The low-productivity South Pacific Gyre (SPG) is Earth's largest oceanic province. Its sediment accumulates extraordinarily slowly (0.1-1 m per million years). This sediment contains a living community that is characterized by very low biomass and very low metabolic activity. At every depth in cored SPG sediment, mean cell abundances are 3 to 4 orders of magnitude lower than at the same depths in all previously explored subseafloor communities. The net rate of respiration by the subseafloor sedimentary community at each SPG site is 1 to 3 orders of magnitude lower than the rates at previously explored sites. Because of the low respiration rates and the thinness of the sediment, interstitial waters are oxic throughout the sediment column in most of this region. Consequently, the sedimentary community of the SPG is predominantly aerobic, unlike previously explored subseafloor communities. Generation of H 2 by radiolysis of water is a significant electron-donor source for this community. The per-cell respiration rates of this community are about 2 orders of magnitude higher (in oxidation/reduction equivalents) than in previously explored anaerobic subseafloor communities. Respiration rates and cell concentrations in subseafloor sediment throughout almost half of the world ocean may approach those in SPG sediment.aerobic ͉ biomass ͉ oxic ͉ radiolysis ͉ respiration

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This review describes recent results regarding voltammetric and amperometric determination of submicromolar concentrations of various environmentally important biologically active organic substances using nontraditional types of electrodes either in batch analysis or in flow liquid systems (especially HPLC or FIA with electrochemical detection). Attention is paid to solid amalgam electrodes (environmentally friendly alternatives to mercury electrodes), to carbon paste electrodes with easily renewable surface, to boron doped diamond film electrodes with very low noise and broad potential window, and to inexpensive solid composite electrodes with high signal-to-noise ratio, compatibility with organic solvents and easy mechanical or electrochemical pretreatment. The review concentrates on our own results in the context of the general development in the filed.

Abstract. 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 O 2 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 O 2 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. Because of the inert nature of the deeper sediment, oxygen that is not consumed within the top centimeters diffuses downward to much greater depth. In deeper zones, a small O 2 flux between 0.05 and 0.3 µmol m −2 d −1 was still present. This flux was nearly constant with depth, indicating extremely low O 2 consumption rates. Modeling of the oxygen profiles suggests that the sediment is probably oxygenated down to the basalt, suggesting an oxygen flux from the sediment into the basaltic basement.