Distribution of post-Last Glacial Maximum Sedimentary Deposits in the Amundsen Sea, Antarctica, from Subbottom Seismic Profiles

Date
2023-12
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Abstract

Marine geologic and geophysical data collected across the Amundsen Sea Embayment of West Antarctica provide insight to geologic and glacial processes that have occurred across the continental shelf since the Last Glacial Maximum (~20 ka), as well as processes that are occurring today. Subbottom profiles collected across the Amundsen Sea Embayment during the austral summers of 2019 and 2020 reveal sediment that has been delivered from two major glaciers: Thwaites and Pine Island. Sediments transported by Thwaites and Pine Island Glaciers have predominantly been studied through analysis of sediment cores which have been collected in specific locations across the Amundsen Sea. This study aims to produce a spatial characterization of sediment deposits and their volumes derived from the post-LGM retreat of Thwaites and Pine Island using the interpretation of ~10,000 km of subbottom profiles. Sediment thickness and sediment geometry were used in conjunction to extrapolate sediment basins and subsequently determine sediment volumes for the study area. Sediment geometry of the deposits was separated into three designated acoustic facies: ponded, draped, and chaotic, based on consistent characteristics across the subbottom profiles. Sediment cores that have previously been interpreted were integrated with sediment geometry characterization for correlation to depositional mechanisms occurring across the Amundsen Sea. 2D thickness was then calculated for interpreted sediment deposits to determine sediment accumulation patterns across the Amundsen Sea. A concentration of high average sediment deposit thickness is seen in areas lacking streamlined geomorphology, specifically proximal to the Eastern Ice Shelf. Geomorphic basin extent and sediment thickness values were used for the extrapolation of sediment basins extending beyond subbottom profile track lines to estimate sediment volumes. In total, 3.53 x 1010 m3 of sediment volume was calculated from glaciers draining into the Amundsen Sea, with Pine Island Glacier sediment delivery accounting for over 50% of the sediment volume. Radiocarbon dated sediment cores are used to demonstrate ages and accumulation rates of sediment interpreted below their maximum depth. Projecting similar sediment accumulation rates from core data to basal sediment interpreted in their corresponding subbottom profiles estimates sediment age of up to ~150,000 years. These projected ages demonstrate potential for pre-LGM sediment deposit preservation, including evidence of paleo-subglacial lake deposits. However, if rates are not assumed similar down section of core acquisition, which is likely, sedimentation rates of up to ~4mm/yr since the LGM would account for current thickness.

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Keywords
Amundsen Sea sediment, subbottom profiles
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