The Espenberg maar lakes in Bering Land Bridge National Preserve, Seward Peninsula, Alaska, are the largest volcanic crater lakes in the world and contain the longest known lake sediment archives in Alaska. These lakes sediments are valuable for understanding the region’s past climate and environmental changes. Further, the sediments may hold information about the timing and dynamics of human migration across the Bering Land Bridge during the last glacial period. This publication documents the discovery of alkenones in maar lake sediments, including White Fish, North Killeak, and Devil Mountain Lakes. Alkenones are a class of organic molecules produced by specific types of algae living in these lakes. Alkenones are stable, or slow to degrade, and can be preserved for long periods of time in lake sediments. The amounts of different alkenones produced by these algae depend upon the temperature at which the algae are living. In this way, alkenones primarily record spring lake temperatures associated with the annual algal bloom. Findings from this study confirm that alkenones originate from haptophyte algae in lake water and will serve excellent proxies for spring temperature reconstructions.
Group I alkenones and Isochrysidales in the world’s largest maar lakes and their potential paleoclimate applications
The Espenberg maar lakes on the Seward Peninsula, Alaska, are the largest volcanic crater lakes in the world and contain the longest known lacustrine sedimentary archives in Alaska. The lack of glacial-aged marine sedimentary archives around the Bering Land Bridge due to exposure of the shelf during sea level low-stands makes these lakes highly valuable for understanding the region’s past climate and environmental changes. Located en route to humanity’s last colonized American continents, the Seward Peninsula’s climate and environments during the last glacial period bear major anthropological significance. However, a lack of quantitative proxies has so far hampered exploration of these lakes for paleoclimate reconstructions. Here we report, for the first time, the discovery of abundant Group I alkenones and Isochrysidales in surface sediments from three maar lakes: White Fish, North Killeak, and Devil Mountain, using a combination of lipid biomarker and 18S rRNA gene sequencing analyses. Our discovery adds to the expanding list of oligotrophic freshwater lakes where Group I alkenones are found, and water chemistry data contribute to the understanding of the environmental controls on Group I Isochrysidales. Our results further confirm the use of the U37K index of Group I alkenones as a proxy for the mean temperature of the spring isotherm (MTSI) and RIK37 as a quantitative measurement for Isochrysidales group mixing. We also demonstrate the analytical challenges for analyzing alkenones in freshwater lakes and the effectiveness of eliminating coelution using silver thiolate chromatographic material (AgTCM).
Wang, K. J., J. A. O’Donnell, W. M. Longo, L. Amaral-Zettler, L. Gaoyuan, Y. Yao, and Y. Huang. 2019. Group I alkenones and Isochrysidales in the World’s large maar lake complexes and their potential paleoclimatic applications. Organic Geochemistry. doi:10.1016/j.orggeochem.2019.103924.