Arctic ocean
Contents
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 [2]. 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).
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 [2]. 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
The stratification in the Arctic Ocean is maintained by fresh water dynamics. The major freshwater sources include: rivers (Arctic Ocean receives around 11 % of the global river runoff discharge), precipitation and ice melt. Low-salinity water from Pacific Ocean inflows via Bering Strait. The low-saline, cold surface waters occupy the upper ~ 50 m and form the Polar Mixed Layer (PML, Fig. 2). Polar halocline (a layer of cold water with a steep salinity gradients) forms below the 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.
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 inner part of the Arctic ocean 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 million km2 in March to 4-7 million km2 in September (Fig. 5). 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 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 than the Arctic Ocean average (Table 1).
| 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 (about 18,000 year 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 6-14,000 year) [5]
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 than other arctic regions[6] (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[8].
Threats
The observed mean temperature trend in the Arctic is 0.73 ∘C/decade and for the globe as a whole 0.19 ∘C/decade for the latest 43-year period of 1979–2021, meaning that the Arctic has warmed nearly four times faster than the globe since 1979[9]. 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[8] and include:
- poleward shift in species distributions – both southern limits of distribution of cold-water 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 ecosystem.
Because sea ice is an effective sunlight reflector, a decrease in sea ice cover implies greater heat absorption by Arctic waters. The decreasing Arctic albedo therefore contributes to the warming of Arctic waters and thus provides a positive feedback to the decrease in Arctic ice cover[10]. 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). This will certainly increase the anthropogenic pressure on the relatively pristine ecosystems of the Arctic Oceans.
Related articles
- Sea ice ecosystem
- Predicted biodiversity changes in the Arctic
- Monitoring keystone components of sub-Arctic foodwebs
References
- ↑ Jakobsson, M., Macnab, R., Mayer, L., Anderson, R., Edwards, M., Hatzky, J., Schenke, H.W. and Johnson, P. 2008. An improved bathymetric portrayal of the Arctic Ocean: Implications for ocean modeling and geological, geophysical and oceanographic analyses. Geophysical Research Letters 35, L07602
- ↑ 2.0 2.1 Jakobsson, M. 2002. Hypsometry and volume of the Arctic Ocean and its constituent's seas, Geochemistry Geophysics Geosystems 3, 5
- ↑ MacDonald, R.W. and Bewers, J.M. 1996. Contaminants in the arctic marine environment: priorities for protection. ICES J Mar Sci 53: 537-563
- ↑ 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
- ↑ 5.0 5.1 5.2 Dunton, K. 1992. Arctic biogeography: the paradox of the marine benthic fauna and flora. TREE 7: 183-189
- ↑ 6.0 6.1 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. Cite error: Invalid
<ref>tag; name "S01" defined multiple times with different content - ↑ Klages, M., Boetius A., Christensen, J.P., Deubel, H., Piepenburg, D., Schewe, I. and 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.
- ↑ 8.0 8.1 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.
- ↑ Rantanen, M., Karpechko, A.Y., Lipponen, A. et al. 2022. The Arctic has warmed nearly four times faster than the globe since 1979. Commun Earth Environ 3, 168
- ↑ Kashiwase, H., Ohshima, K.I., Nihashi, S. and Eicken, H. 2017. Evidence for ice-ocean albedo feedback in the Arctic Ocean shifting to a seasonal ice zone. Nature Scientific Reports 7: 8170
See also
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