Variability of Monthly Radiocarbon During the 1760S in Corals from the Galapagos Islands

Abstract

Radiocarbon (Δ14C) measurements of monthly samples from a Galapagos surface coral are among the first data sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine. An average Δ14C value of −62 is obtained for 144 measurements of samples from monthly coral bands that lived from about AD 1760–1771 (±6 yr). High Δ14C values were found during January through March, when upwelling was weak or absent at the Galapagos Islands. Low Δ14C values were obtained mid-year during strong upwelling. The average seasonal variability of Δ14C was 15–25, which is greater than that at other tropical and subtropical locations in the Pacific Ocean because of intense seasonal upwelling at this site. Periods of sustained high Δ14C values were found during 1762–1763 and 1766. A spectral analysis revealed that the spectral density for the Δ14C data displays most of its variance at the 5-yr cycle, which is reflective of El Niño periodicity during the 20th century.

Holocene marine14C reservoir age variability: Evidence from230Th-dated corals in the South China Sea

“…However, the ΔR values for the other coral (SYO‐28D) are significantly different, with the ΔR value for the decadal sample (362 ± 58 years, OZJ046) being 278 ± 67 years (>2 σ range of the two values) larger than that for the seasonal/annual sample (84 ± 33 years, OZH680). The above difference is larger than any seasonal or inter‐annual 14 C variability observed in modern corals for the past 400 cal BP which has a maximum magnitude of ∼20–25‰ in Δ 14 C or ∼160–200 14 C years [ Druffel and Griffin , 1993; Druffel et al , 2004; Grottoli et al , 2003; Grumet et al , 2004; Guilderson et al , 1998, 2004]. In addition, local recrystallization, which can result in a much younger age for the seasonal/annual sample of SYO‐28D, could not be a reason for the above large difference because all coral samples used in this study were carefully selected after screening for diagenesis as mentioned in section 2.…”

“…Considering possible large seasonal/annual variations in surface ocean 14 C [ Druffel et al , 2004; Hua et al , 2005; Morimoto et al , 2004], we also analyzed 7 decadal samples (each sample covering ∼10 years). The ΔR values derived from these decadal samples are also presented in Table 2 and plotted in Figure 3 (shown as solid symbols).…”

New Marine ΔR Values for the South Pacific Subtropical Gyre Region

“…b Makatea = fossil coral reef. (Taylor and Berger 1967;Druffel et al 2004) which occurs when the wind-driven component of transport in the surface ocean moves perpendicular to the mean wind stress, causing divergence in the surface water and upwelling of water depleted in 14 C (Tomczak and Godfrey 2001:41). Further south, the boundary between Subtropical and Antarctic water (Subtropical Front) forces 14 C-depleted water upwards just off the east coast of the South Island of New Zealand and along the southern flank of the Chatham Rise, resulting in high and variable ΔR values .…”

Zinc Reduction as an Alternative Method for AMS Radiocarbon Dating: Process Optimization at Circe

“…biogeochemical cycles assessment, anthropogenic impact on the cultural heritage, and environment assessment) are becoming 2 of the major fields in which physics methodologies, like ion beam analysis and accelerator mass spectrom etry (AMS), are becoming crucial analyses for clarifying keyhole mechanisms (Tuniz et al 1998;Andersen and Demortier 2004;Calzolai et al 2006). Regarding the carbon biogeochemical cycle, both naturally-and bomb-produced radiocarbon can be used to study dynamics of the different res ervoirs contributing to the global (biogeochemical and/or geochemical) cycle (Hughen et al 1998;Randerson et al 2002;Druffel et al 2004). Reduction of the requested mass of sample needed for 14 C analysis has led AMS to become a feasible tool for the measurement of a series of samples with low carbon contents, a characteristic of most environmental sciences studies (i.e.…”