The distribution of colloids in the North Atlantic and Southern Oceans

Abstract

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 oceanographically distinct regimes, from highly productive nearshore environments to oligotrophic open‐ocean waters. Colloid number concentrations decreased appreciably from the surface to ∼150‐m depth at three of these stations. Concentrations in deep waters of the North Atlantic were high but erratic, suggesting that colloid abundance is regulated by rapid rates of reactions. The colloids were mainly organic and their immediate sources appear to include both autotrophic and heterotrophic activity as well as sediment resuspension. Transmission electron microscope examination of colloid size distributions and morphology indicates that aggregation is the principal removal mechanism for these colloids. Evidence from the cumulative size spectra of small colloids indicates that colloid aggregation is most intense in vertically delineated zones near the surface, around the main thermocline (∼1,000–1,500 m), and in bottom waters. These findings show that the marine colloidal state is abundant but discontinuous in both space and time throughout a wide range of oceanographic environments.