Organic Aggregates in Tropical and Subtropical Surface Waters of the North Atlantic Ocean1

Twenty surface samples taken en route from Bermuda to the west coast of Africa were filtered for subsequent microscopic examination of phytoplankton and organic aggregates (nonliving particulate matter). Fourteen of the samples were accompanied by measurements of particulate organic carbon. All three quantities were significantly correlated. All reached their highest values in a region of upwelling in the Guinea Current, with lower values in the Sargasso Sea, the North Equatorial Current, and nonupwelling equatorial waters. The largest quantity of aggregates observed in these oceanic waters intergraded with the lower range of values previously reported in rich inshore waters of Long Island Sound. Observations and supporting experimental data lead to conclusions that 1) dissolved organic matter secreted by phytoplankton is readily converted to particulate matter by adsorption on near‐surface bubbles, thus producing the direct relation noted above; 2) even in areas where phytoplankton is scarce, there is a sufficient residuum of older dissolved organic matter to permit the formation of significant quantities of aggregates; and 3) the aggregates have a carbon content greatly exceeding that of living phytoplankton.