Wp. Patterson et Lm. Walter, DEPLETION OF C-13 IN SEAWATER SIGMA-CO2 ON MODERN CARBONATE PLATFORMS- SIGNIFICANCE FOR THE CARBON ISOTOPIC RECORD OF CARBONATES, Geology, 22(10), 1994, pp. 885-888
Seawater SIGMACO2 from modern carbonate platforms (Bahama Banks and Fl
orida) is depleted in C-13 by as much as 4 parts per thousand relative
to open-ocean water. Depletion in C-13 is caused by isotopically ligh
t CO2 input from respiration of marine and terrestrial organic matter
during water-mass residence on the bank. As such, depletion in C-13 is
related to changes in water chemistry driven by evaporation, freshwat
er discharge, and CaCO3 withdrawal. Deviation of modern platform seawa
ter deltaC-13 values away from those of surface seawater suggests that
deltaC-13 values of ancient cratonic carbonate must be cautiously int
erpreted. Initial depositional environment, as well as alteration duri
ng diagenesis, must be considered in extracting valid secular trends f
or oceanic deltaC-13 variation.