Correction to the Dynamic Tensile Strength of Ice and Ice-Silicate Mixtures (Lange & Ahrens 1983)

NASA Astrophysics Data System (ADS)

Stewart, S. T.; Ahrens, T. J.

1999-03-01

We present a correction to the Weibull parameters for ice and ice-silicate mixtures (Lange & Ahrens 1983). These parameters relate the dynamic tensile strength to the strain rate. These data are useful for continuum fracture models of ice.

Role of ice sheet dynamics in the collapse of the early-Holocene Laurentide Ice Sheet

NASA Astrophysics Data System (ADS)

Matero, I. S. O.; Gregoire, L. J.; Cornford, S. L.; Ivanovic, R. F.

2017-12-01

The last stage of the deglaciation of the Laurentide Ice Sheet (LIS) during the early Holocene Thermal Maximum ( 9000 to 7000 years ago) provides an analogy and insight to the possible responses of contemporary ice sheets in a warming climate. What makes LIS particularly interesting is that meltwater from the collapse of an ice saddle over Hudson Bay was recently shown to be the primary forcing for the period of abrupt northern hemisphere cooling known as the 8.2 ka event. The evolution of the LIS during this period was likely influenced by its interaction with marginal lakes and the ocean, and its major ice stream, which exported ice towards Hudson Strait. Accurately simulating the early Holocene LIS evolution thus requires a model such as BISICLES, capable of accurately and efficiently resolving ice stream dynamics and grounding line migration thanks to the combined use of higher order physics and adaptive mesh refinement. We drive the BISICLES model using a positive degree day mass balance scheme with monthly precipitation and temperature from the HadCM3 climate model under climatic conditions from 10,000 to 8,000 years ago. We test the effect of varying the initial topographies and ice thicknesses from different timeslices in the ICE-6Gc reconstruction. We also test different parameterisations for the basal friction based on the thicknesses of the underlying sediments. These simulations evaluate the role of the Hudson Strait ice stream, ice sheet dynamics and interactions with the adjacent proglacial Lake Agassiz and North Atlantic Ocean in the collapse of the LIS. Our results highlight that the choice of parameterisation for basal friction has major effects on ice sheet dynamics and evolution.

Gypsum and hydrohalite dynamics in sea ice brines

NASA Astrophysics Data System (ADS)

Butler, Benjamin M.; Papadimitriou, Stathys; Day, Sarah J.; Kennedy, Hilary

2017-09-01

Mineral authigenesis from their dissolved sea salt matrix is an emergent feature of sea ice brines, fuelled by dramatic equilibrium solubility changes in the large sub-zero temperature range of this cryospheric system on the surface of high latitude oceans. The multi-electrolyte composition of seawater results in the potential for several minerals to precipitate in sea ice, each affecting the in-situ geochemical properties of the sea ice brine system, the habitat of sympagic biota. The solubility of two of these minerals, gypsum (CaSO4 ·2H2O) and hydrohalite (NaCl · 2H2O), was investigated in high ionic strength multi-electrolyte solutions at below-zero temperatures to examine their dissolution-precipitation dynamics in the sea ice brine system. The gypsum dynamics in sea ice were found to be highly dependent on the solubilities of mirabilite and hydrohalite between 0.2 and - 25.0 ° C. The hydrohalite solubility between - 14.3 and - 25.0 ° C exhibits a sharp change between undersaturated and supersaturated conditions, and, thus, distinct temperature fields of precipitation and dissolution in sea ice, with saturation occurring at - 22.9 ° C. The sharp changes in hydrohalite solubility at temperatures ⩽-22.9 °C result from the formation of an ice-hydrohalite aggregate, which alters the structural properties of brine inclusions in cold sea ice. Favourable conditions for gypsum precipitation in sea ice were determined to occur in the region of hydrohalite precipitation below - 22.9 ° C and in conditions of metastable mirabilite supersaturation above - 22.9 ° C (investigated at - 7.1 and - 8.2 ° C here) but gypsum is unlikely to persist once mirabilite forms at these warmer (>-22.9 °C) temperatures. The dynamics of hydrohalite in sea ice brines based on its experimental solubility were consistent with that derived from thermodynamic modelling (FREZCHEM code) but the gypsum dynamics derived from the code were inconsistent with that indicated by its

Molecular Dynamics at the Interface between Ice and Poly(vinyl alcohol) and Ice Recrystallization Inhibition.

PubMed

Weng, Lindong; Stott, Shannon L; Toner, Mehmet

2018-05-01

Ice formation is a ubiquitous process that poses serious challenges for many areas. Nature has evolved a variety of different mechanisms to regulate ice formation. For example, many cold-adapted species produce antifreeze proteins (AFPs) and/or antifreeze glycoproteins (AFGPs) to inhibit ice recrystallization. Although several synthetic substitutes for AF(G)Ps have been developed, the fundamental principles of designing AF(G)P mimics are still missing. In this study, we explored the molecular dynamics of ice recrystallization inhibition (IRI) by poly(vinyl alcohol) (PVA), a well-recognized ice recrystallization inhibitor, to shed light on the otherwise hidden ice-binding mechanisms of chain polymers. Our molecular dynamics simulations revealed a stereoscopic, geometrical match between the hydroxyl groups of PVA and the water molecules of ice, and provided microscopic evidence of the adsorption of PVA to both the basal and prism faces of ice and the incorporation of short-chain PVA into the ice lattice. The length of PVA, i.e., the number of hydroxyl groups, seems to be a key factor dictating the performance of IRI, as the PVA molecule must be large enough to prevent the joining together of adjacent curvatures in the ice front. The findings in this study will help pave the path for addressing a pressing challenge in designing synthetic ice recrystallization inhibitors rationally, by enriching our mechanistic understanding of IRI process by macromolecules.

Dynamics of Topological Excitations in a Model Quantum Spin Ice

NASA Astrophysics Data System (ADS)

Huang, Chun-Jiong; Deng, Youjin; Wan, Yuan; Meng, Zi Yang

2018-04-01

We study the quantum spin dynamics of a frustrated X X Z model on a pyrochlore lattice by using large-scale quantum Monte Carlo simulation and stochastic analytic continuation. In the low-temperature quantum spin ice regime, we observe signatures of coherent photon and spinon excitations in the dynamic spin structure factor. As the temperature rises to the classical spin ice regime, the photon disappears from the dynamic spin structure factor, whereas the dynamics of the spinon remain coherent in a broad temperature window. Our results provide experimentally relevant, quantitative information for the ongoing pursuit of quantum spin ice materials.

Proton dynamics and the phase diagram of dense water ice.

PubMed

Hernandez, J-A; Caracas, R

2018-06-07

All the different phases of water ice between 2 GPa and several megabars are based on a single body-centered cubic sub-lattice of oxygen atoms. They differ only by the behavior of the hydrogen atoms. In this study, we investigate the dynamics of the H atoms at high pressures and temperatures in water ice from first-principles molecular dynamics simulations. We provide a detailed analysis of the O-H⋯O bonding dynamics over the entire stability domain of the body-centered cubic (bcc) water ices and compute transport properties and vibrational density-of-states. We report the first ab initio evidence for a plastic phase of water and we propose a coherent phase diagram for bcc water ices compatible with the two groups of melting curves and with the multiple anomalies reported in ice VII around 15 GPa.

Implications of fractured Arctic perennial ice cover on thermodynamic and dynamic sea ice processes

NASA Astrophysics Data System (ADS)

Asplin, Matthew G.; Scharien, Randall; Else, Brent; Howell, Stephen; Barber, David G.; Papakyriakou, Tim; Prinsenberg, Simon

2014-04-01

Decline of the Arctic summer minimum sea ice extent is characterized by large expanses of open water in the Siberian, Laptev, Chukchi, and Beaufort Seas, and introduces large fetch distances in the Arctic Ocean. Long waves can propagate deep into the pack ice, thereby causing flexural swell and failure of the sea ice. This process shifts the floe size diameter distribution smaller, increases floe surface area, and thereby affects sea ice dynamic and thermodynamic processes. The results of Radarsat-2 imagery analysis show that a flexural fracture event which occurred in the Beaufort Sea region on 6 September 2009 affected ˜40,000 km2. Open water fractional area in the area affected initially decreased from 3.7% to 2.7%, but later increased to ˜20% following wind-forced divergence of the ice pack. Energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed-layer of the ocean following flexural fracture. 11.54 MJ m-2 of additional energy for lateral melting of ice floes was identified in affected areas. The impact of this process in future Arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season, and is discussed in context with ocean heat fluxes, atmospheric mixing of the ocean mixed layer, and declining sea ice cover. We conclude that this process is an important positive feedback to Arctic sea ice loss, and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes.

Astronomical Ice: The Effects of Treating Ice as a Porous Media on the Dynamics and Evolution of Extraterrestrial Ice-Ocean Environments

NASA Astrophysics Data System (ADS)

Buffo, J.; Schmidt, B. E.

2015-12-01

With the prevalence of water and ice rich environments in the solar system, and likely the universe, becoming more apparent, understanding the evolutionary dynamics and physical processes of such locales is of great importance. Piqued interest arises from the understanding that the persistence of all known life depends on the presence of liquid water. As in situ investigation is currently infeasible, accurate numerical modeling is the best technique to demystify these environments. We will discuss an evolving model of ice-ocean interaction aimed at realistically describing the behavior of the ice-ocean interface by treating basal ice as a porous media, and its possible implications on the formation of astrobiological niches. Treating ice as a porous media drastically affects the thermodynamic properties it exhibits. Thus inclusion of this phenomenon is critical in accurately representing the dynamics and evolution of all ice-ocean environments. This model utilizes equations that describe the dynamics of sea ice when it is treated as a porous media (Hunke et. al. 2011), coupled with a basal melt and accretion model (Holland and Jenkins 1999). Combined, these two models produce the most accurate description of the processes occurring at the base of terrestrial sea ice and ice shelves, capable of resolving variations within the ice due to environmental pressures. While these models were designed for application to terrestrial environments, the physics occurring at any ice-water interface is identical, and these models can be used to represent the evolution of a variety of icy astronomical bodies. As terrestrial ice shelves provide a close analog to planetary ice-ocean environments, we truth test the models validity against observations of ice shelves. We apply this model to the ice-ocean interface of the icy Galilean moon Europa. We include profiles of temperature, salinity, solid fraction, and Darcy velocity, as well as temporally and spatially varying melt and

Dynamic Ice-Water Interactions Form Europa's Chaos Terrains

NASA Astrophysics Data System (ADS)

Blankenship, D. D.; Schmidt, B. E.; Patterson, G. W.; Schenk, P.

2011-12-01

Unique to the surface of Europa, chaos terrain is diagnostic of the properties and dynamics of its icy shell. We present a new model that suggests large melt lenses form within the shell and that water-ice interactions above and within these lenses drive the production of chaos. This model is consistent with key observations of chaos, predicts observables for future missions, and indicates that the surface is likely still active today[1]. We apply lessons from ice-water interaction in the terrestrial cryosphere to hypothesize a dynamic lense-collapse model to for Europa's chaos terrain. Chaos terrain morphology, like that of Conamara chaos and Thera Macula, suggests a four-phase formation [1]: 1) Surface deflection occurs as ice melts over ascending thermal plumes, as regularly occurs on Earth as subglacial volcanoes activate. The same process can occur at Europa if thermal plumes cause pressure melt as they cross ice-impurity eutectics. 2) Resulting hydraulic gradients and driving forces produce a sealed, pressurized melt lense, akin to the hydraulic sealing of subglacial caldera lakes. On Europa, the water cannot escape the lense due to the horizontally continuous ice shell. 3) Extension of the brittle ice lid above the lense opens cracks, allowing for the ice to be hydrofractured by pressurized water. Fracture, brine injection and percolation within the ice and possible iceberg toppling produces ice-melange-like granular matrix material. 4) Refreezing of the melt lense and brine-filled pores and cracks within the matrix results in raised chaos. Brine soaking and injection concentrates the ice in brines and adds water volume to the shell. As this englacial water freezes, the now water-filled ice will expand, not unlike the process of forming pingos and other "expansion ice" phenomena on Earth. The refreezing can raise the surface and create the oft-observed matrix "domes" In this presentation, we describe how catastrophic ice-water interactions on Earth have

A surface ice module for wind turbine dynamic response simulation using FAST

DOE PAGES

Yu, Bingbin; Karr, Dale G.; Song, Huimin; ...

2016-06-03

It is a fact that developing offshore wind energy has become more and more serious worldwide in recent years. Many of the promising offshore wind farm locations are in cold regions that may have ice cover during wintertime. The challenge of possible ice loads on offshore wind turbines raises the demand of modeling capacity of dynamic wind turbine response under the joint action of ice, wind, wave, and current. The simulation software FAST is an open source computer-aided engineering (CAE) package maintained by the National Renewable Energy Laboratory. In this paper, a new module of FAST for assessing the dynamicmore » response of offshore wind turbines subjected to ice forcing is presented. In the ice module, several models are presented which involve both prescribed forcing and coupled response. For conditions in which the ice forcing is essentially decoupled from the structural response, ice forces are established from existing models for brittle and ductile ice failure. For conditions in which the ice failure and the structural response are coupled, such as lock-in conditions, a rate-dependent ice model is described, which is developed in conjunction with a new modularization framework for FAST. In this paper, analytical ice mechanics models are presented that incorporate ice floe forcing, deformation, and failure. For lower speeds, forces slowly build until the ice strength is reached and ice fails resulting in a quasi-static condition. For intermediate speeds, the ice failure can be coupled with the structural response and resulting in coinciding periods of the ice failure and the structural response. A third regime occurs at high speeds of encounter in which brittle fracturing of the ice feature occurs in a random pattern, which results in a random vibration excitation of the structure. An example wind turbine response is simulated under ice loading of each of the presented models. This module adds to FAST the capabilities for analyzing the response of wind

Discharge of New Subglacial Lake on Whillians Ice Stream: Implication for Ice Stream Flow Dynamics.

NASA Astrophysics Data System (ADS)

Sergienko, O. V.; Fricker, H. A.; Bindschadler, R. A.; Vornberger, P. L.; Macayeal, D. R.

2006-12-01

One of the surprise discoveries made possible by the ICESat laser altimeter mission of 2004-2006 is the presence of a large subglacial lake below the grounding zone of Whillians Ice Stream (dubbed here `Lake Helen' after the discoverer, Helen Fricker). What is even more surprising is the fact that this lake discharged a substantial portion of its volume during the ICESat mission, and changes in lake volume and surface elevation of the ice stream are documented in exquisite detail [Fricker et al., in press]. The presence and apparent dynamism of large subglacial lakes in the grounding zone of a major ice stream raises questions about their effects on ice-stream dynamics. Being liquid and movable, water modifies basal friction spatially and temporally. Melting due to shear heating and geothermal flux reduces basal traction, making the ice stream move fast. However, when water collects in a depression to form a lake, it potentially deprives the surrounding bed of lubricating water, and additionally makes the ice surface flat, thereby locally decreasing the ice stream driving stress. We study the effect of formation and discharge of a subglacial lake at the mouth of and ice stream using a two dimensional, vertically integrated, ice-stream model. The model is forced by the basal friction, ice thickness and surface elevation. The basal friction is obtained by inversion of the ice surface velocity, ice thickness and surface elevation come from observations. To simulate the lake formation we introduce zero basal friction and "inflate" the basal elevation of the ice stream at the site of the lake. Sensitivity studies of the response of the surrounding ice stream and ice shelf flow are performed to delineate the influence of near-grounding-line subglacial water storage for ice streams in general.

Investigation of vapor-deposited amorphous ice and irradiated ice by molecular dynamics simulation.

PubMed

Guillot, Bertrand; Guissani, Yves

2004-03-01

With the purpose of clarifying a number of points raised in the experimental literature, we investigate by molecular dynamics simulation the thermodynamics, the structure and the vibrational properties of vapor-deposited amorphous ice (ASW) as well as the phase transformations experienced by crystalline and vitreous ice under ion bombardment. Concerning ASW, we have shown that by changing the conditions of the deposition process, it is possible to form either a nonmicroporous amorphous deposit whose density (approximately 1.0 g/cm3) is essentially invariant with the temperature of deposition, or a microporous sample whose density varies drastically upon temperature annealing. We find that ASW is energetically different from glassy water except at the glass transition temperature and above. Moreover, the molecular dynamics simulation shows no evidence for the formation of a high-density phase when depositing water molecules at very low temperature. In order to model the processing of interstellar ices by cosmic ray protons and heavy ions coming from the magnetospheric radiation environment around the giant planets, we bombarded samples of vitreous ice and cubic ice with 35 eV water molecules. After irradiation the recovered samples were found to be densified, the lower the temperature, the higher the density of the recovered sample. The analysis of the structure and vibrational properties of this new high-density phase of amorphous ice shows a close relationship with those of high-density amorphous ice obtained by pressure-induced amorphization. Copyright 2004 American Institute of Physics

A dynamical-systems approach for computing ice-affected streamflow

USGS Publications Warehouse

Holtschlag, David J.

1996-01-01

A dynamical-systems approach was developed and evaluated for computing ice-affected streamflow. The approach provides for dynamic simulation and parameter estimation of site-specific equations relating ice effects to routinely measured environmental variables. Comparison indicates that results from the dynamical-systems approach ranked higher than results from 11 analytical methods previously investigated on the basis of accuracy and feasibility criteria. Additional research will likely lead to further improvements in the approach.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

NASA Astrophysics Data System (ADS)

Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

2010-08-01

We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated dynamic calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of streams in this new 3-D marine ice sheet model.

SPH Modelling of Sea-ice Pack Dynamics

NASA Astrophysics Data System (ADS)

Staroszczyk, Ryszard

2017-12-01

The paper is concerned with the problem of sea-ice pack motion and deformation under the action of wind and water currents. Differential equations describing the dynamics of ice, with its very distinct mateFfigrial responses in converging and diverging flows, express the mass and linear momentum balances on the horizontal plane (the free surface of the ocean). These equations are solved by the fully Lagrangian method of smoothed particle hydrodynamics (SPH). Assuming that the ice behaviour can be approximated by a non-linearly viscous rheology, the proposed SPH model has been used to simulate the evolution of a sea-ice pack driven by wind drag stresses. The results of numerical simulations illustrate the evolution of an ice pack, including variations in ice thickness and ice area fraction in space and time. The effects of different initial ice pack configurations and of different conditions assumed at the coast-ice interface are examined. In particular, the SPH model is applied to a pack flow driven by a vortex wind to demonstrate how well the Lagrangian formulation can capture large deformations and displacements of sea ice.

Ice formation on kaolinite: Insights from molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Sosso, Gabriele C.; Tribello, Gareth A.; Zen, Andrea; Pedevilla, Philipp; Michaelides, Angelos

2016-12-01

The formation of ice affects many aspects of our everyday life as well as important technologies such as cryotherapy and cryopreservation. Foreign substances almost always aid water freezing through heterogeneous ice nucleation, but the molecular details of this process remain largely unknown. In fact, insight into the microscopic mechanism of ice formation on different substrates is difficult to obtain even if state-of-the-art experimental techniques are used. At the same time, atomistic simulations of heterogeneous ice nucleation frequently face extraordinary challenges due to the complexity of the water-substrate interaction and the long time scales that characterize nucleation events. Here, we have investigated several aspects of molecular dynamics simulations of heterogeneous ice nucleation considering as a prototypical ice nucleating material the clay mineral kaolinite, which is of relevance in atmospheric science. We show via seeded molecular dynamics simulations that ice nucleation on the hydroxylated (001) face of kaolinite proceeds exclusively via the formation of the hexagonal ice polytype. The critical nucleus size is two times smaller than that obtained for homogeneous nucleation at the same supercooling. Previous findings suggested that the flexibility of the kaolinite surface can alter the time scale for ice nucleation within molecular dynamics simulations. However, we here demonstrate that equally flexible (or non flexible) kaolinite surfaces can lead to very different outcomes in terms of ice formation, according to whether or not the surface relaxation of the clay is taken into account. We show that very small structural changes upon relaxation dramatically alter the ability of kaolinite to provide a template for the formation of a hexagonal overlayer of water molecules at the water-kaolinite interface, and that this relaxation therefore determines the nucleation ability of this mineral.

Inferring Ice Thickness from a Glacier Dynamics Model and Multiple Surface Datasets.

NASA Astrophysics Data System (ADS)

Guan, Y.; Haran, M.; Pollard, D.

2017-12-01

The future behavior of the West Antarctic Ice Sheet (WAIS) may have a major impact on future climate. For instance, ice sheet melt may contribute significantly to global sea level rise. Understanding the current state of WAIS is therefore of great interest. WAIS is drained by fast-flowing glaciers which are major contributors to ice loss. Hence, understanding the stability and dynamics of glaciers is critical for predicting the future of the ice sheet. Glacier dynamics are driven by the interplay between the topography, temperature and basal conditions beneath the ice. A glacier dynamics model describes the interactions between these processes. We develop a hierarchical Bayesian model that integrates multiple ice sheet surface data sets with a glacier dynamics model. Our approach allows us to (1) infer important parameters describing the glacier dynamics, (2) learn about ice sheet thickness, and (3) account for errors in the observations and the model. Because we have relatively dense and accurate ice thickness data from the Thwaites Glacier in West Antarctica, we use these data to validate the proposed approach. The long-term goal of this work is to have a general model that may be used to study multiple glaciers in the Antarctic.

The land-ice contribution to 21st-century dynamic sea level rise

NASA Astrophysics Data System (ADS)

Howard, T.; Ridley, J.; Pardaens, A. K.; Hurkmans, R. T. W. L.; Payne, A. J.; Giesen, R. H.; Lowe, J. A.; Bamber, J. L.; Edwards, T. L.; Oerlemans, J.

2014-06-01

Climate change has the potential to influence global mean sea level through a number of processes including (but not limited to) thermal expansion of the oceans and enhanced land ice melt. In addition to their contribution to global mean sea level change, these two processes (among others) lead to local departures from the global mean sea level change, through a number of mechanisms including the effect on spatial variations in the change of water density and transport, usually termed dynamic sea level changes. In this study, we focus on the component of dynamic sea level change that might be given by additional freshwater inflow to the ocean under scenarios of 21st-century land-based ice melt. We present regional patterns of dynamic sea level change given by a global-coupled atmosphere-ocean climate model forced by spatially and temporally varying projected ice-melt fluxes from three sources: the Antarctic ice sheet, the Greenland Ice Sheet and small glaciers and ice caps. The largest ice melt flux we consider is equivalent to almost 0.7 m of global mean sea level rise over the 21st century. The temporal evolution of the dynamic sea level changes, in the presence of considerable variations in the ice melt flux, is also analysed. We find that the dynamic sea level change associated with the ice melt is small, with the largest changes occurring in the North Atlantic amounting to 3 cm above the global mean rise. Furthermore, the dynamic sea level change associated with the ice melt is similar regardless of whether the simulated ice fluxes are applied to a simulation with fixed CO2 or under a business-as-usual greenhouse gas warming scenario of increasing CO2.

Simulating Ice Dynamics in the Amundsen Sea Sector

NASA Astrophysics Data System (ADS)

Schwans, E.; Parizek, B. R.; Morlighem, M.; Alley, R. B.; Pollard, D.; Walker, R. T.; Lin, P.; St-Laurent, P.; LaBirt, T.; Seroussi, H. L.

2017-12-01

Thwaites and Pine Island Glaciers (TG; PIG) exhibit patterns of dynamic retreat forced from their floating margins, and could act as gateways for destabilization of deep marine basins in the West Antarctic Ice Sheet (WAIS). Poorly constrained basal conditions can cause model predictions to diverge. Thus, there is a need for efficient simulations that account for shearing within the ice column, and include adequate basal sliding and ice-shelf melting parameterizations. To this end, UCI/NASA JPL's Ice Sheet System Model (ISSM) with coupled SSA/higher-order physics is used in the Amundsen Sea Embayment (ASE) to examine threshold behavior of TG and PIG, highlighting areas particularly vulnerable to retreat from oceanic warming and ice-shelf removal. These moving-front experiments will aid in targeting critical areas for additional data collection in ASE as well as for weighting accuracy in further melt parameterization development. Furthermore, a sub-shelf melt parameterization, resulting from Regional Ocean Modeling System (ROMS; St-Laurent et al., 2015) and coupled ISSM-Massachusetts Institute of Technology general circulation model (MITgcm; Seroussi et al., 2017) output, is incorporated and initially tested in ISSM. Data-guided experiments include variable basal conditions and ice hardness, and are also forced with constant modern climate in ISSM, providing valuable insight into i) effects of different basal friction parameterizations on ice dynamics, illustrating the importance of constraining the variable bed character beneath TG and PIG; ii) the impact of including vertical shear in ice flow models of outlet glaciers, confirming its role in capturing complex feedbacks proximal to the grounding zone; and iii) ASE's sensitivity to sub-shelf melt and ice-front retreat, possible thresholds, and how these affect ice-flow evolution.

Rapid replacement of bridge deck expansion joints study - phase I.

DOT National Transportation Integrated Search

2014-12-01

Bridge deck expansion joints are used to allow for movement of the bridge deck due to thermal expansion, dynamics loading, and : other factors. More recently, expansion joints have also been utilized to prevent the passage of winter de-icing chemical...

Dynamical mechanism of antifreeze proteins to prevent ice growth

NASA Astrophysics Data System (ADS)

Kutschan, B.; Morawetz, K.; Thoms, S.

2014-08-01

The fascinating ability of algae, insects, and fishes to survive at temperatures below normal freezing is realized by antifreeze proteins (AFPs). These are surface-active molecules and interact with the diffusive water-ice interface thus preventing complete solidification. We propose a dynamical mechanism on how these proteins inhibit the freezing of water. We apply a Ginzburg-Landau-type approach to describe the phase separation in the two-component system (ice, AFP). The free-energy density involves two fields: one for the ice phase with a low AFP concentration and one for liquid water with a high AFP concentration. The time evolution of the ice reveals microstructures resulting from phase separation in the presence of AFPs. We observed a faster clustering of pre-ice structure connected to a locking of grain size by the action of AFP, which is an essentially dynamical process. The adsorption of additional water molecules is inhibited and the further growth of ice grains stopped. The interfacial energy between ice and water is lowered allowing the AFPs to form smaller critical ice nuclei. Similar to a hysteresis in magnetic materials we observe a thermodynamic hysteresis leading to a nonlinear density dependence of the freezing point depression in agreement with the experiments.

A Model of Icebergs and Sea Ice in a Joint Continuum Framework

NASA Astrophysics Data System (ADS)

VaÅková, Irena; Holland, David M.

2017-11-01

The ice mélange, a mixture of sea ice and icebergs, often present in front of outlet glaciers in Greenland or ice shelves in Antarctica, can have a profound effect on the dynamics of the ice-ocean system. The current inability to numerically model the ice mélange motivates a new modeling approach proposed here. A continuum sea-ice model is taken as a starting point and icebergs are represented as thick and compact pieces of sea ice held together by large tensile and shear strength, selectively introduced into the sea-ice rheology. In order to modify the rheology correctly, an iceberg tracking procedure is implemented within a semi-Lagrangian time-stepping scheme, designed to exactly preserve iceberg shape through time. With the proposed treatment, sea ice and icebergs are considered a single fluid with spatially varying rheological properties. Mutual interactions are thus automatically included without the need for further parametrization. An important advantage of the presented framework for an ice mélange model is its potential to be easily included within sea-ice components of existing climate models.

Temporal dynamics of ikaite in experimental sea ice

NASA Astrophysics Data System (ADS)

Rysgaard, S.; Wang, F.; Galley, R. J.; Grimm, R.; Notz, D.; Lemes, M.; Geilfus, N.-X.; Chaulk, A.; Hare, A. A.; Crabeck, O.; Else, B. G. T.; Campbell, K.; Sørensen, L. L.; Sievers, J.; Papakyriakou, T.

2014-08-01

Ikaite (CaCO3 · 6H2O) is a metastable phase of calcium carbonate that normally forms in a cold environment and/or under high pressure. Recently, ikaite crystals have been found in sea ice, and it has been suggested that their precipitation may play an important role in air-sea CO2 exchange in ice-covered seas. Little is known, however, of the spatial and temporal dynamics of ikaite in sea ice. Here we present evidence for highly dynamic ikaite precipitation and dissolution in sea ice grown at an outdoor pool of the Sea-ice Environmental Research Facility (SERF) in Manitoba, Canada. During the experiment, ikaite precipitated in sea ice when temperatures were below -4 °C, creating three distinct zones of ikaite concentrations: (1) a millimeter-to-centimeter-thin surface layer containing frost flowers and brine skim with bulk ikaite concentrations of >2000 μmol kg-1, (2) an internal layer with ikaite concentrations of 200-400 μmol kg-1, and (3) a bottom layer with ikaite concentrations of <100 μmol kg-1. Snowfall events caused the sea ice to warm and ikaite crystals to dissolve. Manual removal of the snow cover allowed the sea ice to cool and brine salinities to increase, resulting in rapid ikaite precipitation. The observed ikaite concentrations were on the same order of magnitude as modeled by FREZCHEM, which further supports the notion that ikaite concentration in sea ice increases with decreasing temperature. Thus, varying snow conditions may play a key role in ikaite precipitation and dissolution in sea ice. This could have a major implication for CO2 exchange with the atmosphere and ocean that has not been accounted for previously.

Airborne Geophysics and Remote Sensing Applied to Study Greenland Ice Dynamics

NASA Technical Reports Server (NTRS)

Csatho, Beata M.

2003-01-01

Overview of project: we combined and jointly analysed geophysical, remote sensing and glaciological data for investigating the temporal changes in ice flow and the role of geologic control on glacial drainage. The project included two different studies, the investigation of recent changes of the Kangerlussuaq glacier and the study of geologic control of ice flow in NW Greenland, around the Humboldt, Petermann and Ryder glaciers.

A model of icebergs and sea ice in a joint continuum framework

NASA Astrophysics Data System (ADS)

Vaňková, Irena; Holland, David M.

2017-04-01

The ice mélange, a mixture of sea ice and icebergs, often present in front of tidewater glaciers in Greenland or ice shelves in Antarctica, can have a profound effect on the dynamics of the ice-ocean system. The current inability to numerically model the ice mélange motivates a new modeling approach proposed here. A continuum sea-ice model is taken as a starting point and icebergs are represented as thick and compact pieces of sea ice held together by large tensile and shear strength selectively introduced into the sea ice rheology. In order to modify the rheology correctly, a semi-Lagrangian time stepping scheme is introduced and at each time step a Lagrangian grid is constructed such that iceberg shape is preserved exactly. With the proposed treatment, sea ice and icebergs are considered a single fluid with spatially varying rheological properties, mutual interactions are thus automatically included without the need of further parametrization. An important advantage of the presented framework for an ice mélange model is its potential to be easily included in existing climate models.

Dynamic Inland Propagation of Thinning Due to Ice Loss at the Margins of the Greenland Ice Sheet

NASA Technical Reports Server (NTRS)

Wang, Wei Li; Li, Jun J.; Zwally, H. Jay

2012-01-01

Mass-balance analysis of the Greenland ice sheet based on surface elevation changes observed by the European Remote-sensing Satellite (ERS) (1992-2002) and Ice, Cloud and land Elevation Satellite (ICESat) (2003-07) indicates that the strongly increased mass loss at lower elevations (<2000 m) of the ice sheet, as observed during 2003-07, appears to induce interior ice thinning at higher elevations. In this paper, we perform a perturbation experiment with a three-dimensional anisotropic ice-flow model (AIF model) to investigate this upstream propagation. Observed thinning rates in the regions below 2000m elevation are used as perturbation inputs. The model runs with perturbation for 10 years show that the extensive mass loss at the ice-sheet margins does in fact cause interior thinning on short timescales (i.e. decadal). The modeled pattern of thinning over the ice sheet agrees with the observations, which implies that the strong mass loss since the early 2000s at low elevations has had a dynamic impact on the entire ice sheet. The modeling results also suggest that even if the large mass loss at the margins stopped, the interior ice sheet would continue thinning for 300 years and would take thousands of years for full dynamic recovery.

High latitude changes in ice dynamics and their impact on polar marine ecosystems.

PubMed

Moline, Mark A; Karnovsky, Nina J; Brown, Zachary; Divoky, George J; Frazer, Thomas K; Jacoby, Charles A; Torres, Joseph J; Fraser, William R

2008-01-01

Polar regions have experienced significant warming in recent decades. Warming has been most pronounced across the Arctic Ocean Basin and along the Antarctic Peninsula, with significant decreases in the extent and seasonal duration of sea ice. Rapid retreat of glaciers and disintegration of ice sheets have also been documented. The rate of warming is increasing and is predicted to continue well into the current century, with continued impacts on ice dynamics. Climate-mediated changes in ice dynamics are a concern as ice serves as primary habitat for marine organisms central to the food webs of these regions. Changes in the timing and extent of sea ice impose temporal asynchronies and spatial separations between energy requirements and food availability for many higher trophic levels. These mismatches lead to decreased reproductive success, lower abundances, and changes in distribution. In addition to these direct impacts of ice loss, climate-induced changes also facilitate indirect effects through changes in hydrography, which include introduction of species from lower latitudes and altered assemblages of primary producers. Here, we review recent changes and trends in ice dynamics and the responses of marine ecosystems. Specifically, we provide examples of ice-dependent organisms and associated species from the Arctic and Antarctic to illustrate the impacts of the temporal and spatial changes in ice dynamics.

Interior ice/mineral/water interface dynamics (Invited)

NASA Astrophysics Data System (ADS)

Rempel, A. W.

2009-12-01

The search for life begins with the search for liquid water. In our solar system, persistent water reservoirs are invariably found together with ice. On Earth, organisms have evolved to thrive at sub-zero temperatures in ice-bound habitats that have numerous analogues throughout our solar system and beyond. To assess the potential for life requires a thorough investigation of the dynamic interactions within these deposits. Well-established thermodynamic principles govern the stable coexistence of premelted liquid at the interface between ice and other minerals. Foreign constituents are efficiently rejected from the ice crystal lattice and are concentrated in residual liquid regions instead. This gains added importance with the recognition that the most fundamental requirements for survival include a food source and the removal of waste. This talk reviews the astrobiological implications of the availability, behavior, and properties of liquid water in association with the interiors of icy bodies and ice-mineral interfacial regions.

Convection Models for Ice-Water System: Dynamical Investigation of Phase Transition

NASA Astrophysics Data System (ADS)

Allu Peddinti, D.; McNamara, A. K.

2012-12-01

Ever since planetary missions of Voyager and Galileo revealed a dynamically altered surface of the icy moon Europa, a possible subsurface ocean under an icy shell has been speculated and surface features have been interpreted from an interior dynamics perspective. The physics of convection in a two phase water-ice system is governed by a wide set of physical parameters that include melting viscosity of ice, the variation of viscosity due to pressure and temperature, temperature contrast across and tidal heating within the system, and the evolving thickness of each layer. Due to the extreme viscosity contrast between liquid water and solid ice, it is not feasible to model the entire system to study convection. However, using a low-viscosity proxy (higher viscosity than the liquid water but much lower than solid ice) for the liquid phase provides a convenient approximation of the system, and allows for a relatively realistic representation of convection within the ice layer while also providing a self-consistent ice layer thickness that is a function of the thermal state of the system. In order to apply this method appropriately, we carefully examine the upper bound of viscosity required for the low-viscosity proxy to adequately represent the liquid phase. We identify upper bounds on the viscosity of the proxy liquid such that convective dynamics of the ice are not affected by further reductions of viscosity. Furthermore, we investigate how the temperature contrast across the system and viscosity contrast between liquid and ice control ice layer thickness. We also investigate ice shell thickening as a function of cooling, particularly how viscosity affects the conduction-to-convection transition within the ice shell. Finally, we present initial results that investigate the effects that latent heat of fusion (due to the ice-water phase transition) has on ice convection.

The dynamics of climate-induced deglacial ice stream acceleration

NASA Astrophysics Data System (ADS)

Robel, A.; Tziperman, E.

2015-12-01

Geological observations indicate that ice streams were a significant contributor to ice flow in the Laurentide Ice Sheet during the Last Glacial Maximum. Conceptual and simple model studies have also argued that the gradual development of ice streams increases the sensitivity of large ice sheets to weak climate forcing. In this study, we use an idealized configuration of the Parallel Ice Sheet Model to explore the role of ice streams in rapid deglaciation. In a growing ice sheet, ice streams develop gradually as the bed warms and the margin expands outward onto the continental shelf. Then, a weak change in equilibrium line altitude commensurate with Milankovitch forcing results in a rapid deglacial response, as ice stream acceleration leads to enhanced calving and surface melting at low elevations. We explain the dynamical mechanism that drives this ice stream acceleration and its broader applicability as a feedback for enhancing ice sheet decay in response to climate forcing. We show how our idealized ice sheet simulations match geomorphological observations of deglacial ice stream variability and previous model-data analyses. We conclude with observations on the potential for interaction between ice streams and other feedback mechanisms within the earth system.

Last Glacial-Interglacial Transition ice dynamics in the Wicklow Mountains, Ireland

NASA Astrophysics Data System (ADS)

Knight, Lauren; Boston, Clare; Lovell, Harold; Pepin, Nick

2017-04-01

Understanding of the extent and dynamics of former ice masses in the Wicklow Mountains, Ireland, during the Last Glacial-Interglacial Transition (LGIT; 15-10 ka BP) is currently unresolved. Whilst it is acknowledged that the region hosted a local ice cap within the larger British-Irish Ice Sheet at the Last Glacial Maximum (LGM; 27 ka BP), there has been little consideration of ice cap disintegration to a topographically constrained ice mass during the LGIT. This research has produced the first regional glacial geomorphological map, through remote sensing (aerial photograph and digital terrain model interrogation) and field mapping. This has allowed both the style and extent of mountain glaciation and ice recession dynamics during the LGIT to be established. This geomorphological mapping has highlighted that evidence for local glaciation in the Wicklow Mountains is more extensive than previously recognised, and that small icefields and associated outlet valley glaciers existed during the LGIT following disintegration of the Wicklow Ice Cap. A relative chronology based on morphostratigraphic principles is developed, which indicates complex patterns of ice mass oscillation characterised by periods of both sustained retreat and minor readvance. Variations in the pattern of recession across the Wicklow Mountains are evident and appear to be influenced, in part, by topographic controls (e.g. slope, aspect, glacier hypsometry). In summary, this research establishes a relative chronology of glacial events in the region during the LGIT and presents constraints on ice mass extent, dynamics and retreat patterns, offering an insight into small ice mass behaviour in a warming climate.

A Newly Updated Database of Elevation-changes of the Greenand Ice Sheet to Study Surface Processes and Ice Dynamics

NASA Astrophysics Data System (ADS)

Schenk, A. F.; Csatho, B. M.; van den Broeke, M.; Kuipers Munneke, P.

2015-12-01

This paper reports about important upgrades of the Greenland Ice Sheet (GrIS) surface elevation and elevation-change database obtained with our Surface Elevation And Change detection (SERAC) software suite. We have developed SERAC to derive information from laser altimetry data, particularly time series of elevation changes and their partitioning into changes caused by ice dynamics. This allows direct investigation of ice dynamic processes that is much needed for improving the predictive power of ice sheet models. SERAC is different from most other change detection methods. It is based on detecting changes of surface patches, about 1 km by 1 km in size, rather than deriving elevation changes from individual laser points. The current database consists of ~100,000 time series with satellite laser altimetry data from ICESat, airborne laser observations obtained by NASA's Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS). The upgrade is significant, because not only new observations from 2013 and 2014 have been added but also a number of improvements lead to a more comprehensive and consistent record of elevation-changes. First, we used the model that gives in addition to ice sheet also information about ice caps and glaciers (Rastner et al., 2012) for deciding if a laser point is on the ice sheet or ice cap. Then we added small gaps that exist in the ICESat GLA12 data set because the ice sheet mask is not wide enough. The new database is now more complete and will facilitate more accurate comparisons of mass balance studies obtained from the Gravity Recovery and Climate Experiment system (GRACE). For determining the part of a time series caused by ice dynamics we used the new firn compaction model and Surface Mass Balance (SMB) estimates from RACMO2.3. The new database spans the time period from 1993 to 2014. Adding new observations amounts to a spatial densification of the old record and at the same time extends the time domain by two

Ice-shelf Dynamics Near the Front of Filchner-Ronne Ice Shelf, Antarctica, Revealed by SAR Interferometry

NASA Technical Reports Server (NTRS)

Rignot, E.; MacAyeal, D. R.

1998-01-01

Fifteen synthetic-aperture radar (SAR) images of the Ronne Ice Shelf, Antarctica, obtained by the European Space Agency (ESA)'s Earth Remote Sensing satellites (ERS) 1 & 2 are used to study ice-shelf dynamics near two ends of the iceberg-calving front.

Impact of ice-shelf sediment content on the dynamics of plumes under melting ice shelves

NASA Astrophysics Data System (ADS)

Wells, A.

2015-12-01

When a floating ice shelf melts into an underlying warm salty ocean, the resulting fresh meltwater can rise in a buoyant Ice-Shelf-Water plume under the ice. In certain settings, ice flowing across the grounding line carries a basal layer of debris rich ice, entrained via basal freezing around till in the upstream ice sheet. Melting of this debris-laden ice from floating ice shelves provides a flux of dense sediment to the ocean, in addition to the release of fresh buoyant meltwater. This presentation considers the impact of the resulting suspended sediment on the dynamics of ice shelf water plumes, and identifies two key flow regimes depending on the sediment concentration frozen into the basal ice layer. For large sediment concentration, melting of the debris-laden ice shelf generates dense convectively unstable waters that drive convective overturning into the underlying ocean. For lower sediment concentration, the sediment initially remains suspended in a buoyant meltwater plume rising along the underside of the ice shelf, before slowly depositing into the underlying ocean. A theoretical plume model is used to evaluate the significance of the negatively buoyant sediment on circulation strength and the feedbacks on melting rate, along with the expected depositional patterns under the ice shelf.

Estimation of Time-Varying, Intrinsic and Reflex Dynamic Joint Stiffness during Movement. Application to the Ankle Joint

PubMed Central

Guarín, Diego L.; Kearney, Robert E.

2017-01-01

Dynamic joint stiffness determines the relation between joint position and torque, and plays a vital role in the control of posture and movement. Dynamic joint stiffness can be quantified during quasi-stationary conditions using disturbance experiments, where small position perturbations are applied to the joint and the torque response is recorded. Dynamic joint stiffness is composed of intrinsic and reflex mechanisms that act and change together, so that nonlinear, mathematical models and specialized system identification techniques are necessary to estimate their relative contributions to overall joint stiffness. Quasi-stationary experiments have demonstrated that dynamic joint stiffness is heavily modulated by joint position and voluntary torque. Consequently, during movement, when joint position and torque change rapidly, dynamic joint stiffness will be Time-Varying (TV). This paper introduces a new method to quantify the TV intrinsic and reflex components of dynamic joint stiffness during movement. The algorithm combines ensemble and deterministic approaches for estimation of TV systems; and uses a TV, parallel-cascade, nonlinear system identification technique to separate overall dynamic joint stiffness into intrinsic and reflex components from position and torque records. Simulation studies of a stiffness model, whose parameters varied with time as is expected during walking, demonstrated that the new algorithm accurately tracked the changes in dynamic joint stiffness using as little as 40 gait cycles. The method was also used to estimate the intrinsic and reflex dynamic ankle stiffness from an experiment with a healthy subject during which ankle movements were imposed while the subject maintained a constant muscle contraction. The method identified TV stiffness model parameters that predicted the measured torque very well, accounting for more than 95% of its variance. Moreover, both intrinsic and reflex dynamic stiffness were heavily modulated through the

Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets.

PubMed

Pritchard, Hamish D; Arthern, Robert J; Vaughan, David G; Edwards, Laura A

2009-10-15

Many glaciers along the margins of the Greenland and Antarctic ice sheets are accelerating and, for this reason, contribute increasingly to global sea-level rise. Globally, ice losses contribute approximately 1.8 mm yr(-1) (ref. 8), but this could increase if the retreat of ice shelves and tidewater glaciers further enhances the loss of grounded ice or initiates the large-scale collapse of vulnerable parts of the ice sheets. Ice loss as a result of accelerated flow, known as dynamic thinning, is so poorly understood that its potential contribution to sea level over the twenty-first century remains unpredictable. Thinning on the ice-sheet scale has been monitored by using repeat satellite altimetry observations to track small changes in surface elevation, but previous sensors could not resolve most fast-flowing coastal glaciers. Here we report the use of high-resolution ICESat (Ice, Cloud and land Elevation Satellite) laser altimetry to map change along the entire grounded margins of the Greenland and Antarctic ice sheets. To isolate the dynamic signal, we compare rates of elevation change from both fast-flowing and slow-flowing ice with those expected from surface mass-balance fluctuations. We find that dynamic thinning of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic grounding lines, has endured for decades after ice-shelf collapse, penetrates far into the interior of each ice sheet and is spreading as ice shelves thin by ocean-driven melt. In Greenland, glaciers flowing faster than 100 m yr(-1) thinned at an average rate of 0.84 m yr(-1), and in the Amundsen Sea embayment of Antarctica, thinning exceeded 9.0 m yr(-1) for some glaciers. Our results show that the most profound changes in the ice sheets currently result from glacier dynamics at ocean margins.

Effect of knee joint icing on knee extension strength and knee pain early after total knee arthroplasty: a randomized cross-over study.

PubMed

Holm, Bente; Husted, Henrik; Kehlet, Henrik; Bandholm, Thomas

2012-08-01

To investigate the acute effect of knee joint icing on knee extension strength and knee pain in patients shortly after total knee arthroplasty. A prospective, single-blinded, randomized, cross-over study. A fast-track orthopaedic arthroplasty unit at a university hospital. Twenty patients (mean age 66 years; 10 women) scheduled for primary unilateral total knee arthroplasty. The patients were treated on two days (day 7 and day 10) postoperatively. On one day they received 30 minutes of knee icing (active treatment) and on the other day they received 30 minutes of elbow icing (control treatment). The order of treatments was randomized. Maximal knee extension strength (primary outcome), knee pain at rest and knee pain during the maximal knee extensions were measured 2-5 minutes before and 2-5 minutes after both treatments by an assessor blinded for active or control treatment. The change in knee extension strength associated with knee icing was not significantly different from that of elbow icing (knee icing change (mean (1 SD)) -0.01 (0.07) Nm/kg, elbow icing change -0.02 (0.07) Nm/kg, P = 0.493). Likewise, the changes in knee pain at rest (P = 0.475), or knee pain during the knee extension strength measurements (P = 0.422) were not different between treatments. In contrast to observations in experimental knee effusion models and inflamed knee joints, knee joint icing for 30 minutes shortly after total knee arthroplasty had no acute effect on knee extension strength or knee pain.

Melting dynamics of ice in the mesoscopic regime

PubMed Central

Citroni, Margherita; Fanetti, Samuele; Falsini, Naomi; Foggi, Paolo; Bini, Roberto

2017-01-01

How does a crystal melt? How long does it take for melt nuclei to grow? The melting mechanisms have been addressed by several theoretical and experimental works, covering a subnanosecond time window with sample sizes of tens of nanometers and thus suitable to determine the onset of the process but unable to unveil the following dynamics. On the other hand, macroscopic observations of phase transitions, with millisecond or longer time resolution, account for processes occurring at surfaces and time limited by thermal contact with the environment. Here, we fill the gap between these two extremes, investigating the melting of ice in the entire mesoscopic regime. A bulk ice Ih or ice VI sample is homogeneously heated by a picosecond infrared pulse, which delivers all of the energy necessary for complete melting. The evolution of melt/ice interfaces thereafter is monitored by Mie scattering with nanosecond resolution, for all of the time needed for the sample to reequilibrate. The growth of the liquid domains, over distances of micrometers, takes hundreds of nanoseconds, a time orders of magnitude larger than expected from simple H-bond dynamics. PMID:28536197

Towards Quantification of Glacier Dynamic Ice Loss through Passive Seismic Monitoring

NASA Astrophysics Data System (ADS)

Köhler, A.; Nuth, C.; Weidle, C.; Schweitzer, J.; Kohler, J.; Buscaino, G.

2015-12-01

Global glaciers and ice caps loose mass through calving, while existing models are currently not equipped to realistically predict dynamic ice loss. This is mainly because long-term continuous calving records, that would help to better understand fine scale processes and key climatic-dynamic feedbacks between calving, climate, terminus evolution and marine conditions, do not exist. Combined passive seismic/acoustic strategies are the only technique able to capture rapid calving events continuously, independent of daylight or meteorological conditions. We have produced such a continuous calving record for Kronebreen, a tidewater glacier in Svalbard, using data from permanent seismic stations between 2001 and 2014. However, currently no method has been established in cryo-seismology to quantify the calving ice loss directly from seismic data. Independent calibration data is required to derive 1) a realistic estimation of the dynamic ice loss unobserved due to seismic noise and 2) a robust scaling of seismic calving signals to ice volumes. Here, we analyze the seismic calving record at Kronebreen and independent calving data in a first attempt to quantify ice loss directly from seismic records. We make use of a) calving flux data with weekly to monthly resolution obtained from satellite remote sensing and GPS data between 2007 and 2013, and b) direct, visual calving observations in two weeks in 2009 and 2010. Furthermore, the magnitude-scaling property of seismic calving events is analyzed. We derive and discuss an empirical relation between seismic calving events and calving flux which for the first time allows to estimate a time series of calving volumes more than one decade back in time. Improving our model requires to incorporate more precise, high-resolution calibration data. A new field campaign will combine innovative, multi-disciplinary monitoring techniques to measure calving ice volumes and dynamic ice-ocean interactions simultaneously with terrestrial laser

The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

NASA Astrophysics Data System (ADS)

Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

2011-09-01

We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

Ice dynamics of Heinrich events: Insights and implications

NASA Astrophysics Data System (ADS)

Alley, R. B.; Parizek, B. R.; Anandakrishnan, S.

2017-12-01

Physical understanding of ice flow provides important constraints on Heinrich (H) events, which in turn provide lessons for ice dynamics and future sea-level change. Iceberg-rafted debris (IRD), the defining feature of H events, is a complex indicator; however, in cold climates with extensive marine-ending ice, increased IRD flux records ice-shelf loss. Ice shelves fed primarily by inflow from grounded ice experience net basal melting, giving sub-ice-sedimentation rather than open-ocean IRD. Ice-shelf loss has been observed recently in response to atmospheric warming increasing surface meltwater that wedged open crevasses (Larsen B), but also by break-off following thinning from warming of waters reaching the grounding line (Jakobshavn). The H events consistently occurred during cold times resulting from reduced North Atlantic overturning circulation ("conveyor"), but as argued by Marcott et al. (PNAS 2011), this was accompanied by delayed warming at grounding-line depths of the Hudson Strait ice stream, the source of the Heinrich layers, implicating oceanic control. As shown in a rich literature, additional considerations involving thermal state of the ice-stream bed, isostasy and probably other processes influenced why some reduced-conveyor events triggered H-events while others did not. Ice shelves, including the inferred Hudson Strait ice shelf, typically exist in high-salinity, cold waters produced by brine rejection from sea-ice formation, which are the coldest abundant waters in the world ocean. Thus, almost any change in air or ocean temperature, winds or currents can remove ice shelves, because "replacement" water masses are typically warmer. And, because ice shelves almost invariably slow flow of non-floating ice into the ocean, climatic perturbations to regions with ice shelves typically lead to sea-level rise, with important implications.

Unusual dynamic properties of water near the ice-binding plane of hyperactive antifreeze protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuffel, Anna; Czapiewski, Dariusz; Zielkiewicz, Jan, E-mail: jaz@chem.pg.gda.pl

2015-10-07

The dynamical properties of solvation water of hyperactive antifreeze protein from Choristoneura fumiferana (CfAFP) are analyzed and discussed in context of its antifreeze activity. The protein comprises of three well-defined planes and one of them binds to the surface of ice. The dynamical properties of solvation water around each of these planes were analyzed separately; the results are compared with the dynamical properties of solvation water of ice around its two crystallographic planes: basal and prism. Three main conclusions are inferred from our investigations. The first one is that the solvation shell of CfAFP does not seem to be particularlymore » far-ranged, at least not beyond what is usually observed for proteins that do not interact with ice. Therefore, it does not appear to us that the antifreeze activity is enhanced by a long-ranged retardation of water mobility. Also the correlation between the collective mobility of water and the collective mobility of protein atoms highly resembles the one measured for the protein that does not interact with ice. Our second conclusion is that the dynamical properties of solvation water of CfAFP are non-uniform. The dynamics of solvation water of ice-binding plane is, in some respects, different from the dynamics of solvation water of the two remaining planes. The feature that distinguishes the dynamics of solvation water of the three planes is the activation energy of diffusion process. The third conclusion is that—from the three analyzed solvation shells of CfAFP—the dynamical properties of solvation water of the ice-binding plane resemble the most the properties of solvation water of ice; note, however, that these properties still clearly differ from the dynamic properties of solvation water of ice.« less

Sensitivity study of a dynamic thermodynamic sea ice model

NASA Astrophysics Data System (ADS)

Holland, David M.; Mysak, Lawrence A.; Manak, Davinder K.; Oberhuber, Josef M.

1993-02-01

A numerical simulation of the seasonal sea ice cover in the Arctic Ocean and the Greenland, Iceland, and Norwegian seas is presented. The sea ice model is extracted from Oberhuber's (1990) coupled sea ice-mixed layer-isopycnal general circulation model and is written in spherical coordinates. The advantage of such a model over previous sea ice models is that it can be easily coupled to either global atmospheric or ocean general circulation models written in spherical coordinates. In this model, the thermodynamics are a modification of that of Parkinson and Washington (1979), while the dynamics use the full Hibler (1979) viscous-plastic rheology. Monthly thermodynamic and dynamic forcing fields for the atmosphere and ocean are specified. The simulations of the seasonal cycle of ice thickness, compactness, and velocity, for a control set of parameters, compare favorably with the known seasonal characteristics of these fields. A sensitivity study of the control simulation of the seasonal sea ice cover is presented. The sensitivity runs are carried out under three different themes, namely, numerical conditions, parameter values, and physical processes. This last theme refers to experiments in which physical processes are either newly added or completely removed from the model. Approximately 80 sensitivity runs have been performed in which a change from the control run environment has been implemented. Comparisons have been made between the control run and a particular sensitivity run based on time series of the seasonal cycle of the domain-averaged ice thickness, compactness, areal coverage, and kinetic energy. In addition, spatially varying fields of ice thickness, compactness, velocity, and surface temperature for each season are presented for selected experiments. A brief description and discussion of the more interesting experiments are presented. The simulation of the seasonal cycle of Arctic sea ice cover is shown to be robust.

Time-dependence of sea-ice concentration and multiyear ice fraction in the Arctic Basin

USGS Publications Warehouse

Gloersen, P.; Zwally, H.J.; Chang, A.T.C.; Hall, D.K.; Campbell, W.J.; Ramseier, R.O.

1978-01-01

The time variation of the sea-ice concentration and multiyear ice fraction within the pack ice in the Arctic Basin is examined, using microwave images of sea ice recently acquired by the Nimbus-5 spacecraft and the NASA CV-990 airborne laboratory. The images used for these studies were constructed from data acquired from the Electrically Scanned Microwave Radiometer (ESMR) which records radiation from earth and its atmosphere at a wavelength of 1.55 cm. Data are analyzed for four seasons during 1973-1975 to illustrate some basic differences in the properties of the sea ice during those times. Spacecraft data are compared with corresponding NASA CV-990 airborne laboratory data obtained over wide areas in the Arctic Basin during the Main Arctic Ice Dynamics Joint Experiment (1975) to illustrate the applicability of passive-microwave remote sensing for monitoring the time dependence of sea-ice concentration (divergence). These observations indicate significant variations in the sea-ice concentration in the spring, late fall and early winter. In addition, deep in the interior of the Arctic polar sea-ice pack, heretofore unobserved large areas, several hundred kilometers in extent, of sea-ice concentrations as low as 50% are indicated. ?? 1978 D. Reidel Publishing Company.

Dynamics of coupled ice-ocean system in the marginal ice zone: Study of the mesoscale processes and of constitutive equations for sea ice

NASA Technical Reports Server (NTRS)

Hakkinen, S.

1984-01-01

This study is aimed at the modelling of mesoscale processed such as up/downwelling and ice edge eddies in the marginal ice zones. A 2-dimensional coupled ice-ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model (f-plane) through interfacial stresses. The constitutive equations of the sea ice are formulated on the basis of the Reiner-Rivlin theory. The internal ice stresses are important only at high ice concentrations (90-100%), otherwise the ice motion is essentially free drift, where the air-ice stress is balanced by the ice-water stress. The model was tested by studying the upwelling dynamics. Winds parallel to the ice edge with the ice on the right produce upwilling because the air-ice momentum flux is much greater that air-ocean momentum flux, and thus the Ekman transport is bigger under the ice than in the open water. The upwelling simulation was extended to include temporally varying forcing, which was chosen to vary sinusoidally with a 4 day period. This forcing resembles successive cyclone passings. In the model with a thin oceanic upper layer, ice bands were formed.

Joint Chance-Constrained Dynamic Programming

NASA Technical Reports Server (NTRS)

Ono, Masahiro; Kuwata, Yoshiaki; Balaram, J. Bob

2012-01-01

This paper presents a novel dynamic programming algorithm with a joint chance constraint, which explicitly bounds the risk of failure in order to maintain the state within a specified feasible region. A joint chance constraint cannot be handled by existing constrained dynamic programming approaches since their application is limited to constraints in the same form as the cost function, that is, an expectation over a sum of one-stage costs. We overcome this challenge by reformulating the joint chance constraint into a constraint on an expectation over a sum of indicator functions, which can be incorporated into the cost function by dualizing the optimization problem. As a result, the primal variables can be optimized by a standard dynamic programming, while the dual variable is optimized by a root-finding algorithm that converges exponentially. Error bounds on the primal and dual objective values are rigorously derived. We demonstrate the algorithm on a path planning problem, as well as an optimal control problem for Mars entry, descent and landing. The simulations are conducted using a real terrain data of Mars, with four million discrete states at each time step.

Ice-shelf Dynamics Near the Front of Filchner-Ronne Ice Shelf, Antarctica, Revealed by SAR Interferometry: Model/Interferogram Comparison

NASA Technical Reports Server (NTRS)

MacAyeal, D. R.; Rignot, E.; Hulbe, C. L.

1998-01-01

We compare Earth Remote Sensing (ERS) satellite synthetic-aperture radar (SAR) interferograms with artificial interferograms constructed using output of a finite-element ice-shelf flow model to study the dynamics of Filchner-Ronne Ice Shelf (FRIS) near Hemmen Ice Rise (HIR) where the iceberg-calving front itersects Berkener Island (BI).

Double symbolic joint entropy in nonlinear dynamic complexity analysis

NASA Astrophysics Data System (ADS)

Yao, Wenpo; Wang, Jun

2017-07-01

Symbolizations, the base of symbolic dynamic analysis, are classified as global static and local dynamic approaches which are combined by joint entropy in our works for nonlinear dynamic complexity analysis. Two global static methods, symbolic transformations of Wessel N. symbolic entropy and base-scale entropy, and two local ones, namely symbolizations of permutation and differential entropy, constitute four double symbolic joint entropies that have accurate complexity detections in chaotic models, logistic and Henon map series. In nonlinear dynamical analysis of different kinds of heart rate variability, heartbeats of healthy young have higher complexity than those of the healthy elderly, and congestive heart failure (CHF) patients are lowest in heartbeats' joint entropy values. Each individual symbolic entropy is improved by double symbolic joint entropy among which the combination of base-scale and differential symbolizations have best complexity analysis. Test results prove that double symbolic joint entropy is feasible in nonlinear dynamic complexity analysis.

Subglacial Volcanism in West-Antarctica - A Geologic and Ice Dynamical Perspective

NASA Astrophysics Data System (ADS)

Vogel, S. W.; Tulaczyk, S.; Carter, S.; Renne, P.; Turrin, B. D.; Joughin, I.

2004-12-01

Subglacial volcanic eruptions may increase the contribution of the West-Antarctic Ice-Sheet (WAIS) to global sea-level rise in the near-future by enhancing basal melt water production and ice flow lubrication. Geophysical data have led scientists to believe that the ice sheet may be located over an extensive, young volcanic province containing ~1 million cubic kilometers of basalts (Behrendt, 1964; Behrendt et. al., 1991; 1995; 1998). While not all scientists may recognize this theory of widespread subglacial volcanism, so far no scientific paper has challenged its existence. Here we present the first geologic constraints on the presence/absence of widespread Late Cenozoic subglacial volcanism beneath the WAIS and investigate the potential influence of an individual subglacial volcano (Blankenship et. al., 1993) on the flow dynamic of WAIS. Properties of subglacial sediments indicate limited presence of subglacial volcanic rocks. Moreover, the only two basaltic pebbles, recovered from the region, are of Mesozoic-Paleozoic age (~100 to ~500 million years). While these findings reduce the potential for widespread near-future increases in ice discharge from WAIS due to eruptions of subglacial volcanoes, they do not rule out the presence of individual hot spots associated with volcanic centers beneath the WAIS. Fuel for the existence of a proposed volcano (Mt. Casertz) on the Whitmore Mountain Ross Sea Transitional Crust (WRT; Blankenship et. al., 1993), in the southern part of the WAIS, comes from thermo-dynamical modeling in comparison with observed ice velocities. Ice velocities (Joughin et. al., 1999; 2002) downstream of Mt. Casertz indicate significant basal sliding, where thermo-dynamical models suggest that the ice sheet is frozen to its base. Routing of basal melt water, produced in the vicinity of Mt. Casertz, may lubricate the ice base in parts of the WRT, thus enabling basal sliding and enhancing the discharge of ice in this sector of the WAIS. The only

Dynamics of hydrogen guests in ice XVII nanopores

NASA Astrophysics Data System (ADS)

del Rosso, Leonardo; Celli, Milva; Colognesi, Daniele; Rudić, Svemir; English, Niall J.; Burnham, Christian J.; Ulivi, Lorenzo

2017-11-01

The present high-resolution inelastic neutron scattering experiment on ice XVII, containing molecular hydrogen with a different ortho/para ratio, allows one to assign the H2 motion spectral bands to rotational and center-of-mass translational transitions of either para- or ortho-H2. Due to its structure, ice XVII confines H2 molecules to move in spiral channels of molecular size. Reported data demonstrate that H2 molecules rotate almost freely in these nanometric channels, though showing larger perturbation than in clathrate hydrates, and perform a translational motion exhibiting two low-frequency excitations. The agreement between the experimental spectra and the corresponding molecular dynamics results clearly enables one to portray a picture of the confined motions of a hydrophobic guest within a metastable ice framework, i.e., ice XVII.

Tunable nonequilibrium dynamics of field quenches in spin ice

PubMed Central

Mostame, Sarah; Castelnovo, Claudio; Moessner, Roderich; Sondhi, Shivaji L.

2014-01-01

We present nonequilibrium physics in spin ice as a unique setting that combines kinematic constraints, emergent topological defects, and magnetic long-range Coulomb interactions. In spin ice, magnetic frustration leads to highly degenerate yet locally constrained ground states. Together, they form a highly unusual magnetic state—a “Coulomb phase”—whose excitations are point-like defects—magnetic monopoles—in the absence of which effectively no dynamics is possible. Hence, when they are sparse at low temperature, dynamics becomes very sluggish. When quenching the system from a monopole-rich to a monopole-poor state, a wealth of dynamical phenomena occur, the exposition of which is the subject of this article. Most notably, we find reaction diffusion behavior, slow dynamics owing to kinematic constraints, as well as a regime corresponding to the deposition of interacting dimers on a honeycomb lattice. We also identify potential avenues for detecting the magnetic monopoles in a regime of slow-moving monopoles. The interest in this model system is further enhanced by its large degree of tunability and the ease of probing it in experiment: With varying magnetic fields at different temperatures, geometric properties—including even the effective dimensionality of the system—can be varied. By monitoring magnetization, spin correlations or zero-field NMR, the dynamical properties of the system can be extracted in considerable detail. This establishes spin ice as a laboratory of choice for the study of tunable, slow dynamics. PMID:24379372

Results of the US contribution to the joint US/USSR Bering Sea experiment. [atmospheric circulation and sea ice cover

NASA Technical Reports Server (NTRS)

Campbell, W. J.; Chang, T. C.; Fowler, M. G.; Gloersen, P.; Kuhn, P. M.; Ramseier, R. O.; Ross, D. B.; Stambach, G.; Webster, W. J., Jr.; Wilheit, T. T.

1974-01-01

The atmospheric circulation which occurred during the Bering Sea Experiment, 15 February to 10 March 1973, in and around the experiment area is analyzed and related to the macroscale morphology and dynamics of the sea ice cover. The ice cover was very complex in structure, being made up of five ice types, and underwent strong dynamic activity. Synoptic analyses show that an optimum variety of weather situations occurred during the experiment: an initial strong anticyclonic period (6 days), followed by a period of strong cyclonic activity (6 days), followed by weak anticyclonic activity (3 days), and finally a period of weak cyclonic activity (4 days). The data of the mesoscale test areas observed on the four sea ice option flights, and ship weather, and drift data give a detailed description of mesoscale ice dynamics which correlates well with the macroscale view: anticyclonic activity advects the ice southward with strong ice divergence and a regular lead and polynya pattern; cyclonic activity advects the ice northward with ice convergence, or slight divergence, and a random lead and polynya pattern.

Dynamics of Ice/Water Confined in Nanoporous Alumina.

PubMed

Suzuki, Yasuhito; Steinhart, Martin; Graf, Robert; Butt, Hans-Jürgen; Floudas, George

2015-11-19

Dielectric (DS), IR spectroscopy, and (1)H MAS NMR are employed in the study of ice/water confined in nanoporous alumina with pore diameters ranging from 400 nm down to 25 nm. Within nanoporous alumina there is a transformation from heterogeneous nucleation of hexagonal ice in the larger pores to homogeneous nucleation of cubic ice in the smaller pores. DS and IR show excellent agreement in the temperature interval and pore size dependence of the transformation. DS further revealed two dynamic processes under confinement. The "fast" and "slow" processes with an Arrhenius temperature dependence are attributed to ice and supercooled water relaxation, respectively. The main relaxation process of ice under confinement ("slow" process) has an activation energy of 44 ± 2 kJ/mol. The latter is in agreement with the reported relaxation times and activation energy of cubic ice prepared following a completely different route (by pressure). (1)H MAS NMR provided new insight in the state of ice structures as well as of supercooled water. Under confinement, a layer of liquid-like water coexists with ice structures. In addition, both ice structures under confinement appear to be more ordered than bulk hexagonal ice. Supercooled water in the smaller pores is different from bulk water. It shows a shift of the signal toward higher chemical shift values which may suggest stronger hydrogen bonding between the water molecules or increasing interactions with the AAO walls.

Dynamic recrystallization during deformation of polycrystalline ice: insights from numerical simulations.

PubMed

Llorens, Maria-Gema; Griera, Albert; Steinbach, Florian; Bons, Paul D; Gomez-Rivas, Enrique; Jansen, Daniela; Roessiger, Jens; Lebensohn, Ricardo A; Weikusat, Ilka

2017-02-13

The flow of glaciers and polar ice sheets is controlled by the highly anisotropic rheology of ice crystals that have hexagonal symmetry (ice lh). To improve our knowledge of ice sheet dynamics, it is necessary to understand how dynamic recrystallization (DRX) controls ice microstructures and rheology at different boundary conditions that range from pure shear flattening at the top to simple shear near the base of the sheets. We present a series of two-dimensional numerical simulations that couple ice deformation with DRX of various intensities, paying special attention to the effect of boundary conditions. The simulations show how similar orientations of c-axis maxima with respect to the finite deformation direction develop regardless of the amount of DRX and applied boundary conditions. In pure shear this direction is parallel to the maximum compressional stress, while it rotates towards the shear direction in simple shear. This leads to strain hardening and increased activity of non-basal slip systems in pure shear and to strain softening in simple shear. Therefore, it is expected that ice is effectively weaker in the lower parts of the ice sheets than in the upper parts. Strain-rate localization occurs in all simulations, especially in simple shear cases. Recrystallization suppresses localization, which necessitates the activation of hard, non-basal slip systems.This article is part of the themed issue 'Microdynamics of ice'. © 2016 The Author(s).

Assessing the Extent of Influence Subglacial Hydrology Has on Dynamic Ice Sheet Behavior

NASA Astrophysics Data System (ADS)

Babonis, G. S.; Csatho, B. M.

2012-12-01

Numerous recent studies have done an excellent job capturing and quantifying the complex pattern of dynamic changes of the Greenland Ice Sheet (GrIS) over the past several decades. The timing of changes in ice velocities and mass balance indicate that the mechanisms controlling these behaviors, both external and internal, act over variable spatial and temporal regimes, can change in rapid and complex fashion, and have significant effect on ice sheet behavior as well as sea level rise. With roughly half of the estimated ice loss from the GrIS attributed to dynamic processes, these changes account for about 250 Gt/yr (2003-2008), equivalence to 0.6 mm/yr sea level rise. One of the primary influences of dynamic ice behavior is ice sheet hydrology, including the storage and transport of water from the supraglacial to subglacial environment, and the subsequent development of water transport pathways, thus demonstrating the need for further characterization of the subglacial environment. Enhanced dynamic flow of ice due to the influence of meltwater distribution on the subglacial environment has been reported, including In-SAR observations of large velocity increases over short periods of time, suggesting regions where dynamic changes are likely being caused by changes in hydrology. Additionally, building upon the 1993-2011 laser altimetry record, analyzed by our Surface Elevation Reconstruction And Change detection (SERAC) procedure, we have detected complex patterns of rapid thickening and thinning patterns over several outlet glaciers. This study presents a comprehensive investigation of hydrologic control on dynamic glacier behavior for several key sites in Greenland. We combine a high resolution surface digital elevation model (DEM) derived by fusing space- and airborne laser altimetry observations and SPIRIT SPOT DEMs, with a high resolution, hydrologically-corrected bedrock DEM derived from a combination of CResIS and Operation Icebridge ice penetrating radar data

Bed roughness of palaeo-ice streams: insights and implications for contemporary ice sheet dynamics

NASA Astrophysics Data System (ADS)

Falcini, Francesca; Rippin, David; Selby, Katherine; Krabbendam, Maarten

2017-04-01

Bed roughness is the vertical variation of elevation along a horizontal transect. It is an important control on ice stream location and dynamics, with a correspondingly important role in determining the behaviour of ice sheets. Previous studies of bed roughness have been limited to insights derived from Radio Echo Sounding (RES) profiles across parts of Antarctica and Greenland. Such an approach has been necessary due to the inaccessibility of the underlying bed. This approach has led to important insights, such as identifying a general link between smooth beds and fast ice flow, as well as rough beds and slow ice flow. However, these insights are mainly derived from relatively coarse datasets, so that links between roughness and flow are generalised and rather simplistic. Here, we explore the use of DTMs from the well-preserved footprints of palaeo-ice streams, coupled with high resolution models of palaeo-ice flow, as a tool for investigating basal controls on the behaviour of contemporary, active ice streams in much greater detail. Initially, artificial transects were set up across the Minch palaeo-ice stream (NW Scotland) to mimic RES flight lines from past studies in Antarctica. We then explored how increasing data-resolution impacted upon the roughness measurements that were derived. Our work on the Minch palaeo-ice stream indicates that different roughness signatures are associated with different glacial landforms, and we discuss the potential for using these insights to infer, from RES-based roughness measurements, the occurrence of particular landform assemblages that may exist beneath contemporary ice sheets.

Dynamic analysis of clamp band joint system subjected to axial vibration

NASA Astrophysics Data System (ADS)

Qin, Z. Y.; Yan, S. Z.; Chu, F. L.

2010-10-01

Clamp band joints are commonly used for connecting circular components together in industry. Some of the systems jointed by clamp band are subjected to dynamic load. However, very little research on the dynamic characteristics for this kind of joint can be found in the literature. In this paper, a dynamic model for clamp band joint system is developed. Contact and frictional slip between the components are accommodated in this model. Nonlinear finite element analysis is conducted to identify the model parameters. Then static experiments are carried out on a scaled model of the clamp band joint to validate the joint model. Finally, the model is adopted to study the dynamic characteristics of the clamp band joint system subjected to axial harmonic excitation and the effects of the wedge angle of the clamp band joint and the preload on the response. The model proposed in this paper can represent the nonlinearity of the clamp band joint and be used conveniently to investigate the effects of the structural and loading parameters on the dynamic characteristics of this type of joint system.

Arctic ice shelves and ice islands: Origin, growth and disintegration, physical characteristics, structural-stratigraphic variability, and dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeffries, M.O.

1992-08-01

Ice shelves are thick, floating ice masses most often associated with Antarctica where they are seaward extensions of the grounded Antarctic ice sheet and sources of many icebergs. However, there are also ice shelves in the Arctic, primarily located along the north coast of Ellesmere Island in the Canadian High Arctic. The only ice shelves in North America and the most extensive in the north polar region, the Ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands, the tabular icebergs of the Arctic Ocean. The present state of knowledge and understanding ofmore » these ice features is summarized in this paper. It includes historical background to the discovery and early study of ice shelves and ice islands, including the use of ice islands as floating laboratories for polar geophysical research. Growth mechanisms and age, the former extent and the twentieth century disintegration of the Ellesmere ice shelves, and the processes and mechanisms of ice island calving are summarized. Surface features, thickness, thermal regime, and the size, shape, and numbers of ice islands are discussed. The structural-stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described. Large-scale and small-scale dynamics of ice islands are described, and the results of modeling their drift and recurrence intervals are presented. The conclusion identifies some unanswered questions and future research opportunities and needs. 97 refs., 18 figs.« less

Contribution of sea ice microbial production to Antarctic benthic communities is driven by sea ice dynamics and composition of functional guilds.

PubMed

Wing, Stephen R; Leichter, James J; Wing, Lucy C; Stokes, Dale; Genovese, Sal J; McMullin, Rebecca M; Shatova, Olya A

2018-04-28

Organic matter produced by the sea ice microbial community (SIMCo) is an important link between sea ice dynamics and secondary production in near-shore food webs of Antarctica. Sea ice conditions in McMurdo Sound were quantified from time series of MODIS satellite images for Sept. 1 through Feb. 28 of 2007-2015. A predictable sea ice persistence gradient along the length of the Sound and evidence for a distinct change in sea ice dynamics in 2011 were observed. We used stable isotope analysis (δ 13 C and δ 15 N) of SIMCo, suspended particulate organic matter (SPOM) and shallow water (10-20 m) macroinvertebrates to reveal patterns in trophic structure of, and incorporation of organic matter from SIMCo into, benthic communities at eight sites distributed along the sea ice persistence gradient. Mass-balance analysis revealed distinct trophic architecture among communities and large fluxes of SIMCo into the near-shore food web, with the estimates ranging from 2 to 84% of organic matter derived from SIMCo for individual species. Analysis of patterns in density, and biomass of macroinvertebrate communities among sites allowed us to model net incorporation of organic matter from SIMCo, in terms of biomass per unit area (g/m 2 ), into benthic communities. Here, organic matter derived from SIMCo supported 39 to 71 per cent of total biomass. Furthermore, for six species, we observed declines in contribution of SIMCo between years with persistent sea ice (2008-2009) and years with extensive sea ice breakout (2012-2015). Our data demonstrate the vital role of SIMCo in ecosystem function in Antarctica and strong linkages between sea ice dynamics and near-shore secondary productivity. These results have important implications for our understanding of how benthic communities will respond to changes in sea ice dynamics associated with climate change and highlight the important role of shallow water macroinvertebrate communities as sentinels of change for the Antarctic marine

Ice-dammed lateral lake and epishelf lake insights into Holocene dynamics of Marguerite Trough Ice Stream and George VI Ice Shelf, Alexander Island, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Davies, Bethan J.; Hambrey, Michael J.; Glasser, Neil F.; Holt, Tom; Rodés, Angél; Smellie, John L.; Carrivick, Jonathan L.; Blockley, Simon P. E.

2017-12-01

We present new data regarding the past dynamics of Marguerite Trough Ice Stream, George VI Ice Shelf and valley glaciers from Ablation Point Massif on Alexander Island, Antarctic Peninsula. This ice-free oasis preserves a geological record of ice stream lateral moraines, ice-dammed lakes, ice-shelf moraines and valley glacier moraines, which we dated using cosmogenic nuclide ages. We provide one of the first detailed sediment-landform assemblage descriptions of epishelf lake shorelines. Marguerite Trough Ice Stream imprinted lateral moraines against eastern Alexander Island at 120 m at Ablation Point Massif. During deglaciation, lateral lakes formed in the Ablation and Moutonnée valleys, dammed against the ice stream in George VI Sound. Exposure ages from boulders on these shorelines yielded ages of 13.9 to 9.7 ka. Following recession of the ice stream, George VI Ice Shelf formed in George VI Sound. An epishelf lake formed at 15-20 m asl in Ablation and Moutonnée valleys, dated from 9.4 to 4.6 ka, suggesting that the lake was stable and persistent for some 5000 years. Lake-level lowering occurred after this, with the lake level at 12 m at 3.1 ± 0.4 ka and at 5 m asl today. A readvance of the valley glaciers on Alexander Island at 4.4 ± 0.7 ka is recorded by valley glacier moraines overlying epishelf lake sediments. We speculate that the glacier readvance, which occurred during a period of warmth, may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of George VI Ice Shelf.

Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

USGS Publications Warehouse

Mark Torre Jorgenson,; Mikhail Kanevskiy,; Yuri Shur,; Natalia Moskalenko,; Dana Brown,; Wickland, Kimberly P.; Striegl, Robert G.; Koch, Joshua C.

2015-01-01

Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water-filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice-poor transient layer, ice-rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

NASA Astrophysics Data System (ADS)

Jorgenson, M. T.; Kanevskiy, M.; Shur, Y.; Moskalenko, N.; Brown, D. R. N.; Wickland, K.; Striegl, R.; Koch, J.

2015-11-01

Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water-filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice-poor transient layer, ice-rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

Dynamic recrystallization during deformation of polycrystalline ice: insights from numerical simulations

PubMed Central

Griera, Albert; Steinbach, Florian; Bons, Paul D.; Jansen, Daniela; Roessiger, Jens; Lebensohn, Ricardo A.

2017-01-01

The flow of glaciers and polar ice sheets is controlled by the highly anisotropic rheology of ice crystals that have hexagonal symmetry (ice lh). To improve our knowledge of ice sheet dynamics, it is necessary to understand how dynamic recrystallization (DRX) controls ice microstructures and rheology at different boundary conditions that range from pure shear flattening at the top to simple shear near the base of the sheets. We present a series of two-dimensional numerical simulations that couple ice deformation with DRX of various intensities, paying special attention to the effect of boundary conditions. The simulations show how similar orientations of c-axis maxima with respect to the finite deformation direction develop regardless of the amount of DRX and applied boundary conditions. In pure shear this direction is parallel to the maximum compressional stress, while it rotates towards the shear direction in simple shear. This leads to strain hardening and increased activity of non-basal slip systems in pure shear and to strain softening in simple shear. Therefore, it is expected that ice is effectively weaker in the lower parts of the ice sheets than in the upper parts. Strain-rate localization occurs in all simulations, especially in simple shear cases. Recrystallization suppresses localization, which necessitates the activation of hard, non-basal slip systems. This article is part of the themed issue ‘Microdynamics of ice’. PMID:28025295

Stochastic dynamics of melt ponds and sea ice-albedo climate feedback

NASA Astrophysics Data System (ADS)

Sudakov, Ivan

Evolution of melt ponds on the Arctic sea surface is a complicated stochastic process. We suggest a low-order model with ice-albedo feedback which describes stochastic dynamics of melt ponds geometrical characteristics. The model is a stochastic dynamical system model of energy balance in the climate system. We describe the equilibria in this model. We conclude the transition in fractal dimension of melt ponds affects the shape of the sea ice albedo curve.

Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.

PubMed

Csatho, Beata M; Schenk, Anton F; van der Veen, Cornelis J; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R; Simonsen, Sebastian B; Nagarajan, Sudhagar; van Angelen, Jan H

2014-12-30

We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ⋅ y(-1), equivalent to 0.68 mm ⋅ y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers.

Detection and Analysis of Complex Patterns of Ice Dynamics in Antarctica from ICESat Laser Altimetry

NASA Astrophysics Data System (ADS)

Babonis, Gregory Scott

There remains much uncertainty in estimating the amount of Antarctic ice mass change, its dynamic component, and its spatial and temporal patterns. This work remedies the limitations of previous studies by generating the first detailed reconstruction of total and dynamic ice thickness and mass changes across Antarctica, from ICESat satellite altimetry observations in 2003-2009 using the Surface Elevation Reconstruction and Change Detection (SERAC) method. Ice sheet thickness changes are calculated with quantified error estimates for each time when ICESat flew over a ground-track crossover region, at approximately 110,000 locations across the Antarctic Ice Sheet. The time series are partitioned into changes due to surficial processes and ice dynamics. The new results markedly improve the spatial and temporal resolution of surface elevation, volume, and mass change rates for the AIS, and can be sampled at annual temporal resolutions. The results indicate a complex spatiotemporal pattern of dynamic mass loss in Antarctica, especially along individual outlet glaciers, and allow for the quantification of the annual contribution of Antarctic ice loss to sea level rise. Over 5000 individual locations exhibit either strong dynamic ice thickness change patterns, accounting for approximately 500 unique spatial clusters that identify regions likely influenced by subglacial hydrology. The spatial distribution and temporal behavior of these regions reveal the complexity and short-time scale variability in the subglacial hydrological system. From the 500 unique spatial clusters, over 370 represent newly identified, and not previously published, potential subglacial water bodies indicating an active subglacial hydrological system over a much larger region than previously observed. These numerous new observations of dynamic changes provide more than simply a larger set of data. Examination of both regional and local scale dynamic change patterns across Antarctica shows newly

The effects of mixed layer dynamics on ice growth in the central Arctic

NASA Astrophysics Data System (ADS)

Kitchen, Bruce R.

1992-09-01

The thermodynamic model of Thorndike (1992) is coupled to a one dimensional, two layer ocean entrainment model to study the effect of mixed layer dynamics on ice growth and the variation in the ocean heat flux into the ice due to mixed layer entrainment. Model simulations show the existence of a negative feedback between the ice growth and the mixed layer entrainment, and that the underlying ocean salinity has a greater effect on the ocean beat flux than does variations in the underlying ocean temperature. Model simulations for a variety of surface forcings and initial conditions demonstrate the need to include mixed layer dynamics for realistic ice prediction in the arctic.

Pyroclastic density current dynamics and associated hazards at ice-covered volcanoes

NASA Astrophysics Data System (ADS)

Dufek, J.; Cowlyn, J.; Kennedy, B.; McAdams, J.

2015-12-01

Understanding the processes by which pyroclastic density currents (PDCs) are emplaced is crucial for volcanic hazard prediction and assessment. Snow and ice can facilitate PDC generation by lowering the coefficient of friction and by causing secondary hydrovolcanic explosions, promoting remobilisation of proximally deposited material. Where PDCs travel over snow or ice, the reduction in surface roughness and addition of steam and meltwater signficantly changes the flow dynamics, affecting PDC velocities and runout distances. Additionally, meltwater generated during transit and after the flow has come to rest presents an immediate secondary lahar hazard that can impact areas many tens of kilometers beyond the intial PDC. This, together with the fact that deposits emplaced on ice are rarely preserved means that PDCs over ice have been little studied despite the prevalence of summit ice at many tall stratovolcanoes. At Ruapehu volcano in the North Island of New Zealand, a monolithologic welded PDC deposit with unusually rounded clasts provides textural evidence for having been transported over glacial ice. Here, we present the results of high-resolution multiphase numerical PDC modeling coupled with experimentaly determined rates of water and steam production for the Ruapehu deposits in order to assess the effect of ice on the Ruapehu PDC. The results suggest that the presence of ice significantly modified the PDC dynamics, with implications for assessing the PDC and associated lahar hazards at Ruapehu and other glaciated volcanoes worldwide.

Dynamic Nucleation of Ice Induced by a Single Stable Cavitation Bubble

NASA Technical Reports Server (NTRS)

Ohsaka, Kenichi; Trinh, Eugene H.

1997-01-01

Dynamic nucleation of ice induced by caviation bubble in undercooled water is observed using an acoustic levitation technique. The observation indicates that a high pressure pulse associated with a collapsing bubble is indeed responsible for the nucleation of a high pressure phase of ice.

Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics

PubMed Central

Csatho, Beata M.; Schenk, Anton F.; van der Veen, Cornelis J.; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R.; Simonsen, Sebastian B.; Nagarajan, Sudhagar; van Angelen, Jan H.

2014-01-01

We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993–2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt⋅y−1, equivalent to 0.68 mm⋅y−1 sea level rise (SLR) for 2003–2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004–2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland’s outlet glaciers. PMID:25512537

The effect of salt on the melting of ice: A molecular dynamics simulation study.

PubMed

Kim, Jun Soo; Yethiraj, Arun

2008-09-28

The effect of added salt (NaCl) on the melting of ice is studied using molecular dynamics simulations. The equilibrium freezing point depression observed in the simulations is in good agreement with experimental data. The kinetic aspects of melting are investigated in terms of the exchange of water molecules between ice and the liquid phase. The ice/liquid equilibrium is a highly dynamic process with frequent exchange of water molecules between ice and the liquid phase. The balance is disturbed when ice melts and the melting proceeds in two stages; the inhibition of the association of water molecules to the ice surface at short times, followed by the increased dissociation of water molecules from the ice surface at longer times. We also find that Cl(-) ions penetrate more deeply into the interfacial region than Na(+) ions during melting. This study provides an understanding of the kinetic aspects of melting that could be useful in other processes such as the inhibition of ice growth by antifreeze proteins.

Polynya dynamics and associated atmospheric forcing at the Ronne Ice Shelf

NASA Astrophysics Data System (ADS)

Ebner, Lars; Heinemann, Günther

2014-05-01

The Ronne Ice Shelf is known as one of the most active regions of polynya developments around the Antarctic continent. Low temperatures are prevailing throughout the whole year, particularly in winter. It is generally recognized that polynya formations are primarily forced by offshore winds and secondarily by ocean currents. Many authors have addressed this issue previously at the Ross Ice Shelf and Adélie Coast and connected polynya dynamics to strong katabatic surge events. Such investigations of atmospheric dynamics and simultaneous polynya occurrence are still severely underrepresented for the southwestern part of the Weddell Sea and especially for the Ronne Ice Shelf. Due to the very flat terrain gradients of the ice shelf katabatic winds are of minor importance in that area. Other atmospheric processes must therefore play a crucial role for polynya developments at the Ronne Ice Shelf. High-resolution simulations have been carried out for the Weddell Sea region using the non-hydrostatic NWP model COSMO from the German Meteorological Service (DWD). For the austral autumn and winter (March to August) 2008 daily forecast simulations were conducted with the consideration of daily sea-ice coverage deduced from the passive microwave system AMSR-E. These simulations are used to analyze the synoptic and mesoscale atmospheric dynamics of the Weddell Sea region and find linkages to polynya occurrence at the Ronne Ice Shelf. For that reason, the relation between the surface wind speed, the synoptic pressure gradient in the free atmosphere and polynya area is investigated. Seven significant polynya events are identified for the simulation period, three in the autumn and four in the winter season. It can be shown that in almost all cases synoptic cyclones are the primary polynya forcing systems. In most cases the timely interaction of several passing cyclones in the northern and central Weddell Sea leads to maintenance of a strong synoptic pressure gradient above the

Dynamic Analyses Including Joints Of Truss Structures

NASA Technical Reports Server (NTRS)

Belvin, W. Keith

1991-01-01

Method for mathematically modeling joints to assess influences of joints on dynamic response of truss structures developed in study. Only structures with low-frequency oscillations considered; only Coulomb friction and viscous damping included in analysis. Focus of effort to obtain finite-element mathematical models of joints exhibiting load-vs.-deflection behavior similar to measured load-vs.-deflection behavior of real joints. Experiments performed to determine stiffness and damping nonlinearities typical of joint hardware. Algorithm for computing coefficients of analytical joint models based on test data developed to enable study of linear and nonlinear effects of joints on global structural response. Besides intended application to large space structures, applications in nonaerospace community include ground-based antennas and earthquake-resistant steel-framed buildings.

Calibration of sea ice dynamic parameters in an ocean-sea ice model using an ensemble Kalman filter

NASA Astrophysics Data System (ADS)

Massonnet, F.; Goosse, H.; Fichefet, T.; Counillon, F.

2014-07-01

The choice of parameter values is crucial in the course of sea ice model development, since parameters largely affect the modeled mean sea ice state. Manual tuning of parameters will soon become impractical, as sea ice models will likely include more parameters to calibrate, leading to an exponential increase of the number of possible combinations to test. Objective and automatic methods for parameter calibration are thus progressively called on to replace the traditional heuristic, "trial-and-error" recipes. Here a method for calibration of parameters based on the ensemble Kalman filter is implemented, tested and validated in the ocean-sea ice model NEMO-LIM3. Three dynamic parameters are calibrated: the ice strength parameter P*, the ocean-sea ice drag parameter Cw, and the atmosphere-sea ice drag parameter Ca. In twin, perfect-model experiments, the default parameter values are retrieved within 1 year of simulation. Using 2007-2012 real sea ice drift data, the calibration of the ice strength parameter P* and the oceanic drag parameter Cw improves clearly the Arctic sea ice drift properties. It is found that the estimation of the atmospheric drag Ca is not necessary if P* and Cw are already estimated. The large reduction in the sea ice speed bias with calibrated parameters comes with a slight overestimation of the winter sea ice areal export through Fram Strait and a slight improvement in the sea ice thickness distribution. Overall, the estimation of parameters with the ensemble Kalman filter represents an encouraging alternative to manual tuning for ocean-sea ice models.

Isotopic differentiation and sublattice melting in dense dynamic ice

NASA Astrophysics Data System (ADS)

Hermann, Andreas; Ashcroft, N. W.; Hoffmann, Roald

2013-12-01

The isotopes of hydrogen provide a unique exploratory laboratory for examining the role of zero point energy (ZPE) in determining the structural and dynamic features of the crystalline ices of water. There are two critical regions of high pressure: (i) near 1 TPa and (ii) near the predicted onset of metallization at around 5 TPa. At the lower pressure of the two, we see the expected small isotopic effects on phase transitions. Near metallization, however, the effects are much greater, leading to a situation where tritiated ice could skip almost entirely a phase available to the other isotopomers. For the higher pressure ices, we investigate in some detail the enthalpics of a dynamic proton sublattice, with the corresponding structures being quite ionic. The resistance toward diffusion of single protons in the ground state structures of high-pressure H2O is found to be large, in fact to the point that the ZPE reservoir cannot overcome these. However, the barriers toward a three-dimensional coherent or concerted motion of protons can be much lower, and the ensuing consequences are explored.

Dynamics of ice nucleation on water repellent surfaces.

PubMed

Alizadeh, Azar; Yamada, Masako; Li, Ri; Shang, Wen; Otta, Shourya; Zhong, Sheng; Ge, Liehui; Dhinojwala, Ali; Conway, Ken R; Bahadur, Vaibhav; Vinciquerra, A Joseph; Stephens, Brian; Blohm, Margaret L

2012-02-14

Prevention of ice accretion and adhesion on surfaces is relevant to many applications, leading to improved operation safety, increased energy efficiency, and cost reduction. Development of passive nonicing coatings is highly desirable, since current antiicing strategies are energy and cost intensive. Superhydrophobicity has been proposed as a lead passive nonicing strategy, yet the exact mechanism of delayed icing on these surfaces is not clearly understood. In this work, we present an in-depth analysis of ice formation dynamics upon water droplet impact on surfaces with different wettabilities. We experimentally demonstrate that ice nucleation under low-humidity conditions can be delayed through control of surface chemistry and texture. Combining infrared (IR) thermometry and high-speed photography, we observe that the reduction of water-surface contact area on superhydrophobic surfaces plays a dual role in delaying nucleation: first by reducing heat transfer and second by reducing the probability of heterogeneous nucleation at the water-substrate interface. This work also includes an analysis (based on classical nucleation theory) to estimate various homogeneous and heterogeneous nucleation rates in icing situations. The key finding is that ice nucleation delay on superhydrophobic surfaces is more prominent at moderate degrees of supercooling, while closer to the homogeneous nucleation temperature, bulk and air-water interface nucleation effects become equally important. The study presented here offers a comprehensive perspective on the efficacy of textured surfaces for nonicing applications.

Dynamic and thermodynamic impacts of the winter Arctic Oscillation on summer sea ice extent.

NASA Astrophysics Data System (ADS)

Park, H. S.; Stewart, A.

2017-12-01

Arctic summer sea ice extent exhibits substantial interannual variability, as is highlighted by the remarkable recovery in sea ice extent in 2013 following the record minimum in the summer of 2012. Here, we explore the mechanism via which Arctic Oscillation (AO)-induced ice thickness changes impact summer sea ice, using observations and reanalysis data. A positive AO weakens the basin-scale anticyclonic sea ice drift and decreases the winter ice thickness by 15cm and 10cm in the Eurasian and the Pacific sectors of the Arctic respectively. Three reanalysis datasets show that the (upward) surface heat fluxes are reduced over wide areas of the Arctic, suppressing the ice growth during the positive AO winters. The winter dynamic and thermodynamic thinning preconditions the ice for enhanced radiative forcing via the ice-albedo feedback in late spring-summer, leading to an additional 8-10 cm of thinning over the Pacific sector of the Arctic. Because of these winter AO-induced dynamic and thermodynamics effects, the winter AO explains about 22% (r = -0.48) of the interannual variance of September sea ice extent from year 1980 to 2015.

Sea ice dynamics across the Mid-Pleistocene transition in the Bering Sea.

PubMed

Detlef, H; Belt, S T; Sosdian, S M; Smik, L; Lear, C H; Hall, I R; Cabedo-Sanz, P; Husum, K; Kender, S

2018-03-05

Sea ice and associated feedback mechanisms play an important role for both long- and short-term climate change. Our ability to predict future sea ice extent, however, hinges on a greater understanding of past sea ice dynamics. Here we investigate sea ice changes in the eastern Bering Sea prior to, across, and after the Mid-Pleistocene transition (MPT). The sea ice record, based on the Arctic sea ice biomarker IP 25 and related open water proxies from the International Ocean Discovery Program Site U1343, shows a substantial increase in sea ice extent across the MPT. The occurrence of late-glacial/deglacial sea ice maxima are consistent with sea ice/land ice hysteresis and land-glacier retreat via the temperature-precipitation feedback. We also identify interactions of sea ice with phytoplankton growth and ocean circulation patterns, which have important implications for glacial North Pacific Intermediate Water formation and potentially North Pacific abyssal carbon storage.

connecting the dots between Greenland ice sheet surface melting and ice flow dynamics (Invited)

NASA Astrophysics Data System (ADS)

Box, J. E.; Colgan, W. T.; Fettweis, X.; Phillips, T. P.; Stober, M.

2013-12-01

This presentation is of a 'unified theory' in glaciology that first identifies surface albedo as a key factor explaining total ice sheet mass balance and then surveys a mechanistic self-reinforcing interaction between melt water and ice flow dynamics. The theory is applied in a near-real time total Greenland mass balance retrieval based on surface albedo, a powerful integrator of the competing effects of accumulation and ablation. New snowfall reduces sunlight absorption and increases meltwater retention. Melting amplifies absorbed sunlight through thermal metamorphism and bare ice expansion in space and time. By ';following the melt'; we reveal mechanisms linking existing science into a unified theory. Increasing meltwater softens the ice sheet in three ways: 1.) sensible heating given the water temperature exceeds that of the ice sheet interior; 2.) Some infiltrating water refreezes, transferring latent heat to the ice; 3.) Friction from water turbulence heats the ice. It has been shown that for a point on the ice sheet, basal lubrication increases ice flow speed to a time when an efficient sub-glacial drainage network develops that reduces this effect. Yet, with an increasing melt duration the point where the ice sheet glides on a wet bed increases inland to a larger area. This effect draws down the ice surface elevation, contributing to the ';elevation feedback'. In a perpetual warming scenario, the elevation feedback ultimately leads to ice sheet loss reversible only through much slower ice sheet growth in an ice age environment. As the inland ice sheet accelerates, the horizontal extension pulls cracks and crevasses open, trapping more sunlight, amplifying the effect of melt accelerated ice. As the bare ice area increases, the direct sun-exposed crevassed and infiltration area increases further allowing the ice warming process to occur more broadly. Considering hydrofracture [a.k.a. hydrofracking]; surface meltwater fills cracks, attacking the ice integrity

Sea ice type dynamics in the Arctic based on Sentinel-1 Data

NASA Astrophysics Data System (ADS)

Babiker, Mohamed; Korosov, Anton; Park, Jeong-Won

2017-04-01

Sea ice observation from satellites has been carried out for more than four decades and is one of the most important applications of EO data in operational monitoring as well as in climate change studies. Several sensors and retrieval methods have been developed and successfully utilized to measure sea ice area, concentration, drift, type, thickness, etc [e.g. Breivik et al., 2009]. Today operational sea ice monitoring and analysis is fully dependent on use of satellite data. However, new and improved satellite systems, such as multi-polarisation Synthetic Apperture Radar (SAR), require further studies to develop more advanced and automated sea ice monitoring methods. In addition, the unprecedented volume of data available from recently launched Sentinel missions provides both challenges and opportunities for studying sea ice dynamics. In this study we investigate sea ice type dynamics in the Fram strait based on Sentinel-1 A, B SAR data. Series of images for the winter season are classified into 4 ice types (young ice, first year ice, multiyear ice and leads) using the new algorithm developed by us for sea ice classification, which is based on segmentation, GLCM calculation, Haralick texture feature extraction, unsupervised and supervised classifications and Support Vector Machine (SVM) [Zakhvatkina et al., 2016; Korosov et al., 2016]. This algorithm is further improved by applying thermal and scalloping noise removal [Park et al. 2016]. Sea ice drift is retrieved from the same series of Sentinel-1 images using the newly developed algorithm based on combination of feature tracking and pattern matching [Mukenhuber et al., 2016]. Time series of these two products (sea ice type and sea ice drift) are combined in order to study sea ice deformation processes at small scales. Zones of sea ice convergence and divergence identified from sea ice drift are compared with ridges and leads identified from texture features. That allows more specific interpretation of SAR

Dynamic signatures of the transition from stacking disordered to hexagonal ice: Dielectric and nuclear magnetic resonance studies

NASA Astrophysics Data System (ADS)

Gainaru, C.; Vynokur, E.; Köster, K. W.; Fuentes-Landete, V.; Spettel, N.; Zollner, J.; Loerting, T.; Böhmer, R.

2018-04-01

Using various temperature-cycling protocols, the dynamics of ice I were studied via dielectric spectroscopy and nuclear magnetic resonance relaxometry on protonated and deuterated samples obtained by heating high-density amorphous ices as well as crystalline ice XII. Previous structural studies of ice I established that at temperatures of about 230 K, the stacking disorder of the cubic/hexagonal oxygen lattice vanishes. The present dielectric and nuclear magnetic resonance investigations of spectral changes disclose that the memory of the existence of a precursor phase is preserved in the hydrogen matrix up to 270 K. This finding of hydrogen mobility lower than that of the undoped hexagonal ice near the melting point highlights the importance of dynamical investigations of the transitions between various ice phases and sheds new light on the dynamics in ice I in general.

High-precision GPS autonomous platforms for sea ice dynamics and physical oceanography

NASA Astrophysics Data System (ADS)

Elosegui, P.; Wilkinson, J.; Olsson, M.; Rodwell, S.; James, A.; Hagan, B.; Hwang, B.; Forsberg, R.; Gerdes, R.; Johannessen, J.; Wadhams, P.; Nettles, M.; Padman, L.

2012-12-01

Project "Arctic Ocean sea ice and ocean circulation using satellite methods" (SATICE), is the first high-rate, high-precision, continuous GPS positioning experiment on sea ice in the Arctic Ocean. The SATICE systems collect continuous, dual-frequency carrier-phase GPS data while drifting on sea ice. Additional geophysical measurements also collected include ocean water pressure, ocean surface salinity, atmospheric pressure, snow-depth, air-ice-ocean temperature profiles, photographic imagery, and others, enabling sea ice drift, freeboard, weather, ice mass balance, and sea-level height determination. Relatively large volumes of data from each buoy are streamed over a satellite link to a central computer on the Internet in near real time, where they are processed to estimate the time-varying buoy positions. SATICE system obtains continuous GPS data at sub-minute intervals with a positioning precision of a few centimetres in all three dimensions. Although monitoring of sea ice motions goes back to the early days of satellite observations, these autonomous platforms bring out a level of spatio-temporal detail that has never been seen before, especially in the vertical axis. These high-resolution data allows us to address new polar science questions and challenge our present understanding of both sea ice dynamics and Arctic oceanography. We will describe the technology behind this new autonomous platform, which could also be adapted to other applications that require high resolution positioning information with sustained operations and observations in the polar marine environment, and present results pertaining to sea ice dynamics and physical oceanography.

Ice-nucleating bacteria control the order and dynamics of interfacial water

DOE PAGES

Pandey, Ravindra; Usui, Kota; Livingstone, Ruth A.; ...

2016-04-22

Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as Pseudomonas syringae attack plants through frost damage using specialized ice-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering onmore » the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation. Finally, the freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved SFG spectroscopy.« less

Ice-nucleating bacteria control the order and dynamics of interfacial water

PubMed Central

Pandey, Ravindra; Usui, Kota; Livingstone, Ruth A.; Fischer, Sean A.; Pfaendtner, Jim; Backus, Ellen H. G.; Nagata, Yuki; Fröhlich-Nowoisky, Janine; Schmüser, Lars; Mauri, Sergio; Scheel, Jan F.; Knopf, Daniel A.; Pöschl, Ulrich; Bonn, Mischa; Weidner, Tobias

2016-01-01

Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as Pseudomonas syringae attack plants through frost damage using specialized ice-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering on the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice-active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation. The freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved SFG spectroscopy. PMID:27152346

Dynamics of the last glacial maximum Antarctic ice-sheet and its response to ocean forcing

PubMed Central

Golledge, Nicholas R.; Fogwill, Christopher J.; Mackintosh, Andrew N.; Buckley, Kevin M.

2012-01-01

Retreat of the Last Glacial Maximum (LGM) Antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the Northern Hemisphere (NH) as northern ice sheets melted under rising atmospheric temperatures. The extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the Antarctic ice sheet has so far received little attention, however, despite the growing recognition that dynamic effects account for a sizeable proportion of mass-balance changes observed in modern ice sheets. Here we use a 5-km resolution whole-continent numerical ice-sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent. We first simulate the geometry and flow characteristics of an equilibrium LGM ice sheet, using pan-Antarctic terrestrial and marine geological data for constraint, then perturb the system with sea level and ocean heat flux increases to investigate ice-sheet vulnerability. Our results identify that fast-flowing glaciers in the eastern Weddell Sea, the Amundsen Sea, central Ross Sea, and in the Amery Trough respond most rapidly to ocean forcings, in agreement with empirical data. Most significantly, we find that although ocean warming and sea-level rise bring about mainly localized glacier acceleration, concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments—a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets. PMID:22988078

Dynamics of the last glacial maximum Antarctic ice-sheet and its response to ocean forcing.

PubMed

Golledge, Nicholas R; Fogwill, Christopher J; Mackintosh, Andrew N; Buckley, Kevin M

2012-10-02

Retreat of the Last Glacial Maximum (LGM) Antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the Northern Hemisphere (NH) as northern ice sheets melted under rising atmospheric temperatures. The extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the Antarctic ice sheet has so far received little attention, however, despite the growing recognition that dynamic effects account for a sizeable proportion of mass-balance changes observed in modern ice sheets. Here we use a 5-km resolution whole-continent numerical ice-sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent. We first simulate the geometry and flow characteristics of an equilibrium LGM ice sheet, using pan-Antarctic terrestrial and marine geological data for constraint, then perturb the system with sea level and ocean heat flux increases to investigate ice-sheet vulnerability. Our results identify that fast-flowing glaciers in the eastern Weddell Sea, the Amundsen Sea, central Ross Sea, and in the Amery Trough respond most rapidly to ocean forcings, in agreement with empirical data. Most significantly, we find that although ocean warming and sea-level rise bring about mainly localized glacier acceleration, concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments-a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets.

Ice crystal growth in a dynamic thermal diffusion chamber

NASA Technical Reports Server (NTRS)

Keller, V. W.

1980-01-01

Ice crystals were grown in a supersaturated environment produced by a dynamic thermal diffusion chamber, which employed two horizontal plates separated by a distance of 2.5 cm. Air was circulated between and along the 1.2 m length of the plates past ice crystals which nucleated and grew from a fiber suspended vertically between the two plates. A zoom stereo microscope with a magnification which ranged from 3X to 80X and both 35 mm still photographs and 16 mm time lapse cine films taken through the microscope were used to study the variation of the shape and linear growth rate of ice crystals as a function of the ambient temperature, the ambient supersaturation, and the forced ventilation velocity. The ambient growth conditions were varied over the range of temperature 0 to -40 C, over the range of supersaturation 4% to 50% with respect to ice, and over the range of forced ventilation velocities 0 cm/s to 20 cm/s.

Bedrock structure and the interpretation of palaeo ice stream footprints: examples from the Pleistocene British Ice Sheet

NASA Astrophysics Data System (ADS)

Krabbendam, M.; Bradwell, T.

2009-04-01

To model past and future behaviour of ice sheets, a good understanding of both modern and ancient ice streams is required. The study of present-day ice streams provides detailed data of short-term dynamic changes, whilst the study of Pleistocene palaeo-ice streams can provide crucial constraints on the longer-term evolution of ice sheets. To date, palaeo-ice streams, such as the classical Dubawnt Lake palaeo-ice stream of the former Laurentide Ice Sheet, have been recognised largely on the basis of extremely elongate drumlins and megascale glacial lineations; all soft-sediment features. Whilst it appears that topographically unconstrained ice streams (eg. within the West Antarctic Ice Sheet) are generally underlain by deformable till, topographically constrained ice streams such as Jakobshavn Isbrae do not require deformable sediment and may occur on a bedrock-dominated bed. Analysis of DEM data and geomorphology and structural geology fieldwork in Northern Scotland and Northern England has shown the occurrence of highly streamlined bedforms in bedrock of the former base of topographically controlled palaeo-ice streams, which drained parts of the British Ice Sheet. The bedforms are predominantly bedrock megagrooves with asymmetric cross-profiles. In the Ullapool tributary of the Minch palaeo ice stream, bedrock megagrooves form the dominant evidence for ice streaming. The megagrooves are typically 5-15 m deep, 10-30 m wide and 500 - 3000 m long. Spacing of megagrooves is typically 100 - 200 m. In both study areas, the bedrock is strongly anisotropic, either consisting of thin-bedded strata or strongly foliated metasedimentary rocks, with the strata or foliation having a gentle dip. Megagrooves are best developed where the strike of the anisotropy is sub-parallel (within 10 - 20°) with palaeo ice flow. The bedrock in both areas has a well-developed, relatively densely spaced (< 1m), conjugate joint system. We suggest that asymmetric megagrooves are formed by

Dynamic Control of Topological Defects in Artificial Colloidal Ice

DOE PAGES

Libál, A.; Nisoli, C.; Reichhardt, C.; ...

2017-04-05

We demonstrate the use of an external field to stabilize and control defect lines connecting topological monopoles in spin ice. For definiteness we perform Brownian dynamics simulations with realistic units mimicking experimentally realized artificial colloidal spin ice systems, and show how defect lines can grow, shrink or move under the action of direct and alternating fields. Asymmetric alternating biasing forces can cause the defect line to ratchet in either direction, making it possible to precisely position the line at a desired location. Such manipulation could be employed to achieve mobile information storage in these metamaterials.

Dynamic Control of Topological Defects in Artificial Colloidal Ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Libál, A.; Nisoli, C.; Reichhardt, C.

We demonstrate the use of an external field to stabilize and control defect lines connecting topological monopoles in spin ice. For definiteness we perform Brownian dynamics simulations with realistic units mimicking experimentally realized artificial colloidal spin ice systems, and show how defect lines can grow, shrink or move under the action of direct and alternating fields. Asymmetric alternating biasing forces can cause the defect line to ratchet in either direction, making it possible to precisely position the line at a desired location. Such manipulation could be employed to achieve mobile information storage in these metamaterials.

Ice Age Sea Level Change on a Dynamic Earth

NASA Astrophysics Data System (ADS)

Austermann, J.; Mitrovica, J. X.; Latychev, K.; Rovere, A.; Moucha, R.

2014-12-01

Changes in global mean sea level (GMSL) are a sensitive indicator of climate variability during the current ice age. Reconstructions are largely based on local sea level records, and the mapping to GMSL is computed from simulations of glacial isostatic adjustment (GIA) on 1-D Earth models. We argue, using two case studies, that resolving important, outstanding issues in ice age paleoclimate requires a more sophisticated consideration of mantle structure and dynamics. First, we consider the coral record from Barbados, which is widely used to constrain global ice volume changes since the Last Glacial Maximum (LGM, ~21 ka). Analyses of the record using 1-D viscoelastic Earth models have estimated a GMSL change since LGM of ~120 m, a value at odds with analyses of other far field records, which range from 130-135 m. We revisit the Barbados case using a GIA model that includes laterally varying Earth structure (Austermann et al., Nature Geo., 2013) and demonstrate that neglecting this structure, in particular the high-viscosity slab in the mantle linked to the subduction of the South American plate, has biased (low) previous estimates of GMSL change since LGM by ~10 m. Our analysis brings the Barbados estimate into accord with studies from other far-field sites. Second, we revisit estimates of GMSL during the mid-Pliocene warm period (MPWP, ~3 Ma), which was characterized by temperatures 2-3°C higher than present. The ice volume deficit during this period is a source of contention, with estimates ranging from 0-40 m GMSL equivalent. We argue that refining estimates of ice volume during MPWP requires a correction for mantle flow induced dynamic topography (DT; Rowley et al., Science, 2013), a signal neglected in previous studies of ice age sea level change. We present estimates of GIA- and DT-corrected elevations of MPWP shorelines from the U.S. east coast, Australia and South Africa in an attempt to reconcile these records with a single GMSL value.

Experimental Analysis of Sublimation Dynamics for Buried Glacier Ice in Beacon Valley, Antarctica

NASA Astrophysics Data System (ADS)

Ehrenfeucht, S.; Dennis, D. P.; Marchant, D. R.

2017-12-01

The age of the oldest known buried ice in Beacon Valley, McMurdo Dry Valleys (MDV) Antarctica is a topic of active debate due to its implications for the stability of the East Antarctic Ice Sheet. Published age estimates range from as young as 300 ka to as old as 8.1 Ma. In the upland MDV, ablation occurs predominantly via sublimation. The relict ice in question (ancient ice from Taylor Glacier) lies buried beneath a thin ( 30-70 cm) layer of sublimation till, which forms as a lag deposit as underlying debris-rich ice sublimes. As the ice sublimates, the debris held within the ice accumulates slowly on the surface, creating a porous boundary between the buried-ice surface and the atmosphere, which in turn influences gas exchange between the ice and the atmosphere. Additionally, englacial debris adds several salt species that are ultimately concentrated on the ice surface. It is well documented the rate of ice sublimation varies as a function of overlying till thickness. However, the rate-limiting dynamics under varying environmental conditions, including the threshold thicknesses at which sublimation is strongly retarded, are not yet defined. To better understand the relationships between sublimation rate, till thickness, and long-term surface evolution, we build on previous studies by Lamp and Marchant (2017) and evaluate the role of till thickness as a control on ice loss in an environmental chamber capable of replicating the extreme cold desert conditions observed in the MDV. Previous work has shown that this relationship exhibits exponential decay behavior, with sublimation rate significantly dampened under less than 10 cm of till. In our experiments we pay particular attention to the effect of the first several cm of till in order to quantify the dynamics that govern the transition from bare ice to debris-covered ice. We also examine this transition for various forms of glacier ice, including ice with various salt species.

Equivalent dynamic model of DEMES rotary joint

NASA Astrophysics Data System (ADS)

Zhao, Jianwen; Wang, Shu; Xing, Zhiguang; McCoul, David; Niu, Junyang; Huang, Bo; Liu, Liwu; Leng, Jinsong

2016-07-01

The dielectric elastomer minimum energy structure (DEMES) can realize large angular deformations by a small voltage-induced strain of the dielectric elastomer (DE), so it is a suitable candidate to make a rotary joint for a soft robot. Dynamic analysis is necessary for some applications, but the dynamic response of DEMESs is difficult to model because of the complicated morphology and viscoelasticity of the DE film. In this paper, a method composed of theoretical analysis and experimental measurement is presented to model the dynamic response of a DEMES rotary joint under an alternating voltage. Based on measurements of equivalent driving force and damping of the DEMES, the model can be derived. Some experiments were carried out to validate the equivalent dynamic model. The maximum angle error between model and experiment is greater than ten degrees, but it is acceptable to predict angular velocity of the DEMES, therefore, it can be applied in feedforward-feedback compound control.

Long-term evolution of a small ice cap in Greenland: a dynamic perspective from numerical flow modelling

NASA Astrophysics Data System (ADS)

Vieli, Andreas; Lane, Timothy; Adamson, Kathryn

2017-04-01

Small ice caps at the periphery of the Greenland ice sheet are often close to the limit of existence and are therefore expected to respond more sensitively to climate change than the land-margin of the neighboring ice sheet. However, their past evolution and dynamic behavior is poorly understood and their use as climate indicators therefore remains so far limited. We here aim to provide a long-term dynamic reconstruction of Lyngmarksbraeen, a small (32km2) ice cap on Disko Island in West Greenland, with a particular focus on the little ice age (LIA, since 1200AD). We use a 2-dim. time-dependent numerical flow model (SIA) and a PDD-mass balance model in combination with historical observations, geomorphological mapping and exposure dating to simulate its long-term evolution and dynamic behaviour. We specifically focus on retreat since the LIA, which is well constrained by geomorphological evidence and historical maps and length records of several small outlet glaciers and data from local and regional climate stations (Qeqertarssuaq and Ilulisat). We also explore aspects related to flow dynamics and find that the dynamic state of this ice cap is, at any time, far from being balanced and is highly sensitive to the surface elevation mass balance feedback and results in an asynchronous response of the different outlets and hysteresis-type behaviour. The modelling is able to reproduce the observed LIA-extent and the almost continuous retreat over the last hundred years well. It further indicates that the ice cap was already dynamically inert since the 1960s. Today, the ice cap has lost almost its entire accumulation area and even without any further warming in the future, the ice cap is expected to vanish within a couple of decades.

Overview of Ice-Sheet Mass Balance and Dynamics from ICESat Measurements

NASA Technical Reports Server (NTRS)

Zwally, H. Jay

2010-01-01

The primary purpose of the ICESat mission was to determine the present-day mass balance of the Greenland and Antarctic ice sheets, identify changes that may be occurring in the surface-mass flux and ice dynamics, and estimate their contributions to global sea-level rise. Although ICESat's three lasers were planned to make continuous measurements for 3 to 5 years, the mission was re-planned to operate in 33-day campaigns 2 to 3 times each year following failure of the first laser after 36 days. Seventeen campaigns were conducted with the last one in the Fall of 2009. Mass balance maps derived from measured ice-sheet elevation changes show that the mass loss from Greenland has increased significantly to about 170 Gt/yr for 2003 to 2007 from a state of near balance in the 1990's. Increased losses (189 Gt/yr) from melting and dynamic thinning are over seven times larger'than increased gains (25 gt/yr) from precipitation. Parts of the West Antarctic ice sheet and the Antarctic Peninsula are losing mass at an increasing rate, but other parts of West Antarctica and the East Antarctic ice sheet are gaining mass at an increasing rate. Increased losses of 35 Gt/yr in Pine Island, Thwaites-Smith, and Marie-Bryd.Coast are more than balanced by gains in base of Peninsula and ice stream C, D, & E systems. From the 1992-2002 to 2003-2007 period, the overall mass balance for Antarctica changed from a loss of about 60 Gt/yr to near balance or slightly positive.

A coupled ice-ocean model of upwelling in the marginal ice zone

NASA Technical Reports Server (NTRS)

Roed, L. P.; Obrien, J. J.

1983-01-01

A dynamical coupled ice-ocean numerical model for the marginal ice zone (MIZ) is suggested and used to study upwelling dynamics in the MIZ. The nonlinear sea ice model has a variable ice concentration and includes internal ice stress. The model is forced by stresses on the air/ocean and air/ice surfaces. The main coupling between the ice and the ocean is in the form of an interfacial stress on the ice/ocean interface. The ocean model is a linear reduced gravity model. The wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water, while the interfacial stress ice/ocean is proportional to the concentration of ice. A new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium. The upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion. Most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport. On the basis of numerical model, an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model.

Free oscillations in a climate model with ice-sheet dynamics

NASA Technical Reports Server (NTRS)

Kallen, E.; Crafoord, C.; Ghil, M.

1979-01-01

A study of stable periodic solutions to a simple nonlinear model of the ocean-atmosphere-ice system is presented. The model has two dependent variables: ocean-atmosphere temperature and latitudinal extent of the ice cover. No explicit dependence on latitude is considered in the model. Hence all variables depend only on time and the model consists of a coupled set of nonlinear ordinary differential equations. The globally averaged ocean-atmosphere temperature in the model is governed by the radiation balance. The reflectivity to incoming solar radiation, i.e., the planetary albedo, includes separate contributions from sea ice and from continental ice sheets. The major physical mechanisms active in the model are (1) albedo-temperature feedback, (2) continental ice-sheet dynamics and (3) precipitation-rate variations. The model has three-equilibrium solutions, two of which are linearly unstable, while one is linearly stable. For some choices of parameters, the stability picture changes and sustained, finite-amplitude oscillations obtain around the previously stable equilibrium solution. The physical interpretation of these oscillations points to the possibility of internal mechanisms playing a role in glaciation cycles.

The impact of dynamic topography on the bedrock elevation and volume of the Pliocene Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Austermann, Jacqueline; Pollard, David; Mitrovica, Jerry X.; Moucha, Robert; Forte, Alessandro M.; DeConto, Robert M.

2015-04-01

Reconstructions of the Antarctic ice sheet over long timescales (i.e. Myrs) require estimates of bedrock elevation through time. Ice sheet models have accounted, with varying levels of sophistication, for changes in the bedrock elevation due to glacial isostatic adjustment (GIA), but they have neglected other processes that may perturb topography. One notable example is dynamic topography, the deflection of the solid surface of the Earth due to convective flow within the mantle. Numerically predicted changes in dynamic topography have been used to correct paleo shorelines for this departure from eustasy, but the effect of such changes on ice sheet stability is unknown. In this study we use numerical predictions of time-varying dynamic topography to reconstruct bedrock elevation below the Antarctic ice sheet during the mid Pliocene warm period (~3 Ma). Moreover, we couple this reconstruction to a three-dimensional ice sheet model to explore the impact of dynamic topography on the evolution of the Antarctic ice sheet since the Pliocene. Our modeling indicates significant uplift in the area of the Transantarctic Mountains (TAM) and the adjacent Wilkes basin. This predicted uplift, which is at the lower end of geological inferences of uplift of the TAM, implies a lower elevation of the basin in the Pliocene. Relative to simulations that do not include dynamic topography, the lower elevation leads to a smaller Antarctic Ice Sheet volume and a more significant retreat of the grounding line in the Wilkes basin, both of which are consistent with offshore sediment core data. We conclude that reconstructions of the Antarctic Ice Sheet during the mid-Pliocene warm period should be based on bedrock elevation models that include the impact of both GIA and dynamic topography.

Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics

NASA Astrophysics Data System (ADS)

Greenwood, Sarah L.; Clark, Chris D.

2009-12-01

The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid

Reaction Dynamics Following Ionization of Ammonia Dimer Adsorbed on Ice Surface.

PubMed

Tachikawa, Hiroto

2016-09-22

The ice surface provides an effective two-dimensional reaction field in interstellar space. However, how the ice surface affects the reaction mechanism is still unknown. In the present study, the reaction of an ammonia dimer cation adsorbed both on water ice and cluster surface was theoretically investigated using direct ab initio molecular dynamics (AIMD) combined with our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) method, and the results were compared with reactions in the gas phase and on water clusters. A rapid proton transfer (PT) from NH3(+) to NH3 takes place after the ionization and the formation of intermediate complex NH2(NH4(+)) is found. The reaction rate of PT was significantly affected by the media connecting to the ammonia dimer. The time of PT was calculated to be 50 fs (in the gas phase), 38 fs (on ice), and 28-33 fs (on water clusters). The dissociation of NH2(NH4(+)) occurred on an ice surface. The reason behind the reaction acceleration on an ice surface is discussed.

Dynamic Tensile Strength of Low Temperature Ice and Kuiper Belt Size Distributions

NASA Astrophysics Data System (ADS)

Ahrens, Thomas J.; Fat'yanov, O. V.; Engelhardt, H.; Fraser, W. C.

2009-09-01

We model mutual gravitationally driven impact interactions in a nearly gas-free environment of the Kuiper belt (KB) and use low-temperature (< 100 K) ice dynamic strength dependent collisional out-come (accretion vs. erosion and fragmentation) models. These lead to theoretically predictable distributions of object number density, vs. mass distributions. These derived mass distributions are comparable to the now rapidly growing KB survey data. Tensional failure of single and polycrystalline ice in the temperature range from 263 to 128 K was measured for high strain rate, c.a. 104 s-1, dynamic loading conditions. Experiments, similar to Lange and Ahrens(1991)(LA), were conducted using a gas gun launched Lexan projectile. The liquid nitrogen cooled ice target approaching KB-like temperatures was partially confined, rather than using the LA confined geometry. Another set of experiments used a drop tube projectile launcher within the 263 K Caltech Ice Laboratory and at 163 K in a liquid nitrogen cooled chamber. New experiments give tensile strengths of 7.6±1.5 MPa at 263 K and 9.1±1.5 MPa at 163 K for unconfined, free of visual initial defects and measurable imperfections ice samples. The new strengths are lower than the earlier LA data ( 17 MPa). The major differences arise from ice target assembly. LA used polycrystalline ice samples confined in annular stainless steel target rings. New measurements were partially confined, in not initially contacting concentric target rings. Later shots used unconfined configurations with ice pellets affixed to aluminum foil. Circumferential confinement is known to increase the material damage threshold upon both compression and tensile loading. Previous confinement in LA is the main cause of the above discrepancy. Present tensile strengths are only a few times higher than 0.7 - 3.0 MPa summarized in Petrovic (2003) for quasistatic tension at 10-7 to 10-3 s-1 strain rate.

Wave effects on ocean-ice interaction in the marginal ice zone

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Hakkinen, Sirpa; Peng, Chih Y.

1993-01-01

The effects of wave train on ice-ocean interaction in the marginal ice zone are studied through numerical modeling. A coupled two-dimensional ice-ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics. The sea ice model is coupled to the reduced-gravity ocean model through interfacial stresses. The main dynamic balance in the ice momentum is between water-ice stress, wind stress, and wave radiation stresses. By considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves, a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed. The numerical results show significant effects from wave action. The ice edge is sharper, and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days. Upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action; wave action sharpens the ice edge and can produce ice meandering, which enhances local Ekman pumping and pycnocline anomalies. The resulting ice concentration, pycnocline changes, and flow velocity field are shown to be consistent with previous observations.

Biogeochemical Cycling and Sea Ice Dynamics in the Bering Sea across the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Detlef, H.; Sosdian, S. M.; Belt, S. T.; Smik, L.; Lear, C. H.; Hall, I. R.; Kender, S.; Leng, M. J.; Husum, K.; Cabedo-Sanz, P.

2017-12-01

Today the Bering Sea is characterized by high primary productivity (PP) along the eastern shelf, maintained by CO2 and nutrient rich upwelled deep waters and nutrient release during spring sea ice melting. As such, low oxygen concentrations are pervasive in mid-depth waters. Changes in ventilation and export productivity in the past have been shown to impact this oxygen minimum zone. On glacial/interglacial (G/IG) timescales sea ice formation plays a pivotal role on intermediate water ventilation with evidence pointing to the formation of North Pacific Intermediate Water (NPIW) in the Bering Sea during Pleistocene glacial intervals. In addition, sea ice plays a significant role in both long- and short-term climate change via associated feedback mechanisms. Thus, records of sea ice dynamics and biogeochemical cycling in the Bering Sea are necessary to fully understand the interaction between PP, circulation patterns, and past G/IG climates with potential implications for the North Pacific carbon cycle. Here we use a multi-proxy approach to study sea ice dynamics and bottom water oxygenation, across three intervals prior to, across, and after the Mid-Pleistocene Transition (MPT, 1.2-0.7 Ma) from International Ocean Discovery Program Site U1343. The MPT, most likely driven by internal climate mechanisms, is ideal to study changes in sea ice dynamics and sedimentary redox conditions on orbital timescales and to investigate the implications for associated feedback mechanisms. The sea ice record, based on various biomarkers, including IP25, shows substantial increase in sea ice extent across the MPT and the occurrence of a late-glacial/deglacial sea ice spike, with consequences for glacial NPIW formation and land glacier retreat via the temperature-precipitation feedback. U/Mn of foraminiferal authigenic coatings, a novel proxy for bottom water oxygenation, also shows distinct variability on G/IG timescales across the MPT, most likely a result of PP and water mass

The northern Uummannaq Ice Stream System, West Greenland: ice dynamics and and controls upon deglaciation

NASA Astrophysics Data System (ADS)

Lane, Timothy; Roberts, David; Rea, Brice; Cofaigh, Colm Ó.; Vieli, Andreas

2013-04-01

the Uummannaq region. Based upon analysis of fjord bathymetry and width, this ice marginal stabilisation has been shown to have been caused by increases in topographic constriction at Karrat Island. The location of the marginal stillstand is coincident with a dramatic narrowing of fjord width and bed shallowing. These increases in local lateral resistance reduces the ice flux necessary to maintain a stable grounding line, leading to ice margin stabilisation. This acted to negate the effects of the Holocene Thermal Maximum. Following this stabilisation, retreat within Rink-Karrat Fjord continued, driven by calving into the overdeepened Rink Fjord. Rink Isbræ reached its present ice margin or beyond after 5 kyr, during the Neoglacial. In contrast, the southern UISS reached its present margin at 8.7 kyr and Jakobshavn Isbræ reached its margin by 7 kyr. This work therefore provides compelling evidence for topographically forced asynchronous, non-linear ice stream retreat between outlet glaciers in West Greenland. In addition, it has major implications for our understanding and reconstruction of mid-Holocene ice sheet extent, and ice sheet dynamics during the Holocene Thermal Maximum to Neoglacial switch.

Low field domain wall dynamics in artificial spin-ice basis structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, J.; School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798; Goolaup, S.

2015-10-28

Artificial magnetic spin-ice nanostructures provide an ideal platform for the observation of magnetic monopoles. The formation of a magnetic monopole is governed by the motion of a magnetic charge carrier via the propagation of domain walls (DWs) in a lattice. To date, most experiments have been on the static visualization of DW propagation in the lattice. In this paper, we report on the low field dynamics of DW in a unit spin-ice structure measured by magnetoresistance changes. Our results show that reversible DW propagation can be initiated within the spin-ice basis. The initial magnetization configuration of the unit structure stronglymore » influences the direction of DW motion in the branches. Single or multiple domain wall nucleation can be induced in the respective branches of the unit spin ice by the direction of the applied field.« less

Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster

NASA Astrophysics Data System (ADS)

Pohlit, Merlin; Stockem, Irina; Porrati, Fabrizio; Huth, Michael; Schröder, Christian; Müller, Jens

2016-10-01

We study the magnetization dynamics of a spin ice cluster which is a building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition both experimentally and theoretically. The spin ice cluster is composed of twelve interacting Co nanoislands grown directly on top of a high-resolution micro-Hall sensor. By employing micromagnetic simulations and a macrospin model, we calculate the magnetization and the experimentally investigated stray field emanating from a single nanoisland. The parameters determined from a comparison with the experimental hysteresis loop are used to derive an effective single-dipole macrospin model that allows us to investigate the dynamics of the spin ice cluster. Our model reproduces the experimentally observed non-deterministic sequences in the magnetization curves as well as the distinct temperature dependence of the hysteresis loop.

The role of synoptic weather variability in Greenland ice sheet dynamics

NASA Astrophysics Data System (ADS)

Walker, J. M.; Radic, V.

2017-12-01

Much of the large uncertainty in predictions of future global sea level rise is due to our limited understanding of Greenland ice sheet (GrIS) motion and its interactions with climate. Over the next century, climate models predict that the GrIS will experience not only gradual warming, but also changes in atmospheric circulation, hydrology, and weather, including a northward shift of the North Atlantic storm track, with greater frequency and intensity of rain storms over the GrIS. Recent studies of GrIS dynamics have focused on the effects of increased seasonal mean meltwater on ice velocities, finding only a modest impact due to compensation by subglacial drainage systems, but subglacial hydraulic theory indicates that variability on shorter timescales is also relevant: short-term surges in meltwater or rainfall can overload drainage systems at rates faster than they can adjust, leading to water pressure spikes and ice acceleration. If the magnitude or frequency of these transient ice accelerations increase substantially as synoptic weather patterns change over the next century, there could be a significant cumulative impact on seasonal mean ice velocities. However, this issue has not been addressed in the literature and represents a major source of uncertainty. In this study, we investigate the role of synoptic weather variability in GrIS dynamics, with the ultimate goal of evaluating the relationships between extreme weather events and ice sheet flow in different seasons and regions of the GrIS. As a first step, we apply the machine learning technique of self-organizing maps to atmospheric reanalysis data to categorize the predominant synoptic weather systems over the GrIS domain, evaluating atmospheric moisture transport and rainfall to assess the impacts of each weather system on GrIS surface hydrology. The preliminary results presented here will be used in conjunction with ice velocity satellite measurements in future work, to identify any correlations

Inferior olive mirrors joint dynamics to implement an inverse controller.

PubMed

Alvarez-Icaza, Rodrigo; Boahen, Kwabena

2012-10-01

To produce smooth and coordinated motion, our nervous systems need to generate precisely timed muscle activation patterns that, due to axonal conduction delay, must be generated in a predictive and feedforward manner. Kawato proposed that the cerebellum accomplishes this by acting as an inverse controller that modulates descending motor commands to predictively drive the spinal cord such that the musculoskeletal dynamics are canceled out. This and other cerebellar theories do not, however, account for the rich biophysical properties expressed by the olivocerebellar complex's various cell types, making these theories difficult to verify experimentally. Here we propose that a multizonal microcomplex's (MZMC) inferior olivary neurons use their subthreshold oscillations to mirror a musculoskeletal joint's underdamped dynamics, thereby achieving inverse control. We used control theory to map a joint's inverse model onto an MZMC's biophysics, and we used biophysical modeling to confirm that inferior olivary neurons can express the dynamics required to mirror biomechanical joints. We then combined both techniques to predict how experimentally injecting current into the inferior olive would affect overall motor output performance. We found that this experimental manipulation unmasked a joint's natural dynamics, as observed by motor output ringing at the joint's natural frequency, with amplitude proportional to the amount of current. These results support the proposal that the cerebellum-in particular an MZMC-is an inverse controller; the results also provide a biophysical implementation for this controller and allow one to make an experimentally testable prediction.

How dynamic are ice-stream beds?

NASA Astrophysics Data System (ADS)

Davies, Damon; Bingham, Robert G.; King, Edward C.; Smith, Andrew M.; Brisbourne, Alex M.; Spagnolo, Matteo; Graham, Alastair G. C.; Hogg, Anna E.; Vaughan, David G.

2018-05-01

Projections of sea-level rise contributions from West Antarctica's dynamically thinning ice streams contain high uncertainty because some of the key processes involved are extremely challenging to observe. An especially poorly observed parameter is sub-decadal stability of ice-stream beds, which may be important for subglacial traction, till continuity and landform development. Only two previous studies have made repeated geophysical measurements of ice-stream beds at the same locations in different years, but both studies were limited in spatial extent. Here, we present the results from repeat radar measurements of the bed of Pine Island Glacier, West Antarctica, conducted 3-6 years apart, along a cumulative ˜ 60 km of profiles. Analysis of the correlation of bed picks between repeat surveys shows that 90 % of the bed displays no significant change despite the glacier increasing in speed by up to 40 % over the last decade. We attribute the negligible detection of morphological change at the bed of Pine Island Glacier to the ubiquitous presence of a deforming till layer, wherein sediment transport is in steady state, such that sediment is transported along the basal interface without inducing morphological change to the radar-sounded basal interface. Given the precision of our measurements, the upper limit of subglacial erosion observed here is 500 mm a-1, far exceeding erosion rates reported for glacial settings from proglacial sediment yields, but substantially below subglacial erosion rates of 1.0 m a-1 previously reported from repeat geophysical surveys in West Antarctica.

Sensitivity of simulated englacial isochrones to uncertain subglacial boundary conditions in central West Antarctica: Implications for detecting changes in ice dynamics

NASA Astrophysics Data System (ADS)

Muldoon, Gail; Jackson, Charles S.; Young, Duncan A.; Quartini, Enrica; Cavitte, Marie G. P.; Blankenship, Donald D.

2017-04-01

Information about the extent and dynamics of the West Antarctic Ice Sheet during past glaciations is preserved inside ice sheets themselves. Ice cores are capable of retrieving information about glacial history, but they are spatially sparse. Ice-penetrating radar, on the other hand, has been used to map large areas of the West Antarctic Ice Sheet and can be correlated to ice core chronologies. Englacial isochronous layers observed in ice-penetrating radar are the result of variations in ice composition, fabric, temperature and other factors. The shape of these isochronous surfaces is expected to encode information about past and present boundary conditions and ice dynamics. Dipping of englacial layers, for example, may reveal the presence of rapid ice flow through paleo ice streams or high geothermal heat flux. These layers therefore present a useful testbed for hypotheses about paleo ice sheet conditions. However, hypothesis testing requires careful consideration of the sensitivity of layer shape to the competing forces of ice sheet boundary conditions and ice dynamics over time. Controlled sensitivity tests are best completed using models, however ice sheet models generally do not have the capability of simulating layers in the presence of realistic boundary conditions. As such, modeling 3D englacial layers for comparison to observations is difficult and requires determination of a 3D ice velocity field. We present a method of post-processing simulated 3D ice sheet velocities into englacial isochronous layers using an advection scheme. We then test the sensitivity of layer geometry to uncertain boundary conditions, including heterogeneous subglacial geothermal flux and bedrock topography. By identifying areas of the ice sheet strongly influenced by boundary conditions, it may be possible to isolate the signature of paleo ice dynamics in the West Antarctic ice sheet.

Teleseismic Earthquake Signals Observed on an Ice Shelf

NASA Astrophysics Data System (ADS)

Baker, M. G.; Aster, R. C.; Anthony, R. E.; Wiens, D.; Nyblade, A.; Bromirski, P. D.; Stephen, R. A.; Gerstoft, P.

2015-12-01

The West Antarctic Rift System (WARS) is one of Earth's largest continental extension zones. Study of the WARS is complicated by the presence of the West Antarctic Ice Sheet, the Ross Ice Shelf, and the Ross Sea. Recent deployments of broadband seismographs in the POLENET project have allowed passive seismic techniques, such as receiver function analysis and surface wave dispersion, to be widely utilized to infer crustal and mantle velocity structure across much of the WARS and West Antarctica. However, a large sector of the WARS lies beneath the Ross Ice Shelf. In late 2014, 34 broadband seismographs were deployed atop the ice shelf to jointly study deep Earth structure and the dynamics of the ice shelf. Ice shelf conditions present strong challenges to broadband teleseismic imaging: 1) The presence of complicating signals in the microseism through long-period bands due to the influence of ocean gravity waves; 2) The strong velocity contrasts at the ice-water and water-sediment interfaces on either side of the water layer give rise to large amplitude reverberations; 3) The water layer screens S-waves or P-to-S phases originating from below the water layer. We present an initial analysis of the first teleseismic earthquake arrivals collected on the ice shelf at the end of the 2014 field season from a limited subset of these stations.

Reconstructing Interlaced High-Dynamic-Range Video Using Joint Learning.

PubMed

Inchang Choi; Seung-Hwan Baek; Kim, Min H

2017-11-01

For extending the dynamic range of video, it is a common practice to capture multiple frames sequentially with different exposures and combine them to extend the dynamic range of each video frame. However, this approach results in typical ghosting artifacts due to fast and complex motion in nature. As an alternative, video imaging with interlaced exposures has been introduced to extend the dynamic range. However, the interlaced approach has been hindered by jaggy artifacts and sensor noise, leading to concerns over image quality. In this paper, we propose a data-driven approach for jointly solving two specific problems of deinterlacing and denoising that arise in interlaced video imaging with different exposures. First, we solve the deinterlacing problem using joint dictionary learning via sparse coding. Since partial information of detail in differently exposed rows is often available via interlacing, we make use of the information to reconstruct details of the extended dynamic range from the interlaced video input. Second, we jointly solve the denoising problem by tailoring sparse coding to better handle additive noise in low-/high-exposure rows, and also adopt multiscale homography flow to temporal sequences for denoising. We anticipate that the proposed method will allow for concurrent capture of higher dynamic range video frames without suffering from ghosting artifacts. We demonstrate the advantages of our interlaced video imaging compared with the state-of-the-art high-dynamic-range video methods.

Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade.

PubMed

Price, Stephen F; Payne, Antony J; Howat, Ian M; Smith, Benjamin E

2011-05-31

We use a three-dimensional, higher-order ice flow model and a realistic initial condition to simulate dynamic perturbations to the Greenland ice sheet during the last decade and to assess their contribution to sea level by 2100. Starting from our initial condition, we apply a time series of observationally constrained dynamic perturbations at the marine termini of Greenland's three largest outlet glaciers, Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier. The initial and long-term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea-level contribution of approximately 1 ± 0.4 mm from these three glaciers by 2100. Based on scaling arguments, we extend our modeling to all of Greenland and estimate a minimum dynamic sea-level contribution of approximately 6 ± 2 mm by 2100. This estimate of committed sea-level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance. Importantly, > 75% of this value is from the long-term, diffusive response of the ice sheet, suggesting that the majority of sea-level rise from Greenland dynamics during the past decade is yet to come. Assuming similar and recurring forcing in future decades and a self-similar ice dynamical response, we estimate an upper bound of 45 mm of sea-level rise from Greenland dynamics by 2100. These estimates are constrained by recent observations of dynamic mass loss in Greenland and by realistic model behavior that accounts for both the long-term cumulative mass loss and its decay following episodic boundary forcing.

Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade

PubMed Central

Price, Stephen F.; Payne, Antony J.; Howat, Ian M.; Smith, Benjamin E.

2011-01-01

We use a three-dimensional, higher-order ice flow model and a realistic initial condition to simulate dynamic perturbations to the Greenland ice sheet during the last decade and to assess their contribution to sea level by 2100. Starting from our initial condition, we apply a time series of observationally constrained dynamic perturbations at the marine termini of Greenland’s three largest outlet glaciers, Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier. The initial and long-term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea-level contribution of approximately 1 ± 0.4 mm from these three glaciers by 2100. Based on scaling arguments, we extend our modeling to all of Greenland and estimate a minimum dynamic sea-level contribution of approximately 6 ± 2 mm by 2100. This estimate of committed sea-level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance. Importantly, > 75% of this value is from the long-term, diffusive response of the ice sheet, suggesting that the majority of sea-level rise from Greenland dynamics during the past decade is yet to come. Assuming similar and recurring forcing in future decades and a self-similar ice dynamical response, we estimate an upper bound of 45 mm of sea-level rise from Greenland dynamics by 2100. These estimates are constrained by recent observations of dynamic mass loss in Greenland and by realistic model behavior that accounts for both the long-term cumulative mass loss and its decay following episodic boundary forcing. PMID:21576500

DRA/NASA/ONERA Collaboration on Icing Research. Part 2; Prediction of Airfoil Ice Accretion

NASA Technical Reports Server (NTRS)

Wright, William B.; Gent, R. W.; Guffond, Didier

1997-01-01

This report presents results from a joint study by DRA, NASA, and ONERA for the purpose of comparing, improving, and validating the aircraft icing computer codes developed by each agency. These codes are of three kinds: (1) water droplet trajectory prediction, (2) ice accretion modeling, and (3) transient electrothermal deicer analysis. In this joint study, the agencies compared their code predictions with each other and with experimental results. These comparison exercises were published in three technical reports, each with joint authorship. DRA published and had first authorship of Part 1 - Droplet Trajectory Calculations, NASA of Part 2 - Ice Accretion Prediction, and ONERA of Part 3 - Electrothermal Deicer Analysis. The results cover work done during the period from August 1986 to late 1991. As a result, all of the information in this report is dated. Where necessary, current information is provided to show the direction of current research. In this present report on ice accretion, each agency predicted ice shapes on two dimensional airfoils under icing conditions for which experimental ice shapes were available. In general, all three codes did a reasonable job of predicting the measured ice shapes. For any given experimental condition, one of the three codes predicted the general ice features (i.e., shape, impingement limits, mass of ice) somewhat better than did the other two. However, no single code consistently did better than the other two over the full range of conditions examined, which included rime, mixed, and glaze ice conditions. In several of the cases, DRA showed that the user's knowledge of icing can significantly improve the accuracy of the code prediction. Rime ice predictions were reasonably accurate and consistent among the codes, because droplets freeze on impact and the freezing model is simple. Glaze ice predictions were less accurate and less consistent among the codes, because the freezing model is more complex and is critically

Theory of buttressed marine ice sheet dynamics and its application to the assessment of tipping-point conditions

NASA Astrophysics Data System (ADS)

Pegler, S.

2017-12-01

Understanding the fate of the West Antarctic Ice Sheet is constrained by difficulties of resolving the buttressing effect of ice shelves and its dynamic response to grounding-line migration. This effect may be responsible for protecting a large majority of outlet glaciers in Antarctica against surging into the ocean. I present a theoretical methodology for assessing the positions and stability of grounding lines that incorporates closed-form, dynamic descriptions of ice-shelf buttressing and extensional (stretching) viscous stresses. The method is applied to assess the conditions for grounding-line tipping points. Such points are shown to produce abrupt `cliff-edge' transitions to runaway retreat, representing the so-called marine ice sheet instability. Depending on the bed profile, melt and calving rates, a tipping point can either lie very near to a local maximum in the bed topography or potentially far upstream of it, along a reverse bed. The model predictions for both wide and narrow embayments are validated by numerical simulations and laboratory experiments. A case study of Pine Island Glacier indicates the possibility for long-term stabilisation, with the analytical method affording an extensive exploration of scenarios. The theory also elucidates a mode of grounding-line migration controlled entirely by the determinants of the ice-shelf buttressing force, with a loss of sensitivity to basal conditions, contrasting with the conclusion from one-dimensional theory that the ice shelf is irrelevant. The results provide an interpretive framework for understanding grounding-line dynamics, its coupling with ice-shelf dynamics, an efficient exploration of parameter variation, and a complement to large-scale simulation.

Changes in ice dynamics along the northern Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Seehaus, Thorsten; Marinsek, Sebastian; Cook, Alison; Van Wessem, Jan-Melchior; Braun, Matthias

2017-04-01

The climatic conditions along the Antarctic Peninsula have undergone considerable changes during the last 50 years. A period of pronounced air temperature rise, increasing ocean temperatures as well as changes in the precipitation pattern have been reported by various authors. Consequently, the glacial systems showed changes including widespread retreat, surface lowering as well as variations in flow speeds. During the last decades numerous ice shelves along the Antarctic Peninsula retreated, started to break-up or disintegrated completely. The loss of the buttressing effect caused tributary glaciers to accelerate with increasing ice discharge along the Antarctic Peninsula. Quantification of the mass changes is still subject to considerable errors although numbers derived from the different methods are converging. The aim is to study the reaction of glaciers at the northern Antarctic Peninsula to the changing climatic conditions and the readjustments of tributary glaciers to ice shelf disintegration, as well as to better quantify the ice mass loss and its temporal changes. We analysed time series of various satellite sensors (ERS-1/2 SAR, ENVISAT ASAR, RADARSAT-1, ALOS PALSAR, TerraSAR-X/TanDEM-X, ASTER, Landsat) to detect changes in ice dynamics of 74 glacier basins along the northern Antarctic Peninsula (<65°). Intensity feature tracking techniques were applied on data stacks from different SAR satellites over the last 20 years to infer temporal trends in glacier surface velocities. In combination with ice thickness reconstructions and modeled climatic mass balance fields regional imbalances were calculated. Variations in ice front position were mapped based on optical and SAR satellite data sets. Along the west coast of the northern Antarctic Peninsula an increase in flow speeds by 40% between 1992 and 2014 was observed, whereas glaciers on the east side (north of former Prince-Gustav Ice Shelf) showed a strong deceleration. Nearly all former ice shelf

Can xenon in water inhibit ice growth? Molecular dynamics of phase transitions in water-Xe system.

PubMed

Artyukhov, Vasilii I; Pulver, Alexander Yu; Peregudov, Alex; Artyuhov, Igor

2014-07-21

Motivated by recent experiments showing the promise of noble gases as cryoprotectants, we perform molecular dynamics modeling of phase transitions in water with xenon under cooling. We follow the structure and dynamics of xenon water solution as a function of temperature. Homogeneous nucleation of clathrate hydrate phase is observed and characterized. As the temperature is further reduced we observe hints of dissociation of clathrate due to stronger hydrophobic hydration, pointing towards a possible instability of clathrate at cryogenic temperatures and conversion to an amorphous phase comprised of "xenon + hydration shell" Xe·(H2O)21.5 clusters. Simulations of ice-xenon solution interface in equilibrium and during ice growth reveal the effects of xenon on the ice-liquid interface, where adsorbed xenon causes roughening of ice surface but does not preferentially form clathrate. These results provide evidence against the ice-blocker mechanism of xenon cryoprotection.

Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth

NASA Astrophysics Data System (ADS)

Cook, Carys P.; van de Flierdt, Tina; Williams, Trevor; Hemming, Sidney R.; Iwai, Masao; Kobayashi, Munemasa; Jimenez-Espejo, Francisco J.; Escutia, Carlota; González, Jhon Jairo; Khim, Boo-Keun; McKay, Robert M.; Passchier, Sandra; Bohaty, Steven M.; Riesselman, Christina R.; Tauxe, Lisa; Sugisaki, Saiko; Galindo, Alberto Lopez; Patterson, Molly O.; Sangiorgi, Francesca; Pierce, Elizabeth L.; Brinkhuis, Henk; Klaus, Adam; Fehr, Annick; Bendle, James A. P.; Bijl, Peter K.; Carr, Stephanie A.; Dunbar, Robert B.; Flores, José Abel; Hayden, Travis G.; Katsuki, Kota; Kong, Gee Soo; Nakai, Mutsumi; Olney, Matthew P.; Pekar, Stephen F.; Pross, Jörg; Röhl, Ursula; Sakai, Toyosaburo; Shrivastava, Prakash K.; Stickley, Catherine E.; Tuo, Shouting; Welsh, Kevin; Yamane, Masako

2013-09-01

Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century and atmospheric CO2 concentrations similar to today. Estimates for global sea level highstands during these times imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.

Seasonal-to-Interannual Variability in Antarctic Sea-Ice Dynamics, and Its Impact on Surface Fluxes and Water Mass Production

NASA Technical Reports Server (NTRS)

Drinkwater, Mark R.

1999-01-01

Strong seasonal and interannual signals in Antarctic bottom-water outflow remain unexplained yet are highly correlated with anomalies in net sea-ice growth in coastal polynyas. The mechanisms responsible for driving salination and replenishment and rejuvenation of the dense shelf "source" waters likely also generate pulses of bottom water outflow. The objective of this research is to investigate time-scales of variability in the dynamics of sea-ice in the Southern Ocean in order to determine the primary sites for production of dense shelf waters. We are using a merged satellite/buoy sea-ice motion data set for the period 1978-present day to compute the dynamics of opening and closing of coastal polynyas over the continental shelf. The Ocean Circulation and Climate Advanced Model (OCCAM) ocean general circulation model with coupled sea-ice dynamics is presently forced using National Center for Environmental Prediction (NCEP) data to simulate fluxes and the salination impact of the ocean shelf regions. This work is relevant in the context of measuring the influence of polar sea-ice dynamics upon polar ocean characteristics, and thereby upon global thermohaline ocean circulation. Interannual variability in simulated net freezing rate in the Southern Weddell Sea is shown for the period 1986-1993. There is a pronounced maximum of ice production in 1988 and minimum in 1991 in response to anomalies in equatorward meridional wind velocity. This follows a similar approximate 8-year interannual cycle in Sea Surface Temperature (SST) and satellite-derived ice-edge anomalies reported elsewhere as the "Antarctic Circumpolar Wave." The amplitude of interannual fluctuations in annual net ice production are about 40% of the mean value, implying significant interannual variance in brine rejection and upper ocean heat loss. Southward anomalies in wind stress induce negative anomalies in open water production, which are observed in passive microwave satellite images. Thus, cycles of

Overview of ICE Project: Integration of Computational Fluid Dynamics and Experiments

NASA Technical Reports Server (NTRS)

Stegeman, James D.; Blech, Richard A.; Babrauckas, Theresa L.; Jones, William H.

2001-01-01

Researchers at the NASA Glenn Research Center have developed a prototype integrated environment for interactively exploring, analyzing, and validating information from computational fluid dynamics (CFD) computations and experiments. The Integrated CFD and Experiments (ICE) project is a first attempt at providing a researcher with a common user interface for control, manipulation, analysis, and data storage for both experiments and simulation. ICE can be used as a live, on-tine system that displays and archives data as they are gathered; as a postprocessing system for dataset manipulation and analysis; and as a control interface or "steering mechanism" for simulation codes while visualizing the results. Although the full capabilities of ICE have not been completely demonstrated, this report documents the current system. Various applications of ICE are discussed: a low-speed compressor, a supersonic inlet, real-time data visualization, and a parallel-processing simulation code interface. A detailed data model for the compressor application is included in the appendix.

A Dynamic Model for the Evaluation of Aircraft Engine Icing Detection and Control-Based Mitigation Strategies

NASA Technical Reports Server (NTRS)

Simon, Donald L.; Rinehart, Aidan W.; Jones, Scott M.

2017-01-01

Aircraft flying in regions of high ice crystal concentrations are susceptible to the buildup of ice within the compression system of their gas turbine engines. This ice buildup can restrict engine airflow and cause an uncommanded loss of thrust, also known as engine rollback, which poses a potential safety hazard. The aviation community is conducting research to understand this phenomena, and to identify avoidance and mitigation strategies to address the concern. To support this research, a dynamic turbofan engine model has been created to enable the development and evaluation of engine icing detection and control-based mitigation strategies. This model captures the dynamic engine response due to high ice water ingestion and the buildup of ice blockage in the engines low pressure compressor. It includes a fuel control system allowing engine closed-loop control effects during engine icing events to be emulated. The model also includes bleed air valve and horsepower extraction actuators that, when modulated, change overall engine operating performance. This system-level model has been developed and compared against test data acquired from an aircraft turbofan engine undergoing engine icing studies in an altitude test facility and also against outputs from the manufacturers customer deck. This paper will describe the model and show results of its dynamic response under open-loop and closed-loop control operating scenarios in the presence of ice blockage buildup compared against engine test cell data. Planned follow-on use of the model for the development and evaluation of icing detection and control-based mitigation strategies will also be discussed. The intent is to combine the model and control mitigation logic with an engine icing risk calculation tool capable of predicting the risk of engine icing based on current operating conditions. Upon detection of an operating region of risk for engine icing events, the control mitigation logic will seek to change the

NASA Lewis' Icing Research Tunnel Works With Small Local Company to Test Coatings

NASA Technical Reports Server (NTRS)

1998-01-01

Dynamic Coatings, Inc., wanted to test coating products that would enable the company to approach new markets. A Space Act Agreement with NASA Lewis Research Center afforded them this opportunity. They used Lewis' Icing Research Tunnel to test coating products for reduced ice adhesion, industrial and aerospace lubrication applications, a tiremold release coating now used in the production of tires for the Boeing 777, and a product that solidifies asbestos fibers (which is being tested as an insulator in a power plant in Iowa). Not only was the testing a success, but during these activities, Dynamic Coatings met another coating company with whom they now have a joint venture offering a barnacle-repellent coating for marine applications, now on the market in Florida.

Irish Ice Sheet dynamics during deglaciation of the central Irish Midlands: Evidence of ice streaming and surging from airborne LiDAR

NASA Astrophysics Data System (ADS)

Delaney, Catherine A.; McCarron, Stephen; Davis, Stephen

2018-04-01

High resolution digital terrain models (DTMs) generated from airborne LiDAR data and supplemented by field evidence are used to map glacial landform assemblages dating from the last glaciation (Midlandian glaciation; OI stages 2-3) in the central Irish Midlands. The DTMs reveal previously unrecognised low-amplitude landforms, including crevasse-squeeze ridges and mega-scale glacial lineations overprinted by conduit fills leading to ice-marginal subaqueous deposits. We interpret this landform assemblage as evidence for surging behaviour during ice recession. The data indicate that two separate phases of accelerated ice flow were followed by ice sheet stagnation during overall deglaciation. The second surge event was followed by a subglacial outburst flood, forming an intricate esker and crevasse-fill network. The data provide the first clear evidence that ice flow direction was eastward along the eastern watershed of the Shannon River basin, at odds with previous models, and raise the possibility that an ice stream existed in this area. Our work demonstrates the potential for airborne LiDAR surveys to produce detailed paleoglaciological reconstructions and to enhance our understanding of complex palaeo-ice sheet dynamics.

Simulations of Sea-Ice Dynamics Using the Material-Point Method

NASA Technical Reports Server (NTRS)

Sulsky, D.; Schreyer, H.; Peterson, K.; Nguyen, G.; Coon, G.; Kwok, R.

2006-01-01

provide similar overall deformation as the viscous-plastic model; however, explicit regions of opening and shear are predicted. Furthermore, the efficiency of MPM with the elastic-decohesive model is competitive with the current best methods for sea ice dynamics. Simulations will also be presented for an area of the Beaufort Sea, where predictions can be validated against satellite observations of the Arctic.

C-band Joint Active/Passive Dual Polarization Sea Ice Detection

NASA Astrophysics Data System (ADS)

Keller, M. R.; Gifford, C. M.; Winstead, N. S.; Walton, W. C.; Dietz, J. E.

2017-12-01

A technique for synergistically-combining high-resolution SAR returns with like-frequency passive microwave emissions to detect thin (<30 cm) ice under the difficult conditions of late melt and freeze-up is presented. As the Arctic sea ice cover thins and shrinks, the algorithm offers an approach to adapting existing sensors monitoring thicker ice to provide continuing coverage. Lower resolution (10-26 km) ice detections with spaceborne radiometers and scatterometers are challenged by rapidly changing thin ice. Synthetic Aperture Radar (SAR) is high resolution (5-100m) but because of cross section ambiguities automated algorithms have had difficulty separating thin ice types from water. The radiometric emissivity of thin ice versus water at microwave frequencies is generally unambiguous in the early stages of ice growth. The method, developed using RADARSAT-2 and AMSR-E data, uses higher-ordered statistics. For the SAR, the COV (coefficient of variation, ratio of standard deviation to mean) has fewer ambiguities between ice and water than cross sections, but breaking waves still produce ice-like signatures for both polarizations. For the radiometer, the PRIC (polarization ratio ice concentration) identifies areas that are unambiguously water. Applying cumulative statistics to co-located COV levels adaptively determines an ice/water threshold. Outcomes from extensive testing with Sentinel and AMSR-2 data are shown in the results. The detection algorithm was applied to the freeze-up in the Beaufort, Chukchi, Barents, and East Siberian Seas in 2015 and 2016, spanning mid-September to early November of both years. At the end of the melt, 6 GHz PRIC values are 5-10% greater than those reported by radiometric algorithms at 19 and 37 GHz. During freeze-up, COV separates grease ice (<5 cm thick) from water. As the ice thickens, the COV is less reliable, but adding a mask based on either the PRIC or the cross-pol/co-pol SAR ratio corrects for COV deficiencies. In general

Fast Response of the Tropics to an Abrupt Loss of Arctic Sea Ice via Ocean Dynamics

NASA Astrophysics Data System (ADS)

Wang, Kun; Deser, Clara; Sun, Lantao; Tomas, Robert A.

2018-05-01

The role of ocean dynamics in the transient adjustment of the coupled climate system to an abrupt loss of Arctic sea ice is investigated using experiments with Community Climate System Model version 4 in two configurations: a thermodynamic slab mixed layer ocean and a full-depth ocean that includes both dynamics and thermodynamics. Ocean dynamics produce a distinct sea surface temperature warming maximum in the eastern equatorial Pacific, accompanied by an equatorward intensification of the Intertropical Convergence Zone and Hadley Circulation. These tropical responses are established within 25 years of ice loss and contrast markedly with the quasi-steady antisymmetric coupled response in the slab-ocean configuration. A heat budget analysis reveals the importance of anomalous vertical advection tied to a monotonic temperature increase below 200 m for the equatorial sea surface temperature warming maximum in the fully coupled model. Ocean dynamics also rapidly modify the midlatitude atmospheric response to sea ice loss.

An Investigation of Mineral Dynamics in Sea Ice by Solubility Measurements

NASA Astrophysics Data System (ADS)

Butler, B.; Kennedy, H.; Papadimitriou, S.

2016-02-01

Sea ice is a composite material with a sponge-like structure. The framework of the structure is composed of pure ice, and within the pores exists a concentrated seawater brine. When the temperature is reduced, the volume of this residual brine decreases, while its salinity increases. As a result of the paired changes to temperature and salinity, the brine becomes supersaturated with respect to a mineral at several points when cooling sea ice towards -30°C, creating a sequence of minerals that precipitate. The presence of countless microscopic salt crystals encapsulated within the ice, coupled with changes in brine volume associated with their precipitation/dissolution, results in changes to the optical and structural properties of the medium that contribute to the surface energy balance in sea ice environments. Furthermore, attainment of mineral equilibrium can result in abrupt changes in brine composition and osmotic conditions in the isolated brine pockets, imposing challenging conditions upon the biota that habitat the sea ice environment. Mirabilite (Na2SO4.10H2O), gypsum (CaSO4.2H2O) and hydrohalite (NaCl.2H2O) each represent minerals that are understood to exist within sea ice. Previous research has focused upon mineral extraction/detection, and the specific temperature for the onset of each minerals precipitation in sea ice; rather than the overarching dynamics. For this reason, solubility measurements of mirabilite, gypsum and hydrohalite in conditions representative of equilibrium sea ice brines were carried between 0 and -28°C, covering a range of undersaturated and supersaturated conditions for each mineral. Results provide accurate data for the onset of each minerals formation in sea ice, as well as important information on the way in which precipitation and dissolution reactions are affected when sea ice warms or cools. By incorporating the solubility data into a model that simluates the temperature-salinity profiles of first-year sea ice, the

The role of ice particles in the microphysics and dynamics of deep convective storms in various latitudes

NASA Astrophysics Data System (ADS)

Huang, Y. C.; Wang, P. K.

2017-12-01

The role of ice particles in the microphysics and dynamics of deep convective storms in various latitudes Yi-Chih Huang and Pao K. Wang Ice particles contribute to the microphysics and dynamics of severe storms in various regions of the world to a degree that is not commonly recognized. This study is motivated by the need to understand the role of ice particles plays in the development of severe storms so that their impact on various aspects of the storm behavior can be properly assessed. In this study, we perform numerical simulations of thunderstorms using a cloud resolving model WISCDYMM that includes parameterized microphysical processes to understand the role played by ice processes. We simulate thunderstorms occurred over various regions of the world including tropics, substropics and midlatitudes. We then perform statistical analysis of the simulated results to show the formation of various categories of hydrometeors to reveal the importance of ice processes. We will show that ice hydrometeors (cloud ice, snow, graupel/hail) account for 80% of the total hydrometeor mass for the High Plains storms but 50% for the subtropical storms. In addition, the melting of large ice particles (graupel and hail) is the major production process of rain in tropical storms although the ratio of ice-phase mass is responsible for only 40% of the total hydrometeor mass. Furthermore, hydrometeors have their own special microphysical processes in development and depletion over various latitudes. Microphysical structures depend on atmospheric dynamical and thermodynamical conditions which determine the partitioning of hydrometeors. This knowledge would benefit the microphysics parameterization in cloud models and cumulus parameterization in global circulation models.

Dynamic response of an artificial square spin ice

DOE PAGES

Jungfleisch, M. B.; Zhang, W.; Iacocca, E.; ...

2016-03-02

Magnetization dynamics in an artficial square spin-ice lattice made of Ni80Fe20 with magnetic field applied in the lattice plane is investigated by broadband ferromagnetic resonance spectroscopy. The experimentally observed dispersion shows a rich spectrum of modes corresponding to different magnetization states. These magnetization states are determined by exchange and dipolar interaction between individual islands, as is confirmed by a semianalytical model. In the low field regime below 400 Oe a hysteretic behavior in the mode spectrum is found. Micromagnetic simulations reveal that the origin of the observed spectra is due to the initialization of different magnetization states of individual nanomagnets.more » Our results indicate that it might be possible to determine the spin-ice state by resonance experiments and are a first step towards the understanding of artificial geometrically frustrated magnetic systems in the high-frequency regime.« less

Dynamic response of an artificial square spin ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jungfleisch, M. B.; Zhang, W.; Iacocca, E.

Magnetization dynamics in an artficial square spin-ice lattice made of Ni80Fe20 with magnetic field applied in the lattice plane is investigated by broadband ferromagnetic resonance spectroscopy. The experimentally observed dispersion shows a rich spectrum of modes corresponding to different magnetization states. These magnetization states are determined by exchange and dipolar interaction between individual islands, as is confirmed by a semianalytical model. In the low field regime below 400 Oe a hysteretic behavior in the mode spectrum is found. Micromagnetic simulations reveal that the origin of the observed spectra is due to the initialization of different magnetization states of individual nanomagnets.more » Our results indicate that it might be possible to determine the spin-ice state by resonance experiments and are a first step towards the understanding of artificial geometrically frustrated magnetic systems in the high-frequency regime.« less

The effects of ice on methane hydrate nucleation: a microcanonical molecular dynamics study.

PubMed

Zhang, Zhengcai; Guo, Guang-Jun

2017-07-26

Although ice powders are widely used in gas hydrate formation experiments, the effects of ice on hydrate nucleation and what happens in the quasi-liquid layer of ice are still not well understood. Here, we used high-precision constant energy molecular dynamics simulations to study methane hydrate nucleation from vapor-liquid mixtures exposed to the basal, prismatic, and secondary prismatic planes of hexagonal ice (ice Ih). Although no significant difference is observed in hydrate nucleation processes for these different crystal planes, it is found, more interestingly, that methane hydrate can nucleate either on the ice surface heterogeneously or in the bulk solution phase homogeneously. Several factors are mentioned to be able to promote the heterogeneous nucleation of hydrates, including the adsorption of methane molecules at the solid-liquid interface, hydrogen bonding between hydrate cages and the ice structure, the stronger ability of ice to transfer heat than that of the aqueous solution, and the higher occurrence probability of hydrate cages in the vicinity of the ice surface than in the bulk solution. Meanwhile, however, the other factors including the hydrophilicity of ice and the ice lattice mismatch with clathrate hydrates can inhibit heterogeneous nucleation on the ice surface and virtually promote homogeneous nucleation in the bulk solution. Certainly, the efficiency of ice as a promoter and as an inhibitor for heterogeneous nucleation is different. We estimate that the former is larger than the latter under the working conditions. Additionally, utilizing the benefit of ice to absorb heat, the NVE simulation of hydrate formation with ice can mimic the phenomenon of ice shrinking during the heterogeneous nucleation of hydrates and lower the overly large temperature increase during homogeneous nucleation. These results are helpful in understanding the nucleation mechanism of methane hydrate in the presence of ice.

Improved parameterization of marine ice dynamics and flow instabilities for simulation of the Austfonna ice cap using a large-scale ice sheet model

NASA Astrophysics Data System (ADS)

Dunse, T.; Greve, R.; Schuler, T.; Hagen, J. M.; Navarro, F.; Vasilenko, E.; Reijmer, C.

2009-12-01

The Austfonna ice cap covers an area of 8120 km2 and is by far the largest glacier on Svalbard. Almost 30% of the entire area is grounded below sea-level, while the figure is as large as 57% for the known surge-type basins in particular. Marine ice dynamics, as well as flow instabilities presumably control flow regime, form and evolution of Austfonna. These issues are our focus in numerical simulations of the ice cap. We employ the thermodynamic, large-scale ice sheet model SICOPOLIS (http://sicopolis.greveweb.net/) which is based on the shallow-ice approximation. We present improved parameterizations of (a) the marine extent and calving and (b) processes that may initiate flow instabilities such as switches from cold to temperate basal conditions, surface steepening and hence, increases in driving stress, enhanced sliding or deformation of unconsolidated marine sediments and diminishing ice thicknesses towards flotation thickness. Space-borne interferometric snapshots of Austfonna revealed a velocity structure of a slow moving polar ice cap (< 10m/a) interrupted by distinct fast flow units with velocities in excess of 100m/a. However, observations of flow variability are scarce. In spring 2008, we established a series of stakes along the centrelines of two fast-flowing units. Repeated DGPS and continuous GPS measurements of the stake positions give insight in the temporal flow variability of these units and provide constrains to the modeled surface velocity field. Austfonna’s thermal structure is described as polythermal. However, direct measurements of the temperature distribution is available only from one single borehole at the summit area. The vertical temperature profile shows that the bulk of the 567m thick ice column is cold, only underlain by a thin temperate basal layer of approximately 20m. To acquire a spatially extended picture of the thermal structure (and bed topography), we used low-frequency (20 MHz) GPR profiling across the ice cap and the

Dynamic modeling and optimal joint torque coordination of advanced robotic systems

NASA Astrophysics Data System (ADS)

Kang, Hee-Jun

The development is documented of an efficient dynamic modeling algorithm and the subsequent optimal joint input load coordination of advanced robotic systems for industrial application. A closed-form dynamic modeling algorithm for the general closed-chain robotic linkage systems is presented. The algorithm is based on the transfer of system dependence from a set of open chain Lagrangian coordinates to any desired system generalized coordinate set of the closed-chain. Three different techniques for evaluation of the kinematic closed chain constraints allow the representation of the dynamic modeling parameters in terms of system generalized coordinates and have no restriction with regard to kinematic redundancy. The total computational requirement of the closed-chain system model is largely dependent on the computation required for the dynamic model of an open kinematic chain. In order to improve computational efficiency, modification of an existing open-chain KIC based dynamic formulation is made by the introduction of the generalized augmented body concept. This algorithm allows a 44 pct. computational saving over the current optimized one (O(N4), 5995 when N = 6). As means of resolving redundancies in advanced robotic systems, local joint torque optimization is applied for effectively using actuator power while avoiding joint torque limits. The stability problem in local joint torque optimization schemes is eliminated by using fictitious dissipating forces which act in the necessary null space. The performance index representing the global torque norm is shown to be satisfactory. In addition, the resulting joint motion trajectory becomes conservative, after a transient stage, for repetitive cyclic end-effector trajectories. The effectiveness of the null space damping method is shown. The modular robot, which is built of well defined structural modules from a finite-size inventory and is controlled by one general computer system, is another class of evolving

Study of ice cluster impacts on amorphous silica using the ReaxFF reactive force field molecular dynamics simulation method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rahnamoun, A.; Duin, A. C. T. van

We study the dynamics of the collisions between amorphous silica structures and amorphous and crystal ice clusters with impact velocities of 1 km/s, 4 km/s, and 7 km/s using the ReaxFF reactive molecular dynamics simulation method. The initial ice clusters consist of 150 water molecules for the amorphous ice cluster and 128 water molecules for the crystal ice cluster. The ice clusters are collided on the surface of amorphous fully oxidized and suboxide silica. These simulations show that at 1 km/s impact velocities, all the ice clusters accumulate on the surface and at 4 km/s and 7 km/s impact velocities, some of the ice cluster moleculesmore » bounce back from the surface. At 4 km/s and 7 km/s impact velocities, few of the water molecules dissociations are observed. The effect of the second ice cluster impacts on the surfaces which are fully covered with ice, on the mass loss/accumulation is studied. These studies show that at 1 km/s impacts, the entire ice cluster accumulates on the surface at both first and second ice impacts. At higher impact velocities, some ice molecules which after the first ice impacts have been attached to the surface will separate from the surface after the second ice impacts at 7 km/s impact velocity. For the 4 km/s ice cluster impact, ice accumulation is observed for the crystal ice cluster impacts and ice separation is observed for the amorphous ice impacts. Observing the temperatures of the ice clusters during the collisions indicates that the possibility of electron excitement at impact velocities less than 10 km/s is minimal and ReaxFF reactive molecular dynamics simulation can predict the chemistry of these hypervelocity impacts. However, at impact velocities close to 10 km/s the average temperature of the impacting ice clusters increase to about 2000 K, with individual molecules occasionally reaching temperatures of over 8000 K and thus it will be prudent to consider the concept of electron

Ice-sheet dynamics through the Quaternary on the mid-Norwegian continental margin inferred from 3D seismic data.

PubMed

Montelli, A; Dowdeswell, J A; Ottesen, D; Johansen, S E

2017-02-01

Reconstructing the evolution of ice sheets is critical to our understanding of the global environmental system, but most detailed palaeo-glaciological reconstructions have hitherto focused on the very recent history of ice sheets. Here, we present a three-dimensional (3D) reconstruction of the changing nature of ice-sheet derived sedimentary architecture through the Quaternary Ice Age of almost 3 Ma. An extensive geophysical record documents a marine-terminating, calving Fennoscandian Ice Sheet (FIS) margin present periodically on the mid-Norwegian shelf since the beginning of the Quaternary. Spatial and temporal variability of the FIS is illustrated by the gradual development of fast-flowing ice streams and associated intensification of focused glacial erosion and sedimentation since that time. Buried subglacial landforms reveal a complex and dynamic ice sheet, with converging palaeo-ice streams and several flow-switching events that may reflect major changes in topography and basal thermal regime. Lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine-terminating part of the FIS. This palaeo-environmental examination of the FIS provides a useful framework for ice-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of ice-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets.

Wave-induced stress and breaking of sea ice in a coupled hydrodynamic discrete-element wave-ice model

NASA Astrophysics Data System (ADS)

Herman, Agnieszka

2017-11-01

In this paper, a coupled sea ice-wave model is developed and used to analyze wave-induced stress and breaking in sea ice for a range of wave and ice conditions. The sea ice module is a discrete-element bonded-particle model, in which ice is represented as cuboid grains floating on the water surface that can be connected to their neighbors by elastic joints. The joints may break if instantaneous stresses acting on them exceed their strength. The wave module is based on an open-source version of the Non-Hydrostatic WAVE model (NHWAVE). The two modules are coupled with proper boundary conditions for pressure and velocity, exchanged at every wave model time step. In the present version, the model operates in two dimensions (one vertical and one horizontal) and is suitable for simulating compact ice in which heave and pitch motion dominates over surge. In a series of simulations with varying sea ice properties and incoming wavelength it is shown that wave-induced stress reaches maximum values at a certain distance from the ice edge. The value of maximum stress depends on both ice properties and characteristics of incoming waves, but, crucially for ice breaking, the location at which the maximum occurs does not change with the incoming wavelength. Consequently, both regular and random (Jonswap spectrum) waves break the ice into floes with almost identical sizes. The width of the zone of broken ice depends on ice strength and wave attenuation rates in the ice.

Sea ice thermohaline dynamics and biogeochemistry in the Arctic Ocean: Empirical and model results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duarte, Pedro; Meyer, Amelie; Olsen, Lasse M.

Here, large changes in the sea ice regime of the Arctic Ocean have occurred over the last decades justifying the development of models to forecast sea ice physics and biogeochemistry. The main goal of this study is to evaluate the performance of the Los Alamos Sea Ice Model (CICE) to simulate physical and biogeochemical properties at time scales of a few weeks and to use the model to analyze ice algal bloom dynamics in different types of ice. Ocean and atmospheric forcing data and observations of the evolution of the sea ice properties collected from 18 April to 4 Junemore » 2015, during the Norwegian young sea ICE expedition, were used to test the CICE model. Our results show the following: (i) model performance is reasonable for sea ice thickness and bulk salinity; good for vertically resolved temperature, vertically averaged Chl a concentrations, and standing stocks; and poor for vertically resolved Chl a concentrations. (ii) Improving current knowledge about nutrient exchanges, ice algal recruitment, and motion is critical to improve sea ice biogeochemical modeling. (iii) Ice algae may bloom despite some degree of basal melting. (iv) Ice algal motility driven by gradients in limiting factors is a plausible mechanism to explain their vertical distribution. (v) Different ice algal bloom and net primary production (NPP) patterns were identified in the ice types studied, suggesting that ice algal maximal growth rates will increase, while sea ice vertically integrated NPP and biomass will decrease as a result of the predictable increase in the area covered by refrozen leads in the Arctic Ocean.« less

Sea ice thermohaline dynamics and biogeochemistry in the Arctic Ocean: Empirical and model results

DOE PAGES

Duarte, Pedro; Meyer, Amelie; Olsen, Lasse M.; ...

2017-06-08

Here, large changes in the sea ice regime of the Arctic Ocean have occurred over the last decades justifying the development of models to forecast sea ice physics and biogeochemistry. The main goal of this study is to evaluate the performance of the Los Alamos Sea Ice Model (CICE) to simulate physical and biogeochemical properties at time scales of a few weeks and to use the model to analyze ice algal bloom dynamics in different types of ice. Ocean and atmospheric forcing data and observations of the evolution of the sea ice properties collected from 18 April to 4 Junemore » 2015, during the Norwegian young sea ICE expedition, were used to test the CICE model. Our results show the following: (i) model performance is reasonable for sea ice thickness and bulk salinity; good for vertically resolved temperature, vertically averaged Chl a concentrations, and standing stocks; and poor for vertically resolved Chl a concentrations. (ii) Improving current knowledge about nutrient exchanges, ice algal recruitment, and motion is critical to improve sea ice biogeochemical modeling. (iii) Ice algae may bloom despite some degree of basal melting. (iv) Ice algal motility driven by gradients in limiting factors is a plausible mechanism to explain their vertical distribution. (v) Different ice algal bloom and net primary production (NPP) patterns were identified in the ice types studied, suggesting that ice algal maximal growth rates will increase, while sea ice vertically integrated NPP and biomass will decrease as a result of the predictable increase in the area covered by refrozen leads in the Arctic Ocean.« less

Sea ice thermohaline dynamics and biogeochemistry in the Arctic Ocean: Empirical and model results

NASA Astrophysics Data System (ADS)

Duarte, Pedro; Meyer, Amelie; Olsen, Lasse M.; Kauko, Hanna M.; Assmy, Philipp; Rösel, Anja; Itkin, Polona; Hudson, Stephen R.; Granskog, Mats A.; Gerland, Sebastian; Sundfjord, Arild; Steen, Harald; Hop, Haakon; Cohen, Lana; Peterson, Algot K.; Jeffery, Nicole; Elliott, Scott M.; Hunke, Elizabeth C.; Turner, Adrian K.

2017-07-01

Large changes in the sea ice regime of the Arctic Ocean have occurred over the last decades justifying the development of models to forecast sea ice physics and biogeochemistry. The main goal of this study is to evaluate the performance of the Los Alamos Sea Ice Model (CICE) to simulate physical and biogeochemical properties at time scales of a few weeks and to use the model to analyze ice algal bloom dynamics in different types of ice. Ocean and atmospheric forcing data and observations of the evolution of the sea ice properties collected from 18 April to 4 June 2015, during the Norwegian young sea ICE expedition, were used to test the CICE model. Our results show the following: (i) model performance is reasonable for sea ice thickness and bulk salinity; good for vertically resolved temperature, vertically averaged Chl a concentrations, and standing stocks; and poor for vertically resolved Chl a concentrations. (ii) Improving current knowledge about nutrient exchanges, ice algal recruitment, and motion is critical to improve sea ice biogeochemical modeling. (iii) Ice algae may bloom despite some degree of basal melting. (iv) Ice algal motility driven by gradients in limiting factors is a plausible mechanism to explain their vertical distribution. (v) Different ice algal bloom and net primary production (NPP) patterns were identified in the ice types studied, suggesting that ice algal maximal growth rates will increase, while sea ice vertically integrated NPP and biomass will decrease as a result of the predictable increase in the area covered by refrozen leads in the Arctic Ocean.

Coastal sea-ice processes in Alaska and their relevance for sediment dynamics and coastal retreat (Invited)

NASA Astrophysics Data System (ADS)

Eicken, H.; Kapsch, M.; Johnson, M. A.; Weyapuk, W. U., Jr.

2009-12-01

Sea ice plays an important, complicated role in Arctic coastal sediment dynamics. It helps protect the shoreline from wave action and constrains coastal permafrost thaw; at the same time, sea ice is a highly effective sediment erosion and transport agent. For the coastline of (sub-)Arctic Alaska we have examined key processes that govern the role of sea ice as a geologic agent. Based on passive microwave satellite data for the time period 1979 to 2008 and augmented by field measurements and observations conducted by local sea-ice experts in coastal communities from 2006 onwards, we determined the onset of coastal ice spring break-up and fall freeze-up. These two events define the start and end of the open-water season during which the coast is rendered most vulnerable to thermal and dynamic processes promoting erosion. Satellite data show significant trends toward later fall freeze-up in many locations and moreover provide a picture of the statistical significance and variability of such trends in great spatio-temporal detail. Coastal ice observations suggest that important sea-ice processes (such as formation of ice berms) that precede freeze-up as detected by passive microwave data need to be taken into consideration in evaluating the vulnerability of the coastline and the specific threat of individual storms. Field observations, satellite data and local knowledge also highlight the substantial change in winter sea-ice regimes over the past two decades, with a much more mobile ice cover enhancing winter sediment transport. Ultimately, the shorter sea-ice season and the greater mobility and the lack of stability of winter coastal sea ice work in concert to increase the vulnerability of the coastline to erosion and flooding. At the same time, these changes provide a mechanism for effective redistribution and cross-shelf transport of sediments that prepares the stage for further erosive action in subsequent seasons.

The mass balance of the ice plain of Ice Stream B and Crary Ice Rise

NASA Technical Reports Server (NTRS)

Bindschadler, Robert

1993-01-01

The region in the mouth of Ice Stream B (the ice plain) and that in the vicinity of Crary Ice Rise are experiencing large and rapid changes. Based on velocity, ice thickness, and accumulation rate data, the patterns of net mass balance in these regions were calculated. Net mass balance, or the rate of ice thickness change, was calculated as the residual of all mass fluxes into and out of subregions (or boxes). Net mass balance provides a measure of the state of health of the ice sheet and clues to the current dynamics.

Reconstructing the post-LGM decay of the Eurasian Ice Sheets with Ice Sheet Models; data-model comparison and focus on the Storfjorden (Svalbard) ice stream dynamics history

NASA Astrophysics Data System (ADS)

Petrini, Michele; Kirchner, Nina; Colleoni, Florence; Camerlenghi, Angelo; Rebesco, Michele; Lucchi, Renata G.; Forte, Emanuele; Colucci, Renato R.

2017-04-01

The challenge of reconstructing palaeo-ice sheets past growth and decay represent a critical task to better understand mechanisms of present and future global climate change. Last Glacial Maximum (LGM), and the subsequent deglaciation until Pre-Industrial time (PI) represent an excellent testing ground for numerical Ice Sheet Models (ISMs), due to the abundant data available that can be used in an ISM as boundary conditions, forcings or constraints to test the ISMs results. In our study, we simulate with ISMs the post-LGM decay of the Eurasian Ice Sheets, with a focus on the marine-based Svalbard-Barents Sea-Kara Sea Ice Sheet. In particular, we aim to reconstruct the Storfjorden ice stream dynamics history by comparing the model results with the marine geological data (MSGLs, GZWs, sediment cores analysis) available from the area, e.g., Pedrosa et al. 2011, Rebesco et al. 2011, 2013, Lucchi et al. 2013. Two hybrid SIA/SSA ISMs are employed, GRISLI, Ritz et al. 2001, and PSU, Pollard&DeConto 2012. These models differ mainly in the complexity with which grounding line migration is treated. Climate forcing is interpolated by means of climate indexes between LGM and PI climate. Regional climate indexes are constructed based on the non-accelerated deglaciation transient experiment carried out with CCSM3, Liu et al. 2009. Indexes representative of the climate evolution over Siberia, Svalbard and Scandinavia are employed. The impact of such refined representation as opposed to the common use of the NGRIP δ18O index for transient experiments is analysed. In this study, the ice-ocean interaction is crucial to reconstruct the Storfjorden ice stream dynamics history. To investigate the sensitivity of the ice shelf/stream retreat to ocean temperature, we allow for a space-time variation of basal melting under the ice shelves by testing two-equations implementations based on Martin et al. 2011 forced with simulated ocean temperature and salinity from the TraCE-21ka coupled

Ice-Sheet Dynamics and Millennial-Scale Climate Variability in the North Atlantic across the Middle Pleistocene Transition (Invited)

NASA Astrophysics Data System (ADS)

Hodell, D. A.; Nicholl, J.

2013-12-01

During the Middle Pleistocene Transition (MPT), the climate system evolved from a more linear response to insolation forcing in the '41-kyr world' to one that was decidedly non-linear in the '100-kyr world'. Smaller ice sheets in the early Pleistocene gave way to larger ice sheets in the late Pleistocene with an accompanying change in ice sheet dynamics. We studied Sites U1308 (49° 52.7'N, 24° 14.3'W; 3871 m) and U1304 (53° 3.4'N, 33° 31.8'W; 3024 m) in the North Atlantic to determine how ice sheet dynamics and millennial-scale climate variability evolved as glacial boundary conditions changed across the MPT. The frequency of ice-rafted detritus (IRD) in the North Atlantic was greater during glacial stages prior to 650 ka (MIS 16), reflecting more frequent crossing of an ice volume threshold when the climate system spent more time in the 'intermediate ice volume' window, resulting in persistent millennial scale variability. The rarity of Heinrich Events containing detrital carbonate and more frequent occurrence of IRD events prior to 650 ka may indicate the presence of 'low-slung, slippery ice sheets' that flowed more readily than their post-MPT counterparts (Bailey et al., 2010). Ice volume surpassed a critical threshold across the MPT that permitted ice sheets to survive boreal summer insolation maxima, thereby increasing ice volume and thickness, lengthening glacial cycles, and activating the dynamical processes responsible for Laurentide Ice Sheet instability in the region of Hudson Strait (i.e., Heinrich events). The excess ice volume during post-MPT glacial maxima provided a large, unstable reservoir of freshwater to be released to the North Atlantic during glacial terminations with the potential to perturb Atlantic Meridional Overtunring Circulation. We speculate that orbital- and millennial-scale variability co-evolved across the MPT and the interaction of processes on orbital and suborbital time scales gave rise to the changing patterns of glacial

Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline.

PubMed

Bromaghin, Jeffrey F; Mcdonald, Trent L; Stirling, Ian; Derocher, Andrew E; Richardson, Evan S; Regehr, Eric V; Douglas, David C; Durner, George M; Atwood, Todd; Amstrup, Steven C

2015-04-01

In the southern Beaufort Sea of the United States and Canada, prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears (Ursus maritimus). Combined with projections of population decline due to continued climate warming and the ensuing loss of sea ice habitat, those findings contributed to the 2008 decision to list the species as threatened under the U.S. Endangered Species Act. Here, we used mark-recapture models to investigate the population dynamics of polar bears in the southern Beaufort Sea from 2001 to 2010, years during which the spatial and temporal extent of summer sea ice generally declined. Low survival from 2004 through 2006 led to a 25-50% decline in abundance. We hypothesize that low survival during this period resulted from (1) unfavorable ice conditions that limited access to prey during multiple seasons; and possibly, (2) low prey abundance. For reasons that are not clear, survival of adults and cubs began to improve in 2007 and abundance was comparatively stable from 2008 to 2010, with ~900 bears in 2010 (90% CI 606-1212). However, survival of subadult bears declined throughout the entire period. Reduced spatial and temporal availability of sea ice is expected to increasingly force population dynamics of polar bears as the climate continues to warm. However, in the short term, our findings suggest that factors other than sea ice can influence survival. A refined understanding of the ecological mechanisms underlying polar bear population dynamics is necessary to improve projections of their future status and facilitate development of management strategies.

Long-term monitoring of glacier dynamics of Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Friedl, Peter; Seehaus, Thorsten; Wendt, Anja; Braun, Matthias

2017-04-01

The Antarctic Peninsula is one of the world`s most affected regions by Climate Change. Dense and long time series of remote sensing data enable detailed studies of the rapid glaciological changes in this area. We present results of a study on Fleming Glacier, which was the major tributary glacier of former Wordie Ice Shelf, located at the south-western side of the Antarctic Peninsula. Since the ice shelf disintegrated in a series of events starting in the 1970s, only disconnected tidewater glaciers have remained today. As a reaction to the loss of the buttressing force of the ice shelf, Fleming Glacier accelerated and dynamically thinned. However, all previous studies conducted at Wordie Bay covered only relatively short investigation periods and ended in 2008 the latest. Hence it was not well known how long the process of adaption to the changing boundary conditions exactly lasts and how it is characterized in detail. We provide long time series (1994 - 2016) of glaciological parameters (i.e. ice extent, velocity, grounding line position, ice elevation) for Fleming Glacier obtained from multi-mission remote sensing data. For this purpose large datasets of previously active (e.g. ERS, Envisat, ALOS PALSAR, Radarsat-1) as well as currently recording SAR sensors (e.g. Sentinel-1, TerraSAR-X, TanDEM-X) were processed and combined with data from other sources (e.g. optical images, laser altimeter and ice thickness data). The high temporal resolution of our dataset enables us to present a detailed history of 22 years of glacial dynamics at Fleming Glacier after the disintegration of Wordie Ice Shelf. We found strong evidence for a rapid grounding line retreat of up to 13 km between 2008 and 2011, which led to a further amplification of dynamic ice thinning. Today Fleming Glacier seems to be far away from approaching a new equilibrium. Our data show that the current glacier dynamics of Fleming Glacier are not primarily controlled by the loss of the ice shelf anymore, but

Inverse stochastic-dynamic models for high-resolution Greenland ice core records

NASA Astrophysics Data System (ADS)

Boers, Niklas; Chekroun, Mickael D.; Liu, Honghu; Kondrashov, Dmitri; Rousseau, Denis-Didier; Svensson, Anders; Bigler, Matthias; Ghil, Michael

2017-12-01

Proxy records from Greenland ice cores have been studied for several decades, yet many open questions remain regarding the climate variability encoded therein. Here, we use a Bayesian framework for inferring inverse, stochastic-dynamic models from δ18O and dust records of unprecedented, subdecadal temporal resolution. The records stem from the North Greenland Ice Core Project (NGRIP), and we focus on the time interval 59-22 ka b2k. Our model reproduces the dynamical characteristics of both the δ18O and dust proxy records, including the millennial-scale Dansgaard-Oeschger variability, as well as statistical properties such as probability density functions, waiting times and power spectra, with no need for any external forcing. The crucial ingredients for capturing these properties are (i) high-resolution training data, (ii) cubic drift terms, (iii) nonlinear coupling terms between the δ18O and dust time series, and (iv) non-Markovian contributions that represent short-term memory effects.

Human joint motion estimation for electromyography (EMG)-based dynamic motion control.

PubMed

Zhang, Qin; Hosoda, Ryo; Venture, Gentiane

2013-01-01

This study aims to investigate a joint motion estimation method from Electromyography (EMG) signals during dynamic movement. In most EMG-based humanoid or prosthetics control systems, EMG features were directly or indirectly used to trigger intended motions. However, both physiological and nonphysiological factors can influence EMG characteristics during dynamic movements, resulting in subject-specific, non-stationary and crosstalk problems. Particularly, when motion velocity and/or joint torque are not constrained, joint motion estimation from EMG signals are more challenging. In this paper, we propose a joint motion estimation method based on muscle activation recorded from a pair of agonist and antagonist muscles of the joint. A linear state-space model with multi input single output is proposed to map the muscle activity to joint motion. An adaptive estimation method is proposed to train the model. The estimation performance is evaluated in performing a single elbow flexion-extension movement in two subjects. All the results in two subjects at two load levels indicate the feasibility and suitability of the proposed method in joint motion estimation. The estimation root-mean-square error is within 8.3% ∼ 10.6%, which is lower than that being reported in several previous studies. Moreover, this method is able to overcome subject-specific problem and compensate non-stationary EMG properties.

Changes in ice dynamics and mass balance of the Antarctic ice sheet.

PubMed

Rignot, Eric

2006-07-15

The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 degrees C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

Simulation of in vivo dynamics during robot assisted joint movement.

PubMed

Bobrowitsch, Evgenij; Lorenz, Andrea; Wülker, Nikolaus; Walter, Christian

2014-12-16

Robots are very useful tools in orthopedic research. They can provide force/torque controlled specimen motion with high repeatability and precision. A method to analyze dissipative energy outcome in an entire joint was developed in our group. In a previous study, a sheep knee was flexed while axial load remained constant during the measurement of dissipated energy. We intend to apply this method for the investigation of osteoarthritis. Additionally, the method should be improved by simulation of in vivo knee dynamics. Thus, a new biomechanical testing tool will be developed for analyzing in vitro joint properties after different treatments. Discretization of passive knee flexion was used to construct a complex flexion movement by a robot and simulate altering axial load similar to in vivo sheep knee dynamics described in a previous experimental study. The robot applied an in vivo like axial force profile with high reproducibility during the corresponding knee flexion (total standard deviation of 0.025 body weight (BW)). A total residual error between the in vivo and simulated axial force was 0.16 BW. Posterior-anterior and medio-lateral forces were detected by the robot as a backlash of joint structures. Their curve forms were similar to curve forms of corresponding in vivo measured forces, but in contrast to the axial force, they showed higher total standard deviation of 0.118 and 0.203 BW and higher total residual error of 0.79 and 0.21 BW for posterior-anterior and medio-lateral forces respectively. We developed and evaluated an algorithm for the robotic simulation of complex in vivo joint dynamics using a joint specimen. This should be a new biomechanical testing tool for analyzing joint properties after different treatments.

Interaction of Tenebrio Molitor Antifreeze Protein with Ice Crystal: Insights from Molecular Dynamics Simulations.

PubMed

Ramya, L; Ramakrishnan, Vigneshwar

2016-07-01

Antifreeze proteins (AFP) observed in cold-adapting organisms bind to ice crystals and prevent further ice growth. However, the molecular mechanism of AFP-ice binding and AFP-inhibited ice growth remains unclear. Here we report the interaction of the insect antifreeze protein (Tenebrio molitor, TmAFP) with ice crystal by molecular dynamics simulation studies. Two sets of simulations were carried out at 263 K by placing the protein near the primary prism plane (PP) and basal plane (BL) of the ice crystal. To delineate the effect of temperatures, both the PP and BL simulations were carried out at 253 K as well. The analyses revealed that the protein interacts strongly with the ice crystal in BL simulation than in PP simulation both at 263 K and 253 K. Further, it was observed that the interactions are primarily mediated through the interface waters. We also observed that as the temperature decreases, the interaction between the protein and the ice increases which can be attributed to the decreased flexibility and the increased structuring of the protein at low temperature. In essence, our study has shed light on the interaction mechanism between the TmAFP antifreeze protein and the ice crystal. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microwave and physical properties of sea ice in the winter marginal ice zone

NASA Technical Reports Server (NTRS)

Tucker, W. B., III; Perovich, D. K.; Gow, A. J.; Grenfell, T. C.; Onstott, R. G.

1991-01-01

Surface-based active and passive microwave measurements were made in conjunction with ice property measurements for several distinct ice types in the Fram Strait during March and April 1987. Synthesis aperture radar imagery downlinked from an aircraft was used to select study sites. The surface-based radar scattering cross section and emissivity spectra generally support previously inferred qualitative relationships between ice types, exhibiting expected separation between young, first-year and multiyear ice. Gradient ratios, calculated for both active and passive data, appear to allow clear separation of ice types when used jointly. Surface flooding of multiyear floes, resulting from excessive loading and perhaps wave action, causes both active and passive signatures to resemble those of first-year ice. This effect could possibly cause estimates of ice type percentages in the marginal ice zone to be in error when derived from aircraft- or satellite-born sensors.

An ice sheet model validation framework for the Greenland ice sheet

NASA Astrophysics Data System (ADS)

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

2017-01-01

We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013, using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin-scale and whole-ice-sheet-scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of < 1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate a predictive skill with respect to observed dynamic changes that have occurred on

An ice sheet model validation framework for the Greenland ice sheet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.

We propose a new ice sheet model validation framework the Cryospheric Model Comparison Tool (CMCT) that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quanti- tative metricsmore » for use in evaluating the different model simulations against the observations. We find 10 that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, the model initial condition as well as output from idealized and dynamic models all provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CMCT, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few

An ice sheet model validation framework for the Greenland ice sheet

PubMed Central

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

2018-01-01

We propose a new ice sheet model validation framework – the Cryospheric Model Comparison Tool (CmCt) – that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the

An ice sheet model validation framework for the Greenland ice sheet.

PubMed

Price, Stephen F; Hoffman, Matthew J; Bonin, Jennifer A; Howat, Ian M; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P; Evans, Katherine J; Kennedy, Joseph H; Lenaerts, Jan; Lipscomb, William H; Perego, Mauro; Salinger, Andrew G; Tuminaro, Raymond S; van den Broeke, Michiel R; Nowicki, Sophie M J

2017-01-01

We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past

An ice sheet model validation framework for the Greenland ice sheet

DOE PAGES

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; ...

2017-01-17

We propose a new ice sheet model validation framework the Cryospheric Model Comparison Tool (CMCT) that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quanti- tative metricsmore » for use in evaluating the different model simulations against the observations. We find 10 that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, the model initial condition as well as output from idealized and dynamic models all provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CMCT, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few

An Ice Sheet Model Validation Framework for the Greenland Ice Sheet

NASA Technical Reports Server (NTRS)

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas A.; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey R.; Chambers, Don P.; Evans, Katherine J.;

Ocean-ice interaction in the marginal ice zone

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Peng, Chich Y.

1994-01-01

Ocean ice interaction processes in the Marginal Ice Zone (MIZ) by wind, waves, and mesoscale features, such as upwelling and eddies, are studied using ERS-1 Synthetic Aperture Radar (SAR) images and ocean ice interaction model. A sequence of SAR images of the Chukchi Sea MIZ with three days interval are studied for ice edge advance/retreat. Simultaneous current measurements from the northeast Chukchi Sea as well as the Barrow wind record are used to interpret the MIZ dynamics.

The IceCube Neutrino Observatory, the Pierre Auger Observatory and the Telescope Array: Joint Contribution to the 35th International Cosmic Ray Conference (ICRC 2017)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aartsen, M. G.; et al.

Joint contributions of the IceCube Collaboration, the Telescope Array Collaboration, and the Pierre Auger Collaboration to the 35th International Cosmic Ray Conference (ICRC 2017), 12-20 July 2017, Bexco, Busan, Korea.

Validation of Modelled Ice Dynamics of the Greenland Ice Sheet using Historical Forcing

NASA Astrophysics Data System (ADS)

Hoffman, M. J.; Price, S. F.; Howat, I. M.; Bonin, J. A.; Chambers, D. P.; Tezaur, I.; Kennedy, J. H.; Lenaerts, J.; Lipscomb, W. H.; Neumann, T.; Nowicki, S.; Perego, M.; Saba, J. L.; Salinger, A.; Guerber, J. R.

2015-12-01

Although ice sheet models are used for sea level rise projections, the degree to which these models have been validated by observations is fairly limited, due in part to the limited duration of the satellite observation era and the long adjustment time scales of ice sheets. Here we describe a validation framework for the Greenland Ice Sheet applied to the Community Ice Sheet Model by forcing the model annually with flux anomalies at the major outlet glaciers (Enderlin et al., 2014, observed from Landsat/ASTER/Operation IceBridge) and surface mass balance (van Angelen et al., 2013, calculated from RACMO2) for the period 1991-2012. The ice sheet model output is compared to ice surface elevation observations from ICESat and ice sheet mass change observations from GRACE. Early results show promise for assessing the performance of different model configurations. Additionally, we explore the effect of ice sheet model resolution on validation skill.

Modeling brine and nutrient dynamics in Antarctic sea ice: The case of dissolved silica

NASA Astrophysics Data System (ADS)

Vancoppenolle, Martin; Goosse, Hugues; de Montety, Anne; Fichefet, Thierry; Tremblay, Bruno; Tison, Jean-Louis

2010-02-01

Sea ice ecosystems are characterized by microalgae living in brine inclusions. The growth rate of ice algae depends on light and nutrient supply. Here, the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one-dimensional model. The model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component, characterized by one nutrient, namely, dissolved silica (DSi). In the model, DSi follows brine motion and is consumed by ice algae. Depending on physical ice characteristics, the brine flow is either advective, diffusive, or turbulent. The vertical profiles of ice salinity and DSi concentration are solutions of advection-diffusion equations. The model is configured to simulate the typical thermodynamic regimes of first-year Antarctic pack ice. The simulated vertical profiles of salinity and DSi qualitatively reproduce observations. Analysis of results highlights the role of convection in the lowermost 5-10 cm of ice. Convection mixes saline, nutrient-poor brine with comparatively fresh, nutrient-rich seawater. This implies a rejection of salt to the ocean and a flux of DSi to the ice. In the presence of growing algae, the simulated ocean-to-ice DSi flux increases by 0-115% compared to an abiotic situation. In turn, primary production and brine convection act in synergy to form a nutrient pump. The other important processes are the flooding of the surface by seawater and the percolation of meltwater. The former refills nutrients near the ice surface in spring. The latter, if present, tends to expell nutrients from the ice in summer.

Atmosphere-Ice-Ocean-Ecosystem Processes in a Thinner Arctic Sea Ice Regime: The Norwegian Young Sea ICE (N-ICE2015) Expedition

NASA Astrophysics Data System (ADS)

Granskog, Mats A.; Fer, Ilker; Rinke, Annette; Steen, Harald

2018-03-01

Arctic sea ice has been in rapid decline the last decade and the Norwegian young sea ICE (N-ICE2015) expedition sought to investigate key processes in a thin Arctic sea ice regime, with emphasis on atmosphere-snow-ice-ocean dynamics and sea ice associated ecosystem. The main findings from a half-year long campaign are collected into this special section spanning the Journal of Geophysical Research: Atmospheres, Journal of Geophysical Research: Oceans, and Journal of Geophysical Research: Biogeosciences and provide a basis for a better understanding of processes in a thin sea ice regime in the high Arctic. All data from the campaign are made freely available to the research community.

Numerical Investigation of the Dynamic Properties of Intermittent Jointed Rock Models Subjected to Cyclic Uniaxial Compression

NASA Astrophysics Data System (ADS)

Liu, Yi; Dai, Feng; Zhao, Tao; Xu, Nu-wen

2017-01-01

Intermittent jointed rocks, which exist in a myriad of engineering projects, are extraordinarily susceptible to cyclic loadings. Understanding the dynamic fatigue properties of jointed rocks is necessary for evaluating the stability of rock engineering structures. This study numerically investigated the influences of cyclic loading conditions (i.e., frequency, maximum stress and amplitude) and joint geometric configurations (i.e., dip angle, persistency and interspace) on the dynamic fatigue mechanisms of jointed rock models. A reduction model of stiffness and strength was first proposed, and then, sixteen cyclic uniaxial loading tests with distinct loading parameters and joint geometries were simulated. Our results indicate that the reduction model can effectively reproduce the hysteresis loops and the accumulative plastic deformation of jointed rocks in the cyclic process. Both the loading parameters and the joint geometries significantly affect the dynamic properties, including the irreversible strain, damage evolution, dynamic residual strength and fatigue life. Three failure modes of jointed rocks, which are principally controlled by joint geometries, occur in the simulations: splitting failure through the entire rock sample, sliding failure along joint planes and mixed failure, which are principally controlled by joint geometries. Furthermore, the progressive failure processes of the jointed rock samples are numerically observed, and the different loading stages can be distinguished by the relationship between the number of broken bonds and the axial stress.

Measurements of sea ice mass redistribution during ice deformation event in Arctic winter

NASA Astrophysics Data System (ADS)

Itkin, P.; Spreen, G.; King, J.; Rösel, A.; Skourup, H.; Munk Hvidegaard, S.; Wilkinson, J.; Oikkonen, A.; Granskog, M. A.; Gerland, S.

2016-12-01

Sea-ice growth during high winter is governed by ice dynamics. The highest growth rates are found in leads that open under divergent conditions, where exposure to the cold atmosphere promotes thermodynamic growth. Additionally ice thickens dynamically, where convergence causes rafting and ridging. We present a local study of sea-ice growth and mass redistribution between two consecutive airborne measurements, on 19 and 24 April 2015, during the N-ICE2015 expedition in the area north of Svalbard. Between the two overflights an ice deformation event was observed. Airborne laser scanner (ALS) measurements revisited the same sea-ice area of approximately 3x3 km. By identifying the sea surface within the ALS measurements as a reference the sea ice plus snow freeboard was obtained with a spatial resolution of 5 m. By assuming isostatic equilibrium of level floes, the freeboard heights can be converted to ice thickness. The snow depth is estimated from in-situ measurements. Sea ice thickness measurements were made in the same area as the ALS measurements by electromagnetic sounding from a helicopter (HEM), and with a ground-based device (EM31), which allows for cross-validation of the sea-ice thickness estimated from all 3 procedures. Comparison of the ALS snow freeboard distributions between the first and second overflight shows a decrease in the thin ice classes and an increase of the thick ice classes. While there was no observable snowfall and a very low sea-ice growth of older level ice during this period, an autonomous buoy array deployed in the surroundings of the area measured by the ALS shows first divergence followed by convergence associated with shear. To quantify and link the sea ice deformation with the associated sea-ice thickness change and mass redistribution we identify over 100 virtual buoys in the ALS data from both overflights. We triangulate the area between the buoys and calculate the strain rates and freeboard change for each individual triangle

Investigating role of ice-ocean interaction on glacier dynamic: Results from numerical modeling applied to Petermann Glacier

NASA Astrophysics Data System (ADS)

Nick, F. M.; van der Veen, C. J.; Vieli, A.; Pattyn, F.; Hubbard, A.; Box, J. E.

2010-12-01

Calving of icebergs and bottom melting from ice shelves accounts for roughly half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. Petermann Glacier (north Greenland) with its ~17 km wide and ~ 60 km long floating ice-shelf is experiencing high rates of bottom melting. The recent partial disintegration of its shelf (in August 2010) presents a natural experiment to investigate the dynamic response of the ice sheet to its shelf retreat. We apply a numerical ice flow model using a physically-based calving criterion based on crevasse depth to investigate the contribution of processes such as shelf disintegration, bottom melting, sea ice or sikkusak disintegration and surface run off to the mass balance of Petermann Glacier and assess its stability. Our modeling study provides insights into the role of ice-ocean interaction, and on response of Petermann Glacier to its recent massive ice loss.

Calving Geometry of Thwaites Glacier Linked to Semi-brittle Ice Dynamics

NASA Astrophysics Data System (ADS)

Logan, L. C.; Lavier, L.; Choi, E.; Tan, E.; Catania, G. A.; Holt, J.

2016-12-01

In the coming decades the linkage between ice dynamics, basal melt, and calving will play a central role in the flow of Thwaites Glacier, which has undergone vast and recent retreat. We explore this connection using a 3D, transient, thermomechanical ice flow model under different basal melt scenarios. Our use of a semi-brittle ice rheology enables the time-dependent development and tracking of surface and basal crevasses that determine the calving rate at this location. With the use of adaptive re-meshing, we are able to simulate the glacier's retreat response to different boundary forcings. We show that the resulting characteristic pinch-and-swell model geometries in the floating tongue compare well with airborne radar data acquired across the grounding line and floating tongue of Thwaites Glacier. These geometric features may be reproduced using this semi-brittle rheology, and further, are linked directly to the calving rate of Thwaites Glacier (and others). The use of semi-brittle rheology on decadal time scales may help provide constraints on the near-term future behavior of glaciers vulnerable to ocean-induced retreat, as this rheology targets the complex interaction of ice failure, basal melt, and flow.

Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline

USGS Publications Warehouse

Bromaghin, Jeffrey F.; McDonald, Trent L.; Stirling, Ian; Derocher, Andrew E.; Richardson, Evan S.; Regehr, Eric V.; Douglas, David C.; Durner, George M.; Atwood, Todd C.; Amstrup, Steven C.

2015-01-01

In the southern Beaufort Sea of the United States and Canada, prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears (Ursus maritimus). Combined with projections of population decline due to continued climate warming and the ensuing loss of sea ice habitat, those findings contributed to the 2008 decision to list the species as threatened under the U.S. Endangered Species Act. Here, we used mark–recapture models to investigate the population dynamics of polar bears in the southern Beaufort Sea from 2001 to 2010, years during which the spatial and temporal extent of summer sea ice generally declined. Low survival from 2004 through 2006 led to a 25–50% decline in abundance. We hypothesize that low survival during this period resulted from (1) unfavorable ice conditions that limited access to prey during multiple seasons; and possibly, (2) low prey abundance. For reasons that are not clear, survival of adults and cubs began to improve in 2007 and abundance was comparatively stable from 2008 to 2010, with ~900 bears in 2010 (90% CI 606–1212). However, survival of subadult bears declined throughout the entire period. Reduced spatial and temporal availability of sea ice is expected to increasingly force population dynamics of polar bears as the climate continues to warm. However, in the short term, our findings suggest that factors other than sea ice can influence survival. A refined understanding of the ecological mechanisms underlying polar bear population dynamics is necessary to improve projections of their future status and facilitate development of management strategies.

Modeling brine and nutrient dynamics in Antarctic sea ice: the case of dissolved silica

NASA Astrophysics Data System (ADS)

Vancoppenolle, M.; Goosse, H.; de Montety, A.; Fichefet, T.; Tremblay, B.; Tison, J.

2009-12-01

Sea ice ecosystems are characterized by micro-algae living in brine inclusions. The growth rate of ice algae depends on light and nutrient supply. Here, the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one-dimensional model. The model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component, characterized by one nutrient, namely dissolved silica (DSi). In the model, DSi follows brine motion and is consumed by ice algae. Depending on physical ice characteristics, the brine flow is either advective, diffusive or turbulent. The vertical profiles of ice salinity and DSi concentration are solutions of advection-diffusion equations. The model is configured to simulate the typical thermodynamic regimes of first-year Antarctic pack ice. The simulated vertical profiles of salinity and DSi qualitatively reproduce observations. Analysis of results highlights the role of convection in the lowermost 5-10 cm of ice. Convection mixes saline, nutrient-poor brine with comparatively fresh, nutrient-rich seawater. This implies a rejection of salt to the ocean and a flux of DSi to the ice. In presence of growing algae, the simulated ocean-to-ice DSi flux increases by 0-115% compared to an abiotic situation. In turn, primary production and brine convection act in synergy to form a nutrient pump. The other important processes are the flooding of the surface by seawater and the percolation of meltwater. The former refills nutrients near the ice surface in spring. The latter, if present, tends to expell nutrients from the ice in summer. Sketch of salt (left) and nutrient (right) exchanges at the ice-ocean interface proposed in this paper.

Joint symbolic dynamics for the assessment of cardiovascular and cardiorespiratory interactions.

PubMed

Baumert, Mathias; Javorka, Michal; Kabir, Muammar

2015-02-13

Beat-to-beat variations in heart period provide information on cardiovascular control and are closely linked to variations in arterial pressure and respiration. Joint symbolic analysis of heart period, systolic arterial pressure and respiration allows for a simple description of their shared short-term dynamics that are governed by cardiac baroreflex control and cardiorespiratory coupling. In this review, we discuss methodology and research applications. Studies suggest that analysis of joint symbolic dynamics provides a powerful tool for identifying physiological and pathophysiological changes in cardiovascular and cardiorespiratory control.

ICE-VOLC Project: unravelling the dynamics of Antarctica volcanoes

NASA Astrophysics Data System (ADS)

Cannata, Andrea; Del Carlo, Paola; Giudice, Gaetano; Giuffrida, Giovanni; Larocca, Graziano; Liuzzo, Marco

2017-04-01

Melbourne and Rittmann volcanoes are located in the Victoria Land. Whilst Rittmann's last eruption dates probably to Pleistocene, Melbourne's most recent eruption between 1862 and 1922, testifying it is still active. At present, both volcanoes display fumarolic activity. Melbourne was discovered in 1841 by James Clark Ross, Rittmann during the 4th Italian Expedition (1988/1989). Our knowledge on both volcanoes is really little. The position of these volcanoes in the Antarctic region (characterised by absence of anthropic noise) and its proximity with the Italian Mario Zucchelli Station makes them ideal sites for studying volcano seismic sources, geothermal emissions, seismo-acoustic signals caused by cryosphere-hydrosphere-atmosphere dynamics, and volcanic gas impact on environment. Hence, the main aim of the ICE-VOLC ("multiparametrIC Experiment at antarctica VOLCanoes: data from volcano and cryosphere-ocean-atmosphere dynamics") project is the study of Melbourne and Rittmann, by acquisition, analysis and integration of multiparametric geophysical, geochemical and thermal data. Complementary objectives include investigation of the relationship between seismo-acoustic activity recorded in Antarctica and cryosphere-hydrosphere-atmosphere dynamics, evaluation of the impact of volcanic gas in atmosphere. This project involves 26 researchers, technologists and technicians from University of Perugia and from Istituto Nazionale di Geofisica e Vulcanologia of Catania, Palermo, Pisa and Rome. In this work, we show the preliminary results obtained after the first expedition in Antarctica, aiming to perform geochemical-thermal surveys in the volcano ice caves, as well as to collect ash samples and to install temporary seismic stations.

Record low lake ice thickness and bedfast ice extent on Alaska's Arctic Coastal Plain in 2017 exemplify the value of monitoring freshwater ice to understand sea-ice forcing and predict permafrost dynamics

NASA Astrophysics Data System (ADS)

Arp, C. D.; Alexeev, V. A.; Bondurant, A. C.; Creighton, A.; Engram, M. J.; Jones, B. M.; Parsekian, A.

2017-12-01

The winter of 2016/2017 was exceptionally warm and snowy along the coast of Arctic Alaska partly due to low fall sea ice extent. Based on several decades of field measurements, we documented a new record low maximum ice thickness (MIT) for lakes on the Barrow Peninsula, averaging 1.2 m. This is in comparison to a long-term average MIT of 1.7 m stretching back to 1962 with a maximum of 2.1 m in 1970 and previous minimum of 1.3 m in 2014. The relevance of thinner lake ice in arctic coastal lowlands, where thermokarst lakes cover greater than 20% of the land area, is that permafrost below lakes with bedfast ice is typically preserved. Lakes deeper than the MIT warm and thaw sub-lake permafrost forming taliks. Remote sensing analysis using synthetic aperture radar (SAR) is a valuable tool for scaling the field observations of MIT to the entire freshwater landscape to map bedfast ice. A new, long-term time-series of late winter multi-platform SAR from 1992 to 2016 shows a large dynamic range of bedfast ice extent, 29% of lake area or 6% of the total land area over this period, and adding 2017 to this record is expected to extend this range further. Empirical models of lake mean annual bed temperature suggest that permafrost begins to thaw at depths less than 60% of MIT. Based on this information and knowledge of average lake ice growth trajectories, we suggest that future SAR analysis of lake ice should focus on mid-winter (January) to evaluate the extent of bedfast ice and corresponding zones of sub-lake permafrost thaw. Tracking changes in these areas from year to year in mid-winter may provide the best landscape-scale evaluation of changing permafrost conditions in lake-rich arctic lowlands. Because observed changes in MIT coupled with mid-winter bedfast ice extent provide much information on permafrost stability, we suggest that these measurements can serve as Essential Climate Variables (EVCs) to indicate past and future changes in lake-rich arctic regions. The

A parameters optimization method for planar joint clearance model and its application for dynamics simulation of reciprocating compressor

NASA Astrophysics Data System (ADS)

Hai-yang, Zhao; Min-qiang, Xu; Jin-dong, Wang; Yong-bo, Li

2015-05-01

In order to improve the accuracy of dynamics response simulation for mechanism with joint clearance, a parameter optimization method for planar joint clearance contact force model was presented in this paper, and the optimized parameters were applied to the dynamics response simulation for mechanism with oversized joint clearance fault. By studying the effect of increased clearance on the parameters of joint clearance contact force model, the relation of model parameters between different clearances was concluded. Then the dynamic equation of a two-stage reciprocating compressor with four joint clearances was developed using Lagrange method, and a multi-body dynamic model built in ADAMS software was used to solve this equation. To obtain a simulated dynamic response much closer to that of experimental tests, the parameters of joint clearance model, instead of using the designed values, were optimized by genetic algorithms approach. Finally, the optimized parameters were applied to simulate the dynamics response of model with oversized joint clearance fault according to the concluded parameter relation. The dynamics response of experimental test verified the effectiveness of this application.

Thermodynamic and dynamic ice thickness contributions in the Canadian Arctic Archipelago in NEMO-LIM2 numerical simulations

NASA Astrophysics Data System (ADS)

Hu, Xianmin; Sun, Jingfan; Chan, Ting On; Myers, Paul G.

2018-04-01

Sea ice thickness evolution within the Canadian Arctic Archipelago (CAA) is of great interest to science, as well as local communities and their economy. In this study, based on the NEMO numerical framework including the LIM2 sea ice module, simulations at both 1/4 and 1/12° horizontal resolution were conducted from 2002 to 2016. The model captures well the general spatial distribution of ice thickness in the CAA region, with very thick sea ice (˜ 4 m and thicker) in the northern CAA, thick sea ice (2.5 to 3 m) in the west-central Parry Channel and M'Clintock Channel, and thin ( < 2 m) ice (in winter months) on the east side of CAA (e.g., eastern Parry Channel, Baffin Island coast) and in the channels in southern areas. Even though the configurations still have resolution limitations in resolving the exact observation sites, simulated ice thickness compares reasonably (seasonal cycle and amplitudes) with weekly Environment and Climate Change Canada (ECCC) New Ice Thickness Program data at first-year landfast ice sites except at the northern sites with high concentration of old ice. At 1/4 to 1/12° scale, model resolution does not play a significant role in the sea ice simulation except to improve local dynamics because of better coastline representation. Sea ice growth is decomposed into thermodynamic and dynamic (including all non-thermodynamic processes in the model) contributions to study the ice thickness evolution. Relatively smaller thermodynamic contribution to ice growth between December and the following April is found in the thick and very thick ice regions, with larger contributions in the thin ice-covered region. No significant trend in winter maximum ice volume is found in the northern CAA and Baffin Bay while a decline (r2 ≈ 0.6, p < 0.01) is simulated in Parry Channel region. The two main contributors (thermodynamic growth and lateral transport) have high interannual variabilities which largely balance each other, so that maximum ice volume can

Correlation and prediction of dynamic human isolated joint strength from lean body mass

NASA Technical Reports Server (NTRS)

Pandya, Abhilash K.; Hasson, Scott M.; Aldridge, Ann M.; Maida, James C.; Woolford, Barbara J.

1992-01-01

A relationship between a person's lean body mass and the amount of maximum torque that can be produced with each isolated joint of the upper extremity was investigated. The maximum dynamic isolated joint torque (upper extremity) on 14 subjects was collected using a dynamometer multi-joint testing unit. These data were reduced to a table of coefficients of second degree polynomials, computed using a least squares regression method. All the coefficients were then organized into look-up tables, a compact and convenient storage/retrieval mechanism for the data set. Data from each joint, direction and velocity, were normalized with respect to that joint's average and merged into files (one for each curve for a particular joint). Regression was performed on each one of these files to derive a table of normalized population curve coefficients for each joint axis, direction, and velocity. In addition, a regression table which included all upper extremity joints was built which related average torque to lean body mass for an individual. These two tables are the basis of the regression model which allows the prediction of dynamic isolated joint torques from an individual's lean body mass.

Dynamic Distraction External Fixation for Contracture of the Metacarpophalangeal Joint.

PubMed

Seigerman, Daniel A; Tan, Virak

2015-12-01

Metacarpophalangeal (MP) joint contractures are common after traumatic injury, and can be difficult to manage. After surgical capsulectomy, it remains challenging to maintain motion that was obtained at the time of surgery. Our group uses a novel, prefabricated digital external fixator to provide both distraction, and motion therapy across the MP joint after surgical treatment of MP contracture. The purpose of this technique is to demonstrate the effectiveness of an adjunctive dynamic distraction external fixator for the maintenance of joint motion after surgical treatment of MP contractures of the border digits.

Drivers of inorganic carbon dynamics in first-year sea ice: A model study

NASA Astrophysics Data System (ADS)

Moreau, Sébastien; Vancoppenolle, Martin; Delille, Bruno; Tison, Jean-Louis; Zhou, Jiayun; Kotovitch, Marie; Thomas, David N.; Geilfus, Nicolas-Xavier; Goosse, Hugues

2015-01-01

Sea ice is an active source or a sink for carbon dioxide (CO2), although to what extent is not clear. Here, we analyze CO2 dynamics within sea ice using a one-dimensional halothermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice-ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption, and release of CO2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO3·6H2O) and ice-air CO2 fluxes, are also included. The model is evaluated using observations from a 6 month field study at Point Barrow, Alaska, and an ice-tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine-air CO2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice-atmosphere CO2 exchanges, sea ice is a net CO2 source and sink in winter and summer, respectively. The formulation of the ice-atmosphere CO2 flux impacts the simulated near-surface CO2 partial pressure (pCO2), but not the DIC budget. Because the simulated ice-atmosphere CO2 fluxes are limited by DIC stocks, and therefore <2 mmol m-2 d-1, we argue that the observed much larger CO2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO2. Finally, the simulations suggest that near-surface TA/DIC ratios of ˜2, sometimes used as an indicator of calcification, would rather suggest outgassing.

Drivers of inorganic carbon dynamics in first-year sea ice: A model study

NASA Astrophysics Data System (ADS)

Moreau, Sébastien; Vancoppenolle, Martin; Delille, Bruno; Tison, Jean-Louis; Zhou, Jiayun; Kotovich, Marie; Thomas, David; Geilfus, Nicolas-Xavier; Goosse, Hugues

2015-04-01

Sea ice is an active source or a sink for carbon dioxide (CO2), although to what extent is not clear. Here, we analyze CO2 dynamics within sea ice using a one-dimensional halo-thermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice-ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption and release of CO2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO3•6H2O) and ice-air CO2 fluxes, are also included. The model is evaluated using observations from a 6-month field study at Point Barrow, Alaska and an ice-tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine-air CO2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice-atmosphere CO2 exchanges, sea ice is a net CO2 source and sink in winter and summer, respectively. The formulation of the ice-atmosphere CO2 flux impacts the simulated near-surface CO2 partial pressure (pCO2), but not the DIC budget. Because the simulated ice-atmosphere CO2 fluxes are limited by DIC stocks, and therefore < 2 mmol m-2 day-1, we argue that the observed much larger CO2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO2. Finally, the simulations suggest that near surface TA/DIC ratios of ~2, sometimes used as an indicator of calcification, would rather suggest outgassing.

Joint symbolic dynamics for the assessment of cardiovascular and cardiorespiratory interactions

PubMed Central

Baumert, Mathias; Javorka, Michal; Kabir, Muammar

2015-01-01

Beat-to-beat variations in heart period provide information on cardiovascular control and are closely linked to variations in arterial pressure and respiration. Joint symbolic analysis of heart period, systolic arterial pressure and respiration allows for a simple description of their shared short-term dynamics that are governed by cardiac baroreflex control and cardiorespiratory coupling. In this review, we discuss methodology and research applications. Studies suggest that analysis of joint symbolic dynamics provides a powerful tool for identifying physiological and pathophysiological changes in cardiovascular and cardiorespiratory control. PMID:25548272

Global ice sheet/RSL simulations using the higher-order Ice Sheet System Model.

NASA Astrophysics Data System (ADS)

Larour, E. Y.; Ivins, E. R.; Adhikari, S.; Schlegel, N.; Seroussi, H. L.; Morlighem, M.

2017-12-01

Relative sea-level rise is driven by processes that are intimately linked to the evolution ofglacial areas and ice sheets in particular. So far, most Earth System models capable of projecting theevolution of RSL on decadal to centennial time scales have relied on offline interactions between RSL andice sheets. In particular, grounding line and calving front dynamics have not been modeled in a way that istightly coupled with Elasto-Static Adjustment (ESA) and/or Glacial-Isostatic Adjustment (GIA). Here, we presenta new simulation of the entire Earth System in which both Greenland and Antarctica ice sheets are tightly coupledto an RSL model that includes both ESA and GIA at resolutions and time scales compatible with processes suchas grounding line dynamics for Antarctica ice shelves and calving front dynamics for Greenland marine-terminatingglaciers. The simulations rely on the Ice Sheet System Model (ISSM) and show the impact of higher-orderice flow dynamics and coupling feedbacks between ice flow and RSL. We quantify the exact impact of ESA andGIA inclusion on grounding line evolution for large ice shelves such as the Ronne and Ross ice shelves, as well asthe Agasea Embayment ice streams, and demonstate how offline vs online RSL simulations diverge in the long run,and the consequences for predictions of sea-level rise.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

Dynamic ikaite production and dissolution in sea ice - control by temperature, salinity and pCO2 conditions

NASA Astrophysics Data System (ADS)

Rysgaard, S.; Wang, F.; Galley, R. J.; Grimm, R.; Lemes, M.; Geilfus, N.-X.; Chaulk, A.; Hare, A. A.; Crabeck, O.; Else, B. G. T.; Campbell, K.; Papakyriakou, T.; Sørensen, L. L.; Sievers, J.; Notz, D.

2013-12-01

Ikaite is a hydrous calcium carbonate mineral (CaCO3 · 6H2O). It is only found in a metastable state, and decomposes rapidly once removed from near-freezing water. Recently, ikaite crystals have been found in sea ice and it has been suggested that their precipitation may play an important role in air-sea CO2 exchange in ice-covered seas. Little is known, however, of the spatial and temporal dynamics of ikaite in sea ice. Here we present evidence for highly dynamic ikaite precipitation and dissolution in sea ice grown at an out-door pool of the Sea-ice Environmental Research Facility (SERF). During the experiment, ikaite precipitated in sea ice with temperatures below -3 °C, creating three distinct zones of ikaite concentrations: (1) a mm to cm thin surface layer containing frost flowers and brine skim with bulk concentrations of > 2000 μmol kg-1, (2) an internal layer with concentrations of 200-400 μmol kg-1 and (3) a~bottom layer with concentrations of < 100 μmol kg-1. Snowfall events caused the sea ice to warm, dissolving ikaite crystals under acidic conditions. Manual removal of the snow cover allowed the sea ice to cool and brine salinities to increase, resulting in rapid ikaite precipitation. The modeled (FREZCHEM) ikaite concentrations were in the same order of magnitude as observations and suggest that ikaite concentration in sea ice increase with decreasing temperatures. Thus, varying snow conditions may play a key role in ikaite precipitation and dissolution in sea ice. This will have implications for CO2 exchange with the atmosphere and ocean.

Effect of a 6-week dynamic neuromuscular training programme on ankle joint function: A Case report.

PubMed

O'Driscoll, Jeremiah; Kerin, Fearghal; Delahunt, Eamonn

2011-06-09

Ankle joint sprain and the subsequent development of chronic ankle instability (CAI) are commonly encountered by clinicians involved in the treatment and rehabilitation of musculoskeletal injuries. It has recently been advocated that ankle joint post-sprain rehabilitation protocols should incorporate dynamic neuromuscular training to enhance ankle joint sensorimotor capabilities. To date no studies have reported on the effects of dynamic neuromuscular training on ankle joint positioning during landing from a jump, which has been reported as one of the primary injury mechanisms for ankle joint sprain. This case report details the effects of a 6-week dynamic neuromuscular training programme on ankle joint function in an athlete with CAI. The athlete took part in a progressive 6-week dynamic neuromuscular training programme which incorporated postural stability, strengthening, plyometric, and speed/agility drills. The outcome measures chosen to assess for interventional efficacy were: 1 Cumberland Ankle Instability Tool (CAIT) scores, 2 Star Excursion Balance Test (SEBT) reach distances, 3 ankle joint plantar flexion during drop landing and drop vertical jumping, and 4 ground reaction forces (GRFs) during walking. CAIT and SEBT scores improved following participation in the programme. The angle of ankle joint plantar flexion decreased at the point of initial contact during the drop landing and drop vertical jumping tasks, indicating that the ankle joint was in a less vulnerable position upon landing following participation in the programme. Furthermore, GRFs were reduced whilst walking post-intervention. The 6-week dynamic neuromuscular training programme improved parameters of ankle joint sensorimotor control in an athlete with CAI. Further research is now required in a larger cohort of subjects to determine the effects of neuromuscular training on ankle joint injury risk factors.

Earth Structure, Ice Mass Changes, and the Local Dynamic Geoid

NASA Astrophysics Data System (ADS)

Harig, C.; Simons, F. J.

2014-12-01

Spherical Slepian localization functions are a useful method for studying regional mass changes observed by satellite gravimetry. By projecting data onto a sparse basis set, the local field can be estimated more easily than with the full spherical harmonic basis. We have used this method previously to estimate the ice mass change in Greenland from GRACE data, and it can also be applied to other planetary problems such as global magnetic fields. Earth's static geoid, in contrast to the time-variable field, is in large part related to the internal density and rheological structure of the Earth. Past studies have used dynamic geoid kernels to relate this density structure and the internal deformation it induces to the surface geopotential at large scales. These now classical studies of the eighties and nineties were able to estimate the mantle's radial rheological profile, placing constraints on the ratio between upper and lower mantle viscosity. By combining these two methods, spherical Slepian localization and dynamic geoid kernels, we have created local dynamic geoid kernels which are sensitive only to density variations within an area of interest. With these kernels we can estimate the approximate local radial rheological structure that best explains the locally observed geoid on a regional basis. First-order differences of the regional mantle viscosity structure are accessible to this technique. In this contribution we present our latest, as yet unpublished results on the geographical and temporal pattern of ice mass changes in Antarctica over the past decade, and we introduce a new approach to extract regional information about the internal structure of the Earth from the static global gravity field. Both sets of results are linked in terms of the relevant physics, but also in being developed from the marriage of Slepian functions and geoid kernels. We make predictions on the utility of our approach to derive fully three-dimensional rheological Earth models, to

The safety band of Antarctic ice shelves

NASA Astrophysics Data System (ADS)

Fürst, Johannes Jakob; Durand, Gaël; Gillet-Chaulet, Fabien; Tavard, Laure; Rankl, Melanie; Braun, Matthias; Gagliardini, Olivier

2016-05-01

The floating ice shelves along the seaboard of the Antarctic ice sheet restrain the outflow of upstream grounded ice. Removal of these ice shelves, as shown by past ice-shelf recession and break-up, accelerates the outflow, which adds to sea-level rise. A key question in predicting future outflow is to quantify the extent of calving that might precondition other dynamic consequences and lead to loss of ice-shelf restraint. Here we delineate frontal areas that we label as `passive shelf ice’ and that can be removed without major dynamic implications, with contrasting results across the continent. The ice shelves in the Amundsen and Bellingshausen seas have limited or almost no `passive’ portion, which implies that further retreat of current ice-shelf fronts will yield important dynamic consequences. This region is particularly vulnerable as ice shelves have been thinning at high rates for two decades and as upstream grounded ice rests on a backward sloping bed, a precondition to marine ice-sheet instability. In contrast to these ice shelves, Larsen C Ice Shelf, in the Weddell Sea, exhibits a large `passive’ frontal area, suggesting that the imminent calving of a vast tabular iceberg will be unlikely to instantly produce much dynamic change.

Dynamic Cytology and Transcriptional Regulation of Rice Lamina Joint Development.

PubMed

Zhou, Li-Juan; Xiao, Lang-Tao; Xue, Hong-Wei

2017-07-01

Rice ( Oryza sativa ) leaf angle is determined by lamina joint and is an important agricultural trait determining leaf erectness and, hence, the photosynthesis efficiency and grain yield. Genetic studies reveal a complex regulatory network of lamina joint development; however, the morphological changes, cytological transitions, and underlying transcriptional programming remain to be elucidated. A systemic morphological and cytological study reveals a dynamic developmental process and suggests a common but distinct regulation of the lamina joint. Successive and sequential cell division and expansion, cell wall thickening, and programmed cell death at the adaxial or abaxial sides form the cytological basis of the lamina joint, and the increased leaf angle results from the asymmetric cell proliferation and elongation. Analysis of the gene expression profiles at four distinct developmental stages ranging from initiation to senescence showed that genes related to cell division and growth, hormone synthesis and signaling, transcription (transcription factors), and protein phosphorylation (protein kinases) exhibit distinct spatiotemporal patterns during lamina joint development. Phytohormones play crucial roles by promoting cell differentiation and growth at early stages or regulating the maturation and senescence at later stages, which is consistent with the quantitative analysis of hormones at different stages. Further comparison with the gene expression profile of leaf inclination1 , a mutant with decreased auxin and increased leaf angle, indicates the coordinated effects of hormones in regulating lamina joint. These results reveal a dynamic cytology of rice lamina joint that is fine-regulated by multiple factors, providing informative clues for illustrating the regulatory mechanisms of leaf angle and plant architecture. © 2017 American Society of Plant Biologists. All Rights Reserved.

Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics.

PubMed

Cherry, Seth G; Derocher, Andrew E; Thiemann, Gregory W; Lunn, Nicholas J

2013-07-01

Understanding how seasonal environmental conditions affect the timing and distribution of synchronized animal movement patterns is a central issue in animal ecology. Migration, a behavioural adaptation to seasonal environmental fluctuations, is a fundamental part of the life history of numerous species. However, global climate change can alter the spatiotemporal distribution of resources and thus affect the seasonal movement patterns of migratory animals. We examined sea ice dynamics relative to migration patterns and seasonal geographical fidelity of an Arctic marine predator, the polar bear (Ursus maritimus). Polar bear movement patterns were quantified using satellite-linked telemetry data collected from collars deployed between 1991-1997 and 2004-2009. We showed that specific sea ice characteristics can predict the timing of seasonal polar bear migration on and off terrestrial refugia. In addition, fidelity to specific onshore regions during the ice-free period was predicted by the spatial pattern of sea ice break-up but not by the timing of break-up. The timing of migration showed a trend towards earlier arrival of polar bears on shore and later departure from land, which has been driven by climate-induced declines in the availability of sea ice. Changes to the timing of migration have resulted in polar bears spending progressively longer periods of time on land without access to sea ice and their marine mammal prey. The links between increased atmospheric temperatures, sea ice dynamics, and the migratory behaviour of an ice-dependent species emphasizes the importance of quantifying and monitoring relationships between migratory wildlife and environmental cues that may be altered by climate change. © 2013 The Authors. Journal of Animal Ecology © 2013 British Ecological Society.

Nanocluster building blocks of artificial square spin ice: Stray-field studies of thermal dynamics

NASA Astrophysics Data System (ADS)

Pohlit, Merlin; Porrati, Fabrizio; Huth, Michael; Ohno, Yuzo; Ohno, Hideo; Müller, Jens

2015-05-01

We present measurements of the thermal dynamics of a Co-based single building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition. We employ micro-Hall magnetometry, an ultra-sensitive tool to study the stray field emanating from magnetic nanostructures, as a new technique to access the dynamical properties during the magnetization reversal of the spin-ice nanocluster. The obtained hysteresis loop exhibits distinct steps, displaying a reduction of their "coercive field" with increasing temperature. Therefore, thermally unstable states could be repetitively prepared by relatively simple temperature and field protocols allowing one to investigate the statistics of their switching behavior within experimentally accessible timescales. For a selected switching event, we find a strong reduction of the so-prepared states' "survival time" with increasing temperature and magnetic field. Besides the possibility to control the lifetime of selected switching events at will, we find evidence for a more complex behavior caused by the special spin ice arrangement of the macrospins, i.e., that the magnetic reversal statistically follows distinct "paths" most likely driven by thermal perturbation.

Quantification of cardiorespiratory interactions based on joint symbolic dynamics.

PubMed

Kabir, Muammar M; Saint, David A; Nalivaiko, Eugene; Abbott, Derek; Voss, Andreas; Baumert, Mathias

2011-10-01

Cardiac and respiratory rhythms are highly nonlinear and nonstationary. As a result traditional time-domain techniques are often inadequate to characterize their complex dynamics. In this article, we introduce a novel technique to investigate the interactions between R-R intervals and respiratory phases based on their joint symbolic dynamics. To evaluate the technique, electrocardiograms (ECG) and respiratory signals were recorded in 13 healthy subjects in different body postures during spontaneous and controlled breathing. Herein, the R-R time series were extracted from ECG and respiratory phases were obtained from abdomen impedance belts using the Hilbert transform. Both time series were transformed into ternary symbol vectors based on the changes between two successive R-R intervals or respiratory phases. Subsequently, words of different symbol lengths were formed and the correspondence between the two series of words was determined to quantify the interaction between cardiac and respiratory cycles. To validate our results, respiratory sinus arrhythmia (RSA) was further studied using the phase-averaged characterization of the RSA pattern. The percentage of similarity of the sequence of symbols, between the respective words of the two series determined by joint symbolic dynamics, was significantly reduced in the upright position compared to the supine position (26.4 ± 4.7 vs. 20.5 ± 5.4%, p < 0.01). Similarly, RSA was also reduced during upright posture, but the difference was less significant (0.11 ± 0.02 vs. 0.08 ± 0.01 s, p < 0.05). In conclusion, joint symbolic dynamics provides a new efficient technique for the analysis of cardiorespiratory interaction that is highly sensitive to the effects of orthostatic challenge.

Effect of a 6-week dynamic neuromuscular training programme on ankle joint function: A Case report

PubMed Central

2011-01-01

Background Ankle joint sprain and the subsequent development of chronic ankle instability (CAI) are commonly encountered by clinicians involved in the treatment and rehabilitation of musculoskeletal injuries. It has recently been advocated that ankle joint post-sprain rehabilitation protocols should incorporate dynamic neuromuscular training to enhance ankle joint sensorimotor capabilities. To date no studies have reported on the effects of dynamic neuromuscular training on ankle joint positioning during landing from a jump, which has been reported as one of the primary injury mechanisms for ankle joint sprain. This case report details the effects of a 6-week dynamic neuromuscular training programme on ankle joint function in an athlete with CAI. Methods The athlete took part in a progressive 6-week dynamic neuromuscular training programme which incorporated postural stability, strengthening, plyometric, and speed/agility drills. The outcome measures chosen to assess for interventional efficacy were: [1] Cumberland Ankle Instability Tool (CAIT) scores, [2] Star Excursion Balance Test (SEBT) reach distances, [3] ankle joint plantar flexion during drop landing and drop vertical jumping, and [4] ground reaction forces (GRFs) during walking. Results CAIT and SEBT scores improved following participation in the programme. The angle of ankle joint plantar flexion decreased at the point of initial contact during the drop landing and drop vertical jumping tasks, indicating that the ankle joint was in a less vulnerable position upon landing following participation in the programme. Furthermore, GRFs were reduced whilst walking post-intervention. Conclusions The 6-week dynamic neuromuscular training programme improved parameters of ankle joint sensorimotor control in an athlete with CAI. Further research is now required in a larger cohort of subjects to determine the effects of neuromuscular training on ankle joint injury risk factors. PMID:21658224

Grounding Zones, Subglacial Lakes, and Dynamics of an Antarctic Ice Stream: The WISSARD Glaciological Experiment

NASA Astrophysics Data System (ADS)

Tulaczyk, S. M.; Schwartz, S. Y.; Fisher, A. T.; Powell, R. D.; Fricker, H. A.; Anandakrishnan, S.; Horgan, H. J.; Scherer, R. P.; Walter, J. I.; Siegfried, M. R.; Mikucki, J.; Christianson, K.; Beem, L.; Mankoff, K. D.; Carter, S. P.; Hodson, T. O.; Marsh, O.; Barcheck, C. G.; Branecky, C.; Neuhaus, S.; Jacobel, R. W.

2015-12-01

Interactions of West Antarctic ice streams with meltwater at their beds, and with seawater at their grounding lines, are widely considered to be the primary drivers of ice stream flow variability on different timescales. Understanding of processes controlling ice flow variability is needed to build quantitative models of the Antarctic Ice Sheet that can be used to help predict its future behavior and to reconstruct its past evolution. The ice plain of Whillans Ice Stream provides a natural glaciological laboratory for investigations of Antarctic ice flow dynamics because of its highly variable flow rate modulated by tidal processes and fill-drain cycles of subglacial lakes. Moreover, this part of Antarctica has one of the longest time series of glaciological observations, which can be used to put recently acquired datasets in a multi-decadal context. Since 2007 Whillans Ice Stream has been the focus of a regional glaciological experiment, which included surface GPS and passive-source seismic sensors, radar and seismic imaging of subglacial properties, as well as deep borehole geophysical sensors. This experiment was possible thanks to the NSF-funded multidisciplinary WISSARD project (Whillans Ice Stream Subglacial Access Research Drilling). Here we will review the datasets collected during the WISSARD glaciological experiment and report on selected results pertaining to interactions of this ice stream with water at its bed and its grounding line.

On the potential influence of ice nuclei on surface-forced marine stratocumulus cloud dynamics

NASA Astrophysics Data System (ADS)

Harrington, Jerry Y.; Olsson, Peter Q.

2001-11-01

The mixed phase cloudy boundary layer that occurs during off-ice flow in the marine Arctic was simulated in an environment with a strong surface heat flux (nearly 800 W m-2). A two-dimensional, eddy-resolving model coupled to a detailed cloud microphysical model was used to study both liquid phase and mixed phase stratocumulus clouds and boundary layer (BL) dynamics in this environment. Since ice precipitation may be important to BL dynamics, and ice nuclei (IN) concentrations modulate ice precipitation rates, the role of IN in cloud and BL development was explored. The results of several simulations illustrate how mixed phase microphysical processes affect the evolution of the cloudy BL in this environment. In agreement with past studies, BLs with mixed phase clouds had weaker convection, shallower BL depths, and smaller cloud fractions than BLs with clouds restricted to the liquid phase only. It is shown that the weaker BL convection is due to strong ice precipitation. Ice precipitation reduces convective strength directly by stabilizing downdrafts and more indirectly by sensibly heating the BL and inhibiting vertical mixing of momentum thereby reducing surface heat fluxes by as much as 80 W m-2. This feedback between precipitation and surface fluxes was found to have a significant impact on cloud/BL morphology, producing oscillations in convective strength and cloud fraction that did not occur if surface fluxes were fixed at constant values. Increases in IN concentrations in mixed phase clouds caused a more rapid Bergeron-Findeisen process leading to larger precipitation fluxes, reduced convection and lower cloud fraction. When IN were removed from the BL through precipitation, fewer crystals were nucleated at later simulation times leading to progressively weaker precipitation rates, greater cloud fraction, and stronger convective BL eddies.

Dynamic properties of human incudostapedial joint-Experimental measurement and finite element modeling.

PubMed

Jiang, Shangyuan; Gan, Rong Z

2018-04-01

The incudostapedial joint (ISJ) is a synovial joint connecting the incus and stapes in the middle ear. Mechanical properties of the ISJ directly affect sound transmission from the tympanic membrane to the cochlea. However, how ISJ properties change with frequency has not been investigated. In this paper, we report the dynamic properties of the human ISJ measured in eight samples using a dynamic mechanical analyzer (DMA) for frequencies from 1 to 80 Hz at three temperatures of 5, 25 and 37 °C. The frequency-temperature superposition (FTS) principle was used to extrapolate the results to 8 kHz. The complex modulus of ISJ was measured with a mean storage modulus of 1.14 MPa at 1 Hz that increased to 3.01 MPa at 8 kHz, and a loss modulus that increased from 0.07 to 0.47 MPa. A 3-dimensional finite element (FE) model consisting of the articular cartilage, joint capsule and synovial fluid was then constructed to derive mechanical properties of ISJ components by matching the model results to experimental data. Modeling results showed that mechanical properties of the joint capsule and synovial fluid affected the dynamic behavior of the joint. This study contributes to a better understanding of the structure-function relationship of the ISJ for sound transmission. Copyright © 2018. Published by Elsevier Ltd.

Structure, spectroscopy and dynamics of layered H2O and CO2 ices

USGS Publications Warehouse

,; Plattner, Nuria; Meuwly, Markus

2012-01-01

Molecular dynamics simulations of structural, spectroscopic and dynamical properties of mixed water–carbon dioxide (H2O–CO2) ices are discussed over temperature ranges relevant to atmospheric and astrophysical conditions. The simulations employ multipolar force fields to represent electrostatic interactions which are essential for spectroscopic and dynamical investigations. It is found that at the water/CO2 interface the water surface acts as a template for the CO2 component. The rotational reorientation times in both bulk phases agree well with experimental observations. A pronounced temperature effect on the CO2 reorientation time is observed between 100 K and 200 K. At the interface, water reorientation times are nearly twice as long compared to water in the bulk. The spectroscopy of such ices is rich in the far-infrared region of the spectrum and can be related to translational and rotational modes. Furthermore, spectroscopic signatures mediated across the water/CO2 interface are found in this frequency range (around 440 cm−1). These results will be particularly important for new airborne experiments such as planned for SOFIA.

Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

DOE PAGES

Favier, Lionel; Pattyn, Frank; Berger, Sophie; ...

2016-11-09

The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouinmore » ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10%, while omitting the same pinning point in data assimilation decreases it by 10%, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. As a result, pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.« less

Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

DOE Office of Scientific and Technical Information (OSTI.GOV)

Favier, Lionel; Pattyn, Frank; Berger, Sophie

The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouinmore » ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10%, while omitting the same pinning point in data assimilation decreases it by 10%, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. As a result, pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.« less

Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD.

PubMed

Chauve, T; Montagnat, M; Barou, F; Hidas, K; Tommasi, A; Mainprice, D

2017-02-13

Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=-5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the 'parent' ones suggests the possibility of 'spontaneous' nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms.This article is part of the themed issue 'Microdynamics of ice'. © 2016 The Author(s).

Ankle Joint Angle and Lower Leg Musculotendinous Unit Responses to Cryotherapy.

PubMed

Akehi, Kazuma; Long, Blaine C; Warren, Aric J; Goad, Carla L

2016-09-01

Akehi, K, Long, BC, Warren, AJ, and Goad, CL. Ankle joint angle and lower leg musculotendinous unit responses to cryotherapy. J Strength Cond Res 30(9): 2482-2492, 2016-The use of cold application has been debated for its influence on joint range of motion (ROM) and stiffness. The purpose of this study was to determine whether a 30-minute ice bag application to the plantarflexor muscles or ankle influences passive ankle dorsiflexion ROM and lower leg musculotendinous stiffness (MTS). Thirty-five recreationally active college-aged individuals with no history of lower leg injury 6 months before data collection volunteered. On each testing day, we measured maximum passive ankle dorsiflexion ROM (°) and plantarflexor torque (N·m) on an isokinetic dynamometer to calculate the passive plantarflexor MTS (N·m per degree) at 4 joint angles before, during, and after a treatment. Surface electromyography amplitudes (μV), and skin surface and ambient air temperature (°C) were also measured. Subjects received an ice bag to the posterior lower leg, ankle joint, or nothing for 30 minutes in different days. Ice bag application to the lower leg and ankle did not influence passive ROM (F(12,396) = 0.67, p = 0.78). Passive torque increased after ice bag application to the lower leg (F(12,396) = 2.21, p = 0.011). Passive MTS at the initial joint angle increased after ice bag application to the lower leg (F(12,396) = 2.14, p = 0.014) but not at the other joint angles (p > 0.05). Surface electromyography amplitudes for gastrocnemius and soleus muscles increased after ice application to the lower leg (F(2,66) = 5.61, p = 0.006; F(12,396) = 3.60, p < 0.001). Ice bag application to the lower leg and ankle joint does not alter passive dorsiflexion ROM but increases passive ankle plantarflexor torque in addition to passive ankle plantarflexor MTS at the initial joint angle.

Basal friction evolution and crevasse distribution during the surge of Basin 3, Austfonna ice-cap - offline coupling between a continuum ice dynamic model and a discrete element model

NASA Astrophysics Data System (ADS)

Gong, Yongmei; Zwinger, Thomas; Åström, Jan; Gladstone, Rupert; Schellenberger, Thomas; Altena, Bas; Moore, John

2017-04-01

The outlet glacier at Basin 3, Austfonna ice-cap entered its active surge phase in autumn 2012. We assess the evolution of the basal friction during the surge through inverse modelling of basal friction coefficients using recent velocity observation from 2012 to 2014 in a continuum ice dynamic model Elmer/ice. The obtained basal friction coefficient distributions at different time instances are further used as a boundary condition in a discrete element model (HiDEM) that is capable of computing fracturing of ice. The inverted basal friction coefficient evolution shows a gradual 'unplugging' of the stagnant frontal area and northwards and inland expansion of the fast flowing region in the southern basin. The validation between the modeled crevasses distribution and the satellite observation in August 2013 shows a good agreement in shear zones inland and at the frontal area. Crevasse distributions of the summer before and after the glacier reached its maximum velocity in January 2013 (August 2012 and August 2014, respectively) are also evaluated. Previous studies suggest the triggering and development of the surge are linked to surface melt water penetrating through ice to form an efficient basal hydrology system thereby triggering a hydro- thermodynamic feedback. This preliminary offline coupling between a continuum ice dynamic model and a discrete element model will give a hint on future model development of linking supra-glacial to sub-glacial hydrology system.

Dynamic fragmentation of cellular, ice-templated alumina scaffolds

DOE PAGES

Tan, Yi Ming; Cervantes, Octavio; Nam, SeanWoo; ...

2016-01-08

Here, we examine the dynamic failure of ice-templated freeze-cast alumina scaffolds that are being considered as biomimetic hierarchical structures. Three porosities of alumina freeze-cast structures were fabricated, and a systematic variation in microstructural properties such as lamellar width and thickness was observed with changing porosity. Dynamic impact tests were performed in a light-gas gun to examine the failure properties of these materials under high strain-rate loading. Nearly complete delamination was observed following impact, along with characteristic cracking across the lamellar width. Average fragment size decreases with increasing porosity, and a theoretical model was developed to explain this behavior based onmore » microstructural changes. Using an energy balance between kinetic, strain, and surface energies within a single lamella, we are able to accurately predict the characteristic fragment size using only standard material properties of bulk alumina.« less

Dynamic Postural-Stability Deficits After Cryotherapy to the Ankle Joint.

PubMed

Fullam, Karl; Caulfield, Brian; Coughlan, Garrett F; McGroarty, Mark; Delahunt, Eamonn

2015-09-01

Decreased postural stability is a primary risk factor for lower limb musculoskeletal injuries. During athletic competitions, cryotherapy may be applied during short breaks in play or during half-time; however, its effects on postural stability remain unclear. To investigate the acute effects of a 15-minute ankle-joint cryotherapy application on dynamic postural stability. Controlled laboratory study. University biomechanics laboratory. A total of 29 elite-level collegiate male field-sport athletes (age = 20.8 ± 1.12 years, height = 1.80 ± 0.06 m, mass = 81.89 ± 8.59 kg) participated. Participants were tested on the anterior (ANT), posterolateral (PL), and posteromedial (PM) reach directions of the Star Excursion Balance Test before and after a 15-minute ankle-joint cryotherapy application. Normalized reach distances; sagittal-plane kinematics of the hip, knee, and ankle joints; and associated mean velocity of the center-of-pressure path during performance of the ANT, PL, and PM reach directions of the Star Excursion Balance Test. We observed a decrease in reach-distance scores for the ANT, PL, and PM reach directions from precryotherapy to postcryotherapy (P < .05). No differences were observed in hip-, knee-, or ankle-joint sagittal-plane kinematics (P > .05). We noted a decrease in mean velocity of the center-of-pressure path from precryotherapy to postcryotherapy (P < .05) in all reach directions. Dynamic postural stability was adversely affected immediately after cryotherapy to the ankle joint.

Three-dimensional kinematics of the knee and ankle joints for three consecutive push-offs during ice hockey skating starts.

PubMed

Lafontaine, Dany

2007-09-01

Little biomechanical research has been conducted recently on hockey skating despite the sport's worldwide appeal. One reason for this lack of biomechanical knowledge stems from the difficulty of collecting data. The lack of accuracy, the disputable realism of treadmills, and the large field of view required are some of the technical challenges that have to be overcome. The main objective of the current study was to improve our knowledge of the joint kinematics during the skating stroke. A second objective was to improve the data collection system we developed and the third was to establish if a kinematic progression exists in the hockey skating stroke similar to that in speed skating. Relative motions at the knee and ankle joints were computed using a joint coordinate system approach. The differences at the knee joints in push-offs indicated that the skating skill was progressively changing with each push-off. The relative stability of the ankle angles can be attributed to the design of the skate boots, which have recently become very rigid. Further research on ice hockey skating is warranted and should include more skaters and investigate the effect various starting strategies and variations in equipment have on skaters' performance.

Dynamic Wheel-Rail Forces on Mismatched Joints with Ramps

DOT National Transportation Integrated Search

2016-04-12

The discontinuity between rail ends at a joint creates : dynamic wheel-rail forces (i.e. high impact forces and wheel : unloading) that can result in a range of problems including : wear, deterioration, and early failure of the track structure, its :...

Comparison of Ice-shelf Creep Flow Simulations with Ice-front Motion of Filchner-Ronne Ice Shelf, Antarctica, Detected by SAR Interferometry

NASA Technical Reports Server (NTRS)

Hulbe, C. L.; Rignot, E.; MacAyeal, D. R.

1998-01-01

Comparison between numerical model ice-shelf flow simulations and synthetic aperture radar (SAR) interferograms is used to study the dynamics at the Hemmen Ice Rise (HIR) and Lassiter Coast (LC) corners of the iceberg-calving front of the Filchner-Ronne Ice Shelf (FRIS).

Ice bridges and ridges in the Maxwell-EB sea ice rheology

NASA Astrophysics Data System (ADS)

Dansereau, Véronique; Weiss, Jérôme; Saramito, Pierre; Lattes, Philippe; Coche, Edmond

2017-09-01

This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB), is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a Mohr-Coulomb damage criterion that allows for pure (uniaxial and biaxial) tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.

Sensitivity studies with a coupled ice-ocean model of the marginal ice zone

NASA Technical Reports Server (NTRS)

Roed, L. P.

1983-01-01

An analytical coupled ice-ocean model is considered which is forced by a specified wind stress acting on the open ocean as well as the ice. The analysis supports the conjecture that the upwelling dynamics at ice edges can be understood by means of a simple analytical model. In similarity with coastal problems it is shown that the ice edge upwelling is determined by the net mass flux at the boundaries of the considered region. The model is used to study the sensitivity of the upwelling dynamics in the marginal ice zone to variation in the controlling parameters. These parameters consist of combinations of the drag coefficients used in the parameterization of the stresses on the three interfaces atmosphere-ice, atmosphere-ocean, and ice-ocean. The response is shown to be sensitive to variations in these parameters in that one set of parameters may give upwelling while a slightly different set of parameters may give downwelling.

Ice sheet radar altimetry

NASA Technical Reports Server (NTRS)

Zwally, J.

1988-01-01

The surface topography of the Greenland and Antarctic ice sheets between 72 degrees north and south was mapped using radar altimetry data from the U.S. Navy GEOSAT. The glaciological objectives of this activity were to study the dynamics of the ice flow, changes in the position of floating ice-shelf fronts, and ultimately to measure temporal changes in ice surface elevation indicative of ice sheet mass balance.

Effect of static foot posture on the dynamic stiffness of foot joints during walking.

PubMed

Sanchis-Sales, E; Sancho-Bru, J L; Roda-Sales, A; Pascual-Huerta, J

2018-05-01

The static foot posture has been related to the development of lower limb injuries. This study aimed to investigate the dynamic stiffness of foot joints during gait in the sagittal plane to understand the role of the static foot posture in the development of injuries. Seventy healthy adult male subjects with different static postures, assessed by the Foot Posture Index (FPI) (30 normal, 20 highly pronated and 20 highly supinated), were recruited. Kinematic and kinetic data were recorded using an optical motion capture system and a pressure platform, and dynamic stiffness at the different stages of the stance was calculated from the slopes of the linear regression on the flexion moment-angle curves. The effect of foot type on dynamic stiffness and on ranges of motion and moments was analysed using ANOVAs and post-hoc tests, and linear correlation between dynamic stiffness and FPI was also tested. Highly pronated feet showed a significantly smaller range of motion at the ankle and metatarsophalangeal joints and also a larger range of moments at the metatarsophalangeal joint than highly supinated feet. Dynamic stiffness during propulsion was significantly greater at all foot joints for highly pronated feet, with positive significant correlations with the squared FPI. Highly supinated feet showed greater dynamic stiffness than normal feet, although to a lesser extent. Highly pronated feet during normal gait experienced the greatest decrease in the dorsiflexor moments during propulsion, normal feet being the most balanced regarding work generated and absorbed. Extreme static foot postures show greater dynamic stiffness during propulsion and greater absorbed work, which increases the risk of developing injuries. The data presented may be used when designing orthotics or prostheses, and also when planning surgery that modifies joint stiffness. Copyright © 2018 Elsevier B.V. All rights reserved.

Monitoring of Sea Ice Dynamic by Means of ERS-Envisat Tandem Cross-Interferometry

NASA Astrophysics Data System (ADS)

Pasquali, Paolo; Cantone, Alessio; Barbieri, Massimo; Engdahl, Marcus

2010-03-01

The interest in the monitoring of sea ice masses has increased greatly over the past decades for a variety of reasons. These include:- Navigation in northern latitude waters;- transportation of petroleum;- exploitation of mineral deposits in the Arctic, and- the use of icebergs as a source of fresh water.The availability of ERS-Envisat 28minute tandem acquisitions from dedicated campaigns, covering large areas in the northern latitudes with large geometrical baseline and very short temporal separation, allows the precise estimation of sea ice displacement fields with an accuracy that cannot be obtained on large scale from any other instrument. This article presents different results of sea ice dynamic monitoring over northern Canada obtained within the "ERS-Envisat Tandem Cross-Interferometry Campaigns: CInSAR processing and studies over extended areas" project from data acquired during the 2008-2009 Tandem campaign..

An ice-ocean coupled model for the Northern Hemisphere

NASA Technical Reports Server (NTRS)

Cheng, Abe; Preller, Ruth

1992-01-01

The Hibler ice model has been modified and adapted to a domain that includes most of the sea ice-covered areas in the Northern Hemisphere. This model, joined with the Cox ocean model, is developed as an enhancement to the U.S. Navy's sea ice forecasting, PIPS, and is termed PIPS2.0. Generally, the modeled ice edge is consistent with the Navy-NOAA Joint Ice Center weekly analysis, and the modeled ice thickness distribution agrees with submarine sonar data in the central Arctic basin.

Bacterial community dynamics and activity in relation to dissolved organic matter availability during sea-ice formation in a mesocosm experiment.

PubMed

Eronen-Rasimus, Eeva; Kaartokallio, Hermanni; Lyra, Christina; Autio, Riitta; Kuosa, Harri; Dieckmann, Gerhard S; Thomas, David N

2014-02-01

The structure of sea-ice bacterial communities is frequently different from that in seawater. Bacterial entrainment in sea ice has been studied with traditional microbiological, bacterial abundance, and bacterial production methods. However, the dynamics of the changes in bacterial communities during the transition from open water to frozen sea ice is largely unknown. Given previous evidence that the nutritional status of the parent water may affect bacterial communities during ice formation, bacterial succession was studied in under ice water and sea ice in two series of mesocosms: the first containing seawater from the North Sea and the second containing seawater enriched with algal-derived dissolved organic matter (DOM). The composition and dynamics of bacterial communities were investigated with terminal restriction fragment length polymorphism (T-RFLP), and cloning alongside bacterial production (thymidine and leucine uptake) and abundance measurements (measured by flow cytometry). Enriched and active sea-ice bacterial communities developed in ice formed in both unenriched and DOM-enriched seawater (0-6 days). γ-Proteobacteria dominated in the DOM-enriched samples, indicative of their capability for opportunistic growth in sea ice. The bacterial communities in the unenriched waters and ice consisted of the classes Flavobacteria, α- and γ-Proteobacteria, which are frequently found in natural sea ice in polar regions. Furthermore, the results indicate that seawater bacterial communities are able to adapt rapidly to sudden environmental changes when facing considerable physicochemical stress such as the changes in temperature, salinity, nutrient status, and organic matter supply during ice formation. © 2014 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.

Nanocluster building blocks of artificial square spin ice: Stray-field studies of thermal dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pohlit, Merlin, E-mail: pohlit@physik.uni-frankfurt.de; Porrati, Fabrizio; Huth, Michael

We present measurements of the thermal dynamics of a Co-based single building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition. We employ micro-Hall magnetometry, an ultra-sensitive tool to study the stray field emanating from magnetic nanostructures, as a new technique to access the dynamical properties during the magnetization reversal of the spin-ice nanocluster. The obtained hysteresis loop exhibits distinct steps, displaying a reduction of their “coercive field” with increasing temperature. Therefore, thermally unstable states could be repetitively prepared by relatively simple temperature and field protocols allowing one to investigate the statistics of their switching behavior withinmore » experimentally accessible timescales. For a selected switching event, we find a strong reduction of the so-prepared states' “survival time” with increasing temperature and magnetic field. Besides the possibility to control the lifetime of selected switching events at will, we find evidence for a more complex behavior caused by the special spin ice arrangement of the macrospins, i.e., that the magnetic reversal statistically follows distinct “paths” most likely driven by thermal perturbation.« less

Adaptive mesh refinement versus subgrid friction interpolation in simulations of Antarctic ice dynamics

DOE PAGES

Cornford, S. L.; Martin, D. F.; Lee, V.; ...

2016-05-13

At least in conventional hydrostatic ice-sheet models, the numerical error associated with grounding line dynamics can be reduced by modifications to the discretization scheme. These involve altering the integration formulae for the basal traction and/or driving stress close to the grounding line and exhibit lower – if still first-order – error in the MISMIP3d experiments. MISMIP3d may not represent the variety of real ice streams, in that it lacks strong lateral stresses, and imposes a large basal traction at the grounding line. We study resolution sensitivity in the context of extreme forcing simulations of the entire Antarctic ice sheet, using the BISICLES adaptive mesh ice-sheet model with two schemes: the original treatment, and a scheme, which modifies the discretization of the basal traction. The second scheme does indeed improve accuracy – by around a factor of two – for a given mesh spacing, butmore » $$\\lesssim 1$$ km resolution is still necessary. For example, in coarser resolution simulations Thwaites Glacier retreats so slowly that other ice streams divert its trunk. In contrast, with $$\\lesssim 1$$ km meshes, the same glacier retreats far more quickly and triggers the final phase of West Antarctic collapse a century before any such diversion can take place.« less

Mapping of sea ice and measurement of its drift using aircraft synthetic aperture radar images

NASA Technical Reports Server (NTRS)

Leberl, F.; Bryan, M. L.; Elachi, C.; Farr, T.; Campbell, W.

1979-01-01

Side-looking radar images of Arctic sea ice were obtained as part of the Arctic Ice Dynamics Joint Experiment. Repetitive coverages of a test site in the Arctic were used to measure sea ice drift, employing single images and blocks of overlapping radar image strips; the images were used in conjunction with data from the aircraft inertial navigation and altimeter. Also, independently measured, accurate positions of a number of ground control points were available. Initial tests of the method were carried out with repeated coverages of a land area on the Alaska coast (Prudhoe). Absolute accuracies achieved were essentially limited by the accuracy of the inertial navigation data. Errors of drift measurements were found to be about + or - 2.5 km. Relative accuracy is higher; its limits are set by the radar image geometry and the definition of identical features in sequential images. The drift of adjacent ice features with respect to one another could be determined with errors of less than + or - 0.2 km.

Uneven onset and pace of ice-dynamical imbalance in the Amundsen Sea Embayment, West Antarctica

NASA Astrophysics Data System (ADS)

Konrad, Hannes; Gilbert, Lin; Cornford, Stephen L.; Payne, Antony; Hogg, Anna; Muir, Alan; Shepherd, Andrew

2017-01-01

We combine measurements acquired by five satellite altimeter missions to obtain an uninterrupted record of ice sheet elevation change over the Amundsen Sea Embayment, West Antarctica, since 1992. Using these data, we examine the onset of surface lowering arising through ice-dynamical imbalance, and the pace at which it has propagated inland, by tracking elevation changes along glacier flow lines. Surface lowering has spread slowest (<6 km/yr) along the Pope, Smith, and Kohler (PSK) Glaciers, due to their small extent. Pine Island Glacier (PIG) is characterized by a continuous inland spreading of surface lowering, notably fast at rates of 13 to 15 km/yr along tributaries draining the southeastern lobe, possibly due to basal conditions or tributary geometry. Surface lowering on Thwaites Glacier (THG) has been episodic and has spread inland fastest (10 to 12 km/yr) along its central flow lines. The current episodes of surface lowering started approximately 10 years before the first measurements on PSK, around 1990 on PIG, and around 2000 on THG. Ice-dynamical imbalance across the sector has therefore been uneven during the satellite record.

Phased occupation and retreat of the last British-Irish Ice Sheet in the southern North Sea; geomorphic and seismostratigraphic evidence of a dynamic ice lobe

NASA Astrophysics Data System (ADS)

Dove, Dayton; Evans, David J. A.; Lee, Jonathan R.; Roberts, David H.; Tappin, David R.; Mellett, Claire L.; Long, David; Callard, S. Louise

2017-05-01

Along the terrestrial margin of the southern North Sea, previous studies of the MIS 2 glaciation impacting eastern Britain have played a significant role in the development of principles relating to ice sheet dynamics (e.g. deformable beds), and the practice of reconstructing the style, timing, and spatial configuration of palaeo-ice sheets. These detailed terrestrially-based findings have however relied on observations made from only the outer edges of the former ice mass, as the North Sea Lobe (NSL) of the British-Irish Ice Sheet (BIIS) occupied an area that is now almost entirely submarine (c.21-15 ka). Compounded by the fact that marine-acquired data have been primarily of insufficient quality and density, the configuration and behaviour of the last BIIS in the southern North Sea remains surprisingly poorly constrained. This paper presents analysis of a new, integrated set of extensive seabed geomorphological and seismo-stratigraphic observations that both advances the principles developed previously onshore (e.g. multiple advance and retreat cycles), and provides a more detailed and accurate reconstruction of the BIIS at its southern-most extent in the North Sea. A new bathymetry compilation of the region reveals a series of broad sedimentary wedges and associated moraines that represent several terminal positions of the NSL. These former still-stand ice margins (1-4) are also found to relate to newly-identified architectural patterns (shallow stacked sedimentary wedges) in the region's seismic stratigraphy (previously mapped singularly as the Bolders Bank Formation). With ground-truthing constraint provided by sediment cores, these wedges are interpreted as sub-marginal till wedges, formed by complex subglacial accretionary processes that resulted in till thickening towards the former ice-sheet margins. The newly sub-divided shallow seismic stratigraphy (at least five units) also provides an indication of the relative event chronology of the NSL. While there

Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pohlit, Merlin, E-mail: pohlit@physik.uni-frankfurt.de; Porrati, Fabrizio; Huth, Michael

We study the magnetization dynamics of a spin ice cluster which is a building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition both experimentally and theoretically. The spin ice cluster is composed of twelve interacting Co nanoislands grown directly on top of a high-resolution micro-Hall sensor. By employing micromagnetic simulations and a macrospin model, we calculate the magnetization and the experimentally investigated stray field emanating from a single nanoisland. The parameters determined from a comparison with the experimental hysteresis loop are used to derive an effective single-dipole macrospin model that allows us to investigate the dynamicsmore » of the spin ice cluster. Our model reproduces the experimentally observed non-deterministic sequences in the magnetization curves as well as the distinct temperature dependence of the hysteresis loop.« less

Phi-s correlation and dynamic time warping - Two methods for tracking ice floes in SAR images

NASA Technical Reports Server (NTRS)

Mcconnell, Ross; Kober, Wolfgang; Kwok, Ronald; Curlander, John C.; Pang, Shirley S.

1991-01-01

The authors present two algorithms for performing shape matching on ice floe boundaries in SAR (synthetic aperture radar) images. These algorithms quickly produce a set of ice motion and rotation vectors that can be used to guide a pixel value correlator. The algorithms match a shape descriptor known as the Phi-s curve. The first algorithm uses normalized correlation to match the Phi-s curves, while the second uses dynamic programming to compute an elastic match that better accommodates ice floe deformation. Some empirical data on the performance of the algorithms on Seasat SAR images are presented.

Dynamics of landfast sea ice near Jangbogo Antarctic Research Station observed by SAR interferometry

NASA Astrophysics Data System (ADS)

Lee, H.; Han, H.

2015-12-01

Landfast sea ice is a type of sea ice adjacent to the coast and immobile for a certain period of time. It is important to analyze the temporal and spatial variation of landfast ice because it has significant influences on marine ecosystem and the safe operation of icebreaker vessels. However, it has been a difficult task for both remote sensing and in situ observation to discriminate landfast ice from other types of sea ice, such as pack ice, and also to understand the dynamics and internal strss-strain of fast ice. In this study, we identify landfast ice and its annual variation in Terra Nova Bay (74° 37' 4"S, 164° 13' 7"E), East Antarctica, where Jangbogo Antarctic Research Station has recently been constructed in 2014, by using Interferometric Synthetic Aperture Radar (InSAR) technology. We generated 38 interferograms having temporal baselines of 1-9 days out of 62 COSMO-SkyMed SAR images over Terra Nova Bay obtained from December 2010 to January 2012. Landfast ice began to melt in November 2011 when air temperature raised above freezing point but lasted more than two month to the end of the study period in January 2012. No meaningful relationship was found between sea ice extent and wind and current. Glacial strain (~67cm/day) is similar to tidal strain (~40 cm) so that they appear similar in one-day InSAR. As glacial stress is cumulative while tidal stress is oscillatory, InSAR images with weekly temporal baseline (7~9 days) revealed that a consistent motion of Campbell Glacier Tongue (CGT) is pushing the sea ice continuously to make interferometric fringes parallel to the glacier-sea ice contacts. Glacial interferometric fringe is parallel to the glacier-sea ice contact lines while tidal strain should be parallel to the coastlines defined by sea shore and glacier tongue. DDInSAR operation removed the consistent glacial strain leaving tidal strain alone so that the response of fast ice to tide can be used to deduce physical properties of sea ice in various

Dynamic Postural-Stability Deficits After Cryotherapy to the Ankle Joint

PubMed Central

Fullam, Karl; Caulfield, Brian; Coughlan, Garrett F.; McGroarty, Mark; Delahunt, Eamonn

2015-01-01

Context  Decreased postural stability is a primary risk factor for lower limb musculoskeletal injuries. During athletic competitions, cryotherapy may be applied during short breaks in play or during half-time; however, its effects on postural stability remain unclear. Objective  To investigate the acute effects of a 15-minute ankle-joint cryotherapy application on dynamic postural stability. Design  Controlled laboratory study. Setting  University biomechanics laboratory. Patients or Other Participants  A total of 29 elite-level collegiate male field-sport athletes (age = 20.8 ± 1.12 years, height = 1.80 ± 0.06 m, mass = 81.89 ± 8.59 kg) participated. Intervention(s)  Participants were tested on the anterior (ANT), posterolateral (PL), and posteromedial (PM) reach directions of the Star Excursion Balance Test before and after a 15-minute ankle-joint cryotherapy application. Main Outcome Measure(s)  Normalized reach distances; sagittal-plane kinematics of the hip, knee, and ankle joints; and associated mean velocity of the center-of-pressure path during performance of the ANT, PL, and PM reach directions of the Star Excursion Balance Test. Results  We observed a decrease in reach-distance scores for the ANT, PL, and PM reach directions from precryotherapy to postcryotherapy (P < .05). No differences were observed in hip-, knee-, or ankle-joint sagittal-plane kinematics (P > .05). We noted a decrease in mean velocity of the center-of-pressure path from precryotherapy to postcryotherapy (P < .05) in all reach directions. Conclusions  Dynamic postural stability was adversely affected immediately after cryotherapy to the ankle joint. PMID:26285088

Diffusive dynamics during the high-to-low density transition in amorphous ice

NASA Astrophysics Data System (ADS)

Perakis, Fivos; Amann-Winkel, Katrin; Lehmkühler, Felix; Sprung, Michael; Mariedahl, Daniel; Sellberg, Jonas A.; Pathak, Harshad; Späh, Alexander; Cavalca, Filippo; Schlesinger, Daniel; Ricci, Alessandro; Jain, Avni; Massani, Bernhard; Aubree, Flora; Benmore, Chris J.; Loerting, Thomas; Grübel, Gerhard; Pettersson, Lars G. M.; Nilsson, Anders

2017-08-01

Water exists in high- and low-density amorphous ice forms (HDA and LDA), which could correspond to the glassy states of high- (HDL) and low-density liquid (LDL) in the metastable part of the phase diagram. However, the nature of both the glass transition and the high-to-low-density transition are debated and new experimental evidence is needed. Here we combine wide-angle X-ray scattering (WAXS) with X-ray photon-correlation spectroscopy (XPCS) in the small-angle X-ray scattering (SAXS) geometry to probe both the structural and dynamical properties during the high-to-low-density transition in amorphous ice at 1 bar. By analyzing the structure factor and the radial distribution function, the coexistence of two structurally distinct domains is observed at T = 125 K. XPCS probes the dynamics in momentum space, which in the SAXS geometry reflects structural relaxation on the nanometer length scale. The dynamics of HDA are characterized by a slow component with a large time constant, arising from viscoelastic relaxation and stress release from nanometer-sized heterogeneities. Above 110 K a faster, strongly temperature-dependent component appears, with momentum transfer dependence pointing toward nanoscale diffusion. This dynamical component slows down after transition into the low-density form at 130 K, but remains diffusive. The diffusive character of both the high- and low-density forms is discussed among different interpretations and the results are most consistent with the hypothesis of a liquid-liquid transition in the ultraviscous regime.

Dynamic optical imaging of vascular and metabolic reactivity in rheumatoid joints.

PubMed

Lasker, Joseph M; Fong, Christopher J; Ginat, Daniel T; Dwyer, Edward; Hielscher, Andreas H

2007-01-01

Dynamic optical imaging is increasingly applied to clinically relevant areas such as brain and cancer imaging. In this approach, some external stimulus is applied and changes in relevant physiological parameters (e.g., oxy- or deoxyhemoglobin concentrations) are determined. The advantage of this approach is that the prestimulus state can be used as a reference or baseline against which the changes can be calibrated. Here we present the first application of this method to the problem of characterizing joint diseases, especially effects of rheumatoid arthritis (RA) in the proximal interphalangeal finger joints. Using a dual-wavelength tomographic imaging system together with previously implemented model-based iterative image reconstruction schemes, we have performed initial dynamic imaging case studies on a limited number of healthy volunteers and patients diagnosed with RA. Focusing on three cases studies, we illustrated our major finds. These studies support our hypothesis that differences in the vascular reactivity exist between affected and unaffected joints.

Mass Balance Changes and Ice Dynamics of Greenland and Antarctic Ice Sheets from Laser Altimetry

NASA Astrophysics Data System (ADS)

Babonis, G. S.; Csatho, B.; Schenk, T.

2016-06-01

During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA's Ice, Cloud and land Elevation Satellite mission (ICESat) and airborne laser campaigns, such as Airborne Topographic Mapper (ATM) and Land, Vegetation and Ice Sensor (LVIS). For detecting changes in ice sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC) method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local ice caps and the temporal extension from 1993 to 2014 for the Greenland Ice Sheet and for a comprehensive reconstruction of ice thickness and mass changes for the Antarctic Ice Sheets.

Ice stream activity scaled to ice sheet volume during Laurentide Ice Sheet deglaciation.

PubMed

Stokes, C R; Margold, M; Clark, C D; Tarasov, L

2016-02-18

The contribution of the Greenland and West Antarctic ice sheets to sea level has increased in recent decades, largely owing to the thinning and retreat of outlet glaciers and ice streams. This dynamic loss is a serious concern, with some modelling studies suggesting that the collapse of a major ice sheet could be imminent or potentially underway in West Antarctica, but others predicting a more limited response. A major problem is that observations used to initialize and calibrate models typically span only a few decades, and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves over longer timescales. This represents one of the largest sources of uncertainty when predicting the contributions of ice sheets to sea-level rise. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean-climate forcing. Here we reconstruct the activity of 117 ice streams that operated at various times during deglaciation of the Laurentide Ice Sheet (from about 22,000 to 7,000 years ago) and show that as they activated and deactivated in different locations, their overall number decreased, they occupied a progressively smaller percentage of the ice sheet perimeter and their total discharge decreased. The underlying geology and topography clearly influenced ice stream activity, but--at the ice-sheet scale--their drainage network adjusted and was linked to changes in ice sheet volume. It is unclear whether these findings can be directly translated to modern ice sheets. However, contrary to the view that sees ice streams as unstable entities that can accelerate ice-sheet deglaciation, we conclude that ice streams exerted progressively less influence on ice sheet mass balance during the retreat of the Laurentide Ice Sheet.

Compensating for intersegmental dynamics across the shoulder, elbow, and wrist joints during feedforward and feedback control.

PubMed

Maeda, Rodrigo S; Cluff, Tyler; Gribble, Paul L; Pruszynski, J Andrew

2017-10-01

Moving the arm is complicated by mechanical interactions that arise between limb segments. Such intersegmental dynamics cause torques applied at one joint to produce movement at multiple joints, and in turn, the only way to create single joint movement is by applying torques at multiple joints. We investigated whether the nervous system accounts for intersegmental limb dynamics across the shoulder, elbow, and wrist joints during self-initiated planar reaching and when countering external mechanical perturbations. Our first experiment tested whether the timing and amplitude of shoulder muscle activity account for interaction torques produced during single-joint elbow movements from different elbow initial orientations and over a range of movement speeds. We found that shoulder muscle activity reliably preceded movement onset and elbow agonist activity, and was scaled to compensate for the magnitude of interaction torques arising because of forearm rotation. Our second experiment tested whether elbow muscles compensate for interaction torques introduced by single-joint wrist movements. We found that elbow muscle activity preceded movement onset and wrist agonist muscle activity, and thus the nervous system predicted interaction torques arising because of hand rotation. Our third and fourth experiments tested whether shoulder muscles compensate for interaction torques introduced by different hand orientations during self-initiated elbow movements and to counter mechanical perturbations that caused pure elbow motion. We found that the nervous system predicted the amplitude and direction of interaction torques, appropriately scaling the amplitude of shoulder muscle activity during self-initiated elbow movements and rapid feedback control. Taken together, our results demonstrate that the nervous system robustly accounts for intersegmental dynamics and that the process is similar across the proximal to distal musculature of the arm as well as between feedforward (i

The response of grounded ice to ocean temperature forcing in a coupled ice sheet-ice shelf-ocean cavity model

NASA Astrophysics Data System (ADS)

Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.

2010-12-01

Ice shelves provide a pathway for the heat content of the ocean to influence continental ice sheets. Changes in the rate or location of basal melting can alter their geometry and effect changes in stress conditions at the grounding line, leading to a grounded ice response. Recent observations of ice streams and ice shelves in the Amundsen Sea sector of West Antarctica have been consistent with this story. On the other hand, ice dynamics in the grounding zone control flux into the shelf and thus ice shelf geometry, which has a strong influence on the circulation in the cavity beneath the shelf. Thus the coupling between the two systems, ocean and ice sheet-ice shelf, can be quite strong. We examine the response of the ice sheet-ice shelf-ocean cavity system to changes in ocean temperature using a recently developed coupled model. The coupled model consists a 3-D ocean model (GFDL's Generalized Ocean Layered Dynamics model, or GOLD) to a two-dimensional ice sheet-ice shelf model (Goldberg et al, 2009), and allows for changing cavity geometry and a migrating grounding line. Steady states of the coupled system are found even under considerable forcing. The ice shelf morphology and basal melt rate patterns of the steady states exhibit detailed structure, and furthermore seem to be unique and robust. The relationship between temperature forcing and area-averaged melt rate is influenced by the response of ice shelf morphology to thermal forcing, and is found to be sublinear in the range of forcing considered. However, results suggest that area-averaged melt rate is not the best predictor of overall system response, as grounding line stability depends on local aspects of the basal melt field. Goldberg, D N, D M Holland and C G Schoof, 2009. Grounding line movement and ice shelf buttressing in marine ice sheets, Journal of Geophysical Research-Earth Surfaces, 114, F04026.

Evidence for ephemeral middle Eocene to early Oligocene Greenland glacial ice and pan-Arctic sea ice.

PubMed

Tripati, Aradhna; Darby, Dennis

2018-03-12

Earth's modern climate is defined by the presence of ice at both poles, but that ice is now disappearing. Therefore understanding the origin and causes of polar ice stability is more critical than ever. Here we provide novel geochemical data that constrain past dynamics of glacial ice on Greenland and Arctic sea ice. Based on accurate source determinations of individual ice-rafted Fe-oxide grains, we find evidence for episodic glaciation of distinct source regions on Greenland as far-ranging as ~68°N and ~80°N synchronous with ice-rafting from circum-Arctic sources, beginning in the middle Eocene. Glacial intervals broadly coincide with reduced CO 2 , with a potential threshold for glacial ice stability near ~500 p.p.m.v. The middle Eocene represents the Cenozoic onset of a dynamic cryosphere, with ice in both hemispheres during transient glacials and substantial regional climate heterogeneity. A more stable cryosphere developed at the Eocene-Oligocene transition, and is now threatened by anthropogenic emissions.

There goes the sea ice: following Arctic sea ice parcels and their properties.

NASA Astrophysics Data System (ADS)

Tschudi, M. A.; Tooth, M.; Meier, W.; Stewart, S.

2017-12-01

Arctic sea ice distribution has changed considerably over the last couple of decades. Sea ice extent record minimums have been observed in recent years, the distribution of ice age now heavily favors younger ice, and sea ice is likely thinning. This new state of the Arctic sea ice cover has several impacts, including effects on marine life, feedback on the warming of the ocean and atmosphere, and on the future evolution of the ice pack. The shift in the state of the ice cover, from a pack dominated by older ice, to the current state of a pack with mostly young ice, impacts specific properties of the ice pack, and consequently the pack's response to the changing Arctic climate. For example, younger ice typically contains more numerous melt ponds during the melt season, resulting in a lower albedo. First-year ice is typically thinner and more fragile than multi-year ice, making it more susceptible to dynamic and thermodynamic forcing. To investigate the response of the ice pack to climate forcing during summertime melt, we have developed a database that tracks individual Arctic sea ice parcels along with associated properties as these parcels advect during the summer. Our database tracks parcels in the Beaufort Sea, from 1985 - present, along with variables such as ice surface temperature, albedo, ice concentration, and convergence. We are using this database to deduce how these thousands of tracked parcels fare during summer melt, i.e. what fraction of the parcels advect through the Beaufort, and what fraction melts out? The tracked variables describe the thermodynamic and dynamic forcing on these parcels during their journey. This database will also be made available to all interested investigators, after it is published in the near future. The attached image shows the ice surface temperature of all parcels (right) that advected through the Beaufort Sea region (left) in 2014.

On the apparent insignificance of the randomness of flexible joints on large space truss dynamics

NASA Technical Reports Server (NTRS)

Koch, R. M.; Klosner, J. M.

1993-01-01

Deployable periodic large space structures have been shown to exhibit high dynamic sensitivity to period-breaking imperfections and uncertainties. These can be brought on by manufacturing or assembly errors, structural imperfections, as well as nonlinear and/or nonconservative joint behavior. In addition, the necessity of precise pointing and position capability can require the consideration of these usually negligible and unknown parametric uncertainties and their effect on the overall dynamic response of large space structures. This work describes the use of a new design approach for the global dynamic solution of beam-like periodic space structures possessing parametric uncertainties. Specifically, the effect of random flexible joints on the free vibrations of simply-supported periodic large space trusses is considered. The formulation is a hybrid approach in terms of an extended Timoshenko beam continuum model, Monte Carlo simulation scheme, and first-order perturbation methods. The mean and mean-square response statistics for a variety of free random vibration problems are derived for various input random joint stiffness probability distributions. The results of this effort show that, although joint flexibility has a substantial effect on the modal dynamic response of periodic large space trusses, the effect of any reasonable uncertainty or randomness associated with these joint flexibilities is insignificant.

A Tale of Two Forcings: Present-Day Coupled Antarctic Ice-sheet/Southern Ocean dynamics using the POPSICLES model.

NASA Astrophysics Data System (ADS)

Martin, Daniel; Asay-Davis, Xylar; Cornford, Stephen; Price, Stephen; Ng, Esmond; Collins, William

2015-04-01

We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010 resulting from two different choices of climate forcing: a 'normal-year' climatology and the CORE v. 2 interannual forcing data (Large and Yeager 2008). Simulations are performed at 0.1o (~5 km) ocean resolution and adaptive ice sheet resolution as fine as 500 m. We compare time-averaged melt rates below a number of major ice shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and consequent dynamics of the grounded ice sheet. POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).

The role of ice shelves in the Holocene evolution of the Antarctic ice sheet

NASA Astrophysics Data System (ADS)

Bernales, Jorge; Rogozhina, Irina; Thomas, Maik

2014-05-01

Using the continental-scale ice sheet-shelf model SICOPOLIS (Greve, 1997 [1]; Sato and Greve, 2012 [2]), we assess the influence of ice shelves on the Holocene evolution and present-day geometry of the Antarctic ice sheet. We have designed a series of paleoclimate simulations driven by a time-evolved climate forcing that couples the surface temperature record from the Vostok ice core with precipitation pattern using an empirical relation of Dahl-Jensen et al., (1998) [3]. Our numerical experiments show that the geometry of ice shelves is determined by the evolution of climate and ocean conditions over time scales of 15 to 25 kyr. This implies that the initial configuration of ice shelves at the Last Glacial Maximum (LGM, about 21 kyr before present) has a significant effect on the modelled Early Holocene volume of ice shelves (up to 20%) that gradually diminishes to a negligible level for the present-day ice shelf configuration. Thus, the present-day geometry of the Antarctic ice shelves can be attained even if an ice-shelf-free initial condition is chosen at the LGM. However, the grounded ice volume, thickness and dynamic states are found to be sensitive to the ice shelf dynamics over a longer history spanning several tens of thousands of years. A presence of extensive marine ice at the LGM, supported by sediment core reconstructions (e.g. Naish et al., 2009 [4]), has a clear buttressing effect on the grounded ice that remains significant over a period of 30 to 50 kyr. If ice-shelf-free conditions are prescribed at the LGM, the modelled Early Holocene and present-day grounded ice volumes are underestimated by up to 10%, as opposed to simulations incorporating ice shelf dynamics over longer periods. The use of ice-shelf-free LGM conditions thus results in 50 to over 200 meters thinner ice sheet across much of East Antarctica. References [1] Greve, R. (1997). Application of a polythermal three-dimensional ice sheet model to the Greenland ice sheet: response to

Cryotherapy does not impair shoulder joint position sense.

PubMed

Dover, Geoffrey; Powers, Michael E

2004-08-01

To determine the effects of a cryotherapy treatment on shoulder proprioception. Crossover design with repeated measures. University athletic training and sports medicine research laboratory. Thirty healthy subjects (15 women, 15 men). A 30-minute cryotherapy treatment. Joint position sense was measured in the dominant shoulder by using an inclinometer before and after receiving 30 minutes of either no ice or a 1-kg ice bag application. Skin temperature was measured below the tip of the acromion process and recorded every 5 minutes for the entire 30 minutes and immediately after testing. Three different types of error scores were calculated for data analyses and used to determine proprioception. Separate analyses of absolute, constant, and variable error failed to identify changes in shoulder joint proprioception as a function of the cryotherapy application. Application of an ice bag to the shoulder does not impair joint position sense. The control of proprioception at the shoulder may be more complex than at other joints in the body. Clinical implications may involve modifying rehabilitation considerations when managing shoulder injuries.

On Wave-Ice Interaction in the Arctic Marginal Ice Zone: Dispersion, Attenuation, and Ice Response

DTIC Science & Technology

2016-06-01

PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 2. REPORT TYPE1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 6. AUTHOR(S) 8. PERFORMING...schemes and contributes to a change of wave height (and direction) analogous to shoaling and refraction. A method for jointly measuring dispersion and...46 APPENDEX B: WAVE HEIGHTS MEASURED IN ARTIC ICE

Ice Shelf-Ocean Interactions Near Ice Rises and Ice Rumples

NASA Astrophysics Data System (ADS)

Lange, M. A.; Rückamp, M.; Kleiner, T.

2013-12-01

The stability of ice shelves depends on the existence of embayments and is largely influenced by ice rises and ice rumples, which act as 'pinning-points' for ice shelf movement. Of additional critical importance are interactions between ice shelves and the water masses underlying them in ice shelf cavities, particularly melting and refreezing processes. The present study aims to elucidate the role of ice rises and ice rumples in the context of climate change impacts on Antarctic ice shelves. However, due to their smaller spatial extent, ice rumples react more sensitively to climate change than ice rises. Different forcings are at work and need to be considered separately as well as synergistically. In order to address these issues, we have decided to deal with the following three issues explicitly: oceanographic-, cryospheric and general topics. In so doing, we paid particular attention to possible interrelationships and feedbacks in a coupled ice-shelf-ocean system. With regard to oceanographic issues, we have applied the ocean circulation model ROMBAX to ocean water masses adjacent to and underneath a number of idealized ice shelf configurations: wide and narrow as well as laterally restrained and unrestrained ice shelves. Simulations were performed with and without small ice rises located close to the calving front. For larger configurations, the impact of the ice rises on melt rates at the ice shelf base is negligible, while for smaller configurations net melting rates at the ice-shelf base differ by a factor of up to eight depending on whether ice rises are considered or not. We employed the thermo-coupled ice flow model TIM-FD3 to simulate the effects of several ice rises and one ice rumple on the dynamics of ice shelf flow. We considered the complete un-grounding of the ice shelf in order to investigate the effect of pinning points of different characteristics (interior or near calving front, small and medium sized) on the resulting flow and stress fields

Modes of supraglacial lake drainage and dynamic ice sheet response

NASA Astrophysics Data System (ADS)

Das, S. B.; Behn, M. D.; Joughin, I. R.

2011-12-01

We investigate modes of supraglacial lake drainage using geophysical, ground, and remote sensing observations over the western margin of the Greenland ice sheet. Lakes exhibit a characteristic life cycle defined by a pre-drainage, drainage, and post-drainage phase. In the pre-drainage phase winter snow fills pre-existing cracks and stream channels, efficiently blocking past drainage conduits. As temperatures increase in the spring, surface melting commences, initially saturating the snow pack and subsequently forming a surface network of streams that fills the lake basins. Basins continue to fill until lake drainage commences, which for individual lakes occurs at different times depending on the previous winter snow accumulation and summer temperatures. Three styles of drainage behavior have been observed: (1) no drainage, (2) slow drainage over the side into an adjacent pre-existing crack, and (3) rapid drainage through a new crack formed beneath the lake basin. Moreover, from year-to-year individual lakes exhibit different drainage behaviors. Lakes that drain slowly often utilize the same outflow channel for multiple years, creating dramatic canyons in the ice. Ultimately, these surface channels are advected out of the lake basin and a new channel forms. In the post-drainage phase, melt water continues to access the bed typically through a small conduit (e.g. moulin) formed near a local topographic minimum along the main drainage crack, draining the lake catchment throughout the remainder of the melt season. This melt water input to the bed leads to continued basal lubrication and enhanced ice flow compared to background velocities. Lakes that do not completely drain freeze over to form a surface ice layer that persists into the following year. Our results show that supraglacial lakes show a spectrum of drainage behaviors and that these styles of drainage lead to varying rates and timing of surface meltwater delivery to the bed resulting in different dynamic ice

Dynamic Cytology and Transcriptional Regulation of Rice Lamina Joint Development1[OPEN

PubMed Central

2017-01-01

Rice (Oryza sativa) leaf angle is determined by lamina joint and is an important agricultural trait determining leaf erectness and, hence, the photosynthesis efficiency and grain yield. Genetic studies reveal a complex regulatory network of lamina joint development; however, the morphological changes, cytological transitions, and underlying transcriptional programming remain to be elucidated. A systemic morphological and cytological study reveals a dynamic developmental process and suggests a common but distinct regulation of the lamina joint. Successive and sequential cell division and expansion, cell wall thickening, and programmed cell death at the adaxial or abaxial sides form the cytological basis of the lamina joint, and the increased leaf angle results from the asymmetric cell proliferation and elongation. Analysis of the gene expression profiles at four distinct developmental stages ranging from initiation to senescence showed that genes related to cell division and growth, hormone synthesis and signaling, transcription (transcription factors), and protein phosphorylation (protein kinases) exhibit distinct spatiotemporal patterns during lamina joint development. Phytohormones play crucial roles by promoting cell differentiation and growth at early stages or regulating the maturation and senescence at later stages, which is consistent with the quantitative analysis of hormones at different stages. Further comparison with the gene expression profile of leaf inclination1, a mutant with decreased auxin and increased leaf angle, indicates the coordinated effects of hormones in regulating lamina joint. These results reveal a dynamic cytology of rice lamina joint that is fine-regulated by multiple factors, providing informative clues for illustrating the regulatory mechanisms of leaf angle and plant architecture. PMID:28500269

Seismic wave propagation in anisotropic ice - Part 2: Effects of crystal anisotropy in geophysical data

NASA Astrophysics Data System (ADS)

Diez, A.; Eisen, O.; Hofstede, C.; Lambrecht, A.; Mayer, C.; Miller, H.; Steinhage, D.; Binder, T.; Weikusat, I.

2015-02-01

We investigate the propagation of seismic waves in anisotropic ice. Two effects are important: (i) sudden changes in crystal orientation fabric (COF) lead to englacial reflections; (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. Velocities calculated from the polycrystal elasticity tensor derived for the anisotropic fabric from measured COF eigenvalues of the EDML ice core, Antarctica, show good agreement with the velocity trend determined from vertical seismic profiling. The agreement of the absolute velocity values, however, depends on the choice of the monocrystal elasticity tensor used for the calculation of the polycrystal properties. We make use of abrupt changes in COF as a common reflection mechanism for seismic and radar data below the firn-ice transition to determine COF-induced reflections in either data set by joint comparison with ice-core data. Our results highlight the possibility to complement regional radar surveys with local, surface-based seismic experiments to separate isochrones in radar data from other mechanisms. This is important for the reconnaissance of future ice-core drill sites, where accurate isochrone (i.e. non-COF) layer integrity allows for synchronization with other cores, as well as studies of ice dynamics considering non-homogeneous ice viscosity from preferred crystal orientations.

Ecological consequences of sea-ice decline.

PubMed

Post, Eric; Bhatt, Uma S; Bitz, Cecilia M; Brodie, Jedediah F; Fulton, Tara L; Hebblewhite, Mark; Kerby, Jeffrey; Kutz, Susan J; Stirling, Ian; Walker, Donald A

2013-08-02

After a decade with nine of the lowest arctic sea-ice minima on record, including the historically low minimum in 2012, we synthesize recent developments in the study of ecological responses to sea-ice decline. Sea-ice loss emerges as an important driver of marine and terrestrial ecological dynamics, influencing productivity, species interactions, population mixing, gene flow, and pathogen and disease transmission. Major challenges in the near future include assigning clearer attribution to sea ice as a primary driver of such dynamics, especially in terrestrial systems, and addressing pressures arising from human use of arctic coastal and near-shore areas as sea ice diminishes.

Ice interaction with offshore structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cammaert, A.B.; Muggeridge, D.B.

1988-01-01

Oil platforms and other offshore structures being built in the arctic regions must be able to withstand icebergs, ice islands, and pack ice. This reference explain the effect ice has on offshore structures and demonstrates design and construction methods that allow such structures to survive in harsh, ice-ridden environments. It analyzes the characteristics of sea ice as well as dynamic ice forces on structures. Techniques for ice modeling and field testing facilitate the design and construction of sturdy, offshore constructions. Computer programs included.

Diffusive dynamics during the high-to-low density transition in amorphous ice

DOE PAGES

Perakis, Fivos; Amann-Winkel, Katrin; Lehmkuhler, Felix; ...

2017-06-26

Water exists in high- and low-density amorphous ice forms (HDA and LDA), which could correspond to the glassy states of high- (HDL) and low-density liquid (LDL) in the metastable part of the phase diagram. However, the nature of both the glass transition and the high-to-low-density transition are debated and new experimental evidence is needed. Here we combine wide-angle X-ray scattering (WAXS) with X-ray photon-correlation spectroscopy (XPCS) in the small-angle X-ray scattering (SAXS) geometry to probe both the structural and dynamical properties during the high-to-low-density transition in amorphous ice at 1 bar. By analyzing the structure factor and the radial distributionmore » function, the coexistence of two structurally distinct domains is observed at T = 125 K. XPCS probes the dynamics in momentum space, which in the SAXS geometry reflects structural relaxation on the nanometer length scale. The dynamics of HDA are characterized by a slow component with a large time constant, arising from viscoelastic relaxation and stress release from nanometer-sized heterogeneities. Above 110 K a faster, strongly temperature-dependent component appears, with momentum transfer dependence pointing toward nanoscale diffusion. This dynamical component slows down after transition into the low-density form at 130 K, but remains diffusive. In conclusion, the diffusive character of both the high- and low-density forms is discussed among different interpretations and the results are most consistent with the hypothesis of a liquid–liquid transition in the ultraviscous regime.« less

Diffusive dynamics during the high-to-low density transition in amorphous ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perakis, Fivos; Amann-Winkel, Katrin; Lehmkuhler, Felix

Water exists in high- and low-density amorphous ice forms (HDA and LDA), which could correspond to the glassy states of high- (HDL) and low-density liquid (LDL) in the metastable part of the phase diagram. However, the nature of both the glass transition and the high-to-low-density transition are debated and new experimental evidence is needed. Here we combine wide-angle X-ray scattering (WAXS) with X-ray photon-correlation spectroscopy (XPCS) in the small-angle X-ray scattering (SAXS) geometry to probe both the structural and dynamical properties during the high-to-low-density transition in amorphous ice at 1 bar. By analyzing the structure factor and the radial distributionmore » function, the coexistence of two structurally distinct domains is observed at T = 125 K. XPCS probes the dynamics in momentum space, which in the SAXS geometry reflects structural relaxation on the nanometer length scale. The dynamics of HDA are characterized by a slow component with a large time constant, arising from viscoelastic relaxation and stress release from nanometer-sized heterogeneities. Above 110 K a faster, strongly temperature-dependent component appears, with momentum transfer dependence pointing toward nanoscale diffusion. This dynamical component slows down after transition into the low-density form at 130 K, but remains diffusive. In conclusion, the diffusive character of both the high- and low-density forms is discussed among different interpretations and the results are most consistent with the hypothesis of a liquid–liquid transition in the ultraviscous regime.« less

Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.

PubMed

Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

2015-04-24

The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

A coupled dynamic-thermodynamic model of an ice-ocean system in the marginal ice zone

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa

1987-01-01

Thermodynamics are incorporated into a coupled ice-ocean model in order to investigate wind-driven ice-ocean processes in the marginal zone. Upswelling at the ice edge which is generated by the difference in the ice-air and air-water surface stresses is found to give rise to a strong entrainment by drawing the pycnocline closer to the surface. Entrainment is shown to be negligible outside the areas affected by the ice edge upswelling. If cooling at the top is included in the model, the heat and salt exchanges are further enhanced in the upswelling areas. It is noted that new ice formation occurs in the region not affected by ice edge upswelling, and it is suggested that the high-salinity mixed layer regions (with a scale of a few Rossby radii of deformation) will overturn due to cooling, possibly contributing to the formation of deep water.

Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet

NASA Astrophysics Data System (ADS)

Margold, Martin; Stokes, Chris R.; Clark, Chris D.

2018-06-01

This paper reconstructs the deglaciation of the Laurentide Ice Sheet (LIS; including the Innuitian Ice Sheet) from the Last Glacial Maximum (LGM), with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides. We build on a recent inventory of Laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the LIS, which we depict in a series of palaeogeographic maps. Results show that the drainage network at the LGM was similar to modern-day Antarctica. The majority of the ice streams were marine terminating and topographically-controlled and many of these continued to function late into the deglaciation, until the ice sheet lost its marine margin. Ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build-up, peak-phase and collapse of the Cordilleran-Laurentide ice saddle. The south-eastern marine margin in Atlantic Canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the LGM. In contrast, the ice streams draining towards the north-western and north-eastern marine margins in the Beaufort Sea and in Baffin Bay appear to have remained stable throughout most of the Late Glacial, and some of them continued to function until after the Younger Dryas (YD). The YD influenced the dynamics of the deglaciation, but there remains uncertainty about the response of the ice sheet in several sectors. We tentatively ascribe the switching-on of some major ice streams during this period (e.g. M'Clintock Channel Ice Stream at the north-west margin), but for other large ice streams whose timing partially overlaps with the YD, the drivers are less clear and ice-dynamical processes, rather than effects of climate and surface mass balance are viewed as more likely drivers. Retreat

Late Weichselian ice-sheet dynamics and deglaciation history of the northern Svalbard margin

NASA Astrophysics Data System (ADS)

Fransner, O.; Noormets, R. R. N. N.; Flink, A.; Hogan, K.; Dowdeswell, J. A.; O'Regan, M.; Jakobsson, M.

2016-12-01

The glacial evolution of the northern Svalbard margin is poorly known compared with the western margin. Gravity cores, swath bathymetric, sub-bottom acoustic and 2D airgun data are used to investigate the Late Weichselian Svalbard-Barents Ice Sheet history on the northern Svalbard margin. Prograding sequences in Kvitøya and Albertini trough mouths (TMs) indicate ice streaming to the shelf edge multiple times during the Quaternary. While Kvitøya Trough has an associated trough-mouth fan (TMF), Albertini TM is cut back into the shelf edge. Down-faulted bedrock below Albertini TM suggests larger sediment accommodation space there, explaining the absence of a TMF. The bathymetry indicates that ice flow in Albertini Trough was sourced from Duvefjorden and Albertinibukta. Exposed crystalline bedrock likely kept the two ice flows separated before merging north of Karl XII-Øya. Subglacial landforms in Rijpfjorden and Duvefjorden indicate that both fjords accommodated northward-flowing ice streams during the LGM. The deeper fjord basin and higher elongation ratios of landforms in Duvefjorden suggest a more focused and/or larger ice flow there. Easily erodible sedimentary rocks are common in Duvefjorden, which may explain different ice flow dynamics in these fjords. Kvitøya TMF is flanked by gullies, probably formed through erosive downslope gravity flows triggered by sediment-laden meltwater during early deglaciation. Glacial landforms in Albertini Trough comprise retreat-related landforms indicating slow deglaciation. Iceberg scours in Albertini Trough suggest the importance of calving for mass-loss. Sets of De Geer moraines in Rijpfjorden imply that slow, grounded retreat continued in <210 m water depth. Lack of retreat-related landforms in deeper areas of Rijpfjorden and in Duvefjorden indicates floating glacier fronts influenced by calving. 14C ages suggest that deglaciation of inner Rijpfjorden and central Duvefjorden were complete before 10,434 cal a BP and 10

Evidence for a dynamic East Antarctic ice sheet during the mid-Miocene climate transition

NASA Astrophysics Data System (ADS)

Pierce, Elizabeth L.; van de Flierdt, Tina; Williams, Trevor; Hemming, Sidney R.; Cook, Carys P.; Passchier, Sandra

2017-11-01

drill sites proximal to the Antarctic continent provide a previously undocumented record of dynamic ice margin change during the 14.1-13.8 Ma interval in three major East Antarctic drainage basins.

Ice shelf fracture parameterization in an ice sheet model

NASA Astrophysics Data System (ADS)

Sun, Sainan; Cornford, Stephen L.; Moore, John C.; Gladstone, Rupert; Zhao, Liyun

2017-11-01

Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ˜ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

Present-day dynamics and future evolution of the world's northernmost ice cap, Hans Tausen Iskappe (Greenland)

NASA Astrophysics Data System (ADS)

Zekollari, Harry; Huybrechts, Philippe; Noël, Brice; van de Berg, Willem Jan; van den Broeke, Michiel R.

2017-04-01

In this study the dynamics of Hans Tausen Iskappe (western Peary Land, Greenland) are investigated with a coupled ice flow - mass balance model. Precipitation is obtained from the Regional Climate Model RACMO 2.3 and the surface mass balance is calculated from a Positive Degree-Day runoff/retention model, for which the input parameters are derived from field observations. For the ice flow a 3-D higher-order thermo-mechanical model is used, which is run at a 250 m resolution. Under 1961-1990 climatic conditions a steady state ice cap is obtained that is overall similar in geometry to the present-day ice cap. Ice thickness, temperature and flow velocity in the interior agree well with observations. For the outlet glaciers a reasonable agreement with temperature and ice thickness measurements can only be obtained with an additional heat source related to infiltrating meltwater. The simulations indicate that the SMB-elevation feedback has a major effect on the ice cap response time and stability. This causes the southern part of the ice cap to be extremely sensitive to a change in climatic conditions and leads to thresholds in the ice cap evolution. Under constant 2005-2014 climatic conditions the entire southern part of the ice cap cannot be sustained and the ice cap loses about 80% of its present-day volume. The future projected loss of surrounding permanent sea-ice and corresponding potential sharp precipitation increase may however lead to an attenuation of the retreat and even potential stabilization of the ice cap for a warming of up to 2-3°C. In a warmer and wetter climate the ice margin will retreat while the interior is projected to grow, leading to a steeper ice cap, in line with the present-day observed trends. For intermediate (+4°C) and high warming scenarios (+8°C) the ice cap is projected to disappear respectively around 2400 and 2200 A.D., almost irrespective of the projected precipitation regime and the simulated present-day geometry.

Arctic Sea Ice Predictability and the Sea Ice Prediction Network

NASA Astrophysics Data System (ADS)

Wiggins, H. V.; Stroeve, J. C.

2014-12-01

Drastic reductions in Arctic sea ice cover have increased the demand for Arctic sea ice predictions by a range of stakeholders, including local communities, resource managers, industry and the public. The science of sea-ice prediction has been challenged to keep up with these developments. Efforts such as the SEARCH Sea Ice Outlook (SIO; http://www.arcus.org/sipn/sea-ice-outlook) and the Sea Ice for Walrus Outlook have provided a forum for the international sea-ice prediction and observing community to explore and compare different approaches. The SIO, originally organized by the Study of Environmental Change (SEARCH), is now managed by the new Sea Ice Prediction Network (SIPN), which is building a collaborative network of scientists and stakeholders to improve arctic sea ice prediction. The SIO synthesizes predictions from a variety of methods, including heuristic and from a statistical and/or dynamical model. In a recent study, SIO data from 2008 to 2013 were analyzed. The analysis revealed that in some years the predictions were very successful, in other years they were not. Years that were anomalous compared to the long-term trend have proven more difficult to predict, regardless of which method was employed. This year, in response to feedback from users and contributors to the SIO, several enhancements have been made to the SIO reports. One is to encourage contributors to provide spatial probability maps of sea ice cover in September and the first day each location becomes ice-free; these are an example of subseasonal to seasonal, local-scale predictions. Another enhancement is a separate analysis of the modeling contributions. In the June 2014 SIO report, 10 of 28 outlooks were produced from models that explicitly simulate sea ice from dynamic-thermodynamic sea ice models. Half of the models included fully-coupled (atmosphere, ice, and ocean) models that additionally employ data assimilation. Both of these subsets (models and coupled models with data

Modeling the basal melting and marine ice accretion of the Amery Ice Shelf

NASA Astrophysics Data System (ADS)

Galton-Fenzi, B. K.; Hunter, J. R.; Coleman, R.; Marsland, S. J.; Warner, R. C.

2012-09-01

The basal mass balance of the Amery Ice Shelf (AIS) in East Antarctica is investigated using a numerical ocean model. The main improvements of this model over previous studies are the inclusion of frazil formation and dynamics, tides and the use of the latest estimate of the sub-ice-shelf cavity geometry. The model produces a net basal melt rate of 45.6 Gt year-1 (0.74 m ice year-1) which is in good agreement with reviewed observations. The melting at the base of the ice shelf is primarily due to interaction with High Salinity Shelf Water created from the surface sea-ice formation in winter. The temperature difference between the coldest waters created in the open ocean and the in situ freezing point of ocean water in contact with the deepest part of the AIS drives a melt rate that can exceed 30 m of ice year-1. The inclusion of frazil dynamics is shown to be important for both melting and marine ice accretion (refreezing). Frazil initially forms in the supercooled water layer adjacent to the base of the ice shelf. The net accretion of marine ice is 5.3 Gt year-1, comprised of 3.7 Gt year-1 of frazil accretion and 1.6 Gt year-1 of direct basal refreezing.

Isolation and characterisation of sericin antifreeze peptides and molecular dynamics modelling of their ice-binding interaction.

PubMed

Wu, Jinhong; Rong, Yuzhi; Wang, Zhengwu; Zhou, Yanfu; Wang, Shaoyun; Zhao, Bo

2015-05-01

This study aimed to isolate and characterise a novel sericin antifreeze peptide and investigate its ice-binding molecular mechanism. The thermal hysteresis activity of ice-binding sericin peptides (I-SP) was measured and their activity reached as high as 0.94 °C. A P4 fraction, with high hypothermia protective activity and inhibition activity of ice recrystallisation, was obtained from I-SP, and a purified sericin peptide, named SM-AFP, with the sequence of TTSPTNVSTT and a molecular weight of 1009.50 Da was then isolated from the P4 fraction. Treatment of Lactobacillus delbrueckii Subsp. bulgaricus LB340 LYO with 100 μg/ml synthetic SM-AFP led to 1.4-fold increased survival (p < 0.05). Finally, an SM-AFP/ice binding model was constructed and results of molecular dynamics simulation suggested that the binding of SM-AFP with ice and prevention of ice crystal growth could be attributed to hydrogen bond formation, hydrophobic interaction and non-bond interactions. Sericin peptides could be developed into beneficial cryoprotectants and used in frozen food processing. Copyright © 2014 Elsevier Ltd. All rights reserved.

Local dynamic stability of lower extremity joints in lower limb amputees during slope walking.

PubMed

Chen, Jin-Ling; Gu, Dong-Yun

2013-01-01

Lower limb amputees have a higher fall risk during slope walking compared with non-amputees. However, studies on amputees' slope walking were not well addressed. The aim of this study was to identify the difference of slope walking between amputees and non-amputees. Lyapunov exponents λS was used to estimate the local dynamic stability of 7 transtibial amputees' and 7 controls' lower extremity joint kinematics during uphill and downhill walking. Compared with the controls, amputees exhibited significantly lower λS in hip (P=0.04) and ankle (P=0.01) joints of the sound limb, and hip joints (P=0.01) of the prosthetic limb during uphill walking, while they exhibited significantly lower λS in knee (P=0.02) and ankle (P=0.03) joints of the sound limb, and hip joints (P=0.03) of the prosthetic limb during downhill walking. Compared with amputees level walking, they exhibited significantly lower λS in ankle joints of the sound limb during both uphill (P=0.01) and downhill walking (P=0.01). We hypothesized that the better local dynamic stability of amputees was caused by compensation strategy during slope walking.

IceBridge team members

NASA Image and Video Library

2013-11-13

These IceBridge team members aboard a huge U.S. Air Force C-17 transport aircraft are ready to step out into the cold Antarctic air. The C-17 aircraft that fly to Antarctica are operated by the U.S. Air Force's 62nd and 446th Airlift Wings based at Joint Base Lewis-McChord near Seattle, Wash. Credit: NASA/Goddard/Michael Studinger NASA's Operation IceBridge is an airborne science mission to study Earth's polar ice. For more information about IceBridge, visit: www.nasa.gov/icebridge NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Mapping Ross Ice Shelf with ROSETTA-Ice airborne laser altimetry

NASA Astrophysics Data System (ADS)

Becker, M. K.; Fricker, H. A.; Padman, L.; Bell, R. E.; Siegfried, M. R.; Dieck, C. C. M.

2017-12-01

The Ross Ocean and ice Shelf Environment and Tectonic setting Through Aerogeophysical surveys and modeling (ROSETTA-Ice) project combines airborne glaciological, geological, and oceanographic observations to enhance our understanding of the history and dynamics of the large ( 500,000 square km) Ross Ice Shelf (RIS). Here, we focus on the Light Detection And Ranging (LiDAR) data collected in 2015 and 2016. This data set represents a significant advance in resolution: Whereas the last attempt to systematically map RIS (the surface-based RIGGS program in the 1970s) was at 55 km grid spacing, the ROSETTA-Ice grid has 10-20 km line spacing and much higher along-track resolution. We discuss two different strategies for processing the raw LiDAR data: one that requires proprietary software (Riegl's RiPROCESS package), and one that employs open-source programs and libraries. With the processed elevation data, we are able to resolve fine-scale ice-shelf features such as the "rampart-moat" ice-front morphology, which has previously been observed on and modeled for icebergs. This feature is also visible in the ROSETTA-Ice shallow-ice radar data; comparing the laser data with radargrams provides insight into the processes leading to their formation. Near-surface firn state and total firn air content can also be investigated through combined analysis of laser altimetry and radar data. By performing similar analyses with data from the radar altimeter aboard CryoSat-2, we demonstrate the utility of the ROSETTA-Ice LiDAR data set in satellite validation efforts. The incorporation of the LiDAR data from the third and final field season (December 2017) will allow us to construct a DEM and an ice thickness map of RIS for the austral summers of 2015-2017. These products will be used to validate and extend observations of height changes from satellite radar and laser altimetry, as well as to update regional models of ocean circulation and ice dynamics.

Dynamic ocean topography from CryoSat-2: examining recent changes in ice-ocean stress and advancing a theory for Beaufort Gyre stabilization

NASA Astrophysics Data System (ADS)

Dewey, S.; Morison, J.; Kwok, R.; Dickinson, S.; Morison, D.; Andersen, R.

2017-12-01

Model and sparse observational evidence has shown the ocean current speed in the Beaufort Gyre to have increased and recently stabilized. However, full-basin altimetric observations of dynamic ocean topography (DOT) and ocean surface currents have yet to be applied to the dynamics of gyre stabilization. DOT fields from retracked CryoSat-2 retrievals in Arctic Ocean leads have enabled us to calculate 2-month average ocean geostrophic currents. These currents are crucial to accurately computing ice-ocean stress, especially because they have accelerated so that their speed rivals that of the overlying sea ice. Given these observations, we can shift our view of the Beaufort Gyre as a system in which the wind drives the ice and the ice drives a passive ocean to a system with the following feedback: After initial input of energy by wind, ice velocity decreases due to water drag and internal ice stress and the ocean drives the ice, reversing Ekman pumping and decelerating the gyre. This reversal changes the system from a persistently convergent regime to one in which freshwater is released from the gyre and doming of the gyre decreases, without any change in long-term average wind stress curl. Through these processes, the ice-ocean stress provides a key feedback in Beaufort Gyre stabilization.

The Ice Sheet Mass Balance Inter-comparison Exercise

NASA Astrophysics Data System (ADS)

Shepherd, A.; Ivins, E. R.

2015-12-01

Fluctuations in the mass of ice stored in Antarctica and Greenland are of considerable societal importance. The Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE) is a joint-initiative of ESA and NASA aimed at producing a single estimate of the global sea level contribution to polar ice sheet losses. Within IMBIE, estimates of ice sheet mass balance are developed from a variety of satellite geodetic techniques using a common spatial and temporal reference frame and a common appreciation of the contributions due to external signals. The project brings together the laboratories and space agencies that have been instrumental in developing independent estimates of ice sheet mass balance to date. In its first phase, IMBIE involved 27 science teams, and delivered a first community assessment of ice sheet mass imbalance to replace 40 individual estimates. The project established that (i) there is good agreement between the three main satellite-based techniques for estimating ice sheet mass balance, (ii) combining satellite data sets leads to significant improvement in certainty, (iii) the polar ice sheets contributed 11 ± 4 mm to global sea levels between 1992 and 2012, and (iv) that combined ice losses from Antarctica and Greenland have increased over time, rising from 10% of the global trend in the early 1990's to 30% in the late 2000's. Demand for an updated assessment has grown, and there are now new satellite missions, new geophysical corrections, new techniques, and new teams producing data. The period of overlap between independent satellite techniques has increased from 5 to 12 years, and the full period of satellite data over which an assessment can be performed has increased from 19 to 40 years. It is also clear that multiple satellite techniques are required to confidently separate mass changes associated with snowfall and ice dynamical imbalance - information that is of critical importance for climate modelling. This presentation outlines the approach

Modeling Europa's Ice-Ocean Interface

NASA Astrophysics Data System (ADS)

Elsenousy, A.; Vance, S.; Bills, B. G.

2014-12-01

This work focuses on modeling the ice-ocean interface on Jupiter's Moon (Europa); mainly from the standpoint of heat and salt transfer relationship with emphasis on the basal ice growth rate and its implications to Europa's tidal response. Modeling the heat and salt flux at Europa's ice/ocean interface is necessary to understand the dynamics of Europa's ocean and its interaction with the upper ice shell as well as the history of active turbulence at this area. To achieve this goal, we used McPhee et al., 2008 parameterizations on Earth's ice/ocean interface that was developed to meet Europa's ocean dynamics. We varied one parameter at a time to test its influence on both; "h" the basal ice growth rate and on "R" the double diffusion tendency strength. The double diffusion tendency "R" was calculated as the ratio between the interface heat exchange coefficient αh to the interface salt exchange coefficient αs. Our preliminary results showed a strong double diffusion tendency R ~200 at Europa's ice-ocean interface for plausible changes in the heat flux due to onset or elimination of a hydrothermal activity, suggesting supercooling and a strong tendency for forming frazil ice.

Ice Accretions and Full-Scale Iced Aerodynamic Performance Data for a Two-Dimensional NACA 23012 Airfoil

NASA Technical Reports Server (NTRS)

Addy, Harold E., Jr.; Broeren, Andy P.; Potapczuk, Mark G.; Lee, Sam; Guffond, Didier; Montreuil, Emmanuel; Moens, Frederic

2016-01-01

This report documents the data collected during the large wind tunnel campaigns conducted as part of the SUNSET project (StUdies oN Scaling EffecTs due to ice) also known as the Ice-Accretion Aerodynamics Simulation study: a joint effort by NASA, the Office National d'Etudes et Recherches Aérospatiales (ONERA), and the University of Illinois. These data form a benchmark database of full-scale ice accretions and corresponding ice-contaminated aerodynamic performance data for a two-dimensional (2D) NACA 23012 airfoil. The wider research effort also included an analysis of ice-contaminated aerodynamics that categorized ice accretions by aerodynamic effects and an investigation of subscale, low- Reynolds-number ice-contaminated aerodynamics for the NACA 23012 airfoil. The low-Reynolds-number investigation included an analysis of the geometric fidelity needed to reliably assess aerodynamic effects of airfoil icing using artificial ice shapes. Included herein are records of the ice accreted during campaigns in NASA Glenn Research Center's Icing Research Tunnel (IRT). Two different 2D NACA 23012 airfoil models were used during these campaigns; an 18-in. (45.7-cm) chord (subscale) model and a 72-in. (182.9-cm) chord (full-scale) model. The aircraft icing conditions used during these campaigns were selected from the Federal Aviation Administration's (FAA's) Code of Federal Regulations (CFR) Part 25 Appendix C icing envelopes. The records include the test conditions, photographs of the ice accreted, tracings of the ice, and ice depth measurements. Model coordinates and pressure tap locations are also presented. Also included herein are the data recorded during a wind tunnel campaign conducted in the F1 Subsonic Pressurized Wind Tunnel of ONERA. The F1 tunnel is a pressured, high- Reynolds-number facility that could accommodate the full-scale (72-in. (182.9-cm) chord) 2D NACA 23012 model. Molds were made of the ice accreted during selected test runs of the full-scale model

The role of sea ice dynamics in global climate change

NASA Technical Reports Server (NTRS)

Hibler, William D., III

1992-01-01

The topics covered include the following: general characteristics of sea ice drift; sea ice rheology; ice thickness distribution; sea ice thermodynamic models; equilibrium thermodynamic models; effect of internal brine pockets and snow cover; model simulations of Arctic Sea ice; and sensitivity of sea ice models to climate change.

Ice-binding proteins that accumulate on different ice crystal planes produce distinct thermal hysteresis dynamics

PubMed Central

Drori, Ran; Celik, Yeliz; Davies, Peter L.; Braslavsky, Ido

2014-01-01

Ice-binding proteins that aid the survival of freeze-avoiding, cold-adapted organisms by inhibiting the growth of endogenous ice crystals are called antifreeze proteins (AFPs). The binding of AFPs to ice causes a separation between the melting point and the freezing point of the ice crystal (thermal hysteresis, TH). TH produced by hyperactive AFPs is an order of magnitude higher than that produced by a typical fish AFP. The basis for this difference in activity remains unclear. Here, we have compared the time dependence of TH activity for both hyperactive and moderately active AFPs using a custom-made nanolitre osmometer and a novel microfluidics system. We found that the TH activities of hyperactive AFPs were time-dependent, and that the TH activity of a moderate AFP was almost insensitive to time. Fluorescence microscopy measurement revealed that despite their higher TH activity, hyperactive AFPs from two insects (moth and beetle) took far longer to accumulate on the ice surface than did a moderately active fish AFP. An ice-binding protein from a bacterium that functions as an ice adhesin rather than as an antifreeze had intermediate TH properties. Nevertheless, the accumulation of this ice adhesion protein and the two hyperactive AFPs on the basal plane of ice is distinct and extensive, but not detectable for moderately active AFPs. Basal ice plane binding is the distinguishing feature of antifreeze hyperactivity, which is not strictly needed in fish that require only approximately 1°C of TH. Here, we found a correlation between the accumulation kinetics of the hyperactive AFP at the basal plane and the time sensitivity of the measured TH. PMID:25008081

Greenland outlet glacier dynamics from Extreme Ice Survey (EIS) photogrammetry

NASA Astrophysics Data System (ADS)

Hawbecker, P.; Box, J. E.; Balog, J. D.; Ahn, Y.; Benson, R. J.

2010-12-01

Time Lapse cameras fill gaps in our observational capabilities: 1. By providing much higher temporal resolution than offered by conventional airborne or satellite remote sensing. 2. While GPS or auto-theodolite observations can provide higher time resolution data than from photogrammetry, survival of these instruments on the hazardous glacier surface is limited, plus, the maintenance of such systems can be more expensive than the maintenance of a terrestrial photogrammetry installation. 3. Imagery provide a high spatial density of observations across the glacier surface, higher than is realistically available from GPS or other in-situ observations. 4. time lapse cameras provide observational capabilities in Eulerian and Lagrangian frames while GPS or theodolite targets, going along for a ride on the glacier, provide only Lagrangian data. Photogrammetry techniques are applied to a year-plus of images from multiple west Greenland glaciers to determine the glacier front horizontal velocity variations at hourly to seasonal time scales. The presentation includes comparisons between glacier front velocities and: 1. surface melt rates inferred from surface air temperature and solar radiation observations; 2. major calving events identified from camera images; 3. surface and near-surface ocean temperature; 4. land-fast sea ice breakup; 5. tidal variations; 6. supra-glacial melt lake drainage events observed in daily optical satellite imagery; and 7.) GPS data. Extreme Ice Survey (EIS) time lapse camera overlooking the Petermann glacier, installed to image glacier dynamics and to capture the predicted ice "island" detachment.

Interplay of grounding-line dynamics and sub-shelf melting during retreat of the Bjørnøyrenna Ice Stream.

PubMed

Petrini, Michele; Colleoni, Florence; Kirchner, Nina; Hughes, Anna L C; Camerlenghi, Angelo; Rebesco, Michele; Lucchi, Renata G; Forte, Emanuele; Colucci, Renato R; Noormets, Riko

2018-05-08

The Barents Sea Ice Sheet was a marine-based ice sheet, i.e., it rested on the Barents Sea floor during the Last Glacial Maximum (21 ky BP). The Bjørnøyrenna Ice Stream was the largest ice stream draining the Barents Sea Ice Sheet and is regarded as an analogue for contemporary ice streams in West Antarctica. Here, the retreat of the Bjørnøyrenna Ice Stream is simulated by means of two numerical ice sheet models and results assessed against geological data. We investigate the sensitivity of the ice stream to changes in ocean temperature and the impact of grounding-line physics on ice stream retreat. Our results suggest that the role played by sub-shelf melting depends on how the grounding-line physics is represented in the models. When an analytic constraint on the ice flux across the grounding line is applied, the retreat of Bjørnøyrenna Ice Stream is primarily driven by internal ice dynamics rather than by oceanic forcing. This suggests that implementations of grounding-line physics need to be carefully assessed when evaluating and predicting the response of contemporary marine-based ice sheets and individual ice streams to ongoing and future ocean warming.

A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes.

PubMed

Young, Duncan A; Wright, Andrew P; Roberts, Jason L; Warner, Roland C; Young, Neal W; Greenbaum, Jamin S; Schroeder, Dustin M; Holt, John W; Sugden, David E; Blankenship, Donald D; van Ommen, Tas D; Siegert, Martin J

2011-06-02

The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling ∼34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5 km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.

Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models

NASA Astrophysics Data System (ADS)

Levermann, A.; Winkelmann, R.; Nowicki, S.; Fastook, J. L.; Frieler, K.; Greve, R.; Hellmer, H. H.; Martin, M. A.; Meinshausen, M.; Mengel, M.; Payne, A. J.; Pollard, D.; Sato, T.; Timmermann, R.; Wang, W. L.; Bindschadler, R. A.

2014-08-01

The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02-0.14 m; 90% range: 0.0-0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04-0.21 m; 90% range: 0.01-0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these

The future of the Devon Ice cap: results from climate and ice dynamics modelling

NASA Astrophysics Data System (ADS)

Mottram, Ruth; Rodehacke, Christian; Boberg, Fredrik

2017-04-01

The Devon Ice Cap is an example of a relatively well monitored small ice cap in the Canadian Arctic. Close to Greenland, it shows a similar surface mass balance signal to glaciers in western Greenland. Here we use high resolution (5km) simulations from HIRHAM5 to drive the PISM glacier model in order to model the present day and future prospects of this small Arctic ice cap. Observational data from the Devon Ice Cap in Arctic Canada is used to evaluate the surface mass balance (SMB) data output from the HIRHAM5 model for simulations forced with the ERA-Interim climate reanalysis data and the historical emissions scenario run by the EC-Earth global climate model. The RCP8.5 scenario simulated by EC-Earth is also downscaled by HIRHAM5 and this output is used to force the PISM model to simulate the likely future evolution of the Devon Ice Cap under a warming climate. We find that the Devon Ice Cap is likely to continue its present day retreat, though in the future increased precipitation partly offsets the enhanced melt rates caused by climate change.

Using the glacial geomorphology of palaeo-ice streams to understand mechanisms of ice sheet collapse

NASA Astrophysics Data System (ADS)

Stokes, Chris R.; Margold, Martin; Clark, Chris; Tarasov, Lev

2017-04-01

Processes which bring about ice sheet deglaciation are critical to our understanding of glacial-interglacial cycles and ice sheet sensitivity to climate change. The precise mechanisms of deglaciation are also relevant to our understanding of modern-day ice sheet stability and concerns over global sea level rise. Mass loss from ice sheets can be broadly partitioned between melting and a 'dynamic' component whereby rapidly-flowing ice streams/outlet glaciers transfer ice from the interior to the oceans. Surface and basal melting (e.g. of ice shelves) are closely linked to atmospheric and oceanic conditions, but the mechanisms that drive dynamic changes in ice stream discharge are more complex, which generates much larger uncertainties about their future contribution to ice sheet mass loss and sea level rise. A major problem is that observations of modern-day ice streams typically span just a few decades and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves during deglaciation. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean-climate forcing. To address this issue, numerous workers have sought to understand ice stream dynamics over longer time-scales using their glacial geomorphology in the palaeo-record. Indeed, our understanding of their geomorphology has grown rapidly in the last three decades, from almost complete ignorance to a detailed knowledge of their geomorphological products. Building on this body of work, this paper uses the glacial geomorphology of 117 ice streams in the North American Laurentide Ice Sheet to reconstruct their activity during its deglaciation ( 22,000 to 7,000 years ago). Ice stream activity was characterised by high variability in both time and space, with ice streams switching on and off in different locations. During deglaciation, we find that their overall number decreased, they occupied a

High Performance Computing Technologies for Modeling the Dynamics and Dispersion of Ice Chunks in the Arctic Ocean

DTIC Science & Technology

2016-08-23

SECURITY CLASSIFICATION OF: Hybrid finite element / finite volume based CaMEL shallow water flow solvers have been successfully extended to study wave...effects on ice floes in a simplified 10 sq-km ocean domain. Our solver combines the merits of both the finite element and finite volume methods and...ES) U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 sea ice dynamics, shallow water, finite element , finite volume

Leads in Arctic pack ice enable early phytoplankton blooms below snow-covered sea ice

PubMed Central

Assmy, Philipp; Fernández-Méndez, Mar; Duarte, Pedro; Meyer, Amelie; Randelhoff, Achim; Mundy, Christopher J.; Olsen, Lasse M.; Kauko, Hanna M.; Bailey, Allison; Chierici, Melissa; Cohen, Lana; Doulgeris, Anthony P.; Ehn, Jens K.; Fransson, Agneta; Gerland, Sebastian; Hop, Haakon; Hudson, Stephen R.; Hughes, Nick; Itkin, Polona; Johnsen, Geir; King, Jennifer A.; Koch, Boris P.; Koenig, Zoe; Kwasniewski, Slawomir; Laney, Samuel R.; Nicolaus, Marcel; Pavlov, Alexey K.; Polashenski, Christopher M.; Provost, Christine; Rösel, Anja; Sandbu, Marthe; Spreen, Gunnar; Smedsrud, Lars H.; Sundfjord, Arild; Taskjelle, Torbjørn; Tatarek, Agnieszka; Wiktor, Jozef; Wagner, Penelope M.; Wold, Anette; Steen, Harald; Granskog, Mats A.

2017-01-01

The Arctic icescape is rapidly transforming from a thicker multiyear ice cover to a thinner and largely seasonal first-year ice cover with significant consequences for Arctic primary production. One critical challenge is to understand how productivity will change within the next decades. Recent studies have reported extensive phytoplankton blooms beneath ponded sea ice during summer, indicating that satellite-based Arctic annual primary production estimates may be significantly underestimated. Here we present a unique time-series of a phytoplankton spring bloom observed beneath snow-covered Arctic pack ice. The bloom, dominated by the haptophyte algae Phaeocystis pouchetii, caused near depletion of the surface nitrate inventory and a decline in dissolved inorganic carbon by 16 ± 6 g C m−2. Ocean circulation characteristics in the area indicated that the bloom developed in situ despite the snow-covered sea ice. Leads in the dynamic ice cover provided added sunlight necessary to initiate and sustain the bloom. Phytoplankton blooms beneath snow-covered ice might become more common and widespread in the future Arctic Ocean with frequent lead formation due to thinner and more dynamic sea ice despite projected increases in high-Arctic snowfall. This could alter productivity, marine food webs and carbon sequestration in the Arctic Ocean. PMID:28102329

Alaska shorefast ice: Interfacing geophysics with local sea ice knowledge and use

NASA Astrophysics Data System (ADS)

Druckenmiller, Matthew L.

This thesis interfaces geophysical techniques with local and traditional knowledge (LTK) of indigenous ice experts to track and evaluate coastal sea ice conditions over annual and inter-annual timescales. A novel approach is presented for consulting LTK alongside a systematic study of where, when, and how the community of Barrow, Alaska uses the ice cover. The goal of this research is to improve our understanding of and abilities to monitor the processes that govern the state and dynamics of shorefast sea ice in the Chukchi Sea and use of ice by the community. Shorefast ice stability and community strategies for safe hunting provide a framework for data collection and knowledge sharing that reveals how nuanced observations by Inupiat ice experts relate to identifying hazards. In particular, shorefast ice break-out events represent a significant threat to the lives of hunters. Fault tree analysis (FTA) is used to combine local and time-specific observations of ice conditions by both geophysical instruments and local experts, and to evaluate how ice features, atmospheric and oceanic forces, and local to regional processes interact to cause break-out events. Each year, the Barrow community builds trails across shorefast ice for use during the spring whaling season. In collaboration with hunters, a systematic multi-year survey (2007--2011) was performed to map these trails and measure ice thickness along them. Relationships between ice conditions and hunter strategies that guide trail placement and risk assessment are explored. In addition, trail surveys provide a meaningful and consistent approach to monitoring the thickness distribution of shorefast ice, while establishing a baseline for assessing future environmental change and potential impacts to the community. Coastal communities in the region have proven highly adaptive in their ability to safely and successfully hunt from sea ice over the last 30 years as significant changes have been observed in the ice zone

Modeling and analysis of passive dynamic bipedal walking with segmented feet and compliant joints

NASA Astrophysics Data System (ADS)

Huang, Yan; Wang, Qi-Ning; Gao, Yue; Xie, Guang-Ming

2012-10-01

Passive dynamic walking has been developed as a possible explanation for the efficiency of the human gait. This paper presents a passive dynamic walking model with segmented feet, which makes the bipedal walking gait more close to natural human-like gait. The proposed model extends the simplest walking model with the addition of flat feet and torsional spring based compliance on ankle joints and toe joints, to achieve stable walking on a slope driven by gravity. The push-off phase includes foot rotations around the toe joint and around the toe tip, which shows a great resemblance to human normal walking. This paper investigates the effects of the segmented foot structure on bipedal walking in simulations. The model achieves satisfactory walking results on even or uneven slopes.

Dynamics and unsteady morphologies at ice interfaces driven by D2O–H2O exchange

PubMed Central

Holmes-Cerfon, Miranda; Kohn, Robert V.

2017-01-01

The growth dynamics of D2O ice in liquid H2O in a microfluidic device were investigated between the melting points of D2O ice (3.8 °C) and H2O ice (0 °C). As the temperature was decreased at rates between 0.002 °C/s and 0.1 °C/s, the ice front advanced but retreated immediately upon cessation of cooling, regardless of the temperature. This is a consequence of the competition between diffusion of H2O into the D2O ice, which favors melting of the interface, and the driving force for growth supplied by cooling. Raman microscopy tracked H/D exchange across the solid H2O–solid D2O interface, with diffusion coefficients consistent with transport of intact H2O molecules at the D2O ice interface. At fixed temperatures below 3 °C, the D2O ice front melted continuously, but at temperatures near 0 °C a scalloped interface morphology appeared with convex and concave sections that cycled between growth and retreat. This behavior, not observed for D2O ice in contact with D2O liquid or H2O ice in contact with H2O liquid, reflects a complex set of cooperative phenomena, including H/D exchange across the solid–liquid interface, latent heat exchange, local thermal gradients, and the Gibbs–Thomson effect on the melting points of the convex and concave features. PMID:29042511

Seafloor Control on Sea Ice

NASA Technical Reports Server (NTRS)

Nghiem, S. V.; Clemente-Colon, P.; Rigor, I. G.; Hall, D. K.; Neumann, G.

2011-01-01

The seafloor has a profound role in Arctic sea ice formation and seasonal evolution. Ocean bathymetry controls the distribution and mixing of warm and cold waters, which may originate from different sources, thereby dictating the pattern of sea ice on the ocean surface. Sea ice dynamics, forced by surface winds, are also guided by seafloor features in preferential directions. Here, satellite mapping of sea ice together with buoy measurements are used to reveal the bathymetric control on sea ice growth and dynamics. Bathymetric effects on sea ice formation are clearly observed in the conformation between sea ice patterns and bathymetric characteristics in the peripheral seas. Beyond local features, bathymetric control appears over extensive ice-prone regions across the Arctic Ocean. The large-scale conformation between bathymetry and patterns of different synoptic sea ice classes, including seasonal and perennial sea ice, is identified. An implication of the bathymetric influence is that the maximum extent of the total sea ice cover is relatively stable, as observed by scatterometer data in the decade of the 2000s, while the minimum ice extent has decreased drastically. Because of the geologic control, the sea ice cover can expand only as far as it reaches the seashore, the continental shelf break, or other pronounced bathymetric features in the peripheral seas. Since the seafloor does not change significantly for decades or centuries, sea ice patterns can be recurrent around certain bathymetric features, which, once identified, may help improve short-term forecast and seasonal outlook of the sea ice cover. Moreover, the seafloor can indirectly influence cloud cover by its control on sea ice distribution, which differentially modulates the latent heat flux through ice covered and open water areas.

Inferring unknow boundary conditions of the Greenland Ice Sheet by assimilating ICESat-1 and IceBridge altimetry intothe Ice Sheet System Model.

NASA Astrophysics Data System (ADS)

Larour, E. Y.; Khazendar, A.; Seroussi, H. L.; Schlegel, N.; Csatho, B. M.; Schenk, A. F.; Rignot, E. J.; Morlighem, M.

2014-12-01

Altimetry signals from missions such as ICESat-1, CryoSat, EnviSat, as well as altimeters onboard Operation IceBridge provide vital insights into processes such as surface mass balance, mass transport and ice-flow dynamics. Historically however, ice-flow models have been focused on assimilating surface velocities from satellite-based radar observations, to infer properties such as basal friction or the position of the bedrock. Here, we leverage a new methodology based on automatic differentation of the Ice Sheet System Model to assimilate surface altimetry data into a reconstruction of the past decade of ice flow on the North Greenland area. We infer corrections to boundary conditions such as basal friction and surface mass balance, as well as corrections to the ice hardness, to best-match the observed altimetry record. We compare these corrections between glaciers such as Petermann Glacier, 79 North and Zacchariae Isstrom. The altimetry signals exhibit very different patterns between East and West, which translate into very different signatures for the inverted boundary conditions. This study gives us greater insights into what differentiates different basins, both in terms of mass transport and ice-flow dynamics, and what could bethe controlling mechanisms behind the very different evolutions of these basins.

Peculiarities of Vibration Characteristics of Amorphous Ices

NASA Astrophysics Data System (ADS)

Gets, Kirill V.; Subbotin, Oleg S.; Belosludov, Vladimir R.

2012-03-01

Dynamic properties of low (LDA), high (HDA) and very high (VHDA) density amorphous ices were investigated within the approach based on Lattice Dynamics simulations. In this approach, we assume that the short-range molecular order mainly determines the dynamic and thermodynamic properties of amorphous ices. Simulation cell of 512 water molecules with periodical boundary conditions and disordering allows us to study dynamical properties and dispersion curves in the Brillouin zone of pseudo-crystal. Existence of collective phenomena in amorphous ices which is usual for crystals but anomalous for disordered phase was confirmed in our simulations. Molecule amplitudes of delocalized (collective) as well as localized vibrations have been considered.

High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

NASA Astrophysics Data System (ADS)

Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia; Park, Jungsik; Pearson, John E.; Novosad, Valentine; Schiffer, Peter; Hoffmann, Axel

2017-12-01

Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magnetotransport measurements. The experimental findings are described using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.

Modeling of Firn Compaction for Estimating Ice-Sheet Mass Change from Observed Ice-Sheet Elevation Change

NASA Technical Reports Server (NTRS)

Li, Jun; Zwally, H. Jay

2011-01-01

Changes in ice-sheet surface elevation are caused by a combination of ice-dynamic imbalance, ablation, temporal variations in accumulation rate, firn compaction and underlying bedrock motion. Thus, deriving the rate of ice-sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion, which do not involve changes in mass, and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability. We use a 25 year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model. We apply this formulation to ICESat measurements of surface elevation change at three locations on the Greenland ice sheet in order to separate the accumulation-driven changes from the ice-dynamic/ablation-driven changes, and thus to derive the corresponding mass change. Our calculated densities for the accumulation-driven changes range from 410 to 610 kg/cu m, which along with 900 kg/cu m for the dynamic/ablation-driven changes gives average densities ranging from 680 to 790 kg/cu m. We show that using an average (or "effective") density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign.

Cryotherapy impairs knee joint position sense.

PubMed

Oliveira, R; Ribeiro, F; Oliveira, J

2010-03-01

The effects of cryotherapy on joint position sense are not clearly established; however it is paramount to understand its impact on peripheral feedback to ascertain the safety of using ice therapy before resuming exercise on sports or rehabilitation settings. Thus, the aim of the present study was to determine the effects of cryotherapy, when applied over the quadriceps and over the knee joint, on knee position sense. This within-subjects repeated-measures study encompassed fifteen subjects. Knee position sense was measured by open kinetic chain technique and active positioning at baseline and after cryotherapy application. Knee angles were determined by computer analysis of the videotape images. Twenty-minute ice bag application was applied randomly, in two sessions 48 h apart, over the quadriceps and the knee joint. The main effect for cryotherapy application was significant (F (1.14)=7.7, p=0.015) indicating an increase in both absolute and relative angular errors after the application. There was no significant main effect for the location of cryotherapy application, indicating no differences between the application over the quadriceps and the knee joint. In conclusion, cryotherapy impairs knee joint position sense in normal knees. This deleterious effect is similar when cryotherapy is applied over the quadriceps or the knee joint. Georg Thieme Verlag KG Stuttgart.New York.

Spin Ice

NASA Astrophysics Data System (ADS)

Bramwell, Steven T.; Gingras, Michel J. P.; Holdsworth, Peter C. W.

2013-03-01

Pauling's model of hydrogen disorder in water ice represents the prototype of a frustrated system. Over the years it has spawned several analogous models, including Anderson's model antiferromagnet and the statistical "vertex" models. Spin Ice is a sixteen vertex model of "ferromagnetic frustration" that is approximated by real materials, most notably the rare earth pyrochlores Ho2Ti2O7, Dy2Ti2O7 and Ho2Sn2O7. These "spin ice materials" have the Pauling zero point entropy and in all respects represent almost ideal realisations of Pauling's model. They provide experimentalists with unprecedented access to a wide variety of novel magnetic states and phase transitions that are located in different regions of the field-temperature phase diagram. They afford theoreticians the opportunity to explore many new features of the magnetic interactions and statistical mechanics of frustrated systems. This chapter is a comprehensive review of the physics -- both experimental and theoretical -- of spin ice. It starts with a discussion of the historic problem of water ice and its relation to spin ice and other frustrated magnets. The properties of spin ice are then discussed in three sections that deal with the zero field spin ice state, the numerous field-induced states (including the recently identified "kagomé ice") and the magnetic dynamics. Some materials related to spin ice are briefly described and the chapter is concluded with a short summary of spin ice physics.

Simulation of dynamics of beam structures with bolted joints using adjusted Iwan beam elements

NASA Astrophysics Data System (ADS)

Song, Y.; Hartwigsen, C. J.; McFarland, D. M.; Vakakis, A. F.; Bergman, L. A.

2004-05-01

Mechanical joints often affect structural response, causing localized non-linear stiffness and damping changes. As many structures are assemblies, incorporating the effects of joints is necessary to produce predictive finite element models. In this paper, we present an adjusted Iwan beam element (AIBE) for dynamic response analysis of beam structures containing joints. The adjusted Iwan model consists of a combination of springs and frictional sliders that exhibits non-linear behavior due to the stick-slip characteristic of the latter. The beam element developed is two-dimensional and consists of two adjusted Iwan models and maintains the usual complement of degrees of freedom: transverse displacement and rotation at each of the two nodes. The resulting element includes six parameters, which must be determined. To circumvent the difficulty arising from the non-linear nature of the inverse problem, a multi-layer feed-forward neural network (MLFF) is employed to extract joint parameters from measured structural acceleration responses. A parameter identification procedure is implemented on a beam structure with a bolted joint. In this procedure, acceleration responses at one location on the beam structure due to one known impulsive forcing function are simulated for sets of combinations of varying joint parameters. A MLFF is developed and trained using the patterns of envelope data corresponding to these acceleration histories. The joint parameters are identified through the trained MLFF applied to the measured acceleration response. Then, using the identified joint parameters, acceleration responses of the jointed beam due to a different impulsive forcing function are predicted. The validity of the identified joint parameters is assessed by comparing simulated acceleration responses with experimental measurements. The capability of the AIBE to capture the effects of bolted joints on the dynamic responses of beam structures, and the efficacy of the MLFF parameter

Recent dynamic changes on Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Friedl, Peter; Seehaus, Thorsten C.; Wendt, Anja; Braun, Matthias H.; Höppner, Kathrin

2018-04-01

The Antarctic Peninsula is one of the world's regions most affected by climate change. Several ice shelves have retreated, thinned or completely disintegrated during recent decades, leading to acceleration and increased calving of their tributary glaciers. Wordie Ice Shelf, located in Marguerite Bay at the south-western side of the Antarctic Peninsula, completely disintegrated in a series of events between the 1960s and the late 1990s. We investigate the long-term dynamics (1994-2016) of Fleming Glacier after the disintegration of Wordie Ice Shelf by analysing various multi-sensor remote sensing data sets. We present a dense time series of synthetic aperture radar (SAR) surface velocities that reveals a rapid acceleration of Fleming Glacier in 2008 and a phase of further gradual acceleration and upstream propagation of high velocities in 2010-2011.The timing in acceleration correlates with strong upwelling events of warm circumpolar deep water (CDW) into Wordie Bay, most likely leading to increased submarine melt. This, together with continuous dynamic thinning and a deep subglacial trough with a retrograde bed slope close to the terminus probably, has induced unpinning of the glacier tongue in 2008 and gradual grounding line retreat between 2010 and 2011. Our data suggest that the glacier's grounding line had retreated by ˜ 6-9 km between 1996 and 2011, which caused ˜ 56 km2 of the glacier tongue to go afloat. The resulting reduction in buttressing explains a median speedup of ˜ 1.3 m d-1 ( ˜ 27 %) between 2008 and 2011, which we observed along a centre line extending between the grounding line in 1996 and ˜ 16 km upstream. Current median ice thinning rates (2011-2014) along profiles in areas below 1000 m altitude range between ˜ 2.6 to 3.2 m a-1 and are ˜ 70 % higher than between 2004 and 2008. Our study shows that Fleming Glacier is far away from approaching a new equilibrium and that the glacier dynamics are not primarily controlled by the loss of the

Holocene deceleration of the Greenland Ice Sheet.

PubMed

MacGregor, Joseph A; Colgan, William T; Fahnestock, Mark A; Morlighem, Mathieu; Catania, Ginny A; Paden, John D; Gogineni, S Prasad

2016-02-05

Recent peripheral thinning of the Greenland Ice Sheet is partly offset by interior thickening and is overprinted on its poorly constrained Holocene evolution. On the basis of the ice sheet's radiostratigraphy, ice flow in its interior is slower now than the average speed over the past nine millennia. Generally higher Holocene accumulation rates relative to modern estimates can only partially explain this millennial-scale deceleration. The ice sheet's dynamic response to the decreasing proportion of softer ice from the last glacial period and the deglacial collapse of the ice bridge across Nares Strait also contributed to this pattern. Thus, recent interior thickening of the Greenland Ice Sheet is partly an ongoing dynamic response to the last deglaciation that is large enough to affect interpretation of its mass balance from altimetry. Copyright © 2016, American Association for the Advancement of Science.

Temperature and magnetic-field driven dynamics in artificial magnetic square ice

DOE PAGES

Drouhin, Henri-Jean; Wegrowe, Jean-Eric; Razeghi, Manijeh; ...

2015-09-08

Artificial spin ices are often spoken of as being realisations of some of the celebrated vertex models of statistical mechanics, where the exact microstate of the system can be imaged using advanced magnetic microscopy methods. The fact that a stable image can be formed means that the system is in fact athermal and not undergoing the usual finite-temperature fluctuations of a statistical mechanical system. In this paper we report on the preparation of artificial spin ices with islands that are thermally fluctuating due to their very small size. The relaxation rate of these islands was determined using variable frequency focusedmore » magneto-optic Kerr measurements. We performed magnetic imaging of artificial spin ice under varied temperature and magnetic field using X-ray transmission microscopy which uses X-ray magnetic circular dichroism to generate magnetic contrast. Furthermore, we have developed an on-membrane heater in order to apply temperatures in excess of 700 K and have shown increased dynamics due to higher temperature. Due to the ‘photon-in, photon-out' method employed here, it is the first report where it is possible to image the microstates of an ASI system under the simultaneous application of temperature and magnetic field, enabling the determination of relaxation rates, coercivties, and the analysis of vertex population during reversal.« less

Temperature and magnetic-field driven dynamics in artificial magnetic square ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drouhin, Henri-Jean; Wegrowe, Jean-Eric; Razeghi, Manijeh

Artificial spin ices are often spoken of as being realisations of some of the celebrated vertex models of statistical mechanics, where the exact microstate of the system can be imaged using advanced magnetic microscopy methods. The fact that a stable image can be formed means that the system is in fact athermal and not undergoing the usual finite-temperature fluctuations of a statistical mechanical system. In this paper we report on the preparation of artificial spin ices with islands that are thermally fluctuating due to their very small size. The relaxation rate of these islands was determined using variable frequency focusedmore » magneto-optic Kerr measurements. We performed magnetic imaging of artificial spin ice under varied temperature and magnetic field using X-ray transmission microscopy which uses X-ray magnetic circular dichroism to generate magnetic contrast. Furthermore, we have developed an on-membrane heater in order to apply temperatures in excess of 700 K and have shown increased dynamics due to higher temperature. Due to the ‘photon-in, photon-out' method employed here, it is the first report where it is possible to image the microstates of an ASI system under the simultaneous application of temperature and magnetic field, enabling the determination of relaxation rates, coercivties, and the analysis of vertex population during reversal.« less

Water ice is water ice: some applications and limitations of Earth analogues to Mars

NASA Astrophysics Data System (ADS)

Koutnik, M.; Pathare, A.; Waddington, E. D.; Winebrenner, D. P.

2017-12-01

Quantitative and qualitative analyses of ice on Mars have advanced with the acquisition of abundant topography, imagery, and radar data, which have enabled the planetary-science community to tackle sophisticated questions about the martian cryosphere. Over the past decades, many studies have applied knowledge of terrestrial ice-sheet and glacier flow to improve understanding of ice behavior on Mars. A key question for both planets is how we can robustly interpret past climate from glaciological and glacial geomorphological features. Doing this requires deciphering how the history of accumulation, ablation, dust/debris deposition, and flow led to the shape and internal structure of present-day ice. Terrestrial glaciology and glacial geomorphology provide physical relationships that can be extended across environmental conditions to characterize related processes that may act at different rates or on different timescales. However, there remain fundamental unknowns about martian ice rheology and history that often limit our ability to directly apply understanding of ice dynamics learned from Antarctica, Greenland, terrestrial glaciers, and laboratory ice experiments. But the field is rich with opportunity because the constitutive relationship for water ice depends on quantities that can typically be reasonably estimated; water ice is water ice. We reflect on progress to understand the history of the ice-rich North Polar Layered Deposits (NPLD) and of select mid-latitude Lobate Debris Aprons (LDAs), and the utility of terrestrial ice-sheet and glacier analogues for these problems. Our work on Earth and Mars has focused on constraining surface accumulation/ablation patterns and ice-flow histories from topography and radar observations. We present on the challenge of interpreting internal-layer shapes when both accumulation/ablation and ice-flow histories are unknown, and how this non-uniqueness can be broken only by making assumptions about one or the other. In

Ice Streams as the Critical Link Between the Interior Ice Reservoir of the Antarctic Ice Sheet and the Global Climate System - a WISSARD Perspective (Invited)

NASA Astrophysics Data System (ADS)

Tulaczyk, S. M.; Beem, L.; Walter, J. I.; Hossainzadeh, S.; Mankoff, K. D.

2010-12-01

Fast flowing ice streams represent crucial features of the Antarctic ice sheet because they provide discharge ‘valves’ for the interior ice reservoir and because their grounding lines are exposed to ocean thermal forcing. Even with no/little topographic control ice flow near the perimeter of a polar ice sheet self-organizes into discrete, fast-flowing ice streams. Within these features basal melting (i.e. lubrication for ice sliding) is sustained through elevated basal shear heating in a region of thin ice that would otherwise be characterized by basal freezing and slow ice motion. Because faster basal ice motion is typically associated with faster subglacial erosion, ice streams tend to localize themselves over time by carving troughs into underlying rocks and sediments. Debris generated by this erosional activity is carried to the continental shelf and/or continental slope where it may be deposited at very high rates, rivaling these associated with deposition by some of the largest rivers on Earth. In terms of their hydrologic and geological functions, Antarctic ice streams play pretty much the same role as rivers do on non-glaciated continents. However, understanding of their dynamics is still quite rudimentary, largely because of the relative inaccessibility of the key basal and marine boundaries of ice streams where pertinent measurements need to be made. The present elevated interest in predicting future contribution of Antarctica to global sea level changes is driving ambitious research programs aimed at scientific exploration of these poorly investigated environments that will play a key role in defining the response of the ice sheet to near future climate changes. We will review one of these programs, the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) with particular focus on its planned contributions to understanding of ice stream dynamics.

Inverse Dynamics Model for the Ankle Joint with Applications in Tibia Malleolus Fracture

NASA Astrophysics Data System (ADS)

Budescu, E.; Merticaru, E.; Chirazi, M.

The paper presents a biomechanical model of the ankle joint, in order to determine the force and the torque of reaction into the articulation, through inverse dynamic analysis, in various stages of the gait. Thus, knowing the acceleration of the foot and the reaction force between foot and ground during the gait, determined by experimental measurement, there was calculated, for five different positions of the foot, the joint reaction forces, on the basis of dynamic balance equations. The values numerically determined were compared with the admissible forces appearing in the technical systems of osteosynthesis of tibia malleolus fracture, in order to emphasize the motion restrictions during bone healing.

On-Ice Functional Assessment of an Elite Ice Hockey Goaltender After Treatment for Femoroacetabular Impingement.

PubMed

Tramer, Joseph S; Deneweth, Jessica M; Whiteside, David; Ross, James R; Bedi, Asheesh; Goulet, Grant C

2015-01-01

Femoroacetabular impingement (FAI) is a major cause of performance inhibition in elite-level athletes. The condition is characterized by pain, osseous abnormalities such as an increased alpha angle, and decreased range of motion at the affected hip joint. Arthroscopic surgical decompression is useful in reshaping the joint to alleviate symptoms. Functional kinematic outcomes of sport-specific movements after surgery, however, are presently unknown. The ability of an ice hockey goaltender to execute sport-specific movements would improve after arthroscopic surgery. Clinical research. Level 5. An ice hockey goaltender was evaluated after arthroscopic correction of FAI on the symptomatic hip. Passive range of motion and radiographic parameters were assessed from a computed tomography-derived 3-dimensional model. An on-ice motion capture system was also used to determine peak femoral shock and concurrent hip joint postures during the butterfly and braking movements. Maximum alpha angles were 47° in the surgical and 61° in the nonsurgical hip. Internal rotation range of motion was, on average, 23° greater in the surgically corrected hip compared with contralateral. Peak shock was lower in the surgical hip by 1.39 g and 0.86 g during butterfly and braking, respectively. At peak shock, the surgical hip demonstrated increased flexion, adduction, and internal rotation for both tasks (butterfly, 6.1°, 12.3°, and 30.8°; braking, 14.8°, 19.2°, and 41.4°). On-ice motion capture revealed performance differences between hips after arthroscopic surgery in a hockey goaltender. Range of motion and the patient's subjective assessment of hip function were improved in the surgical hip. While presenting as asymptomatic, it was discovered that the contralateral hip displayed measurements consistent with FAI. Therefore, consideration of preemptive treatment in a presently painless hip may be deemed beneficial for young athletes seeking a long career in sport, and future work is

Understanding changes in ice dynamics of southeast Greenland glaciers from high resolution gravimetry data and satellite remote sensing observations

NASA Astrophysics Data System (ADS)

Millan, R.; Rignot, E. J.; Mouginot, J.; Menemenlis, D.; Morlighem, M.; Wood, M.

2016-12-01

Southeast Greenland has been one of the largest contributors to ice mass losses in Greenland in the last few decades mostly as a result of changes in ice dynamics, and to a lesser extent due to the steady increase in runoff. In 1996, the region was thinning up to the ice divide (Krabill et al., 1999) and the change were clearly of ice dynamics nature. Ice-ocean interactions played a central role in triggering a faster, systematic retreat around year 2002-2005 as water of Atlantic origin started to intrude the fjords in larger amounts due to a change in oceanic circulation in the Irminger sea. The glacier response varied significantly from one glacier to the next in response to the oceanic change, which we attribute to variatioins in fjord bathymetry, geometry control on the glaciers and calving speed of the glaciers. This region is however characterized by a dearth of topography data: the fjords have never been mapped and bed topography is challenging to obtain with radio echo sounding techniques. Here, we employ a combination of Operation IceBridge (OIB) high-resolution airborne gravity from 2016, Ocean Melting Greenland (OMG) EVS-2 mission low resolution gravity from 2016, and OMG bathymetry data from 2016 to map the bed elevation of the glaciers and fjords over the entire southeast Greenland combining gravity, thickness, and bathymetry. The data reveal the true depth of the fjords and the glacier thickness at the ice front, in a seamless fashion. We combine these data with a history of ice discharge combining estimates of ice thickness with a time series of ice velocity going back to the early 1990s. We form a time series of ice discharge, glacier per glacier, which is compared with surface mass balance from the RACMO 1-km downscaled model. We compare the results with simulations of ice melt along the calving faces of the glaciers to draw conclusions about the sensitivity of each glacier to climate forcing and re-interpret their pattern of retreat in the last

Linear Parameter Varying Identification of Dynamic Joint Stiffness during Time-Varying Voluntary Contractions

PubMed Central

Golkar, Mahsa A.; Sobhani Tehrani, Ehsan; Kearney, Robert E.

2017-01-01

Dynamic joint stiffness is a dynamic, nonlinear relationship between the position of a joint and the torque acting about it, which can be used to describe the biomechanics of the joint and associated limb(s). This paper models and quantifies changes in ankle dynamic stiffness and its individual elements, intrinsic and reflex stiffness, in healthy human subjects during isometric, time-varying (TV) contractions of the ankle plantarflexor muscles. A subspace, linear parameter varying, parallel-cascade (LPV-PC) algorithm was used to identify the model from measured input position perturbations and output torque data using voluntary torque as the LPV scheduling variable (SV). Monte-Carlo simulations demonstrated that the algorithm is accurate, precise, and robust to colored measurement noise. The algorithm was then used to examine stiffness changes associated with TV isometric contractions. The SV was estimated from the Soleus EMG using a Hammerstein model of EMG-torque dynamics identified from unperturbed trials. The LPV-PC algorithm identified (i) a non-parametric LPV impulse response function (LPV IRF) for intrinsic stiffness and (ii) a LPV-Hammerstein model for reflex stiffness consisting of a LPV static nonlinearity followed by a time-invariant state-space model of reflex dynamics. The results demonstrated that: (a) intrinsic stiffness, in particular ankle elasticity, increased significantly and monotonically with activation level; (b) the gain of the reflex pathway increased from rest to around 10–20% of subject's MVC and then declined; and (c) the reflex dynamics were second order. These findings suggest that in healthy human ankle, reflex stiffness contributes most at low muscle contraction levels, whereas, intrinsic contributions monotonically increase with activation level. PMID:28579954

Estimates of ikaite export from sea ice to the underlying seawater in a sea ice-seawater mesocosm

NASA Astrophysics Data System (ADS)

Geilfus, Nicolas-Xavier; Galley, Ryan J.; Else, Brent G. T.; Campbell, Karley; Papakyriakou, Tim; Crabeck, Odile; Lemes, Marcos; Delille, Bruno; Rysgaard, Søren

2016-09-01

The precipitation of ikaite and its fate within sea ice is still poorly understood. We quantify temporal inorganic carbon dynamics in sea ice from initial formation to its melt in a sea ice-seawater mesocosm pool from 11 to 29 January 2013. Based on measurements of total alkalinity (TA) and total dissolved inorganic carbon (TCO2), the main processes affecting inorganic carbon dynamics within sea ice were ikaite precipitation and CO2 exchange with the atmosphere. In the underlying seawater, the dissolution of ikaite was the main process affecting inorganic carbon dynamics. Sea ice acted as an active layer, releasing CO2 to the atmosphere during the growth phase, taking up CO2 as it melted and exporting both ikaite and TCO2 into the underlying seawater during the whole experiment. Ikaite precipitation of up to 167 µmol kg-1 within sea ice was estimated, while its export and dissolution into the underlying seawater was responsible for a TA increase of 64-66 µmol kg-1 in the water column. The export of TCO2 from sea ice to the water column increased the underlying seawater TCO2 by 43.5 µmol kg-1, suggesting that almost all of the TCO2 that left the sea ice was exported to the underlying seawater. The export of ikaite from the ice to the underlying seawater was associated with brine rejection during sea ice growth, increased vertical connectivity in sea ice due to the upward percolation of seawater and meltwater flushing during sea ice melt. Based on the change in TA in the water column around the onset of sea ice melt, more than half of the total ikaite precipitated in the ice during sea ice growth was still contained in the ice when the sea ice began to melt. Ikaite crystal dissolution in the water column kept the seawater pCO2 undersaturated with respect to the atmosphere in spite of increased salinity, TA and TCO2 associated with sea ice growth. Results indicate that ikaite export from sea ice and its dissolution in the underlying seawater can potentially hamper

Time-lapse joint inversion of geophysical data with automatic joint constraints and dynamic attributes

NASA Astrophysics Data System (ADS)

Rittgers, J. B.; Revil, A.; Mooney, M. A.; Karaoulis, M.; Wodajo, L.; Hickey, C. J.

2016-12-01

Joint inversion and time-lapse inversion techniques of geophysical data are often implemented in an attempt to improve imaging of complex subsurface structures and dynamic processes by minimizing negative effects of random and uncorrelated spatial and temporal noise in the data. We focus on the structural cross-gradient (SCG) approach (enforcing recovered models to exhibit similar spatial structures) in combination with time-lapse inversion constraints applied to surface-based electrical resistivity and seismic traveltime refraction data. The combination of both techniques is justified by the underlying petrophysical models. We investigate the benefits and trade-offs of SCG and time-lapse constraints. Using a synthetic case study, we show that a combined joint time-lapse inversion approach provides an overall improvement in final recovered models. Additionally, we introduce a new approach to reweighting SCG constraints based on an iteratively updated normalized ratio of model sensitivity distributions at each time-step. We refer to the new technique as the Automatic Joint Constraints (AJC) approach. The relevance of the new joint time-lapse inversion process is demonstrated on the synthetic example. Then, these approaches are applied to real time-lapse monitoring field data collected during a quarter-scale earthen embankment induced-piping failure test. The use of time-lapse joint inversion is justified by the fact that a change of porosity drives concomitant changes in seismic velocities (through its effect on the bulk and shear moduli) and resistivities (through its influence upon the formation factor). Combined with the definition of attributes (i.e. specific characteristics) of the evolving target associated with piping, our approach allows localizing the position of the preferential flow path associated with internal erosion. This is not the case using other approaches.

Joint symbolic dynamic analysis of cardiorespiratory interactions in patients on weaning trials.

PubMed

Caminal, P; Giraldo, B; Zabaleta, H; Vallverdu, M; Benito, S; Ballesteros, D; Lopez-Rodriguez, L; Esteban, A; Baumert, M; Voss, A

2005-01-01

Assessing autonomic control provides information about patho-physiological imbalances. Measures of variability of the cardiac interbeat duration RR(n) and the variability of the breath duration TTot(n) are sensitive to those changes. The interactions between RR(n) and TTot(n) are complex and strongly non-linear. A study of joint symbolic dynamics is presented as a new short-term non-linear analysis method to investigate these interactions in patients on weaning trials. 78 patients from mechanical ventilation are studied: Group A (patients that failed to maintain spontaneous breathing and were reconnected) and Group B (patients with successful trials). Using the concept of joint symbolic dynamics, cardiac and respiratory changes were transformed into a word series, and the probability of occurrence of each word type was calculated and compared between both groups. Significant differences were found in 13 words, and the most significant pn(Wc010, r010): 0.0041 ± 0.0036 (group A) against 0.0012 ± 0.0024 (group B), p-value = 0.00001. The number of seldom occurring word types (forbidden words) also presents significant differences fwcr: 6.9 ± 6.6 against 13.5 ± 5.3, p-value = 0.00004. Joint symbolic dynamics provides an efficient non-linear representation of cardiorespiratory interactions that offers simple physiological interpretations.

Dynamic Antarctic ice sheet during the early to mid-Miocene

PubMed Central

DeConto, Robert M.; Pollard, David; Levy, Richard H.

2016-01-01

Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate–ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet–climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52–0.66‰, or a sea level equivalent change of 30–36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability. PMID:26903645

High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia

Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magneto-transport measurements. The experimental findings are describedmore » using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.« less

Altered dynamics of broad-leaved tree species in a Chinese subtropical montane mixed forest: the role of an anomalous extreme 2008 ice storm episode.

PubMed

Ge, Jielin; Xiong, Gaoming; Wang, Zhixian; Zhang, Mi; Zhao, Changming; Shen, Guozhen; Xu, Wenting; Xie, Zongqiang

2015-04-01

Extreme climatic events can trigger gradual or abrupt shifts in forest ecosystems via the reduction or elimination of foundation species. However, the impacts of these events on foundation species' demography and forest dynamics remain poorly understood. Here we quantified dynamics for both evergreen and deciduous broad-leaved species groups, utilizing a monitoring permanent plot in a subtropical montane mixed forest in central China from 2001 to 2010 with particular relevance to the anomalous 2008 ice storm episode. We found that both species groups showed limited floristic alterations over the study period. For each species group, size distribution of dead individuals approximated a roughly irregular and flat shape prior to the ice storm and resembled an inverse J-shaped distribution after the ice storm. Furthermore, patterns of mortality and recruitment displayed disequilibrium behaviors with mortality exceeding recruitment for both species groups following the ice storm. Deciduous broad-leaved species group accelerated overall diameter growth, but the ice storm reduced evergreen small-sized diameter growth. We concluded that evergreen broad-leaved species were more susceptible to ice storms than deciduous broad-leaved species, and ice storm events, which may become more frequent with climate change, might potentially threaten the perpetuity of evergreen-dominated broad-leaved forests in this subtropical region in the long term. These results underscore the importance of long-term monitoring that is indispensible to elucidate causal links between forest dynamics and climatic perturbations.

Altered dynamics of broad-leaved tree species in a Chinese subtropical montane mixed forest: the role of an anomalous extreme 2008 ice storm episode

PubMed Central

Ge, Jielin; Xiong, Gaoming; Wang, Zhixian; Zhang, Mi; Zhao, Changming; Shen, Guozhen; Xu, Wenting; Xie, Zongqiang

2015-01-01

Extreme climatic events can trigger gradual or abrupt shifts in forest ecosystems via the reduction or elimination of foundation species. However, the impacts of these events on foundation species' demography and forest dynamics remain poorly understood. Here we quantified dynamics for both evergreen and deciduous broad-leaved species groups, utilizing a monitoring permanent plot in a subtropical montane mixed forest in central China from 2001 to 2010 with particular relevance to the anomalous 2008 ice storm episode. We found that both species groups showed limited floristic alterations over the study period. For each species group, size distribution of dead individuals approximated a roughly irregular and flat shape prior to the ice storm and resembled an inverse J-shaped distribution after the ice storm. Furthermore, patterns of mortality and recruitment displayed disequilibrium behaviors with mortality exceeding recruitment for both species groups following the ice storm. Deciduous broad-leaved species group accelerated overall diameter growth, but the ice storm reduced evergreen small-sized diameter growth. We concluded that evergreen broad-leaved species were more susceptible to ice storms than deciduous broad-leaved species, and ice storm events, which may become more frequent with climate change, might potentially threaten the perpetuity of evergreen-dominated broad-leaved forests in this subtropical region in the long term. These results underscore the importance of long-term monitoring that is indispensible to elucidate causal links between forest dynamics and climatic perturbations. PMID:25897387

Response of Antarctic ice shelf melt to SAM trend and possible feedbacks with the ice-dynamics

NASA Astrophysics Data System (ADS)

Donat-Magnin, Marion; Jourdain, Nicolas C.; Gallée, Hubert; Spence, Paul; Cornford, Stephen L.; Le Sommer, Julien; Durand, Gaël

2017-04-01

The observed positive trend in the Southern Annular Mode (SAM) may warm the Southern Ocean sub-surface through decreased Ekman downward pumping. Subsequent change in ice-shelves melt has been suggested to trigger glacier acceleration in West Antarctica. Here we use a regional ocean model configuration of the Amundsen Sea that includes interactive ice-shelf cavities. Our results show that the inclusion of ice-shelves changes the ocean response to the projected SAM trend, i.e. it typically inhibits a part of the SAM-induced subsurface warming. Heat budget analysis has been used to propose responsible mechanisms. Regarding Thwaites and Pine Island, sub ice-shelf melt increases above 400m by approximately 40% for Thwaites and 10% for Pine Island and decreases by up to 10% below in response to ocean temperature changes driven by the projected SAM trend. The melt sensitivity to poleward shifting winds is nonetheless small compared to the sensitivity to an ice-sheet instability, i.e. to a projected change in the shape of ice-shelf cavities. For instance, the sub ice-shelf melt are doubled near the grounding line of some glaciers in response to the largest grounding line retreat projected for 2100. Large increase in basal melt close to the grounding line could largely impact instability and glacier acceleration. Our work suggests the need for including ice shelves into ocean models, and to couple ocean models to ice-sheet models in climate projections.

Rewriting Ice Sheet "Glacier-ology"

NASA Astrophysics Data System (ADS)

Bindschadler, R.

2006-12-01

The revolution in glaciology driven by the suite of increasingly sophisticated satellite instruments has been no more extreme than in the area of ice dynamics. Years ago, glaciologists were (probably unwittingly) selective in what properties of mountain glaciers were also applied to ice sheets. This reinforced the view that they responded slowly to their environment. Notions of rapid response driven by the ideas of John Mercer, Bill Budd and Terry Hughes were politely rejected by the centrists of mainstream glaciological thought. How the tables have turned--and by the ice sheets themselves, captured in the act of rapidly changing by modern remote sensors! The saw-toothed record of sea-level change over past glacial-interglacial cycles required the existence of rapid ice loss processes. Satellite based observations, supported by hard-earned field observations have extended the time scale over which ice sheets can suddenly change to ever shorter intervals: from centuries, to decades, to years to even minutes. As changes continue to be observed, the scientific community is forced to consider new or previously ignored processes to explain these observations. The penultimate goal of ice-sheet dynamics is to credibly predict the future of both the Greenland and Antarctic ice sheets. In this important endeavor, there is no substitute for our ability to observe. Without the extensive data sets provided by remote sensing, numerical models can be neither tested nor improved. The impact of remote sensing on our existing ability to predict the future must be compared to our probable state of knowledge and ability were these data never collected. Among many satellite observed phenomena we would be largely or wholly ignorant of are the recent acceleration of ice throughout much of coastal Greenland; the sudden disintegration of multiple ice shelves along the Antarctic Peninsula; and the dramatic thinning and acceleration of the Amundsen Sea sector of West Antarctica. These

Ice Load Project Final Technical Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCoy, Timothy J.; Brown, Thomas; Byrne, Alex

As interest and investment in offshore wind projects increase worldwide, some turbines will be installed in locations where ice of significant thickness forms on the water surface. This ice moves under the driving forces of wind, current, and thermal effects and may result in substantial forces on bottom-fixed support structures. The North and Baltic Seas in Europe have begun to see significant wind energy development and the Great Lakes of the United States and Canada may host wind energy development in the near future. Design of the support structures for these projects is best performed through the use of anmore » integrated tool that can calculate the cumulative effects of forces due to turbine operations, wind, waves, and floating ice. The dynamic nature of ice forces requires that these forces be included in the design simulations, rather than added as static forces to simulation results. The International Electrotechnical Commission (IEC) standard[2] for offshore wind turbine design and the International Organization for Standardization (ISO) standard[3] for offshore structures provide requirements and algorithms for the calculation of forces induced by surface ice; however, currently none of the major wind turbine dynamic simulation codes provides the ability to model ice loads. The scope of work of the project described in this report includes the development of a suite of subroutines, collectively named IceFloe, that meet the requirements of the IEC and ISO standards and couples with four of the major wind turbine dynamic simulation codes. The mechanisms by which ice forces impinge on offshore structures generally include the forces required for crushing of the ice against vertical-sided structures and the forces required to fracture the ice as it rides up on conical-sided structures. Within these two broad categories, the dynamic character of the forces with respect to time is also dependent on other factors such as the velocity and thickness of the

A regional-scale estimation of ice wedge ice volumes in the Canadian High Arctic

NASA Astrophysics Data System (ADS)

Templeton, M.; Pollard, W. H.; Grand'Maison, C. B.

2016-12-01

Ice wedges are both prominent and environmentally vulnerable features in continuous permafrost environments. As the world's Arctic regions begin to warm, concern over the potential effects of ice wedge melt out has become an immediate issue, receiving much attention in the permafrost literature. In this study we estimate the volume of ice wedge ice for large areas in the Canadian High Arctic through the use of high resolution satellite imagery and the improved capabilities of Geographic Information Systems (GIS). The methodology used for this study is similar to that of one performed in Siberia and Alaska by Ulrich et al, in 2014. Utilizing Ulrich's technique, this study detected ice wedge polygons from satellite imagery using ArcGIS. The average width and depth of these ice wedges were obtained from a combination of field data and long-term field studies for the same location. The assumptions used in the analysis of ice wedge volume have been tested, including trough width being representative of ice wedge width, and ice wedge ice content (Pollard and French 1980). This study used specific field sites located near Eureka on Ellesmere Island (N80°01', W85°43') and at Expedition Fiord on Axel Heiberg Island (N79°23', W90°59'). The preliminary results indicate that the methodology used by Ulrich et al, 2014 is transferrable to the Canadian High Arctic, and that ice wedge volumes range between 3-10% of the upper part of permafrost. These findings are similar to previous studies and their importance is made all the more evident by the dynamic nature of ice wedges where it could be argued that they are a key driver of thermokarst terrain. The ubiquitous nature of ice wedges across arctic terrain highlights the importance and the need to improve our understanding of ice wedge dynamics, as subsidence from ice wedge melt-out could lead to large scale landscape change.

Nonlinear structural joint model updating based on instantaneous characteristics of dynamic responses

NASA Astrophysics Data System (ADS)

Wang, Zuo-Cai; Xin, Yu; Ren, Wei-Xin

2016-08-01

This paper proposes a new nonlinear joint model updating method for shear type structures based on the instantaneous characteristics of the decomposed structural dynamic responses. To obtain an accurate representation of a nonlinear system's dynamics, the nonlinear joint model is described as the nonlinear spring element with bilinear stiffness. The instantaneous frequencies and amplitudes of the decomposed mono-component are first extracted by the analytical mode decomposition (AMD) method. Then, an objective function based on the residuals of the instantaneous frequencies and amplitudes between the experimental structure and the nonlinear model is created for the nonlinear joint model updating. The optimal values of the nonlinear joint model parameters are obtained by minimizing the objective function using the simulated annealing global optimization method. To validate the effectiveness of the proposed method, a single-story shear type structure subjected to earthquake and harmonic excitations is simulated as a numerical example. Then, a beam structure with multiple local nonlinear elements subjected to earthquake excitation is also simulated. The nonlinear beam structure is updated based on the global and local model using the proposed method. The results show that the proposed local nonlinear model updating method is more effective for structures with multiple local nonlinear elements. Finally, the proposed method is verified by the shake table test of a real high voltage switch structure. The accuracy of the proposed method is quantified both in numerical and experimental applications using the defined error indices. Both the numerical and experimental results have shown that the proposed method can effectively update the nonlinear joint model.

Modeling of Antarctic Sea Ice in a General Circulation Model.

NASA Astrophysics Data System (ADS)

Wu, Xingren; Simmonds, Ian; Budd, W. F.

1997-04-01

A dynamic-thermodynamic sea ice model is developed and coupled with the Melbourne University general circulation model to simulate the seasonal cycle of the Antarctic sea ice distribution. The model is efficient, rapid to compute, and useful for a range of climate studies. The thermodynamic part of the sea ice model is similar to that developed by Parkinson and Washington, the dynamics contain a simplified ice rheology that resists compression. The thermodynamics is based on energy conservation at the top surface of the ice/snow, the ice/water interface, and the open water area to determine the ice formation, accretion, and ablation. A lead parameterization is introduced with an effective partitioning scheme for freezing between and under the ice floes. The dynamic calculation determines the motion of ice, which is forced with the atmospheric wind, taking account of ice resistance and rafting. The simulated sea ice distribution compares reasonably well with observations. The seasonal cycle of ice extent is well simulated in phase as well as in magnitude. Simulated sea ice thickness and concentration are also in good agreement with observations over most regions and serve to indicate the importance of advection and ocean drift in the determination of the sea ice distribution.

Modeling of Antarctic sea ice in a general circulation model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Xingren; Budd, W.F.; Simmonds, I.

1997-04-01

A dynamic-thermodynamic sea ice model is developed and coupled with the Melbourne University general circulation model to simulate the seasonal cycle of the Antarctic sea ice distributions The model is efficient, rapid to compute, and useful for a range of climate studies. The thermodynamic part of the sea ice model is similar to that developed by Parkinson and Washington, the dynamics contain a simplified ice rheology that resists compression. The thermodynamics is based on energy conservation at the top surface of the ice/snow, the ice/water interface, and the open water area to determine the ice formation, accretion, and ablation. Amore » lead parameterization is introduced with an effective partitioning scheme for freezing between and under the ice floes. The dynamic calculation determines the motion of ice, which is forced with the atmospheric wind, taking account of ice resistance and rafting. The simulated sea ice distribution compares reasonably well with observations. The seasonal cycle of ice extent is well simulated in phase as well as in magnitude. Simulated sea ice thickness and concentration are also in good agreement with observations over most regions and serve to indicate the importance of advection and ocean drift in the determination of the sea ice distribution. 64 refs., 15 figs., 2 tabs.« less

Sediment features at the grounding zone and beneath Ekström Ice Shelf, East Antarctica, imaged using on-ice vibroseis.

NASA Astrophysics Data System (ADS)

Smith, Emma C.; Eisen, Olaf; Hofstede, Coen; Lambrecht, Astrid; Mayer, Christoph

2017-04-01

The grounding zone, where an ice sheet becomes a floating ice shelf, is known to be a key threshold region for ice flow and stability. A better understanding of ice dynamics and sediment transport across such zones will improve knowledge about contemporary and palaeo ice flow, as well as past ice extent. Here we present a set of seismic reflection profiles crossing the grounding zone and continuing to the shelf edge of Ekström Ice Shelf, East Antarctica. Using an on-ice vibroseis source combined with a snowstreamer we have imaged a range of sub-glacial and sub-shelf sedimentary and geomorphological features; from layered sediment deposits to elongated flow features. The acoustic properties of the features as well as their morphology allow us to draw conclusions as to their material properties and origin. These results will eventually be integrated with numerical models of ice dynamics to quantify past and present interactions between ice and the solid Earth in East Antarctica; leading to a better understanding of future contributions of this region to sea-level rise.

Joint-bounded crescentic scars formed by subglacial clast-bed contact forces: Implications for bedrock failure beneath glaciers

NASA Astrophysics Data System (ADS)

Krabbendam, M.; Bradwell, T.; Everest, J. D.; Eyles, N.

2017-08-01

Glaciers and ice sheets are important agents of bedrock erosion, yet the precise processes of bedrock failure beneath glacier ice are incompletely known. Subglacially formed erosional crescentic markings (crescentic gouges, lunate fractures) on bedrock surfaces occur locally in glaciated areas and comprise a conchoidal fracture dipping down-ice and a steep fracture that faces up-ice. Here we report morphologically distinct crescentic scars that are closely associated with preexisting joints, termed here joint-bounded crescentic scars. These hitherto unreported features are ca. 50-200 mm deep and involve considerably more rock removal than previously described crescentic markings. The joint-bounded crescentic scars were found on abraded rhyolite surfaces recently exposed (< 20 years) beneath a retreating glacier in Iceland, as well as on glacially sculpted Precambrian gneisses in NW Scotland and various Precambrian rocks in Ontario, glaciated during the Late Pleistocene. We suggest a common formation mechanism for these contemporary and relict features, whereby a boulder embedded in basal ice produces a continuously migrating clast-bed contact force as it is dragged over the hard (bedrock) bed. As the ice-embedded boulder approaches a preexisting joint in the bedrock, stress concentrations build up in the bed that exceed the intact rock strength, resulting in conchoidal fracturing and detachment of a crescentic wedge-shaped rock fragment. Subsequent removal of the rock fragment probably involves further fracturing or crushing (comminution) under high contact forces. Formation of joint-bounded crescentic scars is favoured by large boulders at the base of the ice, high basal melting rates, and the presence of preexisting subvertical joints in the bedrock bed. We infer that the relative scarcity of crescentic markings in general on deglaciated surfaces shows that fracturing of intact bedrock below ice is difficult, but that preexisting weaknesses such as joints greatly

New insights into West Greenland ice sheet/stream dynamics during the last glacial cycle.

NASA Astrophysics Data System (ADS)

Roberts, David; Lane, Tim; Rea, Brice; Cofaigh, Colm O.; Jamieson, Stewart; Vieli, Andreas; Rodes, Angel

2015-04-01

output which indicates that non-linear retreat, grounding line stability and up-ice surface thinning is heavily influenced by both vertical and lateral constrictions in marine trough systems. While the offshore ice stream corridors are beginning to reveal their dynamic retreat history, knowledge of the inter-stream areas on the continental shelf remains very poor. The western, onshore sector of the GrIS has a much improved deglacial chronology derived from radiocarbon and new cosmogenic surface exposure dating undertaken in the last decade, but the deglacial history of wide swathes of the inner, mid and outer continental shelf remains completely unknown. The Hellefiske moraines on the West Greenland shelf were described in the late 1970's but little is known of ice sheet retreat behaviour across these areas. Understanding the deglacial signature of such regions is important if we are to use palaeo-reconstructions to understand ice sheet collapse/retreat mechanisms and to inform future model predictions.

A molecular model for ice nucleation and growth, attachment 1

NASA Technical Reports Server (NTRS)

Plummer, P. L. M.

1981-01-01

The quantum mechanical technique is used to study ionic, configurational, and impurity defects in the ice surface. In addition to static calculations of the energetics of the water monomer-ice surface interactions, molecular dynamics studies were initiated. The calculations of the monomer-ice surface interaction, molecular dynamics studies were initiated. The calculations of monomer-ice surface interactions indicate that many adsorption sites exist on the ice surfaces and that the barriers between bonding sites are relatively low. Bonding on the prism face of ice is preferentially above lattice sites.

Interlimb symmetry of dynamic knee joint stiffness and co-contraction is maintained in early stage knee osteoarthritis.

PubMed

Collins, A T; Richardson, R T; Higginson, J S

2014-08-01

Individuals with knee OA often exhibit greater co-contraction of antagonistic muscle groups surrounding the affected joint which may lead to increases in dynamic joint stiffness. These detrimental changes in the symptomatic limb may also exist in the contralateral limb, thus contributing to its risk of developing knee osteoarthritis. The purpose of this study is to investigate the interlimb symmetry of dynamic knee joint stiffness and muscular co-contraction in knee osteoarthritis. Muscular co-contraction and dynamic knee joint stiffness were assessed in 17 subjects with mild to moderate unilateral medial compartment knee osteoarthritis and 17 healthy control subjects while walking at a controlled speed (1.0m/s). Paired and independent t-tests determined whether significant differences exist between groups (p<0.05). There were no significant differences in dynamic joint stiffness or co-contraction between the OA symptomatic and OA contralateral group (p=0.247, p=0.874, respectively) or between the OA contralateral and healthy group (p=0.635, p=0.078, respectively). There was no significant difference in stiffness between the OA symptomatic and healthy group (p=0.600); however, there was a slight trend toward enhanced co-contraction in the symptomatic knees compared to the healthy group (p=0.051). Subjects with mild to moderate knee osteoarthritis maintain symmetric control strategies during gait. Copyright © 2014 Elsevier Ltd. All rights reserved.

Interlimb symmetry of dynamic knee joint stiffness and co-contraction is maintained in early stage knee osteoarthritis

PubMed Central

Collins, A.T.; Richardson, R.T.; Higginson, J.S.

2014-01-01

Individuals with knee OA often exhibit greater co-contraction of antagonistic muscle groups surrounding the affected joint which may lead to increases in dynamic joint stiffness. These detrimental changes in the symptomatic limb may also exist in the contralateral limb, thus contributing to its risk of developing knee osteoarthritis. The purpose of this study is to investigate the interlimb symmetry of dynamic knee joint stiffness and muscular co-contraction in knee osteoarthritis. Muscular co-contraction and dynamic knee joint stiffness were assessed in 17 subjects with mild to moderate unilateral medial compartment knee osteoarthritis and 17 healthy control subjects while walking at a controlled speed (1.0 m/s). Paired and independent t-tests determined whether significant differences exist between groups (p < 0.05). There were no significant differences in dynamic joint stiffness or co-contraction between the OA symptomatic and OA contralateral group (p = 0.247, p = 0.874, respectively) or between the OA contralateral and healthy group (p = 0.635, p = 0.078, respectively). There was no significant difference in stiffness between the OA symptomatic and healthy group (p = 0.600); however, there was a slight trend toward enhanced co-contraction in the symptomatic knees compared to the healthy group (p = 0.051). Subjects with mild to moderate knee osteoarthritis maintain symmetric control strategies during gait. PMID:24768278

Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD

PubMed Central

Barou, F.; Hidas, K.; Tommasi, A.; Mainprice, D.

2017-01-01

Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=−5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the ‘parent’ ones suggests the possibility of ‘spontaneous’ nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms. This article is part of the themed issue ‘Microdynamics of ice’. PMID:28025294

Antarctic ice-rafted detritus (IRD) in the South Atlantic: Indicators of iceshelf dynamics or ocean surface conditions?

USGS Publications Warehouse

Nielsen, Simon H.H.; Hodell, D.A.

2007-01-01

Ocean sediment core TN057-13PC4/ODP1094, from the Atlantic sector of the Southern Ocean, contains elevated lithogenic material in sections representing the last glacial period compared to the Holocene. This ice-rafted detritus is mainly comprised of volcanic glass and ash, but has a significant input of what was previously interpreted as quartz during peak intervals (Kanfoush et al., 2000, 2002). Our analysis of these clear mineral grains indicates that most are plagioclase, and that South Sandwich Islands is the predominant source, similar to that inferred for the volcanic glass (Nielsen et al., in review). In addition, quartz and feldspar with possible Antarctic origin occur in conjunction with postulated episodes of Antarctic deglaciation. We conclude that while sea ice was the dominant ice rafting agent in the Polar Frontal Zone of the South Atlantic during the last glacial period, the Holocene IRD variability may reflect Antarctic ice sheet dynamics.

Seasonal Ice Wedge Dynamics in Fosheim Peninsula, Ellesmere Island, Nunavut

NASA Astrophysics Data System (ADS)

Ward, M. K.; Pollard, W. H.

2017-12-01

Areas with ice-rice permafrost are vulnerable to thermokarst (lowering of the land surface from melting ground ice). The Fosheim Peninsula on Ellesmere Island, Nunavut is a high Arctic polar desert system with cold permafrost 500 m thick that is ice-rich in the upper 20 - 30 m. Our team has been monitoring changing permafrost conditions on the Fosheim since 1990. In this area ground ice consists mainly of ice-wedge ice and massive tabular ice bodies. With a mean annual temperature of - 19°C, the area is still sensitive to thermokarst as experienced in 2012; one of the warmest summers on record there was a three-fold increase in thermokarst, with the accelerated deepening of ice wedge troughs and the development of retrogressive thaw slumps. In this study, 7 ice wedges were monitored for 7 weeks in July and August, 2017. Ice wedges were chosen to represent different conditions including varying tough depths (0.36 m to 1.2 m), secondary wedge, varying plant cover (heavily covered to bare soil) and one wedge initially experienced ponding from snow melt that subsequently drained. Data collected included active layer depth measurements, soil moisture, ground temperatures at ice wedge through and polygon centres, dGPS and GPR surveys. Using Worldview 2 satellite imagery from 2008, 2012, 2016, these sites were compared to assess changes in polygons at a landscape scale. Ice wedges are ubiquitous to the arctic but may respond differently within different high Arctic environments. With the majority of studies being focused in the lower arctic, this study provides important field data from a high arctic site.

Preparing and Analyzing Iced Airfoils

NASA Technical Reports Server (NTRS)

Vickerman, Mary B.; Baez, Marivell; Braun, Donald C.; Cotton, Barbara J.; Choo, Yung K.; Coroneos, Rula M.; Pennline, James A.; Hackenberg, Anthony W.; Schilling, Herbert W.; Slater, John W.;

Trajectory design for a cislunar CubeSat leveraging dynamical systems techniques: The Lunar IceCube mission

NASA Astrophysics Data System (ADS)

Bosanac, Natasha; Cox, Andrew D.; Howell, Kathleen C.; Folta, David C.

2018-03-01

Lunar IceCube is a 6U CubeSat that is designed to detect and observe lunar volatiles from a highly inclined orbit. This spacecraft, equipped with a low-thrust engine, is expected to be deployed from the upcoming Exploration Mission-1 vehicle. However, significant uncertainty in the deployment conditions for secondary payloads impacts both the availability and geometry of transfers that deliver the spacecraft to the lunar vicinity. A framework that leverages dynamical systems techniques is applied to a recently updated set of deployment conditions and spacecraft parameter values for the Lunar IceCube mission, demonstrating the capability for rapid trajectory design.

Compression experiments on artificial, alpine and marine ice: implications for ice-shelf/continental interactions

NASA Astrophysics Data System (ADS)

Dierckx, Marie; Goossens, Thomas; Samyn, Denis; Tison, Jean-Louis

2010-05-01

Antarctic ice shelves are important components of continental ice dynamics, in that they control grounded ice flow towards the ocean. As such, Antarctic ice shelves are a key parameter to the stability of the Antarctic ice sheet in the context of global change. Marine ice, formed by sea water accretion beneath some ice shelves, displays distinct physical (grain textures, bubble content, ...) and chemical (salinity, isotopic composition, ...) characteristics as compared to glacier ice and sea ice. The aim is to refine Glen's flow relation (generally used for ice behaviour in deformation) under various parameters (temperature, salinity, debris, grain size ...) to improve deformation laws used in dynamic ice shelf models, which would then give more accurate and / or realistic predictions on ice shelf stability. To better understand the mechanical properties of natural ice, deformation experiments were performed on ice samples in laboratory, using a pneumatic compression device. To do so, we developed a custom built compression rig operated by pneumatic drives. It has been designed for performing uniaxial compression tests at constant load and under unconfined conditions. The operating pressure ranges from about 0.5 to 10 Bars. This allows modifying the experimental conditions to match the conditions found at the grounding zone (in the 1 Bar range). To maintain the ice at low temperature, the samples are immersed in a Silicone oil bath connected to an external refrigeration system. During the experiments, the vertical displacement of the piston and the applied force is measured by sensors which are connected to a digital acquisition system. We started our experiments with artificial ice and went on with continental ice samples from glaciers in the Alps. The first results allowed us to acquire realistic mechanical data for natural ice. Ice viscosity was calculated for different types of artificial ice, using Glen's flow law, and showed the importance of impurities

Tropospheric characteristics over sea ice during N-ICE2015

NASA Astrophysics Data System (ADS)

Kayser, Markus; Maturilli, Marion; Graham, Robert; Hudson, Stephen; Cohen, Lana; Rinke, Annette; Kim, Joo-Hong; Park, Sang-Jong; Moon, Woosok; Granskog, Mats

2017-04-01

Over recent years, the Arctic Ocean region has shifted towards a younger and thinner sea-ice regime. The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in this new ice regime north of Svalbard. Here we analyze upper-air measurements made by radiosondes launched twice daily together with surface meteorology observations during N-ICE2015 from January to June 2015. We study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, sudden increases in moisture content and temperature, temperature inversions and boundary layer dynamics. The influence of synoptic cyclones is strongest under polar night conditions, when radiative cooling is most effective and the moisture content is low. We find that transitions between the radiatively clear and opaque state are the largest drivers of changes to temperature inversion and stability characteristics in the boundary layer during winter. In spring radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. The unique N-ICE2015 dataset is used for case studies investigating changes in the vertical structure of the atmosphere under varying synoptic conditions. The goal is to deepen our understanding of synoptic interactions within the Arctic climate system, to improve model performance, as well as to identify gaps in instrumentation, which precludes further investigations.