Arctic sea ice naturally during the dark, cold winters and during the spring and summer.

Arctic sea ice naturally expands during the dark, cold winters and contracts during the spring and summer.
This is an obvious choice of answers, given that when it is cold, there will be a lot of ice because there isn't enough heat to thaw it, therefore it expands. On the contrary, when it is hot, the Sun emits enough heat so that the ice melts a bit, and naturally, there is less of it.