Chemical Oceanography
Chemical oceanography asks what seawater is made of and why — tracing the dissolved salts, gases, nutrients, and carbon that set the ocean's composition and link it to the atmosphere, the seafloor, and life.
Definition
Chemical oceanography is the study of the chemical composition of seawater and the processes — physical, biological, and geological — that control the distribution and cycling of dissolved and particulate substances in the ocean.
Scope
This area covers the major-ion composition and salinity of seawater, the marine carbonate system and ocean acidification, the cycling of dissolved oxygen and nutrients, the biogeochemical cycles of carbon, nitrogen, and other elements, and the chemical exchanges among ocean, atmosphere, sediments, and biota.
Sub-topics
Core questions
- Why does seawater have a nearly constant ratio of major ions despite varying salinity?
- How does the carbonate system buffer seawater pH, and how is ocean acidification changing it?
- What controls the distribution of dissolved oxygen and the limiting nutrients in the ocean?
- How do biological, physical, and geological processes couple to cycle carbon and other elements?
Key theories
- Constancy of composition
- The major ions of seawater occur in nearly fixed proportions worldwide (the principle associated with Marcet and Dittmar), so a single conservative property — salinity — characterizes the bulk composition.
- Carbonate buffering of seawater
- Equilibria among carbon dioxide, bicarbonate, and carbonate ions buffer ocean pH and govern the storage of inorganic carbon, making the carbonate system central to the ocean's role in climate.
- Redfield stoichiometry
- Marine organic matter forms and decays with a characteristic ratio of carbon, nitrogen, and phosphorus, linking biological production to the distributions of nutrients and oxygen throughout the ocean.
Clinical relevance
Ocean chemistry controls the sea's uptake of anthropogenic carbon dioxide and the progression of ocean acidification, the oxygen budgets that determine the spread of low-oxygen dead zones, and the nutrient supply that sustains fisheries, making it central to climate and marine resource management.
History
Systematic ocean chemistry began with Dittmar's analyses of Challenger expedition samples in the 1880s, confirming the near-constant proportions of seawater's major ions. Redfield's mid-twentieth-century work linked the chemistry of nutrients to biology, and global survey programs such as GEOSECS and WOCE later mapped the ocean's chemical fields.
Key figures
- Alfred Redfield
- William Dittmar
- Lars Gunnar Sillen
Related topics
Seminal works
- pilson2013
- sarmientoGruber2006
Frequently asked questions
- Why is the ocean salty?
- Rivers and hydrothermal systems deliver dissolved ions to the sea, where they accumulate because water leaves mainly by evaporation; over geological time this has produced seawater's characteristic salinity and ion composition.
- How is the ocean becoming more acidic?
- As the ocean absorbs carbon dioxide from the atmosphere, the gas reacts with seawater to form carbonic acid, lowering pH and reducing the carbonate ions that shell-building organisms need.