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The δ13CDIC values range from –18.3‰ to +3.9‰ VPDB (Table T1). At all three sites, the middle Miocene/upper Pliocene unconformity corresponds to an inflection in the slope of downcore profiles in δ13CDIC values (Fig. F1). At Site U1317, δ13CDIC values decrease from –2.5‰ near the top of the core to –8.5‰ to the unconformity at ~148 meters below seafloor (mbsf) (base of lithostratigraphic Unit 1). Below this depth, values increase gradually downcore through Unit 2 to a maximum of +3.9‰ at 257.80 mbsf. The overall trend through Unit 2 is interrupted by two outliers to lower values of –13.8‰ at 207.80 mbsf and –18.5% at 266.01 mbsf. The maximum and minimum δ13CDIC values at this site occur in adjacent samples that represent the two deepest samples recovered from Site U1317. These extremes correspond to a dissolved methane concentration of ~6500 µM, the highest concentration encountered during Expedition 307 (see the “Site U1317” chapter).

Downcore trends in δ13CDIC values are very similar at Sites U1316 and U1318 (Fig. F1). Within the upper ~10 m of Unit 1, δ13CDIC values decrease by ~8‰ to reach minimum values for these sites of –15‰ or lower. Below this depth, δ13CDIC values increase to approximately –6‰ at the middle Miocene/​upper Pliocene unconformity (base of Unit 2), with the rate of change increasing with depth. In Unit 3, δ13CDIC values increase with depth toward maxima of +0.4‰ at Site U1316 and +1.6‰ at Site U1318.