Oceans and water

20 to explore

• Watch Try it What If? Lab What if a coast were made of hard rock? Waves wear coasts away, but not every coast wears at the same speed. In our model, a bare sandy island facing ordinary waves keeps about 72 percent of its land after 50 model years. Make the same island of hard rock and it keeps about 99 percent. That is why hard rock is often left sticking out to sea as headlands.
• Watch Try it What If? Lab What if all the sea ice melted? Sea ice floats, so it is already pushing aside about as much water as it will make when it melts, like an ice cube in a glass. In our model, melting all the Arctic's springtime sea ice raises the sea by only about 2 millimeters. The same ice melting on land would raise it about 7 centimeters.
• Watch Try it What If? Lab What if an ocean food web changed? Antarctic krill are small shrimp-like animals, but they feed a huge number of bigger ones. Take krill out of our model's Southern Ocean food web and all seven other species are affected: every animal in it loses all its food, from silverfish to orcas.
• Watch What If? Lab What if coral reefs could be regrown? Scientists grow broken pieces of coral in underwater nurseries, then plant them back on damaged reefs. Follow how coral gardens work, how scientists search for corals that cope with heat, and what happens when fish come back to a restored reef.
• Watch Try it What If? Lab What if icebergs were made of wood? An iceberg floats with about nine-tenths of it hidden under the water. Swap the ice for wood in our model and watch the block bob up much higher, then find out why how much shows depends on density.
• Watch What If? Lab What if mangroves lined every tropical coast? Mangroves are trees that grow where land meets the sea in warm places, standing on tangled roots. Their roots calm waves, give young fish a safe place to grow, and hold lots of carbon in the mud. Imagine mangroves along every tropical coast and follow three paths: calmer waves, fish nurseries and stored carbon, then find out where mangroves can and can't grow.
• Watch Try it What If? Lab What if orcas left the Southern Ocean? Orcas are apex predators: they eat at the top of the food web. Take them out of our model's Southern Ocean food web and the seals, penguins and fish they eat could become more common, which then changes the food of others. Explore the knock-on effects, and the real orcas that make long trips north.
• Watch What If? Lab What if sea turtles lost their way? Sea turtles cross oceans and return to the coast where they hatched, using Earth's magnetic field like a map. Baby turtles find the sea by heading for the brightest horizon. Imagine them losing their way: follow magnetic maps, bright beach lights, and how people help hatchlings.
• Watch What If? Lab What if sharks disappeared? Sharks catch and eat other sea animals, and just having them around changes where those animals go. Follow what scientists have found in Australia's Shark Bay seagrass meadows and on coral reefs, where the evidence is still debated, and how some shark populations are recovering.
• Watch Try it What If? Lab What if sound traveled through water? Sound does travel through water, and it goes more than four times faster than through air. Send the same sound 1,000 meters through air and then through water in our model, then find out how whale songs carry so far in the real ocean.
• Watch Try it What If? Lab What if the Moon and Sun lined up? The Moon and the Sun both stretch Earth's oceans into tides. When they pull at right angles, at a quarter moon, their stretches partly cancel. In our model, lining them up at new moon makes the tides about 2.7 times as strong: these big tides are called spring tides, and they have nothing to do with the season.
• Watch What If? Lab What if the sea were as clear as glass? Sunlight fades as it goes deeper into the sea, and below about 200 meters there is hardly any. Tiny drifting plants and bits of mud also change how green, blue or murky the water looks. Imagine the sea perfectly clear, then follow how deep light would go, what it would mean for seaweed forests, and what gives the sea its colors.
• Watch What If? Lab What if the sea were not salty? Rain and rivers wash tiny bits of salt out of rocks and carry them to the sea, where they build up. Imagine a sea with no salt: most sea creatures are built for salty water, sea ice would form differently, and deep ocean currents would lose one of their pushes.
• Watch Try it What If? Lab What if the whole Earth were covered by ocean? Water soaks up a lot of heat before it gets hot, and gives it back slowly. Turn a patch of damp ground into ocean in our model and watch the gap between day and night temperatures shrink, then see how the sea already keeps coastal towns mild.
• Watch What If? Lab What if there were no ocean currents? Ocean currents are like rivers in the sea. They carry warm water away from the equator and cold water away from the poles, and some lift food-rich water up from the deep. Imagine them stopping: follow the Gulf Stream, warm and cold coasts, and the rich fishing waters fed by upwelling.
• Watch What If? Lab What if warmer seas changed ocean life? When seawater gets too warm, corals can lose the tiny algae that feed them and turn white. Fish and shellfish move toward cooler water, and a long ocean heatwave can leave whole food webs short of food. Explore what scientists have seen, and what they still study about storms.
• Watch Try it What If? Lab What if waves came from a faraway storm? Some waves are made by wind nearby: short, choppy and close together. Others are swells that have traveled thousands of kilometers from a distant storm: long, smooth and far apart. In our model, waves 1.5 meters high arriving every 14 seconds carry about 2.3 times the power of equally tall waves arriving every 6 seconds, and wear a sandy island away much faster.
• Watch What If? Lab What if waves had no wind? Most ocean waves are made by wind blowing over the water. So what if the wind stopped everywhere? New waves would stop forming, but swells from earlier storms could keep rolling in for a while. And the tide would still come in and go out, because tides are made by the pull of the Moon and the Sun, not by wind.
• Watch What If? Lab What if whales returned to every ocean? Hunting in the last century took away most of the world's great whales, and since a 1985 ban on commercial whaling many are growing in number again. Whale poop feeds the tiny drifting plants at the base of the ocean food web, and whale bodies carry carbon to the deep sea. Imagine whales back in every ocean and follow what they might do.
• Watch What If? Lab What if you could dive to the deepest trench? The Challenger Deep, at the bottom of the Mariana Trench, is about 11 kilometers down: deeper than Mount Everest is tall. Imagine diving there. Discover how strong the water's squeeze becomes, what lives in the dark, and the explorers who have already made the trip.