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Based on the climatological reanalysis data of the European Center for Medium-Range Weather Forecasts and the Arctic sea ice data of the National Snow and Ice Data Center, the relationship between the Arctic sea ice area (SIA) and the interannual variation of atmospheric meridional heat transport (AMHT) was analyzed. The results show that the atmospheric meridional heat transported by transient eddy (TAMHT) dominates the June AMHT in mid-high latitudes of the Northern Hemisphere, while the western Baffin Bay (B) and the eastern Greenland (G) are two gates for TAMHT entering the Arctic. TAMHT in the western Baffin Bay (B-TAMHT) and eastern Greenland (G-TAMHT) has a concurrent variation of reverse phase, which is closely related to the summer Arctic SIA. Possible mechanism is that the three Arctic atmospheric circulation patterns (AD, AO and NAO) in June can cause the concurrent variation of TAMHT in the B and G regions. This concurrent variation helps to maintain AD anomaly in summer through wave action and changes the polar air temperature, thus affecting the summer Arctic SIA. Calling the heat entering the Arctic as warm transport and the heat leaving Arctic as cold transport, then the results are classified into three situations based on B-TAMHT and G-TAMHT: warm B corresponding to cold G (WC), cold B corresponding to warm G (CW), cold B corresponding to cold G (CC), while warm B corresponding to warm G is virtually non-existent. During the WC situation, the SIA in the Pacific Arctic sediments and Kara Sea decreases; during the CW situation, the SIA in the Laptev Sea and Kara Sea decreases; during the CC situation, the SIA in the Kara Sea, Laptev Sea and southern Beaufort Sea increases.

The characteristics and formation conditions of eddy meridional heat transport (MHT) in the eastern equatorial Pacific are studied using the results of eddy-resolving numerical modeling as compared with observational and reanalysis data. Calculations of the eddy MHT convergence at the equator are performed and realistic results in the analyzed region except for its easternmost part are obtained. The interannual variability and velocity of propagation of tropical instability waves are estimated. The errors of the time-averaged model solution are analyzed, and the assumptions on the mechanisms of their occurrence are made.

Climate models show that most of the anthropogenic heat resulting from increased atmospheric CO₂ enters the Southern Ocean near 60°S and is stored around 45°S. This heat is transported to the ocean interior by the meridional overturning circulation (MOC) with wind changes playing an important role in the process. To isolate and quantify the latter effect, we apply an overriding technique to a climate model and decompose the total ocean response to CO₂ increase into two major components: one due to wind changes and the other due to direct CO₂ effect. We find that the poleward-intensified zonal surface winds tend to shift and strengthen the ocean Deacon cell and hence the residual MOC, leading to anomalous divergence of ocean meridional heat transport around 60°S coupled to a surface heat flux increase. In contrast, at 45°S we see anomalous convergence of ocean heat transport and heat loss at the surface. As a result, the wind-induced ocean heat storage (OHS) peaks at 46°S at a rate of 0.07 ZJ yr−1 (° lat)−1 (1 ZJ = 1021 J), contributing 20% to the total OHS maximum. The direct CO₂ effect, on the other hand, very slightly alters the residual MOC but primarily warms the ocean. It induces a small but nonnegligible change in eddy heat transport and causes OHS to peak at 42°S at a rate of 0.30 ZJ yr−1 (° lat)−1, accounting for 80% of the OHS maximum. We also find that the eddy-induced MOC weakens, primarily caused by a buoyancy flux change as a result of the direct CO₂ effect, and does not compensate the intensified Deacon cell.

Despite the recently recomputed time series of the Atlantic Meridional Overturning Circulation (AMOC) suggesting greater stability than previously recognized, AMOC retains the potential to influence regional climate fluctuations across multiple timescales through its considerable variability. The sloshing component of AMOC has been identified as a significant mode of short‐term AMOC variability. While it does not cause permanent changes to the AMOC, this sloshing mode can reshape the ocean's thermal state by redistributing warmer water in the upper layers and altering both basin‐wide and regional ocean heat content (OHC). This study examines how the sloshing AMOC component regulates meridional heat transport and OHC across different timescales in the North Atlantic. It offers insights into the mechanism through which the AMOC could affect regional climate variability, even if it maintains a stable strength in the foreseeable future. Plain Language Summary The Atlantic Meridional Overturning Circulation (AMOC) plays a pivotal role in shaping global and regional climates through its substantial northward heat transport. While a slowdown of the AMOC could have significant impacts on the global climate, 20 years of continuous monitoring have revealed that the AMOC might be more stable than previously believed. Despite this stability, the large‐scale variations in AMOC can still impact regional climate fluctuations ranging from seasonal to decadal periods. This study investigates the dominant processes driving AMOC variability across timescales and examines how they influence tropical and subtropical Atlantic climates by modulating heat conditions in the upper ocean. These findings are important for understanding whether and how the AMOC can affect regional climates, even if its overall state remains stable in the future. Key Points Sloshing component is crucial in shaping the impact of Atlantic overturning on upper‐ocean heat content variability A strengthening overturning circulation may reduce upper‐ocean heat content in eastern boundary of the North Atlantic Sloshing processes drive much of the North Atlantic overturning variability up to decadal scale, dominant in the tropics and subtropics

Meridional heat transport (MHT) is analyzed in ensembles of coupled climate models simulating climate states ranging from the Last Glacial Maximum (LGM) to quadrupled CO₂. MHT is partitioned here into atmospheric (AHT) and implied oceanic (OHT) heat transports. In turn, AHT is partitioned into dry and moist energy transport by the meridional overturning circulation (MOC), transient eddy energy transport (TE), and stationary eddy energy transport (SE) using only monthly averaged model output that is typically archived. In all climate models examined, the maximum total MHT (AHT 1 OHT) is nearly climate-state invariant, except for a modest (4%, 0.3 PW) enhancement of MHT in the Northern Hemisphere (NH) during the LGM. However, the partitioning of MHT depends markedly on the climate state, and the changes in partitioning differ considerably among different climate models. In response to CO₂ quadrupling, poleward implied OHT decreases, while AHT increases by a nearly compensating amount. The increase in annual mean AHT is a smooth function of latitude but is due to a spatially inhomogeneous blend of changes in SE and TE that vary by season. During the LGM, the increase in wintertime SE transport in the NH midlatitudes exceeds the decrease in TE resulting in enhanced total AHT. Total AHT changes in the Southern Hemisphere (SH) are not significant. These results suggest that the net top-of-atmosphere radiative constraints on total MHT are relatively invariant to climate forcing due to nearly compensating changes in absorbed solar radiation and outgoing longwave radiation.However, the partitioning of MHT depends on detailed regional and seasonal factors.

The Kuroshio and Gulf Stream, the subtropical western boundary currents of the North Pacific and North Atlantic, play important roles in meridional heat transport and ocean–atmosphere interaction processes. Using a multimodel ensemble of future projections, we show that a warmer climate intensifies the upper-layer Kuroshio, in contrast to the previously documented slowdown of the Gulf Stream. Our ocean general circulation model experiments show that the sea surface warming, not the wind change, is the dominant forcing that causes the upper-layer Kuroshio to intensify in a warming climate. Forced by the sea surface warming, ocean subduction and advection processes result in a stronger warming to the east of the Kuroshio than to the west, which increases the isopycnal slope across the Kuroshio, and hence intensifies the Kuroshio. In the North Atlantic, the Gulf Stream slows down as part of the Atlantic meridional overturning circulation (AMOC) response to surface salinity decrease in the high latitudes under global warming. The distinct responses of the Gulf Stream and Kuroshio to climate warming are accompanied by different regional patterns of sea level rise. While the sea level rise accelerates along the northeastern U.S. coast as the AMOC weakens, it remains close to the global mean rate along the East Asian coast as the intensifying Kuroshio is associated with the enhanced sea level rise offshore in the North Pacific subtropical gyre.

The Atlantic Meridional Overturning Circulation (AMOC) plays a critical role in the global climate system through the redistribution of heat, freshwater and carbon. At 26.5°N, the meridional heat transport has traditionally been partitioned geometrically into vertical and horizontal circulation cells; however, attributing these components to the AMOC and Subtropical Gyre (STG) flow structures remains widely debated. Using water parcel trajectories evaluated within an eddy‐rich ocean hindcast, we present the first Lagrangian decomposition of the meridional heat transport at 26.5°N. We find that water parcels recirculating within the STG account for 37% (0.36 PW) of the total heat transport across 26.5°N, more than twice that of the classical horizontal gyre component (15%). Our findings indicate that STG heat transport cannot be meaningfully distinguished from that of the basin‐scale overturning since water parcels cooled within the gyre subsequently feed the northward, subsurface limb of the AMOC. Plain Language Summary The Atlantic Meridional Overturning Circulation transports heat northward by converting warm, surface waters into cold waters returning at depth. In the subtropical North Atlantic, the heat transported by the overturning circulation has traditionally been separated from the wind‐driven gyre circulation by assuming that the gyre flows horizontally along constant depth levels. By tracing the pathways of virtual water parcels in a high‐resolution ocean model, we show that the heat transported by the subtropical gyre is larger than traditional estimates because water parcels spiral downwards across depth levels. Our results indicate that the subtropical gyre should not be considered separate from the overturning circulation, since the water parcels cooled within the gyre subsequently flow northwards to form cold, dense waters in the subpolar North Atlantic. Key Points Water parcels recirculating in the subtropical gyre account for 37% of the total heat transport at 26.5°N in an eddy‐rich ocean hindcast The heat transport of the subtropical gyre is associated with shallow vertical overturning rather than the horizontal circulation at 26.5°N Both horizontal and vertical circulation cells are fundamental components of the Atlantic Meridional Overturning Circulation

Previous studies emphasized a significant linkage between Atlantic Meridional Overturning Circulation multidecadal variability (AMOC‐MV) and subsurface temperature in the Tropical North Atlantic (TNA). However, as AMOC‐MV weakens under global warming, it remains unclear whether this linkage persists. Here, we use the Community Earth System Model version 1 Large Ensemble to demonstrate that the connection remains robust under global warming. We highlight that the TNA subsurface response and its changes are primarily confined to the western boundary, regulated by variations in the AMOC‐MV‐related North Brazil Current. In the TNA western boundary, a subsurface temperature dome, which dominates the subsurface thermal response by strengthening meridional heat transport, shifts southward due to changes in mean‐state AMOC and local winds. This southward shift extends the subsurface temperature response equatorward, amplifying the mean TNA response. The sustained linkage supports using TNA subsurface temperature as an indicator for future AMOC‐MV monitoring.

Continuous estimates of the oceanic meridional heat transport in the Atlantic are derived from the Rapid Climate Change–Meridional Overturning Circulation (MOC) and Heatflux Array (RAPID–MOCHA)observing system deployed along 26.5°N, for the period from April 2004 to October 2007. The basinwide meridional heat transport (MHT) is derived by combining temperature transports (relative to a common reference) from 1) the Gulf Stream in the Straits of Florida; 2) the western boundary region offshore of Abaco, Bahamas; 3) the Ekman layer [derived from Quick Scatterometer (QuikSCAT) wind stresses]; and 4) the interior ocean monitored by “endpoint” dynamic height moorings. The interior eddy heat transport arising from spatial covariance of the velocity and temperature fields is estimated independently from repeat hydrographic and expendable bathythermograph (XBT) sections and can also be approximated by the array. The results for the 3.5 yr of data thus far available show a mean MHT of 1.33 ± 0.40 PW for 10-day-averaged estimates, on which time scale a basinwide mass balance can be reasonably assumed. The associated MOC strength and variability is 18.5 ± 4.9 Sv (1 Sv ≡ 10⁶ m³ s−1). The continuous heat transport estimates range from a minimum of 0.2 to a maximum of 2.5 PW, with approximately half of the variance caused by Ekman transport changes and half caused by changes in the geostrophic circulation. The data suggest a seasonal cycle of the MHT with a maximum in summer (July–September) and minimum in late winter (March–April), with an annual range of 0.6 PW. A breakdown of the MHT into “overturning” and “gyre” components shows that the overturning component carries 88% of the total heat transport. The overall uncertainty of the annual mean MHT for the 3.5-yr record is 0.14 PW or about 10% of the mean value.

The recovery of long-term climate proxy records with seasonal resolution is rare because of natural smoothing processes, discontinuities, and limitations in measurement resolution. Yet insolation forcing, a primary driver of multi-millennial-scale climate change, acts through seasonal variations with direct impacts on seasonal climate. Whether the sensitivity of seasonal climate to insolation matches theoretical predictions has not been assessed over long timescales. Here, we analyze a continuous record of water-isotope ratios from the West Antarctic Ice Sheet (WAIS) Divide ice core to reveal summer and winter temperature changes through the last 11,000 years. Summer temperatures in West Antarctica increased through the early-to-mid Holocene, reached a peak at 4.1 ka, and then decreased to the present. Climate model simulations show that these variations primarily reflect changes in maximum summer insolation, confirming the general connection between seasonal insolation and warming, and demonstrating the importance of insolation intensity rather than seasonally integrated insolation or season duration. Winter temperatures varied less overall, consistent with predictions from insolation forcing, but also fluctuated in the early Holocene, likely owing to changes in meridional heat transport. The magnitudes of summer and winter temperature changes constrain the lowering of the WAIS surface since the early Holocene to less than 162 m, and most likely less than 58 m, consistent with geological constraints elsewhere in West Antarctica.