For ships to navigate polar regions, they must have what is called an "Ice Rating". As you'd expect, there are several standards: American, Russian, Swedish, German etc. So be careful to compare like classes when assessing a ship's ability.
One must also bear in mind that an "icebreaker" is a special ship design altogether. As the name suggests, icebreakers are designed to smash through solid sea ice while other (conventional) ships are simply "ice strengthened" and it is their rating in this regard that is most important.
For serious ice work, ships need to be rated 1A or 1A Super. This means they can work with an icebreaker in the heaviest conditions. Then progressively down to 1B, 1C and Class II, the lightest rating.
Some examples of familiar ships:
- MV Orion - Class 1A (Germanischer Lloyd E3)
- Marina Svetaeva - Class 1A
- Lyubov Orlova - Class 1C
- MS Hanseatic - Class 1A Super (Germanischer Lloyd E4)
For the marine engineers among us, here is a heavy technical document to explain it. Here is the easier Wikipedia page.