| Summary: | We present here first results of 14C02 monitoring at two sampling sites in the equatorial region of the South American continent (station Aychapicho, Ecuador and station Llano del Hato, Venezuela). We also include the data for two other stations representing undisturbed marine atmosphere at mid-latitudes of both hemispheres, far from large continental sources and sinks of CO2 (station Izana, Tenerife, Spain and station Cape Grim, Tasmania). Between 1991 and 1993,14C02 levels in the tropical troposphere were generally higher by 2-5%o when compared to mid-latitudes of both hemispheres. This apparent maximum of 14C in the tropics can be explained by two major factors: 1) emissions of 14C-free fossil fuel C02, restricted mainly to mid-latitudes of the northern hemisphere; and 2)14C depletion due to gas exchange with circumpolar Antarctic upwelling water, influencing mainly mid- and high southern latitudes. The e14C record so far available for the Aychapicho station provides direct evidence for a regional reduction of atmospheric 14C02 levels due to gas exchange with 14Cdepleted equatorial surface ocean in the upwelling regions and dilution with the 14C-depleted CO2 released in these areas. Recurrent ENSO events, turning on and off the 14C-depleted CO2 source in the tropical Pacific, lead to relatively large temporal variations of the atmospheric 14C level in this region.
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