106 research outputs found
Changes in Oceanic Radiocarbon and CFCs Since the 1990s
Anthropogenic perturbations from fossil fuel burning, nuclear bomb testing, and chlorofluorocarbon (CFC) use have created useful transient tracers of ocean circulation. The atmospheric 14C/C ratio (â14C) peaked in the early 1960s and has decreased now to preâindustrial levels, while atmospheric CFCâ11 and CFCâ12 concentrations peaked in the early 1990s and early 2000s, respectively, and have now decreased by 10%â20%. We present the first analysis of a decade of new observations (2007 to 2018â2019) and give a comprehensive overview of the changes in ocean â14C and CFC concentration since the WOCE surveys in the 1990s. Surface ocean â14C decreased at a nearly constant rate from the 1990â2010s (20â°/decade). In most of the surface ocean â14C is higher than in atmospheric CO2 while in the interior ocean, only a few places are found to have increases in â14C, indicating that globally, oceanic bomb 14C uptake has stopped and reversed. Decreases in surface ocean CFCâ11 started between the 1990 and 2000s, and CFCâ12 between the 2000â2010s. Strong coherence in model biases of decadal changes in all tracers in the Southern Ocean suggest ventilation of Antarctic Intermediate Water was enhanced from the 1990 to the 2000s, whereas ventilation of Subantarctic Mode Water was enhanced from the 2000 to the 2010s. The decrease in surface tracers globally between the 2000 and 2010s is consistently stronger in observations than in models, indicating a reduction in vertical transport and mixing due to stratification
Radiocarbon content of dissolved organic carbon in the South Indian Ocean
Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 872â879, doi:10.1002/2017GL076295.We report four profiles of the radiocarbon content of dissolved organic carbon (DOC) spanning the South Indian Ocean (SIO), ranging from the Polar Front (56°S) to the subtropics (29°S). Surface waters held mean DOC Î14C values of â426 ± 6â° (~4,400 14C years) at the Polar Front and DOC Î14C values of â252 ± 22â° (~2,000 14C years) in the subtropics. At depth, Circumpolar Deep Waters held DOC Î14C values of â491 ± 13â° (~5,400 years), while values in Indian Deep Water were more depleted, holding DOC Î14C values of â503 ± 8â° (~5,600 14C years). High-salinity North Atlantic Deep Water intruding into the deep SIO had a distinctly less depleted DOC Î14C value of â481 ± 8â° (~5,100 14C years). We use multiple linear regression to assess the dynamics of DOC Î14C values in the deep Indian Ocean, finding that their distribution is characteristic of water masses in that region.National Science Foundation (NSF) Grant Numbers: OPP-1142117, OCE-14367482018-07-2
Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the seawaterâbrine interface
© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 10 (2013): 3175-3183, doi:10.5194/bg-10-3175-2013.Orca Basin, an intraslope basin on the Texas-Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200 m in which limited microbial activity has been reported. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to measurements made in the 1970s. Both DIC and DOC are more "aged" within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon remineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC, allowing for only limited oxidation of methane diffusing upwards from sediments. This conclusion is consistent with previous studies that identify the seawaterâbrine interface as the focus of microbial activity associated with Orca Basin brine. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawaterâbrine interface region as the likely source region for DOC to the brine as well as DIC.This work
was funded by the WHOI Postdoctoral Scholar program, NSF
Cooperative Agreement for the Operation of a National Ocean
Sciences Accelerator Mass Spectrometry Facility (OCE-0753487),
and the US National Science Foundationâs Emerging Frontiers
program (award 0801741 to SBJ)
Carbon dynamics in the western Arctic Ocean : insights from full-depth carbon isotope profiles of DIC, DOC, and POC
© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 9 (2012): 1217-1224, doi:10.5194/bg-9-1217-2012.Arctic warming is projected to continue throughout the coming century. Yet, our currently limited understanding of the Arctic Ocean carbon cycle hinders our ability to predict how changing conditions will affect local Arctic ecosystems, regional carbon budgets, and global climate. We present here the first set of concurrent, full-depth, dual-isotope profiles for dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and suspended particulate organic carbon (POCsusp) at two sites in the Canada Basin of the Arctic Ocean. The carbon isotope composition of sinking and suspended POC in the Arctic contrasts strongly with open ocean Atlantic and Pacific sites, pointing to a combination of inputs to Arctic POCsusp at depth, including surface-derived organic carbon (OC), sorbed/advected OC, and OC derived from in situ DIC fixation. The latter process appears to be particularly important at intermediate depths, where mass balance calculations suggest that OC derived from in situ DIC fixation contributes up to 22% of POCsusp. As in other oceans, surface-derived OC is still a dominant source to Arctic POCsusp. Yet, we suggest that significantly smaller vertical POC fluxes in the Canada Basin make it possible to see evidence of DIC fixation in the POCsusp pool even at the bulk isotope level.The 2008 JOIS hydrographic program
was supported by Fisheries and Oceans Canada, the Canadian
International Polar Year Office, and the US National Science
Foundation (OPP-0424864; lead-PI Andrey Proshutinsky)
Age and growth rate dynamics of an old African baobab determined by radiocarbon dating
Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 727-734.In 2008, a large African baobab (Adansonia digitata L.) from Makulu Makete, South Africa, split vertically
into 2 sections, revealing a large enclosed cavity. Several wood samples collected from the cavity were processed and radiocarbon
dated by accelerator mass spectrometry (AMS) for determining the age and growth rate dynamics of the tree. The 14C
date of the oldest sample was found to be of 1016 ± 22 BP, which corresponds to a calibrated age of 1000 ± 15 yr. Thus, the
Makulu Makete tree, which eventually collapsed to the ground and died, becomes the second oldest African baobab dated
accurately to at least 1000 yr. The conventional growth rate of the trunk, estimated by the radial increase, declined gradually
over its life cycle. However, the growth rate expressed more adequately by the cross-sectional area increase and by the volume
increase accelerated up to the age of 650 yr and remained almost constant over the past 450 yr.This material is based on work supported by a grant from the Romanian
National University Research Council (PN II - IDEI 2354 Nr. 1092) and by US National Science
Foundation under Cooperative Agreement OCE-022828996
Significance of perylene for source allocation of terrigenous organic matter in aquatic sediments.
Author Posting. © American Chemical Society, 2019. This is an open access article published under an ACS AuthorChoice License. The definitive version was published in Environmental Science and Technology 53(14), (2019):8244-8251, doi:10.1021/acs.est.9b02344.Perylene is a frequently abundant, and sometimes the only polycyclic aromatic hydrocarbon (PAH) in aquatic sediments, but its origin has been subject of a longstanding debate in geochemical research and pollutant forensics because its historical record differs markedly from typical anthropogenic PAHs. Here we investigate whether perylene serves as a source-specific molecular marker of fungal activity in forest soils. We use a well-characterized sedimentary record (1735 to 1999) from the anoxic-bottom waters of the Pettaquamscutt River basin, RI, USA to examine mass accumulation rates and isotope records of perylene, and compare them with total organic carbon and the anthropogenic PAH fluoranthene. We support our arguments with radiocarbon (14C) data of higher plant leaf-wax n-alkanoic acids. Isotope-mass balance calculations of perylene and n-alkanoic acids indicate that ~40 % of sedimentary organic matter is of terrestrial origin. Further, both terrestrial markers are pre-aged on millennial time-scales prior to burial in sediments and insensitive to elevated 14C concentrations following nuclear weapons testing in the mid-20th Century. Instead, changes coincide with enhanced erosional flux during urban sprawl. These findings suggest that perylene is definitely a product of soil derived fungi, and a powerful chemical tracer to study spatial and temporal connectivity between terrestrial and aquatic environments.We thank John King, Sean Sylva, Brad Hubeny, Peter Sauer, and Jim Broda for their help in sampling; Carl Johnson and Daniel Montluçon for their incessant help with analyses; as well as Mark Yunker for critical discussion on the perils of perylene. Professor Phil Meyers and two anonymous reviewers provided comments that improved the quality of the manuscript. U.M.H. acknowledges the Swiss National Science Foundation for his postdoctoral fellowship and T.I.E. and K.A.H. acknowledges the NSF for research grants CHE-0089172 and OCE-9708478.2020-06-1
The centenary of Annals of Applied Biology in 2014
Annals of Applied Biology (Annals)â hasâ published the results of original research in applied biology for 100âyears. The journal was established because of the need for a more efficient distribution of scientific information of applied importance, especially in agriculture and horticulture. Over the years, most papers in Annals have reported on crop science, horticulture, pests and diseases of field crops and horticultural plants, and plant breeding. The scope of the journal has remained consistent, although currently the research fields covered in Annals can also be described using the terms agriculture and the environment, crop improvement, pest and invertebrate biology, and plantâpathogen interactions. Maintaining high standards of statistical analysis in the papers published has always been emphasised in Annals.
The Centenary of Annals in 2014 will be celebrated by highlighting some of the most influential papers published in the journal over the 100âyears. These papers have been selected by the Senior Editors (the authors of this editorial), following consultation of the Editorial Board of Annals, which consists of scientists from all parts of the world. Each issue of Annals in 2014 will contain at least one Centenary editorial that introduces an influential paper. Furthermore, the same issue will contain a solicited review article related to the influential paper. The first influential paper introduced in this issue is the study by Chester I. Bliss (1935) on the calculation of the dosageâmortality curve, which has been cited over 850 times and is still regularly referred to today. The editorial has been written by David Finney, who knew Bliss personally and who acted as an unofficial statistical editor of the journal during the period 1942â54. It is noteworthy that this editorial marks 76âyears since David Finney's first publication in 1938 (Finney, 1938). The review article has been written by Roger Payne, who was the Senior Statistical Editor of Annals from 1980 to 1989. The editorials, influential papers and review articles will be made available for free access on the home page of Annals (http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1744â7348).
The Association of Applied Biologists (Association) will organise a Centenary conference under the title âSustainable Intensificationâ in December 2014. For details of the programme and other details, please refer to the home page of the Association in the near future (http://www.aab.org.uk/).
In the following sections we provide some perspectives as to the development of Annals as a scientific journal and statistical data on its impact in the field of applied biology
Comparative AMS radiocarbon dating of pretreated versus non-pretreated tropical wood samples
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 268 (2010): 910-913, doi:10.1016/j.nimb.2009.10.062.Several wood samples collected from Dorslandboom, a large African baobab (Adansonia
digitata L.) from Namibia, were investigated by AMS radiocarbon dating subsequent to
pretreatment and, alternatively, without pretreatment. The comparative statistical
evaluation of results showed that there were no significant differences between fraction
modern values and radiocarbon dates of the samples analyzed after pretreatment and
without pretreatment, respectively. The radiocarbon date of the oldest sample was 993 ± 20
BP. Dating results also revealed that Dorslandboom is a multi-generation tree, with several
stems showing different ages.This material is based on work supported by U.S. National Science
Foundation under Cooperative Agreement OCE-022828996. Part of the research was
supported by grants from the Romanian Academy and the Romanian National University
Research Council (PN II â ID 2354) and also by Nova Research Inc
Quality of Graphite Target for Biological/Biomedical/Environmental Applications of 14C-Accelerator Mass Spectrometry
Catalytic graphitization for 14C-accelerator mass spectrometry (14C-AMS) produced various forms of elemental carbon. Our high-throughput Zn reduction method (C/Fe = 1:5, 500 °C, 3 h) produced the AMS target of graphite-coated iron powder (GCIP), a mix of nongraphitic carbon and Fe3C. Crystallinity of the AMS targets of GCIP (nongraphitic carbon) was increased to turbostratic carbon by raising the C/Fe ratio from 1:5 to 1:1 and the graphitization temperature from 500 to 585 °C. The AMS target of GCIP containing turbostratic carbon had a large isotopic fractionation and a low AMS ion current. The AMS target of GCIP containing turbostratic carbon also yielded less accurate/precise 14C-AMS measurements because of the lower graphitization yield and lower thermal conductivity that were caused by the higher C/Fe ratio of 1:1. On the other hand, the AMS target of GCIP containing nongraphitic carbon had higher graphitization yield and better thermal conductivity over the AMS target of GCIP containing turbostratic carbon due to optimal surface area provided by the iron powder. Finally, graphitization yield and thermal conductivity were stronger determinants (over graphite crystallinity) for accurate/precise/high-throughput biological, biomedical, and environmental14C-AMS applications such as absorption, distribution, metabolism, elimination (ADME), and physiologically based pharmacokinetics (PBPK) of nutrients, drugs, phytochemicals, and environmental chemicals
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