干旱区生态环境知识资源中心

We report an annually laminated sequence spanning the past 530 years from Maar Lake Twintaung, Myanmar. Calcareous varves appear as rhythmic units of light-colored carbonate and dark-colored biogenic-clastic lamina in the sediment. The light-colored carbonate layers are formed in the dry season due to strong evaporation and Spirulina blooms. The varved sequence provides a high-resolution geochemical archive of paleoclimatic variability in this tropical, data sparse area. A synchrotron radiation X-ray fluorescence method was used to analyze elemental data at seasonal to annual time scales. In this arid region, elemental Ca and Sr are mainly regulated by the balance of evaporation and precipitation in this closed lake basin. The elemental variations show distinct interannual and decadal variabilities. On interannual time scales, spectral analysis of the Ca and Sr time series indicates stronger El Nino-Southern Oscillation (ENSO)-like (Indian Ocean Dipole (IOD)-like) variability at periods of 2-7 years. It may suggest that ENSO and/or IOD are two dominant modes of regional rainfall variability on interannual time scales over the past 530 years. The quasiperiodicities of approximately 10 years suggest that solar activity may be a critical driving force of monsoonal rainfall in the region. A notable feature is that decreasing monsoonal rainfall since A. D. 1840 is coupled with tropical sea surface temperature variation. Considering that the monsoonal rainfall is coupled with several atmospheric processes evolving at different spatial and temporal scales, more high-resolution data are required to evaluate and verify the regional rainfall variability and its dynamic links.