Tropical Process In The Western Pacific Warm Pool And Its Influence On PH And PCO₂ Variations In The Upper Water Since 700 Ka

Western Pacific Warm Pool?WPWP?play an important role in heat,moisture and carbon cycles,the same is true in the geologic history.Revealing the variations in the WPWP is significant to understanding the global climate change.In this study,Mg/Ca,?¹⁸O and B/Ca records of surface and subsurface dwelling foraminifera from Core MD06-3047B in the northern margin of WPWP were used to reconstruct temperature,salinity,pH,and partial pressure of carbon dioxide?pCO₂?records in the upper water column since 700 ka.By combining with relative paleo-environment and paleo-climate records from previous studies,we explore the hydrological variability,changes in upper water column structure in the western tropical Pacific and associated controlling factors.Furthermore,the relationship between these tropical process and upper ocean pH and pCO₂ records in our study area are discussed.Through the reconstruction of sea surface temperature?SST?and sea surface residual oxygen isotope composition(?¹⁸O_sw-ice)and comparison with records from other sites in the central,southern part of the WPWP,and eastern tropical Pacific,we draw the following conclusions.The SST and sea surface?¹⁸O_sw-ice records in our study area experienced significant changes on glacial-interglacial timescales.The sea-surface?¹⁸O_sw-ice records over the whole WPWP are characterized by higher values ?lower SSS and thus most likely higher precipitation?during glacials than during interglacials.And this feature might be controlled by exposure of the Maritime Continent due to lower sea level and/or a weakened Atlantic meridional overturning circulation?AMOC?during glacial periods through enhanced Pacific Walker circulation and/or the southward shift of Intertropical Convergence Zone?ITCZ?.Our results also suggest an enhanced tropical zonal Pacific SST gradient during glacial periods,indicating La Ni?a-like conditions and adding weight to the relationship between stronger Walker circulation and higher rainfall in the western tropical Pacific during glacials.Our results also support the idea of an opposite trend in precipitation between continental East Asia and the western tropical Pacific,which may be due to the redistribution of heat controlled by precession and associated variations in monsoon flow according to previous model simulation.Through the reconstruction of thermocline temperature?TWT?and thermocline?¹⁸O_sw-ice records and comparison with SST,Pulleniatina obliquiloculata?¹³C records,we found that SST and TWT records show different characters,with earlier increase in TWT than SST during glacials;TWT records are relatively higher during MIS 16,MIS 12,MIS 8,and MIS 6 than during MIS 14,MIS 10,and MIS 4-2.The difference between SST and TWT(?T _p.obl-G.rub)show obvious glacial-interglacial variation with lower values and thus deeper thermocline depth during glaiclas than during interglacials.The variability in the TWT and?T _p.obl-G.rub in our study area might be controlled by changes in the East Asian Winter Monsoon?EAWM?,the altering and different influence of southern and northern sourced water masses on the tropical Pacific on glacial-interglacial scale.In addition,long-term changes superimposed on glacial cycles are found in the?T _p.obl-G.rub records,which might be controlled by the evolution of East Asian Monsoon?EAM?.The P.obliquiloculata ?¹³C,?T _p.obl-G.rub and thermocline?¹⁸O_sw-icew-ice records from Core MD06-3047B show different changes during different deglacials.Therefore,our result support the idea that different deglacials were triggered by different mechanisms and/or processes since mid-Pleistocene.The sea surface pH and pCO₂ records show higher pH and lower pCO₂ during glacial periods.The surface carbonate system respond to atmospheric pCO₂.Besides,the glacial/interglacial shifts of ENSO-like state might be an interference factor for sea surface p H and p CO₂ changes.While changes in sub-surface pH and pCO₂ records might respond to atmospheric pCO₂ and influenced by the variability in sub-surface water associated with the different influence of southern and northern sourced water masses on the tropical Pacific.Similarly,the long-term changes are also observed in the sea surface pH and pCO₂ records from Core MD06-3047B.And the long-term changes in sea surface pH and pCO₂ may be controlled by changes of upper water column structure caused by variability in EAM.