THE DISTRIBUTION OF COLLOIDS IN THE NORTH-ATLANTIC AND SOUTHERN OCEANS

The concentrations and size distributions of small (<200 nm) colloids were measured at three stations in the North Atlantic and two stations in the Southern Ocean. The stations were chosen to cover a range of o ceanographically distinct regimes, from highly productive nearshore en vironments to oligotrophic open-ocean waters. Colloid number concentra tions decreased appreciably from the surface to approximately 150-m de pth at three of these stations. Concentrations in deep waters of the N orth Atlantic were high but erratic, suggesting that colloid abundance is regulated by rapid rates of reactions. The colloids were mainly or ganic and their immediate sources appear to include both autotrophic a nd heterotrophic activity as well as sediment resuspension. Transmissi on electron microscope examination of colloid size distributions and m orphology indicates that aggregation is the principal removal mechanis m for these colloids. Evidence from the cumulative size spectra of sma ll colloids indicates that colloid aggregation is most intense in vert ically delineated zones near the surface, around the main thermocline (approximately 1,000-1,500 m), and in bottom waters. These findings sh ow that the marine colloidal state is abundant but discontinuous in bo th space and time throughout a wide range of oceanographic environment s.