Podcast: Marine life and climate change

Sea butterfly

Sea butterfly - Clione limacina

17 September 2013 by Richard Hollingham

This week in the Planet Earth podcast, Jason Hopkins of NERC's National Oceanography Centre and Paul Bown of University College London describe how microscopic marine creatures that have been absorbing carbon dioxide for more than 200 million years coped with climate change 56 million years ago.

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

Richard Hollingham: This time in the Planet Earth podcast, what affect will climate change on the organisms that formed the white cliffs of Dover?

I'm Richard Hollingham and I'm at the National Oceanography Centre in Southampton to meet researchers studying coccolithophores - single cell marine plankton - which are crucial to the health of the oceans. I'm in one of the smaller laboratories here with a couple of benches with microscopes on and flasks and the normal computers and the like, and some large refrigerators and with me is PhD student, Jason Hopkins, who is working here at the National Oceanography Centre and Paul Bown from University College London.

Now, Jason, you have in these fridges some coccolithophores, so let's get some out and have a look.

Jason Hopkins: Okay. I'll just open the door. We keep them in small flasks. There's about 15 to 20 millilitres of sea water and if I hold them up to the light you can just about see a cloudy swirl within there, and these are the microscopic coccolithophores.

Richard Hollingham: So it looks as though someone has - I don't know - dropped some chalk into that water.

Jason Hopkins: Well that's exactly what that is. Coccolithophores, the single celled algae, they make a shell on the outside of them, called a coccosphere, and they make it out of calcium carbonate, and if you can imagine a beach ball and you take some paper plates and stick maybe 15 of those plates upside down around it, that's pretty much what a coccolithophores looks like.

Richard Hollingham: Now, Paul, I mentioned that they formed the white cliffs of Dover. The white cliffs of Dover are literally formed of these micro-organisms or rather the calcium plates around them.

Paul Bown: That's correct. The white cliffs of Dover are cretaceous in age, so that means that they're 80-90-100 million years old. If you look at them though in high magnification microscopes, you will see that they're made up of the skeletons of these coccolithophores that Jason was talking about.

Richard Hollingham: How important are they?

Paul Bown: They live in the oceans at the present day and really they form the basis of the food chain of the oceans. So, if you like, the whole of the food of the oceans is built upon these little single cells producing food at the base of the food chain. They're important because they produce carbon and they bury that carbon and so they're part of this huge global planetary carbon cycle. They're important for very applied and economic reasons because they have such a long fossil record going back 200 million years. They've evolved very quickly through that time and so geologists can look at the different species through that time and use them to date rocks, and so if you go out through an oil rig or go and have a look at a geologist mapping an area they might be using those fossils to give very precise dates to the rocks that they're looking at.

Richard Hollingham: Now, if we just come down to the other end of the laboratory here, you've got a microscope set up with some of these coccolithophores on a slide and just if you peer down into this that looks, Jason, almost like diamonds.

Jason Hopkins: That's right. One of the interesting properties of coccolithophores is under polarised light, they're called birefringent, and they basically shine like, as you say, diamonds. So when you look at it there's black background and they stand out like, basically, stars in the sky at night.

Richard Hollingham: These are undoubtedly interesting and they're undoubtedly have been important but why are you working together. I suppose Jason is looking at them now and you were looking at them then, what's the connection?

Paul Bown: We know that our planet is warming up. We know that we're putting more carbon dioxide into the atmosphere, we have warming, but also that carbon dioxide is going into the oceans. It's getting mixed into the oceans and we're getting acidification, it's a phenomenon called ocean acidification. Because these organisms produce calcium carbonate we think that they might be particularly vulnerable to that kind of effect, and so what we've done is we've gone back into the past and looked for examples when ocean acidification occurred in the past.

Richard Hollingham: And have you found anything yet? Have you seen any trends? Because we know that the oceans are becoming more acidic.

Paul Bown: We know that there were periods in the past when there was fog, [unintelligible] carbon dioxide in the atmosphere and that those changes were actually happening quite quickly. In fact there was one event 56 millions years ago called the Paleocene-Eocene Thermal Maximum, a bit of a mouthful, so we call it the PETM and the PETM was a time when the climate warmed by something like 5-6 or 7 degrees, both the surface ocean and the deep ocean, and we think at the same time as this was being driven by carbon dioxide going into the atmosphere, we think there was acidification in the oceans as well. And so what we're doing is we're going back to the rock sediment archive and we're looking at the species of coccolithophores through that time period over thousands of years to see if we can see an effect of ocean acidification.

So that's really what brought Jason in. We started looking at the most beautifully preserved fossils that we could find and actually we could find complete coccospheres, which is unusual. Most coccospheres collapse after death and we just see single coccoliths but we were looking at sediments from New Jersey, from Tanzania where we actually had the full cell preserved and this was the first time that palaeontologists could actually look at these fossils at the cellular level and we started measuring cell size, the coccolith size, the number of coccoliths on the cell and we saw differences through the PETM as more carbon dioxide went into the atmosphere.

But we didn't really know how to interpret this and so we went to the biologists who, thankfully, were in the same lab just down the corridor, and we said we've measured the cell size and the cell size gets a bit bigger but also we've found that there are more coccoliths on those cells at the same time, why is that happening, you must be doing some other kinds of experiments, you're growing living species in little flasks in the fridge that you've just seen, can we compare our measurements with yours.

Jason Hopkins: The advantage we have, we can manipulate some of the conditions that these cells can grow in. Using the incubators that you've just seen we can change the light levels, we can change the temperature levels, we can grow them in different nutrient conditions, we can grow them in different pH conditions-

Richard Hollingham: So you can recreate those conditions of the past?

Jason Hopkins: Exactly. And then we can take live measurements and using those live measurements we can give it to the guys that look at the paleo record and then we can interpret what the paleo record is saying based on what we've see in the lab now.

Richard Hollingham: And are you seeing any changes? Are you seeing any parallels now between now and what happened in the past where there were higher levels of carbon dioxide in the atmosphere?

Paul Bown: One of the species appears to have gone through the PETM with very little change and have been quite happy, often will grow through that period of time, whereas it's the other and in fact it's the species, Coccolithus pelagicus, which is still living today appears to have shown slower growth rates at the PETM so, yes, it showed a reaction at the PETM. It didn't go extinct but it did show different growth behaviour and that's a kind of key observation and probably one of our first observations from the cellular measurements that these species were responding to this warming acidification at the PETM.

Richard Hollingham: What does that mean and what does that mean both for these species but also for the marine food chain if that's what's going to happen as the oceans become more acidic?

Paul Bown: Many of these responses are quite difficult to predict because it's a very complex system, they're at the base of the food chain, so I suppose at the very basic level it's possible that they become less productive, there's less food. The other thing is that they produce these coccoliths and coccoliths are very important because they're relatively heavy little particles and they produce many of these particles and they get shed into the surface ocean, they get stuck together by bits of sticky bacteria and they then accelerate the sinking of carbon out of the system, so they're very important in the carbon cycle of the oceans. Now, if you start to perhaps grow them more slowly or they're effective in some other way then perhaps that ballasting, the weight of those coccoliths and the carbon sinking out of the system may change in a rather subtle way which is difficult to predict but if may effect the function of the ocean and how much carbon the ocean can actually suck up, if you like, and then bury.

Richard Hollingham: I sense though from your answer you're at an early stage of understanding the processes and what's going on here?

Paul Bown: Yeah, very much so. We went to the Paleocene-Eocene Thermal Maximum as one of the most striking examples in the fossil record of a very rapid warming and of ocean acidification and I guess we were looking for a crisis because, perhaps, the first prediction of many of the experiments that were done on these coccolithophores was that they would be greatly affected by ocean acidification and warming or a combination of those two. We go and look at that event 56 million years ago and there were responses from these plankton. We've said that one species slowed down and a number of species we think went extinct, but generally speaking that group continued to function, it didn't lose a great deal of diversity during that time and so I guess one of our thoughts at the moment is that they are actually quite adaptable, they adapt in lots of different ways, they can migrate, they can evolve and even some of the experiments that we're now doing in labs show that over relatively short generation times, and of course these things are dividing many times each day, so we can do experiments over a year where the species is actually dividing over many, many generations and we can actually see them adapting through that time, so it is possible that they are quite adaptable and that's why we don't see a great response of the PETM.

However, there is a caveat and that is that the change that's happening at present is probably far greater in terms of the rate of carbon dioxide being added to the system than the event at the PETM, so we're seeing small responses at the PETM. It may well be that the very rapid carbon cycle changes that are happening now may have even greater effects on coccolithophores.

Richard Hollingham: Paul and Jason thank you very much. As you would expect pictures of coccolithophores and our recording here are available here on our Facebook page and at Planet Earth Online. And that's the Planet Earth podcast from the Natural Environment Research Council. I'm Richard Hollingham from the National Oceanography Centre in Southampton. Thanks for listening.