Dealing with pressure

To understand how pressure affects beaked whales and other deep sea divers, we first must understand what it is. So what is pressure?

You’ve probably noticed pressure without even realising it. It’s the sound of gas escaping from a fizzy drinks bottle when you open it, the way your ears ‘pop’ when you’re in a plane or travelling to higher ground and it’s what causes your head to hurt when you dive down to the bottom of the swimming pool too often. These are all examples of two areas of pressure equalizing, be it between the inside of a drinks bottle and the air or the inside of your ear canal and the air. All the air molecules pressing down on you create pressure. While reading this blog you are currently experiencing what we measure as 1 bar of pressure. 1 bar equates to 10,000 kg per square metre. That’s roughly the weight of a small car pressing down on your head. So why aren’t we currently being crushed? Quite simply, because we are adapted to it. The pressure in the atmosphere in pressing down from all directions, while the pressure in our bodies presses up, ensuring we don’t crumble under pressure (Institute of Physics 2014).

In the ocean, for approximately every 10.6 metres of depth there’s an increase in pressure by 1 bar. So, for example, that record breaking Cuvier’s beaked whale was at a depth of 2992 metres, using this knowledge we can calculate the pressure it was experiencing…

Approximately, 283 bars of pressure!

Styrofoam cups placed on the exterior of the a DSV (deep sea vehicle) during a dive. Deep sea pressure deformed each cup. (Source: Attachment to declassified CIA document, Deep Sea Recovery of HEXAGON Recovery Vehicle 1201-3, dated 24 May 1972.)
Fig 9 . Styrofoam cups placed on the exterior of the a DSV (deep sea vehicle) during a dive. Deep sea pressure deformed each cup. Image source: Attachment to declassified CIA document, Deep Sea Recovery of HEXAGON Recovery Vehicle 1201-3, dated 24 May 1972.)

Remember this animal has dived from the same kind of pressure you’re currently experiencing to one that would shrink a styrofoam cup to an eighth of it’s size (figure 9). That’s a massive change in pressure for an animal that at the same time has to think about controlling its heart rate, monitoring its temperature (the deeper you go in the ocean the colder it gets), thinking about when it needs to come up for air and hunting all at the same time. How beaked whales cope with such extremes of change are still unexplained.

The dangers of deep water diving, however, are well researched and understood. Following models given by dolphins, we can assume that the lungs of beaked whales will collapse at 100m and there will be no further gas exchange from the lungs to the tissue at this point (Scholander 1940) however it has been recorded that the ‘shallow’ recovery dives of beaked whales regularly exceed this (Tyack et al. 2006).

Decompression sickness (DCS), commonly known as ‘the bends’, is a well studied subject in human divers. It is the result of nitrogen bubbles forming in the tissue and causing damage, we say these tissues are ‘supersaturated’. Many beached beaked whales have presented these bubbles in their muscle tissue, the reasons why this might occur will be discussed later (Zimmer & Tyack 2007). However, even though they are deep divers, studies of beaked whales behaving normally suggest that they don’t usually experience DCS, why and how exactly remains a mystery (Tyack et al. 2006).

How does underwater pressure effect humans? Click on the video below to find out:

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A look at extreme mammal divers