The Legend of the Lost Pearl by Moya Huxtable

In the Crystal Caves, hidden far beneath Antarctica, lives an ancient being. Medusa is the last of her kind who escaped from our sister planet, Terralius, before its apocalyptic implosion eons ago. She has seen what unfolds when all warnings of global catastrophe are ignored. After Fleur, estranged daughter of a prominent world leader, is saved from drowning by a massive, green turtle named Midas, they embark on a perilous quest to save the Earth. Midas is no ordinary turtle, and together they journey to the Crystal Caves to seek help from Medusa and her fabled Pearl. Far beneath the waves, Fleur witnesses both the wonder of the marine world and the horrific impact of humankind's destruction and neglect. But will she have the courage and faith to claim the mystical talisman that is our only hope in a race against time and greed?