Vegetation dynamics in arid central Asia over the past two millennia linked to NAO variability and solar forcing

Abstract

The role of NAO modes and solar activity, together with their potential relationship, in driving hydroclimatic variability in arid central Asia over the past two millennia remain controversial—partly due to the limitations of the resolution or time span of existing paleoclimatic records. Vegetation ecosystems at high altitudes are very sensitive to hydroclimate variations. Here, we present a vegetation history for the past two millennia based on a pollen record with an average time resolution of four years from Lake Dalongchi in the Tianshan Mountains. Our results show a millennial-scale drying trend during the past 2000 years, with the vegetation changing from forest-steppe and forest to steppe as the intensity of mid-latitude westerlies gradually decreased. We suggest that the dynamic link between the NAO and moisture variability in arid central Asia depends on the NAO phase in the context of changes in westerlies intensity. The moisture variability in arid central Asia shows a positive relationship with NAO phases when the precipitation delivered by the mid-latitude westerlies exceeded a threshold level in the period of 0–1100 CE. However, over the last millennium, the role of the NAO mode was weakened by solar forcing when the regional moisture gradually decreased below this threshold. The decline of the ancient Silk Road was possibly related to this humid-to-try climate shift at∼1100 CE.