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Monday, 2 November 2009

Hypervelocity impacts and neutron spallation

Hypervelocity impacts and neutron spallation

oxytropidoceras at cox.net oxytropidoceras at cox.net
Mon Nov 2 21:03:36 EST 2009

On Oct. 30, 2009 and in Hypervelocity impacts and neutron spallation
( http://six.pairlist.net/pipermail/meteorite-list/2009-October/057772.html )
E.P. Grondine wrote:

"This would all be blue sky, but for those 14C spikes... Chris,
I think I got the copy of the INTCAL98 chart from one of
Firestone's papers. Stuiver and Volcker (working with Iceland
marine data) were cited as the data sources. Firestone did not
create the INTCAL98 chart. The bumps around 10,900 BCE
were what set Firestone off on his search to find their source,
which led him at first to a nearby supernova and finally to impact."

First a good reference on radiocarbon dating and calibration is:

Hajdas, I., C. Kull, and T. Kiefer, 2006, 14C-Chronology.
PAGES News. vol. 14, no. 3.

http://www.pages-igbp.org/cgi-bin/WebObjects/products.woa/wa/product"id=276
15 MB version http://www.pages-igbp.org/products/newsletters/NL2006_3high_res.pdf
4 MB version http://www.pages-igbp.org/products/newsletters/NL2006_3low_res.pdf

Full references
http://www.pages-igbp.org/products/newsletters/ref2006_3.html

In the above publication, there is an article, "Cosmogenic
isotope 14C: Production and carbon cycle" by K. Hugen,
that discusses the processes that created the radiocarbon
spikes. He states that the changes in 14C concentration
(14C) are "due to changes in either the rate of 14C production
in the atmosphere (a function of geomagnetic field intensity
and solar variability), or the distribution of 14C between
different reservoirs in the global carbon cycle (primarily deep
ocean ventilation). In the Greenland ice cores there is a strong
correlation between the production of beryllium 10 and 14C,
which demonstrates that the radiocarbon spikes are related to
changes in the geomagnetic field intensity associated with the
Laschamp and Mono Lake geomagnetic minima."

Some relevant papers are:

Hughen, K., S. Lehman, J. Southon, J. Overpeck, O. Marchal,
C. Herring, and J. Turnbull, 2004, 14C Activity and Global
Carbon Cycle Changes over the Past 50,000 Years. Science.
vol. 303, no. 5655, pp. 202-207 DOI: 10.1126/science.1090300
http://www.sciencemag.org/cgi/content/abstract/303/5655/202
http://courses.washington.edu/proxies/Hughen-Cariaco_14C_0-50ka_Sci04.pdf

The abstract, in part, for this paper reads:

"Reconstructed 14C activities varied substantially during the
last glacial period, including sharp peaks synchronous with
the Laschamp and Mono Lake geomagnetic field intensity
minimal and cosmogenic nuclide peaks in ice cores and marine
sediments. Simulations with a geochemical box model suggest
that much of the variability can be explained by geomagnetically
modulated changes in 14C production rate together with
plausible changes in deep-ocean ventilation and the global
carbon cycle during glaciation."

Hughen, K. A., J. R. Southon, S. J. Lehman, and J. T.
Overpeck, 2000, Synchronous Radiocarbon and Climate
Shifts During the Last Deglaciation. Science. vol. 290,
pp. 1951-1954.
http://www.whoi.edu/cms/files/llippsett/2007/1/1951_17123.pdf
https://darchive.mblwhoilibrary.org/browse?value=Hughen%2C+K.&type=author

It abstract states:

"Carbon-14 and published beryllium-10 data together
suggest that concurrent climate and carbon-14 changes
were predominantly the result of abrupt shifts in deep
ocean ventilation."

Chiua, T.-C., R. G. Fairbanks, L. Cao, and R. A.
Mortlock, 2007, Analysis of the atmospheric 14C record
spanning the past 50,000 years derived from high-
precision 230Th/234U/238U, 231Pa/235U and 14C dates
on fossil corals. Quaternary Science Reviews. vol. 26,
no. 1-2, pp. 18-36.
http://dx.doi.org/10.1016/j.quascirev.2006.06.015
http://radiocarbon.ldeo.columbia.edu/pubs/2007_Chiu.pdf

Muscheler, R., J. Beer, P. W. Kubik, and H. A. Synal,
2005, Geomagnetic field intensity during the last
60,000 years based on 10Be and 36Cl from the Summit
ice cores and 14C. Quaternary Science Reviews. vol. 24,
pp. 1849-1860.
http://dx.doi.org/10.1016/j.quascirev.2005.01.012

Ice Core Data on Climate and Cosmic Ray Changes by Dr. J.
Beer, Federal Institute of Environmental Science and Technology,
EAWAG, CH-8600 Dubendorf, Switzerland.
http://cdsweb.cern.ch/record/557154/files/p3.pdf

The caption to Figure 7 of the above paper states:
"Figure 7: 14C peaks corresponding to periods of
low solar activity and possibly also reduced solar
irradiance."

Ramsey, C. B., 2008, Radiocarbon Dating: Revolution'
in Understanding. Archaeometry. vol. 50, no. 2,
pp. 249-275.
http://www.arch.unipi.it/Arias/Materiali_Web/Radiocarbonio/Ramsey_2008_C14%20dating

A number of papers about radiocarbon calibration can
be found in "Prof. Richard Fairbanks Publications" at;
http://www.radiocarbon.ldeo.columbia.edu/publications/index.htm

Yours,

Paul H.

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