MESOSCALE PATTERNS OF CHLOROPHYLL-A IN THE CENTRAL NORTH PACIFIC

Within the Central North Pacific along latitude 24°15'N, a mesoscale spatial pattern of chlorophyll a, with a scale of 500 km, dominates basin-wide patterns. West of the Hawaiian Ridge, the dominant scale of near-surface dynamic topography, apparently baroclinic eddy activity, is also 500 km, and the mean variance functions of dynamic height and chlorophyll are coherent. East of the ridge, however, the dynamic topography is dominated by the eastward slope of the isobaric surfaces related to the slow southward transport of near-surface water. Mesoscale patterns of dynamic topography are not apparent, and the relationship between chlorophyll and dynamic topography is unclear. West of the Hawaiian Ridge, higher values of chlorophyll are associated with the centers of cyclonic eddies, lower values with anticyclonic eddies. The pattern of chlorophyll a cannot be explained by concentration and dispersion of cells in the regions of convergence and divergence, but it may involve a combination of growth and depth regulation in response to ambient conditions. There is a loss of nitrate associated with the upward displacement of isopycnal surfaces which accompanies the eddy activity. This doming of subsurface isopycnal surfaces may act as a nutrient pump bringing nitrate into the euphotic zone. Thus, temporal and spatial variations of eddy activity may account for some of the variations in production in the Central North Pacific. © 1990.