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ADVANCING ANTARCTIC SEDIMENT CHRONOLOGY THROUGH COMBINED RAMPED PYROLYSIS OXIDATION AND PYROLYSIS-GC-MS
- Catherine E Ginnane, Jocelyn C Turnbull, Sebastian Naeher, Brad E Rosenheim, Ryan A Venturelli, Andy M Phillips, Simon Reeve, Jeremy Parry-Thompson, Albert Zondervan, Richard H Levy, Kyu-Cheul Yoo, Gavin Dunbar, Theo Calkin, Carlota Escutia, Julia Gutierrez Pastor
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- Journal:
- Radiocarbon , First View
- Published online by Cambridge University Press:
- 08 February 2024, pp. 1-20
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Radiocarbon (14C) dating of sediment deposition around Antarctica is often challenging due to heterogeneity in sources and ages of organic carbon in the sediment. Chemical and thermochemical techniques have been used to separate organic carbon when microfossils are not present. These techniques generally improve on bulk sediment dates, but they necessitate assumptions about the age spectra of specific molecules or compound classes and about the chemical heterogeneity of thermochemical separations. To address this, the Rafter Radiocarbon Laboratory has established parallel ramped pyrolysis oxidation (RPO) and ramped pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) systems to thermochemically separate distinct carbon fractions, diagnose the chemical composition of each fraction, and target suitable RPO fractions for radiocarbon dating. Three case studies of sediment taken from locations around Antarctica are presented to demonstrate the implementation of combined RPO-AMS and Py-GC-MS to provide more robust age determination in detrital sediment stratigraphy. These three depositional environments are good examples of analytical and interpretive challenges related to oceanographic conditions, carbon sources, and other factors. Using parallel RPO-AMS and Py-GC-MS analyses, we reduce the number of radiocarbon measurements required, minimize run times, provide context for unexpected 14C ages, and better support interpretations of radiocarbon measurements in the context of environmental reconstruction.
Linear stability of shallow morphodynamic flows
- Jake Langham, Mark J. Woodhouse, Andrew J. Hogg, Jeremy C. Phillips
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- Journal:
- Journal of Fluid Mechanics / Volume 916 / 10 June 2021
- Published online by Cambridge University Press:
- 12 April 2021, A31
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It is increasingly common for models of shallow-layer overland flows to include equations for the evolution of the underlying bed (morphodynamics) and the motion of an associated sedimentary phase. We investigate the linear stability properties of these systems in considerable generality. Naive formulations of the morphodynamics, featuring exchange of sediment between a well-mixed suspended load and the bed, lead to mathematically ill-posed governing equations. This is traced to a singularity in the linearised system at Froude number ${\textit {Fr}} = 1$ that causes unbounded unstable growth of short-wavelength disturbances. The inclusion of neglected physical processes can restore well posedness. Turbulent momentum diffusion (eddy viscosity) and a suitably parametrised bed load sediment transport are shown separately to be sufficient in this regard. However, we demonstrate that such models typically inherit an associated instability that is absent from non-morphodynamic settings. Implications of our analyses are considered for simple generic closures, including a drag law that switches between fluid and granular behaviour, depending on the sediment concentration. Steady morphodynamic flows bifurcate into two states: dilute flows, which are stable at low ${\textit {Fr}}$, and concentrated flows which are always unstable to disturbances in concentration. By computing the growth rates of linear modes across a wide region of parameter space, we examine in detail the effects of specific model parameters including the choices of sediment erodibility, eddy viscosity and bed load flux. These analyses may be used to inform the ongoing development of operational models in engineering and geosciences.
Contributors
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- By Rony A. Adam, Gloria Bachmann, Nichole M. Barker, Randall B. Barnes, John Bennett, Inbar Ben-Shachar, Jonathan S. Berek, Sarah L. Berga, Monica W. Best, Eric J. Bieber, Frank M. Biro, Shan Biscette, Anita K. Blanchard, Candace Brown, Ronald T. Burkman, Joseph Buscema, John E. Buster, Michael Byas-Smith, Sandra Ann Carson, Judy C. Chang, Annie N. Y. Cheung, Mindy S. Christianson, Karishma Circelli, Daniel L. Clarke-Pearson, Larry J. Copeland, Bryan D. Cowan, Navneet Dhillon, Michael P. Diamond, Conception Diaz-Arrastia, Nicole M. Donnellan, Michael L. Eisenberg, Eric Eisenhauer, Sebastian Faro, J. Stuart Ferriss, Lisa C. Flowers, Susan J. Freeman, Leda Gattoc, Claudine Marie Gayle, Timothy M. Geiger, Jennifer S. Gell, Alan N. Gordon, Victoria L. Green, Jon K. Hathaway, Enrique Hernandez, S. Paige Hertweck, Randall S. Hines, Ira R. Horowitz, Fred M. Howard, William W. Hurd, Fidan Israfilbayli, Denise J. Jamieson, Carolyn R. Jaslow, Erika B. Johnston-MacAnanny, Rohna M. Kearney, Namita Khanna, Caroline C. King, Jeremy A. King, Ira J. Kodner, Tamara Kolev, Athena P. Kourtis, S. Robert Kovac, Ertug Kovanci, William H. Kutteh, Eduardo Lara-Torre, Pallavi Latthe, Herschel W. Lawson, Ronald L. Levine, Frank W. Ling, Larry I. Lipshultz, Steven D. McCarus, Robert McLellan, Shruti Malik, Suketu M. Mansuria, Mohamed K. Mehasseb, Pamela J. Murray, Saloney Nazeer, Farr R. Nezhat, Hextan Y. S. Ngan, Gina M. Northington, Peggy A. Norton, Ruth M. O'Regan, Kristiina Parviainen, Resad P. Pasic, Tanja Pejovic, K. Ulrich Petry, Nancy A. Phillips, Ashish Pradhan, Elizabeth E. Puscheck, Suneetha Rachaneni, Devon M. Ramaeker, David B. Redwine, Robert L. Reid, Carla P. Roberts, Walter Romano, Peter G. Rose, Robert L. Rosenfield, Shon P. Rowan, Mack T. Ruffin, Janice M. Rymer, Evis Sala, Ritu Salani, Joseph S. Sanfilippo, Mahmood I. Shafi, Roger P. Smith, Meredith L. Snook, Thomas E. Snyder, Mary D. Stephenson, Thomas G. Stovall, Richard L. Sweet, Philip M. Toozs-Hobson, Togas Tulandi, Elizabeth R. Unger, Denise S. Uyar, Marion S. Verp, Rahi Victory, Tamara J. Vokes, Michelle J. Washington, Katharine O'Connell White, Paul E. Wise, Frank M. Wittmaack, Miya P. Yamamoto, Christine Yu, Howard A. Zacur
- Edited by Eric J. Bieber, Joseph S. Sanfilippo, University of Pittsburgh, Ira R. Horowitz, Emory University, Atlanta, Mahmood I. Shafi
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- Book:
- Clinical Gynecology
- Published online:
- 05 April 2015
- Print publication:
- 23 April 2015, pp viii-xiv
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Modelling intrusions through quiescent and moving ambients
- Christopher G. Johnson, Andrew J. Hogg, Herbert E. Huppert, R. Stephen J. Sparks, Jeremy C. Phillips, Anja C. Slim, Mark J. Woodhouse
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- Journal:
- Journal of Fluid Mechanics / Volume 771 / 25 May 2015
- Published online by Cambridge University Press:
- 20 April 2015, pp. 370-406
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Volcanic eruptions commonly produce buoyant ash-laden plumes that rise through the stratified atmosphere. On reaching their level of neutral buoyancy, these plumes cease rising and transition to horizontally spreading intrusions. Such intrusions occur widely in density-stratified fluid environments, and in this paper we develop a shallow-layer model that governs their motion. We couple this dynamical model to a model for particle transport and sedimentation, to predict both the time-dependent distribution of ash within volcanic intrusions and the flux of ash that falls towards the ground. In an otherwise quiescent atmosphere, the intrusions spread axisymmetrically. We find that the buoyancy-inertial scalings previously identified for continuously supplied axisymmetric intrusions are not realised by solutions of the governing equations. By calculating asymptotic solutions to our model we show that the flow is not self-similar, but is instead time-dependent only in a narrow region at the front of the intrusion. This non-self-similar behaviour results in the radius of the intrusion growing with time $t$ as $t^{3/4}$, rather than $t^{2/3}$ as suggested previously. We also identify a transition to drag-dominated flow, which is described by a similarity solution with radial growth now proportional to $t^{5/9}$. In the presence of an ambient wind, intrusions are not axisymmetric. Instead, they are predominantly advected downstream, while at the same time spreading laterally and thinning vertically due to persistent buoyancy forces. We show that close to the source, this lateral spreading is in a buoyancy-inertial regime, whereas far downwind, the horizontal buoyancy forces that drive the spreading are balanced by drag. Our results emphasise the important role of buoyancy-driven spreading, even at large distances from the source, in the formation of the flowing thin horizontally extensive layers of ash that form in the atmosphere as a result of volcanic eruptions.
Chapter 10 - Pyroclastic density currents
- Edited by Sarah A. Fagents, University of Hawaii, Manoa, Tracy K. P. Gregg, State University of New York, Buffalo, Rosaly M. C. Lopes, NASA-Jet Propulsion Laboratory, California
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- Book:
- Modeling Volcanic Processes
- Published online:
- 05 March 2013
- Print publication:
- 14 March 2013, pp 203-229
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Summary
Overview
This chapter summarizes the principal experimental and theoretical approaches used to investigate the physics of pyroclastic density currents (PDCs), which are gravity-driven hot gas–particle mixtures commonly generated during explosive volcanic eruptions. PDC behavior ranges from pyroclastic surges, which are dilute turbulent suspensions, to pyroclastic flows, which are dense (fluidized) granular avalanches. Most PDCs consist of a coupled basal flow and an overriding surge, which renders their physics particularly complex. Experiments and phenomenological theory have been used to characterize the propagation and deposition mechanisms of PDCs. Most work has used turbulent gravity currents as an analogue to dilute PDCs and has provided fundamental insight into propagation and deposition dynamics and mixing with their surroundings. Dense PDCs have been investigated as granular and fluidized flows, and these studies have provided insight into deposit levée-channel morphology typical of coarse-grained flows, shown that fines-rich flows may behave as inertial fluid currents, and suggested that deposits of PDCs may form by aggradation. Numerical formulations ranging from continuum depth-averaged to discrete element models have been used to simulate PDC emplacement on real topographies and are fundamental in the context of volcanic hazard assessment and mitigation.
Principal characteristics of pyroclastic density currents
Pyroclastic density currents (PDCs) are common features of explosive volcanic eruptions. They are generated from the gravitational collapse of lava domes (Chapter 7) or eruptive columns (Chapter 8), by lateral explosions in the case of hydromagmatic activity (Chapter 11) or sudden decompression of a magma body (Fig. 10.1), as well as during the formation of collapse calderas. PDCs are hot (up to ~600–800°C), gravity-driven, gas–particle mixtures within which the interstitial fluid may control the flow dynamics. The pyroclasts result from magma fragmentation and their granulometry commonly ranges from micron-sized ash to centimeter-sized lapilli and sometimes meter-sized blocks. PDCs have typical volumes of ~104–108 m3, though their accumulation during an eruptive event can form deposits > 103 km3.
Contributors
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- By Phillip L. Ackerman, Neil Anderson, Jens B. Asendorpf, R. Michael Bagby, Michael Harris Bond, Gregory J. Boyle, Andrea L. Briggs, Giles St J. Burch, Turhan Canli, David Canter, Gianvittorio Caprara, Charles S. Carver, Douglas F. Cellar, Gordon Claridge, Susan Cloninger, Elisabeth D. Conradt, Philip J. Corr, Sharon Dawe, Ian J. Deary, Boele De Raad, Edward L. Deci, Colin G. DeYoung, M. Brent Donnellan, Juris G. Draguns, Marko Elovainio, Aurelio José Figueredo, David C. Funder, Paul Gladden, Rapson Gomez, Samuel D. Gosling, Jeremy R. Gray, Robert D. Hare, B. Austin Harley, Edward Helmes, Robert Hogan, Lauri A. Jensen-Campbell, Daniel Nelson Jones, Mika Kivimäki, Jennifer M. Knack, James T. Lamiell, Natalie J. Loxton, Geoff MacDonald, Gerald Matthews, Robert R. McCrae, Mario Mikulincer, Stephanie N. Mullins-Sweatt, Marcus R. Munafò, Vickie Nam, Craig S. Newmann, Rainer Reisenzein, Madeline Rex-Lear, Richard W. Robins, Michael D. Robinson, Mary K. Rothbart, Richard M. Ryan, Gerard Saucier, Michael F. Scheier, Constantine Sedikides, Phillip R. Shaver, Brad E. Sheese, Yuichi Shoda, Ronald E. Smith, Alice F. Stuhlmacher, Rhonda Swickert, Avril Thorne, David D. Vachon, Geneva Vásquez, Michele Vecchione, Seth A. Wagerman, Fiona Warren, Hannelore Weber, Thomas A. Widiger, Pedro Sofio Abril Wolf, Donna Youngs, Moshe Zeidner
- Edited by Philip J. Corr, University of East Anglia, Gerald Matthews, University of Cincinnati
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- Book:
- The Cambridge Handbook of Personality Psychology
- Published online:
- 05 June 2012
- Print publication:
- 16 July 2009, pp xv-xvii
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The dynamics and mixing of turbulent plumes in a turbulently convecting environment
- FRED WITHAM, JEREMY C. PHILLIPS
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- Journal:
- Journal of Fluid Mechanics / Volume 602 / 10 May 2008
- Published online by Cambridge University Press:
- 25 April 2008, pp. 39-61
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The turbulent motion of buoyant plumes released into turbulently convecting environments is studied. By assuming that the turbulent environment removes fluid from the plume at a rate proportional to a characteristic environmental velocity scale, we derive a model describing the fluid behaviour. For the example of pure buoyancy plumes, entrainment dominates near the source and the plume radius increases with distance, while further from the source removal, or extrainment, of plume material dominates, and the plume radius decreases to zero. Theoretical predictions are consistent with laboratory experiments, a major feature of which is the natural variability of the convection. We extend the study to include the evolution of a finite confined environment, the end-member regimes of which are a well-mixed environment at all times (high convective velocities), and a ‘filling-box’ model similar to that of Baines & Turner (1969) (low convective velocities). These regimes, and the motion of the interface in a ‘filling-box’ experiment, match experimental observations. We find that the convecting filling box is not stable indefinitely, but that the density stratification will eventually be overcome by thermal convection. The model presented here has important applications in volcanology, ventilation studies and environmental science.
Entrainment into two-dimensional and axisymmetric turbulent gravity currents
- Mark A. Hallworth, Herbert E. Huppert, Jeremy C. Phillips, R. Stephen J. Sparks
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- Journal:
- Journal of Fluid Mechanics / Volume 308 / 10 February 1996
- Published online by Cambridge University Press:
- 26 April 2006, pp. 289-311
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Entrainment of ambient fluid into both two-dimensional and axisymmetric gravity currents is investigated experimentally using a novel neutralization technique. The technique involves the titrative neutralization of an alkaline gravity current which intrudes into and entrains an acidic ambient, and is visualized using a pH indicator solution. Using this technique, we can determine quantitative results for the amount of dilution in the head of the current. The head of the current is able to entrain ambient fluid both by shear instabilities on the current/ambient interface and by over-riding (relatively light) ambient fluid. Guided by our experimental observations, we present two slightly different theoretical models to determine the entrainment into the head of the current as a function of distance from the source for the instantaneous release of a constant volume of fluid in a two-dimensional geometry. By dimensional analysis, we determine from both models that the dimensionless entrainment or dilution ratio, E, defined as the ratio of the volumes of ambient and original fluid in the head, is independent of the initial reduced gravity of the current; and this result is confirmed by our experiments in Boussinesq situations. Our theoretical evaluation of E in terms of the initial cross-sectional area of the current agrees very well with our experimental measurements on the incorporation of an entrainment coefficient α, evaluated experimentally to be 0.063 ± 0.003. We also obtain experimental results for constant-volume gravity currents moving over horizontal surfaces of varying roughness. A particularly surprising result from all the experiments, which is reflected in the theoretical models, is that the head remains essentially unmixed – the entrainment is negligible – in the slumping phase. Thus the heads of gravity currents with identical initial cross-sectional areas but different initial aspect ratios (lock lengths) will begin to be diluted by ambient fluid at different positions and hence propagate at different rates. A range of similar results is determined, both theoretically and experimentally, for the instantaneous release of a fixed volume of (heavy) fluid in an axisymmetric geometry. By contrast, the results of our experiments with gravity currents fed by a constant flux exhibit markedly different entrainment dynamics due to the continual replenishment of the fluid in the head by the constant input of undiluted fluid from the tail.
Blocked natural ventilation: the effect of a source mass flux
- ANDREW W. WOODS, C. P. CAULFIELD, JEREMY C. PHILLIPS
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- Journal:
- Journal of Fluid Mechanics / Volume 495 / 25 November 2003
- Published online by Cambridge University Press:
- 11 November 2003, pp. 119-133
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We analyse the density evolution of fluid within a confined ventilated space resulting from the action of a dense turbulent plume originating at the top of the space with finite source volume flux, $Q_0$, and initial source buoyancy flux, $B_0$. The space is ventilated through upper and lower openings of areas $A_u$ and $A_l$ respectively, which are separated by a vertical distance $H$. We show that if $Q_0^3\,{<}\, 2 B_0 H c_l^2 A_l^2$ (where $c_l$ is an empirically determined discharge coefficient) then a two-layer steady stratification becomes established in the room, with outflow through the lower opening and inflow through the upper opening. The interface location depends not only on the geometry of the openings, but also the source conditions. We show that as $Q_0$ increases for fixed $B_0$, the height of the interface, which equals the depth of the lower layer of relatively dense fluid, increases. Eventually, when the source volume flux has a value greater than $Q_m\,{=}\,(c_l A_l)^{2/3}(2B_0 H)^{1/3}$, the natural exchange flow becomes blocked and a steady outflow through both of the openings develops. As a result, the density of the fluid throughout the room gradually evolves towards the density of the incoming dense fluid. We compare our theoretical predictions with a series of laboratory experiments, and discuss the implications of our model for the design of ventilation systems.