HYDROGEN ISOTOPIC COMPOSITIONS OF INDIVIDUAL BIOMARKERS IN LAKE SEDIMENTS AS A RECORD OF PAST CLIMATE CHANGE

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 d18O values as a terrestrial paleoclimate indicator. In this study, we show the potential of the hydrogen isotopic compositions of individual lacustrine biomarkers as a powerful tool for documenting past climate change. We measured the hydrogen isotopic compositions of biomarkers in lacustrine sediments using GC-TC-IRMS or TC/EA-IRMS, and produced isotope stratigraphies from Lake Malawi, East Africa, and two lakes (Berry Pond and Crooked Pond) in New England. By comparing our results with existing paleoclimate records, we find a strong coherence between biomarker dD values and climatic variables. We find evidence of climatic control of both aquatic and terrestrial biomarker dD values, and by comparing the two southern New England records, we find that the results are consistent and repeatable. Lake surface sediment and lake water samples from 19 lakes on a latitudinal transect (29oN to 49oN) in North America provide an additional test and calibration of the method. The results indicate that a range of aquatic biomarkers preserve the dD values of lake water, and carry a clear climatic signal.