We all know that climate change is causing sea levels to rise – the number of images of hapless people wading through floods makes it impossible to forget. But the other impacts of climate change on the oceans, those that take place far away from our most fragile coastlines, are largely invisible to us. Yet scientists know that these hidden impacts cannot be ignored – the oceans are both a vital part of the problem, and a vital part of the solution.
The UK is a world leader when it comes to ocean research and a great deal of it takes place at the National Oceanography Centre (NOC) in Southampton, and its sister site in Liverpool. I visited Southampton on a sunny day in September and made my way through the mildly intimidating military-style security system to get to NOC. Here, the organisation’s huge complex of laboratories, offices and Europe’s largest fleet of autonomous and robotic vehicles overlook the harbour where, on some days (not today, they’re off exploring) the research ships RRS Discovery and RRS James Cook await their next missions.
I am shown around by Chris Pearce, whose research focuses on the processes that cause, and can help mitigate, global climate change. We walk past sparkling white laboratories full of powerful microscopes and other equipment, some used to quantify the carbon content of water and sediment samples, and the occasional room of small tanks that glow blue – Chris thinks these are home to coral research, but it’s not his field. In other rooms engineers tinker with equipment and sensors that will grace the autosubs and surveying equipment being constructed in the robotic centre below – the tools hung on the walls here and the air of organised chaos reminiscent of nothing so much as my dad’s shed. The names on the doors do little to help a novice guess at what takes place within: Microbial Biogeochemistry, the Particle Flux Laboratory. For that, we need the scientists.
CHANGES BIG AND SMALL
‘I always say this to people: the ocean is really big,’ says Stephanie Henson, a principal scientist at NOC and a lead author on the carbon cycle chapter of the latest IPCC report. ‘We can observe the surface with satellites, that’s okay. But once you get below that, we have very poor approaches to sampling what’s going on down there.’ It’s for this reason that Henson’s research relies so much on the new suite of autonomous robotic technologies developed at NOC, which enable data to be gathered from the deepest and furthest reaches of the ocean. For Henson, these data largely relate to phytoplankton and the biological pump – the mechanism by which organic matter (either dead phytoplankton or feaces containing phytoplankton) sinks to the ocean floor, where the carbon is ultimately stored. It’s one of the planet’s most important carbon sequestration tools. Without phytoplankton constantly performing photosynthesis and then dying or being eaten, atmospheric CO2 would be around 50 per cent higher than it is now. ‘That would be a catastrophe,’ says Henson.
Thankfully, a mass die off of these essential primary producers isn’t going to happen any time soon. However, Henson and her team have already noticed changes in their ranks. ‘Phytoplankton vary from absolutely minuscule things, to those that are almost visible with the naked eye,’ she says. ‘The smaller ones tend to take up less carbon dioxide than the big ones, partly because they just don’t need as much when they’re undertaking photosynthesis, but also because they don’t sink very well. We’re seeing a shift towards the smaller end of the size range, which is not ideal, because that implies less carbon uptake.’
She also points to the deleterious impact of ocean acidification, which occurs when the excess CO2 that the ocean naturally absorbs sets off a series of chemical reactions that result in the increased concentration of hydrogen ions: more hydrogen ions translates to higher acidity. ‘We know that ocean acidification affects the way that some phytoplankton build their shells,’ says Henson. ‘Some phytoplankton have calcium carbonate shells, little intricate structures, and when the oceans acidify they can’t build these shells properly and so they become deformed. And if they can’t grow and thrive successfully, then that can have a negative impact as well.’
Scientists don’t yet know the full implications of these changes to phytoplankton or how they will impact our assessment of future climate change, but the signs are worrying. For now, it all comes down to better research and more data. One NOC project, known as GOCART, for which Henson is principal researcher, is key to this goal. ‘For GOCART, we deployed lots of underwater gliders which take really high resolution observations over month-long periods. This allows us to look at the short-timescale variability in particles.’
The gliders (which look like little yellow torpedoes, but are a type of robotic underwater vehicle that can run for many months, with directions being sent remotely via two-way satellite communications) have so far been deployed in four parts of the world: two missions in the Southern Ocean, one off the coast of West Africa, and one at the Porcupine Abyssal Plain – a sustained observatory in the North Atlantic. ‘This is totally new because we haven’t had the techniques to do it until now,’ adds Henson. ‘What we’ll do next is build some equations to feed into a model, and then take a look at what the implications are for carbon storage by biology.’
This work is only one small part of the wider programme at NOC. It appears as if climate change ultimately affects everything in the oceans, from the very smallest creatures to the vast currents that constantly shunt water across the globe. ‘From a climate point of view, the really key thing is that the ocean is one ocean – it’s all connected,’ says Angela Hatton, director of science and technology at NOC. ‘That’s very important because when you have an effect anywhere in the ocean, you have an effect everywhere in the ocean.’
Using satellites, scientists are already observing changes to some of these ocean currents, despite relatively small datasets in terms of duration. The globally significant Atlantic Meridional Overturning Circulation (of which the Gulf Stream, so important for the UK’s mild weather, is one small part) appears to be weakening, or slowing down in the North Atlantic. Projections suggest it will lose even more strength in the decades ahead. This could cause heat and cold extremes in Europe and rapid sea level rise along the east coast of the United States. At the other extreme, recent research by scientists at the Australian National University indicates that the swirling eddies observable in the Southern Ocean have increased in strength.
Hatton refers to the Overturning Circulation as the oceans’ ‘conveyor belt’ and points out several other implications of any changes to it – one of which involves all the nutrients that naturally end up in certain regions. ‘We have highly productive seas around the north of Scotland and around fisheries in the UK, and part of that productivity is because this Overturning Circulation redistributes all the nutrients that plants need to grow. If you start to disrupt the circulation, you stop distributing the nutrients to the right places, and you’ll effect what grows.’
Up until recently it has been hugely difficult to monitor these vast ocean movements, but NOC is on the case. It has set up what’s called an ‘array’ across the North Atlantic, made up of vast moorings, some of which are attached to the sea floor and stand five kilometres tall. ‘They allow us to continually measure this Overturning Circulation,’ says Hatton. ‘Really the fundamental point for me, is about understanding the oceans by increasing our knowledge.’
This central mission – to increase knowledge about the oceans – extends to the second part of the equation: the oceans as a solution. For Claire Evans, a research fellow in the Ocean BioGeosciences group at NOC, this is all important. ‘I started out as a pure scientist, like most scientists do,’ she says, ‘but the older I get, the more mature in my vintage, the more I’m realising that if we’re going to do something useful with this, we have to work with stakeholders, and we have to make our research more applied.’ She is particularly interested in marine carbon sequestration schemes (also known as blue carbon approaches), especially seagrass regeneration.
‘For me personally, the solutions that have the most appeal are those that work within nature. I feel like we’re perturbing nature, and I don’t feel comfortable further perturbing nature to try and push it the other way. I’m not saying we shouldn’t do that, because of course we need to, but for me, using what nature provides to try and sequester that carbon is really, really important.’
According to Evans, the ocean is expected to provide about 21 per cent of emissions offsetting globally and, of that, around two per cent will be met by restoration of coastal habitats such as mangroves, salt marshes and seagrass meadows. Like all plants, seagrass takes in CO2 as part of photosynthesis. What makes it particularly effective as a carbon sink is the fact that this carbon ends up within the sediment of the sea floor where it decomposes much more slowly than on land. Essentially, the sediment traps the carbon in the dead plant material, which may then remain buried for hundreds of years.
Evans’ work hones in on the science behind this process at various pilot sites around the world, including several in the UK. As we speak, she is gearing up for a trip to Antigua where she will oversee coring of the sediment on the sea floor – a process that, at its simplest, involves shoving a drain pipe-like object into the sediment and bringing up samples for analysis at NOC.
‘We have a look at how much organic and inorganic carbon is in there,’ explains Evans. ‘Also, we look at its isotope ratio, which allows us to know where the carbon was fixed. So if it’s organic carbon: is it coming from the terrestrial sphere, or is it from the marine sphere? And then we look at when it was fixed. We can then use those data to say where the sequestered carbon is coming from, how much is there, and how fast it is being sequestered.’
This type of work is important because at most sites it has never been done, meaning a true understanding of the level of sequestration is missing. ‘It’s really important for these countries with large coastlines, because it means their coastal systems can really be an asset, something they can use to meet emissions quotas, or potentially if they wanted to cap and trade using the carbon markets.’
Evans is able to do this work because of NOC’s unique capabilities. ‘There aren’t many research bodies that can operate in submerged habitats,’ she says. Whereas with mangroves or marshes you can pretty much drive right up to them, analysing seagrass is much more difficult as it involves specialist equipment and divers.
Restoration of seagrass meadows still isn’t taking place at scale, but around the world, in Europe, the Caribbean and other locations, pioneering projects are ramping up. As project lead, Evans is particularly invested in ReSOW (Recovery of seagrass for ocean wealth UK) – a government-backed project that aims to provide evidence and a strategic vision for seagrass renewal in UK waters. ‘All around the world, managers are starting to become really aware of how important these environments can be,’ says Evans. ‘I think it’s definitely in the pipeline now.’
BACK FROM WHENCE IT CAME
Down yet another corridor at NOC, geologist Chris Pearce works on an entirely different carbon sequestration scheme. Rather than utilising natural resources, his most recent project focuses on reclaiming those most unnatural of structures: oil and gas rigs.
‘We’ve been extracting fossil fuels, and particularly gas and oil from North Sea oil reservoirs for many decades,’ explains Pearce. ‘We know those reservoirs are quite well-constrained in terms of their geological context and setting. As a climate mitigation tool, we can actually pump the CO2 that’s been extracted and isolated in our power plants back down into the reservoirs from whence it came, and basically keep it stored for many, many years to come.’
To test this vision, Pearce recently travelled to the Central North Sea, specifically to the decommissioned Goldeneye reservoir, as part of an EU-funded project being conducted in collaboration with Shell. The goal was to test the ability of NOC’s submersible equipment to monitor any CO2 leakage that might occur from the sediment overlying the reservoir. For the carbon storage scheme to be practical, the ability to carry out this constant monitoring is essential. ‘We need to have confidence that were there to be any release of CO2, any fractures in the sediment that hadn’t been identified, we would be able to identify them. We also need to be able to differentiate between natural processes that release CO2 and gases such as methane at the sea floor, from those that we are actively injecting.’
It was another big test for NOC’s specialist equipment. ‘We had to come up with a series of tools or technologies that can identify the areas of leakage and differentiate between them.’ While actually in situ, it involved sending a custom-designed cannister of CO2 down to the sea floor. ‘We then injected the CO2 into sediments, and controlled the rates of CO2 release coming out.’ Pearce was delighted to find that the equipment all operated as it should. He can now pass this information on to those with the power to move forward with these type of carbon storage projects.
Such schemes do have many detractors – those who argue that they are too expensive, impractical and give fossil fuel giants a reason to keep on extracting oil and gas. But the EU and the IPCC are still betting big on them. As a scientist, it’s not Pearce who makes these decisions – but he does feel that marine schemes can be part of the solution. ‘Naturally, reducing CO2 emissions has to be the priority,’ he says, ‘but that alone won’t enable us to achieve the 1.5°C or 2°C targets. As a short term fix, this is one of the solutions because we have the infrastructure already there.’ This is one of the key advantages of using old oil rigs. One study by Edinburgh University at a different North Sea site, suggested that over a 30-year period, refitting for a carbon storage scheme would be about 10 times cheaper than decommissioning the structure. ‘I think this is where CCS will play a role,’ adds Pearce. ‘It can be brought online very quickly and obviously within the context of COP26 there’s the net zero goal – the timelines keep creeping closer.’
The ethics of carbon capture aside, it all adds another string to NOC’s bow, and another challenge for its busy engineers who are constantly creating new machines and sensors in light of each new challenge.
Ultimately, all of the work taking place at NOC reveals both how much we still have to learn about the ocean, but also how much research capability has increased. With autonomous vessels and robotic gliders now capable of travelling where humans cannot, and with constant monitoring that over time will reveal the patterns of change – understanding is vastly improving. Given the ever emerging links between climate change and the ocean, it is an understanding that will only prove more vital in the years to come.