The phrase "deepest depths" means the lowest or most extreme part or point of something. It refers to reaching the farthest or most intense extent of a situation or feeling. Full definition
Since the small lens and sensor already have very deep depths of field, closing down the aperture on the S9 has a minimal effect on what's in focus. (theverge.com)
Maybe a wreck at deeper depths or specific plants and coral. (idcthailand.net)
It continually replaces seawater at depth with water from the surface and slowly replaces surface water elsewhere with water rising from deeper depths. (britannica.com)