Latitudinal Gradients of ~(13)C in Atmospheric Methane in the Pacific Ocean Region: Implications for interhemispheric transport

摘要

Measurements of atmospheric methane made on air samples collected on two voyages across the Pacific from about 40deg S to 45deg N in June 1996 and from 35deg S to 32deg N in November 1996 show a 10percent difference in concentration between the hemispheres with an abrupt gradient at the intertropical convergence zone (ITCZ). The concentration gradient observed on the November voyage was marginally greater than that observed in June. The interhemispheric gradient for delta~(13)C in methane, delta~(13)CH_4, appears to be highly dependent on season, however. In June 1996, on a voyage from Auckland, New Zealand, to Seattle, relatively small latitudinal variations in delta~(13)C, with a total range of only 0.15per thousand, were observed. No abroupt change was observed at the ITCZ, which was located at about 10deg N. On a similar voyage in November 1996, however, a large gradient of about 0.5per thousand was measured across the ITCZ. On both voyages, small but consistent excursions in delta~(13)C, < 0.01per thousand, were measured in both hemispheres. These data are the first high precision latitudinal measurements of delta~(13)CH_4 ever reported and show clear correlations with regional convergence zones and meteorological features in the mid-Pacific.