Large-scale 20th Century Warming Identified in the East Siberian Arctic Using Tree-ring Carbon Isotope Records

Carbon isotope measurements (delta13C) across tree rings retain long-term annual and seasonal climate trends that can be used to extend historical records in regions where instrumental observations are limited or unavailable. The delta13C value measured from successive tree-rings reflects changes in stomatal conductance, which varies as a stress response to changes in environmental moisture. In relatively dry environments, a decrease in moisture leads to a reduction in stomatal conductance and causes an observable increase in the measured tree-ring delta 13C composition. Thus, changes in fractionation can be an indicator of varying water-stress associated with changing temperatures. Here, I investigate the use of annually resolved delta13C data to identify twentieth century Arctic temperature trends. I present a new annually resolved delta 13C dataset spanning 50 years (1912-1961) from three Larix cajanderi tree cores collected in far northeastern Siberia. The dataset yields a strong correlation (r = 0.55) with an increase in temperatures associated with the Early Twentieth Century Warming (ETCW) event (1925 to 1946). In order to investigate whether this Arctic-wide temperature anomaly can be identified from other Arctic tree-ring sites, I compiled delta13C data from thirteen previously published high-latitude (>62 ˚N) tree-ring chronologies. The combined dataset, which spanned nearly the entire twentieth century (1900-1998), identified a strong negative relationship (r = -0.53, p < 0.01) between net carbon isotope fractionation and temperature. This Arctic-wide tree-ring dataset showed strong correlation across the ETCW in particular (r = -0.86), as well as across the interval of rapid late twentieth century anthropogenic warming (r = -0.50). Identification of both the natural ETCW and the current anthropogenic Late Twentieth Century Warming (LTCW) event (1966 to 1998) demonstrates the potential for tree-ring delta13C records to extend our knowledge of Arctic temperature change beyond the limited historical record.