Singer from the Sea by Sheri S. Tepper

A good and proper aristocrat on the isolated, seemingly backward planet of Haven, Genevieve has been carefully instructed in the Covenants -- the ancient, inflexible laws governing the women of her class. She knows what is expected of her: marriage in her mid-twenties to a groom of her father's choosing, childbirth at age thirty. And then soon afterwards -- as has been the lot of so many noblewomen before her -- perhaps death.

But there is another Genevieve within who longs to heed the call of the sea -- though she has never once seen the vast waters that cover most of her homeworld's surface. For an unheard voice is crying out to her across the centuries, drawing her ever-closer to a terrible truth hidden beneath a smoke screen of rules, tradition, and propriety. And it is Genevieve who must fulfill a forgotten destiny -- something inborn passed for untold generations from daughter to daughter -- or she and the entire civilization of Haven will be swept away on a cosmic wave of oblivion.