East Antarctic Ice Sheet dynamics during the late Quaternary inferred from marine sediment records of the Indian sector of the Southern Ocean
Final Report Abstract
During expedition ANT-XXIII/9 with RV Polarstern to the southern Indian sector of the Southern Ocean, modern sediments and several sediment cores were recovered on a transect from the Prydz Bay Shelf, MacRobertson Shelf and adjacent continental slope towards the Enderby Basin and the Kerguelen Plateau. The sediment records are studied to gain insights into palaeo glacial dynamics of the East Antarctic Ice Sheet from a marine perspective by the reconstruction of glaciomarine processes in the past. The study area is bordered by the Lambert Glacier-Amery Ice Shelf system that drains about 20% of the East Antarctic Ice Sheet and is considered to be representative for the behaviour of the whole East Antarctic Ice Sheet. The retrieved sediment cores allow the reconstruction of ice-sheet dynamics at different time scales, comprising high-resolution Holocene records, the time interval of the latest glacial-interglacial cycle during the past 130 kyr, and one long-term record back to the mid-Pliocene. Analytical work started in June 2007, comprising granulometric analysis to infer sedimentation patterns and bottom-current activity, counting of lithoclasts >2 mm in x-ray radiographs as a proxy for ice-rafted debris (IRD), examination of mineralogical and geochemical composition of current- and ice-derived detritus for provenance studies, and determination of element distributions by XRF-measurements. Preliminary age models were established according to lithostratigraphy at the Antarctic continental margin (e.g. by defining the transition from lithogenic to biogenic materials as an indicator for the transition from MIS 2 to MIS 1 ) and by the use of diatom stratigraphy for the pelagic records. Following the geological actualistic principle, recent sedimentation patterns and provenance signals were surveyed to establish a basis for the reconstruction of past variations in bottomcurrent activity and origin, as well as shifts in the provenance of material carried by icebergs. Two different source regions of detrial material can be inferred on the basis of heavy-mineral assemblages and clay mineralogy. The dense mineral matter of the fine sand fraction from Prydz Bay Shelf is characterised by predominant hornblende. In contrast, sediments from MacRobertson Land show high amounts of garnet. The clay phases show differences in illite chemistry and in the amount of kaolinite. Very high contents of kaolinite in sediments from MacRobertson Shelf in comparison to material from the Prydz Bay hint to an undefined clay source covered by the ice-sheet in the hinterland of MacRobertson Land. A sediment core from the MacRobertson continental slope, which is investigated in regard to temporal shifts in sediment supply since the last glacial cycle, provides a good record of past variability in the source region both of current derived and ice-transported material. First results lead to the assumption that during interglacial stages and stadials at least sandy material is provided from the Prydz Bay as a result of enhanced iceberg mobility. The anticipated study of a sediment cores from the Kerguelen Plateau will give insight into IRD fluxes and climate-related bottom-water dynamics during the last 130 kyr. Another record from the Enderby Basin reaches back to the mid-Pliocene. Downcore fluctuations in IRD and biogenic opal concentrations are possibly linked with long-term climate changes that took place at the Plio-/Pleistocene boundary and during the mid-Pleistocene climate transition. According to latest publications, both events caused marked responses of the East Anatrctic Ice Sheet behaviour in the Prydz Bay hinterland. In addition to the continuation of the various aspects of laboratory work, future efforts envisage the refinement of chronostratigraphy through the application of sophisticated approaches in palaeomagnetics, biostratigraphy, and radiocarbon dating.
