Final answer:
The depth of water in the Mariana Trench is approximately 11,000 meters. Pressure at this depth can be calculated with the formula P = ρgh, but the assumption of constant seawater density is not entirely accurate. The deep ocean zones also include the aphotic zone, where the Mariana Trench is located.
Step-by-step explanation:
The depth of water in the Mariana Trench is about 11,000 meters (approximately 6.8 miles), making it the deepest part of the world's oceans. To calculate the pressure at the bottom of the Mariana Trench, we use the formula for pressure caused by a fluid column: P = ρgh, where ρ is the density of the seawater, g is the acceleration due to gravity, and h is the depth of the water. Assuming a constant density for seawater, the pressure at a depth of 11.0 km is significant. However, the actual pressure might differ, given that the assumption of constant density is not entirely valid because water is slightly compressible and its density can increase with depth.
The SI unit for pressure is the Pascal (Pa), and indeed, the unit of hρg simplifies to N/m², which is equivalent to Pascal. As for the changes in seawater volume under such pressure, they are calculated using the bulk modulus of water. With increased pressure, seawater's volume decreases, leading to a corresponding increase in its density.
Depth plays a critical role in the categorization of oceanic zones. The pelagic zone includes all open water, while the benthic zone extends along the ocean bottom. The photic zone allows light penetration, unlike the aphotic zone, found in depths greater than 200 meters. Among these, the Challenger Deep in the Mariana Trench represents the aphotic zone and is the site of the greatest ocean depths on Earth.