Holocene Hydroclimate: Multi Millennial-Scale Trends in Proxies and Models

A global-scale, multi-proxy dataset of hydroclimate-sensitive records provides insight into large-scale spatiotemporal changes over terrestrial regions during the Holocene. This new compilation of Holocene Hydroclimate datasets includes 726 records from 612 sites and includes pollen (n=266), speleothem stable isotope (n=106), lake deposit (n=152), lake carbonate (n= 32), sedimentary leaf wax (n= 32), and ice accumulation (n=9) records. The data are provided in the LiPD format and include metadata detailing the climate interpretation and seasonality described by the original author interpretation. 44 proxy regions were identified using a spatially constrained multivariate clustering method to separate common records based on geographic proximity as well as the trend during each of the early (6 0 ka) and late (12 - 6ka) Holocene. For each cluster, a composite time series was computed by standardizing proxy time series over common intervals. Results from these composite records indicate that the first half of the Holocene was a period of general wetting with exceptions in portions of North America and Europe. During the second half of the Holocene, variations in first order trends vary more widely. In the Northern Hemisphere, mid-latitudes generally experienced a shift to wetter conditions while monsoon regions became drier. In the Southern Hemisphere, the composite reconstructions show increased moisture over South America and decreases in Southern Africa and Australia. Comparisons with transient Holocene climate model simulations (Trace-21ka and HadCM3) reveal general agreement in the spatio-temporal pattern of these hydroclimatic trends. 57% and 75% of proxy regions agree with at least one of these transient simulations with respect to the direction of the 1st order trend during the Early and Late Holocene respectively. Agreement is generally highest in monsoon regions and lowest for clusters located in North America and Europe.