How does rising atmospheric CO2 affect marine organisms?

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More Warmth Means a More Stable Climate
Reference
Andrus, C.F.T., Crowe, D.E., Sandweiss, D.H., Reitz, E.J. and Romanek, C.S. 2002. Otolith 18O record of mid-Holocene sea surface temperatures in Peru. Science 295: 1508-1511.

Background
Otoliths are aragonite (CaCO3) structures in fish that are used for acoustic perception and balance. When they are formed, the oxygen that is incorporated into them is in isotopic equilibrium with that of seawater. Hence, the 18O compositions of both modern and ancient otoliths can be used to develop temperature proxies for surrounding ocean waters.

What was done
The authors derived and analyzed the 18O histories of several large otoliths obtained from catfish living in near-shore habitats at two sites off the coast of Peru (650'S and 810'S) that were caught both during and after the strong 1997-98 ENSO event. They then derived and analyzed the 18O histories of several otoliths from two archaeological sites - Ostra (6010 90 yr BP) at 855'S, and Siches (6450 110 yr BP) at 440'S - after which they compared the results from the different sites and time periods.

What was learned
The first exercise yielded a 10-year-long 18O history, which in addition to providing a link to recent sea surface temperatures, clearly revealed the occurrence of both the 1991-92 and 1997-98 El Nios. The older 18O histories suggested that (1) sea surface temperatures some 6000 years ago were 3 to 4C warmer than what they were over the decade of the 1990s, and (2) sea surface temperatures of that earlier time period exhibited better-defined seasonal signals and provided little evidence of any El Nio activity.

What it means
The results of this study confirm the results of several other studies that indicate the mid-Holocene was significantly warmer than it is currently. In addition, the more seasonally-distinct temperature histories of that earlier time period suggest there was much less upwelling of the cool Peru-Chile current near northern Peru before 5000 yr BP, which is also suggested by several other studies. We thus have a situation where a considerably warmer climate than that of the present was apparently unable to sustain significant El Nio activity. This finding is very important, for it demonstrates that future global warming would likely lead to fewer and less intense El Nios, which contradicts the predictions of climate alarmists who fiercely claim the opposite.

Update
The techniques and conclusions of Andrus et al. (2002) are criticized by Bearez et al. (2003). Andrus et al. (2003) respond to this criticism, concluding that their "close examination of the comments and citations of Bearez et al. strengthen our original interpretations."

Update
Bearez, P., DeVries, T.J. and Ortlieb, L. 2003. Comment on "Otolith 18O record of mid-Holocene sea surface temperatures in Peru." Science 299: 203a.

Andrus, C.F.T., Crowe, D.E., Sandweiss, D.H., Reitz, E.J. and Romanek, C.S. 2003. Response to comment on "Otolith 18O record of mid-Holocene sea surface temperatures in Peru." Science 299: 203b.


Reviewed 27 February 2002