A study of triple oxygen isotopes in precipitation from a tropical region
Abstract
Recent advances in analytical technology allow the precise analysis of d17O, making it possible to use 17Oexcess as another tracer of hydrological processes. In this study, we collected about five-years of monthly precipitation samples at Nanyang Technological University (NTU) in Singapore, and analyzed their d2H, d18O, and d17O to understand the drivers of their variabilities. We found that monthly precipitation d18O at NTU shows strong seasonal and intra-annual variabilities. d18O becomes gradually more negative during the monsoon seasons and more positive during inter-monsoons. d18O values are mostly higher than the weighted mean (-6.3‰) during the 2015-2016 El Niño but lower than this value in non El Niño years. Therefore, d18O variabilities record monsoon and El Niño signals. Unlike monthly precipitation in many other tropical regions, d18O at our site shows very low correlation with rainfall amount (r=-0.29,p=0.05), suggesting that the amount effect is not a major control.
17Oexcess and d-excess are weakly correlated (r=-0.32, p=0.03) and exhibit different variabilities. In general, d-excess is lower during the Northeast (NE) monsoon (November to March) relative to the Southwest (SW) monsoon (June to September). This can be attributed to higher humidity over the South China Sea, the major moisture source during the NE monsoon, compared to the Indian Ocean, the major moisture source during the SWmonsoon. d18O negatively and d-excess positively correlate to humidity at different atmospheric levels (from 300hPa to 1000hPa), particuarly to near-surface level humidity. This indicates that rain re-evaporation is a key driver of d18O and d-excess. However, 17Oexcess displays low correlation with d-excess and humidity, implying that re-evaporation is not the primary influence on 17Oexcess. Other processes such as kinetic fractionation during convection or the contribution of stratospheric moisture likely dominate the 17Oexceess variability. In addition, their influence likely varies over time, leading to the gradual decrease in precipitation 17Oexcess.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP14B..02H
- Keywords:
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- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSESDE: 1041 Stable isotope geochemistry;
- GEOCHEMISTRYDE: 1655 Water cycles;
- GLOBAL CHANGEDE: 1833 Hydroclimatology;
- HYDROLOGY