Analysis of the climate controls on the isotopic composition of precipitation (δ18O) at Nuevo Rocafuerte, 74.5°W, 0.9°S, 250 m, Ecuador

The interpretation of the isotopic composition of Andean ice cores (oxygen-18 and deuterium) is still in debate. In 2000, an ice core has been extracted from the Chimborazo glacier, in Ecuador, and the isotopic composition has been measured with a seasonal temporal resolution over the last century. To reliably interpret this isotopic record in terms of climate, an isotopic calibration based on modern precipitation is needed. Thus, since 2001, an Ecuadorian network has been set up to monitor the isotopic composition of precipitation. Here, we present the first results from February 2001 to November 2002 at the site of the Nuevo Rocafuerte station (74.5°W, 0.9°S, 250 m). Our study shows that at both daily and seasonal timescales, the local meteorological parameters are very poor factors to explain the isotopic variability. However, the rainout upstream (intensity of the convection over the Ecuadorian Amazon) can explain up to 70% of the isotopic variability at the seasonal timescale. Thus, the isotopic records from the Chimborazo glacier could offer a record of the past variability of the Ecuadorian precipitation over the Amazon basin.