The premise of temperature effect playing in regions with complex moisture sources – Evidence from high-resolution water vapor isotopes

Abstract

Atmospheric precipitation has widely taken part in the formation and accumulation of many geological archives. In these processes, the isotope fractionations are tightly related to the meteorological factors, such as temperature and precipitation amount. Therefore, precipitation isotopes are usually regarded as an effective proxy to reconstruct the paleoclimate and paleoenvironmental changes. However, with the deepening of research, it is found that the temperature effect is not suitable for all regions and time scales, especially in regions with complex moisture sources. Moreover, the applicable mechanism of the temperature effect is still unclear. Here, we chose Xi’an as our study site, because it is located in the transition zone of the East Asian Summer Monsoon (EASM) and the westerlies with relatively complex water vapor sources. Through conducting a three-year, high-resolution, relatively continuous water vapor isotopic composition measurements in Xi’an, we defined the duration of the EASM here, which normally starts in June and is over in September. By separating the δ18Op into monsoon and non-monsoon seasons, we found a significant temperature effect in the non-monsoon seasons, with a correlation coefficient of 0.54, while no temperature effect is observed in the monsoon seasons and the whole year. Our water vapor isotopic results suggested that the establishment of temperature effect of precipitation isotopes should follow two prerequisites: 1. single water vapor source; 2. large temperature gradient. Our results specify the applicable conditions of temperature effect and potentially help us to better use precipitation isotopes to understand the paleo-temperature variations in different regions.