How does rising atmospheric CO2 affect marine organisms?

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Radical Climate Changes Independent of Atmospheric CO2 Concentration
Darby, D., Bischof, J., Cutter, G., de Vernal, A., Hillaire-Marcel, C., Dwyer, G., McManus, J., Osterman, L., Polyak, L. and Poore, R. 2001. New record shows pronounced changes in Arctic Ocean circulation and climate. EOS, Transactions, American Geophysical Union 82: 601, 607.

What was done
The authors developed a new 10,000-year multi-parameter environmental record from a thick sequence of post-glacial sediments obtained from cores retrieved from the upper continental slope off the Chukchi Sea shelf in the Arctic Ocean.

What was learned
In the words of the authors, their data reveal "previously unrecognized millennial-scale variability in Arctic Ocean circulation and climate," along with evidence that "in the recent past, the western Arctic Ocean was much warmer than it is today." Specifically, they say their data indicate that "during the middle Holocene the August sea surface temperature fluctuated by 5C and was 3-7C warmer than it is today." They also have evidence indicating "rapid and large (1-2C) shifts in bottom water temperature."

What it means
The authors conclude that "Holocene variability in the western Arctic is larger than any change observed in this area over the last century," and that "temperatures may have been 5C warmer only a few thousand years ago." Since there is no evidence the air's CO2 concentration was either higher or fluctuating wildly during this period - it was, in fact, lower and very stable [see Carbon Dioxide (History: The Last 250,000 Years) in our Subject Index] - something else had to have been responsible for the significantly warmer and more variable climate of that time and place. Hence, there is no need to invoke rising atmospheric CO2 concentrations as the cause of the more ordinary climate changes of the past century, or even those predicted for the future, which are supposed to be most evident in high northern latitudes. Any number of as-yet-undiscovered or unappreciated phenomena could well be responsible for them.