Podcast: Insects, sediment and climate change

Cumulonimbus clouds over a lake

Cumulonimbus over the lake at Quistococha

27 May 2014 by Richard Hollingham

This week in the Planet Earth podcast, Frazer Bird and William Gosling of The Open University explain why tiny midges are a powerful tool for telling us about past climate change, and how they can help us predict the future.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Richard Hollingham: I'm Richard Hollingham and this time in the Planet Earth podcast, what midges can tell us about our changing climate. I've come to the Open University in Milton Keynes and I'm standing in a very narrow white lab. There's a bench along one side and then it is dominated by a giant fridge like, I suppose, one of those oversized American fridges you get. And this is one of the laboratories where scientists are studying insects in mud and sediment from tens of thousands of years ago to build up a picture of past climate and help predict future change.

I'm joined by Frazer Bird who is a researcher here. What is in this giant fridge?

Frazer Bird: Hi there. Right, I will take you in. This is our cold store where we store all the cores that we collect on our field work.

Richard Hollingham: So these are cores of sediment and mud - where from?

Frazer Bird: So these lake cores, specifically, and mostly from the tropics of South America. So we have cores from Bolivia, Peru, Ecuador, we have the odd core from Vietnam, pretty much all over the world really.

Richard Hollingham: And when you say cores, there are shelves in this fridge look almost like the rolls that you would have tin foil wrapped around in a kitchen, something like that. But these narrow tubes or poster tubes, perhaps, they're full of mud?

Frazer Bird: Yeah, absolutely. So they are about a metre and a half long aluminium tubes that we drive into the sediment, metre by metre and we retrieve it as it was deposited thousands of years ago. We bring it back to the lab, split it open and there preserved within the layers is the record that we're after.

Richard Hollingham: And you are specifically looking at midges, so tiny insects?

Frazer Bird: I'm looking at midges. They are an aquatic fly that live in lakes and screams and they are really species rich and all the different species seem to live in different environments, so as that lake changes through time different midges will inhabit it and so persevered within the mud are all those different midges and it is a signal of a different lake through time.

Richard Hollingham: So you can get a record of the lake by studying the species of the midges?

Frazer Bird: Absolutely. So, the lake is just sitting there, thousands of years slowly collecting all the organic matter as the world around it changes and different insects will live in it, and so those insects are a representation of the world that they lived in at the time that they died and were deposited.

Richard Hollingham: If we move away from the fridge, which is as you can imagine very cold, to the bench itself and on here you've got, what, half of one of these tubes. It looks a bit like a drainpipe stretched out along the bench here with some of this sediment in it and it just looks like rich peat really.

Frazer Bird: The cores come in in these tubes, as I explained, and then we split them open, one side is kept as an achieve that we store in the fridge indefinitely and then the other is the side that we begin to analyse and so usually people will sample this centimetre by centimetre and as you can see the sediment does change and through those changes we expect the environment to be changing.

Richard Hollingham: We've come into the microscope laboratory where as you would expect there are microscopes and this is where you analyse individual midges under the microscope that you've extracted from the sediment.

Frazer Bird: We sieve the sediment to the size fraction that we know the midges are. We then place them under a low powered microscope and pick through the sediment until we find the midges. We mount those individual heads individually onto microscope slides and then we can put it under a high powered microscope and identify the species.

Richard Hollingham: Now we can look at this under the microscope in just a second, but how big or how small is the actual midge head?

Frazer Bird: So they are about one hundredths of a millimetre. You can actually see them with the naked eye, really big ones, and once they are under the low powered microscope they really pop out and you can pick them up.

Richard Hollingham: Well let's have a look down down the microscope and actually you've hooked up the microscope to a screen. What are we looking at here? It looks like a squashed insect.

Frazer Bird: The midges have four stages to their life cycle. Three are in the lake as an aquatic organism and one as a flying insect which we all know and ruin our holidays. The larvae have a head capsule made out of chitin, which preserves well and this is basically the head capsule of one of those midges. So the rest of its body has rotted away and all you are left with is the head and then on the head there are distinct features that can identify the species.

Richard Hollingham: If we look at this one then under the microscope it looks almost like a set of fingers, quite rounded protrusions coming out, almost like fingers.

Frazer Bird: This is called its mentum, these are its teeth. It's the arrangement of these teeth combined with other features which will tell you what the species is.

Richard Hollingham: So how does this compare to other ones and can you easily tell the difference?

Frazer Bird: Oh, massively. So I can show you another one very quickly. This one is called Chironomus anthracinus.

Richard Hollingham: And that is completely different. That looks more like a Bart Simpson haircut-type teeth arrangement rather than the fingers.

Frazer Bird: Yes, this one has a lot more teeth. They are actually the same family or same sub-family but, again, as you can see a very different species level. It has a lot more teeth and it also has what we call a trifed medium tooth. So a big tooth, two little teeth and then its lateral teeth.

Richard Hollingham: How do you know then what time period these midges are from?

Frazer Bird: We use radio carbon dating on our cores to work out time brackets for different sections of the core and then we can work out roughly how these changes are happening based on changes through time.

Richard Hollingham: Well we are also joined by William Gosling who is overseeing this research, a senior lecturer at the Open University. You've got this record then from midges, how use is that?

William Gosling: Well the record we can reconstruct from midges is really interesting because it can tell us about what past climates were like. It can particularly tell us about past temperatures. Now, understanding how temperatures have changed in the past, how they have varied and then coupling that up with other indicators of past environments, so looking at fossil pollen to reconstruct vegetation, for example, allows us to think about how sensitive things like vegetation are to changes to temperature and this allows us to put the world we see around us today into context.

Richard Hollingham: And you can presumably use this to also help predict future climate?

William Gosling: If you're creating a model that is going to project future climate change one of the really good ways that we can try and think about validating that model, testing if it really works and is accurate is by having a set of data that tells us about what things were actually like in the past and we can run the model backwards, if you like, to see if we can successful predict that. If it can predict the past correctly then we can have more confidence that projects us into the future are likely to be correct.

Richard Hollingham: And South America, this is an area that you've got limited data on in the past. So the midges are, what, helping you fit in a missing link here?

William Gosling: Yeah, absolutely. I mean compared with working in, say, North America or in Europe the amount of samples and locations that we've looked at is very small. To give you an example of that in certain circumstances working in Amazonia it is like trying to tell what the climate was like in London by looking at a sample from Moscow in many instances because we have so few data from South America. So Frazer's work looking at the South American midges and being able to use those midges to create past temperature reconstructions is really novel and pretty unique actually on a continental scale.

Richard Hollingham: So, Frazer, have you found anything surprising so far?

Frazer Bird: What we're seeing with the midges is that they are actually a lot more sensitive to climatic changes. The insects today live on very rapid life cycles, so if the environment changes they too change very quickly and we're seeing this in the fossil record. When we look at the insects they change rapidly through time and they are showing huge changes in the climate that we didn't really know was happening.

Richard Hollingham: So, William, this is proving quite a powerful tool?

William Gosling: Yeah, indeed. I mean looking at sensitivity, if you're looking at rapid climate change protected into the future, what we're seeing with other properties is that they weren't detecting where we saw rapid climate change in the past, whereas the midges really let us get a handle on changes that are happening over decades to hundreds of years which is really important if you want to understand what is going to happen in the future.

Richard Hollingham: William Gosling and Frazer Bird, thank you. We will put some pictures of the midges on our Facebook page and for more podcasts, news from the natural world and the work of the Natural Environment Research Council, visit Plant Earth online. From the lab here at the Open University in Milton Keynes, that's the Planet Earth podcast. Thanks for listening.