The annual cycle of properties derived from CalCOFI data (http://nemo.ucsd.edu) for 1950 to 1997. Monthly averages included data from all years with observations. The major feature of the annual cycle is upwelling of deep waters during the spring, summer and fall. Upwelling brings cold, salty and nutrient (nitrate and phosphate) rich water to the surface. These nutrient rich, upwelled waters are responsible for the great biological production and the diversity of the ecosystem found in central California.