Hello BeefyViking, thank you for posting your question.
I attempted to give my ocean some shadows like in a cave environment as well. I ended up finding out that the inability to give awesome cave-shadows may be from the Shading Model being set to SingleLayerWater for the water’s material. According to this resolved post, this is due to the ocean reflecting the sky.
I hope this give you some insight for now. I look forward to additional replies providing more clarification on this subject.