POLAR GEOPHYSICS (IAGA, IAVCEI, IASPEI, IAG, IAPSO, IAHS,
SCOSTEP)
Location: Muirhead Tower, G08 LT
Location of Poster: Muirhead Tower, Student Room (1st floor)
Tuesday 20 July AM
Presiding Chair: Patrick T Taylor (NASA/GSFC, Greenbelt, MD, USA)
Concurrent Poster Session
JSA09/E/12-A2 0930
ACTIVE VOLCANOES OF THE ANTARCTIC PLATE
Wesley E. LE MASURIER (Department of Geology, University of Colorado, Denver, Colorado,
80217-3364, USA, email: wlemasurier@carbon.cudenver.edu)
It has been estimated that there are 41 active volcanoes on the Antarctic plate, but there are only eight for which Holocene activity is unquestioned. This large uncertainty exists because direct observation is difficult, and because documenting Holocene activity by ^14C dating is not possible where no life forms exist. Fifteen of the 41 "active" volcanoes are in the West Antarctic rift system, including a recently discovered sub-glacial volcano inferred from geophysical data. Twelve others are oceanic islands, 9 are in the South Sandwich arc, and 5 are on the Antarctic Peninsula. The Antarctic plate is almost completely encircled by mid-ocean ridges and has hardly moved since 85 Ma. This environment limits the mechanisms available to sustain volcanic activity on the continent. Thus, mantle plume activity and the interaction of transform faults with the rift system are the main mechanisms that have been invoked to explain volcanism in the rift.
The great enigma of Antarctic volcanism is the extent to which Cenozoic activity has occurred beneath thick ice cover, and the potential it, and associated high heat flow, may have to destabilize the West Antarctic ice sheet. Aeromagnetic surveys suggest the existence of 10^6 km^3 of subglacial volcanic rock, and it has been suggested that the aseismicity of the rift system may be related to magma overpressure. These portend significant subglacial volcanic activity (and high heat flow) in the future, but glaciologists are skeptical that these could be factors in the instability of the ice sheet. Until the potential effects of these factors are modeled, and the causes of the aeromagnetic anomalies verified, the question of how serious this threat might be will remain a matter of speculation.
JSA09/W/14-A2 1000
ICE-VOLCANO INTERACTION DURING SUBGLACIAL ERUPTIONS IN TEMPERATE ICE CAPS IN ICELAND
Magnus T. GUDMUNDSSON (Science Institute, University of Iceland, Hofsvallagata 53,
107 Reykjavik, Iceland, email: mtg@raunvis.hi.is)
Subglacial eruptions occur in volcanic regions at high latitudes and at some large strato-volcanoes in other areas. About 11% of Iceland is ice covered and eruptions within ice caps have been frequent. Some of the most active volcanoes in Iceland are ice covered, notably the Grimsvotn volcano in the Vatnajokull ice cap and the Myrdalsjokull volcano. Jokulhlaups associated with volcanic eruptions in Iceland may drain several cubic kilometers of water and discharge rates of order 100,000 m3/s have been reported. Landscape in the volcanically active zones is dominated by hyaloclastite ridges and tuyas, formed under the Pleistocene ice sheets. The first eruption within a large ice cap that could be monitored was the Gjalp eruption in Vatnajokull in 1996. About 0.4 km3 of magma erupted in 13 days. Melting rates were very fast, 0.5-0.8 km3/day for the first four days when the rate of eruption was highest. This high rate of melting suggests fragmentation of the magma and formation of hyaloclastites. Comparison of the Gjalp eruption with eruptions in the nearby Grimsvotn caldera, illustrates the effect of ice thickness on the response of the surrounding glacier. When the ice is thick, as in Gjalp (500-750 m), the ice deforms and flows into the depression created by melting and drainage. In Gjalp the depressions had a width of several kilometers but the glacier around the depressions was not affected. At known eruption sites in Grimsvotn, ice thickness is about 100 m. Openings are quickly melted in the ice, leading to explosive eruptions that disperse tephra over the ice cap. The ice surrounding the craters is mainly passive and suffers little deformation. Ice-volcano interaction, similar to that observed in Grimsvotn, occurs on ice covered strato-volcanoes in many parts of the world
JSA09/W/08-A2 1045
ARCTIC GRAVITY PROJECT
Rene FORSBERG (Geodynamics Dept., KMS, Rentemestervej 8, DK-2400, Copenhagen NV, Denmark, email: rf@kms.dk)Steve KENYON (NIMA, 3200 S 2nd St, St. Louis, Mo., USA,
63118-3399, email: kenyons@nima.mil)
The gravity field of the Arctic Ocean region is of prime importance for global gravity field and geoid models, for providing information on the geology and tectonics of the Arctic Basin, and for navigation and orbit determination. Planned satellite gravity field missions such as CHAMP, GRACE and GOCE will all to a varying degree be strongly affected by the gravity field of the polar areas, especially for the satellites launched with a non-polar orbit, where a polar gap will remain in the coverage.
Ongoing gravity activities over many years have resulted in a nearly complete coverage of the Arctic with gravity field data. In recent years major airborne and surface survey activities have been carried out in the High Arctic and Greenland, US nuclear submarines have criss-crossed under the ice on scientific cruises, and Russia has continued adecade-long program of surface and airborne gravity measurements. Recently an international initiative, involving a.o. scientists from all circumarctic countries, has been taken to compile all available and releasable gravity data into a 5' uniform, public-domain gravity grid in year 2000. The paper will report on the progress of the project, and showexamples from some recent airborne gravity survey activities.
JSA09/E/02-A2 1115
POLAR GRAVITY MAPPING FROM FUTURE SATELLITE MISSIONS
C.K. SHUM (Department of Civil and Environmental Engineering and Geodetic Science, The Ohio State University, 470 Hitchcock Hall, 2070 Neil Avenue, Columbus, OH 43210-1275, USA,
Email: ckshum@osu.edu) and Andy Trupin (School of Natural Science, Oregon Institute of Techology, Klamath, Oregon, USA, email: trupina@oit.edu)
By the beginning of the next Millennium, GRACE and CHAMP gravity mapping missions are expected to provide a three-fold improvement in our knowledge of the Earth's static gravity field to 1 cm accuracy in geoid at a wavelength of 300 km or longer, and to measure time-varying mass variations of the Earth system with a temporal resolution of days to weeks. With applications to the mass balances of the polar ice sheets, GRACE with a five-year mission is anticipated to provide a measurement accuracy corresponding to better than 0.01 mm/yr of sea level rise for each of Antarctica and Greenland ice sheets, over a spatial scale of 1600 km or longer. The orbital inclinations of GRACE/CHAMP would however limit the coverage of the polar ice caps to within +/- 87 degrees. In 2001, NASA will also launch IceSat, whose instrument Geocience Laser Altimeter System (GLAS) will provide accurate measurements of ice elevation change. Radar altimeters are providing measurements of ice elevation change for interior of Antarctica and Greenland ice sheets. GPS measurements are providing crustal uplift information. In addition, cannon-satellites with satellite laser ranging are enabling determination of long wavelength gravity changes. In this paper, we will discuss the results of pilot studies for the anticipated improvement in the static and temporal gravity fields of the polar regions, and the ability of future satellite missions with combined use of in situ observations to potentially separate ice sheet mass balance, isostatic uplift, and changes in snow accumulation at the surface.
JSA09/W/01-A2 1145
A HIGH RESOLUTION ARCTIC MARINE GRAVITY FIELD FROM ERS ALTIMETRY
Seymour LAXON, Neil Peacock (both at University College London, MSSL, Holmbury St. Mary, Dorking, RH5 6NT, email: swl@mssl.ucl.ac.uk) David McAdoo and Anahita Tikku, (both at U.S. National Oceanic and Atmospheric Administration, NODC/Lab for Satellite Altimetry, SSMC3, Silver Spring, MD, 20910, US, email: dave@comet.grdl.noaa.gov)
A new, detailed, high-accuracy gravity field has been derived from ERS-1 and ERS-2 satellite radar altimeter data over all Arctic seas south of 82 degrees north including permanently ice-covered seas. The entire ERS-1 Geodetic Mission and 22 cycles from the ERS-2 mission have been used in generating this field. In addition to using this larger data set, we have employed enhanced processing techniques, to retrack and reduce these ERS waveform data. Comparisons with airborne measurements show that this new Arctic gravity field resolves features down to crustal scales (i.e., spatial wavelengths as short as 20 km) representing a significant improvement over the 75 km resolution limit of our 1994 Science field (Laxon and McAdoo, Science, vol. 265, 621-624, 1994).
This gravity field should prove a particular help in unravelling the tectonic history and structure of the Canada Basin and Chukchi Borderland. For example, the gravity field clearly shows the anomalies associated with the Alaskan and Canadian continental shelf edges bordering the Canada Basin, shelf edge anomalies bordering the Eurasian Basin as well as a lineated low coincident with the Northwind Ridge. Anomalies and lineations arising from tectonic details imprinted in the seafloor can also be seen including: a north-south trending, negative lineation locating an apparent extinct spreading ridge in the middle of the Canada Basin. Other distinctive anomalies include those due to structures associated with crustal extension in the Chukchi Continental Borderland as well as on the Siberian continental margin and those overlying the active spreading ridge in the Eurasian Basin north of the Laptev Sea. At the other - or Atlantic end - of the Eurasian Basin, anomalies coincident with the Spitsbergen FZ and Lena trough can be seen.
JSA 09/E/04-A2 1200
EARTH TIDES AND OCEAN TIDAL LOADING ON GREENLAND: CORRECTION OF SURFACE DEFORMATIONS BY TIDAL GRAVITY MEASUREMENTS
Gerhard JENTZSCH and Markus Ramatschi (both at Institute for Geosciences, FSU Jena, Burgweg 11, D-07749 Jena, email: jentzsch@geo.uni-jena.de), Per Knudsen (Geodetic Institute, National Survey and Cadastre, DK-2400 Copenhagen, email: pk@kms.dk)
Space and air borne observations of the earth concerning the changes of the Greenland ice cap are related to kinematic GPS measurements connected to fiducial sites. With regard to
the accuracy of these measurements the time variation of the coordinates of the reference stations must be determined. Since most of the reference stations are close to the coast the correction applying standard ocean load models is not sufficient: Due to incomplete ocean
tidal charts especially north of 60° and in shelf areas the computed loading signal does not explain the observation.
With our L & R tidal gravimeter ET 18 we performed gravity tidal measurements from 1993 to 1997 at four sites covering about one year each. The determination of the vertical deformation requires the separation of the Newtonian attraction from the observed load signal by model computations applying a local crust / mantle structure and a local distribution of the ocean tides derived from different models. The vertical deformations obtained for the main tidal waves of up to 35 mm explain about half of the observed effect in gravity only. Thus, the ocean tide models need improvement.
JSA09/W/13-A2 1215
ANALYSIS OF GPS DATA OBSERVED BETWEEN 1997-99 ON PERMANENT STATIONS IN ANTARCTICA AND ITS VICINITY
Xin CHEN*, Falko Menge**, Hans Werner SCHENKE*, Tilo Schoene*, Guenter Seeber**, Christ
of Voelksen** (*Alfred Wegener Institute for Polar- and Marine Research, Columbusstrasse,
D-27568 Bremerhaven, Germany, e-mail: Schenke@AWI-Bremerhaven.DE, **Institut fuer Erdmessung, Universitaet Hannover, Schneiderberg 50, D-30167 Hannover, Germany,
e-mail: menge@mbox.ife.uni-hannover.de)
Under the scientific program GIANT (Geodetic Infrastructure of Antarctica, coordinated under the auspices of the SCAR Working Group on Geodesy and Geographic Information) several new permanent GPS stations were established in Antarctica and its vicinity during 1997 and 1998. The resulting network has enhanced our capability in monitoring crustal deformation in Antarctica. The new stations include: Jubany /Dallmann (DALL), Gough Island (GOUG), Sanae IV (VESL), General Belgrano II (BELG), Mawson (MAW1), Palmer (PALM), Syowa (SYO1), and Dumont d'Urville (DUM1).
The data were processed together with other existing permanent GPS-stations in Antarctica and several permanent IGS-stations in the southern hemisphere, using the GAMIT/GLOBK (Alfred Wegener Institute) and GIPSY-OASIS II (Institut fuer Erdmessung) software packages. Site position time series and site velocities were determined in the ITRF reference frame, and were then compared and analyzed with estimates from other sources.
JSA09/L/02-A2 1230
PLATE DEFORMATIONS AND PLATE KINEMATICS OF ANTARCTICA DERIVED BY GPS
R. DIETRICH, R. Dach, J. Perlt (TU Dresden, Institut für Planetare Geodäsie, D-01062 Dresden),
H.-W. Schenke, T. Schöne, M. Pohl (Alfred-Wegener-Institut für Polar- und Meeresforschung, Columbusstraße, D-27568 Bremerhaven), J. Ihde, G. Engelhardt (Bundesamt für Kartographie und Geodäsie, Außenstelle Leipzig, Karl-Rothe-Straße 10, D-04105 Leipzig), G. Seeber, F. Menge, Ch. Völksen (Universität Hannover, Institut für Erdmessung, Schneiderberg 50, D-30167 Hannover), W. Niemeier, H. Salbach (TU Braunschweig, Institut für Geodäsie und Photogrammetrie, Gaußstraße 22, D-38106 Braunschweig), K. Lindner, H.-J. Kutterer, M. Mayer (Universität Karlsruhe, Geodätisches Institut, Englerstr. 7, D-76128 Karlsruhe), H. Miller, A. Veit (Universität München, Institut für Allgemeine und Angewandte Geologie, Luisenstraße 37, D-80333 München)
Repeated GPS observations are an efficient and accurate tool to study crustal deformations in polar regions. The results presented here are based on data obtained from 1995 until 1998 in the frame of the SCAR GPS Campaigns. A joint German research group contributed substantially to the field activities as well as analyzed the data with different software packages (BERNESE, GAMIT/GLOBK, GIPSY, GEONAP). The resulting network deformations can be used to relate the kinematics of the Antarctic plate to other major tectonic plates. Furthermore, regional deformation patterns, e.g. in the area of the Antarctic Peninsula, are obtained.
Tuesday 20 July PM
Presiding Chair: John Turner (British Antarctic Survey, Cambridge, UK)
JSA09-A2 Introduction 1400
J. DUDENEY, (British Antartic Survey)
JSA09/L/01-A2 1415
THE GEOPHYSICS OF ARCTIC SEA ICE
Donald K. Perovich (USA CRREL, 72 Lyme Road, Hanover NH 03755,
email: perovich@crrel.usace.army.mil)
Perennial sea ice covers much of the Arctic Ocean. The presence of the ice cover profoundly affects energy exchange between the atmosphere and the ocean. The energy exchange process is complicated by the considerable seasonal and spatial variability exhibited in the properties of the ice cover. For instance, due to a combination of thermodynamic and dynamic processes, ice thicknesses can ranges from open water to ridges tens of meters thick. Albedos decrease from peak values of 0.9 in the spring to minima of 0.4 at the height of the summer melt season. General circulation models indicate that Arctic sea ice may be a sensitive indicator of climate change. The sensitivity of the ice pack to climate changes is due in part to the ice-albedo and cloud-radiation feedbacks. This presentation will describe the key geophysical properties of the Arctic sea ice cover and summarize recent sea ice studies. Particular attention will be paid to sea ice feedback processes and the surface heat budget of the Arctic Ocean.
JSA09/L/03-A2 1445
GEOPHYSICS OF THE ANTARCTIC ICE SHEET
CHARLES R. BENTLEY, Geophysical and Polar Research Center, University of Wisconsin, 1215 W. Dayton St., Madison, WI 53706, USA; email: bentley@geology.wisc.edu
The Antarctic ice sheet contains sufficient ice to raise world-wide sea level by more than 60 m if melted completely; the amount of snow deposited annually on its surface is itself equivalent to over 5 mm of global sea level. Thus, the ice sheet could be a major agent of change for the present-day sea level, but it is still not known whether the ice sheet is growing or shrinking and the snow accumulation rate may be changing. The ice sheet is potentially subject to alteration in a modified climate; in fact, it may be shrinking now in response to the end of the last ice age. The West Antarctic ice sheet, which rests on a bed far below sea level, may be particularly capable of rapid retreat. Rates of discharge from some of the major ice streams have changed markedly in recent decades and the grounding line of one of them may be retreating rapidly. Measurements from satellites early in the 21st century are expected to settle the question of current growth or shrinkage, but prediction of the future will remain problematic for many years. Critical to improving our understanding of ice-sheet behavior is to learn more about the key physical processes that govern ice-stream dynamics. These include the interaction between an ice stream and its bed, which may vary with scale; complex temperature-dependent processes at lateral shear margins; interaction with ice shelves; and the spatial and temporal initiation of stream-like flow.
JSA09/L/04-A2 1515
ARCTIC METEOROLOGY AND CLIMATOLOGY : CURRENT UNDERSTANDING AND FUTUREDIRECTIONS
Amanda H. Lynch, University of Colorado, USA
The circulation and surface energy and mass balance of the Arctic atmosphere, land surface, sea ice and ocean system combine to have direct impacts on global climate. For example, the freshwater inputs via runoff and precipitation less evaporation (P-E) play a key role in maintaining the halocline, thereby influencing global ocean circulation as well as regional sea ice cover. The processes determining runoff and P-E include a complex series of feedbacks involving clouds, permafrost, atmospheric circulation, sea ice cover, and many other factors. In addition, the most recent IPCC assessment shows that the largest disagreement between coupled climate model simulations of present day climate remains the polar regions. The disagreement reflects the sensitivity of this interconnected system as well as our limited understanding.
Recent analyses of observations have identified interesting variations in the North Atlantic and Arctic Oscillations, the North Atlantic thermohaline regime, the sea ice distribution, precipitation, permafrost distribution and many other climate variables. It remains to be determined whether these variations are consistent with, or indicators of, the type of polar amplification predicted by global climate model experiments. This presentation will provide an overview of some current findings in the Arctic, and discuss future research directions.
JSA09/E/06-A2 1600
ANTARCTIC METEOROLOGY AND CLIMATOLOGY: RECENT DEVELOPMENTS AND OUTSTANDING PROBLEMS
J.C. KING (British Antarctic Survey, Cambridge CB3 0ET, UK, email: j.c.king@bas.ac.uk)
Over the past two decades, considerable progress has been made in understanding the processes that control the climate of Antarctica and couple this region with the rest of the global climate system. Technological developments have made it feasible to deploy automated measuring systems in previously inacessible areas, while the wealth of data now available from satellite sensors permit continent-wide monitoring of key climatological variables. These advances in measurement technology have been paralelled by improvements in global and regional scale models that, for the first time, provide a synthesis of the workings of the Antarctic climate system. In this talk I will review the advances of the last two decades and will look at some problems that are still outstanding. These include identifying the causes of the recent warming seen in the Antarctic Peninsula and correctly parametrising the processes that control katabatic flow.
JSA09/W/12–A2 1630
THE APE-GAIA CAMPAIGN: AIRBORNE POLAR EXPERIMENT GEOPHYSICAL AIRCRAFT IN ANTARCTICA
Bruno CARLI and Ugo CORTESI (both at IROE-CNR, Via Panciatichi, 64 Firenze, Italy.
E-mail: carli@iroe.fi.cnr.it, cortesi@iroe.fi.cnr.it), Alberto Adriani (IFA-CNR Via del Fosso del Cavaliere, 100 Roma, Italy E-mail: adriani@atmos.ifa.rm.cnr.it), Cornelis Blom (IMK-FZK Postfach 3640, D-76021 Karlsruhe, Germany. E-mail: blom@imk.fzk.de), Stephan Borrmann (FZJ-ICG-1, 52425 Juelich, Germany. E-mail: S.Borrmann@fz-juelich.de), Martyn Chipperfield (University
of Cambridge, Cambridge CB2 1EW, U.K. E-mail: Martyn.Chipperfield@atm.ch.cam.ac.uk),
Giorgio Fiocco (University of Rome, Piazzale Aldo Moro, 2 Roma, Italy.
E-mail: fiocco@g24ux.sci.uniroma1.it), Giorgio Giovanelli (FISBAT-CNR Via Gobetti, 101 Bologna Italy. E-mail: giorgio@atmosphere.fisbat.bo.cnr.it), Valentin Mitev (Observatory of Neuchatel Rue de l'Observatoire, 58 2000 Neuchatel, Switzerland. E-mail: mitev@on.unine.ch), Guido Visconti (University of L'Aquila, Via Vetoio 10, Coppito-L'Aquila, Italy. E-mail: guido.visconti@aquila.infn.it), Michael Volk (University of Frankfurt, Georg Voigt Strasse, 14 D-60325 Frankfurt am Main, Germany. E-mail: M.Volk@meteor.uni-frankfurt.de)
In the frame of the "Airborne Polar Experiment" (APE) a Russian military plane M55 has been converted in a high flying research platform for investigations of the polar lower stratosphere and upper troposphere. A first campaign, carried out in the Arctic during the winter 1996-97 has proved the capability of M55-Geophysica aircraft to access altitude and geographical locations, which are difficult to reach with other platforms.
A new mission of the M55, supported by the Italian National Program for Antarctic Research (PNRA), is now planned over the Antarctic Peninsula for the study of the chemical processes responsible for stratospheric ozone losses, its subsequent recovery and its interaction with
mid-latitude air. The campaign, named APE-GAIA (Geophysica Aircraft In Antarctica), will based in airport of Ushuaia, Argentina (Lat. 54°S, Long. 68°W) from 15 September to 15 October 1999 and will represent the first major mission with a scientific payload of both in-situ and remote sensing instruments conducted on board of a high altitude aircraft in the southern polar region.
JSA09/E/07-A2 1645
SIMULATED VARIABILITY AND TRENDS OF THE ARCTIC SEA-ICE COVER PROPERTIES
Michael Hilmer, Markus HARDER, Peter Lemke
The polar sea-ice caps have received special attention in the context of Global Warming. Especially focussing on detecting trends of the Arctic ice cover as an indication of Climate Change, it is essential to determine its natural variability. The tempora l variations of the Arctic sea-ice cover properties, such as ice thickness and ice extent, are investigated with the dynamic-thermodynamic Kiel Sea-Ice Simulation (KISS). The model is integrated over 40 years (1958 to 1997) with a daily time step. Daily fields of surface wind and air temperature derived from the NCEP/NCAR.
Reanalysis Project provide the atmospheric forcing. The simulation yields both strong inter-annual variability and a statistically significant, decreasing trend in ice thickness. Largest inter-annual variations of the ice thickness occur in the Beaufort Sea and near the Siberian shelves. Statistically significant negative trends of the ice thickness mainly occur near the North Pole and in the Kara and Barent Seas where the inter-annual vari ability is small.
JSA09/E/01-A2 1700
GEOPHYSICAL METHOD OF DETERMINATION OF THE BASE PERMAFROST BOUNDARY IN HOLES
Boris SEDOV (North-East Interdisciplinary Research Institute, the Russian Academy of Sciences, Magadan, Russia)
During the development of deposits in criolithic zone ( production of coal, diamonds, placers etc.) there is a need to know the position of the base permafrost boundary (BPB) that in case of mineralized waters, does not coincide with 0_ isotherm. To determine the position of the base permafrost boundary in the hole, geophysical method was used. This method makes possible to carry out the determinations with any possible precision. For this, multicore cable is installed into the hole after drilling. Every line of such a cable ends with electrode. The distance among the electrodes is chosen according to prescribed precision for (BPB) depth determination. During the recovery of rock temperature in frozen stratum, solution freezes in the hole. Ice is not formed under the BPB. Freezing- in of electrode into the ice increases the earth resistance.
JSA09/W/17-A2 1715
ANTARCTIC PHYSICAL OCEANOGRAPHY: INTERACTIONS WITH SEA ICE, ICE SHELVES AND ICE SHEETS
S.F. ACKLEY, (111 Villa Ann, San Antonio TX 78213, USA, email: jlongbotham@pol.net)
Within the world ocean, a significant fraction of the total water mass has had "contact" with the cold atmosphere in the Antarctic region, and is defined as Antarctic Bottom Water (T< 2°C). Sea ice affects significantly this water mass formation and its circulation in the polar oceans. The seasonal cycle of the ice cover modifies the large-scale density gradients due to the different locations of freezing and melting areas. Circulation beneath ice shelves results in cooling and freshening of water masses, while topography of ice shelves serves to steer water mass circulation, with consequences on their dynamics and thermodynamics. Investigations over the last two decades, when the few (but first) oceanographic expeditions to Antarctica during winter conditions have taken place have shown complex and sensitive interactions between the ocean circulation and sea ice and glacial processes. Event-driven processes originating in the sea ice and glacial ice account for significant variability in water mass modification. Sea ice-atmosphere interaction in the eastern Weddell Sea may, for example, account for the interdecadal variability in the occurrence of the deep water Weddell Polynya (1974-1976). When the Weddell Polynya occurred, total deep water formation of Antarctic Bottom Water was increased substantially, exceeding that occurring from interactions on the continental shelves alone. Ice Shelf Water, a constituent of Antarctic Bottom Water, is formed by modification of inward flowing waters from the continental shelves, that melt a portion of the ice shelves during their transit beneath them. The intensity of the circulation, and seasonal and interannual fluctuations, appear to be linked to the topography of the ice shelves, driven by glacial procesess, and the properties of the continental shelf source waters, driven by sea ice formation in front of the ice shelves. Coastal polynyas, (found extensively around East Antarctica) can occur where glacial tongues from the ice sheet block the flow of sea ice.
JSA09/W/02-A2 1745
MODELLING OF THE ANTARCTIC CIRCUMPOLAR CURRENT: A COMPARISON OF FRAM AND EQUIVALENT BAROTROPIC MODEL RESULTS
Vladimir IVCHENKO (Jet Propulsion Laboratory/NASA, 300-323, 4800 Oak Grove Drive, Pasadena, CA 91109, USA, Email: voi@sundog.jpl.nasa.gov) Alexander Krupitsky (Lehman Brothers Holdings, Inc 3 World Financial Center, New York, NY 10285, USA, Email: akrupits@lehman.com); Vladimir Kamenkovich (Dept. of Marine Science, Institute of Marine Sciences, The University of Southern Mississippi, Stennis Sp.C., MS 39529, USA, Email:kamenkov@sunfish.ssc.usm.edu); Neil Wells (Scool of Ocean and Earth Sciences, Southampton Oceanography Centre, European Way, Southampton SO14 3ZH,UK, Email:n.c.wells@soc.soton.ac.uk)
Analyzing the Fine Resolution Antarctic Model (FRAM) simulations, Killworth (1992) noticed a strong tendency for self-similarity in the vertical structure of the velocity field of the Antarctic Circumpolar Current (ACC). Based on the self-similarity hypothesis, Krupitsky et al.(1996) developed an equivalent barotropic (EB) model of the ACC capable of describing the horizontal structure of the ACC. Compared to the multi-level-primitive-equation GCM, the EB model appeared substantially simpler and therefore useful in process-oriented and sensitivity studies. To assess the applicability of the EB model to the analysis of the horizontal structure of the ACC we performed the comparison of the EB model results with the time-mean depth-averaged results of the FRAM model. The horizontal structure of the ACC transport stream function appears reasonably similar in both models. The more detailed regional analysis shows a rather satisfactorily agreement in the regions with pronounced topographic features (Crozet-Kerquelen area, Macquarie-Ridge Complex and near Pacific-Antarctic Ridge, and to the east from the Drake Passage). In the regions with a more quiet topography (eastern part of the Indian Sector of the Southern Ocean, and in the Southeast Pacific Basin) the agreement is worse but still meaningful. It seems that the EB model satisfactorily describes the influence of the bottom topography on the ACC. It is known (Stevens and Ivchenko 1997) that the averaged (over time, depth and a latitude circle) FRAM zonal momentum equation provides the balance essentially between the wind stress and the bottom pressure drag. The same averaged momentum balance is given by the EB model.
Wednesday 21 July AM
Presiding Chair: R Dietrich (Technische Universität Dresden, Germany)
JSA09/W/15-A3 0830
TECTONICS AND SEISMICITY OF THE ANTARCTIC PENINSULA REGION
Stacey D. ROBERTSON, Douglas A. Wiens, and Gideon P. Smith (Department of Earth & Planetary Sciences, Washington University, St. Louis, MO, email: stacey@izu.wustl.edu), Emilio Vera (Universidad de Chile, Santiago, Chile), George Helffrich (University of Bristol, UK)
The purpose of the Seismic Experiment in Patagonia and Antarctica (SEPA) is to learn more about the seismic and tectonic characteristics of the South Shetland trench and Antarctic peninsula, which are largely unknown. It has been unclear whether subduction is still occurring in the South Shetland trench, and the level of tectonic activity in the backarc Bransfield Strait is also uncertain. Major changes in plate motions over the past 4 million years suggest that this region may provide important insights into several important processes, including very slow subduction, the initiation of rifting, and how plate tectonic systems change through time. The Antarctic portion of the SEPA deployment consists of seven broadband seismic instruments located in the Antarctic Peninsula - South Shetland Islands region. Three of these stations are at inhabited sites and receive occasional support throughout the year, and four are located at field sites which can only be reached during the Antarctic summer and which must receive all their power through solar power and banks of Carbonaire batteries. Fourteen ocean bottom seismographs were recently deployed in the South Shetland trench and Bransfield Strait in conjunction with Leroy Dorman of Scripps Institute of Oceanography.
Although the South Shetland Island area displays a low level of seismicity in global catalogs, the data which we obtained from 1997 and 1998 indicates a high level of local seismicity (mb 2-4). Preliminary locations of these events indicate that the seismicity is concentrated in the South Shetland trench with a few earthquakes located in the Bransfield Strait. The seismicity of the South Shetland trench extends to depths of about 70 km, indicating that subduction is currently occurring. Some earthquakes are concentrated near large seafloor volcanoes along the central rift of the Bransfield Strait, suggesting current eruptive activity. We are also investigating mantle seismic anisotropy from shear wave splitting to provide constraints on the pattern of possible mantle flow through Drake Passage.
JSA09/E/05-A3 0900
SURFACE WAVE TOMOGRAPHY OF THE ARCTIC REGION
Michael Barmin, Anatoli LEVSHIN, Michael Ritzwoller, Alex Padgett (all at Department of Physics, University of Colorado at Boulder, Campus Box 390, Boulder, CO 80309, U.S.A,
e-mail: levshin@lemond.colorado.edu)
Because of the station and earthquake distributions at high northern latitudes, the large-scale structure of the Arctic crust and uppermost mantle is best explored with surface waves. We report on the results of a study of surface wave dispersion at high northern latitudes. We have extended earlier studies of surface wave dispersion across Eurasia in three ways.
(1) Data processing. We have obtained new Rayleigh and Love wave dispersion measurements at GSN, USNSN, and CNSN stations following about 300 earthquakes which occurred around the northern hemisphere from 1995 through 1997.
(2) Isotropic dispersion maps. We have estimated broadband (20 s - 150 s) isotropic group velocity maps across the entire eastern hemisphere north of the equator and for the western hemisphere north of about 50 degree N latitude.
(3) Azimuthally anisotropic dispersion maps. We have simultaneously estimated 2*psi azimuthally anisotropic group velocity maps for the same region at the same periods. We report on the features that appear in the estimated isotropic group velocity maps and on the relation of these features to those apparent in other large-scale dispersion studies. The observed maps display the signatures of sedimentary and oceanic basins, crustal thickness variations, and upper mantle anomalies under both continents and oceans. For example, there are two significant Arctic oceanic low velocity anomalies at long periods. The first and more prominent is associated with the Iceland hotspot and the northward continuation of this anomaly adjacent to the Mohns Ridge toward the Fram Strait between Greenland and Svalbard. The second anomaly runs from the Laptev Sea to the Mendeleev Ridge. The latter anomaly is not obviously coincident with the sismically active Arctic Mid-Oceanic Ridge. At 150 s the low velocities are more nearly coincident with the aseismic Mendeleev Ridge. Finally, we report on the importance of the estimated azimuthal anisotropy in fitting the dispersion data and how its inclusion in the tomographic inversions affects the isotropic maps.
JSA09/W/05-A3 0930
AEROMAGNETICS IN ANTARCTICA.
Massimo CHIAPPINI (Istituto nazionale di Geofisica, Vigna Murata 605, 00143 Roma, Italy;
Email: chiappini@ingrm.it) Fausto Ferraccioli (Dipteris Univ. Genova, Italy,
email: magne@dister.unige.it)John Behrendt (INSTAAR - University of Colorado Boulder, CO 80309-0450 USA, Email: behrendj@stripe.colorado.edu) Julie Ferris (British Antarctic Survey High Cross, Madingley Road Cambridge CB3 OET United Kingdom, Email: JKF@pcmail.nerc-bas.ac.uk).
The Antarctic continent is 99% covered with ice and is the most poorly understood region of the planet. International interest of Earth Sciences in the Antarctic is considerable because of the central role of its tectonics and geology in both Gondwana and Rodinia evolution. Remotely-sensed data, such as magnetic anomaly data provide one of the few ways to obtain geological information over much of the continent, helping to delineate major structural components of the continent, such as cratons, , mobile belts, terranes and rifts. Consequently, numerous near-surface magnetic surveys have been carried out by the international community for site-specific geologic objectives.
Individual magnetic surveys are being combined into regional and ultimately continental scale magnetic synthesis for the Antarctic. In 1995, an international Working Group was established, and initiated efforts to develop an inventory of all magnetic data sources for the Antarctic region south of 60 degrees S, by means of a multinational cooperation called ADMAP, the Antarctic Digital Magnetic Anomaly Project. A number of Antarctic aeromagnetic surveys are reviewed, as a contribution to ADMAP's activities.
JSA09/E/11-A3 1000
A REVIEW OF MAGNETIC ANOMALY FIELD DATA FOR THE ARCTIC REGION: GEOLOGICAL IMPLICATIONS
Patrick T. TAYLOR (Geodynamics Branch, NASA/GSFC, Greenbelt, MD 20771, USA,
email: ptaylor@ltpmail.gsfc.nasa.gov); Ralph von Frese and Daniel R. Roman (both at
Department of Geological Sciences, The Ohio State University, Columbus, OH 43210, USA,
email: vonfrese@geology.ohio-state.edu); James J. Frawley (Herring Bay Geophysics, Dunkirk, MD 20754, USA, email: hbgjjf@ltpmail.gsfc.nasa.gov)
Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, have been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and subject to controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and cAdoo, 1998) are playing a major role in Arctic studies.
JSA09/E/09-A3 1015
MAGNETIC AND GRAVITY COMPILATION OVER VICTORIA LAND (ANTARCTICA): SOME TECTONIC IMPLICATIONS AND PROBLEMS
Fausto FERRACCIOLI, Emanuele Bozzo, Massimo Spano (all at DIP.TE.RIS., Univ. Genova, Italy, email: magne@dister.unige.it) Massimo Chiappini (Istituto Nazionale di Geofisica, Rome, Italy,
email: chiappini@marte.ingrm.it)
Victoria Land (VL) is a key area to study the geology of Antarctica and at a broader scale for the reconstruction of Gondwana assembly, evolution and dispersal. As a first step towards geophysically consistent models for the tectonodynamical evolution of the region we compare magnetic and gravity patterns/trends with geologic and seismic constraints. After hypothized rifting in Precambrian times at the East Antarctic Craton margin, the Early Cambrian to Carboniferous history features subduction, accretion and collision of terranes. Jurassic tholeiitic magmatism at the site of the later Transantarctic Mountains (TAM) was followed by amagmatic(?) crustal extension in the Cretaceous. Finally Cenozoic transtensional and transpressional reactivation of Paleozoic and Mesozoic faults was accompanied by rift-related alkaline magmatism and major uplift of the TAM. Prominent magnetic anomalies have previously been recognized to be associated to Cenozoic plutonism and volcanism. Now it is clear that the pre-existing lower Paleozoic architecture controls its location. New gravity and magnetic data leads to an improved imaging of the Mesozoic to Cenozoic Rennick pull-apart basin and its relationship to VL terrane boundaries. A major magnetic and gravity anomaly break is recognized to correspond to the western boundary of the Wilson Terrane. Extensive Jurassic magmatism focussed in this boundary zone. Open questions regard the nature of the Bowers/Wilson Terrane and the docking mechanisms to the East Antarctic Craton. Unravelling the late-Proterozoic to lower Paleozoic history of VL is still particulary intriguing.
JSA09/W/21-A3 1045
INTERPRETATION OF 'RECONSTRUCTED' MAGNETIC ANOMALY DATA FROM THE BARENTS SEA-EAST GREENLAND SHELF REGION
Jan R. Skilbrei (Geological Survey of Norway, po box 3006, N-7002, Trondheim, Norway,
email: jan.skilbrei@ngu.no)
Potential field anomalies from the Barents shelf and the East-Greenland shelf is interpreted in a pre 'break-up' reconstruction. The geology of the Barents Sea and the Greenland margin is interpreted using the magnetic anomaly in this pre-Eocene context. The magnetic data has been compared with the seismic profiles and the gravity data in order to identify the structural highs and the sedimentary basins, and constrain the interpretation.
The Precambrian and Caledonian geology of Scandinavia and East Greenland is compared with the geophysical data in order to differentiate between intrabasenent and suprabasement sources of the anomalies on the shelves. Long-linear anomalies are related to rift structures of the East Greenland shelf and the Barents Sea. A comparison with the Basin and Range Province of the western U.S. will be made, and the implications of the interpretations for the petroleum industry will be discussed. The lineament patterns as they are illustrated by the potential field images of shelves of the North-Atlantic region will be commented on.
JSA09/W/18-A3 1100
POLAR CRUSTAL ANOMALIES IN SATELLITE MAGNETIC AND GRAVITY OBSERVATIONS
Ralph R.B. VON FRESE, Hyung Rae Kim (both at Dept. of Geological Sciences, The Ohio State University, Columbus, OH 432120, USA, email: vonfrese@osu.edu, kim@geology.ohio-state.edu) Patrick T. Taylor (NASA Code 921, Goddard Space Flight Center, Greenbelt, MD 20771, USA,
email: ptaylor@ltpmail.gsfc.nasa.gov)
Comparing satellite gravity data with terrain gravity effects can help sort crustal from subcrustal components. Crustal thickness variations may be estimated from the spectral correlation between the two data sets. Satellite gravity observations in combination with terrain gravity data may also be used to help estimate crustal components in satellite magnetic measurements. Here the first radial derivative of the terrain gravity effect may be used via Poisson's theorem for correlative potentials to sort crustal from noncrustal components in magnetic observations. Estimates crustal thickness variations and crustal components in satellite gravity and magnetic observations for the Arctic and Antarctic are presented.
JSA09/W/10-A3 1115
POLAR IONOSPHERES
Ted ROSENBERG (Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742-2431 USA, email: rosenberg@uarc.umd.edu)
Quite recently, Newell [Eos, 79(51), 625, 1998] summarized evidence of the importance, even perhaps the controlling influence, of the ionosphere on magnetospheric dynamics, as manifested by the behavior of the aurora and other aspects of magnetosphere-ionosphere coupling. Changes in the background ionospheric conductivity affected by the amount of sunlight is thought to play the crucial role, with the flux of ionizing charged particles perhaps also having some significance. The two polar ionospheres are linked by the extension of the geomagnetic field into space which also provides a path for moving charged particles between hemispheres. Hence the importance of understanding the similarities and differences of the polar ionospheres. New facilities established in both polar regions in recent years have enabled extensive and simultaneous coverage of the polar ionospheres. The distributed high-latitude ground-based observations provide a valuable complement to the measurements being made in space. This has created new opportunities for global (including conjugate) studies of particle precipitation, magnetic pulsations, ionospheric currents, radiowave emissions, and the structure and dynamics of the ionospheric plasma, as will be reported on here.
JSA09/W/20-A3 1130
WHERE ARE THE MAGNETIC POLES ?
Wallace H. CAMPBELL (World Data Center A for Solar Terrestrial Physics, NGDC / NOAA, 325 Broadway, Boulder, CO 80303-3328, USA, email: whc@ngdc.noaa.gov
Cartographers indicate a specific location in the Northern and Southern Hemisphere of the Earth as the place of a "Magnetic Pole." To geomagnetic scientists, it is unclear what is the meaning or value of such map locations. "Magnetic" poles of differing location can be defined by the dip of the International Geomagnetic Reference Field, by a geomagnetic co-ordinate system, by the eccentric geomagnetic field axis or surface dip, by paleomagnetic evidence, or by local (induction anomaly and external disturbance sensitive) determinations of a vertical field. These differing pole locations can be tens of degrees apart. The locations are slowly varying in poisition over the years, although cartographers never attach dates to their "exact" poles. Contrary to some popular beliefs, the mapped spot is, most certainly, not the average global location toward which a compass points.
JSA09/P/01-A3 1145
PECULIAR DECREASE IN THE MAGNITUDE OF VERTICAL GEOMAGNETIC FIELD NEAR THE MAGNETIC POLES IN SUMMER SEASON
Naoshi FUKUSHIMA (Dept. of Earth and Planetary Physics, University of Tokyo, Tokyo 113-0033 Japan. email: fukusima@nipr.ac.jp)
This paper points out a remarkable decrease in the magnitude of vertical geomagnetic field Z (amounting to several tens of nT) observable only in the summer in the polar regions centering the northern or southern magnetic poles. This peculiar phenomenon was known since the Second International Polar Year 1932-1933, through an extensive analysis of world data by Vestine et al. compiled in the Carnegie Institution of Washington Publication No. 580 (1947). Later with the aid of the data during IGY 1957-58 and following years, Mansurov and Mansurova (1971) showed that the same kind of Z-decrease were also observed at Vostok, magnetic south pole station in the Antarctica. It is worth noting here that the geomagnetic anomaly maps published by Langel and Estes (Figs. lb and 2b on pages 2497-8 in JGR 90 [1985] showing the calculated difference of Z-values at 500 km level from their model based on the Magsat data) show the greatest negative anomaly over Vostok, because the Magsat was operative during the austral summer.
The peculiar decrease in geomagnetic Z-field near the magnetic poles in summer seasons has been discussed at present even in connection with the earth's interaction with the solar wind, including the effect of IMF (Interplanetary Magnetic Field) Bz and By. However, it will be more essential for us to study a possible influence of ionized plasma produced in the sunlit polar ionosphere. We must bear in mind that the daily-mean energy received from the sun in the polar area at the summer solstice is even greater than at the equatorial region.
JSA/09/C/GA5.01/W/20-A3 1200
DETERMINATION OF THE MAGNETIC POLES LOCATION
Vladimir V. KUZNETSOV, Vsevolod V. Botvinovsky (Institute of Geophysics SB RAS, Koptyug av.,
3, Novosibirsk 630090, Russia; e-mail: kuz@uiggm.nsc.ru)
The idea of this model is that the magnetic pole drift is caused by change of the intensity of the main dipole field and the field of the global magnetic anomalies which are considered as sources that are quasi-independent from the main geomagnetic dipole field source. We have verified this hypothesis using the data of the geophysical magnetic observatories for the modern drift of the North magnetic pole (NMP) and the South magnetic pole (SMP). In particular, the NMP-1994 location was predicted by us. The observations of this location have confirmed our prediction with high accuracy. Based on the analysis of the magnetic observatories data, we have introduced a correction into the location of the NMP-1831 and the location of the SMP-1909. The application of our hypothesis has permitted us to explain the character of the magnetic pole motion during the reversal. The observations of the magnetic observatories and the hypothesis permit to interpret paleomagnetic data in a new way.
JSA09/E/03-A3 1215
SUB-GLACIAL IMAGING IN SCHIRMACHER OASIS-WOHLTHAT MOUNTAINS REGION IN ANTARCTICA EMPLOYING HELI-MAGNETIC AND SURFACE GRAVITY SURVEYS
Saurabh K. VERMA, H.V. Rambabu, and G.S. Mital (National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, India, email: postmast@csngri.ren.nic.in)
Helicopter-borne magnetic survey was carried out over an area measuring approximately 100 km x 85 km between the Schirmacher Oasis (SO) and Wohlthat Mountains (WM) during the Seventh Indian Antarctic Expedition. Two-dimensional spectral inversion of the data revealed gross features of the topography of the base of the glacier between SO and WM. Subsequently, during the Ninth Indian Antarctic Expedition, Helicopter-supported surface gravity measurements were done along five profiles over the glacial region. Modeling of these profiles provided additional information on the glacial depths, first order structural features, and moho thickness in the region.
Combined interpretation of the magnetic and gravity data has resulted in a more coherent model of the subglacial structure. Imaging of the magnetic map of the region highlights the prominent subglacial features including a graben like structure between SO and WM. Gravity modeling reveals the presence of faults in the subglacial basement that could be correlated with the known faults and structural trends observed in SO.
JSA09/W/22-A3 1230
RESTORATION OF SPACE PARTICLE DATA COLLECTIONS
Nickolay N. Kontor, Nickolay N. PAVLOV, and Elmar N. Sosnovets (Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119899, Russia, email: nnpavlov@taspd.npi.msu.su).
Since 1965, Theoretical and Applied Space Physics Division, Institute of Nuclear Physics, Moscow State University carries out monitoring of charged particles in space with use of Russian far spacecraft and satellites. Significant part of the data from old missions is stored only on paper, many data sets have been saved due to special issues published by the WDC-B. The data sets from both paper and old tapes needed to be restored and transferred to the modern computer media. This work has been supported by NASA, grant NAG5-4656. Useful collaboration with NSSDC has also made this project realizable.
Assuming that similar projects are being currently launched by many research groups for the sake of utilization of the benefits of the new Internet era we would like to share our experience in typical problems, common approaches and software tools used in our work. The main goal is to make the collection living and publicly accessible via Internet. Such issues as data input, data formats, file structure, use of database system, IDL, Java are concerned here. Interactive graphic rectification of raw data sets and creation of the proper documentation are highlighted as the most important for the solving of a key problem of data quality. A simple method of improving the ability of navigation within a multi-spacecraft data collection based on a plain ftp is discussed as well as our approaches to the effective graphic access to the data. Attaching of some simple tools for remote data analysis to the user interface is also considered as a way to make the services more attractive and useful.
Tuesday 20 July AM
Presiding Chair: Ralph von Frese (Ohio State University, USA)
JSA09/W/16-A2 Poster 0930-01
FIRST ABSOLUTE GRAVITY MEASUREMENTS AT THE FRENCH STATION DUMONT D'URVILLE (ANTARCTICA)
Martine Amalvict, Jacques HINDERER (both at Ecole et Observatoire des Sciences de la Terre, 5 rue Descartes, 67084 Strasbourg Cedex, France, e-mail: mamalvict@eost.u-strasbg.fr).
We present the first series of absolute gravity measurements at the French station Dumont d'Urville in Antarctica. These measurements will be performed with a FG-5 (Micro-g Solutions Inc.) absolute gravimeter in a continuous way during a week in March 1999. We will report the conditions of the experiment for which a thermally regulated shelter has been built and discuss the quality of the results. A special attention will be paid to the influence of tidal ocean loading and different corrections according to existing models will be tested. We will also take this opportunity to establish a gravimetric link with a Scintrex CG3-M relative gravimeter to the tide gauge of Dumont d'Urville belonging to the ROSAME network in order to provide a geodetic reference. It is essential to be able to distinguish in the long term any vertical motion of tectonic origin from true sea level changes. A further use of our determination of the gravity field is to allow the establishment of a precise gravimetric calibration line between Hobart (Tasmania) and Dumont d'Urville which should be useful for the marine geophysics campaigns in this region.
JSA09/W/07-A2 Poster 0930-02
INTRAMAP - INTEGRATED TRANSANTARCTIC MOUNTAINS AND ROSS SEA AREA MAGNETIC ANOMALY PROJECT: STATUS & PROGRESS
Massimo CHIAPPINI (Istituto nazionale di Geofisica, Vigna Murata 605, 00143 Roma, Italy;
Email: chiappini@ingrm.it) Fausto Ferraccioli, Emanuele Bozzo (DISTER, Univ. Genova, Italy,
email: magne@dister.unige.it) Detlef Damaske (Bundesanstalt für Geowissenschaften und Rohstoffe Stilleweg 2, 30655 Hannover Germany, Email: d.damaske@bgr.de) John Behrendt (INSTAAR - University of Colorado Boulder, CO 80309-0450 USA, Email: behrendj@stripe.colorado.edu)
Within the framework of the evolving Antarctic Digital Magnetic Anomaly Project (ADMAP), an international consortium called INTRAMAP was initiated in 1997. The aim of INTRAMAP is to compile the aeromagnetic, ground and marine magnetic data acquired throughout the "Ross Sea Antarctic sector" (60 degrees south and 135-255 E) including: the Transantarctic Mountains (TAM), the Ross Sea, Marie Byrd Land, the Pacific Coast, and also to begin the compilation effort to new data over the Wilkes Basin to be collected along the "backside of the TAM" which is the site of proposed future activities within joint Italian, US and German cooperations. Finally the integration of satellite and near-surface magnetic data will result in a compilation that accurately portrays the fullest possible spectrum of magnetic anomalies from the Antarctic lithosphere in the "Ross Sea sector". The final compilation will contribute both in delineating and in studying the major structural and geologic components of the Ross Sea Area. From the geodynamical point of view, the merged magnetic data will permit assessment of different tectonothermal provinces within the West Antarctic Rift System leading to regions of differential uplift along the TAM and in Marie Byrd Land. The status and progress of the project will be presented.
JSA09/W/06-A2 Poster 0930-03
THE HYDROTHERMAL STRUCTURE OF POLYTHERMAL GLACIERS IN SVALBARD USING GROUND PENETRATING RADAR
Anja PÄLLI (Department of Geophysics, University of Oulu, BOX 400, 90571 Oulu, Finland,
E-mail: anjapa@paju.oulu.fi); John Moore (Arctic Centre, University of Lapland, BOX 122, 96101 Rovaniemi, Finland, E-mail: jmoore@levi.urova.fi)
A Ramac (Malå Geosience) Ground Penetrating Radar (GPR) working at 25, 50 and 200 MHz frequencies has been used to map the hydrothermal structure of two polythermal glaciers Hansbreen and Werenskjoldbreen and their tributaries in southeast Spitsbergen. The GPR data was compared with the data from several temperature boreholes instrumented with thermistors and with heights of water tables in moulines. The data collected is of high resolution and the cold ice temperate ice interface was easily detected in all the measured profiles.The bedrock reflection was detected almost everywhere. Many moulins and smaller water channels (probably of metre scale) seen as point reflectors were mapped. The GPR data shows that the hydrothermal structure of Hansbreen is highly variable both along the centre line and on transverse profiles. The temperate firn/cold ice transition appears to show a more gradual transition than observed on other glaciers in northern Svalbard. Water contents in cold and temperate ice were investigated by fitting hyperbolic model reflections to point reflectors. The water content in temperate ice varied from 0 to 2% but water contents up to 5% were calculated from areas associated with surface crevassing and moulins. Isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier.
JSA09/W/11-A2 Poster 0930-04
DETERMINATION OF PLATE TECTONIC MOTION RATES IN THE REGION OF THE ANTARCTIC PENINSULA
MICHAEL MAYER, Klaus Lindner, Hansjoerg Kutterer and Bernhard Heck (all at Geodetic Institute, University of Karlsruhe, Englerstr.7, D-76128 Karlsruhe, Germany,
email: mmayer@gik.uni-karlsruhe.de)
The Geodetic Institute of the University of Karlsruhe (GIK) takes part in a bundle project called "Reference Network Antarctica II" which is sponsored by the Ministry of Science, Research, Education, and Technology of Germany (BMBF). Within this bundle project seven German institutions are co-operating in order to create a three-dimensional velocity field of the atlantic part of Antarctica. The basis and the motivation of this bundle project lays in the previous bundle project "Reference Network Antarctica" which was sponsored by the BMBF, too. The main goal of this bundle project was the creation of a highly precise three-dimensional reference network for the whole Antarctic continent. In the Antarctic summer 1994/95 simultaneous GPS observations (24 h per day, 21 days) were carried out at GPS stations situated on Antarctica and on neighbouring tectonic plates to fulfill the main goal of the first bundle project. This work was done within the framework of the SCAR Epoch 95 Campaign (SCAR95). The GIK working group was responsible for preparatory investigations of the achievable point positioning accuracy by means of spectral analysis, and processing of the GPS observations based on the Bernese GPS Software Version 4.0 (BS). Furthermore several investigations were carried out concerning the accuracy of point positions (influence of atmospheric disturbances, ambiguity resolution strategies, effect of the selection of the ITRF-fiducials). Using the experiences gained from processing a network covering the complete southern hemisphere (SCAR95-data plus IGS-data) - characterized by inhomogeneous baseline lengths (from 1 km up to 4400 km) as well as by an irregular distribution of the sites showing high density in the area of the Antarctic Peninsula and the closeness of some network points to the geomagnetic pole in East Antarctica - the above mentioned second bundleproject was initiated.
JSA09/W/03-A2 Poster 0930-05
HOW GEODETIC OBSERVATIONS CAN CONTRIBUTE TO THE DETERMINATION OF VERTICAL CRUSTAL DEFORMATIONS IN WEST GREENLAND INDUCED BY CHANGING ICE LOADS
Mirko SCHEINERT (Reinhard Dietrich Technische Universität Dresden, Institut für Planetare Geodäsie, D-01062 Dresden, Germany, e-mail:mikro@ipg.geo.tu-dresden.de)
Mass changes of ice sheets induce loading effects on the earth crust. These vertical deformations occur on different time scales. Viscous effects are due to the glaciation history, while elastic effects are mainly caused by recent ice mass changes. These different effects will be reviewed especially for West Greenland.
West Greenland provides a unique research field: large regions along the west coast are ice-free. This allows a comparably easy access to carry out geodetic field measurements in the immediate vicinity of the proceeding ice mass changes, which are the largest at the ice edge. In order to observe the ice-induced vertical deformations a special GPS network between the 61st and 69th parallel was set up. The first epoch observation of this network was carried out in 1995. These GPS observations were densified along the 67th parallel, from the coast up to the ice edge, in the subsequent years. Additional relative gravimetric observations in the region of Kangerlussuaq supplemented the GPS observations. The set-up of the investigations will be reported. The results of the regional observations obtained so far will be presented and discussed.
JSA09/E/10-A2 Poster 0930-06
MORPHOMETRIC PATTERNS AND GEODYNAMICS OF THE LOMONOSOV RIDGE AND ADJUSENT BASINS
Elena DANIEL (All-Russia Research Institute for Geology and Mineral Resources of the World Ocean, 1, Angliysky pr., St.-Peterburg, 190121, Russia, email: dani@vniio.nw.ru)
The new computer bathymetry model reveals essential features of the ocean floor in more detail than in previously published small-scale bathymetric maps. The patterns of the ocean relief forms characterize the deep Arctic basin structures dynamic. Been situated between the Eurasian and Amerasian basins the Lomonosov Ridge has several bends through its extension. These bends coordinate with the such of the Gakkal Ridge and surrounded it basins. These bends are also accompanied by transverse extend line zones. These zones cross the Eurasian and Amerasian basins. The zones characterize ancient tectonic frame to with geometry of temporary spreading is submitted. In the seafloor relief these zones are presented by various forms having the same rout of extension and increased gradient in bathymetry. The escarpments with height of 500-600 m between plains are display of these zones. The plains are characterized by isobaths of 1,600; 2,200 m and of 2,700; 3,200; 3,800 m on the ridges and in the basins, respectively, with is the truth both from the Eurasia and North America point of view. The seismosounding data according the geotransect "De Long islands - Makarov Basin" (Krjukov et al., 1993) show that escarpments are the reflection of the earth crust flexures with accompany its rejuvenation. Probably the formation of the ocean in the Amerasian basin was together with long formation of the surrounded steps, relict of which are saved in temporary seafloor relief.
JSA09/W/19-A2 Poster 0930-07
AEROMAGNETIC FEATURES OF ENDERBY LAND AND EASTERN DRONNING MAUD LAND: IMPLICATIONS FOR GONDWANA ASSEMBLY
Alexander V. GOLYNSKY (VNII Okeangeologia, 1 Angliysky Ave., 190121, St. Petersburg, Russia, email: sasha@gus1.vniio.nw.ru)
In the shield areas of East Antarctica (EA) interpretation of aeromagnetic data allowed to better define the boundaries between the Archean stable blocks and the Proterozoic mobile belts, and to trace these boundaries beneath the ice sheet. Four main boundaries of the EA Shield terranes are distinguished within Enderby Land and eastern Dronning Maud Land from the change of magnetic anomaly pattern. The boundary between the Napier terrane and the Rayner terrane is delineated by the oval band of high-intensity magnetic anomalies. The Napier terrane displays a complex magnetic grain which tends to reflect the lithology of granulites. Metasedimentary rocks and granitoids are associated with magnetic lows, whereas orthogneisses correlate with highs. A broad magnetic low, at least 100 km in width, is associated with the structural grain of the Rayner Complex originated during 1000 Ma event. The boundary between the Rayner - Lützow-Holm Bay (LHB) terranes is clearly visible on the map by distinction of trends. The elongated, fragmented magnetic highs and intervening lows of the LHB terrane is associated with the rocks metamorphosed under granulite facies conditions. Character of distribution and structural pattern of magnetic anomalies do not allow us to accept models of Gondwana reconstruction in which the LHB Complex in EA and Highland Group of Sri Lanka developed in the suture zone at the last phase the Pan-African orogeny and the Late Proterozoic supercontinent was separated by a missing ocean at the position of the LHB Complex. The absence of any well-defined anomalies coherently running in direction of proposed Cambrian orogenic belt allow us to joint to more appropriate conclusion of many authors that the 500 Ma event in East Antarctica was an intraplate phenomenon of Gondwana and restricted to minor though widespread activity.
JSA09/W/04-A2 Poster 0930-08
THE GLENNY ANOMALIES OF ANTARCTICA AND SURROUNDING SEAS
Andrej N.Grushinsky (United Institute of Physics of Earth, Russian Academy of Science, B. Gruzinskaya, 10, Moscow 123810, e-mail: grush@uipe-ras.scgis.ru, Pavel A.Stroev (Sternberg State Astronomical Institute, Moscow State University, Universitesky pr., 13, Moscow 117899,
e-mail: pstroev@sai.msu.su) and Eugenij D.Koryakin (Sternberg State Astronomical Institute, Moscow State University, Universitesky pr., 13, Moscow 117899, e-mail: koryakin@sai.msu.su)
The gravitational effect of far zones and Glenny anomalies for Antarctica has calculated. This calculations take into account the thickness of sediments and their mean densities. The structure of the total correction for middle and far zones was analysed. The main features of this correction is determined by the middle zone one. West Antarctica has a poorly effect on the form of middle zone correction isolines. This fact allows to suppose, that West Antarctica is an active continental margin. The field structure of the far zone gravitational effect connect with the distribution of continents and ocean on the Earth and have clearly expressed long-waved character. The influence of far zones manifests in the total correction by asymmetry: the values of correction for Pacific ocean sector some less, than for Indian ocean one. The structure of Glenny anomalies clearly enough indicates the main geological structures of Antarctica and allows to do some conclusions about the structure of its lithospere. The Glenny anomalies correlation with heat flow was found for South ocean. The preliminary conclusions about isostatical models for different regions of Antarctica may be made from the considerable analysis. Authors are grateful to Russian Fundamental Investigations Foundation, which provided financial support (grant 98-05-64446).