ACTUAL AND ANTICIPATED PETROGRAPHIC EFFECTS OF CARBONATE UNDERSATURATION IN SHALLOW SEAWATER

In the near future, atmospheric CO2 from the combustion of fossil fuels may cause the surface layers of the ocean to become generally undersaturated with CaCO3. The hypothetical sedimentary effects of such an event are discussed in the light of studies in the Skagerrak Bay, North Sea. In this area, nearshore sediments in the depth range 0-40 m are affected by present-day CO3 dissolution. Evidence of inorganic CO3 precipitation is absent. Stages in the dissolution process are microscopic etch patterns on calcareous grains, partially dissolved grains and finally structural breakdown and complete dissolution of skeletal elements. Mineral phases affected are calcite, aragonite and a spectrum of magnesian calcites. Dissolution is quantitatively unimportant in living calcareous organisms, but preservation of shells and skeletons as fossils is much impeded. A future change towards similar conditions in all the world''s shelf seas would certainly mean an end to the typical warm-sea carbonate sedimentation as it is known today on the Bahama Banks and in other supersaturated regions.