A model of the Earth's Dole effect

The Earth's Dole effect describes the isotopic O-18/O-16-enrichment of atmospheric oxygen with respect to ocean water, amounting under today's conditions to 23.5parts per thousand. We have developed a model of the Earth's Dole effect by combining the results of three-dimensional models of the oceanic and terrestrial carbon and oxygen cycles with results of atmospheric general circulation models (AGCMs) with built-in water isotope diagnostics. We obtain a range from 22.4parts per thousand to 23.3parts per thousand for the isotopic enrichment of atmospheric oxygen. We estimate a stronger contribution to the global Dole effect by the terrestrial relative to the marine biosphere in contrast to previous studies. This is primarily caused by a modeled high leaf water enrichment of 5-6parts per thousand. Leaf water enrichment rises by similar to1parts per thousand to 6-7parts per thousand when we use it to fit the observed 23.5parts per thousand of the global Dole effect. The present model is designed to be utilized in forthcoming paleo studies allowing a quantitative analysis of long-term observations from polar ice cores.