Stories & Inspiration

Measuring ocean health with citizen science in Antarctica

The seas around Antarctica teem with life, from penguins by the thousand to enormous humpback whales gorging themselves on krill. But what supports these ecological riches? Phytoplankton, that’s what: tiny single-celled plants converting sunlight into chemical energy to feed the ocean, sucking carbon dioxide out of the atmosphere at the same time. On my most recent Antarctic cruise I joined a citizen science project to find out more about this process, armed with nothing more than an instrument that looked a lot like a dinner plate: a Secchi Disk. 

Citizen science on board Antarctic Cruise ships

I sailed on the Seaventure expedition cruise on Swoop’s Antarctic Peninsula Classic voyage, which spends a chunky five days on the Peninsula. It’s a ship I was keen to travel on, due in part to the way it promotes citizen science as part of the polar experience.

Secchi disk citizen science in Antarctica
Marco, our citizen science guide on Seaventure

Seaventure offers a selection of citizen sciences projects to get involved with. In this way the ship can act in part as a roving research platform, visiting parts of the Antarctic Peninsula and collecting data over an entire cruising season in a way that would be impossible for scientists to replicate. 

Some of the projects can be done on the ship itself, like recording bird sightings for the Southern Ocean Seabird Survey or collecting cloud data for the GLOBE Clouds Survey run by NASA. These are great because they allow anyone to take part, but I wanted to get stuck into the projects that involved signing up for the dedicated citizen science zodiac. For me, this seemed to promise an experience closer to what real scientists get up to in Antarctica, and the chance to get a new angle on the traditional zodiac cruising offered by every cruise ship.  

Introducing the Secchi Disk

As we set out on our first citizen science zodiac cruise off the coast of Cuverville Island on the Antarctic Peninsula, our guide Marco gave us a useful lesson that a lot of science is about data collection, using some pretty basic instruments. After finding a good spot to start our work, he produced the tools of our new trade: a black and white disk about a foot in diameter (or a very precise 30 centimetres as I later found out) plus a spool of measuring tape. This was a Secchi Disk and there was precisely nothing high tech about it at all; these were the kinds of tools I could imagine the earliest explorers using when they first explored these waters a century ago. 

Preparing the Secchi Disk to take a recording

So, what could we possibly use this simple Secchi Disk for that would give us some interesting scientific data? The process, in layman’s terms, was to lower it into the water and then keep on lowering it until we couldn’t see it any more. We’d record the depth that the disk disappeared from sight and that would give us the water’s Secchi depth, a measurement of how transparent the water is. 

At first look, this all sounded a bit bizarre, but Marco assured us that this was real scientific data collection and not just a way to keep a group of polar tourists quiet while everyone else was off looking at a gentoo penguin colony. What was the connection between the water clarity in a pristine-looking place like the Antarctic Peninsula and the health of its ecosystem?

Lowering the Secchi Disk

The key lies with all that phytoplankton, happily sucking in light and carbon dioxide and turning it into the chemical energy that ultimately supports all other life in the sea. The major determinant of water clarity is the amount of life in it – the amount of phytoplankton. The quicker the Secchi Disk disappears from view, the more phytoplankton there is in the water. That ultimately means more krill, more fish, and more penguins, seals and whales. If the disk remains visible for longer, then the water has less life in it. 

Applying some clever maths to the Secchi depth allows you to estimate the amount of biomass in the water – and how much life it can support. Not bad for an overgrown dinner plate and a tape measure! 

Collecting the data

With all this in mind we set to work. Of course, the progress was a bit more vigorous than dropping the Secchi Disk into the water until we couldn’t see it any more. Collecting good data requires good practice. The disk was gently lowered on the zodiac’s offside so we had our backs to the sun to prevent glare affecting our observations. Even the time of day we set out for our measurements was important, because the angle of the sun makes a difference to light penetration. 

Recording the depth of the Secchi Disk

The disk was lowered until it was out of sight and then gently raised again until we could see it. We then repeated the process a number of times so that we could take the average of a set of results to determine the correct depth. All these tiny details in the protocol were designed to ensure that the data we collected was robust enough to be analysed later by researchers. 

With the Secchi Disk measurements collected, we also took water samples for Fjord Phyto, another citizen science project that looks at Antarctic phytoplankton diversity (read my colleague Daniel’s blog about his experience with Fjord Photo). As well as gathering more data, it also gave us the opportunity to look at phytoplankton under the microscope when we were back on board, and get an insight into these tiny building blocks of the polar food web. 

Disappearing from view: a measure of water clarity

It seemed improbable that our little citizen science team should bond over something like plankton, but it felt like we’d been on a research cruise in our own private zodiac, which was a pretty special feeling. Slowing down and seeing Antarctica through a completely novel lens like this also gave us a much broader appreciation for what a complex environment this really is. 

Secchi histories and futures

Back at home after my trip, I was curious to know what had happened to our data, so I reached out to Dr Richard Kirby, who runs the Secchi Disk study. He had received our data before we’d barely warmed up after our zodiac cruise, thanks to Marco uploading it to the Secchi app. He pointed me towards the open data map that allowed me to track where Secchi data had been recorded by citizen scientists across the globe – including on our zodiac by Cuverville Island. 

Graph showing Secchi disk information collected by Seaventure ship in Antarctica
Secchi Disk map showing data collection by citizen scientists on Seaventure.

Dr Kirby also filled in some of the background of the long history of the Secchi Disk as a tool in oceanographic research. Apparently it was all down to the Pope in 1865, who wanted a way to map the currents of the Mediterranean coast to improve navigation for his fleet. He called on his astronomer, Angelo Secchi, to help devise a rigorous scientific method of measuring water clarity. In this way, the Secchi Disk was born, to be widely adopted by marine scientists for the next century. 

Kirby’s own interest came with the publication of research in 2010 that suggested that global phytoplankton was in decline compared to numbers a century ago – data that had been collected using exactly the same method as I had used in Antarctica, and the Pope’s navy before me. The only problem was that in recent decades, phytoplankton and water clarity has been measured in the lab using a different technique. The question therefore was over whether the decline in phytoplankton was real, or was it due to a change of methodology? 

To begin to answer this question, Kirby got out his trusty Secchi Disk. The resulting project, involving citizen scientists around the world, has been recognised for its citizen participation in collecting ocean data by/ the European Innovation in the Framework of the Atlantic Deep Ocean project. Just as crucially, his work has been published in the prestigious scientific journal Nature, showing that the data being collected by non-professionals is just as rigorous as that collected by research scientists.  The Pope’s astronomer apparently knew a thing or two about developing a really sturdy scientific protocol. 

Citizen scientists hard at work!

It felt like a long way from the Papal Navy to peering over the side of a zodiac in Antarctica hoping to get an insight into the health of the region’s phytoplankton, but when you take part in a citizen science project, you can learn the most unexpected things – as well as placing yourself in a great tradition of science at sea! 


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Rebecca Porritt

Polar specialist

Rebecca is a polar specialist at Swoop who has made multiple trips to both Antarctica and the Arctic. On her voyages south, she’s been delighted by orcas on the Peninsula, said hello to the king penguins of South Georgia, and been mad enough to do the polar plunge twice in quick succession.