Assessment of long-chain n-alkanes as a paleoclimate proxy in the Bering Sea sediments

Long-chain n-alkanes are measured in sediment cores (Cores U1341C and UMK-3A) collected from the Bering Sea to evaluate the paleoclimatic utility of n-alkanes in high northern latitude marine sediments. The variations in concentration and molecular composition of long-chain n-alkanes since the end of the last glacial period (the past 18 kyr) have been reconstructed. Sedimentary records of molecular distributions of n-alkanes in Cores U1341C and UMK-3A indicate that they primarily originate from terrestrial vascular plants. The results indicate that concentrations of odd number C25-C31 n-alkanes increased in the last glacial and Younger Dryas (YD) cold pe-riods for Core U1341C, while those in Core UMK-3A increased during the warm Bolling-Allerod period and the cold YD period. These findings suggest that the source and transport pathways differ between the two sites. However, the n-alkanes chain length distribution in Cores U1341C and UMK-3A exhibits a low and a high during the cold and warm periods, respectively. These millennial-scale variability patterns remarkably resemble those of the sea surface temperature records in the proximal sites. This similarity suggests that the sedimentary record of n-alkane chain length distribution reflects surface temperature changes rather than changes in vegetation in the high northern latitudes (including in the Beringia). This study shows that n-alkanes are useful for reconstructing climate change in the high northern latitudes where applicable paleoclimate proxies are limited.