Evidence for the Global Distribution and Uniform Temperature Response of Distinct Alkenones from Group I Haptophytes
Abstract
Alkenones are widely used to reconstruct changes in sea surface temperature. However, their use in many aquatic systems is complicated by species-mixing effects, which overprint the response of alkenone unsaturation to temperature. We recently hypothesized that freshwater lakes are resistant to species-mixing effects because they host Group I haptophyte algae, which feature relatively uniform temperature responses. To test 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). We found that Group I-type alkenone distributions were widespread in freshwater lakes from a range of climates (mean annual air temperature range: -17.3—10.9 °C; mean annual precipitation range: 125—1657 mm year-1; latitude range: 40—81 °N), and were commonly found in neutral to basic lakes. We demonstrate that these freshwater lakes do not feature mixed distributions, providing support for the hypothesis that freshwater lakes are resistant to species effects. In lakes that experienced temporal shifts in salinity, we observed mixed Group I/II alkenone distributions and the alkenone contributions from each producer could be quantified with a mixing model based upon the RIK37 index. We also observed significant correlations of alkenone unsaturation (UK37) with seasonal and mean annual air temperature, with the strongest correlation occurring during the spring transitional season (UK37= 0.029*T - 0.49; r2 = 0.60; p <0.0001). 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) corroborated this finding by demonstrating the highest sedimentary fluxes of alkenones in the spring, concurrent with the period of lake ice melt and isothermal mixing. Together, these findings provide a framework for evaluating lacustrine alkenone distributions and using alkenone unsaturation as a spring lake temperature proxy in freshwater lakes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP31E1708H
- Keywords:
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- 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCESDE: 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCESDE: 1041 Stable isotope geochemistry;
- GEOCHEMISTRYDE: 1055 Organic and biogenic geochemistry;
- GEOCHEMISTRY