Quantification and analysis of mesoscale patchness distribution and productivity in the Adriatic Sea: comparison between data aquired by the towed undulating vehicle (SARAGO) and CTD casts.

A modern approach to the study of pelagic ecosystems requires a quantitative assessment of their major components and their response to physical forcing and dynamics. To achieve the goal of appropriate spatial and temporal resolution and synopticity it may be critical the use of a rapid and high resolution data acquisition tool systems, able to sample over the entire water column. Among other methods, a towed undulating vehicle (TUV) is probably one of the best possible solutions. Within the framework of the Italian National Research Council (CNR) PRISMA 2 Research Project, 8 oceanographic cruises were performed in the Northern Adriatic Sea. The cruises were splitted in two legs: during the first one the SARAGO TUV was used to acquire continuously physical and biological parameters in the water columns, alongshore and cross-shore; during the second one CTD casts were utilised to sample water and analyse the biogeochemical features. The SARAGO data described the frontal system and distribution and abundance of biomass, thus allowing the scheduling of a better sampling plan inshore and offshore the front, that was investigated few days later by CTD casts. The main parameters that were acquired by the SARAGO probe were CTD, Chlorophyll-a concentration, photosynthetic efficiency, PAR and dissolved oxygen. A mathematical model was then applied to estimate the primary production. In this work we compare both the distribution and the quantification of some variables acquired by the two different study methods: the towed undulating vessel and the CTD operated by ship. The two sampling methods were compared by variogram and kriging analysis. The results pointed to a better spatial resolution and continuity of the SARAGO sections that, in turn, allowed a better accuracy in the biomass budget calculations.