142 Fun Facts About Ocean

What percentage of Earth's surface is covered by oceans?

Oceans cover approximately 71% of Earth's surface, making our planet predominantly a water world when viewed from space.

Which of the world's oceanic divisions is the largest by area?

The Pacific Ocean covers about 165 million square kilometres, more than all the planet's land area combined.

What is the deepest known spot on the seabed called?

It reaches about 10,935 metres below sea level, deeper than Everest is tall, and is named for the HMS Challenger expedition that first sounded it in 1875.

What is the average depth of the world's oceans?

The average depth of the world's oceans is approximately 3,688 meters (12,100 feet). This means if you could flatten Earth's surface, the entire planet would be covered in water about 2.5 km deep.

What is the average salinity of ocean water?

Every kilogram of seawater carries roughly 35 grams of dissolved salts, enough that a swimmer floats noticeably higher than in a lake.

Which body of water experiences the highest tidal range on Earth?

The Bay of Fundy, between Nova Scotia and New Brunswick, has a tidal range of about 16 metres; its funnel shape makes the basin resonate with the tide.

What causes ocean tides?

The gravitational pull of the Moon and Sun raises bulges of water on Earth; the Moon's tidal effect is about twice the Sun's, so high tides track the Moon's passage.

What do we call the extra-high tides that arrive when the Sun and Moon line up with Earth?

Spring tides arrive every two weeks, at new and full moon, when the Moon's and Sun's pulls align; the Moon supplies about 69% of the tide-raising force and the Sun 31%.

The deepest known point of the seabed lies in the ocean territory of which country?

The trench itself is named for the Mariana Islands, but its deepest southern end sits in Micronesian waters near Guam.

What is the global ocean 'conveyor belt' of density-driven deep currents called?

Thermohaline circulation takes its name from the Greek for heat and salt; a parcel of water takes roughly a thousand years to complete one lap of the belt.

Which warm ocean current flows northward along the eastern coast of the United States?

The Gulf Stream is a powerful, warm ocean current that originates in the Gulf of Mexico, flows through the Straits of Florida, and travels up the U.S. East Coast before veering toward northwestern Europe.

What is the uppermost zone of the ocean called, where sunlight penetrates?

The epipelagic zone (also called the sunlight zone) extends from the surface to about 200 meters deep. It receives enough sunlight for photosynthesis and contains the vast majority of ocean life.

Roughly what share of animals seen in Monterey Bay's open water can produce their own light?

About 75%: a 2017 MBARI survey of Monterey Bay's water column found 76% of the animals observed were bioluminescent, using light to lure prey, confuse predators and signal mates.

What is the primary compound that makes seawater salty?

Sodium and chloride ions dominate because they linger in the ocean for tens of millions of years, while calcium is pulled out quickly to build shells and reefs.

Which ocean zone is known as the "twilight zone" because only faint light reaches it?

The mesopelagic zone spans roughly 200 to 1,000 metres: too little light for photosynthesis, but enough for animals to see silhouettes above them.

What is the Great Barrier Reef primarily composed of?

Billions of tiny polyps secrete calcium carbonate that piles up over millennia into a system of more than 2,900 reefs stretching 2,300 km.

Off the coast of which country is the Great Barrier Reef located?

The Great Barrier Reef stretches for over 2,300 kilometers along the northeast coast of Australia in the Coral Sea. It is the world's largest coral reef system and is visible from space.

As of 2024, roughly what share of the ocean floor had been mapped at better than satellite resolution?

About 25%: the Seabed 2030 project reported roughly a quarter of the seafloor mapped by ship-based sonar by 2024, leaving the rest known only from coarse satellite-derived gravity data.

Which gas does the ocean absorb from the atmosphere, contributing to ocean acidification?

The ocean absorbs roughly a quarter of human-produced carbon dioxide (CO2) from the atmosphere. When CO2 dissolves in seawater, it forms carbonic acid, lowering the ocean's pH — a process called ocean acidification.

Which explorer made the first solo descent to the bottom of the Mariana Trench in 2012?

James Cameron piloted Deepsea Challenger to the Challenger Deep on 26 March 2012, spending roughly 2.5 hours on the bottom, far longer than Trieste's 20 minutes in 1960.

What is the largest animal to have ever lived on Earth?

The blue whale reaches about 30 metres and up to 200 tonnes, heavier than any dinosaur yet discovered.

What do female anglerfish use their bioluminescent lure for?

Female anglerfish dangle a glowing, bioluminescent lure (called an esca) from a modified dorsal fin spine on their forehead. The light attracts curious prey in the pitch-black deep sea, drawing them close enough to be snapped up.

Which of the world's oceanic divisions is the smallest by area?

It is also the shallowest of the five and spends much of the year under sea ice.

Which underwater mountain range separates the seafloor of the Americas from that of Europe and Africa?

The Mid-Atlantic Ridge marks where the plates pull apart; Iceland is one of the few places it rises above sea level.

What is a tsunami primarily caused by?

Most tsunamis are triggered by underwater earthquakes that suddenly shift the seabed; the word is Japanese for 'harbour wave', and in open ocean the wave can pass under a ship almost unnoticed.

What is the term for the partly enclosed coastal water where a river meets the sea and fresh water mixes with salt?

Estuary, and the brackish mix makes it one of the most productive habitats on the planet, a nursery for fish and birds. A delta is the land a river builds; an estuary is the valley the sea has drowned.

What is the Ring of Fire?

The belt holds around two-thirds of the world's active or dormant volcanoes and most of its largest earthquakes.

What are hydrothermal vents?

Seabed fissures that discharge geothermally heated water, sometimes above 350°C, and the bacteria there live on the chemicals in it rather than sunlight. Those bacteria feed the tube worms, clams and shrimp.

What type of organisms form the base of most ocean food chains?

Phytoplankton are microscopic photosynthetic organisms that form the foundation of nearly all marine food webs. They produce roughly 50% of the world's oxygen through photosynthesis, making them critical for life on Earth.

What is the Great Pacific Garbage Patch?

Most of it is fingernail-sized or smaller plastic suspended in the water column, which is why it is invisible from satellites.

What is the Sargasso Sea unique for among the world's seas?

Currents alone define its edges, and Portuguese sailors named it for the brown Sargassum seaweed drifting across its calm blue surface.

Which shipboard instrument replaced the weighted lead line for measuring water depth?

The echo sounder times a sound pulse's round trip to the seabed, a method that replaced lowering weighted lines from the 1920s and transformed seafloor charting.

Which wind-driven process feeds the world's richest anchovy and sardine fisheries?

Upwelling is a process where deep, cold, nutrient-rich water rises to the surface, typically driven by wind. Upwelling zones are among the most productive areas in the ocean, supporting major fisheries around the world.

What is the deepest ocean zone, found only in trenches below 6,000 meters?

The hadopelagic zone (also called the hadal zone) extends below 6,000 meters and is found only in deep ocean trenches. Named after Hades, the Greek god of the underworld, it is the deepest and least explored ocean zone.

Which two people made the first descent to the bottom of the Mariana Trench in 1960?

Jacques Piccard and Don Walsh took the bathyscaphe Trieste to the Challenger Deep on 23 January 1960, spending about 20 minutes on the bottom; nobody returned for 52 years.

What is the name of the symbiotic algae that live inside coral tissue and give coral its color?

Zooxanthellae are tiny photosynthetic algae that live within coral tissue in a mutually beneficial relationship. They provide the coral with up to 90% of its energy through photosynthesis and give corals their vibrant colors.

Point Nemo, the ocean point farthest from any land, has picked up which grim nickname?

Point Nemo is the spacecraft cemetery: hundreds of dead satellites and the Mir space station were steered to re-enter over it, and the nearest humans are often astronauts passing overhead.

What is a submarine canyon?

A submarine canyon is a steep-sided valley cut into the continental slope; the Great Bahama Canyon's walls rise about 4.3 km, and many canyons are carved by turbidity currents of sliding sediment.

What does El Niño refer to in oceanography?

Weakened trade winds let warm water slosh east; the cool opposite phase is La Niña, and the pair shift weather across the tropics and beyond.

What percentage of Earth's living space (by volume) does the ocean represent?

The ocean represents about 99% of the living space on Earth by volume. Because it extends to depths of over 10,000 meters, the three-dimensional volume of habitable ocean dwarfs the thin layer of land habitat.

Which extinct marine predator had teeth up to 18 centimeters long?

Megalodon, a giant shark that lived from about 23 to 3.6 million years ago, is known almost entirely from its teeth, so its true size remains uncertain.

What is the continental shelf?

The continental shelf is the gently sloping submerged edge of a continent, typically less than 200 metres deep; its shallow shelf seas host most of the world's commercial fishing.

Which creature is known as the largest invertebrate on Earth?

The colossal squid of the Southern Ocean weighs up to about 500 kg and also has the largest eyes of any known animal, roughly 27-30 cm across.

What is the Coriolis effect's role in ocean currents?

Earth's rotation bends moving water and air, which is why the great gyres circle clockwise in the north and anticlockwise in the south.

Which towed camera sled did Robert Ballard's team use when they found the Titanic's debris field in 1985?

Argo, a towed sled of cameras and sonar, sent the first debris images to the research ship Knorr on 1 September 1985; Ballard returned the next year in the submersible Alvin.

Which of these seas has the saltiest water?

The Red Sea's salinity reaches about 40 parts per thousand, against 35 for the open ocean, because it is hot, nearly enclosed and fed by no major rivers.

Which ocean would you cross sailing from New York to Lisbon?

The Atlantic Ocean separates the Americas from Europe and Africa; New York and Lisbon face each other across its northern basin, roughly 5,400 km apart.

What is the unit sailors use to measure a ship's speed at sea?

A knot is one nautical mile (1.852 km) per hour; the name comes from counting the knots on a log line paid out behind a ship while a sandglass ran.

Which whale makes the longest migration of any mammal?

Gray whale, which feeds in the Bering Sea and calves in Baja California's lagoons, where the 'friendly' whales approach tour boats to be touched. Humpbacks travel nearly as far, hence the common confusion.

Which marine ecosystem is nicknamed the 'rainforest of the sea' for its biodiversity?

Coral reefs, which cover less than 1% of the ocean floor yet shelter about a quarter of all marine species. The polyps are animals, relatives of jellyfish, that build limestone skeletons.

Who was the first person to dive to the deepest point of all five oceans?

Victor Vescovo completed the Five Deeps Expedition in 2019, piloting the submersible Limiting Factor to the deepest point of each ocean, including the Challenger Deep.

Which sea lies between Italy's east coast and Croatia?

The Adriatic Sea runs about 800 km from the Gulf of Venice to the Strait of Otranto, with Italy on its western shore and Croatia on its eastern one.

Which species of crab has the largest leg span of any arthropod, around 3.75 metres from tip to tip?

Japanese spider crab, whose Japanese name taka-ashi-gani means 'tall-legged crab'. Adults live 50 to 600 metres down off Japan and can weigh 19 kg, yet they are notably docile.

In the mid-2000s, roughly what share of marine crustaceans caught or farmed were crabs?

About 20%: in the mid-2000s crabs accounted for roughly a fifth of all marine crustaceans caught or farmed for food worldwide, about 1.5 million tonnes a year.

Why does clear, deep ocean water look blue?

Water absorbs red light more than blue: water molecules soak up red and orange wavelengths within a few metres, so the light returning from depth is blue, with sky reflection adding only a little.

Which animals are the closest living relatives of horseshoe crabs?

Spiders and scorpions: horseshoe crabs are chelicerates, with the same pincer-like mouthparts, and have barely changed since the Triassic, around 250 million years ago. Only four species survive.

What colour is horseshoe crab blood, harvested to test for bacterial contamination?

Blue, because it carries oxygen with copper-based hemocyanin instead of iron-based hemoglobin. Its clotting cells make Limulus amebocyte lysate, which detects bacterial endotoxins, and a litre sells for thousands of dollars.

In fiddler crabs, which individuals have one claw dramatically larger than the other?

Only males have the oversized claw, waved to court females and fight rivals; the mismatched pair looks like a fiddle and bow, hence the name.

Why do hermit crabs live inside empty snail shells?

Their abdomen is soft and unarmoured, unlike a true crab's, so without a borrowed shell they are defenceless. They are closer kin to squat lobsters than to crabs, and the size-ordered swap is called a vacancy chain.

How many walking legs does a true crab have, including its claws?

Crabs are decapods, like lobsters and shrimp. Their signature sideways run and tucked-under tail have evolved independently several times, a process biologists call carcinisation.

Which explorer named the Pacific 'Mar Pacífico', meaning peaceful sea, in 1520?

Ferdinand Magellan, who had fought through the strait now named for him and met favourable winds on the far side. He did not survive the circumnavigation; he was killed in the Philippines the next year.

Roughly what share of Earth's water surface does the Pacific cover?

About 46%: the Pacific's 165 million square kilometres make up nearly half of the world's 361 million square kilometres of ocean surface.

What is a 'red tide'?

A red tide is a bloom of toxic algae that discolours the water; dinoflagellates such as Karenia brevis off Florida release toxins that kill fish and taint shellfish.

Which is the warmest of the world's five oceanic divisions?

The Indian Ocean is the warmest of the five: walled off by Asia to the north, it has no Arctic outlet, and its tropical surface waters stay above 28 °C across much of the basin.

Which element's scarcity limits plankton growth across the Southern Ocean and equatorial Pacific?

Iron: in the Southern Ocean and equatorial Pacific nitrate and phosphate are plentiful yet plankton stay sparse, and iron-seeding experiments such as IronEx in 1993 triggered blooms.

Around 5.9 million years ago the Mediterranean was cut off from the Atlantic and largely dried up in what event?

The Messinian salinity crisis, from about 5.97 to 5.33 million years ago, left kilometre-thick salt deposits on the Mediterranean floor before the Zanclean flood refilled the basin.

The Strait of Gibraltar separates Spain from Morocco by only about how many kilometres?

The Strait of Gibraltar narrows to about 14 km between Point Marroquí in Spain and Point Cires in Morocco; the Mediterranean stretches roughly 4,000 km from there to Turkey's coast.

What carved the steep-sided coastal inlets known as fjords?

Glaciers carved fjords as deep U-shaped valleys that the sea flooded once the ice retreated; Norway's Sognefjord reaches 1,308 metres deep.

Over 90% of the deep water of which sea is anoxic, helping preserve ancient shipwrecks?

The Black Sea's deep layer never mixes with the oxygenated surface, so below about 150 metres the water is anoxic; it drains through the Turkish Straits to the Aegean.

Which sea does the Kiel Canal join to the North Sea?

The Baltic Sea: the 98 km Kiel Canal across Schleswig-Holstein links it to the North Sea's German Bight, sparing ships the passage around Denmark.

The Bering Strait is named after an explorer of which nationality?

Vitus Bering, a Danish-born officer in the Russian navy, sailed through the strait in 1728; it is about 82 km wide at its narrowest.

Which strait lies between the Malay Peninsula and Sumatra?

The Strait of Malacca, about 900 km long, links the Indian Ocean to the South China Sea and carries roughly a quarter of the world's traded goods each year.

The Strait of Hormuz provides the only sea passage from the open ocean into which body of water?

The Strait of Hormuz, between Iran and Oman, is the Persian Gulf's only outlet to the Gulf of Oman and Arabian Sea; in the early 2020s about a quarter of seaborne oil trade passed through it.

The Strait of Magellan separates the South American mainland from which archipelago?

Tierra del Fuego, 'Land of Fire', was named by Magellan's expedition in 1520 for the fires of the Selk'nam and other peoples seen along its shores.

Which warm current flows north along the west side of the North Pacific?

The Kuroshio, Japanese for 'Black Stream' after its deep blue water, carries warm tropical water north past Japan and plays the same role there as the Gulf Stream in the North Atlantic.

The cold Humboldt Current flows north along the west coast of which continent?

The Humboldt Current runs north along South America's Pacific coast from Chile to Peru; named for Alexander von Humboldt, it had been described by José de Acosta about two centuries earlier.

What is the largest flow of seawater on Earth, also called the West Wind Drift?

The Antarctic Circumpolar Current flows eastward around Antarctica with a mean transport of about 137 sverdrups, more than 100 times the flow of all the world's rivers combined.

The Agulhas Current flows south along the east coast of which continent?

The Agulhas Current runs south along the east coast of Africa as the western boundary current of the southwest Indian Ocean, one of the strongest currents in the world.

The Mariana Trench's deepest point lies how much farther from sea level than Everest's peak is above it?

Over 2 km: the Challenger Deep's 10,935 metres exceeds Everest's 8,849-metre height by about 2,100 metres, so the mountain would vanish beneath more than 2 km of water.

Which feature holds the deepest points in the Atlantic Ocean?

The Puerto Rico Trench's Milwaukee Deep, at more than 8,300 metres, is the deepest point in the Atlantic Ocean.

The Sunda Trench, near Sumatra, was formerly known by what name?

The Java Trench was renamed the Sunda Trench; it is 3,200 km long and reaches about 7,290 metres deep where the Australian plate subducts beneath Indonesia.

Marie Tharp worked with which geologist on the first scientific map of the Atlantic floor?

Bruce Heezen and Marie Tharp published the first physiographic map of the North Atlantic floor in 1957; her discovery of the Mid-Atlantic Ridge's rift valley helped win acceptance for plate tectonics.

The Bathysphere dives of 1930–1934 by William Beebe and Otis Barton took place off which island?

Beebe and Barton dived off Nonsuch Island, Bermuda, reaching 923 metres in 1934, the first time a marine biologist watched deep-sea animals in their own habitat.

Jacques Cousteau co-invented the Aqua-Lung with which French engineer?

Émile Gagnan, an Air Liquide engineer, adapted a gas regulator into the Aqua-Lung's demand valve with Cousteau in the winter of 1942-1943, making underwater filming far easier.

The research submersible Alvin, commissioned in 1964, is operated by which organisation?

Woods Hole Oceanographic Institution has operated Alvin for the U.S. Navy since 1964; named after WHOI's Allyn Vine, it had logged more than 5,000 dives by 2020, including to the Titanic in 1986.

Which Swiss scientist designed the bathyscaphe Trieste?

Auguste Piccard, the balloonist-physicist, designed the bathyscaphe Trieste, launched in 1953; his son Jacques piloted it to the Challenger Deep with Don Walsh in 1960.

In which country was James Cameron's Deepsea Challenger submersible built?

It reached the Challenger Deep on 26 March 2012 after a descent of two hours and 36 minutes.

What is the biggest living species of fish?

The whale shark, a filter-feeding carpet shark, is the largest living fish; the largest reliably recorded individual measured 18.8 metres.

Which animal has the largest brain on Earth, over five times heavier than a human's?

The sperm whale's brain weighs up to about 8 kg, over five times a human's; it is the largest toothed predator and can dive to roughly 2,250 metres.

How deep was a Cuvier's beaked whale tracked in a record-setting 2014 study?

2,992 metres: a Cuvier's beaked whale tagged off California reached that depth in a 2014 study, and in 2020 one was logged on a 222-minute dive, the longest recorded for a mammal.

Which marine mammal has the densest fur in the animal kingdom?

The sea otter's coat packs up to about 150,000 hairs per square centimetre; unlike most marine mammals it relies on fur rather than blubber, and it uses rocks as tools to open shells.

Sea otters are a keystone species because they control which animal that would otherwise devastate kelp forests?

Sea urchins: without otters to eat them, urchins graze kelp down to 'urchin barrens'; fur hunting between 1741 and 1911 cut otters to as few as 1,000-2,000 animals.

A female seahorse can deposit up to how many eggs in the male's brood pouch?

Up to 1,500 eggs: the female transfers them into the pouch on the front of the male's tail, where he fertilises and carries them for several weeks before giving birth.

How many hearts does an octopus have?

One systemic heart pumps blood round the body and two branchial hearts pump it through the gills.

Which group of fish has a skeleton made of cartilage rather than bone?

Sharks and rays are cartilaginous fish (class Chondrichthyes): their skeletons are cartilage rather than bone, which is why fossil sharks are known mostly from their teeth.

A mantis shrimp's club strike in Odontodactylus scyllarus accelerates at roughly how many g?

About 10,400 g: the peacock mantis shrimp's club reaches 23 metres per second from a standing start, as measured by Sheila Patek's team in 2004.

A male narwhal's spiral tusk is actually what?

The tusk is a protruding left canine tooth that grows 1.5-3 metres long and may serve as a weapon, feeding tool or salinity sensor.

The orca is the largest member of which family?

Individual populations specialise in prey from fish to sharks and other marine mammals.

Which is the largest living sea turtle?

The leatherback is the largest turtle: the record specimen, stranded in Wales in 1988, was 2.9 metres long and 916 kg, and its carapace is oily flesh and leathery skin rather than bone.

Who discovered the first living coelacanth, found off South Africa in 1938?

Marjorie Courtenay-Latimer, curator of the East London museum, spotted the fish in a trawler's catch in December 1938; J.L.B. Smith named the genus Latimeria after her.

What is the longest bony fish alive, growing to about 8 metres?

Its habit of lingering at the surface when dying makes it a likely source of sea serpent tales.

A lion's mane jellyfish measured off Massachusetts in 1865 had tentacles about how long?

Its tentacles were about 36.6 metres (120 feet) long and its bell 210 cm across, making it one of the largest jellyfish specimens ever recorded.

In ideal conditions, giant kelp can grow how much per day?

Giant kelp (Macrocystis) can grow 30-60 cm a day in ideal conditions, among the fastest of any organism; it dominates the northeastern and southeastern Pacific and patches around Australia and South Africa.

Charles Darwin's model explains atoll formation by the sinking of what?

A fringing reef around a volcanic island keeps growing upward as the island slowly subsides beneath the surface, leaving a ring of reef around a lagoon.

Oceanographers define a seamount as rising at least how far above the seafloor?

A seamount rises at least 1,000 metres above the seafloor; most are extinct volcanoes with a conical form and a limited summit area.

Oceanographers define a rogue wave as more than twice which measurement?

Significant wave height is the mean of the largest third of waves in a record.

The Draupner wave, the first rogue wave confirmed by instruments, was recorded in which sea in 1995?

It measured 25.6 metres at the Draupner gas platform in the North Sea, about 160 km off Norway, on New Year's Day 1995.

Which Chinese river has the world's largest tidal bore, up to 9 metres high?

The Qiantang River bore at Hangzhou Bay reaches up to 9 metres and travels at up to 40 km/h, and claims lives most years despite warning signs.

World Oceans Day was first proposed in 1992 at the Earth Summit held in which city?

Canada's International Centre for Ocean Development proposed it at the 1992 Earth Summit in Rio de Janeiro, and the UN officially recognised the day in 2008.

A country's exclusive economic zone extends how far from its coast?

An exclusive economic zone reaches 200 nautical miles (370 km) from the baseline under the 1982 UN Convention on the Law of the Sea, beginning beyond the 12-nautical-mile territorial sea.

The Great Blue Hole, a marine sinkhole 318 metres across, lies off which country?

The Great Blue Hole sits near the centre of Belize's Lighthouse Reef, an atoll about 70 km from the mainland, and is 124 metres deep.

The wreck of the Titanic lies at a depth of roughly how many metres?

The Titanic lies about 3,800 metres (12,500 feet) down, roughly 600 km south-southeast of Newfoundland; it was found in 1985 by a French-American team.

Which French institution co-led the 1985 expedition that located the Titanic wreck?

IFREMER, the French ocean research institute, co-led the search with Woods Hole; Jean-Louis Michel's sonar survey aboard Le Suroît preceded Ballard's Argo find.

A whale fall on the deep seabed can sustain organisms for how long?

Decades: a single carcass feeds a succession of scavengers, bone-eating worms and sulphur-loving bacteria for 50 years or more; some 690,000 carcasses are thought to be decomposing at any one time.

What material are a whale's baleen plates made of?

Baleen is keratin, the same protein as human fingernails; fringed plates hang from the upper jaw and strain krill and small fish from mouthfuls of seawater.

Clownfish rely on which animals for shelter and protection from predators?

In return the fish clean and fan their hosts and drive off anemone-eating fish.

Starfish tube feet are operated by what kind of system?

Hydraulic: a water vascular system pumps seawater into the tube feet to extend them and muscles retract them; most starfish can also regenerate lost arms.

Abyssal plains, among the flattest places on Earth, cover more than what share of the planet's surface?

Abyssal plains cover more than 50% of Earth's surface, lying between 3,000 and 6,000 metres deep, between the continental rise and a mid-ocean ridge.

What is 'marine snow'?

It is a continuous shower feeding creatures in the deep ocean.

Which is the second-largest bay in the world after the Bay of Bengal?

It covers 1,230,000 square kilometres and is named for Henry Hudson, who explored it from August 1610.

The deepest part of the Gulf of Mexico, at 12,467 feet, is known as what?

The Sigsbee Deep, in the southwestern Gulf of Mexico, is the gulf's deepest point; the gulf as a whole is 41% continental slope, 32% shelf and 24% abyssal plain.

Since a 2011 escalation of the Spratly Islands dispute, the Philippines has called nearby waters what?

The West Philippine Sea: Manila adopted the name, made official by a 2012 administrative order, for the parts of the South China Sea within its exclusive economic zone.

In which sea did a major 1942 naval battle between Japan and Allied navies take place?

The Battle of the Coral Sea, 4-8 May 1942, was the first naval battle fought entirely by carrier aircraft; the sea also holds the Great Barrier Reef.

The Denmark Strait cataract, an undersea overflow, lies between which two land masses?

The Denmark Strait, between Greenland and Iceland, hosts the world's largest waterfall: cold Nordic Seas water spills over the sill and cascades about 3,500 metres down, deflected by the Coriolis effect.

What does the Beaufort scale measure at sea?

The Beaufort scale grades wind force from 0 (calm) to 12 (hurricane), devised by Royal Navy officer Francis Beaufort in 1805 from the sea conditions each wind produces.

Which Antarctic ice shelf, the continent's largest, calved iceberg B-15 in 2000?

The Ross Ice Shelf, roughly the size of France, calved B-15 in March 2000; at about 11,000 square kilometres it was the largest iceberg recorded by satellite.

Which manta ray species is the largest, at 7 metres in width?

Mobula (Manta) birostris, the giant oceanic manta, reaches about 7 metres across; mantas have one of the highest brain-to-body ratios of any fish and may recognise themselves in mirrors.

Which vertebrate has the longest known lifespan, estimated at 272 to 510 years?

The Greenland shark: radiocarbon dating of eye lenses in a 2016 study put the oldest individual at about 392 years, give or take 120, making it the longest-lived vertebrate known.

The genus name Vampyroteuthis combines Latin 'vampyrus' with the Greek word for which animal?

Vampyroteuthis infernalis literally means vampire squid from hell; the first specimens were described in 1903.

Hagfish defend themselves against predators by releasing what?

Slime, enough in seconds to clog a shark's gills, after which the hagfish ties itself in a knot to scrape itself clean. Its loose skin holds nearly a third of its blood, which is why it looks like a sack.

Which species is considered the longest-living mammal, at over 200 years?

The bowhead whale: a 2007 harpoon-tip find and amino-acid dating of eye lenses suggest lifespans past 200 years; a newborn calf is around four metres long.

Turritopsis dohrnii is nicknamed the immortal jellyfish because it can revert to which stage?

It can revert to the polyp stage: after maturing, the medusa's cells transform back into a sexually immature colonial polyp, a cycle that can in principle repeat indefinitely.

Though it looks like a jellyfish, the Portuguese man o' war is actually what?

A siphonophore: it is not one animal but a colony of genetically identical zooids, each shaped for a different job such as floating, feeding or reproduction.

Which marine mammal, discovered by Europeans in 1741, was hunted to extinction by 1768?

Steller's sea cow, an 8-9 metre sirenian of the Commander Islands, was described by Georg Steller in 1741 and hunted out by 1768; the dugong is now the only living member of its family Dugongidae.

Antarctic krill in the Southern Ocean has an estimated biomass of roughly how many million tonnes?

About 379 million tonnes, by a 2009 estimate, making Antarctic krill one of the most abundant species on Earth; over half is eaten each year by whales, seals, penguins, seabirds, squid and fish.

The first description of the kraken is usually credited to a Danish bishop writing in which year?

1753: Erik Pontoppidan, Bishop of Bergen, described the kraken in the second volume of his Natural History of Norway, placing it off the Norwegian coast; the word itself is Norwegian.

The word 'ocean' comes from Oceanus, who was what in Greek mythology?

Greeks and Romans imagined him as a vast river encircling the world.

What share of Earth's water is held in the ocean?

About 97% of Earth's water is in the ocean; most of the rest is locked in ice caps and glaciers, and the ocean acts as a huge heat reservoir driving the water cycle.

Deep-sea hydrothermal vent ecosystems were first directly observed in 1977 near which islands?

Geologists diving in Alvin at the Galápagos Rift in 1977 found the vents teeming with life, a shock since no sunlight reaches them and the animals depend on chemosynthetic microbes.

High-temperature 'black smoker' vents were discovered in 1979 on which seafloor spreading ridge?

On the East Pacific Rise at 21°N in 1979, a temperature probe rigged to Alvin recorded about 350-380 °C, and the 'smoke' turned out to be mostly iron sulfide particles.

Runoff from which river feeds the large summer dead zone in the northern Gulf of Mexico?

The Mississippi drains 41% of the contiguous United States, carrying nitrates and phosphorus that fuel algae blooms whose decay strips oxygen from the bottom water.

Between 1950 and 2020, average ocean surface pH fell from roughly 8.15 to what value?

8.05: the pH scale is logarithmic, so the 0.1 drop from 8.15 means about 26% more hydrogen ions; seawater remains alkaline but harder for shell-builders.