Forty-one interstitial water samples recovered from ODP Site 1202, Okinawa Trough, were analyzed for major constituents, B and δ 11B. The geochemical results show that major constituents and boron content varied largely in pore fluids and possibly were affected by sulfate reduction, recrystallization of biogenic carbonate or silica, ash alteration, and organic matter degradation. Mixing of fluids along high-porosity sandy layers or fracture zones also changes the pore water chemical compositions significantly. The down-core distribution of B an d δ 11B in the pore waters are sensitive tracers for assessing fluid migration and water/sediment interaction at various depths. Pore water B content at Site 1202 falls in a range between 0.25 and 1.16 mM compared to that of 0.42 mM in seawater. The δ 1B values, however, vary considerably from ∼32.7 to 50.9‰ relative to the seawater value of 39.5‰. The δ11B vs. 1/B plot indicates that sedimentary B released from clays is the most important source to pore waters, resulting in elevated B with low δ11B. Other processes including precipitation of calcium carbonate, fluid advection through high-porosity permeable sandy horizons, interaction with terrigenous sediments and/or ash alteration may also modify the B and δ 11B distributions.
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