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Life in Icy Waters

02.20.04

As the summer Sun brings warmth to the sea around Antarctica, the vast expanse of winter ice slowly weakens, revealing areas of open water with a link to the food chain.

supply alt text Adeile penguins depend on nutrient-rich polynyas.

These open water areas, known as polynyas, might seem too bleak to support life. But during brief periods each year, microscopic plant life within the polynyas produces organic matter at a higher rate. The increase of nutrients in the water means a greater ability to support a variety of organisms.

Kevin Arrigo, biologist and assistant professor of geophysics at Stanford University, conducted a five-year inventory of the polynyas surrounding the coast of Antarctica. The study showed that in just a few short months each year, some polynyas provide a feeding ground for larger animals like the Adeile penguin.

Polynyas support the growth of phytoplankton, which consist of algae and bacteria and are the foundation of the marine food chain. Icy waters where polynyas occur are the first areas in polar regions to be exposed to the Sun. This exposure promotes the livelihood of phytoplankton and other marine life.

To locate the Antarctic polynyas, researchers analyzed data from a passive-microwave sensor that measures the amount of radiation, known as brightness temperatures, emitted by the Earth's surface.

The coastal polynyas of Antarctica have never before been studied in detail because of the persistent cloudiness that prevents satellites from "seeing" the surface. But passive-microwave sensors measure the Earth's emitted microwave energy that easily penetrates clouds, which allowed the researchers to identify 37 coastal polynyas around Antarctica.

supply alt text This map shows the locations of the 37 polynyas from Arrigo's study.

Arrigo explained that polynyas can create hot spots for a short period of time during the Southern Hemisphere summer, typically December to February. This is when phytoplankton concentrations are highest, providing nutrients for a wide variety of larger organisms.

"Total productivity may not be that high when averaged over an entire year, but when concentrated in a brief time span, it's significant," said Arrigo. "When you think of polynyas as a concentrated food source for larger organisms, then it becomes clear how important they are."

Arrigo found that Adeile penguins depend on these nutrient-rich polynyas throughout much of their life. Besides providing a concentrated food source, the polynyas affect the penguin's reproductive schedule.

"Adeile and Emperor penguins have their chicks in the middle of the winter, so when spring comes, they will have food for the chicks," said Arrigo.

Arrigo plans to study the polynyas on an individual basis, with a longer time series of satellite imagery. He hopes to use this detailed information about each polynya to evaluate patterns of Adeile penguin colonies and focus on their food sources and to learn why some regions are more nutrient-rich than others.

To read the full text of the article, visit:
http://earthobservatory.nasa.gov/Study/icywater/


This article contributed from "Distributed Active Archive Center (DAAC) Alliance:
Supporting Earth Observing Science 2004"
NASA's Kennedy Space Center

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