Late Glacial and Holocene climate variability

Morning All, 

Today I thought a little bit more justification for studying abrupt climate change was needed before pressing on with the Younger Dryas explanation. Therefore, this post reports a brief summary of the climatic changes, mainly recorded in ice cores, since the Last Glacial Maximum.

There are several dating uncertainties inherent in the calculation of the last glacial maximum (LGM), however, as suggested by 37Cl dating by Bowen et al. (2002) (1) the LGM, occurred approximately 22 ka before a period of deglaciation occurred 21.4 ± 1.3 cal yr ka. Global temperatures fell again during the Oldest Dryas, identified in one of the many Greenland ice cores archives, GISP2, by Stuiver et al. (1995) (2), between c. 15.1 to 14.5 cal yr ka. 

Further climate variability occurred in the lead up to the Holocene as summarised by Figure 1 in Steffensen et al. (2008) (3). The Allerod/Bolling warming periods are often separated by a period of cooling known as the Older Dryas, before the Younger Dryas period appeared approximately 12,800 years ago. After 1200 years of cooled climate, an abrupt warming event ended the Younger Dryas and began the present Holocene. The climate of the Holocene has been more stable with fewer abrupt shifts. However, an event at 8200 cal yr BP, among others, will be discussed in the coming months.

Figure 1. Temperatures derived from deuterium analyses on Greenland NGRIP ice core from 14760 - 11660 cal yr BP displaying the major abrupt climate shifts within (Steffensen et al., 2008) (3).

The grey areas on Figure 1 show how quickly abrupt warming can take place. Although the rapid shift of the Atlantic meridional overturning circulation in the Day After Tomorrow is unlikely at the weekly time-scale, shifts in deuterium excess, a proxy for sea surface temperatures (SSTs) in Greenland ice cores, as reported by Steffensen et al. (2008), can take place over 1-3 years.

I think now we are fully set-up to look at the Younger Dryas stadial event, or more colloquially termed as the "Big Freeze" by Berger (1990) (4). To refresh your memory, take a look at the youtube video I posted last week which I've again added below. The Younger Dryas is coming, figuratively speaking.

(1) Bowen et al. (2002) doi: 10.1016/S0277-3791(01)00102-0
(2) Stuiver et al. (1995) doi:10.1006/qres.1995.1079
(3) Steffensen et al. (2008) doi:10.1126/science.1157707

(4) Berger (1990) doi:10.1016/0921-8181(90)90018-8