The 8.2 ka Event Seen from the South

by Ignacio A. Jara

During my usual surfing on the internet catching up with new science content, I stumbled upon a very exciting article published just a few weeks ago in the journal Nature Scientific Reports [1]. In this recent publication, a climate cooling that occurred about 8,200 years ago was clearly identified in a pollen record from South Korea. This particular cooling [SPOILER ALERT] has largely been recognized in many other areas of the Northern Hemisphere. The article presented the first evidence for its occurrence in coastal East Asia. As a trained palynologist with interest in paleoclimatology I have always been fascinated by these kinds of studies. Nonetheless, I was equally intrigued by the fact that, as far as I know, there is not much evidence for such a cooling event in the Southern Hemisphere.


Fig. 1: Things might look quite different from the south.
“América Invertida” by Joaquín Torres Garcías (1943)

The original idea of writing this post was to share some outlooks about Quaternary Sciences from here in the Southern Hemisphere, something I did a few years ago during my PhD times in New Zealand (you can read my early blog entries here). Thus, to show you guys how things look from here in the south, I thought it would be a good idea to perform a simple (and healthy) exercise of wiggle-matching to explore the southern expression of something that should be common to many of you in the north: the cooling event that occurred around 8,200 years ago.

The 8.2 ka what?

If you have no idea what this “event” is, do not panic, I will start with a brief explanation. This particular interval occurred about 8,200 years ago (hereafter I will simply call it the 8.2 ka event) and is - after the ongoing global warming we are facing right now - the most rapid and intense climatic change that has happened in the last 10,000 years. This abrupt cooling event was initially recognized in ice core records from Greenland as a sudden drop in temperatures of 3-5°C that extended for about 160 years [2]. It has also been observed in a great number of terrestrial and marine records across the Northern Hemisphere as a general cooling of 1-3°C and considerable drying, with associated environmental changes and impacts over early agricultural societies in the Middle East [3]. The causes of the 8.2 ka event seem to be clearer now, as it has been linked to a massive discharge of ice-dammed lakes into the North Atlantic Ocean [4]. This freshwater release slowed down the operation of the Atlantic Meridional Overturning Circulation, a large system of currents that transports warm waters from the tropics to the North Atlantic and subsequently releases heat into the atmosphere. Thus, the slowdown of this transport system 8,200 years ago resulted in an overall cooling of the atmosphere in a great part of the northern side of our planet.

Ok, but what about the Southern Hemisphere?

While the Asian and African monsoons north of the equator weakened in response to a general cooler atmosphere, monsoonal activity in the Southern Hemisphere seemed to have been invigorated during the 8.2 ka event [5] (Fig. 2). This opposite response is consistent with a southward movement of tropical rains associated with the monsoon system [1], which might seem like a nice and clean example of the popular bipolar seesaw hypothesis - the premise that one hemisphere heats up while the other chills and vice versa. However, a more detailed look reveals that a comparable response to the rapid 8.2 ka event is found neither in terrestrial reconstructions from the south tropics nor in Antarctic ice records. While the Vostok ice core is perhaps the only exception showing a warming pulse during this interval, the magnitude of this warming is minimal in comparison with the cooling observed in the north [6].

Accordingly, while changes in the tropical monsoons can be observed in both hemispheres, the impacts of the 8.2 ka event are more or less muted in temperature records further south. In other words, what should have been several decades of freezing conditions in Canada, Ireland and even coastal East Asia did not see comparable warming conditions in places like Tasmania, Patagonia or Antarctica, as the bipolar seesaw hypothesis would suggest. However, while temperature responses don’t seem to follow the hemispheric bipolar seesaw during the 8.2 ka event, other climate responses probably occurred in the Southern Hemisphere. Evidence is emerging showing abrupt drying during the 8.2 ka event in South Africa in association with atmospheric teleconnections (rather than with oceanic controls, which are thought to be the driving force behind the bipolar seesaw) [7].

Fig. 2: A little bit of wiggle matching. The 8.2 ka event (blue column in the figure) from temperature records around the world. δ18O records from GISP2 ice core in Greenland [8],  Dongge Cave DA in China [5], Pedro Cave in Brazil [5], and temperatures estimated from deuterium (δD) data in the Antarctic EPICA Dome C Ice Core [9]. All δ18O values are expressed as per mil values relative to the VPDB standard, whereas δD values are expressed as per mil relative to the SMOW standard (see reference for more detail). Additionally, an image of the Atlantic Meridional Overturning Circulation including the location of all sites. All data is freely available at the National Centers for Environmental Information repository

The message

There may be many different climate responses to the 8.2 ka events on the southern side of our planet. Indeed, there is a relatively low number of paleorecords in the Southern Hemisphere and therefore new exciting responses may certainly emerge sooner rather than later. In fact, some very interesting paleoclimate research in recent years has aimed to evaluate the expressions of climate anomalies in the southern latitudes that were originally described in the Northern Hemisphere [10]; I will keep you guys posted.

What is clear is that the 8.2 ka event is a great example of a well-understood period of widespread climate perturbation that offers the possibility to study the responses of the planet as a whole. Furthermore, studying the Earth's responses to this particular event might be especially relevant as evidence is now available that the Atlantic Meridional Overturning Circulation may weaken in the future under anthropogenic greenhouse gas forcing [11]. Here I tried to show you, by adding a Southern Hemisphere perspective, that the spatial extent of this abrupt event was more diverse and complex than many of us might think. What happens on one side of the planet does not necessarily happen in the same way on the other. These differences may be relevant when taking into account the ongoing climate event caused by human impact on the planet.


Ignacio A. Jara
CEAZA Scientific Centre, Chile

About myself

I am Ignacio Jara, a palynologist working in Paleoclimate and Archaeology research who is currently working in northern Chile. I am new to the PAGES early-career community, and have recently been appointed as one of the regional representatives for South America within the PAGES ECN. I won’t lie guys: This is an exciting adventure for me and being able to post here is even more!


If you have questions or comments concerning Ignacio's post, please leave a comment below, or send him an email. You can also connect with him on Twitter.

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References:

[1] Park, J., Park, J., Yi, S., Kim, J.C., Lee, E. and Jin, Q., 2018. The 8.2 ka cooling event in coastal East Asia: High-resolution pollen evidence from southwestern Korea. Scientific reports, 8(1), p.12423.
[2] Thomas, E.R., Wolff, E.W., Mulvaney, R., Steffensen, J.P., Johnsen, S.J., Arrowsmith, C., White, J.W.C., Vaughn, B., Popp, T., 2007. The 8.2 ka event from Greenland ice cores. Quaternary Science Reviews 26, 70-81.
[3] van der Plicht, J., Akkermans, P.M.M.G., Nieuwenhuyse, O., Kaneda, A., Russell, A., 2011. Tell Sabi Abyad, Syria: radiocarbon chronology, cultural change, and the 8.2 ka event. Radiocarbon 53, 229-243.
[4] Alley, R.B. and Ágústsdóttir, A.M., 2005. The 8k event: cause and consequences of a major Holocene abrupt climate change. Quaternary Science Reviews, 24(10-11), pp.1123-1149.
[5] Cheng, H., Fleitmann, D., Edwards, R.L., Wang, X., Cruz, F.W., Auler, A.S., Mangini, A., Wang, Y., Kong, X., Burns, S.J. and Matter, A., 2009. Timing and structure of the 8.2 kyr BP event inferred from δ18O records of stalagmites from China, Oman, and Brazil. Geology, 37(11), pp.1007-1010.
[6] Wiersma, A.P. and Renssen, H., 2006. Model–data comparison for the 8.2 ka BP event: confirmation of a forcing mechanism by catastrophic drainage of Laurentide Lakes. Quaternary Science Reviews, 25(1-2), pp.63-88.
[7] Chase, B.M., Boom, A., Carr, A.S., Carré, M., Chevalier, M., Meadows, M.E., Pedro, J.B., Stager, J.C. and Reimer, P.J., 2015. Evolving southwest African response to abrupt deglacial North Atlantic climate change events. Quaternary Science Reviews, 121, pp.132-136.
[8] Stuiver, M., Grootes, P.M. and Braziunas, T.F., 1995. The GISP2 δ18O climate record of the past 16,500 years and the role of the sun, ocean, and volcanoes. Quaternary Research, 44(3), pp.341-354.
[9] Jouzel, J., Masson-Delmotte, V., Cattani, O., Dreyfus, G., Falourd, S., Hoffmann, G., Minster, B., Nouet, J., Barnola, J., Chappellaz, J. and Fischer, H., 2007. EPICA Dome C ice core 800KYr deuterium data and temperature estimates. IGBP PAGES/World Data Center for Paleoclimatology data contribution series, 91, p.2007.
[10] Moreno, P.I., Vilanova, I., Villa-Martínez, R., Garreaud, R.D., Rojas, M. and De Pol-Holz, R., 2014. Southern Annular Mode-like changes in southwestern Patagonia at centennial timescales over the last three millennia. Nature communications, 5, p.4375.
[11] Fichefet, T., Poncin, C., Goosse, H., Huybrechts, P., Janssens, I. and Le Treut, H., 2003. Implications of changes in freshwater flux from the Greenland ice sheet for the climate of the 21st century. Geophysical Research Letters, 30(17).