δ¹⁸O Signature And Trace Metal As Indicators For Hydrological Pattern And Processes In The North Tropical Pacific

The Tropical Pacific is an area active in atmospheric convection and sensitive to global climate change.Walker circulation above Tropical Pacific is related to El Ni?o/Southern Oscillation events.The hydrogen and oxygen isotope composition in seawater have been used to trace processes,such as melting of sea ice,glacial and river run-off,deep ocean water masses and deep-water formation processes.The trace metal concentration could reflect the budget of input and output,and associate with physical,chemical,and biological ones as well.Based on the investigation from 37^th and 47^thh Chinese research expedition cruises,theδ¹⁸O andδD signature and trace metals from the surface and deep water were measured to detect the hydrological structure and dynamical processes in the Tropical Pacific.The achievement will provide scientific data for exploring the tropical sea-air interaction as well as the response of tropical Pacific to global climate change.The conclusions based onδ¹⁸O andδD signature and trace metals are as follows.（1）For surface water,two different zones were separated at 155oE according to the distributions ofδ¹⁸O andδD signatures and salinity in the surface water of tropical Pacific Ocean from the 47^th cruise.The result was coincided with the behavior of Walker circulation,in which heavier isotopes stay in the residual surface water after evaporation in the Tropic Eastern Pacific,while lighter isotopes precipitate in the western.（2）The results of isotope fractionation model inferred thatδ¹⁸O-enriched water(salinity³5 psu,δ¹⁸O⁰.53‰)occurred at the depth of¹25 m at station CTD03 from the 37^th cruise was derived from the recirculation of Kuroshio extension flow into the warm pool.In contrast,deep water(δ¹⁸O^-0.51‰)from 2000 to 5000 m and bottom water(δ¹⁸O^-0.96‰)were derived from subarctic area or circumpolar water.（3）The correlations between Chl a andδ¹⁸O（R²=0.61,n=9,P=0.04）at station CTD03 indicated that the photosynthesis process may also resulted in a higherδ¹⁸O value in the residual water in the photic zone.（4）Relatively high correlations was found betweenδ¹⁸O orδD signatures and conservative-type trace metals,such as Li and D（R²=0.53）,Mo andδD（R²=0.60）,Cs andδD（R²=0.58）,Rb andδD（R²=0.76）,Cs andδ¹⁸O（R²=0.63）、Rb andδ¹⁸O（R²=0.65）.The result inferred conservative-type trace metals can be used as an indicator of water mass sources.Some nutrient-type trace metals Cu,Y,Ni,Zn and scavenged-type trace metals Mn Pb showed an enrichment tendency above 3000m,reflecting the impacts of nutrient regeneration,dissolution of particulate material,and etc..