METHODS

Pore waters were squeezed from whole-round sediment intervals, acidified with HNO3, and sealed in plastic tubes according to standard procedures aboard the JOIDES Resolution. The samples were shipped to James Cook University (JCU). After cutting each tube, precisely 1.00 mL of solution was removed with a pipette, placed into a plastic vial, and mixed with 8.90 mL of deionized water and 0.10 mL of 1% HNO3 spiked with 10 ppm rhodium for use as an internal standard. All samples were then analyzed for Mn concentrations by inductively coupled plasma-mass spectrometry (ICP-MS) at the JCU Advanced Analytical Centre (AAC). Prepared solutions were injected into a Varian Ultramass ICP-MS with a quadrupole mass analyzer. Manganese concentrations in solution were obtained through standard comparisons to a concentration curve. The curve was constructed by spiking the certified CASS-2 seawater standard with known concentrations of Mn and Ba. Four pore water samples from Leg 181 were prepared and analyzed a second time to assess precision. Repeated analyses of these true replicates are within 6% (Table T1).

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