Arctic Ocean More Vulnerable ToClimate Change Than Antarctic Ocean
09 August, 2013
The Arctic Ocean is more vulnerable to human-induced changes than the Antarctic Ocean according to a study done by a team of scientists. The results were published in Nature's Scientific Reports.
Moreover, another study has found rapid thawing of Arctic sea ice is affecting virtually every species of Arctic wildlife. Loss of algae and plankton is threatening Arctic food chain.
The vulnerable Arctic
After comparing sites in both oceans, scientists have found the Arctic site to be more acidic, warmer during the summer months, and have fewer nutrients. These disparities account for the differences in vulnerability.
The team of scientists included Dalhousie University Oceanography Professor Helmuth Thomas and recent Dalhousie Oceanography PhD graduate Elizabeth Shadwick.
The polar oceans are sensitive to increasing global temperature and increasing concentrations of atmospheric carbon dioxide (CO2). The impact of climate change is expected to be particularly large in ice-covered regions. Up until this project, the Arctic and Southern Oceans remained under-studied at the annual scale compared to other oceans, with the majority of observations restricted to the ice-free summer and autumn seasons.
"Thanks to this research, we now better understand the interplay of various climate and biogeochemical drivers in controlling ocean pH and carbonate saturation state in polar regions," said Dr. Helmuth Thomas. "Climate and biogeochemical conditions make the marine Arctic ecosystem more vulnerable than the Antarctic ecosystem, with potentially severe consequences for peoples living at the Arctic coastline."
The team compared two high-resolution observational data sets of complete annual cycles for sites in the Arctic and Antarctic oceans (Amundsen Gulf and Prydz Bay , respectively).
The scientists found that the Arctic site experienced greater seasonal warming (10 vs 3 degrees Celsius), and freshening (by 3 vs 2 salinity units), had lower alkalinity (2220 vs 2320 µmol/kg), and lower summer pH (8.15 vs 8.5), than the Antarctic site.
The Arctic carbon system showed smaller seasonal changes than the Antarctic system. The team assumes excess surface nutrients in the Antarctic may help reduce the extent of ocean acidification in that area and the Arctic system may be more vulnerable to anticipated future changes in ocean pH and the carbonate saturation state.
Some carbonate shell forming species play crucial roles in polar foodwebs, and are relevant to human food supply. The team expects changes in pH and the carbonate saturation state to have detrimental effects for carbonate shell forming species and therefore potentially for human food supply. The team expects to see these effects decades earlier in the populated Arctic regions than in the unpopulated Antarctic regions.
Threatened Arctic food chain
The polar bear has less chance of catching seals due to melting Arctic ice.
Tim Radford reported:
The loss of Arctic sea ice is bad news for the Pacific walrus and polar bears, but the real problems begin at the base of the food chain.
Since the end of the last century, more than two million square kilometers of sea ice have disappeared, and the loss of summer ice is accelerating. Researchers call this “a stunning loss of habitat for sea ice algae and sub-ice plankton which together account for 57% of the total annual primary production in the Arctic Ocean .”
Eric Post, a biologist at Penn State University in the US, and colleagues report in Science that the seasonal timing of the ice algae bloom is critical to the successful reproduction of the zooplankton copepods (small crustaceans) that graze on the algae, and the bloom in phytoplankton that follows the normal seasonal retreat of the sea ice delivers food for the copepod offspring.
These two “pulses” in productivity in the Arctic are the basis of the food web for all the higher creatures. The copepod explosion provides breakfast, lunch and supper for whales, seabirds, small fish, crustaceans and so on.
But the fact that the total area under ice each summer has been shrinking at 86,000 square kilometers a year, and the annual ice melt season has been extended by at least 20 days, could have profound consequences for the entire ecosystem, and for the big, warm-blooded creatures at the top of the food chain.
“Our team set out to explore the domino effects of sea ice loss on marine mammals, as well as on land dwelling species living adjacent to the ice,” said Post. The ice shelf is a habitat for large mammals: as the ice thins and dwindles so does the habitat, and therefore the hunting opportunities.
Walruses forage for food in shallow waters, and use the sea ice to rest, and to dive from, between foraging. As the ice melts and retreats from the shoreline the ice edge moves over deeper waters, and the walrus community increasingly has to crowd together on the shoreline rather than the ice, making the spread of infection easier, and increasing the dangers of trampling for the young.
As the ice retreats, polar bears have less access to seal populations – and supplies of blubber – and they too have begun to mingle populations: there have been increasing reports of hybridisation with grizzly bears.
Because sea ice in Arctic Canada is decreasing, there is a greater likelihood of contact between eastern and western Arctic seal populations, and a greater chance that phocine distemper virus will spread from the eastern seals to the western population.
Sea ice loss could affect the populations of Arctic fox and wolf because the loss of ice will increase genetic isolation, and the warming of the land surfaces in the Arctic is beginning to alter the vegetation, with consequences for caribou and other grazers.
Another important consequence of sea ice loss is a change in the Arctic albedo – the measure of radiation that normally bounces off the ice and back into space, keeping the Arctic cold.
In Nature Climate Change, Aku Riihelä of the Finnish Meteorological Institute in Helsinki and colleagues report that they looked at satellite data from 1989 to 2002, during the summer months, for both open water and sea ice regions of the Arctic .
They found that all albedo trends show a significant reduction, which is another way of saying that more sunlight is being absorbed into the land and ocean of the Arctic , which will accelerate the rate of warming and the loss of further ice.
The consequences of this for the whole Arctic ecosystem will be considerable, warns Professor Post. As the seas open, they become accessible to shipping traffic and drilling rigs, and any increase in this could affect both terrestrial and marine creatures, among them the bowhead whales and the Pacific walrus.
“By viewing sea ice as essential habitat and a substrate for important species interactions, rather than as a lifeless blank surface, its loss as a result of warming becomes a rather stunning prospect,” he says.
 Story Source:
The story is based on materials provided by Dalhousie University , via Newswise.
E. H. Shadwick, T. W. Trull, H. Thomas, J. A. E. Gibson. Vulnerability of Polar Oceans to Anthropogenic Acidification: Comparison of Arctic and Antarctic Seasonal Cycles. Scientific Reports, 2013; 3 DOI: 10.1038/srep02339
Dalhousie University (2013, August 6). Arctic Ocean more vulnerable to human-induced changes than Antarctic Ocean . ScienceDaily. Retrieved August 9, 2013, from http://www.sciencedaily.com /releases/2013/08/130806155545.htm
 Responding to Climate Change, August 8, 2013, Loss of algae and plankton threatens Arctic food chain,
http://www.rtcc.org/2013/08/08/less-reflective-arctic-ice-threatens-wildlife/ . This article was produced by the Climate News Network.
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