We have better maps of Mars than  we have of our own ocean floor.

And at first glance, this makes no sense, right? I mean, Mars is way farther away  than the bottom of the ocean.

It turns out though, that it's a lot easier  to see through the vastness of space,   than it is to see through all that water . The ocean covers 70% of our planet,  and the deepest parts of it are often   referred to as Earth’s Final Frontier of science. Now, the people calling it that  are mostly the people who study it.

And as a kind of deep sea scientist myself,  I’m probably a little—really biased. But I don’t think that we’re exaggerating! We’ve seen less than 0.001% of the ocean floor,   and the things we have discovered  thus far are absolutely bizarre.

That’s why scientists are so  eager to investigate more of it. From reefs where you’d never expect them  to be, to massive underwater volcanoes,   these are five mysteries of the deep sea that  researchers are the most desperate to explore. [♪ INTRO] The Mariana Trench is the deepest  ocean trench on the planet,   plunging almost 11,000 meters at its  lowest point: called Challenger Deep. And I know what you’re thinking: Denali,  I’ve heard of people going there before.

That doesn’t sound that unexplored. Sure, but the Mariana trench  is almost 2500 kilometers long,   and MOST of that 2500 kilometers  IS completely unexplored! Just because we’ve spent some time at  the bottom doesn’t mean we understand it!

To quote Dr. Drazen, one of the scientists  currently studying the Mariana

Trench: "That's like trying to understand a  mountain by only looking at its summit.” The Mariana Trench is our deepest  trench, but we’ve discovered at   least 20 trenches on Earth so far, and there  are likely many more out of them out there. Most of these are formed by what we  call in geology, a subduction zone. A subduction zone occurs when  two tectonic plates collide. The denser of the two plates gets shoved  underneath the other one, forming a trench.

The Mariana is in what's called the hadal  zone, the deepest region of the ocean. And at this depth, the weight of the water  above creates enormous pressure on the bottom. That pressure can be measured in atmospheres,   which increases by 1 atmosphere  of pressure for every 10 meters.

This means that by the time we get to the  bottom of the Mariana Trench, we’ve reached   a pressure of over 1,000 atmospheres,  that’s about 15,000 lbs per square inch! For comparison, that's like the  weight of 5 USPS postal trucks   pressing down on every inch of your body at once! And understandably, that makes  building equipment that can   survive on the ocean floor pretty difficult.

So why do we bother trying then? Well, there are some things we can only research  if we actually see and sample them in person. Deep trenches serve as  carbon sinks, for one thing.

This means that they absorb more  carbon than they release and they   help regulate how much carbon is in  our atmosphere at any given time. This is really important for studying  and monitoring climate change. And famously, the deep sea is unlike  any other ecosystem on the planet.

There are so many undiscovered organisms  living in the hadal zone that just one study   on the deepest parts of these trenches  revealed more than 5,000 new species. Many species that live in these  zones don't exist anywhere else. For example, the obviously  very majestic Hadal Snailfish,   one of the deepest living fish in existence.

The deepest one we know about, anyway. Some things in the ocean aren’t mysteries  JUST because of how deep they are though,   which brings us to the next place on our list: The Larsen Ice Shelf. This ice shelf is located in Antarctica,   and it’s essentially big blocks of ice  extending from the continent into the ocean.

It formed from 11,000 years worth of ocean  and terrestrial water freezing onto it. The Larsen ice shelf is more than 200m thick  and it's nearly impossible to explore below it, even for deep sea vehicles that actually  have been to the Mariana Trench. So until recently, we’ve known almost nothing  about what’s underneath the ice sheet.

But scientists have been able to get a  sneak peak in the last couple of decades. As climate change progresses, parts of the ice  shelf break off, and each time a section breaks, researchers rush to Antarctica to  try and find out what's below them. In fact, this has happened multiple times.

The first time a chunk broke off was in 1995  when 1500 square kilometers of it drifted away. This part of the shelf was called Larsen A, and  satellite images caught the breakup of the ice. But it wasn’t until 2002 that a chunk  of the shelf called Larsen B broke off   and we actually got the chance to  study the ocean floor beneath it.

Scientists sent camera equipment down 800m to  the bottom and they found something incredible:   the first known chemotrophic  ecosystem in Antarctica. Chemotrophic means that an organism relies   entirely on chemical reactions for  energy instead of photosynthesis. The ocean floor beneath the ice was  covered in clams, other bivalves,   and white bacterial mats with  gas bubbles coming out of them.

The problem was, expeditions to  Antarctica are really hard to do. They’re often planned months or years in advance,   and by the time scientists get  there, where the ice broke off,   the ecosystem has usually already started to  change from how it was before the ice broke. When you take away all that  ice, particles from above start   to fall down on what were previously pretty  isolated organisms and bury those organisms.

Then other species will start to move in  and recolonize that part of the ocean floor,   outcompeting the chemotrophs and  changing that ecosystem forever. So that ecosystem wasn’t pristine by the  time the scientists actually got there. In 2017 though, scientists hit the jackpot.

A part of the Larsen C ice shelf broke  off, a sheet of ice bigger than Delaware. And researchers had been preparing for this for   years by watching satellite photos  for signs of cracks in the ice. Their diligence finally paid off after they  got the first ever glimpse of what these   ecosystems looked like before other  organisms got the chance to move in.

They found these weird geometric  patterns covering the seafloor. And as it turns out, these are nests! Made by thousands of these guys … icefish!

Patterns like this have never been  seen before and the researchers   think that it’s most likely a protective  mechanism from predators and other fish. But why this has only been  seen under the ice shelf,   and WHAT predators may be living down  there, we’re still—really—not sure. It’s amazing how so many species find a way   to make a home somewhere that’s  objectively really hard to live.

And speaking of places it's  objectively REALLY hard to live … The Red Sea is one of the most  unique bodies of water on the planet. At the bottom, you can find something even  stranger than the chemotrophs of Antarctica. This is a lake.

Or something that looks like a lake,  except at the bottom of the ocean. It’s a lake of dense, salty brine. So salty in fact, that it can’t  mix with the seawater above it,   and nothing except a select few microbes  can survive in the actual brine.

It settles into these pools that can  be found more than 1000 meters deep. The brine pools of the Red Sea formed millions of   years ago when that area was cut  off from the rest of the ocean. Being cut off caused it to dry up over time  and leave concentrated salty deposits behind.

These brine pools are also  really hard to access because,   for one thing, it’s still the deep sea,  but they’re also really, really rare. They’re only found in three  known locations: the Red Sea,   the Mediterranean, and the Gulf of Mexico. Aside from the microbes in the brine pools,   there are also several larger species that  have evolved really unique survival tactics   for living directly on the edge of what is  essentially a giant deep sea death trap.

Predators like shrimp and hagfish actually  sit right on the edge of the brine pool and   they wait for things like crabs and other small  animals to be stunned by the high salt content. Then they take them as prey before they  can fully disappear into the brine,   which I think is pretty cool! As a geologist though, my favorite thing  about brine pools is that they preserve   layers of ocean floor sediment.

And they do it in a way that can’t  be done in any other setting. Most material that ends up this deep in the  ocean is made up of really fine particles. And when a major event like a landslide  or a tsunami happens, it brings larger,   coarser grains farther into the ocean  than they would typically reach.

So when scientists see a layer of bigger, coarser  particles surrounded by all the normal fine   particles, that suggests that one of these big  events, like a landslide or tsunami, has happened. This also tells them how often  earthquakes and tsunamis happen,   helping them understand the conditions  and regularity of these kinds of events. It’s an unexpected benefit of  studying these deep sea brine pools!

Next on our list, another  unexpected feature of the deep sea. A coral reef in … Greenland? This is Cape Desolation, off  the southern coast of Greenland.

And there’s actually a deep sea  coral reef here about 800m down. This reef is made up of a hard, specialized  cold-water coral called Eye-coral. Cold water reefs have also been found  in places like Iceland and Norway.

But the Greenland reefs weren’t discovered until   2012, and they’re among the least  explored of these cold water reefs. This is because it’s … still the deep sea… and,   also, Greenland's coastal waters are  notoriously difficult to navigate. On the surface, there’s broken,  shifting ice, fog, and high winds.

And then beneath the surface, there are really  strong, really unpredictable currents. The corals were actually discovered by accident  when a ship sent an instrument down to collect   water samples and their instrument came back  up having been completely smashed by the coral. Now, I’m sure they were mad about the damage.

But the last time I broke a research instrument   I didn’t get to say I discovered a  new coral species at the same time! The existence of these corals is  vital for the entire marine ecosystem. Not just what’s in Greenland but across the globe.

Deep sea corals act as habitat  and breeding grounds for a ton   of marine species like sea  bass, rockfish, and snapper. All of them use different deep sea corals  in different parts of their life cycle. These extreme environments  are also home to organisms   that contain chemical compounds  we can use to fight disease.

The corals of Cape Desolation have a   chemical called Lobophorin K that  is actually toxic to cancer cells. Scientists hope that by studying that compound,  we may be able to develop new cancer treatments. And there are studies happening right  now trying to make that a reality!

It’s one more reason scientists are eager to  learn more about the Cape Desolation reef. Finally, we have my personal  favorite location: the Gakkel ridge. I study underwater volcanoes as part of my PhD,   and the Gakkel ridge is on my  research bucket list for sure… So if anyone on that research team is hiring a   submarine volcanologist in the  next 2-3 years… I’m available.

The Gakkel ridge is located  between Greenland and Siberia,   and it runs 1800km across the Arctic ocean floor. It’s 5,000 meters down at its deepest  point, and it’s so hard to get there   that the first ever submersible dive to  this location didn’t happen until 2025. The sub that made the journey  carried 2 scientists and one pilot,   so only three people have ever  seen this thing in person.

It’s also a great example of  what's called a mid-ocean ridge. Those form where two tectonic plates are moving  away from each other, and as the plates separate,   molten rock from the Earth's interior  comes up between them and causes volcanism. People often picture, like, a river  of lava running through the middle of   the ocean floor where they separate, but  that's not actually what it looks like.

The reality is that the sea water cools the lava   into rock almost immediately  when it reaches the surface. It cools so fast that most of the ocean floor  is covered in a layer of volcanic glass. Not obsidian, though … that's  a completely different kind   of volcanic glass with its own  distinct chemical composition.

This volcanic glass is called MORB  or Mid-Ocean Ridge Basalt glass. Like everything on this list so far, mid-ocean  ridges are really difficult to access. And this is due to how remote they are and  how high the pressure of the deep sea is.

But the Gakkel ridge is also located in the  Arctic and is therefore covered by Arctic sea ice. It’s not as thick as the  200m of the Larsen Ice Shelf,   but it's more than enough to make  it inaccessible to most ships,   including the ones that would have to carry  any underwater vehicles to the dive site. So why would we risk it then?

Well, because deep-sea scientists  are stubborn by nature. And because you can thank mid-ocean ridges for  just about everything you love about the ocean. Ridges are a really significant  source of iron in our ocean,   and iron is really important for a process  you may have heard of called photosynthesis,   where light is converted into chemical energy.

Photosynthesis is used by phytoplankton that serve   as the base for almost the  entire marine food chain. Mid-ocean ridges are also home to one of the   most unique ecosystems on the  planet, hydrothermal vents. As seawater circulates through the ocean floor,   molten material within earth's  crust starts to heat this water up.

The water then returns to  the ocean floor and brings   a bunch of that heat and nutrients up with it. This allows thriving communities of really  unique animals like giant tube worms,   pompeii worms, and chemotropic microbes. The structures of the vent themselves are made of  metal sulfide minerals like iron, copper and zinc.

And if you were to look inside the hydrothermal  vents, this is what you might see. The entire inside is covered in a layer of  pyrite, known more commonly as Fools Gold. So, our deep sea has towers of gold … well, fools gold … surrounded by an entire ocean floor of volcanic glass.

And I don’t know about you, but  to me that sounds pretty magical,   and it’s why I basically sold my  soul to a life researching it. Hydrothermal vents can even be used to  study environments on other planets. The vents at the Gakkel ridge are some of the  only ones on Earth under permanent ice cover.

Which yes, does make them a  huge pain to try and get to. But it also makes them perfect to  study what life might be like on   icy, ocean-covered moons  like Europa and Enceladus. NASA has even funded expeditions  there for this exact reason.

The Gakkel ridge also has something that’s  never been found at any other mid-ocean ridge. It’s the location of the only large  caldera complex… which the media   typically calls a ‘supervolcano’ … to  ever be discovered at a mid-ocean ridge. A large caldera complex is  essentially a giant volcanic crater,   and the caldera at the Gakkel ridge  is about 80km long and 40km wide.

This volcano could have theoretically erupted  as much as 3000 cubic kilometers of material,   a larger eruption than even the biggest  eruption that Yellowstone has had. Explosive eruptions like that are not  impossible underwater, but evidence of   one that size has never been seen at a mid-ocean  ridge before the Gakkel Ridge Caldera discovery. Even today, there is so much about our  ocean floor that remains a mystery.

And everyone in deep-sea science,   from the scientists & engineers to the chefs  and technicians onboard our research vessels,   we’re all working together to uncover  the least explored parts of our ocean. Maybe by the time I retire, we’ll be  able to say we’ve explored 0.002% of it. [♪ OUTRO]