Sedimentary interstitial water samples for nitrate analyses were obtained by standard Rhizon soil moisture samplers (55) (Rhizosphere Research Products, Wageningen, The Netherlands). Rhizon sampling extracted pore water from the sediment core by suction filtering through thin tubes of hydrophilic porous polymer with a mean pore diameter of 0.1 μm. Rhizons (5-cm filter in length) were inserted into one end of a whole round core section, and a total volume of up to 10 ml of interstitial water was extracted. Before deployment, Rhizon samplers were soaked in 18 megohms of deionized water for several hours, followed by rinsing with 30 ml of deionized water that was suction-filtered through each Rhizon. After washing, Rhizons were left to dry on filter paper. Nitrate concentrations were measured shipboard using a Metrohm 844 UV/VIS Compact IC with a 150 mm by 4.0 mm Metrosep A Supp 8 150 column. Approximately 0.8 ml of interstitial water was injected manually into a 250-μl sample loop; the sample was then eluted from the column with a 10% NaCl solution. Absorbance at 215 nm was used for quantification. A 50 μM sodium nitrate standard was run after every fifth or sixth sample to correct for instrument drift. Dissolved oxygen concentrations in the equilibrated core sections were measured with needle-shaped optical O2 sensors (optodes) (PreSens, Regensburg, Germany) as described previously (56). The dissolved O2 data from Expedition KN223 were first reported by D’Hondt et al. (4). They are archived and available online in the Integrated Earth Data Applications (IEDA) database (http://get.iedadata.org/doi/100519).

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