The rate of dissolution of calcium carbonate from the surface of deep-ocean turbidite sediments

Abstract

It is known that past periods of high atmospheric carbon dioxide concentration are associated with poor carbonate preservation in the deep-ocean sedimentary record. Bottom water can become more aggressive towards carbonate sediments during such periods. To interpret the sedimentary record more exactly, and to predict future atmospheric carbon dioxide levels, it is necessary to know the rate of solution of carbonate for a given degree of bottom-water undersaturation. In parts of the Atlantic Ocean, turbidite sedimentation mechanisms have emplaced carbonate-rich material in contact with undersaturated bottom water. The time of the emplacement event can be determined from natural radionuclide distributions, and the degree of carbonate dissolution in this time can be measured. This provides a direct measurement of dissolution rate from a natural sediment surface at a known degree of undersaturation. The range of applicability of the method is explored with a mathematical model, and field data from a 5430 m depth Atlantic site are presented.