Absolute Geostrophic Currents In Global Tropical Oceans And Heat And Salt Transports Across The North Pacific Based On Argo Profiles

A set of monthly absolute geostrophic currents(AGCs) are calculated using the P-vector method based on gridded Argo profiles in the world tropical oceans and are compared with the altimeter geostrophic currents. The comparison shows that over most areas of the tropical oceans, the correlation coefficients pass the 95% significance test, and the Root Mean Square errors of zonal and meridional velocity are smaller than 6 cm/s and 4 cm/s, respectively. Furthermore, the AGCs agree well with the OSCAR currents and the moored current-meter measurements, too. These all suggest that the AGCs are reliable.Based on the AGCs in the upper 2000 meters of the oceans, the characteristics of the mean general circulation in tropical oceans are analyzed, and the classical Sverdrup circulation theory is quantificationally diagnosed in global tropical oceans. The results suggest that the theory agrees well with the AGCs in the eastern tropical and subtropical oceans, while in the western tropical and subtropical oceans the difference between the theory and the AGCs is great. Except for the non-Sverdrup circulation in the northwestern Pacific discovered in previous researches, the differences between the Sverdrup theory and AGCs are also great between the Equatorial Currents and the Euquatorial Counter Currents in the whole tropical South Indian Ocean and the western tropical Atlantic Ocean. Studies show that the diagnosis of the Sverdrup theory in the tropical South Pacific is inconclusive due to the great uncertainties of the wind stress there. However, the differences in other tropical and subtropical areas are not sensitive to the different wind products or the depths of the vertical integration,suggesting that non-Sverdrup circulation may exist in these areas. The diagnosis based on the OFES model(an eddy permitting model) shows a similar result, which also proves our previous findings.The mean characteristics and variation of the meridional heat and salt transports(MHT and MST) in the North Pacific are examined. The results show that the geostrophic transport and the Ekman transport dominates the subtropical and tropical MHT/MST, respectively. Based on the surface heat flux and the salt transport through the Bering Strait, the MHT and MST of the western boundary currents are estimated, whose contribution have the same order of magnitudes as the total interior MHT/MST, but basically opposite direction, and thus the western boundary currents play important roles in maintaining global heat and salt balance. Among them, the MHT and MST of the western boundary currents are estimated for the first time. Additionally, the seasonal variability of the total interior MHT/MST is significant in the tropics, with the transports stronger in summer and autumn, and weaker in winter and spring, and is consistent with the variation of the zonal wind stress. Studies show that, in the North Pacific, the heat transport is mainly controlled by shallow processes, while the salt transport may be affected to a great extent by much deeper ocean circulation.