Diurnal Variations in Some Chemical and Biological Properties of the Sargasso Sea1

Periodic measurements were made during a 24‐hr period in the surface layer (0–300 m) of the Sargasso Sea off Bermuda of the following variables: temperature, salinity, phosphate, nitrite, nitrate, chlorophyll, C 14 assimilation and zooplankton standing crop. Nutrient concentrations, integrated from the surface to 150 m, increased at night and decreased during the day. Chlorophyll concentrations increased during the daylight hours and decreased at night. C 14 assimilation over 24‐hr periods was greater in experiments initiated at night than in those begun in the daytime. Thus changes in the C 14 /chlorophyll relationship appear to have resulted from variations of both parameters. Zooplankton standing crop (0–200 m) increased markedly during the early evening but subsequently decreased throughout the rest of the night and following day.