If you watched the Blue Planet II last night I hope you’ll agree that, if all the world’s a stage, the ocean is a pretty spectacular one!

Well, if the organic carbon coming out of rivers was a performer, I think it would be Houdini.

So, just as onlookers could watch Houdini make his way out from the wings and take position centre stage, we can measure the presence of organic carbon and track its movements, allowing us to ‘see’ it flow out of rivers as it makes its grand entrance into the coastal ocean.

And just like Houdini, one minute it’s right in front of us and the next, it’s vanished without a trace. Or has it?

(Before we go any further, if you haven’t read my last blog post, you can catch up here. Caught up? Then let’s go!)

For marine scientists, nothing ever really vanishes. Ever improving scientific techniques and equipment mean that we are continually getting better and better at being able to track the movement of things beyond what you might expect possible. You just need to know what to look for!

At the most basic level, everything is made up of atoms which make up molecules which make up compounds which make up substances which make up, well, everything. So, like every other living thing, the chemicals and compounds which make up microorganisms have to come from somewhere. We use isotopic tracking to find out where…

We think of carbon as being a singular thing, but it actually comes in 3 different forms. These different forms are called isotopes, and they work a bit like smarties (stick with me!)

Say there are two bowls of smarties, one at each end of a hallway – one is mostly blue, with some red and yellow, and the other is mostly yellow, with some blue and red. If you took a handful of smarties from one of the bowls and walked into another room, I could likely tell which bowl you had taken your smarties from (or which end of the hallway you were at when you picked them up), based on the mix of smarties you had in your hand.

If a plant grows on land, it will pick up a different ‘handful of smarties’ compared to one that grows in the ocean. This is that plants isotopic signature, and it’s like a chemical fingerprint specific to that species and location.

We can take a sample of water from anywhere – a lake, a river, the ocean – and filter everything else out until we are left with just the organic material dissolved in it. From there, we can use a technique called mass spectrometry to determine what that material is made up of. Using this technique, we can separate molecules based on their mass, including 3 different forms of carbon. It’s our way of looking to see what smarties the plant is holding – or the isotopic signature of the organic carbon in the sample, which gives us the fingerprint of where it came from.

And this is how we know that riverine organic carbon is going missing – when we look at samples from rivers, we find an isotopic fingerprint full of land-derived organic carbon,  but when we look at samples from the ocean, we find much, much less.

Still with me? Great!

In my next posts, I’ll talk about some of the leading theories around why we don’t find as much riverine organic carbon in the ocean as we expect to, and how my research is trying to understand where it is going. In the meantime, if you have any questions please ask!

The post The ‘Missing’ Carbon Conundrum… Part 2 appeared first on Exploring our Oceans .

Imagine you have some fish in a tank, and you feed them a mixture of small, easy to digest flakes and larger, more difficult to digest flakes. Assuming you feed enough of each type of food to satisfy their hunger, what would you expect to happen?

You’d expect the fish to take the easy option and eat the smaller, easier to digest flakes, whilst the larger, more difficult to digest flakes are mostly left to sink out and end up on the bottom of the tank, right?

Well, that’s basically what happens in coastal waters when microorganisms have a choice between different kinds of food – they pick the easiest option.  

(Let’s just say that anything which is alive and so small you need a microscope to see it is a microorganism, for anyone who wasn’t sure. And because we are scientists and have to be careful with the meaning of words, when we talk about microorganisms we’ll say that they metabolise (or break down) organic matter rather than saying that they digest food, and we’ll use labile and recalcitrant instead of easy to break down and difficult to break down. Don’t worry, you’ll get the hang of it!)

So, coastal waters tend to be incredibly productive places. The surface waters in these regions are teeming with life, and the phytoplankton and algae which live there turn light and carbon dioxide into lovely, fresh, labile organic matter for other organisms to enjoy.  

At the same time tho, huge amounts of recalcitrant organic matter, mostly produced by land plants, flows out of the rivers that feed into these coastal waters. A lot of this river material is old, having been broken down and recycled by river microorganisms so many times as it travels downstream that it has become nutrient deplete and extremely difficult to metabolise by the time it reaches the sea.

With plenty of fresh food being produced in the surface waters, coastal microorganisms don’t need to spend precious energy breaking down this old river material. So what happens to it? Does it sink out and end up on the bottom, just like the fish food did?

No – and that’s the mystery!

Around 50% of the land-plant-derived organic matter which flows out of rivers and into the ocean goes ‘missing’. It’s not floating around in the water column, it’s not sitting in the sediments, and the scientific literature tells us that microorganisms aren’t eating it. So where does it go? 

This might not seem hugely important at first, but for scientists who study the global carbon cycle, solving this conundrum is vital. You see, a large portion of organic matter is made up of carbon, and we know that carbon is linked to climate. 

So let’s think about it! What could be happening to all that organic matter?  

Some of the biggest scientific breakthroughs have come about because people from different fields of expertise and backgrounds got together and threw around some ideas, so have a go!

In my next blog post, I’ll talk about how we know the organic carbon is going missing. In the mean time, over to you!

The post The ‘Missing’ Carbon Conundrum… Part 1 appeared first on Exploring our Oceans .