Holocene thecamoebians in freshwater lakes on Bylot Island, Northwest Territories, Canada

Thecamoebian assemblages were studied in two short cores from kettle lakes on Bylot Island, Canadian high arctic, within an area bounded by 72 degrees and 74 degrees N and 75 degrees and 82 degrees W. Cores did not provide su itable material for absolute age dating. Based on known sedimentation rates of other arctic takes, however, the time interval covered by lake cores re flect sedimentation during the Holocene of approximately the last 5000 year s. On the Bylot Island lowlands, a low species diversity with eleven thecamoeb ian species was identified whereas five lakes sampled on the Salmon River l owlands around Pond Inlet were barren of thecamoebians. Thecamoebian tests typically have a coarse texture. The shallower of the two lakes on Bylot Is land is dominated by Difflugia globulucs. The assemblage found in the deep lake contains nine taxa with a distinct transition from Difflugia globulus dominance in the lower half of the core to a Difflugia oblonga dominated as semblage in the upper half. D. oblonga prefers organic-rich substrates and its dominance coincides with an increase of organic material in the core. L ate Holocene thecamoebian abundance fluctuates in the shallow lake whereas the deep lake is characterized by more constant numbers. Faunal results in both lakes show that local environmental factors have to be considered to e xplain paleolimnological changes.