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Abstract Theδ18O 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 snowδ18O at 5,680 m in the Andes have not been fully established. We use a proxy system model to simulate how QIC snowδ18O varies by ENSO phase. The model accurately simulates higher and lowerδ18O 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 vaporδ18O values, and (iii) regional temperature. Most (more than two thirds) of the ENSO‐related variability in the QICδ18O 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 vaporδ18O 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 negativeδ18O values. In the forward model, higher initial water vaporδ‐values during El Niño yield higher snowδ18O at the QIC. Our results clarify that the ENSO‐related isotope signal on Quelccaya should not be interpreted as a simple temperature response.
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Influence of Recent Climate Shifts on the Relationship Between ENSO and Asian Monsoon Precipitation Oxygen Isotope Ratios
Abstract Recent studies have revealed robust in‐phase relationships between El Niño–Southern Oscillation (ENSO) and Asian Monsoon precipitation δ18O values (i.e., warm ENSO events with high δ18O values), and this relationship has been used in an attempt to reconstruct past ENSO activity. However, whether this relationship holds in the past is unknown. Here we use precipitation δ18O data from Hong Kong (East Asia) and Bangkok (Southeast Asia) and an ice core δ18O record from Dasuopu glacier (South Asia) to examine the δ18O‐ENSO relationship across two recent climate shifts that occurred during the winters of 1976/1977 and 1988/1989. On an annual scale, the δ18O‐ENSO relationship is weak prior to 1977 and strongest after 1988. We show that the changing δ18O‐ENSO relationship mainly originates from changes in the dry season isotope/climate relationship (which is significant only after 1988), whereas the rainy season relationship is relatively stable. We confirm that, consistent with earlier work on the rainy season, the significant δ18O‐ENSO relationship in the dry season post‐1988 is associated with ENSO's influence on regional convection (Bay of Bengal to South China Sea region). We suggest the insignificant dry season relationship prior to 1989 is due to limited ENSO impacts on convection in the Bay of Bengal to South China Sea region, which is supported by the insignificant relationship between ENSO and vertical velocity at 500 hPa. These findings suggest that without additional constraints, systematic variability in isotope/climate relationships will lead to large uncertainties in ENSO reconstructions based on Asian Monsoon region δ18O data.
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- Award ID(s):
- 1241286
- PAR ID:
- 10460222
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 124
- Issue:
- 14
- ISSN:
- 2169-897X
- Page Range / eLocation ID:
- p. 7825-7835
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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