Modeling shifting oceanscapes; a collective pursuit

19 March 2014 by Liz O'Connell, posted in Modeling Arctic Waters

The Chukchi Sea, Bering Strait, and Bering Sea west of Alaska / Image by Google Earth, accessed March 17, 2014

The Chukchi Sea, Bering Strait, and Bering Sea west of Alaska / Image by Google Earth, accessed March 17, 2014

Azara Mohammadi for Frontier Scientists

In 1996, Dr. Kate Hedstrom travelled to Norway to “Sit on Paul Budgell’s steps,” as she says. She went there to get a piece of code recently improved by Paul Budgell. “He promised his model and I went to Norway to get it!” says Kate.

Hedstrom is an Oceanographic Specialist who has lived and worked in Alaska since 2001, at the Arctic Region Supercomputing Center (ARSC). The rewritten code Hedstrom traveled to Norway to retrieve works within ROMS (the Regional Ocean Modeling System); ROMs is an open source tool made up of many algorithms which model the physics of the ocean and can be coupled with biogeochemical, bio-optical, sediment, and sea ice applications. Hedstrom works with teams of scientists using computer models like ROMS to better understand the changing oceanscapes of the Arctic.

As the Earth changes, scientists are pushed into uncharted territory in which old models no longer apply. Simultaneously, without the patterns of a climatically similar past to guide and inform predictions of the future, scientific models become more important as the most methodologically rigorous way of predicting the future as well as understanding the present.

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Ocean-measuring instruments attached to a tripod.

Hedstrom recalls: “So back in the 70’s when people first started modeling ice the ice was a big, thick, stiff sheet. And now there are areas that are much smaller chunks of thick ice with the first-year ice surrounding it.”

Compared to scientific models purely mapping ocean currents, modeling Arctic oceans when and where sea ice is present requires the inclusion of more factors that increase each model's complexity. In order to create a model that closely represents real Arctic oceans, Kate and her colleagues need to model both ocean currents as well as ice dynamics and thermodynamics.

As one would expect, ice currents do not behave in the same way water currents do. Ice is less dense than water so it floats on top of oceans. Its movement is dependent upon the movement and interaction of the water currents it rests on, as well as other ice. This added layer of complexity becomes more nuanced and unfamiliar as Arctic oceans warm and what would formerly have been large sheets of ice become smaller chunks that vary greatly in shape and size.

Researchers like Hedstrom work on the cutting edge of this unfamiliarity. She and her colleagues practice Arctic oceanography because Polar Regions act as planetary heat sinks. In other words, the poles are where heat is able to escape the Earth’s atmosphere. Thus, the Far North plays an important role in the global climate system. Its role is largely dependent on the role of ocean systems, sea ice, and how they interact with the atmosphere.

Collaboration is important to Hedstrom because she works with highly specialized scientists. Each scientist contributes a new element to the ocean model they produce together. The more aspects included within the model, the more accurately and completely the model represents the real, highly complicated, world.

Hedstrom knew that she and her colleagues could produce more accurate models with a bit of code they refer to as the “Paul Budgell Model.”

Kate did not literally camp out on Budgell’s steps, but she explains: “My going to Norway just forced him to look at the issue, because he knew that would be what it took to make it generally more useful, not just for me but the wider community.”

One of Hedstrom’s collaborators includes Dr. Seth Danielson, a Physical Oceanographer at University of Alaska Fairbanks (UAF) who describes himself as "An observationalist that likes to use modeling results." With the help of ARSC supercomputers, they employ a combination of empirical data and numerical models to add to the scientific community’s understanding and ability to predict ocean processes. “Oceans are largely wind-driven systems,” explains Hedstrom. Danielson’s specialty within their latest collaborative project includes an understanding of how wind drives ocean systems.

Danielson holds up a "bottom-lander" tripod of an Acoustic Doppler Current Profiler that was damaged by ice keels. The ice scoured the bottom of the ocean floor and displaced the tripod by about 250 meters. "It just broke it into smithereens," says Danielson. Unfortunately, most of the instrumentation was not retrievable.

Danielson holds up a "bottom-lander" tripod of an Acoustic Doppler Current Profiler that was damaged by ice keels. The ice scoured the bottom of the ocean floor and displaced the tripod by about 250 meters. "It just broke it into smithereens," says Danielson. Unfortunately, most of the instrumentation was not retrievable.

Currently they are working together on a project funded by the Bureau of Ocean Energy Management (BOEM). Hedstrom and Danielson are creating a new, fine resolution grid (every square in the grid represents 1.5km), to map an area which includes Cook Inlet, Alaska. This grid is large enough to track a hypothetical oil spill in the ocean for 30 to 90 days.

In the fall Hedstrom started using ROMS to place and follow hypothetical tracers in the ocean. “Passive tracers are like dye,” explains Hedstrom. Scientists watch these tracers as they move with the ocean currents, mapping their routes. Hedstrom elaborates: “If there’s a gradient in the dye there’s a velocity. If there’s velocity across the gradient then it will move the dye.”

Hedstrom and her team have recently moved the boundary of their model further south. Getting a larger picture of the southern portion of their model helps them more accurately represent the circulation of the Chukchi and Bering Sea. This allows some of those passive tracers in coastally trapped waves to propagate more easily through the Bering Straight, because coastally trapped waves always follow coasts along a certain direction, influenced by the rotation of the Earth, while other waves are mostly generated by winds.

Hedstrom also works closely with Claudine Hauri, a chemical oceanographer at the Institute of Marine Science at UAF. Hauri focuses her research on the carbon chemistry dynamics and oceanic anthropogenic carbon dioxide (CO2) uptake within the living and nonliving parts of the oceanic ecosystem.

Diatoms, like phytoplankton, are living organisms that are susceptible to the levels of carbon in oceans, and are thus often used as a measure of where the ocean is especially acidic. Unfortunately, the instruments used to measure ocean acidity are used mostly in the summer. These instruments can be damaged by ice scraping against them and leaving scours or gouges.

Danielson has been working with Dr. Thomas Weingartner, a professor at the University of Alaska Fairbanks, since 1994. They deployed the first instruments to collect data under the landfast ice; seasonal ice that is anchored (or "holds fast") as opposed to floating freely with the currents. They distributed roughly 25 instruments over about seven years to measure temperature, conductivity, florescence, and turbidity (water clarity). Another instrument attached to the same tripod sends high frequency signals that bounce off the surface of the ocean and particles within the water. These signals tell scientists about the environments surrounding their instrument. Danielson explains: "The signals off the reflection surface [ice bottom] tell us how fast the ice is moving and that is another useful measurement."

Dr. Thomas Weingartner, Professor at the University of Alaska Fairbanks, Institute of Marine Science

Dr. Thomas Weingartner, Professor at the University of Alaska Fairbanks, Institute of Marine Science

The combined efforts of oceanographers like Hedstrom inform ecosystem studies, climate studies, fisheries management, and oil spill response planning. With the help of high performance computing and empirical data, their models replicate and represent a rich and complicated Arctic through its ocean systems.

Frontier Scientists: presenting scientific discovery in the Arctic and beyond

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