Variability of phytoplankton light absorption in stratified waters of the NW Mediterranean Sea: The interplay between pigment composition and the packaging effect

Abstract The Variability of chlorophyll-specific phytoplankton light absorption [a*ph (λ)] was examined over depth and time in stratified offshore waters the North-Western Mediterranean Sea. Coherent water patches were tracked with Lagrangian drifters during two oceanographic cruises September (late summer) May (post-spring bloom phase). By simultaneously analysing pigment measurements, we explicitly separated impact composition from that packaging on a*ph (λ). We further partitioned effect by comparing variation index [Qa*(440)], community size structure (derived diagnostic analysis), beam attenuation particles [cp* (660)] as an optical photophysiology. In ensemble cruises, around 50% (440) vertical explained changes (ruled decrease photoprotective pigments depth). remaining inter-cruise attributed to effect. found differences cp*(660) (most likely indicating intracellular concentration due photoacclimation) mainly observed Differences cp* (660) coincident either gradient availability or lower mean daily PAR irradiance euphotic layer cruise. These stronger values increasing both relative May. On other hand, did not explain patterns packing Our results highlight importance short-term acclimation prevailing conditions, determining temporal variability A better understanding (λ) its main drivers are key improve different bio-optical applications.