Brine Pools

Brine pools are a semi-magical occurance, common in the abyssal depths of Etharai. They form on ocean shelves, surrounded by Aura mussels that thrive on the magic they give off. These mussels form a mussel bed around the pools, marking them as distinct from the rest of the water. The water within the brine pools is much denser than the ocean around them.
Brine pools are deadly for most creatures - the high salinity of the pools, combined with the excess of magic exuded from the pools. The source of this magic is unclear - however, it can be used in certain deep-sea technologies: the Auras surrounding the pools are often used to power travel upwards.

Hunting Grounds

Due to the deadly nature of the brine pools, some predators will lurk nearby, waiting for unsuspecting prey to wander into the lethal depths. Then, the work of killing their prey having been done for them, they can retrieve and eat their food.

Remnants of the War: A Theory

Some scientiests have theorised that the source of these brine pools, or perhaps simply the source of their magic, originates from the War of World's End. While this is a divisive theory, those who subscribe to it claim that the evidence is clear: defunct weapons have been found sunken at the bottom of the oceans in locations higher up. The weapons that have been found had similar Auras radiating off of them as the brine pools.
However, some believe this association to be the other way around: the weapons found at the bottom of the sea were meant to emulate the brine pools, rather than what caused them.