Introduction
The North Atlantic Current (NAC), often termed the North Atlantic Drift or North Atlantic Sea Movement, is the northeastward continuation of the Gulf Stream and functions as a major warm western‑boundary current in the North Atlantic. As the initial poleward branch of the North Atlantic Subpolar Gyre, the NAC conveys western‑boundary flow from subtropical latitudes into the subpolar circulation, forming an integral element of the basin‑scale gyre system. Geographically it transports warm water northeastward across the basin, creating a zonal‑to‑meridional linkage between subtropical and higher‑latitude subpolar waters. Dynamically, the NAC carries substantial heat, momentum and water mass, thereby shaping regional sea‑surface conditions and the broader structure of North Atlantic ocean circulation.
Characteristics of the North Atlantic Current
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The North Atlantic Current (NAC) originates where the Gulf Stream turns poleward at the Southeast Newfoundland Rise, a submarine ridge extending southeast from the Grand Banks of Newfoundland. From there it flows northward east of the Grand Banks between roughly 40°N and 51°N before turning sharply eastward to cross the Atlantic basin.
In magnitude the NAC is the principal conveyor of warm tropical waters to high northern latitudes among ocean boundary currents, with transport exceeding 40 Sv in its southern reaches and diminishing to about 20 Sv as it traverses the Mid‑Atlantic Ridge. Along the North American continental margin the flow attains peak speeds on the order of 2 knots (≈1.0 m/s), reflecting its strong poleward momentum adjacent to the continental slope.
Seafloor topography exerts a strong control on the NAC’s trajectory, producing pronounced meandering; unlike Gulf Stream meanders, these deflections tend to be persistent and seldom pinch off into isolated eddies. At about 50°W, near the “tail” of the Grand Banks, a bifurcation occurs in which cooler portions of the Gulf Stream turn north while the Azores Current branches south of the Azores. Downstream of this bifurcation the NAC turns northeastward, passing east of the Flemish Cap (≈47°N, 45°W).
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Approaching the Mid‑Atlantic Ridge the current broadens and becomes more diffuse, then splits into a colder northeastern branch and a warmer eastern branch. Much of the subtropical Gulf Stream contribution is routed southward as the warmer branch turns toward lower latitudes, so that the central North Atlantic increasingly receives subpolar waters. Part of this subpolar influence derives from a recirculated input of Labrador Current water incorporated into the NAC circulation near ~45°N, which augments its cooler component.
West of Europe the NAC divides into a southeastward limb that evolves into the Canary Current off northwest Africa and a northward limb that continues along northwestern Europe; regional offshoots include the Irminger and Norwegian Currents. Dynamically, the NAC functions both as the wind‑driven eastward extension of the Gulf Stream and as an element of the global thermohaline circulation, conveying warm, saline waters eastward and northward toward the Arctic.
Climatologically, the NAC (together with the Gulf Stream) contributes to poleward heat transport and thereby influences high‑latitude sea‑ice conditions, but comparative studies indicate that atmospheric circulation patterns — particularly prevailing winds — are the dominant control on the winter climate contrast between North America and Europe. Nonetheless, the NAC’s heat flux remains important in preventing sea‑ice formation at very high latitudes.
Climate change
Model projections under an intermediate‑forcing scenario depict a sequence of increasingly severe states in the North Atlantic circulation, ranging from widespread warming through the 21st century to potential failure of the subpolar gyre and, in more extreme outcomes, collapse of the entire Atlantic Meridional Overturning Circulation (AMOC). Several models identify deep convection in the Labrador–Irminger Seas as a critical driver: sustained shutdown of this deepwater formation undermines the overturning that maintains the North Atlantic subpolar gyre, and in some model realizations can precipitate basin‑scale collapse.
Observations present a mixed picture. Labrador Sea outflow showed no decline between 1997 and 2009, and deep convection intensified beginning in 2012, peaking in 2016 and remaining relatively strong through 2022; this recovery is associated with increased marine primary production. Nevertheless, a 150‑year record indicates that even the recent strengthening is weak compared with the long‑term baseline, underlining the anomalous character of contemporary variability.
Model experiments treat collapse of Labrador–Irminger convection and subsequent subpolar gyre failure as a climatic tipping point: once initiated, recovery is unlikely on human timescales even if temperatures are subsequently reduced, implying marked hysteresis and long‑lived reorganization of ocean circulation. A synthesis of studies places the modal threshold for triggering the convection collapse at roughly 1.8 °C of global warming, with inter‑model estimates spanning about 1.1–3.8 °C; when triggered, collapse most commonly unfolds within about a decade, although plausible durations range from approximately 5 to 50 years.
The climatic consequences would be regionally large despite modest global mean effects. Model syntheses estimate global mean temperature could fall by up to ~0.5 °C, while parts of the North Atlantic and adjacent lands could cool by around 3 °C, with concomitant shifts in regional precipitation that would affect ecosystems and human systems (agriculture, water resources, energy and other sectors). Historical inference further suggests that past disruptions of the subpolar gyre may have contributed to major climatic episodes such as the Little Ice Age, indicating the system’s capacity to drive substantial climate change.
Observed sea‑surface temperature patterns—subpolar cooling, subtropical warming and cool anomalies in the tropics—have increased the meridional SST gradient. This spatial reorganization is not fully captured by the conventional Atlantic Multidecadal Oscillation (AMO) index, revealing limitations of that index for diagnosing contemporary basin‑scale changes.
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Quantifying risk remains model‑dependent. A CMIP6 analysis found subpolar gyre collapse in 4 of 35 models; only 11 of those 35 models reproduce the North Atlantic Current with high fidelity, and all four collapse‑producing models lie within that subset. Using this evidence, the estimated likelihood of an abrupt cooling event over Europe from subpolar gyre collapse was revised to about 36.4%, lower than earlier estimates (≈45.5%) based on previous model generations. Recent 2023 studies have emphasized elevated near‑term risk under high emissions, with some projections placing AMOC or subpolar gyre collapse by mid‑century contingent on continued forcing.
Because many climate models struggle to represent the North Atlantic Current and subpolar gyre dynamics accurately, projections of AMOC/subpolar gyre stability, collapse thresholds and regional impacts carry substantial uncertainty. Improved simulation of the North Atlantic Current appears essential for robust estimates of collapse probability and the magnitude and pattern of associated climate impacts.