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1

Melting Ice  

NSDL National Science Digital Library

Monitor the temperature of a melting ice cube and use temperature probes to electronically plot the data on graphs. Investigate what temperature the ice is as it melts in addition to monitoring the temperature of liquid the ice is submerged in.

Consortium, The C.

2011-12-13

2

The anomalously high melting temperature of bilayer ice  

NASA Astrophysics Data System (ADS)

Confinement of water usually depresses its melting temperature. Here we use molecular dynamics simulations to determine the liquid-crystal equilibrium temperature for water confined between parallel hydrophobic or mildly hydrophilic plates as a function of the distance between the surfaces. We find that bilayer ice, an ice polymorph in which the local environment of each water molecule strongly departs from the most stable tetrahedral structure, has the highest melting temperature (Tm) of the series of l-layer ices. The melting temperature of bilayer ice is not only unusually high compared to the other confined ices, but also above the melting point of bulk hexagonal ice. Recent force microscopy experiments of water confined between graphite and a tungsten tip reveal the formation of ice at room temperature [K. B. Jinesh and J. W. M. Frenken, Phys. Rev. Lett. 101, 036101 (2008)]. Our results suggest that bilayer ice, for which we compute a Tm as high as 310 K in hydrophobic confinement, is the crystal formed in those experiments.

Kastelowitz, Noah; Johnston, Jessica C.; Molinero, Valeria

2010-03-01

3

Melting Ice  

NSDL National Science Digital Library

In this lesson, students explore a discrepant event when they design an experiment to measure the rate that ice melts when in pure water versus salt water. It is designed to help students realize that a carefully-designed experiment may yield unexpected results, due to unseen events, even though the experiment is precisely planned and executed. The addition of a new technology may clarify factors in the experiment which were previously unknown. Note: the experiment requires advance preparation the day before: two buckets of water are set-up (one with plain tap water, the other with as much salt dissolved in it as possible), which need to be at room temperature. It also requires ice cubes of uniform shape (e.g., from an ice maker or ice trays filled to uniform capacity). This lesson is part of the Cosmic Times teachers guide and is intended to be used in conjunction with the 1993 Cosmic Times Poster.

4

Concord Consortium: Melting Ice  

NSDL National Science Digital Library

This activity combines a hands-on lab with a computer simulation, as students investigate and graph the changing temperature of a melting ice cube. In the first step, learners monitor temperature as ice melts in a cup of water. In the second step, the ice cube is melted in a cup of salt water. Interactive graphs allow easy plotting of Temperature vs. Time. The activity concludes with a simulation of the atomic structure of a hot liquid and a cold liquid. Click "Withdraw the Barrier" and watch the changing kinetic energy of the cold liquid particles as they mix with the hot liquid. This item is part of the Concord Consortium, a nonprofit research and development organization dedicated to transforming education through technology. The Concord Consortium develops deeply digital learning innovations for science, mathematics, and engineering.

2011-05-17

5

Melting of Ice under Pressure  

SciTech Connect

The melting of ice under pressure is investigated with a series of first principles molecular dynamics simulations. In particular, a two-phase approach is used to determine the melting temperature of the ice-VII phase in the range of 10 to 50 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 to 40 GPa, ice melts as a molecular solid. For pressures above {approx}45 GPa there is a sharp increase in the slope of the melting curve due to the presence of molecular dissociation and proton diffusion in the solid, prior to melting. The onset of significant proton diffusion in ice-VII as a function of increasing temperature is found to be gradual and bears many similarities to that of a type-II superionic solid.

Schwegler, E; Sharma, M; Gygi, F; Galli, G

2008-07-31

6

Linear relation between TH (homogeneous ice nucleation temperature) and Tm (melting temperature) for aqueous solutions of sucrose, trehalose, and maltose  

NASA Astrophysics Data System (ADS)

Homogeneous ice nucleation temperatures ( THs) of aqueous sucrose, trehalose, and maltose solutions were measured together with melting temperatures ( Tms). It is shown that there is a linear relation between TH and Tm for these solutions. Almost identical supercooling behavior is observed for these aqueous disaccharide solutions.

Kanno, Hitoshi; Soga, Makoto; Kajiwara, Kazuhito

2007-08-01

7

Novel monitoring of Antarctic ice shelf basal melting using a fiber-optic distributed temperature sensing mooring  

NASA Astrophysics Data System (ADS)

basal melting of ice shelves is challenging and represents a critical component toward understanding ocean-ice interactions and climate change. In November 2011, moorings containing fiber-optic cables for distributed temperature sensing (DTS) were installed through the McMurdo Ice Shelf, Antarctica, (~200 m) and extending ~600 m into the ice shelf cavity. The high spatial resolution of DTS allows for transient monitoring of the thermal gradient within the ice shelf. The gradient near the ice-ocean interface is extrapolated to the in situ freezing temperature in order to continuously track the ice-ocean interface. Seasonal melt rates are calculated to be ~1.0 mm d-1 and 8.6 mm d-1, and maximum melting corresponds to the arrival of seasonal warm surface water in the ice shelf cavity between January and April. The development of continuous, surface-based techniques for measuring basal melting represents a significant advance in monitoring ice shelf stability and ice-ocean interactions.

Kobs, Scott; Holland, David M.; Zagorodnov, Victor; Stern, Alon; Tyler, Scott W.

2014-10-01

8

Linear relation between T H (homogeneous ice nucleation temperature) and T m (melting temperature) for aqueous solutions of sucrose, trehalose, and maltose  

Microsoft Academic Search

Homogeneous ice nucleation temperatures (THs) of aqueous sucrose, trehalose, and maltose solutions were measured together with melting temperatures (Tms). It is shown that there is a linear relation between TH and Tm for these solutions. Almost identical supercooling behavior is observed for these aqueous disaccharide solutions.

Hitoshi Kanno; Makoto Soga; Kazuhito Kajiwara

2007-01-01

9

Temperature index melt modelling in mountain areas  

Microsoft Academic Search

Temperature index or degree-day models rest upon a claimed relationship between snow or ice melt and air temperature usually expressed in the form of positive temperatures. Since air temperature generally is the most readily available data, such models have been the most widely used method of ice and snow melt computations for many purposes, such as hydrological modelling, ice dynamic

Regine Hock

2003-01-01

10

Temperature and pressure dependence of the mode Grüneisen parameters close to the melting point in hexagonal ice.  

PubMed

We reexamine the Pippard relations in this study by relating the specific heat CP to the Raman frequency shifts 1/nu (partial differentialnu/partial differentialT) P and the thermal expansivity alphap to the 1/nu (partial differentialnu/partial differentialP) T, when the mode Grüneisen parameter depends on the temperature and pressure close to the melting point in hexagonal ice. From linear relations between them, the values of the slope dP/dT are deduced in this crystal. Our slope values calculated here do not change significantly compared to those obtained when the mode Grüneisen parameter is taken as a constant close to the melting point in hexagonal ice. PMID:16859963

Karacali, H; Yurtseven, H

2007-02-01

11

Local ice melting by an antifreeze protein.  

PubMed

Antifreeze proteins, AFP, impede freezing of bodily fluids and damaging of cellular tissues by low temperatures. Adsorption-inhibition mechanisms have been developed to explain their functioning. Using in silico Molecular Dynamics, we show that type I AFP can also induce melting of the local ice surface. Simulations of antifreeze-positive and antifreeze-negative mutants show a clear correlation between melting induction and antifreeze activity. The presence of local melting adds a function to type I AFPs that is unique to these proteins. It may also explain some apparently conflicting experimental results where binding to ice appears both quasipermanent and reversible. PMID:22657839

Calvaresi, Matteo; Höfinger, Siegfried; Zerbetto, Francesco

2012-07-01

12

Ultrafast superheating and melting of bulk ice.  

PubMed

The superheating of a solid to a temperature beyond its melting point, without the solid actually melting, is a well-known phenomenon. It occurs with many substances, particularly those that can readily be produced as high-quality crystals. In principle, ice should also be amenable to superheating. But the complex three-dimensional network of hydrogen bonds that holds water molecules together and gives rise to unusual solid and liquid properties strongly affects the melting behaviour of ice; in particular, ice usually contains many defects owing to the directionality of its hydrogen bonds. However, simulations are readily able to 'create' defect-free ice that can be superheated. Here we show that by exciting the OH stretching mode of water, it is possible to superheat ice. When using an ice sample at an initial temperature of 270 K, we observe an average temperature rise of 20 +/- 2 K that persists over the monitored time interval of 250 ps without melting. PMID:16407948

Iglev, H; Schmeisser, M; Simeonidis, K; Thaller, A; Laubereau, A

2006-01-12

13

How Does Melting Ice Affect Sea Level?  

NSDL National Science Digital Library

In this activity, students investigate how sea levels might rise when ice sheets and ice caps melt by constructing a pair of models and seeing the effects of ice melt in two different situations. Students should use their markers to predict the increase of water in each box before the ice melts.

Dahlman, Luann; Andrill

14

Growth-Melt Asymmetry in Ice  

NASA Astrophysics Data System (ADS)

It is well known that the Wulff Shape of a crystal is anisotropic at temperatures below the roughening temperatures for the principal facets. In the case of ice in contact with water, the roughening temperature of the prism facet was found by Maruyama to be -16.5 deg C, whereas the basal plane is molecularly smooth up to the bulk transition. Therefore, growth of ice in this range of temperature is anisotropic. We study the anisotropy during melting under small disequilibrium melt drives and extend geometric theory to explain the apparent reorientation of the underlying crystallographic axes observed experimentally. The dynamical melt shapes appear faceted despite the lack of a surface phase transition and we explain the behavior using a geometric treatmen of the basic kinetics of molecular detachment from the surface.

Cahoon, A.; Maruyama, M.; Wettlaufer, J. S.

2005-03-01

15

Ice shelf morphology and the efficiency of basal melting  

Microsoft Academic Search

In the Amundsen Sea sector of Antarctica, changes in basal melting have triggered rapid ice shelf thinning; increasing subsurface ocean temperatures may have initiated this process. A scaling law relating melting to ocean temperature will aid the analysis of observed thinning as well as predictions of ice sheet behavior. Yet it is unclear whether relationships found in prior studies are

C. M. Little; A. Gnanadesikan; M. Oppenheimer

2008-01-01

16

Mountain of Ice: If the Ice Melts  

NSDL National Science Digital Library

This interactive resource portrays what might happen to world coastlines if entire sections of the Antarctic Ice Sheet were to melt. Viewers can see how much land area might be flooded by a relatively modest 17-foot rise in sea level (represented by the collapse of the Western Antarctic Ice Sheet), or a more severe 170-foot rise, represented by the collapse of the Eastern Antarctic Ice Sheet. By comparing present-day coastline positions with those from the peak glacial advance 20,000 years ago, it is possible to appreciate how much water is contained in glaciers, the importance of monitoring their condition, and the impact accelerated global warming could one day have on sea level. A background essay and list of discussion questions are also provided.

17

Trend of melt under Pine Island Glacier ice shelf modulated by high variability in ocean temperature  

NASA Astrophysics Data System (ADS)

Pine Island Glacier and neighbouring outlet glaciers of West Antarctica have thinned and accelerated over the last 2 decades, significantly contributing to global sea level rise. Increased ocean heat transport beneath Pine Island Glacier ice shelf and unpinning from a seabed ridge are thought to be the primary drivers of such changes. However, the acceleration of the glacier paused since 2009, renewing questions about the main processes presently affecting the ice/ocean system, the future behaviour of the glacier and the associated impacts. Here, we present ocean observations taken in austral Spring 2012 to show a 200 m lowering of the thermocline at the glacier calving front and a 50% decrease of meltwater production from 2009. High-resolution simulations of the ocean circulation in the cavity beneath the floating tongue of the glacier demonstrate that for the present ice geometry, the seabed ridge blocks the warmest deep waters from reaching the ice and strongly ties meltwater production to thermocline depth above the ridge, hereby making it susceptible to relatively high variability in time, from intraseasonal to interannual. These results highlight the role of climatic variability in glacial ice loss and the fundamental importance of local ice shelf and seabed geometry for determining ice-ocean dynamics.

Dutrieux, Pierre; De Rydt, Jan; Jenkins, Adrian; Holland, Paul R.; Ha, Ho Kyung; Lee, Sang Hoon; Povl Abrahamsen, E.; Jacobs, Stanley S.

2013-04-01

18

Results from a lab study of melting sea ice  

NASA Astrophysics Data System (ADS)

Sea-ice melting is a complex process which is not fully understood yet. In order to study sea-ice melt in detail we perform lab experiments in an approximately 2x0.7x1.2 m large tank in a cold room. We grow sea ice with different salinities at least 10 cm thick. Then we let the ice melt at different air temperatures and oceanic heat fluxes. During the melt period, we measure the evolution of ice thickness, internal temperature, salinity and surface temperature. We will present results from roughly five months of experiments. Topics will include the influence of bulk salinity on melt rates and the surface temperature. The effects of flushing on the salinity evolution and detailed thermal profiles will also be included. To investigate these processes we focus on the energy budget and the salinity evolution. These topics are linked since the thermodynamic properties of sea ice (heat capacity, heat conductivity and latent heat of fusion) are very sensitive to salinity variations. For example the heat capacity of sea ice increases greatly as the temperature approaches the melting point. This increase results in non-linear temperature profiles and enhances heat conduction into the ice. The salinity evolution during the growth phase has been investigated and measured in multiple studies over the last decades. In contrast there are no detailed lab measurements of melting ice available to quantify the effects of flushing melt water and ponding. This is partially due to the fact that the heterogeneity of melting sea ice makes it much more difficult to measure representative values.

Wiese, M.; Griewank, P.; Notz, D.

2012-04-01

19

The mechanisms of sea ice melt pond formation and evolution  

NASA Astrophysics Data System (ADS)

A series of observations were made on melting first year, landfast Arctic sea ice near Barrow, Alaska to explore the seasonal evolution of melt pond coverage. Observations of pond coverage, albedo, and ice properties are combined with terrestrial lidar measurements of surface topography and meltwater balance to quantitatively identify the timing and role of mechanisms driving pond coverage. The formation of interposed fresh ice is found to eliminate meltwater percolation through early pond formation and allow widespread ponding well above sea level. Pond drainage to sea level occurs principally by horizontal meltwater transport over the ice surface to macroscopic flaws. Freeboard loss, caused by buoyancy decline as the ice thins, controls pond growth late in the melt season after percolation begins. The majority of the macroscopic flaws that drain melt ponds to sea level are observed to develop from brine drainage channels within the ice. A simple thermodynamic model of meltwater percolation illustrates that fresh meltwater inflow causes pores in the ice to either shrink and freeze shut or enlarge based on initial size and ice temperature. This threshold behavior of pore diameter controls both the blockage of smaller pores with interposed ice and the enlargement of larger brine drainage channels to allow meltwater drainage. The results identify links between the temporal evolution of pond coverage and ice temperature, salinity, and thickness, providing new opportunities to realistically parameterize ponds and summer ice albedo within sea ice models.

Polashenski, Chris; Perovich, Donald; Courville, Zoe

2012-01-01

20

Monitoring snow melt characteristics on the Greenland ice sheet using a new MODIS land surface temperature and emissivity product (MOD21)  

NASA Astrophysics Data System (ADS)

Land Surface Temperature (LST) and emissivity are sensitive energy-balance parameters that control melt and energy exchange between the surface and the atmosphere. MODIS LST is currently used to monitor melt zones on glaciers and can be used for glacier or ice sheet mass balance calculations. Much attention has been paid recently to the warming of the Arctic in the context of global warming, with a focus on the Greenland ice sheet because of its importance with sea-level rise. Various researchers have shown a steady decline in the extent of the Northern Hemisphere sea ice, both the total extent and the extent of the perennial or multiyear ice. Surface melt characteristics over the Greenland ice sheet have been traditionally monitored using the MODIS LST and albedo products (e.g. MOD11 and MOD10A1). Far fewer studies have used thermal emissivity data to monitor surface melt characteristics due to the lack of suitable data. In theory, longwave emissivity combined with LST information should give a more direct measure of snow melt characteristics since the emissivity is an intrinsic property of the surface, whereas the albedo is dependent on other factors such as solar zenith angle, and shadowing effects. Currently no standard emissivity product exists that can dynamically retrieve changes in longwave emissivity consistently over long time periods. This problem has been addressed with the new MOD21 product, which uses the ASTER TES algorithm to dynamically retrieve LST and spectral emissivity (bands 29, 31, 32) at 1-km resolution. In this study we show that using a new proposed index termed the snow emissivity difference index (SEDI) derived from the MOD21 longwave emissivity product, combined with the LST, will improve our understanding of snow melt and freezeup dynamics on ice sheets such as Greenland. The results also suggest that synergistic use of both thermal-based and albedo data will help to improve our understanding of snow melt dynamics on glaciers and ice sheets, and reduce uncertainties in estimating magnitudes and trends.

Hulley, G. C.; Hall, D. K.; Hook, S. J.

2013-12-01

21

Monitoring Antarctic ice sheet surface melting with TIMESAT algorithm  

NASA Astrophysics Data System (ADS)

Antarctic ice sheet contributes significantly to the global heat budget by controlling the exchange of heat, moisture, and momentum at the surface-atmosphere interface, which directly influence the global atmospheric circulation and climate change. Ice sheet melting will cause snow humidity increase, which will accelerate the disintegration and movement of ice sheet. As a result, detecting Antarctic ice sheet melting is essential for global climate change research. In the past decades, various methods have been proposed for extracting snowmelt information from multi-channel satellite passive microwave data. Some methods are based on brightness temperature values or a composite index of them, and others are based on edge detection. TIMESAT (Time-series of Satellite sensor data) is an algorithm for extracting seasonality information from time-series of satellite sensor data. With TIMESAT long-time series brightness temperature (SSM/I 19H) is simulated by Double Logistic function. Snow is classified to wet and dry snow with generalized Gaussian model. The results were compared with those from a wavelet algorithm. On this basis, Antarctic automatic weather station data were used for ground verification. It shows that this algorithm is effective in ice sheet melting detection. The spatial distribution of melting areas(Fig.1) shows that, the majority of melting areas are located on the edge of Antarctic ice shelf region. It is affected by land cover type, surface elevation and geographic location (latitude). In addition, the Antarctic ice sheet melting varies with seasons. It is particularly acute in summer, peaking at December and January, staying low in March. In summary, from 1988 to 2008, Ross Ice Shelf and Ronnie Ice Shelf have the greatest interannual variability in amount of melting, which largely determines the overall interannual variability in Antarctica. Other regions, especially Larsen Ice Shelf and Wilkins Ice Shelf, which is in the Antarctic Peninsula region, have relative stable and consistent melt occurrence from year to year.

Ye, Y.; Cheng, X.; Li, X.; Liang, L.

2011-12-01

22

What if the Ice Shelves Melted?  

NSDL National Science Digital Library

This activity is a hands-on guided inquiry activity designed to highlight the role of an ice shelf on slowing the movement of continental ice sheets in Antarctica. Students build a model of Antarctica and both continental glaciers and ice shelves using paper models of the land and slime for glaciers and ice. Students use their model to explore the impact of recent and potential ice shelf melting and break-up.

Dahlman, Luann; Andrill

23

Surface melting on ice shelves and icebergs  

NASA Astrophysics Data System (ADS)

Disintegration of Larsen Ice Shelf A and B, in 1995 and 2002, respectively, were preceded by two decades of extended summer melt seasons and by surface melt-water accumulation in ponds, surface crevasses and depressions produced by the elastic flexure of the ice. The extraordinary rapidity of ice-shelf fragmentation into large iceberg plumes following the appearance of surface melt water implies that the mechanical effects of surface melt water accumulation may represent an unforeseen process allowing abrupt, large-scale change of Antarctica's ice mass. The present study of surface melting and subsequent movement of melt water, both vertically (i.e., downward percolation into underlying firn) and horizontally (e.g., into crevasses and surface depressions created by ice-shelf flexure in response to both side boundary conditions and the melt-water load itself), is motivated by the need to further describe the energy, mass and momentum balances associated with ice shelves and their surrogates-large tabular icebergs-in the face of unprecedented changes in surface mass balance. The goal of this dissertation is to examine both the thermodynamic and mechanical aspects of surface melting on ice shelves and icebergs subject to sudden changes in climate conditions (e.g ., global warming). Thermodynamic aspects of the study include the development and application of surface energy balance models capable of describing the process of surface melting and subsequent vertical movement of melt water through a porous firn. Mechanical aspects of this study include the analysis of vertical melt-water flow, and more particularly, the elastic flexure response of the ice shelf or iceberg to the melt-water loads. Work presented here involves three methodologies, numerical modeling, field observation, and mathematical analysis (e.g., development of analytic solutions to simple, idealized ice-shelf flexure problems).

Sergienko, Olga V.

24

Abrupt grain boundary melting in ice  

E-print Network

The effect of impurities on the grain boundary melting of ice is investigated through an extension of Derjaguin-Landau-Verwey-Overbeek theory, in which we include retarded potential effects in a calculation of the full frequency dependent van der Waals and Coulombic interactions within a grain boundary. At high dopant concentrations the classical solutal effect dominates the melting behavior. However, depending on the amount of impurity and the surface charge density, as temperature decreases, the attractive tail of the dispersion force interaction begins to compete effectively with the repulsive screened Coulomb interaction. This leads to a film-thickness/temperature curve that changes depending on the relative strengths of these interactions and exhibits a decrease in the film thickness with increasing impurity level. More striking is the fact that at very large film thicknesses, the repulsive Coulomb interaction can be effectively screened leading to an abrupt reduction to zero film thickness.

L. Benatov; J. S. Wettlaufer

2004-12-30

25

What controls dead-ice melting under different climate conditions?  

NASA Astrophysics Data System (ADS)

In the geological record, hummocky dead-ice moraines represent the final product of the melt-out of dead- ice. Processes and rates of dead-ice melting in ice-cored moraines and at debris-covered glaciers are commonly believed to be governed by climate. Here, backwasting rates from 14 dead-ice areas are assessed in relation to mean annual air temperature, mean summer air temperature, mean annual precipitation, mean summer precipitation, and the sum of degree days > 0 deg. C. The highest correlation was found between backwasting rate and mean annual air temperature. However, the correlation between melt rates and climate parameters is low, stressing that processes and topography play a major role in governing the rates of backwasting. The rates of dead-ice melting from modern glacial environments should serve as input to de-icing models for ancient dead-ice areas in order to assess the mode and duration of deposition. A challenge for future explorations of dead-ice environments is to obtain long-term records of field-based monitoring of melt progression. Furthermore, many modern satellite-borne sensors have high potentials for recordings of multi-temporal Digital Elevation Models (DEMs) for detection and quantification of changes in dead-ice environments. However, time series of high-resolution aerial photographs remain essential for both visual inspection and high-resolution stereographic DEM production. Reference: Schomacker, A. 2008. What controls dead-ice melting under different climate conditions? Earth- Science Reviews, in press.

Schomacker, A.

2008-12-01

26

Greenland Ice Sheet Melt from MODIS and Associated Atmospheric Variability  

NASA Technical Reports Server (NTRS)

Daily June-July melt fraction variations over the Greenland Ice Sheet (GIS) derived from the MODerate-resolution Imaging Spectroradiometer (MODIS) (2000-2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500hPa height (from NCEPNCAR). Blocking activity with a range of time scales, from synoptic waves breaking poleward ( 5 days) to full-fledged blocks (5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the largest MODIS melt years (2002 and 2012), the area-average temperature anomaly of 2 standard deviations above the 14-year June-July mean, results in a melt fraction of 40 or more. Summer 2007 had the most blocking days, however atmospheric temperature anomalies were too small to instigate extreme melting.

Hakkinen, Sirpa; Hall, Dorothy K.; Shuman, Christopher A.; Worthen, Denise L.; DiGirolamo, Nicolo E.

2014-01-01

27

Quantification of Dead-ice Melting in Ice-Cored Moraines at the High-Arctic Glacier Holmströmbreen, Svalbard  

NASA Astrophysics Data System (ADS)

An extensive dead-ice area has developed at the stagnant snout of the Holmströmbreen glacier on Svalbard following its Little Ice Age maximum. Dead-ice appears mainly as ice-cored moraines, ice-cored eskers and ice- cored kames. The most common dead-ice landform is sediment gravity flows on ice-cored slopes surrounding a large ice-walled, moraine-dammed lake. The lake finally receives the sediment from the resedimentation processes. Dead-ice melting is described and quantified through field studies and analyses of high-resolution, multi-temporal aerial photographs and satellite imagery. Field measurements of backwasting of ice-cored slopes indicate short-term melting rates of c. 9.2 cm/day. Long-term downwasting rates indicate a surface lowering of ice-cored moraines of c. 0.9 m/yr from 1984-2004. Different measures for dead-ice melting are assessed in relation to the temperature record from Svalbard since the termination of the Little Ice Age. The most prominent impact of dead-ice melting is the evolution of the ice-walled lake with an area increasing near-exponentially over the last 40 years. As long as backwasting and mass movement processes prevent build-up of an insulating debris-cover and expose ice-cores to melting, the de-icing continues even though the area is characterized by continuous permafrost.

Schomacker, A.; Kjaer, K. H.

2007-12-01

28

Floating Ice-Algal Aggregates below Melting Arctic Sea Ice  

PubMed Central

During two consecutive cruises to the Eastern Central Arctic in late summer 2012, we observed floating algal aggregates in the melt-water layer below and between melting ice floes of first-year pack ice. The macroscopic (1-15 cm in diameter) aggregates had a mucous consistency and were dominated by typical ice-associated pennate diatoms embedded within the mucous matrix. Aggregates maintained buoyancy and accumulated just above a strong pycnocline that separated meltwater and seawater layers. We were able, for the first time, to obtain quantitative abundance and biomass estimates of these aggregates. Although their biomass and production on a square metre basis was small compared to ice-algal blooms, the floating ice-algal aggregates supported high levels of biological activity on the scale of the individual aggregate. In addition they constituted a food source for the ice-associated fauna as revealed by pigments indicative of zooplankton grazing, high abundance of naked ciliates, and ice amphipods associated with them. During the Arctic melt season, these floating aggregates likely play an important ecological role in an otherwise impoverished near-surface sea ice environment. Our findings provide important observations and measurements of a unique aggregate-based habitat during the 2012 record sea ice minimum year. PMID:24204642

Assmy, Philipp; Ehn, Jens K.; Fernandez-Mendez, Mar; Hop, Haakon; Katlein, Christian; Sundfjord, Arild; Bluhm, Katrin; Daase, Malin; Engel, Anja; Fransson, Agneta; Granskog, Mats A.; Hudson, Stephen R.; Kristiansen, Svein; Nicolaus, Marcel; Peeken, Ilka; Renner, Angelika H. H.; Spreen, Gunnar; Tatarek, Agnieszka; Wiktor, Jozef

2013-01-01

29

Basal terraces on melting ice shelves  

NASA Astrophysics Data System (ADS)

waters melt the margins of Antarctic and Greenland glaciers, and individual glaciers' responses and the integrity of their ice shelves are expected to depend on the spatial distribution of melt. The bases of the ice shelves associated with Pine Island Glacier (West Antarctica) and Petermann Glacier (Greenland) have similar geometries, including kilometer-wide, hundreds-of-meter high channels oriented along and across the direction of ice flow. The channels are enhanced by, and constrain, oceanic melt. New meter-scale observations of basal topography reveal peculiar glaciated landscapes. Channel flanks are not smooth, but are instead stepped, with hundreds-of-meters-wide flat terraces separated by 5-50 m high walls. Melting is shown to be modulated by the geometry: constant across each terrace, changing from one terrace to the next, and greatly enhanced on the ~45° inclined walls. Melting is therefore fundamentally heterogeneous and likely associated with stratification in the ice-ocean boundary layer, challenging current models of ice shelf-ocean interactions.

Dutrieux, Pierre; Stewart, Craig; Jenkins, Adrian; Nicholls, Keith W.; Corr, Hugh F. J.; Rignot, Eric; Steffen, Konrad

2014-08-01

30

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

NASA Astrophysics Data System (ADS)

This presentation is of a 'unified theory' in glaciology that first identifies surface albedo as a key factor explaining total ice sheet mass balance and then surveys a mechanistic self-reinforcing interaction between melt water and ice flow dynamics. The theory is applied in a near-real time total Greenland mass balance retrieval based on surface albedo, a powerful integrator of the competing effects of accumulation and ablation. New snowfall reduces sunlight absorption and increases meltwater retention. Melting amplifies absorbed sunlight through thermal metamorphism and bare ice expansion in space and time. By ';following the melt'; we reveal mechanisms linking existing science into a unified theory. Increasing meltwater softens the ice sheet in three ways: 1.) sensible heating given the water temperature exceeds that of the ice sheet interior; 2.) Some infiltrating water refreezes, transferring latent heat to the ice; 3.) Friction from water turbulence heats the ice. It has been shown that for a point on the ice sheet, basal lubrication increases ice flow speed to a time when an efficient sub-glacial drainage network develops that reduces this effect. Yet, with an increasing melt duration the point where the ice sheet glides on a wet bed increases inland to a larger area. This effect draws down the ice surface elevation, contributing to the ';elevation feedback'. In a perpetual warming scenario, the elevation feedback ultimately leads to ice sheet loss reversible only through much slower ice sheet growth in an ice age environment. As the inland ice sheet accelerates, the horizontal extension pulls cracks and crevasses open, trapping more sunlight, amplifying the effect of melt accelerated ice. As the bare ice area increases, the direct sun-exposed crevassed and infiltration area increases further allowing the ice warming process to occur more broadly. Considering hydrofracture [a.k.a. hydrofracking]; surface meltwater fills cracks, attacking the ice integrity. Because water is 'heavier' than ice, water-filled cracks have unlimited capacity to hydraulically ';jack' open fractures, penetrating, fracturing and disaggregating a solid ice body. This process promotes iceberg calving at more than 150, 1km wide marine terminating Greenland glacier fronts. Resulting from a rising trend of surface melting and sea water temperature, meltwater ejection at the underwater front of marine glaciers drives a an increasing turbulent heat exchange between the glacier front and relatively warm sea water melting it faster. Underwater melting promotes an undercutting of the glacier front leading to ice berg calving. Calving through hydrofracture or marine undercutting provide a direct and immediate ice flow speed response mechanism for surface meltwater production. Ice flow speed reacts because calving reduces flow resistance. The above physical processes interact. Cooling shuts these processes down. Negative feedbacks dampen the warming impulse. Live 21 June, 2013 is a new Danish Web site1 that exploits total mass balance rate of decline as a function of albedo to predict GRACE mass rate of change with 80% explained variance. While surface mass balance explains the mass rate of change slightly higher, surface albedo is an observable quantity as is gravity change.

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

2013-12-01

31

Causes and Effects of Melting Ice  

NSDL National Science Digital Library

In this activity, learners explore the concept of density-driven currents (thermohaline circulation) and how these currents are affected by climate change. Learners use colored ice cubes, water, and salt to explore density as it relates to salinity. This activity helps learners to understand the impact of glacial melt on sea level rise.

Bell, Elizabeth V.; Marshall, Brittney; Bliss, Angela

2012-11-14

32

Onset of convective instabilities in under-ice melt ponds.  

PubMed

The onset of double-diffusive natural convection in under-ice melt ponds is investigated through a linear stability analysis. The three-layer configuration is composed by a fluid layer (melt pond) overlying a saturated porous medium (ice matrix), which in turn overlies another fluid layer (under-ice melt pond). Water density inversion is taken into account by adopting a density profile with a quadratic temperature dependence and a linear concentration dependence. We show that the key parameter affecting stability is the depth of the ice matrix, while the depths of the upper and lower fluid layers play a marginal role. A Hopf bifurcation is observed in the whole range of parameters studied, and the size of the convection cells depends on ice permeability. The influence of the external temperature gradient is investigated by means of the definition of an extra thermal parameter accounting for the relative position of the density maximum. It is shown that convection is favored by larger temperature gradients, which occur during Arctic summer. PMID:23005205

Hirata, Sílvia C; Goyeau, Benoît; Gobin, Dominique

2012-06-01

33

Increased Runoff from Melt from the Greenland Ice Sheet: A Response to Global Warming  

E-print Network

Increased Runoff from Melt from the Greenland Ice Sheet: A Response to Global Warming EDWARD HANNA summer warmth and Greenland Ice Sheet melt and runoff since 1990 to global warming. Southern Greenland Greenland summer temperatures until the early 1990s but not thereafter. Significant warming in southern

Huybrechts, Philippe

34

Acceleration of snow melt in an Antarctic Peninsula ice core during the twentieth century  

NASA Astrophysics Data System (ADS)

Over the past 50 years, warming of the Antarctic Peninsula has been accompanied by accelerating glacier mass loss and the retreat and collapse of ice shelves. A key driver of ice loss is summer melting; however, it is not usually possible to specifically reconstruct the summer conditions that are critical for determining ice melt in Antarctic. Here we reconstruct changes in ice-melt intensity and mean temperature on the northern Antarctic Peninsula since AD 1000 based on the identification of visible melt layers in the James Ross Island ice core and local mean annual temperature estimates from the deuterium content of the ice. During the past millennium, the coolest conditions and lowest melt occurred from about AD 1410 to 1460, when mean temperature was 1.6°C lower than that of 1981-2000. Since the late 1400s, there has been a nearly tenfold increase in melt intensity from 0.5 to 4.9%. The warming has occurred in progressive phases since about AD 1460, but intensification of melt is nonlinear, and has largely occurred since the mid-twentieth century. Summer melting is now at a level that is unprecedented over the past 1,000 years. We conclude that ice on the Antarctic Peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature.

Abram, Nerilie J.; Mulvaney, Robert; Wolff, Eric W.; Triest, Jack; Kipfstuhl, Sepp; Trusel, Luke D.; Vimeux, Françoise; Fleet, Louise; Arrowsmith, Carol

2013-05-01

35

Duration of the Arctic sea ice melt season: Regional and interannual variability, 1979-2001  

USGS Publications Warehouse

Melt onset dates, freeze onset dates, and melt season duration were estimated over Arctic sea ice, 1979-2001, using passive microwave satellite imagery and surface air temperature data. Sea ice melt duration for the entire Northern Hemisphere varied from a 104-day minimum in 1983 and 1996, to a 124-day maximum in 1989. Ranges in melt duration were highest in peripheral seas, numbering 32, 42, 44, and 51 days in the Laptev, Barents-Kara, East Siberian and Chukchi Seas, respectively. In the Arctic Ocean, average melt duration varied from a 75-day minimum in 1987 to a 103-day maximum in 1989. On average, melt onset in annual ice began 10.6 days earlier than perennial ice, and freeze onset in perennial ice commenced 18.4 days earlier than annual ice. Average annual melt dates, freeze dates, and melt durations in annual ice were significantly correlated with seasonal strength of the Arctic Oscillation (AO). Following high-index AO winters (January-March), spring melt tended to be earlier and autumn freeze later, leading to longer melt season durations. The largest increases in melt duration were observed in the eastern Siberian Arctic, coincident with cyclonic low pressure and ice motion anomalies associated with high-index AO phases. Following a positive AO shift in 1989, mean annual melt duration increased 2-3 weeks in the northern East Siberian and Chukchi Seas. Decreasing correlations between consecutive-year maps of melt onset in annual ice during 1979-2001 indicated increasing spatial variability and unpredictability in melt distributions from one year to the next. Despite recent declines in the winter AO index, recent melt distributions did not show evidence of reestablishing spatial patterns similar to those observed during the 1979-88 low-index AO period. Recent freeze distributions have become increasingly similar to those observed during 1979-88, suggesting a recurrent spatial pattern of freeze chronology under low-index AO conditions.

Belchansky, G. I.; Douglas, D. C.; Platonov, N. G.

2004-01-01

36

Simulated melt rates for the Totten and Dalton ice shelves  

NASA Astrophysics Data System (ADS)

The Totten Glacier drains a large proportion of the East Antarctic ice sheet, much of it marine based (grounded below sea level), and is rapidly losing mass. It has been suggested that this mass loss is driven by changes in oceanic forcing; however, the details of the ice-ocean interaction are unknown. Here we present results from an ice shelf-ocean model of the region that includes the Totten, Moscow University and Dalton Ice Shelves, based on the Regional Oceanic Modeling System for the period 1992-2007. Simulated area-averaged basal melt rates (net basal mass loss) for the Totten and Dalton ice shelves are 9.1 m ice yr-1 (44.5 Gt ice yr-1) and 10.1 m ice yr-1 (46.6 Gt ice yr-1), respectively. The melting of the ice shelves varies strongly on seasonal and interannual timescales. Basal melting (mass loss) from the Totten ice shelf spans a range of 5.7 m ice yr-1 (28 Gt ice yr-1) on interannual timescales and 3.4 m ice yr-1 (17 Gt ice yr-1) on seasonal timescales. This study links basal melt of the Totten and Dalton ice shelves to warm water intrusions across the continental shelf break and atmosphere-ocean heat exchange. Totten ice shelf melting is high when the nearby Dalton polynya interannual strength is below average, and vice versa. Melting of the Dalton ice shelf is primarily controlled by the strength of warm water intrusions across the Dalton Rise and into the ice shelf cavity. During periods of strong westwards coastal current flow, Dalton melt water flows directly under the Totten ice shelf further reducing melting. This is the first such modelling study of this region, providing a valuable framework for directing future observational and modelling efforts.

Gwyther, D. E.; Galton-Fenzi, B. K.; Hunter, J. R.; Roberts, J. L.

2013-11-01

37

Simulated melt rates for the Totten and Dalton ice shelves  

NASA Astrophysics Data System (ADS)

The Totten Glacier is rapidly losing mass. It has been suggested that this mass loss is driven by changes in oceanic forcing; however, the details of the ice-ocean interaction are unknown. Here we present results from an ice shelf-ocean model of the region that includes the Totten, Dalton and Moscow University ice shelves, based on the Regional Oceanic Modeling System for the period 1992-2007. Simulated area-averaged basal melt rates (net basal mass loss) for the Totten and Dalton ice shelves are 9.1 m ice yr-1 (44.5 Gt ice yr-1) and 10.1 m ice yr-1 (46.6 Gt ice yr-1), respectively. The melting of the ice shelves varies strongly on seasonal and interannual timescales. Basal melting (mass loss) from the Totten ice shelf spans a range of 5.7 m ice yr-1 (28 Gt ice yr-1) on interannual timescales and 3.4 m ice yr-1 (17 Gt ice yr-1) on seasonal timescales. This study links basal melt of the Totten and Dalton ice shelves to warm water intrusions across the continental shelf break and atmosphere-ocean heat exchange. Totten ice shelf melting is high when the nearby Dalton polynya interannual strength is below average, and vice versa. Melting of the Dalton ice shelf is primarily controlled by the strength of warm water intrusions across the Dalton rise and into the ice shelf cavity. During periods of strong westward coastal current flow, Dalton melt water flows directly under the Totten ice shelf further reducing melting. This is the first such modelling study of this region to provide a valuable framework for directing future observational and modelling efforts.

Gwyther, D. E.; Galton-Fenzi, B. K.; Hunter, J. R.; Roberts, J. L.

2014-05-01

38

Inorganic carbon dynamics of melt pond-covered first year sea ice in the Canadian Arctic  

NASA Astrophysics Data System (ADS)

Melt pond formation is a common feature of the spring and summer Arctic sea ice. However, the role of the melt ponds formation and the impact of the sea ice melt on both the direction and size of CO2 flux between air and sea is still unknown. Here we describe the CO2-carbonate chemistry of melting sea ice, melt ponds and the underlying seawater associated with measurement of CO2 fluxes across first year landfast sea ice in the Resolute Passage, Nunavut, in June 2012. Early in the melt season, the increase of the ice temperature and the subsequent decrease of the bulk ice salinity promote a strong decrease of the total alkalinity (TA), total dissolved inorganic carbon (TCO2) and partial pressure of CO2 (pCO2) within the bulk sea ice and the brine. Later on, melt pond formation affects both the bulk sea ice and the brine system. As melt ponds are formed from melted snow the in situ melt pond pCO2 is low (36 ?atm). The percolation of this low pCO2 melt water into the sea ice matrix dilutes the brine resulting in a strong decrease of the in situ brine pCO2 (to 20 ?atm). As melt ponds reach equilibrium with the atmosphere, their in situ pCO2 increase (up to 380 ?atm) and the percolation of this high concentration pCO2 melt water increase the in situ brine pCO2 within the sea ice matrix. The low in situ pCO2 observed in brine and melt ponds results in CO2 fluxes of -0.04 to -5.4 mmol m-2 d-1. As melt ponds reach equilibrium with the atmosphere, the uptake becomes less significant. However, since melt ponds are continuously supplied by melt water their in situ pCO2 still remains low, promoting a continuous but moderate uptake of CO2 (~ -1mmol m-2 d-1). The potential uptake of atmospheric CO2 by melting sea ice during the Arctic summer has been estimated from 7 to 16 Tg of C ignoring the role of melt ponds. This additional uptake of CO2 associated to Arctic sea ice needs to be further explored and considered in the estimation of the Arctic Ocean's overall CO2 budget.

Geilfus, N.-X.; Galley, R. J.; Crabeck, O.; Papakyriakou, T.; Landy, J.; Tison, J.-L.; Rysgaard, S.

2014-05-01

39

NOTES AND CORRESPONDENCE Surface Melting over Ice Shelves and Ice Sheets as Assessed from Modeled  

E-print Network

NOTES AND CORRESPONDENCE Surface Melting over Ice Shelves and Ice Sheets as Assessed from Modeled, Ronne-Filchner, and Amery ice shelves as well as a large portion of the West Antarctic Ice Sheet (WAIS-day levels avoided significant summer melt over the large Antarctic shelves, the WAIS, and much of the GIS. 1

Meissner, Katrin Juliane

40

Snow melt on sea ice surfaces as determined from passive microwave satellite data  

NASA Technical Reports Server (NTRS)

SMMR data for the year 1979, 1980 and 1984 have been analyzed to determine the variability in the onset of melt for the Arctic seasonal sea ice zone. The results show melt commencing in either the Kara/Barents Seas or Chukchi Sea and progressing zonally towards the central Asian coast (Laptev Sea). Individual regions had interannual variations in melt onset in the 10-20 day range. To determine whether daily changes occur in the sea ice surface melt, the SMMR 18 and 37 GHz brightness temperature data are analyzed at day/night/twilight periods. Brightness temperatures illustrate diurnal variations in most regions during melt. In the East Siberian Sea, however, daily variations are observed in 1979, throughout the analysis period, well before any melt would usually have commenced. Understanding microwave responses to changing surface conditions during melt will perhaps give additional information about energy budgets during the winter to summer transition of sea ice.

Anderson, Mark R.

1987-01-01

41

Deformation-induced melting in the margins of the West Antarctic ice streams  

NASA Astrophysics Data System (ADS)

Flow of glacial ice in the West Antarctic Ice Sheet localizes in narrow bands of fast-flowing ice streams bordered by ridges of nearly stagnant ice, but our understanding of the physical processes that generate this morphology is incomplete. Here we study the thermal and mechanical properties of ice-stream margins, where flow transitions from rapid to stagnant over a few kilometers. Our goal is to explore under which conditions the intense shear deformation in the margin may lead to deformation-induced melting. We propose a 2-D model that represents a cross section through the ice stream margin perpendicular to the downstream flow direction. We limit temperature to the melting point to estimate melt rates based on latent heat. Using rheology parameters as constrained by laboratory data and observations, we conclude that a zone of temperate ice is likely to form in active shear margins.

Suckale, Jenny; Platt, John D.; Perol, Thibaut; Rice, James R.

2014-05-01

42

Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming  

PubMed Central

Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999–2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals. PMID:25246548

Cziko, Paul A.; DeVries, Arthur L.; Evans, Clive W.; Cheng, Chi-Hing Christina

2014-01-01

43

Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming.  

PubMed

Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999-2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals. PMID:25246548

Cziko, Paul A; DeVries, Arthur L; Evans, Clive W; Cheng, Chi-Hing Christina

2014-10-01

44

In-Situ Biological Decontamination of an Ice Melting Probe  

NASA Astrophysics Data System (ADS)

A major concern in space and even many terrestrial missions is the forward contamination of the alien environment with microbes and biological molecules, transported on spacecraft from Earth. Furthermore, organisms and molecules can be brought to the sampling place from the surface. All this can lead to serious misinterpretations of the obtained data and more impor-tantly, could irreversibly alter the pristine nature of the extraterrestrial environments. These issues were addressed and are constantly updated in COSPAR planetary protection policy (20 October 2002; Amended 24 March 2005; 20 July 2008). The objective of our study was to investigate the efficacy of different in-situ decontamination protocols in the conditions of thermo-mechanical ice-melting. We evaluated survival rate of microorganisms on the melting probe as a function of both time and penetration depth. Special focus was made on deter-mination of the optimal concentration of chemical decontaminants (hydrogen peroxide and sodium hypochlorite) the peculiarities of their antimicrobial action at low temperatures (-80 to 0C) combined with constant dilution with melted ice and mechanical abrasion. Common, non-pathogenic microbial strains belonging to different morphological and metabolic groups (Pseudomonas, Micrococcus, Escherichia, Bacillus and others) were chosen as test objects for this study. The working part of the melting probe was first controllably contaminated by in-cubation in suspension of microbial cells. After appropriate sedimentation of microbial cells had been reached, the drilling-melting process was started using specially prepared sterile ice blocks. Every 2 minutes the samples were taken and analyzed. In the control tests, 1 mL of distilled water was injected into the penetration site at the onset of drilling. In the other tests, 1 mL of hydrogen peroxide (30Collected data suggest high efficacy of both used compounds in respect of all tested microbial groups. Typically, 99.9

Digel, Ilya

45

Interactions between snow and melt ponds in sea ice models  

NASA Astrophysics Data System (ADS)

Snow cover on sea ice at the end of the winter persists into the early part of the sea ice melt season, and the spatial distribution of snow affects the surface topography, the distribution of initial melt pond formation and its subsequent evolution. After the initial formation of melt ponds, the low albedo of the ponds compared to snow or bare ice causes the ponds to preferentially absorb solar radiation and therefore further affects surface ice melt. A physically based melt pond model was coupled to the thermodynamic-dynamic Louvain-la-Neuve Sea-Ice Model (LIM, version 3), which recently includes a representation of snow properties and processes. In the new snow scheme, snow is represented in multiple layers with varying thermo-physical properties, and simple parameterizations for blowing snow and fresh water refreezing into the snow were implemented. Several simulations were performed using the combined snow and melt pond configuration to study the impacts of the processes described above on the Arctic sea ice melt pond fractions. Preliminary results lead to two expected but uncorroborated model behaviors. In the simulations, blowing snow tends to decrease the average snow depth on sea ice due to losses into leads, thus allowing wider but shallower ponds on multiyear ice, while no significant effect is noticeable on first-year ice. Similarly, the refreezing of water in the snow curtails the amount of meltwater available to feed melt ponds on thick ice categories, where some snow may persist through the melt season, but has a limited or no impact on thin ice where snow melts away rapidly.

Lecomte, Olivier; Fichefet, Thierry; Flocco, Daniela; Schroeder, David; Vancoppenolle, Martin

2014-05-01

46

High density amorphous ice at room temperature  

PubMed Central

The phase diagram of water is both unusual and complex, exhibiting a wide range of polymorphs including proton-ordered or disordered forms. In addition, a variety of stable and metastable forms are observed. The richness of H2O phases attests the versatility of hydrogen-bonded network structures that include kinetically stable amorphous ices. Information of the amorphous solids, however, is rarely available especially for the stability field and transformation dynamics—but all reported to exist below the crystallization temperature of approximately 150–170 K below 4–5 GPa. Here, we present the evidence of high density amorphous (HDA) ice formed well above the crystallization temperature at 1 GPa—well inside the so-called “no-man’s land.” It is formed from metastable ice VII in the stability field of ice VI under rapid compression using dynamic-diamond anvil cell (d-DAC) and results from structural similarities between HDA and ice VII. The formation follows an interfacial growth mechanism unlike the melting process. Nevertheless, the occurrence of HDA along the extrapolated melt line of ice VII resembles the ice Ih-to-HDA transition, indicating that structural instabilities of parent ice VII and Ih drive the pressure-induced amorphization. PMID:21518902

Chen, Jing-Yin; Yoo, Choong-Shik

2011-01-01

47

Pressure Melting of Ice: While-U-Wait  

NSDL National Science Digital Library

In this demonstration, students get to witness pressure melting and regelation first-hand. A weight is suspended via a thin wire over an ice cube. Over the course of the course of the demonstration, the wire passess through the ice, leaving undamaged ice in its wake.

Demonstration by W.W. Locke, Department of Earth Sciences, Montana State University. Starting Point page by John McDaris.

48

Climate variability, warming and ice melt on the Antarctic Peninsula over the last millennium (Invited)  

NASA Astrophysics Data System (ADS)

The Antarctic Peninsula has experienced rapid warming over the past 50 years, which has led to extensive summer ice melt, the collapse of ice shelves and the acceleration of glacial outflow. But the short observational records of Antarctic climate don't allow for an understanding of how unusual the recent conditions may be. We present reconstructions of temperature and melt history since 1000 AD from a highly resolved ice core record from James Ross Island on the northeastern Antarctic Peninsula. The spatial pattern of temperature variability across networks of palaeoclimate reconstructions demonstrates that the Southern Annular Mode (SAM) has been an important driver of Antarctic Peninsula climate variability over a range of time scales. Rapid warming of the Antarctic Peninsula since the mid-20th century is consistent with strengthening of the SAM by a combination of greenhouse and later ozone forcing. The rare reconstruction of summer melting, from visible melt layers in the ice core, demonstrates the non-linear response of ice melt to increasing summer temperatures. Melting in the region is now more intense than at any other time over the last 1000 years and suggests that the Antarctic Peninsula is now particularly susceptible to rapid increases in ice loss in response to relatively small increases in mean temperature.

Abram, N.; Mulvaney, R.; Wolff, E. W.; Triest, J.; Kipfstuhl, S.; Trusel, L. D.; Vimeux, F.; Fleet, L.; Arrowsmith, C.

2013-12-01

49

Circulation and melting beneath the ross ice shelf.  

PubMed

Thermohaline observations in the water column beneath the Ross Ice Shelf and along its terminal face show significant vertical stratification, active horizontal circulation, and net melting at the ice shelf base. Heat is supplied by seawater that moves southward beneath the ice shelf from a central warm core and from a western region of high salinity. The near-freezing Ice Shelf Water produced flows northward into the Ross Sea. PMID:17734137

Jacobs, S S; Gordon, A L; Ardai, J L

1979-02-01

50

Ising model for melt ponds on Arctic sea ice  

E-print Network

The albedo of melting Arctic sea ice, a key parameter in climate modeling, is determined by pools of water on the ice surface. Recent observations show an onset of pond complexity at a critical area of about 100 square meters, attended by a transition in pond fractal dimension. To explain this behavior and provide a statistical physics approach to sea ice modeling, we introduce a two dimensional Ising model for pond evolution which incorporates ice-albedo feedback and the underlying thermodynamics. The binary magnetic spin variables in the Ising model correspond to the presence of melt water or ice on the sea ice surface. The model exhibits a second-order phase transition from isolated to clustered melt ponds, with the evolution of pond complexity in the clustered phase consistent with the observations.

Ma, Y -P; Golden, K M

2014-01-01

51

Is Global Warming Melting the Greenland Ice Sheet?  

NASA Astrophysics Data System (ADS)

Concerted observational and modelling programmes are underway to determine the mass balance of the Greenland Ice Sheet, and therefore help predict its response to future climatic change. We present results of meteorological modelling based on ERA-40 reanalysis data from the European Centre for Medium Range Weather Forecasts (ECMWF). Our novel surface-mass-balance history of the ice sheet for 1958-2003, is based on accumulation (snowfall minus evaporation/sublimation) modelling and a new monthly melt-water runoff model by Janssens & Huybrechts (Huybrechts 2002). These techniques combined yield valuable insights into the past and present state and variability of the Greenland ice mass and links with climate. Aspects of the validation of the new accumulation, runoff and SMB series are discussed. There was considerable interannual variability in snow accumulation, runoff and mass balance over the last 46 years. By comparing with long-term temperature, precipitation and accumulation records from the meteorological stations and ice cores, we discuss possible climatic factors forcing the ice in this period. There are distinct signals in runoff and SMB following three major volcanic eruptions. Runoff losses from the ice sheet were 280(±28) km^3 yr^-1 in 1961-90 and 391(+-39) km^3 yr^-1 in 1998-2003. Significantly rising runoff since the 1990s has been partly offset by more precipitation. However, our best estimate of overall mass balance declined from -3(±53) km^3 yr^-1 in 1961-90 to -65(±61) km^3 yr^-1 in 1998-2003. Additional dynamical factors that cause an acceleration of ice flow near the margins, and possible enhanced iceberg calving, may have led to a more negative mass balance in the past few years than suggested here. The implication is a significant and accelerating recent contribution from the ice sheet, about 0.22 mm yr^-1 over the last six years, to global sea-level rise. Runoff and thinning of the ice-sheet margins increased substantially since the 1990s. However, massive snow accumulation over south-east Greenland during winter 2002/03, well shown in our analysis, led to unprecedented thickening in recent NASA aircraft LIDAR surveys. Do these recent changes indicate more extreme weather conditions including warming over the Ice Sheet, more storminess and higher accumulation events, due to global warming?

Hanna, E.; Huybrechts, P.; Janssens, I.; McConnell, J.; Das, S.; Cappelen, J.; Steffen, K.; Krabill, W.; Thomas, R.; Stephens, A.

2004-12-01

52

Strong sensitivity of Pine Island ice-shelf melting to climatic variability.  

PubMed

Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice-shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate. PMID:24385606

Dutrieux, Pierre; De Rydt, Jan; Jenkins, Adrian; Holland, Paul R; Ha, Ho Kyung; Lee, Sang Hoon; Steig, Eric J; Ding, Qinghua; Abrahamsen, E Povl; Schröder, Michael

2014-01-10

53

Thin sectioning and surface replication of ice at low temperature.  

USGS Publications Warehouse

We have developed a new technique for making thin sections and surface replicas of ice at temperatures well below 273d K. The ability to make thin sections without melting sample material is important in textural and microstructural studies of ice deformed at low temperatures because of annealing effects we have observed during conventional section making.-from Author

Daley, M.A.; Kirby, S.H.

1984-01-01

54

Melting point of ice in aqueous saccharide solutions  

NASA Astrophysics Data System (ADS)

The melting point of ice in trehalose and sucrose solutions was measured by in situ observations of a minute ice crystal. It was found that the concentration dependence of the melting point of ice in both trehalose and sucrose solutions was identical. Such a concentration dependence of the melting point was in agreement with the equation of freezing point depression for dilute aqueous solutions up to about 1 molal. In addition, the measured values of the melting point decreased rapidly with an increase in the concentration. These experimental results for an equilibrium state were discussed by comparing them with the results for a nonequilibrium state, i.e., the results obtained for growing ice crystals in saccharide solutions.

Sei, Tadanori; Gonda, Takehiko

2006-07-01

55

A model of the threedimensional evolution of Arctic melt ponds on firstyear and multiyear sea ice  

E-print Network

A model of the threedimensional evolution of Arctic melt ponds on firstyear and multiyear sea ice F ice. In the summer the upper layers of sea ice and snow melts producing meltwater that accumulates in Arctic melt ponds on the surface of sea ice. An accurate estimate of the fraction of the sea ice surface

Feltham, Daniel

56

Object-based Image Classification of Arctic Sea Ice and Melt Ponds through Aerial Photos  

NASA Astrophysics Data System (ADS)

The last six years have marked the lowest Arctic summer sea ice extents in the modern era, with a new record summer minimum (3.4 million km2) set on 13 September 2012. It has been predicted that the Arctic could be free of summer ice within the next 25-30. The loss of Arctic summer ice could have serious consequences, such as higher water temperature due to the positive feedback of albedo, more powerful and frequent storms, rising sea levels, diminished habitats for polar animals, and more pollution due to fossil fuel exploitation and/ or increased traffic through the Northwest/ Northeast Passage. In these processes, melt ponds play an important role in Earth's radiation balance since they strongly absorb solar radiation rather than reflecting it as snow and ice do. Therefore, it is necessary to develop the ability of predicting the sea ice/ melt pond extents and space-time evolution, which is pivotal to prepare for the variation and uncertainty of the future environment, political, economic, and military needs. A lot of efforts have been put into Arctic sea ice modeling to simulate sea ice processes. However, these sea ice models were initiated and developed based on limited field surveys, aircraft or satellite image data. Therefore, it is necessary to collect high resolution sea ice aerial photo in a systematic way to tune up, validate, and improve models. Currently there are many sea ice aerial photos available, such as Chinese Arctic Exploration (CHINARE 2008, 2010, 2012), SHEBA 1998 and HOTRAX 2005. However, manually delineating of sea ice and melt pond from these images is time-consuming and labor-intensive. In this study, we use the object-based remote sensing classification scheme to extract sea ice and melt ponds efficiently from 1,727 aerial photos taken during the CHINARE 2010. The algorithm includes three major steps as follows. (1) Image segmentation groups the neighboring pixels into objects according to the similarity of spectral and texture information; (2) random forest ensemble classifier can distinguish the following objects: water, submerged ice, shadow, and ice/snow; and (3) polygon neighbor analysis can further separate melt ponds from submerged ice according to the spatial neighboring relationship. Our results illustrate the spatial distribution and morphological characters of melt ponds in different latitudes of the Arctic Pacific sector. This method can be applied to massive photos and images taken in past years and future years, in deriving the detailed sea ice and melt pond distribution and changes through years.

Miao, X.; Xie, H.; Li, Z.; Lei, R.

2013-12-01

57

Applying Archimedes' Law to Ice Melting in Sea Water  

NASA Astrophysics Data System (ADS)

Archimedes stated that a floating body displaces its own weight of liquid, but his law has been widely misapplied to ice floating in the oceans by scientists who assumed that equal weights correspond to equal liquid volumes. It is often said that when floating ice melts, the sea level does not rise "because of Archimedes' law." True when ice floats in fresh water, but a myth for ice in oceans! Most ice floating in the oceans is nearly pure water. When it melts, the pure water produced has about 2.6% more volume than the salt water that was displaced, and the ocean slightly rises. It is often suggested that students demonstrate the "fact" of no rise in the sea surface by melting ice cubes floating in a glass of water; such a demonstration even appears in the movie "An Inconvenient Truth." Let's teach students to spot such errors. We highlight a couple more "surprise issues." First, the density of the floating ice, if it is free of salt and dirt, is irrelevant, so long as it floats. Next, when "grounded" ice (resting on land), enters the sea, it initially displaces less water than its melted form will eventually add to the sea. Thus, an event of that kind, such as formation of an iceberg, produces a rise of the sea level in two stages. We conclude with a series of thought-experiments that could help teachers and students discern the correct result, and a photo of a demonstration.

Noerdlinger, Peter D.; Brower, K. R.

2006-12-01

58

Winter sea ice melting in the Atlantic Water subduction area, Svalbard Norway  

NASA Astrophysics Data System (ADS)

we study a small area along the shelf west of Spitsbergen, near Prins Karls Forland, where warm, saline Atlantic Water of the West Spitsbergen Current currently first encounters sea ice. This sea ice is drifting in a coastal current that carries Arctic Water originating from the Barents Sea northward over the shelf. Our aim was to investigate whether melting of sea ice by Atlantic Water in this area might be a significant factor that could contribute to the formation of a cold halocline layer that isolates the sea ice from further melting from below. Observations of temperature and salinity profiles were collected during two winters, via CTD-SRDL instruments deployed on harbor seals (Phoca vitulina), and fed into a heat and freshwater budget box model in order to quantify the importance of melting relative to other processes that could transform the shelf water mass during winter. Cross-frontal exchange of Atlantic Water from the West Spitsbergen Current, driven by buoyancy forcing rather than Ekman upwelling, was determined to be the source of the heat that melted drift ice on the shelf. Some local sea ice formation did take place, but its importance in the total heat and freshwater budgets appeared to be minor. The data suggest that the production of a cold halocline layer was preceded by southerly winds and rapid drift ice melting.

Tverberg, V.; Nøst, O. A.; Lydersen, C.; Kovacs, K. M.

2014-09-01

59

Climate Data Records (CDRs) for Ice Motion, Ice Age, and Melt Pond Fraction  

Microsoft Academic Search

Remotely-sensed Arctic sea ice motion, sea ice age, and melt pond coverage have been proposed for development into full CDRs. The first has a considerable history of use, while the latter two are relatively new products. Our technique to estimate sea ice motion utilizes images from SSM\\/I, as well as the Scanning Multichannel Microwave Radiometer (SMMR) and the series of

M. A. Tschudi; J. A. Maslanik; C. Fowler; J. C. Stroeve; I. G. Rigor

2010-01-01

60

Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet.  

PubMed

In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting. PMID:24843158

Keegan, Kaitlin M; Albert, Mary R; McConnell, Joseph R; Baker, Ian

2014-06-01

61

Climate Data Records (CDRs) for Ice Motion, Ice Age, and Melt Pond Fraction  

NASA Astrophysics Data System (ADS)

Remotely-sensed Arctic sea ice motion, sea ice age, and melt pond coverage have been proposed for development into full CDRs. The first has a considerable history of use, while the latter two are relatively new products. Our technique to estimate sea ice motion utilizes images from SSM/I, as well as the Scanning Multichannel Microwave Radiometer (SMMR) and the series of Advanced Very High Resolution Radiometer (AVHRR) sensors to estimate the daily motion of ice parcels. This method is augmented by incorporating ice motion observations from the network of drifting buoys deployed as part of the International Arctic Buoy Program. Our technique to calculate ice age relies on following the actual age of the ice for each ice parcel, categorizing the parcel as first-year ice, second-year ice, etc. based on how many summer melt seasons the ice parcel survives. Our method to estimate melt pond coverage on sea ice involves solving a set of linear equations that relate each surface feature’s individual reflectance within the sensor’s (currently using the MODIS surface reflectance product, MOD09) pixel to the overall reflectance in that pixel. These three research-grade products have been interpolated onto 25x25 km grid points spanning the entire Arctic Ocean using the Equal-Area Scalable Earth (EASE) grid.

Tschudi, M. A.; Maslanik, J. A.; Fowler, C.; Stroeve, J. C.; Rigor, I. G.

2010-12-01

62

Induced ice melting by the snow flea antifreeze protein from molecular dynamics simulations.  

PubMed

Antifreeze proteins (AFP) allow different life forms, insects as well as fish and plants, to survive in subzero environments. AFPs prevent freezing of the physiological fluids. We have studied, through molecular dynamics simulations, the behavior of the small isoform of the AFP found in the snow flea (sfAFP), both in water and at the ice/water interface, of four different ice planes. In water at room temperature, the structure of the sfAFP is found to be slightly unstable. The loop between two polyproline II helices has large fluctuations as well as the C-terminus. Torsional angle analyses show a decrease of the polyproline II helix area in the Ramachandran plots. The protein structure instability, in any case, should not affect its antifreeze activity. At the ice/water interface the sfAFP triggers local melting of the ice surface. Bipyramidal, secondary prism, and prism ice planes melt in the presence of AFP at temperatures below the melting point of ice. Only the basal plane is found to be stable at the same temperatures, indicating an adsorption of the sfAFP on this ice plane as confirmed by experimental evidence. PMID:25353109

Todde, Guido; Whitman, Christopher; Hovmöller, Sven; Laaksonen, Aatto

2014-11-26

63

Modis LST as an Index of Summer Melt Conditions over Arctic Ice Caps  

NASA Astrophysics Data System (ADS)

Despite the large area of glacier ice in the Arctic, very few in situ mass balance and air temperature measurements exist over Arctic ice caps. There is therefore a need to develop proxy records of summer melt conditions on these ice caps in order to identify spatial patterns and temporal trends in surface mass balance across the region. Analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) derived land surface temperatures (LST) may provide a method to evaluate melt and climate trends over Arctic ice caps for the last decade. MODIS LST data were used to derive the seasonal mean of 8-day average values of daytime clear-sky surface temperature over 30 Arctic ice caps for each melt season from 2000 to 2010. LST was retrieved for a specified area within each individual ice cap, defined as the largest contiguous area of ice and snow within that ice cap. The melt season was defined as the period between the 10-year mean of melt onset and freeze-up dates derived from QuikScat. Given the potential biases introduced by the facts that a) LST data are available only for clear sky days and b) cloudiness likely varies substantially across the Arctic glaciated regions, there is a need to verify LST measurements against known changes in air temperature across all these regions. NCEP/NCAR R1 Reanalysis temperatures provide a single consistent dataset with which to evaluate air temperature trends. Ice caps in Alaska, the Canadian Arctic Archipelago (CAA) and Greenland display a common shift toward strong positive anomalies in the 2000's (0.45 to 1.2°C). The Iceland and Svalbard ice caps show weaker positive air temperature anomalies in the same period (0.38 to 0.4°C), while the Novaya Zemlya, Severnaya Zemlya and Franz Josef Land ice caps (Russia) display negative anomalies (-0.10 to -0.25°C). LST track the NCEP air temperature records at 700 hPa in the CAA (r2 0.6 to 0.96) and northern Svalbard (r2 0.6 to 0.76) only. This talk will explore whether the observed differences in degree of correlation between the LST and air temperature records is directly related to regional variations in the number of individual LST measurements contributing to the 8-day LST product and, if so, whether these variations are due primarily to differences in the incidence of cloud cover.

Geai, M. E.; Sharp, M. J.

2011-12-01

64

Climatic warming and basal melting of large ice sheets: possible implications for East Antarctica  

SciTech Connect

Climatic warming is shown to be capable of inducing shear heating instability and basal melting in a model ice sheet that is creeping slowly downslope. Growth times of the instability are calculated from a nonlinear analysis of temperature and flow in the model ice sheet whose surface undergoes a prescribed increase of temperature. The source of instability lies in the decrease of maximum ice thickness for steady downslope creep with increasing surface temperature. A surface temperature increase of 5 to 10 k can cause instability on a 10/sup 4/ year time scale for realistic ice rheology. The instability occurs suddenly after a prolonged period of dormancy. The instability might be relevant to the East Antarctic ice sheet. Warming associated with the Holocene interglacial epoch that heralded the end of the last ice age may have set the East Antarctic ice sheet on a course toward wide-spread instability some 10/sup 4/ years later. The present CO/sub 2/-induced climate warming is also a potential trigger for instability and basal melting of the East Antarctic ice sheet.

Saari, M.R.; Yuen, D.A.; Schubert, G.

1987-01-01

65

Calorimetric study of crystal growth of ice in hydrated methemoglobin and of redistribution of the water clusters formed on melting the ice.  

PubMed Central

Calorimetric studies of the melting patterns of ice in hydrated methemoglobin powders containing between 0.43 and 0.58 (g water)/(g protein), and of their dependence on annealing at subzero temperatures and on isothermal treatment at ambient temperature are reported. Cooling rates were varied between approximately 1500 and 5 K min-1 and heating rate was 30 K min-1. Recrystallization of ice during annealing is observed at T > 228 K. The melting patterns of annealed samples are characteristically different from those of unannealed samples by the shifting of the melting temperature of the recrystallized ice fraction to higher temperatures toward the value of "bulk" ice. The "large" ice crystals formed during recrystallization melt on heating into "large" clusters of water whose redistribution and apparent equilibration is followed as a function of time and/or temperature by comparison with melting endotherms. We have also studied the effect of cooling rate on the melting pattern of ice with a methemoglobin sample containing 0.50 (g water)/(g protein), and we surmise that for this hydration cooling at rates of > or = approximately 150 K min-1 preserves on the whole the distribution of water molecules present at ambient temperature. PMID:7819504

Sartor, G; Mayer, E

1994-01-01

66

What controls dead-ice melting under different climate conditions? A discussion  

NASA Astrophysics Data System (ADS)

In the geological record, hummocky dead-ice moraines represent the final product of the melt-out of dead-ice. Processes and rates of dead-ice melting in ice-cored moraines and at debris-covered glaciers are commonly believed to be governed by climate and debris-cover properties. Here, backwasting rates from 14 dead-ice areas are assessed in relation to mean annual air temperature, mean summer air temperature, mean annual precipitation, mean summer precipitation, and annual sum of positive degree days. The highest correlation was found between backwasting rate and mean annual air temperature. However, the correlation between melt rates and climate parameters is low, stressing that processes and topography play a major role in governing the rates of backwasting. The rates of backwasting from modern glacial environments should serve as input to de-icing models for ancient dead-ice areas in order to assess the mode and duration of deposition. A challenge for future explorations of dead-ice environments is to obtain long-term records of field-based monitoring of melt progression. Furthermore, many modern satellite-borne sensors have high potentials for recordings of multi-temporal Digital Elevation Models (DEMs) for detection and quantification of changes in dead-ice environments. In recent years, high-accuracy DEMs from airborne laser scanning altimetry (LiDAR) are emerging as an additional data source. However, time series of high-resolution aerial photographs remain essential for both visual inspection and high-resolution stereographic DEM production.

Schomacker, Anders

2008-11-01

67

Synoptic and mesoscale climate forcing on Antarctic ice shelf surface melt dynamics  

NASA Astrophysics Data System (ADS)

Given that the polar regions, especially the Antarctic Peninsula, have experienced one of the largest temperature increases on Earth over the last few decades, an understanding of Antarctic climate has become more urgent. Ice shelves themselves are located at the intersection of the atmosphere, hydrosphere and the cryosphere---the air-ice-ocean boundary, and are sensitive to changes in any of these media. In addition to being particularly sensitive to changes in climate, ice shelves play an important role in controlling the flow of glaciers into the ocean, which has important implications for sea level changes. In a warming world, an increased understanding of how climate change is affecting Antarctic ice shelves is valuable for assessing vulnerable regions of the Antarctic that may be prone to further instability. This work focuses on determining the underlying climatic processes controlling energy and mass balance responsible for driving melting over ice shelves. A novel melt-magnitude retrieval method is presented that uses Moderate Resolution Imaging Spectroradiometer (MODIS)-derived near-IR reflectance coupled with ice surface temperature as a proxy for surface melt magnitude. This method has a higher spatial resolution than passive microwave melt detection, has the added benefit of retrieving melt magnitude rather than a binary melt occurrence or non-occurrence, but has a lower temporal resolution than either passive-microwave or microwave-scatterometry melt detection. This limitation is a result of the opacity of cloud cover to both visible and IR radiation, requiring more satellite overpasses to obtain spatially contiguous imagery. This work also examines several weather variables associated with a large-extent, long-duration surface melt event on the Ross Ice Shelf. It is shown that cloudy conditions coupled with increased sensible and latent heat flux to the surface were present during the event, and these conditions are consistent with those that induce surface melting. Finally, an analysis of co-occurring climate conditions and surface melting over a recent 15-year time period (1987-2002) is presented. This analysis examines surface melt extent in three regions: Ross Ice Shelf, Larsen Ice Shelf and the Amundsen-Bellingshausen Region. Self-Organizing Maps (SOMs) are used to categorize weather patterns for each December and January day during the study period, and the average surface melt extent for each SOM pattern is computed. These values are compared to average December and January surface melt extents for each region to determine the SOM patterns associated with significantly greater or significantly less melt than the 15-year average. Over the Ross region, increases in sensible and latent heat fluxes are associated with greater surface melt extent, as is the presence of cyclonic circulation in the Ross Sea that drives mild maritime air poleward. In the Larsen and Amundsen-Bellingshausen regions, radiation fluxes appear to be more closely associated with surface melt extent, although the relationship for the geographically heterogeneous Amundsen-Bellingshausen region is less clear. These results can guide future mesoscale modeling studies that will be able to more precisely determine the causative role of each atmospheric variable in generating surface melting on West Antarctic ice shelves.

Karmosky, Christopher

68

A new approach to the study of interfacial melting of ice: infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Faraday observed in 1850 "that a particle of water which could retain the liquid state whilst touching ice on only one side, could not retain the liquid if it were touched by ice on both" (M. Faraday, Royal Institution Discourse, June 7, 1850; Experimental Researches in Chemistry and Physics (Taylor and Francis, New York, 1991)). Thus began the concept of interfacial melting, and the presence of a liquid water film on the surface of ice at temperatures of 0degreesC and below. Over the past few decades, there have been a number of measurements of interfacial melting. In some studies, the thickness of the thin film, variously called the quasi-liquid layer (QLL), liquid-like layer, surface melting layer, or premelting layer, has been determined. The results of these measurements demonstrate a striking variation depending on the experimental method and the nature of the ice samples. For example, at -0.1degreesC, the thickness values range over two orders of magnitude from around 1 to 100 nm. Although the disagreement can be partially explained by the differences in ice samples, the experimental techniques employed in measurements of the QLL thickness are based on different physical principals, and involve a web of assumptions for their deconvolution. We describe here the technique of infrared attenuated total reflection (ATR) spectroscopy that has been directed to the study of interfacial melting of ice for the first time.

Sadtchenko, V.; Ewing, G. E.

2003-01-01

69

Increased Runoff from Melt from the Greenland Ice Sheet: A Response to Global Warming  

Microsoft Academic Search

The authors attribute significantly increased Greenland summer warmth and Greenland Ice Sheet melt and runoff since 1990 to global warming. Southern Greenland coastal and Northern Hemisphere summer temperatures were uncorrelated between the 1960s and early 1990s but were significantly positively corre- lated thereafter. This relationship appears to have been modulated by the North Atlantic Oscillation, whose summer index was significantly

Edward Hanna; Philippe Huybrechts; Konrad Steffen; John Cappelen; Russell Huff; Christopher Shuman; Tristram Irvine-Fynn; Stephen Wise; Michael Griffiths

2008-01-01

70

The NE Greenland Ice Sheet during the last glacial - a dynamic retreat from the shelf edge triggered by ice melting?  

NASA Astrophysics Data System (ADS)

The dynamics of the north-eastern sector of the Greenland Ice Sheet during the last glacial are still poorly constrained and large uncertainties about its extent exist. We present new swath-bathymetry data and sub-bottom profiles acquired from the outer parts of a shelf-crossing trough. These data reveal glacial landforms suggesting that grounded ice extended to the shelf break. Thus, the hypothesis of a mid-shelf position of the ice sheet in this area during the last glacial maximum is rejected, instead other studies predicting an ice expansion to the shelf break is reinforced. The results presented here also add further details on the behavior of the ice sheet during the initial deglaciation. The outer trough studied was characterized by the formation of a complex pattern of moraine ridges and sediment wedges overlying mega-scale glacial lineations, providing evidence of repeated halts and readvances of the ice sheet during an early phase of its decay. This suggests that the early deglaciation was related to melting of the grounded ice due to temperature increase in the ocean, rather than being triggered by abrupt sea level rise. The latter should, according to established models, result in ice lift-off and a sea floor dominated by landforms formed during full-glacial conditions (mega-scale glacial lineations) and ice disintegration (iceberg plough-marks).

Sverre Laberg, Jan; Forwick, Matthias; Husum, Katrine

2014-05-01

71

Is the Antarctic Ice Sheet melting?  

NASA Astrophysics Data System (ADS)

I review recent research exploring the mass balance of the Antarctic Ice Sheet. Studies based on the comparison of mass input with mass output (flux method) or time-variable gravity (gravity method) indicate that Antarctica is losing mass and the mass loss is increasing with time. These two independent techniques agree on the magnitude of the loss and on its rate of increase with time. A third technique, purely geodetic, indicates that variations in Earth oblateness (J2) require a mass loss from both Greenland and Antarctica in order to be explained, hence confirming an Antarctic contribution. Finally, the discovery of a significant mass loss from Antarctica in the last few years is the main reason we can now confidently close the sea level water budget. A few other studies based on satellite altimetry, have challenged these results and suggested a much lower loss. I will review the reason for the difference. More important, the last twenty years of Antarctic data show that the continent is changing more rapidly and sooner than anticipated by climate models. The mass loss is only a fraction of the annual turn over of mass and only a few regions contribute. The connection between mass loss and global climate is complex and not fully resolved. We detect no long-term change in snowfall. Most losses are caused by glacier acceleration in response to ice shelf collapse (Peninsula) or to the presence of warm waters beneath buttressing ice shelves in front of the glaciers (West Antarctica). Our understanding of the evolution of the Southern Ocean near the ice sheet periphery is however limited and insufficient. Projecting future changes is challenging, data striven, and deeply interdisciplinary. Recent climate modeling studies however indicate that a significant subsurface oceanic warming is possible over the next two centuries which would cause much larger losses of ice mass from Antarctica.

Rignot, E. J.

2011-12-01

72

Antarctic ice-sheet loss driven by basal melting of ice shelves.  

PubMed

Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers. Indeed, recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. But the extent and magnitude of ice-shelf thickness change, the underlying causes of such change, and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow. The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen seas, and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance, and hence global sea level, on annual to decadal timescales. PMID:22538614

Pritchard, H D; Ligtenberg, S R M; Fricker, H A; Vaughan, D G; van den Broeke, M R; Padman, L

2012-04-26

73

A meteorological experiment in the melting zone of the Greenland ice sheet  

SciTech Connect

Preliminary results are described from a glaciometeorological experiment carried out in the margin (melting zone) of the Greenland ice sheet in the summers of 1990 and 1991. This work was initiated within the framework of a Dutch research program on land ice and sea level change. Seven meteostations were operated along a transect running from the tundra well onto the ice sheet. At the ice edge, humidity, temperature, and wind profiles were obtained with a tethered balloon. On the ice sheet, 90 km from the edge, a boundary-layer research unit, including a sound detecting and ranging system (SODAR) and a radio acoustic sounding system (RASS), was established. Although focusing on the relation between surface energy balance, glacier mass balance, and ice flow, the experiment has also delivered a unique dataset on the dynamics of the atmospheric boundary layer around the warm tundra-cold ice sheet transition. Unexpected behavior was found for the surface albedo during the melt season. Lowest values are not found close to the ice edge, which is usual for glaciers, but higher on the ice sheet. Meltwater accumulation due to inefficient surface drainage was found to be the cause for this. The wind regime is dominated by katabatic flow from the ice sheet. The katabatic layer is typically 100-200 m thick. Close to the ice edge, the flow exhibits a very regular daily rhythm, with maximum wind speed in the afternoon. Farther on the ice sheet, the regime changes, and wind speed reaches maximum values in late night/early morning.

Oerlemans, J. (Utrecht Univ. (Netherlands)); Vugts, H.F. (Free Univ. of Amsterdam (Netherlands))

1993-03-01

74

High Geothermal Heat Flow, Basal Melt, and the Origin of Rapid Ice Flow in Central Greenland  

Microsoft Academic Search

Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenland. Melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet. Locally, high melt rates indicate geothermal fluxes 15 to 30 times continental

Mark Fahnestock; Waleed Abdalati; Ian Joughin; John Brozena; Prasad Gogineni

2001-01-01

75

Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt  

E-print Network

Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt Michael Steele,1 summertime upper ocean warming and sea ice melt during the 21st century in the Arctic Ocean. Our first), Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt, J. Geophys. Res., 115, C

Zhang, Jinlun

76

Enhanced Sea Ice Concentration and Ice Temperature Algorithms for AMSR  

NASA Technical Reports Server (NTRS)

Accurate quantification of sea ice concentration and ice temperature from satellite passive microwave data is important because they provide the only long term, spatially detailed and consistent data set needed to study the climatology of the polar regions. Sea ice concentration data are used to derive large-scale daily ice extents that are utilized in trend analysis of the global sea ice cover. They are also used to quantify the amount of open water and thin ice in polynya and divergence regions which together with ice temperatures are in turn needed to estimate vertical heat and salinity fluxes in these regions. Sea ice concentrations have been derived from the NASA Team and Bootstrap algorithms while a separate technique for deriving ice temperature has been reported. An integrated technique that will utilizes most of the channels of AMSR (Advanced Microwave Scanning Radiometer) has been developed. The technique uses data from the 6 GHz and 37 GHz channels at vertical polarization obtain an initial estimate of sea ice concentration and ice temperature. The derived ice temperature is then utilized to estimate the emissivities for the corresponding observations at all the other channels. A procedure for calculating the ice concentration similar to the Bootstrap technique is then used but with variables being emissivities instead of brightness temperatures to minimizes errors associated with spatial changes in ice temperatures within the ice pack. Comparative studies of ice concentration results with those from other algorithms, including the original Bootstrap algorithm and those from high resolution satellite visible and infrared data will be presented. Also, results from a simulation study that demonstrates the effectiveness of the technique in correcting for spatial variations in ice temperatures will be shown. The ice temperature results are likewise compared with satellite infrared and buoy data with the latter adjusted to account for the effects of the snow cover.

Comiso, Josefino C.; Manning, Will; Gersten, Robert

1998-01-01

77

Update on the Greenland Ice Sheet Melt Extent: 1979-1999  

NASA Technical Reports Server (NTRS)

Analysis of melt extent on the Greenland ice sheet is updated to span the time period 1979-1999 is examined along with its spatial and temporal variability using passive microwave satellite data. In order to acquire the full record, the issue of continuity between previous passive microwave sensors (SMMR, SSM/I F-8, and SSM/I F-11), and the most recent SSM/I F-13 sensor is addressed. The F-13 Cross-polarized gradient ratio (XPGR) melt-classification threshold is determined to be -0.0154. Results show that for the 21-year record, an increasing melt trend of nearly 1 %/yr is observed, and this trend is driven by conditions on in the western portion of the ice sheet, rather than the east, where melt appears to have decreased slightly. Moreover, the eruption of Mt. Pinatubo in 1991 is likely to have had some impact the melt, but not as much as previously suspected. The 1992 melt anomaly is 1.7 standard deviations from the mean. Finally, the relationship between coastal temperatures and melt extent suggest an increase in surface runoff contribution to sea level of 0.31 mm/yr for a 1 C temperature rise.

Abdalati, Waleed; Steffen, Konrad

2000-01-01

78

Surface-melt driven Laurentide Ice Sheet retreat during the early A. E. Carlson,1  

E-print Network

Surface-melt driven Laurentide Ice Sheet retreat during the early Holocene A. E. Carlson,1 F. S mechanisms of ice-sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS (2009), Surface-melt driven Laurentide Ice Sheet retreat during the early Holocene, Geophys. Res. Lett

79

Eddy-resolving simulations of the Fimbul Ice Shelf cavity circulation: Basal melting and exchange with open ocean  

NASA Astrophysics Data System (ADS)

Melting at the base of floating ice shelves is a dominant term in the overall Antarctic mass budget. This study applies a high-resolution regional ice shelf/ocean model, constrained by observations, to (i) quantify present basal mass loss at the Fimbul Ice Shelf (FIS); and (ii) investigate the oceanic mechanisms that govern the heat supply to ice shelves in the Eastern Weddell Sea. The simulations confirm the low melt rates suggested by observations and show that melting is primarily determined by the depth of the coastal thermocline, regulating deep ocean heat fluxes towards the ice. Furthermore, the uneven distribution of ice shelf area at different depths modulates the melting response to oceanic forcing, causing the existence of two distinct states of melting at the FIS. In the simulated present-day state, only small amounts of Modified Warm Deep Water enter the continental shelf, and ocean temperatures beneath the ice are close to the surface freezing point. The basal mass loss in this so-called state of “shallow melting” is mainly controlled by the seasonal inflow of solar-heated surface water affecting large areas of shallow ice in the upper part of the cavity. This is in contrast to a state of “deep melting”, in which the thermocline rises above the shelf break depth, establishing a continuous inflow of Warm Deep Water towards the deep ice. The transition between the two states is found to be determined by a complex response of the Antarctic Slope Front overturning circulation to varying climate forcings. A proper representation of these frontal dynamics in climate models will therefore be crucial when assessing the evolution of ice shelf basal melting along this sector of Antarctica.

Hattermann, T.; Smedsrud, L. H.; Nøst, O. A.; Lilly, J. M.; Galton-Fenzi, B. K.

2014-10-01

80

Inference of optical properties from radiation profiles within melting landfast sea ice  

Microsoft Academic Search

Vertical in-ice spectral radiation profiles were measured within melting 1.5- to 1.7-m-thick landfast sea ice in western Hudson Bay on 25 April 2005. Because the surface ice was subject to extensive melting and refreezing, the sea ice had fractioned into two main types, i.e., areas of more reflective white ice and less reflective blue ice. The shortwave albedo was about

J. K. Ehn; T. N. Papakyriakou; D. G. Barber

2008-01-01

81

Sea Ice Melt in Summer 2013 Figure 1. Results from six ice mass balance buoys that operated throughout the summer of 2013. The red  

E-print Network

Sea Ice Melt in Summer 2013 Figure 1. Results from six ice mass balance buoys that operated is the MASIE ice extent on 28 August 2013 mapped on Google Earth. The 2013 Arctic sea ice melt season was observed at a buoy near the ice edge in the Beaufort Sea. This buoy had the largest total amount of melt

82

Basal ice facies and supraglacial melt-out till of the Laurentide Ice Sheet, Tuktoyaktuk Coastlands, western Arctic Canada  

NASA Astrophysics Data System (ADS)

Glacially-deformed massive ice and icy sediments (MI-IS) in the Eskimo Lakes Fingerlands and Summer Island area of the Tuktoyaktuk Coastlands, western Arctic Canada, show, in the same stratigraphic sequences, features characteristic of both basal glacier ice and intrasedimental ice. Basal-ice features comprise (1) ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in Alaska, Greenland and Iceland; (2) ice crystal fabrics similar to those from basal ice in Antarctica and ice-cored moraines on Axel Heiberg Island, Canada; and (3) a thaw or erosional unconformity along the top of the MI-IS, buried by glacigenic or aeolian sediments. Intrasedimental ice consists of pore ice and segregated ice formed within Pleistocene sands deposited before glacial overriding. The co-existence of basal and intrasedimental ice within the MI-IS records their occurrence within the basal ice layer of the Laurentide Ice Sheet. Stagnation of the ice sheet and melt-out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale. The widespread occurrence of supraglacial melt-out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost.

Murton, J. B.; Whiteman, C. A.; Waller, R. I.; Pollard, W. H.; Clark, I. D.; Dallimore, S. R.

2005-03-01

83

Modelling ice melting processes: numerical and experimental validation  

Microsoft Academic Search

Purpose – This work is devoted to the experimental analysis, numerical modelling and validation of ice melting processes. Design\\/methodology\\/approach – The thermally coupled incompressible Navier-Stokes equations including water density inversion and isothermal phase-change phenomena are assumed as the governing equations of the problem. A fixed-mesh finite element formulation is proposed for the numerical solution of such model. In particular, this

Marcela Cruchaga; Diego Celentano

2007-01-01

84

Melt Pond Development on Arctic Land-Fast Sea Ice in Relation to Snow and Ice Properties During the Ice Growth Season  

Microsoft Academic Search

The dynamics of melt pond development on sea ice were studied on a well-defined patch of level land-fast sea ice off the coast of Barrow, Alaska in 2008. The pond development was correlated with both sea ice properties and the history of snow distribution during the ice growth season. In mid January, the ice was covered by an almost level

C. Petrich; H. Eicken; D. Pringle; M. Sturm; D. Perovich; C. Polashenski; D. Finnegan

2008-01-01

85

High geothermal heat flow, Basal melt, and the origin of rapid ice flow in central Greenland.  

PubMed

Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenland. Melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet. Locally, high melt rates indicate geothermal fluxes 15 to 30 times continental background. The southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin. PMID:11743197

Fahnestock, M; Abdalati, W; Joughin, I; Brozena, J; Gogineni, P

2001-12-14

86

Field-calibrated model of melt, refreezing, and runoff for polar ice caps: Application to Devon Ice Cap  

NASA Astrophysics Data System (ADS)

the controls on the amount of surface meltwater that refreezes, rather than becoming runoff, over polar ice masses is necessary for modeling their surface mass balance and ultimately for predicting their future contributions to global sea level change. We present a modified version of a physically based model that includes an energy balance routine and explicit calculation of near-surface meltwater refreezing capacity, to simulate the evolution of near-surface density and temperature profiles across Devon Ice Cap in Arctic Canada. Uniquely, our model is initiated and calibrated using high spatial resolution measurements of snow and firn densities across almost the entire elevation range of the ice cap for the summer of 2004 and subsequently validated with the same type of measurements obtained during the very different meteorological conditions of summer 2006. The model captures the spatial variability across the transect in bulk snowpack properties although it slightly underestimates the flow of meltwater into the firn of previous years. The percentage of meltwater that becomes runoff is similar in both years; however, the spatial pattern of this melt-runoff relationship is different in the 2 years. The model is found to be insensitive to variation in the depth of impermeable layers within the firn but is very sensitive to variation in air temperature, since the refreezing capacity of firn decreases with increasing temperature. We highlight that the sensitivity of the ice cap's surface mass balance to air temperature is itself dependent on air temperature.

Morris, Richard M.; Mair, Douglas W. F.; Nienow, Peter W.; Bell, Christina; Burgess, David O.; Wright, Andrew P.

2014-09-01

87

Bacterial communities of surface mixed layer in the Pacific sector of the western Arctic Ocean during sea-ice melting.  

PubMed

From July to August 2010, the IBRV ARAON journeyed to the Pacific sector of the Arctic Ocean to monitor bacterial variation in Arctic summer surface-waters, and temperature, salinity, fluorescence, and nutrient concentrations were determined during the ice-melting season. Among the measured physicochemical parameters, we observed a strong negative correlation between temperature and salinity, and consequently hypothesized that the melting ice decreased water salinity. The bacterial community compositions of 15 samples, includicng seawater, sea-ice, and melting pond water, were determined using a pyrosequencing approach and were categorized into three habitats: (1) surface seawater, (2) ice core, and (3) melting pond. Analysis of these samples indicated the presence of local bacterial communities; a deduction that was further corroborated by the discovery of seawater- and ice-specific bacterial phylotypes. In all samples, the Alphaproteobacteria, Flavobacteria, and Gammaproteobacteria taxa composed the majority of the bacterial communities. Among these, Alphaproteobacteria was the most abundant and present in all samples, and its variation differed among the habitats studied. Linear regression analysis suggested that changes in salinity could affect the relative proportion of Alphaproteobacteria in the surface water. In addition, the species-sorting model was applied to evaluate the population dynamics and environmental heterogeneity in the bacterial communities of surface mixed layer in the Arctic Ocean during sea-ice melting. PMID:24497990

Han, Dukki; Kang, Ilnam; Ha, Ho Kyung; Kim, Hyun Cheol; Kim, Ok-Sun; Lee, Bang Yong; Cho, Jang-Cheon; Hur, Hor-Gil; Lee, Yoo Kyung

2014-01-01

88

What Will Happen if Climate Variability and Change Cause Glacier and Polar Ice Cap Melting?  

NSDL National Science Digital Library

This demonstration will show how increased temperatures will hasten the melting of ice in the environment, contributing to a rise in sea level and subsequent flooding of coastal areas. Materials required include 2 aquariums, plastic wrap, a clamp light with a 60 watt bulb, modeling clay, ice, pebbles and rocks, and a ruler. Teacher background information, student worksheets and a scoring rubric are included. This is Activity 3 of the learning module, Too Many Blankets, part of the lesson series, The Potential Consequences of Climate Variability and Change.

89

Experimental methods for determining the melting temperature and the heat of melting of clusters and nanoparticles  

Microsoft Academic Search

Unlike macroscopic objects, clusters and nanoparticles lack a definite melting temperature at a given pressure but rather have their solid and liquid phases coexistent in a certain temperature range and their melting temperature dependent on the particle size. As the particle size decreases, the melting temperature becomes fundamentally difficult to define. This review examines methods for measuring the melting temperature

Grigorii N Makarov

2010-01-01

90

Melting temperature of diamond at ultrahigh pressure  

NASA Astrophysics Data System (ADS)

Since Ross proposed that there might be `diamonds in the sky' in 1981 (ref. 1), the idea of significant quantities of pure carbon existing in giant planets such as Uranus and Neptune has gained both experimental and theoretical support. It is now accepted that the high-pressure, high-temperature behaviour of carbon is essential to predicting the evolution and structure of such planets. Still, one of the most defining of thermal properties for diamond, the melting temperature, has never been directly measured. This is perhaps understandable, given that diamond is thermodynamically unstable, converting to graphite before melting at ambient pressure, and tightly bonded, being the strongest bulk material known. Shock-compression experiments on diamond reported here reveal the melting temperature of carbon at pressures of 0.6-1.1TPa (6-11Mbar), and show that crystalline diamond can be stable deep inside giant planets such as Uranus and Neptune. The data indicate that diamond melts to a denser, metallic fluid-with the melting curve showing a negative Clapeyron slope-between 0.60 and 1.05TPa, in good agreement with predictions of first-principles calculations. Temperature data at still higher pressures suggest diamond melts to a complex fluid state, which dissociates at shock pressures between 1.1 and 2.5TPa (11-25Mbar) as the temperatures increase above 50,000K.

Eggert, J. H.; Hicks, D. G.; Celliers, P. M.; Bradley, D. K.; McWilliams, R. S.; Jeanloz, R.; Miller, J. E.; Boehly, T. R.; Collins, G. W.

2010-01-01

91

Homogeneous ice freezing temperatures and ice nucleation rates of aqueous ammonium sulfate and aqueous levoglucosan particles for relevant atmospheric conditions.  

PubMed

Homogeneous ice nucleation from micrometre-sized aqueous (NH4)2SO4 and aqueous levoglucosan particles is studied employing the optical microscope technique. A new experimental method is introduced that allows us to control the initial water activity of the aqueous droplets. Homogeneous ice freezing temperatures and ice melting temperatures of these aqueous solution droplets, 10 to 80 microm in diameter, are determined. Homogeneous ice nucleation from aqueous (NH4)2SO4 particles 5-39 wt% in concentration and aqueous levoglucosan particles with initial water activities of 0.85-0.99 yield upper limits of the homogeneous ice nucleation rate coefficients of up to 1x10(10) cm(-3) s(-1). The experimentally derived homogeneous ice freezing temperatures and upper limits of the homogeneous ice nucleation rate coefficients are compared with corresponding predictions of the water-activity-based ice nucleation theory [T. Koop, B. P. Luo, A. Tsias and T. Peter, Nature, 2000, 406, 611]. It is found that the water-activity-based ice nucleation theory can capture the experimentally derived ice freezing temperatures and homogeneous ice nucleation rate coefficients of the aqueous (NH4)2SO4 and aqueous levoglucosan particles. However, the level of agreement between experimentally derived and predicted values, in particular for homogeneous ice nucleation rate coefficients, crucially depends on the extrapolation method to obtain water activities at corresponding freezing temperatures. It is suggested that the combination of experimentally derived ice freezing temperatures and homogeneous ice nucleation rate coefficients can serve as a better validation of the water-activity-based ice nucleation theory than when compared to the observation of homogeneous ice freezing temperatures alone. The atmospheric implications with regard to the application of the water-activity-based ice nucleation theory and derivation of maximum ice particle production rates are briefly discussed. PMID:19727513

Knopf, Daniel Alexander; Lopez, Miguel David

2009-09-28

92

Simulation of melting ice-phase precipitation hydrometeors for use in passive and active microwave remote sensing algorithms  

NASA Astrophysics Data System (ADS)

Passive and active microwave remote sensing is, by design, sensitive to precipitation-sized particles. The shape of the particles naturally influences the distribution of scattered microwaves. Therefore, we seek to simulate ice-phase precipitation using accurate models of the physical properties of individual snowflakes and aggregate ice crystals, similar to those observed in precipitating clouds. A number of researchers have examined the single-scattering properties of individual ice crystals and aggregates, but only a few have started to look at the properties of melting these particles. One of the key difficulties, from a simulation perspective, is characterizing the distribution of melt-water on a melting particle. Previous studies by the author and others have shown that even for spherical particles, the relative distribution of liquid water on an ice-particle can have significant effects on the computed scattering and absorption properties in the microwave regime. This, in turn, strongly influences forward model simulations of passive microwave TBs, radar reflectivities, and path-integrated attenuation. The present study examines the sensitivity of the single scattering properties of melting ice-crystals and aggregates to variations in the volume fraction of melt water, and the distribution of meltwater. We make some simple simulations 1-D vertical profiles having melting layers, and compute the radar reflectivities consistent with current and planned space-based radars. We also compute the top-of-the-atmosphere brightness temperatures for the same vertical profiles, and discuss the sensitivities to variances in the aforementioned physical properties.

Johnson, B. T.; Olson, W. S.; Skofronick Jackson, G.

2012-12-01

93

Multiparameter Radar Modeling and Observations of Melting Ice.  

NASA Astrophysics Data System (ADS)

This paper uses a microphysically detailed graupel and hail melting model, described by Rasmussen and Heymsfield, which is coupled to a radar model that computes multiparameter variables such as differential reflectivity, linear depolarization ratio, the specific propagation differential phase shift and X-band specific attenuation. The microphysical model is initialized with two different summer-time sounding profiles (Colorado and Alabama). Sensitivity studies are performed with respect to particle shape and orientation distributions. The hail melting model is also initialized with a summertime sounding from the Munich, FRG area, and C-band differential reflectivity is computed for application to radar data from the DFVLR radar. A simple spherical hail melting model is also used to study the effects of absorption and scattering on the X-band attenuation. NCAR CP-2 radar measurements from the MIST (Microburst and Severe Thunderstorm) project and from CINDE (Convective Initiation and Downburst Experiment) are used to illustrate the usefulness of multiparameter data in studying the melting of ice in convective storms.

Vivekanandan, J.; Bringi, V. N.; Raghavan, R.

1990-03-01

94

Observing the Arctic Ocean under melting ice - the UNDER-ICE project  

NASA Astrophysics Data System (ADS)

The sea ice cover of the Arctic Ocean is gradually diminishing in area and thickness. The variability of the ice cover is determined by heat exchange with both the atmosphere and the ocean. A cold water layer with a strong salinity gradient insulates the sea ice from below, preventing direct contact with the underlying warm Atlantic water. Changes in water column stratification might therefore lead to faster erosion of the ice. As the ice recedes, larger areas of surface water are open to wind mixing; the effect this might have on the water column structure is not yet clear. The heat content in the Arctic strongly depends on heat transport from other oceans. The Fram Strait is a crucial pathway for the exchange between the Arctic and the Atlantic Ocean. Two processes of importance for the Arctic heat and freshwater budget and the Atlantic meridional overturning circulation take place here: poleward heat transport by the West Spitzbergen Current and freshwater export by the East Greenland Current. A new project, Arctic Ocean under Melting Ice (UNDER-ICE), aims to improve our understanding of the ocean circulation, water mass distribution, fluxes, and mixing processes, sea ice processes, and net community primary production in ice-covered areas and the marginal ice zone in the Fram Strait and northward towards the Gakkel Ridge. The interdisciplinary project brings together ocean acoustics, physical oceanography, marine biology, and sea ice research. A new programme of observations, integrated with satellite data and state-of-the-art numerical models, will be started in order to improve the estimates of heat, mass, and freshwater transport between the North Atlantic and the Arctic Ocean. On this poster we present the UNDER-ICE project, funded by the Research Council of Norway and GDF Suez E&P Norge AS for the years 2014-2017, and place it in context of the legacy of earlier projects in the area, such as ACOBAR. A mooring array for acoustic tomography combined with "standard" oceanographic measurements of current velocity and water mass properties will be deployed in the Fram Strait in September 2014. The dynamic processes in the marginal ice zone, in particular internal waves, mesoscale eddies, and front instabilities, will be explored using model experiments and high temporal resolution measurements. The results of the observational data analysis and model simulations will be integrated and compared with global climate model simulations (CMIP5). Satellite-derived data products will also be included in the synthesis. As part of the UNDER-ICE project, a web portal for Arctic data will be developed, that will offer open access to metadata and observational and model data products to support studies of Arctic climate and climate change.

Sagen, Hanne; Ullgren, Jenny; Geyer, Florian; Bergh, Jon; Hamre, Torill; Sandven, Stein; Beszczynska-Möller, Agnieszka; Falck, Eva; Gammelsrød, Tor; Worcester, Peter

2014-05-01

95

Modelling the impact of ocean warming on melting and water masses of ice shelves in the Eastern Weddell Sea  

Microsoft Academic Search

The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions\\u000a the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate\\u000a the impact on the temperature–salinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical\\u000a experiments, the

Malte Thoma; Klaus Grosfeld; Keith Makinson; Manfred A. Lange

2010-01-01

96

Real-time Non-contact Millimeter Wave Characterization of Water-Freezing and Ice-Melting Dynamics  

SciTech Connect

We applied millimeter wave radiometry for the first time to monitor water-freezing and ice-melting dynamics in real-time non-contact. The measurements were completed at a frequency of 137 GHz. Small amounts (about 2 mL) of freshwater or saltwater were frozen over a Peltier cooler and the freezing and melting sequence was recorded. Saltwater was prepared in the laboratory that contained 3.5% of table salt to simulate the ocean water. The dynamics of freezing-melting was observed by measuring the millimeter wave temperature as well as the changes in the ice or water surface reflectivity and position. This was repeated using large amounts of freshwater and saltwater (800 mL) mimicking glaciers. Millimeter wave surface level fluctuations indicated as the top surface melted, the light ice below floated up indicating lower surface temperature until the ice completely melted. Our results are useful for remote sensing and tracking temperature for potentially large-scale environmental applications, e.g., global warming.

Sundaram, S. K.; Woskov, Paul P.

2008-11-12

97

Documenting Melting Features of the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

There is an increasing interest in studying the Greenland Ice Sheet, its hydrology and dynamics over the short term and longer term because of the potential impact of a warming Arctic. Major studies concern about whether increased surface melting will lead to changes in production of supraglacial lakes and subglacial water pressures and hence , potentially, rates of ice movement. In this talk I will show movies recorded over the past three years form fieldwork activities carried out over the West Greenland ice sheet. In particular, I will project and comment movies concerning surface streams and supraglacial lakes, as the one at http://www.youtube.com/watch?v=QbuFphwJn4c. I will discuss the importance of observing such phenomena and how the recorded videos can be used to summarize scientific studies and communicate the relevance of scientific findings. I will also show, for the first time, the video of the drainage of a supraglacial lake, an event during which a lake ~ 6 m deep and ~ 1 km drained in ~ 1.5 hours. This section of the movie is under development as video material was collected during our latest expedition in June 2011.

Tedesco, M.

2011-12-01

98

Enhanced high-temperature ice nucleation ability of crystallized aerosol particles after preactivation at low temperature  

NASA Astrophysics Data System (ADS)

cloud chamber experiments with crystallized aqueous ammonium sulfate, oxalic acid, and succinic acid solution droplets, we have studied a preactivation mechanism that markedly enhances the particles' heterogeneous ice nucleation ability. First cloud expansion experiments were performed at a high temperature (267-244 K) where the crystallized particles did not promote any heterogeneous ice nucleation. Ice nucleation at this temperature, however, could be triggered by temporarily cooling the crystallized particles to a lower temperature. This is because upon crystallization, residuals of the aqueous solution are trapped within the crystals. These captured liquids can freeze when cooled below their respective homogeneous or heterogeneous freezing temperature, leading to the formation of ice pockets in the crystalline particles. When warmed again to the higher temperature, ice formation by the preactivated particles occurred via depositional and deliquescence-induced ice growth, with ice active fractions ranging from 1 to 4% and from 4 to 20%, respectively. Preactivation disappeared above the eutectic temperature, which for the organic acids are close to the melting point of ice. This mechanism could therefore contribute to the very small fraction of atmospheric aerosol particles that are still ice active well above 263 K.

Wagner, Robert; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin

2014-07-01

99

How does the mantle melt?How does the mantle melt? 1) Increase the temperature  

E-print Network

the temperatureMelting by raising the temperature Solidus: Temperature of melting, increases with depth (P) #12 the solidus and traverses the shaded melting interval. Dashed lines represent approximate % melting. http amphibole, mica, serpentine minerals in subducting crust · Lowers solidus of overlying mantle · Magmas

Siebel, Wolfgang

100

Summer melt rates on Penny Ice Cap, Baffin Island: Past and recent trends and implications for regional climate  

NASA Astrophysics Data System (ADS)

At latitude 67°N, Penny Ice Cap on Baffin Island is the southernmost large ice cap in the Canadian Arctic, yet its past and recent evolution is poorly documented. Here we present a synthesis of climatological observations, mass balance measurements and proxy climate data from cores drilled on the ice cap over the past six decades (1953 to 2011). We find that starting in the 1980s, Penny Ice Cap entered a phase of enhanced melt rates related to rising summer and winter air temperatures across the eastern Arctic. Presently, 70 to 100% (volume) of the annual accumulation at the ice cap summit is in the form of refrozen meltwater. Recent surface melt rates are found to be comparable to those last experienced more than 3000 years ago. Enhanced surface melt, water percolation and refreezing have led to a downward transfer of latent heat that raised the subsurface firn temperature by 10°C (at 10 m depth) since the mid-1990s. This process may accelerate further mass loss of the ice cap by pre-conditioning the firn for the ensuing melt season. Recent warming in the Baffin region has been larger in winter but more regular in summer, and observations on Penny Ice Cap suggest that it was relatively uniform over the 2000-m altitude range of the ice cap. Our findings are consistent with trends in glacier mass loss in the Canadian High Arctic and regional sea-ice cover reduction, reinforcing the view that the Arctic appears to be reverting back to a thermal state not seen in millennia.

Zdanowicz, Christian; Smetny-Sowa, Anna; Fisher, David; Schaffer, Nicole; Copland, Luke; Eley, Joe; Dupont, Florent

2012-06-01

101

Melt rate predictions for the Totten and Dalton ice shelves from a numerical model  

NASA Astrophysics Data System (ADS)

The Totten Glacier drains a large proportion of the East Antarctic ice sheet, much of it marine based (grounded below sea level) and rapidly losing mass. It has been suggested that mass loss is driven by changes in oceanic forcing; however, the details of the ice-ocean interaction are unknown. Here we present results from an ice shelf-ocean model of the region that includes the Totten, Moscow University and Dalton Ice Shelves, based on the Regional Oceanic Modeling System for the period 1992-2007. Simulated net basal mass loss for the Totten and Dalton ice shelves are 44.5 Gt ice/yr and 46.6 Gt ice/yr, respectively. The melting of the ice shelves varies strongly on seasonal and interannual timescales. Mass loss from the Totten ice shelf has a mean range of variability of 28 Gt ice/yr on interannual timescales and 17 Gt ice/yr on seasonal timescales. This study links basal melt of the Totten and Dalton ice shelves to warm water intrusions across the continental shelf break and atmosphere-ocean heat exchange. Totten ice shelf melting is high when the nearby Dalton polynya interannual strength is below average, and vice versa. Melting of the Dalton ice shelf is primarily controlled by the strength of warm water intrusions across the Dalton Rise and into the ice shelf cavity. During periods of strong westwards coastal current flow, Dalton melt water flows directly into the Totten ice shelf further reducing melting. This is the first such modelling study of this region, providing a valuable framework for directing future observational and modelling efforts.

Gwyther, D.; Galton-Fenzi, B.; Hunter, J. R.; Roberts, J.

2013-12-01

102

ANALYSIS OF ANTARCTIC ICEBERG AND SEA ICE MELTING PATTERNS USING QUIKSCAT  

E-print Network

ANALYSIS OF ANTARCTIC ICEBERG AND SEA ICE MELTING PATTERNS USING QUIKSCAT Keith M. Stuart and David ABSTRACT QuikSCAT tracking of Antarctic icebergs is discussed, and iceberg movement trends are illustrated. Iceberg melting factors are explored and a backscatter time-series is presented. Interactions between ice

Long, David G.

103

A box model of circulation and melting in ice shelf caverns  

Microsoft Academic Search

A simple box model of the circulation into and inside the ocean cavern beneath an ice shelf is used to estimate the melt rates\\u000a of Antarctic glaciers and ice shelves. The model uses simplified cavern geometries and includes a coarse parameterization\\u000a of the overturning circulation and vertical mixing. The melting\\/freezing physics at the ice shelf\\/ocean interface are those\\u000a usually implemented

Dirk Olbers; Hartmut Hellmer

2010-01-01

104

Holocene climate in West Antarctica from the Siple Dome ice core melt-layer record  

Microsoft Academic Search

Summer climate conditions in West Antarctica changed significantly during the Holocene, as recorded by frequency of occurrence of rare melt layers in the Siple Dome deep ice core. We present a record of millennial-scale melt-layer frequency through the Holocene from the Siple Dome ice-core which we interpret as a significant record of changing summer climate conditions for West Antarctica. Melting

S. B. Das; R. B. Alley; J. W. C. White

2003-01-01

105

Sediment Melt-Migration Dynamics in Perennial Antarctic Lake Ice Steven M. Jepsen*  

E-print Network

examined sediment melt-migration dynamics in the ice cover of Lake Fryxell, Taylor Valley, McMurdo Dry of heat losses to shallow, cold ice and the cold, dry atmosphere. Gravity flow of sediment along grain (dry valleys) is the largest (,4000 km2 ) ice-free area of Antarctica (Bull, 1966) and the subject

Priscu, John C.

106

Water isotopic ratios from a continuously melted ice core sample  

E-print Network

A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We built an interface between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneous water isotopic analysis of $\\delta^{18}$O and $\\delta$D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ${\\mu}$l amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100% efficiency in a home made oven. A calibration procedure allows for proper reporting of the data on the VSMOW--SLAP scale. Application of spectral methods yields the combined uncertainty of the system at below 0.1 permil and 0.5 permil for $\\delta^{18}$O and $\\delta$D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sampl...

Gkinis, V; Blunier, T; Bigler, M; Schüpbach, S; Kettner, E; Johnsen, S J

2014-01-01

107

Variability of Basal Melt Beneath the Pine Island Glacier Ice Shelf, West Antarctica  

NASA Technical Reports Server (NTRS)

Observations from satellite and airborne platforms are combined with model calculations to infer the nature and efficiency of basal melting of the Pine Island Glacier ice shelf, West Antarctica, by ocean waters. Satellite imagery shows surface features that suggest ice-shelf-wide changes to the ocean s influence on the ice shelf as the grounding line retreated. Longitudinal profiles of ice surface and bottom elevations are analyzed to reveal a spatially dependent pattern of basal melt with an annual melt flux of 40.5 Gt/a. One profile captures a persistent set of surface waves that correlates with quasi-annual variations of atmospheric forcing of Amundsen Sea circulation patterns, establishing a direct connection between atmospheric variability and sub-ice-shelf melting. Ice surface troughs are hydrostatically compensated by ice-bottom voids up to 150m deep. Voids form dynamically at the grounding line, triggered by enhanced melting when warmer-than-average water arrives. Subsequent enlargement of the voids is thermally inefficient (4% or less) compared with an overall melting efficiency beneath the ice shelf of 22%. Residual warm water is believed to cause three persistent polynyas at the ice-shelf front seen in Landsat imagery. Landsat thermal imagery confirms the occurrence of warm water at the same locations.

Bindschadler, Robert; Vaughan, David G.; Vornberger, Patricia

2011-01-01

108

Seasonal changes in ice sheet motion due to melt water lubrication  

NASA Astrophysics Data System (ADS)

Significant temporal variability of ice flow has been observed at the melting margins of the Greenland ice sheet. Seasonal acceleration and deceleration has been partly attributed to changes in resistance at the ice-bed interface caused by subglacial routing of surface melt water, as is the case for valley glaciers. Larger quantities of melt water do not necessarily reduce resistance, however, and the overall effect of melt water lubrication on the mean annual motion of the ice sheet remains unclear. In this work, numerical models are used to explore the coupling between subglacial drainage of surface melt water and ice sheet motion. A synthetic ice sheet is forced to melt according to a prescribed seasonal cycle and the effect of this melting on the speed of the ice is calculated. The model adopts a distributed-channelized structure for the subglacial drainage system, with opening and closing of drainage space controlled by turbulent dissipation, cavitation around bedrock roughness elements, and creep closure of the ice. Subglacial water pressure is assumed to exert the main hydrological control on ice lubrication and is used to parameterize the basal sliding law for a vertically-integrated higher-order ice flow model. The model results suggest that the fastest ice velocities should be expected soon after the onset of surface melting, when runoff into moulins swamps the existing capacity of the drainage system. Periods of relatively high melting at any stage of the melt season can have the same effect, but the establishment of a more efficient drainage system can also have the effect of reducing water pressure and sliding velocities. This behaviour is in broad agreement with current observations. Comparing years with different total melting rates, the model further suggests that slow-down due to the more efficient drainage system is likely to be confined to close to the ice sheet margins (perhaps within about 20km), whereas further away from the margin a larger annual melt rate is likely to lead to an increase in ice flow. The quantitative behaviour predicted by the model is found to depend sensitively upon the constitutive laws assumed for the structure of the drainage system and the sliding law, underlining the importance of further theoretical studies and detailed measurements to constrain the relationship between sliding and the subglacial hydraulic system.

Hewitt, I.

2012-12-01

109

Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage.  

PubMed

Fluctuations in surface melting are known to affect the speed of glaciers and ice sheets, but their impact on the Greenland ice sheet in a warming climate remains uncertain. Although some studies suggest that greater melting produces greater ice-sheet acceleration, others have identified a long-term decrease in Greenland's flow despite increased melting. Here we use satellite observations of ice motion recorded in a land-terminating sector of southwest Greenland to investigate the manner in which ice flow develops during years of markedly different melting. Although peak rates of ice speed-up are positively correlated with the degree of melting, mean summer flow rates are not, because glacier slowdown occurs, on average, when a critical run-off threshold of about 1.4?centimetres a day is exceeded. In contrast to the first half of summer, when flow is similar in all years, speed-up during the latter half is 62?±?16 per cent less in warmer years. Consequently, in warmer years, the period of fast ice flow is three times shorter and, overall, summer ice flow is slower. This behaviour is at odds with that expected from basal lubrication alone. Instead, it mirrors that of mountain glaciers, where melt-induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient. A model of ice-sheet flow that captures switching between cavity and channel drainage modes is consistent with the run-off threshold, fast-flow periods, and later-summer speeds we have observed. Simulations of the Greenland ice-sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage; a simple model of basal lubrication alone misses key aspects of the ice sheet's response to climate warming. PMID:21270891

Sundal, Aud Venke; Shepherd, Andrew; Nienow, Peter; Hanna, Edward; Palmer, Steven; Huybrechts, Philippe

2011-01-27

110

Antarctic sea ice and temperature variations  

SciTech Connect

Monthly antarctic station temperatures are used in conjunction with grids of sea ice coverage in order to evaluate temporal trends and the strength of associations between the two variables at lags of up to several seasons. The trends of temperature are predominantly positive in winter and summer, but predominantly negative in spring. The spatially aggregated trend of temperature is small but positive, while the corresponding trend of ice coverage is small but negative. Cross-correlations between concurrent anomalies of the two variables are negative over most of the continent and are strongest over the Antarctic Peninsula, especially in winter. In regions other than the Antarctic Peninsula, lag correlations between seasonal anomalies are generally stronger with ice lagging the summer temperatures and with ice leading the winter temperatures.

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

1992-03-01

111

Changes in Arctic Melt Season and Implications for Sea Ice Loss  

NASA Technical Reports Server (NTRS)

The Arctic-wide melt season has lengthened at a rate of 5 days dec-1 from 1979 to 2013, dominated by later autumn freeze-up within the Kara, Laptev, East Siberian, Chukchi and Beaufort seas between 6 and 11 days dec(exp -1). While melt onset trends are generally smaller, the timing of melt onset has a large influence on the total amount of solar energy absorbed during summer. The additional heat stored in the upper ocean of approximately 752MJ m(exp -2) during the last decade, increases sea surface temperatures by 0.5 to 1.5 C and largely explains the observed delays in autumn freeze-up within the Arctic Ocean's adjacent seas. Cumulative anomalies in total absorbed solar radiation from May through September for the most recent pentad locally exceed 300-400 MJ m(exp -2) in the Beaufort, Chukchi and East Siberian seas. This extra solar energy is equivalent to melting 0.97 to 1.3 m of ice during the summer.

Stroeve, J. C.; Markus, T.; Boisvert, L.; Miller, J.; Barrett, A.

2014-01-01

112

Snow to Ice to Water: Melt Ponds, Moulins, and Surging Glaciers  

NSDL National Science Digital Library

This article describes the work of Dr. Jason Box, a researcher studying summer melt ponds on Greenland's ice sheets and the response of glaciers to try to explain the changes in climate that are being observed in the polar regions.

Landis, Carol

113

Forecasting method of ice blocks fall by logistic model and melting degree-days calculation: a case study in northern Gaspésie, Québec, Canada.  

NASA Astrophysics Data System (ADS)

Ice blocks fall is a serious natural hazard that frequently happens in mountainous cold region. The ice blocks result from the melting and collapse of rockwall icings (ice walls or frozen waterfalls). Environment Canada weather data were analysed for 440 cases of ice blocks fall events reported in northern Gaspésie by the "Ministère des Transports du Québec" (M.T.Q.). The analysis shows that the ice blocks fall are mainly controlled by an increase of the air temperature above 0oC. The melting degree-days (DDmelt) can be used to follow the temperature variations and the heat transfer into the ice bodies. Furthermore, large daily temperature changes, especially drastic drops of temperatures and freeze-thaw cycles, can induce enough mechanical stress to favour the opening of cracks and possibly cause the collapse of unstable ice structures such as freestanding ice formations. By following the evolution of the DDmelt and the best logistic model, it is possible to forecast the collapse of some of the most problematic rockwall icings and target the most hazardous periods along the northern Gaspésie roads.

Gauthier, Francis; Hétu, Bernard; Allard, Michel

2013-04-01

114

Investigation of the impact of Antarctic ice-shelf melting in a global ice-ocean model (ORCA2-LIM)  

NASA Astrophysics Data System (ADS)

Ice-shelf melting (ISM) removes heat from and injects fresh water into the adjacent ocean and contributes significantly to the freshwater balance and water mass formation in the Antarctic marginal seas. The thermodynamic interaction between ocean and ice shelf is a complicated process and usually not adequately included in the ocean-ice climate models. In this paper, the ISM from all major ice-shelf areas around Antarctica is added to a global coupled ice-ocean model ORCA2-LIM following the parameterization proposed by Beckmann and Goosse (2003). Using interannual forcing data from 1958 through 2000, the impact of ISM on Southern Ocean hydrography and sea-ice distribution is investigated. The model also shows global signatures of the Antarctic ISM.

Wang, Caixin; Beckmann, Aike

2007-10-01

115

Identification of Ancient Feather Fragments Found in Melting Alpine Ice Patches in Southern Yukon  

Microsoft Academic Search

Twelve ancient artifacts or fragmented feather samples recovered from melting alpine ice patches in southern Yukon were analyzed in order to identify the species of birds associated with the ice patches or used on weapons recovered from these sites. The identification of bird species used by ancient hunters as long ago as 4500 BP enhances our insight into the customs,

CARLA J. DOVE; P. GREGORY HARE; MARCY HEACKER

2005-01-01

116

Arctic sea ice melt onset from passive microwave satellite data: 1979-2012  

NASA Astrophysics Data System (ADS)

An updated version of the Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I-SSMIS Brightness Temperatures is now available. The data record has been re-processed and extended to cover the years 1979-2012. From this data set, a statistical summary of melt onset (MO) dates on Arctic sea ice is presented. The mean MO date for the Arctic Region is 13 May (132.5 DOY) with a standard deviation of ±7.3 days. Regionally, mean MO dates vary from 15 March (73.2 DOY) in the St. Lawrence Gulf to 10 June (160.9 DOY) in the Central Arctic. Statistically significant decadal trends indicate that MO is occurring 6.6 days decade-1 earlier in the year for the Arctic Region. Regionally, MO trends are as great as -11.8 days decade-1 in the East Siberian Sea. The Bering Sea is an outlier and MO is occurring 3.1 days decade-1 later in the year.

Bliss, A. C.; Anderson, M. R.

2014-06-01

117

Implications of increased surface melt under global warming scenarios: Greenland ice-sheet simulations  

Microsoft Academic Search

The Greenland Ice Sheet represents ~10% (by volume) of the cryosphere and ~7 meters of sea-level equivalence. Citing the inherent stability offered by the long glaciological timescales involved in classical ice-sheet dynamics, the elevation of the bedrock on which the ice sheet is perched, and the extremely cold inland surface temperatures, numerical studies on the future of this ice sheet

B. R. Parizek; R. B. Alley

2003-01-01

118

Local Effects of Ice Floes on Skin Sea Surface Temperature in the Marginal Ice Zone from UAVs  

NASA Astrophysics Data System (ADS)

Recent years have seen extreme changes in the Arctic. Particularly striking are changes within the Pacific sector of the Arctic Ocean, and especially in the seas north of the Alaskan coast. These areas have experienced record warming, reduced sea ice extent, and loss of ice in areas that had been ice-covered throughout human memory. Even the oldest and thickest ice types have failed to survive through the summer melt period in areas such as the Beaufort Sea and Canada Basin, and fundamental changes in ocean conditions such as earlier phytoplankton blooms may be underway. Marginal ice zones (MIZ), or areas where the "ice-albedo feedback" driven by solar warming is highest and ice melt is extensive, may provide insights into the extent of these changes. Airborne remote sensing, in particular InfraRed (IR), offers a unique opportunity to observe physical processes at sea-ice margins. It permits monitoring the ice extent and coverage, as well as the ice and ocean temperature variability. It can also be used for derivation of surface flow field allowing investigation of turbulence and mixing at the ice-ocean interface. Here, we present measurements of visible and IR imagery of melting ice floes in the marginal ice zone north of Oliktok Point AK in the Beaufort Sea made during the Marginal Ice Zone Ocean and Ice Observations and Processes EXperiment (MIZOPEX) in July-August 2013. The visible and IR imagery were taken from the unmanned airborne vehicle (UAV) ScanEagle. The visible imagery clearly defines the scale of the ice floes. The IR imagery show distinct cooling of the skin sea surface temperature (SST) as well as a intricate circulation and mixing pattern that depends on the surface current, wind speed, and near-surface vertical temperature/salinity structure. Individual ice floes develop turbulent wakes as they drift and cause transient mixing of an influx of colder surface (fresh) melt water. The upstream side of the ice floe shows the coldest skin SST, and downstream the skin SST is mixed within the turbulent wake over 10s of meters. We compare the structure of circulation and mixing of the influx of cold skin SST driven by surface currents and wind. In-situ temperature measurements provide the context for the vertical structure of the mixing and its impact on the skin SST. Furthermore, comparisons to satellite-derived sea surface temperature of the region are presented. The accuracy of satellite derived SST products and how well the observed skin SSTs represent ocean bulk temperatures in polar regions is not well understood, due in part to lack of observations. Estimated error in the polar seas is relatively high at up to 0.4 deg. C compared to less than 0.2 deg. C for other areas. The goal of these and future analyses of the MIZOPEX data set is to elucidate a basic question that is significant for the entire Earth system. Have these regions passed a tipping point, such that they are now essentially acting as sub-Arctic seas where ice disappears in summer, or instead whether the changes are transient, with the potential for the ice pack to recover?

Zappa, C. J.; Brown, S.; Emery, W. J.; Adler, J.; Wick, G. A.; Steele, M.; Palo, S. E.; Walker, G.; Maslanik, J. A.

2013-12-01

119

Future sea-level rice associated with melting of the Greenland ice sheet  

Microsoft Academic Search

Sea-level rise is one of the major concerns associated with the recent climate change. Thermal expansion of the oceans and melting of glaciers and ice-sheets are all believed to contribute to sea-level change in the next century. The Antarctic and Greenland ice-sheet could potentially rise sea-surface with 60 and 7 meter, respectively, but whereas the Antarctic ice-sheet currently appears to

R. Graversen; S. Drijfhout; W. Hazeleger

2009-01-01

120

Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle in the eastern South Pacific  

E-print Network

Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle of the Patagonian Ice Sheet. We consequently attribute the deglacial onset of marine denitrification in the area), Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle in the eastern South

Demouchy, Sylvie

121

Efficacy of sanitized ice in reducing bacterial load on fish fillet and in the water collected from the melted ice.  

PubMed

This study investigated the efficacy of sanitized ice for the reduction of bacteria in the water collected from the ice that melted during storage of whole and filleted Tilapia fish. Also, bacterial reductions on the fish fillets were investigated. The sanitized ice was prepared by freezing solutions of PRO-SAN (an organic acid formulation) and neutral electrolyzed water (NEW). For the whole fish study, the survival of the natural microflora was determined from the water of the melted ice prepared with PRO-SAN and tap water. These water samples were collected during an 8 h storage period. For the fish fillet study, samples were inoculated with Escherichia coli K12, Listeria innocua, and Pseudomonas putida then stored on crushed sanitized ice. The efficacies of these were tested by enumerating each bacterial species on the fish fillet and in the water samples at 12 and 24 h intervals for 72 h, respectively. Results showed that each bacterial population was reduced during the test. However, a bacterial reduction of < 1 log CFU was obtained for the fillet samples. A maximum of approximately 2 log CFU and > 3 log CFU reductions were obtained in the waters sampled after the storage of whole fish and the fillets, respectively. These reductions were significantly (P < 0.05) higher in the water from sanitized ice when compared with the water from the unsanitized melted ice. These results showed that the organic acid formulation and NEW considerably reduced the bacterial numbers in the melted ice and thus reduced the potential for cross-contamination. PMID:20546415

Feliciano, Lizanel; Lee, Jaesung; Lopes, John A; Pascall, Melvin A

2010-05-01

122

Temperature profile for glacial ice at the South Pole: Implications for life in a nearby subglacial lake  

E-print Network

Inpharmatics, 12040 115th Avenue, Kirkland, WA 98034-4399; ¶Indigo Systems Corporation, 5385 Hollister Avenue-induced melting temperature of freshwater ice. To produce the strong radar signal, the frozen lake must consist

Price, P. Buford

123

Links Between Acceleration, Melting, and Supraglacial Lake Drainage of the Western Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

The impact of increasing summer melt on the dynamics and stability of the Greenland Ice Sheet is not fully understood. Mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding. Here, we compare subdaily ice velocity and uplift derived from nine Global Positioning System stations in the upper ablation zone in west Greenland to surface melt and supraglacial lake drainage during summer 2007. Starting around day 173, we observe speedups of 6-41% above spring velocity lasting 40 days accompanied by sustained surface uplift at most stations, followed by a late summer slowdown. After initial speedup, we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting. Most lake drainages were undetectable in the velocity record, and those that were detected only perturbed velocities for approx 1 day, suggesting preexisting drainage systems could efficiently drain large volumes of water. The dynamic response to melt forcing appears to (1) be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses, and (2) decrease over the course of the summer, presumably as the subglacial drainage system evolves to greater efficiency. The relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers, suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here. Thus, increases in summer melting may not guarantee faster seasonal ice flow.

Hoffman, M. J.; Catania, G. A.; Neumann, T. A.; Andrews, L. C.; Rumrill, J. A.

2011-01-01

124

Snow Dunes: A Controlling Factor of Melt Pond Distribution on Arctic Sea Ice  

NASA Technical Reports Server (NTRS)

The location of snow dunes over the course of the ice-growth season 2007/08 was mapped on level landfast first-year sea ice near Barrow, Alaska. Landfast ice formed in mid-December and exhibited essentially homogeneous snow depths of 4-6 cm in mid-January; by early February distinct snow dunes were observed. Despite additional snowfall and wind redistribution throughout the season, the location of the dunes was fixed by March, and these locations were highly correlated with the distribution of meltwater ponds at the beginning of June. Our observations, including ground-based light detection and ranging system (lidar) measurements, show that melt ponds initially form in the interstices between snow dunes, and that the outline of the melt ponds is controlled by snow depth contours. The resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution.

Petrich, Chris; Eicken, Hajo; Polashenski, Christopher M.; Sturm, Matthew; Harbeck, Jeremy P.; Perovich, Donald K.; Finnegan, David C.

2012-01-01

125

Development of Melting Device for Measurement of Traceable Proxies in Ice Core  

NASA Astrophysics Data System (ADS)

It has been well known that various proxies in ice core can provide useful information about climate change and atmospheric environment in the past. However, ice core sample can be easily contaminated during drilling, shipping, cutting, and handling and especially, its breaks are the primary source of contamination of the inner core. Therefore, decontamination procedure of ice core sample to remove contaminants of outer layers in ice core is very important. Until now, as a decontamination method of ice core sample, conventional method has been broadly used. This indicates removal of pollutants by mechanical scraping with stainless steel knives or by a series of washing-baths with ultra-pure distilled water. It has advantages such as minimization of interferences between samples, flexible adaptation of extraction time, and stable instrumental analysis. As a disadvantage, there have been also reported as low efficiencies of ice core preparation owing to strict and complicated procedures, low resolution (10-20 cm/sample), and difficulties of application to on-line measurement system. As a result, the melting device was developed as an alternative of conventional decontamination method in the early 1990s. Contrary to conventional method, this represented high efficiencies of decontamination, high resolution (? 5 cm/sample), and the possibilities of application to on-line measurement system. However, the artifacts from melting head made of metals, the interferences between samples melted in series, recovery efficiencies of traceable element, and instability of instrumental analysis owing to short extraction time and scanning time have to be overcome. Even if various melting devices have been developed, prior to this study, little researches had been undertaken examining systematically them which would be expected to be important in on-line measurement system. In this study, melting head made of Ti and with 3-channels was constructed to decontaminate discrete ice core samples. The results of performance test of melting device conducted systematically and preliminary results applied to ice core drilled at Alpine and Antarctica will be presented.

Hong, S.; Hwang, H.; Lee, K.; Hur, S.; Hong, S.; Chung, J.; Yoon, A.; Yoon, H.

2009-12-01

126

Sensitivity of the North Atlantic climate to Greenland Ice Sheet melting during the Last Interglacial  

NASA Astrophysics Data System (ADS)

During the Last Interglacial (LIG; ~130 thousand years BP), part of the Greenland Ice Sheet (GIS) melted under the influence of a warmer than present-day climate. However, the impact of this melting on the LIG climate in the North Atlantic region is unknown. Using the LOVECLIM earth system model of intermediate complexity we have systematically tested the sensitivity of the LIG climate to increased freshwater runoff from the GIS. Moreover, additional experiments have been performed to investigate the impact of an idealized reduction of both altitude and extent of the GIS on the LIG climate. By comparing the simulated deep ocean circulation with proxy-based reconstructions, the most realistic simulated climate could be discerned. The resulting climate is characterized by a shutdown of deep convection in the Labrador Sea and a subsequent cooling here by ~6 °C and ~2 °C over the southern part of Baffin Island and the North Atlantic Ocean between 40° N and 60° N. The reduction of altitude and extent of the GIS results in a local warming of up to 6 °C and a reduction in deep convection and accompanying cooling in the Nordic Seas. Combining model results and proxy-based reconstructions enabled us to constrain the possible melt rate of the GIS to a flux between 0.052 Sv and 0.13 Sv. A further comparison of simulated summer temperatures with both continental and oceanic proxy-records reveals that the partial melting of the GIS during the LIG could have delayed maximum summer temperatures in the western part of the North Atlantic region relative to the insolation maximum.

Bakker, P.; van Meerbeeck, C. J.; Renssen, H.

2011-08-01

127

REVIEWS OF TOPICAL PROBLEMS: Experimental methods for determining the melting temperature and the heat of melting of clusters and nanoparticles  

Microsoft Academic Search

Unlike macroscopic objects, clusters and nanoparticles lack a definite melting temperature at a given pressure but rather have their solid and liquid phases coexistent in a certain temperature range and their melting temperature dependent on the particle size. As the particle size decreases, the melting temperature becomes fundamentally difficult to define. This review examines methods for measuring the melting temperature

Grigorii N. Makarov

2010-01-01

128

Thermohaline circulation below the Ross Ice Shelf - A consequence of tidally induced vertical mixing and basal melting  

NASA Technical Reports Server (NTRS)

The warmest water below parts of the Ross Ice Shelf resides in the lowest portion of the water column because of its high salinity. Vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf. A numerical tidal simulation indicates that vertically well-mixed conditions predominate in the southeastern part of the sub-ice shelf cavity, where the water column thickness is small. Basal melting in this region is expected to be between 0.05 and 0.5 m/yr and will drive a thermohaline circulation having the following characteristics: high salinity shelf water (at - 1.8 C), formed by winter sea ice production in the open Ross Sea, flows along the seabed toward the tidal mixing fronts below the ice shelf; and meltwater (at -2.2 C), produced in the well-mixed region, flows out of the sub-ice shelf cavity along the ice shelf bottom. Sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature.

Macayeal, D. R.

1984-01-01

129

Ice Weathering Crust Development and the Contribution of Subsurface Melting to Glacier Ablation and Runoff in the McMurdo Dry Valleys, Antarctica  

NASA Astrophysics Data System (ADS)

In the McMurdo Dry Valleys, Victoria Land, East Antarctica, melting of glacial ice is the primary source of water to streams, lakes, and associated ecosystems. Ablation and runoff was investigated using a surface energy balance model applied to the glaciers of Taylor Valley using 14 years of meteorological data and calibrated to ablation measurements. Inclusion of transmission of solar radiation into the ice through a source term in a one-dimensional heat transfer equation was necessary to accurately model summer ablation and ice temperatures. Model results indicated that ablation was dominated by sublimation and melting was rare across the smooth surfaces of the glaciers, whereas subsurface melt between 5 and 15 cm depth was extensive and lasted for up to six weeks in some summers. The model was better able to predict ablation if some subsurface melt was assumed to drain, lowering ice density, consistent with observations of a low density weathering crust that forms over the course of the summer on Dry Valley glaciers. When applied spatially, the model successfully predicted proglacial streamflow at seasonal and daily time scales. Inclusion of subsurface melt as runoff improved predictions of runoff volume and timing, particularly for the recession of large flood peaks. Because overland flow was rarely observed over much of these glaciers, these model results suggest that runoff may be predominantly transported beneath the surface in a partially melted, permeable layer of weathered ice.

Hoffman, M. J.; Fountain, A. G.; Liston, G. E.

2011-12-01

130

Warm river waters contributed to melting Arctic sea ice  

NASA Astrophysics Data System (ADS)

In 2012 Arctic sea ice extent reached a record low in the satellite-observed record. A new study by Nghiem et al. suggests that warm waters discharged into the Arctic's Beaufort Sea from the Mackenzie River could have contributed to that low ice extent.

Balcerak, Ernie

2014-05-01

131

NASA Finds Thickest Parts of Arctic Ice Cap Melting Faster  

NSDL National Science Digital Library

This interactive NASA webpage displays images of Arctic ice in 1980 and 2012. To facilitate comparison, the visitor can sweep a vertical line from left to right to reveal all of one image or all of the other. Text provides information about the rate of loss of ice and how it is defined.

2013-04-29

132

A data-constrained model for compatibility check of remotely sensed basal melting with the hydrography in front of Antarctic ice shelves  

NASA Astrophysics Data System (ADS)

The ice shelf caverns around Antarctica are sources of cold and fresh water which contributes to the formation of Antarctic bottom water and thus to the ventilation of the deep basins of the World Ocean. While a realistic simulation of the cavern circulation requires high resolution, because of the complicated bottom topography and ice shelf morphology, the physics of melting and freezing at the ice shelf base is relatively simple. We have developed an analytically solvable box model of the cavern thermohaline state, using the formulation of melting and freezing as in Olbers and Hellmer (2010). There is high resolution along the cavern's path of the overturning circulation whereas the cross-path resolution is fairly coarse. The circulation in the cavern is prescribed and used as a tuning parameter to constrain the solution by attempting to match observed ranges for outflow temperature and salinity at the ice shelf front as well as of the mean basal melt rate. The method, tested for six Antarctic ice shelves, can be used for a quick estimate of melt/freeze rates and the overturning rate in particular caverns, given the temperature and salinity of the inflow and the above mentioned constrains for outflow and melting. In turn, the model can also be used for testing the compatibility of remotely sensed basal mass loss with observed cavern inflow characteristics.

Olbers, D.; Hellmer, H. H.; Buck, F. F. J. H.

2014-02-01

133

Arctic sea-ice ridges—Safe heavens for sea-ice fauna during periods of extreme ice melt?  

Microsoft Academic Search

The abundances and distribution of metazoan within-ice meiofauna (13 stations) and under-ice fauna (12 stations) were investigated in level sea ice and sea-ice ridges in the Chukchi\\/Beaufort Seas and Canada Basin in June\\/July 2005 using a combination of ice coring and SCUBA diving. Ice meiofauna abundance was estimated based on live counts in the bottom 30cm of level sea ice

Rolf Gradinger; Bodil Bluhm; Katrin Iken

2010-01-01

134

Melting of ice simulated by a multicanonical method combined with a first-principles calculation  

NASA Astrophysics Data System (ADS)

Water is a ubiquitous material and is both scientifically and technologically important. For the simulation of water, the most common PBE semi-local exchange correlation (XC) functional has an issue: it gives over-structured liquid compared to the experimental one for a given temperature. On the other hand, the PBE0 hybrid XC functional was claimed to be better for the description of water recently [1,2]. In this study, the melting of ice, one of its most fundamental property, was simulated by a multicanonical method combined with a first-principles calculation [3,4]. Both the PBE XC functional and the PBE0 hybrid XC functional were adopted for the simulation. With accelerated computation of the hybrid functional by GPGPU, it was found that the PBE0 XC hybrid functional gave an improved melting temperature compared to that by PBE [5].[4pt] [1] C. Zhang and G. Galli et al., J. Chem. Theory and Comput., 7, 1443 (2011).[0pt] [2] B. Santra and M. Scheffler et al., J. Chem. Phys., 131, 124509 (2009).[0pt] [3] Y. Yoshimoto, J. Chem. Phys., 125, 184103 (2006).[0pt] [4] Y. Yoshimoto, J. Phys. Soc. Jpn., 79, 034602 (2010).[0pt] [5] S. Yoo, X.C. Zeng, and S.S. Xantheas, J. Chem. Phys., 130, 221102 (2009).

Yoshimoto, Yoshihide

2013-03-01

135

Temporal Changes in Spatial Distribution of Basal Melting and Freezing in the Catchment Areas of Whillans Ice Stream and Ice Stream C, West Antarctica: Interplay of Climatic Changes and Ice Dynamics  

Microsoft Academic Search

Basal thermal regimen of West Antarctic Ice Sheet (WAIS) plays the key role in determining the dynamics and stability of this ice sheet. Basal melt water lubricates the ice base allowing fast ice streaming while basal freeze-on increases basal resistance to ice flow. Within WAIS, basal melting is dominant in the interior, where geothermal heat is trapped underneath ~2-to-4-km-thick layer

S. W. Vogel; S. Tulaczyk; I. Joughin

2002-01-01

136

Investigation of seasonal melting of Greenland using GPS records reveals significant ice mass loss in 2010  

NASA Astrophysics Data System (ADS)

Greenland has experienced significant ice mass loss in the past decade. High-precision global positioning system (GPS) data from sites on the rocky margin of Greenland enable measurement of vertical motion of the coastal area, which is an indicator of nearby mass loss. In this study, seasonal melting variation of the Greenland ice sheet (GrIS) is investigated using GPS vertical displacement data. Using a cubic spline fitting model, we retrieve three variables of the seasonal melting pattern for GrIS from 1996 to 2010: date of the beginning and end of melt season, length of melt season, and amount of uplift in the melt season. Data from three long -term sites on the periphery of Greenland show anomalously large uplift in 2010, implying significant melting in 2010. Preliminary results also show an early onset of melting in 2010, about 8 days earlier than the 1996-2009 average. In 2010, Greenland experienced a warmer and drier winter as well as a very warm summer, which presumably contributed to the anomalous ice mass loss of 2010.

Yang, Q.; Dixon, T.; Wdowinski, S.

2011-12-01

137

Is Global Warming Melting the Greenland Ice Sheet?  

Microsoft Academic Search

Concerted observational and modelling programmes are underway to determine the mass balance of the Greenland Ice Sheet, and therefore help predict its response to future climatic change. We present results of meteorological modelling based on ERA-40 reanalysis data from the European Centre for Medium Range Weather Forecasts (ECMWF). Our novel surface-mass-balance history of the ice sheet for 1958-2003, is based

E. Hanna; P. Huybrechts; I. Janssens; J. McConnell; S. Das; J. Cappelen; K. Steffen; W. Krabill; R. Thomas; A. Stephens

2004-01-01

138

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 44, NO. 9, SEPTEMBER 2006 2461 Melt Detection in Antarctic Ice Shelves Using  

E-print Network

the surface melt of Arctic sea ice, e.g., [1]�[3], Antarctic ice sheets [4]�[6], and the Greenland ice sheet more limited has been the use of these instruments in detecting surface melt on Antarctic sea ice [10 Detection in Antarctic Ice Shelves Using Scatterometers and Microwave Radiometers Lukas B. Kunz and David G

Long, David G.

139

Internal stress-induced melting below melting temperature at high-rate laser heating  

NASA Astrophysics Data System (ADS)

In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67 K for a stress-free condition down to 898.1 K for uniaxial strain and to 920.8 K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q ?1.51×1010K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1 K for Q = 1.51 × 1011 K/s and 936.9 K for Q = 1.46 × 1012 K/s.

Hwang, Yong Seok; Levitas, Valery I.

2014-06-01

140

Modeling the Contribution of Tides to the Larsen-C Ice Shelf Basal Melt Rate  

Microsoft Academic Search

Processes affecting the evolution of the Larsen-C Ice Shelf are still too poorly understood to predict whether the shelf will ultimately collapse like the neighboring Larsen-A and Larsen-B; however, evidence that portions of Larsen-C have recently thinned significantly suggests that future collapse is possible. We hypothesize that basal melt under Larsen-C is an important component of the ice shelf mass

R. D. Mueller; L. Padman; H. A. Fricker; M. Dinniman

2008-01-01

141

The melt pond fraction and spectral sea ice albedo retrieval from MERIS data: validation and trends of sea ice albedo and melt pond fraction in the Arctic for years 2002-2011  

NASA Astrophysics Data System (ADS)

The presence of melt ponds on the Arctic sea ice strongly affects the energy balance of the Arctic Ocean in summer. It affects albedo as well as transmittance through the sea ice, which has consequences on the heat balance and mass balance of sea ice. An algorithm to retrieve melt pond fraction and sea ice albedo (Zege et al., 2014) from the MEdium Resolution Imaging Spectrometer (MERIS) data is validated against aerial, ship borne and in situ campaign data. The result show the best correlation for landfast and multiyear ice of high ice concentrations (albedo: R = 0.92, RMS = 0.068, melt pond fraction: R = 0.6, RMS = 0.065). The correlation for lower ice concentrations, subpixel ice floes, blue ice and wet ice is lower due to complicated surface conditions and ice drift. Combining all aerial observations gives a mean albedo RMS equal to 0.089 and a mean melt pond fraction RMS equal to 0.22. The in situ melt pond fraction correlation is R = 0.72 with an RMS = 0.14. Ship cruise data might be affected by documentation of varying accuracy within the ASPeCT protocol, which is the reason for discrepancy between the satellite value and observed value: mean R = 0.21, mean RMS = 0.16. An additional dynamic spatial cloud filter for MERIS over snow and ice has been developed to assist with the validation on swath data. The case studies and trend analysis for the whole MERIS period (2002-2011) show pronounced and reasonable spatial features of melt pond fractions and sea ice albedo. The most prominent feature is the melt onset shifting towards spring (starting already in weeks 3 and 4 of June) within the multiyear ice area, north to the Queen Elizabeth Islands and North Greenland.

Istomina, L.; Heygster, G.; Huntemann, M.; Schwarz, P.; Birnbaum, G.; Scharien, R.; Polashenski, C.; Perovich, D.; Zege, E.; Malinka, A.; Prikhach, A.; Katsev, I.

2014-10-01

142

Reducing the uncertainty in projections of future ice shelf basal melting  

NASA Astrophysics Data System (ADS)

Simulations of ice shelf basal melting in future climate scenarios from the IPCC's Fourth Assessment Report (AR4) have revealed a large uncertainty and the potential of a rapidly increasing basal mass loss particularly for the large cold-water ice shelves in the Ross and Weddell Seas. The large spread in model results was traced back to uncertainties in the freshwater budget on the continental shelf, which is governed by sea ice formation. Differences in sea ice formation, in turn, follow the regional differences between the atmospheric heat fluxes imprinted by the climate models. A more recent suite of BRIOS and FESOM model experiments was performed with output from two members of the newer generation of climate models enganged in the IPCC's Fifth Assessment Report (AR5). Comparing simulations forced with output from the AR5/CMIP5 models HadGem2 and MPI-ESM, we find that uncertainties arising from inter-model differences in high latitudes have reduced considerably. Projected heat fluxes and thus sea ice formation over the Southern Ocean continental shelves have converged to an ensemble with a much smaller spread than between the AR4 experiments. For most of the ten larger ice shelves in Antarctica, a gradual (but accelerating) increase of basal melt rates during the 21st century is a robust feature throughout the various realisations. Both with HadGem2 and with MPI-ESM forcing, basal melt rates for Filchner-Ronne Ice Shelf in FESOM increase by a factor of two by the end of the 21st century in the RCP85 scenario. For the smaller, warm-water ice shelves, inter-model differences in ice shelf basal mass loss projections are still slightly larger than differences between the scenarios RCP45 and RCP85; compared to AR4 projections, however, the model-dependent spread has been strongly reduced.

Timmermann, Ralph; Kauker, Frank

2014-05-01

143

New insights into ice growth and melting modifications by antifreeze proteins  

PubMed Central

Antifreeze proteins (AFPs) evolved in many organisms, allowing them to survive in cold climates by controlling ice crystal growth. The specific interactions of AFPs with ice determine their potential applications in agriculture, food preservation and medicine. AFPs control the shapes of ice crystals in a manner characteristic of the particular AFP type. Moderately active AFPs cause the formation of elongated bipyramidal crystals, often with seemingly defined facets, while hyperactive AFPs produce more varied crystal shapes. These different morphologies are generally considered to be growth shapes. In a series of bright light and fluorescent microscopy observations of ice crystals in solutions containing different AFPs, we show that crystal shaping also occurs during melting. In particular, the characteristic ice shapes observed in solutions of most hyperactive AFPs are formed during melting. We relate these findings to the affinities of the hyperactive AFPs for the basal plane of ice. Our results demonstrate the relation between basal plane affinity and hyperactivity and show a clear difference in the ice-shaping mechanisms of most moderate and hyperactive AFPs. This study provides key aspects associated with the identification of hyperactive AFPs. PMID:22787007

Bar-Dolev, Maya; Celik, Yeliz; Wettlaufer, J. S.; Davies, Peter L.; Braslavsky, Ido

2012-01-01

144

Sea-level rise: Melting glaciers and ice caps  

NASA Astrophysics Data System (ADS)

The contribution of glaciers and ice caps to global sea-level rise is uncertain: they are incompletely counted and the calculation is challenging. A new estimate from the best available data suggests a contribution of about 12 cm by 2100.

Paul, Frank

2011-02-01

145

Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed  

NASA Astrophysics Data System (ADS)

The dynamic response of the Greenland Ice Sheet (GrIS) depends on feedbacks between surface meltwater delivery to the subglacial environment and ice flow. Recent work has highlighted an important role of hydrological processes in regulating the ice flow, but models have so far overlooked the mechanical effect of soft basal sediment. Here we use a three-dimensional model to investigate hydrological controls on a GrIS soft-bedded region. Our results demonstrate that weakening and strengthening of subglacial sediment, associated with the seasonal delivery of surface meltwater to the bed, modulates ice flow consistent with observations. We propose that sedimentary control on ice flow is a viable alternative to existing models of evolving hydrological systems, and find a strong link between the annual flow stability, and the frequency of high meltwater discharge events. Consequently, the observed GrIS resilience to enhanced melt could be compromised if runoff variability increases further with future climate warming.

Bougamont, M.; Christoffersen, P.; Hubbard, A. L.,; Fitzpatrick, A. A.; Doyle, S. H.; Carter, S. P.

2014-09-01

146

Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed.  

PubMed

The dynamic response of the Greenland Ice Sheet (GrIS) depends on feedbacks between surface meltwater delivery to the subglacial environment and ice flow. Recent work has highlighted an important role of hydrological processes in regulating the ice flow, but models have so far overlooked the mechanical effect of soft basal sediment. Here we use a three-dimensional model to investigate hydrological controls on a GrIS soft-bedded region. Our results demonstrate that weakening and strengthening of subglacial sediment, associated with the seasonal delivery of surface meltwater to the bed, modulates ice flow consistent with observations. We propose that sedimentary control on ice flow is a viable alternative to existing models of evolving hydrological systems, and find a strong link between the annual flow stability, and the frequency of high meltwater discharge events. Consequently, the observed GrIS resilience to enhanced melt could be compromised if runoff variability increases further with future climate warming. PMID:25262753

Bougamont, M; Christoffersen, P; Hubbard, A L; Fitzpatrick, A A; Doyle, S H; Carter, S P

2014-01-01

147

Empirical Retrieval of Surface Melt Magnitude from Coupled MODIS Optical and Thermal Measurements over the Greenland Ice Sheet during the 2001 Ablation Season  

PubMed Central

Accelerated ice flow near the equilibrium line of west-central Greenland Ice Sheet (GIS) has been attributed to an increase in infiltrated surface melt water as a response to climate warming. The assessment of surface melting events must be more than the detection of melt onset or extent. Retrieval of surface melt magnitude is necessary to improve understanding of ice sheet flow and surface melt coupling. In this paper, we report on a new technique to quantify the magnitude of surface melt. Cloud-free dates of June 10, July 5, 7, 9, and 11, 2001 Moderate Resolution Imaging Spectroradiometer (MODIS) daily reflectance Band 5 (1.230-1.250?m) and surface temperature images rescaled to 1km over western Greenland were used in the retrieval algorithm. An optical-thermal feature space partitioned as a function of melt magnitude was derived using a one-dimensional thermal snowmelt model (SNTHERM89). SNTHERM89 was forced by hourly meteorological data from the Greenland Climate Network (GC-Net) at reference sites spanning dry snow, percolation, and wet snow zones in the Jakobshavn drainage basin in western GIS. Melt magnitude or effective melt (E-melt) was derived for satellite composite periods covering May, June, and July displaying low fractions (0-1%) at elevations greater than 2500m and fractions at or greater than 15% at elevations lower than 1000m assessed for only the upper 5 cm of the snow surface. Validation of E-melt involved comparison of intensity to dry and wet zones determined from QSCAT backscatter. Higher intensities (> 8%) were distributed in wet snow zones, while lower intensities were grouped in dry zones at a first order accuracy of ? ±2%.

Lampkin, Derrick; Peng, Rui

2008-01-01

148

Vegetation structure in gullies developed by the melting of ice wedges along Kolyma River, northern Siberia  

Microsoft Academic Search

Vegetation structure was surveyed in gullies developed by the melting of ice wedges along the Kolyma River, northern Siberia, using 72–50 × 50 cm plots. The mean total plant cover was approximately 50% on gley soils, which were only distributed in the gullies. Based on twinspan cluster analysis, four vegetation types were recognized: (i) Agrostis purpurascens grassland with Ceratodon purpureus

Shiro Tsuyuzaki; Takeshi Ishizaki; Toshiyuki Sato

1999-01-01

149

Aragonite Undersaturation in the Arctic Ocean: Effects of Ocean Acidification and Sea Ice Melt  

Microsoft Academic Search

The increase in anthropogenic carbon dioxide emissions and attendant increase in ocean acidification and sea ice melt act together to decrease the saturation state of calcium carbonate in the Canada Basin of the Arctic Ocean. In 2008, surface waters were undersaturated with respect to aragonite, a relatively soluble form of calcium carbonate found in plankton and invertebrates. Undersaturation was found

Michiyo Yamamoto-Kawai; Fiona A. McLaughlin; Eddy C. Carmack; Shigeto Nishino; Koji Shimada

2009-01-01

150

Evidence of subglacial drainage expansion during the 2012 Greenland Ice Sheet melt event.  

NASA Astrophysics Data System (ADS)

Extreme melt events of the Greenland Ice Sheet are increasing with multiple occurrences since 2000. The most extensive melt recorded was in July/August 2012 when ~98% of the Ice Sheet surface showed evidence of liquid water. These extreme events influence Ice Sheet dynamics and the surrounding environments but are not well documented. This study fills in some gaps by measuring discharge and chemistry in one of Greenland's largest rivers, the Watson River, during the July 2012 peak melt event. Two distinct peak discharge events were recorded: The first discharge peak was followed by high solute concentration with peak-to-peak lag time of 54 hours between both. Lag time and high ion concentration give evidence for release of multi seasonal water from a subglacial system indicating a shift in the Greenland Ice Sheet basal hydrology towards an expansion of the area affected by seasonal velocity fluctuations which could increase ice mass loss. Lower solute concentrations during the second discharge peak may indicate development of a channelized system with short water residence time. The total water, solute and nutrient flux in 2012 is about 2 times of average of 2007 to 2010. Measured nutrient fluxes such as bioavailable iron and dissolved silica further demonstrate that extension of subglacial drainage area during extreme flood events can potentially have an important effect on the receiving fjords and oceans.

Hagedorn, Birgit; Rennermalm, Asa; Mikkelsen, Andreas; Hasholt, Bent; Choquette, Kyla; Sletten, Ronald

2014-05-01

151

Melting dynamics of large ice balls in a turbulent swirling flow  

NASA Astrophysics Data System (ADS)

We study the melting dynamics of large ice balls in a turbulent von Kármán flow at very high Reynolds number. Using an optical shadowgraphy setup, we record the time evolution of particle sizes. We study the heat transfer as a function of the particle scale Reynolds number textit {Re}D for three cases: fixed ice balls melting in a region of strong turbulence with zero mean flow, fixed ice balls melting under the action of a strong mean flow with lower fluctuations, and ice balls freely advected in the whole apparatus. For the fixed particles cases, heat transfer is observed to be much stronger than in laminar flows, the Nusselt number behaving as a power law of the Reynolds number: textit {Nu} ? textit {Re}D^{0.8}. For freely advected ice balls, the turbulent transfer is further enhanced and the Nusselt number is proportional to the Reynolds number textit {Nu} ? textit {Re}D. Furthermore, the surface heat flux is found to be independent of the particles size, leading to an ultimate regime of heat transfer reached when the thermal boundary layer is fully turbulent.

Machicoane, N.; Bonaventure, J.; Volk, R.

2013-12-01

152

Development of ice thickness retrieval algorithms for large northern lakes from AMSR-E brightness temperature measurements  

Microsoft Academic Search

Ice cover on lakes is a very sensitive to climate variability and change. With climate warming, lakes have the potential to greatly increase their energy and moisture exchanges with the atmosphere due to earlier break-up and warmer lake temperature during the open water season. Lake ice growth occurs between ice-on date and melt-onset as a result of energy loss by

K. Kang; C. R. Duguay; J. Lemmetyinen; Y. Gel

2010-01-01

153

Imbalance and accelerated melting of glaciers and ice caps  

NASA Astrophysics Data System (ADS)

Most glaciers and ice caps (GIC) are out of balance with the current climate. In order to return to equilibrium, these GIC must retreat to higher elevations, losing mass and making a 21st-century sea-level contribution comparable to that of ice sheets. Here, we present data for 140 GIC from 1970-2009 and show that most glaciers and ice caps are farther from balance than previously believed. For the first decade of the 21st century (2000-2009), GIC in this data set have a mean accumulation-area ratio (AAR, the fractional glacier area where accumulation exceeds ablation) of 35%, far below the mean equilibrium value of 56%. If these AARs are assumed to be representative, the Earth's GIC are committed to the future loss of ~40% of their volume, simply to be in balance with the climate of the past decade. Accounting for geographic sampling biases, estimated volume losses are somewhat reduced, but are still substantially larger than previous published values. Extrapolation of recent trends suggests that if recent climate trends continue for the next several decades, the Earth's GIC will ultimately lose more than half their volume.

Mernild, S. H.; Lipscomb, W. H.

2012-04-01

154

Melting Temperature of Irradiated Fast Reactor Mixed Oxide Fuels  

Microsoft Academic Search

The melting (solidus) temperatures of irradiated mixed oxide fuels were measured and the compositions of the fuels on the temperature measurement date were calculated. The fuels contained about 29wt% Pu initially and were irradiated up to 124GWd\\/t in the experimental fast reactor JOYO. A melting temperature correlation was obtained by an experimental regression analysis using 21 measurements:where [Tcirc]m is the

Koichi KONNO; Takashi HIROSAWA

1998-01-01

155

Method For Synthesizing Extremely High-Temperature Melting Materials  

DOEpatents

The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as borides, carbides and transition-metal, lanthanide and actinide oxides, using an Aerodynamic Levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions.

Saboungi, Marie-Louise (Chicago, IL); Glorieux, Benoit (Perpignan, FR)

2005-11-22

156

Method for synthesizing extremely high-temperature melting materials  

DOEpatents

The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as carbides and transition-metal, lanthanide and actinide oxides, using an aerodynamic levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions.

Saboungi, Marie-Louise (Chicago, IL); Glorieux, Benoit (Perpignan, FR)

2007-11-06

157

Method for Synthesizing Extremeley High Temperature Melting Materials  

DOEpatents

The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as borides, carbides and transition-metal, lanthanide and actinide oxides, using an Aerodynamic Levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions.

Saboungi, Marie-Louise and Glorieux, Benoit

2005-11-22

158

Polycrystalline methane hydrate: Synthesis from superheated ice, and low-temperature mechanical properties  

USGS Publications Warehouse

We describe a new and efficient technique to grow aggregates of pure methane hydrate in quantities suitable for physical and material properties testing. Test specimens were grown under static conditions by combining cold, pressurized CH4 gas with granulated H2O ice, and then warming the reactants to promote the reaction CH4(g) + 6H2O(s???1) ??? CH4??6H2O (methane hydrate). Hydrate formation evidently occurs at the nascent ice/liquid water interface on ice grain surfaces, and complete reaction was achieved by warming the system above the ice melting point and up to 290 K, at 25-30 MPa, for approximately 8 h. The resulting material is pure, cohesive, polycrystalline methane hydrate with controlled grain size and random orientation. Synthesis conditions placed the H2O ice well above its melting temperature while reaction progressed, yet samples and run records showed no evidence for bulk melting of the unreacted portions of ice grains. Control experiments using Ne, a non-hydrate-forming gas, showed that under otherwise identical conditions, the pressure reduction and latent heat associated with ice melting are easily detectable in our fabrication apparatus. These results suggest that under hydrate-forming conditions, H2O ice can persist metastably to temperatures well above its ordinary melting point while reacting to form hydrate. Direct observations of the hydrate growth process in a small, high-pressure optical cell verified these conclusions and revealed additional details of the hydrate growth process. Methane hydrate samples were then tested in constant-strain-rate deformation experiments at T = 140-200 K, Pc = 50-100 MPa, and ?? = 10-4 10-6 s-1. Measurements in both the brittle and ductile fields showed that methane hydrate has measurably different strength than H2O ice, and work hardens to an unusually high degree compared to other ices as well as to most metals and ceramics at high homologous temperatures. This work hardening may be related to a changing stoichiometry under pressure during plastic deformation; X-ray analyses showed that methane hydrate undergoes a process of solid-state disproportionation or exsolution during deformation at conditions well within its conventional stability field.

Stern, L.A.; Kirby, S.H.; Durham, W.B.

1998-01-01

159

Southern Ocean warming and increased ice shelf basal melting in the twenty-first and twenty-second centuries based on coupled ice-ocean finite-element modelling  

NASA Astrophysics Data System (ADS)

We utilise a global finite-element sea ice-ocean model (FESOM), focused on the Antarctic marginal seas, to analyse projections of ice shelf basal melting in a warmer climate. Ice shelf-ocean interaction is described using a three-equation system with a diagnostic computation of temperature and salinity at the ice-ocean interface. A tetrahedral mesh with a minimumhorizontal resolution of 4 km and hybrid vertical coordinates is used. Ice shelf draft, cavity geometry, and global ocean bathymetry have been derived from the RTopo-1 data set. The model is forced with the atmospheric output from two climate models: (1) the Hadley Centre Climate Model (HadCM3) and (2) Max Planck Institute’s ECHAM5/MPI-OM coupled climate model. Results from experiments forced with their twentieth century output are used to evaluate the modelled present-day ocean state. Sea ice coverage is largely realistic in both simulations; modelled ice shelf basal melt rates compare well with observations in both cases, but are consistently smaller for ECHAM5/MPI-OM. Projections for future ice shelf basal melting are computed using atmospheric output for the Intergovernmental Panel on Climate Change (IPCC) scenarios E1 and A1B. In simulations forced with ECHAM5 data, trends in ice shelf basal melting are small. In contrast, decreasing convection along the Antarctic coast in HadCM3 scenarios leads to a decreasing salinity on the continental shelf and to intrusions of warm deep water of open ocean origin. In the case of the Filchner-Ronne Ice Shelf (FRIS), this water reaches deep into the cavity, so that basal melting increases by a factor of 4 to 6 compared to the present value of about 90 Gt/year. By the middle of the twenty-second century, FRIS becomes the dominant contributor to total ice shelf basal mass loss in these simulations. Our results indicate that the surface freshwater fluxes on the continental shelves may be crucial for the future of especially the large cold water ice shelves in the Southern Ocean.

Timmermann, Ralph; Hellmer, Hartmut H.

2013-10-01

160

Estimating the time of melt onset and freeze onset over Arctic sea-ice area using active and passive microwave data  

USGS Publications Warehouse

Accurate calculation of the time of melt onset, freeze onset, and melt duration over Arctic sea-ice area is crucial for climate and global change studies because it affects accuracy of surface energy balance estimates. This comparative study evaluates several methods used to estimate sea-ice melt and freeze onset dates: (1) the melt onset database derived from SSM/I passive microwave brightness temperatures (Tbs) using Drobot and Anderson's [J. Geophys. Res. 106 (2001) 24033] Advanced Horizontal Range Algorithm (AHRA) and distributed by the National Snow and Ice Data Center (NSIDC); (2) the International Arctic Buoy Program/Polar Exchange at the Sea (IABP/POLES) surface air temperatures (SATs); (3) an elaborated version of the AHRA that uses IABP/POLES to avoid anomalous results (Passive Microwave and Surface Temperature Analysis [PMSTA]); (4) another elaborated version of the AHRA that uses T b variance to avoid anomalous results (Mean Differences and Standard Deviation Analysis [MDSDA]); (5) Smith's [J. Geophys. Res. 103 (1998) 27753] vertically polarized Tb algorithm for estimating melt onset in multiyear (MY) ice (SSM/I 19V-37V); and (6) analyses of concurrent backscattering cross section (????) and brightness temperature (T b) from OKEAN-01 satellite series. Melt onset and freeze onset maps were created and compared to understand how the estimates vary between different satellite instruments and methods over different Arctic sea-ice regions. Comparisons were made to evaluate relative sensitivities among the methods to slight adjustments of the Tb calibration coefficients and algorithm threshold values. Compared to the PMSTA method, the AHRA method tended to estimate significantly earlier melt dates, likely caused by the AHRA's susceptibility to prematurely identify melt onset conditions. In contrast, the IABP/POLES surface air temperature data tended to estimate later melt and earlier freeze in all but perennial ice. The MDSDA method was least sensitive to small adjustments of the SMMR-SSM/I inter-satellite calibration coefficients. Differences among methods varied by latitude. Freeze onset dates among methods were most disparate in southern latitudes, and tended to converge northward. Surface air temperatures (IABP/POLES) indicated freeze onset well before the MDSDA method, especially in southern peripheral seas, while PMSTA freeze estimates were generally intermediate. Surface air temperature data estimated latest melt onset dates in southern latitudes, but earliest melt onset in northern latitudes. The PMSTA estimated earliest melt onset dates in southern regions, and converged with the MDSDA northward. Because sea-ice melt and freeze are dynamical transitional processes, differences among these methods are associated with differing sensitivities to changing stages of environmental and physical development. These studies contribute to the growing body of documentation about the levels of disparity obtained when Arctic seasonal transition parameters are estimated using various types of microwave data and algorithms. ?? 2004 Elsevier Inc. All rights reserved.

Belchansky, G.I.; Douglas, D.C.; Mordvintsev, I.N.; Platonov, N.G.

2004-01-01

161

Impact of horizontal spreading on light propagation in melt pond covered seasonal sea ice in the Canadian Arctic  

NASA Astrophysics Data System (ADS)

Melt pond covered sea ice is a ubiquitous feature of the summertime Arctic Ocean when meltwater collects in lower-lying areas of ice surfaces. Horizontal transects were conducted during June 2008 above and below landfast sea ice with melt ponds to characterize surface and bottom topography together with variations in transmitted spectral irradiance. We captured a rapid progression from a highly flooded sea ice surface with lateral drainage toward flaws and seal breathing holes to the formation of distinct melt ponds with steep edges. As the mass of the ice cover decreased due to meltwater drainage and rose upward with respect to the seawater level, the high-scattering properties of ice above the water level (i.e., white ice) were continuously regenerated, while pond waters remained transparent compared to underlying ice. The relatively stable albedos observed throughout the study, even as ice thickness decreased, were directly related to these surface processes. Transmission through the ice cover of incident irradiance in the 400-700 nm wave band ranged from 38% to 67% and from 5% to 16% beneath ponded and white ice, respectively. Our results show that this transmission varied not only as a function of surface type (melt ponds or white ice) areal coverage but also in relation to ice thickness and proximity to other surface types through the influence of horizontal spreading of light. Thus, in contrast to albedo, this implies that regional transmittance estimates need to consider melt pond size and shape distributions and variations in optical properties and thickness of the ice cover.

Ehn, Jens K.; Mundy, C. J.; Barber, David G.; Hop, Haakon; Rossnagel, Andrea; Stewart, Jeremy

2011-09-01

162

A Microwave Technique for Mapping Ice Temperature in the Arctic Seasonal Sea Ice Zone  

NASA Technical Reports Server (NTRS)

A technique for deriving ice temperature in the Arctic seasonal sea ice zone from passive microwave radiances has been developed. The algorithm operates on brightness temperatures derived from the Special Sensor Microwave/Imager (SSM/I) and uses ice concentration and type from a previously developed thin ice algorithm to estimate the surface emissivity. Comparisons of the microwave derived temperatures with estimates derived from infrared imagery of the Bering Strait yield a correlation coefficient of 0.93 and an RMS difference of 2.1 K when coastal and cloud contaminated pixels are removed. SSM/I temperatures were also compared with a time series of air temperature observations from Gambell on St. Lawrence Island and from Point Barrow, AK weather stations. These comparisons indicate that the relationship between the air temperature and the ice temperature depends on ice type.

St.Germain, Karen M.; Cavalieri, Donald J.

1997-01-01

163

A microwave technique for mapping ice temperature in the Arctic seasonal sea ice zone  

SciTech Connect

A technique for deriving ice temperature in the Arctic seasonal sea ice zone from passive microwave radiances has been developed. The algorithm operates on brightness temperatures derived from the Special Sensor Microwave/Imager (SSM/I) and uses ice concentration and type from a previously developed thin ice algorithm to estimate the surface emissivity. Comparisons of the microwave derived temperatures with estimates derived from infrared imagery of the Bering Strait yield a correlation coefficient of 0.93 and an RMS difference of 2.1 K when coastal and cloud contaminated pixels are removed. SSM/I temperatures were also compared with a time series of air temperature observations from Gambell on St. Lawrence Island and from Point Barrow, AK weather stations. These comparisons indicate that the relationship between the air temperature and the ice temperature depends on ice type.

St. Germain, K.M. [Naval Research Lab., Washington, DC (United States). Remote Sensing Div.] [Naval Research Lab., Washington, DC (United States). Remote Sensing Div.; Cavalieri, D.J. [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center] [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center

1997-07-01

164

Volume dependence of the melting temperature for aluminium  

NASA Astrophysics Data System (ADS)

We present a simple and straightforward relationship for evaluating the volume dependence of melting temperature based on the Lindemann's melting equation (F.A. Lindemann, Z. Phys. 11 (1910) 609) and the Al'tshular et al. model for the volume dependence of the Gruneisen parameter (L.V. Al'tshuler, S.E. Brusnikin, E.A. Kuz' menkov, J. Appl. Mech. Tech. Phys. 28 (1987) 129). The formula for the volume dependence of melting temperature obtained in the present study has been used to determine the results for aluminium up to a pressure range of 77 GPa. The results obtained for the melting temperature present a good agreement with the available experimental data.

Sharma, S. K.; Sharma, B. K.

2010-08-01

165

Local effects of ice floes and leads on skin sea surface temperature, mixing and gas transfer in the marginal ice zone  

NASA Astrophysics Data System (ADS)

Recent years have seen extreme changes in the Arctic. Marginal ice zones (MIZ), or areas where the "ice-albedo feedback" driven by solar warming is highest and ice melt is extensive, may provide insights into the extent of these changes. Furthermore, MIZ play a central role in setting the air-sea CO2 balance making them a critical component of the global carbon cycle. Incomplete understanding of how the sea-ice modulates gas fluxes renders it difficult to estimate the carbon budget in MIZ. Here, we investigate the turbulent mechanisms driving gas exchange in leads, polynyas and in the presence of ice floes using both field and laboratory measurements. Here, we present measurements of visible and IR imagery of melting ice floes in the marginal ice zone north of Oliktok Point AK in the Beaufort Sea made during the Marginal Ice Zone Ocean and Ice Observations and Processes EXperiment (MIZOPEX) in July-August 2013. The visible and IR imagery were taken from the unmanned airborne vehicle (UAV) ScanEagle. The visible imagery clearly defines the scale of the ice floes. The IR imagery show distinct cooling of the skin sea surface temperature (SST) as well as an intricate circulation and mixing pattern that depends on the surface current, wind speed, and near-surface vertical temperature/salinity structure. Individual ice floes develop turbulent wakes as they drift and cause transient mixing of an influx of colder surface (fresh) melt water. We capture a melting and mixing event that explains the changing pattern observed in skin SST and is substantiated using laboratory experiments. The Gas Transfer through Polar Sea Ice experiment was performed at the US Army Cold Regions Research and Engineering Laboratory (Hanover, NH) under varying ice coverage, winds speed, fetch and currents. Supporting measurements were made of air and water temperature, humidity, salinity and wave height. Air-side profiling provided momentum, heat, and CO2 fluxes. Transfer velocities are also estimated via the active controlled flux technique. Surface turbulence statistics derived from PIV and optical flow applied to infrared imagery are linked to subsurface turbulence and used to investigate how turbulent mechanisms at the ice-water boundary including shear and buoyancy contribute to the magnitude of the transfer. Gas exchange variability with lead size and enhancement near floes will be examined. Thanks are due to the entire MIZOPEX Team.

Zappa, Christopher; Brumer, Sophia; Brown, Scott; LeBel, Deborah; McGillis, Wade; Schlosser, Peter; Loose, Brice

2014-05-01

166

Estimating the time of melt onset and freeze onset over Arctic sea-ice area using active and passive microwave data  

USGS Publications Warehouse

Accurate calculation of the time of melt onset, freeze onset, and melt duration over Arctic sea-ice area is crucial for climate and global change studies because it affects accuracy of surface energy balance estimates. This comparative study evaluates several methods used to estimate sea-ice melt and freeze onset dates: (1) the melt onset database derived from SSM/I passive microwave brightness temperatures (Tbs) using Drobot and Anderson's [J. Geophys. Res. 106 (2001) 24033] Advanced Horizontal Range Algorithm (AHRA) and distributed by the National Snow and Ice Data Center (NSIDC); (2) the International Arctic Buoy Program/Polar Exchange at the Sea (IABP/POLES) surface air temperatures (SATs); (3) an elaborated version of the AHRA that uses IABP/POLES to avoid anomalous results (Passive Microwave and Surface Temperature Analysis [PMSTA]); (4) another elaborated version of the AHRA that uses Tb variance to avoid anomalous results (Mean Differences and Standard Deviation Analysis [MDSDA]); (5) Smith's [J. Geophys. Res. 103 (1998) 27753] vertically polarized Tb algorithm for estimating melt onset in multiyear (MY) ice (SSM/I 19V - 37V); and (6) analyses of concurrent backscattering cross section (rj) and brightness temperature (Tb) from OKEAN-01 satellite series. Melt onset and freeze onset maps were created and compared to understand how the estimates vary between different satellite instruments and methods over different Arctic seaice regions. Comparisons were made to evaluate relative sensitivities among the methods to slight adjustments of the Tb calibration coefficients and algorithm threshold values. Compared to the PMSTA method, the AHRA method tended to estimate significantly earlier melt dates, likely caused by the AHRA's susceptibility to prematurely identify melt onset conditions. In contrast, the IABP/POLES surface air temperature data tended to estimate later melt and earlier freeze in all but perennial ice. The MDSDA method was least sensitive to small adjustments of the SMMR-SSM/I inter-satellite calibration coefficients. Differences among methods varied by latitude. Freeze onset dates among methods were most disparate in southern latitudes, and tended to converge northward. Surface air temperatures (IABP/POLES) indicated freeze onset well before the MDSDA method, especially in southern peripheral seas, while PMSTA freeze estimates were generally intermediate. Surface air temperature data estimated latest melt onset dates in southern latitudes, but earliest melt onset in northern latitudes. The PMSTA estimated earliest melt onset dates in southern regions, and converged with the MDSDA northward. Because sea-ice melt and freeze are dynamical transitional processes, differences among these methods are associated with differing sensitivities to changing stages of environmental and physical development. These studies contribute to the growing body of documentation about the levels of disparity obtained when Arctic seasonal transition parameters are estimated using various types of microwave data and algorithms.

Belchansky, G. I.; Douglas, D. C.; Mordvintsev, I. N.; Platonov, N. G.

2004-01-01

167

Computer simulation study of metastable ice VII and amorphous phases obtained by its melting  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations of metastable ice VII and cubic ice Ic are carried out in order to examine (1) the ability of commonly used water interaction potentials to reproduce the properties of ices, and (2) the possibility of generating low-density amorphous (LDA) structures by heating ice VII, which is known to transform to LDA at ˜135K at normal pressure [S. Klotz, J. M. Besson, G. Hamel, R. J. Nelmes, J. S. Loveday, and W. G. Marshall, Nature (London) 398, 681 (1999)]. We test four simple empirical interaction potentials of water: TIP4P [W. L. Jorgensen, J. Chandrasekhar, J. D. Madura, R. W. Impey, and M. L. Klein, J. Chem. Phys. 79, 926 (1983)], SPC/E [H. J. C. Berendsen, J. R. Grigera, and T. P. Straatsma, J. Phys. Chem. B 91, 6269 (1987)], TIP5P [M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000)], and ST2 [F. H. Stillinger and A. Rahman, J. Chem. Phys. 60, 1545 (1974)]. We have found that TIP5P ice VII melts at 210 K, TIP4P at 90 K, and SPC/E at 70 K. Only TIP5P water after transition has a structure similar to that of LDA. TIP4P and SPC/E have almost identical structures, dissimilar to any known water or amorphous phases, but upon heating both slowly evolve towards LDA-like structure. ST2 ice VII is remarkably stable up to 430 K. TIP4P and SPC/E predict correctly the cubic ice collapse into a high-density amorphous ice (HDA) at ˜1GPa whereas TIP5P remains stable up to ˜5GPa. The densities of the simulated ice phases differ significantly, depending on the potential used, and are generally higher than experimental values. The importance of proper treatment of long-range electrostatic interactions is also discussed.

Slovák, Jan; Tanaka, Hideki

2005-05-01

168

Computer simulation study of metastable ice VII and amorphous phases obtained by its melting.  

PubMed

Molecular dynamics simulations of metastable ice VII and cubic ice Ic are carried out in order to examine (1) the ability of commonly used water interaction potentials to reproduce the properties of ices, and (2) the possibility of generating low-density amorphous (LDA) structures by heating ice VII, which is known to transform to LDA at approximately 135 K at normal pressure [S. Klotz, J. M. Besson, G. Hamel, R. J. Nelmes, J. S. Loveday, and W. G. Marshall, Nature (London) 398, 681 (1999)]. We test four simple empirical interaction potentials of water: TIP4P [W. L. Jorgensen, J. Chandrasekhar, J. D. Madura, R. W. Impey, and M. L. Klein, J. Chem. Phys. 79, 926 (1983)], SPC/E [H. J. C. Berendsen, J. R. Grigera, and T. P. Straatsma, J. Phys. Chem. B 91, 6269 (1987)], TIP5P [M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000)], and ST2 [F. H. Stillinger and A. Rahman, J. Chem. Phys. 60, 1545 (1974)]. We have found that TIP5P ice VII melts at 210 K, TIP4P at 90 K, and SPC/E at 70 K. Only TIP5P water after transition has a structure similar to that of LDA. TIP4P and SPC/E have almost identical structures, dissimilar to any known water or amorphous phases, but upon heating both slowly evolve towards LDA-like structure. ST2 ice VII is remarkably stable up to 430 K. TIP4P and SPC/E predict correctly the cubic ice collapse into a high-density amorphous ice (HDA) at approximately 1 GPa whereas TIP5P remains stable up to approximately 5 GPa. The densities of the simulated ice phases differ significantly, depending on the potential used, and are generally higher than experimental values. The importance of proper treatment of long-range electrostatic interactions is also discussed. PMID:15945757

Slovák, Jan; Tanaka, Hideki

2005-05-22

169

Quantum melting of charge ice and non-Fermi-liquid behavior: An exact solution for the extended Falicov-Kimball model in the ice-rule limit  

E-print Network

An exact solution is obtained for a model of itinerant electrons coupled to ice-rule variables on the tetrahedron Husimi cactus, an analogue of the Bethe lattice of corner-sharing tetrahedra. It reveals a quantum critical point with the emergence of non-Fermi-liquid behavior in melting of the "charge ice" insulator. The electronic structure is compared with the numerical results for the pyrochlore-lattice model to elucidate the physics of electron systems interacting with the tetrahedron ice rule.

Masafumi Udagawa; Hiroaki Ishizuka; Yukitoshi Motome

2010-06-04

170

Significant melting of ice-wedges and formation of thermocirques on hill-slopes of thermokarst lakes in Central Yakutia (Siberia)  

NASA Astrophysics Data System (ADS)

On Earth, permafrost containing a high ice volume (referred as ice-rich) are sensible to climate change, they have been regionally degraded (thermokarst) during the early Holocene climatic optimum forming numerous thermokarst lakes in Central Yakutia (eastern Siberia). Recent temperature increases in the Arctic and Subarctic have been significantly greater than global averages. The frequency and magnitude of terrain disturbances associated with thawing permafrost are increasing in these regions and are thought to intensify in the future. Therefore, understand how is the current development of thermokarst is a critical question. Here, we describe the significant melting of ice-wedges on slopes of thermokarst lakes that leads to formation of amphitheatrical hollows referred as thermocirques. The evolution of thermocirques in Central Yakutia has been little studied and analyzing their formation could help to understand the recent thermokarst in relation to climate change in Central Yakutia. We studied the thermocirques at two scales: (i) field surveys of different thermocirques in July 2009-2010 and October 2012 to examine the processes and origin of melting of ice-wedges and; (ii) photo-interpretation of time series of satellite images (KH-9 Hexagon images of 6-9 m/pixel and GeoEye images of 50 cm/pixel) to study the temporal evolution of thermocirques. The melting of ground-ice on the scarp of thermocirque triggers falls and small mud-flows that induce the retreat of the scarp parallel to itself. Based on field studies and on GeoEye image comparison, we show that their rate of retrogressive growth is 1-2 m/year. On the hill-slopes of lakes, the thermokarst could be initiated by different processes that lead to the uncover and then melting of ice-wedges: thermal erosion by the waves of the ice-rich bluff; active-layer detachment (a form of slope failure linked to detachment of the seasonally thawed upper ground); flowing of water on the slope (precipitation) or; increase of near-surface temperature (insolation, summer temperature). We suggest that the preferential occurrence of thermocirques on south-facing slopes of lakes could emphasize the role of insolation as a factor controlling the preferential melting of ice-wedges. The air temperatures are shown to have increased in Central Yakutia over years and deciphering if ongoing climate warming could lead to an increased development of thermocirques along lake slopes in Central Yakutia is a question that we will address in future study.

Séjourné, Antoine; Costard, François; Gargani, Julien; Fedorov, Alexander; Skorve, Johnny

2013-04-01

171

Substrate effect on the melting temperature of thin polyethylenefilms  

SciTech Connect

Strong dependence of the crystal orientation, morphology,and melting temperature (Tm) on the substrate is observed in thesemicrystalline polyethylene thin films. The Tm decreases with the filmthickness when the film is thinner that a certain critical thickness andthe magnitude of the depression increases with increasing surfaceinteraction. We attribute the large Tm depression to the decrease in theoverall free energy on melting, which is caused by the substrateattraction force to the chains that competes against the interchain forcewhich drives the chains to crystallization.

Wang, Y.; Rafailovich, M.; Sokolov, J.; Gersappe, D.; Araki, T.; Zou, Y.; Kilcoyne, A.D.L.; Ade, H.; Marom, G.; Lustiger, A.

2006-01-17

172

Radar Reflectivity-Ice Water Content Relationships for Use above the Melting Level in Hurricanes.  

NASA Astrophysics Data System (ADS)

Regression equations linking radar reflectivity (Ze) and ice water content (IWC) were calculated from airborne radar and particle image data that were collected above the melting level in two hurricanes. The Ze IWC equation from the stratiform areas of Hurricane Norbert (1984) is similar to the composite equation for thunderstorm anvils derived by Heymsfield and Palmer. The Ze IWC equation from the convective regions of Hurricane Irene (1981) has essentially the same exponent, but a significantly greater coefficient than that from Norbert. The higher density of the graupel and rounded ice in the Irene data accounts for the difference in the coefficients. The hurricane Ze IWC relations have smaller exponents than most of those from midlatitude clouds, which indicates that small ice particles may be more prevalent in these two hurricanes than in midlatitude clouds.

Black, Robert A.

1990-09-01

173

Simulations of the snow covered sea ice surface temperature and microwave effective temperature  

Microsoft Academic Search

The snow surface on thick multiyear sea ice in winter is on average colder than the air because of the negative radiation balance. Beneath the snow surface there is a strong temperature gradient in winter with increasing temperatures towards the ice-water interface temperature at the freezing point around -1.8 °C. The sea ice surface temperature and the thermal microwave brightness

Rasmus T. Tonboe; Gorm Dybkjcr; Jacob L. Høyer

2011-01-01

174

Thermal expansivity, bulk modulus, and melting curve of H2O-ice VII to 20 GPa  

NASA Technical Reports Server (NTRS)

Equation of state properties of ice VII and fluid H2O at high pressures and temperatures have been studied experimentally from 6 to 20 GPa and 300-700 K. The techniques involve direct measurements of the unit-cell volume of the solid using synchrotron X-ray diffraction with an externally heated diamond-anvil cell. The pressure dependencies of the volume and bulk modulus of ice VII at room temperature are in good agreement with previous synchrotron X-ray studies. The thermal expansivity was determined as a function of pressure and the results fit to a newly proposed phenomenological relation and to a Mie-Gruneisen equation of state formalism. The onset of melting of ice VII was determined directly by X-ray diffraction at a series of pressures and found to be in accord with previous volumetric determinations. Thermodynamic calculations based on the new data are performed to evaluate the range of validity of previously proposed equations of state for fluid water derived from static and shock-wave compression experiments and from simulations.

Fei, Yingwei; Mao, Ho-Kwang; Hemley, Russell J.

1993-01-01

175

Sea ice melt pond fraction estimation from dual-polarisation C-band SAR - Part 1: In situ observations  

NASA Astrophysics Data System (ADS)

An understanding of the evolution of melt ponds on Arctic sea ice is important for climate model parameterizations, weather forecast models, and process studies involving mass, energy and biogeochemical exchanges across the ocean-sea ice-atmosphere interface. A field campaign was conducted on landfast first-year sea ice in the Canadian Arctic Archipelago during the summer of 2012, to examine the potential for estimating melt pond fraction from C-band synthetic aperture radar (SAR). In this study, in situ dual-polarisation radar scatterometer observations of pond covered ice are combined with surface physical measurements to analyse the effects of radar and surface parameters on backscatter. LiDAR measurements of ice surface roughness and ultrasonic wind-wave height profiles of melt ponds are used to quantify the sea ice surface rms-height. Variables contributing to the roughness of wind-generated melt pond surface waves within the fetch-limited pond environment are evaluated, and we show that pond roughness and backscatter cannot be explained by wind speed alone. The utility of the VV / HH polarisation ratio (PR) for retrieving melt pond properties including pond fraction, due to the dielectric contrast between free surface water and sea ice, is demonstrated and explained using Bragg scattering theory. Finally, the PR approach is discussed in the context of retrievals from satellite C-, L-, and P-band dual-polarisation SAR.

Scharien, R. K.; Landy, J.; Barber, D. G.

2014-01-01

176

Communication: The Effect of Dispersion Corrections on the Melting Temperature of Liquid Water  

SciTech Connect

We report the results of the melting temperature (Tm) of liquid water for the Becke-Lee- Yang-Parr (BLYP) density functional including Dispersion corrections (BLYP-D) and the TTM3-F ab-initio based classical potential via constant pressure and constant enthalpy (NPH) ensemble molecular dynamics simulations of an ice Ih-liquid coexisting system. The inclusion of dispersion corrections to BLYP lowers the melting temperature of liquid water to Tm=360 K, which is a large improvement over the value of Tm > 400 K obtained with the original BLYP functional. The ab-initio based flexible, polarizable Thole-type model (TTM3-F) produces Tm=248 K from classical molecular dynamics simulations.

Yoo, Soohaeng; Xantheas, Sotiris S.

2011-03-28

177

Response of the Atlantic Ocean circulation to Greenland Ice Sheet melting in a strongly-eddying ocean model  

E-print Network

, and the vulnerability of the Greenland Ice Sheet (GrIS) to global warming, assessing this sensitivity is criticalResponse of the Atlantic Ocean circulation to Greenland Ice Sheet melting in a strongly uncertainties in the climate system. Considering the importance of the AMOC for global heat transports

Weijer, Wilbert

178

Modeling the influence of Greenland ice sheet melting on the Atlantic meridional overturning circulation during the next millennia  

E-print Network

of greenhouse gases into the atmosphere have signif- icantly contributed to the global warming of the EarthModeling the influence of Greenland ice sheet melting on the Atlantic meridional overturning-term evolution of the Greenland ice sheet and its effects on the Atlantic meridional overturning circulation

Huybrechts, Philippe

179

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

PubMed

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. PMID:24264767

Rasmussen, Tine L; Thomsen, Erik

2013-01-01

180

Polarimetric C-/X-band Synthetic Aperture Radar Observations of Melting Sea Ice in the Canadian Arctic Archipelago  

NASA Astrophysics Data System (ADS)

Operational ice information services rely heavily on space-borne synthetic aperture radar (SAR) data for the production of ice charts to meet their mandate of providing timely and accurate sea ice information to support safe and efficient marine operations. During the summer melt period, the usefulness of SAR data for sea ice monitoring is limited by the presence of wet snow and melt ponds on the ice surface, which can mask the signature of the underlying ice. This is a critical concern for ice services whose clients (e.g. commercial shipping, cruise tourism, resource exploration and extraction) are most active at this time of year when sea ice is at its minimum extent, concentration and thickness. As a result, there is a need to further quantify the loss of ice information in SAR data during the melt season and to identify what information can still be retrieved about ice surface conditions and melt pond evolution at this time of year. To date the majority of studies have been limited to analysis of single-polarization C-band SAR data. This study will investigate the potential complimentary and unique sea ice information that polarimetric C- and X-band SAR data can provide to supplement the information available from traditional single co-polarized C-band SAR data. A time-series of polarimetric C- and X-band SAR data was acquired over Jones Sound in the Canadian Arctic Archipelago, in the vicinity of the Grise Fiord, Nunavut. Five RADARSAT-2 Wide Fine Quad-pol images and 11 TerraSAR-X StripMap dual-pol (HH/VV) images were acquired. The time-series begins at the onset of melt in early June and extends through advanced melt conditions in late July. Over this period several ponding and drainage events and two snowfall events occurred. Field observations of sea ice properties were collected using an Ice Mass Balance (IMB) buoy, hourly photos from a time-lapse camera deployed on a coastal cliff, and manual in situ measurements of snow thickness and melt pond depth. Where available, clear-sky data from optical sensors (MODIS, Landsat-8, and WorldView) are also used to provide supplementary information on melt pond coverage and evolution. Meteorological data are available from an Environment Canada weather station in Grise Fiord. In this presentation we will discuss the sea ice information provided by each polarization and frequency and evaluate the impact of melt pond evolution on SAR backscatter. Results to date indicate that C- and X-band provide predominantly redundant information, and cross-polarized backscatter (only acquired at C-band) is often very low and near the system noise floor. Early in the melt season a thick wet snow pack is present and both frequencies provide very little ice information. This is attributed to the strong attenuation of the microwave signal by the wet snow. At this time the underlying ice is effectively obscured. During heavily ponded periods backscatter is highly variable, attributed to changing winds and thus variable melt pond surface roughness. In the final week of observations the fast ice in the region is breaking up and open water is present in some images. In these images C-band appears to provide greater contrast between the melting ice and open water than X-band. Analysis of polarimetric parameters is ongoing.

Casey, J. A.; Beckers, J. F.; Brossier, E.; Haas, C.

2013-12-01

181

A phenomenological model for predicting melting temperatures of DNA sequences.  

PubMed

We report here a novel method for predicting melting temperatures of DNA sequences based on a molecular-level hypothesis on the phenomena underlying the thermal denaturation of DNA. The model presented here attempts to quantify the energetic components stabilizing the structure of DNA such as base pairing, stacking, and ionic environment which are partially disrupted during the process of thermal denaturation. The model gives a Pearson product-moment correlation coefficient (r) of approximately 0.98 between experimental and predicted melting temperatures for over 300 sequences of varying lengths ranging from 15-mers to genomic level and at different salt concentrations. The approach is implemented as a web tool (www.scfbio-iitd.res.in/chemgenome/Tm_predictor.jsp) for the prediction of melting temperatures of DNA sequences. PMID:20865157

Khandelwal, Garima; Bhyravabhotla, Jayaram

2010-01-01

182

Charging in ice-ice collisions as a function of the ambient temperature and the larger particle average temperature  

Microsoft Academic Search

Measurements of charge transfer between ice particles are reported. The ambient temperature and the average graupel temperature are presented as an alternative pair of variables describing the charge transferred between ice particles during a collision. These variables are alternative to the generally used air temperature and liquid water content. A new charging diagram is also presented here. The results suggest

Eldo E. Avila; Guillermo G. Aguirre Varela; Giorgio M. Caranti

1996-01-01

183

Hot Ice  

Microsoft Academic Search

THAT the experiments of Dr. Carnelley on hot ice have excited much interest is not to be wondered at. His statement, however, that ice could be raised to a temperature of 180° without melting was so amazing that many a one could not accept it without repeating the experiments. Soon after the first short notice of Dr. Carnelley appeared in

C. J. E. Brutel de La Rivière; A. van Hasselt

1881-01-01

184

The 1988–2003 Greenland ice sheet melt extent using passive microwave satellite data and a regional climate model  

Microsoft Academic Search

Measurements from ETH-Camp and JAR1 AWS (West Greenland) as well as coupled atmosphere-snow regional climate simulations have highlighted flaws in the cross-polarized gradient ratio (XPGR) technique used to identify melt from passive microwave satellite data. It was found that dense clouds (causing notably rainfall) on the ice sheet severely perturb the XPGR melt signal. Therefore, the original XPGR melt detection

Xavier Fettweis; Hubert Gallée; Filip Lefebre; Jean-Pascal van Ypersele

2006-01-01

185

Development of ice thickness retrieval algorithms for large northern lakes from AMSR-E brightness temperature measurements  

NASA Astrophysics Data System (ADS)

Ice cover on lakes is a very sensitive to climate variability and change. With climate warming, lakes have the potential to greatly increase their energy and moisture exchanges with the atmosphere due to earlier break-up and warmer lake temperature during the open water season. Lake ice growth occurs between ice-on date and melt-onset as a result of energy loss by the conductive heat flow to the atmosphere above from the water under the ice to the ice/snow interface. Previous studies have suggested the potential of using brightness temperatures measured from low-frequency passive microwave sensors to estimate lake ice thickness. In this respect, brightness temperatures from current satellite passive microwave platforms (i.e. AMSR-E and SSM/I) are a viable data source for the development of ice thickness retrieval algorithms from space. The major objective of this study is to develop ice algorithms to estimate ice thickness from brightness temperature (TB) measurements obtained from AMSR-E 18.7 GHz channel over large lakes in northern Canada (e.g. Great Bear Lake and Great Slave Lake). The evolution of the horizontally and vertically polarized TB derived from AMSR-E L2A products was compared with ice thickness obtained with a previously validated lake ice model over the course of seven winter seasons (2002-2009). Given that much of the variations in TB could be explained by ice growth, as demonstrated through the use of a recent version of the Helsinki University of Technology (HUT) model, this relation was exploited to develop global and regional ice thickness retrieval algorithms. Following the application of the algorithms, estimated lake ice thickness on GBL is found to be on average 10-20 cm thicker than on GSL. Overall, this study shows that regression-based algorithms using AMSR-E TB data as input can be used to estimate lake ice thickness routinely on the two large northern lakes.

Kang, K.; Duguay, C. R.; Lemmetyinen, J.; Gel, Y.

2010-12-01

186

Grain boundaries in silicon from zero temperature through melting  

SciTech Connect

Recent atomistic simulations of silicon grain boundaries are reviewed and compared with similar studies in metals. Three aspects are discussed in detail: (i) the zero-temperature structure-energy correlation, (ii) the elastic anomalies near a grain boundary at zero temperature, and (iii) the high-temperature stability of a twist boundary and its role in thermodynamic melting. In each case striking similarities with studies on metals are found. 39 refs., 8 figs.

Phillpot, S.R.; Wolf, D.

1988-12-01

187

Forming of aluminium alloy at temperatures just below melting point  

Microsoft Academic Search

In order to improve the mechanical properties of products, a forming process of a solid material at a temperature just below the melting point is proposed. The material is deformed at the semi-solid temperature due to the heat generation caused by plastic deformation. The tensile strength, elongation, hardness and toughness of the aluminium alloy (Al–7%Si–0.3%Mg) billet extruded at temperatures between

M Shiomi; D Takano; K Osakada; M Otsu

2003-01-01

188

Temperature Temperature is the physical property of a  

E-print Network

of "hot" and "cold". Two systems placed in contact come ultimately into a state of mutual equilibrium interval between melting ice and boiling water under 1 atm pressure shall be 100. @ melting ice temperatureTemperature Scale Solving for T0 : Thus, melting ice temperature corresponds to 273.15 degrees in the absolute

Alexeenko, Alina

189

Temperatures at the base of the Laurentide Ice Sheet inferred from borehole temperature data  

E-print Network

Temperatures at the base of the Laurentide Ice Sheet inferred from borehole temperature data Fre. The GSTH's are consistent with information on the history of the Laurentide ice sheet and provide: Rolandone, F., J.-C. Mareschal, and C. Jaupart, Temperatures at the base of the Laurentide Ice Sheet

Rolandone, Frederique

190

A Climate-Data Record (CDR) of the "Clear-Sky" Surface Temperature of the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

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.

Hall, Dorothy K.; Comiso, Josefino C.; DiGirolamo, Nocolo E.; Shuman, Christopher A.

2011-01-01

191

Abrupt changes in Greenland Ice Sheet runoff and sea water temperature since 1821 recorded by coralline algae  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet (GrIS) contains the largest store of fresh water in the northern hemisphere, equivalent to ~7.4m of eustatic sea level rise, but its impacts on current, past and future sea level, ocean circulation and European climate are poorly understood. Previous estimates of GrIS melt, from satellite observations, temperature driven melt-models and palaeo reconstructions over

Kamenos, Nick; Hoey, Trevor; Claverie, Thomas; Fallick, Anthony; Nienow, Peter; O'Neill, Sean; Thormar, Jonas

2013-04-01

192

Modelling binge-purge oscillations of the Laurentide ice sheet using a plastic ice sheet  

Microsoft Academic Search

A simple combined heat and ice-sheet model has been used to calculate temperatures at the base of the Laurentide ice sheet. We let the ice sheet surge when the basal temperature reaches the pressure-melting temperature. Driving the system with the observed accumulation and temperature records from the GRIP ice core, Greenland, produces surges corresponding to the observed Heinrich events. This

H. C. Steen-Larsen; D. Dahl-Jensen

2008-01-01

193

Large and rapid melt-induced velocity changes in the ablation zone of the Greenland Ice Sheet.  

PubMed

Continuous Global Positioning System observations reveal rapid and large ice velocity fluctuations in the western ablation zone of the Greenland Ice Sheet. Within days, ice velocity reacts to increased meltwater production and increases by a factor of 4. Such a response is much stronger and much faster than previously reported. Over a longer period of 17 years, annual ice velocities have decreased slightly, which suggests that the englacial hydraulic system adjusts constantly to the variable meltwater input, which results in a more or less constant ice flux over the years. The positive-feedback mechanism between melt rate and ice velocity appears to be a seasonal process that may have only a limited effect on the response of the ice sheet to climate warming over the next decades. PMID:18599784

van de Wal, R S W; Boot, W; van den Broeke, M R; Smeets, C J P P; Reijmer, C H; Donker, J J A; Oerlemans, J

2008-07-01

194

Basal ice facies and supraglacial melt-out till of the Laurentide Ice Sheet, Tuktoyaktuk Coastlands, western Arctic Canada  

Microsoft Academic Search

Glacially-deformed massive ice and icy sediments (MI IS) in the Eskimo Lakes Fingerlands and Summer Island area of the Tuktoyaktuk Coastlands, western Arctic Canada, show, in the same stratigraphic sequences, features characteristic of both basal glacier ice and intrasedimental ice. Basal-ice features comprise (1) ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers

J. B. Murton; C. A. Whiteman; R. I. Waller; W. H. Pollard; I. D. Clark; S. R. Dallimore

2005-01-01

195

Modeling Regolith Temperatures and Volatile Ice Processes (Invited)  

NASA Astrophysics Data System (ADS)

Surface and subsurface temperatures are an important tool for exploring the distribution and dynamics of volatile ices on and within planetary regoliths. I will review thermal-analysis approaches and recent applications in the studies of volatile ice processes. Numerical models of regolith temperatures allow us to examine the response of ices to periodic and secular changes in heat sources such as insolation. Used in conjunction with spatially and temporally distributed remotely-sensed temperatures, numerical models can: 1) constrain the stability and dynamics of volatile ices; 2) define the partitioning between phases of ice, gas, liquid, and adsorbate; and 3) in some instances be used to probe the distribution of ice hidden from view beneath the surface. The vapor pressure of volatile ices (such as water, carbon dioxide, and methane) depends exponentially on temperature. Small changes in temperature can result in transitions between stable phases. Cyclic temperatures and the propagation of thermal waves into the subsurface can produce a strong hysteresis in the population and partitioning of various phases (such as between ice, vapor, and adsorbate) and result in bulk transport. Condensation of ice will also have a pronounced effect on the thermal properties of otherwise loose particulate regolith. Cementing grains at their contacts through ice deposition will increase the thermal conductivity, and may enhance the stability of additional ice. Likewise sintering of grains within a predominantly icy regolith will increase the thermal conductivity. Subsurface layers that result from ice redistribution can be discriminated by remote sensing when combined with numerical modeling. Applications of these techniques include modeling of seasonal carbon dioxide frosts on Mars, predicting and interpreting the subsurface ice distribution on Mars and in Antarctica, and estimating the current depth of ice-rich permafrost on Mars. Additionally, understanding cold trapping ices in regions of the regolith of airless bodies, such as Mercury and the Moon, are aided by numerical modeling of regolith temperatures. Thermally driven sublimation of volatiles (water ice on Mars and more exotic species on icy moons in the outer solar system) can result in terrain degradation and collapse.

Mellon, M. T.

2013-12-01

196

High temperature deformation of Bridgman melt-textured YBCO  

Microsoft Academic Search

Large bars were melt-textured using a modified Bridgman method. Neutron diffraction analysis revealed the absence of any large angle grain boundary and a FWHM of < 6 °. Smaller specimens cut from the bars were deformed under flowing oxygen in the temperature range 850–950 °C applying strain rates from 1 × 10?5 to 5 × 10?4 s?1. These high temperature

M. Ullrich; A. Leenders; J. Krelaus; L.-O. Kautschor; H. C. Freyhardt; L. Schmidt; F. Sandiumenge; X. Obradors

1998-01-01

197

Skin Temperature Processes in the Presence of Sea Ice  

NASA Astrophysics Data System (ADS)

Monitoring the sea-ice margins of polar oceans and understanding the physical processes at play at the ice-ocean-air interface is essential in the perspective of a changing climate in which we face an accelerated decline of ice caps and sea ice. Remote sensing and in particular InfraRed (IR) imaging offer a unique opportunity not only to observe physical processes at sea-ice margins, but also to measure air-sea exchanges near ice. It permits monitoring ice and ocean temperature variability, and can be used for derivation of surface flow field allowing investigating turbulence and shearing at the ice-ocean interface as well as ocean-atmosphere gas transfer. Here we present experiments conducted with the aim of gaining an insight on how the presence of sea ice affects the momentum exchange between the atmosphere and ocean and investigate turbulence production in the interplay of ice-water shear, convection, waves and wind. A set of over 200 high resolution IR imagery records was taken at the US Army Cold Regions Research and Engineering Laboratory (CRREL, Hanover NH) under varying ice coverage, fan and pump settings. In situ instruments provided air and water temperature, salinity, subsurface currents and wave height. Air side profiling provided environmental parameters such as wind speed, humidity and heat fluxes. The study aims to investigate what can be gained from small-scale high-resolution IR imaging of the ice-ocean-air interface; in particular how sea ice modulates local physics and gas transfer. The relationship between water and ice temperatures with current and wind will be addressed looking at the ocean and ice temperature variance. Various skin temperature and gas transfer parameterizations will be evaluated at ice margins under varying environmental conditions. Furthermore the accuracy of various techniques used to determine surface flow will be assessed from which turbulence statistics will be determined. This will give an insight on how ice presence may affect the dissipation of turbulent kinetic energy.

Brumer, S. E.; Zappa, C. J.; Brown, S.; McGillis, W. R.; Loose, B.

2013-12-01

198

Deposition Ice Nuclei Concentration at Different Temperatures and Supersaturations  

NASA Astrophysics Data System (ADS)

Ice formation is one of the main processes involved in the initiation of precipitation. Some aerosols serve to nucleate ice in clouds. They are called ice nuclei (IN) and they are generally solid particles, insoluble in water. At temperatures warmer than about -36°C the only means for initiation of the ice phase in the atmosphere involves IN, and temperature and supersaturation required to activate IN are considered as key information for the understanding of primary ice formation in clouds. The objective of this work is to quantify the IN concentration at ground level in Córdoba City, Argentina, under the deposition mode, that is to say that ice deposits on the IN directly from the vapor phase. It happens when the environment is supersaturated with respect to ice and subsaturated with respect to liquid water. Ice nuclei concentrations were measured in a cloud chamber placed in a cold room with temperature control down to -35°C. The operating temperature was varied between -15°C and -30°C. Ice supersaturation was ranged between 2 and 20 %. In order to quantify the number of ice particles produced in each experiment, a dish containing a supercooled solution of cane sugar, water and glycerol was placed on the floor of the cloud chamber. The activated IN grew at the expense of vapor until ice crystals were formed and these then fell down onto the sugar solution. Once there, these crystals could grow enough to be counted easily with a naked eye after a period of about three minutes, when they reach around 2 mm in diameter. In order to compare the present results with previously reported results, the data were grouped in three different ranges of supersaturation: the data with supersaturations between 2 and 8 %, the data with supersaturations between 8 and 14% and the data with supersaturations between 14 and 20 %. In the same way, in order to analize the behavior of IN concentration with supersaturation, the data were grouped for three different temperatures, the data with temperatures between -15°C and -20°C, the data with temperatures between -20°C and -25°C and the data with temperatures between -25°C and -30°C. The results confirm that for each temperature range, the concentration of IN increases at higher supersaturation, and show the tendency of the IN concentration to increase with increasing ice supersaturation. Based on previous parameterizations, a combination of IN concentration in relation with temperature and ice supersaturation is proposed in this work. As far as we know, this is among the first work to measure and parameterize the concentration of deposition ice nuclei in the Southern Hemisphere.

López, M. L.; Avila, E.

2013-05-01

199

Transfer of Escherichia coli O157:H7 to romaine lettuce due to contact water from melting ice.  

PubMed

Ice can be used to chill romaine lettuce and maintain relative humidity during transportation. Escherichia coli O157:H7 may contaminate water used for ice. The objective of this study was to determine the potential for E. coli O157:H7 contamination of romaine lettuce from either ice contaminated with the pathogen or by transfer from lettuce surfaces via melting ice. In experiment 1, lettuce was spot inoculated with E. coli O157:H7 and chilled with ice prepared from uncontaminated tap water. In experiment 2, water inoculated with this pathogen was frozen and used to ice lettuce. Three heads of lettuce were stacked in each container and stored at 4 or 20 degrees C. After the ice melted, E. coli O157:H7 attachment to and recovery from the lettuce leaves were determined. For experiment 1, the population of E. coli O157:H7 attached to inoculated sites averaged 3.8 and 5.5 CFU/cm2 at 4 and 20 degrees C, respectively. Most of the uninoculated sites became contaminated with the pathogen due to ice melt. For experiment 2, 3.5 to 3.8 log CFU E. coli O157:H7 per cm2 was attached to the top leaf on the first head. After rinsing with chlorinated water (200 microg/ml), E. coli O157:H7 remained on the surface of the top head (1.8 to 2.0 log CFU/cm2). There was no difference in numbers of E. coli O157:H7 recovered from each sampling site at 4 and 20 degrees C. Results show that E. coli O157:H7 can be transferred onto other produce layers in shipping containers from melted ice made of contaminated water and from contaminated to uncontaminated leaf surfaces. PMID:18326172

Kim, Jin Kyung; Harrison, Mark A

2008-02-01

200

Abrupt Greenland Ice Sheet runoff and sea water temperature changes since 1821, recorded by coralline algae  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet (GrIS) contains the largest store of fresh water in the northern hemisphere, equivalent to ~7.4m of eustatic sea level rise, but its impacts on current, past and future sea level, ocean circulation and European climate are poorly understood. Previous estimates of GrIS melt, from 26 years of satellite observations and temperature driven melt-models over 48 years, show a trend of increasing melt. There are however no runoff data of comparable duration with which to validate temperature-based runoff models, or relationships between the spatial extent of melt and runoff. Further, longer runoff records that extend GrIS melt records to centennial timescales will enable recently observed trends to be put into a better historical context. We measured Mg/Ca, ?18O and structural cell size in annual growth bands of red coralline algae to reconstruct: (1) near surface sea water temperature; and, (2) melt/runoff from the GrIS. (1) Temperature: we reconstructed the longest (1821-2009) sub-annual resolution record of water temperature in Disko Bugt (western Greenland) showing an abrupt change in temperature oscillation patterns during the 1920s which may be attributable to the interaction between atmospheric temperature and mass loss from Jakobshavn Isbrae glacier. (2) GrIS runoff: using samples from distal parts of Søndre Strømfjord we produced the first reconstruction of decadal (1939-2002) GrIS runoff. We observed significant negative relationships between historic runoff, relative salinity and marine summer temperature. Our reconstruction shows a trend of increasing reconstructed runoff since the mid 1980s. In situ summer marine temperatures followed a similar trend. We suggest that since 1939 atmospheric temperatures have been important in forcing runoff. Subject to locating in situ coralline algae samples, these methods can be applied across hundreds to thousands of years. These results show that our technique has significant potential to enhance understanding of runoff from large ice sheets as it will enable melt reconstruction over centennial-millennial time scales.; Red coralline algal thalli (Lithothamnion glaciale) similar to those used in Greenland reconstructions. Each thallus is 5cm in diameter.

Kamenos, N.; Hoey, T.; Bedford, J.; Claverie, T.; Fallick, A. E.; Lamb, C. M.; Nienow, P. W.; O'Neill, S.; Shepherd, I.; Thormar, J.

2012-12-01

201

High temporal resolution observations of spring fast ice melt and seawater iron enrichment in East Antarctica  

NASA Astrophysics Data System (ADS)

A time series experiment was conducted in late austral spring (November-December 2009) in coastal fast ice, East Antarctica (66°13'07?S, 110°39'02?E). Iron (Fe) measurements were made in sea ice, snow, brines, and underlying seawater, together with meteorological, physical, and biogeochemical measurements to investigate the processes controlling the release of Fe into the underlying water column. Warming air temperatures were clearly associated with decreasing brine volume fractions. Macronutrient profiles revealed very low (<1 ?M) nitrate + nitrite concentrations in the interior of the sea ice, and the brines suggested nitrate + nitrite drawdown exceeded Redfield ratios in comparison to phosphate and silicate. In the basal ice, nitrate + nitrite and silicate were drawn down through time but did not lead to a limiting condition. We found that dissolved Fe tracked the brine volume fraction and was readily transferred from the surface/interior to the underlying water column over time. In contrast, particulate Fe did not show this clear decreasing trend and correlated with particulate organic carbon and chlorophyll a distributions. Over the 28 d of sampling, two distinct mean air temperature warming events were observed (-12.1 to -1.3°C and -6.4 to 0.8°C). This resulted in the release of 419 ?mol of TDFe per m2 of sea ice from our coastal fast ice station into the underlying water column during the study period. Assuming an increase of 1 nM Fe is sufficient for Antarctic diatoms to bloom, our study site presented a fertilization potential for 419 m3 of Fe limited surface Southern Ocean seawater with TDFe and 29 m3 with dFe, per m2 of fast ice.

van der Merwe, P.; Lannuzel, D.; Bowie, A. R.; Meiners, K. M.

2011-09-01

202

Warming, Contraction, and Freshening of Antarctic Bottom Water since the 1990s, with a Potential Ice-Sheet Melt Feedback.  

NASA Astrophysics Data System (ADS)

We analyze changes in Antarctic Bottom Waters (AABW) around the deep Southern Ocean using repeat section data collected between 1981 and 2012. The international World Ocean Circulation Experiment (WOCE) Hydrographic Program collected a global high-quality baseline of full-depth, accurate oceanographic transects in the 1980s and 1990s. Since the 2000s, some of these transects are being reoccupied, again through international collaboration, as part of GO-SHIP (The Global Ocean Ship-Based Hydrographic Investigations Program). The average dates of the first and last data used to estimate these trends are circa 1991 and 2008. Temperature analyses reveal a nearly global-scale signature of warming in the abyssal ocean ventilated from the Antarctic. In the deep basins around Antarctica, AABW warmed at a rate of 0.02 to 0.05 °C per decade below 4000 m. In addition, the waters between 1000 and 4000 m within and south of the Antarctic Circumpolar Current warmed at a rate of about 0.03 °C per decade. With this warming, cold, deep isotherms are sinking in the Southern Ocean. The 0 °C potential isotherm sinking rate is around 100 m per decade, implying a 8.2 (±2.6) Sv contraction rate of AABW, about 7% per decade. In addition to this contraction, AABW freshening is observed within the Indian and Pacific sectors of the Southern Ocean. The freshening signal is stronger closer to AABW sources. Its spatial pattern implies recent changes in AABW formation, perhaps partly owing to freshening of the shelf waters, which has been linked to increases in glacial ice sheet melt. The observed rate of water-mass freshening for AABW colder than 0°C in the Indian and Pacific Sectors of the Southern Ocean is about half of the estimated increase in mass lost by glacial ice sheets there in recent years. A positive feedback loop might link the AABW contraction and ice sheet melt-influenced freshening as follows: Increased ocean heat flux drives enhanced basal melt of floating ice shelves. Increased meltwater freshens shelf waters, increasing their buoyancy and reducing the formation rate and/or density of AABW. The contraction of AABW results in expansion of relatively warm Circumpolar Deep Water (CDW). If expansion of CDW increases the ocean heat flux to the base of the ice shelf, a positive feedback loop is completed. Such a feedback would imply a stronger sensitivity of both AABW formation and mass balance of the Antarctic ice sheet to ocean warming than in the absence of such a process. Deep ocean warming makes a significant contribution to global energy and sea-level rise budgets and influences the rate and magnitude of climate change in response to a given greenhouse gas forcing. Better understanding the potential mechanisms for effecting such deep warming, such as the one proposed here, may aid the goal of improved climate change projections, based on coupled climate models that better represent these processes.

Johnson, Gregory; Purkey, Sarah; Rintoul, Stephen; Swift, James

2013-04-01

203

Light absorption and partitioning in Arctic Ocean surface waters: impact of multi year ice melting  

NASA Astrophysics Data System (ADS)

Ice melting in the Arctic Ocean exposes the surface water to more radiative energy with poorly understood effects on photo-biogeochemical processes and heat deposition in the upper ocean. In August 2009, we documented the vertical variability of light absorbing components at 37 stations located in the southeastern Beaufort Sea including both Mackenzie river-influenced waters and polar mixed layer waters. We found that melting multi-year ice released significant amount of non-algal particulates (NAP) near the sea surface relative to sub-surface waters. NAP absorption coefficients at 440 nm (aNAP(440)) immediately below the sea surface (0-) were on average 3-fold (up to 10-fold) higher compared to sub-surface values measured at 2-3 m depth. The impact of this unusual feature on the light transmission and remote sensing reflectance (Rrs) was further examined using a radiative transfer model. A 10-fold particle enrichment homogeneously distributed in the first meter of the water column slightly reduced photosynthetically available and usable radiation (PAR and PUR) by ~6% and ~8%, respectively, relative to a fully homogenous water column with low particles concentration. In terms of Rrs, the particle enrichment significantly flattered the spectrum by reducing the Rrs by up to 20% in the blue-green spectral region (400-550 nm). These results highlight the impact of melt water on the concentration of particles at sea surface, and the need for considering nonuniform vertical distribution of particles in such systems when interpreting remotely sensed ocean color. Spectral slope of aNAP spectra calculated in the UV domain decreased with depth suggesting that this parameter is sensitive to detritus composition and/or diagenesis state (e.g., POM photobleaching).

Bélanger, S.; Cizmeli, S. A.; Ehn, J.; Matsuoka, A.; Doxaran, D.; Hooker, S.; Babin, M.

2013-03-01

204

Thermohaline Circulation Below the Ross Ice Shelf: A Consequence of Tidally Induced Vertical Mixing and Basal Melting  

Microsoft Academic Search

warm but dense water into contact with the ice shelf. A numerical tidal simulation indicates that vertically well-mixed conditions predominate in the southeastern part of the sub-ice-shelf cavity where the water column thickness is small. Basal melting in this region is expected to be between 0.05 and 0.5 m\\/yr and will drive a thermohaline circulation having the following characteristics: high

Douglas Reed MacAyeal

1984-01-01

205

Basal ice facies and supraglacial melt-out till of the Laurentide Ice Sheet, Tuktoyaktuk Coastlands, western Arctic Canada  

Microsoft Academic Search

Glacially-deformed massive ice and icy sediments (MI–IS) in the Eskimo Lakes Fingerlands and Summer Island area of the Tuktoyaktuk Coastlands, western Arctic Canada, show, in the same stratigraphic sequences, features characteristic of both basal glacier ice and intrasedimental ice. Basal-ice features comprise (1) ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and

J. B. Murton; C. A. Whiteman; R. I. Waller; W. H. Pollard; I. D. Clark; S. R. Dallimore

2005-01-01

206

Equations of state of ice VI and ice VII at high pressure and high temperature  

NASA Astrophysics Data System (ADS)

High-pressure H2O polymorphs among which ice VI and ice VII are abundant in the interiors of large icy satellites and exo-planets. Knowledge of the elastic properties of these pure H2O ices at high-temperature and high-pressure is thus crucial to decipher the internal structure of icy bodies. In this study we assess for the first time the pressure-volume-temperature (PVT) relations of both polycrystalline pure ice VI and ice VII at high pressures and temperatures from 1 to 9 GPa and 300 to 450 K, respectively, by using in situ synchrotron X-ray diffraction. The PVT data are adjusted to a second-order Birch-Murnaghan equation of state and give V0 = 14.17(2) cm3 mol-1, K0 = 14.05(23) GPa, and ?0 = 14.6(14) × 10-5 K-1 for ice VI and V0 = 12.49(1) cm3 mol-1, K0 = 20.15(16) GPa, and ?0 = 11.6(5) × 10-5 K-1 for ice VII.

Bezacier, Lucile; Journaux, Baptiste; Perrillat, Jean-Philippe; Cardon, Hervé; Hanfland, Michael; Daniel, Isabelle

2014-09-01

207

Spatially Distributed Temperature-index Melt Modelling of Glaciers in the Donjek Range, St. Elias Mountains, Yukon Territory  

NASA Astrophysics Data System (ADS)

We apply both classical and enhanced spatially-distributed temperature-index melt models to two small valley glaciers in the Donjek Range of the St. Elias Mountains (Yukon, Canada) in an effort to accurately model glacier melt in this region. The enhanced model is an extension of the classical approach with the addition of potential clear-sky direct solar radiation as developed by Hock (1999). The two study glaciers are located ~10 km apart and are of similar size (~5 km2), but different aspect (north/south) and dynamic regime (normal/surge-type). We calibrate the melt models on one glacier in 2007 and evaluate the models on the same glacier in 2006 and the second glacier in 2007, providing insight into the potential for model extension in both time and space. To drive the melt models we use four to seven temperature records from distal and proximal automatic weather stations (AWS), including AWS located on the glacier surfaces. Model output consists of hourly simulated melt rates at 30 m spatial resolution across each glacier surface. Model skill is examined through comparisons with cumulative surface lowering measured at ablation stakes, as well as with hourly measured surface lowering and hourly melt simulated by an energy balance model at AWS locations on each glacier. Results show that although air temperature lapse rates vary in time and space, daily air temperature over the glaciers can be estimated from off-ice temperature records with reasonable accuracy (maximum r2 = 0.97) when constant lapse rates are applied. With the enhanced model, high model skill in simulating both daily and seasonal melt rates can be achieved even in the absence of accurate estimates of air temperature. Off-ice temperature records generally yield higher model skill than on-ice records. Optimized model parameters (i.e. melt factors) are similar for the two glaciers in 2007, but differ significantly from 2006 to 2007. As a result, the models show greater skill in predicting cumulative melt on the second glacier than predicting melt on the calibration glacier in a different year: mean absolute errors (MAE) are 18 and 23%, respectively. This difference in model skill is partly explained by the surface energy balance computed at the glacier AWS locations: the energy balance is similarly partitioned on the two glaciers in 2007 but shows higher net radiative flux and lower turbulent fluxes in 2006 compared to 2007 on the calibration glacier. The classical 'degree-day' approach matches the skill of the enhanced temperature- index model for cumulative melt simulation during model calibration, but the enhanced model exhibits superior performance in the model evaluation (MAE 11 to 14% lower than classical model) and for daily and sub- daily melt-rate simulations. The spatial transferability of enhanced temperature-index model parameters in this study suggests the potential for reasonable estimation of distributed glacier melt within the study region with minimal data input.

Wheler, B. A.; Flowers, G. E.

2008-12-01

208

Diurnal Melt Detection on Arctic Sea Ice Using Tandem QuikSCAT and SeaWinds Data B.R. Hicks and D.G. Long  

E-print Network

Diurnal Melt Detection on Arctic Sea Ice Using Tandem QuikSCAT and SeaWinds Data B.R. Hicks and D, and applied to the maximum likelihood estimation of melt over Arctic sea-ice. I. INTRODUCTION The tandem

Long, David G.

209

Development of a Climate-Data Record (CDR) of the Surface Temperature of the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

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 deg C to 72+/-0.10 deg 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 0 deg 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. To quantify the ice-surface temperature (IST) of the Greenland Ice Sheet, and to provide an IST dataset of Greenland for modelers that provides uncertainties, we are developing a climate-data record (CDR) of daily "clear-sky" IST of the Greenland Ice Sheet, from 1982 to the present using AVHRR (1982 - present) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data (2000 - present) at a resolution of approximately 5 km. Known issues being addressed in the production of the CDR are: time-series bias caused by cloud cover (surface temperatures can be different under clouds vs. clear areas) and cross-calibration in the overlap period between AVHRR instruments, and between AVHRR and MODIS instruments. Because of uncertainties, mainly due to clouds, time-series of satellite IST do not necessarily correspond with actual surface temperatures. The CDR will be validated by comparing results with automatic-weather station data and with satellite-derived surface-temperature products and biases will be calculated.

Hall, Dorthy K.; Comiso, Josefino C.; Shuman, Christopher A.; DiGirolamo, Nicolo E.; Stock, Larry V.

2010-01-01

210

Light absorption and partitioning in Arctic Ocean surface waters: impact of multiyear ice melting  

NASA Astrophysics Data System (ADS)

Ice melting in the Arctic Ocean exposes the surface water to more radiative energy with poorly understood effects on photo-biogeochemical processes and heat deposition in the upper ocean. In August 2009, we documented the vertical variability of light absorbing components at 37 stations located in the southeastern Beaufort Sea including both Mackenzie River-influenced waters and polar mixed layer waters. We found that melting multiyear ice released significant amount of non-algal particulates (NAP) near the sea surface relative to subsurface waters. NAP absorption coefficients at 440 nm (aNAP(440)) immediately below the sea surface were on average 3-fold (up to 10-fold) higher compared to subsurface values measured at 2-3 m depth. The impact of this unusual feature on the light transmission and remote sensing reflectance (Rrs) was further examined using a radiative transfer model. A 10-fold particle enrichment homogeneously distributed in the first meter of the water column slightly reduced photosynthetically available and usable radiation (PAR and PUR) by ∼6 and ∼8%, respectively, relative to a fully homogenous water column with low particle concentration. In terms of Rrs, the particle enrichment significantly flattered the spectrum by reducing the Rrs by up to 20% in the blue-green spectral region (400-550 nm). These results highlight the impact of meltwater on the concentration of particles at sea surface, and the need for considering non-uniform vertical distribution of particles in such systems when interpreting remotely sensed ocean color. Spectral slope of aNAP spectra calculated in the UV (ultraviolet) domain decreased with depth suggesting that this parameter is sensitive to detritus composition and/or diagenesis state (e.g., POM (particulate organic matter) photobleaching).

Bélanger, S.; Cizmeli, S. A.; Ehn, J.; Matsuoka, A.; Doxaran, D.; Hooker, S.; Babin, M.

2013-10-01

211

Downsag and extension at calderas: new perspectives on collapse geometries from ice-melt, mining, and volcanic subsidence  

Microsoft Academic Search

Structures at calderas may form as a result of precursory tumescence, subsidence due withdrawal of magmatic support, resurgence, and regional tectonism. Structural reactivation and overprinting are common. To explore which types of structures may derive directly from subsidence without other factors, evidence is reviewed from pits caused by the melting of buried ice blocks, mining subsidence, scaled subsidence models, and

M. J. Branney

1995-01-01

212

Using Digital Imagery from a Small Unmanned Aerial Vehicle (UAV) to Estimate Arctic Melt Pond Coverage on Sea Ice  

Microsoft Academic Search

Photo mapping of melt pond coverage on sea ice was undertaken in the Arctic during the summer of 2004 using an Aerosonde. Aerosondes are small, long endurance UAV designed to undertake a wide range of operations in a highly flexible and inexpensive mode. The Aerosonde conducts a defined mission in a completely autonomous mode. All flights are under the command

B. L. Mulac; M. A. Tschudi; J. A. Maslanik; G. J. Holland

2004-01-01

213

BINARY: an optical freezing array for assessing temperature and time dependence of heterogeneous ice nucleation  

NASA Astrophysics Data System (ADS)

A new optical freezing array for the study of heterogeneous ice nucleation in microliter-sized droplets is introduced, tested and applied to the study of immersion freezing in aqueous Snomax® suspensions. In the Bielefeld Ice Nucleation ARraY (BINARY) ice nucleation can be studied simultaneously in 36 droplets at temperatures down to -40 °C (233 K) and at cooling rates between 0.1 K min-1 and 10 K min-1. The droplets are separated from each other in individual compartments, thus preventing a Wegener-Bergeron-Findeisen type water vapor transfer between droplets as well as avoiding the seeding of neighboring droplets by formation and surface growth of frost halos. Analysis of freezing and melting occurs via an automated real time image analysis of the optical brightness of each individual droplet. As an application ice nucleation in water droplets containing Snomax® at concentrations from 1 ng mL-1 to 1 mg mL-1 was investigated. Using different cooling rates a minute time dependence of ice nucleation induced by Class A and Class C ice nucleators contained in Snomax® was detected. For the Class A IN a very strong increase of the heterogeneous ice nucleation rate coefficient with decreasing temperature of ? ≡ -dln(jhet)/dT = 8.7 K-1 was observed emphasizing the capability of the BINARY device. This value is larger than those of other types of IN reported in the literature, suggesting that the BINARY setup is suitable for quantifying time dependence for most other IN of atmospheric interest, making it a useful tool for future investigations.

Budke, C.; Koop, T.

2014-09-01

214

Early Last Interglacial Greenland Ice Sheet melting and a sustained period of meridional overturning weakening: a model analysis of the uncertainties  

NASA Astrophysics Data System (ADS)

Proxy-data suggest that the Last Interglacial (LIG; ~130-116 ka BP) climate was characterized by higher temperatures, a partially melted Greenland Ice Sheet (GIS) and a changed Atlantic meridional overturning circulation (AMOC). Notwithstanding the uncertainties in LIG palaeoclimatic reconstructions, this setting potentially provides an opportunity to evaluate the relation between GIS melt and the AMOC as simulated by climate models. However, first we need to assess the extent to which a causal relation between early LIG GIS melt and the weakened AMOC is plausible. With a series of transient LIG climate simulations with the LOVECLIM earth system model, we quantify the importance of the major known uncertainties involved in early LIG GIS melt scenarios. Based on this we construct a specific scenario that is within the parameter space of uncertainties and show that it is physically consistent that early LIG GIS melting kept the AMOC weakened. Notwithstanding, this scenario is at the extreme end of the parameter space. Assuming that proxy-based reconstructions of early LIG AMOC weakening offer a realistic representation of its past state, this indicates that either (1) the AMOC weakening was caused by other forcings than early LIG GIS melt or (2) the early LIG AMOC was less stable than indicated by our simulations and a small amount of GIS melt was sufficient to keep the AMOC in the weak state of a bi-stable regime. We argue that more intensive research is required because of the high potential of the early LIG to evaluate model performance in relation to the AMOC response to GIS melt.

Bakker, Pepijn; Renssen, Hans; Van Meerbeeck, Cédric J.

2014-08-01

215

Understanding changes in the Arctic basin sea ice mass budget as simulated by CCSM4: Implications from melt season characteristics and the surface albedo feedback  

Microsoft Academic Search

Observations reveal alarming drops in Arctic sea ice extent, and climate models project that further changes will occur that could have global repercussions. An important aspect of this change is the surface albedo feedback, driven by the contrast between the albedos of snow\\/ice and the open ocean. In response to warming, this feedback enhances ice melt and amplifies surface warming

D. A. Pollak; M. M. Holland; D. A. Bailey

2010-01-01

216

Correlations between Inter-Annual Variations in Arctic Sea Ice Extent, Greenland Surface Melt, and Boreal Snow Cover  

NASA Technical Reports Server (NTRS)

Intensification of global warming in recent decades has caused a rise of interest in year-to-year and decadal-scale climate variability in the Arctic. This is because the Arctic is believed to be one of the most sensitive and vulnerable regions to climatic changes. For over two decades satellite passive microwave observations have been utilized to continuously monitor the Arctic environment. Derived parameters include sea ice cover, snow cover and snow water equivalent over land, and Greenland melt extent and length of melt season. Most studies have primarily concentrated on trends and variations of individual variables. In this study we investigated how variations in sea ice cover, Greenland surface melt, and boreal snow cover are correlated. This was done on hemispheric as well as on regional scales. Latest results will be presented including data from the summer of 2004.

Markus, Thorstena; Stroeve, Julienne C.; Armstrong, Richard L.

2004-01-01

217

Measurements of restitution coefficients of ice at low temperatures  

Microsoft Academic Search

Measurements of the restitution coefficient (?) of a smooth water ice sphere (radius = 1.5 cm) are made in a wide range of impact velocities (1??i?700cms?1) and temperatures (113?T?269K). The impact velocity dependence of ? is different in the quasi-elastic and inelastic regimes separated by a critical velocity (?c) at which fracture deformation occurs at the impact point of ice

M. Higa; M. Arakawa; N. Maeno

1996-01-01

218

Evaluation of an ice ablation model to estimate the contribution of melting glacier ice to annual discharge in the Nepal Himalaya  

NASA Astrophysics Data System (ADS)

This study focuses on the contribution of annual glacier ice melt to streamflow along two rivers in two watersheds situated in the monsoon-influenced part of the Nepal Himalaya (Trishuli and Dudh Kosi basins). We used a simple elevation-dependent ice ablation model based on glacier areas from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and IKONOS remote-sensing data combined with hypsometry from the Shuttle Radar Topography Mission (SRTM). Long-term hydrologic measurements were used to calculate the percent contribution of the glacier ice melt component of the water balance to discharge at various elevations and distances from glacier outlets. Glacier ice melt was positively correlated with the basin glacierized area and contributed 58.3% to annual flow in the small Langtang Khola watershed in the Trishuli basin (43.5% glacierized area) and 21.2% in the Hinku watershed in Dudh Kosi basin (34.7% glacierized area). Of this, 17.7% and 4.1% of streamflow, respectively, was due to the contribution of debris-covered glaciers in Langtang Khola and Hinku. The contribution of glacier ice melt to measured discharge decreased substantially toward lowland locations in both study sites, i.e., 9.5% of the streamflow measured at Betrawati (600 m) and 7.4% at Rabuwa Bazaar (470 m), about 50 km from glacier termini. Glacier ice melt contribution decreased to 4.5% of annual discharge further downstream in Trishuli basin (at 325 m, about 75 km from glacier termini). At low elevations, debris-covered tongues contributed a small percent (1.1% and 3.0%) to measured discharge at Betrawati and Rabuwa Bazaar stations, respectively. We independently evaluated the ice ablation approach with synoptic sampling of stable water isotopes (?18O and ?D) collected during the post-monsoon season to quantify the contribution of various sources of water to river flow. Mixing models showed groundwater to be an important component of river flow within only tens of kilometers of the glacier outlets in the post-monsoon season.

Racoviteanu, Adina E.; Armstrong, Richard; Williams, Mark W.

2013-09-01

219

Isotopic probes of ice microphysics at cold temperatures  

NASA Astrophysics Data System (ADS)

Measurements of the isotopic composition of water can provide a valuable probe of cirrus microphysics because the parameters relevant for ice nucleation and growth -- for example, temperature, supersaturation, ice habit, and gas exchange -- all affect isotopic fractionation during ice growth. In particular, isotopic measurements can discriminate between some of the mechanisms proposed to explain apparent persistent supersaturation at very cold temperatures (< 200 K). Proposed mechanisms fall into two broad categories, those that involve partial inhibition of homogeneous ice nucleation and those that involve inhibition of growth of ice particles via some surface effect. The former category results in diffusion limitation of vapor reaching ice particles and a characteristic kinetic fractionation signature; the latter category results in ordinary equilibrium fractionation. We discuss the relevant isotopic physics in relation to potential factors such as aerosol glassification, accommodation coefficient uncertainty, and surface effects of organic or other coatings. We show the magnitudes of the expected effects for different cirrus scenarios, and describe a new measurement program aimed at their diagnosis. ISOCLOUD is a measurement campaign to take place at the AIDA aerosol and cloud simulation chamber during 2012-2014, aimed at obtaining simultaneous isotopic measurements of water vapor in the chamber during cold-temperature cirrus formation experiments.

Moyer, E. J.; Aho, S.; Sarkozy, L.; Saathoff, H.; Möhler, O.; Ebert, V.

2011-12-01

220

Destabilisation of an Arctic ice cap triggered by a hydro-thermodynamic feedback to summer-melt  

NASA Astrophysics Data System (ADS)

Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the Polar Regions. Here we present continuous GPS measurements and satellite synthetic aperture radar based velocity maps from the Austfonna ice cap, Svalbard, that demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of the ice cap's largest drainage basin, Basin-3. The resulting iceberg discharge of 4.2 ± 1.6 Gt a-1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. After accounting for the terminus advance, the related sea-level rise contribution of 7.2 ± 2.6 Gt a-1 matches the recent annual ice-mass loss from the entire Svalbard archipelago. Our study highlights the importance of dynamic glacier wastage and illuminates mechanisms that may trigger a sustained increase in dynamic glacier wastage or the disintegration of ice-sheets in response to climate warming, which is acknowledged but not quantified in global projections of sea-level rise.

Dunse, T.; Schellenberger, T.; Kääb, A.; Hagen, J. O.; Schuler, T. V.; Reijmer, C. H.

2014-05-01

221

The Atlantic Meridional Overturning Circulation Stability Influenced by the Melting of the Greenland Ice Sheet under Various Warming Scenarios  

NASA Astrophysics Data System (ADS)

In this study, we aim to model melting processes of the Greenland ice sheet over the next 1000 years using the Earth system model COSMOS with a dynamic ice sheet module. Of primary interest is the resulting impact on the Atlantic meridional overturning circulation (GMOC/AMOC), which is expected to slow in response to a large freshwater (eg melt water) input. Six warming scenarios will be considered, one set corresponding to the IPCC's RPC Scenario 6, and another set corresponding to RPC Scenario 4.5, each time with 0.5, 1, and 2% increase of greenhouse gas concentration per year. It is expected that the freshwater input will slow down the AMOC overturning; each scenario producing a unique braking signal corresponding to how rapidly the Greenland ice sheet is forced to melt. It will be interesting to see if there is a CO2 threshold level at which the slowdown of the AMOC begins and the melting phenomena becomes unstable and positively reinforces itself or instead, as previous studies have demonstrated with a prescribed amount of melting, if the freshwater input always allows for an eventual recovery of the AMOC to a stable state regardless of the rapidity with which the salinity anomalies develop. The primary difference between this set of experiments and those in previous studies shall be the dynamic nature of the ice sheet model, as we will allow the Greenland ice sheet to melt solely based upon atmospheric conditions rather than prescribing a salinity change directly into the ocean model. It is expected that higher levels of greenhouse gases will result in more rapid melting, which in turn will have a stronger braking affect on the AMOC, possibly with longer recovery times to the starting equilibrium point. It will additionally be of interest to see if it is possible to create a shift in this equilibrium, suggesting that the rapidity with which density anomalies are introduced may create a new stable deep water formation rate. PRELIMINARY RESULTS - AMOC downwelling strength with changes in dynamically modeled Ice Sheet volume. AMOC seems to decrease with varying magnitudes depending upon the rate of carbon dioxide release and the amount of meltwater generated.

Gierz, P.; Lohmann, G.; Wei, W.; Barbi, D.

2012-12-01

222

Transmission and absorption of solar radiation by Arctic sea ice during the melt season  

Microsoft Academic Search

The partitioning of incident solar radiation between sea ice, ocean, and atmosphere strongly affects the Arctic energy balance during summer. In addition to spectral albedo of the ice surface, transmission of solar radiation through the ice is critical for assessing heat and mass balances of sea ice. Observations of spectral irradiance profiles within and transmittance through ice in the Beaufort

Bonnie Light; Thomas C. Grenfell; Donald K. Perovich

2008-01-01

223

Deposition mode ice nucleation reexamined at temperatures below 200 K  

NASA Astrophysics Data System (ADS)

The environmental chamber of a molecular beam apparatus is used to study deposition nucleation of ice on graphite, alcohols and acetic and nitric acids at temperatures between 155 and 200 K. The critical supersaturations necessary to spontaneously nucleate water ice on six different substrate materials are observed to occur at higher supersaturations than are theoretically predicted. This contradictory result motivates more careful examination of the experimental conditions and the underlying basis of the current theories. An analysis based on classical nucleation theory supports the view that at these temperatures nucleation is primarily controlled by the rarification of the vapor and the strength of water's interaction with the substrate surface. The technique enables a careful probing of the underlying processes of ice nucleation and the substrate materials of study. The relevance of the findings to tropospheric temperatures is discussed.

Thomson, E. S.; Kong, X.; Papagiannakopoulos, P.; Pettersson, J. B. C.

2014-09-01

224

Solving the riddle of interglacial temperatures over the last 1.5 million years with a future IPICS "Oldest Ice" ice core  

NASA Astrophysics Data System (ADS)

The sequence of the last 8 glacial cycles is characterized by irregular 100,000 year cycles in temperature and sea level. In contrast, the time period between 1.5-1.2 million years ago is characterized by more regular cycles with an obliquity periodicity of 41,000 years. Based on a deconvolution of deep ocean temperature and ice volume contributions to benthic ?18O (Elderfield et al., Science, 2012), it is suggested that glacial sea level became progressively lower over the last 1.5 Myr, while glacial deep ocean temperatures were very similar. At the same time many interglacials prior to the Mid Brunhes event showed significantly cooler deep ocean temperatures than the Holocene, while at the same time interglacial ice volume remained essentially the same. In contrast, interglacial sea surface temperatures in the tropics changed little (Herbert et al., Science,2010) and proxy reconstructions of atmospheric CO2 using ?11B in planktic foraminifera (Hönisch et al., Science, 2009) suggest that prior to 900,000 yr before present interglacial CO2 levels did not differ substantially from those over the last 450,000 years. Accordingly, the conundrum arises how interglacials can differ in deep ocean temperature without any obvious change in ice volume or greenhouse gas forcing and what caused the change in cyclicity of glacial interglacial cycles over the Mid Pleistocene Transition. Probably the most important contribution to solve this riddle is the recovery of a 1.5 Myr old ice core from Antarctica, which among others would provide an unambiguous, high-resolution record of the greenhouse gas history over this time period. Accordingly, the international ice core community, as represented by the International Partnership for Ice Core Science (IPICS), has identified such an 'Oldest Ice' ice core as one of the most important scientific targets for the future (http://www.pages.unibe.ch/ipics/white-papers). However, finding stratigraphically undisturbed ice, which covers this time period in Antarctica, is not an easy task. Based on a simple ice and heat flow model and glaciological observations (Fischer et al., Climate of the Past, 2013), we conclude that sites in the vicinity of major domes and saddle positions on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, significantly reduced ice thickness is required to avoid bottom melting. The most critical parameter is the largely unknown geothermal heat flux at the bottom of the ice sheet. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 My old ice. If sites with lower geothermal heat flux can be found, also a higher ice thickness is allowed, alleviating the problem of potential flow disturbances in the bottom-most ice to affect a 1.5 Myr climate record.

Fischer, Hubertus

2014-05-01

225

Subglacial drainage of surface melt water affects ice motion: Application of a modeling study to West Greenland  

NASA Astrophysics Data System (ADS)

Subglacial hydrology is one of the main controlling factors in the spatial and temporal evolution of ice flow. The distribution of effective pressure and the form of subglacial drainage networks have important implications on basal sliding. However, subglacial melt water drainage is dynamic in space and time and varies in a complicated manner coupled to surface hydrology. Despite recent conceptual advances, relatively little is known about how the surface hydrology interacts with the subglacial drainage system and how it affects effective pressure and ice flow. Here, we build a 2D numerical model of subglacial drainage to investigate the coupling between drainage of surface melt water and glacier motion. A synthetic glacier geometry is used to obtain the steady-state solutions for effective pressure and subglacial conduit sizes on a rectangular grid. The model has channels and distributed linked cavities that occupy the grid centers and exchange water along the grid edges. The numerical procedure uses Newton's method to compute water pressure and conduit cross-sectional area. The water pressure solution is applied to a sliding law to calculate ice flow speed. We then applied the water model to a 6000 km2 catchment south of Jakobshavn Isbrae along the western margin of Greenland. The water model is forced with surface melt input from the Polar MM5 regional climate model. Surface melt is supplied at discrete locations through supraglacial lakes. The location of supraglacial lakes are identified from satellite imagery. We compare modeled output of ice speed to satellite derived measurements of ice flow and discuss their agreements and discrepancies.

Chu, W.; Creyts, T. T.; Bell, R. E.

2013-12-01

226

The fate of Greenland meltwater: Progress and challenges in understanding the influence of surface melt on ice sheet dynamics and runoff in a highly transient hydrologic system (Invited)  

NASA Astrophysics Data System (ADS)

Melting on polar ice sheets is an important glaciological phenomena. Meltwater runoff directly contributes to ice sheet mass loss and sea level rise; the presence of meltwater changes the physical and biogeochemical nature of the supraglacial, englacial and subglacial environments; and meltwater delivers significant freshwater, chemical and sediment fluxes to the downstream proglacial and marine environments. Furthermore, meltwater has the potential to further influence ice loss through ice dynamic response to melt-induced thinning, and/or by changing the nature of the subglacial hydrologic system. Here we present results from a range of studies across a segment of the west Greenland ice sheet from the ice margin through the wet snow zone highlighting the transient nature of the hydrologic system. We combine satellite, surface and oceanographic observations from the marine ice edge to near the equilibrium line altitude (ELA) to investigate meltwater routing, runoff, and ice dynamic response. At the ice front, we use hydrographic observations to investigate submarine meltwater runoff and interaction with the ice front and fjord. Along the ice margin, large ice-dammed proglacial lakes are observed to form and drain subglacially with increasing frequency (annual to decadal-scale). Further inland, large supraglacial lake drainages provide large pulses of surface melt to the subglacial environment, and create pathways for seasonal melt to access the bed. Across the ablation region we use a network of surface GPS observations to examine the ice surface speed-up in response to diurnal- to seasonal-scale melt variability over multiple summers along a glacial flow line from near the ice margin towards the ELA. Above the ELA, we use ice-core stratigraphy to provide a longer temporal context of past surface melt variability in this region, showing high interannual and decadal melt variability throughout the 20th century. Overall we find that this region is characterized by high spatially and temporally variable melt input to the glacial system. Combined with the inherent difficulty in observing the subglacial and proglacial environments, this presents large challenges towards understanding the overall impact of meltwater on ice sheet processes, and to predicting future behavior of the ice sheet under warming scenarios.

Das, S. B.; Behn, M. D.; Joughin, I. R.; Fahnestock, M. A.; McConnell, J. R.; Stevens, L. A.; Straneo, F.; Plueddemann, A. J.; Singh, H.

2013-12-01

227

Pd-modified Reactive Air Braze for Increased Melting Temperature  

SciTech Connect

Complex high temperature devices such as planar solid oxide fuel cell (pSOFC) stacks often require a two-step sealing process. For example, in pSOFC stacks the oxide ceramic fuel cell plates might be sealed into metallic support frames in one step. Then the frames with the fuel plates sealed to them would be joined together in a separate sealing step to form the fuel cell stack. In this case, the initial seal should have a sufficiently high solidus temperature that it will not begin to remelt at the sealing temperature of the material used for the subsequent sealing step. Previous experience has indicated that, when heated at a rate of 10?C/min, Ag-CuO reactive air braze (RAB) compositions have solidus and liquidus temperatures in the approximate range of 925 to 955?C. Therefore, compositionally modifying the original Ag-CuO braze with Pd-additions such that the solidus temperature of the new braze is between 1025 and 1050?C would provide two RAB compositions with a difference in melting points large enough to allow reactive air brazing of both sets of seals in the fuel cell stack. This study determines the appropriate ratio of Pd to Ag in RAB required to achieve a solidus in the desired range and discusses the wettability of the resulting Pd-Ag-CuO brazes on YSZ substrates. The interfacial microstructures and flexural strengths of Pd-Ag-CuO joints in YSZ will also be presented.

Hardy, John S.; Weil, K. Scott; Kim, Jin Yong Y.; Darsell, Jens T.

2005-03-01

228

Sensitivity of Greenland Ice Sheet surface mass balance to perturbations in sea surface temperature and sea ice cover: a study with the regional climate model MAR  

NASA Astrophysics Data System (ADS)

During recent summers (2007-2012), several surface melt records were broken over the Greenland Ice Sheet (GrIS). The extreme summer melt resulted in part from a persistent negative phase of the North Atlantic Oscillation (NAO), favoring warmer atmospheric conditions than normal over the GrIS. Simultaneously, large anomalies in sea ice cover (SIC) and sea surface temperature (SST) were observed in the North Atlantic, suggesting a possible connection. To assess the direct impact of 2007-2012 SIC and SST anomalies on GrIS surface mass balance (SMB), a set of sensitivity experiments was carried out with the regional climate model MAR forced by ERA-Interim. These simulations suggest that perturbations in SST and SIC in the seas surrounding Greenland do not considerably impact GrIS SMB, as a result of the katabatic wind blocking effect. These offshore-directed winds prevent oceanic near-surface air, influenced by SIC and SST anomalies, from penetrating far inland. Therefore, the ice sheet SMB response is restricted to coastal regions, where katabatic winds cease. A topic for further investigation is how anomalies in SIC and SST might have indirectly affected the surface melt by changing the general circulation in the North Atlantic region, hence favoring more frequent warm air advection towards the GrIS.

Noël, B.; Fettweis, X.; van de Berg, W. J.; van den Broeke, M. R.; Erpicum, M.

2014-10-01

229

Correlation of river water and local sea-ice melting on the Laptev Sea shelf (Siberian Arctic)  

NASA Astrophysics Data System (ADS)

Hydrographic and stable isotope (?18O) data from four summer surveys in the Laptev Sea are used to derive fractions of sea-ice meltwater and river water. Sea-ice meltwater fractions are found to be correlated to river water fractions. While initial heat of river discharge is too small to melt the observed 0-158 km3 of sea-ice meltwater, arctic rivers contain suspended particles and colored dissolved organic material that preferentially absorb solar radiation. Accordingly, heat content in surface waters is correlated to river water fractions. But in years when river water is largely absent within the surface layer, absolute heat content values increase to considerably higher values with extended exposure time to solar radiation and sensible heat. Nevertheless, no net sea-ice melting is observed on the shelf in years when river water is largely absent within the surface layer. The total freshwater volume of the central-eastern Laptev Sea (72-76°N, 122-140°E) varies between ~1000 and 1500 km3 (34.92 reference salinity). It is dominated by varying river water volumes (~1300-1800 km3) reduced by an about constant freshwater deficit (~350-400 km3) related to sea-ice formation. Net sea-ice melt (~109-158 km3) is only present in years with high river water budgets. Intermediate to bottom layer (>25 salinities) contain ~60% and 30% of the river budget in years with low and high river budgets, respectively. The average mean residence time of shelf waters was ~2-3 years during 2007-2009.

Bauch, Dorothea; HöLemann, Jens A.; Nikulina, Anna; Wegner, Carolyn; Janout, Markus A.; Timokhov, Leonid A.; Kassens, Heidemarie

2013-01-01

230

The Holocene thermal maximum in the Nordic Seas: the impact of Greenland Ice Sheet melt and other forcings in a coupled atmosphere-sea-ice-ocean model  

NASA Astrophysics Data System (ADS)

The relatively warm early Holocene climate in the Nordic Seas, known as the Holocene thermal maximum (HTM), is often associated with an orbitally forced summer insolation maximum at 10 ka BP. The spatial and temporal response recorded in proxy data in the North Atlantic and the Nordic Seas reveals a complex interaction of mechanisms active in the HTM. Previous studies have investigated the impact of the Laurentide Ice Sheet (LIS), as a remnant from the previous glacial period, altering climate conditions with a continuous supply of melt water to the Labrador Sea and adjacent seas and with a downwind cooling effect from the remnant LIS. In our present work we extend this approach by investigating the impact of the Greenland Ice Sheet (GIS) on the early Holocene climate and the HTM. Reconstructions suggest melt rates of 13 mSv for 9 ka BP, which result in our model in an ocean surface cooling of up to 2 K near Greenland. Reconstructed summer SST gradients agree best with our simulation including GIS melt, confirming that the impact of the early Holocene GIS is crucial for understanding the HTM characteristics in the Nordic Seas area. This implies that modern and near-future GIS melt can be expected to play an active role in the climate system in the centuries to come.

Blaschek, M.; Renssen, H.

2013-07-01

231

A comparison of surface renewal theory with the observed roughness length for temperature on a melting glacier surface  

NASA Astrophysics Data System (ADS)

The roughness lengths for momentum and temperature are calculated using the profile method on amelting glacier surface. Data from a 5-level 9-m meteorological mastpositioned near the edge of Breidamerkurjökull, an outlet glacier of the Vatnajökull ice cap Iceland, are used for the calculations. The data are selected to avoid the presence of the katabatic wind speedmaximum which would otherwise alter the scaling laws of the surface layer. The surface roughness length for momentum is determined to be 1.0 mm, similar to other estimates made on flat melting ice surfaces. The surface roughness length for temperature is found to be in good agreement with previously proposed surface renewal theories for the observed roughness Reynolds number range of 30 * 70.

Denby, Bruce; Snellen, Henk

232

Temperatures at the base of the Laurentide Ice Sheet inferred from borehole temperature data  

Microsoft Academic Search

We use temperature profiles from 4 deep (>1600 m) boreholes across Canada to determine ground surface temperature histories (GSTH's) through and after the Last Glacial Maximum (LGM). Inversion yields the temperature history at the base of the glacier and the surface temperature evolution after the glacial retreat. The results indicate geographic differences in basal temperature history across the Ice Sheet.

Frédérique Rolandone; Jean-Claude Mareschal; Claude Jaupart

2003-01-01

233

Sea Ice Brightness Temperature as a Function of Ice Thickness, Part II: Computed curves for thermodynamically modelled ice profiles  

E-print Network

Ice thickness is an important variable for climate scientists and is still an unsolved problem for satellite remote sensing specialists. There has been some success detecting the thickness of thin ice from microwave radiometers, and with this in mind this study attempts to model the thickness-radiance relation of sea ice at frequencies employed by the Soil Moisture and Ocean Salinity (SMOS) radiometer and the Advanced Microwave Scanning Radiometer (AMSR): between 1.4 and 89 GHz. In the first part of the study, the salinity of the ice was determined by a pair of empirical relationships, while the temperature was determined by a thermodynamic model. Because the thermodynamic model can be used as a simple ice growth model, in this, second part, the salinities are determined by the growth model. Because the model uses two, constant-weather scenarios representing two extremes ("fall freeze-up" and "winter cold snap"), brine expulsion is modelled with a single correction-step founded on mass conservation. The growt...

Mills, Peter

2012-01-01

234

Antarctic Glaciological Data at NSIDC: field data, temperature, and ice velocity  

NASA Astrophysics Data System (ADS)

An extensive collection of many Antarctic glaciological parameters is available for the polar science community upon request. The National Science Foundation's Office of Polar Programs funds the Antarctic Glaciological Data Center (AGDC) at the National Snow and Ice Data Center (NSIDC) to archive and distribute Antarctic glaciological and cryospheric system data collected by the U.S. Antarctic Program. AGDC facilitates data exchange among Principal Investigators, preserves recently collected data useful to future research, gathers data sets from past research, and compiles continent-wide information useful for modeling and field work planning. Data sets are available via our web site, http://nsidc.org/agdc/. From here, users can access extensive documentation, citation information, locator maps, derived images and references, and the numerical data. More than 50 Antarctic scientists have contributed data to the archive. Among the compiled products distributed by AGDC are VELMAP and THERMAP. THERMAP is a compilation of over 600 shallow firn temperature measurements ('10-meter temperatures') collected since 1950. These data provide a record of mean annual temperature, and potentially hold a record of climate change on the continent. The data are represented with maps showing the traverse route, and include data sources, measurement technique, and additional measurements made at each site, i.e., snow density and accumulation. VELMAP is an archive of surface ice velocity measurements for the Antarctic Ice Sheet. The primary objective of VELMAP is to assemble a historic record of outlet glaciers and ice shelf ice motion over the Antarctic. The collection includes both PI-contributed measurements and data generated at NSIDC using Landsat and SPOT satellite imagery. Tabular data contain position, speed, bearing, and data quality information, and related references. Two new VELMAP data sets are highlighted: the Mertz Glacier and the Institute Ice Stream. Mertz Glacier ice velocity provides an upper limit for change in velocity for this glacier over the past decade. Two pairs of Landsat images were used to compare velocities from 2000-2001 to 1989-2000. No significant change in velocity is observed. A new ice discharge flux of 17.8 km3a-1 was determined, and basal melting at the grounding line was re-calculated at 11 m per year (Berthier et al., 2003, in press). Velocity data for the Institute Ice Stream was compiled at NSIDC using a Landsat images from 1986, 1989, and 1997. The data were recently used in a study outlining the velocity, mass balance, and morphology of the Institute ice stream and nearby Ronne ice shelf area. (Scambos et al., 2003, in review). The study indicates the Institute has regions with flow and morphology characteristics similar to the Ross Embayment ice streams. Ice velocity research contributes to understanding the mass balance and overall stability of the Antarctic Ice Sheet. The archiving of velocity data has proven to be a useful tool to the Antarctic science community, and VELMAP continues to grow as a valuable resource through PI contributions. If you have velocity data that you would like to contribute to the VELMAP archive please contact agdc@nsidc.org. The velocity data used in the two studies presented here can be accessed on the VELMAP web site at http://nsidc.org/data/velmap.

Bauer, R.; Bohlander, J.; Scambos, T.; Berthier, E.; Raup, B.; Scharfen, G.

2003-12-01

235

Hot Ice  

Microsoft Academic Search

THE announcement made some time since by Dr. Carnelley that ice in vacuo could be raised to a temperature far above its ordinary melting-point, seemed so thoroughly in opposition to the experience derived from the great work of Regnault on the tensions of vapours; and as it called for a complete change of ideas in a field in which I

J. B. Hannay

1881-01-01

236

Snow and Ice Melt Flow Features on Devon Island, Nunavut, Arctic Canada as Possible Analogs for Recent Slope Flow Features on Mars  

NASA Astrophysics Data System (ADS)

Based on morphologic and contextual analogs from Devon Island, Arctic Canada, the recent martian slope flow features reported by Malin and Edgett are reinterpreted as being due not necessarily to groundwater seepage but possibly to snow or ice melt.

Lee, P.; Cockell, C. S.; Marinova, M. M.; McKay, C. P.; Rice, J. W., Jr.

2001-03-01

237

Structure and dynamics of magnesium in silicate melts: A high-temperature 25Mg NMR study  

Microsoft Academic Search

Mg NMR spectra for several silicate and aluminosilicate melts were obtained from 1000-1470 8C. The peaks are initially very broad, but narrow with increasing temperature to near 500 Hz at the highest temperatures. The peak positions for most of the melts do not shift noticeably with temperature in the range studied, except for a sodium magnesium silicate composition that was

ANNA M. GEORGE; JONATHAN F. STEBBINS

238

Radiance temperature (at 653 nm) of tungsten at its melting point  

Microsoft Academic Search

The radiance temperature (at 653 nm) of tungsten at its melting point was measured using a subsecond-duration pulse-heating technique. Specimens in the form of strips with initially different surface roughnesses were used. The results do not indicate any dependence of radiance temperature (at the melting point) on initial surface or system operational conditions. The average radiance temperature (at 653 nm)

A. Cezairliyan; A. P. Miiller

1982-01-01

239

Structure and dynamics of Oxide Melts and Glasses : a view from multinuclear and high temperature NMR  

E-print Network

1 Structure and dynamics of Oxide Melts and Glasses : a view from multinuclear and high temperature evidencing µ3 oxygen bridges in aluminate glasses and rediscussion of the structure of high temperature melts temperature molten state in the case of oxide glass forming systems, the mobility is such that only

240

Sea Ice and Ice Temperature Variability as Observed by Microwave and Infrared Satellite Data  

NASA Technical Reports Server (NTRS)

Recent reports of a retreating and thinning sea ice cover in the Arctic have pointed to a strong suggestion of significant warming in the polar regions. It is especially important to understand what these reports mean in light of the observed global warning and because the polar regions are expected to be most sensitive to changes in climate. To gain insight into this phenomenon, co-registered ice concentrations and surface temperatures derived from two decades of satellite microwave and infrared data have been processed and analyzed. While observations from meteorological stations indicate consistent surface warming in both regions during the last fifty years, the last 20 years of the same data set show warming in the Arctic but a slight cooling in the Antarctic. These results are consistent with the retreat in the Arctic ice cover and the advance in the Antarctic ice cover as revealed by historical satellite passive microwave data. Surface temperatures derived from satellite infrared data are shown to be consistent within 3 K with surface temperature data from the limited number of stations. While not as accurate, the former provides spatially detailed changes over the twenty year period. In the Arctic, for example, much of the warming occurred in the Beaufort Sea and the North American region in 1998 while slight cooling actually happened in parts of the Laptev Sea and Northern Siberia during the same time period. Big warming anomalies are also observed during the last five years but a periodic cycle of about ten years is apparent suggesting a possible influence of the North Atlantic Oscillation. In the Antarctic, large interannual and seasonal changes are also observed in the circumpolar ice cover with regional changes showing good coherence with surface temperature anomalies. However, a mode 3 is observed to be more dominant than the mode 2 wave reported in the literature. Some of these spatial and temporal changes appear to be influenced by the Antarctic Circumpolar Wave (ACW) and changes in coastal polynya activities.

Comiso, Josefino C.; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

241

Vibration for controlling of temperature and dopant distributions in melt  

NASA Astrophysics Data System (ADS)

Numerical investigations of the influence of controlled vibrations on mixing, heat and mass transfer are presented. Crystal growth applications for ground-based and microgravity conditions were considered. Mathematical simulation is performed on the solutions of basis unsteady Navier-Stokes equations for incompressible fluid flows. The finite element code ASTRA is used for modeling. The researches of influence of vibrations were carried out for vibrations with small amplitude and frequency up to 100 Hertz The results of parametric calculations for various values of similarity numbers of Prandtl, Reynolds, Grashof and Marangoni are presented including the case of microgravity conditions. The influence of major factors such as thermo-gravitational and thermo-capillary conditions, vibration, rotation on the heat/mass transfer and melt flow was investigated. The averaged vibrational flow (AVF) was investigated by averaging the instant velocity fields found in direct numerical integration of the Navier-Stokes problem. The results illustrate the influence of the form and arrangement of vibrator and the crucible as well as the vibration amplitude-frequency on the hydrodynamics, temperature and mass distributions. The influence of vibrational Reynolds number (amplitude and frequency of vibrations) on AVF was investigated. Numerical results show possibility of controlling of the direction of AVF by variation of vibrational Reynolds number. Numerical results are shown that the vibrations can be used to controlling by the thicknesses of dynamic, thermal and concentration boundary layers, the kinetics of crystal growth and the dopant distribution in crystal. The vibrations can change the history of characteristics of convection in the melt and the dopant segregation at the solid-liquid interface. Influence of the vibration on the shape of melt-crystal interface is also investigated. Possibilities of changing of the curvature of the solid-liquid interface by variation of frequency - amplitude parameters (vibrational Reynolds number) for making more flat shape of interface are shown. The investigations showed that the vibrations can be used as a simple applied and effective tool for controlling of the hydrodynamics, heat and mass transfer, dopant distribution and crystal growth kinetics which to improve the conditions of crystal growth.

Fedyushkin, A. I.; Bourago, N. G.

242

Greenland Ice Sheet's response to global warming (Invited)  

Microsoft Academic Search

Air temperatures along the west coast on the Greenland ice sheet have increased by 2 deg. C per decade since 1991, with largest warming during the winter months. The ice sheet melt area increased by 20% since 1979, and the increase in bare ice area is unmistakable at 13% per year. Warm summers and extended melt seasons are to blame

K. Steffen

2009-01-01

243

Invention of Ozone Inclusion Ice Using Low-Temperature Plasma  

NASA Astrophysics Data System (ADS)

Research on invention of the function ice is actively advanced in the field of perishable foodstuff saving, deodorization, sterilization and cleaning in addition to levelization of electric power in summer. When oxygen low-temperature plasma is generated in a decompressed furnace, a high-dense ozone gas is secondarily formed in the furnace. By utilizing the instant freezing of liquid introduced in the furnace, the purpose of this study is to efficiently store the ozone gas in the ice. The ozone content in the ice was evaluated for each liquid introduction method of a water spray system, a water droplet adsorption system and a gas involvement system on the surface of the water vessel in the furnace.

Nakagawasai, Manabu; Inada, Shigeaki; Ueno, Yusuke; Kawashima, Hisanobu

244

Coexisting methane and oxygen excesses in nitrate-limited polar water (Fram Strait) during ongoing sea ice melting  

NASA Astrophysics Data System (ADS)

Summer sea ice cover in the Arctic Ocean has undergone a reduction in the last decade exposing the sea surface to unforeseen environmental changes. Melting sea ice increases water stratification and induces nutrient limitation, which is also known to play a crucial role in methane formation in oxygenated surface water. We report on a hotspot of methane formation in the marginal ice zone in the western Fram Strait. Our study is based on measurements of oxygen, methane, DMSP, nitrate and phosphate concentrations as well as on phytoplankton composition and light transmission, conducted along the 79° N oceanographic transect. We show that between the eastern Fram Strait, where Atlantic water enters from the south and the western Fram Strait, where Polar water enters from the north, different nutrient limitation occurs and consequently different bloom conditions were established. Ongoing sea ice melting enhances the environmental differences and initiates regenerated production in the western Fram Strait. In a unique biogeochemical feedback process, methane production occurs despite an oxygen excess. We postulate that DMSP (dimethylsulfoniopropionate) released from sea ice may serve as a precursor for methane formation. Thus, feedback effects on cycling pathways of methane are likely, with DMSP catabolism in high latitudes possibly contributing to a warming effect on the earth's climate. This process could constitute an additional component in biogeochemical cycling in a seasonal ice-free Arctic Ocean. The metabolic activity (respiration) of unicellular organisms explains the presence of anaerobic conditions in the cellular environment. Therefore we present a theoretical model which explains the maintenance of anaerobic conditions for methane formation inside bacterial cells, despite enhanced oxygen concentrations in the environment.

Damm, E.; Thoms, S.; Kattner, G.; Beszczynska-Möller, A.; Nöthig, E. M.; Stimac, I.

2011-05-01

245

Did Greenland Ice Sheet melting weaken the AMOC during the early part of the last interglacial? A model analysis of the uncertainties.  

NASA Astrophysics Data System (ADS)

Proxy data suggests that during the early part of the last interglacial, the climate was characterized by a warmer than modern-day climate and a shrinking Greenland Ice Sheet. This may resemble future conditions under the influence of anthropogenic forcings. In addition, for the first several thousand years of the last interglacial period, a weakened overturning circulation has been reconstructed. However, it has not yet been established if there is a causal relationship between the partial melting of the Greenland Ice Sheet and the millennial-scale weakening of the overturning circulation. This intriguing palaeoclimatic setting provides us with the opportunity to investigate with a climate model whether Greenland Ice Sheet melting was the most likely cause of the weakening of the overturning. Concurrently, we can investigate if climate models are capable of realistically simulating the sensitivity of the overturning circulation to Greenland Ice Sheet melting. We performed transient climate simulations for the early last interglacial with the LOVECLIM global climate model of intermediate complexity (Goosse et al., 2010), to investigate if Greenland Ice Sheet melting could have caused the overturning circulation to be substantially weakened for several thousand years. The impact of the uncertainties in the reconstructed volume changes of the Greenland Ice Sheet and the associated melt rates where discussed already in Bakker et al. (2012). In this study we focussed on the importance of the many other uncertainties surrounding this topic: the age constraints, the impact of the preceding deglaciation, high frequency variability in the melt rates, geographical distribution of the melt water into the surrounding oceans and lastly the importance of the model-dependent sensitivity of the overturning circulation to a perturbation of the freshwater budget. Based on our findings we constructed a specific Greenland Ice Sheet melt scenario and show that, within the full uncertainty range, it is physically possible that last interglacial Greenland Ice Sheet melting kept the overturning weakened for 3 to 4 thousand years. However, this scenario is at the very extreme end of the uncertainty envelope. As proxy-based reconstructions are not yet conclusive, this result leads us to propose two different interpretations: If indeed Greenland Ice Sheet melting weakened the overturning, our findings imply that the overturning in most climate models is too stable. The other interpretation however is, that it is not very likely that melting of the Greenland Ice Sheet was the sole reason for the weakened overturning during the early LIG.

Bakker, P.; Renssen, H.; Van Meerbeeck, C. J.

2012-04-01

246

Sea-ice melt CO2-carbonate chemistry in the western Arctic Ocean: meltwater contributions to air-sea CO2 gas exchange, mixed layer properties and rates of net community production under sea ice  

NASA Astrophysics Data System (ADS)

The carbon dioxide (CO2)-carbonate chemistry of sea-ice melt and co-located, contemporaneous seawater has rarely been studied in sea ice covered oceans. Here, we describe the CO2-carbonate chemistry of sea-ice melt (both above sea ice as "melt ponds" and below sea ice as "interface waters") and mixed layer properties in the western Arctic Ocean in the early summer of 2010 and 2011. At nineteen stations, the salinity (~ 0.5 to < 6.5), dissolved inorganic carbon (DIC; ~ 20 to < 550 ?mol kg-1) and total alkalinity (TA; ~ 30 to < 500 ?mol kg-1) of above-ice melt pond water was low compared to water in the underlying mixed layer. The partial pressure of CO2 (pCO2) in these melt ponds was highly variable (~ < 10 to > 1500 ?atm) with the majority of melt ponds acting as potentially strong sources of CO2 to the atmosphere. The pH of melt pond waters was also highly variable ranging from mildly acidic (6.1 to 7) to slightly more alkaline than underlying seawater (8 to 10.7). All of observed melt ponds had very low (< 0.1) saturation states (?) for calcium carbonate (CaCO3) minerals such as aragonite (?aragonite). Our data suggests that sea ice generated "alkaline" or "acidic" melt pond water. This melt-water chemistry dictates whether the ponds are sources of CO2 to the atmosphere or CO2 sinks. Below-ice interface water CO2-carbonate chemistry data also indicated substantial generation of alkalinity, presumably owing to dissolution of calcium CaCO3 in sea ice. The interface waters generally had lower pCO2 and higher pH/?aragonite than the co-located mixed layer beneath. Sea-ice melt thus contributed to the suppression of mixed layer pCO2 enhancing the surface ocean's capacity to uptake CO2 from the atmosphere. Meltwater contributions to changes in mixed-layer DIC were also used to estimate net community production rates (mean of 46.9 ±29.8 g C m-2 for the early-season period) under sea-ice cover. Although sea-ice melt is a transient seasonal feature, above-ice melt pond coverage can be substantial (10 to > 50%) and under-ice interface melt water is ubiquitous during this spring/summer sea-ice retreat. Our observations contribute to growing evidence that sea-ice CO2-carbonate chemistry is highly variable and its contribution to the complex factors that influence the balance of CO2 sinks and sources (and thereby ocean acidification) is difficult to predict in an era of rapid warming and sea ice loss in the Arctic Ocean.

Bates, N. R.; Garley, R.; Frey, K. E.; Shake, K. L.; Mathis, J. T.

2014-01-01

247

Study of inter-annual variations in surface melting over Amery Ice Shelf, East Antarctica, using space-borne scatterometer data  

Microsoft Academic Search

The widespread retreat of glaciers can be considered as a response to the climate change. Being the largest retreating glacier-ice shelf system in East Antarctica, the Amery Ice Shelf-Lambert Glacier system plays an important role in contributing to sea level rise as well as the surrounding environment and climate. The present study is focused on the investigation of surface melting

S. R. Oza; R. K. K. Singh; N. K. Vyas; Abhijit Sarkar

2011-01-01

248

Analysis of surface melting and snow accumulation over the Greenland ice sheet from spaceborne microwave sensors  

Microsoft Academic Search

Continuous monitoring of changes in the Greenland ice sheet from both space and air borne sensors has been conducted since the early 1970's. Since the mid-1990's dramatic changes occurring on the Greenland ice sheet have been observed both from space borne sensors and field work. These changes, primarily mass loss from the ice sheet, are related to the observed trend

Indrajit Bhattacharya

2010-01-01

249

Bubble nucleation in rhyolite and dacite melts: temperature dependence of surface tension  

Microsoft Academic Search

Surface tension (?) profoundly influences the ability of gas bubbles to nucleate in silicate melts. To determine how temperature impacts ?, experiments were carried out in which high-silica rhyolite melts with 5 wt% dissolved water were decompressed at temperatures\\u000a that ranged from 775 to 1,085°C. Decompressions were also carried out using dacite melts with 4.3 wt% dissolved water at 1,150°C.\\u000a Water bubbles

James E. GardnerRichard; Richard A. Ketcham

250

Temperature control of glass melting furnace with fuzzy logic and conventional PI control  

Microsoft Academic Search

This paper presents a practical application of fuzzy logic control of the temperature of glass-melting furnace. Because of the complexity and nonlinearity, temperature control of glass-melting furnace is still delegated to human operator. Though the overall characteristics of glass-melting furnace are complex and nonlinear, one portion of the furnace characteristics can be modeled as a linear system. The linear portion

Un-Chul Moon; Kwang Y. Lee

2000-01-01

251

A survey and new measurements of ice vapor pressure at temperatures between 170 and 250K  

Microsoft Academic Search

Saturated vapor pressures of ice at temperatures below 200K have become more important since the discovery of ice clouds in the polar stratosphere and upper mesosphere. Direct measurements of ice vapor pressures at such low temperatures are sparse and unreliable. This paper summarizes published vapor pressure data and presents new measurements at temperatures between 170 and 250K, extending the range

James Marti; Konrad Mauersberger

1993-01-01

252

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

The impact of a reduced Greenland ice sheet (GrIS) on Greenland's surface climate during the Eemian interglacial is investigated employing the CCSM4 climate model. We find a distinct impact of changes in the GrIS topography on Greenland's surface air temperatures (SAT) even when correcting for changes in surface elevation which influences SAT through the lapse rate effect. The resulting lapse rate corrected SAT anomalies are driven by changes in the surface energy balance. In winter, the variable reacting strongest to changes in the topography is the sensible heat flux (SHFLX). The reason is its dependence on surface winds, which themselves are controlled to a large extent by the shape of the GrIS. Hence, regions where a receding GrIS causes higher surface wind velocities also experience anomalous warming through increased SHFLX. Vice-versa, regions that become flat and ice-free are characterized by low wind speeds, low SHFLX and anomalous cold winter temperatures. In summer, we find surface warming induced by a decrease in surface albedo in deglaciated areas and regions which experience surface melting. The results have implications for the interpretation of Eemian temperature reconstructions based on Greenland proxy archives such as the NEEM ice core. Changing the GrIS topography acts as a local forcing for Greenland's climate, whereas the effect on the climate outside of Greenland is small and mostly negligible. For the NEEM ice core site, our model suggests that up to 3.2 °C of the annual mean Eemian warming can be attributed to these topography-related processes and hence is not linked to large-scale climate variations.

Merz, Niklaus; Born, Andreas; Raible, Christoph; Fischer, Hubertus; Stocker, Thomas

2014-05-01

253

Temperature-resolved SAXS studies of morphological changes in melt-crystallized poly(hexamethylene terephthalate) and its melting upon heating  

Microsoft Academic Search

Temperature-resolved small-angle X-ray scattering (SAXS) on poly(hexamethylene terephthalate) (PHT) samples crystallized from the melt yields direct information about the morphological changes in lamellar crystals and interlamellar amorphous layers upon melt-crystallization and subsequent heating to melting. Absolute intensities of these SAXS patterns were further analyzed via one-dimensional correlation and interface distribution functions. These analyses indicate that melt-crystallization at low temperature produces

Ya-Sen Sun

2006-01-01

254

Regional albedo of Arctic first-year drift ice in advanced stages of melt from the combination of in situ measurements and aerial imagery  

NASA Astrophysics Data System (ADS)

The paper presents a case study of the regional (? 150 km) broadband albedo of first year Arctic sea ice in advanced stages of melt, estimated from a combination of in situ albedo measurements and aerial imagery. The data were collected during the eight day ICE12 drift experiment carried out by the Norwegian Polar Institute in the Arctic north of Svalbard at 82.3° N from 26 July to 3 August 2012. The study uses in situ albedo measurements representative of the four main surface types: bare ice, dark melt ponds, bright melt ponds and open water. Images acquired by a helicopter borne camera system during ice survey flights covered about 28 km2. A subset of > 8000 images from the area of homogeneous melt with open water fraction of ? 0.11 and melt pond coverage of ? 0.25 used in the upscaling yielded a regional albedo estimate of 0.40 (0.38; 0.42). The 95% confidence interval on the estimate was derived using the moving block bootstrap approach applied to sequences of classified sea ice images and albedo of the four surface types treated as random variables. Uncertainty in the mean estimates of surface type albedo from in situ measurements contributed some 95% of the variance of the estimated regional albedo, with the remaining variance resulting from the spatial inhomogeneity of sea ice cover. The results of the study are of relevance for the modeling of sea ice processes in climate simulations. It particularly concerns the period of summer melt, when the optical properties of sea ice undergo substantial changes, which existing sea ice models have significant diffuculty accurately reproducing.

Divine, D. V.; Granskog, M. A.; Hudson, S. R.; Pedersen, C. A.; Karlsen, T. I.; Divina, S. A.; Gerland, S.

2014-07-01

255

Preparation of low melting temperature glass–ceramics from municipal waste incineration fly ash  

Microsoft Academic Search

Glass–ceramics have been prepared from air pollution control residues (fly ash) of a municipal solid waste incineration (MSWI) plant in southern China. The use of additives was investigated in order to decrease the melting temperature of the waste and thus to reduce the costs of production of glass–ceramics from the vitrified waste. Results showed that the melting temperature can be

Jiakuan Yang; Bo Xiao; Aldo R. Boccaccini

2009-01-01

256

Transport properties of low-sanidine single-crystals, glasses and melts at high temperature  

E-print Network

1 Transport properties of low-sanidine single-crystals, glasses and melts at high temperature Maik = 8221 + 9 figures + 5 tables Keywords: laser-flash analysis, high-temperature, thermal diffusivity, viscosity, density, IR spectroscopy, low-sanidine, single-crystal, glass, melt #12;2 Abstract. Thermal

Spera, Frank J.

257

Impact of aerosol intrusions on sea-ice melting rates and the structure Arctic boundary layer clouds  

NASA Astrophysics Data System (ADS)

The Los Alamos National Laboratory sea-ice model (LANL CICE) was implemented into the real-time and research versions of the Colorado State University-Regional Atmospheric Modeling System (RAMS@CSU). The original version of CICE was modified in its structure to allow module communication in an interactive multigrid framework. In addition, some improvements have been made in the routines involved in the coupling, among them, the inclusion of iterative methods that consider variable roughness lengths for snow-covered ice thickness categories. This version of the model also includes more complex microphysics that considers the nucleation of cloud droplets, allowing the prediction of mixing ratios and number concentrations for all condensed water species. The real-time version of RAMS@CSU automatically processes the NASA Team SSMI F13 25km sea-ice coverage data; the data are objectively analyzed and mapped to the model grid configuration. We performed two types of cloud resolving simulations to assess the impact of the entrainment of aerosols from above the inversion on Arctic boundary layer clouds. The first series of numerical experiments corresponds to a case observed on May 4 1998 during the FIRE-ACE/SHEBA field experiment. Results indicate a significant impact on the microstructure of the simulated clouds. When assuming polluted initial profiles above the inversion, the liquid water fraction of the cloud monotonically decreases, the total condensate paths increases and downward IR tends to increase due to a significant increase in the ice water path. The second set of cloud resolving simulations focused on the evaluation of the potential effect of aerosol concentration above the inversion on melting rates during spring-summer period. For these multi-month simulations, the IFN and CCN profiles were also initialized assuming the 4 May profiles as benchmarks. Results suggest that increasing the aerosol concentrations above the boundary layer increases sea-ice melting rates when mixed phase clouds are present.

Cotton, W.; Carrio, G.; Jiang, H.

2003-04-01

258

Future increase of west African monsoon due to sea ice melt  

NASA Astrophysics Data System (ADS)

The decadal variability of African monsoon rainfall from the millennium simulations of a global coupled climate model is analyzed to understand the variability of rainfall in future. We find that the African summer monsoon rainfall increases in future until 2100 compared to the past variability and shows a slight decrease afterwards in the twenty second century. Unlike Indian monsoon or East Asian monsoon, the African monsoon is more confined towards the equator and might depend largely on inter-hemispheric temperature contrast. The shape of the African land adds further to this dependence. We find that in the future global warming scenario, there will be a change in the surface albedo in the northern hemisphere due to changes in sea ice cover. This changes the temperature distribution between northern and southern hemisphere that will affect equatorial monsoonal circulation. For regions like India and east Asia which lie several degrees away from the equator, other external factors like El-Nino, Eurasian snow cover etc plays an important role. But as far as the equatorial monsoon is considered, the inter-hemispheric temperature contrast seems to play the most important role on longer timescales.

Menon, A.; Levermann, A.; Schewe, J.

2012-04-01

259

Temperature regulation in emperor penguins foraging under sea ice  

Microsoft Academic Search

Inferior vena caval (IVC) and anterior abdominal (AA) temperatures were recorded in seven emperor penguins (Aptenodytes forsteri) foraging under sea ice in order to evaluate the hypothesis that hypothermia-induced metabolic suppression might extend aerobic diving time. Diving durations ranged from 1 to 12.5 min, with 39% of dives greater than the measured aerobic dive limit of 5.6 min. Anterior abdominal

P. J Ponganis; R. P Van Dam; T Knower; D. H Levenson

2001-01-01

260

Validation of AVHRR and MODIS ice surface temperature products using in situ radiometers  

Microsoft Academic Search

Ship-borne and airborne infrared radiometric measurements during the ARISE cruise of September-October 2003 permitted in situ validation studies of two satellite-based ice surface skin temperature algorithms: the AVHRR Polar Pathfinder Ice Surface Temperature and the MODIS Sea Ice Surface Temperature. Observations of sea ice from the Aurora Australis ship's rail using a KT-19.82 radiometer were conducted between 25 September and

Ted A. Scambos; Terry M. Haran; Robert Massom

2006-01-01

261

Melting and casting processes for high-temperature intermetallics  

SciTech Connect

Most of the metallic systems thus far identified as promising from the commercial viewpoint are composed of elements which are either susceptible to oxidation, such as Al, or highly reactive, such as Ti; these characteristics entail the use of such melting and casting techniques as vacuum-induction melting, vacuum-arc remelting, electroslag refining, plasma-arc melting, spray casting, and directional solidification. Spray casting is noteworthy both in its ability to produce near-net-shape components and its inherent reduction of the oxygen and hydrogen pickup which has been associated with the embrittlement of aluminides. 24 refs.

Sen, Subhayu; Stefanescu, D.M. (Alabama, University, Tuscaloosa (USA))

1991-05-01

262

Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century  

E-print Network

Global analyses of sea surface temperature, sea ice, and night marine air temperature since and sea surface temperature (SST) data set, HadISST1, and the nighttime marine air temperature (NMAT) data set, HadMAT1. HadISST1 replaces the global sea ice and sea surface temperature (GISST) data sets

263

Temperature profile for glacial ice at the South Pole: Implications for life in a nearby subglacial lake  

PubMed Central

Airborne radar has detected ?100 lakes under the Antarctic ice cap, the largest of which is Lake Vostok. International planning is underway to search in Lake Vostok for microbial life that may have evolved in isolation from surface life for millions of years. It is thought, however, that the lakes may be hydraulically interconnected. If so, unsterile drilling would contaminate not just one but many of them. Here we report measurements of temperature vs. depth down to 2,345 m in ice at the South Pole, within 10 km from a subglacial lake seen by airborne radar profiling. We infer a temperature at the 2,810-m deep base of the South Pole ice and at the lake of ?9°C, which is 7°C below the pressure-induced melting temperature of freshwater ice. To produce the strong radar signal, the frozen lake must consist of a mix of sediment and ice in a flat bed, formed before permanent Antarctic glaciation. It may, like Siberian and Antarctic permafrost, be rich in microbial life. Because of its hydraulic isolation, proximity to South Pole Station infrastructure, and analog to a Martian polar cap, it is an ideal place to test a sterile drill before risking contamination of Lake Vostok. From the semiempirical expression for strain rate vs. shear stress, we estimate shear vs. depth and show that the IceCube neutrino observatory will be able to map the three-dimensional ice-flow field within a larger volume (0.5 km3) and at lower temperatures (?20°C to ?35°C) than has heretofore been possible. PMID:12060731

Price, P. Buford; Nagornov, Oleg V.; Bay, Ryan; Chirkin, Dmitry; He, Yudong; Miocinovic, Predrag; Richards, Austin; Woschnagg, Kurt; Koci, Bruce; Zagorodnov, Victor

2002-01-01

264

In situ observation of partial melting in superplastic aluminum alloy composites at high temperature  

SciTech Connect

The possibility of partial melting and its relations to the superplasticity at high strain rates were studied with transmission electron microscopy and differential scanning calorimetry in Al-Cu-Mg(2124), Al-Mg (5052), and Al-Mg-Si (6061) alloys reinforced with Si[sub 3]N[sub 4] particles. Calorimetry measurements of all three composites showed a sharp endothermic peak at an optimum superplastic temperature. At the same temperature, transmission electron microscopy showed the melting of grain boundaries and interfaces, suggesting direct correlations between partial melting and the superplasticity. Solute segregation was also observed at boundaries and interfaces, and was discussed as causes for partial melting.

Koike, J. (Oregon State Univ., Corvallis, OR (United States). Dept. of Mechanical Engineering); Mabuchi, M. (Government Industrial Research Inst., Nagoya (Japan)); Higashi, K. (Univ. of Osaka Prefecture (Japan). Dept. of Mechanical Systems Engineering)

1995-01-01

265

Alternative ice shelf equilibria determined by ocean environment  

NASA Astrophysics Data System (ADS)

and thermodynamic regimes of ice shelves experiencing weak (?1 m year-1) to strong (~10 m year-1) basal melting in cold (bottom temperature close to the in situ freezing point) and warm oceans (bottom temperature more than half of a degree warmer than the in situ freezing point) are investigated using a 1-D coupled ice/ocean model complemented with a newly derived analytic expression for the steady state temperature distribution in ice shelves. This expression suggests the existence of a basal thermal boundary layer with thickness inversely proportional to the basal melt rate. Model simulations show that ice shelves afloat in warm ocean waters have significantly colder internal ice temperatures than those that float in cold waters. Our results indicate that in steady states, the mass balance of ice shelves experiencing strong and weak melting is controlled by different processes: in ice shelves with strong melting, it is a balance between ice advection and basal melting, and in ice shelves with weak melting, it is a balance between ice advection and deformation. Sensitivity simulations show that ice shelves in cold and warm oceans respond differently to increase of the ocean heat content. Ice shelves in cold waters are more sensitive to warming of the ocean bottom waters, while ice shelves in warm waters are more sensitive to shallowing of the depth of the thermocline.

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

2013-06-01

266

Sudden sea-level change from melting Antarctic ice: How likely?  

SciTech Connect

There has been concern that the West Antarctic marine ice sheet could collapse catastrophically, leading to a 5-meter rise in sea level in a single century. However, that idea was based on a modeled instability at the grounding line that reflected a discontinuity between the mathematical models used for the grounded and floating parts of the ice sheet, respectively. Improved knowledge about ice streams, the active portions of the marine ice sheet, reveals that in the Ross Sea sector, at least, there is in reality a broad, gradual transition zone, rather than a discontinuity, between the inland ice and the ice shelf. Consequently, there probably is no instability; total disappearance of the ice sheet would take a millenium or more. The resulting average contribution to sea-level rise thus would be only a few millimeters per year, comparable to the present rate of rise (from all sources). Furthermore, dynamic response to present-day climate change would not even begin in less than a century. It is still uncertain whether the Antarctic ice sheet is making a positive or negative contribution to sea-level rise now. Whichever the case, however, during the next century or two the effect of climatic warming almost surely will be to increase the mass input to the ice sheet, thus yielding a negative contribution to sea-level rise of the order of a millimeter per year.

Bentley, C.R. [Univ. of Wisconsin, Madison, WI (United States)

1995-12-31

267

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

The influence of a reduced Greenland ice sheet (GrIS) on Greenland's surface climate during the Eemian interglacial is studied using a comprehensive climate model. We find a distinct impact of changes in the GrIS topography on Greenland's surface air temperatures (SAT) even when correcting for changes in surface elevation which influences SAT through the lapse rate effect. The resulting lapse rate corrected SAT anomalies are thermodynamically driven by changes in the local surface energy balance rather than dynamically caused through anomalous advection of warm/cold air masses. The large-scale circulation is indeed very stable among all sensitivity experiments and the NH flow pattern does not depend on Greenland's topography in the Eemian. In contrast, Greenland's surface energy balance is clearly influenced by changes in the GrIS topography and this impact is seasonally diverse. In winter, the variable reacting strongest to changes in the topography is the sensible heat flux (SHFLX). The reason is its dependence on surface winds, which themselves are controlled to a large extent by the shape of the GrIS. Hence, regions where a receding GrIS causes higher surface wind velocities also experience anomalous warming through SHFLX. Vice-versa, regions that become flat and ice-free are characterized by low wind speeds, low SHFLX and anomalous cold winter temperatures. In summer, we find surface warming induced by a decrease in surface albedo in deglaciated areas and regions which experience surface melting. The Eemian temperature records derived from Greenland proxies, thus, likely include a temperature signal arising from changes in the GrIS topography. For the NEEM ice core site, our model suggests that up to 3.2 °C of the annual mean Eemian warming can be attributed to these topography-related processes and hence is not necessarily linked to large-scale climate variations.

Merz, N.; Born, A.; Raible, C. C.; Fischer, H.; Stocker, T. F.

2013-12-01

268

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

The influence of a reduced Greenland Ice Sheet (GrIS) on Greenland's surface climate during the Eemian interglacial is studied using a set of simulations with different GrIS realizations performed with a comprehensive climate model. We find a distinct impact of changes in the GrIS topography on Greenland's surface air temperatures (SAT) even when correcting for changes in surface elevation, which influences SAT through the lapse rate effect. The resulting lapse-rate-corrected SAT anomalies are thermodynamically driven by changes in the local surface energy balance rather than dynamically caused through anomalous advection of warm/cold air masses. The large-scale circulation is indeed very stable among all sensitivity experiments and the Northern Hemisphere (NH) flow pattern does not depend on Greenland's topography in the Eemian. In contrast, Greenland's surface energy balance is clearly influenced by changes in the GrIS topography and this impact is seasonally diverse. In winter, the variable reacting strongest to changes in the topography is the sensible heat flux (SHF). The reason is its dependence on surface winds, which themselves are controlled to a large extent by the shape of the GrIS. Hence, regions where a receding GrIS causes higher surface wind velocities also experience anomalous warming through SHF. Vice-versa, regions that become flat and ice-free are characterized by low wind speeds, low SHF, and anomalous low winter temperatures. In summer, we find surface warming induced by a decrease in surface albedo in deglaciated areas and regions which experience surface melting. The Eemian temperature records derived from Greenland proxies, thus, likely include a temperature signal arising from changes in the GrIS topography. For the Eemian ice found in the NEEM core, our model suggests that up to 3.1 °C of the annual mean Eemian warming can be attributed to these topography-related processes and hence is not necessarily linked to large-scale climate variations.

Merz, N.; Born, A.; Raible, C. C.; Fischer, H.; Stocker, T. F.

2014-06-01

269

PHYSICAL REVIEW B 84, 144435 (2011) Debye-Huckel theory for spin ice at low temperature  

E-print Network

's work already in the context of water ice and it has been observed experimentally.3 The T 0 staticPHYSICAL REVIEW B 84, 144435 (2011) Debye-H¨uckel theory for spin ice at low temperature C October 2011) At low temperatures, spin ice is populated by a finite density of magnetic monopoles

Sheldon, Nathan D.

270

Quaternary Science Reviews 23 (2004) 21132126 Sea surface temperatures and ice rafting in the Holocene North  

E-print Network

Quaternary Science Reviews 23 (2004) 2113­2126 Sea surface temperatures and ice rafting through analyses of sea surface temperature (SST; alkenone unsaturation ratios) and ice rafting were coupled to SST variability and ice rafting. The records outline four major climatic phases: (i

Born, Andreas

271

Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion  

NASA Technical Reports Server (NTRS)

The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that have been attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, and one or more of the following: loss of thrust control (roll back), compressor surge or stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the increase in air temperature causes a portion of the ice crystals to melt. It is hypothesized that this allows the ice-water mixture to cover the metal surfaces of the compressor stationary components which leads to ice accretion through evaporative cooling. Ice accretion causes a blockage which subsequently results in the deterioration in performance of the compressor and engine. The focus of this research is to apply an engine icing computational tool to simulate the flow through a turbofan engine and assess the risk of ice accretion. The tool is comprised of an engine system thermodynamic cycle code, a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor flow path, without modeling the actual ice accretion. A commercial turbofan engine which has previously experienced icing events during operation in a high altitude ice crystal environment has been tested in the Propulsion Systems Laboratory (PSL) altitude test facility at NASA Glenn Research Center. The PSL has the capability to produce a continuous ice cloud which are ingested by the engine during operation over a range of altitude conditions. The PSL test results confirmed that there was ice accretion in the engine due to ice crystal ingestion, at the same simulated altitude operating conditions as experienced previously in flight. The computational tool was utilized to help guide a portion of the PSL testing, and was used to predict ice accretion could also occur at significantly lower altitudes. The predictions were qualitatively verified by subsequent testing of the engine in the PSL. The PSL test has helped to calibrate the engine icing computational tool to assess the risk of ice accretion. The results from the computer simulation identified prevalent trends in wet bulb temperature, ice particle melt ratio, and engine inlet temperature as a function of altitude for predicting engine icing risk due to ice crystal ingestion.

Jorgenson, Philip C. E.; Veres, Joseph P.

2013-01-01

272

Tracking sea ice floes from the Lincoln Sea to Nares Strait and deriving large scale melt from coincident spring and summer (2009) aerial EM thickness surveys  

NASA Astrophysics Data System (ADS)

Satellite observations demonstrate a decreasing summer Arctic sea ice extent over the past ~40 years, as well as a smaller perennial sea ice zone, with a significantly accelerated decline in the last decade. Recent ice extent observations are significantly lower than predicted by any model employed by the Intergovernmental Panel on Climate Change. The disagreement of the modeled and observed results, along with the large variability of model results, can be in part attributed to a lack of consistent and long term sea ice mass balance observations for the High Arctic. This study presents the derivation of large scale (individual floe) seasonal sea ice mass balance in the Lincoln Sea and Nares Strait. Large scale melt estimates are derived by comparing aerial borne electromagnetic induction thickness surveys conducted in spring with surveys conducted in summer 2009. The comparison of coincident floes is ensured by tracking sea ice using ENIVSAT ASAR and MODIS satellite imagery. Only EM thickness survey sections of floes that were surveyed in both spring and summer are analyzed and the resulting modal thicknesses of the distributions, which represent the most abundant ice type, are compared to determine the difference in thickness and therefore total melt (snow+basal ice+surface ice melt). Preliminary analyses demonstrate a bulk (regional ice tracking) seasonal total thickness variability of 1.1m, Lincoln Sea modal thickness 3.7m (April, 2009) and Nares Strait modal thickness 2.6m (August 2009)(Fig1). More detailed floe tracking, in depth analysis of EM surveys and removal of deformed ridged/rafted sea ice (due to inaccuracies over deformed ice) will result in more accurate melt estimates for this region and will be presented. The physical structure of deformed sea ice and the footprint of the EM instrument typically underestimate the total thicknesses observed. Seasonal variations of sea ice properties can add additional uncertainty to the response of the EM instrument over deformed ridged/rafted sea ice. Here we will present additional analysis of the data comparing total thickness to ridge height that will provide some insight into the magnitude of seasonal discrepancies experienced by the EM instrument over deformed ice.

Lange, B. A.; Haas, C.; Beckers, J.; Hendricks, S.

2011-12-01

273

Impacts of sea ice retreat, thinning, and melt-pond proliferation on the summer phytoplankton bloom in the Chukchi Sea, Arctic Ocean  

NASA Astrophysics Data System (ADS)

In 2011, a massive phytoplankton bloom was observed in the Chukchi Sea under first-year sea ice (FYI), an environment in which primary productivity (PP) has historically been low. In this paper, we use a 1-D biological model of the Chukchi shelf ecosystem, in conjunction with in situ chemical and physiological data, to better understand the conditions that facilitated the development of such an unprecedented bloom. In addition, to assess the effects of changing Arctic environmental conditions on net PP (NPP), we perform model runs with varying sea ice and snow thickness, timing of melt, melt ponds, and biological parameters. Results from model runs with conditions similar to 2011 indicate that first-year ice (FYI) with at least 10% melt pond coverage transmits sufficient light to support the growth of shade-adapted Arctic phytoplankton. Increasing pond fraction by 20% enhanced peak under-ice NPP by 26% and produced rates more comparable to those measured during the 2011 bloom, but there was no effect of further increasing pond fraction. One of the important consequences of large under-ice blooms is that they consume a substantial fraction of surface nutrients such that NPP is greatly diminished in the marginal ice zone (MIZ) following ice retreat, where NPP has historically been the highest. In contrast, in model runs with <10% ponds, no under-ice bloom formed, and although peak MIZ NPP increased by 18-30%, this did not result in higher total annual NPP. This suggests that under-ice blooms contribute importantly to total annual NPP. Indeed, in all runs exhibiting under-ice blooms, total annual NPP was higher than in runs with the majority of NPP based in open water. Consistent with this, in model runs where ice melted one month earlier, peak under-ice NPP decreased 30%, and annual NPP was lower as well. The only exception was the case with no sea ice in the region: a weak bloom in early May was followed by low but sustained NPP throughout the entire growth season (almost all of which occurred in deep, subsurface layers), resulting in higher total annual NPP than in cases with sea ice present. Our results also show that both ultraviolet radiation and zooplankton grazers reduce peak open water NPP but have little impact on under-ice NPP, which has important implications for the relative proportion of NPP concentrated in pelagic vs. benthic food webs. Finally, the shift in the relative amount of NPP occurring in under-ice vs. open-water environments may affect total ecosystem productivity.

Palmer, Molly A.; Saenz, Benjamin T.; Arrigo, Kevin R.

2014-07-01

274

In-situ temperature measurement of the McMurdo Ice Shelf and ice shelf cavity using fiber-optic distributed temperature sensing  

NASA Astrophysics Data System (ADS)

Ocean-ice interactions in ice shelf cavities have great potential to affect ice shelf mass balance and stability. In-situ temperature of the ice shelf and ocean water column at Windless Bight, Antarctica, was remotely monitored using fiber-optic distributed temperature sensing (DTS). Fiber-optic cables were installed in two boreholes completed using a combination of electromechanical and hot point drilling. Between November 2011 and January 2013 a set of moorings, comprising of fiber-optic cables for distributed temperature sensing, an independent thermistor string and pressure-temperature transducers were monitored. Data presented summarizes the field deployment of the system between November 2011 and January 2013. Heat serves as natural tracer in environmental systems and is useful for identifying fluxes across boundaries. The heat flux near the ice-ocean interface is estimated from the temperature gradient in the lower ice shelf. Variation in the ice shelf temperature near the ice-ocean interface can be seen. Finally, these new data show the intrusion of warm water under the ice shelf previously observed in 2012.

Kobs, S.; Tyler, S. W.; Holland, D. M.; Zagorodnov, V.; Stern, A. A.

2013-12-01

275

Model group of controlled installation for melting ice on transmission line conductors  

Microsoft Academic Search

Reliability is one of the major index for customers power supply. This fact obligatory should be taken into account when power systems are developed. The power supply disturbances are especially typical for electrical grids located at those climate regions, where the overhead power lines are affected by dangerous meteorological conditions (hoarfrost, snowfall, icing). Our experience shows that icing accidents on

L. L. Baliberdin; M. A. Kozlova; Y. A. Shershnev

2005-01-01

276

Ground surface temperature history in southern Canada: Temperatures at the base of the Laurentide ice sheet and during the Holocene  

E-print Network

climate Holocene ground surface temperature Laurentide ice sheet glacier dynamics We use temperature ice sheet and during the Holocene Christian Chouinard, J.-C. Mareschal GEOTOP-UQAM-McGill, Centre deGround surface temperature history in southern Canada: Temperatures at the base of the Laurentide

Long, Bernard

277

Radiolysis of astrophysical ice analogs by energetic ions: the effect of projectile mass and ice temperature.  

PubMed

An experimental study of the interaction of highly charged, energetic ions (52 MeV (58)Ni(13+) and 15.7 MeV (16)O(5+)) with mixed H(2)O : C(18)O(2) astrophysical ice analogs at two different temperatures is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by cosmic rays inside dense, cold astrophysical environments, such as molecular clouds or protostellar clouds as well at the surface of outer solar system bodies. The measurements were performed at the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a CsI substrate at 13 K and 80 K. In situ analysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross section at 13 K of both H(2)O and CO(2) is about 3-4 times smaller when O ions are employed. The ice temperature seems to affect differently each species when the same projectile was employed. The formation cross section at 13 K of molecules such as C(18)O, CO (with oxygen from water), and H(2)O(2) increases when Ni ions are employed. The formation of organic compounds seems to be enhanced by the oxygen projectiles and at lower temperatures. In addition, because the organic production at 13 K is at least 4 times higher than the value at 80 K, we also expect that interstellar ices are more organic-rich than the surfaces of outer solar system bodies. PMID:21647477

Pilling, Sergio; Duarte, Eduardo Seperuelo; Domaracka, Alicja; Rothard, Hermann; Boduch, Philippe; da Silveira, Enio F

2011-09-21

278

Melting temperature and explosive crystallization of amorphous silicon during pulsed laser irradiation  

Microsoft Academic Search

Measurements during pulsed laser irradiation indicate that amorphous Si melts at a temperature 200 +- 50 K below the crystalline value. Below energy densities required to melt the amorphous layer fully , the data are interpreted in terms of an explosive crystallization. The initial liquid layer solidifies to form coarse grained polycrystalline Si. A thin, self-propagating liquid layer travels through

Michael Thompson; G. J. Galvin; J. W. Mayer; P. S. Peercy; J. M. Poate; D. C. Jacobson; A. G. Cullis; N. G. Chew

1984-01-01

279

Temperature of mantle melts beneath Central America: Integrating petrologic and seismic observations  

Microsoft Academic Search

Mantle melting beneath volcanic arcs is likely polybaric and polythermal, driven by a combination of decompression and hydration. Here we integrate petrologic and seismic observations to constrain the temperature and water content of the bulk melt and the hot zone within the mantle wedge. Results from the TUCAN seismic experiment in Central America show a vertical region, from 150-50 km,

T. Plank; C. Rychert; K. Fischer; G. Abers; E. Syracuse

2007-01-01

280

Melting temperatures of the Allende meteorite: implications for a Hadean magma ocean  

Microsoft Academic Search

Melting temperatures of the silicate fraction of the Allende CV3 meteorite, at upper mantle pressures, are several hundred degrees lower than that of fertile peridotite xenoliths or ‘pyrolite’. If the Earth accreted from material similar to chondrites, then deep mantle melting could have occurred with a relatively modest heat budget. It is concluded that initial chemical composition is an important

Carl B. Agee

1997-01-01

281

Vital role of daily temperature variability in surface mass balance parameterizations of the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

This study aims to demonstrate that the spatial and seasonal effects of daily temperature variability in positive degree-day (PDD) models play a decisive role in shaping the modeled surface mass balance (SMB) of continental-scale ice masses. Here we derive monthly fields of daily temperature standard deviation (SD) across Greenland from the ERA-40 (European Centre for Medium-Range Weather Forecasts 40 yr Reanalysis) reanalysis spanning from 1958 to 2001 and apply these fields to model recent surface responses of the Greenland Ice Sheet (GIS). Neither the climate data set analyzed nor in situ measurements taken in Greenland support the range of commonly used spatially and temporally uniform SD values (~ 5 °C). In this region, the SD distribution is highly inhomogeneous and characterized by low values during summer months (~ 1 to 2.5 °C) in areas where most surface melting occurs. As a result, existing SMB parameterizations using uniform, high SD values fail to capture both the spatial pattern and amplitude of the observed surface responses of the GIS. Using realistic SD values enables significant improvements in the modeled regional and total SMB with respect to existing estimates from recent satellite observations and the results of a high-resolution regional model. In addition, this resolves large uncertainties associated with other major parameters of a PDD model, namely degree-day factors. The model appears to be nearly insensitive to the choice of degree-day factors after adopting the realistic SD distribution.

Rogozhina, I.; Rau, D.

2014-04-01

282

Brief communication "Important role of the mid-tropospheric atmospheric circulation in the recent surface melt increase over the Greenland ice sheet"  

NASA Astrophysics Data System (ADS)

Since 2007, there has been a succession of surface melt records over the Greenland Ice Sheet (GrIS) in continuity of the trend observed since the end of the 1990s towards increasing melt. But, these last two decades are characterized by an increase of negative phases of the North-Atlantic Oscillation (NAO) favouring warmer and drier summers than normal over GrIS. In this context, we use a circulation type classification based on the daily 500 hPa geopotential height to evaluate the role of the atmospheric dynamics in this surface melt acceleration since 20 yr. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June-July-August) mean temperature at 700 hPa over Greenland; analogous atmospheric circulations in the past show that ~70% of the 1992-2011 warming at 700 hPa over Greenland has been driven by changes in the atmospheric flow frequencies. Indeed, the occurrence of anticyclones in surface and at 500 hPa centred over the GrIS has doubled since the end of 1990s which induces southerly warm air advection along the Western Greenland coast and over the neighbouring Canadian islands. These changes in the NAO modes explain also why no significant warming has been observed these last five summers over Svalbard, where northerly atmospheric flows are more frequent than before. Therefore, the recent warmer summers over Greenland, Ellesmere and Baffin Islands can not be considered as a long term climate warming but are more rather a consequence of the NAO variability impacting the atmospheric heat transport. While no global model from the CMIP5 database projects consequent changes in NAO through this century, we can not exclude that these changes in NAO are due to global warming.

Fettweis, X.; Hanna, E.; Lang, C.; Belleflamme, A.; Erpicum, M.; Gallée, H.

2012-09-01

283

Elastic moduli and dynamic yield strength of metals near the melting temperature  

Microsoft Academic Search

Under conditions of shock-wave experiments at elevated temperatures, there was observed an anomalous growth of the Hugoniot elastic limit (HEL) in aluminum and magnesium with increasing temperature. In aluminum, the HEL increased by a factor of four as the temperature approached the melting point. For magnesium, the dependence of the HEL on the temperature achieved a maximum at 857 K.

A. V. Utkin; G. I. Kanel; S. V. Razorenov; A. A. Bogach; D. E. Grady

1998-01-01

284

Mg/Casea surface temperatures during the Marine Isotope Stage 31 collapse of the Ross Ice Shelf  

NASA Astrophysics Data System (ADS)

The recovery of the AND-1b and CRP-1 drill cores from the Southwest Ross Sea highlighted the potential instability in of the Ross Ice Shelf and the West Antarctic Ice Sheet it buttresses. Both cores recovered a few individuals of the planktonic foraminifera Neogloboquadrina pachyderma from marine isotope stage (MIS) 31. This interval is significant because it marks the youngest occurrence of open ocean diatom sediment at AND-1b, which is now situated under the McMurdo Ice Shelf, indicating a substantial retreat of the Ross Ice Shelf occurred during this interglacial. However, sediment deposited after MIS 31 at both sites is represented only by glacial-dominated sediment, suggesting a critical environmental threshold had been crossed enabling the Ross Ice Shelf to form and persist. Numerical modeling by Pollard and DeConto (Nature, 2009) suggested that sub-ice oceanic melting is a critical element in the stability of ice shelves and that "WAIS will begin to collapse when nearby ocean temperatures warm by roughly 5°C." Laser ablation ICPMS measurement of the Mg/Ca content of N. pachyderma shows that although there is considerable heterogeneity in the distribution of Mg in their tests the mean Mg/Ca of a sample population appears proportional to calcification temperature. By empirically calibrating Mg/Ca in CRP-1 N. pachyderma against values measured in modern populations collected from Ross Sea and Southern Ocean sites with SSTs ranging from 1.2°C to 14°C it is concluded that SST during MIS 31 was warmer than today by 5-9°C, consistent with model projections.

Dunbar, G. B.

2012-04-01

285

Morphologies of primary silicon in hypereutectic Al–Si alloys with melt overheating temperature and cooling rate  

Microsoft Academic Search

The morphologies of primary silicon were studied in detail with different cooling rates and melt overheating temperatures. According to the present results, the morphologies of primary silicon are a strong function of the solidification conditions such as cooling rate and melt overheating temperature. With the elevation of melt overheating temperature, the morphologies of primary silicon will change from star-like and

C. L. Xu; Q. C. Jiang

2006-01-01

286

Liquid structure and temperature invariance of sound velocity in supercooled Bi melt  

NASA Astrophysics Data System (ADS)

Structural rearrangement of liquid Bi in the vicinity of the melting point has been proposed due to the unique temperature invariant sound velocity observed above the melting temperature, the low symmetry of Bi in the solid phase and the necessity of overheating to achieve supercooling. The existence of this structural rearrangement is examined by measurements on supercooled Bi. The sound velocity of liquid Bi was measured into the supercooled region to high accuracy and it was found to be invariant over a temperature range of ˜60°, from 35° above the melting point to ˜25° into the supercooled region. The structural origin of this phenomenon was explored by neutron diffraction structural measurements in the supercooled temperature range. These measurements indicate a continuous modification of the short range order in the melt. The structure of the liquid is analyzed within a quasi-crystalline model and is found to evolve continuously, similar to other known liquid pnictide systems. The results are discussed in the context of two competing hypotheses proposed to explain properties of liquid Bi near the melting: (i) liquid bismuth undergoes a structural rearrangement slightly above melting and (ii) liquid Bi exhibits a broad maximum in the sound velocity located incidentally at the melting temperature.

Emuna, M.; Mayo, M.; Greenberg, Y.; Caspi, E. N.; Beuneu, B.; Yahel, E.; Makov, G.

2014-03-01

287

NorthNorth Sea ice and glaciers are melting, permafrost is thawing, tundra  

E-print Network

as a spillway in a dam controls the level of a reservoir, the polar regions con- trol the earth's heat balance coming in winter and spring. Proxy records (ice and peat cores, lake sediments), which tell us mostly

Sturm, Matthew

288

Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century  

Microsoft Academic Search

We present the Met Office Hadley Centre's sea ice and sea surface temperature (SST) data set, HadISST1, and the nighttime marine air temperature (NMAT) data set, HadMAT1. HadISST1 replaces the global sea ice and sea surface temperature (GISST) data sets and is a unique combination of monthly globally complete fields of SST and sea ice concentration on a 1° latitude-longitude

N. A. Rayner; D. E. Parker; E. B. Horton; C. K. Folland; L. V. Alexander; D. P. Rowell; E. C. Kent; A. Kaplan

2003-01-01

289

Thermal Diffusivity for III-VI Semiconductor Melts at Different Temperatures  

NASA Technical Reports Server (NTRS)

The change of the thermal properties of semiconductor melts reflects the structural changes inside the melts, and a fundamental understanding of this structural transformation is essential for high quality semiconductor crystal growth process. This paper focused on the technical development and the measurement of thermal properties of III-VI semiconductor melts at high temperatures. Our previous work has improved the laser flash method for the specialized quartz sample cell. In this paper, we reported the results of our recent progress in further improvements of the measurement system by minimizing the free convection of the melt, adding a front IR detector, and placing the sample cell in a vacuum environment. The results for tellurium and selenium based compounds, some of which have never been reported in the literature, were obtained at different temperatures as a function of time. The data were compared with other measured thermophysical properties to shed light on the structural transformations of the melt.

Ban, H.; Li, C.; Lin, B.; Emoto, K.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

290

The Agulhas Current is said to attenuate the effect of melting ice  

E-print Network

, could in return be offsetting the effects of glacial melting on thermohaline circulation2 and the global helping to maintain worldwide thermohaline circulation. The phenomenon could be partly offsetting

291

DSC Evidence for Microstructure and Phase Transitions in Polyethylene Melts at High Temperatures  

E-print Network

reported previously at temperatures significantly above the melting range. For example, NMR measurements5 5-10 mg) were compressed into aluminum sample pans for testing in a TA Instruments DSC 2910 equipped

Hussein, Ibnelwaleed A.

292

Defects Can Increase the Melting Temperature of DNA-Nanoparticle Assemblies  

E-print Network

DNA-gold nanoparticle assemblies have shown promise as an alternative technology to DNA microarrays for DNA detection and RNA profiling. Understanding the effect of DNA sequences on the melting temperature of the system is central to developing reliable detection technology. We studied the effects of DNA base-pairing defects, such as mismatches and deletions, on the melting temperature of DNA-nanoparticle assemblies. We found that, contrary to the general assumption that defects lower the melting temperature of DNA, some defects increase the melting temperature of DNA-linked nanoparticle assemblies. The effects of mismatches and deletions were found to depend on the specific base pair, the sequence, and the location of the defects. Our results demonstrate that the surface-bound DNA exhibit hybridization behavior different from that of free DNA. Such findings indicate that a detailed understanding of DNA-nanoparticle assembly phase behavior is required for quantitative interpretation of DNA-nanoparticle aggreg...

Harris, Nolan C

2006-01-01

293

Collecting, shipping, storing, and imaging snow crystals and ice grains with low-temperature scanning electron microscopy  

USGS Publications Warehouse

Methods to collect, transport, and store samples of snow and ice have been developed that enable detailed observations of these samples with a technique known as low-temperature scanning electron microscopy (LTSEM). This technique increases the resolution and ease with which samples of snow and ice can be observed, studied, and photographed. Samples are easily collected in the field and have been shipped to the electron microscopy laboratory by common air carrier from distances as far as 5,000 miles. Delicate specimens of snow crystals and ice grains survive the shipment procedures and have been stored for as long as 3 years without undergoing any structural changes. The samples are not subjected to the melting or sublimation artifacts. LTSEM allows individual crystals to be observed for several hours with no detectable changes. Furthermore, the instrument permits recording of photographs containing the parallax information necessary for three-dimensional imaging of the true shapes of snowflakes, snow crystals, snow clusters, ice grains, and interspersed air spaces. This study presents detailed descriptions of the procedures that have been used successfully in the field and the laboratory to collect, ship, store, and image snow crystals and ice grains. Published 2003 Wiley-Liss, Inc.

Erbe, E.F.; Rango, A.; Foster, J.; Josberger, E.G.; Pooley, C.; Wergin, W.P.

2003-01-01

294

Satellite-derived ice data sets no. 2: Arctic monthly average microwave brightness temperatures and sea ice concentrations, 1973-1976  

NASA Technical Reports Server (NTRS)

A summary data set for four years (mid 70's) of Arctic sea ice conditions is available on magnetic tape. The data include monthly and yearly averaged Nimbus 5 electrically scanning microwave radiometer (ESMR) brightness temperatures, an ice concentration parameter derived from the brightness temperatures, monthly climatological surface air temperatures, and monthly climatological sea level pressures. All data matrices are applied to 293 by 293 grids that cover a polar stereographic map enclosing the 50 deg N latitude circle. The grid size varies from about 32 X 32 km at the poles to about 28 X 28 km at 50 deg N. The ice concentration parameter is calculated assuming that the field of view contains only open water and first-year ice with an ice emissivity of 0.92. To account for the presence of multiyear ice, a nomogram is provided relating the ice concentration parameter, the total ice concentration, and the fraction of the ice cover which is multiyear ice.

Parkinson, C. L.; Comiso, J. C.; Zwally, H. J.

1987-01-01

295

Study on the Thermal Drive Type Ice Making Apparatus with Multistage Tray Evaporator  

NASA Astrophysics Data System (ADS)

This report presents the results of ice making and ice melting experiment in bench-scale adsorption type ice making apparatus with adsorption container filling up silica gel and multistage tray evaporator accumulating water. In ice making process, the degree in supercooling of water in tray, cooling speed and heat flux to heat exchanger in adsorbent packed bed are showed. The behaviors of temperature rise in trays in ice melting process are clarified.

Yanadori, Michio; Watabe, Yoshihito

296

Effects of processing parameters on the temperature field of selective laser melting metal powder  

Microsoft Academic Search

Based on temperature-dependent thermophysical parameters and nonlinear phase transformation from powder to liquid, a three-dimensional\\u000a transient thermal finite model of selective laser melting process is developed. Commercial ANSYS software is used to simulate\\u000a the distribution of the temperature field in selective laser melting. The simulation results show that a lower scan speed,\\u000a higher laser power, and a lower scan interval

Ruidi Li; Yusheng Shi; Jinhui Liu; Huashan Yao; Wenxian Zhang

2009-01-01

297

Sea Ice Surface Temperature From the Moderate Resolution Imaging Spectroradiometer (MODIS)  

Microsoft Academic Search

Global sea ice products are produced from the Earth Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) on board both the Terra and Aqua satellites. Daily sea ice extent and ice-surface temperature (IST) products are available at 1- and 4-km resolution. Validation activities have been undertaken to assess the accuracy of the MODIS IST product at the South Pole station

D. K. Hall; J. R. Key; K. A. Casey; G. A. Riggs; D. J. Cavalieri

2003-01-01

298

Analysis of Stress Concentration Effects Around Triple Junctions in Lake Vostok Accretion Ice  

Microsoft Academic Search

Due to the thickness of the Antarctic ice cap, the accretion ice just above Lake Vostok Antarctica exists at temperatures close to the melting point. In addition, the large crystals making up this accretion ice are not highly aligned. Therefore, at triple junctions, substantial stress concentrations may exist. This enhanced stress state may subsequently produce additional melting beyond what would

R. L. Brown; E. E. Adams

2002-01-01

299

Ice Flow History, Basal Melt, and Hydraulic Connections in the Dome C Lake District Headwaters Over the Last Glacial Cycle Inferred from Hyrdopotential, Internal Layers, and Basal Reflectvity in Airborne Radar Sounding Data  

NASA Astrophysics Data System (ADS)

We have tracked 11 dated isochronal layers in the vicinity of Dome C using airborne ice-penetrating radar data for the purposes of calculating vertical strain and estimating horizontal velocity. Using the calculated vertical strain and a back-stripping of the layers we then obtain paleo-accumulation rates for the last 127 k. Combining the strain rate, accumulation history with a surface temperature record from the EPICA Dome C ice core, an assumed lapse rate of 10 degrees per km of elevation and a small linear correction for horizontal advection, we are able to calculate a long-term temperature model for every record of radar data. Characteristically lenticular features in the internal layer structure, associated with accumulation highs at the upstream ends of subglacial lakes Concordia and Horseshoe, are tracked to reveal horizontal velocities of 0.5 and 0.75 m/yr respectively. Velocities in both locations appear to have decreased during glacial maxima to a value nearly half that found during the interglacials. The modern velocities are consistent with those obtained from InSAR satellite measurements. Layer-based paleo-accumulation rates indicate that the present inferred distribution of accumulation rates is broadly equal to the accumulation distribution during the Eemian interglacial. Rates during the last glacial maximum were roughly ½ to 1/3 the rates found presently. Our temperature model reveals that a significant portion of the basal ice in the Dome C region may be at or near the pressure melting point, consistent with other published results from Dome C ice Core. Widely distributed melt rates in the major topographic valleys are generally less than 1 mm/yr throughout the region with slightly higher melts in the basin draining into Vincennes Subglacial Lake. The two largest subglacial lakes within the survey, Concordia and Vincennes are both associated with enhanced basal melting on their upstream shores at rates locally greater than 2 mm/year. Although published estimates for geothermal flux are capable of explaining the behavior of ice and water in most of the area, the two melt anomalies associated with the two largest subglacial lakes require an additional source of basal heat. These results have major implications for the filling rates and histories of several of the known subglacial lakes in this region.

Carter, S. P.; Blankenship, D. D.; Young, D. A.; Holt, J. W.

2007-12-01

300

Study of inter-annual variations in surface melting over Amery Ice Shelf, East Antarctica, using space-borne scatterometer data  

Microsoft Academic Search

The widespread retreat of glaciers can be considered as a response to the climate change. Being the largest retreating glacier–ice\\u000a shelf system in East Antarctica, the Amery Ice Shelf–Lambert Glacier system plays an important role in contributing to sea\\u000a level rise as well as the surrounding environment and climate. The present study is focused on the investigation of surface\\u000a melting

S R Oza; R K K Singh; N K Vyas; Abhijit Sarkar

2011-01-01

301

A Climate-Data Record (CDR) of the "Clear Sky" Surface Temperature of the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

To quantify the ice-surface temperature (IST) we are developing a climate-data record (CDR) of monthly IST of the Greenland ice sheet, from 1982 to the present using Advanced Very High Resolution Radiometer (AVHRR) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data at 5-km resolution. "Clear-sky" surface temperature increases have been measured from the early 1980s to the early 2000s in the Arctic using AVHRR data, showing increases ranging from 0.57-0.02 (Wang and Key, 2005) to 0.72 0.10 deg C per decade (Comiso, 2006). Arctic warming has implications for ice-sheet mass balance because much of the periphery of the ice sheet is near 0 deg C in the melt season and is thus vulnerable to more extensive melting (Hanna et al., 2008). The algorithm used for this work has a long history of measuring IST in the Arctic with AVHRR (Key and Haefliger, 1992). The data are currently available from 1981 to 2004 in the AVHRR Polar Pathfinder (APP) dataset (Fowler et al., 2000). J. Key1NOAA modified the AVHRR algorithm for use with MODIS (Hall et al., 2004). The MODIS algorithm is now being processed over Greenland. Issues being addressed in the production of the CDR are: time-series bias caused by cloud cover, and cross-calibration between AVHRR and MODIS instruments. Because of uncertainties, time series of satellite ISTs do not necessarily correspond with actual surface temperatures. The CDR will be validated by comparing results with in-situ (see Koenig and Hall, in press) and automatic-weather station data (e.g., Shuman et al., 2001).

Hall, Dorothy K.; Comiso, J. C.; DiGirolamo, N. E.; Shuman, C. A.

2011-01-01

302

Molybdenum at high pressure and temperature: melting from another solid phase.  

PubMed

The Gibbs free energies of bcc and fcc Mo are calculated from first principles in the quasiharmonic approximation in the pressure range from 350 to 850 GPa at room temperatures up to 7500 K. It is found that Mo, stable in the bcc phase at low temperatures, has lower free energy in the fcc structure than in the bcc phase at elevated temperatures. Our density-functional-theory-based molecular dynamics simulations demonstrate that fcc melts at higher than bcc temperatures above 1.5 Mbar. Our calculated melting temperatures and bcc-fcc boundary are consistent with the Mo Hugoniot sound speed measurements. We find that melting occurs at temperatures significantly above the bcc-fcc boundary. This suggests an explanation of the recent diamond anvil cell experiments, which find a phase boundary in the vicinity of our extrapolated bcc-fcc boundary. PMID:18517968

Belonoshko, A B; Burakovsky, L; Chen, S P; Johansson, B; Mikhaylushkin, A S; Preston, D L; Simak, S I; Swift, D C

2008-04-01

303

Elastic Modulus and Dynamic Yield Strength of Metals near the Melting Temperature  

Microsoft Academic Search

Under conditions of shock-wave experiments at elevated temperatures, an anomalous growth of the Hugoniot elastic limit (HEL) with increasing temperature was observed in aluminum and magnesium. In the case of aluminum, the peak velocity in the elastic precursor front increased by a factor of three or four when the temperature approached the melting point. For magnesium, the dependence of HEL

A. V. Utkin; G. I. Kanel; S. V. Razorenov; A. A. Bogach; D. E. Grady

1997-01-01

304

Ice Nucleation Temperature of Individual Leaves in Relation to Population Sizes of Ice Nucleation Active Bacteria and Frost Injury  

PubMed Central

Ice nucleation temperatures of individual leaves were determined by a tube nucleation test. With this assay, a direct quantitative relationship was obtained between the temperatures at which ice nucleation occurred on individual oat (Avena sativa L.) leaves and the population sizes of ice nucleation active (INA) bacteria present on those leaves. In the absence of INA bacteria, nucleation of supercooled growth-chamber grown oat leaves did not occur until temperatures were below approximately ?5°C. Both nucleation temperature and population size of INA bacteria were determined on the same individual, field-grown oat leaves. Leaves with higher ice nucleation temperatures harbored larger populations of INA bacteria than did leaves with lower nucleation temperatures. Log10 mean populations of INA bacteria per leaf were 5.14 and 3.51 for leaves with nucleation temperatures of ?2.5°C and ?3.0°C, respectively. Nucleation frequencies (the ratio of ice nuclei to viable cells) of INA bacteria on leaves were lognormally distributed. Strains from two very different collections of Pseudomonas syringae and one of Erwinia herbicola were cultured on nutrient glycerol agar and tested for nucleation frequency at ?5°C. Nucleation frequencies of these bacterial strains were also lognormally distributed within each of the three sets. The tube nucleation test was used to determine the frequency with which individual leaves in an oat canopy harbored large populations of INA bacteria throughout the growing season. This test also predicted relative frost hazard to tomato (Lycopersicon esculentum Mill) plants. PMID:16664039

Hirano, Susan S.; Baker, L. Stuart; Upper, Christen D.

1985-01-01

305

SENSITIVITY OF BRIGHTNESS TEMPERATURES FROM AMSR-E LOW FREQUENCY CHANNELS TO THE SEASONAL EVOLUTION OF LAKE ICE THICKNESS  

Microsoft Academic Search

Lake ice growth and decay include: freeze-up in the autumn; a long period of growth and thickening in winter; a short period of ice melting and thinning, and finally, break-up and the complete disappearance of the ice cover in spring. The sensitivity of freeze-up and break-up dates, and therefore ice cover duration, to climate variability and change has been demonstrated

Kyung-Kuk Kang; Claude R. Duguay; Stephen E. L. Howell; Chris P. Derksen; Richard E. J. Kelly

306

Laser heating of a moving slab: Influence of laser intensity parameter and scanning speed on temperature field and melt size  

Microsoft Academic Search

Laser melting of a moving slab is considered, and the temperature field and the phase-change in the heated region are simulated in-line with experimental conditions. The influence of laser power intensity parameter (?) and laser scanning speed on temperature field and melt depth is examined. An experiment is carried out to compare the melt layer thickness with the predictions. It

S. Z. Shuja; B. S. Yilbas; O. Momin

2011-01-01

307

Low temperature biodegradation of airport de-icing fluids.  

PubMed

The biodegradabilities of glycol- and acetate-based aircraft de-icing fluids on airport surfaces have been investigated at three temperatures between 0 degrees C and 10 degrees C. The aqueous solubilities of these substances can result in high BOD loadings in runoff and pose serious toxicity problems in receiving waters. The measured surface biodegradation rates for de-icing products based on ethylene/diethylene glycol (Konsin), propylene glycol (Kilfrost) and potassium acetate (Clearway) at 4 degrees C were 0.082, 0.073 and 0.033 day(-1). The resulting reductions in the potential BOD loadings, of a single application of a typical mixture of these products, over a 5 day biodegradation period are predicted to be 32.9%, 30.2% and 21.4%, respectively at 8 degrees C, 4 degrees C and 1 degrees C. For consecutive daily applications, the comparable cumulative reductions over 5 days are 20.8%, 18.9% and 13.3%. The subsequent savings in the amount of treatment required for airport runoff prior to safe discharge to receiving waters are discussed and hence the relevance of surface biodegradation processes to the design of stormwater treatment systems involving the wash-off of biodegradable pollutants following retention on urban surfaces. PMID:14703144

Revitt, D M; Worrall, P

2003-01-01

308

Bacterial responses to fluctuations and extremes in temperature and brine salinity at the surface of Arctic winter sea ice.  

PubMed

Wintertime measurements near Barrow, Alaska, showed that bacteria near the surface of first-year sea ice and in overlying saline snow experience more extreme temperatures and salinities, and wider fluctuations in both parameters, than bacteria deeper in the ice. To examine impacts of such conditions on bacterial survival, two Arctic isolates with different environmental tolerances were subjected to winter-freezing conditions, with and without the presence of organic solutes involved in osmoprotection: proline, choline, or glycine betaine. Obligate psychrophile Colwellia psychrerythraea strain 34H suffered cell losses under all treatments, with maximal loss after 15-day exposure to temperatures fluctuating between -7 and -25 °C. Osmoprotectants significantly reduced the losses, implying that salinity rather than temperature extremes presents the greater stress for this organism. In contrast, psychrotolerant Psychrobacter sp. strain 7E underwent miniaturization and fragmentation under both fluctuating and stable-freezing conditions, with cell numbers increasing in most cases, implying a different survival strategy that may include enhanced dispersal. Thus, the composition and abundance of the bacterial community that survives in winter sea ice may depend on the extent to which overlying snow buffers against extreme temperature and salinity conditions and on the availability of solutes that mitigate osmotic shock, especially during melting. PMID:24903191

Ewert, Marcela; Deming, Jody W

2014-08-01

309

Study of close contact melting of ice from a sliding heated flat plate  

Microsoft Academic Search

A study is conducted to examine the effect of the relative motion between a PCM block and a heated flat plate in the process of close contact melting of a high Prandtl number phase change material. An analytical model is proposed and experimental results are reported. Results indicate that the relative velocity between the PCM block and the plate starts

Dominic Groulx; Marcel Lacroix

2006-01-01

310

Pitted rock surfaces on Mars: A mechanism of formation by transient melting of snow and ice  

E-print Network

stable upland zone of the Antarctic Dry Valleys; these form by very localized chemical weathering due in the stable upland zone of the Antarctic Dry Valleys, pit formation by transient melting of small amounts, and combinations of these. [3] On Earth, weathering pits are common features on rocks in the Antarctic Dry Valleys

Marchant, David R.

311

Development of ice slurry for cold storage of foods in wide temperature range  

NASA Astrophysics Data System (ADS)

In order to popularize use of ice slurry, authors have been proposed application of ice slurry to cold storage of foods in place of an air conditioning. For use of the ice slurry in the wide temperature range a new harmless ice slurry to human being was developed by cooling a W/O emulsion made from tap water-edible oil mixture with small amounts of edible emulsifier and food additive. The edible emulsifier is essential to form W/O emulsion, and the food additive is used to dissolve in tap water. In this paper the optimal concentrations of emulsifiers were determined, and the fundamental characteristics such as viscosity, effective latent heat of fusion and usable temperature of ice slurry were clarified. Finally, it was concluded that new ice slurry could be fully applied to cold storage of foods in the wide temperature range because its lower limit usable temperature was about -18°C.

Matsumoto, Koji; Kaneko, Atsushi; Teraoka, Yoshikazu; Igarashi, Yoshito

312

Debye-Hueckel theory for spin ice at low temperature  

SciTech Connect

At low temperatures, spin ice is populated by a finite density of magnetic monopoles--pointlike topological defects with a mutual magnetic Coulomb interaction. We discuss the properties of the resulting magnetic Coulomb liquid in the framework of Debye-Hueckel theory, for which we provide a detailed context-specific account. We discuss both thermodynamical and dynamical signatures and compare Debye-Hueckel theory to experiment as well as numerics, including data for specific heat and AC susceptibility. We also evaluate the entropic Coulomb interaction that is present in addition to the magnetic one and show that it is quantitatively unimportant in the current compounds. Finally, we address the role of bound monopole anti-monopole pairs and derive an expression for the monopole mobility.

Castelnovo, C. [Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP (United Kingdom); SEPnet and Hubbard Theory Consortium, Department of Physics, Royal Holloway University of London, Egham TW20 0EX (United Kingdom); Moessner, R. [Max-Planck-Institut fuer Physik komplexer Systeme, D-01187 Dresden (Germany); Sondhi, S. L. [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States)

2011-10-01

313

Gullies on Mars: Origin by Snow and Ice Melting and Potential for Life Based on Possible Analogs from Devon Island, High Arctic  

NASA Technical Reports Server (NTRS)

Gullies on Devon Island, High Arctic, which form by melting of transient surface ice and snow covers and offer morphologic and contextual analogs for gullies reported on Mars are reported to display enhancements in biological activity in contrast to surrounding polar desert terrain.

Lee, Pascal; Cockell, Charles S.; McKay, Christopher P.

2004-01-01

314

Snow and Ice Melt Flow Features on Devon Island, Nunavut, Arctic Canada as Possible Analogs for Recent Slope Flow Features on Mars  

NASA Technical Reports Server (NTRS)

Based on morphologic and contextual analogs from Devon Island, Arctic Canada, the recent martian slope flow features reported by Malin and Edgett are reinterpreted as being due not necessarily to groundwater seepage but possibly to snow or ice melt. Additional information is contained in the original extended abstract.

Lee, Pascal; Cockell, Charles S.; Marinova, Margarita M.; McKay, Christopher P.; Rice, James W., Jr.

2001-01-01

315

Calculating melting temperatures and pressures of peridotite protoliths: Implications for the origin of cratonic mantle  

NASA Astrophysics Data System (ADS)

The old, stable cores of continents - cratons - are underlain by thick and cold mantle keels, composed of melt-depleted and low density peridotite residues. The origins of these thick keels are debated. Were these thick keels formed in situ, by orogenic thickening, or by underplating of buoyant residual mantle? Key to this debate is determining the temperature and pressure at which the protoliths of cratonic peridotites melted (igneous protolith conditions) and comparing to their metamorphic (subsolidus) temperatures and pressures within the keel. This paper presents a method for explicit calculation of the temperatures and pressures at which the peridotite protoliths melted. The approach relies only on the bulk FeO and MgO of residual peridotites. A system of equations consisting of mass balance and new calibrations of Mg peridotite/melt partitioning and melt productivity is then solved simultaneously. The igneous protoliths of abyssal peridotites are found to have melted at effective pressures of 1-2 GPa and temperatures of 1300-1400 °C, within error of the magmatic temperatures and pressures of melt extraction inferred independently from the SiO2 and MgO contents of mid-ocean ridge basalts. Archean cratonic peridotites, after filtering for the secondary effects of refertilization and orthopyroxene-metasomatism, give igneous protolith pressures and temperatures of 1-5 GPa (30-150 km) and 1400-1750 °C, similar to magmatic temperatures and pressures determined for Archean basalts thought to be representative of the thermal state of the Archean ambient mantle. Most importantly, cratonic peridotite protolith pressures and temperatures are shallower and hotter than their subsolidus equilibration pressures (3-7.5 GPa; 90-200 km) and temperatures (900-1300 °C), which reflects the recent thermal state of the cratonic lithosphere. Specifically, for individual samples with both melting and subsolidus thermobarometric constraints, we find that subsolidus pressures are 1-2 GPa (30-60 km) higher than their igneous protolith pressures although some of the deepest samples experienced minor increases in pressure. Collectively, these results support the suggestion that the building blocks of cratons were generated by hot shallow melting with a mantle potential temperature 200-300 °C warmer than the present. This shallowly generated mantle was subsequently thickened during orogenic episodes, culminating in the formation of a thick, stable craton. Whether such thickening has any modern analogs cannot be answered from this work alone.

Lee, Cin-Ty A.; Chin, Emily J.

2014-10-01

316

Cold ice in the ablation zone: Its relation to glacier hydrology and ice water content  

NASA Astrophysics Data System (ADS)

ice within a polythermal ice body controls its flow dynamics through the temperature dependence of viscosity, and affects glacier hydrology by blocking water flow paths. Lakes on the surface, linked by persistent, deeply incised meltwater streams, are hallmark features of cold ice in the ablation zone of a glacier or ice sheet. Ice radar is a convenient method to map scattering from internal water bodies present in ice at the pressure melting temperature (PMT). Consequently, lack of internal scatters is indicative of cold ice. We use a helicopter-borne 30 MHz ice radar to delineate the extent of cold ice within Grenzgletscher (Zermatt, Swiss Alps). The inferred thermal structure is validated with temperature measurements in 15 deep boreholes, showing excellent agreement. The cold ice occupies 80-90 % of the total ice thickness in a 400 m wide flow band along the central flow line. Quantitative interpretation of ice radar scattering power indicates a decrease of ice water content between PMT and 0.5 K below PMT, as predicted by theory, and observed in the laboratory. The cold ice which emerges at the surface in the lower ablation zone is impermeable to water, and is thus devoid of moulins if not crevassed. The surface water from melt and rain is routed through deeply incised, persistent streams and lakes, and cryoconite holes are frequent, in stark contrast to the adjacent temperate ice from other tributaries. The cold ice thus has a strong control on glacier hydrology, but is likely to change due to continued warming.

Ryser, C.; Lüthi, M.; Blindow, N.; Suckro, S.; Funk, M.; Bauder, A.

2013-06-01

317

Melting temperature and explosive crystallization of amorphous silicon during pulsed laser irradiation  

SciTech Connect

Measurements during pulsed laser irradiation indicate that amorphous Si melts at a temperature 200 +- 50 K below the crystalline value. Below energy densities required to melt the amorphous layer fully , the data are interpreted in terms of an explosive crystallization. The initial liquid layer solidifies to form coarse grained polycrystalline Si. A thin, self-propagating liquid layer travels through the remaining amorphous Si at a velocity of 10--20 m/s, producing fine grained polycrystalline Si.

Thompson, M.O.; Galvin, G.J.; Mayer, J.W.; Peercy, P.S.; Poate, J.M.; Jacobson, D.C.; Cullis, A.G.; Chew, N.G.

1984-06-25

318

Urediospores of Puccinia spp. and other rusts are warm-temperature ice nucleators and harbor ice nucleation active bacteria  

NASA Astrophysics Data System (ADS)

In light of various features of the biology of the rust fungi and of the epidemiology of the plant diseases they cause that illustrate the important role of rainfall in their life history, we have characterized the ice nucleation activity (INA) of the aerially disseminated spores (urediospores) of this group of fungi. Urediospores of this obligate plant parasite were collected from natural infections from 7 species of weeds in France, from coffee in Brazil and from field and greenhouse-grown wheat in France, the USA, Turkey and Syria. Immersion freezing was used to determine freezing onset temperatures and the abundance of ice nuclei in suspensions of washed spores. Microbiological analyses of spores and subsequent tests of the ice nucleation activity of the bacteria associated with spores were deployed to quantify the contribution of bacteria to the ice nucleation activity of the spores. All samples of spores were ice nucleation active having freezing onset temperatures as warm as -4 °C. Spores in most of the samples carried cells of ice nucleation-active strains of the bacterium Pseudomonas syringae (at rates of less than 1 bacterial cell per 100 urediospores), but bacterial INA accounted for only a small fraction of the INA observed in spore suspensions. Changes in the INA of spore suspensions after treatment with lysozyme suggest that the INA of urediospores involves a polysaccharide. Based on data from the literature, we have estimated the concentrations of urediospores in air at cloud height and in rainfall. These quantities are very similar to those reported for other biological ice nucleators in these same substrates. We suggest that air sampling techniques have ignored the spatial and temporal variability of atmospheric concentrations that occur under conditions propitious for precipitation that could increase their local abundance intermittently. Nevertheless, we propose that the relative low abundance of warm-temperature biological ice nucleators in the atmosphere corresponds to optimal conditions for the processes of evolution to positively select for INA.

Morris, C. E.; Sands, D. C.; Glaux, C.; Samsatly, J.; Asaad, S.; Moukahel, A. R.; Gonçalves, F. L. T.; Bigg, E. K.

2012-10-01

319

Antarctica Ice  

NSDL National Science Digital Library

This short video examines the recent melting ice shelves in the Antarctica Peninsula; the potential collapse of West Antarctic ice shelf; and how global sea levels, coastal cities, and beaches would be affected.

Geographic, National

320

Distribution of Temperatures over an Airplane Wing with Reference to the Phenomena of Ice Formation  

NASA Technical Reports Server (NTRS)

The results obtained from the present study of temperature distribution over an airplane wing afford means for making the following statements as regards the conditions of ice accretion and the use of a thermic anti-icer or de-icer: 1) Ice can form on a wing only when the temperature is below or hovering around zero. 2) The thermic effects produced on contact of the air with the moving wing rather oppose ice accretion. 3) The thermic procedure in the fight against ice accretion on the wing consists in electrical heating of the leading edge. 4) It seems that the formation of ice on the wing ought to be accompanied by a temperature rise which brings the accretion to 0 degrees. 5) If the thermic effects of friction favor the operation of the thermic anti-icer, the functioning of the de-icer is facilitated by the release of heat which accompanies the deposit of ice.

Brun, Edmond

1938-01-01

321

Development of a Climate-Data Record of the Surface Temperature of the Greenland Ice Sheet (Invited)  

NASA Astrophysics Data System (ADS)

To quantify the ice-surface temperature (IST) we are developing a climate-data record (CDR) of monthly IST of the Greenland ice sheet, from 1982 to the present using Advanced Very High Resolution Radiometer (AVHRR) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data at 5-km resolution. “Clear-sky” surface temperature increases have been measured from the early 1980s to the early 2000s in the Arctic using AVHRR data, showing increases ranging from 0.57±0.02 (Wang and Key, 2005) to 0.72±0.10 deg C per decade (Comiso, 2006). Arctic warming has implications for ice-sheet mass balance because much of the periphery of the ice sheet is near 0 deg C in the melt season and is thus vulnerable to more extensive melting (Hanna et al., 2008). The algorithm used for this work has a long history of measuring IST in the Arctic with AVHRR (Key and Haefliger, 1992). The data are currently available from 1981 to 2004 in the AVHRR Polar Pathfinder (APP) dataset (Fowler et al., 2000). J. Key/NOAA modified the AVHRR algorithm for use with MODIS (Hall et al., 2004). The MODIS algorithm is now being processed over Greenland. Issues being addressed in the production of the CDR are: time-series bias caused by cloud cover, and cross-calibration between AVHRR and MODIS instruments. Because of uncertainties, time series of satellite ISTs do not necessarily correspond with actual surface temperatures. The CDR will be validated by comparing results with in-situ (see Koenig and Hall, in press) and automatic-weather station data (e.g., Shuman et al., 2001). References Comiso, J. C., 2006: Arctic warming signals from satellite observations, Weather, 61(3): 70- 76. Fowler, C. et al., 2000: updated 2007. AVHRR Polar Pathfinder Twice-daily 5 km EASE-Grid Composites V003, [used dates from 2000 - 2004], Boulder, CO: NSIDC. Digital media. Hall, D.K., J.Key, K.A. Casey, G.A. Riggs and D. J. Cavalieri, 2004: Sea ice surface temperature product from the Moderate-Resolution Imaging Spectroradiometer (MODIS), IEEE TGRS, 42(5):1076-1087. Hanna, E., P. Huybrechts, K. Steffen, J. Cappelen, R. Huff, C.A. Shuman, T. Irvine-Fynn and S. Wise, 2008: Increased runoff from melt from the Greenland Ice Sheet: a response to global warming? J. Climate, vol. 21(2):331-341. Key, J., and M. Haefliger, 1992: Arctic ice surface temperature retrieval from AVHRR thermal channels, JGR, 97:5885-5893. Koenig, L.S. and D.K. Hall, in press: Comparison of satellite, thermochron and station temperatures at Summit, Greenland, during the winter of 2008-09, J. Glaciol. Shuman, C.A., K. Steffen, J.E. Box and C.R. Stearns, 2001: A dozen years of temperature observations at the Summit: Central Greenland automatic weather stations 1987-1999, JAM, 40(4):741-752. Wang, X., and J. Key, 2005: Arctic surface, cloud, and radiation properties based on the AVHRR Polar Pathfinder data set. Part II: Recent trends, J. Climate, 18, 2575- 2593.

Hall, D. K.; Comiso, J. C.; Digirolamo, N. E.; Shuman, C. A.

2010-12-01

322

Correlation between the surface temperature and thickness of Arctic sea ice  

NASA Astrophysics Data System (ADS)

A study was conducted to investigate a possible correlation between the surface temperature and thickness of Arctic sea ice. Surface temperatures were measured with an infrared (IR) sensor while the ice thickness was determined using a capacitively coupled resistivity array. It was postulated that there would be an inverse correlation between the thickness and surface temperature of the sea ice. Thicker sea ice should better insulate the surface from the warmer seawater underneath, causing the surface temperature to vary inversely with sea ice thickness. This study was performed on the Chukchi Sea ice just offshore from Barrow, Alaska. Data was collected along two survey lines, each over 200m long, one parallel and one perpendicular to the shoreline. An IR sensor measured ice surface temperature, and this data was compared to both ground penetrating radar (250MHz and 500MHz) and capacitively coupled resistivity data. Ground penetrating radar was unable to yield a determination of the thickness of the ice. This was not surprising given the ice-to-water transition that starts with solid ice, proceeds through an intervening region of cracked ice and slush, and finally ends with seawater. [1] Resistivity data was collected at approximately 3 points per horizontal meter. With multiple receivers and passes along the survey lines, data was obtained at more than 8 vertical depths in the ice that was approximately 3 meters thick. The resistivity array yielded images indicating the thickness of the sea ice and the location and shape of the ice/water boundary. While the model-dependent nature of resistivity data processing is acknowledged, we have reasonable confidence in the results for the relative thickness of the ice. The temperature of the ice surface was determined via a calibrated (±0.1°C) IR sensor controlled with a data logger. Temperature measurements were collected at approximately 50 points per linear meter. The comparison of the temperature and resistivity data showed a strong visual correlation between the two, with the surface temperature being lower where the resistivity models indicated the ice was thicker. A full statistical analysis of this correlation will be discussed. This work suggests a possible future method for quickly determining the volume of sea ice over large areas using thermal imagery. The temperature of the seawater below the ice gives one boundary condition for the heat conduction equation, while IR imagery may yield the other boundary condition. The nature of the thermal conductivity "k" has been investigated. [2] Thus IR temperature readings for the ice surface may yield an efficient method for determining sea ice thickness over large areas. [1] The geophysics of sea ice. N. Untersteiner (editor). 1986. New York, Plenum Press. (NATO ASI Series B, 146). [2] Petrich, C. and H. Eicken (2009) "Growth, structure and properties of sea ice," in Thomas, D. N. and G. S. Dieckmann (eds.) Sea Ice, Wiley-Blackwell, pp. 23-77.

Frazier, A. H.; Vaccaro, A.; Phillips, S.; Blake, D.; Herman, R. B.

2012-12-01

323

Climate Data Records (CDRs) for Ice Motion and Ice Age  

NASA Astrophysics Data System (ADS)

Climate Data Records (CDRs) for remotely-sensed Arctic sea ice motion and sea ice age are under development by our group at the University of Colorado, Boulder. The ice motion product, archived at NSIDC, has a considerable history of use, while sea ice age is a relatively new product. Our technique to estimate sea ice motion utilizes images from SSM/I, as well as SMMR and the series of AVHRR sensors to estimate the daily motion of ice parcels. This method is augmented by incorporating ice motion observations from the network of drifting buoys deployed as part of the International Arctic Buoy Program. Our technique to calculate ice age relies on following the actual age of the ice for each ice parcel, categorizing the parcel as first-year ice, second-year, ice, etc. based on how many summer melt seasons the ice parcel survives. Both of these research-grade products have been interpolated onto 25x25 km grid points spanning the entire Arctic Ocean using the Equal-Area Scalable Earth (EASE) grid. Datasets generated from this program have shown that the Arctic ice cover has experienced a significant (> 70%) decline in multiyear ice over the last 20 years, leaving a younger ice cover in 2011. By comparing ice age derived by the Lagrangian tracking method to ice thickness estimated by Ice, Cloud and land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) data, it is observed that ice age is linearly related to ice thickness, up to an age of 10 years. Therefore, the shift in dominance of multiyear ice to first-year ice relates to a significant thinning of the ice. This thinning is estimated to correspond to a 40% reduction in ice volume in the last 20 years. An ancillary dataset (APP-X) produced by the University of Wisconsin, Madison has been combined with the ice motion product to monitor the properties of the sea ice parcels tracked by the ice motion product. This dataset includes ice surface and 2-meter air temperature, albedo, downwelling shortwave and longwave radiation, first year, multiyear, and total ice concentration, and passive microwave brightness temperatures. The combination of sea ice motion and sea ice surface properties can therefore be utilized to observe the evolution of these properties as the ice ages. Using this dataset, we observe that the evolution of albedo through the summer months varies between first year and mutliyear ice types, resulting in a greater amount of shortwave radiation absorbed per unit area over first-year ice through the melt season vs. multiyear ice. Given that a larger portion of the ice cover is now first-year ice, the total shortwave energy absorbed by the pack through the melt season has increased from two decades ago, a feedback associated with the change in predominant ice type.

Tschudi, M. A.; Fowler, C.; Maslanik, J. A.; Stroeve, J. C.

2011-12-01

324

Breakdown of time-temperature superposition in a bead-spring polymer melt near the glass transition temperature  

E-print Network

The breakdown of the time-temperature superposition (TTS) near its glass transition temperature (Tg) in simple bead-spring polymer melts with and without the chain angle potential was numerically investigated. The stress relaxation modulus at different temperatures G(t,T) was calculated by the Green-Kubo relation. The TTS of G(t,T) of bead-spring polymer melts worked well at temperatures sufficiently higher than its Tg. However, when the system temperature is approaching the glass transition regime, the breakdown of TTS is observed. At temperatures near the Tg, the temperature dependence of the shift factor aTB, which is defined at the time scale between the bond relaxation and the chain relaxation regimes of a G(t)-function, is significantly stronger than ones aTA defined by the time scale of the chain relaxation modes. In direct relation to the breakdown of TTS of G(t,T), the decoupling of Stokes-Einstein law of diffusion-viscosity relation also appears in the glass transition regime. The analysis of the van Hove function Gs(r,t) and non-gaussian parameter, a2(t), of the bead motions strongly suggest that the TTS breakdown is concerned with the dynamic heterogeneity. The effect of the chain stiffness on the temperature dependence of the shift factors was also investigated in this study. The stiffer chains melt has a stronger temperature dependence of the shift factors than the ones of the flexible chains melt. However, regardless of the chain stiffness, the stress relaxation modulus functions of the bead-spring polymer melts will begin to breakdown the TTS at a similar Tg-normalized temperature around T/Tg ~ 1.2.

Tamio Yamazaki

2014-04-03

325

Temperature measurement of ratio pyrometers of melting pool surfaces  

Microsoft Academic Search

The errors in measurement employing quotient pyrometry are a function of the temperature and the effective wavelengths used. They are generated by the spectral emission coefficients of the surface of the test specimen and the spectral transmissivity of the media in the beam path. Temperature-independent deviations up to -30°K have been found for various imaging lenses using calibrated tungsten strip

Mack

1978-01-01

326

Relationship between Crystal Thickness and Isothermal Crystallization Temperature for Determination of Equilibrium Melting Temperature for Syndiotatic Polypropylene  

NASA Astrophysics Data System (ADS)

Syndiotatic polypropylene (sPP) was used to investigate the relationship between isothermal crystallization temperature (Tc = 70-115^oC), crystal thickness and subsequent melting using simultaneous synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) in conjunction with DSC. The thickest lamellar crystals melt at the end of the DSC endotherm. At this temperature, the SAXS intensity (corrected formelt scattering) showed a diffuse profile, and the crystalline feature in the WAXD pattern was completely absent. This crystal thickness was estimated using an approach based on the single lamella structure factor, which will also be compared to the value determined by the interface distribution function. The equilibrium melting temperature obtained this way will be contrasted by other methods such as the Hoffman-Weeks approach. Acknowledgement: This work was supported by by a NSF grant (DMR 9732653).

Wang, Zhi-Gang; Hsiao Hsiao, Benjamin; Srinivas, Srivatsan; Crist, Buckley

2000-03-01

327

Vanishing Polar Ice Sheets  

Microsoft Academic Search

\\u000a Global temperatures have increased by 0.8°C since instrumental records began, and the last decade has been the warmest. This\\u000a warming has been closely linked to increasing greenhouse gas concentrations due to human activities. Arctic warming is leading\\u000a to thinning and disappearance of sea ice on the Arctic Ocean and the increased melting of the Greenland ice sheet. In the\\u000a last

Nancy A. N. Bertler; Peter J. Barrett

328

Sensitive response of the Greenland Ice Sheet to surface melt drainage over soft bed  

E-print Network

by frictional and geothermal heating accumulates at the 136 bed over the course of winter and is released together with the first SGL drainage 137 events. With either one of these factors included, our model was able to reproduce the 138 2010 spring... -sheet simulations. Quaternary 516 Science Reviews 23, 1013-1027 (2004). 517 32 Shannon, S. R. et al. Enhanced basal lubrication and the contribution of the 518 Greenland ice sheet to future sea-level rise. Proceedings of the National 519 Academy of Sciences...

Bougamont, M H; Christoffersen,P.; Hubbard, A. L.; Fitzpatrick, A. A.; Doyle, S. H.; Carter, S. P.

2014-09-29

329

Temperature and melt solid interface control during crystal growth  

NASA Technical Reports Server (NTRS)

Findings on the adaptive control of a transparent Bridgman crystal growth furnace are summarized. The task of the process controller is to establish a user specified axial temperature profile by controlling the temperatures in eight heating zones. The furnace controller is built around a computer. Adaptive PID (Proportional Integral Derivative) and Pole Placement control algorithms are applied. The need for adaptive controller stems from the fact that the zone dynamics changes with respect to time. The controller was tested extensively on the Lead Bromide crystal growth. Several different temperature profiles and ampoule's translational rates are tried. The feasibility of solid liquid interface quantification by image processing was determined. The interface is observed by a color video camera and the image data file is processed to determine if the interface is flat, convex or concave.

Batur, Celal

1990-01-01

330

Melting and metallization of silica in the cores of gas giants, ice giants and super Earths  

E-print Network

The physical state and properties of silicates at conditions encountered in the cores of gas giants, ice giants and of Earth like exoplanets now discovered with masses up to several times the mass of the Earth remains mostly unknown. Here, we report on theoretical predictions of the properties of silica, SiO$_2$, up to 4 TPa and about 20,000K using first principle molecular dynamics simulations based on density functional theory. For conditions found in the Super-Earths and in ice giants, we show that silica remains a poor electrical conductor up to 10 Mbar due to an increase in the Si-O coordination with pressure. For Jupiter and Saturn cores, we find that MgSiO$_3$ silicate has not only dissociated into MgO and SiO$_2$, as shown in previous studies, but that these two phases have likely differentiated to lead to a core made of liquid SiO$_2$ and solid (Mg,Fe)O.

Mazevet, S; Taniuchi, T; Benuzzi-Mounaix, A; Guyot, F

2014-01-01

331

Atomistic simulations of melting and solidification using temperature accelerated molecular dynamics  

NASA Astrophysics Data System (ADS)

A detailed understanding of melting/solidification mechanisms in metals remains obscure, though over the years many simulations and experiments have been performed for clarifying it. We have applied the enhanced-sampling method, Temperature-Accelerated Molecular Dynamics, to study the melting/solidification of FCC metals like copper, nickel under the constant temperature and pressure conditions. Free energy surfaces along Steinhardt order parameters and local density are obtained and minimum free energy path (MFEP) between the metastable states are calculated. An analysis of the atomic structure along the MFEP, reveals that an interplay between orientation ordering and positional ordering governs this phase transition.

Yu, Tang-Qing; Samanta, Amit; E, Weinan; Tuckerman, Mark; vanden-Eijnden, Eric

2013-03-01

332

Temperature modulated DSC studies of melting and recrystallization in polymers exhibiting multiple endotherms  

Microsoft Academic Search

Temperature-modulated DSC (TMDSC) is used to characterize melting and recrystallization in polymers exhibiting multiple melting endotherms. Poly(ethylene-2,6-naphthalenedicarboxylate)(PEN) and poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene)(PEEK) are chosen, and the data show the detailed contributions of thermal and processing histories to properties. The results are supplemented by standard DSC at different heating rates. By independent very rapid heating rate methods, the temperature at which the polymer first

B. B Sauer; W. G Kampert; E Neal Blanchard; S. A Threefoot; B. S Hsiao

2000-01-01

333

Are seasonal calving dynamics forced by buttressing from ice mélange or undercutting by melting? Outcomes from full-Stokes simulations of Store Gletscher, West Greenland  

NASA Astrophysics Data System (ADS)

We use a full-Stokes 2-D model (Elmer/Ice) to investigate the flow and calving dynamics of Store Gletscher, a fast flowing outlet glacier in West Greenland. Based on a new, subgrid-scale implementation of the crevasse depth calving criterion, we perform two sets of simulations; one to identify the primary forcing mechanisms and another to constrain future stability. We find that the mixture of icebergs and sea-ice, known as ice mélange or sikussak, is principally responsible for the observed seasonal advance of the ice front, whereas submarine melting plays a secondary role. Sensitivity analysis demonstrates that the glacier's calving dynamics are sensitive to seasonal perturbation, but are stable on interannual timescales due to the glacier's topographic setting. Our results shed light on the dynamics of calving glaciers while explaining why neighbouring glaciers do not necessarily respond synchronously to changes in atmospheric and oceanic forcing.

Todd, J.; Christoffersen, P.

2014-07-01

334

Generation of Primary Kilauea Magmas: Constraints on Pressure, Temperature and Composition of Melts  

NASA Astrophysics Data System (ADS)

Picrite glasses from the submarine extension of Kilauea, Puna Ridge, which contain up to 15.0 wt% MgO, are the most magnesian glass samples reported from Hawaii. Their compositions form a distinct olivine fractionation trend. A comparison of this trend with phase relations of garnet lherzolite in the CaO-MgO-Al2O3-SiO2 (CMAS) and CaO-MgO-Al2O3-SiO2-Na2O-FeO (CMASNF) system indicates that melts parental to the Hawaiian picrites are produced by melting of a garnet lherzolite source at a pressure of 5 ± 1 GPa. The primary melt composition for Kilauea proposed by Clague et al. (1995), which has 18.4 wt% MgO, is close to the expected 5 GPa melt composition. By using the pressure-independent CMASNF geothermometer (Gudfinnsson and Presnall, 2001), we obtain a temperature of formation of 1450° C for the most magnesian Puna Ridge glass after correction for the presence of 0.4 wt% H2O and 0.7 wt% CO2. This assumes that the glass is not much modified after separation from the lherzolite source. However, comparison with phase relations in the CMAS system strongly suggests that the most magnesian Puna Ridge glasses are the product of some olivine fractionation, and therefore give temperature considerably lower than that of the source. When applied to the proposed Kilauea primary melt composition of Clague et al. (1995), the CMASNF geothermometer gives a melting temperature of 1596° C or about 1565° C after correction for the presence of volatiles. This compares well with the anhydrous solidus temperature of 1600 ± 15° C at 5 GPa for the fertile KR4003 lherzolite (Lesher et al., 2003), which has the complete garnet lherzolite phase assemblage present at the solidus at this pressure. This consistency supports use of phase relations from the CMAS system and the CMASNF geothermometer to the Puna Ridge picrite compositions. With the pressure and temperature of melting known, one can calculate the potential temperature of the Hawaiian mantle, provided certain conditions are met. The calculation assumes that the temperature at the point of melt segregation is close to the temperature of the solid adiabat. If extensive melting has occurred prior to the segregation, this will be incorrect. Secondly, it is assumed that the melting is occurring at the non-conducting part of the geotherm. Provided this is the case and the Kilauea primary melt composition truly represents a near-primary melt composition, we derive a potential temperature for the mantle beneath Kilauea of about 1500° C. The very high temperature and pressure conditions for magma generation at Hawaii appear to be unmatched by any other currently active volcanism on the Earth. Thus, of all the candidates for plume status, Hawaii appears to be the most robust.

Gudfinnsson, G. H.; Presnall, D. C.

2004-12-01

335

A Climate-Data Record of the "Clear-Sky" Surface Temperature of the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

We are developing a climate-data record (CDR of daily "clear-sky" ice-surface temperature (IST) of the Greenland Ice Sheet, from 1982 to the present using Advanced Very High Resolution Radiometer (AVHRR) (1982 - present) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data (2000 - present) at a resolution of approximately 5 km. The CDR will be continued in the National Polar-orbiting Operational Environmental Satellite System Visible/Infrared Imager Radiometer Suite era. Two algorithms remain under consideration. One algorithm under consideration is based on the split-window technique used in the Polar Pathfinder dataset (Fowler et al., 2000 & 21007). Another algorithm under consideration, developed by Comiso (2006), uses a single channel of AVHRR data (channel 4) in conjunction with meteorological-station data to account for atmospheric effects and drift between AVHRR instruments. Known issues being addressed in the production of the CDR are: tune-series bias caused by cloud cover (surface temperatures can be different under clouds vs. clear areas) and cross-calibration in the overlap period between AVHRR instruments, and between AVHRR and MODIS instruments. Because of uncertainties, mainly due to clouds (Stroeve & Steffen, 1998; Wang and Key, 2005; Hall et al., 2008 and Koenig and Hall, submitted), time-series of satellite 1S'1" do not necessarily correspond to actual surface temperatures. The CDR will be validated by comparing results with automatic-,",eather station (AWS) data and with satellite-derived surface-temperature products. Regional "clear-sky" surface temperature increases in the Arctic, measured from AVHRR infrared data, range from 0.57+/-0.02 deg C (Wang and Key, 2005) to 0.72+/-0.10 deg C (Comiso, 2006) per decade since the early 1980s. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near 0 deg C during the melt season, and is thus vulnerable to rapid melting if temperatures continue to increase. References

Hall, D. K.; Comiso, J. C.; Digirolamo, N. E.; Stock, L. V.; Riggs, G. A.; Shuman, C. A.

2009-01-01

336

Tools made of ice facilitate forming of soft, sticky materials  

NASA Technical Reports Server (NTRS)

Tools made of ice facilitate the forming or shaping of materials that are soft and sticky in the uncured state. The low-temperature of the ice slows the curing of the material, extending the working time available before setup. Handling problems are eliminated because the material does not adhere to the tool, and the melting ice serves as a lubricant.

Harris, J. E.; Ramsey, J. G., Jr.; Schinbeckler, K. D.

1969-01-01

337

Sensitivity of AMSR-E Brightness Temperatures to the Seasonal Evolution of Lake Ice Thickness  

Microsoft Academic Search

The sensitivity of brightness temperature (TB) at 6.9, 10.7, and 18.7 GHz from Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) observations is investigated over five winter seasons (2002-2007) on Great Bear Lake and Great Slave Lake, Northwest Territories, Canada. The TB measurements are compared to ice thicknesses obtained with a previously validated thermodynamic lake ice model. Lake ice thickness is

Kyung-Kuk Kang; Claude R. Duguay; Stephen E. L. Howell; Chris P. Derksen; Richard E. J. Kelly

2010-01-01

338

Temperature Dependence of Density, Viscosity and Electrical Conductivity for Hg-Based II-VI Semiconductor Melts  

NASA Technical Reports Server (NTRS)

The relaxation phenomenon of semiconductor melts, or the change of melt structure with time, impacts the crystal growth process and the eventual quality of the crystal. The thermophysical properties of the melt are good indicators of such changes in melt structure. Also, thermophysical properties are essential to the accurate predication of the crystal growth process by computational modeling. Currently, the temperature dependent thermophysical property data for the Hg-based II-VI semiconductor melts are scarce. This paper reports the results on the temperature dependence of melt density, viscosity and electrical conductivity of Hg-based II-VI compounds. The melt density was measured using a pycnometric method, and the viscosity and electrical conductivity were measured by a transient torque method. Results were compared with available published data and showed good agreement. The implication of the structural changes at different temperature ranges was also studied and discussed.

Li, C.; Ban, H.; Lin, B.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

339

Black carbon concentrations from a Tibetan Plateau ice core spanning 1843-1982: recent increases due to emissions and glacier melt  

NASA Astrophysics Data System (ADS)

Black carbon (BC) deposited on snow and glacier surfaces can reduce albedo and lead to accelerated melt. An ice core recovered from Guoqu glacier on Mt. Geladaindong and analyzed using a Single Particle Soot Photometer provides the first long-term (1843-1982) record of BC concentrations from the Central Tibetan Plateau. The highest concentrations are observed from 1975-1982, which corresponds to a 2.0-fold and 2.4-fold increase in average and median values, respectively, relative to 1843-1940. BC concentrations post-1940 are also elevated relative to the earlier portion of the record. Causes for the higher BC concentrations include increased regional BC emissions and subsequent deposition, and melt induced enrichment of BC, with the melt potentially accelerated due to the presence of BC at the glacier surface. A qualitative comparison of the BC and Fe (used as a dust proxy) records suggests that if changes in the concentrations of absorbing impurities at the glacier surface have influenced recent glacial melt, the melt may be due to the presence of BC rather than dust. Guoqu glacier has received no net ice accumulation since the 1980s, and is a potential example of a glacier where an increase in the equilibrium line altitude is exposing buried high impurity layers. That BC concentrations in the uppermost layers of the Geladaindong ice core are not substantially higher relative to deeper in the ice core suggests that some of the BC that must have been deposited on Guoqu glacier via wet or dry deposition between 1983 and 2005 has been removed from the surface of the glacier, potentially via supraglacial or englacial meltwater.

Jenkins, M.; Kaspari, S.; Kang, S.; Grigholm, B.; Mayewski, P. A.

2013-10-01

340

Combined influence of temperature forcing and lapse rate on empirical melt-model performance  

NASA Astrophysics Data System (ADS)

Temperature-index models are popular tools for glacier melt-modeling at a variety of scales and are widely used in projections of glacier mass change. Though minimal input data are required to drive these models, the necessary data may only exist distal from the area of interest. Here we explore the combined effects of temperature forcing provenance and surface lapse rate on the performance of an empirical melt model. The model is applied to a polythermal glacier in the St. Elias Mountains of northwestern Canada over five melt seasons. Air temperature records come from three different environments: (1) glacier surfaces, (2) glacier-proximal locations, and (3) low elevation valleys, and are combined with constant lapse rates spanning the range of measured values from the temperature stations to the study site. Model performance is assessed by comparing measured and modeled cumulative summer ablation at a network of stakes and by evaluating the transferability of the model to a second site. We find that the temperature forcings and lapse rates have a modest impact on model performance, relative to the inter-annual variability of model performance due to melt-season conditions and calibration data quality. Despite < 30% variation in estimated summer ablation arising from the combined influences of temperature forcing and lapse rate, the resulting variations in estimated annual mass balance are >100% in some cases. We hypothesize that the quality and quantity of mass-balance data available for model calibration may play a larger role than the combined temperature forcing and lapse rate in dictating empirical melt-model performance.

Flowers, G. E.; Wheler, B.; MacDougall, A. H.; Petersen, E. I.; Whitfield, P. H.; Kohfeld, K. E.

2013-12-01

341

Recent variations of sea ice and air temperature in high latitudes  

SciTech Connect

Feedbacks resulting from the retreat of sea ice and snow contribute to the polar amplification of the greenhouse warming projected by global climate models. A gridded sea-ice database, for which the record length is now approaching four decades for the Arctic and two decades for the Antarctic, is summarized here. The sea-ice fluctuations derived from the data set are characterized by (1) temporal scales of several seasons to several years and (2) spatial scales of 30[degrees]-180[degrees] of longitude. The ice data are examined in conjunction with air temperature data for evidence of recent climate change in the polar regions. The arctic sea-ice variations over the past several decades are compatible with the corresponding air temperatures, which show a distinct warming that is strongest over northern land areas during the winter and spring. The temperature trends over the sub arctic seas are smaller and even negative in the southern Greenland region. Statistically significant decreases of the summer extent of arctic ice are apparent in the sea-ice data, and new summer minima have been achieved three times in the past 15 years. There is no significant trend of ice extent in the Arctic during winter or in the Antarctic during any season. The seasonal and geographical changes of sea-ice coverage are consistent with the more recent greenhouse experiments performed with coupled atmosphere-ocean models.

Chapman, W.L.; Walsh, J.E. (Univ. of Illinois, Urbana (United States))

1993-01-01

342

Sensitivity of a distributed temperature-radiation index melt model based on a four melt season AWS record from Hurd Peninsula glaciers, Livingston Island, Antarctica  

NASA Astrophysics Data System (ADS)

We use an automatic weather station and mass balance dataset spanning four melt seasons collected on Hurd Peninsula Glaciers, South Shetland Islands, to investigate the point surface energy balance, to determine the absolute and relative contribution of the various energy fluxes acting on the glacier surface and to estimate the sensitivity of melt to ambient temperature changes. Long-wave incoming radiation is the main energy source for melt, while short-wave radiation is the most important flux controlling the variation of both seasonal and daily mean surface energy balance. Short-wave and long-wave radiation fluxes do in general balance each other, resulting in a high correspondence between daily mean net radiation flux and available melt energy flux. We calibrate a distributed melt model driven by air temperature and an expression for the incoming short-wave radiation. The model is calibrated with the data from one of the melt seasons and validated with the data of the three remaining seasons. The model results deviate at most 0.14 m w.e. from the corresponding observations using the glaciological method. The model is very sensitive to changes in ambient temperature: a 0.5 °C increase results in 56 % higher melt rates.

Jonsell, U. Y.; Navarro, F. J.; Bañón, M.; Lapazaran, J. J.; Otero, J.

2011-11-01

343

Remote sensing D/H ratios in methane ice: Temperature-dependent absorption coefficients of CH 3D in methane ice and in nitrogen ice  

NASA Astrophysics Data System (ADS)

The existence of strong absorption bands of singly deuterated methane (CH 3D) at wavelengths where normal methane (CH 4) absorbs comparatively weakly could enable remote measurement of D/H ratios in methane ice on outer Solar System bodies. We performed laboratory transmission spectroscopy experiments, recording spectra at wavelengths from 1 to 6 ?m to study CH 3D bands at 2.47, 2.87, and 4.56 ?m, wavelengths where ordinary methane absorption is weak. We report temperature-dependent absorption coefficients of these bands when the CH 3D is diluted in CH 4 ice and also when it is dissolved in N 2 ice, and describe how these absorption coefficients can be combined with data from the literature to simulate arbitrary D/H ratio absorption coefficients for CH 4 ice and for CH 4 in N 2 ice. We anticipate these results motivating new telescopic observations to measure D/H ratios in CH 4 ice on Triton, Pluto, Eris, and Makemake.

Grundy, W. M.; Morrison, S. J.; Bovyn, M. J.; Tegler, S. C.; Cornelison, D. M.

2011-04-01

344

Sea ice-albedo climate feedback mechanism  

SciTech Connect

The sea ice-albedo feedback mechanism over the Arctic Ocean multiyear sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice-atmosphere system. In its simplest form, ice-albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature, further decreasing the area cover of snow and ice. It is shown that the sea ice-albedo feedback can operate even in multiyear pack ice, without the disappearance of this ice, associated with internal processes occurring within the multiyear ice pack (e.g., duration of the snow cover, ice thickness, ice distribution, lead fraction, and melt pond characteristics). The strength of the ice-albedo feedback mechanism is compared for several different thermodynamic sea ice models: a new model that includes ice thickness distribution., the Ebert and Curry model, the Mayjut and Untersteiner model, and the Semtner level-3 and level-0 models. The climate forcing is chosen to be a perturbation of the surface heat flux, and cloud and water vapor feedbacks are inoperative so that the effects of the sea ice-albedo feedback mechanism can be isolated. The inclusion of melt ponds significantly strengthens the ice-albedo feedback, while the ice thickness distribution decreases the strength of the modeled sea ice-albedo feedback. It is emphasized that accurately modeling present-day sea ice thickness is not adequate for a sea ice parameterization; the correct physical processes must be included so that the sea ice parameterization yields correct sensitivities to external forcing. 22 refs., 6 figs., 1 tab.

Schramm, J.L.; Curry, J.A. [Univ. of Colorado, Boulder, CO (United States); Ebert, E.E. [Bureau of Meterology Research Center, Melbourne (Australia)

1995-02-01

345

Ice surface temperature retrieval from AVHRR, ATSR, and passive microwave satellite data: Algorithm development and application  

NASA Technical Reports Server (NTRS)

One essential parameter used in the estimation of radiative and turbulent heat fluxes from satellite data is surface temperature. Sea and land surface temperature (SST and LST) retrieval algorithms that utilize the thermal infrared portion of the spectrum have been developed, with the degree of success dependent primarily upon the variability of the surface and atmospheric characteristics. However, little effort has been directed to the retrieval of the sea ice surface temperature (IST) in the Arctic and Antarctic pack ice or the ice sheet surface temperature over Antarctica and Greenland. The reason is not one of methodology, but rather our limited knowledge of atmospheric temperature, humidity, and aerosol vertical, spatial and temporal distributions, the microphysical properties of polar clouds, and the spectral characteristics of snow, ice, and water surfaces. Over the open ocean the surface is warm, dark, and relatively homogeneous. This makes SST retrieval, including cloud clearing, a fairly straightforward task. Over the ice, however, the surface within a single satellite pixel is likely to be highly heterogeneous, a mixture of ice of various thicknesses, open water, and snow cover in the case of sea ice. Additionally, the Arctic is cloudy - very cloudy - with typical cloud cover amounts ranging from 60-90 percent. There are few observations of cloud cover amounts over Antarctica. The goal of this research is to increase our knowledge of surface temperature patterns and magnitudes in both polar regions, by examining existing data and improving our ability to use satellite data as a monitoring tool. Four instruments are of interest in this study: the AVHRR, ATSR, SMMR, and SSM/I. Our objectives are as follows. Refine the existing AVHRR retrieval algorithm defined in Key and Haefliger (1992; hereafter KH92) and applied elsewhere. Develop a method for IST retrieval from ATSR data similar to the one used for SST. Further investigate the possibility of estimating surface temperature from passive microwave data (in conjunction with AVHRR clear sky samples) through the use of 'effective emissivities' and physical relationships between skin temperature and subsurface temperature. Use the general method outlined in MK93 to calculate a 12-year record of clear sky equivalent surface temperatures, or possibly all-sky snow-ice interface physical temperatures, from SMMR and SSM/I, compare these temperatures to climatologies, ECMWF modeled surface temperatures, and surface temperatures predicted by a 2-D ice model. And intercompare several ice surface retrieval methods and validate them against ground measurements from the Swiss Camp on the Greenland ice sheet. Additionally, we intend to develop a surface temperature product based on AVHRR data and possibly blended with drifting buoy and meteorological station temperatures.

Key, Jeff; Maslanik, James; Steffen, Konrad

1994-01-01

346

NEW IRONMAKING PROCESS FROM THE VIEWPOINT OF CARBURIZATION AND IRON MELTING AT LOW TEMPERATURE  

Microsoft Academic Search

A new ironmaking process is required for the reduction of CO2 emission and energy consumption. One of the most effective factors of environmental conservation is to lower temperature and shorten time in the ironmaking process. Therefore, the carburization and melting stage of iron, which are essential processes in ironmaking, has been discussed. The important factors are the realization of direct

TAICHI MURAKAMI; KAZUHIRO NAGATA

2003-01-01

347

A Theoretical Study of the Variation of Ice Crystal Habits with Temperature  

Microsoft Academic Search

A theory is presented to explain the temperature dependence of the velocity of step-growth and the interaction distance between two approaching steps on the basal plane of ice. Numerical calculations based on this theory are shown to be in reasonable agreement with experimental results. It is suggested that an ice crystal grows from the vapor phase by steps being nucleated

P. V. Hobbs; W. D. Scott

1965-01-01

348

Untangling the formation of the cyclic carbon trioxide isomer in low temperature carbon dioxide ices  

E-print Network

Untangling the formation of the cyclic carbon trioxide isomer in low temperature carbon dioxide of the cyclic carbon trioxide isomer, CO3(X 1 A1), in carbon-dioxide-rich extraterrestrial ices and in the atmospheres of Earth and Mars were investigated experimentally and theoretically. Carbon dioxide ices were

Kaiser, Ralf I.

349

Ice Sheet Temperature Records - Satellite and In Situ Data from Antarctica and Greenland  

Microsoft Academic Search

Recently completed decadal-length surface temperature records from Antarctica and Greenland are providing insights into the challenge of detecting climate change. Ice and snow cover at high latitudes influence the global climate system by reflecting much of the incoming solar energy back to space. An expected consequence of global warming is a decrease in area covered by snow and ice and

C. A. Shuman; J. C. Comiso

2001-01-01

350

PLS Road surface temperature forecast for susceptibility of ice occurrence  

NASA Astrophysics Data System (ADS)

Winter maintenance relies on many operational tools consisting in monitoring atmospheric and pavement physical parameters. Among them, road weather information systems (RWIS) and thermal mapping are mostly used by service in charge of managing infrastructure networks. The Data from RWIS and thermal mapping are considered as inputs for forecasting physical numerical models, commonly in place since the 80s. These numerical models do need an accurate description of the infrastructure, such as pavement layers and sub-layers, along with many meteorological parameters, such as air temperature and global and infrared radiation. The description is sometimes partially known, and meteorological data is only monitored on specific spot. On the other hand, thermal mapping is now an easy, reliable and cost effective way to monitor road surface temperature (RST), and many meteorological parameters all along routes of infrastructure networks, including with a whole fleet of vehicles in the specific cases of roads, or airports. The technique uses infrared thermometry to measure RST and an atmospheric probes for air temperature, relative humidity, wind speed and global radiation, both at a high resolution interval, to identify sections of the road network prone to ice occurrence. However, measurements are time-consuming, and the data from thermal mapping is one input among others to establish the forecast. The idea was to build a reliable forecast on the sole data from thermal mapping. Previous work has established the interest to use principal component analysis (PCA) on the basis of a reduced number of thermal fingerprints. The work presented here is a focus on the use of partial least-square regression (PLS) to build a RST forecast with air temperature measurements. Roads with various environments, weather conditions (clear, cloudy mainly) and seasons were monitored over several months to generate an appropriate number of samples. The study was conducted to determine the minimum number of samples to get a reliable forecast, considering inputs for numerical models do not exceed five thermal fingerprints. Results of PLS have shown that the PLS model could have a R² of 0.9562, a RMSEP of 1.34 and a bias of -0.66. The same model applied to establish a forecast on past event indicates an average difference between measurements and forecasts of 0.20 °C. The advantage of such approach is its potential application not only to winter events, but also the extreme summer ones for urban heat island.

Marchetti, Mario; Khalifa, Abderrhamen; Bues, Michel

2014-05-01

351

Oxygen adsorption and the magnetic susceptibility of ice at low temperatures  

USGS Publications Warehouse

WHEN dealing with the magnetic susceptibility of tumour tissue1, we reported the magnetic susceptibility of ice at various temperatures from 273??K. down to 77??K. Since this publication, the authors have made many susceptibility measurements of ice, using the same equipment, and have obtained similar results, that is, a relatively large increase in diamagnetism below 150??K. Normal diamagnetism is not dependent on temperature, and hence further experiments were made of the magnetic susceptibility of ice at low temperatures in an attempt to determine some extraneous cause of the increased diamagnetism. ?? 1962 Nature Publishing Group.

Senftle, F. E.; Thorpe, A.

1962-01-01

352

A reconstruction of temperature, ice volume and atmospheric CO2 over the past 40 million years  

NASA Astrophysics Data System (ADS)

Knowledge on past climate change largely emerges from sediment records drilled from the ocean floor and ice-core records from the Antarctic and Greenland ice sheets. From these records proxy data is obtained indicating changes in, for example, temperature, sea level and greenhouse gas concentrations. A key parameter that emerges from the sediment records is the oxygen isotope ratio, ?18O, from fossilised benthic foraminiferal shells. The benthic ?18O data serves as a proxy for changes in local deep-water temperatures and global ice volume. With an innovative modelling approach surface-air temperatures relative to present day are derived from changes in benthic ?18O. This temperature anomaly is used to derive the two contributions to the benthic ?18O data with ice-sheet models and a simple deep-water temperature coupling function. With multiple 1-D ice-sheet models a continuous record of temperature and sea level over the past 40 million years has been derived from the observed benthic ?18O. The obtained data is shown to compare well with observations and other modelling results. It is shown that both the relation of ice volume with temperature and ice volume with sea water ?18O are highly variable and not constant through time. Therefore the use of a global coverage of ice volume changes is important for interpreting the benthic ?18O records in a transient mode. Using the temperature reconstruction from the 1-D ice-sheet models, a variety of different CO2 proxies are tested for their coherence with the observed ice-core CO2 data. The most coherent records are selected to derive a self-consistent and continuous CO2 record over the past 20 million years. Moreover, the long-term climate sensitivity of temperature to CO2 changes is derived, which includes radiative forcing of CO2, short and fast feedbacks and a correction for other greenhouse gasses. The large sensitivity derived here implies that subtle changes in atmospheric CO2 could be related to the Mid-Pleistocene Transition and the initiation of NH glaciation. With comprehensive 3-D ice-sheet models a more in-depth analysis has been performed on ice volume changes over the past million years. For the first time the separate contributions of these four ice sheets have been calculated explicitly over this time interval. With respect to eustatic sea level, the large NH ice sheets are naturally responsible for the largest variability during the Plio-Pleistocene. Coherently, these ice sheets also provide the largest contribution to sea water ?18O. The Antarctic and Greenland ice sheets contribute about 10 % to changes in eustatic sea level. For sea water ?18O the contribution is even larger, between 10 and 20 %, mainly due to the relatively much lower ?18Oice values of the Antarctic ice sheet. With a simple linear forcing of temperature and/or sea level it is shown that ice volume on Antarctica is increased due to lowering of sea level, which is enhanced by decreasing temperatures. On the contrary, ice growth on Eurasia and North America starts when temperatures drop, due to a positive surface mass balance which is enhanced by lowering of sea level.

de Boer, B.

2012-02-01

353

Mullite Decomposition Kinetics and Melt Stabilization in the Temperature Range 19002000C  

E-print Network

, in which gas-phase SiO2 reacts with carbon to form SiO and CO, is proposed; both IR analysis and kinetic of mullite ( 0.2 Pa s)3 at high temperatures (1900­2000°C) that makes mullite streams susceptible to Rayleigh investigated the influence of CO atmosphere on the melting behavior of mullite5,6 in the temperature range 1000

Mitchell, Brian S.

354

Dehydration-melting of amphibolite at 10 kbar: the effects of temperature and time  

Microsoft Academic Search

We have simulated the dehydration-melting of a natural, low-K, calcic amphibolite (67.4% hornblende, 32.5% anorthite) in piston-cylinder experiments at 10 kbar and 750–1000°C, for 1–9 days. The solidus temperature is lower than 750°C; garnet appears at 850°C. The overall reaction is: Hb+P?L+Cpx+Al-Hb+Ca-Hb+Ga+Opx. Three stages of reaction are: (1) melting dominated by the growth of clinopyroxene and garnet, with little change

Michael B. Wolf; Peter J. Wyllie

1994-01-01

355

Recent Changes in the Arctic Melt Season  

NASA Technical Reports Server (NTRS)

Melt-season duration, melt-onset and freeze-up dates are derived from satellite passive microwave data and analyzed from 1979 to 2005 over Arctic sea ice. Results indicate a shift towards a longer melt season, particularly north of Alaska and Siberia, corresponding to large retreats of sea ice observed in these regions. Although there is large interannual and regional variability in the length of the melt season, the Arctic is experiencing an overall lengthening of the melt season at a rate of about 2 weeks decade(sup -1). In fact, all regions in the Arctic (except for the central Arctic) have statistically significant (at the 99% level or higher) longer melt seasons by greater than 1 week decade(sup -1). The central Arctic shows a statistically significant trend (at the 98% level) of 5.4 days decade(sup -1). In 2005 the Arctic experienced its longest melt season, corresponding with the least amount of sea ice since 1979 and the warmest temperatures since the 1880s. Overall, the length of the melt season is inversely correlated with the lack of sea ice seen in September north of Alaska and Siberia, with a mean correlation of -0.8.

Stroeve, Julienne; Markus, Thorsten; Meier, Walter N.; Miller, Jeff

2007-01-01

356

Estimating water temperatures and time of ice formation on the Saint Lawrence River  

E-print Network

Estimating water temperatures and time of ice formation on the Saint Lawrence River Charles E by a simple linear relation with air-water temperature differential. It is suggested however estimates of water temperature changes for the period of study. The water temperature decline equation

357

The Evolution of Remnant Ice at the Lunar South Pole from Diviner Surface Temperature Results  

NASA Technical Reports Server (NTRS)

The Diviner lunar radiometer instrument aboard the Lunar Reconnaissance Orbiter mission has revealed large areas of lunar polar terrain with surface temperatures well below 100K. At these temperatures, the sublimation rate of water ice is well below 1 mm per billion years. In contrast, the loss rate at 120K is more than 1 meter of ice in that time consequently volatiles delivered to the coldest locations can be trapped for over 1 Ga, but will be quickly lost from warmer locales. Here we investigate the loss or retention of a layer of ice-bearing regolith at the lunar south poe, assuming contemporary surface temperature conditions and no other loss processes. We use an analytic solution for the one-dimensional diffusion equation of water ice, assuming an isothermal regolith with pore space comparable to mean grain size, 75 micrometers. Only the top meter of soil is assumed to be ice-bearing. We can then calculate the history of ice content with time based on local temperature, and predict what the epithermal neutron output would be in the presence of such a concentration of hydrogen. We compare the present, observed distribution of hydrogen with what one would expect from the temperature-dependent loss or retention of ice for various times since emplacement.

Elphic, Richard C.; Siegler, Mathew; Paige, David; Teodoro, Luis Filipe; Vasavada, Ashwin R.

2010-01-01

358

Climate scenarios of sea level rise for the northeast Atlantic Ocean: a study including the effects of ocean dynamics and gravity changes induced by ice melt  

Microsoft Academic Search

Here we present a set of regional climate scenarios of sea level rise for the northeast Atlantic Ocean. In this study, the\\u000a latest observations and results obtained with state-of-the-art climate models are combined. In addition, regional effects\\u000a due to ocean dynamics and changes in the Earth’s gravity field induced by melting of land-based ice masses have been taken\\u000a into account.

Caroline A. Katsman; Wilco Hazeleger; Sybren S. Drijfhout; Geert Jan van Oldenborgh; Gerrit J. H. Burgers

2008-01-01

359

Modeling englacial radar attenuation at Siple Dome, West Antarctica, using ice chemistry and temperature data  

USGS Publications Warehouse

The radar reflectivity of an ice-sheet bed is a primary measurement for discriminating between thawed and frozen beds. Uncertainty in englacial radar attenuation and its spatial variation introduces corresponding uncertainty in estimates of basal reflectivity. Radar attenuation is proportional to ice conductivity, which depends on the concentrations of acid and sea-salt chloride and the temperature of the ice. We synthesize published conductivity measurements to specify an ice-conductivity model and find that some of the dielectric properties of ice at radar frequencies are not yet well constrained. Using depth profiles of ice-core chemistry and borehole temperature and an average of the experimental values for the dielectric properties, we calculate an attenuation rate profile for Siple Dome, West Antarctica. The depth-averaged modeled attenuation rate at Siple Dome (20.0 ?? 5.7 dB km-1) is somewhat lower than the value derived from radar profiles (25.3 ?? 1.1 dB km-1). Pending more experimental data on the dielectric properties of ice, we can match the modeled and radar-derived attenuation rates by an adjustment to the value for the pure ice conductivity that is within the range of reported values. Alternatively, using the pure ice dielectric properties derived from the most extensive single data set, the modeled depth-averaged attenuation rate is 24.0 ?? 2.2 dB km-1. This work shows how to calculate englacial radar attenuation using ice chemistry and temperature data and establishes a basis for mapping spatial variations in radar attenuation across an ice sheet. Copyright 2007 by the American Geophysical Union.

MacGregor, J.A.; Winebrenner, D.P.; Conway, H.; Matsuoka, K.; Mayewski, P.A.; Clow, G.D.

2007-01-01

360

Can a melting Greenland ice sheet act as a nutrient source that compensates projected nutrient deficits in Atlantic surface water masses?  

NASA Astrophysics Data System (ADS)

Numerous studies have shown that under severe climate warming the northern Atlantic Ocean is more stratified, because an enhanced hydrological cycle and warming of upper ocean layers hampers water mass exchange with deeper layers. Therefore the supply of nutrient-rich deep water masses, which replenish the nutrients in the photic zone, is weakened in many climate warming scenarios. Consequently biological activities in the photic zone are stronger limited by the availability of nutrients. On the other side several studies, addressing in particular the release of organic material from melting glaciers or outlet glaciers of Greenland, suggest that intensified melting of glaciers and ice sheet might impact the nutrient supply to the ocean. This leads to the question: Does a strongly melting Greenland ice sheet can compensate the restrained nutrient supply from deep water masses? We've performed simulations with the MPI-ESM under different scenarios to address the question. A run under pre-industrial conditions serves as a base line experiment, while simulations under the strong warming scenario RCP8.5 shall represent the conditions in a warming world. To mimic the influence of a melting Greenland ice sheet, we discharge homogenously 0.1 Sv (105 m3/s) of fresh water along the coast of Greenland for 40 years. The continuous discharge of 0.1 Sv comes from common hosing experiments, while the setup with the uniformly release along the coast follows two comprehensive studies about the melting water influence on the Atlantic Meridional Overturning Circulation (AMOC) under historical and future warming conditions (RCP8.5). Proportional to the melting strength, nutrients (NO3, PO4, SiO2, and Iron) have been released, whereby the proportionalities have been compiled from a range of published values. In terms of release concentration a high end and a conservative setup have been analyzed. The simulations highlight, that the additionally released nutrients, have indeed a significant impact on the nutrient distribution. The nutrients flow with the general circulation from the coastal areas of Greenland into the Labrador Sea and spread afterwards into the North Atlantic. In particular the primary production is much stronger than in scenarios where meltwaters have been released without nutrients. All in all it seems, that even in the here assumed high nutrient supply scenarios the loss of nutrients due to increased stratification cannot be compensated for by nutrient input of a melting Greenland ice sheet.

Rodehacke, Christian; Gröger, Matthias

2014-05-01

361

Thermal diffusivity of rhyolitic glasses and melts: effects of temperature, crystals and dissolved water  

NASA Astrophysics Data System (ADS)

Thermal diffusivity ( D) was measured using laser-flash analysis on pristine and remelted obsidian samples from Mono Craters, California. These high-silica rhyolites contain between 0.013 and 1.10 wt% H2O and 0 to 2 vol% crystallites. At room temperature, D glass varies from 0.63 to 0.68 mm2 s-1, with more crystalline samples having higher D. As T increases, D glass decreases, approaching a constant value of ˜0.55 mm2 s-1 near 700 K. The glass data are fit with a simple model as an exponential function of temperature and a linear function of crystallinity. Dissolved water contents up to 1.1 wt% have no statistically significant effect on the thermal diffusivity of the glass. Upon crossing the glass transition, D decreases rapidly near ˜1,000 K for the hydrous melts and ˜1,200 K for anhydrous melts. Rhyolitic melts have a D melt of ˜0.51 mm2 s-1. Thermal conductivity ( k = D· ?· C P) of rhyolitic glass and melt increases slightly with T because heat capacity ( C P) increases with T more strongly than density ( ?) and D decrease. The thermal conductivity of rhyolitic melts is ˜1.5 W m-1 K-1, and should vary little over the likely range of magmatic temperatures and water contents. These values of D and k are similar to those of major crustal rock types and granitic protoliths at magmatic temperatures, suggesting that changes in thermal properties accompanying partial melting of the crust should be relatively minor. Numerical models of shallow rhyolite intrusions indicate that the key difference in thermal history between bodies that quench to obsidian, and those that crystallize, results from the release of latent heat of crystallization. Latent heat release enables bodies that crystallize to remain at high temperatures for much longer times and cool more slowly than glassy bodies. The time to solidification is similar in both cases, however, because solidification requires cooling through the glass transition in the first case, and cooling only to the solidus in the second.

Romine, William L.; Whittington, Alan G.; Nabelek, Peter I.; Hofmeister, Anne M.

2012-12-01

362

A study of the surface temperature and the thickness of the Arctic sea ice  

NASA Astrophysics Data System (ADS)

In March 2010, a study was performed to investigate a possible correlation between the surface temperature and the thickness of the Arctic sea ice just offshore from Barrow, Alaska. Temperature readings were acquired using Thermochron digital temperature data loggers at 1-meter intervals along a 500-meter line. Electrical resistivity data and snow depth readings were obtained concurrently along this line. In addition, resistivity data was obtained repeatedly along this line over the course of two weeks to investigate the time scale over which the meter-scale structure of the sea ice might change. A number of problems with the temperature measurements were encountered including having a limited number of Thermochrons, their measurement relaxation times, contamination by the ambient air temperature, and moving them along the survey line without contaminating the data by touching them. The Thermochron data will be compared with the resistivity and snow depth data. A possible model of heat transfer through the ice will be discussed. This model could allow the thickness of the sea ice to be determined from the temperature on the surface of the ice along with an assumption of the temperature of the water below the ice.

Herman, R. B.; Zhao, B.; Blake, D.

2010-12-01

363

Intrinsic nano-transformation of Al55 clusters below the melting temperature  

NASA Astrophysics Data System (ADS)

A recent series of experiments [1] have shown diverse melting behaviors in size-selected Al nanoclusters (Aln). In particular, Al55 is a magic cluster that serves as a boundary for abrupt change of melting points when n is around 55. Here, resulting from first-principles molecular dynamics simulations of Al55 clusters, we reveal a new dynamic melting state that has both solid and liquid characteristics. In thermal fluctuations near the melting point, the low-energy tetrahedral Al55 survives through rapid, collective surface transformations --- such as parity conversions and intervened row hopping --- without losing its structural orders. The emergence of the collective motions is due to efficient thermal excitation of soft phonon modes at nanoscale. A series of spontaneous surface reconfigurations result in a mixture or effective flow of surface atoms as is random color shuffling of a Rubik's cube. This novel ``lattice-liquid'' state will provide useful insights into understanding stability and functionality of nano systems near or below melting temperatures. [1] G. A. Breaux et al., Phys. Rev. Lett. 94, 173401 (2005).

Kang, Joongoo; Wei, Su-Huai; Kim, Yong-Hyun

2010-03-01

364

Analytical Comparisons of Tree Ring Data, Greenland Ice Core Temperatures and Temperature Fluctuations of the Sargasso Sea  

Microsoft Academic Search

Embedded in various events on Earth are data that allow us to map the temperature of the Earth over many years. In this work we have chosen the temperature fluctuations in the Sargasso Sea, the changing patterns in tree ring growth and temperature fluctuations in Greenland ice core samples for comparison with a goal to understanding the patterns in global

James Roberts; Jai Dahiya

2010-01-01

365

Entropy and heat capacity of DNA melting from temperature dependence of single molecule stretching.  

PubMed Central

When a single molecule of double-stranded DNA is stretched beyond its B-form contour length, the measured force shows a highly cooperative overstretching transition. We have measured the force at which this transition occurs as a function of temperature. To do this, single molecules of DNA were captured between two polystyrene beads in an optical tweezers apparatus. As the temperature of the solution surrounding a captured molecule was increased from 11 degrees C to 52 degrees C in 500 mM NaCl, the overstretching transition force decreased from 69 pN to 50 pN. This reduction is attributed to a decrease in the stability of the DNA double helix with increasing temperature. These results quantitatively agree with a model that asserts that DNA melting occurs during the overstretching transition. With this model, the data may be analyzed to obtain the change in the melting entropy DeltaS of DNA with temperature. The observed nonlinear temperature dependence of DeltaS is a result of the positive change in heat capacity of DNA upon melting, which we determine from our stretching measurements to be DeltaC(p) = 60 +/- 10 cal/mol K bp, in agreement with calorimetric measurements. PMID:11259306

Williams, M C; Wenner, J R; Rouzina, I; Bloomfield, V A

2001-01-01

366

The impact of a phase-change cooling vest on heat strain and the effect of different cooling pack melting temperatures.  

PubMed

Cooling vests (CV) are often used to reduce heat strain. CVs have traditionally used ice as the coolant, although other phase-change materials (PCM) that melt at warmer temperatures have been used in an attempt to enhance cooling by avoiding vasoconstriction, which supposedly occurs when ice CVs are used. This study assessed the effectiveness of four CVs that melted at 0, 10, 20 and 30 °C (CV?, CV??, CV??, and CV??) when worn by 10 male volunteers exercising and then recovering in 40 °C air whilst wearing fire-fighting clothing. When compared with a non-cooling control condition (CON), only the CV? and CV?? vests provided cooling during exercise (40 and 29 W, respectively), whereas all CVs provided cooling during resting recovery (CV? 69 W, CV?? 66 W, CV?? 55 W and CV?? 29 W) (P < 0.05). In all conditions, skin blood flow increased when exercising and reduced during recovery, but was lower in the CV? and CV?? conditions compared with control during exercise (observed power 0.709) (P < 0.05), but not during resting recovery (observed power only 0.55). The participants preferred the CV?? to the CV?, which caused temporary erythema to underlying skin, although this resolved overnight after each occurrence. Consequently, a cooling vest melting at 10 °C would seem to be the most appropriate choice for cooling during combined work and rest periods, although possibly an ice-vest (CV?) may also be appropriate if more insulation was worn between the cooling packs and the skin than used in this study. PMID:23160652

House, James R; Lunt, Heather C; Taylor, Rowan; Milligan, Gemma; Lyons, Jason A; House, Carol M

2013-05-01

367

Temperature profile for glacial ice at the South Pole: Implications for life nearby subglacial lake  

E-print Network

, Avenue, Kirkland, 98034­4399; ¶ Indigo Systems Corporation, 5385 Hollister Avenue, 103, Barbara, 93111 deep of South of #9°C, which is 7°C below pressure­induced melting temperature freshwater produce

Woschnagg, Kurt

368

Surface Transformations and Water Uptake on Liquid and Solid Butanol near the Melting Temperature  

E-print Network

Water interactions with organic surfaces are of central importance in biological systems and many Earth system processes. Here we describe experimental studies of water collisions and uptake kinetics on liquid and solid butanol from 160 to 200 K. Hyperthermal D2O molecules (0.32 eV) undergo efficient trapping on both solid and liquid butanol, and only a minor fraction scatters inelastically after an 80% loss of kinetic energy to surface modes. Trapped molecules either desorb within a few ms, or are taken up by the butanol phase during longer times. The water uptake and surface residence time increase with temperature above 180 K indicating melting of the butanol surface 4.5 K below the bulk melting temperature. Water uptake changes gradually across the melting point and trapped molecules are rapidly lost by diffusion into the liquid above 190 K. This indicates that liquid butanol maintains a surface phase with limited water permeability up to 5.5 K above the melting point. These surface observations are indic...

Papagiannakopoulos, Panos; Thomson, Erik S; Markovic, Nikola; Pettersson, Jan B C

2013-01-01

369

The role of sea ice in the temperature-precipitation feedback of glacial cycles  

NASA Astrophysics Data System (ADS)

The response of the hydrological cycle to climate variability and change is a critical open question, where model reliability is still unsatisfactory, yet upon which past climate history can shed some light. Sea ice is a key player in the climate system and in the hydrological cycle, due to its strong albedo effect and its insulating effect on local evaporation and air-sea heat flux. Using an atmospheric general circulation model with specified sea surface temperature and sea-ice distribution, the role of sea ice in the hydrological cycle is investigated under last glacial maximum (LGM) and present day conditions, and by studying its contribution to the "temperature-precipitation feedback". By conducting a set of sensitivity experiments in which the albedo and thickness of the sea ice are varied, the various effects of sea ice in the hydrological cycle are isolated. It is demonstrated that for a cold LGM like state, a warmer climate (as a result of reduced sea-ice cover) leads to an increase in snow precipitation over the ice sheets. The insulating effect of the sea ice on the hydrological cycle is found to be larger than the albedo effect. These two effects interact in a nonlinear way and their total effect is not equal to summing their separate contribution.

Gildor, Hezi; Ashkenazy, Yosef; Tziperman, Eli; Lev, Ilit

2014-08-01

370

Influence of Crucible Materials on High-temperature Properties of Vacuum-melted Nickel-chromium-cobalt Alloy  

NASA Technical Reports Server (NTRS)

A study of the effect of induction-vacuum-melting procedure on the high-temperature properties of a titanium-and-aluminum-hardened nickel-base alloy revealed that a major variable was the type of ceramic used as a crucible. Reactions between the melt and magnesia or zirconia crucibles apparently increased high-temperature properties by introducing small amounts of boron or zirconium into the melts. Heats melted in alumina crucibles had relatively low rupture life and ductility at 1,600 F and cracked during hot-working as a result of deriving no boron or zirconium from the crucible.

Decker, R F; Rowe, John P; Freeman, J W

1957-01-01

371

Greenland palaeotemperatures derived from GRIP bore hole temperature and ice core isotope profiles  

Microsoft Academic Search

Modelling the temperature profile along the GRIP deep bore at the summit of the Greenland ice sheet leads to conversion factors that allow interpretation of the dated stable isotope profile as a climatic temperature record spanning the last 113,000 years. When corrected for surface elevation changes, the late glacial to Boreal temperature shift appears to have been 22°C in central

Sigfus J. Johnsen; Dorthe Dahl-Jensen; Willi Dansgaard; Niels Gundestrup

1995-01-01

372

International Equations for the Pressure Along the Melting and Along the Sublimation Curve of Ordinary Water Substance  

Microsoft Academic Search

In order to define the phase boundary between the solid phase (ice) and the fluid phase (liquid and gas) of ordinary (light) water substance in pressure-temperature coordinates, correlation equations for the pressure along the melting curve of the various modifications of ice as well as for the pressure along the sublimation curve are presented. The five equations for the melting

Wolfgang Wagner; A. Saul; A. Pruss

1994-01-01

373

Link between depressions of melting temperature and Debye temperature in nanowires and its implication on Lindeman relation  

NASA Astrophysics Data System (ADS)

In this paper we investigate a possible link between the depressions of the melting temperature Tm and the Debye Temperature ?D in metal nanowires and check the validity of Lindeman relation on size reduction that connects these two physical quantities. From direct measurements of the ?D and Tm, we show that the depressions in these physical quantities are such that ?Tm(d) and ??D2(d) have nearly the same inverse power law dependence on the diameter d (with the exponent ?-0.6) for nanowires with diameters down to 30 nm. However the ratio ?/DTm1/2 is strictly not constant showing a reduction of nearly 9% when the sample size is taken from bulk to 30 nm. We discuss the physical significance of this observation and its impact on Lindeman criterion for melting.

Ghosh, Sabyasachi; Raychaudhuri, A. K.

2013-12-01

374

Spatial and temporal variability of air temperature on a melting glacier: atmospheric controls, extrapolation methods and their effect on melt modelling  

NASA Astrophysics Data System (ADS)

Air temperature is a key control in the exchange of energy fluxes at the glacier-atmosphere interface and is also the main input variable in many of the melt models currently used to predict glacier melt across a variety of scales, be these energy balance or temperature-index type of models. The commonly used approach to derive distributed temperature inputs is extrapolation from point measurements with a Lapse Rate (LR) that is often assumed to be constant in time and uniform in space. In this work, temperature data from three Automatic Weather Stations and twelve Temperature Loggers are used to investigate the spatio-temporal variability of temperature over a glacier, its main atmospheric controls, the suitability of extrapolation techniques and their effect on melt modelling. We use data collected on Juncal Norte Glacier, central Chile, during one ablation season. We examine temporal and spatial variability in LRs, together with alternative statistical interpolation methods. Our main result is that the main control over the glacier thermal regime is the development of a katabatic boundary layer (KBL). Katabatic wind occurs at night and in the morning and is eroded in the afternoon. LRs reveal strong diurnal variability, with steeper LRs during the day when the katabatic wind weakens and shallower LRs during the night and morning. We suggest that temporally variable LRs should be used to account for the observed change. They tend to be steeper than equivalent constant LRs, and therefore result in a reduction in simulated melt compared to use of constant LRs. In addition to the temporal variability, the temperature-elevation relationship varies also in space. Differences are evident between local LRs and including such variability in melt modelling affects melt simulations. The LR used for the upper glacier is a key control on the area contributing to melt, and thus on total melt. Extrapolation methods based on the spatial variability of the observations after removal of the elevation trend, such as Inverse Distance Weighting or Kriging, do not seem necessary for simulations of gridded temperature data over a glacier.

Pellicciotti, F.; Petersen, L.; Carenzo, M.

2011-12-01

375

The influence of glacier ice temperature on the long-term evolution of longitudinal valley profiles: Can a landscape escape from the "glacial buzzsaw"?  

NASA Astrophysics Data System (ADS)

The long-term pattern of glacial erosion in alpine valleys leads to characteristic longitudinal valley profiles. While landscape evolution models commonly take glacier sliding velocity to be the dominant control on erosion, the influence of spatial and temporal variations in glacier ice temperature on the efficiency of erosion over long timescales (>1 Ma) remains largely unexplored. Yet, the thermal field of a glacier can strongly influence the pattern of sliding. Temperate glaciers, with basal temperatures at the pressure melting point (PMP), slide whenever and wherever the glacial hydrology produces high water pressures. In contrast, in polythermal glaciers, erosion efficiency is strongly linked to basal ice temperature; when and where basal ice temperatures are below the PMP sliding, and hence erosion, are limited. We present results from numerical models in which we explore the influence of variations in glacier ice temperature on long-term glacial erosion processes in alpine valleys. These simulations are motivated by the persistent appeal of geomorphologists to polar glacial conditions to explain sites of unusually low glacial erosion rates. We employ a transient 1D (flowline) ice flow model that numerically solves the continuity equation for ice, and includes a depth-averaged approximation for longitudinal coupling stress. We prescribe separate winter and summer surface mass balance profiles: a capped elevation-dependent snowfall pattern in winter, and we capture both daily and seasonal oscillations in ablation using a positive degree day algorithm in summer. The steady-state ice temperature within the glacier is calculated using the conventional 2D (cross-sectional) heat equation (i.e. diffusion, advection and production terms) at a prescribed interval. The ice temperature model uses the surface temperature at the end of each melt season as the surface boundary condition, and a prescribed geothermal gradient as the basal boundary condition. Basal sliding is limited to sites where the basal ice is at the PMP. Glacial erosion rate is parameterized as a function of sliding velocity, which in turn depends upon a flotation fraction that is parameterized to account for annual variations in the glacial hydrologic system. We explore the long-term glacial erosion pattern when the landscape is subjected to different rock uplift rates, and to climates ranging from continental to maritime. Of specific interest to us are conditions that favor polythermal glaciers in which the basal ice at high elevations becomes cold. In such cases, rock uplift can outpace limited glacial erosion, allowing high peaks to escape from the "glacial buzzsaw" while basal ice at lower elevations remains at the PMP, allowing sliding and erosion. These simulations also allow a more formal assessment of the conditions under which cold basal ice can be invoked to explain low glacial erosion rates, and the conditions under which variations in rock erodibility may instead be invoked as the major control on erosion.

Dühnforth, M.; Anderson, R. S.; Colgan, W.

2012-04-01

376

Simulation of the temperature distribution in the selective beam melting process for polymer material  

NASA Astrophysics Data System (ADS)

In the present contribution the temperature distribution in the selective beam melting process for polymer materials is simulated to better understand the influence of process parameters on the properties of the produced part. The basis for the developed simulation tool is the nonlinear heat equation including temperature dependent functions for the heat capacity and the heat conduction which were obtained by experimental measurements. The effect of latent heat occurring in the process is also taken into account. The heat equation is discretized in time and space where a Runge-Kutta method of Radau IIA type is used for time integration. An adaptive finite element method is applied for the discretization in space and the model is implemented into the finite element library deal.II. The heat and cooling rate as important process parameters are simulated for different beam velocities. The ability for computing these process parameters makes the simulation tool suited for optimizing the process management of selective beam melting plants.

Riedlbauer, D.; Mergheim, J.; Steinmann, P.

2014-05-01

377

Comparison of CORCON-MOD1 predictions with experimental melt temperature histories  

SciTech Connect

The interaction between molten core materials and the concrete substructure has been identified as a significant phenomenon in Light Water Reactor (LWR) fuel meltdown accidents. High temperature melt/contrete interactions are being studied both experimentally and analytically at Sandia National Laboratories. As part of this program, the CORCON (core/concrete interaction) computer model is being developed to provide quantitative estimates of pertinent phenomena suitable for risk assessment of LWR's. The first version of this program, CORCON-MOD1, has been completed. As an initial code assessment effort, prediction clculations have been performed for the Sandia Code Comparison tests. This paper compares the measured and calculated melt temperature histories and examines their differences.

Muir, J.F.; Corradini, M.L.; Cole, R.K. Jr.

1981-01-06