Analysis of the atmospheric 14C record spanning the past 50,000 years derived from high-precision 230Th/234U/238U, 231Pa/235U and 14C dates on fossil corals

Changes in the geomagnetic field intensity, solar variability, and the internal changes of the carbon cycle are believed to be the three controlling factors of past atmospheric radiocarbon (14C) concentrations (denoted as Δ14C). Of these three, it is believed that the field intensity is the dominant factor. We analyze an atmospheric Δ14C record spanning the past 50,000 years based on previously-published 230Th/234U/238U and 14C dates of fossil corals from Kiritimati, Barbados, Araki and Santo Islands, and identify the role of the Laschamp geomagnetic field excursion on the long term trend of the Δ14C record. There is a general consistency between the coral Δ14C record and the Δ14C output from carbon cycle models based on the global 14C production estimates. High-precision, high-accuracy 230Th/234U/238U dates and redundant 231Pa/235U dates anchor the timing of this Δ14C record. We propose that a significant fraction of the long-term Δ14C trend may be due to inaccuracies in the generally accepted 14C decay constant. The uncertainty in estimating the shape of 14C beta spectrum below 20 keV leads to one of the greatest errors in decay constant estimates. Once the 14C half-life is validated via redundant techniques, Δ14C records will provide a better opportunity to examine the roles of carbon cycle and 14C production influences.