Australia: The Land Where Time Began
Toba Eruption 74 ka BP – Direct Linking between Ice Cores from Greenland and Antarctica
About 74 ka Mt Toba in Sumatra, Indonesia erupted
in one of the largest volcanic events on Earth for the last 2 million
years. Close to the boundary between marine isotope stages (MIS) 4 and
5, the eruption spread tephra over vast Areas of Asia, where it
constitutes a major time marker. According to the authors1 no
tephra that could be associated with the Mount Toba eruption has been
identified in the Greenland or Antarctic ice cores. New accurate dating
of tephra in Malaysia that was deposited following the Mt Toba eruption
and accurate dating of stalagmites in Europe the Toba Event is now known
to have occurred between the onset of the Greenland Interstadials (GI)
19 and 20. Also, the linking that exists between the ice cores from
The authors1 suggest in this paper that the Greenland ice cores (NGRIP) and the Antarctic ice cores (EDML) are synchronized at the Toba eruption, basing their suggestion on a matching pattern of bipolar volcanic spikes. Counting the annual layers in the ice cores between volcanic spikes allows for a unique match. The authors 1 tested their bipolar matching technique on the Laschamp geomagnetic excursion (41 ka BP) prior to applying it to the suggested Toba interval. The pattern of the Toba synchronisation covers about 2,000 years in GI-20 and AIM 19/20, including 9 peaks of acidity that are recognised in both ice cores.
The bipolar synchronisation that is suggested has decadal precision. Therefore, an exact phasing of interhemisphere climate in a time interval of ice core records that are poorly constrained, and allows for a discussion of the impact on climate of the Toba eruption in a global perspective. A way of placing palaeoenvironmental records, other than ice cores, into a precise climate context is also provided by their bipolar match technique.
It has been possible to obtain bipolar volcanic matches at the Laschamp geomagnetic excursion, about 41 ka BP, and at about 74 ka BP, the time of the mega-eruption of Mt Toba, by application of high resolution records of impurity from tie Greenland NGRIP and the Antarctic EDML ice cores by applying bipolar ice core synchronisations that already exist.
The authors1 say they are certain the Toba event occurred close to the onset of GS-20 in Greenland, and in Antarctica, between AIM-19 and AIM-20, by the use of constraints from precise Ar-Ar dating of the Toba ash in Malaysia, and from precise U-Th dating of the stalagmites in Europe. The Toba event is suggested by the ice core records to have comprised up to 4 individual eruptions which occurred within 400 years, though they say they have no means of determining how many of those events originated from Toba.
The bipolar seesaw hypothesis, acting with no or little time lag, in the boundary region of MIS 4-5 is given very strong support by their direct bipolar Toba synchronisation. The climate pattern in the EDML site in Dronning Maud Land is somewhat different from that of the East Antarctic Plateau, which suggests that local effects, such as the extent of sea ice cover, may have an important role in the region.
Temperature proxies in Greenland and Antarctica suggest there could be a cooling episode that lasted 100 years that was associated with the Toba eruption or eruptions, though they exclude the possibility of a global cooling period lasting longer than 100 years. Antarctica underwent a rapid warming following the eruption or eruptions.
The authors1 say their approach to synchronising the ice cores from Greenland with those from Antarctica by matching volcanic sequences could potentially be expanded to other periods of the glacial phase.
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|