A submarine uses tanks that can be filled with either water or air so that the submarine can have “neutral buoyancy.” That means its average density is equal to the density of water where it is located so that it will remain at that level under water. The density of water changes a small amount with depth in the ocean due to the changes in pressure and temperature. How much additional mass must a submarine take on to sit at the ocean bottom at a depth of 500 m? At this depth, the density of water is about 0.25% larger than at atmospheric pressure. Assume the volume of the submarine is 3.0 × 10⁴ m³ and it is initially floating at the surface, fully covered with water.