Ocean Wolves by Theresa Beachman

A life-threatening discovery mined from the bottom of the North Atlantic Ocean turns a routine mission deadly for Becca’s scientific team. Her only chance of survival will involve trusting a team of black-ops mercenaries led by the one man she swore to forget.
Dr. Becca Johnson has buried herself in her work after a painful past taught her she’s better off alone. She loves the isolation of ocean research but as her six month deep sea rotation draws to a close, events rapidly escalate into life-threatening chaos. Struggling to hold her team together, she is forced against her wishes to accept the help of the Ocean Wolves.
Ethan Carter joined the Ocean Wolves after his career in the elite Special Boat Services ended, when his troubled past led to a forces psychiatrist deeming him unfit for duty. Now, he’s a hired gun with the Wolves, paid to protect the interests of the world’s biggest ocean-based multi-national, Triton Core. When his team is tasked to escort crucial research to the surface, he discovers events spiraling out of control and the woman from his past he has tried desperately to forget. The woman who reignites emotions hidden deep in his heart.
Fighting escalating dangers that threaten the lives of everyone in the habitat and a rogue AI, Ethan vows to protect Becca at all costs.
But as their options dwindle, leaving Ethan and Becca trapped nearly 8000 feet below the surface, will it be enough to keep her alive?