浮游生物记录了数百年气候变化 | Nature Podcast

来源：Nature自然科研

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Shamini Bundell

If we want to fully understand the ongoing environmental impacts of climate change, one important thing to look at is how ecosystems have changed over time. The ocean is the Earth’s largest ecosystem, and it’s also one that keeps its own record of the past. Within the marine environment there floats a community of very small, very informative zooplankton – they’re called foraminifera. These single-celled drifters can be found remarkably preserved in ocean floor sediments, providing a microscopic record of their historical communities. Lucas Jonkers from MARUM – the Center for Marine Environmental Sciences at the University of Bremen in Germany – drew on mountains of data on these animals, from both before and after the Industrial Revolution. Reporter Geoff Marsh called him up and asked why it’s useful to know what the marine ecosystem was like before the Industrial Revolution. 

Interviewee: Lucas Jonkers

At the moment, we observe changes in marine ecosystems and we say that they are in a direction that is consistent with global change, but we have no clue what these ecosystems looked like before human input, and so that makes it really difficult to say that the changes that we are seeing now are due to global change.

Interviewer: Geoff Marsh

Because presumably we’ve got lots of nice marine ecosystem data over the last sort of hundred years.

Interviewee: Lucas Jonkers

Well, it’s even less. I think it’s maybe since World War II. We need longer time periods.

Interviewer: Geoff Marsh

So, the way that you’re probing these historical marine ecosystems is by using these zooplankton, the foraminifera. Tell us why you use those and why do they make a useful organism.

Interviewee: Lucas Jonkers

These little plankton, they form a calcite or carbonate shell that is very well preserved in the sediment. We can look in the sediment and see exactly what their species community looked like at the time when the sediment was deposited.

Interviewer: Geoff Marsh

Listeners should probably just go on their computer or smartphones and just Google them because they’re really beautiful, aren’t they, but they’re microscopic almost.

Interviewee: Lucas Jonkers

They are.

Interviewer: Geoff Marsh

What do they look like?

Interviewee: Lucas Jonkers

Well, if you’re disrespectful, you’d say they look like little popcorn, but they can be very beautiful. I think it’s magic. They’re unicellular organisms and very, very simple, but their skeletons are very beautiful. They have globular chambers and when they’re alive they have spines that extend double their body size sometimes and this is what they use to catch food. They’ve got intricate shapes and beautiful colours, at least the living ones – the dead ones all look white. 

Interviewer: Geoff Marsh

So, you’re looking at the foraminifera living in the ocean at the moment, seeing which species are there and then by looking at the old sediment that may have floated down 170 years ago, you’re comparing those two communities to see how the ecosystems have shifted post-industrialisation. 

Interviewee: Lucas Jonkers

Exactly.

Interviewer: Geoff Marsh

You’re doing this at a global scale, right? That sounds like a massive job.

Interviewee: Lucas Jonkers

It is a massive job, but I didn’t do that work. The data compiled has been collected by generations of scientists over decades, so It is really a lot of work but I didn’t do it. I just put data together.

Interviewer: Geoff Marsh

We all stand on the shoulders of giants, Lucas.

Interviewee: Lucas Jonkers

Exactly. Yeah, I’m indebted to other people.

Interviewer: Geoff Marsh

Well, good on you for jumping in at the end and writing a Nature paper. So, when you compared these old communities to the current communities of these zooplankton, what sort of shifts came up in the data?

Interviewee: Lucas Jonkers

The first thing that we tried to do is to compare the modern communities with what’s directly on the seafloor below, and we saw that they are different. We saw that that difference is bigger in locations where the climate has been warming more. So, then we thought there might be a link with global change and then we looked at where in the sediment, where on the seafloor, do we find species communities that are most similar to what we find in the water. And then we found that in almost all cases, that the most similar sediment species community, the sort of pre-industrial community, was in a warmer area. So, this means that the modern communities represent a warmer species community than you find below them.

Interviewer: Geoff Marsh

I mean the ocean hasn’t just homogenously heated up across industrialisation has it – some parts of the ocean have got colder.

Interviewee: Lucas Jonkers

In those situations, we also saw that the planktonic foraminifera changed in a direction towards colder temperatures.

Interviewer: Geoff Marsh

Can we be sure that temperature is what’s affecting these communities because by definition almost plankton are these free-floating organisms that are kind of at the will of all sorts of variables and currents and whatnot. How confident are you that it is to do with temperature?

Interviewee: Lucas Jonkers

I am very, very confident about that. Previous studies have already demonstrated that the distribution of these foraminifera is primarily controlled by temperature, certainly on an ocean-scale, and this is also the way we can use fossil species assemblages to reconstruct temperature back in the past. 

Interviewer: Geoff Marsh

Is this compositional shift benign because I understand that all sorts of plankton form the basis of the marine food chain, does it worry you?

Interviewee: Lucas Jonkers

Yes, it worries me that we are changing not only the physical state of the ocean but also the biological state of the ocean, but it’s very difficult, at the moment, to predict what those consequences exactly are. But we’re definitely changing ecological interaction networks and things in the food chain, and this puts all the studies that have a shorter timestamp into a longer-term perspective and so we now are sure that the ecosystems are different and I expect that they will keep on changing into states that we haven’t seen before.

Host: Shamini Bundell

That was Lucas Jonkers from MAREM at the University of Bremen chatting to Geoff Marsh. ⓝ

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