ROLE OF THE CONTINENTAL-MARGIN IN THE GLOBAL CARBON BALANCE DURING THE PAST 3 CENTURIES

The global continental margins are important sites of deposition and r egeneration of terrestrial organic carbon and of calcium carbonate pro duced in situ. The material balance of organic carbon in the coastal z one determines to a large extent its role as either a source or sink o f CO2 relative to the atmosphere. We explore the role of the continent al margin in the global cycling of carbon during the recent geologic p ast using a new model, TOTEM (Terrestrial Ocean aTmosphere Ecosystem M odel). We conclude that during the past 300 yr, the coastal zone has b een a site of relatively stable calcium carbonate deposition, as well as a Site of greater input, recycling, and storage of terrestrial orga nic carbon. As a result, more organic carbon in the coastal zone is re mineralized than produced in situ by photosynthesis (i.e., the coastal zone is net heterotrophic), and this reduces its sink strength for an thropogenic CO2. Continuation of this trend in the future will weaken the ability of the coastal zone to act as a sink for the rising anthro pogenic CO2 in the atmosphere. Reversal of the carbon biogeochemical b alance from net remineralization (heterotrophy) to net production (aut otrophy) may occur in those continental margin sections where bioprodu ction is enhanced by elevated inorganic nutrient inputs (e.g., coastal upwelling zones) and/or where there is efficient carbon storage.