Editorial: “Arctic melt, smash and grab ahead“
“WE ARE witnessing the early stages of the transformation of the Arctic,” says Louis Fortier of Laval University in Quebec City, Canada. For millennia, the top of the planet has been the preserve of specialist organisms, from fish with antifreeze running through their veins to bears capable of fasting for months. That’s all changing. An increasingly ice-free Arctic is opening a new frontier for life on Earth.
There are some windows into this warmer future: natural open-water hotspots that have always been present in the Arctic. Called polynyas, they are found in places where wind patterns and natural upwellings of warm water prevent ice from forming. The archetypal polynya is the North Water in northern Baffin Bay, says Fortier, “perhaps the most productive ecosystem beyond the Arctic Circle where marine mammals – including large whales – and humans have congregated for centuries”.
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Relatively few creatures have evolved to survive at Arctic temperatures, so the fate of entire food chains can pivot on a few species. Shift things slightly in time, space or volume and everything can tip.
Timing is a particular concern. Climate change means the sun is reaching into Arctic waters earlier. Ice that only formed the previous winter lets light through more readily than a 10-metre-thick floe that has been building for several years. This means the annual cycle of life can kick off earlier, creating a problem for large species like whales, whose migrations have evolved to coincide with the historical onset of spring.
In the Amundsen Gulf of north-west Canada, nutrient upwellings have become a recurrent feature since 2002, boosting local biodiversity, says Fortier. In June 2008, the nutrients triggered a phytoplankton bloom. In just three weeks, local primary productivity shot up to more than twice the annual amount. In the Beaufort Sea to the north of Alaska, the biomass of ice algae – which cling to the underside of ice floes and occupy the lowest link of the food chain – was more than three times that reported in 35 years of seasonal observations (Climatic Change, ).
Algal blooms are just the beginning. They feed tiny zooplankton, which provide vital energy supplies for organisms higher up the food chain – the polar bears that eat the seals, which eat the fish. Less ice, says of the University of Washington in Seattle, could cause a cascade of changes to these food chains.
Some of the transformations have already taken place and appear to be here to stay. , took water samples from the Beaufort Sea between 2003 and 2010, and used DNA analysis to see what algae, plankton and bacteria it contained. The species composition was constant between 2003 and 2006, but in 2007, when summer ice cover was abnormally low, photosynthetic organisms suddenly seemed to take over. Although the following years saw more summer ice cover, the community never reverted to its initial make-up (PLoS One, ).
“Some of the changes have already taken place and appear to be here to stay”
Elsewhere, species are moving in from further south. The polar cod once dominated the Hudson Bay and Beaufort Sea, but capelin and sand lance are now making appearances. Pacific salmon are also moving into the Arctic Basin, says Fortier. For now, the local polar cod and Arctic charr seem unaffected. But that could change if further warming brings in more competitive generalists, which can thrive in a wide range of environments. They might be able to outcompete the wildlife that has taken millennia to adapt to the unique conditions of the Arctic.
In the short run, the top of the world looks set to bloom, at least in parts. Some will profit: industrial fisheries are already keen to move in. But at what cost? Fortier hesitantly predicts that Pacific plankton and fish will dominate by 2050 and many marine mammals and birds could be gone entirely by the end of the century.
“It might take decades until we observe the final ‘new state’,” says Rolf Gradinger of the University of Alaska Fairbanks. “But once a tipping point has been reached, there might be no way back – although we’ll see oscillations around a new centre.”
For more on the Arctic’s record low in ice coverage, see “Arctic ice low heralds end of 3-million-year cover“
Future not all bad for bears
Thin ice could be good news for some species, at least initially. It’s a habitat in which seals thrive. “They want to slip up on an ice floe and slip back in,” says Marine Mammal Laboratory in Seattle. Thin ice that formed the previous winter also crumples more easily than thick multi-year floes, forming ridges and gaps that offer breathing holes.
That makes this first-year ice attractive to the animal at the top of the Arctic food chain: the polar bear. Some areas have seen an increase in Ursus maritimus, says . Polar bears typically move to thicker ice during the autumn but can move onto land to den as well.
In the short run, then, some polar bear populations could benefit from thinner ice. Others won’t. Melissa McKinney and Robert Letcher of Environment Canada in Ottawa studied polar bears near Hudson Bay and found they ate different seal species in years when the sea ice broke up early. That could be a problem: some species live in water with high levels of PCBs, flame retardants and other toxic chemicals from fertiliser runoff. The contaminants move up the food chain, but the consequences are unclear as yet.
Although the changes might bring benefits in the short term, the long-term picture is very different. Seals could lose breeding ground if the ice pulls away from the shore before they can give birth, for example. And more open water means polar bears need to spend more time swimming than they can afford. As the open-water season lengthens, so will their fasting time. Other species from further south – such as brown bears – may stand a better chance.
