Vulnerable environment in the marginal ice zone

The marginal ice zone from the open ocean inwards through the pack ice to dense pack ice, fast ice and multiyear ice will be more vulnerable to pressures for large parts of the year. This is because of high production and biodiversity under the water as far as the light penetrates, and the high density of seabirds, marine mammals and polar bears.

Biological activity in the marginal ice zone through the year. Illustration: Paul Wassmann, University of Tromsø

The marginal ice zone is biologically important because the stable upper layer of the water is mixed here by a combination of ice melting and wind. This leads to a comparatively brief, but intense production of phytoplankton (primary production) in the water masses near the ice edge and in the marginal ice zone itself (see the illustration). Zooplankton, fish, marine mammals and seabirds exploit this and gather at the ice edge.

A large part of the biological production sinks through the water column and forms a basis for rich communities of benthic? organisms in ice-influenced areas. Ice algae, too, which are tied to the actual ice, will contribute to the total production in the area. The bloom of ice algae starts earlier than the phytoplankton bloom in the water masses, thus prolonging the productive season in the marginal ice zone.

The marginal ice zone and ice-edge habitats in general are also essential for the total annual energy budget of many arctic, endemic species like ivory gulls, ringed seals, polar bears, narhvals, beluga whales and bowhead whales. Several of these are Red Listed nationally and internationally. These habitats are also important for many migratory species, like kittiwakes and black guillemots. Disturbances to the habitats may therefore have consequences for the population levels of many species.

Sea ice as a habitat has a unique status and value. The sea ice is the platform on which some species of seals, like harp seals and hooded seals, reproduce and have their pups, and it is also a habitat where arctic whales find protection. The great concentrations of many species, often in very limited areas in the marginal ice zone, mean that these species are very vulnerable when they are there. For instance, in late summer, 80–90% of the global population of ivory gulls are in the marginal ice zone in the Barents Sea.