Preprints
https://doi.org/10.5194/egusphere-2022-1437
https://doi.org/10.5194/egusphere-2022-1437
 
19 Dec 2022
19 Dec 2022
Status: this preprint is open for discussion.

All about Nitrite: Exploring Nitrite Sources and Sinks in the Eastern Tropical North Pacific Oxygen Minimum Zone

John C. Tracey1,2, Andrew R. Babbin3, Elizabeth Wallace1, Xin Sun1,4, Katherine L. DuRussel1,5, Claudia Frey1,6, Donald E. Martocello III3, Tyler Tamasi3, Sergey Oleynik1, and Bess B. Ward1 John C. Tracey et al.
  • 1Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ, USA 08544
  • 2Department of Biology and Paleo Environment, Lamont Doherty Earth Observatory, Columbia University, Palisades, NY, USA 10964
  • 3Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA 02138
  • 4Department of Global Ecology, Carnegie Institution for Science, Stanford, CA, USA 94305
  • 5Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL, USA 60208
  • 6Department of Environmental Sciences, University of Basel, Bernoullistrasse 30, 4056 Basel, Switzerland

Abstract. Oxygen minimum zones (OMZs), due to their large volumes of perennially deoxygenated waters, are critical regions for understanding how the interplay between anaerobic and aerobic nitrogen (N) cycling microbial pathways affects the marine N budget. Here we present a suite of measurements of the most significant OMZ N cycling rates, which all involve nitrite (NO2) as a product, reactant, or intermediate, in the Eastern Tropical North Pacific (ETNP) OMZ. These measurements and comparisons to data from previously published OMZ cruises present additional evidence that NO3 reduction is the predominant OMZ N flux, followed by NO2 oxidation back to NO3. The combined rates of both of these N recycling processes were observed to be much greater (up to nearly 200x) than the combined rates of the N loss processes of anammox and denitrification, especially in waters near the anoxic / oxic interface. We also show that NO2 oxidation can occur in functionally anoxic incubations, measurements that further strengthen the case for truly anaerobic NO2 oxidation. We also evaluate the possibility that NO2 dismutation provides the oxidative power for anaerobic NO2 oxidation. Although almost all treatments returned little evidence for dismutation (as based on product inhibition, substrate stimulation, and stoichiometric hypotheses), results from one treatment under conditions closest to in situ NO2 values may support the occurrence of NO2 dismutation. The partitioning of N loss between anammox and denitrification differed widely from stoichiometric predictions of at most 29 % anammox; in fact, N loss rates at many depths consisted entirely of anammox. Through investigating the magnitudes of NO3 reduction and NO2 oxidation, testing for anaerobic NO2 oxidation, examining the possibility of NO2 dismutation, and further documenting the balance of N loss processes, these new data shed light on many open questions in OMZ N cycling research.

John C. Tracey et al.

Status: open (until 13 Feb 2023)

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John C. Tracey et al.

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Short summary
Nitrogen (N) is essential for life. Thus, its availability plays a key role in determining marine productivity. Using incubations of seawater spiked with a rare form of N measurable on a mass spectrometer, we quantified microbial pathways that determine marine N availability. The results highlight the central role of nitrite in the N cycle, provide new data towards understanding how much N is available for marine productivity, and answer several open questions in marine N biogeochemistry.