Making of an Arctic Sea

The northeastern part of Midrêth is a dangerous area for travelers.  There is the Cube of Infinity, sometimes used to terminate extremely dangerous criminals.  Around this unimaginably large cube is the Forbidden Sea.  In these waters, you risk being lost to freak tidal waves.  Beyond both of these is

Silfergath, making his own prison

the Prison Continent, more commonly known as Denerra.  During the Dawn War, this continent was used to imprison primordials and some of their powerful minions.    One of those imprisoned here was a icy monstrosity named Silfergath.

Silfergath was not a thinker, he was made by Thyrm and others to serve as a living war machine.  Twice he ended up creating his own
icy prison.  His final resting place is in the cold depths of Nautrek.  This sea changed when Silfergath became entombed in its depths.  It went from being a temperate ocean to be an arctic one.