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I thought you guys would like to see this that was kindly passed along to me by someone working in the field:

June 1 2011 issue of Radiocarbon (vol. 53 no. 2, pp. 303-323) by Paul LaViolette:

"Evidence for a Solar Flare Cause of the Pleistocene Mass Extinction".

Published paper is available here:

http://digitalcommons.arizona.edu/holdings/journal/issue?r=http://radiocarbon.library.arizona.edu/Volume53/Number2/

Also a preprint may be downloaded here:
Starburstfound.org/downloads/superwave/SPE.html

Paper abstract:
The hypothesis is presented that an abrupt rise in atmospheric radiocarbon concentration evident in the Cariaco Basin varve record at 12,837±10 cal yrs BP contemporaneous with the Rancholabrean termination, may have been produced by a super-sized solar proton event (SPE) having a fluence of ~1.3 X 10^11 protons/cm^2. A SPE of this magnitude would have been large enough to deliver a lethal radiation dose of at least 3 - 6 Sv to the Earth's surface, and hence could have been a principal cause of the final termination of the Pleistocene megafauna and several genera of smaller mammals and birds. The event time-correlates with a large magnitude acidity spike found at 1708.65 m in the GISP2 Greenland ice record, which is associated with high NO^-3 ion concentrations and a rapid rise in ^10Be deposition rate, all of which are indicators of a sudden cosmic ray influx. The depletion of nitrate ion within this acidic ice layer suggests that the snowpack surface at that time was exposed to intense UV for a prolonged period which is consistent with a temporary destruction of the polar ozone layer by solar cosmic rays. The acidity event also coincides with a large magnitude, abrupt climatic excursion and is associated with elevated ammonium ion concentrations, an indicator of global fires.

Below is a summary of the paper's principle findings.
• The Pleistocene megafaunal extinction likely had a solar cause.

• An extinction level solar proton event (SPE) likely occurred around 12,837 ± 10 calendar years BP. (This date is based on the varve chronology established for Cariaco Basin ocean sediment core drilled off the coast of Venezuela.)

• The proposed super SPE is estimated to have been roughly 125 times more intense than the February 1956 SPE. On the assumption that its cosmic ray energy spectrum had a hardness comparable to the 1956 event, it is estimated to have produced a ground level radiation exposure ranging from 3 Sieverts (Sv) to over 6 Sv delivered over a two-day period. By comparison, LD-100 (lethal exposure) for most mammals is in the range of 3 to 8 Sv. Lethal dose for humans is 3.5 Sv.

• The magnitude of the super SPE is based on the size of a radiocarbon production spurt registered in the Cariaco Basin radiocarbon excess record. This spurt, which occurs during the early younger Dryas, is one of the two largest to have occurred during the four-millennia-long Cariaco Basin radiocarbon record.

• Correlations made between the Cariaco Basin climate profile and the GISP2 Greenland ice core climate profile show that this candidate radiocarbon spurt correlates with an acidity spike present in the Greenland ice record at a depth of 1708.65 meters, and which is the largest acidity spike to occur during the Younger Dryas period. Also this spike is found to be flanked by two nitrate ion concentration peaks which are the highest of the Younger Dryas period. It is also spanned by a large increase in beryllium-10 concentration. All of these are good indicators for the occurrence of a solar proton event.

• The acidity spike event is found to coincide with a nitrate ion minimum, which indicates that the nitrate ions were photolytically dissociated by exposure to intense UV radiation at the time of their deposition. This strongly suggests that the 12,837 years BP super SPE likely destroyed the polar ozone layer for a period of several years following its impact. This ozone hole may even have extended to mid latitudes allowing harmful UV radiation to penetrate through the Earth's atmosphere.

• Both the high levels of solar cosmic ray radiation and solar UV radiation associated with this event were responsible for the sharp decline in mammal population marked by the Rancholabrean termination which dates close to the time of this event, around 12,883 ± 60 calendar years BP (when converted to calendar years using the Cariaco Basin radiocarbon chronology). This super SPE date also follows the Clovis paleoIndian cut-off date, which lies in the interval 12,880 to 12,840 calendar years BP (Cariaco Basin chronology), and it precedes the black mat stratum at the Murray Springs, Arizona site, which lies between 12,750 and 11,850 Cariaco calendar years BP.

• The 12,837 years BP super SPE was sufficiently large that the main phase decrease produced by its storm time radiation belt ring current could have partially or totally collapsed the geomagnetic field, allowing a large fraction of the impacting cosmic rays to contact the Earth's atmosphere and produce a substantially enhanced particle shower.

• The Greenland ice record suggests that an abrupt climatic cooling occurred at the time of the 12,837 years BP super SPE acidity spike, which is an expected consequence of the generation of high concentrations of condensation nuclei in the stratosphere. The event is also found to be flanked by two very warm episodes separated from one another by about one solar cycle period. The warming following the SPE was one of the most pronounced Dansgaard/Oeschger climatic events of the entire Younger Dryas with polar temperatures reaching Allerod levels. High ammonium ion concentrations, occurring during each of these warm periods, indicate the occurrence of widespread wildfires. Hazards associated with these fires as well as the associated destruction of food supplies and habitats would have been a contributing factor in megafaunal termination.

• A second equally large radiocarbon production spurt is reported to date 12,639 ± 10 calendar years BP, separated by 198 years (one Suess solar cycle or 9 Hale solar cycles) from the primary super SPE event. Also two smaller C-14 spurts are shown to precede the primary event, each separated from one another by three Hale solar cycles. In addition, the GISP2 ice record is shown to record a more minor acidity spike event, i.e., a SPE of lesser intensity, that occurred about 18 years after the primary 12,837 years BP super SPE.

• Lunar rock studies suggest that the Sun was in an unusually active state close to the end of the last ice age. This could explain why these super SPEs were occurring during the terminal Pleistocene and have not occurred more recently.

• In the event that the geomagnetic field would have been substantially disturbed and possibly even temporarily collapsed at the time of SPE and coronal mass ejection impact, large amounts of extraterrestrial dust residing in the circumterrestrial dust sheath would have been consequently jettisoned into the stratosphere. This could account for the extraterrestrial debris-rich layer that has been sporadically reported to underlie the black mat layer in the early YD sediments and the nanodiamond rich layer found in Greenland ice. The comet impact scenario proposed by Firestone et al. to account for this layer is unlikely to have occurred since it has been reported that a comet impact should have produced a nitrate ion signal 10^5 times higher than the upper limit observed in the Greenland ice record.