[meteorite-list] Cometary airbursts and atmospheric chemistry: Tunguska and a candidate Younger Dryas event, Adrian L Melott et al, 2009.10.04 to be in Geology, 13p text: Rich Murray 2009.11.07

[Rich Murray]

Cometary airbursts and atmospheric chemistry: Tunguska and a candidate 
Younger Dryas event, Adrian L Melott et al, 2009.10.04 to be in Geology, 13p 
text: Rich Murray 2009.11.07

http://cargo.ucsc.edu/coffee/2009/10/04/cometary-airbursts-and-atmospheric-chemistry-tunguska-and-a-candidate-younger-dryas-event-replacement/

Cometary airbursts and atmospheric chemistry: Tunguska and a candidate 
Younger Dryas event [Replacement]
Adrian L. Melott (Kansas),
Brian C. Thomas (Washburn),
Gisela Dreschhoff (Kansas),
Carey K. Johnson (Kansas)
ArXiv #: 0907.1067 (PDF, PS, Other)
Comments: Accepted for publication in Geology.
Numerous minor revisions in wording; no change in conclusions

We estimate atmospheric chemistry changes from ionization for the 1908 
Tunguska airburst event, finding agreement with nitrate enhancement in 
GISP2H and GISP2 ice cores, noting an unexplained accompanying ammonium 
spike.
We then consider the candidate cometary impact at the onset of the Younger 
Dryas (YD).
The estimated NOx production and O3 depletion are large, beyond accurate 
extrapolation, but the ice core peak is lower than predicted, possibly 
because of insufficient sampling resolution.
Ammonium has been attributed to biomass burning, with a coincident nitrate 
spike found at YD onset in both GRIP and GISP2 ice cores.
A similar result is well-resolved in Tunguska ice core data, but that forest 
fire was far too small to account for this.
Direct input of ammonia from a comet into the atmosphere is adequate to 
explain ice core data at the YD event, but not Tunguska data.
An analog of the Haber process with hydrogen contributed by cometary or 
surface water, atmospheric nitrogen, high temperatures, pressures, and the 
possible presence of catalytic iron from a comet could in principle produce 
ammonia, accounting for the peaks in both sets of ice core data.

Tags: atmospheric nitrogen, minor revisions, sampling resolution, younger 
dryas, gisp2 ice

http://arxiv.org/ftp/arxiv/papers/0907/0907.1067.pdf  13 pages