The primary research goal of the project is to understand the biotic and abiotic processes that govern the molecular composition of dissolved organic matter (DOM) in hydrothermally influenced deep subseafloor sediments. To reach this goal, we have received a comprehensive set of porewater and sediment samples from the Guaymas Basin, recovered in the frame of IODP Expedition 385 (Sep. – Nov. 2019). The samples were obtained from up to 500-meter-long cores from eight drill sites, exhibiting different hydrothermal gradients. By determining the molecular composition of porewater DOM and water-extractable organic matter from the sediment, we will assess their hydrothermal and microbial alteration. Using ultrahigh-resolution mass spectrometry (FT-ICR-MS), modern molecular biological methods and sophisticated carbon-isotope analysis, we aim to fill the current knowledge gaps around the molecular properties of deep subsurface DOM. We will 1) characterize the molecular composition of DOM in the high heat-flow and organic-rich sediments versus the off-axis sediments, and 2) decipher the connection of the molecular DOM composition with deep biosphere-related microbial metabolism along temperature and redox gradients. The results will also be compared with samples from the water column obtained during an RV Atlantis cruise to the Guaymas Basin in 2018 to investigate the transport of hydrothermal DOM into the deep ocean. The following hypotheses will be tested in the frame of the project: I) Hydrothermal heating of deep subsurface sediments produces and releases large amounts of reactive and refractory DOM, II) Hydrothermal dissolved black carbon (DBC) contributes to the marine stable carbon isotopic signature and the radiocarbon age of the refractory oceanic DBC, III) The subsurface microbial community structure is influenced by geochemical and thermal gradients and is related to specific reactive, hydrothermally produced DOM compounds. Overall, the project offers the unique opportunity to study the biogeochemistry of DOM across hydrothermal gradients in the deep subsurface and across the lithosphere-hydrosphere interface.

Funding

DFG Infrastructure Priority Programs (SPP IODP)

International Ocean Discovery Program
 

List of people involved:

Michael Seidel

Melina Knoke

Bert Engelen

Thorsten Dittmar
 

External Collaborators:

Andreas Teske

Alysha Inez Coppola

Florence Schubotz

Jonas Brünjes