Enhanced Recent Local Moisture Recycling on the Northwestern Tibetan Plateau Deduced From Ice Core Deuterium Excess Records

Abstract

Local moisture recycling plays an essential role in maintaining an active hydrological cycle of the Tibetan Plateau (TP). Previous studies were largely limited to the seasonal time scale due to short and sparse observations, especially for the northwestern TP. In this study, we used a two‐component mixing model to estimate local moisture recycling over the past decades from the deuterium excess records of two ice cores (i.e., Chongce and Zangser Kangri) from the northwestern TP. The results show that on average almost half of the precipitation on the northwestern TP is provided by local moisture recycling. In addition, the local moisture recycling ratio has increased evidently on the northwestern TP, suggesting an enhanced hydrological cycle. This recent increase could be due to the climatic and environmental changes on the TP in the past decades. Rapid increases in temperature and precipitation have enhanced evaporation. Changes of land surface of plateau have significantly increased evapotranspiration. All of these have intensified local moisture recycling. However, the mixing model used in this study only includes a limited number of climate factors. Some of the extreme values of moisture recycling ratio could be caused by large‐scale atmospheric circulation and other climatic and weather events. Moreover, the potential mechanisms for the increase in local recycling need to be further examined, since the numeric simulations from climate models did not reproduce the increased contribution of local moisture recycling in precipitation.

Controls on Deuterium Excess across Asia

“…Temporal records from ice cores in Asia go back 10 s to 100 s of years, and show seasonal variability in d-excess, where high values are associated with Mediterranean-derived moisture and/or continental recycling, and low values are associated with Indian or Arctic Ocean-derived moisture and/or arid conditions that promote subcloud evaporation [5,50,51]. Because falling snow at high elevations does not evaporate much due to cold temperatures and a cloud base that is relatively close to the ground, seasonal changes in d-excess are more likely controlled by distinct moisture sources (oceanic and continental), as opposed to variations in subcloud evaporation.…”

Long‐distance atmospheric moisture dominates water budget in permafrost regions of the Central Qinghai‐Tibet plateau

“…Similar results were also found in the northwestern QTP (6,100 m a.s.l.) by An et al (2017). Froehlich et al (2008) confirmed that the impact of subcloud evaporation on d‐excess of precipitation could be ignored in the high elevation regions due to the shorter distance between the ground and cloud base.…”

“…Notably, the latter two areas had the lowest ratios on the QTP among existing results. Based on the ice core records at Chongce and Zangser Kangri, An et al (2017) found the moisture recycling ratio were 15% ‐ 82.6% from 1979 to 2012 and 24.7% ‐ 81.6% from 1979 to 2008, respectively.…”

“…The high elevation, low air temperature, and short growing season resulted in a limited contribution of plant transpiration to recycled moisture. The evaporation vapour from the soil and open water body dominates the recycled moisture in this area (An et al, 2017; Kong et al, 2013; Liu et al, 2013). As a result, a two‐component mixing model based on d‐excess ( d‐excess = δ 2 H‐8δ 18 O) was adopted to analyse local moisture recycling in our study area.…”

How old are the Tibetan ice cores?

“…使 用 Picarro L2120-i液 态 水 同位 素分析仪对58.8和135.8 m崇测冰芯进 行了稳定同位素分析, 样品δ 18 O的分 析精度小于0.1‰ [12] . 58.8 m崇测冰芯 共采集了1956个样品, 采样分辨率为 2~3 cm/样品 [13] ; 135.8 m崇测冰芯从…”