Response of lower trophic level ecosystems to decadal scale variation of climate system in the North Pacific Ocean

The changes related to interdecadal climate variations, such as the Pacific Decadal Oscillation and the 18.6-y tidal cycle, have been discussed in many marine ecosystem studies. The climate regime shift of 1976/77 played an important role in both lower and higher trophic ecosystem change, especially in the North Pacific. By analyzing data from observation of nutrient concentrations, decreasing and increasing trends of nutrients in the surface and subsurface layers, have been reported in many studies. Changes have also been observed in the biomass of phytoplankton and zooplankton. However, quantitative understanding of ecosystems remains a major research challenge because of the complex biodiversity and food web structure. This review focuses on primary producers and zooplankton as key links to higher trophic levels, with the aim of elucidating the mechanism that sustains marine ecosystems.