Helen Czerski on the deck of the research vessel Maria S Merian. One of the consequences is that animals that live about two-thirds of a mile below the surface and never see the sun’s light, from the petite lanternfish to the giant squid, can still breathe oxygen. It’s like an open plughole into the deep ocean – anything that enters the sea here can just keep going down – and this forms a crucial part of what’s called the “overturning circulation”, the slow global shunting of seawater between the surface and the depths. But in this corner of the north Atlantic in winter, the surface water cools so much that the continual storms can mix the top layer a long way downwards. Over most of the global ocean, the top layer of water (usually a few tens of metres thick) floats on colder, denser water underneath, staying quite separate.

The ocean breathing that happens here in the Labrador Sea is particularly important because this is one of the few areas where its surface is sometimes directly connected to its depths. Our seas are doing us an enormous favour by removing additional carbon from the atmosphere, but we don’t understand all the details of this process at the surface, or how this may change in the future. These processes are not currently balanced – the ocean is taking in extra CO 2 because we have increased the atmospheric concentration by burning fossil fuels and altering the land surface. Near the equator, for example, CO 2 comes out of the water to rejoin the atmosphere, while up here in the high latitudes, it goes the other way. And where the sea’s vast surface touches the atmosphere, these gases can be transferred in both directions, changing their concentrations in the water and the air. It is a huge reservoir for heat and gases: carbon dioxide (CO 2), oxygen, nitrogen and more.

The connected global ocean is an engine, a dynamic 3D system with internal anatomy that is constantly doing things that shape the world we take for granted. Our society tends to view the big blue expanses on maps as mere liquid filler with fish in it. Our seas are doing us an enormous favour by removing additional carbon from the atmosphere I’m part of the UK contingent of an international team of scientists here to study how that happens. Cooling between late November and February causes a deep mixing between surface waters and the waters at depth, facilitating a vital transport of gases. All around us, the ocean is taking a deep breath – literally. We’re here to learn about a process that is fundamental to the way our planetary engine ticks. In this north-west corner of the Atlantic, between the southern tip of Greenland and Newfoundland, in winter – in the cold and continually stormy weather – we can live inside a particular scientific phenomenon for many weeks. While the views are dramatic, we’re here in the Labrador Sea because of something that no human can see directly.

Blue planet the seas of life