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Address : 1Alfred Wegener Institute For Polar and Marine Research, Germany; 2University of Tromsّ, Norway
Celebration date : 29 Monday September 2008
Author name : Hass, H. Christian1; Kuhn, Gerhard1; Forwick, Matthias2; Vorren, Tore O.2

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  • Article title : The medieval warm period and the Little Ice Age in marine sediments from Maxwell Bay, King George Island, West Antarctic Peninsula
    Article type : Environmetal Geology
    Location : International Geological Congress,oslo 2008

    Fulltext :

    The West Antarctic Peninsula (WAP) is a region of considerable changes in the climate system. The global warming trend is most significant in this region (>2°C in 50 years) which makes it a perfect place to compare warm phases of the past with the recent trend. Maxwell Bay is a > 500 m deep fjord system between King George and Nelson islands, WAP. Here we present results of a high-resolution gravity core taken at 461 m of water depth close to the mouth of Potter Cove, one of the tributary fjords that feed Maxwell Bay. Methods applied include AMS radiocarbon age determinations, X-ray investigations of the sediment structure, investigations of the magnetic susceptibility and XRF scanning to discriminate different sediment source areas, granulometry at 1-cm intervals to characterize the depositional environment, and TOC and carbonate analyses to gain information on marine productivity and sea-ice coverage.
    The sediment core is 928 cm long and is basically composed of terrigeneous silty clay with only scattered IRD and some intercalated tephra layers. Five radiocarbon dates reveal that it covers the past 2000 years; a reservoir correction of 1370 years was applied. The grain-size mean values suggest coarser sediments during colder climate episodes such as the Little Ice Age (LIA, c. AD 1350-1900) and finer sediments during warmer climate phases such as the past 100 years or the Medieval Warm Period (MWP, c. AD 700-1350). The magnetic susceptibility has been relatively stable before AD 1400. Few clear minima that correspond with elevated TOC values are likely reflecting episodes of increased productivity and reduced sea-ice cover during the MWP. A significant change in the sediment source areas is suggested at the beginning of the LIA. Magnetic-susceptibility values decrease rapidly and never return to the values before the LIA. XRF data that are being measured will provide more information on that issue.
    Summer temperatures in the investigated area exceed 2°C and thus summer discharge of meltwater is immense and forms the main sediment transport mechanism. Large plumes of suspended fine-grained sediment exiting e.g. Potter Cove can be detected on satellite images. Under cooler climate conditions the amount of fine-grained sediment decreased with the likely decrease of meltwater during summer. The reduction of fine material led to a coarsening of the sediments during the cooler phases. The opposite was the case during warmer climate phases (fining of sediments). The synopsis of the measured parameters shows clear evidence of the recent warming, the LIA, and the MWP. Conditions of the MWP appear to have started already around AD 400. The climate reconstruction presented here correlates well with EPICA-DML ice-core results and it resembles the global temperature record for the past 2000 years in great detail.

     
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