If the ocean pressure can break human bones, why don't whales and other species die?

Thank you for sending in such a great question!

The short answer to this is because of the weight of the water being pulled down by gravity.  On land, we have the atmosphere pushing down on us, which we are designed to cope with.  In the ocean, however, we have this air but also water being pulled down by gravity.  The water is heavier than air, and therefore puts more pressure on us and objects in the sea.  The deeper you go into the ocean, the more water there is above you, so there is more pressure.

Our human bodies - specifically our lungs - are only designed to manage one atmosphere’s worth of pressure (like we do on land). As the pressure is greater in the ocean, we have to use pressurised vehicles to travel down into the deep sea.  Most ocean species, however, are specially adapted to live in the ocean.  Many sea creatures are made of mostly water.  Water cannot be compressed, or squeezed, by pressure like air can.  This means that animals in the sea can stay safe when in the depths of the sea, as their body is balanced with the pressure around them, whereas we have air in our bodies that would be crushed.  For marine mammals, like whales, the situation is a bit different, as they breathe air like we do.  Whales are adapted in amazing ways to cope with the pressure.  For instance, whales can collapse their lungs when they dive deep into the ocean, to avoid their lungs being damaged by the pressure!

As you can see from the picture above, whales manage to dive very deep in the ocean – these are some record-breakers! Image credit: Anaïs Remili.

There is a world-famous ocean research centre, which I was lucky enough to visit when studying for my PhD, called the Woods Hole Oceanographic Institution, who have written a webpage all about pressure in the ocean. I would recommend taking a look, as they have a cool, interactive section on ‘how much pressure can we take?’ which you might enjoy.  They also share a picture of one of my favourite ocean pressure experiments… When scientists go on research ships to explore the deep sea, they often send down equipment to video or take samples from the ocean floor. As they do this, they often attach polystyrene coffee cups to the machines to take down and bring them back up, because the pressure turns them into fun, mini cups, which make great souvenirs of their expedition, like the ones shown below!  I hope you think these are as cool as I do!

Thanks again for sending in your question and have a good day!

(Feature image credit: R. Rayner and A. Zych, High Pressure in the Deep Ocean)