Wild Dark Shore by Charlotte McConaghy

Dominic Salt is the caretaker of Shearwater, a remote island near Antarctica where he lives with his three children, Raff, Fen, and Orly. The island is mostly inhabited by seals but visiting researchers have created a vast seed bank – which would help the world replant if there were a natural disaster. Because the sea is rising, the island will soon be uninhabitable so the Salts, after many isolated years, will be forced to begin again somewhere on the mainland. If they really leave.