Past ice dynamics and unusual ramp bedforms offshore Brunt Ice Shelf, Weddell Sea


Contact
Jan.Erik.Arndt [ at ] awi.de

Abstract

Past ice dynamics are so far only poorly resolved in the southern Weddell Sea. This is highlighted by previous studies that led to two contradicting scenarios for the grounding line location during the Last Glacial Maximum (LGM), which differed by up to ~650 km. Another study suggested that the maximum ice extent locally was not reached during the LGM but in the early Holocene, indicating that there was also a highly dynamic ice sheet system during deglaciation. There is ambiguity about the history of ice advance and retreat in the region offshore Brunt Ice Shelf based on current data. Only one radiocarbon dated marine geological core is available, contains age reversals, and can be interpreted as indicating ice free conditions during the LGM or having been overrun by grounded ice between 30.2-20.3 cal ka BP. Today, the Brunt Ice Shelf itself is a focus of interest due to the critical crack/fracture development since 2016. This endangers Halley research station, which is situated on the ice shelf, and has resulted in the third consecutive year of austral winter closure. Geophysical ice shelf investigations revealed that, unlike usual ice shelves, the Brunt Ice Shelf consists of numerous blocks of meteoric/glacial ice that are “glued” together by freezing sea ice and snow drift. It is hypothesized that the Brunt Ice Shelf sustains its stability due to buttressing at the McDonald Ice Rumples, which form the only remaining ice shelf pinning point. Improved understanding of the past development of the ice shelf system may also aid understanding the processes active today. We investigated hydroacoustic data that were acquired offshore Brunt Ice Shelf over the last decades with RV Polarstern and RRS James Clark Ross for geomorphological indications of past ice sheet dynamics. The identified landforms show that major ice discharge during the LGM was not via Brunt Basin just in front of the modern-day Brunt Ice Shelf, but via an ice stream that occupied Stancomb-Wills Trough, which is located northeast of Brunt Ice Shelf and extends about 200 km upstream of the modern-day grounding line. We identified at least three still stand phases during retreat in this trough. Marine geological data revealed a minimum age for grounding line retreat before 8.5 cal ka BP. In contrast, we found no indications of fast flowing ice in Brunt Basin. Instead, we infer slow flowing, cold-based ice and found uniquely formed ramp-shaped bedforms. We suggest that these ramps were formed due to the unusual structure of the ice shelf, which led to temporary grounding of ice shelf keels that acted as buttressing points for a more extensive ice shelf in the past. We will present the new ice sheet reconstruction and will discuss the formation process of the ramps.



Item Type
Conference (Talk)
Authors
Divisions
Primary Division
Programs
Primary Topic
Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
ISAES 2019, Incheon, South Korea.
Eprint ID
53415
Cite as
Arndt, J. E. , Hillenbrand, C. D. , Larter, R. D. , Dorschel, B. , Sørlie, S. H. , Forwick, M. , Smith, J. A. and Wacker, L. (2019): Past ice dynamics and unusual ramp bedforms offshore Brunt Ice Shelf, Weddell Sea , ISAES 2019, Incheon, South Korea .


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