The Eastern Arctic Seas Encyclopedia

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

Laptev Sea

Reference work entry
Laptev Sea – a marginal, predominantly continental sea of the Arctic Ocean in Russia, located between the Severnaya Zemlya Archipelago and Taymyr Peninsula in the west and the New Siberian Islands to the east. It bears the name of Russian sea explorers – the Laptev brothers. Its western boundary runs along the eastern shore of the Severnaya Zemlya from the Arctic Cape (the Komsomolets Island), through the Strait of the Red Army along the eastern coast of the October Revolution Island to Anuchin Cape, across the Strait of Shokalskiy to Cape Peschanyi on Bolshevik Island and along its eastern coast to Cape Vaygach, then along the eastern border of the Vilkitsky Strait, and further along the mainland shore to the top of the Khatanga Bay. The northern boundary of the sea runs from the Arctic Cape to the point of intersection of the meridian of the northernmost point of Kotelnyi Island (Cape Anissiy) with the edge of the continental shelf (79°N, 139°E); the eastern border extends from this point by the meridian 139°E to the Kotelnyi Island, further along its western shore, through the Sannikov Strait, along the western shores of the Big and Small Lyakhovskiy Islands and the western boundary of the Dmitry Laptev Strait to Cape Svyatoy Nos (St. Nose).

The southern boundary runs along the mainland coast from this Cape to the top Khatanga Bay. With the East Siberian Sea, the L.S. is linked by the straits of Sannikov, Eterikan, and Dmitry Laptev, with the Kara Sea by Vilkitsky, Shokalskiy, and the Red Army straits.

The L.S. belongs to continental marginal seas. Its area is 662,000 km2, the volume is 353,000 km3, the average depth is 533 m, and the maximum depth is 3,385 m.

Near the L.S. coasts, there are several groups of islands, as well as dozens of islands, most of which are located in the western part of the sea. Their area is 3,784 km2. Komsomolskaya Pravda, Faddey, and Peter islands are near the Taymyr coast. Among individual islands the largest are Starokadomskiy, Malyi Taymyr islands near the eastern coast of Severnaya Zemlya, Begichev Island at the entry to the Gulf of Khatanga, and Yarok Island in the Yana Bay. Of the New Siberian Islands, only Stolbovoy and Belkovskiy islands are fully located in the L.S. Many small islands are located in the river deltas.

Seashores are severely rugged and form bays, gulfs, embayments, peninsulas, and headlands of multiple shapes and sizes. Eastern coasts of Severnaya Zemlya and the Taymyr Peninsula are significantly embayed. To the east of the peninsula, the shoreline forms several gulfs and bays (Khatanga, Anabar, Olenyok, Yana, Kozhevnikov, Noordwijk, Tiksi, Buor-Khaya, Vankin) and peninsulas (Hara-Tumus, Noordwijk). The west coast of the New Siberian Islands is less rugged.

By its nature, the coast is quite varied. There are abrasion and accumulative and icy shores. Sometimes, low mountains reach the sea; most of the coasts are lowlands. The L.S. is characterized by the predominance of terrigenous sediments. On the coast there are widely spread Quaternary sediments, shackled by permafrost.

The bottom of the L.S. is an almost non-segmented plain gently descending to the north. Here one can separate some troughs, small uplands, and benchlands. A wide but short trough is located against the Lena Delta, a funnel-shaped trough is at Olenyok Bay, and a long and narrow trough goes from Stolbovoy Island to the north. In the eastern part of the sea, there are Semyonovskiy and Vasilyevskiy benchlands. Half of the total area is occupied by the sea depths up to 50 m, and south from 76°N, they do not exceed 25 m. The northern part of the sea is much deeper. At a depth of 100 m, the bottom drops sharply. The sea is mostly shaped by waters of the southern part with the depths of 25–100 m.

The L.S. is one of the most severe arctic seas. It generally has a polar marine, sometimes continental, climate that is most evident in the relatively large annual fluctuations of air temperature.

In the cold season, the sea is primarily in the area of high atmospheric pressure – the Siberian Anticyclone. In the autumn, unstable winds gradually take the southern direction increasing to stormy ones. Less common are cyclones, with less cloudiness. In winter, the L.S. is under impact of three major pressure systems. In the southeastern part, there is the Siberian Anticyclone wedge line, which center is located near the Yana Bay. From the north there is an extending polar maximum wedge. In the western part of the sea, sometimes there are effects of the Icelandic minimum wedge. In accordance with such baric conditions, southern and southwesterly winds with an average speed of about 8 m/s dominate in this season. By the end of winter, their speed decreases; calm sea is frequently observed. The air is strongly cooled. The air temperature over the sea, in general, decreases from the northwest to the southeast in January, and near the Bay of Tiksi it is equal to −26…–29 °C. Calm and mainly clear winter weather is sometimes interrupted by cyclones passing rather south of the sea. They cause severe cold northerly winds and blizzards, which last only a few days. At the beginning of the warm season, the destruction of atmospheric pressure begins. The baric situation is generally similar to the winter, but a little more blurred, so the spring winds are very unstable in direction.

In addition to the southern winds, northerly winds also blow sometimes. Usually, the winds are gusty, but not strong. The air temperature steadily rises. Cloudy and relatively cold weather prevails.

In summer, the Siberian maximum is absent, and the polar maximum is quite weak. South from the sea, the pressure is slightly reduced; over the sea itself, it is slightly higher. Consequently, northerly winds blowing at a rate of 3–4 m/s are the most frequent. Strong winds (with speeds greater than 20 m/s) in summers are not observed. The average monthly temperature in August is the annual maximum; in the central part of the sea, the temperature is equal to 1–5 °C. On the coast, in enclosed bays, the air sometimes (though rarely) warms up very significantly (up to 32.7 °C in Tiksi). Summers are characterized by increased cyclonic activity. At this time, cyclones move over the southern part of the sea, where they also fill up with air. This results in a cloudy weather over the sea with a continuous drizzle. In late August, the Siberian maximum pressure begins to form that signifies the transition to autumn. Thus, most of the year, the L.S. is under the influence of the Siberian Anticyclone. This leads to a relatively weak cyclonic activity and mostly weak winds of monsoonal character.

Long and strong cooling under calm wind winter conditions is an important climatic feature of the sea. Another very important factor of the formation of natural image of the L.S. is the continental runoff, which is contributed by many small and few large rivers. Most of them are the Lena, which annually brings an average of approx. 530 km3 of water; the Khatanga, over 105 km3; the Yana –32 km3; the Olenyok – 40 km3; and the Anabar – approx. 25 km3. All other rivers deliver about 20 km3 of water per year. The total volume of annual runoff into the sea is about 720–767 km3, accounting for 30 % of the total flow to all the Arctic Sea. Due to precipitation, the sea receives 164 km3, with the evaporating capacity from its area of 63 km3. In summer, desalinated water masses in the surface layer are transferred through the straits of the New Siberian Islands to the East Siberian Sea, while more salty ocean masses come from the west.

However, the runoff distribution is very uneven in time and space. About 90 % of the annual runoffs fall on the summer months (June–September), of which on August fall about 35–40 % of annual runoffs, whereas in January, this value barely reaches 5 %. Such a distribution of runoffs during the year is due to the fact that the rivers, which flow into the L.S., are snow fed, and the vast majority of their water flows to the southeastern part of the sea (the Lena only gives 70 % of the continental runoff). Depending on the amount of water brought by the rivers and hydrometeorological conditions, river waters are distributed either to the northeast, reaching the northernmost point of Kotelnyi Island, or far to the east, flowing through the straits in the East Siberian Sea. A large continental runoff leads to the desalination of water in the vast expanses of the sea, especially in the southern and eastern parts. In general, the L.S. area, subjected to the influence of desalinated rivers, totals approx. 145,000 km2. The overall solid runoff volume is more than 20 million tons/year, sometimes reaching up to 30 million tons/year, although other data are available as well.

Surface Arctic waters prevail in the L.S. In the areas of strong influence of the continental runoff, the mixing of river and Arctic surface waters leads to the formation of the water of a relatively high temperature and low salinity. At their interface (subsurface horizon of 5–7 m), there are large gradients of salinity and density. In the north, warm Atlantic waters flows in a deep trench over the Arctic surface water, but their temperature is somewhat lower than in trenches of the Kara Sea. These steams penetrate here 2.5–3 years after starting they flow at Spitsbergen. The bulk of the deep Atlantic water penetrates to the L.S. via the Sadko Trench up to 77°N. In the L.S., which is deeper (as compared to the Kara Sea), the horizons from 800–1,000 m to the bottom are filled with Arctic cold bottom water with a temperature −0.4…–0.9 °C and almost homogeneous salinity (34.90–34.95 ‰).

For most of the year, the water temperature is close to freezing temperature and decreases rapidly after the summer maximum. In winter, the surface water temperature varies from −0.8 °C (near Mostakh Island) to −1.7 °C (near Cape Chelyuskin) due to differences in salinity in these areas. In the early spring months, ice is melting, so the water temperature is almost the same as in winter. Only in coastal areas (especially in estuarine areas) which get cleared of ice before the others, the water temperature is slightly higher than in the central regions. It generally decreases from south to north and from east to west. Over the summer, the sea surface warms significantly. In August, the south (Buor-Khaya Bay) surface water temperature can reach 10 °C or even 14 °C, in the central regions, it is 3–5 °C; at the northernmost point of Kotelnyi Island, it is 0.8 °C; and at Cape Chelyuskin, it is 1 °C. In general, the western part of the sea, where cold waters of the Arctic Basin come, is characterized by low (2–3 °C) water temperatures than in the eastern part, where the main mass of warm river waters is concentrated, and the surface temperature can reach 6–8 °C here.

The water temperature decreases rapidly with depth. In winter, in the areas with depths up to 50–60 m, the water temperature is the same as from the surface to the bottom. In the coastal zone, it is −1…–1.2 °C, and in the open sea, it is around 1.6 °C. In the northern areas at depths of 50–60 m, the water temperature rises by 0.1–0.2 °C due to the inflow of other waters.

In the north, in the area of the deep trench, a negative temperature is observed from the surface to 100 m deep. Here it begins to rise (to 0.6–0.8 °C) to a depth of about 300 m and then slowly lowers till the bottom. High temperature values (above zero) in the layer of 100–300 m are associated with the penetration to the L.S. of warm Atlantic waters from the Central Arctic Basin.

In summer, the 10–15 m thick upper layer is well warmed to a temperature of 8–10 °C in the southeastern part and to 3–4 °C in the central regions. Below these horizons the temperature decreases sharply and reaches −1.4… −1.5 °C in the horizon of 25 m. These values or those close to them are preserved till the bottom. In the western part of the sea, where the warming is less, no such sharp differences in temperature are observed.

Salinity in the L.S. is very inhomogeneous: in summer it varies from 1 to almost 31 ‰, but in the surface layer desalinated water with a salinity of 20–30 ‰ is predominant, and its distribution is very complicated. In general, it increases from the southeast to northwest and north. In winter, with the minimum river runoff and intensive ice formation, the salinity increases. At that (as in summer) it is higher in the west (near Cape Chelyuskin – 34 ‰) than in the east (at Kotelnyi Island – 25 ‰). This salinity remains high for a long time; only in June the ice begins to melt and salinity decreases. In summer, the southeastern part of the sea is the most desalinated. In the Buor-Khaya Bay, the salinity drops to below 5 ‰, and to the west of Lyakhovskiy Island, it increases (10–15 ‰). In the western part of the sea, there are more salted waters (30–32 ‰). They are slightly north of the line from Peter Island to Cape Anissiy. Thus, desalinated waters go north in the eastern part of the sea, and salt waters go down to the south in the western part of the sea.

With the depth the salinity increases, but there are seasonal differences in its distribution. In winter, in shallow water, it increases from the surface to the horizons of 10–15 m, and below it and till the bottom, salinity remains almost unchanged. At greater depths, salinity increases markedly not from the surface itself but from the underlying horizons. The spring-time vertical distribution of salinity starts from the moment of intensive melting of snow and ice. At this time, salinity decreases rapidly in the surface layer and preserves its winter values on lower horizons.

In summer, in the zone of distribution of river waters, the upper layer (5–10 m) is very much desalinated; below there is a very sharp increase in salinity. In the layer of 10–25 m, the salinity gradient sometimes reaches 20 ‰ per 1 m. In northern part of the sea, salinities increase relatively rapidly from the surface to 50 m; from here to 300 m, salinity slowly increases (ranging from 29 ‰ to 33–34 ‰); deeper it is almost unchanged.

In autumn, in southern area, the summer salinity jump is gradually diffused.

In the L.S., the density distribution rather relates to salinity than the temperature. This is due to a large range of salinity and a weak influence of the water low temperature on the density.

The density increases from the southeast to the northwest. In winter and autumn, the water is denser than in summer and spring. In winter and early spring, it has almost the same density from surface to bottom. In summer, large gradients of salinity and temperatures at depths of 10–15 m determine a sharp decrease of their density. In autumn, due to cooling and salinization of surface waters, their density increases. Density stratification of the waters can clearly be seen from late spring to early autumn. It is very distinctive in the southeastern and central parts of the sea and near the ice edge.

Wind mixing in the ice-free sea spaces is weak due to the relatively weak winds during warm seasons and a large sea ice cover. During spring and summer, the wind stirs only the uppermost layers up to 5–7 m thick in the east and up to 10 m in the western part of the sea.

Strong autumn and winter cooling and intensive ice formation cause the active development of convective mixing. Due to the relatively high degree of uniformity of waters and early ice formation, the density mixing penetrates most deeply (to the horizons of 90–100 m) to the north of the sea. In the central part, the convection reaches the bottom (40–50 m) by the beginning of winter, and in the southern part because of the large vertical gradients of salinity, it extends to the bottom even at low depths only by the end of winter.

Surface currents form a cyclonic gyre. The coastal flow moving along the mainland coast from west to east deviates off the eastern shores to the north and northwest and, in the form of Novosibirsk Stream, goes beyond the sea, connecting with the Transarctic Stream of the Central Arctic Basin. Away from it, near the northernmost point of Severnaya Zemlya, the East Taymyr Stream branches off it to the south and moves to the south along the eastern coast of Severnaya Zemlya and Taymyr Peninsula and closes the cyclonic ring. A small amount of the coastal waters flows out through Dmitry Laptev and Sannikov straits to the East Siberian Sea. The flow velocity in this gyre is low (2 cm/s). Depending on a large-scale baric situation, the center of cyclonic circulation can shift from the middle of the northern part of the sea toward Severnaya Zemlya. Accordingly, this creates branches from the mainstream. The permanent streams are overlapped with tidal currents.

In the L.S., tides are very distinctive everywhere with their anomalous semidiurnal character. The tidal waves enter from the north, from the Central Arctic Basin, fading and deforming along its way to the south. The tidal range is usually small, preferably about 0.5 m. Only in Khatanga Bay, the range of oscillations of the tidal level exceeds 2 m in spring tides. This is due to the well-known “funnel” effect observed, for example, in the Bay of Fundy. The tidal wave that came to Khatanga Bay (“funnel”) grows in size and extends to almost 500 km up the river of Khatanga. This is one of the examples of deep upriver penetrations of tidal waves. However, the effects of boron in Khatanga are not observed. To other rivers, which flow into the L.S., tides hardly penetrate. They fade away very close to the mouths, as tidal waves are damped in deltas of these rivers.

In addition to the tidal level fluctuations, seasonal and storm surges are observed in the L.S. Seasonal level changes are insignificant, in general. Most of all, they are distinctive in the southeastern part of the sea, in the areas close to the mouths of rivers, where the fluctuations reaches 40 cm. The minimum level is observed in winter, the maximum – in summer.

Storm surges are observed everywhere and in any season, but they are the most significant in the southeastern part. Positive and negative surges cause the greatest decreases and increases in the L.S. levels. The range of fluctuations of surge levels is 1–2 m and sometimes reaches up to 2.5 m (Tiksi Bay). Most often, positive and negative surges are observed in autumn with strong and steady winds. In general, northern winds cause positive surges and southern winds negative surges, but depending on the configuration of the coast, fluctuations of positive–negative surge levels are caused in each particular area by winds of certain directions. So, in the southeastern part of the sea, the most effective are westerly and northwesterly surge winds.

On average, surges of force 2–4 with wave heights of about 1 m prevail in the L.S. In summer (July–August) in the western and central parts of the sea, storms occasionally reach the force of 5, when the wave height reaches 4–5 m. Autumn is the most stormy season of the year when the maximum high waves (up to 6 m) can be observed. However, in this season, waves about 4 m high prevail, which is predetermined by the acceleration distance and depths. Wave processes are the main factors affecting the coasts. They lead to coastal destruction and the subsequent transformation of the sedimentary material to its abrasion, turning it into a subtle and migratory slurry carried for significant distances from the source areas.

Most of the year (October to May), the L.S. is covered with ice. Ice formation begins in late September and lasts simultaneously over the whole of the sea. In winter, extensive fast ice develops in its shallow eastern part with a thickness up to 2 m. The boundary of the propagation of fast ice is the depth of about 25 m, which in this area of the sea is remote for several hundred kilometers from the coast. The fast ice area is about 30 % of its sea. In the western and northwestern parts of the sea, the shore ice is small, and during some winters, it is entirely absent. North of the landfast ice zone is the drifting ice area.

With almost continuous carryover of ice from the sea to the north in winter, behind the landfast ice, significant spaces of polynyas and young ice are preserved almost through the whole winter. The width of the zone varies from dozens to several hundred kilometers. Its separate parts are called the Vostochno-Severozemelskaya, Taymyrskaya, Lenskaya, and Novosibirskaya polynyas. The latter two at the beginning of the warm season become enormously huge (thousands of km2) in size. Ice melting begins in June and July, and by August large areas of the sea are free of ice. In summer, ice edges frequently change their position under the influence of winds and currents. The western part of the sea is more arctic in general than its east. The oceanic Taymyr ice massif comes down to the sea along the eastern coast of Taymyr, which bears frequent heavy multiyear ice. It is well preserved until the new ice formation, depending on the prevailing winds, moving either to the north or to then south. The local Yana ice massif formed by landfast ice, by the second half of August, usually melts “on the scene” or is partially carried away to the north beyond the sea limits.

Flora and Fauna are of the Arctic origin. Phytoplankton is represented mainly by diatom algae both marine and brackish freshwater. In zooplankton the most common are ciliates, rotifers, copepods, and among the benthic fauna (bents), foraminifera, polychaetes, isopods crustaceans, mollusks, and bryozoans prevail.

Due to harsh environmental conditions, the biological productivity of the L.S. is low, and life in its waters is generally poor both quantitatively and qualitatively. 37 species of fish live here. Ichthyofauna is represented by marine anadromous and semi-anadromous fish species. The most common are Siberian whitefish, trout, cisco, whitefish, white salmon, and sturgeon. Of marine mammals, there are walruses, bearded seals, eared seals, and toothed whales – belukha.

The deltas of rivers are nesting areas for many birds in summer, including geese, gulls, and others. The permanent residents of the coastal tundra are snowy owl and ptarmigan. In some places on the rocky cliffs, there are multiple rookeries (diving pigeons, guillemots, gulls, etc.). Along the banks are deer, lemming, and gopher and predators such as foxes and wolves; on the ice and on the islands, polar bears.

Estuaries and deltas of the local are fishery areas. Whitefish, cisco, and sometimes muksun are caught in small quantities. Of great commercial importance is walrus. In the tundra the industries include hunting for fur (mainly polar fox), animals, and reindeer.

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© Springer International Publishing Switzerland 2016