Diurnal Fluctuation in Photosynthetic Rate and Chlorophyll “a” Content of Phytoplankton from Eastern Pacific Waters

Measurements were made of photosynthetic activity and chlorophyll “a” content of phytoplankton samples taken at regular intervals over a 46‐hour period in May 1957, from surface waters near Clarion Island in the eastern Pacific Ocean. Results confirm previous observations of a diurnal periodicity in photosynthesis which, in this particular instance, appears to be correlated with variations in chlorophyll content. The photosynthesis‐chlorophyll relationship gives an estimated value of 4.24 mg C/hr per mg of chlorophyll “a” at a light intensity of 1000 foot‐candles.