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HOLOCENE LAKE ONTOGENY IN RELATION TO CLIMATIC FORCING AND CATCHMENT DEVELOPMENT IN THE KANGERLUSSUAQ REGION, WEST GREENLAND

PERREN, BIANCA B  University of Toronto.
Anderson, N. John  Loughborough University.
Birks, Hilary H  University of Bergen.
Douglas, Marianne S.V.  University of Toronto.

The 170 km-wide, ice-free area of West Greenland near Kangerlussuaq (67N, 51W) contains thousands of lakes ranging from dilute sites on the coast to evaporatively-enriched closed basin systems that reflect the more continental climate of the ice sheet margin. Sediment cores from these lakes are being used to generate a detailed spatial network of multi-proxy records (isotopes, diatoms, macrofossils, pollen, zooplankton, chironomids, metals) of Holocene environmental change in West Greenland. In the present study, diatoms from four lakes along this strong climatic gradient are being analysed to assess the spatial and temporal variability of post-glacial lake ontogeny in the region with regard to changing Holocene climatic and catchment influences. Here, we present a preliminary, 14C-dated Holocene diatom stratigraphy from lake SS16, a small, dilute, dimictic lake in the ice-proximal region. Low lake productivity (inferred from LOI) and early colonizing diatom assemblages characterize the immediate postglacial environment of SS16 (approximately 8.5 ka BP). With the arrival of Betula nana and stabilization of the terrestrial environment after 7.5 ka BP, LOI-inferred lake productivity increased, aquatic macrophytes and invertebrates became abundant, and diatom assemblages changed to small, benthic Fragilaria-dominated communities. The stratigraphic record is then punctuated by long periods in which no diatoms are present (6.5-4 ka BP). As there is little visual indication of diatom dissolution, the absence of diatoms during the early- to mid- Holocene strongly suggests nutrient (Si) limitation. Effective moisture (precipitation-evaporation) was extremely negative in the early-mid Holocene in West Greenland (McGowan, et al., 2003). Catchment weathering and nutrient inputs were thus limited to levels below the minimum required to sustain siliceous algal production. A marked shift occurred in the lake approximately 4 ka BP, when a predominantly planktonic community of diatoms and chrysophytes reappeared in the lake. Increased nutrient flux resulting from aeolian activity or increased precipitation is a likely explanation for the shift from benthic to planktonic diatoms in the later Holocene. This interpretation is corroborated by records from the West Greenland saline lakes that show a shift to increased precipitation at that time. The late Holocene record from SS16 is characterized by century-scale variability, but does not show the historically unprecedented recent changes seen in other circumarctic paleolimnological records. The diatom history of SS16, a dilute freshwater system, demonstrates the importance of catchment and biotic factors in structuring the diatom community response to climatic variability in arctic lakes, particularly at millennial timescales.


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