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ARCTIC SEMINAR SERIES: Past Arctic sea-ice variability, forcing mechanisms and impact on Norse settlements

by Professor Marit-Solveig Seidenkrantz, Department for Geoscience

2014.09.03 | Mia Korsbæk

Date Tue 23 Sep
Time 14:00 15:00
Location AIAS, Aarhus Institute of Advanced Studies, Høegh-Guldbergs Gade 6B, building 1632, room 203

Title: Past Arctic sea-ice variability, forcing mechanisms and impact on Norse settlements

Abstract: Arctic sea ice represents an important component of the climate system, being an effective insulator between the oceans and the atmosphere as well as impacting ecosystems and society. The ongoing severe reduction of Arctic sea ice is largely ascribed to anthropogenic effects, but the current rate of sea-ice reduction is nevertheless much faster than predicted by models, suggesting that other factors may play a role as well. However, little is known about natural changes in sea-ice cover and the underlying forcing mechanisms. Hence, there is a need for longer sea-ice time series to establish a baseline for natural Arctic sea-ice variability. The present talk will discuss possibilities for estimating sea ice extent also for the pre-satellite period, discuss causes for natural sea ice variability and give an example of how changes in sea ice may have influenced human habitation in Greenland.

Past records of sea ice variability can be reconstructed based on various methods, especially IP25, dinocysts and diatoms. In a recent study we use diatom assemblages from marine sediment cores collected from West Greenland to reconstruct changes in sea-ice cover over the past 6,700 years. Our results demonstrate a strong link between changes in sea-ice cover and solar variability over the past 4000 years, in particular during the last millennium, driving sea ice export from the Arctic Ocean. In contrast, solar forcing appears to have been less important for sea-ice concentrations during earlier millennia, underlining the complex link between solar forcing and sea-ice cover.

When comparing such records of past sea ice from areas of Norse settlement sites along the Greenland west coast, an important difference is seen between the timing of sea-ice expansion for the Western and Eastern Settlement regions. The Western Settlement, as well as the northern hunting grounds around Disko Bugt, already experienced major climate deterioration in the first decades after 1200 CE with an expansion of fjord and sea ice in coastal waters, while environmental conditions in the Eastern Settlement deteriorated notably later, around 1400 CE. Summer blockage of the fjord entrance by thick, multi-year sea ice is a specific feature of the Eastern Settlement area, whereas in the Western Settlement region, the seasonal sea ice would have threatened Norse sailing in late winter. Shortly after 1200 CE living conditions in the Western Settlement thus likely became less attractive, making the Western Settlement increasingly dependent on supplies from the Eastern Settlement, where milder climate conditions continued to prevail for another century. Around 1400 increased summer blockage of the Eastern Settlement fjords by sea ice would have imposed serious limitations to sailing and pasture productivity in coastal areas and may have played a crucial role in the final demise of the Eastern Settlement a few decades later.

The Arctic Seminars is a forum for interdisciplinary discussions on research perspectives in the Arctic region. The presenters in the Seminar series come from a variety of disciplines across the four faculties involved in ARC. 

All interested are welcome to participate. There will be coffee and tea during the seminar.