This story is a year old but Ive fished it out as it offers an alternative explanation for the Younger Dryas event – see http://archaeologynewsnetwork.blogspot.com/2011/06/was-pleistocene-mass-… and is the hypothesis of Paul LaViolette of the Starburst Foundation in a paper published in the journal Radiocarbon (last year). It is interesting in that he notes there were radiocarbon 'spurts' when radiocarbon levels in the atmosphere shot up suddenly in which he attempts to tie in with solar Hale cycles (and the de Vreis 200 year solar cycle period). LaViolette then claims to have found evidence for a solar flare in the GISP2 Greenland ice core acidity spike in association with a high nitrate ion concentration peak and a rapid rise in beryllium-10 – all good indicators, he says, of an influx of cosmic rays. In his opinion the solar flare was so strong it was able to destroy the ozone layer over the Poles to allow solar UV to penetrate deep into the atmosphere. Further, LaViolette links the acidity spike to the abrupt cooling of the Younger Dryas event, a consequence, he says, of solar cosmic ray exposure. The impact of the solar proton event would have generated a high concentration of conduction nuclei in the atratosphere, he goes on, which would account for the cooling effect – but the Younger Dryas lasted some 1300 years.
The warming that followed the Younger Dryas was pronounced, it continues, also a consequence of a solar cycle – but the fact that high ammonium ion concentrations coincided with each of the warm intervals, before and after the Younger Dryas cooling, is also significant, the result of wildfires. In contrast, we may note at this point, that Mike Baillie (in his book New Light on the Black Death) associated ammonium spikes with cosmic events (such as Tunguska, or the 1014AD spike). However, LaViolette then takes a look at the YD boundary impact hypothesis and throws cold water at it, saying the solar flare was huge enough to disturb and drastically shrink the geomagnetic field. As a consequence large amounts of extraterrestrial dust residing in a circumterrestrial dust sheaf were oergaos jettisoned into the stratosphere which account for the debris rich layer (or black mat formation) associated with the early Younger Dryas period. He rejects the idea of an impacting comet – but does not mention a storm of fireballs. He adds, the extinctions did not happen all at the same time but was an extended event which is more in keeping with a solar photon event. LaViolette is the author of Earth Under Fire and various articles. He atttributes elevated solar activity to the presence in the solar system of high concentrations of interstellar dust drived inwards by a wall of galactic cosmic rays. Presumably, the earlier Heinrich events, precursors of the Younger Dryas, have a similar origin in super solar flares and galactic cosmic rays.