Dissolved organic sulfur is known to be produced in areas with abundant sulfide and abundant organic matter, however less is known about its production in oligotrophic carbonate systems with relatively low organic matter content, as dominates the coastal tropics and subtropics.  Here, we explore a seagrass meadow in central Florida Bay. Using a combination of stable isotopes (C, S, O) and Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS), we reveal the connections between vegetation, sulfurization of carbonate-associated organic matter, and its release to the water column. We find that seagrass mediated oxygen pumping in the rhizosphere fuels sulfide oxidation, which determines the low net rates of sulfate reduction observed despite high gross rates. This sulfide oxidation in turn contributes to localized carbonate dissolution, while carbonate precipitation elsewhere leads to low net rates of precipitation. FT-ICR-MS analysis reveals intense sulfurization of carbonate-associated “dissolvable” organic matter likely through a combination of reactions with sulfide, polysulfides, and other sulfur intermediates, while the rapid cycling of carbonate dissolution and precipitation allows for the connectivity of this pool with the porewater and water column. Despite low net rates of sulfate reduction and carbonate dissolution, this system is a factory for the sulfurization of already highly photodegraded and likely recalcitrant, dissolved organic sulfur.

Primary Presenter: Mary Zeller, University of Bremen (maryazeller@gmail.com)

Authors:

Mary Zeller, MARUM-Center for Marine Environmental Science-University of Bremen  (mzeller@marum.de)

Bryce Van Dam, Helmholtz Zentrum Hereon  (bryce.dam@hereon.de)

Amy McKenna, National High Magnetic Field Laboratory  (mckenna@magnet.fsu.edu)

Christian Lopes, Florida International University  (diverchris23@gmail.com)

Christopher Osburn, North Carolina State University  (closburn@ncsu.edu)

James Fourqurean, Florida International University  (fourqure@fiu.edu)

John Kominoski, Florida International University  (jkominos@fiu.edu)

Michael Böttcher, Leibniz Institute for Baltic Sea Research (IOW)  (michael.boettcher@io-warnemuende.de)