ORCID Profile
0000-0002-8501-8730
Current Organisations
University of Leeds
,
University of Tasmania
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Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-12078
Abstract: & & Antarctic ice flow shows deviation from the deformation regimes of pure and simple shear. By analysing the vorticity number from surface velocity data it is found that approximately 80% of the flow is outside these regimes. These deformations are both between pure and simple shear, as well as highly rotational, highlighting the need for fabric predictions away from the commonly studied regimes of pure and simple shear.& & / & & & We use the numerical scheme SpecCAF, which has been shown to accurately reproduce experimentally observed fabrics with no free parameters, to study ice fabrics in such general deformations. By exploring the parameter space of temperature and vorticity number, we present a definitive classification of fabrics patterns which arise, and construct a universal regime diagram for ice fabrics under general two-dimensional deformation. We find that intermediate deformations see a smooth transition between a cone-shape fabric and a secondary cluster. We present the first investigation of the fabrics produced in highly rotational deformations, which produce a weak girdle fabric with the axis aligned to the vorticity axis. We also show that across deformation and temperature space fabrics only reach a true steady-state above strains of 200%, and there is significant variation in this across the parameter space. & & / &
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-3743
Abstract: & & Accurately predicting ice crystal fabrics is key to understanding the processes and deformation in ice-sheets. Here we use SpecCAF, a continuum fabric evolution model validated against laboratory experiments, to predict the fabric evolution with an active ice stream. This is done by predicting the fabrics at the East Greenland Ice core Project (EGRIP) site. We do this using satellite data and inferred particle paths, combined with the shallow ice approximation (with basal slip) to infer a leading order approximation for the deformation through the ice sheet. We find that SpecCAF is able to predict the patterns observed at EGRIP - a girdle/horizontal maxima fabric perpendicular to the flow direction. By reducing the rate of rotational recrystallization in the model we are also able to predict the fabric strength at EGRIP. This suggests the effect of rotational recrystallization on the fabric may be primarily strain-rate/stress dependent. These results show SpecCAF can be applied to real-world conditions and provide insights into the deformation and basal-conditions of the ice sheet. As the model only considers deformation and recrystallization through dislocation creep, the results imply that - for the ice stream modelled - no other process is significantly influencing both the produced ice fabric and the deformation. We find that the model gives best results for full slip at the base of the ice sheet, implying that the level of sliding at the base of the ice sheet in the North Greenland Ice stream may be very high. The methodology used here can be extended to other ice core locations in Greenland and Antarctica.& &
Publisher: Copernicus GmbH
Date: 28-10-2022
Abstract: Abstract. Ice fabrics – the distribution of crystal orientations in a polycrystal – are key for understanding and predicting ice flow dynamics. Despite their importance, the characteristics and evolution of fabrics produced outside of the deformation regimes of pure and simple shear flow has largely been neglected, yet they are a common occurrence within ice sheets. Here, we use a recently developed numerical model (SpecCAF) to classify all fabrics produced over a continuous spectrum of incompressible two-dimensional deformation regimes and temperatures. The model has been shown to accurately predict ice fabrics produced in experiments, where the ice has been deformed in either uniaxial compression or simple shear. Here we use the model to reveal fabrics produced in regimes intermediate to pure and simple shear, as well as those that are more rotational than simple shear. We find that intermediate deformation regimes between pure and simple shear result in a smooth transition between a fabric characterised by a girdle and a secondary cluster pattern. Highly rotational deformation regimes are revealed to produce a weak girdle fabric. Furthermore, we provide regime diagrams to help constrain deformation conditions of measured ice fabrics. We also obtain predictions for the strain scales over which fabric evolution takes place at any given temperature. The use of our model in large-scale ice flow models and for interpreting fabrics observed in ice cores and seismic anisotropy provides new tools supporting the community in predicting and interpreting ice flow in a changing climate.
Publisher: Copernicus GmbH
Date: 26-04-2021
DOI: 10.5194/TC-2021-118
Abstract: Abstract. Ice fabrics are key for understanding and predicting ice flow dynamics. Despite its importance, the characteristics and evolution of ice fabrics beyond pure and simple shear flow has largely been neglected. However, 80 % of the flow of ice in Antarctica is outside the regimes of pure and simple shear. We use a new validated numerical model (SpecCAF), which has been shown to accurately reproduce experimentally observed fabrics in both compression and simple shear, to explore the fabrics produced between pure and simple shear, as well as those that are highly rotational. We present a definitive classification of all fabric patterns. We find that intermediate deformations between pure and simple shear result in a smooth transition between a fabric characterised by a cone-shape and a secondary cluster pattern. Highly-rotational fabrics are found to produce a weak girdle fabric. In addition we obtain complete predictions for the strain required for any fabric under a 2D deformation to reach steady state at any given temperature. Use of our data in current ice flow models as well as for ice core fabric and seismic anisotropy interpretation will enhance the communities' ability to predict future ice flow in a changing climate.
Publisher: Elsevier BV
Date: 09-2019
DOI: 10.1016/J.AJO.2019.03.027
Abstract: We aimed to externally validate the performance of new screening criteria for retinopathy of prematurity (ROP) developed in the Postnatal Growth and Retinopathy of Prematurity (G-ROP) study among a Japanese cohort. Validation of screening criteria. We reviewed premature infants screened for ROP between September 2009 and May 2017 at a single institution. The G-ROP criteria, except hydrocephalus, were applied as a prediction model for infants with both a known outcome of ROP and serial measurements of weight gain. We assessed sensitivity and specificity for treatment-requiring ROP, and reduction in the number of infants who receive ROP screening and in the number of retinal examinations. Of 692 premature infants screened for ROP, 537 had information of ROP outcome and weight gain. In this cohort, 81 infants required treatment for ROP in 218 infants, ROP regressed spontaneously and 238 infants did not develop any ROP. The G-ROP model reached a sensitivity of 100% (95% confidence interval [CI], 95.4%-100%) and specificity of 28.9% (95% CI, 24.9%-33.2%). No infants required any treatment for ROP before the date of risk determination. The number of infants requiring screening and the number of examinations would have been reduced by 24.5% and 12.9%, respectively. This is the first validation study of the G-ROP criteria in a developed country other than North America. The criteria demonstrated high sensitivity in this Japanese cohort, even though the criterion of hydrocephalus was excluded.
Publisher: Elsevier BV
Date: 02-2021
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Daniel Richards.