Ariel and the Aquamarine Jewel

Ariel and the Aquamarine Jewel is a The Little Mermaid book released around 2009. The story dealt with Ariel  having to become a mermaid again to aid her father, King Triton, in recovering the palace treasures after a storm blew them all away. Afterwards, she was allowed to keep an aquamarine jewel necklace as a gift and memento.

Description
Ariel helps search for lost jewels in the underwater kingdom of Atlantica