scholarly journals The influence of layering and barometric pumping on firn air transport in a 2-D model

2018 ◽  
Vol 12 (6) ◽  
pp. 2021-2037 ◽  
Author(s):  
Benjamin Birner ◽  
Christo Buizert ◽  
Till J. W. Wagner ◽  
Jeffrey P. Severinghaus
Keyword(s):  
Dispersion Model ◽  
Noble Gas ◽  
Ice Core ◽  
Transport Processes ◽  
Air Transport ◽  
Atmospheric Composition ◽  
Elemental Ratios ◽  
Barometric Pumping ◽  
Kinetic Fractionation ◽  
D Model

Abstract. Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. However, the influence of low-permeability layers and barometric pumping (driven by surface pressure variability) on firn air transport is not well understood and is not readily captured in conventional one-dimensional (1-D) firn air models. Here we present a two-dimensional (2-D) trace gas advection–diffusion–dispersion model that accounts for discontinuous horizontal layers of reduced permeability. We find that layering or barometric pumping individually yields too small a reduction in gravitational settling to match observations. In contrast, when both effects are active, the model's gravitational fractionation is suppressed as observed. Layering focuses airflows in certain regions in the 2-D model, which acts to amplify the dispersive mixing resulting from barometric pumping. Hence, the representation of both factors is needed to obtain a realistic emergence of the lock-in zone. In contrast to expectations, we find that the addition of barometric pumping in the layered 2-D model does not substantially change the differential kinetic fractionation of fast- and slow-diffusing trace gases. Like 1-D models, the 2-D model substantially underestimates the amount of differential kinetic fractionation seen in actual observations, suggesting that further subgrid-scale processes may be missing in the current generation of firn air transport models. However, we find robust scaling relationships between kinetic isotope fractionation of different noble gas isotope and elemental ratios. These relationships may be used to correct for kinetic fractionation in future high-precision ice core studies and can amount to a bias of up to 0.45 °C in noble-gas-based mean ocean temperature reconstructions at WAIS Divide, Antarctica.

scholarly journals The influence of layering and barometric pumping on firn air transport in a 2D model

2017 ◽  
Author(s):  
Benjamin Birner ◽  
Christo Buizert ◽  
Till J. W. Wagner ◽  
Jeffrey P. Severinghaus
Keyword(s):  
Dispersion Model ◽  
Noble Gas ◽  
Ice Core ◽  
Transport Processes ◽  
Air Transport ◽  
Atmospheric Composition ◽  
Elemental Ratios ◽  
Barometric Pumping ◽  
Kinetic Fractionation ◽  
2D Model

Abstract. Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. However, the influence of impermeable layers and barometric pumping (driven by surface pressure variability) on firn air transport is not well understood and cannot be captured in conventional 1-dimensional firn air models. Here we present a 2-dimensional (2D) trace gas advection-diffusion-dispersion model that accounts for discontinuous horizontal layers of reduced permeability. We find that layering and barometric pumping individually yield too small a reduction in gravitational settling to match observations. In contrast, a combination of both effects more strongly suppresses gravitational fractionation. Layering locally focuses airflows in the 2D model and thus amplifies the dispersive mixing resulting from barometric pumping. Hence, the representation of both factors is needed to obtain a more natural emergence of the lock-in zone. Moreover, we find that barometric pumping in the layered 2D model does not substantially change the differential kinetic fractionation of fast and slow diffusing trace gases, which is observed in nature. This suggests that further subgrid-scale physics may be missing in the current generation of firn air transport models. However, we find robust scaling relationships between kinetic isotope fractionation of different noble gas isotope and elemental ratios. These relationships may be used to correct for kinetic fractionation in future high precision ice core studies.

scholarly journals Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland

2011 ◽  
Vol 11 (5) ◽  
pp. 15975-16021 ◽  
Author(s):  
C. Buizert ◽  
P. Martinerie ◽  
V. V. Petrenko ◽  
J. P. Severinghaus ◽  
C. M. Trudinger ◽  
...  
Keyword(s):  
Ice Core ◽  
Effective Diffusivity ◽  
Air Transport ◽  
Ice Age ◽  
Atmospheric Composition ◽  
Advective Transport ◽  
Mixing Ratios ◽  
The Difference ◽  
Model Tuning ◽  
Intercomparison Study

Abstract. Compacted snow (firn) preserves a continuous record of atmospheric composition up to a century back in time. Firn air transport modeling is essential for interpretation of firn gas records. Each site needs to be characterised individually through a tuning procedure, in which the effective diffusivity at each depth is adjusted to optimise the agreement between modeled and measured mixing ratios of a selected reference gas (usually CO2). We present the characterisation of the NEEM site, Northern Greenland (77.45° N 51.06° W), where an ensemble of ten reference tracers is used to constrain the diffusivity reconstruction. By analysing uncertainties in both data and the reference gas atmospheric histories, we can objectively assign weights to each of the gases used for the model tuning, and define a root mean square criterion that is minimised in the tuning. Each tracer constrains the firn profile differently through its unique atmospheric history and free air diffusivity, making our multiple-tracer characterisation method a clear improvement over the commonly used single-tracer tuning. Six firn air transport models are tuned to the NEEM site; all models successfully reproduce the data within a 1σ Gaussian distribution. The modern day Δage, i.e. the difference between gas age and ice age, is calculated to be 182 ± 8 yr. We find evidence that diffusivity does not vanish completely in the firn lock-in zone, as is commonly assumed. We further present the first intercomparison study of firn air models, where we introduce diagnostic scenarios designed to probe specific aspects of the model physics. Our results show that there are major differences in the way the models handle advective transport. Furthermore diffusive fractionation of isotopes in the firn is poorly constrained by the models, which has consequences for attempts to reconstruct the isotopic composition of trace gases back in time using firn air and ice core records.

scholarly journals Intercontinental transport of biomass burning pollutants over the Mediterranean Basin during the summer 2014 ChArMEx-GLAM airborne campaign

2017 ◽  
Author(s):  
Vanessa Brocchi ◽  
Gisèle Krysztofiak ◽  
Valéry Catoire ◽  
Jonathan Guth ◽  
Virginie Marécal ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Mediterranean Basin ◽  
Transport Model ◽  
Dispersion Model ◽  
Particle Dispersion ◽  
Transport Processes ◽  
Atmospheric Composition ◽  
Air Masses ◽  
The Mediterranean ◽  
The Mediterranean Basin

Abstract. The Gradient in Longitude of Atmospheric constituents above the Mediterranean basin (GLAM) campaign was set up in August 2014, as part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) project. This campaign aimed at studying the chemical variability of gaseous pollutants and aerosols in the troposphere along a West-East transect above the Mediterranean Basin (MB). In the present work, we focus on two biomass burning events detected at 5.4 and 9.7 km altitude above sea level (asl) above Sardinia (from 39°12 N–9°15 E to 35°35 N–12°35 E and at 39°30 N–8°25 E, respectively). Concentration variations in trace gas carbon monoxide (CO) and aerosols were measured thanks to the standard instruments on-board the Falcon-20 aircraft operated by the Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE) and the Spectromètre InfraRouge In situ Toute Altitude (SPIRIT) developed by LPC2E. 20-day backward trajectories with Lagrangian particle dispersion model FLEXPART (FLEXible PARTicle) help understanding the transport processes and the origin of the emissions that contributed to these pollutions detected above Sardinia. Biomass burning emissions came (i) on 10 August from the Northern American continent with air masses transported during 5 days before arriving over the MB, and (ii) on 6 August from Siberia with air masses travelling during 12 days and enriched in fire emission products above Canada 5 days before arriving over the MB. In combination with the Global Fire Assimilation System (GFAS) inventory and the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite fire locations, FLEXPART reproduces well the contribution of those fires to CO and aerosols enhancements under adjustments of the injection height to 10 km in both cases, and application of an amplification factor of 2.5 on CO GFAS emissions for the 10 August event. The chemistry transport model (CTM) MOCAGE is used as a complementary tool for the case of 6 August to confirm the origin of the emissions by tracing the CO global atmospheric composition reaching the MB. For this event, both models agree on the origin of air masses with CO concentrations simulated with MOCAGE lower than the observed ones, likely caused by the coarse model horizontal resolution that yields the dilution of the emissions and diffusion during transport. In combination with wind fields, the analysis of the transport of the air mass documented on 6 August suggests the subsidence of CO pollution from Siberia towards North America and then a transport to the MB via fast jet winds located at around 5.5 km in altitude.

scholarly journals New methods for measuring atmospheric heavy noble gas isotope and elemental ratios in ice core samples

2018 ◽  
Vol 32 (10) ◽  
pp. 801-814 ◽  
Author(s):  
Bernhard Bereiter ◽  
Kenji Kawamura ◽  
Jeffrey P. Severinghaus
Keyword(s):  
Noble Gas ◽  
Ice Core ◽  
Elemental Ratios ◽  
Core Samples ◽  
New Methods ◽  
Noble Gas Isotope

Investigation of volcanic emissions in Antikythera PANGEA station using near-real-time alerts

2021 ◽  
Author(s):  
Anna Kampouri ◽  
Vassilis Amiridis ◽  
Stavros Solomos ◽  
Anna Gialitaki ◽  
Eleni Marinou ◽  
...  
Keyword(s):  
Real Time ◽  
Dispersion Model ◽  
Atmospheric Composition ◽  
Dust Particles ◽  
Volcanic Plume ◽  
Observation Data ◽  
National Observatory ◽  
Development Fund ◽  
Model Simulations ◽  
Geophysical Observatory

<p>In the last years, several Etna eruption events are documented, forming lava flows and explosive activity. The Pilot EO4D_ash – Earth observation data for detection, discrimination & distribution (4D) of volcanic ash of the e-shape project provides the PANhellenic GEophysical observatory of Antikythera (PANGEA) of the National Observatory of Athens (NOA), in Greece with near-real-time alerts from Etna volcano eruptions. These alerts are used in the PANGEA station to monitor and reveal the presence of volcanic particles above the area the days following an eruption, also the station is supported by a volcanic particle monitoring and forecasting warning system. In this work, we investigate the volcano eruption between 30 May and 6 June 2019 which affected the southern parts of Greece and reaching the Antikythera station. Due to the prevailing meteorological conditions, volcanic particles and gases followed an easterly direction and were dispersed towards Greece. FLEXPART dispersion model simulations confirm the volcanic plume transport from Etna towards PANGEA, mixing also with co-existing desert dust particles. Model simulations are evaluated with Polly<sup>XT</sup> lidar measurements performed at PANGEA and satellite-based SO<sub>2</sub> observations from the TROPOspheric Monitoring Instrument onboard the Sentinel-5 Precursor (TROPOMI/S5P). This is the first time that Etna volcanic products are monitored at the Antikythera station, in Greece with implications for the investigation of their role in the Mediterranean weather and climate.</p><p><strong>Acknowledgments</strong>: We acknowledge the support by EU H2020 E-shape project (Grant Agreement n. 820852). Also, this research was supported by data and services obtained from the PANhellenic Geophysical Observatory of Antikythera (PANGEA) of the National Observatory of Athens (NOA), Greece, and by the project “PANhellenic infrastructure for Atmospheric Composition and climatE change” (MIS 5021516) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund). NOA team acknowledges the support of the Stavros Niarchos Foundation (SNF).</p>

scholarly journals The Community Firn Model (CFM) v1.0

2020 ◽  
Author(s):  
C. Max Stevens ◽  
Vincent Verjans ◽  
Jessica M.D. Lundin ◽  
Emma C. Kahle ◽  
Annika N. Horlings ◽  
...  
Keyword(s):  
Climate Model ◽  
Noble Gas ◽  
Regional Climate ◽  
Ice Core ◽  
Ice Cores ◽  
Elevation Change ◽  
Model Framework ◽  
Modular Model ◽  
Surface Elevation Change ◽  
Air Diffusion

Abstract. Models that simulate evolution of polar firn are important for several applications in glaciology, including converting ice-sheet elevation-change measurements to mass change and interpreting climate records in ice cores. We have developed the Community Firn Model (CFM), an open-source, modular model framework designed to simulate numerous physical processes in firn. The modules include firn densification, heat transport, meltwater percolation and refreezing, water-isotope diffusion, and firn-air diffusion. The CFM is designed so that new modules can be added with ease. In this paper, we first describe the CFM and its modules. We then demonstrate the CFM's usefulness in two model applications that utilize two of its novel aspects. The CFM currently has the ability to run any of 13 previously published firn-densification models, and in the first application we compare those models' results when they are forced with regional climate model outputs for Summit, Greenland. The results show that the models do not agree well (spread greater than 10 %) when predicting depth-integrated porosity, firn age, or trend in surface-elevation change trend. In the second application, we show that the CFM's coupled firn-air and firn-densification models can simulate noble-gas records from an ice core better than a firn-air model alone.

Constraining ice core chronologies with 39Ar and 81Kr

2021 ◽  
Author(s):  
Florian Ritterbusch ◽  
Jinho Ahn ◽  
Ji-Qiang Gu ◽  
Wei Jiang ◽  
Giyoon Lee ◽  
...  
Keyword(s):  
Sample Size ◽  
Half Life ◽  
Earth Science ◽  
Noble Gas ◽  
Ice Core ◽  
Ice Cores ◽  
High Mountain ◽  
National Academy Of Sciences ◽  
Geophysical Research ◽  
Mountain Glaciers

<p>Paleoclimate reconstructions from ice core records can be hampered due to the lack of a reliable chronology, especially when the stratigraphy is disturbed and conventional dating methods cannot be readily applied. The noble-gas radioisotopes <sup>81</sup>Kr and <sup>39</sup>Ar can in these cases provide robust constraints as they yield absolute, radiometric ages. <sup>81</sup>Kr (half-life 229 ka) covers the time span of 50-1300 ka, which is particularly relevant for polar ice cores, whereas <sup>39</sup>Ar (half-life 269 a) with a dating range of 50-1800 a is suitable for high mountain glaciers. For a long time the use of <sup>81</sup>Kr and <sup>39</sup>Ar for dating of ice samples was hampered by the lack of a detection technique that can meet its extremely small abundance at a reasonable sample size.</p><p>Here, we present <sup>81</sup>Kr and <sup>39</sup>Ar dating of Antarctic and Tibetan ice cores with the detection method Atom Trap Trace Analysis (ATTA), using 5-10 kg of ice for <sup>81</sup>Kr and 2-5 kg for <sup>39</sup>Ar. Recent advances in further decreasing the sample size and increasing the dating precision will be discussed. Current studies include <sup>81</sup>Kr dating in shallow ice cores from the Larsen Blue ice area, East Antarctica, in order to retrieve climate signals from the last glacial termination. Moreover, an <sup>39</sup>Ar profile from a central Tibetan ice core has been obtained in combination with layer counting based on isotopic and visual stratigraphic signals. The presented studies demonstrate how <sup>81</sup>Kr and <sup>39</sup>Ar can constrain the age range of ice cores and complement other methods in developing an ice core chronology.</p><p> </p><p>[1] Z.-T. Lu, Tracer applications of noble gas radionuclides in the geosciences, Earth-Science Reviews 138, 196-214, (2014)<br>[2] C. Buizert, Radiometric <sup>81</sup>Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica, Proceedings of the National Academy of Sciences, <strong>111</strong>, 6876, (2014)</p><p>[3] L. Tian, <sup>81</sup>Kr Dating at the Guliya Ice Cap, Tibetan Plateau, Geophysical Research Letters, (2019)</p><p>http://atta.ustc.edu.cn</p>

Chapter 6.2 Englacial tephras of East Antarctica

2021 ◽  
pp. M55-2018-86
Author(s):  
Biancamaria Narcisi ◽  
Jean Robert Petit
Keyword(s):  
Late Quaternary ◽  
Ice Core ◽  
Ice Cores ◽  
Explosive Volcanism ◽  
Current Data ◽  
Atmospheric Composition ◽  
Antarctic Continent ◽  
South Sandwich Islands ◽  
Eastern Periphery ◽  
Age Range

AbstractDriven by successful achievements in recovering high-resolution ice records of climate and atmospheric composition through the Late Quaternary, new ice–tephra sequences from various sites of the East Antarctic Ice Sheet (EAIS) have been studied in the last two decades spanning an age range of a few centuries to 800 kyr. The tephrostratigraphic framework for the inner EAIS, based on ash occurrence in three multi-kilometre-deep ice cores, shows that the South Sandwich Islands represent a major source for tephra, highlighting the major role in the ash dispersal played by clockwise circum-Antarctic atmospheric circulation penetrating the Antarctic continent. Tephra records from the eastern periphery of the EAIS, however, are obviously influenced by explosive activity sourced in nearby Antarctic rift provinces. These tephra inventories have provided a fundamental complement to the near-vent volcanic record, in terms of both frequency/chronology of explosive volcanism and of magma chemical evolution through time. Despite recent progress, current data are still sparse. There is a need for further tephra studies to collect data from unexplored EAIS sectors, along with extending the tephra inventory back in time. Ongoing international palaeoclimatic initiatives of ice-core drilling could represent a significant motivation for the tephra community and for Quaternary Antarctic volcanologists.

scholarly journals Determining the origin of the building blocks of the Ice Giants based on analogue measurements from comets

2019 ◽  
Vol 491 (1) ◽  
pp. 488-494 ◽  
Author(s):  
K E Mandt ◽  
O Mousis ◽  
S Treat
Keyword(s):  
Noble Gas ◽  
Giant Planet ◽  
Solid Material ◽  
Building Blocks ◽  
Atmospheric Composition ◽  
Isotopic Ratios ◽  
Carbon And Nitrogen ◽  
Formation Conditions ◽  
Comet 67P

ABSTRACT The abundances of the heavy elements and isotopic ratios in the present atmospheres of the giant planets can be used to trace the composition of volatiles that were present in the icy solid material that contributed to their formation. The first definitive measurements of noble gas abundances and isotope ratios at comet 67P/Churyumov–Gerasimenko (67P/C–G) were recently published by Marty et al. (2017) and Rubin et al. (2018, 2019). The implications of these abundances for the formation conditions of the 67P/C–G building blocks were then evaluated by Mousis et al. (2018a). We add here an analysis of the implications of these results for understanding the formation conditions of the building blocks of the Ice Giants and discuss how future measurements of Ice Giant atmospheric composition can be interpreted. We first evaluate the best approach for comparing comet observations with giant planet composition, and then determine what would be the current composition of the Ice Giant atmospheres based on four potential sources for their building blocks. We provide four scenarios for the origin of the Ice Giants building blocks based on four primary constraints for building block composition: (1) the bulk abundance of carbon relative to nitrogen, (2) noble gas abundances relative to carbon and nitrogen, (3) abundance ratios Kr/Ar and Xe/Ar, and (4) Xe isotopic ratios. In situ measurements of these quantities by a Galileo-like entry probe in the atmosphere(s) of Uranus and/or Neptune should place important constraints on the formation conditions of the Ice Giants.

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