Tree-Ring Stable Carbon Isotope as a Proxy for Hydroclimate Variations in Semi-Arid Regions of North-Central China

Carbon and oxygen isotope ratios (delta C-13 and delta O-18) were measured in annual tree-ring cellulose samples dated from 1756 to 2015 CE. These samples were extracted from Chinese pine (Pinus tabulaeformis Carr.) trees located in a semi-arid region of north-central China. We found that tree-ring delta C-13 and delta O-18 values both recorded similar climatic signals (e.g., temperature and moisture changes), but found that tree-ring delta C-13 exhibited a stronger relationship with mean temperature, precipitation, average relative humidity, self-calibrating Palmer drought severity index (scPDSI), and standard precipitation evaporation index (SPEI) than delta O-18 during the period 1951-2015 CE. The strongest correlation observed was between tree-ring delta C-13 and scPDSI (previous June to current May), which explains similar to 43% of the variance. The resulting 130-year reconstruction reveals severe drought events in the 1920s and a sustained drying trend since the 1980s. This hydroclimate record based on tree-ring delta C-13 data also reveals similar dry and wet events to other proxy data (i.e., tree-ring width and historical documentation) that have allowed reconstructions to be made across the northern fringe of the Asian summer monsoon region. Our results suggest that both large-scale modes of climate variability (e.g., El Nino-Southern Oscillation, Pacific Decadal Oscillation, and North Atlantic Oscillation) and external forcing (e.g., solar variability) may have modulated moisture variability in this region. Our results imply that the relationship between tree-ring delta O-18 and local climate is less well-characterized when compared to delta C-13 and may be affected more strongly by the influences of these different atmospheric circulation patterns. In this semi-arid region, tree-ring delta C-13 appears to represent a better tool with which to investigate historical moisture changes (scPDSI).

Automated summary

Carbon and oxygen isotope ratios in tree-ring cellulose samples from Chinese pine trees in a semi-arid region of north-central China were measured to investigate their relationship with climatic changes. The results showed that both delta C-13 and delta O-18 values in tree-ring cellulose recorded similar climatic signals, but delta C-13 exhibited a stronger relationship with temperature, precipitation, humidity, and drought severity index compared to delta O-18. The tree-ring delta C-13 data provided a valuable record of historical moisture changes and revealed severe drought events in the past.