Abstract
Abstract. An equilibrium simulation of Marine Isotope Stage 3 (MIS3) climate with boundary conditions characteristic of Greenland Interstadial 8 (GI-8; 38 kyr BP) is carried out with the Norwegian Earth System Model (NorESM). A computationally efficient configuration of the model enables long integrations at relatively high resolution, with the simulations reaching a quasi-equilibrium state after 2500 years. We assess the characteristics of the simulated large-scale atmosphere and ocean circulation, precipitation, ocean hydrography, sea ice distribution, and internal variability. The simulated MIS3 interstadial near-surface air temperature is 2.9 ∘C cooler than the pre-industrial (PI). The Atlantic meridional overturning circulation (AMOC) is deeper and intensified by ∼13 %. There is a decrease in the volume of Antarctic Bottom Water (AABW) reaching the Atlantic. At the same time, there is an increase in ventilation of the Southern Ocean, associated with a significant expansion of Antarctic sea ice and concomitant intensified brine rejection, invigorating ocean convection. In the central Arctic, sea ice is ∼2 m thicker, with an expansion of sea ice in the Nordic Seas during winter. Attempts at triggering a non-linear transition to a cold stadial climate state, by varying atmospheric CO2 concentrations and Laurentide Ice Sheet height, suggest that the simulated MIS3 interstadial state in the NorESM is relatively stable, thus underscoring the role of model dependency, and questioning the existence of unforced abrupt transitions in Greenland climate in the absence of interactive ice sheet–meltwater dynamics.
Highlights
IntroductionMarine Isotope Stage 3 (MIS3), a period about 60–30 kyr BP (thousand years before present) during the last glacial, was characterised by millennial-scale abrupt climate transitions
Marine Isotope Stage 3 (MIS3), a period about 60–30 kyr BP during the last glacial, was characterised by millennial-scale abrupt climate transitions
We present a MIS3 interstadial equilibrium simulation employing a new version of the Norwegian Earth System Model (NorESM) designed for multi-millennial and ensemble studies (Guo et al, 2019)
Summary
Marine Isotope Stage 3 (MIS3), a period about 60–30 kyr BP (thousand years before present) during the last glacial, was characterised by millennial-scale abrupt climate transitions These events are known as Dansgaard–Oeschger (D-O) events, as revealed by the Greenland oxygen isotope ice core records (Dansgaard et al, 1993). Towards the end of every few stadial periods, the marine sediments show evidence of massive calving of the Laurentide Ice Sheet, with large numbers of icebergs transversing and melting in the North Atlantic. These events are known as Heinrich events (Heinrich, 1988). The freshwater from these melting icebergs is thought to have weakened the Atlantic meridional overturning circulation (AMOC), possibly causing further cooling of the Northern Hemisphere (e.g. Broecker, 1994)
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