Coupling of sulfur, nitrogen and carbon biogeochemistry in oxygen minimum zone sediments covered by giant sulfur bacteria mats (Santa Barbara Basin, California)

Tina Treude1, David W Valentine Jr2, Kelsey Gosselin3, Felix Janssen4, Frank Kinnaman5, Sebastian Krause6, Na Liu7, Xuefeng Peng8, Qianhui Qin9, De'Marcus Robinson10, Jonathan Tarn11, Frank Wenzhofer4 and David John Yousavich12, (1)University of California Los Angeles, Department of Earth, Planetary and Space Sciences, Los Angeles, United States, (2)University of California Santa Barbara, Santa Barbara, United States, (3)University of California Santa Barbara, Interdepartmental Graduate Program in Marine Science, Santa Barbara, United States, (4)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, HGF-MPG Joint Research Group for Deep-Sea Ecology and Technology, Bremerhaven, Germany, (5)University of California Santa Barbara, Earth Science, Santa Barbara, CA, United States, (6)University of California Los Angeles, Los Angeles, United States, (7)University of California Santa Barbara, Inderdepartmental Graduate Program in Marine Science, Santa Barbara, United States, (8)University of South Carolina, School of Earth, Ocean and Environment, Columbia, United States, (9)University of California Los Angeles, United States, (10)University of California Los Angeles, Atmospheric and Oceanic Science Department, Los Angeles, United States, (11)University of California Santa Barbara, Santa Barbara, CA, United States, (12)University of California Los Angeles, Earth, Planetary, and Space Science, Los Angeles, United States
Abstract:
The dynamics of oxygen minimum zones along continental margins, and their potential for future expansion, are important because of their intersection with global biogeochemical cycles and because of their far-reaching impacts on ocean ecosystems. However, the impacts of transient deoxygenation on sediment biogeochemical cycles of carbon, nitrogen and sulfur are not well established and are the focus of this study.

Specifically, our study will test the overarching hypothesis that deoxygenation triggers a positive feedback loop between sulfide-consuming bacterial mats and underlying communities of anaerobic, sulfide-producing bacteria. By this hypothesis, the establishment of benthic mats following deoxygenation focuses and accelerates nitrogen cycling in the uppermost sediment horizon and allows for upward expansion of bacterial sulfate reduction, which in-turn provides a shallow source of sulfide as substrate to further support nitrogen cycling in the benthic mats.

To investigate the relationship between oxygen dynamics and sediment biogeochemical processes involving carbon, sulfur and nitrogen, our study tests specific hypotheses to assess the extent to which benthic mats remove nitrate from seawater, the extent to which shallow sulfide production and nitrogen cycling is stimulated by the development of benthic mats, and the extent to which benthic mats occur regionally and are scalable.

This poster will present preliminary results from the R/V Atlantis expedition AT42-19 to the Santa Barbara Basin (Fall 2019). The seasonally hypoxic/anoxic basin is home to the so far largest recorded sulfur bacterial mat spanning over 1.6 km between 487 and 523 m water depth in a zone where oxygen is deficient and nitrate is present. Data collected include a combination of in-situ measurements made at the sea floor (benthic chamber, microsensor profiler, photomosaic mapping), shipboard experiments (radiotracer incubations, 15N-labelling, porewater geochemistry), and shore-based measurements (microbial diversity analyses and microscopic identifications).

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