DO Events

During the last glacial period, the North Atlantic basin experienced a number of large and abrupt millennial-scale fluctuations in climate referred to as Dansgaard-Oeschger (D/O) cycles. Ice cores from Greenland reveal that each cycle began with an abrupt warming from stadial to interstadial conditions within a few decades (Johnsen et al., 1992; Dansgaard et al., 1993; Grootes et al., 1993; Huber et al., 2006). The ensuing period of interglacial conditions persisted for several centuries, over which time gradual surface cooling occurred. At the end of this interstadial phase, a more rapid decline in temperature marked a return to glacial conditions. The amplitudes and rates of the high-frequency fluctuations in air temperature over central Greenland were substantial and reached up to 16°C over a few decades (Lang et al., 1999; Jouzel, 1999; Kindler et al., 2014). The effects of this warming extended across much of the Northern Hemisphere (Bond et al. 1993; Voelker, 2002; Overpeck and Cole, 2006; Spötl et al., 2006). D/O-induced climate change is centred on the North Atlantic and on regions with strong atmospheric response to changes in that region (Bond et al., 1993; van Kreveld et al., 2000; Margari et al., 2010; Dokken et al., 2013). Millennial-scale fluctuations in sea-surface temperature (Hendy and Kennett, 2000; Schmidt et al., 2006) and upwelling intensity (Schulz et al., 1998, Kim et al., 2012) with striking similarities to the Greenland Interstadials (GIS) have, however, also been reported from other oceanic sites. Most importantly, variations of the methane content of ice in both Greenland and Antarctica parallel Greenland warmings (Blunier and Brook, 2001), thus providing strong evidence that this rhythmic pattern occurred on a global scale during glacial times.