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In Brief August 2009


JMcCBuried mountains


A very important article in Nature1 reports on an extensive radar investigation of these mountains beneath the East Antarctica ice sheet. The team led by Sun Bo from China travelled 1235km by tractor train during the survey. The area surveyed was 30 km x 30 km. The radar waves bounce back and the two-way travel time is measured, giving you the ice thickness. The ice is up to 3km thick and the peaks in the topography below rise to 1km depth2.

Ice sheet development in Antarctica was the result of significant and rapid global climatic change commencing about 34 million years ago, during the Oligocene. The cause is believed to be a major natural reduction in atmospheric carbon dioxide (“greenhouse gases”) coupled with development of the Circumpolar Current, though orbital changes of the planet may have also been involved. The ice covering the mountains started to form ~14 million years ago. The study focused on Dome A, the centre of the ice sheet, at 4093m above sea level. The radar information revealed Alpine topography beneath the ice, with pre-existing river valleys deepened by valley glaciers when the main summer temperature was ~3oC, a landscape that developed in the initial phases of the Antarctic glaciation. There was a second cooling phase with a summer temperature of 6-7oC, when the ice cover started to form. JMcC

References

  1. Sun Bo, Siegert, M J Mudd, S M et al. 2009. The Gamburtsev mountains and the origins and evolution of the Antarctic Ice sheet. Nature 459, 690-693.
  2. http://news.bbc.co.uk/1/hi/sci/tech/8079767.stm 

The Zechstein SeaOld salt’s tale


Did volatile halogenated gases from giant salt lakes contribute to the mass extinction at the end of the Permian, the biggest in the geological record? Researchers from Russia, Austria, South Africa and Germany have found that in both Russia and South Africa microbial processes in present-day salt lakes naturally emit highly volatile halogens such as chloroform, tri- and tetra-chlorethene. They then applied their results to the Zechstein Sea, which covered 600,000km2 250 million years ago. The hypersaline sea was exposed to a dry continental climate1,2: climatic considerations, under the global warming at that time created, according to these authors, at least 1.3 million tonnes each of tri- and tetra-chlorethene, 1.1 million tonnes of choloroform and some methyl chloroform being produced - with a potentially catastrophic effect on life.

It should be borne in mind that at this time Pangaea existed, surrounded by Panthalassa, according to Plate Tectonic theory3,4, and any climatic modelling would have to take this into account. These authors sensibly accept that this new toxic agent may well have contributed to the mass extinction, alongside other causes5,6 - rather than being the sole cause. JMcC

References

  1. Weissflog, L , Elanskii, N F , Kotte K , Keppler,F , Pfennigsdorff, A, Lange, K Putz, E , Lisitzina, L V 2009 O wosmojnoi roli galogenoderjaschtschaich gasow w ismenii sostojanija atmosferi I prirodnoi sredi w posdnii permskii period Dokladi Akademii Nauk, 424, 1-6 (in Russian)
  2. Weissflog, L , Elanskii, N F Kotte K , Keppler,F , Pfennigsdorff, A, Lange, C A Putz, E , Lisitzina, L V 2009 Late Permian changes in conditions of the atmosphere and environments caused by halogenated gases Dokladi Earth Sciences, 424(6), 818-823 (in English)
  3. McCall, G J H 2008 All at sea (Panthalassa) Geoscientist 18(10), 3
  4. McCall, G J H 2009 (in the press) Panthalassa, the ocean of ignorance Earth Science Reviews
  5. Hallam, A 2004 Catastrophes and lesser calamities Oxford University Press, 274 pp
  6. McCall, G J H 2009 Half a century of progress on terrestrial impact structures: a review Earth Science Reviews 92, 99-116