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Microscopic view of crucigenia phytoplankton.
—Photo courtesy of U.S. Environmental Protection Agency Great Lakes National Program office
—Photo courtesy of NASA.
MODIS image of the Southern Ocean (centered on the Falkland Islands) on 22 November 2004, showing various levels of chlorophyll. The more phytoplankton present in the ocean water, the greater the concentration of plant pigments.
—Image courtesy of the MODIS Ocean Science Team at Goddard Space Flight Center.
Phytoplankton consist mostly of algae and bacteria and are the foundation of the marine food chain. Phytoplankton, shrimp, and other small organisms feed the fish. These, in turn, feed the seals, which feed the bears. Like plants on land, phytoplankton use sunlight and nutrients to produce their own food. Cold, polar water is the perfect breeding ground for phytoplankton.
Each spring when sea ice melts in the Arctic or Antarctic, the ice leaves behind a layer of fresh water on the ocean surface that is full of nutrients. Microorganisms use the nutrients to develop, forming the basis for organisms higher in the food chain. Another source of nutrient-rich water appears when cold, dense polar water sinks to the ocean bottom, forcing deep, nutrient-laden water to the surface. Polynyas also have rich nutrients that support the growth of phytoplankton.
Phytoplankton "blooms" occur in the surface water each spring, when sunlight easily penetrates the water and provides the energy needed for rapid phytoplankton population growth. Phytoplankton blooms in the Bering Sea appear when ice melts early or later in the season as sunlight increases. The Southern Ocean that surrounds Antarctica is one of the most productive areas on Earth, but only during the Antarctic summer--a few months around December each year--when abundant sunlight provides the perfect conditions for phytoplankton to multiply in vast quantities.
These blooms feed krill, tiny, shrimp-like animals, which in turn are eaten by Adélie penguins, seabirds, seals, whales, and other animals. Phytoplankton also support the development of different species of fish. The fisheries of the North Pacific Ocean and the Bering Sea are among the most productive in the world, in part because of the large concentration of phytoplankton there.
In Antarctica, Adélie penguins depend on polynyas, where phytoplankton are abundant, throughout much of their lives. In eastern Antarctica, more than 90 percent of all Adélie penguin colonies live next to coastal polynyas. The open water provides a concentrated food source for the penguins, who time their cycles with food availability. Adélie penguins have their chicks in the late spring or early summer, so that food is abundant when the chicks need it.
Because phytoplankton are so vital to many different species, scientists want to monitor where the highest concentrations occur. One way to do this is with satellites.
Different types and quantities of phytoplankton show slightly different colors when viewed from space. The more phytoplankton present in the ocean water, the greater the concentration of plant pigments and the greener the water. The Sea-viewing Wide Field-of-View Sensor (SeaWiFS) satellite mission was designed to monitor changes in ocean color as an indicator of primary productivity, the amount of organic material produced by phytoplankton. Visit the SeaWiFS project at the NASA Goddard Space Flight Center Web site for more information. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Aqua and Terra satellites is also used to detect ocean color from space. Visit the OceanColor Web at the NASA Goddard Space Flight Center Web site.
To learn more about remote sensing studies of phytoplankton, see the following articles at the NASA Earth Observatory Web site:
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