Laminated stalagmite - based mean annual temperature reconstruction for middle reaches of the Yangtze River during the past 1200 years

Temperature changes in the middle reaches of the Yangtze River (MRYR) have affected more than one billion people. In contrast to the warming trend in the Northern Hemisphere (NH), there was a sustained cooling trend of mean annual temperatures in the MRYR from 1930s to 1980s. Due to long-term mean annual temperature record has so far been lacking in the MRYR, it remains unclear to what extent regional peculiarities reflect region-specific internal climate variability or differences in driving mechanisms. Here, we present a reconstruction of temperature variability over the MRYR for the period CE 800-1998 using a laminated stalagmite (HS4) from Heshang cave, Yichang region, China. Observations of Heshang cave suggest that the growth of HS4 stalagmite is mainly affected by the temperature because of the stability of dripping water composition. Based on a significant positive correlation between the growth rate and the observed temperature, we reconstructed the mean annual temperature (MAT) for Yichang region with an explained variance of 39.8%, the correlation in interdecadal scale (10-yr low pass) was significantly improved (r=0.86). The new MAT reconstruction shows an almost similar trend with existing low resolution mean annual temperature records from historical document, which confirms the credibility of the reconstruction. Four warm (800s-880s, 1260-1450s, 1650s-1800s, 1900s-1950s) and three cold (890s-1250s, 1460s-1640s, 1810s-1890s) period were identified in MAT record. Our reconstruction shows a significant cooling in the MRYR during the MCA period, which may differ from previous NH temperature records. We suggested that the unique temperature variation in the MRYR may be driven by El Niño-Southern Oscillation (ENSO), as there was a significant positive correlation between MAT record and ENSO over the past 1200 years on the multidecadal scale. When sea surface temperatures in the eastern Pacific rise, so do temperatures in the MRYR, and vice versa. Our study provided the longest mean annual temperature record in the MRYR, and we also highlight that ENSO may be related to the temperature variation of the East Asian monsoon region, which has generally been ignored in past studies.