Tree-ring cellulose oxygen isotopes indicate atmospheric aridity in the western Kunlun Mountains

As an important indicator of atmospheric aridity, the vapor pressure deficit (VPD) is being paid increasing attention in global change researches during recent decades. However, available proxy data with the capability to represent VPD is still scarce in the globe. Herein we demonstrated a hidden frequency-dependent indication of tree-ring cellulose oxygen isotope (delta(OTRC)-O-18) to atmospheric aridity in the western Kunlun Mountains, Central Asia. In applying correlation and partial correlation analysis, frequency-dependent climatic drivers triggering the delta(OTRC)-O-18 values were detected. For the raw data with inter-decadal variability, delta(OTRC)-O-18 variations mainly indicated May-August precipitation (Local: r = -0.59, p < 0.001; Moisture source: r = -0.53, p < 0.001), evapotranspiration (ET) (Local: r = -0.57, p < 0.001; Moisture source: r = -0.51, p < 0.001). After a 5-year high-pass filter, the delta(OTRC)-O-18 series revealed highly significant correlation with May-August VPD (Local: r = 0.82, p < 0.001; Moisture source: r = 0.80, p < 0.001). The partial correlation further confirmed the strong linkages with high-frequency VPD when the impact of any additional eco-climatological variable (precipitation, temperature, ET, soil moisture 0-40 cm) was excluded. In contrast, if the effect of May-August VPD was excluded, relationships between delta(OTRC)-O-18 and other variables turned insignificant. Collectively, it was concluded that delta 18OTRC from the western Kunlun Mountains may indicate VPD at timescales < 5 years. Our results suggest that frequency dependent climatic significances should be considered when interpreting multi-process determined delta(OTRC)-O-18 as a climate-proxy.

Automated summary

Vapor pressure deficit (VPD) is an important indicator of atmospheric aridity, but there is a lack of data to represent VPD globally. In this study, tree-ring cellulose oxygen isotope (δ(OTRC)-O-18) in the western Kunlun Mountains is shown to be a hidden frequency-dependent indication of atmospheric aridity. The results reveal that δ(OTRC)-O-18 values are strongly correlated with VPD at timescales < 5 years.