PP33D-08
Inter-annual Controls on Oxygen Isotopes of Precipitaion in the Asian Monsoon Region

Wednesday, 16 December 2015: 15:25
2012 (Moscone West)
Hongying Yang1, Kathleen R Johnson1, Michael L Griffiths2 and Kei Yoshimura3, (1)University of California Irvine, Irvine, CA, United States, (2)William Paterson University of New Jersey, South River, NJ, United States, (3)Atmosphere and Ocean Research Institute University of Tokyo, Tokyo, Japan
Abstract:
The complex nature of speleothem δ18O from the Asian monsoon region is a result of the varying influences of monsoon strength, moisture source region, transport history, local cave hydrology and other effects on cave dripwater δ18O. In order to provide a more robust interpretation of speleothem δ18O data from the broader Asian monsoon region, we utilize existing simulations from the isotope-enabled GCM, IsoGSM (Yoshimura el al. 2008), to investigate the climatic controls on precipitation δ18O (δ18Op) at four cave locations: Dongge Cave, China (25°17′ N, 108°5′ E); Tham Mai Cave, Laos (20.75 N, 102.65 E); Mawmluh Cave, India (25°15′44′′N, 91°52′54′′E); and Qunf Cave, Oman (17°10′ N, 54°18′ E). Our composite speleothem records from Laos—a key site at the interface between the Indian and East Asian monsoon systems—will be used as a case study for interpreting speleothem δ18O in the South-East Asian Monsoon (SEAM) region.

Our results show that δ18Op extracted from the grid point closest to four cave sites from IsoGSM shows very low correlation between δ18Op and local precipitation. δ18Op at Dongge cave reveals a negative correlation (0.4 to 0.5) with precipitation in the Bay of Bengal, suggesting that δ18Op from the East Asian monsoon area reflects upstream distillation over the Indian monsoon region. δ18Op in Laos exhibits a negative correlation with precipitation over the broad Indo-Pacific warm pool region, indicating increased convection over this area leads to more negative δ18Op over SE Asia. Given the low correlation between local precipitation and δ18Op at all four cave sites, we interpret the δ18Op at these locales as reflective of regional changes in hydroclimate, rather than local precipitation amount. In addition, δ18Op from IsoGSM at all fours sites, especially Qunf, Mawnluh, and Tham Mai cave, show a positive correlation with Pacific SSTs over the NINO3.4 region and in the western and northern Indian Ocean, suggesting that the δ18Op of annual rainfall may be influenced by ENSO and IOD.As a case study, after detrending, Laos δ18Op from IsoGSM since 1900 AD is moderately correlated with the NINO3.4 index (r=0.53) and with the IOD index at a lag of 1 year (r = -0.35). This indicates that interannual variability of δ18Op at our site is likely controlled by ENSO.