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Stable isotope variations in monsoon precipitation related to atmospheric moisture transport in southern Peru

Olson-Water-Poster.pdf (6.77 MB)
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Elizabeth Olson1, Lisa Welp1, Jonathan DeGraw1, Adriana Larrea Valdivia2, Juan Reyes Larico2, Greg Michalski1 

1Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA 

2Department of Chemistry, Universidad Nacional San Augustin, Arequipa, Peru

Monsoon circulation in South America carries Atlantic water vapor across the continent to the western slopes of the Andes. Previous research into the isotopic variability of western Andean rainfall found Atlantic moisture to be the sole source of atmospheric water vapor despite significant influence by El Niño- Southern Oscillation (ENSO) in the Pacific. To study the impact of monsoon and ENSO strength on the isotopic composition of Andean precipitation, samples were collected across the Central Andean department of Arequipa, Peru; a large area of approximately 25,000 km2. Fifteen volunteer field stations were established to collect daily precipitation samples during the 2019 monsoon (January to March). The weighted LMWL from this data is δD = 8.3 x δ18O + 13.8 is based on 344 samples. A weak El Niño in the Pacific during 2019 allows for investigations into the influence of Pacific temperature anomalies on Andean atmospheric phenomenon. Within the city of Arequipa precipitation isotope values are on average δ 18O = -4.2‰ and δ D = -23‰), with the exception of a two week anomaly during which isotope values are lower (avg. δ18O = -9.8‰, avg. δ D = -71‰). Despite this excursion in isotope values there is no change in d-excess. Atmospheric moisture transport modeling is done using NOAA’s Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) back trajectory model for the periods Jan 15- 31, Feb 1-15, and Feb 16-28. Reanalysis data from the National Centers for Environment Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) was used to plot geopotential height and wind speed vectors for these time periods. Both the HYSPLIT and the reanalysis data show a strong influence from the Bolivian high on upper and mid-level air circulation in Arequipa, Peru during Jan 15-31 and Feb 16-28. Atmospheric models show displacement of the Bolivian High, which coincides with the isotope drop, suggesting that short-term changes in regional circulation can strongly influence precipitation isotope values.

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