Answer:
D. Subordinate clause with subordinating conjunction "because".
Explanation:
The option that displays the type of change done to the original sentence to form a new one is a subordinate clause with a subordinate conjunction "because".
The new sentence illustrates a complex sentence beginning with the subordinate clause linked with the subordinating conjunction "because" which is introducing the dependent clause. The subordinate conjunction redefines the main clause as it provides the reason(Because a measurable physical difference for in the ocean) that tells why "the water surrounding the Antarctic continent is considered an ocean unto itself".