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Freediving turns the absence of breath into a survival skill and a sport. Ancient Greek sponge divers rode a skandalopetra stone of up to 15 kilograms to depths of about 30 meters and were hauled back by a partner. In the Peloponnesian War, divers slipped under blockades to carry messages and supplies, and at the Siege of Tyre in 332 BC they cut the anchor cables of Alexander the Great's ships. Japan's Ama, traditionally women, have gathered pearls for some 2,000 years, and in the Sulu Archipelago the largest pearls belonged to the Sultan by law, with death for secret sales. Dottie Frazier broke barriers for women in the 1940s and designed rubber suits for Navy divers.

Cold water on the face triggers the mammalian dive reflex, slowing the heart and pulling blood to the brain and heart, and the spleen squeezes out stored red blood cells. The Bajau sea nomads of Southeast Asia have evolved genetically larger spleens. The urge to breathe comes from rising carbon dioxide, not falling oxygen, so hyperventilating before a dive silences the alarm while oxygen keeps dropping, inviting a blackout with no warning. On ascent, expanding lung gas drops oxygen pressure and can pull oxygen from the brain. Competitive apnea under AIDA and CMAS pits athletes against time and depth.

• Stephane Mifsud holds an AIDA static apnea record of 11 minutes 35 seconds.
• In constant weight, Alexey Molchanov reached 133 meters and Alessia Zecchini 123 meters.
• Herbert Nitsch rode a sled to 214 meters in No Limits, a discipline AIDA no longer recognizes.
• Safety divers meet athletes at a third to a quarter of target depth and seal the airway of anyone who blacks out.
• Aquathlon, underwater wrestling from the 1980s USSR, and underwater hockey, invented by Alan Blake in England in 1954, test breath-hold under exertion.

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Peruvian fishermen named El Nino after the Christ child because the coastal water turned warm and the anchovies vanished around Christmas. The El Nino Southern Oscillation, or ENSO, is a coupled conversation between ocean and atmosphere. In the neutral state, trade winds push the sun-warmed surface of the Pacific west until sea level near Indonesia sits about a foot and a half higher than off Peru, while cold, nutrient-rich water wells up along South America. The western Pacific runs 8 to 10 degrees Celsius warmer, driving the Walker circulation, first pieced together by Gilbert Walker, in which moist air rises over Indonesia and sinks dry over the east. Jacob Bjerknes described the self-reinforcing loop in 1969.

A burst of westerly winds, often from the Madden-Julian Oscillation, can break the loop, sending warm water sloshing east. The warm pool caps the upwelling, rain follows it east, and Australia, Indonesia, and India face drought while the eastern Pacific floods. La Nina, once called El Viejo or anti-El Nino, exaggerates the neutral state, and ENSO Modoki, from a Japanese word for similar but different, stalls warm water mid-Pacific. Released heat expands the troposphere and shoves the jet streams through teleconnections, shifting storms far from the Pacific. NOAA declares El Nino when the Nino 3.4 region holds 0.5 degrees Celsius above average for consecutive overlapping seasons.

• The 2023 El Nino cut maize output by up to 70 percent in parts of Zimbabwe, Zambia, and Malawi.
• A 2014 University of Cambridge study found El Nino lowers GDP in Australia, India, and South Africa while the US, Canada, and Mexico often gain.
• Columbia University researchers linked ENSO to 21 percent of civil conflicts since 1950, with civil war risk doubling in El Nino years.
• The strong events of 1997 to 1998 and 2015 to 2016 killed up to 99 percent of live coral on some equatorial reefs.
• The Southern Oscillation Index compares air pressure at Tahiti and Darwin, Australia.

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In 2012 teenager Boyan Slat took a TED stage with a sketch of a passive barrier that would let ocean currents sweep plastic into its arms, delighting the public and drawing eye rolls from oceanographers. He founded The Ocean Cleanup in 2013 and raised 2 million dollars through crowdfunding in 2014 for a 100-kilometer barrier moored to the seabed with a conveyor belt. Testing ran through 273 scale models and six prototypes, and a North Sea test in 2016 shredded a conventional oil boom. Slat scaled down to a free-floating, 2-kilometer design made of flexible high-density polyethylene pipe.

System 001 reached the Great Pacific Garbage Patch in 2018 but drifted at the same speed as the plastic, which washed back out, and an 18-meter section of pipe snapped off, forcing a tow back to Hawaii. System 001B in 2019 added a deep parachute anchor to slow the barrier and finally held trash. Passive drift was still too slow, so System 002, nicknamed Jenny, was towed by two crewed ships in 2021, followed by the 2.25-kilometer System 03 in 2023. A 30-ship Mega Expedition in 2015 and a 2016 C-130 flight with LIDAR helped show that 86 percent of ocean plastic comes from rivers, leading to the solar-powered Interceptor barge in 2019.

• System 03 uses 15-millimeter mesh, cameras, acoustic deterrents, and a Marine Animal Safety Hatch to free trapped animals.
• Flash floods in Jakarta broke an early Interceptor barrier.
• After a 2024 storm, a fortified barrier on Guatemala's Las Vacas River caught 1.4 million kilograms of waste in hours.
• Scientists including Miriam Goldstein argued near-shore collection is cheaper, and ecologists warn the nets skim neuston such as blue buttons.
• Funding came from 200-euro sunglasses, partners Kia and MrBeast, and a 121 million dollar Audacious Project grant.

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Scrimshaw began on 19th century whaling ships, where men endured months of empty horizon between hunts. Carved from sperm whale teeth, bone, baleen, and sometimes walrus tusks, it started in the late 18th century as practical tools and grew into detailed art made by scrimshanders. The word's origin is unknown, and its first written appearance is an 1826 entry in the logbook of the brig By Chance. Ship's wood was a costly, counted resource, while whale teeth and bone were free waste after the oil was rendered. The spark came in 1815, when US Navy Captain David Porter's published journal exposed where whale teeth came from and how plentiful they were, and their market value collapsed so ordinary sailors could keep them.

The earliest authenticated pictorial sperm whale scrimshaw dates to 1817, inscribed as a tooth from a whale taken near the Galapagos that yielded 100 barrels of oil. Sailors carved with sail needles and scrap iron and rubbed lamp black, soot from the try-works, or tobacco juice into the lines, often copying illustrations from books and newspapers. Many pieces survived because they were stored in barrels of whale oil. Today collectors who fill teeth with baby oil and car wax clash with conservators, who warn that oils oxidize and yellow the ivory and instead control light, humidity, and temperature.

• Sailors made jagging wheels for crimping pie crusts, corset busks, and children's toys for the women and families at home.
• Herman Melville described whaling sketches carved on sperm whale teeth and busks cut from right whale bone in Moby-Dick.
• Scrimshaw falls under the Marine Mammal Protection Act of 1972, the Endangered Species Act, and CITES.
• Legal marine ivory scrimshaw must predate 1973, and elephant ivory pieces must predate the 1989 ban.
• Modern scrimshanders work in fossil mammoth ivory, Alaskan walrus tusk carved by Indigenous Alaskans, micarta, and polychrome inks.

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When Spanish galleons entered the Pacific, a priest aboard called them sluggish lead weights beside local boats that flew across the water like birds. The outrigger solved the conflict between speed and stability: a long, narrow hull cuts form drag, and a float on booms supplies the balance a wide hull would. It likely emerged around 1500 BCE among Austronesian-speaking peoples of island Southeast Asia, driven by the crab claw sail, a V-shaped rig whose spiraling vortices generate lift much like a delta wing. Outriggers carried the Austronesian expansion east to Polynesia, Micronesia, Hawaii, and Easter Island, and west across the Indian Ocean to Madagascar.

Designs evolved from lashed logs to asymmetric double canoes, single outriggers, and finally double outriggers, which arose in Southeast Asia after Pacific voyagers had already left. To keep a single float on the windward side, Pacific sailors shunted, walking the sail's base to the other end so the stern became the bow. Linguists trace the migration through shared words: banca and waka for boat, ama for the float, iako for the booms. In the Philippines, double outriggers grew into karakoa warships holding hundreds of warriors, and the barangay, the smallest political unit, is named for the balangay boats of the first settlers.

• Sri Lanka's oruwa and Tanzania's ngalawa show non-Austronesian cultures adopting the outrigger.
• Outrigger canoe racing is Hawaii's official state sport, raced in six-person OC6 and single-person OC1 hulls of carbon fiber.
• OC6 paddlers switch sides on the caller's command to counter the ama's drag, and the steersman in seat six prevents a huli.
• The Molokai Hoe is a 43-mile race across the Kaiwi Channel, the Channel of Bones.
• Nine-person crews make water changes, dropping relief paddlers into the sea to climb aboard a moving canoe.

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In 1878 engineer Henry Fleuss built the first commercially practical closed-circuit rebreather: a rubber mask, a breathing bag, pure oxygen from a copper cylinder, and rope yarn soaked in caustic potash to scrub carbon dioxide. It gave up to three hours underwater with no bubbles, so British, Italian, and German frogmen adopted the technology in World War II. In the US, Major Christian J. Lambertsen built a free-swimming oxygen rebreather in 1939 and in 1952 patented an improved version under the name SCUBA. Pure oxygen, though, becomes a neurotoxin under pressure and causes sudden convulsions. In 1942 Jacques Cousteau and Emile Gagnan created the open-circuit Aqua-Lung with a demand valve, and in 1952 Ted Eldred's single-hose design set the pattern divers still use.

Water rewrites the senses. A mask's air space lets the cornea focus but makes objects look about 34 percent bigger and 25 percent closer, and red light vanishes within 15 to 20 feet, so blood looks green at 100 feet. Boyle's law makes holding your breath on ascent deadly, since expanding air can rupture the lungs and cause an arterial gas embolism. Neutral buoyancy is a positive feedback loop as a wetsuit and BCD compress with depth, so skilled divers fine-tune it with their lungs. Henry's law drives nitrogen into tissue, causing the bends on fast ascents, and deep divers answer with blended gases.

• Scuba is an acronym for self-contained underwater breathing apparatus.
• Nitrox at 32 or 36 percent oxygen extends bottom time but shrinks maximum depth.
• Trimix and heliox replace nitrogen with helium to avoid narcosis on deep technical dives.
• Technical divers may carry four to six cylinders and switch gases as depth changes.
• Modern closed-circuit rebreathers use computers and oxygen sensors to inject gas in real time.

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In 1554 French physician Guillaume Rondelet labeled the great white Lamia, after a child-eating monster of Greek myth, centuries before Peter Benchley's 1974 Jaws. The real animal is the sole living species of Carcharodon, a mackerel shark with a strikingly stable genome, reliably measured to about 6 meters and 2,500 kilograms, with females far larger than males. It is partially warm-blooded, warming its brain, eyes, and swimming muscles up to 25 degrees Fahrenheit above the water, and an oily liver of over a quarter of its body weight replaces a swim bladder and stores energy. One tagged shark swam from South Africa to northwestern Australia and back, 20,000 kilometers in under nine months, and California sharks gather at the White Shark Cafe midway to Hawaii.

Hunting is tactical. Off South Africa, sharks rise from about 20 meters to strike Cape fur seals hard enough to breach 3 meters into the air, and they target sea lions behind the torso to avoid their fore flippers. Rather than wrestle a 4,000-pound elephant seal, they bite and wait. Rivals settle disputes over carcasses with tail-slapping splash fights, and persistence can beat size. Pups feed on uterine milk and unfertilized eggs through a 12-month gestation, litters run two to ten, and a 2015 study found males mature at about 26 years and females at 33.

• A 2023 drone video off Carpinteria, California captured a pale newborn white shark shedding an embryonic skin layer.
• Great whites abandoned a major South African aggregation site when liver-hunting orcas moved in.
• A 2023 paper recast bites on surfers as exploratory, and a 2025 drone study saw no aggression during close encounters.
• Mexico banned white shark tourism at Guadalupe Island in 2023 after cage-diving safety violations.
• Critically endangered in the Mediterranean, they have had only four confirmed sightings there in a decade.

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Kelp is not a plant. It is a brown macroalga in the kingdom Protista with no roots and no vascular plumbing: the holdfast only anchors it, the flexible stipe gives it structure, and each frond absorbs nutrients straight from the water while gas-filled pneumatocysts lift it toward the light. Fed by cold upwelling water, giant kelp grows 30 to 60 centimeters a day. Kelp forests and coral reefs cover one tenth of one percent of Earth's surface yet account for almost a full percent of global primary productivity. As a passive ecosystem engineer, kelp builds a layered city: a canopy of nudibranchs, an understory sheltering juvenile rockfish and perch, and holdfasts packed with crabs and brittle stars, while winter storms tear light gaps that let the lower layers grow.

Balance depends on predators. When fur hunters nearly wiped out Alaska's sea otters, sea urchins exploded, chewed through holdfasts, and left urchin barrens. Urchins stay passive while drift kelp keeps them fed and march only when it runs out, and in Southern California spiny lobsters and California sheephead stand in for otters. The Kelp Highway hypothesis argues that early people reached the Americas by boat along an unbroken kelp coast from Japan to Chile that offered consistent food and calm water. In the 2010s, marine heat waves known as the blob stratified the Pacific, starved the kelp, and wiped out 95 percent of Northern California's kelp ecosystems.

• A predictive model led a submarine team to deep tropical kelp forests near the Galapagos, once thought impossible.
• Kelp-derived alginic acid forms the gel that keeps toothpaste from separating.
• Macroalgae lock away roughly 200 million tons of carbon dioxide a year as blue carbon on the deep seafloor.
• Sea star wasting disease wiped out sunflower sea stars, the urchin hunters of Northern California.
• Divers now smash urchins, and Bodega Marine Laboratory, Humboldt State, and Ocean Rainforest near Santa Barbara grow kelp to replant.

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Dreadnought means fear nothing, and following the name through the Royal Navy traces 500 years of naval technology. The first was a 40-gun ship of 1553; a 41-gun successor launched in 1573 fought the Spanish Armada in 1588 and at Cadiz in 1596, and was rebuilt in 1592 and 1614. Oak was so scarce that ships were stripped to the keel and rebuilt around their sound timbers, so sailors could fight aboard the same hull for decades. A 52-gun Dreadnought fought at the Four Days Battle in 1666 and the brutal melee at Solebay in 1672, and 60-gun versions followed in 1691, 1723, and 1742.

The 98-gun second-rate Dreadnought of 1801 fought at Trafalgar in 1805 and became a hospital ship in 1827, as did a later Dreadnought, the former Caledonia, in 1856. In 1906 HMS Dreadnought made every battleship afloat obsolete: steam turbines gave her a sustained 21 knots, and ten 12-inch guns of one caliber let spotters read a single salvo's splashes and correct their aim. Every later battleship was a dreadnought and everything before it a pre-dreadnought, triggering the arms race that preceded World War I, yet she was sold for breaking up in 1921. In the atomic age the name went to Britain's first nuclear submarine, and fearing nothing came to mean staying unseen.

• During the 1782 siege of Gibraltar, a Dreadnought gunboat carried 21 men from the Brilliant and a single 18-pounder.
• A small Dreadnought gunboat captured the schooners Polly and Cyrus in North American waters in 1813.
• Before 1906, mixed batteries threw so many splashes that spotters could not tell which came from the main guns.
• Submarine S101 Dreadnought served from 1960 until it was decommissioned in 1980.
• Britain's new ballistic missile submarines carry the Dreadnought class name to sustain continuous at-sea deterrence.

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Roud Folk Song Index number 322, the shanty about what to do with a very inebriated sailor early in the morning, was built as a tool, not a song. Its first published appearance is an 1839 account of a whaling voyage out of New London, Connecticut, and sailors recalled using it while tacking ships on Maine's Penobscot River in the 1820s. It shares its chord progression and structure with the Irish song Oro Se do Bheatha 'Bhaile, and its Dorian mode gives a weathered minor edge to a driving tempo. It was a stamp-and-go shanty: 30 or 40 men gripped a line and marched down the deck in step, so every boot struck together and the load never faltered.

When packet ships and clippers cut crew sizes, walkaway hauling died and the song adapted to hand-over-hand hauling, capstans, and even dragging a scraper under an iron hull, as an 1870s sailor told folklorist Alan Lomax in 1939. An English sailor of the 1860s recalled only two working verses, a drunken sailor and a drunken soldier, and the catalog of punishments grew later. By the early 1900s it was sung at Eton College and London's Savage Club, then absorbed by Percy Grainger in 1924, Malcolm Arnold in a 1943 woodwind quintet, the Robert Shaw Chorale, and a Fred Kaan Easter hymn. Fiddler John Baltzell recorded it as a dance medley in 1923.

• Pere Ubu turned it into the post-punk track Caligari's Mirror in 1978.
• An Irish pop group took a disco version into the Irish top 20 in 1981.
• It turns up in Ringo Starr's You're Sixteen, The Truman Show, SpongeBob SquarePants, and the 2019 film Fisherman's Friends.
• Parody verses have targeted the Exxon Valdez spill, the Tailhook scandal, and the ship that blocked the Suez Canal.
• In 2026 an Iranian Lego-themed video used it to ask what should be done with Pete Hegseth.