Takao
The Bunker Group
The Ocean Shield and Ocean Protector are both at the bottom edge of the Ice Class range and are not intended in or through heavy ice, however, they are entirely satisfactory for southern ocean patrols.
For the most part a 50 cal is more than enough for illegal fishermen and other policing activities.
It is not just the hull structure that is important it is how the vessel is operated. Adelaide operated deep into the southern ocean to rescue Tony Bullimore. The issue there was taking time to ‘normalise’ the hull to the temperature. Racing into very cold waters without doing this can result in brittle cracking.
Building on what @alexsa said, often one vessel designed for one climate doesn't do well in the other - look at the issues with RN ships operating in the Pacific, especially in 1944/45. Again, taking lessons from the IJN/USN/RN CV's in the 1930/40s, you have to pick a likely environment to operate in, and for us it's to the north. We can cover our responsibilities to the south for the foreseeable future (which I grant you, if 2020 is any indication so far, is about 37 minutes....)