Phytoplankton are photosynthetic, meaning they convert sunlight into chemical energy and give off oxygen. Phytoplankton capture sunlight via pigments in their cells, which alter the wavelength and quantity of the light reflected back out to space. Because satellites measure the radiation reflected from the oceans, their data help document pigment levels and, thus, phytoplankton activity. This visualization shows satellite observations of phytoplankton activity from January 2000 through December 2003 as measured by NASA's MODIS instrument on the Terra satellite.

Examining patterns of phytoplankton activity worldwide reveals how microscopic plants respond to the seasons and ocean currents. Sunlight and nutrients are the primary resources phytoplankton need to flourish. Plenty of sunlight shines on the tropics year-round, but at higher latitudes, the amount changes with the seasons. (When it is winter in either hemisphere, that hemisphere's pole is angled away from the Sun because of Earth's tilt.) Therefore, when it is summer in the Northern Hemisphere, large blooms of phytoplankton occur in the North Atlantic. Six months later, blooms occur the Southern Hemisphere.

Nutrients are more concentrated in cold water. Along the continental shelf surrounding the Falkland Islands, east of Argentina, perennial winds kick up waves that bring cold, nutrient-rich water to the ocean surface year-round. When the Sun's rays illuminate the Falkland Shelf during the Southern Hemisphere's summer months, large phytoplankton blooms occur. The blooms provide food for invertebrates, fishes, and mammals in the ocean, bolstering food webs.

Satellites provide a global view of life's response to the seasons. This data visualization reveals seasonal and annual patterns in the growth rate, or productivity, of phytoplankton.

Educator Resources for "Ocean Primary Productivity"