Coral Oxygen Isotopic Records Capture the 2015/2016 El Niño Event in the Central Equatorial Pacific




Baum, Julia K.
O'Connor, Gemma K.
Cobb, Kim M.
Sayani, Hussein R.
Atwood, Alyssa R.
Grothe, Pamela R.
Stevenson, Samantha
Chen, Tianran
Claar, Danielle C.
Hitt, Nicholas T.

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Geophysical Research Letters


Coral oxygen isotopes (δ18O) from the central equatorial Pacific provide monthly resolved records of El Niño-Southern Oscillation activity over past centuries to millennia. However, calibration studies using in situ data to assess the relative contributions of warming and freshening to coral δ18O records are exceedingly rare. Furthermore, the fidelity of coral δ18O records under the most severe thermal stress events is difficult to assess. Here, we present six coral δ18O records and in situ temperature, salinity, and seawater δ18O data from Kiritimati Island (2°N, 157°W) spanning the very strong 2015/16 El Niño event. Local sea surface temperature (SST) anomalies of +2.4 ± 0.4°C and seawater δ18O anomalies of −0.19 ± 0.02‰ contribute to the observed coral δ18O anomalies of −0.58 ± 0.05‰, consistent with a ∼70% contribution from SST and ∼30% from seawater δ18O. Our results demonstrate that Kiritimati coral δ18O records can provide reliable reconstructions even during the largest class of El Niño events. Plain Language Summary Oxygen isotope anomalies in coral skeletons are a well-established proxy for changes in tropical Pacific Ocean temperature variations, which have a profound impact on weather extremes around the planet. However, only a handful of calibrations exist that quantify the relationship between ocean temperature and coral oxygen isotopic composition at a given site, especially across extreme events where this relationship may vary most strongly. Here we compare ocean temperature data from loggers installed on the reef at Kiritimati Island (2°N, 157°W) to coral oxygen isotopic records spanning the record-breaking 2015/16 El Niño event. We find that oxygen isotopes in corals provide accurate reconstructions of ocean temperature extremes during this very strong El Niño event, with ∼70% of the signal originating from ocean temperature and the remainder from increased rainfall.


We acknowledge the Republic of Kiribati for granting us permits to collect samples and conduct research on Kiritimati Island (number 005/13), provided by the Environment and Conservation Division. We especially thank Tiito Teabi for his support and expertise in the field on numerous expeditions to Kiritimati from 2012 to 2016.


Pacific Ocean temperature variations, coral oxygen isotopic composition, El Niño, 2015/16 temperature variations


O’Connor, G. K., Cobb, K. M., Sayani, H. R., Atwood, A. R., Grothe, P. R., Stevenson, S., et al. (2021). Coral oxygen isotopic records capture the 2015/2016 El Niño event in the central equatorial Pacific. Geophysical Research Letters, 48(24).