Pore fluid concentrations of iodine and boron are presented in Table T1. In addition, the iodine and boron pore water content is also presented in millimoles per cubic meter of wet sediment, based on measured concentrations and shipboard determinations of sediment porosity. Depth profiles of iodine (Fig. F2B) show shallow concentrations starting at seawater values and reaching a maximum (~800 然) at just over 20 meters below seafloor (mbsf). The deep iodine concentrations far exceed seawater (0.44 然) and therefore must be derived from either mineral dewatering reactions or diagenesis of locally deposited marine organic material. Concentrations of iodine are also well above the typical value for high-temperature island arc fumaroles (13.06 然) (Snyder et al., 2002; Tedesco and Toutain, 1991) as well as that of pore water samples recovered from the relatively shallow d嶰ollement of the Nankai accretionary prism (35 然) (You et al., 1993). They are also above those of waters derived from seafloor mud volcanoes not associated with serpentinization (Aloisi et al., 2004). Because the chloride concentrations of the pore fluids do not vary appreciably with depth, normalizing iodine concentrations to chloride concentrations (Fig. F2B) produced a similar pattern.
The boron contents of the pore fluids show a dramatic increase with increasing core depth, after which they stabilize at ~3500 痠ol/kg (Fig. F2C) at a depth of ~10 mbsf. This is consistent with results from previous investigations of the Conical Seamount (Mottl et al., 2003; Mottl, 1992). As with iodine, boron concentrations in the deep fluids exceed those of both seawater (420 然) (Spivack and Edmond, 1987) and high-temperature fumarolic condensates (1795 然) (Goff and McMurtry; 2000). Unlike iodine, the boron abundances of the deep fluids from the South Chamorro Seamount are indistinguishable from d嶰ollement fluids of the Nankai Trough (3210 然) (You et al., 1993, 1995). The similarity is also true with respect to B/Cl ratios (Fig. F2D), despite the fact that the Nankai is a shallow accretionary system and the Marianas system is a nonaccretionary system where the fluids are derived from much greater depths.
The maximum concentration of iodine in serpentinized clasts (61 痠ol/kg; 139 mbsf) is, to the author's knowledge, the highest concentration measured in nonsedimentary rock types (Fig. F3A). Maximum iodine concentrations in the muds are even greater than the clasts (102 痠ol/kg; 32 mbsf). The iodine concentrations for both are an order of magnitude lower than the average values for marine sediment (332 痠ol/kg) (Martin et al., 1993) and yet more than three orders of magnitude greater than accepted values for the depleted upper mantle (0.003 痠ol/kg) (Burgess et al., 2002) and more than two orders of magnitude greater than those measured in rocks associated with island arc volcanism (0.079 痠ol/kg) (Muramatsu and Wedepohl, 1998). No appreciable difference was observed between the samples obtained from the Conical Seamount and those obtained from the South Chamorro Seamount. Although the total number of samples was limited and the depth resolution was low, iodine concentrations decrease somewhat with depth, perhaps because of diagenetic loss as both mud and clasts are buried by fresher deposits. Iodine concentrations in the clasts and muds were normalized to the bulk wet sediment volume (and expressed in millimoles per cubic meter) using onboard porosity and grain density determinations (Salisbury, Shinohara, Richter, et al., 2002; Fryer, Pearce, Stokking, et al., 1990). Although pore fluid samples were only available for the upper 60 m, they clearly show that the amount of iodine residing in the pore fluids is greater than that residing in the sediments, except at depths <26 mbsf (Fig. F3B).
The boron concentrations in the serpentinized peridotites and serpentinite muds from the South Chamorro Seamount (Savov et al., this volume, 2002) and Conical Seamount (Benton, 1997; Savov et al., 2000) do not change appreciably with depth (Fig. F3C). The average boron concentration of the clasts is 2050 痠ol/kg, whereas that of the muds is 1190 痠ol/kg. This difference becomes even more apparent if the concentrations are normalized to the volume of wet sediment because the intervals with clasts have lower porosity and greater grain density (Fig. F3D). The concentrations in serpentinites from both seamounts are an order of magnitude lower than concentrations generally found in marine sediments (Ishikawa and Nakamura, 1993; Leeman, 1996) and are two orders of magnitude greater than values associated with fresh mid-ocean-ridge basalt glasses, representing depleted upper mantle values (23 痠ol/kg) (Ryan and Langmuir, 1993). Boron concentrations in the serpentinized ultramafics and muds are also very similar to those of the Izu-Bonin-Mariana island arc products (Straub and Layne, 2002), as well as island arc lavas globally (Ryan and Langmuir 1993; Leeman, 1996). Unlike iodine, the pore fluids contribute less to the bulk boron content than do the mud and clasts. Although the pore fluids achieve higher concentrations of boron than iodine with depth (Fig. F2), the relative proportion of residual boron in the fluid phase is less.