How the oceans work, and how we affect them

You’ve no doubt heard the news, and the projections, and the doom surrounding pretty much all aspects of the marine world as a result of climate change. This is nothing new and certainly isn’t going away any time soon. We’re in a mass extinction event, currently projected to lose 50-60% of species worldwide if we carry on at current level of consumption. It is a bleak prospect. But there are of course many people out there for whom protecting the oceans has become their life’s work. So this show hopes to highlight some of the perhaps lesser known strategies being deployed to alleviate the stress on our seas, and the life therein. And to have any hope of doing this, we must first understand how the ocean itself operates, and what humans are doing to that system. Helen Czerski is a physicist at University College London, and author of new book, ‘Blue Machine’.

Helen - Well, we have this cultural perception that the ocean is a void, that it's kind of big and empty, that it's just the space between the interesting bits. And the problem is that that's rubbish <laugh>. The ocean is doing things. We don't talk about it very much in society. When we talk about the ocean, we talk about the fish or the whales or the pollution. We talk about the things in the water, but not what the water itself is doing. The water itself is this engine. It's distinct, it's different in different places. It's got different components. They are moving over and around each other to form this engine. So it's not random, it's not that the ocean kind of just is a pool of water. And sometimes there's a current, on the surface there's this three dimensional engine where it's, it's turning over from the top to the bottom very, very slowly. And then it's kind of moving horizontally at the surface. And then there's these smaller little swirls at the surface. And then there's tiny, tiny things that happen at the ocean surface and further down. So like the breaking waves and bubbles that I study. And all of this forms an engine. It's a physical entity that is doing different things in different places and different parts of it are moving around.

Will - If the ocean is an engine, then it probably doesn't run on diesel. And please don't pour in any to check. So what powers it instead?

Helen - So the big drivers of the way the engine works on a larger scale are ultimately it's all solar energy and heating and surface currents are pushed by the wind, which is ultimately, that energy comes from the sun, but it's shaped by the Coriolis force and by the shape of the different ocean basins. And so there's a huge amount of energy in the ocean. They also get quite a lot of energy in there from the tides, so the moon is slowly drifting further and further away from the earth. And we are kind of capturing some of that energy, that tide energy that ends up in the ocean. So it's being driven by all these different things, but it's shaped by the land and the spin of the earth.

Will - But natural processes are not the sole drivers behind oceanic activity. Humans play their part too. The ocean weighs 1.5 million, million, million tonnes. The combined mass of humans on earth is 13 orders of magnitude less than that. So how much damage can we really do?

Helen - Well on the face of it, you'd think that just as for the atmosphere, you know, we puny little humans are too small to affect the ocean in any important way. And of course as we have discovered with the atmosphere, that's not true. So we're affecting the ocean in a few ways. The biggest one of course is global heating. So the extra carbon dioxide we put up into the atmosphere acts like a kind of block to energy flowing away into space. So what that means is the energy flowing in is more or less the same, but the energy flowing out is slowed down. And so we're kind of accumulating energy. 93% of that ends up in the ocean, mostly close to the surface. And the reason that matters is because, well, it matters for a few reasons, but one of them is the structure of the ocean. I said it's got different types of water in different places. And the thing that distinguishes those water masses is temperature and salinity. And it's the density of water that determines where it sits in the water column. So if you've got less dense water, it sits at the top. Now the reason that solar heating matters is that if you heat that surface water up even more, it's even more likely to stay at the top and less likely to mix downwards. And so you are creating a lid on the top of the ocean. I mean it's already there, but you're strengthening that lid. The energy, the sunlight is all at the top, but as time goes on and things live and die, the nutrients that you need for life tend to end up at the bottom. So you've got the nutrients at the bottom and the sunlight at the top. And so the places where you can mix cold water up to the surface, that's where you get loads of life. That's really important for biodiversity. But if you make that upper lid really, really strong because you've heated it up, you kind of shut down that system. You make it harder for nutrients to come up from underneath. And so you've got a physical thing which is caused by climate change, which is affecting how many nutrients there are for life in the places where life needs it.

Will - So what is the upshot of our mistreatment of the sea? What will happen to both the marine and atmospheric processes if some don't change their carbon heavy lifestyles?

Helen - A lot of studies are trying to work out the extent of this. And you know that film the day after tomorrow where they said the Gulf Stream was going to shut down, that is probably not going to happen. But you can have a lot of things that sound less serious, that will have enormous consequences. So because the ocean moves around heat and nutrients, so for example, if you weaken the overturning circulation, which is what takes water from the surface down into the deeps for a few hundred years and and brings it back up somewhere else, if you weaken that, you weaken the exchange between the surface water and the deepen. So you kind of change the structure of what can live where. And then in terms of physical currents and things like that, it's unlikely I think that currents are really going to disappear because the wind is still going to blow. It's still going to push things around. But if you move those currents, so the temperature of the water in the current is not the same as it used to be and perhaps the warmer water is further north than it used to be, then animals that depended on the current and depended on the temperature can't find them both in the same place. So the problem is not so much that the engine is just going to shut down, it's that it's going to change shape and life in the ocean and us. We all depend on that ocean engine kind of having the shape that it does because it brings rain to the land in certain places. It brings fish to the surface, provides a place for them to live in a good environment in certain places and that's going to move and those species are going to have to adapt. But our whole system, we just take for granted that the weather we have in every country is, well that's the weather in that country, right? We take it for granted that Britain is a bit warmer than it should be because of the Gulf stream and that it rains quite a bit and all that kind of thing. And it's not, the weather is going to stop, it's just the patterns are going to change and our infrastructure is going to be a bit left behind. And it's the same for the animals in the ocean. Animals are going to have to move perhaps to cooler water, but then the other things that they need won't be in those places. And so they will need to adapt. The engine is going to keep turning, but it's just going to change shape and that's going to change things that we take for granted.