Publications by authors named "Andrew C Scott"

23 Publications

  • Page 1 of 1

TOX is a critical regulator of tumour-specific T cell differentiation.

Nature 2019 07 17;571(7764):270-274. Epub 2019 Jun 17.

Immunology Program, Memorial Sloan Kettering Cancer Center, New York, NY, USA.

Tumour-specific CD8 T cell dysfunction is a differentiation state that is distinct from the functional effector or memory T cell states. Here we identify the nuclear factor TOX as a crucial regulator of the differentiation of tumour-specific T (TST) cells. We show that TOX is highly expressed in dysfunctional TST cells from tumours and in exhausted T cells during chronic viral infection. Expression of TOX is driven by chronic T cell receptor stimulation and NFAT activation. Ectopic expression of TOX in effector T cells in vitro induced a transcriptional program associated with T cell exhaustion. Conversely, deletion of Tox in TST cells in tumours abrogated the exhaustion program: Tox-deleted TST cells did not upregulate genes for inhibitory receptors (such as Pdcd1, Entpd1, Havcr2, Cd244 and Tigit), the chromatin of which remained largely inaccessible, and retained high expression of transcription factors such as TCF-1. Despite their normal, 'non-exhausted' immunophenotype, Tox-deleted TST cells remained dysfunctional, which suggests that the regulation of expression of inhibitory receptors is uncoupled from the loss of effector function. Notably, although Tox-deleted CD8 T cells differentiated normally to effector and memory states in response to acute infection, Tox-deleted TST cells failed to persist in tumours. We hypothesize that the TOX-induced exhaustion program serves to prevent the overstimulation of T cells and activation-induced cell death in settings of chronic antigen stimulation such as cancer.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41586-019-1324-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7698992PMC
July 2019

Depleting T regulatory cells by targeting intracellular Foxp3 with a TCR mimic antibody.

Oncoimmunology 2019;8(7):1570778. Epub 2019 Apr 15.

Molecular Pharmacology Program, Sloan Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.

Depletion of T regulatory cells (Tregs) in the tumor microenvironment is a promising cancer immunotherapy strategy. Current approaches for depleting Tregs are limited by lack of specificity and concurrent depletion of anti-tumor effector T cells. The transcription factor forkhead box p3 (Foxp3) plays a central role in the development and function of Tregs and is an ideal target in Tregs, but Foxp3 is an intracellular, undruggable protein to date. We have generated a T cell receptor mimic antibody, "Foxp3-#32," recognizing a Foxp3-derived epitope in the context of HLA-A*02:01. The mAb Foxp3-#32 selectively recognizes CD4 + CD25 + CD127 and Foxp3 + Tregs also expressing HLA-A*02:01 and depletes these cells via antibody-mediated cellular cytotoxicity. Foxp3-#32 mAb depleted Tregs in xenografts of PBMCs from a healthy donor and ascites fluid from a cancer patient. A TCRm mAb targeting intracellular Foxp3 epitope represents an approach to deplete Tregs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/2162402X.2019.1570778DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6527296PMC
April 2019

A Tournaisian (earliest Carboniferous) conglomerate-preserved non-marine faunal assemblage and its environmental and sedimentological context.

PeerJ 2019 3;6:e5972. Epub 2019 Jan 3.

Department of Zoology, University of Cambridge, Cambridge, UK.

A conglomerate bed from the Tournaisian Ballagan Formation of Scotland preserves a rich array of vertebrate and other nonmarine fossils providing an insight into the wider ecosystem and paleoenvironment that existed during this pivotal stage of Earth history. It challenges hypotheses of a long-lasting post-extinction trough following the end-Devonian extinction event. The fauna recovered includes a wide size range of tetrapods, rhizodonts, and dipnoans, from tiny juveniles or small-bodied taxa up to large adults, and more than one taxon of each group is likely. Some fauna, such as actinopterygians and chondrichthyans, are rare as macrofauna but are better represented in the microfossil assemblage. The fauna provides evidence of the largest Carboniferous lungfish ever found. The specimens are preserved in a localized, poorly-sorted conglomerate which was deposited in the deepest part of a river channel, the youngest of a group of channels. In addition to the fossils (micro- and macro-), the conglomerate includes locally-derived clasts of paleosols and other distinctive elements of the surrounding floodplains. Charcoal fragments represent small woody axes and possible larger trunk tissue from arborescent pteridosperms. Preservation of the fossils indicates some aerial exposure prior to transport, with abrasion from rolling. The findings presented here contrast with other published trends in vertebrate size that are used to interpret a reduction in maximum sizes during the Tournaisian. The richness of the fauna runs counter to the assumption of a depauperate nonmarine fauna following the end-Devonian Hangenberg event, and charcoal content highlights the occurrence of fire, with the requisite levels of atmospheric oxygen during that stage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7717/peerj.5972DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6321757PMC
January 2019

Chromatin states define tumour-specific T cell dysfunction and reprogramming.

Nature 2017 05 17;545(7655):452-456. Epub 2017 May 17.

Immunology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA.

Tumour-specific CD8 T cells in solid tumours are dysfunctional, allowing tumours to progress. The epigenetic regulation of T cell dysfunction and therapeutic reprogrammability (for example, to immune checkpoint blockade) is not well understood. Here we show that T cells in mouse tumours differentiate through two discrete chromatin states: a plastic dysfunctional state from which T cells can be rescued, and a fixed dysfunctional state in which the cells are resistant to reprogramming. We identified surface markers associated with each chromatin state that distinguished reprogrammable from non-reprogrammable PD1 dysfunctional T cells within heterogeneous T cell populations from tumours in mice; these surface markers were also expressed on human PD1 tumour-infiltrating CD8 T cells. Our study has important implications for cancer immunotherapy as we define key transcription factors and epigenetic programs underlying T cell dysfunction and surface markers that predict therapeutic reprogrammability.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature22367DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5693219PMC
May 2017

Fire history on the California Channel Islands spanning human arrival in the Americas.

Philos Trans R Soc Lond B Biol Sci 2016 06;371(1696)

Oxford Radiocarbon Accelerator Unit (ORAU), Research Laboratory for Archaeology and the History of Art (RLAHA), University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, UK.

Recent studies have suggested that the first arrival of humans in the Americas during the end of the last Ice Age is associated with marked anthropogenic influences on landscape; in particular, with the use of fire which, would have given even small populations the ability to have broad impacts on the landscape. Understanding the impact of these early people is complicated by the dramatic changes in climate occurring with the shift from glacial to interglacial conditions. Despite these difficulties, we here attempt to test the extent of anthropogenic influence using the California Channel Islands as a smaller, landscape-scale test bed. These islands are famous for the discovery of the 'Arlington Springs Man', which are some of the earliest human remains in the Americas. A unifying sedimentary charcoal record is presented from Arlington Canyon, Santa Rosa Island, based on over 20 detailed sedimentary sections from eight key localities. Radiocarbon dating was based on thin, fragile, long fragments of charcoal in order to avoid the 'inbuilt' age problem. Radiocarbon dating of 49 such fragments has allowed inferences regarding the fire and landscape history of the Canyon ca 19-11 ka BP. A significant period of charcoal deposition is identified approximately 14-12.5 ka BP and bears remarkable closeness to an estimated age range of the first human arrival on the islands.This article is part of the themed issue 'The interaction of fire and mankind'.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rstb.2015.0167DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4874405PMC
June 2016

The interaction of fire and mankind: Introduction.

Philos Trans R Soc Lond B Biol Sci 2016 06;371(1696)

Department of Anthropology, Southern Methodist University, Dallas, TX 75275-0336, USA.

Fire has been an important part of the Earth system for over 350 Myr. Humans evolved in this fiery world and are the only animals to have used and controlled fire. The interaction of mankind with fire is a complex one, with both positive and negative aspects. Humans have long used fire for heating, cooking, landscape management and agriculture, as well as for pyrotechnologies and in industrial processes over more recent centuries. Many landscapes need fire but population expansion into wildland areas creates a tension between different interest groups. Extinguishing wildfires may not always be the correct solution. A combination of factors, including the problem of invasive plants, landscape change, climate change, population growth, human health, economic, social and cultural attitudes that may be transnational make a re-evaluation of fire and mankind necessary. The Royal Society meeting on Fire and mankind was held to address these issues and the results of these deliberations are published in this volume.This article is part of the themed issue 'The interaction of fire and mankind'.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rstb.2015.0162DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4874400PMC
June 2016

The interaction of fire and mankind.

Philos Trans R Soc Lond B Biol Sci 2016 06;371(1696)

Department of Anthropology, Southern Methodist University, Dallas, TX 75275-0336, USA.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rstb.2016.0149DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4874423PMC
June 2016

Living on a flammable planet: interdisciplinary, cross-scalar and varied cultural lessons, prospects and challenges.

Philos Trans R Soc Lond B Biol Sci 2016 06;371(1696)

School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5C8.

Living with fire is a challenge for human communities because they are influenced by socio-economic, political, ecological and climatic processes at various spatial and temporal scales. Over the course of 2 days, the authors discussed how communities could live with fire challenges at local, national and transnational scales. Exploiting our diverse, international and interdisciplinary expertise, we outline generalizable properties of fire-adaptive communities in varied settings where cultural knowledge of fire is rich and diverse. At the national scale, we discussed policy and management challenges for countries that have diminishing fire knowledge, but for whom global climate change will bring new fire problems. Finally, we assessed major fire challenges that transcend national political boundaries, including the health burden of smoke plumes and the climate consequences of wildfires. It is clear that to best address the broad range of fire problems, a holistic wildfire scholarship must develop common agreement in working terms and build across disciplines. We must also communicate our understanding of fire and its importance to the media, politicians and the general public.This article is part of the themed issue 'The interaction of fire and mankind'.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rstb.2015.0469DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4874422PMC
June 2016

Global combustion: the connection between fossil fuel and biomass burning emissions (1997-2010).

Philos Trans R Soc Lond B Biol Sci 2016 06;371(1696)

School of Biological Sciences, The University of Tasmania, Hobart, TAS 7011, Australia.

Humans use combustion for heating and cooking, managing lands, and, more recently, for fuelling the industrial economy. As a shift to fossil-fuel-based energy occurs, we expect that anthropogenic biomass burning in open landscapes will decline as it becomes less fundamental to energy acquisition and livelihoods. Using global data on both fossil fuel and biomass burning emissions, we tested this relationship over a 14 year period (1997-2010). The global average annual carbon emissions from biomass burning during this time were 2.2 Pg C per year (±0.3 s.d.), approximately one-third of fossil fuel emissions over the same period (7.3 Pg C, ±0.8 s.d.). There was a significant inverse relationship between average annual fossil fuel and biomass burning emissions. Fossil fuel emissions explained 8% of the variation in biomass burning emissions at a global scale, but this varied substantially by land cover. For example, fossil fuel burning explained 31% of the variation in biomass burning in woody savannas, but was a non-significant predictor for evergreen needleleaf forests. In the land covers most dominated by human use, croplands and urban areas, fossil fuel emissions were more than 30- and 500-fold greater than biomass burning emissions. This relationship suggests that combustion practices may be shifting from open landscape burning to contained combustion for industrial purposes, and highlights the need to take into account how humans appropriate combustion in global modelling of contemporary fire. Industrialized combustion is not only an important driver of atmospheric change, but also an important driver of landscape change through companion declines in human-started fires.This article is part of the themed issue 'The interaction of fire and mankind'.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rstb.2015.0177DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4874414PMC
June 2016

The impact of fire on the Late Paleozoic Earth system.

Front Plant Sci 2015 23;6:756. Epub 2015 Sep 23.

State Key Laboratory of Coal Resources and Safe Mining, and School of Geosciences and Survey Engineering, China University of Mining and Technology Beijing, China.

Analyses of bulk petrographic data indicate that during the Late Paleozoic wildfires were more prevalent than at present. We propose that the development of fire systems through this interval was controlled predominantly by the elevated atmospheric oxygen concentration (p(O2)) that mass balance models predict prevailed. At higher levels of p(O2), increased fire activity would have rendered vegetation with high-moisture contents more susceptible to ignition and would have facilitated continued combustion. We argue that coal petrographic data indicate that p(O2) rather than global temperatures or climate, resulted in the increased levels of wildfire activity observed during the Late Paleozoic and can, therefore, be used to predict it. These findings are based upon analyses of charcoal volumes in multiple coals distributed across the globe and deposited during this time period, and that were then compared with similarly diverse modern peats and Cenozoic lignites and coals. Herein, we examine the environmental and ecological factors that would have impacted fire activity and we conclude that of these factors p(O2) played the largest role in promoting fires in Late Paleozoic peat-forming environments and, by inference, ecosystems generally, when compared with their prevalence in the modern world.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fpls.2015.00756DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4585212PMC
October 2015

Mechanisms of resistance to high and low linear energy transfer radiation in myeloid leukemia cells.

Blood 2012 Sep 24;120(10):2087-97. Epub 2012 Jul 24.

Molecular Pharmacology and Chemistry Program and Leukemia Service, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.

Low linear energy transfer (LET) ionizing radiation (IR) is an important form of therapy for acute leukemias administered externally or as radioimmunotherapy. IR is also a potential source of DNA damage. High LET IR produces structurally different forms of DNA damage and has emerged as potential treatment of metastatic and hematopoietic malignancies. Therefore, understanding mechanisms of resistance is valuable. We created stable myeloid leukemia HL60 cell clones radioresistant to either γ-rays or α-particles to understand possible mechanisms in radioresistance. Cross-resistance to each type of IR was observed, but resistance to clustered, complex α-particle damage was substantially lower than to equivalent doses of γ-rays. The resistant phenotype was driven by changes in: apoptosis; late G2/M checkpoint accumulation that was indicative of increased genomic instability; stronger dependence on homology-directed repair; and more robust repair of DNA double-strand breaks and sublethal-type damage induced by γ-rays, but not by α-particles. The more potent cytotoxicity of α-particles warrants their continued investigation as therapies for leukemia and other cancers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1182/blood-2012-01-404509DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3437596PMC
September 2012

The human dimension of fire regimes on Earth.

J Biogeogr 2011 Dec;38(12):2223-2236

Humans and their ancestors are unique in being a fire-making species, but 'natural' (i.e. independent of humans) fires have an ancient, geological history on Earth. Natural fires have influenced biological evolution and global biogeochemical cycles, making fire integral to the functioning of some biomes. Globally, debate rages about the impact on ecosystems of prehistoric human-set fires, with views ranging from catastrophic to negligible. Understanding of the diversity of human fire regimes on Earth in the past, present and future remains rudimentary. It remains uncertain how humans have caused a departure from 'natural' background levels that vary with climate change. Available evidence shows that modern humans can increase or decrease background levels of natural fire activity by clearing forests, promoting grazing, dispersing plants, altering ignition patterns and actively suppressing fires, thereby causing substantial ecosystem changes and loss of biodiversity. Some of these contemporary fire regimes cause substantial economic disruptions owing to the destruction of infrastructure, degradation of ecosystem services, loss of life, and smoke-related health effects. These episodic disasters help frame negative public attitudes towards landscape fires, despite the need for burning to sustain some ecosystems. Greenhouse gas-induced warming and changes in the hydrological cycle may increase the occurrence of large, severe fires, with potentially significant feedbacks to the Earth system. Improved understanding of human fire regimes demands: (1) better data on past and current human influences on fire regimes to enable global comparative analyses, (2) a greater understanding of different cultural traditions of landscape burning and their positive and negative social, economic and ecological effects, and (3) more realistic representations of anthropogenic fire in global vegetation and climate change models. We provide an historical framework to promote understanding of the development and diversification of fire regimes, covering the pre-human period, human domestication of fire, and the subsequent transition from subsistence agriculture to industrial economies. All of these phases still occur on Earth, providing opportunities for comparative research.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/j.1365-2699.2011.02595.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3263421PMC
December 2011

Fire and the spread of flowering plants in the Cretaceous.

New Phytol 2010 Dec 2;188(4):1137-50. Epub 2010 Sep 2.

Botany Department, University of Cape Town, Rondebosch, South Africa.

We suggest that the spread of angiosperms in the Cretaceous was facilitated by novel fire regimes. Angiosperms were capable of high productivity and therefore accumulated flammable biomass ('fuel') more rapidly than their predecessors. They were capable of rapid reproduction, allowing populations to spread despite frequent disturbance. We evaluate the evidence for physical conditions conducive to fires in the Cretaceous. These included high temperatures, seasonally dry climate and higher atmospheric oxygen than current levels. We evaluate novel properties of angiosperms that contributed to rapid biomass accumulation, and to their ability to thrive in frequently disturbed environments. We also review direct evidence for Cretaceous fires. Charcoal mesofossils are common in Cretaceous deposits of the Northern Hemisphere. Inertinite, the charcoal component of coal, is common throughout the Cretaceous and into the Palaeocene, but declined steeply from the Eocene when angiosperm-dominated forests became widespread. Direct and indirect evidence is consistent with angiosperms initiating novel fire regimes, promoting angiosperm spread in the Cretaceous. Several traits are consistent with frequent surface fires. We suggest that forest was slow to develop until the Eocene, when fire activity dropped to very low levels. The causes and consequences of fires in the deep past warrant greater attention.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/j.1469-8137.2010.03418.xDOI Listing
December 2010

No evidence of nanodiamonds in Younger-Dryas sediments to support an impact event.

Proc Natl Acad Sci U S A 2010 Sep 30;107(37):16043-7. Epub 2010 Aug 30.

Department of Physics and Center for Materials Innovation, Washington University in St Louis, MO 63130, USA.

The causes of the late Pleistocene megafaunal extinctions in North America, disappearance of Clovis paleoindian lithic technology, and abrupt Younger-Dryas (YD) climate reversal of the last deglacial warming in the Northern Hemisphere remain an enigma. A controversial hypothesis proposes that one or more cometary airbursts/impacts barraged North America ≈12,900 cal yr B.P. and caused these events. Most evidence supporting this hypothesis has been discredited except for reports of nanodiamonds (including the rare hexagonal polytype) in Bølling-Ållerod-YD-boundary sediments. The hexagonal polytype of diamond, lonsdaleite, is of particular interest because it is often associated with shock pressures related to impacts where it has been found to occur naturally. Unfortunately, previous reports of YD-boundary nanodiamonds have left many unanswered questions regarding the nature and occurrence of the nanodiamonds. Therefore, we examined carbon-rich materials isolated from sediments dated 15,818 cal yr B.P. to present (including the Bølling-Allerod-YD boundary). No nanodiamonds were found in our study. Instead, graphene- and graphene/graphane-oxide aggregates are ubiquitous in all specimens examined. We demonstrate that previous studies misidentified graphene/graphane-oxide aggregates as hexagonal diamond and likely misidentified graphene as cubic diamond. Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the YD impact hypothesis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1003904107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2941276PMC
September 2010

Fire in the Earth system.

Science 2009 Apr;324(5926):481-4

University of Tasmania, Hobart, TAS 7001, Australia.

Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1163886DOI Listing
April 2009

Scanning electron microscopy and synchrotron radiation x-ray tomographic microscopy of 330 million year old charcoalified seed fern fertile organs.

Microsc Microanal 2009 Apr;15(2):166-73

Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW200EX, UK.

Abundant charcoalified seed fern (pteridosperm) pollen organs and ovules have been recovered from Late Viséan (Mississippian 330 Ma) limestones from Kingswood, Fife, Scotland. To overcome limitations of data collection from these tiny, sometimes unique, fossils, we have combined low vacuum scanning electron microscopy on uncoated specimens with backscatter detector and synchrotron radiation X-ray tomographic microscopy utilizing the Materials Science and TOMCAT beamlines at the Swiss Light Source of the Paul Scherrer Institut. In combination these techniques improve upon traditional cellulose acetate peel sectioning because they enable study of external morphology and internal anatomy in multiple planes of section on a single specimen that is retained intact. The pollen organ Melissiotheca shows a basal parenchymatous cushion bearing more than 100 sporangia on the distal face. Digital sections show the occurrence of pollen in some sporangia. The described ovule is new and has eight integumentary lobes that are covered in spirally arranged glandular hairs. Virtual longitudinal sections reveal the lobes are free above the pollen chamber. Results are applied in taxonomy and will subsequently contribute to our understanding of the former diversity and evolution of ovules, seeds, and pollen organs in the seed ferns, the first seed-bearing plants to conquer the land.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1017/S1431927609090126DOI Listing
April 2009

Geochemical evidence for combustion of hydrocarbons during the K-T impact event.

Proc Natl Acad Sci U S A 2009 Mar 26;106(11):4112-7. Epub 2009 Feb 26.

Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom.

It has been proposed that extensive wildfires occurred after the Cretaceous-Tertiary (K-T) impact event. An abundance of soot and pyrosynthetic polycyclic aromatic hydrocarbons (pPAHs) in marine K-T boundary impact rocks (BIRs) have been considered support for this hypothesis. However, nonmarine K-T BIRs, from across North America, contain only rare occurrences of charcoal yet abundant noncharred plant remains. pPAHs and soot can be formed from a variety of sources, including partial combustion of vegetation and hydrocarbons whereby modern pPAH signatures are traceable to their source. We present results from multiple nonmarine K-T boundary sites from North America and reveal that the K-T BIRs have a pPAH signature consistent with the combustion of hydrocarbons and not living plant biomass, providing further evidence against K-T wildfires and compelling evidence that a significant volume of hydrocarbons was combusted during the K-T impact event.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.0813117106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2657452PMC
March 2009

Increased terrestrial methane cycling at the Palaeocene-Eocene thermal maximum.

Nature 2007 Sep;449(7160):332-5

Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.

The Palaeocene-Eocene thermal maximum (PETM), a period of intense, global warming about 55 million years ago, has been attributed to a rapid rise in greenhouse gas levels, with dissociation of methane hydrates being the most commonly invoked explanation. It has been suggested previously that high-latitude methane emissions from terrestrial environments could have enhanced the warming effect, but direct evidence for an increased methane flux from wetlands is lacking. The Cobham Lignite, a recently characterized expanded lacustrine/mire deposit in England, spans the onset of the PETM and therefore provides an opportunity to examine the biogeochemical response of wetland-type ecosystems at that time. Here we report the occurrence of hopanoids, biomarkers derived from bacteria, in the mire sediments from Cobham. We measure a decrease in the carbon isotope values of the hopanoids at the onset of the PETM interval, which suggests an increase in the methanotroph population. We propose that this reflects an increase in methane production potentially driven by changes to a warmer and wetter climate. Our data suggest that the release of methane from the terrestrial biosphere increased and possibly acted as a positive feedback mechanism to global warming.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature06012DOI Listing
September 2007

The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration.

Proc Natl Acad Sci U S A 2006 Jul 10;103(29):10861-5. Epub 2006 Jul 10.

Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom.

By comparing Silurian through end Permian [approximately 250 million years (Myr)] charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long-term variations in fire occurrence and fire system diversification are related to fluctuations in Late Paleozoic atmospheric oxygen concentration. Charcoal, a proxy for fire, occurs in the fossil record from the Late Silurian (approximately 420 Myr) to the present. Its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13% to 35% (the "fire window"). Herein, we observe that, as predicted, atmospheric oxygen levels rise from approximately 13% in the Late Devonian to approximately 30% in the Late Permian so, too, fires progressively occur in an increasing diversity of ecosystems. Sequentially, data of note include: the occurrence of charcoal in the Late Silurian/Early Devonian, indicating the burning of a diminutive, dominantly rhyniophytoid vegetation; an apparent paucity of charcoal in the Middle to Late Devonian that coincides with a predicted atmospheric oxygen low; and the subsequent diversification of fire systems throughout the remainder of the Late Paleozoic. First, fires become widespread during the Early Mississippian, they then become commonplace in mire systems in the Middle Mississippian; in the Pennsylvanian they are first recorded in upland settings and finally, based on coal petrology, become extremely important in many Permian mire settings. These trends conform well to changes in atmospheric oxygen concentration, as predicted by modeling, and indicate oxygen levels are a significant control on long-term fire occurrence.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.0604090103DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1544139PMC
July 2006

Evaluating phenanthrene sorption on various wood chars.

Water Res 2005 Feb 23;39(4):549-58. Epub 2004 Dec 23.

School of Civil Engineering and Environmental Science, University of Oklahoma, Norman, OK 73019, USA.

A certain amount of wood char or soot in a soil or sediment sample may cause the sorption of organic compounds to deviate significantly from the linear partitioning commonly observed with soil organic matter (SOM). Laboratory produced and field wood chars have been obtained and analyzed for their sorption isotherms of a model solute (phenanthrene) from water solution. The uptake capacities and nonlinear sorption effects with the laboratory wood chars are similar to those with the field wood chars. For phenanthrene aqueous concentrations of 1 microg l(-1), the organic carbon-normalized sorption coefficients (log K(oc)) ranging from 5.0 to 6.4 for field chars and 5.4-7.3 for laboratory wood chars, which is consistent with literature values (5.6-7.1). Data with artificial chars suggest that the variation in sorption potential can be attributed to heating temperature and starting material, and both the quantity and heterogeneity of surface-area impacts the sorption capacity. These results thus help to corroborate and explain the range of logK(oc) values reported in previous research for aquifer materials containing wood chars.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.watres.2004.10.015DOI Listing
February 2005