ESTIMATES OF THE MAGNITUDE (TOP PANEL) AND ONSET (BOTTOM PANEL) OF THE SPRING BLOOM IN CENTRAL PRINCE WILLIAM SOUND (SAME DATA AS FIGURE ABOVE). THE MAGNITUDE OF THE BLOOM WAS ESTIMATED BY NUMERICALLY INTEGRATING CHLOROPHYLL CONCENTRATION FROM MARCH 1 TO AUGUST 15 IN EACH YEAR USING THE TRAPEZOID RULE. THE ONSET OF THE BLOOM WAS ESTIMATED AS THE DAY OF THE YEAR WHEN SURFACE CHLOROPHYLL CONCENTRATIONS FIRST EXCEEDED 2 ΜG L-1. ON DATES WHEN THERE WAS AN ESTIMATE FROM BOTH THE SEAWIFS (ADJUSTED FOR OFFSETS) AND THE MODIS TIME SERIES AVAILABLE, THE MIDPOINT WAS USED.