The role of CO_(2) decline for the onset of Northern Hemisphere glaciation

• Published in: Quaternary Science Reviews
• Main Authors: Willeit, Matteo, Ganopolski, Andrey, Calov, Reinhard, Robinson, Alexander James, Maslin, Mark
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon-Elsevier Science Ltd 2015
• Subjects: 52; Greenland ice-sheet; Pliocene sea-level; Benthic Delta-O-18 records; Atlantic coastal-plain; Climate system model; Sub-Artic Pacific; Intermediate complexity; United-States; Progressive intensification; Middle Pliocene; Física atmosférica; 2501 Ciencias de la Atmósfera; Greenland; Pacific; Ice Sheet
• Online Access: https://hdl.handle.net/20.500.14352/23858; https://doi.org/10.1016/j.quascirev.2015.04.015

© 2015 The Authors. M.W. acknowledges support by the German Science Foundation DFG grant GA 1202/2-1. A.R. was funded by the Marie Curie 7th Framework Programme (Project PIEF-GA-2012-331835, EURICE). The comments of two anonymous reviewers helped to improve the paper. The PlioceneePleistocene Transition (PPT), from around 3.2 to 2.5 million years ago (Ma), represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern Eurasia and North America. Paleo evidence indicates that the PPT was accompanied and possibly caused by a decrease in atmospheric CO_(2), but the temporal resolution of CO_(2) reconstructions is low for this period of time and uncertainties remain large. Therefore, instead of applying existent CO_(2) reconstructions we solved an ‘inverse’ problem by finding a schematic CO_(2) concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records. To this end, we performed an ensemble of transient simulations with an Earth system model of intermediate complexity from which we derived a best guess transient CO_(2) scenario for the interval from 3.2 to 2.4 Ma that gives the best fit between the simulated and reconstructed benthic δ^(18)O and global sea surface temperature evolution. Our data-constrained CO_(2) scenarios are consistent with recent CO_(2) reconstructions and suggest a gradual CO_(2) decline from 375-425 to 275-300 ppm, between 3.2 and 2.4 Ma. In addition to a gradual decline, the best fit to paleoclimate data requires the existence of pronounced CO_(2) variability coherent with the 41-kyr (1 kyr = 1000 years) obliquity cycle. In our simulations the long-term CO_(2) decline is accompanied by a relatively abrupt intensification of Northern Hemisphere glaciation at around 2.7 Ma. This is the result of a threshold behaviour of the ice sheets response to gradual CO_(2) decrease and orbital forcing. The simulated Northern ...