@article{e45476593d8647109c8b5e459f9a6b0d,
title = "Dissolved organic matter compositions in 0.6–3.4 km deep fracture waters, Kaapvaal Craton, South Africa",
abstract = "The composition of dissolved organic matter (DOM) in extremely deep groundwaters has rarely been investigated. Focusing on deep fracture waters in billion year old rocks in South Africa, we hypothesized the DOM would be predominantly derived from in situ microbial sources, consistent with H2-driven lithoautotrophic ecosystems previously documented in these fluids. We collected groundwater from 0.6 to 3.4 km depths via boreholes in mines, and characterized the DOM by a variety of analytical methods. Dissolved organic carbon concentrations ranged from 0.25 to 4.9 mg C/L. Low molecular weight organic acids (formate, acetate, lactate, propanoate) and amino acids (after hydrolysis) accounted for varying fractions of the total dissolved organic carbon. UV spectrophotometry, scanning fluorimetry, and nuclear magnetic resonance (NMR) spectra indicated lower concentrations of aromatic compounds than are commonly found in surface waters and shallow groundwaters. Molecular weights of aromatic compounds measured by size-exclusion chromatography were dominantly 500–1000 Da. Scanning fluorimetry revealed humic substances in two shallow (578 and 1300 m) samples; deeper samples showed peaks indicating aromatic amino acids. Intensive study of one sample from a previously sampled borehole in Beatrix mine resulted in large NMR peaks for aliphatics and carboxyls with lesser aromatics peaks; negative electrospray ion Fourier transform ion cyclotron resonance-mass spectrometry detected protein-, lipid-, and lignin-like compounds. These results are consistent with DOM in the form of microbial metabolites, and modified cell components (membrane lipids and proteins). These findings support previous geomicrobiological reports of chemolithoautotrophic microbial ecosystems functioning in isolation from photosynthetic primary production.",
keywords = "Aliphatics, Aromatics, Carboxyls, Dissolved organic matter, Fluorescence, Groundwater, Negative electrospray ion Fourier transform ion cyclotron resonance-mass spectrometry, Proteins, Solid state NMR, UV–vis spectrophotometry",
author = "Kieft, {Thomas L.} and Walters, {Clifford C.} and Higgins, {Meytal B.} and Mennito, {Anthony S.} and Clewett, {Catherine F.M.} and Verena Heuer and Pullin, {Michael J.} and Sarah Hendrickson and {van Heerden}, Esta and {Sherwood Lollar}, Barbara and Lau, {Maggie C.Y.} and Onstott, {Tullis C.}",
note = "Funding Information: This work was supported by funding from the National Science Foundation (NSF) to Tullis C. Onstott ( EAR-0948659 ) and to Thomas L. Kieft and Michael J. Pullin (EAR-0948335), from the National Geographic Society to Tullis C. Onstott (Grant no. 8990-11 ), from the Deep Carbon Observatory to Thomas L. Kieft, and from the National Aeronautics and Space Administration{\textquoteright}s Lewis and Clark Fund for Exploration and Field Research in Astrobiology to Sarah Hendrickson. The NMR work was partially supported by NSF grant 1428605 and by Sandia National Laboratories through the Basic Energy Science Program of the U.S. Department of Energy (DOE). Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the DOE, National Nuclear Security Administration under contract DE-AC04-94AL85000. We thank Gold Fields Ltd., Sibanye Gold Ltd., Harmony Gold Co. Mining Ltd., Petra Diamonds, AngloGold Ashanti Ltd., South Africa; the management and staff of Beatrix, Driefontein, Masimong, Kloof, Tau Tona, and Joel gold mines and Finsch, Star, and Koffiefontein diamond mines for providing access and assistance during sampling. We especially appreciate the efforts of S. Maphanga of Beatrix gold mine; H. van Niekerk of Driefontein gold mine; S. Sparks of Finsch diamond mine; O. Muthelo, L. Joubert, and J. Ackermann of Masimong gold mine; F. Vermeulen, M. Pienaar, and A. Munro of Tau Tona gold mine; K. Sibeko of Kloof gold mine; W. Nkaletshane of Joel gold mine; E. van der Westhuizen-Coetzer of Koffiefontein diamond mine; and B. Visser of Star Diamond mine. We thank B. Linage, O. Kuloyo, C. Magnabosco, B. Pfeiffer, C. Simon, M. Lindsay, L. Li, K. Wilkie, D. Simkus, L. Snyder, J.-G. Vermeulen, A.M. Meyer, M. Maleke, T. Tlalajoe, V. Mescheryakov, and G. Borgonie for their assistance in the collection, preservation, and field analyses of the fracture water samples. We thank Associate Editor Paul Greenwood and two anonymous reviewers for helpful comments. Publisher Copyright: {\textcopyright} 2018 Elsevier Ltd",
year = "2018",
month = apr,
doi = "10.1016/j.orggeochem.2018.02.003",
language = "English (US)",
volume = "118",
pages = "116--131",
journal = "Organic Geochemistry",
issn = "0146-6380",
publisher = "Elsevier Limited",
}