Oceans
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149 free Oceans trivia questions with answers — nature quiz, new questions added Oct 2026.
10 free Oceans trivia questions with answers. Oceans trivia lives in two places on BrainPickle. This page is the shorter set; the main quiz is Ocean trivia, with our deepest question pool on the topic and a source behind every answer.
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Q 01Which is the smallest and shallowest of Earth's five oceans?
Arctic Ocean
The Arctic Ocean is mostly covered by sea ice, which reflects far more of the Sun's energy than open water, so as the ice melts, the darker water absorbs more heat and speeds the melting.
Q 02In which sea creature does the male, rather than the female, carry the young and give birth?
Seahorse
Seahorses: the female places her eggs in the male's brood pouch, and he carries them for weeks before pushing the young out with muscular contractions.
Q 03Ocean phytoplankton produce about half of Earth's oxygen through which process?
Photosynthesis
Photosynthesis: because phytoplankton need light to make food, they drift in the ocean's top layer, and they form the base of most marine food webs.
Q 04Which sea creature's internal shell gives pet birds extra calcium?
Cuttlefish
Cuttlefish: the cuttlebone is divided into chambers, and the animal changes their mix of gas and liquid to rise or sink.
Q 05Which whale migrates each year between icy northern feeding grounds and calving lagoons in Mexico's Baja California?
Gray whale
Gray whales make one of the longest annual migrations of any mammal, and after whaling drove them to near extinction, the eastern population recovered enough to leave the US endangered list.
Q 06Which fish makes its home among the stinging tentacles of a sea anemone?
Clownfish
Clownfish: a mucus coating stops the anemone from stinging them, and in return they chase off anemone-eating fish and feed their host with their waste.
Q 07Which process brings cold, nutrient-rich deep water to the ocean surface, creating rich fishing grounds?
Upwelling
Upwelling: winds push surface water aside and deeper water rises to replace it, so when El Niño weakens those winds, fewer nutrients rise and fish stocks suffer.
Q 08Which marine ecosystem is nicknamed the 'rainforests of the sea' for its biodiversity?
Coral reefs
Coral reefs cover under 1% of the ocean yet shelter at least a quarter of marine species, and when water gets too warm, corals expel their food-making algae and bleach white.
Q 09Which US Navy lieutenant reached the Challenger Deep with Jacques Piccard in 1960?
Don Walsh
Don Walsh: past 9,000 metres one of Trieste's outer windows cracked with a bang that shook the craft, but the pair kept going and spent about 20 minutes on the bottom.
Q 10Which 'sea', really a salt lake, is bordered by Jordan, Israel and the West Bank?
Dead Sea
The Dead Sea is about 9.6 times saltier than the ocean, so swimmers float with ease, while fish and plants can't live in it at all.
Q 11Which effect deflects ocean currents to the right in the Northern Hemisphere?
Coriolis effect
The Coriolis effect comes from Earth's rotation and steers winds and ocean currents into huge swirls, yet it is far too weak to decide which way a sink or toilet drains.
Q 12Which undersea mountain range surfaces at Iceland, where two tectonic plates pull apart?
Mid-Atlantic Ridge
The Mid-Atlantic Ridge crosses Iceland at Þingvellir National Park, where divers in the Silfra fissure swim in a water-filled rift between the North American and Eurasian plates.
Q 13Which raft did Thor Heyerdahl sail across the Pacific in 1947?
Kon-Tiki
Q 21Which fish hatches in a river, grows up at sea, then swims back to its home stream to spawn?
Salmon
Salmon find their way back to the stream where they hatched largely by smell, and every Pacific species dies within days or weeks of spawning.
Q 22Which explorer's 1770s voyages proved that water encircled the globe's southern latitudes?
James Cook
James Cook's second voyage sailed deep into polar southern waters and over most of the predicted sites of Terra Australis, proving no such continent lay in temperate latitudes.
Q 23The Mariana Trench is named after islands whose largest is which US territory?
Guam
Guam: Spain named the islands Las Marianas in 1668 to honour Queen Mariana of Austria, then ceded Guam to the United States after losing the Spanish–American War.
Kon-Tiki: Heyerdahl set out to show South Americans could have settled Polynesia, but the evidence points to settlers from Island Southeast Asia instead.
Q 14Balboa sighted the Pacific in 1513, but which explorer gave it its name in 1520?
Ferdinand Magellan
Ferdinand Magellan called it Mar Pacífico, the 'peaceful sea', but his fleet then spent three months and twenty days crossing it, and many of the crew died of scurvy.
Q 15What mainly causes the twice-daily rise and fall of Earth's ocean tides?
The Moon's gravity
The Moon's gravity drives the tides, and when the Sun lines up with it at new and full moon, the extra pull makes 'spring tides', a name with nothing to do with the season.
Q 16Which scale rates wind at sea from calm to hurricane force?
Beaufort
Beaufort: Admiral Francis Beaufort devised the scale in 1805 so sailors could estimate wind strength from what they saw.
Q 17The Atlantic's deepest point lies in a trench named after which Caribbean island?
Puerto Rico
Puerto Rico: the trench runs just north of the island, and in 1918 an earthquake off its northwest coast sent a tsunami onto its west coast, killing dozens.
Q 18Which is the warmest of the world's oceans?
The Indian Ocean
The Indian Ocean is the world's warmest, and Asia's landmass to its north drives its monsoon, with winds blowing from the southwest in summer and from the northeast in winter.
Q 19Which whale's songs filled a best-selling 1970 album produced by Roger Payne?
Humpback whale
Humpback whales: Songs of the Humpback Whale helped build momentum for the Save the Whales movement against commercial whaling.
Q 20Which marine mammal often wraps itself in kelp to keep from drifting away while it rests?
Sea otter
Sea otters eat the sea urchins that graze on kelp, so coasts that lose their otters can turn into urchin barrens with no kelp forest left.
Q 24Water pressure at the bottom of the Mariana Trench is roughly how many times that at sea level?
About 1,000 times
About 1,000 times: the deepest-living fish, found near 8,000 metres, carry high levels of a molecule called TMAO, which stops their proteins being squashed out of shape.
Q 25Which sea creature's blue blood is harvested to test injectable drugs and medical devices for bacterial toxins?
Horseshoe crab
Horseshoe crabs: despite the name, they aren't true crabs at all, and they are more closely related to spiders and scorpions.
Q 26Which sea creature has three hearts and blue blood?
Octopus
Octopuses: two hearts pump blood through the gills and one through the body, and the blood turns blue because it carries oxygen on a copper-based protein rather than iron.
Q 27Divers on the Great Barrier Reef cull which coral-eating starfish by injecting it with vinegar or bile salts?
Crown-of-thorns starfish
Crown-of-thorns starfish: during an outbreak they can strip a reef of most of its living coral.
Q 28The Sargasso Sea is unusual among seas because it is bounded by what rather than land?
Four ocean currents
Four ocean currents, led by the Gulf Stream, swirl around it, so floating sargassum seaweed gathers in its calm centre, and so does a heavy load of plastic waste.
Q 29Which fish, whose breeding was a mystery since Aristotle, did Johannes Schmidt trace to the Sargasso Sea?
The European eel
The European eel: Schmidt found ever-smaller larvae the farther he sailed toward the Sargasso Sea, yet no one has ever watched these eels spawn in the wild.
Q 30Which American polymath charted the Gulf Stream?
Benjamin Franklin
Benjamin Franklin noticed that mail ships from England took longer to reach America, so he charted the current with whaling captain Timothy Folger.