出典:Wikipedia
出典:『Wikipedia』 (2011/03/20 00:43 UTC 版)
The Dole effect describes an inequality in the ratio of the heavy isotope 18O (a 'standard' oxygen atom with two additional neutrons) to the lighter 16O, measured in the atmosphere and seawater. This ratio is usually denoted δ18O. It was noticed in 1935 that air contained more 18O than seawater; this was quantified in 1975 to 23.5‰. The imbalance arises mainly as a result of respiration in plants and in animals. Due to thermodynamics, respiration removes the lighter — hence more reactive — 16O in preference to 18O, increasing the relative amount of 18O in the atmosphere.