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Holocene paleoenvironmental record from southern Greenland
Department of Geology and Geophysics, University of Wisconsin, Madison, WI, 53706
Institute of Arctic and Alpine Research and Dept. of Geological Sciences, Univ. of Colorado, CO, 80309
A 2.6 m sediment core from Qipisarqo Lake, southern Greenland (7 m asl; 61N; 48W), provides a continuous Holocene paleoenvironmental record of environmental change. The lake is situated in a drainage that can be fed by inland ice meltwater when the ice advances. Moraine and vegetation kill zones indicate the ice was sufficiently advanced during the Little Ice Age to divert meltwater into Qipisarqo Lake, but it has subsequently retreated and meltwater no longer reaches the lake.
Following an interval of rapid marine sedimentation, Qipisarqo Lake became isolated from the sea about 9 cal ka. Lacustrine gyttja sedimentation extends from the isolation event until ca. 500 yr ago, when glacial-lacustrine sediments appear abruptly. A thin gyttja (4 cm) that overlies the glacial-lacustrine unit reflects sedimentation since meltwater was diverted from the lake's drainage within the last 100 yrs.
Environmental change is preserved in the sedimentary characteristics, organic matter content, biogenic silica and magnetic susceptibility. Following isolation of the lake from the sea, the paleoproductivity proxies increase in concentration until ca. 5.5 cal ka. Subsequently, the paleoproductivity proxies decrease in concentration (and minerogenic component increases), especially after ca. 2.5 cal ka. In the last 2.5 cal ka, productivity minima occurred at ca. 1.8, 1.1, ca. 0.5 to 0.1 cal ka. Only during the Little Ice Age was the inland ice thick enough to deliver meltwater to the lake since at least 9 cal ka. Brief intervals of high productivity occurred at ca. 1.5 and 0.6 cal ka and recently.
We interpret the proxy record to indicate that the early and middle Holocene were characterized by more abundant vegetation, stabilizing slopes in the catchment and optimal primary productivity in the lake. Conditions diminished slightly after 5 cal ka, but by ca. 2.5 cal ka a substantial increase in the flux of clastic sediment indicates diminished terrestrial vegetation cover and regional landscape instability. Advancing inland ice finally breached a col in the headwaters of the lake's drainage about 500 yr ago, and meltwater dominated lake sedimentation until ice recession in the early 20th century.