ESTIMATION OF STICKING AND CONTACT EFFICIENCIES IN AGGREGATION OF PHYTOPLANKTON - THE 1993 SIGMA TANK EXPERIMENT

The coagulation of phytoplankton, a fundamental mechanism for vertical flux in the oceans and a possible predatory escape mechanism, is a fu nction of the density of suspended particles and at least three enigma tic system processes: the encounter rate of the particles; the contact efficiency of various sized particles upon encounter; and the efficie ncy of sticking upon contact. A variant of a continuous coagulation mo del, including the second-order aggregation rate representation and da ta obtained from the 1993 SIGMA tank experiment at Santa Barbara, are used first to estimate 'stickiness', the efficiency of sticking given that a collision occurs. Primary tools are an inverse, least squares m ethodology, an aggregation model, and an individual growth model for p hytoplankton. The model output corresponds well with the data for smal ler sized particles (<0.4 mm(3)); however, predicted densities for lar ger particles were less than observed, and the predicted timing of the bloom was earlier than observed. These anomalies led to an investigat ion of the interacting roles of stickiness, contact efficiency, and nu trient storage in individual cells. The analyses suggest that (i) aggr egation is relatively insensitive to the sticking efficiency, and thus it is difficult to estimate stickiness accurately by fitting aggregat ion data; (ii) contact efficiency appears to be more functionally vari able than assumed in traditional representations, and estimating conta ct efficiency, jointly with the sticking efficiency, generally produce s better agreement with the SIGMA experimental size particle data spec trum; (iii) for the SIGMA tank environment, estimates of contact effic iency are dimensionally more closely related to diameter than to the t raditional surface area representation; and (iv) stored nutrient reser ves may play a fundamental role in governing timing of peak algal bloo m and dynamics of aggregates; inclusion of nutrient storage improves e stimation of peak bloom, but does not significantly improve prediction of aggregate dynamics in the SIGMA tank experiment.