Radiocarbon variability in the western equatorial Pacific inferred from a high‐resolution coral record from Nauru Island

We have generated a high resolution coral Δ 14 C record spanning the last 50 years to document the seasonal and interannual redistribution of surface waters in the western tropical Pacific. Prebomb (1947–1956) Δ 14 C values average −63‰ and have a total range of 30‰. Values begin to increase in 1957, reaching a maximum of 137‰ in mid‐1983. Large interannual variability of up to 80‰ closely follows the El Niño‐Southern Oscillation (ENSO). During each ENSO warm phase, Δ 14 C values begin to increase, reflecting the reduction of low‐ 14 C water upwelling in the east and the invasion of subtropical water into the western equatorial tropical Pacific. Maximum Δ 14 C values are in phase or lag the corresponding sea surface temperature maxima in the eastern tropical Pacific, whereas the rapid return to more negative Δ 14 C is in phase with eastern Pacific ENSO indices. The highest‐amplitude excursions occur during the 1965/1966 and 1972/1973 events, when the 14 C contrast is highest between the eastern Pacific and subtropics. The 1982/1983 El Niño, although a larger ENSO event, has a lower Δ 14 C amplitude, reflecting the penetration of bomb radiocarbon into the equatorial undercurrent and the reduced contrast in Δ 14 C between thermocline and subtropical surface waters at that time. This coral record demonstrates the potential for using similar radiocarbon time series for documenting variability in Pacific shallow circulation over interannual and decadal timescales.