Answer: D) weathering
Phosphorus is a chemical organic element that is found in numerous compounds of the Earth typically found in water, sediments and soils. The phosphorus in the soil is being added up by the chemical fertilizers. In the ocean or marine water the phosphorus is deposited as animal waste and by the weathering of the rocks and minerals.
The weathering is a process by which the rocks are broken down into small parts and sediments by the action of the physical agents such as water, wind and chemicals. In the given situation the weathering is the process by which the element phosphorus will be added to the bottom bed of the ocean.