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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.

 

ABSTRACT Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.