Holocene moisture variations in arid central Asia: Reassessment and reconciliation

Abstract

During the past two decades there have been numerous studies of Holocene moisture variations in arid central Asia (ACA). However, these available records show contradictory results regarding the long-term trends. Moreover, most hypotheses that have been proposed to reconcile contradictory interpretations have failed to resolve the inconsistencies. Therefore, an up-to-date and comprehensive study incorporating all published high-quality records from the whole of ACA is urgently needed to determine the potential reasons (such as proxy interpretations, geomorphological context, precipitation seasonality) for these contradictory moisture reconstructions. We present a compilation of 36 records of the Holocene moisture evolution of ACA that are supported by reliable chronologies. The compilation reveals an overall long-term wetting trend (31 out of 36 records) during the Holocene, and it also shows that the records with inconsistent variations were based mainly on pollen assemblages from the Altai Mountains and on stalagmite δ18O records. The complex patterns of pollen-based precipitation reconstructions from the Altai Mountains can at least partly be attributed to the varying influences of temperature on vegetation change at different elevations. Additionally, the stalagmite δ18O records were significantly affected by the moisture source and water vapor transport pathways, which adversely affected their reliability as a direct regional moisture indicator. After excluding the records based on ambiguous proxies, we found almost no significant differences between the long-term moisture trends in the remaining records. Therefore, we suggest that the previous contradictory moisture reconstructions are caused mainly by proxy ambiguity. Finally, by preliminarily reconciling the trends of moisture evolution, isotopic variations, temperature changes, and vegetation dynamics in ACA, we attempt to present a possible framework of the circulation-hydroclimate-ecosystem evolution in ACA during the Holocene.