Widespread occurrence of distinct alkenones from Group I haptophytes in freshwater lakes: implications for paleotemperature and paleoenvironmental reconstructions

Longo, W. M. et al. (2018) Widespread occurrence of distinct alkenones from Group I haptophytes in freshwater lakes: implications for paleotemperature and paleoenvironmental reconstructions. Earth and Planetary Science Letters, 492, pp. 239-250. (doi: 10.1016/j.epsl.2018.04.002)

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Alkenones are C35–C42 polyunsaturated ketone lipids that are commonly employed to reconstruct changes in sea surface temperature. However, their use in coastal seas and saline lakes can be hindered by species-mixing effects. We recently hypothesized that freshwater lakes are immune to species-mixing effects because they appear to exclusively host Group I haptophyte algae, which produce a distinct distribution of alkenones with a relatively consistent response of alkenone unsaturation to temperature. To evaluate this hypothesis and explore the geographic extent of Group I haptophytes, we analyzed alkenones in sediment and suspended particulate matter samples from lakes distributed throughout the mid- and high latitudes of the Northern Hemisphere (n=30). Our results indicate that Group I-type alkenone distributions are widespread in freshwater lakes from a range of different climates (mean annual air temperature range: −17.3–10.9 °C; mean annual precipitation range: 125–1657 mm yr−1; latitude range: 40–81°N), and are commonly found in neutral to basic lakes (pH > 7.0), including volcanic lakes and lakes with mafic bedrock. We show that these freshwater lakes do not feature alkenone distributions characteristic of Group II lacustrine haptophytes, providing support for the hypothesis that freshwater lakes are immune to species-mixing effects. In lakes that underwent temporal shifts in salinity, we observed mixed Group I/II alkenone distributions and the alkenone contributions from each group could be quantified with the RIK37 index. Additionally, we observed significant correlations of alkenone unsaturation (UK37) with seasonal and mean annual air temperature with this expanded freshwater lakes dataset, with the strongest correlation occurring during the spring transitional season (UK37=0.029⁎T-0.49; r2=0.60; p<0.0001). We present new sediment trap data from two lakes in northern Alaska (Toolik Lake, 68.632°N, 149.602°W; Lake E5, 68.643°N, 149.458°W) that demonstrate the highest sedimentary fluxes of alkenones in the spring transitional season, concurrent with the period of lake ice melt and isothermal mixing. Together, these data provide a framework for evaluating lacustrine alkenone distributions and utilizing alkenone unsaturation as a lake temperature proxy.

Item Type:Articles
Additional Information:This work was primarily funded by NSF grant PLR-1503846 to Y. Huang, NSF grant DEB-1026843 to G. Shaver, and the National Geographic Society. We would like to thank A. Carter and D. White for assistance in the field, L. Wang and J. Dillon for discussions on alkenone separations methods, and R. Tarozo who provided laboratory support. Icelandic lake samples were provided by LacCore (National Lacustrine Core Facility), Department of Earth Sciences, University of Minnesota-Twin Cities. We thank R. Bradley for providing the Upper Murray Lake sample. The ARC LTER and Toolik Field Station Environmental Data Center provided air and lake temperature data. Six samples and environmental data from lakes in south Siberia and north Mongolia were supported by RSF, grant 17-77-10086, RFBR and Government of the Novosibirsk Region, grant 17-45-540527, and the Ministry of Education and Science of the Russian Federation (project no. 14.Y26.31.0018). Two samples from Lake Ichino-megata were collected with funding from MEXT –Japan KAKENHI grant nos. 24651019, 2621101002 and 101002. Two samples from volcanic lakes in NE China were collected with funding from the National Natural Science Foundation of China (grant no. 41573113) to Y. Huang
Glasgow Author(s) Enlighten ID:Toney, Professor Jaime
Authors: Longo, W. M., Huang, Y., Yao, Y., Zhao, J., Giblin, A. E., Wang, X., Zech, R., Haberzettl, T., Jardillier, L., Toney, J., Liu, Z., Krivonogov, S., Kolpakova, M., Chu, G., D'Andrea, W. J., Harada, N., Nagashima, K., Sato, M., Yonenobu, H., Yamada, K., Gotanda, K., and Shinozuka, Y.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Earth and Planetary Science Letters
ISSN (Online):1385-013X
Published Online:17 April 2018
Copyright Holders:Copyright © 2018 Elsevier
First Published:First published in Earth and Planetary Science Letters 492:239-250
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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