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doi:10.2204/iodp.proc.310.108.2007 GeochemistryAll geochemical pore water data are presented in tables allsitesIW.xls and IWsaturation.xls in “Supplementary Material.” pH, alkalinity, ammonia, chloride, and sulfateThe pH of all pore water samples from the Tiarei outer ridge is generally like seawater, with samples from Hole M0009A having slightly lower pH (Fig. F81A). Alkalinity in these pore waters is generally that of seawater or slightly lower (Fig. F81B). Of the few pore water samples obtained from Tiarei outer ridge sites, ammonia was only detected in a single sample (Sample 310-M0025A-11R-1, 130 cm). Chloride and sulfate concentrations do not significantly deviate from seawater values, indicating that no freshwater influence is observed on the interstitial water (IW) geochemistry. Mg, K, Ca, and SrMg, K, and Ca (Fig. F81C) concentrations are within error of seawater values in all pore water samples from the Tiarei outer ridge. Sr is elevated above seawater values only in Hole M0009A samples (Fig. F81D), suggesting some aragonite dissolution may have occurred as a result of the lower pH values in these pore waters. Li, P, Mn, Fe, and BaCompared to a seawater Li concentration of 174 µg/L, Li is enriched in some samples but depleted in others (Fig. F81E), suggesting the presence of both sinks and sources of Li in Tiarei outer ridge material. Most samples display P concentrations in the same range as those found for Tahitian seawaters sampled during drilling operations (53–90 µg/L; M. Kölling, unpubl. data), but a couple of the samples are slightly enriched (Fig. F81F). Mn, Fe, and Ba are highly elevated compared to seawater in most samples (Fig. F81G–F81I), and the source of these cations is most likely the dissolution of microbialites (Camoin et al., 2006). |
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