WASHINGTON — A NASA mission to study the tiny algae vital to the ocean's food chain has turned up a massive amount of phytoplankton where scientists least expected it -- under the Arctic ice.

In a project that uses both satellites and on-site measurements to study this important food source for many of the ocean's creatures, NASA sent a team to sample the ice pack off the Chukchi Sea along Alaska's coast.

Researchers aboard the US Coast Guard icebreaker ship, Healy, sampled beneath the 0.8-1.3 meter (2.4-4.0 feet) thick sea ice and found phytoplankton biomass was "extremely high, about fourfold greater than in open water."

The "massive under-ice bloom" also appeared to extend about 100 kilometers (60 miles) into the ice shelf, until "the waters literally looked like pea soup," mission leader Kevin Arrigo told reporters.

"We were astonished. It was completely unexpected. It was literally the most intense phytoplankton bloom I have ever seen in my 25 years of doing this type of research," said Arrigo, a scientist at Stanford University in California.

"Just like the tomatoes in your garden, these and all phytoplankton require light and they require nutrients to grow," Arrigo explained.

"It has been presumed that there was very little light under the ice and we didn't expect to see much."

Known formally as "Impacts of Climate on Ecosystems and Chemistry of the Arctic Pacific Environment," or ICESCAPE, mission scientists went on two expeditions in June-July of 2010 and 2011.

The latest findings are published in the June 7 edition of the journal Science.

Arrigo said the discovery caused "a fundamental shift in our understanding of the Arctic ecosystem," which was previously believed to be cold and desolate.

Before, the tiny single-celled plants were not believed to grow until the ice melted.

"If you rank all the phytoplankton blooms anywhere in the world by the amount of phytoplankton that is contained in them, the under-ice bloom that we saw during ICESCAPE would finish at the very top of the list," he added.

"And it was growing beneath a layer of sea ice as thick as a five-year-old child is tall."

Phytoplankton were scarcer and deeper in the open waters, and were "greatest at depths of 20 to 50 meters (66-164 feet) because of nutrient depletion near the surface," said the study.

More research is needed to determine how these under-ice phytoplankton affect local ecosystems.

Phytoplankton blooms in the Arctic have been observed to peak as many as 50 days earlier than they did a dozen years ago, a development that could have implications for the larger food web, scientists have said.

"My concern is that if phytoplankton continue to develop and grow earlier and earlier in the year, it is going to become increasingly difficult for those animals that time their life cycle to be in the Arctic... to be there at the right time of year," Arrigo said.

The microscopic organisms are the base of the food chain and drive the food and reproductive cycles of fish, seabirds and polar bears. How larger animals may react to phytoplankton changes remains unknown.

Phytoplankton are also important because through the process of photosynthesis they remove about half of the harmful carbon dioxide produced by the burning of fossil fuels worldwide.

Previous research has shown the microscopic organisms have been disappearing globally at a rate of one percent per year.

Since 1950, phytoplankton mass has dropped by about 40 percent, most likely due to the accelerating impact of global warming, said a 2010 study in the journal Nature.