How does rising atmospheric CO2 affect marine organisms?

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A Warning Sign of Cooler Times to Come?
Reference
Sachs, J.P. 2007. Cooling of Northwest Atlantic slope waters during the Holocene. Geophysical Research Letters 34: 10.1029/2006GL028495.

What was done
Working with a sediment core from the continental slope east of Virginia (37N, 75W, 1049 m depth), a second core from the margin east of Nova Scotia (44N, 63W, 250 m depth), and a third core from abyssal depths of the Laurentian Fan (43N, 55W, 3975 m depth), with age control derived from radiocarbon dates of planktonic foraminifera, the author derived three Holocene sea surface temperature (SST) histories by means of alkenone paleothermometry employing the temperature calibration of Prahl et al. (1988).

What was learned
Cooling in the range of 4-10C occurred at each of the three locations "more or less continuously throughout the Holocene," in the words of Sachs, who reports that "warmest SSTs of 19C off Virginia, 18C on the Laurentian Fan, and 15C on the Scotian Margin occurred at the beginning of the Holocene," while "coldest SSTs of 14.5C, 8.5C, and 8C, respectively, occurred within the last few centuries."

What it means
In providing some context for his findings, Sachs states that "a decline in summer and mean annual insolation at middle and high northern latitudes during the last 11,000 years (e.g., by 48, 40 & 36 W/m2 at 65, 45, & 20N, respectively, during summer, and by 9, 8 & 7% in the annual mean (Berger, 1978)) to levels last reached during the Last Glacial Maximum [our italics] provides a direct radiative mechanism for cooling North Atlantic surface waters (Renssen et al., 2005)." Consequently, Sachs concludes his analysis by stating that "perhaps cooling of the northwest Atlantic slope waters is a harbinger of climate deterioration preceding the next glacial period," which should give everyone pause to wonder whether it is such a good idea to attempt to stop what climate alarmists claim is a strong impetus for warming, i.e., the ongoing rise in the air's CO2 content, when (if they are correct on this latter point) it may be needed to forestall an imminent descent into a full-fledged ice age. Surely, such a possibility should not be dismissed out of hand without a careful consideration of what Sachs' findings might imply.

References
Berger, A. 1978. Long-term variations of daily insolation and Quaternary climate change. Journal of the Atmospheric Sciences 35: 2362-2367.

Prahl, F.G. et al. 1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52: 2303-2310.

Renssen, H., Goosse, H. and Fichefet, T. 2005. Contrasting trends in North Atlantic deep-water formation in the Labrador Sea and Nordic Seas during the Holocene. Geophysical Research Letters 32: 10.1029/2005GL022462.

Reviewed 14 November 2007