This paper presents a compilation of atmospheric radiocarbon for the period 1950–2019, derived from atmospheric CO2 sampling and tree rings from clean-air sites. Following the approach taken by Hua ...et al. (2013), our revised and extended compilation consists of zonal, hemispheric and global radiocarbon (14C) data sets, with monthly data sets for 5 zones (Northern Hemisphere zones 1, 2, and 3, and Southern Hemisphere zones 3 and 1–2). Our new compilation includes smooth curves for zonal data sets that are more suitable for dating applications than the previous approach based on simple averaging. Our new radiocarbon dataset is intended to help facilitate the use of atmospheric bomb 14C in carbon cycle studies and to accommodate increasing demand for accurate dating of recent (post-1950) terrestrial samples.
The El Niño–Southern Oscillation (ENSO) represents the largest source of year‐to‐year global climate variability. While Earth system models suggest a range of possible shifts in ENSO properties under ...continued greenhouse gas forcing, many centuries of preindustrial climate data are required to detect a potential shift in the properties of recent ENSO extremes. Here we reconstruct the strength of ENSO variations over the last 7,000 years with a new ensemble of fossil coral oxygen isotope records from the Line Islands, located in the central equatorial Pacific. The corals document a significant decrease in ENSO variance of ~20% from 3,000 to 5,000 years ago, coinciding with changes in spring/fall precessional insolation. We find that ENSO variability over the last five decades is ~25% stronger than during the preindustrial. Our results provide empirical support for recent climate model projections showing an intensification of ENSO extremes under greenhouse forcing.
Plain Language Summary
Recent modeling studies suggest that El Niño will intensify due to greenhouse warming. Here new coral reconstructions of the El Niño–Southern Oscillation (ENSO) record sustained, significant changes in ENSO variability over the last 7,000 years and imply that ENSO extremes of the last 50 years are significantly stronger than those of the preindustrial era in the central tropical Pacific. These records suggest that El Niño events already may be intensifying due to anthropogenic climate change.
Key Points
Line Island corals provide 1,751 years of monthly resolved ENSO variability from the mid‐Holocene to present
ENSO strength is significantly weaker between 3,000 and 5,000 years ago compared to the 2,000‐year periods both before and after
ENSO extremes of the last 50 years are significantly stronger than those of the preindustrial era in the central tropical Pacific
In their review, Song et al. (2016) overstate the validity of the atmospheric carbon sequestration potential of phytoliths as they misrepresent recent literature on the topic and omit any evidence ...that calls into question this concept. Here, we evaluate and present the full range of the misrepresented and omitted literature, and question the representativeness of their original assumptions. We also address Song et al.'s concerns regarding isotopic fractionation and/or the negative effects of over-rigorous oxidation on the isotopic analysis of phytoliths. Finally, we call for further data acquisition to properly quantify all the fluxes involved in the phytolith carbon cycle.
For proper interpretation of radiocarbon (14C) age results, the carbon fraction being dated must be identified beforehand, ideally as a single homogeneous entity that best represents the event being ...studied. Radiocarbon dating of fossil phytoliths (biosilica formed in living higher-plants) has been used in a number of archaeology and paleoenvironmental studies. More precisely, the carbon occlusion (phytC) has been 14C dated. This method relies on the phytC being photosynthetic in origin, so that its 14C signature is similar to that of the host plant. However, we have recently presented overwhelming evidence that phytC in modern plants is made up of a mixture of carbon photosynthesized by the plant (from atmospheric CO2) and soil carbon comprised of multiple 14C signatures (ages). The discussion presented here is based on our assessments of phytC 14C signatures, their chemical nature, location, origin and fate as well as the current state of knowledge on plant cell silica interactions with biomolecules. Finally, regardless of the fact that there are cases where fossil phytC 14C results appear to match expected values, the impossibility of establishing a priori either the amount of the soil carbon contribution to phytC or the mean 14C age of its occluded mixed pool precludes the use of phytoliths as a reliable 14C dating tool.
In response to a strong El Niño, fires in Indonesia during September and October 2015 released a large amount of carbon dioxide and created a massive regional smoke cloud that severely degraded air ...quality in many urban centers across Southeast Asia. Although several lines of evidence indicate that peat burning was a dominant contributor to emissions in the region, El Niñ
-induced drought is also known to increase deforestation fires and agricultural waste burning in plantations. As a result, uncertainties remain with respect to partitioning emissions among different ecosystem and fire types. Here we measured the radiocarbon content (
C) of carbonaceous aerosol samples collected in Singapore from September 2014 through October 2015, with the aim of identifying the age and origin of fire-emitted fine particulate matter (particulate matter with an aerodynamic diameter less than or equal to 2.5 μm). The Δ
C of fire-emitted aerosol was -76 ± 51‰, corresponding to a carbon pool of combusted organic matter with a mean turnover time of 800 ± 420 y. Our observations indicated that smoke plumes reaching Singapore originated primarily from peat burning (∼85%), and not from deforestation fires or waste burning. Atmospheric transport modeling confirmed that fires in Sumatra and Borneo were dominant contributors to elevated PM
in Singapore during the fire season. The mean age of the carbonaceous aerosol, which predates the Industrial Revolution, highlights the importance of improving peatland fire management during future El Niño events for meeting climate mitigation and air quality commitments.
South American tropical climate is strongly related to the tropical low-pressure belt associated with the South American monsoon system. Despite its central societal role as a modulating agent of ...rainfall in tropical South America, its long-term dynamical variability is still poorly understood. Here we combine a new (and world's highest) tree-ring 14C record from the Altiplano plateau in the central Andes with other 14C records from the Southern Hemisphere during the second half of the 20th century in order to elucidate the latitudinal gradients associated with the dissemination of the bomb 14C signal. Our tree-ring 14C record faithfully captured the bomb signal of the 1960's with an excellent match to atmospheric 14C measured in New Zealand but with significant differences with a recent record from Southeast Brazil located at almost equal latitude. These results imply that the spreading of the bomb signal throughout the Southern Hemisphere was a complex process that depended on atmospheric dynamics and surface topography generating reversals on the expected north-south gradient in certain years. We applied air-parcel modeling based on climate data to disentangle their different geographical provenances and their preformed (reservoir affected) radiocarbon content. We found that air parcel trajectories arriving at the Altiplano during the bomb period were sourced i) from the boundary layer in contact with the Pacific Ocean (41%), ii) from the upper troposphere (air above the boundary layer, with no contact with oceanic or continental carbon reservoirs) (38%) and iii) from the Amazon basin (21%). Based on these results we estimated the ∆14C endmember values for the different carbon reservoirs affecting our record which suggest that the Amazon basin biospheric 14C isoflux could have been reversed from negative to positive as early as the beginning of the 1970's. This would imply a much faster carbon turnover rate in the Amazon than previously modelled.
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•The world’s highest elevation tree records the 14C produced by nuclear detonations in northern latitudes during the 1960s•During the initial 14C spike, there were reversals on the north-south atmospheric ∆14C gradient in the southern hemisphere•Air parcel trajectories show that altitude and carbon provenance influenced the atmospheric ∆14C in Tropical South America
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.
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•Nuclear bomb derived 14CO2 has been detected in tree rings from Equatorial Amazon.•A continuous atmospheric 14C record from 1940 to 2016 was built with 175 measurements.•Timing of tree-ring growth was verified by 14C results of intra-annual wood slices.•Longitudinal asymmetry has been found as well as terrestrial biosphere enrichment.•Fossil 14CO2 intrusion, mostly from the NH, has been detected from the 2000s onwards.
An ammonia-oxidizing, carbon-fixing archaeon, Candidatus "Nitrosopumilus maritimus," recently was isolated from a salt-water aquarium, definitively confirming that chemoautotrophy exists among the ...marine archaea. However, in other incubation studies, pelagic archaea also were capable of using organic carbon. It has remained unknown what fraction of the total marine archaeal community is autotrophic in situ. If archaea live primarily as autotrophs in the natural environment, a large ammonia-oxidizing population would play a significant role in marine nitrification. Here we use the natural distribution of radiocarbon in archaeal membrane lipids to quantify the bulk carbon metabolism of archaea at two depths in the subtropical North Pacific gyre. Our compound-specific radiocarbon data show that the archaea in surface waters incorporate modern carbon into their membrane lipids, and archaea at 670 m incorporate carbon that is slightly more isotopically enriched than inorganic carbon at the same depth. An isotopic mass balance model shows that the dominant metabolism at depth indeed is autotrophy (83%), whereas heterotrophic consumption of modern organic carbon accounts for the remainder of archaeal biomass. These results reflect the in situ production of the total community that produces tetraether lipids and are not subject to biases associated with incubation and/or culture experiments. The data suggest either that the marine archaeal community includes both autotrophs and heterotrophs or is a single population with a uniformly mixotrophic metabolism. The metabolic and phylogenetic diversity of the marine archaea warrants further exploration; these organisms may play a major role in the marine cycles of nitrogen and carbon.
The science of tropical dendrochronology is now emerging in regions where tree-ring dating had previously not been considered possible. Here, we combine wood anatomical microsectioning techniques and ...radiocarbon analysis to produce the first tree-ring chronology with verified annual periodicity for a new dendrochronological species,
(commonly known as "algarrobo blanco") in the tropical Andes of Bolivia. First, we generated a preliminary chronology composed of six trees using traditional dendrochronological methods (i.e., cross-dating). We then measured the
C content on nine selected tree rings from two samples and compared them with the Southern Hemisphere (SH) atmospheric
C curves, covering the period of the bomb
C peak. We find consistent offsets of 5 and 12 years, respectively, in the calendar dates initially assigned, indicating that several tree rings were missing in the sequence. In order to identify the tree-ring boundaries of the unidentified rings we investigated further by analyzing stem wood microsections to examine anatomical characteristics. These anatomical microsections revealed the presence of very narrow terminal parenchyma defining several tree-ring boundaries within the sapwood, which was not visible in sanded samples under a stereomicroscope. Such newly identified tree rings were consistent with the offsets shown by the radiocarbon analysis and allowed us to correct the calendar dates of the initial chronology. Additional radiocarbon measurements over a new batch of rings of the corrected dated samples resulted in a perfect match between the dendrochronological calendar years and the
C dating, which is based on good agreement between the tree-ring
C content and the SH
C curves. Correlations with prior season precipitation and temperature reveal a strong legacy effect of climate conditions prior to the current
growing season. Overall, our study highlights much potential to complement traditional dendrochronology in tree species with challenging tree-ring boundaries with wood anatomical methods and
C analyses. Taken together, these approaches confirm that
can be accurately dated and thereby used in climatic and ecological studies in tropical and subtropical South America.
Worldwide monitoring of fossil fuel carbon dioxide (FFCO2) has been fragmented, and mostly devoted to developed countries. Here we compare a previously published FFCO2 dataset with socio-economic ...characteristics in order to better tailor FFCO2 urban point-sources for a megacity of the Global South, the Metropolitan Area of Rio de Janeiro (MARJ), Brazil. Evaluations were performed by superimposing maps of the FFCO2 measurements on urban data acquired from the Brazilian Institute of Geography and Statistics, the latest Origin-Destination Survey of the MARJ, and correlation and regression analyses between FFCO2 and socioeconomic variables. While we confirmed that population density and the transportation sector are important drivers of FFCO2 concentrations, the centrality of urban activities within MARJ also creates undesirable clustered zones (e.g., the city centers and the main intercity bridge). At the intra-urban scale, both high- and low-income residents play important roles in FFCO2 levels. For instance, higher-income populations tend to produce more carbon pollution at their own residential areas, where most urban activities are located. Low FFCO2 levels were found in low-income areas with poor infrastructure. However, distance from the city center, age distribution, job availability, lack of basic services, and car ownership force low-income populations to commute through high-traffic areas, adding high FFCO2 levels to the same already clustered places. By integrating FFCO2 monitoring with many socioeconomic variables, we believe that we capture its spatial distribution as well as better understand the causes of its emission patterns. Therefore, future CO2 monitoring and assessment studies conducted in megacities can benefit from the insights and discussions presented in this study.
•Low FFCO2 levels were found in low-income areas with poor infrastructure.•A spatial regression model was used to analyze drivers of FFCO2 concentration.•High FFCO2 levels were found mostly on city centers and near intercity bridge.•A polycentric development model could mitigate emissions by reducing traffic demands.•FFCO2 remains a challenge even in areas with wide biofuel use, such as MARJ.
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