IP12b

Sea Level Changes, Tide and Surges at Borollus and Ras El-Barr along the Mediterranean Coast of Egypt

Ahmed Abdel Hamid El-Gindy and Zeinab Moursy

Oceanography Department, Faculty of Science, Alexandria University, Egypt
National Institute of Oceanography and Fisheries, Alexandria, Egypt

The study of the sea level changes with its components: tides and surges as well as the relative importance of their contributions is quite important for coastal management and protection. The main ports along the Egyptian Mediterranean coast (Alexandria and Port Said) were to some extent studied because of the availability of long sea level records. Therefore, our objective in this paper is to investigate other sites affected by significant active shore processes; Borollus and Ras El-Barr, using the available relatively short sea level time series, From January to September, 1984, collected at the Institute of Coastal Protection Research, Alexandria, Egypt.

The aims of the study are: 1. Estimation of the amplitudes and phases of the tidal harmonics at the above positions, using Dodson and Mike Forman methods. 2. Estimation of predicted tidal elevations in the period of the time series used. 3. Extraction of hourly surge. 4. The study of frequency and probability distributions of water level and surge which is important in coastal engineering work. 5. The study of the behaviour of the time series of water level and surge, using spectral analysis, and the relative contribution of surge and tide in the water level.

The results indicated that the surge contribution is comparable with or even greater than the tidal contribution. It has a daily range of -35 to 35 cm, with a mean close to zero cm. It is also characterised by semi-diurnal oscillations; these are probably related to atmospheric pressure cycles and external edge waves. The frequency distributions and the statistical measures at Ras El-Barar and Borollus were quite similar in values. The water level and surges were found normally distributed with defined means and standard deviations. All these information are new in such areas where data are generally not well documented.

IP12c

A Generalized Set of Equations for Coastal Ocean Circulation and its Application to the East China Sea

Shizuo Feng, Dexing Wu, Hui Wang and Kai Wang

Institute of Physical Oceanography, Ocean University of Qingdao, Qingdao, China

A turbulent closure three-dimensional nonlinear baroclinic coastal water system, in which tidal currents and a quasi-steady flow are dominant over the flow field and supposed to be of the same order of magnitude, is presented and examined. In view of dominant tidal currents, associated with tides as gravitational long waves, the scale analysis on the system reveals a small parameter characterizing and measuring the order of nonlinear convection, and using a perturbation approach with the small parameter the coastal water system is systematically treated. The inter-tidal transport equations for the tidally time-averaged concentration, temperature, salinity, turbulent kinetic energy and its dissipation rate are derived, in which the convective transport velocity is the sum of velocity of the dominant quasi-steady flow and the mass-transport velocity and is termed a ‘generalized mass transport velocity’. The generalized mass transport velocity as a solenoid can be viewed as a Eulerian field variable and the aggregate of such local velocities can be specified as a Eulerian field of flow of an incompressible fluid. Thus, a set of field equations governing the generalized mass transport velocity is derived and a turbulent closure problem for the coastal ocean circulation of which the velocity is embodied by the generalized mass transport velocity, nonlinearly coupled with the dominant tidal circulation through the eddy viscosity, is proposed and used to describe and understand the dynamics of
wind-, density- and tide-driven circulation and the inter-tidal transport processes. Based on the set of field equations, the nonlinear effects of the convection and the sea surface elevation of the quasi-steady flow on the circulation, and in particular, the dynamic mechanism of the nonlinear coupling between the tidal and the tidally time-averaged circulation are revealed and examined. Finally, a preliminary application of the proposed model to simulating the winter-time and the summer-time circulations in the East China Sea and to understanding their dynamics is briefly described and discussed.

IP12d

Black Sea Large-scale Circulation and Water Stratification - Buoyancy Flux Impact

S.N. Bulgakov

Marine Hydrophysical Institute Ukrainian Academy of Sciences, UKRAINE

The origin of the Black Sea circulation and water stratification is studied. ‘Haline hypothesis’ is proposed to investigate the general patterns of the kinematic and hydrological seawater structures, which can be formed by the buoyancy flux through the open lateral boundaries (river estuaries, straits). The present study of this problem is carried out using a complex method of approach: analytical and numerical methods of theoretical analysis, laboratory modelling based on the similarity of dynamic processes in a rotating basin and at the Black Sea, analysis of the current velocity data and CTD measurements in the Black Sea, using information from the data base and especially organized field observations.

An important role of the inflows of river discharges and salty Marmara Sea waters through the Bosphorus strait is demonstrated for the large-scale circulation and water stratification generation in the Black Sea. It is established that buoyancy flux forms a three-layered vertical structure of the horizontal circulation with the countercurrent at the depth of the main pycnocline. The distinctive feature of the corresponding hydrological fields is an expansion of the main pycnocline.

The present and recently obtained current velocity data and CTD observations demonstrated the existence of the similar elements of the kinematic and hydrological water structures in the Black Sea and in other marginal seas.

IP12E

Coastal Upwelling in the North-Western Black sea

A.I. Ginzburg, A.G. Kostianoy and S.V. Stanichny

Institute of Oceanology, Russian Academy of Science, Moscow, RUSSIA,
Marine Hydrophysical Institute, Sevastopol, UKRAINE

An investigation of coastal upwelling in the north-western Black Sea, which is spacious and predominantly shallow shelf area, has been carried out on the basis of analysis of NOAA-11 infrared high resolution (1.1 km) satellite imagery (20 images for summer 1993 and a few images for other years) and available mean-daily hydrometeorological information for seaports in the area (summer 1993), together with archived hydrological data set of many years. It was revealed that upwelling with dissimilar intensity and alongshore extent occurred in the following coastal zones with distinct spatial orientation and character of shore line: regions of the Danube delta (I) and from the Zhebrjanskaya Bay to Odessa (II), Tendrovskaya spit (III) and the Crimea coastal zone between Cape Tarhankut and Cape Hersones (IV). Time difference between the onset (relaxation) of upwelling and the beginning (termination) of upwelling favourable wind and predominant velocity of 5 m/s did not exceed 24 hours (it was impossible to define time response more exactly because of absence of hourly wind measurements). The upwelling front was at a distance up to about 20 and 50 km from the coast in zones I-III and IV, respectively. It was zone III where upwelling was most often observed because of prevalence of north-westerly winds, cold water band appearing along the whole of the spit. Temperature of upwelled water was about 11-14ƒC (4-7ƒC colder than that beyond the front), which corresponded to a depth less than 20-30 m (within seasonal thermocline or just below).

Transversal filaments of transformed upwelling water 4-14 km width propagated offshore from the front to a distance up to about 40-50 km in zones I-III and even farther in the vicinity of capes and in bays in zone IV. Entrainment of the water by two anticyclonic mesoscale eddies over the continental slope southwest of Sevastopol conditioned its propagation from Cape Hersones for a distance of more than 150 km. The filaments terminated sometimes in vortex or vortex dipole in areas both with freshened surface water (zones I, II and western region of zone III) and with complete vertical homohalinity (eastern region of zone III, zone IV). Most often they were observed along the whole Tendrovskaya spit, the number of them being from 1 to 6 and a distance between them from 20-45 km.

A non-dimensional parameter, which determined dynamics of coastal upwelling in laboratory experiments of Narimousa and Maxworthy (1987), was estimated using observed width of upwelling zone and wind velocity as well as known density stratification. The estimated values met their criteria for formation of the filaments.

ip12f

Sensitivity of Vertical Temperature, Velocity and Viscosity Profiles with Regard to Different Model Realisations

Thomas Pohlmann

Zentrum f¸r Meeres und Klimaforschung der Universitat Hamburg, Hamburg, Germany

A three-dimensional baroclinic shelf sea model driven with realistic atmospheric forcing data was calibrated with the help of temperature profiles measured during the Fladenground Experiment FLEX '76 in the year 1976. The influence of the vertical turbulent scheme was investigated very carefully. A second order closure scheme originally developed by Kochergin gave very satisfactory results. For this study FLEX '76 data were of particular value because they cover the period of thermocline formation, ie. the spring period when the thermal structure reacts very sensitively to the characteristics of the turbulent scheme.

Firstly, the influence of horizontal advection in the FLEX '76 region will be estimated, comparing the results of the complete three-dimensional model run with results from a rim in which horizontal advection is neglected. Since one of the major assumption for the interpretation of the FLEX '76 experiment was that far-field processes are negligible, this study will help to bring some light into the still ongoing discussion.

Secondly, results of a three-dimensional and a one-dimensional column model are compared. Although both models use the same set of parameters to describe the local processes, differences are significant and cannot only be attributed to the missing horizontal advection. One of the possible explanations for this discrepancy is a too small dissipation of the inertial oscillation in column models caused by the lack of horizontal viscosity. Since the vertical eddy viscosity decisively depends on the vertical shear of the velocity, this also explains why one-dimensional models produce significantly different vertical eddy viscosity profiles compared to models, comprising the complete three-dimensional physics. This finding clearly demonstrates the limited applicability of column models, in particular if obtained parameters are intended to be transferred to three-dimensional modelling.

ip12g

CIRCULATION in south china sea with kuroshio intrusion and pacific to indian ocean throughflow

Longfei Ye

South China Sea Institute of Oceanology, Chinese Academy of Science Guangzhou, CHINA

1.  
2. Kuroshio Intrusion through the Luzon Strait may result from "thermal forcing" in winter and "salinity forcing" in summer. Its transport may be expressed roughly as:

where A ª 4.5 Sv, B ª 3.6 Sv (with phase lead t₀ ª 0.5) are annual mean and seasonal variation respectively, and t is the number of months.

2. Two anti-parallel currents, namely the Kuroshio South China Sea Branch (KSCSB) and the South China Sea Warm Current (SCSWC), exist along the continental slope south of China throughout the whole year. The KSCSB is formed by the Kuroshio intrusion "trapped" by the continental slope. In winter, the SCSWC is driven by the strong thermal gradient developed by the Kuroshio intrusion and becomes even stronger against the strong NE monsoon. In summer, it may be drawn by the less saline output through the Taiwan Strait due to heavy precipitation similar to an "inflow basin" with inflow and outflow in different passages as in the case of the "American Mediterranean"

3. Contribution to the Pacific to Indian Ocean Throughflow may result from an output transport to the Sulu Sea through the Mindoro Strait. This may be shared with the outward transports through both the Taiwan Strait and the SCSWC as well as the Sunda Shelf/Java Sea.

ip12h

simulation of baroclinic processes in the southern north sea

Roger Proctor

Proudman Oceanographic Laboratory, Bidston Observatory,
Birkenhead Merseyside, UK

Baroclinic processes play an important role in the circulation of the southern North Sea. Coastal currents are modified by inflowing river plumes and seasonal heating induces thermal stratification, whose regional distribution is controlled by the tides. A 3-D hydrodynamic model with a gridsize small enough to resolve the internal Rossby radius, and hence simulate certain baroclinic motions, has been run for a 6-month period (March-September 1989). The period coincides with the extensive data set collected during the UK NERC North Sea Project. The model shows features observed in the data, e.g. internal tides and tidal straining. A comparison between the model and observation will be given to indicate the model’s ability to resolve the baroclinic motions.

ip12I

Development of a 3D Operational Tide-surge Model on the North West European Shelf

C.M. Kwong, A.M. Davies and R.A. Flather

Proudman Oceanographic Laboratory, Bidston Observatory,
Merseyside, UK

A three dimensional hydrodynamic model of the European continental shelf (12 km grid), using a spectral approach in the vertical and finite differences in the horizontal has been developed for operational tide-surge prediction (UKOPMOD - UK waters OPerational MODel). A very brief outline of the major steps in formulating the 3D model will be presented together with some comparison with observation.

Calculations using up to fifteen tidal constituents will be described. The model is used to examine the spatial distribution, both the elevations and currents of the major tides in the region. Detailed comparisons are made between model computed profiles and harmonic analyses of 278 current time series, at a range of locations in varying water depths. Comparisons between the observed and computed tidal elevation amplitudes and phases are also shown. These detailed comparisons are used to determine any bias in the model and the accuracy of predicted elevations and currents derived with the model.

Calculations have also been performed to examine the wind induced flows on the continental shelf. By using idealized wind much insight has been gained on the effects of wind turbulence on the current structure and sea surface elevation. Results will also be presented for the storm event in January 1993.

ip12j

Modelling wind driven circulation on the North West European Shelf during the storm in January 1993

C.M. Kwong and A.M. Davies

Proudman Oceanographic Laboratory, Bidston Observatory,
Merseyside, UK

A three dimensional hydrodynamic model of the European continental shelf (12 km grid), is used to study the wind driven response of the shelf to a major storm event in January 1993, the period of oil spill due to the grounding of the tanker Braer on the Shetland. A number of calculations have been carried out to examine the sensitivity of the wind driven flow, in particular the near surface currents, to a number of eddy viscosity parameterizations and methods of accounting for wind driven turbulence. Effects of including a wave-dependent eddy viscosity term in the flow model are also shown.

Results are also shown from a high resolution (of order 0.924 km) limited area model of the Shetland sea regions. The importance of including a high resolution grid and taking account of 'far field' effects computed with the shelf wide model, together with the accuracy of local winds in determining the circulation in the vicinity of Shetland, is considered.

ip12k

APPLICATION of micom and VENTILATION of the east (JAPan) sea

Y.H. Seung and K.J. Kim

Department of Oceanography, Inha University, SOUTH KOREA

The MICOM is applied to the East (Japan) Sea to investigate the process of renewal of intermediate and deep water of the basin. The basin is forced by inflow-outflow of warm surface water and local forcings, both mechanical and thermodynamic. A warm current named Tsushima Current enters the basin from, and flows out to the north Pacific. Below the Tsushima Current Water, an intermediate water is found which is characterised by minimum salinity and maximum dissolved oxygen. It has long been suspected that this water is produced at the surface in the northern part of the basin. Further below the Intermediate Water, a deep homogeneous water named the Japan Sea Proper Water is found. Many questions have also been raised about its formation. To numerically model these processes, MICOM, an isopycnic coordinate model, is applied. The original model is slightly modified to incorporate the inflow-outflow open boundary conditions. The known temperature, salinity volume transport and mixed layer depth are imposed at the inflow open boundary while the radiation condition is applied at the outflow open boundary. Surface winds calculated from the daily atmospheric pressure charts are applied to the surface. The mixed-layer temperature and salinity are relaxed to the temperature and salinity of historical data. Model results show a surface circulation pattern similar to those obtained in previous models. Tracer experiment appears useful in determining the time scale of renewal and understanding its dynamics. It seems that the renewal is mostly done by local convective overturning. It then expands over the whole basin by slow advection. It takes several years to replace the whole intermediate layer with newly formed water. However, the time scale of renewal of deep water is beyond the model integration time. For further dynamical analyses, the model results are compared with a simple analytic solution obtained by applying the ventilation theory developed by Luyten et al (1983) to the basin.

IP12l

The "separation formula" and the Indonesian Throughflow

Doron Nof

Department of Oceanography, Florida State University, Tallahassee, USA

The "separation formula", a new analytical method for computing the inter-hemispheric transport of thermocline water (recently introduced by Nof and Van Gorder, JPO, 1996) is applied to the Pacific Ocean. The method involves an integration of the wind stress along a "horseshoe" path. The integration begins at the separation point of the poleward flowing western boundary current in the southern hemisphere, continuing eastward across the ocean, progressing northward along the continental boundary, and then turning back westward across the ocean to the separation point of the western boundary current in the northern hemisphere. In the case of the Pacific (which is closed on the northern side), such an integration gives the wind-driven upper water mass flux through the Indonesian passages.

The analytical formulas show that, in order for a such wind-driven throughflow to exist, it is necessary that there will be an asymmetry in the winds associated with the two zonal cross-sections connecting the (northern and southern) separation points in the west to the continents in the east. It turns out that these asymmetries in the Pacific are relatively small and, consequently, do not allow for an Indonesian transport of more than one Sverdrup. Furthermore, in the southern Pacific, this wind-driven transport is directed to the south implying a net Indian to Pacific transport rather than a Pacific to Indian transport.

When an upwelling (of intermediate water into thermocline water) is added to the model, however, then one obtains that all the water upwelled in the Pacific must exit the Pacific via the Indonesian Seas, i.e., the wind field is effectively blocking the South Pacific, forcing the upwelled water into the Indian Ocean. This upwelling model suggests, therefore, that the observed Pacific to Indian throughflow (5-6 Sv according to recent analyses) is a measure of the upwelling in the Pacific.

These results are not in agreement with previous calculations based on the Island Rule which does not allow for any upwelling (i.e., the flow is strictly wind-driven) and yet gives a Pacific to Indian transport of 15-20 Sv. It is argued that the discrepancy is mainly due to the proximity of the Australian continent to Asia which introduces dramatic alterations to the Island Rule estimate.

IP12m

Air-Sea Interaction Studies in the Eastern Mediterranean and Alboran Seas

Simon A. Josey and Peter K. Taylor

James Rennell Division for Ocean Circulation, Southampton Oceanography Centre, Empress Dock, Southampton SO17 7NS, UK

The inter-annual variability of air-sea heat and momentum exchange in the Eastern Mediterranean as deduced from climatological fields based on in situ reports in the COADS 1a dataset covering the period 1980-93 will be discussed. A shift in the dominant region of late winter heat loss from the Southern Adriatic to the Aegean Sea is observed during 1991-93. The potential for this change in surface forcing to explain the change in water characteristics in the Eastern Mediterranean reported by Roether et al (1996) will be examined. Results from a recent cruise in the Alboran Sea in which the air-sea interaction in the vicinity of the Almeria-Oran front was investigated (specifically changes in the longwave flux across the front, the effect of atmospheric aerosols on the surface shortwave flux and an evaluation of the various bulk formulae that have been advanced to estimate the longwave flux) will also be presented.

Roether, W., B. B. Manca, B. Klein, D. Bregant, D. Georgopolous, V. Beitzel, V. Kovacevic and A. Luchetta, 1996: Recent changes in eastern Mediterranean deep waters. Science, 271(5247), 333-335.

ip12n

Decadal Variability on the Northwest European Shelf

J¸rgen S¸ndermann

Zentrum f¸r Meeres und Klimaforschung, Universit”t Hamburg, GERMANY

The seasonal cycles of sea surface temperature and other parameters at eight sites on the Northwest European shelf show an interannual variability in the range of years to decades for the years 1970-1995. Statistical methods like spectral analysis or phase diagrams prove that only a few frequency peaks beyond the annual cycle are of real significance. Most prominent signals for temperature and salinity in the southern North Sea are at periods around 8 and 17 years. The time series are too short to identify definitely long-term trends or transitions between different states of equilibrium.

Explanations for the decadal variability can be given by the intrinsic time scales of the internal shelf dynamics as well as by external periods. A spectral analysis of calculated mass fluxes through the Shetland-Orkneys section shows that there is little energy in periods beyond the seasonal cycle. This does not suggest a major advective influence from the Atlantic Ocean. The most probable external source of decadal variability on the Northwest European shelf is the atmosphere. This hypothesis means that no phase shift can be expected between corresponding signals of time series at different North Sea sites as is indeed observed.

ip12o

An Investigation of the Circulation Induced in a Coral Reef Lagoon by the Radiation Stress of Breaking Incident Waves

J.R. Hunter and C.J. Hearn

CSIRO Division of Oceanography, Hobart, Australia
ADFA Campus of University of New South Wales, Canberra, Australia

Two-dimensional depth-averaged hydrodynamic models, in which the bottom stress is derived from a time-convolution over the forcing (e.g. wind), have existed for over 20 years. The full three-dimensional velocity field may be derived from these models by a separate integration of the depth-dependent horizontal dynamic equations. Such models, which are often called 'two and a half dimensional', offer some computational gains over more conventional three-dimensional hydrodynamic models. Developments of the technique have involved various approximations to the convolution kernel, including one which yields the exact steady-state three-dimensional solution to the linearised equations (e.g. Hunter and Hearn, 1989).

A steady-state two and a half dimensional model is particularly useful for the investigation of the three-dimensional velocity field generated by the radiation stress of breaking waves. Such a model is here applied to Kaneohe Bay, Hawaii, which is a coral reef lagoon, 15 km long, 6 km wide and with a maximum depth of 16 m. The model is used to investigate the effect of different spatial distributions of radiation stress on the velocity field, and on the flushing characteristics of the Bay.

Hunter, J.R. and Hearn, C.J., 1989: The single relaxation approximation for bottom stress in two-dimensional hydrodynamic models of shallow seas, Continental Shelf Research, 9 (5) 465-478.

IP12Q

Rapid change of sediment and nutrient discharges from the yellow and yangtze rivers by human activities

Dunxin Hu

Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, P.R. CHINA

The Yellow and Yangtze Rivers are two of the biggest rivers surrounding the Pacific Ocean, which empty a huge amount of sediment and nutrient into the ocean, occupying more than 10% of the world total of riverine sediment discharge in the past. However, with human activities along the river basins rapid change has taken place. For example, owing to dam construction, such as Sanmenzia completed in late 1960’s and Ziaolangdi at present, etc. the sediment discharge of the Yellow River dropped from a mean (1950-1969) of 1.2 billion ton/yr to a mean (1970-1992) of 0.7 billion ton/yr (by about 40% decrease) and the Yellow River dried up for more than 4 months for each of the last two years (1995 and 1996). Due to the dramatic increase of fertiliser applications in China, which went up almost 100 times in the last 40 years, nitrogen concentration in the Yangtze River mouth increased by 4-5 times from early 1960’s to early 1980’s and the dissolved nitrogen flux of the River increased by 5 times from late 1950’s to early 1980’s.

In the future, dam construction will be heavily continued for economic development in China, which will definitely cause a decrease of riverine sediment discharge. On the other hand, soil erosion will cause increase of the sediment. We cannot predict at present how serious the soil erosion, determined by land use, will be.

In the present paper, the history of anthropogenic impact on coastal marine sediment is reviewed with the Yellow River as example with special reference to the recent change since 1950 and the future tendency is considered.

IP12s

statistical assessment of trace metal geochemical associations in sediments from a tropical estuary on bay of bengal, a marginal sea along east coast of india

K.C. Sahu, U.C. Panda and B.K. Rath

P.G. Department of Marine Sciences, Barhampur University, Berhampur, Orissa, INDIA
ONGC, Bombay, INDIA

Geochemical associations of certain trace metals in Rushikulya estuary on a marginal sea, India, were studied and trace metals in sediments were sequentially extracted. Fe-Mn oxides bound fraction is the most dominant phase in the non-lithogeneous fraction, containing 7-48% Fe, 10-55% Mn, 10-41% Zn. This is attributed to the strong scavenging properties of Fe-Mn oxides to many trace metals. In non-residual fraction the exchangeable or easily leachable fraction is geochemically insignificant. The carbonate-bound fraction appears to be the least dominant phase. Most trace meetals were shown to be associated with the reducible and organic phases. The lithogeneous (residual) fraction is generally considered as a guide to the natural background as determined to contain 46-99% Fe, 14-67% Mn,
24-66% Co, 6-56% Zn, 14-61% Cu, 53-83% Cr and 37-61% Ni.

Multivariate analytical results for the geochemical speciation of estuarine sediments suggest that no single factor has a maximum percentage of total variance. It has been found that Mn, Zn and Cu are from organic sources. Mn and Cu, along with Fe in exchangeable sides are mostly with silt and clay. The carbonaceous fraction is biochemically rather than chemically precipitated. Significant loading on mud contents, carbonates with heavy metals and the negative loading on sand content demonstrate the vital role of textural parameters for the fixation of heavy metals.

ip12t

Integrated Modeling of Port Phillip Bay

John Parslow and Stephen Walker

CSIRO Division of Marine Research, Hobart, Australia

From 1992 to 1996, CSIRO directed a large integrated study of the fate and effect of nutrient and toxicant discharges into Port Phillip Bay, designed to provide a basis for future management of discharges to the Bay. An important outcome from this study was the development of an integrated model of the Bay, capable of simulating the physics and ecology of the Bay over periods ranging from hours to decades.

Numerical models of waves, tides and currents were developed, able to simulate any period in the last decade. These models were coupled using particle tracking techniques to a transport model which described the movement of substances, dissolved and particulate, organic and inorganic, around the Bay. The transport model was extended to include a module describing the fate and impacts of nutrient loads (nitrogen, phosphorus and silicate) in the Bay. The resulting integrated ecological model was used both to synthesize observations and process studies, and to produce scenarios to guide decisions about future discharges.

The issues involved in the design, development and calibration of these models, and their implications for the ecology and management of the Bay, will be presented.

IP12u

Spectral Modelling of Optical Properties of Turbid Waters.

T. Kutser and H. Arst

Estonian Marine Institute, Tallinn, Estonia

Blue to green ratios or the same kind of algorithms have been widely used in interpretation of remote sensing data measured on the clear ocean waters. We have carried out a number of optical experiments in the Baltic Sea, Estonian and Finnish lakes to verify the usefulness of the algorithms, elaborated by our group and other authors, in the case of turbid coastal and inland waters. Dramatic changes in concentration, spatial distribution and optical properties of phytoplankton, dissolved organic matter (yellow substance), and suspended sediments are causing high variation in shape and multitude of water reflectance spectra. Therefore the remote sensing algorithms elaborated for estimation of concentrations of optically active substances in Case I waters cannot be used in turbid waters. Moreover, our results (supported by other authors) confirm that the remote sensing algorithms for turbid waters are site specific and vary seasonally.

To avoid shortcomings of the above-mentioned method we elaborated a simple mathematical model that enables us to simulate water reflectance spectra in the visible part of spectrum. Using specific absorption and scattering coefficients of phytoplankton, yellow substance and suspended matter we calculate reflectance beneath and just above the water surface. The shape of the full simulated spectrum is compared with the measured spectrum. We assume that concentrations of optically-active substances that were used in the simulation correspond to real ones in the waterbody under investigation based on the case where the calculated spectrum fits with the measured one.

Prototype of the model based on specific absorption and scattering coefficients available in literature (measured mainly in clear waters) gives good estimations of concentrations of chlorophyll, yellow substance and suspended matter if tested using underwater and remotely measured spectral data . Taking into account specific optical properties of material typically present in the waterbody under investigation we can improve correlation between measured and estimated concentrations of optically active substances. Preliminary knowledge about dominating algae species, type and size distribution of suspended particles, their specific absorption and scattering properties should significantly improve reliability of model estimations.

IP12V

Monitoring Circulation Pattern and Water Masses Distributions in northern part of red sea by AVHRR imagery

M.M. Farag

Department of Environmental Studies, Institute of Graduate Studies and Research, University of Alexandria, Alexandria, EGYPT

In spite of many investigations made in the Northern Red Sea, it seems that more detailed studies are needed to understand the variability of the dynamic structures. On the basis of the available AVHRR data, we investigate the characteristics that are involved in the process of water exchange between the Red Sea, and Gulf of Suez and Gulf of Akaba. Also, sea surface temperature, different water masses, water intrusion and circulation patterns will be monitored by using AVHRR images. The classified images present a local study of water masses in and out of the gulfs (Suez and Akaba), and general circulation patterns of the interested area.

The general approach of this study is the use of remote sensing techniques for detecting and monitoring difference structures of circulation and drawing synoptic maps of dynamical processes.

IP12W

Circulation pattern of the eastern Mediterranean sea studied using satellite data

M.M. Farag, A.M. Ashor and F.M. Eid

Department of Environmental Studies, Institute of Graduate Studies and Research, University of Alexandria, Alexandria, EGYPT
Oceanography Department, Faculty of Science, University of Alexandria, Alexandria, EGYPT

The Eastern Mediterranean Sea is considered, almost, an isolated basin. It is characterised by synoptic circulation and variabilities that occur on three scales: (1) basin scale (water exchange between eastern and western basins through Strait of Sicily); (2) sub-basin scale (Levantine, Ionian, Adriatic and Agean basins circulation); and (3) mesoscale which is associated with cyclonic and anti-cyclonic gyres. These circulations patterns are affected by four water masses:

1.  
2. Surface water mass;
3.  
1. Atlantic water mass;
2.  
1. Intermediate water mass; and
2.  
1. Deep water mass.

The aim of the study is to determine the gyres’ parameters in the Eastern Mediterranean Sea by using satellite data (NOAA-AVHRR). Visible bands (1,2) were used to monitor circulation patterns and coastal boundaries. Thermal bands (4,5) are used to determine absolute Sea Surface Temperature (SST) by using a developed algorithm. Also, surface current velocities are calculated from sequential images of SST by two different methods:

1.  
2. objective method using maximum cross correlation between time-lapsed images.
3.  
1. subjective method using feature-tracking technique.

The resulted images have been compared with ground measurements and showed high agreement between them. Generally, the determined gyres’ parameters are found very useful to understanding the gyres’ system in the Eastern Mediterranean.

IP12X

Laboratory experiments on the preconditioning and mixing phases of deep ocean convection

S. N. Dikarev

P. P. Shirshov Institute of Oceanology, Moscow, RUSSIA

It is well-known that there are two different types of deep water formation in the World ocean. Together with the common "shelf" type there exists "open ocean deep convection" type, firstly discovered in the northwestern Mediterranean sea in late sixties. The process of deep convection observed in the central parts of few cyclonic gyres during the winter cooling is usually divided into three general phases: preconditioning, violent mixing, lateral spreading. The analysis of this process over quite long periods of time (30 years) clearly shows its variable, non-stationary nature strongly influenced by climate change. That is why we need to know more about physics of this valuable process and laboratory experiments seem to be a suitable tool.

The key internal hydrologic parameter, which controls the existence of the second phase and so the whole process, is the minimum buoyancy content of the quasi-homogeneous upper ocean layer (UL). Due to the general baroclinic structure of a cyclonic gyre this minimum naturally exists in its central part. The question is: how UL in cyclonic gyre evolves during convective buoyancy loss in the preconditioning phase?

One of the aspects of deep convection is: if the gyre current at the periphery moves water out of the region of large atmospheric convective impact, then the maximum heat loss will be achieved in the central part of the gyre. We have made preliminary lab experiments in order to estimate the efficiency of local overturning in two layers stratified fluid, created by a turbulent buoyant vertical jet. We obtained, that overall background uniform rotation of the fluid enhances the efficiency of local overturning.

For the phase of violent mixing we examined the inertial oscillations mechanism of very big vertical current (10 cm/s) usually observed in the ocean deep convection process. In the lab experiments few regimes of water motion have been discovered. We used resonant conditions in the slightly inclined to the vertical rotating cylinder of water with free surface. The possible applications of lab results to the ocean will be discussed.

IP12y

Observations of Tidally Generated Internal Bores in the Strait of Messina

P. Brandt, D. Quadfasel, A. Rubino, W. Alpers,
J.O. Backhaus, J. Sellschopp and H.V. Fiekas

Institut f¸r Meereskunde, Universit”t Hamburg, Hamburg, GERMANY
SACLANT Undersea Research Centre, La Spezia, ITALY
Forschungsanstalt der Bundeswehr f¸r Wasserschall- und Geophysik, Kiel, GERMANY

During the Atlantic-Ionian-Stream '95 cruise in October 1995, the space-time evolution of tidally induced internal bores was observed in the Strait of Messina. The measurements were carried out by means of a CTD (conductivity, temperature, depth) chain and an ADCP (acoustic Doppler current profiler) providing high resolution density and velocity fields. During the experiment, a strong seasonal thermocline was observed in the Strait of Messina, characterized by a discontinuity near the Strait’s sill: the Tyrrhenian surface water north of the sill was heavier than the Ionian surface water south of the sill. As a consequence, while the northward propagating internal bore, consisting of Ionian surface water, developed as a surface jet, the southward propagating internal bore, consisting of heavier Tyrrhenian surface water, developed as a subsurface jet, intruding at a depth of about 100 m. These data indicate that horizontal density gradients play a crucial role in the evolution of tidally generated internal bores.

ip12z

tides and tidal energetics of the strait of gibraltar: model results and observational evidence

Luis T. Martinez, Alfredo I. Gonz·lez, Dmitrii V. Sein
and Boris A. Kagan

Departamento de Fisica Aplicada, Universidad de Cadiz, SPAIN
P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences,
St. Petersburg, RUSSIA

The main semidiurnal (M2 and S2) and diurnal (O1 and K1) tidal waves in the Strait of Gibraltar are simulated by employing a 2D non-linear, boundary-fitted coordinate model with a nominal resolution of 0.5 km. Agreement between predicted and observed tidal constants at coastal tide gauge and bottom pressure stations as well as between predicted and observed tidal ellipse parameters at sites of current measurements is good for the M2 and S2 waves and satisfactory for the O1 and K1 waves. The model reproduces all the known features of the tidal regime of the Strait, namely, a more than two-fold decrease in the M2 and S2 amplitudes eastward with a concurrent south-western phase propagation, a nearly constant amplitude ratio and phase difference between M2 and S2 waves and great variations in amplitude ratio and phase difference between the O1 and K1 waves throughout the Strait. Moreover, the model predicts some new features of the spatial structure and energetics of the Strait’s tides. These new features are the O1 amphidrome with anticlockwise rotation of cotidal lines in the Tarifa Narrows, small-scale eddies in the O1 mean tidal energy flux field near open boundaries of the Strait, and the general direction of the M2 and S2 mean tidal energy fluxes to the west. The latter fact eliminates the contradiction between observed south-western phase propagation and a commonly used mean tidal transport eastward.

IP12AA

Interaction of Hydrothermal solutions with sea water (results of physico-chemical modelling)

L.M. Gramm-Osipova, V.N. Gramm-Osipova
and V.M. Shul’kin

Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, Vladivostok RUSSIA,
Far Eastern State University, Vladivostok, RUSSIA
Pacific Institute of Geography, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, RUSSIA

The modelling of process interaction of sea water (pH 8.00) and hydrothermal solution (pH 3.76) in the Matupi Harbour (New Guinea), carried out by a method of Gibbs Energy minimisation on computer is described. During modelling to 1 liter of the hydrothermal solution the portions of the sea water were added. A result was observed of continuous evolution of a moisture solution. Three stages of mixture are allocated. At the first stage there is increasing of alkali of the solution, and growth in pH from 3.76 till 4.53. On the second, a sharp decrease up to 1.27. At the third stage there occurs gradual increase pH till 8.00, characteristic for the sea water. A geochemical barrier is allocated on which there is a sharp change of the forms of migration of iron, manganese, lead and zinc, formation of solid phases Fe and Mn. It is marked, that the formation of iron solid phases begins at pH 3.38, and Mn -5.54. An explanation of the physico-chemical evolution of the mixture solution, macro- and micro-components of the system behaviour is given. The described method and approach may be useful for the investigations and analysis mixing processes of polluted waters with river or sea waters.

IP12BB

Construction of thermodynamic models of fresh and salt waters

V.N. Gramm-Osipova and E. Obolochkova

Far Eastern State University, Chemical Department, Vladivostok, RUSSIA

The form of main ions of principal salts in the river and sea waters are calculated with an ion-associative model. Modelling was carried out with help of program complex "Selector" by method of minimisation of Gibb’s energy. The data of chemical composition of river and sea waters in the region, modern data of thermodynamic base and apparently constants of stability were used. Models of fresh and salt waters were constructed for different hydrological seasons.

Model of fresh water is:

CO₃^-2, Ca(CO₃), Ca(HCO₃)⁺, Ca⁺², CaCl⁺, CaSO₄, Cl^-, HCO₃^-, HSO₄^-, K⁺, KSO₄^-, Mg(CO₃), Mg(HCO₃)⁺, Mg⁺², MgCl⁺, Na⁺, NaCl, SO₄^-2, NO₃^-, OH^-, H⁺. (concentration till 0.1 g/1)

Model of salt water is:

B(OH)₃, BO₂^-, Br^-, CO₃^-2, Ca(CO₃), Ca(HCO₃)⁺, Ca⁺², CaCl⁺, CaCl₂, CaF⁺, CaSO₄, Cl^-, F^-, HCO₃^-, HSO₄^-, K⁺, KBr, KCl, KSO₄^-, Mg(CO₃), Mg(HCO₃)⁺, Mg⁺², MgCl⁺, MgF⁺, NO₂^-, Na⁺, NaBr, NaCl, NaF, SO₄^-2, SrCO₃, Sr|₂, SrCl⁺, SrF⁺, NO₃^-, OH^-, H⁺ (salinity 28-30%).

The ions Ca⁺² and HCO₃^- prevail in river waters, Na⁺, M⁺², Cl^-, SO₄^-2 is in the sea. Minimal concentration of substances is in the summer both in river and in the sea solutions. Maximal concentration of all matters in the sea waters is in the spring.

Maximal contents of HCO₃^-, Ca⁺², Mg⁺², Na⁺, CaFu⁺, CaHu⁺, MgFu⁺ are in autumn, SO₄^-2, Cl^-, K⁺ are in the spring. Relation of chloride complexes during one year in the salt water is:

NaCl > MgCl⁺ > CaCl⁺ > CaCl₂ > KCl

in the fresh water is:

MgCl⁺ > NaCl > CaCl⁺ > KCl > CaCl₂

Correlation for sulphates and hydrosulphates during all the year is the same for sea and river:

SO₄^-2 > CaSO₄ > KSO₄^- > HSO₄^- > KHSO₄

Content of hydrocarbonate ion and its complexes with calcium and magnesium in both environments is more than concentration carbonate ion and its compounds. It is till 99.9% of sodium in river to be in the Na⁺, and besides one, ion NaCl composes from 8.5 to 12.9% in the sea water. Potassium presents till 98-99% as K⁺ in river water. Compounds KOH and KSO₄^- are presented in insignificant quantities. Free ion K⁺ composes from 72.6% to 38.2% in salt water, KOH from 8.6% to 53%, KSO₄^- from 8.1% to 17.8%. Calcium is on 77.9 - 81.3% in the form of free ion Ca⁺², from 9.8% to 11.9% - as CaFu, from 5.7% to 7.8% as CaHu in the fresh water. CaSO₄ is in the sea waters from 51.6% to 64.5%, but quantity of free ion decreases to 28.6 - 43.1%. Complexes CaCl⁺ and CaCl₂ is 1.1 - 2.8% and organic compounds are less 0.1% in the sea. Magnesium prevail as Mg⁺² to 80% in the river waters and to 65% in the sea waters. MgFu⁺ and MgHu⁺ present from 13.5% to 22.6% in the river waters. In the sale water MgCl⁺ is considerable quantity. Constructed models show quantity and quality difference in the forms of elements in natural waters of different compositions.

ip12cc

Surface Circulation Statistics in the Straits of Sicily as Computed From Drifter Measurements

E. Zambianchi and P.-M. Poulain

Istituto Universario Navale Napoli, Naples, ITALY
Naval Postgraduate School, Monterey, California, USA

The Straits of Sicily region connects the western and eastern subbasins of the Mediterranean Sea and plays a major role in the water mass exchange between the two basins and in the global circulation of the entire Mediterranean Sea. Starting in fall 1994, satellite-tracked drifters were deployed in the Straits region in order to study the spatial characteristics and the temporal variability of its surface circulation. The drifter program continued for about 3 years and by the end of summer 1997, more than 60 surface drifters had been released.

The drifter trajectories revealed important characteristics of the circulation in the Straits region and in the Ionian Sea. In particular, they showed that the main pathway of the surface Atlantic-Ionian Stream consists of a swift main current flowing eastward between Malta and Sicily, subsequently turning northward on the Ionian shelfbreak and proceeding in the form of a quasi-permanent anticyclonic gyre in the northern Ionian Sea.

Preliminary statistical analyses of the drifter data set are presented, with special focus on the region of the Straits of Sicily. The data were studied from two different perspectives. First, they were processed in the so-called pseudo-Eulerian way, i.e., by binning them into subdomains in which the flow is characterized by a mean velocity and a mean kinetic energy. This was first done over the whole data set, and then focusing the attention to seasonal and interannual variabilities of the average quantities. Second, Lagrangian statistics were estimated to evaluate the typical parameters of the surface mesoscale turbulence, such as the Lagrangian typical time and space decorrelation scales and their spatial variations.

ip12dd

Lagrangian Measurements of Surface Circulation in the Straits of Sicily

P.-M. Poulain, E. Zambianchi, J. Sellschopp and M. Ribera

Naval Postgraduate School, Monterey, California, USA
Istituto Universario Navale Napoli, Naples, ITALY
SACLANT Undersea Research Centre, La Spezia, ITALY
Stazione Zoologica Napoli, Naples, ITALY

The region of the Straits of Sicily is of crucial importance for the circulation in the Mediterranean Sea as it connects its western and eastern subbasins, and plays a major role in the water mass exchanges between the two basins. The Straits dynamics have been investigated in the past using mainly hydrographic measurements and subsurface current meter data from which it was possible to describe the seasonal and interannual variability of the mean axial flow both at the surface and in the intermediate layer. No details of the surface circulation in the Straits of Sicily, however, were documented by these experiments, nor was clear the destiny of the surface Modified Atlantic Water exiting eastward from the Straits into the Ionian Sea.

Starting in fall 1994, satellite-tracked drifters were deployed in the Straits region to study the spatial characteristics and the temporal variability of its surface circulation. Two surface drifter designs were utilized, the CODE or Davis (within the first meter of water) and the WOCE/TOGA (drogued to 15 m depth) types. One cluster of 6 drifters and 2 groups of 8 drifters were released in 1994 and 1995, respectively. Seasonal deployments of clusters of typically 5 drifters continued until summer 1997. More than 60 drifters were deployed in less than three years. As the drifters moved eastward with the prevailing Atlantic-Ionian Stream (AIS), they provided information on the surface circulation in the Ionian basin and even in the Adriatic Sea.

The drifter data are presented in terms of individual or clustered trajectories from which the major circulation patterns in the Straits of Sicily and the eastern Ionian are described. Despite the complexity of the drifter trajectories produced by the mesoscale variability, the drifter tracks reveal the main pathway of the surface AIS, consisting of swift mean currents (speeds of the order of 40 cm/s) transporting Modified Atlantic Water into the Ionian almost entirely through the Malta Channel (between Malta and Sicily). Subsequently, the AIS turns northward over the sharp Ionian shelfbreak, where it is identified as the Maltese front, and proceeds in the form of a mean anticyclonic gyre in the northern Ionian Sea.

South of the Straits of Sicily (i.e., south of 36ƒN), and in particular on the Tunisian shelf, currents are generally weaker and dominated by mesoscale eddies, mostly anticyclonic. Counter-currents (to the NW) were occasionally observed. Some of the drifters meandered southward and eventually approached the African coast. Except for a single drifter that moved eastward in a coastal current off Libya, negligible eastward surface mean transport is found between Malta and the African continent.

The seasonal and interannual variabilities of the above circulation picture is explored. In particular the shape and strength of the AIS in the Straits of Sicily and in the northeastern Ionian are discussed. Except for a few drifters moving south and southeastward upon leaving the Malta shelf in summer 1995, the drifter observations indicate that the main circulation in the northeastern Ionian remained essentially anticyclonic throughout the three years of the program. The reversal into a cyclonic pattern in winter, as suggested by hydrographic observations and computer simulations, is not substantiated by the surface drifters.

IP12EE

Tides, Tidal currents and residual currents in rotating semi-enclosed basin

Hidekazu Yasuda

Chugoku National Industrial Research Institute, Hiro-Suehiro, Kure-City, JAPAN

Tides and tide-induced currents in a rotating semi-enclosed basin are investigated theoretically to verify the tide-induced residual current observed in a rotating hydraulic basin. The basin in this study is assumed to be rectangular for simplicity and as long as the period of the longitudinal free oscillation is longer than the tidal period. The basin width is smaller than Rossby’s external radius of deformation.

The node of the tidal oscillation is formed in such a long basin and the position is shifted by the rotation effect. The node shift is related to the result obtained in this analysis that the period of the free oscillation of the rotating basin gets shorter with increase of the rotation effect. This means that the period of free oscillation of the basin is shorter in higher latitudes.

The tidal current ellipse is formed near the basin floor by the rotation effect through the tidal current oscillates rectilinearly in the outside of the boundary layer in a narrow basin like this model. The ellipticity of the tidal current near the floor gets larger with increase of the Coriolis effect.

It has been known that the bottom boundary layer (Stokes layer) generates residual circulations vertically even in the basin with no rotation. The lateral component of the tidal current (the tidal current ellipse) near the floor generated by the rotation effect produces the residual circulation horizontally in the rotating basin. It also gets stronger with increase of the rotation effect. The horizontal circulation is divided into some pieces in a long basin, while only a cyclonic circulation is formed in a short basin. Such residual circulations play an important role in matter distribution in enclosed basins.

IP12ff

Baroclinic Eddies and Basin Oscillations in Semi-enclosed Basins. Model Study on the Black Sea Circulation and Biological Processes.

Emil Vassilev Stanev

Department of Meteorology and Geophysics, University of Sofia,
Sofia, Bulgaria

Eddy dynamics of the Black Sea are analyzed on the basis of model simulated data. The data are produced using Bryan-Semtner-Cox modular ocean model with grid intervals 1/9ƒ x1/12ƒ in the longitude/latitude. The model variability is dominated by basin oscillations, which are strongly modified by baroclinicity and topography. The simulations support the concept that the anticyclonic circulation in the Black Sea is observed between the jet-current and the coast, where meanders and eddies with changing amplitudes are spontaneously formed. The baroclinic instability results in pronounced quasi-periodic changes of the circulation. The meanders increase, and spectacular intrusions of coastal water into the open sea are simulated. In the extreme cases, the gyre breaks into sub-basin scale eddies. Satellite data, which are already available for this basin support the model simulated patterns, as well as the characteristics of the model variability.

Some hypotheses about the mechanisms of cold water formation, based on observations, are validated using model simulations. The results indicate that the cold water is formed mostly on the shelf and continental slope and then is transported by the main cyclonic gyre into the basin interior and into the deeper layers (up to 100-120 m). Anticyclonic eddies between the Black Sea front and the coast enhance the penetration of cold water into the halocline. This mechanism is very efficient west of Crimea Peninsula. The areas of maximum cooling of the sea and the ones of formation of extremely low temperatures do not coincide. This suggests that the ocean-atmosphere heat exchange is strongly controlled by the basin dynamics.

Five and seven compartment biological models including nitrates, ammonium, phytoplancton, zooplancton detritus (and bacteria and dissolved organic nitrogen) are coupled with the physical model. The simulations are tuned to the specific Black Sea conditions. Model behaviour under different physical conditions, resulting from the atmospheric forcing and model dynamics, are analysed. The results of different scenarios are intercompared with the focus on the impact of physical, biological and combined effects on the model performance.

IP12gg

Variabilities of Particulate Fluxes and Currents in the Western Slope of the South Okinawa Trough

Yu-chia Chung and Guo-wei Hung

Institute of Marine Geology and Chemistry, National Sun Yat-sen University Kaohsiung, Taiwan

Since October, 1992, fourteen mooring strings, each with several time-series sediment traps (PPS 3/3) and current meters (RCM 8) have been deployed to collect data on particulate fluxes and associated currents at 14 sites in the western slope area of the South Okinawa Trough. This project was undertaken as an integral part of the KEEP (Kuroshio Edge Exchange Processes) studies conducted by the oceanographic community in Taiwan.

Parts of the results obtained were presented at earlier international scientific meetings (IUGG at Boulder, 1995 and WPGM at Brisbane, 1996). This paper presents new results and summarises all the data gathered to date. The data show large temporal and spatial variabilities in particulate fluxes, averaging about 40 gm^-2d^-1, are observed in a canyon where the water flows outward as a counter current generated by the Kuroshio intrusion. The particulate fluxes drop by an order of magnitude outside and away from the canyon. There is a good correlation between the mean particulate flux and the mean current speed within the canyon and its outlet. Such a correlation disappears at the other mooring sites. The particulate fluxes at each site increase toward the ocean bottom, suggesting that lateral transport of the particulates resuspended by slumping in the upper slope of shelf area provides a major source for the trapped particulates in this marginal sea environment.

IP12hh

Groundwater in salt and water regime of the inland seas (with the Caspian Sea as an example).

I.S. Zektser and R.G. Dzhamalov

Water Problems Institute, Russian Academy of Sciences, Moscow, RUSSIA

Groundwater exchange between land and sea is the least studied and most difficult to determine component in salt and water balance investigations of inland seas. Groundwater exchange includes two opposite and non-equivalent processes : groundwater discharge from land into the sea and sea water intrusion into the coast. Here, groundwater discharge into the sea is prevailing, it is formed in the water-saturated rocks under the sea draining impact. Sea water intrusion into the coast is considerably less spread , mainly in the local areas with intensive groundwater withdrawal.

Role of groundwater discharge in water and salt balance of the Caspian Sea is examined in the report, basing the results on perennial investigations. Certainly, the Caspian Sea problem, due to its level considerable fluctuations, in the last 15-20 years attracted fixed attention of both Russian and foreign scientists. Trying to find the reason for level changes, scientists make attempts to define more precisely separate components of its balance including groundwater inflow. It is clear from the report, that hydrodynamic method of groundwater flow rate calculation is the most reliable quantitative method for groundwater discharge into the inland seas. Using this method and actual hydrodynamic parameters, the authors of this report jointly with A.V. Meskheteli, made calculations of groundwater discharge into the Caspian Sea. In so doing, common values of groundwater inflow for separate calculated areas and for the whole sea, as well as specific characteristics have been
obtained : mean perennial modules of groundwater discharge into the sea in l/s for 1 sq.km of the catchment area and linear groundwater inflow in m/s for 1 km of the sea coast line. It appeared, that groundwater inflow into the sea does not exceed 5 km /year , that is not more that 1.5 - 2% for the whole Caspian Sea on the average. However, groundwater role in the salt balance of the Caspian Sea is much more considerable and amounts to 30% if compared with salt flushed out by surface water. Under detailed studies of groundwater discharge into the sea, it is recommended to use the method, based on direct studying the anomalies in physical properties and chemical composition of bed sediments and bottom water, caused by groundwater discharge. Examples and results of such investigations, the Caspian Sea included, are given in the report.

IP12ii

DETERMINATION of SPM FLUX in the COASTAL ZONE FROM LONG-TERM TRANSMISSOMETER RECORDS.

C.F.J. Bull and C.F. Jago

School of Ocean Sciences, University of Wales, Bangor,
Menai Bridge, Anglesey, UK.

Transmissometers are now routinely attached to either benthic or pelagic mooring packages to measure the suspended particulate matter (SPM) concentration over time. A calibration between the beam attenuance of the transmissometer and SPM load is normally determined by carrying out a linear regression between this and the gravimetric analysis of a number of water samples. The fact that it is necessary to calibrate for a specific site has been reported by a number of workers. However, such calibration may still produce a significant error between the interpolated SPM concentration from the transmissometer record and the actual SPM concentration determined by gravimetric analysis.

At a number of study sites in the North Sea off the east coast of the U.K., we have obtained transmissometer data concurrent with gravimetric, particle size, settling velocity, and current velocity data over several tidal cycles as part of the Natural Environment Research Council's, Land Ocean Interaction Study, the principle aim of which is to measure nett fluxes. The transmissometer calibrations using all the gravimetric samples over a tidal cycle can in some cases only provide an R² = 0.47. However, by introducing the textural characteristics of the suspended matter, a time varying calibration, (which in conjunction with salinity and current velocity data) has been derived which gives a calibration with an R² = 0.85.

To determine the error in the flux calculations, interpolated data from the transmissometer has been compared with flux calculations using actual gravimetric samples. At one site the flux error has been reduced from 485% to 37% and at another site from 150% to 3%. Thus by increasing our understanding of the physical and hydraulic properties of SPM over a tidal cycle it is becoming possible to reduce the error in the flux determinations below the level of the nett flux.

IP12jj

The Measurement of Suspended Sediment Transport Processes in the Nearshore Zone off the Holderness Coast - Southern North Sea, England

J.C. Blewett and D.A. Huntley

Institute of Marine Studies, University of Plymouth, Drake Circus, Plymouth, UK

Investigations show that the Holderness Cliffs are retreating at a rate of 1.7m a year. It is suggested that storm events play a major role in transporting the cliff material away from the coast. A field campaign was set up as part of the LOIS-RACS coastal program, to determine the hydrodynamic processes responsible for transporting the sediment offshore, and to quantify the total sediment flux. Three Boundary Layer Intelligent Sensor System (BLISS) tripods (built by NERC Plymouth Marine Laboratories) were deployed at predetermined mooring sites off the Holderness Coast in February, July, November, 1995 and February, 1996. Two bi-axial electromagnetic current meters were aligned to measure the horizontal (u v) and vertical components of flow, at 0.4 meters above the seabed. Two optical backscatter sensors and a beam transmissometer were positioned at three different heights to monitor suspended sediment concentration. Additional measurements of pressure, conductivity and temperature were also collected. Data was collected over a period of two weeks each deployment and recorded at 5Hz for 17 minutes every hour, on the same data acquisition system.

Estimates of sediment flux based on measurements taken from the BLISS July 1995 and February 1996 deployment phase will be presented. The results will be discussed in the context of various time scales. Such time scales will include short term effects, such as turbulence, hourly effects such as the tide, the monthly spring/neap tidal cycle, through to the seasons and finally long-term i.e. years. In addition to the different time scales mentioned above, the response of fluxes to the changing weather conditions, will be examined and special attention will be given to North Sea storm events, which are thought to play a major role in eroding and carrying the sediment away from the Holderness Coast.

IP12kk

Storm Surges and Waves Along the Mediterranean Coast of Egypt

Abdel Aziz Abdel Baeth Hamed

College of Maritime Transport and Technology, Arab Academy for Science and Technology, EGYPT

Lack of sufficient knowledge of coastal wave climates and storm surges hinders management and treatment of coastal problems. This limits the data applicability for describing the basic stochastic processes which govern beach changes along the Mediterranean coast of Egypt. The main purposes of this paper are:

1. Examination of the effect of the different depressions during their courses over the Eastern Mediterranean on the wave generation along the Egyptian coast. 2. Comparison between the wave measurements in the area of interest and the estimated wave characteristics from the synoptic charts. 3. Classification of the storm surges according to their heights and the associated synoptic situations. 4. Establishing an empirical formula to predict the storm surge height. 5. Finding out the wave climates along the Mediterranean coast of Egypt.

Data used are: the hourly sea level heights the hourly wind velocity and atmospheric pressure, the mean sea level synoptic charts over the Mediterranean Sea every 6 hours from 1968 to 1988 and the wave observations during 1981, 1982, 1985 and 1986. Results indicated the following: 1. Highly significant correlation coefficient between the observed and predicted surges using the newly derived empirical equation obtained in this work. 2. There is a highly significant correlation coefficient between wind waves and the predicted waves using a new empirical formula obtained during this study. 3. Five types of storm surge were identified: A, B, C, D and E. Type A represents the simple case of storm surge (16 cm) and type E has the strongest surge (43 cm).

IP12LL

The variability of nutrients and primary production in coastal waters of the south china sea

A.P. Nedashkovsky and V.I. Zvalinsky

Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, Vladivostok 690041, RUSSIA

During winter 1994–1995 in the South China shelf area near to east coast of Vietnam (18-16ƒN; 107-109ƒE) in the cruise R/V "Professor Bogorov" the distribution of dissolved oxygen, chlorophyll-a, phosphate, nitrate, silicate PO₃^-, NO₃^- (on separate stations was measured ammonium and total nitrogen) was studied.

The average concentrations of nutrients and Chl-a are (in mkmol/1): phosphate ~ 0.84; nitrate ~ 0.42; nitrite ~ 0.08; ammonium ~0.1; organic N~5.5; silicate ~ 9.2; Chl-a ~ 1.4 mkg/1.

From the given data it follows, that for the researched region the ratios N:P:Si = 0.5:1:11 these differ from the Richard-Redfield ratios (16:1:23).

Therefore the primary production in the research zone is limited by nitrogen and the distribution of nitrate concentration is largely determined by biological processes. For this reason, an inverse correlation between vertical distribution of average concentration inorganic nitrogen and % oxygen is observed.

The phosphate and silicate distribution, as a rule, is characterised by the higher contents in the surface horizons and is defined basically by hydrological processes.

The primary production (PP) was estimated: on base of data of the contents of Chl-a (assimilation number ~ 35 mgC/mgChl*d, the effective thickness of the photic layer ~ 25 m) and on base of the oxygen budget. The results of PP, estimated by two ways, are close among themselves and made 0.9 - 1.2 gC/m²*d. Assimilation of the nitrogen, appropriate to given PP, should make about 0.5 mkmol/1*d. A nitrogen budget was constructed: ~ 0.3 mkmol/1*d is compensated for the account destruction Norg, ~ 0.1 mkmol/1*d is transported from below; ~ 0.05 mkmol/1*d acts with river and with coastal flow; disbalance ~0 .15 mkmol/1*d apparently connected with disregarding other forms of nitrogen (eg. ammonium and urea).

IP12mm

IMPACT OF SEA LEVEL RISE ON THE TIDE, STORM SURGE AND PROBABLE HIGHEST WATER LEVEL IN SHANGHAI

Yi-Hong Duan, Zeng-Hao Qin and Yong-Ping Li

Shanghai Typhoon Institute, Shanghai, CHINA

Tides and storm surges, caused by the estimated sea level rises in 2010 and 2030 for the coastal tide-stations in Shanghai, are numerically computed in this paper using a traditional nonlinear 2-D hydrodynamic model with slight revision. Estimation to the probable highest water levels resulting from the sea level rises in 2010 and 2030 are completed as well. It is shown that the coming sea level rise could result in a decrease in storm surges depending upon the track and intensity of the impinging tropical cyclone as well as the geographic location of the tide-station.

The effect of the coming sea level rise on tide oscillates with the period as same as that of the tide. There are no effects of the sea level rise on tide at both high water and low water. Its effect on tide is positive for the duration of rise below the mean sea level, whereas the negative effect occurs for the duration of (ebb) fall. The opposite conclusion holds true in case it occurs below the mean sea level.

The impact of the sea level rise on tide becomes intense when the amplitude of rising sea level increases.

Three intense tropical cyclones impinging Shanghai and its neighborhood, are chosen in computation and intensities of these tropical cyclones are forced to altered hypothetically to ensure that the tropical cyclone case matches the most dangerous storm surges that happened to Shanghai. After nonlinearly matching the most dangerous storm surge with appropriate spring tide, the computational results give the probable highest water levels for Shanghai in 2010 and 2030 respectively to be 745cm and 752cm in the background of the known relative sea level rise estimation done by the present authors elsewhere. These figures seem to be useful to the coastal engineering design in the future for Shanghai harbor. The method suggested may be effectual for other metropolis in dealing with similar situations.

IP12NN

Physical, chemical and biological processes in the East China Sea

Tetsuo Yanagi and Xinyu Guo

Department of Civil & Ocean Engineering, Ehime University, Matsuyama, JAPAN

The East China Sea is one of the most developed shelf seas in the world and much anthropogenic materials including nutrients are supplied from large rivers such as Changjiang and the Yellow River. The primary production rate is very high at 500 mgC.m^-2 day^-1 (Hama.1995). From the box model analysis (Yanagi et al., 1996), organic carbon of 16 mgC m^-2 day^-1 (about 3% of the primary production) is lost from the East China Sea to the Pacific Ocean or sea bottom. Such facts suggest that the East China Sea is a sink for the atmospheric carbon dioxide.

A three-dimensional ecological model is developed to reproduce the physical, chemical and biological processes in the East China Sea and to predict the change of material flux there relative to the global change. The calculation results reproduce well the observed distributions of phytoplankton, zooplankton and detritus in April 1994. The detailed physical, chemical and biological processes which are revealed by this numerical model will be presented.

IP12oo

Oceanographic Conditions near the Spawning Ground of Southern Bluefin Tuna off the Northwest Coast of Australia

Takashige Sugimoto and Hiroshi Matsuura

Ocean Research Institute, University of Tokyo, Japan
Japan Marine Science and Technology Center, Yokosuka City, Japan

Hydrographic surveys and surface current observations using satellite tracked buoys were conducted in winter of 1992-1993 and 1993-1994, near the spawning ground of southern bluefin tuna, Thunnus maccoyii, in the water between Australia and Indonesia to make clear the larval transport environment. Surface geopotential anomalies along the meridional observation line west of Australia showed eastward geostrophic flow. Trajectories of satellite tracked drifting buoys showed meso-scale dominating current with eddies of about 100~300 km in diameter with weak mean westward current which was about 6 cm/s.

Horizontal dispersion coefficients estimated from Lagrangian auto-correlation function increased almost linearly at first and became almost constant at about 3.6x10³m²/s after about 6 days from release. Concentration of particles off the Northwest Cape was computed using simple advection/dispersion model to study the effects of dispersion coefficient and advection speed on the influx rate of the larvae in the upstream of Leeuwin Current.

IP12pp

An inverse model for ocean surface velocities from satellite altimeter and temperature data using a direct minimization approach

John L. Wilkin

CSIRO Division of Marine Research, Hobart, Australia

An inverse model is presented that estimates mesoscale sea surface height and velocity from satellite altimeter, sea surface temperature, and other data. A cost functional is constructed comprising several terms that express the misfit between the solution and data, and other prescribed conditions, including conservation of temperature and relative vorticity, and smoothness. The solution is determined by direct minimization of the cost functional with respect to the sea surface height, and is therefore able to accommodate nonlinear constraints. The relative weighting applied to the terms of the cost functional is determined by evaluating the skill of the inverse solution compared to withheld data. The technique has been used to produce analyses every 10 days, at 25 km resolution, for the Tasman and Coral Seas, using TOPEX/POSEIDON altimeter and AVHRR SST data. ERS-1 altimeter data were used as the independent verifying dataset.

IP12QQ

Variability of current and water property between Mindanao and New Guinea

Yuji Kashino, Hidetoshi Watanabe, Bambang Herunadi, Djoko Hartoyo and Michio Aoyama

Japan Marine Science and Technology Centre, JAPAN
Sanyo Techno Marine Inc., JAPAN,
Badan Pengkajian Dan Penerapan Teknologi, INDONESIA, Meteorological Research Institute, JAPAN

Current and water property variability at the Pacific entrance of the Indonesian throughflow was investigated using mooring data and hydrographic observation data.

Three current meters and one CTD were deployed at 3ƒ-11’N, 128ƒ-27’ E and 4ƒ-1’N, 127ƒ-31’E between Talaud Islands and Morotai Island from February, 1994 to June, 1995. The hydrographic observations were conducted at October, 1992, February, 1994, January, 1995, July, 1995 and June, 1996 in the western boundary area of the equatorial Pacific.

At the both mooring stations, the oscillation with the period of two months was revealed in the current meter and CTD data. In addition, change of current direction and strength was abruptly observed in November 1994 at the southern station (north of Morotai Island). After November 1994, northwestward flow transporting low-salinity water from the North Pacific water was probably advected southward by the anticyclonic eddy (Halmahera eddy) located at 4ƒN, 130ƒE, once, and turned northwestward. This result implies that Halmahera eddy plays some role in controlling the property of water entering into the Indonesian seas.

IP12rr

One Dimensional physical-Biochemical coupled modelling for the Mediterranean sea: Applications to open sea and coastal ecosystems

E. Napolitano, T. Oguz, P. Malanotte-Rizzoli
and M. Ribera d’Alcala

Istituto di Meteorologia e Oceanografia, I.U.N., Napoli, ITALY, Institute of Marine Sciences, M.E.T.U., Erdemli, TURKEY, Department of Earth, Atmospheric and Planetary Sciences, M.I.T., Cambridge, USA
Stazione Zoologica "A. Dohrn", Napoli, ITALY

The main interactions between physical and biochemical processes in two different areas of the Mediterranean sea were studied by a one-dimensional vertically resolved physical-biological upper ocean model, coupled with the Mellor-Yamada level 2.5 turbulence closure scheme. The biochemical model involves interactions between the inorganic nitrogen (nitrate, ammonium), phytoplankton and herbivorous zooplankton biomasses, and detritus. The two areas, the central Mediterranean sea (Sicily channel area) and the Gulf of Naples (Tyrrhenian sea) were chosen in order to study the ecosystem dynamics of two different Mediterranean environments.

A process study was carried out for the central part of the Mediterranean sea. The seasonal structure and dynamics of the mixed layer and the effect of the external forcing variability with idealized forcing functions (monochromatic wind-stress, heat flux and surface salinity) were studied in order to analyse the response of the model under different forcing conditions. The model simulated various local vertical thermal structures observed in the Sicily channel area, in which the different intensity of the wind stress and different heat fluxes play an important role. A series of sensitivity experiments were carried out on a biochemical submodel with these physical conditions in order to study the different responses of the model in different ecological conditions. Vertical advective transport has not been considered and the coupling with the biochemical submodel is through the vertical mixing coefficients.

The Gulf of Naples, an important coastal area of the Mediterranean sea subject to strong environmental alterations, is studied as a coastal application. This area is a wide bay on the west coast of Italy and is strongly linked to off shelf Tyrrhenian waters. The hydrographic characteristics of the gulf are very similar to those in the Tyrrhenian sea, while lower salinity waters are found only in the vicinity of the local freshwater sources. Anomalous high concentrations of nutrients results from land run-off and are observed only in the littoral area. Therefore, two subsystems within the gulf can be identified: a wide oligotrophic area similar to the offshore Tyrrhenian waters, and a narrower eutrophic coastal zone. The one dimensional model has been applied to study the seasonal dynamics of an ecosystem which is controlled by external sources of nutrient rich freshwaters. Therefore, the model was forced by realistic forcing functions including a surface nitrates forcing function constructed from a wide data set from Stazione Zoologica "A. Dohrn" of Naples, which includes five years of biweekly sampling of physical, chemical and biological parameters. In this communication we presented preliminary results obtained by numerical experiments.

IP12tt

Seasonal and Year-to-Year Variations in Throughflow of the Straits of Malacca

Tetsuo Yanagi

Department of Civil and Ocean Engineering, Ehime University, Matsuyama, Japan

Seasonal and year-to-year variations in monthly mean sea level difference between the eastern and western coasts of the Malay peninsula and those of monthly mean sea surface wind in the east, west and south seas of the Malay peninsula are investigated. Sea level difference between the eastern and western coasts is large in boreal winter and at the period of El NiÒo, that is, the throughflow of the Straits of Malacca is considered to be intensified at the period of El NiÒo. It is due to the larger depression of mean sea level along the western coasts than that along the eastern coast by the intensified northwestward wind in the eastern Indian Ocean at the period of El NiÒo.

IP12vv

Diagnosing the mean strength of the Indonesian Throughflow in an Ocean GCM

J.S. Godfrey and Y. Masumoto

CSIRO Division of Oceanography, Hobart, AUSTRALIA
Geophysical Institute, Department of Science, University of Tokyo, Bunkyo-ku, Tokyo, JAPAN

A recent version of the Island Rule is used to diagnose the dynamical processes setting the long-term mean magnitude of the Indonesian Throughflow, in a numerical model. If flow were in perfect Sverdrup balance above the Indonesian sill depth, the Island Rule would suggest a magnitude of 10.6 Sv, for the wind and topography of the model (1 Sv = 10⁶ m³s^-1). The full model value was 9.5 Sv. However, considerable cancellation of terms was involved in producing this apparent near-Sverdrup balance. The largest non-Sverdrup term was due to the fact that there was strong net northward flow across the Pacific at 39ƒS, at the Indonesian sill depth (629 m in this model). This added 3.9 Sv to the estimate based on a "level of no motion" at the sill depth. Pressure differences across New Zealand reduced the northward flow by about 2.0 Sv, while a downward flow of 0.5 Sv throughout the Pacific, through 629 m, further reduced the Throughflow magnitude. Nonlinear and frictional terms along 39ƒS account for the remaining 0.2 Sv.

The flow at 629 m implies a pressure difference across the Pacific at 39ƒS equivalent to a head of 0.058 m of water. We describe results of an approximate analysis along a path up the South American coast, across the equator and down the western Australian coast, to find the dynamical source of this pressure head. This proves to be quite difficult in the Bryan and Cox code, next to the irregular coastal bottom topography.

IP12ww

Long-term Salinity Changes in the Adriatic Sea

M. Morovic and B. Grbec

Institute of Oceanography and Fisheries, Croatia

Salinity fluctuations have been very intense from year to year in the Adriatic. Mediterranean waters permanently enter the Adriatic but in some years this phenomena was intensified and larger amounts of saltier Mediterranean waters reflected upon the higher salinity of the southern and middle Adriatic. The data series for station Stoncica (open middle Adriatic) were analyzed at standard oceanographic depths. Resulting components from the PC analysis of salinity data were compared to the meteorological factors (pressure difference between the northern and the southern Adriatic and water flux in the sea-atmosphere interface) leading to the conclusion that salinity fluctuation in the surface layer (0-20 m) was highly correlated with the E-P and the wind, while the intermediate layer (30-100 m) responded to the pressure gradient between the northern and the southern Adriatic. To describe the advection mechanism additional attention was paid to the pressure field, analysing frequency of cyclones and anti-cyclones locations over the larger area (from 70ƒW-40ƒE and 20ƒN-80ƒN).

From analysis of the salinity field it can be concluded that PCA was successfully applied to these time-series, separating two levels whose salinity properties change due to difference processes. In the surface layer salinity change due to water flux was influenced by the wind e.g. by processes at the air-sea interface. In the intermediate layer, salinity is under considerable influence of horizontal advection. Salinity change in the intermediate layer is highly correlated to horizontal pressure gradient between northern and southern Adriatic. Pressure gradient is influenced by the distribution of cyclone and anticyclone centers over the wide area from Atlantic to Europe. Interannual salinity changes seems to be related to frequency distribution of low and high pressure centers in this area, which enhance dynamics of saltier water advection from the Mediterranean into the Adriatic.

IP12xx

Climatic Changes and their Influence on Oceanographic Properties of the Adriatic Sea

B. Grbec and M. Morovic

Institute of Oceanography and Fisheries, Croatia

In this work the influences of climatic changes and fluctuations are studied. Possible influences of climatic changes on sea surface temperature, sea level and on thermohaline properties in the vertical profile of the middle Adriatic are investigated. Linear trends are determined analysing the low frequency components of monthly mean meteorological and oceanographic data. Basic climatic oscillations were determined for the time series with long oscillating periods. At the secular time scale, significant air pressure and sea level trends amounting to (1.01 ± 0.04) hPa/100 year and (14.4 ± 0.6) cm/100 year respectively, were obtained. Precipitation decreased trend of 109.5 mm/year per 100 year was found. Temperature changes at the secular scale were stationary with a climatic wave period of 121 years. Approximately the same length was found for pressure secular changes while climatic oscillation for precipitation was found for pressure secular changes while climatic oscillation for precipitation was half of the mentioned interval. Mean processes that cause changes of sea-level and temperature at the long-term scale were determined using Principal Component Analysis. Sea level rise at the secular scale cannot be connected to precipitation decreased trend nor to increased pressure trend over the Adriatic, pointing to the global scale causes. The influence of global sea level rise is diminished in the Adriatic due to precipitation decrease. Salinity is influenced by atmospheric input. Due to precipitation decrease and stronger horizontal advection of saltier Mediterranean water, increased salinity can be expected. Temperature increase in the surface layer is not anticipated since there is no additional heating from the atmosphere. Eventual temperature increase in the Mediterranean should influence the temperature of intermediate layer in the Adriatic.

IP12yy

Numerical Simulation of the Anoxic Water Mass in the Southwestern Part of the Seto-Inland Sea, Japan

Atsuhiko Isobe

Dept. Earth System Science and Technology, Kyushu University, JAPAN

The anoxic water mass often appears in the Suo Sea, southwestern part of the Seto Inland Sea, Japan in summer. In this area, anoxic water mass is intensively formed near the coast, where the water depth is less than 10 m. Previous studies (Isobe et al.,1993; Kamizono et al., 1994) show that the generation of the anoxic water mass near the coast results from the large oxygen consumption rate in the bottom water, which is due mainly to the decomposition of the detritus tidally resuspended in situ. We carried out the numerical simulation on the formation of the anoxic water mass in this area. The calculated properties are momentum, temperature/salinity (diagnostically controlled by using the observed values in July, 1991 in which the anoxic water mass remarkably appeared), DIN, DIP, detritus, phytoplankton and dissolved oxygen. Consequently, we could reproduce the anoxic water mass near the coast as we observed. The detritus is gradually accumulated toward the coast due to the resuspension by the tidal current and the estuarine circulation typically developed in coastal ocean in summer. It is considered that detritus resuspending and decomposing intensively near the coast generates local anoxic water mass in Suo Sea.

IP12zz

Simulation of Annual Plankton Productivity Cycle in the Black Sea by a coupled Physical-Biological Model

Temel Oguz, Hugh Ducklow and Paola Malanotte-Rizzoli

Middle East Technical University, Institute of Marine Sciences, Erdemli, Icel, TURKEY
Virginia Institute of Marine Sciences, The College of William and Mary, Gloucester Point, USA
Massachussets Institute of Technology, Earth, Atmospheric and Planetary Sciences, USA

The annual cycle of the plankton dynamics in the central Black Sea is studied by a one-dimensional vertically resolved physical-biological upper ocean model, coupled with the Mellor-Yamada level 2.5 turbulence closure scheme. The biological model involves interactions between the inorganic nitrogen (nitrate, nitrite and ammonium), size-fractionated phytoplankton and zooplankton biomasses, detritus and microbial loop. Given a knowledge of physical forcing, the model simulates main observed seasonal and vertical characteristic features; in particular, formation of the cold intermediate water mass and yearly evolution of the upper layer stratification, the annual cycle of production with the fall and the spring blooms, as well as the subsurface phytoplankton maximum layer in summer. Initiation of the spring bloom is shown to be critically dependent on the water column stability. It commences as soon as the convective mixing process ceases and before the seasonal stratification of surface waters is developed. It is followed by a weaker phytoplankton production at the time of establishment of the seasonal thermocline towards the beginning of May. While summer nutrient concentrations in the mixed layer are low enough to limit production, the layer between the thermocline and the base of the euphotic zone provides sufficient light and nutrient to support the subsurface phytoplankton development. The autumn bloom takes place some time within November and December months; its period of development depends on the environmental conditions. In the case of weak grazing pressure to control the growth rate it is found that, once it commences, relatively high phytoplankton concentrations persist for the whole winter season. The system therefore may possess either a two distinct blooms (spring and fall) or one unified continuous bloom structure during November-to-March depending on variabilities in the oceanographic characteristics. These bloom structures are similar to the year-to-year variabilities present in the data.

IP12aaa

A Simple Box Model of Paleoclimatic Variability in the Japan Sea

F. Suzuki and M. Ikeda

Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan

The analysis of piston core data shows that, in last 60,000 years, the Japan Sea experienced drastic changes: during the last glacier (until 15,000 years ago), the near-surface temperature was lower than the present value by 5-7 degrees. The Sea was extremely freshened (~27 ppt) at the glacier maximum (20,000~18,000 years ago). For a few thousands years after the glacier, the surface temperature and the salinity were similar to those of the Oyashio. Hence, it is suggested that the inflow/outflow reversed: opposite to the present exchange with a warm inflow through Tsushima Strait, a cold inflow occurred through Tsugaru Strait.

A two-box model is employed to investigate this variability. The boxes represent the northern and the southern half domains in the upper (300-m thick) layer. This model is based on Stommel's model, which was driven by atmospheric forcing with different time scales between fast heat flux and slow fresh water flux. The volume exchange between the boxes is proportional to a density difference. A major modification is inflow/outflow; e.g., under the present state, a warm inflow (Tsushima Current) is given to the southern box, while an outflow is taken from the northern box.

The exchange coefficient between the boxes is an uncertain parameter and first determined by matching the solution with the present state. The model is then run for examining the three paleoclimatic states. It is straightforward to reproduce the cold surface layer during the glacier by giving low air temperatures. The fresh surface layer in 20,000~18,000 years ago is attributed to a near shutoff of the inflow due to the low sea level. However, the transition from the glacier to the present state is harder to determine. Here, two possible scenarios are suggested: one is the reversed inflow/outflow that brings the Oyashio into the Sea, and the other is the fresh northern box, which is under the salinity-driven state following the freshened period.

IP12bbb

Monitoring the outflow from the Japan Sea by using a submarine cable across the Tsugaru Strait

Kunio Rikiishi, M. Michigami, T. Araki, K. Shiowaki, R. Eto, K. Taira, and J.C. Larsen

Department of Earth Sciences, Hirosaki University, JAPAN
Ocean Research Institute, University of Tokyo, JAPAN
Pacific Marine Environmental Laboratory, NOAA, USA

The general circulation in Japan Sea is believed to be basically controlled by the inflow and outflow through Tsushima Strait and Tsugaru Strait, respectively. In order to monitor the outflow from Japan Sea to Pacific (Tsugaru Warm Current), differences of electrical potential across the Tsugaru Strait have been measured by using a submarine cable for more than two years. This is because the motion of the sea water, in the earth's magnetic fields, induces a cross-stream voltage proportional to the volume transport of the ocean current. The voltages across the Tsugaru Strait are measured at about 5 second intervals, and their 10 minute averages are transmitted automatically via the commercial telephone line to a hard disk of a personal computer at the remote laboratory. The geomagnetism is also measured to check the influence of geomagnetic variation on the electrical potential.

The measured voltages have been compared dynamically with the sea level differences both in the cross-stream and along-stream directions. It has been found that the voltages and the sea level differences are dynamically in good balance both for the tidal and ocean current components. As for the ocean current component, however, disagreements are sometimes seen when the sea levels are affected significantly by strong winds. The voltages have also been compared with the volume transports observed by using ADCP during March 14-15 and September 21-24 of 1995. A clear linear relation has again been shown, with a voltage of 100 mv corresponding to a volume transport of 1.5 Sv.

ip12ccc

Interannual Variability of the Seasonal Coastal Upwelling in the Caspian Sea

V.S. Arkhipkin and A.N. Kosarev

Department of Oceanology, Moscow State University,
Moscow, RUSSIA

A strong seasonal upwelling along the eastern coast of the Middle Caspian is formed in the summer period. The present analysis of coastal upwelling was done on the basis of hydrometeorological observations at a number of shore stations over 60 years. The spectral analysis of the average months water temperature for August shows the presence of oscillations with periods 2-3, 4-5 and 10-12 years. The energy of oscillations increases with the growth of oscillations' period. It is shown also that the energy of oscillations for the alongshore wind speed in the synoptic scale is much more in the years with very low average months temperature than in the other years. The presence of clearly distinguished interannual oscillations of the average months water temperature near the eastern coast of the Middle Caspian deals with the efficient action on the sea by the large-scale atmospheric fluctuations that produces in common action of the local physico-geographical factors and prevailing wind field.

IP12ddd

Edge waves and their effect on sediments on the Sydney coast

Bradley D. Morris and Jason H. Middleton

Oceanography, School of Mathematics, University of New South Wales, Sydney, Australia

Edge waves are well known for their effects on sediment distribution inside the surf zone. Less well understood are their effect on sediments in deeper water well outside the surf zone.

Observations of stationary sand lobes in the relatively straight cliff lined coast between Bondi and South Head in the Sydney region have prompted questions concerning their continued presence. Previous studies have indicated the presence of edge waves in the Sydney region, and the present observational and theoretical study is designed to test the hypothesis that the sand lobe distribution is related to edge wave current fields.

Edge wave theory was used along with real bottom topography to determine expected dispersion relations and velocity fields for the study area. An experimental array of current meters was deployed in July 1996 using this knowledge.

A brief overview of the theory is given and some of the results from this field work are discussed. Field data is compared to edge wave theory using various frequency and time domain methods. The apparent coupling between the energy in the infragravity band of the spectra with the energy in the wind wave band of the spectra is discussed as is the relation between calculated standing edge wave spatial scales and the spatial scales of the sediment distribution in the study region .

IP12eee

MODELING the ANOXIC CONDITION FORMATION AND ESTIMATING THE DENITRIFICATION RATE OF THE BLACK SEA

Evgeniy V. Yakushev

Shirshov Institute of Oceanology, Moscow, Russia

The investigations of anoxic conditions in natural waters appears to be very significant because these conditions can be formed by natural and by anthropogenic ways, as a result of local ecological catastrophes. The Black Sea is characterised by the largest in the world anoxic zone of natural origin and has also local regions, where hydrogen sulphide waters form by anthropogenic way. The one-dimensional model describing nitrogen, manganese and sulphur cycles in suboxic and anoxic conditions is considered. The modelled vertical distributions of nitrogen compounds (total organic nitrogen, ammonium, nitrate, nitrite), dissolved and particulate manganese and inorganic reduced sulphur compounds (hydrogen sulphide, elemental sulphur, thiosulphate, sulphate) as well as dissolved oxygen adequately correspond to the observed situation. The model takes into account the processes of turbulent diffusion, sedimentation and biogeochemical transformation of compounds. On the base of the model it was demonstrated, that the anoxic and suboxic conditions form because of organic matter mineralisation in condition of restricted oxygen influx. The vertical distribution of rates of sulphur and nitrogen cycles processes were calculated within the frames of the model. According to model the total for the Black Sea amount of gaseous nitrogen formation connected with denitrification equals 1 Tg N/yr. The share of the Black Sea in the global process of N₂ production in the World Ocean (120 Tg/year [Codispoti et al., 1985]), is about 1%. The model rate of this process - 0.11 mol/day per square meter - can be typical for the regions, where anoxic conditions take place.

IP12ggg

Comparison of the in situ ADCP measurements and Satellite Image derived Currents of the Mesoscale Eddies in the East (Japan) Sea

Young Jae Ro and Alexander Kazansky,

Department of Oceanography, Chungnam National University, Taejon, Korea
Institute for Automation and Control Processes, Vladivostok, Russia

Mesoscale eddy activities are understood to play a vital role in the East (Japan) Sea hydrography. Mesoscale eddies are being generated in the various areas near polar front as well as coastal front around Ulleung Island in the East Sea. Satellite images are particularly useful in detecting these eddies and following those in time sequence. However, few studies have been attempted to use these image data to define the surface current field. We estimate the current vectors using time sequential satellite images and validate those estimates with in situ ADCP and CTD measurements.

Manual tracking is employed to define visible objects on the AVHRR images and follow those by estimating their translational and rotational speed in time frames. In validating our estimates of the current vectors (sdcv), we develop the appropriate scheme, namely synoptic approach between in situ ADCP data and sdcv. We will show five pairs of AVHRR images for the period of Apr. 3, 1993 to Apr. 16, 1993 which contain remarkable eddies in two locations and the results of the estimated current vectors.

We will present various statistics of eddy parameters such as size of eddy, axis direction, rotational speed based on the estimates from two data sets. In conclusion, we have obtained agreeable comparison between sdcv and in situ ADCP measurements and thus will expand our efforts to apply the technique to all available sets of satellite images to get the statistics of the mesoscale eddies in the East Sea.

IP12hhh

An integrated and multiscale approach of the Mediterranean Sea

Andre Monaco

University of Perpignan, CNRS URA, Perpignan, FRANCE

The aim of the Mediterranean Targeted Project (Marine Science and Technology programme of the European Commission) is to study the functioning of the Regional Sea with a strong multidisciplinary approach considering physical, chemical and biological processes.

The MATER project which stands for Mass Transfer and Ecosystem Response proposes : i) to study and quantify the triggering and controlling processes of mass and energy transfer (transport and transformation) between the different compartments (land-sea, sea-atmosphere, water-sediment, living-non living, pelagos-benthos) and in contrasting environments (from eutrophic to oligotrophic), ii) to appraise the time and space scales of the phenomena in identified physical structures of the system, iii) to investigate the ecosystem response to these transfers and its evolution with time as recorded in the water masses, in the biological communities and in the sediments.

The climatic sensitivity of the Mediterranean Sea, due to its critical latitudinal situation between the arid North Africa and the temperate European mainland records long and short term changes, both natural and man-induced.

Among the various studies performed during the project pilot-phase (MTP I) and the starting MTP II phase, those dedicated to the complex processes controlling the particle fluxes will be presented in order to: - investigate the relationship between downward fluxes and water mass dynamics and surface productivity, - test the effect of external forcing (climate) on biogeochemical compounds and temporal variability, - draw up quantitative mass budgets of key biogeochemicals in representative hydrographical systems.

IP12iii

Examining Mesoscale Circulation and Biological Distributions at the Almeria-Oran Front.

J.T. Allen , A. Corzo, S. Alderson, S. Ruiz, S. Fielding,
N. Crisp, V. Hart, C. Garcia, F. Jimenez-Gomez,
P. Cipollini and J. Schwarz

Southampton Oceanography Centre, Empress Dock,
Southampton, UK
Universitat de Cadiz, Institut de CiËncies del Mar,
Barcelona, SPAIN
Universitat de Malaga, SPAIN

During the observational phase of OMEGA, an EU funded project under the MAST programme, high resolution hydrographic and current profiling measurements to 350 m water depth were made at the eastern end of the Alboran Sea. Here, upwelled Modified Atlantic Water along the Spanish coast and the variability of a second 'eastern' Alboran gyre form a complex frontal zone between the Alboran Sea and the rest of the western Mediterranean Sea known as the Almeria-Oran Front. Instability of this front to perturbations at the mesoscale (10-100 km) is clearly visible in satellite IR images. Additionally, there are large horizontal variations in stratification below the halocline and T/S profiles indicate a recirculation/transport of water from the east. Optical, acoustic and direct sampling techniques were used to observe and quantify biological distributions both at the surface and in vertical profile to over 350 m. For the first time we can combine an almost continuous size spectrum of biological activity from dissolved organic material to shrimps and small fish a few cms in length with simultaneous physical data at similar temporal and spatial resolutions.

IP12jjj

Numerical Investigation on Internal Tides in the Eastern Indonesian Seas and Their Effect on the Modification of the Throughflow Water

Takaki Hatayama, Toshiyuki Awaji, Tomohiro Nakamura
and Kazunori Akitomo

Department of Geophysics, Kyoto University, JAPAN

It has been thought that vertical mixing enhanced by tides in the Indonesian Seas affects the regional and global ocean circulations (e.g., Ffield and Gordon, 1996; Godfrey, 1996). Past studies suggested that this mixing process is likely due to the breaking of internal waves generated through strong tidal interactions with sloping bottom topography. However, little is known about the detailed physical processes. Thus, to identify the time-dependent behaviours of internal tides in the Indonesian seas and their effect on vertical mixing responsible for modification of the Indonesian throughflow water properties, we have performed numerical experiments using the 2-dimensional non-hydrostatic model, in which we focus on the region around the Manipa Strait with sill-shaped topography between the Seram and Banda Seas. With the barotropic M2 current simulated by Hatayama et al.(1996) as forcing for internal waves, a time series of the velocity, temperature and salinity fields are calculated. The prominent feature is that, as barotropic tidal flow becomes strongest, a hydraulic-like current structure accompanying a large isopycnal depression appears in the downslope portion of the sill despite the presence of the subcritical condition in terms of the conventional Froude number (Fr=U/C<1). This phenomenon cannot be explained by the steady hydraulic theory. Close examination revealed that non-linear tidal interactions with an abrupt topographic change can cause the hydraulic-like transition from a barotropic flow upstream to a baroclinic flow downstream through the generation of bottom intensified currents, basically similar to the result by Kuroda and Mitsudera (1995). Thus, this is a transient phenomenon. As tidal flow slackens, the hydraulic jump is formed, subsequently evolving into a travelling internal bore. This bore grows mainly by an intensive internal beam along the critical slope, eventually leading to its partial breaking. These processes can produce a high vertical diffusion of the order of 100 cm²/s, probably enough to considerably reduce the salinity maximum of the incoming throughflow water. Further, when a steady shear flow in the upper 300 m that simplifies the vertical profile of the throughflow is added, the Kelvin-Helmholtz instability occurs around the lower thermocline, promoting vertical mixing much more to such an extent as almost loss of the salinity maximum of the throughflow water observed in the Banda Sea.

IP12kkk

The Eastward Extension of the South Java Current in December, 1995

W.M.L. Morawitz, N.A. Bray, A.G. Ilahude, S. Hautala,
J. Chong and W. Pandoe

Center for Coastal Studies/Scripps Institution of Oceanography,
La Jolla, USA
Indonesian Institute of Science, Jakarta, INDONESIA
University of Washington, Seattle, WA, USA
BPP Teknologi, Jakarta, INDONESIA

Towed ADCP and CTD data from a cruise aboard the Indonesian R/V Baruna Jaya 1 in December of 1995, showed an energetic extension of the South Java Current (SJC) as far east as Sumba Strait, well east of Lombok Strait. Over the top 100 to 150 m of the water column, the current was observed to be eastward at 0.5 to 1.5 m/s along the Indian Ocean boundary of the Indonesian Archipelago, and northward at comparable speeds through Lombok, Alas and Sape Straits. The watermass characteristics of the extension were similar to those found in the Java Sea. The observed pattern of near-surface flow in the eastern archipelago in the December survey is opposite to the direction expected for the throughflow. The extension of the SJC did not extend as far east as Timor Passage. In addition, the eastward-flowing waters are significantly fresher and colder than the throughflow. The temperature/salinity structure of the eastward and westward flowing water is quite distinct: the westward-flowing water has canonical throughflow characteristics, while the eastward-flowing water is typical of the Java Sea. This implies that the SJC may extend much farther east than is reported in the literature, at least during its November maximum, and that it provides an efficient mechanism for transporting very low-salinity water out of the Java Sea, through Sunda Strait and into the eastern part of the archipelago along the southern coast of Java and Nusa Tenggara. The pattern of flow we observe in December is consistent with drifters deployed by Michida and Yoritaka [1996]. In contrast to the near-surface pattern, the velocity from 200-300 m looks much more like the expected throughflow: there is southward flow through Lombok Strait, and westward flow through Timor Passage.

IP12lll

Late Pleistocene - Holocene paleoproductivity circulation in the Japan Sea: Sea-level control on carbon and nitrogen isotope records of sediment organics.

Koji Minoura and Koichi Hoshino

Institute of Geology and Paleontology, Faculty of Science,
Tohoku University, Sendai, Miyagi, JAPAN.

Organic carbon and total nitrogen contents and their isotope ratios were determined in a sediment core recovered from the Japan Sea to investigate the record of organic matter resources and paleoproductivity in a semi-closed marginal sea. d ¹³C-d ¹⁵N relationships show that the composition of sediment organics resulted from the mixing of terrestrial and marine organic matter. We found synchronous down-core variations in the carbon and nitrogen isotope records, which are explained by surface productivity control on the composition of sediment organics. Moreover, these variations are related to sea level changes, which caused variable surface water inflows.

Last-glacial sea-level lowering increased continental runoff, leading to water-column stratification in the Japan Sea. Anaerobic conditions due to basin-water stagnation led to the deposition of laminated clay. Sediment organic C/N and isotope ratios fluctuated markedly in the transitional stage from aerobic to anaerobic conditions. The fluctuations are likely to have been caused by large-scale oscillations in sea level just before the last glacial maximum.

IP12mmm

Tidal Exchange and Mixing At the Kuril Islands

Tomohiro Nakamura, Toshiyuki Awaji, Takaki Hatayama
and Kazunori Akitomo

Department of Geophysics, Kyoto University, JAPAN

It is of great importance to clarify the transport and modification processes of the waters around the Kuril Straits between the Okhotsk Sea and the North Pacific, because these processes are indispensable for the formation of low salinity Oyashio Water and hence the Okhotsk Sea could be the source of the North Pacific Intermediate Water (NPIW), e.g. Talley (1991). Since past studies strongly suggested that tidal activities there must be responsible for these processes, so we have investigated the tides and tidal currents around the Kuril Straits and their effect on transport and mixing through the following numerical experiments. First, the barotropic K1 and M2 fields are simulated with our regional model. The calculated harmonic constants of the K1 and M2 tides agree well with extensive tide gauge observations below the mean rms errors of 6.75 cm. Essentially, the predominant component K1 is forced by cyclonic propagation of the tidal wave along the coast passing through the northern Straits from the North Pacific. The peak velocity near the Kuril Straits exceeds 1.5 m/s. Consequently, tidal rectification over variable topography there induces significant bi-directional mean flows through the Straits, producing the total mean outflow of about 5.0 Sv towards the North Pacific primarily via the Bussol', Kruzenshterna and Chetvertty Straits. This value is basically similar to the net transport of the NPIW reported by Talley et al. (1995). Next, the behaviours of internal waves generated by interactions of the predominant K1 tidal current with sill-shaped topography are studied to identify the role played by the internal waves in transport and mixing around the Kuril Straits, using the 2-dimensional non-hydrostatic model. The result shows that intense internal waves are confined to the limited region nearby the sill because the Kuril Straits are located over the critical latitude for K1. Such confinement of the wave energy around the sill eventually leads to the breaking of large-amplitude internal waves, causing a high vertical diffusion corresponding to 10²cm²/s. This strong vertical mixing can produce low salinity water observed in the Bussol' Strait regarded as the major entrance of the NPIW to the North Pacific.

IP12nnn

Is the Mediterranean Sea a Coastal Ocean?

M. Ribera d’Alcalý, V. Saggiomo, A. Bergamasco,
G. Civitarese, A. Luchetta and F. Conversano

Stazione Zoologica, Napoli, Italy
CNR-Istituto per lo Studio delle Grandi Masse, Venezia, Italy
CNR-Istituto Talassografico di Trieste, Trieste, Italy
Istituto di Scienze Ambientali, Universitý di Genova, Genova, Italy

The Mediterranean Sea is certainly the most known among the semi-enclosed basins of the global ocean and, very likely, one of the most investigated. Yet, some of the intriguing aspects of its functioning remain largely unexplored. The larger of its two main basins, the Eastern one, is the only oceanic region where P limitation has been convincingly demonstrated to occur in anticyclonic gyres, at least for a part of the year, where recent (thousand years) anoxia episodes took place, thus following a different history than the Western basin, where internal deep water formation, which is in any case a peculiarity for mid-latitudinal seas, occurs in marginal seas , and not within the main basin, where an anthropogenic action, such as the Nile damming, has been shown to affect significantly and at the scale of the basin a basic property like salinity.

By contrast the Western basin follows more familiar schemes with a more evident seasonality, dense water formation in the interior of the main basin, absence of marginal seas, etc. Yet, from a bio-geochemical point of view the Western Mediterranean resembles more the Eastern one than the open ocean. The turnover time of Mediterranean deep water masses is 0.5 to 1 order of magnitude faster that the open ocean ones, it has a larger boundary-to-volume ratio which makes the basin more affected by terrestrial contributions, particularly considering the dominant role of internal thermohaline cells as compared with the external one.

By contrast the basin can be ranked in the oligotrophic range, the shelf area, with the exception of the Adriatic Sea (a marginal sea) and the Sicily Channel and surrounding regions, is quite restricted as compared with the surface of the basin and for many aspects, large regions, such as the Ionian sea, display strong similarities with corresponding areas of oceanic basins. Because of the cooperative effort of man