干旱区生态环境知识资源中心

Ocean systems were traditionally thought to be static aqueous deserts of low productivity with a low "steady-state" diffusional supply of nitrate across the thermocline. Over the last decade, this view has been increasingly challenged due to several factors: the adoption of new methodologies, increased sampling frequency, and the discovery of a diverse picophytoplankton (< 2-mu-m) that provides most of the primary production. Our current view of oceanic nutrient supply recognizes the importance of episodic events that increase the nitrate flux to surface waters and rapidly enhance photosynthetic rates. Recent estimates of oceanic primary production and that portion supported by nitrate have been revised upwards, which has a direct impact upon calculations of global carbon fluxes. We now believe that there is a rapid cycling of carbon and nitrogen in the open sea that is driven by synergistic picoplankton interactions between photoautotrophs, chemoautotrophs, methanotrophs, heterotrophic bacteria, and their protozooplankton grazers in the water column and on microaggregates.