Magnetic anisotropy and debris-dependent rheological heterogeneity within stratified basal ice

Hopkins, Nathan R.; Evenson, Edward B.; Bilardello, Dario; Alley, Richard B.; Berti, Claudio; Kodama, Kenneth P.

doi:10.1017/jog.2019.51

Cited by 6 publications

(4 citation statements)

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“…8), which suggests that cumulative strain was unevenly distributed and probably varied time‐transgressively as the till accreted, or that there was deformation partitioning at the microscale. In general, differences in strain may result from variations in till rheology caused by different clay contents or particle sorting (Underhill and Woodcock, 1987; Hopkins et al, 2019), or porewater pressure variations that would affect the style of deformation (van der Meer et al, 2003; Piotrowski et al, 2006; Menzies et al, 2016; Phillips et al, 2018; Narloch et al, 2020). The different orientations of microshears may also result from rotation of the stress field (Ahlgren, 2001; Shipton and Cowie, 2001) but this is typically associated with pebble‐ or boulder‐sized clasts.…”

Section: Discussionmentioning

confidence: 99%

Till kinematics in the Stargard drumlin field, NW Poland constrained by microstructural proxies

Hermanowski

Piotrowski

Duda

2020

J Quaternary Science

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Deciphering the relationships between streamlined subglacial landforms and deposits therein helps to constrain the dynamics of past ice sheets. Here we present microstructural analyses of till from the largest drumlin field in the North European Lowland generated by a major palaeo-ice stream of the Scandinavian Ice Sheet. Data derived from thin sections and X-ray microtomography (μCT) reveal multiple microstructures including microshears, circular structures, grain stacks and crushed grains. Long axes of micro-clasts measured in thin sections are directionally clustered and have low, down-ice-oriented dip angles. Some samples reveal subordinate clustering oriented at high angles to the main direction. The μCT data show low clustering strengths of clasts and no systematic fabric pattern in the entire set of samples. There is no correspondence between the clast orientations and the directions of drumlin long axes, suggesting that the till is antecedent in relation to the drumlin-shaping process. The observations indicate spatially and temporally variable, shallow-seated brittle and ductile deformation controlled by porewater pressure fluctuations and generated time-transgressively parallel to till accretion. Consistently with previous studies, the data suggest that the Stargard drumlins are erosional remnants of a pre-existing terrain shaped by material removal from the inter-drumlin areas.

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Section: Discussionmentioning

confidence: 99%

Till kinematics in the Stargard drumlin field, NW Poland constrained by microstructural proxies

Hermanowski

Piotrowski

Duda

2020

J Quaternary Science

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“…Goldsby and Kohlstedt, 2001) to describe the rheological effects of debris particles in ice are broadly consistent with the conceptual framework developed by Moore (2014) in an attempt to explain the, at times, paradoxical field observations and laboratory measurements of the constitutive properties of debris-laden ice. Field measurements often indicate that the presence of debris can weaken ice (enhancing the flow rate), in contrast to the strengthening implied by most laboratory experiments (as reviewed in detail by Moore, 2014; see also Hopkins et al, 2019). Moore (2014) identified three main components of this framework: (1) in the “dirty ice” regime (i.e.…”

Section: Contextualizing Debris-covered Ice On Mars With Debris-cmentioning

confidence: 98%

Contextualizing lobate debris aprons and glacier-like forms on Mars with debris-covered glaciers on Earth

Koutnik

Pathare

2021

Progress in Physical Geography: Earth and Environment

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Debris-covered glaciers from around the world offer distinct environmental, climatic, and historical conditions from which to study the effects of debris on glacier-ice evolution. A rich literature on debris-covered glaciers exists from decades of field work, laboratory studies, remote-sensing observations, and numerical modeling. In general, the base of knowledge established by studying periglacial, glacial, and paraglacial landforms on Earth has been applied to aid interpretation of ice-rich or ice-remnant landforms on Mars, but research has progressed on both planets. For Mars, the spatial distribution of lobate debris aprons and glacier-like forms, in particular, is critical to constraining past climate conditions when such features were active, reconstructing past ice extent, and estimating the total inventory of buried ice remaining in the mid-latitudes of Mars. This review spans a range of knowledge about debris-covered glaciers on Earth, in order to add context to investigations of dust and debris-covered ice on Mars and to put research on both planets in a perspective aimed at maximizing process-based understanding of glacier evolution. The state of knowledge and some gaps in knowledge on Mars are discussed in relation to possible avenues for future research in how landforms are classified, advances in comparative planetology, and new understanding from future missions. While this review is focused primarily on processes controlling active debris-covered glaciers, a key to understanding glacier change through time is to consider individual landforms in context with the full-system environment in which they are found. For Earth, this includes understanding local and regional controls on current glacier change, and how these processes relate to landform development in the past as well as what may develop in the future. For Mars, this includes evaluating how present-day landforms elucidate past ice activity and environmental conditions during epochs when orbital parameters, climate, and water ice distribution were substantially different.

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“…b Number of microbial genomes estimated using 2.5 fg of DNA per genome. cHopkins et al (2019). n.d.: no data.…”

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confidence: 99%

Variation in bacterial composition, diversity, and activity across different subglacial basal ice types

Doyle

Christner

2022

Preprint

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Abstract. Glaciers and ice sheets possess layers of basal ice characterized by high amounts of entrained debris that can serve as sources of nutrients and organic matter, providing habitat for microorganisms adapted to the frozen conditions. Basal ice forms through various mechanisms and is classified based on its ice and debris content; however, little is known about variation in microbial composition, diversity, and activity across different basal ice types. We investigated these parameters in four different types of basal ice from a cold-based and temperate glacier and used a meta-analysis to compare our findings with microbiome studies from other frozen environments. We found basal ice environments harbor a diverse range of microbiomes whose composition and activity can vary significantly between basal ice types, even within adjacent facies from the same glacier. In some debris-rich basal ices, elevated ATP concentrations, isotopic gas signatures, and high ratios of amplified sequences for 16S rRNA relative to that for 16S rRNA genes implicated certain bacterial taxa (e.g., Paenisporosarcina, Desulfocapsa, Syntrophus, Desulfosporosinus) as being potentially active, with ice temperature appearing to be an important predictor for the diversity of taxa inferred to be active. Compared to those of other sympagic environments, these microbiomes often resembled those found in permafrost or perennial cave ice rather than other glacial ice environments. In contrast, debris-poor basal ices harbored microbiomes more like those found in oligotrophic englacial ice. Collectively, these results suggest that different basal ice types contain distinct microbiomes that are actively structured by the diagenesis of their habitat.

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Magnetic anisotropy and debris-dependent rheological heterogeneity within stratified basal ice

Cited by 6 publications

References 68 publications

Till kinematics in the Stargard drumlin field, NW Poland constrained by microstructural proxies

Till kinematics in the Stargard drumlin field, NW Poland constrained by microstructural proxies

Contextualizing lobate debris aprons and glacier-like forms on Mars with debris-covered glaciers on Earth

Variation in bacterial composition, diversity, and activity across different subglacial basal ice types

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