Data report: d18O in pore fluids from NanTroSEIZE Expeditions 322 and 333

Abstract

We report on analyses of the oxygen isotopic composition of pore fluids in sediments from two sites drilled in the Shikoku Basin as part of the Nankai Trough Seismogenic Zone Experiment. Both Sites C0011 and C0012 were cored to sample the input section to the subduction zone offshore southern Japan during Integrated Ocean Drilling Program Expeditions 322 and 333. Pore fluid δ 18 O analysis was performed using gas chromatography interfaced with isotope ratio mass spectrometry at the Institut de Physique du Globe de Paris. At both sites, pore fluids are depleted in 18 O relative to modern seawater: δ 18 O decreases with depth to values of -4.66‰ (Site C0011) and -3.97‰ (Site C0012) at the bottom of lithologic Unit II and remains relatively constant at -4.5‰ in lithologic Units III and IV. In lithologic Unit V at Site C0011, δ 18 O slightly decreases to a value of -5.30‰ at 858 meters below seafloor (mbsf), whereas at Site C0012, the δ 18 O depth profile shows a reverse trend with δ 18O values increasing with depth from -4.5‰ to -3.15‰ at 529.2 mbsf.