L. Shimek, Ph.D.
My contribution to this month's reading list was published
on 29 September, 2005, in the journal, Nature. All reef aquarists
are familiar with the necessity of maintaining alkalinity
within "natural" levels in their systems. But what
is going to happen to the world's ecosystems when that "natural"
level of alkalinity changes? This article discusses some of
the consequences of the upcoming change in the global oceanic
alkalinity changes that will be occurring over the next few
Orr, J. C., V. J. Fabry, O. Aumont, L. Bopp, S. C. Doney,
R. A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos,
R. M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray,
A. Mouchet, R. G. Najjar, G-K. Plattner, K. B. Rodgers, C.
L. Sabine, J. L. Sarmiento, R. Schlitzer, R. D. Slater, I.
J. Totterdell, M-F. Weirig, Y. Yamanaka and A. Yool. 2005.
Anthropogenic ocean acidification over the twenty-first century
and its impact on calcifying organisms. Nature. 437: 681-686.
Today's surface ocean is saturated with respect to calcium
carbonate, but increasing atmospheric carbon dioxide concentrations
are reducing ocean pH and carbonate ion concentrations, and
thus the level of calcium carbonate saturation. Experimental
evidence suggests that if these trends continue, key marine
organisms-such as corals and some plankton-will have difficulty
maintaining their external calcium carbonate skeletons. Here
we use 13 models of the ocean-carbon cycle to assess calcium
carbonate saturation under the IS92a 'business-as-usual' scenario
for future emissions of anthropogenic carbon dioxide. In our
projections, Southern Ocean surface waters will begin to become
undersaturated with respect to aragonite, a metastable form
of calcium carbonate, by the year 2050. By 2100, this undersaturation
could extend throughout the entire Southern Ocean and into
the subarctic Pacific Ocean. When live pteropods were exposed
to our predicted level of undersaturation during a two-day
shipboard experiment, their aragonite shells showed notable
dissolution. Our findings indicate that conditions detrimental
to high-latitude ecosystems could develop within decades,
not centuries as suggested previously.