marine oxygen isotopic record

paleontology

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June 30, 2026

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The marine oxygen isotope record is a method used to reconstruct past climate conditions, primarily focusing on global ice volume and ocean temperatures. This record is derived from the analysis of oxygen isotopes (oxygen-16 and oxygen-18) found in the calcium carbonate shells of microfossils, such as foraminiferans, that accumulate on the seafloor.12

The ratio of these isotopes in the shells is influenced by two main factors: the temperature of the seawater when the shell was formed and the isotopic composition of the seawater itself. Colder water leads to shells with a higher proportion of oxygen-18, while warmer water results in shells with more oxygen-16.1

Crucially, the isotopic composition of seawater is directly linked to the amount of water stored in large ice sheets on land. During glacial periods, more water is locked up in ice, making the remaining ocean water relatively "heavier" (richer in oxygen-18). Conversely, during warmer interglacial periods, less ice means the ocean water is relatively "lighter" (richer in oxygen-16). Therefore, the marine oxygen isotope record primarily serves as a proxy for past glaciations on the continents. This continuous record is invaluable for correlating with terrestrial climate data and understanding long-term climate cycles.13

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Pleistocene Epoch
Marine oxygen isotope record
The isotopic record is based on the ratio of two oxygen isotopes, oxygen-16 (¹⁶O) and oxygen-18 (¹⁸O), which is determined on calcium carbonate from shells of microfossils that accumulated year by year on the seafloor. The ratio depends on two
Read More
The isotopic record is based on the ratio of two oxygen isotopes, oxygen-16 (¹⁶O) and oxygen-18 (¹⁸O), which is determined on calcium carbonate from shells of microfossils that accumulated year by year on the seafloor. The ratio depends on two
Read More

Pleistocene Epoch
Cause of the climatic changes and glaciations
…glaciations as inferred from the marine oxygen isotope record were milestones in testing the astronomical theory. Early spectral analysis of the oxygen isotope record of cores from the deep ocean showed frequencies of climatic variation at essentially the same frequencies as the orbital cycles—that is to say, at 100,000 years,…
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…glaciations as inferred from the marine oxygen isotope record were milestones in testing the astronomical theory. Early spectral analysis of the oxygen isotope record of cores from the deep ocean showed frequencies of climatic variation at essentially the same frequencies as the orbital cycles—that is to say, at 100,000 years,…
Read More