The northernmost part of the Antarctic mainland, the Antarctic Peninsula extends 1,300 kilometers (800 miles) from Cape Adams on the Weddell Sea. The entire peninsula is made up of a string of bedrock islands covered beneath a permanent sheet of ice; each of these islands is separated by channels. Because it has the mildest climate in Antarctica, the peninsula is dotted with research stations from many different nations, including Argentina, Chile and the United Kingdom, each having overlapping and competing claims to sovereignty. Although naval historians dispute the peninsula's discovery by Europeans, most concur that it was first sighted in 1820 by a Russian Imperial Navy expedition led by Fabian Gottlieb von Bellingshausen, even though it was presumed to be an ice field, not a landmass. Only days later, a British expedition headed by Edward Bransfield and William Smith became the first to actually chart the peninsula.