Fusing the thermohaline circulation - the 8200-Year Event

Having concluded the Younger Dryas in my last post, it is time to move onto the second major abrupt cooling event within my time-series. 8400 cal yr BP, an abrupt cooling occurred before temperatures rebounded to 8000 cal yr BP. Today's post will consider the causes of the 8200-yr Event by looking at one paper in particular, a review by Barber et al (1997) (1).

Although the reasons for this abrupt change are still unknown, several papers have attributed the event to the final retreat of the Laurentide Ice Sheet releasing a series of outbursts from Lake Aggasiz through the Hudson Strait to the Northern Atlantic. This freshwater flux has been estimated at >10¹⁴m³ occurring c. 8470 cal yr BP. Just like in the case of the Younger Dryas, such a deposit of freshwater into the North Atlantic would prevent the formation of North Atlantic Deep Water preventing heat transfer to the high-latidudes of the Northern Hemisphere.

Evidence for this event can be found through many sources. Alley et al. (1997) (2) present a useful diagram as shown in Figure 1. Across many proxies, the 8200 year downward spike can be seen through ice accumulation, a decrease in methane, temperature and other substances. Further evidence from Klitgaard-Kristensen et al., (1998) (3) present data from marine records in the North Sea and dendrochronology in Germany which show evidence for a 2 C drop in temperature in correlation with the Greenland ice core data.

Figure 1. - Holocene climate clearly showing 8200-yr Event (2)

Today's short post has continued to explain abrupt climate events within this blog's time-series. My next post will prevent further evidence of the event found in the literature. From then on, I will look at a few less pronounced climate changes, including the Medieval Warm Period and the Little Ice Age, before relating the changes in the thermohaline circulation to what could potentially occur in our future.

1. Barber et al., 1997 doi: 10.1038/22504
2. Alley et al., 1997 doi: 10.1130/0091-7613(1997)​025<0483:HCIAPW>2.3.CO;2
​3. Klitgaard-Kristensen 1998 doi: 10.1002/(SICI)1099-1417(199803/04)13:2<165::AID-JQS365>3.0.CO;2-#