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The Bright Side of Arctic Ice

by Julie Zeidner Russo

Floating above the vast frozen continental shelves of the Arctic--an amazing 25 percent of the shallow ocean waters--a small crew of biological oceanographers aboard an icebreaker would brave the elements for discovery's sake. A combination of good timing and persistence would help them make some scientific breakthroughs last spring. It would be the first attempt ever performed by researchers at studying early season phenomena in the deeper portions of the Arctic using a Remotely Operated Vehicle (ROV). They cruised up through the Bering Strait to the ice-covered Chukchi Sea northwest of Alaska.

Misperceived as a biological desert because of the bitter cold, perennial ice cover and restricted growing season, scientists have recently come to discover a bright side to this hostile environment. The whales, seals, and walruses have always known better. Attracted to polynyas, which are areas of open water surrounded by sea ice, the mammals have luck finding food. The appeal of these great, rugged creatures at the top of the food pyramid draws in many scientists, who soon find themselves fascinated by the "tiny giants" or simplest life forms at the bottom of the pyramid supporting the entire ecosystem.

That's where William Ambrose, an associate professor of biology at Bates College, and his research colleagues would focus. By studying the relationship between the algae growing on top, inside and underneath sea ice and the small organisms that live on the bottom and in the mud of the Chukchi Sea, the researchers learned more about a complex food web in an extreme environment.
Far from finding a barren desert, they discovered an impressive amount of animals, on and in the sediment. Many of them were consuming ice algae. These startling observations also helped fill in an important part of the equation related to carbon cycling in the Arctic Ocean and its potential impact on global warming.

Ice algae in the Chukchi Sea.

There's been a lot of research in the Arctic, but it's been late in the season when the shelves are ice free and the ice covered areas are more accessible. It was luck that the Coast Guard's icebreaker the Polar Sea was available to assist researchers in reaching the Chukchi in late May of '98 during a time of year previously sealed off. The research would be supported by the NOAA's Undersea Research Program (NURP) and the Cold Regions Research and Environmental Laboratory (CRREL.)

The research team included Ambrose, and oceanographers Lisa Clough of East Carolina University, Jody Deming of the University of Washington, and Terry Tucker of CRREL. The group was determined to reach the sea early in the season based on results Ambrose and Clough obtained during projects in Greenland and the Chukchi Sea between 1992 and 1996 that were supported by the National Science Foundation (NSF) and the Coast Guard. In Greenland they had observed ice algae getting to the bottom and some typical ice algae species in the sediment.

"The perception has been that when you take a system and cover it with ice, light doesn't get through," Ambrose said. "It's cold and dark, and there isn't much plant life fueled by this." Scientists call the fueling of plant life primary productivity.

A brittle star on the bottom of the Chukchi Sea

The theory that the Arctic was a barren environment was dispelled in the early '90s when researchers on a NSF cruise across the Chukchi Sea documented high rates of primary productivity occurring. It was groundbreaking research. Clough was on the transarctic cruise in 1994 when researchers began to quantify the contribution of ice algae.

She and Tucker went to the Chukchi Sea in 1996 seeking evidence that ice algae might be reaching the bottom and serving as an early season fuel to the benthos and maybe an important fuel sustaining it the rest of the year. All the evidence they had came from a box core taken from the mud, but that was enough to convince NURP that they should be supported to return to the region better equipped in 1998, Ambrose said.

Most of the previous Arctic research also focused on the role of phytoplankton, a floating photosynthesizing algae that is abundant in the summer months. Phytoplankton is the object of intense scientific scrutiny because of its ability to convert atmospheric carbon dioxide into a food source. If the planet is getting warmer as a result of increased inputs of carbon dioxide into the atmosphere, scientists are trying to determine what impact this will have on the environment. Marine plants and animals are biological storehouses of carbon. Because the ocean is the largest reservoir of carbon--taking in and storing as much as 75 percent of the carbon on earth--scientists are trying to determine the potential effects of global warming on this cycle.

Early in the season before the ice is gone and phytoplankton bloom, Arctic algae growing on ice may play as important a role in converting carbon dioxide into carbon. This process fuels secondary production--the process by which animals turn plant food into animal bodies--contributing to the very high amount of bottom--dwelling organisms, Ambrose theorized.

Using NURP's Remotely Operated Vehicle (ROV), the scientists could determine what role ice algae played in fueling the benthic ecosystem. It was the first time an ROV had ever been used in the western Arctic. NURP pilot Lance Horn navigated the RS2 Super Phantom. It couldn't have been better than if the researchers were riding in a luxury car. From the relative comfort of the icebreaker, the scientists observed on video what the submersible robot piloted by Horn was filming 50 to 100 m below the frigid water. They looked for ice algae and counted the number of creatures they observed. NURP'S RS2 Super Phantom

Ambrose's suspicion that algae was getting to the bottom where it was an important early season contribution to benthic activity was correct. Sunlight was getting through the ice fueling a lush lawn of algae. "We saw big curtains of algae. It looked like someones lawn had gone wild," Ambrose said. "At almost all stations over many meters we found huge amounts--it was phenomenal." Norweigan Polar Institute biologist Cecilie Quillfeldt found more than 260 species of ice algae from cores of ice. This suggested that there are a variety of ice algae providing an abundance of food.

The ROV also recorded ice algae at just about every station along the bottom. With the exception of some earlier observations made by divers in shallow water, this was the first time ice algae had been observed rolling along the bottom of the Arctic by an ROV.

At each station, box core samples of what was in the mud were taken from aboard the ship. Back in the laboratory, researchers quantified 180,000 individual ice algal cells per millimeter of mud, as well as lipids in the mud associated with ice algae.

"The ice algae is making it to the bottom," Ambrose said, "but then what? The organisms that live on the surface seem to gather up the algal tumbleweeds, and we have some evidence to show that they start to crank up their activity levels too." Additional proof that the organisms were consuming ice algae came from observing sand dollars, brittle stars, star fish (part of the epibenthos living on the surface of the mud) that were brought onto the ship and fed it.

Along with the lush algae, researchers also found an abundance of animals--more than 250 brittle stars per meter squared. These kind of organisms can account for upwards of 70 percent of the carbon being consumed on the bottom, Ambrose said. The other 30 percent of the carbon is being consumed by organisms that are in the mud . It also showed ice algae and benthic organisms playing a big role in the processing of carbon. "This was a huge piece of the puzzle that was missing," Ambrose said.

These results were just the tip of the ice. The researchers had enough data from 1996 and 1998 to make some comparisons. What they discovered was the ice was much thinner in 1998 than it was two years earlier, and there was much more ice algae. They found 4 to 5 times more plant pigment from the algae on the bottom in '98 than in '96. The thinner ice had created a much more active system, with higher respiration rates and bacterial activity. "The whole system was kicking over, and the difference was big," Ambrose said.

What is interesting about the discovery is that some researchers believe Arctic ice is getting thinner as a result of global warming. "Thinner seasonal continental shelves are likely to promote luxuriant growth of algae," Ambrose said. "This will be good for the critters on the bottom. In that sense a little bit of global warming would be good for the organisms on the bottom."

But Ambrose cautioned that too much atmospheric warming would have the opposite effect. "If the ice melts enough so that the shelves are ice free," he said. "Then there won't be ice algae, and that would be a loss of a unique, complete food source of primary productivity getting to the bottom."

The bottom line is that ice algae are important, even critical, early in the season when phytoplankton are not yet abundant. Previously, their contribution to the benthos had been completely ignored. This critical piece of information will reshape our understanding of arctic ecology, future models of global carbon cycling, and the potential effects of global warming.

Additional information about this project can be found at the Bates College Web site. The participating principal investigators are as follows: Drs.William Ambrose, Bates College, Lisa Clough, East Carolina University, Jody Deming, University of Washington, and Terry Tucker, Cold Regions Research and Environmental Laboratory (CRREL). The Research was supported through a grant from the NOAA's Undersea Research Program's West Coast and Polar Regions Undersea Research Center. Additional funding was provided by the Howard Hughes Medical Institute.

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Updated: April 1, 2005