This research provides a critical baseline for chemical and macromolecular characteristics of organic matter (OM) sources in high-elevation lake sediments. Such studies are essential for accurate paleoenvironmental interpretation of organic matter characteristics, particularly in mountain regions where steep environmental gradients lead to spatially variable OM inputs among lakes. We analyzed the carbon- and nitrogen-isotope compositions (δ13CTOC, δ15NTN), and total organic carbon to total nitrogen atomic ratios (TOC:TN), of whole tissues of modern vegetation, lichen and algae from Uinta Mountain lakes, along with the abundances and carbon- and hydrogen-isotope compositions of n-alkanes (δ13Cn-alkane, δ2Hn-alkane). TOC:TN can be used to distinguish between aquatic and terrestrial sources, but the differentiating values are higher in the Uinta Mountains than in low-elevation regions. Chain lengths of n-alkanes are more useful than n-alkane isotope compositions for differentiating between terrestrial and semi-aquatic sources in the Uinta Mountains. The ratio of n-alkanes C23 to C27 in mountain lake sediment OM can be used to detect inputs from coniferous krummholz trees and may serve as a proxy for treeline position. We used the isotope data from n-alkanes to calculate the carbon-isotope fractionation between atmospheric carbon dioxide and the n-alkane C23 (ɛbulk), and the hydrogen-isotope fractionation between source water and the n-alkane C25 (ɛwater). These fractionation factors, and the isotope compositions of n-alkanes extracted from lake sediments, suggest that the δ13C of atmospheric CO2 was − 7.0 ± 2‰ and the δ2H of precipitation was − 133 ± 7‰ at ~ 1400 CE in this region. These calculations demonstrate potential applications of our results for obtaining additional paleoclimatic information from paleolimnological organic matter archives.
|Number of pages||17|
|Journal||Journal of Paleolimnology|
|Early online date||16 Sep 2022|
|Publication status||Published - Feb 2023|
Bibliographical noteFunding Information:
We thank Chris Plunkett, Mark Muir, Darlene Koerner, Helen Kempenich, Christy Oprandy, Nick Oprandy, Mike Devito and the rest of the Ashley National Forest personnel for assistance with sample collection. We are also grateful to Kim Law, Grace Yau and Li Huang of the Laboratory for Stable Isotope Science (LSIS) at the University of Western Ontario for assistance with stable isotope analysis, and Erika Hill at the Lake and Reservoir Systems Research Facility (LARS) for assistance with fieldwork preparation. We also thank Karen Van Kerkoerle from the University of Western Ontario for help with designing graphics. Funding was provided by an NSERC Alexander Graham Bell Canada Graduate Scholarship (RD), Natural Sciences and Engineering Research Council (NSERC) Discovery Grant (FJL), the Canada Research Chairs Program (FJL), the Canada Foundation for Innovation (FJL) and the Ontario Research Fund (FJL). Additional funding was provided by the Ashley National Forest (KAM). This is LSIS contribution #393.
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