Tree-ring δ18O, a tool to crack the paleo-hydroclimatic code in subtropical China

Abstract

Tree ring plays an important role in deciphering the paleoclimatic signals. Although tree-ring width (TRW) has obvious advantages in studying the hydroclimatic history in the middle-high latitudes, it has certain limitation in hydroclimatic signal extraction in the tropical to subtropical areas, which greatly limits our fully understanding about the hydroclimatic history in these areas. In this work, tree-ring δ18O (δ18Otree) records from five independent tree-ring cores were measured and a composite δ18Otree record (1939–2014) was developed in Guilin, subtropical southwest China. No “juvenile effect” existed in this δ18Otree record and no relationship was found between δ18Otree and TRW. Correlation analysis with the climatic parameters demonstrated that the δ18Otree record significantly (p < 0.01) and negatively correlated with all the hydroclimatic parameters during the growing season (e.g. April–October precipitation, August–October relative humidity and April–November standardized precipitation–evapotranspiration index), while it only positively correlated with the August–September mean temperature (p < 0.05). At high frequency, the above relationships were greatly strengthened. Compared with the temperature-limited TRW in Guilin and other areas of subtropical China, δ18Otree was a better choice for hydroclimatic reconstruction. Moreover, the δ18Otree record in Guilin showed high consistency with other moisture-sensitive δ18Otree records in a large area of central-southeastern China. Analysis revealed that both large-scale circulation system (e.g. Indian summer monsoon, ENSO, westerlies) and local weather system significantly influenced the growing-season hydroclimatic variation in the study area. This study provides great potential for extracting hydroclimatic information from longer-living trees in subtropical China.