Knock-on effects for wildlife as the Arctic loses ice
- 01 Aug 2013, 19:30
- Freya Roberts
Credit: Eric Post
Many of the impacts of retreating Arctic sea ice
are reasonably well
known. But the loss of sea ice isn't just a
climate issue, it's also an ecological one. A new
review article in the journal Science examines the effect of
climate change in the Arctic on the plants, animals and ecosystems
of the region.
Temperatures in the Arctic have risen
twice as fast as the global average in
recent decades. Sea ice cover is in long term decline. In the
summer of 2012, sea ice reached its lowest
level since satellite records began in
Scientists agree that the decline will
consequences for the climate - extra heating
and possible changes to weather patterns. But, as the new review
article explores, the loss of sea ice and warming oceans will have
an impact on the Arctic's wildlife too.
Working up the food chain
The Science article examines a range of
scientific literature to explain how changes in the region affect
life at all scales.
At the lowest levels of the food chain, some of
the simplest underwater creatures like algae and phytoplankton are
feeling the effects of sea ice loss. Algae and
phytoplankton have a short and dramatic life cycle. They have one
growth spurt each season, when the sea ice thins and retreats
exposing them to the sunlight they need to make energy.
With sea ice melting earlier each year, algae
and phytoplankton populations are peaking earlier, and starting to
decline sooner. This can mean that by the time predators looking to
feed on them arrive, much of the food source is gone.
The fallout from this mismatch in timing spreads
through the food chain, affecting bigger animals. Crustaceans and
fish like the Arctic cod struggle to find enough food. Mammals
which feed on cod, like seals, go hungry. Polar bears feed on
seals, and can struggle to lay down enough fat to survive long
Sea ice loss also alters the physical landscape
of the region, limiting the movement of Arctic animals. Some
species use the sea ice to hunt and sleep, while land-based animals
Arctic fox and
wolves use it as a bridge to reach other places,
allowing them to breed with other populations and maintain a
healthy gene pool. Without it, these populations will become
isolated and could decline, the paper concludes.
Being increasingly bound to the land as sea ice
retreats has other risks, including the easy spread of disease and
crossbreeding. For polar bears, more time on land increases
the likelihood of crossbreeding with
A leaner, greener Arctic
It's not just animals affected by changes in the
region. More heat will be absorbed by the open ocean as sea ice
retreats - known as the albedo effect - leading to further warming
in the region.
That extra heat will affect surrounding icy land
masses too, the article explains. Much of the
land in the Arctic circle is frozen, with a layer on top which
thaws during the warmer months of the year.
This semi-frozen land, or permafrost
, is expected to thaw more extensively and for a longer
period of time as Arctic sea ice shrinks, temperatures rise and the
summer season lengthens. This could release methane - a powerful
Another consequence of longer thaw seasons is
that plants are likely to start growing earlier in the year. In
parts of Greenland, frozen areas are
already greening up early, with the growth
spurt of simple plant species peaking before migrating Caribou
arrive to feed. This is causing a timing mismatch similar to that
taking place in the ocean food chain.
Taking the land areas in the Arctic as a whole,
plant growth does seem to have increased as sea ice has declined,
the authors say.
The upside of this is that more carbon may be
being stored in plant life, rather than the atmosphere. But with
the potential for extra methane to be released from thawing
permafrost it's hard to say whether a greener Arctic is speeding up
or slowing down climate change.
Directly or indirectly, the loss of Arctic sea
ice poses the risk of serious impacts on wildlife in the region. In
some cases it's already happening. Changes at the bottom of the
food chain are likely to be felt at the top, and a warming ocean
will likely thaw its neighbouring land.
As the Science review article points out, sea
ice loss isn't just a warning sign of climate change - it's
something which actively drives ecological change. With climate
change adding to a host of other pressures on the region, from
fishing to shipping and mineral exploration, the Arctic's wildlife
is facing a difficult future.
Post et al. (2013) Ecological Consequences of
Sea-Ice Decline. Science. DOI: 10.1126/science.1235225
Note: All images in this blog are property of lead author
Eric Post and co-author Jeffrey Kirby, University of