Sources and transformations of organic matter as deduced from FDOM variability in a transatlantic section along 7.5º N

Abstract

The vertical and horizontal distributions of fluorescent dissolved organic matter (FDOM) were determined by fluorometry from water samples taken at 28 stations during MOC2-Equatorial cruise. The stations were allocated along 7.5ºN transect (a repetition of the A06 WOCE line) in the equatorial Atlantic Ocean. In the upper layer the vertical variability of FDOM was associated with light attenuation and plankton distribution while in deep layers FDOM variability responded to the thermohaline water-mass characteristics. In the range of intermediate waters all profiles showed peaks of fluorescent humic substances between 300 and 600 meters, such peaks became more conspicuous in the eastern sector of the transect. This West-East FDOM gradient appears to be related to changes in nutrient concentration and Apparent Oxygen Utilization (AOU). The biological transformations within each water mass, as they shape the vertical and horizontal distribution of FDOM, are discussed