HR: 17:00h
AN: U52C-05    [PDF]
TI: Dynamics of the Neoproterozoic Carbon Cycle
AU: * Rothman, D H
EM: dan@segovia.mit.edu
AF: Department of Earth, Atmospheric,and Planetary Sciences, MIT, Cambridge, MA 02139 United States
AU: Hayes, J M
EM: jhayes@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Summons, R E
EM: summons@mit.edu
AF: Department of Earth, Atmospheric,and Planetary Sciences, MIT, Cambridge, MA 02139 United States
AB: The Neoproterozoic (1000-543 Ma) record of the isotopic composition of inorganic carbon exhibits extraordinarily large fluctuations, of a magnitude not seen in the ensuing Phanerozoic (543 Ma--present). Thus a key feature of the long-term carbon cycle changed at the Proterozoic-Phanerozoic boundary. Moreover it almost certainly was related, but not necessarily causally, to the Cambrian radiation of multicellular animal life that began at that time. Here we address these changes quantitatively, by a dynamical interpretation of the carbon-isotopic record. Information on the evolution of the carbon cycle is encoded in the coupled fluctuations of the isotopic content of inorganic carbon and the fractionation between inorganic and marine organic carbon. Whereas significant fluctuations in the Phanerozoic record are consistent with steady-state models of the carbon cycle, their larger Neoproterozoic counterparts are not. The Neoproterozoic records can be well understood, however, as deriving from the nonsteady dynamics of two reactive pools of carbon. The lack of a steady state is traced to an unusually large oceanic reservoir of organic carbon. We suggest that the most significant of the Neoproterozoic negative carbon-isotopic excursions resulted from increased oxidation of this reservoir, possibly as a result of severe global cooling. The terminal Neoproterozoic isotopic event, at the Proterozoic-Cambrian boundary, signals the final diminution of the reservoir, a process that was likely initiated by evolutionary innovations that increased export of organic matter to the deep sea. The terminal event also signals a change from a carbon cycle evolving dynamically, permanently out of steady state, to one evolving quasistatically, from one steady state to another.
UR: http://segovia.mit.edu/publications/2003/neoprot.abs.html
DE: 1055 Organic geochemistry
DE: 1615 Biogeochemical processes (4805)
DE: 4806 Carbon cycling
DE: 4870 Stable isotopes
DE: 9619 Precambrian
SC: U
MN: 2003 Fall Meeting