Water content estimates of a first-year sea-ice pressure ridge keel from surface-nuclear magnetic resonance tomography

Abstract

The porosity of a sea-ice pressure ridge keel is an important but poorly known variable, relevant for determining the mass budget and evolution of the Arctic sea-ice cover. Determination of keel porosity from drillholes is time-intensive and only yields limited information because of their limited lateral extent. Since the porosity within a keel equals its liquid water content, surface-nuclear magnetic resonance (surface-NMR) methods can be used to estimate porosity within such features. Surface-NMR tomography measurements were made in April 2011 using seven surface coil positions across a first-year pressure ridge on landfast sea ice near Barrow, Alaska, USA. The inversion results indicate water contents of 30 ± 7% and 40 ±10% in the ridge’s shallow and deep parts, respectively. These values are much higher than those obtained from drillholes, which are ∼10% and ∼27%, respectively. In contrast to drilling, surface-NMR tomography yields average porosity values for the entire subsurface volume. However, the inversion process is sensitive to the electrical conductivity distribution; uncertain conductivity estimates limit the reliability of the inverted water contents. Nevertheless, the results suggest that ridge porosities obtained from invasive measurements such as drilling may lead to substantially overestimated sea-ice volume.

Landfast sea ice breakouts: Stabilizing ice features, oceanic and atmospheric forcing at Barrow, Alaska

“…Directly related to the ridge keel geometry is the porosity of the ridge keel. In 774 this study, we assumed a porosity of 0.3, also taken from Nuber et al (2013). Figure 775 11 displays the strength of the ridge keels' frictional coupling to the sea floor for the 776 grounded ridges in February 2009 and March 2010 for different ridge keel 777 porosities.…”

“…In order to determine the cross-sectional size of a ridge created through 381 convergence, we need to know the parent ice sheet thickness and the fraction of the 382 ridge volume occupied by voids. Taking a keel porosity of 0.3 (Nuber et al, 2013), 383 the sail porosity would be 0.22 according to 384…”

A Variational Method for Sea Ice Ridging in Earth System Models

“…Nuclear magnetic resonance tomography indicates that the macroporosity between keel blocks can exceed 40% (Nuber et al, 2013), as do sectional and incisional ridge surveys (Bowen & Topham, 1996;Høyland, 2007). These measurements typically yield a lower bulk macroporosity for entire ridges of between ∼20% and 30% due to refreezing between blocks near the waterline, otherwise known as ridge consolidation (Johnston & Barker, 2000;Leppäranta & Hakala, 1992;Strub-Klein & Sudom, 2012;Timco & Burden, 1997); R often exceeds the bulk microporosity, , of first-year ridge blocks caused by brine and air pockets within their crystal structure, where typically ranges between ∼2% and 12% in mildly frigid to near-melting conditions (Kovacs, 1997;Pringle et al, 2009).…”

Torus-nuclear magnetic resonance: Quasicontinuous airborne magnetic resonance profiling by using a helium-filled balloon

“…Many recent and past studies have shown the beneficial usage of surface nuclear magnetic resonance (NMR) for various hydrogeological issues, such as characterization of aquifers in sedimentary (Legchenko et al, 2004;Mohnke and Yaramanci, 2008;Vouillamoz et al, 2008) and fractured rocks (Baltassat et al, 2005;Vouillamoz et al, 2005), in karst (Vouillamoz et al, 2003) and thermokarst environments (Parsekian et al, 2013), identification and characterization of freshwater resources within saltwater environments (Guenther and Müller-Petke, 2012;Vouillamoz et al, 2012;Siemon et al, 2015), melting glaciers (Lehmann-Horn et al, 2012;Legchenko et al, 2014), or arctic sea ice thickness (Nuber et al, 2013). Moreover, the ongoing technical and methodological improvement of the surface NMR method opens new and expands existing application fields.…”