Australia: The Land Where Time Began

A biography of the Australian continent 

Antarctic and Greenland Ice Cores Directly Linked at the Toba Eruption - 74 ka BP

About 74 ka BP the Toba eruption in Sumatra, Indonesia, among the largest volcanic event in the last 2 My, spread tephra over vast areas of Asia, the tephra deposits being sufficient to form a marker close to the Marine Isotope Stage (MIS) 4/5 boundary, but no tephra association has been identified in ice cores from either Antarctica or Greenland. The Toba event is known to have occurred between the Greenland interstadials (GI) 19 and 20, based on new, accurate dating of the Toba tephra and European stalagmites that have been accurately dated. The existing linking between the ice cores from Greenland and Antarctica by gas records and by the seesaw hypothesis suggests the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM) 19 and 20. In this report of the study carried out by the authors¹ a direct synchronisation of the Greenland (NGRIP) and Antarctic (EDML) ice cores at the Toba eruption is suggested, based on matching of the pattern of bipolar volcanic spikes, and a unique match is found by counting the annual layers between volcanic spikes in ice cores from Antarctica and Greenland. The authors¹ tested this technique of bipolar matching on the Laschamp geomagnetic excursion at 41 ka BP, that has already been synchronised, before applying it to the Toba interval that had been suggested. Covering about 2,000 years in the GI-20 and the AIM 19/20 which includes 9 activity peaks that are recognised in both ice cores.

The Toba synchronisation that has been suggested has precision on a decadal timescale. An exact  phasing of the climate between both the Northern and Southern Hemisphere, in a time interval in which the ice records are poorly constrained, is therefore allowed, which allows a discussion of the impact of climate of the Toba eruption in a global perspective. The suggested long-term global cooling that has been suggested to have been caused by the Toba eruption is not supported by the link between the poles, with Antarctica undergoing a warming interval a short time following the Toba eruption. The bipolar match obtained by the authors¹ also provides a way to place palaeoenvironmental records other than ice core records into a precise climatic context.

Authors conclusions 

The authors found it was possible to obtain bipolar volcanic matches at the Laschamp geomagnetic excursion, about 41 ka b2k, by applying high resolution impurity records from the Greenland NGRIP and the Antarctic EDML ice cores and applying existing bipolar ice core synchronisations. The authors¹ say they are certain the Toba event occurred close to the onset of the GS-20 in Greenland and in Antarctica between the AIM-19 and AIM-20, based on constraints obtained from precise Ar-Ar dating of the Toba tephra, and form precise dating of stalagmites in Europe. In the ice core records there is evidence of 4 large bipolar eruptions occurring within 400 years close to the onset of the GS-20, though the number of events that can be attributed to the Toba eruption, based only on the evidence from the ice cores, could not be determined by the authors¹. The authors¹ suggest the fact that none of the bipolar ice core events are as outstanding as expected, based on the geological evidence, could be explained by several Toba eruptions occurring in this time interval.

The bipolar seesaw hypothesis acting with little if any time lag in the boundary region of the MIS4/5 is strongly supported by the bipolar Toba synchronisation obtained by the authors¹. The climate pattern at the EDML site in Dronning Maud Land differs somewhat from that of the East Antarctic Plateau, which the authors¹ suggesting an important role may be played in the region by local effects such as sea ice cover. The possibility of a global cooling impact of the Toba eruption(s) that lasted longer than 100 years is excluded by Antarctica temperature proxies, as Antarctica warmed up shortly following the bipolar events. There is a link, that the authors¹ describe as "very uncertain", with 1 of the ice core Toba candidates that is potentially associated with an Antarctic cooling episode that lasted for 100 years. In the AIM-20 there are several other Antarctic cooling episodes that appear similar, that are not related to volcanism. The authors¹ suggest any long-term cooling must involve feedback mechanisms, as the high atmospheric loadings of sulphate that are associated with bipolar volcanic events don't last more than about 10 years.

The authors¹ suggest the approach they used to synchronise the ice cores from Greenland and Antarctica by the matching of volcanic sequences has the potential to be expanded by other time intervals in the last glacial period.

Sources & Further reading

1. Svensson, A., Bigler, M., Blunier, T., Clausen, H. B., Dahl-Jensen, D., Fischer, H., Fujita, S., Goto-Azuma, K., Johnsen, S. J., Kawamura, K., Kipfstuhl, S., Kohno, M., Parrenin, F., Popp, T., Rasmussen, S. O., Schwander, J., Seierstad, I., Severi, M., Steffensen, J. P., Udisti, R., Uemura, R., Vallelonga, P., Vinther, B. M., Wegner, A., Wilhelms, F., and Winstrup, M.: Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP), Clim. Past, 9, 749-766, doi:10.5194/cp-9-749-2013, 2013