How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Meteorites and Climate Change
Usoskin, I.G., Solanki, S.K., Taricco, C., Bhandari, N. and Kovaltsov, G.A. 2006. Long-term solar activity reconstructions: direct test by cosmogenic 44Ti in meteorites. Astronomy & Astrophysics 457: 10.1051/0004-6361:20065803.

Many people believe that changes in solar activity have been responsible for changes in climate; but to demonstrate that such is truly the case, a record of past variations in solar activity is required. With respect to this need, the authors note that "long-term solar activity in the past is usually estimated from cosmogenic isotopes, 10Be or 14C, deposited in terrestrial archives such as ice cores and tree rings," because "the production rate of cosmogenic isotopes in the atmosphere is related to the cosmic ray flux impinging on Earth," which "is modulated by the heliospheric magnetic field and is thus a proxy of solar activity." A nagging concern, however, is that the isotope records may suffer from what the five scientists call "uncertainties due to the sensitivity of the data to several terrestrial [our italics] processes." Consequently, they devised a plan to attempt to resolve this issue.

What was done
Noting that the activity of a cosmogenic isotope in a meteorite represents "the time integrated cosmic ray flux over a period determined by the mean life of the radioisotope," Usoskin et al. reasoned that (1) "by measuring abundance of cosmogenic isotopes in meteorites which fell through the ages, one can evaluate the variability of the cosmic ray flux, since the production of cosmogenic isotopes ceases after the fall of the meteorite," and that (2) if they could develop such a meteoritic-based cosmogenic isotope record they could use it "to constrain [other] solar activity reconstructions using cosmogenic 44Ti activity in meteorites which is not affected by terrestrial processes [our italics]."

The researchers' choice of 44Ti for this purpose was driven by the fact that it has a half-life of about 59 years and is thus "relatively insensitive to variations of the cosmic ray flux on decadal or shorter time scales, but is very sensitive to the level of the cosmic ray flux and its variations on a centennial scale." Hence, they compared the results of different long-term 10Be- and 14C-based solar activity reconstruction models with measurements of 44Ti in 19 stony meteorites (chondrites) that fell between 1766 and 2001, as reported by Taricco et al. (2006).

What was learned
Usoskin et al. ultimately determined that "most recent reconstructions of solar activity, in particular those based on 10Be data in polar ice (Usoskin et al., 2003, 2004; McCracken et al., 2004) and on 14C in tree rings (Solanki et al., 2004), are consistent with the 44Ti data."

What it means
The results of this study give ever more credence to the findings of the many studies that have reported strong correlations between various climatic changes and 10Be- and 14C-based reconstructions of solar activity.

Solanki, S.K., Usoskin, I.G., Kromer, B., et al. 2004. Nature 431: 1084.

Taricco, C., Bhandari, N., Cane, D., et al. 2006. Journal of Geophysical Research 111: A08102.

Usoskin, I.G., Solanki, S.K., Schussler, M., et al. 2003. Physical Review Letters 91: 211101.

Usoskin, I.G., Mursula, K., Solanki, S.K., et al. 2004. Astronomy & Astrophysics 413: 745.

Reviewed 21 February 2007