George Howard, on his web site/ blog http://cosmictusk.com is reporting on the Fall Meeting of the AGU which included a session on the Younger Dryas boundary event. In the first of what will be several reports George begins with two speakers, Wally Broecker on the sceptics side, and Allen West, on the pro.
Wally Broecker was the man who advanced the Ocean Circulation model as the trigger of Heinrich events and spontaneous sudden shutdowns causing sudden and abrupt climate change as occurred at Heinrich boundaries (cooling events) and Dansgaard-Oeschger boundaries (sudden warming events). He long ago recognised the YD was a typical Heinrich (cooling) which ended in an abrupt warming so it is not surprising Broecker was in the sceptic camp as far as a YD comet impact was concerned. Heinrich and Dansgaard-Oeschger events litter the Late Pleistocene – and this is a problem for the comet hypothesis. Could there have been multiple comet impacts – and what might have caused the warmings? Broecker ruled out a comet – and flooding. Presumably this is a reference to floods of cold water entering the North Atlantic and shutting down the Ocean Circulation System.
Allen West’s presentation was more interesting as far as George Howard is concerned as he calculated evidence accumulated worldwide for a cosmic encounter of some kind, including a discussion of nano diamonds as marker evidence. This was in response to a couple of papers in 2009 that had purportedly discredited the comet hypothesis (Surovell and Gill). West considers the nano diamonds are the most important evidence and have now been found on three continents at 21 sites within discrete YD stratigraphy. Identical diamonds are found at the KT boundary event (end of the Dinosaur age) and in appropriate stratigraphy at the Tunguska site in Siberia (from 1908). Hence, evidence is mounting for an impact or airburst event, according to West. He went on to produce a photograph (slide) of a YD black mat layer in Pennsylvania (investigated by Demitroff and Lecompte) with nearly 1000 spherules per kilogram of sample, the highest yet found at any site. There was Aluminosilicate spherules, nano and micro tektites, and suspected impact glass found in the layer – not above or below it but within it and formed at temperatures of 1500 to 1800 C. The melted glass and spherules were formed from melted terrestrial clay or shale which is absolutely earth bound geochemistry, he went on. An impact (of some kind) is the best explanation according to West who then went on to describe some recent work of Marie Agnes Courty, a French soil scientist. She is best known to the SIS as a speaker at one of our Cambridge Conferences. In that instance she produced evidence of a cosmic event at the end of the Akkadian dynasty in the late third millennium BC. It seems she has found evidence very similar to that of West at three sites, one near the Caspian Sea, another on the coast of Peru, and the third on the Atlantic coast of France. She claims such sites contain oxogenous air transported micro debris that is part of a complex time series of recurrent fine dust/ wild fire events mingled with micro tektites, glassy spherules, devitrified glass shards, unmelted to partly melted sedimentary and igneous clasts, terrestrial native metals and carbonaceous components (grape clustered polymers, vitrified graphic carbon, amorphous carbon spherules with a honeycomb pattern and green carbon fibres with crystalised quartz and metal blebs). The evidence is of high temperature transformation possibly from a high energy airburst.
Its all of course a matter of interpretation to what might have caused the anomalies but there are a lot more papers from the conference to appear on George Howard’s web site, which will be updated as and when.