GROUNDING LINE AND CALVING FRONT RETREAT IN GLOMAR CHALLENGER BASIN AND PENNELL TROUGH OF ROSS SEA, ANTARCTICA RECONSTRUCTED FROM DIATOM ABUNDANCES AND ASSEMBLAGES

• Main Author: Bradford, Jaren
• Format: Text
• Language: unknown
• Published: LSU Scholarly Repository 2023
• Subjects: Fragilariopsis curta; calving cliff; ice sheet retreat; Whales Deep Basin; Geology; Glaciology; Antarc*; Antarctic; Antarctica; Ice Sheet; Ice Shelf; Ross Sea; Sea ice
• Online Access: https://repository.lsu.edu/gradschool_theses/5835; https://repository.lsu.edu/context/gradschool_theses/article/6922/viewcontent/bradford_thesis.pdf

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. McGlannan et 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 ice shelf 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.These contrasting retreat histories between the basins west and east of Ross Bank show that the retreat style is partly related to local factors.