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

Abstract

Ice loss in the Southern Hemisphere has been greatest over the past 30 years 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 ∼1.2 Ma 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.

A review of Eupholidoptera (Orthoptera, Tettigoniidae) from Crete, Gavdos, Gavdopoula, and Andikithira

“…Following the above pattern, populations in the western and southwestern corner of Crete (subgroup 4) represent a genetically well-outlined lineage, sharing the nuclear ITS fragment and its mitochondrial genome with the population on Andikithira (subgroup 5) (genetic distances of the nuclear internal transcribed spacers show very low variation among Eupholidoptera ). The two islands have been isolated since the beginning of the Pleistocene (2.6 Mya), with only a narrow length of sea separating them during the Last Glacial Maximum ( Lykousis 2009 ; Simaiakis et al 2017 ; Fassoulas 2018 ; Bailey et al 2022 ). This, combined with the small but stable morphological differences between the two isolated lineages and the deep marine strait between Crete and Andikithira suggest that the Eupholidoptera populations of Crete and Andikithira, have been isolated for a considerable length of time.…”

Unraveling the Deep‐Sea Sedimentary Record of Ice Sheet History

“…Accessing and understanding this sedimentary archive has never been more important than today, when marine ice shelves and outlet glaciers are destabilizing due to atmospheric and ocean warming (DeConto et al., 2021; IPCC, 2022). In this sense, past records of ice retreat recorded in deep sea sediment cores provide insight into how ice sheets behaved during past warm climate intervals, which offers a glimpse into future vulnerability of marine ice sheets in Greenland and Antarctica (i.e., Bailey et al., 2022; Weber et al., 2021).…”

“…Accessing and understanding this sedimentary archive has never been more important than today, when marine ice shelves and outlet glaciers are destabilizing due to atmospheric and ocean warming (DeConto et al, 2021;IPCC, 2022). In this sense, past records of ice retreat recorded in deep sea sediment cores provide insight into how ice sheets behaved during past warm climate intervals, which offers a glimpse into future vulnerability of marine ice sheets in Greenland and Antarctica (i.e., Bailey et al, 2022;Weber et al, 2021).Although the concept of IRD seems simple, its identification and measurement within marine sediment is not. Glaciers can incorporate the full range of particle sizes into icebergs, from clay to boulders, quantification of IRD within marine sediment is largely limited to a narrow range of sizes.…”

A Geochemical Mechanism for >10 m Apparent Downward Offsets of Magnetic Reversals Inferred From Comparison of Two Scotia Sea Drill Sites

“…U1538 data transferred to the U1537 splice depth scale following the correlation of Bailey et al. (2022). Data include: inclination after 20 mT alternating field (AF) demagnetization.…”

“…Inclination after 15 mT AF demagnetization (Inc 15mT ) with the expected values for a geocentric axial dipole are plotted. The expected Matuyama‐Brunhes reversal location is indicated based on assignment of marine isotope stage 19 (Bailey et al., 2022; Weber et al., 2022). The last occurrence of the radiolarian, P. trilobum , is also indicated, which is expected to be found in C1r.1r at around 860 ka.…”