Asian Summer Monsoon‐Related Relative Humidity Recorded by Tree Ring δ¹⁸O During Last 205 Years

Abstract

To deeply understand the Asian summer monsoon (ASM) strength variation in its fringe region, we established a 205-year stable oxygen isotope (δ 18 O) chronology based on four individual Pinus tabulaeformis Carr. from Ordos Plateau, China. First, we found that δ 18 O in tree rings inherits the signals of summer (June to August) monsoonal precipitation δ 18 O (δ 18 O P ). Second, relative humidity (RH) was observed to have a large effect on the δ 18 O of pine trees. The tree ring δ 18 O series significantly correlates with the observed local RH from June to August (RH JJA ) with r = −0.65 (N = 56, p < 0.001). The RH over Ordos Plateau is greatly influenced by ASM-related precipitation. As such, it could well reflect the variations of ASM intensity. Thus, we reconstructed the RH JJA over Ordos, the center of the ASM fringe region (ASMFR), for the last two centuries. Our reconstructed RH JJA series has a large geographical and spatial representativeness, which is well compared with other precipitation reconstructions in ASMFR and jointly reflects ASM variations in the past. The RH JJA reconstruction showed that the 1870s-1890s were the wettest years in the entire reconstruction, while the middle-late 1920s were the driest. From 1930 to 2012, the RH of the study area continuously decreased. We found significantly negative correlations between RH JJA and the Central Pacific sea surface temperature. This finding means that if the El Niño-Southern Oscillation of the Central Pacific continues to increase in the future, the aridification in the ASMFR will be intensified.

A 210-year tree-ring &#x003B4;¹⁸O record in North China and its relationship with large-scale circulations

“…Previous studies have shown that d 18 O TR can be a good indicator of hydrological climate factors (Lorrey et al, 2016;Brunello et al, 2019), such as RH (An et al, 2014;Grießinger et al, 2017;Liu, Wang et al, 2019), PDSI (Sano et al, 2011;Liu, Fang et al, 2019), SPEI (Labuhn et al, 2016), precipitation (Anchukaitis et al, 2008;Baker, Hunt et al, 2015;Xu, Shi et al, 2019), vapour pressure deficit , even cloud cover (Liu et al, 2014). The results of the spatial correlation between d 18 O TR in Baotou and the vapour pressure, precipitation, and PDSI in this study (Fig.…”

“…To further demonstrate that the d 18 O TR record can represent the regional hydrological conditions, we performed spatial d 18 O TR records in Baotou and Ordos Plateau of Inner Mongolia (Liu, Wang et al, 2019) were correlated both on the interannual (Fig. 7a) and interdecadal (Fig.…”

“…This was because the RH directly controlled the d 18 O TR fractionation, while precipitation and temperature could only indirectly influence the d 18 O TR through d 18 O P and RH (McCarroll and Loader, 2004). Lower RH would result in an increasing vapour pressure gradient between the atmosphere and interstitial leaf space, leading to preferred 16 O loss and thereby 18 O enrichment in leaf water (Sano et al, 2011;Liu, Wang et al, 2019), and vice versa. Therefore, d 18 O TR exhibited a negative correlation with RH.…”

“…In China, many d 18 O TR studies have revealed the history of the AM and highlighted the impact of El Niño-Southern Oscillation (ENSO) on the AM on the interannual timescale (Xu et al, 2013(Xu et al, , 2016Zeng et al, 2016;Liu, Fang et al, 2019;Liu, Wang et al, 2019). In the Yaoshan region of Central China and the Ordos Plateau of North China (Liu, Wang et al, 2019), the d 18 O TR -based RH reconstructions reflected the weakening trend of the Asian summer monsoon (ASM) since the 1930s. More evidence about the weakening trend of ASM is needed.…”

Seasonality of moisture supplies to precipitation over the Third Pole: a stable water isotopic perspective

“…So far, water stable isotopes in precipitation have demonstrated wide applications to earth sciences on the TP, having been used to detect moisture source and intensity of related atmospheric circulations [12][13][14][15][16] , reflect the influences of local and/or large-scale atmospheric circulation processes on precipitation that pertains closely to the water cycle [17][18][19][20][21] , transcend time to link modern variation features with climate significances in paleoproxies 5,12,[22][23][24][25][26] and inform of the plateau uplift history with their imprints on rock records 27,28 . Various studies on water stable isotope compositions have been conducted in the southern, southeastern, northeastern and northwestern parts of TP [29][30][31][32] , revealing the dependency of δ 18 O in precipitation on moisture sources 17,33 , relative humidity 22 , cloudiness 34 , and integrated convective activity along upstream air mass trajectories 17,30,[35][36][37] . Those studies highlighted the spatial heterogeneity of precipitation and its water stable isotopic compositions across the TP, which pertains to atmospheric circulations.…”