Oceanic Fronts
When two currents (in this case the Oyashio and Kuroshio currents) collide, they create eddies. The blue-green color in this image is caused by phytoplankton which are concentrated along the boundaries of the eddie. Source: Spring Bloom Colors the Pacific Near Hokkaido | NOAA
Similar to fronts between air masses, oceanic fronts are boundaries between surface ocean currents. Like weather fronts, they exist between the water of different temperatures and densities. When these fronts meet, a portion of the boundary current can break off and develop into a closed circulation called a whirling eddy. Eddies can have impacts on climate and huge impacts on coastal waters.