Oceanography is the scientific study of Earth's oceans and marine environments, including their physical properties, chemical composition, biological communities, geological structures and interactions with the atmosphere and solid Earth. It is an interdisciplinary science because oceans involve fluid dynamics, chemistry, biology, geology, climate processes and planetary physics. Oceanographers investigate ocean currents, waves, tides, temperature, salinity, marine organisms, seafloor structures, sediments, dissolved gases, nutrients and the movement of heat and carbon. Oceans cover most of Earth's surface and contain the majority of the planet's liquid water, making their behaviour essential to understanding weather, climate, ecosystems and the global water cycle.
Physical oceanography examines the movement and physical properties of seawater. Temperature and salinity influence seawater density, while density differences help drive large scale circulation. Wind transfers momentum to the ocean surface and contributes to currents and waves. Tides arise principally from gravitational interactions involving the Moon and Sun combined with Earth's rotation and the geometry of ocean basins. Surface currents can transport heat across enormous distances, while deep ocean circulation is influenced strongly by differences in density associated with temperature and salinity. The resulting circulation helps redistribute energy and materials around the planet and contributes substantially to Earth's climate system.
Chemical oceanography studies the composition and chemical behaviour of seawater. Important variables include salinity, dissolved oxygen, carbon dioxide, nutrients, acidity, alkalinity and concentrations of many trace substances. The ocean is a major reservoir for carbon and plays an important role in the global carbon cycle. Carbon dioxide dissolves in seawater and participates in chemical equilibria involving carbonic acid, bicarbonate and carbonate ions. Human increases in atmospheric carbon dioxide have consequently altered ocean chemistry and contributed to ocean acidification. Chemical oceanographers investigate these changes as well as nutrient cycling, pollutants, dissolved metals and interactions between seawater, sediments and organisms.
Biological oceanography, also called marine biology in many contexts, investigates organisms living in marine environments and the ecological processes connecting them. Marine ecosystems include microscopic phytoplankton, zooplankton, bacteria, algae, corals, fish, marine mammals, seabirds and organisms living on or within the seafloor. Phytoplankton are particularly important because they perform photosynthesis and form the foundation of many marine food webs. Ocean productivity depends on light, nutrients, temperature, mixing and other conditions. Deep ocean ecosystems can operate without sunlight, including communities associated with hydrothermal vents where chemosynthetic microorganisms use chemical energy.
Geological oceanography examines the seafloor, marine sediments, plate tectonics, submarine volcanoes, trenches, ridges, continental margins and the geological history preserved beneath the oceans. Mid ocean ridges are associated with seafloor spreading and the creation of new oceanic crust. Deep ocean trenches can form where one tectonic plate is subducted beneath another. Sediments accumulate from biological remains, material transported from land, volcanic particles and chemical precipitation. Studying these sediments provides evidence about past ocean conditions, climate, biological productivity and geological events.
Oceanography is essential to climate science because the ocean stores and transports enormous quantities of heat. Seawater can absorb solar energy at the surface, while currents redistribute heat between different regions. The ocean also exchanges gases with the atmosphere and absorbs a substantial fraction of anthropogenic carbon dioxide emissions. Ocean circulation therefore affects atmospheric temperature, precipitation patterns and climate variability. Phenomena such as El Nino and La Nina demonstrate how changes in ocean temperatures and atmospheric circulation can interact across the tropical Pacific and influence weather patterns far beyond the Pacific region.
Scientists study oceans using research vessels, autonomous underwater vehicles, remotely operated vehicles, satellites, moorings, floats, buoys, sonar, sediment cores and chemical sampling systems. Satellite instruments can measure sea surface temperature, ocean colour, sea level and other properties over enormous areas. Autonomous floats can measure temperature and salinity at different depths and transmit observations by satellite. Sonar is used to map the seafloor and detect underwater features. Deep sea vehicles can investigate environments that are inaccessible to ordinary divers. These technologies allow oceanographers to study a vast environment that remains difficult to observe directly.
Oceanography has practical significance for fisheries, maritime transport, coastal management, offshore energy, conservation, pollution monitoring, climate assessment and hazard prediction. Coastal and marine systems face pressures from warming, sea level rise, habitat loss, pollution, overfishing and chemical changes. Oceanographers provide evidence needed to understand these processes and manage marine environments. Oceanography is therefore not a single narrow discipline but a broad scientific framework combining physical, chemical, biological and geological approaches to understand the world's oceans and their role within the Earth system.
