The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctica.
The Antarctic Peninsula is part of the larger peninsula of West Antarctica, protruding 1,300 km (810 miles) from a line between Cape Adams (Weddell Sea) and a point on the mainland south of the Eklund Islands. Beneath the ice sheet that covers it, the Antarctic Peninsula consists of a string of bedrock islands; these are separated by deep channels whose bottoms lie at depths considerably below current sea level. They are joined by a grounded ice sheet. Tierra del Fuego, the southernmost tip of South America, is about 1,000 km (620 miles) away across the Drake Passage.
The marine ecosystem around the western continental shelf of the Antarctic Peninsula (WAP) has been subjected to rapid physical climate change. Over the past 50 years, the warm, moist maritime climate of the northern WAP has shifted south. This climatic change increasingly displaces the once dominant cold, dry continental Antarctic climate. This regional warming has caused multi-level responses in the marine ecosystem such as increased heat transport, decreased sea ice extent and duration, local declines in ice-dependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition as well as changes in krill recruitment, abundance and availability to predators.
The Antarctic Peninsula is currently dotted with numerous research stations, and nations have made multiple claims of sovereignty. The peninsula is part of disputed and overlapping claims by Argentina, Chile, and the United Kingdom. None of these claims have international recognition and, under the Antarctic Treaty System, the respective countries do not attempt to enforce their claims. The British claim, however, is recognised by Australia, France, New Zealand, and Norway. Argentina has the most bases and personnel stationed on the peninsula.