Climate variation in the equatorial and North Pacific

1 Climate variation in the equatorial and North Pacific A number of large-scale climatic cycles and their impacts have been recognized and thoroughly studied in the 1990s. Two of the climatic cycles that impact the central and northern Pacific are the ENSO and the Pacific Decadal Oscillation (PDO). 

ENSO events are characterized by reversals of the atmospheric pressure systems in the south and central Pacific and switching of the sources of the intensely upwelled water masses along the southeastern Pacific continental margin. An El Nino event results in warmer surface waters, greater stratification and reduced upwelling of nutrients in the central and eastern equatorial Pacific, reducing primary productivity. While reduced equatorial-subequatorial productivity during El Nino is observed in the central eastern Pacific in all studied events (Barber Chavez, 1983 Barber etal., 1996 Strutton Chavez, 2000), the effects of ENSO events on POC flux to the seafloor are not clear. 

20th century (Trenberth Hoar, 1996, 1997 Timmermann etal., 1999) and the defining role of POC fluxes on NEPAP communities, the impact of ENSO events on the seafloor is yet to be resolved. 

In particular, it has been suggested that chlorophyll concentrations in the euphotic zone at stations Climax and ALOHA document the impact of PDO, and specifically the climate shift of 1976-77 on oligotrophic gyre productivity (Karl, 1999 Karl etal., 2001b). The current hypothesis suggests a shift from a eukaryotic phytoplankton community to one dominated by nitrogen-fixing prokaryotes. The shift to prokaryotic dominance is caused by physical conditions 

---