Pickled Pools: Briney Ecosystems

Brine pools in the Gulf of Mexico. Image via Nautilus Live.

On the surface the ocean can often look idyllic and inviting. Exploration of the sea floor, however, reveals a harsh and unforgiving domain. Full of toxic compounds, it is hard to imagine a more hostile habitat than the Gulf of Mexico brine pools. Subject to salinity more than four times the amount of normal seawater, the pools are so desolate they have garnered the nickname the “Jacuzzi of Despair.” Despite such severe conditions, certain creatures can live or even thrive in close proximity; mussels make their home along the edge, and fish skim the surface. While life exists on the periphery of the pools, any animal that ventures into the brine will not survive.

Brine pool exploration. Video via Nautilus Live.

Brine pools form through a geologic process known as salt tectonics. Long ago the Gulf of Mexico was a shallow sea which was cut off from the rest of the ocean and eventually dried out. This caused the salt in the seawater to crystalize as the liquid evaporated. The salt crystals were then covered by sediment and compressed into an underlying layer. Eventually worldwide sea levels rose again filling the gulf. The additional water pressure caused salt to seep through cracks in the sediment layers and recombine with the liquid above. This process resulted in a brine so dense and incompatible with the surrounding seawater that it created a visible “lake” within the ocean.

Remotely operated vehicle dips into brine pool. Video via Nautilus Live.

A halocline, or a visible boundary between two fluids, is what generates the bizarre phenomena of a lake at the bottom of the ocean. Haloclines occur in areas where differences in salinity, and therefore density, separate two bodies of water. Just like a fluid boundary between air and water, disturbing the surface of the brine pool can even create waves. Haloclines can be found around the world, especially in areas where two separate bodies of water meet.

Poor pickled crab. Image via Nautilus Live.

The pools’ composition is another notable feature. Alone the brine’s high salt content is caustic to marine organisms, but toxic compounds such as methane and sulfide are also dissolved into the brine. Furthermore the immense pressure at 3300ft below the surface reduces the available oxygen. These conditions create a nearly uninhabitable environment. Yet, specialized mussels use this location to their advantage. Symbiotic bacteria in the mussel’s gills use chemosynthesis to convert methane and sulfide into energy. The bacteria are provided a place to live, and the mussels can use the energy created by the bacteria to grow. This exchange makes it viable for the mussels to exist in such an uninviting place.

Unfortunately, any large organisms that fall into the pool suffocate from the lack of oxygen. Then, like pickling a cucumber, the salt causes water to leach from the organism’s cells, preserving them indefinitely. Their bodies remain as a warning for any who might try to venture in.

The Gulf of Mexico brine pools are a fascinating discovery, but they can also lead to a greater understanding of the natural world. Knowledge gleaned from researching the pools can be useful for developing new technology. Perhaps chemosynthetic organisms can lead us to new processes for creating energy.

Alternatively extremophiles, like methane breathing bacteria, could inform our search for extraterrestrial life. Environments like the brine pools may be similar enough to those on other planets that one could imagine life surviving in space. With this in mind it is important to value the ocean and protect marine ecosystems. Discoveries like the brine pools are not possible if they are destroyed before we ever know of their existence.

Originally published at athensscienceobserver.com on December 15, 2016.