Paper No. 6
Presentation Time: 9:20 AM
EXTRACTING PALEOCLIMATE INFORMATION FROM LAKE SEDIMENTS USING COMPOUND-SPECIFIC HYDROGEN ISOTOPE ANALYSIS OF INDIVIDUAL SEDIMENTARY ORGANIC COMPOUNDS
Oxygen isotopic compositions of carbonate sediments are important indicators of past climate change, in both marine and terrestrial settings. Unfortunately, carbonate minerals are absent from most lake sediments, or frequently contain significant detrital carbonate contamination, prohibiting the widespread use of their Delta18O values as a terrestrial paleoclimate indicator. We studied the hydrogen isotopic compositions of a number of lacustrine sedimentary compounds from lake surface sediments of 33 North American lakes and corresponding lake water. We demonstrate that several compounds have nearly constant hydrogen isotope fractionation relative to the lake water, and carry the signals of lake water hydrogen isotope ratios. We also produced hydrogen isotope stratigraphies from a sediment core at Crooked Pond in New England. By comparing our results with existing pollen-derived paleoclimate records, we find a strong coherence between compound DeltaD values and climatic variables, particularly temperature. The results indicate that a range of compounds of aquatic origin preserve the DeltaD values of lake water, and carry a clear climatic signal. We also determined the variations in hydrogen isotopes for higher plant biomarkers (leaf waxes) in a sediment core from Lake Tulane, Florida. The DeltaD values of the plant biomarkers vary little during the Holocene, but are ca. 40 to 70 per mils higher between 13,000 to 24,000 years BP than the early Holocene. The abrupt decrease in DeltaD from the last glacial to the Holocene suggests an increase in P-E, which is generally consistent with pollen results. Our results also provide support for future use of hydrogen-isotope values of biomarkers as an additional proxy for paleoclimate (temperature and/or moisture balance) in lake sediments.