Tree-ring C14 data across the ITCZ over South America and Central Africa: filling the gaps in atmospheric post-AD1950 C14 curves

LAIA ANDREU-HAYLES; QUAN HUA; DARWIN PUCHA-COFREP; PETER GROENENDIJK; GUACIARA M. SANTOS; RICARDO DE POL-HOLZ; EDILSON J. REQUENA-ROJAS; ARNO F.N. BRANDES; ROSE OELKERS; DANIELA GRANATO-SOUZA; MARIA E. FERRERO; SILVANA PATIÑO-ROSARIO; ANA C.C. BARBOSA

Dublin

Congreso; 20th Congress of the International Union for Quaternary Research (INQUA); 2019

International Union for Quaternary Research (INQUA)

Radiocarbon (14C) dating allows us to better understand the human past and the carbon cycle. The technique?s success relies on very precise measurements of 14C activity in carbonaceous material remains. Independently-dated biological materials that exhibit annual layers, such as tree rings, are necessary for a precise reconstruction of the atmospheric 14C, as radiocarbon ages do not represent exact calendar dates. Ongoing efforts to optimize the 14C timescale have produced calibration curves back to 50 kyrs BP. Nevertheless, several gaps still remain. While it is well established that during the Holocene atmospheric 14C signatures have varied between the Northern Hemisphere (NH) and Southern Hemisphere (SH) through the inter-hemispheric offset, there is still little data to better define intra-hemispheric offsets for the last 70 years. The intra-hemispheric offsets define the 14C geographical division known as zones NH1, NH2, and NH3 for Northern Hemisphere, and SH1-2 and SH3 for Southern Hemisphere. Currently, the 14C geographical divisions, zones SH1-2 and SH3, are basically defined using data from eastern SH sites (New Zealand, Australia, and Indonesia). Consequently, the 14C boundary between zones SH1-2, SH3, and NH3 over South America and Africa at lower latitudes are defined based on the mean position of the Inter Tropical Convergence Zone (ITCZ). To overcome a dearth of suitable 14C records at lower-latitudes, we selected six tree species across the Amazon basin and Central Africa (i.e., Ecuador, Peru, Bolivia, Brazil and Cameroon). The main goal of this project is to extend the observational record by developing annually-resolved atmospheric post-AD1950 14C data using cellulose material from dendrochronologically-dated tree rings across the ITCZ mixed band. These newly developed datasets will be used to model observed 14C gradients of each species/site for backtracking air-mass parcels to better constrain the new global atmospheric 14CO2 global distribution map. Additionally, we will develop isotopic synoptic maps based on both δ13C and δ18O tree-ring series to examine spatial and temporal patterns of carbon cycle changes that can influence 14C spatial distributions. The project showcase will be discussed and preliminary results will be presented.