The Bering Strait throughflow — roughly 0.8 Sv (1 Sv = 1 million cubic meters per second) of relatively fresh Pacific water entering the Arctic Ocean, carrying a net freshwater transport of about 80 mSv — is the only oceanic link between the Pacific and the Arctic–North Atlantic system. Model studies since the 1990s agree that it modifies the Atlantic Meridional Overturning Circulation (AMOC), so the open problem is not whether the strait matters but how strongly, in which direction, and through which mechanisms, once model realism and forcing realism are imposed. A 2026 Earth-system-model-of-intermediate-complexity study showed that a constructed closure of the strait can extend the AMOC's safe carbon budget by up to 500 PgC, but only if applied while the AMOC is still strong, and all its thresholds are specific to a 5-degree grid with a parameterized strait under idealized forcing. An idealized two-basin study indicates that the throughflow can also generate North Atlantic multidecadal variability through a western-boundary freshwater-tongue instability, unconfirmed in realistic models, and two decades of observations constrain the inflow trend but not its downstream Atlantic effect. The open problem is to quantify how changes in the Pacific inflow — both the observed multidecadal increase and any engineered closure — propagate through the Arctic to North Atlantic circulation.

Background

The Bering Strait (about 85 km wide, sill depth about 50 m) is the only oceanic passage between the Pacific and the Arctic oceans. About 0.8 Sv (1 Sv = 10^6 m^3/s) of relatively fresh (salinity near 32.5 g/kg) northward-flowing Pacific water enters the Arctic Ocean through it, corresponding to a net freshwater transport of roughly 80 mSv. The Arctic Mediterranean — the collective name for the Arctic Ocean, the Nordic Seas, and their adjacent shelf seas — receives this Pacific inflow plus a larger Atlantic inflow across the Greenland–Scotland Ridge, and exports modified water both through the deep overflow branches of that ridge (the dense water that feeds the lower limb of the Atlantic Meridional Overturning Circulation) and through the shallow Canadian Arctic Archipelago, where most of the Pacific-derived water leaves. The Atlantic Meridional Overturning Circulation (AMOC) is the global-scale overturning in which warm, salty Atlantic surface water flows northward, cools and densifies in the Nordic and Labrador Seas, sinks, and returns south as North Atlantic Deep Water; it is a major tipping element of the climate system, meaning a subsystem that can undergo self-amplifying, potentially irreversible transitions when forced past a threshold. A standard probe of AMOC stability is the 'hosing' experiment, in which a prescribed freshwater flux is added to the North Atlantic; the 'safe carbon budget' of the AMOC is the cumulative CO2 emission beyond which the circulation collapses.

That the Bering Strait throughflow influences the North Atlantic at all is established model knowledge, not an open question. Shaffer and Bendtsen (1994) and Goosse et al. (1997) first showed in ocean and ice–ocean models that the throughflow freshens the North Atlantic and weakens deep water formation. Hu and Meehl (2005) and Hu et al. (2012) demonstrated with the CCSM coupled model that the throughflow acts as a stabilizing feedback on an active AMOC: when the AMOC weakens, Arctic sea level rises, the throughflow slows or reverses, and freshwater is diverted to the Pacific — so an open strait narrows the hysteresis loop (the multiple-equilibrium loop between an active and a collapsed circulation obtained by varying and then removing forcing) of the 'ocean conveyor belt'. Hu et al. (2015) found that a Bering Strait closure strengthens the present-day AMOC by about 2.5 Sv but that the sign and magnitude of the effect depend on the background climate. Hu et al. (2023) then identified a dichotomy: the open strait's stabilizing effect under freshwater hosing is not as pronounced under CO2-driven warming, because heating rather than freshening then dominates the surface buoyancy change.

Three recent results define the currently open part of the question. First, Soons and Dijkstra (2026), using the Earth-system model of intermediate complexity CLIMBER-X (an emulator-class coupled model on a 5∘×5∘5^\circ\times5^\circ grid in which the strait is represented as a baroclinic tracer exchange rather than a resolved barotropic current), showed that a constructed closure of the strait can prevent a CO2-forced AMOC tipping and extend the safe carbon budget by up to 500 PgC, provided the AMOC has weakened by less than (6.1±0.5)%(6.1\pm0.5)\% from pre-industrial at closure time; they themselves stress that all thresholds are model-specific, that the hosing magnitudes (up to 0.15 Sv) and the 1%-per-year CO2 increase are unrealistic, and that closure experiments in more detailed models with more valid Arctic freshwater transports under realistic forcing have not yet been carried out. Second, Yang and Cessi (2023), in an idealized two-basin configuration with a shallow northern strait, found that the Bering-Strait freshwater transport forms a tongue along the western boundary of the Atlantic-like basin that sharpens the horizontal density gradient until the boundary region becomes unstable to large-scale baroclinic anomalies — oscillations growing by extracting energy from the lateral density contrast — thereby generating multidecadal (20–70 year) variability like that observed in North Atlantic sea-surface-temperature records; they frame this only as a potential role, demonstrated in an idealized model. Third, the observational anchor: Østerhus et al. (2019) assembled a consistent volume budget for the Arctic Mediterranean from two decades of gateway measurements and found that only the Pacific inflow through the Bering Strait shows a statistically significant (positive) transport trend — the inflow roughly increased over 1990–2015 (Woodgate 2018) — while the downstream branches remain incompletely constrained, and Pacific water, exiting mostly through the Canadian Arctic Archipelago, is judged unlikely to contribute appreciably to overflow formation, though it may affect water transformation in the Labrador Sea.

Beyond the circulation response, changes in North Atlantic sea-surface temperature, sea ice, and convection also bear on the physical habitat conditions underlying North Atlantic ecosystems — a downstream consequence that the closure-intervention literature explicitly leaves unassessed.

Problem Statement

Overarching objective: establish quantitatively, and with a defensible causal account, how changes in Bering Strait Pacific-water inflow propagate through the Arctic Ocean to North Atlantic circulation — a question whose current evidence base rests on coarse intermediate-complexity models, idealized two-basin configurations, and incomplete gateway observations. The linked components of this one objective are: (1) the response of the mean AMOC strength — defined as the maximum of the Atlantic meridional overturning streamfunction, with the response measured as the change in its multi-decadal mean relative to the pre-industrial control — and of its tipping behavior — critical freshwater forcing, critical cumulative carbon emission, and the delay window within which an intervention remains beneficial — to inflow changes (both the observed multidecadal increase and a constructed closure), under realistic forcing pathways (SSP-type emission scenarios and observationally bounded freshwater-flux magnitudes and rates), including how the sign and magnitude of the response depend on forcing type (freshwater versus CO2-driven warming) and on the AMOC state at the time of the change, thereby testing the thresholds of Soons & Dijkstra (2026) outside their 5∘×5∘5^\circ\times5^\circ tracer-exchange model; (2) the response of deep convection in the Labrador and Nordic Seas, the formation regions of the AMOC's lower limb; (3) the role of the inflow in generating and sustaining Atlantic multidecadal variability on 20-70 year time scales, in particular whether the western-boundary freshwater-tongue/baroclinic-instability mechanism of Yang & Cessi (2023) operates in realistic bathymetry, sea-ice, and air-sea-coupling conditions or is suppressed by them; and (4) observational constraints linking the measured Bering Strait transport variability and trend to downstream North Atlantic quantities, closing the gap between the well-observed inflow and the under-constrained export and convection branches identified by Østerhus et al. (2019). The four circulation components above are independent, self-contained sub-questions of one objective — a single Pacific–Arctic–Atlantic gateway control on North Atlantic circulation. Each component may be answered on its own, and a rigorous resolution of any one component resolves its corresponding sub-question and stands as a result in its own right; the overarching objective is the integration of the four into one causal account of how the inflow changes propagate through the Arctic to North Atlantic circulation.

References

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