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doi:10.2204/iodp.proc.336.205.2015

Results

Solid-phase P at North Pond is mainly present in mineral phases. The most abundant geochemical forms of sedimentary P are (1) P adsorbed onto iron oxyhydroxides and (2) P present in authigenic/biogenic apatite and P bound to calcium carbonate (Figs. F2, F3; Tables T1, T2, T3). Organic P is also present in small amounts throughout the sediment core, even at deep sections of the sedimentary column (Figs. F2, F3; Tables T1, T2, T3). These results suggest that P bioavailability to the deep biosphere is highly impeded since mineral forms are considered to be less labile for microorganisms. However, buried organic P could constitute a bioavailable P source to the deep biosphere. Alternatively, it is possible that deep subseafloor microorganisms have mechanisms to utilize mineral P.

Total solid-phase P concentrations measured fall within the ranges of concentrations measured for other open-ocean regions (Filippelli, 1997). Total sedimentary P content varies little throughout the sediment column, with the exception of sediment layers near the sediment/basement interface. Solid-phase P content is greatest at 91.9 meters below seafloor (mbsf) in Hole U1384A and at 89.1 mbsf in Hole U1382B (Fig. F2). To a lesser extent, a similar increase in P is observed in Hole U1383E at 42.7 mbsf but is absent in Hole U1383D (Fig. F3). The increase in P content downcore could be indicative of higher P accumulation rates when those sediment layers were deposited.

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