The Upper Water Body Structure Evolution In The Core Region Of The Western Pacific Warm Pool And Its Correlation To The ENSO-like Process And ITCZ Shift Since MIS10

In the warming world, Western Pacific Warm Pool(WPWP) variation has been paid a great deal of attention on account of its enormous influence on global climate change, particularly the ENSO(El Ni?o and Southern Oscillation) process. To determine the role of tropical Pacific in the past climate change, we provide new high-resolution proxy records of magnesium/calcium ratios, oxygen and carbon isotope in multi-foraminiferal calcites from core KX97322-4(00o01.73’S,159o14.66’E, water depth 2362 m, total core length of 6.3 m) on Ontong Java Plateau to reconstruct the upper water structure and hydrological variation in the core region of the WPWP over the last 360,000 years.The age model reestablishment is based on the 14 C dating and the benthic foraminiferal(Cibicidoides wuellerstorfi) δ18O records. Multi-foraminiferal(Globigerinoides ruber, Globigerinella aequilateralis and Neogloboquadrina dutertrei) calcites Mg/Ca were used to reconstruct different layers temperature of the upper water during the last 360 kyr. The glacial-interglacial cycle of temperature variation is obvious and the Sea Surface Temperature(SST) in the Last Glacial Maximum was lower than late Holocene 2.9±0.7 ℃. In terminations, the SST variation was synchronous with the planktonic δ18O, while ahead the benthic δ18O 2-3 kyr. In the interglacial, there would be a SST threshold value(~29 ℃) controlling the change of global ice volume. Since the WPWP cooling more quickly than the δ18O variation in the following time, there also could be a threshold value at which ice volume began to grow rapidly. In terminations, the SST change may be not the direct driver of warming and no threshold value was found. In the Marine isotope stage(MIS) 6, the SST variation was contradictory to the δ18O. The warm SST would benefit the high latitude glaciation via transport more water vapor to polar.In the glacial cycle, sub-SST variation amplitude is greater than SST. Sub-SST warming was leading the surface and ahead of δ18O variation. Spectral analysis shows that the SST variation of the WPWP was mainly controlled by tropical process, while the primary driver of sub-SST change was high latitude process.Horizontal and vertical comparing of Mg/Ca-derived temperature records suggests that, in a relatively stable condition, like the Last Glacial Maximum(LGM) and other glacial, the tropical Pacific appears to be a La Ni?a-like state, and Walker and Hadley circulation are synchronously enhanced. While the El Ni?o-like condition could have happened in the tropical Pacific in rapidly changing periods, both the cooling stages in interglacial and terminations. Compare to the WPWP, the Eastern Pacific Cold Tongue(EPCT) is more sensitive to the insolation. We hypothesize that an inter-restricted relationship between the WPWP and EPCT would control the zonal gradient variation of SST and influence the climate change. Tropical Pacific could regulate the thermal and water provisions of middle-high latitude through the ENSO-like process. However, the ENSO-like signal was imprinted on the salinity variation of sub-surface waters. The sub-SST may impact on SST and SSS variation by altering the barrier layer thickness.Considering the linear correlation between the sea water δ18O(δ18Osw) and salinity, the heavier δ18Osw values in glacial and lighter values in interglacial would reflect the upper water-body salinity variation in the WPWP. The results demonstrate that the sub-surface salinity had a wider variation range than the surface. The vertical salinity variation amplitude comparison is supposed that the barrier layer was existing in the central WPWP in the glacial when La Ni?a-like prevailed. While in interglacial when El Ni?o-like to proceed, the barrier layer was absent or feeble.Furthermore, the δ18Osw-iv is closely tied with local precipitation, which is dominated by ENSO process and associated ITCZ shift. The opposite variation trend of rainfall in the core region of WPWP to the East Asian summer monsoon indicates the periodical swing of the Intertropical Convergence Zone(ITCZ) on precession scale. Meanwhile, precipitation also affected by the SST and ENSO-like process. The ENSO-like process may modify the extent of ITCZ shift.In the past 360 kyr, the biogeochemical processes in the upper water-body of the central WPWP also endured relevant evolution. The δ13C difference between the planktonic and benthic species(Δδ13Cp-b) values in terminations are extra low. It comes before low productivity times in interglacial. It probably induced by the enhanced deep ventilation or mid-deep water upwelling. The Δδ13Cp-b values correspond to the broad δ13C deglacial minimum. Moreover, the decline magnitude of δ13C in deeper living species calcite is larger. The broad δ13C deglacial minimum could be caused by the recovery of thermohaline circulation in terminations induced the intensive upwelling of southerly mid-deep waters. During terminations, the WPWP thermocline shoaled and the enhanced deep water ventilation released large amounts of CO2 to the atmosphere and brought the world into a warm time.In the interglacial, the δ13C difference between the surface and sub-surface species shows a low productivity with a poor mixing degree of upper waters. It is consistent with the lack of deep living species and paleoproductivity evidence from the benthic foraminifer. The productivity was relatively high in the glacial with the abundance of deep living species. The planktonic foraminiferal δ13C in the central WPWP could not represent past productivity variation and the low value in glacial may link to the ventilation between the Southern Ocean intermediate waters and the tropical sub-surface waters.