IP5a
Biogeochemical Cycling of Nutrients in the Estuarine and Shelf Regions of Godavari River (Bay of Bengal)
D. Satyanarayana, D. Padmarathi and K. Srinivas
Chemical Oceanography Division, School of Chemistry, Andhra University, India
The distribution of nutrients in the estuarine region of
Godavari and its adjoining shelf region of the Bay of Bengal
(Lat: 160’ - 1720’N and Long: 8130’ -
8230’E) has been studied over a period of one year in
premonsoon (March-May), Monsoon (June-November) and postmonsoon
(December-February) seasons. Silicon (SiO4-Si) and
Ammonium (NH4-N) exhibited distinct non-conservative
behaviour with a net removal of 8-27% and 12-26% respectively,
while Nitrate (NO3-N) and Phosphate (PO4-P)
showed semi-conservative behaviour in the estuary. This is
attributed to their biological uptake by diatoms and
phytoplankton. The overall nutrient/chlorinity ratios computed
are in the range NO3-N=0.140±0.01, NH4-N=0.142±0.005,
PO4-P=0.116±0.005 and SiO4-Si=2.17±0.18
(x 10-5) respectively in the chlorinity range 15-19x10-3.
Based on the average annual river discharge and the concentration
of nutrients at zero salinity, the net flux of nutrients are
estimated as 0.39, 0.88, 0.83 and 17.3 x (1010) g.y-1
for NO3-N, NH4-N, PO4-P and SiO4-Si
respectively.
Nutrients exhibited distinct temporal and spatial variations in estuarine and coastal waters. For example, they showed a decreasing trend from riverine and estuarine and shelf regions indicating their predominant occurrence with fresh water. Further, they recorded an increasing trend from surface (0m) to the bottom (50m) indicating their utilisation by phytoplankton in the surface and their remineralisation in the water column. Nutrients in general, showed enrichment in monsoon/post-monsoon seasons due to dominant fresh water influx and depletion in pre-monsoon season due to their relatively high utilisation in photosynthesis. Distinct spatial and temporal variations are also observed in the particulate (POC, PON and POP) and sedimentary (OC, TN and TP) constituents.
Nutrients exhibited distinct diurnal variations. For example, they showed an increasing trend (particularly evident with SiO4-Si) during ebb tide reaching maximum at lowest low tide period, and a decreasing trend during flood tide reaching minimum at the highest high tide period both at the head and the mouth of the estuary in all the seasons which are attributed to the variation in fresh water and sea water proportions during a tidal cycle.
The biogeochemical cycling of nutrients in the estuarine region of Godavari river and its adjoining shelf region (Bay of Bengal) is discussed in detail based on their distribution and temporal and spatial variations in water, particular matter and sediments.
IP5b
Biochemical cycles of hydrocarbons (aliphatic and pah) in the coastal regions of the okhotsk and bering seas (distribution, transport, mobile forms)
Nemirovskaya, Inna
P. P. Shirshov Institute of Oceanography RAS, Moscow, RUSSIA
Data are presented on the concentrations and composition of aliphatic hydrocarbons (HC), normal and branch alkanes, polycyclic aromatic hydrocarbons (PAH) in the surface microlayer, water column, the surface layer of the bottom sediments and the biota of the southern Bering Sea and coastal regions of the Okhotsk Sea (near the Kurily Islands, the East Okhotsk Sea shelf, the Sakhalin Bay and the North-East Sakhalin Island shelf).
Our study assesses hydrocarbon levels and distributions; sources, including biogenic, anthropogenic and natural seepage, and potential pathways of HC transport. Sediments from the Sakhalin Islands shelf (100 samples) contain marine autochtonous HC (41%,) terrestrial allochthonous HC (40%) and petroleum HC from natural seepage (19%) An accounting was also conducted of the contents of mobile forms of aliphatic HC.
IP5C
MANGANESE FROM MID OCEAN RIDGES: A PARTICLE REACTIVE TRACER IN THE DEEP SEA
J. Segschneider and E. Maier-Reimer
Max-Planck-Institute for Meteorology, Hamburg, Germany
Manganese is injected into the deep ocean by hydrothermal vents along the mid oceanic ridges. The source strength can be quantified as the spreading rates of the oceanic ridges are known as well as the relationship between hydrothermal manganese concentrations with those of injected mantle helium. In contrast to mantle helium, manganese is particle reactive and thus scavenged from the water column by microorganisms and marine snow. Here, a numerical experiment is described in which the spreading of hydrothermal manganese by advection and diffusion as well as scavenging by biogenic particles is investigated. An annual outflux of 1010 kg manganese from a mid ocean ridge source is advected with OGCM currents by means of a Lagrangian transport model. Biogenic particle fluxes are computed with a global carbon cycle model and the adsorbtion rate of manganese onto the particles are prescribed.
The model was run for 1000 years. In the final year, bottom concentrations were determined. The comparison of these concentrations with observations show, that the distribution is to first order determined by the spreading rates.
ip5e
sinking particle flux and the related P CO2 change in the central pacific
Hodaka Kawahata, Atsushi Suzuki and Hidekazy Ohta
Maine Geology Department, Geological Survey
of Japan,
Tsukuba-higashi, JAPAN
Kansai Environmental Engineering Centre, Osaka, JAPAN
Export production plays an important role in the interaction of carbon transfer between the ocean and the atmosphere. Few data on sinking particles have been reported from the open sea of the Central Pacific. Here we present the results on sinking particles collected with six moorings of sediment traps which were deployed along 175 E. The sites were located at 0 N, 8 N, 30 N, 34 N (178 E), 37.5 N and 46 N respectively. Surface water in the Central Pacific can be classified into four zones. The first one is the equatorial region, second the subtropical gyre, third the Kuroshio extension and lastly the subarctic region. Sediment trap experiments suggest an organic carbon export flux of 19 mgC m-2 day-1 from the equatorial region (0 N and 8 N), 28 mgC m-2 day-1 from the subtropical gyre (30 N), 46 mgC m-2 day-1 from the Kuroshio extension (34 N and 37.5 N) and 79 mgC m-2 day-1 from the subarctic region (46 N).
Carbon cycling in the ocean is often affected by the fluxes and composition of primary producers, the settling of particulate organic carbon decreases the total carbon dioxide and partial pressure of CO2 (PCO2) of the surface layers, whereas the production of carbonate from surface waters raises PCO2 by shifting the carbonate ion equilibria. Therefore, export flux as well as differences in the initial production Corg/Ccarbonate ratio can effect significant variation in PCO2 in the surface water. The measurement of PCO2 in the surface water was carried out from 0 N to 8 N in May 1992 and from 8 N to 48 N in May 1993. Surface water PCO2 values were smaller than the atmospheric pCO2 between 0 N and 48 N. Especially the difference between the PCO2 of the surface ocean and the atmospheric pCO2 was the largest between 30 N and 40 N. The maximum PCO2 difference was more than 50 ΅atm. These features indicate large net transfer of CO2 from the atmosphere to the surface seawater in the middle latitude. The high export flux of organic carbon in the sinking particles was substantially responsible for removal of CO2 from the surface water in the middle latitude in the late spring of the Central Pacific.
IP5f
The Variations of the Radium-226 Concentration in the Waters of the Pacific
Mikhail Domanov, Nikolay Surin, Aleksandr Permyakov and Elena Vodyanaay
P.P.Shirshov Institute of Oceanology Russian Academy of Sciences, Moscow, Russia
The Radium-226 concentration was measured in the waters of the West Pacific ( 35N - 0) across the oceanic hydrological fronts and in the equatorial pelagic water of the central part of the Pacific. The meso-scale variations are discussed. It is shown that variations in the surface water can be caused by biogeochemical extraction of Radium-226 from the surface layer in quasistationary macrocirculation systems and expresses the zonal distribution of primary production. Vertical distribution of Radium-226 in the photosynthetic layer (0-150 m) and in the system of the equatorial contercurrent (Cromwell current) will also be discussed.
IP5g
THE PHYSICO-CHEMICAL MODELING OF THE URANIUM BEHAVIOUR IN DIFFERENT NATURAL ENVIRONMENTS
Lev M. Gramm-Osipova and Valentina N. Gramm-Osipova
Pacific Oceanological Institute, Far Eastern
Branch,
Russian Academy of Sciences, Vladivostok, RUSSIA
Far Eastern State University, Vladivostok, RUSSIA
The investigation of radioactive pollution is very important. Uranium is a natural radioactive element, which is widely distributed in the natural environment. In what physico-chemical form migrates this element in natural waters, as it behaves in various physico-chemical conditions? These questions represent significant interest study of radioactive pollution on an environment. To answer these questions the physico-chemical modeling of behaviour of uranium in sea water zone of mixture river and sea waters, and also behaviour of uranium under influence of hydrogen sulphide infection was carried out. The modeling was carried out by computer programs WATEQ4F and SELECTOR-S. Results of modeling have shown, that in sea water the main forms of uranium are ions UO2(CO3)2-2 and UO2(CO3)3-4. At pH7.5 amount UO2(CO3)2-2 makes 25.5 %, and UO2(CO3)3-4- 64.2 %, at increase pH up to 8.5 quantity UO2(CO3)2-2 decreases up to 5.2 %, and UO2(CO3)3-4is increased up to 94.6 %. The behaviour of uranium in a zone of mixture of river and sea waters was carried out in estuarine zone of the river Razdol'naja and the Amur Gulf (The Sea of Japan). It is established, that in the waters with salinity till 2.31%. of the prevailing form of uranium is an ion UO2 (HPO4)2- 2, in waters with salinity 4.21-24.74 %. ions UO2(CO3)2-2 and UO2(CO3)3-4prevail. Under a conditions of hydrogen sulphide infection a prevailing role of ions UO2(CO3)2-2 and UO2(CO3)3-4 is saved, but at Eh =3D 0.053V the ion UO2+ appears, and at Eh=3D-0.237V the ion U(OH)+3 appears also. Physico-chemical modeling carried out by us predicts behaviour of uranium in natural environment, so as to organize more effective struggle for prevention of radioactive pollution.
ip5h
th-234 scavenging and particle export fromthe upper arabian sea: jgofs results
M.M Sarin, R. Rengarajan and V. Ramaswamy
Physical Research Laboratory, Ahmedabad,
INDIA
National Institute of Oceanography, Goa, INDIA
The removal of dissolved Th-234 from seawater by adsorption onto sinking particles is an important mechanism controlling its spatial distribution which can be used to study the processes of chemical scavenging, particle export and new production in the ocean. In this context, spatial and temporal distribution of dissolved and particulate Th-234 activities have been measured in the central-eastern Arabian Sea during the winter (February-March), inter-monsoon (April-May) and monsoon (July-August) cruises of the JGOFS (India) programme.
At all stations, marked deficiencies of both dissolved and total (dissolved + particulate) Th-234 exist relative to U-238 in the mixed layer but secular equilibrium with respect to total Th-234 activity is attained at depths below 100 m. Modelling of this Th-234 : U-238 disequilibrium yields a mean residence time of a few weeks for dissolved Th-234 with respect to particle scavenging in the upper 100 m. The spatial distribution of total Th-234 has been used to estimate the flux of particulate Th-234 out of the surface layer down to 100 m. The predicted Th-234 export flux (at open ocean sites) ranges between 1250 to 2170 dpm/m2/d with enhanced export occurring over the northern Arabian Sea: a region characterized by higher rates of Primary Production. However, the particulate Th-234 export rates do not change significantly between the winter and inter-monsoon. Using this export flux and the measured specific activity of Th-234 and C/Th-234 ratio in the sinking particles (collected by free-floating traps) from the upper 100 m, the magnitude of particulate matter and carbon export has been determined for this region. The calculated export flux of particulates varies spatially and temporally in the central Arabian Sea, ranging from 725 to 3280 mg/m2/d. In general, the trap fluxes are lower than those derived from the water column data. These results suggest that sampling by the floating traps (deployed for 3-5 days) may not be representative of the sinking particulate pool in the Arabian Sea.
IP5I
ANThROPOGENIC CO2 IN THE INTERMEDIATE WATER OF THE NORTHWEST PACIFIC
Andrey G. Andreev, Igor A. Zabin and Alexandr S. Bychkov
Pacific Oceanological Institute Far Eastern
Branch
Russian Academy of Sciences, Vladivostok, RUSSIA
PICES Secretariat, c/o IOS, Sidney, CANADA
World ocean used to be considered as the main sink for the anthropogenic CO2. Due to the lack of the deep and bottom water formation in the North Pacific, the penetration depth of the chemical tracers such as freons, tritium, anthropogenic CO2, etc. is limited by the lower boundary of the intermediate layer. The northwest Pacific, including the marginal seas, is generally believed to be a region where the transformation of intermediate water characteristics occurs. The anthropogenic CO2 concentrations in the northwest Pacific were calculated based on observations of temperature, salinity, carbonate parameters and oxygen from the joint Canada-Russian expeditions aboard the R/V Akademik A.Vinogradov in April-May 1991 (cruise AV19) and in August 1992 (AV23). Discussion dwelt on the vertical profiles and the anthropogenic CO2 distribution on isopycnal surfaces in the different structural zones of the intermediate water. The surface of 27.6 sigma-theta with zero concentration of the anthropogenic CO2 was chosen as a reference to determine the anthropogenic CO2 concentration on the isopycnal surfaces of 26.8, 27.2 and 27.4-.5 sigma-theta. The data analysis in the layer of 26.8-27.5 sigma-theta of the study area suggests that linear relations exist between anthropogenic CO2 and freons concentrations and salinity; in the layer of 27.2-27.5 sigma-theta the most "fresh" waters with high freons and anthropogenic CO2 concentrations are located in the Bussol' Strait; from the subarctic to subtropic zone the increase in salinity of the intermediate layer is accompanied by a decrease of freons and anthropogenic CO2 concentrations a result of isopycnal and diapycnal mixing; The difference in the intermediate layer between the anthropogenic CO2 vertical profiles from GEOSECS expedition (1973) and recent observations (1991) let us qualify the role of advection, lateral and vertical mixing in the anthropogenic CO2 distribution in the subarctic and subtropical zones of the northwest Pacfic.
IP5j
Application of Isotope Tracers to Study
ocean circulation. Validation of numerical simulations against
observed Chernobyl
137Cs and 90Sr
data
Joanna Staneva, Ken Buesseler, Emil Stanev
and Hugh Livingston
Department of Meteorology and Geophysics,
University of Sofia, Sofia, Bulgaria
National Science Foundation, Ocean Sciences Division,
Arlington, USA
Isotope techniques have contributed greatly to the progress of marine environmental studies, and in particular to better understanding of fundamental oceanographic processes, distribution of pollutants, reconstruction of past and prediction of future states of the ocean. The distribution of artificial radionuclides, 137Cs and 90Sr, is used in this paper to investigate mixing and ventilation in the Black Sea. Samples were collected between 1986 and 1992. The time-series of vertical radionuclide data are used to follow the magnitude and depth of penetration of surface oxic water into intermediate depths, below the oxic/anoxic interface. A tracer model is coupled to 3-D Black Sea circulation model. Three radioactive tracers are considered: pre-Chernobyl 137Cs (weapon testing 137Cs); Chernobyl 137Cs, and 90Sr. Initial data are constructed using experimentally derived data for radionuclides. The main output from the simulations is the identification of the contribution of different processes (diffusion, entrainment, transport) in the formation of radioactive pollution of the Black Sea. The trend of tracers to penetrate into the deep layers following the isopycnic surfaces, which is a major characteristic of the Black Sea circulation, is well demonstrated in the model. The correlation between the activities of radionuclides and salinity, found in the experimental data, is supported in the simulations. This independent estimate proves that the analysis of the fate of tracers, made against isopycnic depths, or salinity, is consistent with the Black Sea physics. Model results illustrate that the time-space abundance of experiment data, which seems not to be always sufficient for mapping purposes, is quite good for reliable estimates of the penetration rates of radionuclides into the intermediate and deep layers.
IP5n
The CO2 system and carbon cycle in the lagoon water of the Great Barrier Reef
Atsushi Suzuki, Hodaka Kawahata, Koichi Goto and Tenshi Ayukai
Marine Geology Dept, Geological Survey of
Japan, Tsukuba, Ibaraki, Japan
Graduate School of Science, Tohoku University, Sendai, Japan
Kansai Environmental Eng. Center Co., Ltd., Osaka, Japan
Australian Institute of Marine Science, Queensland, Australia
The carbon cycle of coral reefs and its effect on the surrounding ocean have drawn considerable attention. However, few direct measurements of CO2 system parameters have been conducted for large scale (> 500 km) reef systems. Parameters of the CO2 system in the lagoon water of the Great Barrier Reef (GBR) were examined in order to ascertain the net effect of reef and lagoon systems on air-sea CO2 exchange. A survey was carried out during the R/V Hakurei-maru cruise in May, 1996, corresponding to the austral winter and the dry season of the GBR area.
The lagoon water in the GBR showed wide variations in temperature and salinity. Generally, the sea surface temperature in the lagoon was lower than that in the offshore area, probably due to its shallow depth and surface cooling. Salinity in the surface water changed locally and appeared to be well correlated with local precipitation and freshwater runoff. Lagoon salinity was higher than offshore salinity in the Central Section of the GBR off Townsville, whereas salinity in the Cairns Section was lower than the offshore values. The effect of precipitation and freshwater runoff on the lagoon water was also seen as an increase in sea surface DOC concentration.
The fugacity of CO2 in seawater (fCO2) in the lagoon water and the offshore water ranged between 335-350 ΅atm and 320-330 ΅atm, respectively. The fCO2 in the atmosphere over this area averaged 360 ΅atm. Therefore, these regions could be expected to act as potential sinks of atmospheric CO2 overall. However, the fCO2 in the GBR lagoon was significantly higher compared to the offshore values. This relative increase suggests that the presence of a large mass of coral reefs reduces the ability of seawater to absorb CO2 from the atmosphere.
The effects of salinity and temperature on fCO2 in seawater were minor and could not account for the relatively high fCO2 in the GBR lagoon. Alkalinity depletion in the lagoon water indicates that this high fCO2 is the result of the calcification by reef organisms, together with the decomposition of organic matter in the lagoon. The Great Barrier Reef, which is an example of large scale coral reef systems, seems to act as a potential source for atmospheric CO2.
IP5o
Assessing the Effect of Variability in the Composition and Formation Processes of Antarctic Intermediate Water on the South Pacific Oxygen Maximum
J. Russell and A.G. Dickson
Scripps Institution of Oceanography, University of California, San Diego, USA
The South Pacific oxygen maximum is created by the outcropping of isopycnals in the Southern Ocean where high winds, very cold water, and upwelling of oxygen-undersaturated deep water enhance the uptake of oxygen by the surface water. Some of this water, when subducted as Antarctic Intermediate Water, eventually feeds into the Equatorial Undercurrent through the Vitiaz Straits. This high-oxygen, high-nutrient input helps drive the equatorial biological pump as water is upwelled to the surface along the equator. Without this continued influx of oxygen and nutrients from Antarctic Intermediate Water, it is possible that the extremely low oxygen conditions in the Eastern Pacific basin would extend westward, increasing denitrification on the equator. Thus, variability in the oxygen content of surface waters in the Southern Ocean can be relayed to the equator via Antarctic Intermediate Water.
To assess the potential importance of such variability in the composition and formation of Antarctic Intermediate Water, we have used data from WOCE cruises P16, P18 and P19 to examine the export of oxygen from the Southern Ocean in Antarctic Intermediate Water along 165 W, 110 W, and 88 W. We interpolated the oxygen and nutrient data from these cruises onto isopycnal surfaces. The oxygen data were then corrected for the effects of remineralization using Redfield calculations and the nutrient data. The results of these calculations imply that there is significant variability in the surface mixing processes affecting the uptake of oxygen in Antarctic Intermediate Water. We will present these results and speculations about the possible causes and effects of such variability in the export of oxygen into the South Pacific.
IP5p
South Atlantic NADW CFC-concentrations interpreted by using age distributions
Alfred Putzka and O. Huhn
Institut fΈr Umweltphysik, Universitaet Bremen, FB1, Bremen, Germany
Transient tracer concentrations in the ocean deliver information about the ventilation ages of the water. Conventional dating concepts using tracer concentrations or ratios to determine ages lead to different results for tracers with different input history. The reason for this is mixing in the ocean which causes the superposition of different vintages of the water mass in question. Age distributions represent a concept which explicitly takes into account different ages of different components within a water parcel.
Using simple transport models it is possible to define an analytical expression for age distributions depending on only three parameters. This concept will be explained and applied to interpret F-11, F-12 and CCl4-concentrations of North Atlantic Deep Water (NADW) measured between 10 and 30 S in the South Atlantic. The dilution with water of different origin will be accounted for by a multiparameter analysis. Mean ages, the age distributions and resulting transport parameters for the upper NADW will be discussed.
IP5q
The tracer signature of Antarctic Bottom Water and its spread in the Southwest Indian Ocean
Stephen Boswell, Denise Smythe-Wright and Sue Holley
Southampton Oceanography Centre, Empress
Dock,
Southampton UK
Antarctic Bottom Water (AABW) is a major contributor to the
deep and bottom waters of the world's oceans. Its influence can
be seen in all ocean basins penetrating far to the north of its
source regions. Besides having a distinctive cold signature, AABW
can be distinguished by its elevated dissolved silica
concentrations. Many previous studies of the spread of AABW have
been based on a combination of classical hydrography and silica
content. However, the use of silica as a quantitative tracer of
AABW movement is often inhibited because of non-conservative
input from the dissolution of falling diatomaceous particles and
from the diagenetic release of silica from sediments. In recent
years the use of the anthropogenic CFCs as time-clock tracers has
provided a tool for estimating the rate at which both physical
and chemical processes occur in the oceans. Using a T/S based
mixing model we have investigated the dilution of AABW and the
development of its silica anomaly as it moves away from the
Weddell Gyre. The model has allowed us to calculate CFC-derived
translation rates of AABW between the Weddell Gyre and the
Southwest Indian Ocean, and we have used these results to
estimate the contribution of diagenesis and remineralisation to
the development of the AABW silica maximum. In this way it was
hoped to correct for this non-conservative input and hence allow
silica to be used as an adjunct to classical temperature and
salinity methods for establishing mixing relationships. However,
diagenetic silica fluxes to the bottom waters in the Southwest
Indian Ocean range between 270 and 730 mmol
m-2 yr-1, with remineralisation fluxes
below 360 mmol m-2 yr-1, showing wide
geographical variation. These studies indicate that these fluxes
preclude the use of silica as a quantitative tracer in this
region of the ocean.
IP5r
A Study of Diacpycnal Mixing and Winter Convection in the Open Ocean: the Greenland Sea Tracer Release Experiment - ESOP 2
Marie-Jose Messias, Andrew J. Watson, Elisabet Fogelqvist, Kim A. Van Scoy and Truls Johannessen
School of Environ. Sciences, Univ. of East
Anglia, Norwich, UK
Dept of Analytical & Marine Chem., Univ. of Goteborg, Sweden
Atmospheric & Ocean Sciences, Univ. of Wisconsin, Madison,
USA
Geophysical Institut, University of Bergen, Bergen, Norway
To explore the processes involved in the formation and rate of overturning of bottom and deep waters in the Greenland Sea, a tracer release (SF6) experiment is being carried out in the region.
The main objectives are to investigate:
(1) the late summer diapycnal mixing in the weakly stratified waters below the surface mixed layer,
(2) the efficiency of winter-time deep convection in mixing the water column,
(3) how much and how quickly water leaves the Greenland Sea towards the North Atlantic.
Three steps of the experiment have already been achieved as of January 1997. During the first cruise in August 1996, an hydrological and geochemical survey was performed before the tracer release in order to locate the center of the Greenland Sea gyre and to establish the SF6 background concentrations. Chimney-like structures were observed in the SF6 distribution, marking the extent of vertical mixing over previous years, which are dated using SF6/CFCs ratios. Second, the tracer was injected in an area of approximately 50 square km in the centre of the gyre (approx 7430’N, 30W) along the sigma-theta = 28.049 isopycnal surface (at a depth of 350 ± 10 m). Third, during a second cruise in Nov/Dec 1996, the redistribution of the tagged water showed an important summer diapycnal mixing when compared to previous studies made in less active areas. The horizontal spreading was also found to be quite important, the initial SF6 patch being distributed over 3 or 4 times its injection area only after 3 to 4 months.
These measurements also yielded the initial conditions of tracer distribution before the convective season starts. The next steps involve several sampling surveys in February and March 1997, during or just subsequent to winter convection and then in May after the convection occurred. The tracer is expected to be subject to redistribution and deep mixing due to convective events and thus to provide an estimate of the penetrative convection and an insight on the associated processes.
IP5s
A coupled 3-d carbon cycle model for the Atlantic and Arctic Oceans
Helge Drange
Nansen Environmental and Remote Sensing Center, Solheimsviken, NORWAY
Atmospheric carbon dioxide has characteristic life times ranging from decades to centuries, and about two-thirds of the man-generated greenhouse forcing is caused by increasing concentrations of atmospheric CO2. It is therefore of paramount importance to improve our understanding of the past and present transport, mixing and cycling of carbon within and between the atmosphere, the terrestrial biosphere and ocean carbon reservoirs, if reliable predictions of the future global carbon cycle are to be made.
In this paper, a coupled 3-dimensional physical-biochemical model for the cycling of carbon and plant nutrients in the ocean is presented. The coupled model consists of the Miami Isopycnic Coordinate Ocean Model (MICOM), a dynamic-thermodynamic sea ice model, an ecosystem formulation including phytoplankton, zooplankton and bacteria, and a chemical module for the carbonic acid system in seawater. The coupled model has been set up for the North Atlantic Ocean, the Nordic Seas and the Arctic Basin in order to model the cycling of carbon and plant nutrients, and the associated carbon fluxes, on seasonal time scales for the present climate.
After an initial spin-up integration of the ice-ocean model, several multi year simulations have been carried out with the coupled model. A comparison with observations indicates that the model is able to reproduce the main features of the seasonal cycling of carbon and plant nutrients over large parts of the model domain. In the paper, the main processes that govern the exchange of CO2 across the air-sea interface at high northern latitudes are discussed, together with the seasonal cycling in the biogenic primary, regenerated and export productions.