Dongmin Kim

The Korea–Japan (KJ) region has experienced warming faster than the global average, culminating in a record-breaking heatwave during the summer of 2025. Although the three summers from 2023 to 2025 all developed under a persistently negative Pacific decadal oscillation, only 2025 produced such an event. We show that the meridional structure of the underlying thermal forcing was decisive: in 2023, broad tropical–subtropical warming associated with El Niño distributed the thermal forcing across a wide latitudinal band; in 2024, a similarly broad tropical warming signal persisted; and in 2025, with the tropics having relatively cooled, warming was confined to the midlatitude North Pacific. This narrow midlatitude-confined forcing triggered the dynamical chain that drove the surface heatwave: a weakened upper-tropospheric temperature gradient on the equatorward flank of the jet, a weakened and poleward-displaced jet, persistent blocking, suppressed cloud cover, and enhanced surface shortwave radiation. The enhanced radiation then warmed the underlying ocean, and the air–sea coupling (ASC) further amplified and sustained the event. We further demonstrate that ASC over this region has strengthened since 2016, with 2025 representing its most extreme expression on record. These findings indicate that anticipating future KJ heatwave risk requires understanding the spatial structure of thermal forcing and the evolving strength of regional ASC, beyond projections of global-mean warming alone.

The historical evolution of the Atlantic Meridional Overturning Circulation (AMOC) remains debated due to limited continuous observations. To bridge this gap, we leverage historical hydrographic data spanning 1955 to 2022 to constrain a high-resolution global ocean model. Here, we show an overall weakening of the AMOC relative to a 1955–1964 baseline, interrupted by a transient recovery during 1995–2004. The regional footprint of this weakening shifts over time. While earlier reductions (~ 7% during 1965–1994) are driven by suppressed dense water formation in the subpolar North Atlantic, steeper recent declines (~ 11% during 2005–2022) stem from combined reductions across the subpolar North Atlantic and Nordic Seas, despite partially compensating increases in the Arctic Ocean. Sensitivity experiments reveal that the AMOC weakening is overwhelmingly driven by a long-term freshening regime, manifested by repeated episodes of high-latitude salinity anomalies—occurring during the 1970s–1990s and again in recent years—that are broadly tied to Arctic export and Greenland ice melt. Finally, while a relatively cold thermal state during 1975–2004 partially buffers the freshwater-driven decline, this thermal compensation is absent during 2005–2022 due to anomalous warming of the Nordic Seas and the Labrador Current, acting alongside the freshwater forcing to drive the steeper modern decline of the AMOC.

We used a high-resolution (1/12°) Modular Ocean Model version 6 implementation for the Northwest Atlantic Ocean (MOM6-NWA12) to dynamically downscale Geophysical Fluid Dynamics Laboratory Earth System Model version 4.1 (GFDL-ESM4.1) projections for the 21st century. Simulations were conducted under four different Coupled Model Intercomparison Project Phase 6 emission scenarios. MOM6-NWA12 accurately simulates the spatial patterns of sea surface temperature, salinity, and dynamic sea surface height (SSH) during the historical period. In particular, the Gulf Stream's strength, position, recirculation, and separation from the US East Coast are significantly improved in MOM6-NWA12 compared to the coarse-resolution GFDL-ESM4.1. Projected end-of-century warming varied strongly between scenarios, from ∼4 °C under prior “worst case” emissions scenarios (SSP-585), 2∼3 °C under intermediate scenarios (SSP-245, SSP-370) more consistent with current trajectories, to ∼1 °C under aggressive mitigation (SSP-126). Consistent with a significant weakening of the Atlantic Meridional Overturning Circulation projected by GFDL-ESM4.1, MOM6-NWA12 shows a substantial volume transport reduction in the Western Boundary Current (WBC) system (i.e., Yucatan Current, Florida Current, Antilles Current, and the Deep Western Boundary Current) toward the late 21st century (between 23 % and 38 %, varying by scenario). This projected weakening of the WBC system and the associated reduction in the coastal upwelling of cold, fresh subsurface waters lead to a significant increase in ocean temperature, salinity, and dynamic SSH along the US southeast and northeast Coasts, particularly in the South Atlantic Bight.

Future ocean conditions will likely alter habitat suitability for many species, potentially resulting in range shifts. Climate models simulate environmental conditions under climate scenarios and serve as a valuable tool for projecting future changes in habitat suitability. Here, we use ocean bottom temperature patterns from a multi-model ensemble mean of 6 Coupled Model Intercomparison Project (CMIP6) models for ‘low’, ‘medium’, and ‘high’ emission socioeconomic climate scenarios (SSP2-4.5, SSP3-7.0, SSP5-8.5) to estimate changes in thermal habitat availability for 6 commercially important fish species along the US Atlantic coast from 2015 to 2100. Thermal preferences were derived from survey data, and modeled bottom temperatures were adjusted to better reflect observed habitat conditions. Projections indicated declines in suitable thermal habitat for all species, although rates varied, with poleward shifts in northern range edges evident by the end of the century. Projected changes in suitable thermal habitat are likely to contribute to shifts in species distributions, which may require fisheries management bodies to co-develop strategies that address the reorganization of marine ecosystems under climate change. Enhancing model resolution and accounting for regional factors should significantly improve these predictions, allowing for the use of robust species distribution models.

We used a high-resolution (1/12°) Modular Ocean Model version 6 implementation for the the Northwest Atlantic Ocean (MOM6-NWA12) to dynamically downscale Geophysical Fluid Dynamics Laboratory Earth System Model version 4.1 (GFDL-ESM4.1) projections for the 21st century. Simulations were conducted under four different Coupled Model Intercomparison Project Phase 6 emission scenarios. MOM6-NWA12 accurately simulates the spatial patterns of sea surface temperature, salinity, and dynamic sea surface height (SSH) during the historical period. In particular, the Gulf Stream's strength, position, recirculation, and separation from the U.S. East Coast are significantly improved in MOM6-NWA12 compared to the coarse-resolution GFDL-ESM4.1. Projected end-of-century warming varied strongly between scenarios, from ~ 4 °C under prior "worst case" emissions scenarios (SSP-585), 2~3 °C under intermediate scenarios (SSP-245, SSP-370) more consistent with current trajectories, to ~ 1 °C under aggressive mitigation (SSP-126). Consistent with a significant weakening of the Atlantic Meridional Overturning Circulation projected by GFDL-ESM4.1, MOM6-NWA12 shows a substantial volume transport reduction in the Western Boundary Current (WBC) system (i.e., Yucatan Current, Florida Current, Antilles Current, and the Deep Western Boundary Current) toward the late 21st century (between 23 and 38 %, varying by scenario). This projected weakening of the WBC system and the associated reduction in the coastal upwelling of cold, fresh subsurface waters lead to a significant increase in ocean temperature, salinity, and dynamic SSH along the U.S. southeast and northeast Coasts, particularly in the South Atlantic Bight. These localized changes have significant implications for future sea level rise, marine ecosystems, and fish populations in these highly vulnerable regions.

We used a high-resolution (1/12°) Modular Ocean Model version 6 implementation for the the Northwest Atlantic Ocean (MOM6-NWA12) to dynamically downscale Geophysical Fluid Dynamics Laboratory Earth System Model version 4.1 (GFDL-ESM4.1) projections for the 21st century. Simulations were conducted under four different Coupled Model Intercomparison Project Phase 6 emission scenarios. MOM6-NWA12 accurately simulates the spatial patterns of sea surface temperature, salinity, and dynamic sea surface height (SSH) during the historical period. In particular, the Gulf Stream's strength, position, recirculation, and separation from the U.S. East Coast are significantly improved in MOM6-NWA12 compared to the coarse-resolution GFDL-ESM4.1. Projected end-of-century warming varied strongly between scenarios, from ~ 4 °C under prior "worst case" emissions scenarios (SSP-585), 2~3 °C under intermediate scenarios (SSP-245, SSP-370) more consistent with current trajectories, to ~ 1 °C under aggressive mitigation (SSP-126). Consistent with a significant weakening of the Atlantic Meridional Overturning Circulation projected by GFDL-ESM4.1, MOM6-NWA12 shows a substantial volume transport reduction in the Western Boundary Current (WBC) system (i.e., Yucatan Current, Florida Current, Antilles Current, and the Deep Western Boundary Current) toward the late 21st century (between 23 and 38 %, varying by scenario). This projected weakening of the WBC system and the associated reduction in the coastal upwelling of cold, fresh subsurface waters lead to a significant increase in ocean temperature, salinity, and dynamic SSH along the U.S. southeast and northeast Coasts, particularly in the South Atlantic Bight. These localized changes have significant implications for future sea level rise, marine ecosystems, and fish populations in these highly vulnerable regions.

We used a high-resolution (1/12°) Modular Ocean Model version 6 implementation for the the Northwest Atlantic Ocean (MOM6-NWA12) to dynamically downscale Geophysical Fluid Dynamics Laboratory Earth System Model version 4.1 (GFDL-ESM4.1) projections for the 21st century. Simulations were conducted under four different Coupled Model Intercomparison Project Phase 6 emission scenarios. MOM6-NWA12 accurately simulates the spatial patterns of sea surface temperature, salinity, and dynamic sea surface height (SSH) during the historical period. In particular, the Gulf Stream's strength, position, recirculation, and separation from the U.S. East Coast are significantly improved in MOM6-NWA12 compared to the coarse-resolution GFDL-ESM4.1. Projected end-of-century warming varied strongly between scenarios, from ~ 4 °C under prior "worst case" emissions scenarios (SSP-585), 2~3 °C under intermediate scenarios (SSP-245, SSP-370) more consistent with current trajectories, to ~ 1 °C under aggressive mitigation (SSP-126). Consistent with a significant weakening of the Atlantic Meridional Overturning Circulation projected by GFDL-ESM4.1, MOM6-NWA12 shows a substantial volume transport reduction in the Western Boundary Current (WBC) system (i.e., Yucatan Current, Florida Current, Antilles Current, and the Deep Western Boundary Current) toward the late 21st century (between 23 and 38 %, varying by scenario). This projected weakening of the WBC system and the associated reduction in the coastal upwelling of cold, fresh subsurface waters lead to a significant increase in ocean temperature, salinity, and dynamic SSH along the U.S. southeast and northeast Coasts, particularly in the South Atlantic Bight. These localized changes have significant implications for future sea level rise, marine ecosystems, and fish populations in these highly vulnerable regions.

We used a high-resolution (1/12°) Modular Ocean Model version 6 implementation for the the Northwest Atlantic Ocean (MOM6-NWA12) to dynamically downscale Geophysical Fluid Dynamics Laboratory Earth System Model version 4.1 (GFDL-ESM4.1) projections for the 21st century. Simulations were conducted under four different Coupled Model Intercomparison Project Phase 6 emission scenarios. MOM6-NWA12 accurately simulates the spatial patterns of sea surface temperature, salinity, and dynamic sea surface height (SSH) during the historical period. In particular, the Gulf Stream's strength, position, recirculation, and separation from the U.S. East Coast are significantly improved in MOM6-NWA12 compared to the coarse-resolution GFDL-ESM4.1. Projected end-of-century warming varied strongly between scenarios, from ~ 4 °C under prior "worst case" emissions scenarios (SSP-585), 2~3 °C under intermediate scenarios (SSP-245, SSP-370) more consistent with current trajectories, to ~ 1 °C under aggressive mitigation (SSP-126). Consistent with a significant weakening of the Atlantic Meridional Overturning Circulation projected by GFDL-ESM4.1, MOM6-NWA12 shows a substantial volume transport reduction in the Western Boundary Current (WBC) system (i.e., Yucatan Current, Florida Current, Antilles Current, and the Deep Western Boundary Current) toward the late 21st century (between 23 and 38 %, varying by scenario). This projected weakening of the WBC system and the associated reduction in the coastal upwelling of cold, fresh subsurface waters lead to a significant increase in ocean temperature, salinity, and dynamic SSH along the U.S. southeast and northeast Coasts, particularly in the South Atlantic Bight. These localized changes have significant implications for future sea level rise, marine ecosystems, and fish populations in these highly vulnerable regions.

In the South Atlantic Bight (SAB), changes in the Gulf Stream (GS), particularly its strength and proximity to the coast, are thought to be primary factors determining the shelf‐break upwelling rate. However, it is still not entirely clear if and to what extent those factors influence cross‐shelf nutrient fluxes and shape the ocean biogeochemistry at interannual and longer timescales. Here, we use a high‐resolution regional ocean‐biogeochemical model and an ocean reanalysis product (1993–2022), along with a satellite‐derived chlorophyll data set (1997–2022), to investigate the interannual ocean‐biogeochemical variability in the SAB. Regional model outputs suggest that year‐to‐year changes in phytoplankton production are indeed largely driven by upwelling of cold and nutrient‐rich water to the shelf‐break. The upwelling variability, reflected in bottom temperature and vertically integrated production patterns, is strongly linked to surface velocity changes in the GS near the shelf break, but weakly related to the depth‐integrated GS transport. The GS's velocity changes, and the temperature and production anomalies, are well correlated to the alongshore wind stress, suggesting that local wind is the leading driver of the shelf‐break upwelling variability at interannual timescales. Those relationships are also supported by circulation patterns from ocean reanalysis and satellite chlorophyll anomalies. Finally, examining the simulated shelf‐slope interchanges in the carbonate system, we find that shelf‐break upwelling significantly increases bottom acidification, a pattern linked to the low carbonate concentration in the slope waters. This study thus provides new insight for understanding and predicting GS and winds impacts on biogeochemical patterns from the SAB.