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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-489
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-489
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Jan 2020

Submitted as: research article | 28 Jan 2020

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This preprint is currently under review for the journal BG.

Sediment release of dissolved organic matter to the oxygen minimum zone off Peru

Alexandra N. Loginova1, Andrew W. Dale1, Frédéric A. C. LeMoigne1,2, Sören Thomsen1,3, Stefan Sommer1, Klaus Wallmann1, and Anja Engel1 Alexandra N. Loginova et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
  • 2Mediterranean Institute of Oceanography, UM110, Aix Marselle Université, CNRS, IRD, 13288, Marselle, France
  • 3LOCEAN-IPSL, IRD/CNRS/Sorbonnes Universites (UPMC)/MNHN, Paris, France

Abstract. The eastern tropical South Pacific (ETSP) represents one of the most productive areas in the ocean that is characterized by a pronounced oxygen minimum zone (OMZ). Particulate organic matter (POM) that sinks out of the euphotic zone is supplied to the anoxic sediments and utilized by microbial communities. The degradation of POM is associated with dissolved organic matter (DOM) production and reworking. The release of recalcitrant DOM to the overlying waters may represent an important organic matter escape mechanism from remineralization within sediments but received little attention in OMZ regions so far. Here, we combine measurements of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) with DOM optical properties in the form of chromophoric (CDOM) and fluorescent (FDOM) DOM from pore waters and near-bottom waters of the ETSP off Peru. We evaluate diffusion–driven fluxes and net in situ fluxes of DOC and DON in order to investigate processes affecting DOM cycling at the sediment–water interface along a transect 12° S. To our knowledge, these are the first data for sediment release of DON and pore water CDOM and FDOM for the ETSP off Peru. Pore-water DOC and DON accumulated with increasing sediment depth, suggesting an imbalance between DOM production and remineralization within sediments. High DON accumulation resulted in very low pore water DOC / DON ratios (> 1) which could be caused by either an imbalance in DOC and DON remineralization, or to the presence of an additional nitrogen source. Diffusion driven fluxes of DOC and DON exhibited high spatial variability. They varied from 0.2–0.1 mmol m−2 d−1 to 2.52–1.3 mmol m−2 d−1 and from −0.042–0.02 mmol m−2 d−1 to 3.32–1.7 mmol m−2 d−1, respectively. Generally low net in situ DOC and DON fluxes as well as steepening of spectral slope (S) of CDOM and accumulation of humic-like FDOM at the near-bottom waters over time indicated active microbial DOM utilization at the sediment–water interface, potentially stimulated by nitrate (NO3) and nitrite (NO2). The microbial DOC utilization rates, estimated in our study, may be sufficient to support denitrification rates of 0.2–1.4 mmol m−2 d−1, suggesting that sediment release of DOM contributes substantially to nitrogen loss processes in the ETSP off Peru.

Alexandra N. Loginova et al.

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Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Alexandra N. Loginova et al.

Alexandra N. Loginova et al.

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Latest update: 07 Jul 2020
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Short summary
The eastern tropical South Pacific is highly productive. Particles that sink out of the surface ocean reach anoxic sediments and are utilized by microbes. Thereby a fraction of organic matter is released in dissolved form (DOM). Here, we quantify DOM release from pore waters and near-bottom waters, and examine DOM cycling at the sediment-water interface. Our results suggest that sediment release of DOM contributes substantially to nitrogen loss processes in the ETSP off Peru.
The eastern tropical South Pacific is highly productive. Particles that sink out of the surface...
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