Exploring the impact of temperature on dissolved organic matter and life in the deep biosphere off Muroto, Nankai Trough (IODP Expedition 370)
Mineralogy, Petrology and Geochemistry
Final Report Abstract
IODP Expedition 370 “Temperature Limit of the Deep Biosphere off Muroto (T-Limit)” (September 10 – November 23, 2016) was designed to fill our vast gaps of knowledge about the response of microbial life to the increase of temperature with depth. Using DV Chikyu, the expedition established Site C0023 at the deformation front of the Nankai Trough subduction zone off Cape Muroto, Japan. Due to high heat flow in this region, in situ temperatures of up to 120°C were reached at the 1180 m deep bottom of the borehole. This post-cruise study aimed to elucidate the impact of temperature on dissolved organic matter (DOM) and microbial life. To this end, 112 interstitial water samples were analyzed with respect to the concentration and stable carbon isotopic composition of acetate and other water-soluble organic metabolites using isotope-ratio-monitoring liquid chromatography/mass spectrometry (irm-LC/MS), and with respect to DOM composition using three-dimensional fluorescence spectroscopy excitationemission matrices (3D-EEMs) coupled with parallel factor analysis (PARAFAC). For 13 selected samples, the elemental composition and molecular size of individual DOM forming molecules was analyzed using ultrahigh resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). Our high-resolution depth profiles for the concentration and carbon isotopic composition of acetate contributed to a reliable detection of microbial activity in >100°C hot sediments, and thus to the conclusion that subseafloor life is not limited by an upper temperature limit below 120°C. Together, the concentration and carbon isotopic composition of acetate, propionate and butyrate and the composition of fluorescent DOM reveal distinct changes in DOM quality with depth, that point to changes and in the availability und turnover of microbial substrates during sediment burial and heating. Our study suggests that tectonically driven inflow of hot fluids into sediments below the décollement goes along with distinct changes in DOM quality, which might result from both thermal alteration of sedimentary organic matter and changes in microbial activity.
Publications
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Temperature limits to deep subseafloor life in the Nankai Trough subduction zone. Science, 370, 1230-1234
V.B. Heuer, F. Inagaki, Y. Morono, Y. Kubo, A.J. Spivack, B. Viehweger, T. Treude, F. Beulig, F. Schubotz, S. Tonai, S. Bowden, M. Cramm, S. Henkel, T. Hirose, K. Homola, T. Hoshino, A. Ijiri, H. Imachi, N. Kamiya, M. Kaneko, L. Lagostina, H. Manners, H.-L. McClelland, K. Metcalfe, N. Okutsu, D. Pan, M. J. Raudsepp, J. Sauvage, M.-Y. Tsang, D.T. Wang, E. Whitaker, Y. Yamamoto, K. Yang, L. Maeda, R.R. Adhikari, C. Glombitza, Y. Hamada, J. Kallmeyer, J. Wendt, L. Wörmer, Y. Yamada, M. Kinoshita, K.-U. Hinrichs
