CHLOROPHYLL-A CONCENTRATIONS IN THE NORTH PACIFIC - DOES A LATITUDINAL GRADIENT EXIST

Chlorophyll a concentrations were measured as a function of depth from 28 to 48-degrees-N along 152-degrees-W in March 1991 with Whatman GF/ F and 0.2-mum Nuclepore filters. Surface Chl a concentrations measured with 0.2-mum Nuclepore filters were up to fourfold higher than those measured with Whatman GF/F filters. The largest difference between the two filter types was found in subtropical waters, where picoplankton were a major constituent of the phytoplankton assemblage. Chl a concen trations integrated from 0 to 175 m showed a threefold increase (9-26 mg Chl a m-2) between 28 and 48-degrees-N when Whatman GF/F filters we re used. However, integrated Chl a concentrations based on measurement s with 0.2-mum Nuclepore filters were nearly constant (25-31 mg Chl a m-2) over the transect. These results lead us to question the existenc e of previously reported latitudinal gradients in integrated Chl a con centrations in the North Pacific Ocean.