ANCHORAGE (AP) ― The grounding of a petroleum drilling ship on a remote Alaska island has refueled the debate over oil exploration in the U.S. Arctic Ocean, where critics for years have said the conditions are too harsh and the stakes too high to allow dangerous industrial development.

The drilling sites are 1,600 kilometers from Coast Guard resources, and environmentalists argue offshore drilling in the Arctic’s fragile ecosystem is too risky. So when a Royal Dutch Shell PLC ship went aground on New Year’s Eve on an uninhabited island in the Gulf of Alaska, they pounced ― saying the incident foreshadowed what will happen north of the Bering Strait if drilling is allowed.

For oil giant Shell, which leads the way in drilling in the frontier waters of the U.S Arctic, a spokesman said the grounding will be a learning experience in the company’s yearslong effort to draw oil from beneath the ocean floor, which it maintains it can do safely. Though no wells exist there yet, Shell has invested billions of dollars gearing up for drilling in the Beaufort and the Chukchi seas, off Alaska’s north and northwest coast.

The potential bounty is high: The U.S. Geological Survey estimates 26.6 billion barrels of recoverable oil and 3.68 trillion cubic meters of natural gas exist below Arctic waters.

Environmentalists note the Beaufort and the Chukchi seas are some of the wildest and most remote ecosystems on the planet. They also are among the most fragile, supporting polar bears, the ice seals they feed on, walrus, endangered whales and other marine mammals that Alaska Natives depend on for their subsistence culture.

“The Arctic is just far different than the Gulf of Alaska or even other places on earth,’’ said Marilyn Heiman, U.S. Arctic director for the Pew Environment Group.

Royal Dutch Shell PLC in 2008 spent $2.1 billion on Chukchi Sea leases and estimates it has spent a total of nearly $5 billion on drilling efforts there and in the Beaufort.

Shell Alaska spokesman Curtis Smith said the company has a long, successful history of working offshore in Alaska and is confident it can build another multidecade business in the Arctic.

“Our success here is not by accident,” Smith said. “We know how to work in regions like this. Having said that, when flawless execution does not happen, you learn from it, and we will.’’

The drill ship that operated in the Beaufort Sea, the Kulluk, a circular barge with a funnel-shape hull and no propulsion system, ran ashore Monday on Sitkalidak Island, which is near the larger Kodiak Island in the gulf.

The ship had left Dutch Harbor in the Aleutian Island under tow behind the 100-meter anchor handler Aiviq on Dec. 22. It was making its way to a Pacific Northwest shipyard for maintenance and upgrades when it ran into a vicious storm ― a fairly routine winter event for Alaska waters.

The tow line snapped Dec. 27. Shell vessels and the Coast Guard reattached tow lines at least four times. High wind and seas that approached 15 meters frustrated efforts to control the rig, and it ran aground on a sand and gravel beach.

Shell, the drill ship operators and transit experts, and the Coast Guard are planning the salvage operation.

Calmer weather conditions on Wednesday allowed a team of six salvage experts to be lowered by a helicopter to the Kulluk to conduct a three-hour structural assessment. Information the team gathered will be used for the final salvage plans, officials said late Wednesday in a release. Also taken to the Kulluk was a state-owned emergency towing system for use in the operation.