Biotic and Abiotic Controls on Dissolved Organic Matter in Hydrothermal Sediments: Transformations, Mobilization, and Discharge to the Deep Ocean

It is poorly understood how thermogenic transformations and advective transport shape dissolved organic matter (DOM) in deep, organic-rich hydrothermal sediments. These processes may have far-field effects on DOM biogeochemistry in the deep ocean. Here we hypothesize that in organic-rich hydrothermal systems, the DOM composition is shaped by depth- and temperature dependent processes, including microbial transformations in shallow sediments and hydrothermal alterations at deeper, high-temperature zones. Additionally, both recalcitrant and bioavailable DOM may be released into the ocean via hydrothermal fluid flow. To test this, we analyzed solid-phase extracted (SPE) DOM from porewater and sediment samples from IODP Expedition 385 from down to ~330 meters below seafloor in the Guaymas Basin (Gulf of California) and simulated DOM mobilization using hot-water Soxhlet extractions of sediments. Ultrahigh-resolution mass spectrometry (FT-ICR-MS) revealed that microbial processes enhance DOM oxygenation in shallow sediments, while sulfurization and hydrothermal alteration modify DOM in deeper layers. Our findings suggest that hydrothermal discharge introduces both labile and recalcitrant DOM into the deep ocean, influencing carbon cycling on a global scale.

Presentation Preference: Oral

Primary Presenter: Michael Seidel, University of Oldenburg (m.seidel@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 Guenther, University of Oldenburg  (jana.guenther@uni-oldenburg.de)

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

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

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