The variability of the rainfall stable isotopic values (2Hp, 18Op) in the Ecuadorian Amazon
to the Andes presents a marked local “altitude” effect. At the same time, this complex orography
creates diverse precipitation regimes (unimodal, bimodal, and three-modal) that make it difficult
to establish a relationship with the local amount. Nevertheless, stations along these regions show
a similar intra-annual isotopic variability, with lower values during MAM and ON. In contrast,
higher values are found during DJF and JAS in a w-shaped pattern, suggesting a common regional
controller. A monthly 2Hp and 18Op collection campaign was established in Central Ecuador
(n = 30) to complement stations biased towards the northern and southern parts. Based on back
trajectory analysis, the results demonstrated that moisture arrives from two primary sources: the
Tropical North Atlantic (DJFM) and the Amazon Basin (JAS). Nevertheless, their convergence (AMJ
and ON) is the crucial factor modulating the lowest isotopic values. Precisely, this convergence is
stronger at the V-Index region (5 S–5 N, 65–75 W), where the wind seasonality and reversal at
low levels are enhanced, allowing the inter-hemispheric moisture flux transport (cross-equatorial
flow). We propose that the amount of rainfall located at the V-Index region is a more robust approach
for explaining the 2Hp and 18Op variability rather than the local amount.

Accurate knowledge of the Ne isotopic composition of air is essential for planetary science. While the uncertainty of the noble gas isotopic composition of air has been drastically reduced to the level of ∼0.1% in the last few years thanks to modern techniques, the most widely accepted value of the 22Ne/20Ne ratio of air (0.102 ± 0.0008, Eberhardt et al., 1965) has an uncertainty of ±0.78% (1σ). Here we present the first multi-laboratory re-determination of the atmospheric 22Ne/20Ne. An artificial, high purity mixture of 20Ne and 22Ne was prepared and the 22Ne/20Ne (0.11888 ± 0.00001, 1σ) and 20Ne/22Ne (8.4118 ± 0.0007, 1σ) determined gravimetrically. This gas was used to determine the mass fractionation of five mass spectrometers allowing the air 22Ne/20Ne to be determined (n = 234 analyses). Each laboratory sampled their own local air, used a different gas preparation system and analysis procedure as well as doing their own expansion of the high-pressure artificial Ne gas. Individual air 22Ne/20Ne determinations have uncertainties in the range of 0.01–0.08%. The overall reproducibility of the calculated 22Ne/20Ne of air between the laboratories shows no overdispersion with respect to the individual uncertainties. We report a global value for the atmospheric 22Ne/20Ne of 0.10196 ± 0.00007 (0.07%, 1σ), equivalent of 20Ne/22Ne of 9.808 ± 0.007. This is almost identical to the Eberhardt et al. (1965) value although its uncertainty shows a 12 times reduction. Our study did not verify any of the other previous determinations of atmospheric 22Ne/20Ne. This highly accurate and precise atmospheric 22Ne/20Ne value provides a new reference for atmospheric 21Ne/20Ne determinations and we recalculate (21Ne/20Ne)air of five recent determinations. While this exercise resulted in no significant change to the absolute values, it gives more confidence with respect to the correctness of (21Ne/20Ne)air. We suggest that the revised value for atmospheric 22Ne/20Ne be used routinely in all geoscience applications.