Concentrations of iron measured at the surface on a transect from Monterey Bay, California to a point about 300 km offshore during upwelling and non-upwelling conditions (Johnson, K. S., F. P. Chavez and G. E. Friederich. 1999. Continental-shelf sediment as a primary source of iron for coastal phytoplankton. Nature, 398, 697 - 700).