Black reflections with Cycle's Glossy Material This is a common problem I've found in a few jobs related with ocean. When the camera is close to the surface, looking at the horizon, those black areas appear. Either with a normal texture or not.




It looks there's a problem with ocean's self reflection, but I can't avoid this by adjusting the bounces. Any ideas?

Here is the .blend file. As you can see, the environment is visible only through camera and glossy, and the problem keeps with a blank environment too. The scene is lit with a sun lamp and plain color environment.
I'm not completely sure what's causing this, I suspect it is just how Cycles works and is not strictly a bug - similar to the terminator issue.

In order to work around it, we can modify the surface normals slightly in the material:



From the manual:


  Incoming
  
  Vector pointing towards the point the shading point is being viewed from.


Thus adding a tiny bit of the Incoming vector will skew the surface normal just enough to hide the artifacts.

Note that changing the surface normal means our reflections will be incorrect - so we need to change it as little as possible, otherwise the reflections of objects and clouds will be noticeably weird.