Climate change: effects on marine ecosystems
In polar seas, ongoing climate change is causing other major changes. The physical properties of water are altered; circulation patterns change and sea ice cover is shrinking. These rapid climate changes lead to shifts and upheavals in marine ecosystems and in the biogeochemical cycle. Climate change can affect marine organisms through many different processes that are interlinked in complex and unpredictable ways.
In spring and summer, the oceans of the Arctic are extremely productive; masses of different seabirds and sea mammals come to the Arctic to feed on zooplankton and small fish. Changes in the marine environment in the Arctic can thus affect species that spend much of the year elsewhere. A wide range of alterations in the arctic marine environment have been shown to be caused by climate change. For example, some sub-arctic species and a few from temperate regions have experienced a northward shift in habitat. This led to changes both in the occurrence of key species and in the food web. Simultaneously, the occurrence and reproductive rate of some arctic species declined, especially the ice-dependent species.
There is documentation showing increased primary production in open water in Arctic Ocean. Overall, available studies imply that the effects of climate change arise mainly through increased inflow of warm water from the Atlantic and Pacific Oceans to the Arctic Ocean, longer residence time for these warm water masses, and changes in sea ice, rather than through direct warming.
With higher water temperatures, more warmth-craving species can survive in the Arctic and compete successfully with some of the species that currently live there. The copepod Calanus finmarchicus is a crucial species in the marine ecosystem in the High North, not least as food for commercially important species of fish. With rising water temperatures, these copepods may be displaced by species from farther south, with lower nutrient content. In the same way, C. finmarchicus may displace the lipid-rich arctic zooplankton species that live farther north, thus reducing the availability of nutrients for seabirds and arctic fish.
Commercially important fish such as cod and capelin may shift their range to the north and east and migrate into Russian waters. Seabirds and sea mammals follow their prey: zooplankton or small fish. If the ranges of these prey species shift, the occurrence of seabirds and sea mammals in the open sea will also change.
Melting glaciers will probably increase the inflow of fresh water, sediments and some nutrients to coastal areas in the Arctic. This can affect water circulation, biological productivity and ecosystem structure in fjords and along coasts.
When tidal glaciers retreat up onto land, important feeding grounds for seabirds and sea mammals can be lost. At the terminus of a tidal glacier, upwelling nutrient-rich water increases plankton productivity, and seals use icebergs calved from the glacier as resting places. In Svalbard, these areas are particularly important feeding grounds for ringed seals and white (beluga) whales in summer and autumn. Cold fresh water from melting glaciers can paralyse or kill plankton and crustaceans, attracting polar cod (Boreogadus saida) and capelin (Mallotus villosus), which feed on them. Polar cod and capelin are in turn important prey species not only for white whales and ringed seals, but also a multitude of seabird and marine mammal species.
Major changes that are occurring in the climate of the Southern Ocean will have significant impact on the marine ecosystem. Over the past 50 years, many changes have been documented, particularly on the western side of the Antarctic Peninsula, where the rise in temperature has been greatest, and where the extent of sea ice has decreased. Krill populations are declining; in some places, primary production is increasing, in others it is decreasing. Some species, for example a few species of salps, have shifted their range southward.
- Paul Wassmann et al. 2010. Footprints of climate change in the Arctic marine ecosystem. Global Change Biology. (Vol. 17): 1235–1249. DOI:10.1111/j.1365-2486.2010.02311.x
- Arctic Monitoring and Assessment Programme (AMAP), 2012. Arctic Climate Issues 2011: Changes in Arctic Snow, Water, Ice and Permafrost. Snow, Water, Ice and Permafrost in the Arctic (SWIPA) 2011 Overview Report.