Sedimentary lipids as a paleoclimate proxy in greenland jamie mcfarlin
The hydrogen isotope ratios of sedimentary lipids in lacustrine archives are a valuable tool for reconstructing paleohydrology1. Compounds with identifiable sources allow for differentiation between aquatic and terrestrial plant lipids2,3, which offer insight into integrated (lake) water balance vs. growth-season precipitation. The hydrogen isotope ratio, d2H, of precipitation varies primarily with temperature and moisture source4,5, with substantial seasonal differences observed in the Arctic6. Documenting changes in precipitation from sedimentary archives is particularly significant in Greenland where comparisons of past warm periods to the present are needed to better constrain the impacts of ongoing warming on the hydrologic cycle7. However, few paleoclimate studies of Arctic Holocene records include hydrologic reconstruction8 largely due to limitations in available proxies. The emerging use of plant lipid d2H as a proxy for paleo lake-water and paleoprecipitation in the Arctic is promising. However, further calibration and application of this proxy is needed, in part because plants at high latitudes endure extremes in growth-season daylight and climate9,10.
Here we present ongoing work to calibrate and apply sedimentary lipid isotope proxies in Greenland. We discuss the application of hydrogen isotope ratios in sedimentary short and long-chain n-alkanes in a down-core record ~2 km from the present margin of the Greenland Ice Sheet. This archive includes both the Holocene and the Last Interglacial and provides direct comparison of two warm periods. We compare plant lipid d2H to other proxy work from the same core, including independent proxies for summer temperature and lake water oxygen isotope ratios. This synthesis allows us to place archival lake water isotopes onto local evaporation lines and the global meteoric water line. We also discuss our ongoing efforts to document d2H of sedimentary lipids along a latitudinal transect on the western coast of Greenland, that spans from low to high Arctic climate zones. We investigate the chain-length profile and d2H of sedimentary lipids from a suite of ~20 lakes, including proglacial and non-glacial lakes. Together, these studies will inform the modern relationship between d2H of sedimentary lipids and their source waters in Greenland as well as the application of this proxy in conjunction with other climate proxies on lacustrine archives.