How does rising atmospheric CO2 affect marine organisms?

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Secrets of the Mediterranean Sea ... Revealed!
Cini Castagnoli, G.C., Bonino, G., Taricco, C. and Bernasconi, S.M. 2002. Solar radiation variability in the last 1400 years recorded in the carbon isotope ratio of a Mediterranean sea core. Advances in Space Research 29: 1989-1994.

What was done
Variations in 13C from symbiontic foraminifera record the effects of productivity and of photosynthetic activity, varying with the ambient light level. Because 13C time series can provide information on sea surface illumination at the time of planktonic foraminifera growth, they can be utilized as proxies of solar radiation variability. In this study, the authors search for possible solar-induced variations in the 13C record of the foraminifera Globigerinoides rubber obtained from a sea core located in the Gallipoli terrace of the Gulf of Taranto (3945'53"N, 1753'33"E, depth of 178 m) over the past 1400 years.

What was learned
Starting at the beginning of the 1400-year record, the 13C values increased from about 0.4 per mil around 600 A.D. to a value of 0.8 per mil by 900 A.D. Thereafter, the 13C record remained relatively constant until about 1800, when it rose another 0.2 per mil to its present day value of around 1.0 per mil. Using a statistical procedure known as singular spectrum analysis, the authors were able to identify three important cyclical components of the record, having periods of approximately 11.3, 100 and 200 years. Comparison of both the raw 13C and component data with the historical aurorae and sunspot time series, respectively, revealed that the records are "associable in phase" and "disclose a statistically significant imprint of the solar activity in a climate record."

What it means
The authors note that the initial increase in their 13C values coincides with the climatic transition from the Dark Ages Cold Period to the Medieval Warm Period, over which time frame oceanic productivity would indeed have been expected to increase. The other major 13C increase starting at about 1800 coincides with the increase in atmospheric CO2 concentration that accompanied the development and progression of the Industrial Revolution (see Carbon Dioxide - History: The Last 1000 Years in our Subject Index). Hence, the authors suggest that this latter productivity increase may be "possibly due to fossil fuel CO2 fertilization." Altogether, therefore, their work appears to harmonize with what is known about decadal, centennial and millennial periodicities in solar activity, the effects of these phenomena on climate, and the beneficent effects of atmospheric CO2 enrichment on the biosphere.

Reviewed 18 September 2002