Dissolved organic sulfur (DOS) and dissolved black carbon (DBC) are quantitatively important fractions of the global recalcitrant marine dissolved organic matter (DOM) pool. DOS is formed by marine microorganisms and abiotic sulfurization. DBC is mainly produced during incomplete combustion of biomass on land and marine asphalt seepage was identified to contribute to the oceanic DBC and DOS pools. However, the hydrothermal sources are still not well constrained. We hypothesize that DOS and DBC are mobilized from deep subsurface sediments via hydrothermal heating. The Guaymas Basin (GB) is ideal to study these processes since sill intrusions into the sediments result in thermal alteration of organic matter and thus pore water chemistry. We investigated pore water and sediments collected during IODP Expedition 385. DOM was characterized molecularly using ultrahigh-resolution mass spectrometry (FT-ICR-MS). DOS concentrations were quantified with elemental analysis and DBC as benzenepolycarboxylic acids. Our results revealed three reaction zones in the GB subsurface: the upper sediments were characterized by active microbial decomposition of DOM. In the deeper sediments, DOM accumulated, partly due to in situ formation of DOS and BC solubilization from sediments. At the sill contact zone, heat-induced molecular alterations reduced the DOM molecular diversity. We conclude that hydrothermal heating stimulates the release and formation of recalcitrant DOM in the GB sediments which can be released to the deep ocean during advective hydrothermal events.

Primary Presenter: Melina Knoke, University of Oldenburg (melina.knoke@uni-oldenburg.de)

Authors:

Melina Knoke, University of Oldenburg  (melina.knoke@uni-oldenburg.de)

Thorsten Dittmar, University of Oldenburg  (thorsten.dittmar@uni-oldenburg.de)

Jana Günther, University of Oldenburg  (jana.guenther@uni-oldenburg.de)

Philipp Böning, University of Oldenburg  (p.boening@uni-oldenburg.de)

Bert Engelen, University of Oldenburg  (bert.engelen@uni-oldenburg.de)

Jutta Niggemann, University of Oldenburg  (jutta.niggemann@uni-oldenburg.de)

Andreas Teske, University of North Carolina at Chapel Hill  (teske@email.unc.edu)

Michael Seidel, University of Oldenburg  (m.seidel@uni-oldenburg.de)