The first linked Master's Thesis presents evidence from the IODP Expedition 374 (in the Ross Sea, see the second linked reference) that the WAIS most likely collapsed during the MIS 5e (Eemian). I also remind readers ice-rafter debris (IRD) can only occur due to MICI-types of marine glacier collapse and that there is plenty of evidence IRD in the coastal Southern Ocean in this timeframe.
Master's Thesis: "PLIO-PLEISTOCENE PALEOCEONOGRAPHY OF THE ROSS SEA, ANTARCTICA BASED ON FORAMINIFERA FROM IODP SITES U1523, U1522, AND U1521" by JULIA L. SEIDENSTEIN May 2020
https://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1988&context=masters_theses_2Abstract: "The West Antarctic Ice Sheet (WAIS) is currently thinning and retreating because shifting oceanic currents are transporting warmer waters to the ice margin, which could lead to a collapse of the ice sheet and global sea level rise. International Ocean Discovery Program (IODP) Expedition 374 sailed to the Ross Sea in 2018 to study the history of the WAIS over the last 20 million years. Previous geologic drilling projects into Ross Sea sediments that record the history of the WAIS (DSDP Leg 28, RISP, MSSTS, Cape Roberts Drilling Project, ANDRILL), as well as modeling studies, show considerable variability of ice-sheet extent during the Neogene and Quaternary including ice sheet collapse during times of extreme warmth.
The purpose of this study is to reconstruct paleoenvironments on the Ross Sea and confirm modeling studies that show warming waters in the Southern Ocean led to the loss of Antarctic ice in the past. Site U1523 is a key site as it is located close to the shelf break and therefore sensitive to warm water incursions from modified Circumpolar Deep Water (mCDW) onto the Ross Sea continental shelf as the Antarctic Slope Current weakens with a changing climate. Shelf sites U1522 and U1521 provide perspective for what was happening closer to the Ross Ice Shelf. Multiple incursions of subpolar or temperate planktic foraminifera taxa occurred during the latest Pliocene and early Pleistocene prior to ~1.8 Ma at Site U1523 indicating times of warmer than present conditions and less ice in the Ross Sea. Especially high abundances of foraminifera are recorded in the late Pleistocene associated with Marine Isotope Stage (MIS) 31, MIS 11, and MIS 5e might also indicate reduced ice and relatively warmer conditions. The interval of abundant foraminifera around MIS 31 (MIS 37 to 21) suggests multiple warmer interglacials during the Mid-Pleistocene Transition (MPT). A change in benthic foraminiferal assemblages and a large increase in foraminiferal fragments after the MPT (~800 ka) indicate stronger currents at the seafloor and perhaps corrosive waters, suggesting a major change in water masses entering (mCDW) or exiting the Ross Sea (AABW) since the MPT."
Extract: "Increased foram abundances at MIS 11, and particularly during MIS 5, suggest that these periods were also much less ice covered. We suspect MIS 5 rather than MIS11 32 could be associated with collapse of the West Antarctic Ice Sheet (Scherer et al., 1998)."
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McKay, R.M., De Santis, L., Kulhanek, D.K., and the Expedition 374 Scientists (August 10, 2019), " Proceedings of the International Ocean Discovery Program Volume 374",
https://doi.org/10.14379/iodp.proc.374.101.2019http://publications.iodp.org/proceedings/374/101/374_101.htmlAbstract
The marine-based West Antarctic Ice Sheet (WAIS) is currently locally retreating because of shifting wind-driven oceanic currents that transport warm waters toward the ice margin, resulting in ice shelf thinning and accelerated mass loss. Previous results from geologic drilling on Antarctica’s continental margins show significant variability in ice sheet extent during the late Neogene and Quaternary. Climate and ice sheet models indicate a fundamental role for oceanic heat in controlling ice sheet variability over at least the past 20 My. Although evidence for past ice sheet variability is available from ice-proximal marine settings, sedimentary sequences from the continental shelf and rise are required to evaluate the extent of past ice sheet variability and the associated forcings and feedbacks. International Ocean Discovery Program Expedition 374 drilled a latitudinal and depth transect of five sites from the outer continental shelf to rise in the central Ross Sea to resolve Neogene and Quaternary relationships between climatic and oceanic change and WAIS evolution. The Ross Sea was targeted because numerical ice sheet models indicate that this sector of Antarctica responds sensitively to changes in ocean heat flux. Expedition 374 was designed for optimal data-model integration to enable an improved understanding of Antarctic Ice Sheet (AIS) mass balance during warmer-than-present climates (e.g., the Pleistocene “super interglacials,” the mid-Pliocene, and the Miocene Climatic Optimum). The principal goals of Expedition 374 were to
• Evaluate the contribution of West Antarctica to far-field ice volume and sea level estimates;
• Reconstruct ice-proximal oceanic and atmospheric temperatures to quantify past polar amplification;
• Assess the role of oceanic forcing (e.g., temperature and sea level) on AIS variability;
• Identify the sensitivity of the AIS to Earth’s orbital configuration under a variety of climate boundary conditions; and
• Reconstruct Ross Sea paleobathymetry to examine relationships between seafloor geometry, ice sheet variability, and global climate.
To achieve these objectives, postcruise studies will
• Use data and models to reconcile intervals of maximum Neogene and Quaternary ice advance and retreat with far-field records of eustatic sea level;
• Reconstruct past changes in oceanic and atmospheric temperatures using a multiproxy approach;
• Reconstruct Neogene and Quaternary sea ice margin fluctuations and correlate these records to existing inner continental shelf records;
• Examine relationships among WAIS variability, Earth’s orbital configuration, oceanic temperature and circulation, and atmospheric pCO2; and
• Constrain the timing of Ross Sea continental shelf overdeepening and assess its impact on Neogene and Quaternary ice dynamics.
Expedition 374 departed from Lyttelton, New Zealand, in January 2018 and returned in March 2018. We recovered 1292.70 m of high-quality core from five sites spanning the early Miocene to late Quaternary. Three sites were cored on the continental shelf (Sites U1521, U1522, and U1523). At Site U1521, we cored a 650 m thick sequence of interbedded diamictite and diatom-rich mudstone penetrating seismic Ross Sea Unconformity 4 (RSU4). The depositional reconstructions of past glacial and open-marine conditions at this site will provide unprecedented insight into environmental change on the Antarctic continental shelf during the late early and middle Miocene. At Site U1522, we cored a discontinuous late Miocene to Pleistocene sequence of glacial and glaciomarine strata from the outer shelf with the primary objective of penetrating and dating RSU3, which is interpreted to reflect the first continental shelf–wide expansion of East and West Antarctic ice streams. Site U1523, located on the outer continental shelf, targeted a sediment drift beneath the westward-flowing Antarctic Slope Current (ASC) to test the hypothesis that changes in ASC vigor regulate ocean heat flux onto the continental shelf and thus ice sheet mass balance.
We also cored two sites on the continental rise and slope. At Site U1524, we recovered a Plio–Pleistocene sedimentary sequence from the levee of the Hillary Canyon, one of the largest conduits of Antarctic Bottom Water from the continental shelf to the abyssal ocean. Site U1524 was designed to penetrate into middle Miocene and older strata, but coring was initially interrupted by drifting sea ice that forced us to abandon coring in Hole U1524A at 399.5 m drilling depth below seafloor (DSF). We moved to a nearby alternate site on the continental slope (Site U1525) to core a single hole designed to complement the record at Site U1524. We returned to Site U1524 after the sea ice cleared and cored Hole U1524C with the rotary core barrel system with the intention of reaching the target depth of 1000 m DSF. However, we were forced to terminate Hole U1524C at 441.9 m DSF because of a mechanical failure with the vessel that resulted in termination of all drilling operations and forced us to return to Lyttelton 16 days earlier than scheduled. The loss of 39% of our operational days significantly impacted our ability to achieve all Expedition 374 objectives. In particular, we were not able to recover continuous middle Miocene sequences from the continental rise designed to complement the discontinuous record from continental shelf Site U1521. The mechanical failure also meant we could not recover cores from proposed Site RSCR-19A, which was targeted to obtain a high-fidelity, continuous record of upper Neogene and Quaternary pelagic/hemipelagic sedimentation. Despite our failure to recover a continental shelf-to-rise Miocene transect, records from Sites U1522, U1524, and U1525 and legacy cores from the Antarctic Geological Drilling Project (ANDRILL) can be integrated to develop a shelf-to-rise Plio–Pleistocene transect.