Data-Model Comparisons of the Tropical Hydroclimate Response to the 8.2 ka Event with an Isotope Enabled Climate Model
Authors: Moore Andrea L. , Atwood Alyssa R. , Pauly Raquel E. 
Published: December 2024

Abstract. The 8.2 ka Event, a prominent climate anomaly that occurred approximately 8,200 years before present (8.2 ka), has been the subject of extensive research due to its potential implications for understanding the characteristics and mechanisms of abrupt climate change events. We characterize the tropical hydroclimate response to the 8.2 ka Event based on a multiproxy compilation of 61 tropical hydroclimate records and assess the consistency between the reconstructed hydroclimate changes and those simulated by a new isotope-enabled climate model simulation of the 8.2 ka Event with iCESM. The timing and duration of the hydroclimate anomalies is calculated using two event detention methods, one of which uses a new changepoint detection algorithm to account for age uncertainty. When age uncertainties are explicitly accounted for, significant hydroclimate anomalies associated with the 8.2 ka Event are detected in 30 % of the records in the compilation, with a mean onset age of 8.28±0.12 ka (1σ), mean termination age of 8.11±0.09 ka (1σ), and mean duration of 152±70 years (1σ; with a range of 50–289 years), comparing well with previous estimates, and lending support to a regionally-variable tropical hydroclimate response to the 8.2 ka Event, with events that span decadal to multi-centennial timescales in the proxy record. Notably, the hydroclimate anomalies are not hemispherically uniform, but rather display rich regional structure. Anomalous conditions are characterized by pronounced isotopic enrichment across East Asia, South Asia, and the Arabian Peninsula. In the Americas, drying and isotopic enrichment occurred in southern Central America, contrasting with isotopic depletion in central/eastern Brazil. In contrast, no robust signatures of the 8.2 ka Event were found over the Maritime Continent. Many of these regional patterns generally agree with the new set of iCESM simulations of the 8.2 ka Event. In iCESM, the North Atlantic meltwater forcing leads to a broad southward shift in tropical rainfall, resulting in a generally drier Northern Hemisphere and wetter Southern Hemisphere, but with large regional variations in precipitation amount and the isotopic composition of precipitation. Over the oceans, the precipitation δ18O anomalies are generally consistent with the ”amount effect”, wherein areas characterized by drying have more isotopically enriched precipitation and areas of wetting have more isotopically depleted precipitation. However, the precipitation δ18O anomalies are more decoupled from changes in precipitation amount over land. iCESM captures many of the regional hydroclimate responses observed in the reconstructions, including the large-scale isotopic enrichment pattern in precipitation δ18O in South and East Asia and the Arabian Peninsula, drying and isotopic enrichment in precipitation δ18O in southern Central America, isotopic depletion in parts of northeastern South America, and a muted hydroclimate response in the Maritime Continent. Overall, this study provides new insights into the tropical hydroclimate response to the 8.2 ka Event, emphasizing the importance of accounting for age uncertainty in the hydroclimate reconstructions and the value of using isotope-enabled model simulations for data-model intercomparison.