Oceanographic influences on the stability of the Cosgrove Ice Shelf, Antarctica

Ferrero Bay, located in eastern Pine Island Bay (PIB) of the Amundsen Sea Embayment, is one of the largest and southernmost fjords yet studied in Antarctica. High-resolution multibeam swath bathymetric data, chirp sonar sub-bottom profiles, and three Kasten cores were collected in Ferrero Bay during the IB Oden Southern Ocean 2009–2010 cruise (OSO0910). Core KC-15 from the inner bay yielded two carbonate ages providing a minimum age for ice sheet recession from this sector of PIB by ~11 cal. kyr BP. In total, seven additional acid insoluble organic (AIO) fraction radiocarbon ages provide a linear age model with an R2 of 0.99. Variations in magnetic susceptibility, grain size, total organic carbon (TOC) and nitrogen, diatom abundance, and foraminiferal assemblage and abundance are used to interpret glacial history and paleoceanographic conditions. Grounding line retreat was characterized by advection of planktic foraminifera beneath an ice shelf that may have extended across the middle continental shelf. Following initial deglaciation, the Cosgrove Ice Shelf covered Ferrero Bay, and productivity was virtually absent during the mid-Holocene, while benthic foraminifera indicate periodic incursion of warm Circumpolar Deep Water. The ice shelf persisted until 2.3 cal. kyr BP, when TOC and diatom abundance increased as the bay opened and coastal areas deglaciated. Abundant diatoms demonstrate open marine conditions and seasonal sea ice during the recent open water phase, while high benthic foraminiferal abundance indicates active benthos. The retreat of the Cosgrove Ice Shelf was out of phase with Antarctic Peninsula ice shelves and ice-core proxy temperatures, implying that it did not respond to Holocene climate events but rather to the influence of Circumpolar Deep Water and possibly to internal glacial dynamics.