Mid-ocean ridges and their influence on the large-scale patterns of chlorophyll and production in the North Pacific

Abstract

Ocean-wide spatial patterns of chlorophyll a and productivity are investigated along two transects, one through the central North Pacific at 24°15′N and one through the subarctic Pacific at 47°N. In the south, large-scale gradients are absent across most of the ocean. In the north, largescale gradients are significant.Three mid-ocean ridge systems are crossed by these transects: the Hawaiian Ridge and the Mariana Ridge in the central North Pacific and the Emperor Seamount Chain in the subarctic. Significant reductions in chlorophyll a are seen for more than 900 km west of the shallow Hawaiian Ridge in the oligotrophic central North Pacific. A similar band of reduced chlorophyll lies above the deep Emperor Sea Mount Chain in the eutrophic subarctic Pacific. No change in chlorophyll a is associated with the Mariana Ridge. The effect of mid-ocean ridges on the epipelagic ecosystem does not depend directly on the depth of the bottom topography or the ambient nutrient concentration in the euphoric layer. The effect may be more widespread than previously realized.