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Benthic iron and phosphorus fluxes across the Peruvian oxygen minimum zone
Author(s) -
Noffke A.,
Hensen C.,
Sommer S.,
Scholz F.,
Bohlen L.,
Mosch T.,
Graco M.,
Wallmann K.
Publication year - 2012
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2012.57.3.0851
Subject(s) - benthic zone , oxygen minimum zone , anoxic waters , total organic carbon , oceanography , bottom water , organic matter , environmental chemistry , redfield ratio , flux (metallurgy) , ferrous , phosphorus , water column , biogeochemical cycle , eutrophication , chemistry , environmental science , nutrient , geology , phytoplankton , upwelling , organic chemistry
Benthic fluxes of dissolved ferrous iron (Fe 2+ ) and phosphate (TPO 4 ) were quantified by in situ benthic chamber incubations and pore‐water profiles along a depth transect (11°S, 80‐1000 m) across the Peruvian oxygen minimum zone (OMZ). Bottom‐water O 2 levels were < 2 µmol L −1 down to 500‐m water depth, and increased to ∼ 40 µmol L −1 at 1000 m. Fe 2+ fluxes were highest on the shallow shelf (maximum 316 mmol m −2 yr −1 ), moderate (15.4 mmol m −2 yr −1 ) between 250 m and 600 m, and negligible at deeper stations. In the persistent OMZ core, continuous reduction of Fe oxyhydroxides results in depletion of sedimentary Fe : Al ratios. TPO 4 fluxes were high (maximum 292 mmol m −2 yr −1 ) throughout the shelf and the OMZ core in association with high organic carbon degradation rates. Ratios between organic carbon degradation and TPO 4 flux indicate excess release of P over C when compared to Redfield stoichiometry. Most likely, this is caused by preferential P release from organic matter, dissolution of fish debris, and/or P release from microbial mat communities, while Fe oxyhydroxides can only be inferred as a major P source on the shallow shelf. The benthic fluxes presented here are among the highest reported from similar, oxygen‐depleted environments and highlight the importance of sediments underlying anoxic water bodies as nutrient sources to the ocean. The shelf is particularly important as the periodic passage of coastal trapped waves and associated bottom‐water oxygenation events can be expected to induce a transient biogeochemical environment with highly variable release of Fe 2+ and TPO 4 .