Ocean deoxygenation effects on dissolved organic matter sequestration in a changing ocean

• Applicant: Gonzalo V. Gomez-Saez, Ph.D.
• Subject Area: Oceanography
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491444019

Seawater stores as much carbon in the form of dissolved organic matter (DOM) as there is CO2 in the atmosphere. Over a period of just 50 years (from 1960 to 2010) global oceanic oxygen reserves have been reduced by 2% and the anoxic waters have quadrupled, mainly due to anthropogenic global warming and eutrophication. Ocean deoxygenation leads to an expansion of oxygen minimum zones (OMZs), which contain higher concentrations of DOM (carbon and sulfur) than the oxygenated ocean. While there is no consensus about the reasons behind DOM sequestration in OMZs, it is well established that microbes are directly responsible for the production, degradation and recycling of marine DOM. Recent advances in analytical chemistry characterize the DOM at the molecular level in unprecedented detail, revealing new insights into its source and history by Fourier transform ion-cyclotron resonance mass spectrometry (FT-ICR-MS). Current progress in sequencing technology can predict specific functions contributing to the molecular activity of microbial communities in environmental samples by metatranscriptomics. The synergistic coupling of FT-ICR-MS and metatranscriptomics is therefore of great importance to connect DOM cycling with microbial activities in OMZs, in order to measure the response of this major carbon reservoir to ocean deoxygenation and climate change. This Emmy Noether project aims to identify the effects of ocean deoxygenation on DOM sequestration due to interactions with microbial communities and the marine carbon and sulfur cycles. Synergistic chemical and microbiological datasets and experiments will be used to test (1) if indigenous DOM accumulates in OMZs because the anoxic conditions decrease the metabolic activity of microbes; (2) if the concentration of sulfur-containing substrates is a major control on the heterotrophic activity of specific groups of microbes degrading dissolved organic sulfur (DOS) from OMZs; (3) if highly active microbes from different biomes can degrade presumably recalcitrant DOM from OMZs; and (4) if sulfurized DOM from OMZs is chemically so stable that it cannot be microbially degraded and accumulates over long timescales. This project builds on my previous research and includes novel implementation of state-of-art methods to elucidate new links between the microbial biosphere with the chemical diversity of DOM in the context of a changing, deoxygenated ocean.

• DFG Programme: Independent Junior Research Groups