Chemical and isotopic composition of interstitial water from Deep Sea Drilling Project Sites 533 and 534.

Abstract

Low salinities and strong opposing fluctuations between chlorinity and interstitial water delta18O and deltaD characterize the region of gas-hydrate occurrence at Site 533. In addition to the hydrate recovered from 243m sub-bottom, thin, diffuse layers of hydrate composing about 10% of the total pore space may have been cored around 290m. Decomposition during recovery could account for the high oxygen isotope value and low chlorinity observed at this depth. High alkalinity and dissolved ammonia indicate substantial microbial activity. Chlorinity gradually increases with depth in the 1600m thick sediment column at Site 534, perhaps due to deep-seated alteration-hydration reactions or to the presence of nearby evaporites. Delta18O and deltaD decrease with depth and are well correlated, suggesting that a common mechanism is fractionating both.-from Authors