Latitudinal variation in oxygen-18 of atmospheric CO₂

Abstract

This report provides information on a potentially important new atmospheric tracer of large-scale behaviour at the Earth's surface, the oxygen isotope composition of CO₂. We use measurements on flask air collected from Alaska, Hawaii, Samoa, Tasmania, coastal Antarctica and the South Pole. Recently, we examined 1982–84 measurements of δ¹⁸O in CO₂ extracted in situ from marine air at Cape Grim, Tasmania¹. Here we report on a comparison of Cape Grim flask and in situ data that gives a measure of precision and serves to demonstrate a marked improvement over previous infrequent measurements. While previous data^2,3 suggests a north-south gradient, our flask data establish a strong, asymmetric meridional gradient. We argue that this reflects the oxygen isotope ratio in ground water, via mechanisms involving gross catalysed CO₂ exchange with leaf (and possibly soil) water. Very large CO₂ fluxes are involved, of the order of 200 Gt carbon (C) yr⁻¹.