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Sea Ice Melt has Implications for Acidification of Arctic Waters 11/2009
12/04/2009 | Marilyn Sigman, Alaska SeaGrant/MAP
Tags: Arctic Ocean, Changing Arctic Sea Ice, Climate Change, Ocean Acidification

Two scientific journal articles published in November, 2009, related the extent of sea ice melt to undersaturation of aragonite which is required for shell-building by many plankton and invertebrate species in Arctic waters. A combination of processes are now working to increase acidification and lower the concentrations of forms of calcite used for shell-building: 1) increased carbon dioxide in the ocean from anthropogenic sources, 2) freshening and dilution as ice melts, 3) increased biological activity after the ice melts which takes up calcite from surface waters and depletes it in subsurface waters as organic matters decays and produced CO2, and 4) upwellings of low pH waters.

Yamamoto-Kawai et. al. published an article in the November 20th issue of Science concerning their measurements of undersaturated surface waters in the Canada Basin of the Western Arctic Ocean in 2008 which concluded that this was a direct consequence of the recent extensive melting of sea ice in that Basin. According to the abstract “the retreat of the ice edge well past the shelf-break has produced conditions favorable to enhanced upwelling of subsurface, aragonite-undersaturated water onto the Arctic continental shelf."

The “take-away” messages from the article were summarized by the Teaching Climate Law blog as:

    • The Southern Ocean is predicted to become undersaturated with respect to aragonite by 2030, and in the North Pacific by 2100; Arctic surface waters will become undersaturated with aragonite within a decade. This is attributable to freshening related to sea ice melting and increased carbon uptake related to sea ice retreat;
    • Aragonite saturation has already decreased in the top 50 meters of the Canada Basin; this is the layer in which rapid uptake of carbon dioxide occurs and increased freshwater inputs take place; this could have serious implications for many species of marine organisms, including coccolithophore, foraminfera, pteropods, mussels and clams. For example, aragonite shell-forming pteropods are concentrated in the top 50 meters
    • Populations of both planktonic and benthic calcifying organisms in the Canadian Basin are already being affected by the rapid transition to undersaturation in the Arctic environment, another “canary in the coal mine” in terms of climate impacts.
Full text available by subscription or pay-per-article

Yamamoto-Kawai, M., F. A. McLaughlin, E. C. Carmack, S. Nishino, K, Shimada. Aragonite Undersaturation in the Arctic Ocean: Effects of Ocean Acidification and Sea Ice Melt. Science, November 20, 2009. Vol. 326. no. 5956, pp. 1098 - 1100
DOI: 10.1126/science.117419

In a related article, Bates, Mathis, and Cooper (2009) published the calculated calcium carbonate mineral saturation states for aragonite and calcite for waters of the Chukchi Sea shelf and Canada Basin during an oceanographic study conducted from 2002 to 2004. The surface waters were seasonally undersaturated in areas where the sea ice had melted over the Chukchi Shelf and in patches over the deeper Canada Basin. They considered the phenomenon to be likely a recent one that resulted from the uptake of anthropogenic CO2 and subsequent ocean acidification.

They also related the seasonal nature of change in saturation rates to the high productivity that occurred after the ice retreated, which would have served to increase aragonite and calcite in surface waters while subsurface waters became undersaturated with respect to aragonite as organic matter decayed and released CO2. The abstract concluded “The benthic ecosystem of the Chukchi Sea (and other Arctic Ocean shelves) is thus potentially vulnerable to future ocean acidification and suppression of CaCO3 saturation states.”

Bates, N.R., J.T. Mathis, and L.W. Cooper. Ocean acidification and biologically induced seasonality of carbonate mineral saturation states in the western Arctic Ocean. Journal of Geophysical Research Oceans. Published 11/5/09

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