In response to:Isotopic problem
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         ISOGEOCHEM Digest 190

Dear Alaa,

Drs. Hendry and Grossman have addressed the issue of alteration of your
worm tubes.  I would just like to add that volcanic injection of light CO2
into the oceans is an unlikely explanation for low d13C values in your
samples.  The oceans contain enough carbon that any such injection would
have to be extremely large to cause even a 1 per mil shift in the oceanic
d13C budget.  A "quick and dirty" mixing calculation using d13C values for
Cretaceous seawater and volcanic gasses should demonstrate this quite
easily.  For an initial Cretaceous value of 2 per mil, to drop it down to
-3 per mil by the addition of volcanic CO2 (at -5 per mil) would require on
the order of 70% of the oceanic C reservoir to be replaced by volcanic CO2
over a short time scale.  This is a LOT of carbon.  I don't think this is
your mechanism.  Good luck,


Dr. Louis A. Derry
Cornell University
Dept.of Geological Sciences
Ithaca, NY 14853-1504
tel. (607)255-9354
fax  (607)254-4780