The two distinct migration signal found for the two functional species that have a realistic pattern can be explained by the presence of a thermocline at 40m. This temperature difference impacts then the metabolism of the population above and below it, influencing thence the lipid accumulation timing and the time of entering into diapause. Once the population at the surface goes into diapause, the population below the thermocline keeps migrating/diffusing toward the active target depth seeding a second surface population. With the homogenisation of the temperature towards the fall season, the second population experience the same temperature at the surface allowing the biomass remaining surface to uniformly reach the high C:N threshold.