The Mariana Trench

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Hello In eighteen seventy five in the western Pacific, the crew of HMS Challenger discovered the Mariana Trench, which turned out to be deeper than Everest is high by some two kilometers. Now trenches like Mariana form when one tectonic plate slips under another and heads downwards towards the Earth's mantle, and there are around fifty of them globally.

Now some people used to think that it was too dark and deep for life to exist there. Others imagined monsters lurking at the bottom of the ocean. The truth has proved to be more intriguing than either of those. With me to discuss the Mariana Trench are three people who were all veterans of this kind of environment.

Alan Jameson, Director of the Deep Sea Research Centre at the University of Western Australia. John Copley, Professor of Ocean Exploration and Science Communication at the University of Southampton. And Heather Stewart director of Kelpie Geoscience and Associate Professor at the University of Western Australia. Heather, I'd like to come to you first. Can you just describe the Mariana Trench to us? How big is it? Where is it? And if we could see it, what would it look like?

Yeah, fantastic. Uh the Mariana Trench is what's called a subduction trench, and what it looks like is this long deep within the western Pacific, and that's formed as you introduced through a process of plate tectonics. So we have denser oceanic lithosphere, so the Pacific plate. That plate encompasses the entire Pacific Ocean, And that is being thrust and pulled underneath the adjoining continental plates. So this process of plate tectonics by which

these oceanic plates are getting taken down into the mantle and recycled. That downward flexure causes these ultra deep parts of our world, most famously the Mariana Trench and the other trenches that surround the Pacific, the so called Pacific Ring of Fire. Dyma'r hyn y mae'r unrhyw beth sy'n ymwneud â'r unrhyw beth sy'n ymwneud â'r unrhyw beth sy'n ymwneud â'r unrhyw beth.

of St Paul's Cathedral, which is just it's a really hard number to sort of visualise in your head when you start to think about these sort of in deep water environments. And how long is it exactly? It's about two thousand five hundred and fifty kilometers um long and it's sort of arched. around the the Mariana Isles in the the Western Pacific there. Now you're all experienced divers in these terrains. Heather, what's it like to go down a trench?

It's absolutely incredible. I mean, all three of us around the table here have been in submersibles, but from my personal point of view there's the moment when you're sitting on the sea surface and you get the the clear to dive call. And that colour change as you start to fall through the water column and the change from the sort of clear waters on the sea surface through the brightest sh shades of blue down to absolute pitch blackness.

But then of course all of that you're you're sitting in silence. And that is so humbling as well as very, very exciting,'cause of course after a few hours you start to come to the seafloor in these sort of deep subduction trenches, and I've been lucky enough to dive to the bottom of the Tonga Trench. But that moment when you turn on the the s lights of the submersible

and you start to see the sea floor coming up underneath you is absolutely fantastic. And as a geologist, knowing that you're the first person to set eyes on this um seascape, if you will, But also starting to look and your brain is already starting to process what you're seeing out of the viewports and trying to put that into some sort of geological context, you know.

Are we landing on sort of soft sediment seafloor or are we coming down on rocks? What type of rocks are there? Are there any structure in those rocks? Are we seeing faults? You know, what life is encrusting and are being associated with that?

habitat down there. So you're constantly taking this information in and trying to form a sort of hypothesis and and that you're testing during the submersible dive itself. But I mean it's absolutely You know, the the very first dive I did, um, the the pilot sort of joked that, you know, he had to turn up the oxygen because I I was getting very excited so I was using up more oxygen in the environment inside the sub. But it's it's truly, you know, the being there

and sort of seeing it yourself is something that can't be replicated through other means. Fascinating. And Alan, I believe that you have gone amongst our guests the furthest down the Mariana Trench.

Can you tell us about that experience? Yeah, it was uh a good few years ago now, but it was uh it was a mistake. I wasn't really supposed to do that. How can you? How can you go down the Mariana trench by mistake? It wasn't planned. It was we went there to do I think it was four or five dives. on the deepest place on earth and it was the f like I think the first one was the third time it's ever been done and

No one thought we'd ever do it. We'd figured that it we'd probably get one in, maybe two, before the sub breaks or we're run out of time where there's weather or whatever and For some reason we just did one every two days for a week and we got all we ticked all the boxes'cause some of the dyes have to do with the classification of the sub.

Some of them because of the owner wants to do it at the time, uh other ones were to do with the manufacturer. Um we did four. Um no one no one nobody expected us to do that. And so Interestingly the guy called Don Walsh who was the guy who did the first dive ever in nineteen sixty. He was with us and he came in one day and said, uh

There's another one. But it's it's time for another one, do you wanna do it? I was like, Yeah, sure, yeah And they said, Well where do you wanna dive? And I said, Well, I don't really wanna dive challenge a deep because it's we've just done it four times and there's actually nothing much there. Uh but is similar. Yeah, yeah. We've done it twenty two times now, so I was right. There isn't much there. But uh

I said I want to go next door. There's a place next door called the Serenity which is like ten thousand seven hundred and there was reason to believe it would be a slightly more interesting. So yeah, and before not, next morning we were down at ten thousand seven hundred and something meters and we found these big sulphur mounds and All sorts of interesting stuff. It was brilliant. So it wasn't it wasn't planned, it wasn't really supposed to happen.

Uh what are the challenges for the submersibles themselves? I mean because they must be operating under immense pressure and yet They've got to sustain an environment in which humans can live uh or or exist for four or five hours or whatever. Yeah, there's two parts to it. So we've gone down to environments which are pressure wise are about one tonne per square centimetre, if not a bit more.

So the engineering for that is actually relatively easy'cause it's linear. So i you just make things thicker thicker. We use titanium inside the spear and we use all sorts of materials that can get us back to the surface and so on. But the other problem we have is not just the pressure at depth, is actually the distance from the surface.

So communication with the surface is very difficult for all sorts of safety reasons we have protocols in place where we have to contact the surface every fifteen minutes. Every half hour it has to be a voice one. So we have an underwater telephone where we can talk to the surface. That's the biggest problem, it's trying to punch an acoustic signal through seven miles of water.

and then trying to listen for them coming back. And we've kinda nailed it now. But some of the other problems we have is tracking. Is quite often well, up until recently, there hasn't been any products on the market that we can use to track where the sub is. So for the last five, six, seven years we've been doing it with no tracking at all.

So we've got very rudimentary tracking, but not like you would in shallow water. So there's a certain degree of challenges to do with just being very, very far away from the ship. As well as the pressure at the bottom. How does the sound travel back and forth between the ship and the submersives? We have a thing called an underwater modem, uh and it's an old Australian military device.

that we push a button and say hello and then you release the button and it scrambles into an acoustic signal goes up. And you can kinda tell. It's weird. It scrambles into acoustic signal but you can tell who's talking. It's really bizarre. You can almost hear the accent in it and it's and then they hear it and then they they talk back and you have a little we've got text message now as well, which is quite nice.

John, these depths are often called hedel zones. What does that what does that mean? What is a hadl zone? So the idea is this is the the greatest depths of the ocean. So this is uh th there are these popular schemes for dividing the ocean up into different depth zones and giving them names, but Environmentally, ecologically, most of them don't make sense. The Hedel Zone is one that, in a way, does make sense if we just say, well, that's ocean trench.

Ocean trenches tend to start at about six thousand meters. But that said, there are some environments in the deep ocean that aren't ocean trench, which are at more than six thousand meters, which is where these zones kind of break down. But in a way you can think of it as a shorthand for being ocean trench. Right, that's nice and simple.

How was it discovered? The Mariana Trench in particular? So uh you mentioned in your introduct introduction HMS Challenger. So this is a global voyage of discovery in the early eighteen seventies. And it has two main goals. One is scientific, to map the ocean floor, understand its undulations and the extent of life in the deep ocean, and also a strategic goal as well. Uh and that's to scout the routes for submarine telegraph cables, which are such a huge technological revolution.

of that time. I mean, I think right up there with with the invention of the printing press and the impact they had on the world. Yeah, so we had telegraph cables across the Atlantic in the eighteen sixties. Presumably the Pacific was even more challenging. Exactly. And people wanted to wire up the British Empire. Uh so eight one of the goals of HMS Challenger and the reason it got funded was this strategic goal.

Anyway, twenty third of march eighteen seventy five, HMS Challenger has been it's in the Pacific and it has been pushed off course by baffling winds, as they record in their log, and they decide to make a depth measurement where they've ended up. So they lower a weighted line and they record a depth of four thousand four hundred and seventy five fathoms, which is eight thousand one hundred and eighty four meters, I think.

So that was the deepest place that they measured on their voyage. It's not actually the deepest point in the ocean, and it's not even the deepest place that had been measured at that time. So where they made that measurement, they were actually about twenty five kilometers. From what we now recognise as the deepest part of the Mariana Trench, the Challenger Deep, and about 2,700 metres short of that.

And it wasn't then thought to be the deepest part of the world's oceans, because a year earlier a ship called the USS Tuscarora, which was also scouting submarine telegraph cable routes in the Pacific for the United States, had measured 8,513 meters fur much further north in the Pacific in what we now recognise as the Kiral Kamchatka trench.

So HMS Challenger found this deep depression, literally by accident, near the Mariana Islands, and there were no other depth measurements in that area for another twenty four years. So they found a deep spot. Uh it they didn't know it was part of a trench. It wasn't called the Mariana Trench at all at that time, and it wasn't even the deepest known point at that time.

So if we jump forward a little bit, 1894 uh HMS Penguin measures just over 9,100 meters in the southwest Pacific and what we now recognize as the Kermadec Trench, so that then becomes the deepest known place uh on earth. But not for very long. Eighteen ninety nine, a ship called USS Nero.

Again, scouting submarine cable routes near the Philippines measures nine thousand six hundred and thirty six meters. That becomes the deepest known place on Earth, what we now recognise as the Philippine Trench. And that stayed as what people thought was the deepest place on Earth. until 1951. And these were individual depth measurements and people didn't realise they were part of these trenches and these features that that Heather's described.

That came also, though, at the end of the nineteenth century. So there was a map published of the depths of the world's oceans by a cartographer called Alexander Supan, And he showed that some of these places where there've been these big depth measurements were trench like features. Not actually the Mariana one on his map, but he identified the Aleutian trench and he also proposed that these things should be named after the geographic features that they're near to.

So that people don't get confused. So that's why Mariana turns out to be Mariana because it's near the Mariana Islands. Indeed, and Challenger Deep, which is what it was called before on an earlier map in eighteen seventy seven, that becomes eventually the deepest known bit of the Mariana Trent.

Heather, what do we see when we get down to the bottom of the trench, on the on the b uh on the beds of the trenches, in geological terms? Is this like a sort of conveyor belt of rock? Yes, indeed. In in that sort of really large scale, big geological processes frame, then we're looking at a conveyor belt of oceanic plate coming into the trench being bent and thrust down underneath that overriding plate. So that's where we get that conveyor belt.

But in terms of when we're actually looking at the seascape, you know, it can it can vary quite a lot. So we have what are called hemipelagic and clay rich sediments that drape that seascape, that topography of rock But once we're actually in the trench, we you know we don't only have that oceanic plate which are composed of volcanic rocks like basalts and things. We actually have, you know, the the forearch, so all these rocks and sediments are also getting scraped off.

onto the overriding plate as it's been subducted in, so we get this mélange of but we can also see bits of exposed mantle in these trench environments as well. So these are sort of scabbros. What does mantle look like? It's actually really cool and we've got some amazing footage of that. And it it's these massive dark rocks, but they've got really big major faults and joints in them. So it I mean it's very characteristic and it's got a lovely sheen to them as well. So in terms of

what you're looking at out of the the viewports and what you're looking back on the on the video that's recorded. It's a very striking environment. But what's also really cool is that when the process of subduction is happening, it almost

starts this catalyst of other things that are happening. So we see mud volcanoes and we see vent systems. You know, there's a the Shinkai vent system is on that forearc of the Mariana Trench. And it's not like what we might think in terms of black smokers and, you know, those amazing documentaries that we see where you've got that sort of pump of of black material kind of coming out of the the seafloor and those very dark brown big edifices and stuff.

These vent systems in the Mariana, the Shinkai vent system, for example, are made out of carbonates. So they're white, pristine, white chimneys that are preserved on the sea floor, and the fluids that are erupting from these and systems are being sampled and tested for the chemistry so they're we're looking at what minerals are being dissolved by the water that is being taken down by this process of subduction and is percolating through the rock mass.

and it's dissolving out all of these minerals and then it's reprecipitating them and that's when Alan was talking about the the sulfur mounds in the in the Serena Deep, you know, the sort of bright yellows. I mean, the colours that you can see on the seafloor can take your breath away. Some of the other footage that we have from the Java trench, for example, I mean Alan, we've got yellows and blues and

and all of these hemosynthetic bacteria that are living off the mineral content coming out of these vents and the the cracks and fissures on the seafloor. And uh just explain to us quickly what turbidity currents are. So turbidity currents they're not going to be able to do.

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uh slope that is being loaded with sediment. Much like whenever you're driving through the highlands and you look, especially after heavy rainfall, you might see the the sort of sides of the glen that you're driving through. You know, you can see the material is sort of slipping down slope. So

we can get the same comparable processes underwater in these trench systems as well. But then of course we've got the more dramatic, perhaps the the more sort of well known events that are triggered by earthquakes or volcanic eruptions, for example. But basically these trigger movement of vast quantities of material down slope at huge speeds as well. and it is a really great mechanism for transporting not just sediment from higher slopes down into these trench basins.

But also it's transporting food and nutrients for the communities that live down there. Well, let's go on to those communities and uh Alan let me ask you, what kinds of life are we seeing at these decks? Ah, there's all sorts. So there's there's kind of you can kinda categorize all deep sea animals into two different categories. There's those that go down to about eight thousand and there's those that go beyond that. So when you look at things like fish, prawns, urchins, brittle stars, sea stars

Squid Octopus. You find all them deeper than six thousand meters, but they rarely ever go beyond eight. So it's obviously there's a barrier there which is quite difficult. If the species is adapted to high pressure and go beyond that, they go all the way and they don't seem to care about pressure at all. So there you've got things like little tiny hoppers called anthipods. Uh there are things called isopods and polychetes which are pill bugs and scale worms and there's uh

Normal looking jellyfish, there's anemones down there. But once they seem once an animal seems to have evolved to break the eight thousand meter barrier, it almost adopts this complete resilience to pressure. And sometimes their depth range can be five thousand metres, which is incredible. So but so at the very very bottom there's one animal which I I think has become kind of

really important to us'cause we're finding it at the bottom of every single deep trench we go to. And you have to be deeper than about eight and a half to nine thousand meters to see it. And it's just an anemone. It's called a galothienthemum and they live in a little tube and they look like a little white flower Really quite beautiful looking thing. But we can't find them anywhere else except at the very deepest points of the really deepest trenches. So there's there's that.

Uh everything else tends to be quite small at the deepest points, but when you as I say when you get to eight thousand y there's quite a lot of large animals still kicking around, which is people will find quite surprising. And they don't look weird. They look if anything kind of goofy. And you I I believe you discovered or named one called the snail fish.

Oh the snailfish is is a known family. We we discovered the Mariana snail fish. We discovered heaps of fish, we just don't name them anymore'cause it's too difficult. Yeah, we find snail fish all the time. So we named the Mariana one because it was quite prestigious. So for for quite a few years it was the deepest fish in the world. Unfortunately it's not anymore. There's one further north off Japan which is slightly deeper, but they're all kind of the same. They all look goofy and weird and

They're sort of flaccid looking little things. But they are the deepest in the world. And then weirdly the the family of fish of snail fish are not actually deep sea fish, they're shallow water fish. They've just they've completely taken over. So there's three hundred species. You find them up estuaries and stuff and Nailfish are now a thousand meters deeper than actual proper well, I c consider proper deep seafish. Preamrefine HVO100 på utvalda stationer. från fossil olja.

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John, how did these Animals and the anemones and so on, how do they withstand pressure at ten thousand meters below? How does it happen? Well the the challenge of pressure for animals at i in the deep sea is is really often not what we perhaps imagine it is. So I mean to illustrate that, uh I was on the last expedition I was on in the Arctic. We took an ordinary uncooked chicken egg.

And we sent it down to three and a half thousand meters on the outside of one of our deep diving vehicles. That's about the average depth of the world's ocean. And it came back without a crack on it. And that's not because it's somehow stronger than our submersibles, you know, we then cracked it open in the in the galley to show that it was it was it it was an ordinary egg.

That's because if you think about that chicken egg, what's it made of? It's made of solid matter for its shell and it's filled with liquid. And those are pretty much incompressible forms of matter. You know, if you imagine dropping a stone into the Mariana trench, it sinks down into the ocean, it doesn't at some point suddenly implode because there's no gas filled space inside it for it to get squashed down into by the pressure.

Similarly with liquids, if you get a syringe of water, you know, stick your thumb over the air and try and push down that plunger, you won't budge it compared to a syringe of air. The same kind of thing. So for deep sea animals whose bodies are made of solid matter in their tissues, liquid body fluids

in a sense they're not mechanically withstanding pressure, a difference in pressure between their insides and their outsides, in the same way that our deep diving vehicles do. Our vehicles have to maintain you know, a gas filled space inside them at normal atmospheric pressure, either to keep us alive as occupants or to keep electronics dry if it's an uncrewed vehicle.

But it's not like that for deep sea life. There is a challenge, but it's it's about what happens with molecules in cells. But it's not about mechanically with withstanding pressure. Can you just go into that a bit about the molecules in the in the cells? Because They act in a rather different way than than the molecules in our cells do. So some of the problems with pressure, for example, uh involve protein molecules.

folding up into the right three dimensional shape that they need to be to work as enzymes. And, you know, we need the enzymes in are carrying out all the living processes in cells. And that's a big problem because high pressure traps water molecules on the unfolded protein as it's been kind of put together inside the cell and prevent it from folding up into the right shape to do its job.

So that's one challenge of pressure, and so a lot of deep sea animals have these small molecules that we call chaperones that help to pull the water molecules off the unfolded proteins so they fold up into the right shape. Sometimes the animals have a different kind of protein structure. Their protein is made of a different sequence of these little like bead like amino acids, which again helps them form the right s structure under pressure.

And it's also the cell membranes, the things that enclose the cells. Now that's normally a very fluid bilayer of of lipid molecules, fat like molecules. Under high pressure that can become very rigid and that can stop, you know, messages getting in and out of the cell and so on. So again, a lot of deep sea animals have different composition of lipid molecules in their in their membranes to overcome that. So a fundamentally different evolutionary path from from say humans.

Well adaptations. Adaptations to their environment just tweaks if you like, as to you know, n nature coming up with a a solution to these challenges. Heather, back to what we were talking about, you mentioned the landfalls and earthquakes and and volcanoes. How stable is that? And does that impact on the the animals living at the m at the bottom or or in the trench?

In terms of stability, I mean it it is a very dynamic environment. You know, being part of the the Ring of Fire, the Pacific Ring of Fire, of course, you know, we've got um volcanic eruptions, we've got volcanics going on, we've got the earthquakes and everything. It is quite what we might call a a sort of slippy boundary at the at the Mariana, so we don't we see a lot of earthquakes. I mean it is an active subducting margin.

but it's not stuck. There are other margins that are sort of become stuck and then we've got a huge build up of geological forces that are trying to sort of unstick that margin. And that's where we get these huge earthquakes that cause such devastation. So in terms of the Marianne. So as I was saying earlier, in terms of keeping the movement of nutrients and sediments from the shallower

four arc down into the trench basin. So that's a constant evolving and occurring process. So there it is constantly changing. And we've got some amazing footage from up and round the corner a little bit, the Japan trench. Where you can see rock failures and the block failures. So sort of going back to the basics of sort of geotechnical elements.

we can see that happening, not just in this rock mass, but also with this sort of semi consolidated so the sediments that are a bit stuck together and are starting to behave more like a a coherent rock than a soft, squishy substrate. And we can see those failure planes and mechanisms happening as we traverse in the submersibles and the remotely operated vehicles that we're using. Alan, what happens when you go down there? What do you see? Is it a pristine environment?

I think I've probably done a better Oh probably over thirty dives now and I don't necessarily recall any dive that haven't seen s something man made. Probably everyone. Maybe maybe there's one or two that haven't. Some of them are really bad. So I remember doing a a ten thousand meter dive on the Philippine trench, which was the the spot where the Galathea expedition in the fifties had found a rock that

Which was a Galatin Galathientum one by the way, the one I was mentioning earlier. So so we dove on that spot and we filmed them alive and I thought that's great. But we also saw about something like nineteen plastic bags on the same dive. Just floating around, you could read the logos off them. There was a eco friendly plastic bag that came past and you're like, Really is that how eco friendly is that? you know?

Uh and then there are other dives which I more serious, so going back to Mariana Trench, dive in the Challenger Deep, the whole western side of Challenger Deep, which is where Don and a guy called Picard dove in nineteen sixties now a no go zone because That whole area is just covered in discarded fibro optic cable.

And so someone in the last ten, twenty years, maybe it's got something to do with listening to the naval base on Guam, or maybe it's in guys in the military, I don't know, but people have been doing a lot of experiments at the deepest point. And now we have hours and hours of footage of fibre optic cable either just discarded or actually taut and tight across and you if you're g in in a self propelled vehicle like a sub, you do not want to be anywhere near fibre optic cable.

Very, very dangerous. And it's everywhere now. But it's only on Challenger D. But it's not anywhere else in the Mariana and it's not seen anywhere else in any other trench. So there are things like that where that's kinda almost deliberate. That's someone's been doing something there. But one of the weirdest ones I think was last year we were down I think it's 5,000 meters somewhere just on the equator and four days north of Samoa and we're driving along.

Doing the usual thing. I was telling the pilot to go and have a look at this, go and have a look at that. And we saw this red thing. I thought that's that's weird, I wonder what that is. Let's go and have a look and pulled up alongside it. And it was just a packet of Chinese cigarettes just lying there thousands of miles away from anywhere, as if someone had just dropped them out of their pocket and

You know, it's i it it's bizarre. It's really quite bizarre. It can really throw you as well when you're sort of gonna like'cause you're so focused on trying to

you know, record as much scientific data and information in the commentary that as you're going along on the sea floor. And then add out of the gloom. Well out of the gloom you sort of see something, you know, and I think, you know, on the Nova Canton Trough as well, I had a dive at six and a half thousand metres and I sort of said to the

the pilot was like, Oh God, there's there's something over that like that's gonna be and it was a a cardboard box. And it's just, you know, you're like, oh Oh sugar, I've just like deviated from the plan because I thought that was gonna be something, you know, geologically or or ecologically monumental and it's like, Oh, okay, yeah.

The Puerto Rico trench was pretty bad. The Puerto Rico had gates and magazines and plates and coke cans and beer bottles and but I mean th it's s sitting in hurricane alleys, so I think when these hurricanes it's not necessarily a story of human folly. I think when you have

tsunamis and hurricanes, a lot of material just goes offshore and if you happen to be next to a trench it's gonna end up there and it's it's quite it's quite depressing. Although the point you make about um fibre optic cables on Challenger D seems to me to be quite Well, the coolest thing about Marianne in terms of man made naughtiness.

Is there's an SR seventy one Blackbird. You know the old aircraft from the nineteen sixties, a big black, really cool looking thing? And one of them crashed. They didn't want the Chinese to get it, so they took it out of Guam out to the Mariana and threw it off the back. You can see pictures of it online. So there's somewhere in the Mariana there's a blackbird. Which would be the coolest I've ever.

I I think to differ, you know. They haven't released the coordinates for exactly where it is. So I bet the Chinese have found it. Yeah by now. Um John, I wanna come back to the to the animals down there.

How do they feed? What's what are they feeding on apart from human junk? Most of the time they're feeding on what rains down into the trench. And trenches are interesting because they act a little bit like a funnel, in that there's this stuff that we has the poetic name marine snow, but basically it is

poo of all the animals that are living in the ocean, and it is dead bodies of all things living in the ocean. And this marine snow sinks down. It does get concentrated in the trenches through this sort of funnel effect. And so y the bottom of your trench, I mean, it's combination of both a toilet and a mortuary, but that's what things will make a make a meal of. And they'll make a meal of anything that they can.

So oddly enough, some of the animals that live at the bottom of the trenches are able to digest things like wood, which a lot of animals in the ocean don't bother with. It's quite hard to kind of crack. uh the molecules in wood to make a meal of it. But if that sinks and nothing has made has eaten it on the way down, that's what you get at the bottom of the trench, then there's

A strong driver for any organism that that can make a meal of it. Now there are some places in trenches though that are really exciting where there are chemical fuelled islands of life. that break all the rules. So they're what we call cold seeps. They're as Heather mentioned, where you got these plates For subducting you get the sediment being scraped and squeezed on the subducting plate, and that squeezes whatever's in that sediment out of it.

And so if that's had rotting organic matter in it over, you know, many, many uh millennia, that's broken down into methane. Methane gets pushed out of the seabed, you get these what we call cold seep communities. And that's where life is incredibly abundant.

Now they haven't been seen yet uh in terms of animal colonies uh in cold seeps in the Marianas, but they have been seen in the Kural Kamchatka and the Aleutian trenches, more than nine thousand metres deep, which are the the deepest known islands of this chemically powered life uh which we have on earth, which are hugely exciting.

Uh Alan, from a scientific perspective The Mariana must be uh an achievement to go down there. But is it the most interesting scientifically or is it just the feather in your cap of having been deeper than anywhere else? It's not it's certainly not the most interesting. I think it's the most prestigious and it's Sometimes when you have Something with a prestigious name to it, it does kind of cloud.

the reputation it's got and stuff. It's well from a purely scientific point, I think we've spent a lot of time going to other trenches. We've done Marianne about six times, but for various different reasons and different boats and different nationalities, whatever. There's been reasons for doing it but it's it No one trench represents all other trenches. And so it's the deepest one, therefore it's an outlier. It's not the same as the rest of them because it's deeper than them.

lie along a coastline. So all that organic matter that comes into the surface that rains down as food, it's the only one that doesn't have it. The rest of them are somehow attached to or associated with a continental landmass. It's also quite low to the equ it's near the equator. Rydyn ni'n mynd a lot of food on the surface there anyway, so it's what we call oligotrophic, which means it's in an area of the ocean that doesn't have a lot of energy.

And it doesn't have any seasonality. And so there's lots of reasons why Mariana doesn't represent anything other than the fact it's super deep. So if the question you're trying to ask is what happens at mega deep depth?

I guess it's your one. But if it's if it's the question is what happens in trenches or what happens across a massive depth range, there are many other places you need to go to as well. The analogy I always use is like if you're trying to understand high altitude biology or high altitude flora and fauna, how much would Mount Everest tell you about every other mountain in the world?

Not very much. It would tell you a little bit about altitude, but it won't tell you anything about a mountain goat and Kilimanjaro, right? So uh do I get John in that case? It's the implication of what Alan's saying that the environment in Mariana is actually very static and constant compared to to others.

Uh it depends on what timescale we're talking here. Now everywhere in the deep ocean is changing as a result of impacts of human activity. Uh so climate change affects all of the ocean, including the deepest depths in the ocean. And it affects it in in several different ways. I mean we are getting warming of waters and that is getting deeper and so on. Fundamentally for deep ocean, what's changing is the flow of oxygen that's that reaches

the deepest parts of the ocean. So all the animals that we've been talking about, they're animals. They need oxygen. That oxygen's dissolved in seawater. Where does that oxygen come from? Well, it dissolves from the atmosphere into the ocean in the polar regions, the surface. Where dense deep currents form and sink and then they spill out across the ocean basins. So life at somewhere like the bottom of Mariama Trench.

The oxygen that those animals are consuming began its journey into the deep actually in the Antarctic. And it takes several hundred years for it to kind of flow and and get there. And that flow is getting weaker as a result of climate change. Yes, although does that mean that climate change is going to affect them in three hundred years time? It does, yes indeed. And and that change is already on its way from changes that we've made in the atmosphere.

So we already know that overall globally the deep ocean will end up with about ten percent less oxygen than it had in pre industrial times. Now, it's very patchy and different bits will be affected. more than some others, but overall globally it's on track for ten percent less than it had already. It's gonna change the distributions of species around the world. Some can tolerate that, some can't. Their distributions are gonna are going to shift.

And that's a change that's already baked in. That's already happened. It's on its way to the deep ocean. It just hasn't reached the deepest places yet.

Heather, it strikes me that w when you're looking at something like the the trenches, it involves a lot of different skills. It involves geologists, it involves engineers, it involves biologists, all sorts of people. How do they work together? Do they understand what the other is doing? Very much so. I think I think I can speak on all of us, you know, like I think the most rewarding expeditions have been the cross, multidisciplinary ones and

Each discipline, you know, thinks a little bit differently, you know, the the engineers, to the geologists, to the physical oceanographers, to the biogeochemists. And I think that.

fusion and that sort of spark between the different disciplines and making you know, hearing about their research questions and their concerns or their technological challenges or what aspects they're trying to overcome. And then you can sort Oh well actually, you know, we we do it this way or, you know, you can take and learn from each other.

But I mean, you know, I've worked you know over 20 years now with all these different disciplines and learned so much. And I think in order to undertake successful research you need to be able to work together with everyone in these environments. And it's certainly I've learned a lot in terms of, you know, I'm a geologist, not an engineer.

in terms of the the challenges in terms of how you build vehicles to put down to these sort of depths and things, you know, working with Alan, for example, as an engineer. Yn yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw'n yw. How can we get um physical samples and cores from these deep areas without using a big drill ship like the Japanese vehicle Chikyu? You know, trying to think a little bit more out of the box.

But I think also in terms of the big discoveries. I think if you look back at how those expeditions and how the people on board have worked together, that's helped contribute to some of these big discoveries that we're making in the deep sea now as well. It's struck me in this discussion how uh remarkable the research into biology has been.

Uh, John, I've got a question for you. How do you study these animals when presumably if you bring them up to the surface, they're not gonna survive, are they? They they don't survive, no. They don't explode, okay, because of the pressure thing that we talked about in r in reverse. Okay. They're not there's nothing in them to expand as they come up, big if it's solid tissue and and liquid body fluid. ond we can learn a lot from the specimens that we do get of course.

Um we can look at the adaptations they've got. We can we can look at what molecules are in their cells and and so on. Uh these days though we're also able to preserve animals actually at the seafloor. uh which is really useful. So for example you can collect a specimen and you can process it in a way that its tissues are preserved in something that allows you to see what genes are actually switched on at the moment that you encountered it.

So that you know, otherwise we we can do that with specimens we bring up, but of course they'll have gone through a lot of changes on on the way up. But actually being able to preserve things in situ is giving us really big insights in what we call genomics and transcriptomics, seeing what genes are actually being switched on uh in that organism, in its environment, to understand how it's adapted to the conditions down there. Historically, Alan, um people have believed that

this is an area of giant monsters and uh uh all sorts of mysterious creatures. Do you encounter that sort of attitude today despite the fact that we now have a much better idea of what's down there and they're not giant monsters. Yes, all the time. It's one of the most common questions you get is about questions about Megalodon and stuff like that and you know, I think when you start looking into

the energy in these systems they c it could never ever support a large animal, especially not of that kind of size. But even bigger than a a shoe is quite difficult to maintain at those kind of depths. So it's it's just all to do with

education I think in the way in which Deepsy's portrayed in the media and things like that. I think we can probably do it a bit more responsibly in Stop referring to monsters and creatures and stop making movies about it and but then you know, little snail fish aren't gonna make a Hollywood movie, right?'Cause you know, they don't even have any teeth.

Well they did make a Disney movie about a clownfish, so maybe maybe the snail fish could come next. Yeah, different type. Who knows? I'm very interested in d deep sea vents and

deep sea mining. Is that something that you have to engage with that that debate about whether the minerals should be exploited in this way? I mean I work primarily on deep sea vents, which we don't get in subduction trenches in the same in the same way, these black smoker systems and so on.

Yes, deep sea m that is one of the environments that's being targeted for a form of deep sea mining. There are others as well. People get very excited these days about the manganese nodules. That's a totally different environment, totally different set of ecological kind of challenges involved there. For deep sea vents, uh the active ones, which have these incredible colonies of of uh species living around them,

We don't actually need to do any more research to say that mining active deep sea vents would risk extinction of species. And we've been very clear to that to the international regulators. And I hope when they drew do draw up some kind of code for this activity in the future. That'll be the top line for this environment is that active deep sea vents must be protected.

And one final question, is the Mariana Trench less interesting now because it's pretty well known what's what's down there and it's not as active as as the other trenches? Uh or will people still want to go down? Hallo? Alan hinted at, you know, just because it is the deepest, of course, you know, there's still gonna be a lot of interest and activity down there.

But I mean, for me, you know, the South Sandwich Trench, the um Tonga Trench, the Kermadek Trench are much more interesting from a a geological perspective in terms of the activity going on there. We're managing to document sort of volcanic uh pyroclastic density currents at, you know, and the the rocks that have been deposited by those features at eight thousand meters wash depth, which has never been done before. So we're starting to look at new

processes. We're getting little glimpses as to volcanic processes at depth in these environments now that hadn't been noticed before. So there's still a lot to be learned. from these environments. But I think certainly sort of widening and working elsewhere and engaging with with uh

with other researchers as well. There's also another way to look at it because the Mariana is massive, right? If the volume of the Mariana is about the same as the volume of the Himalaya and the size of a submersible might let's say is the size of a Land Rover.

Yeah. So if you put a Land Rover on the Himalayan and said, Look, how long is it going to take for you to document everything on this thing? It's going to take you a while. Right? So you could theoretically spend your entire life just working on that thing. But again

within the the book ends of it being this is what happens in the Mayan trench, you can't necessarily make bigger statements about this is what happens in every trench, but it's still valid. And the Mayan trench weirdly is actually five different areas. There are subducting semanks which partition it.

So from an animal like Challenger Deep, for example, could not get to the top of Mariana Trench without having to decompress by thousands and thousands of metres. So there's technically it's five bins. So yeah, so there's all sorts of interesting things to do. My thanks to John Copley, Heather Stewart and Alan Jameson. And next week it's the Roman Arena and the role of gladiator fights in imperial politics.

Thank you for listening. And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Misha and his guests.

So tell me, what did we miss out? John Uh I I personally am really fascinated in kind of like the inner space race that took people to the bottom Mariana Trench for the first time and the context for that. There were various private individuals who were designing these vehicles and engaged in this work and innovating and and so on and then the French Navy wanted to get involved and then they had a bit of a bust up and Eventually the US Navy got involved and bought up the technology.

Uh, at a time when they were rea uh in during the Cold War, this is around about nineteen sixty, when they were really flexing their muscles publicly in terms of capability in the ocean. They sent a submarine underneath the North Pole for the first time, they surfaced one at the North Pole, they had the first circumnavigation submerged by a nuclear submarine and they wanted to be the people to get to the deepest point for the first time.

So that whole story I think is a very interesting story. Sort of mirroring the space story about the side. To some extent the Russia the Soviet Union really weren't weren't involved in sending people. I mean they were sampling deep trenches uh in the late nineteen fifties. and looking at life down there, but they weren't looking at these kinds of demonstrations of of capability in the same way. Hather, what did we miss um?

The evolution of the Pacific ocean as a whole is really interesting. So if we go back sort of two hundred, three hundred million years we had um a supercontinent called Pangea and it was surrounded by a a super ocean called Pantalassa. And basically Pacific is the last remnant of that ancient ocean. And that's why it's so much older than the Indian and Atlantic. So they opened at sort of two hundred million years ago as this supercontinent Pangaea.

started to break apart, that's when the Atlantic and the Indian Ocean starting to to open. But what is really cool is that in the northwest Pacific, actually just near the Mariana, is where they sampled the oldest oceanic crust in nineteen eighty nine. And it was drilled by a a big international uh collaboration called the Ocean Drilling Programme.

and that was a hundred and s it prove rocks that are Jurassic in age, a hundred and seventy million years old. And that is just fantastic. And I love the fact that The Pacific Ocean is this old ocean made of old geological rocks, the oldest oceanic rocks that we have on our planet.

ac mae'n yw'n meddwl mae'r pacific oceaniaeth wedi'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i rather than the Atlantic and Indian that are still opening and widening at the time. So so that's still the breakup of Pangea? Yes. Yeah. And I I I love that. I love that the geological time scale is still sort of trundling on and it's just this

this uh conveyor belt of sort of motion. So if we think about plate tectonics and the earth being made up of these sort of jigsaw pieces all sort of moving relative to each other and some are sliding past one another, that's a sort of strike slip. yw'r yw'r yw'r yw'r yw'r yw'r yw'r yw'r yw'r yw'r yw'r yw'r yw'r

areas and other ones are are sort of where we get new crust being formed. And I just love that conveyor belt of evolution. John. The the thing that surprises me as a biologist though when I hear about this th the just geological history is is that nevertheless, even though the Pacific is the oldest bit of ocean crust we've got, it's still really to me very young, you know, compared to three and a half billion year rocks on land in some places.

Four point six billion year central of central Canada and even the northwest of Scotland, that's some of the oldest rocks on our planet, is four point three million But I think it shows how dynamic the ocean is. Yes. You know, uh that that's that's the thing. Is it it's much more dynamic than the land. Yeah.

But uh uh Alan, anything you feel we've missed out? I've got a funny story about a party. Go on then. So yeah, so b the Challenger Deep was not discovered in eighteen seventy five. It was discovered in nineteen fifty two. Right, but challenger to you, right? So I read this book once, it was called The Hydrographer's Tale and it's it's by a guy called Steve Ritchie, who t ended up Rear Admiral Steve Ritchie, he was the highest ranking hydrographer in the Royal Navy.

And he had done the soundings for the D Day landings. He ended up on Challenger two and he sounded what is now Challenger Deep the ten thousand and I I remember talking to my boss at I used to work in Aberdeen for many years. I said to my boss, like this guy's this is the guy who discovered Challenger Deep My boss said, Yeah, he lives just uh up the road. I was like, You kidding me? So I ended up at his ninety third birthday party.

He he lived in a town called Colliston, he and his family had been there for two hundred years and then w we turned up thinking there's gonna be this frail old man in this cottage. I really hope there's rum. Oh it was an admiral story, you know. You know, it's like I've actually met went to the birthday party with a guy discovered.

Challenger Deep was only really identified by him and it's murky because someone gets a deep siding which says there's something big there, but then refining just exactly where the deepest point is takes a little time. So so Challenger Deep is a feature on a map. Turns up in eighteen seventy seven. Okay, but it's not you know, that's before there was a Mariana trench or whatever, and it's just and that's one measurement.

And they just drawn a kind of a circle around it. Did they have to did the did the Challenger, the original Challenger, did they have to have rope going down five kilometres or something? Yeah, um the it was Phenomenal. I was they covered 70,000 Nosco miles, but they had 144 miles of Italian hemp.

for the soundings that they were doing. And quite often they had a bucket on the end of that rope so they could take like a little sample and of the the sort of sediment that was down there. But I mean imagine have like keeping track Of all of that wire and it wasn't actually the absolute cutting edge technology at the time. So uh Lord Kelvin, the absolute polymath genius Uh, eighteen seventy two he'd invented a a wire sounding

machine using piano wire to to measure the depth. So what they do is they lower a weighted line and they kind of look at the rate at which the line is paying out and and when it slows down they assume the bottom of it is now touching the C. Um and it's you know In really deep water. In really deep water, yeah. The ocean currents can take it and so anyway, th that's why a lot of the early measurements are are way off um for things.

Lord Kelvin's piano wire machine is much more reliable. Now he sent one to the HMS Challenger, but they couldn't get it to work properly. It was still a prototype, and so they just shelved it and they went with tried and tested. But they they still had was it twelve and a half miles of piano wire with them as well. You know, it's just something that because of the the

popularity of upright pianos amongst the middle classes of the nineteenth century m led to mass production of piano wire, which meant it was available in these huge lengths for ocean sounding. Yeah. What do we use for ocean sounding today? Acoustics. Yeah.

But very, very accurate, right? Yeah. Yeah, yeah. So I I mean yeah, we know that, you know, Challenger D for example is ten thousand nine hundred and twenty five met meters. Plus or minus six. Yeah, plus or minus six, you know. At our margin, you know, and it You know, that's that's using sort of a a sound to sort of it goes from the ship down to the seafloor, bounces off the seafloor and comes back up. What's interesting is um the meteor in nineteen twenty six used

Sound to measure water depth for scientific purposes. It had been used by the military pre-1926, but the first use for scientific purposes was actually in the South Atlantic, in the South Sandwich Trench. and it was an expedition and they measure and we went back and surveyed it in 2019 yeah And we were within one metre of what they recorded in nineteen twenty six. It was the Germans that had been out on um R V Meteor.

And it was ju you know, that way that it's just you know you're like that's it was almost a hundred years later. There is a sort of and they actually had it so it's meteor deep. In between the ropes and the acoustics there was a thing called bomb sounding which was brilliant. So you'd stand on the back of the boat, you'd like a stick of dynamite.

You throw it off so it blows up on the surface and there's a kid in the hull who pushes a stopwatch when the bang goes off and then pushes the stopwatch When you hear the echo. The the stock on the the dynamite as well as the thing. And so some of the there's a guy called uh was it Bob Fisher and Cullenberg and these guys, they would

sort of draw it based on these things. It would and there's hand drawn one in the Philippine trench. I think we went there and tell you what, it's not bad. It's not bad because given they're just lobbing dynamite off the back of the boat, right? cake a case of TNT. It's just like lighting it off a cigar and just lobbing it in the ocean. And then eventually when we get echo sounding after bomb sounding, that was in part because of the Titanic.

So there was a German inventor who after Titanic came up with a way, well can we detect, you know, potential collision obstacles using sound looking ahead and then people said, Well if we turn that vertically we can use that to measure ocean depth. Got it. Yeah. Well, just a little bit, yeah. Yeah. I was also very interested by the way in the uh the fact that the fiber optic cables are only at Challenger Deep and I

I can just imagine the type of the endless covert activity that is going on in places like it. Yeah. It really is. And you don't want to get tangled up in it'cause you have no idea if it's a thousand meters long or ten thousand meters, but it's everywhere. And we don't know if there's someone on the end of it.

So when y whenever you're going along there you've got to keep your eye out and and as soon as it's seen it it's cut the die if you just move. We've published all we've we we've actually drew a map of it and try to recommend an area to not take a tethered or an untethered vehicle because it's it's pretty Why do you want to get rid of the um get rid of the uh fibre optic cable?'Cause presumably you can reuse it.

Oh there's lots of different reasons. There's some of it's obviously under who we think is doing it, but you can do that by having uh a surface boy that gets It's winched below the surface so no one can see it. So you can if you imagine you had a a flotation device with a beacon on it a hundred meters under the surface and it's connected all the way to the bottom. Now you can listen to submarines coming out of Guam, which is

Let's be honest, this is what's got something to do with that. Yeah. But you don't want someone being able to steal your listening device. So you have a little winch that then comes up for an hour, beams all your information back itself and then pulls itself back down again. Right. And so there are those in the area we think.

Uh, but to to get that technology right and to get stuff down there, fibre optic is the way to go. And the the vehicle John talked about, the fibre optic ROV, we had that out and it was it was it was terrible. Uh we happened to be there when it imploded. The whole thing imploded. It was just a very experimental, but it was just a complete disaster.

All that fibre optic is gone now and it's all lying in the bottom of the sea again. So it's it's it's I think that's what I was hinting at. It's just like today, you know, we don't have anything apart from submersibles that go that depth.

Technology is moving forward and I think we need to move away from those sort of things. Yeah, there were two solutions to it. One was super fine fiber optic, and the other one was super heavy. Japanese went real big heavy stuff and then the Americans went super thin and both turned out to be the wrong and then someone's recently did a completely untethered one and that got lost as well. So it's not easy, so we've gone somewhere in between

Feels like the right thing to do. If it was easy, other people would you know we wouldn't be doing it as a group. Yeah. Yeah. Yeah. I've come across quite a lot of fiber stuff in terms of drones as well now. Yes. So that's the same stuff that was in the American uh it was torpedo wire. That's what it's like. So it just it just falls out. So the faster you go the better it works. If you stop and try to do anything it breaks. Yeah. Yeah.

Which of course from a research perspective we're wanting to stop to pick up the samples of the the communities and the rocks and and things that are that are down there. Yeah. Was it something that occurred to me as um when you were talking about the the life down there and I think it's one of the sort of funnier thing is i is the snail fish eating the amphopods, but of course anthropods eat

soft things that have fallen down and are decaying. So what do the snailfish do to stop the the amphipods eating them from the inside out? They have an internal jaw. So they have two mouths. They've got the big mouth at the front that you suck an animal in. But if they just swallow it, the animal then just bore itself out its stomach. So it has a second jaw inside its head that when it swallows it just grinds the animal to make sure it's dead.

Oh my god. But what is really from a from a non biologist sort of you know, and that's what I was talking about when it you know, you pick up things from um lots of different disciplines so that, you know

if you come across something unusual or noteworthy that isn't from your own discipline, you know that it's it's important. Right. But when I'm looking back at some of the video and watching the snail fish so you see them sort of soup up the amphipod But then as it's the second internal jaw is working, they sort of collapse and they have a little food coma.

on the sea floor as this is working, don't they? And you just see them. Yeah, they're just sort of sat, sort of, you know, doing a beach well, what what my family call a beached whale impression after you've had too big a meal. And they're just all sort of sat on the sea floor going, Oh, crikey, you know. But really at least it it means I'm not going to get consumed by my dinner from the inside out. You know, it's just sort of funny things like that that keep you going.

But I mean I think as we're sort of exploring more and more of these environments and stuff, you know, that

the discoveries that we're making is is makes it all worthwhile. It makes the the sort of trips away or away from family and friends. But also the other thing that I failed to ask you about, which I should have done, was uh about what the implications of the research are for human health. Uh, because that was a fascinating aspect of it in terms of I think it's to do with the enzymes and the protein folding. Is that right, John?

Well there are a lot of insights we can get um from deep sea animals. I mean n I'm not so so familiar with actual trench organisms, but it's something I I keep an eye on and You know, deep sea life can inspire us in two different ways. Actually for material science. So I was co author and description of a species called the scalyfoot snail and it's teaching us how to make better solar panels.

uh because it can create tiny crystals of a metal mineral that at room temperature and this is what people want to be able to do for solar panels. And now people have been able to recreate this process in the lab with kind of off the shelf ingredients. Uh, I also was involved in describing a species of deep sea shrimp which has got tiny little bristles on it, which have inspired a new nano material that's fantastic for heat and sound insulation.

Uh so there's those sorts of things. And then there's a lot on the biomedical side. Um one of the chaperone molecules that you get in a lot of deep sea life uh in laboratory studies, you know, can help to rescue human proteins that get bent out of shape, which involving quite a few human diseases. Well look, thank you all very much. This has been absolutely fascinating. Really appreciate it. Ah Simon Does anyone want tea or coffee or rum?

It's if the chances of finding a glass of rum in the BBC are actually less than zero. Oh thank you. Brilliant. Thank you. In Our Time with Misha Glenny is produced by Simon Tillotson and it's a BBC Studios production. I'm Paul Kenyon, and for Radio 4 and the History Podcast, this is Two Nottingham Lads. When the invasion happened, Completely hell on earth. The sad thing about war is people lose. I want to know how two men from Nottingham

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