The relevance of stable oxygen and carbon isotopes in oceanography and paleoclimatology

Sediment deposits at the sea floor comprise the most extensive archive of  short and long-term variations of the earth's climate. They contain information about changes in the oceanic and atmospheric circulation as well as about variations in the chemical composition of sea water. The main carrier of information for the reconstruction of past climates and oceanic circulations are stable oxygen and carbon isotope ratios (¹⁸O/¹⁶O; ¹³C/¹²C). They are determined e.g. on fossil calcareous shells of marine organisms (e.g., monocellular zooplankton), which has been sampled from sediment cores. The isotope ratios contain approximate values for numerous climatic and oceanic variables such as ice volume, water temperature, salinity, nutrients, and the CO₂ content of the ocean.