ClimaTea Lecture: "Understanding the continuum of Dansgaard-Oeschger variability"

Speaker: Axel Timmermann (U Hawaii)

Millennial-scale variability associated with Dansgaard Oeschger (DO) and Heinrich events (HE) is one of the most puzzling glacial climate features found in paleo-climate archives.  The presentation will  describe the results of the first transient global climate hindcast simulation covering the period  50 ka B.P. to 30 ka B.P. The climate model is forced by time-varying external boundary conditions (greenhouse gasses, orbital forcing, and ice-sheet orography and albedo) and anomalous North Atlantic freshwater fluxes, which mimic the effects of changing Northern Hemisphere ice-volume on millennial timescales. Together these forcings generate a realistic global climate trajectory, as demonstrated by an extensive model/paleo data comparison. The analysis presented is consistent with the idea that ice-sheet instabilities and subsequent forced changes of the Atlantic Meridional Overturning Circulation were the main driver for the continuum of DO and HE variability seen in paleo-records across the globe. The talk will further assess the role of ocean and sea-level feedbacks in synchronizing ice-sheet instabilities in different regions and conclude with a critical discussion of alternative DO mechanisms.