Natural Radiocarbon Activity of the Dissolved Organic Carbon in the North-east Pacific Ocean

Abstract

THE “age” of the dissolved organic matter in the deep sea relative to its origin in the euphotic zone has been, a matter of conjecture for some time^1–3. Photosynthetic fixation of carbon dioxide into plant carbon by phytoplankton and subsequent biochemical oxidation or solubilization of organic carbon takes place primarily in the upper 0–300 m of the sea. A small, as yet unknown, fraction of this organic carbon is transferred into the deep water by physical processes such as turbulent mixing and sinking of surface water at high latitudes. In addition, particulate organic carbon which sinks from the surface may be converted into dissolved organic matter at depth. In order to determine how “old” this dissolved organic carbon is, its natural radiocarbon activity has been measured for two deep-water samples taken off southern California.