Climate Variability Reconstruction Using Coral Proxies

Coral skeletons serve as remarkable archives of past oceanographic conditions, continuously recording environmental signals through variations in their chemical and isotopic composition. Two principal proxies—stable oxygen isotopes (δ18O) and strontium-to-calcium ratios (Sr/Ca)—provide complementary chronologies of sea surface temperature (SST) and seawater composition. Coral δ18O reflects a combination of SST and seawater δ18O, which itself is influenced by local salinity and hydrological balance, whereas coral Sr/Ca is primarily a thermometer for SST. High‐resolution coral records, often spanning centuries to millennia, furnish insights into interannual phenomena such as El Niño–Southern Oscillation (ENSO), decadal modes like the Pacific Decadal Oscillation, and longer‐term changes in tropical warm pools. By integrating multi‐core records from diverse ocean basins and applying rigorous calibration techniques, researchers reconstruct regional and basin‐scale climate variability, evaluate climate model simulations, and unravel the interplay between ocean–atmosphere forcing and hydrological cycles over the Common Era and beyond. These reconstructions are indispensable for understanding the magnitude and drivers of natural variability, placing recent warming in a long‐term context, and improving skill in future climate projections.

Research from Nature Portfolio

Studies of mid‐Holocene corals from the western Indian Ocean have revealed a marked reduction in seasonal SST range compared to modern records, implying a significant westward expansion of the Indian Ocean warm pool under altered orbital forcing. This finding challenges modelled insolation-driven seasonality and highlights the role of ocean–atmosphere feedbacks. Investigations of coral geochemistry in northern Borneo have provided a multi‐decadal perspective on ENSO and Pacific Decadal Oscillation influences, documenting synchronous shifts in sea surface temperature and seawater δ18O during major El Niño and La Niña events since the early 1980s. These records demonstrate the value of tropical coral archives in capturing both interannual extremes and longer‐term trends in hydrological balance and thermal stress. Earlier work has used multi‐core Porites records from the western Indian Ocean to identify biases in twentieth century SST products, showing that coral reconstructions offer an independent benchmark for evaluating instrumental datasets and refining estimates of regional warming patterns.

Climate Variability Reconstruction Using Coral Proxies publication trend

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

Technical terms

Stable oxygen isotopes (δ18O): The ratio of heavy to light oxygen isotopes in coral aragonite, reflecting SST and seawater isotopic composition related to salinity and precipitation.

Strontium-to-calcium ratio (Sr/Ca): The proportion of strontium to calcium in coral skeletons, serving as a temperature‐dependent proxy for sea surface temperatures.

Palaeoclimate proxy: A natural recorder of past environmental conditions, such as coral skeletons, tree rings or ice cores, used to infer climate variability before instrumental records.

Coral core: A cylindrical sample extracted from massive coral colonies, enabling the reconstruction of sequential environmental data at monthly to annual resolution.

References

1. Mid-Holocene expansion of the Indian Ocean warm pool documented in coral Sr/Ca records from Kenya. Scientific Reports (2023).
2. Corals reveal ENSO-driven synchrony of climate impacts on both terrestrial and marine ecosystems in northern Borneo. Scientific Reports (2020).
3. Indian Ocean corals reveal crucial role of World War II bias for twentieth century warming estimates. Scientific Reports (2017).
4. The CoralHydro2k database: a global, actively curated compilation of coral δ18O and Sr / Ca proxy records of tropical ocean hydrology and temperature for the Common Era. Earth System Science Data (2023).
5. Equatorial Undercurrent Influence on Surface Seawater δ18O Values in the Galápagos. Geophysical Research Letters (2023).