A Molecular Isotopic Proxy for Precipitation in Arctic Lakes
Arctic Research Initiative
2007 Funded Project
Accurate records of the pattern and timing of climate change in the Arctic are important to understanding how the global climate system functions. The Arctic is a significant region with respect to climate, and the effects of global climate change might be identifiable in the Arctic before they can be found elsewhere, as suggested by the large and rapid changes documented throughout the Arctic environment in recent years. In addition to showing sensitivity to global changes in climate, the Arctic may also be capable of forcing widespread climate shifts. Changes in Arctic precipitation and river runoff could alter the freshwater flux to the high latitude North Atlantic Ocean and influence the rate of thermohaline circulation, thus impacting hemispheric heat transport and possibly global climate. Models predict that warmer global conditions will generate increases in high-latitude precipitation, and such changes have been observed in syntheses of 20th-century freshwater discharge from Eurasian rivers into the Arctic Ocean. Evidence for correlation between Arctic precipitation and global mean temperature (and thus predictions of continued increase in the future) is controversial however, and additional records of precipitation change in the Arctic are critical to resolving this important question. Accurate calibrations of precipitation proxies are needed to enable reconstruction of precipitation change throughout the Arctic for comparison to large temperature changes in the past.
This work will develop and refine a new precipitation proxy based on compound-specific hydrogen isotopic analysis of organic biomarkers for use in lakes throughout the Arctic. Accurate estimates of past precipitation change from Arctic lakes are currently difficult to obtain, and proxies are often available only on a lake-by-lake basis. We will measure independent δD values from organic compounds synthesized by vascular plants and aquatic algae, respectively. The terrestrial δD will be contrasted with values from aquatic biomarkers in order to produce an index reflecting plant evapotranspiration and soil evaporation. We will compare this aridity index to steep precipitation and temperature gradients across the Baffin Island region as well as northern Labrador, southern Greenland and the Canadian High Arctic. This surface sediment network will provide calibration of a novel precipitation proxy that will be applicable to small lake catchments throughout the Arctic. As part of this proposed work, long sediment cores will be targeted for high-resolution measurements for comparison to paleo-precipitation records previously constructed from independent proxies.
In previous work, surface lake sediments were collected from Baffin Island and the Labrador coast, to be compared with climate data (mean annual, mean January and mean July precipitation) available as a 25-km gridded climatology. The surface sediment samples have already been obtained and are being analyzed as part of funded work to develop new temperature and runoff indices from archeal membrane lipids. Therefore, the organic lipid extractions have already been completed. Downcore samples will also be obtained from sites with known histories of precipitation change, to extend the calibration into the temporal as well as spatial dimension. This proposed work will leverage substantially against funded work to investigate these samples for a similar purpose, but using a very different analytical tool. We request funding only for the costs associated with the additional chemical procedures necessary to isolate and purify the leaf waxes and algal biomarkers, and for the compound-specific δD analyses in the Fye Facility at WHOI, using previously established techniques. Results from these calibrations will be applicable to extensive networks of lake sediment records already collected and being analyzed for paleotemperature synthesis as a part of the SEARCH (Study of Environmental Arctic Change) Science Implementation and the International Polar Year. This degree of coordination could allow us to construct a spatial network of Arctic precipitation changes in relatively short time, compared to the decades required to construct the original paleotemperature records used for the synthesis efforts to date. If this proposed work is successful, it will provide the preliminary data necessary to support proposals to NSF and NOAA, potentially as part of the end of IPY (synthesis) and as part of continued SEARCH funding for the next several years.