Oceanic Origin of A Recent La Nina-Like Trend in the Tropical Pacific

Global ocean temperature has been rising since the late 1970s at a speed unprecedented during the past century of recordkeeping. This accelerated warming has profound impacts not only on the marine ecosystem and oceanic carbon uptake but also on the global water cycle and climate. During this rapid warming period, the tropical Pacific displays a pronounced La Nina-like trend, characterized by an intensification of west--east SST gradient and of atmospheric zonal overturning circulation, namely the Walker circulation. This La Nina-like trend differs from the El Nino-like trend in warm climate projected by most climate models, and cannot be explained by responses of the global water cycle to warm climate. The results of this study indicate that the intensification of the zonal SST gradient and the Walker circulation are associated with recent strengthening of the upper-ocean meridional overturning circulation.