Postbomb Subtropical North Pacific Surface Water Radiocarbon History

Abstract

We have generated a high-resolution coral Δ14C record from the leeward side of the Big Island of Hawai’i in the subtropical North Pacific. The record spans 1947–1992, when the coral was collected, and includes a brief prebomb interval as well as the postbomb era. Mean prebomb (1947–1954) values average −55‰ (±1, SE of the mean) with a clear seasonal cycle. Values are less positive during winter when vertical exchange mixes surface and lower-14C subsurface waters. The postbomb annual maximum occurs in 1971 (+160‰) and decreases in a series of shifts to +105‰ in 1991, the end of our coral-based reconstruction. The decrease is not monotonic and has inflection points during the La Niña years of 1973, 1977, and 1984. Imbedded in the Δ14C record is interannual variability in the El Nino-Southern Oscillation band which is interpreted to reflect the lateral advection of low latitude surface waters as part of the oceanic Hadley Cell driven by Sverdrup dynamics.