On this second layer, Effects > Stylize > Engrave/Emboss

I like to keep the same pixel width as I use in the land, and while I usually use Emboss as I did on the land, I occasionally find that Engraving the sea, looks better. Try it both ways to see which you like. You could also adjust the pixel width to diminish the differences in ocean depth and give a smoother, more "surface"-like appearance.

In the layers window, select Layer Properties. Change the Blend Mode to Overlay.

Hide Layer.

Yeah, the ocean operates a little differently from the other layers. There are fewer steps in setting up the texture, mainly because we can't use any masking until later or the sea will look weird.Go back to the very bottom layer of clouds, and hide everything else. (Even if you're experimenting with what layers to use, your ocean has to be made from the lowest "elevation" layer.)Duplicate once only  we're not making a mask yet  and ignore the bottom layer.For the impatient: Since so much of what you're doing is repeated on each layer, you could choose to lump each action together: duplicate everything, rename everything, run the Emboss on everything, run the Threshold and Alpha Mask on everything, and then merge everything. The Repeat Effect command, CTRL-F, would become your friend for quite a lot of these steps.