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Amu Darya (آمودریا)
Amu Darya (آمودریا), the ancient Oxus, is a ~2,500 km Central Asian river flowing from the Pamirs to the Aral Sea, shared by five states and contested by Afghanistan's Qosh Tepa Canal.
Amundsen Basin
Amundsen Basin: deep Arctic Ocean basin (~4,400 m) of the Eurasian Basin, between the Lomonosov and Gakkel ridges, named for Roald Amundsen; fresher Transpolar Drift surface water, NP-28 channel, MOSAiC drift start site.
Amundsen Gulf
Amundsen Gulf: Arctic embayment, 400 km long, between Banks Island and Canada's mainland coast, westernmost Northwest Passage entrance; named for Roald Amundsen, entered 1905; Cape Bathurst polynya.
Amundsen Sea
Amundsen Sea (Amundsenhavet), a marginal sea of the Southern Ocean off Marie Byrd Land, West Antarctica, named in 1929 for Roald Amundsen; warm Circumpolar Deep Water melts Thwaites and Pine Island ice shelves, driving Antarctic sea-level rise.
Amur (river, China)
The Amur (Heilong Jiang) is a 2,824 km Northeast Asian river formed by the Argun and Shilka confluence, flowing to the Sea of Okhotsk and forming the Russia-China border for 1,880 km, with a basin shared by Russia, China, and Mongolia.
Anabranch
Anabranch: a stream channel that leaves a river and rejoins it downstream, from "anastomotic branch" (1834). Anabranching rivers have stable vegetated islands, unlike braided rivers, and cover 51% of global alluvial channel length.
Anacostia River
The Anacostia River is a 9-mile tidal Potomac tributary in Washington, D.C. and Maryland, once heavily polluted by industry and sewage overflows, now improving through DC Water's tunnel project and sediment cleanup.
Anadyr
The Anadyr is a river in the Chukotka Autonomous Okrug of northeastern Siberia, Russia, that is the second largest to empty into the Bering Sea after the Yukon.
Ancylus Lake
Ancylus Lake was a freshwater lake stage in the postglacial Baltic Sea basin, following the Yoldia Sea and preceding the Littorina Sea, lasting roughly from 8800 to 6700 BC.
Andaman Basin
Andaman Basin: active back-arc basin in the NE Indian Ocean behind the Sunda subduction zone, extending ~1,250 km from Myanmar to Sumatra; spreading began ~4 Ma; Indian Category II frontier hydrocarbon basin with 371 MMTOE estimated resources.
Andaman Islands
The Andaman Islands is a large archipelago located in the Bay of Bengal, forming the union territory of India that encompasses the Nicobar Islands.
Andaman Sea
Andaman Sea, or Burma Sea, a ~790,000 km2 marginal sea of the eastern Indian Ocean between the Andaman-Nicobar Islands and Myanmar and Thailand, defined by IHO limits, monsoon-driven circulation, coral reefs, mangroves, seagrass, and the 2004 earthquake zone.
Anderson (landform)
Anderson River, Northwest Territories (Inuvialuktun Kuuk, Dene Beghula), an Arctic-draining river forming a delta and migratory bird sanctuary near Tuktoyaktuk; distinct from the smaller Anderson River tributary of the Fraser River in British Columbia.
Andvord Bay
Andvord Bay: glaciomarine fjord on the Danco Coast, Western Antarctic Peninsula, in Gerlache Strait; ~20 km long, five tidewater glaciers, deep >400 m basins; FjordEco study site 2015-2017.
Ang Laren
Ang Laren, also called Ngangla Ringco, is a large brackish salt lake in Zhongba County, Tibet, China, lying at about 4,700 m on the western Tibetan Plateau.
Angara
The Angara (Ангара́) is a river in Irkutsk Oblast and Krasnoyarsk Krai, Russia, the only outflow of Lake Baikal and the largest tributary of the Yenisei, dammed for hydropower.
Angel Falls
Angel Falls (Salto Ángel, Kerepakupai Merú), Venezuela's 979 m waterfall on Auyán-tepui in Canaima National Park, is the world's tallest, with an 807 m single drop, named for aviator Jimmie Angel.
Angola Basin
Angola Basin (Ангольская Котловина), also Southeastern Atlantic Basin or Buchanan Deep: undersea basin of the eastern South Atlantic off Angola and Namibia, bounded by the Walvis Ridge, with Aptian salt, DSDP Leg 75 black shales, and a three-layer deep circulation.
Antarctic Circumpolar Current
The Antarctic Circumpolar Current, also known as the West Wind Drift, is the world's largest ocean current, flowing eastward around Antarctica and connecting the Atlantic, Pacific, and Indian Oceans.
Antarctic continental shelf
The Antarctic continental shelf is the deep (average 450 m, over 1,000 m in places), wide (~125 km) seabed around Antarctica, shaped by glacial overdeepening, source of Antarctic Bottom Water, and conduit for warm Circumpolar Deep Water toward ice shelves.
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.
Anzali Lagoon (تالاب انزلی)
Anzali Lagoon (Mordāb-e Anzalī, تالاب انزلی) is a Caspian coastal freshwater lagoon in Gilan, Iran, a 1975 Ramsar site on the Montreux Record, shrinking from ~258 km2 (1930) toward projected seasonal desiccation by 2058.
Apalachicola River
Apalachicola River: Florida's largest river, flowing over 100 miles from Jim Woodruff Dam at Lake Seminole (Chattahoochee-Flint confluence) to Apalachicola Bay; ACF basin water wars, dredging history, and oyster fishery collapse distinguish it.
Aponus
Aponus (Aponi fons) was the Venetic god of the Euganean hot springs near Padua, later identified with Apollo; his name survives in Abano Terme, and his sacred spring, the fons Aponi, drew healing pilgrims and Tiberius's golden dice.
Apure (landform)
Apure (Río Apure) is a whitewater river in western Venezuela, known for having the largest basin of any Orinoco tributary. It drains the Venezuelan Llanos and the Andes.
Aquae Albulae (Italy)
Aquae Albulae (Acque Albule): sulphurous hypothermal springs near Tivoli, Rome, used since Roman times by Augustus and Hadrian, now the Terme di Roma spa with SSN-accredited cures.
Aquae Sinuessanae
Aquae Sinuessanae: sulphurous Roman thermal springs and baths of the colony of Sinuessa near Mondragone, Campania; cited by Livy, Strabo, and Pliny, visited by Narcissus, and still in therapeutic use today.
Aquatic plant
Aquatic plants (hydrophytes, macrophytes) are plants adapted to water, in emergent, floating-leaved, free-floating, and submerged forms. Derived from terrestrial ancestors, they use bicarbonate-based carbon uptake, provide habitat and water-quality benefits, and are managed as invasive nuisances.