05 Apr 2024
 | 05 Apr 2024
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

A global Data Assimilation of Moisture Patterns from 21,000–0 BP (DAMP-21ka) using lake level proxy records

Christopher L. Hancock, Michael P. Erb, Nicholas P. McKay, and Sylvia G. Dee

Abstract. Global hydroclimate significantly differed from modern climate during the mid-Holocene (6 ka) and Last Glacial Maximum (21 ka). Consequently, both periods have been described as either a partial or reverse analogue for current climate change. To reconstruct past hydroclimate, an offline paleoclimate data assimilation methodology is applied to a dataset of 130 lake status records which provide relative estimates of water level measured using percentile units. The proxy observations are integrated with the climate dynamics of two transient simulations (TraCE-21ka and HadCM3) using a multivariate proxy system model (PSM) which estimates relative lake status from available climate simulation variables. The resulting DAMP-21ka (Data Assimilation of Moisture Patterns 21,000–0 BP) reanalysis reconstructs annual lake status and precipitation values at 500-year resolution and represents the first application of the methodology to global hydroclimate on timescales spanning the Holocene and longer. Validation using Pearson’s correlation coefficients indicates that the reconstruction (0.33) is more skillful, on average, than model simulations (0.10), particularly in portions of North America and East Africa where data density is high and proxy-model disagreement is prominent during the Holocene. Results of the PSM and assimilation are used to evaluate climatic controls on lake status, spatiotemporal patterns of moisture variability, and proxy-model disagreement. During the mid-Holocene, wetter conditions are reconstructed for North and East Africa, Asia, and southern Australia, but, in contrast to the model prior, negative anomalies are observed in North America resulting in drier than modern conditions throughout the Northern Hemisphere midlatitudes. Proxy-model disagreement in western North America may reflect a bias in model simulations to stronger sea level pressure gradients in the North Pacific during the mid-Holocene. The data assimilation framework is able to reconcile these differences by integrating the constraints of proxy observations with the dynamics of the model prior to produce a more robust estimation of hydroclimate variability during the past 21,000 years.

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Christopher L. Hancock, Michael P. Erb, Nicholas P. McKay, and Sylvia G. Dee

Status: open (until 31 May 2024)

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  • RC1: 'Comment on egusphere-2024-746', Anonymous Referee #1, 10 May 2024 reply
Christopher L. Hancock, Michael P. Erb, Nicholas P. McKay, and Sylvia G. Dee
Christopher L. Hancock, Michael P. Erb, Nicholas P. McKay, and Sylvia G. Dee


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Short summary
We reconstruct global hydroclimate anomalies for the past 21,000 years using a data assimilation methodology blending observations recorded in lake sediments with the climate dynamics simulated by climate models. The reconstruction resolves data-model disagreement in East Africa and North America, and we find that changing global temperatures and associated circulation patterns as well as orbital forcing are the dominant controls on global precipitation over this interval.