The Timing and Amplitude of Holocene Neoglaciation in the Arctic

Abstract:

Evidence for late Holocene cooling (Neoglaciation) has been observed in proxy records from lake and marine sediments, ice cores, glacier moraines, and other archives. Despite the prevalence of such observations, an Arctic-wide quantitative analysis of the onset of Neoglaciation has not been undertaken. Here we use the proxy climate records in the Arctic Holocene Transitions (AHT) database to characterize the timing of the onset of Arctic Neoglaciation, as well as the amplitude of temperature change across the mid-Holocene transition. We then compare the results with a Holocene transient climate model simulation from the Community Climate System Model v3 (CCSM3 - TraCE-21 experiment). We applied both a broken-stick regression algorithm and a Bayesian change-point detection algorithm to systematically evaluate the presence and timing of the onset of Neoglaciation in the paleoclimate time series, propagating age uncertainty through both analyses. The resulting distribution of onset ages allows us to reject the hypothesis that there was a single Arctic-wide interval of Neoglacial cooling; rather, there were multiple onsets. Remarkably, we find similar results applying the same algorithms to surface temperatures simulated by the TraCE-21 experiment. CCSM3 also simulated multiple intervals of Neoglacial onsets, which are associated in the model with variability in Atlantic Meridional Overturning Circulation. Consistent with the model simulations, observed temperature change across observed transitions ranged from 0 to 4ºC, with most sites showing less than 1.5ºC cooling. The similarities between the transient model simulations and the observed Arctic Neoglaciation are striking, especially given the discrepancies between simulated and observed Holocene temperature evolution based on global means.