Interstitial waters from six sites of the Western Mediterranean Basin (Sites 974-979; Fig. 1) were retrieved during Leg 161 of the Ocean Drilling Program (ODP) and analyzed for stable isotopes of dissolved sulfate (34S/32S, 18O/16O), water (18O/16O), and inorganic carbonate species (13C/12C), in addition to major and minor ions. Site 974 was drilled in the central Tyrrhenian Sea. Site 975 was located on the South Balearic Margin, between the Balearic Promontory (Menorca and Mallorca Islands) and the Algerian Basin. Sites 977 and 978 are situated in the Eastern Alboran Sea, and Sites 976 and 979 were drilled in the Western and Southern Alboran Sea, respectively (Comas, Zahn, Klaus, et al., 1996). The recovered sediments span a time interval from the Pleistocene to the Miocene (Comas, Zahn, Klaus, et al., 1996). Several sapropel layers with organic carbon contents up to 6.3% by weight (Comas, Zahn, Klaus, et al., 1996) were found at almost all sites and reflect periods of enhanced organic matter production and/or preservation.
Pore waters were retrieved from all sites drilled during Leg 161 to characterize the early and late diagenetic microbial degradation of organic matter within the sediment column and the influence of evaporites or brines at depth on the interstitial waters of the sediments.