he is the depth in the ocean at which calcareous skeletal material first begins to dissolve. Multiple choice question.

lysocline

Explanation:

Lysocline is the depth in the ocean at which calcareous skeletal material first begins to dissolve. It is the depth of the ocean whereby the dissolution rate of calcite has a dramatic rise.

Lysocline is also referred to as the transition zone upper bound where the CaCO3 content drops.

a:

by the combination of an unlimited number of elements