Aircraft measurements show strong enhancements of methane above central Amazonia.
Miller, University of Colorado and NOAA/ESRL, email@example.com
Gatti, IPEN, firstname.lastname@example.org
D'amelio, IPEN, email@example.com
Martins, IPEN, firstname.lastname@example.org
Polakiewizc, IPEN, email@example.com
Crotwell, University of Colorado and NOAA/ESRL, firstname.lastname@example.org
Tans, NOAA/ESRL, email@example.com
Artaxo, USP, firstname.lastname@example.org
Recent results at chamber [Keppler, 2006], field [Melack, 2004; do Carmo, 2006] and satellite scales [Frankenburg, 2005] suggest the presence of large methane emissions from the Amazon basin. Here we present regionally integrating trace gas observations from two aircraft sites that confirm the presence of large enhancements of methane above Amazônia. Air samples collected on aircraft near Santarém (2 deg S) and Manaus (2 deg S) in eastern and central Amazônia since 2001 show large enhancements of CH4 compared to those collected at the NOAA/ESRL site at Ascension Island (8 deg S) in the tropical Atlantic Ocean. From the surface to 3500 m, enhancements averaging 30 ppb and up to 120 ppb occur throughout the year. Wet season profiles are more uniformly enhanced from the surface to 3500 m above sea level, while dry season profiles tend to show stronger enhancements closer to the surface. To assess the validity of using Ascension Island CH4 measurements as proxies we examine differences in SF6 between Ascension and Amazônia. This analysis suggests that while Ascension is representative of source air, some of the observed continental enhancement, especially during the wet season, results from air of more northerly origin. The remaining elevation above background can be most easily explained as wetland emissions during the wet season and biomass burning emissions during the dry season. Direct emissions from plants in oxic environments can also not be ruled out as a source but are not required to explain the observations. While existing measurements cannot distinguish between the various sources, we will discuss strategies to separately account for biomass burning, wetland and putative direct plant emissions at the basin scale. Our measurements represent a substantial gradient between South America and adjacent oceans and a tropical bulge in the global north-south methane gradient that are not captured by sampling sites in the marine boundary layer.