The color scale for this image is the same as for the previous image. The land is colored grey-brown and the black sections in the ocean are parts of the image where the satellite was unable to get enough information for a variety of reasons. Beginning with the image from March on the left, have the students locate the highest phytoplankton concentrations. They should be able to identify higher concentrations in coastal areas and towards the Artic Circle. There is more phytoplankton in September than March because the summer sunlight has allowed phytoplankton to bloom in the North Atlantic.
Cold water has more carbon dioxide than warm water.
Therefore, there is more phytoplankton in cold waters, i.e. near the Artic Circle. Phytoplankton also take advantage of nutrients in runoff to bloom along coastlines. Compare the image from March with the one from September. Notice that the September image has more phytoplankton around the Amazon River. That is the end of the rainy season, hence there are more nutrients which ultimately result in more phytoplankton.