Q 1991, by the American Society of Limnology and Oceanography, Inc. Geographic variation of oceanic 14C dark uptake

In a series of midocean stations extending from high northern to high southern latitudes in both the Pacific and Atlantic Oceans we found that 14C dark uptake followed a definite geographic pattern. In temperate and equatorial regions the dark uptake was normally 5 10 % of that in the light, but in the subtropical gyres and at high southern latitudes the average dark uptake varied from 10 to>50 % of the light uptake. There was a significant and complex relationship between dark uptake, production, and standing stock that seemed to depend on the structure ofthe plankton community, but a relatively simple pattern could also be discerned. At production levels of s 1 fig C liter- ’ h-l or at standing stock levels of>40 rg C liter-‘, the average dark uptake was low. At lower levels the average dark uptake was high. It is not surprising that when the 14C method was first described (Steemann Niel-sen 1952) it rapidly became accepted as a standard. Prior to 1952, the methods used for measuring primary production in the sea were neither accurate nor precise. The al