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 data2,3 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.