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Petroleum News: Researchers unraveling the secrets of the Arctic Ocean

Alan Bailey
The big problem with researching what’s under the Arctic Ocean is that much of the ocean is covered with ice for much of the year. That’s the fundamental reason that so little is known about that particular region of the Earth. But scientists believe that the Arctic Ocean contains many missing clues to several aspects of the Earth’s history and geography.
“If you want to make this global model, this global paleoclimate model, this global tectonic model, you need the Arctic. The Arctic is the missing piece,” Bernard Coakley, associate professor of geology and geophysics at the University of Alaska Fairbanks, told an audience at the Pac Com conference in Anchorage on Feb. 23.
Coakley explained how complementary approaches to Arctic Ocean research are gradually building an understanding of the ocean.
“Logistics dictate our (research) opportunities — no single platform is adequate,” Coakley said. “This is the rule of the study of the Arctic.”
Amundsen and the Fram
In the earliest Arctic research, about 100 years ago, Norwegian explorer Amundsen deliberately allowed his ship, the Fram, to freeze into the pack ice and be carried across the ocean, Coakley explained. In a similar type of approach, characterized by Coakley as a “drifting station,” people still successfully operate research stations on drifting ice. The Russians, for example, are currently operating their 33rd floating ice station since World War II.
Other means of Arctic Ocean research include the use of icebreakers, submarines, aerial surveys and satellite surveillance. Each approach has its strengths and weaknesses. Taken together, the various approaches have resulted in a substantial body of data, Coakley said.
Scientists have been painstakingly piecing together this data. And this integration of the data is bringing into focus an ever-clearer picture of how the Arctic Ocean is structured.
“It has allowed us not merely to see the sea floor clearly but also to start to articulate very specific questions about the history and development of the Arctic Ocean,” Coakley said.
One of the most impressive results of this data compilation is the International Bathymetric Chart of the Arctic Ocean, a stunningly detailed image of the physical relief of the ocean floor.
The chart clearly depicts how the ocean consists of two major basins: the Eurasian basin lying north of Europe and western Russia; and the Amerasian basin to the north of North America and eastern Russia. A major subsea ridge, called the Lomonosov Ridge, running almost under the North Pole in a fairly straight line between northern Greenland and northern Siberia, divides the two basins. A pair of in-line subsea ridges, the Alpha and Mendeleev ridges, divides the Amerasian basin into the Canada basin, offshore Alaska and northern Canada, and the Makarov basin, between Ellesmere Island and northeastern Siberia.
Oceanic and continental crust
In general, the Earth’s crust consists of oceanic crust and continental crust. Oceanic crust forms deep under the oceans as a result of the splitting apart of the plates that structure the Earth’s surface. Continental crust forms the building material of the Earth’s continents.
All of the Earth’s oceans are floored by oceanic crust. And the Arctic Ocean is no exception, with oceanic crust under both the Eurasian and Amerasian basins. But we now know that the histories of these two basins are very different, Coakley explained.
The Eurasian basin has formed during the past 60 million years through the continuing propagation across the Arctic region of the vast central ridge that marks the splitting apart and spreading of the Atlantic Ocean — it’s a bit like a giant coat zipper being pulled open from the bottom. The sub-sea Gakkel Ridge, a spectacular feature with a huge central canyon, marks the fissure where the Eurasian Basin is opening up.
Geologists interpret the Lomonosov Ridge as a sliver of continental crust that was split off from northern Europe and Siberia when the Eurasian Basin started to form.
In contrast to the Eurasian basin, the Amerasian basin formed during the Mesozoic era, more than 60 million years ago. And, despite a number of theories, no one really understands the mechanism of formation for the basin; features such as the Alpha-Mendeleev Ridge and the Canada basin remain perplexing puzzles.
“We don’t really understand how they hook up with the global system of plate boundaries that existed during the Mesozoic,” Coakley said.
Data from submarines
But research continues.
Coakley described how submarines play a critical role in revealing the ocean structure. Although aerial and satellite gravity and magnetic surveys can cover vast areas, submarines can enable almost any form of detailed survey anywhere under the ice, Coakley said.
“Submarines have really been the way that we’ve come to know the bathymetry of most of the Arctic Ocean,” he said.
Coakley described his participation in a series of six unclassified cruises by U.S. Navy submarines under the Arctic ice between 1993 and 1999. Known as the SCICEX program, the cruises gathered extensive information about the deep Arctic Ocean, using a variety of geophysical instruments.
Each cruise built on the results of the previous cruise. And the last two cruises were able to perform particularly high-resolution surveys using what are known as swath bathymetry and chirp sub-bottom profiling. Working rather like a conventional sonar system, a swath bathymetry system gathers acoustic reflection data from a swath around a vessel’s track. Chirp is a sonic system that gathers high-resolution reflection data down to 50 to 70 meters below the sea floor, Coakley said.
The Lomonosov Ridge
Chirp data from the Lomonosov Ridge proved particularly revealing.
“Sediments are all parallel, railroad track reflectors,” Coakley said. “There’s no indication of any kind of erosion (within the sedimentary layers).”
However, where the ridge projects above a water depth of about 1,000 meters, there is a very distinctive erosion surface at the top of the layered sediments, with a capping lens of sediment sloping down into the Amerasian basin.
“The only way you can explain this kind of erosion is if you had a huge ice sheet grounded against Lomonosov Ridge,” Coakley said, noting the thickness of ice implied by the depth of the erosion surface below sea level.
“The only place an ice sheet of this dimension might be possible to have come from is the St. Anna trough,” Oakley said. The St. Anna Trough is a huge submarine canyon that connects the deep Eurasian basin with the Barents Sea continental shelf.
The submarine surveys were also able to delineate detailed profiles of the Gakkel Ridge, in the middle of the Eurasian basin. One surprising find was that the base of the canyon running along the axis of this ridge reaches depths of 5,206 meters below sea level, the deepest part of the entire Arctic Ocean.
Arctic drilling
A major reason for the submarine survey of the Lomonosov Ridge was to help determine a drilling location for a summer 2004 Arctic Ocean drilling project. That project drilled to about 400 meters below the sea floor on the Lomonosov Ridge (see “Pioneering drilling in Arctic pack ice” in the Oct. 30, 2005, edition of Petroleum News). During the drilling, a huge Russian nuclear icebreaker and a smaller Swedish icebreaker opened up the pack ice, so that the drill ship (a converted icebreaker) could remain stationary.
“They never had to break off drilling because of ice,” Coakley said.
The drilling recovered a continuous record of sediments through much of the Cenozoic, Coakley said. One of the more startling discoveries was rock with high total organic content in some of the sediments.
The organic material included azolla pollen, indicating warm temperatures near the North Pole many millions of years ago — nowadays azolla only exists in the rice paddies of Southeast Asia, Coakley said. But what adds to the interest of this find is that preservation of the organic material would have required water devoid of oxygen at a position high in the ocean basin. Nowadays, such oxygen-free conditions only exist in deep, restricted basins.
The bottom of the hole encountered Cretaceous-age sands that geologists interpret as what is known as a passive margin, a slowly sinking shelf that sloped into an ancient ocean.
“This is the passive margin that once formed the edge of the Amerasian basin, before the rifting took place that separated the Lomonosov Ridge from the Barents Shelf,” Coakley said.
The icebreaker Healy
The 2004 drilling set the stage for a summer 2005 research cruise by the U.S. Coast Guard icebreaker Healy. Coakley was a co-chief on that cruise.
Equipped with multi-channel seismic equipment using streamers and sonobuoys, as well as equipment for swath bathymetry and chirp surveying, the cruise gathered detailed information about the ocean basin structure and history. The cruise also collected sediment cores from the ocean floor for the study of ancient climate records and oceanography.
After setting out from Dutch Harbor in the Aleutian Islands, the Healy traversed the Chukchi Sea and achieved the first crossing of the Mendeleev Ridge by western research scientists, Coakley said. From the Mendeleev Ridge, the Healy crossed the Makarov basin before rendezvousing with the Swedish icebreaker Oden. The two icebreakers then sailed in tandem across the remainder of the Arctic Ocean, eventually reaching Tromso in Norway.
Relatively open ice conditions for the first half of the cruise enabled the straightforward collection of multi-channel seismic data.
“We got excellent data on the Chukchi and on the Mendeleev Ridge,” Coakley said.
Then worsening ice turned the seismic data acquisition into a significant challenge. Coakley described how large chunks of ice flew up from under the ship’s transom, lifting the seismic air guns above the water. The ship’s propellers would also mill through some of the ice blocks, causing considerable vibration and noise.
“You can see, flying out from under the transom, blocks about half the size of this room that have two big semicircular cutouts in them with spirals from the props milling in the ice,” Coakley said.
Sometimes the ice floated the receivers on the seismic streamer to the surface, and twice the whole streamer broke off.
“One of the interesting things about doing multi-channel seismic acquisition in the Arctic is that anything towed is expendable,” Coakley said. “ … Your streamer is a consumable.”
However, the seismic data gathered during the cruise is providing invaluable knowledge about the ocean floor. For example, a seismic section shows a continuous drape of sediment across the Mendeleev Ridge.
You can see this continuous drape “almost everywhere in the Amerasian basin except on top of the Chukchi, where it was probably eliminated by glacial erosion, and down in the low between the Mendeleev and Alpha ridges,” Coakley said.
The seismic data also detected numerous extensional geologic faults in the Amerasian basin.
What next?
Coakley sees drilling on the Chukchi plateau as the probable next step in Arctic Ocean scientific research.
“I think it will provide a very nice contrast to the record that’s come off Lomonosov Ridge,” Coakley said. “It will also complement a group that’s come together to propose drilling in the Bering Sea.” In conjunction with the Alaska Ocean Observing System, the Barrow Arctic Science Consortium and Barrow itself, Coakley is working to develop permanent seafloor observatories off Barrow, at the northeast end of Alaska’s North Slope. The area near Barrow is one of the best places to see how the sea is changing and how the currents are interacting, he said.
The current federal budget also includes provision for a new University of Alaska Fairbanks vessel known as the Alaska Region Research Vessel. Capable of continuously breaking two-and-a-half feet of level ice, the vessel could operate in the Bering, Chukchi and Beaufort seas.
As a driver for future research Coakley sees strong incentives for nations to measure and map the Arctic Ocean, to clearly define offshore economic exclusion zones, under Article 76 of the United Nations — the United Nations has specified a series of EEZ criteria based on parameters such as a depth contour on the continental slope or the point of maximum curvature on the slope. The Canadians, the Greenlanders and the Danes are particularly anxious to obtain Arctic Ocean data in the area near Ellesmere Island and Greenland, where the ice piles up and is double and triple thickness, he said.
So they’ve invited a submarine to work in their waters. It means that the whole northern edge of North America is open to exploration by submarine.
“I think it’s an incredible opportunity,” Coakley said.

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