DOI: 10.5061/dryad.xsj3tx9rd
title: Data from: A novel post-1950 CE atmospheric 14C record for the tropics using absolutely dated tree rings in the equatorial Amazon

description: 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.
description: Sample selection: For this atmospheric tree-ring based
 <sup>14</sup>C dataset, a <em>Cedrela odorata</em>
 specimen was sourced from an established 231-year tree-ring chronology
 (Granato-Souza et al., 2019, 2020; https://www.ncei.noaa.gov/access/paleo-search/study/24110). A wood segment (P45) with clear tree ring boundaries was then used, and 77 tree rings spanning the period 1940 to 2016 were individually sampled from it for high-precision <sup>14</sup>C accelerator mass spectrometry (AMS) and stable isotope (δ<sup>13</sup>C) analysis. Cellulose extraction:  Tree-ring cellulose extraction to alpha-cellulose was performed at three laboratories, i.e., the Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI), the Lamont-Doherty Earth Observatory (LDEO), and the Australian Nuclear Science and Technology Organization (ANSTO). Once KCCAMS/UCI completed the microscope inspection of all tree rings singled out, samples and/or subsamples were accordingly redistributed to other labs for alpha-cellulose extractions. The largest load of samples went to LDEO for batch-mode chemical extractions using a semiautomated bath device. At the KCCAMS/UCI facility the tree ring slices of 1962 and 1963, and replicates of the counterpart whole rings, were extracted in 13mm culture tubes. The ANSTO <sup>14</sup>C-AMS facility was responsible for 10 duplicates of raw wood tree rings between 1999 and 2000 for cross-laboratory validation. Expanded descriptions of sample preparation processes and <sup>14</sup>C analysis alongside images of the main devices/apparatus used by each laboratory have been added to the main text and in the supplementary material of Santos et al. 2024 https://doi.org/10.1016/j.scitotenv.2024.170686. Graphite production for <sup>14</sup>C analysis and measurements: Graphite production from cellulose extracts for <sup>14</sup>C-AMS analysis were employed by two <sup>14</sup>C-AMS facilities, KCCAMS/UCI and ANSTO. KCCAMS/UCI produced filamentous graphite from in-house alpha-cellulose fibers and LDEO cellulose extracts using the sealed-tube Zn reduction method (Santos & Xu 2017), while ANSTO used the H<sub>2</sub>/Fe method for graphite production (Hua et al. 2001). Both <sup>14</sup>C-AMS facilities employ distinct spectrometers during their <sup>14</sup>C analysis, i.e., the KCCAMS/UCI runs an in-house modified NEC 0.5MV 1.5SDH-1 system (Beverly et al 2010) and ANSTO operates a 1-MV NEC VEGA instrument (Fink et al., 2004). High accuracy and precision were obtained at both <sup>14</sup>C-AMS facilities based on consistent results of reference materials and replicated cellulose data. Stable carbon isotope (δ<sup>13</sup>C) determination: Remaining aliquots of chemically extracted alpha cellulose containing 0.6 to 0.7 mg each were weighed out into tin boats to take stable isotope ratio mass spectrometer (IRMS) measurements, using a Delta Plus CFIRMS interfaced with a Fisons NA 1500NC elemental analyzer (EA) at the KCCAMS/UCI facility. This instrument has a typical precision of 0.1‰ based on measurements of several standards, such as USGS-24, IAEA-600, and Atropine (C<sub>17</sub>H<sub>23</sub>NO<sub>3</sub>). For further details, refer to Santos et al. 2024 https://doi.org/10.1016/j.scitotenv.2024.170686. Citation information in this document: Beverly, R.K., Beaumont, W., Tauz, D., Ormsby, K.M., von Reden, K.F., Santos, G.M., Southon, J.R., 2010. The Keck Carbon Cycle AMS Laboratory, University of California, Irvine: status report. Radiocarbon 52 (2), 301–309. DOI: https://doi.org/10.1017/S0033822200045343 Fink, D., Hotchkis, M., Hua, Q., Jacobsen, G., Smith, A.M., Zoppi, U., Child, D., Mifsud, C., van der Gaast, H., Williams, A., Williams, M., 2004. The ANTARES AMS Facility at ANSTO. Nucl. Instrum. Methods Phys. Res. B 223–224, 109–115. https://doi.org/10.1016/j.nimb.2004.04.025 Granato-Souza, D., Stahle, D.W., Barbosa, A.C., Feng, S., Torbenson, M.C., de Assis Pereira, G., Schongart, J., Barbosa, J.P., Griffin, D., 2019. Tree rings and rainfall in the equatorial Amazon. Climate Dynam. 52 (3), 1857–1869. https://doi.org/10.1007/s00382-018-4227-y. Granato-Souza, D., Stahle, D.W., Torbenson, M.C., Howard, I.M., Barbosa, A.C., Feng, S., Fernandes, K., Schongart, J., 2020. Multidecadal changes in wet season precipitation totals over the Eastern Amazon. Geophys. Res. Lett. 47 (8) (p.e2020GL087478).  https://doi.org/10.1029/2020GL087478 Hua, Q., Jacobsen, G.E., Zoppi, U., Lawson, E.M., Williams, A.A., Smith, A.M., McGann, M.J., 2001. Progress in radiocarbon target preparation at the ANTARES AMS Centre. Radiocarbon 43, 275–282. DOI: https://doi.org/10.1017/S003382220003811X Santos, G.M., Xu, X., 2017. Bag of tricks: a set of techniques and other resources to help <sup>14</sup>C laboratory setup, sample processing, and beyond. Radiocarbon 59 (3), 785–801. DOI: https://doi.org/10.1017/RDC.2016.43
description: # Data from: A novel post-1950 CE atmospheric 14C record for the tropics
 using absolutely dated tree rings in the equatorial Amazon ## Data S1 and
 S2 S1. EAB_14C_record_weighted mean S2. EAB_14C_dataset complete ## Brief
 description of dataset contents \***Data file S1** (EAB 14C record -
 averaged data) contains the annual data (Weighed mean ± larger of error of
 the mean or standard error of replicated data, when applicable) of the 77
 *Cedrela odorata* tree rings from Eastern Equatorial Amazon, Brazil (1°S,
 53°W; 1940-2016). Variables (columns from left to right) listed are
 described as follows: 1: “#” = The sample number. 2: “Calendar year AD” =
 Dendrochronological calendar dates were adjusted to the calendar’s
 sub-annual level of 0.34 yrs based on the climate diagram in Granato-Souza
 et al. (2020) and intra-annual Delta14C values of 1962 and 1963 rings. 3:
 “IRMS-delta13C” = Values of IRMS-delta13C were obtained from
 alpha-cellulose extracts produced at LDEO and KCCAMS/UCI only. Missing
 result for 1960 calendar year indicates that no remaining cellulose
 extract was available to provide EA-IRMS data. 4: “Age corrected Delta14C
 (‰)” = decay corrected Delta14C values, expressed in parts per thousand
 (‰), as per equation (1) in Santos et al. 2024
 [https://doi.org/10.1016/j.scitotenv.2024.170686](https://doi.org/10.1016/j.scitotenv.2024.170686) 5: “±1s” = 1 sigma or one standard deviation from the measured value. 6: “# of measurements” = Total number of 14C measurements that were obtained from alpha cellulose extracts produced by using the extraction methods of the LDEO lab, and/or the 14C-AMS facilities of KCCAMS/UCI and ANSTO. Graphite targets and AMS measurements were carried out at the aforementioned facilities (i.e., KCCAMS/UCI and ANSTO). **S1 dataset notes** ꟷ Cells under IRMS-delta13C with "-" imply that the measurement was not taken, as no extra alpha cellulose extract was available. ꟷ Radiocarbon results are given as Delta14C corrected for radioactive decay to 1950 and mass-dependent fractionation (Stuiver and Polach 1977). Delta14C corrected weighed mean ± larger of error of the mean or standard error (see data file S2 for details on individual 14C results and errors). \***Data file S2** (EAB 14C record - complete dataset) contains the complete 14C dataset for the 77 *Cedrela odorata* tree rings from Eastern Equatorial Amazon, Brazil (1°S, 53°W; 1940-2016). A total of 175 radiocarbon results are shown. Variables (columns from left to right) listed are described as follows: 1: “# meas.” = number of 14C measurements performed. 2: “Radiocarbon AMS facility#” = The assigned numeric entries UCIAMS# and ANSTO# that correspond to the 14C-AMS facility identifier where samples were measured for their 14C content. UCIAMS# is the identifier for one of the spectrometers run at KCCAMS/UCI facility. A total of 155 measurements/results produced at the KCCAMS/UCI involved 8 wheels, while ANSTO produced 20 results in a single run. 3: “Sample ID” = Sample ID are the wood-segment (P45) and calendar year in which ring formation begins. At Eastern Amazon Basin Cedrela odorata ring growth occurs from February to July of every year. Sample ID's followed by capital letters A, B, C & D are the intra-annual 14C signatures spread between February to July. 4: “Extraction lab/14C-AMS” = LDEO-KCCAMS/UCI, KCCAMS/UCI and ANSTO indicate where tree ring samples were chemically extracted to alpha cellulose before 14C sample processing took place at either 14C-AMS facility aforementioned. 5: “Year of growth” = Dendrochronological calendar dates were adjusted to the calendar’s sub-annual level of 0.34 yrs based on the climate diagram in Granato-Souza et al. (2020), and intra-annual 14C values of 1962 and 1963 rings. 6: “IRMS-delta13C” = Values of IRMS-delta13C were obtained from alpha cellulose extract remains of LDEO and KCCAMS/UCI. Missing result for 1960 indicates that no remaining cellulose extract was available for a measurement. 7: “F14C”= fraction of the modern standard (F14C), following the description in Reimer et al. (2014). 8: “±1s” = 1 sigma or one standard deviation from the measured value. 9: “Age corrected Delta14C (‰)” = decay corrected Delta14C values, expressed in parts per thousand (‰), as per equation (1) in Santos et al. 2024 [https://doi.org/10.1016/j.scitotenv.2024.170686](https://doi.org/10.1016/j.scitotenv.2024.170686) 10: “±1s” = 1 sigma or one standard deviation from the measured value. 11: “Weighed Mean Delta14C (‰)” = each Delta14C values per cal. year was multiplied by its assigned weight, summed and divided by the total number of Delta14C values produced. 12: “Propagated Error” = square root of the sum of squares. 13: “Standard Error” = standard deviation of the sample and "n" is the sample size. 14: “# of pairs” = number of pairs or replicated data produced. **S2 dataset notes** ꟷ Uncertainty between IRMS-delta13C duplicates is in the order of ±0.1‰, and matches with instrumental uncertainty based on measurement of a series of reference materials. ꟷ Cells under IRMS-delta13C with "-" imply that the measurement was not taken, as no extra alpha cellulose extract was available. ꟷ Cells under “Weighed Mean Delta14C (‰)”, “Propagated Error” and “Standard Error” discriminated by "n/a" imply that just one 14C measurement has been done per calendar year (Year of growth). On other words, there is no other data point to compare it to. ꟷ Radiocarbon results are given as fraction of the modern standard (F14C; Reimer et al 2014) and Delta14C corrected for radioactive decay to 1950 and mass-dependent fractionation (Stuiver and Polach 1977). Delta14C corrected weighed mean ± larger of error of the mean or standard error. ꟷ Simple pooled standard deviation calculation (by Cohen 1988) based on 69 replicated measurements yielded a precision of 0.13%. **Mentioned publications in these notes:** Cohen, J. (1988), Statistical Power Analysis for the Behavioral Sciences, 2nd Edition, Hillsdale: Lawrence Erlbaum, 567++, eBook published in 12 May 2013 - New York. DOI: [https://doi.org/10.4324/9780203771587](https://doi.org/10.4324/9780203771587)  Granato-Souza, D., Stahle, D.W., Torbenson, M.C., Howard, I.M., Barbosa, A.C., Feng, S., Fernandes, K., Sch¨ongart, J., 2020. Multidecadal changes in wet season precipitation totals over the Eastern Amazon. Geophys. Res. Lett. 47 (8) (p.e2020GL087478). DOI: [ [https://doi.org/10.1029/2020GL087478](https://doi.org/10.1029/2020GL087478)] Reimer PJ, Brown TA, Reimer RW. 2004. Discussion: reporting and calibration of postbomb 14C data. Radiocarbon 46(3):1299–1304. DOI: [https://doi.org/10.1017/S0033822200033154](https://doi.org/10.1017/S0033822200033154) Stuiver M, Polach HA. 1977. Discussion reporting of 14C data. Radiocarbon 19(3):355–363. DOI: [https://doi.org/10.1017/S0033822200003672](https://doi.org/10.1017/S0033822200003672) ## Description of the data and file structure Data files S1 and S2 are both Excel sheets. They each contain radiocarbon (14C) and IRMS stable isotope (delta13C) data. **##Access information##** The dataset shown here has been produced and curated for the purpose of atmospheric 14C reconstructions, and has been thoroughly discussed in the Santos et al. 2024 manuscript ([https://doi.org/10.1016/j.scitotenv.2024.170686](https://doi.org/10.1016/j.scitotenv.2024.170686)). Rules on use and distribution of this data: * Researchers are encouraged to use the original data formats for their analyses to ensure the accuracy and reliability of their results. However, we understand that some file formats may require specific software or tools for access. In such cases, or for any assistance with data conversion and analysis, researchers are welcome to contact Guaciara dos Santos ([gdossant@uci.edu](mailto:gdossant@uci.edu)), responsible for the accuracy of the dataset. Dr. Santos is committed to providing support and guidance to facilitate the effective use of this comprehensive dataset in further research and analysis. * Use of this data MUST be accompanied by a citation of these datafiles and/or the original manuscript. Any alternations made to either dataset must be disclosed. ## Purpose and Utility * This file is a resource for researchers aiming to conduct detailed analyses of pantropical atmospheric 14C concentrations. * Offering raw data in this format empowers researchers to draw comparisons, fostering diverse investigations in radiocarbon and other relevant research fields, such as monitor and understand long-term changes in the global cycle, or help on separate fossil, biomass burning, and biogenic contributions in the terrestrial/atmospheric reservoir. ## Dataset funding This 14C dataset is a result of an US National Science Foundation fund granted to Dr. Guaciara dos Santos (AGS-1903690).