The history and impacts of farming activities in south Greenland: an insight from lake deposits.

International audienceAgriculture in southern Greenland has a two-phase history: with the Norse, who first settled and farmed the region between 985ad and circa 1450ad, and with the recent reintroduction of sheep farming (1920ad to the present). The agricultural sector in Greenland is expected to grow over the next century as anticipated climate warming extends the length of the growing season and increases productivity. This article presents a synthesis of results from a well-dated 1500-year lake sediment record from Lake Igaliku, south Greenland (61°00′N, 45°26′W, 15m asl) that demonstrates the relative impacts of modern and Norse agricultural activities. Pollen, non-pollen palynomorphs (NPPs), sediment mass accumulation rates, diatoms and stable isotopes of nitrogen provide a comprehensive history of both phases of agriculture and their associated impacts on the landscape and adjacent lake. The initial colonisation of southern Greenland is marked by a loss of tree birch pollen, a rise in weed taxa, and an increase in coprophilous fungi and sediment accumulation rate consistent with land-use changes. The biological and chemical proxies within the lake, however, show only slight changes in diatom taxa, and a rise in δ15N. After the Norse demise and during the Little Ice Age, most of the markers return to pre-settlement conditions. However, the continuation of non-indigenous plant taxa suggests that the landscape did not completely return to a pre-disturbance state. After 1988, the character of the lake changed markedly: mesotrophic diatoms and N isotopes all reveal major shifts consistent with a trophic shift, together with a sharp rise in sediment accumulation rate. The post-1988 lake environment, affected by modern farming development, is unprecedented within the context of the last 1500 years. These results demonstrate the potential of lake sediment studies paired with archaeological investigations to reveal the relationship between climate, environment and human societies