Variability of summer humidity during the past 800 years on the eastern Tibetan Plateau inferred from δ<sup>18</sup>O of tree-ring cellulose

Abstract

Abstract. We present an 800-year δ 18 O chronology from the eastern part of the Tibetan Plateau (TP). The chronology dates back to AD 1193 and was sampled in AD 1996 from living Juniperus tibetica trees. This first long-term tree-ringbased δ 18 O chronology for eastern Tibet provides a reliable archive for hydroclimatic reconstructions. Highly significant correlations were obtained with hydroclimatic variables (relative humidity, vapour pressure, and precipitation) during the summer season. We applied a linear transfer model to reconstruct summer season relative humidity variations over the past 800 years. More moist conditions prevailed during the termination of the Medieval Warm Period while a systematic shift during the Little Ice Age is not detectable. A distinct trend towards more dry conditions since the 1870s is apparent. The moisture decline weakened around the 1950s but still shows a negative trend. The mid-19th century humidity decrease is in good accordance with several multiproxy hydroclimate reconstructions for south Tibet. However, the pronounced summer relative humidity decline is stronger on the central and eastern TP. Furthermore, the relative humidity at our study site is significantly linked to the relative humidity at large parts of the TP. Therefore, we deduce that the reconstructed relative humidity is mostly controlled by local and mesoscale climatic drivers, although significant connections to the higher troposphere of west-central Asia were observed.

Modelling tree ring cellulose <i>δ</i><sup>18</sup>O variations in two temperature-sensitive tree species from North and South America

“…They have been widely used to reconstruct past atmospheric conditions such as air temperature (Naulier et al, 2015), drought (Labuhn et al, 2016), precipitation amount (Rinne et al, 2013), isotopic composition of precipitation (Danis et al, 2006), relative air humidity (Wernicke et al, 2015), cloud cover (Shi et al, 2012), and even atmospheric circulation patterns (Brienen et al, 2012). This diversity of climatic targets possibly reconstructed based on oxygen isotopes hints at the challenge of understanding the complexity of the climatic and biological processes that control isotopic fractionation of oxygen in trees .…”

Decreasing Indian summer monsoon on the northern Indian sub-continent during the last 180 years: evidence from five tree-ring cellulose oxygen isotope chronologies

“…A reduction in the monsoon precipitation and relative humidity of the ISM in the last 200 years is also evident in other areas influenced by the ISM. Maar lake sediments in Myanmar exhibit a decreasing trend of monsoonal rainfall since 1840 CE (Sun et al, 2016); a tree-ring δ 18 O record from southeast Asia exhibits a drying trend since 1800 CE (Xu et al, 2013a); a stalagmite δ 18 O record from southwest China reveals an overall decreasing trend in monsoon precipitation since 1760 CE (Tan et al, 2016); tree-ring δ 18 O and maar lake records in southwest China indicate reduced monsoon precipitation, relative humidity and cloud cover since 1840 or 1860 CE (Chu et al, 2011;Grießinger et al, 2017;Liu et al, 2014;Wernicke et al, 2015;Xu et al, 2012). Monsoon precipitation in northwestern India shows a significant decreasing trend during the period of 1866(Bhutiyani et al, 2010.…”

“…However, oxygen isotopes in tree rings and ice cores from the Tibetan Plateau revealed a weakening trend ISM since 1840 or 1860 (Duan et al, 2004;Grießinger et al, 2017;Liu et al, 2014;Wernicke et al, 2015). In addition, a stalagmite oxygen isotope record from northern India indicated that the ISM experienced a 70-year pattern of variation over the last 200 years, with no clear trend (Sinha et al, 2015).…”

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

“…Indeed, the stable isotopes of oxygen and hydrogen (δ 18 O and δD) of tree rings can be influenced by several parameters other than humidity (precipitation source, temperature). This limits the interpretation of tree ring isotope series in terms of humidity changes to places where variations of these other parameters are well constrained (Grießinger et al, 2016;Wernicke et al, 2015). A promising method relies on the δ 18 O and δD of plant biomarkers (e.g., n-alkanes and fatty acids from leaf waxes) recovered from soils (or buried soils) and sediments.…”