Atmospheric ¹⁴CO₂ Variations in the Equatorial Region

Abstract

We present here first results of 14CO2 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 Izaña, Tenerife, Spain and station Cape Grim, Tasmania). Between 1991 and 1993, 14CO2 levels in the tropical troposphere were generally higher by 2–5‰ 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 CO2, 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 δ14C record so far available for the Aychapicho station provides direct evidence for a regional reduction of atmospheric 14CO2 levels due to gas exchange with 14C-depleted 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.

Sources and transport of Δ<sup>14</sup>C in CO<sub>2</sub> within the Mexico City Basin and vicinity

“…Levin, personal communication, 2009). Earlier observations by Rozanski et al (1995) and Levin and Hesshaimer (2000) revealed <4‰ difference between 14 CO 2 levels within the Northern Hemisphere tropical troposphere compared to mid-latitudes. Hsueh et al (2007) …”

“…The isotopic analysis of CO 2 in the lower atmosphere has resulted in a better understanding of the 14 C exchange with the biosphere and the role of anthropogenic activity (Zondervan and Meijer, 1996;Dutta et al, 2002). More than 40 years of direct tropospheric 14 CO 2 observations from maritime and continental stations in both hemispheres are now available since the nuclear test ban treaty in 1962 (Mook, 1980;Rozanski et al, 1995;Levin and Hesshaimer, 2000;Kitagawa et al, 2004). Seasonal and regional variability in atmospheric 14 C is clearly visible in many contemporary observations and has the potential to provide additional information about the source, age, and magnitude of regional fluxes (Randerson et al 2002).…”

“…Anthropogenic perturbations, mainly attributable to landuse changes, fossil fuel burning, and atmospheric nuclear detonations, have markedly affected the natural balance of the 14 C in CO 2 cycle (Suess, 1955;Tans et al, 1979;Stuiver and Quay, 1981;Rozanski et al, 1995;and Caldeira et al, 1998). The isotopic analysis of CO 2 in the lower atmosphere has resulted in a better understanding of the 14 C exchange with the biosphere and the role of anthropogenic activity (Zondervan and Meijer, 1996;Dutta et al, 2002).…”

Spatial distribution of Δ&lt;sup&gt;14&lt;/sup&gt;CO&lt;sub&gt;2&lt;/sub&gt; across Eurasia: measurements from the TROICA-8 expedition

“…While there have been numerous studies of the temporal change in 14 CO 2 , only a few observations of the synoptic spatial distribution have been made (Hsueh et al, 2007;Rozanski et al, 1995 Several trace gas species have been used or proposed as fossil fuel CO 2 tracers, based on estimates of the ratio of tracer to CO 2 emissions (which may vary in space and time) and assuming co-location of the tracer and fossil fuel CO 2 sources. Such tracers have the advantage over 14 CO 2 in ease and lower cost of measurement, although their empirical correlation with fossil fuel CO 2 emissions appears to be weaker than for 14 CO 2 (Turnbull et al, 2006).…”

Atmospheric 14C Variability Recorded in Tree Rings from Peninsular India: Implications for Fossil Fuel CO2 Emission and Atmospheric Transport

“…Thus, during the mid-1960s, oceanic evasion of CO 2 could have potentially decreased terrestrial atmospheric Δ 14 C records near the Arabian Sea coasts, providing that sufficient contact time existed for ocean-atmosphere CO 2 exchange. Atmospheric Δ 14 C records from coastal regions are reported to be influenced by coastal upwelling, as observed in pre-bomb tree rings (Damon et al 1999) and atmospheric 14 CO 2 measurements in the post-bomb period (Rozanski et al 1995). The back-trajectory analysis shows that during the summer (May-Sep), which encompasses the main growing season of the tree rings, the predominant flow of wind was from the middle of the Arabian Sea towards peninsular India.…”