Chemical Oceanography

Chemical oceanography examines the distributions, sources, transformations and cycling of chemical species in the marine environment. It encompasses the study of major ions that determine salinity, the carbonate system that buffers pH and governs air–sea CO₂ exchange, the nutrient cycles that sustain marine productivity, and the trace-metal and organic-compound dynamics that modulate biogeochemical feedbacks. By combining field observations, laboratory experiments and numerical modelling, chemical oceanographers characterise processes ranging from molecular-scale reactions to basin-scale transports. These processes underpin the ocean’s role in climate regulation, carbon sequestration and ecosystem health, and inform our understanding of ocean acidification, deoxygenation and pollutant dispersal.

Research from Nature Portfolio

Global observational and modelling analyses have demonstrated that precipitation delivers substantial freshwater and dissolved CO₂ to the surface ocean, increasing regional salinity dilution and enhancing net carbon uptake by up to 0.2 Pg C yr⁻¹. This rainfall-driven perturbation of surface pCO₂ and stratification amplifies tropical ocean CO₂ sinks by 5–7 % over the past decade. Complementary mesocosm experiments reveal that intense rainfall events at the sea surface create millimetre-scale salinity anomalies of more than 6 g kg⁻¹ in calm conditions and up to 14 g kg⁻¹ in the surface microlayer. These near-surface salinity pulses persist over tens of centimetres depth under mixing and can alter local carbonate chemistry and gas-exchange rates, highlighting rainfall as a previously underappreciated control on coastal and open-ocean carbon fluxes.

Research from all publishers

High-resolution coastal time‐series spanning 2008–2018 in a large urban estuary have provided decade-long records of temperature, salinity, oxygen, nutrients, total alkalinity, dissolved inorganic carbon and pH. These data elucidate episodic acidification and hypoxia driven by river discharge, redox processes and seasonal heating, offering benchmarks for acidification monitoring and model validation. At basin scale, reanalyses of multiple carbonate parameters reveal that subsurface waters (100–600 m) often experience larger acidification signals than the surface due to weaker buffer capacity and accumulation of remineralised carbon. In many regions, pCO₂, Revelle factor and [H⁺] have risen by more than the atmospheric pCO₂ increase, with implications for deep-ocean carbon storage, ventilation and the potential re-emergence of high-pCO₂ waters at the surface.

Chemical Oceanography publication trend

The graph below shows the total number of articles in chemical oceanography across all publications each year (not limited to Nature Index journals).

Technical terms

Dissolved inorganic carbon (DIC): The sum of aqueous CO₂, bicarbonate and carbonate ions in seawater, reflecting the total inorganic carbon reservoir.

Total alkalinity (TAlk): The excess of proton acceptors (primarily bicarbonate and carbonate) over proton donors, determining seawater buffering capacity.

Partial pressure of CO₂ (pCO₂): The effective pressure that dissolved CO₂ would exert if in equilibrium with a gas phase, driving air–sea gas exchange.

Buffer capacity: The resistance of seawater pH to change upon addition or removal of acid or base, governed chiefly by the carbonate system.

Aragonite saturation state (Ωarag): The ratio of seawater calcium and carbonate ion activity to the solubility product of aragonite; values below unity imply conditions favouring mineral dissolution.

Air–sea CO₂ flux: The net transfer of carbon dioxide across the ocean surface per unit area, driven by the pCO₂ gradient between water and atmosphere and modulated by wind and stratification.

References

1. Global ocean carbon uptake enhanced by rainfall. Nature Geoscience (2024).
2. The impact of rainfall on the sea surface salinity: a mesocosm study. Scientific Reports (2024).
3. A decade-long cruise time series (2008–2018) of physical and biogeochemical conditions in the southern Salish Sea, North America. Earth System Science Data (2024).
4. Amplified Subsurface Signals of Ocean Acidification. Global Biogeochemical Cycles (2023).