Climatic-Oceanographic Controls On The PH And P CO₂ In The Upper Water From Tropical West Pacific Since MIS 6

The B/Ca ratios of planktonic foraminifera is mainly controlled by seawater pH,thus a proxy for past carbonate chemistry,then providing evidence for atmospheric pCO₂ and ocean carbon cycle in the geological history.However,recent studies have revealed uncertainty as to whether seawater temperature or[CO₃^2-]is the dominant control on the partition coefficient K_D of planktonic foraminiferal B/Ca,except for the planktonic foraminifera that has been determined formula or method.Furthermore,it has been suggested that dissolution may influence planktonic foraminiferal B/Ca.To improve our understanding of how planktonic foraminiferal B/Ca may be applied as a proxy,B/Ca ratios in the tests of Neogloboquadrina dutertrei and Pulleniatina obliquiloculata in surface sediment samples from the tropical western Pacific and the South China Sea were measured in this study,and then revising the relationship between B/Ca values in thermocline-dweelling and temperature and[CO₃^2-].In addition,B/Ca ratios in the the tests of Globigerinoides ruber and N.dutertrei in Core MD06-3052 from the tropical western Pacific were also measured in this study,coupled with the revised relationship between B/Ca values in thermocline-dweelling and temperature and[CO₃^2-],pH and pCO₂ in the upper water from tropical west Pacific were reconstructed,the climatic-oceanographic controls on upper water pH and pCO₂ in the tropical western Pacific were investigated,and then the role of the ocean on the glacial-interglacial atmospheric CO₂ variations were analysed.Before analysed the climatic-oceanographic controls on the upper water pH and pCO₂ in the study area,compared the variation of Cd/Ca ratio of planktonic foraminifera G.ruber for core MD06-3052 with the reconstructive results of terrigenous input,upper ocean structure and marine primary productivity,from the two aspects of nutrient contribution and utilization,we investigate the variations and controls of surface ocean nutrient concentration in the West Philippine Sea since MIS 6,which lays a foundation for the exploration of climatic and oceanographic controls in the study area.B/Ca ratios in the tests of N.dutertrei and P.obliquiloculata in surface sediment samples from the tropical western Pacific and the South China Sea were unaffected by increasing water depth,which suggests that B/Ca ratios are not influenced by dissolution.In addition,the relationship between these B/Ca ratios and bottom water calcite saturation states(?[CO₃^2–])is weak,thus suggesting only a small dissolution effect on the B/Ca of the two species.The correlation coefficients?R²?between the B/Ca ratios of N.dutertrei and P.obliquiloculata and environmental parameters?e.g.,temperature,salinity,phosphate,DIC,and ALK?in the study area are not high enough to justify using B/Ca ratios as a palaeoenvironmental proxy.The significant correlation between K_D values of N.dutertrei and P.obliquiloculata and carbonate system parameters in the study area reflect chemical links between the K_D denominator and these variables.Based on our surface sediment calibration,an empirical relationship between the K_D of thermocline-dwelling foraminiferal N.dutertrei and temperature is proposed in the tropical western Pacific:K_D?×1000?=-0.0689×T+2.83R²=0.660Sea surface pCO₂ in the tropical western Pacific is mainly response to atmosphere pCO₂.Marine biogeochemical processes such as nutrient utilization and biological pump,tropical process of ENSO-like,and changes of AAIW/SAMW can break the balance beween sea and air.The increases in Luzon-sourced terrigenous inputs during MIS 6 and MIS 5e,led to the increase of nutrient,and then resulted in the increase in G.ruber Cd/Ca during thid period.In addition,the study of marine bilgeochemical processes for pH and pCO₂ in the sea surface of the tropical western Pacific shows that the respiration of the sea surface in the tropical western Pacific is greater than photosynthesis in the MIS 6 and MIS 5e due to the increase of nutrient,making the sea surface producing more CO₂ and then breaking the balance between sea snd air,causing ocean as strong carbon source to atmosphere.The carbonate system of upper water in the tropical western Pacific are affected by the ENSO process,and the upper water responds to the increased ventilation in the Southern Ocean.In El Ni?o,the thermocline becomes shallower,resulting in the decreased pH and increased pCO₂ of the upper water in the tropical western Pacifc;the situation in La Ni?a is contrary to the El Ni?o.When the ventilation in the Southern Ocean is enhanced,the increased AAIW/SAMW conveyed the minimum signal of?¹³C and a large number of DIC to the study area,and then influenced the carbonate system of the upper water body in the tropical western Pacific.On the glacial-interglacial scale,the exchange of carbon between sea and air in the tropical western Pacific is not balanced,which is different from the sea-air balance of modern process in the study area.This is mainly caused by the effects of nutrient and productivity,ENSO-like process,and the ventilation in the Southern Ocean on carbonate system in upper water from tropical western Pacific.