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HOLMGREN, SOFIA  Department of Earth Sciences, Goteborg University, Sweden, and UNIS, Svalbard.
Wolfe, Alex P  Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada.
Ingolfsson, Olafur  Department of Geology and Geography, University of Iceland, Reykjavik, Iceland.

Gravity cores from four lakes in western Spitsbergen, Svalbard, register marked stratigraphical changes in the 20th century. At Skardtjørna and Tjørnskardet on Nordenskiöldkysten, there is an apparent diatom floristic change coupled to increased diatom concentrations in the uppermost c.10 cm of sediment, which at the former site corresponds to the last c. 40 years. At Istjørna and Istjørnelva, 25 km southwest of Longyearbyen, striking changes occur in siliceous algal assemblages contained in the uppermost c. 5 cm of sediment. At both sites, diatom and chrysophyte cyst concentrations increase dramatically in the most recent sediments. We hypothesize that algal production has increased in all four lakes in the 20th century, perhaps as a synergistic response to climate warming (longer growing seasons) and atmospheric nutrient deposition.

There is also evidence of increased inorganic sedimentation rates at all four sites, suggesting accelerated geomorphic activity in their catchments. We have observed dramatic dilutions of sediment 210Pb activities in the unsupported inventories from each lake. Marked and near-synchronous crashes in diatom concentrations and organic carbon content correspond with these 210Pb reversals, suggesting dilution of autochthonous sediment by inputs of predominantly inorganic material. Taken together, these data suggest that lakes of western Spitsbergen have entered new limnological and geomorphic states for which no adequate Holocene analogues exist

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