Mid-to-late Pleistocene Depositional Environments at the Ross Sea Continental margin: Implications for Antarctic Ice Sheet Dynamics

Abstract

This study investigates a sediment core (RS15-LC47) from the Ross Sea continental rise to reconstruct ice sheet dynamics and paleodepositional environments over the past 800 ka. We employed a multi-proxy approach in this study, integrating whole-core magnetic susceptibility (MS), total organic carbon (TOC), calcium carbonate (CaCO₃), biogenic silica, sedimentological features, and the isotopic ratio of authigenic beryllium ((10Be/9Be)reac). The interval between 750 and 550 ka represents an intensified glacial phase characterized by expanded ice sheets, strengthened bottom currents, and reduced marine productivity. The dominance of contourite deposits interspersed with slumped sediments suggests that the sediment deposition occurred under highly dynamic and unstable conditions driven by intensified bottom currents. The presence of poorly sorted sediments and millimetre-scale faults further indicates gravity flow deposition, likely triggered by ice-sheet advances. Low (10Be/9Be)reac ratios in this interval suggest limited scavenging in open marine settings, likely due to reduced sediment transit time to the coring site as advancing ice sheets extended toward the shelf edge. Although TOC values are highest in this interval, a high total organic carbon/nitrogen (TOC/TN) ratio and low excess Barium (Baex) suggest increased terrestrial input from the advancing ice sheets and a reduced marine productivity under intense glacial conditions in the Ross Sea. Following the Mid-Pleistocene Transition (MPT), between 550 and 250 ka, MS values remained consistently low, while (10Be/9Be)reac ratios were notably elevated, indicating relatively warmer conditions with diminished glacial influence. The TOC/TN ratios during this interval resemble those observed in the euphotic layer of the Ross Sea, with relatively higher Baex and TOC suggesting enhanced marine productivity under relatively warmer conditions between 550 and 250 ka. During the late Pleistocene (>250 ka), the depositional environment became increasingly influenced by glacial-interglacial cycles, with warmer interglacials driving enhanced productivity. During this interval, coarser grain sizes point to stronger bottom currents, while the sharp rise in (10Be/9Be)reac ratios indicates interglacial conditions associated with ice sheet retreat. The longer sediment transit from the subglacial zone to the depositional site during these warmer periods enhanced scavenging of Be isotopes in open marine settings, resulting in elevated (10Be/9Be)reac values. A positive correlation between OpalMAR, TOC%, and (10Be/9Be)reac during interglacials reflects a direct link between increased marine productivity and warmer climatic phases. Our findings emphasize how ice-sheet expansion and retreat control the depositional processes in the region.