The seafarer's kiss
(Book)

Series information from Goodreads.com

Having long wondered what lives beyond the ice shelf, nineteen-year-old mermaid Ersel learns of the life she wants when she rescues and befriends Ragna, a shield-maiden stranded on the merfolk's fortress. But when Ersel's childhood friend and suitor catches them together, he gives Ersel a choice: say goodbye to Ragna or face justice at the hands of the glacier's brutal king. Determined to forge a different fate, Ersel seeks help from the divine Loki. But such deals are never straightforward, and the outcome sees her exiled from the only home and protection she's known. To save herself from perishing in the barren, underwater wasteland and be reunited with the human she's come to love, Ersel must try to outsmart the God of Lies.