Analysis of Deuterium from Fossil Pollen to Reconstruct Paleoclimates

Abstract

We propose a method to reconstruct paleotemperatures and to determine paleo-air mass source areas from deuterium isotopes (δD) extracted from fossil pollen originating from Lake Lisan (precursor to the Dead Sea), Jordan, and encompassing the period ∼ 23.3 – 13.8 cal kyr BP. Previous isotopic studies on fossil pollen depend on analyses of δ13C and δ18O values, which can vary significantly between and within plant species according to environmental setting and photosynthetic pathway. In addition, carbon chemicals introduced during acetylosis processing of pollen samples can contaminate carbon isotopes. In contrast, δD data from pollen are not affected by variation in organic carbon, and thus, do not require non-carbon bearing extraction techniques. We propose that pollen extraction can follow standard palynological methods of acid digestion and acetylosis. A paleotemperature curve is reconstructed by converting δD data from pollen to δ18O values using a localized meteoric water line and a standard temperature relationship between δD and δ18O. We estimate temperatures for the Late Glacial Maximum and the Bølling-Allerød warm period based on δD from fossil pollen. These results compare favorably with other temperature estimates for the Eastern Mediterranean region based on δ18O.