This chart of 1975 hydrographic and satellite data shows the path of the Gulf Stream and a number of warm-core and cold-core rings (north and south of the stream, respectively) that have spun off it. This was the first attempt to create a “weather map” for the northwestern Atlantic Ocean. The flow is charted using the depth (in hundreds of meters) of a water layer registering 59°F (15°C), which years of research have shown to be a reliable indicator of the surface current. (Figure courtesy of Phil Richardson)

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