洞庭湖流域夏季旱涝与降水同位素丰度的关系

Stable isotopes are scarce in the environment, but they respond very sensitively to the environmental evolution and record it in different geological archives. Tracing methods derived from the stable isotope composition of water have been widely applied in researches on hydrometeorology, weather diagnosis, and palaeoclimate reconstruction. The investigated area, Dongting Lake basin(24.4°~30.9°N, 107.3°~114.7°E), is located in central-southern China, surrounded by mountains with a plain in its center and north. The Dongting Lake basin has a subtropical monsoon climate, which is alternately dominated by SWM and SEM in summer(JJA). It is an ideal region to study the evolution of the East Asian Summer Monsoon(EASM). The main rainy season of the basin is spring(MAM) and summer. In recent years, the isotopologues of oxygen stable isotope composition of precipitation in Southern China have been controversial, partly because the global observation sites, without widespread enough, collected data for a short period(several years or even several months). In this paper, there are three sources of the observed stable isotopic composition of atmospheric precipitation(δ18Op) in Changsha, which are (1) from GNIP Changsha Station(28°07'12″N, 113°02'24″E) (from January 1988 to December 1992), (2) cited from Yang et al. (2011) (from June 2006 to March 2009), and (3) measured daily data from Site1(28°11'29.76″N, 112°56'27.78″E) (from January 2010 to December 2019). The measured daily stable isotopic composition of the Xiangjiang River water(δ18Or) was derived from Site2(28°12'10.08″N, 112°57'33.12″E) (from January 2010 to December 2019). Based on the observed and simulated data(from isoGSM2) on stable isotope composition of water, the relationship between summer precipitation(JJA P) and oxygen stable isotope composition(δ18O) is determined in the Dongting Lake Basin under monthly, seasonal and annual timescales. Their possible influencing factors are demonstrated, and the contribution rate of different factors is analyzed by multiple linear stepwise regression. The results indicate that the temporal variation of JJA δ18Op was consistent with that of annual δ18Op. Besides, the annual δ18Op and JJA δ18Op were both significantly negatively correlated with JJA P. In dry and wet summers, the mean JJA Δδ 18Op were 0.48 ‰ and -0.66 ‰, respectively, indicating that the amount effect was observed in the basin. The amount effect was examined in river water to some extent, and in the wet summer of 2017, the fluctuation range of δ18Or was large with relatively low δ18Or. Statistically, on an interannual timescale, the more south-westerly(or north-easterly) the WPSH extended(or retreated), the higher(or lower) the JJA δ18Op was, indicating that the circulation effect was observed in the basin. On an inter-decadal timescale, the JJA P was the dominant control of annual δ18Op, accounting for ca. 75% of the contribution rate of the total variance. The δ18Os from Lianhua Cave(29°29'N, 109°32'E; 455 m a.s.l.) was expected to record the summer precipitation at Longshan Station(29°25'12″N, 109°22'48″E), and the rainout intensity was -0.3 ‰/100 mm. It demonstrates that the value of stable isotopes in precipitation may be considered a proxy of summer precipitation over Dongting Lake Basin. These results can potentially improve the reconstruction of paleoclimate in the East Asian monsoon region. Further study is needed to determine the contribution rate of local factors and large-scale factors on the oxygen stable isotope composition of precipitation.