Decadal-scale changes in meridional heat transport across 24 degree N in the Pacific Ocean

We investigated the long-term variability of the meridional heat transport across 24 degree N in the Pacific Ocean in two ways: (1) by adding the surface net heat flux to the temporal change rate of the ocean heat content (OHC) north of 24 degree N and (2) by integrating the product of meridional velocity and potential temperature over the 24 degree N section in numerical models. Decadal-scale changes with amplitudes of approximately 0.1-0.2 PW were detected consistently in the 5-year running means of the meridional heat transport in the 1980s and 1990s from these different analyses. The heat transport increased during the 1980s, which is closely linked with the change in the OHC. While both the Ekman and Kuroshio transports were responsible for the change in the 1980s, the contribution of the former was dominant. On the other hand, the variation in the Kuroshio temperature transport dominated meridional heat transport in the 1990s. The air-sea net heat fluxes of the atmospheric reanalysis data sets integrated north of 24 degree N increased in the 1990s, which indicates that the increase of the lateral heat transport was distributed mainly to the atmosphere, particularly in the Kuroshio and Kuroshio-Oyashio Extension (KOE) regions. However, there are also large discrepancies in the surface heat flux among the data sets. To reveal the impact of the decadal-scale changes in meridional heat transport on the atmosphere, it is crucial to obtain more accurate values for the air-sea heat exchange and OHC by using a sustainable observing system and numerical models.