The Variation Of Upper Ocean Structure In The North Margin Of The Western Pacific Warm Pool During The Last 700 Kyr

Core MD06-3047B(17o 00.44’ N, 124o 47.93’ E, length 8.90 m, water depth 2510 m) was retrieved during Marco Polo2 IMAGES XIV Cruise, east off Luzon Island in the Western Philippine Sea, from the Benham Rise, was used to investiga te paleoceanographic variations at the north margin of the Western Pacific Warm Pool(WPWP) over the past 700,000 years.The age model of Core MD06-3047 B was established by comparing benthic foraminifera C. wuellerstorfi δ18O curve with the LR04 stack combining the last appearance datum of C. wuellerstorfi(pink) which indicates a numerical age of 120 ka. Core MD06-3047 B contains 17 MIS and about 700 000 years.The results of the stable oxygen isotope records of C. wuellerstorfi, G. ruber and P. obliquiloculata show obvious changes over glacial- interglacial cycle except of the stable oxygen isotope records of G. ruber during MIS 14-13. The stable carbon isotope records of C. wuellerstorfi also show glacial- interglacial changes, small in glacia l periods and large in interglacial periods. The results of the stable carbon isotope records of G. ruber become progressively lager in glacial periods and become progressive ly smal er in interglacial periods, and the P. obliquiloculata have opposite characterist ics. And the stable carbon isotope records of P. obliquiloculata occur intense negative excursions during termination Ⅰ, Ⅱ, Ⅳ and Ⅴ and obvious positive excursion during MIS13 and MIS3.The δ18O difference between the subsurface dwelling P. obliquiloculata and the surface dwelling G. ruber in the Core MD06-3047 B suggests shal ower thermocline during most glacial episodes and deeper thermocline during interglacial intervals. The results of the stable carbon isotope records of G. ruber and P. obliquiloculata, the δ18O difference between the benthic foraminifera C. wuellerstorfi and the subsurface dwelling P. obliquiloculata shows that the productivity are higher in glacial periods and lower in interglacial periods. By comparing the δ18O differences of Core MD06-3047 B in the north margin of WPWP, Site ODP805 in the center of WPWP and Site ODP847 in the eastern tropical Pacific, we infer that equatorial Pacific was in ENSO-like variation mode since 70,000 ka, just like El Ni?o condition in glacial periods, and La Ni?a condition in interglacial periods.The intense negative δ13C excursions at thermocline during termination Ⅰ, Ⅱ, Ⅳand Ⅴ indicates that the low δ13C waters from Southern Ocean had arrived at the north margin of the WPWP.The Mg/Ca temperature of surface and subsurface water shows changes over glacia linterglacial cycles. Glacial- interglacial amplitudes of the surface temperature are 6℃.