Chukchi Sea depths hold vast environmental complexities

Research finds gray surface shields hugely varied environment.

Petroleum NewsApril 23, 2012 

The barrier island on which the village of Kivalina is located stretches along the edge of the Chukchi Sea as seen from a U.S. Coast Guard C-130 in 2008.

BOB HALLINEN / DAILY NEWS ARCHIVE 2008

In summer, the gray surface of Alaska's Chukchi Sea looks monotonously uniform, except for an occasional scattering of small ice floes, which are the remnants of the winter ice pack.

Hidden beneath the surface, however, is a remarkably varied environment according to industry-funded researchers working in areas of planned oil and gas exploratory drilling by Shell, Conoco Phillips and Statoil.

"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 recently.

Day was referring to differences in the underwater environment between the areas around the Conoco Phillips Devil's Paw prospect, the Burger prospect, where Shell plans to drill, and around Statoil's Chukchi Sea leases. Day referred to the Conoco Phillips area as the "Klondike."

The Klondike lies about 120 miles west of the Chukchi coastal village of Wainwright. The two other areas are farther north: Statoil is about 100 miles northwest of Wainwright, while Burger lies to the south of Statoil and about 60 miles northeast of Klondike.

The objective of the research is to obtain baseline environmental data, get information needed for permitting and National Environmental Policy Act assessments and provide information needed to plan future industrial operations, Day said. The findings presented to the Open Water Meeting covered research cruises conducted between July and October in 2008, 2009 and 2010, with research in the Statoil area starting in 2010. The research continued in 2011 with an expanded study area, Day said.

During the cruises, scientists used a computer system to merge data from environmental sampling with continuous records of vessel navigation and other data, including weather. Data were also collected from subsea acoustic recorders.

Day attributed the environmental differences among the three areas in part to a complex interaction between ocean currents, seafloor topography and year-to-year variations in weather.

At a simplistic level, the Chukchi Sea, having a surface slightly higher at its southern extremity than in the north, can be viewed as a northward tilting table, with relatively warm Bering Sea water flowing north through the Bering Strait, through the Chukchi and into the Arctic Ocean, Day said.

The water flow is 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 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 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.

The Klondike area, being relatively far south, tends to be affected by the Bering Sea water more than the other two prospect areas, he said. 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, spinning in place rather than moving out.

Because cold water can carry more carbon dioxide than warm water, water temperature affects the acidity caused by carbon dioxide dissolving in the water, Day said. During one cruise, scientists found the acidity of the water at Burger to be high enough to dissolve aragonite, a form of calcium carbonate found in some fish bones and 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 Bering Sea water only observed in the more southerly Klondike area. 2009, on the other hand, saw warm weather early in the 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 the two earlier years, Day said.

Strong winds can also significantly impact the sea-ice melt, he said.

The differences in the water columns between the different areas, and between different years in the same areas, in turn affect the mix of life forms, including plankton carried by water currents. At the same time, marked differences in the nature of the seafloor affects the types of animals on the seafloor.

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