The Planet Earth podcast - 'Microscopic plants, using volcanic ash for dating'.
23 April 2012
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Richard Hollingham:Hello, I'm Richard Hollingham. Welcome to the Plant Earth Podcast from the United Kingdom's most easterly point, Lowestoft. We will be contemplating the colour of the North Sea. Also this time the secrets revealed by volcanic dust.
Victoria Cullen:Every blast from a single eruption has one composition, one chemical composition, which is frozen at the time of the explosion and that composition acts like a finger print.
Richard Hollingham:Growing up in East Anglia I spent much of my holidays on North Sea beaches in biting wind like this and the water, well it's never looked that inviting. Here on the beach at Lowestoft, and to be fair a fairly clear sky, the North Sea just looks brown, slopping against the sandy beach here, but even the clearest sea water is teaming with microscopic life and that's what Katy Owen from the University of East Anglia is studying. You're looking at phytoplankton. Now, what is a phytoplankton?
Katy Owen:Phytoplankton - you have to think of them a little bit like the grass of the sea, they're tiny microscopic plants, thinner in diameter than a strand of human hair and you find them everywhere in seas and oceans around the world, hot, cold water, they're tiny little powerhouses, they photosynthesise and in doing remove carbon dioxide from the atmosphere and convert it into a organic carbon as part of their bodies.
Richard Hollingham:So they're really the base of the food chain in the sea?
Katy Owen:Exactly right, yeah, they underpin everything. They're eaten by things as varied as crab larvae, bacteria, all the way up to fishes and whales - a huge range of animals eat them.
Richard Hollingham:Okay, let's get a bit closer to the water. We're not going to be able to see them, presumably, are we?
Katy Owen:No, they're very small in diameter, really, really thin. Thinner than a sheet of cling film, so you can't see them with the naked eye at all.
Richard Hollingham:Let me just get a handful of water. So, I've got a handful of water and wet feet! How many plankton are there in there? Is that really just full of plankton?
Katy Owen:Absolutely teaming and you can have as many as 20,000 individual cells in just a millilitre of water, so huge quantities in a very small amount of volume.
Richard Hollingham:You're interested in this not just because it's important because of the food chain but its role in the global climate?
Katy Owen:Exactly right. Because they photosynthesise it's really key. They remove this carbon dioxide from the atmosphere and they take it out of circulation and they incorporate into their bodies and then as they die or are eaten by something else in the food web that carbon is recycled or it is taken to the deep ocean so it's out of the way, it's removed, so it's a really good way of reducing carbon dioxide levels in the atmosphere.
Richard Hollingham:Are they under appreciated synch, if you like, for carbon?
Katy Owen:Yeah, I would think so. I mean if you think about all of the publicity that the rain forests get which do a similar role but obviously trees are much more obvious. I mean you can take a quick glance and have a look at what's going on with an ecosystem on land and you can see the state of the grass, you can see the state of the forest but phytoplankton you look at the sea and you have no idea what's going on with them so it's really important that we understand a bit more about them.
Richard Hollingham:So what are you doing - before I ask that question let's just move a little further away from the waves. Let me ask that question again - what are you doing?
Katy Owen:I use a machine called a flow cytometer which is borrowed from Biomedical Research, normally it's used to scan blood cells but I am applying it to marine science and using it to count these phytoplankton.
Richard Hollingham:Why? What are you trying to find out?
Katy Owen:Everything really. We know very little about them. Because they're so small it's only really recently with the development of this machine that we've been able to count them properly. In the past since the Victorian times we've looked down microscopes to count them but obviously that's limited to what you can see with the human eye. If you do it electronically with a machine you can count them much more accurately and you can count a much larger size range and you can count them a lot faster. So using this machine is going to give you a really detailed image of what's going on with phytoplankton and where they're most abundant, what makes them tick and what nutrients and condition they prefer, everything like that.
Richard Hollingham:And I suppose that will give us a better handle on where the carbon is going and how it's moving around.
Katy Owen:Exactly, it's also to do with carbon cycling, that's what's so important and we need to know whether it is all small cells which are more likely to be recycled in the surface waters or perhaps it's concentrated in larger cells which are more likely to sink through the water column and be deposited in the deep ocean and we might not see that carbon again unless there is some kind of storm vent. It could be hundreds of years.
Richard Hollingham:Well let's get out of the wind here to your laboratory which is up there on the cliff.
Katy Owen:Sure why not.
Richard Hollingham:Well here we are in the molecular biology laboratory at CEFAS.
Katy Owen:The Centre of Environment, Fisheries and Aquaculture Science.
Richard Hollingham:And you have, rather helpfully, some flasks of phytoplankton and this looks completely green and this is, presumably, very concentrated.
Katy Owen:This is a very concentrated culture. These are some cells that grow here in the lab just for testing purposes and you can see how dense that is and you normally you wouldn't get that concentration in a natural sample. Here's one that I collected from the North Sea last week and you can see that it is more of that typical North Sea colour, brown.
Richard Hollingham:That's really just an opaque brownish colour.
Katy Owen:A lot of that will be sediment but it has been concentrated and there are quite a lot of phytoplankton cells in there as well.
Richard Hollingham:So this one here, this almost totally green one which looks almost like a rather nasty synthetic limeade. That's a plant essentially, a plant in water, lots of plants in water.
Katy Owen:Lots of tiny microscopic plants altogether in a special media that we use to grow them. There's no many of them because we enhance it with sort of special vitamins that they need to grow happily.
Richard Hollingham:And next to them on the laboratory bench is this curious looking machine - it's about the size of a beer barrel I suppose but with the outside exposed and it's full of circuit boards and tubes. It does look almost like a device out of a science fiction film.
Katy Owen:Yeah, I get that a lot actually. It's not normally like this when I take it to sea, it's out of its protective casing now that I'm here in the lab but it looks horrible, it looks really horribly complicated but it's actually quite a simple principle. It's a machine we use as a pump and we pump water, a stream of water, a stream of sea water through the path of a laser beam and as the laser beam hits anything in that seawater such as debris or, hopefully, phytoplankton cells that laser light is scattered and we collect that information which gives us a lot of details on the size and the shape and the structure and also the pigment content of the phytoplankton cells.
Richard Hollingham:So individual phytoplankton. So you can count them but you can also see the size and shape of them.
Katy Owen:That's right and something that we've been doing for a little while now at CEFAS. Traditionally CEFAS is a great place for phytoplankton taxonomy, we have a whole lab which is dedicated to counting phytoplankton cells by light microscope which is, as I mentioned earlier, something that we've done for hundreds of years now but the problem with that is that is only covers a very small range of sizes things that we call the nano and the net plankton which are from 20 to 200 microns, but there is a real whole wealth of phytoplankton below that size range something called the picoplankton which are less than 3 microns so we're talking a fraction of the size of a human hair follicle and you can't see them with a light microscope and they're just too small to be counted or identified accurately, so this machine is not only capable of measuring them we can also approximately identify them and do thousounds of these cells within a few minutes.
Richard Hollingham:And these picoplankton have they been overlooked do you think?
Katy Owen:Yes, definitely. I mean we know very little about them within the North Sea just because they are so hard to count. We only really discovered that they existed about 20 years ago in the 1980s, the end of the 1980s and we're still discovering new species. In fact this machine here, not this one exactly, but a machine like this discovers what is now a hugely important species called Synechococcus and Pyrococcus which we just didn't know existed and now it is essentially vital in carbon cycling.
Richard Hollingham:So is phytoplankton something we should all learn to appreciate a lot more?
Katy Owen:Definitely. I find them fascinating but I'm probably slightly biased but I find it amazing that things that are so small and so tiny we know just so little about. They are so important. We sail on them, we swim amongst them every day but we know very little information about them, so I think it's really key that they become more appreciated and loved a little bit more.
Richard Hollingham:Katy Owen, thank you very much. This is the Planet Earth Podcast. You can see some photos of Katy on the beach here at Lowestoft on our Facebook page and for the latest news and features on the science of the natural world do visit Planet Earth Online. To find both search for Planet Earth Online.
When a volcano explodes it ejects material known as tefra. Now this can range from rocks the size of cars to the smallest particle of ash. This ash can travel thousands of miles forming an invisible layer on the landscape, but my studying these microscopic grains scientists can date archaeological sites and this can help clarify the effects of environmental and climatic change or even determine, get this, the movement of the human population within the last 100,000 years. Well, Sue Nelson met up with Dr Christine Lane and Victoria Cullen at the University of Oxford's Research Laboratory for Archaeology to find out more as they both work on the reset project which is investigating the response of humans to abrupt environmental transitions.
Christine Lane:These are some samples that I collected in the field from various places which are close to volcanic sources but different to what we look at normally. In this bag I've got two samples from Lepari which is one of the Aeolian Islands from Italy and one of them is a pumice, a bit like you would use in the bath, a very light rock full of air.
Sue Nelson:Oh yes it is incredibly light and it's got that rough scaly feel that you know you want to put on some hard skin. Oh, and this is black and shiny.
Christine Lane:This rock is what we call an obsidian and it's actually made of exactly the same material as this pumice, it's glass, but it's got no air bubbles in it so it's really heavy and it's much denser, so even though the glass is about the same size you will feel that that is a much heavier rock.
Sue Nelson:So they're exactly the same?
Christine Lane:Yeah, the composition is exactly the same, they're both formed from the magma from the eruption, one flows out of the volcano and cools very quickly which creates a glass and one is erupted with a lot of gas in the eruption which causes a very explosive eruption, so it's full of bubbles. All of these examples were found fairly close to the volcano itself but what we're looking at in the lab here is the same material but it's travelled maybe thousands up to maybe three to five thousand kilometres from the source. So what we're looking at now is volcanic ash rather than pumice, so again it's the same material just much smaller. And you can see it looks much more like dust, just particles of dust or very small grains like sand size grains.
Sue Nelson:And do you have a specific name for this scale, this size of ash?
Christine Lane:All material erupted from a volcano when its erupted explosively we call tefra and tefra is actually the Greek word for ash, so we use the word tefra generally when we're talking about this material and in particular when its travelled a long way from the volcano.
Sue Nelson:Victoria, you're going to show me aren't you exactly what this looks like.
Victoria Cullen:As Christine says it is actually glass and if you can imagine when you break a glass in your house it fractures in very distinct ways, very sharp edges and in some locations you get these bubbles as well which also kept all the glass shards, so if I get some slides out for you know we can actually look at what it looks like down a microscope.
If I get you to look down there and you can see some very pinky purply looking shards of glass.
Sue Nelson:Do you know it reminds me of a child's kaleidoscope.
Victoria Cullen:Very much.
Sue Nelson:It is quite mesmerising because it is so pretty.
Victoria Cullen:It's very beautiful isn't it? If you were to find this in an archaeological environmental site you wouldn't actually be able to see if physically looking at the site, it's invisible to the naked eye. So this is why it's called cryptotephra or hidden secret tefra also known as microtefra. So when we look at certain sites because it's travelled so far, it's so fine, it's so small, when it is deposited it is just invisible to the naked eye so we have to take samples down these sites, take them to a laboratory, process the samples and then they come onto the microscope and actually look if tefra is there in the first place.
Sue Nelson:So now that we know, obviously, that we've got tefra because these are samples where you know they've got them, where do you go from here?
Victoria Cullen:We take them down to the microprobe and we analyse them for their chemistry. Every blast from a single eruption has one composition, one chemical composition which is frozen at the time of the explosion and that composition acts like a fingerprint so we can identify from a tefra the composition of a tefra shard which eruption it came from.
Sue Nelson:This looks like a giant microscope effectively - more than a metre high but with computer screens on either side and a console.
Victoria Cullen:Yes, this is our electro microprobe. It is like a giant microscope but it works at much higher resolutions, much smaller sizes but it also has four different, what we call spectrometers, and these are effectively the detectors that record the composition of the material that we put in there.
If I choose a little grain to focus in on we can now on the computer console we can have a look at that here - and it looks quite complicated because there's a lot of different columns on it but the one we want to look at is this column here which is the weight percent oxide and this tells us for each element-
Sue Nelson:I can see there it's sodium, magnesium, aluminium, silicea. These are all in ash?
Victoria Cullen:Yeah, these are just what we call the major and minor elements, so these are the main constituents of this ash. There are other trace elements in there but we can't analyse those on this machine. But usually, and in this case nine or 11 elements we can fairly well characterise our eruption. So you can see that the greatest composition is silicea, there are silicate materials like all volcanic rock, so silicea, aluminum, sodium, iron and potassium and sometimes calcium are the main elements that we're measuring.
Sue Nelson:There's one I don't quite recognise - TI.
Victoria Cullen:That's titanium.
Sue Nelson:It is titanium.
Victoria Cullen:Yeah, titanium oxide. So some volcanic centres such as Icelandic ones have quite a lot of titanium oxide in their systems.
Sue Nelson:And what can you actually learn from analysing these bits of ash, this tefra.
Victoria Cullen:We're looking in records where we have a story already, so we might have an archaeological site which tells a story of what the population in that site had been doing when they've been there, what sort of behaviour they've been doing and what tools they've been making or we might be working in an environmental records, so sediments accumulated in the bottom of the lake over time which record changes in vegetation or the landscape around the lake basin. And we're finding these tefra layers or the same tefra layers in different sites we can link up those records, so where we have a population in a cave and we find evidence then just below a tefra layer, if we find the same tefra layer in a lake record that tells us what the climate was doing at the time that eruption took place we can infer that that was always the climate at the time of that that population was there. So we're using them as marker layers to transfer climatic and environmental information between sites.
Sue Nelson:Victoria, you're looking at the same type of ash, the same tefra but slightly different further afield.
Victoria Cullen:What I'm trying to do with my research is to use these tefra layers to look at sites in specific regions in the Caucasus so that's Georgia, Armenia Azerbaijan, a small part of southern Russia and the [unintelligible 0:15:42.0] and it's just between the Black Sea and the Caspian Sea our little land mass there. What we're finding from these sites there is that sites that have been redated using radio carbon are now showing that the coexistence of these two species isn't as much as we had previously thought. So what I'm trying to do is use these tefras to try and test further. Because we can look at different sites in the same region on one time level with these tefras I can see, well first of all people or [unintelligible 0:16:11.8] occupying the same space at the same time. So I might find one tefra layer in another Palaeolithic case site and then in another Palaeolithic case site I might not find that. Now is that because it's not getting into there or is that because it is actually different times when people are exploiting this landscape, so I'm trying to build up a picture about how people move around this landscape and it actually can be proved that these two species co inhabit the same space in the same time in this one region.
Sue Nelson:So does the ash help with everything else be it archaeological radio carbon dating and what have you, does it act as sort of an extra test in a way in terms of learning whether different species coexist.
Victoria Cullen:So the wondrous thing about tefra chronology is ash dating is the fact that it is a blanket of time, so we can look at sites across massive geographical region and including environmental sites on one plane of time and see what was happening at that one time across, say, Europe, for example. So, if I find an ash in one case site and then find the same ash in another case site I never [unintelligible 0:17:13.5] at the same time. So then I can look at the archaeology at both sites and actually start to directly compare them and whether that is coexistence or not that's where the questions come from.
Richard Hollingham:Victoria Cullen and Dr Christine Lane from the University of Oxford talking to Sue Nelson. We will put some pictures of Christine and Victoria on our Facebook page. Meanwhile right now on Plant Earth Online you can read about the engineering that goes into orangutan nests and discover how many Emperor penguins there are in Antarctica among other things. And that's the Plant Earth podcast. It is produced for the National Environment Research Council. I'm Richard Hollingham, thanks for listening.