Changes In Tropical Pacific Salinity Under Global Warmin

The observations and reanalysis data of salinity were evaluated in this paper,based on which the variability characteristics of long-term trends of salinity in the tropical Pacific Ocean were analyzed to further investigate the changes of temperature-salinity relationship in the tropical Pacific Ocean and its relative contribution to the upper oceanic stratification.At the same time,the model data were used to attribute the changes of salinity under global warming and further analyze the differences in salinity changes forced by different sea surface flux forcing.First,we compare the salinity characteristics and ocean stratification in the tropical Pacific derived from the Array for real-time geostrophic oceanography data(Argo),Ensemble 4analysis(EN4),the Simple Ocean Data Assimilation reanalysis(SODA),Institute of Atmospheric Physics data(IAP)and the Ocean Reanalysis System 4(ORAS4).The results show that the region with low salinity showing large deviation and strong dispersion.The position with the largest deviation is located near the dateline while the IAP shows high-salinity deviations relative to other datasets.The Argo and EN4 show thicker barrier layer relative to the ensemble mean while the SODA displays the largest negative deviation in the tropical western Pacific.The deviation of N~2 indicates that the EN4,ORAS4,and IAP underestimate the stability in the upper ocean,while Argo overestimates ocean stability.The salinity becomes lighter in the tropical western and southern Pacific convergence zones and saltier in the southeastern Pacific.Meanwhile,the trend of temperature and salinity are not synchronous,and their relationship is closer with time.When the temperature changes 1℃in the past decade,the salinity changes about 0.22 psu,while the relationship between temperature and salinity in the subsurface layer changes less.Under the combined influence of temperature and salinity changes,the surface density decreases significantly in the tropical Pacific,with the large value centered in the warm pool.The subsurface density changes are dominated by temperature,and the density in the tropical western Pacific increases in the subsurface layer.At the same time,the mixed layer becomes shallower near the equatorial dateline and deeper in the warm pool,which is mainly influenced by salinity.The contributions of salinity and temperature to barrier layer variability are located in different regions,with salinity thickening the BLT east of 160°E of the equator and temperature thickening the barrier layer west of 160°E of the equator.The response of salinity to freshwater fluxes,heat fluxes,and wind stress fluxes shows commonalities and differences,with sea surface salinity in the tropical western Pacific decreased in the tropical western Pacific mainly influenced by heat fluxes and freshwater fluxes,while the contribution of wind stresses is relatively small.In addition,heat fluxes have the greatest influence on sea surface density,mixed layer and barrier layer,resulting in a large reduction of sea surface density in the tropical Pacific.The regression of sea surface salinity anomalies with Ni?o3.4 index reveals that the center of negative sea surface salinity anomalies west of the equatorial day boundary is enhanced by adding flux perturbations,which is especially evident in the freshwater flux experiments.