B077-0004
Sulfur-Oxidizing Microbial Mats Affect Sulfur and Nitrogen Cycling in the Santa Barbara Basin

Monday, 14 December 2020
Poster
David John Yousavich, University of California Los Angeles, Earth, Planetary, and Space Science, Los Angeles, CA, United States, De'Marcus Robinson, University of California Los Angeles, Los Angeles, United States, Sebastian Krause, University of California Los Angeles, Los Angeles, CA, United States, Jonathan Tarn, University of California Santa Barbara, Santa Barbara, CA, United States, Na Liu, University of California Santa Barbara, Inderdepartmental Graduate Program in Marine Science, Santa Barbara, CA, United States, Frank Wenzhofer, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, HGF-MPG Group for Deep Sea Ecology and Technology, Bremerhaven, Germany, Felix Janssen, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany, David L Valentine, University of California Santa Barbara, Marine Science Institute, Santa Barbara, CA, United States and Tina Treude, University of California Los Angeles, Department of Earth, Planetary and Space Sciences, Los Angeles, United States
Abstract:
Sulfate reduction, a crucial metabolic pathway in the remineralization of organic matter in marine sediments, produces hydrogen sulfide that can be subsequently utilized by chemoautotrophic organisms. In November 2019, during the AT42-19 expedition aboard the RV Atlantis, equipped with ROV Jason and AUV Sentry, sediment samples were collected at several stations along a bimodal depth transect traversing the Santa Barbara Basin to examine sulfur and nitrogen cycling in microbial mats. This basin experiences temporary oxygen depletion with a water column that becomes transiently anoxic and nitrate-depleted from approximately October to January. During these months, large benthic microbial mats of sulfur-oxidizing bacteria have been observed at the bottom of the basin but their metabolism has, so far, not been assessed. In order to elucidate the metabolic mechanisms of the mats in the Santa Barbara Basin, the consumption and production of sulfur and nitrogen species in the sediment porewater was examined. Sediment push cores were taken at various depths to study depth profiles of sulfate reduction rates (SRR) as well as porewater sulfur and nitrogen species (SO42-, sulfide, NO3-, NO2-, NH4+). SRR were highest at the depocenter in the deepest part of the basin (approx. 574 m depth), where mats were most abundant, with depth-integrated rates of more than 5 mmol SO42- m-2 d-1. SRR were an order of magnitude lower at shallower stations with higher bottom water oxygen concentrations, signs of bioturbation, and without mats. Additionally, ammonium concentrations were an order of magnitude higher at the sediment/water interface where mats were present versus stations without mats. At stations with mats, sulfide concentrations in the upper 2-3 cm were near-zero, despite higher SRR and ammonium accumulation than stations without mats. Our results suggest microbial mats of sulfur-oxidizing bacteria in the Santa Barbara Basin are consuming nitrate from the water column and sulfide produced by sulfate reducers, possibly through the process of dissimilatory nitrate reduction to ammonium coupled to sulfide oxidation.
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