METHODS

Samples were oven-dried at 60°C and sieve washed. Well-preserved specimens were chosen from the coarse-fraction (>154 µm) residues and cleaned with ethanol (99.7%) in an ultrasonic bath. They were dried again in an oven at 60°C and reacted with orthophosphoric acid in an automatic carbonate device (Kiel III) at 70°C to generate CO₂. The escaping CO₂ was then transferred to a Finnigan MAT252 mass spectrometer at the Laboratory of Marine Geology in Tongji University, People's Republic of China, for measurement of stable isotopes. Benthic foraminifers Cibicidoides wuellerstorfi (diameter = 300-900 µm, 1-3 specimens) or Uvigerina spp. (length = 400-900 µm, 1-3 specimens), and planktonic foraminifers Globigerinoides ruber (diameter = 300-360 µm, 5-7 specimens) or Globigerinoides obliquus (diameter = 200-340 µm, 3-7 specimens) were analyzed. A total of 1896 planktonic samples (Table T1) and 1717 benthic samples (Table T2) were analyzed. Because of isotopic differences between species and according to the adjustment factors proposed by Shackleton et al. (1995), a constant 0.64 was added to each ¹⁸O value of C. wuellerstorfi and a constant 0.9 was added to each ¹³C value of Uvigerina in order to merge the values of the two. No adjustment factors were used for G. ruber and G. obliquus, as both species display similar isotope values according to the work of Lourens et al. (1996). Precision was regularly checked with the Chinese national carbonate standard GBW04405. Conversion to the international Peedee belemnite (PDB) scale was performed using NBS19 and NBS18 standards: ¹³C = 0.57 PDB, ¹⁸O = -8.49 PDB); the standard deviation = 0.07 for ¹⁸O and 0.04 for ¹³C during the year 2000.