Holocene paleoceanographic variability in Robertson Bay, Ross Sea, Antarctica: A marine record of ocean, ice sheet, and climate connectivity

Abstract

Accelerating ocean-driven basal melting of Antarctic ice shelves in recent decades has implications for sea level rise and global overturning circulation. Here, we reconstruct oceanographic conditions at the confluence of the Ross Sea and the Southern Ocean by analyzing a multi-proxy Holocene marine sedimentary record collected from Robertson Bay. A ramped pyrolysis oxidation radiocarbon age-depth model provides a timeline for glacial behavior and oceanographic changes over the last 6700 years. The diatom assemblage, magnetic susceptibility, grain size, total organic carbon and nitrogen, trace elements, and bulk delta 13C are used as proxies for changing ocean and glacial conditions, which we interpret in the context of modern oceanographic measurements. Our record shows evidence of persistent ice cover in the northwestern Ross Sea during the Antarctic midHolocene climate optimum (ca. 5 cal kyr BP). Based on this observation, we suggest that meltwater and iceberg discharge associated with ice sheet retreat in the Ross Sea region altered local oceanography during the mid-Holocene. The onset of modern style oceanographic conditions in Robertson Bay occurred at ca. 4 cal kyr BP. Stable late Holocene conditions in are punctuated by a period of enhanced polynya activity and upwelling of nutrient rich Circumpolar Deep Water ca. 0.8 cal kyr BP and an increase in the seasonal duration of sea ice after 0.7 cal kyr BP, during the Little Ice Age. The response of the marine environment in Robertson Bay to midHolocene ice sheet retreat and natural climate variability during the last millennium underscores the sensitivity of the Antarctic ice-ocean interface to projected changes in coming decades.