Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 8 2009 10.5194/bg-6-1467-2009 http://www.biogeosciences.net/6/1467/2009/ http://www.biogeosciences.net/6/1467/2009/bg-6-1467-2009.html http://www.biogeosciences.net/6/1467/2009/bg-6-1467-2009.pdf 1467 1478 2009-08-07 Oxygen penetration deep into the sediment of the South Pacific gyre J. P. Fischer jfischer@mpi-bremen.de T. G. Ferdelman S. D'Hondt H. Røy F. Wenzhöfer Max Planck Institute for Marine Microbiology, Bremen, Germany Graduate School of Oceanography, University of Rhode Island, USA Center for Geomicrobiology, University of Aarhus, Denmark Sediment oxygen concentration profiles and benthic microbial oxygen consumption rates were investigated during an IODP site survey in the South Pacific Gyre. Primary production, particle fluxes and sedimentation rates are extremely low in this ultra-oligotrophic oceanic region. We derived O₂ consumption rates from vertical oxygen profiles in sediments obtained on different spatial scales ex situ (in piston cores and multi cores), and in situ (using a benthic lander equipped with a microelectrode profiler). Along a transect in the area 24 to 46° S and 165 to 117° W, cores from 10 out of 11 sites were oxygenated over their entire length (as much as 8 m below seafloor), with deep O₂ concentrations >150 μmol L^−1. This represents the deepest oxygen penetration ever measured in marine sediments. High-resolution microprofiles from the surface sediment layer revealed a diffusive oxygen uptake between 0.1 and 1.3 mmol m^−2 d^−1, equal to a carbon mineralization rate of ~0.4–4.5 gC m^−2 yr^−1. This is in the lower range of previously reported fluxes for oligotrophic sediments but corresponds well to the low surface water primary production. Half of the pool of reactive organic matter was consumed in the top 1.5–6 mm of the sediment. 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