How does rising atmospheric CO2 affect marine organisms?

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North Atlantic Millennial-Scale Oscillations
Bianchi, G.G. and McCave, I.N.  1999.  Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland.  Nature 397: 515-517.

What was done
Grain-sizes of deep-sea sediments were examined in cores extracted from a region of the northeast Atlantic Ocean covering the time interval of the last 11,000 years.

What was learned
Sediment grain-size was shown to be related to the flow rate of the thermohaline circulation in this region, which, in turn, was shown to be related to well-known climatic events in Europe.  Several warm/cool oscillations with a quasi-periodicity of about 1,500 years were documented.  These millennial-scale climatic oscillations, according to the authors, were comparable to the Little Ice Age and the Medieval Warm Period, and are a "recurrent feature of earlier parts of Holocene climatic history."  However, they indicate that their data do not provide an explanation for the forcing mechanism(s) for such changes.

What it means
The authors of this paper demonstrate that the climate of the Holocene has experienced many oscillations that were independent of any change in atmospheric CO2 concentration.  With respect to the future, the authors suggest that a significant increase in the melting of the Greenland ice sheet may trigger a feedback response in the thermohaline circulation causing Europe to cool.  This consequence is the result of a melt water-induced input of freshwater into this ocean region, which, depending on the amount, could reduce the density of the water that drives the thermohaline circulation, thus triggering a slower flow rate.  Without such perturbations, according to the authors, "the climate looks likely to be warm for several hundred years."

Reviewed 15 March 1999