Increasing atmospheric CO2 levels results in increased seawater CO2 concentrations which consequently alter the seawater carbonate equilibrium and decreases the pH. This effect can influence planktic foraminifera and lead to loss of biodiversity and chang es in biocalcification. Because of the natural low water temperatures and concentration of carbonate ions, low buffering capacity, freshening and increased carbon uptake in response to accelerating sea ice retreat due to Arctic warming, the atmospheric CO 2 enters the Arctic waters more rapidly than elsewhere. The project focuses on reconstruction and quantification of the response of planktic foraminifera to changes in surface ocean chemistry in the Fram Strait. The proposed project aims to increase the u nderstanding of consequences of changes in Arctic Ocean carbonate chemistry due to increased atmospheric CO2 concentration on calcifying planktic foraminifera and study the past and present impacts of Arctic Ocean acidification.New geochemical proxies as well as well tested approaches reflecting sea water chemistry will be applied. Marine sediment cores, surface samples and sediment traps from the Fram Strait will be examined with the focus on polar planktic foraminifera. Shell weight, degree of fragment ation and measurements of degree of dissolution based on SEM images will be used to establish the state of dissolution/preservation. Boron isotopes (d11B, a proxy for pH), B/Ca ratios (a proxy for carbonate ion concentration), and Mg/Ca ratios will be per formed. The project will be carried out in collaboration with scientists from the University of Tromsø (Norway) and the Alfred Wegener Institute for Polar and Marine Research (Germany). It will be based on analyses of marine sediment samples collected in previous and new (planned for 2012 and 2013) research cruises to the Fram Strait and sediment traps collected in the HAUSGARTEN deep-sea observatory in the Fram Strait.