Journal
ORGANIC GEOCHEMISTRY
Volume 138, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.orggeochem.2019.103909
Keywords
Antarctica; Lacustrine sediments; n-Alkanes; n-Alkanoic acids; Carbon isotopic ratios; Vascular plant leaf waxes; Microbial origin; Long chain
Categories
Funding
- National Natural Science Foundation of China [41576183, 41776188]
- United States National Science Foundation [OPP-1503846, EAR-1762431]
- Chinese Arctic and Antarctic Administration of the State Oceanic Administration
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Long-chain n-alkyl lipids are traditionally ascribed to an origin from terrestrial vascular plants because these compounds are major constituents of higher plant leaf waxes. Over the past half century, numerous studies have taken advantage of these sedimentary biomarkers and their isotopic ratios to reconstruct paleo-environmental and paleo-climatological changes at a variety of time scales. However, it is uncertain and extremely difficult to determine if these compounds can also derive from microbes because of the prevalence of higher plants in most environments around the globe. Here we show, for the first time from natural sediment samples, that long-chain n-alkyl lipids can predominantly originate from aquatic microbial sources at three high-latitude (>69 degrees S latitude) Antarctic lakes, where no vascular plants are present in the surrounding land mass. The high carbon isotopic values (up to -12 parts per thousand) of these long-chain n-alkyl lipids exclude the possibility that these compounds are transported by wind from adjacent vegetated land masses. Instead, these isotope values are similar to lipids produced by aquatic microbial mats with an average bulk delta C-13 value of -14.2 +/- 1.7 parts per thousand, indicating heterotrophic microbes are the likely source of these long-chain n-alkyl lipids. For comparison, we also show that when even small amount of vascular plants and mosses are present in the study region, for instance at Long Lake (similar to 62 degrees S latitude) in the Antarctic Peninsula, the carbon isotopic values of sedimentary long-chain n-alkyl lipids decline dramatically, suggesting a rapid proportional increase in the relative contribution of leaf wax sources to total long-chain n-alkyl lipid inventory in lake sediments. (C) 2019 Published by Elsevier Ltd.
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