Our relationship to the deep sea

Today, we have a different set of tools that we can use to explore the ocean, but the questions we’re asking are not really very different from the questions that our ancestors asked. First and foremost, we’re really interested in understanding what this deep sea is about. What does it look like? We’ve only seen a tiny percentage of the deep ocean, and a lot of us are wondering how these organisms relate to those we’re more familiar with – like the coral reefs that you see in the shallow ocean, or the sharks, swordfish and tuna – and, of course, ultimately to try and better understand our relationship with the ocean: how they influence us and how we, in turn, influence them.

So, today, exploration takes place in many different ways. One is just exploration in the purest sense of the word: trying to understand and explore an environment that we really know very little about. However, we also explore with an eye towards improving our relationship with the deep ocean: understanding how our activities are adversely impacting processes in the deep sea and how we can manage those better to maintain not just the health of the deep sea, but the entire biosphere.

So many people, including those of us who study this professionally, make some assumptions about what the deep sea is, or we make blanket statements: it’s large; it’s cold; it’s expansive. What’s amazing is that when you look at the deep ocean below a kilometre of depth it is all in permanent darkness, but there’s a lot of diversity. Don’t get me wrong, there are parts of it that are large, expansive and relatively stable, but stable is not the same as boring, nor does it imply that there isn’t a diversity of environments or organisms.

Let me give you a few examples. The deep sea harbours, I would argue, Earth’s most extreme environments. There are large areas of the deep sea that are very cold and very stable, and food doesn’t get there very often. It’s extreme because it’s a nutrient-limited environment. They are not benefiting from sunlight, not directly. Anything in the shallow waters that dies and sinks is what they have to eat, hence it’s very nutrient-limited. It’s like a starving ecosystem. However, the organisms there, the microbes and animals, have evolved many interesting adaptations to live in these low-energy conditions. At the same time, the deep sea harbours hydrothermal vents or underwater hot springs. These are fantastic environments that are at the opposite end of a kind of food or nutrient spectrum. Their environment is fuelled by volcanism, by the chemical energy of the earth that microbes can harness. Just the same way plants harness sunlight, microbes in vents harness chemical energy, and they grow by the billions.

This is very important because we know that our atmosphere is warming. This is fact. It has been measured and shown. We know that sea surface temperatures are also warming, which has also been measured and shown. We’re starting to see temperatures creep up in the deep sea – a 10th of a degree here, a 20th of a degree there. While those may seem like small numbers, there are two really important things to remember. One: the organisms that live there have evolved in an environment where temperatures have been stable for millennia, so a 10th of a degree has a big impact on them. How? We’re just beginning to understand and study that, so that’s the work being done. However, there’s a second thing: there are chemical effects of that increase in temperature. For example, there is a lot of methane that is tied up in the deep sea as methane ice, an extraordinary material that is methane literally trapped in water ice. It’s very stable until you warm it up. A 10th of a degree is enough to release a lot of methane. What happens to that methane next? We don’t know. Is it eaten by microbes? Maybe, but there’s a chance that it’s so much methane that it’ll escape the ocean, enter our atmosphere and make the problem of a warming planet even worse.

Deep sea exploration today is conducted by human-occupied submarines – which is an extraordinary experience – by robotic submarines – which are basically submarines on a cable – and by autonomous vehicles or robots, more or less. All three of those are really powerful tools. Then there’s a fourth tool, which is that we have the technologies now to actually make maps of the deep sea, very high-resolution maps from ships floating on the surface. So, we can actually interrogate the deep sea through sound. It’s really hard to work in the deep sea. I think we can all agree on that. Remarkably, though, the advances in communications technology are allowing us to bring the deep-sea experience to the ship, then from the ship back to land by satellite.

One thing that my colleagues and I have been working a lot on is developing the technologies and methods for using robot subs connected with wire to take video and make observations in the deep sea, to then bring that video up to the ship and beam it by satellite to a shore-based facility – where scientists can sit and participate in the expedition alongside us – or to your home. There are a couple of websites that have been set up where scientists like myself invite the public to join us on a deep-sea expedition. You, too, can keep your eyes on the new discoveries we’re making, but also contribute. My hope personally is that we can continue to develop these telepresence technologies to democratise access to the deep sea.

The deep sea is playing a much larger role in contributing to those trace nutrients than we thought. In other words, hydrothermal vents in the deep sea that release iron are kind of like the ocean’s multivitamin. They’re producing these and releasing these elements that are really important to the surface organisms for their growth and productivity. What that means is that, as we think about the blue economy, we really need to think about how the deep sea plays into this. If we’re going to turn to the ocean to increase protein production for human populations, we should think about how the deep sea can help bolster that.

We should also recognise that the deep ocean is Earth’s natural sink for carbon. Much of the carbon that’s produced in the ocean ends up going into the deep sea and some of it stays there for millennia. The ocean is acting like a giant heat buffer, dampening the effects of warming that are caused by our activities. So, if we’re really thinking about a sustainable blue economy, we should think about the ways in which the deep sea can bolster it, but also how we protect the deep sea environment so that we don’t end up adversely affecting it and crashing the very economy we’re trying to create.