The correct answer is A. Oceans.
The main abiotic reservoir for elements involved in biogeochemical cycles, such as calcium and phosphorus, is the oceans. The oceans contain a vast amount of dissolved and solid substances, including various elements essential for life. Calcium and phosphorus, for example, are present in the oceans in the form of dissolved salts and sediments.
The oceans play a crucial role in the cycling of elements through processes like weathering, erosion, and deposition. Elements like calcium and phosphorus can enter the oceans through runoff from land, atmospheric deposition, and volcanic activity. These elements then participate in various biological and geological processes within the marine environment, including the formation of shells, skeletons, and sediments.
