Spring Bloom Colors the Pacific Near Hokkaido

In the northwest Pacific Ocean, the Oyashio Current flows down out of the Arctic, past Siberia and the Kamchatka Peninsula. Around the latitude of Hokkaido, Japan, it begins to veer eastward and converges with the warmer Kuroshio Current, flowing into the area from the south.

When two currents with different temperatures and densities (cold, Arctic water is saltier and denser than subtropical waters) collide, they create eddies. Phytoplankton growing in the surface waters become concentrated along the boundaries of these eddies, tracing out the motions of the water. The swirls of color visible in the waters southeast of Hokkaido (upper left), show where different kinds of phytoplankton are using chlorophyll and other pigments to capture sunlight and produce food. The bright blues just offshore of Hokkaido may be churned up sediment, rather than phytoplankton.