The first time you will encounter Ice Sheets is during Sequence 2, Mission 1, One Little Victory. If you sail straight through, following the ship as per the mission, you will not break enough ice to unlock this achievement. To get the remainder that you need, you want to travel the the North Arctic Passage. Alternatively, if you have not yet played that mission, PunkRawkSoldier
suggests the following.
You can also go back the way you came after completing that mission. That's exactly what I did and it popped. That way, you can avoid the fort.
The North Arctic Passage is located in the North Atlantic region, and can be entered from (580,-80) or (660, -100). There is a fort on the western side, so do your best to avoid mortars if you are approaching from there. As you approach the Passage, you want to aim towards the iced-over areas of water. There is more than enough ice in this area to unlock the achievement. Simply sail through and you will unlock it. If for some reason you don't simply turn around and travel through again.
This video below shows the location of the North Arctic Passage.