Oceanography is the interdisciplinary scientific study of the oceans, encompassing all aspects of the marine environment. This Earth science draws heavily upon physics, chemistry, biology, and geology to understand the world’s seas. Oceanographers investigate the vast bodies of water that cover over 70% of the planet, analyzing their properties, processes, and life forms. The goal is to develop a holistic understanding of the oceans, from the atmosphere-ocean boundary down to the deepest seafloor trenches. This study is traditionally organized into four major branches: physical, chemical, biological, and geological oceanography.
Physical Oceanography
Physical oceanography focuses on the properties and movement of seawater, examining how water dynamics influence global systems. Scientists investigate how energy and momentum are transferred through the water column, studying phenomena like waves, tides, and ocean currents. Waves are generated by wind, while tides result from the gravitational pull of the Moon and Sun, creating predictable, cyclical water movement.
Ocean currents are continuous flows of water, driven by surface winds and differences in temperature and salinity. The large-scale, deep-ocean circulation is known as the thermohaline circulation, often called the “global conveyor belt,” which is powered by density variations. Cold, dense water formed in the polar regions sinks and moves along the ocean floor, while warmer surface waters flow poleward to replace it. This massive circulation system plays a significant role in regulating the Earth’s climate by redistributing heat across the globe.
The ocean absorbs a majority of the solar radiation reaching the Earth’s surface, acting as a massive heat reservoir due to water’s high heat capacity. This heat is then exchanged with the atmosphere through processes like evaporation, which forms rain and storms, linking ocean dynamics directly to weather patterns on land. Studying the distribution of temperature and salinity is paramount, as these properties determine seawater density and influence sea level changes.
Chemical Oceanography
Chemical oceanography investigates the composition of seawater and the complex processes governing the distribution of elements and compounds within the marine environment. Seawater is a complex solution containing virtually every element found on Earth, with dissolved salts like sodium chloride making up a significant portion. Scientists track the biogeochemical cycling of essential elements such as carbon, nitrogen, and oxygen, which are fundamental to marine life and global climate systems.
The ocean functions as a substantial carbon sink, absorbing about 25% of annual anthropogenic carbon dioxide (CO2) emissions from the atmosphere. When CO2 dissolves into seawater, it reacts with water molecules to form carbonic acid (\(\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3\)). This reaction lowers the pH of the water, a phenomenon known as ocean acidification. Acidification reduces the availability of carbonate ions needed by organisms like corals and shellfish to build their calcium carbonate structures.
Researchers analyze the transport and fate of various pollutants, including heavy metals and plastics. Understanding how these contaminants are distributed and chemically interact with seawater and sediments is important for assessing environmental impacts. Unique environments like hydrothermal vents, which spew hot, mineral-rich water from the seafloor, are also studied for their contributions to deep-ocean chemical environments.
Biological Oceanography
Biological oceanography focuses on the marine biosphere, studying the distribution, abundance, and production of life in the ocean. This field examines the structure of marine ecosystems, from microscopic bacteria and phytoplankton to large marine mammals. The base of the marine food web is formed by phytoplankton, which use sunlight and dissolved nutrients to convert CO2 into organic carbon through photosynthesis. This process produces about half of the world’s oxygen.
The productivity of these organisms supports a complex food web that includes zooplankton (tiny floating animals) and nekton (actively swimming organisms like fish and squid). Benthos are the organisms that live on or in the seafloor, occupying a wide range of habitats. Scientists study how the distribution of these organisms is regulated by environmental factors, such as light availability and nutrient concentrations.
A major focus is the biological pump, the biologically driven transfer of carbon from the surface ocean to the deep ocean interior and seafloor sediments. When surface organisms die or produce fecal pellets, this organic carbon sinks. This process sequesters carbon away from the atmosphere for decades to millennia.
Geological Oceanography
Geological oceanography, sometimes called marine geology, is the study of the ocean floor, the structure beneath the water, and the processes that shape these features. This branch investigates the topography of the seafloor, known as bathymetry, which reveals an underwater landscape as complex as any on land. Scientists map out features such as abyssal plains, vast flat areas in the deep ocean, and the steep continental margins, which include the shelf, slope, and rise.
The shape and structure of the ocean floor are largely a result of plate tectonics, the theory that the Earth’s outer layer is broken into large, moving plates. Major features include mid-ocean ridges, where new oceanic crust is created, and deep-sea trenches, formed where one plate subducts beneath another. The deepest parts of the ocean, such as the Mariana Trench, are found in these subduction zones.
Geological oceanographers analyze marine sediments, which are particles of rock, mineral, and organic material that accumulate on the seafloor. These sediments, which can be terrigenous (from land) or biogenous (from organisms), hold a long record of Earth’s past climate and geological history. The study of this solid earth beneath the waves is important for understanding coastal erosion processes and the long-term evolution of the planet’s ocean basins.