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doi:10.2204/iodp.proc.307.206.2009 Data report: carbon isotope composition of total dissolved inorganic carbon in interstitial water, Sites U1316, U1317, and U1318, Porcupine Seabight1Tracy D. Frank2AbstractThe carbon isotope composition of total dissolved inorganic carbon (DIC) was measured on 111 samples of interstitial water from Sites U1316–U1318 drilled during Integrated Ocean Drilling Program Expedition 307 to the Porcupine Seabight, southwest of Ireland. The analyses were performed to aid in understanding processes involved in the origin and development of Challenger Mound, a deepwater coral mound that was the focus of the expedition. Site U1317 was drilled into the northwest shoulder of Challenger Mound, whereas Sites U1316 and U1318 penetrated siliciclastic slope facies that accumulated downslope and upslope of the mound, respectively. The δ13CDIC values in interstitial water range from –18.3‰ to +3.9‰ Vienna Peedee belemnite. Maximum and minimum values occur in juxtaposition in the two deepest samples recovered from Site U1317 and correspond to a maximum in dissolved methane. At all three sites, downhole profiles of δ13CDIC values show a marked change in slope across a major unconformity between the middle Miocene and upper Pliocene series. At Site U1317, δ13CDIC values decrease from –2.5‰ to –8.5‰ from the top of the core to the unconformity at ~122 meters below seafloor (mbsf). Below this depth, values increase overall to a maximum value of +3.9‰. At Sites U1316 and U1318, the δ13CDIC values decrease markedly over the uppermost 10 m to values lower than –15‰ before increasing with depth to approximately –6‰ at the middle Miocene/upper Pliocene unconformity. Below the unconformity, δ13CDIC values increase with depth toward maxima ranging between 0‰ and +1.5‰. |
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