Light in the Deepest Depths, Part 1

If asked to imagine a place on Earth unexplored by humans and bereft of our influence, mythical Utopias such as Shangri-La and the Garden of Eden springs to mind. But such a place does exist, with slightly better accessibility yet no less mysterious: The Deep Sea. What in the world goes on down there?

It was first speculated that the deep ocean would contain little to no life at all, owing to the absence of light. When the first probes were sent to the bottom, scientists were shocked to discover thriving communities of living organisms. (How light is associated with life and the implications of this discovery – such as the possibility of life on planets and moons far from their sun – will not be discussed here, but perhaps in a later post…).

But exactly how deep is deep? The most popular destination for deep sea research – I use popular very loosely here, as there have been more missions to the moon than to this part of Earth – is part of the Pacific Ocean called the Mariana Trench, measured to be about 11km in depth.

‘Pssshh’ you say, ‘I can run that distance and be home for supper’. But remember the cumulative force exerted by the water above as you begin the descent. By the time you reach the bottom, the amount of pressure you would have to endure is equivalent to 1000 times that of the standard atmospheric pressure. Imagine trying to move with the weight of ten cows on your shoulders.

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Deciding who gets to be on top.

Remember when your high school science teacher that a gas can be compressed but a liquid can’t? Well, you can throw that out the window – at that kind of pressure even liquid water is compressed, increasing its density by 5%. Organisms present in these deep waters have adaptations to cope with this intense pressure. Firstly, they have to ensure that their bodies contain no pockets of air – so no cavities, no lungs, no conventional swim bladders. This is to ensure there is no pressure differential between their insides and their outsides, otherwise their bodies would cave in upon itself. Inversely if a deep sea fish filled with air rose to shallower depths, they would literally explode from within! But wait, didn’t you say that water can also compress and expand? To avoid this issue, these organisms decrease their tissue density through high fat content along with reduction of skeletal weight.

The next issue here occurs at a chemical level, where many metabolic processes that occur on the surface can be accelerated or retarded under these pressures. To cope with this, our deep sea friends have put to use a whole lot of amazing chemistry, but I’d like to highlight this one peculiar molecule. Before I get to that, you have to understand that every molecule that isn’t water present in the cells of sea creatures are osmolytes – that is, they serve to counteract osmosis and maintain cellular volume, along with their primary roles in redox and metabolism.

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TMAO: Not your everyday tertiary amine N-oxide.

The organic molecule Trimethylamine N-oxide (TMAO) is one of these, but what is amazing is it directly counteracts the destabilization of protein structure and binding – a key part of any biological process – caused by the intense pressures. In vitro studies on TMAO show that it is also able to offset the effects of high pressure by preserving enzymatic activity1. As you dive deeper down, organisms contain higher and higher concentrations of TMAO – this protein protecting, pressure offsetting molecule. Damn.

A lot of the chemistry and life processes that occur in deep sea organisms is yet to be discovered, due to the difficulty of obtaining live specimens. Their chemical makeup is so different to creatures that live nearer to the surface that they do not thrive when brought into a laboratory.

I figured this post would be rather long if I added the next section in, so I’ve decided to build suspense and release Part 2 as a separate entry, lucky you!

Reference:

  1. P. H. Yancey, Organic osmolytes as compatible, metabolic and counteracting cytoprotectants in high osmolarity and other stresses,