Tree-Ring Stable Carbon Isotope-Based Mean Maximum Temperature Reconstruction in Northwest China and Its Connection with Atmospheric Circulations

The inter-annual stable carbon isotope ratio (delta C-13) of three tree-ring cores of P. euphratica (Populus euphratica Oliv.) was determined from Ejina Oasis in Northwest China. A robust and representative delta C-13 chronology is generated from the three delta C-13 series using an arithmetic mean method. After eliminating the influence of the delta C-13 from elevated atmospheric carbon dioxide (CO2) concentration, we obtained a carbon isotopic discrimination (Delta C-13) chronology. According to the significant correlation between the tree-ring Delta C-13 and instrumental data, we reconstructed the mean maximum temperature anomalies from previous December to current September (T-DS) for the period 1901-2011. The reconstruction explained 43.6% of the variance over the calibration period. Three high-temperature periods (1929-1965, 1972-1974, and 1992-2006) and three low-temperature periods (1906-1926, 1966-1968, and 1975-1991) were found in the reconstructed series. Comparisons between the reconstructed T-DS and the observed mean temperature from previous December to current September in Anxi meteorological station and the temperature index in north-central China demonstrated the reconstructed T-DS has the advantage of reliability and stability. The significant spatial correlation declared that the reconstruction has a broad spatial representation and can represent the temperature variation characteristics in a wide geographical area. In addition, we found that the area of Ejina Oasis is smaller (larger) when the mean maximum temperature is higher (lower), which may be due to a conjunction effect of natural and anthropogenic activities. Significant periodicities and correlations suggested that the T-DS variations in Ejina Oasis were regulated by solar radiation and atmospheric circulations at the interannual and interdecadal time scales.