About the author: Brian Van Pay is a Maritime Geographer with the Bureau of Oceans and International Environmental and Scientific Affairs. He is currently on the U.S. Coast Guard Cutter Healy on the Arctic Ocean.
In my previous two entries, I discussed why the United States is working in the Arctic to define its continental shelf, but for this entry I'll discuss what we are doing, specifically the types of data we are collecting.
I'll spare you my hour-long Power Point on how a country determines an extended continental shelf and boil it down to this: a country can use one of two formulas in any combination to determine the edge of its extended continental shelf as provided in the Convention on the Law of the Sea. But the Convention also says there are two constraint lines that those two formulas cannot go past. Here, too, a country can use any combination of those constraint lines to maximize its shelf. So the line that ultimately defines the U.S. extended continental shelf could be a combination of one or all of those four factors -- the two formula lines and the two constraint lines. Keep in mind this legal definition of the continental shelf is not the same as what a geologist would call a continental shelf.
There are two primary datasets that a country needs to collect to determine the two formula lines and the two constraint lines. The first is bathymetric data that provides a three-dimensional map of the ocean floor. We are currently collecting bathymetric data from Healy using a multibeam echosounder (called the Seabeam 2112), which is mounted on the hull of Healy. Every few seconds, the multibeam echosounder sends out a ping and when the energy is returned to the ship we collect up to 121 individual depth measurements. I can hear the ping every few seconds right now as I write on my laptop in my room.
The second required dataset is seismic reflection data, which provides a cross-section view of what's beneath the ocean floor. From that cross-section view, scientists can derive information on the thickness, geometry, and other characteristics of the geologic layers that are stacked on top of one another. Canada's icebreaker, Louis S. St. Laurent, is collecting seismic data now. Louis is towing a sound source behind it that emits acoustic energy at regular intervals. The transmitted energy is reflected or refracted from the various geologic layers and received by an array of hydrophones also towed behind the ship. The signals that are picked up by the hydrophones are recorded in digital form and stored on high-speed computers for subsequent processing and analysis.
As you can imagine, collecting this kind of data is not trivial, especially in ice-covered conditions in the Arctic. Check back for my next DipNote entry on how the United States and Canada are working together to collect this data.
Editor's Note: Read Brian's previous entry on Why Does Defining the U.S. Extended Continental Shelf Matter?