Arctic ecosystems

Considerable development of offshore oil reserves in the Beaufort Sea threatens arctic marine ecosystems with oil con- tamination, Offshore well and pipeline structures must with- stand enormous forces from ice, and ship transport of oil is highly hazardous. Failures of buried pipelines would first contaminate benthic ecosystems. Oil well blowouts will pollute open water as well as over-ice and Under-ice ecosystems.

Prudhoe crude oil was found to degrade very slowly in most of the arctic ecosystems. During the first month following a spill on water, the oil lost all light hydrocarbons; but during the following month almost no further changes in composition occurred. Essentially no biodégradation of over-ice oil occur- red during the winter and only slow changes occurred during the summer, Under-ice oil degraded at even slower rates. More light hydrocarbons remained in the under-ice spills after three weeks than in the over-ice spills. The ice cover clearly limits evaporative losses, and dissolution probably accounts for the slow loss of light hydrocarbons. Prudhoe Bay oil had conside- rable impact on a variety of invertebrates in the benthos. The oil was toxic to some amphipods, but the isopods were as abun­dant in oil-contaminated sediment as in uncontaminated sedi­ment. Some polyehaete species seemed to be attracted to oil whereas others were killed by the oil. Some invertebrates deco- lonized contaminated sediments within a couple of months? however, the community composition was markedly different from what it was prior to contaminations

Offshore oil ,

Potential oil deposits lie off the coastlines of all conti­nents. Drilling is going on in many of these continental shelf areas at the present time. Several thousand oil and gas wells have operated in the Gulf of Mexico nearshore waters for ma­ny years.

Drilling at sea may be done from rigs or ships. Rigs may be mounted on the sea bottom or may be floating, as is the semi-

submersible rig. Rigs mounted on the seabed are limited to depths of less than 100 m. The semisubmersible rig is used in deep water. Drill ships, which have a hole through the hull for the drilling apparatus, have mobility but must be moored by cables and anchors when drilling. They have drilled wells in water depths of 800 m and, in at least one instance, of 2000 m.

In 1968, scientists aboard the Glomar Challenger, a specially designed ship for scientific exploration in the Deep Sea Drilling Project sponsored by the National Science Foundation, found oil and gas beneath 12,000 feet of water in the middle of the Gulf of Mexico. It was one of the first pieces of evidence that there is oil at great depths in the ocean. Now the oil companies are collaborating with the National Science Foundation in a 10-year, $ 700-million ocean margin drilling program at depths up to 13,000 feet. The U.S. Geological Survey estimates that the United States has between 12.5 and 38 million barrels of undiscovered, but recoverable oil offshore along the edge of the continental shelf.

When exploratory drilling operations discover petroleum, permanent platforms are installed. These platforms are huge structures from which 30 or more development wells may be drilled, many at an angle. The platforms contain within their superstructures living quarters, storage areas, and operating space. Most oil platforms must be guyed and moored in position. Each anchor must weigh 20 tons. Offshore structures in the Gulf of Mexico are built to endure 140-mph winds and 70-foot waves; in the arctic they must withstand the enormous pressure of sea ice as well as high winds and waves. In Labrador, drilling contractors have had to tow icebergs away from rigs. Wells in the ocean have subsurface safety valves installed in the well hole beneath the ocean floor. These valves are designed to close automatically and shut off the flow of oil or gas in the event of a blowout. Despite precautions, some blowouts do occur. When this happens, an auxiliary well is drilled at an angle until it comes close to the bottom of the

blowout well. Mud is then pumped under high pressure down the auxiliary well until it gets caught up in the uncontrolled well, where it stops the flow. Often blowout wells will stop flowing of their own accord.

During the years 1971 through 1978, there were 7553 new wells drilled on the U.S. outer continental shelf, and 30 blowouts occurred. The total oil lost from these blowouts was less than 300 tons. In June 1979 the Ixtoc-I blowout occurred in the Bay of Campeche, in offshore Mexico, during the drilling of an exploratory well; 450,000 tons of oil were re- leased into the sea before the blowout was capped in March 1980.