4C bomb peak and the onset of the Anthropocene

The unprecedented environmental changes resulting from anthropogenic activities initiated during the Great Acceleration of the mid-20th century can be traced using radiocarbon analysis. The cosmogenic isotope 14C, which is produced in the atmosphere, is well-known as the geochronological tool applied to archives of the last 55 thousand years. However, during the last 200 years, the natural signal of 14C in the atmosphere and connected reservoirs (biosphere, ocean, soils, etc.,) has been perturbed by human activities. Two anthropogenic effects are observed: a decreasing trend observed in 14C concentration of the atmosphere (Suess effect) which has been temporarily reversed by aboveground thermonuclear tests of the 1950/60s. The excess of the artificially produced 14C (bomb pulse) is a useful time marker for the mid-20th century and the detection of the bomb peak in natural archives has thus been proposed as a tool to locate and date the onset of a proposed new epoch, the Anthropocene [1]. Here we present the results of radiocarbon analysis conducted as a part of the research dedicated to establishing the Global boundary Stratotype Section and Point (GSSP) for the proposed Anthropocene series. The studied sites include corals (Flinders Reef, AU and Flower Garden Banks, USA)[2, 3], peat (Śnieżka peatland, PL)[4], lake sediment (Crawford Lake, CA and Searsville Lake, USA)[5, 6] and marine sediment (East Gotland Basin, Baltic Sea)[7]. The variety of records (different carbon reservoirs) required site and sample-specific treatment prior to analysis and site-specific interpretation of the measured 14C. Nevertheless, the mid-20th century bomb peak was detected at all but one of these sites (Searsville Lake)[6]. In all records, the observed onset of the 14C bomb peak always postdates 1954, the year of the first atmospheric 14C bomb increase. The specific reservoir effects and corrections will be discussed. References The Anthropocene Review, 2023. 10(1): 1.    Waters, C.N., et al. (Eds.), Candidate sites and other reference sections for the Global boundary Stratotype Section and Point of the Anthropocene series.  p. 3-24. 2.    Zinke, J., et al., North Flinders Reef (Coral Sea, Australia) Porites sp. corals as a candidate Global boundary Stratotype Section and Point  for the Anthropocene series.  p. 201-224. 3.    DeLong, K.L., et al., The Flower Garden Banks Siderastrea siderea coral as a candidate Global boundary Stratotype Section and Point  for the Anthropocene series. p. 225-250. 4.    Fiałkiewicz-Kozieł, B., et al., The Śnieżka peatland as a candidate for the Global boundary Stratotype Section and Point  for the Anthropocene series.  p. 288-315. 5.    McCarthy, F.M.G., et al., The varved succession of Crawford Lake, Milton, Ontario, Canada as a candidate Global boundary Stratotype Section and Point for the Anthropocene series.  p. 146-176. 6.    Stegner, M.A., et al., The Searsville Lake Site (California, USA) as a candidate Global boundary Stratotype Section and Point for the Anthropocene Series. p. 116-145. 7.    Kaiser, J., et al., The East Gotland Basin (Baltic Sea) as a candidate Global boundary Stratotype Section and Point for the Anthropocene series. p. 25-48.