UPPER WATER COLUMN TEMPERATURE VARIATIONS IN EQUATORIAL PACIFIC DURING LATE PLEISTOCENE

A 524cm-long piston core (KODOS-313) recovered from the Ontong-Java Plateau, western equatorial Pacific (02°00'037"N, 164°33'761"E, 4259m deep) was investigated for stable isotope composition of planktonic foraminifera and CaCO₃ content to delineate the paleoceanographic variation around the equatorial Pacific. The oxygen isotope stratigraphy was established on the basis of marine isotope stages (MIS) using oxygen isotope ratios of Neogloboquadrina dutertrei (thermocline dwelling planktonic foraminifera) with comparison to SPECMAP. The core KODOS-313 spans less than 800 kyr, late Pleistocene. Linear sedimentation rate was relatively low, ranging from 0.4 to 1.2cm kyr^-1 with an average of 0.74 cm kyr^-1. CaCO₃ contents show obvious 100 kyr cycle variations, high in glacials and low in interglacials. Temperature variations of thermocline between eastern and western equatorial Pacific was inferred using oxygen isotope values of N. dutertrei. δ¹⁸O values of N. dutertrei. in KODOS-313 are consistently lighter than those in ODP-847 core from the eastern equatorial Pacific. However, offset values of N. dutertrei. δ¹⁸O between two cores reveal significant change at the boundary of MISs 5 and 6. From core top down to MIS 5, offset values show a little variation between glacial and interglacial stages, ranging from 1.11 to 1.59 permil. Prior to MIS 6, however, magnitude of offset is relatively small and shows systematic variations between glacial and interglacial stages. Averaged offset values of glacial stages are larger than surrounding interglacial values about 0.2 to 0.6 permil, which translated into 1°C to 2.7°C (Erez and Luz, 1983). This indicates upwelling or advection of cooler current to eastern equatorial Pacific intensified during glacial stages prior to MIS 6. Similar patterns are observed from Globigerinoides sacculifer (surface mixed water dwelling planktonic foraminifera) δ¹⁸O values, also suggesting the importance of upwelling in eastern equatorial Pacific during glacial times prior to MIS 6.