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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 temperature of ice at positive and negative pressures  

Microsoft Academic Search

The pressure of an equilibrium mixture of water and ice contained in helically wound Pyrex capillary tubes was measured as a function of temperature. The sealed helices function as Berthelot tubes, allowing the measurements to extend to negative pressures, and as pressure gauges using the Bourdon tube principle. The locus of the melting line for ice I was measured up

Stephen J. Henderson; Robin J. Speedy

1987-01-01

4

Reevaluation of the reconstruction of summer temperatures from melt features in Belukha ice cores, Siberian Altai  

Microsoft Academic Search

In a previous study, past summer temperatures were reconstructed from melt features in the Belukha ice core, Siberian Altai. We evaluated the climatic representativeness of net accumulation and melt features by comparing two Belukha ice cores retrieved at neighboring sites by different institutions and dated by different methods. Melt features in both cores showed a significant correlation, but the trends

Sachiko Okamoto; Koji Fujita; Hideki Narita; Jun Uetake; Nozomu Takeuchi; Takayuki Miyake; Fumio Nakazawa; Vladimir B. Aizen; Stanislav A. Nikitin; Masayoshi Nakawo

2011-01-01

5

Reevaluation of past summer temperature reconstruction by melt features in Belukha ice cores, Russian Altai  

Microsoft Academic Search

Past summer temperature has been reconstructed by melt features in Belukha ice core in a previous study. We evaluated a climatic representativeness of isotope, net accumulation and melt feature by comparing two Belukha ice cores retrieved by different institutions and dated by different methods. We find a significant correlation between seasonal changes in stable isotope in precipitation and air temperature.

S. Okamoto; K. Fujita; H. Narita; J. Uetake; N. Takeuchi; T. Miyake; F. Nakazawa; V. Aizen; S. Nikitin; M. Nakawo

2009-01-01

6

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 use a sensor to 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.

7

Novel Monitoring of Ice Shelf and Shelf Cavity Temperatures and Melt Rates  

NASA Astrophysics Data System (ADS)

Ice shelf and ice shelf cavity melting represents a critical unknown in the assessment of potential Antarctic ice sheet collapse. However, continuous measurement of both subshelf ocean temperatures and ice shelf melting is extremely difficult, due to the thickness of the ice shelves, the harsh sub-shelf ocean conditions of high pressure, currents and icing and the difficulties of maintaining operating temperature sensing instruments for long periods of time. With the development and widespread use of Raman backscatter sensing on standard fiber-optic cables in industrial and environmental applications, significantly reduced downhole instrumentation may now be needed to continuously measure, in time and depth, ice shelf and ocean temperatures. Coupling this distributed fiber temperature system (DTS) with novel hot point drilling methods suggests that low cost and low impact drilling, installation and long term monitoring of sub-ice shelf temperatures may be practical. We present the design and operating parameters of a combined hot point drilling system/optical fiber installation, and low power temperature sensing/data telemetry system for the Ross Ice shelf at Windless Bight planned for installation in November 2011. The system is designed for rapid deployment, ~800 deployment water depth, continuous overwinter temperature and depth measurements and near-real time telemetry of data. Preliminary temperature and drilling results from Windless Bight will also be presented if available.

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

2011-12-01

8

Greenland ice sheet surface temperature, melt and mass loss: 2000-06  

USGS Publications Warehouse

A daily time series of 'clear-sky' surface temperature has been compiled of the Greenland ice sheet (GIS) using 1 km resolution moderate-resolution imaging spectroradiometer (MODIS) land-surface temperature (LST) maps from 2000 to 2006. We also used mass-concentration data from the Gravity Recovery and Climate Experiment (GRACE) to study mass change in relationship to surface melt from 2003 to 2006. The mean LST of the GIS increased during the study period by ???0.27??Ca-1. The increase was especially notable in the northern half of the ice sheet during the winter months. Melt-season length and timing were also studied in each of the six major drainage basins. Rapid (<15 days) and sustained mass loss below 2000 m elevation was triggered in 2004 and 2005 as recorded by GRACE when surface melt begins. Initiation of large-scale surface melt was followed rapidly by mass loss. This indicates that surface meltwater is flowing rapidly to the base of the ice sheet, causing acceleration of outlet glaciers, thus highlighting the metastability of parts of the GIS and the vulnerability of the ice sheet to air-temperature increases. If air temperatures continue to rise over Greenland, increased surface melt will play a large role in ice-sheet mass loss.

Hall, D. K.; Williams, Jr. , R. S.; Luthcke, S. B.; Digirolamo, N. E.

2008-01-01

9

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

10

Melting of ice under pressure.  

PubMed

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 10-50 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 and 40 GPa, ice melts as a molecular solid. For pressures above approximately 45 Gpa, there is a sharp increase in the slope of the melting curve because of the presence of molecular dissociation and proton diffusion in the solid before 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. PMID:18809909

Schwegler, Eric; Sharma, Manu; Gygi, François; Galli, Giulia

2008-09-22

11

Greenland ice sheet surface temperature, melt and mass loss: 2000–06  

Microsoft Academic Search

A daily time series of 'clear-sky' surface temperature has been compiled of the Greenland ice sheet (GIS) using 1 km resolution moderate-resolution imaging spectroradiometer (MODIS) land- surface temperature (LST) maps from 2000 to 2006. We also used mass-concentration data from the Gravity Recovery and Climate Experiment (GRACE) to study mass change in relationship to surface melt from 2003 to 2006.

Dorothy K. Hall; Richard S. Williams; Scott B. Luthcke; Nicolo E. Digirolamo

2008-01-01

12

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

13

Melting ice cubes  

NSDL National Science Digital Library

Explore how melting of ice cubes floating in water is influenced by the salinity of the water. Important oceanographic concepts like density and density driven currents are visualized and can be discussed on the basis of this experiment.

Glessmer, Mirjam

14

Melting Sea Ice  

NSDL National Science Digital Library

This activity uses a mix of multimedia resources and hands-on activities to support a storyline of investigation into melting sea ice. The lesson begins with a group viewing of a video designed to get students to consider both the local and global effects of climate change. The class then divides into small groups for inquiry activities on related topics followed by a presentation of the findings to the entire class. A final class discussion reveals a more complex understanding of both the local and global impacts of melting sea ice.

Domain, Wgbh E.

15

Melting Ice Rising Seas  

NSDL National Science Digital Library

This NASA video presents animations, photos and footage of melting polar ice as a result of climate change, the resulting sea-level rise, and selected consequences of that rise. Excellent animations, interviews with scientists, and clear step-by-step explanations provide a solid introduction to one facet of sea level rise and its consequences.

Noaa

16

Ultrafast superheating and melting of bulk ice  

NASA Astrophysics Data System (ADS)

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 270K, we observe an average temperature rise of 20 +/- 2K that persists over the monitored time interval of 250ps without melting.

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

2006-01-01

17

Melting Ice Caps  

NSDL National Science Digital Library

From the remote village of Gambell, Alaska, listener Bob Woolf can see the polar ice melting, and emailed us to ask if global warming would ever become irreversible. According to senior scientist Warren Washington of the National Center for Atmospheric Research, it probably already is, at least for the short term. That's because the greenhouse gases that are in the atmosphere now can last for decades or even centuries.

Science Update (AAAS;)

2006-08-15

18

Melting of horizontal ice layer from above by combined effect of temperature and concentration of aqua-solvent  

Microsoft Academic Search

This paper is concerned with the melting of horizontal ice layer from above by aqua-solvent with low solidification point. The solute used in this experiment are Sodium chloride NaCl, Calcium chloride CaCl2, Magnesium chloride MgCl2, and Urea CO(NH2)2- The upper surface of aqua-solvent melt layer is heated by an infrared lamp, whose temperature is in the range of about 8

M. Sugawara; H. Inaba; H. Nishimura; M. Mizuno

1987-01-01

19

Melting Temperature of Ice Ih calculated from coexisting solid-liquid phases  

SciTech Connect

In a previous paper we report the calculated melting temperature of the proton-disordered hexagonal ice I{sub h} using a four-site water model, the TIP4P (Ref. 2) and a five-site model, the TIP5P. In that work, we used a free-energy method. For the TIP4P model, the calculated melting temperature at 1 bar is T{sub m} = 229 {+-} 9 K, whereas for the TIP5P model, T{sub m} = 268 {+-} 6 K. For both models, the long-ranged interactions were truncated at 17 {angstrom}. Interestingly, these values of Tm are very close to T{sub m} = 232 {+-} 5 K and T{sub m} = 273.9 K reported by Sanz et al. and Vega et al. who used a slightly different free-energy method along with Ewald summation technique, although both the TIP4P and TIP5P models were originally developed for use with a truncated Coulomb interaction. The purpose of this paper is twofold: (1) to compute the melting temperature (T{sub m}) of ice I{sub h} with both TIP4P and TIP5P models by using the two-phase coexistence method and to compare with previously obtained T{sub m}; (2) to compute the T{sub m} using recently improved TIP4P and TIP5P models, namely, the TIP4P-Ew (Ref. 6) and TIP5P-Ew (Ref. 7) models. Both models are developed specifically for use with Ewald techniques. The TIP4P-Ew model, in particular, has shown substantial improvement over the original TIP4P model as it can reproduce the density maximum at about 274 K, very close to 277 K of the real water. The original TIP5P model can reproduce the measured T{sub m}. It will be of interest to see whether the improved TIP5P-Ew model can still hold the same level of prediction as far as the T{sub m} is concerned.

Wang, J. [University of Nebraska, Lincoln; Yoo, S. [University of Nebraska, Lincoln; Bai, J. [University of Nebraska, Lincoln; Morris, James R [ORNL; Zeng, X.C. [University of Nebraska, Lincoln

2005-01-01

20

Why does salt melt ice?  

NSDL National Science Digital Library

This tutorial on the chemical interaction between salt and ice explains how molecules on the surface of the ice escape into the water (melting), and how molecules of water are captured on the surface of the ice (freezing). It was created by the Chemistry Department at Frostburg State University (no, really).

Senese, Fred

21

Melting characteristics of horizontal ice surfaces in cold saline water  

Microsoft Academic Search

The results of an experimental investigation of the buoyancy driven flow adjacent to and below a horizontal ice surface melting in cold water at near oceanic salinity are presented. This melting configuration is characteristic of circumistances encountered by sea ice, for example, by new ice and, also, on the bottom of tabular ice floes. Several ambient water temperatures t, are

Benjamin Gebhart; Bahgat Sammakia; Tore Audunson

1983-01-01

22

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

23

Isotope thermometry in melt-affected ice cores  

Microsoft Academic Search

Summertime melt at ice core sites can lead to enrichment of isotopic valuesIsotopic enrichment results in overestimation of ice core-derived temperaturesCorrection of isotopic enrichment improves temperature estimates

T. Moran; S. J. Marshall; M. J. Sharp

2011-01-01

24

What controls dead-ice melting under different climate conditions?  

Microsoft Academic Search

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

A. Schomacker

2008-01-01

25

Shock and Post-Shock Temperatures in an Ice-Quartz Mixture: Implications for Melting During Planetary Impact Events  

NASA Astrophysics Data System (ADS)

Melting of H2O ice during planetary impact events is a widespread phenomenon. On planetary surfaces, ice is often mixed with other materials; yet, at present, how energy is partitioned between the components of a shocked mixture is still an open question in the shock physics community. Knowledge of how energy is partitioned to the ice component would help to predict and interpret a wide range of processes including shock-induced melting and chemistry. In this work, we construct a conceptual framework to elucidate the thermodynamic pathways of the components in a mixture and define three broad regimes based on the relative particle size with respect to the thickness of the shock front: (1) small length scale mixtures that reach pressure and temperature equilibration immediately behind the shock front; (2) intermediate length scales where pressure but not temperature equilibrium is achieved behind the shock front; and (3) long length scales where pressure equilibration requires multiple wave reflections. Here, we conduct shock temperature experiments in an H2O ice-SiO2 quartz mixture in the intermediate length scale regime. For shock pressures between 8 and 23 GPa, we determine the shock and post-shock temperatures of the H2O component. We find that the mixture is shocked to pressure equilibrium but not thermal equilibrium immediately behind the shock front. The shock and post-shock temperatures of the H2O component demonstrate that it is shocked to the principal Hugoniot. Therefore, in the intermediate length scale regime, the shock energy initially partitions according to the Hugoniots of the components. At present, the complexity of the thermodynamics of icy mixtures are not captured by available hydrocodes; however, using educated constraints on length and time scales, more accurate estimates of volumes of melt may be attained. We discuss energy partitioning in mixtures over the wide range of length and time scales encountered during planetary impact events. In some cases, the criteria for shock induced melting are the same as for pure H2O ice.

Stewart, S. T.; Kraus, R. G.; Seifter, A.; Obst, A. W.

2009-12-01

26

Numerical simulation of melting of ice around a horizontal cylinder  

Microsoft Academic Search

The problem of outward melting of ice around a horizontal isothermal cylinder is considered. A numerical model in which natural convection induced in the molten water encompassing density inversion is taken into consideration has been developed. Via finite-difference solution of the melting model, numerical simulation of melting of ice has been performed for the cylinder surface temperature T(i) = 4,

C. J. Ho; S. Chen

1986-01-01

27

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

28

Ultrafast superheating and melting of bulk ice  

Microsoft Academic Search

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

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

2006-01-01

29

Cool thermal discharge obtained with air flowing over melting ice  

Microsoft Academic Search

A model of ice melting has been developed to produce chilled air during on-peak power consumption. Equations have been derived for estimating the thickness of the melted ice and the temperature distribution in the liquid region with convection boundary condition. Three test cases have been studied in which the air temperature was specified and varied with time. Results are given

Chii-Dong Ho; Ho-Ming Yeh; Wen-Pen Wang

1998-01-01

30

Polar ice melting  

Microsoft Academic Search

Shrinking polar ice caps may be causing the earth's sea level to rise and its days to lengthen. `Rising mean sea level is a significant indication of global climate change,' R. Etkins and E. Epstein report, pointing out that global sea levels have risen slightly more than one-tenth of an inch each year, on the average, since 1940, for a

Jack G. Calvert

1982-01-01

31

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.

32

Does sea ice influence Greenland ice sheet surface-melt?  

Microsoft Academic Search

Recent decreases in Arctic sea ice and increases in Greenland ice sheet surface-melt may have global impacts, but the interactions between these two processes are unknown. Using microwave satellite data, we explore the spatial and temporal covariance of sea ice extent and ice sheet surface-melt around Greenland from 1979 to 2007. Significant covariance is discovered in several loci in the

Asa K Rennermalm; Laurence C Smith; Julienne C Stroeve; Vena W Chu

2009-01-01

33

MELTING OF ICE AROUND A HORIZONTAL ISOTHERMAL CYLINDRICAL HEAT SOURCE  

Microsoft Academic Search

Processes during melting from a horizontal cylindrical heat source of uniform surface temperature embedded in ice have been studied experimentally. The volume of the melt and its shape were photographed at different times for various constant temperatures of the heat source. At early times and under all conditions, the melt occupied a cylindrical annulus. At later times free convective motion

JORG HERRMANN; WOLFGANG LEIDENFROST; RAYMOND VISKANTA

1984-01-01

34

Quantum melting of spin ice  

NASA Astrophysics Data System (ADS)

A quantum melting of the spin ice is proposed for pyrochlore-lattice magnets Pr2TM2O7 (TM =Ir, Zr, and Sn). The quantum pseudospin-1/2 model is derived from the strong-coupling perturbation of the f-p electron transfer in the basis of atomic non-Kramers magnetic doublets. The ground states are characterized by a cooperative ferroquadrupole and pseudospin chirality in the cubic unit cell, forming a magnetic analog of smectic liquid crystals. Then, pinch points observed in spin correlations for dipolar spin-ice systems are replaced with the minima. The relevance to experiments is discussed.

Onoda, Shigeki; Tanaka, Yoichi

2010-03-01

35

Satellite-derived, melt-season surface temperature of the Greenland Ice Sheet (2000-2005) and its relationship to mass balance  

USGS Publications Warehouse

Mean, clear-sky surface temperature of the Greenland Ice Sheet was measured for each melt season from 2000 to 2005 using Moderate-Resolution Imaging Spectroradiometer (MODIS)-derived land-surface temperature (LST) data-product maps. During the period of most-active melt, the mean, clear-sky surface temperature of the ice sheet was highest in 2002 (-8.29 ?? 5.29??C) and 2005 (-8.29 ?? 5.43??C), compared to a 6-year mean of -9.04 ?? 5.59??C, in agreement with recent work by other investigators showing unusually extensive melt in 2002 and 2005. Surface-temperature variability shows a correspondence with the dry-snow facies of the ice sheet; a reduction in area of the dry-snow facies would indicate a more-negative mass balance. Surface-temperature variability generally increased during the study period and is most pronounced in the 2005 melt season; this is consistent with surface instability caused by air-temperature fluctuations. Copyright 2006 by the American Geophysical Union.

Hall, D. K.; Williams, Jr. , R. S.; Casey, K. A.; DiGirolamo, N. E.; Wan, Z.

2006-01-01

36

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

37

AN EXPERIMENTAL STUDY OF MELTING VERTICAL ICE CYLINDERS IN COLD WATER  

Microsoft Academic Search

Short vertical ice cylinders were melted in quiescent ambient cold fresh water to visualize the melting and the resulting convective motions. Melting rates and heat transfer parameters were also determined. The cylinder penetrated the water surface, to model the melting of floating surface ice. Melting experiments over the ambient medium temperature range, t ?, from 2 to 7°C covered the whole

BENJAMIN GEBHART; T. WANG

1982-01-01

38

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

39

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

40

Rapid bottom melting widespread near Antarctic Ice Sheet grounding lines.  

PubMed

As continental ice from Antarctica reaches the grounding line and begins to float, its underside melts into the ocean. Results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed. The melting rate is positively correlated with thermal forcing, increasing by 1 meter per year for each 0.1 degrees C rise in ocean temperature. Where deep water has direct access to grounding lines, glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature. PMID:12065835

Rignot, Eric; Jacobs, Stanley S

2002-06-14

41

Ice Melting Characteristics of an Ice Thermal Storage Container Filled with Harvest Ice  

NASA Astrophysics Data System (ADS)

This paper deals with ice melting characteristics of an ice thermal storage container filled up with harvest ice. The change in outlet water temperature and its stability over time are examined when the position of the inlet pipe in the ice thermal storage container, the time taken for the water in the container to be replaced once, and the method of spraying water into the container are changed. The following results were obtained for the harvest ice thermal storage container : (1) Outlet water temperature in the ice thermal storage container is influenced by the position of the inlet pipe; that is, when the water from the inlet pipe flows slowly through the ice packed bed, the lower outlet water temperature is able to be supplied to a heat exchanger for a longer time. (2) When water is sprayed from above the container, the outlet water temperature change against the nondimensional time is represented by one correlation curve even when the water replacing once in the container is changed, and the outlet temperature stays under 2°C up to a nondimensional time of about 0.8. (3) When water is sprayed from above the container, total heat release rate is also represented by one line. (4) Period of time during which the outlet temperature remains under 2°C is proportional to the time taken for the water in the container to be replaced once for three types of ice thermal storage in this experiment are used. (5) Heat transfer coefficient and modified Stanton number defined by volume flow rate are useful parameter for representation of ice melting characteristics.

Ohira, Akiyoshi; Yanadori, Michio

42

Surface melting on Larsen Ice Shelf, Antarctica  

Microsoft Academic Search

The disintegration of Larsen A and B ice shelves in 1995 and 2002, respectively, was preceded by intense surface melting during the summer of ice-shelf collapse and previous summers. To understand the transition of the ice-shelf surface from dry to wet conditions, we developed a one-dimensional model, describing the mass, heat and force balances of water and firn within the

Olga Sergienko; Douglas R. Macayeal

2005-01-01

43

Diamond stabilization of ice multilayers at human body temperature  

Microsoft Academic Search

Diamond is a promising material for wear-resistant medical coatings. Here we report a remarkable increase in the melting point of ice resting on a diamond (111) surface modified with a submonolayer of Na+ . Our molecular dynamics simulations show that the interfacial ice bilayer melts at a temperature 130K higher than in free ice, and relatively thick ice films (

Alexander D. Wissner-Gross; Efthimios Kaxiras

2007-01-01

44

Sea-ice melting processes inferred from ice–upper ocean relationships in the Ross Sea, Antarctica  

Microsoft Academic Search

Sea-ice melting processes are inferred from various summer sea-ice and upper ocean data obtained in the Ross Sea in January 1999. Using spatially (30 km) averaged continuous data, an ice concentration–water temperature plot (CT-plot) shows that the temperature at a depth of ?7 m increases as ice concentration decreases in the ice interior region. The CT-plot is explained by a

Sohey Nihashi; Kay I. Ohshima; Martin O. Jeffries; Toshiyuki Kawamura

2005-01-01

45

Relationship between the upper ocean and sea ice during the Antarctic melting season  

NASA Astrophysics Data System (ADS)

During the Antarctic ice-melting season, high-resolution sea ice data were collected with the video monitoring system aboard the icebreaker Shirase along with the monitoring of temperature and salinity in the upper ocean. On the basis of these data, relationships among sea ice concentration, temperature, and salinity are investigated. In the ice interior region away from the ice-free ocean, ice concentration is negatively correlated with temperature and positively correlated with salinity for the spatially averaged data, which suggests that the local balances of heat and salt nearly hold in a bulk area. At the ice margin, ice concentration is negatively correlated with both temperature and salinity, suggesting that the local balances are overwhelmed by the effects of ice advection. The expendable bathythermograph profiles at the ice margin also show that a considerable amount of sea ice was advected into the ice-free ocean and subsequently melted there. It is pointed out that a polynya works as an "ice-melting factory" in summer; it absorbs solar radiation during the period of opening, and then melts the ice advected there. Prom a heat budget analysis and ocean structure in the melting season, we propose a simple ice-upper ocean coupled model in which sea ice melts on the bottom and lateral faces with the heat source supplied to the open water area by solar radiation. The relations among ice concentration, temperature, and salinity derived from the model are consistent with the observed relations. The analytic solution for the no lateral melting case shows that the concentration-temperature relation converges to a certain asymptotic curve with time, which explains that the temperature-concentration plot shows a similar relation for any region. Dependence of the relations among ice concentration, temperature, and salinity on the spatial scale is also discussed.

Ohshima, Kay I.; Yoshida, Kazumasa; Shimoda, Haruhito; Wakatsuchi, Masaaki; Endoh, Tatsuo; Fakuchi, Mitsuo

1998-04-01

46

Spontaneous melting of ice in a CaCl 2 solution  

Microsoft Academic Search

This paper is concerned with the melting of a vertical ice plate into a calcium chloride aqueous solution inside a square\\u000a cavity. The initial temperatures of the ice and the liquid are ?5°C and 0°C respectively, and the initial solute (i.e. CaCl2) concentration of the liquid is 20wt% at the beginning of melting. The ice melts spontaneously with decreasing temperature

Masahiro Sugawara; Makoto Tago

1999-01-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

48

An estimate of the impact of trapped melt ponds on sea ice thinning  

NASA Astrophysics Data System (ADS)

Melt ponds form on Arctic sea ice during the melting season and their presence affects the heat and mass balance of the ice cover. Towards the end of the melt season melt ponds cover up to 50% of the sea ice area decreasing the value of the surface albedo by up to 20%. The dramatic impact of melt ponds on the albedo feedback mechanism for sea ice melt has been demonstrated in previous studies. Here, we focus on the refreezing of melt ponds. As the ponds freeze from above, they gradually release latent heat that inhibits basal ice growth. The refreezing process can take up to three months. Freezing of the melt pond comes to an halt if the pond's freezing point reaches the air temperature since the Stefan condition for sea ice growth is not met anymore. Since the ice in presence of melt pond will stay thinner and flatter for longer, the areas where ponds are present are likely location for pond formation in the subsequent years. The presence of a pond trapped in the ice delays significantly the sea ice growth at locations where melt ponds form. The potential volume loss of sea ice per year in the Arctic considering a melt pond cover of 20% is up to 1000 km3 without considering the presence of snow. Within the ASBO (Arctic Synoptic Basin-wide Observations) project we have developed a model of refreezing melt ponds that uses mushy layer theory to describe the sea ice and takes account of the presence of salt in the refreezing melt pond. We use this model to investigate the rate at which melt ponds refreeze, releasing latent heat, and their impact on sea ice growth. In this work we would like to present model result with climatology input. We will give an estimate of the impact of the melt pond presence on sea ice growth in the Arctic basin.

Flocco, Daniela; Feltham, Daniel; Schroeder, David

2013-04-01

49

How does an ice block assembly melt?  

PubMed

The melting of an assembly of ice blocks contained in a vertical cylinder and under an unidirectional load was investigated. The total volume occupied by the ice blocks and the volume of ice were simultaneously measured which allowed one to determine the volume fraction of the ice in the cylinder. While the ice volume continuously decreases, sudden breakdowns of the total volume were observed. Large reorganizations of the whole assembly occur. However, the maximal volume fraction found just after a large reorganization decreased with time. In addition, the modifications of the pile structure were investigated using an x-ray tomography imaging before and after one collapse. As the packing is better ordered along the walls, we suggest that the motion of the piston is governed by the layer of ice blocks located along the container wall. This layer was modeled by a two-dimensional assembly of disks. The model supports the idea that the geometrical frustrations explain the dynamics of the successive reorganization due to the shrinkage of the grains. Finally, numerical simulations allow one to conclude that the dynamics of the melting of the ice blocks is governed (i) by the confinement effect which induces defects in the packing and (ii) by the low friction between the ice blocks. PMID:23004753

Dorbolo, S; Ludewig, F; Vandewalle, N; Laroche, C

2012-05-24

50

How does an ice block assembly melt?  

NASA Astrophysics Data System (ADS)

The melting of an assembly of ice blocks contained in a vertical cylinder and under an unidirectional load was investigated. The total volume occupied by the ice blocks and the volume of ice were simultaneously measured which allowed one to determine the volume fraction of the ice in the cylinder. While the ice volume continuously decreases, sudden breakdowns of the total volume were observed. Large reorganizations of the whole assembly occur. However, the maximal volume fraction found just after a large reorganization decreased with time. In addition, the modifications of the pile structure were investigated using an x-ray tomography imaging before and after one collapse. As the packing is better ordered along the walls, we suggest that the motion of the piston is governed by the layer of ice blocks located along the container wall. This layer was modeled by a two-dimensional assembly of disks. The model supports the idea that the geometrical frustrations explain the dynamics of the successive reorganization due to the shrinkage of the grains. Finally, numerical simulations allow one to conclude that the dynamics of the melting of the ice blocks is governed (i) by the confinement effect which induces defects in the packing and (ii) by the low friction between the ice blocks.

Dorbolo, S.; Ludewig, F.; Vandewalle, N.; Laroche, C.

2012-05-01

51

Modeling the summertime evolution of sea-ice melt ponds  

Microsoft Academic Search

We present a mathematical model describing the summer melting of sea ice. We simulate the evolution of melt ponds and determine area coverage and total surface ablation. The model predictions are tested for sensitivity to the melt rate of unponded ice, enhanced melt rate beneath the melt ponds, vertical seepage, and horizontal permeability. The model is initialized with surface topographies

M. Lüthje; D. L. Feltham; P. D. Taylor; M. G. Worster

2006-01-01

52

Ice, Ice, Baby: Examining the Causes and Effects of Melting Ice Formations in Antarctica  

NSDL National Science Digital Library

In this lesson, students learn about the causes and effects of the melting ice formations in Antarctica. They are directed to examine the causes and effects of melting ice shelves and perform an experiment to learn how melting ice affects water levels. As part of an associated activity, students research different aspects of the topic and create a news special. Objectives, a materials list, procedures, discussion questions, and extension activities are provided. Academic content standards and links to additional information are also included.

53

Abrupt grain boundary melting in ice  

Microsoft Academic Search

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

Latchezar Benatov; J. S. Wettlaufer; Larry Wilen

2004-01-01

54

A PIV and CFD Analysis of Natural Convection Ice Melting  

Microsoft Academic Search

An experimental (PIV) and numerical (CFD) analysis of the melting of a vertical cylindrical ice cube in water at different temperatures has been carried out. The objective was to examine the effects of the density inversion of water, which occurs at 4°C approximately. In this experiment a PIV analysis was carried out and vector maps of the flow field were

T J Scanlon; M T Stickland; M Lacombe

55

Islands uncovered by melting polar ice  

NASA Astrophysics Data System (ADS)

Thawing glaciers north of Norway's Svalbard archipelago have revealed at least two unmapped and unclaimed islands, one roughly the size of a basketball court, according to a 20 August Reuters report. In addition, information released in August by the U.S. National Snow and Ice Data Center indicated that with one month left in the melting season, Arctic sea ice is already below the record minimum. "Reductions of snow and ice are happening at an alarming rate," said Norwegian Environment Minister Helen Bjoernoy. She suggested that these observations may indicate that the loss of sea ice is perhaps accelerating faster than predicted by the Intergovernmental Panel on Climate Change, which warned in February that summer sea ice could almost vanish by the end of this century.

Kumar, Mohi

56

Sub-ice shelf circulation and basal melting of the Fimbul Ice Shelf  

NASA Astrophysics Data System (ADS)

The Fimbul Ice Shelf is the largest of the ice shelves in Dronning Maud Land. Due to a narrow and some places non-existent continental shelf, the ice shelves in Dronning Maud Land are situated close to the Warm Deep Water. The Antarctic Slope Front separates the Warm Deep Water from the ice shelves and complicated exchange processes working across this front controls the melting of the Fimbul Ice Shelf and the other ice shelves in Dronning Maud Land. Here we will present analysis of unique data from the Dronning Maud Land coastal zone, as well as preliminary results from the 2009/2010 field work on the Fimbul Ice Shelf. In 2008 eight elephant seals equipped with CTD data loggers collected hydrographic data in the Dronning Maud Land coastal zone from February through October. Analysis of these data shows that overturning of the Antarctic Slope Front is the main process exchanging heat into the ice shelf cavities. This overturning together with an onshore surface Ekman flow leads to a seasonal cycle in the salinity of the coastal water masses, while glacial melting sea ice formation has little influence. During the 2009/2010 field season on the Fimbul Ice Shelf glaciological and oceanographic data were collected. We will show preliminary results of ice flow, ice thickness and basal melting measured using stake nets and phase sensitive radar. Oceanographic data were collected through three hot water drilled access holes in the ice shelf. These data show a water column with temperatures close to the surface freezing point over most of the water column. Relatively warmer water was observed near the bottom on one of the CTD stations. Maximum observed temperature is -1.57 °C. We compare the sub iceshelf hydrography with the hydrography observed by the elephant seals near the ice front in an attempt to reveal the sub ice shelf circulation. We also compare estimated melt rates from the oceanographic data with melt rates estimated with the phase sensitive radar and stake nets. Our primary goal for the project is to estimate the mass balance of the Fimbul Ice Shelf, and preliminary mass balance estimates will be presented.

Nost, Ole Anders

2010-05-01

57

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

58

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

2012-06-08

59

Onset of convective instabilities in under-ice melt ponds  

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

60

Experimental Investigation and Theoretical Modeling of Ice-Melting Processes  

Microsoft Academic Search

In this article, ice-melting phenomena have been investigated experimentally. The geometrical shapes studied were cylindrical and right circular truncated cones. Ice blocks were left floating on a large water container in order to be melted. The rate of melting was measured experimentally. A relation was developed for the remaining mass of the ice in respect to time, considering the turbulent

R. Hosseini; M. Rahaeifard

2009-01-01

61

Modelling of melt ponds on a sea ice floe  

NASA Astrophysics Data System (ADS)

During winter the ocean surface at the poles freezes over to form sea ice. Sea ice floats on the ocean surface and has a matrix structure caused by the rejection of salts during freezing. In the summer sea ice melts at its surface creating melt ponds. An accurate estimate of the fraction of the upper sea-ice surface covered in melt ponds during the summer melt season is essential for a realistic estimate of the albedo for global climate models. We present a sea ice model that simulates the two-dimensional (areal) evolution of melt ponds on an Arctic sea-ice surface. Water transport across and through the sea-ice surface is described by the major hydraulic processes believed to be present. Thermodynamic processes are modelled using heat flux equations. Lateral and vertical melt water transport is described by Darcy's Law. The model simulates a section of a sea ice floe where edge effects such as the presence of leads are neglected. The model consists of a grid of cells, each of which can be in one of four possible configurations: snow covered ice; bare ice; melt pond covered ice or open water. A cluster of adjacent cells containing melt water may be considered to have formed a melt pond. The model is initialised with ice topographies that represent either first-year or multi-year sea ice, these are reconstructed from ice thickness data using standard statistical methods; in this way characteristic examples of both first-year ice and multi-year ice can be constructed. The roughness of the ice and snow surfaces were altered and the sensitivity of the model to the initial data was tested. First-year ice and multi-year ice simulations agreed with observed differences in individual pond size and depth. Sensitivity studies showed that pond fraction is most sensitive to mean initial snow depth in first-year ice simulations and reduction of ice permeability all cases.

Scott, F.; Feltham, D.

2009-04-01

62

The pressure melting of ice under a body with flat base  

SciTech Connect

One of the anomalous thermodynamic properties of water is that the melting point of ice decreases as the pressure increases. This behavior was discovered independently by Kirchhoff and Thomson. It inspired Reynolds to speculate that the pressure-melting of ice and snow might be responsible for the low coefficient of friction experienced during skating and skiing. According to him, the pressure applied by the skate on the ice surface would cause superficial melting, which in turn would lubricate the relative motion between skate and ice. Although the pressure-melting phenomenon received some attention from early tribologists, this interest decreased after Bowden and Hughes' work, which showed that the superficial melting under the skate is due to friction (viscous dissipation) in the water film. In this note the authors consider a different fundamental aspect of the pressure-melting of ice, namely the indentation caused by a flat solid that is pressed against a block of ice. Unlike in the work referenced above, there is no lateral motion between the solid body and the ice block. The only motion that occurs is the normal progress that the solid body makes into the ice. This motion is made possible by the melting of the ice situated in front of the body. In this way, the pressure melting process is related to the contact melting process that occurs when a temperature difference ({Delta}T) is maintained between the solid body and the phase-change material.

Bejan, A. (Duke Univ., Durham, NC (United States)); Tyvand, P.A.

1992-05-01

63

Cool thermal discharge obtained with air flowing over melting ice by complete removal of melt  

Microsoft Academic Search

A new device of ice melting with performance improved has been developed by complete removal of melt to produce chilled air during on-peak power consumption. Energy equations have been derived, from the integral boundary-layer analysis, for estimating the thickness of the ice melted and the thermal penetration distance in ice layer region with convective boundary condition on free surface. Numerical

C. D. Ho; H. M. Yeh; W. P. Wang; J. K. Wang

2000-01-01

64

Transmission of sunlight through melting Arctic sea ice (Invited)  

Microsoft Academic Search

The transmission of solar radiation through sea ice affects internal warming and melting of the ice cover, contributes heat to the ocean, and determines light availability for primary productivity within and beneath the ice cover. In situ measurements of the spectral extinction of shortwave radiation in sea ice were made for both bare and ponded multiyear ice and bare first-year

B. Light; D. K. Perovich; T. C. Grenfell; K. Runciman

2009-01-01

65

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

66

Past and Future Vulnerability of the West Antarctic Ice Sheet to Surface Ice-Shelf Melt  

NASA Astrophysics Data System (ADS)

New sediment core records from the Ross Embayment (ANDRILL) imply dramatic, orbitally paced variability of the West Antarctic Ice Sheet (WAIS) over the last five million years (Naish et al., 2009). Time-continuous model simulations of the coupled Antarctic ice sheet-shelf system over this interval are capable of simulating this implied WAIS variability, including sudden, orbitally triggered retreats and subsequent regrowth of nearly all marine ice in West Antarctica. In the model, simulated episodes of WAIS retreat are common during the warm Pliocene, but they also occur during some of the strongest interglacials of the colder Pleistocene. Clearly, the magnitude and millennial timescale of simulated WAIS retreat in response to relatively modest past forcing hints at the potential future vulnerability of the ice sheet. In previous long-term simulations (Pollard and DeConto, 2009), the ice-sheet model was driven by parameterized climatologies (surface temperature, precipitation, sea level, and oceanic sub-ice shelf melt), scaled mainly to deep- sea benthic oxygen isotope records. The model WAIS was found to be highly sensitive to sub-ice-shelf melt rates, with modest increases (~2 m/yr) capable of triggering sudden grounding-line retreat and dynamic thinning in the Ross, Weddell and Amundsen Sea sectors - largely in response to reduced ice-shelf buttressing. Here we present new ice sheet-shelf simulations of specific Pliocene and Pleistocene interglacials, using atmospheric climatologies from a new high-resolution Regional Climate Model. The results show that in addition to increased sub-ice-shelf melt rates, surface melting on ice-shelf surfaces could have been a contributing factor to past episodes of WAIS retreat, providing a simple explanation (orbital forcing of Antarctic surface air temperatures) for the orbital pacing of the events. Simulated increases in surface ice-shelf melt rates in response to elevated greenhouses gas levels are also evaluated, to assess their influence on WAIS retreat and sea-level rise in the near and long-term future.

DeConto, R.; Pollard, D.; Kowalewski, D. E.

2011-12-01

67

Ocean circulation and fronts as related to ice melt-back in the Chukchi Sea  

Microsoft Academic Search

In summer at the edge of the retreating ice pack in the Chukchi Sea, a sharp temperature and salinity front is formed as the result of ice melt by warm surface water from the south. Beneath this front another front is present, formed from the juxtaposition of the resident winter bottom water under the ice and a water transitional between

Robert G. Paquette; Robert H. Bourke

1981-01-01

68

The melting history of the late Pleistocene Antarctic ice sheet  

Microsoft Academic Search

Spatial and temporal variations in the sea levels of the past 20,000 years around the globe place constraints on the melting history of the major late Pleistocene ice sheets. The Antarctic ice sheets provided a significant contribution to the sea-level rise at a rate that was approximately synchronous with the melting of the Laurentide ice sheet, except for the interval

M. Nakada; K. Lambeck

1988-01-01

69

Summer and Fall Sea Ice Processes in the Amundsen Sea: Bottom melting, surface flooding and snow ice formation  

NASA Astrophysics Data System (ADS)

Two ice mass balance buoys were deployed on the Amundsen Sea, Antarctica, ice pack near January 1, 2011. Below freezing air and snow temperatures and sea ice and seawater temperatures at the freezing point at this time indicated that summer melt had not yet commenced. Over the next two months, however, while snow depths changed by less than 0.1m, ice thickness decreased, from bottom melting, by 0.9-1.0m. As snow temperature records did not show temperatures ever reaching the melting point, no surface melt was recorded during the summer period and the small snow depth changes were presumed to occur by consolidation or wind scouring. Water temperatures above the freezing point caused the observed bottom melting from mid January to late February. During the ice loss periods, progressive flooding by sea water at the base of the snow pack was recorded by temperature sensors, showing an increase in the depth of flooded snow pack of 0.4m by the end of the summer period in late February. We hypothesize that progressive flooding of the surface snow pack gives a mechanism for nutrient replenishment in these upper layers, and continuous high algal growth can therefore occur in the flooded snow layer during summer. An underice radiometer recorded light transmission through the ice and snow at selective wavelengths sensitive to chlorophyll. These radiometric results will be presented to examine this algal growth hypothesis. This flooded layer then refroze from the top down into snow ice as air temperatures dropped during March and April, showing that the layer had refrozen as snow ice on the top surface of the ice. Refreezing of the flooded layer gives an ice growth mechanism at the end of summer of 0.2 m to 0.4m of new ice growth over the majority of the ice pack. The snow ice growth in areas covered with pack ice gives salt fluxes commensurate with new ice growth in the autumn expansion of the ice edge over open water. These high salt fluxes therefore represent a marked contrast to the lower values of salt flux under the Arctic summer ice pack where salt fluxes are only associated with new ice forming in fall over a smaller percentage of the area than the widespread snow ice growth in the Antarctic pack ice zone.

Ackley, S. F.; Perovich, D. K.; Weissling, B.; Elder, B. C.

2011-12-01

70

Response of Southern Ocean circulation to global warming may enhance basal ice shelf melting around Antarctica  

Microsoft Academic Search

We investigate the large-scale oceanic features determining the future ice shelf–ocean interaction by analyzing global warming\\u000a experiments in a coarse resolution climate model with a comprehensive ocean component. Heat and freshwater fluxes from basal\\u000a ice shelf melting (ISM) are parameterized following Beckmann and Goosse [Ocean Model 5(2):157–170, 2003]. Melting sensitivities to the oceanic temperature outside of the ice shelf cavities

Tore Hattermann; Anders Levermann

2010-01-01

71

New Equations for the Sublimation Pressure and Melting Pressure of H2O Ice Ih  

NASA Astrophysics Data System (ADS)

New reference equations, adopted by the International Association for the Properties of Water and Steam (IAPWS), are presented for the sublimation pressure and melting pressure of ice Ih as a function of temperature. These equations are based on input values derived from the phase-equilibrium condition between the IAPWS-95 scientific standard for thermodynamic properties of fluid H2O and the equation of state of H2O ice Ih adopted by IAPWS in 2006, making them thermodynamically consistent with the bulk-phase properties. Compared to the previous IAPWS formulations, which were empirical fits to experimental data, the new equations have significantly less uncertainty. The sublimation-pressure equation covers the temperature range from 50 K to the vapor-liquid-solid triple point at 273.16 K. The ice Ih melting-pressure equation describes the entire melting curve from 273.16 K to the ice Ih-ice III-liquid triple point at 251.165 K. For completeness, we also give the IAPWS melting-pressure equation for ice III, which is slightly adjusted to agree with the ice Ih melting-pressure equation at the corresponding triple point, and the unchanged IAPWS melting-pressure equations for ice V, ice VI, and ice VII.

Wagner, Wolfgang; Riethmann, Thomas; Feistel, Rainer; Harvey, Allan H.

2011-12-01

72

Haline circulation induced by formation and melting of sea ice  

Microsoft Academic Search

A three-dimensional, coupled ice-ocean model is developed, and basic numerical experiments for examining effects of freshwater budget associated with formation and melting of sea ice on the thermohaline circulation are performed. Motion of sea ice affects the freshwater budget in two ways. First, if horizontally transports freshwater in the form of sea ice. Second, it alters the conditions of sea

Hiroyasu Hasumi; Nobuo Suginohara

1995-01-01

73

Melt season duration on Canadian Arctic ice caps, 2000-2004  

NASA Astrophysics Data System (ADS)

The extent and duration of summer melt on ice caps in the Queen Elizabeth Islands (QEI), Nunavut, Canada, in 2000-2004 were mapped using enhanced resolution QuikSCAT (QSCAT) scatterometer images. The mean melt duration depends mainly on surface elevation and distance from Baffin Bay. Over most ice caps, inter-annual variations in melt duration and the variation in melt duration with elevation are closely related to variations in the July 500 hPa height over the QEI. Pressure-related variability in the vertical gradient of near-surface air temperature appears to be a major control on the inter-annual variations in average melt duration.

Wang, L.; Sharp, M. J.; Rivard, B.; Marshall, S.; Burgess, D.

2005-10-01

74

Picosecond temperature and pressure jumps in ice  

NASA Astrophysics Data System (ADS)

A sensitive picosecond thermometer and manometer for hydrogen-bonded systems is demonstrated. The technique is applied for temperature jumps in ice by the help of subpicosecond pulses in the mid-infrared. The hydroxilic stretching vibrations (OH or OD) are applied for energy deposition and for the fast and sensitive spectral probing of local structure and thermodynamic condition. The method is verified in isotopically mixed ice at 200 K and ambient pressure. The transient data show that the local quasi-equilibrium in ice builds up within 25 ps allowing definition of a local temperature. Measurements performed close to the melting point provide no evidence for melting after energy deposition, but for substantial superheating of the ice lattice to 300 K that persists over the monitored time interval of 1.3 ns.

Schmeisser, Marcus; Thaller, Andy; Iglev, Hristo; Laubereau, Alfred

2006-06-01

75

Effects of a melted greenland ice sheet on climate, vegetation, and the cryosphere  

Microsoft Academic Search

This paper investigates the possible implications for the earth-system of a melting of the Greenland ice-sheet. Such a melting is a possible result of increased high latitude temperatures due to increasing anthropogenic greenhouse gas emissions. Using an atmosphere-ocean general circulation model (AOGCM), we investigate the effects of the removal of the ice sheet on atmospheric temperatures, circulation, and precipitation. We

Daniel J. Lunt; Nathalie de Noblet-Ducoudré; Sylvie Charbit

2004-01-01

76

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.

Chen, Jing-Yin; Yoo, Choong-Shik

2011-01-01

77

Modeling sea level change in response of ice sheet melting  

NASA Astrophysics Data System (ADS)

Variations in regional and global sea level are caused by different mechanisms. A major contributor is the change of temperature of the ocean. Furthermore, there are also changes in sea level caused by ocean mass variations, mostly due to the mass loss of mountain glaciers, and major ice sheets in Greenland and the West Antarctic. We study relative sea level change including the changes originating from the mass loss of the major ice sheets and of the glaciers in Alaska. The oceanic change is modeled with the finite element sea-ice ocean model. The gravitational sea level response to the surface loading are computed using Green's functions. Furthermore, the regional changes caused by the viscous Earth response to past glacial loading are taken into account. In our study, we apply realistic melting rates and compare our results to time series from tide gauges in the North Atlantic. The modeled relative sea level change, without applying the melt scenarios, compares reasonably well with tide gauge records in different coastal regions in the North Atlantic. Including the mass loss of the major ice sheets and of the glaciers in Alaska into the ocean model further improves modeled relative sea level change. Its correlation with tide gauges increases from around 0.7 to above 0.8.

Brunnabend, Sandra; Schröter, Jens; Kusche, Jürgen; Rietbroek, Roelof; Ivchenko, Vladimir

2013-04-01

78

Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation  

NASA Astrophysics Data System (ADS)

This study uses the eddy correlation technique to examine fluxes across the ice-water interface. Temperature eddy correlation systems were used to determine rates of ice melting and freezing, and O2 eddy correlation systems were used to examine O2 exchange rates as driven by biological and physical processes. The research was conducted below 0.7 m thick sea ice in mid March 2010 in a southwest Greenland fjord and revealed low average rates of ice melt amounting to a maximum of 0.80 ± 0.09 mm d-1 (SE, n=31). The corresponding calculated O2 flux associated with release of O2 depleted melt water was less than 13 % of the average daily O2 respiration rate. Ice melt and insufficient vertical turbulent mixing due to low current velocities caused periodic stratification immediately below the ice. This prevented the determination of fluxes during certain time periods, amounting to 66 % of total deployment time. The identification of these conditions was evaluated by examining the velocity and the linearity and stability of the cumulative flux. The examination of unstratified conditions through velocity and O2 spectra and their cospectra revealed characteristic fingerprints of well-developed turbulence. From the observed O2 fluxes, a photosynthesis/irradiance curve was established by least-squares fitting. This relation showed that light limitation of net photosynthesis began at 4.2 ?mol photons m-2 s-1, and that the algal communities were well-adapted to low-light conditions as they were light saturated for 75 % of the day during this early spring period. However, the sea ice associated microbial and algal community was net heterotrophic with a daily gross primary production of 0.69 ± 0.02 mmol O2 m-2 d-1 (SE, n=4) and a respiration rate of -2.13 mmol O2 m-2 d-1 (no SE, see text for details) leading to a net primary production of -1.45 ± 0.02 mmol O2 m-2 d-1 (SE, n=4). Modeling the observed fluxes allowed for the calculation of fluxes during time periods when no O2 fluxes were extracted. This application of the eddy correlation technique produced high temporal resolution O2 fluxes and ice melt rates that were measured without disturbing the environmental conditions while integrating over a large area of approximately 50 m2 which encompassed the highly variable activity and spatial distributions of sea ice algal communities.

Long, M. H.; Koopmans, D.; Berg, P.; Rysgaard, S.; Glud, R. N.; Søgaard, D. H.

2011-11-01

79

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

80

Ice core evidence for extensive melting of the greenland ice sheet in the last interglacial.  

PubMed

Evidence from ice at the bottom of ice cores from the Canadian Arctic Islands and Camp Century and Dye-3 in Greenland suggests that the Greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka (thousand years ago), in contrast to earlier interpretations. The presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed. However, the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller. Ice texture, gas content, and other evidence also suggest that the basal ice at each drill site is superimposed ice, a type of ice typical of the early growth stages of an ice cap or ice sheet. If the present-day ice masses began their growth during the last interglacial, the ice sheet from the earlier (Illinoian) glacial period must have competely or largely melted during the early part of the same interglacial period. If such melting did occur, the 6-meter higher-than-present sea level during the Sangamon cannot be attributed to disintegration of the West Antarctic ice sheet, as has been suggested. PMID:17731883

Koerner, R M

1989-05-26

81

A model of melt pond evolution on sea ice  

Microsoft Academic Search

A one-dimensional, thermodynamic, and radiative model of a melt pond on sea ice is presented that explicitly treats the melt pond as an extra phase. A two-stream radiation model, which allows albedo to be determined from bulk optical properties, and a parameterization of the summertime evolution of optical properties, is used. Heat transport within the sea ice is described using

P. D. Taylor; D. L. Feltham

2004-01-01

82

The Radiation Budget of Sea Ice during the Springtime Melt  

NASA Astrophysics Data System (ADS)

The energy budget of sea ice in the melt season has significant spatial variability at scales much smaller than a model cell or satellite pixel. This variability results primarily from albedo variation caused by different surface characteristics such as melt ponds of varying depth, snow of varying thickness, and sediment content within the snow, ice, or surface water. There may also be variation in the longwave energy emitted by the surface, mostly resulting from temperature variations. Understanding this variability and how it affects the progress of the melt is necessary for improving energy-budget parameterizations in models or retrievals from satellite sensors. To gain a better understanding of this variability, we have developed a radiation sled that quickly measures the upwelling and downwelling broadband longwave and shortwave radiation, along with the spectral albedo. In addition, it photographs the sky and surface at the time of the measurement, measures the surface temperature with a narrowband infrared thermometer, and records the measurement location and the air temperature and humidity. The sled is set up to allow many measurements in an area to be made during a short period by one or two people. From this we can see the large scale effect of small scale variations in the surface energy budget. This sled was deployed for the first time during the first two weeks of June this year. Data were collected every 5 m along a 200-m line located on fast ice about 3 km southwest of Point Barrow, Alaska. Observations were made around local noon each day from 5 to 13 June, when the progression of the melt forced us to bring the instruments back to land. During most of the observation period, we had refreezing of melt ponds that were prevalent at the start. Midway through, there was some light snowfall, before melt resumed on the last days. The line included a variety of surfaces, including bare ice with a scattering layer, melt ponds of varying depths with a refrozen layer on the surface, and deep, sediment-laden melt ponds that remained open throughout the period. Broadband albedos varied from 0.15 to 0.73, with temporal variations at individual locations of about 0.2 to 0.25. Some locations showed almost no temporal variation, however, so that while the large scale albedo increased as ponds refroze and new snow fell, some areas were unaffected, allowing melt to continue in those areas. The net radiation budget was always positive (net gain by the ice) during our measurements, even on days when the surface remained dry during the midday hours. Net absorption ranged from 75 to 530 W m-2. Spatial variability in the net radiation was dominated by spatial variability of albedo, while temporal variability was dominated by temporal variability of incoming solar radiation, which varied from 265 to 925 W m-2. From these data, the role that clouds and surface temporal and spatial variability play in affecting the progression and spatial distribution of melt will be examined.

Hudson, S. R.; Granskog, M.; Elder, B. C.; Perovich, D. K.; Petrich, C.; Nicolaus, M.

2011-12-01

83

The Radiation Budget of Sea Ice during the Springtime Melt  

NASA Astrophysics Data System (ADS)

The energy budget of sea ice in the melt season has significant spatial variability at scales much smaller than a model cell or satellite pixel. This variability results primarily from albedo variation caused by different surface characteristics such as melt ponds of varying depth, snow of varying thickness, and sediment content within the snow, ice, or surface water. There may also be variation in the longwave energy emitted by the surface, mostly resulting from temperature variations. Understanding this variability and how it affects the progress of the melt is necessary for improving energy-budget parameterizations in models or retrievals from satellite sensors. To gain a better understanding of this variability, we have developed a radiation sled that quickly measures the upwelling and downwelling broadband longwave and shortwave radiation, along with the spectral albedo. In addition, it photographs the sky and surface at the time of the measurement, measures the surface temperature with a narrowband infrared thermometer, and records the measurement location and the air temperature and humidity. The sled is set up to allow many measurements in an area to be made during a short period by one or two people. From this we can see the large scale effect of small scale variations in the surface energy budget. This sled was deployed for the first time during the first two weeks of June 2011. Data were collected every 5 m along a 200-m line located on fast ice about 3 km southwest of Point Barrow, Alaska. Observations were made around local noon each day from 5 to 13 June, when the progression of the melt forced us to bring the instruments back to land. During most of the observation period, we had refreezing of melt ponds that were prevalent at the start. Midway through, there was some light snowfall, before melt resumed on the last days. The line included a variety of surfaces, including bare ice with a scattering layer, melt ponds of varying depths with a refrozen layer on the surface, and deep, sediment-laden melt ponds that remained open throughout the period. Broadband albedos varied from 0.15 to 0.73, with temporal variations at individual locations of about 0.2 to 0.25. Some locations showed almost no temporal variation, however, so that while the large scale albedo increased as ponds refroze and new snow fell, some areas were unaffected, allowing melt to continue in those areas. The net radiation budget was always positive (net gain by the ice) during our measurements, even on days when the surface remained dry during the midday hours. Net absorption ranged from 75 to 530 W m-2. Spatial variability in the net radiation was dominated by spatial variability of albedo, while temporal variability was dominated by temporal variability of incoming solar radiation, which varied from 265 to 925 W m-2. From these data, the role that clouds and surface temporal and spatial variability play in affecting the progression and spatial distribution of melt will be examined.

Hudson, S.; Granskog, M. A.; Elder, B. C.; Perovich, D. K.; Petrich, C.; Nicolaus, M.

2012-04-01

84

Pine Island glacier ice shelf melt distributed at kilometre scales  

NASA Astrophysics Data System (ADS)

By thinning and accelerating, West Antarctic ice streams are contributing about 10% of the observed global sea level rise. Much of this ice loss is from Pine Island Glacier, which has thinned since at least 1992, driven by changes in ocean heat transport beneath its ice shelf and retreat of the grounding line. Details of the processes driving this change, however, remain largely elusive, hampering our ability to predict the future behaviour of this and similar systems. Here, a Lagrangian methodology is developed to measure oceanic melting of such rapidly advecting ice. High-resolution satellite and airborne observations of ice surface velocity and elevation are used to quantify patterns of basal melt under the Pine Island Glacier ice shelf and the associated adjustments to ice flow. At the broad scale, melt rates of up to 100 m yr-1 occur near the grounding line, reducing to 30 m yr-1 just 20 km downstream. Between 2008 and 2011, basal melting was largely compensated by ice advection, allowing us to estimate an average loss of ice to the ocean of 87 km3 yr-1, in close agreement with 2009 oceanographically constrained estimates. At smaller scales, a network of basal channels typically 500 m to 3 km wide is sculpted by concentrated melt, with kilometre-scale anomalies reaching 50% of the broad-scale basal melt. Basal melting enlarges the channels close to the grounding line, but farther downstream melting tends to diminish them. Kilometre-scale variations in melt are a key component of the complex ice-ocean interaction beneath the ice shelf, implying that greater understanding of their effect, or very high resolution models, are required to predict the sea-level contribution of the region.

Dutrieux, P.; Vaughan, D. G.; Corr, H. F. J.; Jenkins, A.; Holland, P. R.; Joughin, I.; Fleming, A. H.

2013-09-01

85

Pine Island Glacier ice shelf melt distributed at kilometre scales  

NASA Astrophysics Data System (ADS)

By thinning and accelerating, West Antarctic ice streams are contributing about 10% of the observed global sea level rise. Much of this ice loss is from Pine Island Glacier, which has thinned since at least 1992, driven by changes in ocean heat transport beneath its ice shelf and retreat of the grounding line. Details of the processes driving this change, however, remain largely elusive, hampering our ability to predict the future behaviour of this and similar systems. Here, a Lagrangian methodology is developed to measure oceanic melting of such rapidly advecting ice. High-resolution satellite and airborne observations of ice surface velocity and elevation are used to quantify patterns of basal melt under the Pine Island Glacier ice shelf and the associated adjustments to ice flow. At the broad scale, melt rates of up to 100 m yr-1 occur near the grounding line, reducing to 30 m yr-1 just 20 km downstream. Between 2008 and 2011, basal melting was largely compensated by ice advection, allowing us to estimate an average loss of ice to the ocean of 87 km3 yr-1, in close agreement with 2009 oceanographically-constrained estimates. At smaller scales, a network of basal channels typically 500 m to 3 km wide is sculpted by concentrated melt, with kilometre-scale anomalies reaching 50% of the broad-scale basal melt. Basal melting enlarges the channels close to the grounding line, but farther downstream melting tends to diminish them. Kilometre-scale variations in melt are a key component of the complex ice-ocean interaction beneath the ice shelf, implying that greater understanding of their effect, or very high resolution models, are required to predict the sea-level contribution of the region.

Dutrieux, P.; Vaughan, D. G.; Corr, H. F. J.; Jenkins, A.; Holland, P. R.; Joughin, I.; Fleming, A.

2013-04-01

86

The pressure melting of ice due to an embedded cylinder  

Microsoft Academic Search

In this note the authors consider the motion of a cylinder through a block of ice. The cylinder is pushed laterally through the ice block. The ice melts over the leading portion of the cylinder, the water films acts as lubricant (flows around the cylinder), and refreezes over the trailing portion of the cylinder. A cross section through the embedded

P. A. Tyvand; A. Bejan

1992-01-01

87

Candidate Volcanic Ice-Cauldrons on Mars: Estimates of Ice Melt, Magma Volume, and Astrobiological Implications  

NASA Astrophysics Data System (ADS)

The morphological properties of two martian depressions suggest ice-cauldron formation. We conduct volumetric and calorimetric estimates showing that up to a cubic km of ice may have been removed in these depressions (melted and/or vaporized).

Levy, J. S.; Head, J. W.; Fassett, C. I.; Fountain, A. G.

2010-03-01

88

The effect of footwear sole abrasion on the coefficient of friction on melting and hard ice  

Microsoft Academic Search

Footwear sole wear by natural use or artificial abrasion either increases or decreases slip resistance on floors with and without lubricant. The objectives of this paper were to study the effect of footwear sole abrasive wear on slip resistance on ice with respect to temperature, and to compare the slip resistance of abraded soles on melting and hard ice with

Chuansi Gao; John Abeysekera; Mikko Hirvonen; Carita Aschan

2003-01-01

89

Numerical study of convection heat transfer during the melting of ice in a porous layer  

SciTech Connect

A numerical study is made of the melting of ice in a rectangular porous cavity heated from above. The Landau transformation is used to immobilize the ice-water interface, and the Darcy-Boussinesq equations are solved by a finite-difference technique. Results are analyzed in terms of the heating temperature and the aspect ratio of the cavity. A comparison is made with the case of melting from below. It was found that melting from above is more effective than melting from below when the heating temperature is between 0 and 8 C: convection arises earlier, the melting process is faster, and the total melt at steady state is thicker. The critical time for onset of convection is minimum when the upper boundary is heated at 6 C. At this heating temperature, one also obtains a maximum heat transfer rate (Nusselt number).

Zhang, X.; Nguyen, T.H. (Ecole Polytechnique de Montreal, Quebec (Canada). Dept. of Mechanical Engineering)

1994-05-01

90

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

91

Impact of tide-topography interactions on basal melting of Larsen C Ice Shelf, Antarctica  

NASA Astrophysics Data System (ADS)

Basal melting of ice shelves around Antarctica contributes to formation of Antarctic Bottom Water and can affect global sea level by altering the offshore flow of grounded ice streams and glaciers. Tides influence ice shelf basal melt rate (wb) by contributing to ocean mixing and mean circulation as well as thermohaline exchanges with the ice shelf. We use a three-dimensional ocean model, thermodynamically coupled to a nonevolving ice shelf, to investigate the relationship between topography, tides, andwb for Larsen C Ice Shelf (LCIS) in the northwestern Weddell Sea, Antarctica. Using our best estimates of ice shelf thickness and seabed topography, we find that the largest modeled LCIS melt rates occur in the northeast, where our model predicts strong diurnal tidal currents (˜0.4 m s-1). This distribution is significantly different from models with no tidal forcing, which predict largest melt rates along the deep grounding lines. We compare several model runs to explore melt rate sensitivity to geometry, initial ocean potential temperature (?0), thermodynamic parameterizations of heat and freshwater ice-ocean exchange, and tidal forcing. The resulting range of LCIS-averagedwb is ˜0.11-0.44 m a-1. The spatial distribution of wb is very sensitive to model geometry and thermodynamic parameterization while the overall magnitude of wb is influenced by ?0. These sensitivities in wbpredictions reinforce a need for high-resolution maps of ice draft and sub-ice-shelf seabed topography together with ocean temperature measurements at the ice shelf front to improve representation of ice shelves in coupled climate system models.

Mueller, R. D.; Padman, L.; Dinniman, M. S.; Erofeeva, S. Y.; Fricker, H. A.; King, M. A.

2012-05-01

92

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

93

Arctic Sea Ice Melt in the Summer of 2008  

NASA Astrophysics Data System (ADS)

There has been a marked decline in the summer extent of Arctic sea ice over the past few decades. To enhance our understanding of this decline, autonomous ice mass balance buoys were deployed in the sea ice cover as part of the North Pole Environmental Observatory, the Beaufort Gyre Environmental Observatory, and the Developing Arctic Modeling and Observing Capabilities for Long-term Environmental Studies Program. These buoys monitor changes in snow deposition and ablation, ice growth, and ice surface and bottom melt. Results during the summer of 2008 showed considerable spatial variability in the amount of surface and bottom melt. In the vicinity of the North Pole the amounts of surface and bottom ablation were comparable to values observed in recent years. Modest (less than 0.5 m total) amounts of melting were observed north of Greenland. Melting in the Southern Beaufort Sea was quite large, with 0.85 m of surface melt and more than 1 m of bottom melt. Reduced ice concentration in this region led to a buildup of solar heat in the upper ocean. This absorbedsolar heat was released gradually and also through abrupt episodes when peak bottom melt rates exceeded several cm per day.

Perovich, D. K.; Richter-Menge, J. A.; Elder, B. C.; Polashenski, C. M.

2008-12-01

94

Basal melt rate at the Larsen-C Ice Shelf  

NASA Astrophysics Data System (ADS)

During the past decade, the Larsen Ice Shelf has progressively thinned and two large sections have collapsed, catastrophically, leading to increased ice discharge into the oceans and a global sea level rise of about 0.07 mm yr-1. If similar events are to occur at the remaining Larsen-C section, the fate of a tenfold greater ice reservoir hangs in the balance. Although the origin of the underlying instability has yet to be determined, only three processes can realistically be to blame; enhanced basal or surface melting, or accelerated flow. To quantify rates of basal ice melting, we deployed a phase sensitive radar at the Larsen-C Ice Shelf in 2008. The radar is a high-precision instrument that directly measures changes in ice thickness at the base of the ice shelf, in contrast to indirect methods which infer basal melting from surface observation while assuming steady state equilibrium. During the spring 2008, we established three sites at the Larsen-C where time-series of satellite altimeter data are also available. In the spring 2009, the 3 sites have been re-visited twice with the objective of measuring yearly and summer rates of basal melting. We combine the phase sensitive radar observations with measurement of surface mass balance, gps-determined strain rates, surface velocity field from InSAR and elevation changes from altimetry to quantify the role of basal melting in the overall mass balance of the Larsen-C Ice Shelf.

Gourmelen, Noel; Shepherd, Andrew; Jenkins, Adrian; Houlie, Nicolas

2010-05-01

95

Basal melt rate at the Larsen-C Ice Shelf  

NASA Astrophysics Data System (ADS)

During the past decade, the Larsen Ice Shelf has progressively thinned and two large sections have collapsed, catastrophically, leading to increased ice discharge into the oceans and a global sea level rise of about 0.07 mm yr-1. If similar events are to occur at the remaining Larsen-C section, the fate of a tenfold greater ice reservoir hangs in the balance. Although the origin of the underlying instability has yet to be determined, only three processes can realistically be to blame; enhanced basal or surface melting, or accelerated flow. To quantify rates of basal ice melting, we deployed a phase sensitive radar at the Larsen-C Ice Shelf in 2008. The radar is a high-precision instrument that directly measures changes in ice thickness at the base of the ice shelf, in contrast to indirect methods which infer basal melting from surface observation while assuming steady state equilibrium. During the spring 2008, we established three sites at the Larsen-C where time-series of satellite altimeter data are also available. In the spring 2009, the 3 sites are to be re-visited twice with the objective of measuring yearly and summer rates of basal melting. We combine the phase sensitive radar observations with measurement of surface mass balance, gps-determined strain rates, surface velocity field from InSAR and elevation chanes from altimetry to quantify the role of basal melting in the overall mass balance of the Larsen-C Ice Shelf.

Gourmelen, N.; Shepherd, A.; Jenkins, A.; Houlie, N.

2009-12-01

96

Dissociative melting of ice VII at high pressure.  

PubMed

We have used x-ray diffraction to determine the structure factor of water along its melting line to a static pressure of 57 GPa (570 kbar) and a temperature of more than 1500 K, conditions which correspond to the lower mantle of the Earth, and the interiors of Neptune and Uranus up to a depth of 7000 km. We have also performed corresponding first principles and classical molecular dynamics simulations. Above a pressure of 4 GPa the O-O structure factor is found to be very close to that of a simple soft sphere liquid, thus permitting us to determine the density of liquid water near the melting line. By comparing these results with the density of ice, also determined in this study, we find that the enthalpy of fusion (DeltaH(f)) increases enormously along the melting line, reaching approximately 120 kJ/mole at 40 GPa (compared to 6 kJ/mole at 0 GPa), thus revealing significant molecular dissociation of water upon melting. We speculate that an extended two-phase region could occur in planetary processes involving the adiabatic compression of water. PMID:19334858

Goncharov, Alexander F; Sanloup, Chrystele; Goldman, Nir; Crowhurst, Jonathan C; Bastea, Sorin; Howard, W M; Fried, Laurence E; Guignot, Nicolas; Mezouar, Mohamed; Meng, Yue

2009-03-28

97

Dissociative melting of ice VII at high pressure  

SciTech Connect

We have used x-ray diffraction to determine the structure factor of water along its melting line to a static pressure of 57 GPa (570 kbar) and a temperature of more than 1500 K, conditions which correspond to the lower mantle of the Earth, and the interiors of Neptune and Uranus up to a depth of 7000 km. We have also performed corresponding first principles and classical molecular dynamics simulations. Above a pressure of 4 GPa the O-O structure factor is found to be very close to that of a simple soft sphere liquid, thus permitting us to determine the density of liquid water near the melting line. By comparing these results with the density of ice, also determined in this study, we find that the enthalpy of fusion ({Delta}H{sub f}) increases enormously along the melting line, reaching approximately 120 kJ/mole at 40 GPa (compared to 6 kJ/mole at 0 GPa), thus revealing significant molecular dissociation of water upon melting. We speculate that an extended two-phase region could occur in planetary processes involving the adiabatic compression of water.

Goncharov, Alexander F.; Sanloup, Chrystele; Goldman, Nir; Crowhurst, Jonathan C.; Bastea, Sorin; Howard, W.M.; Fried, Laurence E.; Guignot, Nicolas; Mezouar, Mohamed; Meng, Yue; (UPMC); (LLNL); (CIW); (ESRF)

2009-04-02

98

Water isotopic ratios from a continuously melted ice core sample  

NASA Astrophysics Data System (ADS)

A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We build an interface between an Infra Red Cavity Ring Down Spectrometer (IR-CRDS) and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of ?18O and ?D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ?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 at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on humidity levels. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1 ‰ and 0.5 ‰ for ?18O and ?D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of ?18O and ?D, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the framework of the NEEM deep ice core drilling project in Greenland, during the 2010 field season.

Gkinis, V.; Popp, T. J.; Blunier, T.; Bigler, M.; Schüpbach, S.; Johnsen, S. J.

2011-06-01

99

The melting of floating ice raises the ocean level  

NASA Astrophysics Data System (ADS)

It is shown that the melting of ice floating on the ocean will introduce a volume of water about 2.6 per cent greater than that of the originally displaced sea water. The melting of floating ice in a global warming will cause the ocean to rise. If all the extant sea ice and floating shelf ice melted, the global sea level would rise about 4cm. The sliding of grounded ice into the sea, however, produces a mean water level rise in two parts; some of the rise is delayed. The first part, while the ice floats, is equal to the volume of displaced sea water. The second part, equal to 2.6 per cent of the first, is contributed as it melts. These effects result from the difference in volume of equal weights of fresh and salt water. This component of sea rise is apparently unrecognized in the literature to date, although it can be interpreted as a form of halosteric sea level change by regarding the displaced salt water and the meltwater (even before melting) as a unit. Although salinity changes are known to affect sea level, all existing analyses omit our calculated volume change. We present a protocol that can be used to calculate global sea level rise on the basis of the addition of meltwater from grounded and floating ice; of course thermosteric volume change must be added.

Noerdlinger, Peter D.; Brower, Kay R.

2007-07-01

100

Level-ice melt ponds in the Los Alamos sea ice model, CICE  

NASA Astrophysics Data System (ADS)

A new meltpond parameterization has been developed for the CICE sea ice model, taking advantage of the level ice tracer available in the model. The ponds evolve according to physically based process descriptions, assuming a depth-area ratio for changes in pond volume. A novel aspect of the new scheme is that the ponds are carried as tracers on the level ice area of each thickness category, thus limiting their spatial extent based on the simulated sea ice topography. This limiting is meant to approximate the horizontal drainage of melt water into depressions in ice floes. Simulated melt pond processes include collection of liquid melt water and rain into ponds, drainage through permeable sea ice or over the edges of floes, infiltration of snow by pond water, and refreezing of ponds. Furthermore, snow that falls on top of ponds whose top surface has refrozen blocks radiation from penetrating into the ponds and sea ice below.

Hunke, Elizabeth C.; Hebert, David A.; Lecomte, Olivier

2013-11-01

101

Anisotropy of the Reflected Radiation Field Over Melting Glacier Ice  

Microsoft Academic Search

In this article we analyze the anisotropy of the reflected radiation field over melting glacier ice using 118 ground-based radiance measurements in Landsat TM Bands 2 and 4. The measurements were carried out on the tongue of the Morteratschgletscher, Switzerland. On the basis of directional measurements several bidirectional reflectance distribution functions (BRDFs) were derived for dirty and clean glacier ice

Wouter H. Knap; Carleen H. Reijmer

1998-01-01

102

Ion fractionation and percolation in ice cores with seasonal melting  

Microsoft Academic Search

We examine the impact that post- depositional change has on ion concentrations in ice cores that suffer limited seasonal melting. We show that the impact in the case of at least one Svalbard ice core is limited to decreasing resolution of signals to about 3 years - a similar accuracy as the best dating can usually provide. We model various

John C. Moore; Aslak Grinsted

103

An investigation of the heat transfer at the liquid/solid interface of rapidly melting ice  

NASA Astrophysics Data System (ADS)

This paper describes an experimental and analytical investigation of a system capable of rapidly melting ice. The melting technique used involved forcing a cylindrical ice slug against a heated surface, letting the effluent fluid exit radially. An analytical model based on fundamental physical principles was developed and used to predict the behavior of the system. Liquid layer thickness, liquid bulk temperature, radial pressure distribution in the liquid layer, convective heat transfer coefficient, and ice melt rate were all computed for steady state operation of the system. Experiments were performed to verify the model predictions. The tests measured the ice melt velocity and exit bulk temperature at a known supply pressure. The input heat flux was determined using two independent methods of calculation. One technique found the conduction heat flux leaving the heated block by using two heated block temperature measurements spaced a known distance apart near the liquid/block surface. The second method applied the measured ice melt velocity and liquid bulk temperature to an energy balance on the liquid film to yield an input heat flux value. A comparison of the experimental results with the analytical model predictions is made demonstrating satisfactory agreement.

Fredley, J. E.

1980-03-01

104

Organochlorine compounds in ice melt water from Italian Alpine rivers  

Microsoft Academic Search

Organochlorine chemicals (OCs) (dichlorodiphenyltrichloroethanes, hexachlorocyclohexanes, and hexachlorobenzene) were measured in ice melt water from five glaciers in the Italian Alps. Even though the data collected may not be sufficient for a precise description of persistent organic pollutant release patterns from glacier melting, they have, however, highlighted the potential for surface water contamination. Concentrations were of the same order of magnitude

Sara Villa; Christian Negrelli; Antonio Finizio; Onelio Flora; Marco Vighi

2006-01-01

105

The effects of localized deformation on melting processes in ice  

Microsoft Academic Search

Polycrystalline ice deformed in pure shear and in plane strain at approximately ?1°C exhibited plastic flow, accommodated by intracrystalline slip and grain boundary migration. A film record of the plastic flow shows that deformation becomes localized along slip-lines that correspond to zones of high resolved shear stress. During this deformation melting occurs. While a simple calculation shows that more melt

C. J. L. Wilson; Y. Zhang; K. Stüwe

1996-01-01

106

Topological defects and bulk melting of hexagonal ice  

Microsoft Academic Search

We use classical molecular dynamics combined with the recently developed metadynamics method [A. Laio and M. Parrinello, Procs. Natl. Acad. Sci. USA 99, 20 (2002)] to study the process of bulk melting in hexagonal ice. Our simulations show that bulk melting is mediated by the formation of topological defects which preserve the coordination of the tetrahedral network. Such defects cluster

Davide Donadio; Paolo Raiteri; Michele Parrinello

2005-01-01

107

Physical Basis for the Temperature-Based Melt-Index Method  

Microsoft Academic Search

The close relationship between air temperature measured at standard screen level and the rate of melt on snow and ice has been widely used to estimate the rate of melt. The parameterization of the melt rate using air temperature usually takes a simple form as a function of either the mean temperature for the relevant period or positive degree-day statistics.

Atsumu Ohmura

2001-01-01

108

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

NASA Astrophysics Data System (ADS)

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 30 cm of level sea ice based on triplicate ice core sampling at each location, and in individual ice chunks from ridges at four locations. Under-ice amphipods were counted in situ in replicate ( N=24-65 per station) 0.25 m 2 quadrats using SCUBA to a maximum water depth of 12 m. In level sea ice, the most abundant ice meiofauna groups were Turbellaria (46%), Nematoda (35%), and Harpacticoida (19%), with overall low abundances per station that ranged from 0.0 to 10.9 ind l -1 (median 0.8 ind l -1). In level ice, low ice algal pigment concentrations (<0.1-15.8 ?g Chl a l -1), low brine salinities (1.8-21.7) and flushing from the melting sea ice likely explain the low ice meiofauna concentrations. Higher abundances of Turbellaria, Nematoda and Harpacticoida also were observed in pressure ridges (0-200 ind l -1, median 40 ind l -1), although values were highly variable and only medians of Turbellaria were significantly higher in ridge ice than in level ice. Median abundances of under-ice amphipods at all ice types (level ice, various ice ridge structures) ranged from 8 to 114 ind m -2 per station and mainly consisted of Apherusa glacialis (87%), Onisimus spp. (7%) and Gammarus wilkitzkii (6%). Highest amphipod abundances were observed in pressure ridges at depths >3 m where abundances were up to 42-fold higher compared with level ice. We propose that the summer ice melt impacted meiofauna and under-ice amphipod abundance and distribution through (a) flushing, and (b) enhanced salinity stress at thinner level sea ice (less than 3 m thickness). We further suggest that pressure ridges, which extend into deeper, high-salinity water, become accumulation regions for ice meiofauna and under-ice amphipods in summer. Pressure ridges thus might be crucial for faunal survival during periods of enhanced summer ice melt. Previous estimates of Arctic sea ice meiofauna and under-ice amphipods on regional and pan-Arctic scales likely underestimate abundances at least in summer because they typically do not include pressure ridges.

Gradinger, Rolf; Bluhm, Bodil; Iken, Katrin

2010-01-01

109

Influence of air temperature on flashover along ice surfaces  

Microsoft Academic Search

In the present study, the maximum withstand, the minimum flashover and the 50% withstand voltages of triangular ice samples were determined and compared during ice melting. The influence of the surrounding air temperature on the maximum withstand voltage, the critical leakage current and the time interval between voltage application and flashover occurrence were studied. The results obtained will contribute to

J. Zhang; M. Farzaneh; X. Chen

1996-01-01

110

Effective control of gas hydrate dissociation above the melting point of ice.  

PubMed

Direct measurements of the dissociation behaviors of pure methane and ethane hydrates trapped in sintered tetrahydrofuran hydrate through a temperature ramping method showed that the tetrahydrofuran hydrate controls dissociation of the gas hydrates under thermodynamic instability at temperatures above the melting point of ice. PMID:21938303

Kida, Masato; Jin, Yusuke; Narita, Hideo; Nagao, Jiro

2011-09-22

111

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

112

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

113

Coupling of ice-shelf melting and buttressing is a key process in ice-sheets dynamics  

Microsoft Academic Search

Increase in ice-shelf melting is generally presumed to have triggered recent coastal ice-sheet thinning. Using a full-Stokes finite element model which includes a proper description of the grounding line dynamics, we investigate the impact of melting below ice shelves. We argue that the influence of ice-shelf melting on the ice-sheet dynamics induces a complex response, and the first naive view

O. Gagliardini; G. Durand; T. Zwinger; R. C. A. Hindmarsh; E. Le Meur

2010-01-01

114

Control of the width of West Antarctic ice streams by internal melting in the ice sheet near the margins  

NASA Astrophysics Data System (ADS)

Could the 40 to 80 km widths of West Antarctic (Ross Shelf) ice streams be controlled by onset of melting within the ice sheet at the stream margins? The streams are driven by gravity which is resisted by basal drag, inferred to be small, and by shear stress at the lateral margins, assuming longitudinal stress gradients are unimportant [Whilans & van der Veen, JG'93]. Lateral shear stress in the sheet scales with the difference between gravitational stress and basal drag, and increases linearly with the lateral distance X from the center of a stream. With increasing X, that lateral shear stress times the creep strain rate it induces becomes a significant heat source within the ice sheet (proportional to X4 using Glen's law), and must ultimately induce internal melting. We study this possibility using data for a set of 5 ice stream profiles (A, WNar, C, D, E) of Joughin et al. [JGR'02]. They used measured lateral shear strain rates at the margins, and a depth-averaged values of the Glen's law creep parameter, based on a 1-D conduction-advection heat transfer analysis, without internal heating, to estimate the lateral drag. We find that when we incorporate the product of their drag stress and strain rate as a source in a conductive heat transfer model, the predicted margin temperatures are in excess of melting over some depth range for all five profiles. This supports the possibility that internal melting within the ice sheet is indeed related to why the margins are where they are. Next, we reformulated the 1-D vertical heat flux problem allowing some lower depth range of the of ice sheet to be partially melted ice at the melting temperature, with the rest of the sheet frozen and undergoing conductive heat transfer. The sheet was subjected to a uniform lateral shear rate, allowing the Glen's law parameter and local shear stress to be different for the two zones. The predicted fraction of the thickness that is molten, if any, depends on the lateral shear strain rate (or, equivalently, on the thickness-averaged lateral stress). For the profiles (A, WNar, C, D, E), the observed strain rates are respectively (1.2, 2.4, 0.6, 0.9, 1.9) times the levels at which internal melting should begin; with the exception of C (upper tributary of Kamb), the results are compatible with the hypothesis that the margin is undergoing internal melting. Also, the model predicts that a 5% increase in lateral stress, and hence in ice stream width, is enough to go from onset of internal melting to melting half the sheet thickness. The liquid production rate in the melting zone is also predicted. Using the permeability model of Nye and Frank [JG'73], melt rains downward to the bed via a vein system, and a permeability of ~10-16 m2 is reached at the bottom of the sheet, corresponding to a Darcy flux of ~5 m/yr. We expect that the massive drainage to the bed associated with melting causes R-channel development, with channel fluid pressure sufficiently below the ice overburden pressure that the effective normal stress on the bed adjacent to the channel is notably larger than in the central regions of the stream. That is conjectured to lock the ice sheet to the bed outboard of the R-channel and hence create the limit to width of the stream of fast-flowing ice.

Perol, T.; Rice, J. R.

2011-12-01

115

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

Microsoft Academic Search

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

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

2011-01-01

116

Sensitivity analysis of Pine Island Glacier ice flow to increased melting rates,computed from the ECCO2 project and new IceBridge bathymetry data.  

NASA Astrophysics Data System (ADS)

The acceleration of Pine Island Glacier in the last decade correlates significantly with an increase in ocean temperatures in the Amundsen Sea during the same period. Although studies have been carried out to try and link both phenomenons, the demonstration of a significant link between sub-cavity ice shelf melting and ice flow acceleration remains an open question. Here, we present a new coupled ocean circulation/ice flow model, based on the MITgcm and ISSM models, that includes significant offline coupling between the sub-ice shelf cavity ocean circulation and the glacier ice flow. Computed melting rates are used to constrain ice flow, which in turn is used to constrain geometry of the sub-ice shelf cavity. The model is applied to the Amundsen Sea/Pine Island Glacier and Thwaites Glacier, to try and assess the sensitivity of ice flow acceleration to a scenario of increased melting under the ice shelf. The results show significant ice flow acceleration on a short term basis (10 to 100 years), as well as modification of the ocean circulation under the ice shelf, in response to a changing sub-ice shelf cavity geometry. These results demonstrate that there are significant links between changing ocean circulation patterns in the Amundsen Sea and sudden ice flow acceleration of Pine Island Glacier in the last decade. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

Larour, E. Y.; Rignot, E. J.; Menemenlis, D.; Schodlok, M.; Seroussi, H. L.; Morlighem, M.

2011-12-01

117

Simulation of melt pond evolution on level ice  

NASA Astrophysics Data System (ADS)

A melt pond model is presented that predicts pond size and depth changes, given an initial ice thickness field and representative surface fluxes. The model is based on the assumption that as sea ice melts, fresh water builds up in the ice pore space and eventually saturates the ice. Under these conditions, a water table is defined equal to the draft of the ice or sea level, and ponds are produced in ice surface depressions, much like lakes in a watershed. Pond evolution is forced by applying fluxes of heat at the pond surface and a radiative transfer model for solar radiation that penetrates the pond. Results from the model using forcing data from the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment and representative pond parameters indicate that the model accurately simulates pond depth and fractional area over the summer melt season, with fractional area increasing linearly. Overall, ice albedo is affected primarily by the increase in pond coverage. Decrease in pond albedo from pond deepening has a much lower influence on the total albedo. Cases with predominately sunny conditions are shown to produce more rapid pond expansion than overcast cases. In both sunny and cloudy cases the fractional area increases linearly.

Skyllingstad, Eric D.; Paulson, Clayton A.; Perovich, Donald K.

2009-12-01

118

Surface melting of ice Ih single crystals revealed by glancing angle x-ray scattering  

Microsoft Academic Search

We present glancing angle x-ray scattering experiments at [00.1], [10.0], and [11.0] surfaces of ice Ih single crystals. The temperature dependence of the evanescent Bragg scattering upon heating reveals a quasiliquid surface layer well below the melting point of each investigated ice surface. At [10.0] and [11.0] surfaces, thermal faceting is observed, which is briefly discussed. The ``oxygen-forbidden'' (00.4) Bragg

A. Lied; H. Dosch; J. H. Bilgram

1994-01-01

119

Circulation and melting beneath George VI Ice Shelf, Antarctica  

Microsoft Academic Search

Oceanographic data are presented from the eastern Bellingshausen Sea, representing the first near-contemporaneous sampling of conditions near both the northern and southern ice fronts of George VI Ice Shelf. Circumpolar Deep Water (CDW) with a temperature in excess of 1°C floods the entire continental shelf and forms the main inflow to the cavity beneath the ice shelf. We use measurements

Adrian Jenkins; Stan Jacobs

2008-01-01

120

Antarctic ice sheet response to combined surface and oceanic sub-ice shelf melt during past interglacials and in the future  

NASA Astrophysics Data System (ADS)

New sediment core records from the Ross Embayment (ANDRILL; Naish et al., Nature, 2009) and time-continuous modeling of the Antarctic ice sheet-shelf system (Pollard and DeConto, Nature, 2009) imply dramatic, orbitally paced variability of the West Antarctic Ice Sheet (WAIS) through the Plio-Pleistocene. Model-simulated episodes of WAIS retreat are common during the warm Pliocene, but they also occur during some interglacials in the colder Pleistocene. The relatively modest forcing of these simulated past retreats hints at the future vulnerability of the ice sheet. In our previous long-term simulations, the ice-sheet model was driven by parameterized climatologies (surface temperature, precipitation, sea level, and oceanic sub-ice shelf melt) scaled mainly to deep-sea benthic oxygen isotope records. In the model, WAIS was found to be highly sensitive to sub-ice-shelf melt rates, with modest increases (~2 m/yr) capable of triggering sudden grounding-line retreat and dynamic thinning in the Ross, Weddell and Amundsen Sea sectors- largely in response to reduced ice-shelf buttressing. Here we present new ice sheet-shelf simulations of specific past interglacials and future scenarios with elevated greenhouse gasses. The model is driven by atmospheric climatologies from a new high-resolution Regional Climate Model adapted to the South Polar region and modest increases in circum-Antarctic ocean temperatures. The model (accounting for past greenhouse gas and orbital forcing) shows that melt on ice-shelf surfaces played a contributing role in prior Pleistocene WAIS retreats, but increased oceanic sub ice-shelf melt was likely the dominant mechanism driving those past retreats. At levels of atmospheric CO2 exceeding 2x preindustrial levels (560 ppmv), surface melt on ice-shelf surfaces becomes increasingly important. As CO2 levels approach 4x preindustrial levels, surface melt on ice shelves and the low-elevation flanks of WAIS is sufficient to cause near complete WAIS collapse within several thousand years, without any increase in ocean temperature and oceanic sub-ice melt. On millennial timescales, the loss of WAIS ice is partially compensated by increased accumulation on East Antarctica, but the transfer of mass from West to East Antarctica has significant implications for local relative sea level adjustment. These results suggest oceanic sub-ice melt likely played the dominant role in previous Pleistocene WAIS retreats, but surface melt will begin to play an increasingly important role in the long-term future dynamic response of WAIS in response to elevated greenhouse gas concentrations.

DeConto, R.; Pollard, D.; Kowalewski, D.

2012-04-01

121

Water isotopic ratios from a continuously melted ice core sample  

NASA Astrophysics Data System (ADS)

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 simultaneuous water isotopic analysis of ?18O and ?D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ?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 at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW-SLAP scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on the water concentration in the optical cavity. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1‰ and 0.5‰ for ?18O and ?D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the temporal resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of ?18O and ?D, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the field during the 2010 season as part of the NEEM deep ice core drilling project in North Greenland.

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

2011-11-01

122

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

Microsoft Academic Search

In most cases when eruptions occur within glaciers they lead to rapid ice melting, jokulhlaups and\\/or lahars. Many parameters influence the style of activity and its impact on the environment. These include ice thickness (size of glacier), bedrock geometry, magma flow rate and magma composition. The eruptions that have been observed can roughly be divided into: (1) eruptions under several

M. T. Gudmundsson

2005-01-01

123

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

NASA Astrophysics Data System (ADS)

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 of earth's warmer climate in recent decades both in peer reviewed journals and in popular media. This dissertation addresses two parameters that contribute to Greenland ice sheet mass balance estimates. The first factor is characterization of surface melting of the Greenland ice sheet from satellite-based passive and active microwave sensors. We use a wavelet based edge detection technique to delineate surface melt from brightness temperature measured by passive microwave sensors. Along with brightness temperature data, we also use normalized backscatter data from the Quick Scatterometer (QuikSCAT) as an independent sensor for comparison with the radiometer derived results. We use a semi-empirical threshold based method for surface melt detection from QuikSCAT. Our results show a step-like, consistent increase in melt area of the Greenland ice sheet since 1995. This step-like increase is also observed in the mean summer air temperature along portions of the Greenland coast. The 1995 step-like increase of melt area (and melt index, a measure of melt intensity) is correlated with a distinct change of the North Atlantic Oscillation (NAO) index (from positive to negative) after 1995. The second factor is mass accumulation in the upper reaches of the ice-sheet. We use an empirical model that correlates mean annual brightness temperature to annual accumulation rate. We apply a microwave emission model for the dry snow region of Greenland to show that 37 GHz vertically polarized brightness temperature data are better suited to capture the inter-annual variability of snow accumulation. Using our model we estimate a snow accumulation time series from brightness temperature for 150 km x 150 km area around Summit Camp in central Greenland. Using measured surface velocities and ice thickness we calculate the surface mass balance for our study area. We find a positive mass balance of 3.18 +/- 6.0 cm/yr. Our mass balance derived elevation change is in agreement with satellite altimeter data and published results of other researchers.

Bhattacharya, Indrajit

124

Investigation of Factors Affecting the Melt Down of Soft Serve Imitation Ice Milk.  

National Technical Information Service (NTIS)

The effect of stabilizer and emulsifier combinations, position size, type of fat, amount of fat, level of serum solids, level of sucrose, combinations of sucrose and corn syrup solids and draw temperature, on the melt down of soft serve ice milk tested un...

C. C. Walts G. C. Walker J. M. Tuomy

1971-01-01

125

Sea-ice melt onset associated with ice deformation events during early summer near the North Pole in the Arctic Ocean  

NASA Astrophysics Data System (ADS)

In the central Arctic Ocean, autonomous observations of ocean mixed layer and ice documented the transition from cold spring to early summer. Our ice motion measurements using GPS drifters captured three events of lead opening and ice ridge formation in May and June. We clarify how these ice deformation events are linked with the onset of sea ice melt. In early June, the buoy array detected a shear deformation coincident with a temperature peak at 6 m below the ice bottom. At this time, an autonomous profiler shows there was a slow decrease of temperature with depth and nearly homogeneous salinity profiles, with persistently stable mixed layer. We use a one-dimensional numerical simulation incorporating the Local Turbulence Closure (LTC) scheme to investigate the mechanisms controlling basal melt onset. According to the simulation, a combination of the extremely slow ice motion and incoming solar energy input at the open lead, followed by a transient low pressure system, produced a thin, low density surface layer by advection of warm lead water under the ice. This enhanced stratification near the surface facilitates storage of solar radiation within the thin layer, instead of exchange with deeper layers, leading to early onset of basal ice melt preceding the upper surface melt.

Kawaguchi, Yusuke; Huthchings, Jennifer; Vivire, Frederic; Kikuchi, Takashi; Morison, James; Noguchi, Tomohide; Lourenco, Antonio

2013-04-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

127

Future projections of the Greenland ice sheet energy balance driving the surface melt  

NASA Astrophysics Data System (ADS)

In this study, simulations at 25 km resolution are performed over the Greenland ice sheet (GrIS) throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios from three CMIP5 global circulation models (GCMs), in order to investigate the projected changes of the surface energy balance (SEB) components driving the surface melt. Analysis of 2000-2100 melt anomalies compared to melt results over 1980-1999 reveals an exponential relationship of the GrIS surface melt rate simulated by MAR to the near-surface air temperature (TAS) anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are preferentially driven by stronger sensible heat fluxes, induced by enhanced warm air advection over the ice sheet. Over the central dry snow zone, the surface albedo positive feedback induced by the increase in summer melt exceeds the negative feedback of heavier snowfall for TAS anomalies higher than 4 °C. In addition to the incoming longwave flux increase associated with the atmosphere warming, GCM-forced MAR simulations project an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. However, it should be noted that this trend in the cloud cover is contrary to that simulated by ERA-Interim-forced MAR for recent climate conditions, where the observed melt increase since the 1990s seems mainly to be a consequence of more anticyclonic atmospheric conditions. Finally, no significant change is projected in the length of the melt season, which highlights the importance of solar radiation absorbed by the ice sheet surface in the melt SEB.

Franco, B.; Fettweis, X.; Erpicum, M.

2013-01-01

128

Significant contribution of insolation to Eemian melting of the Greenland ice sheet  

NASA Astrophysics Data System (ADS)

The Eemian (130 to 114 ky BP) was characterized by a warmer Northern Hemisphere climate and by higher summer insolation. As a result, the Greenland ice sheet was 30 to 60% smaller than today. The primary driver of this retreat was enhanced surface melt. Although most energy for melt is provided by short wave radiation, temperature is regarded as the key parameter to determine surface melt. In this model study, we show that Eemian changes in insolation were as important as Eemian temperature changes. For this, four regional climate model simulations are preformed with Eemian or preindustrial climate and with Eemian or preindustrial orbital parameters. These four simulations separate the individual contributions of insolation and temperature on the Eemian ablation increase. About 55% of the Eemian ablation increase, compared to preindustrial climate, is due to increased temperatures. The other 45% is due to stronger insolation and non-linear effects. Temperature-melt relations neglecting insolation fail to reproduce this effect. These result show that the direct effect of insulation cannot be neglected if simplified melt relations are used. Furthermore, it shows that the Eemian is not a good analogue of future Greenland melt. Since insolation changes not significantly on timescales of one century, the response of the Greenland ice sheet to future warming is less strong than on the Eemian warming.

van de Berg, W. J.; van den Broeke, M. R.; Ettema, J.; van Meijgaard, E.; Kaspar, F.

2012-04-01

129

Seasonal melting of surface water ice condensing in martian gullies  

Microsoft Academic Search

In this work we consider when and how much liquid water during present climate is possible within the gullies observed on the surface of Mars. These features are usually found on poleward directed slopes. We analyse the conditions for melting of H2O ice, which seasonally condenses within the gullies. We follow full annual cycle of condensation and sublimation of atmospheric

Konrad J. Kossacki; Wojciech J. Markiewicz

2004-01-01

130

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

131

Atmospheric and oceanic climate forcing of the exceptional Greenland Ice Sheet surface melt in summer 2012  

NASA Astrophysics Data System (ADS)

The NASA announcement of record surface melting of the Greenland ice sheet in July 2012 led us to examine the atmospheric and oceanic climatic anomalies that are likely to have contributed to these exceptional conditions and also to ask the question of how unusual these anomalies were compared to available records. Our analysis allows us to assess the relative contributions of these two key influences to both the extreme melt event and ongoing climate change. In 2012, as in recent warm summers since 2007, a blocking high pressure feature, associated with negative NAO conditions, was present in the mid-troposphere over Greenland for much of the summer. This circulation pattern advected relatively warm southerly winds over the western flank of the ice sheet, forming a "heat dome" over Greenland that led to the widespread surface melting. Both sea-surface temperature and sea-ice cover anomalies seem to have played a minimal role in this record melt, relative to atmospheric circulation. Two representative coastal climatological station averages and several individual stations in S, W and NW Greenland set new surface air temperature records for May, June, July and the whole (JJA) summer. The unusually warm summer 2012 conditions extended to the top of the ice sheet at Summit, where our reanalysed (1994-2012) DMI Summit weather station summer (JJA) temperature series set new record high mean and extreme temperatures in 2012; 3-hourly instantaneous 2-m temperatures reached an exceptional value of 2.2degC at Summit on 11 July 2012. These conditions translated into the record observed ice-sheet wide melt during summer 2012. However, 2012 seems not to be climatically representative of future "average" summers projected this century.

Hanna, Edward; Fettweis, Xavier; Mernild, Sebastian; Cappelen, John; Ribergaard, Mads; Shuman, Christopher; Steffen, Konrad; Wood, Len; Mote, Thomas

2013-04-01

132

Ocean circulation and fronts as related to ice melt-back in the Chukchi Sea  

NASA Astrophysics Data System (ADS)

In summer at the edge of the retreating ice pack in the Chukchi Sea, a sharp temperature and salinity front is formed as the result of ice melt by warm surface water from the south. Beneath this front another front is present, formed from the juxtaposition of the resident winter bottom water under the ice and a water transitional between it and warm summer water flowing northward from Bering Strait. The two fronts may be coincident where the current shears parallel to the ice with low to moderate lateral mixing. They may also be widely separated in areas where the current impinges normal to the ice, most often within ice embayments. On the flanks of rapidly moving streams, wedge-like frontal interfaces in the lower layer are likely to be found. These fronts are often rich in temperature fine structure. The ice melt-back patterns and the various frontal arrangements appear to be controlled by steering of the currents by bottom bathymetry.

Paquette, Robert G.; Bourke, Robert H.

1981-05-01

133

Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow  

Microsoft Academic Search

Ice flow at a location in the equilibrium zone of the west-central Greenland Ice Sheet accelerates above the midwinter average rate during periods of summer melting. The near coincidence of the ice acceleration with the duration of surface melting, followed by deceleration after the melting ceases, indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the

H. Jay Zwally; Waleed Abdalati; Tom Herring; Kristine Larson; Jack Saba; Konrad Steffen

2002-01-01

134

Sea ice melting in the marginal ice zone.  

USGS Publications Warehouse

The heat and salt flux boundary conditions together with the freezing curve relationship are a necessary component of any ice- sea water thermodynamic model. A neutral two-layer oceanic planetary boundary layer model that incorporates these boundary conditions is used. The results are discussed. -from Author

Josberger, E. G.

1983-01-01

135

Aggregation of algae released from melting sea ice: implications for seeding and sedimentation  

Microsoft Academic Search

Factors influencing the fate of ice algae released from melting sea ice were studied during a R V Polarstern cruise (EPOS Leg 2) to the northwestern Weddell Sea. The large-scale phytoplankton distribution patterns across the receding ice edge and small-scale profiling of the water column adjacent to melting ice floes indicated marked patchiness on both scales. The contribution of typical

U. Riebesell; I. Schloss; V. Smetacek

1991-01-01

136

Effects of basal-melting distribution on the retreat of ice-shelf grounding lines  

Microsoft Academic Search

The stability of marine ice streams depends on the distribution as well as the magnitude of melting beneath the adjacent ice shelf, as shown by new model results. Recent observations of rapid retreat of ice-shelf grounding lines in the Amundsen Sea sector of West Antarctica have highlighted the need for understanding how basal melting of ice shelves by warm ocean

R. T. Walker; T. K. Dupont; B. R. Parizek; R. B. Alley

2008-01-01

137

Rapid barotropic sea level rise from ice sheet melting  

NASA Astrophysics Data System (ADS)

Sea level rise associated with idealized Greenland and Antarctic ice sheet melting events is examined using a global coupled ocean sea-ice model that has a free surface formulation and thus can simulate fast barotropic motions. The perturbation experiments follow the Coordinated Ocean-ice Reference Experiment (CORE) version III. All regions of the global ocean experience a sea level rise within 7-8 days of the initialization of a polar meltwater input of 0.1 Sv (1 Sv ? 106 m3 s-1). The fast adjustment contrasts sharply with the slower adjustment associated with the smaller steric sea level evolution that is also connected with melt events. The global mean sea level rises by 9 mm yr-1 when this forcing is applied either from Greenland or Antarctica. Nevertheless, horizontal inter-basin gradients in sea level remain. For climate adaption in low-lying coastal and island regions, it is critical that the barotropic sea level signal associated with melt events is taken into consideration, as it leads to a fast sea level rise from melting ice sheets for the bulk of the global ocean. A linear relation between sea level rise and global meltwater input is further supported by experiments in which idealized melting occurs only in a region east or west of the Antarctic Peninsula, and when melting rates are varied between 0.01 Sv and 1.0 Sv. The results indicate that in ocean models that do not explicitly represent the barotropic signal, the barotropic component of sea level rise can be added off-line to the simulated steric signal.

Lorbacher, K.; Marsland, S. J.; Church, J. A.; Griffies, S. M.; Stammer, D.

2012-06-01

138

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

139

Sea Ice Melting in the Marginal Ice Zone  

Microsoft Academic Search

The heat and salt flux boundary conditions together with the freezing curve relationship are a necessary component of any ice-sea water thermodynamic model. A neutral two-layer oceanic planetary boundary layer model that incorporates these boundary conditions gives the following results: The interfacial salinity is within 10% of the far-field salinity for conditions commonly encountered in the MIZ and depends only

Edward G. Josberger

1983-01-01

140

Current measurements near Ronne Ice Shelf: Implications for circulation and melting  

NASA Astrophysics Data System (ADS)

We present the first year-long current meter records ever obtained near the floating Filchner-Ronne Ice Shelf in the Weddell Sea. The currents are steered along the ice front, but in the lower layer where the bottom topography is descending toward the west the current has a component toward the ice front of about 3 cm s-1. During winter the temperature stayed near the surface freezing point, while the salinity increased, indicating that ice was formed and brine released. The seasonal variation in salinity was 0.15±0.05 psu, corresponding to the formation of 1-2 m of ice on a shelf depth of 400 m. The transport of High-Salinity Shelf Water (HSSW) into the ice shelf cavity was found to be of the order 0.5×106 m3 s-1. The production of this water due to oscillating tides and off shelf winds was found to be of the same order of magnitude. In contact with glacial ice at great depths, and because of the depression of the freezing point, the HSSW is transformed to Ice Shelf Water (ISW) by cooling and melting processes. The melting rate was estimated to 1×1011 ton yr-1. This corresponds to the melting of 0.2 m ice per year if the melting is evenly distributed over the Filchner-Ronne Ice Shelf. If the melting is concentrated along a path from the Berkner Shelf around the Berkner Island to the Filchner Depression, then melting rates up to 7 m yr-1 must be expected. A comparison of HSSW characteristics in the Ronne Depression, our winter observations on the Berkner Shelf, and the ISW flowing out of the Filchner Depression indicates that very little water passes through the cavity from the Ronne to the Filchner Depression. It appears that most of the ISW originating from processes on the Berkner Shelf escapes the cavity in the Filchner Depression. This leaves the Berkner Shelf as the important source of ISW and subsequently of the Weddell Sea Bottom Water formed from ISW.

Foldvik, A.; GammelsrøD, T.; Nygaard, E.; ØSterhus, S.

2001-03-01

141

Modelling the Areal Evolution of Arctic Melt Ponds on Sea Ice  

NASA Astrophysics Data System (ADS)

During winter the ocean surface at the poles freezes over to form sea ice. Sea ice floats on the ocean surface and has a matrix structure caused by the rejection of salts during freezing. In the summer sea ice melts at its surface creating melt ponds. An accurate estimate of the fraction of the upper sea-ice surface covered in melt ponds during the summer melt season is essential for a realistic estimate of the albedo for global climate models. We present a sea ice model that simulates the two-dimensional (areal) evolution of melt ponds on an Arctic sea-ice surface. Water transport across and through the sea-ice surface is described by the major hydraulic processes believed to be present. Thermodynamic processes are modelled using heat flux equations. Lateral and vertical melt water transport is described by Darcy's Law. The model simulates a section of a sea ice floe where edge effects such as the presence of leads are neglected. The model consists of a grid of cells, each of which can be in one of four possible configurations: snow covered ice; bare ice; melt pond covered ice or open water. A cluster of adjacent cells containing melt water may be considered to have formed a melt pond. The model is initialised with ice topographies that represent either first-year or multi-year sea ice, these are reconstructed from ice thickness data using standard statistical methods; in this way characteristic examples of both first-year ice and multi-year ice can be constructed. The roughness of the ice and snow surfaces were altered and the sensitivity of the model to the initial data was tested. First-year ice and multi-year ice simulations agreed with observed differences in individual pond size and depth. Sensitivity studies showed that pond fraction is most sensitive to mean initial snow depth in first-year ice simulations and reduction of ice permeability all cases.

Feltham, D. L.; Scott, F.

2009-12-01

142

Airborne laser scanning based quantification of dead-ice melting in recently deglaciated terrain  

NASA Astrophysics Data System (ADS)

Dead-ice is explained as stagnant glacial ice, not influenced by glacier flow anymore. Whenever glaciers have negative mass balances and an accumulation of debris-cover on the surface, dead-ice may form. Although, there are numerous conceptual process-sediment-landform models for the melt-out of dead-ice bodies and areas of dead-ice environments at glacier margins are easily accessible, just a few quantitative studies of dead-ice melting have been carried out so far. Processes and rates of dead-ice melting are commonly believed to be controlled by climate and debris-cover properties, but there is still a lack of knowledge about this fact. This study has a focus on the quantification of process induced volumetric changes caused by dead-ice melting. The research for this project was conducted at Hintereisferner (Ötztal Alps, Austria), Gepatschferner (Ötztal Alps, Austria) and Schrankar (Stubai Alps, Austria), areas for which a good data basis of ALS (Airborne Laser Scanning) measurements is available. 'Hintereisferner' can be characterized as a typical high alpine environment in mid-latitudes, which ranges between approximately 2250 m and 3740 m a.s.l.. The Hintereisferner region has been investigated intensively since many decades. Two dead ice bodies at the orographic right side and one at the orographic left side of the Hintereisferner glacier terminus (approx. at 2500 m to 2550 m a.s.l.) were identified. Since 2001, ALS measurements have been carried out regularly at Hintereisferner resulting in a unique data record of 21 ALS flight campaigns, allowing long-term explorations of the two dead-ice areas. The second study area of 'Gepatschferner' in the Kaunertal ranges between 2060 m and 3520 m a.s.l. and is the second largest glacier of Austria. Near the glacier tongue at the orographic right side a significant dead ice body has formed. The ALS data used for quantification include a period of time of 4 years (2006 - 2010). 'Schrankar' is located in the Western Stubai Alps in a north to south aligned valley, with 12 rockglaciers of different activities between elevations of 2400 m and 2800 m a.s.l.. Beside the rockglaciers, a big dead ice body (approx. at 2800 m to 2850 m a.s.l.) next to the terminus of the southern Schrankarferner was identified. For the quantification of dead-ice melting, ALS data was used from 2006 - 2009. Additionally, a time series of digital elevation models (DEM) derived from aerial images of different periods (1953 -2003) were integrated in the analysis. In recent years, high-accuracy DEMs from ALS altimetry are emerging as an additional data source to existing field measurements. We present inter annual and annual trends of topographic changes caused by dead-ice melting. These trends are determined from multitemporal DEM differencing. The DEMs are generated from aerial images and ALS data. First results on the three dead-ice bodies of Hintereisferner show significant changes (-0.48 m and -2.24 m respectively per year). The derived melt rates are discussed, summarized and assessed in relation to climate parameters, like mean annual air temperature, mean summer air temperature, mean annual precipitation, mean summer precipitation, and annual sum of positive degree days.

Klug, C.; Sailer, R.; Schümberg, M.; Stötter, J.

2012-04-01

143

Interfacial Melting of Ice in Contact with SiO2  

Microsoft Academic Search

The physical behavior of condensed matter can be drastically altered in the presence of interfaces. Using a high-energy x-ray transmission-reflection scheme, we have studied ice-SiO2 model interfaces. We observed the formation of a quasiliquid layer below the bulk melting temperature and determined its thickness and density as a function of temperature. The quasiliquid layer has stronger correlations than water and

S. Engemann; H. Reichert; H. Dosch; J. Bilgram; V. Honkimäki; A. Snigirev

2004-01-01

144

Space-time variation of mixed-layer properties, heat and salt fluxes, and ice melt in the Newfoundland marginal ice zone  

NASA Astrophysics Data System (ADS)

Oceanographic data collected in the Newfoundland marginal ice zone in March 1992 are analyzed to study the variation of mixed-layer properties across the ice zone. The mixed-layer depth decreases from 80 m in the interior of the pack ice to 25 m at the eastern ice edge over a distance of 120 km. In the open ocean without ice cover, the depth is considerably greater, 150˜200 m. The temperature under the pack ice is near freezing. A sharp increase in both the temperature and salinity occurs across the ice edge. The variation of the mixed-layer properties is simulated by integrating a one-dimensional bulk mixed-layer model coupled to sea ice, from November 1991 to March 1992. The initial ocean conditions are obtained from an objective analysis of archived data of November 1991. The forcings are 6-hourly meteorological data from the European Centre for Medium-Range Weather Forecasts. Ice concentration and thickness are treated as prescribed functions of time extracted from daily ice maps since ice in the area is not locally formed. The model simulation is in good agreement with the observations. From the model results, a detailed analysis of the roles of wind stress, ice melt, surface cooling, and shortwave radiation in the water mass transformation of the upper ocean is carried out. There are large differences in the melt rate and water-ice heat flux between the times when ice enters the shelf and after the water has been cooled by the ice to near freezing: 15˜20 cm d-1 and 500˜700 Wm-2, and 0˜2 cm a-1 and 20˜50 Wm-2 respectively. A large portion of the heat in the water column is expended for ice melting from January to March. Calculations that use surface data such as surface wind and sea surface temperature without considering ice melt can underestimate the net ocean-to-air heat flux, especially at the eastern ice edge in March.

Tang, C. L.; Detracey, B. M.

1998-01-01

145

A new sea ice albedo scheme including melt ponds for ECHAM5 general circulation model  

Microsoft Academic Search

Today we experience an accelerated melting of sea ice in the Arctic which global circulation models are inadequate to predict. We believe one of the reasons is the shortcomings in the sea ice albedo schemes for these models. This paper investigates a physically based sea ice albedo scheme for ECHAM5 GCM, which separates between snow-covered sea ice, bare sea ice,

Christina A. Pedersen; Erich Roeckner; Mikael Lüthje; Jan-Gunnar Winther

2009-01-01

146

Calving fluxes and basal melt rates of Antarctic ice shelves.  

PubMed

Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000?gigatonnes per year. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321?±?144?gigatonnes per year and a total basal mass balance of -1,454?±?174?gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering and enhanced discharge. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing. PMID:24037377

Depoorter, M A; Bamber, J L; Griggs, J A; Lenaerts, J T M; Ligtenberg, S R M; van den Broeke, M R; Moholdt, G

2013-09-15

147

Glacier winds on Vatnajökull ice cap, Iceland, and their relation to temperatures of its lowland environs  

Microsoft Academic Search

During the ablation season, the ice cap Vatnajökull (8100 km2) develops its own microclimate that we describe by meteorological data collected during the summers of 1994-2003. Persistent glacier winds are generated down the melting ice cap, whose variations in speed can be related empirically to the temperature fluctuations of the lowland environs of the ice cap. This suggests that climate

Helgi Björnsson; Sverrir Gudmundsson; Finnur Pálsson

2005-01-01

148

Sensitivity of Microwave Properties to Melting Ice-Phase Precipitation  

NASA Astrophysics Data System (ADS)

Microwave remote sensing is ideally suited for detecting and estimating precipitation due the fact that microwave radiation strongly interacts with precipitation hydrometeors, while remaining relatively insensitive to clouds and atmospheric gases. For rain, the relationships between observed microwave quantities (whether passive or active) are fairly well established. For ice-phase precipitation, such as snow, graupel, frozen rain, etc., the relationship between what is observed and the physical properties of the precipitation is much more uncertain. The shape of ice-phase hydrometeors can be highly variable, even when the total particle mass is the same. Because microwave remote sensing of ice-phase precipitation often exploits the fact that ice is a strong scatterer of microwave radiation, the shape of the particles within the field of view have a non-trivial impact on the scattered field of radiation. This becomes further complicated when these particles begin to melt, due to the presence and distribution of liquid water. The present study examines the role of particle shape and melting in simulating observable quantities for both passive and active microwave applications. We specifically focus on the Global Precipitation Measurement Mission and the CloudSat mission for the selection of microwave frequencies examined; ranging from 10.65 GHz to 183.31 GHz for the passive, and 13.4, 35.6, and 94.0 GHz for radar remote sensing.

Johnson, B. T.; Skofronick Jackson, G.

2011-12-01

149

Changes of CDW on the Amundsen Sea Shelf as a major cause for Ice Sheet melt  

NASA Astrophysics Data System (ADS)

From February to March 2010 a joint geophysical and oceanographic German expedition with RV Polarstern into the Amundsen Sea will provide an important contribution to the long-term monitoring of CDW characteristics on the Amundsen Sea continental shelf, continuously conducted by colleagues in the US (LDEO) and UK (BAS), as part of the international ASEP (Amundsen Sea Embayment Project). For the Amundsen Sea it is entirely plausible that ocean influence on the WAIS (West-Antarctic Ice Sheet) could increase from changes in ocean temperature, heat transport and vertical thermohaline structure, in response to altered atmospheric forcing, sea ice production, and ice shelf morphology. Previous work has revealed that the ‘warm,' salty CDW gains access to the continental shelf near the sea floor, particularly in the eastern sector, and ponds in glacially scoured troughs that extend deep beneath the ice shelves. The oceanic heat drives basal ice shelf melting rates orders of magnitude faster than beneath the largest ice shelves. Substantial thermohaline variability is apparent in some of the repeated late summer observations, but little is yet known about the seasonal cycle or interannual variability. Heat transport from the continental shelf break to the ice shelf caverns may be influenced by mixing over the rough bottom topography, tidal currents, winds, sea ice production, icebergs, and meltwater impacts on the pycnocline. The talk will focus on first results form CTD measurements conducted during the just finished cruise and the comparison with previous hydrographic data.

Schroeder, Michael; Hellmer, Hartmut; Wisotzki, Andreas; Jacobs, Stan

2010-05-01

150

Extending remote sensing estimates of Greenland ice sheet melting  

NASA Astrophysics Data System (ADS)

The Melt Area Detection Index (MADI), a remote sensing algorithm to discriminate between dry and wet snow, has been previously developed and applied to the western portion of the Greenland ice sheet for the years 2000-2006, using Moderate Resolution Imaging Radiospectrometer (MODIS) data (Chylek et al, 2007). We extend that work both spatially and temporally by taking advantage of newly available data, and developing algorithms that facilitate the sensing of cloud cover and the automated inference of wet snow regions. The automated methods allow the development of a composite melt area data product with 0.25 km^2 spatial resolution and approximately two week temporal resolution. We discuss melt area dynamics that are inferred from this high resolution composite melt area. Chylek, P., M. McCabe, M. K. Dubey, and J. Dozier (2007), Remote sensing of Greenland ice sheet using multispectral near-infrared and visible radiances, J. Geophys. Res., 112, D24S20, doi:10.1029/2007JD008742.

Heavner, M.; Loveland, R.

2010-12-01

151

Phytoplankton production from melting ponds on Arctic sea ice  

NASA Astrophysics Data System (ADS)

Recently, the areal extent of melt ponds within sea ice has rapidly increased during the Arctic Ocean summer. However, the biological impacts of melt ponds on the Arctic marine ecosystem have rarely been studied. Carbon and nitrogen uptake rates of phytoplankton were measured at 26 different melt ponds in 2005 and 2008, using a 13C-15N dual stable isotope tracer technique. Generally, the open ponds had relatively higher nutrients than closed ponds, but the nutrient concentrations in the open ponds were within a range similar to those in surrounding surface seawaters. Chlorophyll a (Chl a) concentrations in melt ponds ranged from 0.1 to 2.9 mg Chl a m-3 with a mean of 0.6 mg Chl a m-3 (SD = ±0.8 mg Chl a m-3) in the Canada Basin in 2005, whereas the range of the Chl a concentrations was from 0.1 to 0.3 mg Chl a m-3 with a mean of 0.2 mg Chl a m-3 (SD = ±0.1 mg Chl a m-3) in the central Arctic Ocean in 2008. The average annual carbon production in sea ice melt ponds was 0.67 g C m-3 (SD = ±1.03 g C m-3) in the Arctic Ocean. Based on this study, recent annual carbon production of all melt ponds was roughly estimated to be approximately 2.6 Tg C, which is less than 1% of the total production in the Arctic Ocean.

Lee, Sang H.; Stockwell, Dean A.; Joo, Hyoung-Min; Son, Young Baek; Kang, Chang-Keun; Whitledge, Terry E.

2012-04-01

152

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

Microsoft Academic Search

The effect of added salt (NaCl) on the melting of ice is studied using molecular dynamics simulations. The equilibrium freezing point depression observed in the simulations is in good agreement with experimental data. The kinetic aspects of melting are investigated in terms of the exchange of water molecules between ice and the liquid phase. The ice\\/liquid equilibrium is a highly

Jun Soo Kim; Arun Yethiraj

2008-01-01

153

Effective viscosity of partially melted ice in the ammonia-water system  

Microsoft Academic Search

The steady-state deformation of paritally melted ice in the ammonia-water system was studied by means of a concentric cylinder viscometer in shear stresses, 10 kPa approximately 0.1 MPa, temperatures, 180 approximately 210 K and NH3 contents, 4.0 approximately 8.4%. The flow law found was of a non-Newtonian power-law type; the stress exponent was 4.0 +\\/- 0.1. The activation energy at

M. Arakawa; N. Maeno

1994-01-01

154

Melting by temperature-modulated calorimetry  

SciTech Connect

Well-crystallized macromolecules melt irreversibly due to the need of molecular nucleation, while small molecules melt reversibly as long as crystal nuclei are present to assist crystallization. Furthermore, imperfect crystals of low-molar-mass polymers may have a sufficiently small region of metastability between crystallization and melting to show a reversing heat-flow component due to melting of poor crystals followed by crystallization of imperfect crystals which have insufficient time to perfect before the modulation switches to heating and melts the imperfect crystals. Many metals, in turn. melt sharply and reversibly as long as nuclei remain after melting for subsequent crystallization during the cooling cycle. Their analysis is complicated, however, due to thermal conductivity limitations of the calorimeters. Polymers of sufficiently high molar mass, finally, show a small amount of reversible. local melting that may be linked to partial melting of individual molecules. Experiments by temperature-modulated calorimetry and model calculations are presented. The samples measured included poly(ethylene terephthalate)s, poly(ethylene oxide)s, and indium. Two unsolved problems that arose from this research involve the origin of a high, seemingly stable, reversible heat capacity of polymers in the melting region, and a smoothing of melting and crystallization into a close-to-elliptical Lissajous figure in a heat-flow versus sample-temperature plot.

Wunderlich, B.; Okazaki, Iwao; Ishikiriyama, Kazuhiko; Boller, A. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry]|[Oak Ridge National Lab., TN (United States)

1997-09-01

155

Melt-water accumulation on the surface of the Greenland ice sheet: Effect on albedo and mass balance  

NASA Astrophysics Data System (ADS)

Satellite-derived albedo maps of the western part of the Greenland ice sheet (between 64.5 and 70.5 degreesN) reveal a north-south extending zone with relatively low albedos at some distance from the ice margin. In the literature it has been hypothesized that this "dark zone" is due to a local maximum in melt-water accumulation on the ice-covered surface. A plausible explanation for this maximum in melt-water accumulation is that relative to the situation within the "dark zone", melt-water accumulation is reduced at higher elevations by a smaller melt-water production rate whereas runoff occurs more easily at lower elevations where slopes are generally steeper. For the present paper AVHRR images from eight years (1990-1997) were analysed. The following indications confirming the "melt-water accumulation hypothesis" were found: (1) there is a significant correlation between the annual mean albedo lowering within the "dark zone" and the annual amount of melt as inferred from local mass-balance measurements: and (2) within each summer season the albedo lowering within the "dark zone" seems to respond to the melt-water production rate as inferred from local temperature measurements. The effect of melt-water accumulation on the albedo implies a positive feedback between the albedo and the amount of melt. It is estimated that approximately 40% of the interannual mass-balance variations in the ''dark zone" are due to this feedback.

Greuell, W.

156

Crystallization, melting, and structure of water nanoparticles at atmospherically relevant temperatures.  

PubMed

Water nanoparticles play an important role in atmospheric processes, yet their equilibrium and nonequilibrium liquid-ice phase transitions and the structures they form on freezing are not yet fully elucidated. Here we use molecular dynamics simulations with the mW water model to investigate the nonequilibrium freezing and equilibrium melting of water nanoparticles with radii R between 1 and 4.7 nm and the structure of the ice formed by crystallization at temperatures between 150 and 200 K. The ice crystallized in the particles is a hybrid form of ice I with stacked layers of the cubic and hexagonal ice polymorphs in a ratio approximately 2:1. The ratio of cubic ice to hexagonal ice is insensitive to the radius of the water particle and is comparable to that found in simulations of bulk water around the same temperature. Heating frozen particles that contain multiple crystallites leads to Ostwald ripening and annealing of the ice structures, accompanied by an increase in the amount of ice at the expense of the liquid water, before the particles finally melt from the hybrid ice I to liquid, without a transition to hexagonal ice. The melting temperatures T(m) of the nanoparticles are not affected by the ratio of cubic to hexagonal layers in the crystal. T(m) of the ice particles decreases from 255 to 170 K with the particle size and is well described by the Gibbs-Thomson equation, T(m)(R) = T(m)(bulk) - K(GT)/(R - d), with constant K(GT) = 82 ± 5 K·nm and a premelted liquid of width d = 0.26 ± 0.05 nm, about one monolayer. The freezing temperatures also decrease with the particles' radii. These results are important for understanding the composition, freezing, and melting properties of ice and liquid water particles under atmospheric conditions. PMID:22452637

Johnston, Jessica C; Molinero, Valeria

2012-04-05

157

Modeling of thermal processes for internal melt ice-on-coil tank including ice-water density difference  

Microsoft Academic Search

The internal melt ice-on-coil tank with horizontal tubes is used widely for thermal storage. Its discharge process is greatly affected by the ice-water density different. The existing models developed for internal melt ice-on-coil tanks are concentric cylinder models which are applicable to tanks with vertical tubes or when all the water in the tank is frozen, but they do not

Yingxin Zhu; Yan Zhang

2001-01-01

158

An experimental study of crystallization and crystal growth of methane hydrates from melting ice  

Microsoft Academic Search

An experiment with well defined gas-water interfacial surface area was developed to study the crystallization and crystal growth of methane hydrates. Measurable formation rates were observed only when melting ice was involved. No hydrates nucleated from liquid water or from non-melting ice. It is concluded that melting ice, which like hydrate water is hydrogen-bonded, provides a template for hydrate nucleation

M. J. Hwang; D. A. Wright; A. Kapur; G. D. Holder

1990-01-01

159

Melt season duration on Canadian Arctic ice caps, 2000-2004  

Microsoft Academic Search

The extent and duration of summer melt on ice caps in the Queen Elizabeth Islands (QEI), Nunavut, Canada, in 2000-2004 were mapped using enhanced resolution QuikSCAT (QSCAT) scatterometer images. The mean melt duration depends mainly on surface elevation and distance from Baffin Bay. Over most ice caps, inter-annual variations in melt duration and the variation in melt duration with elevation

L. Wang; M. J. Sharp; B. Rivard; S. Marshall; D. Burgess

2005-01-01

160

Melt season duration on Canadian Arctic ice caps, 2000–2004  

Microsoft Academic Search

The extent and duration of summer melt on ice caps in the Queen Elizabeth Islands (QEI), Nunavut, Canada, in 2000–2004 were mapped using enhanced resolution QuikSCAT (QSCAT) scatterometer images. The mean melt duration depends mainly on surface elevation and distance from Baffin Bay. Over most ice caps, inter-annual variations in melt duration and the variation in melt duration with elevation

L. Wang; M. J. Sharp; B. Rivard; S. Marshall; D. Burgess

2005-01-01

161

Recent melt rates of Canadian arctic ice caps are the highest in four millennia  

Microsoft Academic Search

There has been a rapid acceleration in ice-cap melt rates over the last few decades across the entire Canadian Arctic. Present melt rates exceed the past rates for many millennia. New shallow cores at old sites bring their melt series up-to-date. The melt-percentage series from the Devon Island and Agassiz (Ellesmere Island) ice caps are well correlated with the Devon

David Fisher; James Zheng; David Burgess; Christian Zdanowicz; Christophe Kinnard; Martin Sharp; Jocelyne Bourgeois

162

A finite-volume approach for coupled simulations of ice, sediment, and melt-water transport  

NASA Astrophysics Data System (ADS)

Glaciers and ice-sheets are highly dynamic systems showing temporal changes occurring over several timescales, ranging from days/weeks (glacier surges), to years/centuries (e.g. ice streams), to millennia (ice ages). While long-term variability relates primarily to changes in global earth surface temperatures, feedbacks related to water- and sediment-modulated basal sliding is thought to provide the main control on the short-term and spatially localised variability. Process oriented computational exploration of the importance of such feedbacks requires numerical platforms for simulating the coupled flow of glacier ice, melt-water, and sediments. Here we present a new computational approach for simulating coupled ice-related flow processes on a three-dimensional topographic surface. The method employs 1) irregular finite volume discretization of the topographic surface, 2) local 2nd order polynomial approximation of the bed topography and ice surface and 3) explicit time marching. Ice flow is computed using a second-order shallow-ice approximation (SOSIA) including contributions from longitudinal stress gradients, rugged bed topographies, and localised ice-thickness variations. The finite-volume approach leads to a general and highly parallel algorithm based on discrete cell interactions, which is well suited for simulating coupled sub-glacial flow systems as well as other types of surface flow processes, like fluvial and hill-slope related sediment transport. The inherent benefit of the method thus relates primarily to the ease with which several types of earth surface processes may be simulated simultaneously. We illustrate the potentials of the approach by simple model scenarios related to the dynamics of alpine glaciers.

Egholm, D. L.; Piotrowski, J. A.; Lesemann, J.-E.; Nielsen, S. B.

2009-04-01

163

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

164

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

165

Heat of Freezing and Melting of Sea Ice.  

National Technical Information Service (NTIS)

Computations are presented which show that the latent heat of freezing ice in equilibrium with sea water is less than that associated with freezing pure water at 0C. The difference is due primarily to a temperature effect that is opposed to some extent by...

D. Anderson

1966-01-01

166

Onset and end of the summer melt season over sea ice: thermal structure and surface energy perspective from SHEBA  

NASA Astrophysics Data System (ADS)

Various measurements from the Surface Heat Flux of the Arctic Ocean (SHEBA) experiment have been combined to study structures and processes producing the onset and end of summer melt over Arctic sea ice. The analysis links the surface energy budget to free-troposphere synoptic variables, clouds, precipitation, and in-ice temperatures. The key results are (1) SHEBA melt-season transitions are associated with atmospheric synoptic events (2) onset of melt clearly occurs on May 28, while the end of melt is produced by a sequence of three atmospheric storm events over a 28-day period producing step-like reductions in the net surface energy flux. The last one occurs on August 22.; (3) melt onset is primarily due to large increases in the downwelling longwave radiation and modest decreases in the surface albedo; (4) decreases in the downwelling longwave radiation occur for all end-of-melt transition steps, while increases in surface albedo occur for the first two; (5) decreases in downwelling shortwave radiation contribute only to the first end-of-melt transition step; (6) springtime free-tropospheric warming preconditions the atmosphere-ice system for the subsequent melt onset; and (7) melt-season transitions also mark transitions in system responses to radiative energy flux changes because of invariant melt-season surface temperatures. The extensive SHEBA observations enable an understanding of the complex processes not available from other field program data. The analysis provides a basis for future testing of the generality of the results, and contributes to better physical understanding of multi-year analyses of melt-season trends from less extensive data sets.

Persson, P. Ola G.

2012-09-01

167

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

168

Can Marine Micro-organisms Influence Melting of the Arctic Pack Ice?  

NASA Astrophysics Data System (ADS)

The Arctic Ocean Expedition of 2001 (AOE-2001) to the central Arctic mostly north of latitude 85°N was conducted to study marine life forms and their products in water and ice, how their products may get into the air, the evolution of the particles produced, and their growth up to sizes large enough for activation into clouds. The expedition also investigated whether these naturally generated particles and clouds constitute a positive or negative climate feedback upon temperature forcing, as schematically shown in Figure 1. Indeed, biological activity of the open lead surface micro-layer was found to strongly influence particle production over the pack ice region, and this would influence cloud properties there. Similar processes transferring particulates from the surface micro-layer to the air-bubble bursting-should be operative over the world's oceans. So, can marine micro-organisms influence the melting of the Arctic pack ice? The answer must be yes, but to determine whether that influence is significant or not, we have to contend with many unknown factors. For example, will biological activity and airborne particle production increase or decrease with melting of the pack ice, and will resultant changes in warmer oceans oppose or reinforce the Arctic changes? Will cloud cover and the feeble mixing between surface and higher air remain unchanged? To have identified a possible influence on climate change is important, but assessing the extent of that influence will be a far harder problem.

Leck, Caroline; Tjernström, Michael; Matrai, Patrica; Swietlicki, Erik; Bigg, Keith

2004-01-01

169

Extreme melt on Canada's Arctic ice caps in the 21st century  

NASA Astrophysics Data System (ADS)

Canada's Queen Elizabeth Islands contain ˜14% of Earth's glacier and ice cap area. Snow accumulation on these glaciers is low and varies little from year to year. Changes in their surface mass balance are driven largely by changes in summer air temperatures, surface melting and runoff. Relative to 2000-2004, strong summer warming since 2005 (1.1 to 1.6°C at 700 hPa) has increased summer mean ice surface temperatures and melt season length on the major ice caps in this region by 0.8 to 2.2°C and 4.7 to 11.9 d respectively. 30-48% of the total mass lost from 4 monitored glaciers since 1963 has occurred since 2005. The mean rate of mass loss from these 4 glaciers between 2005 and 2009 (-493 kg m-2 a-1) was nearly 5 times greater than the 1963-2004 average. In 2007 and 2008, it was 7 times greater (-698 kg m-2 a-1). These changes are associated with a summer atmospheric circulation configuration that favors strong heat advection into the Queen Elizabeth Islands from the northwest Atlantic, where sea surface temperatures have been anomalously high.

Sharp, Martin; Burgess, David O.; Cogley, J. Graham; Ecclestone, Miles; Labine, Claude; Wolken, Gabriel J.

2011-06-01

170

The pressure melting of ice under a body with flat base  

Microsoft Academic Search

One of the anomalous thermodynamic properties of water is that the melting point of ice decreases as the pressure increases. This behavior was discovered independently by Kirchhoff and Thomson. It inspired Reynolds to speculate that the pressure-melting of ice and snow might be responsible for the low coefficient of friction experienced during skating and skiing. According to him, the pressure

A. Bejan; P. A. Tyvand

1992-01-01

171

Melting heat transfer of liquid ice in a rectangular cavity with a heated vertical wall  

SciTech Connect

The melting characteristics of liquid ice in a rectangular cavity were studied experimentally. The liquid ice, mixture of ice particles and ethylene-glycol aqueous solution, was heated from one of the vertical walls of the cavity. The shape of the mush-liquid interface, melting rate, and local/mean heat-transfer coefficient at the heated vertical wall were observed and measured under a variety of conditions of heat flux and initial concentration of the aqueous binary solution. It was found that the formation of double-diffusive layers based on the thermal and solutal buoyancy forces exerted a great influence on the melting process of the liquid ice.

Fukusako, Shoichiro; Yamada, Masahiko; Kim, Myounghwan (Hokkaido Univ. (Japan). Dept. of Mechanical Engineering)

1993-12-01

172

A Five-Year Record of Summer Melt on Eurasian Arctic Ice Caps  

Microsoft Academic Search

Climatologies and annual anomaly patterns (2000-04) of melt season duration and dates of melt onset\\/ freeze-up on Eurasian Arctic ice masses were derived from Quick Scatterometer (QuikSCAT) backscatter data. Severnaya Zemlya, Russia, has later melt onset, earlier freeze-up, and shorter melt seasons than Svalbard, Norway\\/Novaya Zemlya, Russia. In all three archipelagos 2001 was the longest melt season and 2000 was

Martin Sharp; Libo Wang

2009-01-01

173

Melting-driven evolution of an ice-shelf coupled to a buoyant meltwater plume  

NASA Astrophysics Data System (ADS)

Melting at the base of ice shelves can impact ice-sheet flow and hence have consequences for sea-level rise. Recent measurements have revealed significant heterogeneities in ice-shelf thickness, including channels and undulations in the ice-shelf base. However, the precise conditions for genesis remain unclear. The buoyancy-driven flow of meltwater under an ice shelf is sensitive to ice-shelf geometry, with faster flow under steeper basal slopes providing a feedback that increases melting rates. To build insight into the potential for melting-driven instability, I consider the simplified setting of a two-dimensional stationary ice shelf melting into a warmer ocean. A theoretical model is developed to describe the coupling of a meltwater plume to an evolving ice-shelf geometry. When there is negligible subglacial discharge, the subsequent weak-flow regime near to the grounding line results in a planar ice-water interface being neutrally stable to small perturbations. Hence, the amplitude of perturbations to the basal slope neither grows, nor decays. In the absence of ice-deformation, the nonlinear evolution of melting results in cusp-like features in the ice-shelf base.

Wells, Andrew J.

2013-04-01

174

Future projections of the Greenland ice sheet energy balance driving the surface melt, developed using the regional climate MAR model  

NASA Astrophysics Data System (ADS)

In this study, 25 km-simulations are performed over the Greenland ice sheet (GrIS) throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios from two CMIP5 global circulation models, in order to investigate the projected changes of the surface energy balance (SEB) components driving the surface melt. Analysis of 2000-2100 melt anomalies compared to melt results over 1980-1999 reveals an exponential relationship of the GrIS surface melt rate simulated by MAR to the near-surface temperature (TAS) anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are rather driven by stronger sensible heat fluxes, induced by enhanced warm air advections over the ice sheet. Over the central dry snow zone, the increase of melt surpasses the negative feedback from heavier snowfall inducing therefore a decrease of the summer surface albedo even at the top of the ice sheet. In addition to the incoming longwave flux increase associated to the atmosphere warming, MAR projects an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. However, it should be noted that this trend in the cloud cover is contrary to that simulated by ERA-INTERIM-forced MAR over current climate, where the observed melt increase since the 1990's seems rather to be a consequence of more anticyclonic atmospheric conditions. Finally, no significant change is projected in the length of the melt season. This timing highlights the importance of solar radiation in the melt SEB.

Franco, B.; Fettweis, X.; Erpicum, M.

2012-07-01

175

Rapidly Melting Ice Caps of Northern Baffin Island: Insights From Cosmogenic and Conventional Radiocarbon Dating  

Microsoft Academic Search

The interior plateau of northern Baffin Island in the eastern Canadian Arctic is home to several small (< 50 km2) ice caps whose melt has been well recorded since 1949. Modern equilibrium line altitude (ELA) is well above all existing ice and a continuation of current climatic conditions will lead to the disappearance of all ice on the plateau in

R. K. Anderson; G. H. Miller; J. P. Briner; N. Lifton; S. B. Devogel

2006-01-01

176

Application of the theory of dispersion forces to the surface melting of ice  

Microsoft Academic Search

We apply the theory of Dzyaloshinskii, Lifshitz, and Pitaevskii to ice, water, and vapor at the triple point and find that electromagnetic interactions do not permit a liquid film of macroscopic thickness at the ice-vapor interface. Hence the surface melting of ice is at most incomplete. However, the thickness of the film which is permitted is surprisingly large, with retardation

Michael Elbaum; M. Schick

1991-01-01

177

DSC study and computer modelling of the melting process in ice slurry  

Microsoft Academic Search

In order to understand the non-isothermal melting kinetics in the ice slurry, a differential scanning calorimetry (DSC) was used. Experimental results were compared to those obtained by a numerical simulation in which a general enthalpy method was applied. In this work the ice slurry studied consists of ice particles uniformly dispersed within a water–antifreeze liquid mixture. The effects of the

T. Kousksou; A. Jamil; Y. Zeraouli; J.-P. Dumas

2006-01-01

178

Time and space variability of freshwater content, heat content and seasonal ice melt in the Arctic Ocean  

NASA Astrophysics Data System (ADS)

The Arctic Ocean water column is strongly stratified in salinity due to large freshwater input from river runoff, net precipitation and the inflow of low salinity Pacific water through Bering Strait: The strong stability allows sea ice to form in winter and to be exported. In summer seasonal ice melt adds freshwater to the stability in the upper part of the water column. The distribution of heat, relative to -1.9C, and freshwater, relative to 34.9, in the upper 1000m of the water column and in different areas of the Arctic Ocean, as well as the amount and distribution of seasonal ice melt have been determined from hydrographic data obtained from ice breaker cruises conducted in the Arctic Ocean during the last 15 years. The water column is subdivided into six layers: the Polar Mixed Layer, the upper halocline (S<34), the lower halocline (S>34, T<0C), two Atlantic layers (T>0C) separated at the temperature maximum, and the intermediate layer (T<0C) down to 1000m. The time variability of thickness, freshwater content and heat content in these layers is then determined for the Nansen Basin, the Gakkel Ridge, the Amundsen Basin, the Lomonosov Ridge, the Makarov Basin, the northern Canada Basin and the southern Canada Basin. The temporal variations in freshwater content are largest in the uppermost layers, the Polar Mixed Layer and the upper halocline and magnify towards Bering Strait. The seasonal ice melt is estimated from the freshwater stored in the Polar Surface Layer above the temperature minimum indicating the depth of the local winter convection and homogenisation. The melt water content is computed relative to the salinity at the temperature minimum. The required latent heat of melting and the sensible heat stored above the temperature minimum are compared with the NCEP/NCAR reanalysis heat input data. The estimated freshwater input is 1-2m, in Nansen Basin usually below 1m and over the Lomonosov Ridge and in the Makarov Basin sometimes above 2m. This is close to but generally less than the potential ice melt deduced from the reanalyses. The differences could be due to melt water stored onto or beneath the ice floes, to advection of freshwater and to the neglect of the heat capacity of sea ice.

Korhonen, Meri; Rudels, Bert; Zhou, Jinping

2010-05-01

179

MELT TEMPERATURE MODELS OF EXTRUDED WHEY PROTEINS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Empirical models of corn meal extrudates with whey protein isolate (WPI) based on melt temperature (MT) were derived for high shear extrusion conditions with temperatures ranging from 100 to 150C, ramped at 5 C intervals. WPI was added to corn meal at concentrations of 15, 25 and 35 wt%. Adding W...

180

Stratigraphic analysis of an ice core from the Prince of Wales Icefield, Ellesmere Island, Arctic Canada, using digital image analysis: High-resolution density, past summer warmth reconstruction, and melt effect on ice core solid conductivity  

NASA Astrophysics Data System (ADS)

High-resolution (1 mm) stratigraphic information was derived from digital image analysis of an ice core from the Prince of Wales (POW) Icefield, Central Ellesmere Island, Canada. Following careful image processing, a profile of ice core transmitted light was derived from the greyscale images and used to reconstruct high-resolution density variations for the unfractured sections of the core. Images were further classified into infiltration and glacier ice using an automatic thresholding procedure, and were converted to a high-resolution melt percentage index. The mean annual melt percentage over the last 580 years was 9%, and melting occurred in 8 years out of 10. Melting obliterated most of the original depositional sequence, and seasonal density cycles were mostly unrecognizable. The ice core solid conductivity was greater and more variable in melt features than in glacier ice, owing to washout of strong acids by meltwater (elution) and chemical enrichment upon refreezing. This hindered the identification of acid volcanic layers and further compromised dating by annual layer counting. Comparison of the melt record with those from other Arctic ice caps shows that the melt-temperature relationship on POW Icefield is site-specific. We speculate that this is due to the peculiar position of the icefield, which rests on the periphery of the Baffin Bay maritime climate zone, and to the proximity of the North Open Water polynya, which controls snow accumulation variability on the icefield and affects the melt percentage index.

Kinnard, Christophe; Koerner, Roy M.; Zdanowicz, Christian M.; Fisher, David A.; Zheng, Jiancheng; Sharp, Martin J.; Nicholson, Lindsey; Lauriol, Bernard

2008-12-01

181

Measurement of Latent Heat of Melting of Thermal Storage Materials for Dynamic Type Ice Thermal Storage  

NASA Astrophysics Data System (ADS)

In order to measure the latent heat of melting of ice slurries with various solute concentrations, an adiabatic calorimeter was constructed. Ice slurries were made from each aqueous solution of ethanol, ethylene glycol and silane coupling agent. The latent heat of melting of ice made from tap water was measured with the present calorimeter and the uncertainty of the result was one percent. Ice slurries were made both by mixing ice particles made from water with each aqueous solution and by freezing each aqueous solution with stirring in a vessel. The latent heat of melting of these ice slurries was measured with various concentrations of solution. The latent heat of melting decreased as the solute concentration or the freezing point depression increased. The latent heat of ice slurries made from ethanol or ethylene glycol aqueous solution agreed with that of ice made from pure water known already. The latent heat of melting of ice slurries made from silane coupling agent aqueous solution got smaller than that of ice made from pure water as the freezing point depression increased.

Sawada, Hisashi; Okada, Masashi; Nakagawa, Shinji

182

Basal Melting of a CO2-rich Ice Cap on Mars  

Microsoft Academic Search

Basal melting of the permanent polar caps of Mars is often inferred from terrain features. We show that a water ice cap cannot melt under likely conditions, so either the cap contains large amounts of CO2, or the evidence for melting is incorrect.

N. Hoffman; J. S. Kargel; K. L. Tanaka

2002-01-01

183

Using shallow ice coring experiments and melt modelling to determine mass balance of Devon Ice Cap, Canada  

Microsoft Academic Search

A combination of shallow ice-coring field experiments and degree-day melt modelling was employed to reconstruct the spatial pattern of mass balance across the Devon Ice Cap. This research is part of a wider program to quantify and to determine the causes of changes in the geometry and mass of the Devon Ice Cap over the last 40 years. In April-May

D. Mair; D. Burgess; M. Sharp

2003-01-01

184

Communication: Growing room temperature ice with graphene  

NASA Astrophysics Data System (ADS)

Water becomes ordered in the form of hexagonal ice at room temperature under controlled humidity conditions upon confinement in the nanometer range between protective graphene sheets and crystalline (111) surfaces with hexagonal symmetry of the alkali earth fluoride BaF2. Interfacial water/substrate pseudoepitaxy turns out to be a critical parameter since ice is only formed when the lattice mismatch is small, an observation based on the absence of ice on (111) surfaces of isostructural CaF2

Verdaguer, Albert; Segura, Juan José; López-Mir, Laura; Sauthier, Guillaume; Fraxedas, Jordi

2013-03-01

185

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

PubMed

The effect of added salt (NaCl) on the melting of ice is studied using molecular dynamics simulations. The equilibrium freezing point depression observed in the simulations is in good agreement with experimental data. The kinetic aspects of melting are investigated in terms of the exchange of water molecules between ice and the liquid phase. The ice/liquid equilibrium is a highly dynamic process with frequent exchange of water molecules between ice and the liquid phase. The balance is disturbed when ice melts and the melting proceeds in two stages; the inhibition of the association of water molecules to the ice surface at short times, followed by the increased dissociation of water molecules from the ice surface at longer times. We also find that Cl(-) ions penetrate more deeply into the interfacial region than Na(+) ions during melting. This study provides an understanding of the kinetic aspects of melting that could be useful in other processes such as the inhibition of ice growth by antifreeze proteins. PMID:19045033

Kim, Jun Soo; Yethiraj, Arun

2008-09-28

186

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

NASA Astrophysics Data System (ADS)

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

Kim, Jun Soo; Yethiraj, Arun

2008-09-01

187

Ice-melt collapse pits and associated features in the 1991 lahar deposits of Volcán Hudson, Chile: criteria to distinguish eruption-induced glacier melt  

Microsoft Academic Search

In subaerial volcaniclastic sequences structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcán Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50 km down the Rio de los Huemules valley to the sea. Large

M. J. Branney; J. S. Gilbert

1995-01-01

188

Ice-melt collapse pits and associated features in the 1991 lahar deposits of Volcán Hudson, Chile: criteria to distinguish eruption-induced glacier melt  

Microsoft Academic Search

In subaerial volcaniclastic sequences, structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcán Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50?km down the Rio de los Huemules valley to the sea. Large current

Michael J. Branney; Jennie S. Gilbert

1995-01-01

189

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

PubMed

Glaciers and ice sheets on many active volcanoes are rapidly receding. There is compelling evidence that melting of ice during the last deglaciation triggered a dramatic acceleration in volcanic activity. Will melting of ice this century, which is associated with climate change, similarly affect volcanic activity and associated hazards? This paper provides a critical overview of the evidence that current melting of ice will increase the frequency or size of hazardous volcanic eruptions. Many aspects of the link between ice recession and accelerated volcanic activity remain poorly understood. Key questions include how rapidly volcanic systems react to melting of ice, whether volcanoes are sensitive to small changes in ice thickness and how recession of ice affects the generation, storage and eruption of magma at stratovolcanoes. A greater frequency of collapse events at glaciated stratovolcanoes can be expected in the near future, and there is strong potential for positive feedbacks between melting of ice and enhanced volcanism. Nonetheless, much further research is required to remove current uncertainties about the implications of climate change for volcanic hazards in the twenty-first century. PMID:20403841

Tuffen, Hugh

2010-05-28

190

Analysis of summer 2002 melt extent on the Greenland ice sheet using MODIS and SSM/I data  

USGS Publications Warehouse

Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0?? isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave/Imager (SSM/I)-derived melt, at the time of the maximum melt extent in 2002. To validate the MODIS-derived land-surface temperatures (LSTs), we compared the MODIS LSTs with air temperatures from nine stations (using 11 different data points) and found that they agreed to within 2.3??2.09??C, with station temperatures consistently lower than the MODIS LSTs. According to the MODIS LST, the maximum surface melt extended to ???2300 m in southern Greenland; while the SSM/I measurements showed that the maximum melt extended to nearly 2700 m in southeastern Greenland. The MODIS and SSM/I data are complementary in providing detailed information about the progression of surface and near-surface melt on the Greenland ice sheet.

Hall, D. K.; Williams, Jr. , R. S.; Steffen, K.; Chien, J. Y. L.

2004-01-01

191

Defect pair separation as the controlling step in homogeneous ice melting.  

PubMed

On being heated, ice melts into liquid water. Although in practice this process tends to be heterogeneous, it can occur homogeneously inside bulk ice. The thermally induced homogeneous melting of solids is fairly well understood, and involves the formation and growth of melting nuclei. But in the case of water, resilient hydrogen bonds render ice melting more complex. We know that the first defects appearing during homogeneous ice melting are pairs of five- and seven-membered rings, which appear and disappear repeatedly and randomly in space and time in the crystalline ice structure. However, the accumulation of these defects to form an aggregate is nearly additive in energy, and results in a steep free energy increase that suppresses further growth. Here we report molecular dynamics simulations of homogeneous ice melting that identify as a crucial first step not the formation but rather the spatial separation of a defect pair. We find that once it is separated, the defect pair--either an interstitial (I) and a vacancy (V) defect pair (a Frenkel pair), or an L and a D defect pair (a Bjerrum pair)--is entropically stabilized, or 'entangled'. In this state, defects with threefold hydrogen-bond coordination persist and grow, and thereby prepare the system for subsequent rapid melting. PMID:23783630

Mochizuki, Kenji; Matsumoto, Masakazu; Ohmine, Iwao

2013-06-20

192

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

National Technical Information Service (NTIS)

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 th...

D. G. Vaughan P. Vornberger R. Bindschadler

2011-01-01

193

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

194

Sum-frequency spectroscopic studies: I. Surface melting of ice, II. Surface alignment of polymers  

SciTech Connect

Surface vibrational spectroscopy via infrared-visible sum-frequency generation (SFG) has been established as a useful tool to study the structures of different kinds of surfaces and interfaces. This technique was used to study the (0001) face of hexagonal ice (Ih). SFG spectra in the O-H stretch frequency range were obtained at various sample temperatures. For the vapor(air)/ice interface, the degree of orientational order of the dangling OH bonds at the surface was measured as a function of temperature. Disordering sets in around 200 K and increases dramatically with temperature, which is strong evidence of surface melting of ice. For the other ice interfaces (silica/OTS/ice and silica/ice), a similar temperature dependence of the hydrogen bonded OH stretch peak was observed; the free OH stretch mode, however, appears to be different from that of the vapor (air)/ice interface due to interactions at the interfaces. The technique was also used to measure the orientational distributions of the polymer chains on a rubbed polyvinyl alcohol surface. Results show that the polymer chains at the surface appear to be well aligned by rubbing, and the adsorbed liquid crystal molecules are aligned, in turn, by the surface polymer chains. A strong correlation exists between the orientational distributions of the polymer chains and the liquid crystal molecules, indicating that the surface-induced bulk alignment of a liquid crystal film by rubbed polymer surfaces is via an orientational epitaxy-like mechanism. This thesis also contains studies on some related issues that are crucial to the above applications. An experiment was designed to measure SFG spectra in both reflection and transmission. The result confirms that SFG in reflection is generally dominated by the surface contribution. Another issue is the motional effect due to fast orientational motion of molecules at a surface or interface. Calculations show that the effect is significant if the molecular orientation varies over a broad range within the vibrational relaxation time. The stretch vibration of the free OH bonds at the vapor/water interface is used to illustrate the importance of the effect.

Wei, Xing

2000-12-21

195

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

NASA Astrophysics Data System (ADS)

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 Sea during the summer of 1998 during the Surface Heat Budget of the Arctic Ocean (SHEBA) are presented. Sites representative of melting multiyear and first-year ice, along with ponded ice were measured. Observed spectral irradiance extinction coefficients (K?) show broad minima near 500 nm and strong increases at near-infrared wavelengths. The median K? at 600 nm for the bare ice cases is close to 0.8 m-1 and about 0.6 m-1 for ponded ice. Values are considerably smaller than the previously accepted value of 1.5 m-1. Radiative transfer models were used to analyze the observations and obtain inherent optical properties of the ice. Derived scattering coefficients range from 500 m-1 to 1100 m-1 in the surface layer and 8 to 30 m-1 in the ice interior. While ponded ice is known to transmit a significant amount of shortwave radiation to the ocean, the irradiance transmitted through bare, melting ice is also shown to be significant. The findings of this study predict 3-10 times more solar radiation penetrating the ice cover than predicted by a current GCM (CCSM3) parameterization, depending on ice thickness, pond coverage, stage of the melt season, and specific vertical scattering coefficient profile.

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

2008-03-01

196

Sea Surface Temperatures and their Relationship to Melt and Freeze Onset in the Central Arctic  

NASA Astrophysics Data System (ADS)

With the advent of polar orbiting satellites in the late 1970’s we have been able to study remote locations like the Arctic in great detail and are now able to observe trends in Arctic ice extent. The Arctic has warmed 2 to 3 C since the 1950’s and sea surface temperatures (SST) have been increasing since 1995. Arctic sea ice extent has been decreasing at a rate of -10.2 to -11.4% per decade from 1979 to 2007 and the ice pack has been decreasing in thickness as well, moving from a predominately thick multi-year ice pack to a more vulnerable thin first-year ice pack. This decrease in ice extent and thickness has allowed a larger area of open ocean in the summer months, strengthening the ice-ocean interactions in the Arctic. These trends have also influenced the onset of ice melt in the spring and freezing in the fall. A new dataset of melt and freeze onset has been created from passive-microwave data using SMMR and SSM/I from 1979-2009 A recent analysis of this data has shown that the melt season length has increased by 6.4 days/decade for the entire Arctic. Regions like the Chukchi/Beaufort Seas, Laptev/East Siberian Seas, East Greenland Sea, and Hudson Bay show melt season increasing by more than 10 days/decade. This dataset shows that some areas of the Arctic have increased their melt season by 20 days since 1979.This could have profound impact on the stability of the ice pack. The timing of melt onset is crucial to the maintenance of the ice pack for the duration of the melt season, especially where the first-year ice pack melts and exposes the Arctic Ocean. This enhances the ice-albedo feedback and causes a large input of heat into the ocean, which then has to be released in order for freezing to occur in the fall. In these areas, early melting allows for the SSTs to increase and for more heat to be absorbed by the system. This large the amount of heat absorbed delays freeze-up because it takes longer for this heat to be lost. In years when the SST is warmer than average we should expect to see the melt season length to be longer than years when the SST is below average. In this study we focus primarily on the first-year ice pack of the Chukchi/Beaufort Seas, the Laptev/East Siberian Seas and the Kara/Barents Seas to determine how SSTs are influenced by melt onset and how they impact freeze-up in the fall. This is accomplished by analysis of the SST dataset produced by the National Climate Data Center using optimum interpolation between the Pathfinder Advanced Very High Resolution Radiometer (AVHRR), observational AVHRR and in-situ observations for the years 1982-2009. Using both satellite and in-situ data results in reduced errors. This product has a spatial resolution of 1/4° and temporal resolution of 1 day. The dataset will be compared with melt and freeze onset datasets. The goal was to better understand the role of first-year ice-ocean interactions and the role that SSTs play in impacting melt season length.

Boisvert, L.; Markus, T.; Parkinson, C.

2010-12-01

197

An experimental investigation into the icing and melting process of a water droplet impinging onto a superhydrophobic surface  

NASA Astrophysics Data System (ADS)

The freezing and melting process of a small water droplet on a superhydrophobic cold surface was investigated using the Laser Induced Fluorescence (LIF) technique. The superhydrophobic surface was prepared using a sol-gel method on a red copper test plate. From the obtained fluorescence images, the phase transition characteristics during the freezing and melting process of a water droplet were clearly observed. It was found that, at the beginning of the droplet freezing process, liquid water turned into ice at a very fast rate. Such phase transition process decreased gradually with time and the volume of frozen ice approached a constant value at the end of the icing process. In addition, the freezing time was found to reduce with the decrease of the test plate temperature. Besides, when the test plate temperature is relatively high, the effect of droplet volume on the freezing time is very significant. Over all, we provide some tentative insights into the microphysical process related to the icing and melting process of water droplets.

Jin, ZheYan; Jin, SongYue; Yang, ZhiGang

2013-09-01

198

Emissivities of High Temperature Metallic Melts  

NASA Astrophysics Data System (ADS)

The mathematical modeling of heat flow in high temperature processes has been a useful means of obtaining more efficient process design and stricter process control. At high temperatures heat can be transferred by three mechanisms, that is, conduction, convection, and radiation. Analysis of heat transfer requires physical property data of a medium through which heat is transferred, relevant to the respective mechanisms: the thermal conductivity is indispensable to heat flux calculation by conduction from Fourier's law, and the viscosity, density, and heat capacity are indispensable to heat flux calculation by convection. On the other hand, the emissivity plays a key role in heat transfer analysis by radiation because it quantifies how well a substance radiates energy in the form of light. The emissivity is more important in the analysis for materials processing involving metallic melts since the radiation contribution becomes more predominant as temperature rises. Thus, emissivity measurements have been conventionally attempted on various metallic melts at high temperatures, data of which have been published in the handbook [1], for example. However, the data have not been abundant enough for practical use in mathematical modeling, and measurements are still now being made continuously. This chapter focuses on emissivities of metallic melts and reviews recent measurement techniques and data for the emissivity, mainly on and after the publication of the handbook.

Susa, Masahiro; Endo, Rie K.

199

Studies of ice-snow melt debris flows in the western Tian Shan Mountains, China  

Microsoft Academic Search

The ice-snow melt debris flow in the west part of the Tian Shan Mountains is an important natural hazard. The sediment for the debris flows is derived from the thick Quaternary deposits which occur in the Tain Shan Mountains. Another cause of the debris flows is the ice- snow meltwater and the abundant precipitation in the western part of the

WEI WENSHOU; GAO CUNHAI

1992-01-01

200

Onset of Convection in a Layer of Water Formed by Melting Ice from Below  

Microsoft Academic Search

The onset of convection, or the critical Rayleigh number in a layer of water formed continuously by melting ice from below, has been determined experimentally. Homogeneous, bubble-free ice was prepared, and used in all the experiments. The critical Rayleigh number Rac for a fluid undergoing phase change and density inversion is not a single value but may be correlated empirically

Yin-Chao Yen

1968-01-01

201

Modeled steric and mass-driven sea level change caused by Greenland Ice Sheet melting  

Microsoft Academic Search

Meltwater from the Greenland Ice Sheet (GIS) has been a major contributor to sea level change in the recent past. Global and regional sea level variations caused by melting of the GIS are investigated with the finite element sea-ice ocean model (FESOM). We consider changes of local density (steric effects), mass inflow into the ocean, redistribution of mass, and gravitational

S.-E. Brunnabend; J. Schröter; R. Timmermann; R. Rietbroek; J. Kusche

202

Anisotropic elastocreep in glacial ice: A mechanism for intergranular melt and recrystallization  

Microsoft Academic Search

Bonded ice crystals under pressure are in a heterogeneous stress state because of the mechanical anisotropy of constituent grains. This condition plays a role in intergranular melt and recrystallization, which in turn influence properties such as permeability and biologic habitability. To examine this, we develop an anisotropic elastocreep model simulating subgrain-scale stresses in polycrystalline ice, choosing in particular the thermal

Steven M. Jepsen; Edward E. Adams

2008-01-01

203

Coupling snow densification and melt-water retention in a large-scale ice sheet model  

Microsoft Academic Search

The physics of snow and how the annual snow changes during a melting season is important for the surface mass balance of the Greenland Ice Sheet. Densification when meltwater is present will generally go much faster than the dry snow densification due to percolation and refreezing of meltwater in the snow-pack and it needs to be considered in ice sheet

R. S. Fausto; A. P. Ahlstrøm; S. J. Johsen

2008-01-01

204

Effect of heat transmission through melt ponds and ice on melting during summer in the Arctic Ocean  

Microsoft Academic Search

To observe sea ice and ocean conditions in the Arctic in summer, a trans-Arctic research cruise of the U.S. Coast Guard Cutter Healy was conducted from 5 August to 30 September 2005. The relationship between the ice concentration observed by the on-board ice-watch and the temperature above the freezing point (?T) measured by expendable conductivity-temperature-depth (XCTD) sensors had a negative

Jun Inoue; Takashi Kikuchi; Donald K. Perovich

2008-01-01

205

Effect of heat transmission through melt ponds and ice on melting during summer in the Arctic Ocean  

Microsoft Academic Search

To observe sea ice and ocean conditions in the Arctic in summer, a trans-Arctic research cruise of the U.S. Coast Guard Cutter Healy was conducted from 5 August to 30 September 2005. The relationship between the ice concentration observed by the on-board ice-watch and the temperature above the freezing point (DeltaT) measured by expendable conductivity-temperature-depth (XCTD) sensors had a negative

Jun Inoue; Takashi Kikuchi; Donald K. Perovich

2008-01-01

206

Melting of small Arctic ice caps observed from ERS scatterometer time series  

Microsoft Academic Search

Time series of active microwave backscatter data from the ERS Wind Scatterometers are used to demonstrate (1) the timing of melt onset can be observed over small ice caps, as well as the major ice sheets and multi-year sea ice; and (2) temporally integrated backscatter reduction (R) is strongly correlated with total annual positive-degree-days (PDD), as measured at four automated

Laurence C. Smith; Yongwei Sheng; Richard R. Forster; Konrad Steffen; Karen E. Frey; Douglas E. Alsdorf

2003-01-01

207

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

Microsoft Academic Search

The Greenland ice sheet is likely to make a faster contribution to sea-level rise in a warming world than previously believed, based on numerical modelling using a parameterization of recent results showing surface-meltwater lubrication of ice flow. Zwally et al. (Science 297(557) (2002) 218) documented correlation between increased ice velocity and increased surface melt (as parameterized by positive degree days).

Byron R. Parizek; Richard B. Alley

2004-01-01

208

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

209

The peculiarities of water crystallization and ice melting processes in the roots of one-year plants (Plantago major L.).  

PubMed

Results are presented of a water phase transition study in plantain (Plantago major L.) roots, which were used as a model system to research the peculiarities of water crystallization and ice melting processes in complex heterogeneous biological systems. It was confirmed that water in such systems is crystallized in two clearly distinguished temperature ranges: -10 to -25 degree capital ES, Cyrillic and -25 to -45 degree capital ES, Cyrillic. These water fractions are conditionally attributed to extracellular (-10 to -25 degree capital ES, Cyrillic) and intracellular (-25 to -45 degree capital ES, Cyrillic) solutions. A possible explanation is given for such significant supercooling of the intracellular solution. The values of osmotic pressures of extra- and intracellular solutions were determined according to ice melting curves. It is noted that the intracellular solution, which crystallized at lower temperatures, had a lower osmotic pressure. PMID:18754062

Bakradze, N; Kiziria, E; Sokhadze, V; Gogichaishvili, S

210

Can Arctic Sea Ice Summer Melt be Accelerated by Changes in Spring Cloud Properties?  

NASA Astrophysics Data System (ADS)

Ice-albedo feedback remains the major factor accelerating recently observed decline in the Arctic sea ice extent and thickness. The immediate effect of this feedback is offset by clouds, which decrease the amount of solar radiation reaching the surface in summer. However, once the surface albedo is decreased due to an increase in the open water fraction or enhanced snow melt, larger amounts of solar radiation are absorbed by the ocean mixed layer. This can cause earlier spring snow/ice melt, a delay in the fall freeze-up, and an overall decrease in the ice thickness. Studies with the Surface Heat Budget of the Arctic (SHEBA) data showed that the Arctic stratus clouds produce a net warming of 20 W m-2 in the surface layer during the spring season, which may accelerate the spring time melting of the ice pack. In the Arctic where the cloudiness is usually high, cloud radiative forcing depends mostly on the cloud microphysical properties, rather than on the cloud fraction. Liquid clouds have an order of magnitude larger optical thickness compared to ice clouds. Using the SHEBA data, we relate the seasonal changes in cloud short-wave and long-wave radiative forcing to the cloud ice/liquid water content. We will also present the results from a simple thermodynamic sea ice model to show the cloud effects on sea ice thickness and concentration.

Gorodetskaya, I.; Tremblay, B.; Liepert, B.; Cane, M.

2006-12-01

211

A Multiband Remote Sensing Study of Melting Shorefast Sea Ice  

Microsoft Academic Search

Near-shore waters along Alaska's Beaufort sea coast are covered by shorefast sea ice 9 to 10 months each year, and by April the fast ice extends 10 to 50 km seaward along the coast. Recent scientific interest in sea ice dynamics (Maykut et al., 1972) and the prospects for offshore petroleum development in the region (Clark, 1976) highlight the need

Richard E. Moritz; Luis A. Bartolucci

1977-01-01

212

Internal melting in Antarctic sea ice: Development of “gap layers”  

Microsoft Academic Search

An internal “gap” layer of deteriorated sea ice is co-located with a significant microbial biological community in late first year and second year Antarctic sea ice in summer. We modeled gap layer formation using a thermal flux model based on the summer reversal in thermal gradient and the thermal conductivity found in the upper ice column. The conductive model gives

S. F. Ackley; M. J. Lewis; C. H. Fritsen; Hongjie Xie

2008-01-01

213

Temperature dependence of ice critical nucleus size.  

PubMed

We present a molecular dynamics study of ice growth from supercooled water. By performing a series of simulations with different initial conditions, we have quantitative established the relationship existing between the critical nucleus size and the temperature. The results show that ice embryos containing hundreds or thousands of molecules are needed for the system to crystallize macroscopically, even at high degrees of supercooling. Our findings explain the difficulty in observing spontaneous ice nucleation in atomistic simulations and the relative ease with which water droplets can be supercooled under controlled experiments. PMID:21787014

Pereyra, Rodolfo G; Szleifer, Igal; Carignano, Marcelo A

2011-07-21

214

Rapidly Melting Ice Caps of Northern Baffin Island: Insights From Cosmogenic and Conventional Radiocarbon Dating  

NASA Astrophysics Data System (ADS)

The interior plateau of northern Baffin Island in the eastern Canadian Arctic is home to several small (< 50 km2) ice caps whose melt has been well recorded since 1949. Modern equilibrium line altitude (ELA) is well above all existing ice and a continuation of current climatic conditions will lead to the disappearance of all ice on the plateau in the future. Between 2000 and 2005, approximately 1 km2 of ice was lost per year, equivalent to ~1.3% of the total ice cover on the plateau. To put this current melt into a larger picture of ice-cap history on the plateau since deglaciation 6 ka, several techniques have been used in concert. The recent extent of the ice caps during the Little Ice Age can be estimated from the preservation of lichen trimlines across much of the plateau. These trimlines represent previous multi-year snow or ice cover and their aerial extent can be measured via satellite imagery. Based on these measurements, modern ice caps represent only ~3% of ice-cap extent during the Little Ice Age. Radiocarbon dating of moss, preserved beneath the ice caps due to their cold-based nature, suggests a sudden expansion of ice cover around 520 calendar years before present (cal BP), indicated by a mode of 7 dates of approximately this age. This coincides with a pulse of global volcanic activity; predicted cooling from increased aerosol loading may have triggered rapid ice-cap growth. However, dead moss emerging at three sites is more than 1000 years old, with a maximum age of 1326±15 cal BP, indicating that portions of the remaining ice caps have remained intact from more than 1000 years Further constraints on ice cap size are provided by 14C cosmogenic exposure dating. 14C concentrations in rocks at the modern ice margin are too low to be the result of continuous exposure since deglaciation followed by shielding for 500-1000 years by ice cover. Exposure history modeling indicates at least one additional prior period of ice cover of approximately 1000 years. This cold interval most likely occurred sometime since 4 ka, after the Holocene Thermal Maximum in the Arctic and coeval with the onset of Neoglaciation. Radiocarbon dating reveals that some plateau ice caps have been continuously present for more than 1000 years, whereas others formed early in the Little Ice Age (~520 cal BP). Even without additional warming, continuation of current climatic conditions on northern Baffin Island will result in the demise of all ice on the plateau, a condition that has not occurred for more than 1300 years.

Anderson, R. K.; Miller, G. H.; Briner, J. P.; Lifton, N.; Devogel, S. B.

2006-12-01

215

Links between acceleration, melting, and supraglacial lake drainage of the western Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

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 ˜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.

2011-12-01

216

Molecular transport and phase transition of polycrystalline ice doped with HCl and SO2 near its melting point  

NASA Astrophysics Data System (ADS)

HCl and SO2 are major trace gases in atmosphere, which greatly affects chemical properties of atmospheric ice particles. A particular interest to atmospheric science is the effects of impurities on molecular transport and phase transition at grain boundaries in polycrystalline ice. Effects of doped HCl and SO2 on transport and phase transition at grain boundary of 2-4 micrometer polycrystalline ice were studied using a novel technique - Fast Thermal Desorption Spectroscopy (FTDS) [1] in the temperature range from -2 to -20 deg. C. In these experiments, H2O/D2O/H2O sandwich-like polycrystalline ice films doped with HCl and SO2 were vapor- deposited on the surface of a thin filament positioned in a vacuum chamber and maintained initially at cryogenic temperatures. After the deposition, the temperature of the filament was rapidly raised to a value near ice melting point, thus, initiating rapids H/D exchange reaction at the interface of H2O and D2O layers. Diffusion controlled rate of isotopic exchange in the desorbing film was monitored with a sensitive mass-spectrometer making it possible to gain quantitative information of the extent of diffusion of chemical species along the grain boundaries in polycrystalline ice samples. Comparisons of the experimental results in pure and doped polycrystalline ice show that water self diffusivity at the grain boundaries is significantly enhanced (by at least an order of magnitude) in the presence of HCl or SO2. The strong, non- Arrhenius, dependence of the water self-diffusivity on temperature indicates that this is due to grain boundary premelting [2], which may occur at temperatures as low as 10 deg. below ice melting point. We will discuss implication of this and other results of our FTDS experiments to various environmental phenomena. References: 1. Haiping Lu, Stephanie A. McCartney, M. Chonde, D. Smyla, and Vlad Sadtchenko, Fast thermal desorption spectroscopy study of morphology and vaporization kinetics of polycrystalline ice films, J. Chem. Phys., 125, 044709, 2006. 2. Dash, J.G., A.W. Rempel and J.S. Wettlaufer, The physics of premelted ice and its geophysical consequences, Rev. Mod. Phys., 78, 695, 2006.

Lu, H.; McCartney, S.; Sadtchenko, V.

2007-12-01

217

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

218

A Warmer Atmosphere on Mars Near the Noachian-Hesperian Boundary: Evidence from Basal Melting of the South Polar Ice Cap (Dorsa Argentea Formation)  

Microsoft Academic Search

Dorsa Argentea Formation (Noachian-Hesperian) eskers are evidence for basal melting. Ice-flow models show that the mean annual south polar temperature must be raised to -50° to -75°C, providing an independent estimate of elevated lower latitude surface temperature.

J. L. Fastook; J. W. Head; D. R. Marchant; F. Forget; J.-B. Madeleine

2011-01-01

219

A Warmer Atmosphere on Mars Near the Noachian-Hesperian Boundary: Evidence from Basal Melting of the South Polar Ice Cap (Dorsa Argentea Formation)  

NASA Astrophysics Data System (ADS)

Dorsa Argentea Formation (Noachian-Hesperian) eskers are evidence for basal melting. Ice-flow models show that the mean annual south polar temperature must be raised to -50° to -75°C, providing an independent estimate of elevated lower latitude surface temperature.

Fastook, J. L.; Head, J. W.; Marchant, D. R.; Forget, F.; Madeleine, J.-B.

2011-03-01

220

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

221

CO2-H2O Phase Equilibria: Residual Ice Layers and Basal Melting of the Martian Polar Ice Caps  

Microsoft Academic Search

Shifts in saturation surfaces with pressure favor residual layers of solid CO_2 at the martian south pole. Basal melting of solid-CO_2 layers within polar ice caps during periods of low obliquity may lead to storage of liquid CO_2 in the Martian crust.

J. Longhi

2004-01-01

222

CO2-H2O Phase Equilibria: Residual Ice Layers and Basal Melting of the Martian Polar Ice Caps  

NASA Astrophysics Data System (ADS)

Shifts in saturation surfaces with pressure favor residual layers of solid CO_2 at the martian south pole. Basal melting of solid-CO_2 layers within polar ice caps during periods of low obliquity may lead to storage of liquid CO_2 in the Martian crust.

Longhi, J.

2004-03-01

223

On the Question of Accumulation of Ice-Melt Water South of the Ice in the Chukchi Sea.  

National Technical Information Service (NTIS)

The processes controlling the distribution of melt water from the retreating ice edge in summer in the Chukchi Sea were examined in order to provide evidence of the flow regime. Current and salinity data from National Oceanogrpahic Data Center files and f...

R. G. Handlers

1977-01-01

224

Perception of melting and flavor release of ice cream containing different types and contents of fat.  

PubMed

Temporal effects of dairy and vegetable fats (0 to 18%) on perception of strawberry flavor release and melting of ice cream were studied using the time intensity sensory method. Also, aroma and flavor attributes of the ice cream samples were evaluated. Only slight effects of fat on the rate of flavor release and flavor intensity were perceived. A slightly faster flavor release from the vegetable fat compared with dairy fat was noticed. Polydextrose and maltodextrin as bodying agents in the fat-free ice cream significantly increased flavor release and melting rate of the ice cream. Increasing fat content slightly retarded melting of ice cream in the mouth. No significant effect of the fat quality on perceived melting was noticed. Significant differences in aroma and flavor attributes of the fat-free and other samples were perceived. Intensity and sharpness of the strawberry aroma and flavor were greater in fat-free samples and they were perceived as nontypical. Fattiness and creaminess were highly correlated. Maltodextrin and polydextrose increased perceived fattiness and creaminess of fat-free ice cream. PMID:12741536

Hyvönen, L; Linna, M; Tuorila, H; Dijksterhuis, G

2003-04-01

225

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

226

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

227

ERS-1 SAR analysis of Arctic ice concentration during the melt season  

Microsoft Academic Search

Ice concentration can be derived with high accuracy (a few percent) from SAR images using the so called “global” ice concentration algorithm. The concentration error increases if surface properties change systematically, e.g. due to temperature or wind shifts. Properties of importance for the accuracy of the algorithm have been studied over an Arctic ice area in August 1991. The algorithm

J. Askne; L. M. H. Ulander; D. Birkeland

1993-01-01

228

The influence of coastal polynyas on the basal melting of ice shelves.  

NASA Astrophysics Data System (ADS)

The dense water production from coastal polynyas can strongly modify local circulation patterns with implications for both net basal melting of ice shelves and dense water formation. Results are presented from two different ice-shelf/ocean models: one of the Amery Ice Shelf/Prydz Bay region; and one of the Mertz Glacier Ice Tongue region. The models are based on the Regional Ocean Modeling System (ROMS). Two important modifications have been made to improve the simulation of thermodynamic processes beneath ice shelves: the inclusion of direct basal melt/freeze processes; and the inclusion of frazil ice dynamics. The models are forced with tides and with a smoothy varying seasonal cycle of winds. Thermohaline and circulation fields are relaxed to a smoothly varying seasonal climatology at the lateral boundaries. The open ocean surface fluxes are modified by an imposed climatological sea-ice cover that includes the seasonal effect of polynyas. It was found that the Prydz Bay gyre and Mertz gyre are summertime features. Both the strength and direction of the gyres are controlled by the production of dense water from local coastal polynyas. The production of dense water creates a current that blocks the westward flowing coastal current and diverts it northward away from the coast. For the Amery region, the coastal current bypasses the Amery Ice Shelf and flows out of the Prydz Bay channel and westward along the slope front. During summer, when the polynyas in Prydz Bay are inactive, Modified Circumpolar Deep Water (MCDW) is entrained with the eastward flowing coastal current as part of the gyre circulation. Observations of sea-ice confirm the presence of the Prydz Bay gyre under these conditions. The melt rates are higher in winter (~0.8 m ice per year) compared with summer (~0.7 m ice per year). The melting is primarily driven by dense shelf waters, with sufficient negative bouyancy, that drain to the deepest parts of the ice shelf at ~2500m below mean sea level. Preliminary studies of the Mertz region show that times of highest basal melting correspond to the summertime movement of MCDW onto the shelf from the deep ocean. The model shows that the circulation in the Mertz depression is controlled seasonally by the formation of dense water that is formed in the polynya. The Mertz polynya also acts to block the movement of MCDW onto the shelf region and thus leads to lower melt rates during winter. Simulations that include a dynamic sea-ice model, without accounting for the effect of subgrid scale features, such as coastal polynyas, can potentially underestimate the production of dense shelf water, which has consequences for the basal melting of ice shelves. This research contributes to understanding how interaction between ice shelves and various forcing mechanisms can lead to changes in basal melt/freeze and dense water formation, which has major implications for the stability of ice shelves, sea level rise, and the salt budget of the global oceans.

Galton-Fenzi, Benjamin; Marsland, Simon; Meijers, Andrew; Fraser, Alex

2010-05-01

229

A measurement method of ice layer thickness based on resistance-capacitance circuit for closed loop external melt ice storage tank  

Microsoft Academic Search

The measurement of the ice layer thickness in closed loop external melt ice storage tank not only affects the optimal operation of the ice storage system but also directly determines the safety of the system. The traditional methods could not satisfy the needs of rapidity and accuracy very well. A measurement method to quickly and accurately predict the thickness of

Wenxing Shi; Baolong Wang; Xianting Li

2005-01-01

230

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

231

The relationship between melt, refreezing and runoff across a transect on the Greenland ice sheet  

Microsoft Academic Search

Across the accumulation zone of the Greenland ice sheet (GrIS), a spatially-variable (but unknown) proportion of the summer meltwater does not become runoff, but percolates into the sub-surface snowpack and underlying firn where it refreezes, forming ice layers and lenses. This process causes sub-surface density to increase after melt events, leading to surface elevation change without corresponding mass change. These

R. M. Morris; D. Mair; V. Parry; P. W. Nienow

2010-01-01

232

Geophysical implications of presen-day and late Pleistocene ice melting across New Zealand  

NASA Astrophysics Data System (ADS)

According to the estimation given by Chinn (2001) in total a 53 km3 of ice volume was accumulated over New Zealand during the Pleistocene covering an area of about 1160 km2 concentrated mainly along the South Island between 42 and 46 arc-deg of southern latitudes. Most recently a new mass balance monitoring program has been established with on-site support by the World Glaciers Monitoring Service (WGMS). Chinn (1996) suggests an increase retreating of glaciers with a net ice volume loss between 1977 and 2005 of about 11% (Unep, 2008). In this study we investigate the sensitivity of New Zealand's coastal regions to decadal glaciers melting (estimated by Chinn 1996) by means of sea level change and bedrock deformations. A regional present-day ice melting model, composed by disc loads with fixed positions spaced in order to minimize the overlaps, is developed and applied. We provide an estimate of the global patterns of sea level (fingerprints) associated with the melting of New Zealand's glaciers assuming an incompressible and elastic earth model. The predicted elastic deformation field is combined with the estimates of the visco-elastic deformation field associated with the melting of the late-Pleistocene ice sheets according to a set of plausible combinations of ice chronology and mantle viscosity. The total deformation field is then compared with GPS observations.

Ruggieri, G.; Tenzer, R.; Spada, G.; Fadil, A.

2012-04-01

233

Response of a Coupled Ocean–Atmosphere Model to Greenland Ice Melting  

Microsoft Academic Search

We investigate the transient response of the global coupled ocean–atmosphere system to enhanced freshwater forcing representative\\u000a of melting of the Greenland ice sheets. A 50-year long simulation by a coupled atmosphere–ocean general circulation model\\u000a (CGCM) is compared with another of the same length in which Greenland melting is prescribed. To highlight the importance of\\u000a coupled atmosphere–ocean processes, the CGCM results

D. Stammer; N. Agarwal; P. Herrmann; A. Köhl; C. R. Mechoso

2011-01-01

234

Seasonal to interannual variability in Antarctic sea-ice surface melt  

Microsoft Academic Search

Satellite remote sensing time-series images are used to illustrate the spatial and temporal variability in Antarctic-wide sea-ice surface melting during the austral summer. Combinations of collocated data from the Active Microwave Instrument onboard the ERS-1\\/2 spacecraft, RadarSat synthetic aperture radar (SAR), and special sensor microwave\\/imager (SSM\\/I) passive microwave radiometer are used in characterizing the effects of surface melting on measured

Mark R. Drinkwater; Xiang Liu

2000-01-01

235

Can Arctic sea-ice melt be explained by atmospheric meridional transports? (Invited)  

NASA Astrophysics Data System (ADS)

The Arctic summer sea ice is melting away at an alarming rate, and it is now expected that an principally sea-ice free Arctic summer will occur much earlier than projected by the IPCC AR4 models. At the same time Arctic near-surface temperatures are rising at a rate much faster than the global average. The processes responsible for these changes are debated and many claim that local feedbacks, such as the surface albedo feedback, are the main culprits while other argue that remote effects, such as atmospheric circulation changes on synoptic and hemispheric scales, are the most important. We will explore the effects of the meridional transport by synoptic and larger scale atmospheric circulation on recent changes, using reanalysis data. It will be illustarated how this transport can contribute significant amounts of sensible heat, but also of atmospheric moisture such that local cloud feedbacks as well as the direct greenhouse effect of the water vapor contributes significantly to the surface energy balance over the Arctic polar cap.

Tjernstrom, M. K.; Graversen, R. G.

2010-12-01

236

Melting temperature of MgO at high pressures  

NASA Astrophysics Data System (ADS)

In this study, the melting temperature of MgO is determined at high pressures using the laser-heated diamond-anvil cell. Single-crystal MgO is coated with a variety of refractory metals as a laser absorber and laser heated from both sides. The melting is identified by recrystallization of the single crystal upon quenching, which is shown through the appearance of powder x-ray diffraction. Determining the melting temperature of MgO has profound implications for mantle rheology and melting relations at high pressure, furthermore, providing a crucial test for theoretical models of high-pressure melting.

Du, Z.; Lee, K. K.

2010-12-01

237

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.

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

2012-01-01

238

New insights into ice growth and melting modifications by antifreeze proteins.  

PubMed

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

2012-07-11

239

Sea-level rise: Melting glaciers and ice caps  

Microsoft Academic Search

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.

Frank Paul

2011-01-01

240

Melting of ice slurry under forced convection conditions in tubes  

Microsoft Academic Search

The paper presents the results of experimental research on heat transfer of ice slurry during its flow through tubes of circular, rectangular and slit cross-sections. Moreover, the work discusses the influence of solid particles, type of motion and cross-section on the changes in the heat transfer coefficient. The analysis presented in the paper allows for an identification of the criterial

Beata Niezgoda-?elasko; Jerzy ?elasko

2008-01-01

241

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

242

Can Marine Microorganisms Influence Melting of the Arctic Pack Ice?  

Microsoft Academic Search

The Arctic Ocean Expedition of 2001 (AOE-2001) to the central Arctic mostly north of latitude 85°N was conducted to study marine life forms and their products in water and ice, how their products may get into the air, the evolution of the particles produced, and their growth up to sizes large enough for activation into clouds. The expedition also investigated

Caroline Leck; Michael Tjernström; Patrica Matrai; Erik Swietlicki; Keith Bigg

2004-01-01

243

Natural convection for the melting of ice in porous media in a rectangular enclosure  

Microsoft Academic Search

The transient behavior and heat transfer for the melting of ice in porous media within a rectangular enclosure is simulated by the numerical method SIMPLE C. The solid-liquid interface becomes irregular due to the presence of porous media. The mushy zone of the finite thickness is taken into consideration in this investigation. The entire flow field is modeled by the

Wen-Jeng Chang; Dong-Fang Yang

1996-01-01

244

Models of ice melting and edifice growth at the onset of subglacial basaltic eruptions  

Microsoft Academic Search

Models of the early stages of basaltic eruptions beneath temperate glaciers are presented that consider the evolving sizes of volcanic edifices emplaced within subglacial cavities. The cavity size reflects the competing effects of enlargement by melting and closure by downward ductile deformation of the ice roof, which occurs when the cavity pressure is less than glaciostatic due to meltwater drainage.

Hugh Tuffen

2007-01-01

245

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

246

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

Microsoft Academic Search

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

Robert A. Black

1990-01-01

247

Thermal Instability in a Layer of Water Formed by Melting Ice from Below.  

National Technical Information Service (NTIS)

The transition in the mode of heat transfer from conduction to convection in a layer of water formed continuously by melting ice from below has been determined experimentally. This was accomplished by locating the inflection point on the curve relating th...

Y. C. Yen

1969-01-01

248

Simulation of ice speedup events in Greenland from seasonal surface melt signals via explicit modelling of basal water pressure  

NASA Astrophysics Data System (ADS)

We model the glacial dynamic response of Greenland to seasonal patterns of surface melt. Our aim is to produce a model that can explain a number of aspects of observed speed-up behaviour in Greenland. These include: a seasonal acceleration of ice, differing speed-up of outlet and land terminating ice, and inter-annual variability of sliding velocity. The model is based on an ice-sheet scale model of basal water pressure HYDRO, originally developed to consider basal melt inputs to the subglacial environment. This is coupled to the community ice sheet model GLIMMER, via two principle mechanisms. First, the basal water pressure is incorporated into a function to describe a basal drag coefficient. This in turn is used in a sliding law which has a linear dependence on shear stress. Second, the model also defines a friction coefficient which explicitly defines basal heating rates as a function of basal ice velocity and water pressure. Water pressure distribution is predicted by resolving large-scale water production and flow over the ice sheet domain driven by hydraulic pressure gradients. This is based on a simple Darcian expression, but the model has the capacity to represent areas of efficient and inefficient flow by modifying the overall basal hydraulic conductivity as a function of water flux. Thus with high water throughput, the model can switch to an efficient mode, serving as a simple large-scale proxy to the development of basal water conduits without explicit specification of the system. The bed becomes impermeable where it is frozen. The surface system is coupled to the basal model by, a) developing a simple expression to pond any surface melt locally on the ice sheet surface (surface flow is omitted for simplicity) b) developing a simple proxy mechanism to hydrofracturing by allowing ponded water to reach the bed instantaneously once its depth is greater than a specific threshold, but controlled probabilistically c) such water is then included as if it were instantaneous basal melt. d) any further melt in the same season goes directly to the bed. An approximation to present Greenland is first modelled assuming quasi-equilibrium with present climate. This provides an ice temperature field and initial basal pressure regime. The model is then run for a further period using monthly time steps and surface water inputs. In doing so we can demonstrate a variety of speed-up behaviour at the margin linked to seasonal melt patterns. Given there is no explicit description of longitudinal stresses in the model we show a) a small response inland from where water reaches the bed, b) seasonal speed-up in some margins, but less so in those which already experience low effective pressures (e.g. Ilulissat), c) multi-seasonal pressure build-up and speed-up in some areas, d) a relative insensitivity to the overall magnitude of surface melt input fluxes but complex behaviour resulting from the triggered inclusion of surface water into the basal system.

Karatay, Mehmet; Hulton, Nick

2010-05-01

249

Effect of Thermal Radiation on Melting Times of DT Ice Layers in Polymer-Capsule Targets for IFE Reactors  

SciTech Connect

Estimates of the time-to-melt for cryogenic DT inertial fusion targets in the presence of thermal radiation are presented. This time is defined as that required for thermal radiation in a hypothetical reactor to raise the temperature of small polymer capsules containing solid DT by 1 K and to fully liquefy the contents. The time estimates are in turn based on estimates of the infrared absorption spectra of both solid DT and the polymer capsule material. Assuming typical target dimensions and rapid equilibration of the target temperature, the estimates show that the absorption of thermal radiation and subsequent heating of likely capsule materials will dominate the corresponding quantities of DT ice and thus that the former effect largely determines the time-to-melt of the target. Specific estimates are made for capsules fabricated from Kapton{sup TM} polyimide. Comparisons are also made for capsules coated with reflective metal coatings, and the potential benefit of these coatings is discussed.

Gosnell, Timothy R.; Hoffer, James K. [Los Alamos National Laboratory (United States)

2004-06-15

250

Partitioning of melt energy and meltwater fluxes in the ablation zone of the west Greenland ice sheet  

NASA Astrophysics Data System (ADS)

We present four years (August 2003-August 2007) of surface mass balance data from the ablation zone of the west Greenland ice sheet along the 67° N latitude circle. Sonic height rangers and automatic weather stations continuously measured accumulation/ablation and near-surface climate at distances of 6, 38 and 88 km from the ice sheet margin at elevations of 490, 1020 and 1520 m a.s.l. Using a melt model and reasonable assumptions about snow density and percolation characteristics, these data are used to quantify the partitioning of energy and mass fluxes during melt episodes. The lowest site receives very little winter accumulation, and ice melting is nearly continuous in June, July and August. Due to the lack of snow accumulation, little refreezing occurs and virtually all melt energy is invested in runoff. Higher up the ice sheet, the ice sheet surface freezes up during the night, making summer melting intermittent. At the intermediate site, refreezing in snow consumes about 10% of the melt energy, increasing to 40% at the highest site. The sum of these effects is that total melt and runoff increase exponentially towards the ice sheet margin, each time doubling between the stations. At the two lower sites, we estimate that radiation penetration causes 20-30% of the ice melt to occur below the surface.

van den Broeke, M.; Smeets, P.; Ettema, J.; van der Veen, C.; van de Wal, R.; Oerlemans, J.

2008-12-01

251

Multiparameter Radar Modeling and Observations of Melting Ice  

Microsoft Academic Search

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

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

1990-01-01

252

Properties of Ice Cloud and Melting Layer from GPM Validation Projects  

NASA Astrophysics Data System (ADS)

This study characterizes the properties of ice clouds and through the melting layer from observations during three field programs: LPVEX (Finland, 2010), MC3E (Oklahoma, 2011) and GCPEX (Canada, 2012). A combination of level-flight passes and Lagrangian spiral descents by aircraft, together with co-located radar observations, are used in the analysis. Excellent detail of the microphysics from 10 microns to more than 1 cm and direct measurements of the condensed water content were obtained in stratiform through convectively-generated clouds. We report on the ice cloud properties, fine details of the melting processes through the melting layer, and the development of multi-wavelength radar reflectivity-snowfall(rainfall) rate relationships that express these properties with this complete set of observations in a range of cloud types and geographical locations.

Heymsfield, Andrew; Bansemer, Aaron; Poellot, Mike; Oolman, Larry

2013-04-01

253

Significant Reduction in Arctic Perennial Sea Ice  

Microsoft Academic Search

Increasing temperature in summer can further decrease Arctic sea ice extent and ice thickness by stronger melting. Here, we examine a different mechanism, ice export by strong or persistent wind forcing, which can cause an anomalous decrease in perennial ice extent. An excessive perennial ice export may result in an effective thinning of the ice cover consisting less of thicker

S. V. Nghiem; Y. Chao; G. Neumann; P. Li; D. K. Perovich; P. Clemente-Colon

2006-01-01

254

Effects of initial parameters on the internal-melt ice-on-tube while icing  

Microsoft Academic Search

Numerical simulation method is widely used in studying ice-storage process in an ice-storage system. In this paper, the three-dimensional\\u000a dynamical mathematical model of the ice-storage process in a single tube is established and the process is solved by the enthalpy\\u000a method. Effects on the performance of heat-exchange, caused by variation of velocity of the refrigerant, inner diameter of\\u000a the tube,

Bingxi Li; Xinhai Xu; Yi Liu; Linhua Liu

2009-01-01

255

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

NASA Astrophysics Data System (ADS)

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 and the heat of melting of clusters and nanoparticles. The temperature (internal energy) of the particles is defined and how it affects the properties of and processes involving the particles is discussed. The melting features of clusters and nanoparticles versus bulk materials are examined. Early methods of determining the melting temperature of large clusters are described. New precision methods of measuring the melting temperature and the heat of melting of clusters are discussed, which use the clusters themselves as 'high-sensitivity calorimeters' to measure energy. Laser-based nanoparticle melting techniques are outlined.

Makarov, Grigorii N.

2010-05-01

256

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

257

Impact of melt ponds on decrease of Arctic summer sea ice based on simulations from 1980 to 2012  

NASA Astrophysics Data System (ADS)

Melt ponds form on Arctic sea ice during the melting season and their presence affects the heat and mass balances of the ice cover, mainly by decreasing the value of the surface albedo by up to 20%. We have developed a melt pond model suitable for forecasting the presence of melt ponds based on sea ice conditions. This model has been incorporated into the Los Alamos CICE sea ice model, the sea ice component of several IPCC climate models. Simulations for the period 1980 to 2012 are in good agreement with observed ice concentration. The maximum pond area occurs in the beginning of July with an Arctic mean of 25% (fraction of sea ice). The inter-annual variability is strong with the lowest maximum fraction of 15% occurring in years with the largest September ice extent and the highest maximum fraction of nearly 40% in years with the lowest September ice extent. Can the pond fraction in July be used to predict the following September ice extent? Based on our 33 year long time series the connection and correlation of pond fraction and minimum sea ice extent will be quantified.

Schroeder, David; Feltham, Daniel; Flocco, Daniela

2013-04-01

258

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

259

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.

2013-08-01

260

The Effects of Freezing, Melting and Partial Ice Cover on Gas Transport in Laboratory Seawater Experiments  

NASA Astrophysics Data System (ADS)

Sea ice physico-chemical processes affect gas dynamics, which may be relevant to polar ocean budgets of climatically-active gases. We used SF6 and O2 as inert gas tracers in a tank experiment to observe the transport of gases between water, ice and air during freezing/melting and partial ice cover. The results show that during ice growth, the rejection of O2 and SF6 was greater than the rejection of salt per unit of ambient concentration in seawater. Unconsolidated ice crystal growth produced an increase in dissolved O2 concentration, indicating that the water-air gradient may favor gas evasion during the early stages of sea-ice formation. Measurements of the gas transfer velocity (k), using SF6 and O2 during conditions of partial ice cover exceed the proportionality between the fraction of open water and k determined between 0% and 100% open water conditions. At 15% open water, k equals 35% of k during ice-free conditions, indicating the importance of under-ice turbulence for gas exchange. In our experiments most of this turbulence was produced by pumps installed for circulation of the water in the tank to avoid density stratification. Varying the turbulent kinetic energy (TKE) delivered to the water by these pumps produced a correspondent variation in k. Measurements of TKE using particle velocimetry suggest that turbulence in the ice-water boundary layer dominated the convection driven by heat loss through the open water, and the magnitude of net TKE production was similar to that measured beneath drifting ice in the field.

Loose, B.; McGillis, W.; Schlosser, P.; Perovich, D.; Takahashi, T.

2008-12-01

261

Impact of Antarctic ice shelf basal melting on sea ice and deep ocean properties  

Microsoft Academic Search

An approximation of Antarctica's rocky and icy coastline normally forms the southern boundary in global climate models. Such a configuration neglects extensive ice shelf areas where ocean-ice interaction initiates a net freshwater flux to the circumpolar continental shelf equal to ~75% of the annual mean net precipitation in coastal seas. The results of a numerical model for the Southern Ocean

H. H. Hellmer

2004-01-01

262

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

263

MHD technology for the production of Pb-Li eutectic melt with low melting temperature  

Microsoft Academic Search

The lead-based Pb-Li eutectic melt with the low melting temperature has been chosen as a promising blanket material for thermoelectric fusion reactors (for example, in breeding blanket test facilities). The main problem in the production of this material is a great difference in the densities of the both components (Pb and Li). They differ in more than 20 times, therefore,

J. Freibergs; J. Klavins; O. Lielausis; A. Mikelsons; J. Zandarts

2006-01-01

264

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.; Cavalieri, D.J. [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center

1997-07-01

265

Melt and collapse of buried water ice: An alternative hypothesis for the formation of chaotic terrains on Mars  

NASA Astrophysics Data System (ADS)

Chaotic terrains and the associated massive outflow channels are some of the most enigmatic features on Mars. Over hundreds of kilometres of rock units are fractured, tilted, and have subsided, forming chaotic terrain basins (Sharp, 1973). Large quantities of water emanated from these chaotic terrains in short periods of time in the Hesperian epoch (~ 3.7-3.3 Ga), carving huge outflow channels, thousands of kilometres long, and more than 1 km deep (Baker, 2001). However, the subsurface mechanism by which chaotic terrains form, and thereby suddenly produce very large quantities of water (> 10 5 km 3) is poorly understood. Here we explore if these features can form by melting and collapse of buried water ice in a confined basin. 2D thermal modelling, using boundary conditions derived from the geology of Aram Chaos, demonstrates that a buried ice unit will start melting when 1-2 km of overburden has accumulated. The thickness of the liquid subsurface layer depends primarily on the crustal heat flux, the thermal conductivity of the overburden sediments, and the surface temperature. A subsurface liquid water layer of 1 to 2 km can be achieved under present day surface temperature conditions and a crustal heat flux of 15-30 mW m - 2 . To a first order, the geological features of chaotic terrains and their outflow channels are consistent with a scenario in which a subsurface lake forms by melting of buried water ice, followed by collapse and rapid outflow of water. If correct, this hypothesis suggests that subsurface lakes on Mars may have existed for extensive (> 100 Ma) periods of time. Such subsurface lakes would be of major interest for astrobiology.

Zegers, Tanja E.; Oosthoek, Jelmer H. P.; Rossi, Angelo P.; Blom, Jan Kees; Schumacher, Sandra

2010-09-01

266

Energy budget of first-year Arctic sea ice in advanced stages of melt  

NASA Astrophysics Data System (ADS)

During an 8 day drift in July-August 2012 in the Nansen Basin, all components of the energy budget of melting first-year sea ice were observed. Absorption of solar radiation by the ice and ponds was the largest source of energy to the ice at almost all times during the drift. However, oceanic heat flux also provided significant heating and dominated during one wind event. Longwave fluxes provided a relatively small cooling effect, and atmospheric heat fluxes were negligible. The aggregate scale albedo of this younger, thinner ice was significantly lower than at Surface Heat Budget of the Arctic Ocean (SHEBA), and the transmittance was significantly higher here, despite similar pond and open water fractions. The oceanic heat flux was only half of the solar flux through the ice to the water, producing warm water near the surface that might delay ice growth in autumn, an important effect of the transition to thinner first-year ice in the high Arctic.

Hudson, Stephen R.; Granskog, Mats A.; Sundfjord, Arild; Randelhoff, Achim; Renner, Angelika H. H.; Divine, Dmitry V.

2013-06-01

267

Simulation of snow and ice melt discharge into the Gepatsch reservoir (Kaunertal/Austrian Alps)  

NASA Astrophysics Data System (ADS)

We present an enhanced method to simulate snow and ice melt discharge into an Alpine reservoir (Gepatsch reservoir, Ötztal Alps, Tyrol/Austria) by combining a process based snow model with sophisticated data assimilation techniques. Within the frame of the alpS project MUSICALS (MUltiscale Snow/ICemelt Discharge Simulation into ALpine ReservoirS), snow cover distribution is analysed based on a set of high-resolution surface elevation datasets acquired from airborne laserscan (ALS) flights over the entire catchments (approx. 580 km², 23% glacierized) contributing directly or by diversion to discharge into the Gepatsch reservoir. The resulting maps of spatially distributed snow water equivalent (SWE) are compared to SWE maps produced by the snow model AMUNDSEN, a distributed physically based energy balance model specifically designed for high mountain regions. AMUNDSEN distinguishes between different types of snow and ice (new snow, old snow, firn and glacier ice) and accounts for their distinct properties. The initial ice thickness distribution is modeled based on digital elevation models and glacier outlines from the Austrian glacier inventory. This is required to account for changing runoff generated from glacier melt under conditions of glacier retreat. Discharge generation from calculated meltwater production and precipitation is simulated in AMUNDSEN using a linear reservoir model with five parallel reservoir cascades considering the distinct storage properties of snow, firn, ice, unglacierized areas and soil. Calibration of the recession coefficients is done separately for each subcatchment. MUSICALS aims to model discharge generated by spatially differentiated snow and ice melt more realistically and to develop a robust simulation tool that is able to calculate short-, middle- and long-term forecasts of reservoir inflow based on weather predictions and climate scenarios.

Hanzer, Florian; Helfricht, Kay; Schneider, Katrin; Marke, Thomas; Kuhn, Michael; Strasser, Ulrich

2013-04-01

268

Effect of Sweetener, Stabilizer, and Storage Temperature on Ice Recrystallization in Ice Cream  

Microsoft Academic Search

ABSTRACT In ice cream manufacturing, control of ice crystal growth,through,proper formulation,and storage tem- perature is important,for stability during storage. The objective of this study was,to investigate the influence of sweetener (sucrose, 20 dextrose equivalent corn syrup, 42 dextrose equivalent corn syrup, and 42 high fructose corn syrup), with and without stabilizer, on ice recrystallization in ice cream,at three storage temperatures.

Tadashi Hagiwara; Richard W. Hartelt

1996-01-01

269

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

270

Investigations of the temperature regimes of the selective laser melting  

NASA Astrophysics Data System (ADS)

The principles of measuring the surface temperature of powder bed in the focal spot of the laser radiation while scanning the surface using galvoscanner with F-teta lens have been elaborated. Investigation of the melting of overhang layers has been conducted under full temperature monitoring. Temperature regimes of the selective laser melting process of the 3D object from steel 316L powder have been investigated.

Chivel, Yu.

2012-05-01

271

Scanning electron microscopy investigations of laboratory-grown gas clathrate hydrates formed from melting ice, and comparison to natural hydrates  

USGS Publications Warehouse

Scanning electron microscopy (SEM) was used to investigate grain texture and pore structure development within various compositions of pure sI and sII gas hydrates synthesized in the laboratory, as well as in natural samples retrieved from marine (Gulf of Mexico) and permafrost (NW Canada) settings. Several samples of methane hydrate were also quenched after various extents of partial reaction for assessment of mid-synthesis textural progression. All laboratory-synthesized hydrates were grown under relatively high-temperature and high-pressure conditions from rounded ice grains with geometrically simple pore shapes, yet all resulting samples displayed extensive recrystallization with complex pore geometry. Growth fronts of mesoporous methane hydrate advancing into dense ice reactant were prevalent in those samples quenched after limited reaction below and at the ice point. As temperatures transgress the ice point, grain surfaces continue to develop a discrete "rind" of hydrate, typically 5 to 30 ??m thick. The cores then commonly melt, with rind microfracturing allowing migration of the melt to adjacent grain boundaries where it also forms hydrate. As the reaction continues under progressively warmer conditions, the hydrate product anneals to form dense and relatively pore-free regions of hydrate grains, in which grain size is typically several tens of micrometers. The prevalence of hollow, spheroidal shells of hydrate, coupled with extensive redistribution of reactant and product phases throughout reaction, implies that a diffusion-controlled shrinking-core model is an inappropriate description of sustained hydrate growth from melting ice. Completion of reaction at peak synthesis conditions then produces exceptional faceting and euhedral crystal growth along exposed pore walls. Further recrystallization or regrowth can then accompany even short-term exposure of synthetic hydrates to natural ocean-floor conditions, such that the final textures may closely mimic those observed in natural samples of marine origin. Of particular note, both the mesoporous and highly faceted textures seen at different stages during synthetic hydrate growth were notably absent from all examined hydrates recovered from a natural marine-environment setting.

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

2004-01-01

272

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

273

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

274

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

275

Depolarization, Scattering, and Attenuation of Circularly Polarized Radio Waves by Spherically Asymmetric Melting Ice Particles  

Microsoft Academic Search

The eccentric spheres model and an extended Mie solution are used to formulate scattering of a plane, electromagnetic wave by a single melting ice particle as well as by a horizontal layer of such particles. The incident wave is left-hand circularly polarized, whereas the scattered wave, as a result of depolarization by the spherically asymmetric particles, comprises left-hand and right-hand

Melina P. Ioannidou; Dimitris P. Chrissoulidis

2007-01-01

276

Gas hydrate fast nucleation from melting ice and quiescent growth along vertical heat transfer tube  

Microsoft Academic Search

During the observation of HCFC141b gas hydrate growth processes outside a vertical heat transfer tube, two exciting phenomena\\u000a were found: fast nucleation of gas hydrate from melting ice, and the spontaneous permeation of water into the guest phases\\u000a along the surface of heat transfer tube to form gas hydrate continuously. These two phenomena were explained with Zhou & Sloan’s\\u000a hypothesis

Yingming Xie; Kaihua Guo; Deqing Liang; Shuanshi Fan; Jianming Gu; Jinggui Chen

2005-01-01

277

Effect of ice melting on bacterial carbon fluxes channelled by viruses and protists in the Arctic Ocean  

Microsoft Academic Search

During the last few years, extensive sea ice melting in the Arctic due to climate change has been detected, which could potentially\\u000a modify the organic carbon fluxes in these waters. In this study, the effect of sea ice melting on bacterial carbon channelling\\u000a by phages and protists has been evaluated in the northern Greenland Sea and Arctic Ocean. Grazing on

Julia A. BorasM; M. Montserrat Sala; Jesus M. Arrieta; Elisabet L. Sà; Jorge Felipe; Susana Agustí; Carlos M. Duarte; Dolors Vaqué

2010-01-01

278

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

279

Substrate effect on the melting temperature of gold nanoparticles  

NASA Astrophysics Data System (ADS)

Previous experimental, molecular dynamics, and thermodynamic researches on the melting temperature of Au nanoparticles on tungsten substrate provide entirely different results. To account for the substrate effect upon the melting point of nanoparticles, three different substrates were tested by using a thermodynamic model: tungsten, amorphous carbon, and graphite. The results reveal that the melting point suppression of a substrate-supported Au nanoparticle is principally ruled by the free surface-to-volume ratio of the particle or the contact angle between the particle and the substrate. When the contact angle ? is less than 90°, a stronger size-dependent melting point depression compared with those for free nanoparticles is predicted; when the contact angle ? is greater than 90°, the melting temperature of the supported Au nanoparticles are somewhat higher than those for free nanoparticles.

Luo, Wenhua; Su, Kalin; Li, Kemin; Liao, Gaohua; Hu, Nengwen; Jia, Ming

2012-06-01

280

Structure of Cu-Sn Melt at High Temperature  

NASA Astrophysics Data System (ADS)

The temperature-dependent viscosity and X-ray diffraction (XRD) patterns of a Cu65Sn35 melt were investigated at high temperatures. The viscosity of the melt changed discontinuously at about 1283 K (1010 °C). An XRD analysis of the Cu65Sn35 melt revealed no obvious changes in the correlation radius, whereas the coordination number increased abruptly at a similar temperature with that mentioned previously, i.e., 1283 K (1010 °C) during the cooling process. The results indicate a redistribution of atoms in the nearest environment. The structural transition at the higher temperature was attributed to a change of combination mode of nearest atoms in the short-range order cluster of the Cu65Sn35 melt.

Hou, J. X.; Zhan, C. W.; Tian, X. L.; Chen, X. C.; Kim, Yong-Suk; Choe, Heeman

2012-11-01

281

Thermal equivalence of DNA duplexes without calculation of melting temperature  

NASA Astrophysics Data System (ADS)

The common key to nearly all processes involving DNA is the hybridization and melting of the double helix: from transmission of genetic information and RNA transcription, to polymerase chain reaction and DNA microarray analysis, DNA mechanical nanodevices and DNA computing. Selecting DNA sequences with similar melting temperatures is essential for many applications in biotechnology. We show that instead of calculating these temperatures, a single parameter can be derived from a statistical-mechanics model that conveniently represents the thermodynamic equivalence of DNA sequences. This parameter is shown to order experimental melting temperatures correctly, is much more readily obtained than the melting temperature, and is easier to handle than the numerous parameters of empirical regression models.

Weber, Gerald; Haslam, Niall; Whiteford, Nava; Prügel-Bennett, Adam; Essex, Jonathan W.; Neylon, Cameron

2006-01-01

282

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

283

Formation of local melting regions in a solid body near the melting temperature  

NASA Astrophysics Data System (ADS)

The formation of local melting regions is shown to be ensured by the fluctuation of the vibrational (kinetic) energy in a crystal. This approach is based on the Frenkel' idea about heterophase fluctuations. Equations that relate the additional volume (? V( T)), electrical resistivity (??( T)), or enthalpy (? H( T)) increment in solids to the presence of local melting regions are obtained. An analysis of the experimental data demonstrates that 6% of the solid body atoms have the properties of a liquid at the melting temperature. This approach is used to explain some unexpected facts and to calculate the energy of formation ( E f) and concentration ( C m) of vacancies in some metals.

Solov'ev, V. A.

2013-05-01

284

The WAIS Melt Monitor: An automated ice core melting system for meltwater sample handling and the collection of high resolution microparticle size distribution data  

NASA Astrophysics Data System (ADS)

Paleoclimate data are often extracted from ice cores by careful geochemical analysis of meltwater samples. The analysis of the microparticles found in ice cores can also yield unique clues about atmospheric dust loading and transport, dust provenance and past environmental conditions. Determination of microparticle concentration, size distribution and chemical makeup as a function of depth is especially difficult because the particle size measurement either consumes or contaminates the meltwater, preventing further geochemical analysis. Here we describe a microcontroller-based ice core melting system which allows the collection of separate microparticle and chemistry samples from the same depth intervals in the ice core, while logging and accurately depth-tagging real-time electrical conductivity and particle size distribution data. This system was designed specifically to support microparticle analysis of the WAIS Divide WDC06A deep ice core, but many of the subsystems are applicable to more general ice core melting operations. Major system components include: a rotary encoder to measure ice core melt displacement with 0.1 millimeter accuracy, a meltwater tracking system to assign core depths to conductivity, particle and sample vial data, an optical debubbler level control system to protect the Abakus laser particle counter from damage due to air bubbles, a Rabbit 3700 microcontroller which communicates with a host PC, collects encoder and optical sensor data and autonomously operates Gilson peristaltic pumps and fraction collectors to provide automatic sample handling, melt monitor control software operating on a standard PC allowing the user to control and view the status of the system, data logging software operating on the same PC to collect data from the melting, electrical conductivity and microparticle measurement systems. Because microparticle samples can easily be contaminated, we use optical air bubble sensors and high resolution ice core density profiles to guide the melting process. The combination of these data allow us to analyze melt head performance, minimize outer-to-inner fraction contamination and avoid melt head flooding. The WAIS Melt Monitor system allows the collection of real-time, sub-annual microparticle and electrical conductivity data while producing and storing enough sample for traditional Coulter-Counter particle measurements as well long term acid leaching of bioactive metals (e.g., Fe, Co, Cd, Cu, Zn) prior to chemical analysis.

Breton, D. J.; Koffman, B. G.; Kreutz, K. J.; Hamilton, G. S.

2010-12-01

285

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

Microsoft Academic Search

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

A. Schomacker; K. H. Kjaer

2007-01-01

286

The melt anomaly of 2002 on the Greenland Ice Sheet from active and passive microwave satellite observations  

Microsoft Academic Search

Active and passive microwave satellite data are used to map snowmelt extent and duration on the Greenland ice sheet. The passive microwave (PM) data reveal the extreme melt extent of 690,000 km2 in 2002 as compared with an average extent of 455,000 km2 from 1979-2003. A statistical analysis of the melt time series affirms an increased melt extent earlier in

K. Steffen; S. V. Nghiem; R. Huff; G. Neumann

2004-01-01

287

Transient response of the MOC and climate to potential melting of the Greenland Ice Sheet in the 21st century  

Microsoft Academic Search

The potential effects of Greenland Ice Sheet (GrIS) melting on the Atlantic meridional overturning circulation (MOC) and global climate in the 21st century are assessed using the Community Climate System Model version 3 with prescribed rates of GrIS melting. Only when GrIS melting flux is strong enough to be able to produce net freshwater gain in upper subpolar North Atlantic

Aixue Hu; Gerald A. Meehl; Weiqing Han; Jianjun Yin

2009-01-01

288

Formation of recent martian debris flows by melting of near-surface ground ice at high obliquity.  

PubMed

The observation of small gullies associated with recent surface runoff on Mars has renewed the question of liquid water stability at the surface of Mars. The gullies could be formed by groundwater seepage from underground aquifers; however, observations of gullies originating from isolated peaks and dune crests question this scenario. We show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity. Our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in Greenland and numerical simulations that show that above-freezing temperatures can occur at high obliquities in the near surface of Mars, and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on Mars. PMID:11729267

Costard, F; Forget, F; Mangold, N; Peulvast, J P

2001-11-29

289

Sum-frequency spectroscopic studies. I. Surface melting of ice. II. Surface alignment of polymers  

Microsoft Academic Search

Surface vibrational spectroscopy via infrared-visible sum-frequency generation (SFG) has been established as a useful tool to study the structures of different kinds of surfaces and interfaces. This technique was used to study the (0001) face of hexagonal ice (Ih). SFG spectra in the O-H stretch frequency range were obtained at various sample temperatures. For the vapor(air)\\/ice interface, the degree of

Xing Wei; Xing

2000-01-01

290

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

291

Melting Temperature of Mixed Oxide Fuels for Fast Reactors  

Microsoft Academic Search

Alternation of the melting temperature of irradiated mixed oxide (MOX) fuel in fast reactors with progress of burnup was determined in relation to the actinide fractions contained and of the oxygen-to-metal (O\\/M) ratio. Based on ideal solution models of UO2-PuO2 and UO2-PuO2-Am2O3 systems and on correlations obtained of the measured melting with O\\/M ratio and with burnup, an equation was

Koichi KONNO; Takashi HIROSAWA

2002-01-01

292

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

293

Surface formation of CO2 ice at low temperatures  

NASA Astrophysics Data System (ADS)

The surface formation of CO2 at low temperatures through the reaction CO + OH and direct dissociation of the resulting HO-CO complex is shown by hydrogenation of a CO:O2 ice mixture. Such a binary ice is not fully representative for an interstellar ice, but the hydrogenation of O2 ice produces OH radicals, which allows the investigation of the interstellar relevant CO + OH solid state reaction under fully controlled laboratory conditions. Similar recent astrophysical ice studies have focused on the investigation of isolated surface reaction schemes, starting from the hydrogenation of pure ices, like solid CO or O2. For such ices, no CO2 formation is observed upon H-atom exposure. The hydrogenation of binary ice mixtures presented here allows to investigate for the first time the influence of the presence of other species in the ice on the pure ice reaction shemes. Mixtures of CO:O2 are deposited on a substrate in an ultra high vacuum setup at low temperatures (15 and 20 K) and subsequently hydrogenated. The ice is monitored by means of Reflection Absorption InfraRed Spectroscopy (RAIRS). Results show that solid CO2 is formed in all studied CO:O2 mixtures under our laboratory conditions. Within the experimental uncertainties no dependency on ice temperature or composition is observed. The laboratory results show a correlation between the formation of CO2 and H2O, which is consistent with the astronomical observation of solid CO2 in water-rich environments. The results also show that the contemporary presence of CO and O2 molecules in the ice influences the final product yields of the separate CO + H (H2CO, CH3OH) and O2+ H (H2O2 and H2O) channels, even though the formation rates are not significantly affected.

Ioppolo, S.; van Boheemen, Y.; Cuppen, H. M.; van Dishoeck, E. F.; Linnartz, H.

2011-05-01

294

Recent increase in snow-melt area in the Greenland Ice sheet as an indicator of the effect of reduced surface albedo by snow impurities  

NASA Astrophysics Data System (ADS)

Recent rapid decline of cryosphere including mountain glaciers, sea ice, and seasonal snow cover tends to be associated with global warming. However, positive feedback is likely to operate between the cryosphere and air temperature, and then it may not be so simple to decide the cause-and-effect relation between them. The theory of heat budget for snow surface tells us that sensible heat transfer from the air to the snow by atmospheric warming by 1°C is about 10 W/m2, which is comparable with heat supply introduced by reduction of the snow surface albedo by only 0.02. Since snow impurities such as black carbon and soil- origin dusts have been accumulated every year on the snow surface in snow-melting season, it is very important to examine whether the snow-melting on the ice sheets, mountain glaciers, and sea ice is caused by global warming or by accumulated snow impurities originated from atmospheric pollutants. In this paper we analyze the dataset of snow-melt area in the Greenland ice sheet for the years 1979 - 2007 (available from the National Snow and Ice Data Center), which is reduced empirically from the satellite micro-wave observations by SMMR and SMM/I. It has been found that, seasonally, the snow-melt area extends most significantly from the second half of June to the first half of July when the sun is highest and sunshine duration is longest, while it doesn't extend any more from the second half of July to the first half of August when the air temperature is highest. This fact may imply that sensible heat required for snow-melting comes from the solar radiation rather than from the atmosphere. As for the interannual variation of snow-melt area, on the other hand, we have found that the growth rate of snow-melt area gradually increases from July, to August, and to the first half of September as the impurities come out to and accumulated at the snow surface. However, the growth rate is almost zero in June and the second half of September when fresh snow of high albedo covers the surface. This fact may imply that the combined operation of solar radiation and snow impurities is responsible for the recent global decline of cryosphere. Discussion about other research works will be given in the presentation in order to support the above idea.

Rikiishi, K.

2008-12-01

295

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

296

MODELS FOR INDIRECT TEMPERATURE MEASUREMENTS OF MELT IN LD CONVERTER  

Microsoft Academic Search

This paper deals with refinement of steel in LD converter, where are the processes, which run near high temperature and in very aggressive environment. For these reasons a continual measurement of some values is not possible during the converter process by direct measuring (sensors). One of their values is the temperature of melt, which is very important for tapping of

Marek LACIAK; Karol KOSTÚR

297

Isothermal plastic forming of high melting temperature alloys  

Microsoft Academic Search

This paper deals with the problem of an unconventional plastic forming process—deformation of high melting temperature alloys under isothermal conditions. The test were performed for alloyed steel containing 0.5% C. The upsetting process at various temperatures and strain rates was used to determine the optimum parameters of deformation. In order to obtain fine grains prior to deformation and create the

J Sinczak; W Lapkowski; S Rusz

1997-01-01

298

Seasonal and decadal expansions of the snow-melt area in the Greenland ice sheet and its possible relation with the decrease in snow surface albedo  

NASA Astrophysics Data System (ADS)

Rapid decline of the entire cryosphere in recent years is generally considered to be caused by global warming. However, estimates of the heat budget at the snow surface lead to the conclusion that the sensible heat transfer from air to snow by the air temperature rise by 1 K is only about 10 W/m2. Consequently, it seems uncertain whether or not this amount of heat addition is large enough to cause the simultaneous decline of ice sheets, mountain glaciers, sea ice, and seasonal snow cover all over the world. In this paper we have analyzed the dataset of snow-melt area in the Greenland ice sheet for the years 1979 - 2007 (available from the National Snow and Ice Data Center). The melt-area is estimated empirically from the satellite micro-wave observations by SMMR and SMM/I. It has been found that the seasonal expansion of snow-melt area is more significant during the periods when the sun is higher and sunshine duration is longer rather than during the periods when the air temperature is higher. On the other hand, the decadal growth rate of snow-melt area shows maximum values in the first half of September when the snow surface is covered with accumulated snow impurities, and minimum values in June and the second half of September when the surface is covered with clean or newly fallen snow. We have then analyzed the dataset of clear-sky surface albedo over the Greenland for the years 1981 - 2005 (available from the National Snow and Ice Data Center). The albedo values are estimated from visible imageries by making corrections for the effects of water vapor, cloud, and angles between the zenith and sun and satellite. Similar trends have been found in terms of the seasonal expansion and the decadal growth rate for the snow surface albedo. These facts imply that the snow-melting in the Greenland ice sheet may be caused by the decrease in snow surface albedo (or by the increase in snow impurities) rather than the air temperature rise.

Rikiishi, K.

2009-04-01

299

Communication: The effect of dispersion corrections on the melting temperature of liquid water  

NASA Astrophysics Data System (ADS)

The melting temperature (Tm) of liquid water with the Becke-Lee-Yang-Parr (BLYP) density functional including dispersion corrections (BLYP-D) and the Thole-type, version 3 (TTM3-F) ab-initio based flexible, polarizable classical potential is reported via constant pressure and constant enthalpy (NPH) molecular dynamics simulations of an ice Ih-liquid coexisting system. Dispersion corrections to BLYP lower Tm to about 360 K, a large improvement over the value of Tm > 400 K previously obtained with the original BLYP functional under the same simulation conditions. For TTM3-F, Tm = 248 K from classical molecular dynamics simulations.

Yoo, Soohaeng; Xantheas, Sotiris S.

2011-03-01

300

The physical radiative and microwave scattering characteristics of melt ponds on Arctic landfast sea ice  

Microsoft Academic Search

Abstract. Melt ponds,are an important,characteristic,of Arctic sea ice because of their control,on,the,surface,radiation,balance.,Little is known,about,the physical,nature,of these features,and,to date there is no operational,method,for detection,of their formation,or estimation,of their aerial fraction. Coincident in situ observations, aerial surveys and synthetic aperture radar data from a field site in Arctic Canada are compared in an evaluation of the physical, radiative and,electrito,The integrated shortwave albedo,was,measured,in

D. G. Barber; J. Yackel

301

Cyclone Occurrence in the Arctic: Coupling With Teleconnections and the Impacts on Ice Sheet Melt Cycles  

NASA Astrophysics Data System (ADS)

Evidence assembled over the past several decades shows the Arctic system as in the midst of significant environmental change. This includes pronounced warming over most land areas, reductions in sea ice extent, alterations in precipitation, melt-water discharge and sea ice circulation, and warming and increased aerial extent of the Arctic Ocean's Atlantic section [Serreze et al., 2000; SEARCH SSC, 2001]. The accepted paradigm is that these changes are related to the general dominance of the positive phase of the Arctic Oscillation (AO) in recent decades [Thompson and Wallace, 1998; 2000]. While the AO/NAO (North Atlantic Oscillation) has proven to be a valuable integrating framework, many aspects of climatic variability and change are fundamentally driven by events at synoptic space and time scales, in particular, by the individual or aggregate effect of extratropical cyclones. The polar basin is considered a transit area or a sink for cyclones that develop elsewhere [Putnins, 1970]. In the Northern Hemisphere, warming and cooling trends are associated, respectively, with increases and decreases in cyclone occurrence [McCabe et al., 2001]. As presented by McCabe et al. [2001], differences in extratropical cyclone frequency and strength have a direct influence on surface climate through effects on cloud cover, winds, and precipitation frequency, duration, and magnitude. Melt cycles and precipitation over the terrestrial Arctic drainage are predominantly determined by the frequency and strength of cyclones [Mote, 1998a, 1998b; Serreze et al., 2002]. Cyclone activity also has pronounced effects on the circulation and concentration of sea ice cover with attendant feedbacks. This paper uses NCEP global sea-level pressure data over the past forty years and passive microwave data of the Greenland ice sheet over the past twelve years to address the importance of cyclone processes in the moderation of melt cycles on the Greenland ice sheet. The relationship between the intensity of these processes and differences in the general synoptic environment associated with the positive and negative phases of the AO/NAO will also be addressed.

McAllister, M. J.; Steffen, K.

2003-12-01

302

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

2010-08-26

303

Probing the microscopic flexibility of DNA from melting temperatures  

NASA Astrophysics Data System (ADS)

The microscopic flexibility of DNA is a key ingredient for understanding its interaction with proteins and drugs but is still poorly understood and technically challenging to measure. Several experimental methods probe very long DNA samples, but these miss local flexibility details. Others mechanically disturb or modify short molecules and therefore do not obtain flexibility properties of unperturbed and pristine DNA. Here, we show that it is possible to extract very detailed flexibility information about unmodified DNA from melting temperatures with statistical physics models. We were able to retrieve, from published melting temperatures, several established flexibility properties such as the presence of highly flexible TATA regions of genomic DNA and support recent findings that DNA is very flexible at short length scales. New information about the nanoscale Na+ concentration dependence of DNA flexibility was determined and we show the key role of ApT and TpA steps when it comes to ion-dependent flexibility and melting temperatures.

Weber, Gerald; Essex, Jonathan W.; Neylon, Cameron

2009-10-01

304

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

NASA Astrophysics Data System (ADS)

We use temperature profiles from 7 deep (? 2000 m) boreholes located in southern Canada to infer ground surface temperature histories (GSTH) during the Last Glacial Maximum (LGM) and the Holocene. Visual inspection of the heat flow and of the reduced temperature depth profiles reveals significant regional differences with some sites showing conspicuous signs of post glacial warming, and other indicating only very small changes in ground surface temperature. These differences are confirmed by the inversions of the temperature profiles. The most prominent variations in GST are found at the Sudbury, Ontario, sites where the present ground surface temperature is high. With the exception of Sept-Iles, Quebec, the other sites only show moderate or no variation in GST. For all the sites, except possibly Sept-Iles, temperatures at the base of the ice sheet during the LGM were at or slightly below the melting point of ice. Temperatures might have been lower, a few degrees below 0 °C, at Sept-Iles. These results are consistent with field observations and model predictions suggesting high velocity basal flows in the ice sheet above the studied regions. These new data on basal temperatures will provide better quantitative constraints on glacier flow dynamics. The inversions give a chronology for the retreat of the ice sheet comparable to other proxies. Inversion and direct modeling show that, following the ice retreat, there was a warm period between 2 and 5 ka with temperatures 1-2 K higher than present. The inversion yields a time for this episode 1-2 kyr more recent than that inferred by other proxies for the Holocene climate optimum (HCO).

Chouinard, Christian; Mareschal, J.-C.

2009-01-01

305

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 towards increasing melt observed since the end of the 1990s. 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 for the last two decades. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June-July-August) mean temperature from reanalyses at 700 hPa over Greenland; analogous atmospheric circulations in the past show that ~70% of the 1993-2012 warming at 700 hPa over Greenland has been driven by changes in the atmospheric flow frequencies. Indeed, the occurrence of anticyclones centred over the GrIS at the surface and at 500 hPa has doubled since the end of 1990s, which induces more frequent southerly warm air advection along the Western Greenland coast and over the neighbouring Canadian Arctic Archipelago (CAA). These changes in the NAO modes explain also why no significant warming has been observed these last summers over Svalbard, where northerly atmospheric flows are twice as frequent as before. Therefore, the recent warmer summers over GrIS and CAA cannot be considered as a long term climate warming but are 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 cannot exclude that these changes in NAO are due to global warming. Indeed, we have performed several sensitivity experiments performed with the regional climate model MAR over an integration domain large enough for allowing MAR to simulate its own general circulation independently of the forcing (ERA-INTERIM). These MAR simulations seem to suggest that the NAO anomalies over summers 2007-2012 are due to changes in the Sea Ice Cover (SIC) and Sea Surface Temperatures (SST) in the Arctic.

Fettweis, Xavier; Hanna, Edward; lang, Charlotte; Belleflamme, Alexandre; Erpicum, Michel; Gallée, Hubert

2013-04-01

306

Using singlet molecular oxygen to probe the solute and temperature dependence of liquid-like regions in/on ice.  

PubMed

Liquid-like regions (LLRs) are found at the surfaces and grain boundaries of ice and as inclusions within ice. These regions contain most of the solutes in ice and can be (photo)chemically active hotspots in natural snow and ice systems. If we assume all solutes partition into LLRs as a solution freezes, freezing-point depression predicts that the concentration of a solute in LLRs is higher than its concentration in the prefrozen (or melted) solution by the freeze-concentration factor (F). Here we use singlet molecular oxygen production to explore the effects of total solute concentration ([TS]) and temperature on experimentally determined values of F. For ice above its eutectic temperature, measured values of F agree well with freezing-point depression when [TS] is above ?1 mmol/kg; at lower [TS] values, measurements of F are lower than predicted from freezing-point depression. For ice below its eutectic temperature, the influence of freezing-point depression on F is damped; the extreme case is with Na2SO4 as the solute, where F shows essentially no agreement with freezing-point depression. In contrast, for ice containing 3 mmol/kg NaCl, measured values of F agree well with freezing-point depression over a range of temperatures, including below the eutectic. Our experiments also reveal that the photon flux in LLRs increases in the presence of salts, which has implications for ice photochemistry in the lab and, perhaps, in the environment. PMID:23841666

Bower, Jonathan P; Anastasio, Cort

2013-07-22

307

Melting temperature of diamond at ultrahigh pressure  

Microsoft Academic Search

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

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

2010-01-01

308

Liquidus Temperature Depression in Cryolitic Melts  

NASA Astrophysics Data System (ADS)

The electrolyte in Hall-Héroult cells for the manufacture of primary aluminum nominally contains only cryolite (Na3AlF6) with additions of AlF3, CaF2, and Al2O3. However, impurities are present, entering the process with the feedstock. The effect on the liquidus temperature by the impurities cannot be calculated correctly by the well-known equation for freezing-point depression in binary systems simply because the electrolyte cannot be regarded as a binary system. By extending the equation for freezing-point depression to the ternary system NaF-AlF3-B, it appeared that the acidity of the impurity B plays a major role. Some calculations were made using an ideal Temkin model, and for most types of impurities, the effect on the liquidus temperature will be larger in an industrial electrolyte than what can be estimated from the equation for freezing-point depression in cryolite. Experimental data on the liquidus temperature in the system Na3AlF6-AlF3-Al2O3-CaF2-MgF2 show that the effect of MgF2 on the liquidus temperature increases strongly with decreasing NaF/AlF3 molar ratio, and it is suggested that MgF2 forms an anion complex, probably MgF{4/2-}.

Solheim, Asbjørn

2012-08-01

309

Electronic Desorption from Internal Surfaces of Porous Low Temperature Ice  

NASA Astrophysics Data System (ADS)

Radiation induced surface desorption from low temperature water ice plays a crucial role in the astrochemistry of icy planetary surfaces, comets and ice-covered interstellar grains. Excitations from low energy electrons (5- 100 eV) or VUV photons can hop between the strongly coupled hydrogen bonding network and migrate until they encounter a surface or a defect where they localize and induce dissociation. Ices deposited at very low temperatures, such as those in interstellar space, exhibit an exceptionally low density and have a highly porous amorphous structure. These pores represent large open structures and enclose a volume of vacuum and give the porous ice an enormous internal surface area. These pores are also likely to play an important role in spontaneous segregation of hydrophobic organic contaminants. The electronic structure of ice at the interface of these pores should resemble that of the outer surface vacuum interface. The effects of porosity and morphology of amorphous and crystalline D2O ices on the electron stimulated generation and trapping of D2 and O2 have been studied by post-irradiation thermal desorption. Molecular deuterium is released in the temperature range from 55 - 105 K for each of the samples, with two notable bursts at 115 and 132 K for porous amorphous ice. The majority of trapped O2 coevolves with desorption of the ice matrix, suggesting that clathrate hydrates may be important trapping sites. Production and trapping of organic polymers within pores from coadsorbed methane and ammonia are also discussed.

Grieves, G. A.; Orlando, T. M.

2006-05-01

310

Temperature and salinity beneath Ronne Ice Shelf, Antarctica  

NASA Astrophysics Data System (ADS)

Salinity and temperature measurements have been made beneath Ronne Ice Shelf, Antarctica. Access to the seawater was gained by hot-water drilling through 562 m of ice at a site 300 km from the ice front. The ice column is composed of 516 m of meteoric-origin ice, underlain by 31 m of consolidated saline ice, with a further 15 m of unconsolidated slush at the base. The 360-m-deep water column beneath the ice shelf consists broadly of a 210-m layer of Ice Shelf Water (ISW) at a potential temperature of -2.30°C and salinity 34.53, overlying a 100-m-thick layer of modified Western Shelf Water (-2.03°C, 34.64). The layers are separated by a weak 50-m-thick pycnocline. Isotopic analyses of water samples support this interpretation of the water types. Comparison of the data with published oceanographic observations from the shore lead indicate that the source of the water is either the western Berkner shelf or north of the ice front in the Ronne Depression. The measurements from the drill site broadly match predictions from a simple plume model of the sub-ice-shelf water circulation. In that model the basal slope of the ice shelf plays a central role in determining the properties of the ISW plume. With the exception of the upper few tens of meters the temperature and salinity of the entire water column vary by about 0.04°C and 0.03 on tidal timescales, and there is evidence for a longer-term drift, presumably connected with shifts in the larger-scale circulation. There is also much variability from internal wave activity. The salinity and deuterium budgets indicate that the meltwater fraction in the ISW observed at the drill site was between 5.3 and 6.5‰, in reasonable agreement with values previously found for ISW in the open ocean.

Nicholls, Keith W.; Jenkins, Adrian

1993-12-01

311

Potential methane emission from north-temperate lakes following ice melt  

USGS Publications Warehouse

Methane, a radiatively active 'greenhouse' gas, is emitted from lakes to the atmosphere throughout the open-water season. However, annual lake CH4 emissions calculated solely from open-water measurements that exclude the time of spring ice melt may substantially underestimate the lake CH4 source strength. We estimated potential spring CH4 emission at the time of ice melt for 19 lakes in northern Minnesota and Wisconsin. Lakes ranged in area from 2.7 to 57,300 ha and varied in littoral zone sediment type. Regression analyses indicated that lake area explained 38% of the variance in potential CH4 emission for relatively undisturbed lakes; as lake area increases potential CH4 emission per unit area decreases. Inclusion of a second term accounting for the presence or absence of soft organic-rich littoral-zone sediments explained 83% of the variance in potential spring CH4 emission. Total estimated spring CH4 emission for 1993 for all Minnesota lakes north of 45?? with areas ???4 ha was 1.5 x 108 mol CH4 assuming a 1 : 1 ratio of soft littoral sediment to hard littoral sediment lakes. Emission estimates ranged from 5.3 x 107 tool assuming no lakes have soft organic-rich littoral sediments to 4.5 x 108 mol assuming all lakes have soft organic-rich littoral sediments. This spring CH4 pulse may make up as much as 40% of the CH4 annually emitted to the atmosphere by small lakes.

Michmerhuizen, C. M.; Striegl, R. G.; McDonald, M. E.

1996-01-01

312

Reduced North Atlantic Central Water formation in response to early Holocene ice-sheet melting  

NASA Astrophysics Data System (ADS)

Central waters of the North Atlantic are fundamental for ventilation of the upper ocean and are also linked to the strength of the Atlantic Meridional Overturning Circulation (AMOC). Here, we show based on benthic foraminiferal Mg/Ca ratios, that during times of enhanced melting from the Laurentide Ice Sheet (LIS) between 9.0-8.5 thousand years before present (ka) the production of central waters weakened the upper AMOC resulting in a cooling over the Northern Hemisphere. Centered at 8.54 ± 0.2 ka and 8.24 ± 0.1 ka our dataset records two ˜150-year cooling events in response to the drainage of Lake Agassiz/Ojibway, indicating early slow-down of the upper AMOC in response to the initial freshwater flux into the subpolar gyre (SPG) followed by a more severe weakening of both the upper and lower branches of the AMOC at 8.2 ka. These results highlight the sensitivity of regional North Atlantic climate change to the strength of central-water overturning and exemplify the impact of both gradual and abrupt freshwater fluxes on eastern SPG surface water convection. In light of the possible future increase in Greenland Ice Sheet melting due to global warming these findings may help us to better constrain and possibly predict future North Atlantic climate change.

Bamberg, Audrey; Rosenthal, Yair; Paul, André; Heslop, David; Mulitza, Stefan; Rühlemann, Carsten; Schulz, Michael

2010-09-01

313

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

314

Summer basal melt rate at the Larsen-C ice shelf, Antarctic Peninsula, measured by phase sensitive radar  

NASA Astrophysics Data System (ADS)

During the past decade, the Larsen Ice Shelf (LIS) has progressively thinned and two large sections have collapsed, catastrophically, leading to increased ice discharge into the oceans and a global sea level rise of about 0.07 mm yr-1. If similar events are to occur at the remaining Larsen-C section, the fate of a tenfold greater ice reservoir hangs in the balance. Although the origin of the underlying instability has yet to be determined, only three processes can realistically be to blame; enhanced basal or surface melting, or accelerated flow. To quantify rates of basal ice melting, we deployed a phase sensitive radar at the Larsen-C Ice Shelf (LCIS) during the austral summers of 2008-2009 and 2009-2010. The radar is a high-precision instrument that directly measures changes in ice thickness at the base of the ice shelf, in contrast to indirect methods, which infer basal melting from surface observation while assuming steady state equilibrium. During the 2008-2009 we established three campsites, collocated with time-series of satellite altimeter height measurements, we performed an average of 15 radar measurements per campsites. During the 2009-2010, the 3 sites were re-visited twice at 1-month interval with the objective of measuring yearly and summer rates of basal melting. The field experiment also included surface density measurement from gravimetry and neutron probe analysis and surface strain measurement from campaign GPS. Here, we are presenting the estimated basalt melt rate from the analysis of the phase sensitive radar measurements performed during the Antarctic summers of 2008 and 2009.

Gourmelen, N.; Shepherd, A.; McMillan, M.; Jenkins, A.; King, M.

2010-12-01

315

Nitric acid adsorption on ice at environmental temperatures  

Microsoft Academic Search

Nitric acid has become an important pollutant in areas which depend on snowpack melt for their water supply. The adsorption of HNO3 on the ice surface was investigated at [-]20oC using artificial snow packed into glass columns and exposed to nitric acid vapor in a flow system. It was observed that, given sufficient acid vapor, HNO3 would adsorb in multilayers

Susan Kay Laird

1998-01-01

316

Calibration of gas pressure using the mercury melting curve in conjunction with eutectic ice-salt mixtures  

Microsoft Academic Search

Eutectic freezing mixtures of ice-KNO3, ice-KCl, ice-NH4Cl and ice-NaCl provide a convenient method of obtaining uniform temperatures close to -2.8, -10.6, -15.3 and -21.1 degrees C, respectively. Calibration to better than +or-0.1% is achievable for gas pressures between 344 and 701 MPa when these mixtures are used in conjunction with a mercury pressure cell and a resistance thermometer accurate to

J. Lusk

1990-01-01

317

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

318

Correlations between Raman frequency shifts and the thermodynamic quantities close to the melting point in D2O ice  

Microsoft Academic Search

The Raman frequency shifts (1\\/) (\\/T)P and (1\\/) (\\/P)T of the translational mode are correlated to the specific heat Cp and to the thermal expansivity p, respectively, in D2O ice. Close to the melting point, they correlate linearly, from which the values of the slope dP\\/dT have been deduced in D2O ice. Our calculated values of dP\\/dT are in very

H. Karacali; H. Yurtseven

2005-01-01

319

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

320

Comparison of AMSR-E derived Antarctic snow-ice interface temperatures with previous surface observations  

Microsoft Academic Search

The AMSR-E Sea Ice Temperature (L3 25 km) data product derived from passive microwave emissions at 6.9 GHz is available from the National Snow and Ice Data Center. The Sea Ice Temperature data represents the temperature at the surface of the sea ice, or the temperature corresponding to the snow-ice interface. Antarctic sea ice images from 2005 were obtained at

M. Lewis; S. F. Ackley; H. Xie; B. Cicek

2006-01-01

321

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

322

Parameterization and testing of a surface melt and water routing model for the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

Rapid supraglacial lake drainages are thought to cause temporary spikes in subglacial water pressure, reductions in basal friction and transient ice sheet accelerations. In order to model potential lake drainage events of the correct magnitude and timing, it is necessary to accurately model: i) the temporal and spatial variability of surface melt; and ii) the surface routing of this water to lakes / moulins. This study is focussed on the Paakitsoq region of western Greenland and is composed of two key components. First, we parameterize a high resolution surface energy / mass balance model by comparing modelled accumulation, melt and albedo against measurements made at the GC-NET stations JAR 1, JAR 2 and Swiss Camp; and modelled snowline position against measurements derived from Landsat 7 ETM+ imagery. Snowline position is obtained from the satellite imagery using a combination of Normalised Difference Snow Index (NDSI) calculations and image thresholding. Second, we parameterize a surface routing and lake filling model using field data collected in June 2011. We focus on the filling of two supraglacial lakes in the Paakitsoq region: 'Lake Ponting' and 'Lake Half Moon'. Using the parameterized distributed surface energy balance model we generate hourly melt output per DEM cell for a 100 km2 area containing these two lakes. Using the Darcian equation for flow at the bottom of a saturated snow pack and the Manning Strickler equation for flow over a bare ice surface, hourly discharge hydrographs into each lake are calculated. These are used in conjunction with the DEM to calculate the temporal changes in lake depths and compared to pressure sensor data from both lakes.

Banwell, A. F.; Willis, I. C.; Arnold, N. S.; Tedesco, M.; Messerli, A.; Ahlstrom, A. P.

2011-12-01

323

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

NASA Astrophysics Data System (ADS)

Pits in rocks on the surface of Mars have been observed at several locations. Similar pits are observed in rocks in the Mars-like hyperarid, hypothermal stable upland zone of the Antarctic Dry Valleys; these form by very localized chemical weathering due to transient melting of small amounts of snow on dark dolerite boulders preferentially heated above the melting point of water by sunlight. We examine the conditions under which a similar process might explain the pitted rocks seen on the surface of Mars (rock surface temperatures above the melting point; atmospheric pressure exceeding the triple point pressure of H2O; an available source of solid water to melt). We find that on Mars today each of these conditions is met locally and regionally, but that they do not occur together in such a way as to meet the stringent requirements for this process to operate. In the geological past, however, conditions favoring this process are highly likely to have been met. For example, increases in atmospheric water vapor content (due, for example, to the loss of the south perennial polar CO2 cap) could favor the deposition of snow, which if collected on rocks heated to above the melting temperature during favorable conditions (e.g., perihelion), could cause melting and the type of locally enhanced chemical weathering that can cause pits. Even when these conditions are met, however, the variation in heating of different rock facets under Martian conditions means that different parts of the rock may weather at different times, consistent with the very low weathering rates observed on Mars. Furthermore, as is the case in the stable upland zone of the Antarctic Dry Valleys, pit formation by transient melting of small amounts of snow readily occurs in the absence of subsurface active layer cryoturbation.

Head, James W.; Kreslavsky, Mikhail A.; Marchant, David R.

2011-09-01

324

Melting behavior of H[subscript 2]O at high pressures and temperatures  

SciTech Connect

Water plays an important role in the physics and chemistry of planetary interiors. In situ high pressure-temperature Raman spectroscopy and synchrotron x-ray diffraction have been used to examine the phase diagram of H{sub 2}O. A discontinuous change in the melting curve of H{sub 2}O is observed at approximately 35 GPa and 1040 K, indicating a triple point on the melting line. The melting curve of H{sub 2}O increases significantly above the triple point and may intersect the isentropes of Neptune and Uranus. Solid ice could therefore form in stratified layers at depth within these icy planets. The extrapolated melting curve may also intersect with the geotherm of Earth's lower mantle above 60 GPa. The presence of solid H{sub 2}O would result in a jump in the viscosity of the mid-lower mantle and provides an additional explanation for the observed higher viscosity of the mid-lower mantle.

Lin, Jung-Fu; Gregoryanz, Eugene; Struzhkin, Viktor V.; Somayazulu, Maddury; Mao, H.-K.; Hemley, R.J. (CIW)

2010-07-19

325

Antarctic ice sheet and sea ice regional albedo and temperature change, 1981–2000, from AVHRR Polar Pathfinder data  

Microsoft Academic Search

Spring–summer (November, December, January) ice sheet and sea ice regional surface albedo, surface temperature, sea ice concentration and sea ice extent averages and trends from 1981 to 2000 have been calculated for the Antarctic area. In this research the AVHRR Polar Pathfinder 5-km EASE-Grid Composites and the combined SMMR and SSMI data sets from the National Snow and Ice Data

Vesa Laine

2008-01-01

326

Anomalous Proton Dynamics in Ice at Low Temperatures  

SciTech Connect

We present incoherent quasielastic neutron scattering measurements on ice Ih (ordinary ice) and Ic (cubic ice) which show the existence of nonharmonic motion of hydrogen at low temperatures, down to 5 K. We show that this dynamics is localized, nonvibrational, and related to the hydrogen disorder since it is absent in ordered ice VIII. A main jump distance of 0.75 A is identified, hence close to the distance between the two possible proton sites along the oxygen-oxygen bond. The dynamics is non-Arrhenius, has a large time rate of 2.7x10{sup 11} s{sup -1}, and affects only a few percent of the total number of hydrogen atoms in the crystal. These results give evidence for the existence of concerted proton tunneling in these ice phases.

Bove, L. E.; Klotz, S. [IMPMC, CNRS-UMR 7590, Universite P and M Curie, F-75252 Paris (France); Paciaroni, A.; Sacchetti, F. [CNR-INFM CRS-Soft, c/o Dipartimento di Fisica, Universita di Perugia, I-06123 Perugia (Italy)

2009-10-16

327

On the use of multi-year ice ERS-1 as a proxy indicator of melt period sea ice albedo  

Microsoft Academic Search

Sea ice albedo is a critical factor determining the overall energy balance of the ocean--sea ice-atmosphere interface (hereafter referred to as the marine cryosphere) and the seasonal processes of sea ice growth and decay. Small changes in sea ice albedo can affect regional and global climate through the existence of positive feedback loops such as those proposed by Budyko (Tellus,

A. THOMAS; D. G. BARBER

1998-01-01

328

Ultrafast Superheating of Ice  

NASA Astrophysics Data System (ADS)

Ultrafast temperature jump technique for ice is demonstrated using IR double resonant spectroscopy. Measurements performed close to the melting point show substantial superheating to 301 K that persists beyond 1.3 ns.

Iglev, Hristo; Schmeisser, Marcus; Laubereau, Alfred

329

Polymerization and diamond formation from melting methane and their implications in ice layer of giant planets  

Microsoft Academic Search

High-pressure and high-temperature experiments of solid methane were performed using a laser-heated diamond anvil cell. X-ray diffractometry and Raman spectroscopy revealed the melting conditions to be above approximately 1100K in a wide pressure range of 10–80GPa. Above 1100K, polymerizations occurred to produce ethane molecules and further polymerized hydrocarbons. Above 3000K, diamond was produced. These changes proceeded depending on temperature rather

Hisako Hirai; Keisuke Konagai; Taro Kawamura; Yoshitaka Yamamoto; Takehiko Yagi

2009-01-01

330

The melting parameters of high-temperature nonmetallic nitrides  

SciTech Connect

The ranges of temperatures and pressures for the existence of condensed boron, aluminum, and silicon nonmetallic nitrides in thermodynamic equilibrium with an ambient gas were calculated on the basis of reference data. The melting parameters of the high-temperature nitrides mentioned above were investigated experimentally in the nitrogen pressure range of 5200 MPa. The 99% purity nitride samples were prepared in the form of 4 x 4-mm plates with a thickness of 1 mm. The surfaces of samples were heated with stationary laser beam and analyzed by X-ray technique. The brightness temperature of nonmetallic nitrides was measured at 0.633-{mu}m wavelength using the optical pyrometry method. The apparent melting temperatures were found from the analysis of heating and cooling thermograms. Based on the available literature data on normal spectral emmissivity, the true melting temperatures of nonmetallic nitrides were estimated as 3370 K for BN, 3025 K for AlN, and 2775 K for Si{sub 3}N{sub 4}.

Kostanovsky, A.V. [Inst. for High Temperatures, Moscow (Russian Federation); Kirillin, A.V. [Russian Foundation for Basic Research, Moscow (Russian Federation)

1996-03-01

331

Winter sea-ice melt in the Canada Basin, Arctic Ocean  

NASA Astrophysics Data System (ADS)

Recent warming and freshening of the Canada Basin has led to the year-round storage of solar radiation as the near-surface temperature maximum (NSTM). Using year-round ocean (from ice tethered profilers and autonomous ocean flux buoys), sea-ice (from ice mass balance buoys), and atmosphere (from NCEP/NCAR reanalysis) data from 2005-2010, we find that heat from the NSTM is entrained into the surface mixed layer (SML) during winter. Entrainment can only occur when the base of the SML reaches the top of the NSTM. If this condition is met, the surface forcing and stratification together determine whether the SML deepens into the NSTM. Heat transfer occurs by diffusion or by the erosion of the summer halocline. The average temperature of the SML warmed by as much as 0.06°C during storm events. Solar radiation began warming the SML about 1 month early during the winter of 2007-2008 and this can be explained by thin sea ice.

Jackson, Jennifer M.; Williams, William J.; Carmack, Eddy C.

2012-02-01

332

Ice Shelves and Landfast Ice on the Antarctic Perimeter: Revised Scope of Work.  

National Technical Information Service (NTIS)

Ice shelves respond quickly and profoundly to a warming climate. Within a decade after mean summertime temperature reaches approx. O C and persistent melt pending is observed, a rapid retreat and disintegration occurs. This link was documented for ice she...

T. Scambos

2002-01-01

333

Viscosity and Density Measurements of High Temperature Melts  

NASA Astrophysics Data System (ADS)

Since the viscosity and density are most fundamental properties for any fluids, many efforts to obtain reliable values have been made. However, the measurements are not so easy, especially at high temperature in molten state. The high temperature melts are typically classified into molten metals, molten salts, and molten oxides. They appear in many industrial processes, for example, steelmaking, nonferrous metallurgy, aluminum smelting, foundry, glass making, etc. The adaptable methods for the measurements should be chosen carefully by considering some physical and chemical properties of the melt. Iida published the review on the properties including viscosity and density of molten metals [1], and the comparison among the viscosities of molten iron reported by many researchers showed considerable difference of several dozen percent. The viscosity value is in considerably wide range depending on the groups of the melts, for example, in general low for molten metals and high for molten silicates, including slag and glass, and the difference reaches more than ten orders by reflecting the difference in the melt structure. On the other hand, density is mainly depending on atomic mass and not so different to each other because of not so big difference in molar volumes of the components. Various methods for viscosity and density measurement were also introduced [2] and also the viscometries were summarized [3].

Sato, Yuzuru

334

Quality assessment of MODIS land surface temperatures over an Arctic ice cap  

NASA Astrophysics Data System (ADS)

Surface temperature is governed by the surface energy balance and therefore a key variable in climate monitoring, ecology and also in glacier melt observation and modelling. With thermal satellite remote sensing land surface temperature (LST) can be obtained with high spatial and temporal coverage. Clear sky LST derived from the Moderate Resolution Imaging Spectrometer (MODIS) has a reported uncertainty of below 1K under most circumstances. However, there are only few studies validating the product over snow and ice surface, indicating a much higher uncertainty of up to 4K. The MODIS LST level 3 product is compared with 8 years of meteorological data of an automatic weather station (AWS) located on the Austfonna ice cap, Svalbard. The smoothness of the ice cap in terms of topography, temperature and emissivity makes it an ideal site for comparing point measurements with the 1 km MODIS resolution. We find an overall RMS between MODIS LST and measured air temperature of 6.2K; however, melting conditions are nicely reproduced by the MODIS LST. Clouds are opaque in the range of the spectrum used for LST and therefore, cloudy scenes have to be removed. The MODIS LST product considers cloudiness by an automatic cloud-detection procedure. We derive a cloud index from the meteorological data of the AWS to assess the possibility of LST being affected by deficient cloud-detection. We find that over snow and ice the MODIS procedure detects too few clouds. Of the scenes classified as cloudy according to AWS data, MODIS interpreted 42% as clear sky during winter and 20% during summer. In contrast, on bare ground outside the glacier not far from the AWS, 65% of the sunny days are interpreted as cloudy during summer. Due to prevailing cloud condition at Austfonna, 42% of the successfully produced LST are acquired during a cloudy sky, 36% during a mixed sky and only 22% during clear sky. The effect of cloud miss detection is demonstrated by the RMS of 7.4K under cloudy conditions, in contrast to the 4.5K under clear sky conditions. The MODIS LST and air temperature discrepancy increases with decreasing sun angles, indicating that the MODIS cloud algorithm performs unsatisfactory under low solar illumination. The under-detection of clouds leads to a considerable cold bias in the LST product since top-of-cloud temperatures typically are much lower than surface temperatures. The LST-data set has a great potential for glaciological applications on larger glaciers and ice caps. Nevertheless, thermal remote sensing over snow and ice surface in cloud prone areas like Svalbard remains challenging.

Østby, Torbjørn I.; Schuler, Thomas V.; Westermann, Sebastian

2013-04-01

335

Protective Coverings for Ice and Snow.  

National Technical Information Service (NTIS)

Summer deterioration of snow and ice surfaces due to high solar radiation and near-melting temperatures hampers the year-round use of natural ice islands and smooth sea-ice areas in the Arctic Ocean, and permanent snow and ice areas in the Antarctic. Sawd...

N. S. Stehle

1966-01-01

336

Measuring the temperature of the glass melt in a furnace with a cooled metal baffle plate  

Microsoft Academic Search

The temperature field inthe volume of the melt was determined by the method normally used in studying the temperature of the melt in the drawing pot of uondebiteuse drawing systems [4]. The measurement of the temperature in the melting end, however, particularly in the maximum temperature zone and in the region where the heaps of batch are distributed, has necessitated

A. G. Gurkov; V. I. Pokolenko; V. N. Ruslov

1973-01-01

337

Trace element analyses of spheres from the melt zone of the Greenland ice cap using synchrotron X ray fluorescence  

Microsoft Academic Search

Synchrotron X ray fluorescence spectra of unpolished iron and chondritic spheres extracted from sediments collected on the melt zone of the Greenland ice cap allow the analysis of Ni, Cu, Zn, Ga, Ge, Pb, and Se with minimum detection limits on the order of several parts per million. All detected elements are depleted relative to chondritic abundance with the exception

P. Chevallier; C. Jehanno; M. Maurette; S. R. Sutton

1987-01-01

338

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

339

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

340

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.

2013-09-01

341

An Artificial Neural Network Approach to Surface Melt Magnitude Retrieval over West Antarctic Ice Shelves Using Coupled MODIS Optical and Thermal Satellite Measurements  

NASA Astrophysics Data System (ADS)

Ice shelf stability is of crucial importance in the Antarctic because shelves serve as buttresses to glacial ice advancing from the Antarctic Ice Sheet. Surface melt has been increasing over recent years, especially over the Antarctic Peninsula, contributing to disintegration of shelves such as Larsen. Satellite based assessments of melt from passive microwave systems are limited in that they only provide an indication of melt occurrence and have coarse resolution. Though this is useful in tracking the duration of melt, melt amount of magnitude is still unknown. Coupled optical/thermal surface measurements from MODIS were calibrated by estimates of liquid water fraction (LWF) in the upper 1cm of the firn derived from a one-dimensional thermal snowmelt model (SNTHERM). SNTHERM was forced by hourly meteorological data from automatic weather station data at seven reference sites spanning a range of melt conditions across several West Antarctic ice shelves. A calibration “curve” was developed using an artificial neural network platform to derive LWF for satellite composite periods covering the Antarctic summer months at a 4km resolution over the Larsen Ice Shelf, Ronne-Filchner Ice Shelf and the Ross Ice Shelf, ranging from near 0% LWF to upwards of 5% LWF on the Larsen Ice Shelf during the time of peak surface melt. Spatial and temporal variations in the amount of surface melt are seen to be related to both katabatic wind strength and wind shifts due to the progression of cyclones along the circumpolar vortex. Sea ice concentration along the ice shelf front, specifically the formation of polynyas, are also thought to be driving factors for surface melt as latent and sensible heat fluxes increase by one to three orders of magnitude as polynyas form.

Karmosky, C. C.; Lampkin, D. J.

2009-12-01

342

A mixed layer beneath melting sea ice in the marginal ice zone using a one-dimensional turbulent closure model  

Microsoft Academic Search

A level 2 second-order turbulent closure model is employed to study the surface mixed layer developing between sea ice and a relatively warmer background water in the marginal ice zone. The model is driven by a suddenly imposed ice-water stress and warming in the water. The mixed layer rapidly develops in 1 day and afterwards is gradually eroded at its

Motoyoshi Ikeda

1986-01-01

343

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

344

21 CFR 1250.85 - Drinking fountains and coolers; ice; constant temperature bottles.  

Code of Federal Regulations, 2013 CFR

...fountains and coolers; ice; constant temperature bottles. 1250.85 Section 1250...fountains and coolers; ice; constant temperature bottles. (a) Drinking fountains...contact with water in coolers or constant temperature bottles. (c) Constant...

2013-04-01

345

Basal melting and freezing beneath Antarctic ice shelves derived from glaciological modelling and remote sensing compared with results from oceanographic models  

NASA Astrophysics Data System (ADS)

To fully capture the sensitivity of the Antarctic ice sheet to changes in the ocean, coupled numerical models of ocean and marine ice sheets will be needed. If coupled models are to provide accurate predictions of the sea level contribution from the Antarctic ice sheet, they will need careful initialisation, so that the flow speed, rate of thickness change and surface mass balance of floating ice shelves are consistent with the basal mass balance, from melting or freezing, estimated from the oceanographic model. Any inconsistency would cause the forecast of ice thickness to suffer from spurious drift, and this in turn would affect the buttressing and flow of grounded ice in the interior of Antarctica. A sensible first step before proceeding with any coupled simulation is to compare maps of basal melt from the two different sources. Here, a new comprehensive map of basal melt/freeze for all Antarctic ice shelves is derived from a combination of remote sensing and glaciological modelling. In this approach, the viscosity of the floating ice shelves is selected using inverse methods to agree with satellite velocity measurements and the basal rate of melting or freezing is inferred using conservation of mass. Corrections are applied for surface mass balance and for satellite observations of ice shelf thickness change. We compare this map with estimates of basal melt/freeze from oceanographic models.

Arthern, Robert; Pritchard, Hamish; Makinson, Keith; Holland, Paul

2013-04-01

346

The Effects of Rotation and Ice Shelf Topography on Frazil-Laden Ice Shelf Water Plumes  

Microsoft Academic Search

A model of the dynamics and thermodynamics of a plume of meltwater at the base of an ice shelf is presented. Such ice shelf water plumes may become supercooled and deposit marine ice if they rise (because of the pressure decrease in the in situ freezing temperature), so the model incorporates both melting and freezing at the ice shelf base

Paul R. Holland; Daniel L. Feltham

2006-01-01

347

Ice Shelf Water plume flow beneath Filchner-Ronne Ice Shelf, Antarctica  

Microsoft Academic Search

A two-dimensional plume model is used to study the interaction between Filchner-Ronne Ice Shelf, Antarctica and its underlying ocean cavity. Ice Shelf Water (ISW) plumes are initiated by the freshwater released from a melting ice shelf and, if they rise, may become supercooled and deposit marine ice due to the pressure increase in the in situ freezing temperature. The aim

Paul R. Holland; Daniel L. Feltham; Adrian Jenkins

2007-01-01

348

Melting and Frustration in Temperature-Sensitive Colloids  

NASA Astrophysics Data System (ADS)

I will review experiments from my laboratory that employ temperature-sensitive microgel particles to induce novel phase behavior in suspension. This phenomenon offers a fantastic new variable for control of lyotropic suspensions. Recent experiments, for example, have enabled us to learn how three-dimensional crystals first begin to melt [1], to directly observe melting in 2-D wherein intermediate hexatic phases form [2], and to create geometrically frustrated colloidal ``anti-ferromagnets'' [3]. [4pt] References: [0pt] [1] Alsayed, A.M., Islam, M.F., Zhang, J., Collings, P.J., Yodh, A.G., Science 309, 1207-1210, (2005). [0pt] [2] Han Y, Ha NY, Alsayed AM and Yodh AG, Phys. Rev. E, Vol. 77 (2008). [0pt] [3] Y. Han, Y. Shokef, A. M. Alsayed, P. Yunker, T. C. Lubensky, and A. G. Yodh, ``Geometric frustration in buckled colloidal monolayers,'' to be published in Nature (2008).

Yodh, Arjun

2009-03-01

349

Arctic Melting  

NSDL National Science Digital Library

In this radio broadcast, a panel of experts joins National Public Radio journalist Diane Rehm to discuss rising temperatures at the North Pole and what the melting may mean for the climate, national boundaries, and oil exploration. There is discussion of the 1982 U.N. convention, Law of the Sea, which is guiding new mapping due to arctic melting and changing coastlines; and why the decreasing need for Arctic ice-breakers is making oil exploration mapping easier. There is explanation of why the Antarctic may melt a couple of decades after the Arctic; why we know sea levels will rise as polar ice melts; and why we know humans are causing the melting, as opposed to astronomical configurations or other natural causes leading to melting cycles. The broadcast is 51 minutes in length, but the discussion about the Arctic starts 32 minutes into the program and lasts 19 minutes. You may listen to the archived broadcast in Windows Media or Real Audio format.

2011-06-15

350

High temperature steady shear and oscillatory rheometry of basaltic melt  

NASA Astrophysics Data System (ADS)

There is a paucity of linear viscoelastic data on low viscosity (basaltic) silicate melts. We report here the initial results of a rheometrical characterisation (steady rotation, small angle oscillation) study on a geochemically well constrained aphyric basalt from Ethiopia (SiO2 48.51 wt.%, Mg# 0.44), in the temperature range 1200-1400 Celsius. Experiments were done using a recently developed commercial instrument (Anton Paar FRS 1600) and a wide gap Couette geometry. To the best of our knowledge these are the first reported silicate melt viscosity data obtained using small amplitude oscillatory shear and a rheometer with a high performance electrically commutated actuator. Results show that in the temperature range the system was very fluid, with the measured shear viscosity falling to ~ 2.3 Pa s at T = 1400 C. The melt exhibited a linear (Newtonian) response, with the shear viscosity remaining constant across two decades of deformation rate. As expected for a Newtonian fluid, the phase angle was 90 degrees across the entire range of angular frequencies studied. Correspondingly, the storage modulus (G') was zero and the loss modulus finite exhibiting a linear increase with frequency. The complex viscosity (oscillation) and shear viscosity (steady rotation) were equal in magnitude ('Cox-Merz' equivalence). These data are best interpreted in terms of a system with relatively low 'connectivity'/polymeric character and rapid relaxation dynamics, consistent with the mafic composition of the melt. As detailed compositional data are available the experimentally determined shear viscosity values are compared with those predicted from multicomponent chemical models in the literature. Discrepancies between the experimental and theoretical values are discussed.

Petford, N.; English, R.; Williams, R.; Rogers, N.

2012-04-01

351

Correcting the Cenozoic ? 18O deep-sea temperature record for Antarctic ice volume  

Microsoft Academic Search

The oxygen isotope signal in benthic foraminifera from deep-sea cores is mainly determined by deep-ocean temperature and land ice volume. Separating the temperature and ice volume signals is a key step in understanding the evolution of Cenozoic climate. Except for the last few million years, fluctuations in land ice volume were determined mainly by the size of the Antarctic ice

Johannes Oerlemans

2004-01-01

352

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

353

The impact of a seasonally ice free Arctic Ocean on the temperature, precipitation and surface mass balance of Svalbard  

NASA Astrophysics Data System (ADS)

The observed decline in summer sea ice extent since the 1970s is predicted to continue until the Arctic Ocean is seasonally ice free during the 21st Century. This will lead to a much perturbed Arctic climate with large changes in ocean surface energy flux. Svalbard, located on the present day sea ice edge, contains many low lying ice caps and glaciers and is expected to experience rapid warming over the 21st Century. The total sea level rise if all the land ice on Svalbard were to melt completely is 0.02 m. The purpose of this study is to quantify the impact of climate change on Svalbard's surface mass balance (SMB) and to determine, in particular, what proportion of the projected changes in precipitation and SMB are a result of changes to the Arctic sea ice cover. To investigate this a regional climate model was forced with monthly mean climatologies of sea surface temperature (SST) and sea ice concentration for the periods 1961-1990 and 2061-2090 under two emission scenarios. In a novel forcing experiment, 20th Century SSTs and 21st Century sea ice were used to force one simulation to investigate the role of sea ice forcing. This experiment results in a 3.5 m water equivalent increase in Svalbard's SMB compared to the present day. This is because over 50 % of the projected increase in winter precipitation over Svalbard under the A1B emissions scenario is due to an increase in lower atmosphere moisture content associated with evaporation from the ice free ocean. These results indicate that increases in precipitation due to sea ice decline may act to moderate mass loss from Svalbard's glaciers due to future Arctic warming.

Day, J. J.; Bamber, J. L.; Valdes, P. J.; Kohler, J.

2012-01-01

354

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

355

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 reveal 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 a 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 a 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 early Holocene GIS is crucial for understanding the HTM characteristics in the Nordic Seas area. This implies that the 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.

2012-10-01

356

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

357

Holocene melting history of Antarctic ice sheet inferred from relative sea-level records around the Lutzow-Holm Bay, Antarctica.  

NASA Astrophysics Data System (ADS)

The relative sea-level record from the last glacial period around the Antarctica is very important to infer the melting history of Antarctic ice sheet, since it is significantly dependent on crustal movements due to rebound after ice retreat. The relative sea-level variations from last glacial maximum around Antarctica are, however, more poorly defined than on any other continents. Recently, Miura et al. (2002) determined the accurate sea-level curve using in situ fossil shells and sequence stratigraphy of raised beach deposits at Skarvsnes, Lutzow-Holm Bay region, East Antarctica, and they deduced that the rapid sea-level falling event which magnitude is about 6 m for about 1000 yrs occurred in the mid-Holocene (4000 - 2700 yrBP). This event is attributed to the rapid removal of a regional ice load as a response to a warmer climatic event, which has been reported as ``mid-Holocene climatic optimum'' from various records around the Antarctica. Then we estimate the melting ice volume around Lutzow-Holm Bay region in the mid-Holocene by comparing the observations and predictions using the glacio-isostatic-adjustment model. In this study, we examine the possibility of the episodic melting of Antarctic ice sheet, and evaluate the spatial distribution, temporal change and volume of the melting ice loads by precise calculations. In our preliminary results, we can??t explain the rapid sea-level falling event unless the regional ice loads of 150 - 200 m melt around the Lutzow-Holm Bay. This result means that the volume of melting ice loads is corresponding to about 1 m for eustatic sea level (ESL) rise. Since previous authors have ascribed about 2 m for ESL to the Holocene Antarctic ice melting on the basis of relative sea-level variations at far-field, so this 1 m ESL rise is equivalent to 30 - 50 percent of the previous Antarctic melting estimate.

Okuno, J.; Miura, H.; Maemoku, H.

2004-12-01

358

Greenland Ice Sheet  

NSDL National Science Digital Library

A study of the Greenland ice sheet has shown it is melting faster than expected. This radio broadcast describes how the ice sheet thickness is measured and how this factors into the fight over whether pollution is raising global temperatures. The broadcast from 1999 is 3 minutes and 46 seconds in length.

359

Characterizing and Predicting Surface Melt in Antarctica  

NASA Astrophysics Data System (ADS)

The presence of surface melting on ice sheets and ice shelves marks an important climatic and geophysical threshold in the cryosphere. Wetting of snow reduces albedo and encourages additional melt, meltwater runoff contributes to mass loss from ice sheets, and penetration of meltwater to the glacier bed can lubricate faster flow and contribute to ice-sheet mass loss. Meltwater may also contribute to ice-shelf collapse through wedging open of crevasses. While fringing ice-shelf collapse along the Antarctic Peninsula is probably the best known example of the cryospheric response to a warming atmosphere (and ocean), surface melting is also present in inland portions of West Antarctica. In addition to potentially contributing to ice sheet dynamics, surface melt occurrence is a valuable proxy for changing atmospheric temperature conditions. Combining satellite remote sensing with atmospheric modeling, we diagnose the meteorological conditions associated with surface melting on the Antarctic ice sheet and its fringing ice shelves. With these results, we plan to predict whether the regional warming associated with anticipated anthropogenic global warming and related atmospheric circulation changes will lead to a future increase of melting. We present case studies of selected West Antarctic melt events that document the utility and skill of our meteorological datasets (reanalyses, RCMs, selected CMIP5 GCMs) in the development of diagnostic tools for identifying surface melt as observed by satellite and simulated by models.

Reusch, D. B.; Karmosky, C. C.; Lampkin, D. J.; Schneider, D. P.

2011-12-01

360

Infrared spectroscopy used to study ice formation: the effect of trehalose, maltose, and glucose on melting.  

PubMed

We report the use of infrared (IR) spectroscopy to detect ice crystals in biological solutions. The method is based on the temperature dependence of the OH bending and stretch bands of water. By using mixtures of D(2)O and H(2)O, water's absorption bands can be made to be on-scale in transmission mode. Water's stretch band moves to lower frequency and sharpens with freezing, and the bending band goes to higher frequency and becomes less sharp. The technique is demonstrated for the study of the hysteresis of freezing in the presence of glucosyl sugars, namely glucose, maltose, and trehalose. PMID:19376080

Zelent, B; Vanderkooi, J M

2009-04-17

361

Liquidus Temperatures of Cryolite Melts With Low Cryolite Ratio  

NASA Astrophysics Data System (ADS)

The effect of calcium fluoride on liquidus temperatures of the cryolite melts with a low cryolite ratio (CR) was studied. The systems KF-NaF-AlF3 and KF-LiF-AlF3 with CRs of 1.3, 1.5, and 1.7 have been investigated. The liquidus curves of systems containing CaF2 are different and depend on the K/(K + Na) and K/(K + Li) ratios. In potassium cryolite with CRs of 1.3 and 1.5, the calcium fluoride solubility is low and increases with NaF (LiF) concentration.

Apisarov, Alexei; Dedyukhin, Alexander; Nikolaeva, Elena; Tinghaev, Pavel; Tkacheva, Olga; Redkin, Alexander; Zaikov, Yurii

2011-02-01

362

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...  

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Cargo viscosity and melting point information; measuring cargo temperature...Information § 153.908 Cargo viscosity and melting point information; measuring cargo temperature...has a written statement of the cargo's melting point in °C from the cargo's...

2010-10-01

363

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...  

Code of Federal Regulations, 2010 CFR

...2009-10-01 false Cargo viscosity and melting point information; measuring cargo temperature...Information § 153.908 Cargo viscosity and melting point information; measuring cargo temperature...has a written statement of the cargo's melting point in °C from the cargo's...

2009-10-01

364

Perchlorate Found by Phoenix Could Provide a Mobile Brine Sludge at the Bed of Mars Northern Ice Cap that Would Allow Flow with Very Low Basal Temperatures: Possible Mechanism for Water Table ReCharge  

Microsoft Academic Search

The north cap of Mars has basal temperature that precludes the flow of ice. Phoenix discovered polar soils contain perchlorate salts. These salts depress the melting point so it could form a sludge that provides a mobile bed that moves the ice outwards.

D. A. Fisher; M. Hecht; S. Kounaves; D. Catling

2009-01-01

365

Perchlorate Found by Phoenix Could Provide a Mobile Brine Sludge at the Bed of Mars Northern Ice Cap that Would Allow Flow with Very Low Basal Temperatures: Possible Mechanism for Water Table Re-Charge  

NASA Astrophysics Data System (ADS)

The north cap of Mars has basal temperature that precludes the flow of ice. Phoenix discovered polar soils contain perchlorate salts. These salts depress the melting point so it could form a sludge that provides a mobile bed that moves the ice outwards.

Fisher, D. A.; Hecht, M.; Kounaves, S.; Catling, D.

2009-03-01

366

Temperature and ice layer trends in the summer middle atmosphere  

NASA Astrophysics Data System (ADS)

We present results from our LIMA model (Leibniz Institute Middle Atmosphere Model) which nicely reproduces mean conditions of the summer mesopause region and also mean characteristics of ice layers known as noctilucent clouds. LIMA nudges to ECMWF data in the troposphere and lower stratosphere which influences the background conditions in the mesosphere. We study temperature trends in the mesosphere at middle and polar latitudes and compared with temperature trends from satellites, lidar, and phase height observations. For the first time large observed temperature trends in the summer mesosphere can be reproduced and explained by a model. As will be shown, stratospheric ozone has a major impact on temperature trends in the summer mesosphere. The temperature trend is not uniform in time: it is moderate from 1961 (the beginning of our record) until the beginning of the 1980s. Thereafter, temperatures decrease much stronger until the mid 1990s. Thereafter, temperatures are nearly constant or even increase with time. As will be shown, trends in ozone and carbon dioxide explain most of this behavior. Ice layers in the summer mesosphere are very sensitive to background conditions and are therefore considered to be appropriate tracers for long term variations in the middle atmosphere. We use LIMA background conditions to determine ice layer characteristics in the mesopause region. We compare our results with measurements, for example with albedos from the SBUV satellites, and show that we can nicely reproduce observed trends. It turns out that temperature trends are positive (negative) in the upper (lower) part of the ice layer regime. This complicates an interpretation of NLC long term variations in terms of temperature trends.

Lübken, F.-J.; Berger, U.

2012-04-01

367

Temperature Regimes in Traditional Iñupiat Ice Cellars in Barrow, Alaska  

NASA Astrophysics Data System (ADS)

Historically ice cellars excavated in permafrost (perennially frozen ground) have been essential to Arctic residents and remain so today. These traditional facilities allow secure, year-round frozen storage of subsistence harvests over long periods. Iñupiat peoples in Barrow, Alaska, have many of these cellars, some of which were created more than a century ago. Others were established recently and continue to be enlarged. Temperatures within the cellars are critical because bacteria can damage meat even at temperatures below the freezing point. These cellars generally have temperatures close to those of surrounding permafrost. Climatic change has been suspected of compromising and causing damage to ice cellars in some northern communities, with thaw and spoilage of meat occurring in some cases. Beginning in 2005, local residents and the Native Village of Barrow organization provided access to their ice cellars and miniature temperature data loggers programmed to record at hourly intervals were installed. Cellars at a variety of depths, locations relative to the coast, and age were included in the survey. Analysis of the five years of record revealed seasonal variations within each cellar, temperature changes over time within some cellars, and temperature differences between the five cellars examined. Winter ventilation to artificially cool the cellars, local snow drifting, and proximity to brine-saturated sediments contribute to differences in ambient ground conditions. Long-term temperature measurements in these and other cellars are needed to better understand the observed changes.

Klene, A. E.; Yoshikawa, K.; Streletskiy, D. A.; Brown, J.; Nelson, F. E.; Shiklomanov, N. I.

2011-12-01

368

Thirty-seven year mass balance of Devon Ice Cap, Nunavut, Canada, determined by shallow ice coring and melt modeling  

Microsoft Academic Search

In April–May 2000, eight boreholes were drilled to ?15–20 m depth on the Devon Ice Cap. 137Cs ? activity profiles of each borehole showed a peak count rate at depth that is associated with fallout from atmospheric thermonuclear weapons testing in 1963. Snow, firn, and ice densities were measured at each core site and were used to estimate the average

Douglas Mair; David Burgess; Martin Sharp

2005-01-01

369

Carbon dioxide partial pressure and 13C content of north temperate and boreal lakes at spring ice melt  

USGS Publications Warehouse

Carbon dioxide (CO2) accumulates under lake ice in winter and degasses to the atmosphere after ice melt. This large springtime CO2 pulse is not typically considered in surface-atmosphere flux estimates, because most field studies have not sampled through ice during late winter. Measured CO2 partial pressure (pCO2) of lake surface water ranged from 8.6 to 4,290 Pa (85-4,230 ??atm) in 234 north temperate and boreal lakes prior to ice melt during 1998 and 1999. Only four lakes had surface pCO2 less than or equal to atmospheric pCO2, whereas 75% had pCO2 >5 times atmospheric. The ??13CDIC (DIC = ??CO2) of 142 of the lakes ranged from -26.28??? to +0.95.???. Lakes with the greatest pCO2 also had the lightest ??13CDIC, which indicates respiration as their primary CO2 source. Finnish lakes that received large amounts of dissolved organic carbon from surrounding peatlands had the greatest pCO2. Lakes set in noncarbonate till and bedrock in Minnesota and Wisconsin had the smallest pCO2 and the heaviest ??13CDIC, which indicates atmospheric and/or mineral sources of C for those lakes. Potential emissions for the period after ice melt were 2.36 ?? 1.44 mol CO2 m-2 for lakes with average pCO2 values and were as large as 13.7 ?? 8.4 mol CO2 m-2 for lakes with high pCO2 values.

Striegl, R. G.; Kortelainen, P.; Chanton, J. P.; Wickland, K. P.; Bugna, G. C.; Rantakari, M.

2001-01-01

370

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

371

Flush at room temperature followed by storage on ice creates the best lung graft preservation in rats.  

PubMed

Current clinical lung preservation techniques have not eliminated ischaemia-reperfusion (I/R) injury, despite many improvements. The optimal combination of flush and storage temperatures remain unclear in lung preservation. This is the first study to investigate a range of temperatures with 24-h inflated storage using consistent state-of-the-art preservation techniques. A rat lung transplant model was used to investigate the optimal combination of flush and storage temperatures. In six groups, rat lungs were flushed at 4 °C, 10 °C or room temperature (F(4) /F(10) /F(Rt)) with Perfadex and stored inflated for 24 h in Perfadex on melting ice or at 10 °C (S(ice) /S(10)). Left donor lungs were transplanted for analysis. During 2-h reperfusion, the lung graft function was measured (blood gases, maximum ventilation pressure and static compliance) and lung graft injury was also assessed (W/D ratio, total lung protein, Tryptase, Myeloperoxidase). Right donor lungs were assessed for W/D ratio only after flush and storage. For baseline measurements, left lungs without intervention were used. The combination of F(Rt) -S(ice) showed a significantly higher pO(2), lower P(max), low W/D ratios and total protein levels of left lungs after reperfusion when compared with F(4) -S(ice) and baseline. Storage at 10 °C did not improve preservation. We conclude that F(Rt) -S(ice) creates the best lung graft preservation. PMID:23668661

Munneke, Anita J; Rakhorst, Gerhard; Petersen, Arjen H; van Oeveren, Wim; Prop, Jochum; Erasmus, Michiel E

2013-05-14

372

Effect of storage temperature on quality of light and full-fat ice cream  

Microsoft Academic Search

Ice cream quality is dependent on many factors including storage temperature. Currently, the industry standard for ice cream storage is ?28.9°C. Ice cream production costs may be decreased by increasing the temperature of the storage freezer, thus lowering energy costs. The first objective of this research was to evaluate the effect of 4 storage temperatures on the quality of commercial

J. R. Buyck; R. J. Baer; J. Choi

2011-01-01

373

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

374

The Creep of Polycrystalline Ice  

Microsoft Academic Search

Polycrystalline blocks of ice have been tested under compressive stresses in the range from 1 to 10 bars at temperatures from -13 degrees C to the melting-point. Under these conditions ice creeps in a manner similar to that shown by metals at high temperatures; there is a transient creep component and also a continuing or quasi-viscous component. The relation between

J. W. Glen

1955-01-01

375

Thirty-seven year mass balance of Devon Ice Cap, Nunavut, Canada, determined by shallow ice coring and melt modeling  

Microsoft Academic Search

In April-May 2000, eight boreholes were drilled to ~15-20 m depth on the Devon Ice Cap. 137Cs gamma activity profiles of each borehole showed a peak count rate at depth that is associated with fallout from atmospheric thermonuclear weapons testing in 1963. Snow, firn, and ice densities were measured at each core site and were used to estimate the average

Douglas Mair; David Burgess; Martin Sharp

2005-01-01

376

Melting probes as a means to explore planetary glaciers and ice caps  

Microsoft Academic Search

On many planetary bodies thick layers of frozen volatiles cover the surface. Examples are: The polar ice caps of Earth and Mars, consisting of H2O-ice and an mixture of H2O- and CO2-ice, respectively; Neptune's satellite Triton, whose polar areas are composed of nitrogen (N2)-ice, and the icy satellites of Jupiter (in particular Europa), which most probably host liquid layers below

N. I. Kömle; G. Kargl; M. Steller

2002-01-01

377

Incorporation of a new melt pond model into a GCM sea ice model component  

Microsoft Academic Search

The Arctic sea ice cover has retreated in the past few decades: submarine data gathered from 1958 to 1976 indicates a decrease of sea ice thickness of about 1.5m (Rothrock et al, 1999) in the region of observation. Satellite observations show that the ice cover is continuing to thin (Laxon et al, 2003). In September 2005 and 2007 historical minima

D. Flocco; D. L. Feltham; A. K. Turner

2009-01-01

378

Modeling the heating and melting of sea ice through light absorption by microalgae  

Microsoft Academic Search

In sea ice of polar regions, high concentrations of microlgae are observed during the spring. Algal standing stocks may attain peak values of over 300 mg chl a m - in the congelation ice habitat. As of yet, the effect of additional heating of sea ice through conversion of solar radiation into heat by algae has not been investigated in

Richard E. Zeebe; Hajo Eicken; Dale H. Robinson; Dieter Wolf-Gladrow; Gerhard S. Dieckmann

1996-01-01

379

Sediment plume response to surface melting and supraglacial lake drainages on the Greenland ice sheet  

Microsoft Academic Search

Increased mass losses from the Greenland ice sheet and inferred contributions to sea-level rise have heightened the need for hydrologic observations of meltwater exiting the ice sheet. We explore whether temporal variations in ice-sheet surface hydrology can be linked to the development of a downstream sediment plume in Kangerlussuaq Fjord by comparing: (1) plume area and suspended sediment concentration from

Vena W. Chu; Laurence C. Smith; Asa K. Rennermalm; Richard R. Forster; Jason E. Box; Niels Reehy

2009-01-01

380

Spin Polarized Liquid 3 He Obtained by Rapid Melting : Towards Lower Temperatures and Larger Pressures?  

Microsoft Academic Search

Our variant of the rapid melting technique enables us to study strongly polarized liquid3He around 80 mK below 29 bars, the minimum of the melting curve. Analysis of our results suggests that lower temperatures or larger pressures could only be obtained using a Pomeranchuk cell to control the pressure during melting. This paper describes an attempt in this direction.

O. Buu; A. C. Forbes; L. Puech; P. E. Wolf

1998-01-01

381

Temperature Independent Thermal Expansivities of Silicate Melts in the System Anorthite-Wollastonite-Gehlenite (CAS) system  

Microsoft Academic Search

Calcium aluminosilicate melts are, in addition to their model role in geochemistry, also important for both the glass and stone wool industry. Contributions to the PVT equation of state of such melts are needed for geochemical and geophysical modelling, as well as for providing tests of structure-property relationships for magma. The temperature-independent thermal expansivities of ten melts included in the

M. Solvang; M. Potuzak; D. B. Dingwell

2004-01-01

382

Melting Curve of Water Studied in Externally Heated Diamond-Anvil Cell  

Microsoft Academic Search

The melting curve of ice VII was measured to a maximum pressure of 38GPa (temperature of about 1000 K). Experiments were carried out in an externally heated diamond anvil cell and melting was monitored by the disappearance of X-ray difiraction from ice VII. The melting line of H2O was found to be well described by the Simon equation P =

Natalia Dubrovinskaia; Leonid Dubrovinsky

2003-01-01

383

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

PubMed

Airborne radar has detected approximately 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 degrees C, which is 7 degrees 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 km(3)) and at lower temperatures (-20 degrees C to -35 degrees 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

2002-06-11

384

Non-melting and self-wetting of alkali halide surfaces at high temperatures  

Microsoft Academic Search

We investigated theoretically the high temperature thermodynamic properties and the (lack of) self-wetting of ionic crystal surfaces, with NaCl(100) as a prototype case. We found by classical molecular dynamics simulations that NaCl(100) is a non-melting crystal surface and can be overheated to a spinodal temperature TS 150 K above the bulk melting temperature (T_M). While surface non-melting is in itself

Davide Ceresoli; Tania Zykova-Timan; Ugo Tartaglino; Wassila Sekkal; Edoardo Jagla; Erio Tosatti

2004-01-01

385

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

386

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

Microsoft Academic Search

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

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

1993-01-01

387

Method to determine the melting temperatures of metals under megabar shock pressures  

NASA Astrophysics Data System (ADS)

Based on the model that the high-pressure melting temperatures of metals approximately equal the experimentally measured interface temperatures between the metallic plate sample and the transparent window when shock- and/or release-induced melting falls into the mixed phase region, we proposed a method to determine the melting temperatures of metals under megabars of shock compression. Experiments were conducted by using the oxygen-free high-conductivity copper, and pure iron plate sample with single-crystal lithium fluoride windows. Results showed that the measured melting temperatures are in good agreement with reported theoretical calculations.

Tan, H.; Dai, C. D.; Zhang, L. Y.; Xu, C. H.

2005-11-01

388

Physics of ice friction  

NASA Astrophysics Data System (ADS)

Although the study of friction has a long history, ice friction has only been investigated during the last century. The basic physical concepts underlying the different friction regimes, such as boundary, mixed, and hydrodynamic friction are also relevant to ice friction. However, these friction regimes must be described with respect to the thickness of the lubricating liquidlike layer on ice. In this review the state of knowledge on the physics of ice friction is discussed. Surface melting theories are introduced. These theories attempt to explain the existence and nature of the liquidlike surface layer on ice at any temperature and without any load applied. Pressure melting, as the long-time explanation for the ease of ice friction, is discussed, together with the prevailing theory of frictional heating. The various laboratory setups for ice friction measurements are presented as well as their advantages and disadvantages. The individual influence of the different parameters on the coefficient of ice friction is discussed; these include the effects of temperature, sliding velocity, normal force exerted by the sliding object, the contact area between ice and slider, relative humidity, and also properties of the slider material such as surface roughness, surface structure, wettability, and thermal conductivity. Finally, the most important ice friction models based on the frictional heating theory are briefly introduced and research directions on the subject of ice friction are discussed.

Kietzig, Anne-Marie; Hatzikiriakos, Savvas G.; Englezos, Peter

2010-04-01

389

Migration of air bubbles in ice under a temperature gradient, with application to “Snowball Earth”  

Microsoft Academic Search

To help characterize the albedo of “sea glaciers” on Snowball Earth, a study of the migration rates of air bubbles in freshwater ice under a temperature gradient was carried out in the laboratory. The migration rates of air bubbles in both natural glacier ice and laboratory-grown ice were measured for temperatures between ?36°C and ?4°C and for bubble diameters of

Ruzica Dadic; Bonnie Light; Stephen G. Warren

2010-01-01

390

Effects of temperature on the microstructure of first-year Arctic sea ice  

Microsoft Academic Search

While the apparent optical properties of sea ice vary with ice type and temperature throughout the annual cycle, they depend more fundamentally on how inclusions of brine, gas, precipitated salts, and other impurities are distributed within the ice. Since little is known about these distributions or about how they evolve with temperature, experiments were designed to collect detailed information on

B. Light; G. A. Maykut; T. C. Grenfell

2003-01-01

391

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.

392

Basal drainage system response to increasing surface melt on the Greenland ice sheet.  

PubMed

Surface meltwater reaching the bed of the Greenland ice sheet imparts a fundamental control on basal motion. Sliding speed depends on ice/bed coupling, dictated by the configuration and pressure of the hydrologic drainage system. In situ observations in a four-site transect containing 23 boreholes drilled to Greenland's bed reveal basal water pressures unfavorable to water-draining conduit development extending inland beneath deep ice. This finding is supported by numerical analysis based on realistic ice sheet geometry. Slow meltback of ice walls limits conduit growth, inhibiting their capacity to transport increased discharge. Key aspects of current conceptual models for Greenland basal hydrology, derived primarily from the study of mountain glaciers, appear to be limited to a portion of the ablation zone near the ice sheet margin. PMID:23950535

Meierbachtol, T; Harper, J; Humphrey, N

2013-08-16

393

High-Temperature Vibrational Properties and Melting Curve of Aluminum  

NASA Astrophysics Data System (ADS)

The mean-field theory due to Wang and Li (Phys Rev B 63:196, 2000) to calculate the effective mean potential experienced by vibrating ions in a crystal is used to compute the ion-motional free energy. An improvement is sought by treating the parameter ?, entering an expression of the mean-field potential (MFP), as a free parameter for the case of aluminum. Although a corresponding expression for the Grüneisen parameter ( ?) is significantly different then the known cases, namely, those due to (i) Slater, (ii) Dugdale and MacDonald, (iii) free volume theory, and (iv) Barton and Stacey, its value is very close to the experimental result. Significant improvement is observed for high-temperature thermodynamics of aluminum with the new choice of ?, or equivalently ?. Also, the present improved scheme is extended to measure the vibrational response of the crystal. Recently, Bhatt et al. (Philos Mag 90:1599, 2010) have demonstrated that the mean frequency ( ?') calculated by the MFP approach in conjunction with the density-dependent local pseudopotential suffices to characterize the crystal at finite temperatures. Relating ?' to the Debye frequency, vibrational properties like the Debye temperature, the mean-square displacement, and entropy are obtained as a function of temperature. Further, a generalized melting law is derived by combining the MFP approach to Lindemann's law, where the effect of different choices of the parameter ? is now explicitly included into the description. Results so obtained for different physical properties are analyzed and discussed in the light of recent first principles and experimental findings.

Bhatt, N. K.; Thakore, B. Y.; Vyas, P. R.; Jani, A. R.

2010-12-01

394

Unlabeled Oligonucleotides as Internal Temperature Controls for Genotyping by Amplicon Melting  

PubMed Central

Amplicon melting is a closed-tube method for genotyping that does not require probes, real-time analysis, or allele-specific polymerase chain reaction. However, correct differentiation of homozygous mutant and wild-type samples by melting temperature (Tm) requires high-resolution melting and closely controlled reaction conditions. When three different DNA extraction methods were used to isolate DNA from whole blood, amplicon Tm differences of 0.03 to 0.39°C attributable to the extractions were observed. To correct for solution chemistry differences between samples, complementary unlabeled oligonucleotides were included as internal temperature controls to shift and scale the temperature axis of derivative melting plots. This adjustment was applied to a duplex amplicon melting assay for the methylenetetrahydrofolate reductase variants 1298A>C and 677C>T. High- and low-temperature controls bracketing the amplicon melting region decreased the Tm SD within homozygous genotypes by 47 to 82%. The amplicon melting assay was 100% concordant to an adjacent hybridization probe (HybProbe) melting assay when temperature controls were included, whereas a 3% error rate was observed without temperature correction. In conclusion, internal temperature controls increase the accuracy of genotyping by high-resolution amplicon melting and should also improve results on lower resolution instruments.

Seipp, Michael T.; Durtschi, Jacob D.; Liew, Michael A.; Williams, Jamie; Damjanovich, Kristy; Pont-Kingdon, Genevieve; Lyon, Elaine; Voelkerding, Karl V.; Wittwer, Carl T.

2007-01-01

395

Spin liquid regimes at nonzero temperature in quantum spin ice  

NASA Astrophysics Data System (ADS)

Quantum spin liquids are highly entangled ground states of quantum systems with an emergent gauge structure, fractionalized spinon excitations, and other unusual properties. While these features clearly distinguish quantum spin liquids from conventional, mean-field-like states at zero temperature (T), their status at T>0 is less clear. Strictly speaking, it is known that most quantum spin liquids lose their identity at nonzero temperature, being then adiabatically transformable into a trivial paramagnet. This is the case for the U(1) quantum spin liquid states recently proposed to occur in the quantum spin ice pyrochlores. Here we propose, however, that in practical terms, the latter quantum spin liquids can be regarded as phases distinct from the high-temperature paramagnet. Through a combination of gauge mean-field theory calculations and physical reasoning, we argue that these systems sustain both quantum spin liquid and thermal spin liquid phases, dominated by quantum fluctuations and entropy, respectively. These phases are separated by a first-order “thermal confinement” transition such that, for temperatures below the transition, spinons and emergent photons are coherently propagating excitations, and above it the dynamics is classical. Even for parameters for which the ground state is magnetically ordered and not a quantum spin liquid, this strong first-order transition occurs, preempting conventional Landau-type criticality. We argue that this picture explains the anomalously low-temperature phase transition observed in the quantum spin ice material Yb2Ti2O7.

Savary, Lucile; Balents, Leon

2013-05-01

396

Effects of Fat Replacers on the Sensory Properties, Color, Melting, and Hardness of Ice Cream1  

Microsoft Academic Search

We examined the effects of individual fat replacers on the physical and sensory properties of fat-free ice cream. Ice creams (? 0.5% milk fat) were formulated with maltodextrin, milk protein concentrate, or poly- dextrose. Lactose-reduced, freeze-concentrated skim milk was used to prepare a 1.6% fat ice cream mix. Experimental mixes were formulated to maintain the sweetness intensity and freezing characteristics

Ann M. Roland; Lance G. Phillips; Kathryn J. Boor

1999-01-01

397

Ti 4+ in silicate melts: Energetics from high-temperature calorimetric studies and implications for melt structure  

NASA Astrophysics Data System (ADS)

The drop solution calorimetric method was used to determine the enthalpy of solution of rutile ( ?Hsol) in silicate melts. High-temperature (1760 K) in situ calorimetric data show that ?Hsol is a strong function of melt composition. For potassium endmember melts, potassium disilicate, and trisilicate, ?Hsol increases (from 28-48 kJ/mol) as TiO 2 concentration increases. For calcium disilicate melts ?Hsol is constant (69 kJ/mol). For mixed potassium-calcium compositions, ?Hsol is more exothermic than for the calcium endmember but remains constant at 43.9 kJ/mol. The enthalpy of solution of rutile at 1760 K and the enthalpy of mixing at 978 K derived from lead borate solution calorimetry for Ti-bearing potassium aluminosilicate glasses have been used to model the homogeneous equilibria among Ti species in the potassium-bearing melts. The energetics of Ti speciation were used to predict quantitatively the excess heat capacity of titanium-bearing silicate melts previously observed by Lange and Navrotsky (1993), suggesting that heat capacities, mixing properties, and rutile solubility are all controlled by the temperature and composition dependence of the same set of homogenous equilibria among titanium species in the melts. Though knowing the exact microscopic nature of these species is not necessary for macroscopic thermodynamic modeling, the model is consistent with a gradual variation with composition and temperature in mid-range order involving five-coordinated titanyl groups and alkali atoms as proposed by Farges et al. (1996a,b,c).

Gan, Hao; Wilding, Martin C.; Navrotsky, Alexandra

1996-11-01

398

Plasma-melting and plasma-melt-gas-atomization of high temperature intermetallic compounds (Nb3Al)  

NASA Astrophysics Data System (ADS)

There has been much interest in rapidly solidified niobium-aluminides (Nb3Al) as structural materials for ultrahigh temperature applications. Pressurizing melting atmosphere to approximately 0.25 MPa can reduce Al vaporization during plasma melting. A unique plasma-melt-gas-atomization process (PMGA) has been developed for making rapidly-solidified powder of high temperature intermetallic compounds such as Nb3Al. In this technique, we use only water-cooled copper as a tundish for bottom poring, instead of refractories or refractory metals. The crystal structure of PMGA'ed Nb3Al powder consists of an almost Al-saturated solid solution of niobium (bcc). This fact means that the solidification rate of PMGA is sufficiently high.

Kohno, T.; Kohmoto, H.; Murahashi, N.

399

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

2011-06-06

400

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

401

Growth–melt asymmetry in ice crystals under the influence of spruce budworm antifreeze protein  

Microsoft Academic Search

Here we describe studies of the crystallization behavior of ice in an aqueous solution of spruce budworm antifreeze protein (sbwAFP) at atmospheric pressure. SbwAFP is an ice binding protein with high thermal hysteresis activity, which helps protect Choristoneura fumiferana (spruce budworm) larvae from freezing as they overwinter in the spruce and fir forests of the north eastern United States and

Natalya Pertaya; Yeliz Celik; Carlos L DiPrinzio; J S Wettlaufer; Peter L Davies; Ido Braslavsky

2007-01-01

402

Optical properties of melting landfast sea ice and underlying seawater in Santala Bay, Gulf of Finland  

Microsoft Academic Search

In March and early April 2000, spectral irradiance measurements were conducted on 10 occasions above and beneath the landfast sea ice in Santala Bay near the entrance to the Gulf of Finland. The measurements included the spectral albedo and transmittance of the sea ice and the downwelling and upwelling spectral irradiance at different depths in the water column. Spectral albedos

Jens Ehn; Mats A. Granskog; Anu Reinart; Ants Erm

2004-01-01

403

SEASAT SAR Sea Ice Imagery from Summer Melt to Fall Freeze-up.  

National Technical Information Service (NTIS)

Some salient aspects of SEASAT L-band SAR sea ice imagery are presented. High backscatter attributed to water-saturated surface layers reduces the ability to interpret ice conditions. Slush on water areas produces a strong backscatter which could be misin...

R. D. Ketchum

1982-01-01

404

Isolation and characterization of hydroxylamine-induced mutations in the Erwinia herbicola ice nucleation gene that selectively reduce warm temperature ice nucleation activity.  

PubMed

Cells of ice nucleation active bacterial species catalyse ice formation over the temperature range of -2 to -12 degrees C. Current models of ice nucleus structure associate the size of ice nucleation protein aggregates with the temperature at which they catalyse ice formation. To better define the structural features of ice nucleation proteins responsible for the functional heterogeneity of ice nuclei within a genetically homogeneous collection of cells we used in vitro chemical mutagenesis to isolate mutants with reduced ability to nucleate ice at warm assay temperatures but which retain normal or near normal nucleation activity at cold temperatures (WIND, i.e. warm ice nucleus-deficient mutants). Nearly half of the mutants obtained after hydroxylamine mutagenesis of the iceE gene from Erwinia herbicola had this phenotype. The phenotypes and location of lesions on the genetic map of iceE were determined for a number of mutants. All WIND mutations were restricted to the portion of iceE encoding the repetitive region of the polypeptide. DNA sequencing of two WIND mutants revealed single nucleotide substitutions changing a conserved serine or glycine residue to phenylalanine and serine, respectively. The implications of these findings in structure/function models for the ice nucleation protein are discussed. PMID:8412688

Gurian-Sherman, D; Lindow, S E; Panopoulos, N J

1993-07-01

405

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

406

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 series of surface melt records over the Greenland ice sheet (GrIS), continuing the trend towards increased melt observed since the end of the 1990's. The 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 daily 500 hPa geopotential height to evaluate the role of atmospheric dynamics in this surface melt acceleration for the last two decades. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June-July-August) mean temperature from reanalyses at 700 hPa over Greenland; analogous atmospheric circulations in the