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  • Leo R

The Secret World of Underwater Lakes

If our dear childhood obsession Spongebob Squarepants got one thing right about the biology of the oceans, it's probably not what you'd expect. No, there's no burger joint run by a money-grabbing crab, locked in perpetual warfare with an oversized zooplankton. But there are seas that sit on the ocean-floor. Great expanses of gentle white waves rolling away into the distance.

However, visit these shores and you're not likely to find a whole lot of beach-goers. No, instead you'll be faced with an apparent dead zone, scattered corpses, and perhaps the odd slimy hagfish worming its way through the darkness. These are the brine pools of the deep sea. Lakes of ultra-salty water - too salty to support a community of life - which form when water seeps into cracks in the sea-floor and begins to dissolve salt deposits beneath the sediment.

Watch the video above to see some footage from these brine pools, or scroll down to continue with the article.

Above: These underwater lakes can be expansive, but you certainly wouldn't want to take a dip here.

Below: You alright there, Mr Krabs? Well, the likely answer is no. You see, when organisms enter this super-salty brine, they suffer a toxic shock! The fluid contains almost no oxygen and is full of toxic chemicals like hydrogen sulphide and methane, which almost instantly kills any sea life that come into contact with it.

But although life cannot be found within the pools, there is still a surprising diversity of life that gathers on their shores. In fact, brine pools support chemosynthetic activity in which specialised bacteria convert the toxic chemicals into energy! Think of this as a similar process to photosynthesis in plants. And just like plants, the bacteria therefore provide nutrients and energy for other life.

Because of this, we find a stark contrast at the very edge of the 'jacuzzis of despair. A hard edge between the death trap, and a sprawling array of clustered life. Often, this comes in the form of beds of mussels that live in symbiosis with the chemosynthetic bacteria, and predators that feed on those mussels.

Above: The stark edge of the 'jacuzzi of despair'. There is a fine line between where life is able to thrive in great abundance, and where survival is altogether impossible. Photograph sourced from EV Nautilus.

Mussels are not the only organisms found here. Their predators include eels and deep sea crabs, while some fish such as the odd-looking chimaera frequent the pools too.


Formation of a Brine Pool:

So how do these hot tubs of despair form? I briefly mentioned earlier that it's due to water seeping into salt deposits, but it's a bit more complicated than that.

Let's take a look at the Gulf of Mexico, where brine pools are very well documented due to there being huge deep buried salt plates under the sea floor. When water intrudes into these plates, it dissolves some of their minerals.

Tectonic movement causes the salt plates to warp and crack, allowing more water to seep into the sea floor and push out the brine. This brine flows into a divot or basin, forming a brine pool. Mineral deposits left behind by the mineral-rich water creates colourful ridge structures.


Below: A small brine pool. The ridges that border the briny source are mineral deposits.

Discover more about the life in the deep over on the Deep Sea Hub.

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