SDOO

Abrupt warming episodes punctuate Greenland ice core records throughout the last glacial period. These events were first identified in two Greenland stable water isotope records (Dansgaard et al., 1993), and are generally referred to as Dansgaard-Oeschger (DO) events. During an event, Greenland transitions from cold stadial (GS) to warmer Greenland Interstadial (GI) conditions within a decade (Kindler et al., 2014; Huber et al., 2006). Surface air temperatures (SATs) over Greenland increase by 10-15°C and local snow accumulation almost doubles (Andersen et al., 2006; Kindler et al., 2014; Huber et al., 2006). These events occur at the onset of an oscillation that is of millennial timescale and are rather pronounced during Marine Isotope Stage3 (MIS3; between approximately 25 – 60 thousand of years BP, hereafter ka) (Fig. 1; Johnsen et al. (2001), Voelker et al.(2002)).

There are currently few examples of spontaneous DO-type oscillations occurring in coupled climate models, under any climate conditions, glacial-state or otherwise. For example the Max-Planck Institute Earth System Model (MPI-ESM) model is able to reproduce spontaneous millennial-scale AMOC oscillations when implementing PI ice sheet distribution in combination with a CO2 concentration range of 195-217 ppm (Klockmann et al., 2018, 2020) (See Figure 1). Under full glacial conditions, Peltier and Vettoretti (2014) found regular cycles of DO-type oscillations with the University of Toronto version of CCSM4 (UofT CCSM4) (See Figure 1). Authors term this behaviour as a “kicked” salt oscillator. Under late glacial conditions, at 30 ka, a quasi-oscillating AMOC is produced by the HadCM3 model (Armstrong et al., 2021) and results from a North Atlantic salt oscillator mechanism similar to that in UofT CCSM4 (Peltier and Vettoretti, 2014; Vettoretti and Peltier, 2016; Peltier et al., 2020) (See Figure 1).

Figure 1. MIS3 temperature reconstruction from North Greenland Ice Core Project (NGRIP) based on δ¹⁸O and  δ¹⁵N records (NGRIP Project Members, 2004; Kindler et al., 2014). Also shown, stack of anomalous (relative to the past millennium) Antarctic Temperature based on δD and δ¹⁸O records from six ice cores: EPICA Dronning Maud Land(EDML), EPICA Dome C, Talos Dome, Vostok, WAIS Divide Core and Dome Fuji as published in (Pedro et al., 2018). (b-d) MPI-ESM, (e-h) HadCM3 and (i-l) CCSM4 time series of modelled surface air temperature in Greenland and Antarctica at the grid points closest to the NGRIP (blue) and WDC (red) ice core sites, respectively. Modelled data is in timeseries of decadal average and smoothed with a 100-year running mean.