The Alaska Current is a broad, northward-flowing ocean current that carries relatively warm water along the coast of British Columbia and southeastern Alaska before curving westward across the northern Gulf of Alaska. It forms when the North Pacific Current splits as it approaches the west coast of North America, sending one branch north toward Alaska and another south as the California Current.1Progress in Oceanography. Variability of the North Pacific Current and its bifurcation As the eastern boundary current of the subarctic gyre, it shapes everything from regional weather patterns to salmon migration routes and the productivity of one of the world’s richest marine ecosystems.
Where the Alaska Current Comes From
The Alaska Current does not originate on its own. It exists because of a fork in a much larger flow. The North Pacific Current is a broad, slow, eastward-moving band of water that spans the open Pacific roughly between 40°N and 50°N. As this current nears the coast of North America, it divides. The portion that turns south becomes the California Current, feeding the eastern boundary of the subtropical gyre. The portion that turns north becomes the Alaska Current, feeding the eastern boundary of the subarctic gyre.2Progress in Oceanography. Variability of the North Pacific Current and its bifurcation The latitude where this split happens is not fixed. It shifts north or south from year to year depending on large-scale wind patterns, which means the relative strength of the Alaska Current and the California Current also fluctuates.
Once the split occurs, the Alaska Current flows northwestward along the outer continental shelf of British Columbia and southeastern Alaska. It is not a tight, well-defined jet at this stage. Instead, it is broad, relatively slow, and riddled with meanders, behaving like a typical eastern boundary current.3Continental Shelf Research. Meteorology and oceanography of the Northern Gulf of Alaska If you picture the California Current as its mirror image on the other side of the bifurcation, the comparison holds: both are wide, sluggish, and eddy-prone compared with the fast western boundary currents like the Kuroshio or the Gulf Stream.
The Path Around the Gulf of Alaska
The Alaska Current sweeps counterclockwise around the Gulf of Alaska. After flowing northwestward along the coast, it reaches the head of the gulf and bends southwestward, following the curve of the continental slope. At this point, its character begins to change. The broad, diffuse flow compresses as it follows the narrowing shelf along the Alaska Peninsula. By the time it passes Kodiak Island, near 155°W, it has become a much more concentrated current. Oceanographers give this concentrated downstream continuation a different name: the Alaskan Stream.4Continental Shelf Research. Meteorology and oceanography of the Northern Gulf of Alaska
The Alaskan Stream is a fast, narrow, deep western boundary current, roughly the subarctic Pacific’s equivalent of the Gulf Stream in the Atlantic. Off Kodiak Island it is about 60 km wide, extends deeper than 3,000 meters, and carries an annual mean transport of roughly 20 Sverdrups, meaning about 20 million cubic meters of water per second.5Oceanography. Progress of Fisheries-Oceanography Coordinated Investigations in the Gulf of Alaska and Aleutian Passes The original Alaska Current, broad and slow, and the Alaskan Stream, narrow and fast, are really two phases of the same circulation loop. The transition between them is gradual, not a sharp boundary, but the difference in speed and width is pronounced enough that oceanographers treat them as distinct features.
The Alaskan Stream continues southwestward along the Alaska Peninsula and the Aleutian Islands. Some of its water leaks through passes in the Aleutian chain into the Bering Sea, while the rest continues westward. This leakage has major consequences for the Bering Sea’s temperature and productivity, a connection explored further below.
The Alaska Coastal Current Is a Separate Flow
People often conflate the Alaska Current with the Alaska Coastal Current, but they are different features occupying different parts of the water column and shelf. The Alaska Coastal Current (ACC) is a narrow, fast, buoyancy-driven flow that hugs the inner continental shelf, typically within about 20 to 40 km of shore. It is powered largely by the massive volume of freshwater runoff from coastal Alaska’s glaciers, rivers, and rain. This freshwater is lighter than the saltier offshore water, so it rides along the coast as a distinct surface layer, steered rightward by Earth’s rotation.
The ACC’s transport is much smaller than the offshore Alaska Current’s. Measurements from the mid-1980s put its mean volume transport at roughly 0.85 million cubic meters per second, with a seasonal peak in winter driven by strong storm winds and a secondary peak in autumn as freshwater from summer and fall rains accumulated on the shelf.6NOAA PMEL. Volume transport in the Alaska Coastal Current Freshwater transport in the ACC averages about 880 cubic kilometers per year, and the flushing time for the freshwater over the roughly 1,500-km stretch of coast is about a year or less.7Deep Sea Research Part II. Freshwater variability and predictability in the Alaska Coastal Current
Why does the distinction matter? Because many of the ecological and climate stories in the Gulf of Alaska depend on which current you are talking about. The offshore Alaska Current and its eddies transport nutrients and iron into the open ocean. The nearshore ACC carries freshwater and sediment along the coast, creates sharp fronts where its low-salinity water meets saltier offshore water, and aggregates prey for marine mammals. Lumping them together misses these distinct roles.
What Drives the Seasonal Swings
The entire Gulf of Alaska circulation system pulses with the seasons, and the main driver is the Aleutian Low, a semi-permanent low-pressure system that dominates the North Pacific atmosphere in winter. When the Aleutian Low intensifies and shifts position, it changes the wind field over the gulf, which in turn alters the strength and direction of both the Alaska Current and the ACC.8Journal of Biogeography. Southeast Alaska: oceanographic habitats and linkages
In winter, strong cyclonic (counterclockwise) winds spin up the subarctic gyre, strengthening the Alaska Current and pushing more water along the coast. Coastal downwelling intensifies, pressing warm, nutrient-poor surface water against the shelf and suppressing upwelling. At the same time, powerful storms deliver enormous rainfall and drive the ACC’s peak winter transport. In summer, the Aleutian Low weakens and retreats. Winds relax, the gyre slows modestly, and the nearshore freshwater influence shifts toward the glacial melt season. Coastal freshwater discharge is large year-round in this region, but its seasonal timing and the winds that organize it create very different shelf conditions from month to month.
These seasonal swings matter because they control when and where nutrients reach the sunlit surface layer. Winter storms mix the water column and replenish surface nutrients, setting the stage for spring phytoplankton blooms once light returns. The interplay between wind forcing, freshwater input, and current strength creates a biological calendar that the entire food web depends on.
Eddies That Fertilize the Open Ocean
One of the most striking things about the Alaska Current is how many eddies it spawns. These are rotating parcels of water, typically 100 to 200 km across, that pinch off from the main flow and drift into the interior of the Gulf of Alaska. Most are anticyclonic, spinning clockwise in the Northern Hemisphere, and they form preferentially along the continental margin where the current is unstable.
The eddy formation process is tied to the same downwelling-favorable winds that strengthen the coastal circulation. Stronger southwesterly winds, such as those during El Niño winters, generate positive sea-surface height anomalies along the coast. These anomalies grow through a combination of wave dynamics and instability until they detach from the coast as large, coherent eddies.9Progress in Oceanography. Intrinsic and forced interannual variability of the Gulf of Alaska mesoscale circulation Once formed, the eddies propagate slowly westward into the basin interior, carrying coastal water with them.
This is where the biology gets interesting. The open Gulf of Alaska is one of the world’s “high-nutrient, low-chlorophyll” (HNLC) regions, meaning it has plenty of nitrogen and phosphorus but not enough iron to support large phytoplankton blooms. Coastal waters, by contrast, are loaded with iron from rivers, glaciers, and seafloor sediments. When eddies trap that iron-rich coastal water and carry it offshore, they deliver the missing ingredient to the open ocean.
A detailed two-year study of Haida eddies, which form off the west coast of Canada and drift into the Gulf of Alaska, showed that newly formed eddies carried dissolved iron concentrations nearly two orders of magnitude higher than the open ocean around them. Total iron in their surface waters was more than 13 nanomolar higher than surrounding waters. Even 16 months after formation, the eddies still contained about 1.5 to 2 times more iron than the water around them.10Deep Sea Research Part II: Topical Studies in Oceanography. Iron transport by mesoscale Haida eddies in the Gulf of Alaska As these eddies slowly decay, their internal structure relaxes and pushes iron-rich deeper water upward, providing a slow, steady fertilization effect that can sustain elevated phytoplankton growth far from shore.11Progress in Oceanography. Mesoscale eddies dominate surface phytoplankton in northern Gulf of Alaska
In satellite images, you can sometimes see rings of elevated chlorophyll wrapped around the outer edges of these eddies, where the entrained coastal water still carries its original biological load. The eddies essentially act as slow-release capsules of iron, keeping the open gulf more productive than it would be if nutrients could only reach it through deep mixing or atmospheric dust.
How the Current Shapes Marine Life
The Gulf of Alaska supports one of the most productive marine ecosystems on Earth, and the Alaska Current and its associated flows are a big part of the reason. The current system does not just move water; it moves heat, nutrients, plankton, and larvae, connecting coastal nursery habitats with offshore feeding grounds.
Salmon are a prime example. Sockeye salmon from British Columbia’s Fraser River spend years feeding in the North Pacific before returning to their natal streams. Computer simulations have shown that the strength of the Alaska Gyre circulation in a given year affects when and where these fish arrive on the coast. In years with stronger gyre circulation, fish that were south of about 48°N were carried closer to Vancouver Island, potentially returning earlier. Fish further north experienced the opposite pattern.12Canadian Journal of Fisheries and Aquatic Sciences. Computer Simulations of the Influence of Ocean Currents on Fraser River Sockeye Salmon (Oncorhynchus nerka) Return Times The interplay between current strength and fish position means that year-to-year variability in the Alaska Current translates directly into variability in the timing and success of salmon runs.
Further north, the Alaska Coastal Current plays a role in the distribution of beluga whales near Barrow, Alaska. When the ACC flow is strong, it creates a well-defined front where its lower-salinity water meets the saltier Arctic basin water. This front concentrates prey species, and researchers have found that beluga whales are more abundant and vocalize more frequently in these conditions, likely reflecting better foraging opportunities.13Marine Ecology Progress Series. Correlation of a strong Alaska Coastal Current with the presence of beluga whales Delphinapterus leucas near Barrow, Alaska
Seabird communities along the Aleutian Islands also track the current. A study of seabird distribution, abundance, and diet across the eastern and central Aleutians found that bird communities could be split into two distinct groups corresponding to marine environments shaped by the extent of the Alaska Coastal Current.14Fisheries Oceanography. Seabird distribution, abundance and diets in the eastern and central Aleutian Islands Where the ACC’s influence reached, one set of species and diets prevailed; beyond it, a different assemblage took over. The current essentially draws an ecological boundary line through the Aleutian chain.
The Alaskan Stream’s Influence on the Bering Sea
The Alaskan Stream does not simply circle the gulf and dissipate. As it flows southwestward along the Aleutian Islands, portions of it pour through passes in the island chain into the Bering Sea. This inflow is one of the main ways the Bering Sea receives heat and nutrients from the North Pacific, and changes in the stream’s transport have measurable effects on Bering Sea conditions.
Modeling studies have shown that the relationship is not straightforward. When the Alaskan Stream’s transport increases from moderate to strong levels (roughly 10 to 25 Sverdrups), the Bering Sea shelf warms by about a quarter of a degree Celsius on average, with local maxima around half a degree, because more warm Pacific water flows through the eastern Aleutian passes. But if the transport increases further, from roughly 25 to 40 Sverdrups, the pattern reverses: the Bering shelf cools slightly.15Journal of Geophysical Research: Oceans. The role of the Alaskan Stream in modulating the Bering Sea climate The likely reason is that at very high transport levels, the flow dynamics shift which passes carry the most water, and cooler water from deeper layers ends up being what enters the Bering Sea.
The connectivity extends below the surface as well. Warm subsurface water from the Alaskan Stream travels westward along the southern slope of the Aleutian Islands, passes through gaps like Amchitka Pass at roughly 180°W, then turns eastward along the northern slope. This water can reach as far as Bering Canyon, and its transport is modulated by tidal mixing within the passes themselves.16Journal of Geophysical Research: Oceans. Connectivity of the Aleutian North Slope Current and Bering Sea Basin Waters at the Level of the Subsurface Temperature Maximum The Bering Sea’s walleye pollock fishery, one of the largest in the world, depends on conditions influenced by these inflows, making the Alaskan Stream’s behavior a matter of direct economic concern.
Marine Heatwaves and the “Blob”
The Alaska Current region has been at the center of some of the most dramatic ocean temperature events in recent memory. During the winter of 2013–2014, a persistent ridge of high atmospheric pressure over the northeastern Pacific suppressed the usual winter storms that cool and mix the surface ocean. Sea-surface temperatures soared, and a massive area of anomalously warm water developed, eventually dubbed “the Blob” by researchers and media alike.
Near Station Papa, a long-monitored site in the Gulf of Alaska, sea-surface temperature anomalies reached more than 4.5 standard deviations above normal, an extraordinary departure. Temperature anomalies exceeding 4 standard deviations persisted in subsurface waters well into 2017.17Deep-Sea Research Part I. ‘The Blob’ – or, how unusual were ocean temperatures in the Northeast Pacific during 2014-2018? The warm anomaly disrupted the usual nutrient supply to the surface by strengthening stratification (warm water sits on top of cold and does not mix easily), which reduced phytoplankton production and cascaded up the food web. Seabird die-offs, shifts in fish distribution, and harmful algal blooms all followed in the Blob’s wake.
Events like the Blob are superimposed on the Alaska Current’s normal variability, but they highlight how sensitive the region is to changes in atmospheric forcing. When the winds that normally drive the subarctic gyre weaken or shift, the entire circulation system responds, and the effects ripple through the ecosystem. With ocean temperatures in the North Pacific trending upward over recent decades, the question of whether such marine heatwaves will become more frequent is a live area of research.
The Subarctic Gyre and Decadal Patterns
The Alaska Current does not exist in isolation; it is one limb of the subarctic gyre, and that gyre’s strength fluctuates on timescales much longer than a single season. The Pacific Decadal Oscillation (PDO) is a pattern of sea-surface temperature variability across the North Pacific that shifts between warm and cool phases over periods of roughly 20 to 30 years. During positive (warm) phases of the PDO, the subarctic gyre tends to be stronger, which means a more vigorous Alaska Current.18Oceanography. Progress of Fisheries-Oceanography Coordinated Investigations in the Gulf of Alaska and Aleutian Passes
A stronger gyre pushes more warm water northward along the eastern boundary, shifts the bifurcation point of the North Pacific Current, and generally creates warmer conditions across the Gulf of Alaska. These decadal shifts have been linked to major changes in marine ecosystem structure, including salmon productivity regimes, groundfish community composition, and the distribution of marine mammals. Fisheries managers in Alaska have long recognized that what looks like a change in fish stock health may actually be a change in the physical ocean environment driven by the PDO or related large-scale climate modes. That awareness has pushed Gulf of Alaska fisheries management toward ecosystem-based approaches that account for ocean conditions, not just fish counts.
The interplay between decadal oscillations and shorter-term events like El Niño or marine heatwaves makes prediction difficult. A strong El Niño occurring during a positive PDO phase can amplify the Alaska Current and its eddy production beyond what either pattern alone would produce. A marine heatwave arriving during a negative PDO phase may have somewhat different ecosystem effects than one arriving during a positive phase, because the baseline gyre circulation is different. Researchers continue to work at disentangling these overlapping signals, and long-term ocean monitoring stations like Station Papa and mooring arrays across the Aleutian passes remain critical to that effort.