PHYTOPLANKTON SEASONALITY IN THE CENTRAL NORTH PACIFIC - THE ENDLESS SUMMER RECONSIDERED

Seventeen years of phytoplankton data from the eastern basin of the central North Pacific near 28-degrees-N, 155-degrees-W indicate that winter mixing is often deep enough to mix species from the deep phytoplankton association to the surface and that this mixing stimulates growth of these species. The frequency of deep winter mixing may be sufficient to have allowed the deep-living species to evolve a strategy of enhanced growth during a short winter, enabling them to survive a prolonged summer of restricted growth. In contrast, winter mixing may be unfavorable for the shallow flora, most species of which declined in abundance during winter. These seasonal cycles of shallow and deep-living species are independent. Hence, studies which consider only phytoplankton integrated through the euphotic zone may fail to detect pattern.