The Bering Sea ranges from near-freezing to surprisingly mild depending on the season, the depth, and how far north you go. Winter surface temperatures in the northern shelf drop to roughly −1.8 °C (about 28.8 °F), the freezing point of seawater, while summer surface waters in the southeastern region can climb above 10 °C (50 °F). That enormous swing, combined with one of the most dynamic sea-ice systems on the planet, makes the Bering Sea far more than just “cold.” Its temperatures and ice patterns shape fisheries worth billions of dollars, feed nutrients into the Arctic Ocean, and have been shifting in ways that recently collapsed an entire crab population.
Winter Temperatures and the Freezing Shelf
The coldest the Bering Sea gets is on its vast continental shelf north of about 60°N, where the water column is reset to the freezing point of seawater, around −1.8 °C, by the end of each winter.1Elsevier / Continental Shelf Research. Thermal and haline variability over the central Bering Sea shelf: Seasonal and interannual perspectives That is about as cold as ocean water gets before it turns to ice. The shelf here is shallow, in many places less than 200 meters deep, which means it does not take long for Arctic winds to cool the entire water column from surface to seafloor. By contrast, the deep Bering Sea basin to the west, which plunges to nearly 4,000 meters in places, holds stratified layers of water at different temperatures, with deep water hovering around 1.5–2 °C year-round.
As spring arrives, rapid melting begins in May, driven by the seasonal increase in solar radiation and southerly winds that push thinning ice northward. Solar heating through spring and summer builds strong thermal stratification, creating a two-layer system on the mid-shelf: a warming upper layer mixed by wind, and a cold bottom layer maintained by tidal mixing of leftover winter water. This bottom layer is the source of one of the Bering Sea’s most ecologically important features.
The Cold Pool
Every winter, a pool of extremely cold bottom water, below 2 °C, forms across the eastern Bering Sea shelf. It is created by cooling and vertical mixing as sea ice grows and releases brine into the water beneath it.2PubMed Central. On the variability of the Bering Sea Cold Pool and implications for the biophysical environment This cold pool persists through summer, sitting on the seafloor like a slab of near-freezing water even while the surface warms overhead. Its size varies enormously from year to year, and that variation is largely controlled by how far south sea ice extends the preceding winter.
Think of the cold pool as a thermal footprint of the previous ice season. In heavy ice years, the cold pool stretches across much of the shelf and can reach south past the Pribilof Islands. In low-ice years, it shrinks to a narrow band in the north or nearly vanishes altogether. This matters because the cold pool acts as a physical barrier and habitat boundary for many species. Walleye pollock, the most commercially valuable fish in the Bering Sea, shift their distribution dramatically in response to it: in cold years with a large cold pool, adult pollock concentrate over the outer shelf in a narrow, southerly band, while in warm years they spread northward past St. Lawrence Island.3Deep Sea Research Part II: Topical Studies in Oceanography. Environmental impacts on walleye pollock (Gadus chalcogrammus) distribution across the Bering Sea shelf The cold pool’s extent also correlates with pollock body condition, prey availability, and growth rates, making it a kind of master switch for the shelf ecosystem.4Progress in Oceanography. Synthesis of interannual variability in spatial demographic processes supports the strong influence of cold-pool extent on eastern Bering Sea walleye pollock (Gadus chalcogrammus)
How Sea Ice Forms and Moves
Bering Sea ice is not a static sheet. Most of it forms in polynyas, open-water areas in the northern Bering Sea where fierce Arctic winds blow existing ice away from the coast, exposing seawater to the frigid air. Beginning around November, episodic outbreaks of northerly winds cool the water, form new ice, and push it southward. As this ice drifts over warmer water to the south, its leading edge melts, rapidly chilling the water column beneath it and building the cold pool described above.5Deep Sea Research Part II: Topical Studies in Oceanography. On the recent warming of the southeastern Bering Sea shelf The process is sometimes called an “ice factory”: ice is continuously manufactured in the north, conveyed south by wind, and melted at its southern margin.
Maximum ice extent can arrive as early as January or as late as May, depending on winter wind patterns. At its peak in a heavy ice year, sea ice can cover most of the eastern shelf down to about 57°N, roughly the latitude of Bristol Bay. In a light year, ice may barely extend past St. Lawrence Island. This variability is enormous and has consequences that cascade through the physical and biological systems of the entire region.
During ice formation in the polynyas, brine is rejected into the water beneath, making it saltier and denser. Measurements from one such polynya showed salinity increasing at a rate of about 0.008 grams per kilogram per hour during a typical event lasting around 65 hours, with a corresponding heat flux of roughly 535 watts per square meter, enough to produce about 5 meters of ice over a single winter.6Journal of Geophysical Research: Oceans. Effects of a shelf polynya on flow and water properties in the northern Bering Sea That dense, salty water sinks and can even temporarily reverse local currents, pulling water toward the polynya.
Summer Warming and the Temperature Swing
By midsummer, the contrast with winter is stark. Surface temperatures in the southeastern Bering Sea routinely reach 8–12 °C. Even in the northern shelf areas that were at −1.8 °C a few months earlier, surface waters warm to 4–8 °C. The Bering Strait, where the sea funnels northward into the Arctic, shows a seasonal range from about −1.8 °C in winter to roughly 2.3 °C in summer, with salinity swinging between about 31.9 and 33 parts per thousand.7Geophysical Research Letters. Monthly temperature, salinity, and transport variability of the Bering Strait through flow The relatively modest summer warming at the Strait reflects the fact that it sits at the far northern end of the sea, squeezed between Alaska and Russia, where cold Arctic air and the shallow depth keep temperatures in check even at the height of summer.
This seasonal cycle is driven primarily by solar radiation, wind patterns, and the heat content of water flowing in through the Aleutian passes. Warmer Pacific water enters the Bering Sea through gaps in the Aleutian Island chain, with the largest net northward transport, over 4 million cubic meters per second, passing through Amukta Pass.8Fisheries Oceanography. Observations from moorings in the Aleutian Passes: temperature, salinity and transport This inflow carries heat and nutrients from the North Pacific onto the shelf and ultimately through the Bering Strait into the Arctic Ocean, making the Bering Sea a critical thermal gateway between the Pacific and Arctic basins.
Recent Warming and Marine Heatwaves
The Bering Sea has warmed over recent decades, and the warming has not been gradual or even. Long-term trends show increasing sea surface temperatures, and marine heatwaves, which are sustained periods of abnormally high ocean temperature, have become more frequent and longer-lasting.9Journal of Climate. Atmospheric Variability Drives Anomalies in the Bering Sea Air–Sea Heat Exchange The most recent decade, 2010 to 2019, saw the highest frequency and total number of marine heatwave days recorded, with the northern Bering Sea also experiencing increases in heatwave intensity.10Journal of Hydrology. Bering Sea marine heatwaves: Patterns, trends and connections with the Arctic
The winters of 2017–2018 were a particularly dramatic example. Sea ice that winter hit the lowest extent ever recorded for the Bering Sea. Ice arrived late because warm southerly winds dominated in November. More typical northerly winds in December and January pushed ice forward, but then strong, warm southerlies in February and March forced it to retreat again.11Geophysical Research Letters. Extreme Conditions in the Bering Sea (2017–2018): Record‐Breaking Low Sea‐Ice Extent The result was a winter with almost no cold pool to speak of, weakened water column stratification, a delayed spring phytoplankton bloom, and low abundances of large crustacean zooplankton in both the northern and southeastern Bering Sea.12Geophysical Research Letters. Responses of the Northern Bering Sea and Southeastern Bering Sea Pelagic Ecosystems Following Record‐Breaking Low Winter Sea Ice
Whether this pattern represents a permanent shift is not settled. Interannual variability still matters: during 2021–2024, the Aleutian Low pressure system returned to a regionally dominant position and sea-ice conditions bounced back to near the historical average.13International Journal of Climatology. Future Climate Change in the Northern Bering Sea In other words, a few warm, low-ice years do not mean the Bering Sea has permanently flipped to a warm state. The atmospheric circulation patterns that set each winter’s temperature and ice conditions can still produce cold years. But the trend is clear: cold years are becoming less common and warm extremes are becoming more intense.
What Happens When the Ice Retreats Early or Late
The timing of sea-ice retreat in spring has outsized effects on the Bering Sea’s biology, separate from how much ice there was. When ice sticks around late, phytoplankton blooms happen at the retreating ice edge in cold water, around 0–1 °C. When ice retreats early, the spring bloom happens in open water at warmer temperatures, sometimes up to 5.4 °C, and the blooms are substantially more productive, roughly 70% higher in primary production compared to cold-water ice-edge blooms.14Journal of Geophysical Research: Oceans. Sea ice impacts on spring bloom dynamics and net primary production in the Eastern Bering Sea Early ice retreat also leads to higher summer productivity, likely because the weaker thermal stratification that follows allows more nutrient mixing. Overall, warm years with early ice retreat saw annual net primary production enhanced by 40–50% in the southeastern Bering Sea compared to late-retreat years.
The relationship between ice timing and phytoplankton community composition adds another layer. Earlier ice retreat tends to favor larger phytoplankton, especially diatoms, because the prolonged open-water period allows a longer window of nitrate supply. Later ice retreat can actually trigger under-ice blooms, because by the time the ice is melting it is thin enough for enough sunlight to penetrate.15Biogeosciences. Influence of timing of sea ice retreat on phytoplankton size during marginal ice zone bloom period on the Chukchi and Bering shelves These differences in the base of the food web ripple upward, affecting zooplankton, forage fish, and ultimately the seabirds and marine mammals that depend on them.
The Snow Crab Collapse
Perhaps the starkest illustration of what Bering Sea temperature changes can do came with the snow crab. Since 2018, more than 10 billion snow crab vanished from the eastern Bering Sea, and the population crashed to historical lows by 2021.16Science. The collapse of eastern Bering Sea snow crab Researchers linked this collapse to the marine heatwave of 2018–2019. Snow crab are cold-water specialists closely associated with the cold pool. When the cold pool shrank dramatically, the crabs were packed into a smaller area. Their calculated caloric requirements exceeded what the diminished habitat could support, and evidence from body condition measurements pointed to starvation as a key driver. The fishery was shut down entirely for the 2022–2023 season, the first closure in its history.
The crab collapse underscored something that temperature data alone does not convey: the cold pool is not just cold water, it is habitat. When it shrinks, the species that depend on it do not simply move, they crowd together, compete for dwindling food, and, as the crabs showed, can die in staggering numbers.
The Bering Sea as an Arctic Gateway
Water flowing north through the Bering Strait carries heat, freshwater, and nutrients from the Bering Sea into the Arctic Ocean. The volume of this flow varies seasonally from roughly 0.4 to 1.2 sverdrups (millions of cubic meters per second), but its temperature and salinity have far-reaching consequences for Arctic sea ice and water-column structure.7Geophysical Research Letters. Monthly temperature, salinity, and transport variability of the Bering Strait through flow Maximum summer salinities passing through the Strait have remained remarkably stable at about 33.1 parts per thousand over at least a decade, which helps set the salinity of the western Arctic’s cold halocline, a layer that insulates Arctic sea ice from warmer water below.17Geophysical Research Letters. Observed increases in Bering Strait oceanic fluxes from the Pacific to the Arctic from 2001 to 2011 and their impacts on the Arctic Ocean water column
This means that warming in the Bering Sea does not stay in the Bering Sea. Warmer water flowing through the Strait can accelerate sea-ice melt in the Chukchi Sea and alter the thermal structure of the western Arctic. At the same time, wind patterns over the Bering Sea influence how much ice and cold air reach the northern shelf each winter. A weakened Arctic frontal system, where the boundary between cold northern air and warmer southern air shifts or breaks down, can allow storms and mild air to penetrate northward, reducing ice formation.13International Journal of Climatology. Future Climate Change in the Northern Bering Sea Before 2017, this front acted as a fairly reliable barrier keeping the northern Bering and Chukchi seas firmly in a cold Arctic climate. Its weakening in recent warm years helped create the record-low ice conditions.
The Bering Sea’s Ice Compared to the Sea of Okhotsk
The Bering Sea is not the only sub-Arctic sea with seasonal ice. The Sea of Okhotsk, on the opposite side of the North Pacific between Russia and Japan, also freezes extensively each winter. Interestingly, the ice covers of the two seas sometimes fluctuate out of phase, meaning that when one has more ice than usual, the other has less. This seesaw pattern is driven by the same large-scale atmospheric circulation patterns: when the Aleutian Low shifts westward, it tends to push cold air over the Okhotsk and warm air over the Bering, and vice versa.18Journal of Geophysical Research: Oceans. On the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the Bering and Okhotsk Seas For anyone tracking North Pacific ice trends, a warm Bering Sea winter does not necessarily mean a warm Okhotsk winter. The two are coupled through the atmosphere, often in opposite directions.
Coastal Communities and the Changing Ice
For the Yup’ik communities along the Yukon-Kuskokwim Delta of western Alaska, Bering Sea ice is not an abstract climate variable. Sea ice historically buffered the coastline from winter storm waves, provided hunting platforms, and regulated coastal erosion. As ice extent has declined, these communities face compounding threats: storm surges reach shore unimpeded, coastal erosion accelerates, and permafrost that once held the ground together is thawing.19Earth’s Future. Interacting Sea‐Level Rise, Sea‐Ice Loss, Storm Flooding, Erosion, and Permafrost Thaw Threaten Ecosystems, Wildlife, and Communities on the Yukon‐Kuskokwim Delta Some villages are already facing relocation, a process that is enormously expensive and culturally wrenching. The loss of sea ice here is not just an oceanographic event; it is an existential threat to communities that have lived on this coast for thousands of years.
What Ancient Sediments Say About Past Temperatures
The Bering Sea’s temperature swings are not new, even if the recent extremes may be. Sediment cores from the Bering Sea floor preserve chemical records stretching back roughly 18,000 years, to the end of the last ice age. The chain-length distribution of certain organic molecules in these sediments tracks surface temperature changes over millennia, with patterns that align remarkably well with known cold periods like the Younger Dryas (about 12,800–11,600 years ago) and warm intervals like the Bølling-Allerød.20Progress in Oceanography. Assessment of long-chain n-alkanes as a paleoclimate proxy in the Bering Sea sediments These records confirm that the Bering Sea has cycled between dramatically warmer and cooler states many times. What distinguishes the current warming is its speed and its coupling with reduced ice that historically would have returned each winter.