Heidi M. Sosik
1,442,733 views • 10:01

I bet all of you are familiar with this view of the ocean, but the thing is, most of the ocean looks nothing like this. Below the sunlit surface waters, there's an otherworldly realm known as the twilight zone. At 200 to 1,000 meters below the surface, sunlight is barely a glimmer. Tiny particles swirl down through the darkness while flashes of bioluminescence give us a clue that these waters teem with life: microbes, plankton, fish. Everything that lives here has amazing adaptations for the challenges of such an extreme environment. These animals help support top predators such as whales, tuna, swordfish and sharks. There could be 10 times more fish biomass here than previously thought. In fact, maybe more than all the rest of the ocean combined. There are countless undiscovered species in deep waters, and life in the twilight zone is intertwined with earth's climate.

Yet the twilight zone is virtually unexplored. There are so many things we still don't know about it.

I think we can change that. I was drawn to oceanography by just this kind of challenge. To me it represents the perfect intersection of science, technology and the unknown, the spark for so many breakthrough discoveries about life on our planet.

As a college student, I went on an expedition across the Atlantic with a team of scientists using a high-powered laser to measure microscopic algae. The wild thing that happened on that trip is that we discovered what everyone who looked before had completely missed: photosynthetic cells smaller than anyone thought possible. We now know those tiny cells are the most abundant photosynthetic organisms on earth. This amazing discovery happened because we used new technology to see life in the ocean in a new way. I am convinced that the discoveries awaiting us in the twilight zone will be just as breathtaking.

We know so little about the twilight zone because it's difficult to study. It's exceedingly large, spanning from the Arctic to the Southern Ocean and around the globe. It's different from place to place. It changes quickly as the water and animals move. And it's deep and dark and cold, and the pressures there are enormous.

What we do know is fascinating. You may be imagining huge monsters lurking in the deep sea, but most of the animals are very small, like this lantern fish. And this fierce-looking fish is called a bristlemouth. Believe it or not, these are the most abundant vertebrates on earth and many are so small that a dozen could fit in this one tube.

It gets even more interesting, because small size does not stop them from being powerful through sheer number. Deep, penetrating sonar shows us that the animals form dense layers. You can see what I mean by the red and yellow colors around 400 meters in these data. So much sound bounces off this layer, it's been mistaken for the ocean bottom. But if we look, it can't be, because the layer is deep during the day, it rises up at night and the pattern repeats day after day. This is actually the largest animal migration on earth. It happens around the globe every day, sweeping through the world's oceans in a massive living wave as twilight zone inhabitants travel hundreds of meters to surface waters to feed at night and return to the relative safety of deeper, darker waters during the day.

These animals and their movements help connect the surface and deep ocean in important ways. The animals feed near the surface, they bring carbon in their food into the deep waters, where some of that carbon can stay behind and remain isolated from the atmosphere for hundreds or even thousands of years. In this way, the migration may help keep carbon dioxide out of our atmosphere and limit the effects of global warming on our climate.

But we still have many questions. We don't know which species are migrating, what they're finding to eat, who is trying to eat them or how much carbon they are able to transport.

So I'm a scientist who studies life in the ocean. For me, curiosity about these things is a powerful driver, but there's more to the motivation here. We need to answer these questions and answer them quickly, because the twilight zone is under threat. Factory ships in the open ocean have been vacuuming up hundreds of thousands of tons of small, shrimp-like animals called krill. The animals are ground into fish meal to support increasing demands for aquaculture and for nutraceuticals such as krill oil. Industry is on the brink of deepening fisheries such as these into the mid-water in what could start a kind of twilight zone gold rush operating outside the reach of national fishing regulations. This could have irreversible global-scale impacts on marine life and food webs. We need to get out ahead of fishing impacts and work to understand this critical part of the ocean.

At Woods Hole Oceanographic Institution, I'm really fortunate to be surrounded by colleagues who share this passion. Together, we are ready to launch a large-scale exploration of the twilight zone. We have a plan to begin right away with expeditions in the North Atlantic, where we'll tackle the big challenges of observing and studying the twilight zone's remarkable diversity. This kind of multiscale, multidimensional exploration means we need to integrate new technologies.

Let me show you a recent example that has changed our thinking. Satellite tracking devices on animals such as sharks are now showing us that many top predators regularly dive deep into the twilight zone to feed. And when we map their swimming patterns and compare them to satellite data, we find that their feeding hot spots are linked to ocean currents and other features. We used to think these animals found all of their food in surface waters. We now believe they depend on the twilight zone. But we still need to figure out how they find the best areas to feed, what they're eating there and how much their diets depend on twilight zone species.

We will also need new technologies to explore the links with climate. Remember these particles? Some of them are produced by gelatinous animals called salps. Salps are like superefficient vacuum cleaners, slurping up plankton and producing fast-sinking pellets of poop — try saying that 10 times fast — pellets of poop that carry carbon deep into the ocean. We sometimes find salps in enormous swarms. We need to know where and when and why and whether this kind of carbon sink has a big impact on earth's climate.

To meet these challenges, we will need to push the limits of technology. We will deploy cameras and samplers on smart robots to patrol the depths and help us track the secret lives of animals like salps. We will use advanced sonar to figure out how many fish and other animals are down there. We will sequence DNA from the environment in a kind of forensic analysis to figure out which species are there and what they are eating. With so much that's still unknown about the twilight zone, there's an almost unlimited opportunity for new discovery. Just look at these beautiful, fascinating creatures. We barely know them. And imagine how many more are just down there waiting for our new technologies to see them.

The excitement level about this could not be higher on our team of ocean scientists, engineers and communicators. There is also a deep sense of urgency. We can't turn back the clock on decades of overfishing in countless regions of the ocean that once seemed inexhaustible. How amazing would it be to take a different path this time?

The twilight zone is truly a global commons. We need to first know and understand it before we can be responsible stewards and hope to fish it sustainably. This is not just a journey for scientists, it is for all of us, because the decisions we collectively make over the next decade will affect what the ocean looks like for centuries to come.

Thank you.