14-8 Sensitivity Testing of the Alkenone UK37 Paleothermometer to Ice Cover and Air Temperature in High Arctic Lakes

Session: Lake Sedimentary Records of Past Climate and Environment

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Abstract:

Alkenones are long-chain ketones produced by haptophyte algae in marine and lacustrine environments. The unsaturation index (UK37) of alkenones produced by Group I haptophytes, common in high-latitude, freshwater lakes, varies linearly with lake surface temperature during the algal growing season. Alkenones preserved in Arctic lake sediments therefore act as a powerful local paleothermometer and have been widely used to reconstruct past climate variability. Lake temperature reconstructions from alkenone UK37 values are typically inferred to represent spring/summer conditions, with a roughly stable relationship to air temperature through time. 

In polar lakes with seasonal to perennial ice cover, however, the timing of ice-off is strongly influenced by winter temperature and precipitation, wind-speed, and lake-specific parameters including depth, fetch, shading by local topography, and water clarity. Variability in the timing of lake thaw may therefore impart non-linearities in the lake temperature signal recorded by alkenone UK37, ultimately masking the primary climatic variable of interest: air temperature. Here, we apply PRYSM 2.0, a proxy system model for lacustrine archives, to explore the climatic and environmental controls on UK37 in two neighboring lakes from Wandel Dal valley, North Greenland, which are subject to the same meteorological conditions but differ from one another in size and shape. We compare model results with two sedimentary UK37 records from the same systems, in order to elucidate a shared climate history for the mid-late Holocene. This work highlights the importance of considering internal lake dynamics when interpreting paleoclimate records from the High Arctic and builds a new UK37 sensor model for PRYSM. 

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