Postglacial climate reconstruction based on compound-specific D/H ratios of fatty acids from Blood Pond, New England

Abstract

We determined hydrogen isotope ratios of individual fatty acids in a sediment core from Blood Pond, Massachusetts, USA, in order to reconstruct climate changes during the past 15 kyr. In addition to palmitic acid (C16 n-acid), which has been shown to record lake water D/H ratios, our surface sediments and down core data indicate that behenic acid (C22 n-acid), produced mainly by aquatic macrophytes, is also effective for capturing past environmental change. Calibration using surface sediments from two transects across eastern North America indicates that behenic acid records dD variation of lake water. Down core variations in dD values of behenic acid and pollen taxa are consistent with the known climate change history of New England. By evaluating the hypothesis that D/H fractionations of long chain even numbered fatty acids (C24-C32 n-acids) relative to lake water provide independent estimates of relative humidity during the growing season, we find that differences between lake-level records and isotopically inferred humidity estimates may provide useful insight into seasonal aspects of the hydrologic cycle. Combined analyses of D/H of short and long chain fatty acids from lake sediment cores thus allow reconstructions of both past temperature and growing season relative humidity. Comparison of dD records from two lakes in New England provides critical information on regional climate variation and abrupt climate change, such as the 8.2 ka event.