Coral Geochemistry and Climate Reconstruction

Coral skeletons, composed of aragonitic calcium carbonate, sequester a suite of geochemical signals that reflect past ocean conditions. Variations in elemental ratios (for example Sr/Ca, U/Ca and Ba/Ca) and stable-isotope compositions (notably δ18O, δ13C and δ11B) provide quantitative reconstructions of sea surface temperature, salinity, pH and nutrient dynamics over seasonal to millennial timescales. The fidelity of these proxies is governed by physicochemical partitioning, seawater chemistry and biologically mediated “vital effects” associated with coral calcification and metabolic processes. By combining high‐resolution coral records from multiple sites and species, researchers can resolve regional climate variability, monsoon intensities, upwelling events and long-term trends in ocean heat content, providing critical context for modern climate change and projections of future marine environmental change.

Research from Nature Portfolio

Recent work has defined a robust inverse relationship between coral skeletal δ13C and both tissue photosynthesis and growth rate, revealing that mean δ13C decreases systematically with increasing water depth. This calibrated depth–δ13C framework enhances the precision of palaeo-sea-level reconstructions by accounting for metabolic influences on carbon isotopes in Porites and other genera. In parallel, a high‐resolution monthly coral Sr/Ca and δ18O record from the tropical North Atlantic during the end of the last interglacial (~118 kyr BP) has demonstrated that seasonal temperature amplitude was comparable to the present. These results confirm that orbital insolation remains the primary control on tropical seasonality and validate coral proxy performance under markedly different climate boundary conditions.

Coral Geochemistry and Climate Reconstruction publication trend

The graph below shows the total number of articles in coral geochemistry and climate reconstruction across all publications each year (not limited to Nature Index journals).

Technical terms

Sr/Ca ratio: The molar ratio of strontium to calcium in coral aragonite, used as a palaeothermometer because Sr incorporation inversely correlates with seawater temperature.

δ18O: The deviation in 18O/16O ratio of coral carbonate relative to a standard, reflecting both temperature and the δ18O of seawater (linked to salinity and ice volume).

δ13C: The deviation in 13C/12C ratio of coral carbonate, sensitive to photosynthetic activity, metabolic rate and ambient carbon isotopic composition, and used in sea-level and growth-rate studies.

Proxy: An indirect measurement preserved in a natural archive that can be calibrated to reconstruct past environmental variables such as temperature or pH.

Calcification: The biologically mediated precipitation of calcium carbonate in the coral’s extracellular calcifying medium, influenced by seawater chemistry and organismal physiology.

Vital effects: The suite of organismal processes (for example ion pumping, organic matrix synthesis and respiration) that induce departures of skeletal geochemistry from equilibrium inorganic partitioning.

References

1. Coral carbon isotope sensitivity to growth rate and water depth with paleo-sea level implications. Nature Communications (2019).
2. Tropical Atlantic temperature seasonality at the end of the last interglacial. Nature Communications (2015).
3. Coral skeletal proxy records database for the Great Barrier Reef, Australia. Earth System Science Data (2024).
4. Geochemical responses of scleractinian corals to nutrient stress. Geochimica et Cosmochimica Acta (2023).