ABSTRACT Analyses of water samples taken by means of an in-hole sampler generally show good agreement with analyses of samples collected by routine shipboard squeezing techniques. At Sites 438 and 439, a decrease in salinity with depth is related to former freshwater flow from an aquifer that crops out at an anticline on a deep sea terrace between Japan and the top of the trench slope of the Japan Trench. This former subaerial recharge suggests significant late Cenozoic subsidence of the terrace, because it now lies at a water depth of 1500 meters. Samples from the trench slope at Site 440 have extremely high values of alkalinity and ammonia, presumably because of a favorable combination of high sedimentation rate and organic carbon content. Diagenetic conditions on the trench slope favor formation of the Fe-Mg carbonate mineral, ankerite; at Site 440 it first occurs at a depth below the sea floor of only 29 meters in late Pleistocene strata. Undissolved diatoms persist to relatively great depth at the sites of Leg 57 because of a low geothermal gradient caused by subduction. Secondary silica lepispheres first appear at 851 meters at the most landward and warmest site, Site 438, in strata 16 million years old with an ambient temperature of 31 °C. SAMPLING AND ANALYTICAL PROCEDURES During Leg 57 Shipboard in-hole data on pH, alkalinity, chlorinity, calcium, and magnesium (except Mg from Site 438) generally show good agreement with the samples obtained by routine shipboard squeezing techniques The results for ammonia and silica were obtained from the overflow water of the in-hole sampler and had to be corrected for dilution by distilled water. Agreement for Site 438 with routinely collected samples is good In general, however, we conclude that the in-hole samples essentially confirm the validity of the interstitial water sample data collected by routine squeezing, even for the minor constituents, silica and ammonia. This is in agreement with the conclusions of Barnes and others (1979). SALINITY DECREASE WITH DEPTH An interesting phenomenon at Sites 438 and 439 (water depth about 1600 m) is a downhole decrease in salinity and chlorinity. The chlorinity at the deepest sample at Site 438 is only about 50 per cent of that of seawater. These data imply that fresh water has been advected to the sites from an outcrop area. A possible source of fresh water is through sandstone and conglomerate layers in the deeper strata of the sites. Because boulders in the conglomerate are very large, 126
