Bermuda is a group of low-forming volcanoes located in the Atlantic Ocean, near the western edge of the Sargasso Sea, roughly 578 nautical miles (1,070 km (665 mi)) east-southeast of Cape Hatteras on the Outer Banks of North Carolina and about 594 nautical miles (1,100 km (684 mi)) southeast of Martha's Vineyard of Massachusetts. Bermuda is on the western fringe of what Sea?