Marine plants measured from space

With up to 30m precision, scientists can track carbon locked away by marine microbes from space
20 July 2021

Interview with 

Gemma Kulk, Plymouth Marine Laboratory


An underwater view of the ocean surface.


These days we take for granted that we can take pictures of the earth from space, whereas in the past scientists were chiefly focused on taking pictures of space, from earth! As we heard from the Royal Society's Keith Moore...

Keith - Photography was an important part of the 19th-century summer science exhibition. So people like Norman Lockyer the astronomer would demonstrate very regularly photographs of the latest discoveries. But also this is an area where some women scientists got involved. The Irish astronomer Annie Maunder showed her photographic skills at several summer science exhibitions in the 1890s. So this was an exhibition that women were beginning to participate in as well as men.

And nowadays we can look down on the Earth using cameras mounted on orbiting satellites. This can be used to study weather patterns and predict storms and heatwaves; monitor how the continents are moving and where volcanic eruptions might be brewing; or where pollution and other gases go. Another group is using this technology to find out how tiny marine green plants called phytoplankton take up the carbon dioxide we pump into the atmosphere. Gemma Kulk is from the Plymouth Marine Laboratory and spoke to Chris Smith...

Gemma - It seems like a huge contradiction that we can see phytoplankton from space because indeed they are so small, but collectively, so all phytoplankton together become visible through their impact on the colour of the ocean. So the greener the water, the more phytoplankton there are. So similar to plants on land, phytoplankton are green.

Chris - And what are they actually doing with the carbon? How is the carbon going from the atmosphere and ending up in these plants in the ocean then?

Gemma - So phytoplankton photosynthesize. So if you are familiar with the process of photosynthesis, that means that phytoplankton use sunlight, so energy from the Sun, to convert carbon dioxide and water into oxygen and organic particles.

Chris - And so if they're doing that to grow, is your sort of inference then that the greener the water is the more they're growing and therefore the more carbon they must be using?

Gemma - Exactly. That's true.

Chris - And how precise is that? So if I've got a camera watching the ocean, how subtle is the difference in greenness and how accurately does that map onto what the phytoplankton are actually doing when you look from space?

Gemma - The satellites that we are using in the open ocean, such as the North Atlantic ocean, for example, have a resolution of 300 metres. So for every 300 metre by 300 metre square, we have an image, we have data available. If we look closer to the coast, we have a resolution of up to 30 metres, which is very high resolution. So we can see phytoplankton in quite a lot of detail. And the colours; it's not just a green colour that is measured, but there are different colours that we use to identify phytoplankton. So yeah, the precision is quite high.

Chris - And what are you learning through doing this? Have we spotted anything that we didn't realise before, or are you able to just confirm "Yep, we pump out CO2, it goes into the atmosphere and it ends up in the ocean"?

Gemma - Well, I think that's true, but what I find really exciting about my work with satellites is that we can watch the entire ocean at a global scale for very long periods of time. So the ocean colour satellites that we now have, have a record of over two decades. So over 20 years of data, which is really exciting because we can watch phytoplankton over those two decades and see what happens. So what scientists originally thought was that maybe phytoplankton globally was decreasing over time, so there's less phytoplankton now than there was 20 years ago, but we don't actually see that at the global scale. It seems to go up and down a little bit. So we don't see a clear trend or clear decrease or increase.

Chris - Now we heard earlier in the program about the issue of climate change and you know, that's never far from anyone's mind, is it? Can this be useful in terms of monitoring where carbon's going and how we mitigate against climate change? Because we think carbon's at the root of climate change, don't we?

Gemma - Yes, definitely. I think the oceans play a really important role in the global carbon cycle and we often forget about it because it's not very visible. But phytoplankton take up about 50 gigatons of carbon each year, which makes them equally important to all plants on land. So they're really essential. And that also means that they play a role in climate change. What we do not know yet is how phytoplankton respond to climate change because our time series of over two decades is not quite long enough to understand the changes that are occurring at the sort of climate change scale. So this is something that we have to wait for. We gather more data, but it might take us another 10 years to have a better understanding of that.

Chris - Of course, something we don't have to wait for is to come and visit your virtual stall for the Royal Society summer exhibition this year. So what will I see if I come and inspect your wares?

Gemma - Hopefully you will see lots of phytoplankton, but there are also other things to see. So people can explore the global carbon cycle from space, not only in the oceans, but also how carbon moves through the atmosphere and is stored on land. It was very much a collaboration between different scientists, so we are looking at the total global carbon cycle.


Add a comment