"Once a perpetual winter wonderland of snow and ice, the walrus and the polar bear are losing their beautiful icebound world as it melts from underneath them."

Контекст следующий:
From National Geographic Films, the people who brought you MARCH OF THE PENGUINS and Paramount Classics, the studio that brought you AN INCONVENIENT TRUTH, ARCTIC TALE is an epic adventure that explores the vast world of the Great North. The film follows the walrus, Seela and the polar bear, Nanu, on their journey from birth to adolescence to maturity and parenthood in the frozen Arctic wilderness. Once a perpetual winter wonderland of snow and ice, the walrus and the polar bear are losing their beautiful icebound world as it melts from underneath them.

Сам перевел это страшное предложение как
"Полярная медведица и моржиха теряют свой прекрасный, скованный льдами мир, казавшийся вечной и чудесной страной снега и льда, так как он тает незаметно от них."
НО уверенности нет никакой :)