C04_07

Tree species in Central Amazon basin show uniform levels of ¹⁴C bomb-peak as well as fossil-CO₂ contributions from mining operations

Santos G¹, Albuquerque R², Barros C², Ancapichun S^3,4, Oelkers  R⁵, Andreu-Hayles L⁵, de Faria S⁶, De Pol-Holz R³, Brandes A⁷

¹University of California, Irvine, Irvine,, United States, ²Escola Nacional de Botânica Tropical, Rio de Janeiro, , Brazil, ³Universidad de Magallanes, Punta Arenas, Chile, ⁴Universidad de Concepción, Concepción, Chile, ⁵Columbia University, Palisades, , USA, ⁶Empresa Brasileira de Pesquisa Agropecuária, Seropédica, , Brazil, ⁷Universidade Federal Fluminense, Niterói, , Brazil

Tree rings has been widely used for atmospheric radiocarbon (¹⁴C) calibration purposes, but such records have been limited along tropical latitudes. Here we report precisely measured ¹⁴C dates in tree rings (1937 to 2007) of the parenchyma-rich Hymenolobium petraeum tree species from the Central Brazilian Amazon (Porto Trombetas, 1°S, 56°W). Bomb-peak tree-ring ¹⁴C reconstruction coincides with the broader changes associated with reported values of the Southern Hemisphere ¹⁴C curve (Hua et al. 2021), suggesting that inter-hemispheric air-mass transport of excess-¹⁴C injected into the stratosphere during aboveground nuclear tests is relatively uniform across distinct longitudinal regions. From the early 1970s onwards, H. petraeum had lower ¹⁴C values than recently developed pantropical ¹⁴C records (e.g., Camanducaia; Santos et al. 2015, and Altiplano; Ancapichún et al. 2021). Through ¹⁴C-based estimation, we found a strong influence of local fossil-fuel CO₂ contributions. While the Oriximiná district’s population density (0.5/km²) cannot be considered as its main cause, mining operations and waterway shipping traffic are potentially responsible for the local dilution of atmospheric ¹⁴CO₂. In addition, air parcels reaching Porto Trombetas during the growing season follow the Amazon River path, which handles most of export shipments of country’s ore, soybean and corn by transnational business giants. Our findings invite further ¹⁴C analyses using tree rings of tropical tree species as a potential tracer for a wide range of environmental sources of atmospheric ¹⁴C-variability.

Hua et al. 2021. Radiocarbon, 1-23. DOI: https://doi.org/10.1017/RDC.2021.95

Santos et al. 2015. QUAGEO 25, 96-103

Ancapichún et al. 2021. STOTEN 774, 145126