How does rising atmospheric CO2 affect marine organisms?

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Millennial-Scale Changes in Ocean Circulation
Marchitto Jr., T.M., Curry, W.B. and Oppo, D.W.  1998.  Millennial-scale changes in North Atlantic circulation since the last glaciation.  Nature 393: 557-561.

What was done
The authors studied cadmium/calcium ratios in benthic foraminifera shells contained in sediment cores retrieved from the Bahama Banks region of the Northwest Providence Channel that connects the North Atlantic basin (Sargasso Sea) to the Florida Straits.

What was learned
The evidence obtained in this investigation demonstrates that, in the authors' own words, "periods of enhanced intermediate-water production alternate with periods of enhanced deep-water formation on both orbital and millennial timescales."  They also note that "analogous dynamics operate in the modern North Atlantic on much shorter (decadal) timescales."

What it means
This work adds to the mounting evidence that there are relatively short period cycles in oceanic circulation characteristics that operate within intermediate length cycles occurring within much longer cycles.  This complex nested cyclical behavior of the oceans has a complex nested cyclical impact on climate that must clearly be considered in interpreting the meaning of current climatic trends.  Simply put, there are a variety of reasons why the earth - depending on who you believe - may or may not be warming.  The temperature trend, in and by itself, tells one very little about the reason(s) for its existence.  Studies like this one, which identify past repeated behavior, along with similar investigations in a number of other fields, are needed to make this crucial determination.

Reviewed 1 October 1998