2.2. Stable isotope analysis
Stable isotope analyses of precipitation and surface water samples were
conducted at the Stable Isotopes Research Group facilities of
Universidad Nacional (Heredia, Costa Rica) using a cavity ring down
spectroscopy water isotope analyser L2120-i (Picarro, USA) and a
LWIA-45-EP water isotope analyzer (Los Gatos, USA).18O/16O and2H/1H ratios are presented in the
established delta notation δ (‰), with reference to the VSMOW-SLAP
scale. Deuterium excess was calculated as d -excess =
δ2H-8·δ18O (Dansgaard, 1964). The
analytical long‐term uncertainty is ±0.5‰ (1σ) for δ2H
and ± 0.1‰ (1σ) for δ18O.