The Bright Side of Arctic Ice
by Julie Zeidner Russo
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
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
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.
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.
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
NURP'S RS2 Super Phantom
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.
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,"
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."
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."
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.