The Eastern Arctic Seas Encyclopedia

2016 Edition
| Editors: Igor S. Zonn, Andrey G. Kostianoy, Aleksandr V. Semenov

Chukchi Sea

Reference work entry
DOI: https://doi.org/10.1007/978-3-319-24237-8_131
Chukchi Sea – an adjacent sea of the Arctic Ocean, the easternmost of its Arctic seas. It bathes the northern coast of the Chukchi Peninsula (Russia) and the northwestern coast of Alaska (USA). Its western boundary extends from the intersection of the meridian 180 ° with the edge of the continental shelf (76 °N, 180 °E) along the 180° meridian to Wrangel Island, Cape Zapadnyy, and then through the De Long Strait and Cape Yakan, along the eastern border of the East Siberian Sea. The northern boundary extends from a point at 72 °N, 156 °W to Cape Barrow in Alaska, where it connects to the Beaufort Sea, then along the mainland coast from the southern entrance of the bay of Cape Shishmareva (Seward Peninsula, USA). The southern border of Ch.S. goes along the northern border of the Bering Strait from the southern entrance of the bay of Cape Shishmareva to Cape Unikyn (Chukchi Peninsula) and further along the continental coast to Cape Yakan. The Bering Strait connects the Ch.S. with the Bering Sea of the Pacific Ocean. The Long Strait is part of the Ch.S., and its western border runs from Cape Blossom to Cape Yakan. The eastern boundary of the strait extends from cape Pillar (Wrangel Island) to Cape Schmidt.

The Chukchi Sea (Source: https://en.wikipedia.org/wiki/Chukchi_Sea)

The Ch.S. is one of the continental-adjacent seas. Its area is 595 (589) thousand km2, its volume is 42 (45) thousand km3, and the average depth is 71 m, with 1,256 m at the deepest. The Ch.S. has only three islands – Wrangel Island (7,300 km2), Herald Island, and Kolyuchin Island; along the American coast, in the Gulf of Kotzebue, there are also Chamisso Island and Puffin Island.

From the spurs of the mountain ranges that stretch inside the Chukchi Peninsula and Alaska, numerous small rivers and streams flow into the many coastal lagoons. The largest of them are the Anguema River, the Vankarem River on the Chukchi Peninsula, as well as Kobuk, Noatak, and Utukok and others in Alaska. The total flow of all rivers flowing into the Ch.S. (including Alaska) is 82.6 km3. The estimated sediment runoff from the side of Chukotka is 1 million tons per year and from Alaska – 2.7 million tons per year. The muddiness of the rivers of Chukchi Peninsula ranges from 25 to 100 g/m3, with an average of 50 g/m3.

The coastline of the Ch.S. (including islands) is approx. 1,600 km. The coastline is slightly indented. The bays include Kolyuchinskaya Bay, Kotzebue Bay, and Shishmareva Bay. The coast is mountainous almost throughout its length. On the eastern coast of Wrangel Island, there are low hills that drop off sharply into to the sea. Low mountains stretch along the northern coast of Alaska and Chukotka, but they are usually far from the water’s edge. The coastline is formed by low gravel and sand bars, separating the lagoons from the sea. Such a landscape is typical of the coast of the Ch.S.

Along the coasts of the Ch.S., there are capes such as Cape Yakan, Cape Schmidt, Cape Vankarem, Cape Serdtse-Kamen, Cape Krusenstern, Cape Hope, Icy Cape, Cape Lisburne, Cape Barrow, etc.

The Ch.S. is mostly located on the continental shelf with the depths of 40–60 m. The shelf is comprised of abrasion-accumulative plains of varying age. A characteristic feature of the continental margin within the sea is the existence of a special intermediate zone between the continental shelf and the slope, the so-called avanshelf – an inclined plane, at times stepped, lowered to the depth of several hundred meters. The amount of sediments in the sea today varies widely, from 0 to 10 m. The relief of the seafloor is rather flat. The depth of water is generally less than 50 m (56 %), while the maximum depth (in the north) does not exceed 1,300 m. Isobaths of 10 and 25 m are located close to the coast. There are shallows with depth of water up to 13 m. The bottom is split by two canyons: the Herald Canyon with a depth of 90 m and the Barrow Canyon with the maximum depth of 160 m. The seafloor is covered with silt with sand and gravel. Numerous lagoons are located on the mainland coast of the Russian part of the sea. The largest of them are Kanygtokynmanky, Neskynpilgyn, Tenkergykynmangky, and Nutauge.

The climate of the sea is that of the polar zone. Its characteristics include little solar heat and small annual fluctuations of the air temperature. In autumn and winter, the sea is influenced by several large-scale pressure systems. At the start of the season, it is subject to the spurs of the Siberian and Arctic Anticyclones and the Aleutian Low. Because of this distribution of pressure systems, the direction of the wind over the sea is very changeable. Wind speeds average 6–8 m/s. The air temperature in autumn falls quickly, and in October on Cape Schmidt and Wrangel Island, it reaches −8 °C. In November, northwesterly winds begin to dominate, and in February the low pressure trough disappears. Siberian and North American wind spurs come close above the sea, at times merging and forming a “bridge” of high pressure between the continents. Because of this, the north part of the sea is dominated by northerly and northeasterly winds, while the south is subject to northerly and northwesterly winds. In the second half of winter, southerly bearings generally blow over the sea. The wind speed is usually about from 5 to 6 m/s. The air temperature in the coldest month (February) averages −28 °C in Uelen and about −25 °C on Wrangel Island and −28 °C on Schmidt Island. This temperature distribution is due to the warming effect of the Pacific Ocean and cooling effect of the Asian continent. Winter is characterized by dull, cold weather with gusty winds, which is sometimes changed by flows of warm air from the Bering Sea.

In the warm time of the year, the North American and the Siberian Anticyclone are not present in the region, and the North Polar Maximum becomes weakened and moves to the north. In spring, a field of low pressure exists to the south of the sea, extending from the Icelandic Low to the east and connecting to the trough of mild Aleutian Low. Toward the end of the season, unstable winds acquire a predominantly southern direction. Their speed typically does not exceed 3–4 m/s. In spring, as a rule, the weather is cloudy, quiet, dry, and cold. The temperature in April averages −12 °C on Uelen and −17 °C on Wrangel.

In summer, a spur of the Pacific Maximum comes closer to Alaska, and over the ice-free spaces, water pressure is slightly elevated. In the southern part of the sea, the winds of the southerly and southeasterly direction are predominant, and in the northern regions, there are northerly and northwesterly winds. Their speed usually reaches 4–5 m/s. The temperature of the warmest month (July) is on average 6 °C in Uelen, about 2.5 °C on Wrangel, and 3.5 °C on Schmidt. In areas along the coast, sheltered from the winds, it can reach 10 °C and higher. Summer weather is cloudy, with rain and snow. The summer is very short, and the transition to the next season begins already in August.

The continental runoff in the Ch.S. is rather insignificant. Only 72 km3 of river water per year flows here, which is about 5 % of the total coastal runoff in all Arctic seas and just a fraction of a percentage point of the volume of its waters. Of this amount, 54 km3/year flows from the rivers of Alaska, and 18 km3/year comes from Chukotka River. This modest coastal runoff does not change the hydrological conditions of the sea significantly, but it affects the temperature and the salinity characteristics of coastal waters.

In a much greater extent, the nature of the Ch.S. is affected by the water exchange with the Central Arctic Basin and the Pacific Ocean through the Bering Strait. A slight increase in water temperature at the bottom layers in the north of the Sea is connected to the transformed warm Atlantic waters flowing here.

The hydrological structure of the sea is generally similar to the water composition in other Siberian Arctic seas, but it has its own characteristics. In western and central areas of the sea, surface Arctic waters are typical. In the narrow coastal zone, especially where the rivers flow into the sea, one can find warm desalinated water, formed by the mixing of seawater with river flows. At the northern edge of the sea, the continental slope is cut deep by the Chukotka Trough, along which Atlantic waters spread at the depth of 400–450 m, with a maximum temperature of 0,7–0,8 °C. These waters come into the sea 5 years after they enter into the Arctic Basin in the Svalbard area. A middle layer lies between the surface and the Atlantic waters.

The eastern part of the sea has relatively warm and salty waters coming from the Bering Sea. They arrive here in the volume of 30,000 km3/year. They usually move to the north and the east, but in some years the De Long branch is significantly more developed. This branch has warm currents that get to the East Siberian Sea through the De Long Strait. Moving toward the Ch.S., Pacific waters mix with the local waters, cool down, and sink into the subsurface layers. In the eastern part of the sea with depths of 40–50 m, they extend from the surface to the bottom. In the northern parts of the sea, where it is deeper, the waters form a layer with its center located at the depth of 40–100 m, under which there is deep water. In the surface Arctic and Pacific waters, seasonal layers form and are destroyed, which is linked to the intra-annual variability of oceanographic characteristics. Temperature in winter and early spring in the under-ice layer is distributed fairly evenly over the space of the sea and is −1,6 °… −1,8 °C. In late spring on the surface of pure water, it rises up to −0,5 °C… −0,7 °C near the ice edge and up to 2–3 °C in the Bering Strait. Due to the influx of summer warmth and the waters from the Pacific with an average temperature of 0,2–4 °C, the temperature of the water surface rises. The temperature in the marginal ice zone in August is −0,1…–0,3 °C; in the western part of the coast, it is approximately 4 °C; to the east of the meridian of 168 °W, where it lies the axis of the flow of the Pacific, it rises up to 7–8 °C; while in the eastern Bering Strait, it can even reach 14 °C. In general, the western part of the sea is cooler than the eastern.

The vertical distribution of water temperature in winter and early spring is homogeneous almost throughout the sea. From the surface to the bottom, it is −1,7…–1,8 °C, and only in the Bering Strait on the level of 30 m, it rises to −1.5 °C. In spring, the temperature of the water surface rises, but at levels of 5–10 m, it lowers toward the bottom, at first rather sharply, but then more smoothly. In summer, in the south and east of the sea, the radiation heating goes fairly deep, and in some shallow areas, it goes down to the bottom.

The surface temperature of 6–7 °C is observed at the levels of 10–12 m, where it decreases with depth, and even at the bottom, it is 2–2,5 °C. In the central part of the sea, the influence from the Bering Sea waters appears smaller. The surface temperature (about 5 °C) covers a layer with a thickness of 5–7 m, and then it decreases fairly rapidly to the bottom. In the northern part of the sea in the Chukchi troughs in the upper layer at about 20 m, the temperature is 2–3 °C, then it falls to 1.6 °C on the level of 100 m, then it rises again, and at the bottom layer, it is close to zero. This is caused by the influence of warm Atlantic waters coming from the Central Arctic Basin. In autumn, the cooling of the surface spreads from the inside, which leads to equalization of temperature along the vertical direction. Winter vertical circulation reaches the bottom, and in winter the temperature of all the water in the sea is about 0 °C.

The levels and the distribution of salinity on the surface of the sea are influenced by different seasonal influx of the Pacific and – in the coastal zone – of river waters. Winter and early spring are characterized by increased salinity of the ice layer. In the west it is about 31 ‰; in the central and northeastern parts, it is close to 32 ‰; but it is highest in the Bering Strait with 33–33.5 ‰. From the end of spring and during the summer, when the inflow of waters through the Bering Strait is enhanced and there is an increased continental runoff, the salinity distribution pattern on the surface of the sea becomes quite varied. In general, the salinity increases from west to east from about 28 ‰ to 30–32 ‰. At the edges of the ice, it decreases and is 24 ‰, while near the mouths of the rivers, it drops to 3–5 ‰. In the Bering Strait, the salinity remains the largest – 32.5 ‰. In autumn, with the start of the ice formation, there is a general increase in salinity, and then it becomes equal throughout the surface of the sea. In winter and early spring, the salinity typically changes very little, almost throughout the whole sea. To the northwest of the Bering Strait, where the influence of the Pacific waters is strong, the salinity is quite significantly higher and varies from 31.5 ‰ to 32.5 ‰ between the levels of 20 and 30 m. Moving away from this zone, the increase in water salinity with depth is not as great and happens more smoothly. As a result of the spring thaw, it rises sharply in the layer of 5–10 m from 30 ‰ to 31–32 ‰. Below it grows very slowly, and at the bottom it is close to 33 ‰. Such a vertical change of salinity can be observed in the coastal strip, but the surface layer is much stronger, and desalinated water is underlain with waters of lower salinity – 30–31 ‰. In summer, the freshened surface layers of the sea decrease as a result of the inflow of the Pacific waters, and in autumn they disappear completely. In the central part of the sea, with the influence of the Bering Sea waters, the salinity steeply increases from 32 ‰ to 33 ‰ from the surface to the bottom. In the area of drifting ice and along the coast of the Chukchi Sea coastline, the salinity in the surface layer with a thickness of 5–10 m is lower, then there is its sharp increase (up to 31–31.5 ‰) in the layer of 10–20 m, and then it gradually increases to the bottom, where it reaches 33–33.5 ‰. In autumn and especially in winter, the salinity increases due to salinization during the ice formation. In some areas, the salinity levels become equal everywhere in the autumn, while in others it does so only at the end of winter.

In accordance with the distribution and seasonal changes in salinity and temperature changes, the density of water also changes. In autumn and winter, when the salinity is increased and the water is extremely low, its density is quite high. Similar to the distribution of salinity, the high density on the surface is found in the southern and eastern parts of the sea, and to the northwest, the density decreases slightly. In the warmer half of the year, the surface water gets desalinated, gets warmer, and their density decreases. Due to the relatively intensive introduction of salt water from the Bering Sea at this time of the year, more dense waters are located in the southern and eastern parts of the sea. In the north and west, the density on the surface is reduced, because the top layer of the sea gets fresh water due to ice melting and due to an inflow of the low salinity waters of the East Siberian Sea. In winter, the density increases from the bottom surface rather evenly throughout the water column. In spring and summer, near the ice edge and in the coastal strip, the top layer of water with a thickness of 10–20 m is very different in density from the underlying layer below, under which the density increases uniformly to the bottom. In the central part of the sea, the density varies vertically more smoothly. In autumn, due to the cooling of the sea surface, the density begins to increase. The changeable winds and a varying vertical dispersion of density largely determine the conditions and opportunities for water mixing in the sea.

In spring and summer, the water spaces free from sea ice differ in density, and relatively weak winds mix only the uppermost layers. The same depth of wind mixing is in the estuarine areas. In autumn, the vertical stratification of water is reduced, and the winds are intensified, so wind mixing penetrates to the horizons of 10–15 m. Deeper it is prevented in its spread by significant vertical density gradients. This picture is especially characteristic of the western part of the sea. Stable structure of water is beginning to be destroyed by the autumn convective mixing, which penetrates only 3–5 m below the wind mixing. Relatively small (up to 5 m) increases are seen in the thickness of the upper homogeneous layer due to thermal convection in autumn. Only at the end of winter, at depths of 40–50 m (which occupy about 90 % of the sea), winter vertical circulation extends to the bottom. At greater depths, the ventilation occurs when lower layers backslide into the water down the slopes, toward the bottom.

The total water circulation in the sea, besides the basic factors that influence the flow of the Arctic seas, is largely determined by flows coming through the Bering Strait and the De Long Strait. Surface currents of the sea as a whole form a weakly pronounced cyclonic gyre. Coming out of the Bering Strait, Pacific waters spread like waves. Their main flow is directed almost to the north. At the latitudes of Kotzebue Bay, they are joined by the freshened continental runoff waters from this bay. Moving further to the north, the Bering Sea water flow near Cape Hope is divided into three streams. One of them, Alaska, continues to move to the north, and Cape Lisburne turns northeast to mount Barrow. The second one goes from Cape Hope and deviates to the northwest. Meeting on the way to the Herald Canyon, this stream is divided into two branches. One of them – Longovskaya Branch – is to the west, while the southern shores of Wrangel Island, where it merges with the current, envelops the island on the east side. The other one – the Geraldovskaya Branch – continues to spread in the northwest direction through the Herald Canyon which goes up to 73–74 °N. Here it meets with local cold water and turns east, forming an ever-present cold Chukchi flow. The flow of water is introduced into the Ch.S. across the De Long Strait, flowing along the coast toward the southeast. With sufficiently strong development, in winter it brings out surface water and ice from the Ch.S. to the Bering Sea, forming the so-called polar flow.

Tidal range is insignificant along the coast of Chukotka. At some points it is only 10–15 cm. At Wrangel Island tides are higher. In Rogers Bay level rises above the high water level at low tide 150 cm, because here comes the wave formed by the addition of waves coming from the north and west. The same value of the tide is observed at the top of Kotzebue Sound, but there are large tides which are caused by the configuration of the coasts and topography of the bay.

Almost the whole year, the sea is covered with ice. In winter, from November–December to May–June, the sea is completely covered with ice. Fast ice is slightly developed. Its width varies in different places, but not more than 10–20 km. Drifting ice is located beyond the fast ice. Most of these are 1- and 2-year ice formations, with the thickness of 150–180 cm. In the north of the sea, there are many years of heavy ice.

In summer the ice edge retreats northward. In the Chukchi Sea, the Chukchi and Wrangel ice massifs are formed. The first of these consists of heavy ice. The minimum amount of ice in the sea is usually in the second half of August until the first half of October. In some years, the ice accumulates in the Long Strait and stretches along the coast of Chukotka. In such years, navigation is extremely difficult. In other years, the ice, on the other hand, departs far from the coast of the Chukchi Peninsula, which is very favorable for navigation. In late September, new ice begins to form, which over time continues to increase and covers all the winter sea.

According to estimates, the shelf of the Ch.S. contains up to 30 billion barrels of oil. In February 2008, the US government announced the successful bidding for the production (the total price of $2.6 billion). The decision has been criticized by environmentalists.

The population of the coast is not numerous – the Chukchi, Eskimos, and Russians. Small settlements mainly consist of one-story wooden houses. The largest settlements are Cape Schmidt village and the village of Uelen.

Major ports include Uelen (Russia) and Barrow (USA).

The Ch.S. is not rich in fish. It has 37 species of fish. Of local commercial importance are char (polar cod), smelt, polar flounder, polar cod, and a few other species. Hunting sea mammals (seals) is developed. There are polar bears in the Ch.S.

Through the Chukchi Sea passes the Northern Sea Route. It is the easternmost link between the ports of the Far East, the mouths of Siberian rivers, and the European part of Russia. The eastern part of the sea connects foreign Pacific ports in Canada and the USA and the mouth of the Mackenzie River. The navigation in the sea is quite complicated, which is due to a lack of coastal landmarks and ice conditions. In the period of 1914–1983, six ships perished in the sea. During a voyage in 1983, as a result of compression of ice, 57 vessels got captured by the ice; 30 of them were damaged to varying degrees, including five icebreakers.

The name of the sea comes from the Chukchi Peninsula and its peoples – the Chukchi.

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