TOWARD A RECONSTRUCTION OF LONG-TERM CLIMATE VARIABILITY USING SEDIMENTS FROM AN ANOXIC ESTUARINE BASIN

Reconstructing climate over the past several centuries to millenia is necessary for placing the unusual climate of the late 20th Century and now early 21st Century in the context of longer-term natural variability. Because instrumental records of climate typically span little more than the last century, our understanding of climate variability in prior centuries must come from natural climate recorders, or climate proxies. These proxies can be used to understand how a particular environment has responded to climate variability (e.g. precipitation) in the past, or be used to reconstruct large-scale atmospheric patterns (e.g the Southern Oscillation or North Atlantic Oscillationc [NAO]) prior to the existance of instrumental records.

We have developed an organic carbon record from the Pettaquamscutt River Estuary in Rhode Island. The depositional setting is a kettle hole with anoxic bottom water and sedimentation rates are on the order of millimeters/yr. A five-meter-long piston core was collected and sampled at 2 cm resolution and the organic carbon content was determined by Loss on Ignition. In the top three meters, organic carbon content averages 28 percent followed by a decline to an average of 20 percent over next meter and finally falling to less than five percent in glacial sands at the bottom of the core.

Using a preliminary age model based on magnetic paleosecular variations, we found a marginally significant correlation between the organic carbon variability and a multicentury, annually resolved reconstruction of the winter NAO index at periods greater than 40 years. We are hopeful that with a refined age model and additional analysis, this site can yield information on the long term behaviour of the NAO, one of the major climate patterns in the Northern Hemisphere.