Drastic changes in Depositional Environments at the Ross Sea Continental Margin since the Mid-Pleistocene: More evidence for West Antarctic Ice Sheet collapse

Abstract. This study investigates a sediment core (RS15-LC47) from the Ross Sea continental rise to elucidate the sea-ice interaction and resulting paleodepositional changes over the past 800 ka. By integrating whole-core Magnetic Susceptibility (MS), sediment biogenic components (TOC, CaCO₃, and biogenic silica), sedimentological features, and the isotopic ratio of authigenic beryllium (¹⁰Be/⁹Be)_reac, we unravel the paleoenvironmental changes and their influence on the sedimentary processes. The lower segment of the investigated interval (750–550 ka) exhibits distinct lithological characteristics, including parallel and cross laminations, along with millimeter-scale faults, suggestive of contourite depositional processes. This section also displays irregular trends in MS values due to poorly sorted sediments, characteristics feature of sediment slumping. The lowest (¹⁰Be/⁹Be)_reac ratio in this interval suggests reduced Circumpolar Deep Water (CDW) inflow due to strengthened Antarctic Slope Current (ASC). Although the Total Organic Carbon (TOC) is highest in this interval, high Carbon-to-Nitrogen (C/N) ratio and low Barium excess (Ba_ex) suggests reduced marine productivity due to increased terrestrial input likely from advancing ice sheets. Following the Mid-Pleistocene Transition (MPT), MS values remain consistently low until MIS 8 (~250 ka) and (¹⁰Be/⁹Be)_reac relatively increases, indicating persistent lukewarm condition. We hypothesize this timeframe favorable for ice-shelf disintegration and possible collapse of the West Antarctic Ice Sheet (WAIS). Between 550 and 250 ka, TOC/TN levels resemble those observed in the euphotic layer of the Ross Sea, with relatively higher Ba_ex and TOC, indicating higher productivity during an extended lukewarm condition. During the late Pleistocene (> 250 ka), coarser grain size and IRD-rich layers suggest strengthening of bottom currents. The upwelling of CDW facilitated a drastic increase in the (¹⁰Be/⁹Be)_reac ratio during the late Pleistocene. Opal_MAR and TOC % exhibit positive trends with (¹⁰Be/⁹Be)_reac during the late Pleistocene interglacials, suggesting increased productivity during warmer periods.