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Oceanic mesoscale eddies are important dynamical processes in the Southern Ocean. Using high-resolution (∼0.1° for the ocean) Community Earth System Model (CESM-HR) simulations under a high-carbon emission scenario, we investigate the role of mesoscale eddies in regulating the response of the Subantarctic Front (SAF) to global warming. The CESM-HR simulates more realistic oceanic fronts and mesoscale eddies in the Southern Ocean than a coarse-resolution (∼1° for the ocean) CESM. Under global warming, the SAF is projected to intensify. The mean flow temperature advection intensifies the front, whereas the mesoscale-eddy-induced temperature advection and atmospheric dampening play primary (∼67%) and secondary (∼28%) roles in counteracting the effect of mean flow temperature advection. Our study suggests the importance of mesoscale eddies on inhibiting the SAF intensification under global warming and necessity of mesoscale-eddy-resolving simulations for faithful projection of future climate changes in the Southern Ocean.

The Antilles Current (AC) off the Bahamas Islands is an important component for both wind-driven and thermohaline circulation system in the North Atlantic. The evolution of AC intensity could exert substantial impacts on mid-latitude climate and surrounding environment. For instance, an anomalous weaker AC is found to decelerate the nutrient transport in the shelf regions, risking the deep-water corals. In addition, a weaker AC could reduce the poleward heat transport of the Gulf Stream and the North Atlantic Drift and further influence the climate in Western Europe. Based on nine high-resolution coupled climate models, we find a 3.8 Sv weakening of the AC, which is equivalent to 63% of its climatology transport during 1950–2050. The deceleration of AC introduces a −0.17 PW of heat transport decrement, dominating the total heat transport change across 26.5° N. Further analysis reveals that change of AC is mainly attributed to the evolution of thermohaline circulation in a changing climate and is partly influenced by wind stress curl in the North Atlantic. Our finding highlights the needs to establish a long-term monitoring network for the AC and a comprehensive understanding of associated impacts.

The Kuroshio Current (KC) in the East China Sea is one of the most prominent components of the ocean circulation system in the North Pacific. The onshore intensification of the KC is found to drive nutrient-rich upwelling in the shelf regions, induce anomalous warming that leads to coastal marine heatwaves, and reduce the ability of the oceans to absorb anthropogenic carbon dioxide. Based on altimeter and in situ observations, we find an onshore acceleration and offshore deceleration of the KC over the past three decades. This intensification is characterized by a spatial mean onshore acceleration (offshore deceleration) of 0.39 (−0.63) cm s ^−1 per decade. This phenomenon can be attributed to changes in wind stress curl (WSC) and oceanic stratification over the subtropical North Pacific. The weakened WSC decreases the vertical extent of the KC by reducing its transport and contributes to the offshore deceleration, whereas the enhanced stratification drives the uplift of the KC and contributes to the onshore acceleration. Our findings underscore the importance of establishing and maintaining a long-term monitoring network for the zonal variations of the KC in the future to obtain a comprehensive understanding of the associated impacts.

Marine heatwaves (MHWs) can cause various adverse effects on marine ecosystems associated with complicated social ramifications. It has been well established that the gradually rising sea surface temperature (SST) due to anthropogenic carbon emission will cause an increase of the MHW duration and intensity. However, for species with strong adaptation capacity or mobility, MHW changes due to the altered SST variability under greenhouse warming are more crucial but so far remain poorly assessed. Under the high carbon emission scenario, we show that the cumulative duration (intensity) of MHWs, with the effect of secular SST increase excluded, is projected to be 60% (100%) higher by the end of this century than in the 1990s due to an amplified SST seasonal cycle. This increase becomes more evident for stronger MHWs, reaching up to 8 (30) folds for the extreme MHW category. The amplified SST seasonal cycle also causes pronounced seasonality of MHWs, making them more active in summer-autumn than winter-spring. Our results suggest that MHWs are likely to have increasingly devastating impacts on a wide range of marine species in the future without taking effective steps for carbon emission reduction.