Holocene history of water convection and ice-rafting in the Burton Basin, Mac.Robertson Shelf, and its implications on the distribution of ice masses and bottom-water production in this region.

gerhard.kuhn [ at ] awi.de


In the scope of the research project Late Quaternary East Antarctic Ice SheetDynamics inferred from marine sediments a sediment core recovered from Burton Basin with RV Polarstern was investigated by sedimentological and mineralogical means. The sediment basin is located on MacRobertson shelf west of Prydz Bay and Cape Darnley. There the Lambert Glacier, representing the world`s largest outlet glacier, drains about 20 % of the East Antarctic Ice Sheet. The goal of our study is to offer clues to the ice configuration in the MacRobertson region from the Last Glacial to modern times and to decipher the impact of global sea-level rise and meltwater pulses on East Antarctic Ice Sheet floating forced by Northern Hemispheric ice sheet decay. We therefore reconstruct the convection of water in the basin as a possible indicator for the activity of the Antarctic Coastal Current or production of Antarctic Bottom Water as well as the timing of ice-rafting processes with the help of grain size analysis and X-radiographs. The provenance of current-derived and ice transported material (IRD) is determined by clay mineral- and heavy mineral analysis, respectively. In order to decompose high resolution grain size distributions that emerge from mixing of different transport and sedimentation processes, we apply end-member modeling to the sediment record.Results point to lifting of the grounded ice sheet on MacRobertson shelf prior to thebeginning of glacial retreat that started around 12.0 14C ka. This potentially indicates linkages to pulses in postglacial global sea level rise. During the local glacial retreat convection of water masses within the Burton Basin strongly increased with a maximum strength at 9.5 14C ka possibly hinting to invigoration of the Antarctic Coastal Current in the nearshore region. At the same time a first decline in the input of ice-rafted debris suggests the retreat of the calving line of the floating ice sheet farther inland with respect to the position of the sediment core. During the mid-Holocene optimum calm water conditions in the sediment basin aredistinguished by sediment texture and down-settling of suspension load. This could be referred to either a weakened Antarctic Coastal Current, a decrease in sea ice production and associated less formation of dence bottom water (AABW) or increased input of meltwater. The timing is consistent with a period of warming in ice core records e.g. from Taylor Dome. The last occurence of IRD is dated to 6.0 14C ka which coincides with diminished sea level rise at this time. This timing suggests a strong coupling of the ice sheet on MacRobertson Shelf to global sea-level changes. During the neoglacial period of the last about 3.0 14C ka strengthened water convection in Burton Basin is tentatively related to times of strong brine rejection processes associated to sea ice production. The latter itself is coupled to the strength of katabatic winds and westward flow of Antarctic Coastal Current.As the region off Cape Darnley is found to be the second largest area in Antarctica inregard to the production of sea ice it is speculated to be a region of possible AABW formation. Insights into variations of the water convection during the past are therefore a useful tool to reconstruct sea ice cover on the one hand side and changing AABW production in times of warming on the other hand.

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Conference (Talk)
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First SCAR ACE Symposium, 07.09. - 11.09.2009, Granada, Spain..
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Borchers, A. , Hartmann, K. , Kuhn, G. and Diekmann, B. (2009): Holocene history of water convection and ice-rafting in the Burton Basin, Mac.Robertson Shelf, and its implications on the distribution of ice masses and bottom-water production in this region. , First SCAR ACE Symposium, 07.09. - 11.09.2009, Granada, Spain. .

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