The physical basis for gas transport through polar firn: a case study at Summit, Greenland

Abstract. Compared to other natural porous materials, relatively little is known about the physical nature of polar firn. This intricate network of ice and pore space that comprises the top 60–100 m of the polar ice sheets is the framework that forms the natural archive of past climate information. Despite the many implications for ice core interpretation, direct measurements of physical properties throughout the firn column are limited. Models of gas transport through firn are used to interpret in-situ chemical data which is retrieved to analyze past atmospheric composition. These traditional models treat the firn as a "black box," with gas transport parameters tuned to match gas concentrations with depth to known atmospheric histories. Though this method has been largely successful and provided very useful insights, there are still many questions and uncertainties to be addressed. This work seeks to understand the impact of firn structure on gas transport in firn from a first principles standpoint through direct measurements of permeability, gas diffusivity and microstructure. The relationships between gas transport properties and microstructure will be characterized and compared to existing relationships for general porous media. Direct measurements of gas diffusivity are compared to diffusivities deduced from models based on firn air chemical sampling. Our comparison illuminates the primary importance of including microstructural parameters, beyond just porosity or density, in mass transport modeling, and it provides insights about the nature of gas transport throughout the firn column. Guidance is provided for development of next-generation firn air transport models.

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Exploring ice core sea ice proxies through process-based modelling

10.5194/egusphere-egu2020-9013 ◽

2020 ◽

Author(s):

Rachael Rhodes ◽

Xin Yang ◽

Eric Wolff

Keyword(s):

Sea Ice ◽

Atmospheric Chemistry ◽

Ice Core ◽

Ice Cores ◽

Sea Salt ◽

Atmospheric Composition ◽

The Arctic ◽

Sea Salt Aerosol ◽

Aerosol Emission ◽

The Impact

It is important to understand the magnitude and rate of past sea ice changes, as well as their timing relative to abrupt shifts in other components of Earth&#8217;s climate system. Furthermore, records of past sea ice over the last few centuries are urgently needed to assess the scale of natural (internal) variability over decadal timescales. By continuously recording past atmospheric composition, polar ice cores have the potential to document changing sea ice conditions if atmospheric chemistry is altered. &#160;Sea salt aerosol, specifically sodium (Na), and bromine enrichment (Brenr, Br/Na enriched relative to seawater ratio) are two ice core sea ice proxies suggested following this premise.Here we aim to move beyond a conceptual understanding of the controls on Na and Brenr in ice cores by using process-based modelling to test hypotheses. We present results of experiments using a 3D global chemical transport model (p-TOMCAT) that represents marine aerosol emission, transport and deposition. Critically, the complex atmospheric chemistry of bromine is also included. Three fundamental issues will be examined: 1) the partitioning of Br between gas and aerosol phases, 2) sea salt aerosol production from first-year versus multi-year sea ice, and 3) the impact of increased acidity in the atmosphere due to human activity in the Arctic.

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The impact of ice layers on gas transport through firn at the North Greenland Eemian Ice Drilling (NEEM) site, Greenland

The Cryosphere ◽

10.5194/tc-8-1801-2014 ◽

2014 ◽

Vol 8 (5) ◽

pp. 1801-1806 ◽

Cited By ~ 10

Author(s):

K. Keegan ◽

M. R. Albert ◽

I. Baker

Keyword(s):

Gas Transport ◽

Ice Core ◽

Polar Regions ◽

Air Concentration ◽

Transport Models ◽

Transport Dynamics ◽

The North ◽

Transition Depth ◽

The Impact ◽

North Greenland

Abstract. Typically, gas transport through firn is modeled in the context of an idealized firn column. However, in natural firn, imperfections are present, which can alter transport dynamics and therefore reduce the accuracy of reconstructed climate records. For example, ice layers have been found in several firn cores collected in the polar regions. Here, we examined the effects of two ice layers found in a NEEM, Greenland firn core on gas transport through the firn. These ice layers were found to have permeability values of 3.0 and 4.0 × 10−10 m2, and are therefore not impermeable layers. However, the shallower ice layer was found to be significantly less permeable than the surrounding firn, and can therefore retard gas transport. Large closed bubbles were found in the deeper ice layer, which will have an altered gas composition than that expected because they were closed near the surface after the water phase was present. The bubbles in this layer represent 12% of the expected closed porosity of this firn layer after the firn-ice transition depth is reached, and will therefore bias the future ice core gas record. The permeability and thickness of the ice layers at the North Greenland Eemian Ice Drilling (NEEM) site suggest that they do not disrupt the firn-air concentration profiles and that they do not need to be accounted for in gas transport models at NEEM.

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The impact of ice layers on gas transport through firn

The Cryosphere Discussions ◽

10.5194/tcd-8-1095-2014 ◽

2014 ◽

Vol 8 (1) ◽

pp. 1095-1110

Author(s):

K. Keegan ◽

M. R. Albert ◽

I. Baker

Keyword(s):

Gas Transport ◽

Ice Core ◽

Polar Regions ◽

Concentration Profiles ◽

Air Concentration ◽

Transport Models ◽

Transport Dynamics ◽

The Impact ◽

Firn Core ◽

Age Estimates

Abstract. Typically, gas transport through firn is modeled in the context of an idealized firn column. However, in natural firn, imperfections are present which may alter transport dynamics in ways that may reduce the accuracy of climate records. For example, ice layers have been found in several firn cores collected in the polar regions. Here, we examined the effects of two ice layers found in a NEEM, Greenland firn core on gas transport through the firn. Both ice layers were somewhat permeable. However, only the shallower ice layer was significantly less permeable than the surrounding firn and is therefore likely to retard gas transport. Large closed bubbles were found in one ice layer, which would contain older atmospheric samples than expected. Theses bubbles are likely to significantly bias age estimates. Conversely, the permeability and thickness of ice layers at NEEM suggest that they will not significantly bias the expected firn air concentration profiles at the present spatial resolution at which these data are collected. Therefore, ice layers do not need to be accounted for in gas transport models at NEEM. However, the microstructure of these ice layers indicates that larger melting events could significantly bias ice core records.

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Gas diffusivity and permeability through the firn column at Summit, Greenland: measurements and comparison to microstructural properties

The Cryosphere ◽

10.5194/tc-8-319-2014 ◽

2014 ◽

Vol 8 (1) ◽

pp. 319-328 ◽

Cited By ~ 13

Author(s):

A. C. Adolph ◽

M. R. Albert

Keyword(s):

Gas Transport ◽

Atmospheric Composition ◽

Coarse Grained ◽

Storm Event ◽

Microstructural Properties ◽

Near Surface ◽

Site Specific ◽

Archie’S Law ◽

Gas Diffusivity ◽

Starting Point

Abstract. The physical structure of polar firn plays a key role in the mechanisms by which glaciers and ice sheets preserve a natural archive of past atmospheric composition. This study presents the first measurements of gas diffusivity and permeability along with microstructural information measured from the near-surface firn through the firn column to pore close-off. Both fine- and coarse-grained firn from Summit, Greenland are included in this study to investigate the variability in firn caused by seasonal and storm-event layering. Our measurements reveal that the porosity of firn (derived from density) is insufficient to describe the full profiles of diffusivity and permeability, particularly at porosity values above 0.5. Thus, even a model that could perfectly predict the density profile would be insufficient for application to issues involving gas transport. The measured diffusivity profile presented here is compared to two diffusivity profiles modeled from firn air measurements from Summit. Because of differences in scale and in firn processes between the true field situation, firn modeling, and laboratory measurements, the results follow a similar overall pattern but do not align; our results constitute a lower bound on diffusive transport. In comparing our measurements of both diffusivity and permeability to previous parameterizations from numerical 3-D lattice-Boltzmann modeling, it is evident that the previous relationships to porosity are likely site-specific. We present parameterizations relating diffusivity and permeability to porosity as a possible tool, though use of direct measurements would be far more accurate when feasible. The relationships between gas transport properties and microstructural properties are characterized and compared to existing relationships for general porous media, specifically the Katz–Thompson (KT), Kozeny–Carman (KC), and Archie's law approximations. While those approximations can capture the general trend of gas transport relationships, they result in high errors for individual samples and fail to fully describe firn variability, particularly the differences between coarse- and fine-grained firn. We present a direct power law relationship between permeability and gas diffusivity based on our co-located measurements; further research will indicate if this type of relationship is site-specific. This set of measurements and relationships contributes a unique starting point for future investigations in developing more physically based models of firn gas transport.

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Horizontal ice flow impacts the firn structure of Greenland's percolation zone

The Cryosphere ◽

10.5194/tc-14-1703-2020 ◽

2020 ◽

Vol 14 (5) ◽

pp. 1703-1712 ◽

Cited By ~ 1

Author(s):

Rosemary Leone ◽

Joel Harper ◽

Toby Meierbachtol ◽

Neil Humphrey

Keyword(s):

Pore Space ◽

Ice Core ◽

Heat Content ◽

Greenland Ice Sheet ◽

Ice Flow ◽

One Dimensional ◽

Climate Gradients ◽

Horizontal Advection ◽

The Impact ◽

Percolation Zone

Abstract. One-dimensional simulations of firn evolution neglect horizontal advection from ice flow, which transports the firn column across climate gradients as it is buried by accumulation. Using a suite of model runs, we demonstrate the impacts of horizontal advection on the development of firn density, temperature, and the stratigraphy of melt features through the Greenland ice sheet percolation zone. The simulations isolate processes in synthetic runs and investigate four specific transects and an ice core site. Relative to one-dimensional simulations, the horizontal advection process tends to increase the pore close-off depth, reduce the heat content, and decrease the frequency of melt features with depth by emplacing firn sourced from higher locations under increasingly warm and melt-affected surface conditions. Preservation of the advected pore space and cold content is strongly dependent upon the depth of meltwater infiltration. Horizontal ice flow interacts with topography, climate gradients, and meltwater infiltration to influence the evolution of the firn column structure; the interaction between these variables modulates the impact of horizontal advection on firn at locations around Greenland. Pore close-off and firn temperature are mainly impacted in the lowermost 20–30 km of the percolation zone, which may be relevant to migration of the lower percolation zone. Relatively high in the percolation zone, however, the stratigraphy of melt features can have an advection-derived component that should not be conflated with changing climate.

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Atmospheric composition 1 million years ago from blue ice in the Allan Hills, Antarctica

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1420232112 ◽

2015 ◽

Vol 112 (22) ◽

pp. 6887-6891 ◽

Cited By ~ 56

Author(s):

John A. Higgins ◽

Andrei V. Kurbatov ◽

Nicole E. Spaulding ◽

Ed Brook ◽

Douglas S. Introne ◽

...

Keyword(s):

Ice Core ◽

Ice Cores ◽

Atmospheric Composition ◽

Glacial Period ◽

Climate Cycles ◽

Direct Measurements ◽

Ice Core Record

Here, we present direct measurements of atmospheric composition and Antarctic climate from the mid-Pleistocene (∼1 Ma) from ice cores drilled in the Allan Hills blue ice area, Antarctica. The 1-Ma ice is dated from the deficit in 40Ar relative to the modern atmosphere and is present as a stratigraphically disturbed 12-m section at the base of a 126-m ice core. The 1-Ma ice appears to represent most of the amplitude of contemporaneous climate cycles and CO2 and CH4 concentrations in the ice range from 221 to 277 ppm and 411 to 569 parts per billion (ppb), respectively. These concentrations, together with measured δD of the ice, are at the warm end of the field for glacial–interglacial cycles of the last 800 ky and span only about one-half of the range. The highest CO2 values in the 1-Ma ice fall within the range of interglacial values of the last 400 ka but are up to 7 ppm higher than any interglacial values between 450 and 800 ka. The lowest CO2 values are 30 ppm higher than during any glacial period between 450 and 800 ka. This study shows that the coupling of Antarctic temperature and atmospheric CO2 extended into the mid-Pleistocene and demonstrates the feasibility of discontinuously extending the current ice core record beyond 800 ka by shallow coring in Antarctic blue ice areas.

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Gas Transport Parameters in the Vadose Zone: Gas Diffusivity in Field and Lysimeter Soil Profiles

Vadose Zone Journal ◽

10.2136/vzj2006.0014 ◽

2006 ◽

Vol 5 (4) ◽

pp. 1194-1204 ◽

Cited By ~ 32

Author(s):

Ken Kawamoto ◽

Per Moldrup ◽

Per Schjønning ◽

Bo V. Iversen ◽

Dennis E. Rolston ◽

...

Keyword(s):

Vadose Zone ◽

Gas Transport ◽

Soil Profiles ◽

Transport Parameters ◽

Gas Diffusivity

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Review of the relationship between aggregates geology and Los Angeles and micro-Deval tests

Bulletin of Engineering Geology and the Environment ◽

10.1007/s10064-020-02097-y ◽

2021 ◽

Vol 80 (3) ◽

pp. 1963-1980

Author(s):

Solomon Adomako ◽

Christian John Engelsen ◽

Rein Terje Thorstensen ◽

Diego Maria Barbieri

Keyword(s):

Los Angeles ◽

Crystal Size ◽

Grain Shape ◽

Mechanical Performance ◽

Pore Space ◽

Construction Material ◽

Engineering Properties ◽

Coarse Grained ◽

The Impact ◽

The Relationship

AbstractRock aggregates constitute the enormous volume of inert construction material used around the globe. The petrologic description as igneous, sedimentary, and metamorphic types establishes the intrinsic formation pattern of the parent rock. The engineering properties of these rocks vary due to the differences in the transformation process (e.g. hydrothermal deposits) and weathering effect. The two most common mechanical tests used to investigate the performance of aggregates are the Los Angeles (LA) and micro-Deval (MD) tests. This study reviewed the geological parameters (including mineralogy, grain and crystal size, grain shape, and porosity) and the relationship to Los Angeles and micro-Deval tests. It was found that high content of primary minerals in rocks (e.g. quartz and feldspar) is a significant parameter for performance evaluation. Traces of secondary and accessory minerals also affect the performance of rocks, although in many cases it is based on the percentage. Furthermore, some studies showed that the effect of mineralogic composition on mechanical strength is not sufficient to draw final conclusions of mechanical performance; therefore, the impact of other textural characteristics should be considered. The disposition of grain size and crystal size (e.g. as result of lithification) showed that rocks composed of fine-grain textural composition of ≤ 1 mm enhanced fragmentation and wear resistance than medium and coarse grained (≥ 1 mm). The effect of grain shape was based on convex and concave shapes and flat and elongated apexes of tested samples. The equidimensional form descriptor of rocks somehow improved resistance to impact from LA than highly flat and elongated particles. Lastly, the distribution of pore space investigated by means of the saturation method mostly showed moderate (R = 0.50) to strong (R = 0.90) and positive correlations to LA and MD tests.

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Using Satellite Data for CBRN (Chemical, Biological, Radiological, and Nuclear) Threat Detection, Monitoring, and Modelling

Surveys in Geophysics ◽

10.1007/s10712-021-09637-5 ◽

2021 ◽

Author(s):

Gary Sutlieff ◽

Lucy Berthoud ◽

Mark Stinchcombe

Keyword(s):

Satellite Data ◽

Meteorological Data ◽

Atmospheric Composition ◽

Chemical Detection ◽

List Type ◽

Data Types ◽

Wide Range ◽

Future Technologies ◽

The Impact ◽

Near Future

Abstract CBRN (Chemical, Biological, Radiological, and Nuclear) threats are becoming more prevalent, as more entities gain access to modern weapons and industrial technologies and chemicals. This has produced a need for improvements to modelling, detection, and monitoring of these events. While there are currently no dedicated satellites for CBRN purposes, there are a wide range of possibilities for satellite data to contribute to this field, from atmospheric composition and chemical detection to cloud cover, land mapping, and surface property measurements. This study looks at currently available satellite data, including meteorological data such as wind and cloud profiles, surface properties like temperature and humidity, chemical detection, and sounding. Results of this survey revealed several gaps in the available data, particularly concerning biological and radiological detection. The results also suggest that publicly available satellite data largely does not meet the requirements of spatial resolution, coverage, and latency that CBRN detection requires, outside of providing terrain use and building height data for constructing models. Lastly, the study evaluates upcoming instruments, platforms, and satellite technologies to gauge the impact these developments will have in the near future. Improvements in spatial and temporal resolution as well as latency are already becoming possible, and new instruments will fill in the gaps in detection by imaging a wider range of chemicals and other agents and by collecting new data types. This study shows that with developments coming within the next decade, satellites should begin to provide valuable augmentations to CBRN event detection and monitoring. Article Highlights There is a wide range of existing satellite data in fields that are of interest to CBRN detection and monitoring. The data is mostly of insufficient quality (resolution or latency) for the demanding requirements of CBRN modelling for incident control. Future technologies and platforms will improve resolution and latency, making satellite data more viable in the CBRN management field

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Characterization of Gas Transport Properties of Compacted Solid Waste Materials

Environments ◽

10.3390/environments8040026 ◽

2021 ◽

Vol 8 (4) ◽

pp. 26

Author(s):

Muhammad Rashid Iqbal ◽

Hiniduma Liyanage Damith Nandika ◽

Yugo Isobe ◽

Ken Kawamoto

Keyword(s):

Hydraulic Conductivity ◽

Solid Waste ◽

Gas Transport ◽

Bottom Ash ◽

Gas Diffusion ◽

Saturated Hydraulic Conductivity ◽

Dry Density ◽

Transport Parameters ◽

Functional Relations ◽

Mixed Waste

Gas transport parameters such as gas diffusivity (Dp/D0), air permeability (ka), and their dependency on void space (air-filled porosity, ε) in a waste body govern convective air and gas diffusion at solid waste dumpsites and surface emission of various gases generated by microbial processes under aerobic and anaerobic decompositions. In this study, Dp/D0(ε) and ka(ε) were measured on dumping solid waste in Japan such as incinerated bottom ash and unburnable mixed waste as well as a buried waste sample (dumped for 20 years). Sieved samples with variable adjusted moistures were compacted by a standard proctor method and used for a series of laboratory tests for measuring compressibility, saturated hydraulic conductivity, and gas transport parameters. Results showed that incinerated bottom ash and unburnable mixed waste did not give the maximum dry density and optimum moisture content. Measured compressibility and saturated hydraulic conductivity of tested samples varied widely depending on the types of materials. Based on the previously proposed Dp/D0(ε) models, the diffusion-based tortuosity (T) was analyzed and unique power functional relations were found in T(ε) and could contribute to evaluating the gas diffusion process in the waste body compacted at different moisture conditions.

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