SEASONAL-VARIATION IN NITRATE PHOSPHATE RATIOS IN THE ENGLISH-CHANNEL1923-1987/

Nutrient concentrations measured at station El in the English Channel from 1930 to 1987 show a wide range in nitrate:phosphate ratio. A larg e number of samples, the majority of which were taken in the summer mo nths, have low nitrate:phosphate ratios. Detailed analysis of the time series revealed that, in a significant number of years, mid-summer va lues of phosphate increased for short periods of time whilst nitrate c oncentrations remained low. These transient increases in phosphate con centration occurred both in the surface mixed water and in water below the seasonal thermocline; equivalent transients in nitrate concentrat ion were less common. The changes in nitrate:phosphate ratio are discu ssed in relation to phytoplankton assimilation and nutrient regenerati on. (C) 1998 Academic Press Limited.