‘Every bit of data is precious’: my life on a boat tracking how the ocean breathes
Darkness is falling and I’m up at the top of the research vessel Maria SMerian, on the bridge. This is its control centre, with big windows providing an uninterrupted view of the stormy sea in all directions, and long banks of screens and maps displaying data funnelled from inside, around, above and below the ship. Out here in the open ocean, keeping a close eye on what nature is up to is essential. The lights are off so that dark-adapted eyes can scan the waves, and the first officer is using the speakers to fill the space with smooth jazz and calm.
I am holding on to the rail beneath the window with both hands, one leg braced against the desk behind me, as the ship rides up a wave about 8 metres (26ft) high, then plunges down the other side. It’s like a large rollercoaster; you feel yourself floating just after the peak of the wave and then, as the ship hits the trough, you tense to withstand the additional force from the floor.
While the views are dramatic, we’re here in the Labrador Sea because of something that no human can see directly. 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. We’re here to learn about a process that is fundamental to the way our planetary engine ticks. All around us, the ocean is taking a deep breath – literally. Cooling between late November and February causes a deep mixing between surface waters and the waters at depth, facilitating a vital transport of gases. I’m part of the UK contingent of an international team of scientists here to study how that happens.
Our society tends to view the big blue expanses on maps as mere liquid filler with fish in it. Nothing could be further from the truth. 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. It is a huge reservoir for heat and gases: carbon dioxide (CO2), oxygen, nitrogen and more. 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.
Near the equator, for example, CO2 comes out of the water to rejoin the atmosphere, while up here in the high latitudes, it goes the other way. These processes are not currently balanced – the ocean is taking in extra CO2 because we have increased the atmospheric concentration by burning fossil fuels and altering the land surface. 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.
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. 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. 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. 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. One of the consequences is that animals that live about twothirds 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.
Big winter storms at this location add oxygen to the surface water, which sinks downward, then sideways and onward into the rest of the Atlantic, oxygenating the whole middle layer of the ocean. But our best computer models for how much oxygen flows in this way don’t match what we actually measure. This matters, because the whole global ocean is slowly losing oxygen – there’s now about 2% less than there was in the 1960s. To predict what will happen in the future and its implications, we need to understand the conveyor belt that gets it there.
The Maria S Merian is a German research vessel, and there are 22 scientists and 24 crew on board. Each team within this collaboration of researchers from Germany, Canada, the US and the UK is studying a different aspect of the complex breathing process. The only way to progress is to keep track of ocean physics and chemistry, and what the surface and atmosphere are doing, and then put the data together – assemble the jigsaw once we’re back on dry land. There have been relatively few experiments that could directly measure gases moving between the atmosphere and stormy open waters, and the last one (which I was also involved in) was 10 years ago.
A decade on, we have new and more accurate measuring instruments and we know we need to study a wider range of interlinked processes. This is a huge opportunity, and we are all aware that (for logistical and resource reasons) it won’t come again for a long time. None of this is easy: these are novel experiments in a violent environment; there is no guarantee that anything you put over the side of the ship will come back intact, or that the wind and waves will let us carry out our plans. Every bit of data we get is precious.
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There are two methods of measuring ocean breathing, one from a tall mast perched on the bow of the ship that tracks the minutest details of wind direction and CO2 concentration, and one that depends on measuring inert tracer gases that we injected into the water 10 days ago (I’m writing in late December), now at concentrations of about one in a million billion. Some on board are taking water samples continually, both from the surface as the ship zigzags about, and from a range of depths, mapping the 3D structures (water masses made distinct by temperature or salinity) beneath us. Others have small underwater or surface vehicles, which are dragged behind the ship or “fly” short missions in the water.
I’m measuring the bubbles from breaking waves at the surface – and how their sizes change over time – because these are thought to speed up the transfer of some gases into the water. The difficulty is that all the interesting bubble processes are happening in the top 2 to 3 metres, but the surface itself is frequently moving up and down by between 5 and 10 metres. To give me access to that awkward top layer, the mechanical engineering workshop at University College London, where I’m based, made me a buoy that is basically a big hollow yellow stick with a heavy base that floats upright and is mostly submerged.
This provides a platform for my eyes and ears just below the water line: with specialised bubble cameras, acoustical devices and dissolved gas sensors. It can float freely for several