Deglacier variability of the Filcher Ice Shelf, Antarctica

• Main Author: Lamping, Nele
• Format: Thesis
• Language: unknown
• Published: Univ. Bremen 2016
• Subjects: Antarctic; Austral; Filchner Trough; Southern Ocean; The Antarctic; Weddell; Weddell Sea; Antarc*; Antarctica; antartic*; Ice Sheet; Ice Shelf; Sea ice
• Online Access: https://epic.awi.de/id/eprint/42177/; https://hdl.handle.net/10013/epic.48935

The Weddell Sea Embayment (WSE) in Antarctica is one of the least explored environments on Earth. Ice streams and glaciers draining into it discharge more than 22 % of Antartic continental ice to the Southern Ocean. Due to extensive sea ice cover and harsh weather conditions throughout the year, this region is largely inaccessible, leaving it with only sparse knowledge about the deglacial history since the Last Glacial Maximum (LGM). Understanding the post–LGM evolution of the Antarctic Ice Sheet (AIS) in this sector is crucial in order to test and calibrate numerical ice sheet models that aim at predicting future AIS stability and dynamics. Especially the grounded ice sheet extent and retreat history within the cross–shelf Filchner Trough, a paleo–ice stream trough incising the southern continental shelf of the WSE, is controversial. For this thesis I investigated giant gravity cores (GGC) recovered from the deepest parts of the inner Filchner Trough, just seawards the ice shelf edge position during the Austral summer 1987/1988. Apart from describing the sedimentary lithologies and structures, a multi–proxy approach, including the determination of grain–size distributions, TC/TOC contents, magnetic susceptibilities, water contents and shear strengths has been applied in order to define sedimentary facies. Furthermore, ten new and reliable 14C radiocarbon ages, derived from calcareous foraminifera, are provided in order to reach a better understanding about the deglacial history of the WSE. Detailed analyses of the sediments reveal a retreat stratigraphy on the southern Wed-dell Sea continental shelf, containing distal glaciomarine sediments overlying sediments that have been deposited rather proximal to the ice sheets grounding line (GL). The distinction between these two sedimentary facies is largely based on grain–size analysis, determination of water contents, wet bulk densities (WBD) and shear strengths. These results in combination with the constrained 14C radiocarbon ages indicate that since the last ~5.8 cal. 14C ka BP the depositional environment in the Southern Weddell Sea must have been comparable to those observed today and hence, that the ice sheet must have started its landward retreat prior to that. Unusually high TOC contents in only one of the two investigated cores not only show that the GGC’s must have been fed from different catchments, but also that TOC contents in this region have to be treated with caution, since fossil carbon from the hinterland may contaminate samples significantly and would have a˙ected potential AIO ages, thereby leading to erroneous interpretations of postglacial retreat. This fact shows that 14C radiocarbon dating of calcareous microfossils is the most reliable dating method for sediments from Antarctic continental shelves, thus for reliably characterising long–term glacial changes in Antarctica.