TESTING A NEW ISOTOPIC PALEOTHERMOMETER IN A MULTI-PROXY CONTEXT: CHIRONOMID d¹⁸O AS A PROXY FOR HOLOCENE TEMPERATURE CHANGE IN ICELAND

New 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 paleothermometer, which uses the oxygen isotopic composition (d¹⁸O) of subfossil chironomid larval head capsules as a proxy for past mean annual air temperatures (MATs).

d¹⁸O of precipitation is highly correlated with MAT in cold regions. In suitable stream-fed arctic lakes, d¹⁸O of precipitation determines d¹⁸O of lakewater, which in turn controls d¹⁸O of chironomid larvae living at the sediment-water interface. In a pilot study by Wooler et al. (2003), d¹⁸O of chironomid chitin extracted from lake sediments at four sites in Greenland, arctic Canada, and Massachusetts, was well correlated with local precipitation d¹⁸O and MAT. The follow-up work described here is focused on testing the relationship between MAT and chironomid d¹⁸O in Iceland, and identifying any confounding effects of watershed processes and biological fractionation.

Chironomid d¹⁸O will be used, in combination with more established paleoclimate proxies including chironomid taxonomy, to reconstruct late-glacial and Holocene temperature changes in northern Iceland. The magnitude of Holocene climate variability in Iceland may have been exceptionally large: North Iceland lies at a major front between warm (Atlantic) and cold (polar) ocean surface currents, and is therefore sensitive to small shifts in ocean circulation. The North Iceland shelf has experienced significant oceanographic changes during the Holocene (e.g., Eiríksson et al., 2000; Andrews et al., 2001), and historical records document large changes in Iceland’s climate over the past millennium, including economically devastating advances of sea ice (e.g., Ogilvie and Jónsson, 2001). Thus Iceland’s lakes may be ideal sites for reconstructing Holocene climate variability, especially changes in North Atlantic circulation, which may drive rapid climate changes that propagate around the globe. This poster presents the initial results of our ongoing research.