Fluorescent dissolved organic matter production via microbial respiration: A comparison between the equatorial Atlantic Ocean and the subantarctic zone of the South Atlantic Ocean

Abstract

The distribution of humic-like fluorescent dissolved organic matter (FDOM) at two different Ex/Em wavelengths, 340/440 nm and 320/410 nm, were obtained for both the equatorial Atlantic Ocean and the subantarctic zone of the South Atlantic Ocean. Water samples for FDOM measurements in the equatorial Atlantic Ocean were taken during the MOC2-equatorial cruise, along 7.5ºN section. In the subantarctic zone of the South Atlantic Ocean, the FDOM measurements were acquired during the MOC2-austral cruise, which was divided in two transects, one located in the Argentine Basin and the other in the Cape Basin. The relationships of FDOM with Apparent Oxygen utilization (AOU) and with the inorganic nutrients (both as proxies of organic matter mineralization through heterotrophic respiration) are evaluated once the effect of water mass mixing is corrected. In this way, the influence of in situ microbial activity on FDOM variability for intermediate and deep waters is identified. The differences between these two oceanic zones relative to FDOM production through microbial respiration are also discussed.