I think for all of us, there's just something so thrilling about how unknown the deep ocean is. Most of us will never go down there, just the odd scientist. Sperm whales on the other hand routinely dive 2, 3, 6,000 feet, or over a mile below sea level. They are perfectly adapted for high-octane battles with deep sea colossal squid.

We're not going to look too much into the overall facts about sperm whales:

• _{Can be found everywhere but the polar regions}
• _{20 metres long, up to 65 tons}
• _{Biggest brain in the world}
• _{Biggest toothed animals, hunts giant squid.}
• _{Vulnerable as a species}
  
  

No, here we are going to look at exactly how they are able to survive deep down there in the depths of darkness. It's pretty impressive. I mean, if you tripped and fell off a boat into the Marianas Trench and just so happened to get a bowling ball all knotted up on a bootlace that just refused to come off, you'd fall down, down, deep below and be crushed by the extreme pressures long before you got to the deepest ocean dwellers the sperm whale likes to feed on. That is, of course, if you can hold your breath really well.

er... anyway. We better start off back at school:

Atmospheric pressure _{Skip this section if you know all about this}




In short, atmospheric pressure is the weight of all the air molecules from above, pushing down below due to Earth's gravity. There is a greater density of molecules at sea level because there is more stuff above it pushing down.

There it a lot of air in our bodies. Aside from the lungs, we have air in our ears, sinuses, blood and so on. Thankfully this air pushes out against the air pushing down and around us at the same time, which balances out the whole thing so we don't feel it.

But when we go swimming underwater, things change.

You see, unlike air, water can't really be compressed, not under normal conditions. We'll get back to 'normal conditions' in part 2.

So when diving, the pressure of the water on our bodies is greater than the air within us, and so it starts to add more pressure, compressing the air inside us until, well, if you can swim deep enough, your eardrums would burst, your lungs would collapse, and you'd suffocate while bleeding internally. And that's only a couple of thousand feet down.

But there's more. If we go back up too fast, dissolved air - I'm looking at you, Nitrogen - starts to decompress into bubbles of air in our bodies. Have you ever tried injecting air into your body? Presumably not because you're still alive. Please don't do that, you will die.

This is because any small bubbles can simply block the blood streams going into all your vital organs like, you know, the brain. This is why nurses squeeze a little of their medicine out of the syringe before injecting you; to make sure no air pocket is in the tip of the needle.

Anyway back to diving. When going up too fast, the Nitrogen bubbles make the same thing happen. If those minuscule bubbles get big enough, they can block blood flow or even stretch and tear the vessels or nerves. This is called The Bends, and The symptoms are many.

So with all these horrifying issues in mind, how come these air-breathing whales get to dive over 3,000 metres (in the case of the Cuvier's Beaked Whale)?



Enter Evolution

The problems whales have to overcome are plenty, but let's start with the sperm whale's head.

The head

The middle-ear cavity is an air-filled space that falls victim to pressure and can be very troublesome if you find yourself thousands of feet below the sea.

The primary solution for the whale is to line the whole cavity with something called Venous Plexus which is basically a cluster of veins, which are flexible and prevent the squeeze of the outside pressure from taking effect.

In fact, sperm whales and some other cetaceans have invested a lot of their bodily system into Venous Plexus's throughout their ears and sinuses, something only recently described in detail (2012) when looking at dolphins.

Often times occupying every available space within cavities and between tissues. In the head and neck, venous plexuses are seen investing the IMFBs and EMFBs, the cranial sinuses, ophthalmic regions, nasal passages, tracheal mucosa, surrounding the esophagus, within the epidural spaces, and inside the brain case.



The paper referenced is a fascinating read and goes into how this can also be fatal when artificial circumstances occur to the animals, along with much more cool info, you can read it below.

The spermaceti, a... spermy substance that the sperm whale gets its name from resides in a bulging head, and some theories suggest this aids the whale in buoyancy. By filling the area with cold water, cooling the wax and solidifying it, which reduces its volume. This creates a relative density difference of about 88lbs, making it easier to sink.



So what about the lungs? You can't fill the lungs with blood vessels galore, right?

Well, the sperm whale has a technique for this. They move the air out of their lungs and keep it instead in a cartilage-reinforced airway. But with no oxygen in the lungs, you'd think they couldn't thrive below for 2 hours or so.

The chest

First the whale practices deep breathing, which exhales up to 90% of the air in the lungs, compared to 15% or so capable from a human. This removes all that deadly air, thanks to collapsible lungs. By breathing deeply, oxygen diffuses into the blood more completely, meaning the whale depends on the oxygen already dissolved within the bloodstream.

This also helps reduce Nitrogen levels in the blood which, as stated above, can be pretty dangerous. HIgh levels of Nitrogen in general can at the very least create a narcotic effect called nitrogen narcosis.

To complement this, it has a large blood-body ratio for their body size compared to other animals, with lots of red blood cells, lots of hemoglobin (Transports oxygen) and lots of myoglobin (oxygen storage) - Sperm whales have up to 10 times the amount of myglobin in their muscles compared to dogs.



It goes on. With an extra efficient distribution of blood vessels through those venus plexuses, the oxygen gets focused on the heart and the brain, and metabolism slows greatly, reducing the need to use that oxygen.

The sperm whale's heart is itself quite special. It's big, bigger than you, at about 115kgs, or 0.5% of the whole body mass. The aortic arch, simple a bend in the aorta, is elastic and gets bigger as it leaves the heart, which ensures a steady blood flow at various depths.

Lifestyle

Behaviourally speaking, the animals, like birds, decrease their 'swimming' activity and concentrate more on 'gliding' and following currents. Or just... sinking, which conserves energy.

To avoid the bends on the way up, they have learned through evolution to take their time to prevent any nitrogen doing its deathly thing, which can at first make them seem drunk and dizzy, which isn't good when you're 9,000 feet under the sea and running out of breath.

So if you ever drop your wedding ring off the side of your boat and need a ride, ask the nearest sperm whale, it has your back!

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As noted above, the deepest dive ever comes from the Cuvier's beaked whale at 10,000 feet down. Any seasoned oceanographers out there may know that the ocean goes much, much deeper than that; as deep as 11,000 metres/ 36,000 feet. That's about 6,000 me's standing on top of each other. No whale is getting down there.

No, these creatures need some extra-special-super-extreme adaptations, adaptations that mean instant death if they were to ever try to swim upwards any distance.

But for that, you will have to wait until part 2!



Image Sources:

Whale depths
Whale head & blood system - Wikimedia user Kurzon
Other images CC0 Licensed

Sources:

Bubbles in your blood = death
Study on Dolphin sinuses etc
Animal structure and function
Scientific American