Productivity - (n.)
The amount of carbon fixed by photosynthesis in the uppermost layers of the ocean. Radiocarbon measurements suggest a total productivity of 30 billion tons of carbon per year. About half of this is fixed within a few hundred kilometers of the coast, the "green" coastal ocean, and the rest is found in the vast expanses of the "blue" ocean. This pattern reflects the fact that vertical mixing is greatest in the coastal ocean. Along many coastlines, also, there is a strong upward motion of cold deep waters from the thermocline, called "coastal upwelling." Strong seasonal coastal upwelling occurs off the shores of California (where this cold upwelling water makes surfers wear wetsuits), off Peru, off northwestern Africa, off Namibia, and in the Arabian Sea. In these areas productivity is especially high and fish are potentially plentiful. There is one important exception to this overall blue-ocean/green-ocean dichotomy: a strip of high productivity along the equator. The equatorial upwelling results from effects introduced by the rotation of the Earth, on the motion of water masses driven westward by the trade winds. It is especially strong in the eastern equatorial regions of the Pacific and the Atlantic, and high-sea fisheries are correspondingly intense in these regions.