Separating temperature from precipitation signals encoded in tree-ring widths over the past millennium on the northeastern Tibetan Plateau, China

Abstract

Tree-ring width chronologies from the upper timberline are an important material to reconstruct past temperature variability on the northeastern Tibetan Plateau (NTP). However, precipitation signals are often encoded in the upper timberline chronologies, which complicate the temperature reconstructions and should be removed properly. Here, we propose to use the chronologies from the middle to lower forest zones to remove the precipitation signals encoded in the upper timberline chronologies on the NTP, as tree growth at the two elevation zones records similar precipitation signals but has different temperature responses. We compiled a dataset of 13 Qilian juniper (Sabina przewalskii Kom.) tree-ring width chronologies, and employed two independent methods to develop millennial (AD 1000–2000) temperature reconstructions on the NTP. The two reconstructions are very consistent with each other over the past millennium, with a correlation of 0.97, and account for more than 50% of the observed temperature variance during 1958–2000. Both reconstructions contain little precipitation signals, suggesting that we have extracted purer temperature information than before. Our reconstructions show similar warm-cold patterns to the temperature records from the surrounding areas, indicating that they are capable of representing large-scale temperature variability during the past millennium. Comparison of our reconstructions with five millennial Northern Hemisphere (NH) temperature series indicates that temperature changes on the NTP are generally distinct from the NH temperature patterns except for the long-term trend during the past millennium, suggesting specific characteristics of regional temperature variability. The distinct variations may be related to the influence of local precipitation, which generally has inverse variations with the temperature on multi-decadal timescales. Our results also show that temperature variability on the NTP has a strong linkage with the strength of the Indian summer monsoon (ISM), with the warm and cool phases of NTP temperature associated with strong and weak ISM, respectively.