Equatorial Undercurrent Influence on Surface Seawater δ¹⁸O Values in the Galápagos

Stable isotopes of oxygen (δ 18 O) in seawater reflect the combined influences of ocean circulation and atmospheric moisture balance. However, it is difficult to disentangle disparate ocean and atmosphere influences on modern seawater δ 18 O values, partly because continuous time series of seawater δ 18 O are rare. Here we present a nearly nine‐year, continuous record of seawater δ 18 O values from the Galápagos. Seawater δ 18 O values faithfully track sea surface salinity and salinity along the equator at 50 m depth. Zonal current velocity within the Equatorial Undercurrent (EUC), directly west of the Galápagos, is strongly correlated with Galápagos surface seawater δ 18 O values with a 1‐month lag. Reconstructions of Galápagos seawater δ 18 O values could thus provide a window into past variations in the strength of the EUC, an important influence on large‐scale tropical Pacific climate.