Instability of the Atlantic overturning circulation during Marine Isotope Stage 3

Abstract

Variations in the strength of the Atlantic meridional overturning circulation (AMOC) were involved in the occurrences of Dansgaard-Oeschger (D-O) events during Marine Isotope Stage 3 (MIS3). The stability of the AMOC to North Atlantic freshwater perturbations is studied using a comprehensive climate model under MIS3 boundary conditions. An AMOC stability diagram constructed from a series of equilibrium freshwater perturbation experiments reveals a highly nonlinear dependence of AMOC strength on freshwater forcing. The MIS3 baseline state is remarkably unstable with respect to minor perturbations. The global climate signal associated with a change in AMOC strength is consistent with a transition from an interstadial to a stadial state including an annual mean surface air temperature drop of~8 K in central Greenland. We suggest that minor freshwater perturbations in the hydrologic cycle, e.g., related to ice sheet processes, had the potential to trigger D-O-type climate shifts associated with a threshold in the atmosphere-ocean system.

Black Sea temperature response to glacial millennial‐scale climate variability

“…Interstadial warming was shown to be strongest in Greenland [Kindler et al, 2014] and HE cooling most prominent in the midlatitude North Atlantic and western Mediterranean Sea [Bard et al, 2000;Martrat et al, 2004Martrat et al, , 2007. Climate models suggest that this spatial heterogeneity in the North Atlantic climate response was transmitted to the continental interior, with DO cycle temperature anomalies penetrating deeper into the continent than HE-associated cooling [Ganopolski and Rahmstorf, 2001;Zhang et al, 2014]. Pollen and stalagmite records from eastern and southern Europe reveal a pronounced variability in rainfall that coincided with DO cycles characterized by wetter conditions and lower wind stress during interstadials [Allen et al, 1999;Tzedakis et al, 2004;Fleitmann et al, 2009;Fletcher et al, 2010] BLACK SEA TEMPERATURE AND DO CYCLES 1 differences between HE and non-HE stadials, the detailed patterns of DO cycles and HE in the eastern Mediterranean region seem to be more ambiguous [Tzedakis et al, 2004;Fleitmann et al, 2009;Shumilovskikh et al, 2014].…”

“…Stadials associated with massive iceberg discharges occurring on a multimillennial timescale, referred to as Heinrich events (HE) [Heinrich, 1988;Bond et al, 1993], were significantly colder in some areas of the midlatitude North Atlantic [Heinrich, 1988;Bond et al, 1993;Bard et al, 2000;Martrat et al, 2007]. These abrupt climate changes associated with DO cycles and HE were probably caused by major reorganizations in the Atlantic Meridional Overturning Circulation (AMOC) and strongly amplified by shifts in sea ice expansion and other forms of climate feedback [Bond et al, 1993;Ganopolski and Rahmstorf, 2001;Van Meerbeeck et al, 2011;Zhang et al, 2014]. Climate model simulations [Ganopolski and Rahmstorf, 2001;Zhang et al, 2014] suggest very different spatial patterns of oceanic and continental temperature anomalies during DO cycles and HE in the Northern Hemisphere.…”

“…These abrupt climate changes associated with DO cycles and HE were probably caused by major reorganizations in the Atlantic Meridional Overturning Circulation (AMOC) and strongly amplified by shifts in sea ice expansion and other forms of climate feedback [Bond et al, 1993;Ganopolski and Rahmstorf, 2001;Van Meerbeeck et al, 2011;Zhang et al, 2014]. Climate model simulations [Ganopolski and Rahmstorf, 2001;Zhang et al, 2014] suggest very different spatial patterns of oceanic and continental temperature anomalies during DO cycles and HE in the Northern Hemisphere. While stadials (interstadials) have been attributed to a weak (strong) AMOC associated with decreased (increased) ocean heat transport and most likely sea ice controlled, HE can be explained by an off mode of the AMOC [Bond et al, 1993;Ganopolski and Rahmstorf, 2001;Van Meerbeeck et al, 2011;Zhang et al, 2014].…”

“…Climate model simulations [Ganopolski and Rahmstorf, 2001;Zhang et al, 2014] suggest very different spatial patterns of oceanic and continental temperature anomalies during DO cycles and HE in the Northern Hemisphere. While stadials (interstadials) have been attributed to a weak (strong) AMOC associated with decreased (increased) ocean heat transport and most likely sea ice controlled, HE can be explained by an off mode of the AMOC [Bond et al, 1993;Ganopolski and Rahmstorf, 2001;Van Meerbeeck et al, 2011;Zhang et al, 2014].…”

Impact of meltwater on high-latitude early Last Interglacial climate

“…It is worth noting that mechanisms other than freshwater fluxes have been invoked which could cause millennial-scale variations in climate through changes in AMOC behaviour. These include a salt oscillator in the North Atlantic (Peltier and Vet- toretti, 2014) and wind stresses over the subpolar gyre caused by changes in the Laurentide ice-sheet geometry (Zhang et al, 2014). Furthermore, high-latitude climates are influenced by changes in the mode of atmospheric circulation (e.g.…”