ocean color.

Ocean color varies from green to blue, depending on the type and concentration of phytoplankton, or algae, in any given area. A deep blue ocean typically means there is little phytoplankton present. The more phytoplankton present, the more green the water appears. According to NASA, when sunlight hits the ocean, some of the light is reflected back directly, but most of it penetrates the ocean surface and interacts with the water molecules it encounters. By keeping a close watch on ocean colors, scientists can better understand phytoplankton and how they impact the world around them.

Phytoplankton live at the ocean surface, where they use sunlight and carbon dioxide to engage in photosynthesis. They pull carbon into the ocean while giving off oxygen. When these organisms die, they bury carbon in the deep ocean, a crucial process that helps to regulate the global climate.

 paying close attention to changes in the oceans' color can offer the first clues of the changes that are underway.