Isotopic variations in precipitation at Bangkok and their climatological significance

Abstract

Abstract:The stable isotopic composition of precipitation from low to mid latitudes contains information about changes of some climatic factors, such as temperature, precipitation and atmospheric circulation patterns. However, the isotopic variations in the area are very complicated because of the combined influences of these factors. Proper interpretation of the patterns of isotopic variations for palaeoclimate reconstructions in this area requires a detailed understanding of these complex stable isotope controls. The isotopic data (υ 18 O and υ 2 D) in precipitation at the International Atomic Energy Agency-World Meteorological Organization Bangkok station were collected and analysed because of the relatively long and unbroken isotopic records and the particular geographical location. The isotopic variations at Bangkok have strong seasonal patterns owing to distinct source regions in different seasons. In summer, the remote sources of water there can influence the υ 18 O values significantly, which is verified by the simple Rayleigh model. In winter, the mixing of isotopically distinct air masses with different origins, i.e. the continental and oceanic air masses, accounts for the isotopic variations. In the transition periods of the Asia-Australia monsoon, namely in May and October, the local vapour contribution may play a role in the isotopic ratios. On the interannual time-scale, the influences of El Niño-southern oscillation (ENSO) and the Indian Ocean dipole (IOD) on isotopic composition are examined. The indications are that both the ENSO and IOD indices have a significant correlation with the υ 18 O ratios, and that the υ 18 O ratio in summer rains is significantly more enriched (depleted) during the warm (cold) phase of ENSO/IOD events. All the results suggest that it is useful for us in understanding the water cycling process and may be helpful in palaeoclimate reconstruction in this monsoon region.

Inter‐annual and multi‐decadal variability of monsoon season rainfall in central Thailand during the period 1804–1999, as inferred from tree ring oxygen isotopes

“…Tree ring cellulose δ 18 O is controlled by δ 18 O of rainfall and relative humidity, both of which are related to monsoon season precipitation in Asia monsoonal area. The negative relationship between rainfall and precipitation δ 18 O, known as the “amount effect,” has been documented throughout Southeast Asia (Araguas‐Araguas et al ., ) and is particularly apparent in Bangkok during the rainy season (Ichiyanagi and Yamanaka, ; He et al ., ). In the present study area, for example, tree ring δ 18 O for the period 1970–1999 varied in step with the δ 18 O of May–October precipitation in Bangkok (Figure ).…”

Characteristics of water isotopes and hydrograph separation during the wet season in the Heishui River, China

“…At temporal scale, by t-test for pooled data at a 0.05 level of significance (Learning, 2000) between wet and the dry season, significant difference of dD existed at the most of tributary sampling sites except for K, and insignificant difference of d 18 O occurred at the most of tributary sampling sites except H and I between the dry and wet season. The most difference between the dry and wet season was that the numbers and amount of rain were increasing with time, and the isotopic values of rain became more negative in the wet season than that in the dry season (He et al, 2006). At the same site, comparison of electrical conductivity (EC) between the dry and wet season showed that the EC of the wet season became lower for participation of rain (Fan et al, 2006).…”

Factors controlling isotopic composition of precipitation on Okinawa Island, Japan: Implications for paleoclimate reconstruction in the East Asian Monsoon region

“…The data should instead be interpreted in a larger perspective with hydrological and meteorological datasets. Many studies, for example, have shown the importance of the air mass origin in the isotope signal (Gonzalez et al, 2009;He et al, 2006;Liotta et al, 2008). The isotope incorporated General Circulation Model (GCM) is also a useful tool for such analysis.…”