At a depth of 13,000 feet (approximately 4,000 meters) in the "bathypelagic" zone of the ocean, the temperature is consistently near-freezing, typically hovering around 39 degrees Fahrenheit (4 degrees Celsius). This area is known as the "Midnight Zone" because it is completely void of sunlight, and the water is remarkably uniform in its chill regardless of the surface climate above. The extreme cold is caused by the slow circulation of dense, oxygen-rich polar water that sinks and flows across the ocean floor. In addition to the freezing temperatures, any creature or vessel at this depth must withstand crushing pressures of over 5,800 pounds per square inch (psi), which is more than 390 times the pressure at the surface. While there is no seasonal variation at this depth, localized areas near hydrothermal vents (underwater volcanoes) can see temperatures spike to over 700 degrees Fahrenheit, creating a bizarre and deadly contrast with the surrounding near-freezing seawater.