The melting of Arctic sea ice as the climate warms is such a dramatic change to northern ecosystems that it will have a serious impact not just on ocean dwellers such as whales and seals, but land animals such as caribou and foxes, scientists say.
The proportion of the Arctic covered by sea ice during the summer hit a record low in 2012. Since 1979, the summer sea ice coverage has declined by about three-million kilometres squared, losing an area larger than the province of New Brunswick each year, scientific records show. Because dark open water reflects far less sunlight than ice, warming accelerates with sea ice loss, which in turn causes the ice to melt more quickly.
While most people see the loss of sea ice as a sign or indicator of climate change, it's far more than that, say U.S. and Canadian scientists in a paper published Thursday online in the journal Science.
Sea ice in the Arctic is analogous to trees in a forest, said Jedediah Brodie, a conservation ecologist at the University of British Columbia who co-authored the paper.
"When you cut the trees, you alter the entire ecosystem — every other species that lives in a forest in some way depends on those trees," he said in a phone interview.
'Loss of a globally important ecosystem'
The loss of sea ice is "actually the loss of a habitat," he added, "and that's the loss of a globally important ecosystem."
Sea ice plays a huge role in the Arctic because 80 per cent of the low-lying tundra is within 100 kiometres of the ocean that is covered by ice for at least part of the year.
Penn State University biologist Eric Post, lead author of the paper, wanted to examine the relationships among Arctic organisms from algae to whales to bears, and compile the ways in which they might be affected by the loss of sea ice. He sought help from experts in the U.S. and Canada, including Brodie, who researches how environmental change affects ecosystems; University of Calgary veterinary medicine researcher Susan Kutz; and University of Alberta polar bear specialist Ian Stirling.
It's most obvious that sea ice loss will affect marine organisms, but some of the specific effects are not intuitive.
For example, the loss of ice reduces the fat content of algae that live between layers of ice, making them less nourishing to marine animals, the researchers noted.
The melting ice is also changing the timing each summer of huge blooms of phytoplankton that form the base of the Arctic food chain, which may shorten the season for the blooms, causing ripples all the way up the food chain to fish, seabirds and marine mammals such as seals and whales.
Many marine mammals such as seals also rely on sea ice as a place to raise their young or even just to rest after long dives in search of fish. As the sea ice disappears, animals such as walruses have been crowding onto shorelines, which can lead to their young being trampled or the spread of disease through the population.
The loss of sea ice also has many indirect, inintuitive effects on both marine and land animals.
"It can have pretty dramatic effects on climate even far inland," Brodie said.
That in turn can affect the growth of vegetation on land, disrupting food sources for animals such as caribou.
Indirect effects on migration, breeding
The article notes a number of other potential indirect effects of sea ice loss on land animals:
- Isolation and increased inbreeding among populations of wolves and arctic foxes, which currently use ice to travel between populations during most of the year.
- Increased interbreeding and hybridization between grizzly bears and polar bears because polar bears are spending more time on land, where they come into contact with grizzlies.
- The spread of diseases that were once restricted by sea ice barriers to a certain part of the Arctic, such as phocine distemper virus, which currently affects only eastern Arctic seals.
- Increased shipping in the Canadian Arctic and the later freeze up of the ice could affect the annual migration of the Dolphin and Union caribou herd.
The paper noted that it is a challenge to forsee how sea ice decline will increase human activities such as shipping and industrial development in the Arctic, which could also have negative consequences for many species.