Wikipedia's article on the colossal squid gives the distribution as in the Southern Ocean only.
It makes sense for many animals found in the Antarctic to not also be found in the Artic even if the environments are similar, simply because there's no way for the species to get from the Antarctic to the Artic. However if colossal squids can range more than a kilometer under sea level, then by that depth, the ocean should look the same in every direction: it would be so dark and cold that there's no easy way to tell if one is on the equator or under the North Pole. In other words the squid should be found in every ocean, not just the Southern Ocean.
What is wrong with this reasoning?