ANTARCTIC PENINSULA FJORD GLACIAL MARGINS DURING THE MIDDLE HOLOCENE, AND CIRCUM-ANTARCTIC CONNECTIONS

A growing body of data suggests significantly reduced glacial cover on the Antarctic Peninsula (AP) during the early to middle Holocene with ice margins more retracted than today. Evidence includes dated marine and terrestrial materials from both sides of the AP; glacial sediments from modern tidewater fronts of AP glaciers contain marine mollusc fragments that date to the middle Holocene. Multi-proxy data from western AP fjord and shelf marine sediment cores, including Eucampia abundance, symmetry and colony length records, and organic geochemistry, suggest decreased sea ice extent and a more productive marine ecosystem. The middle Holocene optimum is also seen in the more severely glaciated portions of the eastern AP. For example, in sediments deposited beneath the Larsen B Ice Shelf, a middle Holocene biofacies acme is observed that must reflect major oceanographic changes in Weddell Sea circulation, as there are no local sediment accumulation rate changes that can explain the increase in microfossil abundance, nor is there any evidence for open water in the embayment. Similarly, cores in front of the Larsen C Ice Shelf record a middle Holocene biofacies acme, and Larsen A embayment cores document the absence of an ice shelf. Finally, marine sediments record a mid-Holocene productivity maximum in the Ross Sea, and sedimentologic data from the East Antarctic margin suggest that the mid-Holocene glacial minimum extends well beyond the Antarctic Peninsula. These data provide clues to potential forcing mechanisms, including southward migration of westerly winds that may have driven greater upwelling of relatively warm and nutrient rich UCDW on the shelf. In turn, this may have resulted in more extended growing seasons and greater iron fertilization, as well as increased oceanic warmth and the retreat of glacial margins. Rising sea level coupled to glacial isostatic adjustment, also may have contributed to retracted ice margins during the middle Holocene. The climate records from the AP provide a glimpse into just how far retracted the near-modern Antarctic glacial cover can reach -- under the momentum of accelerated sea level rise and warming atmospheric temperatures and might provide an analogy to conditions proposed during warmer interglacial epochs of the Late Pleistocene.