Arctic Ocean

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Local environment

Definition and basic facts

The Arctic Ocean consists of a deep Ocean Basin, the broad shelves of the Barents, Kara, Laptev, East Siberian, Chukchi and Beaufort Seas, the White Sea, the Lincoln Sea and the narrow shelf off Canadian Arctic Archipelago and northern Greenland [1]. Its spatial extent is constrained by the Fram Strait, the western limit of the Barents Sea, the Bering Strait and the Canadian Archipelago (Fig. 1).
Figure 1: Arctic Ocean and its constituent seas. Red dotted line indicates the limits of the Arctic Ocean. Main basins of the deep Arctic Ocean basin: NB – Nansen Basin, AB – Amundsen Basin, MB – Makarov Basin, CB – Canada Basin. The bathymetric map is based on IBCAO model v.2.[2]

Arctic Ocean and its constituent seas make around 3 % of the total ocean area and only about 1 % of the volume. The Arctic Ocean is the shallowest (mean depth 1361 m) and has significantly larger continental shelves than other oceans.

The deep central Arctic Ocean Basin consists of four abyssal plains separated by submarine ridges. The abyssal plains make 12 %, while ridges make 16 % of the total area of the Arctic Ocean [1]. Lomonosov Ridge divide the Arctic Basin into two major sub-basins: Eurasian Basin and Amerasian Basin. Gakkel Ridge subdivides Eurasian Basin into Amundsen and Nansen Basins, while the Alpha-Mendelejev Ridge subdivides Amerasian Basin into Canada and Makarov Basins (Fig. 1).

Continental shelves encompass broad shelves of Eurasia and narrow shelves off North America and northern Greenland and altogether make up as much as 53 % of the total area of the Arctic Ocean. The Barents Sea is the largest of the epicontinental seas. The Laptev and East Siberian Seas are the shallowest (mean depths – 48 and 58 m, respectively). The Lincoln Sea and the adjacent area of the Northern Canadian Arctic Archipelago are the deepest portions of the Arcic Ocean shelve seas (mean depths – 257 and 338 m, respectively).

Arctic Ocean is nearly landlocked, the only connections to the other oceans are: 1) Bering Strait (depth 45 m), 2) Canadian Archipelago (depth 220 m) and 3) Fram Strait (depth 2600 m).

Stratification and circulation

Figure 2: Stratification of the Arctic Ocean water masses and seawater exchange with Pacific and Atlantic Oceans. (modified from MacDonald and Bewers [3])

The stratification in the Arctic Ocean is maintained by the fresh water dynamics. The major freshwater sources include: rivers (Arctic Ocean receives around 11 % of the global river runoff discharge), precipitation and ice melt. The low-salinity water from Pacific Ocean inflows via Bering Strait. The low-saline, cold surface waters occupy the upper ~ 50 m and form PML (Polar Mixed Layer) (Fig. 2). Polar halocline (a layer of cold water with a steep salinity gradients) forms below PML and limits the exchange between surface and deep ocean water masses. Deeper water masses are formed by transformed Atlantic waters.


The dominant features of the surface circulation are the clockwise Beaufort Gyre (over the Canadian Basin) and the Transpolar Drift (flowing from the Siberian coast towards the Fram Strait) (Fig. 3). The cold and low salinity Arctic surface waters are exported to the North Atlantic Ocean by East Greenland Current and through the Canadian Archipelago. Warm and high salinity Atlantic water inflow the Arctic Ocean via the Fram Strait and the Barents Sea.

Figure 3: Surface circulation and sea ice extent in the Arctic Ocean. A graphic produced by Philippe Rekacewicz, (UNEP/GRID-Arendal) and available at http://maps.grida.no/go/graphic/ocean_currents_and_sea_ice_extent (Last visited March 11, 2009)


Sea ice

The polar halocline isolates surface water masses and sea-ice from warm deep water and thus acts as a determining factor for the existence of all-year sea ice cover. The ocean’s interior is all year covered with perennial (multi-year) pack ice, while seasonal (first-year) ice-cover is formed on the marginal seas from October to June. The spatial extent of sea ice varies from 14-15 mln km2 in March to 6-7 mln km2 in September (Fig. 3). The inflows of warm Atlantic waters usually keeps the southern part of the Barents sea ice-free year round. The average thickness of sea ice in the Arctic Ocean is about 3 m. Land-fast ice (up to 2 m in thickness) grows seaward from the shore and usually extends to the 20 m isobath. Two forms of open water areas can occur in the winter ice-cover: 1) flaw lead systems – discontinuities between the land-fast ice and off-shore sea-ice or 2) polynyas – where ice is carried away by winds or currents or melted by the local convection of warm deep water masses.








Primary production

Primary productivity in the Arctic Ocean is relatively low, but can vary considerably between regions[4]. The productivity of the central Arctic Basin is among the lowest recorded in the world seas. The primary production is limited by the presence of multiyear ice- cover and very short growing season. The Siberian shelf seas also exhibit low productivity that is mostly nutrient-limited: the Siberian rivers are phosphorous-poor and the multi-year ice covers the shelf break, thus hindering the wind-driven upwelling of nutrient-rich deep waters at the shelf edge. In contrast, Barents Sea (that is kept ice-free by the inflows of warm Atlantic waters) and Chukchi Sea (that is supplied with nutrient-rich Bering Sea waters) can have primary production several times higher that the Arctic Ocean average (Table 1).


Table 1. Average annual primary production (av PP [gC m-2 y-1]) and total areal primary production (tot PP [106 t C]) in the Arctic Ocean and its constituent seas. After several authors compiled by Sakshaug [4]
area av PP tot PP
Arctic Ocean Basin >11 >50
Arctic shelves 32 279
Barents Sea 20-200 136
White Sea 25 2
Kara Sea 30-50 237
Laptev Sea 25-40 16
East Siberian Sea 25-40 30
Chukchi Sea 20->400 42
Beaufort Sea 30-70 8
Lincoln Sea 20-40 3
total Arctic Ocean >26 >329

Specific biodiversity issues

Arctic Ocean fauna is relatively young and comprise few endemics, it is mostly composed of species of Pacific or Atlantic affinity[5]. The origin and evolution of the arctic biota was summarized by Dunton[5] :

  • north polar sea originated as a large northern embayment of the North Pacific in the Mesozoic,
  • in late Cretaceous large connections to subtropical Gulf of Mexico and to tropical Tethys sea were developed (that could result in some subtropical taxa migrations and may explain the origin of some Arctic species with phylogenetic affinities with warm-water taxa)
  • about the end of Cretaceous the deep-water connection (and the exchange of bathyal and abyssal fauna) between Arctic Ocean and North Pacific was closed by continental plate movements,
  • deep-water seaways between Arctic Ocean and North Atlantic (and the migration of Atlantic taxa) occurred by the end of Eocene, that coincided with a large cooling of the northern high latitude areas (temperature decreased to below 10˚C)
  • successive cooling (temperatures dropped to below 5˚C in late Miocene) and the exchange with the North Atlantic led to the development of cool-temperate arctic biota of the Atlantic character
  • in late Pliocene the Bering Land Bridge was breached and the shallow water passage between Pacific Ocean and Arctic Ocean opened – the arctic fauna was strongly supplemented by migrants from Pacific Ocean
  • perennial ice cover developed in Pleistocene, when the Arctic was subjected to numerous glacial and interglacial intervals; during the maximum of the last major glaciation (18 ky ago) the Arctic shelves were either covered with permanent ice sheets or emergent and so the shallow water fauna was nearly completely eradicated. Arctic shallow seas are now considered to remain in a phase of colonization (after the last deglaciation, i.e. for the last 6-14 ky) [5].
Figure 4: Numbers of invertebrate species recorded in the Arctic deep basin and in the eurasian Arctic marginal seas according to Sirenko[6]

There are only few records of the fauna of the deep Arctic basin, and they are limited to a low number of samples. All the up-to date records show very low biomass (from 5 to 32 mg C m-2) and species diversity (from 1 to 11 species per 0.02 m2) of macrozoobenthos dwelling in arctic deep basins[7]. The fauna of the Siberian shallow shelf seas is also relatively impoverished as it is confronted with the low primary productivity and physical stress produced by massive riverine inflows. The productive waters of the Barents Sea host much higher numbers of species that other arctic regions[8] (Fig. 4). The local hot-spots of both productivity and biodiversity in the Arctic include flaw lead systems, polynyas, areas of oceanographic fronts where mixing between cold polar and temperate waters occur and marginal ice zone[9].



Threats

Figure 5: The decrease of Arctic Ocean multiyear sea ice: minimum sea-ice extent in 1982 and 2007, and projections of the future successive decrease of sea-ice extent within this century (according to the Arctic Climate Impact Assessment ). The graphic was produced by Hugo Ahlenius (UNEP/GRID-Arendal) and is available at http://maps.grida.no/go/graphic/the-decrease-of-arctic-sea-ice-minimum-extent-in-1982-and-2007-and-climate-projections. (Last visited March 11, 2009).

The main threats to biodiversity in this region are generated by the potential effects of the global warming. Land-surface air temperatures increased with an average rate of 0.09˚C/decade in the Arctic form 1900 to 2003 that is greater than overall trend documented for the northern hemisphere (0.06˚C/decade)[10]. The warming is accompanied by the decrease of both spatial extent and thickness of the Arctic sea-ice cover (Fig. 5).


The possible effects of the climate warming on the marine ecosystems of the Arctic Ocean were summarized by Loeng et al[9] and include:

  • poleward shift in species distributions – both southern limits of distribution of coldwater species and northern limits of warm water temperate species will move northward,
  • increase of primary productivity (driven by the removal of light limitation after the disappearance of sea ice cover) and possible change of timing of the blooms – that can affect the pelago-benthic coupling processes,
  • the dramatic decrease of the sea-ice extent will affect the sea ice ecosystems.


The decline of the sea-ice extent will improve the accessibility of the Arctic Ocean to shipping and exploration of the natural resources (extensive fishing and exploration of large oil and gas reserves). That will certainly largely increase the anthropogenic pressure on the relatively pristine ecosystems of the Arctic Oceans.

References

  1. 1.0 1.1 Jakobsson, M., 2002, Hypsometry and volume of the Arctic Ocean and its constituent's seas, Geochemistry Geophysics Geosystems, v. 3, no. 2.
  2. Jakobsson, M., R. Macnab, L. Mayer, R. Anderson, M. Edwards, J. Hatzky, H. W. Schenke, and P. Johnson (2008), An improved bathymetric portrayal of the Arctic Ocean: Implications for ocean modeling and geological, geophysical and oceanographic analyses, Geophysical Research Letters, DOI: doi: 10.1029/2008gl033520. http://www.ibcao.org
  3. MacDonald, R.W., Bewers, J.M., 1996, Contaminants in the arctic marine environment: priorities for protection. ICES J Mar Sci 53: 537-563
  4. 4.0 4.1 Sakshaug, E., 2003, Primary and Secondary Production in the Arctic Seas. in: Stein, R., MacDonald, R.W., The organic carbon cycle in the Arctic Ocean. Springer, pp 57-81
  5. 5.0 5.1 5.2 Dunton, K., 1992, Arctic biogeography: the paradox of the marine benthic fauna and flora. TREE 7, 183-189.
  6. Sirenko, B.I., 2001, List of species of free-living invertebrates of eurasian arctic seas and adjacent deep waters. Explorations of the fauna of the seas 51(59) St Petersburg, 1-129.
  7. Klages, M., Boetius A., Christensen, J.P., Deubel, H., Piepenburg, D., Schewe, I., Soltwedel, T., 2003, The benthos of Arctic Seas and its role for the organic carbon cycle at the seafloor. in: Stein, R., MacDonald, R.W., The organic carbon cycle in the Arctic Ocean. Springer, pp 139-167.
  8. Sirenko, B.I., 2001, List of species of free-living invertebrates of eurasian arctic seas and adjacent deep waters. Explorations of the fauna of the seas 51(59) St Petersburg, 1-129.
  9. 9.0 9.1 Loeng H, Brander K, Carmack E, Denisenko S and others (2005) Marine systems. In: Symon C, Arris L, Heal B (eds) Arctic climate impact assessment, ACIA. Cambridge University Press, Cambridge, p 453–538. available at http://www.acia.uaf.edu/PDFs/ACIA_Science_Chapters_Final/ACIA_Ch09_Final.pdf
  10. McBean, G, Alekseev, G., Chen, D., Forland, E. and others (2005) Arctic Climate: Past and Present. In: Symon C, Arris L, Heal B (eds) Arctic climate impact assessment, ACIA. Cambridge University Press, Cambridge, p 21- 60. available at http://www.acia.uaf.edu/PDFs/ACIA_Science_Chapters_Final/ACIA_Ch02_Final.pdf

See also


The main author of this article is Włodarska- Kowalczuk, Maria
Please note that others may also have edited the contents of this article.