Publication Date:
2022-10-26
Description:
© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Elling, F. J., Hemingway, J. D., Kharbush, J. J., Becker, K. W., Polik, C. A., & Pearson, A. Linking diatom-diazotroph symbioses to nitrogen cycle perturbations and deep-water anoxia: insights from Mediterranean sapropel events. Earth and Planetary Science Letters, 571, (2021): 117110, https://doi.org/10.1016/j.epsl.2021.117110.
Description:
Elevated organic matter (OM) export flux promotes marine anoxia, thus increasing carbon sequestration efficiency and decreasing atmospheric carbon dioxide levels. However, the mechanisms that trigger and sustain anoxic events—particularly those associated with nutrient-poor, oligotrophic surface waters—remain poorly constrained. Mediterranean Sea sapropels are well-preserved sediments deposited during episodic anoxic events throughout the Plio-Pleistocene; as such, they may provide unique insight into the biogeochemical and ecological drivers of—and responses to—marine anoxia. Using biomarker distributions, we demonstrate that anaerobic ammonium oxidizing (anammox) bacteria and diazotrophic endosymbionts of mat- and/or raft-forming diatoms were both abundant during sapropel events, particularly in the Ionian and Libyan seas. In these sapropels, the carbon isotope compositions of anammox biomarkers directly capture progressive 13C-depletion in deep-water dissolved inorganic carbon, indicating sustained carbon sequestration. To explain these observations, we propose a reinforcing feedback whereby initial nutrient and/or circulation perturbations promote fixed nitrogen loss via intensified anammox and heterotrophic denitrification, which in turn favors proliferation of rapidly sinking diatom-diazotroph symbiotic consortia, increases OM burial flux, and sustains anoxia. This mechanism resolves the long-standing conundrum that small and buoyant diazotrophs are apparently associated with high OM export during periods of marine anoxia and oligotrophy.
Description:
This work was funded through the Gordon and Betty Moore Foundation and US National Science Foundation grants 1843285, 1702262 and 1349126 (to A.P.). Additional financial support was provided by the Postdoctoral Program at the Woods Hole Oceanographic Institution and U.S. Geological Survey (K.W.B.).
Keywords:
Nammox
;
Anoxia
;
Compound-specific, δ13, C
;
Diatom-diazotroph symbioses
;
N2-fixation
;
Mediterranean sapropels
Repository Name:
Woods Hole Open Access Server
Type:
Article
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