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32nd Annual Arctic Workshop Abstracts
March 14-16, 2002
INSTAAR, University of Colorado at Boulder

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FINNEY, BRUCE P. Institute of Marine Science, University of Alaska Fairbanks.
Brown, Tom . Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory.

A change in carbon cycling in arctic and subarctic regions has the potential to be an important feedback to the global climate system. While much research has been focused on reconstructing northern high-latitude paleoclimatic change, less effort has been concerned with determining past changes in the carbon cycle in this region. Lake sediments have the potential to provide important information on past changes in carbon cycling, as they contain information on both aquatic and watershed processes. In some regions (i.e., the Alaskan Arctic Coastal Plain) lakes constitute a significant proportion of the surface area of the landscape. To learn more about how lakes record information regarding carbon cycling, a transect of 51 lakes in Alaska spanning 60 70 degrees N was sampled in summer. In addition, several lakes were sampled at weekly to bi-weekly periods for up to 2 years. Lake water characteristics include temperature, pH, pCO2, DO, Chl-a and nutrients. Lake suspended POM (primarily phytoplankton) and surface sediments were analyzed for C and N content, stable carbon and nitrogen isotope ratios, and in some cases radiocarbon content. Similar to recent data from other regions, the surface water of most of the study lakes is supersaturated with respect to CO2 (pCO2 ranged from < 50 - ~10,000 ppm). This implies a net transfer to lakes of respired CO2 from their watersheds. The C-13 ratio of lake POM, which ranged from 15 to 45 o/oo, is inversely related to surface water pCO2. The pCO2 of lake surface waters, in turn, is related to a number of factors, including basin hydrology, soil/vegetation characteristics, and lake productivity. Radiocarbon analyses of POM (phytoplankton) revealed that non-contemporary ages (several hundred to several thousand years BP) are common. In general, lakes with higher pCO2 had phytoplankton (lake POM) with lower fractions of radiocarbon relative to modern. This implies that lakes may have significant reservoir effects, even in the absence of carbonate bedrock, due to input of CO2 from watershed organic matter of non-modern age. This reservoir effect is likely to be ubiquitous in high-latitudes, and has significant implications for radiocarbon dating of lake sediments.


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