Grant from the Danish Council for Independent Research (DFF) awarded to Bo Barker Jørgensen

Project: "The cryptic sulfur cycle of marine sediments".

2017.05.15 | Maj Thimm Carlsen

The seabed is Earth’s greatest anaerobic bioreactor where organic material produced in the ocean is mineralized to CO2 and inorganic nutrients that subsequently return to the element cycles of the ocean. Microbial respiration with sulfate to produce sulfide is quantitatively the most important process of anaerobic degradation of organic matter, but the net consumption of sulfate and the rate of sulfate respiration do not seem to match. It is the hypothesis of the project that a cryptic sulfur cycle may explain the discrepancy whereby a part of the produced sulfide is oxidized back to sulfate by reaction with iron minerals in the seabed. This hypothesis will be tested through a novel design of experiments where radioactive (35S) and stable (33S, 34S, 18O) isotopes are used to track and measure concurrent processes of sulfate reduction and sulfide oxidation. By retarding the turnover at individual steps in the sulfide oxidation pathway, the added tracer will accumulate in these sulfur pools whereby their importance as intermediates by the sulfide oxidation can be calculated. The complex competition between sulfate respiration, iron respiration and sulfide oxidation with iron is also differentiated through these experiments. The project thereby aims to reveal the complexity of processes behind well-established net reactions in iron and sulfur geochemistry.

Center for Geomicrobiology, Awards