Interstellar matrices: the chemical composition and evolution of interstellar ices as observed by ISO.

PubMed

d'Hendecourt, L; Dartois, E

2001-03-15

Matrix isolation techniques have been developed in the early sixties as a tool for studying the spectroscopic properties of out of equilibrium species (atoms, radicals, ions, reactive molecules), embedded in rare gas inert matrices at low temperatures. Cold interstellar grains surfaces are able to condense out gas phase molecules, routinely observed by radioastronomy. These grain 'mantles' can be considered as 'interstellar matrices'. However, these matrices are not clean and unreactive. They are made principally of dirty ices whose composition must be determined carefully to assess the importance of the solid state chemistry that takes place in the Interstellar Medium. Infrared spectroscopy, both in astronomy and in the laboratory, is the unique tool to determine the chemical composition of these ices. Astronomical spectra can directly be compared with laboratory ones obtained using classical matrix isolation techniques. Furthermore, dedicated experiments may be undertaken to further improve the understanding of the basic physico-chemical processes that take place in cosmic ices.

Dirty Snow, Atmospheric Warming, and Climate Feedbacks from Boreal Black Carbon Emissions

NASA Astrophysics Data System (ADS)

Flanner, M. G.; Zender, C. S.; Randerson, J. T.; Jin, Y.

2005-12-01

Black carbon (BC) emitted from boreal fires darkens snow and sea-ice surfaces, increases solar absorption in the atmosphere, and decreases the incident flux at the surface. Although global surface forcing of darkened snow/ice is small relative to atmospheric forcing, the former directly triggers ice-albedo feedback, whereas the latter directly alters the atmospheric lapse rate. This highlights the importance of examining climate feedback strength as well as instantaneous forcings. We used a coupled land-atmosphere GCM (NCAR CAM3) to compare the relative forcings and climate feedbacks of BC emitted from a suite of boreal forest fires over the last decade, accounting for both enhanced snow/ice and atmospheric absorption by BC. The net change in absorbed energy at the surface was about three times greater than the instantaneous surface forcing when BC interactively heated the snow. Timing and location of fires determined the magnitude of darkened snow/ice feedback potential. We also assessed climate feedback strength from BC emitted globally during extreme high and low fire years, including the 1998 fire season.

Attitudes and perceptions of urban African Americans of a "dirty bomb" radiological terror event: results of a qualitative study and implications for effective risk communication.

PubMed

Bass, Sarah Bauerle; Greener, Judith R; Ruggieri, Dominique; Parvanta, Claudia; Mora, Gabriella; Wolak, Caitlin; Normile, Rebecca; Gordon, Thomas F

2015-02-01

Radiological terror presents a real threat, but little is known about how low-income, urban African Americans may respond to such threats. The aim of this study was to understand the unique challenges of this group and to explore their knowledge of what a "dirty bomb" is, their intended behaviors should one occur, and their barriers to complying with "shelter in place" recommendations. Thirty-seven 18-65-year-olds who were users of community centers in disadvantaged areas participated in 3 focus groups in Philadelphia. Results were analyzed by using the Krueger method of analyzing narrative text. The responses highlighted little knowledge or concern about a dirty bomb. Lack of trust in local authorities was expressed, with participants indicating that they did not feel their needs were addressed. While shelter in place was understood, most said they would still check on family or talk with others to get the "whole truth" because the most trusted information sources were neighbors and community leaders. Our results indicate that a risk communication intervention for urban minorities may support desirable behaviors in the event of a dirty bomb, but successful communication will require establishing a local leader as a spokesperson to convince people of the importance of sheltering in place.

Low temperature self-cleaning properties of superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Wang, Fajun; Shen, Taohua; Li, Changquan; Li, Wen; Yan, Guilong

2014-10-01

Outdoor surfaces are usually dirty surfaces. Ice accretion on outdoor surfaces could lead to serious accidents. In the present work, the superhydrophobic surface based on 1H, 1H, 2H, 2H-Perfluorodecanethiol (PFDT) modified Ag/PDMS composite was prepared to investigate the anti-icing property and self-cleaning property at temperatures below freezing point. The superhydrophobic surface was deliberately polluted with activated carbon before testing. It was observed that water droplet picked up dusts on the cold superhydrophobic surface and took it away without freezing at a measuring temperature of -10 °C. While on a smooth PFDT surface and a rough surface base on Ag/PDMS composite without PFDT modification, water droplets accumulated and then froze quickly at the same temperature. However, at even lower temperature of -12 °C, the superhydrophobic surface could not prevent the surface water from icing. In addition, it was observed that the frost layer condensed from the moisture pay an important role in determining the low temperature self-cleaning properties of a superhydrophobic surface.

Mannann'an Crater

NASA Technical Reports Server (NTRS)

1998-01-01

This composite view taken by NASA's Galileo spacecraft shows the rim and interior of the impact crater, Mannann'an, on Jupiter's moon, Europa. A high resolution image (20 meters per picture element) was combined with lower resolution (80 meters per picture element) color images taken through violet, green and near-infrared filters, to produce this synthetic color composite image. The color data can be used to distinguish between regions of purer (clean) and more contaminated (dirty) ice on the surface, and also offers information on the size of the ice grains. The reddish brown material is thought to be dirty ice, while the bluish areas inside the crater are purer ice. The crater rim is on the left at the boundary between the reddish brown material and the gray material.

The high resolution data show small features inside the crater, including concentric fractures and a spider-like set of fractures near the right (east) edge of the image. For a more regional perspective, the Mannann'an crater can be seen as a large circular feature with bright rays in the lower left corner of a regional image from Galileo's first orbit of Jupiter in June 1996.

North is to the top of the picture and the Sun illuminates the scene from the east (right). The image, centered at 3 degrees north latitude and 240 degrees west longitude, covers an area approximately 18 by 4 kilometers (11 by 2.5 miles). The finest details that can be discerned in this picture are about 40 meters (44 yards) across. The images were taken by the spacecraft's onboard solid state imaging camera when Galileo flew by Europa on March 29th, 1998 at a distance of 1,934 kilometers (1,200 miles).

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

Attitudes and Perceptions of Urban African Americans of a “Dirty Bomb” Radiological Terror Event: Results of a Qualitative Study and Implications for Effective Risk Communication

PubMed Central

Bass, Sarah Bauerle; Greener, Judith R.; Ruggieri, Dominique; Parvanta, Claudia; Mora, Gabriella; Wolak, Caitlin; Normile, Rebecca; Gordon, Thomas F.

2017-01-01

Objectives Radiological terror presents a real threat, but little is known about how low-income, urban African Americans may respond to such threats. The aim of this study was to understand the unique challenges of this group and to explore their knowledge of what a “dirty bomb” is, their intended behaviors should one occur, and their barriers to complying with “shelter in place” recommendations. Methods Thirty-seven 18–65-year-olds who were users of community centers in disadvantaged areas participated in 3 focus groups in Philadelphia. Results were analyzed by using the Krueger method of analyzing narrative text. Results The responses highlighted little knowledge or concern about a dirty bomb. Lack of trust in local authorities was expressed, with participants indicating that they did not feel their needs were addressed. While shelter in place was understood, most said they would still check on family or talk with others to get the “whole truth” because the most trusted information sources were neighbors and community leaders. Conclusion Our results indicate that a risk communication intervention for urban minorities may support desirable behaviors in the event of a dirty bomb, but successful communication will require establishing a local leader as a spokesperson to convince people of the importance of sheltering in place. PMID:25611688

Combining a Distributed Melt Model and Meteorological Data of Shackleton Glacier, Canadian Rockies

NASA Astrophysics Data System (ADS)

Mueller, M.; Jiskoot, H.

2010-12-01

Runoff from the Canadian Rocky Mountains into the Upper Columbia and Kootenay basins is strongly dominated by winter snow accumulation and spring melt, and it has been suggested that future reductions in snowpack will create increased competition for water between spring and early fall (Hamlet & Lettenmaier, 1999). Although the glacierised area is substantial for affecting summer flows in these basins, there are no measurements or quantified estimates of glacier runoff contribution. In an effort to provide an estimate of glacier runoff for the region, we measured ablation over 5 years, set up weather stations and temperature sensors in Summers 2009 and 2010 and developed a melt model for Shackleton Glacier (42.5 km2), the largest outlet of the Clemenceau Icefield Group (271 km2), which is the major local ice mass feeding into the Upper Columbia basin. Two HOBO weather stations (WS) were installed on the glacier for two weeks in Summer 2010, one near the left lateral moraine on very dirty ice, and one mid-glacier on relatively clean ice. Instrumentation included pyranometers (solar radiation and albedo), and temperature, wind speed and direction, relative humidity and barometric pressure sensors. A weather station off ice provided additional temperature and precipitation data. Other data included daily ablation stake measurements, surface roughness measurements, temperature data from Tidbit loggers on and off ice, and daily manual weather observations. Yearly ablation stake measurements and summer weather observations have been made by our team since 2005. A BC River Forecast Centre automatic snow pillow station provides additional temperature and precipitation data. Using these meteorological and ablation data for parameterisation and optimisation, a distributed GIS melt model was constructed from a simple energy balance model. The model is driven by hourly direct and diffuse radiation and DEM hillshading, an albedo parameterisation based on four ice/snow zones identified from a satellite image and field measurements, constant daily values of longwave radiation as a function of percent cloud cover, and sensible heat input as a function of air temperature, katabatic wind, surface roughness and elevation. Latent heat was considered negligible. Novel aspects of the melt model include a valley temperature threshold for katabatic wind (using on and off ice temperatures and katabatic wind speed) and slope corrected area melt and radiation calculations. In an attempt to quantify energy balance effects of tributary-trunk detachment due to glacier recession related glacier fragmentation, special attention was paid to the potential influence from lateral moraines and valley walls and very dirty ice on the ablation in ice marginal regions. Observations suggest that, when katabatic wind diminishes, heat advection from an even moderately warmer lateral moraine can raise nearby glacier temperature substantially. This suggests that a combination of katabatic wind fields and proximity to lateral moraines/rock walls may be important in calculations of sensible heat contribution to surface melt in recently fragmented glacier systems.

Coupled energy-balance/ice-sheet model simulations of the glacial cycle: A possible connection between terminations and terrigenous dust

NASA Astrophysics Data System (ADS)

Peltier, W. Richard; Marshall, Shawn

1995-07-01

We apply a coupled energy-balance/ice-sheet climate model in an investigation of northern hemisphere ice-sheet advance and retreat over the last glacial cycle. When driven only by orbital insolation variations, the model predicts ice-sheet advances over the continents of North America and Eurasia that are in good agreement with geological reconstructions in terms of the timescale of advance and the spatial positioning of the main ice masses. The orbital forcing alone, however, is unable to induce the observed rapid ice-sheet retreat, and we conclude that additional climatic feedbacks not explicitly included in the basic model must be acting. In the analyses presented here we have parameterized a number of potentially important effects in order to test their relative influence on the process of glacial termination. These include marine instability, thermohaline circulation effects, carbon dioxide variations, and snow albedo changes caused by dust loading during periods of high atmospheric aerosol concentration. For the purpose of these analyses the temporal changes in the latter two variables were inferred from ice core records. Of these various influences, our analyses suggest that the albedo variations in the ice-sheet ablation zone caused by dust loading may represent an extremely important ablation mechanism. Using our parameterization of "dirty" snow in the ablation zone we find glacial retreat to be strongly accelerated, such that complete collapse of the otherwise stable Laurentide ice sheet ensues. The last glacial maximum configurations of the Laurentide and Fennoscandian complexes are also brought into much closer accord with the ICE-3G reconstruction of Tushingham and Peltier (1991,1992) and the ICE-4G reconstruction of Peltier (1994) when this effect is reasonably introduced.

Climate Effects and Efficacy of Dust and Soot in Snow

NASA Astrophysics Data System (ADS)

Zender, C. S.; Flanner, M. G.; Randerson, J. T.; Mahowald, N. M.; Rasch, P. J.; Yoshioka, M.; Painter, T.

2006-12-01

Dust and industrial and biomass burning emissions from low and mid-latitudes dominate the absorbing impurities trapped in snow at mid- and high-latitudes. We study the effects of dust and smoke on global and regional climate using a general circulation model driven by observed and predicted aerosol emissions determined from satellite and in situ observations. The model has sophisticated treatments of aerosol and snowpack radiative and thermodynamic processes that compare well with observations of snow albedo evolution and impurity concentration. This presentation focuses on the individual and combined contributions of present day dust and soot to snow-albedo forcing and on the global temperature and snowpack responses. Results are emphasized near India and East Asia, where the anthropogenic aerosol forcing of surface albedo and hydrology is greatest. We find that dust and black carbon (BC) aerosols have climate change efficacies (surface temperature change per unit forcing) about 3--4 times greater than CO2, making them the most efficacious forcing agents known. We estimate present day dust and soot snowpack-forcing of ~ 0.050 W m-2 warms global climate by ~ 0.16 °K. Anthropogenic soot from fossil fuel sources causes more than 50% of this warming, and biomass burning can account for up to 30% in strong tropical or boreal burn years. The greatest forcings occur in the Tarim/Mongol region (due to dust), northeastern China (due to soot), and the Tibetan Plateau (both). Dirty springtime snow in these regions can darken albedo by more than 0.1 and increase surface absorption by more than 20 W m-2. These results have implications for the strength of the Asian Monsoon, which is negatively correlated with antecedent snow cover in non-ENSO years. Dust and soot have such strong efficacies because they increase spring melt rates thus reduce summer snow cover. In some regions and seasons, dirty snow reduces snowpack depth and cover by 50%, triggering strong snow and sea-ice albedo feedbacks.

Martian neutron leakage spectra

NASA Astrophysics Data System (ADS)

Drake, D. M.; Feldman, W. C.; Jakosky, B. M.

1988-06-01

A high-energy nucleon-meson transport code is used to calculate energy spectra of Martian leakage neutrons. Four calculations are used to simulate a uniform surface layer containing various amounts of water, different burial depths of a 50 percent water layer underneath a 1 percent water layer, changing atmospheric pressure, and a thick carbon dioxide ice sheet overlying a "dirty" water ice sheet. Calculated spectra at energies less than about 1000 eV were fitted by a superposition of thermal and epithermal functions having four free parameters, two of which (thermal and epithermal amplitudes) were found to vary systematically and to specify uniquely the configuration in each of the series. Parameter variations depend on the composition of the assumed surface layers through the average atomic mass and the macroscopic scattering and absorption cross sections. It is concluded that measurements of leakage neutron spectra should allow determination of the hydrogen content of surface layers buried to depths up to about 100 g/sq. cm and determination of the thickness of a polar dry ice cap up to a thickness of about 250 g/sq. cm.

Prebiotic significance of extraterrestrial ice photochemistry: detection of hydantoin in organic residues.

PubMed

de Marcellus, Pierre; Bertrand, Marylène; Nuevo, Michel; Westall, Frances; Le Sergeant d'Hendecourt, Louis

2011-11-01

The delivery of extraterrestrial organic materials to primitive Earth from meteorites or micrometeorites has long been postulated to be one of the origins of the prebiotic molecules involved in the subsequent apparition of life. Here, we report on experiments in which vacuum UV photo-irradiation of interstellar/circumstellar ice analogues containing H(2)O, CH(3)OH, and NH(3) led to the production of several molecules of prebiotic interest. These were recovered at room temperature in the semi-refractory, water-soluble residues after evaporation of the ice. In particular, we detected small quantities of hydantoin (2,4-imidazolidinedione), a species suspected to play an important role in the formation of poly- and oligopeptides. In addition, hydantoin is known to form under extraterrestrial, abiotic conditions, since it has been detected, along with various other derivatives, in the soluble part of organic matter of primitive carbonaceous meteorites. This result, together with other related experiments reported recently, points to the potential importance of the photochemistry of interstellar "dirty" ices in the formation of organics in Solar System materials. Such molecules could then have been delivered to the surface of primitive Earth, as well as other telluric (exo-) planets, to help trigger first prebiotic reactions with the capacity to lead to some form of primitive biomolecular activity.

The (mis)measurement of the Dark Triad Dirty Dozen: exploitation at the core of the scale

PubMed Central

Kajonius, Petri J.; Persson, Björn N.; Rosenberg, Patricia

2016-01-01

Background. The dark side of human character has been conceptualized in the Dark Triad Model: Machiavellianism, psychopathy, and narcissism. These three dark traits are often measured using single long instruments for each one of the traits. Nevertheless, there is a necessity of short and valid personality measures in psychological research. As an independent research group, we replicated the factor structure, convergent validity and item response for one of the most recent and widely used short measures to operationalize these malevolent traits, namely, Jonason’s Dark Triad Dirty Dozen. We aimed to expand the understanding of what the Dirty Dozen really captures because the mixed results on construct validity in previous research. Method. We used the largest sample to date to respond to the Dirty Dozen (N = 3,698). We firstly investigated the factor structure using Confirmatory Factor Analysis and an exploratory distribution analysis of the items in the Dirty Dozen. Secondly, using a sub-sample (n = 500) and correlation analyses, we investigated the Dirty Dozen dark traits convergent validity to Machiavellianism measured by the Mach-IV, psychopathy measured by Eysenck’s Personality Questionnaire Revised, narcissism using the Narcissism Personality Inventory, and both neuroticism and extraversion from the Eysenck’s questionnaire. Finally, besides these Classic Test Theory analyses, we analyzed the responses for each Dirty Dozen item using Item Response Theory (IRT). Results. The results confirmed previous findings of a bi-factor model fit: one latent core dark trait and three dark traits. All three Dirty Dozen traits had a striking bi-modal distribution, which might indicate unconcealed social undesirability with the items. The three Dirty Dozen traits did converge too, although not strongly, with the contiguous single Dark Triad scales (r between .41 and .49). The probabilities of filling out steps on the Dirty Dozen narcissism-items were much higher than on the Dirty Dozen items for Machiavellianism and psychopathy. Overall, the Dirty Dozen instrument delivered the most predictive value with persons with average and high Dark Triad traits (theta > −0.5). Moreover, the Dirty Dozen scale was better conceptualized as a combined Machiavellianism-psychopathy factor, not narcissism, and is well captured with item 4: ‘I tend to exploit others towards my own end.’ Conclusion. The Dirty Dozen showed a consistent factor structure, a relatively convergent validity similar to that found in earlier studies. Narcissism measured using the Dirty Dozen, however, did not contribute with information to the core of the Dirty Dozen construct. More importantly, the results imply that the core of the Dirty Dozen scale, a manipulative and anti-social trait, can be measured by a Single Item Dirty Dark Dyad (SIDDD). PMID:26966673

The (mis)measurement of the Dark Triad Dirty Dozen: exploitation at the core of the scale.

PubMed

Kajonius, Petri J; Persson, Björn N; Rosenberg, Patricia; Garcia, Danilo

2016-01-01

Background. The dark side of human character has been conceptualized in the Dark Triad Model: Machiavellianism, psychopathy, and narcissism. These three dark traits are often measured using single long instruments for each one of the traits. Nevertheless, there is a necessity of short and valid personality measures in psychological research. As an independent research group, we replicated the factor structure, convergent validity and item response for one of the most recent and widely used short measures to operationalize these malevolent traits, namely, Jonason's Dark Triad Dirty Dozen. We aimed to expand the understanding of what the Dirty Dozen really captures because the mixed results on construct validity in previous research. Method. We used the largest sample to date to respond to the Dirty Dozen (N = 3,698). We firstly investigated the factor structure using Confirmatory Factor Analysis and an exploratory distribution analysis of the items in the Dirty Dozen. Secondly, using a sub-sample (n = 500) and correlation analyses, we investigated the Dirty Dozen dark traits convergent validity to Machiavellianism measured by the Mach-IV, psychopathy measured by Eysenck's Personality Questionnaire Revised, narcissism using the Narcissism Personality Inventory, and both neuroticism and extraversion from the Eysenck's questionnaire. Finally, besides these Classic Test Theory analyses, we analyzed the responses for each Dirty Dozen item using Item Response Theory (IRT). Results. The results confirmed previous findings of a bi-factor model fit: one latent core dark trait and three dark traits. All three Dirty Dozen traits had a striking bi-modal distribution, which might indicate unconcealed social undesirability with the items. The three Dirty Dozen traits did converge too, although not strongly, with the contiguous single Dark Triad scales (r between .41 and .49). The probabilities of filling out steps on the Dirty Dozen narcissism-items were much higher than on the Dirty Dozen items for Machiavellianism and psychopathy. Overall, the Dirty Dozen instrument delivered the most predictive value with persons with average and high Dark Triad traits (theta > -0.5). Moreover, the Dirty Dozen scale was better conceptualized as a combined Machiavellianism-psychopathy factor, not narcissism, and is well captured with item 4: 'I tend to exploit others towards my own end.' Conclusion. The Dirty Dozen showed a consistent factor structure, a relatively convergent validity similar to that found in earlier studies. Narcissism measured using the Dirty Dozen, however, did not contribute with information to the core of the Dirty Dozen construct. More importantly, the results imply that the core of the Dirty Dozen scale, a manipulative and anti-social trait, can be measured by a Single Item Dirty Dark Dyad (SIDDD).

Ice in Caspian Sea and Aral Sea, Kazakhstan

NASA Technical Reports Server (NTRS)

2002-01-01

In this MODIS image from December 3, 2001, winter sea ice can be seen forming in the shallow waters of the northern Caspian (left) and Aral (upper right) Seas. Despite the inflow of the Volga River (upper left), the northern portion of the Caspian Sea averages only 17 ft in depth, and responds to the region's continental climate, which is cold in winter and hot and dry in the summer. The southern part of the Sea is deeper and remains ice-free throughout the winter. The dirty appearance of the ice may be due to sediment in the water, but may also be due to wind-driven dust. The wind in the region can blow at hurricane-force strength and can cause the ice to pile up in hummocks that are anchored to the sea bottom. The eastern portion of the Aral Sea is also beginning to freeze. At least two characteristics of the Aral Sea 'compete' in determining whether its waters will freeze. The Sea is shallow, which increases the likelihood of freezing, but it is also very salty, which means that lower temperatures are required to freeze it than would be required for fresh water. With average December temperatures of 18o F, it's clearly cold enough to allow ice to form. As the waters that feed the Aral Sea continue to be diverted for agriculture, the Sea becomes shallower and the regional climate becomes even more continental. This is because large bodies of water absorb and retain heat, moderating seasonal changes in temperature. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

The rheology of icy satellites

NASA Technical Reports Server (NTRS)

Sammis, C. G.

1984-01-01

High-temperature creep in orthoenstatite under conditions of controlled oxygen fugacity was studied. It was found that creep was conttrolled by the extremely thin layer of SiO2 which wetted the grain boundaries. Slight reduction of the (Mg, Fe)SiO3 enstatite during hot pressing produced microscopic particles of Fe and the thin film of intergranular SiO2. This result highlights another complication in determining the flow properties of iron bearing silicates which constitute the bulk of terrestrial planets and moons. The Phenomenon may be important in the ductile formation of any extraterrestrial body which is formed in a reducing environment. The rheology of dirty ice was studied. This involves micromechanical modeling of hardening phenomena due to contamination by a cosmic distribution of silicate particles. The larger particles are modeled by suspension theory. In order to handle the distribution of particles sizes, the hardening is readed as a critical phenomenon, and real space renormalization group techniques are used. Smaller particles interact directly with the dislocations. The particulate hardening effect was studied in metals. The magnitude of such hardening in ice and the defect chemistry of ice are studied to assess the effects of chemical contamination by methane, ammonia, or other likely contaminants.

How to measure the thickness of dirty, wet Himalayan glaciers with low-frequency radar

NASA Astrophysics Data System (ADS)

Pritchard, Hamish; Mayer, Christoph; Lambrecht, Astrid

2017-04-01

High Mountain Asia holds 90,000 glaciers of which only around ten have any ice thickness measurements at all, and on any one glacier these tend to be sparsely distributed and not well suited to calculating glacier ice volume. Existing regional ice volume estimates come from indirect methods (based on area-volume scaling or modelled ice flux) that are poorly constrained in this region and so have a wide spread (e.g., 1670 to 6500 km3 (Bolch et al., 2012; Huss and Faranotti, 2012)). Sufficiently extensive measurements of ice thickness can be used to calculate ice volumes directly, or can be used to calibrate and hence improve the indirect estimates. Unfortunately, measuring ice thickness on such glaciers on a useful scale is difficult. They are often remote with very rough, water-logged and debris-covered ablation areas, a lossy environment for radar and quite different to clean and cold polar glaciers that lend themselves well to rapid radar surveying by snowmobile or aeroplane. A possible solution is to develop a low-frequency, helicopter-borne radar that can access remote mountain valleys and penetrate to the beds of the thickest of these mountain glaciers. But the lower the frequency, the longer the dipole and the more cumbersome the radar: what frequency do we need to detect the bed? Here we report results from pilot studies on the ground in the Langtang Valley and on Ngozumpa, Nepal's largest glacier, that show how bed detectability depends on frequency both in terms of signal attenuation and clutter, and what this means for a planned regional-scale glacier thickness surveys.

Debris-bed friction of hard-bedded glaciers

USGS Publications Warehouse

Cohen, D.; Iverson, N.R.; Hooyer, T.S.; Fischer, U.H.; Jackson, M.; Moore, P.L.

2005-01-01

[1] Field measurements of debris-bed friction on a smooth rock tablet at the bed of Engabreen, a hard-bedded, temperate glacier in northern Norway, indicated that basal ice containing 10% debris by volume exerted local shear traction of up to 500 kPa. The corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0.05 and 0.08. A model of friction in which nonrotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if the power law exponent for ice flowing past large clasts is 1. A small exponent (n < 2) is likely because stresses in ice are small and flow is transient. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed using n = 1 show that this force can reach values several hundred times that on a sphere isolated from the bed, thus drastically increasing frictional resistance. Various estimates of basal friction are obtained from this model. For example, the shear traction at the bed of a glacier sliding at 20 m a-1 with a geothermally induced melt rate of 0.006 m a-1 and an effective pressure of 300 kPa can exceed 100 kPa. Debris-bed friction can therefore be a major component of sliding resistance, contradicting the common assumption that debris-bed friction is negligible. Copyright 2005 by the American Geophysical Union.

Overcoming a Dirty Category: Cross-Cultural Experience in the American Classroom.

ERIC Educational Resources Information Center

Kim, Kyong L.

According to Edmund Leach (1976), boundaries are dirty. Yet power resides in the boundaries. As foreign-born instructors, the authors fall into a dirty category because they exist in cultural boundaries. This paper recognizes the American style of communication studies as a dirty category. This paper suggests that the authors' role be redefined in…

Development and applications of a radar-attenuation model for polar ice sheets

NASA Astrophysics Data System (ADS)

MacGregor, Joseph A.

Modern ice sheets are currently responding to significant climatic forcings and undergoing ice-dynamics changes that are not yet well understood. Ice-penetrating radar surveys are often used to infer their basal condition (e.g., is the bed wet or dry?) and internal properties. However, such inferences typically require a model of the electromagnetic attenuation through the ice sheet. Here I first develop and test a radar-attenuation model that is based on a synthesis of existing laboratory measurements of the dielectric properties of ice. This synthesis shows that radar attenuation in polar ice has a strong non-linear temperature dependence and a weaker linear dependence on the concentrations of acid and sea-salt chloride. This model was tested at Siple Dome, West Antarctica, using ice-core-chemistry and borehole-temperature data, and the model agreed well with an existing radar-attenuation measurement. I then use this model to investigate the nature of radar detection of accreted ice over Lake Vostok, East Antarctica. My analysis of ice-core and radar data found that the observed reflection is likely due to a fabric contrast near the boundary between the dirty and clean accreted ices. This reflection mechanism is also consistent with the spatial pattern of detection of the reflection. In anticipation of the requirements of a thermomechanical ice-sheet model to predict the spatial variation of attenuation over Lake Vostok, I develop an accumulation-rate map for the Lake Vostok region using radar data, a steady-state flow-band model, and inverse methods. I found that accumulation rates there are not inversely correlated with surface elevation, that there is a broad maximum above the lake's northwestern corner, and a minimum above most of its eastern shoreline. Finally, I investigate the spatial variability of attenuation in an ice sheet, using the flowline that crosses through the Vostok ice core as an example. I use radar layers and ice-velocity and temperature outputs from an ice-sheet model to estimate the spatial variation of attenuation using a series of progressively more complex models. I found that an attenuation-rate model that uses non-uniform ice temperatures and radar layers to rescale impurity-conentration profiles can satisfactorily capture most of the spatial variability of attenuation.

Unexpected Patterns in Snow and Dirt

NASA Astrophysics Data System (ADS)

Ackerson, Bruce J.

2018-01-01

For more than 30 years, Albert A. Bartlett published "Thermal patterns in the snow" in this journal. These are patterns produced by heat sources underneath the snow. Bartlett's articles encouraged me to pay attention to patterns in snow and to understanding them. At winter's end the last snow becomes dirty and is heaped into piles. This snow comes from the final clearing of sidewalks and driveways. The patterns observed in these piles defied my intuition. This melting snow develops edges where dirt accumulates, in contrast to ice cubes, which lose sharp edges and become more spherical upon melting. Furthermore, dirt absorbs more radiation than snow and yet doesn't melt and round the sharp edges of snow, where dirt accumulates.

ARC-1979-A79-7097

NASA Image and Video Library

1979-07-08

Range : 85,000 kilometers (53,000 miles) This photo of Jupiter's satellite Ganymede shows ancient cratered terrain. A variety of impact craters of different ages are shown. The brightest craters are the youngest. The ejecta blankets fade with age. The center shows a bright patch that represents the rebounding of the floor of the crater. The dirty ice has lost all topography except for faint circular patterns. Also shown are the 'Callisto type' curved troughs and ridges that mark an ancient enormous impact basin. The basin itself has been destroyed by later geologic processes. Only the ring features are preserved on the ancient surface. Near the bottom of the picture, these curved features are trumcated by the younger grooved terrain.

Exterior egg quality as affected by enrichment resources layout in furnished laying-hen cages.

PubMed

Li, Xiang; Chen, Donghua; Meng, Fanyu; Su, Yingying; Wang, Lisha; Zhang, Runxiang; Li, Jianhong; Bao, Jun

2017-10-01

This study aimed to investigate the effects of enrichment resources (a perch, dustbath, and nest) layout in furnished laying-hen cages (FC) on exterior quality of eggs. One hundred and sixty-eight (168) Hy-Line Brown laying hens at 16 weeks of age were randomly distributed to four treatments: small furnished cages (SFC), medium furnished cages type I (MFC-I), medium furnished cages type II (MFC-II), and medium furnished cages type III (MFC-III). Each treatment had 4 replicates or cages with 6 hens for SFC (24 birds for each SFC) and 12 hen/cage for MFC-I, -II, and -III (48 birds for each MFC-I, -II and -III). Following a 2-week acclimation, data collection started at 18 weeks of age and continued till 52 weeks of age. Dirtiness of egg surface or cracked shell as indicators of the exterior egg quality were recorded each week. The results showed that the proportion of cracked or dirty eggs was significantly affected by the FC type (p<0.01) in that the highest proportion of cracked or dirty eggs was found in MFC-I and the lowest proportion of dirty eggs in SFC. The results of this showed that furnished cage types affected both dirty eggs and cracked eggs (p<0.01). The results also indicated that not nest but dustbath lead to more dirty eggs. Only MFC-I had higher dirty eggs at nest than other FC (p< 0.01). The results of dirty eggs in MFC-I and MFC-II compared with SFC and MFC-III seemed suggest that a low position of dustbath led to more dirty eggs. SFC design affected exterior egg quality and the low position of dustbath in FC resulted in higher proportion of dirty eggs.

Caspian Sea

NASA Technical Reports Server (NTRS)

2002-01-01

In this Moderate-resolution Imaging Spectroradiometer (MODIS) image from December 3, 2001, winter sea ice can be seen forming in the shallow waters of the northern Caspian (left) and Aral (upper right) Seas. Despite the inflow of the Volga River (upper left), the northern portion of the Caspian Sea averages only 17 feet in depth, and responds to the region's continental climate, which is cold in winter and hot and dry in the summer. The southern part of the Sea is deeper and remains ice-free throughout the winter. The dirty appearance of the ice may be due to sediment in the water, but may also be due to wind-driven dust. The wind in the region can blow at hurricane-force strength and can cause the ice to pile up in hummocks that are anchored to the sea bottom. The eastern portion of the Aral Sea is also beginning to freeze. At least two characteristics of the Aral Sea 'compete' in determining whether its waters will freeze. The Sea is shallow, which increases the likelihood of freezing, but it is also very salty, which means that lower temperatures are required to freeze it than would be required for fresh water. With average December temperatures of 18oF, it's clearly cold enough to allow ice to form. As the waters that feed the Aral Sea continue to be diverted for agriculture, the Sea becomes shallower and the regional climate becomes even more continental. This is because large bodies of water absorb and retain heat, moderating seasonal changes in temperature. Image courtesy Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC

Domestic use of dirty energy and its effects on human health: empirical evidence from Bhutan

NASA Astrophysics Data System (ADS)

Rahut, Dil Bahadur; Ali, Akhter; Behera, Bhagirath

2017-11-01

Use of dirty fuels such as fuelwood, charcoal, cow dung and kerosene is common in developing countries, which adversely affects the health of people living in the dwellings, especially children and women. Using the data from a comprehensive and nationally representative Bhutan Living Standard Survey 2012, the present study examines the effects of dirty fuels on human health and household health expenditure. The result from propensity score-matching approach indicate that households using dirty fuels have a higher incidence of respiratory disease by 2.5-3% compared to households using cleaner fuels. The chances of household contracting tuberculosis are higher for households using dirty fuel in the range of 5-6%. It is also observed that the incidence of eye diseases and health expenditures among households using dirty fuels is higher. Hence the policy should focus on providing access to clean sources of energy to wider population.

Optical properties and molecular diversity of dissolved organic matter in the Bering Strait and Chukchi Sea

NASA Astrophysics Data System (ADS)

Gonsior, Michael; Luek, Jenna; Schmitt-Kopplin, Philippe; Grebmeier, Jacqueline M.; Cooper, Lee W.

2017-10-01

Changes in the molecular composition of dissolved organic matter (DOM) and its light absorbing chromophoric component (CDOM) are of particular interest in the Arctic region because of climate change effects that lead to warmer sea surface temperatures and longer exposure to sunlight. We used continuous UV-vis (UV-vis) spectroscopy, excitation emission matrix fluorescence and ultrahigh resolution mass spectrometry during a transect from the Aleutian Islands in the Bering Sea to the Chukchi Sea ice edge through Bering Strait to determine the variability of DOM and CDOM. These data were combined with discrete sampling for stable oxygen isotopes of seawater, in order to evaluate the contributions of melted sea ice versus runoff to the DOM and CDOM components. This study demonstrated that high geographical resolution of optical properties in conjunction with stable oxygen ratios and non-targeted ultrahigh resolution mass spectrometry was able to distinguish between different DOM sources in the Arctic, including identification of labile DOM sources in Bering Strait associated with high algal blooms and sampling locations influenced by terrestrially-derived DOM, such as the terrestrial DOM signal originating from Arctic rivers and dirty/anchor sea ice. Results of this study also revealed the overall variability and chemodiversity of Arctic DOM present in the Bering and Chukchi Seas.

Near-Infrared Monitoring of Volatiles in Frozen Lunar Simulants While Drilling

NASA Technical Reports Server (NTRS)

Roush, Ted L.; Colaprete, Anthony; Elphic, Richard C.; Forgione, Joshua; White, Bruce; McMurray, Robert; Cook, Amanda M.; Bielawski, Richard; Fritzler, Erin L.; Thompson, Sarah J.;

Dynamical conductivity at the dirty superconductor-metal quantum phase transition.

PubMed

Del Maestro, Adrian; Rosenow, Bernd; Hoyos, José A; Vojta, Thomas

2010-10-01

We study the transport properties of ultrathin disordered nanowires in the neighborhood of the superconductor-metal quantum phase transition. To this end we combine numerical calculations with analytical strong-disorder renormalization group results. The quantum critical conductivity at zero temperature diverges logarithmically as a function of frequency. In the metallic phase, it obeys activated scaling associated with an infinite-randomness quantum critical point. We extend the scaling theory to higher dimensions and discuss implications for experiments.

Ultrasound and Perforated Viscus; Dirty Fluid, Dirty Shadows, and Peritoneal Enhancement.

PubMed

Shokoohi, Hamid; S Boniface, Keith; M Abell, Bruce; Pourmand, Ali; Salimian, Mohammad

2016-01-01

Early detection of free air in the peritoneal cavity is vital in diagnosis of life-threatening emergencies, and can play a significant role in expediting treatment. We present a series of cases in which bedside ultrasound (US) in the emergency department accurately identified evidence of free intra-peritoneal air and echogenic (dirty) free fluid consistent with a surgical final diagnosis of a perforated hollow viscus. In all patients with suspected perforated viscus, clinicians were able to accurately identify the signs of pneumoperitoneum including enhanced peritoneal stripe sign (EPSS), peritoneal stripe reverberations, and focal air collections associated with dirty shadowing or distal multiple reflections as ring down artifacts. In all cases, hollow viscus perforation was confirmed surgically. It seems that, performing US in patients with suspected perforated viscus can accurately identify presence of intra-peritoneal echogenic or "dirty" free fluid as well as evidence of free air, and may expedite patient management.

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.

Modeling North American Ice Sheet Response to Changes in Precession and Obliquity

NASA Astrophysics Data System (ADS)

Tabor, C.; Poulsen, C. J.; Pollard, D.

2012-12-01

Milankovitch theory proposes that changes in insolation due to orbital perturbations dictate the waxing and waning of the ice sheets (Hays et al., 1976). However, variations in solar forcing alone are insufficient to produce the glacial oscillations observed in the climate record. Non-linear feedbacks in the Earth system likely work in concert with the orbital cycles to produce a modified signal (e.g. Berger and Loutre, 1996), but the nature of these feedbacks remain poorly understood. To gain a better understand of the ice dynamics and climate feedbacks associated with changes in orbital configuration, we use a complex Earth system model consisting of the GENESIS GCM and land surface model (Pollard and Thompson, 1997), the Pennsylvania State University ice sheet model (Pollard and DeConto, 2009), and the BIOME vegetation model (Kaplan et al., 2001). We began this study by investigating ice sheet sensitivity to a range of commonly used ice sheet model parameters, including mass balance and albedo, to optimize simulations for Pleistocene orbital cycles. Our tests indicate that choice of mass balance and albedo parameterizations can lead to significant differences in ice sheet behavior and volume. For instance, use of an insolation-temperature mass balance scheme (van den Berg, 2008) allows for a larger ice sheet response to orbital changes than the commonly employed positive degree-day method. Inclusion of a large temperature dependent ice albedo, representing phenomena such as melt ponds and dirty ice, also enhances ice sheet sensitivity. Careful tuning of mass balance and albedo parameterizations can help alleviate the problem of insufficient ice sheet retreat during periods of high summer insolation (Horton and Poulsen, 2007) while still accurately replicating the modern climate. Using our optimized configuration, we conducted a series of experiments with idealized transient orbits in an asynchronous coupling scheme to investigate the influence of obliquity and precession on the Laurentide and Cordillera ice sheets of North America. Preliminary model results show that the ice sheet response to changes in obliquity are larger than for precession despite providing a smaller direct insolation variation in the Northern Hemisphere high latitudes. A combination of enhanced Northern Hemisphere mid-latitude temperature gradient and longer cycle duration allow for a larger ice sheet response to obliquity than would be expected from insolation forcing alone. Conversely, a shorter duration dampens the ice sheet response to precession. Nevertheless, the precession cycle does cause significant changes in ice volume, a feature not observed in the Early Pleistocene δ18O records (Raymo and Nisancioglu, 2003). Future work will examine the climate response to an idealized transient orbit that includes concurrent variations in obliquity, precession, and eccentricity.

Dynamical conductivity at the dirty superconductor-metal quantum phase transition

NASA Astrophysics Data System (ADS)

Hoyos, J. A.; Del Maestro, Adrian; Rosenow, Bernd; Vojta, Thomas

2011-03-01

We study the transport properties of ultrathin disordered nanowires in the neighborhood of the superconductor-metal quantum phase transition. To this end we combine numerical calculations with analytical strong-disorder renormalization group results. The quantum critical conductivity at zero temperature diverges logarithmically as a function of frequency. In the metallic phase, it obeys activated scaling associated with an infinite-randomness quantum critical point. We extend the scaling theory to higher dimensions and discuss implications for experiments. Financial support: Fapesp, CNPq, NSF, and Research Corporation.

Ice Nucleation in the Tropical Tropopause Layer: Implications for Cirrus Occurrence, Cirrus Microphysical Properties, and Dehydration of Air Entering the Stratosphere

NASA Technical Reports Server (NTRS)

Jensen, Eric; Kaercher, Bernd; Ueyama, Rei; Pfister, Leonhard

2017-01-01

Recent laboratory experiments have advanced our understanding of the physical properties and ice nucleating abilities of aerosol particles atlow temperatures. In particular, aerosols containing organics will transition to a glassy state at low temperatures, and these glassy aerosols are moderately effective as ice nuclei. These results have implications for ice nucleation in the cold Tropical Tropopause Layer (TTL; 13-19 km). We have developed a detailed cloud microphysical model that includes heterogeneous nucleation on a variety of aerosol types and homogeneous freezing of aqueous aerosols. This model has been incorporated into one-dimensional simulations of cirrus and water vapor driven by meteorological analysis temperature and wind fields. The model includes scavenging of ice nuclei by sedimenting ice crystals. The model is evaluated by comparing the simulated cloud properties and water vapor concentrations with aircraft and satellite measurements. In this presentation, I will discuss the relative importance of homogeneous and heterogeneous ice nucleation, the impact of ice nuclei scavenging as air slowly ascends through the TTL, and the implications for the final dehydration of air parcels crossing the tropical cold-point tropopause and entering the tropical stratosphere.

Diverging effects of clean versus dirty money on attitudes, values, and interpersonal behavior.

PubMed

Yang, Qing; Wu, Xiaochang; Zhou, Xinyue; Mead, Nicole L; Vohs, Kathleen D; Baumeister, Roy F

2013-03-01

Does the cue of money lead to selfish, greedy, exploitative behaviors or to fairness, exchange, and reciprocity? We found evidence for both, suggesting that people have both sets of meaningful associations, which can be differentially activated by exposure to clean versus dirty money. In a field experiment at a farmers' market, vendors who handled dirty money subsequently cheated customers, whereas those who handled clean money gave fair value (Experiment 1). In laboratory studies with economic games, participants who had previously handled and counted dirty money tended toward selfish, unfair practices-unlike those who had counted clean money or dirty paper, both of which led to fairness and reciprocity. These patterns were found with the trust game (Experiment 2), the prisoner's dilemma (Experiment 4), the ultimatum game (Experiment 5), and the dictator game (Experiment 6). Cognitive measures indicated that exposure to dirty money lowered moral standards (Experiment 3) and reduced positive attitudes toward fairness and reciprocity (Experiments 6-7), whereas exposure to clean money had the opposite effects. Thus, people apparently have 2 contradictory sets of associations (including behavioral tendencies) to money, which is a complex, powerful, and ubiquitous aspect of human social life and cultural organization. PsycINFO Database Record (c) 2013 APA, all rights reserved

The Harmon Memorial Lectures in Military History 1959-1987

DTIC Science & Technology

1988-01-01

more treasure, eroded more humanity than the great conflicts. Dirty , grim combats they were, replete with piteous patriotism, with :.hining hero- ism...and the United States proved no exception. Americans had to learn to fight dirty and to keep what they won. Harsh as it seemed to many, this appeared...proper victory for a grim and dirty war. But Versailles statisfied no one, and Pershing noted with distaste the "Gen. .lon J. Pershing at general

Multilocus genetic characterization of two ant vectors (Group II "Dirty 22" species) known to contaminate food and food products and spread foodborne pathogens.

PubMed

Sulaiman, Irshad M; Anderson, Mickey; Oi, David H; Simpson, Steven; Kerdahi, Khalil

2012-08-01

The U.S. Food and Drug Administration utilizes the presence of filth and extraneous materials as one of the criteria for implementing regulatory actions and assessing adulteration of food products of public health importance. Twenty-two prevalent pest species (also known as the ''Dirty 22'' species) have been considered by this agency as possible vehicles for the spread of foodborne diseases, and the presence of these species is considered an indicator of unsanitary conditions in food processing and storage facilities. In a previous study, we further categorized the Dirty 22 species into four groups: group I includes four cockroach species, group II includes two ant species, group III includes 12 fly species, and group IV includes four rodent species. Here, we describe the development of three nested PCR primer sets and multilocus genetic characterization by amplifying the small subunit rRNA, elongation factor 1-alpha, and wingless (WNT-1) genes of group II Dirty 22 ant species Monomorium pharaonis and Solenopsis molesta. These novel group II Dirty 22 species-specific nested PCR primer sets can be used when the specimens cannot be identified using conventional microscopic methods. These newly developed assays will provide correct identification of group II Dirty 22 ant species, and the information can be used in the control of foodborne pathogens.

The Hidden Complexity of Biological "Dirty Bombs": Implications for Special Operations Medical Personnel.

PubMed

Washington, Michael A; Blythe, Jauchia

The recent capture of a terrorist in Belgium carrying explosives, fecal matter, and animal tissue may indicate a shift from conventional weapons to crude bacteriological preparations as instruments of terror. It is important to note that although such weapons lack technological sophistication, bacteria are inherently complex, unpredictable, and undetectable in the field. Therefore, it is important that Special Operations medical personnel understand the complications that such seemingly simple devices can add to the treatment of casualties in the field and subsequent evaluation in the clinic. 2016.

Ice-atmosphere interactions in the Canadian High Arctic: Implications for the thermo-mechanical evolution of terrestrial ice masses

NASA Astrophysics Data System (ADS)

Wohlleben, Trudy M. H.

Canadian High Arctic terrestrial ice masses and the polar atmosphere evolve codependently, and interactions between the two systems can lead to feedbacks, positive and negative. The two primary positive cryosphere-atmosphere feedbacks are: (1) The snow/ice-albedo feedback (where area changes in snow and/or ice cause changes in surface albedo and surface air temperatures, leading to further area changes in snow/ice); and (2) The elevation - mass balance feedback (where thickness changes in terrestrial ice masses cause changes to atmospheric circulation and precipitation patterns, leading to further ice thickness changes). In this thesis, numerical experiments are performed to: (1) quantify the magnitudes of the two feedbacks for chosen Canadian High Arctic terrestrial ice masses; and (2) to examine the direct and indirect consequences of surface air temperature changes upon englacial temperatures with implications for ice flow, mass flux divergence, and topographic evolution. Model results show that: (a) for John Evans Glacier, Ellesmere Island, the magnitude of the terrestrial snow/ice-albedo feedback can locally exceed that of sea ice on less than decadal timescales, with implications for glacier response times to climate perturbations; (b) although historical air temperature changes might be the direct cause of measured englacial temperature anomalies in various glacier and ice cap accumulation zones, they can also be the indirect cause of their enhanced diffusive loss; (c) while the direct result of past air temperature changes has been to cool the interior of John Evans Glacier, and its bed, the indirect result has been to create and maintain warm (pressure melting point) basal temperatures in the ablation zone; and (d) for Devon Ice Cap, observed mass gains in the northwest sector of the ice cap would be smaller without orographic precipitation and the mass balance---elevation feedback, supporting the hypothesis that this feedback is playing a role in the evolution of the ice cap.

Space Science Reference Guide, 2nd Edition

NASA Technical Reports Server (NTRS)

Dotson, Renee (Editor)

2003-01-01

This Edition contains the following reports: GRACE: Gravity Recovery and Climate Experiment; Impact Craters in the Solar System; 1997 Apparition of Comet Hale-Bopp Historical Comet Observations; Baby Stars in Orion Solve Solar System Mystery; The Center of the Galaxy; The First Rock in the Solar System; Fun Times with Cosmic Rays; The Gamma-Ray Burst Next Door; The Genesis Mission: An Overview; The Genesis Solar Wind Sample Return Mission; How to Build a Supermassive Black Hole; Journey to the Center of a Neutron Star; Kepler's Laws of Planetary Motion; The Kuiper Belt and Oort Cloud ; Mapping the Baby Universe; More Hidden Black Hole Dangers; A Polarized Universe; Presolar Grains of Star Dust: Astronomy Studied with Microscopes; Ring Around the Black Hole; Searching Antarctic Ice for Meteorites; The Sun; Astrobiology: The Search for Life in the Universe; Europa and Titan: Oceans in the Outer Solar System?; Rules for Identifying Ancient Life; Inspire ; Remote Sensing; What is the Electromagnetic Spectrum? What is Infrared? How was the Infrared Discovered?; Brief History of Gyroscopes ; Genesis Discovery Mission: Science Canister Processing at JSC; Genesis Solar-Wind Sample Return Mission: The Materials ; ICESat: Ice, Cloud, and Land Elevation Satellite ICESat: Ice, Cloud, and Land; Elevation Satellite ICESat: Ice, Cloud, and Land Elevation Satellite ICESat: Ice, Cloud, and Land Elevation Satellite ICESat: Ice, Cloud, and Land Elevation Satellite Measuring Temperature Reading; The Optical Telescope ; Space Instruments General Considerations; Damage by Impact: The Case at Meteor Crater, Arizona; Mercury Unveiled; New Data, New Ideas, and Lively Debate about Mercury; Origin of the Earth and Moon; Space Weather: The Invisible Foe; Uranus, Neptune, and the Mountains of the Moon; Dirty Ice on Mars; For a Cup of Water on Mars; Life on Mars?; The Martian Interior; Meteorites from Mars, Rocks from Canada; Organic Compounds in Martian Meteorites May be Terrestrial Contaminants; Bands on Europa;Big Mountain, Big Landslide on Jupiter's Moon, Io; Cratering of the Moon; Europa's Salty Surface; The Europa Scene in the Voyager-Galileo Era; Explosive Volcanic Eruptions on the Moon; Ice on the Bone Dry Moon; Jupiter's Hot, Mushy Moon; The Moon Beyond 2002 ; Phases of the Moon; The Ph-D Project: Manned Expedition to the Moons of Mars; and Possible Life in a Europan Ocean.

Enhancement of the Accelerating Gradient in Superconducting Microwave Resonators

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

Checchin, Mattia; Grassellino, Anna; Martinello, Martina

2017-05-01

The accelerating gradient of superconducting resonators can be enhanced by engineering the thickness of a dirty layer grown at the cavity's rf surface. In this paper the description of the physics behind the accelerating gradient enhancement by meaning of the dirty layer is carried out by solving numerically the the Ginzburg-Landau (GL) equations for the layered system. The calculation shows that the presence of the dirty layer stabilizes the Meissner state up to the lower critical field of the bulk, increasing the maximum accelerating gradient.

Reality Before Rhetoric: Toward An Air Force Narrative For The Early Mid 21st Century

DTIC Science & Technology

2016-06-01

politicians, and military leaders assumed that clean bombs were ideal for intervening in dirty wars where the adversary purposely blurred the...and Political Overview,” 15 21 Chivvis, “Strategic and Political Overview,” 19 22 Robert H. Gregory. Clean Bombs and Dirty Wars: Air Power in Kosovo...the ground are always " dirty " for those on the ground, and it is only an illusion that they can be won cheaply and "cleanly" through airpower

Integrating terrestrial and marine records of the LGM in McMurdo Sound, Antarctica: implications for grounded ice expansion, ice flow, and deglaciation of the Ross Sea Embayment

NASA Astrophysics Data System (ADS)

Christ, A. J.; Marchant, D. R.

2017-12-01

During the LGM, grounded glacier ice filled the Ross Embayment and deposited glacial drift on volcanic islands and peninsulas in McMurdo Sound, as well as along coastal regions of the Transantarctic Mountains (TAM), including the McMurdo Dry Valleys and Royal Society Range. The flow geometry and retreat history of this ice remains debated, with contrasting views yielding divergent implications for both the fundamental cause of Antarctic ice expansion as well as the interaction and behavior of ice derived from East and West Antarctica during late Quaternary time. We present terrestrial geomorphologic evidence that enables the reconstruction of former ice elevations, ice-flow paths, and ice-marginal environments in McMurdo Sound. Radiocarbon dates of fossil algae interbedded with ice-marginal sediments provide a coherent timeline for local ice retreat. These data are integrated with marine-sediment records and multi-beam data to reconstruct late glacial dynamics of grounded ice in McMurdo Sound and the western Ross Sea. The combined dataset suggest a dominance of ice flow toward the TAM in McMurdo Sound during all phases of glaciation, with thick, grounded ice at or near its maximum extent between 19.6 and 12.3 calibrated thousands of years before present (cal. ka). Our data show no significant advance of locally derived ice from the TAM into McMurdo Sound, consistent with the assertion that Late Pleistocene expansion of grounded ice in McMurdo Sound, and throughout the wider Ross Embayment, occurs in response to lower eustatic sea level and the resulting advance of marine-based outlet glaciers and ice streams (and perhaps also reduced oceanic heat flux), rather than local increases in precipitation and ice accumulation. Finally, when combined with allied data across the wider Ross Embayment, which show that widespread deglaciation outside McMurdo Sound did not commence until 13.1 ka, the implication is that retreat of grounded glacier ice in the Ross Embayment did not add significantly to SLR during Meltwater Pulse 1a (14.0-14.5 ka).

The adsorption of fungal ice-nucleating proteins on mineral dusts: a terrestrial reservoir of atmospheric ice-nucleating particles

NASA Astrophysics Data System (ADS)

O'Sullivan, Daniel; Murray, Benjamin J.; Ross, James F.; Webb, Michael E.

2016-06-01

The occurrence of ice-nucleating particles (INPs) in our atmosphere has a profound impact on the properties and lifetime of supercooled clouds. To date, the identities, sources and abundances of particles capable of nucleating ice at relatively low supercoolings (T > -15 °C) remain enigmatic. While biomolecules such as proteins and carbohydrates have been implicated as important high-temperature INPs, the lack of knowledge on the environmental fates of these species makes it difficult to assess their potential atmospheric impacts. Here we show that such nanoscale ice-nucleating proteins from a common soil-borne fungus (Fusarium avenaceum) preferentially bind to and confer their ice-nucleating properties to kaolinite. The ice-nucleating activity of the proteinaceous INPs is unaffected by adsorption to the clay, and once bound the proteins do not readily desorb, retaining much of the activity even after multiple washings with pure water. The atmospheric implications of the finding that biological residues can confer their ice-nucleating ability to dust particles are discussed.

Nuclear Radiation and the Thyroid

MedlinePlus

... can cause thyroid cancer. For example, a “dirty bomb” is not likely to contain radioactive iodine because it has a short half- life. (A “dirty bomb” is a conventional bomb mixed with radioactive material, ...

7 CFR 29.6012 - Dirty.

Code of Federal Regulations, 2010 CFR

2010-01-01

... INSPECTION Standards Definitions § 29.6012 Dirty. The state of tobacco containing an abnormal amount of dirt or sand, or tobacco to which additional quantities of dirt or sand have been added. (See Rule 17.) ...

7 CFR 29.1013 - Dirty.

Code of Federal Regulations, 2010 CFR

2010-01-01

... Type 92) § 29.1013 Dirty. The state of tobacco containing moderate to excessive amounts of dirt or sand, or tobacco to which additional quantities of dirt or sand have been added. (See Rule 24.) ...

Evidence that dirty electricity is causing the worldwide epidemics of obesity and diabetes.

PubMed

Milham, Samuel

2014-01-01

The epidemics of obesity and diabetes most apparent in recent years had their origins with Thomas Edison's development of distributed electricity in New York City in 1882. His original direct current (DC) generators suffered serious commutator brush arcing which is a major source of high-frequency voltage transients (dirty electricity). From the onset of the electrical grid, electrified populations have been exposed to dirty electricity. Diesel generator sets are a major source of dirty electricity today and are used almost universally to electrify small islands and places unreachable by the conventional electric grid. This accounts for the fact that diabetes prevalence, fasting plasma glucose and obesity are highest on small islands and other places electrified by generator sets and lowest in places with low levels of electrification like sub-Saharan Africa and east and Southeast Asia.

Fluctuating snow line altitudes in the Hunza basin (Karakoram) using Landsat OLI imagery

NASA Astrophysics Data System (ADS)

Racoviteanu, Adina; Rittger, Karl; Brodzik, Mary J.; Painter, Thomas H.; Armstrong, Richard

2016-04-01

Snowline altitudes (SLAs) on glacier surfaces are needed for separating snow and ice as input for melt models. When measured at the end of the ablation season, SLAs are used for inferring stable-state glacier equilibrium line altitudes (ELAs). Direct measurements of snowlines are rarely possible particularly in remote, high altitude glacierized terrain, but remote sensing data can be used to separate these snow and ice surfaces. Snow lines are commonly visible on optical satellite images acquired at the end of the ablation season if the images are contrasted enough, and are manually digitized on screen using various satellite band combinations for visual interpretation, which is a time-consuming, subjective process. Here we use Landsat OLI imagery at 30 m resolution to estimate glacier SLAs for a subset of the Hunza basin in the Upper Indus in the Karakoram. Clean glacier ice surfaces are delineated using a standardized semi-automated band ratio algorithm with image segmentation. Within the glacier surface, snow and ice are separated using supervised classification schemes based on regions of interest, and glacier SLAs are extracted on the basis of these areas. SLAs are compared with estimates from a new automated method that relies on fractional snow covered area rather than on band ratio algorithms for delineating clean glacier ice surfaces, and on grain size (instead of supervised classification) for separating snow from glacier ice on the glacier surface. The two methods produce comparable snow/ice outputs. The fSCA-derived glacierized areas are slightly larger than the band ratio estimates. Some of the additional area is the result of better detection in shadows from spectral mixture analysis (true positive) while the rest is shallow water, which is spectrally similar to snow/ice (false positive). On the glacier surface, a thresholding the snow grain size image (grain size > 500μm) results in similar glacier ice areas derived from the supervised classification, but there is noise (snow) on edges of dirty ice/ moraines at the glacier termini and around rock outcrops on the glacier surface. Neither of the two methods distinguishes the debris-covered ice, so these were mapped separately using a combination of topographic indices (slope, terrain curvature), along with remote sensing surface temperature and texture data. Using average elevation of snow and ice areas, we calculate an ELA of 5260 m for 2013. We construct yearly time series of the ELAs around the centerlines of selected glaciers in the Hunza for the period 2000 - 2014 using Landsat imagery. We explore spatial trends in glacier ELAs within the region, as well as relationships between ELA and topographic characteristics extracted on a glacier-by-glacier basis from a digital elevation model.

Electromagnetic hypersensitivity: biological effects of dirty electricity with emphasis on diabetes and multiple sclerosis.

PubMed

Havas, Magda

2006-01-01

Dirty electricity is a ubiquitous pollutant. It flows along wires and radiates from them and involves both extremely low frequency electromagnetic fields and radio frequency radiation. Until recently, dirty electricity has been largely ignored by the scientific community. Recent inventions of metering and filter equipment provide scientists with the tools to measure and reduce dirty electricity on electrical wires. Several case studies and anecdotal reports are presented. Graham/Stetzer (GS) filters have been installed in schools with sick building syndrome and both staff and students reported improved health and more energy. The number of students needing inhalers for asthma was reduced in one school and student behavior associated with ADD/ADHD improved in another school. Blood sugar levels for some diabetics respond to the amount of dirty electricity in their environment. Type 1 diabetics require less insulin and Type 2 diabetics have lower blood sugar levels in an electromagnetically clean environment. Individuals diagnosed with multiple sclerosis have better balance and fewer tremors. Those requiring a cane walked unassisted within a few days to weeks after GS filters were installed in their home. Several disorders, including asthma, ADD/ADHD, diabetes, multiple sclerosis, chronic fatigue, fibromyalgia, are increasing at an alarming rate, as is electromagnetic pollution in the form of dirty electricity, ground current, and radio frequency radiation from wireless devices. The connection between electromagnetic pollution and these disorders needs to be investigated and the percentage of people sensitive to this form of energy needs to be determined.

Rays as weapons.

PubMed

Vogel, H

2007-08-01

Ionizing radiation is being regarded as life threatening. Therefore, accidents in nuclear power plants are considered equal threatening as nuclear bomb explosions, and attacks with dirty bombs are thought as dangerous as nuclear weapon explosions. However, there are differences between a nuclear bomb explosion, the largest imaginable accident in a nuclear power plant, and an attack with a dirty bomb. It is intended to point them out. The processes are described, which damage in a nuclear bomb explosion, in the largest imaginable accident in a nuclear power plant, and in an attack with a dirty bomb. Their effects are compared with each other, i.e. explosion, heat, shock wave (blast), ionizing radiation, and fallout. In the center of the explosion of a nuclear bomb, the temperature rises to 100Mio degrees C, this induces damaging heat radiation and shock wave. In the largest imaginable accident in a nuclear power plant and in the conventional explosion of a dirty bomb, the temperature may rise up to 3000 degrees C, heat radiation and blast are limited to a short distance. In nuclear power plants, explosions due to oxyhydrogen gas or steam may occur. In nuclear explosions the dispersed radioactive material (fall out) consists mainly of isotopes with short half-life, in nuclear power plants and in dirty bomb attacks with longer half-life. The amount of fall out is comparable in nuclear bomb explosions with that in the largest imaginable accident in a nuclear power plant, it is smaller in attacks with dirty bombs. An explosion in a nuclear power plant even in the largest imaginable accident is not a nuclear explosion. In Hiroshima and Nagasaki, there were 200,000 victims nearly all by heat and blast, some 300 died by ionizing radiation. In Chernobyl, there have been less than 100 victims due to ionizing radiation up till now. A dirty bomb kills possibly with the explosion of conventional explosive, the dispersed radioactive material may damage individuals. The incorporation of irradiating substances may kill and be difficult to detect (Litvinenko). A new form of (government supported) terrorism/crime appears possible. The differences are important between a nuclear weapon explosion, the largest imaginable accident in a nuclear power plant, and an attack with a dirty bomb. Nuclear weapons kill by heat and blast; in the largest imaginable accident in a nuclear power plant, they are less strong and limited to the plant; an attack with a dirty bomb is as life threatening as an ("ordinary") bomb attack, dispersed radiating material may be a risk for individuals.

Dirty Electricity Elevates Blood Sugar Among Electrically Sensitive Diabetics and May Explain Brittle Diabetes

PubMed Central

Havas, Magda

2008-01-01

Transient electromagnetic fields (dirty electricity), in the kilohertz range on electrical wiring, may be contributing to elevated blood sugar levels among diabetics and prediabetics. By closely following plasma glucose levels in four Type 1 and Type 2 diabetics, we find that they responded directly to the amount of dirty electricity in their environment. In an electromagnetically clean environment, Type 1 diabetics require less insulin and Type 2 diabetics have lower levels of plasma glucose. Dirty electricity, generated by electronic equipment and wireless devices, is ubiquitous in the environment. Exercise on a treadmill, which produces dirty electricity, increases plasma glucose. These findings may explain why brittle diabetics have difficulty regulating blood sugar. Based on estimates of people who suffer from symptoms of electrical hypersensitivity (3–35%), as many as 5–60 million diabetics worldwide may be affected. Exposure to electromagnetic pollution in its various forms may account for higher plasma glucose levels and may contribute to the misdiagnosis of diabetes. Reducing exposure to electromagnetic pollution by avoidance or with specially designed GS filters may enable some diabetics to better regulate their blood sugar with less medication and borderline or pre-diabetics to remain non diabetic longer. PMID:18568931

7 CFR 29.3515 - Dirty.

Code of Federal Regulations, 2010 CFR

2010-01-01

... Type 95) § 29.3515 Dirty. The state of tobacco containing an abnormal amount of dirt or sand, or tobacco to which additional quantities of dirt or sand have been added. (See Rule 24, § 29.3625.) ...

Implications of Contingency Planning Support for Weather and Icing Information

NASA Technical Reports Server (NTRS)

Vigeant-Langlois, Laurence; Hansman, R. John, Jr.

2003-01-01

A human-centered systems analysis was applied to the adverse aircraft weather encounter problem in order to identify desirable functions of weather and icing information. The importance of contingency planning was identified as emerging from a system safety design methodology as well as from results of other aviation decision-making studies. The relationship between contingency planning support and information on regions clear of adverse weather was investigated in a scenario- based analysis. A rapid prototype example of the key elements in the depiction of icing conditions was developed in a case study, and the implications for the components of the icing information system were articulated.

The relationship between dairy cow hygiene and somatic cell count in milk.

PubMed

Sant'anna, A C; Paranhos da Costa, M J R

2011-08-01

Corporal hygiene is an important indicator of welfare for dairy cows and is dependent on facilities, climate conditions, and the behavior of the animals. The objectives of this study were to describe how the hygiene conditions of dairy cows vary over time and to assess whether a relationship exists between hygiene and somatic cell count (SCC) in milk. Monthly hygiene evaluations were conducted on lactating cows in 2 dairy farms for 9 consecutive months, totaling 3,554 evaluations from 545 animals. Hygiene was measured using a 4-point scoring system (very clean, clean, dirty, and very dirty) for 4 areas of the animal's body (leg, flank, abdomen, and udder) and combining these scores to generate a composite cleanliness score. A total of 2,218 milk samples was analyzed from 404 cows to determine SCC and somatic cell linear scores (SCLS). Individual variation was observed in the hygiene of cows throughout the year, with the highest proportion of clean cows being observed in August and the lowest in January. In spite of this seasonal variation, approximately half (55.62%) of the cows displayed consistent cleanliness scores, with 45.86% of them remaining consistently clean (very clean or clean) and 9.76% remaining dirty (very dirty or dirty) over the course of the study. The very clean cows had the lowest SCLS, followed by the clean, dirty, and very dirty cows (no statistically significant differences were found between the latter 2 groups). The most critical months for cow hygiene were those with the greatest rainfall, when a reduction in the welfare of cows and higher SCC values were observed. The evaluation and control of dairy cow hygiene are useful in defining management strategies to reduce problems with milk and improve the welfare of the animals. Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Mudstone sedimentation at high latitudes: Ice as a transport medium for mud and supplier of nutrients

USGS Publications Warehouse

Macquaker, J.H.S.; Keller, M.A.

2005-01-01

Controls on mudstone deposition at high latitudes are poorly known relative to low latitudes. In recent sediments deposited in these environments, ice significantly influences sediment transport and primary productivity. The products of ice transport are relatively well known in glacimarine settings, but are less well known from below melting sea ice. This latter setting is significant as today it is associated with high primary organic productivity. The aim of this study is to assess how sea ice might have controlled lithofacies variability and organic-matter distribution and preservation in an ancient marine, siliciclastic mudstone-dominated succession deposited at high latitudes. Combined sedimentary logging, optical and electron optical (back-scatte red electron imagery), geochemical, and isotopic methods were used to determine sample variability in forty-five samples collected from the Lower Cretaceous succession in the Mikkelsen Bay State #1 borehole (North Slope, Alaska). The succession overall fines upward and contains muddy sandstones and sand- and silt-bearing, clay-rich mudstones towards its base in contrast to clay-rich and clay-dominated mudstones towards its top. Some of the mudstone units exhibit thin (< 5 mm), relic-beds that fine upward weakly. In some units small (0.5 mm), bed-parallel silt-filled microburrows disrupt depositional laminae whereas in others pervasive burrowing completely obliterates original depositional textures. Many of the units are pelleted. These mudstones are unusual in that they contain minor but very striking outsize grains, composed of subrounded to rounded sand and granule-size material. In addition, they are good petroleum source rocks, with between 2.8 and 5.9 wt % total organic carbon, of predominantly Type II kerogen. The organic matter has an isotopic signature ranging from -25.4??? ??13C to -28.1??? ??13C. Thin tuffs (< 20 mm) and carbonate-cemented units are also present. Given the absence of significant polar ice in the Early Cretaceous the outsized grains are interpreted to have been deposited from a combination of melting, dirty anchor, and fast ice. The mud fraction, which forms the bulk of the sediment, is interpreted to have been deposited from melting, sediment-laden frazil ice, and fast ice. After deposition sediments were partially reworked by bottom currents generated by brine rejection during sea ice formation. Sympagic organisms, grazing on algae and bacteria both within and below the ice, pelleted the sediment. Bioturbation, which varies through the succession, indicates that sedimentation probably occurred beneath a predominantly oxic or dysoxic water column. In this setting productivity was fueled by nutrients released from melting sea ice in the marginal ice zone. The good petroleum source potential of these mudstones is attributed to high organic productivity coupled to episodic and rapid sedimentation rather than existence of bottom-water anoxia linked to upwelling. Because sea-ice rafting was probably the dominant sediment transport mechanism it is not appropriate to use sequence stratigraphic methodology to predict lithofacies variability in this environment. Copyright ?? 2005, SEPM (Society for Sedimentary Geology).

Induction signals from Callisto's ionosphere and their implications on a possible subsurface ocean

NASA Astrophysics Data System (ADS)

Hartkorn, Oliver; Saur, Joachim

2017-11-01

We investigate whether induction within Callisto's electrically conductive ionosphere can explain observed magnetic fields which have previously been interpreted as evidence of induction in a saline, electrically conductive subsurface ocean. Callisto's ionosphere is subject to the flow of time-periodic magnetized plasma of Jupiter's magnetosphere, which induces electric fields and electric currents in Callisto's electrically conductive ionosphere. We develop a simple analytic model for a first quantitative understanding of the effects of induction in Callisto's ionosphere caused by the interaction with a time-variable magnetic field environment. With this model, we also investigate how the associated ionospheric currents close in the ambient magnetospheric plasma. Based on our model, we find that the anisotropic nature of Callisto's ionospheric conductivity generates an enhancement effect on ionospheric loop currents which are driven by the time-variable magnetic field. This effect is similar to the Cowling channel effect known from Earth's ionosphere. Subsequently, we numerically calculate the expected induced magnetic fields due to Jupiter's time-variable magnetic field in an anisotropic conductive ionosphere and compare our results with the Galileo C-3 and C-9 flybys. We find that induction within Callisto's ionosphere is responsible for a significant part of the observed magnetic fields. Ionospheric induction creates induced magnetic fields to some extent similar as expected from a subsurface water ocean. Depending on currently unknown properties such as Callisto's nightside ionosphere, the existence of layers of "dirty ice" and the details of the plasma interaction, a water ocean might be located much deeper than previously thought or might not exist at all.

Pitted terrains on (1) Ceres and implications for shallow subsurface volatile distribution.

PubMed

Sizemore, H G; Platz, T; Schorghofer, N; Prettyman, T H; De Sanctis, M C; Crown, D A; Schmedemann, N; Neesemann, A; Kneissl, T; Marchi, S; Schenk, P M; Bland, M T; Schmidt, B E; Hughson, K H G; Tosi, F; Zambon, F; Mest, S C; Yingst, R A; Williams, D A; Russell, C T; Raymond, C A

2017-07-16

Prior to the arrival of the Dawn spacecraft at Ceres, the dwarf planet was anticipated to be ice-rich. Searches for morphological features related to ice have been ongoing during Dawn's mission at Ceres. Here we report the identification of pitted terrains associated with fresh Cerean impact craters. The Cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on Mars (where ice is implicated in pit development) and Vesta (where the presence of ice is debated). We employ numerical models to investigate the formation of pitted materials on Ceres and discuss the relative importance of water ice and other volatiles in pit development there. We conclude that water ice likely plays an important role in pit development on Ceres. Similar pitted terrains may be common in the asteroid belt and may be of interest to future missions motivated by both astrobiology and in situ resource utilization.

Pitted terrains on (1) Ceres and implications for shallow subsurface volatile distribution

USGS Publications Warehouse

Sizemore, H.G.; Platz, Thomas; Schorghofer, Norbert; Prettyman, Thomas; De Sanctis, Maria Christina; Crown, David A.; Schmedemann, Nico; Nessemann, Andeas; Kneissl, Thomas; Simone Marchi,; Schenk, Paul M.; Bland, Michael T.; Schmidt, B.E.; Hughson, Kynan H.G.; Tosi, F.; Zambon, F; Mest, S.C.; Yingst, R.A.; Williams, D.A.; Russell, C.T.; Raymond, C.A.

2017-01-01

Prior to the arrival of the Dawn spacecraft at Ceres, the dwarf planet was anticipated to be ice-rich. Searches for morphological features related to ice have been ongoing during Dawn's mission at Ceres. Here we report the identification of pitted terrains associated with fresh Cerean impact craters. The Cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on Mars (where ice is implicated in pit development) and Vesta (where the presence of ice is debated). We employ numerical models to investigate the formation of pitted materials on Ceres and discuss the relative importance of water ice and other volatiles in pit development there. We conclude that water ice likely plays an important role in pit development on Ceres. Similar pitted terrains may be common in the asteroid belt and may be of interest to future missions motivated by both astrobiology and in situ resource utilization.

Cocaine

MedlinePlus

... use among the nation’s youth. View Online Dirty Money and Cocaine Published: December 18, 2014 Dirty money: find out just how much of your cash ... June 27, 2018 NOTE: PDF documents require the free Adobe Reader . Flash content requires the free Adobe ...

The infrared spectral properties of frozen volatiles. [in cometary nuclei

NASA Technical Reports Server (NTRS)

Fink, U.; Sill, G. T.

1982-01-01

Since Whipple's dirty snowball model of comet nuclei, it has been generally accepted that volatile ices help to explain cometary phenomena. The infrared spectral properties of many substances that are potential candidates for frozen volatiles in the solar system are being pursued; indeed some of these frozen materials have been found in the solar system: H2O, CO2, and SO2. A review of laboratory spectra in the range 1 to 20 microns of H2O, CO2, SO2, CH4, NH3, H2S, CO, NH4HS and NH3.H2O is presented. Both reflection spectra of thick frosts and transmission spectra of thin films are shown, and their main characteristics are described. Hydrates, clathrates, and composite spectra are discussed. When it is possible to observe the nuclei of comets at close range, it may be possible to identify frozen volatiles by their infrared spectra.

Controls on Arctic sea ice from first-year and multi-year survival rates

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

Hunke, Jes

2009-01-01

The recent decrease in Arctic sea ice cover has transpired with a significant loss of multi year ice. The transition to an Arctic that is populated by thinner first year sea ice has important implications for future trends in area and volume. Here we develop a reduced model for Arctic sea ice with which we investigate how the survivability of first year and multi year ice control the mean state, variability, and trends in ice area and volume.

Driven by excess? Climatic implications of new global mapping of near-surface water-equivalent hydrogen on Mars

NASA Astrophysics Data System (ADS)

Pathare, Asmin V.; Feldman, William C.; Prettyman, Thomas H.; Maurice, Sylvestre

2018-02-01

We present improved Mars Odyssey Neutron Spectrometer (MONS) maps of near-surface Water-Equivalent Hydrogen (WEH) on Mars that have intriguing implications for the global distribution of "excess" ice, which occurs when the mass fraction of water ice exceeds the threshold amount needed to saturate the pore volume in normal soils. We have refined the crossover technique of Feldman et al. (2011) by using spatial deconvolution and Gaussian weighting to create the first globally self-consistent map of WEH. At low latitudes, our new maps indicate that WEH exceeds 15% in several near-equatorial regions, such as Arabia Terra, which has important implications for the types of hydrated minerals present at low latitudes. At high latitudes, we demonstrate that the disparate MONS and Phoenix Robotic Arm (RA) observations of near surface WEH can be reconciled by a three-layer model incorporating dry soil over fully saturated pore ice over pure excess ice: such a three-layer model can also potentially explain the strong anticorrelation of subsurface ice content and ice table depth observed at high latitudes. At moderate latitudes, we show that the distribution of recently formed impact craters is also consistent with our latest MONS results, as both the shallowest ice-exposing crater and deepest non-ice-exposing crater at each impact site are in good agreement with our predictions of near-surface WEH. Overall, we find that our new mapping is consistent with the widespread presence at mid-to-high Martian latitudes of recently deposited shallow excess ice reservoirs that are not yet in equilibrium with the atmosphere.

Formation of Mesospheric Clouds on Mars

NASA Astrophysics Data System (ADS)

Plane, J. M. C.; Audouard, J.; Listowski, C.; Mangan, T.; Maattanen, A. E.; Montmessin, F.; Forget, F.; Millour, E.; Spiga, A.; Crismani, M. M. J.; Schneider, N. M.

2017-12-01

Martian Mesospheric Clouds (MMCs) are observed intermittently in the Martian atmosphere between 60 and 100 km, occurring particularly at low latitudes. The clouds consist mainly of CO2-ice particles around 1 mm in radius. Explaining the nucleation and growth of these particles is challenging: it has been assumed that - by analogy with polar mesospheric clouds in the terrestrial atmosphere - nucleation occurs on meteoric smoke particles (very small metal-silicate particles resulting from the condensation of the vapor produced by cosmic dust ablation). Indeed, 1D modeling of CO2 microphysics suggests that an exogenous source of nuclei is necessary to model CO2 MMCs, in agreement with observations in cold pockets produced by the coupling of gravity waves and thermal tides. However, a recent laboratory study has shown that smoke particles, which would be around 1 nm in size - require extremely high CO2 supersaturations to nucleate CO2 ice. Here we present an alternative picture of the nucleation of CO2-ice particles. The major meteoric metals - Mg and Fe - should form MgCO3 and FeCO3 molecules in the Mars atmosphere below 90 km. These molecules have enormous electric dipole moments (11.6 and 9.3 Debye, respectively), and so will immediately form stable clusters with 3 CO2 molecules, which then slowly exchange with H2O to produce hexa-hydrated carbonate molecules. These primary particles polymerize readily to form a background population of "dirty" water-ice particles. Using MAVEN-IUVS measurements of the background Mg+ ion layer to constrain the injection rates of Mg and Fe from meteoric ablation, and a 1D model of metal chemistry coupled to an aerosol coagulation model, we show that the population of these water-ice particles with radii greater than 10 nm should be around 200 cm-3 at 80 km, thus providing a population of effective CO2-ice nuclei. When these nuclei are input in the Laboratoire de Météorologie Dynamique (LMD) Mars GCM, first results show that they can be activated in the upper mesosphere cold pockets and hence contribute to form CO­2-ice clouds whose characteristics (spatial and seasonal distribution, opacities, and particle sizes) are in agreement with observations.

Expanded Craters on Mars: Implications for Shallow, Mid-latitude Excess Ice

NASA Astrophysics Data System (ADS)

Viola, Donna

Understanding the age and distribution of shallow ice on Mars is valuable for interpreting past and present climate conditions, and has implications on habitability and future in situ resource utilization. Many ice-related features, such as lobate debris aprons and concentric crater fill, have been studied using a range of remote sensing techniques. Here, I explore the distribution of expanded craters, a form of sublimation thermokarst where shallow, excess ice has been destabilized and sublimated following an impact event. This leads to the collapse of the overlying dry regolith to produce the appearance of diameter widening. The modern presence of these features suggests that excess ice has remained preserved in the terrain immediately surrounding the craters since the time of their formation in order to maintain the surface. High-resolution imagery is ideal for observing thermokarst features, and much of the work described here will utilize data from the Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO). Expanded craters tend to be found in clusters that emanate radially from at least four primary craters in Arcadia Planitia, and are interpreted as secondary craters that formed nearly simultaneously with their primaries. Crater age dates of the primaries indicate that the expanded secondaries, as well as the ice layer into which they impacted, must be at least tens of millions of years old. Older double-layer ejecta craters in Arcadia Planitia commonly have expanded craters superposed on their ejecta - and they tend to be more expanded (with larger diameters) in the inner ejecta layer. This has implications on the formation mechanisms for craters with this unique ejecta morphology. Finally, I explore the distribution of expanded craters south of Arcadia Planitia and across the southern mid-latitudes, along with scalloped depressions (another form of sublimation thermokarst), in order to identify the modern excess ice boundary in this region and any longitudinal variations. This study identifies some potential low-latitude locations with patchy excess ice, possibly preserved during a past climate. Through these studies, I will infer regions that contain abundant ice today and consider the implications that this ice has on both the martian climate and future exploration.

The Aftermath of the Largest Cometary Outburst in Recorded History - An In-Depth Study of Comet 17P/Holmes

NASA Astrophysics Data System (ADS)

Stevenson, Rachel Ann

On UT 2007 Oct. 23, Jupiter Family comet 17P/Holmes underwent the largest cometary outburst in recorded history when it brightened by a factor of nearly a million in less than 2 days. This unprecedented event prompted a four-month observing campaign to observe the aftermath of the outburst. The wide field imager, MegaCam mounted on the Canada-France-Hawaii telescope was used to obtain r' images of the nucleus and the rapidly expanding dust coma. These images are unequaled in their quality and scope, and form a unique dataset with which to study the outburst aftermath. This original work examines the morphology of the outburst, and constrains the characteristics of the ejected material. Spatial filtering of images obtained in 2007 Nov. revealed numerous fragments moving away from the nucleus. The fragments were too bright to have been inactive, monolithic blocks and must have been acting as mini-comets with their own sources of sublimating volatiles and dust comae. They represented a significant (~ 10%) of the total ejected mass. The fragments had unusually high velocities relative to the nucleus, suggesting that they were accelerated by high gas pressure inside the nucleus prior to ejection. This work presents the first detection of such large, rapidly moving cometary fragments. The scarcity of similar ejecta around other fragmenting comets may be due to observational biases, rather than being unique to 17P/Holmes. Aperture photometry was used to study the evolution of the inner coma, which faded rapidly in the weeks and months following the initial outburst. Despite the observed fading, the nucleus must have remained active, continuing to supply fresh material to the inner coma. A second, much smaller outburst was detected on UT 2007 Nov. 12, which released an estimated 106 kg of dust into the inner coma. The secondary outburst showed that the nucleus remained unstable for several weeks after the initial event. Surface brightness profiles of the inner coma were constructed for each night of observation. The slopes of the profiles between 10000 km and 25000 km are consistent with dust grains fragmenting near the nucleus. Such fragmenting may be caused by thermal stressing or sublimation of cohesive volatiles. As the comet moved away from the Sun, the profiles also showed a persistent bump, interpreted as a halo of freshly released ice grains. The expected sublimation rates of such grains were examined, and it is concluded that the ice grains must have been contaminated with albedo-lowering regolith that significantly shortened their life-times. The possible characteristics of these dirty ice grains are examined within the context of the observations. The mini-comet fragments, dirty ice grains, and continuing but declining activity together suggest that the outburst of 17P/Holmes excavated material from within the nucleus, and left exposed patches of sublimating volatiles on its surface. The long-term fate of 17P/Holmes is uncertain, but micro-outbursts are likely as the nucleus settles over coming apparitions.

Development of a PCR-restriction fragment length polymorphism protocol for rapid detection and differentiation of four cockroach vectors (group I "Dirty 22" species) responsible for food contamination and spreading of foodborne pathogens: public health importance.

PubMed

Sulaiman, Irshad M; Anderson, Mickey; Khristova, Marina; Tang, Kevin; Sulaiman, Nikhat; Phifer, Edwin; Simpson, Steven; Kerdahi, Khalil

2011-11-01

Assessing the adulteration of food products and the presence of filth and extraneous materials is one of the measures that the U.S. Food and Drug Administration (FDA) utilizes in implementing regulatory actions of public health importance. To date, 22 common pest species (also known as the "Dirty 22" species) have been regarded by this agency as the spreaders of foodborne diseases. We have further categorized the Dirty 22 species into four groups: I has four cockroach species, II has two ant species, III has 12 fly species, and IV has four rodent species. The presence of any Dirty 22 species is also considered an indicator of unsanitary conditions in food processing and storage facilities. In this study, we describe the development of a two-step nested PCR protocol to amplify the small subunit ribosomal gene of group I Dirty 22 species that include four cockroach species: Blattella germanica, Blatta orientalis, Periplaneta americana, and Supella longipalpa, along with the development of a PCR-restriction fragment length polymorphism method for rapid detection and differentiation of these violative species. This method will be utilized when the specimen cannot be identified with conventional microscopic taxonomic methods, especially when only small body parts are separated and recovered from food samples for analysis or when these body parts are in a decomposed state. This new PCR-restriction fragment length polymorphism will provide correct identification of group I Dirty 22 species; this information can then be used in regulation and prevention of foodborne pathogens.

Impact of egg disinfection of hatching eggs on the eggshell microbiome and bacterial load.

PubMed

Olsen, R; Kudirkiene, E; Thøfner, I; Pors, S; Karlskov-Mortensen, P; Li, L; Papasolomontos, S; Angastiniotou, C; Christensen, J

2017-09-01

Disinfection of hatching eggs is essential to ensure high quality production of broilers. Different protocols are followed in different hatcheries; however, only limited scientific evidence on how the disinfection procedures impact the microbiome is available. The aim of the present study was to characterize the microbiome and aerobic bacterial load of hatching eggs before disinfection and during the subsequent disinfection steps. The study included a group of visibly clean and a group of visibly dirty eggs. For dirty eggs, an initial wash in chlorine was performed, hereafter all eggs were submitted to two times fumigation and finally spray disinfection. The eggshell microbiome was characterized by sequencing of the total amount of 16S rRNA extracted from each sample, consisting of shell surface swabs of five eggs from the same group. In addition, the number of colony forming units (cfu) under aerobic conditions was established for each disinfection step. The disinfection procedure reduced the bacterial load from more than 104 cfu (initially visibly clean eggs) and 105 cfu (initially visibly dirty eggs) to less than 10 cfu per sample after disinfection for both groups of eggs. The microbiome of both initially visibly clean and initially visibly dirty eggs had the highest abundances of the phyla Firmicutes, Proteobacteria and Bacteroidetes. Within the phyla Firmicutes the relative abundances of Clostridiales decreased while Lactobacillus increased from before to after final disinfection. In conclusion, the investigated disinfection procedure is effective in reducing the bacterial load, and by adding a chlorine wash for initially visibly dirty eggs, the microbiome of initially visibly clean and initially visibly dirty eggs had a highly similar microflora after the final disinfection step. © 2017 Poultry Science Association Inc.

Effect of housing conditions (clean vs. dirty) on growth performance and feeding behavior in growing pigs in a tropical climate.

PubMed

Renaudeau, D

2009-04-01

The effect of bad sanitary conditions on growth performance and feeding behaviour were studied on a total of 48 Large White pigs between 95 and 130 d of age. This experiment carried out during the hot season in a tropical humid climate. Two groups of 12 pigs each were housed in a clean environment in which the pens were disinfected thoroughly prior to stocking and maintained in a clean state by daily washing the pens and by weekly emptying the manure stored beneath the partial concrete floor. The dirty environment was achieved by not cleaning the pens prior to stocking or throughout the experiment and by storing the manure beneath the floor slats throughout the experimental period. The microbial pressure was increased by introducing 5 additional non experimental pigs near each experimental dirty pen. Feeding behaviour parameters were measured using automatic feed dispensers. Pigs housed in a clean environment consumed more feed (2.283 vs. 1.953 kg/d; P < 0.001) and grew faster (871 vs. 780 g/d; P < 0.05) than those housed in the dirty environment. No significant effect on treatment was reported for the feed conversion efficiency (2.70 kg/kg on average). The reduced average daily feed intake in dirty pens was associated with a reduction of the meal size (334 vs. 282 g/meal; P = 0.10) whereas the meal frequency was not affected by treatment (7.5 meals/d on average). The rate of feed intake was significantly higher in the clean than in the dirty environment (34.0 vs. 29.9 g/min; P < 0.05).

Ice cover extent drives phytoplankton and bacterial community structure in a large north-temperate lake: implications for a warming climate.

PubMed

Beall, B F N; Twiss, M R; Smith, D E; Oyserman, B O; Rozmarynowycz, M J; Binding, C E; Bourbonniere, R A; Bullerjahn, G S; Palmer, M E; Reavie, E D; Waters, Lcdr M K; Woityra, Lcdr W C; McKay, R M L

2016-06-01

Mid-winter limnological surveys of Lake Erie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice-free waters in 2012. Consistent with a warming climate, ice cover on the Great Lakes is in decline, thus the ice-free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally important shifts in phytoplankton and bacterial community structure. Expansive ice cover supported phytoplankton blooms of filamentous diatoms. By comparison, ice free conditions promoted the growth of smaller sized cells that attained lower total biomass. We propose that isothermal mixing and elevated turbidity in the absence of ice cover resulted in light limitation of the phytoplankton during winter. Additional insights into microbial community dynamics were gleaned from short 16S rRNA tag (Itag) Illumina sequencing. UniFrac analysis of Itag sequences showed clear separation of microbial communities related to presence or absence of ice cover. Whereas the ecological implications of the changing bacterial community are unclear at this time, it is likely that the observed shift from a phytoplankton community dominated by filamentous diatoms to smaller cells will have far reaching ecosystem effects including food web disruptions. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.

The Darkening of the Greenland Ice Sheet: Trends, Drivers and Projections (1981-2100)

NASA Technical Reports Server (NTRS)

Tedesco, Marco; Doherty, Sarah; Fettweis, Xavier; Alexander, Patrick; Jeyaratnam, Jeyavinoth; Stroeve, Julienne

2016-01-01

The surface energy balance and meltwater production of the Greenland ice sheet (GrIS) are modulated by snow and ice albedo through the amount of absorbed solar radiation. Here we show, using space-borne multispectral data collected during the 3 decades from 1981 to 2012, that summertime surface albedo over the GrIS decreased at a statistically significant (99 %) rate of 0.02 decade(sup -1) between 1996 and 2012. Over the same period, albedo modelled by the Modele Atmospherique Regionale (MAR) also shows a decrease, though at a lower rate (approximately -0.01 decade(sup -1)) than that obtained from space-borne data. We suggest that the discrepancy between modelled and measured albedo trends can be explained by the absence in the model of processes associated with the presence of light-absorbing impurities. The negative trend in observed albedo is confined to the regions of the GrIS that undergo melting in summer, with the dry snow zone showing no trend. The period 1981-1996 also showed no statistically significant trend over the whole GrIS. Analysis of MAR outputs indicates that the observed albedo decrease is attributable to the combined effects of increased near-surface air temperatures, which enhanced melt and promoted growth in snow grain size and the expansion of bare ice areas, and to trends in light-absorbing impurities (LAI) on the snow and ice surfaces. Neither aerosol models nor in situ and remote sensing observations indicate increasing trends in LAI in the atmosphere over Greenland. Similarly, an analysis of the number of fires and BC emissions from fires points to the absence of trends for such quantities. This suggests that the apparent increase of LAI in snow and ice might be related to the exposure of a "dark band" of dirty ice and to increased consolidation of LAI at the surface with melt, not to increased aerosol deposition. Albedo projections through to the end of the century under different warming scenarios consistently point to continued darkening, with albedo anomalies averaged over the whole ice sheet lower by 0.08 in 2100 than in 2000, driven solely by a warming climate. Future darkening is likely underestimated because of known underestimates in modelled melting (as seen in hindcasts) and because the model albedo scheme does not currently include the effects of LAI, which have a positive feedback on albedo decline through increased melting, grain growth, and darkening.

Ice formation in subglacial Lake Vostok, Central Antarctica

NASA Astrophysics Data System (ADS)

Souchez, R.; Petit, J. R.; Tison, J.-L.; Jouzel, J.; Verbeke, V.

2000-09-01

The investigation of chemical and isotopic properties in the lake ice from the Vostok ice core gives clues to the mechanisms involved in ice formation within the lake. A small lake water salinity can be reasonably deduced from the chemical data. Possible implications for the water circulation of Lake Vostok are developed. The characteristics of the isotopic composition of the lake ice indicate that ice formation in Lake Vostok occurred by frazil ice crystal generation due to supercooling as a consequence of rising waters and a possible contrast in water salinity. Subsequent consolidation of the developed loose ice crystals results in the accretion of ice to the ceiling of the lake.

Iapetus Bright and Dark Terrains

NASA Technical Reports Server (NTRS)

1990-01-01

Saturn's outermost large moon, Iapetus, has a bright, heavily cratered icy terrain and a dark terrain, as shown in this Voyager 2 image taken on August 22, 1981. Amazingly, the dark material covers precisely the side of Iapetus that leads in the direction of orbital motion around Saturn (except for the poles), whereas the bright material occurs on the trailing hemisphere and at the poles. The bright terrain is made of dirty ice, and the dark terrain is surfaced by carbonaceous molecules, according to measurements made with Earth-based telescopes. Iapetus' dark hemisphere has been likened to tar or asphalt and is so dark that no details within this terrain were visible to Voyager 2. The bright icy hemisphere, likened to dirty snow, shows many large impact craters. The closest approach by Voyager 2 to Iapetus was a relatively distant 600,000 miles, so that our best images, such as this, have a resolution of about 12 miles. The dark material is made of organic substances, probably including poisonous cyano compounds such as frozen hydrogen cyanide polymers. Though we know a little about the dark terrain's chemical nature, we do not understand its origin. Two theories have been developed, but neither is fully satisfactory--(1) the dark material may be organic dust knocked off the small neighboring satellite Phoebe and 'painted' onto the leading side of Iapetus as the dust spirals toward Saturn and Iapetus hurtles through the tenuous dust cloud, or (2) the dark material may be made of icy-cold carbonaceous 'cryovolcanic' lavas that were erupted from Iapetus' interior and then blackened by solar radiation, charged particles, and cosmic rays. A determination of the actual cause, as well as discovery of any other geologic features smaller than 12 miles across, awaits the Cassini Saturn orbiter to arrive in 2004.

Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales.

PubMed

Curran, P J; Desoky, W M; Milosević, M V; Chaves, A; Laloë, J-B; Moodera, J S; Bending, S J

2015-10-23

Scanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our films have much higher levels of disorder than bulk single crystals and therefore both superconducting condensates are expected to be pushed deep into the type 2 regime with purely repulsive vortex interactions. We observe broken symmetry vortex patterns at low fields in all samples after field-cooling from above Tc. These are consistent with those seen in systems with competing repulsions on disparate length scales, and remarkably similar structures are reproduced in dirty two band Ginzburg-Landau calculations, where the simulation parameters have been defined by experimental observations. This suggests that in our dirty MgB2 films, the symmetry of the vortex structures is broken by the presence of vortex repulsions with two different lengthscales, originating from the two distinct superconducting condensates. This represents an entirely new mechanism for spontaneous symmetry breaking in systems of superconducting vortices, with important implications for pinning phenomena and high current density applications.

Requirements for estimation of doses from contaminants dispersed by a 'dirty bomb' explosion in an urban area.

PubMed

Andersson, K G; Mikkelsen, T; Astrup, P; Thykier-Nielsen, S; Jacobsen, L H; Hoe, S C; Nielsen, S P

2009-12-01

The ARGOS decision support system is currently being extended to enable estimation of the consequences of terror attacks involving chemical, biological, nuclear and radiological substances. This paper presents elements of the framework that will be applied in ARGOS to calculate the dose contributions from contaminants dispersed in the atmosphere after a 'dirty bomb' explosion. Conceptual methodologies are presented which describe the various dose components on the basis of knowledge of time-integrated contaminant air concentrations. Also the aerosolisation and atmospheric dispersion in a city of different types of conceivable contaminants from a 'dirty bomb' are discussed.

Digital cleaning and "dirt" layer visualization of an oil painting.

PubMed

Palomero, Cherry May T; Soriano, Maricor N

2011-10-10

We demonstrate a new digital cleaning technique which uses a neural network that is trained to learn the transformation from dirty to clean segments of a painting image. The inputs and outputs of the network are pixels belonging to dirty and clean segments found in Fernando Amorsolo's Malacañang by the River. After digital cleaning we visualize the painting's discoloration by assuming it to be a transmission filter superimposed on the clean painting. Using an RGB color-to-spectrum transformation to obtain the point-per-point spectra of the clean and dirty painting images, we calculate this "dirt" filter and render it for the whole image.

Pitted terrains on (1) Ceres and implications for shallow subsurface volatile distribution

PubMed Central

Platz, T.; Schorghofer, N.; Prettyman, T. H.; De Sanctis, M. C.; Crown, D. A.; Schmedemann, N.; Neesemann, A.; Kneissl, T.; Marchi, S.; Schenk, P. M.; Bland, M. T.; Schmidt, B. E.; Hughson, K. H. G.; Tosi, F.; Zambon, F.; Mest, S. C.; Yingst, R. A.; Williams, D. A.; Russell, C. T.; Raymond, C. A.

2017-01-01

Abstract Prior to the arrival of the Dawn spacecraft at Ceres, the dwarf planet was anticipated to be ice‐rich. Searches for morphological features related to ice have been ongoing during Dawn's mission at Ceres. Here we report the identification of pitted terrains associated with fresh Cerean impact craters. The Cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on Mars (where ice is implicated in pit development) and Vesta (where the presence of ice is debated). We employ numerical models to investigate the formation of pitted materials on Ceres and discuss the relative importance of water ice and other volatiles in pit development there. We conclude that water ice likely plays an important role in pit development on Ceres. Similar pitted terrains may be common in the asteroid belt and may be of interest to future missions motivated by both astrobiology and in situ resource utilization. PMID:28989206

Arctic sea ice trends, variability and implications for seasonal ice forecasting

PubMed Central

Serreze, Mark C.; Stroeve, Julienne

2015-01-01

September Arctic sea ice extent over the period of satellite observations has a strong downward trend, accompanied by pronounced interannual variability with a detrended 1 year lag autocorrelation of essentially zero. We argue that through a combination of thinning and associated processes related to a warming climate (a stronger albedo feedback, a longer melt season, the lack of especially cold winters) the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. These findings have implications for seasonal ice forecasting. In particular, while advances in observing sea ice thickness and assimilating thickness into coupled forecast systems have improved forecast skill, there remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability. PMID:26032315

The significance of clean and dirty animals for bacterial dynamics along the beef chain.

PubMed

Hauge, Sigrun J; Nesbakken, Truls; Moen, Birgitte; Røtterud, Ole-Johan; Dommersnes, Sissel; Nesteng, Ole; Østensvik, Øyvin; Alvseike, Ole

2015-12-02

This study investigated the bacterial dynamics along the beef chain for clean and dirty cattle in the slaughter and processing lines, using classic quantitative methods and molecular analyses. In addition, the Norwegian national guidelines for Good Hygiene Practices in Norway were evaluated. In these guidelines, cattle presented for slaughter are categorised according to hide cleanliness, resulting in separate processing lines for meat from very dirty animals and reduced prices to farmers. The study was conducted in two commercial abattoirs in Norway. Two groups were compared; 40 visually clean cattle and 40 visually dirty cattle presented for slaughter, with 20 from each group at each abattoir. The same animals were sampled at five sampling sites: hides, carcass surfaces after dehiding, just before chilling, after chilling, and meat trimmings. Meat trimmings were sampled in only one abattoir. Three hundred and sixty samples were collected by swabbing 100 cm(2) of the brisket area at the first four sampling sites, and sampling 200 g of meat trimmings at the fifth site. The results showed that the hides of dirty cattle had more Enterobacteriaceae and higher Aerobic Plate Counts (APC) than visually clean cattle (P<0.05), however there was no significant difference for Escherichia coli. For the other sampling sites, there were no differences between the dirty and the clean group. An effect of chilling/drying of the carcass surfaces was demonstrated by the significant reduction in the number of carcasses on which E. coli and Enterobacteriaceae were detected; from 11% and 39% before chilling to 1% and 16% after chilling, respectively. Enterobacteriaceae and E. coli were detected in only three and one of the meat trimming samples, respectively. Amplification and sequencing of the 16S rRNA gene from 643 Enterobacteriaceae colonies derived from 107 samples demonstrated that Escherichia/Shigella were dominant within this family on the hides. However, after dehiding, after grading, and after chilling, the genera Citrobacter and Enterobacter dominated. The meat trimmings were dominated by the genera Kluyvera, Hafnia, and unclassified Enterobacteriaceae. The relative proportions of Escherichia/Shigella were higher for dirty animals than for clean animals, and were higher on hides than from sampling sites further down the chain (P<0.05). The minor differences in contamination on carcass surfaces and meat trimmings between clean and dirty cattle indicate that separate processing lines in Norwegian abattoirs seem to be unnecessary. Copyright © 2015 Elsevier B.V. All rights reserved.

The Depth of Ice Inside the Smallest Cold-Traps on Mercury: Implications for Age and Origin

NASA Astrophysics Data System (ADS)

Rubanenko, L.; Mazarico, E.; Neumann, G. A.; Paige, D. A.

2018-05-01

We use Mercury Laser Altimeter data and an illumination model to constrain the depth of the smallest ice deposits on Mercury. By comparing this depth to modeled gardening rates, we estimate the age and delivery method of this ice.

DirtyGrid I: 3D Dust Radiative Transfer Modeling of Spectral Energy Distributions of Dusty Stellar Populations

NASA Astrophysics Data System (ADS)

Law, Ka-Hei; Gordon, Karl D.; Misselt, Karl A.

2018-06-01

Understanding the properties of stellar populations and interstellar dust has important implications for galaxy evolution. In normal star-forming galaxies, stars and the interstellar medium dominate the radiation from ultraviolet (UV) to infrared (IR). In particular, interstellar dust absorbs and scatters UV and optical light, re-emitting the absorbed energy in the IR. This is a strongly nonlinear process that makes independent studies of the UV-optical and IR susceptible to large uncertainties and degeneracies. Over the years, UV to IR spectral energy distribution (SED) fitting utilizing varying approximations has revealed important results on the stellar and dust properties of galaxies. Yet the approximations limit the fidelity of the derived properties. There is sufficient computer power now available that it is now possible to remove these approximations and map out of landscape of galaxy SEDs using full dust radiative transfer. This improves upon previous work by directly connecting the UV, optical, and IR through dust grain physics. We present the DIRTYGrid, a grid of radiative transfer models of SEDs of dusty stellar populations in galactic environments designed to span the full range of physical parameters of galaxies. Using the stellar and gas radiation input from the stellar population synthesis model PEGASE, our radiative transfer model DIRTY self-consistently computes the UV to far-IR/sub-mm SEDs for each set of parameters in our grid. DIRTY computes the dust absorption, scattering, and emission from the local radiation field and a dust grain model, thereby physically connecting the UV-optical to the IR. We describe the computational method and explain the choices of parameters in DIRTYGrid. The computation took millions of CPU hours on supercomputers, and the SEDs produced are an invaluable tool for fitting multi-wavelength data sets. We provide the complete set of SEDs in an online table.

The Dirty Water Challenge

ERIC Educational Resources Information Center

Walker, Mark; Kremer, Angelika; Schluter, Kirsten

2007-01-01

"The Dirty Water Challenge" is a fun activity that teaches children about their environment in an engaging and practical way. Inquiry is embedded within the practical--students have to design, plan, and then build their own design of water filter. Students are exposed to important concepts from a variety of scientific disciplines, including how…

Spectral properties of ice-particulate mixtures and implications for remote sensing. 1. Intimate mixtures.

USGS Publications Warehouse

Clark, R.N.; Lucey, P.G.

1984-01-01

The spectral properties of water ice-partitioning mixtures are studied for the purpose of deriving the ice and particulate abundances from remotely obtained spectra (particulates referring to non-icy materials in the form of grains). Reflectance levels and ice absorption band depths are a complex function of the single scattering albedo of the particulates embedded in the ice. The ice absorption band depths are related to the mean optical path length of photons in ice through Beers law, Fresnel reflection from the ice-crystal faces on the surface, and ice absorption coefficient as a function of wavelength. Laboratory spectra of many ice- particulate mixtures are studied with high-, medium-, and low-albedo particulates.-from Authors

Surgical considerations in the management of combined radiation blast injury casualties caused by a radiological dirty bomb.

PubMed

Williams, Geraint; O'Malley, Michael

2010-09-01

The capacity for surgical teams to respond appropriately to the consequences caused by the detonation of a radiological dirty bomb will be determined by prior knowledge, familiarity and training for this type unique terrorist event. This paper will focus on the surgical aspects of this scenario with particular emphasis on the management of combined trauma-radiological injury. The paper also describes some of the more serious explosion-contamination incidents from nuclear industrial sources, summarises learning points and parallels taken from these scenarios in relation to subject of a radiological dirty bomb and describes the likely radioactive substances involved. 2010 Elsevier Ltd. All rights reserved.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Khain, A.; Simpson, S.

2004-01-01

Cloud microphysics are inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles (i.e., pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail). Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region, in the sub-tropics (Florida) and in the mid-latitude using identical thermodynamic conditions but with different concentrations of CCN: a low 'clean' concentration and a high 'dirty' concentration.

‘Schizophrenia is a dirty word’: service users’ experiences of receiving a diagnosis of schizophrenia

PubMed Central

Howe, Lorna; Tickle, Anna; Brown, Ian

2014-01-01

Aims and method To explore service users’ experiences of receiving a diagnosis of schizophrenia and the stigma associated with the diagnostic label. Seven participants were interviewed about their perceptions of these experiences. Interviews were analysed using interpretative phenomenological analysis. Results Five superordinate themes resulted from the analysis: (1) avoidance of the diagnosis of schizophrenia; (2) stigma and diagnostic labels; (3) lack of understanding of schizophrenia; (4) managing stigma to maintain normality; (5) being ‘schizophrenic’. These, together with their subthemes, highlighted avoidance of the term schizophrenia by participants and use of alternative terms by professionals, which limited opportunities for understanding the label and challenging associated stigma. Participants strived to maintain normality despite potential stigma. Clinical implications There is a need to address the process of giving a diagnosis as a phenomenon of consequence within its own terms. Implications relate to how professionals deliver and discuss the diagnosis of schizophrenia. PMID:25237536

Credibility of the threat from a radiological dispersal device by terrorists within the United States

DTIC Science & Technology

2016-06-10

on assessing the probability of an RDD attack, otherwise known as a “dirty bomb ,” within the US and its territories. Currently, there is an...officials arrested plotters planning to employ a dirty bomb utilizing americium obtained from smoke detectors.7 Officials thought it extremely unlikely

How training and experience affect the benefits of autonomy in a dirty-bomb experiment

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

David J. Bruemmer; Curtis W. Nielsen; David I. Gertman

2008-03-01

A dirty-bomb experiment conducted at the INL is used to evaluate the effectiveness and suitability of three different modes of robot control. The experiment uses three distinct user groups to understand how participants’ background and training affect the way in which they use and benefit from autonomy. The results show that the target mode, which involves automated mapping and plume tracing together with a point and click tasking tool, provides the best performance for each group. This is true for objective performance such as source detection and localization accuracy as well as subjective measures such as perceived workload, frustration andmore » preference. The best overall performance is achieved by the Explosive Ordinance Disposal group which has experience in both robot teleoperation and dirty bomb response. The user group that benefits least from autonomy is the Nuclear Engineers that have no experience with either robot operation or dirty bomb response. The group that benefits most from autonomy is the Weapons of Mass Destruction Civil Response Team that has extensive experience related to the task, but no robot training.« less

The Latest IceCube Results and the Implications

NASA Astrophysics Data System (ADS)

Mase, Keiichi

IceCube was built at the South Pole and aims to detect high energy neutrinos from the universe mainly above 100 GeV. The transparent ice media allows us to build a 1 km3 large detection volume to detect the rarely interacting particles. Neutrinos are thought to be generated at astrophysical sources such as active galactic nuclei and gamma-ray bursts. Nature of the rare interaction with matters and little deflection by a magnetic field makes it possible to explore such sources located at the deep universe. Since the neutrinos are produced through collisions of hadronic particles, the observation can elucidate the origin of cosmic rays, which is still mystery after the discovery 100 years ago. The detector was completed at the end of 2010 and is running smoothly. Recently, IceCube has found the first evidence of extraterrestrial neutrinos with energies above approximately 60 TeV. IceCube also contributes to elementary particle physics by searching for neutrinos produced in self-annihilation of SUSY particles such as neutralinos and by investigating atmospheric neutrino oscillations. The latest IceCube results and the corresponding implications are presented.

ULTRAVIOLET PHOTON-INDUCED SYNTHESIS AND TRAPPING OF H{sub 2}O{sub 2} AND O{sub 3} IN POROUS WATER ICE FILMS IN THE PRESENCE OF AMBIENT O{sub 2}: IMPLICATIONS FOR EXTRATERRESTRIAL ICE

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

Shi, J.; Raut, U.; Kim, J.-H.

2011-09-01

The mass uptake of ambient oxygen in nanoporous ice is enhanced by irradiation with 193 nm photons, due to conversion of O{sub 2} into H{sub 2}O{sub 2} and O{sub 3}, with an efficiency that increases with decreasing temperature. These findings show a new way to form H{sub 2}O{sub 2} and O{sub 3} on icy surfaces in the outer solar system at depths much larger than are accessible by typical ionizing radiation, with possible astrobiological implications.

Arctic sea ice trends, variability and implications for seasonal ice forecasting.

PubMed

Serreze, Mark C; Stroeve, Julienne

2015-07-13

September Arctic sea ice extent over the period of satellite observations has a strong downward trend, accompanied by pronounced interannual variability with a detrended 1 year lag autocorrelation of essentially zero. We argue that through a combination of thinning and associated processes related to a warming climate (a stronger albedo feedback, a longer melt season, the lack of especially cold winters) the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. These findings have implications for seasonal ice forecasting. In particular, while advances in observing sea ice thickness and assimilating thickness into coupled forecast systems have improved forecast skill, there remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Sulfur dioxide reactions on ice surfaces: Implications for dry deposition to snow

Treesearch

Martha H. Conklin; Richard A. Sommerfeld; S. Kay Laird; John E. Villinski

1993-01-01

Controlled exposure of ice to a reactive gas, SO2, demonstrated the importance of the chemical composition of the ice surface on the accumulation of acidity in snow. In a series of bench-scale continuous-flow column experiments run at four temperatures (-1, -8, -30 and -60°C), SO2 was shown to dissolve and to react with other species in the ice-air interfacial region...

Comets: Dirty snowballs or icy dirtballs

NASA Astrophysics Data System (ADS)

Keller, H. U.

1989-12-01

The observations of comet Halley show that the non-volatile (dust) component of the cometary nucleus has become more dominant if compared to the perception based on the icy conglomerate nucleus. The in-situ observations on the Giotto spacecraft revealed an excess of large dust particles that dominate the mass distribution. Even larger particles were derived from the attitude changes of the spacecraft bridging the gap to the cloud of particles observed by radar techniques. A dust to gas ratio larger than one was derived for comet Halley. The importance of dust for the structure of the nucleus is corroborated by the amount of particles and their lifetime in meteor streams. Fireballs show that large (meter size) objects separate from the nucleus and are stable enough to survive hundreds of orbital periods. From the various lines of evidence it is concluded that the structure of cometary nuclei is determined by the non-volatile component rather than by ice or snow. Laboratory models based on icy agglomerations do not seem realistic as nucleus analogs.

Klyuchevskaya, Volcano, Kamchatka Peninsula, CIS

NASA Image and Video Library

1991-05-06

STS039-77-010 (28 April 1991) --- The Kamchatka Peninsula, USSR. This oblique view of the eastern margin of the Kamchatka Peninsula shows pack-ice along the coast, which is drifting along with local currents and delineates the circulation patterns. Also visible are the Kamchatka River (left of center), and the volcanic complex with the active volcano Klyuchevskaya (Kloo-chevs'-ska-ya), 15,584 feet in elevation. The last reported eruption of the volcano was on April 8, but an ash and steam plume extending to the south can be seen in this photograph, taken almost three weeks later (April 28). On April 29, the crew observed and photographed the volcano again, and it was no longer visibly active. However, the flanks of the mountain are dirty from the ash fall. Just north of the Kamchatka River (to the left, just off frame) is Shiveluch, a volcano which was active in early April. There are more than 100 volcanic edifices recognized on Kamchatka, with 15 classified as active.

4.6 micron absorption features due to solid phase CO and cyano group molecules toward compact infrared sources

NASA Technical Reports Server (NTRS)

Lacy, J. H.; Baas, F.; Allamandola, L. J.; Van De Bult, C. E. P.; Persson, S. E.; Mcgregor, P. J.; Lonsdale, C. J.; Geballe, T. R.

1984-01-01

Spectra obtained at a resolving power of 840, for seven protostellar sources in the region of the 4.67-micron fundamental vibrational band of CO, indicate that the deep absorption feature in W33A near 4.61 microns consists of three features which are seen in other sources, but with varying relative strength. UV-irradiation laboratory experiments with 'dirty ice' temperature cycling allow the identification of two of the features cited with solid CO and CO complexed to other molecules. Cyano group-containing molecules have a lower vapor pressure than CO, and can therefore survive in much warmer environments. The formation and location of the CO- and CN-bearing grain mantles and sources of UV irradiation in cold molecular clouds are discussed. Plausible UV light sources can produce the observed cyano group features, but only under conditions in which local heat sources do not cause evaporation of the CO molecules prior to their photoprocessing.

Sexual Learning and the Seaside: Relocating the "Dirty Weekend" and Teenage Girls' Sexuality

ERIC Educational Resources Information Center

Hemingway, Judy

2006-01-01

This paper explores the geographical constitution of the "dirty weekend" and teenage girls' sexuality by interrogating the cultural habitus of the seaside resort. It reidentifies the littoral pleasure zone as an active agent in sexual learning and disrupts taken-for-granted inscriptions of the seaside as an inert backdrop against which…

What "Dirty Dancing" Taught Me about Media Literacy Education

ERIC Educational Resources Information Center

Fuxa, Robin

2012-01-01

The author reflects on her youthful viewing of "Dirty Dancing" on video against her parents' wishes as one example of the ineffectiveness of a protectionist approach to media. She offers ideas on how she and her students (pre-service and in-service educators) think through how to navigate selection of materials for effective media literacy…

Give Earth a Chance Series, Dirty Air, Trash Is Taking Over, Sounds and Silence, Pesticides Are Perilous, Tragedy in the Laundromat, Troublesome Tail Pipes.

ERIC Educational Resources Information Center

Minneapolis Independent School District 275, Minn.

These six booklets in the "Give Earth a Chance Series" are titled, "Dirty Air,""Trash is Taking Over,""Sounds and Silence,""Pesticides are Perilous,""Tragedy in the Laundromat," and "Troublesome Tail Pipes." The booklets are suitable for elementary use, and are intended to…

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.

Compression Freezing Kinetics of Water to Ice VII

DOE PAGES

Gleason, A. E.; Bolme, C. A.; Galtier, E.; ...

2017-07-11

Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6 nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. In conclusion, these first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

Compression Freezing Kinetics of Water to Ice VII

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

Gleason, A. E.; Bolme, C. A.; Galtier, E.

Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6 nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. In conclusion, these first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

Buried glacier ice in southern Iceland and its wider significance

NASA Astrophysics Data System (ADS)

Everest, Jeremy; Bradwell, Tom

2003-06-01

Geo-electrical resistivity surveys have been carried out at recently deglaciated sites in front of three glaciers in southern Iceland: Skeiðarájökull, Hrútárjökull, and Virkisjökull. The results show the presence of old glacier ice beneath debris mantles of various thickness. We conclude that buried glacier ice has survived for at least 50 years at Virkisjökull and Hrútárjökull, and probably for over 200 years at Skeiðarájökull. Additional data from a further site have identified a discontinuous ice core within 18th-century jökulhlaup deposits. Photographic and lichenometric evidence show that the overlying debris has been relatively stable, and hence melting of the ice at all four sites is proceeding slowly due to the heat-shielding properties of the overburden. The geomorphic implications are pertinent when considering the potential longevity of buried ice. The possible implications for dating techniques, such as lichenometry, radiocarbon dating and cosmogenic surface-exposure dating are also important, as long-term readjustments of surface forms may lead to dating inaccuracy. Finally, it is recognised that landscape development in areas of stagnant ice topography may post-date initial deglaciation by a considerable degree.

Climate, icing, and wild arctic reindeer: past relationships and future prospects.

PubMed

Hansen, Brage Bremset; Aanes, Ronny; Herfindal, Ivar; Kohler, Jack; Saether, Bernt-Erik

2011-10-01

Across the Arctic, heavy rain-on-snow (ROS) is an "extreme" climatic event that is expected to become increasingly frequent with global warming. This has potentially large ecosystem implications through changes in snowpack properties and ground-icing, which can block the access to herbivores' winter food and thereby suppress their population growth rates. However, the supporting empirical evidence for this is still limited. We monitored late winter snowpack properties to examine the causes and consequences of ground-icing in a Svalbard reindeer (Rangifer tarandus platyrhynchus) metapopulation. In this high-arctic area, heavy ROS occurred annually, and ground-ice covered from 25% to 96% of low-altitude habitat in the sampling period (2000-2010). The extent of ground-icing increased with the annual number of days with heavy ROS (> or = 10 mm) and had a strong negative effect on reindeer population growth rates. Our results have important implications as a downscaled climate projection (2021-2050) suggests a substantial future increase in ROS and icing. The present study is the first to demonstrate empirically that warmer and wetter winter climate influences large herbivore population dynamics by generating ice-locked pastures. This may serve as an early warning of the importance of changes in winter climate and extreme weather events in arctic ecosystems.

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

Connell, Leonard W.

We examined the relative risk and impact of a dirty bomb employing Co-60 and Cs-137, the two most common high activity source materials. We found that the risk of an area denial dirty bomb attack is greater for Cs-137 due to the form and chemistry of CsCl, the soft, powdery salt form currently in use for high activity Cs-137 sources, found in blood and research irradiators.

Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages.

USGS Publications Warehouse

Croft, S.K.; Kieffer, S.W.; Ahrens, T.J.

1979-01-01

We produced a series of decimeter-sized impact craters in blocks of ice near 0oC and -70oC and in ice-saturated sand near -70oC as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar satellites. Crater diameters in the ice-saturated sand were 2 times larger than craters in the same energy and velocity range in competent blocks of granite, basalt and cement. Craters in ice were c.3 times larger. Martian impact crater energy versus diameter scaling may thus be a function of latitude. -from Authors

Bifurcations of the Creation of Low-Temperature Maxima of the Tunneling Conductance of a "Dirty" N-I-N Junction

NASA Astrophysics Data System (ADS)

Kirpichenkov, V. Ya.; Kirpichenkova, N. V.; Lozin, O. I.; Pukhlova, A. A.

2017-05-01

The representation of the tunneling conductance G(T) of the "dirty" (with low concentrations of the same nonmagnetic impurities in the I layer) N-I-N junction (where N is a normal metal and I is an insulator) in the form of a sum of conductances of random quantum jumpers penetrating the disordered I layer is obtained in the low-temperature region. It is shown that the axis of the parameter δ = |ɛ0 - ɛF| giving the deviation of the energy of ɛ0 the quasi-local electron state on the impurity in the I layer from the Fermi energy of ɛF the dirty N-I-N junction contains a series of bifurcation points, at the transition through each of which (in the direction of the increase in δ) the number of maxima on the temperature dependence G(T) increases by unity; i.e., a new maximum is "born" on the curve G(T). Numerical estimates are given for the characteristic parameters of dirty N-I-N junctions indicating the possibility of the experimental observation of at least the first of these maxima.

Mitigation implications of an ice-free summer in the Arctic Ocean

NASA Astrophysics Data System (ADS)

González-Eguino, Mikel; Neumann, Marc B.; Arto, Iñaki; Capellán-Perez, Iñigo; Faria, Sérgio H.

2017-01-01

The rapid loss of sea ice in the Arctic is one of the most striking manifestations of climate change. As sea ice melts, more open water is exposed to solar radiation, absorbing heat and generating a sea-ice-albedo feedback that reinforces Arctic warming. Recent studies stress the significance of this feedback mechanism and suggest that ice-free summer conditions in the Arctic Ocean may occur faster than previously expected, even under low-emissions pathways. Here we use an integrated assessment model to explore the implications of a potentially rapid sea-ice-loss process. We consider a scenario leading to a full month free of sea ice in September 2050, followed by three potential trajectories afterward: partial recovery, stabilization, and continued loss of sea ice. We analyze how these scenarios affect the efforts to keep global temperature increase below 2°C. Our results show that sea-ice melting in the Arctic requires more stringent mitigation efforts globally. We find that global CO2 emissions would need to reach zero levels 5-15 years earlier and that the carbon budget would need to be reduced by 20%-51% to offset this additional source of warming. The extra mitigation effort would imply an 18%-59% higher mitigation cost to society. Our results also show that to achieve the 1.5°C target in the presence of ice-free summers negative emissions would be needed. This study highlights the need for a better understanding of how the rapid changes observed in the Arctic may impact our society.

Implications of a electroweak triplet scalar leptoquark on the ultra-high energy neutrino events at IceCube

NASA Astrophysics Data System (ADS)

Mileo, Nicolas; de la Puente, Alejandro; Szynkman, Alejandro

2016-11-01

We study the production of scalar leptoquarks at IceCube, in particular, a particle transforming as a triplet under the weak interaction. The existence of electroweak-triplet scalars is highly motivated by models of grand unification and also within radiative seesaw models for neutrino mass generation. In our framework, we extend the Standard Model by a single colored electroweak-triplet scalar leptoquark and analyze its implications on the excess of ultra-high energy neutrino events observed by the IceCube collaboration. We consider only couplings between the leptoquark to first generation of quarks and first and second generations of leptons, and carry out a statistical analysis to determine the parameters that best describe the IceCube data as well as set 95% CL upper bounds. We analyze whether this study is still consistent with most up-to-date LHC data and various low energy observables.

Selected physical, biological and biogeochemical implications of a rapidly changing Arctic Marginal Ice Zone

NASA Astrophysics Data System (ADS)

Barber, David G.; Hop, Haakon; Mundy, Christopher J.; Else, Brent; Dmitrenko, Igor A.; Tremblay, Jean-Eric; Ehn, Jens K.; Assmy, Philipp; Daase, Malin; Candlish, Lauren M.; Rysgaard, Søren

2015-12-01

The Marginal Ice Zone (MIZ) of the Arctic Ocean is changing rapidly due to a warming Arctic climate with commensurate reductions in sea ice extent and thickness. This Pan-Arctic review summarizes the main changes in the Arctic ocean-sea ice-atmosphere (OSA) interface, with implications for primary- and secondary producers in the ice and the underlying water column. Changes in the Arctic MIZ were interpreted for the period 1979-2010, based on best-fit regressions for each month. Trends of increasingly open water were statistically significant for each month, with quadratic fit for August-November, illustrating particularly strong seasonal feedbacks in sea-ice formation and decay. Geographic interpretations of physical and biological changes were based on comparison of regions with significant changes in sea ice: (1) The Pacific Sector of the Arctic Ocean including the Canada Basin and the Beaufort, Chukchi and East Siberian seas; (2) The Canadian Arctic Archipelago; (3) Baffin Bay and Hudson Bay; and (4) the Barents and Kara seas. Changes in ice conditions in the Barents sea/Kara sea region appear to be primarily forced by ocean heat fluxes during winter, whereas changes in the other sectors appear to be more summer-autumn related and primarily atmospherically forced. Effects of seasonal and regional changes in OSA-system with regard to increased open water were summarized for photosynthetically available radiation, nutrient delivery to the euphotic zone, primary production of ice algae and phytoplankton, ice-associated fauna and zooplankton, and gas exchange of CO2. Changes in the physical factors varied amongst regions, and showed direct effects on organisms linked to sea ice. Zooplankton species appear to be more flexible and likely able to adapt to variability in the onset of primary production. The major changes identified for the ice-associated ecosystem are with regard to production timing and abundance or biomass of ice flora and fauna, which are related to regional changes in sea-ice conditions.

Symmetry conditions of a nodal superconductor for generating robust flat-band Andreev bound states at its dirty surface

NASA Astrophysics Data System (ADS)

Ikegaya, Satoshi; Kobayashi, Shingo; Asano, Yasuhiro

2018-05-01

We discuss the symmetry property of a nodal superconductor that hosts robust flat-band zero-energy states at its surface under potential disorder. Such robust zero-energy states are known to induce the anomalous proximity effect in a dirty normal metal attached to a superconductor. A recent study has shown that a topological index NZES describes the number of zero-energy states at the dirty surface of a p -wave superconductor. We generalize the theory to clarify the conditions required for a superconductor that enables NZES≠0 . Our results show that NZES≠0 is realized in a topological material that belongs to either the BDI or CII class. We also present two realistic Hamiltonians that result in NZES≠0 .

Separation and Sealing of a Sample Container Using Brazing

NASA Technical Reports Server (NTRS)

Bar-Cohen, Yoseph; Rivellini, Tommaso P.; Wincentsen, James E.; Gershman, Robert

2007-01-01

A special double-wall container and a process for utilizing the container are being developed to enable (1) acquisition of a sample of material in a dirty environment that may include a biological and/or chemical hazard; (2) sealing a lid onto the inner part of the container to hermetically enclose the sample; (3) separating the resulting hermetic container from the dirty environment; and (4) bringing that hermetic container, without any biological or chemical contamination of its outer surface, into a clean environment. The process is denoted S(exp 3)B (separation, seaming, and sealing using brazing) because sealing of the sample into the hermetic container, separating the container from the dirty environment, and bringing the container with a clean outer surface into the clean environment are all accomplished simultaneously with a brazing operation.

Numerical modeling the formation of impact craters: Implications for the structure of Europa's ice shell

NASA Astrophysics Data System (ADS)

Silber, E. A.; Johnson, B. C.

2017-12-01

Craters produced by hypervelocity impacts are an invaluable tool for studying planetary surfaces. The observed impact crater depth-diameter (d-D) on the Galilean moon Europa exhibits three distinct transition regimes, two of which may correspond to the presence of warm convecting ice at depths of 7-8 km and a liquid ocean at 19-25 km, respectively [1]. In our study, we use iSALE2D to model formation of impact craters on Europa to investigate thickness and internal structure of its ice shell. This study is different from previous modeling studies [2,3] in that we consider the both fully conductive ice shell over ocean, as well as conductive lid overlying warm convecting ice, to discern the boundary conditions at the interface between the ice and the underlying ocean. Moreover, our model includes implementation of the full viscoelastic-plastic rheology for ice. Our results suggest that both conductive shell over ocean and conductive lid over warm convective ice are equally probable on Europa. We will discuss the implications and relevance of these results. The plausible scenarios are either a 6 - 7 km thick conductive ice lid overlying warm convecting ice at 265 K, or an 8 km completely conductive ice shell over ocean. Acknowledgements: We gratefully acknowledge the developers of iSALE-2D (www.isale-code.de), the simulation code used in our research, including G. Collins, K. Wünnermann, D. Elbeshausen, B. Ivanov and J. Melosh. References: [1] Schenk P. (2002) Nature, 417, 419-421. [2] Bray V.J. et al. (2014) Icarus, 231, 394-406. [3] Cox R. and Beuer A.W. (2015) JGR - Planets, 120(10), 1708-1719.

A national outbreak of Salmonella enteritidis infections from ice cream. The Investigation Team.

PubMed

Hennessy, T W; Hedberg, C W; Slutsker, L; White, K E; Besser-Wiek, J M; Moen, M E; Feldman, J; Coleman, W W; Edmonson, L M; MacDonald, K L; Osterholm, M T

1996-05-16

In September 1994, the Minnesota Department of Health detected an increase in the number of reports of Salmonella enteritidis infections. After a case-control study implicated a nationally distributed brand of ice cream (Schwan's) in the outbreak, the product was recalled and further epidemiologic and microbiologic investigations were conducted. We defined an outbreak-associated case of S. enteritidis infection as one in which S. enteritidis was cultured from a person who became ill in September or October 1994. We established national surveillance and surveyed customers of the implicated manufacturer. The steps involved in the manufacture of ice cream associated with cases of S. enteritidis infection were compared with those of products not known to be associated with infection matched for the date of manufacture. Cultures for bacteria were obtained from ice cream samples, the ice cream plant, and tanker trailers that had transported the ice cream base (premix) to the plant. We estimate that S. enteritidis gastroenteritis developed in 224,000 persons in the United States after they ate Schwan's ice cream. The attack rate for consumers was 6.6 percent. Ice cream associated with infection contained a higher percentage of premix that had been transported by tanker that had carried nonpasteurized eggs immediately before (P = 0.02). S. enteritidis was isolated from 8 of 226 ice cream products (3 percent), but not from environmental samples obtained from the ice cream plant (n = 157) or tanker trailers (n = 204). This nationwide outbreak of salmonellosis was most likely the result of contamination of pasteurized ice cream premix during transport in tanker trailers that had previously carried nonpasteurized liquid eggs containing S. enteritidis. To prevent further outbreaks, food products not destined for repasteurization should be transported in dedicated containers.

A review of the physics of ice surface friction and the development of ice skating.

PubMed

Formenti, Federico

2014-01-01

Our walking and running movement patterns require friction between shoes and ground. The surface of ice is characterised by low friction in several naturally occurring conditions, and compromises our typical locomotion pattern. Ice skates take advantage of this slippery nature of ice; the first ice skates were made more than 4000 years ago, and afforded the development of a very efficient form of human locomotion. This review presents an overview of the physics of ice surface friction, and discusses the most relevant factors that can influence ice skates' dynamic friction coefficient. It also presents the main stages in the development of ice skating, describes the associated implications for exercise physiology, and shows the extent to which ice skating performance improved through history. This article illustrates how technical and materials' development, together with empirical understanding of muscle biomechanics and energetics, led to one of the fastest forms of human powered locomotion.

Fracture propagation and stability of ice shelves governed by ice shelf heterogeneity

NASA Astrophysics Data System (ADS)

Borstad, Chris; McGrath, Daniel; Pope, Allen

2017-05-01

Tabular iceberg calving and ice shelf retreat occurs after full-thickness fractures, known as rifts, propagate across an ice shelf. A quickly evolving rift signals a threat to the stability of Larsen C, the Antarctic Peninsula's largest ice shelf. Here we reveal the influence of ice shelf heterogeneity on the growth of this rift, with implications that challenge existing notions of ice shelf stability. Most of the rift extension has occurred in bursts after overcoming the resistance of suture zones that bind together neighboring glacier inflows. We model the stresses in the ice shelf to determine potential rift trajectories. Calving perturbations to ice flow will likely reach the grounding line. The stability of Larsen C may hinge on a single suture zone that stabilizes numerous upstream rifts. Elevated fracture toughness of suture zones may be the most important property that allows ice shelves to modulate Antarctica's contribution to sea level rise.

Transport Processes in the Ice Shell of Europa — A Review

NASA Astrophysics Data System (ADS)

Rhoden, A. R.

2017-11-01

Recent models and observations of Europa's geologic activity suggest a dynamic ice shell, rich with liquid water, that may change in thickness and activity over time. Implications for Europa's habitability and future exploration will be discussed.

Reverse osmosis and ultrafiltration for recovery and reuse of larval rearing water in Anopheles arabiensis mass production: Effect of water quality on larval development and fitness of emerging adults.

PubMed

Mamai, Wadaka; Hood-Nowotny, Rebecca; Maiga, Hamidou; Ali, Adel Barakat; Bimbile-Somda, Nanwintoun S; Soma, Diloma Dieudonné; Yamada, Hanano; Lees, Rosemary Susan; Gilles, Jeremie R L

2017-06-01

Countries around the world are showing increased interest in applying the sterile insect technique against mosquito disease vectors. Many countries in which mosquitoes are endemic, and so where vector control using the sterile insect technique may be considered, are located in arid zones where water provision can be costly or unreliable. Water reuse provides an alternate form of water supply. In order to reduce the cost of mass rearing of Anopheles arabiensis mosquitoes, the possibility of recycling and reusing larval rearing water was explored. The used rearing water ('dirty water') was collected after the tilting of rearing trays for collection of larvae/pupae, and larvae/pupae separation events and underwent treatment processes consisting of ultrafiltration and reverse osmosis. First-instar An. arabiensis larvae were randomly assigned to different water-type treatments, 500 larvae per laboratory rearing tray: 'clean' dechlorinated water, routinely used in rearing; dirty water; and 'recycled' dirty water treated using reverse osmosis and ultrafiltration. Several parameters of insect quality were then compared: larval development, pupation rate, adult emergence, body size and longevity. Water quality of the samples was analyzed in terms of ammonia, nitrite, nitrate, sulphate, dissolved oxygen, chloride, and phosphate concentrations after the larvae had all pupated or died. Surface water temperatures were also recorded continuously during larval development. Pupation rates and adult emergence were similar in all water treatments. Adult body sizes of larvae reared in recycled water were similar to those reared in clean water, but larger than those reared in the dirty larval water treatment, whereas the adult longevity of larvae reared in recycled water was significantly increased relative to both 'clean' and 'dirty' water. Dirty larval water contained significantly higher concentrations of ammonium, sulfate, phosphate and chloride and lower levels of dissolved oxygen than clean water. These parameters significantly varied during the period of larval development. After dirty water was recycled by ultrafiltration and reverse osmosis, all the parameters measured were the same as those in clean water. This study demonstrated the potential for using recycled larval rearing water to supplement clean dechlorinated water supplies. Recycling used water improved its quality and of the reared mosquitoes. As water demands and environmental pressures grow, recycling of larval rearing water will improve the sustainability and affordability of mosquito mass-rearing. Copyright © 2017 Elsevier B.V. All rights reserved.

Measuring the muon content of air showers with IceTop

NASA Astrophysics Data System (ADS)

Gonzalez, Javier G.

2015-08-01

IceTop, the surface component of the IceCube detector, has been used to measure the energy spectrum of cosmic ray primaries in the range between 1.58 PeV and 1.26 EeV. It can also be used to study the low energy muons in air showers by looking at large distances (> 300 m) from the shower axis. We will show the muon lateral distribution function at large lateral distances as measured with IceTop and discuss the implications of this measurement. We will also discuss the prospects for low energy muon studies with IceTop.

Controls on Arctic sea ice from first-year and multi-year ice survival rates

NASA Astrophysics Data System (ADS)

Armour, K.; Bitz, C. M.; Hunke, E. C.; Thompson, L.

2009-12-01

The recent decrease in Arctic sea ice cover has transpired with a significant loss of multi-year (MY) ice. The transition to an Arctic that is populated by thinner first-year (FY) sea ice has important implications for future trends in area and volume. We develop a reduced model for Arctic sea ice with which we investigate how the survivability of FY and MY ice control various aspects of the sea-ice system. We demonstrate that Arctic sea-ice area and volume behave approximately as first-order autoregressive processes, which allows for a simple interpretation of September sea-ice in which its mean state, variability, and sensitivity to climate forcing can be described naturally in terms of the average survival rates of FY and MY ice. This model, used in concert with a sea-ice simulation that traces FY and MY ice areas to estimate the survival rates, reveals that small trends in the ice survival rates explain the decline in total Arctic ice area, and the relatively larger loss of MY ice area, over the period 1979-2006. Additionally, our model allows for a calculation of the persistence time scales of September area and volume anomalies. A relatively short memory time scale for ice area (~ 1 year) implies that Arctic ice area is nearly in equilibrium with long-term climate forcing at all times, and therefore observed trends in area are a clear indication of a changing climate. A longer memory time scale for ice volume (~ 5 years) suggests that volume can be out of equilibrium with climate forcing for long periods of time, and therefore trends in ice volume are difficult to distinguish from its natural variability. With our reduced model, we demonstrate the connection between memory time scale and sensitivity to climate forcing, and discuss the implications that a changing memory time scale has on the trajectory of ice area and volume in a warming climate. Our findings indicate that it is unlikely that a “tipping point” in September ice area and volume will be reached as the climate is further warmed. Finally, we suggest novel model validation techniques based upon comparing the characteristics of FY and MY ice within models to observations. We propose that keeping an account of FY and MY ice area within sea ice models offers a powerful new way to evaluate model projections of sea ice in a greenhouse warming climate.

An Examination of the Dirty Dozen Measure of Psychopathy: A Cautionary Tale about the Costs of Brief Measures

ERIC Educational Resources Information Center

Miller, Joshua D.; Few, Lauren R.; Seibert, L. Alana; Watts, Ashley; Zeichner, Amos; Lynam, Donald R.

2012-01-01

Given substantial interest in the traits conceived of as part of the "Dark Triad"--psychopathy, narcissism, and Machiavellianism--assessment of these traits is of great importance. The Dirty Dozen (DD; Jonason & Webster, 2010) is a brief measure of the Dark Triad constructs that uses 4 items to assess each of these constructs. In the present…

The defective nature of ice Ic and its implications for atmospheric science

NASA Astrophysics Data System (ADS)

Kuhs, W. F.; Hansen, T. C.

2009-04-01

The possible atmospheric implication of ice Ic (cubic ice) has already been suggested some time ago in the context of snow crystal formation [1]. New findings from air-borne measurements in cirrus clouds and contrails have put ice Ic into the focus of interest to understand the so-called "supersaturation puzzle" [2,3,4,5]. Our recent microstructural work on ice Ic [6,7] appears to be highly relevant in this context. We have found that ice Ic is characterized by a complex stacking fault pattern, which changes as a function of temperature as well as time. Indeed, from our own [8] and other group's work [9] one knows that (in contrast to earlier believe) ice Ic can form up to temperatures at least as high as 240K - thus in the relevant range for cirrus clouds. We have good preliminary evidence that the "cubicity" (which can be related to stacking fault probabilities) as well as the particle size of ice Ic are the relevant parameters for this correlation. The "cubicity" of stacking faulty ice Ic (established by diffraction) correlates nicely with the increased supersaturation at decreasing temperatures observed in cirrus clouds and contrails, a fact, which may be considered as further evidence for the presence of ice Ic. Moreover, the stacking faults lead to kinks in the outer shapes of the minute ice Ic crystals as seen by cryo scanning electron microscopy (cryo-SEM); these defective sites are likely to play some role in heterogeneous reactions in the atmosphere. The cryo-SEM work suggests that stacking-faulty ice Ic has many more active centres for such reactions than the usually considered thermodynamically stable form, ice Ih. [1] T Kobayashi & T Kuroda (1987) Snow Crystals. In: Morphology of Crystals (ed. I Sunagawa), Terra Scientific Publishing, Tokyo, pp.649-743. [2] DM Murphy (2003) Dehydration in cold clouds is enhanced by a transition from from cubic to hexagonal ice. Geophys.Res.Lett.,30, 2230, doi:10.1029/2003GL018566. [3] RS Gao & 19 other authors (2004) Evidence that nitric acid increases relative humidity in low-temperature cirrus clouds. Science 303, 516-520. [4] T Peter, C Marcolli, P Spaichinger, T Corti, MC Baker & T Koop (2006) When dry air is too humid. Science 314, 1399-1402. [5] JE Shilling, MA Tolbert, OB Toon, EJ Jensen, BJ Murray & AK Bertram (2006) Measurements of the vapor pressure of cubic ice and their implications for atmospheric ice clouds. Geophys.Res.Lett. 33, 026671. [6] TC Hansen, MM Koza & WF Kuhs (2008) Formation and annealing of cubic ice: I Modelling of stacking faults. J.Phys.Cond.Matt. 20, 285104. [7] TC Hansen, MM Koza, P Lindner & WF Kuhs (2008) Formation and annealing of cubic ice: II. Kinetic study. J.Phys.Cond.Matt. 20, 285105. [8] WF Kuhs, G Genov, DK Staykova & AN Salamatin (2004) Ice perfection and the onset of anomalous preservation of gas hydrates. Phys.Chem.Chem.Phys. 6, 4917-4920. [9] BJ Murray, DA Knopf & AK Bertram (2005) The formation of cubic ice under conditions relevant to Earth's atmosphere. Nature 434, 292-205.

Sea Ice Topography Profiling using Laser Altimetry from Small Unmanned Aircraft Systems

NASA Astrophysics Data System (ADS)

Crocker, Roger Ian

Arctic sea ice is undergoing a dramatic transition from a perennial ice pack with a high prevalence of old multiyear ice, to a predominantly seasonal ice pack comprised primarily of young first-year and second-year ice. This transition has brought about changes in the sea ice thickness and topography characteristics, which will further affect the evolution and survivability of the ice pack. The varying ice conditions have substantial implications for commercial operations, international affairs, regional and global climate, our ability to model climate dynamics, and the livelihood of Arctic inhabitants. A number of satellite and airborne missions are dedicated to monitoring sea ice, but they are limited by their spatial and temporal resolution and coverage. Given the fast rate of sea ice change and its pervasive implications, enhanced observational capabilities are needed to augment the current strategies. The CU Laser Profilometer and Imaging System (CULPIS) is designed specifically for collecting fine-resolution elevation data and imagery from small unmanned aircraft systems (UAS), and has a great potential to compliment ongoing missions. This altimeter system has been integrated into four different UAS, and has been deployed during Arctic and Antarctic science campaigns. The CULPIS elevation measurement accuracy is shown to be 95±25 cm, and is limited primarily by GPS positioning error (<25 cm), aircraft attitude determination error (<20 cm), and sensor misalignment error (<20 cm). The relative error is considerably smaller over short flight distances, and the measurement precision is shown to be <10 cm over a distance of 200 m. Given its fine precision, the CULPIS is well suited for measuring sea ice topography, and observed ridge height and ridge separation distributions are found to agree with theoretical distributions to within 5%. Simulations demonstrate the inability of course-resolution measurements to accurately represent the theoretical distributions, with differences up to 30%. Future efforts should focus on reducing the total measurement error to <20 cm to make the CULPIS suitable for detecting ice sheet elevation change.

Ice sublimation and rheology - Implications for the Martian polar layered deposits

NASA Astrophysics Data System (ADS)

Hofstadter, M. D.; Murray, B. C.

1990-04-01

If the sublimation and creep of water ice are important processes in the Martian polar layered deposits, ice-rich scenario formation and evolution schemes must invoke a mechanism for the inhibition of sublimation, such as a dust layer derived from the residue of the sublimating deposits. This layer could be of the order of 1 m in thickness. If the deposits are ice-rich, flows of more than 1 km should have occurred. It is noted that the dust particles in question may be cemented by such ice that may be present, but that impurities may also have served to cement dust particles together even in the absence of ice.

Ice sublimation and rheology - Implications for the Martian polar layered deposits

NASA Technical Reports Server (NTRS)

Hofstadter, Mark D.; Murray, Bruce C.

1990-01-01

If the sublimation and creep of water ice are important processes in the Martian polar layered deposits, ice-rich scenario formation and evolution schemes must invoke a mechanism for the inhibition of sublimation, such as a dust layer derived from the residue of the sublimating deposits. This layer could be of the order of 1 m in thickness. If the deposits are ice-rich, flows of more than 1 km should have occurred. It is noted that the dust particles in question may be cemented by such ice that may be present, but that impurities may also have served to cement dust particles together even in the absence of ice.

Possible significance of cubic water-ice, H2O-Ic, in the atmospheric water cycle of Mars

NASA Technical Reports Server (NTRS)

Gooding, James L.

1988-01-01

The possible formation and potential significance of the cubic ice polymorph on Mars is discussed. When water-ice crystallizes on Earth, the ambient conditions of temperature and pressure result in the formation of the hexagonal ice polymorph; however, on Mars, the much lower termperature and pressures may permit the crystallization of the cubic polymorph. Cubic ice has two properties of possible importance on Mars: it is an excellant nucleator of other volatiles (such as CO2), and it undergoes an exothermic transition to hexagonal ice at temperatures above 170 K. These properties may have significant implications for both martian cloud formation and the development of the seasonal polar caps.

Tandem transmission/reflection mode XRD instrument including XRF for in situ measurement of Martian rocks and soils

NASA Astrophysics Data System (ADS)

Delhez, Robert; Van der Gaast, S. J.; Wielders, Arno; de Boer, J. L.; Helmholdt, R. B.; van Mechelen, J.; Reiss, C.; Woning, L.; Schenk, H.

2003-02-01

The mineralogy of the surface material of Mars is the key to disclose its present and past life and climates. Clay mineral species, carbonates, and ice (water and CO2) are and/or contain their witnesses. X-ray powder diffraction (XRPD) is the most powerful analytical method to identify and quantitatively characterize minerals in complex mixtures. This paper discusses the development of a working model of an instrument consisting of a reflection mode diffractometer and a transmission mode CCD-XRPD instrument, combined with an XRF module. The CCD-XRD/XRF instrument is analogous to the instrument for Mars missions developed by Sarrazin et al. (1998). This part of the tandem instrument enables "quick and dirty" analysis of powdered (!) matter to monitor semi-quantitatively the presence of clay minerals as a group, carbonates, and ices and yields semi-quantitative chemical information from X-ray fluorescence (XRF). The reflection mode instrument (i) enables in-situ measurements of rocks and soils and quantitative information on the compounds identified, (ii) has a high resolution and reveals large spacings for accurate identification, in particular of clay mineral species, and (iii) the shape of the line profiles observed reveals the kind and approximate amounts of lattice imperfections present. It will be shown that the information obtained with the reflection mode diffractometer is crucial for finding signs of life and changes in the climate on Mars. Obviously this instrument can also be used for other extra-terrestrial research.

Were micrometeorites a source of prebiotic molecules on the early Earth?

PubMed

Maurette, M; Brack, A; Kurat, G; Perreau, M; Engrand, C

1995-03-01

"Interplanetary Dust Particles" with sizes approximately 10 micrometers collected in the stratosphere (IDPs), as well as much larger "giant" micrometeorites retrieved from Antarctic ice melt water (AMMs), are mostly composed of unequilibrated assemblages of minerals, thus being related to primitive unequilibrated meteorites. Two independent evaluations of the mass flux of micrometeorites measuring approximately 50 micrometers to approximately 200 micrometers, recovered from either the Greenland or the Antarctic ice sheets have been reported (approximately 20,000 tons/a). A comparison with recent evaluation of the flux of meteorites reaching the Earth's surface (up to masses of 10,000 tons), indicates that micrometeorites represent about 99.5% of the extraterrestrial material falling on the Earth's surface each year. As they show carbon concentrations exceeding that of the most C-rich meteorite (Orgueil), they are the major contributors of extraterrestrial C-rich matter accreting to the Earth today. Moreover they are complex microstructured aggregates of grains. They contain not only a variety of C-rich matter, such as a new "dirty" magnetite phase enriched in P, S, and minor elements, but also a diversity of potential catalysts (hydrous silicates, oxides, sulfides and metal grains of Fe/Ni composition, etc.). They could have individually functioned on the early Earth, as "micro-chondritic-reactors" for the processing of prebiotic organic molecules in liquid water. Future progress requires the challenging development of meaningful laboratory simulation experiments, and a better understanding of the partial reprocessing of micrometeorites in the atmosphere.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Khain, A.; Simpson, S.; Johnson, D.; Remer, L.

2004-01-01

Cloud microphysics is inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensembel (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region and in the mid-latitude continent with different concentrations of CCN: a low "c1ean"concentration and a high "dirty" concentration. In addition, differences and similarities between bulk microphysics and spectral-bin microphysical schemes will be examined and discussed.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Khain, A.; Simpson, S.; Johnson, D.; Remer, L.

2004-01-01

Cloud microphysics is inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, r d a U production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensembe1 (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and platelike), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region and in the mid-latitude continent with different concentrations of CCN: a low "c1ean"concentration and a high "dirty" concentration. In addition, differences and similarities between bulk microphysics and spectral-bin microphysical schemes will be examined and discussed.

Do European Standard Disinfectant tests truly simulate in-use microbial and organic soiling conditions on food preparation surfaces?

PubMed

Meyer, B; Morin, V N; Rödger, H-J; Holah, J; Bird, C

2010-04-01

The results from European standard disinfectant tests are used as one basis to approve the use of disinfectants in Europe. The design of these laboratory-based tests should thus simulate as closely as possible the practical conditions and challenges that the disinfectants would encounter in use. No evidence is available that the organic and microbial loading in these tests simulates actual levels in the food service sector. Total organic carbon (TOC) and total viable count (TVC) were determined on 17 visibly clean and 45 visibly dirty surfaces in two restaurants and the food preparation surfaces of a large retail store. These values were compared to reference values recovered from surfaces soiled with the organic and microbial loading, following the standard conditions of the European Surface Test for bactericidal efficacy, EN 13697. The TOC reference values for clean and dirty conditions were higher than the data from practice, but cannot be regarded as statistical outliers. This was considered as a conservative assessment; however, as additional nine TOC samples from visibly dirty surfaces were discarded from the analysis, as their loading made them impossible to process. Similarly, the recovery of test organisms from surfaces contaminated according to EN 13697 was higher than the TVC from visibly dirty surfaces in practice; though they could not be regarded as statistical outliers of the whole data field. No correlation was found between TVC and TOC in the sampled data, which re-emphasizes the potential presence of micro-organisms on visibly clean surfaces and thus the need for the same degree of disinfection as visibly dirty surfaces. The organic soil and the microbial burden used in EN disinfectant standards represent a realistic worst-case scenario for disinfectants used in the food service and food-processing areas.

Ugly ducklings-the dark side of plastic materials in contact with potable water.

PubMed

Neu, Lisa; Bänziger, Carola; Proctor, Caitlin R; Zhang, Ya; Liu, Wen-Tso; Hammes, Frederik

2018-01-01

Bath toys pose an interesting link between flexible plastic materials, potable water, external microbial and nutrient contamination, and potentially vulnerable end-users. Here, we characterized biofilm communities inside 19 bath toys used under real conditions. In addition, some determinants for biofilm formation were assessed, using six identical bath toys under controlled conditions with either clean water prior to bathing or dirty water after bathing. All examined bath toys revealed notable biofilms on their inner surface, with average total bacterial numbers of 5.5 × 10 6  cells/cm 2 (clean water controls), 9.5 × 10 6  cells/cm 2 (real bath toys), and 7.3 × 10 7  cells/cm 2 (dirty water controls). Bacterial community compositions were diverse, showing many rare taxa in real bath toys and rather distinct communities in control bath toys, with a noticeable difference between clean and dirty water control biofilms. Fungi were identified in 58% of all real bath toys and in all dirty water control toys. Based on the comparison of clean water and dirty water control bath toys, we argue that bath toy biofilms are influenced by (1) the organic carbon leaching from the flexible plastic material, (2) the chemical and biological tap water quality, (3) additional nutrients from care products and human body fluids in the bath water, as well as, (4) additional bacteria from dirt and/or the end-users' microbiome. The present study gives a detailed characterization of bath toy biofilms and a better understanding of determinants for biofilm formation and development in systems comprising plastic materials in contact with potable water.

Seasonal predictability of Arctic Sea Ice: assessing its limits and potential in a GCM and implications for observations.

NASA Astrophysics Data System (ADS)

Blanchard-Wrigglesworth, E.

2012-12-01

Arctic sea ice has exhibited a dramatic decrease both in area and thickness over the recent decades, particularly during the summer months. This decrease has led to growing interest in the potential predictability of summer sea ice, spurred in part by the socioeconomic implications. Here we present results of several parallel experiments designed to assess and understand the limits and potential for seasonal predictability of Arctic sea ice, with an emphasis on the summer minimum. Building on our experience from the SEARCH Outlook, we present results of a coupled general circulation model (GCM) hindcast simulation of Arctic summer sea ice variability for the satellite period (1979-present). These are initialized with spring sea ice volume anomalies obtained from a modelling and assimilation system, considered to be a close representation of reality. We show that there is significant predictability, yet the stochastic forcing imparted mainly by the atmosphere can lead to large errors in the hindcast. The model, however, can simulate anomalous runs that lie beyond a Gaussian distribution. Additionally, we investigate the regional characteristics of predictability and its links to sea ice dynamics and the spatio-temporal behavior of sea ice anomalies. We show a distinct difference between models. Unfortunately, observational data of thickness are not yet detailed enough to assess the models. Our results indicate the potential for detailed ice thickness observations in improving regional predictability. Finally, we discuss the importance of experiment design in predictability experiments, and show that predictions made with models that have a large mean state bias in sea ice require a careful initialization in order to fully capture all initial value predictability.

Assessment of the efficacy of benzalkonium chloride and sodium hypochlorite against Acanthamoeba polyphaga and Tetrahymena spp.

PubMed

Vaerewijck, M J M; Sabbe, K; Baré, J; Spengler, H-P; Favoreel, H W; Houf, K

2012-03-01

The efficacy of benzalkonium chloride and sodium hypochlorite against Acanthamoeba polyphaga and two Tetrahymena spp. was determined based on the European Standard EN 1276:2009 suspension test. Trophozoite viability was assessed by determination of the membrane integrity using flow cytometry as a fast screening technique. Bovine serum albumin was added to simulate clean (0.3 g/liter) and dirty (3 g/liter) conditions. Benzalkonium chloride caused cell lysis at concentrations above 50 mg/liter under clean and dirty conditions. A concentration of 50 mg of free chlorine per liter had a strong biocidal effect on acanthamoebae and tetrahymenae after 15 min under clean and dirty conditions. Our results suggest that benzalkonium chloride and sodium hypochlorite were effective against the three microorganisms at concentrations commonly applied in the food industry.

River-ice break-up/freeze-up: a review of climatic drivers, historical trends and future predictions

NASA Astrophysics Data System (ADS)

Prowse, T. D.; Bonsal, B. R.; Duguay, C. R.; Lacroix, M. P.

2007-10-01

River ice plays a fundamental role in biological, chemical and physical processes that control freshwater regimes of the cold regions. Moreover, it can have enormous economic implications for river-based developments. All such activities and processes can be modified significantly by any changes to river-ice thickness, composition or event timing and severity. This paper briefly reviews some of the major hydraulic, mechanical and thermodynamic processes controlling river-ice events and how these are influenced by variations in climate. A regional and temporal synthesis is also made of the observed historical trends in river-ice break-up/freeze-up occurrence from the Eurasian and North American cold regions. This involves assessment of several hydroclimatic variables that have influenced past trends and variability in river-ice break-up/freeze-up dates including air-temperature indicators (e.g. seasonal temperature, 0°C isotherm dates and various degree-days) and large-scale atmospheric circulation patterns or teleconnections. Implications of future climate change on the timing and severity of river-ice events are presented and discussed in relation to the historical trends. Attention is drawn to the increasing trends towards the occurrence of mid-winter break-up events that can produce especially severe flood conditions but prove to be the most difficult type of event to model and predict.

The Radiolytic Destruction of Glycine Diluted in H2O and CO2 Ice: Implications for Mars and Other Planetary Environments

NASA Astrophysics Data System (ADS)

Gerakines, Perry A.; Hudson, R. L.

2013-10-01

Future missions to Mars and other planetary surfaces will probe under the surfaces of these worlds for signs of organic chemistry. In previous studies we have shown that glycine and other amino acids have radiolytic destruction rates that depend on temperature and on dilution within an H2O ice matrix (Gerakines et al., 2012; Gerakines and Hudson 2013). In the new work presented here, we have examined the destruction of glycine diluted in CO2 ice at various concentrations and irradiated with protons at 0.8 MeV, typical of cosmic rays and solar energetic particles. Destruction rates for glycine were measured by infrared spectroscopy in situ, without removing or warming the ice samples. New results on the half life of glycine in solid CO2 will be compared to those found in H2O ice matrices. The survivability of glycine in icy planetary surfaces rich in H2O and CO2 ice will be discussed, and the implications for planetary science missions will be considered. References: Gerakines, P. A., Hudson, R. L., Moore, M. H., and Bell, J-L. (2012). In-situ Measurements of the Radiation Stability of Amino Acids at 15 - 140 K. Icarus, 220, 647-659. Gerakines, P. A. and Hudson, R. L. (2013). Glycine's Radiolytic Destruction in Ices: First in situ Laboratory Measurements for Mars. Astrobiology, 13, 647-655.

Evaporation of ice in planetary atmospheres - Ice-covered rivers on Mars

NASA Technical Reports Server (NTRS)

Wallace, D.; Sagan, C.

1979-01-01

The existence of ice covered rivers on Mars is considered. It is noted that the evaporation rate of water ice on the surface of a planet with an atmosphere involves an equilibrium between solar heating and radiative and evaporative cooling of the ice layer. It is determined that even with a mean Martian insolation rate above the ice of approximately 10 to the -8th g per sq cm/sec, a flowing channel of liquid water will be covered by ice which evaporates sufficiently slowly that the water below can flow for hundreds of kilometers even with modest discharges. Evaporation rates are calculated for a range of frictional velocities, atmospheric pressures, and insolations and it is suggested that some subset of observed Martian channels may have formed as ice-choked rivers. Finally, the exobiological implications of ice covered channels or lakes on Mars are discussed.

Massive subsurface ice formed by refreezing of ice-shelf melt ponds

PubMed Central

Hubbard, Bryn; Luckman, Adrian; Ashmore, David W.; Bevan, Suzanne; Kulessa, Bernd; Kuipers Munneke, Peter; Philippe, Morgane; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Tison, Jean-Louis; O'Leary, Martin; Rutt, Ian

2016-01-01

Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km across, several kilometres long and tens of metres deep, located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and radar measurements with remote sensing and firn modelling to investigate the layer, found to be ∼10 °C warmer and ∼170 kg m−3 denser than anticipated in the absence of ponding and hitherto used in models of ice-shelf fracture and flow. Surface ponding and ice layers such as the one we report are likely to form on a wider range of Antarctic ice shelves in response to climatic warming in forthcoming decades. PMID:27283778

Multilocus genetic characterization of two ant vectors (Group II ‘‘Dirty 22’’ species) known to contaminate food and food products and spread foodborne pathogens

USDA-ARS?s Scientific Manuscript database

The U.S. Food and Drug Administration utilizes the presence of filth and extraneous materials as one of the criteria for implementing regulatory actions and assessing adulteration of food products of public health importance. Twenty-two prevalent pest species (also known as the ‘‘Dirty 22’’ species)...

Mental contamination: the effects of imagined physical dirt and immoral behaviour.

PubMed

Elliott, Corinna M; Radomsky, Adam S

2012-06-01

There is a growing body of empirical support for Rachman's (1994, 2004, 2006) conceptualization of mental contamination. The aim of this study was to tease apart manipulations of imagined physical descriptions (i.e., clean versus dirty), in the context of both morally sound and reprehensible acts (i.e., consensual versus non-consensual kiss) to expand our understanding of the experimental variables which may evoke mental contamination and address limitations of previous research. Female undergraduate student participants (n = 140) were randomly assigned to listen to one of four audio recordings and imagine receiving either a consensual or non-consensual kiss from a man described as either physically clean or physically dirty. Results indicated that participants who imagined a non-consensual kiss from a physically dirty man reported the greatest feelings of mental contamination; whereas, participants who imagined a consensual kiss from a physically clean man reported the lowest feelings of mental contamination. However, there were few significant differences in mental contamination feelings between those who imagined a consensual kiss from a physically dirty man and those who imagined a non-consensual kiss from a physically clean man. Results are discussed in terms of cognitive-behavioural conceptualizations of and treatments for contamination fears. Copyright © 2012 Elsevier Ltd. All rights reserved.

Investigating the Equatorial Gaps in Snowball Earth Sea Glaciers

NASA Astrophysics Data System (ADS)

Spaulding-Astudillo, F.; Ashkenazy, Y.; Tziperman, E.; Abbot, D. S.

2017-12-01

The way photosynthetic life survived the Neoproterozoic Snowball Earth events is still a matter of debate that has deep implications for planetary habitability. One option is that gaps in thick, semi-global ice coverage (sea glaciers) could be maintained at the equator by ocean-ice-atmosphere dynamics. We investigate this idea by modifying a global ocean-thick-marine-ice model developed for modeling Neoproterozoic Snowball Events to account for gaps in thick ice and interactions with atmospheric dynamics. Our hypothesis is that in the parameter regime that allows for sea glacier flow, ice flow will make gaps in the thick ice, and therefore an open ocean solution, less likely. This would suggest that oases in thick ice are a more viable survival mechanism for photosynthetic life during a Snowball Earth event.

Boreal pollen contain ice-nucleating as well as ice-binding ‘antifreeze’ polysaccharides

NASA Astrophysics Data System (ADS)

Dreischmeier, Katharina; Budke, Carsten; Wiehemeier, Lars; Kottke, Tilman; Koop, Thomas

2017-02-01

Ice nucleation and growth is an important and widespread environmental process. Accordingly, nature has developed means to either promote or inhibit ice crystal formation, for example ice-nucleating proteins in bacteria or ice-binding antifreeze proteins in polar fish. Recently, it was found that birch pollen release ice-nucleating macromolecules when suspended in water. Here we show that birch pollen washing water exhibits also ice-binding properties such as ice shaping and ice recrystallization inhibition, similar to antifreeze proteins. We present spectroscopic evidence that both the ice-nucleating as well as the ice-binding molecules are polysaccharides bearing carboxylate groups. The spectra suggest that both polysaccharides consist of very similar chemical moieties, but centrifugal filtration indicates differences in molecular size: ice nucleation occurs only in the supernatant of a 100 kDa filter, while ice shaping is strongly enhanced in the filtrate. This finding may suggest that the larger ice-nucleating polysaccharides consist of clusters of the smaller ice-binding polysaccharides, or that the latter are fragments of the ice-nucleating polysaccharides. Finally, similar polysaccharides released from pine and alder pollen also display both ice-nucleating as well as ice-binding ability, suggesting a common mechanism of interaction with ice among several boreal pollen with implications for atmospheric processes and antifreeze protection.

Boreal pollen contain ice-nucleating as well as ice-binding ‘antifreeze’ polysaccharides

PubMed Central

Dreischmeier, Katharina; Budke, Carsten; Wiehemeier, Lars; Kottke, Tilman; Koop, Thomas

2017-01-01

Ice nucleation and growth is an important and widespread environmental process. Accordingly, nature has developed means to either promote or inhibit ice crystal formation, for example ice-nucleating proteins in bacteria or ice-binding antifreeze proteins in polar fish. Recently, it was found that birch pollen release ice-nucleating macromolecules when suspended in water. Here we show that birch pollen washing water exhibits also ice-binding properties such as ice shaping and ice recrystallization inhibition, similar to antifreeze proteins. We present spectroscopic evidence that both the ice-nucleating as well as the ice-binding molecules are polysaccharides bearing carboxylate groups. The spectra suggest that both polysaccharides consist of very similar chemical moieties, but centrifugal filtration indicates differences in molecular size: ice nucleation occurs only in the supernatant of a 100 kDa filter, while ice shaping is strongly enhanced in the filtrate. This finding may suggest that the larger ice-nucleating polysaccharides consist of clusters of the smaller ice-binding polysaccharides, or that the latter are fragments of the ice-nucleating polysaccharides. Finally, similar polysaccharides released from pine and alder pollen also display both ice-nucleating as well as ice-binding ability, suggesting a common mechanism of interaction with ice among several boreal pollen with implications for atmospheric processes and antifreeze protection. PMID:28157236

Glacial/interglacial changes in subarctic north pacific stratification.

PubMed

Jaccard, S L; Haug, G H; Sigman, D M; Pedersen, T F; Thierstein, H R; Röhl, U

2005-05-13

Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.

New transformations between crystalline and amorphous ice

NASA Technical Reports Server (NTRS)

Hemley, R. J.; Chen, L. C.; Mao, H. K.

1989-01-01

High-pressure optical and spectroscopic techniques were used to obtain directly the ice I(h) - hda-ice transformation in a diamond-anvil cell, and the stability of the amorphous form is examined as functions of pressure and temperature. It is demonstrated that hda-ice transforms abruptly at 4 GPa and 77 K to a crystalline phase close in structure to orientationally disordered ice-VII and to a more highly ordered, ice-VIII-like structure at higher temperatures. This is the first time that an amorphous solid is observed to convert to a crystalline solid at low temperatures by compression alone. Phase transitions of this type may be relevant on icy planetary satellites, and there may also be implications for the high-pressure behavior of silica.

A DirtI Application for LBT Commissioning Campaigns

NASA Astrophysics Data System (ADS)

Borelli, J. L.

2009-09-01

In order to characterize the Gregorian focal stations and test the performance achieved by the Large Binocular Telescope (LBT) adaptive optics system, two infrared test cameras were constructed within a joint project between INAF (Observatorio Astronomico di Bologna, Italy) and the Max Planck Institute for Astronomy (Germany). Is intended here to describe the functionality and successful results obtained with the Daemon for the Infrared Test Camera Interface (DirtI) during commissioning campaigns.

A Survey of Rollback-Recovery Protocols in Message-Passing Systems

DTIC Science & Technology

1999-06-01

and M.A. Castillo. "Checkpointing through garbage collection." Technical report. Departamento de Ciencia de la Computation, Escuela de Ingenieria ...between consecutive checkpoints. It can be implemented by using the dirty-bit of the memory protection hardware or by emulating a dirty-bit in software [4...compare the program’s state with the previous checkpoint in software , and writing the difference in a new checkpoint [46]. The required storage and

The Dirty Dozen Scale: Validation of a Polish Version and Extension of the Nomological Net.

PubMed

Czarna, Anna Z; Jonason, Peter K; Dufner, Michael; Kossowska, Małgorzata

2016-01-01

In five studies (total N = 1300) we developed and validated a Polish version of the Dirty Dozen measure (DTDD-P) that measures the three traits of the Dark Triad, Machiavellianism, psychopathy, and narcissism. We detail the presence and stability of a bifactor structure of the 12 items and present evidence for good internal consistency and test-retest reliability. We examine the nomological network surrounding the Dark Triad and show that both the Dark Triad total score and the subscales have acceptable validity. We also present evidence on the Dark Triad and moral behavior. Dark Triad predicts utilitarian moral choice (e.g., approval for sacrificing somebody's life for the sake of saving others) and this link is mediated by low empathic concern. In total, our results suggest that the Polish Dirty Dozen-Parszywa Dwunastka-is valid, stable, and useful for the study of lingering puzzles in the literature.

Multi-decadal Arctic sea ice roughness.

NASA Astrophysics Data System (ADS)

Tsamados, M.; Stroeve, J.; Kharbouche, S.; Muller, J. P., , Prof; Nolin, A. W.; Petty, A.; Haas, C.; Girard-Ardhuin, F.; Landy, J.

2017-12-01

The transformation of Arctic sea ice from mainly perennial, multi-year ice to a seasonal, first-year ice is believed to have been accompanied by a reduction of the roughness of the ice cover surface. This smoothening effect has been shown to (i) modify the momentum and heat transfer between the atmosphere and ocean, (ii) to alter the ice thickness distribution which in turn controls the snow and melt pond repartition over the ice cover, and (iii) to bias airborne and satellite remote sensing measurements that depend on the scattering and reflective characteristics over the sea ice surface topography. We will review existing and novel remote sensing methodologies proposed to estimate sea ice roughness, ranging from airborne LIDAR measurement (ie Operation IceBridge), to backscatter coefficients from scatterometers (ASCAT, QUICKSCAT), to multi angle maging spectroradiometer (MISR), and to laser (Icesat) and radar altimeters (Envisat, Cryosat, Altika, Sentinel-3). We will show that by comparing and cross-calibrating these different products we can offer a consistent multi-mission, multi-decadal view of the declining sea ice roughness. Implications for sea ice physics, climate and remote sensing will also be discussed.

Future sea ice conditions and weather forecasts in the Arctic: Implications for Arctic shipping.

PubMed

Gascard, Jean-Claude; Riemann-Campe, Kathrin; Gerdes, Rüdiger; Schyberg, Harald; Randriamampianina, Roger; Karcher, Michael; Zhang, Jinlun; Rafizadeh, Mehrad

2017-12-01

The ability to forecast sea ice (both extent and thickness) and weather conditions are the major factors when it comes to safe marine transportation in the Arctic Ocean. This paper presents findings focusing on sea ice and weather prediction in the Arctic Ocean for navigation purposes, in particular along the Northeast Passage. Based on comparison with the observed sea ice concentrations for validation, the best performing Earth system models from the Intergovernmental Panel on Climate Change (IPCC) program (CMIP5-Coupled Model Intercomparison Project phase 5) were selected to provide ranges of potential future sea ice conditions. Our results showed that, despite a general tendency toward less sea ice cover in summer, internal variability will still be large and shipping along the Northeast Passage might still be hampered by sea ice blocking narrow passages. This will make sea ice forecasts on shorter time and space scales and Arctic weather prediction even more important.

Sea ice type maps from Alaska synthetic aperture radar facility imagery: An assessment

NASA Technical Reports Server (NTRS)

Fetterer, Florence M.; Gineris, Denise; Kwok, Ronald

1994-01-01

Synthetic aperture radar (SAR) imagery received at the Alaskan SAR Facility is routinely and automatically classified on the Geophysical Processor System (GPS) to create ice type maps. We evaluated the wintertime performance of the GPS classification algorithm by comparing ice type percentages from supervised classification with percentages from the algorithm. The root mean square (RMS) difference for multiyear ice is about 6%, while the inconsistency in supervised classification is about 3%. The algorithm separates first-year from multiyear ice well, although it sometimes fails to correctly classify new ice and open water owing to the wide distribution of backscatter for these classes. Our results imply a high degree of accuracy and consistency in the growing archive of multiyear and first-year ice distribution maps. These results have implications for heat and mass balance studies which are furthered by the ability to accurately characterize ice type distributions over a large part of the Arctic.

Predictability of the Arctic sea ice edge

NASA Astrophysics Data System (ADS)

Goessling, H. F.; Tietsche, S.; Day, J. J.; Hawkins, E.; Jung, T.

2016-02-01

Skillful sea ice forecasts from days to years ahead are becoming increasingly important for the operation and planning of human activities in the Arctic. Here we analyze the potential predictability of the Arctic sea ice edge in six climate models. We introduce the integrated ice-edge error (IIEE), a user-relevant verification metric defined as the area where the forecast and the "truth" disagree on the ice concentration being above or below 15%. The IIEE lends itself to decomposition into an absolute extent error, corresponding to the common sea ice extent error, and a misplacement error. We find that the often-neglected misplacement error makes up more than half of the climatological IIEE. In idealized forecast ensembles initialized on 1 July, the IIEE grows faster than the absolute extent error. This means that the Arctic sea ice edge is less predictable than sea ice extent, particularly in September, with implications for the potential skill of end-user relevant forecasts.

A dirty animal is a scary animal! Effects of disgust-related information on fear beliefs in children.

PubMed

Muris, Peter; Mayer, Birgit; Huijding, Jorg; Konings, Tjeerd

2008-01-01

The present study investigated whether disgust-valenced information has an impact on children's fear beliefs about animals. Non-clinical children aged between 9 and 13 years (n=159) were presented with disgust-related and cleanliness-related information about unknown animals (Australian marsupials). Before and after information, beliefs of disgust and fear regarding the animals were assessed. Results showed that disgust-related information not only induced higher levels of disgust but also increased children's fear beliefs in relation to these animals. The other way around, cleanliness-related information decreased levels of disgust and resulted in lower levels of fear. The implications for the role of disgust in the development of animal fear are briefly discussed.

Hopane Biomarkers Traced from Bedrock to Recent Sediments and Ice at the Haughton Impact Structure, Devon Island: Implications for the Search for Biomarkers on Mars

NASA Technical Reports Server (NTRS)

Parnell, J.; Osinski, G. R.; Lee, P.; Cockell, C. C.; Taylor, C. W.

2004-01-01

Hopanoid biomarkers have been successsfully traced from Palaeozoic target bedrock to Miocene impact-processed rocks, post-impact sediments, and Qu aternary ice at the Haughton impact Structure, Devon Island, High Arctic, suggesting that similar biomarkers and techniques to detect them might provide a promising strategy in the search for biomarkers in rocks, sediments and ice on Mars.

Arctic Ice Melting: National Security Implications

DTIC Science & Technology

2011-02-01

be a curse rather than a good, and under no conditions can it either lead into freedom or constitute a proof for its existence. - Hannah ... Arendt 39 How will the domestic or foreign economic policies of the United States be affected by Arctic ice melting? Increased access to the

The time-dependence of the defective nature of ice Ic (cubic ice) and its implications for atmospheric science

NASA Astrophysics Data System (ADS)

Sippel, Christian; Koza, Michael M.; Hansen, Thomas C.; Kuhs, Werner F.

2010-05-01

The possible atmospheric implication of ice Ic (cubic ice) has already been suggested some time ago in the context of snow crystal formation [1]. New findings from air-borne measurements in cirrus clouds and contrails have put ice Ic into the focus of interest to understand the so-called "supersaturation puzzle" [2,3,4]. Our recent microstructural work on ice Ic [5,6] appears to be highly relevant in this context. We have found that ice Ic is characterized by a complex stacking fault pattern, which changes as a function of temperature as well as time. Indeed, from our own [7] and other group's work [8] one knows that (in contrast to earlier believe) ice Ic can form up to temperatures at least as high as 240K - thus in the relevant range for cirrus clouds. We have good preliminary evidence that the "cubicity" (which can be related to stacking fault probabilities) as well as the particle size of ice Ic are the relevant parameters for this correlation. The "cubicity" of stacking faulty ice Ic (established by diffraction) correlates nicely with the increased supersaturation at decreasing temperatures observed in cirrus clouds and contrails, a fact, which may be considered as further evidence for the presence of ice Ic. Recently, we have studied the time-dependency of the changes in both "cubicity" and particle size at various temperatures of relevance for cirrus clouds and contrails by in-situ neutron powder diffraction. The timescales over which changes occur (several to many hours) are similar to the life-time of cirrus clouds and contrails and suggest that the supersaturation situation may change within this time span in the natural environment too. Some accompanying results obtained by cryo-SEM (scanning electron microscopy) work will also be presented and suggest that stacking-faulty ice Ic has kinky surfaces providing many more active centres for heterogeneous reactions on the surface than in the usually assumed stable hexagonal form of ice Ih with its rather flat low-indexed crystal faces. [1] T Kobayashi & T Kuroda (1987) Snow Crystals. In: Morphology of Crystals (ed. I Sunagawa), Terra Scientific Publishing, Tokyo, pp.649-743. [2] RS Gao & 19 other authors (2004) Evidence that nitric acid increases relative humidity in low-temperature cirrus clouds. Science 303, 516-520. [3] T Peter, C Marcolli, P Spichtinger, T Corti, MC Baker & T Koop (2006) When dry air is too humid. Science 314, 1399-1402. [4] JE Shilling, MA Tolbert, OB Toon, EJ Jensen, BJ Murray & AK Bertram (2006) Measurements of the vapor pressure of cubic ice and their implications for atmospheric ice clouds. Geophys.Res.Lett. 33, 026671. [5] TC Hansen, MM Koza & WF Kuhs (2008) Formation and annealing of cubic ice: I Modelling of stacking faults. J.Phys.Cond.Matt. 20, 285104. [6] TC Hansen, MM Koza, P Lindner & WF Kuhs (2008) Formation and annealing of cubic ice: II. Kinetic study. J.Phys.Cond.Matt. 20, 285105. [7] WF Kuhs, G Genov, DK Staykova & AN Salamatin, T Hansen (2004) Ice perfection and the onset of anomalous preservation of gas hydrates. Phys.Chem.Chem.Phys. 6, 4917-4920. [8] BJ Murray, DA Knopf & AK Bertram (2005) The formation of cubic ice under conditions relevant to Earth's atmosphere. Nature 434, 292-205.

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.

Self-perceived effects of sexual trauma among women who smoke crack.

PubMed

Young, Amy M; Boyd, Carol; Hubbell, Amy

2002-10-01

This descriptive study examined how Black women who smoke crack cocaine spoke about their experiences of sexual trauma, drug use, and the implications of these experiences for their lives. The authors also explored whether the women's perceptions of the effects of sexual abuse were related to objective indicators of mental health and drug use. The most commonly reported effects of sexual trauma were feeling dirty or ashamed or blaming self, having negative feelings toward the perpetrator, experiencing a general dislike of men or sex, and reporting a conscious reluctance to cope with the incident. In addition, conscious or unconscious denial of the effects of sexual trauma was associated with use of drugs to cope with intrapersonal and interpersonal feelings, inwardly directed responses to the trauma (e.g., self-blaming, feeling ashamed) were positively related to depression, and outwardly directed responses to the trauma (e.g., anger at the perpetrator) were positively related to self-esteem. These findings are discussed in terms of their implications for the self-medication model of substance use, treatment implications for women who have been sexually abused, and the role of self-perception in the relationship between sexual trauma and long-term outcomes.

Further Research on the Electrification of Pyrocumulus Clouds

NASA Technical Reports Server (NTRS)

Lang, Timothy J.; Laroche, Kendell; Baum, Bryan; Bateman, Monte; Mach, Douglas

2015-01-01

Past research on pyrocumulus electrification has demonstrated that a variety of lightning types can occur, including cloud-to-ground (CG) flashes, sometimes of dominant positive polarity, as well as small intra-cloud (IC) discharges in the upper levels of the pyro-cloud. In Colorado during summer 2012, the first combined polarimetric radar, multi-Doppler radar, and three-dimensional lightning mapping array (LMA) observations of lightning-producing pyrocumulus were obtained. These observations suggested that the National Lightning Detection Network (NLDN) was not sensitive enough to detect the small IC flashes that appear to be the dominant mode of lightning in these clouds. However, after an upgrade to the network in late 2012, the NLDN began detecting some of this pyrocumulus lightning. Multiple pyrocumulus clouds documented by the University of Wisconsin for various fires in 2013 and 2014 (including over the Rim, West Fork Complex, Yarnell Hill, Hardluck, and several other incidents) are examined and reported on here. This study exploits the increased-sensitivity NLDN as well as the new nationwide U.S. network of polarimetric Next-generation Radars (NEXRADs). These observations document the common occurrence of a polarimetric "dirty ice" signature - modest reflectivities (20-40+ dBZ), near-zero differential reflectivity, and reduced correlation coefficient (less than 0.9) - prior to the production of lightning. This signature is indicative of a mixture of ash and ice particles in the upper levels of the pyro-cloud (less than -20 C), with the ice interpreted as being necessary for pyro-cloud electrification. Pseudo-Geostationary Lightning Mapper (GLM) data will be produced from the 2012 LMA observations, and the ability of GLM to detect small pyrocumulus ICs will be assessed. The utility of lightning and polarimetric radar for documenting rapid wildfire growth, as well as for documenting pyrocumulus impacts on the composition of the upper troposphere/lower stratosphere (UTLS), will be discussed.

Strain in shore fast ice due to incoming ocean waves and swell

NASA Astrophysics Data System (ADS)

Fox, Colin; Squire, Vernon A.

1991-03-01

Using a development from the theoretical model presented by Fox and Squire (1990), this paper investigates the strain field generated in shore fast ice by normally incident ocean waves and swell. After a brief description of the model and its convergence, normalized absolute strain (relative to a 1-m incident wave) is found as a function of distance from the ice edge for various wave periods, ice thicknesses, and water depths. The squared transfer function, giving the relative ability of incident waves of different periods to generate strain in the ice, is calculated, and its consequences are discussed. The ice is then forced with a Pierson-Moskowitz spectrum, and the consequent strain spectra are plotted as a function of penetration into the ice sheet. Finally, rms strain, computed as the incoherent sum of the strains resulting from energy in the open water spectrum, is found. The results have implications to the breakup of shore fast ice and hence to the floe size distribution of the marginal ice zone.

The Arctic-Subarctic Sea Ice System is Entering a Seasonal Regime: Implications for Future Arctic Amplication

NASA Astrophysics Data System (ADS)

Haine, T. W. N.; Martin, T.

2017-12-01

The loss of Arctic sea ice is a conspicuous example of climate change. Climate models project ice-free conditions during summer this century under realistic emission scenarios, reflecting the increase in seasonality in ice cover. To quantify the increased seasonality in the Arctic-Subarctic sea ice system, we define a non-dimensional seasonality number for sea ice extent, area, and volume from satellite data and realistic coupled climate models. We show that the Arctic-Subarctic, i.e. the northern hemisphere, sea ice now exhibits similar levels of seasonality to the Antarctic, which is in a seasonal regime without significant change since satellite observations began in 1979. Realistic climate models suggest that this transition to the seasonal regime is being accompanied by a maximum in Arctic amplification, which is the faster warming of Arctic latitudes compared to the global mean, in the 2010s. The strong link points to a peak in sea-ice-related feedbacks that occurs long before the Arctic becomes ice-free in summer.

Antarctic Sea ice variations and seasonal air temperature relationships

NASA Technical Reports Server (NTRS)

Weatherly, John W.; Walsh, John E.; Zwally, H. J.

1991-01-01

Data through 1987 are used to determine the regional and seasonal dependencies of recent trends of Antarctic temperature and sea ice. Lead-lag relationships involving regional sea ice and air temperature are systematically evaluated, with an eye toward the ice-temperature feedbacks that may influence climatic change. Over the 1958-1087 period the temperature trends are positive in all seasons. For the 15 years (l973-l987) for which ice data are available, the trends are predominantly positive only in winter and summer, and are most strongly positive over the Antarctic Peninsula. The spatially aggregated trend of temperature for this latter period is small but positive, while the corresponding trend of ice coverage is small but negative. Lag correlations between seasonal anomalies of the two variables are generally stronger with ice lagging the summer temperatures and with ice leading the winter temperatures. The implication is that summer temperatures predispose the near-surface waters to above-or below-normal ice coverage in the following fall and winter.

Radical formation, chemical processing, and explosion of interstellar grains

NASA Technical Reports Server (NTRS)

Greenberg, J. M.

1976-01-01

The ultraviolet radiation in interstellar space is shown to create a sufficient steady-state density of free radicals in the grain mantle material consisting of oxygen, carbon, nitrogen, and hydrogen to satisfy the critical condition for initiation of chain reactions. The criterion for minimum critical particle size for maintaining the chain reaction is of the order of the larger grain sizes in a distribution satisfying the average extinction and polarization measures. The triggering of the explosion of interstellar grains leading to the ejection of complex interstellar molecules is shown to be most probable where the grains are largest and where radiation is suddenly introduced; i.e., in regions of new star formation. Similar conditions prevail at the boundaries between very dark clouds and H II regions. When the energy released by the chemical activity of the free radicals is inadequate to explode the grain, the resulting mantle material must consist of extremely large organic molecules which are much more resistant to the hostile environment of H II regions than the classical dirty-ice mantles made up of water, methane, and ammonia.

Exopolymer alteration of physical properties of sea ice and implications for ice habitability and biogeochemistry in a warmer Arctic

PubMed Central

Krembs, Christopher; Eicken, Hajo; Deming, Jody W.

2011-01-01

The physical properties of Arctic sea ice determine its habitability. Whether ice-dwelling organisms can change those properties has rarely been addressed. Following discovery that sea ice contains an abundance of gelatinous extracellular polymeric substances (EPS), we examined the effects of algal EPS on the microstructure and salt retention of ice grown from saline solutions containing EPS from a culture of the sea-ice diatom, Melosira arctica. We also experimented with xanthan gum and with EPS from a culture of the cold-adapted bacterium Colwellia psychrerythraea strain 34H. Quantitative microscopic analyses of the artificial ice containing Melosira EPS revealed convoluted ice-pore morphologies of high fractal dimension, mimicking features found in EPS-rich coastal sea ice, whereas EPS-free (control) ice featured much simpler pore geometries. A heat-sensitive glycoprotein fraction of Melosira EPS accounted for complex pore morphologies. Although all tested forms of EPS increased bulk ice salinity (by 11–59%) above the controls, ice containing native Melosira EPS retained the most salt. EPS effects on ice and pore microstructure improve sea ice habitability, survivability, and potential for increased primary productivity, even as they may alter the persistence and biogeochemical imprint of sea ice on the surface ocean in a warming climate. PMID:21368216

Exopolymer alteration of physical properties of sea ice and implications for ice habitability and biogeochemistry in a warmer Arctic.

PubMed

Krembs, Christopher; Eicken, Hajo; Deming, Jody W

2011-03-01

The physical properties of Arctic sea ice determine its habitability. Whether ice-dwelling organisms can change those properties has rarely been addressed. Following discovery that sea ice contains an abundance of gelatinous extracellular polymeric substances (EPS), we examined the effects of algal EPS on the microstructure and salt retention of ice grown from saline solutions containing EPS from a culture of the sea-ice diatom, Melosira arctica. We also experimented with xanthan gum and with EPS from a culture of the cold-adapted bacterium Colwellia psychrerythraea strain 34H. Quantitative microscopic analyses of the artificial ice containing Melosira EPS revealed convoluted ice-pore morphologies of high fractal dimension, mimicking features found in EPS-rich coastal sea ice, whereas EPS-free (control) ice featured much simpler pore geometries. A heat-sensitive glycoprotein fraction of Melosira EPS accounted for complex pore morphologies. Although all tested forms of EPS increased bulk ice salinity (by 11-59%) above the controls, ice containing native Melosira EPS retained the most salt. EPS effects on ice and pore microstructure improve sea ice habitability, survivability, and potential for increased primary productivity, even as they may alter the persistence and biogeochemical imprint of sea ice on the surface ocean in a warming climate.

Impact of solid second phases on deformation mechanisms of naturally deformed salt rocks (Kuh-e-Namak, Dashti, Iran) and rheological stratification of the Hormuz Salt Formation

NASA Astrophysics Data System (ADS)

Závada, P.; Desbois, G.; Urai, J. L.; Schulmann, K.; Rahmati, M.; Lexa, O.; Wollenberg, U.

2015-05-01

Viscosity contrasts displayed in flow structures of a mountain namakier (Kuh-e-Namak - Dashti), between 'weak' second phase bearing rock salt and 'strong' pure rock salt types are studied for deformation mechanisms using detailed quantitative microstructural study. While the solid inclusions rich ("dirty") rock salts contain disaggregated siltstone and dolomite interlayers, "clean" salts reveal microscopic hematite and remnants of abundant fluid inclusions in non-recrystallized cores of porphyroclasts. Although the flow in both, the recrystallized "dirty" and "clean" salt types is accommodated by combined mechanisms of pressure-solution creep (PS), grain boundary sliding (GBS), transgranular microcracking and dislocation creep accommodated grain boundary migration (GBM), their viscosity contrasts observed in the field outcrops are explained by: 1) enhanced ductility of "dirty" salts due to increased diffusion rates along the solid inclusion-halite contacts than along halite-halite contacts, and 2) slow rates of intergranular diffusion due to dissolved iron and inhibited dislocation creep due to hematite inclusions for "clean" salt types Rheological contrasts inferred by microstructural analysis between both salt rock classes apply in general for the "dirty" salt forming Lower Hormuz and the "clean" salt forming the Upper Hormuz of the Hormuz Formation and imply strain rate gradients or decoupling along horizons of mobilized salt types of different composition and microstructure.

Submarine melt rates under Greenland's ice tongues

NASA Astrophysics Data System (ADS)

Wilson, Nat; Straneo, Fiametta; Heimbach, Patrick; Cenedese, Claudia

2017-04-01

The few remaining ice tongues (ice-shelf like extensions) of Greenland's glaciers are undergoing rapid changes with potential implications for the stability of the ice sheet. Submarine melting is recognized as a major contributor to mass loss, yet the magnitude and spatial distribution of melt are poorly known or understood. Here, we use high resolution satellite imagery to infer the magnitude and spatial variability of melt rates under Greenland's largest remaining ice tongues: Ryder Glacier, Petermann Glacier and Nioghalvfjerdsbræ (79 North Glacier). We find that submarine plus aerial melt approximately balance the ice flux from the grounded ice sheet for the first two while at Nioghalvfjerdsbræ the total melt flux exceeds the inflow of ice indicating thinning of the ice tongue. We also show that melt rates under the ice tongues vary considerably, exceeding 60 m yr-1 near the grounding zone and decaying rapidly downstream. Channels, likely originating from upstream subglacial channels, give rise to large melt variations across the ice tongues. Using derived melt rates, we test simplified melt parameterizations appropriate for ice sheet models and find the best agreement with those that incorporate ice tongue geometry in the form of depth and slope.

Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

USGS Publications Warehouse

Todd, Brian J.; Valentine, Page C.; Longva, Oddvar; Shaw, John

2007-01-01

The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (

Limited Impact of Subglacial Supercooling Freeze-on for Greenland Ice Sheet Stratigraphy

NASA Astrophysics Data System (ADS)

Dow, Christine F.; Karlsson, Nanna B.; Werder, Mauro A.

2018-02-01

Large units of disrupted radiostratigraphy (UDR) are visible in many radio-echo sounding data sets from the Greenland Ice Sheet. This study investigates whether supercooling freeze-on rates at the bed can cause the observed UDR. We use a subglacial hydrology model to calculate both freezing and melting rates at the base of the ice sheet in a distributed sheet and within basal channels. We find that while supercooling freeze-on is a phenomenon that occurs in many areas of the ice sheet, there is no discernible correlation with the occurrence of UDR. The supercooling freeze-on rates are so low that it would require tens of thousands of years with minimal downstream ice motion to form the hundreds of meters of disrupted radiostratigraphy. Overall, the melt rates at the base of the ice sheet greatly overwhelm the freeze-on rates, which has implications for mass balance calculations of Greenland ice.

How will melting of ice affect volcanic hazards in the twenty-first century?

PubMed

Tuffen, Hugh

2010-05-28

Glaciers and ice sheets on many active volcanoes are rapidly receding. There is compelling evidence that melting of ice during the last deglaciation triggered a dramatic acceleration in volcanic activity. Will melting of ice this century, which is associated with climate change, similarly affect volcanic activity and associated hazards? This paper provides a critical overview of the evidence that current melting of ice will increase the frequency or size of hazardous volcanic eruptions. Many aspects of the link between ice recession and accelerated volcanic activity remain poorly understood. Key questions include how rapidly volcanic systems react to melting of ice, whether volcanoes are sensitive to small changes in ice thickness and how recession of ice affects the generation, storage and eruption of magma at stratovolcanoes. A greater frequency of collapse events at glaciated stratovolcanoes can be expected in the near future, and there is strong potential for positive feedbacks between melting of ice and enhanced volcanism. Nonetheless, much further research is required to remove current uncertainties about the implications of climate change for volcanic hazards in the twenty-first century.

Practical Application of NASA-Langley Advanced Satellite Products to In-Flight Icing Nowcasts

NASA Technical Reports Server (NTRS)

Bernstein, Ben C.; Wolff, Cory A.; Minnis, Patrick

2006-01-01

Experimental satellite-based icing products developed by the NASA Langley Research Center provide new tools to identify the locations of icing and its intensity. Since 1997, research forecasters at the National Center for Atmospheric Research (NCAR) have been helping to guide the NASA Glenn Research Center's Twin Otter aircraft into and out of clouds and precipitation for the purpose of characterizing in-flight icing conditions, including supercooled large drops, the accretions that result from such encounters and their effect on aircraft performance. Since the winter of 2003-04, the NASA Langley satellite products have been evaluated as part of this process, and are being considered as an input to NCAR s automated Current Icing Potential (CIP) products. This has already been accomplished for a relatively straightforward icing event, but many icing events have much more complex characteristics, providing additional challenges to all icing diagnosis tools. In this paper, four icing events with a variety of characteristics will be examined, with a focus on the NASA Langley satellite retrievals that were available in real time and their implications for icing nowcasting and potential applications in CIP.

Combined observations of Arctic sea ice with near-coincident colocated X-band, C-band, and L-band SAR satellite remote sensing and helicopter-borne measurements

NASA Astrophysics Data System (ADS)

Johansson, A. M.; King, J. A.; Doulgeris, A. P.; Gerland, S.; Singha, S.; Spreen, G.; Busche, T.

2017-01-01

In this study, we compare colocated near-coincident X-, C-, and L-band fully polarimetry SAR satellite images with helicopter-borne ice thickness measurements acquired during the Norwegian Young sea ICE 2015 (N-ICE2015) expedition in the region of the Arctic Ocean north of Svalbard in April 2015. The air-borne surveys provide near-coincident snow plus ice thickness, surface roughness data, and photographs. This unique data set allows us to investigate how the different frequencies can complement one another for sea ice studies, but also to raise awareness of limitations. X-band and L-band satellite scenes were shown to be a useful complement to the standard SAR frequency for sea ice monitoring (C-band) for lead ice and newly formed sea ice identification. This may be in part be due to the frequency but also the high spatial resolution of these sensors. We found a relatively low correlation between snow plus ice thickness and surface roughness. Therefore, in our dataset ice thickness cannot directly be observed by SAR which has important implications for operational ice charting based on automatic segmentation.

The non-commutative topology of two-dimensional dirty superconductors

NASA Astrophysics Data System (ADS)

De Nittis, Giuseppe; Schulz-Baldes, Hermann

2018-01-01

Non-commutative analysis tools have successfully been applied to the integer quantum Hall effect, in particular for a proof of the stability of the Hall conductance in an Anderson localization regime and of the bulk-boundary correspondence. In this work, these techniques are implemented to study two-dimensional dirty superconductors described by Bogoliubov-de Gennes Hamiltonians. After a thorough presentation of the basic framework and the topological invariants, Kubo formulas for the thermal, thermoelectric and spin Hall conductance are analyzed together with the corresponding edge currents.

24. Station Oil Tanks, view to the south. The four ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

24. Station Oil Tanks, view to the south. The four oil storage tanks located along the east wall (left side of photograph) are, from foreground to background: dirty transformer oil tank, clean transformer oil tank, dirty lubricating oil tank, and clean lubricating oil tank. An oil filter system is also visible in background along the far wall. - Washington Water Power Clark Fork River Noxon Rapids Hydroelectric Development, Powerhouse, South bank of Clark Fork River at Noxon Rapids, Noxon, Sanders County, MT

Evolution of United States Army Deployment Operations: The Santiago Campaign

DTIC Science & Technology

2015-09-03

direction that suits them, looking for the nearest place where they may cook their pork and beans.ൺ Private Charles Post of the Seventy-First New York... Dirty Little War: The Spanish-American War of 1898 (Westport, CT: Praeger, 2000), 94. 82 Trask, War with Spain, 182. 23 oppressive heat...United States Army (London: Smith, Elder, 1899), 51. 84 Rosenfeld, Diary of a Dirty Little War, 85. 85 FM 3-35, 4-10. 86 Huston, Sinews of War

Multiphase Reactive Transport and Platelet Ice Accretion in the Sea Ice of McMurdo Sound, Antarctica

NASA Astrophysics Data System (ADS)

Buffo, J. J.; Schmidt, B. E.; Huber, C.

2018-01-01

Sea ice seasonally to interannually forms a thermal, chemical, and physical boundary between the atmosphere and hydrosphere over tens of millions of square kilometers of ocean. Its presence affects both local and global climate and ocean dynamics, ice shelf processes, and biological communities. Accurate incorporation of sea ice growth and decay, and its associated thermal and physiochemical processes, is underrepresented in large-scale models due to the complex physics that dictate oceanic ice formation and evolution. Two phenomena complicate sea ice simulation, particularly in the Antarctic: the multiphase physics of reactive transport brought about by the inhomogeneous solidification of seawater, and the buoyancy driven accretion of platelet ice formed by supercooled ice shelf water onto the basal surface of the overlying ice. Here a one-dimensional finite difference model capable of simulating both processes is developed and tested against ice core data. Temperature, salinity, liquid fraction, fluid velocity, total salt content, and ice structure are computed during model runs. The model results agree well with empirical observations and simulations highlight the effect platelet ice accretion has on overall ice thickness and characteristics. Results from sensitivity studies emphasize the need to further constrain sea ice microstructure and the associated physics, particularly permeability-porosity relationships, if a complete model of sea ice evolution is to be obtained. Additionally, implications for terrestrial ice shelves and icy moons in the solar system are discussed.

Active volcanism beneath the West Antarctic ice sheet and implications for ice-sheet stability

USGS Publications Warehouse

Blankenship, D.D.; Bell, R.E.; Hodge, S.M.; Brozena, J.M.; Behrendt, John C.; Finn, C.A.

1993-01-01

IT is widely understood that the collapse of the West Antarctic ice sheet (WAIS) would cause a global sea level rise of 6 m, yet there continues to be considerable debate about the detailed response of this ice sheet to climate change1-3. Because its bed is grounded well below sea level, the stability of the WAIS may depend on geologically controlled conditions at the base which are independent of climate. In particular, heat supplied to the base of the ice sheet could increase basal melting and thereby trigger ice streaming, by providing the water for a lubricating basal layer of till on which ice streams are thought to slide4,5. Ice streams act to protect the reservoir of slowly moving inland ice from exposure to oceanic degradation, thus enhancing ice-sheet stability. Here we present aerogeophysical evidence for active volcanism and associated elevated heat flow beneath the WAIS near the critical region where ice streaming begins. If this heat flow is indeed controlling ice-stream formation, then penetration of ocean waters inland of the thin hot crust of the active portion of the West Antarctic rift system could lead to the disappearance of ice streams, and possibly trigger a collapse of the inland ice reservoir.

Temperature Dependence of Cryogenic Ammonia-Water Ice Mixtures and Implications for Icy Satellite Surfaces

NASA Technical Reports Server (NTRS)

Dalton, J. B., III; Curchin, J. M.; Clark, R. N.

2001-01-01

Infrared spectra of ammonia-water ice mixtures reveal temperature-dependent absorption bands due to ammonia. These features, at 1.04, 2.0, and 2.25 microns, may shed light on the surface compositions of the Galilean and Saturnian satellites. Additional information is contained in the original extended abstract.

Impacts and management implications of ice storms on forests in the southern United States

Treesearch

Don C. Bragg; Michael G Shelton; Boris Zeide

2003-01-01

Abstract: This review explores the ecological and silvicultural impacts of ice storms on forests in the southern United States. Different environmental factors like weather conditions, topography, vegetation, stand density, and management practices influence the degree of glaze damage a particular forest may experience. Additionally, the frequent...

Evidence of local and regional freshening of Northeast Greenland coastal waters.

PubMed

Sejr, Mikael K; Stedmon, Colin A; Bendtsen, Jørgen; Abermann, Jakob; Juul-Pedersen, Thomas; Mortensen, John; Rysgaard, Søren

2017-10-13

The supply of freshwater to fjord systems in Greenland is increasing as a result of climate change-induced acceleration in ice sheet melt. However, insight into the marine implications of the melt water is impaired by lack of observations demonstrating the fate of freshwater along the Greenland coast and providing evaluation basis for ocean models. Here we present 13 years of summer measurements along a 120 km transect in Young Sound, Northeast Greenland and show that sub-surface coastal waters are decreasing in salinity with an average rate of 0.12 ± 0.05 per year. This is the first observational evidence of a significant freshening on decadal scale of the waters surrounding the ice sheet and comes from a region where ice sheet melt has been less significant. It implies that ice sheet dynamics in Northeast Greenland could be of key importance as freshwater is retained in southward flowing coastal currents thus reducing density of water masses influencing major deep water formation areas in the Subarctic Atlantic Ocean. Ultimately, the observed freshening could have implications for the Atlantic meridional overturning circulation.

The Production of Amino Acids in Interstellar Ices: Implications for Meteoritic Organics

NASA Technical Reports Server (NTRS)

Sandford, A.; Bernstein, M. P.; Dworkin, J. P.; Cooper, G. W.; Allamandola, L. J.; DeVincenzi, D. (Technical Monitor)

2002-01-01

Indigenous amino acids have been detected in a number of meteorites, over 70 in the Murchison meteorite alone. It has been generally accepted that the amino acids in meteorites formed in liquid water on an asteroid or comet parent-body. However, the water in the Murchison meteorite, for example, was depleted of deuterium, making the distribution of deuterium in organic acids in Murchison difficult to explain. Similarly, occasional but consistent meteoritic biases for non-terrestrial L amino acids cannot be reasonably rationalized by liquid water parent-body reactions. We will present the results of a laboratory demonstration showing that the amino acids glycine, alanine, and serine should result from the UV (ultraviolet) photolysis of interstellar ice grains. This suggests that some meteoritic amino acids may be the result of interstellar ice photochemistry, rather than having formed by reactions in liquid water. We will describe some of the potential implications of these findings for the organic materials found in primitive meteorites, in particular how interstellar ice synthesis might more easily accommodate the presence and distribution of deuterium, and the meteoritic bias for L amino acids.

Palaeoclimate: ocean tides and Heinrich events.

PubMed

Arbic, Brian K; Macayeal, Douglas R; Mitrovica, Jerry X; Milne, Glenn A

2004-11-25

Climate varied enormously over the most recent ice age--for example, large pulses of ice-rafted debris, originating mainly from the Labrador Sea, were deposited into the North Atlantic at roughly 7,000-year intervals, with global climatic implications. Here we show that ocean tides within the Labrador Sea were exceptionally large over the period spanning these huge, abrupt ice movements, which are known as Heinrich events. We propose that tides played a catalytic role in liberating iceberg armadas during that time.

On the size dependence of the scattering greenhouse effect of CO2 ice particles

NASA Astrophysics Data System (ADS)

Kitzmann, D.; Patzer, A. B. C.; Rauer, H.

2011-10-01

In this contribution we study the potential greenhouse effect due to scattering of CO2 ice clouds for atmospheric conditions of terrestrial extrasolar planets. Therefore, we calculate the scattering and absorption properties of CO2 ice particles using Mie theory for assumed particle size distributions with different effective radii and particle densities to determine the scattering and absorption characteristics of such clouds. Implications especially in view of a potential greenhouse warming of the planetary surface are discussed.

Ice Shelf Microbial Ecosystems in the High Arctic and Implications for Life on Snowball Earth

NASA Astrophysics Data System (ADS)

Vincent, W. F.; Gibson, J. A. E.; Pienitz, R.; Villeneuve, V.; Broady, P. A.; Hamilton, P. B.; Howard-Williams, C.

The Ward Hunt Ice Shelf (83°N, 74°W) is the largest remaining section of thick (>10m) landfast sea ice along the northern coastline of Ellesmere Island, Canada. Extensive meltwater lakes and streams occur on the surface of the ice and are colonized by photosynthetic microbial mat communities. This High Arctic cryo-ecosystem is similar in several of its physical, biological and geochemical features to the McMurdo Ice Shelf in Antarctica. The ice-mats in both polar regions are dominated by filamentous cyanobacteria but also contain diatoms, chlorophytes, flagellates, ciliates, nematodes, tardigrades and rotifers. The luxuriant Ward Hunt consortia also contain high concentrations (107-108cm-2) of viruses and heterotrophic bacteria. During periods of extensive ice cover, such as glaciations during the Proterozoic, cryotolerant mats of the type now found in these polar ice shelf ecosystems would have provided refugia for the survival, growth and evolution of a variety of organisms, including multicellular eukaryotes.

New constraints on the structure and dynamics of the East Antarctic Ice Sheet from the joint IPY/Ice Bridge ICECAP aerogeophysical project

NASA Astrophysics Data System (ADS)

Blankenship, D. D.; Young, D. A.; Siegert, M. J.; van Ommen, T. D.; Roberts, J. L.; Wright, A.; Warner, R. C.; Holt, J. W.; Young, N. W.; Le Meur, E.; Legresy, B.; Cavitte, M.; Icecap Team

2010-12-01

Ice within marine basins of East Antarctica, and their outlets, represent the ultimate limit on sea level change. The region of East Antarctica between the Ross Sea and Wilkes Land hosts a number of major basin, but has been poorly understood. Long range aerogeophysics from US, Australian and French stations, with significant British and IceBridge support, has, under the banner of the ICECAP project, greatly improved our knowledge of ice thickness, surface elevation, and crustal structure of the Wilkes and Aurora Subglacial Basins, as well as the Totten Glacier, Cook Ice Shelf, and Byrd Glacier. We will discuss the evolution of the Wilkes and Aurora Subglacial Basins, new constraints on the geometry of the major outlet glaciers, as well as our results from surface elevation change measurements over dynamic regions of the ice sheet. We will discuss the implications of our data for the presence of mid Pleistocene ice in central East Antarctica. Future directions for ICECAP will be discussed.

The role of ice nuclei recycling in the maintenance of cloud ice in Arctic mixed-phase stratocumulus

DOE PAGES

Solomon, Amy; Feingold, G.; Shupe, M. D.

2015-09-25

This study investigates the maintenance of cloud ice production in Arctic mixed-phase stratocumulus in large eddy simulations that include a prognostic ice nuclei (IN) formulation and a diurnal cycle. Balances derived from a mixed-layer model and phase analyses are used to provide insight into buffering mechanisms that maintain ice in these cloud systems. We find that, for the case under investigation, IN recycling through subcloud sublimation considerably prolongs ice production over a multi-day integration. This effective source of IN to the cloud dominates over mixing sources from above or below the cloud-driven mixed layer. Competing feedbacks between dynamical mixing andmore » recycling are found to slow the rate of ice lost from the mixed layer when a diurnal cycle is simulated. Furthermore, the results of this study have important implications for maintaining phase partitioning of cloud ice and liquid that determine the radiative forcing of Arctic mixed-phase clouds.« less

The role of ice nuclei recycling in the maintenance of cloud ice in Arctic mixed-phase stratocumulus

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

Solomon, Amy; Feingold, G.; Shupe, M. D.

This study investigates the maintenance of cloud ice production in Arctic mixed-phase stratocumulus in large eddy simulations that include a prognostic ice nuclei (IN) formulation and a diurnal cycle. Balances derived from a mixed-layer model and phase analyses are used to provide insight into buffering mechanisms that maintain ice in these cloud systems. We find that, for the case under investigation, IN recycling through subcloud sublimation considerably prolongs ice production over a multi-day integration. This effective source of IN to the cloud dominates over mixing sources from above or below the cloud-driven mixed layer. Competing feedbacks between dynamical mixing andmore » recycling are found to slow the rate of ice lost from the mixed layer when a diurnal cycle is simulated. Furthermore, the results of this study have important implications for maintaining phase partitioning of cloud ice and liquid that determine the radiative forcing of Arctic mixed-phase clouds.« less

Large-Scale Structure and Hyperuniformity of Amorphous Ices

NASA Astrophysics Data System (ADS)

Martelli, Fausto; Torquato, Salvatore; Giovambattista, Nicolas; Car, Roberto

2017-09-01

We investigate the large-scale structure of amorphous ices and transitions between their different forms by quantifying their large-scale density fluctuations. Specifically, we simulate the isothermal compression of low-density amorphous ice (LDA) and hexagonal ice to produce high-density amorphous ice (HDA). Both HDA and LDA are nearly hyperuniform; i.e., they are characterized by an anomalous suppression of large-scale density fluctuations. By contrast, in correspondence with the nonequilibrium phase transitions to HDA, the presence of structural heterogeneities strongly suppresses the hyperuniformity and the system becomes hyposurficial (devoid of "surface-area fluctuations"). Our investigation challenges the largely accepted "frozen-liquid" picture, which views glasses as structurally arrested liquids. Beyond implications for water, our findings enrich our understanding of pressure-induced structural transformations in glasses.

Risk factors for bacterial contamination during boar semen collection.

PubMed

Goldberg, Ana Maria G; Argenti, Laura E; Faccin, Jamil E; Linck, Lídia; Santi, Mônica; Bernardi, Mari Lourdes; Cardoso, Marisa R I; Wentz, Ivo; Bortolozzo, Fernando P

2013-10-01

The aim of this study was to evaluate the influence of multiple factors on bacterial contamination in 213 ejaculates from four boar studs. Semen contamination by aerobic mesophiles increased in ejaculates where the preputial fluid flowed into the collection container, collection glove was dirty, preputial hair was long (>1.0 cm), the collection lasted >7 min and boars were older than 18 months. An increase in coliforms occurred when preputial fluid dripped into the collection container, collections lasted >7 min or when penis escaped during collection. Semen contamination increased when two or more factors related to hygiene (poor hygiene of the boar, dirty preputial ostium, large preputial diverticulum, long preputial hair, dirty gloves, preputial liquid trickling from the hand of the technician into the semen container and penis escaping) were present. A vigilant protocol of collection must be followed to minimize bacterial contamination, especially avoiding dripping of preputial liquid into the semen container. Copyright © 2013 Elsevier Ltd. All rights reserved.

Agnosia Interferes With Daily Hygiene in Patients With Dementia

PubMed Central

Hamdy, R. C.; Kinser, A.; Culp, J.E.; Kendall-Wilson, T.; Depelteau, A.; Copeland, R.; Whalen, K.

2018-01-01

Patients with dementia, particularly Alzheimer’s disease, may not recognize that their clothes are dirty. They may see the food stains and discoloration of the clothes and yet because of their agnosia are unable to integrate these observations and deduce that their clothes are dirty and need to be changed. They will, therefore, resist attempts to get them to change clothes, especially if these clothes happen to be their favorite ones. This often causes caregivers to become frustrated, especially, if it represents a change in the patient’s previous habits of only wearing clean clothes. In this case study, we present a 72-year-old woman with moderate Alzheimer’s disease who lives with her daughter, who adamantly refuses to change the clothes she has been wearing for a few days and which are now clearly dirty. We report the interaction, highlight what went wrong in the patient–daughter interaction, and discuss how the catastrophic ending could have been avoided or averted. PMID:29900188

Water Ice in 2060 Chiron and Its Implications for Centaurs and Kuiper Belt Objects.

PubMed

Luu; Jewitt; Trujillo

2000-03-10

We report the detection of water ice in the Centaur 2060 Chiron, based on near-infrared spectra (1.0-2.5 µm) taken with the 3.8 m United Kingdom Infrared Telescope and the 10 m Keck Telescope. The appearance of this ice is correlated with the recent decline in Chiron's cometary activity: the decrease in the coma cross section allows previously hidden solid-state surface features to be seen. We predict that water ice is ubiquitous among Centaurs and Kuiper Belt objects, but its surface coverage varies from object to object and thus determines its detectability and the occurrence of cometary activity.

Penetration of Solar Radiation into Solid Carbon Dioxide

NASA Astrophysics Data System (ADS)

Chinnery, H. E.; Hagermann, A.; Kaufmann, E.; Lewis, S. R.; Grady, M. M.

2017-09-01

Carbon dioxide ice exists naturally on the surface of Mars. This is a unique environment, with no Earth analogues, and so determining the properties of such a surface is important to further our understanding of the Martian environment. Laboratory experiments have determined the e-folding scale, or absorption scale length, for carbon dioxide slab ice, granular ice and snow. This is a universal measure of how transparent a material is to visible light, and so has implications for the radiative budget of carbon dioxide ice covered surfaces, as well as physical processes, such as the so-called spider formations in the cryptic region near the Martian south pole.

Studies of proton irradiated H2O + CO2 and H2O + CO ices and analysis of synthesized molecules

NASA Technical Reports Server (NTRS)

Moore, M. H.; Khanna, R.; Donn, B.

1991-01-01

Infrared spectra of H2O + CO2 and H2O + CO ices before and after proton irradiation showed that a major reaction in both mixtures was the interconversion of CO2 yields CO. Radiation synthesized organic compounds such as carbonic acid were identified in the H2O + CO2 ice. Different chemical pathways dominate in the H2O + CO ice in which formaldehyde, methanol, ethanol, and methane were identified. Sublimed material was also analyzed using a mass spectrometer. Implications of these results are discussed in reference to comets.

Relation of attitude toward body elimination to parenting style and attitude toward the body.

PubMed

Corgiat, Claudia A; Templer, Donald I

2003-04-01

The purpose was to estimate the relation of attitude toward body elimination in 93 college students (27 men and 66 women), to authoritarian personality features, participants' perception of their mothers' parenting style, and attitudes toward cleanliness, sex, and family nudity. Subjects were administered the Body Elimination Attitude Scale, the Four-item F Scale, the Parental Authority Questionnaire Pertaining to Mothers, and the items "Sex is dirty," "Cleanliness is next to godliness," and "Children should never see other family members nude." Larger scores for disgust toward body elimination were associated with authoritarian personality characteristics, being less likely to describe mother's parenting style as authoritative (open communication) and more likely to describe it as authoritarian and lower scores for tolerance for family nudity. Implications for further research were suggested.

In situ observations of Arctic cloud properties across the Beaufort Sea marginal ice zone

NASA Astrophysics Data System (ADS)

Corr, C.; Moore, R.; Winstead, E.; Thornhill, K. L., II; Crosbie, E.; Ziemba, L. D.; Beyersdorf, A. J.; Chen, G.; Martin, R.; Shook, M.; Corbett, J.; Smith, W. L., Jr.; Anderson, B. E.

2016-12-01

Clouds play an important role in Arctic climate. This is particularly true over the Arctic Ocean where feedbacks between clouds and sea-ice impact the surface radiation budget through modifications of sea-ice extent, ice thickness, cloud base height, and cloud cover. This work summarizes measurements of Arctic cloud properties made aboard the NASA C-130 aircraft over the Beaufort Sea during ARISE (Arctic Radiation - IceBridge Sea&Ice Experiment) in September 2014. The influence of surface-type on cloud properties is also investigated. Specifically, liquid water content (LWC), droplet concentrations, and droplet size distributions are compared for clouds sampled over three distinct regimes in the Beaufort Sea: 1) open water, 2) the marginal ice zone, and 3) sea-ice. Regardless of surface type, nearly all clouds intercepted during ARISE were liquid-phase clouds. However, differences in droplet size distributions and concentrations were evident for the surface types; clouds over the MIZ and sea-ice generally had fewer and larger droplets compared to those over open water. The potential implication these results have for understanding cloud-surface albedo climate feedbacks in Arctic are discussed.

Ask about ice, then consider iron

PubMed Central

Rabel, Antoinette; Leitman, Susan F.; Miller, Jeffery L.

2015-01-01

Background and purpose To review a condition defined by the desire to consume ice in order to satisfy an addictive-like compulsion, rather than for purposes of hydration or pain relief. This condition is called ice pica, or pagophagia. Explain the association between ice pica and iron deficiency. Suggest to clinicians how to perform clinical screening for patients at risk for ice pica. Recommend treatment and follow-up care, if needed. Methods Extensive published literature review of original research articles, reviews, clinical practice manuscripts and scientific publications on pica and pagophagia. Conclusions A compulsion or craving for the consumption of ice is often overlooked in clinical practice. It is therefore important for clinicians to include ice pica as part of the review of systems for certain patient populations. Ice pica is frequently associated with iron deficiency, and iron supplementation is an effective therapy in most cases. Implications for practice Knowledge gained from screening for ice pica can generate valuable patient information and lead to the diagnosis and treatment of iron deficiency. The populations at risk include young women and blood donors of either sex. PMID:25943566

Impact of surface melt and ponding on the stability of Larsen C Ice Shelf, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Kulessa, Bernd; Luckman, Adrian; Hubbard, Bryn; Bevan, Suzanne; O'Leary, Martin; Ashmore, David; Kuipers Munneke, Peter; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Holland, Paul; McGrath, Daniel; Brisbourne, Alex; Rutt, Ian

2017-04-01

Several ice shelves on the Antarctic Peninsula have disintegrated rapidly in recent decades, and surface meltwater is strongly implicated as a driver. The Larsen C Ice Shelf is the largest ice shelf on the peninsula and one of the largest in Antarctica, and is subject to pronounced surface melting and meltwater ponding, especially in the northern sectors and landward inlets. As part of the MIDAS project we have investigated the structure and physical properties of the firn and ice layers in the 2014/15 and 2015/16 austral summers, using a combination of radar and seismic geophysical surveys together with hot water drilling and borehole optical televiewing and temperature measurements. We found that Larsen C's firn column and ice temperatures are modified strongly by surface melting and ponding, including the presence of massive ice bodies in the Cabinet and Whirlwind inlets. Numerical modelling reveals that these modifications have been altering ice shelf deformation, flow and fracture significantly. The findings from our MIDAS project thus suggest that the response of Antarctic ice shelves to climatic warming is more complex than previously thought.

Sensitivity of Cirrus Properties to Ice Nuclei Abundance

NASA Technical Reports Server (NTRS)

Jensen, Eric

2014-01-01

The relative importance of heterogeneous and homogeneous ice nucleation for cirrus formation remains an active area of debate in the cloud physics community. From a theoretical perspective, a number of modeling studies have investigated the sensitivity of ice number concentration to the nucleation mechanism and the abundance of ice nuclei. However, these studies typically only addressed ice concentration immediately after ice nucleation. Recent modeling work has shown that the high ice concentrations produced by homogeneous freezing may not persist very long, which is consistent with the low frequency of occurrence of high ice concentrations indicated by cirrus measurements. Here, I use idealized simulations to investigate the impact of ice nucleation mechanism and ice nuclei abundance on the full lifecycle of cirrus clouds. The primary modeling framework used includes different modes of ice nucleation, deposition growth/sublimation, aggregation, sedimentation, and radiation. A limited number of cloud-resolving simulations that treat radiation/dynamics interactions will also been presented. I will show that for typical synoptic situations with mesoscale waves present, the time-averaged cirrus ice crystal size distributions and bulk cloud properties are less sensitive to ice nucleation processes than might be expected from the earlier simple ice nucleation calculations. I will evaluate the magnitude of the ice nuclei impact on cirrus for a range of temperatures and mesoscale wave specifications, and I will discuss the implications for cirrus aerosol indirect effects in general.

Airborne thickness and freeboard measurements over the McMurdo Ice Shelf, Antarctica, and implications for ice density

NASA Astrophysics Data System (ADS)

Rack, Wolfgang; Haas, Christian; Langhorne, Pat J.

2013-11-01

We present airborne measurements to investigate the thickness of the western McMurdo Ice Shelf in the western Ross Sea, Antarctica. Because of basal accretion of marine ice and brine intrusions conventional radar systems are limited in detecting the ice thickness in this area. In November 2009, we used a helicopter-borne laser and electromagnetic induction sounder (EM bird) to measure several thickness and freeboard profiles across the ice shelf. The maximum electromagnetically detectable ice thickness was about 55 m. Assuming hydrostatic equilibrium, the simultaneous measurement of ice freeboard and thickness was used to derive bulk ice densities ranging from 800 to 975 kg m-3. Densities higher than those of pure ice can be largely explained by the abundance of sediments accumulated at the surface and present within the ice shelf, and are likely to a smaller extent related to the overestimation of ice thickness by the electromagnetic induction measurement related to the presence of a subice platelet layer. The equivalent thickness of debris at a density of 2800 kg m-3 is found to be up to about 2 m thick. A subice platelet layer below the ice shelf, similar to what is observed in front of the ice shelf below the sea ice, is likely to exist in areas of highest thickness. The thickness and density distribution reflects a picture of areas of basal freezing and supercooled Ice Shelf Water emerging from below the central ice shelf cavity into McMurdo Sound.

Ice Lens Formation and Frost Heave at the Phoenix Landing Site

NASA Technical Reports Server (NTRS)

Zent, A. P.; Sizemore, H. G.; Remple, A. W.

2011-01-01

Several lines of evidence indicate that the volume of shallow ground ice in the martian high latitudes exceeds the pore volume of the host regolith. Boynton et al. found an optimal fit to the Mars Odyssey Gamma Ray Spectrometer (GRS) data at the Phoenix landing site by modeling a buried layer of 50-75% ice by mass (up to 90% ice by volume). Thermal and optical observations of recent impact craters in the northern hemisphere have revealed nearly pure ice. Ice deposits containing only 1-2% soil by volume were excavated by Phoenix. The leading hypothesis for the origin of this excess ice is that it developed in situ by a mechanism analogous to the formation of terrestrial ice lenses and needle ice. Problematically, terrestrial soil-ice segregation is driven by freeze/thaw cycling and the movement of bulk water, neither of which are expected to have occurred in the geologically recent past on Mars. If however ice lens formation is possible at temperatures less than 273 K, there are possible implications for the habitability of Mars permafrost, since the same thin films of unfrozen water that lead to ice segregation are used by terrestrial psychrophiles to metabolize and grow down to temperatures of at least 258 K.

Ice Lens Formation, Frost Heave, Thin Films, and the Importance of the Polar H2O Reservoir at High Obliquity

NASA Technical Reports Server (NTRS)

Zent, A. P.; Sizemore, H. G.; Rempel, A. W.

2011-01-01

Several lines of evidence indicate that the volume of shallow ground ice in the martian high latitudes exceeds the pore volume of the host regolith. Boynton et al. found an optimal fit to the Mars Odyssey Gamma Ray Spectrometer (GRS) data at the Phoenix landing site by modeling a buried layer of 50-75% ice by mass (up to 90% ice by volume). Thermal and optical observations of recent impact craters in the northern hemisphere have revealed nearly pure ice. Ice deposits containing only 1-2% soil by volume were excavaged by Phoenix. One hypothesis for the origin of this excess ice is that it developed in situ by a mechanism analogous to the formation of terrestrial ice lenses and needle ice. Problematically, terrestrial soil-ice segregation is driven by freeze/thaw cycling and the movement of bulk water, neither of which are expected to have occurred in the geologically recent past on Mars. If however ice lens formation is possible at temperatures less than 273 K, there are possible implications for the habitability of Mars permafrost, since the same thin films of unfrozen water that lead to ice segregation are used by terrestrial psychrophiles to metaboluze and grow down to temperatures of at least 258 K.

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.

Formation of melt channels on ice shelves

NASA Astrophysics Data System (ADS)

Sergienko, Olga

2013-04-01

Melt channels have been observed on ice shelves experiencing strong melting in both Greenland (Petermann Glacier) and Antarctica (Pine Island Glacier). Using a fully-couple ice-shelf/sub-ice-shelf-ocean flow model, it is demonstrated that these channels can form spontaneously in laterally confined ice shelves. These channels have transverse extent of a few kilometers and a vertical relief of about a few hundred meters. Meltrates and sea-water transport in the channels are significantly higher than in between the channels on the smooth flat ice bottom. In circumstances where an ice shelf has no-slip conditions at its lateral boundaries, the ice-shelf/sub-ice-shelf-cavity system exhibits equilibrium periodic states, where the same configurations repetitively appear with a periodicity of about 30-35 years. This peculiar dynamics of the system has strong implications on the interpretation of the remote and in-situ observations and inferences of the system parameters (e.g., melt rates) based on these observations. For instance, the persistent temporal changes in the ice-shelf thickness are caused by internal dynamics of the melt channels, and, in contrast to traditional interpretation, can be independent of the oceanic forcings.

Collisions with ice-volatile objects: Geological implications

NASA Technical Reports Server (NTRS)

Wilde, P.; Quinby-Hunt, M. S.; Berry, W. B. N.

1988-01-01

The collision of the Earth with extra-terrestrial ice-volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record. These bodies would be analogs of the ice satellites found for the Jovian planets and suspected for comets and certain low density bodies in the Asteroid belt. Five generic end-members are postulated: (1) water ice; (2) dry ice: carbon-carbon dioxide rich, (3) oceanic (chloride) ice; (4) sulfur-rich ice; (5) ammonia hydrate-rich ice; and (6) clathrate: methane-rich ice. Due to the volatile nature of these bodies, evidence for their impact with the Earth would be subtle and probably best reflected geochemically or in the fossil record. Actual boloids impacting the Earth may have a variable composition, generally some admixture with water ice. However for discussion purposes, only the effects of a dominant component will be treated. The general geological effects of such collisions, as a function of the dominant component would be: (1) rapid sea level rise unrelated to deglaciation, (2) decreased oceanic pH and rapid climatic warming or deglaciation; (3) increased paleosalinities; (4) increased acid rain; (5) increased oceanic pH and rapid carbonate deposition; and (6) rapid climatic warming or deglaciation.

Modeling Studying the Role of Bacteria on ice Nucleation Processes

NASA Astrophysics Data System (ADS)

Sun, J.

2006-12-01

Certain air-borne bacteria have been recognized as active ice nuclei at the temperatures warm than - 10°C. Ice nucleating bacteria commonly found in plants and ocean surface. These ice nucleating bacteria are readily disseminated into the atmosphere and have been observed in clouds and hailstones, and their importance in cloud formation process and precipitation, as well as causing diseases in plants and animal kingdom, have been considered for over two decades, but their significance in atmospheric processes are yet to be understood. A 1.5-D non-hydrostatic cumulus cloud model with bin-resolved microphysics is developed and is to used to examine the relative importance of sulphate aerosol concentrations on the evolution of cumulus cloud droplet spectra and ice multiplication process, as well as ice initiation process by ice nucleating bacteria in the growing stage of cumulus clouds and the key role of this process on the ice multiplication in the subsequent dissipating stage of cumulus clouds. In this paper, we will present some sensitivity test results of the evolution of cumulus cloud spectra, ice concentrations at various concentrations of sulfate aerosols, and at different ideal sounding profiles. We will discuss the implication of our results in understanding of ice nucleation processes.

Scenario of a dirty bomb in an urban environment and acute management of radiation poisoning and injuries.

PubMed

Chin, F K C

2007-10-01

In the new security environment, there is a clear and present danger of terrorists using non-conventional weapons to inflict maximum psychological and economic damage on their targets. This article examines two scenarios of radiation contamination and injury, one accidental in nature leading to environmental contamination, and another of deliberate intent resulting in injury and death. This article also discusses the management of injury from radiological dispersion devices or dirty bombs, with emphasis on the immediate aftermath as well as strategy recommendations.

CBRN Weapons of Mass Destruction: The Relevance of the United States Armys Chemical Corps in the Support of Homeland Security and Defense against State and Non-State Actors

DTIC Science & Technology

2017-06-09

scorpion- bombs /6.html. 42 Smart, 12. 19 infecting clothing with smallpox and yellow fever and then sold the clothing to unsuspicious Union troops...focusing on the use of biological warfare by terrorists.43 Radiological An example of a radiological dispersal device (RDD) is a “dirty bomb .” It is a...combination of explosives and radioactive material. Most dirty bombs will not release enough radiation to kill people or cause severe illness

Using the Patriot Act to Turn North Korea’s Dirty Money into a Bargaining Chip

DTIC Science & Technology

2009-01-01

Dirty Money: The Fight Against Money Laundering (Washington, DC: Institute for International Economics, 2004), 81–87. 17. Wechsler, “ Follow the Money ,” 49...and Wechsler, “ Follow the Money ,” 55–56. 26. The FATF adopted Eight Special Recommendations on Terrorist Financing in October 2001. It added a ninth... the Money ,” Foreign Affairs 80, no. 4 (July/August, 2001): 48–49. 15. Ibid., 48. Tracey.indd 138 4/30/09 1:21:17 PM Using the Patriot Act to

Emergency care centers--an efficient method for mitigation of consequences after a dirty bomb attack.

PubMed

Miska, Horst

2012-08-01

For emergency preparedness and response with respect to nuclear power plant accidents, the concept of Emergency Care Centers has been developed in Germany. This setup aims at monitoring contamination, to decontaminate if needed, assess the dose, and perform an initial medical evaluation of people who might have been affected by the accident. The concept has been tested in many exercises. In response to a terrorist attack involving a dirty bomb, this concept may prove useful for attending contaminated people who are not severely injured.

Scratching the surface of ice: Interfacial phase transitions and their kinetic implications

NASA Astrophysics Data System (ADS)

Limmer, David

The surface structure of ice maintains a high degree of disorder down to surprisingly low temperatures. This is due to a number of underlying interfacial phase transitions that are associated with incremental changes in broken symmetry relative to the bulk crystal. In this talk I summarize recent work attempting to establish the nature and locations of these different phase transitions as well as how they depend on external conditions and nonequilibrium driving. The implications of this surface disorder is discussed in the context of simple kinetic processes that occur at these interfaces. Recent experimental work on the roughening transition is highlighted.

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

Kulkarni, Gourihar R.; Zhang, Kai; Zhao, Chun

Changes in the ice nucleation characteristics of atmospherically relevant mineral dust particles due to nitric acid coating are not well understood. Further, the atmospheric implications of dust coating on ice-cloud properties under different assumptions of primary ice nucleation mechanisms are unknown. We investigated ice nucleation ability of Arizona test dust, illite, K-feldspar and quartz as a function of temperature (-25 to -30°C) and relative humidity with respect to water (75 to 110%). Particles were size selected at 250 nm and transported (bare or coated) to the ice nucleation chamber to determine the fraction of particles nucleating ice at various temperaturemore » and water saturation conditions. All dust nucleated ice at water-subsaturated conditions, but the coated particles showed a reduction in their ice nucleation ability compared to bare particles. However, at water-supersaturated conditions, we observed that bare and coated particles had nearly similar ice nucleation characteristics. X-ray diffraction patterns indicated that structural properties of bare dust particles modified after acid treatment. We found that lattice parameters were slightly different, but crystallite sizes of the coated particles were reduced compared to bare particles. Next, single-column model results show that simulated ice crystal number concentrations mostly depends upon fraction of particles that are coated, primary ice nucleation mechanisms, and the competition between ice nucleation mechanisms to nucleate ice. In general, we observed that coating modify the ice-cloud properties and the picture of ice and mixed-phase cloud evolution is complex when different primary ice nucleation mechanisms are competing for fixed water vapor mass.« less

Ice stream motion facilitated by a shallow-deforming and accreting bed

PubMed Central

Spagnolo, Matteo; Phillips, Emrys; Piotrowski, Jan A.; Rea, Brice R.; Clark, Chris D.; Stokes, Chris R.; Carr, Simon J.; Ely, Jeremy C.; Ribolini, Adriano; Wysota, Wojciech; Szuman, Izabela

2016-01-01

Ice streams drain large portions of ice sheets and play a fundamental role in governing their response to atmospheric and oceanic forcing, with implications for sea-level change. The mechanisms that generate ice stream flow remain elusive. Basal sliding and/or bed deformation have been hypothesized, but ice stream beds are largely inaccessible. Here we present a comprehensive, multi-scale study of the internal structure of mega-scale glacial lineations (MSGLs) formed at the bed of a palaeo ice stream. Analyses were undertaken at macro- and microscales, using multiple techniques including X-ray tomography, thin sections and ground penetrating radar (GPR) acquisitions. Results reveal homogeneity in stratigraphy, kinematics, granulometry and petrography. The consistency of the physical and geological properties demonstrates a continuously accreting, shallow-deforming, bed and invariant basal conditions. This implies that ice stream basal motion on soft sediment beds during MSGL formation is accommodated by plastic deformation, facilitated by continuous sediment supply and an inefficient drainage system. PMID:26898399

The impact of lower sea-ice extent on Arctic greenhouse-gas exchange

USGS Publications Warehouse

Parmentier, Frans-Jan W.; Christensen, Torben R.; Sørensen, Lise Lotte; Rysgaard, Søren; McGuire, A. David; Miller, Paul A.; Walker, Donald A.

2013-01-01

In September 2012, Arctic sea-ice extent plummeted to a new record low: two times lower than the 1979–2000 average. Often, record lows in sea-ice cover are hailed as an example of climate change impacts in the Arctic. Less apparent, however, are the implications of reduced sea-ice cover in the Arctic Ocean for marine–atmosphere CO2 exchange. Sea-ice decline has been connected to increasing air temperatures at high latitudes. Temperature is a key controlling factor in the terrestrial exchange of CO2 and methane, and therefore the greenhouse-gas balance of the Arctic. Despite the large potential for feedbacks, many studies do not connect the diminishing sea-ice extent with changes in the interaction of the marine and terrestrial Arctic with the atmosphere. In this Review, we assess how current understanding of the Arctic Ocean and high-latitude ecosystems can be used to predict the impact of a lower sea-ice cover on Arctic greenhouse-gas exchange.

Investigation of 2-Dimensional Isotropy of Under-Ice Roughness in the Beaufort Gyre and Implications for Mixed Layer Ocean Turbulence

DTIC Science & Technology

2008-03-01

this roughness is important for numerical modeling and prediction of the Arctic air-ice-ocean system, which will play a significant role as the US Navy...is important for numerical modeling and prediction of the Arctic air-ice-ocean system, which will play a significant role as the US Navy increases... Model 1 is based on a sequence of plane parallel layers each with a constant gradient whereas Model 2 is based on a series of flat layers of

Radar evidence for ice in lobate debris aprons in the mid-northern latitudes of Mars

NASA Astrophysics Data System (ADS)

Plaut, Jeffrey J.; Safaeinili, Ali; Holt, John W.; Phillips, Roger J.; Head, James W.; Seu, Roberto; Putzig, Nathaniel E.; Frigeri, Alessandro

2009-01-01

Subsurface radar sounding data indicate that lobate debris aprons found in Deuteronilus Mensae in the mid-northern latitudes of Mars are composed predominantly of water ice. The position in time delay and the relatively low amount of signal loss of the apparent basal reflectors below the debris aprons indicate that aprons contain only a minor component of lithic material. The current presence of large ice masses at these latitudes has important implications for the climate evolution of Mars, and for future targets for in situ exploration.

The condensation and vaporization behavior of ices containing SO2, H2S, and CO2 - Implications for Io

NASA Astrophysics Data System (ADS)

Sandford, Scott A.; Allamandola, Louis J.

1993-12-01

The present compilation of measurements of the physical and IR spectral properties of ices whose molecular compositions are relevant to the case of Io encompasses ice systems containing SO2, H2S, and CO2. Surface-binding energies used to calculate the residence times of molecules on a surface as a function of temperature furnish crucially important parameters for models attending to the transport of such molecules to the surface of Io. The values thus derived show that SO2 frosts anneal rapidly.

Constraining ice sheet history in the Weddell Sea, West Antarctica, using ice fabric at Korff Ice Rise

NASA Astrophysics Data System (ADS)

Brisbourne, A.; Smith, A.; Kendall, J. M.; Baird, A. F.; Martin, C.; Kingslake, J.

2017-12-01

The grounding history of ice rises (grounded area of independent flow regime within a floating ice shelf) can be used to constrain large scale ice sheet history: ice fabric, resulting from the preferred orientation of ice crystals due to the stress regime, can be used to infer this grounding history. With the aim of measuring the present day ice fabric at Korff Ice Rise, West Antarctica, a multi-azimuth wide-angle seismic experiment was undertaken. Three wide-angle common-midpoint gathers were acquired centred on the apex of the ice rise, at azimuths of 60 degrees to one another, to measure variation in seismic properties with offset and azimuth. Both vertical and horizontal receivers were used to record P and S arrivals including converted phases. Measurements of the variation with offset and azimuth of seismic traveltimes, seismic attenuation and shear wave splitting have been used to quantify seismic anisotropy in the ice column. The observations cannot be reproduced using an isotropic ice column model. Anisotropic ray tracing has been used to test likely models of ice fabric by comparison with the data. A model with a weak girdle fabric overlying a strong cluster fabric provides the best fit to the observations. Fabric of this nature is consistent with Korff Ice Rise having been stable for the order of 10,000 years without any ungrounding or significant change in the ice flow configuration across the ice rise for this period. This observation has significant implications for the ice sheet history of the Weddell Sea sector.

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.

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.

Tropical Glaciers in the Common Era: Papua, Indonesia, Quelccaya Ice Cap, Peru and Kilimanjaro, Tanzania

NASA Astrophysics Data System (ADS)

Thompson, L. G.; Mosley-Thompson, E. S.; Davis, M. E.

2011-12-01

High-resolution ice core stratigraphic records of δ18O (temperature proxy) demonstrate that the current warming at high elevations in mid- to lower latitudes is unprecedented for at least the last two millennia, although at many sites the Early Holocene was much warmer than at present. Here we discuss the interaction of El Niño-Southern Oscillation (ENSO) variability and warming trends as recorded in ice core records from high-altitude tropical glaciers and the implications of the warming trends for the future of these glaciers. ENSO has strong impacts on meteorological phenomena that either directly or indirectly affect most regions on the planet and their populations, particularly throughout the Tropics. Here we examine similarities and differences among ice core records from Papua (Indonesia), Quelccaya Ice Cap (Peru) and Kilimanjaro (Tanzania). Quelccaya, Earth's largest tropical ice cap, has provided continuous, annually-resolved proxy records of climatic and environmental variability preserved in many measurable parameters, especially oxygen and hydrogen isotopic ratios (δ18O, δD) and the net mass balance (accumulation) spanning the last 1800 years. The remarkable similarity between changes in the highland and coastal cultures of Peru and climate variability in the Andes, especially with regard to precipitation, implies a strong connection between prehistoric human activities and climate in this region. The well-documented ice loss on Quelccaya, Kilimanjaro in eastern Africa and the ice fields near Puncak Jaya in Papua, Indonesia presents a possible analog for glacier response in the tropics during the Holocene. The ongoing melting of these ice fields is consistent with model predictions of a vertical amplification of temperature in the Tropics. A sequence of over 50 recently exposed, rooted, soft-bodied plant deposits collected between 2002 and 2011 from the retreating margins of the Quelccaya ice cap provide a longer term perspective for the recent glacier retreat. The ongoing glacier retreat in the Tropics and associated loss of natural resources has dire implications for people living in these areas. These recent changes are examined in the context of the Common Era from a glacier derived paleoclimate perspective as recorded in the glaciers on the world's highest mountains.

Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow

PubMed Central

Kulessa, Bernd; Hubbard, Alun L.; Booth, Adam D.; Bougamont, Marion; Dow, Christine F.; Doyle, Samuel H.; Christoffersen, Poul; Lindbäck, Katrin; Pettersson, Rickard; Fitzpatrick, Andrew A. W.; Jones, Glenn A.

2017-01-01

The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self-regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms. PMID:28835915

Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow.

PubMed

Kulessa, Bernd; Hubbard, Alun L; Booth, Adam D; Bougamont, Marion; Dow, Christine F; Doyle, Samuel H; Christoffersen, Poul; Lindbäck, Katrin; Pettersson, Rickard; Fitzpatrick, Andrew A W; Jones, Glenn A

2017-08-01

The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self-regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms.

Effects of an Arctic under-ice phytoplankton bloom on bio-optical properties of surface waters during the Norwegian Young Sea Ice Cruise (N-ICE2015)

NASA Astrophysics Data System (ADS)

Pavlov, A. K.; Granskog, M. A.; Hudson, S. R.; Taskjelle, T.; Kauko, H.; Hamre, B.; Assmy, P.; Mundy, C. J.; Nicolaus, M.; Kowalczuk, P.; Stedmon, C. A.; Fernandez Mendez, M.

2016-02-01

A thinner and younger Arctic sea-ice cover has led to an increase in solar light transmission into the surface ocean, especially during late spring and summer. A description of the seasonal evolution of polar surface water optical properties is essential, in order to understand how changes are affecting light availability for photosynthetic organisms and the surface ocean energy budget. The development of the bio-optical properties of Arctic surface waters under predominantly first-year sea ice in the southern Nansen Basin were studied from January to June 2015 during the Norwegian Young Sea Ice Cruise (N-ICE2015). Observations included inherent optical properties, absorption by colored dissolved organic matter and particles, as well as radiometric measurements. We documented a rapid transition from relatively clear and transparent waters in winter to turbid waters in late May and June. This transition was associated with a strong under-ice phytoplankton bloom detected first under the compact ice pack and then monitored during drift across the marginal ice zone. We discuss potential implications of underwater light availability for photosynthesis, heat redistribution in the upper ocean layer, and energy budget of the sea-ice - ocean system.

Effects of Carbohydrate Intake Before and During An Ice Hockey Game on Blood and Muscle Energy Substrates.

ERIC Educational Resources Information Center

Simard, Clermont; And Others

1988-01-01

Study of the effect of a supplemental carbohydrate intake for seven elite ice hockey players before and during a game demonstrated that the supplement could result in less glycogen usage per distance skated, which had important implications for athletes who may participate in more than one game a day. (Author/CB)

What color should snow algae be and what does it mean for glacier melt?

NASA Astrophysics Data System (ADS)

Dial, R. J.; Ganey, G. Q.; Loso, M.; Burgess, A. B.; Skiles, M.

2017-12-01

Specialized microbes colonize glaciers and ice sheets worldwide and, like all organisms, they are unable to metabolize water in its solid form. It is well understood that net solar radiation controls melt in almost all snow and ice covered environments, and theoretical and empirical studies have documented the substantial reduction of albedo by these microbes both on ice and on snow, implicating a microbial role in glacier melt. If glacial microbiomes are limited by liquid water, and the albedo-reducing properties of individual cells enhance melt rates, then natural selection should favor those microbes that melt ice and snow crystals most efficiently. Here we: (1) argue that natural selection favors a red color on snow and a near-black color on ice based on instantaneous radiative forcing. (2) Review results of the first replicated, controlled field experiment to both quantify the impact of microbes on snowmelt in "red-snow" communities and demonstrate their water-limitation and (3) show the extent of snow-algae's spatial distribution and estimate their contribution to snowmelt across a large Alaskan icefield using remote sensing. On the 700 km2 of a 2,000 km2 maritime icefield in Alaska where red-snow was present, microbes increased snowmelt over 20% by volume, a percentage likely to increase as the climate warms and particulate pollution intensifies with important implications for models of sea level rise.

The effect of under-ice melt ponds on their surroundings in the Arctic

NASA Astrophysics Data System (ADS)

Feltham, D. L.; Smith, N.; Flocco, D.

2016-12-01

In the summer months, melt water from the surface of the Arctic sea ice can percolate down through the ice and flow out of its base. This water is relatively warm and fresh compared to the ocean water beneath it, and so it floats between the ice and the oceanic mixed layer, forming pools of melt water called under-ice melt ponds. Sheets of ice, known as false bottoms, can subsequently form via double diffusion processes at the under-ice melt pond interface with the ocean, trapping the pond against the ice and completely isolating it from the ocean below. This has an insulating effect on the parent sea ice above the trapped pond, altering its rate of basal ablation. A one-dimensional, thermodynamic model of Arctic sea ice has been adapted to study the evolution of under-ice melt ponds and false bottoms over time. Comparing simulations of sea ice evolution with and without an under-ice melt pond provides a measure of how an under-ice melt pond affects the mass balance of the sea ice above it. Sensitivity studies testing the response of the model to a range of uncertain parameters have been performed, revealing some interesting implications of under-ice ponds during their life cycle. By changing the rate of basal ablation of the parent sea ice, and so the flux of fresh water and salt into the ocean, under-ice melt ponds affect the properties of the mixed layer beneath the sea ice. Our model of under-ice melt pond refreezing has been coupled to a simple oceanic mixed layer model to determine the effect on mixed layer depth, salinity and temperature.

Rheological stratification of the Hormuz Salt Formation in Iran - microstructural study of the dirty and pure rock salts from the Kuh-e-Namak (Dashti) salt diapir

NASA Astrophysics Data System (ADS)

Závada, Prokop; Desbois, Guillaume; Urai, Janos; Schulmann, Karel; Rahmati, Mahmoud; Lexa, Ondrej; Wollenberg, Uwe

2014-05-01

Significant viscosity contrasts displayed in flow structures of a mountain namakier (Kuh-e-Namak - Dashti), between 'weak' terrestrial debris bearing rock salt types and 'strong' pure rock salt types are questioned for deformation mechanisms using detailed quantitative microstructural study including crystallographic preferred orientation (CPO) mapping of halite grains. While the solid impurity rich ("dirty") rock salts contain disaggregated siltstone and dolomite interlayers, "clean" salts (debris free) reveal microscopic hematite and remnants of abundant fluid inclusions in non-recrystallized cores of porphyroclasts. Although flow in both, the recrystallized dirty and clean salt types is accommodated by combined mechanisms of pressure-solution creep (PS), grain boundary sliding (GBS) and dislocation creep accommodated grain boundary migration (GBM), their viscosity contrasts are explained by significantly slower rates of intergranular diffusion and piling up of dislocations at hematite inclusions in clean salt types. Porphyroclasts of clean salts deform by semi-brittle and plastic mechanisms with intra-crystalline damage being induced also by fluid inclusions that explode in the crystals at high fluid pressures. Boudins of clean salt types with coarse grained and original sedimentary microstructure suggest that clean rock salts are associated with dislocation creep dominated power law flow in the source layer and the diapiric stem. Rheological contrasts between both rock salt classes apply in general for the variegated and terrestrial debris rich ("dirty") Lower Hormuz and the "clean" rock salt forming the Upper Hormuz, respectively, and suggest that large strain rate gradients likely exist along horizons of mobilized salt types of different composition and microstructure.

Comparative study of ice nucleating efficiency of K-feldspar in immersion and deposition freezing modes

NASA Astrophysics Data System (ADS)

Hiron, T.; Hoffmann, N.; Peckhaus, A.; Kiselev, A. A.; Leisner, T.; Flossmann, A. I.

2016-12-01

One of the main challenges in understanding the evolution of Earth's climate resides in the understanding the role of ice nucleation on the development of tropospheric clouds as well as its initiation. K-feldspar is known to be a very active ice nucleating particle and this study focuses on the characterization of its activity in two heterogeneous nucleation modes, immersion and deposition freezing.We use a newly built humidity-controlled cold stage allowing the simultaneous observation of up to 2000 identical 0.6-nanoliter droplets containing suspension of mineral dust particles. The droplets are first cooled down to observe immersion freezing, the obtained ice crystals are then evaporated and finally, the residual particles are exposed to the water vapor supersaturated with respect to ice.The ice nucleation abilities for the individual residual particles are then compared for the different freezing modes and correlation between immersion ice nuclei and deposition ice nuclei is investigated.Based on the electron microscopy analysis of the residual particles, we discuss the possible relationship between the ice nucleation properties of feldspar and its microstructure. Finally, we discuss the atmospheric implications of our experimental results, using DESCAM, a 1.5D bin-resolved microphysics model.

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.

Superfluid density and carrier concentration across a superconducting dome: The case of strontium titanate

NASA Astrophysics Data System (ADS)

Collignon, Clément; Fauqué, Benoît; Cavanna, Antonella; Gennser, Ulf; Mailly, Dominique; Behnia, Kamran

2017-12-01

We present a study of the lower critical field, Hc 1, of SrTi1 -xNbxO3 as a function of carrier concentration with the aim of quantifying the superfluid density. At low carrier concentration (i.e., the underdoped side), superfluid density and the carrier concentration in the normal state are equal within experimental margin. A significant deviation between the two numbers starts at optimal doping and gradually increases with doping. The inverse of the penetration depth and the critical temperature follow parallel evolutions as in the case of cuprate superconductors. In the overdoped regime, the zero-temperature superfluid density becomes much lower than the normal-state carrier density before vanishing all together. We show that the density mismatch and the clean-to-dirty crossover are concomitant. Our results imply that the discrepancy between normal and superconducting densities is expected whenever the superconducting gap becomes small enough to put the system in the dirty limit. A quantitative test of the dirty BCS theory is not straightforward, due to the multiplicity of the bands in superconducting strontium titanate.

The Milankovitch Signature of the air Content Along the EPICA DC Ice Record: a Tool Towards an Absolute Dating and Implication for ice Flow Modeling

NASA Astrophysics Data System (ADS)

Raynaud, D.; Duval, P.; Lemieux-Dudon, B.; Lipenkov, V.; Parrenin, F.

2006-12-01

Air content of polar ice, V, depends primarily on air pressure, temperature and pore volume at close-off prevailing at the site of ice formation. Here we present the recently measured V record of the EPICA DC (EDC) Antarctic ice core covering the last 650,000 years. The first 440,000 years remarkably displays the fundamental Milankovitch orbital frequencies. The 100 kyr period, corresponding to the eccentricity of the Earth's orbit and found in the V record, likely reflects essentially the pressure/elevation signature of V. But most of the variations observed in the V record cannot be explained neither by air pressure nor by temperature changes, and then should reflect properties influencing the porosity at close-off other than temperature. A wavelet analysis indicates a dominant period around 41 kyr, the period characteristic of the obliquity variations of the Earth's axis. We propose that the local insolation, via the solar radiation absorbed by the snow, leaves its imprint on the snow structure, then affects the snow-firn transition, and therefore is one of the controlling factors for the porosity at close-off. Such mechanism could account for the observed anti-correlation between local insolation and V. We estimate the variations of the absorbed solar flux in the near-surface snow layers on the basis of a simple albedo model (Lemieux-Dudon et al., this session). We compare the dating of the ice obtained using the local insolation signal deduced from the V record with a chronology based on ice flow modelling. We discuss the glaciological implications of the comparison between the two chronologies, as well as the potential of local insolation markers for approaching an absolute dating of ice core. The latest results covering the period 440-650 kyr BP will also be presented.

Parameterizations of Cloud Microphysics and Indirect Aerosol Effects

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

Tao, Wei-Kuo

1. OVERVIEW Aerosols and especially their effect on clouds are one of the key components of the climate system and the hydrological cycle [Ramanathan et al., 2001]. Yet, the aerosol effect on clouds remains largely unknown and the processes involved not well understood. A recent report published by the National Academy of Science states "The greatest uncertainty about the aerosol climate forcing - indeed, the largest of all the uncertainties about global climate forcing - is probably the indirect effect of aerosols on clouds [NRC, 2001]." The aerosol effect on clouds is often categorized into the traditional "first indirect (i.e.,more » Twomey)" effect on the cloud droplet sizes for a constant liquid water path [Twomey, 1977] and the "semi-direct" effect on cloud coverage [e.g., Ackerman et al., 2000]. Enhanced aerosol concentrations can also suppress warm rain processes by producing a narrow droplet spectrum that inhibits collision and coalescence processes [e.g., Squires and Twomey, 1961; Warner and Twomey, 1967; Warner, 1968; Rosenfeld, 1999]. The aerosol effect on precipitation processes, also known as the second type of aerosol indirect effect [Albrecht, 1989], is even more complex, especially for mixed-phase convective clouds. Table 1 summarizes the key observational studies identifying the microphysical properties, cloud characteristics, thermodynamics and dynamics associated with cloud systems from high-aerosol continental environments. For example, atmospheric aerosol concentrations can influence cloud droplet size distributions, warm-rain process, cold-rain process, cloud-top height, the depth of the mixed phase region, and occurrence of lightning. In addition, high aerosol concentrations in urban environments could affect precipitation variability by providing an enhanced source of cloud condensation nuclei (CCN). Hypotheses have been developed to explain the effect of urban regions on convection and precipitation [van den Heever and Cotton, 2007 and Shepherd, 2005]. Recently, a detailed spectral-bin microphysical scheme was implemented into the Goddard Cumulus Ensemble (GCE) model. Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region and summertime convection over a mid-latitude continent with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. The impact of atmospheric aerosol concentration on cloud and precipitation will be investigated. 2. MODEL DESCRIPTION AND CASE STUDIES 2.1 GCE MODEL The model used in this study is the 2D version of the GCE model. Modeled flow is anelastic. Second- or higher-order advection schemes can produce negative values in the solution. Thus, a Multi-dimensional Positive Definite Advection Transport Algorithm (MPDATA) has been implemented into the model. All scalar variables (potential temperature, water vapor, turbulent coefficient and all five hydrometeor classes) use forward time differencing and the MPDATA for advection. Dynamic variables, u, v and w, use a second-order accurate advection scheme and a leapfrog time integration (kinetic energy semi-conserving method). Short-wave (solar) and long-wave radiation as well as a subgrid-scale TKE turbulence scheme are also included in the model. Details of the model can be found in Tao and Simpson (1993) and Tao et al. (2003). 2.2 Microphysics (Bin Model) The formulation of the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (cloud droplets and raindrops), and six types of ice particles: pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail. Each type is described by a special size distribution function containing 33 categories (bins). Atmospheric aerosols are also described using number density size-distribution functions (containing 33 bins). Droplet nucleation (activation) is derived from the analytical calculation of super-saturation, which is used to determine the sizes of aerosol particles to be activated and the corresponding sizes of nucleated droplets. Primary nucleation of each type of ice crystal takes place within certain temperature ranges. A detailed description of these explicitly parameterized processes can be found in Khain and Sednev (1996) and Khain et al. (1999, 2001). 2.3 Case Studies Three cases, a tropical oceanic squall system observed during TOGA COARE (Tropical Ocean and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment, which occurred over the Pacific Ocean warm pool from November 1992 to February 1993), a midlatitude continental squall system observed during PRESTORM (Preliminary Regional Experiment for STORM-Central, which occurred in Kansas and Oklahoma during May-June 1985), and mid-afternoon convection observed during CRYSTAL-FACE (Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cumulus Experiment, which occurred in Florida during July 2002), will be used to examine the impact of aerosols on deep, precipitating systems. 3. SUMMARY of RESULTS • For all three cases, higher CCN produces smaller cloud droplets and a narrower spectrum. Dirty conditions delay rain formation, increase latent heat release above the freezing level, and enhance vertical velocities at higher altitude for all cases. Stronger updrafts, deeper mixed-phase regions, and more ice particles are simulated with higher CCN in good agreement with observations. • In all cases, rain reaches the ground early with lower CCN. Rain suppression is also evident in all three cases with high CCN in good agreement with observations (Rosenfeld, 1999, 2000 and others). Rain suppression, however, only occurs during the first hour of simulation. This result suggests that microphysical processes dominate the impact of aerosols on precipitation in the early stage of precipitation development. • During the mature stage of the simulations, the effect of increasing aerosol concentration ranges from rain suppression in the PRESTORM case to little effect on surface rainfall in the CRYSTAL-FACE case to rain enhancement in the TOGA COARE case. • The model results suggest that evaporative cooling is a key process in determining whether higher CCN reduces or enhances precipitation. Cold pool strength can be enhanced by stronger evaporation. When cold pool interacts with the near surface wind shear, the low-level convergence can be stronger, facilitating secondary cloud formation and more vigorous precipitation processes. Evaporative cooling is more than two times stronger at low levels with higher CCN for the TOGA COARE case during the early stages of precipitation development. However, evaporative cooling is slightly stronger at lower levels with lower CCN for the PRESTORM case. The early formation of rain in the clean environment could allow for the formation of an earlier and stronger cold pool compared to a dirty environment. PRESTORM has a very dry environment and both large and small rain droplets can evaporate. Consequently, the cold pool is relatively weaker, and the system is relatively less intense with higher CCN. • Sensitivity tests are conducted to determine the impact of ice processes on aerosol-precipitation interaction. The results suggested that ice processes are crucial for suppressing precipitation due to high CCN for the PRESTORM case. More and smaller ice particles are generated in the dirty case and transported to the trailing stratiform region. This reduces the heavy convective rain and contributes to the weakening of the cold pool. Warm rain processes dominate the TOGA COARE case. Therefore, ice processes only play a secondary role in terms of aerosol-precipitation interaction. • Two of the three cloud systems presented in this paper formed a line structure (squall system). A 2D simulation, therefore, gives a good approximation to such a line of convective clouds. Since the real atmosphere is 3D, further 3D cloud-resolving simulations are needed to address aerosol-precipitation interactions. 4. REFERENCES Tao, W.-K., X. Li, A. Khain, T. Matsui, S. Lang, and J. Simpson, 2007: The role of atmospheric aerosol concentration on deep convective precipitation: Cloud-resolving model simulations. J. Geophy. Res., 112, D24S18, doi:10.1029/2007JD008728. All other references can be found in above paper. 5. Acknowledgements The GCE model is mainly supported by the NASA Headquarters Atmospheric Dynamics and Thermodynamics Program and the NASA Tropical Rainfall Measuring Mission (TRMM). The research was also supported by the Office of Science (BER), U. S. Department of Energy/Atmospheric Radiation Measurement (DOE/ARM) Interagency. The authors acknowledge NASA Goddard Space Flight Center for computer time used in this research.« less

Seasonal thickness changes of Arctic sea ice north of Svalbard and implications for satellite remote sensing, ecosystem, and environmental management

NASA Astrophysics Data System (ADS)

Gerland, S.; Rösel, A.; King, J.; Spreen, G.; Divine, D.; Eltoft, T.; Gallet, J. C.; Hudson, S. R.; Itkin, P.; Krumpen, T.; Liston, G. E.; Merkouriadi, I.; Negrel, J.; Nicolaus, M.; Polashenski, C.; Assmy, P.; Barber, D. G.; Duarte, P.; Doulgeris, A. P.; Haas, C.; Hughes, N.; Johansson, M.; Meier, W.; Perovich, D. K.; Provost, C.; Richter-Menge, J.; Skourup, H.; Wagner, P.; Wilkinson, J.; Granskog, M. A.; Steen, H.

2016-12-01

Sea-ice thickness is a crucial parameter to consider when assessing the status of Arctic sea ice, whether for environmental management, monitoring projects, or regional or pan-arctic assessments. Modern satellite remote sensing techniques allow us to monitor ice extent and to estimate sea-ice thickness changes; but accurate quantifications of sea-ice thickness distribution rely on in situ and airborne surveys. From January to June 2015, an international expedition (N-ICE2015) took place in the Arctic Ocean north of Svalbard, with the Norwegian research vessel RV Lance frozen into drifting sea ice. In total, four drifts, with four different floes were made during that time. Sea-ice and snow thickness measurements were conducted on all main ice types present in the region, first year ice, multiyear ice, and young ice. Measurement methods included ground and helicopter based electromagnetic surveys, drillings, hot-wire installations, snow-sonde transects, snow stakes, and ice mass balance and snow buoys. Ice thickness distributions revealed modal thicknesses in spring between 1.6 and 1.7 m, which is lower than reported for the region from comparable studies in 2009 (2.4 m) and 2011 (1.8 m). Knowledge about the ice thickness distribution in a region is crucial to the understanding of climate processes, and also relevant to other disciplines. Sea-ice thickness data collected during N-ICE2015 can also give us insights into how ice and snow thicknesses affect ecosystem processes. In this presentation, we will explore the influence of snow cover and ocean properties on ice thickness, and the role of sea-ice thickness in air-ice-ocean interactions. We will also demonstrate how information about ice thickness aids classification of different sea ice types from SAR satellite remote sensing, which has real-world applications for shipping and ice forecasting, and how sea ice thickness data contributes to climate assessments.

Dynamics of the global meridional ice flow of Europa's icy shell

NASA Astrophysics Data System (ADS)

Ashkenazy, Yosef; Sayag, Roiy; Tziperman, Eli

2018-01-01

Europa is one of the most probable places in the solar system to find extra-terrestrial life1,2, motivating the study of its deep ( 100 km) ocean3-6 and thick icy shell3,7-11. The chaotic terrain patterns on Europa's surface12-15 have been associated with vertical convective motions within the ice8,10. Horizontal gradients of ice thickness16,17 are expected due to the large equator-to-pole gradient of surface temperature and can drive a global horizontal ice flow, yet such a flow and its observable implications have not been studied. We present a global ice flow model for Europa composed of warm, soft ice flowing beneath a cold brittle rigid ice crust3. The model is coupled to an underlying (diffusive) ocean and includes the effect of tidal heating and convection within the ice. We show that Europa's ice can flow meridionally due to pressure gradients associated with equator-to-pole ice thickness differences, which can be up to a few km and can be reduced both by ice flow and due to ocean heat transport. The ice thickness and meridional flow direction depend on whether the ice convects or not; multiple (convecting and non-convecting) equilibria are found. Measurements of the ice thickness and surface temperature from future Europa missions18,19 can be used with our model to deduce whether Europa's icy shell convects and to constrain the effectiveness of ocean heat transport.

Basal channels on ice shelves

NASA Astrophysics Data System (ADS)

Sergienko, O. V.

2013-09-01

Recent surveys of floating ice shelves associated with Pine Island Glacier (Antarctica) and Petermann Glacier (Greenland) indicate that there are channels incised upward into their bottoms that may serve as the conduits of meltwater outflow from the sub-ice-shelf cavity. The formation of the channels, their evolution over time, and their impact on ice-shelf flow are investigated using a fully-coupled ice-shelf/sub-ice-shelf ocean model. The model simulations suggest that channels may form spontaneously in response to meltwater plume flow initiated at the grounding line if there are relatively high melt rates and if there is transverse to ice-flow variability in ice-shelf thickness. Typical channels formed in the simulations have a width of about 1-3 km and a vertical relief of about 100-200 m. Melt rates and sea-water transport in the channels are significantly higher than on the smooth flat ice bottom between the channels. The melt channels develop through melting, deformation, and advection with ice-shelf flow. Simulations suggest that both steady state and cyclic state solutions are possible depending on conditions along the lateral ice-shelf boundaries. This peculiar dynamics of the system has strong implications on the interpretation of observations. The richness of channel morphology and evolution seen in this study suggests that further observations and theoretical analysis are imperative for understanding ice-shelf behavior in warm oceanic conditions.

Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications

NASA Astrophysics Data System (ADS)

DeWeaver, Eric T.; Bitz, Cecilia M.; Tremblay, L.-Bruno

This volume addresses the rapid decline of Arctic sea ice, placing recent sea ice decline in the context of past observations, climate model simulations and projections, and simple models of the climate sensitivity of sea ice. Highlights of the work presented here include • An appraisal of the role played by wind forcing in driving the decline; • A reconstruction of Arctic sea ice conditions prior to human observations, based on proxy data from sediments; • A modeling approach for assessing the impact of sea ice decline on polar bears, used as input to the U.S. Fish and Wildlife Service's decision to list the polar bear as a threatened species under the Endangered Species Act; • Contrasting studies on the existence of a "tipping point," beyond which Arctic sea ice decline will become (or has already become) irreversible, including an examination of the role of the small ice cap instability in global warming simulations; • A significant summertime atmospheric response to sea ice reduction in an atmospheric general circulation model, suggesting a positive feedback and the potential for short-term climate prediction. The book will be of interest to researchers attempting to understand the recent behavior of Arctic sea ice, model projections of future sea ice loss, and the consequences of sea ice loss for the natural and human systems of the Arctic.

Constraints on Nubular Electromagnetic Pulses

NASA Astrophysics Data System (ADS)

Eisenhour, D. D.; Buseck, P. R.

1993-07-01

Chondritic meteorites contain an abundance of silicate minerals with opaque inclusions of oxides, sulfides, and metals. These host silicates interact differently from their enclosed opaques to electromagnetic (EM) radiation; specifically, silicates are inefficient at absorbing EM energy in the visible and near infrared while metals, sulfides, and Fe oxides absorb strongly in this frequency range. In the presence of a strong electromagnetic pulse (EMP), this preferential absorption leads to the selective heating of the opaque inclusions and can produce unique textures ("dirty snowballs": intimate, ~spherical intergrowths of silicate and opaque minerals with radii of < 1 to 10 micrometers) that record the passage of the EMP. Many chondrules, CAIs, and isolated silicate grains within chondritic meteorites exhibit these unique features, suggesting that strong EMPs were common in the early solar nebula [1]. Here we discuss new constraints on nebular EMPs obtained from both experimental simulations and calculations of radiative heat transport. To test the feasibility of producing "dirty snowball" textures by EMP heating, olivines and pyroxenes containing metal and sulfide inclusions were heated with a 10 watt, argon-ion, CW laser operated at 514 nm. Comparisons between meteoritic "dirty snowball" textures and experimentally produced textures confirm the ability to produce the meteoritic textures by EMP heating and suggest heating times and fluxes of 0.25 to 10 seconds and 10^9 to 10^10 ergs cm^-2 sec^-1. Fluxes less than 10^9 ergs cm^-2 sec^-1 were insufficient to melt metal and sulfide inclusions, while fluxes greater than 10^10 ergs cm^-2 sec^-1 resulted in complete melting of metal, sulfide, and silicates. The experimentally determined heating time scales suggest that radiative equilibrium was reached in the "dirty snowball" formation process, indicating that the range of observed textures is controlled by cooling rates. Calculations of radiative absorption and emission allow further constraints to be placed on the EMPs responsible for "dirty snowball" formation. The absorption and emission efficiencies of grains in a blackbody radiation field were determined by calculating Planck mean cross sections for olivine, pyroxene, and iron as a function of grain size [2,3]. This information was combined with conductive heat flow calculations to determine the behavior of olivine and pyroxene grains with small inclusions of metal. Results indicate that "dirty snowball" formation results only over a narrow flux range for a given multiphase assemblage, with higher fluxes required for smaller, more transparent, or more refractory grains. For a 100-mm olivine chondrule containing a 10-micrometer "dirty snowball," the required flux is ~9 +- 1 x 10^8 ergs cm^-2 sec^-1, with a minimum pulse duration of 4 seconds (assuming an initial grain temperature of 500 K prior to heating). These values are in good agreement with experimentally determined values. The results show that pulses energetic enough to create "dirty snowballs" are also capable of producing the total melting required for chondrule formation with only slight increases in flux, or with only marginally different grain properties (e.g., more opaque inclusions, lower melting points, higher absorption cross sections). Because of the temperature and grain size dependence of the Planck mean cross sections of silicates, an EMP of the type described above will selectively melt larger aggregates and individual grains (>100 micrometer) while leaving smaller aggregates and grains unmelted. Therefore, natural products of EMP heating are: 1) the formation of chondrules in a sustained dusty environment, 2) a paucity of small chondrules, and 3) residual grains relatively unaffected by the EMPs. References: [1] Eisenhour D. D. and Buseck P. R. (1993) LPSC XXIV, 435-436. [2] Falk S. W. and Scalo J. M. (1975) Ap. J., 202, 690-695. [3] Gilman R. C. (1974) Ap. J. Supp., 268, 28, 397-403.

The "Dirty Weather" diaries of Reverend Richard Davis: insights about early Colonial-era meteorology and climate variability for Northern New Zealand, 1839-1851

NASA Astrophysics Data System (ADS)

Lorrey, A. M.; Chappell, P. R.

2015-08-01

Reverend Richard Davis (1790-1863) was a Colonial-era missionary stationed in the Far North of New Zealand who was a key figure in the early efforts of the Church Mission Society. He kept meticulous meteorological records for the early settlements of Waimate North and Kaikohe, and his observations are preserved in a two-volume set in the rare manuscripts archive at the Auckland City Library. The Davis diary volumes are significant because they constitute some of the earliest land-based meteorological measurements that were continually chronicled for New Zealand. The diary measurements cover nine years within the 1839-1851 timespan that are broken into two parts: 1839-1844 and 1848-1851. Davis' meteorological recordings include daily 9 AM and noon temperatures and mid-day pressure measurements. Qualitative comments in the diary note prevailing wind flow, wind strength, cloud cover, climate variability impacts, bio-indicators suggestive of drought, and notes on extreme weather events. "Dirty weather" comments scattered throughout the diary describe disturbed conditions with strong winds and driving rainfall. The Davis diary entries coincide with the end of the Little Ice Age (LIA) and they indicate southerly and westerly circulation influences and cooler winter temperatures were more frequent than today. A comparison of climate field reconstructions derived from the Davis diary data and tree ring-based winter temperature reconstructions are supported by tropical coral palaeotemperature evidence. Davis' pressure measurements were corroborated using ship log data from vessels associated with iconic Antarctic exploration voyages that were anchored in the Bay of Islands, and suggest the pressure series he recorded are robust and can be used as `station data'. The Reverend Davis meteorological data are expected to make a significant contribution to the Atmospheric Circulation Reconstructions across the Earth (ACRE) project, which feeds the major data requirements for the longest historical reanalysis - the 20th Century Reanalysis Project (20CR). Thus these new data will help extend surface pressure-based re-analysis reconstructions of past weather covering New Zealand within the data-sparse Southern Hemisphere.

The "dirty weather" diaries of Reverend Richard Davis: insights about early colonial-era meteorology and climate variability for northern New Zealand, 1839-1851

NASA Astrophysics Data System (ADS)

Lorrey, Andrew M.; Chappell, Petra R.

2016-03-01

Reverend Richard Davis (1790-1863) was a colonial-era missionary stationed in the Far North of New Zealand who was a key figure in the early efforts of the Church Mission Society. He kept meticulous meteorological records for the early settlements of Waimate North and Kaikohe, and his observations are preserved in a two-volume set in the Sir George Grey Special Collections in the Auckland Central Library. The Davis diary volumes are significant because they constitute some of the earliest land-based meteorological measurements that were continually chronicled for New Zealand. The diary measurements cover nine years within the 1839-1851 time span that are broken into two parts: 1839-1844 and 1848-1851. Davis' meteorological recordings include daily 9 a.m. and noon temperatures and midday pressure measurements. Qualitative comments in the diary note prevailing wind flow, wind strength, cloud cover, climate variability impacts, bio-indicators suggestive of drought, and notes on extreme weather events. "Dirty weather" comments scattered throughout the diary describe disturbed conditions with strong winds and driving rainfall. The Davis diary entries coincide with the end of the Little Ice Age (LIA) and they indicate southerly and westerly circulation influences and cooler winter temperatures were more frequent than today. A comparison of climate field reconstructions derived from the Davis diary data and tree-ring-based winter temperature reconstructions are supported by tropical coral palaeotemperature evidence. Davis' pressure measurements were corroborated using ship log data from vessels associated with iconic Antarctic exploration voyages that were anchored in the Bay of Islands, and suggest the pressure series he recorded are robust and can be used as "station data". The Reverend Davis meteorological data are expected to make a significant contribution to the Atmospheric Circulation Reconstructions across the Earth (ACRE) project, which feeds the major data requirements for the longest historical reanalysis - the 20th Century Reanalysis Project (20CR). Thus these new data will help extend surface pressure-based reanalysis reconstructions of past weather covering New Zealand within the data-sparse Southern Hemisphere.

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 changes in relation to sea ice dynamics. Additional records of benthic foraminiferal assemblages and biogenic opal accumulation rates further elucidate the influence of PP on U/Mn, which can help to investigate the strength of NPIW formation along the eastern Bering slope, important for CO2 outgassing and abyssal North Pacific carbon storage.

High pressure ices are not the end of the story for large icy moons habitability: experimental studies of salts effects on high pressure ices and the implications for icy worlds large hydrosphere structure and chemical evolution

NASA Astrophysics Data System (ADS)

Journaux, Baptiste; Abramson, Evan; Brown, J. Michael; Bollengier, Olivier

2017-10-01

The presence of several phases of deep high-pressure ices in large icy moons hydrosphere has often been pointed as a major limitation for the habitability of an uppermost ocean. As they are gravitationally stable bellow liquid H2O, they are thought to act as a chemical barrier between the rocky bed and the ocean. Solutes, including salt species such as NaCl and MgSO4, have been suggested inside icy world oceans from remote sensing, magnetic field measurements and chondritic material alteration models. Unfortunately, the pressures and temperatures inside these hydrospheres are very different from the one found in Earth aqueous environments, so most of our current thermodynamic databases do not cover the range of conditions relevant for modeling realistically large icy worlds interiors.Recent experimental results have shown that the presence of solutes, and more particularly salts, in equilibrium with high pressure ices have large effects on the stability, buoyancy and chemistry of all the phases present at these extreme conditions.In particular brines have been measured to be sometimes more dense than the high pressure ices at melting conditions, possibly creating several oceanic layer "sandwiched" in between two ices shells or in contact with the rocky bed.Other effects currently being investigated by our research group also covers ice melting curve depressions that depend on the salt species and incorporation of solutes inside the crystallographic lattice of high pressure ices. Both of these could have very important implication at the planetary scale, enabling thicker/deeper liquid oceans, and allowing chemical transportation through the high pressure ice layer in large icy worlds.We will present the latest results obtained in-situ using diamond anvil cell high pressure allowing to probe the density, chemistry and thermodynamic properties of high pressure ice and aqueous solutions in equilibrium with Na-Mg-SO4-Cl ionic species.We will also discuss the new planetary evolution scenarios implied by these new material and thermodynamic properties and how this could suggest the existence of new habitable environments in large icy worlds, even when high pressure ices dominate the total volume of the hydrosphere.

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.

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.

Implications of Observed High Supersaturation for TTL Cloud Formation and Dehydration

NASA Technical Reports Server (NTRS)

Jensen, Eric

2004-01-01

In situ measurements of water vapor concentration made during the CRYSTAL-FACE and Pre-AVE missions indicate higher than expected supersaturations in both clear and cloudy air near the cold tropical tropopause: (1) steady-state ice supersaturations of 20-30% were measured within cirrus at T < 200 K; (2) supersaturations exceeding 100% (near water saturation) were observed under cloud-free conditions near 187 K. The in-cloud measurements challenge the conventional belief that any water vapor in excess of ice saturation should be depleted by crystal growth given sufficient time. The high clear-sky supersaturations imply that thresholds for ice nucleation due to homogeneous freezing of aerosols (or any other mechanism) are much higher than those inferred from laboratory measurements. We will use simulations of Tropical Tropopause Layer (TTL) transport and cloud formation throughout the tropics to show that these effects have important implications for TTL cloud frequency and freeze-drying of air crossing the tropical tropopause cold trap.

Exploration and protection of Europa's biosphere: implications of permeable ice.

PubMed

Greenberg, Richard

2011-03-01

Europa has become a high-priority objective for exploration because it may harbor life. Strategic planning for its exploration has been predicated on an extreme model in which the expected oceanic biosphere lies under a thick ice crust, buried too deep to be reached in the foreseeable future, which would beg the question of whether other active satellites might be more realistic objectives. However, Europa's ice may in fact be permeable, with very different implications for the possibilities for life and for mission planning. A biosphere may extend up to near the surface, making life far more readily accessible to exploration while at the same time making it vulnerable to contamination. The chances of finding life on Europa are substantially improved while the need for planetary protection becomes essential. The new National Research Council planetary protection study will need to go beyond its current mandate if meaningful standards are to be put in place. © Mary Ann Liebert, Inc.

How experimentally to detect a solitary superconductivity in dirty ferromagnet-superconductor trilayers?

NASA Astrophysics Data System (ADS)

Avdeev, Maxim V.; Proshin, Yurii N.

2017-10-01

We theoretically study the proximity effect in the thin-film layered ferromagnet (F) - superconductor (S) heterostructures in F1F2S design. We consider the boundary value problem for the Usadel-like equations in the case of so-called ;dirty; limit. The ;latent; superconducting pairing interaction in F layers taken into account. The focus is on the recipe of experimental preparation the state with so-called solitary superconductivity. We also propose and discuss the model of the superconducting spin valve based on F1F2S trilayers in solitary superconductivity regime.

Saturn's satellites - Near-infrared spectrophotometry (0.65-2.5 microns) of the leading and trailing sides and compositional implications

NASA Technical Reports Server (NTRS)

Steele, A.; Clark, R. N.; Brown, R. H.; Owensby, P. D.

1984-01-01

Water ice absorptions at 2.0, 1.5, and 1.25 microns are noted in near-IR spectra of Tethys, Dione, Rhea, Iapetus, and Hyperion, and the weak 1.04-micron ice absorption, which is detected for Rhea and Dione, is studied to establish band depth upper limits. The leading-trailing side 1.04-micron ice band depth differences on Saturn's satellites are similar to those for the Galilean satellites, indicating possible surface modification by magnetospheric charged particle bombardment. Limits are obtained for the amounts of particulates, trapped gases, and ammonium hydroxide on the surface. With the exception of the dark side of Iapetus, the surfaces of all of Saturn's satellites are nearly pure ice water.

The interaction between sea ice and salinity-dominated ocean circulation: implications for halocline stability and rapid changes of sea-ice cover

NASA Astrophysics Data System (ADS)

Jensen, M. F.; Nilsson, J.; Nisancioglu, K. H.

2016-02-01

In this study, we develop a simple conceptual model to examine how interactions between sea ice and oceanic heat and freshwater transports affect the stability of an upper-ocean halocline in a semi-enclosed basin. The model represents a sea-ice covered and salinity stratified ocean, and consists of a sea-ice component and a two-layer ocean; a cold, fresh surface layer above a warmer, more saline layer. The sea-ice thickness depends on the atmospheric energy fluxes as well as the ocean heat flux. We introduce a thickness-dependent sea-ice export. Whether sea ice stabilizes or destabilizes against a freshwater perturbation is shown to depend on the representation of the vertical mixing. In a system where the vertical diffusivity is constant, the sea ice acts as a positive feedback on a freshwater perturbation. If the vertical diffusivity is derived from a constant mixing energy constraint, the sea ice acts as a negative feedback. However, both representations lead to a circulation that breaks down when the freshwater input at the surface is small. As a consequence, we get rapid changes in sea ice. In addition to low freshwater forcing, increasing deep-ocean temperatures promote instability and the disappearance of sea ice. Generally, the unstable state is reached before the vertical density difference disappears, and small changes in temperature and freshwater inputs can provoke abrupt changes in sea ice.

Meltwater storage in low-density near-surface bare ice in the Greenland ice sheet ablation zone

NASA Astrophysics Data System (ADS)

Cooper, Matthew G.; Smith, Laurence C.; Rennermalm, Asa K.; Miège, Clément; Pitcher, Lincoln H.; Ryan, Jonathan C.; Yang, Kang; Cooley, Sarah W.

2018-03-01

We document the density and hydrologic properties of bare, ablating ice in a mid-elevation (1215 m a.s.l.) supraglacial internally drained catchment in the Kangerlussuaq sector of the western Greenland ice sheet. We find low-density (0.43-0.91 g cm-3, μ = 0.69 g cm-3) ice to at least 1.1 m depth below the ice sheet surface. This near-surface, low-density ice consists of alternating layers of water-saturated, porous ice and clear solid ice lenses, overlain by a thin (< 0.5 m), even lower density (0.33-0.56 g cm-3, μ = 0.45 g cm-3) unsaturated weathering crust. Ice density data from 10 shallow (0.9-1.1 m) ice cores along an 800 m transect suggest an average 14-18 cm of specific meltwater storage within this low-density ice. Water saturation of this ice is confirmed through measurable water levels (1-29 cm above hole bottoms, μ = 10 cm) in 84 % of cryoconite holes and rapid refilling of 83 % of 1 m drilled holes sampled along the transect. These findings are consistent with descriptions of shallow, depth-limited aquifers on the weathered surface of glaciers worldwide and confirm the potential for substantial transient meltwater storage within porous low-density ice on the Greenland ice sheet ablation zone surface. A conservative estimate for the ˜ 63 km2 supraglacial catchment yields 0.009-0.012 km3 of liquid meltwater storage in near-surface, porous ice. Further work is required to determine if these findings are representative of broader areas of the Greenland ice sheet ablation zone, and to assess the implications for sub-seasonal mass balance processes, surface lowering observations from airborne and satellite altimetry, and supraglacial runoff processes.

Pink marine sediments reveal rapid ice melt and Arctic meltwater discharge during Dansgaard-Oeschger warmings.

PubMed

Rasmussen, Tine L; Thomsen, Erik

2013-01-01

The climate of the last glaciation was interrupted by numerous abrupt temperature fluctuations, referred to as Greenland interstadials and stadials. During warm interstadials the meridional overturning circulation was active transferring heat to the north, whereas during cold stadials the Nordic Seas were ice-covered and the overturning circulation was disrupted. Meltwater discharge, from ice sheets surrounding the Nordic Seas, is implicated as a cause of this ocean instability, yet very little is known regarding this proposed discharge during warmings. Here we show that, during warmings, pink clay from Devonian Red Beds is transported in suspension by meltwater from the surrounding ice sheet and replaces the greenish silt that is normally deposited on the north-western slope of Svalbard during interstadials. The magnitude of the outpourings is comparable to the size of the outbursts during the deglaciation. Decreasing concentrations of ice-rafted debris during the interstadials signify that the ice sheet retreats as the meltwater production increases.

Life in ice: implications to astrobiology

NASA Astrophysics Data System (ADS)

Hoover, Richard B.; Pikuta, Elena V.

2009-08-01

During previous research expeditions to Siberia, Alaska and Antarctica, it was observed that glaciers and ice wedges contained bacterial cells that became motile as soon as the ice melted. This phenomenon of live bacteria in ice was first documented for microbes in ancient ice cores from Vostok, Antarctica. The first validly published species of Pleistocene bacteria alive on Earth today was Carnobacterium pleistocenium. This extremophile had remained for 32,000 years, encased in ice recently exposed in the Fox Tunnel of Alaska. These frozen bacteria began to swim as soon as the ice was thawed. Dark field microscopy studies revealed that large numbers of bacteria exhibited motility as soon as glacial ice was melted during our recent Expeditions to Alaska and Antarctica led to the conclusion that microbial life in ice was not a rare phenomenon. The ability of bacteria to remain alive while frozen in ice for long periods of time is of great significance to Astrobiology. In this paper, we describe the recent observations and advance the hypothesis that life in ice provides valuable clues to how we can more easily search for evidence of life on the Polar Caps of Mars, comets and other icy bodies of our Solar System. It is suggested that cryopanspermia may have played a far more important role in Origin of Life on Earth and the distribution of Life throughout the Cosmos and than previously thought possible.

Prospecting for Martian Ice from Orbit

NASA Technical Reports Server (NTRS)

Kanner, L. C.; Bell, M. S.; Allen, C. C.

2003-01-01

Recent data from the Gamma-Ray Spectrometer (GRS) on Mars Odyssey indicate the presence of a hydrogen-rich layer tens of centimeters thick in high latitudes on Mars. This hydrogen-rich layer correlates to previously determined regions of ice stability. It has been suggested that the subsurface hydrogen is ice and constitutes 35 plus or minus 15% by weight near the north and south polar regions. This study constrains the location of subsurface ice deposits on the scale of kilometers or smaller by combining GRS data with surface features indicative of subsurface ice. The most recognizable terrestrial geomorphic indicators of subsurface ice, formed in permafrost and periglacial environments, include thermokarst pits, pingos, pseudocraters and patterned ground. Patterned ground features have geometric forms such as circles, polygons, stripes and nets. This study focuses on the polygonal form of patterned ground, selected for its discernable shape and subsurface implications. Polygonal features are typically demarcated by troughs, beneath which grow vertical ice-wedges. Ice-wedges form in thermal contraction cracks in ice-rich soil and grow with annual freezing and thawing events repeated over tens of years. Ice wedges exist below the depth of seasonal freeze-thaw. Terrestrial ice wedges can be several meters deep and polygons can be tens of meters apart, and, on rare occasions, up to 1 km. The crack spacing of terrestrial polygons is typically 3 to 10 times the crack depth.

The condensation and vaporization behavior of ices containing SO2, H2S, and CO2: Implications for Io

NASA Technical Reports Server (NTRS)

Sandford, Scott A.; Allamandola, Louis J.

1993-01-01

In an extension of previously reported work on ices containing CO, CO2, H2O, CH3OH, NH3, and H2, measurements of the physical and infrared spectral properties of ices containing molecules relevant to Jupiter's moon Io are presented. These include studies on ice systems containing SO2, H2S, and CO2. The condensation and sublimation behaviors of each ice system and surface binding energies of their components are discussed. The surface binding energies can be used to calculate the residence times of the molecules on a surface as a function of temperature and thus represent important parameters for any calculation that attempts to model the transport of these molecules on Io's surface. The derived values indicate that SO2 frosts on Io are likely to anneal rapidly, resulting in less fluffy, 'glassy' ices and that H2S can be trapped in the SO2 ices of Io during night-time hours provided that SO2 deposition rates are on the order of 5 micrometers/hr or larger.

"I Don't Shag Dirty Girls": Marginalized Masculinities and the Use of Partner Selection as a Sexual Health Risk Reduction Strategy in Heterosexual Young Men.

PubMed

Limmer, Mark

2016-03-01

Understanding and addressing the sexual risk taking of young men remains a key research, policy, and practice concern in attempts to improve the emotional and physical sexual health of young men and their sexual partners. This article explores one of the ways in which young men attempt to mitigate sexual risk through the assigning of labels to particular young women and using these as a basis for their decisions in relation to sexual activity, contraception, and condom use. The article uses the lens of hegemonic masculinities theory to increase understanding of the role played by the construction and performance of marginalized masculinities and how these in turn are influenced by social exclusionary processes. The article draws on focus group and interview data from 46 young men aged 15 to 17 years living in the northwest of England, purposively selected on the basis of the prevailing policy definitions of social inclusion and exclusion. The article describes a form of marginalized masculinity pertaining to socially excluded young men, which as a result of limited access to other tenets of hegemonic masculinity, is disproportionately reliant on sexual expertise and voracity alongside overt demonstrations of their superiority over women. It is in this context that young women are assigned the labels of "dirty" or "clean" on the basis of a selection of arbitrary judgments relating to dress, demeanor, area of residence, and perceived sexual activities. The motivations of the young men, the impact on young women, and the policy and practice implications are all discussed. © The Author(s) 2014.

New age constraints for the Saalian glaciation in northern central Europe: Implications for the extent of ice sheets and related proglacial lake systems

NASA Astrophysics Data System (ADS)

Lang, Jörg; Lauer, Tobias; Winsemann, Jutta

2018-01-01

A comprehensive palaeogeographic reconstruction of ice sheets and related proglacial lake systems for the older Saalian glaciation in northern central Europe is presented, which is based on the integration of palaeo-ice flow data, till provenance, facies analysis, geomorphology and new luminescence ages of ice-marginal deposits. Three major ice advances with different ice-advance directions and source areas are indicated by palaeo-ice flow directions and till provenance. The first ice advance was characterised by a southwards directed ice flow and a dominance of clasts derived from southern Sweden. The second ice advance was initially characterised by an ice flow towards the southwest. Clasts are mainly derived from southern and central Sweden. The latest stage in the study area (third ice advance) was characterised by ice streaming (Hondsrug ice stream) in the west and a re-advance in the east. Clasts of this stage are mainly derived from eastern Fennoscandia. Numerical ages for the first ice advance are sparse, but may indicate a correlation with MIS 8 or early MIS 6. New pIRIR290 luminescence ages of ice-marginal deposits attributed to the second ice advance range from 175 ± 10 to 156 ± 24 ka and correlate with MIS 6. The ice sheets repeatedly blocked the main river-drainage pathways and led to the formation of extensive ice-dammed lakes. The formation of proglacial lakes was mainly controlled by ice-damming of river valleys and major bedrock spillways; therefore the lake levels and extends were very similar throughout the repeated ice advances. During deglaciation the lakes commonly increased in size and eventually drained successively towards the west and northwest into the Lower Rhine Embayment and the North Sea. Catastrophic lake-drainage events occurred when large overspill channels were suddenly opened. Ice-streaming at the end of the older Saalian glaciation was probably triggered by major lake-drainage events.

The Role of Aerosols on Precipitation Processes: Cloud Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Matsui, T.

2012-01-01

Cloud microphysics is inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, a detailed spectral-bin microphysical scheme was implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e., 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region, the sub-tropics (Florida) and midlatitudes using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CeN case but has less cloud water mass aloft. Because the spectral-bin model explicitly calculates and allows for the examination of both the mass and number concentration of species in each size category, a detailed analysis of the instantaneous size spectrum can be obtained for these cases. It is shown that since the low (CN case produces fewer droplets, larger sizes develop due to greater condensational and collection growth, leading to a broader size spectrum in comparison to the high CCN case. Sensitivity tests were performed to identify the impact of ice processes, radiation and large-scale influence on cloud-aerosol interactive processes, especially regarding surface rainfall amounts and characteristics (i.e., heavy or convective versus light or stratiform types). In addition, an inert tracer was included to follow the vertical redistribution of aerosols by cloud processes. We will also give a brief review from observational evidence on the role of aerosol on precipitation processes.

Effect of Ice-Shell Thickness Variations on the Tidal Deformation of Enceladus

NASA Astrophysics Data System (ADS)

Choblet, G.; Cadek, O.; Behounkova, M.; Tobie, G.; Kozubek, T.

2015-12-01

Recent analysis of Enceladus's gravity and topography has suggested that the thickness of the ice shell significantly varies laterally - from 30-40 km in the south polar region to 60 km elsewhere. These variations may influence the activity of the geysers and increase the tidal heat production in regions where the ice shell is thinned. Using a model including a regional or global subsurface ocean and Maxwell viscoelasticity, we investigate the impact of these variations on the tidal deformation of the moon and its heat production. For that purpose, we use different numerical approaches - finite elements, local application of 1d spectral method, and a generalized spectral method. Results obtained with these three approaches for various models of ice-shell thickness variations are presented and compared. Implications of a reduced ice shell thickness for the south polar terrain activity are discussed.

The physical and infrared spectral properties of CO2 in astrophysical ice analogs

NASA Technical Reports Server (NTRS)

Sandford, S. A.; Allamandola, L. J.

1990-01-01

Results of measurements of the infrared spectroscopic and condensation-vaporization properties of CO2 in pure and mixed ices are presented. Detailed examination of five infrared CO2 bands, 2.20, 2.78, 4.27, 15.2, and 4.39 microns, shows that the peak position, FWHM, and profile of the bands provide important information about the composition, formation, and subsequent thermal history of the ices. Absorption coefficients and their temperature dependence for all five CO2 bands are determined. The temperature dependence variation is found to be less than 15 percent from 10 to 150 K, i.e., the temperature at which H2O ice sublimes. The number of parameters associated with the physical behavior of CO2 in CO2- and H2O-rich ices, including surface binding energies, and condensation and sublimation temperatures, are determined under experimental conditions. The implications of the data obtained for cometary models are considered.

Scale structure: Processing Minimum Standard and Maximum Standard Scalar Adjectives

PubMed Central

Frazier, Lyn; Clifton, Charles; Stolterfoht, Britta

2008-01-01

Gradable adjectives denote a function that takes an object and returns a measure of the degree to which the object possesses some gradable property (Kennedy, 1999). Scales, ordered sets of degrees, have begun to be studied systematically in semantics (Kennedy, to appear, Kennedy & McNally, 2005, Rotstein & Winter, 2004). We report four experiments designed to investigate the processing of absolute adjectives with a maximum standard (e.g., clean) and their minimum standard antonyms (dirty). The central hypothesis is that the denotation of an absolute adjective introduces a ‘standard value’ on a scale as part of the normal comprehension of a sentence containing the adjective (the “Obligatory Scale” hypothesis). In line with the predictions of Kennedy and McNally (2005) and Rotstein and Winter (2004), maximum standard adjectives and minimum standard adjectives systematically differ from each other when they are combined with minimizing modifiers like slightly, as indicated by speeded acceptability judgments. An eye movement recording study shows that, as predicted by the Obligatory Scale hypothesis, the penalty due to combining slightly with a maximum standard adjective can be observed during the processing of the sentence; the penalty is not the result of some after-the-fact inferencing mechanism. Further, a type of ‘quantificational variability effect’ may be observed when a quantificational adverb (mostly) is combined with a minimum standard adjective in sentences like The dishes are mostly dirty, which may receive either a degree interpretation (e.g. 80% dirty) or a quantity interpretation (e.g., 80% of the dishes are dirty). The quantificational variability results provide suggestive support for the Obligatory Scale hypothesis by showing that the standard of a scalar adjective influences the preferred interpretation of other constituents in the sentence. PMID:17376422

Mass Fluxes of Ice and Oxygen Across the Entire Lid of Lake Vostok from Observations of Englacial Radiowave Attenuation

NASA Astrophysics Data System (ADS)

Winebrenner, D. P.; Kintner, P. M. S.; MacGregor, J. A.

2017-12-01

Over deep Antarctic subglacial lakes, spatially varying ice thickness and the pressure-dependent melting point of ice result in areas of melting and accretion at the ice-water interface, i.e., the lake lid. These ice mass fluxes drive lake circulation and, because basal Antarctic ice contains air-clathrate, affect the input of oxygen to the lake, with implications for subglacial life. Inferences of melting and accretion from radar-layer tracking and geodesy are limited in spatial coverage and resolution. Here we develop a new method to estimate rates of accretion, melting, and the resulting oxygen input at a lake lid, using airborne radar data over Lake Vostok together with ice-temperature and chemistry data from the Vostok ice core. Because the lake lid is a coherent reflector of known reflectivity (at our radar frequency), we can infer depth-averaged radiowave attenuation in the ice, with spatial resolution 1 km along flight lines. Spatial variation in attenuation depends mostly on variation in ice temperature near the lid, which in turn varies strongly with ice mass flux at the lid. We model ice temperature versus depth with ice mass flux as a parameter, thus linking that flux to (observed) depth-averaged attenuation. The resulting map of melt- and accretion-rates independently reproduces features known from earlier studies, but now covers the entire lid. We find that accretion is dominant when integrated over the lid, with an ice imbalance of 0.05 to 0.07 km3 a-1, which is robust against uncertainties.

Reconstruction of historic sea ice conditions in a sub-Arctic lagoon

USGS Publications Warehouse

Petrich, Chris; Tivy, Adrienne C.; Ward, David H.

2014-01-01

Historical sea ice conditions were reconstructed for Izembek Lagoon, Bering Sea, Alaska. This lagoon is a crucial staging area during migration for numerous species of avian migrants and a major eelgrass (Zostera marina) area important to a variety of marine and terrestrial organisms, especially Pacific Flyway black brant geese (Branta bernicla nigricans). Ice cover is a common feature of the lagoon in winter, but appears to be declining, which has implications for eelgrass distribution and abundance, and its use by wildlife. We evaluated ice conditions from a model based on degree days, calibrated to satellite observations, to estimate distribution and long-term trends in ice conditions in Izembek Lagoon. Model results compared favorably with ground observations and 26 years of satellite data, allowing ice conditions to be reconstructed back to 1943. Specifically, periods of significant (limited access to eelgrass areas) and severe (almost complete ice coverage of the lagoon) ice conditions could be identified. The number of days of severe ice within a single season ranged from 0 (e.g., 2001) to ≥ 67 (e.g., 2000). We detected a slight long-term negative trend in ice conditions, superimposed on high inter-annual variability in seasonal aggregate ice conditions. Based on reconstructed ice conditions, the seasonally cumulative number of significant or severe ice days correlated linearly with mean air temperature from January until March. Further, air temperature at Izembek Lagoon was correlated with wind direction, suggesting that ice conditions in Izembek Lagoon were associated with synoptic-scale weather patterns. Methods employed in this analysis may be transferable to other coastal locations in the Arctic.

Ikaite crystal distribution in Arctic winter sea ice and implications for CO2 system dynamics

NASA Astrophysics Data System (ADS)

Rysgaard, S.; Søgaard, D. H.; Cooper, M.; Pućko, M.; Lennert, K.; Papakyriakou, T. N.; Wang, F.; Geilfus, N. X.; Glud, R. N.; Ehn, J.; McGinnnis, D. F.; Attard, K.; Sievers, J.; Deming, J. W.; Barber, D.

2012-12-01

The precipitation of ikaite (CaCO3·6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74° N, 20° W) of NE Greenland. Ikaite crystals, ranging in size from a few µm to 700 µm were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea-ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surfaceice values of 700-900 µmol kg-1 ice (~ 25 × 106 crystals kg-1) to bottom-layer values of 100-200 µmol kg-1 ice (1-7 × 106 kg-1), all of which are much higher (4-10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration whereas TA concentrations in bottom layers were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolved in bottom layers. From these findings and model calculations we relate sea ice formation and melt to observed pCO2 conditions in polar surface waters, and hence, the air-sea CO2 flux.

The ice VII-ice X phase transition with implications for planetary interiors

NASA Astrophysics Data System (ADS)

Aarestad, B.; Frank, M. R.; Scott, H.; Bricker, M.; Prakapenka, V.

2008-12-01

A significant amount of research on the high pressure polymorphs of H2O have detailed the lattice structure and density of these phases, namely ice VI, ice VII, and ice X. These high pressure ices are noteworthy as they may comprise a considerable part of the interior of large icy planets and satellites. However, there is a dearth of data on how the incorporation of an impurity, charged or non-charged, affects the ice VII-ice X transition. This study examined the ice VII-ice X transition that occurs at approximately 62 GPa with a pure system and two select impure systems. Solutions of pure H2O, 1.6 mole percent NaCl in H2O, and 1.60 mole percent CH3OH in H2O were compressed in a diamond anvil cell (DAC). The experiments were performed at the GSECARS 13-BM-D beam line at the Advanced Photon Source at Argonne National Laboratory. Powder diffraction data of the ice samples were collected using monochromatic X-ray radiation, 0.2755 Å, and a MAR 345 online imaging system at intervals of approximately 2 GPa up to ~71.5, ~74.5, and ~68 GPa, respectively. Analyses of the data provided volume-pressure relations (at 298 K) which were used to detail the ice VII-ice X phase transition. The pressure of the phase transition, based upon an interpretation of the X-ray diffraction data, was found to vary as a function of the impurity type. Thus, the depth of the ice VII-ice X phase transition within an ice-rich planetary body can be influenced by trace-level impurities.

Satellite-derived submarine melt rates and mass balance (2011-2015) for Greenland's largest remaining ice tongues

NASA Astrophysics Data System (ADS)

Wilson, Nat; Straneo, Fiammetta; Heimbach, Patrick

2017-12-01

Ice-shelf-like floating extensions at the termini of Greenland glaciers are undergoing rapid changes with potential implications for the stability of upstream glaciers and the ice sheet as a whole. While submarine melting is recognized as a major contributor to mass loss, the spatial distribution of submarine melting and its contribution to the total mass balance of these floating extensions is incompletely known and understood. Here, we use high-resolution WorldView satellite imagery collected between 2011 and 2015 to infer the magnitude and spatial variability of melt rates under Greenland's largest remaining ice tongues - Nioghalvfjerdsbræ (79 North Glacier, 79N), Ryder Glacier (RG), and Petermann Glacier (PG). Submarine melt rates under the ice tongues vary considerably, exceeding 50 m a-1 near the grounding zone and decaying rapidly downstream. Channels, likely originating from upstream subglacial channels, give rise to large melt variations across the ice tongues. We compare the total melt rates to the influx of ice to the ice tongue to assess their contribution to the current mass balance. At Petermann Glacier and Ryder Glacier, we find that the combined submarine and aerial melt approximately balances the ice flux from the grounded ice sheet. At Nioghalvfjerdsbræ the total melt flux (14.2 ± 0.96 km3 a-1 w.e., water equivalent) exceeds the inflow of ice (10.2 ± 0.59 km3 a-1 w.e.), indicating present thinning of the ice tongue.

The microbiome of glaciers and ice sheets.

PubMed

Anesio, Alexandre M; Lutz, Stefanie; Chrismas, Nathan A M; Benning, Liane G

2017-01-01

Glaciers and ice sheets, like other biomes, occupy a significant area of the planet and harbour biological communities with distinct interactions and feedbacks with their physical and chemical environment. In the case of the glacial biome, the biological processes are dominated almost exclusively by microbial communities. Habitats on glaciers and ice sheets with enough liquid water to sustain microbial activity include snow, surface ice, cryoconite holes, englacial systems and the interface between ice and overridden rock/soil. There is a remarkable similarity between the different specific glacial habitats across glaciers and ice sheets worldwide, particularly regarding their main primary producers and ecosystem engineers. At the surface, cyanobacteria dominate the carbon production in aquatic/sediment systems such as cryoconite holes, while eukaryotic Zygnematales and Chlamydomonadales dominate ice surfaces and snow dynamics, respectively. Microbially driven chemolithotrophic processes associated with sulphur and iron cycle and C transformations in subglacial ecosystems provide the basis for chemical transformations at the rock interface under the ice that underpin an important mechanism for the delivery of nutrients to downstream ecosystems. In this review, we focus on the main ecosystem engineers of glaciers and ice sheets and how they interact with their chemical and physical environment. We then discuss the implications of this microbial activity on the icy microbiome to the biogeochemistry of downstream ecosystems.

Genetic profiling links changing sea-ice to shifting beluga whale migration patterns

PubMed Central

Mahoney, Andrew R.; Suydam, Robert; Quakenbush, Lori; Whiting, Alex; Lowry, Lloyd; Harwood, Lois

2016-01-01

There is increasing concern over how Arctic fauna will adapt to climate related changes in sea-ice. We used long-term sighting and genetic data on beluga whales (Delphinapterus leucas) in conjunction with multi-decadal patterns of sea-ice in the Pacific Arctic to investigate the influence of sea-ice on spring migration and summer residency patterns. Substantial variations in sea-ice conditions were detected across seasons, years and sub-regions, revealing ice–ocean dynamics more complex than Arctic-wide trends suggest. This variation contrasted with a highly consistent pattern of migration and residency by several populations, indicating that belugas can accommodate widely varying sea-ice conditions to perpetuate philopatry to coastal migration destinations. However, a number of anomalous migration and residency events were detected and coincided with anomalous ice years, and in one case with an increase in killer whale (Orcinus orca) sightings and reported predation on beluga whales. The behavioural shifts were likely driven by changing sea-ice and associated changes in resource dispersion and predation risk. Continued reductions in sea-ice may result in increased predation at key aggregation areas and shifts in beluga whale behaviour with implications for population viability, ecosystem structure and the subsistence cultures that rely on them.

Detection of cryogenic water ice contaminants and the IR AI&T environment

NASA Astrophysics Data System (ADS)

Lynch, David K.; Russell, Ray W.

2000-12-01

Several remote sensing/infrared space surveillance programs in the midst of assembly, integration and test have recently experienced delays when water vapor was deposited as ice on cold surfaces in a sensor under test or calibration. When these surfaces were at critical locations, the sensitivity or response of the sensor decreased significantly because the ice absorbed the incoming signal. The source of water vapor could be from a chamber leak or outgassing from the sensor system or the vacuum chamber itself. In order to quantify the effects of ice deposits on signals in various spectral bands, published optical constants for amorphous and crystalline water ice have been used to calculate the transmission of water ice films as a function of wavelength from 1 to 20 microns. The results are presented in two ways: spectra of the physical thickness of a layer of ice whose absorption optical depth is unity, and transmission spectra for several characteristic layer thicknesses. These tools can be used in estimating the amount of ice - and by inference water vapor - present in the system. Related calculations can also be used to assess the probability that a given hardware setup or resulting data set is showing signs of degradation of response due to ice absorption, and the implications for those trying to interpret the results.

The Classification and Geomorphic Implications of Thaw Lakes on the Arctic Coastal Plain, Alaska

DTIC Science & Technology

1975-12-01

Plain is underlain by ice-rich marine sediments , the product of several marine transgressions and regressions. Numerous thaw lake basins of...variable morphology and distribution have developed on the perennially frozen sediments (permafrost) of this low-lying plain. Most notable are the large...mechanism of thaw lake formation was recognized whereby sediment laden ice rafts initiated thawing of the permafrost and formation of lake basins

Glacier crevasses: Observations, models, and mass balance implications

NASA Astrophysics Data System (ADS)

Colgan, William; Rajaram, Harihar; Abdalati, Waleed; McCutchan, Cheryl; Mottram, Ruth; Moussavi, Mahsa S.; Grigsby, Shane

2016-03-01

We review the findings of approximately 60 years of in situ and remote sensing studies of glacier crevasses, as well as the three broad classes of numerical models now employed to simulate crevasse fracture. The relatively new insight that mixed-mode fracture in local stress equilibrium, rather than downstream advection alone, can introduce nontrivial curvature to crevasse geometry may merit the reinterpretation of some key historical observation studies. In the past three decades, there have been tremendous advances in the spatial resolution of satellite imagery, as well as fully automated algorithms capable of tracking crevasse displacements between repeat images. Despite considerable advances in developing fully transient three-dimensional ice flow models over the past two decades, both the zero stress and linear elastic fracture mechanics crevasse models have remained fundamentally unchanged over this time. In the past decade, however, multidimensional and transient formulations of the continuum damage mechanics approach to simulating ice fracture have emerged. The combination of employing damage mechanics to represent slow upstream deterioration of ice strength and fracture mechanics to represent rapid failure at downstream termini holds promise for implementation in large-scale ice sheet models. Finally, given the broad interest in the sea level rise implications of recent and future cryospheric change, we provide a synthesis of 10 mechanisms by which crevasses can influence glacier mass balance.

Human-Centered Systems Analysis of Aircraft Separation from Adverse Weather: Implications for Icing Remote Sensing

NASA Technical Reports Server (NTRS)

Vigeant-Langlois, Laurence; Hansman, R. John, Jr.

2003-01-01

The objective of this project was to propose a means to improve aviation weather information, training procedures based on a human-centered systems approach. Methodology: cognitive analysis of pilot's tasks; trajectory-based approach to weather information; contingency planning support; and implications for improving weather information.

Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene.

PubMed

Kingslake, J; Scherer, R P; Albrecht, T; Coenen, J; Powell, R D; Reese, R; Stansell, N D; Tulaczyk, S; Wearing, M G; Whitehouse, P L

2018-06-01

To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters 1 . Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so) 2-4 . Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today's grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance 5 . Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity-parameters that are difficult to measure and to incorporate into ice-sheet models.

Initiation of the ice phase by marine biogenic surfaces in supersaturated gas and supercooled aqueous phases.

PubMed

Alpert, Peter A; Aller, Josephine Y; Knopf, Daniel A

2011-11-28

Biogenic particles have the potential to affect the formation of ice crystals in the atmosphere with subsequent consequences for the hydrological cycle and climate. We present laboratory observations of heterogeneous ice nucleation in immersion and deposition modes under atmospherically relevant conditions initiated by Nannochloris atomus and Emiliania huxleyi, marine phytoplankton with structurally and chemically distinct cell walls. Temperatures at which freezing, melting, and water uptake occur are observed using optical microscopy. The intact and fragmented unarmoured cells of N. atomus in aqueous NaCl droplets enhance ice nucleation by 10-20 K over the homogeneous freezing limit and can be described by a modified water activity based ice nucleation approach. E. huxleyi cells covered by calcite plates do not enhance droplet freezing temperatures. Both species nucleate ice in the deposition mode at an ice saturation ratio, S(ice), as low as ~1.2 and below 240 K, however, for each, different nucleation modes occur at warmer temperatures. These observations show that markedly different biogenic surfaces have both comparable and contrasting effects on ice nucleation behaviour depending on the presence of the aqueous phase and the extent of supercooling and water vapour supersaturation. We derive heterogeneous ice nucleation rate coefficients, J(het), and cumulative ice nuclei spectra, K, for quantification and analysis using time-dependent and time-independent approaches, respectively. Contact angles, α, derived from J(het)via immersion freezing depend on T, a(w), and S(ice). For deposition freezing, α can be described as a function of S(ice) only. The different approaches yield different predictions of atmospheric ice crystal numbers primarily due to the time evolution allowed for the time-dependent approach with implications for the evolution of mixed-phase and ice clouds.

Suspension freezing of bottom sediment and biota in the Northwest Passage and implications for Arctic Ocean sedimentation

USGS Publications Warehouse

Reimnitz, E.; Marincovich, L.; McCormick, M.; Briggs, W.M.

1992-01-01

No evidence was seen for entrainment by bottom adfreezing, bluff slumping, river flooding, dragging ice keels, or significant eolian transport from land to sea. Muddy sediment with pebbles and cobbles, algae with holdfasts, ostracodes with appendages, and well-preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice. These materials indicate that suspension freezing reaching to a water depth of 25-30 m during the previous fall was responsible for entrainment. This mechanism requires rapid ice formation in open, shallow water during a freezing storm, when the ocean becomes supercooled, and frazil and anchor ice attach to and ultimately lift sediment and living organisms to the sea surface. -from Authors

New eyes in the sky measure glaciers and ice sheets

USGS Publications Warehouse

Kieffer, Hugh; Kargel, Jeffrey S.; Barry, Roger G.; Bindschadler, Robert; Bishop, Michael P.; MacKinnon, David; Ohmura, Atsumu; Raup, Bruce; Antoninetti, Massimo; Bamber, Jonathan; Braun, Mattias; Brown, Ian; Cohen, Denis; Copland, Luke; DueHagen, Jon; Engeset, Rune V.; Fitzharris, Blair; Fujita, Koji; Haeberli, Wilfried; Hagen, Jon Oue; Hall, Dorothy; Hoelzle, Martin; Johansson, Maria; Kaab, Andi; Koenig, Max; Konovalov, Vladimir; Maisch, Max; Paul, Frank; Rau, Frank; Reeh, Niels; Rignot, Eric; Rivera, Andres; De Ruyter de Wildt, Martiyn; Scambos, Ted; Schaper, Jesko; Scharfen, Greg; Shroder, Jack; Solomina, Olga; Thompson, David; van der Veen, Kees; Wohlleben, Trudy; Young, Neal

2000-01-01

The mapping and measurement of glaciers and their changes are useful in predicting sea-level and regional water supply, studying hazards and climate change [Haeberli et al., 1998],and in the hydropower industry Existing inventories cover only about 67,000 of the world's estimated 160,000 glaciers and are based on data collected over 50 years or more [e.g.,Haeberli et al., 1998]. The data available have proven that small ice bodies are disappearing at an accelerating rate and that the Antarctic ice sheet and its fringing ice shelves are undergoing unexpected, rapid change. According to many glaciologists, much larger fluctuations in land ice—with vast implications for society—are possible in the coming decades and centuries due to natural and anthropogenic climate change [Oppenheimer, 1998].

Radar measurements of melt zones on the Greenland Ice Sheet

NASA Technical Reports Server (NTRS)

Jezek, Kenneth C.; Gogineni, Prasad; Shanableh, M.

1994-01-01

Surface-based microwave radar measurements were performed at a location on the western flank of the Greenland Ice Sheet. Here, firn metamorphasis is dominated by seasonal melt, which leads to marked contrasts in the vertical structure of winter and summer firn. This snow regime is also one of the brightest radar targets on Earth with an average backscatter coefficient of 0 dB at 5.3 GHz and an incidence angle of 25 deg. By combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winter's snow pack. This observation has important implications for monitoring and understanding changes in ice sheet volume using spaceborne microwave sensors.

Remote Characterization of Ice Shelf Surface and Basal Processes: Examples from East Antarctica

NASA Astrophysics Data System (ADS)

Greenbaum, J. S.; Blankenship, D. D.; Grima, C.; Schroeder, D. M.; Soderlund, K. M.; Young, D. A.; Kempf, S. D.; Siegert, M. J.; Roberts, J. L.; Warner, R. C.; van Ommen, T. D.

2017-12-01

The ability to remotely characterize surface and basal processes of ice shelves has important implications for conducting systematic, repeatable, and safe evaluations of their stability in the context of atmospheric and oceanic forcing. Additionally, techniques developed for terrestrial ice shelves can be adapted to orbital radar sounding datasets planned for forthcoming investigations of icy moons. This has been made possible through recent advances in radar signal processing that enable these data to be used to test hypotheses derived from conceptual and numerical models of ice shelf- and ice shell-ocean interactions. Here, we present several examples of radar sounding-derived characterizations of surface and basal processes underway on ice shelves in East Antarctica. These include percolation of near-surface meltwater in warm austral summers, brine infiltration along ice shelf calving fronts, basal melt rate and distribution, and basal freeze distribution. On Europa, near-surface brines and their migration may impact local geological variability, while basal processes likely control the distribution of melt and freeze. Terrestrially, we emphasize radar-sounding records of the Totten Glacier Ice Shelf which hosts each of these processes as well as the highest known density of basal melt channels of any terrestrial ice shelf. Further, with a maximum floating ice thickness of over 2.5 km, the pressure at Totten's basal interface may be similar to that at Europa's ice-ocean interface; therefore, evaluating surface and basal processes of Totten Glacier and other ice shelves could serve as analogs for understanding melting processes of Europa's ice shell.

Release of Oxidized Bromine Species From Diatoms: Implication for the Polar Troposphere and Oceanic Polyhalomethane Production

NASA Astrophysics Data System (ADS)

Manley, S. L.; Hill, V. L.

2006-12-01

Marine and ice diatoms are known producers of polybromomethanes. These trace gases produced from ice algae have been implicated as a source of photochemically active bromine involved in polar surface ozone depletion events. A more dominant source of reactive bromine, however, has been attributed to the reaction on ice particles and in sea spray aerosols of atmospherically derived HOBr with bromide and chloride to produce the dihalogens Br2 and BrCl. We have measured the release of oxidized bromine species (Brox = HOBr, Br2, Br3-1) from polar and temperate diatoms. The highest rates were measured from Porosira glaciales (CCMP 651). Release rates are range from 0.84 to 180 fmoles bromine/hour/cell depending on the species or an approximate maximum of 950 nmoles bromine/mg chl a/hr (P. glaciales). The flux from the diatoms is 0.1 to 7.5 nmoles bromine/cm2 diatom surface/hr. This release occurs from an extracellular bromoperoxidase when a suitable organic substrate is absent. At 0.84 mM bromide (average seawater concentration), the optimal pH for Brox release is 6.5, which is the putative pH of the apoplastic space, and the optimal H2O2 concentration is 250 nM. Based on these results, it is estimated that the amount of bromine released from ice algae as Brox is 10 to 200 times greater than the release of bromine as bromoform from ice algae. The Brox so produced could participate in the abiotic formation of dihalogens in sea ice. Also, Brox released from diatoms may react with specific components of DOC, if present, to indirectly produce polybromomethanes both in sea ice and seawater. The amount of polyhalomethanes produced is not only dependent on the algal species present but also on the composition of DOC.

Ensuring the safety of surgical teams when managing casualties of a radiological dirty bomb.

PubMed

Williams, Geraint; O'Malley, Michael; Nocera, Antony

2010-09-01

The capacity for surgical teams to ensure their own safety when dealing with the consequences caused by the detonation of a radiological dirty bomb is primarily determined by prior knowledge, familiarity and training for this type of event. This review article defines the associated radiological terminology with an emphasis on the personal safety of surgical team members in respect to the principles of radiological protection. The article also describes a technique for use of hand held radiation monitors and will discuss the identification and management of radiologically contaminated patients who may pose a significant danger to the surgical team. 2010 Elsevier Ltd. All rights reserved.

Unwanted sexual experiences and cognitive appraisals that evoke mental contamination.

PubMed

Ishikawa, Ryotaro; Kobori, Osamu; Shimizu, Eiji

2015-01-01

Mental contamination is a psychological sense of contamination that involves an internal, emotional feeling of dirtiness that may be evoked by unwanted thoughts and images, such as sexual assaults. This study aimed to investigate which types of unwanted sexual experiences evoke the strongest mental contamination, and to test the hypothesis that cognitive appraisals of an unwanted sexual experience predict indices of mental contamination (i.e. feeling of dirtiness, urge to wash, internal negative emotions, and external negative emotions). 148 female participants were asked to recall their most distressing unwanted sexual experiences. Indices of mental contamination and cognitive appraisals of the experience were then assessed. Our findings indicated that individuals recalling experiences related to rape felt more intense feelings of dirtiness than individuals recalling other types of unwanted sexual experience, such as verbal sexual assault, visual sexual assault, and forcible touching/frottage. In addition, hierarchical regression analyses demonstrated that a cognitive appraisal of perceived violation predicted all of the indices of mental contamination after controlling anxiety, depression, and fear of contact contamination. The present study demonstrated that an individual is at greatest risk of mental contamination if she has experienced rape/attempted rape, and if she makes a cognitive appraisal of violation regarding the incident.

Bacterial populations associated with the dirty area of a South African poultry abattoir.

PubMed

Geornaras, I; de Jesus, A E; von Holy, A

1998-06-01

Bacterial populations associated with three sample types from the neck region of poultry carcasses in the dirty area of an abattoir were characterized. Sample types before and after scalding were skin only, feathers only, and a skin and feather combination. The neck skin of carcasses after the defeathering processing stage was also sampled. Bacterial populations associated with water from the scald tank, rubber fingers at the exit of the defeathering machine, and air in the dirty area were also characterized. Bacterial colonies (751) were randomly isolated from yeast extract-supplemented tryptone soya agar plates exhibiting 30 to 300 colonies. Micrococcus spp. were isolated in the highest proportion from pre-and postscalded carcass samples (63.5 to 86.1% of isolates), regardless of the sample type. Conversely, Enterobacteriaceae (40.3%), Acinetobacter (19.4%), and Aeromonas/Vibrio (12.5%) species predominated on neck skin samples taken from mechanically defeathered carcasses. Isolates from the rubber fingers were, however, predominantly Micrococcus spp. (94.4%). Bacterial groups isolated in the highest proportion from scald tank water samples were Micrococcus spp. (38.3%), species of Enterobacteriaceae (29.1%), and lactic acid bacteria (17.0%). Corynebacterium spp., species of Enterobacteriaceae, and Micrococcus spp. were dominant on air settle plates.

Firn structure of Larsen C Ice Shelf, Antarctic Peninsula, from in-situ geophysical surveys

NASA Astrophysics Data System (ADS)

Kulessa, B.; Brisbourne, A.; Kuipers Munneke, P.; Bevan, S. L.; Luckman, A. J.; Hubbard, B. P.; Ashmore, D.; Holland, P.; Jansen, D.; King, E. C.; O'Leary, M.; McGrath, D.

2015-12-01

Rising surface temperatures have been causing firn layers on Antarctic Peninsula ice shelves to compact, a process that is strongly implicated in ice shelf disintegration. Firn compaction is expected to warm the ice column and given sufficiently wet and compacted firn layers, to allow meltwater to penetrate into surface crevasses and thus enhance the potential for hydrofracture. On Larsen C Ice Shelf a compacting firn layer has previously been inferred from airborne radar and satellite data, with strongly reduced air contents in Larsen C's north and north-west. The hydrological processes governing firn compaction, and the detailed firn structures they produce, have so far remained uncertain however. Using integrated seismic refraction, MASW (Multi-Channel Analysis of Surface Waves), seismoelectric and ground-penetrating radar (GPR) data, we reveal vertical and horizontal changes in firn structure across Larsen C Ice Shelf. Particular attention is paid to the spatial prevalence of refrozen meltwaters within firn, such as the massive subsurface ice layer discovered recently by the NERC-funded MIDAS project in Cabinet Inlet in Larsen C's extreme northwest. Such ice layers or lenses are particularly dramatic manifestations of increased ice shelf densities and temperatures, and contrast sharply with the relatively uncompacted firn layers present in the ice shelf's southeast. We consider our observations in the context of a one-dimensional firn model for Larsen C Ice Shelf that includes melt percolation and refreezing, and discuss temporal changes in firn layer structures due to surface melt and ponding.

UV irradiation of polycyclic aromatic hydrocarbons in ices: production of alcohols, quinones, and ethers

NASA Technical Reports Server (NTRS)

Bernstein, M. P.; Sandford, S. A.; Allamandola, L. J.; Gillette, J. S.; Clemett, S. J.; Zare, R. N.

1999-01-01

Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis.

Thermal evolution of a differentiated Ganymede and implications for surface features

NASA Technical Reports Server (NTRS)

Kirk, R. L.; Stevenson, D. J.

1987-01-01

Thermodynamic models are developed for the processes which controlled the evolution of the surface Ganymede, an icy Jovian satellite assumed to have a rock-rich core surrounded by a water-ice mantle. Account is taken of a heat pulse which would have arisen from a Rayleigh-Taylor instability at a deep-seated liquid-solid water interface, rapid fracturing from global stresses imposed by warm ice diapiric upwelling, impacts by large meteorites, and resurfacing by ice flows (rather than core formation). Comparisons are made with existing models for the evolution of Callisto, and the difficulties in defining a mechanism which produced the groove terrain of Ganymede are discussed.

Lot quality assurance sampling for monitoring immunization programmes: cost-efficient or quick and dirty?

PubMed

Sandiford, P

1993-09-01

In recent years Lot quality assurance sampling (LQAS), a method derived from production-line industry, has been advocated as an efficient means to evaluate the coverage rates achieved by child immunization programmes. This paper examines the assumptions on which LQAS is based and the effect that these assumptions have on its utility as a management tool. It shows that the attractively low sample sizes used in LQAS are achieved at the expense of specificity unless unrealistic assumptions are made about the distribution of coverage rates amongst the immunization programmes to which the method is applied. Although it is a very sensitive test and its negative predictive value is probably high in most settings, its specificity and positive predictive value are likely to be low. The implications of these strengths and weaknesses with regard to management decision-making are discussed.

Disgust as a Unique Affective Predictor of Mental Contamination Following Sexual Trauma

PubMed Central

Badour, Christal L.; Ojserkis, Rachel; McKay, Dean; Feldner, Matthew T.

2014-01-01

Mental contamination has been described as an internal experience of dirtiness that can arise and persist in the absence of contact with observable physical contaminants. Recent research has examined mental contamination specifically related to unwanted physical contact and sexual trauma. This study evaluated the degree to which disgust propensity and both self-focused and perpetrator-focused peritraumatic disgust were associated with mental contamination in a sample of women who experienced sexual trauma (n = 72). Results showed that peritraumatic self-focused disgust, but not peritraumatic perpetrator-focused disgust or fear, was significantly associated with mental contamination. Additionally, disgust propensity contributed significantly to the incremental validity of the model. These findings support the nascent literature showing that disgust plays a significant role in mental contamination, particularly following sexual trauma. Future research directions, and clinical/theoretical implications of these results are discussed. PMID:25129888

Social problem-solving abilities and personality disorder characteristics among dual-diagnosed persons in substance abuse treatment.

PubMed

Herrick, S M; Elliott, T R

2001-01-01

We examined the relation of self-appraised social problem-solving abilities and personality-disorder characteristics to the adjustment and compliance of persons with dual diagnoses in substance-abuse treatment. It was hypothesized that elements of the problem-orientation component would remain predictive of depressive behavior and distress after considering personality-disorder characteristics among 117 persons receiving inpatient-substance-abuse treatment. Furthermore, self-appraised problem-solving abilities were expected to predict the occurrence of "dirty" drug and alcohol screens during treatment and compliance with the first scheduled community follow-up visit. Results supported predictions concerning the relation of problem-solving confidence to depressive behavior, distress, and substance-use screens; however, a paradoxical relation was observed between the problem-orientation variables and compliance with the first outpatient visit. The results are interpreted within the context of contemporary models of social problem solving and the implications for cognitive-behavioral assessment and intervention are considered.

Close packing effects on clean and dirty snow albedo and associated climatic implications

NASA Astrophysics Data System (ADS)

He, C.; Liou, K. N.; Takano, Y.

2017-12-01

Previous modeling of snow albedo, a key climate feedback parameter, follows the independent scattering approximation (ISA) such that snow grains are considered as a number of separate units with distances longer than wavelengths. Here we develop a new snow albedo model for widely observed close-packed snow grains internally mixed with black carbon (BC) and demonstrate that albedo simulations match closer to observations. Close packing results in a stronger light absorption for clean and BC-contaminated snow. Compared with ISA, close packing reduces pure snow albedos by up to 0.05, whereas it enhances BC-induced snow albedo reduction and associated surface radiative forcing by up to 15% (20%) for fresh (old) snow, with larger enhancements for stronger structure packing. Finally, our results suggest that BC-snow albedo forcing and snow albedo feedback (climate sensitivity) are underestimated in previous modeling studies, making snow close packing consideration a necessity in climate modeling and analysis.

Close packing effects on clean and dirty snow albedo and associated climatic implications

NASA Astrophysics Data System (ADS)

He, Cenlin; Takano, Yoshi; Liou, Kuo-Nan

2017-04-01

Previous modeling of snow albedo, a key climate feedback parameter, follows the independent scattering approximation (ISA) such that snow grains are considered as a number of separate units with distances longer than wavelengths. Here we develop a new snow albedo model for widely observed close-packed snow grains internally mixed with black carbon (BC) and demonstrate that albedo simulations match closer to observations. Close packing results in a stronger light absorption for clean and BC-contaminated snow. Compared with ISA, close packing reduces pure snow albedos by up to 0.05, whereas it enhances BC-induced snow albedo reduction and associated surface radiative forcing by up to 15% (20%) for fresh (old) snow, with larger enhancements for stronger structure packing. Finally, our results suggest that BC-snow albedo forcing and snow albedo feedback (climate sensitivity) are underestimated in previous modeling studies, making snow close packing consideration a necessity in climate modeling and analysis.

A metaphor analysis of recovering substance abusers' sensemaking of medication-assisted treatment.

PubMed

Malvini Redden, Shawna; Tracy, Sarah J; Shafer, Michael S

2013-07-01

In this study, we examined metaphors invoked by people recovering from opioid dependence as they described the challenges and successes of using medication-assisted treatment. Metaphors provide linguistic tools for expressing issues that are confusing, complex, hidden, and difficult to state analytically or literally. Using data from eight focus groups with 68 participants representing four ethnic minority groups, we conducted a grounded analysis to show how recovering substance users communicatively constructed addiction and recovery. The primary medication, methadone, was framed as "liquid handcuffs" that allowed those in recovery to quit "hustling," get "straight," and find "money in their pockets." Nonetheless, methadone also served as a "crutch," leaving them still feeling like "users" with "habits" who "came up dirty" to friends and family. In this analysis, we tease out implications of these metaphors, and how they shed light on sensemaking, agency, and related racial- and class-based structural challenges in substance abuse recovery.

Geodynamic Modeling of Planetary Ice-Oceans: Evolution of Ice-Shell Thickness in Convecting Two-Phase Systems

NASA Astrophysics Data System (ADS)

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

2016-12-01

Along with the newly unveiled icy surface of Pluto, several icy planetary bodies show indications of an active surface perhaps underlain by liquid oceans of some size. This augments the interest to explore the evolution of an ice-ocean system and its surface implications. The geologically young surface of the Jovian moon Europa lends much speculation to variations in ice-shell thickness over time. Along with the observed surface features, it suggests the possibility of episodic convection and conduction within the ice-shell as it evolved. What factors would control the growth of the ice-shell as it forms? If and how would those factors determine the thickness of the ice-shell and consequently the heat transfer? Would parameters such as tidal heating or initial temperature affect how the ice-shell grows and to what significance? We perform numerical experiments using geodynamical models of the two-phase ice-water system to study the evolution of planetary ice-oceans such as that of Europa. The models evolve self-consistently from an initial liquid ocean as it cools with time. The effects of presence, absence and magnitude of tidal heating on ice-shell thickness are studied in different models. The vigor of convection changes as the ice-shell continues to thicken. Initial modeling results track changes in the growth rate of the ice-shell as the vigor of the convection changes. The magnitude and temporal location of the rate change varies with different properties of tidal heating and values of initial temperature. A comparative study of models is presented to demonstrate how as the ice-shell is forming, its growth rate and convection are affected by processes such as tidal heating.

Ice Thickness, Melting Rates and Styles of Activity in Ice-Volcano Interaction

NASA Astrophysics Data System (ADS)

Gudmundsson, M. T.

2005-12-01

In most cases when eruptions occur within glaciers they lead to rapid ice melting, jokulhlaups and/or lahars. Many parameters influence the style of activity and its impact on the environment. These include ice thickness (size of glacier), bedrock geometry, magma flow rate and magma composition. The eruptions that have been observed can roughly be divided into: (1) eruptions under several hundred meters thick ice on a relatively flat bedrock, (2) eruptions on flat or sloping bed through relatively thin ice, and (3) volcanism where effects are limitied to confinement of lava flows or melting of ice by pyroclastic flows or surges. This last category (ice-contact volcanism) need not cause much ice melting. Many of the deposits formed by Pleistocene volcanism in Iceland, British Columbia and Antarctica belong to the first category. An important difference between this type of activity and submarine activity (where pressure is hydrostatic) is that pressure at vents may in many cases be much lower than glaciostatic due to partial support of ice cover over vents by the surrounding glacier. Reduced pressure favours explosive activity. Thus the effusive/explosive transition may occur several hundred metres underneath the ice surface. Explosive fragmentation of magma leads to much higher rates of heat transfer than does effusive eruption of pillow lavas, and hence much higher melting rates. This effect of reduced pressure at vents will be less pronounced in a large ice sheet than in a smaller glacier or ice cap, since the hydraulic gradient that drives water away from an eruption site will be lower in the large glacier. This may have implications for form and type of eruption deposits and their relationship with ice thickness and glacier size.

The interaction between sea ice and salinity-dominated ocean circulation: implications for halocline stability and rapid changes of sea ice cover

NASA Astrophysics Data System (ADS)

Jensen, Mari F.; Nilsson, Johan; Nisancioglu, Kerim H.

2016-11-01

Changes in the sea ice cover of the Nordic Seas have been proposed to play a key role for the dramatic temperature excursions associated with the Dansgaard-Oeschger events during the last glacial. In this study, we develop a simple conceptual model to examine how interactions between sea ice and oceanic heat and freshwater transports affect the stability of an upper-ocean halocline in a semi-enclosed basin. The model represents a sea ice covered and salinity stratified Nordic Seas, and consists of a sea ice component and a two-layer ocean. The sea ice thickness depends on the atmospheric energy fluxes as well as the ocean heat flux. We introduce a thickness-dependent sea ice export. Whether sea ice stabilizes or destabilizes against a freshwater perturbation is shown to depend on the representation of the diapycnal flow. In a system where the diapycnal flow increases with density differences, the sea ice acts as a positive feedback on a freshwater perturbation. If the diapycnal flow decreases with density differences, the sea ice acts as a negative feedback. However, both representations lead to a circulation that breaks down when the freshwater input at the surface is small. As a consequence, we get rapid changes in sea ice. In addition to low freshwater forcing, increasing deep-ocean temperatures promote instability and the disappearance of sea ice. Generally, the unstable state is reached before the vertical density difference disappears, and the temperature of the deep ocean do not need to increase as much as previously thought to provoke abrupt changes in sea ice.

Implementing an empirical scalar constitutive relation for ice with flow-induced polycrystalline anisotropy in large-scale ice sheet models

NASA Astrophysics Data System (ADS)

Graham, Felicity S.; Morlighem, Mathieu; Warner, Roland C.; Treverrow, Adam

2018-03-01

The microstructure of polycrystalline ice evolves under prolonged deformation, leading to anisotropic patterns of crystal orientations. The response of this material to applied stresses is not adequately described by the ice flow relation most commonly used in large-scale ice sheet models - the Glen flow relation. We present a preliminary assessment of the implementation in the Ice Sheet System Model (ISSM) of a computationally efficient, empirical, scalar, constitutive relation which addresses the influence of the dynamically steady-state flow-compatible induced anisotropic crystal orientation patterns that develop when ice is subjected to the same stress regime for a prolonged period - sometimes termed tertiary flow. We call this the ESTAR flow relation. The effect on ice flow dynamics is investigated by comparing idealised simulations using ESTAR and Glen flow relations, where we include in the latter an overall flow enhancement factor. For an idealised embayed ice shelf, the Glen flow relation overestimates velocities by up to 17 % when using an enhancement factor equivalent to the maximum value prescribed in the ESTAR relation. Importantly, no single Glen enhancement factor can accurately capture the spatial variations in flow across the ice shelf generated by the ESTAR flow relation. For flow line studies of idealised grounded flow over varying topography or variable basal friction - both scenarios dominated at depth by bed-parallel shear - the differences between simulated velocities using ESTAR and Glen flow relations depend on the value of the enhancement factor used to calibrate the Glen flow relation. These results demonstrate the importance of describing the deformation of anisotropic ice in a physically realistic manner, and have implications for simulations of ice sheet evolution used to reconstruct paleo-ice sheet extent and predict future ice sheet contributions to sea level.

Future Antarctic bed topography and its implications for ice sheet dynamics

NASA Astrophysics Data System (ADS)

Adhikari, Surendra; Ivins, Erik; Larour, Eric; Seroussi, Helene; Morlighem, Mathieu; Nowicki, Sophie

2014-05-01

A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has been generally losing its mass since the last glacial maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that the past loading is relatively less important than future loading on the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years 2100 and 2500 AD, respectively, and that the East Antarctic Ice Sheet (EAIS) is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector of WAIS in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay approaches roughly 45 mm/yr in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is associated with the flattening of reverse bed, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote the stability to marine portions of the ice sheet in the future.

Cloud Response to Arctic Sea Ice Loss and Implications for Feedbacks in the CESM1 Climate Model

NASA Astrophysics Data System (ADS)

Morrison, A.; Kay, J. E.; Chepfer, H.; Guzman, R.; Bonazzola, M.

2017-12-01

Clouds have the potential to accelerate or slow the rate of Arctic sea ice loss through their radiative influence on the surface. Cloud feedbacks can therefore play into Arctic warming as clouds respond to changes in sea ice cover. As the Arctic moves toward an ice-free state, understanding how cloud - sea ice relationships change in response to sea ice loss is critical for predicting the future climate trajectory. From satellite observations we know the effect of present-day sea ice cover on clouds, but how will clouds respond to sea ice loss as the Arctic transitions to a seasonally open water state? In this study we use a lidar simulator to first evaluate cloud - sea ice relationships in the Community Earth System Model (CESM1) against present-day observations (2006-2015). In the current climate, the cloud response to sea ice is well-represented in CESM1: we see no summer cloud response to changes in sea ice cover, but more fall clouds over open water than over sea ice. Since CESM1 is credible for the current Arctic climate, we next assess if our process-based understanding of Arctic cloud feedbacks related to sea ice loss is relevant for understanding future Arctic clouds. In the future Arctic, summer cloud structure continues to be insensitive to surface conditions. As the Arctic warms in the fall, however, the boundary layer deepens and cloud fraction increases over open ocean during each consecutive decade from 2020 - 2100. This study will also explore seasonal changes in cloud properties such as opacity and liquid water path. Results thus far suggest that a positive fall cloud - sea ice feedback exists in the present-day and future Arctic climate.

Turbulent heat exchange between water and ice at an evolving ice-water interface

NASA Astrophysics Data System (ADS)

Ramudu, E.; Hirsh, B.; Olson, P.; Gnanadesikan, A.

2016-02-01

Experimental results are presented on the time evolution of ice subject to a turbulent shear flow in a layer of water of uniform depth. Our study is motivated by observations in the ocean cavity beneath Antarctic ice shelves, where shoaling of Circumpolar Deep Water into the cavity has been implicated in the accelerated melting of the ice shelf base. Measurements of inflow and outflow at the ice shelf front have shown that not all of the heat entering the cavity is delivered to the ice shelf, suggesting that turbulent transfer to the ice represents an important bottleneck. Given that a range of turbulent transfer coefficients has been used in models it is important to better constrain this parameter. We measure as a function of time in our experiments the thickness of the ice, temperatures in the ice and water, and fluid velocity in the shear flow, starting from an initial condition in which the water is at rest and the ice has grown by conduction above a cold plate. The strength of the applied turbulent shear flow is represented in terms of a Reynolds number Re, which is varied over the range 3.5 × 103 ≤ Re ≤ 1.9 × 104. Transient partial melting of the ice occurs at the lower end of this range of Re and complete transient melting of the ice occurs at the higher end of the range. Following these melting transients, the ice reforms at a rate that is independent of Re. We fit to our experimental measurements of ice thickness and temperature a one-dimensional model for the evolution of the ice thickness in which the turbulent heat transfer is parameterized in terms of the friction velocity of the shear flow. Comparison with the Pine Island Glacier Ice Shelf yields qualitative agreement between the transient ice melting rates predicted by our model and the shelf melting rate inferred from the field observations.

A Detailed Geophysical Investigation of the Grounding of Henry Ice Rise, with Implications for Holocene Ice-Sheet Extent.

NASA Astrophysics Data System (ADS)

Wearing, M.; Kingslake, J.

2017-12-01

It is generally assumed that since the Last Glacial Maximum the West Antarctic Ice Sheet (WAIS) has experienced monotonic retreat of the grounding line (GL). However, recent studies have cast doubt on this assumption, suggesting that the retreat of the WAIS grounding line may have been followed by a significant advance during the Holocene in the Weddell and Ross Sea sectors. Constraining this evolution is important as reconstructions of past ice-sheet extent are used to spin-up predictive ice-sheet models and correct mass-balance observations for glacial isostatic adjustment. Here we examine in detail the formation of the Henry Ice Rise (HIR), which ice-sheet model simulations suggest played a key role in Holocene ice-mass changes in the Weddell Sea sector. Observations from a high-resolution ground-based, ice-penetrating radar survey are best explained if the ice rise formed when the Ronne Ice Shelf grounded on a submarine high, underwent a period of ice-rumple flow, before the GL migrated outwards to form the present-day ice rise. We constrain the relative chronology of this evolution by comparing the alignment and intersection of isochronal internal layers, relic crevasses, surface features and investigating the dynamic processes leading to their complex structure. We also draw analogies between HIR and the neighbouring Doake Ice Rumples. The date of formation is estimated using vertical velocities derived with a phase-sensitive radio-echo sounder (pRES). Ice-sheet models suggest that the formation of the HIR and other ice rises may have halted and reversed large-scale GL retreat. Hence the small-scale dynamics of these crucial regions could have wide-reaching consequences for future ice-sheet mass changes and constraining their formation and evolution further would be beneficial. One stringent test of our geophysics-based conclusions would be to drill to the bed of HIR to sample the ice for isotopic analysis and the bed for radiocarbon analysis.

Worldwide Emerging Environmental Issues Affecting the U.S. Military. March 2007 Report

DTIC Science & Technology

2007-03-01

some existent climate regions (mainly in tropical mountain areas, Amazon and Indonesian rainforests , and towards the poles) and the prospects of...ice sheets and floating sea ice. Military Implications: In view of the increasing importance of the Arctic in military planning and the oil reserves...95080 4.2 Malacca Straits Need Increased Protection from Various Security Threats The Malacca Strait, one of the most important shipping lanes in the

High pressure study of water-salt systems, phase equilibria, partitioning, thermodynic properties and implication for large icy worlds hydrospheres.

NASA Astrophysics Data System (ADS)

Journaux, B.; Brown, J. M.; Abramson, E.; Petitgirard, S.; Pakhomova, A.; Boffa Ballaran, T.; Collings, I.

2017-12-01

Water salt systems are predicted to be present in deep hydrosphere inside water-rich planetary bodies, following water/rock chemical interaction during early differentiation stages or later hydrothermal activity. Unfortunately the current knowledge of the thermodynamic and physical properties of aqueous salt mixtures at high pressure and high temperature is still insufficient to allow realistic modeling of the chemical or dynamic of thick planetary hydrospheres. Recent experimental results have shown that the presence of solutes, and more particularly salts, in equilibrium with high pressure ices have large effects on the stability fields, buoyancy and chemistry of all the phases present at these extreme conditions. Effects currently being investigated by our research group also covers ice melting curve depressions that depend on the salt species and incorporation of solutes inside the crystallographic lattice of high pressure ices. Both of these could have very important implication at the planetary scale, enabling thicker/deeper liquid oceans, and allowing chemical transportation through the high pressure ice layer in large icy worlds. We will present the latest results obtained in-situ using diamond anvil cell, coupled with Synchrotron X-Ray diffraction, Raman Spectroscopy and optical observations, allowing to probe the crystallographic structure, equations of state, partitioning and phase boundary of high pressure ice VI and VII in equilibrium with Na-Mg-SO4-Cl ionic species at high pressures (1-10 GPa). The difference in melting behavior depending on the dissolved salt species was characterized, suggesting differences in ionic speciation at liquidus conditions. The solidus P-T conditions were also measured as well as an increase of lattice volumes interpreted as an outcome of ionic incorporation in HP ice during incongruent crystallization. The measured phase diagrams, lattice volumes and important salt incorporations suggest a more complex picture of the structure, dynamic and evolution of icy worlds hydrospheres that could allow, among others, deep liquid reservoirs, chemical transport at the solid state through HP ices layers and/or complex dynamic due to salt exsolutions at HP ices solid-solid phase boundaries.

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.

A New Discrete Element Sea-Ice Model for Earth System Modeling

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

Turner, Adrian Keith

Sea ice forms a frozen crust of sea water oating in high-latitude oceans. It is a critical component of the Earth system because its formation helps to drive the global thermohaline circulation, and its seasonal waxing and waning in the high north and Southern Ocean signi cantly affects planetary albedo. Usually 4{6% of Earth's marine surface is covered by sea ice at any one time, which limits the exchange of heat, momentum, and mass between the atmosphere and ocean in the polar realms. Snow accumulates on sea ice and inhibits its vertical growth, increases its albedo, and contributes to pooledmore » water in melt ponds that darken the Arctic ice surface in the spring. Ice extent and volume are subject to strong seasonal, inter-annual and hemispheric variations, and climatic trends, which Earth System Models (ESMs) are challenged to simulate accurately (Stroeve et al., 2012; Stocker et al., 2013). This is because there are strong coupled feedbacks across the atmosphere-ice-ocean boundary layers, including the ice-albedo feedback, whereby a reduced ice cover leads to increased upper ocean heating, further enhancing sea-ice melt and reducing incident solar radiation re ected back into the atmosphere (Perovich et al., 2008). A reduction in perennial Arctic sea-ice during the satellite era has been implicated in mid-latitude weather changes, including over North America (Overland et al., 2015). Meanwhile, most ESMs have been unable to simulate observed inter-annual variability and trends in Antarctic sea-ice extent during the same period (Gagne et al., 2014).« less

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.

The effects of snow and salt on ice table stability in University Valley, Antarctica

USGS Publications Warehouse

Williams, Kaj; Heldmann, Jennifer L.; McKay, Christopher P.; Mellon, Michael T.

2018-01-01

The Antarctic Dry Valleys represent a unique environment where it is possible to study dry permafrost overlaying an ice-rich permafrost. In this paper, two opposing mechanisms for ice table stability in University Valley are addressed: i) diffusive recharge via thin seasonal snow deposits and ii) desiccation via salt deposits in the upper soil column. A high-resolution time-marching soil and snow model was constructed and applied to University Valley, driven by meteorological station atmospheric measurements. It was found that periodic thin surficial snow deposits (observed in University Valley) are capable of drastically slowing (if not completely eliminating) the underlying ice table ablation. The effects of NaCl, CaCl2 and perchlorate deposits were then modelled. Unlike the snow cover, however, the presence of salt in the soil surface (but no periodic snow) results in a slight increase in the ice table recession rate, due to the hygroscopic effects of salt sequestering vapour from the ice table below. Near-surface pore ice frequently forms when large amounts of salt are present in the soil due to the suppression of the saturation vapour pressure. Implications for Mars high latitudes are discussed.

Bacteria beneath the West Antarctic ice sheet.

PubMed

Lanoil, Brian; Skidmore, Mark; Priscu, John C; Han, Sukkyun; Foo, Wilson; Vogel, Stefan W; Tulaczyk, Slawek; Engelhardt, Hermann

2009-03-01

Subglacial environments, particularly those that lie beneath polar ice sheets, are beginning to be recognized as an important part of Earth's biosphere. However, except for indirect indications of microbial assemblages in subglacial Lake Vostok, Antarctica, no sub-ice sheet environments have been shown to support microbial ecosystems. Here we report 16S rRNA gene and isolate diversity in sediments collected from beneath the Kamb Ice Stream, West Antarctic Ice Sheet and stored for 15 months at 4 degrees C. This is the first report of microbes in samples from the sediment environment beneath the Antarctic Ice Sheet. The cells were abundant ( approximately 10(7) cells g(-1)) but displayed low diversity (only five phylotypes), likely as a result of enrichment during storage. Isolates were cold tolerant and the 16S rRNA gene diversity was a simplified version of that found in subglacial alpine and Arctic sediments and water. Although in situ cell abundance and the extent of wet sediments beneath the Antarctic ice sheet can only be roughly extrapolated on the basis of this sample, it is clear that the subglacial ecosystem contains a significant and previously unrecognized pool of microbial cells and associated organic carbon that could potentially have significant implications for global geochemical processes.

Introducing the North Water: Histories of exploration, ice dynamics, living resources, and human settlement in the Thule Region.

PubMed

Hastrup, Kirsten; Mosbech, Anders; Grønnow, Bjarne

2018-04-01

The North Water is a recurrent polynya in the High Arctic situated between Northwest Greenland and Ellesmere Island of Canada. The North Water makes a dynamic space, where various processes may enhance or obstruct each other, accelerating or halting particular modes of human-animal relations in the region, where life itself depends on the North Water. This will be discussed in four steps. The first step posits the North Water as a perceived oasis for explorers and whalers hailing from Europe or America in the nineteenth century. The second step concentrates on the diverse rhythms inherent in the ice conditions, as affected by trends that are set in motion elsewhere. The third step highlights the implications of the dynamics of the ice and sea currents for animal life in the region. The fourth step gives an overview of human settlement patterns around the North Water across the ages. The article shows how natural and social features are deeply implicated in each other, even if they are not directly co-variant.

Adsorption of CO on oxide and water ice surfaces - Implications for the Martian atmosphere

NASA Technical Reports Server (NTRS)

Leu, M.-T.; Blamont, J. E.; Anbar, A. D.; Keyser, L. F.; Sander, S. P.

1992-01-01

The adsorption of carbon monoxide (CO) on water ice and on the oxides Fe2O3, Fe3O4, Al2O3, SiO2, CaO, MgO, and TiO2 (rutile and anatase) has been investigated in a flow reactor. A mass spectrometer was employed as a detector to monitor the temporal concentrations of CO. Adsorption coefficients as large as 1 x 10 exp -4 were measured for CO on TiO2 solids in helium at 196 K. The fractional surface coverage for CO on TiO2 solids in helium was also determined to be approximately 10 percent at 196 K. The upper limits of the fractional surface coverage for the other oxides (Fe2O3, Fe3O4, Al2O3, SiO2, CaO, and MgO) and water ice were also measured to be less than 1 percent. The implications for the stability of CO2 in the Martian atmosphere and the 'CO hole' observed by the Phobos/ISM experiment are discussed.

The Role of Arctic Sea Ice in Last Millennium Climate Variability: Model-Proxy Comparisons Using Ensemble Members and Novel Model Experiments.

NASA Astrophysics Data System (ADS)

Gertler, C. G.; Monier, E.; Prinn, R. G.

2016-12-01

Variability in sea ice extent is a prominent feature of forced simulations of the last millennium and reconstructions of paleoclimate using proxy records. The rapid 20th century decline in sea ice extent is most likely due to greenhouse gas forcing, but the accuracy of future projections depend on the characterization of natural variability. Declining sea ice extent affects regional climate and society, but also plays a large role in Arctic amplification, with implications for mid-latitude circulation and even large-scale climate oscillations. To characterize the effects of natural and anthropogenic climate forcing on sea ice and the related changes in large-scale atmospheric circulation, a combination of instrumental record, paleoclimate reconstructions, and general circulation models can be employed to recreate sea ice extents and the corresponding atmosphere-ocean states. Model output from the last millennium ensemble (LME) is compared to a proxy-based sea ice reconstruction and a global proxy network using a variety of statistical and data assimilation techniques. Further model runs using the Community Earth Systems Model (CESM) are performed with the same inputs as LME but forced with experimental sea ice extents, and results are contextualized within the larger ensemble by a variety of metrics.

Reconciling biases and uncertainties of AIRS and MODIS ice cloud properties

NASA Astrophysics Data System (ADS)

Kahn, B. H.; Gettelman, A.

2015-12-01

We will discuss comparisons of collocated Atmospheric Infrared Sounder (AIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) ice cloud optical thickness (COT), effective radius (CER), and cloud thermodynamic phase retrievals. The ice cloud comparisons are stratified by retrieval uncertainty estimates, horizontal inhomogeneity at the pixel-scale, vertical cloud structure, and other key parameters. Although an estimated 27% globally of all AIRS pixels contain ice cloud, only 7% of them are spatially uniform ice according to MODIS. We find that the correlations of COT and CER between the two instruments are strong functions of horizontal cloud heterogeneity and vertical cloud structure. The best correlations are found in single-layer, horizontally homogeneous clouds over the low-latitude tropical oceans with biases and scatter that increase with scene complexity. While the COT comparisons are unbiased in homogeneous ice clouds, a bias of 5-10 microns remains in CER within the most homogeneous scenes identified. This behavior is entirely consistent with known sensitivity differences in the visible and infrared bands. We will use AIRS and MODIS ice cloud properties to evaluate ice hydrometeor output from climate model output, such as the CAM5, with comparisons sorted into different dynamical regimes. The results of the regime-dependent comparisons will be described and implications for model evaluation and future satellite observational needs will be discussed.

Relationship between sea ice freeboard and draft in the Arctic Basin, and implications for ice thickness monitoring

NASA Technical Reports Server (NTRS)

Wadhams, P.; Tucker, W. B., III; Krabill, W. B.; Swift, R. N.; Comiso, J. C.; Davis, N. R.

1992-01-01

This study confirms the finding of Comiso et al. (1991) that the probability density function (pdf) of the ice freeboard in the Arctic Ocean can be converted to a pdf of ice draft by applying a simple coordinate factor. The coordinate factor, R, which is the ratio of mean draft to mean freeboard pdf is related to the mean material (ice plus snow) density, rho(m), and the near-surface water density rho(w) by the relationship R = rho(m)/(rho(w) - rho(m)). The measured value of R was applied to each of six 50-km sections north of Greenland of a joint airborne laser and submarine sonar profile obtained along nearly coincident tracks from the Arctic Basin north of Greenland and was found to be consistent over all sections tested, despite differences in the ice regime. This indicates that a single value of R might be used for measurements done in this season of the year. The mean value R from all six sections was found to be 7.89.

A Review of Recent Changes in Southern Ocean Sea Ice, Their Drivers and Forcings

NASA Technical Reports Server (NTRS)

Hobbs, William R.; Massom, Rob; Stammerjohn, Sharon; Reid, Phillip; Williams, Guy; Meier, Walter

2016-01-01

Over the past 37years, satellite records show an increase in Antarctic sea ice cover that is most pronounced in the period of sea ice growth. This trend is dominated by increased sea ice coverage in the western Ross Sea, and is mitigated by a strong decrease in the Bellingshausen and Amundsen seas. The trends in sea ice areal coverage are accompanied by related trends in yearly duration. These changes have implications for ecosystems, as well as global and regional climate. In this review, we summarize the researchto date on observing these trends, identifying their drivers, and assessing the role of anthropogenic climate change. Whilst the atmosphere is thought to be the primary driver, the ocean is also essential in explaining the seasonality of the trend patterns. Detecting an anthropogenic signal in Antarctic sea ice is particularly challenging for a number of reasons: the expected response is small compared to the very high natural variability of the system; the observational record is relatively short; and the ability of global coupled climate models to faithfully represent the complex Antarctic climate system is in doubt.

Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia

PubMed Central

Kumpula, Timo; Meschtyb, Nina; Laptander, Roza; Macias-Fauria, Marc; Zetterberg, Pentti; Verdonen, Mariana; Kim, Kwang-Yul; Boisvert, Linette N.; Stroeve, Julienne C.; Bartsch, Annett

2016-01-01

Sea ice loss is accelerating in the Barents and Kara Seas (BKS). Assessing potential linkages between sea ice retreat/thinning and the region's ancient and unique social–ecological systems is a pressing task. Tundra nomadism remains a vitally important livelihood for indigenous Nenets and their large reindeer herds. Warming summer air temperatures have been linked to more frequent and sustained summer high-pressure systems over West Siberia, Russia, but not to sea ice retreat. At the same time, autumn/winter rain-on-snow (ROS) events have become more frequent and intense. Here, we review evidence for autumn atmospheric warming and precipitation increases over Arctic coastal lands in proximity to BKS ice loss. Two major ROS events during November 2006 and 2013 led to massive winter reindeer mortality episodes on the Yamal Peninsula. Fieldwork with migratory herders has revealed that the ecological and socio-economic impacts from the catastrophic 2013 event will unfold for years to come. The suggested link between sea ice loss, more frequent and intense ROS events and high reindeer mortality has serious implications for the future of tundra Nenets nomadism. PMID:27852939

Effects of ocean acidification on the physiological performance and carbon production of the Antarctic sea ice diatom Nitzschia sp. ICE-H.

PubMed

Qu, Chang-Feng; Liu, Fang-Ming; Zheng, Zhou; Wang, Yi-Bin; Li, Xue-Gang; Yuan, Hua-Mao; Li, Ning; An, Mei-Ling; Wang, Xi-Xi; He, Ying-Ying; Li, Lu-Lu; Miao, Jin-Lai

2017-07-15

Ocean acidification (OA) resulting from increasing atmospheric CO 2 strongly influences marine ecosystems, particularly in the polar ocean due to greater CO 2 solubility. Here, we grew the Antarctic sea ice diatom Nitzschia sp. ICE-H in a semicontinuous culture under low (~400ppm) and high (1000ppm) CO 2 levels. Elevated CO 2 resulted in a stimulated physiological response including increased growth rates, chlorophyll a contents, and nitrogen and phosphorus uptake rates. Furthermore, high CO 2 enhanced cellular particulate organic carbon production rates, indicating a greater shift from inorganic to organic carbon. However, the cultures grown in high CO 2 conditions exhibited a decrease in both extracellular and intracellular carbonic anhydrase activity, suggesting that the carbon concentrating mechanisms of Nitzschia sp. ICE-H may be suppressed by elevated CO 2 . Our results revealed that OA would be beneficial to the survival of this sea ice diatom strain, with broad implications for global carbon cycles in the future ocean. Copyright © 2017. Published by Elsevier Ltd.

Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia.

PubMed

Forbes, Bruce C; Kumpula, Timo; Meschtyb, Nina; Laptander, Roza; Macias-Fauria, Marc; Zetterberg, Pentti; Verdonen, Mariana; Skarin, Anna; Kim, Kwang-Yul; Boisvert, Linette N; Stroeve, Julienne C; Bartsch, Annett

2016-11-01

Sea ice loss is accelerating in the Barents and Kara Seas (BKS). Assessing potential linkages between sea ice retreat/thinning and the region's ancient and unique social-ecological systems is a pressing task. Tundra nomadism remains a vitally important livelihood for indigenous Nenets and their large reindeer herds. Warming summer air temperatures have been linked to more frequent and sustained summer high-pressure systems over West Siberia, Russia, but not to sea ice retreat. At the same time, autumn/winter rain-on-snow (ROS) events have become more frequent and intense. Here, we review evidence for autumn atmospheric warming and precipitation increases over Arctic coastal lands in proximity to BKS ice loss. Two major ROS events during November 2006 and 2013 led to massive winter reindeer mortality episodes on the Yamal Peninsula. Fieldwork with migratory herders has revealed that the ecological and socio-economic impacts from the catastrophic 2013 event will unfold for years to come. The suggested link between sea ice loss, more frequent and intense ROS events and high reindeer mortality has serious implications for the future of tundra Nenets nomadism. © 2016 The Authors.

Ion Irradiation of H2-Laden Porous Water-ice Films: Implications for Interstellar Ices

NASA Astrophysics Data System (ADS)

Raut, U.; Mitchell, E. H.; Baragiola, R. A.

2015-10-01

To understand the effects of cosmic-ray (CR) impacts on interstellar icy grains immersed in H2 gas, we have irradiated porous water-ice films loaded with H2 with 100 keV H+. The ice films were exposed to H2 gas at different pressures following deposition and during irradiation. A net H2 loss is observed during irradiation due to competition between ion-induced sputtering and gas adsorption. The initial H2 loss cross-section, 4(1) × 10-14 cm2, was independent of film thickness, H2, and proton fluxes. In addition to sputtering, irradiation also closes nanopores, trapping H2 in the film with binding that exceeds physical absorption energies. As a result, 2%-7% H2 is retained in the ice following irradiation to high fluences. We find that the trapped H2 concentration increases with decreasing Φ, the ratio of ion to H2 fluxes, suggesting that as high as 8% solid H2 can be trapped in interstellar ice by CR or stellar wind impacts.

A customer value analysis of Taiwan ice cream market: a means-end chain approach across consumption situations.

PubMed

Chen, Yan-Kwang; Tsai, Pei-Shan; Chiu, Fei-Rung

2015-01-01

In the highly competitive market, it is increasingly hard for ice cream stores to develop creative marketing strategies to retain existing customers and attract new ones. This study applies the means-end chain approach to identify the customer value, consequences, and attributes of ice cream and to suggest useful information for ice cream sellers to develop differential marketing strategies across various consumption situations (i.e. on a date, gathering with friends, craving for ice cream). This study conducted one-on-one in-depth interviews with participants. The interview content was subsequently analyzed and coded to produce an implication matrix and a hierarchical value map, which was further used to determine customers' value perceptions. The results indicate the terminal values of the highest strength comprised economy, pleasure, and efficiency. Pleasure was emphasized among consumers who were on a date or gathering with friends, whereas satisfaction was emphasized among consumers who craved ice cream. Based on the results, the study also provides suggestions to the industry and future researchers.

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.

Sensitivity of Antarctic sea ice to the Southern Annular Mode in coupled climate models

NASA Astrophysics Data System (ADS)

Holland, Marika M.; Landrum, Laura; Kostov, Yavor; Marshall, John

2017-09-01

We assess the sea ice response to Southern Annular Mode (SAM) anomalies for pre-industrial control simulations from the Coupled Model Intercomparison Project (CMIP5). Consistent with work by Ferreira et al. (J Clim 28:1206-1226, 2015. doi: 10.1175/JCLI-D-14-00313.1), the models generally simulate a two-timescale response to positive SAM anomalies, with an initial increase in ice followed by an eventual sea ice decline. However, the models differ in the cross-over time at which the change in ice response occurs, in the overall magnitude of the response, and in the spatial distribution of the response. Late twentieth century Antarctic sea ice trends in CMIP5 simulations are related in part to different modeled responses to SAM variability acting on different time-varying transient SAM conditions. This explains a significant fraction of the spread in simulated late twentieth century southern hemisphere sea ice extent trends across the model simulations. Applying the modeled sea ice response to SAM variability but driven by the observed record of SAM suggests that variations in the austral summer SAM, which has exhibited a significant positive trend, have driven a modest sea ice decrease. However, additional work is needed to narrow the considerable model uncertainty in the climate response to SAM variability and its implications for 20th-21st century trends.

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.

High Arctic Holocene temperature record from the Agassiz ice cap and Greenland ice sheet evolution

PubMed Central

Lecavalier, Benoit S.; Fisher, David A.; Milne, Glenn A.; Vinther, Bo M.; Tarasov, Lev; Lacelle, Denis; Main, Brittany; Zheng, James; Bourgeois, Jocelyne; Dyke, Arthur S.

2017-01-01

We present a revised and extended high Arctic air temperature reconstruction from a single proxy that spans the past ∼12,000 y (up to 2009 CE). Our reconstruction from the Agassiz ice cap (Ellesmere Island, Canada) indicates an earlier and warmer Holocene thermal maximum with early Holocene temperatures that are 4–5 °C warmer compared with a previous reconstruction, and regularly exceed contemporary values for a period of ∼3,000 y. Our results show that air temperatures in this region are now at their warmest in the past 6,800–7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene. The warmer early Holocene inferred from the Agassiz ice core leads to an estimated ∼1 km of ice thinning in northwest Greenland during the early Holocene using the Camp Century ice core. Ice modeling results show that this large thinning is consistent with our air temperature reconstruction. The modeling results also demonstrate the broader significance of the enhanced warming, with a retreat of the northern ice margin behind its present position in the mid Holocene and a ∼25% increase in total Greenland ice sheet mass loss (∼1.4 m sea-level equivalent) during the last deglaciation, both of which have implications for interpreting geodetic measurements of land uplift and gravity changes in northern Greenland. PMID:28512225

Ikaite crystals in melting sea ice - implications for pCO2 and pH levels in Arctic surface waters

NASA Astrophysics Data System (ADS)

Rysgaard, S.; Glud, R. N.; Lennert, K.; Cooper, M.; Halden, N.; Leakey, R. J. G.; Hawthorne, F. C.; Barber, D.

2012-03-01

A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO2 exchange. This has been complicated by the recent discoveries of ikaite (CaCO3·6H2O) in Arctic and Antarctic sea ice, which indicate that multiple chemical transformations occur in sea ice with a possible effect on CO2 and pH conditions in surface waters. Here we report on biogeochemical conditions, microscopic examinations and x-ray diffraction analysis of single crystals from an actively melting 1.7 km2 (0.5-1 m thick) drifting ice floe in the Fram Strait during summer. Our findings show that ikaite crystals are present throughout the sea ice but with larger crystals appearing in the upper ice layers. Ikaite crystals placed at elevated temperatures gradually disintegrated into smaller crystallites and dissolved. During our field campaign in late June, melt reduced the ice flow thickness by ca. 0.2 m per week and resulted in an estimated 1.6 ppm decrease of pCO2 in the ocean surface mixed layer. This corresponds to an air-sea CO2 uptake of 11 mmol m-2 sea ice d-1 or to 3.5 ton km-2 ice floe week-1.

Detecting Aerosol Effect on Deep Precipitation Systems: A Modeling Study

NASA Astrophysics Data System (ADS)

Li, X.; Tao, W.; Khain, A.; Kummerow, C.; Simpson, J.

2006-05-01

Urban cities produce high concentrations of anthropogenic aerosols. These aerosols are generally hygroscopic and may serve as Cloud Condensation Nuclei (CCN). This study focuses on the aerosol indirect effect on the deep convective systems over the land. These deep convective systems contribute to the majority of the summer time rainfall and are important for local hydrological cycle and weather forecast. In a companion presentation (Tao et al.) in this session, the mechanisms of aerosol-cloud-precipitation interactions in deep convective systems are explored using cloud-resolving model simulations. Here these model results will be analyzed to provide guidance to the detection of the impact of aerosols as CCN on summer time, deep convections using the currently available observation methods. The two-dimensional Goddard Cumulus Ensemble (GCE) model with an explicit microphysical scheme has been used to simulate the aerosol effect on deep precipitation systems. This model simulates the size distributions of aerosol particles, as well as cloud, rain, ice crystals, snow, graupel, and hail explicitly. Two case studies are analyzed: a midlatitude summer time squall in Oklahoma, and a sea breeze convection in Florida. It is shown that increasing the CCN number concentration does not affect the rainfall structure and rain duration in these two cases. The total surface rainfall rate is reduced in the squall case, but remains essentially the same in the sea breeze case. For the long-lived squall system with a significant portion of the stratiform rain, the surface rainfall PDF (probability density function) distribution is more sensitive to the change of the initial CCN concentrations compared with the total surface rainfall. The possibility of detecting the aerosol indirect effect in deep precipitation systems from the space is also studied in this presentation. The hydrometeors fields from the GCE model simulations are used as inputs to a microwave radiative transfer model. It is found that Tb at higher frequencies (35 GHz and 85 GHz) are quite sensitive to the CCN concentration variations. This is because the higher frequency brightness temperatures are sensitive to large, ice-phase particles. In a clean environment, the deep convections produce larger cloud particles. When these cloud particles are transported above the freezing level by strong updrafts, they form larger precipitable ice particles (snow, graupel and hail) compared with dirty environment simulations. These larger ice particles result in significantly colder brightness temperatures at high frequencies in the clean scenario simulations.

The influence of the hydrologic cycle on the extent of sea ice with climatic implications

NASA Technical Reports Server (NTRS)

Dean, Kenneson G.; Stringer, William J.; Searcy, Craig

1993-01-01

Multi-temporal satellite images, field observations, and field measurements were used to investigate the mechanisms by which sea ice melts offshore from the Mackenzie River delta. Advanced Very High Resolution Radiometer (AVHRR) satellite data recorded in 1986 were analyzed. The satellite data were geometrically corrected and radiometrically calibrated so that albedo and temperature values could be extracted. The investigation revealed that sea ice melted approximately 2 weeks earlier offshore from the Mackenzie River delta than along coasts where river discharge is minimal or non-existent. There is significant intra-delta variability in the timing and patterns of ice melt. An estimation of energy flux indicates that 30 percent more of the visible wavelength energy and 25 percent more of the near-infrared wavelength energy is absorbed by water offshore of the delta compared to coastal areas with minimal river discharge. The analysis also revealed that the removal of sea ice involves the following: over-ice-flooding along the coast offshore from river delta channels; under-ice flow of 'warm' river water; melting and calving of the fast ice; and, the formation of a bight in the pack ice edge. Two stages in the melting of sea ice were identified: (1) an early stage where heat is supplied to overflows largely by solar radiation, and (2) a later stage where heat is supplied by river discharge in addition to solar radiation. A simple thermodynamic model of the thaw process in the fast ice zone was developed and parameterized based on events recorded by the satellite images. The model treats river discharge as the source of sensible heat at the base of the ice cover. The results of a series of sensitivity tests to assess the influence of river discharge on the near shore ice are presented.

Monitoring Subsurface Ice-Ocean Processes Using Underwater Acoustics in the Ross Sea

NASA Astrophysics Data System (ADS)

Haxel, J. H.; Dziak, R. P.; Matsumoto, H.; Lee, W. S.; Yun, S.

2016-12-01

The Ross Sea is a dynamic area of ice-ocean interaction, where a large component of the Southern Ocean's sea ice formation occurs within regional polynyas in addition to the destructive processes happening at the seaward boundary of the Ross Ice Shelf. Recent studies show the sea-ice season has been lengthening and the sea ice extent has been growing with more persistent and larger regional polynyas. These trends have important implications for the Ross Sea ecosystem with polynyas supporting high rates of primary productivity in the area. Monitoring trends in sea ice and ice shelf dynamics in the Southern Ocean has relied heavily on satellite imagery and remote sensing methods despite a significant portion of these physical processes occurring beneath the ocean surface. In January 2014, an ocean bottom hydrophone (OBH) was moored on the seafloor in the polynya area of Terra Nova Bay in the northwest region of the Ross Sea, north of the Drygalski Ice Tongue. The OBH recorded a year long record of the underwater low frequency acoustic spectrum up to 500 Hz from January 29 until it was recovered the following December 17, 2014. The acoustic records reveal a complex annual history of ice generated signals with over 50,000 detected events. These ice generated events related to collisions and cracking provide important insight for the timing and intensity of the ice-ocean dynamics happening below the sea surface as the polynya grows and expands and the nearby Drygalski ice tongue flows into Terra Nova Bay. Additionally, high concentrations of baleen whale vocalizations in frequencies ranging from 200-400 Hz from September - December suggest a strong seasonal presence of whales in this ecologically important polynya region.

An Expanded Analysis of Nitrogen Ice Convection in Sputnik Planum

NASA Astrophysics Data System (ADS)

Umurhan, Orkan M.; Lyra, Wladimir; Wong, Teresa; McKinnon, William B.; Nimmo, Francis; Howard, Alan D.; Moore, Jeffrey M.; Binzel, Richard; White, Oliver; Stern, S. Alan; Ennico, Kimberly; Olkin, Catherine B.; Weaver, Harold A.; Young, Leslie; New Horizons Geology and Geophysics Science Team

2016-10-01

The New Horizons close-encounter flyby of Pluto revealed 20-35 km scale ovoid patterns on the informally named Sputnik Planum. These features have been recently interpreted and shown to arise from the action of solid-state convection of (predominantly) nitrogen ice driven by Pluto's geothermal gradient. One of the major uncertainties in the convection physics centers on the temperature and grain-size dependency of nitrogen ice rheology, which has strong implications for the overturn times of the convecting ice. Assuming nitrogen ice in Sputnik Planum rests on a passive water ice bedrock that conducts Pluto's interior heat flux, and, given the uncertainty of the grain-size distribution of the nitrogen ice in Sputnik Planum, we examine a suite of two-dimensional convection models that take into account the thermal contact between the nitrogen ice layer and the conducting water-ice bedrock for a given emergent geothermal flux. We find for nitrogen ice layers several km deep, the emerging convection efficiently cools the nitrogen-ice water-ice bedrock interface resulting in temperature differences across the convecting layer of 10-20 K (at most) regardless of layer depth. For grain sizes ranging from 0.01 mm to 5 mm the resulting horizontal size to depth ratios of the emerging convection patterns go from 4:1 up to 6:1, suggesting that the nitrogen ice layer in Sputnik Planum may be anywhere between 3.5 and 8 km deep. Such depths are consistent with Sputnik Planum being a large impact basin (in a relative sense) analogous to Hellas on Mars. In this grain-size range we also find, (i) the calculated cell overturn times are anywhere from 1e4 to 5e5 yrs and, (ii) there is a distinct transition from steady state to time dependent convection.

Ikaite crystals in melting sea ice - implications for pCO2 and pH levels in Arctic surface waters

NASA Astrophysics Data System (ADS)

Rysgaard, S.; Glud, R. N.; Lennert, K.; Cooper, M.; Halden, N.; Leakey, R. J. G.; Hawthorne, F. C.; Barber, D.

2012-08-01

A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO2 exchange. This has been complicated by the recent discoveries of ikaite (a polymorph of CaCO3·6H2O) in Arctic and Antarctic sea ice, which indicate that multiple chemical transformations occur in sea ice with a possible effect on CO2 and pH conditions in surface waters. Here, we report on biogeochemical conditions, microscopic examinations and x-ray diffraction analysis of single crystals from a melting 1.7 km2 (0.5-1 m thick) drifting ice floe in the Fram Strait during summer. Our findings show that ikaite crystals are present throughout the sea ice but with larger crystals appearing in the upper ice layers. Ikaite crystals placed at elevated temperatures disintegrated into smaller crystallites and dissolved. During our field campaign in late June, melt reduced the ice floe thickness by 0.2 m per week and resulted in an estimated 3.8 ppm decrease of pCO2 in the ocean surface mixed layer. This corresponds to an air-sea CO2 uptake of 10.6 mmol m-2 sea ice d-1 or to 3.3 ton km-2 ice floe week-1. This is markedly higher than the estimated primary production within the ice floe of 0.3-1.3 mmol m-2 sea ice d-1. Finally, the presence of ikaite in sea ice and the dissolution of the mineral during melting of the sea ice and mixing of the melt water into the surface oceanic mixed layer accounted for half of the estimated pCO2 uptake.

Ultraviolet Irradiation of Naphthalene in H2O Ice: Implications for Meteorites and Biogenesis

NASA Technical Reports Server (NTRS)

Bernstein, Max P.; Dworkin, Jason; Sandford, Scott A.; Allamandola, Louis J.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

The polycyclic aromatic hydrocarbon (PAH) naphthalene was exposed to ultraviolet radiation in H2O ice under astrophysical conditions, and the products were analyzed using infrared spectroscopy and high performance liquid chromatography. As we found in our earlier studies on the photoprocessing of coronene in H2O ice, aromatic alcohols and ketones (quinones) were formed. The regiochemistry of the reactions is described and leads to specific predictions of the relative abundances of various oxidized naphthalenes that should exist in meteorites if interstellar ice photochemistry influenced their aromatic inventory. Since oxidized PAHs are present in carbon-rich meteorites and interplanetary dust particles (IDPs), and ubiquitous in and fundamental to biochemistry, the delivery of such extraterrestrial molecules to the early Earth may have played a role in the origin and evolution of life.

Channelized melting drives thinning under Dotson ice shelf, Western Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Gourmelen, N.; Goldberg, D.; Snow, K.; Henley, S. F.; Bingham, R. G.; Kimura, S.; Hogg, A.; Shepherd, A.; Mouginot, J.; Lenaerts, J.; Ligtenberg, S.; Van De Berg, W. J.

2017-12-01

The majority of meteoric ice that forms in West Antarctica leaves the ice sheet through floating ice shelves, many of which have been thinning substantially over the last 25 years. A significant proportion of ice-shelf thinning has been driven by submarine melting facilitated by increased access of relatively warm (>0.6oC) modified Circumpolar Deep Water to sub-shelf cavities. Ice shelves play a significant role in stabilising the ice sheet from runaway retreat and regulating its contribution to sea level change. Ice-shelf melting has also been implicated in sustaining high primary productivity in Antarctica's coastal seas. However, these processes vary regionally and are not fully understood. Under some ice shelves, concentrated melting leads to the formation of inverted channels. These channels guide buoyant melt-laden outflow, which can lead to localised melting of the sea ice cover. The channels may also potentially lead to heightened crevassing, which in turn affects ice-shelf stability. Meanwhile, numerical studies suggest that buttressing loss is sensitive to the location of ice removal within an ice-shelf. Thus it is important that we observe spatial patterns, as well as magnitudes, of ice-shelf thinning, in order to improve understanding of the ocean drivers of thinning and of their impacts on ice-shelf stability. Here we show from high-resolution altimetry measurements acquired between 2010 to 2016 that Dotson Ice Shelf, West Antarctica, thins in response to basal melting focussed along a single 5 km-wide and 60 km-long channel extending from the ice shelf's grounding zone to its calving front. The coupled effect of geostrophic circulation and ice-shelf topography leads to the observed concentration of basal melting. Analysis of previous datasets suggests that this process has been ongoing for at least the last 25 years. If focused thinning continues at present rates, the channel would melt through within 40-50 years, almost two centuries before it is projected from the average thinning rate. Our findings provide evidence of basal melt-driven sub-ice shelf channel formation and its potential for accelerating the weakening of ice shelves.

Mapping and assessing variability in the Antarctic marginal ice zone, pack ice and coastal polynyas in two sea ice algorithms with implications on breeding success of snow petrels

NASA Astrophysics Data System (ADS)

Stroeve, Julienne C.; Jenouvrier, Stephanie; Campbell, G. Garrett; Barbraud, Christophe; Delord, Karine

2016-08-01

Sea ice variability within the marginal ice zone (MIZ) and polynyas plays an important role for phytoplankton productivity and krill abundance. Therefore, mapping their spatial extent as well as seasonal and interannual variability is essential for understanding how current and future changes in these biologically active regions may impact the Antarctic marine ecosystem. Knowledge of the distribution of MIZ, consolidated pack ice and coastal polynyas in the total Antarctic sea ice cover may also help to shed light on the factors contributing towards recent expansion of the Antarctic ice cover in some regions and contraction in others. The long-term passive microwave satellite data record provides the longest and most consistent record for assessing the proportion of the sea ice cover that is covered by each of these ice categories. However, estimates of the amount of MIZ, consolidated pack ice and polynyas depend strongly on which sea ice algorithm is used. This study uses two popular passive microwave sea ice algorithms, the NASA Team and Bootstrap, and applies the same thresholds to the sea ice concentrations to evaluate the distribution and variability in the MIZ, the consolidated pack ice and coastal polynyas. Results reveal that the seasonal cycle in the MIZ and pack ice is generally similar between both algorithms, yet the NASA Team algorithm has on average twice the MIZ and half the consolidated pack ice area as the Bootstrap algorithm. Trends also differ, with the Bootstrap algorithm suggesting statistically significant trends towards increased pack ice area and no statistically significant trends in the MIZ. The NASA Team algorithm on the other hand indicates statistically significant positive trends in the MIZ during spring. Potential coastal polynya area and amount of broken ice within the consolidated ice pack are also larger in the NASA Team algorithm. The timing of maximum polynya area may differ by as much as 5 months between algorithms. These differences lead to different relationships between sea ice characteristics and biological processes, as illustrated here with the breeding success of an Antarctic seabird.

On the state of water ice on saturn's moon Titan and implications to icy bodies in the outer solar system.

PubMed

Zheng, Weijun; Jewitt, David; Kaiser, Ralf I

2009-10-22

The crystalline state of water ice in the Solar System depends on the temperature history of the ice and the influence of energetic particles to which it has been exposed. We measured the infrared absorption spectra of amorphous and crystalline water ice in the 10-50 K and 10-140 K temperature ranges, respectively, and conducted a systematic experimental study to investigate the amorphization of crystalline water ice via ionizing radiation irradiation at doses of up to 160 +/- 30 eV per molecule. We found that crystalline water ice can be converted only partially to amorphous ice by electron irradiation. The experiments showed that a fraction of the 1.65 microm band, which is characteristic for crystalline water ice, survived the irradiation, to a degree that strongly depends on the temperature. Quantitative kinetic fits of the temporal evolution of the 1.65 mum band clearly demonstrate that there is a balance between thermal recrystallization and irradiation-induced amorphization, with thermal recrystallizaton dominant at higher temperatures. Our experiments show the amorphization at 40 K was incomplete, in contradiction to Mastrapa and Brown's conclusion (Icarus 2006, 183, 207.). At 50 K, the recrystallization due to thermal effects is strong, and most of the crystalline ice survived. Temperatures of most icy objects in the Solar System, including Jovian satellites, Saturnian satellites (including Titan), and Kuiper Belt Objects, are equal to or above 50 K; this explains why water ice detected on those objects is mostly crystalline.

Sea ice decline and 21st century trans-Arctic shipping routes

NASA Astrophysics Data System (ADS)

Melia, N.; Haines, K.; Hawkins, E.

2016-09-01

The observed decline in Arctic sea ice is projected to continue, opening shorter trade routes across the Arctic Ocean, with potentially global economic implications. Here we quantify, using Coupled Model Intercomparison Project Phase 5 global climate model simulations calibrated to remove spatial biases, how projected sea ice loss might increase opportunities for Arctic transit shipping. By midcentury for standard open water vessels, the frequency of navigable periods doubles, with routes across the central Arctic becoming available. A sea ice-ship speed relationship is used to show that European routes to Asia typically become 10 days faster via the Arctic than alternatives by midcentury, and 13 days faster by late century, while North American routes become 4 days faster. Future greenhouse gas emissions have a larger impact by late century; the shipping season reaching 4-8 months in Representative Concentration Pathway (RCP)8.5 double that of RCP2.6, both with substantial interannual variability. Moderately, ice-strengthened vessels likely enable Arctic transits for 10-12 months by late century.

Topographic variations in chaos on Europa: Implications for diapiric formation

NASA Technical Reports Server (NTRS)

Schenk, Paul M.; Pappalardo, Robert T.

2004-01-01

Disrupted terrain, or chaos, on Europa, might have formed through melting of a floating ice shell from a subsurface ocean [Cam et al., 1998; Greenberg et al., 19991, or breakup by diapirs rising from the warm lower portion of the ice shell [Head and Pappalardo, 1999; Collins et al., 20001. Each model makes specific and testable predictions for topographic expression within chaos and relative to surrounding terrains on local and regional scales. High-resolution stereo-controlled photoclinometric topography indicates that chaos topography, including the archetypal Conamara Chaos region, is uneven and commonly higher than surrounding plains by up to 250 m. Elevated and undulating topography is more consistent with diapiric uplift of deep material in a relatively thick ice shell, rather than melt-through and refreezing of regionally or globally thin ice by a subsurface ocean. Vertical and horizontal scales of topographic doming in Conamara Chaos are consistent with a total ice shell thickness >15 km. Contact between Europa's ocean and surface may most likely be indirectly via diapirism or convection.

Topographic variations in chaos on Europa: Implications for diapiric formation

NASA Astrophysics Data System (ADS)

Schenk, Paul M.; Pappalardo, Robert T.

2004-08-01

Disrupted terrain, or chaos, on Europa, might have formed through melting of a floating ice shell from a subsurface ocean [Carr et al., 1998; Greenberg et al., 1999], or breakup by diapirs rising from the warm lower portion of the ice shell [Head and Pappalardo, 1999; Collins et al., 2000]. Each model makes specific and testable predictions for topographic expression within chaos and relative to surrounding terrains on local and regional scales. High-resolution stereo-controlled photoclinometric topography indicates that chaos topography, including the archetypal Conamara Chaos region, is uneven and commonly higher than surrounding plains by up to 250 m. Elevated and undulating topography is more consistent with diapiric uplift of deep material in a relatively thick ice shell, rather than melt-through and refreezing of regionally or globally thin ice by a subsurface ocean. Vertical and horizontal scales of topographic doming in Conamara Chaos are consistent with a total ice shell thickness >15 km. Contact between Europa's ocean and surface may most likely be indirectly via diapirism or convection.

Commentary: The Feasibility of Subduction and Implications for Plate Tectonics on Jupiter's Moon Europa

NASA Astrophysics Data System (ADS)

Kattenhorn, Simon A.

2018-03-01

A new modeling-based study by Johnson et al. (2017, https://doi.org/10.1002/2017JE005370) lends support to the hypothesis that portions of Europa's surface may have been removed by the process of subduction, as suggested by Kattenhorn and Prockter (2014, https://doi.org/10.1038/NGEO2245). Using a simple 1-D model that tracks the thermal and density structure of a descending ice plate, Johnson et al. show that ice plates with 10% porosity and overall salt contents of 5%, which differ in salt content by 2.5% from the surrounding reference ice shell, are nonbuoyant and thus likely to sink through the underlying, convecting portion of the ice shell. The feasibility of subduction in an ice shell is critical to the existence of icy plate tectonics, which is hypothesized to exist at least locally on Europa, potentially making it the only other Solar System body other than Earth with a surface modified by plate tectonics.

Lunar and Planetary Science XXXV: Special Session: Mars Climate Change

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Mars Climate Change" contained the following reports:Geological Evidence for Climate Change on Mars; A New Astronomical Solution for the Long Term Evolution of the Insolation Quantities of Mars; Interpreting Martian Paleoclimate with a Mars General Circulation Model; History and Progress of GCM Simulations on Recent Mars Climate Change; Northern and Southern Permafrost Regions on Mars with High Content of Water Ice: Similarities and Differences; Periods of Active Permafrost Layer Formation in the Recent Geological History of Mars; Microclimate Zones in the Dry Valleys of Antarctica: Implications for Landscape; Evolution and Climate Change on Mars; Geomorphic Evidence for Martian Ground Ice and Climate Change; Explaining the Mid-Latitude Ice Deposits with a General Circulation Model; Tharsis Montes Cold-based Glaciers: Observations and Constraints for Modeling and Preliminary Results; Ice Sheet Modeling: Terrestrial Background and Application to Arsia Mons Lobate Deposit, Mars; Enhanced Water-Equivalent Hydrogen on the Western Flanks of the Tharsis Montes and Olympus Mons: Remnant Subsurface Ice or Hydrate Minerals?; and New Age Mars.

Lunar and Planetary Science XXXV: Special Session: Mars Climate Change

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Mars Climate Change" included the following topics:Geological Evidence for Climate Change on Mars; A New Astronomical Solution for the Long Term Evolution of the Insolation Quantities of Mars; Interpreting Martian Paleoclimate with a Mars General Circulation Model; History and Progress of GCM Simulations on Recent Mars Climate Change; Northern and Southern Permafrost Regions on Mars with High Content of Water Ice: Similarities and Differences; Periods of Active Permafrost Layer Formation in the Recent Geological History of Mars; Microclimate Zones in the Dry Valleys of Antarctica: Implications for Landscape Evolution and Climate Change on Mars; Geomorphic Evidence for Martian Ground Ice and Climate Change; Explaining the Mid-Latitude Ice Deposits with a General Circulation Model; Tharsis Montes Cold-based Glaciers: Observations and Constraints for Modeling and Preliminary Results; Ice Sheet Modeling: Terrestrial Background and Application to Arsia Mons Lobate Deposit, Mars; Enhanced Water-Equivalent Hydrogen on the Western Flanks of the Tharsis Montes and Olympus Mons: Remnant Subsurface Ice or Hydrate Minerals?; and New Age Mars.

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 collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution.

Studies of contemporary glacier basal ice cryostructures to identify buried basal ice in the permafrost: an example from the Matanuska Glacier, Alaska.

NASA Astrophysics Data System (ADS)

Stephani, E.; Fortier, D.; Kanevskiy, M.; Dillon, M.; Shur, Y.

2007-12-01

In the permafrost, massive ice bodies occur as buried glacier ice, aufeis ice, recrystalized snow, massive segregated ice, injection ice, ice wedges or ice formed in underground cavities ("pool ice", "thermokarst-cave ice"). The origin of massive ice bodies in the permafrost bears considerable implications for the reconstructions of paleoenvironments and paleoclimates. Our work aims to help the permafrost scientists working on massive icy sediments to distinguish buried basal glacier ice from other types of buried ice. To do so, the properties and structure of contemporary basal ice must be well known. Field investigations at the Matanuska Glacier (Chugach range, South-central Alaska), consisted in descriptions and sampling of natural basal ice exposures. We have used the basal ice facies classification of Lawson (1979) which is simple, easy to use in the field and provides a good framework for the description of basal ice exposures. Cores were extracted and brought back to the laboratory for water and grain-size analyses. The sediments forming the cryostructure were mostly polymodal, poorly sorted gravelly silt to gravelly fine sand, with mud contents generally over 50%. These data will be used to calibrate three-dimensional (3D) models produced from micro-tomographic scans of basal ice which will produce quantitative estimates of volumetric ice and sediments contents of basal ice cryostructures. Ultimately, visual qualitative and quantitative characterization of the basal ice components of 3D models together with field observations and laboratory analysis will allow for a new micro-facies and cryostructures classification of the basal ice. Our work will also have applications in glaciology, glacial geology, geomorphology, Quaternary and paleo-climatological studies based on inferences made from the structure of basal glacier ice. This paper presents the internal composition of the basal ice facies in terms of cryostructures assemblages (Fortier et al.: 2007) and sedimentological properties. Fortier, D., Kanevskiy, M, Stephani, E., Dillon, M., Shur, Y. 2007. Facies and cryostructures of glacier basal ice as an object of permafrost study, an example from the Matanuska Glacier, Alaska. Canadian Quaternary Association Conference, Ottawa, June 2007: 75. Lawson, D.E. 1979. Sedimentological analysis of the western terminus region of the Matanuska Glacier, Alaska. Cold Regions Engineering and Research Laboratory, Hanover, N.H., Report 79-9.

Implications of the pseudo-Dirac scenario for ultra high energy neutrinos from GRBs

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

Esmaili, Arman; Farzan, Yasaman, E-mail: aesmaili@ifi.unicamp.br, E-mail: yasaman@theory.ipm.ac.ir

2012-12-01

The source of Ultra High Energy Cosmic Rays (UHECR) is still an unresolved mystery. Up until recently, sources of Gamma Ray Bursts (GRBs) had been considered as a suitable source for UHECR. Within the fireball model, the UHECR produced at GRBs should be accompanied with a neutrino flux detectable at the neutrino telescope such as IceCube. Recently, IceCube has set an upper bound on the neutrino flux accompanied by GRBs about 3.7 times below the prediction. We investigate whether this deficit can be explained by the oscillation of the active neutrinos to sterile neutrinos en route from the source tomore » the detectors within the pseudo-Dirac scenario. We then discuss the implication of this scenario for diffuse supernova relic neutrinos.« less

Nanowires from dirty multi-crystalline Si for hydrogen generation

NASA Astrophysics Data System (ADS)

Li, Xiaopeng; Schweizer, Stefan L.; Sprafke, Alexander; Wehrspohn, Ralf B.

2013-09-01

Silicon nanowires are considered as a promising architecture for solar energy conversion systems. By metal assisted chemical etching of multi-crystalline upgraded metallurgical silicon (UMG-Si), large areas of silicon nanowires (SiNWs) with high quality can be produced on the mother substrates. These areas show a low reflectance comparable to black silicon. More interestingly, we find that various metal impurities inside UMG-Si are removed due to the etching through element analysis. A prototype cell was built to test the photoelectrochemical (PEC) properties of UMG-SiNWs for water splitting. The on-set potential for hydrogen evolution was much reduced, and the photocurrent density showed an increment of 35% in comparison with a `dirty' UMG-Si wafer.

The Environment and Directed Technical Change.

PubMed

Acemoglu, Daron; Aghion, Philippe; Bursztyn, Leonardo; Hemous, David

2012-02-01

This paper introduces endogenous and directed technical change in a growth model with environmental constraints. The final good is produced from "dirty" and "clean" inputs. We show that: (i) when inputs are sufficiently substitutable, sustainable growth can be achieved with temporary taxes/subsidies that redirect innovation toward clean inputs; (ii) optimal policy involves both "carbon taxes" and research subsidies, avoiding excessive use of carbon taxes; (iii) delay in intervention is costly, as it later necessitates a longer transition phase with slow growth; and (iv) use of an exhaustible resource in dirty input production helps the switch to clean innovation under laissez-faire. (JEL O33, O44, Q30, Q54, Q56, Q58).

On the Radiolysis of Ethylene Ices by Energetic Electrons and Implications to the Extraterrestrial Hydrocarbon Chemistry

NASA Astrophysics Data System (ADS)

Zhou, Li; Maity, Surajit; Abplanalp, Matt; Turner, Andrew; Kaiser, Ralf I.

2014-07-01

The chemical processing of ethylene ices (C2H4) by energetic electrons was investigated at 11 K to simulate the energy transfer processes and synthesis of new molecules induced by secondary electrons generated in the track of galactic cosmic ray particles. A combination of Fourier transform infrared spectrometry (solid state) and quadrupole mass spectrometry (gas phase) resulted in the identification of six hydrocarbon molecules: methane (CH4), the C2 species acetylene (C2H2), ethane (C2H6), the ethyl radical (C2H5), and—for the very first time in ethylene irradiation experiments—the C4 hydrocarbons 1-butene (C4H8) and n-butane (C4H10). By tracing the temporal evolution of the newly formed molecules spectroscopically online and in situ, we were also able to fit the kinetic profiles with a system of coupled differential equations, eventually providing mechanistic information, reaction pathways, and rate constants on the radiolysis of ethylene ices and the inherent formation of smaller (C1) and more complex (C2, C4) hydrocarbons involving carbon-hydrogen bond ruptures, atomic hydrogen addition processes, and radical-radical recombination pathways. We also discuss the implications of these results on the hydrocarbon chemistry on Titan's surface and on ice-coated, methane-bearing interstellar grains as present in cold molecular clouds such as TMC-1.

Sputtering of water ice films: A re-assessment with singly and doubly charged oxygen and argon ions, molecular oxygen, and electrons

NASA Astrophysics Data System (ADS)

Galli, A.; Vorburger, A.; Wurz, P.; Tulej, M.

2017-07-01

We studied the erosion rates from thin water ice films on a microbalance upon irradiation with ions (O+, O2+, O2+ , Ar+ , and Ar2+) and electrons at energies between 0.1 keV and 80 keV. The results with O+ and Ar+ irradiation confirm previous results of other research groups that relied on the same experiment set-up. In addition, we assessed how the ice film thickness affects the results and we compared the results for singly versus doubly charged ions and for O+ versus O2+ ions. The irradiation with 1 keV and 3 keV electrons offer the first experimental results at these energies. Our results confirm theoretical predictions that the yield per impacting electron does not increase with energy ad infinitum but rather levels off between 0.1 and 1 keV. The results for ion and electron sputtering have important implications for atmosphere-less icy bodies in a plasma environment. We briefly discuss the implications for the icy moons of Jupiter. Finally, the experiments also allow us to assess the viability of two methods to measure the erosion rate in the case that the icy sample cannot be attached on a microbalance. This is an important step for future laboratory studies where regolith ice samples and their reaction to particle irradiation are to be characterized.

Planetary Ice-Oceans: Numerical Modeling Study of Ice-Shell Growth in Convecting Two-Phase Systems

NASA Astrophysics Data System (ADS)

Allu Peddinti, Divya; McNamara, Allen

2017-04-01

Several icy bodies in the Solar system such as the icy moons Europa and Enceladus exhibit signs of subsurface oceans underneath an ice-shell. For Europa, the geologically young surface, the presence of surface features and the aligned surface chemistry pose interesting questions about formation of the ice-shell and its interaction with the ocean below. This also ties in with its astrobiological potential and implications for similar ice-ocean systems elsewhere in the cosmos. The overall thickness of the H2O layer on Europa is estimated to be 100-150 km while the thickness of the ice-shell is debated. Additionally, Europa is subject to tidal heating due to interaction with Jupiter's immense gravity field. It is of interest to understand how the ice-shell thickness varies in the presence of tidal internal heating and the localization of heating in different regions of the ice-shell. Thus this study aims to determine the effect of tidal internal heating on the growth rate of the ice-shell over time. We perform geodynamic modeling of the ice-ocean system in order to understand how the ice-shell thickness changes with time. The convection code employs the ice Ih-water phase diagram in order to model the two-phase convecting ice-ocean system. All the models begin from an initial warm thick ocean that cools from the top. The numerical experiments analyze three cases: case 1 with no tidal internal heating in the system, case 2 with constant tidal internal heating in the ice and case 3 with viscosity-dependent tidal internal heating in the ice. We track the ice-shell thickness as a function of time as the system cools. Modeling results so far have identified that the shell growth rate changes substantially at a point in time that coincides with a change in the planform of ice-convection cells. Additionally, the velocity vs depth plots indicate a shift from a conduction dominant to a convection dominant ice regime. We compare the three different cases to provide a comprehensive understanding of the temporal variation in the ice-shell thickness due to the addition of heating in the ice.

A glimpse beneath Antarctic sea ice: observation of platelet-layer thickness and ice-volume fraction with multifrequency EM

NASA Astrophysics Data System (ADS)

Hoppmann, Mario; Hunkeler, Priska A.; Hendricks, Stefan; Kalscheuer, Thomas; Gerdes, Rüdiger

2016-04-01

In Antarctica, ice crystals (platelets) form and grow in supercooled waters below ice shelves. These platelets rise, accumulate beneath nearby sea ice, and subsequently form a several meter thick, porous sub-ice platelet layer. This special ice type is a unique habitat, influences sea-ice mass and energy balance, and its volume can be interpreted as an indicator of the health of an ice shelf. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In the present study, we applied a lateral constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the ice-shelf influenced fast-ice regime of Atka Bay, eastern Weddell Sea. We adapted the inversion algorithm to incorporate a sensor specific signal bias, and confirmed the reliability of the algorithm by performing a sensitivity study using synthetic data. We inverted the field data for sea-ice and platelet-layer thickness and electrical conductivity, and calculated ice-volume fractions within the platelet layer using Archie's Law. The thickness results agreed well with drillhole validation datasets within the uncertainty range, and the ice-volume fraction yielded results comparable to other studies. Both parameters together enable an estimation of the total ice volume within the platelet layer, which was found to be comparable to the volume of landfast sea ice in this region, and corresponded to more than a quarter of the annual basal melt volume of the nearby Ekström Ice Shelf. Our findings show that multi-frequency EM induction sounding is a suitable approach to efficiently map sea-ice and platelet-layer properties, with important implications for research into ocean/ice-shelf/sea-ice interactions. However, a successful application of this technique requires a break with traditional EM sensor calibration strategies due to the need of absolute calibration with respect to a physical forward model.

Radar Detection of Layering in Ice: Experiments on a Constructed Layered Ice Sheet

NASA Astrophysics Data System (ADS)

Carter, L. M.; Koenig, L.; Courville, Z.; Ghent, R. R.; Koutnik, M. R.

2016-12-01

The polar caps and glaciers of both Earth and Mars display internal layering that preserves a record of past climate. These layers are apparent both in optical datasets (high resolution images, core samples) and in ground penetrating radar (GPR) data. On Mars, the SHARAD (Shallow Radar) radar on the Mars Reconnaissance Orbiter shows fine layering that changes spatially and with depth across the polar caps. This internal layering has been attributed to changes in fractional dust contamination due to obliquity-induced climate variations, but there are other processes that can lead to internal layers visible in radar data. In particular, terrestrial sounding of ice sheets compared with core samples have revealed that ice density and composition differences account for the majority of the radar reflectors. The large cold rooms and ice laboratory facility at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) provide us a unique opportunity to construct experimental ice sheets in a controlled setting and measure them with radar. In a CRREL laboratory, we constructed a layered ice sheet that is 3-m deep with a various snow and ice layers with known dust concentrations (using JSC Mars-1 basaltic simulant) and density differences. These ice sheets were profiled using a commercial GPR, at frequencies of 200, 400 and 900 MHz, to determine how the radar profile changes due to systematic and known changes in snow and ice layers, including layers with sub-wavelength spacing. We will report results from these experiments and implications for interpreting radar-detected layering in ice on Earth and Mars.

Solid and gaseous inclusions in the EDML deep ice core: origins and implications for the physical properties of polar ice

NASA Astrophysics Data System (ADS)

Faria, S. H.; Kipfstuhl, S.; Garbe, C. S.; Bendel, V.; Weikusat, C.; Weikusat, I.

2010-12-01

The great value of polar deep ice cores stems mainly from two essential features of polar ice: its crystalline structure and its impurities. They determine the physical properties of the ice matrix and provide proxies for the investigation of past climates. Experience shows that these two essential features of polar ice manifest themselves in a multiscale diversity of dynamic structures, including dislocations, grain boundaries, solid particles, air bubbles, clathrate hydrates and cloudy bands, among others. The fact that these structures are dynamic implies that they evolve with time through intricate interactions between the crystalline structure, impurities, and the ice flow. Records of these interactions have been carefully investigated in samples of the EPICA deep ice core drilled in Dronning Maud Land, Antarctica (75°S, 0°E, 2882 m elevation, 2774.15 m core length). Here we show how the distributions of sizes and shapes of air bubbles correlate with impurities and the crystalline structure, how the interaction between moving grain boundaries and micro-inclusions changes with ice depth and temperature, as well as the possible causes for the abrupt change in ice rheology observed in the MIS6-MIS5e transition. We also discuss how these observations may affect the flow of the ice sheet and the interpretation of paleoclimate records. Micrograph of an EDML sample from 555m depth. One can identify air bubbles (dark, round objects), microinclusions (tiny defocused spots), and a grain boundary pinned by a bubble. The width of the image is 700 micrometers.

Sedimentary record of a fluctuating ice margin from the Pennsylvanian of western Gondwana: Paraná Basin, southern Brazil

NASA Astrophysics Data System (ADS)

Vesely, Fernando F.; Trzaskos, Barbara; Kipper, Felipe; Assine, Mario Luis; Souza, Paulo A.

2015-08-01

The Paraná Basin is a key locality in the context of the Late Paleozoic Ice Age (LPIA) because of its location east of the Andean proto-margin of Gondwana and west of contiguous interior basins today found in western Africa. In this paper we document the sedimentary record associated with an ice margin that reached the eastern border of the Paraná Basin during the Pennsylvanian, with the aim of interpreting the depositional environments and discussing paleogeographic implications. The examined stratigraphic succession is divided in four stacked facies associations that record an upward transition from subglacial to glaciomarine environments. Deposition took place during deglaciation but was punctuated by minor readvances of the ice margin that deformed the sediment pile. Tillites, well-preserved landforms of subglacial erosion and glaciotectonic deformational structures indicate that the ice flowed to the north and northwest and that the ice margin did not advance far throughout the basin during the glacial maximum. Consequently, time-equivalent glacial deposits that crop out in other localities of eastern Paraná Basin are better explained by assuming multiple smaller ice lobes instead of one single large glacier. These ice lobes flowed from an ice cap covering uplifted lands now located in western Namibia, where glacial deposits are younger and occur confined within paleovalleys cut onto the Precambrian basement. This conclusion corroborates the idea of a topographically-controlled ice-spreading center in southwestern Africa and does not support the view of a large polar ice sheet controlling deposition in the Paraná Basin during the LPIA.

The volume- and surface-binding energies of ice systems containing CO, CO2, and H2O

NASA Technical Reports Server (NTRS)

Sandford, Scott A.; Allamandola, Louis J.

1990-01-01

Laboratory-measured, temperature-dependent sticking efficiencies are presently used to derive the surface-binding energies of CO and CO2 on H2O-rich ices, with a view to determining the condensation and vaporization properties of these systems as well as to the measured energies' implications for both cometary behavior and the evolution of interstellar ices. The molecular volume and the surface binding energies are not found to be necessarily related on the basis of simple nearest-neighbor scaling in surface and bulk sites; this may be due to the physical constraints associated with matrix structure-associated physical constraints, which sometimes dominate the volume-binding energies.

Changes and variations in the turning angle of Arctic sea ice

NASA Astrophysics Data System (ADS)

Ukita, J.; Honda, M.; Ishizuka, S.

2012-12-01

The motion of sea ice is under influences of forcing from winds and currents and of sea ice properties. In facing rapidly changing Arctic climate we are interested in whether we observe and quantify changes in sea ice conditions reflected in its velocity field. Theoretical consideration on the freedrift model predicts a change in the sea ice turning angle with respect to the direction of forcing wind in association with thinning sea ice thickness. Possible changes in atmospheric and ocean boundary layer conditions may be reflected in the sea ice turning angle through modification of both atmospheric and oceanic Ekman spirals. With these in mind this study examines statistical properties of the turning angle of the Arctic sea ice and compares them with atmospheric/ice/ocean conditions for the period of 1979-2010 on the basis of IABP buoy data. Preliminary results indicate that over this period the turning angle has varying trends depending on different seasons. We found weakly significant (>90% level) changes in the turning angle from August to October with the maximum trend in October. The direction of trends is counter-clockwise with respect to the geostrophic wind direction, which is consistent with the thinning of sea ice. The interannual variability of the turning angle for this peak season of the reduced sea ice cover is not the same as that of the Arctic SIE. However, in recent years the turning angle appears to covary with the surface air temperature, providing supporting evidence for the relationship between the angle and sea ice thickness. In the presentation we will provide results on the relationships between the turning angle and atmospheric and oceanic variables and further discuss their implications.

A theory-based parameterization for heterogeneous ice nucleation and implications for the simulation of ice processes in atmospheric models

NASA Astrophysics Data System (ADS)

Savre, J.; Ekman, A. M. L.

2015-05-01

A new parameterization for heterogeneous ice nucleation constrained by laboratory data and based on classical nucleation theory is introduced. Key features of the parameterization include the following: a consistent and modular modeling framework for treating condensation/immersion and deposition freezing, the possibility to consider various potential ice nucleating particle types (e.g., dust, black carbon, and bacteria), and the possibility to account for an aerosol size distribution. The ice nucleating ability of each aerosol type is described using a contact angle (θ) probability density function (PDF). A new modeling strategy is described to allow the θ PDF to evolve in time so that the most efficient ice nuclei (associated with the lowest θ values) are progressively removed as they nucleate ice. A computationally efficient quasi Monte Carlo method is used to integrate the computed ice nucleation rates over both size and contact angle distributions. The parameterization is employed in a parcel model, forced by an ensemble of Lagrangian trajectories extracted from a three-dimensional simulation of a springtime low-level Arctic mixed-phase cloud, in order to evaluate the accuracy and convergence of the method using different settings. The same model setup is then employed to examine the importance of various parameters for the simulated ice production. Modeling the time evolution of the θ PDF is found to be particularly crucial; assuming a time-independent θ PDF significantly overestimates the ice nucleation rates. It is stressed that the capacity of black carbon (BC) to form ice in the condensation/immersion freezing mode is highly uncertain, in particular at temperatures warmer than -20°C. In its current version, the parameterization most likely overestimates ice initiation by BC.

Improving Arctic Sea Ice Observations and Data Access to Support Advances in Sea Ice Forecasting

NASA Astrophysics Data System (ADS)

Farrell, S. L.

2017-12-01

The economic and strategic importance of the Arctic region is becoming apparent. One of the most striking and widely publicized changes underway is the declining sea ice cover. Since sea ice is a key component of the climate system, its ongoing loss has serious, and wide-ranging, socio-economic implications. Increasing year-to-year variability in the geographic location, concentration, and thickness of the Arctic ice cover will pose both challenges and opportunities. The sea ice research community must be engaged in sustained Arctic Observing Network (AON) initiatives so as to deliver fit-for-purpose remote sensing data products to a variety of stakeholders including Arctic communities, the weather forecasting and climate modeling communities, industry, local, regional and national governments, and policy makers. An example of engagement is the work currently underway to improve research collaborations between scientists engaged in obtaining and assessing sea ice observational data and those conducting numerical modeling studies and forecasting ice conditions. As part of the US AON, in collaboration with the Interagency Arctic Research Policy Committee (IARPC), we are developing a strategic framework within which observers and modelers can work towards the common goal of improved sea ice forecasting. Here, we focus on sea ice thickness, a key varaible of the Arctic ice cover. We describe multi-sensor, and blended, sea ice thickness data products under development that can be leveraged to improve model initialization and validation, as well as support data assimilation exercises. We will also present the new PolarWatch initiative (polarwatch.noaa.gov) and discuss efforts to advance access to remote sensing satellite observations and improve communication with Arctic stakeholders, so as to deliver data products that best address societal needs.

Compatibility of amino acids in ice Ih and high-pressure phases: implications for the origin of life

NASA Astrophysics Data System (ADS)

Hao, J.; Giovenco, E.; Pedreira-Segade, U.; Montagnac, G.; Daniel, I.

2017-12-01

Icy environments may have been common on the early Earth due to the faint young sun. Previous studies have proposed that the formation of large icy bodies in the early ocean could concentrate the building blocks of life in eutectic fluids and therefore facilitate the polymerization of monomers. This hypothesis is based on the untested assumption that organic molecules are virtually incompatible in ice Ih. In this study, we conducted freezing experiments to explore the partitioning behavior of selected amino acids (glycine, L-alanine, L-proline, and L-phenylalanine) between ice Ih and aqueous solutions analogous to seawater. We let ice crystals grow slowly from a few seeds in equilibrium with the solution and used Raman spectroscopy to analyze in situ the relative concentrations of amino acids in the ice and aqueous solution. During freezing, there was no precipitation of amino acid crystals, indicating that the concentrations in solution never reached their solubility limit, even when the droplet was mostly frozen. Analyses of the Raman spectra of ice and eutectic solution showed that considerable amounts of amino acids existed in the ice phase with partition coefficients ranging between 0.2 and 0.5. This study also explored the partitioning of amino acids between other phases of ice (ice VI and ice VII) and solutions at high pressures and observed similar results. These observations implied little incompatibility of amino acids in ice during the freezing of the solutions, rendering the hypothesis of a cold origin of life unwarranted. However, incorporation into ice could significantly improve the efficiency of extraterrestrial transport of small organics. Therefore, this study supports the hypothesis of extraterrestrial delivery of organic molecules in the icy comets and asteroids to the primitive Earth as suggested by an increasing number of independent observations.

Test methods and response surface models for hot, humid air decontamination of materials contaminated with dirty spores of Bacillus anthracis ∆Sterne and Bacillus thuringiensis Al Hakam.

PubMed

Buhr, T L; Young, A A; Barnette, H K; Minter, Z A; Kennihan, N L; Johnson, C A; Bohmke, M D; DePaola, M; Cora-Laó, M; Page, M A

2015-11-01

To develop test methods and evaluate survival of Bacillus anthracis ∆Sterne or Bacillus thuringiensis Al Hakam on materials contaminated with dirty spore preparations after exposure to hot, humid air using response surface modelling. Spores (>7 log10 ) were mixed with humic acid + spent sporulation medium (organic debris) or kaolin (dirt debris). Spore samples were then dried on five different test materials (wiring insulation, aircraft performance coating, anti-skid, polypropylene, and nylon). Inoculated materials were tested with 19 test combinations of temperature (55, 65, 75°C), relative humidity (70, 80, 90%) and time (1, 2, 3 days). The slowest spore inactivation kinetics was on nylon webbing and/or after addition of organic debris. Hot, humid air effectively decontaminates materials contaminated with dirty Bacillus spore preparations; debris and material interactions create complex decontamination kinetic patterns; and B. thuringiensis Al Hakam is a realistic surrogate for B. anthracis. Response surface models of hot, humid air decontamination were developed which may be used to select decontamination parameters for contamination scenarios including aircraft. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors

NASA Astrophysics Data System (ADS)

Garaud, Julien; Corticelli, Alberto; Silaev, Mihail; Babaev, Egor

2018-02-01

In multiband systems, such as iron-based superconductors, the superconducting states with locking and antilocking of the interband phase differences are usually considered as mutually exclusive. For example, a dirty two-band system with interband impurity scattering undergoes a sharp crossover between the s± state (which favors phase antilocking) and the s++ state (which favors phase locking). We discuss here that the situation can be much more complex in the presence of an external field or superconducting currents. In an external applied magnetic field, dirty two-band superconductors do not feature a sharp s±→s++ crossover but rather a washed-out crossover to a finite region in the parameter space where both s± and s++ states can coexist for example as a lattice or a microemulsion of inclusions of different states. The current-carrying regions such as the regions near vortex cores can exhibit an s± state while it is the s++ state that is favored in the bulk. This coexistence of both states can even be realized in the Meissner state at the domain's boundaries featuring Meissner currents. We demonstrate that there is a magnetic-field-driven crossover between the pure s± and the s++ states.

Popular Beliefs about the Infectivity of Water among School Children in Two Hyperendemic Schistosomiasis Areas of Brazil

PubMed Central

Gazzinelli, Maria Flávia Carvalho; Kloos, Helmut; de Cássia Marques, Rita; dos Reis, Dener Carlos; Gazzinelli, Andrea

2009-01-01

This article examines changing common knowledge of elementary school children to scientific knowledge related to the relationship between water characteristics and the transmission of schistosomiasis through health education. A review of the literature and two case studies from rural elementary schools in Brazil show how the prevailing concept of dirty and polluted water, which has operated as an epistemological obstacle for acquiring scientific knowledge, may be related to symbolic thought and cultural parameters. Through an educational intervention not commonly applied to health programs involving elementary school students in two schistosomiasis-endemic rural communities in Brazil this paper describes the difficulties researchers encountered in changing the prevailing perception that very dirty and polluted water provides optimal conditions for schistosome transmission, to the scientifically accepted view that transmission occurs most often in visually clean, although fecally contaminated water. This conceptual difficulty may be largely explained in terms of the symbolism involved in clean and dirty water and the life-giving quality of water. Based on our results, we recommend that knowledge about water-related beliefs and concepts among school children should be considered in school-based health education programs in areas of endemic schistosomiasis and possibly other intestinal infections. PMID:18599008

Ikaite crystal distribution in winter sea ice and implications for CO2 system dynamics

NASA Astrophysics Data System (ADS)

Rysgaard, S.; Søgaard, D. H.; Cooper, M.; Pućko, M.; Lennert, K.; Papakyriakou, T. N.; Wang, F.; Geilfus, N. X.; Glud, R. N.; Ehn, J.; McGinnis, D. F.; Attard, K.; Sievers, J.; Deming, J. W.; Barber, D.

2013-04-01

The precipitation of ikaite (CaCO3 ⋅ 6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74° N, 20° W) of NE Greenland. Ikaite crystals, ranging in size from a few μm to 700 μm, were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surface-ice values of 700-900 μmol kg-1 ice (~25 × 106 crystals kg-1) to values of 100-200 μmol kg-1 ice (1-7 × 106 crystals kg-1) near the sea ice-water interface, all of which are much higher (4-10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration, whereas TA concentrations in the lower half of the sea ice were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolve in layers below. Melting of sea ice and dissolution of observed concentrations of ikaite would result in meltwater with a pCO2 of <15 μatm. This value is far below atmospheric values of 390 μatm and surface water concentrations of 315 μatm. Hence, the meltwater increases the potential for seawater uptake of CO2.

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 accretion rates. A porous medium is an ideal place for the coalescence of nutrients and the formation of energy gradients, key controllers of biological activity. Understanding the physics that influence ice-ocean exchange is thus essential in assessing the habitability of Europa and its contemporaries.

Experimental Insights on Natural Lava-Ice/Snow Interactions and Their Implications for Glaciovolcanic and Submarine Eruptions

NASA Astrophysics Data System (ADS)

Edwards, B. R.; Karson, J.; Wysocki, R.; Lev, E.; Bindeman, I. N.; Kueppers, U.

2012-12-01

Lava-ice-snow interactions have recently gained global attention through the eruptions of ice-covered volcanoes, particularly from Eyjafjallajokull in south-central Iceland, with dramatic effects on local communities and global air travel. However, as with most submarine eruptions, direct observations of lava-ice/snow interactions are rare. Only a few hundred potentially active volcanoes are presently ice-covered, these volcanoes are generally in remote places, and their associated hazards make close observation and measurements dangerous. Here we report the results of the first large-scale experiments designed to provide new constraints on natural interactions between lava and ice/snow. The experiments comprised controlled effusion of tens of kilograms of melted basalt on top of ice/snow, and provide insights about observations from natural lava-ice-snow interactions including new constraints for: 1) rapid lava advance along the ice-lava interface; 2) rapid downwards melting of lava flows through ice; 3) lava flow exploitation of pre-existing discontinuities to travel laterally beneath and within ice; and 4) formation of abundant limu o Pele and non-explosive vapor transport from the base to the top of the lava flow with minor O isotope exchange. The experiments are consistent with observations from eruptions showing that lava is more efficient at melting ice when emplaced on top of the ice as opposed to beneath the ice, as well as the efficacy of tephra cover for slowing melting. The experimental extrusion rates are as within the range of those for submarine eruptions as well, and reproduce some features seen in submarine eruptions including voluminous production of gas rich cavities within initially anhydrous lavas and limu on lava surfaces. Our initial results raise questions about the possibility of secondary ingestion of water by submarine and glaciovolcanic lava flows, and the origins of apparent primary gas cavities in those flows. Basaltic melt moving down ice channel over thermocouples (flow approx 30 cm in width).

Expanded secondary craters in the Arcadia Planitia region, Mars: evidence for tens of Myr-old shallow subsurface ice

USGS Publications Warehouse

Viola, Donna; McEwen, Alfred S.; Dundas, Colin M.; Byrne, Shane

2015-01-01

A range of observations indicates widespread subsurface ice throughout the mid and high latitudes of Mars in the form of both pore-filling and excess ice. It is generally thought that this ice was recently emplaced and is not older than a hundred thousand to a few millions of years old based on ice stability and orbital-induced climate change. We analyze the distribution of subsurface ice in Arcadia Planitia, located in the northern mid latitudes, by mapping thermokarstically expanded secondary craters, providing additional evidence for extensive excess ice down to fairly low latitudes (less than 40°N). We further infer the minimum age of this subsurface ice based on the ages of the four primary craters that are thought to be the source of a large portion of these secondaries, which yields estimates on the order of tens of millions of years old – much more ancient than anticipated. This estimated ancient age suggests that ice can be preserved in the shallow subsurface for long periods of time, at least in some parts of Arcadia Planitia where expanded secondary craters are especially abundant. We estimate the amount of ice lost to sublimation during crater expansion based on measurements of expanded secondary craters in HiRISE Digital Terrain Models. The loss is equivalent to a volume of ice between ∼140 and 360 km3, which would correspond to a global layer of 1–2.5 mm thick. We further argue that much more ice (at least 6000 km3) is likely preserved beneath the un-cratered regions of Arcadia Planitia since significant loss of this excess ice would have caused extensive terrain dissection and the removal of the expanded secondary craters. Both the loss of ice due to secondary crater expansion and the presence of this ice today have implications for the martian climate.

Future Antarctic bed topography and its implications for ice sheet dynamics

NASA Astrophysics Data System (ADS)

Adhikari, S.; Ivins, E. R.; Larour, E.; Seroussi, H.; Morlighem, M.; Nowicki, S.

2014-06-01

The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45 mm yr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.

Future Antarctic bed topography and its implications for ice sheet dynamics

NASA Astrophysics Data System (ADS)

Adhikari, S.; Ivins, E.; Larour, E.; Seroussi, H.; Morlighem, M.; Nowicki, S.

2014-01-01

The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A~recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) is generally losing its mass since the last glacial maximum (LGM). In a sustained warming climate, the AIS is predicted to retreat at a greater pace primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that the past loading is relatively less important than future loading on the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years 2100 and 2500 AD, respectively, and that the East Antarctic Ice Sheet (EAIS) is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay approaches roughly 45 mm yr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is associated with the flattening of reverse bed, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote the stability to marine portions of the ice sheet in future.

Future Antarctic Bed Topography and Its Implications for Ice Sheet Dynamics

NASA Technical Reports Server (NTRS)

Adhikari, Surendra; Ivins, Erik R.; Larour, Eric Y.; Seroussi, Helene L.; Morlighem, Mathieu; Nowicki, S.

2014-01-01

The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves.We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS.We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45mmyr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.

Large thermal Hall effect in a frustrated pyrochlore magnet

NASA Astrophysics Data System (ADS)

Hirschberger, Max; Krizan, Jason; Cava, Robert J.; Ong, N. Phuan

2015-03-01

In frustrated magnetism, the nature of the ground state and its elementary excitations are a matter of considerable debate. We present a detailed study of the full thermal conductivity tensor κij, including the Righi-Leduc (or thermal Hall) effect, in single crystals of the frustrated quantum spin-ice pyrochlore Tb2Ti2O7. The off-diagonal response κxy / T is large in this insulating material, despite the absence of itinerant electrons experiencing the Lorentz force. Our experiments over the temperature range of 0 . 8 - 200 K and in fields up to 14 T reveal a remarkable phenomenology: A sizeable field-linear Hall effect κxy / T is observed below 100 K, and its slope with respect to magnetic field increases strongly as we cool the sample. We observe significant curvature in the field dependence of κxy / T below 15 K. At the lowest temperatures, both κxx / T and the initial slope limB-->0 [κxy / TB ] are constant in temperature, behavior reminiscent of fermionic heat conduction in dirty metals. Experimental methods and verification of the intrinsic nature of the effect will be discussed. R.J.C. and N.P.O. are supported by a MURI Grant (ARO W911NF-12-1-0461) and by the US National Science Foundation (Grant Number DMR 0819860).

SU-F-P-24: Radiological Disperse Device

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

Alam, R

Purpose: We are now living in a society of constant fear of terrorism. This topic is pertaining to give a general knowledge of what is a radiological dispersion device or RDD and in case of its detonation, what are the options open to public for a safe action in terms of reducing the exposure and knowing the proper steps. These RDD are also called dirty bombs. Methods: Compared to nuclear weapons, dirty bombs are easy to make. In order for a terrorist organization to construct and detonate a dirty bomb, it must acquire radioactive material by stealing it or buyingmore » it through legal or illegal channels. Possible RDD material could come from the millions of radioactive sources used in the industry, for medical purposes and in academic applications mainly for researches. These are, americium-{sup 241}, californium-{sup 252}, caesium-{sup 137}, cobalt-{sup 60}, iridium-{sup 192}, plutonium-{sup 238}, polonium-{sup 210}, radium-{sup 226} and strontium-{sup 90}. Results: Prompt detection of the type of radioactive material used will greatly assist advising people on the protective measures, like sheltering in place, or quickly leaving the immediate area. The effects of radiation are determined by:°the amount of radiation absorbed by body°the type of radiation °the distance from the radiation to an individual°the means of exposure absorbed by the skin, inhaled, or ingested; and length of time exposed. Conclusion: In any facility it is now much more important to keep a log list of all radioactive materials in use. In case there is a dirty bomb explosion, the chaos and economic cost could be enormous. The economic cost for the evaluation of the contamination, survey of people and surroundings and the after treatment, decontamination cost and effort will be a big challenge in any country. So awareness and preparation is the start to face this new type of challenge.« less

The role of the sand in chemical warfare agent exposure among Persian Gulf War veterans: Al Eskan disease and "dirty dust".

PubMed

Korényi-Both, A L; Svéd, L; Korényi-Both, G E; Juncer, D J; Korényi-Both, A L; Székely, A

2000-05-01

The purpose of this paper is to inquire into the relationship between Al Eskan disease and the probable exposure to chemical warfare agents by Persian Gulf War veterans. Al Eskan disease, first reported in 1991, compromises the body's immunological defense and is a result of the pathogenic properties of the extremely fine, dusty sand located in the central and eastern region of the Arabian peninsula. The disease manifests with localized expression of multisystem disorder. Signs and symptoms of Al Eskan disease have been termed by the news media "Persian Gulf syndrome." The dust becomes a warfare agent when toxic chemicals are microimpregnated into inert particles. The "dirty dust" concept, that the toxicity of an agent could be enhanced by absorption into inactive particles, dates from World War I. A growing body of evidence shows that coalition forces have encountered Iraqi chemical warfare in the theater of operation/Persian Gulf War to a much greater extent than early U.S. Department of Defense information had indicated. Veterans of that war were exposed to chemical warfare agents in the form of direct (deliberate) attacks by chemical weapons, such as missiles and mines, and indirect (accidental) contamination from demolished munition production plants and storage areas, or otherwise. We conclude that the microimpregnated sand particles in the theater of operation/Persian Gulf War depleted the immune system and simultaneously acted as vehicles for low-intensity exposure to chemical warfare agents and had a modifying-intensifying effect on the toxicity of exposed individuals. We recommend recognition of a new term, "dirty sand," as a subcategory of dirty dust/dusty chemical warfare agents. Our ongoing research efforts to investigate the health impact of chemical warfare agent exposure among Persian Gulf War veterans suggest that Al Eskan disease is a plausible and preeminent explanation for the preponderance of Persian Gulf War illnesses.

Causes of ice age intensification across the Mid-Pleistocene Transition

PubMed Central

Foster, Gavin L.; Rohling, Eelco J.; Sexton, Philip F.; Cherry, Soraya G.; Hasenfratz, Adam P.; Haug, Gerald H.; Martínez-García, Alfredo; Pälike, Heiko; Pancost, Richard D.; Wilson, Paul A.

2017-01-01

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets. PMID:29180424

Debris-Covered Glaciers in the Sierra Nevada, California, and Their Implications for Snowline Reconstructions

USGS Publications Warehouse

Clark, D.H.; Clark, M.M.; Gillespie, A.R.

1994-01-01

Ice-walled melt ponds on the surfaces of active valley-floor rock glaciers and Matthes (Little Ice Age) moraines in the southern Sierra Nevada indicate that most of these landforms consist of glacier ice under thin (ca. 1 - 10 m) but continuous covers of rock-fall-generated debris. These debris blankets effectively insulate the underlying ice and greatly reduce rates of ablation relative to that of uncovered ice. Such insulation explains the observations that ice-cored rock glaciers in the Sierra, actually debris-covered glaciers, are apparently less sensitive to climatic warming and commonly advance to lower altitudes than do adjacent bare-ice glaciers. Accumulation-area ratios and toe-to-headwall-altitude ratios used to estimate equilibrium-line altitudes (ELAs) of former glaciers may therefore yield incorrect results for cirque glaciers subject to abundant rockfall. Inadvertent lumping of deposits from former debris-covered and bare-ice glaciers partially explains an apparently anomalous regional ELA gradient reported for the pre-Matthes Recess Peak Neoglacial advance. Distinguishing such deposits may be important to studies that rely on paleo-ELA estimates. Moreover, Matthes and Recess Peak ELA gradients along the crest evidently depend strongly on local orographic effects rather than latitudinal climatic trends, indicating that simple linear projections and regional climatic interpretations of ELA gradients of small glaciers may be unreliable.

Causes of ice age intensification across the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Chalk, Thomas B.; Hain, Mathis P.; Foster, Gavin L.; Rohling, Eelco J.; Sexton, Philip F.; Badger, Marcus P. S.; Cherry, Soraya G.; Hasenfratz, Adam P.; Haug, Gerald H.; Jaccard, Samuel L.; Martínez-García, Alfredo; Pälike, Heiko; Pancost, Richard D.; Wilson, Paul A.

2017-12-01

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth's orbitally paced ice age cycles intensified, lengthened from ˜40,000 (˜40 ky) to ˜100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ˜43 to ˜75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.

The adsorption of fungal ice-nucleating proteins on mineral dusts: a terrestrial reservoir of atmospheric ice-nucleating particles

NASA Astrophysics Data System (ADS)

O'Sullivan, Daniel; Murray, Benjamin J.; Ross, James; Webb, Michael E.

2016-04-01

The occurrence of ice-nucleating particles (INPs) in our atmosphere has a profound impact on the properties and lifetime of supercooled clouds. However, the identities, sources and abundances of airborne particles capable of efficiently nucleating ice at relatively low supercoolings (T > -15 °C) remain enigmatic. Recently, several studies have suggested that unidentified biogenic residues in soil dusts are likely to be an important source of these efficient atmospheric INPs. While it has been shown that cell-free proteins produced by common soil-borne fungi are exceptional INPs, whether these fungi are a source of ice-nucleating biogenic residues in soils has yet to be shown. In particular, it is unclear whether upon adsorption to soil mineral particles, the activity of fungal ice-nucleating proteins is retained or is reduced, as observed for other soil enzymes. Here we show that proteins from a common soil fungus (Fusarium avenaceum) do in fact preferentially bind to and impart their ice-nucleating properties to the common clay mineral kaolinite. The ice-nucleating activity of the proteinaceous INPs is found to be unaffected by adsorption to the clay, and once bound the proteins do not readily desorb, retaining much of their activity even after multiple washings with pure water. The atmospheric implications of the finding that nanoscale fungal INPs can effectively determine the nucleating abilities of lofted soil dusts are discussed.

Influence of Arctic Sea Ice Extent on Polar Cloud Fraction and Vertical Structure and Implications for Regional Climate

NASA Technical Reports Server (NTRS)

Palm, Stephen P.; Strey, Sara T.; Spinhirne, James; Markus, Thorsten

2010-01-01

Recent satellite lidar measurements of cloud properties spanning a period of 5 years are used to examine a possible connection between Arctic sea ice amount and polar cloud fraction and vertical distribution. We find an anticorrelation between sea ice extent and cloud fraction with maximum cloudiness occurring over areas with little or no sea ice. We also find that over ice!free regions, there is greater low cloud frequency and average optical depth. Most of the optical depth increase is due to the presence of geometrically thicker clouds over water. In addition, our analysis indicates that over the last 5 years, October and March average polar cloud fraction has increased by about 7% and 10%, respectively, as year average sea ice extent has decreased by 5% 7%. The observed cloud changes are likely due to a number of effects including, but not limited to, the observed decrease in sea ice extent and thickness. Increasing cloud amount and changes in vertical distribution and optical properties have the potential to affect the radiative balance of the Arctic region by decreasing both the upwelling terrestrial longwave radiation and the downward shortwave solar radiation. Because longwave radiation dominates in the long polar winter, the overall effect of increasing low cloud cover is likely a warming of the Arctic and thus a positive climate feedback, possibly accelerating the melting of Arctic sea ice.

Implications for an Enhanced Biological Pump in the Sea-Ice Reduction Region of the Western Arctic Ocean

NASA Astrophysics Data System (ADS)

Nishino, S.; Shimada, K.; Itoh, M.; Yamamoto-Kawai, M.; Chiba, S.

2009-12-01

Since the late 1990s, catastrophic sea-ice reduction during summer has been observed in the western Arctic Ocean. Regions of decreasing sea ice might be associated with increased biological production compared to ice-covered ocean areas due to light intensification in the water column. The R/V Mirai field experiments in summer 2004 revealed that the algal biomass (chlorophyll a) in the open water region of the western Canada Basin increased from that observed in summer 1994, when the sea ice covered that area. Under the euphotic zone of the increased algal biomass area, evidence of diatom detritus decomposition was found, while such evidence was not observed in 1994, suggesting an enhancement of biological pump (see figure). The increase of algal biomass was not found throughout the sea-ice reduction region; rather, it was observed western Canada Basin where nutrients are effectively supplied from shelf regions. Further west from the Canada Basin, Russian river water with relatively high nutrients may play an important role in the biogeochemical cycles. Monthly sea-ice concentrations (white = 100%, black = 0%) in September of (a) 1994 and (b) 2004 (National Ice Center), and (c) vertical profiles of silicate obtained from the field experiments of Arctic Ocean Section 94 in 1994 (○) and Mirai04 in 2004 (■). The positions where the profiles were obtained are depicted by dots in (a) and (b), respectively.

Mechanisms and implications of α-HCH enrichment in melt pond water on Arctic sea ice.

PubMed

Pućko, M; Stern, G A; Barber, D G; Macdonald, R W; Warner, K-A; Fuchs, C

2012-11-06

During the summer of 2009, we sampled 14 partially refrozen melt ponds and the top 1 m of old ice in the pond vicinity for α-hexachlorocyclohexane (α-HCH) concentrations and enantiomer fractions (EFs) in the Beaufort Sea. α-HCH concentrations were 3 - 9 times higher in melt ponds than in the old ice. We identify two routes of α-HCH enrichment in the ice over the summer. First, atmospheric gas deposition results in an increase of α-HCH concentration from 0.07 ± 0.02 ng/L (old ice) to 0.34 ± 0.08 ng/L, or ~20% less than the atmosphere-water equilibrium partitioning concentration (0.43 ng/L). Second, late-season ice permeability and/or complete ice thawing at the bottom of ponds permit α-HCH rich seawater (~0.88 ng/L) to replenish pond water, bringing concentrations up to 0.75 ± 0.06 ng/L. α-HCH pond enrichment may lead to substantial concentration patchiness in old ice floes, and changed exposures to biota as the surface meltwater eventually reaches the ocean through various drainage mechanisms. Melt pond concentrations of α-HCH were relatively high prior to the late 1980-s, with a Melt pond Enrichment Factor >1 (MEF; a ratio of concentration in surface meltwater to surface seawater), providing for the potential of increased biological exposures.

Ice Nucleation of Bare and Sulfuric Acid-coated Mineral Dust Particles and Implication for Cloud Properties

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

Kulkarni, Gourihar R.; Sanders, Cassandra N.; Zhang, Kai

2014-08-27

Ice nucleation properties of different dust species coated with soluble material are not well understood. We determined the ice nucleation ability of bare and sulfuric acid coated mineral dust particles as a function of temperature (-25 to -35 deg C) and relative humidity with respect to water (RHw). Five different mineral dust species: Arizona test dust (ATD), illite, montmorillonite, quartz and kaolinite were dry dispersed and size-selected at 150 nm and exposed to sulfuric acid vapors in the coating apparatus. The condensed sulfuric acid soluble mass fraction per particle was estimated from the cloud condensation nuclei activated fraction measurements. Themore » fraction of dust particles nucleating ice at various temperatures and RHw was determined using a compact ice chamber. In water-subsaturated conditions, compared to bare dust particles, we found that only coated ATD particles showed suppression of ice nucleation ability while other four dust species did not showed the effect of coating on the fraction of particles nucleating ice. The results suggest that interactions between the dust surface and sulfuric acid vapor are important, such that interactions may or may not modify the surface via chemical reactions with sulfuric acid. At water-supersaturated conditions we did not observed the effect of coating, i.e. the bare and coated dust particles had similar ice nucleation behavior.« less

Low temperature and high field regimes of connected kagome artificial spin ice: the role of domain wall topology.

PubMed

Zeissler, Katharina; Chadha, Megha; Lovell, Edmund; Cohen, Lesley F; Branford, Will R

2016-07-22

Artificial spin ices are frustrated magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, reversal occurs along one-dimensional chains by propagation of ferromagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges. At room temperature, it is established that the topological edge-charges determine the exact switching reversal path taken. However, magnetic reversal at low temperatures has received much less attention and how these chiral objects interact at reduced temperature is unknown. In this study we use magnetic force microscopy to image the magnetic reversal process at low temperatures revealing the formation of quite remarkable high energy remanence states and a change in the dynamics of the reversal process. The implication is the breakdown of the artificial spin ice regime in these connected structures at low temperatures.

Detection prospects for GeV neutrinos from collisionally heated gamma-ray bursts with IceCube/DeepCore.

PubMed

Bartos, I; Beloborodov, A M; Hurley, K; Márka, S

2013-06-14

Jet reheating via nuclear collisions has recently been proposed as the main mechanism for gamma-ray burst (GRB) emission. In addition to producing the observed gamma rays, collisional heating must generate 10-100 GeV neutrinos, implying a close relation between the neutrino and gamma-ray luminosities. We exploit this theoretical relation to make predictions for possible GRB detections by IceCube + DeepCore. To estimate the expected neutrino signal, we use the largest sample of bursts observed by the Burst and Transient Source Experiment in 1991-2000. GRB neutrinos could have been detected if IceCube + DeepCore operated at that time. Detection of 10-100 GeV neutrinos would have significant implications, shedding light on the composition of GRB jets and their Lorentz factors. This could be an important target in designing future upgrades of the IceCube + DeepCore observatory.

Reply to comment received from J. C. Knight regarding "Last Glacial Maximum cirque glaciation in Ireland and implications for reconstructions of the Irish Ice Sheet" by Barth et al. (2016), Quaternary Science Reviews 141, 85-93

NASA Astrophysics Data System (ADS)

Barth, Aaron M.; Clark, Peter U.; Clark, Jorie; McCabe, A. Marshall; Caffee, Marc

2016-10-01

We concluded that our new 10Be chronology records onset of retreat of a cirque glacier within the Alohart basin of southwestern Ireland 24.5 ± 1.4 ka, placing limiting constraints on reconstructions of the Irish Ice Sheet (IIS) and Kerry-Cork Ice Cap (KCIC) during the Last Glacial Maximum (LGM) (Barth et al., 2016). Knight (2016) raises two main arguments against our interpretation: (1) the glacier in the Alohart basin was not a cirque glacier, but instead a southern-sourced ice tongue from the KCIC overtopping the MacGillycuddy's Reeks, and (2) that the boulders we sampled for 10Be exposure dating were derived from supraglacial rockfall rather than transported subglacially, experienced nuclide inheritance, and are thus too old. In the following, we address both of these arguments.

The influence of the hydrologic cycle on the extent of sea ice with climatic implications

NASA Technical Reports Server (NTRS)

Dean, Ken; Gosink, Joan

1991-01-01

The role was analyzed of the hydrologic cycle on the distribution of sea ice, and its influence on forcings and fluxes between the marine environment and the atmosphere. River discharge plays a significant role in degrading the sea ice before any melting occurs elsewhere along the coast. The influence is considered of river discharge on the albedo, thermal balance, and distribution of sea ice. Quantitative atmospheric-hydrologic models are being developed to describe these processes in the coastal zone. Input for the models will come from satellite images, hydrologic data, and field observations. The resulting analysis provides a basis for the study of the significance of the hydrologic cycle throughout the Arctic Basin and its influence on the regional climate as a result of possible climatic scenarios. The area offshore from the Mackenzie River delta was selected as the study area.

Routine single particle CryoEM sample and grid characterization by tomography

PubMed Central

Noble, Alex J; Brasch, Julia; Chase, Jillian; Acharya, Priyamvada; Tan, Yong Zi; Zhang, Zhening; Kim, Laura Y; Scapin, Giovanna; Rapp, Micah; Eng, Edward T; Rice, William J; Cheng, Anchi; Negro, Carl J; Shapiro, Lawrence; Kwong, Peter D; Jeruzalmi, David; des Georges, Amedee; Potter, Clinton S

2018-01-01

Single particle cryo-electron microscopy (cryoEM) is often performed under the assumption that particles are not adsorbed to the air-water interfaces and in thin, vitreous ice. In this study, we performed fiducial-less tomography on over 50 different cryoEM grid/sample preparations to determine the particle distribution within the ice and the overall geometry of the ice in grid holes. Surprisingly, by studying particles in holes in 3D from over 1000 tomograms, we have determined that the vast majority of particles (approximately 90%) are adsorbed to an air-water interface. The implications of this observation are wide-ranging, with potential ramifications regarding protein denaturation, conformational change, and preferred orientation. We also show that fiducial-less cryo-electron tomography on single particle grids may be used to determine ice thickness, optimal single particle collection areas and strategies, particle heterogeneity, and de novo models for template picking and single particle alignment. PMID:29809143

Implications of rapid environmental change for polar bear behavior and sociality

USGS Publications Warehouse

Atwood, Todd C.

2017-01-01

Historically, the Arctic sea ice has functioned as a structural barrier that has limited the nature and extent of interactions between humans and polar bears (Ursus maritimus). However, declining sea ice extent, brought about by global climate change, is increasing the potential for human-polar bear interactions. Loss of sea ice habitat is driving changes to both human and polar bear behavior—it is facilitating increases in human activities (e.g., offshore oil and gas exploration and extraction, trans-Arctic shipping, recreation), while also causing the displacement of bears from preferred foraging habitat (i.e., sea ice over biologically productive shallow) to land in some portions of their range. The end result of these changes is that polar bears are spending greater amounts of time in close proximity to people. Coexistence between humans and polar bears will require imposing mechanisms to manage further development, as well as mitigation strategies that reduce the burden to local communities.

Ices on the Satellites of Jupiter, Saturn, and Uranus

NASA Technical Reports Server (NTRS)

Cruikshank, Dale P.; Brown, Robert H.; Calvin, Wendy M.; Roush, Ted L.

1995-01-01

Three satellites of Jupiter, seven satellites of Saturn, and five satellites of Uranus show spectroscopic evidence of H2O ice on their surfaces, although other details of their surfaces are highly diverse. The icy surfaces contain contaminants of unknown composition in varying degrees of concentration, resulting in coloration and large differences in albedo. In addition to H2O, Europa has frozen SO2, and Ganymede has O2 in the surface; in both of these cases external causes are implicated in the deposition or formation of these trace components. Variations in ice exposure across the surfaces of the satellites are measured from the spectroscopic signatures. While H2O ice occurs on the surfaces of many satellites, the range of bulk densities of these bodies shows that its contribution to their overall compositions is highly variable from one object to another.

Cordilleran Ice Sheet mass loss preceded climate reversals near the Pleistocene Termination

NASA Astrophysics Data System (ADS)

Menounos, B.; Goehring, B. M.; Osborn, G.; Margold, M.; Ward, B.; Bond, J.; Clarke, G. K. C.; Clague, J. J.; Lakeman, T.; Koch, J.; Caffee, M. W.; Gosse, J.; Stroeven, A. P.; Seguinot, J.; Heyman, J.

2017-11-01

The Cordilleran Ice Sheet (CIS) once covered an area comparable to that of Greenland. Previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost Canada as late as 12.5 thousand years ago (ka). New data indicate that substantial areas throughout westernmost Canada were ice free prior to 12.5 ka and some as early as 14.0 ka, with implications for climate dynamics and the timing of meltwater discharge to the Pacific and Arctic oceans. Early Bølling-Allerød warmth halved the mass of the CIS in as little as 500 years, causing 2.5 to 3.0 meters of sea-level rise. Dozens of cirque and valley glaciers, along with the southern margin of the CIS, advanced into recently deglaciated regions during the Bølling-Allerød and Younger Dryas.

Ceres: predictions for near-surface water ice stability and implications for plume generating processes

USGS Publications Warehouse

Titus, Timothy N.

2015-01-01

This paper will constrain the possible sources and processes for the formation of recently observed H2O vapor plumes above the surface of the dwarf planet Ceres. Two hypotheses have been proposed: (1) cryovolcanism where the water source is the mantle and the heating source is still unknown or (2) comet-like sublimation where near-surface water ice is vaporized by seasonally increasing solar insolation. We test hypothesis #2, comet-like near-surface sublimation, by using a thermal model to examine the stability of water-ice in the near surface. For a reasonable range of physical parameters (thermal inertia, surface roughness, slopes), we find that water ice is only stable at latitudes higher than ~40-60 degrees. These results indicate that either (a) the physical properties of Ceres are unlike our expectations or (b) an alternative to comet-like sublimation, such as the cryovolcanism hypothesis, must be invoked.

Is snow-ice now a major contributor to sea ice mass balance in the western Transpolar Drift region?

NASA Astrophysics Data System (ADS)

Graham, R. M.; Merkouriadi, I.; Cheng, B.; Rösel, A.; Granskog, M. A.

2017-12-01

During the Norwegian young sea ICE (N-ICE2015) campaign, which took place in the first half of 2015 north of Svalbard, a deep winter snow pack (50 cm) on sea ice was observed, that was 50% thicker than earlier climatological studies suggested for this region. Moreover, a significant fraction of snow contributed to the total ice mass in second-year ice (SYI) (9% on average). Interestingly, very little snow (3% snow by mass) was present in first-year ice (FYI). The combination of sea ice thinning and increased precipitation north of Svalbard is expected to promote the formation of snow-ice. Here we use the 1-D snow/ice thermodynamic model HIGHTSI forced with reanalysis data, to show that for the case study of N-ICE2015, snow-ice would even form over SYI with an initial thickness of 2 m. In current conditions north of Svalbard, snow-ice is ubiquitous and contributes to the thickness growth up to 30%. This contribution is important, especially in the absence of any bottom thermodynamic growth due to the thick insulating snow cover. Growth of FYI north of Svalbard is mainly controlled by the timing of growth onset relative to snow precipitation events and cold spells. These usually short-lived conditions are largely determined by the frequency of storms entering the Arctic from the Atlantic Ocean. In our case, a later freeze onset was favorable for FYI growth due to less snow accumulation in early autumn. This limited snow-ice formation but promoted bottom thermodynamic growth. We surmise these findings are related to a regional phenomenon in the Atlantic sector of the Arctic, with frequent storm events which bring increasing amounts of precipitation in autumn and winter, and also affect the duration of cold temperatures required for ice growth in winter. We discuss the implications for the importance of snow-ice in the future Arctic, formerly believed to be non-existent in the central Arctic due to thick perennial ice.

The Arctic sea ice cover of 2016: a year of record-low highs and higher-than-expected lows

NASA Astrophysics Data System (ADS)

Petty, Alek A.; Stroeve, Julienne C.; Holland, Paul R.; Boisvert, Linette N.; Bliss, Angela C.; Kimura, Noriaki; Meier, Walter N.

2018-02-01

The Arctic sea ice cover of 2016 was highly noteworthy, as it featured record low monthly sea ice extents at the start of the year but a summer (September) extent that was higher than expected by most seasonal forecasts. Here we explore the 2016 Arctic sea ice state in terms of its monthly sea ice cover, placing this in the context of the sea ice conditions observed since 2000. We demonstrate the sensitivity of monthly Arctic sea ice extent and area estimates, in terms of their magnitude and annual rankings, to the ice concentration input data (using two widely used datasets) and to the averaging methodology used to convert concentration to extent (daily or monthly extent calculations). We use estimates of sea ice area over sea ice extent to analyse the relative "compactness" of the Arctic sea ice cover, highlighting anomalously low compactness in the summer of 2016 which contributed to the higher-than-expected September ice extent. Two cyclones that entered the Arctic Ocean during August appear to have driven this low-concentration/compactness ice cover but were not sufficient to cause more widespread melt-out and a new record-low September ice extent. We use concentration budgets to explore the regions and processes (thermodynamics/dynamics) contributing to the monthly 2016 extent/area estimates highlighting, amongst other things, rapid ice intensification across the central eastern Arctic through September. Two different products show significant early melt onset across the Arctic Ocean in 2016, including record-early melt onset in the North Atlantic sector of the Arctic. Our results also show record-late 2016 freeze-up in the central Arctic, North Atlantic and the Alaskan Arctic sector in particular, associated with strong sea surface temperature anomalies that appeared shortly after the 2016 minimum (October onwards). We explore the implications of this low summer ice compactness for seasonal forecasting, suggesting that sea ice area could be a more reliable metric to forecast in this more seasonal, "New Arctic", sea ice regime.

Implication of azelaic acid in a Greenland Ice Core for oceanic and atmospheric changes in high latitudes

NASA Astrophysics Data System (ADS)

Kawamura, K.; Yokoyama, K.; Fujii, Y.; Watanabe, O.

A Greenland ice core (450 years) has been studied for low molecular weight dicarboxylic acids (C2-C10) using a capillary gas chromatography and mass spectrometer. Their molecular distribution generally showed a predominance of succinic acid (C4) followed by oxalic (C2), malonic (C3), glutaric (C5), adipic (C6), and azelaic (C9) acids. Azelaic acid, that is a specific photochemical reaction product of biogenic unsaturated fatty acids, gave a characteristic historical trend in the ice core; i.e., the concentrations are relatively low during late 16th to 19th century (Little Ice Age) but become very high in late 19th to 20th century (warmer periods) with a large peak in 1940s AD. Lower concentrations of azelaic acid may have been caused by a depressed emission of unsaturated fatty acids from seawater microlayers due to enhanced sea ice coverage during Little Ice Age. Inversely, increased concentrations of azelaic acid in late 19th to 20th century are likely interpreted by an enhanced sea-to-air emission of the precursor unsaturated fatty acids due to a retreat of sea ice and/or by the enhanced production due to a potentially increased oxidizing capability of the atmosphere.

Laboratory IR Studies and Astrophysical Implications of C2H2-Containing Binary Ices

NASA Technical Reports Server (NTRS)

Knez, C.; Moore, M.; Ferrante, R.; Hudson, R.

2012-01-01

Studies of molecular hot cores and protostellar environments have shown that the observed abundance of gas-phase acetylene (C2H2) cannot be matched by chemical models without the inclusion of C2H2 molecules subliming from icy grain mantles. Searches for infrared (IR) spectral features of solid-phase acetylene are under way, but few laboratory reference spectra of C2H2 in icy mixtures, which are needed for spectral fits to observational data, have been published. Here, we report a systematic study of the IR spectra of condensed-phase pure acetylene and acetylene in ices dominated by carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and water (H2O). We present new spectral data for these ices, including band positions and intrinsic band strengths. For each ice mixture and concentration, we also explore the dependence of acetylene's nu5-band position (743 cm-1, 13.46 micrometers) and FWHM on temperature. Our results show that the nu5 feature is much more cleanly resolved in ices dominated by non-polar and low-polarity molecules, specifically CO, CO2, and CH4, than in mixtures dominated by H2O-ice. We compare our laboratory ice spectra with observations of a quiescent region in Serpens.

Measures of Local Segregation for Monitoring Health Inequities by Local Health Departments.

PubMed

Krieger, Nancy; Waterman, Pamela D; Batra, Neelesh; Murphy, Johnna S; Dooley, Daniel P; Shah, Snehal N

2017-06-01

To assess the use of local measures of segregation for monitoring health inequities by local health departments. We analyzed preterm birth and premature mortality (death before the age of 65 years) rates for Boston, Massachusetts, for 2010 to 2012, using the Index of Concentration at the Extremes (ICE) and the poverty rate at both the census tract and neighborhood level. For premature mortality at the census tract level, the rate ratios comparing the worst-off and best-off terciles were 1.58 (95% confidence interval [CI] = 1.36, 1.83) for the ICE for income, 1.66 (95% CI = 1.43, 1.93) for the ICE for race/ethnicity, and 1.63 (95% CI = 1.40, 1.90) for the ICE combining income and race/ethnicity, as compared with 1.47 (95% CI = 1.27, 1.71) for the poverty measure. Results for the ICE and poverty measures were more similar for preterm births than for premature mortality. The ICE, a measure of social spatial polarization, may be useful for analyzing health inequities at the local level. Public Health Implications. Local health departments in US cities can meaningfully use the ICE to monitor health inequities associated with racialized economic segregation.

PHYSICAL THERAPY MANAGEMENT OF ICE HOCKEY ATHLETES: FROM THE RINK TO THE CLINIC AND BACK.

PubMed

Wolfinger, Christopher R; Davenport, Todd E

2016-06-01

The increasing number of athletes playing hockey compels rehabilitation professionals working in orthopedic and sports settings to understand the unique functional demands of ice hockey and the patterns of injuries they may promote. The purpose of this clinical perspective is to: (1) discuss the functional implications of different positions and age levels on injury prevalence within the sport; (2) summarize the seven most common injuries sustained by ice hockey athletes; and (3) present a conceptual model for the clinical management and prevention of these injuries by rehabilitation professionals. A narrative review and synthesis was conducted of currently available literature on prevalence, etiology, rehabilitative intervention, prognosis, and prevention of ice hockey injuries. Research evidence is available to support the prevalence of injuries sustained while participating in ice hockey, as well as the most effective clinical treatment protocols to treat them. Most of the existing protocols are based on clinical and sports experience with incorporation of scientific data. This clinical commentary reviews the current concepts of ice hockey injury care and prevention, based on scientific information regarding the incidence, mechanism, rehabilitation protocols, prognosis, and prevention of injuries. Science-based, patient-centered reasoning is integral to provide the highest quality of rehabilitative and preventative care for ice hockey athletes by physical therapists. 5.

Laboratory experiments to investigate sublimation rates of water ice in nighttime lunar regolith

NASA Astrophysics Data System (ADS)

Piquette, Marcus; Horányi, Mihály; Stern, S. Alan

2017-09-01

The existence of water ice on the lunar surface has been a long-standing topic with implications for both lunar science and in-situ resource utilization (ISRU). Cold traps on the lunar surface may have conditions necessary to retain water ice, but no laboratory experiments have been conducted to verify modeling results. We present an experiment testing the ability to thermally control bulk samples of lunar regolith simulant mixed with water ice under vacuum in an effort to constrain sublimation rates. The simulant used was JSC-1A lunar regolith simulant developed by NASA's Johnson Space Center. Samples with varying ratios of water ice and JSC-1A regolith simulant, totally about 1 kg, were placed under vacuum and cooled to 100 K to simulate conditions in lunar cold traps. The resulting sublimation of water ice over an approximately five-day period was measured by comparing the mass of the samples before and after the experimental run. Our results indicate that water ice in lunar cold traps is stable on timescales comparable to the lunar night, and should continue to be studied as possible resources for future utilization. This experiment also gauges the efficacy of the synthetic lunar atmosphere mission (SLAM) as a low-cost water resupply mission to lunar outposts.

Ice sheets on plastically-yielding beds

NASA Astrophysics Data System (ADS)

Hewitt, Ian

2016-11-01

Many fast flowing regions of ice sheets are underlain by a layer of water-saturated sediments, or till. The rheology of the till has been the subject of some controversy, with laboratory tests suggesting almost perfectly plastic behaviour (stress independent of strain rate), but many models adopting a pseudo-viscous description. In this work, we consider the behaviour of glaciers underlain by a plastic bed. The ice is treated as a viscous gravity current, on a bed that allows unconstrained slip above a critical yield stress. This simplified description allows rapid sliding, and aims to investigate 'worst-case' scenarios of possible ice-sheet disintegration. The plastic bed results in an approximate ice-sheet geometry that is primarily controlled by force balance, whilst ice velocity is determined from mass conservation (rather than the other way around, as standard models would hold). The stability of various states is considered, and particular attention is given to the pace at which transitions between unstable states can occur. Finally, we observe that the strength of basal tills depends strongly on pore pressure, and combine the model with a description of subglacial hydrology. Implications for the present-day ice sheets in Greenland and Antarctica will be discussed. Funding: ERC Marie Curie FP7 Career Integration Grant.

Magnetic Charge Organization and Screening in Thermalized Artificial Spin Ice

NASA Astrophysics Data System (ADS)

Gilbert, Ian

2014-03-01

Artificial spin ice is a material-by-design in which interacting single-domain ferromagnetic nanoislands are used to model Ising spins in frustrated spin systems. Artificial spin ice has proved a useful system in which to directly probe the physics of geometrical frustration, allowing us to better understand materials such as spin ice. Recently, several new experimental techniques have been developed that allow effective thermalization of artificial spin ice. Given the intense interest in magnetic monopole excitations in spin ice materials and artificial spin ice's success in modeling these materials, it should not come as a surprise that interesting monopole physics emerges here as well. The first experimental investigation of thermalized artificial square spin ice determined that the system's monopole-like excitations obeyed a Boltzmann distribution and also found evidence for monopole-antimonopole interactions. Further experiments have implicated these monopole excitations in the growth of ground state domains. Our recent study of artificial kagome spin ice, whose odd-coordinated vertices always possess a net magnetic charge, has revealed a theoretically-predicted magnetic charge ordering transition which has not been previously observed experimentally. We have also investigated the details of magnetic charge interactions in lattices of mixed coordination number. This work was done in collaboration with Sheng Zhang, Cristiano Nisoli, Gia-Wei Chern, Michael Erickson, Liam O'Brien, Chris Leighton, Paul Lammert, Vincent Crespi, and Peter Schiffer. This work was primarily funded by the US Department of Energy, Office of Basic Energy Sciences, Materials Science and Engineering Division, grant no. DE-SC0005313.

A Mathematical Model of Melt Lake Development on an Ice Shelf

NASA Astrophysics Data System (ADS)

Buzzard, S. C.; Feltham, D. L.; Flocco, D.

2018-02-01

The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. Melt lakes have been implicated in ice shelf collapse; Antarctica's Larsen B Ice Shelf was observed to have a large amount of surface melt lakes present preceding its collapse in 2002. Such collapse can affect ocean circulation and temperature, cause habitat loss and contribute to sea level rise through the acceleration of tributary glaciers. We present a mathematical model of a surface melt lake on an idealized ice shelf. The model incorporates a calculation of the ice shelf surface energy balance, heat transfer through the firn, the production and percolation of meltwater into the firn, the formation of ice lenses, and the development and refreezing of surface melt lakes. The model is applied to the Larsen C Ice Shelf, where melt lakes have been observed. This region has warmed several times the global average over the last century and the Larsen C firn layer could become saturated with meltwater by the end of the century. When forced with weather station data, our model produces surface melting, meltwater accumulation, and melt lake development consistent with observations. We examine the sensitivity of lake formation to uncertain parameters and provide evidence of the importance of processes such as lateral meltwater transport. We conclude that melt lakes impact surface melt and firn density and warrant inclusion in dynamic-thermodynamic models of ice shelf evolution within climate models, of which our model could form the basis for the thermodynamic component.

Diagnosing sea ice from the north american multi model ensemble and implications on mid-latitude winter climate

NASA Astrophysics Data System (ADS)

Elders, Akiko; Pegion, Kathy

2017-12-01

Arctic sea ice plays an important role in the climate system, moderating the exchange of energy and moisture between the ocean and the atmosphere. An emerging area of research investigates how changes, particularly declines, in sea ice extent (SIE) impact climate in regions local to and remote from the Arctic. Therefore, both observations and model estimates of sea ice become important. This study investigates the skill of sea ice predictions from models participating in the North American Multi-Model Ensemble (NMME) project. Three of the models in this project provide sea-ice predictions. The ensemble average of these models is used to determine seasonal climate impacts on surface air temperature (SAT) and sea level pressure (SLP) in remote regions such as the mid-latitudes. It is found that declines in fall SIE are associated with cold temperatures in the mid-latitudes and pressure patterns across the Arctic and mid-latitudes similar to the negative phase of the Arctic Oscillation (AO). These findings are consistent with other studies that have investigated the relationship between declines in SIE and mid-latitude weather and climate. In an attempt to include additional NMME models for sea-ice predictions, a proxy for SIE is used to estimate ice extent in the remaining models, using sea surface temperature (SST). It is found that SST is a reasonable proxy for SIE estimation when compared to model SIE forecasts and observations. The proxy sea-ice estimates also show similar relationships to mid-latitude temperature and pressure as the actual sea-ice predictions.

Two-phase convection in Ganymede's high-pressure ice layer - Implications for its geological evolution

NASA Astrophysics Data System (ADS)

Kalousová, Klára; Sotin, Christophe; Choblet, Gaël; Tobie, Gabriel; Grasset, Olivier

2018-01-01

Ganymede, the largest moon in the solar system, has a fully differentiated interior with a layer of high-pressure (HP) ice between its deep ocean and silicate mantle. In this paper, we study the dynamics of this layer using a numerical model of two-phase ice-water mixture in two-dimensional Cartesian geometry. While focusing on the generation of water at the silicate/HP ice interface and its upward migration towards the ocean, we investigate the effect of bottom heat flux, the layer thickness, and the HP ice viscosity and permeability. Our results suggest that melt can be generated at the silicate/HP ice interface for small layer thickness ( ≲ 200 km) and high values of heat flux ( ≳ 20 mW m-2) and viscosity ( ≳ 1015 Pa s). Once generated, the water is transported through the layer by the upwelling plumes. Depending on the vigor of convection, it stays liquid or it may freeze before melting again as the plume reaches the temperate (partially molten) layer at the boundary with the ocean. The thickness of this layer as well as the amount of melt that is extracted from it is controlled by the permeability of the HP ice. This process constitutes a means of transporting volatiles and salts that might have dissolved into the melt present at the silicate/HP ice interface. As the moon cools down, the HP ice layer becomes less permeable because the heat flux from the silicates decreases and the HP ice layer thickens.

Rapid grounding line migration induced by internal variability of a marine-terminating ice stream

NASA Astrophysics Data System (ADS)

Robel, A.; Schoof, C.; Tziperman, E.

2013-12-01

Numerous studies have found significant variability in the velocity of ice streams to be a prominent feature of geomorphologic records in the Siple Coast (Catania et al. 2012) and other regions in West Antarctica (Dowdeswell et al. 2008). Observations indicate that grounding line position is strongly influenced by ice stream variability, producing rapid grounding line migration in the recent past (Catania et al. 2006) and the modern (Joughin & Tulaczyk 2002). We analyze the interaction of grounding line mass flux and position in a marine-terminating ice stream using a stretch-coordinate flowline model. This model is based on that described in Schoof (2007), with a mesh refined near the grounding line to ensure accurate resolution of the mechanical transition zone. Here we have added lateral shear stress (Dupont & Alley 2005) and an undrained plastic bed (Tulaczyk et al. 2000). The parameter dependence of ice stream variability seen in this model compares favorably to both simpler (Robel et al. 2013) and more complex (van der Wel et al. 2013) models, though with some key differences. We find that thermally-induced internal ice stream variability can cause very rapid grounding line migration even in the absence of retrograde bed slopes or external forcing. Activation waves propagate along the ice stream length and trigger periods of rapid grounding line migration. We compare the behavior of the grounding line due to internal ice stream variability to changes triggered externally at the grounding line such as the rapid disintegration of buttressing ice shelves. Implications for Heinrich events and the Marine Ice Sheet Instability are discussed.

Ice-walled-lake plains: Implications for the origin of hummocky glacial topography in middle North America

USGS Publications Warehouse

Clayton, L.; Attig, J.W.; Ham, N.R.; Johnson, M.D.; Jennings, C.E.; Syverson, K.M.

2008-01-01

Ice-walled-lake plains are prominent in many areas of hummocky-till topography left behind as the Laurentide Ice Sheet melted from middle North America. The formation of the hummocky-till topography has been explained by: (1) erosion by subglacial floods; (2) squeezing of subglacial till up into holes in stagnant glacial ice; or (3) slumping of supraglacial till. The geomorphology and stratigraphy of ice-walled-lake plains provide evidence that neither the lake plains nor the adjacent hummocks are of subglacial origin. These flat lake plains, up to a few kilometers in diameter, are perched as much as a few tens of meters above surrounding depressions. They typically are underlain by laminated, fine-grained suspended-load lake sediment. Many ice-walled-lake plains are surrounded by a low rim ridge of coarser-grained shore sediment or by a steeper rim ridge of debris that slumped off the surrounding ice slopes. The ice-walled lakes persisted for hundreds to thousands of years following glacial stagnation. Shells of aquatic molluscs from several deposits of ice-walled-lake sediment in south-central North Dakota have been dated from about 13 500 to 10 500??B.P. (calibrated radiocarbon ages), indicating a climate only slightly cooler than present. This is confirmed by recent palaeoecological studies in nearby non-glacial sites. To survive so long, the stagnant glacial ice had to be well-insulated by a thick cover of supraglacial sediment, and the associated till hummocks must be composed primarily of collapsed supraglacial till. ?? 2007 Elsevier B.V. All rights reserved.

Photochemical degradation of hydroxy PAHs in ice: Implications for the polar areas.

PubMed

Ge, Linke; Li, Jun; Na, Guangshui; Chen, Chang-Er; Huo, Cheng; Zhang, Peng; Yao, Ziwei

2016-07-01

Hydroxyl polycyclic aromatic hydrocarbons (OH-PAHs) are derived from hydroxylated PAHs as contaminants of emerging concern. They are ubiquitous in the aqueous and atmospheric environments and may exist in the polar snow and ice, which urges new insights into their environmental transformation, especially in ice. In present study the simulated-solar (λ > 290 nm) photodegradation kinetics, products and pathways of four OH-PAHs (9-Hydroxyfluorene, 2-Hydroxyfluorene, 1-Hydroxypyrene and 9-Hydroxyphenanthrene) in ice were investigated, and the corresponding implications for the polar areas were explored. It was found that the kinetics followed the pseudo-first-order kinetics with the photolysis quantum yields (Φs) ranging from 7.48 × 10(-3) (1-Hydroxypyrene) to 4.16 × 10(-2) (2-Hydroxyfluorene). These 4 OH-PAHs were proposed to undergo photoinduced hydroxylation, resulting in multiple hydroxylated intermediates, particularly for 9-Hydroxyfluorene. Extrapolation of the lab data to the real environment is expected to provide a reasonable estimate of OH-PAH photolytic half-lives (t1/2,E) in mid-summer of the polar areas. The estimated t1/2,E values ranged from 0.08 h for 1-OHPyr in the Arctic to 54.27 h for 9-OHFl in the Antarctic. In consideration of the lower temperature and less microorganisms in polar areas, the photodegradation can be a key factor in determining the fate of OH-PAHs in sunlit surface snow/ice. To the best of our knowledge, this is the first report on the photodegradation of OH-PAHs in polar areas. Copyright © 2016 Elsevier Ltd. All rights reserved.

Fathoms Below: Propagation of Deep Water-driven Fractures and Implications for Surface Expression and Temporally-varying Activity at Europa

NASA Astrophysics Data System (ADS)

Walker, C. C.; Craft, K.; Schmidt, B. E.

2015-12-01

The fracture and failure of Europa's icy shell are not only observable scars of variable stress and activity throughout its evolution, they also serve key as mechanisms in the interaction of surface and subsurface material, and thus crucial aspects of the study of crustal overturn and ice shell habitability. Galileo images, our best and only reasonable-resolution views of Europa until the Europa Multiple Flyby Mission arrives in the coming decades, illustrates a single snapshot in time in Europa's history from which we deduce many temporally-based hypotheses. One of those hypotheses, which we investigate here, is that sub-surface water-both in the form of Great Lake-sized perched water pockets in the near-surface and the larger global ocean below-drives the deformation, fracture, and failure of the surface. Using Galileo's snapshot in time, we use a 2D/3D hydraulic fracturing model to investigate the propagation of vertical fractures upward into the ice shell, motion of water within and between fractures, and the subsequent break-up of ice over shallow water, forming the chaos regions and other smaller surface features. We will present results from a cohesive fragmentation model to determine the time over which chaos formation occurs, and use a fracking model to determine the time interval required to allow water to escape from basal fractures in the ice shell. In determining the style, energy, and timescale of these processes, we constrain temporal variability in observable activity and topography at the surface. Finally, we compare these results to similar settings on Earth-Antarctica-where we have much higher resolution imagery and observations to better understand how sub-surface water can affect ice surface morphology, which most certainly have implications for future flyby and surface lander exploration.

Marine Ice Crevassing Imaged with Side-looking GPR: Implications for Stability within the McMurdo Shear Zone

NASA Astrophysics Data System (ADS)

Arcone, S. A.; Ray, L.; Lever, J.; Koons, P. O.; Kaluzienski, L. M.

2017-12-01

Shearing along ice shelf margins threatens shelf stability if crevassing results throughout the ice. We are investigating a 28 km2 section of the McMurdo Shear Zone (MSZ), which lies between the Ross Ice Shelf (RIS) and the McMurdo Ice Shelf (MIS). Our gridded transects are east-west, ice flow is nearly due north and the RIS compresses against the MIS from east to west. We find nearly synchronized firn and marine ice crevassing; the marine ice is stratified. However, the lack of any radar evidence for crevassing or fracture within the intermediate 120 m of meteoric ice is so far, enigmatic. The marine ice crevassing is interpreted from ground-penetrating radar (GPR) trace signatures within 100 m swaths of the interface between the meteoric and marine ice; thus the GPR performs like side-looking radar. Symmetric and deformed diffraction hyperbolas indicate crevasses oriented at 43-76 degrees relative to ice flow, as seen in the firn. Those near 45 degrees are interpreted as recently formed while those at greater angles are likely older and rotated. Many traces indicate crevasse warping, lateral faulting, and down-faulting. Traces nearly perpendicular to flow indicate possible wing cracks that grew from the tips of crevasses into the direction of compression from the RIS. We interpret the marine crevasses to have originated at the meteoric-marine interface, and to have extended to the shelf bottom because they appear filled with unstratified frozen seawater. In view of these observations, and that the intermediate meteoric ice must be under similar although not exactly the same stresses, the lack of fracturing within the meteoric ice may imply that suturing following brittle and ductile shear deformation provides stability for the MSZ and may result from this east-west compression of the RIS against the MIS.

Recent Glaciers on Mars: Description and Solar System Perspective

NASA Astrophysics Data System (ADS)

Kargel, J. S.

2001-11-01

Active or recently active ice deposits occur on Mars at middle and high latitudes in fretted terrain, around massifs in highlands east of Hellas and in southern Argyre, on crater walls in the highlands, and in the south polar cap. Most mid-latitude icy flows are debris covered, apparently stagnant, and eroded by partial sublimation. Others are scarred by fresh crevasses and gullies, thus suggesting recent deformation and surface melting. Erosional features include a variety of small-scale relief elements due mainly to sublimation, but sublimation has not obliterated evidence of flow. Similar to terrestrial glaciers in many respects, there are also notable differences, especially in the nature of accumulation. Deformation of the south polar cap is indicated by folding, boudinage, strike-slip or normal faulting, forebulge tectonics near scarps, and thrust faulting. The north polar cap locally also exhibits flow indicators. The south cap's glacial features suggest interbedding of two or more types of ice of differing volatility and rheology, plus a locally deforming surficial dry-ice cap overlying the other materials. Major ice types may include two (or more) of the following, in order of highest to lowest mechanical strength: CO2 clathrate hydrate, water ice, water ice containing traces of liquid-soluble salts, water ice containing traces of solid-soluble acids, and CO2 ice; dust is another variable. Within our Solar System, the closest geomorphic analog to icy Martian flows are Earth's alpine glaciers, rock glaciers, and continental ice sheets, though key differences are apparent. If made dominantly of water ice, important and recent climatic shifts seem to be implicated. Ice-flow landforms also occur on some outer planet satellites; among them are Io, Europa, Enceladus, Ariel, and Triton. Volatile flows on these bodies may involve diverse materials, such as sulfur, water ice, hydrated salts, ammonia-water ices, and nitrogen ice. Most of these would not be suitable materials on Mars. This work was funded by grants from the NASA Mars Data Analysis Program.

The kinematic response of Petermann Glacier, Greenland to ice shelf perturbation

NASA Astrophysics Data System (ADS)

Hubbard, A.; Box, J. E.; Bates, R.; Nick, F.; Luckman, A. J.; van de Wal, R.; Doyle, S. H.

2010-12-01

The acceleration and dynamic thinning of interior zones of the polar ice sheets due to outlet/ice shelf retreat has been identified as a factor hastening their demise and contribution to global sea-level rise. The detachment of a 275 square km area of the Petermann Glacier ice shelf in August, 2010 presents a natural experiment to investigate the timing, mechanisms and efficacy of upstream dynamic feedbacks resulting from a singular but potentially significant frontal perturbation. In 2009, a permanent geodetic/differential GPS strain network logging every 10 seconds was deployed along a 200 km longitudinal profile from the ice front across the grounding line extending into the interior of Petermann Glacier to characterize the system’s state before, during and after any such event. We present an overview of the geophysical measurements conducted and analyze the kinematics of the shelf detachment in relation to local environmental forcing. Finally, we discuss the postulated instantaneous and ongoing evolution in force-balance and concomitant dynamic response resulting from the perturbation along with its implications for Petermann's ongoing stability. Petermann Glacier GNSS base & telemetric GPS facility: community AA & rehab meet point. On ice geodetic-GPS station flat out & reading 0 Volts

Composition and structure of the shallow subsurface of Ceres revealed by crater morphology

NASA Astrophysics Data System (ADS)

Bland, Michael T.; Raymond, Carol A.; Schenk, Paul M.; Fu, Roger R.; Kneissl, Thomas; Pasckert, Jan Hendrik; Hiesinger, Harry; Preusker, Frank; Park, Ryan S.; Marchi, Simone; King, Scott D.; Castillo-Rogez, Julie C.; Russell, Christopher T.

2016-07-01

Before NASA’s Dawn mission, the dwarf planet Ceres was widely believed to contain a substantial ice-rich layer below its rocky surface. The existence of such a layer has significant implications for Ceres’s formation, evolution, and astrobiological potential. Ceres is warmer than icy worlds in the outer Solar System and, if its shallow subsurface is ice-rich, large impact craters are expected to be erased by viscous flow on short geologic timescales. Here we use digital terrain models derived from Dawn Framing Camera images to show that most of Ceres’s largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres’s shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content.

Discovery of a hypersaline subglacial lake complex beneath Devon Ice Cap, Canadian Arctic

PubMed Central

Blankenship, Donald D.; Schroeder, Dustin M.; Dowdeswell, Julian A.

2018-01-01

Subglacial lakes are unique environments that, despite the extreme dark and cold conditions, have been shown to host microbial life. Many subglacial lakes have been discovered beneath the ice sheets of Antarctica and Greenland, but no spatially isolated water body has been documented as hypersaline. We use radio-echo sounding measurements to identify two subglacial lakes situated in bedrock troughs near the ice divide of Devon Ice Cap, Canadian Arctic. Modeled basal ice temperatures in the lake area are no higher than −10.5°C, suggesting that these lakes consist of hypersaline water. This implication of hypersalinity is in agreement with the surrounding geology, which indicates that the subglacial lakes are situated within an evaporite-rich sediment unit containing a bedded salt sequence, which likely act as the solute source for the brine. Our results reveal the first evidence for subglacial lakes in the Canadian Arctic and the first hypersaline subglacial lakes reported to date. We conclude that these previously unknown hypersaline subglacial lakes may represent significant and largely isolated microbial habitats, and are compelling analogs for potential ice-covered brine lakes and lenses on planetary bodies across the solar system. PMID:29651462

The chemical composition of cirrus forming aerosol: Lessons from the MACPEX field study

NASA Astrophysics Data System (ADS)

Cziczo, D. J.; Froyd, K. D.; Murphy, D. M.

2012-12-01

Cirrus clouds are an important factor in the Earth's climate system. These clouds exert a large radiative forcing due to their extensive global coverage and high altitude despite minimal physical and optical thickness. During the Mid-latitude Aerosol and Cloud Properties EXperiment (MACPEX) we measured chemical and physical properties of the aerosols on which cirrus ice crystals formed in situ and in real time using a laser ablation single particle mass spectrometry technique deployed aboard the NASA WB-57 research aircraft. Ice residual particles were also collected for off-line laboratory investigation including electron microscopy. Flights spanned from the Gulf of Mexico to the mid-latitudes over the United States. In most cases heterogeneous freezing was the inferred mechanism of cloud formation and aerosol composition had a significant impact on the nucleation of the ice phase. Mineral dust and some metallic particles were highly enhanced in the ice phase when compared to their abundance outside of cloud. Particles such as soot and biological material, previously suggested as ice nuclei, were not found either due to an inability to nucleate ice or low abundance. Atmospheric implications of these measurements and more advanced future analyses will be discussed.

Composition and structure of the shallow subsurface of Ceres revealed by crater morphology

USGS Publications Warehouse

Bland, Michael T.; Carol A. Raymond,; Schenk, Paul M.; Roger R. Fu,; Thomas Kneisl,; Hendrick Pasckert, Jan; Hiesinger, Harald; Frank Preusker,; Ryan S. Park,; Simone Marchi,; Scott King,; Castillo-Rogez, Julie C.; Christopher T. Russell,

2016-01-01

Before NASA’s Dawn mission, the dwarf planet Ceres was widely believed to contain a substantial ice-rich layer below its rocky surface. The existence of such a layer has significant implications for Ceres’s formation, evolution, and astrobiological potential. Ceres is warmer than icy worlds in the outer Solar System and, if its shallow subsurface is ice-rich, large impact craters are expected to be erased by viscous flow on short geologic timescales. Here we use digital terrain models derived from Dawn Framing Camera images to show that most of Ceres’s largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres’s shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content.

Poleward upgliding Siberian atmospheric rivers over sea ice heat up Arctic upper air.

PubMed

Komatsu, Kensuke K; Alexeev, Vladimir A; Repina, Irina A; Tachibana, Yoshihiro

2018-02-13

We carried out upper air measurements with radiosondes during the summer over the Arctic Ocean from an icebreaker moving poleward from an ice-free region, through the ice edge, and into a region of thick ice. Rapid warming of the Arctic is a significant environmental issue that occurs not only at the surface but also throughout the troposphere. In addition to the widely accepted mechanisms responsible for the increase of tropospheric warming during the summer over the Arctic, we showed a new potential contributing process to the increase, based on our direct observations and supporting numerical simulations and statistical analyses using a long-term reanalysis dataset. We refer to this new process as "Siberian Atmospheric Rivers (SARs)". Poleward upglides of SARs over cold air domes overlying sea ice provide the upper atmosphere with extra heat via condensation of water vapour. This heating drives increased buoyancy and further strengthens the ascent and heating of the mid-troposphere. This process requires the combination of SARs and sea ice as a land-ocean-atmosphere system, the implication being that large-scale heat and moisture transport from the lower latitudes can remotely amplify the warming of the Arctic troposphere in the summer.

Low-pressure clathrate-hydrate formation in amorphous astrophysical ice analogs

NASA Technical Reports Server (NTRS)

Blake, D. F.; Allamandola, L. J.; Sandford, S.; Hudgins, D.; Freund, F.

1991-01-01

In modeling cometary ice, the properties of clathrate hydrates were used to explain anomalous gas release at large radial distances from the Sun, and the retention of particular gas inventories at elevated temperatures. Clathrates may also have been important early in solar system history. However, there has never been a reasonable mechanism proposed for clathrate formation under the low pressures typical of these environments. For the first time, it was shown that clathrate hydrates can be formed by warming and annealing amorphous mixed molecular ices at low pressures. The complex microstructures which occur as a result of clathrate formation from the solid state may provide an explanation for a variety of unexplained phenomena. The vacuum and imaging systems of an Hitachi H-500H Analytical Electron Microscope was modified to study mixed molecular ices at temperatures between 12 and 373 K. The resulting ices are characterized by low-electron dose Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED). The implications of these results for the mechanical and gas release properties of comets are discussed. Laboratory IR data from similar ices are presented which suggest the possibility of remotely observing and identifying clathrates in astrophysical objects.

Influence of the Structural Dichotomy of Antarctic Lithosphere on Regional Glacial-Isostatic Adjustment

NASA Astrophysics Data System (ADS)

Klemann, V.; Rau, D.; Martinec, Z.; Wolf, D.

2009-05-01

The strong structural dichotomy between East and West Antarctica is related to the West Antarctic Rift. The rheological implications are a reduction of the elastic-lithosphere thickness by a factor of more than 2 from East to West Antarctica as well as a strongly reduced mantle viscosity below West Antarctica and the Antarctic Peninsula. For modelling glacial-isostatic adjustment, we use a global viscoelastic earth model and apply the spectral finite-element method for the solution of the field equations. Ice models ICE-5G and IJ05 are used for parameterizing the last Pleistocene deglaciation. Lateral viscosity variations in the upper mantle are derived from variations in seismic velocity by applying scaling laws. Considering also lateral variations in the lithosphere structure, we study the implications of lateral variability on the glacial-isostatic adjustment of Antarctica.

Mars Global Surveyor Data Analysis Program. Origins of Small Volcanic Cones: Eruption Mechanisms and Implications for Water on Mars

NASA Technical Reports Server (NTRS)

Fagents, Sarah A.; Greeley, Ronald; Thordarson, Thorvaldur

2002-01-01

The goal of the proposed work was to determine the origins of small volcanic cones observed in Mars Global Surveyor (MGS) data, and their implications for regolith ice stores and magma volatile contents. For this 1-year study, our approach involved a combination of: Quantitative morphologic analysis and interpretation of Mars Orbiter Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) data; Numerical modeling of eruption processes responsible for producing the observed features; Fieldwork on terrestrial analogs in Iceland. Following this approach, this study succeeded in furthering our understanding of (i) the spatial and temporal distribution of near-surface water ice, as defined by the distribution and sizes of rootless volcanic cones ("pseudocraters"), and (ii) the properties, eruption conditions, and volatile contents of magmas producing primary vent cones.

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 content and ice crystallography (grain size, ice fabrics...) on the deformation behaviour. Glacier ice was also used in our experiments. Calculations of the flow parameter A give a value of 3.10e-16 s-1 kPa-3 at a temperature of -10° C. These results are in accordance with previous lab deformation studies. Compression tests show the effectiveness of the deformation unit for uniaxial strain experiment. In the future, deformation of marine ice and of the ice mélange (consisting of a melange of marine ice, broken blocks of continental ice and blown snow further metamorphosed into firn and then ice) will be studied, to obtain a comprehensive understanding of the parameters that influence the behaviour of both ice types and how they affect the overall flow of the ice shelf and potential future sea level rise.

Nonlinear Spectral Mixture Modeling to Estimate Water-Ice Abundance of Martian Regolith

NASA Astrophysics Data System (ADS)

Gyalay, Szilard; Chu, Kathryn; Zeev Noe Dobrea, Eldar

2017-10-01

We present a novel technique to estimate the abundance of water-ice in the Martian permafrost using Phoenix Surface Stereo Imager multispectral data. In previous work, Cull et al. (2010) estimated the abundance of water-ice in trenches dug by the Mars Phoenix lander by modeling the spectra of the icy regolith using the radiative transfer methods described in Hapke (2008) with optical constants for Mauna Kea palagonite (Clancy et al., 1995) as a substitute for unknown Martian regolith optical constants. Our technique, which uses the radiative transfer methods described in Shkuratov et al. (1999), seeks to eliminate the uncertainty that stems from not knowing the composition of the Martian regolith by using observations of the Martian soil before and after the water-ice has sublimated away. We use observations of the desiccated regolith sample to estimate its complex index of refraction from its spectrum. This removes any a priori assumptions of Martian regolith composition, limiting our free parameters to the estimated real index of refraction of the dry regolith at one specific wavelength, ice grain size, and regolith porosity. We can then model mixtures of regolith and water-ice, fitting to the original icy spectrum to estimate the ice abundance. To constrain the uncertainties in this technique, we performed laboratory measurements of the spectra of known mixtures of water-ice and dry soils as well as those of soils after desiccation with controlled viewing geometries. Finally, we applied the technique to Phoenix Surface Stereo Imager observations and estimated water-ice abundances consistent with pore-fill in the near-surface ice. This abundance is consistent with atmospheric diffusion, which has implications to our understanding of the history of water-ice on Mars and the role of the regolith at high latitudes as a reservoir of atmospheric H2O.

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.

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.

Ice Particle Impact on Cloud Water Content Instrumentation

NASA Technical Reports Server (NTRS)

Emery, Edward F.; Miller, Dean R.; Plaskon, Stephen R.; Strapp, Walter; Lillie, Lyle

2004-01-01

Determining the total amount of water contained in an icing cloud necessitates the measurement of both the liquid droplets and ice particles. One commonly accepted method for measuring cloud water content utilizes a hot wire sensing element, which is maintained at a constant temperature. In this approach, the cloud water content is equated with the power required to keep the sense element at a constant temperature. This method inherently assumes that impinging cloud particles remain on the sensing element surface long enough to be evaporated. In the case of ice particles, this assumption requires that the particles do not bounce off the surface after impact. Recent tests aimed at characterizing ice particle impact on a thermally heated wing section, have raised questions about the validity of this assumption. Ice particles were observed to bounce off the heated wing section a very high percentage of the time. This result could have implications for Total Water Content sensors which are designed to capture ice particles, and thus do not account for bouncing or breakup of ice particles. Based on these results, a test was conducted to investigate ice particle impact on the sensing elements of the following hot-wire cloud water content probes: (1) Nevzorov Total Water Content (TWC)/Liquid Water Content (LWC) probe, (2) Science Engineering Associates TWC probe, and (3) Particle Measuring Systems King probe. Close-up video imaging was used to study ice particle impact on the sensing element of each probe. The measured water content from each probe was also determined for each cloud condition. This paper will present results from this investigation and attempt to evaluate the significance of ice particle impact on hot-wire cloud water content measurements.

Cool Science Explains a Warming World: Using Ice Core Science to Bridge the Gap Between Researchers and the K-12 Classroom

NASA Astrophysics Data System (ADS)

Huffman, L. T.

2017-12-01

Changing ice has urgent implications for people around the world. The Ice Drilling Program Office (IDPO) provides scientific leadership and oversight of ice coring and drilling activities funded by the US National Science Foundation and also has goals to enhance education and communication of current research information. In a time when misinformation is rampant and climate change science is suspect, it is essential that students receive accurate scientific information and engage in learning activities that model complex ideas through engaging and age appropriate ways, while also learning to validate and recognize reliable sources. The IDPO Education and Outreach (EO) office works to create resources, activities and professional development that bridge the gap between ice core science research and educators and their students. Ice core science is on the cutting edge of new discoveries about climate change and understanding better the past to predict the future. Hands-on inquiry activities based on ice core data allow teachers to lead their students to new discoveries about climate secrets hidden deep in the ice. Capitalizing on the inherent interest in the extremes of the Polar Regions, IDPO materials engage students in activities aligned with NGSS standards. Ice drilling technologies make an ideal platform for intertwining engineering concepts and practices with science research to meet the SEP (Science and Engineering Practices) in the NGSS. This session will highlight how the IDPO EO office has built a community of ice core scientists willing to take part in education and outreach projects and events and share some of the resources available to K-12 educators. We will highlight some of the successes and lessons learned as we continually evolve our work toward more effective science education and communication highlighting ice core and climate change science.

Basal crevasses and suture zones in the Larsen C Ice Shelf, Antarctica: Implications for ice shelf stability in a warming climate

NASA Astrophysics Data System (ADS)

McGrath, Daniel J.

Understanding ice shelf structure and processes is paramount to future predictions of sea level rise, as nearly 75% of the ice flux from the Antarctic Ice Sheet (AIS) passes through these gates. The breakup of an ice shelf removes the longitudinal back stress acting on the grounded inland ice and leads to flow acceleration, dynamic thinning and frontal retreat, processes that can be sustained for more than a decade. Increased ice discharge to the ocean contributes to global sea level rise. This dissertation investigates basal crevasses and suture zones, two key structural components of ice shelves, in order to understand how the structure of an ice shelf influences its stability in a warming climate. Ground penetrating radar, high-resolution satellite imagery and a variety of modeling approaches are utilized to assess these features on the Larsen C Ice Shelf but in a manner that considers their influence on ice shelf stability around the AIS. Basal crevasses are large-scale (~66% of ice thickness and ten's of kms in length) and abundant features that are significant structural weaknesses. The viscoplastic deformation of the ice shelf in response to the perturbed hydrostatic balance leads to the formation of both surface depressions and crevasses, hence weakening the ice shelf further. Basal crevasses increase the local ice-ocean interface by ~30%, thereby increasing basal roughness and altering ice-ocean interactions. Ice-shelf fractures frequently terminate where they encounter suture zones, regions of material heterogeneity that form at the lateral bounds of meteoric inflows to ice shelves. The termination of a 25 km-long rift in the Churchill Peninsula suture zone is investigated and found to contain ~60 m of accreted marine ice. Steady-state basal melting/freezing rates are determined for the ice shelf and applied to a flowline model to examine the along-flow evolution of ice shelf structure. The thickening surface wedge of locally accumulated meteoric ice, which likely has limited lateral variation in its mechanical properties, accounts for ~60% of the total ice thickness near the calving front. This suggests that the material heterogeneities present in the lower ~40% of the ice column are responsible for resisting fracture propagation and thereby delaying tabular calving events. This represents a highly sensitive aspect of ice-shelf stability, as changes in the oceanic forcing may lead to the loss of this heterogeneity.

Down and Dirty.

ERIC Educational Resources Information Center

Greeley, Geoffrey

2001-01-01

Offers 10 tips that can help school and university custodial staffs maintain a healthy physical environment. Suggestions include ideas for carpet cleaning, maintenance planning, and trapping outside dirt.(GR)

Laboratory, Computational and Theoretical Investigations of Ice Nucleation and its Implications for Mixed Phase Clouds

NASA Astrophysics Data System (ADS)

Yang, Fan

Ice particles in atmospheric clouds play an important role in determining cloud lifetime, precipitation and radiation. It is therefore important to understand the whole life cycle of ice particles in the atmosphere, e.g., where they come from (nucleation), how they evolve (growth), and where they go (precipitation). Ice nucleation is the crucial step for ice formation, and in this study, we will mainly focus on ice nucleation in the lab and its effect on mixed-phase stratiform clouds. In the first half of this study, we investigate the relevance of moving contact lines (i.e., the region where three or more phases meet) on the phenomenon of contact nucleation. High speed video is used to investigate heterogeneous ice nucleation in supercooled droplets resting on cold substrates under two different dynamic conditions: droplet electrowetting and droplet vibration. The results show that contact-line motion is not a sufficient condition to trigger ice nucleation, while locally curved contact lines that can result from contact-line motion are strongly related to ice nucleation. We propose that pressure perturbations due to locally curved contact lines can strongly enhance the ice nucleation rate, which gives another interpretation for the mechanism for contact nucleation. Corresponding theoretical results provide a quantitative connection between pressure perturbations and temperature, providing a useful tool for ice nucleation calculations in atmospheric models. In this second half of the study, we build a minimalist model for long lifetime mixed-phase stratiform clouds based on stochastic ice nucleation. Our result shows that there is a non-linear relationship between ice water contact and ice number concentration in the mixed-phase cloud, as long as the volume ice nucleation rate is constant. This statistical property may help identify the source of ice nuclei in mixed-phase clouds. In addition, results from Lagrangian ice particle tracking in time dependent fields show that long lifetime ice particles exist in mixed-phase stratiform clouds. We find that small ice particle can be trapped in eddy-like structures. Whether ice particles grow or sublimate depends on the thermodynamic field in the trapping region. This dynamic-thermodynamic coupling effect on the lifetime of ice particles might explain the fast phase-partition change observed in the mixed phase cloud.

Degradation and stabilization of ice wedges: Implications for assessing risk of thermokarst in northern Alaska

NASA Astrophysics Data System (ADS)

Kanevskiy, Mikhail; Shur, Yuri; Jorgenson, Torre; Brown, Dana R. N.; Moskalenko, Nataliya; Brown, Jerry; Walker, Donald A.; Raynolds, Martha K.; Buchhorn, Marcel

2017-11-01

Widespread degradation of ice wedges has been observed during the last decades in numerous areas within the continuous permafrost zone of Eurasia and North America. To study ice-wedge degradation, we performed field investigations at Prudhoe Bay and Barrow in northern Alaska during 2011-2016. In each study area, a 250-m transect was established with plots representing different stages of ice-wedge degradation/stabilization. Field work included surveying ground- and water-surface elevations, thaw-depth measurements, permafrost coring, vegetation sampling, and ground-based LiDAR scanning. We described cryostratigraphy of frozen soils and stable isotope composition, analyzed environmental characteristics associated with ice-wedge degradation and stabilization, evaluated the vulnerability and resilience of ice wedges to climate change and disturbances, and developed new conceptual models of ice-wedge dynamics that identify the main factors affecting ice-wedge degradation and stabilization and the main stages of this quasi-cyclic process. We found significant differences in the patterns of ice-wedge degradation and stabilization between the two areas, and the patterns were more complex than those previously described because of the interactions of changing topography, water redistribution, and vegetation/soil responses that can interrupt or reinforce degradation. Degradation of ice wedges is usually triggered by an increase in the active-layer thickness during exceptionally warm and wet summers or as a result of flooding or disturbance. Vulnerability of ice wedges to thermokarst is controlled by the thickness of the intermediate layer of the upper permafrost, which overlies ice wedges and protects them from thawing. In the continuous permafrost zone, degradation of ice wedges rarely leads to their complete melting; and in most cases wedges eventually stabilize and can then resume growing, indicating a somewhat cyclic and reversible process. Stabilization of ice wedges after their partial degradation makes them better protected than before degradation because the intermediate layer is usually 2 to 3 times thicker on top of stabilized ice wedges than on top of initial ice wedges in undisturbed conditions. As a result, the likelihood of formation of large thaw lakes in the continuous permafrost zone triggered by ice-wedge degradation alone is very low.

[On new screening biomarker to evaluate health state in personnel engaged into chemical weapons extinction].

PubMed

Voitenko, N G; Garniuk, V V; Prokofieva, D S; Gontcharov, N V

2015-01-01

The work was aimed to find new screeding parameters (biomarkers) for evaluation of health state of workers engaged into enterprises with hazardous work conditions, as exemplified by "Maradykovskyi" object of chemical weapons extinction. Analysis of 27 serum cytokines was conducted in donors and the object personnel with various work conditions. Findings are statistically significant increase of serum eotaxin in the personnel of "dirty" zone, who are regularly exposed to toxic agents in individual filter protective means over the working day. For screening detection of health disorders in the object personnel, the authors suggested new complex biomarker--ratio Eotaxin* IFNγ/TNFα that demonstrates 67.9% sensitivity and 87.5% specificity in differentiating the "dirty" zone personnel and other staffers.

A dirty word or a dirty world?: Attribute framing, political affiliation, and query theory.

PubMed

Hardisty, David J; Johnson, Eric J; Weber, Elke U

2010-01-01

We explored the effect of attribute framing on choice, labeling charges for environmental costs as either an earmarked tax or an offset. Eight hundred ninety-eight Americans chose between otherwise identical products or services, where one option included a surcharge for emitted carbon dioxide. The cost framing changed preferences for self-identified Republicans and Independents, but did not affect Democrats' preferences. We explain this interaction by means of query theory and show that attribute framing can change the order in which internal queries supporting one or another option are posed. The effect of attribute labeling on query order is shown to depend on the representations of either taxes or offsets held by people with different political affiliations.

Medieval Warm Period and Little Ice Age Signatures in the Distribution of Modern Ocean Temperatures

NASA Astrophysics Data System (ADS)

Gebbie, G.; Huybers, P. J.

2017-12-01

It is well established both that global temperatures have varied overthe last millenium and that the interior ocean reflects surfaceproperties inherited over these timescales. Signatures of theMedieval Warm Period and Little Ice Age are thus to be expected in themodern ocean state, though the magnitude of these effects and whetherthey are detectable is unclear. Analysis of changes in temperatureacross those obtained in the 1870s as part of the theH.M.S. Challenger expedition, the 1990s World Ocean CirculationExperiment, and recent Argo observations shows a consistent pattern:the upper ocean and Atlantic have warmed, but the oldest waters inthe deep Pacific appear to have cooled. The implications of pressureeffects on the H.M.S. Challenger thermometers and uncertainties indepth of observations are non-negligible but do not appear tofundamentally alter this pattern. Inversion of the modern hydrographyusing ocean transport estimates derived from passive tracer andradiocarbon observations indicates that deep Pacific cooling could bea vestige of the Medieval Warm Period, and that warming elsewhere reflects thecombined effects of emergence from the Little Ice Age and modernanthropogenic warming. Implications for longterm variations in oceanheat uptake and separating natural and anthropogenic contributions to themodern energy imbalance are discussed.

Context for the Recent Massive Petermann Glacier Calving Event

NASA Astrophysics Data System (ADS)

Falkner, Kelly K.; Melling, Humfrey; Münchow, Andreas M.; Box, Jason E.; Wohlleben, Trudy; Johnson, Helen L.; Gudmandsen, Preben; Samelson, Roger; Copland, Luke; Steffen, Konrad; Rignot, Eric; Higgins, Anthony K.

2011-04-01

On 4 August 2010, about one fifth of the floating ice tongue of Petermann Glacier (also known as “Petermann Gletscher”) in northwestern Greenland calved (Figure 1). The resulting “ice island” had an area approximately 4 times that of Manhattan Island (about 253±17 square kilometers). The ice island garnered much attention from the media, politicians, and the public, who raised concerns about downstream implications for shipping, offshore oil and gas operations, and possible connections to Arctic and global warming. Does this event signal a change in the glacier's dynamics? Or can it be characterized as part of the glacier's natural variability? Understanding the known historical context of this event allows scientists and the public to judge its significance.

Bromoalkane production by Antarctic ice algae

NASA Technical Reports Server (NTRS)

Sturges, W. T.; Sullivan, C. W.; Schnell, R. C.; Heidt, L. E.; Pollock, W. H.

1993-01-01

Ice microalgae, collected from the underside of annual sea ice in McMurdo Sound, Antarctica, were found to contain and release to seawater a number of brominated hydrocarbons. These included bromoform, dibromomethane, mixed bromochloromethanes, and methyl bromide. Atmospheric measurements in the McMurdo Sound vicinity revealed the presence of bromoform and methyl bromide in the lower atmosphere, with lowest concentrations inland, further indicating that biogenic activity in the Sound is a source of organic bromine gases to the Antarctic atmosphere. This may have important implications for boundary layer chemistry in Antarctica. In the Arctic, the presence of bromoform has been linked to loss of surface ozone in the spring. We report here preliminary evidence for similar surface ozone loss at McMurdo Station.

Improved limits on dark matter annihilation in the Sun with the 79-string IceCube detector and implications for supersymmetry

NASA Astrophysics Data System (ADS)

Aartsen, M. G.; Abraham, K.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Altmann, D.; Anderson, T.; Ansseau, I.; Anton, G.; Archinger, M.; Arguelles, C.; Arlen, T. C.; Auffenberg, J.; Bai, X.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Becker Tjus, J.; Becker, K.-H.; Beiser, E.; BenZvi, S.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Börner, M.; Bos, F.; Bose, D.; Böser, S.; Botner, O.; Braun, J.; Brayeur, L.; Bretz, H.-P.; Buzinsky, N.; Casey, J.; Casier, M.; Cheung, E.; Chirkin, D.; Christov, A.; Clark, K.; Classen, L.; Coenders, S.; Collin, G. H.; Conrad, J. M.; Cowen, D. F.; Cruz Silva, A. H.; Danninger, M.; Daughhetee, J.; Davis, J. C.; Day, M.; de André, J. P. A. M.; De Clercq, C.; del Pino Rosendo, E.; Dembinski, H.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de Wasseige, G.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; di Lorenzo, V.; Dumm, J. P.; Dunkman, M.; Eberhardt, B.; Edsjö, J.; Ehrhardt, T.; Eichmann, B.; Euler, S.; Evenson, P. A.; Fahey, S.; Fazely, A. R.; Feintzeig, J.; Felde, J.; Filimonov, K.; Finley, C.; Flis, S.; Fösig, C.-C.; Fuchs, T.; Gaisser, T. K.; Gaior, R.; Gallagher, J.; Gerhardt, L.; Ghorbani, K.; Gier, D.; Gladstone, L.; Glagla, M.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Góra, D.; Grant, D.; Griffith, Z.; Groß, A.; Ha, C.; Haack, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Hansen, E.; Hansmann, B.; Hanson, K.; Hebecker, D.; Heereman, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hignight, J.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Holzapfel, K.; Homeier, A.; Hoshina, K.; Huang, F.; Huber, M.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; In, S.; Ishihara, A.; Jacobi, E.; Japaridze, G. S.; Jeong, M.; Jero, K.; Jones, B. J. P.; Jurkovic, M.; Kappes, A.; Karg, T.; Karle, A.; Katz, U.; Kauer, M.; Keivani, A.; Kelley, J. L.; Kemp, J.; Kheirandish, A.; Kiryluk, J.; Klein, S. R.; Kohnen, G.; Koirala, R.; Kolanoski, H.; Konietz, R.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krings, K.; Kroll, G.; Kroll, M.; Krückl, G.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Lanfranchi, J. L.; Larson, M. J.; Lesiak-Bzdak, M.; Leuermann, M.; Leuner, J.; Lu, L.; Lünemann, J.; Madsen, J.; Maggi, G.; Mahn, K. B. M.; Mandelartz, M.; Maruyama, R.; Mase, K.; Matis, H. S.; Maunu, R.; McNally, F.; Meagher, K.; Medici, M.; Meier, M.; Meli, A.; Menne, T.; Merino, G.; Meures, T.; Miarecki, S.; Middell, E.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Neer, G.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke Pollmann, A.; Olivas, A.; Omairat, A.; O'Murchadha, A.; Palczewski, T.; Pandya, H.; Pankova, D. V.; Paul, L.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Quinnan, M.; Raab, C.; Rädel, L.; Rameez, M.; Rawlins, K.; Reimann, R.; Relich, M.; Resconi, E.; Rhode, W.; Richman, M.; Richter, S.; Riedel, B.; Robertson, S.; Rongen, M.; Rott, C.; Ruhe, T.; Ryckbosch, D.; Sabbatini, L.; Sander, H.-G.; Sandrock, A.; Sandroos, J.; Sarkar, S.; Savage, C.; Schatto, K.; Schimp, M.; Schlunder, P.; Schmidt, T.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schulte, L.; Schumacher, L.; Scott, P.; Seckel, D.; Seunarine, S.; Silverwood, H.; Soldin, D.; Song, M.; Spiczak, G. M.; Spiering, C.; Stahlberg, M.; Stamatikos, M.; Stanev, T.; Stasik, A.; Steuer, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Ström, R.; Strotjohann, N. L.; Sullivan, G. W.; Sutherland, M.; Taavola, H.; Taboada, I.; Tatar, J.; Ter-Antonyan, S.; Terliuk, A.; Te{š}ić, G.; Tilav, S.; Toale, P. A.; Tobin, M. N.; Toscano, S.; Tosi, D.; Tselengidou, M.; Turcati, A.; Unger, E.; Usner, M.; Vallecorsa, S.; Vandenbroucke, J.; van Eijndhoven, N.; Vanheule, S.; van Santen, J.; Veenkamp, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Wallace, A.; Wallraff, M.; Wandkowsky, N.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whelan, B. J.; Wiebe, K.; Wiebusch, C. H.; Wille, L.; Williams, D. R.; Wills, L.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, D. L.; Xu, X. W.; Xu, Y.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zoll, M.

2016-04-01

We present an improved event-level likelihood formalism for including neutrino telescope data in global fits to new physics. We derive limits on spin-dependent dark matter-proton scattering by employing the new formalism in a re-analysis of data from the 79-string IceCube search for dark matter annihilation in the Sun, including explicit energy information for each event. The new analysis excludes a number of models in the weak-scale minimal supersymmetric standard model (MSSM) for the first time. This work is accompanied by the public release of the 79-string IceCube data, as well as an associated computer code for applying the new likelihood to arbitrary dark matter models.

Side Group Addition to the PAH Coronene by UV Photolysis in Cosmic Ice Analogs

NASA Technical Reports Server (NTRS)

Bernstein, Max P.; Elsila, Jamie E.; Dworkin, Jason P.; Sandford, Scott A.; Allamandola, Louis J.; Zare, Richard N.; DeVincenzi, D. (Technical Monitor)

2002-01-01

Ultraviolet photolysis of various ice mixtures at low temperature and pressure caused the addition of amino (-NH2), methyl (-CH3), methoxy (-OCH3), and cyano (-CN) functional groups to the polycyclic aromatic hydrocarbon (PAH) coronene (C22H12). The implications of these results for interstellar and meteoritic chemistry are discussed. Previously only simple PAH photo-oxidation had been reported. This work represents the first experimental evidence that ice photochemistry may have contributed to aromatics bearing carbon and nitrogen containing side groups that are detected in primitive meteorites and interplanetary dust particles. Furthermore, these results suggest a wider range of modified PAHs should be expected in interstellar lees and materials predating solar system formation.

Integrating Observations and Models to Better Understand a Changing Arctic Sea Ice Cover

NASA Astrophysics Data System (ADS)

Stroeve, J. C.

2017-12-01

TThe loss of the Arctic sea ice cover has captured the world's attention. While much attention has been paid to the summer ice loss, changes are not limited to summer. The last few winters have seen record low sea ice extents, with 2017 marking the 3rdyear in a row with a new record low for the winter maximum extent. More surprising is the number of consecutive months between January 2016 through April 2017 with ice extent anomalies more than 2 standard deviations below the 1981-2010 mean. Additionally, October 2016 through April 2017 saw 7 consecutive months with record low extents, something that had not happened before in the last 4 decades of satellite observations. As larger parts of the Arctic Ocean become ice-free in summer, regional seas gradually transition from a perennial to a seasonal ice cover. The Barents Sea is already only seasonally ice covered, whereas the Kara Sea has recently lost most of its summer ice and is thereby starting to become a seasonally ice covered region. These changes serve as harbinger for what's to come for other Arctic seas. Given the rapid pace of change, there is an urgent need to improve our understanding of the drivers behind Arctic sea ice loss, the implications of this ice loss and to predict future changes to better inform policy makers. Climate models play a fundamental role in helping us synthesize the complex elements of the Arctic sea ice system yet generally fail to simulate key features of the sea ice system and the pace of sea ice loss. Nevertheless, modeling advances continue to provide better means of diagnosing sea ice change, and new insights are likely to be gained with model output from the 6th phase of the Coupled Model Intercomparison Project (CMIP6). The CMIP6 Sea-Ice Model Intercomparison Project (SIMIP) aim is to better understand biases and errors in sea ice simulations so that we can improve our understanding of the likely future evolution of the sea ice cover and its impacts on global climate. To reach this goal, a community-defined set of model output has been recommended that will allow scientists to better characterize the heat, momentum and mass budget of Arctic sea ice. This will allow for better quantification of the role of internal variability, external forcing and model deficiencies.

On the radiolysis of ethylene ices by energetic electrons and implications to the extraterrestrial hydrocarbon chemistry

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

Zhou, Li; Maity, Surajit; Abplanalp, Matt

2014-07-20

The chemical processing of ethylene ices (C{sub 2}H{sub 4}) by energetic electrons was investigated at 11 K to simulate the energy transfer processes and synthesis of new molecules induced by secondary electrons generated in the track of galactic cosmic ray particles. A combination of Fourier transform infrared spectrometry (solid state) and quadrupole mass spectrometry (gas phase) resulted in the identification of six hydrocarbon molecules: methane (CH{sub 4}), the C2 species acetylene (C{sub 2}H{sub 2}), ethane (C{sub 2}H{sub 6}), the ethyl radical (C{sub 2}H{sub 5}), and—for the very first time in ethylene irradiation experiments—the C4 hydrocarbons 1-butene (C{sub 4}H{sub 8}) andmore » n-butane (C{sub 4}H{sub 10}). By tracing the temporal evolution of the newly formed molecules spectroscopically online and in situ, we were also able to fit the kinetic profiles with a system of coupled differential equations, eventually providing mechanistic information, reaction pathways, and rate constants on the radiolysis of ethylene ices and the inherent formation of smaller (C1) and more complex (C2, C4) hydrocarbons involving carbon-hydrogen bond ruptures, atomic hydrogen addition processes, and radical-radical recombination pathways. We also discuss the implications of these results on the hydrocarbon chemistry on Titan's surface and on ice-coated, methane-bearing interstellar grains as present in cold molecular clouds such as TMC-1.« less

Aerosol-driven increase in Arctic sea ice over the middle of the twentieth century

NASA Astrophysics Data System (ADS)

Gagné, Marie-Ève; Fyfe, John C.; Gillett, Nathan P.; Polyakov, Igor V.; Flato, Gregory M.

2017-07-01

Updated observational data sets without climatological infilling show that there was an increase in sea ice concentration in the eastern Arctic between 1950 and 1975, contrary to earlier climatology infilled observational data sets that show weak interannual variations during that time period. We here present climate model simulations showing that this observed sea ice concentration increase was primarily a consequence of cooling induced by increasing anthropogenic aerosols and natural forcing. Indeed, sulphur dioxide emissions, which lead to the formation of sulphate aerosols, peaked around 1980 causing a sharp increase in the burden of sulphate between the 1950s and 1970s; but since 1980, the burden has dropped. Our climate model simulations show that the cooling contribution of aerosols offset the warming effect of increasing greenhouse gases over the midtwentieth century resulting in the expansion of the Arctic sea ice cover. These results challenge the perception that Arctic sea ice extent was unperturbed by human influence until the 1970s, suggesting instead that it exhibited earlier forced multidecadal variations, with implications for our understanding of impacts and adaptation in human and natural Arctic systems.

Water in Inhomogeneous Nanoconfinement: Coexistence of Multilayered Liquid and Transition to Ice Nanoribbons.

PubMed

Qiu, Hu; Zeng, Xiao Cheng; Guo, Wanlin

2015-10-27

Phase behavior and the associated phase transition of water within inhomogeneous nanoconfinement are investigated using molecular dynamics simulations. The nanoconfinement is constructed by a flat bottom plate and a convex top plate. At 300 K, the confined water can be viewed as a coexistence of monolayer, bilayer, and trilayer liquid domains to accommodate the inhomogeneous confinement. With increasing liquid density, the confined water with uneven layers transforms separately into two-dimensional ice crystals with unchanged layer number and rhombic in-plane symmetry for oxygen atoms. The monolayer water undergoes the transition first into a puckered ice nanoribbon, and the bilayer water transforms into a rhombic ice nanoribbon next, followed by the transition of trilayer water into a trilayer ice nanoribbon. The sequential localized liquid-to-solid transition within the inhomogeneous confinement can also be achieved by gradually decreasing the temperature at low liquid densities. These findings of phase behaviors of water under the inhomogeneous nanoconfinement not only extend the phase diagram of confined water but also have implications for realistic nanofluidic systems and microporous materials.

Delayed deglaciation or extreme Arctic conditions 21-16 cal. kyr at southeastern Laurentide Ice Sheet margin?

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

Peteet, D. M.; Beh, M.; Orr, C.

The conventionally accepted ages of the Last Glacial Maximum (LGM) retreat of the southeastern Laurentide Ice Sheet (LIS) are 26–21 cal. kyr (derived from bulk-sediment radiocarbon ages) and 28–23 cal. kyr (varve estimates). By utilizing accelerator mass spectrometry (AMS) 14C dating of earliest macrofossils in 13 lake/bog inorganic clays, we find that vegetation first appeared on the landscape at 16–15 cal. kyr, suggesting ice had not retreated until that time. The gap between previous age estimates and ours is significant and has large implications for our understanding of ocean-atmosphere linkages. Older ages imply extreme Arctic conditions for 9–5 cal kyr;more » a landscape with no ice, yet no deposition in lakes. Also, our new AMS chronology of LIS retreat is consistent with marine evidence of deglaciation from the N. Atlantic, showing significant freshwater input and sea level rise only after 19 cal kyr with a cold meltwater lid, perhaps delaying ice melt.« less

Delayed deglaciation or extreme Arctic conditions 21-16 cal. kyr at southeastern Laurentide Ice Sheet margin?

DOE PAGES

Peteet, D. M.; Beh, M.; Orr, C.; ...

2012-06-15

The conventionally accepted ages of the Last Glacial Maximum (LGM) retreat of the southeastern Laurentide Ice Sheet (LIS) are 26–21 cal. kyr (derived from bulk-sediment radiocarbon ages) and 28–23 cal. kyr (varve estimates). By utilizing accelerator mass spectrometry (AMS) 14C dating of earliest macrofossils in 13 lake/bog inorganic clays, we find that vegetation first appeared on the landscape at 16–15 cal. kyr, suggesting ice had not retreated until that time. The gap between previous age estimates and ours is significant and has large implications for our understanding of ocean-atmosphere linkages. Older ages imply extreme Arctic conditions for 9–5 cal kyr;more » a landscape with no ice, yet no deposition in lakes. Also, our new AMS chronology of LIS retreat is consistent with marine evidence of deglaciation from the N. Atlantic, showing significant freshwater input and sea level rise only after 19 cal kyr with a cold meltwater lid, perhaps delaying ice melt.« less

Experimental investigation of insolation-driven dust ejection from Mars' CO2 ice caps

NASA Astrophysics Data System (ADS)

Kaufmann, E.; Hagermann, A.

2017-01-01

Mars' polar caps are - depending on hemisphere and season - partially or totally covered with CO2 ice. Icy surfaces such as the polar caps of Mars behave differently from surfaces covered with rock and soil when they are irradiated by solar light. The latter absorb and reflect incoming solar radiation within a thin layer beneath the surface. In contrast, ices are partially transparent in the visible spectral range and opaque in the infrared. Due to this fact, the solar radiation can penetrate to a certain depth and raise the temperature of the ice or dust below the surface. This may play an important role in the energy balance of icy surfaces in the solar system, as already noted in previous investigations. We investigated the temperature profiles inside CO2 ice samples including a dust layer under Martian conditions. We have been able to trigger dust eruptions, but also demonstrated that these require a very narrow range of temperature and ambient pressure. We discuss possible implications for the understanding of phenomena such as arachneiform patterns or fan shaped deposits as observed in Mars' southern polar region.

10Be in ice at high resolution: Solar activity and climate signals observed and GCM-modeled in Law Dome ice cores

NASA Astrophysics Data System (ADS)

Pedro, Joel; Heikkilä, Ulla; van Ommen, T. D.; Smith, A. M.

2010-05-01

Changes in solar activity modulate the galactic cosmic ray flux, and in turn, the production rate of 10Be in the earth's atmosphere. The best archives of past changes in 10Be production rate are the polar ice cores. Key challenges in interpreting these archives as proxies for past solar activity lie in separating the useful solar activity (or production) signal from the interfering meteorological (or climate) signal, and furthermore, in determining the atmospheric source regions of 10Be deposited to the ice core site. In this study we use a new monthly resolution composite 10Be record, which spans the past decade, and a general circulation model (ECHAM5-HAM), to constrain both the production and climate signals in 10Be concentrations at the Law Dome ice core site, East Antarctica. This study differs from most previous work on 10Be in Antarctica due to the very high sample resolution achieved. This high resolution, through a time period where accurate instrumental measurements of solar activity and climate are available, allows us to examine the response of 10Be concentrations in ice to short-term (monthly to annual) variations in solar activity, and to short-term variations in climate, including seasonality. We find a significant correlation (r2 = 0.56, P < 0.005, n = 92) between observed 10Be concentrations and solar activity (represented by the neutron counting rate). The most pervasive climate influence is a seasonal cycle, which shows maximum concentrations in mid-to-late-summer and minimum concentrations in winter. Model results show reasonable agreement with observations; both a solar activity signal and seasonal cycle in 10Be are captured. However, the modeled snow accumulation rate is too high by approximately 60%. According to the model, the main atmospheric source region of 10Be deposited to Law Dome is the 30-90°S stratosphere (~50%), followed by the 30-90°S troposphere (~30%). An enhancement in the fraction of 10Be arriving to Law Dome from the stratosphere is found by the model during the mid-to-late summer, we suggest this pattern is implicated in the seasonality of observed 10Be concentrations in ice. Our results have implications for interpretation of longer term records of 10Be from ice cores. Firstly, the strong production signal supports the use of 10Be as a solar proxy. Secondly, the short term climate processes operating here, may provide clues to how longer term shifts in climate impact on ice core 10Be.

Implications of sea-ice biogeochemistry for oceanic production and emissions of dimethyl sulfide in the Arctic

NASA Astrophysics Data System (ADS)

Hayashida, Hakase; Steiner, Nadja; Monahan, Adam; Galindo, Virginie; Lizotte, Martine; Levasseur, Maurice

2017-06-01

Sea ice represents an additional oceanic source of the climatically active gas dimethyl sulfide (DMS) for the Arctic atmosphere. To what extent this source contributes to the dynamics of summertime Arctic clouds is, however, not known due to scarcity of field measurements. In this study, we developed a coupled sea ice-ocean ecosystem-sulfur cycle model to investigate the potential impact of bottom-ice DMS and its precursor dimethylsulfoniopropionate (DMSP) on the oceanic production and emissions of DMS in the Arctic. The results of the 1-D model simulation were compared with field data collected during May and June of 2010 in Resolute Passage. Our results reproduced the accumulation of DMS and DMSP in the bottom ice during the development of an ice algal bloom. The release of these sulfur species took place predominantly during the earlier phase of the melt period, resulting in an increase of DMS and DMSP in the underlying water column prior to the onset of an under-ice phytoplankton bloom. Production and removal rates of processes considered in the model are analyzed to identify the processes dominating the budgets of DMS and DMSP both in the bottom ice and the underlying water column. When openings in the ice were taken into account, the simulated sea-air DMS flux during the melt period was dominated by episodic spikes of up to 8.1 µmol m-2 d-1. Further model simulations were conducted to assess the effects of the incorporation of sea-ice biogeochemistry on DMS production and emissions, as well as the sensitivity of our results to changes of uncertain model parameters of the sea-ice sulfur cycle. The results highlight the importance of taking into account both the sea-ice sulfur cycle and ecosystem in the flux estimates of oceanic DMS near the ice margins and identify key uncertainties in processes and rates that should be better constrained by new observations.

Englacial layer mapping correlation and consistency techniques: an example from airborne ice penetrating radar profiles in West Antarctica

NASA Astrophysics Data System (ADS)

Sudunagunta, V.; Ballal, S.; Albach, R.; Muldoon, G.; Quartini, E.; Cavitte, M. G.; Young, D. A.; Blankenship, D. D.

2016-12-01

Ice sheets are important considerations in projections of sea level rise and studies of climate history. Satellite imagery, ice-penetrating radar, and ground penetrating radar are commonly used to understand the dynamics and health of ice sheets. We focus on how to accurately interpret ice-penetrating radar data by tracing isochrones dated by comparison to deep ice cores so that an extensive knowledge of the West Antarctic Ice Sheet's internal stratigraphy is obtained. The radar data shows englacial reflectors and isochrones are interpreted englacial reflectors. We analyze these features and attempt to understand their possible origins. Accurate interpretation of radar data is crucial because the data will be used to evaluate ice flow evolution and boundary conditions. It can also be used to validate simulated ice sheet models. However to do so, isochrones must be traced and connected correctly. Our approach accomplishes this and has the potential to be applied to other ice sheets on Earth and in extraterrestrial systems. We discuss the methodology utilized by our team to interpret data from the West Antarctic Ice Sheet collected using airborne ice-penetrating radar. The seismic reflection interpretation environment Landmark DecisionSpace was adapted to display and interpret the radar returns. When tracing isochrones, a group approach is used to maximize accuracy. In gridded surveys, loops are used to continuously check isochrones, in addition to retracing of isochrones by different group members to check for errors in interpretation. As loops are made, areas of possible scientific merit, such as isochrone drawdowns or Raymond bumps, are documented. A key aspect of this approach is the ability to work in a shared environment with a collaborative database like DecisionSpace. We will explore how we identified these features, their root causes, and subsequent implications for understanding ice sheet dynamics.

Extenstional terrain formation in icy satellites: Implications for ocean-surface interaction

NASA Astrophysics Data System (ADS)

Howell, Samuel M.; Pappalardo, Robert T.

2017-10-01

Europa and Ganymede, Galilean satellites of Jupiter, exhibit geologic activity in their outer H2O ice shells that might convey material from water oceans within the satellites to their surfaces. Imagery from the Voyager and Galileo spacecraft reveal surfaces rich with tectonic deformation, including dilational bands on Europa and groove lanes on Ganymede. These features are generally attributed to the extension of a brittle ice lithosphere overlaying a possibly convecting ice asthenosphere. To explore band formation and interaction with interior oceans, we employ fully visco-elasto-plastic 2-D models of faulting and convection with complex, realistic pure ice rheologies. In these models, material entering from below is tracked and considered to be “fossilized ocean,” ocean material that has frozen into the ice shell and evolves through geologic time. We track the volume fraction of fossil ocean material in the ice shell as a function of depth, and the exposure of both fresh ice and fossil ocean material at the ice shell surface. To explore the range in extensional terrains, we vary ice shell thickness, fault localization, melting-temperature ice viscosity, and the presence of pre-existing weaknesses. Mechanisms which act to weaken the ice shell and thin the lithosphere (e.g. vigorous convection, thinner shells, pre-existing weaknesses) tend to plastically yield to form smooth bands at high strains, and are more likely to incorporate fossil ocean material in the ice shell and expose it at the surface. In contrast, lithosphere strengthened by rapid fault annealing or increased viscosity, for example, exhibits large-scale tectonic rifting at low strains superimposed over pre-existing terrains, and inhibits the incorporation and delivery of fossil ocean material to the surface. Thus, our results identify a spectrum of extensional terrain formation mechanisms as linked to lithospheric strength, rather than specific mechanisms that are unique to each type of band, and discuss where in this spectrum ocean material incorporated at the bottom of the ice shell may be exposed on the satellite surface.

Long-term patterns of benthic irradiance and kelp production in the central Beaufort sea reveal implications of warming for Arctic inner shelves

NASA Astrophysics Data System (ADS)

Bonsell, Christina; Dunton, Kenneth H.

2018-03-01

This study synthesizes a multidecadal dataset of annual growth of the Arctic endemic kelp Laminaria solidungula and corresponding measurements of in situ benthic irradiance from Stefansson Sound in the central Beaufort Sea. We incorporate long-term data on sea ice concentration (National Sea Ice Data Center) and wind (National Weather Service) to assess how ice extent and summer wind dynamics affect the benthic light environment and annual kelp production. We find evidence of significant changes in sea ice extent in Stefansson Sound, with an extension of the ice-free season by approximately 17 days since 1979. Although kelp elongation at 5-7 m depths varies significantly among sites and years (3.8-49.8 cm yr-1), there is no evidence for increased production with either earlier ice break-up or a longer summer ice-free period. This is explained by very low light transmittance to the benthos during the summer season (mean daily percent surface irradiance ± SD: 1.7 ± 3.6 to 4.5 ± 6.6, depending on depth, with light attenuation values ranging from 0.5 to 0.8 m-1), resulting in minimal potential for kelp production on most days. Additionally, on month-long timescales (35 days) in the ice-free summer, benthic light levels are negatively related to wind speed. The frequent, wind-driven resuspension of sediments following ice break-up significantly reduce light to the seabed, effectively nullifying the benefits of an increased ice-free season on annual kelp growth. Instead, benthic light and primary production may depend substantially on the 1-3 week period surrounding ice break-up when intermediate sea ice concentrations reduce wind-driven sediment resuspension. These results suggest that both benthic and water column primary production along the inner shelf of Arctic marginal seas may decrease, not increase, with reductions in sea ice extent.

Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap

USGS Publications Warehouse

Brown, Adrian J.; Piqueux, Sylvain; Titus, Timothy N.

2014-01-01

The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) ( Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap ( Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a ‘minimum apparent‘ amount of deposition corresponding to a thin H2O ice layer of 0.2 mm (with 70% porosity). This amount of H2O ice deposition is 0.6–6% of the total Martian atmospheric water budget. We compare our ‘minimum apparent’ quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.

Future Interannual Variability of Arctic Sea Ice Area and its Implications for Marine Navigation

NASA Astrophysics Data System (ADS)

Vavrus, S. J.; Mioduszewski, J.; Holland, M. M.; Wang, M.; Landrum, L.

2016-12-01

As both a symbol and driver of ongoing climate change, the diminishing Arctic sea ice pack has been widely studied in a variety of contexts. Most research, however, has focused on time-mean changes in sea ice, rather than on short-term variations that also have important physical and societal consequences. In this study we test the hypothesis that interannual Arctic sea ice variability will increase in the future by utilizing a set of 40 independent simulations from the Community Earth System Model's Large Ensemble for the 1920-2100 period. The model projects that ice variability will indeed grow substantially in all months but with a strong seasonal dependence in magnitude and timing. The variability increases most during late autumn (November-December) and least during spring. This increase proceeds in a time-transgressive manner over the course of the year, peaking soonest (2020s) in late-summer months and latest (2090s) during late spring. The variability in every month is inversely correlated with the average melt rate, resulting in an eventual decline in both terms as the ice pack becomes seasonal by late century. These projected changes in sea ice variations will likely have significant consequences for marine navigation, which we assess with the empirical Ice Numeral (IN) metric. A function of ice concentration and thickness, the IN quantifies the difficulty in traversing a transect of sea ice-covered ocean as a function of vessel strength. Our results show that although increasingly open Arctic seas will mean generally more favorable conditions for navigation, the concurrent rise in the variability of ice cover poses a competing risk. In particular, future intervals featuring the most rapid declines in ice area that coincide with the highest interannual ice variations will offer more inviting shipping opportunities tempered by less predictable navigational conditions.

Extensional terrain formation on Europa and Ganymede: Implications for ocean-surface interaction

NASA Astrophysics Data System (ADS)

Howell, S. M.; Pappalardo, R. T.

2017-12-01

Europa and Ganymede, Galilean satellites of Jupiter, exhibit geologic activity in their outer H2O ice shells that might convey material from water oceans within the satellites to their surfaces. Imagery from the Voyager and Galileo spacecraft reveal surfaces rich with tectonic deformation, including dilational bands on Europa and groove lanes on Ganymede. These features are generally attributed to the extension of a brittle ice lithosphere overlaying a possibly convecting ice asthenosphere. To explore band formation and interaction with interior oceans, we employ fully visco-elasto-plastic 2-D models of faulting and convection with complex, realistic pure ice rheologies. In these models, material entering from below is tracked and considered to be "fossilized ocean," ocean material that has frozen into the ice shell and evolves through geologic time. We track the volume fraction of fossil ocean material in the ice shell as a function of depth, and the exposure of both fresh ice and fossil ocean material at the ice shell surface. We vary ice shell thickness, fault localization, melting-temperature ice viscosity, and the presence of pre-existing weaknesses. Mechanisms which act to weaken the ice shell and thin the lithosphere (e.g. vigorous convection, thinner shells, pre-existing weaknesses) tend to plastically yield to form smooth bands at high strains, and are more likely to incorporate fossil ocean material in the ice shell and expose it at the surface. In contrast, lithosphere strengthened by rapid fault annealing or increased viscosity, for example, exhibits large-scale tectonic rifting at low strains superimposed over pre-existing terrains, and inhibits the incorporation and delivery of fossil ocean material to the surface. Thus, our results identify a spectrum of extensional terrain formation mechanisms as linked to lithospheric strength, rather than any specific mechanism being unique to each type of band, and where in this spectrum ocean material incorporated at the bottom of the ice shell may be exposed on the satellite surface.

Statistical Analyses of High-Resolution Aircraft and Satellite Observations of Sea Ice: Applications for Improving Model Simulations

NASA Astrophysics Data System (ADS)

Farrell, S. L.; Kurtz, N. T.; Richter-Menge, J.; Harbeck, J. P.; Onana, V.

2012-12-01

Satellite-derived estimates of ice thickness and observations of ice extent over the last decade point to a downward trend in the basin-scale ice volume of the Arctic Ocean. This loss has broad-ranging impacts on the regional climate and ecosystems, as well as implications for regional infrastructure, marine navigation, national security, and resource exploration. New observational datasets at small spatial and temporal scales are now required to improve our understanding of physical processes occurring within the ice pack and advance parameterizations in the next generation of numerical sea-ice models. High-resolution airborne and satellite observations of the sea ice are now available at meter-scale resolution or better that provide new details on the properties and morphology of the ice pack across basin scales. For example the NASA IceBridge airborne campaign routinely surveys the sea ice of the Arctic and Southern Oceans with an advanced sensor suite including laser and radar altimeters and digital cameras that together provide high-resolution measurements of sea ice freeboard, thickness, snow depth and lead distribution. Here we present statistical analyses of the ice pack primarily derived from the following IceBridge instruments: the Digital Mapping System (DMS), a nadir-looking, high-resolution digital camera; the Airborne Topographic Mapper, a scanning lidar; and the University of Kansas snow radar, a novel instrument designed to estimate snow depth on sea ice. Together these instruments provide data from which a wide range of sea ice properties may be derived. We provide statistics on lead distribution and spacing, lead width and area, floe size and distance between floes, as well as ridge height, frequency and distribution. The goals of this study are to (i) identify unique statistics that can be used to describe the characteristics of specific ice regions, for example first-year/multi-year ice, diffuse ice edge/consolidated ice pack, and convergent/divergent ice zones, (ii) provide datasets that support enhanced parameterizations in numerical models as well as model initialization and validation, (iii) parameters of interest to Arctic stakeholders for marine navigation and ice engineering studies, and (iv) statistics that support algorithm development for the next-generation of airborne and satellite altimeters, including NASA's ICESat-2 mission. We describe the potential contribution our results can make towards the improvement of coupled ice-ocean numerical models, and discuss how data synthesis and integration with high-resolution models may improve our understanding of sea ice variability and our capabilities in predicting the future state of the ice pack.

Sediments in Arctic sea ice: Implications for entrainment, transport and release

USGS Publications Warehouse

Nurnberg, D.; Wollenburg, I.; Dethleff, D.; Eicken, H.; Kassens, H.; Letzig, T.; Reimnitz, E.; Thiede, Jorn

1994-01-01

Despite the Arctic sea ice cover's recognized sensitivity to environmental change, the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood. Sea ice sediment inclusions were studied in the central Arctic Ocean during the Arctic 91 expedition and in the Laptev Sea (East Siberian Arctic Region Expedition 1992). Results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central Arctic Ocean. This study documents the regional distribution and composition of particle-laden ice, investigates and evaluates processes by which sediment is incorporated into the ice cover, and identifies transport paths and probable depositional centers for the released sediment. In April 1992, sea ice in the Laptev Sea was relatively clean. The sediment occasionally observed was distributed diffusely over the entire ice column, forming turbid ice. Observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment. In the central Arctic Ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes. The surface sediment accumulation in central Arctic multi-year sea ice exceeds by far the amounts observed in first-year ice from the Laptev Sea in April 1992. Sea ice sediments are generally fine grained, although coarse sediments and stones up to 5 cm in diameter are observed. Component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles. The biogenous components, namely shells of pelecypods and benthic foraminiferal tests, point to a shallow, benthic, marine source area. Apparently, sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing. Clay mineralogy of ice-rafted sediments provides information on potential source areas. A smectite maximum in sea ice sediment samples repeatedly occurred between 81??N and 83??N along the Arctic 91 transect, indicating a rather stable and narrow smectite rich ice drift stream of the Transpolar Drift. The smectite concentrations are comparable to those found in both Laptev Sea shelf sediments and anchor ice sediments, pointing to this sea as a potential source area for sea ice sediments. In the central Arctic Ocean sea ice clay mineralogy is significantly different from deep-sea clay mineral distribution patterns. The contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms. ?? 1994.

Boosted dark matter and its implications for the features in IceCube HESE data

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

Bhattacharya, Atri; Gandhi, Raj; Gupta, Aritra

2017-05-01

We study the implications of the premise that any new, relativistic, highly energetic neutral particle that interacts with quarks and gluons would create cascade-like events in the IceCube (IC) detector. Such events would be observationally indistinguishable from neutral current deep-inelastic (DIS) scattering events due to neutrinos. Consequently, one reason for deviations, breaks or excesses in the expected astrophysical power-law neutrino spectrum could be the flux of such a particle. Motivated by features in the recent 1347-day IceCube high energy starting event (HESE) data, we focus on particular boosted dark matter (χ) related realizations of this premise. Here, χ is assumedmore » to be much lighter than, and the result of, the slow decay of a massive scalar (φ ) which constitutes a major fraction of the Universe's dark matter (DM) . We show that this hypothesis, coupled with a standard power-law astrophysical neutrino flux is capable of providing very good fits to the present data, along with a possible explanation of other features in the HESE sample. These features include a) the paucity of events beyond ∼ 2 PeV b) a spectral feature resembling a dip or a spectral change in the 400 TeV–1 PeV region and c) an excess in the 50−100 TeV region. We consider two different boosted DM scenarios, and determine the allowed mass ranges and couplings for four different types of mediators (scalar, pseudoscalar, vector and axial-vector) which could connect the standard and dark sectors.We consider constraints from gamma-ray observations and collider searches. We find that the gamma-ray observations provide the most restrictive constraints, disfavouring the 1σ allowed parameter space from IC fits, while still being consistent with the 3σ allowed region. We also test our proposal and its implications against the (statistically independent) sample of six year through-going muon track data recently released by IceCube.« less

Evidence for stabilization of the ice-cemented cryosphere in earlier martian history: Implications for the current abundance of groundwater at depth on Mars

NASA Astrophysics Data System (ADS)

Weiss, David K.; Head, James W.

2017-05-01

The present-day martian mean annual surface temperature is well below freezing at all latitudes; this produces a near-surface portion of the crust that is below the freezing point of water for > 2 consecutive years (defined as permafrost). This permafrost layer (i.e., the cryosphere) is a few to tens of km thick depending on latitude. Below the base of the permafrost (i.e., the cryosphere), groundwater is stable if it exists, and can increase and decrease in abundance as the freezing isotherm rises and falls. Where water is available, ice fills the pore space within the cryosphere; this region is known as the ice-cemented cryosphere (ICC). The potential for a large reservoir of pore ice beneath the surface has been the subject of much discussion: previous studies have demonstrated that the theoretical thickness of the martian cryosphere in the Amazonian period ranges from up to ∼9 km at the equator to ∼10-22 km at the poles. The total thickness of ice that might fill the pore space within the cryosphere (the ICC), however, remains unknown. A class of martian crater, the Hesperian-Amazonian-aged single-layered ejecta crater, is widely accepted as having formed by impact into an ice-cemented target. Although the target structure related to the larger multiple-layered ejecta craters remains uncertain, they have recently been interpreted to be formed by impact crater excavation below the ice-cemented target, and here we tentatively adopt this interpretation in order to infer the thickness of the ice-cemented cryosphere. Our global examination of the excavation depths of these crater populations points to a Hesperian-Amazonian-aged ice-cemented cryosphere that is ∼1.3 km thick at the equator, and ∼2.3 km thick at the poles (corresponding to a global equivalent water layer of ∼200 m assuming ∼20% pore ice at the surface). To explore the implications of this result on the martian climatic and hydrologic evolution, we then assess the surface temperature, atmospheric pressure, obliquity, and surface heat flux conditions under which the downward-propagating cryosphere freezing front matches the inferred ice-cemented cryosphere. The thermal models which can best reproduce the inferred ice-cemented cryosphere occur for obliquities between 25° and 45° and CO2 atmospheric pressures ≤600 mbar, but require increased heat fluxes and surface temperatures/pressures relative to the Amazonian period. Because the inferred ice-cemented cryosphere is much thinner compared with Amazonian-aged cryosphere thermal models, we suggest that the ice-cemented cryosphere ceased growing when it exhausted the underlying groundwater supply (i.e., ICC stabilization) in a more ancient period in Mars geologic history. Our thermal analysis suggests that this ICC stabilization likely occurred sometime before or at ∼3.0-3.3 Ga (during or before the Late Hesperian or Early Amazonian period). If groundwater remained below the ICC during the earlier Late Noachian period, our models predict that mean annual surface temperatures during this time were ≥212-227 K. If the Late Noachian had a pure CO2 atmosphere, this places a minimum bound on the Late Noachian atmospheric pressure of ≥390-850 mbar. These models suggest that deep groundwater is not abundant or does not persist in the subsurface of Mars today, and that diffusive loss of ice from the subsurface has been minimal.

Visible and near-infrared reflectance spectroscopy of planetary analog materials. Experimental facility at Laboratoire de Planetologie de Grenoble.

NASA Astrophysics Data System (ADS)

Pommerol, A.; Brissaud, O.; Schmitt, B.; Quirico, E.; Doute, S.

2007-08-01

We have developed an original experimental facility designed to measure the bidirectional reflectance spectra of planetary analog materials. These measurements are helpful to interpret the observations of the spectrometers on board space probes in orbit around various Solar System bodies. The central part of the facility is the LPG spectrogonio- radiometer (Brissaud et al., 2004). This instrument provides measurements of samples BRDF (Bidirectional Reflectance Distribution Function) with high photometric and spectrometric accuracy in the spectral range of visible and near-infrared (0.3 - 4.8 microns). Measurements can be made at any value of incidence and emergence angle up to 80°. Azimuth angle is allowed to vary between 0 and 180°. The instrument was recently installed in a cold room allowing ambient temperatures as low as -20°C. This makes possible the measurements on different kinds of water ice samples (slab ice, frost, snow...) and mixtures of minerals and water ice with unprecedented accuracy. We also have designed and built a simulation chamber to measure spectra of samples (water ice and/or minerals) under an atmosphere with perfectly controlled temperature, pressure and composition. The main objective of this last improvement is the study of water exchange between planetary regolith analogs and atmosphere (adsorption/ desorption, condensation/sublimation). Experimental results will mainly apply to Martian water cycle and hydrated mineralogy. This simulation chamber also provides an efficient way to obtain bidirectional reflectance spectra of dry materials (removal of adsorbed water) with implications for planetary bodies without atmospheric or surface water (Titan, asteroids...). The reflectance spectroscopy facility is part of a large panel of instruments and techniques available at Laboratoire de Planetologie de Grenoble that provide complementary measurements on the same samples: infrared transmission spectroscopy of thin ice films, thick liquid and solid samples and samples diluted in KBr pellets, infrared imaging microscope, numerical modeling of bidirectional reflectance spectra using laboratory-measured optical constants. We will present different examples of experimental results obtained on the reflectance spectroscopy facility: - Effects of particle size, mixtures between samples with different albedo and measurement geometries on the water-of-hydration near-infrared absorption signatures with implications for the Martian regolith water content. - BRDF of regolith analogs and natural snow. - Hydration and dehydration of planetary analogs. - Spectra of different kinds of mixtures between water ice and minerals. We will briefly discuss the planetary implications of each of these measurements and detail the future investigations that will be undertaken on our experimental facility.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Khain, A.; Simpson, S.; Johnson, D.; Li, X.; Remer, L.

2003-01-01

Cloud microphysics are inevitable affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distribution parameterized as spectral bin microphysics are needed to explicitly study the effect of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensembel (GCE) model. The formulation for the explicit spectral-bim microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e., pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), groupel and frozen drops/hall] Each type is described by a special size distribution function containing many categories (i.e., 33 bins). Atmospheric aerosols are also described using number density size-distribution functions.A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region and in the mid-latitude using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Besides the initial differences in aerosol concentration, preliminary results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CCN case but has less cloud water mass aloft. Because the spectral-bim model explicitly calculates and allows for the examination of both the mass and number concentration of cpecies in each size category, a detailed analysis of the instantaneous size spectrum can be obtained for the two cases. It is shown that since the low CCN case produces fever droplets, larger size develop due to greater condencational and collectional growth, leading to a broader size spectrum in comparison to the high CCN case.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Khain, A.; Simpson, S.; Johnson, D.; Li, X.; Remer, L.

2003-01-01

Cloud microphysics are inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e.,pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions.A spectral-bin microphysical model is very expensive from a from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Besides the initial differences in aerosol concentration, preliminary results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CCN case but has less cloud water mass aloft. Because the spectral-bin model explicitly calculates and allows for the examination of both the mass and number concentration of species in each size categor, a detailed analysis of the instantaneous size spectrum can be obtained for the two cases. It is shown that since the low CCN case produces fewer droplets, larger sized develop due to the greater condensational and collectional growth, leading to a broader size spectrum in comparison to the high CCN case.

H{sub 2} MOLECULAR CLUSTERS WITH EMBEDDED MOLECULES AND ATOMS AS THE SOURCE OF THE DIFFUSE INTERSTELLAR BANDS

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

Bernstein, L. S.; Clark, F. O.; Lynch, D. K., E-mail: larry@spectral.com, E-mail: dave@thulescientific.com

2013-05-01

We suggest that the diffuse interstellar bands (DIBs) arise from absorption lines of electronic transitions in molecular clusters primarily composed of a single molecule, atom, or ion ({sup s}eed{sup )}, embedded in a single-layer shell of H{sub 2} molecules. Less abundant variants of the cluster, including two seed molecules and/or a two-layer shell of H{sub 2} molecules, may also occur. The lines are broadened, blended, and wavelength-shifted by interactions between the seed and surrounding H{sub 2} shell. We refer to these clusters as contaminated H{sub 2} clusters (CHCs). We show that CHC spectroscopy matches the diversity of observed DIB spectralmore » profiles and provides good fits to several DIB profiles based on a rotational temperature of 10 K. CHCs arise from {approx}centimeter-sized, dirty H{sub 2} ice balls, called contaminated H{sub 2} ice macro-particles (CHIMPs), formed in cold, dense, giant molecular clouds (GMCs), and later released into the interstellar medium (ISM) upon GMC disruption. Attractive interactions, arising from Van der Waals and ion-induced dipole potentials, between the seeds and H{sub 2} molecules enable CHIMPs to attain centimeter-sized dimensions. When an ultraviolet (UV) photon is absorbed in the outer layer of a CHIMP, it heats the icy matrix and expels CHCs into the ISM. While CHCs are quickly destroyed by absorbing UV photons, they are replenished by the slowly eroding CHIMPs. Since CHCs require UV photons for their release, they are most abundant at, but not limited to, the edges of UV-opaque molecular clouds, consistent with the observed, preferred location of DIBs. An inherent property of CHCs, which can be characterized as nanometer size, spinning, dipolar dust grains, is that they emit in the radio-frequency region. We also show that the CHCs offer a natural explanation for the anomalous microwave emission feature in the {approx}10-100 GHz spectral region.« less

Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implications

NASA Astrophysics Data System (ADS)

Wendt, Jens; Dietrich, Reinhard; Fritsche, Mathias; Wendt, Anja; Yuskevich, Alexander; Kokhanov, Andrey; Senatorov, Anton; Lukin, Valery; Shibuya, Kazuo; Doi, Koichiro

2006-09-01

In the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed. The derived ice flow velocity for Vostok Station is 2.00ma-1 +/- 0.01ma-1. Along the flowline of Vostok Station an extension rate of about 10-5a-1 (equivalent to 1cm km-1 a-1) was determined. This significant velocity gradient results in a new estimate of 28700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4mma-1 along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years.

Analysis of ERS 1 synthetic aperture radar data of frozen lakes in northern Montana and implications for climate studies

USGS Publications Warehouse

Hall, Dorothy K.; Fagre, Daniel B.; Klasner, Fritz; Linebaugh, Gregg; Liston, Glen E.

1994-01-01

Lakes that freeze each winter are good indicators of regional climate change if key parameters, such as freeze-up and breakup date and maximum ice thickness, are measured over a decade-scale time frame. Synthetic aperture radar (SAR) satellite data have proven to be especially useful for measurement of climatologically significant parameters characteristic of frozen lakes. In this paper, five lakes in Glacier National Park, Montana, have been studied both in the field and using Earth Remote-Sensing Satellite (ERS) 1 SAR data during the 1992-1993 winter. The lakes are characterized by clear ice, sometimes with tubular or rounded bubbles, and often with a layer of snow ice on top of the clear ice. They are also often snow covered. Freeze-up is detected quite easily using ERS 1 SAR data as soon as a thin layer of ice forms. The effect of snow ice on the backscatter is thought to be significant but is, as yet, undetermined. On the five lakes studied, relative backscatter was found to increase with ice thickness until a maximum was reached in February. Breakup, an often ill-defined occurrence, is difficult to detect because surface water causes the SAR signal to be absorbed, thus masking the ice below. Comparison of the bubble structure of thaw lakes in northern Alaska with lakes in northern Montana has shown that the ice structure is quite different, and this difference may contribute to differential SAR signature evolution in the lakes of the two areas.

Implications of basal micro-earthquakes and tremor for ice stream mechanics: Stick-slip basal sliding and till erosion

NASA Astrophysics Data System (ADS)

Barcheck, C. Grace; Tulaczyk, Slawek; Schwartz, Susan Y.; Walter, Jacob I.; Winberry, J. Paul

2018-03-01

The Whillans Ice Plain (WIP) is unique among Antarctic ice streams because it moves by stick-slip. The conditions allowing stick-slip and its importance in controlling ice dynamics remain uncertain. Local basal seismicity previously observed during unstable slip is a clue to the mechanism of ice stream stick-slip and a window into current basal conditions, but the spatial extent and importance of this basal seismicity are unknown. We analyze data from a 2010-2011 ice-plain-wide seismic and GPS network to show that basal micro-seismicity correlates with large-scale patterns in ice stream slip behavior: Basal seismicity is common where the ice moves the least between unstable slip events, with small discrete basal micro-earthquakes happening within 10s of km of the central stick-slip nucleation area and emergent basal tremor occurring downstream of this area. Basal seismicity is largely absent in surrounding areas, where inter-slip creep rates are high. The large seismically active area suggests that a frictional sliding law that can accommodate stick-slip may be appropriate for ice stream beds on regional scales. Variability in seismic behavior over inter-station distances of 1-10 km indicates heterogeneity in local bed conditions and frictional complexity. WIP unstable slips may nucleate when stick-slip basal earthquake patches fail over a large area. We present a conceptual model in which basal seismicity results from slip-weakening frictional failure of over-consolidated till as it is eroded and mobilized into deforming till.

Snow depth of the Weddell and Bellingshausen sea ice covers from IceBridge surveys in 2010 and 2011: An examination

NASA Astrophysics Data System (ADS)

Kwok, R.; Maksym, T.

2014-07-01

We examine the snow radar data from the Weddell and Bellingshausen Seas acquired by eight IceBridge (OIB) flightlines in October of 2010 and 2011. In snow depth retrieval, the sidelobes from the stronger scattering snow-ice (s-i) interfaces could be misidentified as returns from the weaker air-snow (a-s) interfaces. In this paper, we first introduce a retrieval procedure that accounts for the structure of the radar system impulse response followed by a survey of the snow depths in the Weddell and Bellingshausen Seas. Limitations and potential biases in our approach are discussed. Differences between snow depth estimates from a repeat survey of one Weddell Sea track separated by 12 days, without accounting for variability due to ice motion, is -0.7 ± 13.6 cm. Average snow depth is thicker in coastal northwestern Weddell and thins toward Cape Norvegia, a decrease of >30 cm. In the Bellingshausen, the thickest snow is found nearshore in both Octobers and is thickest next to the Abbot Ice Shelf. Snow depth is linearly related to freeboard when freeboards are low but diverge as the freeboard increases especially in the thicker/rougher ice of the western Weddell. We find correlations of 0.71-0.84 between snow depth and surface roughness suggesting preferential accumulation over deformed ice. Retrievals also seem to be related to radar backscatter through surface roughness. Snow depths reported here, generally higher than those from in situ records, suggest dissimilarities in sample populations. Implications of these differences on Antarctic sea ice thickness are discussed.

Crystal Structure of an Insect Antifreeze Protein and Its Implications for Ice Binding*

PubMed Central

Hakim, Aaron; Nguyen, Jennifer B.; Basu, Koli; Zhu, Darren F.; Thakral, Durga; Davies, Peter L.; Isaacs, Farren J.; Modis, Yorgo; Meng, Wuyi

2013-01-01

Antifreeze proteins (AFPs) help some organisms resist freezing by binding to ice crystals and inhibiting their growth. The molecular basis for how these proteins recognize and bind ice is not well understood. The longhorn beetle Rhagium inquisitor can supercool to below −25 °C, in part by synthesizing the most potent antifreeze protein studied thus far (RiAFP). We report the crystal structure of the 13-kDa RiAFP, determined at 1.21 Å resolution using direct methods. The structure, which contains 1,914 nonhydrogen protein atoms in the asymmetric unit, is the largest determined ab initio without heavy atoms. It reveals a compressed β-solenoid fold in which the top and bottom sheets are held together by a silk-like interdigitation of short side chains. RiAFP is perhaps the most regular structure yet observed. It is a second independently evolved AFP type in beetles. The two beetle AFPs have in common an extremely flat ice-binding surface comprising regular outward-projecting parallel arrays of threonine residues. The more active, wider RiAFP has four (rather than two) of these arrays between which the crystal structure shows the presence of ice-like waters. Molecular dynamics simulations independently reproduce the locations of these ordered crystallographic waters and predict additional waters that together provide an extensive view of the AFP interaction with ice. By matching several planes of hexagonal ice, these waters may help freeze the AFP to the ice surface, thus providing the molecular basis of ice binding. PMID:23486477

Surface-atmosphere decoupling limits accumulation at Summit, Greenland.

PubMed

Berkelhammer, Max; Noone, David C; Steen-Larsen, Hans Christian; Bailey, Adriana; Cox, Christopher J; O'Neill, Michael S; Schneider, David; Steffen, Konrad; White, James W C

2016-04-01

Despite rapid melting in the coastal regions of the Greenland Ice Sheet, a significant area (~40%) of the ice sheet rarely experiences surface melting. In these regions, the controls on annual accumulation are poorly constrained owing to surface conditions (for example, surface clouds, blowing snow, and surface inversions), which render moisture flux estimates from myriad approaches (that is, eddy covariance, remote sensing, and direct observations) highly uncertain. Accumulation is partially determined by the temperature dependence of saturation vapor pressure, which influences the maximum humidity of air parcels reaching the ice sheet interior. However, independent proxies for surface temperature and accumulation from ice cores show that the response of accumulation to temperature is variable and not generally consistent with a purely thermodynamic control. Using three years of stable water vapor isotope profiles from a high altitude site on the Greenland Ice Sheet, we show that as the boundary layer becomes increasingly stable, a decoupling between the ice sheet and atmosphere occurs. The limited interaction between the ice sheet surface and free tropospheric air reduces the capacity for surface condensation to achieve the rate set by the humidity of the air parcels reaching interior Greenland. The isolation of the surface also acts to recycle sublimated moisture by recondensing it onto fog particles, which returns the moisture back to the surface through gravitational settling. The observations highlight a unique mechanism by which ice sheet mass is conserved, which has implications for understanding both past and future changes in accumulation rate and the isotopic signal in ice cores from Greenland.

Spatiotemporal Variability of Meltwater Refreezing in Southwest Greenland Ice Sheet Firn

NASA Astrophysics Data System (ADS)

Rennermalm, A. K.; Hock, R.; Tedesco, M.; Corti, G.; Covi, F.; Miège, C.; Kingslake, J.; Leidman, S. Z.; Munsell, S.

2017-12-01

A substantial fraction of the summer meltwater formed on the surface of the Greenland ice sheet is retained in firn, while the remaining portion runs to the ocean through surface and subsurface channels. Refreezing of meltwater in firn can create impenetrable ice lenses, hence being a crucial process in the redistribution of surface runoff. To quantify the impact of refreezing on runoff and current and future Greenland surface mass balance, a three year National Science Foundation funded project titled "Refreezing in the firn of the Greenland ice sheet: Spatiotemporal variability and implications for ice sheet mass balance" started this past year. Here we present an overview of the project and some initial results from the first field season in May 2017 conducted in proximity of the DYE-2 site in the percolation zone of the Southwest Greenland ice sheet at elevations between 1963 and 2355 m a.s.l.. During this fieldwork two automatic weather stations were deployed, outfitted with surface energy balance sensors and 16 m long thermistor strings, over 300 km of ground penetrating radar data were collected, and five 20-26 m deep firn cores were extracted and analyzed for density and stratigraphy. Winter snow accumulation was measured along the radar tracks. Preliminary work on the firn-core data reveals increasing frequency and thickness of ice lenses at lower ice-sheet elevations, in agreement with other recent work in the area. Data collected within this project will facilitate advances in our understanding of the spatiotemporal variability of firn refreezing and its role in the hydrology and surface mass balance of the Greenland Ice Sheet.

Surface-atmosphere decoupling limits accumulation at Summit, Greenland

PubMed Central

Berkelhammer, Max; Noone, David C.; Steen-Larsen, Hans Christian; Bailey, Adriana; Cox, Christopher J.; O’Neill, Michael S.; Schneider, David; Steffen, Konrad; White, James W. C.

2016-01-01

Despite rapid melting in the coastal regions of the Greenland Ice Sheet, a significant area (~40%) of the ice sheet rarely experiences surface melting. In these regions, the controls on annual accumulation are poorly constrained owing to surface conditions (for example, surface clouds, blowing snow, and surface inversions), which render moisture flux estimates from myriad approaches (that is, eddy covariance, remote sensing, and direct observations) highly uncertain. Accumulation is partially determined by the temperature dependence of saturation vapor pressure, which influences the maximum humidity of air parcels reaching the ice sheet interior. However, independent proxies for surface temperature and accumulation from ice cores show that the response of accumulation to temperature is variable and not generally consistent with a purely thermodynamic control. Using three years of stable water vapor isotope profiles from a high altitude site on the Greenland Ice Sheet, we show that as the boundary layer becomes increasingly stable, a decoupling between the ice sheet and atmosphere occurs. The limited interaction between the ice sheet surface and free tropospheric air reduces the capacity for surface condensation to achieve the rate set by the humidity of the air parcels reaching interior Greenland. The isolation of the surface also acts to recycle sublimated moisture by recondensing it onto fog particles, which returns the moisture back to the surface through gravitational settling. The observations highlight a unique mechanism by which ice sheet mass is conserved, which has implications for understanding both past and future changes in accumulation rate and the isotopic signal in ice cores from Greenland. PMID:27386509

Does modifying personal responsibility moderate the mental contamination effect?

PubMed

Kennedy, Tinisha S; Simonds, Laura M

2017-12-01

Mental contamination is the psychological sense of internal dirtiness that arises in the absence of physical contact with a perceived contaminant. Mental contamination can be evoked through imagining perpetrating a moral transgression. This study experimentally evoked mental contamination by asking men to imagine perpetrating a non-consensual kiss. It explored whether reducing sense of personal responsibility for the kiss moderated the mental contamination effect. Male students (N = 60) imagined giving either a consensual or non-consensual kiss. Personal responsibility for the kiss was manipulated in one of two non-consensual kiss conditions by way of the inclusion of social influence information. Feelings of mental contamination were assessed by self-report and through a behavioural index. Mental contamination was successfully induced in the two non-consensual kiss conditions. There was evidence to support the hypothesis that reducing personal responsibility might moderate specific components of mental contamination (shame, dirtiness and urge to cleanse). The effect of responsibility modification was evident in the self-report measures, but not in the behavioural index. The sample comprised male university students which limits generalizability of the findings. The behavioural assessment of mental contamination was limited to a proxy measure. Imagined moral violations are associated with increases in indices of mental contamination. Further research should investigate whether feelings of shame, dirtiness and urge to cleanse are particularly responsive to responsibility modifications. Copyright © 2017 Elsevier Ltd. All rights reserved.

Mid-Wisconsin Laurentide Ice Sheet growth and decay: Implications for Heinrich events 3 and 4

NASA Astrophysics Data System (ADS)

Kirby, Matthew E.; Andrews, John T.

1999-04-01

A close look at the sedimentology of Heinrich event 4 from the northwest Labrador Sea indicates that an extended ice margin, perhaps greater than before Heinrich events 1 or 2 (H-1 and H-2), existed in the Hudson Strait region pre-Heinrich event 4 (H-4) and, that on the basis of characteristics of the sediment unit, Heinrich event-4 was different than Heinrich events 1 or 2 (i.e., larger ice sheet collapse(?), longer duration(?), "dirtier" icebergs(?)). Other data from across the southern and eastern margin of the Laurentide Ice Sheet, as well as Greenland and the North Atlantic, support this interpretation, possibly indicating a relative mid-Wisconsin glacial maximum pre-Heinrich event 4. Many of these data also indicate that Heinrich event 4 (35 ka) resulted in serious climatic and oceanographic reorganizations. We suggest that Heinrich event 4 gutted the Hudson Strait, leaving it devoid of ice for Heinrich event 3. We further hypothesize that Heinrich event 3 did not originate from axial ice transport along the Hudson Strait; thus Heinrich event 3 may be more analogous to the proposed northward advancing ice from Ungava Bay during Heinrich event 0 than to the more typical down-the-strait flow during H-1, H-2, and H-4. Consequently, the climatic and oceanographic impacts resulting from Heinrich events are highly susceptible to the type, origin, and magnitude of ice sheet collapse, something which varied per Heinrich event during the last glacial period.

Correspondence between North Pacific Ocean ventilation, Cordilleran Ice Sheet variations, and North Atlantic Heinrich Events

NASA Astrophysics Data System (ADS)

Walczak, M. H.; Mix, A.; Fallon, S.; Praetorius, S. K.; Cowan, E. A.; Du, J.; Hobern, T.; Padman, J.; Fifield, L. K.; Stoner, J. S.; Haley, B. A.

2017-12-01

Much remains unresolved concerning the origin and global implications of the episodes of rapid glacial failure in the North Atlantic known as Heinrich Events. Thought to occur during or at the termination of the coldest of the abrupt stadial climate events known as Dansgaard-Oschger cycles, various trigger mechanisms have been theorized, including external forcing in the form of oceanic or atmospheric warming, internal dynamics of the large Laurentide ice sheet, or the episodic failure of another (presumably European) ice sheet. Heinrich events may also be associated with a decrease in North Atlantic deep-water formation. New results from Gulf of Alaska IODP Expedition 341 reveal events of Cordilleran Ice Sheet retreat (based on ice-rafted detritus and sedimentation rates) synchronous with reorganization of ocean circulation (based on benthic-planktic 14C pairs) spanning the past 45,000 years on an independent high-resolution radiocarbon-based chronology. We document the relationship between these Pacific records and the North Atlantic Heinrich events, and find the data show an early Pacific expression of ice sheet instability in the form of pulses of Cordilleran glacial discharge. The benthic radiocarbon anomalies in the Northeast Pacific contemporaneous with Cordilleran discharge events indicate a close coupling of ice-ocean dynamics throughout Marine Isotope Stage 2. These data are hard to reconcile with triggering in the North Atlantic or internal to the Laurentide ice sheet, requiring us to re-think both the mechanisms that generate Heinrich events and their far-field impacts.

A Climate-Data Record (CDR) of the "Clear-Sky" Surface Temperature of the Greenland Ice Sheet

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.; Comiso, Josefino C.; DiGirolamo, Nocolo E.; Shuman, Christopher A.

2011-01-01

We have developed a climate-data record (CDR) of "clear-sky" ice-surface temperature (IST) of the Greenland Ice Sheet using Moderate-Resolution Imaging Spectroradiometer (MODIS) data. The CDR provides daily and monthly-mean IST from March 2000 through December 2010 on a polar stereographic projection at a resolution of 6.25 km. The CDR is amenable to extension into the future using Visible/Infrared Imager Radiometer Suite (VIIRS) data. Regional "clear-sky" surface temperature increases since the early 1980s in the Arctic, measured using Advanced Very High Resolution Radiometer (AVHRR) infrared data, range from 0.57 +/- 0.02 to 0.72 +/- 0.1 c per decade. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near O C during the melt season, and is thus vulnerable to rapid melting if temperatures continue to increase. An increase in melting of the ice sheet would accelerate sea-level rise, an issue affecting potentially billions of people worldwide. The IST CDR will provide a convenient data set for modelers and for climatologists to track changes of the surface temperature of the ice sheet as a whole and of the individual drainage basins on the ice sheet. The daily and monthly maps will provide information on surface melt as well as "clear-sky" temperature. The CDR will be further validated by comparing results with automatic-weather station data and with satellite-derived surface-temperature products.

The Influence of Arctic Sea Ice Extent on Polar Cloud Fraction and Vertical Structure and Implications for Regional Climate

NASA Technical Reports Server (NTRS)

Palm, Stephen P.; Strey, Sara T.; Spinhirne, James; Markus, Thorsten

2010-01-01

Recent satellite lidar measurements of cloud properties spanning a period of five years are used to examine a possible connection between Arctic sea ice amount and polar cloud fraction and vertical distribution. We find an anti-correlation between sea ice extent and cloud fraction with maximum cloudiness occurring over areas with little or no sea ice. We also find that over ice free regions, there is greater low cloud frequency and average optical depth. Most of the optical depth increase is due to the presence of geometrically thicker clouds over water. In addition, our analysis indicates that over the last 5 years, October and March average polar cloud fraction has increased by about 7 and 10 percent, respectively, as year average sea ice extent has decreased by 5 to 7 percent. The observed cloud changes are likely due to a number of effects including, but not limited to, the observed decrease in sea ice extent and thickness. Increasing cloud amount and changes in vertical distribution and optical properties have the potential to affect the radiative balance of the Arctic region by decreasing both the upwelling terrestrial longwave radiation and the downward shortwave solar radiation. Since longwave radiation dominates in the long polar winter, the overall effect of increasing low cloud cover is likely a warming of the Arctic and thus a positive climate feedback, possibly accelerating the melting of Arctic sea ice.

Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments.

PubMed

La Farge, Catherine; Williams, Krista H; England, John H

2013-06-11

Across the Canadian Arctic Archipelago, widespread ice retreat during the 20th century has sharply accelerated since 2004. In Sverdrup Pass, central Ellesmere Island, rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550-1850 AD). The exhumed bryophyte assemblages have exceptional structural integrity (i.e., setae, stem structures, leaf hair points) and have remarkable species richness (60 of 144 extant taxa in Sverdrup Pass). Although the populations are often discolored (blackened), some have developed green stem apices or lateral branches suggesting in vivo regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were collected for in vitro growth experiments. Our results include a unique successful regeneration of subglacial bryophytes following 400 y of ice entombment. This finding demonstrates the totipotent capacity of bryophytes, the ability of a cell to dedifferentiate into a meristematic state (analogous to stem cells) and develop a new plant. In polar ecosystems, regrowth of bryophyte tissue buried by ice for 400 y significantly expands our understanding of their role in recolonization of polar landscapes (past or present). Regeneration of subglacial bryophytes broadens the concept of Ice Age refugia, traditionally confined to survival of land plants to sites above and beyond glacier margins. Our results emphasize the unrecognized resilience of bryophytes, which are commonly overlooked vis-a-vis their contribution to the establishment, colonization, and maintenance of polar terrestrial ecosystems.

Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments

PubMed Central

La Farge, Catherine; Williams, Krista H.; England, John H.

2013-01-01

Across the Canadian Arctic Archipelago, widespread ice retreat during the 20th century has sharply accelerated since 2004. In Sverdrup Pass, central Ellesmere Island, rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550–1850 AD). The exhumed bryophyte assemblages have exceptional structural integrity (i.e., setae, stem structures, leaf hair points) and have remarkable species richness (60 of 144 extant taxa in Sverdrup Pass). Although the populations are often discolored (blackened), some have developed green stem apices or lateral branches suggesting in vivo regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were collected for in vitro growth experiments. Our results include a unique successful regeneration of subglacial bryophytes following 400 y of ice entombment. This finding demonstrates the totipotent capacity of bryophytes, the ability of a cell to dedifferentiate into a meristematic state (analogous to stem cells) and develop a new plant. In polar ecosystems, regrowth of bryophyte tissue buried by ice for 400 y significantly expands our understanding of their role in recolonization of polar landscapes (past or present). Regeneration of subglacial bryophytes broadens the concept of Ice Age refugia, traditionally confined to survival of land plants to sites above and beyond glacier margins. Our results emphasize the unrecognized resilience of bryophytes, which are commonly overlooked vis-a-vis their contribution to the establishment, colonization, and maintenance of polar terrestrial ecosystems. PMID:23716658

Single-scattering properties of ice particles in the microwave regime: Temperature effect on the ice refractive index with implications in remote sensing

NASA Astrophysics Data System (ADS)

Ding, Jiachen; Bi, Lei; Yang, Ping; Kattawar, George W.; Weng, Fuzhong; Liu, Quanhua; Greenwald, Thomas

2017-03-01

An ice crystal single-scattering property database is developed in the microwave spectral region (1 to 874 GHz) to provide the scattering, absorption, and polarization properties of 12 ice crystal habits (10-plate aggregate, 5-plate aggregate, 8-column aggregate, solid hexagonal column, hollow hexagonal column, hexagonal plate, solid bullet rosette, hollow bullet rosette, droxtal, oblate spheroid, prolate spheroid, and sphere) with particle maximum dimensions from 2 μm to 10 mm. For each habit, four temperatures (160, 200, 230, and 270 K) are selected to account for temperature dependence of the ice refractive index. The microphysical and scattering properties include projected area, volume, extinction efficiency, single-scattering albedo, asymmetry factor, and six independent nonzero phase matrix elements (i.e. P11, P12, P22, P33, P43 and P44). The scattering properties are computed by the Invariant Imbedding T-Matrix (II-TM) method and the Improved Geometric Optics Method (IGOM). The computation results show that the temperature dependence of the ice single-scattering properties in the microwave region is significant, particularly at high frequencies. Potential active and passive remote sensing applications of the database are illustrated through radar reflectivity and radiative transfer calculations. For cloud radar applications, ignoring temperature dependence has little effect on ice water content measurements. For passive microwave remote sensing, ignoring temperature dependence may lead to brightness temperature biases up to 5 K in the case of a large ice water path.

Cloud chamber experiments on the origin of ice crystal complexity in cirrus clouds

NASA Astrophysics Data System (ADS)

Schnaiter, Martin; Järvinen, Emma; Vochezer, Paul; Abdelmonem, Ahmed; Wagner, Robert; Jourdan, Olivier; Mioche, Guillaume; Shcherbakov, Valery N.; Schmitt, Carl G.; Tricoli, Ugo; Ulanowski, Zbigniew; Heymsfield, Andrew J.

2016-04-01

This study reports on the origin of small-scale ice crystal complexity and its influence on the angular light scattering properties of cirrus clouds. Cloud simulation experiments were conducted at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber of the Karlsruhe Institute of Technology (KIT). A new experimental procedure was applied to grow and sublimate ice particles at defined super- and subsaturated ice conditions and for temperatures in the -40 to -60 °C range. The experiments were performed for ice clouds generated via homogeneous and heterogeneous initial nucleation. Small-scale ice crystal complexity was deduced from measurements of spatially resolved single particle light scattering patterns by the latest version of the Small Ice Detector (SID-3). It was found that a high crystal complexity dominates the microphysics of the simulated clouds and the degree of this complexity is dependent on the available water vapor during the crystal growth. Indications were found that the small-scale crystal complexity is influenced by unfrozen H2SO4 / H2O residuals in the case of homogeneous initial ice nucleation. Angular light scattering functions of the simulated ice clouds were measured by the two currently available airborne polar nephelometers: the polar nephelometer (PN) probe of Laboratoire de Métérologie et Physique (LaMP) and the Particle Habit Imaging and Polar Scattering (PHIPS-HALO) probe of KIT. The measured scattering functions are featureless and flat in the side and backward scattering directions. It was found that these functions have a rather low sensitivity to the small-scale crystal complexity for ice clouds that were grown under typical atmospheric conditions. These results have implications for the microphysical properties of cirrus clouds and for the radiative transfer through these clouds.

Effects of ice and floods on vegetation in streams in cold regions: implications for climate change

PubMed Central

Lind, Lovisa; Nilsson, Christer; Weber, Christine

2014-01-01

Riparian zones support some of the most dynamic and species-rich plant communities in cold regions. A common conception among plant ecologists is that flooding during the season when plants are dormant generally has little effect on the survival and production of riparian vegetation. We show that winter floods may also be of fundamental importance for the composition of riverine vegetation. We investigated the effects of ice formation on riparian and in-stream vegetation in northern Sweden using a combination of experiments and observations in 25 reaches, spanning a gradient from ice-free to ice-rich reaches. The ice-rich reaches were characterized by high production of frazil and anchor ice. In a couple of experiments, we exposed riparian vegetation to experimentally induced winter flooding, which reduced the dominant dwarf-shrub cover and led to colonization of a species-rich forb-dominated vegetation. In another experiment, natural winter floods caused by anchor-ice formation removed plant mimics both in the in-stream and in the riparian zone, further supporting the result that anchor ice maintains dynamic plant communities. With a warmer winter climate, ice-induced winter floods may first increase in frequency because of more frequent shifts between freezing and thawing during winter, but further warming and shortening of the winter might make them less common than today. If ice-induced winter floods become reduced in number because of a warming climate, an important disturbance agent for riparian and in-stream vegetation will be removed, leading to reduced species richness in streams and rivers in cold regions. Given that such regions are expected to have more plant species in the future because of immigration from the south, the distribution of species richness among habitats can be expected to show novel patterns. PMID:25505542

Effects of ice and floods on vegetation in streams in cold regions: implications for climate change.

PubMed

Lind, Lovisa; Nilsson, Christer; Weber, Christine

2014-11-01

Riparian zones support some of the most dynamic and species-rich plant communities in cold regions. A common conception among plant ecologists is that flooding during the season when plants are dormant generally has little effect on the survival and production of riparian vegetation. We show that winter floods may also be of fundamental importance for the composition of riverine vegetation. We investigated the effects of ice formation on riparian and in-stream vegetation in northern Sweden using a combination of experiments and observations in 25 reaches, spanning a gradient from ice-free to ice-rich reaches. The ice-rich reaches were characterized by high production of frazil and anchor ice. In a couple of experiments, we exposed riparian vegetation to experimentally induced winter flooding, which reduced the dominant dwarf-shrub cover and led to colonization of a species-rich forb-dominated vegetation. In another experiment, natural winter floods caused by anchor-ice formation removed plant mimics both in the in-stream and in the riparian zone, further supporting the result that anchor ice maintains dynamic plant communities. With a warmer winter climate, ice-induced winter floods may first increase in frequency because of more frequent shifts between freezing and thawing during winter, but further warming and shortening of the winter might make them less common than today. If ice-induced winter floods become reduced in number because of a warming climate, an important disturbance agent for riparian and in-stream vegetation will be removed, leading to reduced species richness in streams and rivers in cold regions. Given that such regions are expected to have more plant species in the future because of immigration from the south, the distribution of species richness among habitats can be expected to show novel patterns.

Bacterial Ice Nucleation in Monodisperse D2O and H2O-in-Oil Emulsions.

PubMed

Weng, Lindong; Tessier, Shannon N; Smith, Kyle; Edd, Jon F; Stott, Shannon L; Toner, Mehmet

2016-09-13

Ice nucleation is of fundamental significance in many areas, including atmospheric science, food technology, and cryobiology. In this study, we investigated the ice-nucleation characteristics of picoliter-sized drops consisting of different D2O and H2O mixtures with and without the ice-nucleating bacteria Pseudomonas syringae. We also studied the effects of commonly used cryoprotectants such as ethylene glycol, propylene glycol, and trehalose on the nucleation characteristics of D2O and H2O mixtures. The results show that the median freezing temperature of the suspension containing 1 mg/mL of a lyophilized preparation of P. syringae is as high as -4.6 °C for 100% D2O, compared to -8.9 °C for 100% H2O. As the D2O concentration increases every 25% (v/v), the profile of the ice-nucleation kinetics of D2O + H2O mixtures containing 1 mg/mL Snomax shifts by about 1 °C, suggesting an ideal mixing behavior of D2O and H2O. Furthermore, all of the cryoprotectants investigated in this study are found to depress the freezing phenomenon. Both the homogeneous and heterogeneous freezing temperatures of these aqueous solutions depend on the water activity and are independent of the nature of the solute. These findings enrich our fundamental knowledge of D2O-related ice nucleation and suggest that the combination of D2O and ice-nucleating agents could be a potential self-ice-nucleating formulation. The implications of self-nucleation include a higher, precisely controlled ice seeding temperature for slow freezing that would significantly improve the viability of many ice-assisted cryopreservation protocols.

Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

DOE PAGES

de la Peña, S.; Howat, I. M.; Nienow, P. W.; ...

2015-06-11

Atmospheric warming over the Greenland Ice Sheet during the last 2 decades has increased the amount of surface meltwater production, resulting in the migration of melt and percolation regimes to higher altitudes and an increase in the amount of ice content from refrozen meltwater found in the firn above the superimposed ice zone. Here we present field and airborne radar observations of buried ice layers within the near-surface (0–20 m) firn in western Greenland, obtained from campaigns between 1998 and 2014. We find a sharp increase in firn-ice content in the form of thick widespread layers in the percolation zone,more » which decreases the capacity of the firn to store meltwater. The estimated total annual ice content retained in the near-surface firn in areas with positive surface mass balance west of the ice divide in Greenland reached a maximum of 74 ± 25 Gt in 2012, when compared to the 1958–1999 average of 13 ± 2 Gt, while the percolation zone area more than doubled between 2003 and 2012. Increased melt and column densification resulted in surface lowering averaging -0.80 ± 0.39 m yr -1 between 1800 and 2800 m in the accumulation zone of western Greenland. Since 2007, modeled annual melt and refreezing rates in the percolation zone at elevations below 2100 m surpass the annual snowfall from the previous year, implying that mass gain in the region is retained after melt in the form of refrozen meltwater. Furthermore, if current melt trends over high elevation regions continue, subsequent changes in firn structure will have implications for the hydrology of the ice sheet and related abrupt seasonal densification could become increasingly significant for altimetry-derived ice sheet mass balance estimates.« less

Sea ice algae chlorophyll a concentrations derived from under-ice spectral radiation profiling platforms

NASA Astrophysics Data System (ADS)

Lange, Benjamin A.; Katlein, Christian; Nicolaus, Marcel; Peeken, Ilka; Flores, Hauke

2016-12-01

Multiscale sea ice algae observations are fundamentally important for projecting changes to sea ice ecosystems, as the physical environment continues to change. In this study, we developed upon previously established methodologies for deriving sea ice-algal chlorophyll a concentrations (chl a) from spectral radiation measurements, and applied these to larger-scale spectral surveys. We conducted four different under-ice spectral measurements: irradiance, radiance, transmittance, and transflectance, and applied three statistical approaches: Empirical Orthogonal Functions (EOF), Normalized Difference Indices (NDI), and multi-NDI. We developed models based on ice core chl a and coincident spectral irradiance/transmittance (N = 49) and radiance/transflectance (N = 50) measurements conducted during two cruises to the central Arctic Ocean in 2011 and 2012. These reference models were ranked based on two criteria: mean robustness R2 and true prediction error estimates. For estimating the biomass of a large-scale data set, the EOF approach performed better than the NDI, due to its ability to account for the high variability of environmental properties experienced over large areas. Based on robustness and true prediction error, the three most reliable models, EOF-transmittance, EOF-transflectance, and NDI-transmittance, were applied to two remotely operated vehicle (ROV) and two Surface and Under-Ice Trawl (SUIT) spectral radiation surveys. In these larger-scale chl a estimates, EOF-transmittance showed the best fit to ice core chl a. Application of our most reliable model, EOF-transmittance, to an 85 m horizontal ROV transect revealed large differences compared to published biomass estimates from the same site with important implications for projections of Arctic-wide ice-algal biomass and primary production.

Geomorphological Evidence for Excess Ice in the Southern Hemisphere of Mars

NASA Astrophysics Data System (ADS)

Viola, D.; McEwen, A. S.

2016-12-01

Abundant water ice is present in the polar caps and in the subsurface at mid to high latitudes on Mars. Subsurface ice can either be confined to regolith pore spaces (pore-filling) or "excess ice" that exceeds the available pore space. The latitudinal bounds of modern excess ice in the northern hemisphere of Mars have been constrained by observations of recent ice-exposing impacts (Dundas et al., 2014, JGR: Planets): >25 have been found as of July 2016 at latitudes above 38°N. However, new impact craters are less commonly found in the southern hemisphere since impacts into relatively dust-free surfaces are difficult to discover; only 5 ice-exposing impacts have been found, all at >55°S. Therefore, we propose the use of other surface morphological features to define the present mid-latitude excess ice boundary in the southern hemisphere. We primarily focus on "expanded craters" that show evidence for thermokarstic diameter enlargement. These craters likely form when an impact exposes a subsurface excess ice layer that subsequently sublimates, leading to an apparent widening of the crater. It is important to note that expanded craters suggest that ice was present both at the time of impact and today, since the widespread loss of an excess ice layer would lead to the collapse of these features. Expanded craters have been mapped across a broad region of the northern plains, and their distribution is consistent with the latitudinal limits of new ice-exposing craters. We also observe expanded craters in and around Hellas Planitia, and will use images from the Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) to conduct preliminary mapping of their broader distribution across the southern hemisphere. We will also identify additional features that suggest present or past ice: scallops, polygonal patterned ground, and pedestal craters. This data will be used to infer the latitudinal limit and longitudinal variations of modern excess ice in the southern hemisphere of Mars. This has implications on the history and preservation of water ice on Mars, and may be of interest for future human exploration.

Geomicrobiology of basal ice in a temperate glacier: implications for primary microbial production and export, elemental cycling and soil formation

NASA Astrophysics Data System (ADS)

Toubes-Rodrigo, Mario; Potgieter-Vermaak, Sanja; Sen, Robin; Elliott, David R.; Cook, Simon J.

2017-04-01

Basal ice is a significant sub-glacial component of glaciers and ice sheets that arises from ice-bedrock/substrate interaction. As a result, basal ice of a glacier retains a distinctive physical and chemical signature characterised by a high sediment- and low bubble-content and selective ionic enrichment. Previous research concluded that sediment entrapped in the basal ice matrix originates from the bedrock/substrate, and harbours an active microbial community. However, the nature and significance of the microbial community inhabiting basal ice facies remains poorly characterised. This paper reports on an integrated chemical, mineralogical, and microbial community analysis of basal ice in the subglacial environment at Svínafellsjökull, in south-east Iceland. Basal ice sediment supported 10E7 cells g^-1 and, based on glacier velocity and sediment flux, an estimated 10E17 cells a^-1 are exported to the glacier foreland. Furthermore, 16S rRNA gene analysis highlighted a glacier basal ice bacterial community dominated by Proteobacteria, Acidobacteria, Actinobacteria, and Chloroflexi. Sequences ascribed to chemolithotrophic-related species (Thiobacillus, Syderoxidans) were highly abundant. Minerological analyses of basal ice sediment confirmed dominant silicates and iron-containing minerals that represent susceptible substrates open to oxidation by the aforementioned chemolithotrophs. Previous studies have suggested that basal ice could constitute a good analogue for astrobiology. Svínafellsjökull and Mars geology are similar - volcanically derived rocks with a high abundance of silicates and iron-rich minerals, reinforcing this idea. Understanding where the limits of life in extreme environments, such as debris-rich basal ice, could help to unravel how life on other planets could succeed, and could help to identify which markers to use in order to find it. In dark and isolated basal ice niches, the dominating chemolithotrophic bacterial community are likely to act as primary producers, fixing carbon while weathering minerals and thus providing a plausible mechanism to explain how a basal ice microbial ecosystem can be sustained.

PHYSICAL THERAPY MANAGEMENT OF ICE HOCKEY ATHLETES: FROM THE RINK TO THE CLINIC AND BACK

PubMed Central

Davenport, Todd E.

2016-01-01

ABSTRACT Background The increasing number of athletes playing hockey compels rehabilitation professionals working in orthopedic and sports settings to understand the unique functional demands of ice hockey and the patterns of injuries they may promote. Purpose The purpose of this clinical perspective is to: (1) discuss the functional implications of different positions and age levels on injury prevalence within the sport; (2) summarize the seven most common injuries sustained by ice hockey athletes; and (3) present a conceptual model for the clinical management and prevention of these injuries by rehabilitation professionals. Methods A narrative review and synthesis was conducted of currently available literature on prevalence, etiology, rehabilitative intervention, prognosis, and prevention of ice hockey injuries. Results Research evidence is available to support the prevalence of injuries sustained while participating in ice hockey, as well as the most effective clinical treatment protocols to treat them. Most of the existing protocols are based on clinical and sports experience with incorporation of scientific data. Conclusion This clinical commentary reviews the current concepts of ice hockey injury care and prevention, based on scientific information regarding the incidence, mechanism, rehabilitation protocols, prognosis, and prevention of injuries. Science-based, patient-centered reasoning is integral to provide the highest quality of rehabilitative and preventative care for ice hockey athletes by physical therapists. Level of Evidence 5 PMID:27274432

Mixing water ice into regolith in low-velocity impact experiments

NASA Astrophysics Data System (ADS)

Brisset, J.; Colwell, J. E.; Dove, A.; Rascon, A. N.; Mohammed, N.; Cox, C.

2016-12-01

Collisions between dust and ice grains of different sizes lead to particle growth both in Saturn's rings and in the protoplanetary disk (PPD). Low-velocity collisions (a few m/s or less) among ring or PPD particles produce ejecta and play an important role in this growth process as ejected particles accrete on larger grains. We report on the results of a series of experiments to study the ejecta mass-velocity distribution from impacts of cm-scale particles into granular media at speeds below 3 m/s. These experiments were performed using the lunar regolith simulant JSC-1 in both microgravity and 1-g conditions, under vacuum and at room temperature. As most planetesimal formation occurred beyond the frost line and as Satrun's rings particles are mostly composed of water ice, we proceeded to perform impact experiments at 1-g into JSC-1 lunar regolith simulant mixed with water ice particles at low temperatures (<150 K). We will present the results of the cryogenic impacts and compare them to the study performed at room temperature without water ice. The inclusion of water ice into the target sample is a first step towards better understanding the influence of the presence of water ice in the production of ejecta in response to low-velocity impacts. We will discuss the implications of our results for planetary ring particle collisions as well as planetesimal formation.

The Formation of Organic Compounds of Astrobiological Interest by the Irradiation Processing of Astrophysical Ices

NASA Technical Reports Server (NTRS)

Sandford, Scott A.

2015-01-01

Many environments in space contain very low temperature mixed molecular ices that are exposed to ionizing radiation in the form of cosmic rays and high-energy photons. While traditional chemistry would not be expected to occur at the temperatures typical of these ices (T < 50 K), ionizing radiation can break bonds in the original molecules in the ices to form highly reactive ions and radicals. These ions and radicals are subsequently free to react despite the low temperatures of the original ices. Laboratory experiments, many of them carried out at the Astrochemistry Laboratory at NASA-Ames, show that the irradiation of ices made of even simple molecules like H2O, CO, CO2, CH4, NH3, etc. can result in the robust formation of large numbers of far more complex organic compounds. Many of these new products are of direct interest to astrobiology. For example, the irradiation of mixed molecular ices has been shown to produce amino acids, amphiphiles, quinones, sugars, heterocyclic compounds, and nucleobases, all molecular building blocks used by terrestrial life. Insofar as the presence of these materials plays a role in the origin of life on planets, this has profound implications for the potential abundance of life in the universe since these experiments simulate universal conditions that are expected to be found wherever new stars and planets form.

A New Data Base of Supercooled Cloud Variables for Altitudes up to 10, 000 Feet AGL (Above Ground Level) and the Implications for Low Altitude Aircraft Icing

DTIC Science & Technology

1983-08-01

moist and the mountains are higher. The greatest Icing hazards occur in warm weather cumulonimbus (Cb) clouds, or developing thunderstorms, where LWCs...Washington data apply to aircraft operations which normally do not take place cloqe to the summit or sides of mountains in Instrument Meteorological...of the Sierra Nevada mountains , but MVDs larger than 35 pm do not appear to be unambiguously present In supercooled layer clouds. Other large

Ice polyamorphism in the minimal Mercedes-Benz model of water.

PubMed

Cartwright, Julyan H E; Piro, Oreste; Sánchez, Pedro A; Sintes, Tomás

2012-12-28

We investigate ice polyamorphism in the context of the two-dimensional Mercedes-Benz model of water. We find a first-order phase transition between a crystalline phase and a high-density amorphous phase. Furthermore, we find a reversible transformation between two amorphous structures of high and low density; however, we find this to be a continuous and not an abrupt transition, as the low-density amorphous phase does not show structural stability. We discuss the origin of this behavior and its implications with regard to the minimal generic modeling of polyamorphism.

Ice polyamorphism in the minimal Mercedes-Benz model of water

NASA Astrophysics Data System (ADS)

Cartwright, Julyan H. E.; Piro, Oreste; Sánchez, Pedro A.; Sintes, Tomás

2012-12-01

We investigate ice polyamorphism in the context of the two-dimensional Mercedes-Benz model of water. We find a first-order phase transition between a crystalline phase and a high-density amorphous phase. Furthermore, we find a reversible transformation between two amorphous structures of high and low density; however, we find this to be a continuous and not an abrupt transition, as the low-density amorphous phase does not show structural stability. We discuss the origin of this behavior and its implications with regard to the minimal generic modeling of polyamorphism.

Summer 2007 and 2008 Arctic Sea Ice Loss in Context: OUTLOOK 2008

NASA Astrophysics Data System (ADS)

Overland, J. E.; Eicken, H.; Wiggins, H. V.

2008-12-01

The Arctic is changing faster than the publication cycle for new information. In response, the SEARCH and DAMOCLES Programs initiated an OUTLOOK 2008 to provide broad-based communication and assessment within the arctic science community on the causes of rapid summer sea ice loss, synthesizing information from Arctic observing networks and model simulations. The question for summer 2008 was whether the previous loss of multi-year sea ice and delay in sea ice formation in autumn 2007 would still allow sufficient winter growth of sea ice thickness to last through the summer 2008, potentially allowing for recovery from the 2007 minimum. The answer is no; summer 2008 was a second sequential year of extremely low minimum sea ice extent. To organize OUTLOOK 2008, respondents were asked in May, June and July to provide a rationale and semi-quantitative assessment of arctic sea ice extent anticipated for September 2008. OUTLOOK 2008 supplemented information maintained by ice centers, universities and other data providers. Using a range of methods, all of the approximately 20 groups responded that summer sea ice would not return to climatological mean conditions, with a median response near the 2007 extent. The range of responses depended on the relative weight given to "initial conditions," e.g., age and thickness of sea ice at the end of spring, versus whether summer winds in 2008 would be as supportive for ice loss as in 2007. Initial conditions turned out to be a primary factor for summer 2008, with implications for continued sea ice loss in future years. OUTLOOK 2008 highlighted aspects of the observation and modeling efforts that require further attention such as interpretation of summer microwave signatures, in situ buoy measurements, and data assimilation in models. We appreciate the contributions from respondents and reviewers who made OUTLOOK 2008 a success.

Phylogeographic diversity and mosaicism of the Helicobacter pylori tfs integrative and conjugative elements.

PubMed

Delahay, Robin M; Croxall, Nicola J; Stephens, Amberley D

2018-01-01

The genome of the gastric pathogen Helicobacter pylori is characterised by considerable variation of both gene sequence and content, much of which is contained within three large genomic islands comprising the cag pathogenicity island ( cag PAI) and two mobile integrative and conjugative elements (ICEs) termed tfs3 and tfs4 . All three islands are implicated as virulence factors, although whereas the cag PAI is well characterised, understanding of how the tfs elements influence H. pylori interactions with different human hosts is significantly confounded by limited definition of their distribution, diversity and structural representation in the global H. pylori population. To gain a global perspective of tfs ICE population dynamics we established a bioinformatics workflow to extract and precisely define the full tfs pan-gene content contained within a global collection of 221 draft and complete H. pylori genome sequences. Complete (ca. 35-55kbp) and remnant tfs ICE clusters were reconstructed from a dataset comprising > 12,000 genes, from which orthologous gene complements and distinct alleles descriptive of different tfs ICE types were defined and classified in comparative analyses. The genetic variation within defined ICE modular segments was subsequently used to provide a complete description of tfs ICE diversity and a comprehensive assessment of their phylogeographic context. Our further examination of the apparent ICE modular types identified an ancient and complex history of ICE residence, mobility and interaction within particular H. pylori phylogeographic lineages and further, provided evidence of both contemporary inter-lineage and inter-species ICE transfer and displacement. Our collective results establish a clear view of tfs ICE diversity and phylogeographic representation in the global H. pylori population, and provide a robust contextual framework for elucidating the functional role of the tfs ICEs particularly as it relates to the risk of gastric disease associated with different tfs ICE genotypes.

Asynchronous behavior of the Antarctic Ice Sheet and local glaciers during and since Termination 1, Salmon Valley, Antarctica

NASA Astrophysics Data System (ADS)

Jackson, Margaret S.; Hall, Brenda L.; Denton, George H.

2018-01-01

The stability of the Antarctic Ice Sheet under future warming remains an open question with broad implications for sea-level prediction and adaptation. In particular, knowledge of whether the ice sheet has the capacity for rapid drawdown or collapse, or whether it can remain stable during periods of warming, is essential for predicting its future behavior. Here we use 55 radiocarbon dates, coupled with geomorphologic mapping, to reconstruct the timing of changes in ice extent and elevation during the last ice-age termination in Salmon Valley, adjacent to McMurdo Sound in the western Ross Sea Embayment. Results indicate that a grounded ice sheet in the Ross Sea Embayment achieved its maximum elevation and extent along the headlands of Salmon Valley at ∼18,000 yr BP, during a period of increasing temperatures and accumulation over the Antarctic continent. This ice remained at or near its maximum on the headlands near the valley mouth until after ∼14,000 yr BP. Removal of grounded Ross Sea ice from Salmon Valley was complete shortly after ∼7900 yr BP, indicating that the grounding line had retreated through southern McMurdo Sound by that time. We suggest the primary driver of Ross Sea ice removal from McMurdo Sound was marine-based, either through basal melting or calving due to sea-level rise. When combined with regional data, the Salmon Valley record suggests that this sector of the Antarctic Ice Sheet did not contribute in a significant way to deglacial meltwater pulses, such as meltwater pulse 1a. In contrast to the Ross Sea ice, our work also shows that local, independent alpine glaciers in Salmon Valley have advanced through the Holocene. Land-terminating glaciers such as these elsewhere in the region show a similar pattern, and may reflect the continued influence of increased accumulation following the termination of the last ice age.

Ice sintering timescales at the surface of Europa and implications for surface properties

NASA Astrophysics Data System (ADS)

Phillips, C. B.; Molaro, J.; Meirion-Griffith, G.

2017-12-01

The planned exploration of Europa by NASA's Europa Clipper Mission and the possibility of a future Europa lander have driven the need to characterize its surface strength, roughness, porosity, thermal conductivity, and regolith depth in order to accurately interpret remote sensing data and develop appropriate spacecraft landing systems. Many processes contribute to Europa's landscape evolution, such as sputtering, mass wasting, thermal segregation, and impact gardening, driving the creation and distribution of icy regolith across the surface. While the efficacy of these processes are not well constrained, any amount of regolith emplaced at the surface will undergo subsequent processing due to sintering. Ice sintering is a form of frost metamorphism whereby contacting ice grains experience the diffusion of material into their contact region, forming a "neck" between them and densifying over time. Over long enough timescales, ice aggregates will sinter into solid material, which may contribute to the incorporation of non-ice material into Europa's subsurface and help to drive subsurface chemistry. Sintering also interacts with other processes, adding to the complexity of icy surface evolution. For example, sputtering preferentially removes larger grains and may enhance sintering rates, and changes in ice porosity may affect the response of the surface to micrometeorite impacts. Quantifying the effects of ice sintering will allow us to predict the microstructural properties of Europa's surface at spacecraft scales. To this end, we have modeled pressure-less (no overburden) sintering of spherical water-ice grains and validated the results with a laboratory experiment. We also modeled ice at the surface of Europa to obtain a first-order approximation of the sintering timescale and surface properties. Preliminary results indicate that ice grains will experience neck growth but not significant densification over Europa's surface age, suggesting that loose surface ice forms a weak and porous crust. Furthermore, our results suggest that existing models do not accurately quantify all stages of the sintering process for ice, emphasizing the need for more laboratory studies on this topic.