Indian summer monsoon and winter Total Solar Irradiance signals in the tree-ring δ18O from foothills of High Asia, northern Pakistan

A tree-ring stable oxygen isotope (delta O-18) chronology was developed for the past 171 years by four Abies pindrow trees growing in southwest foothills of High Asia, northern Pakistan, which is correlated with observed and modelled delta O-18 of precipitation in Islamabad over the instrumental period. The averaged tree-ring delta O-18 chronology is significantly negative correlated with local (r = -.651, p < .001, n = 38) and regional (r = -.664, p < .001, n = 65) summer precipitation variations. Analysis of vertically integrated water vapour flux and surface wind field suggests that the sampling site is located at the northern limit of the Indian summer monsoon (ISM). Our tree-ring delta O-18 series is significantly (p < .001, n = 143) negatively correlated with observed Homogenous India rainfall, All Indian rainfall, Core-Monsoon India rainfall and Northwest India rainfall. This is the first detected ISM signal from tree-ring delta O-18 over northern Pakistan. Several ISM-related paleoclimate proxies, including three stalagmites delta O-18 series (Sahiya cave, Jhumar cave and Qunf cave) and a tree-ring delta O-18 series (Manali), show consistent variability and a correlation coefficient of .566 (p < .001, n = 165) with our tree-ring delta O-18, suggesting that a combination of multiple proxies may be potentially useful to understand the full perspective of ISM before instrumental era. In addition, we found that the satellite-observed winter Total Solar Irradiance exerts influence on the tree-ring delta O-18 variation (r = .643, p < .001, n = 38), which may be linked to runoff of the Indus River and ISM precipitation.