Pleistocene oceanographic variability in the Ross Sea: A multiproxy approach to age model development and paleoenvironmental analyses

Abstract

Understanding how ocean circulation has varied around Antarctica in the past is vital because significant volumes of ice are grounded below sea level, and therefore ice sheet variations are strongly coupled with oceanographic variability at the continental shelf margin. This study investigates the 11.75？m sediment core RS15-LC42, retrieved from the Central Basin of the Ross Sea. A magneto-biostratigraphic age model was constructed from a magnetic reversal stratigraphy, diatom biostratigraphy, and the relative paleointensity of the geomagnetic field. The core spans the last 1.34 Myr with a mean sedimentation rate of 0.88？cm/kyr, providing insights into paleoceanographic variability in the Ross Sea throughout the Pleistocene. Winnowed deposits enriched in iceberg rafted debris were formed when the ice-sheet was not grounded in the outer Joides Trough due to a combination of enhanced glacial calving during glacial retreats, and export of Dense Shelf Water during interglacial and weak glacial periods. During periods of expanded ice sheets on the outer Ross Sea continental shelf, laminated sediments rich in reworked diatoms are interpreted to have formed due to glacial scouring on the continental shelf, transporting shelf sediments to the mouth of the Joides Trough, where slope failures and meltwater pulses remobilized this material onto the continental slope. Dense shelf water formation is inferred to be most intense during interglacial periods, with reduced export from the Joides Trough during ice-sheet advances. The study does not find any evidence for prolonged ice-sheet grounding in the outer Ross Sea since ~0.3？Ma, however, we conclude that the grounding line reached the outer shelf frequently between 0.3 and 1.2？Ma, supporting higher Antarctic ice volumes during glacial periods in this interval.