What Controls Phytoplankton Production in Nutrient-Rich Areas of the Open Sea

摘要

The oceans play a critical role in regulating the global carbon cycle. Deep-oceanwaters are roughly 200% supersaturated with CO2 compared to surface waters, which are in contact with the atmosphere. The difference is due to the flux of photosynthetically derived organic material from surface to deep waters and its subsequent remineralization, i.e. the 'biological pump'. The pump is a complex phytoplankton-based ecosystem. It is driven by sunlight, and fueled by the supply of inorganic nutrients derived primarily from the deep ocean. In areas of the oceans where inorganic N and P are effectively exhausted by phytoplankton in surface waters during the growing season, the pump functions at maximal efficiency: The transport of carbon to depth is limited by the flux of N and P into the surface waters. In the Southern Ocean, near the equator, and in the subarctic Pacific, however, relatively high concentrations of nitrate and phosphate are found in the surface waters throughout the year, and phytoplankton biomass and net production are much lower than would be expected based on the availability of major nutrients. (Copyright (c) 1991, by the American Society of Limnology and Oceanography, Inc.)