Vertical distribution of pico- and nano-sized Dapi yellow particles at Dyfamed time-series station, NW Mediterranean Distribution verticale des particules colorées au Dapi (Dapi yellow particles) de taille pico- et nano-planctonique à la station d’observation permanente Dyfamed en Méditerranée nord-occidentale

We measured abundance and surface area of picoand nano-sized organic particles that are stained by 4’6-diamidino-2-phenylindole (Dapi), namely Dapi yellow particles. This study was done monthly from April 1999 to March 2000 from surface down to 2000 m at the French-JGOFS time-series station Dyfamed in the NW Mediterranean. Dapi yellow particles were always observed throughout the water column and the total surface area of Dapi yellow particles 0.2–10 μm ranged from 0.5 to 51.5 mm l. Dapi yellow particles were generally less abundant in the surface layer, greater between 70 and 500 m and decreased toward 2000 m. During the mixing period, Dapi yellow particles were homogeneous throughout the upper 200 m, suggesting that distribution of Dapi yellow particles was influenced by the hydrological structure. Dapi yellow particles correlated positively with inorganic nutrients (NO3, PO4 and Si) and negatively with dissolved oxygen concentration (P < 0.05). These results suggest that abundant Dapi yellow particles from the bottom of the euphotic layer to the intermediate layer reflect the process of particle degradation in the ocean. © 2003 Éditions scientifiques et médicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.