ENSO's Impact on the Pacific Intertropical Convergence Zone: New Insights from a Network of Pacific Coral Records

El Niño-Southern Oscillation (ENSO) events are fundamentally intertwined with the behavior of the Intertropical Convergence Zone (ITCZ). For example, sea surface temperature anomalies during El Niño events draw the Pacific ITCZ equatorward and thus alter patterns of rainfall across the Pacific. However, the behavior of the Pacific ITCZ on time scales longer than that of the satellite era (1979-present) remains poorly constrained due to the scarcity of rain gauge sites across the tropical Pacific, which limits understanding of long-term interactions between the ITCZ and ENSO.

This study uses a network of coral geochemical records to reconstruct the location of the western/central Pacific ITCZ from 1950 to 1995, overlapping and extending satellite-based ITCZ indices. We present three new records of coral δ¹⁸O, which reconstruct sea surface temperature and seawater δ¹⁸O, from Onotoa (1 coral, 1.8°S, 175.6°E) and Majuro Atolls (2 corals, 7.1°N, 171.4°E). These records primarily reflect changes in seawater δ¹⁸O associated with salinity and therefore precipitation, and provide key northerly and southerly endpoints for a network of coral records from the western and central Pacific ITCZ (8 sites total). The reconstructed, instrumental, and reanalysis-based ITCZ locations correlate significantly and respond similarly to ENSO events, shifting southward during El Niño and northward during La Niña. We assess changes in the relationship between ENSO and the ITCZ through time, and explore low-frequency variability and long-term trends in ITCZ position that result from Pacific decadal variability, inter-hemisphere differences in aerosol production, and anthropogenic warming. Ultimately, this work extends instrumental records of the ITCZ's position, explores the stability of the ENSO-ITCZ relationship on decadal timescales, and assesses precipitation and drought trends in Pacific island nations.