Understanding Tropical Convection Through Triple Oxygen Isotopes Of Precipitation From The Maritime Continent

Monthly precipitation samples from Singapore were collected between 2013 and 2019 for stable isotope analysis to further our understanding of the drivers of tropical precipitation isotopes, in particular, O-17-excess. delta O-18 ranges from -11.34 parts per thousand to -2.34 parts per thousand, with a low correlation to rainfall (r = -0.31, p = 0.014), suggesting a weak amount effect. d-excess is relatively consistent and has an average value of 10.89 parts per thousand +/- 3.45 parts per thousand. Compared to high-latitude regions, O-17-excess in our samples generally falls in a narrower range from 2 to 47 per meg with an average of 21 +/- 11 per meg. Moreover, O-17-excess shows strong periodic variability; spectral analysis reveals 3-month, 6-month, and 2.7-year periodicities, likely corresponding to intraseasonal oscillations, monsoons, and the El Nino-Southern Oscillation (ENSO), respectively. In contrast, d-excess shows no clear periodicities. Although spectral analysis only identifies 6-month periodicity in the delta O-18 time series, delta O-18 tracks the Nino3.4 sea surface temperature variability; the average delta O-18 value (-5.2 parts per thousand) is higher during El Nino years than ENSO neutral years (-7.6 parts per thousand). Therefore, regional convection associated with monsoons and ENSO has different impacts on delta O-18, d-excess, and O-17-excess. O-17-excess and d-excess are anticorrelated and do not relate to the relative humidity in moisture source regions. Extremely low humidity and drought conditions in moisture source regions would be required to account for high O-17-excess. Processes during transport and precipitation likely modify these two parameters, especially O-17-excess, which no longer record humidity conditions of moisture source regions. Our findings will be useful for further modeling studies to identify physical processes during convection that alter d-excess and O-17-excess.