“Ocean Guru” Studies Arctic Water Movement

Dr. Kevin Arrigo is a Professor in the Department of Environmental Earth System Science at Stanford University. He is the Chief Scientist for NASA’s ICESCAPE (Impact of Climate change on the Eco-Systems and Chemistry of the Arctic Pacific Environment) mission this summer onboard US Coast Guard Cutter HEALY.

The motion of the ocean. It moves sea ice around like the pieces of an uncompleted puzzle. It brings nutrients such as nitrogen and phosphorus from the Pacific Ocean into the Arctic where they fuel luxuriant phytoplankton growth. It also moves particles up and down like tiny yo-yo’s on a string. It sometimes flows in circuitous paths determined by wind patterns and the shape of the ocean floor, and at other times, it zips northward, hugging the Alaska coastline. Every place we sample and everything we measure is affected by the nervous energy of the restless ocean.

That’s why it is so important that ICESCAPE have its own ocean guru. Dr. Bob Pickart (Woods Hole Oceanographic Institution) has been studying water movement in the Arctic Ocean for the last decade. He understands its idiosyncrasies better than most and his expertise makes him a particularly valuable asset to the ICESCAPE team. He is always ready with suggestions for alternative sampling strategies when the sea ice isn’t cooperating, which has been most of our expedition. Because of his sage advice, ICESCAPE is capturing an unprecedented picture of the flow of water from the Pacific Ocean, over the Chukchi Shelf, and out into the deep Canada Basin.

How does he do it? His primary tool is the CTD – an instrument that’s lowered into the ocean from a wire and measures Conductivity (a proxy for salinity), Temperature, and Depth continuously as it slowly descends from the surface to the bottom. By dropping the CTD every few miles along a predetermined line, he puts together a two-dimensional picture of the ocean’s salinity and temperature, kind of like the pictures you get from an MRI or CT scan.

He combines this information with data collected by Frank Bahr (Woods Hole Oceanographic Institution) using the HEALY’s Acoustic Doppler Current Profiler, a gizmo that bounces sound off of little particles in the water to get a measure of the water’s speed. The result? A series of strategically placed slices through the Arctic Ocean showing where that water has come from, where it is going, how fast it is moving, and even what it is carrying with it.

Without this information, we would be unable to interpret the patterns we observe in our other measurements – like nutrient levels, phytoplankton abundance, and concentrations of carbon dioxide. As a physical oceanographer once told me, “You got nuthin if you don’t got the physics!”