A fourth government probe is under way into Royal Dutch Shell's mishap-prone 2012 Alaska drilling season, this time for possible violations of international marine environmental rules, a U.S. Coast Guard official said on Wednesday, March 27, according to Reuters.

The Coast Guard has asked federal prosecutors to consider taking action on possible violations of the International Convention for the Prevention of Pollution from Ships (MARPOL) committed in the operations of Shell's Kulluk drillship, said Rear Admiral Thomas Ostebo, head of the Coast Guard in Alaska.

Shell, which had planned to drill up to five wells offshore Alaska in 2012 and a similar number this year, has previously said it will pause its Alaska operations to regroup due to complications faced in the harsh northern environment, but it expects to resume drilling next year.

Ostebo said he had commissioned one investigation already launched into the December 31 grounding of the Kulluk and that the Coast Guard has forwarded findings of safety and environmental violations on the Noble Discoverer, Shell's other Alaska drillship, to U.S. prosecutors for possible enforcement action.

Shell's 2012 drill season had earlier been the subject of a 60-day review by the U.S. Department of Interior that concluded Shell was ill-prepared for Alaska's marine rigors, had not adequately overseen contractors and had committed other lapses.

With two rigs out of service, Shell last month said it will pause its Alaska drilling operations in 2013.

It still expects to resume drilling in 2014, and may be joined in the Chukchi Sea by ConocoPhillips, which holds extensive leases in the basin.

Regulators required Shell to have a special barge with an oil-containment dome to respond to any blowouts. Shell was unable to get the dome and barge working right for 2012, so it was not allowed to drill into hydrocarbon-bearing zones.