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.