Large-scale atmospheric circulation controls intra-annual tree-ring oxygen isotope in the lower Yangtze River basin

Abstract

In the Asian monsoon region, the oxygen isotope ratios in precipitation (δ¹⁸O_ppt) are widely reported to be influenced by upstream convective activity, but short-term measurements have limited their further application. Tree-ring cellulose δ¹⁸O (δ¹⁸O_cell) is mainly influenced by δ¹⁸O_ppt and local relative humidity, and it has great potential for extending the application of δ¹⁸O_ppt. We present the intra-annual and annual variabilities of δ¹⁸O_cell of Pinus taiwanensis Hayata in the lower Yangtze River basin, China. Intra-annual δ¹⁸O_cell values show typical “V”-shaped patterns with the most depleted values occurring in the centre of each growth ring, similar to the variation of δ¹⁸O_ppt. Using statistical analysis and forward modeling on different timescales, we found that the seasonal tree-ring isotopic cycle was primarily controlled by δ¹⁸O_ppt, which depends on the large-scale atmospheric circulation. Additionally, seasonal δ¹⁸O_cell profiles were significantly linked with upstream processes, such as the tropical monsoon and outgoing longwave radiation (OLR) in the late or post monsoon season, across the upstream area. Local moisture conditions have a limited effect on intra-annual δ¹⁸O_cell. On the annual scale, δ¹⁸O_cell variability was controlled by both local moisture conditions and δ¹⁸O_ppt during the growing season; however, these relationships were unstable during the past 40 years. Due to the diverse primary drivers of δ¹⁸O_cell on different timescales, annual and seasonal δ¹⁸O_cell records of multi-centennial length may enable us to infer long-term variations in different climate signals separately, such as the strength of upstream convective activity, especially in the late or post monsoon season, on the seasonal scale.