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doi:10.2204/iodp.proc.307.202.2009

Material and methods

The analyzed interval of Hole U1318B ranges from 0.05 meters below seafloor (mbsf) (interval 307-U1318B-1H-1, 5 cm; top of Unit 1) to 90.5 mbsf (interval 307-U1318B-10H-CC, 23 cm; Subunit 3A). The sampling interval was 20 cm. After excluding large skeletal grains, 422 samples were dried and powdered for carbon and oxygen isotope measurement.

Isotopic compositions were measured using mass spectrometry (Finnigan Mat Delta Plus) coupled with an automatic gas separation system (Gas Bench). In this system, the samples were reacted with purified H₃PO₄ under 1 atm He in a sealed glass bottle. Reaction temperature and time were 55°C and 3 h, respectively. The reactant CO₂ was, together with He, sent to the gas chromatograph, which separated components such as H₂O. The separated CO₂ was introduced into the mass spectrometer, where its isotopic compositions were measured. The measured carbon and oxygen isotopic ratios were normalized with the laboratory standard (Solnhofen Limestone; δ¹³C = –0.47‰, δ¹⁸O = –5.04‰) that was calibrated against National Bureau of Standards (NBS) 19 (δ¹³C = +1.95‰, δ¹⁸O = –2.20‰ versus Vienna Peedee belemnite). Repeated measurements of the laboratory standard (n = 22) showed that the reproducibility of δ¹³C and δ¹⁸O was within ±0.20 and ±0.27‰, respectively. Outliers were measured twice to check their accuracy.

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