Volume 15, issue 16 | Copyright
Biogeosciences, 15, 5093-5111, 2018
https://doi.org/10.5194/bg-15-5093-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Aug 2018

Research article | 27 Aug 2018

Modulation of the vertical particle transfer efficiency in the oxygen minimum zone off Peru

Marine Bretagnon1,2, Aurélien Paulmier1, Véronique Garçon1, Boris Dewitte1,3,4,5, Séréna Illig1,6, Nathalie Leblond7, Laurent Coppola7, Fernando Campos8,9,10, Federico Velazco11, Christos Panagiotopoulos12, Andreas Oschlies13, J. Martin Hernandez-Ayon14, Helmut Maske15, Oscar Vergara1, Ivonne Montes9, Philippe Martinez16, Edgardo Carrasco11, Jacques Grelet17, Olivier Desprez-De-Gesincourt18, Christophe Maes1,19, and Lionel Scouarnec18 Marine Bretagnon et al.
  • 1Laboratorie d'Etude en Géophysique et Océanographie Spatiales (UPS/CNRS/IRD/CNES), Toulouse, France
  • 2ACRI, Sophia Antipolis, France
  • 3Centro de Estudios Avanzado en Zonas Áridas (CEAZA), Coquimbo, Chile
  • 4Departamento de Biología, Facultad de Ciencias del Mar, Universidad Católica del Norte, Coquimbo, Chile
  • 5Millennium Nucleus for Ecology and Sustainable Management of Oceanic Islands (ESMOI), Coquimbo, Chile
  • 6Department of Oceanography, MARE Institute, LMI ICEMASA, University of Cape Town, Cape Town, Rondebosch, South Africa
  • 7Sorbonne Université, CNRS, Laboratoire d'Océanographie de Villefanche, LOV, Villefranche-sur-Mer, France
  • 8UNAC, Lima, Peru
  • 9IGP, Lima, Peru
  • 10CICESE, Ensenada, Mexico
  • 11IMARPE, Callao, Peru
  • 12Aix-Marseille Université, Université de Toulon, CNRS, IRD, Mediterranean Institute of Oceanography (MIO), UM 110, Marseille, France
  • 13GEOMAR/SFB754, Kiel, Germany
  • 14UABC, Ensenada, Mexico
  • 15CICESE, Ensenada, Mexico
  • 16EPOC, Bordeaux, France
  • 17US IMAGO/IRD, Brest, France
  • 18INSU/CNRS, DT, Brest, France
  • 19LOPS, Brest, France

Abstract. The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth's system. The OM produced through photosynthesis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive eastern boundary upwelling systems (EBUSs) associated with oxygen minimum zones (OMZs) would be expected to foster OM preservation due to low O2 conditions. But their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru. Data provided high-temporal-resolution O2 series characterising two seasonal steady states at the upper trap: suboxic ([O2] < 25µmolkg−1) and hypoxic–oxic (15 < [O2] < 160µmolkg−1) in austral summer and winter–spring, respectively. The OMZ vertical transfer efficiency of particulate organic carbon (POC) between traps (Teff) can be classified into three main ranges (high, intermediate, low). These different Teff ranges suggest that both predominant preservation (high Teff > 50%) and remineralisation (intermediate Teff 20 < 50% or low Teff < 6%) configurations can occur. An efficient OMZ vertical transfer (Teff > 50%) has been reported in summer and winter associated with extreme limitation in O2 concentrations or OM quantity for OM degradation. However, higher levels of O2 or OM, or less refractory OM, at the oxycline, even in a co-limitation context, can decrease the OMZ transfer efficiency to below 50%. This is especially true in summer during intraseasonal wind-driven oxygenation events. In late winter and early spring, high oxygenation conditions together with high fluxes of sinking particles trigger a shutdown of the OMZ transfer (Teff < 6%). Transfer efficiency of chemical elements composing the majority of the flux (nitrogen, phosphorus, silica, calcium carbonate) follows the same trend as for carbon, with the lowest transfer level being in late winter and early spring. Regarding particulate isotopes, vertical transfer of δ15N suggests a complex pattern of 15N impoverishment or enrichment according to Teff modulation. This sensitivity of OM to O2 fluctuations and particle concentration calls for further investigation into OM and O2-driven remineralisation processes. This should include consideration of the intermittent behaviour of OMZ towards OM demonstrated in past studies and climate projections.

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