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 timing of Tiwanaku's collapse remains contested. Here we present a generational-scale chronology of Tiwanaku using Bayesian models of 102 radiocarbon dates, including 45 unpublished dates. This ...chronology tracks four community practices: residing short- vs. long-term, constructing monuments, discarding decorated ceramics, and leaving human burials. Tiwanaku was founded around AD 100 and around AD 600, it became the region's principal destination for migrants. It grew into one of the Andes' first cities and became famous for its decorated ceramics, carved monoliths, and large monuments. Our Bayesian models show that monument building ended ~AD 720 (the median of the ending boundary). Around ~AD 910, burials in tombs ceased as violent deaths began, which we document for the first time in this paper. Ritualized murders are limited to the century leading up to ~AD 1020. Our clearest proxy for social networks breaking down is a precise estimate for the end of permanent residence, ~AD 1010 (970-1050, 95%). This major inflection point was followed by visitors who used the same ceramics until ~AD 1040. Temporary camps lasted until roughly ~AD 1050. These four events suggest a rapid, city-wide collapse at ~AD 1010-1050, lasting just ~20 years (0-70 years, 95%). These results suggest a cascading breakdown of community practices and social networks that were physically anchored at Tiwanaku, though visitors continued to leave informal burials for centuries. This generation-scale chronology suggests that collapse 1) took place well before reduced precipitation, hence this was not a drought-induced societal change and 2) a few resilient communities sustained some traditions at other sites, hence the chronology for the site of Tiwanaku cannot be transposed to all sites with similar material culture.
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
The Southeast Pacific Subtropical Anticyclone (SPSA) extends over the entire South Pacific Basin and it is the dominant forcing of the Humboldt Current System. The SPSA has seasonal, interannual, and ...decadal (interdecadal) variability. The latter variability has been associated with the Pacific Decadal Oscillation (PDO), recognized as a Pan-Pacific mode. However, most of the ocean–atmosphere studies on interdecadal scales have been conducted in the Northern Hemisphere, and very few in the Southern Hemisphere. Thus, through reanalysis model outputs and satellite data, this research mainly establishes the relationship between SPSA and PDO in the period 1949–2012 and its impact on sea surface temperature along the north-central coast of Chile between 2000 and 2012. For this purpose we first analyzed the seasonal and interannual variability of the SPSA. An analysis of correlation between air pressure at sea level and the PDO and Southern Annular Mode (SAM) indices established that, at the interdecadal scale, these oscillations explained 49% and 40% of the variance, respectively; however, SAM had a time lag of six years to explain this variance. The PDO, in the air pressure field, produced similar changes to El Niño–Southern Oscillation. Over the past 13 years, the SPSA has intensified and shifted toward the southwest, increasing the offshore Ekman transport and Ekman suction, which would explain much of the observed coastal cooling south of 33º S (central Chile).
The chronology of Machu Picchu was traditionally associated with the period attributed to the reign of Pachacuti Inca Yupanqui. Within the scheme of the so-called “historical chronology”, proposed by ...John H. Rowe in 1945, the ascension to power of Pachacuti Inca took place around 1438 CE, and the construction of Machu Picchu began by 1450–1460 CE. Several radiocarbon-dated samples may help to understand the chronology of the construction of llaqta of Machu Picchu, Chachabamba, and Choqesuysuy. However, there is a lack of consensus between different radiocarbon-based Inca chronologies because of the lack of information of which calibration curves to use: Northern Hemisphere (NH), Southern Hemisphere (SH), or a mixed calibration curve? Thus, the main goal of the present investigation is to develop a new methodological approach to reconstruct a radiocarbon-based Incan chronology, an approach based on the determination, through modeling, of the proportion of NH and SH air parcels arriving at three relevant Inca settlements. We found air parcel contributions from the NH and SH for Machu Picchu (51% NH and 49% SH), Chamical (29% NH and 71% SH), and Tiquischullpa (41% NH and 59% SH). Thereby, our investigation brings three proportions to mix NH and SH 14C curves, based on an empirical method and supported by a high-resolution paleoclimatic tracer, for Inca radiocarbon dating studies. Our study emphasizes that great attention should be paid when applying radiocarbon calibration to radiocarbon measurements of samples originating from regions under the influence of the atmospheric circulation-boundary between hemispheres.
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.
El Anticiclón Subtropical del Pacífico Sudeste (ASPS) se extiende sobre toda la cuenca oceánica del Pacífico Sur y es el forzamiento dominante del Sistema de la Corriente de Humboldt. El ASPS ...presenta variabilidades estacionales, interanuales y decadales (interdecadales). Esta última variabilidad se ha asociado a la Oscilación Decadal del Pacífico (ODP), reconocida como un modo de la cuenca del Pacífico. Sin embargo, la mayoría de los estudios sobre la relación entre el océano y la atmósfera a escala interdecadal han sido conducidos en el hemisferio norte, y muy pocos en el hemisferio sur. Así, a través de información de salida de modelos de reanálisis y datos satelitales, esta investigación establece principalmente la relación entre el ASPS y la ODP en el periodo 1949-2012 y su repercusión en la temperatura superficial del mar a lo largo de la costa centro-norte de Chile entre 2000 y 2012. Para esto, primero se analizó la variabilidad estacional e interanual del ASPS. Mediante un análisis de correlación entre el campo de presión del aire a nivel de mar y los índices de la ODP y el Modo Anular del Sur (MAS), se estableció que a escala interdecadal éstas oscilaciones explicaron el 49% y 40% de la varianza, respectivamente; sin embargo, el MAS presentó un desfase de seis años para explicar esa varianza. La ODP, en el campo de la presión del aire, produjo cambios parecidos a los de El Niño-Oscilación del Sur. En los últimos 13 años, el ASPS se ha intensificado y dirigido hacia el suroeste, incrementando el transporte de Ekman hacia afuera de la costa y la succión de Ekman, lo cual explicaría gran parte la disminución de la temperatura superficial del mar observada hacia el sur de 33º S (costa central de Chile).
Atmospheric radiocarbon (14C) recorded in tree rings has been widely used for atmospheric 14C calibration purposes and climate studies. But atmospheric 14C records have been limited along tropical ...latitudes. Here we report a sequence from 1938 to 2007 of precisely measured 14C dates in tree rings of the parenchyma-rich Hymenolobium petraeum tree species (Porto Trombetas, 1°S, 56°W) from the Central Brazilian Amazon. H. petraeum has discernible growth ring boundaries that allow dating techniques to be employed to produce calendrical dates. Bomb-peak tree-ring 14C reconstruction coincides with the broader changes associated with reported values of the Southern Hemisphere atmospheric 14C curve (SH zone 3; values within the ±2σ interval), suggesting that inter-hemispheric air-mass transport of excess-14C injected into the stratosphere during intensive atmospheric nuclear tests is relatively uniform across distinct longitudinal regions. From the early 1980s onwards, H. petraeum had lower 14C values than other pantropical 14C records. Through 14C-based estimation, we found a strong influence of fossil-fuel CO2 contributions from Porto Trombetas mining operations and shipping traffic on inland waterways. An increase of at least 6.3 ± 0.8 ppm of fossil-fuel CO2 has been detected by 14C. 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.
•Bomb-peak radiocarbon (14C) levels were investigated at a site in Central Amazon.•High-resolution 14C tree-ring analysis of parenchyma-rich tree species was attained.•Inter-hemispheric air-mass transfer seems to be uniform across longitudinal regions.•Fossil fuel emissions associated with mining and transportation have been identified.•No evidence of “slow nonstructural carbon” biasing alpha-cellulose has been found.
In this study, we present a comprehensive atmospheric radiocarbon (
C) 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
C measurements obtained through accelerator mass spectrometry (AMS), offers a detailed chronology of post-1950 CE (Common Era)
C fluctuations in the Tropical Low-Pressure Belt (TLPB). To ensure accuracy and reliability, we included
C-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,
C 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-CO
emissions from mining and trade activities in the Central Amazon Basin on the
C record. Our findings reveal a notable increase in
C from land-respired CO
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
C record, when compared with a shorter record from Muna Island, Indonesia, highlights regional differences and contributes to a more nuanced understanding of global
C variations at low latitudes. This study not only fills critical spatial gaps in existing
C compilations but also aids in refining the demarcation of
C variations over South America. The extended tree-ring
C 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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