:"hadal" designating or of the ecological zone (hadal zone) of the ocean floor trenches below c. 3,300 fathoms (c. 6,000 m)

Well, then what designates ocean floor trenches above 3,300 fathoms (c.6000 m)?

And how is this hadal pronounced? I know I could LIU, but I'd rather see it spelled out here.

Best regards,
BubBub