Abstract
Abstract. Millennial-scale variability associated with Dansgaard–Oeschger events is arguably one of the most puzzling climate phenomena ever discovered in paleoclimate archives. Here, we set out to elucidate the underlying dynamics by conducting a transient global hindcast simulation with a 3-D intermediate complexity earth system model covering the period 50 to 30 ka BP. The model is forced by time-varying external boundary conditions (greenhouse gases, orbital forcing, and ice-sheet orography and albedo) and anomalous North Atlantic freshwater fluxes, which mimic the effects of changing northern hemispheric ice volume on millennial timescales. Together these forcings generate a realistic global climate trajectory, as demonstrated by an extensive model/paleo data comparison. Our results are consistent with the idea that variations in ice-sheet calving and subsequent changes of the Atlantic Meridional Overturning Circulation were the main drivers for the continuum of glacial millennial-scale variability seen in paleorecords across the globe.
Highlights
The glacial climate system during Marine Isotope Stage 3 (MIS3, 59.4–27.8 ka BP) experienced massive variability on timescales of centuries to millennia (Masson-Delmotte et al, 2013), referred to as Dansgaard–Oeschger (DO) variability
The applied North Atlantic freshwater forcing F (t) captures the dominant meltwater pulses associated with Heinrich stadials (Fig. 2)
Except for the simulated sea level rise associated with Heinrich event 5, which is not captured in these eastern North Atlantic paleorecords, we find a relatively good match between model simulation and reconstruction, supporting the realism of the applied freshwater forcing
Summary
The glacial climate system during Marine Isotope Stage 3 (MIS3, 59.4–27.8 ka BP) experienced massive variability on timescales of centuries to millennia (Masson-Delmotte et al, 2013), referred to as Dansgaard–Oeschger (DO) variability. We observe that within the age uncertainties, all DO stadials between 30–50 ka BP were accompanied by iceberg surges, which originated from the adjacent northern hemispheric ice sheets According to these marine records and other data sets from the northern North Atlantic (e.g., Elliot et al, 1998; Grousset et al, 2001; Elliot et al, 2002), the iceberg calving increased during interstadial periods and peaked at the end of the stadials, after which it decayed rapidly. Possible feedbacks between the Atlantic meridional overturning circulation (AMOC) and ice sheets may have further modulated the evolution of iceberg and freshwater discharges into the North Atlantic as previously suggested
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