Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period

Abstract

Abstract. Since its discovery in Greenland ice cores, the millennial scale climatic variability of the last glacial period has been increasingly documented at all latitudes with studies focusing mainly on Marine Isotopic Stage 3 (MIS 3; 28–60 thousand of years before present, hereafter ka) and characterized by short Dansgaard-Oeschger (DO) events. Recent and new results obtained on the EPICA and NorthGRIP ice cores now precisely describe the rapid variations of Antarctic and Greenland temperature during MIS 5 (73.5–123 ka), a time period corresponding to relatively high sea level. The results display a succession of long DO events enabling us to highlight a sub-millennial scale climatic variability depicted by i) short-lived and abrupt warming events preceding some Greenland InterStadial (GIS) (precursor-type events) and ii) abrupt warming events at the end of some GIS (rebound-type events). The occurrence of these secondary events is suggested to be driven by the Northern Hemisphere summertime insolation at 65° N together with the internal forcing of ice sheets. Thanks to a recent NorthGRIP-EPICA Dronning Maud Land (EDML) common timescale over MIS 5, the bipolar sequence of climatic events can be established at millennial to sub-millennial timescale. This provides evidence that a linear relationship is not satisfactory in explaining the link between Antarctic warming amplitudes and the duration of their concurrent Greenland Stadial (GS) for the entire glacial period. The conceptual model for a thermal bipolar seesaw permits a reconstruction of the Antarctic response to the northern millennial and sub-millennial scale variability over MIS 5. However, we show that when ice sheets are extensive, Antarctica does not necessarily warm during the whole GS as the thermal bipolar seesaw model would predict.

Abrupt millennial variability and interdecadal-interstadial oscillations in a global coupled model: sensitivity to the background climate state

“…This period was characterized by relatively high sea level and CO 2 concentrations compared to full glacial conditions. The nature of the variability during that period appears to be quite different from that developing during MIS 3, with Greenland interstadials exhibiting a multi-millennial cooling trend sometimes followed by the presence of rebound-type events (Capron et al 2010). These events are associated with a relatively small, but abrupt, Greenlandic temperature increase compared to the DO events that punctuated MIS 3.…”

“…These events are associated with a relatively small, but abrupt, Greenlandic temperature increase compared to the DO events that punctuated MIS 3. Capron et al (2010) suggested that these rebound events are the consequence of orbitally forced cooling during extended interglacial-like periods. This could have resulted in progressively larger northern latitude sea ice extent and saltier surface waters, ultimately leading to a small resumption of the AMOC.…”

Eurasian contribution to the last glacial dust cycle: how are loess sequences built?

“…The climate trend, cooling and increase in dustiness, within these particular events is variable as well. High-resolution studies of the temperature signal in older interstadials show the occurrence of sub-millennialscale elements like precursor events of about centennial duration before the interstadial itself, rebound events exhibiting abrupt cooling towards stadial conditions, and cooling events occurring towards the end of the interstadial (Capron et al, 2010). These sub-millennial events make the understanding of the climate variability during these interstadials even more complicated than a simple warming followed by a two-step cooling.…”

Astronomical forcing of sub-Milankovitch climate oscillations during the late Quaternary

“…Capron, 2010;Fairbanks et al, 2005). Skinner (2008) rightly points out that these models may be considered hypotheses, as the glaciological models are heavily reliant upon modelling beyond the range of radiocarbon dating and layer counting (Clemens, 2005).…”

“…Capron et al, 2010;Clemens, 2005;Davis and Brewer, 2011;Ditlevsen et al, 2007;Hays et al, 1976;Imbrie et al, 1984). The Sun is clearly the primary driver of Earth's climate.…”