Pacific water entering the Arctic Ocean through Bering Strait carries a distinctive nutrient signature - nitrate depleted by sedimentary denitrification on the Bering and Chukchi shelves, leaving excess phosphate and silicate - and is exported, after transit through the Canadian Arctic Archipelago and Baffin Bay, through Davis Strait into the Labrador Current system and along the northwest Atlantic margin, where nutrient-ratio and nitrate-isotope tracers track it as a recognized control on biological productivity. The unresolved problem is to quantify this exchange: the fluxes of Pacific-derived macronutrients (nitrate, phosphate, silicate) and dissolved micronutrients (iron, manganese, cobalt, nickel, copper, zinc) delivered through the Arctic gateways to the North Atlantic; the fraction of that supply which reaches and fuels productivity on the northwest Atlantic shelf rather than being diluted into the interior ocean; the net effect on Arctic-Atlantic basin nutrient balances, including excess-phosphate export and its implications for North Atlantic nitrogen fixation; and the sensitivity of this supply to the documented increase, warming, and freshening of the Pacific inflow and to changing sea-ice and shelf conditions in the Arctic. Recent work has advanced the individual ingredients, but no study closes the integrated budget or productivity attribution.

Background

The Arctic Ocean is the intermediary through which Pacific and Atlantic waters exchange properties. Pacific water enters through the narrow, shallow Bering Strait and flows north across the highly productive Bering and Chukchi shelves, where intense seasonal phytoplankton blooms export organic matter to the sediments. There, sedimentary denitrification - the bacterial reduction of nitrate to nitrogen gas in low-oxygen sediments - removes fixed nitrogen from the water column without a matching removal of phosphate or silicate. The resulting Pacific-origin water therefore carries a characteristic signature: a deficit of nitrate relative to phosphate, usually summarized as a negative value of the tracer N* (nitrate minus 16 times phosphate, a standard index of nitrogen loss or gain), together with excess silicate and phosphate. This water forms the cold, salty halocline layer of the Canada Basin (a layer of rapid salinity change that insulates sea ice from Atlantic heat) and is then exported toward the Atlantic along two distinct limbs. The western limb flows through the channels of the Canadian Arctic Archipelago (CAA - the islands and straits north of mainland Canada, including Lancaster Sound, Jones Sound, and Nares Strait) into Baffin Bay and through Davis Strait, feeding the Labrador Current and the northwest Atlantic continental shelf. The eastern limb exits through Fram Strait and the Barents Sea Opening into the Nordic Seas. Nutrient-ratio tracing and, more recently, the nitrogen and oxygen isotope composition of nitrate (delta-15N and delta-18O, which record the sources and cycling history of the nitrate pool) allow the fraction of Pacific water, abbreviated fPW, to be quantified along these pathways; Sherwood et al. (2021, doi:10.5194/bg-18-4491-2021) showed that isotopically distinct Pacific nitrate (delta-15N about 8.3 per mil) mixes conservatively with Atlantic nitrate (about 4.8 per mil) from Baffin Bay to the Labrador shelf, with fPW exceeding 0.6 in the halocline core waters, providing a framework for interpreting delta-15N records in modern and paleo archives along the margin. In transit, the CAA also acts as a trace-metal source: sediment resuspension and sediment-water interactions enrich the transiting Pacific-derived waters in iron (Colombo et al., 2021, doi:10.1029/2021GB007058), so the exported water carries both a macronutrient and a micronutrient signature of its Pacific and shelf history. The NW Atlantic continental shelf (Scotian Shelf, Laurentian Channel, Grand Banks) is a productive system whose subsurface nutrient supply is delivered by slope-water advection, winter mixing, and along-shelf transport; optimum multiparameter analysis (a least-squares decomposition of a water sample into defined source water types) shows North Atlantic Central Water and Cold Intermediate Water dominating the Scotian Shelf supply (Lehmann et al., 2025, doi:10.1029/2024GB008409), while decadal nutrient variability there tracks the relative influence of the Gulf Stream and Labrador Current (Lehmann et al., 2023, doi:10.1029/2023JC019928), and Labrador Sea interior productivity is tied to winter deep convection (Tesdal et al., 2022, doi:10.1016/j.pocean.2022.102848). How much of the shelf's nutrient supply and productivity is specifically attributable to the Pacific-derived component has not been quantified. For micronutrients (dissolved trace metals that limit or co-limit phytoplankton growth, principally Fe, Mn, Co, Ni, Cu, Zn), the GEOTRACES program (an international survey of trace elements and isotopes in the ocean) produced the first gateway-scale flux estimates: combining observations at the Barents Sea Opening, Fram Strait, and Davis Strait, Krisch et al. (2022, doi:10.1029/2021GB007191) estimated a net southward Arctic-to-Atlantic flux of dissolved iron of 2.7 plus or minus 2.4 gigagrams per year (with comparable relative uncertainties for other metals), concluding from the paucity of gateway trace-element data that how Arctic-Atlantic exchange shapes micronutrient availability in the two basins remains unclear; the Nordic Seas, fed by the eastern limb, show Arctic-inflow waters depleted in nitrate but enriched in silicate and trace metals, with future changes in Arctic export expected to alter regional nutrient stoichiometry (Ruan et al., 2026, doi:10.1029/2025GB008954). The forward-looking dimension is anchored in the Bering Strait mooring record: the Pacific inflow increased at about 0.01 sverdrups per year (1 sverdrup = 1 million cubic meters per second) over 1990-2015 (Woodgate, 2018, doi:10.1016/j.pocean.2017.12.007) and warmed and freshened over 1990-2019 (Woodgate and Peralta-Ferriz, 2021, doi:10.1029/2021GL092528), mooring-based nutrient parameterizations yield annually averaged Bering Strait fluxes of 16 plus or minus 6, 1.5 plus or minus 0.5, and 30 plus or minus 11 kilomoles per second of nitrate, phosphate, and silicate, about 50 percent higher than earlier estimates (Hennon et al., 2022, doi:10.1029/2022GL098908), and the first overwinter in-situ nitrate time series gives a year-round Pacific-to-Arctic nitrate flux of 10.4 plus or minus 1.6 kilomoles per second and suggests a multi-decadal increase, while showing that the salinity-nutrient relationships used to infer wintertime concentrations break down (Woodgate et al., 2025, doi:10.1029/2025GL117737). The ecological motivation is longstanding: remote climate forcing, mediated in part by Arctic-origin waters, has been proposed to drive decadal-scale regime shifts in northwest Atlantic shelf ecosystems (Greene et al., 2013, doi:10.4319/lo.2013.58.3.0803), and the Pacific carbon (dissolved inorganic carbon) export through the CAA has been estimated directly (Shadwick et al., 2011, doi:10.1016/j.csr.2011.01.014). What is missing is the integrated, observationally constrained quantification linking the changing Pacific inflow, the modifying Arctic transit, the gateway exports, and the nutrient supply and productivity of the northwest Atlantic.

Problem Statement

Determine, quantitatively and with defensible uncertainties, how the flow of Pacific water through the Arctic Ocean into the North Atlantic controls nutrient balances between the two basins and fuels biological productivity on the northwest Atlantic shelf, and how this supply will change as Pacific inflow and Arctic conditions evolve. Concretely: (1) the fluxes of Pacific-derived macronutrients (nitrate, phosphate, silicate) and dissolved micronutrients (iron, manganese, cobalt, nickel, copper, zinc) delivered through the Arctic gateways to the North Atlantic - principally the western pathway (Bering Strait, Canadian Arctic Archipelago channels, Davis Strait) that feeds the Labrador Current and the northwest Atlantic margin, together with the eastern Fram Strait / Barents Sea Opening limb of Arctic-Atlantic micronutrient exchange - including the modifications these waters undergo in transit (sedimentary denitrification, shelf trace-metal inputs, mixing with Atlantic water); (2) the fraction of this supply that reaches and supports biological productivity on the northwest Atlantic continental shelf, as opposed to being diluted or exported into the interior ocean - that is, the attribution of shelf nutrient supply and new production (the part of phytoplankton production supported by externally supplied nutrients rather than locally regenerated ones) among Pacific-derived, Atlantic slope-water, and locally regenerated sources; (3) the net effect of this exchange on Arctic-Atlantic basin-scale nutrient balances, including the export of phosphate in excess of nitrate and its consequences for nitrogen fixation in the North Atlantic; and (4) the sensitivity of this supply to the documented increase, warming, and freshening of the Pacific inflow through Bering Strait and to changing Arctic conditions such as sea-ice retreat, Nares Strait ice-arch stability (the seasonal sea-ice jams that block drift through the strait), and altered shelf processes.

References

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