Distribution of suspended particulate matter at the equatorial transect in the Atlantic Ocean

Abstract

Studied oceanographic transect across the Equatorial Atlantic is considered as a “screenshot” of suspended particulate matter distribution against a hydrographical background. The area of abnormal high suspended matter volume concentrations was found above the Sierra Leone Rise from top to bottom (eastern part of the transect). The suggested explanation for the anomaly is based on the ballast hypothesis whereby solid particles are incorporated as ballast into suspended biogenic aggregates, leading to increased velocities of sinking. This process is located within the Northwest African upwelling area since the plankton exposed to the Saharan dust abundance form a significant number of aggregates lately transported equatorward via Canary Current. The intermediate nepheloid layer associated with the Deep Western Boundary Current was recorded from the American Slope at the 3200–3700 m to the depth of 4300 m above the Para Abyssal Plain. Antarctic Bottom Water enriched in the suspended matter was found mostly in the troughs at 40–41° W. It was detached from the bottom, coinciding with the core of the flow due to the bottom rise (“dam”) located up-stream. The grain size of particles was in accordance with polymodal distribution – the 2–4 μm and the 8–13 μm modes. The registered rise in the percentage of the 7–21 μm-sized particles suggests the presence of the well-known coarse mode (20–60 μm) formed by aggregation of transparent exopolymer particles (mucus).