Papers by Guaciara M Santos
Radiocarbon, 2003
Author(s): Southon, John R; Santos, Guaciara M; Druffel-Rodriguez, K C; Druffel, Ellen R. M; Trum... more Author(s): Southon, John R; Santos, Guaciara M; Druffel-Rodriguez, K C; Druffel, Ellen R. M; Trumbore, Susan E; Xu, Xiaomei; Griffin, Sheila; Ali, S; Mazon, M | Abstract: A new 14C accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5 MV AMS system was installed in mid-2002 and has operated routinely sinceOctober of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported radiocarbonAMS background: charge exchange tails from 14N beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator.
Proceedings of the National Academy of Sciences, 2018
Significance We report radiocarbon ( 14 C) measurements of carbonaceous aerosol originating from ... more Significance We report radiocarbon ( 14 C) measurements of carbonaceous aerosol originating from fires on the islands of Sumatra and Borneo. These data provide information about what types of ecosystems burned and are critical for linking the human health effects of fires to the anthropogenic build-up of atmospheric CO 2 . Our measurements confirm that peat emissions were the dominant source of aerosols in Singapore during the 2015 El Niño and provide a means for monitoring the success of policies designed to protect peatland areas during future drought events.
Geochimica et Cosmochimica Acta, 2019
Relatively little is known about the amount of time that lapses between the photosynthetic fixati... more Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter
Quaternary Geochronology, 2017
We investigate the local marine reservoir effect at Kalba, United Arab Emirates (UAE), between th... more We investigate the local marine reservoir effect at Kalba, United Arab Emirates (UAE), between the Neolithic and Bronze Age with respect to possible changes through time and mollusk species diversity. Two distinctive species living in close proximity to the mangrove of Khor Kalba provide insights into ocean circulation patterns in this coastal environment. The species selected are the bivalve Anadara uropigimelana, and the gastropod Terebralia palustris. They have been an important local food resource for humans since at least the Neolithic. Our results show that for the Neolithic and Bronze Age, the reservoir effects DR are quite different for the species selected. For Anadara spp. the DR decreases from 576 ± 90 to 112 ± 44 years, while for Terebralia spp. the reduction ranges from 389 ± 66 to À19 ± 36 years. These results are coeval with other multi-proxies (stalagmite records and sea level changes) for the middle Holocene, and suggest that the main cause of the decreasing reservoir effect is a changing e in this case declining-sea level and an increasingly drier climate.
Radiocarbon, 2004
Radiocarbon (Δ14C) measurements of monthly samples from a Galapagos surface coral are among the f... more Radiocarbon (Δ14C) measurements of monthly samples from a Galapagos surface coral are among the first data sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine. An average Δ14C value of −62 is obtained for 144 measurements of samples from monthly coral bands that lived from about AD 1760–1771 (±6 yr). High Δ14C values were found during January through March, when upwelling was weak or absent at the Galapagos Islands. Low Δ14C values were obtained mid-year during strong upwelling. The average seasonal variability of Δ14C was 15–25, which is greater than that at other tropical and subtropical locations in the Pacific Ocean because of intense seasonal upwelling at this site. Periods of sustained high Δ14C values were found during 1762–1763 and 1766. A spectral analysis revealed that the spectral density for the Δ14C data displays most of its variance at the 5-yr cycle, which is reflective of El Niño periodicity during the ...
Radiocarbon, 2011
Marine radiocarbon (14C) is a widely used tracer of past ocean circulation, but very few high-res... more Marine radiocarbon (14C) is a widely used tracer of past ocean circulation, but very few high-resolution records have been obtained. Here, we report a time series of carbon isotope abundances of dissolved inorganic carbon (DIC) in surface seawater collected from the Newport Beach pier in Orange County, within the Southern California Bight, from 2005 to 2010. Surface seawater was collected bimonthly and analyzed for Δ14C, δ13C, and salinity. Results from May 2005 to November 2010 show no long-term changes in δ13C DIC values and no consistent variability that can be attributed to upwelling. Δ14C DIC values have lowered from ∼34‰ to about ∼16‰, an 18‰ decrease from the beginning of this project in 2005, and is consistent with the overall 14C depletion from the atmospheric thermonuclear bomb pulse at the end of the 1950s. Δ14C DIC values, paired with salinity, do appear to be suitable indicators of upwelling strength with periods of upwelling characterized by more saline and lower DIC Δ...
Radiocarbon, 2004
A new radiocarbon accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has bee... more A new radiocarbon accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5MV AMS system was installed in mid-2002 and has operated routinely since October of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported 14C AMS background: charge exchange tails from 14N beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator.
Radiocarbon, 2010
The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has devel... more The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has developed protocols for analyzing radiocarbon in samples as small as ∼0.001 mg of carbon (C). Mass-balance background corrections for modern and 14C-dead carbon contamination (MC and DC, respectively) can be assessed by measuring 14C-free and modern standards, respectively, using the same sample processing techniques that are applied to unknown samples. This approach can be validated by measuring secondary standards of similar size and 14C composition to the unknown samples. Ordinary sample processing (such as ABA or leaching pretreatment, combustion/graphitization, and handling) introduces MC contamination of ∼0.6 ± 0.3 μg C, while DC is ∼0.3 ± 0.15 μg C. Today, the laboratory routinely analyzes graphite samples as small as 0.015 mg C for external submissions and ≅0.001 mg C for internal research activities with a precision of ∼1% for ∼0.010 mg C. However, when analyzing ultra-small samples ...
Radiocarbon, 2010
Over the past decades, analysis of occluded carbon in phytoliths (opaline silica mineral bodies t... more Over the past decades, analysis of occluded carbon in phytoliths (opaline silica mineral bodies that form in and between plant cells) has become a workhorse of paleoclimate and archaeological studies. Since different plant types exhibit distinctive phytolith morphologies, their assemblages are used in identifying vegetation histories or food culture adaptations. A few direct radiocarbon AMS measurements of phytoliths have been carried out, but these measurements are difficult due to the low concentrations of phytoliths in some plant species, and the small amount of C per phytolith (<2%). In addition, no phytoliths samples of a known14C age are available to verify measurement accuracy and precision, and to check sample preparation protocols. Background corrections are also difficult to address due to the lack of suitable material. In this work, we designed a procedure to quantify a suitable blank using SiO2powder samples (close to the opal structure, and free of14C). The full phyt...
Radiocarbon, 2007
We present an overview of accelerator mass spectrometry (AMS) radiocarbon sample preparation and ... more We present an overview of accelerator mass spectrometry (AMS) radiocarbon sample preparation and measurements, describing the technical upgrades that now allow us to routinely obtain 0.2–0.3% precision for 1-mg carbon samples. A precision of ∼1% on samples with 100 μg of carbon can also be achieved. We have also developed graphitization techniques and AMS procedures for ultra-small samples (down to 0.002 mg of carbon). Detailed time series are presented for large and small aliquots of standards such as NIST OX-I and OX-II; FIRI-C and -D; IAEA-C6, -C7 and -C8; and 14C-free samples.
Radiocarbon, 2010
We report carbon isotope abundances of dissolved inorganic carbon (DIC) in surface seawater colle... more We report carbon isotope abundances of dissolved inorganic carbon (DIC) in surface seawater collected from a time-series site off the Newport Beach Pier in Orange County, California. These data represent the first time series of Δ14C data for a coastal southern California site. From a suite of samples collected daily from 16 October to 11 November 2004, Δ14C values averaged 32.1 ± 4.4‰. Freshwater input from the Santa Ana River to our site caused Δ14C and δ13C values to decrease. Since this initial set of measurements, a time-series site has been maintained from November 2004 to the present. Surface seawater has been collected bimonthly and analyzed for Δ14C, δ13C, salinity, and ΣCO2 concentrations. Water samples from the Santa Ana River were collected during the wet season. California sea mussels and barnacle shells, ranging from 4 to 6 months old, were also collected and analyzed. Results from May 2005 to January 2008 show no long-term changes in δ13C DIC values. Δ14C DIC values o...
Journal of Archaeological Science, 2016
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Geochemistry, Geophysics, Geosystems, 2016
Time‐consuming and expensive radiometric dating techniques limit the number of dates available to... more Time‐consuming and expensive radiometric dating techniques limit the number of dates available to construct absolute chronologies for high‐resolution paleoclimate reconstructions. A recently developed rapid‐screen 14C dating technique reduces sample preparation time and per sample costs by 90%, but its accuracy has not yet been tested on shallow‐water corals. In this study, we test the rapid‐screen 14C dating technique on shallow‐water corals by comparing 44 rapid‐screen 14C dates to both high‐precision 14C dates and U/Th dates from mid‐ to late‐Holocene fossil corals collected from the central tropical Pacific (2–4°N, 157–160°W). Our results show that 42 rapid‐screen 14C and U/Th dates agree within uncertainties, confirming closed‐system behavior and ensuring chronological accuracy. However, two samples that grew ∼6500 years ago have calibrated 14C ages ∼1000 years younger than the corresponding U/Th ages, consistent with diagenetic alteration as indicated by the presence of 15–23%...
Biogeosciences, 2016
Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the... more Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the assumptions that phytC is of photosynthetic origin and a closed system, claims were recently made that phytoliths from several agriculturally important monocotyledonous species play a significant role in atmospheric CO 2 sequestration. However, anomalous phytC radiocarbon (14 C) dates suggested contributions from a non-photosynthetic source to phytC. Here we address this non-photosynthetic source hypothesis using comparative isotopic measurements (14 C and δ 13 C) of phytC, plant tissues, atmospheric CO 2 , and soil organic matter. State-of-the-art methods assured phytolith purity, while sequential stepwise-combustion revealed complex chemicalthermal decomposability properties of phytC. Although photosynthesis is the main source of carbon in plant tissue, it was found that phytC is partially derived from soil carbon that can be several thousand years old. The fact that phytC is not uniquely constituted of photosynthetic C limits the usefulness of phytC either as a dating tool or as a significant sink of atmospheric CO 2. It additionally calls for further experiments to investigate how SOM-derived C is accessible to roots and accumulates in plant biosilica, for a better understanding of the mechanistic processes underlying the silicon biomineralization process in higher plants.
Global Biogeochemical Cycles, 2015
Black carbon (BC) aerosol emitted by boreal fires has the potential to accelerate losses of snow ... more Black carbon (BC) aerosol emitted by boreal fires has the potential to accelerate losses of snow and ice in many areas of the Arctic, yet the importance of this source relative to fossil fuel BC emissions from lower latitudes remains uncertain. Here we present measurements of the isotopic composition of BC and organic carbon (OC) aerosols collected at two locations in interior Alaska during the summer of 2013, as part of NASA's Carbon in Arctic Reservoirs Vulnerability Experiment. We isolated BC from fine air particulate matter (PM2.5) and measured its radiocarbon (Δ14C) content with accelerator mass spectrometry. We show that fires were the dominant contributor to variability in carbonaceous aerosol mass in interior Alaska during the summer by comparing our measurements with satellite data, measurements from an aerosol network and predicted concentrations from a fire inventory coupled to an atmospheric transport model. The Δ14C of BC from boreal fires was 131 ± 52‰ in the year ...
Biogeosciences Discussions, 2015
Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the... more Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the assumptions that phytC is of photosynthetic origin and a closed system, claims were recently made that phytoliths from grasslands play a significant role in atmospheric CO<sub>2</sub> sequestration. However, anomalous phytC radiocarbon (<sup>14</sup>C) dates suggested contributions from a non-photosynthetic source to phytC. Here we address this non-photosynthetic source hypothesis using comparative isotopic measurements…
Frontiers in Plant Science, 2015
Many plants, including grasses and some important human food sources, accumulate, and precipitate... more Many plants, including grasses and some important human food sources, accumulate, and precipitate silica in their cells to form opaline phytoliths. These phytoliths contain small amounts of organic matter (OM) that are trapped during the process of silicification. Previous work has suggested that plant silica is associated with compounds such as proteins, lipids, lignin, and carbohydrate complexes. It is not known whether these compounds are cellular components passively encapsulated as the cell silicifies, polymers actively involved in the precipitation process or random compounds assimilated by the plant and discarded into a "glass wastebasket." Here, we used Raman spectroscopy to map the distribution of OM in phytoliths, and to analyze individual phytoliths isolated from Sorghum bicolor plants grown under different laboratory treatments. Using mapping, we showed that OM in phytoliths is distributed throughout the silica and is not related to dark spots visible in light microscopy, previously assumed to be the repository for phytolith OM. The Raman spectra exhibited common bands indicative of C-H stretching modes of general OM, and further more diagnostic bands consistent with carbohydrates, lignins, and other OM. These Raman spectra exhibited variability of spectral signatures and of relative intensities between sample treatments indicating that differing growth conditions altered the phytolith carbon. This may have strong implications for understanding the mechanism of phytolith formation, and for use of phytolith carbon isotope values in dating or paleoclimate reconstruction.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015
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Papers by Guaciara M Santos
a) Resultados Recentes do Programa Brasileiro de AMS, J.C. Acquadro et al; p.3
b) Espalhamento Elástico, Inelástico e Fusão do Sistema 14N + 59Co, C. Muri et al; p. 45
c) Elastic Scattering of 27Al + 27Al at near Barrier Energies, A. Zerwekh; p. 8
a) Resultados Recentes do Programa Brasileiro de AMS, J.C. Acquadro et al; p.3
b) Espalhamento Elástico, Inelástico e Fusão do Sistema 14N + 59Co, C. Muri et al; p. 45
c) Elastic Scattering of 27Al + 27Al at near Barrier Energies, A. Zerwekh; p. 8
a) AMS no Laboratório Pelletron: Desenvolvimento e Testes, R. Liguori Neto et al; p. 66
b) Espalhamento Elástico do 6,7Li + 138Ba a Energia Próxima a Barreira Coulombiana, A.M.M. Maciel et al; p. 126
a) AMS no Laboratório Pelletron: Desenvolvimento e Testes, R. Liguori Neto et al; p. 66
b) Espalhamento Elástico do 6,7Li + 138Ba a Energia Próxima a Barreira Coulombiana, A.M.M. Maciel et al; p. 126
a) Status and Plans for the Brazilian AMS Program, R. Liguori Neto et al; p.47
b) The Brazilian Bragg Curve Detector Built for AMS Studies", G.M. Santos, P.R.S. Gomes et al; p. 81
c) 14C AMS Dating of Fires in the Central Amazon Rain Forest ", R.C. Cordeiro, G.M. Santos, P.R.S. Gomes et al; p.175
a) Status and Plans for the Brazilian AMS Program, R. Liguori Neto et al; p.47
b) The Brazilian Bragg Curve Detector Built for AMS Studies", G.M. Santos, P.R.S. Gomes et al; p. 81
c) 14C AMS Dating of Fires in the Central Amazon Rain Forest ", R.C. Cordeiro, G.M. Santos, P.R.S. Gomes et al; p.175
a) Status and Plans for the Brazilian AMS Program, R. Liguori Neto et al; p.47
b) The Brazilian Bragg Curve Detector Built for AMS Studies", G.M. Santos, P.R.S. Gomes et al; p. 81
c) 14C AMS Dating of Fires in the Central Amazon Rain Forest ", R.C. Cordeiro, G.M. Santos, P.R.S. Gomes et al; p.175
a) Palaeoenvironmental Change on Land and at Sea in the Vicinity of Cape Range of Western Australia - 50,000 years Record un Ravelled using Numerous Proxies on Deep-sea Core, P. De Deckker et al; p. 21
b) Cronologies from Accelerator Mass Spectrometry, L.K. Fifield et al; p. 34
a) Palaeoenvironmental Change on Land and at Sea in the Vicinity of Cape Range of Western Australia - 50,000 years Record un Ravelled using Numerous Proxies on Deep-sea Core, P. De Deckker et al; p. 21
b) Cronologies from Accelerator Mass Spectrometry, L.K. Fifield et al; p. 34
a) Initial Operation of the Keck Carbon Cycle AMS Laboratory, University of California, Irvine. J. Southon, G.M. Santos, E Druffel, S Trumbore and Xaiomei Xu; p135
b) Use of Radioactive and Stable Carbon Isotopes to Assess the Coastal Upwelling Contribution of Arraial do Cabo (Cabo Frio) – Brazil , K.C. Ferraz, A.N. Marques Jr, E.G. Rodriguez, GM Santos, S.G. Tims, LK Fifield, and PRS Gomes; p.104
c) 14 C AMS as a Tool for the Investigation of Mercury Deposition at Remote Amazon Region, J.A. Barbosa, RC Cordeiro, EV Silva, b Turcq, GM Santos, PRS Gomes, A Sifedinne, ALS Albuquerque, LD Lacerda, PA Hausladen, S.G. Tims, LK Fifield and V. Levchenco; p115
a) Initial Operation of the Keck Carbon Cycle AMS Laboratory, University of California, Irvine. J. Southon, G.M. Santos, E Druffel, S Trumbore and Xaiomei Xu; p135
b) Use of Radioactive and Stable Carbon Isotopes to Assess the Coastal Upwelling Contribution of Arraial do Cabo (Cabo Frio) – Brazil , K.C. Ferraz, A.N. Marques Jr, E.G. Rodriguez, GM Santos, S.G. Tims, LK Fifield, and PRS Gomes; p.104
c) 14 C AMS as a Tool for the Investigation of Mercury Deposition at Remote Amazon Region, J.A. Barbosa, RC Cordeiro, EV Silva, b Turcq, GM Santos, PRS Gomes, A Sifedinne, ALS Albuquerque, LD Lacerda, PA Hausladen, S.G. Tims, LK Fifield and V. Levchenco; p115