Past 250 Kyr Paleoceanography In Central West Pacific Warm Pool

Core WP7, which was recovered from the south west Ontong Java Plateau and the heart area of the West Pacific Warm Pool, was chosen to reconstruct the variation of the upper water column structure, to find out the main reason of the productivity changes and its contribution to Atmosphere CO₂ oscillation. Theδ¹⁸O,δ¹³C, and Mg/Ca of the planktonic foraminifer G. ruber and N. dutertrei were analyzed, with sediments'chemistry analysis also performed.Upper water structure variation based on differences between surface dwelling G. ruber and subsurface dwelling N. dutertrei's Mg/Ca temperature, seawaterδ¹⁸O and shellδ¹³C show great coherence, which also coincide with equatorial pacific eolian flux and central equatorial pacificΔpCO₂ records. High eolian flux, highΔpCO₂, and WP7 strong mixing of the upper water, high primary productivity appeared at the same time; while low eolian flux, lowΔpCO₂, and WP7 weak upper water mixing, low primary productivity emerged coincidently. It is quite possible that the upper water structure variation in West Pacific Warm Pool results from changes of the equatorial Pacific wind field and determines local primary productivity. By spectrum analysis of G. ruber and N. dutertrei's shell Mg/Ca,δ¹⁸O andδ¹³C, strong half-precessional cycles exist, demonstrating that solar radiation of equatorial and low latitudes determines the local climate and environment changes.With primary components analysis of the sediments'element composition, layers containing significant amount of tephra were recognized, with detritus and biogenic always exist. The appearance of the tephra indicates that the volcanoes in the west and southwest island arcs off Ontong Java Plateau were once quite active. These tephra dilute the biogenic CaCO₃ and constrain the application of some geochemistry proxies. Behaviours of redox sensitive elements showed that the very up top of the sediment is in oxic environment, most sediments appear in suboxic environments, except some layers containing high amounts of organic carbon shows weak anoxic characteristics.The excess Ba was primarily from biogenic and has suffered no redox effects, indicating that it could be used as a proxy of organic carbon leaving from euphotic zone in biological pump process. With CaCO₃ as the inorganic carbon leaving the euphotic zone, the ratio of excess Ba to CaCO₃ could be used as the rain ratio index, which was high during inter-glacials but low in glacials.