midocean

Midocean, or open ocean, denotes the vast regions of the world's oceans distant from coastlines and continental shelves. It includes the pelagic zone from the sunlit epipelagic layer to the deep mesopelagic, bathypelagic, and abyssopelagic zones, as well as the mid-ocean basins and their seafloor features.

Geographically, the midocean contains most of the ocean's volume. The global mid-ocean ridge system—the long, continuous volcanic mountain chain created by seafloor spreading—stretches about 65,000 kilometers across all oceans. The deep-sea floor comprises abyssal plains, seamounts, and fracture zones. Average ocean depth is about 3,700 meters; depths commonly exceed 4,000 meters, and trenches near margins can surpass 7,000 meters.

Physical conditions vary with latitude. Surface waters range from warm in the tropics to cold in polar regions; the water column is strongly stratified. The sunlit epipelagic layer reaches roughly 200 meters, after which light diminishes rapidly. In open subtropical gyres, nutrients are typically scarce, leading to low primary productivity, while higher productivity occurs in high-latitude seas, coastal upwelling zones, and around hydrothermal vents on spreading ridges.

Biologically, the open ocean hosts diverse planktonic communities and larger migratory animals. Deep-sea habitats near mid-ocean ridges support unique ecosystems sustained by chemosynthesis around hydrothermal vents.

Human activities include exploration and scientific drilling programs, and potentially deep-sea mining, which raises concerns about ecosystem impacts. The midocean is important for global climate and carbon cycling and remains a major focus of oceanographic research.