Late summer chlorophyll blooms in the oligotrophic North Pacific subtropical gyre

Cara Wilson, Ph.D.
NOAA/NMFS
Pacific Fisheries Environmental Laboratory

Wednesday, June 25, 2003
3:00 p.m. – Pacific Forum

In the late summer of 1997, 1999, and 2000, SeaWiFS recorded large chlorophyll blooms in the oligotrophic North Pacific subtropical gyre (NPSG) near 30°N and 150°W. These blooms covered up to 40,000 km² and lasted as long as 4 months. They are distinct from the surface seasonal cycle in both timing and amplitude, and they are not associated with either SSH or SST anomalies that would indicate changes in subsurface structure. The chlorophyll blooms are not forced by nutrient fertilization from dust deposition or rainfall. It is hypothesized that the chlorophyll blooms are fueled by NO3 supplied from summer Trichodesmium blooms, and that wind forcing could be a factor in their development. The existence of these blooms supports previous research indicating that there are inputs of primary production in the NPSG outside of the understood seasonal cycle.