The "Water Depth" plugin makes easy mixing MW Ocean Depth with other water depth nodes like "TZ_RiverDepth".
Usage is extremely simple: just put a "Water Depth" node at the output of the other water depth node.
The "Water Depth" node add the local ocean depth to the input value. Care is taken that either ocean depth and input value are clamped to 0.0 in case they tend to become negative.