Diatom-based reconstructions of climate and ocean conditions from Svalbard and Baffin Bay since the Last Glacial Maximum

The recent changes in the Arctic region, e.g. decreased Arctic sea ice cover and accelerated ice mass loss from the Greenland ice sheet, have an alarming rate and magnitude. The ongoing climate warming has a profound impact on the sensitive Arctic region known as polar amplification. To better understand the changes taking place in the Arctic region, and to project the future impacts of the ongoing climate change, we need to look into the past in order to obtain analogues of past climate conditions and past interactions between climate system components (ocean, ice sheet, and atmosphere). High-latitude marine proxy records provide indirect information of past long-term oceanic conditions and climate variability. Paleoceanographic records, from the vicinity of ice margins, can be employed to investigate past interactions between the ocean and ice sheets, which are crucial in order to understand the future impacts of the ocean surface warming on the marine terminating parts of ice sheets. This work examines ocean surface conditions (August sea surface temperatures, sea ice and ocean surface water masses) from high northern latitudes after the Last Glacial Maximum using marine fossil diatom assemblages. Long-term paleoclimatic and -oceanographic records are obtained from two study sites (northern Svalbard and central-eastern Baffin Bay) using quantitative and qualitative diatom analyses, and sediment grain size distribution analysis. An additional focus of this work was to study the ecology of common northern North Atlantic diatom species and define their relationship to environmental variables (August sea surface temperatures and April sea ice) in order to identify the best indicator species for these environmental variables and to improve their reliability as paleoceanographic indicators for high latitude paleoclimatic reconstructions. The Baffin Bay study site was investigated for the deglacial period (10−14 kyr BP), and the results suggest a warmer ocean surface in central-eastern Baffin Bay during the cold Younger Dryas period (11.7−12.9 kyr BP) indicating that the ocean was out of phase with atmospheric conditions over Greenland. The warmer conditions were caused by enhanced inflow of Atlantic-sourced waters and increased solar insolation on the Northern Hemisphere, which amplified seasonality over Baffin Bay and had a significant role triggering the retreat of the Jakobshavn Isbræ ice stream in West Greenland, which is visible in the sedimentological evidence. The paleoceanographic record from northern Svalbard represents the late Holocene (last ca. 4 200 years), and the results show a clear climate shift at 2.5 kyr BP, as the study location changed from stable, glacier-proximal conditions into fluctuating glacier-distal conditions, emphasizing the sensitivity of the Arctic environment to climate oscillations. Diatoms are widely used as indicators for past climate change, which emphasizes that understanding the species` relationship to environmental variables is essential when employing diatoms as a paleoclimate proxy. The study of the main northern North Atlantic diatom taxa ́s ecology and responses to environmental variables identifies robust indicators for cold, temperate and warm waters and for sea ice. The