Climatic and Environmental Controls on the Occurrence and Distributions of Long Chain Alkenones in Lakes of the Interior United States

Authors

Jaime L. Toney, Brown UniversityFollow
Yongsong Huang, Brown UniversityFollow
Sherilyn C. Fritz, University of Nebraska-LincolnFollow
Paul A. Baker, Duke UniversityFollow
Eric Grimm, Illinois State Museum, Springfield, IL
Paul Nyren, North Dakota State UniversityFollow

Document Type

Article

Date of this Version

2010

Comments

Published in Geochimica et Cosmochimica Acta 74:5 (March 1, 2010), pp. 1563–1578; doi: 10.1016/j.gca.2009.11.021 Copyright © 2009 Elsevier Ltd. Used by permission. http://www.sciencedirect.com/science/journal/00167037

Abstract

Long chain alkenones (LCA) are temperature-sensitive lipids with great potential for quantitative reconstruction of past continental climate. We conducted the first survey for alkenone biomarkers from 55 different lakes in the Northern Great Plains and Nebraska Sand Hills of the United States. Among those surveyed, we found 13 lakes that contain LCAs in the surface sediments. The highest concentrations of alkenones in sediments are found in cold (mean annual air temperature ~11 °C versus 17 °C in our warmest sites), brackish to mesosaline (salinity = 8.5–9.7 g/L), and alkaline (pH = 8.4–9.0) lakes with high concentrations of sodium and sulfate. The dynamics of stratification and nutrient availability also appear to play a role in LCA abundance, as early spring mixing promotes a bloom of alkenone-producing haptophytes. Four of the alkenone-containing sites contain the C_37:4 alkenone; however, we discovered an unprecedented lacustrine alkenone distribution in a cluster of lakes, with a total absence of C_37:4 alkenone. We attribute this unusual composition to a different haptophyte species and show that the sulfate:carbonate ratio may control the occurrence of these two distinct populations. We created a new in-situ temperature calibration for lacustrine sites that contain C_37:4 using a water-column calibration from Lake George, ND and show that U^K₃₇ is linearly correlated to lake water temperature (R² = 0.74), but U^K'₃₇ is not. A number of lakes contain an unidentified compound series that elutes close to the LCAs, highlighting the importance of routine GC–MS examination prior to using lacustrine LCAs for paleotemperature reconstructions.