Arctic Expedition Reaches 88.5 Degrees North LatitudeFourth Joint U.S.-Canada Survey for Purpose of Delineating Extended Continental Shelf
The United States and Canada joined forces once again in August and September 2011 to survey the seafloor in remote and ice-covered regions of the Arctic Ocean. The two-icebreaker expedition was the last of four joint cruises designed to collect data that each country will use to define its “extended continental shelf”—the area beyond 200 nautical miles (nm) from shore where a nation has sovereign rights over resources on and beneath the seafloor according to the Law of the Sea Convention. (Visit http://www.un.org/Depts/los/ to learn more.)
The criteria for delimiting extended continental shelf as set forth in the convention require detailed information about the shape (“morphology”) of the seafloor and the thickness of sediment beneath the seafloor. To map seafloor morphology, scientists used a multibeam bathymetric-mapping system aboard the U.S. Coast Guard Cutter Healy. To acquire information about sediment thickness, they used a multichannel seismic-reflection system on the Canadian Coast Guard Ship Louis S. St-Laurent (the Louis).
The Healy and Louis worked together to collect data between lat 78° and 88° N. along some of the most poorly mapped ridges and basins of the Arctic Ocean. The 2011 work started with a 1,200-km seismic-reflection transect northward from the Chukchi Plateau, across Alpha Ridge and the Makarov Basin, to Lomonosov Ridge (see map below). Along the return tracks southward, the expedition acquired primarily multibeam bathymetric data, although four additional short seismic-reflection lines were collected in the Stephenson Basin and on Sever Spur. Before joining the Louis for the two-icebreaker work, the Healy collected approximately 25,000 km2 of multibeam bathymetric soundings in deep water of the Alaskan margin east-northeast of Barrow (map B).
Each summer since 2008, the two icebreakers Healy and Louis have worked together to enable scientists to collect morphologic and sediment-thickness data in the Arctic, primarily beyond 200 nm from shore. In 2008 the fieldwork was conducted mainly in the southern and central Canada Basin, and in 2009 primarily in the central and northern Canada Basin. The 2010 fieldwork was conducted along both the Alaskan and Canadian Beaufort margins, with additional lines along Northwind Ridge and the Stephenson Basin. Profiling conducted in 2011 expanded the previous surveys northward.
Throughout the 4 years of joint icebreaker work, the primary U.S. and Canadian focus was on collecting multichannel seismic-reflection data, with the Healy breaking ice in front of the Louis. Canada and the United States also had bathymetric objectives, and where those objectives were a priority, the Louis broke ice ahead of the Healy. Together, the joint surveys have added approximately 15,000 km of high-quality multichannel seismic-reflection data, many thousands of kilometers of multibeam bathymetric data, and more than 120 sonobuoy seismic-refraction lines in parts of the Arctic where surface ships have rarely been able to operate. (Seismic-refraction data, commonly collected by deploying an instrument called a sonobuoy, are required for correct calculation of sub-seafloor sediment thickness from the seismic-reflection data; they also provide information about sediment composition.) The multichannel seismic-reflection profile acquired from the Chukchi Plateau northward to Lomonosov Ridge is the first continuous seismic-reflection profile collected in this part of the Arctic Ocean, providing some of the first images across Alpha Ridge and the Makarov Basin that show clear sedimentary stratigraphy and basement morphology. (“Basement” is the hard rock beneath the sediment, into which the sound waves used to collect sediment data typically do not penetrate.)
Chief scientists for the 2011 cruises were David Mosher (Geological Survey of Canada) on the Louis and Larry Mayer (University of New Hampshire) and Andy Armstrong (National Oceanic and Atmospheric Administration) on the Healy. For the third year, Deborah Hutchinson (U.S. Geological Survey [USGS] Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts) was the U.S. liaison on the Louis. Aboard the Healy, Lisa Robbins (USGS St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida) led a group of scientists—Paul Knorr and Brian Buczkowski of the USGS and Jonathan Wynne of the University of South Florida—in a “science of opportunity” study of ocean acidification in the Arctic Ocean. Gravity data were collected on both ships, monitored by Hutchinson on the Louis and Buczkowski on the Healy.
The ocean-acidification measurements taken from the Healy, which expand the region sampled in the 2010 joint icebreaker cruise, represent the first continuous sample transect taken near the North Pole from surface ships (see “USGS Arctic Ocean Research: A Polar Ocean Acidification Study,” published before the cruise in Sound Waves, August 2011). More than 9,000 continuous samples (collected from seawater flowing through a shipboard system) were analyzed, as well as 515 discrete surface samples collected for pH measurement and 350 discrete surface samples collected for measurement of carbonate concentration. At eight sites, water samples were collected from selected water-column depths during deployment of a “CTD”—an assembly of instruments that measure conductivity (related to salinity), temperature, and depth while being lowered through the water. The CTD frame holds a ring, or “rosette,” of water-sampling bottles triggered to collect water at selected depths as the assembly is raised back toward the surface. Ice samples were taken at three sites. The 2011 measurements provide a rich dataset for comparing CO2 saturations and fluxes among the Canada, Nautilus, Makarov, and Stephenson Basins, as well as understanding how the carbon values relate to other physical and biological parameters. A blog and additional information about the ocean-acidification studies is posted at http://coastal.er.usgs.gov/ocean-acidification/arcticcruise2011/.
Several “firsts” took place aboard the Louis during the 2011 trip. For the first time, an autonomous underwater vehicle (AUV) was deployed in the ice and completed a successful 20-hour mission acquiring multibeam bathymetric data from a height of approximately 100 m above the seafloor along the ice-covered Canadian margin. Although recovery of the vehicle was challenging in the ice, the successful mission demonstrated the potential for using AUVs in remote and difficult environments, such as the ice-covered Arctic, where movement of surface ships is restricted. Another first was the use of a drone unmanned aerial vehicle (UAV) for scientific purposes in the Arctic. U.S. Air Force Captain Steve Wackowski flew nine missions using cameras aboard Raven UAVs to image ice conditions and search for marine mammals. An ozone buoy (O-buoy) was deployed on the ice near lat 88° N. to collect air-quality measurements integrated with physical-environment data and hourly camera images in this remote part of the Arctic (visit http://obuoy.datatransport.org/ and click on “OBuoy #4”). Finally, near the northernmost extent of the expedition, samples from throughout the water column were taken with CTD rosettes to add to a limited number of observations of full-depth physical oceanography and water-mass interactions in the area.
The Healy and Louis rafted together twice during the expedition, once at the beginning of the cruise for the Louis to take on fuel from the Healy after high winds prevented the Louis from refueling from a barge off Tuktoyaktuk, Northwest Territories, Canada, and again at the end of the cruise, for the third year of joint-operations celebration. (Logistical complexities prevented a celebration raft-up in 2010.) This year’s end-of-cruise raft-up included nautical-skills competitions (the Healy excelled), musical entertainment (the Louis excelled), and a feast of amazing treats (everyone excelled). A set of blogs about life aboard Louis is posted at http://blogs.science.gc.ca/arctic-arctique/?lang=en. Finally, a USGS flag flown on the Louis to the northernmost point of the journey was given to the captain and crew of the Louis in appreciation of the 4 years of successful joint operations with the USGS.
The Extended Continental Shelf Project is operated through the U.S. Extended Continental Shelf Task Force, an interagency body chaired by the Department of State with co-vice chairs from the Department of the Interior and the National Oceanic and Atmospheric Administration. The task force, which reports to the National Ocean Council, includes representatives from the USGS, the Executive Office of the President, the Joint Chiefs of Staff, the U.S. Navy, the U.S. Coast Guard, the U.S. Department of Energy, the National Science Foundation, the U.S. Environmental Protection Agency, the Bureau of Ocean Energy Management, and the U.S. Arctic Research Commission. Additional information on the joint U.S.-Canadian Extended Continental Shelf cruise is posted at http://continentalshelf.gov/ and http://ess.nrcan.gc.ca/scient_e.php.
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