Age‐Related Climate Response of Tree‐Ring δ¹³C and δ¹⁸O From Spruce in Northwestern China, With Implications for Relative Humidity Reconstructions

Abstract

Abstract Understanding varying climate responses in tree‐ring data across tree ages is important, but little is known about tree‐age effects on climate responses in tree‐ring stable isotopes. To detect whether age differences in tree‐ring δ 13 C and δ 18 O could lead to differing climate responses, we measured tree‐ring cellulose δ 13 C and δ 18 O (1901–2010) from Schrenk spruce ( Picea schrenkiana ) trees in northwestern China with ages ranging from 110 to 470 years, which we binned into three age groups. Tree‐ring δ 13 C (pin‐corrected) and δ 18 O exhibited similar year‐to‐year variability between age groups and did not feature age‐related trends. δ 13 C series from old trees (270–470 years) showed stronger legacy effects, reflecting influences from the antecedent period (due to carbohydrate reserves and climate), compared to young trees (110–125 years). Both tree‐ring δ 13 C and δ 18 O values decreased with increasing relative humidity (RH) and precipitation and with decreasing mean and maximum temperatures during the main growing season (May–August). δ 13 C and δ 18 O exhibited age‐dependent climate responses: Young trees had a stronger climate response in δ 13 C but a weaker or similar climate response in δ 18 O compared to old trees. We developed multiple growing‐season RH reconstructions based on composite chronologies using δ 13 C and δ 18 O series from different age groups. In particular, we found that including δ 13 C from young trees improved the skill of RH reconstructions because of the age‐specific mechanisms driving the δ 13 C‐climate relationship, but that caution is warranted with regard to extreme values. We therefore suggest that young trees should be considered when using stable isotopes, particularly in δ 13 C, for climate reconstruction.

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