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Exploring the Arctic Basin
From: Woods Hole Oceanographic Institution
| By:
Robert SohnHanumant SinghSpahr C. Webb |
EDITOR'S INTRODUCTION |
The Arctic Ocean, located in a deep basin beneath a thick layer of permanent ice, has been an area of great scientific interest since the first major expedition to the region by Captain Otto Sverdrup in 1889. The extreme  temperatures and ice cover have thwarted most traditional forms of oceanographic observation, and few scientists have had the equipment or the funding to research this area. As a result the deep ocean remains largely unexplored. The Arctic Ocean, however, holds important clues for understanding the effects of global climate change, the origin of life on Earth and the genetic evolution of deep-sea microbial communities. This has motivated many scientists to develop novel instrumentation for accessing this extreme environment.
In this feature, WHOI scientists Rob Sohn and Hanumant Singh, and Spahr Webb of Columbia University's Lamont Doherty Earth Observatory describe their designs for an Autonomous Polar Geophysical Explorer (APOGEE), shown on right, that would capture deep-sea measurements of the Arctic Basin, providing valuable data on the volcanic processes that form the Earth's crust in this region, and the exotic deep-sea hydrothermal systems they create. |
 he Gakkel Ridge in the Eastern Arctic Basin represents a vast and largely unexplored region beneath the permanent Arctic ice cap. The northern boundary between the North American and Eurasian plates, the Gakkel Ridge is the slowest divergent plate boundary on Earth, which results in a mountain chain with spectacular topographic relief and complex architecture. |
These factors have the potential to profoundly impact the nature of hydrothermal circulation and biological colonization on the Gakkel Ridge. In addition, the Arctic Basin is essentially a self-contained feature, with communication to the rest of the world's oceans limited to exchange across shallow sills. This hydrographic isolation has important implications for the evolution and ecology of resident chemosynthetic fauna. |
The very existence of hydrothermal systems in the Arctic was a matter of speculation until the 2001 joint US-German expedition to the Gakkel Ridge discovered numerous hydrothermal plumes in the water column and retrieved massive sulfide deposits in dredge hauls. These discoveries provided tantalizing evidence of deep-sea hydrothermal activity on the ridge, but images of the vent fields and their biological communities could not be obtained because the dynamic nature of the ice pack precludes the use of Remotely Operated Vehicles (ROVs) and submersibles. |
This information served as the background for our special research initiative, designed to give scientists the tools to learn more about this previously unexplored region, and to study the impact this region could have on the world's oceans and, indeed, environment. |
A historical perspective on Arctic research
"...notwithstanding I can greatly commend those valiant minds that doe attempt such voyages, and the rather when they doe it for knowledge sake, and profit all their countrie, and not altogether for private gaine and lucre."
--Thomas Blundeville, 1613, Of Arctic Voyages (from the comfort of a London fireside) |
Of all the world's oceans, the Arctic has been the most reluctant to divulge her secrets. Positioned at the top of the world and covered with a permanent layer of ice, the Arctic Ocean remains largely unexplored and poorly understood, even in the face of twentieth-century technology. |
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| Map projections of the Arctic Basin. Glaciers larger than 90 square-kilometers are plotted in white, irrespective of elevation. | |
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In 1889 Captain Otto Sverdrup sailed the Fram ship into the East Siberian Sea and let it freeze into the pack ice northeast of the New Siberian Islands. Over the next three years the Fram drifted in the transpolar current and became the first scientific station to drift across the Arctic Ocean. During this expedition, bathymetric (or water-depth) soundings in excess of 3,000 meters were recorded, and the existence of a deep ocean basin beneath the ice cap was discovered. |
Since that time a multitude of international expeditions and scientific programs have been carried out to map the Arctic Basin and to unravel its tectonic history. The extreme logistical difficulty associated with Arctic investigations, however, has severely curtailed the quality and amount of data collected. On the basis of fairly sparse data the major geologic features of the Basin have been delineated, but their relation to one another, and the evolution of the Basin as a whole, remains largely unknown. |
Modern explorations of the Arctic Basin
In this regard the Woods Hole APOGEE (Autonomous Polar Geophysical Explorer) project is simply one of the more recent attempts to penetrate and explore the ice-covered Arctic Basin. Our approach is to use Autonomous Underwater Vehicle (AUV) technology to get beneath the ice and to make scientific observations. |
The idea of getting beneath the ice to avoid many of the obstacles to Arctic Ocean navigation is not new. In 1648, Bishop John Wilkins of England proposed that "voyages to the polar regions by submarine vessels would be safe from the uncertainty of tides, the violence of tempests, and from ice and great frosts." |
Wilkins was apparently a man of great vision, but little good it did him personally since submarine technology didn't mature until some 300 years later. Submarines have in fact proven to be tremendously useful for exploring and mapping the Arctic Basin, though much of the data acquired by militaries remains classified. |
The US Navy and the National Science Foundation teamed up from 1995-9 with the Scientific Ice Expeditions (SCICEX) program to use the nuclear submarine USS Hawkbill for unclassified, scientific investigations in the Arctic. A variety of fascinating observations were made, but the cost of operating nuclear submarines is essentially beyond the financial means allocated for civilian polar research, and this has put further plans on hold. |
AUVs are much less expensive to operate than nuclear submarines. You don't need a nuclear reactor, for one thing, nor do you need to accommodate a sub full of hungry sailors. They're also much less expensive to build (a gross understatement), so all in all they have the potential to provide an extremely cost effective means of making scientific observations beneath the ice cap. We're hoping that our WHOI development effort will allow us to contribute to Arctic Basin exploration and investigation in a significant way, and at a price that is consistent with civilian polar research budgets. |
APOGEE explorations
APOGEE is an Autonomous Underwater Vehicle (AUV) specially designed to conduct scientific investigations under ice-covered bodies of water, and under the polar ice caps, in particular. In the open ocean autonomous oceanographic equipment is typically recovered by snatching up a piece of gear that has surfaced for recovery. This approach doesn't work so well in polar seas because the equipment doesn't frequently surface for recovery as it traps itself under the ice. |
The APOGEE is deployed in the usual way, which is to say it is lowered into the ocean and released. The vehicle goes about its business making observations of various kinds. When the mission is over we use acoustic homing methods to recover the vehicle. |
An acoustic beacon is lowered on a wire through a hole in the ice. Ideally this would be the hole created by the passage of a polar class icebreaker, but any hole large enough for the vehicle (about 3 feet diameter) will do. The nose of the vehicle is equipped with a phased transducer array that receives acoustic signals from the beacon and allows it to determine azimuth and bearing to the source. This information is passed to the navigation system, which steers the vehicle "home" (i.e., acoustic homing). The vehicle is equipped with a side latch system that allows it to fasten itself to the trawl wire as it swims past the homing beacon, at which point it is ready to be raised onto the icebreaker and the ice platform. |
Broadband seismology in the Arctic
APOGEE is a Bluefin Robotics Odyssey III vehicle measuring 21 inches (53 centimeters) in diameter, and about 8 feet (2.5 meters) long. It weighs about 450 pounds (200 kilograms). It is capable of operating at water depths up to 4,500 meters with a nominal velocity of 3 knots (1.5 meters-per-second). In a survey mode it has a maximum range of about 50 kilometers (30 miles). |
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| A diagram showing the basic dimensions of the APOGEE. | |
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The original motivation behind APOGEE was to make broadband seismic (or vibration) measurements in the high Arctic to study the massive volcanoes along the Gakkel Ridge. To do this the vehicle must be capable of remaining stationary on the deep seafloor for long periods of time. A heavy weight is affixed to the bottom of the vehicle for this purpose. The weight is jettisoned after the measurements have been made, and a flotation package then carries the vehicle up to the sea/ice interface on a tether. The tether is released in shallow water, and the vehicle is then free to navigate itself to the homing beacon for recovery. |
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| Picture of the APOGEE vehicle, which includes an internal navigation system, acoustic sounding device and computer for collecting and recording data. | |
Seismology missions, however, do not take advantage of the vehicle's ability to conduct intelligent surveys of unexplored terrain, a capability that can be exploited to great advantage in the Arctic Basin. Once we have a vehicle that can reliably operate beneath the ice cap it would be a bit of a shame to simply leave it sitting on the seafloor when it could be swimming around acquiring all sorts of data in the deep ocean. For example, we have yet to locate a deep-sea hydrothermal field on the seafloor in the Arctic Basin. The US-German AMORE expedition in 2001 came tantalizingly close, but in the end it simply wasn't going to happen by lowering a camera off the side and hoping the icebreaker would drift over a hydrothermal field. Deep-sea AUVs that can operate under the ice have the potential to revolutionize our methods for locating hydrothermal fields in the Arctic, and this is a powerful vision for APOGEE. |
Our approach is to equip the vehicle with a suite of optical, chemical and physical sensors capable of detecting hydrothermal fluids in the water column. APOGEE would then fly missions under the ice searching for telltale hydrothermal plume tracers and mapping these plumes in detail once they are found. After a plume is located and mapped in the water column, a systematic search for the seafloor hydrothermal field and its biological communities can be undertaken. Ideally this search would include optical imagery so that the biological communities around the vents could be characterized, and we plan to accomplish this by utilizing the SeaBED AUV for fine-scale optical, bathymetric, and side-scan surveys of the hydrothermal fields. |
Testing APOGEE and SeaBED: The Bermuda trials, 2001-2
We carried out two sets of sea trials for the APOGEE and SeaBED vehicles in the waters off Bermuda, a small island in the sub-tropical western Atlantic, in the summers of 2001 and 2002. Why test vehicles for Arctic research in the warm waters off a resort island? |
Bermuda is a superb location to test deep water AUVs because it sticks up like a sort of giant space needle from the deep ocean. It is two hours from the pier to water depths of 3 km (1.5 miles). By comparison it would take something like 15 hours of steaming from virtually any East Coast harbor to comparable water depths. This enables us to conduct deep-water trials close to shore, an important convenience during the prototype stage of development. |
In 2001 we conducted engineering trials, deep-water pressure tests, and homing trials for APOGEE. In 2002 we conducted optical imaging trials for SeaBED by making linear strip and 2-D photomosaics of coral reef communities off Bermuda's south shore. All of these tests have been successful, and AUV trials in the Arctic will begin in 2002. |
The APOGEE project is a joint effort between the Woods Hole Oceanographic Institution, Columbia University's Lamont Doherty Earth Observatory, and the Bluefin Robotics Corporation. Initial funding to develop and test a prototype vehicle was obtained from the National Science Foundation Office of Polar Programs. This article was published in September 2002. Copyright Woods Hole Oceanographic Institution. |
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