This book is on pre-order until restock arrives. 
 
In Violent Waves (Tidal Tithe #1) by JA Townsend:
 
On the eve of her arranged marriage, Princess Lyra is bound to the Tidal Tithe, a ritual demanding the sacrifice of a human heart. But before the offering can be made, she is stolen away by a rival kingdom.

Torn from the sea, Lyra enters into a dangerous bargain to appease ancient magic unraveling around her. Her only ally? The enemy she was foretold to hate.

As treachery deepens and tides rise, Lyra must choose: obey the rules of her kingdom, or seize the forbidden magic hidden in within her voice—and risk everything to change the tides.

A story of sacrifice, rebellion, and love as fierce as the sea itself.