Exploring the ¹⁴C Bomb Peak with Tree Rings of Tropical Species from the Amazon Forest

Abstract

In this work we explore the radiocarbon (14C) signal as an independent tool to assess the year of formation of individual tree rings of tropical species in northern Brazil. Three different species were analyzed in this work: Dipteryx magnifica, Enterolobium maximum, and Hymenolobium petraeum. The studied samples are from the stem of only one individual of each species, all cut down in 2008 in Porto Trombetas, Pará, Brazil. Individual tree rings were identified based on wood anatomy and they were counted from bark to pith. Several rings were selected for 14C analysis in order to cover the overall shape of the 14C atmospheric bomb peak (after 1955). The 14C content was measured at Laboratory of Radiocarbon, Universidade Federal Fluminense (LAC-UFF). Results are compared with the Southern Hemisphere 14C atmospheric calibration curves. For E. maximum and H. petraeum the 14C signal exhibits an overall good match with the SH zone 3 and suggests annual seasonality in the growth-ring formation. These species offer suitable characteristics for dendrochronology. The D. magnifica shows mismatches in the 14C measurements that are likely a result of difficulties in identifying ring boundaries with certainty. Additional techniques may be helpful to disentangle the origin of this discrepancy.

Annually Verified Growth of Cedrela Fissilis from Central Brazil

“…However, a strong correlation of growth with rain season can produce reliable annual records in some species from tropical South America (Baker et al 2017). Studies based on species such as Cedrela sp., Araucaria angustifolia, Enterolobium maximum and Hymenolobium petraeum have shown encouraging results (Santos et al 2015;Baker et al 2017;Linares et al 2017). With the aim of validating dendrochronological records as reliable 14 C datasets, the first step is to evaluate the known atmospheric 14 C concentration in comparison to 14 C-dated rings, preferably in a period when subtle variations can be perceived.…”

Historical droughts recorded in extended Juniperus procera ring-width chronologies from the Ethiopian Highlands

“…For example, the initial J. procera chronology from the Blue Nile River basin showed a 1-year difference from bomb radiocarbon dates and the chronology was revised (Wils et al 2010). In another tropical study, Linares et al (2017) showed that in some years, the radiocarbon dating revealed 7-12 missing rings between two consecutive dendrochronologically dated tree-rings. False rings can also lead to incorrect dating, as several false rings can occur within 2 years.…”

High resolution <sup>14</sup>C bomb-peak dating and climate response analyses of subseasonal stable isotope signals in wood of the African baobab – A case study from Oman

“…Reliable age estimates of tropical and subtropical trees can be obtained from radiocarbon dating (Swart, 1963;Worbes, 1989). Using the bomb peak caused by extensive nuclear testing in the 1950s and 60s, radiocarbon dating was proven a reliable tool in plant sciences that enables dendrochronological studies on trees with indistinct growth boundaries (Fichtler et al, 2003;Hua et al, 2003;Robertson et al, 2006;Andreu-Hayles et al, 2015;Ohashi et al, 2016;Baker et al, 2017;Linares et al, 2017). The vast majority of bomb tests have been carried out in the Northern Hemisphere.…”