News / Research Highlights / Computer Modeling of the Arctic: A Coupled Marine Ecosystem-Physical Model

Computer Modeling of the Arctic:   A Coupled Marine Ecosystem-Physical Model

July 22, 2005

Arctic sea ice is home to some of the largest and smallest life forms on earth.   From polar bears to diatoms, researchers are studying this diverse ecosystem.   Some of the smaller organisms that inhabit this extreme environment are sea-ice algae.   Ice algae communities are found in several areas of the ocean including brine channels, the small vertical spaces between ice crystals that fill with a salty water solution.   They may attach to the underside of ice, which provides a platform for algae in the upper ocean, or can hang from the ice in strand-like filaments.   Algae can also be free-floating under the surface of the ice (Fig. 1).

Sea-ice algae are part of the food web in the Arctic and by using sunlight (solar energy) they convert carbon dioxide, an inorganic form of carbon, into organic carbon molecules. This process is essential for small life forms living below the ice.   Ice algae provide nourishment for tiny krill and small crustaceans, which, in turn, provide sustenance to large mammals like whales and, eventually, man (Fig. 2).  

There are few studies of tiny ice organisms in the Arctic due to the remote location, extreme weather, and dangerous condition of sea ice during spring thaw. Computer models provide a valuable method for researchers to synthesize information, simulate the ocean's biological and physical processes, and project scenarios of future climate.   Models often include variables like temperature, sunlight, and water chemistry and they can link numerical data with chemical process studies over a specific period of time.

IARC Researcher Clara Deal and her colleagues are developing a model that couples sea-ice algae production off the coast of Barrow, Alaska with a physical ice-ocean model.   The ice algae portion of the model represents a single location on a horizontal time line from February through June, covering the spring bloom period through ice melt.   Data for the model comes from ice cores collected off the coast of Barrow from March to June, from 2001 to 2004.

Research on tiny diatoms in sea ice indicates that their growth and distribution is mainly determined by the amount of sunlight available. At certain times, sea ice can filter out more than 90% of the available light.   Sediment particles in the ice and snow cover also affect the amount of sunlight that reaches ice algae.   In first-year ice, most primary productivity takes place during the spring season.

From March to June of 2002 through 2004, ice core observations were conducted off the coast of Barrow by IARC scientists and researchers form other institutions. They found that most of the ice-algal biomass exists in the bottom two centimeters of the sea ice, and that it's production peaked in early May (Fig. 4, top panel).

The ice core observation data for May through June of 2002 and 2003 suggested "three distinct periods of ice algal bloom: an exponential growth period from March to April, slow variation in early May, and sharp decline period from late May to early June for both years," according to Deal.

When Deal and her colleagues compared the ice algae model results to observation data, they found that the model simulations of ice algal biomass were very similar. The model indicates that the above three consecutive periods are largely controlled by light, the availability of nutrients, and meltwater flushing. They found a higher biomass of phytoplankton from March to May in 2002 (Fig. 4, bottom panel) than in 2003, and speculate that this difference could be from advection, the horizontal movement of phytoplankton from one area to another, or by a species of diatom that was able to grow under low light conditions.

Scientists formerly thought that sea-ice algae had little significance in the Arctic, but recent studies now indicate that ice algae make up fifty percent or more of the total primary production in the Arctic Ocean¹ .

IARC researchers recognize the sensitivity of sea-ice algae to changes in the physical environment.   Water temperature, salinity, ice extent and thickness can have an influence on the productivity and survival of ice algae and other ocean organisms.   For the past several decades, there has been a warming trend in the Arctic and sea-ice extent and thickness have been decreasing.   At least a hundred different species of diatom could be affected by these climate changes, which, in turn, could have a large impact on the higher level arctic food chain.

¹Gosselin, M., M. Levasseur, P.A. Wheeeler, and B.C. Booth, 1997.  New measurements of phytoplankton and ice algal production in the Arctic Ocean.  Deep-Sea Res., 44:1623-1644

Fig. 4. Ice algal biomass, Mar-May 2002 (top). Phytoplankton biomass, Mar-May 2002 (bottom).

Tiny diatoms in sea ice (from NOAA Arctic Theme Page)

Maps showing the research area.