Isotope compositions in precipitation across Mexico: 2018-2021

Here we report on the spatial and temporal isotope variations of 21 precipitation monitoring stations across Mexico. Our database includes 608 monthly samples collected from 2018 to 2021 over four main domains (between 5 and 2,365 m asl): the Pacific coast, the Gulf of Mexico/Caribbean Sea region, and the Central and Northern Plateaus. All linear regressions and statistical diagnostics were computed using R (R Core Team, 2022). The nationwide isotopic lapse rate (-1.75‰ in δ18O/km) (including monitoring sites influenced by tropical cyclones (TCs) (Loreto, Culiacan, and Hermosillo) explained 65% (p<0.001) of the total variance. The direct influence of TCs passages and landfalls across the Pacific coast resulted in depleted monthly compositions in low-elevation coastal sites. By removing these sites, the isotopic lapse rate increased to -2.20‰ in δ18O/km (85% of the total variance explained, p<0.001). The precipitation-weighted isotope lapse rate (including all sites) resulted in a similar slope -2.10‰ in δ18O/km (72% of the total variance explained, p<0.001). Raster interpolations were performed in ArcGIS 10.8.1 (ESRI, USA) using a 10m digital elevation model.