Temporal and spatial variations of atmospheric radiocarbon in the Mexico City metropolitan area

This work is licensed under a Creative Commons Attribution 3.0 License.-- et al.Proceedings of the 1st International Radiocarbon in the Environment Conference 18–22 August 2014, Queen’s University Belfast, Belfast, Northern Ireland (UK).The Mexico City Metropolitan Area (MCMA) produces a complex mixture of gases and aerosols from diverse sources, including burning of fossil fuels, biomass, and wastes, with a significant biogenic contribution. We present the first results of ongoing projects to study temporal and spatial variations of 14CO2 in the area. Temporal variations reconstructed from tree rings of Taxodium mucronatum indicate a considerable radiocarbon depletion, in accordance to the vast amount of fossil fuels burnt inside Mexico Valley, with values between 62 and 246‰ lower than background values for the 1962–1968 period, and lower by 51–88‰ for the 1983–2010 period. The lower dilution found for the last decades might indicate an increase in enriched 14CO2 sources. Results from the spatial distribution, as revealed from integrated CO2 samples and grasses from six points within the MCMA collected during the 2013 dry season, show variations between sites and sample types. For integrated CO2 samples, values range from 35.6‰ to 54.0‰, and for grasses between –86.8‰ and 40.7‰. For three of the sampling points, the grasses are significantly depleted, by up to ~133‰, as compared to the corresponding integrated CO2 sample. This may result from differences in the carbon assimilation period and exposure to different CO2 sources. Higher-than-background Δ14C values were found for all integrated CO2 samples, presumably resulting from 14C-enriched CO2 derived from forest fires in the mountains during the sampling period. Results obtained so far confirm the complexity of the 14C cycle in the MCMA.This research is funded by DGAPA-UNAM through project PAPIIT-IN106113. Scholarships from CONACyT for AMJ and AMR and from Instituto de Geología and DGAPA-UNAM for AGS are gratefully acknowledged.Peer Reviewe

Dynamic and Thermodynamic Influences on Precipitation in Northeast Mexico on Orbital to Millennial Timescales

The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region

Catalytic hydropyrolysis of wood to prepare lignin-enriched residues for stable carbon isotope analysis

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Modern radiocarbon levels for northwestern Mexico derived from tree rings: A comparison with northern hemisphere zones 2 and 3 curves

Proceedings of the 20th International Radiocarbon Conference.-- This work is licensed under a Creative Commons Attribution 3.0 License.-- et al.The radiocarbon variation for northwestern Mexico during the period 1950-2004 was studied by accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) analyses of tree rings. Two tree-ring sequences of Pseudotsuga menziesii, sampled in a site isolated from urban centers and active volcanoes (26.18°N, 106.3°W, 3000 m asl), were dendrochronologically dated and separated in annual rings prior to 14C analysis. Results obtained show a similar profile to the values reported for the Northern Hemisphere (NH), having significant correlation coefficients with the compilation curves for NH zone 2 (r = 0.987, p < 0.001) and NH zone 3 (r = 0.993, p < 0.001). The maximum peak is centered at 1964.5 with a Δ14C value of 713.15 ± 9.3‰. The values obtained for the period 1958-1965 are lower than zone 2 values and higher than zone 3 values. For the period 1975-2004, the values obtained are higher than the NH compilation curve and other NH records. We attribute the first divergence to the North American monsoon that may have carried 14C-depleted air from the south during the summer months; the second divergence may be attributable to 14C-enriched biospheric CO2. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.The financial support from DGAPA–UNAM (Project IN-111608) is gratefully acknowledged.Peer Reviewe

Radiocarbon Laboratory at the National Autonomous University of Mexico: First Set of Samples and New 14

This contribution reports the first set of samples and the creation of an internal reference material at the recently opened Radiocarbon Laboratory at the National Autonomous University of Mexico (UNAM). Samples for the initial measurements were selected from archaeological and dating projects on Teotihuacán, one of the largest and best-studied Mesoamerican urban and ceremonial centers. The 14C dates were compared to results obtained by 2 other laboratories in order to assess the results obtained at UNAM and validate the adopted methodology. As part of the quality assurance protocol, an internal reference material was created that consists of charred wood from the Teotihuacán site with a 14C activity in the value range expected for samples from Mesoamerican archaeological sites. Results from 7 analyses have a mean of 1750 +/16 BP (80.43 +/0.16 pMC).The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Radiocarbon Laboratory at the National Autonomous University of Mexico: First Set of Samples and New 14C Internal Reference Material

This contribution reports the first set of samples and the creation of an internal reference material at the recently opened Radiocarbon Laboratory at the National Autonomous University of Mexico (UNAM). Samples for the initial measurements were selected from archaeological and dating projects on Teotihuacán, one of the largest and best-studied Mesoamerican urban and ceremonial centers. The 14C dates were compared to results obtained by 2 other laboratories in order to assess the results obtained at UNAM and validate the adopted methodology. As part of the quality assurance protocol, an internal reference material was created that consists of charred wood from the Teotihuacán site with a 14C activity in the value range expected for samples from Mesoamerican archaeological sites. Results from 7 analyses have a mean of 1750 +/16 BP (80.43 +/0.16 pMC).The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Changes in CO2 emission sources in Mexico city metropolitan area deduced from radiocarbon concentrations in tree rings

We present radiocarbon (C) in tree rings from Mexico City and a reconstruction of fossil CO concentrations for the last five decades, as part of a research program to understand the C dynamics in this complex urban area. Background values were established by C concentrations in tree rings from a nearby clean area. Agreement between background and NH-zone 2 values indicate Taxodium mucronatum is a good biomonitor for annual atmospheric C variations. Values for the urban tree rings were significantly lower than background values, indicating a C depletion from fossil CO emissions. There is an increasing trend of fossil CO between 1960 and 1990, in agreement with the population growth and the increasing demand for fossil fuels in Mexico City. Between 1990 and 2000, there is an apparent decrease in fossil CO concentration, increasing again after 2000. The decrease in 2000, despite being of the same magnitude as the overall uncertainty, may reflect environmental policies that improved the energy efficiency and reduced CO emissions in the area. The increase in fossil CO concentration between 2000 and 2010 may be attributable to the significant growth of motor vehicle usage in Mexico City, which made transportation the main energy-demanding and -emitting sector.This research was funded by DGAPA–UNAM (project PAPIIT-IN106113). Scholarships from CONACyT and Instituto de Geología for AMR are gratefully acknowledged. Thanks are also due to the authorities of Bosque de Chapultepec for granting permission for sampling the tree-ring sequences. The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://www.ready.noaa.gov) used in this publication. Comments by Jocelyn C Turnbull and an anonymous reviewer helped to improve this article.Peer reviewe

Modern Radiocarbon Levels for Northwestern Mexico Derived from Tree Rings: A Comparison with Northern Hemisphere Zones 2 and 3 Curves

From the 20th International Radiocarbon Conference held in Kona, Hawaii, USA, May 31-June 3, 2009.The radiocarbon variation for northwestern Mexico during the period 1950-2004 was studied by accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) analyses of tree rings. Two tree-ring sequences of Pseudotsuga menziesii, sampled in a site isolated from urban centers and active volcanoes (26.18 degrees N, 106.3 degrees W, 3000 m asl), were dendrochronologically dated and separated in annual rings prior to 14C analysis. Results obtained show a similar profile to the values reported for the Northern Hemisphere (NH), having significant correlation coefficients with the compilation curves for NH zone 2 (r = 0.987, p < 0.001) and NH zone 3 (r = 0.993, p < 0.001). The maximum peak is centered at 1964.5 with a ∆14C value of 713.15 +/- 9.3‰. The values obtained for the period 1958-1965 are lower than zone 2 values and higher than zone 3 values. For the period 1975-2004, the values obtained are higher than the NH compilation curve and other NH records. We attribute the first divergence to the North American monsoon that may have carried 14C-depleted air from the south during the summer months; the second divergence may be attributable to 14C-enriched biospheric CO2.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Modern Radiocarbon Levels for Northwestern Mexico Derived from Tree Rings: A Comparison with Northern Hemisphere Zones 2 and 3 Curves

From the 20th International Radiocarbon Conference held in Kona, Hawaii, USA, May 31-June 3, 2009.The radiocarbon variation for northwestern Mexico during the period 1950-2004 was studied by accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) analyses of tree rings. Two tree-ring sequences of Pseudotsuga menziesii, sampled in a site isolated from urban centers and active volcanoes (26.18 degrees N, 106.3 degrees W, 3000 m asl), were dendrochronologically dated and separated in annual rings prior to 14C analysis. Results obtained show a similar profile to the values reported for the Northern Hemisphere (NH), having significant correlation coefficients with the compilation curves for NH zone 2 (r = 0.987, p < 0.001) and NH zone 3 (r = 0.993, p < 0.001). The maximum peak is centered at 1964.5 with a ∆14C value of 713.15 +/- 9.3‰. The values obtained for the period 1958-1965 are lower than zone 2 values and higher than zone 3 values. For the period 1975-2004, the values obtained are higher than the NH compilation curve and other NH records. We attribute the first divergence to the North American monsoon that may have carried 14C-depleted air from the south during the summer months; the second divergence may be attributable to 14C-enriched biospheric CO2.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Dynamic and thermodynamic influences on precipitation in Northeast Mexico on orbital to millennial timescales.

The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region