ALBERT

Description: ABSTRACT FINAL ID: PP31A-1838 High concentrations of carbonate in surface sediments of the Nordic Seas are generally related to warm Atlantic Water (AW) inflow. This relationship was recently used to infer the Holocene dynamics of Atlantic-derived water off North-West Iceland (Giraudeau et al, 2010; QSR vol. 29) following suggestions that carbonate production in the vicinity of Denmark Strait is tightly linked with inputs of warm, nutrient-rich Irminger Current waters. The present study aims at testing this assumption in the two main passageways of AW to the Arctic Ocean: Fram Strait and the Barents Sea, with a focus on a high resolution Holocene sediment record collected off western Svalbard. Our datasets on extant coccolithophores, as well as estimates of coccolith-carbonate contents within the studied marine cores suggest that sedimentation of calcium carbonate in the northernmost North Atlantic essentially reflects production rates of coccolithophores, and that sedimentation of their fossil remains is driving to a high extent the Holocene variations in net CaCO3 accumulation in Fram Strait and the SW Barents Sea. Our coccolith-based proxy records are indicative of a complex regional dynamics of Holocene surface water changes in these two regions. With the exception of a ca. 2 000 years delayed recovery of surface AW influence to the SW Barents Sea in the early Holocene, both regions experienced the same history of surface water temperature changes until ca. 3 000 cal.yrs BP. A Holocene sea-surface thermal optimum is clearly recognized in both regions during the 8 000 to 7 000 cal. yrs BP interval, followed by a large scale surface cooling triggered by reduced poleward inflow of AW across the Iceland-Scotland Ridge. A decoupling in the pattern of coccolith-carbonate sedimentation between Fram Strait and the SW Barents Sea characterizes the late Holocene. While near continuous surface water warming impacted the southern Barents Sea throughout the last 3 000 years, the eastern Fram Strait was affected by the settling, during maximum AW inflow to the Arctic Ocean, of a strong stratification separating a fresh, sea-ice rich surface mixed-layer of polar origin from an AW-derived poleward water mass.

Description: Scattered and indirect evidence suggests that sea ice occurred as far south as the Iceland Sea during the Early Pliocene, when the global climate was warmer than present. However, conclusive evidence as well as potential mechanisms governing sea ice occurrence outside the Arctic Ocean during a time with elevated greenhouse gas concentrations are still elusive. Here we present a suite of organic biomarkers and palynological records from the Iceland Sea and Yermak Plateau. We show that sea ice appeared as early as ~4.5 Ma in the Iceland Sea. The sea ice either occurred seasonally or was transported southward with the East Greenland Current. The Yermak Plateau mostly remained free of sea ice and was influenced dominantly by Atlantic water. From ~4.0 Ma, occurrence of extended sea ice conditions at both the Yermak Plateau and Iceland Sea document a substantial expansion of sea ice in the Arctic. The expansion occurred contemporaneous with increased northward heat and moisture transport in the North Atlantic region, which likely led to a fresher Arctic Ocean that favors sea ice formation. This extensive sea ice cover along the pathway of the East Greenland Current gradually isolated Greenland from warmer Atlantic water in the Late Pliocene, providing a positive feedback for ice sheet expansion in Greenland.