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Waters of the Chukchi bring surprises Industry research team finds major variations in marine environment and unexpectedly small fish in areas of planned oil drilling Alan Bailey Petroleum News
In the summer, from the air, the grey surface of Alaska’s Chukchi Sea, extending out to the horizon, looks monotonously uniform, other than perhaps for a scattering of small ice floes, the remnants of the winter ice pack. But the water below the ocean surface contains some remarkable environmental variation. Or, at least, that is the finding to date of an industry-funded research team, investigating the subsea environment in the area of planned oil and gas exploratory drilling by Shell, ConocoPhillips and Statoil.
Dramatic changes “I’ve never seen a system in which you can have such dramatic changes, environmentally, in such a short distance,” Robert Day, senior scientist with environmental research firm ABR Inc., told the National Marine Fisheries Service’s annual Arctic Open Water Meeting on March 8.
Day was referring to differences in the underwater environment between the areas around the ConocoPhillips Devil’s Paw prospect; around the Burger prospect, where Shell plans to drill; and around Statoil’s Chukchi Sea leases. Day referred to the ConocoPhillips area as the “Klondike” area, referencing an earlier name for the ConocoPhillips prospect.
The Klondike area lies about 120 miles west of the Chukchi Sea coastal village of Wainwright. The two other areas are farther north: The Statoil area is about 100 miles northwest of Wainwright, while Burger lies to the south of the Statoil area and about 60 miles northeast of the Klondike area.
The objective of the industry-funded research is to obtain baseline environmental data; to obtain information needed for permitting and National Environmental Policy Act assessments; and to provide information needed to plan any future industrial operations, Day said. The findings that Day presented to the Open Water Meeting related to research cruises conducted between July and October in the years 2008 to 2010, with research in the Statoil area starting in 2010. However, the research continued in 2011 with an expanded study area, Davis said.
During the cruises, the research scientists used a computer system to merge data from environmental sampling with continuous records of vessel navigation data and other data such as weather information. Data were also obtained from arrays of subsea acoustic recorders.
Day attributed the environmental differences between the three areas in part to a complex interaction between ocean currents, seafloor topography and year-to-year variations in the Arctic weather.
At a very simplistic level, the Chukchi Sea, having a sea surface slightly higher at its southern extremity than in the north, can be viewed as a northward inclining table, with relatively warm Bering Sea water flowing north through the Bering Strait, through the Chukchi and into the Arctic Ocean, Day said. That water flow becomes funneled into several huge north-south subsea channels, including the Barrow Canyon, off northwest Alaska, and a channel that is more central to the Chukchi Sea shelf. The water tends to flow around some major shoals that form high points in the subsea topography.
During the winter, cold Chukchi Sea water sits under the annual cover of sea ice, resulting in two competing water systems: the cold, static, low salinity water from under the ice, and the warmer, higher salinity water trying to flow north from the Bering Sea. The extent to which the Bering Sea water displaces the cold winter water at a particular location appears to depend on how far south that location is; the relative positions of the various subsea channels and shoals; the weather patterns in a particular year; and unexplained variations in the strength of the current from the Bering Sea from one year to another, Day said.
Klondike to south The Klondike area, being relatively far south, tends to be impacted by the Bering Sea water more than the other two prospect areas, he said. And because of the locations of the Statoil leases and the Burger prospect on the south side of a major shoal called the Hanna Shoal, cold water tends to persist in these areas, tending to spin in place rather than be moved out.
Because cold water can carry more carbon dioxide than warm water, the water temperature impacts the ocean water acidity caused by dissolved carbon dioxide, Davis said. During one cruise the research scientists found the acidity of the water at Burger to be high enough to start dissolving aragonite, a form of calcium carbonate found in some fish bones and in a few marine snail shells, he said.
But the weather can have a dramatic effect. 2008 saw very cold weather, with persistent sea ice and with Bering Sea water only being observed in the more southerly Klondike area. 2009, on the other hand, saw warm weather early in the Arctic open water season and the complete melting of ice over the entire Chukchi Sea shelf. Bering Sea water flowed into much of the region, at least near the surface. The weather in 2010 turned out to be somewhat intermediate between those two earlier years, Davis said.
Strong winds can also significantly impact the sea-ice melt, he said.
Variations in life forms The differences in the water columns between the different areas, and between different years in the same areas, in turn impact the mix of life forms in the water column, including the plankton which are dragged around by the water currents. At the same time, marked differences in the nature of the seafloor, with Burger being very muddy and Klondike being clean but rocky, impacts the types of animal found on the seafloor in each area. And that in turn impacts the types of marine mammal and seabird that inhabit an area, seeking food, Day said.
The Burger area, for example, with its muddy seafloor, has a particular abundance of bottom-living creatures which, in turn, attract bearded seals and walruses. Ringed and spotted seals are more abundant in the Klondike area, Davis said.
However, one surprising feature common to all three areas is the absence of large fish. The average length of the fish is just two to three inches, Davis said.
“A big fish out there is less than six inches long,” he said.
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