The region that is characterized by a vast realm of open, blue water is called the zone.

~Hello there! ^_^

Your question: The region that is characterized by a vast realm of open, blue water is called the zone.

Your  The region that is characterized by a vast realm of open, blue water is called the oceanic pelagic zone.

The answer to fill up the blank is ocean pelagic.

Hope this helps! :D

Answer (d) may increase or decrease porosity through dissolution or deposition;