English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The physical structure of polar firn plays a key role in the mechanisms bywhich glaciers and ice sheets preserve a natural archive of past atmosphericcomposition. This study presents the first measurements of gas diffusivityand permeability along with microstructural information measured from thenear-surface firn through the firn column to pore close-off. Both fine- andcoarse-grained firn from Summit, Greenland are included in this study toinvestigate the variability in firn caused by seasonal and storm-eventlayering. Our measurements reveal that the porosity of firn (derived fromdensity) is insufficient to describe the full profiles of diffusivity andpermeability, particularly at porosity values above 0.5. Thus, even a modelthat could perfectly predict the density profile would be insufficient forapplication to issues involving gas transport. The measured diffusivityprofile presented here is compared to two diffusivity profiles modeled fromfirn air measurements from Summit. Because of differences in scale and infirn processes between the true field situation, firn modeling, andlaboratory measurements, the results follow a similar overall pattern but donot align; our results constitute a lower bound on diffusive transport. Incomparing our measurements of both diffusivity and permeability to previousparameterizations from numerical 3-D lattice-Boltzmann modeling, it isevident that the previous relationships to porosity are likely site-specific.We present parameterizations relating diffusivity and permeability toporosity as a possible tool, though use of direct measurements would be farmore accurate when feasible. The relationships between gas transportproperties and microstructural properties are characterized and compared toexisting relationships for general porous media, specifically theKatz–Thompson (KT), Kozeny–Carman (KC), and Archie's law approximations.While those approximations can capture the general trend of gas transportrelationships, they result in high errors for individual samples and fail tofully describe firn variability, particularly the differences between coarse-and fine-grained firn. We present a direct power law relationship betweenpermeability 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 startingpoint for future investigations in developing more physically based models offirn gas transport

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