Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 299

In the spring, the combination of sea ice melt and the arrival of freshwater river runoff
results in these lower-density waters lying above the more salty waters below. The water
columnissaidtobehighlystratified, whichresultsinsomeofthemostintense phytoplank-
tonprimary production knownanywhere. Onthe eastern Bering Sea shelf, this intense pho-
tosynthetic activity removes most of the CO 2 from the surface waters, which allows for yet
more CO 2 to enter from the atmosphere. A great deal of the organic matter produced by
the phytoplankton during the spring phytoplankton bloom falls to deeper depths, where it
eventually decays - either directly or indirectly. This leads to an injection of CO 2 into these
waters. This further lowers the pH and significantly depresses the Ω by about 0.2. Accord-
ing to a study reported in 2010 and 2011, these subsurface waters became undersaturated
with respect to aragonite (but not calcite).
Undersaturation has also been observed in the Chukchi Sea and in the surface waters
of the Canada Basin. Here, it was attributed to the new ice-free state, which allowed more
atmospheric CO 2 to dissolve into the ocean. This is thought to have lowered alkalinity and
calcium ion concentrations of the low salinity freshwater that has been accumulating in the
basin.
The AMAP assessment judged that the short and simple food web structure of Arctic
marine ecosystems leaves them potentially vulnerable to acidification. They considered
that shellfish, fish eggs and early fish larval stages are likely to be adversely impacted.
However, how organisms will cope with ocean acidification in the Arctic (and elsewhere)
remains a topic in need of answers. As a general rule, organisms that require calcium grow
more slowly under acidifying conditions in laboratory experiments. This is thought to in-
dicate that they are diverting more energy resources to the task of acquiring and maintain-
ing calcium.
The eastern Bering Sea supports one of the most intensive fisheries in the world. It
supplies about 47% of the U.S. fish catch. However, it is looking as if it may hold the un-
fortunate distinction ofbeing the first ocean area adjacent to North America to be adversely
impacted by climate-induced ocean acidification. How much or when the fishery will be
impacted is unclear, but it is perhaps safe to assume that shellfish and organisms that har-