HR: 08:45h
AN: OS31C-04    [Abstracts]
TI: Strontium Isotopes, Basalt Weathering and Phanerozoic CO2
AU: * Berner, R A
EM: robert.berner@yale.edu
AF: Dept. of Geology and Geophysics, Yale University, New Haven, CT 06520-8109,
AB: Using a combined model for the strontium and carbon cycles that distinguishes the weathering of volcanic and non-volcanic silicate rocks, the weathering of younger and older carbonates, basalt-seawater reaction, and marine carbonate burial, the ratio of volcanic (mainly basalt) weathering to total silicate weathering is calculated as a function of time from the oceanic record of 87Sr/86Sr. The volcanic proportion is then used to modify the equations for calculating atmospheric CO2 in the GEOCARBSULF model by the addition of a new non- dimensional volcanic weathering factor. The effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales, and not Sr isotopic data that had been used previously. Results indicate large variations in the volcanic proportion of silicates undergoing weathering over time and uniformly lower CO2 values than GEOCARBSULF for the early Paleozoic and for the Mesozoic with the degree of lowering depending upon the 87Sr/86Sr of nonvolcanics undergoing weathering and the ratio of the intrinsic weatherability of volcanics to nonvolcanics. An increased minimum in CO2 during the Late Ordovician is in agreement with the presence of a continental glaciation at that time, and, using intrinsic volcanic/non-volcanic weatherability = 10, variations of Jurassic and Cretaceous CO2 agree with the independent work of Fletcher et al (2007) based on liverwort delta 13C values.
DE: 0428 Carbon cycling (4806)
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting