A solid brass sphere is initially surrounded by air, and the air pressure exerted on it is 1.0 \times 10^{5} N / m ^{2} (normal atmospheric pressure). The sphere is lowered into the ocean to a depth where the pressure is 2.0 \times 10^{7} N / m ^{2} . The volume of the sphere in air is 0.50 m³. By how much does this volume change once the sphere is submerged?