Ross Sea West Antarctic Ice Sheet History

Abstract

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 pCO 2 ; 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 R.M. McKay et al. Expedition 374 summary IODP Proceedings 2 V o l u m e 3 7 4

Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

“…The sites are located along the present-day middle continental shelf of the Ross Sea (Fig. 1), and the age models developed from biostratigraphic and paleomagnetic techniques show relatively expanded sequences of Miocene sediments (Hayes et al, 1975;Bart, 2003;McKay et al, 2019). However, it should be noted that all age models are subject to future refinement through improved resolution of biostratigraphic observations and development of a consistent biostratigraphic framework between recent and legacy cores that is beyond the scope of this study.…”

“…Core and wireline (downhole) logging measurements were completed in the site to 650.1 m below seafloor (mbsf), above which depth average core recovery was 63%. Details on the coring techniques and logging tools are provided in McKay et al (2019). DSDP Site 272 is located at 77°07.62′S, 176°45.61′W in Glomar Challenger Basin at 629 m wd (Fig.…”

“…Here, we aim to constrain the regional spatial extent of ice sheet and ice cap advances and retreats that influenced sedimentation in the middle to outer continental shelf of the central Ross Sea during the early and middle Miocene. We correlate seismic records with drill-site physical properties and lithostratigraphy from Deep Sea Drilling Project (DSDP) sites 272 and 273 (Hayes et al, 1975), and IODP Site U1521 (McKay et al, 2019) (Fig. 1).…”

The Antarctic Ice Sheet: A Paleoclimate Modeling Perspective

“…Clearly defined modeling targets, such as quantitative icevolume estimates or locations with evidence for meltwater, are incredibly useful (e.g., Lewis et al, 2006;Warny et al, 2009;Mudelsee et al, 2014;Gulick et al, 2017). The recent retrieval of new ice-proximal records from three sectors of Antarctica as part of the International Ocean Discovery Program are already providing some of these key records (Escutia et al, 2019;McKay et al, 2019).…”

Neogene Development of the Terror Rift, Western Ross Sea, Antarctica

“…A revision of the depth and age of the RSU5 unconformity is ongoing after the recent IODP Expedition 374, which drilled site U1521; this site is located near the western edge of the Eastern Basin (Figures 1 and 4) and that reached sediments dated ca. 18 Ma near the bottom of the hole (McKay et al, 2019). Therefore, we used the names RSU5B_vlb (19 Ma) and RSU5C_vlb (21 Ma) labels in the Victoria Land Basin (extension "_vlb" stands for Victoria Land Basin).…”