IODP Proceedings    Volume contents     Search
iodp logo


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.