MODELING THE SEASONAL CYCLE OF DISSOLVED ORGANIC-CARBON AT STATION E-1 IN THE ENGLISH-CHANNEL

Seasonal cycles of DOC and DON at Station E-I in the English Channel w ere investigated using an ecosystem model. Important features of the m odel are: (i) both carbon and nitrogen are incorporated by means of a set of varying C/N ratios; (ii) separate labile and semi-labile dissol ved organic pools are distinguished; and (iii) there is a detailed tre atment of processes associated with DOM production. The model yields a seasonality in DOM C/N ratios. Results suggest that the observed DOC increase of 34.4 mmol m(-3) is almost entirely due to a buildup of a s emi-labile pool (turnover similar to 1% per day), with phytoplankton e xcretion acting as a major contributary flux (with lesser additions vi a zooplankton messy feeding, detrital breakdown, bacterial lysis and p hytoplankton mortality). The model indicates that the food supply from DOM via bacteria may provide up to 50% of the needs of zooplankton at certain times of year, notably during the overwintering period. (C) 1 998 Academic Press Limited.