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TESTING A NEW ISOTOPIC PALEO-THERMOMETER IN A MULTI-PROXY CONTEXT: CHIRONOMID δ18O AS A PROXY FOR HOLOCENE TEMPERATURE CHANGE IN ICELAND

AXFORD, YARROW  INSTAAR - University of Colorado.
Miller, Gifford H.  INSTAAR - University of Coloradoe.
Wooller, Matthew J.  Alaska Stable Isotope Facility, University of Alaska Fairbanks.
Francis, Donna  Dept. of Geosciences, University of Massachusetts.
Geirsdóttir, Áslaug  Dept. of Geosciences, University of Iceland.

Additional quantitative paleoclimate records are needed for further testing general circulation models and for understanding the magnitudes and rates of natural climate changes. Here we describe initial tests of a new paleo-thermometer, which uses the oxygen isotopic composition (δ18O) of subfossil chironomid larval head capsules as a proxy for past mean annual air temperatures (MATs).

δ18O of precipitation is highly correlated with MAT in cold regions. In suitable stream-fed arctic lakes, δ18O of precipitation determines δ18O of lakewater, which in turn controls δ18O of chironomid larvae living at the sediment-water interface. In a pilot study by Wooler et al. (2003), δ18O of chironomid chitin extracted from lake sediments at four sites in Greenland, arctic Canada, and Massachusetts, was well correlated with local precipitation δ18O and MAT. The work described here is focused on characterizing the relationship between lakewater δ18O and MAT across Iceland, and identifying any confounding effects of meteorology and/or watershed processes. Our results indicate that the δ18O of large lakes in Iceland is indeed strongly correlated with MAT; thus the chironomid δ18O paleothermometer holds promise for reconstructing paleotemperatures in Iceland.



Figure 1. The δ18O of lakewater in large Icelandic lakes is well correlated with mean annual air temperature.


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