HB-1-3

Sea ice is a critical component of global climate, contributing to heat reduction (albedo) and deep-water formation, a driving mechanism of the global thermohaline circulation. The impacts of sea ice on oceanic-atmospheric interactions as well as biological processes (primary production), together with its response to climate change, are strongly demonstrated by variations in its spatial and temporal distributions. In order to understand processes controlling recent dramatic reductions in sea ice cover in the polar regions, it is essential to determine these changes in sea ice occurrence and its natural variability in the past on time scales going back in time beyond the period of direct measurements/observations. Despite the importance of sea-ice cover in the global climate system, however, detailed information about the extent and variability of paleosea ice is still very sparse. Here, a novel biomarker approach („IP25“) which is based on the determination of sea-ice diatom specific isoprenoids (C25 HBIs), seems to be a major step forward in filling this important gap of knowledge. Since about 20 years, R. Stein and his AWI working group are/were involved in multidisciplinary marine-geological research program dealing with detailed studies of changes in paleoclimate, paleoceanic circulation, paleoproductivity, and sea-ice distribution in the central Arctic Ocean and the adjacent continental margin on various time scales from the Cretaceous and Early Cenozoic to the Late Quaternary (especially postglacial-Holocene). Most recently, the novel IP25 approach for reconstruction of sea-ice cover has been further developed by combining the sea-ice proxy IP25 with biomarkers indicative for openwater primary productivity. The good correlation between modeled sea-ice parameters and the biomarker-based estimate of sea-ice coverage substantiates that linking proxy and model data occurs to be a promising concept in terms of a cross-evaluation. This combinatory data-model approach by Müller et al. (2011) may provide a first step towards more quantitative sea ice reconstructions by means of IP25. Furthermore, these data allow studying the interrelationships between sea-ice cover, ocean circulation and primary productivity. Sediment data indicating an increase in Arctic Ocean freshwater discharge and sea-ice formation during the onset of the Younger Dryas may support the hypothesis of increased freshwater/sea-ice export through Fram Strait as trigger for reduced NADW formation.

Concentrating on organic-geochemical bulk parameters (TOC content, C/N ratios, Rock-Eval data) and specific biomarkers, reconstructions of surface-water characteristics in the (sub-) polar North Atlantic and Arctic Ocean and their changes through late Quaternary times will be carried-out. Of special interest will be the interrelationship between sea-ice cover, meltwater/freshwater discharge and primary productivity, as well as the Laurentide and Greenland ice-sheet history. We will concentrate on specific warm/cold intervals (i.e., Last Glacial Maximum, Heinrich Events, Bølling-Allerød, the Younger Dryas, and the 8.2-kyr event as well as the Warm Medieval Period (MWP) and the Little Ice Age (LIA)). Our biomarker data will be related to palynological as well as isotope data indicative for sea-ice cover, meltwater discharge and/or productivity, the main focus of research of our Canadian project partners.