Abstract
Glacier-derived dissolved organic matter represents a quantitatively significant source of ancient, yet highly bioavailable carbon to downstream ecosystems1. This finding runs counter to logical perceptions of age–reactivity relationships, in which the least reactive material withstands degradation the longest and is therefore the oldest2. The remnants of ancient peatlands and forests overrun by glaciers have been invoked as the source of this organic matter1,3,4. Here, we examine the radiocarbon age and chemical composition of dissolved organic matter in snow, glacier surface water, ice and glacier outflow samples from Alaska to determine the origin of the organic matter. Low levels of compounds derived from vascular plants indicate that the organic matter does not originate from forests or peatlands. Instead, we show that the organic matter on the surface of the glaciers is radiocarbon depleted, consistent with an anthropogenic aerosol source. Fluorescence spectrophotometry measurements reveal the presence of protein-like compounds of microbial or aerosol origin. In addition, ultrahigh-resolution mass spectrometry measurements document the presence of combustion products found in anthropogenic aerosols. Based on the presence of these compounds, we suggest that aerosols derived from fossil fuel burning are a source of pre-aged organic matter to glacier surfaces. Furthermore, we show that the molecular signature of the organic matter is conserved in snow, glacier water and outflow, suggesting that the anthropogenic carbon is exported relatively unchanged in glacier outflows.
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Acknowledgements
K. Butler is thanked for help with measurements of DOC concentrations and DOM optical properties, R. Dyda for help with lignin analyses, A. Wozniak for discussions regarding aerosol OM, A. Boyette for assistance with design and production of figures, and the College of Sciences Major Instrumentation Cluster (COSMIC) at ODU for FTICR-MS instrument time. NorthStar Trekkers and the US forest Service are thanked for providing transport and access to Mendenhall Glacier. This work was funded by the US National Science Foundation (DEB-1146161/-1145313/-1145932/-11455885, OCE-0728634, EAR-0943599/-0838587), the Climate Effects Network of the US Geological Survey, and a Fellowship from the Hanse Institute for Advanced Studies (HWK, Delmenhorst, Germany) granted to A. Stubbins. The use of brand names is for identification purposes only and does not imply endorsement. Any opinions, findings, conclusions or recommendations expressed are those of the authors and do not necessarily reflect the views of the funding bodies.
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A.S., E.H., R.G.M.S. and G.R.A. designed the research. E.H. led the fieldwork at Mendenhall and Herbert glaciers with assistance from R.G.M.S., A.W.V. and D.T.S., and G.R.A., P.S. and R.G.S. led the fieldwork at Gulkana and Fremont glaciers. P.A.R. and D.B. analysed samples for radiocarbon ages. P.J.H. and R.G.M.S. ran lignin analyses. G.R.A. and A.W.V. ran DOC, absorbance and fluorescence analyses. FTICR-MS data acquisition and analysis were conducted by R.L.S., H.A.N.A., P.G.H. and A.S. Writing and data integration were done by A.S. with significant contributions from E.H., R.G.M.S, and P.A.R. All authors commented on the manuscript.
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Stubbins, A., Hood, E., Raymond, P. et al. Anthropogenic aerosols as a source of ancient dissolved organic matter in glaciers. Nature Geosci 5, 198–201 (2012). https://doi.org/10.1038/ngeo1403
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DOI: https://doi.org/10.1038/ngeo1403
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