The Kuroshio system and the Gulf Stream serve as the primary poleward heat transporters in the Northern Hemisphere. Anomalous changes in these systems can have significant implications for the climate, particularly in mid-latitude regions. However, due to the limitations of available observational data and the coarse resolution of climate models, previous studies mainly focused on surface currents, such as the East China Sea Kuroshio (ECSK) and the Florida Current (FC), overlooking the evolution of subsurface currents including the Ryukyu Current (RC) and the Antilles Current (AC). In this study, we utilize high-resolution coupled climate models to examine the trends of both surface and subsurface currents from 1950 to 2050. Our findings reveal a significant deceleration of the RC and AC, with reductions of 6.2 Sv and 3.8 Sv, respectively, over the 100-year period. This corresponds to a 45% weakening of the RC and a 63% reduction in the AC. The decline of the RC is primarily driven by a weakened subtropical wind field and increased ocean stratification. In contrast, the weakening of the AC is more closely associated with the decreasing strength of the Atlantic Meridional Overturning Circulation (AMOC). Moreover, our results demonstrate that the weakening of subsurface currents is a major factor in the evolution of poleward heat transport, accounting for a reduction of 1.1 PW in the Pacific and 0.17 PW in the Atlantic. These findings highlight the critical role of subsurface currents in shaping heat transport and stress the importance of these currents when assessing the impacts of climate change on ocean circulation and global climate systems.
 

global warming, western boundary current, subsurface current