Seasonal size spectra of transparent exopolymeric particles (TEP) in a coastal sea and comparison with those predicted using coagulation theory

Abstract

The abundance and size distribution of transparent exopolymeric particles (TEP) were monitored in the Kattegat (Denmark) during 1 yr. TEP number concentration ranged from 0.5 X 105 to 3.8 X 105 ml-' and the volume concentration between 3 and 310 ppm. TEP volume concentration peaked during the spring bloon~ and again during the summer period. The observed accun~ulation of TEP during summer is consistent with the recent observation that dissolved organic matter (DOM) concentration has a similar seasonal distribution and suggests that TEP are formed from DOM. The supposed mode of formation of TEP (coagulation of colloidal organic particles) was tested by companng the observed TEP size spectra with those predicted by means of a coagulation model. The model used was a steady-state version of a particle coagulation model extended to include interactions between TEP and non-TEP particles. The spectra generated by the model were fitted to the observed TEP size spectra. The spectra predicted from the model fitted the observations relatively well, suggesting that the model provides a good description of the hnetics of TEP coagulation and that coagulation of colloids is an important mode of TEP formation. The best fits of the simulated steady-state TEP spectra to the observed ones were used to estimate TEP turnover rates. Seasonal estimates of TEP turnover rates, calculated assuming a sticlung coefficient of 0.6 for TEP-TEP interactions and 0.3 for interactions between TEP and non-TEP particles, ranged between 0.1 and 0.9 d-l. TEP turnover rate appeared to be most sensitive to interactions between TEP and non-TEP particles. Relative TEP carbon fluxes were compared with histoncal primary production estimates and showed almost identical seasonal patterns. According to TEP concentration, turnover times and estlrnates of carbon content, TEP carbon accumulation may represent an important fraction of the primary production and, thus, TEP and their colloidal precursors may represent a significant pathway for dissolved organic carbon in the ocean.