On the Vertical Mixing of Sea-Water and its Importance for the Algal Plankton

Abstract

1. Measurements of hydrogen ion concentration, of phosphate concentration, and of temperature all show at certain seasons a well-marked gradient from surface to bottom. The upper 10–20 metres is more alkaline, notably depleted of phosphates and warmer.2. Settled summer weather and deep water, free from irregularities of the bottom, favour the formation of such a gradient. Its breaking up is occasioned by wave action and the cooling of the surface water in autumn.3. Thermal stratification in the English Channel arises at each station, and is not due to the inflow of warm over colder water.