Pacific Ocean climate change: atmospheric forcing, ocean circulation and ecosystem response.

A major climate change event that affected atmospheric forcing, ocean circulation and ecosystem structure of the Pacific Ocean began in the mid-1970s. Changes in biomass, and presumably productivity, of the lower trophic levels (phytoplankton and Zooplankton) were directly attributed to this event. It also appears that some individual species at higher trophic levels were influenced, but cause-and-effect relationships are more difficult to document at the species level. Recent work shows that at least five major pelagic ecosystems responded to this event, but in different ways, and both increases and decreases in biomass were seen. Changes of this magnitude are well documented in the paleo-oceanographic record. However, it remains to be determined to what extent the changes were caused by natural cycles versus anthropogenic change (global warming).