An international team of scientists led by the Cambridge University Institute of Computing for Climate Science recently explored the role of deep sea turbulence in the regulation of Atlantic currents. A global network of currents helps regulate our climate, by removing heat and carbon dioxide from the atmosphere and drawing them down into the deep ocean. New insights on the vertical mixing of water demonstrates that there may be more up and down movement within the currents than previously thought, which has serious implications for how long carbon and heat get stored in the ocean.
To understand how all this works, imagine a Florida beach. A water balloon fight has just begun. Your toes grip into the sand as you hurl a red balloon at the person closest to you. You aimed well, but missed. The balloon tumbles down the beach and into the waves.
Image of imaginary balloon on its journey at sea was created using Neural Love AI.
Thanks to an array of floating probes and ocean modelling systems, we can now predict, with increasing accuracy, the path that this balloon might take. It would likely get swept up in the gulf stream, a warm ocean current that could deposit it somewhere in the vicinity of Greenland. Learn more about ocean currents with this video.
In the north, a cold wind chills the surface of the ocean, causing ice crystals to form. The lattice structure of ice leaves much of the salt behind which makes the surrounding water saltier and denser. Since surface water is in contact with the air, some carbon dioxide, oxygen and other nutrients are absorbed. These components are called tracers and are mixed into the denser water. Denser water sinks, taking everything down with it. By this stage in its journey our balloon has a small leak, allowing the dense water in. It starts to sink, carrying a little bit of carbon dioxide all the way down to the bottom of the ocean.
Did you know that cooler water can take up more carbon from the atmosphere than warmer water? In fact, almost a third of all carbon dioxide released by humans is dissolved into the oceans. The darkest red marks on the map below show where most of the ocean carbon is concentrated. The location on the east side of North America is where deep water is formed and trapped carbon has sunk down. This deep water formation is a key process that drives the Atlantic ocean conveyor belt.
Map of the concentration of carbon in the ocean (source)
Cold water flows southward until it comes up in the Southern Ocean. This is primarily caused by winds that are linked to the temperature imbalance and rotation of the earth. Yet, ICCS researchers also found that tracers like carbon might be moving between ocean layers more vigorously than previously assumed. This is due to waves breaking at the points where the less dense water above meets denser water below. Just like waves that break at the beach, the change in density layers can cause enough disturbance that the same thing happens underwater. Crucially, the team found that wave-break turbulence caused more upwelling than downwelling. This means that our balloon is more likely to be pulled upward than downward when ocean layers mix.
This net transformation of water from dense to light is important because ocean currents move faster in the lighter layers. If our balloon got caught in turbulence, it could resurface much faster, and we’re talking centuries versus millennia. Without disruption, carbon could stay in the depths for thousands of years, buying us time to solve the climate crisis.
Next time you see floating ocean debris, or think about a single drop of water in the ocean, picture the long journey of possibilities they could have taken to end up right next to you.