Laptev Sea


The Laptev Sea is a marginal sea of the Arctic Ocean. It is located between the northern coast of Siberia, the Taimyr Peninsula, Severnaya Zemlya, and the New Siberian Islands. Its northern boundary passes from the Arctic Cape to a point with co-ordinates of 79°N and 139°E, and ends at the Anisiy Cape. The Kara Sea lies to the west, the East Siberian Sea to the east.
The sea is named after Russian explorers Dmitry Laptev and Khariton Laptev; formerly, it had been known under various names, the last being Nordenskiöld Sea, after explorer Adolf Erik Nordenskiöld. The sea has a severe climate with temperatures below 0 °C for more than nine months per year; low water salinity; scarcity of flora, fauna, and human population; and shallow depths. It is frozen most of the time, though generally clear in August and September.
The sea shores were inhabited for thousands of years by indigenous tribes of Yukaghirs and then Evens and Evenks, which were engaged in fishing, hunting and reindeer husbandry. They were then settled by Yakuts and later by Russians. Russian explorations of the area started in the 17th century. They came from the south via several large rivers which empty into the sea, such as the prominent Lena River, the Khatanga, the Anabar, the Olenyok, the Omoloy and the Yana. The sea contains several dozen islands, many of which contain well-preserved mammoth remains.

Extent

The International Hydrographic Organization defines the limits of the Laptev Sea as follows:

On the West The eastern limit of Kara Sea
Komsomolets Island from Cape Molotov to South Eastern Cape; thence to Cape Vorochilov, Oktiabrskaya Revolutziya Island to Cape Anuchin. Then to Cape Unslicht on Bolshevik Island. Bolshevik Island to Cape Yevgenov. Thence to Cape Pronchisthehev on the main land.
On the North A line joining Cape Molotov to the Northern extremity of Kotelni Island.
On the East From the Northern extremity of Kotelni Island – through Kotelni Island to Cape Madvejyi. Then through Malyi Island , to Cape Vaguin on Great Liakhov Island. Thence to Cape Sviatoy Nos on the main land.

Using current geographic names and transcription this definition corresponds to the area shown in the map.
  1. The sea's border starts at Arctic Cape on Komsomolets Island at and connects to Cape Rosa Luxemburg , the southeastern cape of the island.
  2. The next segment crosses Red Army Strait and leads to Cape Vorochilov on October Revolution Island and afterwards through that island to Cape Anuchin at.
  3. Next, the border crosses Shokalsky Strait to Cape Unslicht at on Bolshevik Island. It goes further through the island to Cape Yevgenov at.
  4. From there, the border goes through Vilkitsky Strait to Cape Pronchishchev at on the Tamyr peninsula.
  5. The southern boundary is the shore of the Asian mainland. Prominent features are the Khatanga Gulf and the delta of the Lena River.
  6. In the east, the polygon crosses the Dmitry Laptev Strait. It connects Cape Svyatoy Nos at with Cape Vagin at in the very east of Bolshoy Lyakhovsky Island.
  7. Next, the Laptev Sea border crosses the Eterikan Strait to Little Lyakhovsky Island at up to Cape Medvezhiy.
  8. Finally, there is a segment through Kotelny Island to Cape Anisy, its northernmost headland.
  9. The last link reaches from there back to Arctic Cape.

    Geography

The Lena River, with its large delta, is the biggest river flowing into the Laptev Sea, and is the second largest river in the Russian Arctic after Yenisei. Other important rivers include the Khatanga, the Anabar, the Olenyok or Olenek, the Omoloy and the Yana.
The sea shores are winding and form gulfs and bays of various sizes. The coastal landscape is also diverse, with small mountains near the sea in places. The main gulfs of the Laptev Sea coast are the Khatanga Gulf, the Olenyok Gulf, the Buor-Khaya Gulf and the Yana Bay.
There are several dozens of islands with the total area of, mostly in the western part of the sea and in the river deltas. Storms and currents due to the ice thawing significantly erode the islands, so the Semenovsky and Vasilievsky islands which were discovered in 1815 have already disappeared. The most significant groups of islands are Severnaya Zemlya, Komsomolskaya Pravda, Vilkitsky and Faddey, and the largest individual islands are Bolshoy Begichev, Belkovsky, Maly Taymyr, Stolbovoy, Starokadomsky, and Peschanyy.
More than half of the sea rests on a continental shelf with the average depths below, and the areas south from 76°N are shallower than 25 m. In the northern part, the sea bottom sharply drops to the ocean floor with the depth of the order of . There it is covered with silt, which is mixed with ice in the shallow areas.
The Laptev Sea is bound to the south by the East Siberian Lowland, an alluvial plain mainly composed of sediments of marine origin dating back to the time when the whole area was occupied by the Verkhoyansk Sea, an ancient sea at the edge of the Siberian Craton in the Permian period. As centuries went by, gradually, most of the area limiting the sea to the south became filled with the alluvial deposits of modern rivers.

Climate

The climate of the Laptev Sea is Arctic continental and, owing to the remoteness from both the Atlantic and Pacific oceans, is one of the most severe among the Arctic seas. Polar night and midnight sun last about three months per year on the south and five months on the north. Air temperatures stay below 0 °С 11 months a year on the north and nine months on the south. The average temperature in January varies across the sea between and and the minimum is. In July, the temperature rises to 0 °С in the north and to 5 °С in the south, however, it may reach 22–24 °С on the coast in August. The maximum of was recorded in Tiksi. Strong winds, blizzards and snow storms are common in winter. Snow falls even in summer and is alternating with fogs.
The winds blow from south and south-west in winter with the average speed of 8 m/s which subsides toward the spring. In summer, they change direction to the northerly, and their speed is 3–4 m/s. Relatively weak winds result in low convection in the surface waters, which occurs only to the depth of 5–10 meters.

Ice

The Laptev Sea is a major source of arctic sea ice. With an average outflow of 483,000 km2 per year over the period 1979–1995, it contributes more sea ice than the Barents Sea, Kara Sea, East Siberian Sea and Chukchi Sea combined. Over this period, the annual outflow fluctuated between 251,000 km2 in 1984–85 and 732,000 km2 in 1988–89. The sea exports substantial amounts of sea ice in all months but July, August and September.
Usually, ice formation starts in September on the north and October on the south, though it has progressively begun later because of human-driven climate change. In 2020 Siberia experienced record-breaking heat and formation did not begin until late October, marking the latest start ever recorded. The ice formation results in a large continuous sheet of ice, with the thickness up to in the south-eastern part of the sea as well as near the coast. The coastal sheet ends at the water depth of 20–25 m which occurs at several hundred kilometers from the shore, thus this coastal ice covers some 30% of the sea area. Ice is drifting north to this coastal band, and several polynyas are formed by the warm south winds around there. They have various names, such as the Great Siberian Polynya, and can stretch over many hundreds kilometers. The ice sheet usually starts melting from late May to early June, creating fragmented ice agglomerates on the north-west and south-east and often revealing remains of the mammoths. The ice formation varies from year to year, with the sea either clear or completely covered with ice.

Hydrology

The sea is characterized by the low water temperatures, which ranges from in the north to in the south-eastern parts. The medium water layer is warmer, up to 1.5 °С because it is fed by the warm Atlantic waters. It takes them 2.5–3 years to reach the Laptev Sea from their formation near Spitsbergen. The deeper layer is colder at about −0.8 °С. In summer, the surface layer in the ice-free zones warms up by the sun up to 8–10 °С in the bays and 2–3 °С in the open sea, and remains close to 0 °С under ice. The water salinity is significantly affected by the thawing of ice and river runoff. The latter amounts to about 730 km3 and would form a 135 cm freshwater layer over the entire sea; it is the second largest in the world after the Kara Sea. The salinity values vary in winter from 20 to 25‰ in the south-east to 34‰ in the northern parts of the sea; it decreases in summer to 5–10‰ and 30–32‰ respectively.
Most of the river runoff is contributed by the Lena River. Other major contributions are from Khatanga, Olenyok, Yana and Anabar, with other rivers contributing about 20 km3. Owing to the ice melting season, about 90% of the annual runoff occurs between June and September with 35–40% in August alone, whereas January contributes only 5%.
Sea currents form a cyclone consisting of the southward stream near Severnaya Zemlya which reaches the continental coast and flows along it from west to east. It is then amplified by the Lena River flow and diverts to the north and north-west toward the Arctic Ocean. A small part of the cyclone leaks through the Sannikov Strait to the East Siberian Sea. The cyclone has a speed of 2 cm/s which decreases toward the center. The center of the cyclone drifts with time that slightly alters the flow character.
The tides are mostly semi-diurnal, with the average amplitude of. In the Khatanga Gulf it may reach 2 m because of the funnel-like shape of the gulf. This tidal wave is then noticeable up to the unusually long distance of 500 km up to the Khatanga River – the tidal wave is damped at much shorter distance in other rivers of the Laptev Sea.
The seasonal variations of the sea level are relatively small – the sea level rises up to in summer near the river deltas and lowers in winter. Wind-induced changes are observed all through the year, but are more frequent in autumn when the winds are strong and steady. In general, the sea level rises with northern and lowers with southern winds, but depending on the area, the maximum amplitude is observed for a specific wind direction. They average amplitudes are 1–2 m and may exceed near Tiksi.
Owing to the weak winds and shallow waters, the sea is relatively calm with the waves typically within. In July–August waves up to 4–5 m are observed near the sea center, and they may reach in autumn.