Organic carbon in shelf seas: sinks or sources, processes and products

The preservation of Corg in various shelf seas from different geological, hydrological and climatological settings is compared. Most of these shelves have been studied extensively over the last two to three decades, often within the framework of large (inter)national research projects. Various factors (physical oceanography, chemical conditions, sedimentation rates) that could influence the preservation of Corg are discussed. Not only recent conditions, but also longer time scale fluctuations (glacials versus inter-glacials, sea level variations) are dealt with. Most (>95%) of the Corg introduced onto shelves by primary production and imported from the oceans and continents is mineralized in the water column and sediments. It appears that the role of shelves as sinks for Corg is sometimes overestimated. Large areas of the continental shelves do not show any accumulation of organic matter under present day conditions. Only locally, where hydrological and sedimentological conditions are favourable for organic matter accumulation considerable amounts of Corg are buried. On longer time scales the role of shelves as sinks for Corg is limited, even more than under recent conditions. Continental slopes, canyons and deep-sea fans are thought to be the main sinks for Corg.