October BRGS Meeting: Grounding Line and Calving Front Retreat in Glomar Challenger Basin and Pennell Trough of Ross Sea, Antarctica: Reconstructed from Diatom Abundances and Assemblages

Join us October 13, 2023

Mr.  Jaren Bradford 

Leaaf Environmental, LLC

Grounding Line and Calving Front Retreat in Glomar Challenger Basin and Pennell Trough of Ross Sea, Antarctica:  Reconstructed from Diatom Abundances and Assemblages

Abstract

Previous studies showed that West Antarctic Ice Sheet (WAIS) retreat from the Whales Deep Basin continental shelf edge in eastern Ross Sea was underway by 14.7± 0.4 cal kyr BP.  Following an ice-shelf breakup at 12.3 ± 0.6 cal kyr BP, a calving cliff margin remained within 60 km of the shelf edge until 11.5 ± 0.3 cal kyr BP. McGlannanet al. (2017) inferred that an ice shelf reformed immediately during a subsequent rapid retreat.  That interpretation of grounding-line retreat with an intact ice shelf is being reevaluated by Sivils (in prep.).   Here, we conducted a similar synthesis of sedimentology with diatom assemblages and abundances to determine whether retreat in the Glomar Challenger and Pennell basins occurred with an ice shelf or calving cliff.  Two legacy sediment cores from Glomar Challenger Basin bottom in till deposited below grounded ice. The till is directly overlain by sub-ice-shelf facies characterized by a low abundance of diatoms, most of which are reworked.  The overlying open marine sediment is dominated by an assemblage of sea-ice associated diatom species.  The sub-ice-shelf facies show that retreat of grounded ice from Glomar Challenger occurred with an intact ice shelf.  A core from the Pennell Trough also bottoms in till deposited in a subglacial environment and has a low abundance of reworked diatoms.  The till has a sharp upcore transition directly to open-marine sediment that contains sea ice associated diatoms such as Fragilariopsis curta.  This sharp transition and lack of an intermediate sub-ice shelf sediment facies suggests that a calving cliff and/or at most a small iceshelf retreated as grounded ice retreated in Pennell Trough.  The absence of a large ice shelf during retreat from the Pennell Trough may have been a consequence of its significantly smaller catchment for the basin and hence relatively low discharge of grounded ice.

Biography

Jaren Bradford is currently employed as a Geologist at Leaaf Environmental, LLC in Gretna, Louisiana. He received his B.S. in Geology and Geophysics from Louisiana State University (LSU) in 2018 and plans on receiving his M.S. this Fall.  In the middle of his M.S. program, Jaren was able to travel to Ross Sea, Antarctica aboard the RVIB Nathaniel B. Palmer in the Fall of 2022.  During this research cruise, he and the rest of the crew helped to collect sediment cores that will be used in future ice sheet retreat studies. In addition to growing his skills within the Soil and Groundwater Division, he looks forward to also being able to use his microscopy background to further minimize environmental risks.