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Die Expedition ANTARKTIS-VIII/1-2, 1989 mit der Winter Weddell Gyre Study der Forschungsschiffe "POLARSTERN" und "Akademik Fedorov"

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Augstein, E. , Bagriantsev, N. and Schenke, H. W. (1991): Die Expedition ANTARKTIS-VIII/1-2, 1989 mit der Winter Weddell Gyre Study der Forschungsschiffe "POLARSTERN" und "Akademik Fedorov" , Reports on Polar Research, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, 134 p. .
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Abstract:

The Polarstern-Expedition ANT VIII/ 1 was separated into twosections. During the first part from Bremerhaven to Vigo, Spain, thenew hydroacoustic sonar systems Hydrosweep and Parasound, whichwere installed in summer 1989, were calibrated in the North Seaand tested in the deep sea of the Bay of Biscay and at the Frenchcontinental shelf. During the second part of the cruise from Vigo toPuerto Madryn, Argentina, deep sea trials and special tests wereperformed at the Romanche Fracture Zone with both systemsHydrosweep and Parasound.During the entire cruise, various groups carried out air chemistryobservations in the Atlantic along the north-south profile. In additionozone observations in the lower atmosphere and water sampling inthe upper water column were performed systematically. Data fromradiosondes were collected continuously during the cruise and usedfor an improved modeling of the atmospheric correction of AVHRR-datafrom NOAA satellites. CTD-measurements were carried out inthe Hydrosweep test areas, and XBT's were launched regularly everyone degree of latitude.For the deep sea trials and comparisons with external data, Seabeammeasurements from the French R/V Jean Charcot and Hydrosweepdata from the German R/V Meteor were made available for thisproject by the originators of the data. For the determination of theinternal accuracy, repetitive measurements of selected profiles werecarried out.Another goal was the verification and analysis of the Hydrosweepcross-fan calibration technique used for the determination of themean sound speed value. For these investigations, special profileswere measured in the abyssal plain of the Bay of Biscay. The meanwater sound velocity, derived from Hydrosweep measurements, wascompared to the results from independent CTD-data in the samearea. The maximum observed difference was ± 5 m/s, which wouldcreate an error of about 3% of the water depth. The generalprecision for the mean sound velocity from a period of calibrations is± 1 m/s.The most important prerequisite for a precise sea floor survey withmultibeam sonar is the precise positioning of the ship. Positioningwith the Global Positioning System GPS/NAVSTAR can be performedin the single station or in the relative navigation mode. To secure agood position accuracy for the sea trials in the Bay of Biscay, therelative navigation mode was used. A reference station was deployedat the French marine research institute IFREMER near Brest.Relative navigation with GPS/NAVSTAR is based on the technique ofpseudo range code corrections.Simultaneous operation of both systems Hydrosweep and Parasoundwas checked in the deep waters of the Bay of Biscay. At the end ofthe sea trials and performance tests, the acceptance procedure wasclosed. Polarstern arrived in Vigo on the 14 August 1989, and 20engineers and scientists disembarked.On the transit from Vigo to the Romanche Fracture Zone, a numberof additional tests and trials in shallow and deep sea waters weredone with the new hydroacoustic sonar systems. Studies of thesystem performance in areas with different morphological structuresand topographic features were performed en route. Training coursesfor maintenance, repair and operation of Hydrosweep and Parasoundwere given by technicians of the manufacturer. The investigationduring the transit confirmed that Hydrosweep and Parasoundproduced excellent results, even under difficult hydroacousticconditions. However, the main requirement is to have a well trainedoperator to observe and control the measurements.At the Romanche Fracture Zone, first the re-survey of the 12 testprofiles was performed. The parallel profiles are arrangedperpendicular to the fracture zone. These profiles were firstestablished and measured in 1984 during the deep sea calibration ofSeabeam on the Polarstern-Expedition ANT III/l. The second surveyof these profiles was performed for Hydrosweep sea trials on theMeteor-Expedition M 6/4 from 28 December 1987 until 12 January1988. The comparisons between the three surveys on identicalprofiles indicate an excellent correspondence. Even on large scalemaps, small structures and features on the sea floor can be verifiedfrom different surveys.The vast Romanche Fracture Zone (R.F.Z.) is the most prominentdepression of the Mid-Atlantic-Ridge (MAR). The 920 km long east-westtransverse ridge has its the deepest point at the Vema Depthwith nearly 8 000 m. The southem slope has inclinations of up to45°. The central part of the trench bottom is covered with sedimentlayers or sediment bridges.During recent years, intensive marine geophysical and geological studieshave been carried out there. Physiographic and geomorphological investigationhave been done with GLORIA images (R/V Discovery) and Seabambathymetry (R/V Jean Charcot). The Romanche Fracture Zone has alsoattracted the attention of physical oceanographers,since it is assumed that the cold Antarctic Bottom Water passes through this area. For additional investigations in this area, the survey area was enlarged during this cruise in a western direction. The area between 17°3O'W and 19°30'W along theRomanche Fracture Zone is now completely surveyed with multibeamsonar. However, prior to the postprocessing of the multibeam data,correction of the GPS-navigation must still be performed in order toproduce high precision large scale bathymetric maps.A new satellite tracking system for AVHRR-data from NOAA-satelliteswas installed on board Polarstern in the summer 1989. The remotesensing data shall be mainly used for sea-ice studies in the polarregions. During the first part of this leg, the system was tested andcalibrated. On the Atlantic, more than 15 satellite passes weretracked. The data were recorded on magnetic tapes and will be usedfor additional investigations at the institute. Measurements of thephysical and meteorological parameters, necessary for theatmospheric correction of the satellite data, were obtained fromradiosonde ascents and from observations on board.During this leg, air chemistry and ozone measurements wereperformed by various groups in continuation of their investigationsduring the Polarstern-cruise ANT VII/1 in 1988. The series ofinvestigations of the marine atmosphere and its chemistry wascontinued during this cruise. The first results indicate a goodagreement with the data from earlier expeditions.

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