LATE PLEISTOCENE PALEOCEANOGRAPHIC CHANGES OF THE WEST EQUATORIAL PACIFIC

To delineate Late Pleistocene paleoceanographic change of the West Pacific, we analyzed the oxygen and carbon isotopic ratios of two planktonic foraminifera species (G. sacculifer and N. dutertrei) from a piston core (KODOS-313) taken from the West equatorial Pacific (02^o00′N, 164^o33′E), and they are compared with the published results of the East Pacific (ODP site 847 and RC 11-210), in terms of relative amounts and mass accumulation rates of CaCO₃ and eolian component, back to marine isotopic stage (MIS) 6. Differences in oxygen and carbon isotope values between two foraminifera species (0.75 permil in δ¹⁸O, 0.05 permil in δ¹³C) are less than those of the East Pacific (1.30 permil in δ¹⁸O, 0.14 permil in δ¹³C), which indicates smaller vertical contrasts in both temperature and nutrient between mixing-zone and thermocline in the West Pacific. Strong deviation in δ¹⁸O of G. sacculifer from SPECMAP suggests the carbonate fraction of KODOS-313 was subjected to partial dissolution by bottom water under lysocline. Lower accumulation rates of CaCO₃ and eolian component during glacial times are likely due to low sedimentation rate (ave. 0.75cm/1000 yr) combined with carbonate dissolution in KODOS-313 site. However, the high CaCO₃ contents during the glacial periods clearly follow the general pattern of equatorial Pacific ocean.