Previous   |    Next

doi:10.2204/iodp.proc.308.201.2008

Materials and methods

Hole U1322B (28°5.9642′N, 89°1.4995′W) is located on the southern slope of the Mississippi Fan in the northern Gulf of Mexico, in a water depth of 1319.5 m (Expedition 308 Scientists, 2005). The hole penetrated to 234.5 meters below seafloor (mbsf), and core recovery is slightly more than 100% because of core expansion. The sediment is dominated by dark-colored organic-rich mud accumulated in a rapid depositional environment.

A total of 141 samples (20 cm³), mostly at 1.5 m spacing, were collected from Hole U1322B. Samples were oven-dried at 60°C and then washed through a 0.063 mm sieve. All well-preserved specimens of the planktonic foraminifer Globigerina ruber (clean, intact, with no signs of dissolution) were picked from the >100–250 µm fraction. Specimens >250 µm are extremely rare in most samples. Therefore, only 97 samples yielded 5 or more individuals of G. ruber suitable for isotopic measurement.

The specimens picked were washed with ethanol (~99.7%) in an ultrasonic bath. They were then dried in an oven at 60°C and reacted with orthophosphoric acid in an automated carbonate device (Kiel III) at 70°C to generate CO₂. Afterward, they were transferred to a Finnigan MAT252 mass spectrometer for measuring stable isotopes in the Laboratory of Marine Geology of Tongji University. Precision was regularly checked with a Chinese national carbonate standard GBW04405; the standard deviation is 0.07‰ for δ¹⁸O and 0.05‰ for δ¹³C. Finally, a NBS19 standard was used to convert the results to the international Peedee belemnite scale.

Top of page   |    Previous   |    Next