Seasonal cycle of phosphate in the open ocean

The seasonal cycle of phosphate in the world ocean is described using all h istorical data lover 170,000 profiles) held at the U.S. National Oceanograp hic: Data Center and World Data Center-A for Oceanography. Generally, phosp hate concentrations are depressed in the season of highest primary producti on, in conformance with phosphate's role as a major nutrient. Mean phosphat e concentration in the North Pacific are twice those in the North Atlantic. The largest seasonal differences occur in the sub-polar North Atlantic and Pacific, where changes in concentration are as large as a factor of two. T emperate and equatorial regions exhibit less seasonal variability. High lat itudes, upwelling areas, and river mouths exhibit a notable seasonal signal in phosphate. Enrichment of phosphate from the Amazon and Orinoco rivers a ppears to dominate the seasonal signal in the tropical Atlantic. In fact, t he extent of the rivers' effects extend so far north into the North Atlanti c gyre that it obscures the normal pattern of summer depletion occurring el sewhere in the basin. The seasonal signal in the tropical Pacific Ocean is a function of seasonal variability in the winds, which affect the strength of coastal upwelling. Published by Elsevier Science Ltd.