A synoptic sampling method applied to Calanus finmarchicus population on the Norwegian mid-shelf in 1997

The majority of studies of marine processes are based on data from signific ant field efforts. This was also the case for the Trans-Atlantic Study of C alanus finmarchicus (TASC). Three cruises were conducted in 1997 as part of a field programme, covering the most important reproductive period of C, f inmarchicus at the latitude of the Norwegian shelf. Conventional sampling p rovides distribution maps for selected life stages and species without taki ng into consideration errors introduced by internal rates of the biological components, behavior and advection. An understanding of physical-biologica l processes studied is best acquired by reconstructing a synoptic spatial d istribution of plankton from samples including advective effects. We have d eveloped a method for transforming conventionally sampled data into synopti c distributions (Synoptic Sampling Scheme, SSS transform) by removing the a dvective component. This is achieved by forward and backward Lagrangian par ticle tracking, both in physical xyz space and stage space. The method incl udes the application of hydrodynamical flowfields and physiological models featuring the population dynamics of C. finmarchicus. We have assessed the method by comparing and contrasting distribution maps based on untreated an d normalised synoptic data on the demography of C. finmarchicus. The data w ere taken from 2 of the cruises conducted during the spring and summer of 1 997 on the Norwegian mid-shelf sector. The results show that the lowest sta ges are more affected by the SSS transform than the older stages, due to sh orter turnover time. Samples taken in regions with high current magnitudes contribute most to the reconfiguration of the cruise polygon. It is also sh own that the SSS transform appears to have greater effects on small concent rations. The controlling factor is probably the fluxes amongst the stages. An effect indicated by the scheme is that the end regions will be most affe cted by the SSS, while the general ecological interpretations are not drama tically changed. Due to the effect advection and stage dynamics will have d uring the time of the cruise, the study recommends the use of new semi-syno ptic sampling technology. This could eliminate the use of the SSS transform . To a certain extent the optical plankton counter (OPC) and acoustic Doppl er current profiler (ADCP) could prove efficient in that context. Generally , interpretations based on uncorrected data should be made with extreme car e.