14.8 The next glaciation

Fig. 14.1 The Pleistocene climatic madhouse

a) Pleistocene subdivisions according to the International Commission on Stratigraphy. b) LR04 stack of 57 benthic cores record of !18O, an ice and temperature proxy, subdivided between ocean (dark blue), and ice (light blue) at the level that identifies the generally accepted interglacials. !18O in essence measures the distribution of water between ice and oceans. Numbers correspond to marine isotope stages (after Lisiecki & Raymo 2005). c) Pleistocene hominins showing the main species of the genus Homo, and the Australophitecus and Paranthropus genera, as well as the approximate time for some of the main cultural advances. No species distinction is made between ergaster and erectus, and between antecessor and heildebergensis. No inference is made regarding evolutionary relationship.

Fig. 14.2 Average of six of the past ten interglacials

An average interglacial (black curve and 1' grey bands) was constructed from EPICA Dome C deuterium data for interglacials MIS 5e, 7c–a, 9e, 15a, 15c and 19c, after aligning them at the zero date, corresponding to 787.0, 624.4, 579.6, 335.5, 214.7, and 131.4 ka in EDC3 dates. The obliquity average for all of them (grey sinusoid continuous line) and the insolation average at 65°N on 21st June for all but MIS 7c–a (grey dotted line) were also averaged from the alignment. The thick line represents the different global substages of a typical interglacial. Antarctica leads in deglaciation, with the rest of the planet lagging (Jouzel, et al. 2007; Laskar et al. 2004).

Fig. 14.3 Comparison of MIS 9e interglacial and Daansgard–Oechsger event 8

With a different time-scale, MIS 9e (black line, EPICA) and DO–8 (red dashed line, GISP2) present a fast (excitation) transition from an excitable point, and a slow (relaxation) transition from an unstable point, between a stable cold state and a quasi–stable warm state. Data from Jouzel, et al. (2007) and Alley (2000).

in a relaxation-type dynamic until the conditions are met for a new interglacial. During the past 2.3 million years no interglacial has been able to continue from one obliquity oscillation to the next. Low obliquity conditions have always led to the end of the interglacial.

Despite their very different temporal scale, the similarities between Antarctic interglacial records and Greenland Dansgaard–Oeschger oscillations (Fig. 14.3; see also Chap. 3) suggest similar dynamics are at play. Both have been proposed to be astronomically paced (Milankovi# 1920; Rahmstorf 2003). The warming phase is explosive, fed by a fast ice-melting feedback, producing an early peak. It appears to constitute an excitable system from a stable glacial state. A slow declining phase from the peak towards an inflection point (unstable point, Fig. 14.3) suggests a quasi-stable warm phase as the warming conditions wane. At the inflection point the intensification of the slow ice-accumulation feedback accelerates the cooling phase increasing the climatic instability and producing a faster relaxation towards the stable state. Fast-slow dynamics acting on excitation cycles have been discussed as an explanation for both Dansgaard–Oeschger events and interglacials (Crucifix 2012), in which the cold stable and