Global Outlook for Ice & Snow

ever, the sea-ice habitat is of most important for larvae and juvenile stages of the krill species Euphausia su- perba . Concentrations up to 3000 individuals per square metre have been observed in under-ice crevices during spring 60 . Sea-ice algae and bacterial assemblages on the underside of ice floes enable the krill larvae to survive the winter months when food in the water column is absent. Sea ice also provides them with an important refuge from predators. Marine mammals endemic to polar regions have evolved into specialists that deal extraordinarily well with condi- tions that would be considered very harsh for most other mammals 61 – 63 . Their morphology, life history and behav- iour patterns are all finely tuned to deal with cold temper- atures and the high degree of variation in temperatures and conditions between seasons and from year to year. Mammals and birds dependent on sea ice

The presence of extensive areas of sea ice is of overrid- ing importance to many polar marine mammals. Most of the marine mammals that are year-round residents of the Arctic or the Antarctic spend much of the year in close association with sea ice. Predictions for changes in sea-ice conditions in polar regions due to global warm- ing are a cause for great concern with respect to polar marine mammal populations. Worst case scenarios cer- tainly include the extinction of some species in the com- ing decades in the Arctic 31 , 64 . Climate change also poses risks to these polar marine mammals beyond the direct impacts on habitat brought about by alterations to the physical environment. These include 31 , 65 – 67 : changes to their forage base (such as shifts in the spe- cies, density and distribution of prey species); increased competition from temperate species expand- ing northward;

Figure 5.15a: Underside of multi-year sea ice. Photo: Haakon Hop, Norwegian Polar Institute

Figure 5.15b: Gammarus wilkitzkiii , one of the most abundant ice amphipods associated with under-ice habitats. Photo: Haakon Hop, Norwegian Polar Institute

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GLOBAL OUTLOOK FOR ICE AND SNOW