Observation and simulation of the spring bloom in the northwestern Irish Sea

A two-layer, coupled physical-biological model was used to investigate phytoplankton dynamics in the north-western Irish Sea. The model was parameterized with values obtained from the published literature, and predicted the concentration of chlorophyll and dissolved inorganic nitrogen in an upper and lower layer. Simulations were driven with measured hourly values of meteorological data. The timings of the spring bloom predicted by the model at a summer thermally stratified site and a vertically mixed site were compared with observations made during 1992. At the mixed site, good agreement was found between the model and observations. At the stratified site, the results are less satisfactory and show that the model predicted a spring bloom 13 days later than observed. The difference was probably due to overestimation of the surface mixed-layer depth leading to underestimation of upper-layer irradiance. A simple numerical experiment demonstrated that the timing of the spring bloom was best simulated using the maximum theoretically justifiable value for photosynthetic efficiency.