Seas, oceans, and coastal waters

Antarctic sea ice

Antarctic sea ice is frozen seawater around Antarctica, measured by satellite since November 1978 as extent (ocean at least 15% ice covered). It rose slightly until 2014, then collapsed after 2016 to record lows in 2023–2025.

Antarctic Sound

Antarctic Sound, nicknamed Iceberg Alley for its giant tabular icebergs, is a 30-mile strait between Joinville Island and the Antarctic Peninsula, first navigated in 1902.

Antongil Bay

Antongil Bay (French: Baie d'Antongil) is the largest bay in Madagascar, a 2,800 km² embayment on the northeastern coast sheltered by the Masoala Peninsula and a major humpback whale breeding ground.

Arabian Basin

Arabian Basin: an undersea basin of the Arabian Sea near 12°N, 65°E in the GEBCO gazetteer, and the asymmetric Upper Precambrian-Phanerozoic sedimentary basin on the Arabian Plate, about 8 km deep.

Arabian Sea

The Arabian Sea is the northwestern Indian Ocean between India, Arabia, and Iran-Pakistan, linked to the Red Sea and Persian Gulf, driven by reversing monsoon winds, and hosting the world's thickest oxygen minimum zone.

Arafura Sea

The Arafura Sea is a shallow tropical sea lying between northern Australia and southeastern New Guinea, bounded by the Timor Sea, Torres Strait, and Gulf of Carpentaria.

Arctic Archipelago

The Arctic Archipelago, also known as the Canadian Arctic Archipelago, is a group of roughly 36,500 islands off northern Canada containing Baffin Island and the Northwest Passage.

Arctic Basin

The Arctic Basin is the deep central Arctic Ocean, comprising the Eurasian and Amerasian Basins (Nansen, Amundsen, Canada, Makarov sub-basins) separated by the Lomonosov Ridge, 3,800-4,500 m deep, with Atlantic and Pacific water inflows and rapid climate change.

Arctic bays and inlets

Arctic bays and inlets are the coastal indentations of the Arctic Ocean, including shallow estuarine gulfs like the Ob Gulf, Yenisey Gulf, and Kolyma Gulf.

Arctic convoys of World War II

The Arctic convoys of World War II, also called the Murmansk Run, carried Lend-Lease supplies from Britain and Iceland to Murmansk and Arkhangelsk between 1941 and 1945.

Arctic dipole anomaly

The Arctic dipole anomaly, also called the Arctic Dipole, is a pattern of sea-level pressure variability in the Arctic that drives sea ice toward the Atlantic.

Arctic Ocean

The Arctic Ocean is the pole-centered, land-enclosed ocean, about 4,000 m deep and divided by the Lomonosov Ridge, covered by thin sea ice that is rapidly thinning and shrinking, with gateways at Fram Strait, Barents Sea Opening, and Bering Strait.

Arctic Ocean circulation

Arctic Ocean circulation is the system of currents and water-mass transformations moving heat and freshwater between the North Atlantic and the ice-covered Arctic basin, driven by winds, river freshwater, and warm Atlantic inflow.

Arctic sea ice

Arctic sea ice is the frozen seawater covering most of the Arctic Ocean, ranging from seasonal sheets to ridged multi-year floes that can circulate for seven to ten years.

Argentine Basin

Argentine Basin: deep abyssal basin of the western South Atlantic off Argentina and Uruguay, south of the Rio Grande Rise. Formed ~138 Ma during Gondwana breakup; over 4000 m deep; hosts the Zapiola Drift and exports Antarctic Bottom Water via the Vema Channel.

Argentine Sea

The Argentine Sea is the shallow marginal sea over Argentina's continental shelf in the southwestern Atlantic, stretching about 2,400 km from the Río de la Plata toward Cape Horn.

Arrugado

Arrugado (ARRU) is a GeoNames undersea feature code for an area of subdued corrugations off Baja California; also the Spanish adjective for wrinkled. Only 2 toponyms use the code.

Ascension Island

Ascension Island, in the UK Overseas Territory of St Helena, Ascension and Tristan da Cunha, is a volcanic South Atlantic island discovered in 1501, garrisoned by Britain in 1815 as HMS Ascension, with no permanent population and a 2019 EEZ-wide marine protected area.

Athos / Ormos Vatopediou

Ormos Vatopediou (Vatopedi Bay) is the broad bay on the northeast coast of the Athos peninsula, Greece, named for Vatopedi Monastery and its harbour Arsanas Vatopedi; boat-only access, Diamonitirion permit, male pilgrims only.

Oct 15, 2026

Atlantic meridional mode

The Atlantic meridional mode (AMM) is the dominant mode of coupled ocean-atmosphere variability in the tropical Atlantic, an anomalous north-south sea surface temperature gradient across the equator.

Atlantic meridional overturning circulation

Atlantic meridional overturning circulation (AMOC): basin-scale Atlantic current system moving ~17 Sv northward and ~1.2 PW of heat, driven by Labrador and Nordic Seas deep-water formation; monitored by RAPID since 2004 and projected to weaken 18–43% by 2100.

Oct 15, 2026

Atlantic multidecadal oscillation

The Atlantic multidecadal oscillation (AMO), or Atlantic multidecadal variability (AMV), is a fluctuation of North Atlantic sea surface temperature on a 60–80 year time scale, linked to rainfall and hurricanes.

Oct 15, 2026

Atlantic Niño

The Atlantic Niño is an episodic warming of the eastern equatorial Atlantic Ocean, a smaller, shorter counterpart of Pacific El Niño that peaks in boreal summer and affects Sahel rainfall.

Atlantic Northwest Africa

Atlantic Northwest Africa is FEOW freshwater ecoregion 501, a Palearctic temperate coastal rivers unit along Morocco, Western Sahara, Mauritania, Algeria, and Spain, with Iberian faunal elements, Africa's only native salmonid, and high endemism.

Atlantic Ocean

The Atlantic Ocean is Earth's second largest ocean basin, about 106,460,000 km² (20% of Earth's surface), between the Americas and Europe-Africa, home of the AMOC and Gulf Stream.

Atlantic slave trade

Atlantic slave trade (transatlantic slave trade): forced transport of 10-12 million enslaved Africans to the Americas, 16th-19th centuries, via the triangular trade and Middle Passage; about 2 million died at sea; documented in the SlaveVoyages database.