What was the notable accomplishment of the Scottish brothers Jamie, Ewan, and Lachlan Maclean?

The notable accomplishment of the Scottish brothers Jamie, Ewan, and Lachlan Maclean is the fastest unsupported row across the Pacific. This achievement is significant for several reasons: it highlights their extraordinary endurance and strength while promoting awareness and interest in adventurous and challenging expeditions. Unsupported means they completed the journey without the assistance of support boats, relying solely on their skills and supplies, which adds to the difficulty and prestige of the accomplishment. Their record showcases not only their physical capabilities but also their planning and teamwork, crucial elements in successfully navigating such a vast and challenging body of water.

The other options represent different types of extreme sports challenges, each with its unique demands and circumstances, but the Maclean brothers are specifically recognized for their record in rowing across the Pacific, making this the correct choice.