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Abstract A limitation in fine-tuned tree-ring radiocarbon (¹⁴C) data is normally associated with overall data uncertainty. Tree-ring¹⁴C data variance as a result of sample heterogeneity can be reduced by adopting best practices at the time of sample collection and subsequent preparation and analysis. Variance-reduction of¹⁴C data was achieved by meticulous sample handling during increment core or cross-sectional cuttings, in-laboratory wood reductions, and cellulose fiber homogenization of whole rings. To demonstrate the performance of those procedures to final¹⁴C results, we took advantage of the replicated data from assigned calendar years of two Pantropical post-1950 AD tree-ring¹⁴C reconstructions. TwoCedrela fissilisVell. trees spaced 22.5 km apart, and two trees of this species together with onePeltogyne paniculataBenth tree spaced 0.2 to 5 km apart were sampled in a tropical dry and moist forest, respectively. Replicate¹⁴C data were then obtained from grouped tree-ring samples from each site. A total of 88% of the replicated¹⁴C results fell into a remarkably consistent precision/accuracy range of 0.3% or less, even though multiple tree species were used as pairs/sets. This finding illustrates how adopting a few simple strategies, in tandem with already established chemical extraction procedures and high-precision¹⁴C analysis, can improve¹⁴C data results of tropical trees. 

In this study, we present a comprehensive atmospheric radiocarbon (14C) record spanning from 1940 to 2016, derived from 77 single tree rings of Cedrela odorata located in the Eastern Amazon Basin (EAB). This record, comprising 175 high-precision 14C measurements obtained through accelerator mass spectrometry (AMS), offers a detailed chronology of post-1950 CE (Common Era) 14C fluctuations in the Tropical Low-Pressure Belt (TLPB). To ensure accuracy and reliability, we included 14C-AMS results from intra-annual successive cuts of the tree rings associated to the calendar years 1962 and 1963 and conducted interlaboratory comparisons. In addition, 14C concentrations in 1962 and 1963 single-year cuts also allowed to verify tissue growth seasonality. The strategic location of the tree, just above the Amazon River and estuary areas, prevented the influence of local fossil-CO2 emissions from mining and trade activities in the Central Amazon Basin on the 14C record. Our findings reveal a notable increase in 14C from land-respired CO2 starting in the 1970s, a decade earlier than previously predicted, followed by a slight decrease after 2000, signaling a transition towards the fossil fuel era. This shift is likely attributed to changes in reservoir sources or global atmospheric dynamics. The EAB 14C record, when compared with a shorter record from Muna Island, Indonesia, highlights regional differences and contributes to a more nuanced understanding of global 14C variations at low latitudes. This study not only fills critical spatial gaps in existing 14C compilations but also aids in refining the demarcation of 14C variations over South America. The extended tree-ring 14C record from the EAB is pivotal for reevaluating global patterns, particularly in the context of the current global carbon budget, and underscores the importance of tropical regions in understanding carbon-climate feedbacks. 

To ensure unbiased tree-ring radiocarbon (14C) results, traditional pretreatments carefully isolate wood cellulose from extractives using organic solvents, among other chemicals. The addition of solvents is laborious, time ­consuming, and can increase the risk of carbon contamination. Tropical woods show a high diversity in wood­ anatomical and extractive composition, but the necessity of organic-solvent extraction for the 14C dating of these diverse woods remains untested. We applied a chemical treatment that excludes the solvent step on the wood of 8 tropical tree species sampled in South-America and Africa, with different wood-anatomical and extractive properties. We analyzed the success of the extractive removal along with several steps of the a-cel­lulose extraction procedure using Fourier Transform Infrared (FTIR) spectroscopy and further confirmed the quality of 14C measurements after extraction. The ex-cellulose extracts obtained here showed FTIR-spectra free of signals from various extractives and the 14C results on these samples showed reliable results. The chemical method evaluated reduces the technical complexity required to prepare a-cellulose samples for 14C dating, and therefore can bolster global atmospheric 14C applications, especially in the tropics. 

In this study, we present a comprehensive atmospheric radiocarbon (14C) record spanning from 1940 to 2016, derived from 77 single tree rings of Cedrela odorata located in the Eastern Amazon Basin (EAB). This record, comprising 175 high-precision 14C measurements obtained through accelerator mass spectrometry (AMS), offers a detailed chronology of post-1950 CE (Common Era) 14C fluctuations in the Tropical Low-Pressure Belt (TLPB). To ensure accuracy and reliability, we included 14C-AMS results from intra-annual successive cuts of the tree rings associated to the calendar years 1962 and 1963 and conducted interlaboratory comparisons. In addition, 14C concentrations in 1962 and 1963 single-year cuts also allowed to verify tissue growth seasonality. The strategic location of the tree, just above the Amazon River and estuary areas, prevented the influence of local fossil-CO2 emissions from mining and trade activities in the Central Amazon Basin on the 14C record. Our findings reveal a notable increase in 14C from land-respired CO2 starting in the 1970s, a decade earlier than previously predicted, followed by a slight decrease after 2000, signaling a transition towards the fossil fuel era. This shift is likely attributed to changes in reservoir sources or global atmospheric dynamics. The EAB 14C record, when compared with a shorter record from Muna Island, Indonesia, highlights regional differences and contributes to a more nuanced understanding of global 14C variations at low latitudes. This study not only fills critical spatial gaps in existing 14C compilations but also aids in refining the demarcation of 14C variations over South America. The extended tree-ring 14C record from the EAB is pivotal for reevaluating global patterns, particularly in the context of the current global carbon budget, and underscores the importance of tropical regions in understanding carbon-climate feedbacks. 

Tree-ring width chronologies of cedro (Cedrela fissilis Vell.) (1875 to 2018), jatobá (Hymenaea courbaril L.) (1840 to 2018) and roxinho Peltogyne paniculata Benth.) (1910 to 2018) were developed by dendrochronological techniques in the southern Amazon Basin. Acceptable statistics for the tree-ring chronologies were obtained, and annual calendar dates were assigned. Due to the lack of long-term chronologies for use in paleoclimate reconstructions in degraded forest areas, dendrochronological dating was validated by 14C analysis. Tree-rings selected for analysis corresponded to 1957, 1958, 1962, 1963, 1965, 1971, and 1972. Those are critical calendar years in which atmospheric 14C changes were the highest, and therefore their tree-ring cellulose extracts 14C signatures when in alignment with existing post-AD 1950 atmospheric 14C atmospheric curves would indicate annual periodicity. Throughout our correlated calendar years and post-AD 1950 14C signatures, we indicate that H. courbaril shows an erratic sequence of wood ages. The other two tree species, C. fissilis and P. paniculata, are annual in nature and can be used successfully as paleoclimate proxies. Moreover, due to the sampling site’s strategic location in relation to the Tropical Low-Pressure Belt over South America, these trees can be used to enhance the limited amount of observational data in Southern Hemisphere atmospheric 14C calibration curves. 

Abstract Instrumental observations indicate that Amazon precipitation and streamflow extremes have increased during the last 40 years, possibly due to anthropogenic changes and natural variability. How unprecedented these changes might be is difficult to determine because some paleoclimatic, instrumental, and climate model simulations suggest that Amazonian precipitation and streamflow may be subject to multidecadal variability with return intervals longer than most direct observations. A new 258‐yearlong tree‐ring chronology ofCedrela odoratahas been developed in the eastern Amazon and has been used to reconstruct wet season precipitation totals from 1759–2016. Reconstructed drought extremes are associated with significant sea surface temperature anomalies over the tropical Pacific and Atlantic Oceans. Strong multidecadal variance is identified in the reconstruction that may reflect a component of natural rainfall variability relevant to forest ecosystem dynamics and suggesting that recent hydroclimate changes over the eastern Amazon may not be unprecedented over the past 258 years.