A team including Dalhousie University Oceanography Professor Helmuth Thomas and recent Dalhousie Oceanography PhD graduate Elizabeth Shadwick found evidence suggesting that the Arctic Ocean is more vulnerable to human-induced changes than the Antarctic Ocean. After comparing sites in both oceans, they found the Arctic site to be more acidic, warmer during the summer months, and have fewer nutrients; those disparities account for the differences in vulnerability.
The results were published in Nature's Scientific Reports.
The polar oceans are sensitive to increasing global temperature and increasing concentrations of atmospheric carbon dioxide (CO2). The impacts of climate change are 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," says 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). They 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 believes excess surface nutrients in the Antarctic may help reduce the extent of ocean acidification in that area and they believe that 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.
- 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
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