The Paleoceanographic Records During The Past150Kyr B.P. In The Northern Part Of Western Pacific Warm Pool

International Marine Global Change Study Program (IMAGES) CoreMD06-3052（14°48.6042’N,123°29.3983’E,732m water depth) was recovered withthe Calypso Giant Piston Corer on board R/V Marion-Dufresne during the IMAGEScruise ‘Marco Polo2’ in June2006. The core lied in the northern edge of westernPacific Warm Pool, near the bifurcation of North Equatorial Current, which provideda good material for investigating paleoceanography of western Pacific Warm Pool andcomparing with high latitudes since late Pleistocene. The core is19.48m long withseveral turbidite layers. We established the age model of core MD06-3052byAMS14C dating and correlating with the standard LR04curve. The results showed thatthe age of bottom of the core was about150kyr B.P.(late MIS6), and the temporalresolution between samples was~300yr.Mg/Ca-based SST results showed that SST records of MD06-3052led δ18O by~2-3kyr, similar to the paleorecords from eastern Pacific, southern ocean and centreof western pacific warm pool, although the mechanism was of great debate. Duringthe penultimate deglacial, SST increased in timing with Antarctic temperature, andfollowed changes of Northern Hemisphere Summer Insolation. Similar recordsoccurred in eastern equatorial pacific and southern ocean. The most popularmechanisms included ENSO-like ocean-atmosphere activities and green house gasCO2forcing and our records didn’t support the latter one.δ18C of both surface and subsurface dwelling foraminifera showed minimumevents during deglacials, i.e., MIS6/5, MIS4/3and MIS2/1, which was globaldistributed and parallelled. δ18C increased gradually since150kyr B.P., which was thelatter part of long-term δ18Cmax events, although several δ18Cmin events punctuatedduring the increase of surface-dwelling foraminifera. Notably, surface δ18Cmin eventsled subsurface, indicating different controlling factors and forcing machanisms ofsurface and subsurface waters.Δδ18CG-Nresults showed glacial-interglacial changes of depth of upper nutricline.Low Δδ18CG-Nduring glacials indicated strong mixing of upper ocean, resulting inincrease of Primary Productivity. Contrarily, high Δδ18CG-Nduring interglacialsindicated strong stratification of upper ocean, resulting in decrease of PP. Δδ18CG-Nincreased during each deglacial, i.e., MIS6/5, MIS4/3and MIS2/1, which reflected gradual deepening of the nutricline during deglacial. Δδ18CG-Nchanges resemblesAntarctic Vostok CO2records and PP records from Sulu Sea and Mindanao Sea.The surface δ18Oresidualshowed similar trends of local summer insolation,however, high δ18Oresidualvalues corresponded to high insolation, which showedsimilarity to precession cycles. We inferred that high insolation resulted in highevaporation-precipitation, which finally led to increased of sea surface salinity.δ18Oresidualof subsurface was specially behaved during Termination II (increased),last interglacial (remaining high) and the inception of last glacial (increased).δ18Oresidualwas calculated by removing temperature and ice volume effect from thecarbonate δ18O, so it mostly reflected local hydrographic changes, i.e., water masschanges in our research area. We inferred that a water mass with high salinity wascontrolling the thermocline changes of MD06-3052. From modern observations, wededuced that the water mass was from north pacific tropical water, which formed insubtropical gyre. The Evaporation was way too much stronger than Precipitation inthe subtropical gyre, which resulted in the high salinity of the water mass. The northpacific tropical water subducted into subsurface with its high salinity as itscharacteristic.ΔTG-N(temperature differences between surface and subsurface water) reflectedthe thermal gradients between the upper water, i.e., the structure of upper water overthe last150kyr B.P.. Our results ΔTG-Nrecords showed similar trends like surfaceδ18Oresidualand high surface δ18Oresidualcorresponded with high ΔTG-N, which meanshigh surface salinity occurred concurrently with shoaling of thermocline depth ofwestern Pacific Warm Pool, an anolog condition of modern El Ni o.We found thatduring MIS5e, ΔTG-Nwas the smallest over the last150kyr B.P., which indicated thethermal gradients between the upper water was smallest, i.e., the depth of thethermocline was deepest, coherent with records from Kurishio source region. We inferthat the latitudinal displace of the bifurcation of north equatorial current influenced byENSO-like climate changes should have been responsible for the strengthening of thePacific subtropical circulation, which would resulted in intensified Kurishio.