Tropical precipitation anomalies and d -excess evolution during El Niño 2014-16

Abstract

The last 2014-16 El Nino event was among the three strongest episodes on record. El Nino considerably changes annual and seasonal precipitation across the tropics. Here, we present a unique stable isotope data set of daily precipitation collected in Costa Rica prior to, during, and after El Nino 2014-16, in combination with Lagrangian moisture source and precipitation anomaly diagnostics. δ2H composition ranged from -129.4 to +18.1 (‰) while δ18O ranged from -17.3 to +1.0 (‰). No significant difference was observed among δ18O (P = 0.0186) and δ2H (P = 0.664) mean annual compositions. However, mean annual d-excess showed a significant decreasing trend (from +13.3 to +8.7 ‰) (P < 0.001) with values ranging from +26.6 to -13.9 ‰ prior to and during the El Nino evolution. The latter decrease in d-excess can be partly explained by an enhanced moisture flux convergence across the southeastern Caribbean Sea coupled with moisture transport from northern South America by means of an increased Caribbean Low Level Jet regime. During 2014-15, precipitation deficit across the Pacific domain averaged 46% resulting in a very severe drought; while a 94% precipitation surplus was observed in the Caribbean domain. Understanding these regional moisture transport mechanisms during a strong El Nino event may contribute to a) better understanding of precipitation anomalies in the tropics and b) re-evaluate past stable isotope interpretations of ENSO events in paleoclimatic archives within the Central America region. This article is protected by copyright. All rights reserved.