Ecosystem assessment of the Central Arctic Ocean: Description of the ecosystem

The report provides a description of the ecosystem in the Central Arctic Ocean, or CAO. This is a deep-sea area with two main basins of depths to 4–5 km, separated by the Lomonosov Ridge. The CAO is a globally unique ecosystem, characterized by presence of sea ice and very low primary production by phytoplankton and ice algae. Atlantic water flows into the CAO through the deep Fram Strait and across the Barents Sea shelf, and continues as a set of boundary currents anti-clockwise around the slopes of the CAO basins. The circulation of the boundary currents takes place at an intermediate depth of about 200–1000 m, underneath a gradient layer with strong salinity and density stratification, and a seasonally dynamic top layer with two prominent circulation features: the Beaufort Gyre in Canada Basin, and the Transpolar Drift across the North Pole that exits in Fram Strait. A smaller amount of Pacific water (ratio of about 1:5 to Atlantic water) flows north through the Chukchi Sea and into the gradient layer between the surface polar water and the deeper Atlantic water of the boundary currents. The Pacific water exits primarily through Canadian Arctic Archipelago passages into Baffin Bay.

The circulating waters and floating sea ice form the dynamic habitats of the animals and plants that constitute the living part of the CAO ecosystem. Large calanoid copepods, with Calanus hyperboreus as the most important species in terms of zooplankton biomass, reproduce successfully mainly in the peripheral parts of the CAO with seasonal ice cover. Sea ice amphipods, with Gammarus wilkitzkii and Apherusa glacialis as the two most prominent species, are the dominant group among the sea ice invertebrate fauna. An important issue addressed in the report, is how the ice fauna can maintain their populations by recolonizing new sea ice as it forms in autumn and winter. 

About 50 species of fish have been either found (39 species), or are considered likely to occur (14 species), in the CAO. Most of them are small species, dominated by eelpouts along the basin slopes, and sculpins on the upper slopes and surrounding shelves. Two small cods, polar cod (Boreogadus saida) and Arctic cod (Arctogadus glacialis), are assumed to be the most important fishes in the CAO foodwebs. Thirty-five species of birds and 35 species of marine mammals have been recorded in the CAO. Most of them are seasonal visitors, and  the CAO plays small roles for their populations overall. Exceptions to this are two species of gulls, ivory gull (Pagophila eburnea) and Ross’s gull (Rhodostethia rosea), for which the marginal ice zone of the CAO in late summer provides a habitat for large parts of their global populations. Polar bear (Ursus maritimus) is the marine mammal with strongest dependence on sea ice habitats in the CAO. Considerable parts of several subpopulations of polar bear (Barents Sea, Laptev Sea, Chukchi Sea, Southern and Northern Beaufort Sea subpopulations) move seasonally with the retreating sea ice into the CAO in summer.

There has been a large loss in sea ice since the 1990s in what is termed the “Great melt”, with a pronounced change from heavier multiyear pack ice to thinner annual ice. The report describes some of the associated changes in the CAO ecosystem associated with the loss and change in sea ice habitats. However, the main aim of this report is to provide detailed descriptions of the current CAO ecosystem and its various components, thereby providing a basis for more in-depth assessments on the impacts of climate change and other human activities in future. 

Changes carried out on 18/08/2022: PICES and PAME logos added, and information added to the disclaimer.