Summary Keywords:
northwards, measure, carbon, weakening, climate, atmosphere, temperature, called, Atlantic, simulations, data,
water, heat, big, flowing, years, timescales, North Atlantic, climate change, ocean circulation, conveyor belt, overturning,
warming, cooling, ecosystem
Speakers:
Daniel Tulloch (MOCA Team)
Dr Neil Fraser (SAMS) - Physical Oceanographer
Part 1 (Part 2 to follow)
Daniel Tulloch
So have you been in SAMS for long?
Dr Neil Fraser
Yes, I did my PhD in SAMS. So, I first came to SAMS during my undergrad actually, I did a couple of summer placements here in 2011 and 2012, then a PhD here from 2013 - 2017, and then I've been doing a postdoc here since, so I’ve been here quite a long time now, actually.
D T
So what's your main focus?
Dr N F
So I work on, we basically measure the currents in the North Atlantic. And so how much water is being transported by the currents, and also how much heat is being moved around by the currents. So is the current flowing faster? And how warm is it basically? So in the North Atlantic, warm water near the surface is heated around the equator, and it flows northwards towards the sub-polar regions, and the Arctic regions, where it then becomes dense, because it gets cooled by the atmosphere there, it becomes dense and it sinks.
And then you have the dense water flowing southwards, again, at depth. So if you can think about, you know, in a room with a radiator at one side, you have this kind of convection, overturning, so that's what we call it in the ocean as well, overturning circulation. It’s this idea that you have water, it's being heated at one end, at the equator end, and being cooled up at the polar end. And so the warm water goes along the top surface of the ocean, it goes down, and then back along the bottom.
So we just want to measure the strength of that circulation. So how strong is that? And also how much heat is it taking northwards? And it’s an important driver of the of the climate.
So you can think of the climate as being, the earth is heated mostly around the equator, that's where most of the sunlight hits it, that's where the atmosphere and the ocean get warmed up. But then the atmosphere and the ocean, both being fluids, they both kind of transfer that heat towards the poles. And this is one way that the ocean does that, and the Atlantic in particular is an important pathway for global heat to get towards the pole.
So you can think about that as the climate: the transport of heat towards the poles.
At the same time, you can think of the climate as the long term average of weather.
So you think, ‘what’s the climate here?’, well, it's what the weather does on average. And that's also applicable here, because the ocean taking heat northwards, kind of dictates what the weather is over Europe, say?
So for instance, if you take the latitude we’re at now, we’re at 56 degrees north in Scotland, it maybe doesn't seem like it today, but it's actually relatively warm here compared to other places in the same latitude. If you go to Siberia or something, then it'll be much colder. And that's because we don't have this, the warm water flowing northward, essentially, the Gulf Stream, you think of it intuitively as the Gulf Stream. And the Gulf Stream is, it's not wrong to call it the Gulf Stream, but we kind of talk about it a bit more technically as this overturning circulation, which is, the Gulf Stream then becomes the North Atlantic current, and that's the bit that takes the heat northwards, and then you also have this deep cold part coming southwards, and it’s the difference between the two, that’s what takes the heat north.
D T
Right. Okay. So, it’s almost like, the cold almost repels the heat?
Dr N F
Yeah, exactly. So it's the water -
D T
The cold undercurrent, is almost like a conveyor belt?
Dr N F
Exactly. Some people call it the conveyor belt as well. So exactly the right word.
Right, so people call it the ocean conveyor belt. It's this conveyor belt, it's basically delivering heat into the atmosphere.
When that water gets to sub-polar regions, it loses its heat to the atmosphere, warms up the atmosphere, and in doing so, the water loses heat and sinks. So that process is actually what's driving the kind of relatively warm air, the warm atmosphere around the European regions.
D T
And is that causing the ice to melt? Is that part of the reason…?
Dr N F
So I suppose I'd say no, I think there's a bit more to it than that. So what's happening there? Let me think.
So if you look at a map of global warming, so in the latest IPCC report, there's maps that show observed global surface warming, so the surface of the ocean or the land, you know, and there are darker reds where it's warming faster, and kind of paler reds, where it's still warming, but not as much, and then it's blue in the regions which are actually cooling. And there's only one place on the map that's cooling.
There's a big blue spot, right over the northern North Atlantic, the sub-polar North Atlantic. So just below Iceland, there's it's actually the only region of the surface of the earth that's actually getting colder. And that's been attributed to the idea that this, this overturning circulation might be slowing down.
So what's happening is that, due to climate change, as the circulation slows down, it's delivering less heat northwards. So it's a bit of a counterintuitive idea that climate change is warming most regions, but the effect of that is that this this current, this current system is slowing down. And so it's delivering less heat northward. So in the northern North Atlantic, we're actually seeing cooling right now. It's kind of the only place you're seeing cooling. So it's quite a sort of counterintuitive and surprising result, that. And there was a bit of debate about what's causing it, and I'll just say one more thing there about that, about this overturning circulation that drives heat northwards to the Atlantic:
If you look at the whole globe, you know, it's not just important in the Atlantic, it's important globally, because if you look at the entire globe, and you look at the temperature difference, the average temperature difference in the Northern Hemisphere and the Southern Hemisphere, the Northern Hemisphere is, on average, about four degrees warmer than the Southern Hemisphere. So the average temperature in the air and ocean in the Northern Hemisphere is four degrees warmer, and a major reason reason for that is that the ocean currents in the Atlantic are driving heat northwards, much more than driving them southwards. It's not like the heat goes to the equator, and then kind of goes north and south; the ocean gets heated at the equator and it goes north.
D T
And why is that, is that something to do with tides…?
Dr N F
It's not so much to do with tides, it's to do more with, it’s much more kind of a long-term process than that.
So why does it happen? Well, there’s a lot of things going on: It’s partly due to the wind, okay, but it's more due to, large scale ocean currents are driven by pressure differences. So if you have high, intuitively if you have high pressure over here and low pressure over here, then high pressure over on the right and low pressure over on the left and the water wants to flow from high to low pressure, from right to left.
We measure what we have, we're measuring the temperature and salinity and the currents in the North Atlantic. We take boats out every couple of years across the entire North Atlantic and we see-
D T
CTDs (instrument for measuring Conductivity, Temperature, and Depth)?
Dr N F
CTDs yeah, and we have both CTDs that we measure directly from the ship and we also deploy hydrographic mooring, so these are you know, moorings which are near the surface right to the seabed and all along the chain, there's the CTDs measuring temperature, the salinity, we have current metres, so we can get measurements all the way through the water depth.
So, you might think the current metres are the most useful thing for that, but actually more useful than the current metres, are the CTDs, tell you a lot about the currents as well.
I talk about pressure differences: so if you think about some water where the sea surface is tilted, say you have a coffee cup here, but if I kind of do that, if I kind of shake it, the surface tilts, and when it's tilted high on one side, the flow kind of acts to correct that tilt, the water wants to flow to flatten out the sea surface. And that happens on global scales as well. So if we have a sea surface height difference, across the whole Atlantic of just a few centimetres, that's actually enough to drive a huge amount of flow, the water wants to move so as to flatten out that flow.
And when I'm talking about sea surface height differences, I'm not really talking about waves, or anything like that, it's much more kind of large-scale and long-term. So just a few centimetres difference between, say, here and North America, will drive, will push the water. But there's another aspect as well.
So the ocean is also stratified, so it's made up of layers of light, light layers above denser layers. So if you think about a light layer sitting above a dense layer. And if you think about it, in that case, if we have a light layer sitting above a dense layer, and you have the interface between those two layers, if there's a tilt in that interface, then the same kind of thing happens. So if you imagine you have a light layer here, and the dense layer here, and the interface is tilted, the water above wants to flow, this way to flatten out and the water below want to move this way, basically, the same idea happens that the water wants to move so as to flatten out the tilt.
So if you know the density profile of the water, if you know how the density layers are changing throughout the ocean, then you can work out what the currents are doing due to that.
And the way we do that is, well, density depends on two things. It depends on the temperature and the salinity, because as you know, when you warm water up, it gets less dense, it expands, and when water gets saltier, it becomes more dense. So if you know the temperature and the salinity of the water, you can actually use that to calculate the density. And then based on the density of the water, you can work out, well, are these density surfaces tilted? And if they are, how much are they tilted? In what direction are they tilted? And what are the currents trying to do?
D T
So you can make a sort of correlation between…?
Dr N F
Yeah, you can, so… it’s kind of like a physical law. Actually, you can say with kind of certainty. If the density surfaces are tilted, we've measured the density layers over here, measured the density layers over here. So we know there's a tilt, and we can work out from that what the currents have to be doing.
D T
Wow, that’s fascinating, really interesting!
Dr N F
Yeah, when I got into it all, I was just surprised how exact you could be about it. You kind of think the ocean, and the atmosphere and things like this, I was surprised that you could be so precise with the physics of it. You kind of think it's, it's all just mixing around. You can measure it. See what happens. But actually, there are laws you can appeal to, real physical laws that you can use to work this out.
And so, just to add another layer of complexity to that and I don't want to get too much more complicated because you know, this idea that if you if you know the tilt in the density layers or you know the tilt in the sea surface. So both of those, if you know both of those, then you can kind of work out which way the water is getting pushed.
But to add up to, literally add spin on things. Yeah, the Earth is spinning, right? So water doesn't actually go in the direction it's pushed, because we've got the Coriolis effect. So the Coriolis effect means that things, if you try and push something in the northern hemisphere, it will kind of go to the right of the direction you're pushing it. In the southern hemisphere, it'll go to the left of the direction you're pushing it. So yeah, that kind of adds another level of complexity. But you know, we can easily, you know, we've been doing ocean science enough, long enough now that we can quite easily account for that.
The main thing is, you know, we need to measure the density of the ocean. And we also need to measure the sea surface height changes, so it’s these tilts in the density surfaces, so the density layers, the tilts in the density layers, and the tilts in the sea surface that we need. We measure the tilts in the density by going out and putting instruments in the water measuring the temperature and salinity. And we measure the tilts in the sea surface using satellites. We have satellites, satellite altimeters, so you know, satellites basically, can measure the height of the sea surface as it’s changing over time.
So with a combination of satellite data, and what we call in-situ ocean data measurements that we've taken, and yeah, so that's how we do it.
There’s a major programme we've been involved with since 2014, which is this cross section across the whole Atlantic, from Scotland, to Greenland, and across to Canada, we measure the strength of the currents, and how much heat they're transporting northwards through that cross section.
And, yeah, so we’ve been doing it since 2014, eight years now, and it's told us a huge amount, it's still not long enough to really talk about changes on a climate timescale. Because, you know, climate change is something that we can't really be exact about, is the climate changing based on eight years, eight years of data? So for longer time series, we appeal to older data, which has been gathered, you know, here and they’re kind of scattered around, but not not really with the same focus of trying to measure / monitor this, this one current. And also people use computer simulations of the ocean. So, you know, if we can use the observations we have to make the computer simulations very accurate, then we can look at further.
So first of all, we can look back in time and say, you know, has the circulation changed over the last 150 years since the onset of the industrial era? But then, like you say, more importantly, is look to the future, and say, is it going to change more?
D T
So what sort of findings, generally speaking, is… do you find that the currents are slowing down? Is that a trend that you're seeing?
Dr N F
So over the eight years since we've been measuring the overturning circulation, how much heat is being delivered northwards in the Atlantic, we haven't really found a major change in that in those eight years. So that's, you know, maybe somewhat surprising because there's a lot of other evidence and theories that the overturning is weakening and has weakened since the Industrial Revolution. So how do we reconcile those two things? Well, again, it's only eight years. So you know, there's a lot of sort of what you may call high frequency noise, you know, things are changing between different years and over sort of five to ten year timescales there's a lot of ups and downs that are not necessarily climate, nothing to do with anthropogenic climate change signals. Yeah. So we haven't found that the it's been weakening over those timescales.
What have we found? Well, you know how I said that the warm water comes northwards, and then it gets cooled down and sinks and goes - where that cooling down takes place. People used to always think that all that water was getting cooled down and sinking West of Greenland, and that the Labrador Sea, which is the region west of Greenland, and east of Canada, we've actually found that there's actually not much of it going on there. Most of this kind of cooling down and sort of formation of dense water, this deep, dense water is probably happening to the east of Greenland. So in the kind of around Iceland, maybe just the the region sort of south of Iceland, maybe some north of Iceland. So that's the main finding from the project so far.
I think the thing is we, because there's a lot of evidence that the overturning circulation has weakened over the last 100 years. And there's a lot of simulations indicating that it will continue to weaken drastically over the next 100 years.
I think what's really important is that we keep this monitoring up, we keep the project going and keep measuring this current for longer. Eight years just isn't long enough to answer the questions we really want to answer.
D T
What sort of implications that would have? Would it be quite catastrophic?
Dr N F
Yeah, yeah. Absolutely. Yeah. So if the overturning circulation were to slow down, which, which some people think it already has started to significantly, then then what we would see is a cooling and freshening in the sub-polar North Atlantic. So you know, the water becoming less salty and cooler. Just because there's less warm, salty water being delivered northwards in the Gulf Stream, and the North Atlantic current.
And we’re already potentially seeing evidence for that, because, like I said, if you look at a map of global warming, the most eye-catching place where it's not warming is the region south of Iceland, the sub-polar north. People are theorising that is evidence of the overturning circulation slowing down.
That also has implications for the future, because if you have this very fresh water on the surface, which is kind of what we have right now, that's not going to become as dense and it's not going to sink as well. So the idea is, if you have warm salty water, and you cool it down, you get cold, salty water, and cold salty water is basically the densest type of water you can get. It's very cold and very salty. It will sink and it'll sink right down and it'll drive this overturning. You can get fresh water and pull it down, but it won't get as dense, so it won't drive the engine quite as strong.
D T
It’s kind of a vicious cycle really?
Dr N F
It is, exactly.
There are a lot of questions right now about which way it's going to go, are the Arctic and sub-polar regions, are they going to get warmer or are they going to get colder? The Arctic right now is the place where we're seeing the most warming. We're losing sea ice, glaciers are melting, you know that, you can see pictures of polar bears on very small icebergs, of course. That’s one of the reasons the Arctic is feeling the effects of climate change, of global warming the most, right. However, if the the overturning circulation in the Atlantic slows down drastically, then you might actually expect that the Northern Hemisphere might get colder.
So it's it's a difficult one. I wouldn't want to say exactly which way it's going to go. But the implications would be massive for the marine life, obviously, because we're already seeing in the Arctic regions as they get warmer, species of animal that like the cold Arctic waters, for instance in the in the fjords and Svalbard, you have these zooplankton, they like Arctic waters, like cold arctic water. But as those fjords are getting filled with warmer Atlantic water, as the Atlantic warms, there's less habitat for them. And they're getting getting displaced further and further northwards, and they're being replaced with kind of more warm Atlantic type species, which aren't really adapted to live in Arctic climates, so it throws everything off the balance.
The other thing is that the Arctic species, they can only go so far north, there's a limit to how far north you will run out of space. So yes, it has a huge effect on the on the on ecosystem? I'm not an ecologist. I'm not going to comment too much on that, but as the conditions, the temperature and the salinity conditions in the ocean, they create the environment for the species, ecosystem. So it's a very direct link.
D T
It’s hard to summarise or pinpoint climate change, and what they say, it's a lot things happening at once isn't it?
Dr N F
I suppose the easiest thing to say is, well, temperatures are increasing. But then they're not changing the same everywhere. And like I say, in this specific part of the North Atlantic, they actually they seem to be decreasing, or have done for the last ten years, especially. Which is still climate change. You might think, “Oh, it's getting colder here. So what's the big problem?” But actually that's a symptom. The current is misbehaving, and something's going wrong in the system that we rely on.
I’ll just say one thing about, we've been measuring these currents, the project I work on, for almost ten years, and for about for eighteen years, they've been measuring the same current but further south, a project called the Rapid Array (Rapid MOC), which goes between Florida and Africa. So we’ve got these concrete records of the strength of the overturning for fifteen years.
But how do we go back further than that? Well, there's been a lot of work on something called proxy records. So what they do is they they take global simulations, and they say, well, in my global simulation, which run for maybe, I don't know, 1000 years or hundreds of years, right? They know everything in the simulation, they don't have the issue that they don't have measurements everywhere, no measurements going back in time. They can see everything. So they can say, well, let's look at the strength of the overturning in my simulation, and we'll find something which correlates in the simulation, with the strength of the overturning.
So, some work for instance, has been done on looking at the surface temperature, saying let you know, in the simulations, whenever the the overturning is strong, the surface temperature is warm here, in this specific location, say, and then they say, it's weak, it's cold here, so we have a correlation. So then they can say well, but, let's look at the historical record of the temperature at that location and assume that the correlation in the computer simulation also exists in real life and then use that to reconstruct the ocean circulation going back.
That’s a big area of research and those studies tend to apply that the circulation has been weakening a lot in the last 100 years. Whereas the ocean data we have available, it's not quite so clear from that. So it’s difficult, you know, you always end up relying on simulations, and simulations are really useful. And the end goal, if you like, is to have really accurate simulations that will tell us about the future. But you need to data as well. You need the data to compare with them.
D T
Yeah, exactly. And to strengthen your your argument, I suppose.
Dr N F
Yeah, absolutely. If you have a simulation, which compares really well with the real data, yeah, for the time that you have real data, then you can trust that simulation much more going further back in time and also, for the future.
D T
Right. Yeah. Would you say yourself? Are you personally concerned about climate change?
Dr N F
Yes, definitely. Yeah, absolutely. I think the most concerning thing? I mean, in terms of, there's my personal thoughts and my professional thoughts.
Personally, I'm very concerned by the changes, and extreme increase in extreme weather events throughout the globe, you know, fires in California, and also, you know, what's going on in the Arctic. With the loss of ice there. You know, just a couple of examples. I think the evidence if you look at the latest IPCC report, it's absolutely irrefutable.
Professionally, I specifically look at this aspect of the climate, which is this Atlantic overturning? And am I concerned about that? Well, yes, though we haven't seen evidence that it's weakened. And so we've been measuring it over the last decade or decade or so. You know, that's a short record, like I've already said, that's a relatively short amount of time. And the simulations. And so there’s hundreds and hundreds of different computer simulations have been run by different groups all over the world, the IPCC report, and the they show that the strength of the circulation may or may not have changed over the last 100 years, but they have various different answers, quite a large spread, actually, of what it has been doing for the last 100 years, this circulation. Quite concerning is how little we actually know about what it's been doing for the last 100 years.
But what they agree much more on is what it’s going to do in the next 100 years, with increased carbon emissions, is that it's going to weaken substantially. All of the simulations more or less agree in the next 10 years, we're going to see it just start to drop off and it's going to continue to drop off.
Again, these are simulations, all simulations have a degree of uncertainty, but the concerning thing is that all these different independent simulations all say the same thing.
D T
Do you ever, your work that you're doing here? Do you pass that data on to other people doing work in, you know, fish routes and migration routes? And that sort of thing?
Dr N F
Yeah, almost certainly, you know, the data that we collect is all made openly available for any other researcher who wants it, or anybody who wants it. The project has a website, it's called the OSNAP Project, O S N A P stands for Overturning in a Sub-Polar North Atlantic. And if you go on the website, you can download all our data.
I don't know exactly who uses it, almost certainly people who want to know, whether or not people who are in fisheries and stuff will use that data directly? I'm not sure, I think what's more likely to happen, because it's very large-scale ocean and climate data, I think that the people who are doing fisheries and stuff probably want to know more about like, small-scale close to coast, and on a short timescale, you know, “if I go fishing tomorrow, where should I go next?” “Fishing next week, where should I go?”. The data that we collect is probably not directly useful for that.
This data will be fed into large scale, global simulations, and it'll make them more accurate. And then it will also be fed into smaller-scale regional simulations and make them more accurate, or what might even happen is that the data gets fed into a large-scale simulation, and the data from the large-scale simulation then gets fed into a smaller-scale simulation, which is a very high resolution regional one of the west coast of Scotland. And that’s what, people who run fish farms, if they want to know what the ocean conditions are going to be doing, they'd probably be looking at that. So there's a few steps in between. But I don’t actually know who all uses our data. I think it's mostly used for research purposes, and also gets fed into simulations. And you think of these ocean simulations as big, large-scale, very slow moving weather forecasts. It's kind of like that.
D T
It’s like a weather forecasts for just the sea essentially?
Dr N F
Exactly, you can also get what are called coupled climate models, which have the ocean and the atmosphere running simultaneously. And that's good, because they do speak to each other. If you have the atmosphere moving around, that's the wind and that blows the ocean around, creates waves. And if you have very cold air coming off of Greenland, say, that will have an effect on the surface temperatures in the ocean. So it’s the coupled climate models, coupled meaning the surface and ocean components, then they speak to each other.
D T
I know because I work on boats as well. I’ve been across to Halifax in Canada, and I've been across the Atlantic quite a few times. And I remember coming down across the Labrador Sea, and that area just seemed… A lot of the time there was a lot of fog. I have a feeling that has to do with the currents? The warm and cold air, you know, this meeting point of warm and cold?
Dr N F
Yeah, so I guess that would make sense if there's a lot of evaporation there, it’s saturating the atmosphere and causing fog. So yeah, you're right. I mean, you can think of, if it's foggy one day, that's the weather. But if one particular region tends to be foggy, like the default is that it's just foggy, if it's foggy nine times out of ten in a specific region, then that’s the climate and that's more likely to be driven by the ocean.
Because the climate is driven by the changes in the atmosphere and in the ocean, but the ocean moves much more slowly and has like a longer memory, you know, the atmosphere moves quickly, but there's lots of high-frequency noise. The ocean is more likely to be responsible for these low-frequency changes in weather, and very low-frequency changes in weather, you would actually say changes in climate.
D T
What about ocean acidification? Does that have any impact do you think?
Dr Neil Fraser
It's not something that I really study. Ocean acidification linked to higher carbon concentrations in the ocean; co2 levels in the atmosphere, that co2 gets absorbed by the ocean and increases the acidification.
It's something that we are starting to look at more. We have, on our array, on our instruments that we have across the North Atlantic, they measure the temperature and the salinity. And some of them are starting to, more and more, measure the oxygen level in the water, dissolved oxygen level. And obviously, the the amount of dissolved oxygen is very important for marine life, you know, you need to have oxygen. So that’s very useful for the ocean ecosystems and biogeochemistry.
But it's also useful for the carbon, it's hard to measure the carbon content directly. But if you know the temperature, and the salinity, and the oxygen level, the carbon content correlates very highly; you can work out from those three, with a high degree of accuracy. So that's something that we're doing more and more of, for exactly that reason, we want to know if the carbon saturation in the ocean is going up.
That’s something that's kind of increasing across the board of ocean observations. So another huge global programme for observing the oceans is this thing called the Argo programme. I noticed that Jennifer emailed me, her name's Jennifer Argo, so it came, this email, and it was ‘Jennifer Argo and NERC’ (the Natural Environment Research Council), and I was like, it's somebody from the Argo programme, this big international initiative. I was reading it like, this doesn't make any sense, then I was like, oh, wait, that's actually her surname! It just took me a couple of minutes just to be like ‘ohh right!’.
Anyway, the ARGO programme; Argo Floats are these big, tall cylinders, two metres tall, and you throw them in the water, and they float around in the water. They don't swim, they can't control their movement at all.
D T
Are they fixed to the seabed?
Dr N F
No, they just float. They go down to 1000 metres depth, and they just move with the current, and they measure the temperature, and the salinity.
D T
And the at a certain time they’ll just pop to the surface?
Dr N F
Every 10 days, they pop up, and they send all their data. They get an Iridium fix, a satellite fix, and they also get a GPS location. So you kind of get two things, they measure the water properties when they're underwater, but also the fact that they've drifted, the fact that they just move with the currents, means that every time they pop up, you can use the fact that in the last ten days, it's gone from here to here, and that tells you what the currents are doing. So they're really useful, and recently; ARGOs have been going since about 2002 / 2004, there’s been a lot of Argo floats in the water for the last ten years, you can have global coverage with them.
And and they just float around until they run out of battery, and they actually just wash up and people think, oh you know, that chucking these things in the water is a bit reckless.
D T
But I mean, it’s important to have that data?
Dr N F
I think it's a toss up, you know? I can see the argument both ways. There's a few thousand of them, but it's still a tiny amount compared to the amount off crap that’s already in the ocean.
But recently the Argo programme, they are now putting oxygen sensors on there as well, and that will be really useful for constraining the carbon content, getting a better handle on it? Because measuring the carbon content directly is not that easy, but if you have temperature, salinity, and oxygen measurements, then from those three, you can estimate the carbon content quite accurately, and that’s easier and cheaper to do than measure of carbon directly.
It's a worrying thing, like I said, the ocean has a long memory compared to the atmosphere. So if we were to, say tomorrow, globally, we stopped emitting co2, it's not going happen, but suppose we did. The amount of carbon in the atmosphere would stop increasing so quickly. And if we were to have carbon capture technologies, say, or more carbon sequestration in our land use, and marine carbon sequestration, we could reduce the amount of carbon in the atmosphere. And that would be an ambitious, but potentially achievable goal to get the carbon atmosphere back down to a reasonable level.
But the problem is that the whole time we've been emitting all this carbon, the ocean has been absorbing it. And like I said, and in the sub-polar North Atlantic, where this dense water forms and sinks, it sinks and it also takes carbon down with it, down into the deep ocean. So all this carbon has been sucked down to the deep ocean, and it’s started flowing southwards. So this dense water in the sub-polar North Atlantic, where this dense water forms and sinks, it takes carbon down with it. So you have this dense layer of cold, southward flowing water in the Atlantic, but also, the stuff from the last 100 years or so has a higher carbon content. And at some point, that stuff's going to pop up again, it's going to come back to the surface, what we call outgassing.
The ocean is going to basically start releasing carbon; if that deep water which is flowing southwards, will probably get down to the southern ocean or around about Antarctica, or at the continental boundaries, tends to be where the water flows back up again, and closes the circuit.
I've talked so far about the stuff sinking in the high northern latitudes, but elsewhere around the equator and moving more so further south, you have what you call as the upwelling limb, so that’s the the deep stuff going back up to the surface. And so that's gonna cause what did you call outgassing. So that's causing a huge, well, that has the potential to cause a big lag in the global carbon levels.
Even if we're sucking stuff out of the atmosphere in the short to medium term, there is going to be, for a long time, the signal of carbon in the ocean, it kind of causes a lag, you know, the ocean has a long memory, it absorbs this carbon. Keeps it under under there for hundreds, maybe even 1000s of years. And at some point, it's going to pop up again.
I don't know over what region, over what timescales it will be released. I mean, there will be simulations of this. I don't know exactly what they say. But in terms of carbon released into the atmosphere, the stuff in the ocean, that's going to be there a lot longer. Even if we do fix the problem with emissions, the oceans would be a harder problem to fix. You can't go down and start getting carbonated water, extract it at 2000 metres depth, that’s impractical. That high carbon signal, it's kind of like, you got this conveyor belt, and then it moving very slowly. And then, you know, recently that stuff sinking and flowing down the system, high carbon saturation, and where's it going to come out? And when? It’s hard to say.
D T
Is there anything positive, would you say about your findings?
Well, I suppose that you could say the fact that we've been measuring the overturning circulation for the last eight years; further south, they’ve been measuring it for the last coming on twenty years, they haven't seen a weakening trend in that time. It is a cause for, I wouldn’t go as far as to say it’s a cause for optimism, but it's better than if it was just a downward trend all the time.
When they started measuring the overturning down in the subtropics in 2004, for the first few years, they saw quite a steep drop off, and the first few papers that came out of that were saying, ‘Look at this, this is seriously weakening very quickly. That was 2007 / 2008, there was a real step down, real weakening, since then, actually is levelled off and is even showing signs of recovering again. So that's a cause for optimism, but on climate timescales, 20 years is nothing, it's hard to see the way things are gonna go based on the snapshot we have.
I think once we have, you know, 20, 30, 50 years of data, I probably wouldn't be working on the project. Then then we'll be in a position to answer some big, you know, big questions. Not that we're not in position right now to answer big questions. Because what we're doing right now, we're understanding how it works much better which will aid our ability to predict. But the best way to predict how something's going to change over 50 years is to measure it over 50 years and see these kinds of long term changes.
I'm a major advocate, obviously, for keeping these monitoring projects going. It's quite a difficult one, because if you measure something for six years, and it's an expensive thing to do to measure these currents, and then you say, well, we want funding to measure it for another two years, it’s like, well, what are you gonna tell me after eight years? I couldn't tell them after six, right? Well, maybe not all that much. It's going to be an extra two years. The data set will be more valuable, but it'll have less impact, because it's just trying to add on another two years. Obviously, once you get to 20 years, that’s 20 - 30 years, it’s much more valuable. But you're trying to do continuous monitoring.
D T
It's bizarre to me that you need to get funded for something that’s, well, seems quite fundamental…
Dr N F
We have to show we have scientific outputs, we have to publish papers based on the data as we get it, and it's really valuable data, it tells us a lot, but there's always this long term goal in mind of, we want to lengthen the time series, we want to lengthen the record, so, of course, the longer it is, the more valuable it is, but it's maybe not as high impact, the impact isn't as high because you're going,
D T
Do you always monitor very specific points, do you go to on the ship to certain positions?
Dr N F
Yeah, we do, we have a set of moving locations dotted right across the North Atlantic. From Scotland, to Greenland and Greenland to Canada. And I don't know how many moorings there are 30, or something, these different marine locations. So every two years, the boat will go across, take all the old moorings out, get instruments off, get the data and put new moorings in the same location. And those locations are chosen very carefully. They're kind of chosen, as you know, they're chosen to be the optimal locations to measure the ocean, basically, to get the maximal information right out of the ocean by choosing these specific locations. And although the instruments are recovered every two years and redeployed, they're deployed in the same place, to have a continuous record. So that's how the moorings work.
We also, for the last couple of years, we have been measuring part of the section using these underwater robots called gliders. So these, are they look like a kind of torpedo.
D T
I’ve seen one of those before, because I was on Discovery and the James Cook; I was like, are we a war ship now, or…?
Dr N F
Yeah. They look for the they look quite militaristic. Quite often they're bright yellow or bright, which if they were like, grey, gunmetal grey…
D T
Yeah, exactly. (Laughs)
Dr N F
But yeah, we use these underwater robots called gliders to fill in some of the section and they swim around, tell you the temperature, salinity, they kind of get pushed around by the currents a bit. So they don't stay in one place quite like the mornings. But they’re really useful, because we basically send them to kind of patrol their little bit of the section.
If you imagine the, the our section, our ocean section going across the North Atlantic, in Scotland, and Canada. That's like, we're kind of patrolling that with our instruments and with the boats, and also with these robots, you know, they just have their little bit like prison guards, they just walk back and forward and take the data and basically just monitor anything that's going through how much heat, how much flow, how much fresh water? And they make we can put them out for as much as a year or 18 months at a time. They can just sit around on their own. You'd have to check in on them on a computer every now and again. But for the most part, they just do their own thing. They know what they're supposed to be doing. And they just stick to it. So yeah, they're really really valuable. They've been a big asset in terms of, it’s a lot cheaper to have a robot; they’re expensive but then once you start telling them (funders) how expensive it is to have a ship like the Discovery at sea for a day with the crew and its fuel, you know, they pay for themselves very quickly because we we go from Oban, you know, we'll take a rib out to kind of between Tyree and Berra, Chuck one in the water usually, recover another one, chuck one in the water and it'll swim off and just do its thing. Six months later, we'll go out in a rib again. Pick it up. We'll tell it, come swim back home again.
It is really useful, you think about going for a scientific cruise, and I'm not, I don't want, my boss would kill me if I put any shade on scientific research cruises; they’re still absolutely the workhorse of ocean of physical oceanography. But that's a big endeavour, going off on a scientific cruise for a month. It's you know, it's expensive -
D T
And it can be quite dangerous as well, sometimes.
Dr N F
Yeah. Whereas we can go, I can get to SAMS at nine o'clock in the morning, we’d jump in a rib, we’re out past Tyree, lunchtime, chuck a glider in the water, take another glider out of the water, have a cup of tea and be back here for one o’ clock. That's that's us done our instrument deployment. There's a lot of bonuses there. So they're out there a lot of fun.
D T
Are you from Oban?
Dr N F
Originally, I'm from just outside Edinburgh, I moved up to Easdale Island, just south of Oban, when I was 15. I went to Oban High School for the last few years of school. So kind of from this area, but also originally from the Edinburgh area.
D T
Would you say, this is more on personal thoughts about the local environment: have you noticed any changes to the weather yourself? Since you've been living here? Or, or any significant changes to marine life? Or increase in marine life, or decrease? Or I don't know, if you go fishing..?
Dr N F
So one thing I've noticed, I mean, I quite like spending time in the hills, and you do notice that the winters seem to be less cold, you don't get such proper a winter, mountaineering season in Scotland these days, it seems to be less and less likely you get proper snow coverage. Only on the odd year recently; the Beast in East, for instance, last year, actually as well, but we were in lockdown for most of it.
But yeah, that's a that's a big, that's a noticeable thing, in terms of, I mean, I'm from a coastal community and Easdale Island. I wouldn't know, to be honest. In terms of the frequency and severity of storms. I think there might be an increase in the last ten years, but I'm not 100% Sure.
My boss who lives in Taynuilt, he has a back garden weather station, and he's been looking at the rainfall statistics. Every year, I think he is noticing changes like rainfall. Last year was the was the rainiest year on record, since he's lived in there for 10 years. But need to double check with them. I'd be interested to be totally honest with you. It's not something that I suppose I, beyond what the average person thinks. For instance, it's very difficult to separate, to be objective; I remember last July, we had that incredibly hot spell, the whole of the country?
D T
It was just like, wow, this is, ridiculous. It was like being in Italy or something!
Dr N F
The off the charts, temperature, and for how long as well, for a week or two weeks? And you're thinking, well this is obviously a climate signal, but you can't really attribute a two week, or a month-long warm period, to long-term anthropogenic climate change. As much as at the back of your head, you're thinking this is what we're in store for? You’re internally conflicted about that. (Both laugh)
D T
There's a lot, you know, a lot of, I mean, a lot of people in Scotland that I've spoken to, they're sort of like, bring it on, bring on the heat. I don't know if they're joking or being serious. I mean, I can understand, you know, where they're coming from, in Scotland, obviously, we've got to deal with awful weather, but yeah, it’s… I think climate change isn't just about climate warming, as you were saying before, it’s, climate change is the extremes.
Dr N F
The extremes as well. People say, you know, it's not so much that the climate is just going to the kind of, that the average will change. But also the variability will change. The climate will become much more erratic. The weather events will become much more, less predictable and more erratic.
A lot of work has been done by colleagues of mine on the frequency of marine heat waves, are marine heat waves more frequent and more severe? That's a different question to saying is the climate changing? Is the temperature trend changing? It’s more saying, is the temperature variability, is the amplitude of the temperature swings, warm or cold, are they getting, is it becoming a more energetic signal? Is the temperature going up and down more vigorously, with a bigger amplitude?
It's a different question, but also related to climate change. I think that's a big part of it is, if you live at the, on the coast, you're worried about sea level rise, and as a large-scale, physical oceanographer, we think about sea level rise, the average sea level is going up in this location, by what seems like a small amount, a few millimetres, but it's not, it's actually quite significant.
If you’re living by the coast, you're not really concerned about the average sea level, you're concerned about how high the highest tide can be, cause that’s what's gonna do the damage. And so if the extremes get bigger, that’s as important, if not more important than the long-term status changing.
So there's a lot of things about how the tides might change as well, as the as the sea level rises, the tides could be altered, the tidal patterns that we recognise can be altered quite substantially. So you know, places where you used to get very large tides might actually get lower tides. But then in other locations, you might get a larger tide because, the way the tide interacts with the shape of the seabed underwater plays a big role in the tidal signals that you see at the coast.
So, for instance, an extreme example would be in the Severn Estuary, you have the southern border, we have absolutely huge tides, they're seven metre tides or something, and that's because the tides gets funnelled and amplified in the Severn Estuary. And you might find that as the mean, sea level changes, increases, that some places which have large tides, because of that effect, might have less of that effect, the funnelling might change. But the other places might have more of an amplification. That's just talking about extremes in general, it’s true of tides specifically.
There’s also kind of an analogy for extremes, if you're a fish, and you like to live in water between 10 - 15 degrees C. If the average water temperature of Scotland changes from 10 to 12 C, it’s still in your comfort zone, and you're like, oh, that's fine. I'm not bothered by that. But if the extremes change, if the very warmest temperatures you experience, get higher, so if the water goes above 15 degrees, more often higher out of your comfort zone, that's really going to kill you off, basically, you're going to have to move somewhere else. That's an example, in terms of the impact on the ecology and the impact on us as humans. The change in the extremes is as important if not more important than the change in the mean climate state.