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Analysis of helicopter and ship-borne magnetic data in the Amundsen Sea Embayment, West Antarctica

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Citation:
Denk, A. , Gohl, K. and Wobbe, F. (2010): Analysis of helicopter and ship-borne magnetic data in the Amundsen Sea Embayment, West Antarctica , 24. Internationale Polartagung der DGP, Obergurgl.-10. Sept. 2010. .
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Abstract:

In the last years, the Amundsen Sea sector of West Antarctica has attracted increasing attention due to the role of the marine-based West Antarctic Ice Sheet which partly drains into the Amundsen Sea. For instance, the Pine Island and Thwaites glacier systems exhibit an amplifying ice-flow velocity and a retreat of their grounding zones. Arising questions concern the regime of the underlying tectonically and magmatically formed basement which forms the controlling morphology geometry for past ice-sheet dynamics. Accurate models of the geodynamic-tectonic evolution contain some of the most important parameters for understanding and reconstruction of the paleoenvironment. The objectives comprise the identification of the boundaries between suspected crustal blocks and volcanic zones in Pine Island Bay. The glacier troughs and Pine Island Bay are thought to have developed along such tectonic boundaries.During two expeditions with RV Polarstern in the years 2006 and 2010 to West Antarctic continental margin, a considerable amount of magnetic data has been acquired in the Amundsen Sea, particularly in Pine Island Bay. In both years, the data acquisition was conducted with a permanent ship borne magnetometer system and a variable helicopter borne magnetometer system. Helicopter borne magnetic measurements were performed with a caesium vapour magnetometer, towed 30 m below the helicopter to avoid magnetic disturbances. During the flight campaign of 2010, in which 15000 km of flight data was gathered, a densification and supplement of the grid of 2006 containing 20000 km flight data, was achieved. The resulting grid covers an area of about 20000 km² and ranges from Pine Island Bay on the inner shelf to the outer shelf and above continental slope. Shipborne magnetic measurements were made by two fluxgate vector magnetometers, which are permanently mounted at the crow's nest of RV Polarstern. The data were sampled at one-second intervals. To take account of the influence of the metallic bulk of the ship, the ship undertook compensation loops. In the small area of a compensation loop the variation of the magnetic field due to the crustal magnetization are assumed to be negligible. The loops thus provide coefficients that relate the ship's heading, roll, and pitch movements to the variations in magnetometer measurements that they cause. Using these coefficients it is possible to correct the ship borne magnetic measurements in the wider area around the compensation loop.A fundamental division exists between the magnetic styles of the inner, middle and outer shelf. Short wavelength anomalies characterize the inner shelf and adjacent land. These short wavelength anomalies can be associated with the existence of magmatic structures which also can be observed in several magmatic exposures on small islands. In contrast, long wavelength anomalies are visible on the outer shelf. Parallel belts of similar magnetic signature can be identified here. These linear features are up to 500 km long and strike approximately southwest-northeast. Similar but less distinct features strike in a direction perpendicular to these. The magnetic anomaly pattern shows at least two phases of tectonic and magmatic processes in the Amundsen Sea Embayment.

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