In Our Time: The Mariana Trench

25:59Follow NerdWallet's Smart Money podcast on your favorite podcast app. Alan, we've talked about how the Mariana Trench was created how it was discovered, the geology and so on but what happens when you actually go down there? What do you see? Is it a pristine environment? No. Sometimes there are places that look very pristine but I've probably done over 30 dives now and I don't necessarily recall any dive that haven't seen something man-made. Probably every one. Maybe there's one or two that haven't. Some of them are really bad. So I remember doing a 10 ,000-meter dive on the Philippine Trench, which was the spot where the Galatia expedition in the 50s had found a rock, which was a Galatia enthe moon, by the way, the one I was mentioning earlier.

26:50So we dove on that spot and we filmed them live. I thought, that's great. But we also saw something like 19 plastic bags on the same dive, just floating around. You could read the logos off them. There was an eco-friendly plastic bag came past and you're like, really? How eco-friendly is that? And then there are other dives where it's actually more serious. So going back to Mariana Trench, diving the Challenger Deep, the whole Western side of Challenger Deep, which is where Don and a guy called Picard dove in 1960, is now in no-go zone because that whole area is just covered in discarded fibre optic cable.

27:22And so someone in the last 10, 20 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 if you're 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 Deep. It's not anywhere else in the Mariana and it's not seen anywhere else in any other trench.

27:52So there are things like that where that's kind of almost deliberate. Someone's been doing something there. But one of the weirdest ones, I think, was last year we were down, I think it was 5 ,000 metres somewhere, just on the equator four days north of Samoa and we were driving along and doing the usual thing. I was telling the pilot, go and have a look at this, go and have a look at that. And we saw this red thing. I thought, 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.

28:21And, you know, it's bizarre. It's really quite bizarre. It can really throw you as well when you're sort of going out because you're so focused on trying to, you know, record as much scientific data and information and the commentary that as you're going along on the seafloor and then 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 meters and i said to the the pilot i was like oh god there's there's something over there like that's gonna be and it was a cardboard box it's just you know you're like oh oh sugar i've just like deviated from the plan because I thought that was going to be something geologically or ecologically monumental.

29:00It's like, oh, okay. The Port Rico trench was probably bad. The Port Rico had gates and magazines and plates and Coke cans and beer bottles. But I mean, it's sitting in hurricane alleys. 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 going to end up there. And it's quite depressing to see it. Although the point you make about fibre optic cables on Challenger D seems to me to be quite interesting. The coolest thing about Mariana in terms of man-made naughtiness is there's an SR-71 Blackbird you know the old aircraft from the 60s, a big black really cool looking thing?

29:40One 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 somewhere in the Mariana there's a Blackbird which would be the coolest I've ever. I beg to differ. they haven't released the coordinates for exactly where it is I bet the Chinese have found it by now John, I want to come back to the animals down there how do they feed? 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 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 the bottom of your trench i mean it's a 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 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 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 fueled islands of life that break all the rules.

31:16They're what we call cold seeps. As Heather mentioned, where you've got these plates 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 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 in terms of animal colonies in cold seeps in the Marianas but they have been seen in the Kirol Kamchatka and the Aleutian Trenches more than 9 ,000 metres deep which are the deepest known islands of this chemically powered life which we have on earth which are hugely exciting.

32:01Alan from a scientific perspective the Mariana must be 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 a bit of both it's not certainly not the most interesting i think it's 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 from a purely scientific point i think we've spent a lot of time going to other trenches we've done mariana about six times but for various different reasons and different boats and different nationalities whatever.

32:36There's been reasons for doing it but 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. The biggest problem in Mariana we've got is that one of the only big trenches in the world that does not lie along a coastline so all that organic matter that comes into the surface that rains down its food, it's the only one that doesn't have it. The rest of them are somehow attached to or associated with the continental landmass. It's also quite low near the equator and so there's not a lot of food on the surface there anyway so it is 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 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?

33:41Not very much. It would tell you a little bit about altitude, but it wouldn't tell you anything about a mountain goat in Kilimanjaro, right? So do I get, John, in that case, the implication of what Alan's saying, that the environment in Mariana is actually very static and constant compared to others? 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. So climate change affects all of the ocean, including the deepest depths in the ocean. And it affects it in several different ways. I mean, we are getting warming of waters and that is getting deeper and so on.

34:20But fundamentally for deep ocean, what's changing is the flow of oxygen that reaches the deepest parts of the ocean. So all the animals that we've been talking about, they're animals. They need oxygen. The oxygen is 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 the Mariana Trench, the oxygen that those animals are consuming began its journey into the deep actually in the Antarctic.

34:53And it takes several hundred years for it to kind of flow 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 300 years' time? It does, yes, indeed. 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 10 % 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 10 % less than it had already.

35:29It's going to change the distributions of species around the world. Some can tolerate that. Some can't. Their distributions 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 when you're looking at something like 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 can speak on all of us.

36:06I think the most rewarding expeditions have been the cross, multidisciplinary ones. and each discipline, you know, thinks a little bit differently, you know, the engineers, 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 of, oh, well, actually, you know, we do it this way. or you can take and learn from each other.

36:44But I mean, I've worked 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, I'm a geologist, not an engineer, in terms of 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. You know, it's fascinating and it's allowed me to think better and more strategically and more creatively about how to sort of address geological questions, you know, like how can we get 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.

37:36but 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 remarkable the research into biology has been 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 going to survive are they they they don't survive no they don't explode okay because of the pressure thing that we talked about in in reverse okay they're not there's nothing in them to expand as they come up if it's solid tissue and liquid body fluids um but 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 these days though we're also able to preserve animals actually at the seafloor, which is really useful.

38:39So 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 can do that with specimens we bring up, but of course they'll have gone through a lot of changes 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 in that organism, in its environment, to understand how it's adapted to the conditions down there.

39:11Historically, Alan, people have believed that this is an area of giant monsters and 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, it could never, ever support a large animal, especially not of that kind of size. But even bigger than a shoe is quite difficult to maintain at those kind of depth.

39:49So it's just all to do with education, I think, and the way in which deep sea is portrayed in the media and things like that, I think we can probably do it a bit more responsibly and stop referring to monsters and creatures and stop making movies about it. But then, you know, little snailfish aren't going to make a Hollywood movie, right? So, you know, they don't even have any teeth. Well, they did make a Disney movie about a clownfish, so maybe the snailfish could come next. Yeah, different type. Who knows? I'm very interested in deep sea vents and deep sea mining. Is that something that you have to engage with, that debate about whether the minerals should be exploited in this way?

40:32I mean, I work primarily on deep sea vents, which we don't get in subduction trenches in the same way, these black smoker systems and so on. Yes, deep sea, 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, the active ones, which have these incredible colonies of 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.

41:07And we've been very clear to that to the international regulators. And I hope when they 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 down there and it's not as active as the other trenches? Or will people still want to go down? Heather? I think as Alan hinted at, you know, just because it is the deepest, of course, you know, there's still going to be a lot of interest and activity down there.

41:46But I mean, for me, you know, the South Sandwich Trench, the Tonga Trench, the Kermadec Trench are much more interesting from a geological perspective in terms of the activity going on there. We're managing to document sort of volcanic pyroclastic density currents at, you know, and the rocks that have been deposited by those features at 8000 metres 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.

42:23But I think certainly sort of widening and working elsewhere and engaging with other researchers as well. There's also another way to look at it because the Mariana is massive, right? If the volume in the Mariana is about the same as the volume in the Himalaya and the size of a submersible might, let's say, is the size of a Land Rover. so if you put a land rover on the Himalaya 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 so you could theoretically spend your entire life just working on that thing but again within the bookends of it being this is what happens in the Mariana Trench you can't necessarily make bigger statements about this is what happens in every trench but it's still valid and the Mariana Trench weirdly is actually five different areas there are subducting semen which partition it so from an animal at Challenger Deep for example, could not get to the top of Mariana Trench without having to decompress by thousands and thousands of metres.

43:13So technically it's five bins of really deep ones. So, yeah, there's all sorts of interesting things to do. Well, that's all I wanted to ask. What would you like to add? I personally am really fascinated in kind of like the inner space race that took people to the bottom of 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 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.

43:48At a time when they were, during the Cold War, this is around about 1960, 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 one. Sort of mirroring the space story. To some extent. The Russia, the Soviet Union really weren't involved in sending people. I mean, they were sampling deep trenches in the late 1950s and looking at life down there, but they weren't looking at these kinds of demonstrations of capability in the same way.

44:30Heather, what did we miss out? I think the evolution of the Pacific Ocean as a whole is really interesting. So if we go back 200, 300 million years, we had a supercontinent called Pangaea, and it was surrounded by a superocean called Pantalassa. And basically, the 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 200 million years ago as the supercontinent Pangaea started to break apart. That's when the Atlantic and the Indian Ocean started to open. But what's really cool is that in the northwest Pacific, actually just near the Mariana, is where they sampled the oldest oceanic crust in 1989.

45:19And it was drilled by a big international collaboration called the Ocean Drilling Programme. and that was a hundred and a few rocks that are Jurassic in age 170 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 and that and that's why the the Pacific Ocean technically is contracting as it's getting consumed rather than the Atlantic and Indian that are still opening and widening at this time. So that's still the breakup of Pangaea? Yes, yeah. And I love that. I love that the geological timescale is still sort of trundling on and it's just this conveyor belt of sort of motion.

46:05So if we think about plate tectonics and the Earth being made up with 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 sort of margin or one's being consumed by another, that's your convergent, that's your subduction areas and other ones are sort of where we get new crust being formed and i just love that conveyor belt of evolution john the thing that surprises me as a biologist though when i hear about this this 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 yeah well 4.6 billion year yeah so central of central Canada and even the northwest of Scotland, that's some of the oldest rocks on our planet is 4.3 million billion, sorry.

46:52But I think it shows how dynamic the ocean is. Yes. That's the thing. It's much more dynamic than the land. But, Alan, anything you feel we've missed out? I've got a funny story about a party. Go on then. So, yeah, so the Challenger Deep was not discovered in 1875. It was discovered in 1952. Right, by Challenger Deep, right? So I read this book once, it was called The Hydrographer's Tale, and it's by a guy called Steve Ritchie who 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 2 and he sounded what is now Challenger Deep, the 10 ,000.

47:27And I remember talking to my boss. I used to work in Aberdeen for many years. I said to my boss, this guy's just a guy who discovered Challenger Deep. My boss said, yeah, he lives just up the road. I was like, you're kidding me? So I ended up at his 93rd birthday party. He lived in a town called Colliston and his family had been there for 200 years. And we turned up thinking there's going to be this frail old man in this cottage. I really hope there's rum at that party. Oh, there was lots of rum. Admiral's story. It was wearing some African poncho, and his house is all oil-on-canvas drawings of some harbour in Borneo somewhere.

47:56It was brilliant. Unfortunately, he died a couple of years later, but it was great to just, you know, it's like I've actually met and went to the birthday party of the guy who discovered Challenger Deep. So, hold on, let me get this straight. The Challenger Deep was only really identified by him. It's murky because someone gets the deep sounding which says there's something big there, but then refining just exactly where the deepest point is takes a little time. So Challenger Jeep as a feature on a map turns up in 1877, 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've just drawn a kind of a circle around it.

48:28By the way, did the Challenger, the original Challenger, did they have to have rope going down five kilometres or something? They did. I wrote it down actually. Hang on, let me... It took the other wire. Yeah, it was phenomenal. They covered 70 ,000 nautical 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 of the sediment that was down there. But I mean, imagine keeping track of all of that wiring. And it wasn't actually the absolute cutting edge technology at the time.

49:06so Lord Kelvin the absolute polymath genius 1872 he'd invented a a wire sounding machine using piano wire to measure that 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 when it slows down they assume the bottom of it is now touching the seabed and it's you know in really deep water in really deep water yeah the ocean The incurrence can take it. Anyway, that's why a lot of the early measurements are way off 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.

49:44It was still a prototype. And so they just shelved it and they went with tried and tested hemp. But they still had, was it, 12 and a half miles of piano wire with them as well. And actually, that's something that because of the popularity of upright pianos amongst the middle classes of the 19th century, led to mass production of piano wire, which meant it was available in these huge lengths for ocean sounding. What do we use for ocean sounding today? Acoustics. Sound, yeah. But very, very accurate, right? Yeah. Something that occurred to me is when you were talking about the life down there, and I think it's one of the sort of funnier thing, is the snailfish eating the amphipods, but of course amphipods eat soft things that are falling down and are decaying.

50:27So what do the snailfish do to stop the amphipods eating them from the inside out? They have an internal jaw. So they have two mouths. The big mouth at the front, they just suck an animal in. But if they just swallow it, the animal then just bore itself out of 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 non-biologist, and that's what I was talking about when you pick up things from lots of different disciplines, so that if you come across something unusual or noteworthy that isn't from your own discipline, you know that it's important.

51:03But when I'm looking back at some of the video and watching the snailfish, so you see them sort of suck up the amphipod, but then as 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 doing a beach, well, 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 seafloor going oh crikey you know but really at least 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 sort of trips away away from family and friends My thanks to Heather Stewart, John Copley and Alan Jameson.

51:53And thank you for listening to In Our Time from the BBC World Service. In Our Time won't normally be here in the documentary, so if you'd like to hear more episodes on topics from the Roman arena to the microorganisms that live in volcanic springs, then just search In Our Time wherever you get your BBC podcasts. In Our Time is presented by me, Misha Glennie. It's produced by Simon Tillotson and is a BBC Studios production.

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