Episodes of Early Pleistocene West Antarctic Ice Sheet Retreat Recorded by Iceberg Alley Sediments

• Main Authors: Bailey, Ian, Hemming, Sidney, Reilly, Brendan T, Rollinson, Gavyn, Williams, Trevor, Weber, Michael E, Raymo, Maureen E, Peck, Victoria L, Ronge, Thomas A, Brachfeld, Stefanie, O'Connell, Suzanne, Tauxe, Lisa, Warnock, Jonathan P, Armbrecht, Linda, Cardillo, Fabricio G, Du, Zhiheng, Fauth, Gerson, Garcia, Marga, Glueder, Anna, Guitard, Michelle, Gutjahr, Marcus, Hernández‐Almeida, Iván, Hoem, Frida S, Hwang, Ji‐Hwan, Iizuka, Mutsumi, Kato, Yuji, Kenlee, Bridget, Martos, Yasmina M, Pérez, Lara F, Seki, Osamu, Tripathi, Shubham, Zheng, Xufeng
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2022
• Subjects: Earth Sciences; Physical Geography and Environmental Geoscience; Geology; Climate Action; provenance; Ar-Ar; SEM; QEMSCAN; MicroCT; IODP; scotia sea; pirie basin; southern ocean; ice rafted debris; Antarctic Ice Sheet; West Antarctic Ice Sheet; ice-sheet retreat; deglaciation; IODP expedition 382; iceberg alley; Ar‐Ar; ice‐sheet retreat; Geochemistry; Oceanography; Ecology; Paleontology; Antarctic; Southern Ocean; Weddell Sea; West Antarctica; Scotia Sea; Amundsen Sea; Pacific; Weddell; Pirie; Antarc*; Antarctica; Ice Sheet; Iceberg*
• Online Access: https://escholarship.org/uc/item/56v8x2wc

Ice loss in the Southern Hemisphere has been greatest over the past 30years in West Antarctica. The high sensitivity of this region to climate change has motivated geologists to examine marine sedimentary records for evidence of past episodes of West Antarctic Ice Sheet (WAIS) instability. Sediments accumulating in the Scotia Sea are useful to examine for this purpose because they receive iceberg-rafted debris (IBRD) sourced from the Pacific- and Atlantic-facing sectors of West Antarctica. Here we report on the sedimentology and provenance of the oldest of three cm-scale coarse-grained layers recovered from this sea at International Ocean Discovery Program Site U1538. These layers are preserved in opal-rich sediments deposited ∼1.2Ma during a relatively warm regional climate. Our microCT-based analysis of the layer's in-situ fabric confirms its ice-rafted origin. We further infer that it is the product of an intense but short-lived episode of IBRD deposition. Based on the petrography of its sand fraction and the Phanerozoic 40Ar/39Ar ages of hornblende and mica it contains, we conclude that the IBRD it contains was likely sourced from the Weddell Sea and/or Amundsen Sea embayment(s) of West Antarctica. We attribute the high concentrations of IBRD in these layers to "dirty" icebergs calved from the WAIS following its retreat inland from its modern grounding line. These layers also sit at the top of a ∼366-m thick Pliocene and early Pleistocene sequence that is much more dropstone-rich than its overlying sediments. We speculate this fact may reflect that WAIS mass-balance was highly dynamic during the ∼41-kyr (inter)glacial world.