| 1. |
- Hunkeler, Priska A., et al.
(författare)
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A glimpse beneath Antarctic sea ice : Platelet layer volume from multifrequency electromagnetic induction sounding
- 2016
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:1, s. 222-231
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Tidskriftsartikel (refereegranskat)abstract
- In Antarctica, ice crystals emerge from ice-shelf cavities and accumulate in unconsolidated layers beneath nearby sea ice. Such sub-ice platelet layers form a unique habitat, and serve as an indicator for the state of an ice shelf. However, the lack of a suitable methodology impedes an efficient quantification of this phenomenon on scales beyond point measurements. In this study, we inverted multi-frequency electromagnetic (EM) induction soundings of > 100 km length, obtained on fast ice with an underlying platelet layer in the eastern Weddell Sea. EM-derived platelet-layer thickness and conductivity are consistent with other field observations. Our results further suggest that platelet-layer volume is higher than previously thought in this region, and that platelet-layer ice-volume fraction is proportional to its thickness. We conclude that multi-frequency EM is a suitable tool to determine platelet-layer volume, with the potential to obtain crucial knowledge of associated processes in otherwise inaccessible ice-shelf cavities.
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| 2. |
- Hunkeler, Priska A., et al.
(författare)
-
Improved 1D inversions for sea ice thickness and conductivity from electromagnetic induction data : Inclusion of nonlinearities caused by passive bucking
- 2016
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Ingår i: Geophysics. - 0016-8033 .- 1942-2156. ; 81:1, s. WA45-WA58
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Tidskriftsartikel (refereegranskat)abstract
- The porosity of sea ice is a fundamental physical parameter that governs the mechanical strength of sea ice and the mobility of gases and nutrients for biological processes and biogeochemical cycles in the sea ice layer. However, little is known about the spatial distribution of the sea ice porosity and its variability between different sea ice types; an efficient and nondestructive method to measure this property is currently missing. Sea ice porosity is linked to the bulk electrical conductivity of sea ice, a parameter routinely used to discriminate between sea ice and seawater by electromagnetic (EM) induction sensors. Here, we have evaluated the prospect of porosity retrieval of sea ice by means of bulk conductivity estimates using 1D multi-frequency EM inversion schemes. We have focused on two inversion algorithms, a smoothness-constrained inversion and a Marquardt-Levenberg inversion, which we modified for the nonlinear signal bias caused by a passive bucking coil operated in such a highly conductive environment. Using synthetic modeling studies, 1D inversion algorithms and multiple frequencies, we found that we can resolve the sea ice conductivity within +/- 0.01 S/m. Using standard assumptions for the conductivity-porosity relation of sea ice, we were able to estimate porosity with an uncertainty of +/- 1.2%, which enables efficient and nondestructive surveys of the internal state of the sea ice cover.
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