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On the Interpretation of the ENSO Signal Embedded in the Stable Isotopic Composition of Quelccaya Ice Cap, Peru
Author(s) -
Hurley J. V.,
Vuille Mathias,
Hardy Douglas R.
Publication year - 2019
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd029064
Subject(s) - climatology , water vapor , snow , environmental science , atmospheric sciences , el niño southern oscillation , forcing (mathematics) , ice core , geology , geomorphology , physics , meteorology
The δ 18 O signal in ice cores from the Quelccaya Ice Cap (QIC), Peru, corresponds with and has been used to reconstruct Niño region sea surface temperatures (SSTs), but the physical mechanisms that tie El Niño–Southern Oscillation (ENSO)‐related equatorial Pacific SSTs to snow δ 18 O at 5,680 m in the Andes have not been fully established. We use a proxy system model to simulate how QIC snow δ 18 O varies by ENSO phase. The model accurately simulates higher and lower δ 18 O values during El Niño and La Niña, respectively. We then explore the relative roles of ENSO forcing on different components of the forward model: (i) the seasonality and amount of snow gain and loss at the QIC, (ii) the initial water vapor δ 18 O values, and (iii) regional temperature. Most (more than two thirds) of the ENSO‐related variability in the QIC δ 18 O can be accounted for by ENSO's influence on South American summer monsoon (SASM) activity and the resulting change in the initial water vapor isotopic composition. The initial water vapor δ 18 O values are affected by the strength of upstream convection associated with the SASM. Since convection over the Amazon is enhanced during La Niña, the water vapor over the western Amazon Basin—which serves as moisture source for snowfall on QIC—is characterized by more negative δ 18 O values. In the forward model, higher initial water vapor δ ‐values during El Niño yield higher snow δ 18 O at the QIC. Our results clarify that the ENSO‐related isotope signal on Quelccaya should not be interpreted as a simple temperature response.