A sea of change: Biogeochemical variability in the North Pacific Subtropical Gyre

The North Pacific Subtropical Gyre (NPSG) is the largest ecosystem on our p lanet. However, this expansive habitat is also remote, poorly sampled, and therefore not well understood. For example, the most abundant oxygenic phot otroph in the NPSG, Prochlorococcus, was described only a decade ago. Other novel Bacteria, Archaea and Eukarya, recently identified by nucleic acid s equence analysis, have not been isolated. In October 1988, an ocean time-se ries research program was established to study ecosystem processes in the g yre, including rates and pathways of carbon and energy flow, spatial and te mporal scales of variability, and coupling of ocean physics to biogeochemic al processes. After a decade of ecosystem surveillance, this sentinel obser vatory has produced an unprecedented data set and some new views of an old ocean. Foremost is evidence for dramatic changes in microbial community str ucture and in mechanisms of nutrient cycling in response to large-scale oce an-atmosphere interactions. These and other observations demand reassessmen t of current views of physical-biogeochemical processes in this and other o pen-ocean ecosystems.