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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.

2012-07-19

2

Melting Ice  

NSDL National Science Digital Library

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

2012-08-03

3

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

4

Concord Consortium: Melting Ice  

NSDL National Science Digital Library

This activity combines a hands-on lab with a computer simulation, as students investigate and graph the changing temperature of a melting ice cube. In the first step, learners 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.

5

Surface Temperature and Melt on the Greenland Ice Sheet, 2000 - 2011  

NASA Technical Reports Server (NTRS)

Enhanced melting along with surface-temperature increases measured using infrared satellite data, have been documented for the Greenland Ice Sheet. Recently we developed a climate-quality data record of ice-surface temperature (IST) of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) IST product -- http://modis-snow-ice.gsfc.nasa.gov.Using daily and mean-monthly MODIS IST maps from the data record we show maximum extent of melt for the ice sheet and its six major drainage basins for a 12-year period extending from March of 2000 through December of 2011. The duration of the melt season on the ice sheet varies in different drainage basins with some basins melting progressively earlier over the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. The short time of the study period (approx 12 years) precludes an evaluation of statistically-significant trends. However the dataset provides valuable information on natural variability of IST, and on the ability of the MODIS instrument to capture changes in IST and melt conditions in different drainage basins of the ice sheet.

Hall, Dorothy K.; Comiso, Josefino C.; Shuman, Christopher A.; Koeing, Lora S.; Box, Jason E.; DiGirolamo, Nicolo E.

2012-01-01

6

Variability of Surface Temperature and Melt on the Greenland Ice Sheet, 2000-2011  

NASA Technical Reports Server (NTRS)

Enhanced melting along with surface-temperature increases measured using infrared satellite data, have been documented for the Greenland Ice Sheet. Recently we developed a climate-quality data record of ice-surface temperature (IST) of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) 1ST product -- http://modis-snow-ice.gsfc.nasa.gov. Using daily and mean monthly MODIS 1ST maps from the data record we show maximum extent of melt for the ice sheet and its six major drainage basins for a 12-year period extending from March of 2000 through December of 2011. The duration of the melt season on the ice sheet varies in different drainage basins with some basins melting progressively earlier over the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. The short time of the study period (approximately 12 years) precludes an evaluation of statistically-significant trends. However the dataset provides valuable information on natural variability of IST, and on the ability of the MODIS instrument to capture changes in IST and melt conditions indifferent drainage basins of the ice sheet.

Hall, Dorothy K.; Comiso, Josefino, C.; Shuman, Christopher A.; Koenig, Lora S.; DiGirolamo, Nicolo E.

2012-01-01

7

Pressure melting and ice skating  

Microsoft Academic Search

Pressure melting cannot be responsible for the low friction of ice. The pressure needed to reach the melting temperature is above the compressive failure stress and, if it did occur, high squeeze losses would result in very thin films. Pure liquid water cannot coexist with ice much below -20 °C at any pressure and friction does not increase suddenly in

S. C. Colbeck

1995-01-01

8

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

9

Melting of ice under pressure  

PubMed Central

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 ?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

2008-01-01

10

Relationship Between Ice Nucleation Temperature Depression and Equilibrium Melting Points Depression of Medaka (Oryzias latipes) Embryos  

NASA Astrophysics Data System (ADS)

We measured the ice nucleation temperature depression , ?Tf , and equilibrium melting points depression, ?Tm, of Medaka (Oryzias latipes) embryos with different cryoprotectant (ethylene glycol, 1.3-propanediol, 1.4-butanediol, glycerol aqueous solutions) treatments. Our obtained results showed the good relationship between the ?Tf ,and ?Tm all samples. In addition the value of ? , which can be obtained from the linear relationship, ?Tf =? ?Tm, were confirmed to show correlation with the value of ? , as obtained by the W/O emulsion method.

Kimizuka, Norihito; Suzuki, Toru

11

Quantum path integral simulation of isotope effects in the melting temperature of ice Ih  

E-print Network

The isotope effect in the melting temperature of ice Ih has been studied by free energy calculations within the path integral formulation of statistical mechanics. Free energy differences between isotopes are related to the dependence of their kinetic energy on the isotope mass. The water simulations were performed by using the q-TIP4P/F model, a point charge empirical potential that includes molecular flexibility and anharmonicity in the OH stretch of the water molecule. The reported melting temperature at ambient pressure of this model (T = 251 K) increases by 6.5+-0.5 K and 8.2+-0.5 K upon isotopic substitution of hydrogen by deuterium and tritium, respectively. These temperature shifts are larger than the experimental ones (3.8 K and 4.5 K, respectively). In the classical limit, the melting temperature is nearly the same as that for tritiated ice. This unexpected behavior is rationalized by the coupling between intermolecular interactions and molecular flexibility. This coupling makes the kinetic energy o...

Ramirez, R; 10.1063/1.3503764

2011-01-01

12

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

13

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.

WGBH Educational Foundation Teachers' Domain

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.

2007-01-01

15

Testing recent charge-on-spring type polarizable water models. I. Melting temperature and ice properties.  

PubMed

We determined the freezing point of eight molecular models of water. All models use the charge-on-spring (COS) method to express polarization. The studied models were the COS/G2, COS/G3 [H. Yu and W. F. van Gunsteren, J. Chem. Phys. 121, 9549 (2004)], the COS/B2 [H. Yu, T. Hansson, and W. F. van Gunsteren, J. Chem. Phys. 118, 221 (2003)], the SWM4-DP [G. Lamoureux, A. D. MacKerell, Jr., and B. Roux, J. Chem. Phys. 119, 5185 (2003)], the SWM4-NDP [G. Lamoureux, E. Harder, I. V. Vorobyov, B. Roux, and A. D. MacKerell, Jr., Chem. Phys. Lett. 418, 245 (2006)], and three versions of our model, the BKd1, BKd2, and BKd3. The BKd1 is the original Gaussian model [P. T. Kiss, M. Darvas, A. Baranyai, and P. Jedlovszky, J. Chem. Phys. 136, 114706 (2012)] with constant polarization and with a simple exponential repulsion. The BKd2 applies field-dependent polarizability [A. Baranyai and P. T. Kiss, J. Chem. Phys. 135, 234110 (2011)], while the BKd3 model has variable size to approximate the temperature-density (T-?) curve of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 137, 084506 (2012)]. We used the thermodynamic integration (TI) and the Gibbs-Helmholtz equation to determine the equality of the free energy for liquid water and hexagonal ice (Ih) at 1 bar. We used the TIP4P and the SPC/E models as reference systems of the TI. The studied models severely underestimate the experimental melting point of ice Ih. The calculated freezing points of the models are the following: COS/G2, 215 K; COS/G3, 149 K; SWM4-DP, 186 K; BKd1, 207 K; BKd2, 213 K; BKd3, 233 K. The freezing temperature of the SWM4-NDP system is certainly below 120 K. It might even be that the water phase is more stable than the ice Ih at 1 bar in the full temperature range. The COS/B2 model melts below 100 K. The best result was obtained for the BKd3 model which indicates that correct description of the (T-?) curve improves the estimation of the freezing point. We also determined and compared the densities of high-pressure polymorphs of ice for these models. PMID:23181289

Kiss, Péter T; Bertsyk, Péter; Baranyai, András

2012-11-21

16

Testing recent charge-on-spring type polarizable water models. I. Melting temperature and ice properties  

NASA Astrophysics Data System (ADS)

We determined the freezing point of eight molecular models of water. All models use the charge-on-spring (COS) method to express polarization. The studied models were the COS/G2, COS/G3 [H. Yu and W. F. van Gunsteren, J. Chem. Phys. 121, 9549 (2004), 10.1063/1.1805516], the COS/B2 [H. Yu, T. Hansson, and W. F. van Gunsteren, J. Chem. Phys. 118, 221 (2003), 10.1063/1.1523915], the SWM4-DP [G. Lamoureux, A. D. MacKerell, Jr., and B. Roux, J. Chem. Phys. 119, 5185 (2003), 10.1063/1.1598191], the SWM4-NDP [G. Lamoureux, E. Harder, I. V. Vorobyov, B. Roux, and A. D. MacKerell, Jr., Chem. Phys. Lett. 418, 245 (2006), 10.1016/j.cplett.2005.10.135], and three versions of our model, the BKd1, BKd2, and BKd3. The BKd1 is the original Gaussian model [P. T. Kiss, M. Darvas, A. Baranyai, and P. Jedlovszky, J. Chem. Phys. 136, 114706 (2012), 10.1063/1.3692602] with constant polarization and with a simple exponential repulsion. The BKd2 applies field-dependent polarizability [A. Baranyai and P. T. Kiss, J. Chem. Phys. 135, 234110 (2011), 10.1063/1.3670962], while the BKd3 model has variable size to approximate the temperature-density (T-?) curve of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 137, 084506 (2012), 10.1063/1.4746419]. We used the thermodynamic integration (TI) and the Gibbs-Helmholtz equation to determine the equality of the free energy for liquid water and hexagonal ice (Ih) at 1 bar. We used the TIP4P and the SPC/E models as reference systems of the TI. The studied models severely underestimate the experimental melting point of ice Ih. The calculated freezing points of the models are the following: COS/G2, 215 K; COS/G3, 149 K; SWM4-DP, 186 K; BKd1, 207 K; BKd2, 213 K; BKd3, 233 K. The freezing temperature of the SWM4-NDP system is certainly below 120 K. It might even be that the water phase is more stable than the ice Ih at 1 bar in the full temperature range. The COS/B2 model melts below 100 K. The best result was obtained for the BKd3 model which indicates that correct description of the (T-?) curve improves the estimation of the freezing point. We also determined and compared the densities of high-pressure polymorphs of ice for these models.

Kiss, Péter T.; Bertsyk, Péter; Baranyai, András

2012-11-01

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

Does Ice Dissolve or Does Halite Melt? A Low-Temperature Liquidus Experiment for Petrology Classes.  

ERIC Educational Resources Information Center

Measurement of the compositions and temperatures of H2O-NaCl brines in equilibrium with ice can be used as an easy in-class experimental determination of a liquidus. This experiment emphasizes the symmetry of the behavior of brines with regard to the minerals ice and halite and helps to free students from the conceptual tethers of one-component…

Brady, John B.

1992-01-01

19

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).

Fred Senese

20

Sliding temperatures of ice skates  

Microsoft Academic Search

The two theories developed to explain the low friction of ice, pressure melting and frictional heating, require opposite temperature shifts at the ice-skate interface. The arguments against pressure melting are strong, but only theoretical. A set of direct temperature measurements shows that frictional heating is the dominant mechanism because temperature behaves in the manner predicted by the theory of frictional

S. C. Colbeck; L. Najarian; H. B. Smith

1997-01-01

21

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.

LuAnn Dahlman

22

Climatology of increased temperatures and melt at Swiss Camp, western slope of Greenland ice sheet, 1991-2012  

NASA Astrophysics Data System (ADS)

Climate observations (1991-2012) will be discussed from the Swiss Camp (69deg 33?53?N, 49deg 19?51?W, 1176 m), located at the western slope of the Greenland ice sheet, 60 km inland from Ilulissat. The mean annual temperature of -12 C increased 3.6 C between 1991 and 2012 (1.7 C per decade) with large interannual variability in all seasons. The mean spring temperature increased from -16.0 C to -13.8 C, and the fall temperature increased from -12.4 C to -11.3 C in the same time. The winter temperature showed the largest increase of 6.5 C, whereas summer temperatures increased 3.0 C during the 21 years (1991 - 2012). Radiation has been monitored continuously at Swiss Camp since 1993. Net radiation of 50 W/ m2 was recorded in 2012, the warmest summer month on record. The entire annual snow cover melted at Swiss Camp, reducing the monthly albedo value to 0.4 with bare ice exposed. Interannual variability of snow accumulation ranged between 0.07 and 0.70 m water equivalent, whereas annual snow and ice ablation varied between +0.35 (net gain) and -1.8 m (net loss) for the time period 1991-2012. The equilibrium line altitude (ELA) is no longer located at Swiss Camp (1176 m elevation) with a net surface lowering of 9.5 m since 1991. Increasing summer air temperatures have resulted in an upward migration of both the percolation facies and ablation area of the Greenland ice sheet. The 0°C isothermal migrated upward at a rate of 35 m/a over the 1995-2012 period in West Greenland. There is a 50% probability of the mean annual dry snow line migrating above Summit by 2025, at which time Summit will experience routine melt on an annual basis. The surface mass balance observations similarly indicate that the ELA has migrated upwards at a rate of 44 m/a over the 1997-2011 period in West Greenland, resulting in a more than doubling of the ablation zone width during this period. Inter-annual variability of monthly mean albedo at the Swiss Camp (1993 - 2012). Albedo at 0.5 is shown with a yellow contour line. The lowest surface albedo with 0.35 was recorded in summer 2010 and 2012.

Steffen, K.; McGrath, D.

2013-12-01

23

Ice Cream Structural Elements that Affect Melting Rate and Hardness  

Microsoft Academic Search

Statistical models were developed to reveal which structural elements of ice cream affect melting rate and hardness. Ice creams were frozen in a batch freezer with three types of sweetener, three levels of the emulsifier polysorbate 80, and two different draw temperatures to produce ice creams with a range of microstructures. Ice cream mixes were analyzed for viscosity, and finished

M. R. Muse; R. W. Hartel

2004-01-01

24

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.

25

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

26

Monte Carlo Study of Melting of a Model Bulk Ice  

Microsoft Academic Search

The methods of NVT (constant number, volume and temperature) and NPT (constant number, pressure and temperature) Monte Carlo computer simulations are used to examine the melting of a periodic hexagonal ice (ice Ih) sample with a unit cell of 192 (rigid) water molecules interacting via the revised central force potentials of Stillinger and Rahman (RSL2). In NVT Monte Carlo simulation

Kyu-Kwang Han

1989-01-01

27

Ice-Shelf Melting Around Antarctica  

NASA Astrophysics Data System (ADS)

We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines.

Rignot, E.; Jacobs, S.; Mouginot, J.; Scheuchl, B.

2013-07-01

28

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.

LuAnn Dahlman

29

Surface melting on ice shelves and icebergs  

NASA Astrophysics Data System (ADS)

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

Sergienko, Olga V.

30

Monte Carlo Study of Melting of a Model Bulk Ice.  

NASA Astrophysics Data System (ADS)

The methods of NVT (constant number, volume and temperature) and NPT (constant number, pressure and temperature) Monte Carlo computer simulations are used to examine the melting of a periodic hexagonal ice (ice Ih) sample with a unit cell of 192 (rigid) water molecules interacting via the revised central force potentials of Stillinger and Rahman (RSL2). In NVT Monte Carlo simulation of P-T plot for a constant density (0.904g/cm^3) is used to locate onset of the liquid-solid coexistence region (where the slope of the pressure changes sign) and estimate the (constant density) melting point. The slope reversal is a natural consequence of the constant density condition for substances which expand upon freezing and it is pointed out that this analysis is extremely useful for substances such as water. In this study, a sign reversal of the pressure slope is observed near 280 K, indicating that the RSL2 potentials reproduce the freezing expansion expected for water and support a bulk ice Ih system which melts <280 K. The internal energy, specific heat, and two dimensional structure factors for the constant density H_2O system are also examined at a range of temperatures between 100 and 370 K and support the P-T analysis for location of the melting point. This P-T analysis might likewise be useful for determining a (constant density) freezing point, or, with multiple simulations at appropriate densities, the triple point. For NPT Monte Carlo simulations preliminary results are presented. In this study the density, enthalpy, specific heat, and structure factor dependences on temperature are monitored during a sequential heating of the system from 100 to 370 K at a constant pressure (1 atm.). A jump in density upon melting is observed and indicates that the RSL2 potentials reproduce the melting contraction of ice. From the dependences of monitored physical properties on temperature an upper bound on the melting temperature is estimated. In this study we made the first analysis and calculation of the P-T curve for ice Ih melting at constant volume and the first NPT study of ice and of ice melting. In the NVT simulation we found for rho = 0.904g/cm^3 T_ {rm m} ~eq 280 K which is much closer to physical T_ {rm m} than any other published NVT simulation of ice. Finally it is shown that RSL2 potentials do a credible job of describing the thermodynamic properties of ice Ih near its melting point.

Han, Kyu-Kwang

31

Surface melting on Larsen Ice Shelf, Antarctica  

NASA Astrophysics Data System (ADS)

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 ice-shelf surface layer. The model is run using atmospheric data from an automatic weather station on Larsen C ice shelf (World Meteorological Organization station 'Larsen Ice Site') located south of Larsen A and B. The model's derived melting rate is greater than melting predicted by the positive degree-day (PDD) approach, common in studies of ablating ice sheets, such as Greenland. The model shows that the years of ice-shelf break-up (1995 and 2002) are distinguished from previous years by local maxima in the number of melting days. When the PDD approach is considered, however, a maximum in the number of positive degree-days appears in the 2002 break-up year, but not in 1995.

Sergienko, Olga; Macayeal, Douglas R.

32

Freezing, melting and structure of ice in a hydrophilic nanopore.  

PubMed

The nucleation, growth, structure and melting of ice in 3 nm diameter hydrophilic nanopores are studied through molecular dynamics simulations with the mW water model. The melting temperature of water in the pore was T(m)(pore) = 223 K, 51 K lower than the melting point of bulk water in the model and in excellent agreement with experimental determinations for 3 nm silica pores. Liquid and ice coexist in equilibrium at the melting point and down to temperatures as low as 180 K. Liquid water is located at the interface of the pore wall, increasing from one monolayer at the freezing temperature, T(f)(pore) = 195 K, to two monolayers a few degrees below T(m)(pore). Crystallization of ice in the pore occurs through homogeneous nucleation. At the freezing temperature, the critical nucleus contains approximately 75 to 100 molecules, with a radius of gyration similar to the radius of the pore. The critical nuclei contain features of both cubic and hexagonal ice, although stacking of hexagonal and cubic layers is not defined until the nuclei reach approximately 150 molecules. The structure of the confined ice is rich in stacking faults, in agreement with the interpretation of X-ray and neutron diffraction experiments. Though the presence of cubic layers is twice as prevalent as hexagonal ones, the crystals should not be considered defective Ic as sequences with more than three adjacent cubic (or hexagonal) layers are extremely rare in the confined ice. PMID:20379503

Moore, Emily B; de la Llave, Ezequiel; Welke, Kai; Scherlis, Damian A; Molinero, Valeria

2010-04-28

33

Floating Ice-Algal Aggregates below Melting Arctic Sea Ice  

PubMed Central

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

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

2013-01-01

34

Floating ice-algal aggregates below melting arctic sea ice.  

PubMed

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

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

2013-01-01

35

Will Melting Ice Caps Increase Global Warming?  

NSDL National Science Digital Library

In this hands-on activity, students will test one aspect of a theory that reduction in the polar caps will speed global warming. They simulate a polar region with pans of water, one painted white to represent a glacier, and one painted black or blue to represent the same area after the ice has melted. They place the covered pans in the sun with water in the bottom, and measure and compare the temperature of the water in the two pans over time. A thermometer is needed in the investigation. The investigation is supported by the textbook, Climate Change, part of Global System Science, an interdisciplinary course for high school students that emphasizes how scientists from a wide variety of fields work together to understand significant problems of global impact.

36

Indirect measurement of interfacial melting from macroscopic ice observations  

NASA Astrophysics Data System (ADS)

Premelted water that is adsorbed to particle surfaces and confined to capillary regions remains in the liquid state well below the bulk melting temperature and can supply the segregated growth of ice lenses. Using macroscopic measurements of ice-lens initiation position in step-freezing experiments, we infer how the nanometer-scale thicknesses of premelted films depend on temperature depression below bulk melting. The interfacial interactions between ice, liquid, and soda-lime glass particles exhibit a power-law behavior that suggests premelting in our system is dominated by short-range electrostatic forces. Using our inferred film thicknesses as inputs to a simple force-balance model with no adjustable parameters, we obtain good quantitative agreement between numerical predictions and observed ice-lens thickness. Macroscopic observations of lensing behavior have the potential as probes of premelting behavior in other systems.

Saruya, Tomotaka; Kurita, Kei; Rempel, Alan W.

2014-06-01

37

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

38

Greenland ice sheet melt from MODIS and associated atmospheric variability  

PubMed Central

Daily June-July melt fraction variations over the Greenland ice sheet (GIS) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) (2000–2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500 hPa height. Blocking activity with a range of time scales, from synoptic waves breaking poleward (<5 days) to full-fledged blocks (?5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the years with the greatest melt (2002 and 2012) during the MODIS era, the area-average temperature anomaly of 2 standard deviations above the 14 year June-July mean results in a melt fraction of 40% or more. Though the summer of 2007 had the most blocking days, atmospheric temperature anomalies were too small to instigate extreme melting. Key Points Short-term atmospheric blocking over Greenland contributes to melt episodes Associated temperature anomalies are equally important for the melt Duration and strength of blocking events contribute to surface melt intensity

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

2014-01-01

39

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.

40

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

41

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

42

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.

Elizabeth Vernon Bell

2012-11-14

43

Ocean variability contributing to basal melt rate near the ice front of Ross Ice Shelf, Antarctica  

NASA Astrophysics Data System (ADS)

Basal melting of ice shelves is an important, but poorly understood, cause of Antarctic ice sheet mass loss and freshwater production. We use data from two moorings deployed through Ross Ice Shelf, ˜6 and ˜16 km south of the ice front east of Ross Island, and numerical models to show how the basal melting rate near the ice front depends on sub-ice-shelf ocean variability. The moorings measured water velocity, conductivity, and temperature for ˜2 months starting in late November 2010. About half of the current velocity variance was due to tides, predominantly diurnal components, with the remainder due to subtidal oscillations with periods of a few days. Subtidal variability was dominated by barotropic currents that were large until mid-December and significantly reduced afterward. Subtidal currents were correlated between moorings but uncorrelated with local winds, suggesting the presence of waves or eddies that may be associated with the abrupt change in water column thickness and strong hydrographic gradients at the ice front. Estimated melt rate was ˜1.2 ± 0.5 m a-1 at each site during the deployment period, consistent with measured trends in ice surface elevation from GPS time series. The models predicted similar annual-averaged melt rates with a strong annual cycle related to seasonal provision of warm water to the ice base. These results show that accurately modeling the high spatial and temporal ocean variability close to the ice-shelf front is critical to predicting time-dependent and mean values of meltwater production and ice-shelf thinning.

Arzeno, Isabella B.; Beardsley, Robert C.; Limeburner, Richard; Owens, Breck; Padman, Laurie; Springer, Scott R.; Stewart, Craig L.; Williams, Michael J. M.

2014-07-01

44

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

45

Projections of ice shelf basal melting in a global finite element sea ice - ice shelf - ocean model  

NASA Astrophysics Data System (ADS)

In the framework of the EU project Ice2sea we utilize a global finite element sea ice - ice shelf - ocean model (FESOM), focused on the Antarctic marginal seas, to quantify heat and freshwater fluxes in the Antarctic ice shelf cavities and to assess 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 minimum horizontal resolution of 4 minutes and hybrid vertical coordinates is used. Ice shelf draft, cavity geometry, and global ocean bathymetry have been derived from the RTopo-1 data set. Additional simulations were carried out with the circumpolar coarse-scale finite-difference model developed as part of the Bremerhaven Regional Ice Ocean Simulations (BRIOS). Simulations for present-day climate were forced with the NCEP reanalysis product and the atmospheric output from 20th century simulations of the Hadley Centre Climate Model (HadCM3). The projections for the period 2000-2199 use the output of HadCM3 simulations for the IPCC scenarios A1B and E1. Results from both models indicate a strong sensitivity of basal melting to increased ocean temperatures for the ice shelves in Amundsen Sea. An even stronger impact is found for warm water starting to pulse onto the southern Weddell Sea continental shelf in the middle of the 21st century, originating from a redirected coastal current. As these pulses propagate far into the Filchner-Ronne Ice Shelf (FRIS) cavity, basal melting increases significantly compared to the present value of about 100 Gt/yr. At the end of the 21st / beginning of the 22nd century both models suggest a stabilization of FRIS basal mass loss on a high level.

Timmermann, R.; Hellmer, H. H.

2012-04-01

46

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

47

The refreezing of melt ponds on Arctic sea ice  

NASA Astrophysics Data System (ADS)

The presence of melt ponds on the surface of Arctic sea ice significantly reduces its albedo, inducing a positive feedback leading to sea ice thinning. While the role of melt ponds in enhancing the summer melt of sea ice is well known, their impact on suppressing winter freezing of sea ice has, hitherto, received less attention. Melt ponds freeze by forming an ice lid at the upper surface, which insulates them from the atmosphere and traps pond water between the underlying sea ice and the ice lid. The pond water is a store of latent heat, which is released during refreezing. Until a pond freezes completely, there can be minimal ice growth at the base of the underlying sea ice. In this work, we present a model of the refreezing of a melt pond that includes the heat and salt balances in the ice lid, trapped pond, and underlying sea ice. The model uses a two-stream radiation model to account for radiative scattering at phase boundaries. Simulations and related sensitivity studies suggest that trapped pond water may survive for over a month. We focus on the role that pond salinity has on delaying the refreezing process and retarding basal sea ice growth. We estimate that for a typical sea ice pond coverage in autumn, excluding the impact of trapped ponds in models overestimates ice growth by up to 265 million km3, an overestimate of 26%.

Flocco, Daniela; Feltham, Daniel L.; Bailey, Eleanor; Schroeder, David

2015-02-01

48

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

PubMed Central

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

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

2014-01-01

49

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

50

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

51

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

52

Estimation of surface melt and absorbed radiation on the Greenland ice sheet using passive microwave data  

NASA Astrophysics Data System (ADS)

Passive microwave data from the Defense Meteorological Satellite Program (DMPS) Special Sensor Microwave/Imager (SSM/I) and Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) were used to estimate the extent of melt, melt duration and length of melt season on the Greenland ice sheet for the years 1979--1997. Three techniques---a maximum likelihood classification (MLC), a spectral technique and an edge detection method---were implemented. The MLC and spectral techniques provided estimates of the melt extent, while estimates of the melt extent, the length of the melt season and the duration of melt were obtained from the edge method. Comparisons of the surface melt results with global and coastal (Greenland) temperature data indicated that melt extents were better related to global than coastal temperatures. The reverse was noted for melt season and duration trends. The results suggest an overall increase in warmer spells in summer for the period 1979--1997, as indicated by increasing maximum melt extent on the ice sheet. However, there was no corresponding increase in the overall total melt season and total duration of melt. The annual melt extent and the total melt season/duration showed a sharp drop in 1992, due to the eruption of Mt. Pinatubo in June, 1991. The results indicated that melt extents alone cannot be used to estimate warming or cooling on the ice sheet and that melt duration and season trends should also be examined. These surface melt results were then extended to obtain the absorbed radiation flux on the Greenland ice sheet. The monthly albedo on the ice sheet was estimated by assigning an albedo value that was a function of the length of the melt season. The monthly albedo was used with a solar radiation model to estimate the monthly and annual absorbed shortwave flux on the ice sheet. The computation of absorbed radiation on the Greenland ice sheet gave results consistent with those derived from the Earth Radiation Budget Experiment (ERBE). The estimation of absorbed shortwave radiation using satellite passive microwave data demonstrates a new method for determining absorbed shortwave flux on the Greenland ice sheet.

Joshi, Maneesha D.

1999-09-01

53

High density amorphous ice at room temperature  

PubMed Central

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

Chen, Jing-Yin; Yoo, Choong-Shik

2011-01-01

54

Interactions between snow and melt ponds in sea ice models  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

55

Strong surface melting preceded collapse of Antarctic Peninsula ice shelf  

Microsoft Academic Search

During the austral summer of 2001\\/02, melting at the surface of Larsen Ice Shelf in the Antarctic Peninsula was three times greater than the average of five previous summers. This exceptional melt event lasted for three months and was followed by the collapse of Larsen B Ice Shelf, during which 3,200 km2 of ice shelf surface was lost. The strong

Michiel van den Broeke

2005-01-01

56

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

57

Pressure Melting of Ice: While-U-Wait  

NSDL National Science Digital Library

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

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

58

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

E-print Network

of recent climate change and have focused attention on causal factors that promote ice shelf retreat. Ice shelves. While the Larsen B ice shelf was preweakened by at least a decade of thinning largely resulting, 2003). The Wilkins ice shelf, which currently undergoes extensive summer melting, also experienced

Meissner, Katrin Juliane

59

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

PubMed

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

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

2014-01-10

60

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

61

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

62

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

63

Applying Archimedes' Law to Ice Melting in Sea Water  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

64

Rapid bottom melting widespread near Antarctic ice sheet grounding lines  

NASA Technical Reports Server (NTRS)

As continental ice from Antartica 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.

Rignot, E.; Jacobs, S.

2002-01-01

65

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

PubMed

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

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

2014-06-01

66

On the phase diagram of water with density functional theory potentials: the melting temperature of Ice I-h with the Perdew-Burke-Ernzerhof and Becke-Lee-Yang-Parr functionals  

SciTech Connect

The melting temperature (Tm) of ice Ih was determined from constant enthalphy (NPH) Born-Oppenheimer Molecular Dynamics (BOMD) simulations to be 417±3 K for the Perdew-Burke-Ernzerhof (PBE) and 411±4 K for the Becke-Lee-Yang-Parr (BLYP) density functionals using a coexisting ice (Ih)-liquid phase at constant pressures of P = 2,500 and 10,000 bar and a density ? = 1 g/cm3, respectively. This suggests that ambient condition simulations at ? = 1 g/cm3 will rather describe a supercooled state that is overstructured when compared to liquid water. This work was supported by the US Department of Energy Office of Basic Energy Sciences' Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Yoo, Soohaeng; Zeng, Xiao Cheng; Xantheas, Sotiris S.

2009-06-11

67

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

68

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

69

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

70

2 Internal melting in Antarctic sea ice: Development of ``gap layers'' 3 S. F. Ackley,1  

E-print Network

of the snow cover, followed by melt pond formation on 50 top of the ice is the dominant surface characteristic of Arctic 51summer sea ice [Perovich et al., 2002]. Melt ponds are not 52often observed on Antarctic sea ice accelerate melting by 63increasing the absorption of solar radiation within the sea 64ice. Algal blooms

Texas at San Antonio, University of

71

Large melt channels discovered underneath Antarctic ice shelves  

NASA Astrophysics Data System (ADS)

New radar observations reveal melt channels 500 meters to 3 kilometers wide and up to 200 meters deep underneath the ice shelf buttressing the Pine Island Glacier in West Antarctica; researchers suggest that these subglacial channels could be a “prelude to eventual collapse” of the ice shelves, which cover about 10% of the areal extent of the West Antarctic Ice Sheet (WAIS). A complete collapse of WAIS could increase global sea level by at least 3-4 meters. Taking advantage of a dense network of radar lines designed to penetrate ice thicknesses of more than 2 kilometers, Vaughan et al. combine indirect satellite observations with direct echo-sounding measurements from submersibles to show what scientists have suspected: Thinning ice shelves lead to crevassing of the ice shelves. Echo sounding reveals 50-to 100-meter-wide crevasses aligned with the subglacial channels; the basal crevasses penetrate up to one third of the ice thickness in the shelves buttressing the Pine Island Glacier, even leaving their mark on the surface of the glacier. Melting at the base of floating ice shelves creates subglacial channels. Using stress models, the authors show that when the subglacial channels form sufficiently rapidly, they create crevasses, which the authors found on the surface and at the base of the ice shelf bordering the Pine Island Glacier.

Bhattacharya, Atreyee

2012-10-01

72

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

NASA Astrophysics Data System (ADS)

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

Karmosky, Christopher

73

Response of the Antarctic Ice Sheet to increased ice-shelf oceanic melting  

NASA Astrophysics Data System (ADS)

A numerical ice sheet-shelf model is used to simulate the large-scale response of the Antarctic Ice Sheet to prescribed future increases in oceanic melting at the base of floating ice shelves. The model is driven forward in time starting from modern conditions, with step-function perturbations in parameterized sub-ice oceanic melt rates that crudely represent possible ranges due to future anthropogenic warming. It is found that with melt rates under the interiors of large shelves increased to ~2 m/y or more (from modern 0.1 m/y), drastic grounding line retreat in the Ross, Filchner-Ronne and Pine Island/Thwaites embayments leads to collapse of nearly all marine West Antarctic ice. The time scale of collapse depends on the magnitude of oceanic melt: ~1500 years for 2 m/y, and ~300 years for "infinite" melt (no floating ice). The WAIS collapse causes ~3 m of global sea-level rise. Further results are presented which include surface mass-balance changes, time-dependent future forcing, and spatial differences in ocean melting between embayments.

Pollard, David; Deconto, Robert

2010-05-01

74

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

Microsoft Academic Search

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

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

2008-01-01

75

Modelling of Superimposed Ice Formation and SubSurface Melting in the Baltic Sea  

Microsoft Academic Search

Superimposed ice formation and sub-surface melting were modelled using a one-dimensional thermodynamic sea ice model with the Baltic Air-Sea-Ice Study (BASIS) field data. During a thermal equilibrium stage in winter 1997\\/98, ice showed little mass change at the ice-water interface. The observations indicated snow-to-ice transformation at the snow-ice interface. Numerical modelling suggested that the re-freezing of the surface melt water

Bin Cheng; Jouko Launianen; Timo Vihma

76

Greenland ice sheet melt area, volume, and runoff from satellite and in situ observations  

NASA Astrophysics Data System (ADS)

Remote sensing provides surface melt area and regional mass change. In situ automatic weather station (AWS) data provide a relatively precise, but very local surface mass budget. Combining the two methods allows melt quantification for the entire Greenland ice sheet. We use interpolated near-surface air temperature from the GC-Net and PROMICE AWS networks, and remotely-sensed MODIS surface albedo to calculate melt with a temperature/albedo-index melt model. The calculations make use of albedo, combined with top-of-the-atmosphere solar radiation and cloud cover, to take into account absorbed shortwave radiation, the dominant melt parameter. In so doing the darkening due to the melt-albedo feedback is accounted. Calculated ablation is calibrated using AWS data. Assuming that surface albedo is a first-order indicator of the firn's available pore space and cold content, refreezing is parameterized as a function of it. Meltwater runoff for selected catchments is validated with river discharge data. The product: observation-based daily maps of near-surface air temperature, melt (extent and volume), and runoff for the Greenland ice sheet.

van As, D.; Box, J. E.; Fausto, R. S.; Petersen, D.; Citterio, M.; Ahlstrom, A. P.; Andersen, S. B.; Steffen, K.

2013-12-01

77

Experiments on melting of a vertical ice layer immersed in immiscible liquid  

NASA Astrophysics Data System (ADS)

Experiments on the melting of a vertical ice layer immersed in immiscible liquid yielded quantitative results both for the timewise evolution of the melting front and the heat transfer. Vegetable oil, which was contained in a rectangular vessel, was adopted as a testing liquid. A bubble-free ice block stuck on a cooled wall was installed vertically in the vessel. The experiments were carried out for the immiscible liquid temperatures from 7.6 to 30.0 °C, while for the cooled wall temperatures from 0 to -11.5 °C. The flow structure of the liquid and the melting front were extensively observed and recorded photographically. It was found that the heat transfer and the rate of melting are significantly affected by a couple of fluid motions of both the water melt induced by melting of ice and the immiscible liquid based on free convection. Zusammenfassung Experimente bezüglich einer in eine nichtmischbare Flü ssigkeit eintauchend vertikal Eisschicht lieferten quantitative Ergebnisse für die zeitliche Entwicklung der Schmelzfront und des Wärmeübergangs. Als Testfluid wurde Pflanzenöl in einem rechteckigen Behälter verwendet. Ein blasenfreier Eisblock wurde senkrecht an der gekühlten Wand des Behälters befestigt. Die Temperaturen der nichtmischbaren Flüssigkeit variierten von 7,6 bis 30 °C, die der Kühlwand von 0 bis -11,5 °C. Flüssigkeitsstruktur und Schmelzfront konnten beobachtet und photographisch aufgezeichnet werden. Wärmeübergang und Schmelzrate zeigten deutlich den Einfluß von Fluidbewegungen, die im Wasser durch den Schmelzvorgang, in der nichtmischbaren Flüssigkeit durch freie Konvektion induziert wurden.

Yamada, M.; Fukusako, S.; Sayed, M. Eman-Bellah

78

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

79

Did Davy melt Ice by Friction in a Vacuum?  

Microsoft Academic Search

QUITE firmly entrenched in scientific literature, including some very recent English histories of science, is the statement that Sir Humphry Davy contrived a clockwork by which two pieces of ice were rubbed together and made to melt under the exhausted receiver of an air-pump. This is incorrect. A reference to Davy's works (Davy, ``Collected Works'', vol. 2, 1839, p. 11,

Florian Cajori

1926-01-01

80

Absence of superheating for ice Ih with a free surface : a new method of determining the melting point of different water models  

E-print Network

Molecular dynamic simulations were performed for ice Ih with a free surface. The simulations were carried out at several temperatures and each run lasted more than 7ns. At high temperatures the ice melts. It is demonstrated that the melting process starts at the surface and propagates to the bulk of the ice block. Already at the temperatures below the melting point, we observe a thin liquid layer at the ice surface, but the block of ice remains stable along the run. As soon as the temperature reaches the melting point the entire ice block melts. Our results demonstrate that, unlike in the case of conventional simulations in the NpT ensemble, overheating of the ice Ih with a free surface does not occur. That allows to estimate the melting point of ice at zero pressure. We applied the method to the following models of water: SPC/E, TIP4P, TIP4P/Ew, TIP4P/Ice and TIP4P/2005, and found good agreement between the melting temperatures obtained by this procedure and the values obtained either from free energy calculations or from direct simulations of the ice/water interface.

Carlos Vega; Maria Martin-Conde; Andrzej Patrykiejew

2013-04-18

81

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

PubMed

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

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

2012-04-26

82

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

E-print Network

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

Zhang, Jinlun

83

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

84

A continuum model of melt pond evolution on Arctic sea ice Daniela Flocco1  

E-print Network

A continuum model of melt pond evolution on Arctic sea ice Daniela Flocco1 and Daniel L. Feltham1 the Northern Hemisphere summer, absorbed solar radiation melts snow and the upper surface of Arctic sea ice to generate meltwater that accumulates in ponds. The melt ponds reduce the albedo of the sea ice cover during

Feltham, Daniel

85

A model of melt pond evolution on sea ice P. D. Taylor and D. L. Feltham  

E-print Network

short-wave radiation. The difference in solar energy ab- sorption between pond-covered and bare sea iceA model of melt pond evolution on sea ice P. D. Taylor and D. L. Feltham Centre for Polar-dimensional, thermodynamic, and radiative model of a melt pond on sea ice is presented that explicitly treats the melt pond

Feltham, Daniel

86

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

87

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

NASA Technical Reports Server (NTRS)

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

Abdalati, Waleed; Steffen, Konrad

2000-01-01

88

Enhanced Sea Ice Concentration and Ice Temperature Algorithms for AMSR  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

89

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

90

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

91

Continental heat anomalies and the extreme melting of the Greenland ice surface in 2012 and 1889  

NASA Astrophysics Data System (ADS)

Recent decades have seen increased melting of the Greenland ice sheet. On 11 July 2012, nearly the entire surface of the ice sheet melted; such rare events last occurred in 1889 and, prior to that, during the Medieval Climate Anomaly. Studies of the 2012 event associated the presence of a thin, warm elevated liquid cloud layer with surface temperatures rising above the melting point at Summit Station, some 3212 m above sea level. Here we explore other potential factors in July 2012 associated with this unusual melting. These include (1) warm air originating from a record North American heat wave, (2) transitions in the Arctic Oscillation, (3) transport of water vapor via an Atmospheric River over the Atlantic to Greenland, and (4) the presence of warm ocean waters south of Greenland. For the 1889 episode, the Twentieth Century Reanalysis and historical records showed similar factors at work. However, markers of biomass burning were evident in ice cores from 1889 which may reflect another possible factor in these rare events. We suggest that extreme Greenland summer melt episodes, such as those recorded recently and in the late Holocene, could have involved a similar combination of slow climate processes, including prolonged North American droughts/heat waves and North Atlantic warm oceanic temperature anomalies, together with fast processes, such as excursions of the Arctic Oscillation, and transport of warm, humid air in Atmospheric Rivers to Greenland. It is the fast processes that underlie the rarity of such events and influence their predictability.

Neff, William; Compo, Gilbert P.; Martin Ralph, F.; Shupe, Matthew D.

2014-06-01

92

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

93

Supplement A: In Fig.1 we show a schematic picture that described the effects of solutes upon ice melting  

E-print Network

the colligative melting point depression line. In water activity space, this line is identical for any solute reduces the ice melting point temperature by the melting point depression Tm. Similarly, solutes do also. From these caluclations we obtain aw values of 0.99378 and 0.99160 for the pH 5.9 and pH 4.1/NaCl

Meskhidze, Nicholas

94

Sea ice melting increase in the eastern Barents Sea during the last ca. 500 years  

NASA Astrophysics Data System (ADS)

Climate conditions in the Arctic have changed considerably in the last decades. Sea ice cover is declining, temperatures are rising and the latest projections point to an ice free Arctic ocean at around 2040. To understand better climatic processes on such a sensitive and climatically significant region on the globe it is necessary to gain knowledge on the drivers of climate over time. Here we show a reconstruction of past sea ice and sea surface temperature (SST) variations in the eastern Barents Sea from sediment core PL96-126 (73° 37.5' N, 50° 43.0' E; 270m water depth) that spans the last ca. 4.400 years (Voronina et al. 2001). To achieve this goal, we used a recently developed biomarker based on highly branched isoprenoid lipid (IP25) synthesized by sea ice diatoms (Belt et al. 2007) to infer variations in past sea ice cover, together with the concentration of alkenones - algae synthesized lipids - from which we also estimated past SST (UK37' index) and fresh water mass variation (%C37:4). At lower resolution, we also analyzed the distributions of terrigenous lipids to obtain information on the origin of the organic matter, and finally the glycerol dialkyl glycerol tetraethers (GDGTs) which give an estimate of past sea surface temperature (TEX86) and air temperature (MBT/CBT indices). Three climatically distinct periods can be distinguished in the sediment record under study. A period from ca. 4.4 to 2.5 Kyr BP, had a generally stable sea ice cover and relatively short ice melting season, as inferred from the low IP25 and algal lipids concentrations, together with cold and freshened surface water. From ca. 2.5 to 1 Kyr BP there was a transition period with rather unstable conditions characterized by fluctuations in the biomarker indices. From ca. 1 Kyr BP until present, our data indicate a gradual increase in ice melting that accelerated during the last ca. 0.5 Kyr BP. This is in agreement with a previous reconstruction (Vare et al. 2010) suggesting a reduced sea ice cover for the last centuries. In contrast, a reconstruction for the last 7 Kyr BP from the central Canadian Arctic Archipelago (Belt et al. 2010) interpreted an increase in IP25 flux for the last 0.8 Kyr as higher sea ice occurrence. Here we interpret our IP25 data as suggested by Müller et al. (2011). The recent increase in IP25 represents an acceleration in ice melting during the last 500 years in the Barents Sea.

Rueda, G.; Rosell-Melé, A.; Massé, G.; Polyak, L.

2012-04-01

95

Aluminosilicate melts: structure, composition and temperature  

NASA Astrophysics Data System (ADS)

The anionic structure of aluminosilicate melts of intermediate degree of polymerization (NBO/T = 0.5) and with along the composition join (LS4-LA4) has been examined in-situ to 1480°C, and compared with recent data for melts along the analog composition join and with less polymerized melts along the join and O_5. With , the anionic equilibrium, (1) , adequately describes the structure. With , a second expression, (2) , is required because an additional structural unit, Q1, is stabilized in the melts. The enthalpy, , of reaction (1) increases from - 36 +/-4 kJ/mol in the absence of aluminum to 34+/- 5 kJ/mol at and 64 +/- 4 kJ/mol at Al/(Al + Si) = 0.45. Similar trends are reported for other alkali aluminosilicate melts. Least-squares fitting of abundance of structural units as a function of temperature and bulk composition has been conducted. The unit abundance is dominantly a function of temperature, Al/(Al +Si), and bulk melt polymerization. Configurational entropy and heat capacity of mixing of melts above their glass transition temperatures have been calculated with the aid of the least-squares fitted equations. The values of these parameters indicate that as the ionization potential of the metal cations increases, configurational heat capacity of alkali aluminosilicate melts becomes temperature dependent. As a result, transport properties (viscosity, diffusivity, and conductivity) of such melts will not show Arrhenian behavior even in the high-temperature range. Further, discontinuous changes in entropy and heat capacity of mixing results from temperature-induced changes in types of structural units in the melts. Such discontinuous changes would also be reflected in discontinuous changes of temperature-dependent transport properties.

Mysen, B.

96

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

2013-10-01

97

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

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

98

Isotope thermometry in melt-affected ice cores  

NASA Astrophysics Data System (ADS)

A statistically significant relationship is observed between stable water isotopes (?18O) and melt amounts in a melt-affected firn core (SSummit) taken from the Prince of Wales Icefield, Ellesmere Island, Canada. By contrast, a low-melt firn core taken from a higher-elevation, higher-latitude location on the same icefield shows no relationship between these variables. We interpret this as evidence for meltwater-induced isotopic enrichment at SSummit. A percent melt-based correction slope is applied to isotopic values from SSummit. Uncorrected and corrected temperature records derived from the raw and corrected ?18O values are compared to bias-corrected temperature data from the NCEP Reanalysis. Improvements are observed in the isotopic reconstruction of SSummit annual precipitation-weighted temperatures when we correct for meltwater enrichment, with a reduction from +0.6°C to 0.0°C in the mean annual error and a decrease in root-mean-square error from 1.8°C to 1.6°C. The correction factor appears to overcorrect isotopic modification during high melt years such as 1999, during which SSummit experienced nearly 70% more melt than the average from 1975 to 2000. Excluding 1999 data from the correction analysis results in a slight reduction in mean absolute error from 1.4°C to 1.3°C. These results suggest that melt-induced isotopic modification cannot be corrected in very high melt years.

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

2011-06-01

99

Bacterial Communities of Surface Mixed Layer in the Pacific Sector of the Western Arctic Ocean during Sea-Ice Melting  

PubMed Central

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

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

2014-01-01

100

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

PubMed

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

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

2014-01-01

101

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

NSDL National Science Digital Library

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

102

Melt Detection in Antarctic Ice-Sheets Using Spaceborne Scatterometers and Radiometers  

E-print Network

Recently, longer melt season duration and surface melt ponds on Antarctic ice-shelves have been linked duration and in observing surface melt pond formation. These measurements are sen- sitive to changing ice regions regardless of cloud cover or solar illumination. The SSM/I radiometers record Tb measurements

Long, David G.

103

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

2012-04-18

104

Influence of NaCl on ice VI and ice VII melting curves up to 6 GPa, implications for large icy moons  

NASA Astrophysics Data System (ADS)

The influence of sodium chloride salt on the liquidus of ice VI and ice VII has been measured for concentrations ranging between 0.01 and 4 mol kg-1 NaCl. Dissolved NaCl significantly increases the melting pressure or decreases the melting temperature as a function of the salt concentration and induces a density crossover between ice VI and the brine. For NaCl concentrations higher than 2.5 mol kg-1 ice VI is more buoyant than the brine. The liquidus points are fitted to a second order polynomial law and a model is provided to predict the melting pressures of ice VI and ice VII (Pm,VI and Pm,VII), respectively as a function of temperature T (K) and NaCl concentration XNaCl (mol kg-1): Pm,VI(T,XNaCl)=9.27+0.996XNaCl-(6.99×10-2+7.6×10-3XNaCl)·T+(1.414×10-4+1.541×10-5XNaCl)·T2 Pm,VII(T,XNaCl)=-0.133+0.122XNaCl-(1.28×10-4+4.17×10-4XNaCl)·T+(1.86×10-5+8.56×10-7XNaCl)·T2 The temperature of the triple point between ice VI, ice VII and the brine shifts of -7 K/XNaCl along the 2.17 GPa isobar. The consequences of potentially dissolved NaCl for the internal structure of water rich planetary bodies are discussed. The density crossover between ice VI and brines suggests that migration of brines through a deep ice VI layer is enhanced for high thermal profiles and is unlikely for colder thermal conditions. It also suggests that patches of brines may actually be gravitationally stable at the interface between the bedrock and a deep ice VI basal layer allowing for a potential new class of exobiological habitat.

Journaux, B.; Daniel, I.; Caracas, R.; Montagnac, G.; Cardon, H.

2013-09-01

105

Ross ice shelf cavity circulation, residence time, and melting: Results from a model of oceanic chlorofluorocarbons  

NASA Astrophysics Data System (ADS)

Despite their harmful effects in the upper atmosphere, anthropogenic chlorofluorocarbons dissolved in seawater are extremely useful for studying ocean circulation and ventilation, particularly in remote locations. Because they behave as a passive tracer in seawater, and their atmospheric concentrations are well-mixed, well-known, and have changed over time, they are ideal for gaining insight into the oceanographic characteristics of the isolated cavities found under Antarctic ice shelves, where direct observations are difficult to obtain. Here we present results from a modeling study of air-sea chlorofluorocarbon exchange and ocean circulation in the Ross Sea, Antarctica. We compare our model estimates of oceanic CFC-12 concentrations along an ice shelf edge transect to field data collected during three cruises spanning 16 yr. Our model produces chlorofluorocarbon concentrations that are quite similar to those measured in the field, both in magnitude and distribution, showing high values near the surface, decreasing with depth, and increasing over time. After validating modeled circulation and air-sea gas exchange through comparison of modeled temperature, salinity, and chlorofluorocarbons with field data, we estimate that the residence time of water in the Ross Ice Shelf cavity is approximately 2.2 yr and that basal melt rates for the ice shelf average 10 cm yr -1. The model predicts a seasonal signature to basal melting, with highest melt rates in the spring and also the fall.

Reddy, Tasha E.; Holland, David M.; Arrigo, Kevin R.

2010-04-01

106

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

NASA Astrophysics Data System (ADS)

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 net mass balance and show a large increase in melt since the middle 1990s. Arctic ice core melt series (latitude range of 67 to 81 N) show the last quarter century has had the highest melt in two millennia and The Holocene-long Agassiz melt record shows that the last 25 years has the highest melt in 4200 years. The Agassiz melt rates since the middle 1990s resemble those of the early Holocene thermal maximum over 9000 years ago.

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

2012-03-01

107

Reconstruction of Past Temperatures of Glaciers Subjected to Subsurface Melting  

Microsoft Academic Search

Many glaciers are subjected to melting due to high summer air temperatures. Melt water percolates into the snow-firn sequences. Melting intensity during summer months is proportional to the third power of the mean air temperature. Hence, small changes of summer air temperatures induce large changes of the active layer temperatures. The refreezing of melt water results in the sub-surface heat

O. V. Nagornov; Y. Konovalov; O. Sergienko

2002-01-01

108

On thin ice: surface order and disorder during pre-melting.  

PubMed

The effect of temperature on the structure of the ice Ih (0001) surface is considered through a series of molecular dynamics simulations on an ice slab. At relatively low temperatures (200 K) a small fraction of surface self-interstitials (i.e. admolecules) appear that are formed exclusively from molecules leaving the outermost bilayer. At higher temperatures (ca. 250 K), vacancies start to appear in the inner part of the outermost bilayer exposing the underlying bilayer and providing sites with a high concentration of dangling hydrogen bonds. Around 250-260 K aggregates of molecules formed on top of the outermost bilayer from self-interstitials become more mobile and have diffusivities approaching that of liquid water. At approximately 270-280 K the inner bilayer of one surface noticeably destructures and it appears that at above 285 K both surfaces are melting. The observed disparity in the onset of melting between the two sides of the slab is rationalised by considering the relationship between surface energy and the spatial distribution of protons at the surface; thermodynamic stability is conferred on the surface by maximising separations between dangling protons at the crystal exterior. Local hotspots associated with a high dangling proton density are suggested to be susceptible to pre-melting and may be more efficient at trapping species at the external surface than regions with low concentrations of protons thus potentially helping ice particles to catalyse reactions. A preliminary conclusion of this work is that only about 10-20 K below the melting temperature of the particular water potential employed is major disruption of the crystalline lattice noted which could be interpreted as being "liquid", the thickness of this film being about a nanometre. PMID:19227362

Bishop, C L; Pan, D; Liu, L M; Tribello, G A; Michaelides, A; Wang, E G; Slater, B

2009-01-01

109

Southern Ocean warming and increased ice shelf basal melting in the 21st and 22nd centuries based on coupled ice-ocean finite-element modelling  

NASA Astrophysics Data System (ADS)

In the framework of the EU project Ice2sea we utilize a global finite element sea ice - ice shelf - ocean model (FESOM), focused on the Antarctic marginal seas, to assess 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 minimum horizontal resolution of 4 minutes 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. Data from their 20th-century simulations are used to evaluate the modeled present-day ocean state. Sea-ice coverage is largely realistic in both simulations. Modeled 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 IPCC scenarios E1 and A1B. Trends in sea ice coverage depend on the scenario chosen but are largely consistent between the two forcing models. In contrast to this, variations of ocean heat content and ice shelf basal melting are only moderate in simulations forced with ECHAM5/MPI-OM data, while a substantial shift towards a warmer regime is found in experiments forced with HadCM3 output. A strong sensitivity to salinity distribution at the continental shelf break is found for the Weddell Sea, where in the HadCM3-A1B experiment warm water starts to pulse onto the southern continental shelf during the 21st century. As these pulses reach deep into the Filchner-Ronne Ice Shelf (FRIS) cavity, basal melting increases by a factor of three to six compared to the present value of about 100 Gt/yr. By the middle of the 22nd century, FRIS becomes the largest contributor to total ice shelf basal mass loss in this simulation.

Timmermann, Ralph; Hellmer, Hartmut

2013-04-01

110

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

111

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

112

Attribution of Recent Arctic Sea Ice Melting to Human Influence  

NASA Astrophysics Data System (ADS)

During recent three decades Arctic sea ice extent (SIE) has been decreasing with its rate accelerating. There have been, however, limited studies which have identified human influence on the Arctic sea ice using a formal detection approach. This study conducts an updated detection analysis of recent Arctic SIE during 1979-2012 by comparing observed changes with those from CMIP5 (Coupled Model Intercomparison Project Phase 5) multi-model simulations. We use the NSIDC (National Snow and Ice Data Center) sea ice index as observations. The simulated Arctic SIEs are calculated from available ensembles of CMIP5 multi-models which have been performed under natural plus anthropogenic forcing (ALL: historical combined with RCP4.5, 112 runs from 40 models), natural forcing only (NAT: historicalNat, 48 runs from 10 models) and greenhouse gas forcing only (GHG: historicalGHG, 35 runs from 9 models). Anthropogenic forcing (ANT) responses are estimated from differences between ALL and NAT. We apply an optimal fingerprinting method where observations are regressed onto model-simulated signals (multi-model means of ALL, NAT, and GHG). Here the internal variability noise is estimated from historical simulations after removing multi-model averages. The observations display decreasing trends across all months with stronger amplitude in summer than other seasons, which is reasonably reproduced by CMIP5 simulations. Results from one-signal analyses show that the ALL, ANT, and GHG signals are all detected when considering four months (Mar, Jun, Sep, and Dec) together and also from September to January when looking at individual months. Results from two-signal analyses show that ANT is separable from NAT and also that GHG is separable from other non-GHG forcings. Scaling factors of the detected ANT and GHG signals include unity, indicating that observed Arctic sea ice melting during the satellite period is largely attributable to human-induced increases in GHGs.

Heo, Joonghyeok; Min, Seung-Ki

2014-05-01

113

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

114

Evaluation of Surface and Near-Surface Melt Characteristics on the Greenland Ice Sheet using MODIS and QuikSCAT Data  

NASA Technical Reports Server (NTRS)

The Greenland Ice Sheet has been the focus of much attention recently because of increasing melt in response to regional climate warming. To improve our ability to measure surface melt, we use remote-sensing data products to study surface and near-surface melt characteristics of the Greenland Ice Sheet for the 2007 melt season when record melt extent and runoff occurred. Moderate Resolution Imaging Spectroradiometer (MODIS) daily land-surface temperature (LST), MODIS daily snow albedo, and a special diurnal melt product derived from QuikSCAT (QS) scatterometer data, are all effective in measuring the evolution of melt on the ice sheet. These daily products, produced from different parts of the electromagnetic spectrum, are sensitive to different geophysical features, though QS- and MODIS-derived melt generally show excellent correspondence when surface melt is present on the ice sheet. Values derived from the daily MODIS snow albedo product drop in response to melt, and change with apparent grain-size changes. For the 2007 melt season, the QS and MODIS LST products detect 862,769 square kilometers and 766,184 square kilometers of melt, respectively. The QS product detects about 11% greater melt extent than is detected by the MODIS LST product probably because QS is more sensitive to surface melt, and can detect subsurface melt. The consistency of the response of the different products demonstrates unequivocally that physically-meaningful melt/freeze boundaries can be detected. We have demonstrated that these products, used together, can improve the precision in mapping surface and near-surface melt extent on the Greenland Ice Sheet.

Hall, Dorothy K.; Nghiem, Son V.; Schaaf, Crystal B.; DiGirolamo, Nicolo E.

2009-01-01

115

Strong Isotope Effects on Melting Dynamics and Ice Crystallisation Processes in Cryo Vitrification Solutions  

PubMed Central

The nucleation and growth of crystalline ice during cooling, and further crystallization processes during re-warming are considered to be key processes determining the success of low temperature storage of biological objects, as used in medical, agricultural and nature conservation applications. To avoid these problems a method, termed vitrification, is being developed to inhibit ice formation by use of high concentration of cryoprotectants and ultra-rapid cooling, but this is only successful across a limited number of biological objects and in small volume applications. This study explores physical processes of ice crystal formation in a model cryoprotective solution used previously in trials on vitrification of complex biological systems, to improve our understanding of the process and identify limiting biophysical factors. Here we present results of neutron scattering experiments which show that even if ice crystal formation has been suppressed during quench cooling, the water molecules, mobilised during warming, can crystallise as detectable ice. The crystallisation happens right after melting of the glass phase formed during quench cooling, whilst the sample is still transiting deep cryogenic temperatures. We also observe strong water isotope effects on ice crystallisation processes in the cryoprotectant mixture. In the neutron scattering experiment with a fully protiated water component, we observe ready crystallisation occurring just after the glass melting transition. On the contrary with a fully deuteriated water component, the process of crystallisation is either completely or substantially supressed. This behaviour might be explained by nuclear quantum effects in water. The strong isotope effect, observed here, may play an important role in development of new cryopreservation strategies. PMID:25815751

Kirichek, Oleg; Soper, Alan; Dzyuba, Boris; Callear, Sam; Fuller, Barry

2015-01-01

116

Environmental impact of melting buried ice blocks (North Poland)  

NASA Astrophysics Data System (ADS)

The aim of the research was to decipher the impacts of the role of dead ice melting on landscape evolution in the Lateglacial and early Holocene Central Europe. Here, we present the paleoecological results from the middle section of the Wda river which is located in northern Poland (Central Europe), on the outwash plain formed during the Pomeranian phase of the last (Vistulian) glacial period ca 16,000 14C yrs BP. The Wda river has a typical polygenetic valley in young glacial areas of the northern central European lowlands. We reconstructed environmental changes using biotic proxies (plant macrofossil and pollen analyses) and geomorphological investigations. In this study we focused on a short terrestrial sediment core (48 cm) representing four phases of landscape evolution: telmatic, lacustrine, lacustrine-fluvial and alluvial. Abrupt changes in lithology and sediment structures show rapid changes and threshold processes in environmental conditions. The AMS 14C dating of terrestrial plant remains reveals an age for the basal sediments of 11 223 × 23 cal yr BP and thus falls within the Preboreal biozone. Our results showed that existence of buried ice blocks in northern Poland even at the beginning of the Holocene is clear evidence that locally discontinuous permafrost still was present at that time. The results of our study prove a strong influence of melting buried ice blocks on the geomorphological development, hydrological changes in the catchment, and the biotic environment even in the early Holocene. The research was supported by the National Science Centre Poland (grants No. NN 306085037 and NCN 2011/01/B/ST10/07367). This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution (ICLEA) of the Helmholtz Association. Financial support by the COST Action ES0907 INTIMATE is gratefully acknowledged.

Ott, F.; Slowinski, M. M.; Blaszkiewicz, M.; Brauer, A.; Noryskiewicz, B.; Tyszkowski, S.

2013-12-01

117

Melt detection in Antarctic ice-sheets using spaceborne scatterometers and radiometers  

Microsoft Academic Search

Backscatter measurements from the Sea Winds on QuikSCAT scatterometer are used to determine periods of surface freeze and melt on Antarctic ice-shelves. A maximum likelihood method is used to infer the daily ice-surface conditions for various study points located on the Ronne, Ross, Larsen, Fimbul, Amery, and Shackleton ice-shelves. Criteria for determining the dates of melt-onset and freeze-up for each

Lukas B. Kunz; David G. Long

2004-01-01

118

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

119

Lagrangian analysis of ICESat altimetry reveals patterns of ice shelf basal melting  

NASA Astrophysics Data System (ADS)

Iceberg calving and ice shelf basal melting are normal mass-loss processes that over time roughly balance the outflow of ice from the Antarctic Ice Sheet. Most basal melting is thus compensated by ice advection and is not detected by the traditional methods of analyzing surface elevation changes in a fixed geographic coordinate system (Eulerian). Here we present a new method that derive elevation changes in a "Lagrangian" sense from repeat-track ICESat laser altimetry, where specific locations are followed on the advancing ice shelf surface. We use a published ice shelf velocity field to correct for ice advection between consecutive repeats, and then convert the Lagrangian dh/dt estimates into ice thickness changes based on a model of the firn layer. In some locations, the derived ice thickness changes are much larger the Eulerian approach. The Lagrangian approach reduces the noise level of the derived ice thickness changes and reveals clear spatial patterns that we interpret as variations in basal melting. For the largest Antarctic ice shelves (Ross and Filchner-Ronne), we find that the Lagrangian thinning rates increase progressively towards the fronts, which is consistent with oceanographic models that suggest higher basal melt rates in the frontal zone. There are few examples of localized Lagrangian thickening, suggesting that basal melting is likely dominating over basal freezing in the interior of most ice shelves. Combined with data on surface mass balance and firn compaction, our Lagrangian approach can provide new insights into the magnitude and extent of basal melting, as well as being an important validation for models of ice-ocean interaction.

Moholdt, G.; Fricker, H. A.; Padman, L.

2012-12-01

120

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

121

A Model of Ice-Shelf Thermodynamics and Surface Hydrology Under Melting Conditions With an Application to the Recent Disintegration of the Larsen A and B Ice Shelves  

NASA Astrophysics Data System (ADS)

Break-up of Larsen A and B ice shelves in 1995 and 2002, respectively, is thought to be a consequence of extensive warming within the Antarctic Peninsula region observed in recent decades. The most notable glaciological effect of this warming has been the emergence of pervasive surface melting on the two ice shelves in the summers prior to their disintegration.Indeed, the mechanical effects of surface meltwater in the propagation and deepening of surface and basal crevasses has been proposed as the mechanism by which the ice shelves were fractured to the point of disintegration. To develop an understanding of how surface conditions on the Larsen Ice Shelves converted from essentially dry, polar conditions to wet, temperate conditions, we have developed a simple model that describes the hydrological and thermodynamic evolution of surface firn and melt under warming environments. Energy conservation aspects of the model are designed to simulate the formation of subsurface melt due to the absorbtion of solar radiation and the formation of in situ ice layers in response to latent heat release. Hydrological aspects of the model are concerned with how meltwater percolates down and re-freezes at colder horizons. Storage aspects of the surface hydrology are parameterized in a simple manner so that the evolution of metwater ponds and water-filled surface crevasses can be simulated as a consequence of progressively saturating the firn with meltwater and impermeable re-frozen ice lenses. The model is tested by comparing its evolution with observations of the Larsen Ice shelf under model forcing conditions (atmospheric pressure, temperature, precipitation, specific humidity and wind speed) representative of conditions on Larsen B ice shelf in the years prior to it's disintegration.

Sergienko, O.; Macayeal, D. R.

2003-12-01

122

Melt ponds on Arctic sea ice determined from MODIS satellite data using an artificial neural network  

NASA Astrophysics Data System (ADS)

Melt ponds on sea ice strongly reduce the surface albedo and accelerate the decay of Arctic sea ice. Due to different spectral properties of snow, ice, and water, the fractional coverage of these distinct surface types can be derived from multispectral sensors like the Moderate Resolution Image Spectroradiometer (MODIS) using a spectral unmixing algorithm. The unmixing was implemented using a multilayer perceptron to reduce computational costs. Arctic-wide melt pond fractions and sea ice concentrations are derived from the level 3 MODIS surface reflectance product. The validation of the MODIS melt pond data set was conducted with aerial photos from the MELTEX campaign 2008 in the Beaufort Sea, data sets from the National Snow and Ice Data Center (NSIDC) for 2000 and 2001 from four sites spread over the entire Arctic, and with ship observations from the trans-Arctic HOTRAX cruise in 2005. The root-mean-square errors range from 3.8 % for the comparison with HOTRAX data, over 10.7 % for the comparison with NSIDC data, to 10.3 % and 11.4 % for the comparison with MELTEX data, with coefficient of determination ranging from R2=0.28 to R2=0.45. The mean annual cycle of the melt pond fraction per grid cell for the entire Arctic shows a strong increase in June, reaching a maximum of 15 % by the end of June. The zonal mean of melt pond fractions indicates a dependence of the temporal development of melt ponds on the geographical latitude, and has its maximum in mid-July at latitudes between 80° and 88° N. Furthermore, the MODIS results are used to estimate the influence of melt ponds on retrievals of sea ice concentrations from passive microwave data. Results from a case study comparing sea ice concentrations from ARTIST Sea Ice-, NASA Team 2-, and Bootstrap-algorithms with MODIS sea ice concentrations indicate an underestimation of around 40 % for sea ice concentrations retrieved with microwave algorithms.

Rösel, A.; Kaleschke, L.; Birnbaum, G.

2012-04-01

123

Changes in Arctic Melt Season and Implications for Sea Ice Loss  

NASA Technical Reports Server (NTRS)

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

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

2014-01-01

124

Dynamics of surface melting over Amery and Ross ice shelf in Antarctic using OSCAT data  

NASA Astrophysics Data System (ADS)

Antarctic sea ice sheets play an important role in modulating the climate system. The present study investigates the dynamics of melt/freeze over Amery and Ross ice shelf located in Eastern and Southern part of continent using OSCAT, the microwave scatterometer data from OCEANSAT2. The study utilizes the sensitivity of backscatter coefficient values of scatterometer data to presence of liquid water in the snow caused due to melt conditions. The analysis carried out for four austral winters from 2010-2013 and five austral summer from 2009-2014 showed spatial and temporal variations in average backscatter coefficient over Amery and Ross shelf areas. A dynamic threshold based on the austral winter mean and standard deviation of HH polarization is considered for pixel by pixel analysis for the shelf area. There is significant spatio-temporal variability in melt extent, duration and melt index as observed in the analysis. Spatially, the melt over Amery shelf moves from South to North along coast and West towards inner shelf area. Maximum mean melt occurs on 9th January with January 1-15 fortnight accounting for 80 % of the melt. Extreme low melt conditions were observed during summer 2010-11 and 2011-12 indicating cold summer. Summer 2012-13 and 2013-14 were warm summer. Year 2014 experienced melt only in the month of January with entire shelf under melt conditions. Practically no melt was observed over Ross ice shelf.

Bothale, R. V.; Rao, P. V. N.; Dutt, C. B. S.; Dadhwal, V. K.

2014-11-01

125

Glaciation in the Late Noachian Icy Highlands: Ice accumulation, distribution, flow rates, basal melting, and top-down melting rates and patterns  

NASA Astrophysics Data System (ADS)

Geological evidence for extensive non-polar ice deposits of Amazonian age indicates that the current cold and dry climate of Mars has persisted for several billion years. The geological record and climate history of the Noachian, the earliest period of Mars history, is less certain, but abundant evidence for fluvial channels (valley networks) and lacustrine environments (open-basin lakes) has been interpreted to represent warm and wet conditions, including rainfall and runoff. Alternatively, recent atmospheric modeling results predict a "cold and icy" Late Noachian Mars in which moderate atmospheric pressure accompanied by a full water cycle produce an atmosphere where temperature declines with elevation following an adiabatic lapse rate, in contrast to the current situation on Mars, where temperature is almost completely determined by latitude. These results are formulated in the Late Noachian Icy Highlands (LNIH) model, in which these cold and icy conditions lead to the preferential deposition of snow and ice at high elevations, such as the southern uplands. What is the fate of this snow and ice and the nature of glaciation in such an environment? What are the prospects of melting of these deposits contributing to the observed fluvial and lacustrine deposits? To address these questions, we report on a glacial flow-modeling analysis using a Mars-adapted ice sheet model with LNIH climate conditions. The total surface/near-surface water inventory is poorly known for the Late Noachian, so we explore the LNIH model in a "supply-limited" scenario for a range of available water abundances and a range of Late Noachian geothermal fluxes. Our results predict that the Late Noachian icy highlands (above an equilibrium line altitude of approximately +1 km) were characterized by extensive ice sheets of the order of hundreds of meters thick. Due to extremely cold conditions, the ice-flow velocities in general were very low, less than a few mm/yr, and the regional ice-flow pattern was disorganized and followed topography, with no radial flow pattern typical of an equilibrium ice sheet. Virtually the entire ice sheet is predicted to be cold-based, and thus the range of wet-based features typically associated with temperate glaciers (e.g., drumlins, eskers, etc.) is not predicted to occur. Wet-based conditions are predicted only locally in the thickest ice (on the floors of the deepest craters), where limited subglacial lakes may have formed. These LNIH regional ice-sheets provide a huge reservoir of potential meltwater as a source for forming the observed fluvial and lacustrine features and deposits. Top-down melting scenarios applied to our LNIH ice sheet model predict that periods of punctuated warming could lead to elevated temperatures sufficient to melt enough snow and ice to readily account for the observed fluvial and lacustrine features and deposits. Our model indicates that such melting should take place preferentially at the margins of the ice sheets, a prediction that can be tested with further analyses.

Fastook, James L.; Head, James W.

2015-02-01

126

Delineation of Surface and Near-Surface Melt on the Greenland Ice Sheet Using MODIS and QuikSCAT data  

NASA Technical Reports Server (NTRS)

This slide presentation reviews the use of MODIS and QuikSCAT data to measure the surface and sub-surface melting on the Greenland Ice Sheet. The project demonstrated the consistence of this technique for measuring the ice melt on the Greenland Ice Sheet. The blending of the two instruments data allows for determination of surface vs subsurface melting. Also, the use of albedo maps can provide information about the intensity of the melting.

Hall, Dorothy K.; Nghiem, Son V.; DiGirolamo, Nicolo E.; Neumann, Gregory; Schaaf, Crystal B.

2010-01-01

127

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.

Carol Landis

128

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

129

Sensitivity of the Weddell Sea sector ice streams to sub-shelf melting and surface accumulation  

NASA Astrophysics Data System (ADS)

A recent ocean modelling study indicates that possible changes in circulation may bring warm deep-ocean water into direct contact with the grounding lines of the Filchner-Ronne ice streams, suggesting the potential for future ice losses from this sector equivalent to ~0.3 m of sea-level rise. Significant advancements have been made in our knowledge of both the basal topography and ice velocity in the Weddell Sea sector, and the ability to accurately model marine ice sheet dynamics, thus enabling an assessment to be made of the relative sensitivities of the diverse collection of ice streams feeding the Filchner-Ronne Ice Shelf. Here we use the BISICLES ice sheet model, which employs adaptive-mesh refinement to resolve grounding line dynamics, to carry out such an assessment. The impact of realistic perturbations to the surface and sub-shelf mass balance forcing fields from our 2000-year "reference" model run indicate that both the Institute and Möller ice streams are highly sensitive to changes in basal melting either near to their respective grounding lines, or in the region of the ice rises within the Filchner-Ronne Ice Shelf. These same perturbations have little impact, however, on the Rutford, Carlson or Foundation ice streams, while the Evans Ice Stream is found to enter a phase of unstable retreat only after melt at its grounding line has increased by 50% of likely present-day values.

Wright, A. P.; Le Brocq, A. M.; Cornford, S. L.; Bingham, R. G.; Corr, H. F. J.; Ferraccioli, F.; Jordan, T. A.; Payne, A. J.; Rippin, D. M.; Ross, N.; Siegert, M. J.

2014-11-01

130

Freezing and melting behavior of an octyl ?-D-glucoside-water binary system--inhibitory effect of octyl ?-D-glucoside on ice crystal formation.  

PubMed

Phase transition behavior of lyotropic liquid crystals of an octyl ?-D-glucoside (OG)-water binary system during ice freezing and melting was studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Not the thermotropic, but the lyotropic phase transition due to the change of OG concentration during ice freezing and melting was observed. The concentration-temperature phase diagram of the binary system was constructed. Melting temperature of ice, T(m), lyotropic phase transition temperature, T(tr), and glass transition temperatures of unfrozen phases in the absence and presence of ice, T(g) and T(g)', were shown in the phase diagram. The phase diagram indicated that the OG aqueous system was concentrated to ca. 90-92 wt% by ice freezing and exhibited glass transition at T(g)'. An observation of the concentration-gradient specimen by the cryo-POM showed the evidence of the inhibitory effects of OG on nucleation and growth of ice crystals in the extremely high OG concentration system in which the lamellar liquid crystalline phase was formed. This study provided the importance of the influence of concentration change by ice freezing on the behaviour of the sugar-based surfactant-water system under low temperature conditions. PMID:23133837

Ogawa, Shigesaburo; Asakura, Kouichi; Osanai, Shuichi

2012-12-21

131

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

132

Perception of Melting and Flavor Release of Ice Cream Containing Different Types and Contents of Fat  

Microsoft Academic Search

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 inten- sity 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 wereperceived. Aslightly fasterflavor release

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

2003-01-01

133

Shifting Arctic Sea-ice Formation and Melt Patterns in a Warming World  

NASA Astrophysics Data System (ADS)

As the Arctic warms, sea-ice formation and melt regions are shifting. Ice retreats earlier, open water extends farther north, and fall freeze-up comes later. The changes are already having an impact on important features of the aquatic Arctic system such as surface productivity, water-column stratification, sea-ice velocities, and the export of freshwater (and buoyancy) to the Nordic Seas. These changes are likely to amplify as the trend toward warmer conditions continues. In this contribution we present ice formation and melt patterns over the duration of the polar satellite observation period, from 1979 to the current. The changes are complex, reflecting latitudinal and temporal shifts with warming of the Northern Hemisphere as well as dynamical trends, such as changes in the prevailing surface wind stress patterns and reduction of internal ice stress. We analyze the satellite-derived sea-ice formation and melt dataset with an eye on: the potential impacts on melt/deposition regions (nutrient delivery, water column stratification, contaminant release); the timing of ice formation anddeposition; changes in bathymetric regimes of the formatino and deposition (which imply changes in sea-ice rafted material transport); shifting freshwater transport patterns; and the underlying dynamical mechanisms driving the observed changes.

Newton, R.; Fowler, C.; Tremblay, B.; Pfirman, S. L.

2011-12-01

134

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

E-print Network

Response of Southern Ocean circulation to global warming may enhance basal ice shelf melting around determining the future ice shelf­ocean interaction by ana- lyzing global warming experiments in a coarse Antarctica Tore Hattermann � Anders Levermann Received: 28 January 2009 / Accepted: 25 July 2009 / Published

Levermann, Anders

135

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

Microsoft Academic Search

In this study, we use a numerical sea-ice-ocean model to examine what causes summertime upper ocean warming and sea ice melt during the 21st century in the Arctic Ocean. Our first question is, “What causes the ocean to warm in the Pacific Sector during the summer”? We find that about 80% of total heating over this region comes from ocean

Michael Steele; Jinlun Zhang; Wendy Ermold

2010-01-01

136

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

Microsoft Academic Search

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

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

2005-01-01

137

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

138

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

2008-01-01

139

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

140

Sensitivity of the Weddell Sea sector ice streams to sub-shelf melting and surface accumulation  

NASA Astrophysics Data System (ADS)

A recent ocean modelling study indicates that possible changes in circulation may bring warm deep ocean water into direct contact with the grounding lines of the Filchner-Ronne ice streams, suggesting the potential for future ice losses from this sector equivalent to ~ 0.3 m of sea-level rise. Significant advancements have been made in our knowledge of both the basal topography and ice velocity in the Weddell Sea sector, thus enabling an assessment to be made of the relative sensitivities of the diverse collection of ice streams feeding the Filchner-Ronne Ice Shelf. Here we use the BISICLES ice sheet model, which employs adaptive-mesh refinement to resolve grounding line dynamics, to carry out such an assessment. The impact of perturbations to the surface and sub-shelf mass balance forcing fields from our 2000 yr "reference" model run indicate that both the Institute and Möller Ice Streams are highly sensitive to changes in basal melting either near to their respective grounding lines, or in the region of the ice rises within the Filchner-Ronne Ice Shelf. These same perturbations have little impact, however, on Rutford, Carlson or Foundation ice streams, while Evans Ice Stream is found to enter a phase of unstable retreat only after melt at its grounding line has increased by an order-of-magnitude from likely present-day values.

Wright, A. P.; Le Brocq, A. M.; Cornford, S. L.; Siegert, M. J.; Bingham, R. G.; Corr, H. F. J.; Ferraccioli, F.; Jordan, T. A.; Rippin, D. M.; Ross, N.

2013-11-01

141

Volcanic unrest primed by ice cap melting: A case study of Snæfellsjökull volcano, Western Iceland  

NASA Astrophysics Data System (ADS)

The most dramatic effect of global warming is the water level rise due to rapid melting of ice sheets. In addition, recent studies suggest that accelerated glacial retreat and associated lithospheric relaxation may enhance upwelling of magmatic fluids through the crust. Here, we investigate whether, also at short geological timescales, shallow magmatic systems may be affected by rapid melting of ice caps. As a case study, we chose the Snæfellsjökull volcanic system in western Iceland, whose ice cap is rapidly melting with 1.25 m(w.e.)/year. To investigate the role of deglaciation in promoting volcanic unrest we use a cross-disciplinary approach integrating geophysical field data, laboratory rheological rock tests, and numerical finite-element analysis. Initial results from seismic data acquisition and interpretation in 2011 show seismic activity (occasionally in swarm sequences) at around a depth range of 8-13 km, indicating the presence of a magmatic reservoir in the crust. In addition, a temporary seismic network of 21 broad-band stations has been deployed in spring 2013 and continuously collected data for several months, which will help better constrain the subsurface geometry. During summer 2013 we collected samples of Tertiary basaltic bedrock from the flanks of Snæfellsjökull, which we assume to be representative for the subsurface volcanic system. Cores drilled from these samples were tri-axially deformed in a Paterson-type apparatus at a constant strain rate of 10-5 s-1, a confining pressure of 50 MPa (i.e. ~2 km depth), and a temperature ranging from 200 °C to 1000 °C (i.e. various proximities to magma chamber). From the obtained stress-strain curves the static Young's modulus is calculated to be around 35 (±2) GPa, which is not significantly influenced by increasing temperatures up to 800 °C. Beyond the elastic domain, cataclastic shear bands develop, accommodating up to 7% strain before brittle failure. The subsurface geometrical constraints from geophysical field data and the rheological parameters from laboratory testing are fed into a numerical finite-element model solving for the pressure in the magma chamber and the stress field in the surrounding basement rock before and after the retreat of an assumed 200 m thick ice cap. Preliminary results show that ice unloading has two effects. First, it leads to significant stress release at the base of the volcanic edifice, possibly resulting in a destabilization of the flanks, which in turn leads to further unloading of the volcanic cone by means of landslides. Second, the pressure change around the magma chamber is in the order of 0.5 MPa. This may be sufficient to induce volatile exsolution and accelerated pressurization of the magmatic reservoir, ultimately leading volcanic unrest, in particular in critically stressed environments prior to glacial retreat. We point out ice cap melting as a possible mechanism for triggering volcanic unrest of shallow magmatic systems.

Bakker, Richard; Lupi, Matteo; Frehner, Marcel; Berger, Julien; Fuchs, Florian

2014-05-01

142

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

143

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

NASA Technical Reports Server (NTRS)

The impact of increasing summer melt on the dynamics and stability of the Greenland Ice Sheet is not fully understood. Mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding. Here, we compare subdaily ice velocity and uplift derived from nine Global Positioning System stations in the upper ablation zone in west Greenland to surface melt and supraglacial lake drainage during summer 2007. Starting around day 173, we observe speedups of 6-41% above spring velocity lasting approximately 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 approximately 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.; Newmann, T. A.; Andrews, L. C.; Rumrill, J. A.

2012-01-01

144

A three-phase free boundary problem with melting ice and dissolving gas  

E-print Network

We develop a mathematical model for a three-phase free boundary problem in one dimension that involves the interactions between gas, water and ice. The dynamics are driven by melting of the ice layer, while the pressurized gas also dissolves within the meltwater. The model incorporates a Stefan condition at the water-ice interface along with Henry's law for dissolution of gas at the gas-water interface. We employ a quasi-steady approximation for the phase temperatures and then derive a series solution for the interface positions. A non-standard feature of the model is an integral free boundary condition that arises from mass conservation owing to changes in gas density at the gas-water interface, which makes the problem non-self-adjoint. We derive a two-scale asymptotic series solution for the dissolved gas concentration, which because of the non-self-adjointness gives rise to a Fourier series expansion in eigenfunctions that do not satisfy the usual orthogonality conditions. Numerical simulations of the original governing equations are used to validate the series approximations.

Maurizio Ceseri; John M. Stockie

2014-11-05

145

Sea ice conditions and melt season duration variability within the Canadian Arctic Archipelago: 1979-2008  

NASA Astrophysics Data System (ADS)

Sea ice conditions and melt season duration within the Canadian Arctic Archipelago (CAA) were investigated from 1979-2008. The CAA is exhibiting statistically significant decreases in average September total sea ice area at -8.7% decade-1. The melt season duration within the CAA is increasing significantly at 7 days decade-1. 2008 represented the longest melt season duration within the CAA over the satellite record at 129 days. Average September multi-year ice (MYI) area is decreasing at -6.4% decade-1 but has yet to reach statistical significance as a result of increasing MYI dynamic import from the Arctic Ocean. Results also find that the Western Parry Channel (WPC) region of the Northwest Passage (NWP) will continue to be susceptible to MYI as the transition to a summer-time sea ice free Arctic continues. The processes responsible for the temporary clearing of the WPC region of the NWP in 2007 were also identified.

Howell, Stephen E. L.; Duguay, Claude R.; Markus, Thorsten

2009-05-01

146

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

147

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

148

Contribution of Greenland ice sheet melting to sea level rise during the last interglacial period: an approach combining ice sheet modelling and proxy data  

NASA Astrophysics Data System (ADS)

In the context of global warming, the contribution of the two major ice sheets, Antarctica and Greenland, to global sea level rise is a subject of key importance for the scientific community (4th assessment report of the Intergovernmental Panel on climate change, IPCC-AR4, Meehl et al., 2007). By the end of the next century, a 3-5 °C warm up is expected in Greenland. Similar temperatures in this region were reached during the last interglacial (LIG) period due to a change in orbital configuration rather than to anthropogenic forcing. Ice core evidence suggests that the Greenland Ice Sheet (GIS) has survived this warm period but great uncertainties remain about the total Greenland ice reduction during the LIG and its sea level rise contribution. In order to improve our confidence in future state projections, we first intend to reconstruct the past states of the GIS using ice sheet modelling, and confront the simulations with paleo data. The chosen methodoly of paleoclimate reconstruction is strongly based on proxy data. Proxy data are also used to constrain the ice sheet model during the calibration phase. Our estimates of Greenland melting contribution to sea level rise during the LIG period range from 0.65 to 1.5 m of sea level equivalent.

Quiquet, A.; Ritz, C.; Punge, H. J.; Salas y Mélia, D.

2012-08-01

149

Surface Melt Magnitude Retrieval Over Ross Ice Shelf, Antarctica Using Coupled MODIS Optical and Thermal Satellite Measurements During the 2002-03 Melt Season  

Microsoft Academic Search

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. Unfortunately, we are not realistically able to quantify surface snowmelt from ground-based methods because there

C. C. Karmosky; D. J. Lampkin

2008-01-01

150

Influence of tides on melting and freezing beneath Filchner-Ronne Ice Shelf, Antarctica  

NASA Astrophysics Data System (ADS)

An isopycnic coordinate ocean circulation model is applied to the ocean cavity beneath Filchner-Ronne Ice Shelf, investigating the role of tides on sub-ice shelf circulation and ice shelf basal mass balance. Including tidal forcing causes a significant intensification in the sub-ice shelf circulation, with an increase in melting (3-fold) and refreezing (6-fold); the net melt rate and seawater flux through the cavity approximately doubles. With tidal forcing, the spatial pattern and magnitude of basal melting and freezing generally match observations. The 0.22 m a-1 net melt rate is close to satellite-derived estimates and at the lower end of oceanographic values. The Ice Shelf Water outflow mixes with shelf waters, forming a cold (<-1.9°C), dense overflow (0.83 Sv) that spills down the continental slope. These results demonstrate that tidal forcing is fundamental to both ice shelf-ocean interactions and deep-water formation in the southern Weddell Sea.

Makinson, Keith; Holland, Paul R.; Jenkins, Adrian; Nicholls, Keith W.; Holland, David M.

2011-03-01

151

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

152

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

NASA Astrophysics Data System (ADS)

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

Yoshimoto, Yoshihide

2013-03-01

153

Warm river waters contributed to melting Arctic sea ice  

NASA Astrophysics Data System (ADS)

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

Balcerak, Ernie

2014-05-01

154

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

SciTech Connect

In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67?K for a stress-free condition down to 898.1?K for uniaxial strain and to 920.8?K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q?1.51×10{sup 10}K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1?K for Q?=?1.51?×?10{sup 11?}K/s and 936.9?K for Q?=?1.46?×?10{sup 12?}K/s.

Hwang, Yong Seok, E-mail: yshwang@iastate.edu [Department of Aerospace Engineering, Iowa State University, Ames, Iowa 50011 (United States); Levitas, Valery I., E-mail: vlevitas@iastate.edu [Departments of Aerospace Engineering, Mechanical Engineering, and Material Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States)

2014-06-30

155

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

156

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

E-print Network

Detection in Antarctic Ice Shelves Using Scatterometers and Microwave Radiometers Lukas B. Kunz and David G to 2003 are analyzed and found to be effective in determining periods of melt in Antarctic ice sheets of the seasonal and interannual melting of the Antarctic ice sheets. Index Terms--Antarctic, ice, ice shelves

Long, David G.

157

Superimposed ice formation and surface energy fluxes on sea ice during the spring melt freeze period in the Baltic Sea  

NASA Astrophysics Data System (ADS)

The development of land-fast sea ice and overlying snow was monitored during a 4 week period, until the snow cover had completely disappeared, at a site in the Gulf of Bothnia, Baltic Sea (63.57° N, 19.85° E). The meteorological and radiative boundary conditions were continuously recorded. During the observation period, a 15 cm thick snow layer on the ice was transformed into a 7 cm thick granular ice layer (superimposed ice) on the ice surface, contributing significantly (about 11%) to the total ice thickness. Approximately 1 cm w.e. of the snow was sublimated. Neither snow-ice formation nor basal ice growth was significant during the same period. The salinity and isotopic (?18O) composition of the ice indicated that prior to the experiment a 7 cm layer of superimposed ice had already formed. Hence, superimposed ice layers contributed 22% of the total ice thickness by the time all snow had disappeared. The advancing spring, decrease in surface albedo, diurnal cycle in the incoming solar radiation, and synoptic-scale changes in the cloud cover and the air ice turbulent heat fluxes caused variations in the heat budget of the snowpack. Superimposed ice formation due to refreezing of meltwater occurred during most nights of the study period, and the most important refreezing periods were under such synoptic conditions that the air and snow surface temperatures also remained below zero during daytime. In contrast to typical summer conditions in polar oceans, low snow surface temperatures acted as the primary heat sink for the refreezing of meltwater.

Granskog, Mats A.; Vihma, Timo; Pirazzini, Roberta; Cheng, Bin

158

Channelized ice melting in the ocean boundary layer beneath Pine Island Glacier, Antarctica.  

PubMed

Ice shelves play a key role in the mass balance of the Antarctic ice sheets by buttressing their seaward-flowing outlet glaciers; however, they are exposed to the underlying ocean and may weaken if ocean thermal forcing increases. An expedition to the ice shelf of the remote Pine Island Glacier, a major outlet of the West Antarctic Ice Sheet that has rapidly thinned and accelerated in recent decades, has been completed. Observations from geophysical surveys and long-term oceanographic instruments deployed down bore holes into the ocean cavity reveal a buoyancy-driven boundary layer within a basal channel that melts the channel apex by 0.06 meter per day, with near-zero melt rates along the flanks of the channel. A complex pattern of such channels is visible throughout the Pine Island Glacier shelf. PMID:24031016

Stanton, T P; Shaw, W J; Truffer, M; Corr, H F J; Peters, L E; Riverman, K L; Bindschadler, R; Holland, D M; Anandakrishnan, S

2013-09-13

159

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

NASA Astrophysics Data System (ADS)

The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate the impact on the temperature-salinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical experiments, the warming is imposed homogeneously along the open inflow boundaries of the model domain, leading to a warming of the warm deep water (WDW) further downstream. Our modelling results indicate a weak quadratic dependence of the melt rate at the ice shelf base on the imposed amount of warming, which is consistent with earlier studies. The total melt rate has a strong dependence on the applied ocean warming depth. If the warming is restricted to the upper ocean (above 1,000 m), the water column (aside from the mixed surface layer) in the vicinity of the ice shelves stabilises. Hence, reduced vertical mixing will reduce the potential of Antarctic Bottom Water formation further downstream with consequences on the global thermohaline circulation. If the warming extends to the abyss, the WDW core moves significantly closer to the continental shelf break. This sharpens the Antarctic Slope Front and leads to a reduced density stratification. In contrast to the narrow shelf bathymetry in the EWIS region, a wider continental shelf (like in the southern Weddell Sea) partly protects ice shelves from remote ocean warming. Hence, the freshwater production rate of, e.g., the Filchner-Ronne Ice Shelf increases much less compared with the EWIS for identical warming scenarios. Our study therefore indicates that the ice-ocean interaction has a significant impact on the temperature-salinity distribution and the water column stability in the vicinity of ice shelves located along a narrow continental shelf. The effects of ocean warming and the impact of increased freshwater fluxes on the circulation are of the same order of magnitude and superimposed. Therefore, a consideration of this interaction in large-scale climate studies is essential.

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

2010-06-01

160

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

161

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

162

Experimental Discussion for Characteristics of Ice Formation and Melting of Latent Heat Thermal Energy Storage Cell Using Resin Tube-Mat  

NASA Astrophysics Data System (ADS)

The experimental discussion was performed to the process of ice formation and melting in the ice thermal energy storage cell employing the resin tube-mat for the heat transfer surface. The experiments were carried out by varying the size of resin tube-mat and the arrangement of the tubes by measuring the ice formation rate and the melting rate, and by measuring the temperature change of the brine. As a result, in the solidification process, the steady performance for the storing of cold energy was achieved during about 4-6 hours by the brine of - 5°C and in the melting process, the performance for the utilizing of cold energy was achieved during about 3-5 hours by the brine of 10°C. It was found that the heat transfer characteristics becomes better for the case of the thin pipe thickness and the large pipe diameter.

Hirasawa, Yoshio; Kosaka, Akio; Kitano, Kazuyuki

163

Massively parallel molecular-dynamics simulation of ice crystallisation and melting: The roles of system size, ensemble, and electrostatics  

NASA Astrophysics Data System (ADS)

Ice crystallisation and melting was studied via massively parallel molecular dynamics under periodic boundary conditions, using approximately spherical ice nano-particles (both "isolated" and as a series of heterogeneous "seeds") of varying size, surrounded by liquid water and at a variety of temperatures. These studies were performed for a series of systems ranging in size from ˜1 × 106 to 8.6 × 106 molecules, in order to establish system-size effects upon the nano-clusters" crystallisation and dissociation kinetics. Both "traditional" four-site and "single-site" and water models were used, with and without formal point charges, dipoles, and electrostatics, respectively. Simulations were carried out in the microcanonical and isothermal-isobaric ensembles, to assess the influence of "artificial" thermo- and baro-statting, and important disparities were observed, which declined upon using larger systems. It was found that there was a dependence upon system size for both ice growth and dissociation, in that larger systems favoured slower growth and more rapid melting, given the lower extent of "communication" of ice nano-crystallites with their periodic replicae in neighbouring boxes. Although the single-site model exhibited less variation with system size vis-à-vis the multiple-site representation with explicit electrostatics, its crystallisation-dissociation kinetics was artificially fast.

English, Niall J.

2014-12-01

164

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

165

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

E-print Network

Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle), Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle in the eastern South off northern Chile based on sedimentary nitrogen isotopes. Our results show a relatively early, large

Demouchy, Sylvie

166

Reducing the uncertainty in projections of future ice shelf basal melting  

NASA Astrophysics Data System (ADS)

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

Timmermann, Ralph; Kauker, Frank

2014-05-01

167

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

PubMed Central

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

Lampkin, Derrick; Peng, Rui

2008-01-01

168

Distinguishing ice from snow for melt modeling using daily observations from MODIS  

NASA Astrophysics Data System (ADS)

In high mountainous regions of the Earth during melt periods, both seasonal snow and glacier ice melt may contribute to surface water and ground water feeding streams. In these regions there are often few in-situ observations that can help distinguish between the two components of melt, particularly across large mountain ranges. Understanding the contribution of melt water from the seasonal snow and glacier ice sources informs us about the current state of the water cycle and how a changing climate may alter the water cycle. In this study, we analyze daily time series of MODIS data products to distinguish ice from snow as the seasonal snowpack recedes, revealing melt over glacier ice surfaces. Broadband albedo increases as ice is exposed because of larger grain sizes and dust/debris on the glacier surface. To investigate the grain sizes we use estimates from the MODIS Snow Covered Area and Grain Size Model (MODSCAG) and MODIS Dust Radiative Forcing in Snow (MODDRFS) derived from MODIS surface reflectance (MOD09GA). MODSCAG uses the shape of the spectrum selected by a spectral mixture analysis model while MODDRFS uses the Normalized Difference Grain Size Index (NDGSI). Comparison of the grain sizes with grain sizes derived from the Airborne Visible/Infrared Imaging Spectrometer have demonstrated higher accuracy for the NDGSI approach. In addition to analysis of grain sizes, we use 2 standard albedo products from the MODIS, the Terra Daily Snow Cover algorithm (MOD10A1) that uses a narrow-to-broadband conversion scheme to create an integrated broadband albedo and Surface Reflectance BRDF/Albedo (MOD43) product that provides albedo in three broad bands. We focus on the Hunza River basin, in the Upper Indus located in Northern Pakistan. We use the annual minimum ice and snow from the MODICE Persistent Ice and Snow (MODICE) algorithm to identify glaciated regions for analysis. The methods (MODSCAG, MODDRFS, MOD10A1, MOD43) all show sensitivity to exposed glacier surfaces. Further work will use a time series of melt modeling in this region to determine the contributions from seasonal snow versus glacier ice melt.

Rittger, Karl; Bryant, Anne C.; Brodzik, Mary J.; Painter, Thomas H.; Armstrong, Richard

2014-05-01

169

New insights into ice growth and melting modifications by antifreeze proteins  

PubMed Central

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

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

2012-01-01

170

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

171

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

PubMed

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

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

2014-01-01

172

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

Microsoft Academic Search

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

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

2010-01-01

173

Method for Synthesizing Extremeley High Temperature Melting Materials  

DOEpatents

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

Saboungi, Marie-Louise and Glorieux, Benoit

2005-11-22

174

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

175

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

176

ANALYSIS OF ANTARCTIC ICEBERG AND SEA ICE MELTING PATTERNS USING QUIKSCAT  

E-print Network

ANALYSIS OF ANTARCTIC ICEBERG AND SEA ICE MELTING PATTERNS USING QUIKSCAT Keith M. Stuart and David ABSTRACT QuikSCAT tracking of Antarctic icebergs is discussed, and iceberg movement trends are illustrated, a threshold algorithm to de- tect polynyas is developed. The 2006-2007 Antarctic ablation sea- son is analyzed

Long, David G.

177

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

178

Cumulate maturation and melt migration in a temperature gradient  

Microsoft Academic Search

A potential driving force for cumulate compaction and melt segregation in magmas arises from the change in crystal solubility with temperature. Spatial thermal variation in a cumulus crystal pile sets up a gradient in interstitial melt composition, which in turn provides a diffusion potential for silicate liquid species. Mass transport in response to this potential, referred to as thermal migration,

C. E. Lesher; D. Walker

1988-01-01

179

Can Nano-Particle Melt below the Melting Temperature of Its Free Surface Partner?  

NASA Astrophysics Data System (ADS)

The phonon thermal contribution to the melting temperature of nano-particles is inspected. The discrete summation of phonon states and its corresponding integration form as an approximation for a nano-particle or for a bulk system have been analyzed. The discrete phonon energy levels of pure size effect and the wave-vector shifts of boundary conditions are investigated in detail. Unlike in macroscopic thermodynamics, the integration volume of zero-mode of phonon for a nano-particle is not zero, and it plays an important role in pure size effect and boundary condition effect. We find that a nano-particle will have a rising melting temperature due to purely finite size effect; a lower melting temperature bound exists for a nano-particle in various environments, and the melting temperature of a nano-particle with free boundary condition reaches this lower bound. We suggest an easy procedure to estimation the melting temperature, in which the zero-mode contribution will be excluded, and only several bulk quantities will be used as input. We would like to emphasize that the quantum effect of discrete energy levels in nano-particles, which is not present in early thermodynamic studies on finite size corrections to melting temperature in small systems, should be included in future researches.

Sui, Xiao-Hong; Wang, Zong-Guo; Kang, Kai; Qin, Shao-Jing; Wang, Chui-Lin

2015-02-01

180

Towards Estimate of Present Day Ice Melting in Polar Regions From Altimetry, Gravity, Ocean Bottom Pressure and GPS Observations  

NASA Astrophysics Data System (ADS)

The ice sheet in Polar Regions stores the largest freshwater bodies on Earth, sufficient to elevate global sea level by more than 65 meters if melted. The earth may have entered an intensive ice-melting episode, possibly due to anthropogenic global warming rather than natural orbit variations. Determining present-day ice mass balance, however, is complicated by the fact that most observations contain both present day ice melting signal and residual signals from past glacier melting. Despite decades of progress in geodynamic modeling and new observations, significant uncertainties remain in both. The key to separate present-day ice mass change and signals from past melting is to include data of different physical characteristics. We conducted a new global kinematic inversion scheme to estimate both present-day ice melting and past glacier signatures simultaneously and assess their contribution to current and future global mean sea level change. Our approach is designed to invert and separate present-day melting signal in the spherical harmonic domain using a globally distributed interdisciplinary data with distinct physical information. Interesting results with unprecedented precisions have been achieved so far. We will present our results of the estimated present-day ice mass balance trend in both Greenland and Antarctica ice sheet as well as other regions where significant mass change occurs.

Jiang, Y.; Wu, X.; van den Broeke, M. R.; Munneke, P. K.; Simonsen, S. B.; van der Wal, W.; Vermeersen, B. L.

2013-12-01

181

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

182

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

183

The melt-freeze cycle of the Arctic Ocean ice cover and its dependence on ocean stratification  

NASA Astrophysics Data System (ADS)

A time-dependent, 1-D coupled ice-ocean model is used to quantify the impact of ocean stratification on the Arctic ice cover. The model results show that the ice growth during winter equals the ice melt in summer for areas with a well-developed cold halocline layer (CHL), provided that the initial ice thickness is around 3 m, while thinner initial ice thickness results in net growth. Areas with weak salt stratification can have a negative annual thickness change irrespective of the initial ice thickness and are thus dependent on ice import in order to remain ice covered. The model results also show that ocean stratification is mostly important for ice-thickness development during the growing season. Areas with weak stratification have an ocean heat flux up to 8 W m-2 reaching the ice during the growing season, while areas with a CHL have an average of about 0.7 W m-2. In the extreme area, north of Svalbard, the ocean heat fluxes are typically around 25 W m-2 but can be up to 400 W m-2 during the initial adjustment, when the warm Atlantic water has direct contact with the ice. A general outcome of the study is that, depending on ocean stratification, the ice cover of Arctic Ocean can be divided into one part with net ice growth (the major part) and another part with net ice melt (mainly in the Nansen Basin).

Linders, Johanna; Björk, Göran

2013-11-01

184

Unusually loud ambient noise in tidewater glacier fjords: a signal of ice melt  

USGS Publications Warehouse

In glacierized fjords, the ice-ocean boundary is a physically and biologically dynamic environment that is sensitive to both glacier flow and ocean circulation. Ocean ambient noise offers insight into processes and change at the ice-ocean boundary. Here we characterize fjord ambient noise and show that the average noise levels are louder than nearly all measured natural oceanic environments (significantly louder than sea ice and non-glacierized fjords). Icy Bay, Alaska has an annual average sound pressure level of 120?dB (re 1 ?Pa) with a broad peak between 1000 and 3000?Hz. Bubble formation in the water column as glacier ice melts is the noise source, with variability driven by fjord circulation patterns. Measurements from two additional fjords, in Alaska and Antarctica, support that this unusually loud ambient noise in Icy Bay is representative of glacierized fjords. These high noise levels likely alter the behavior of marine mammals.

Pettit, Erin C.; Lee, Kevin M.; Brann, Joel P.; Nystuen, Jeffrey A.; Wilson, Preston S.; O'Neel, Shad R.

2015-01-01

185

Water solubility in phonolite melts: Influence of melt composition and temperature  

Microsoft Academic Search

The water solubility in various phonolite melts was determined experimentally at pressures between 50 and 395 MPa and at temperatures between 850 and 1200 °C. The aim of this study was to elucidate to which extent chemical and physical parameters such as relative amounts of alkali and alkaline earth elements or temperature affect the water solubility. For this purpose a total of

Burkhard C. Schmidt; Harald Behrens

2008-01-01

186

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

187

Arctic warming: nonlinear impacts of sea-ice and glacier melt on seabird foraging.  

PubMed

Arctic climate change has profound impacts on the cryosphere, notably via shrinking sea-ice cover and retreating glaciers, and it is essential to evaluate and forecast the ecological consequences of such changes. We studied zooplankton-feeding little auks (Alle alle), a key sentinel species of the Arctic, at their northernmost breeding site in Franz-Josef Land (80°N), Russian Arctic. We tested the hypothesis that little auks still benefit from pristine arctic environmental conditions in this remote area. To this end, we analysed remote sensing data on sea-ice and coastal glacier dynamics collected in our study area across 1979-2013. Further, we recorded little auk foraging behaviour using miniature electronic tags attached to the birds in the summer of 2013, and compared it with similar data collected at three localities across the Atlantic Arctic. We also compared current and historical data on Franz-Josef Land little auk diet, morphometrics and chick growth curves. Our analyses reveal that summer sea-ice retreated markedly during the last decade, leaving the Franz-Josef Land archipelago virtually sea-ice free each summer since 2005. This had a profound impact on little auk foraging, which lost their sea-ice-associated prey. Concomitantly, large coastal glaciers retreated rapidly, releasing large volumes of melt water. Zooplankton is stunned by cold and osmotic shock at the boundary between glacier melt and coastal waters, creating new foraging hotspots for little auks. Birds therefore switched from foraging at distant ice-edge localities, to highly profitable feeding at glacier melt-water fronts within <5 km of their breeding site. Through this behavioural plasticity, little auks maintained their chick growth rates, but showed a 4% decrease in adult body mass. Our study demonstrates that arctic cryosphere changes may have antagonistic ecological consequences on coastal trophic flow. Such nonlinear responses complicate modelling exercises of current and future polar ecosystem dynamics. PMID:25639886

Grémillet, David; Fort, Jérôme; Amélineau, Françoise; Zakharova, Elena; Le Bot, Tangi; Sala, Enric; Gavrilo, Maria

2015-03-01

188

Modelling the impact of submarine frontal melting and ice mélange on glacier dynamics  

NASA Astrophysics Data System (ADS)

Two mechanisms are generally proposed to explain seasonal variations in the calving front of tidewater glaciers: submarine melting of the calving face and the mechanical back-force applied by the ice mélange. However, the way these processes affect the calving rate and the glacier dynamics remains uncertain. In this study, we used the finite element model Elmer/Ice to simulate the impact of these forcings on more than 200 two dimensional theoretical flowline glacier configurations. The model, which includes calving processes, suggests that frontal melting affects the position of the terminus only slightly (< a few hundred meters) and does not affect the pluriannual glacier mass balance at all. However, the ice mélange has a greater impact on the advance and retreat cycles of the glacier front (more than several 1000 m) and its consequences for the mass balance are not completely negligible, stressing the need for better characterization of forcing properties. We also show that ice mélange forcing against the calving face can mechanically prevent crevasse propagation at sea level and hence prevent calving. Results also revealed different behaviors in grounded and floating glaciers: in the case of a floating extension, the heaviest forcings can disrupt the glacier equilibrium by modifying its buttressing and ice flux at the grounding line.

Krug, J.; Durand, G.; Gagliardini, O.; Weiss, J.

2015-01-01

189

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

190

Aircraft observations of the evolution of ice surface conditions at the onset of the melt season in the Beaufort Sea  

NASA Astrophysics Data System (ADS)

At the onset of the melt season in the Arctic, the energy exchange between atmosphere, sea ice, and ocean undergoes strong changes. Caused by melting of snow and formation of melt ponds and open leads the areally averaged albedo decreases dramatically and absorption of solar radiation is enhanced. To investigate these changes, the aircraft campaign MELTEX was performed from 11 May to 7 June, 2008 over the Beaufort Sea (region 69°N-74°N, 133°W-144°W). During the campaign, the sea ice cover experienced several episodes with strong on-ice warm-air advection from the Canadian Coast. Between these warm episodes, northerly flow with cold-air advection from the inner Arctic caused an interruption of melting and melt pond evolution and even a temporary refreezing. To quantify the evolution of ice surface conditions, the aircraft POLAR 5 was equipped with a digital reflex camera, broadband radiation sensors, a spectral albedometer with active horizontal stabilization, and further meteorological instruments. Images of seven flights were analyzed by means of a supervised classification employing the maximum likelihood method to derive the areal fraction of different surface classes. Areally averaged broadband and spectral albedo was derived for clear-sky conditions only to allow for a better comparison of values. On 11 May, the ice conditions were still characteristic for late winter. The maximum broadband albedo for snow covered ice was 0.82. On 26 May, already 21,6% of the sea ice surface right north of a coastal polynya consisted of wet ice (19,4%) and shallow melt ponds (2,2%). Broadband albedo measurements indicated an average value of 0.57 for melting snow and bare ice. The most enhanced stage of melting was encountered on 6 June for fast ice in Franklin and Darnley Bay, south of the Amundsen Gulf. The total fraction of melt ponds and particle-laden sea ice amounted to 45,0±16,7% with an average broadband albedo of 0.16. The average albedo of the remaining clean bare ice was 0.48. On 7 June, the last day of the campaign, a distinct north-south gradient in melt pond fraction was observed. On the northernmost flight leg between 72°N and 73°N, only 11,1±10,3% of the sea ice surface consisted of wet ice and shallow melt ponds. For areas where the sum of melting snow and melt ponds was larger than 90%, the average broadband albedo ? showed a nearly linear dependence on the area fraction fp of melt ponds. Results can be fitted as ? = ?s - 0.18 * fp , where ?s = 0.63 is the average albedo of the melting snow. Hence, the average albedo of the shallow melt ponds observed can be estimated to be 0.45. Areally averaged spectral albedo was measured in the range 350 nm to 2150 nm. Largest differences in the spectral signature of different surface classes occurred in the visible range. In contrast, differences were very small for wavelengths larger than 1500 nm. Here, the areally averaged spectral albedo was nearly independent of the melt pond fraction. Future aircraft campaigns will focus on the measurement of additional key parameters influencing albedo of summer sea ice, e.g., ice thickness and melt pond depth.

Birnbaum, G.; Ehrlich, A.; Schwarz, P.; Lüpkes, C.; Dierking, W.; Hartmann, J.

2012-12-01

191

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

192

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

USGS Publications Warehouse

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

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

2004-01-01

193

Pressure Dependence of the Melting Temperature: A Theoretical Approach  

NASA Astrophysics Data System (ADS)

A new universal equation of state (EoS) was derived by using zero pressure and temperature reference frame and separating the initial volume, elastic and thermal components in the volume. The new equation of state works comparably or better in wide range of temperature with respect to conventional EoS (i.e. Burch-Murnaghan and Vinet EoS) in fitting published experimental P-V-T data of perovskite and epsilon iron. In this study, we use this universal equation of state to investigate melting temperature of iron. Under the hypothesis that the ratio of thermal volume to the solid volume at zero temperature remains constant along melting curve, melting temperature of iron is studied. Using the six parameters of the EoS determined based experimental data and applying the proposed melting criteria, the melting curve of iron is calculated. The result is consistent with lower bound of experimental data. In addition, expanding the calculation to extremely high pressure leads to an interesting phenomenon that the thermal volume does not increase with temperature above a critical pressure. research.com/php/EOS_Iron.php

Garai, J.

2008-05-01

194

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

195

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

196

A Model of Ice-Shelf Thermodynamics and Surface Hydrology Under Melting Conditions With an Application to the Recent Disintegration of the Larsen A and B Ice Shelves  

Microsoft Academic Search

Break-up of Larsen A and B ice shelves in 1995 and 2002, respectively, is thought to be a consequence of extensive warming within the Antarctic Peninsula region observed in recent decades. The most notable glaciological effect of this warming has been the emergence of pervasive surface melting on the two ice shelves in the summers prior to their disintegration.Indeed, the

O. Sergienko; D. R. Macayeal

2003-01-01

197

Basal Melt and Thickness Change of the Antarctic Ice Shelves Revealed by the Lagrangian Elevation Measurement from Satellite Laser Altimetry  

NASA Astrophysics Data System (ADS)

We present a novel method for estimating the elevation change on the Antarctic ice shelves using laser altimetry data from the Ice Cloud and land Elevation Satellite (ICESat; 2003-2009). Unlike the conventional crossover or repeat-track analysis fixed on the geodetic position, we estimate the elevation change rate at points fixed on the surface of moving ice, i.e. in the Lagrangian coordinate system. The ICESat ground tracks are relocated into the Lagrangian coordinate system based on the velocity field from the interferometric synthetic aperture radar (InSAR) and then the elevation change rate is measured from their crossover differences. The thickness change rates converted from the elevation change rates through a hydrostatic formula are applied to the mass conservation equation in the Lagrangian coordinate system, in order to derive the basal melt rate. In Lagrangian approach, the crossover difference is less affected by the small-scale surface relief on the moving ice, which causes the large uncertainty of elevation change rate in the conventional (Eulerian) crossover analysis. The basal melt derived from the mass conservation equation is also less sensitive to the noises of gridded ice thicknesses in the Largrangian approach than in the Eulerian approach. Our analysis provides a reliable map of basal melt rate and thickness change rate in the Antarctic ice shelves, which is a snapshot for the ICESat period. The highest ice thinning rates, accompanying strongest basal melts, are observed in the small ice shelves along the Amundsen Sea coast. In the Ross Ice Shelf, the ice thickness change is mainly controlled by the shutdown of Kamb Ice Stream. The ice thinning is dominant in the Filchner-Ronne Ice Shelf and strong within 150 km from the ice front.

Lee, C.; Seo, K.; Scambos, T.

2012-12-01

198

Quantum Melting of Charge Ice and Non-Fermi-Liquid Behavior: An Exact Solution for the Extended Falicov-Kimball Model in the Ice-Rule Limit  

NASA Astrophysics Data System (ADS)

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

Udagawa, Masafumi; Ishizuka, Hiroaki; Motome, Yukitoshi

2010-06-01

199

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

200

Volcano-Ice Interactions During Recent Eruptions of Aleutian Arc Volcanoes and Implications for Melt Water Generation  

NASA Astrophysics Data System (ADS)

Recent eruptions in Alaska (Redoubt 2009; Pavlof 2007, 2013; Veniaminof 2013) all involved ice eruptive-product interactions that led to variable amounts of melt water generation. Production of melt water during explosive eruptions is the primary mechanism for lahar generation, which is a significant and sometimes-deadly hazard at snow and ice clad volcanoes. During the 2009 eruption of Redoubt Volcano, pyroclastic flows produced by explosive destruction of lava domes swept across and eroded glacier ice and generated large quantities of melt water that formed correspondingly large lahars (107-109 m3) in the Drift River valley north of the volcano. Three of the twenty lahars generated during the eruption were large enough to threaten an oil storage facility 40 km from the volcano. During eruptions of Pavlof Volcano in 2007 and 2013 spatter-fed lava flows and minor pyroclastic flows descended over snow and ice on the upper flanks of the volcano and produced some melt water that generated lahars in the associated drainages. These lahars were smaller than those associated with the 2009 eruption of Redoubt Volcano because the melt water generation mechanism was different. At Veniaminof Volcano, a low-level eruption beginning in June 2013 produced small lava flows that flowed passively over glacier ice and produced only limited amounts of melt water. Although melt pits surrounding the lava flows eventually developed, the rate of melt water production was gradual and no significant outflows of water occurred. These eruptions and comparison with past events highlight the various mechanisms for melt water production during eruptive activity at snow and ice clad Alaskan volcanoes. Dynamic emplacement of eruptive products over glacier ice that involves significant erosion of ice and snow leads to production of large volumes of melt water. Less dynamic, but still energetic interactions such as those that have occurred at Pavlof Volcano, produce smaller amounts of melt and correspondingly smaller volume lahars whose distribution is controlled in part by changes in the location of the summit vent. Effusive, subaerial eruptions at Veniaminof Volcano result in the smallest amount of meltwater production, mainly because the lava-ice interaction is not very dynamic and only a small proportion of the heat flux goes to melt ice.

Waythomas, C. F.

2013-12-01

201

Mixing of the Immiscible: Hydrocarbons in Water-Ice near the Ice Crystallization Temperature.  

PubMed

Structural changes in hydrocarbon-doped water-ice during amorphous to crystalline phase conversion are investigated using polycyclic aromatic hydrocarbons (PAHs) as probes. We show that aggregation of impurity molecules occurs due to the amorphous-crystalline transition in ice, especially when they are hydrophobic molecules such as PAHs. Using ultraviolet-visible (UV-vis), Fourier-transform Infrared (FTIR), and laser-induced-fluorescence (LIF) spectroscopic techniques, we show that, although ice infrared absorption features change from a broad structureless band corresponding to amorphous ice to a sharp structured crystalline ice bands, simultaneously, sharper isolated PAH UV absorption features measured in the amorphous ice host turn broad upon ice crystallization. A simultaneous decrease in the monomer fluorescence and increase in the excimer emission band is observed, a clear indication for the formation of PAH molecular aggregates when amorphous ice is converted to crystalline ice at higher temperatures. Similar to the irreversible amorphous-crystalline phase transitions, the UV, fluorescence, and excimer emissions indicate that PAHs undergo irreversible aggregation. Our studies suggest that organic impurities exist as aggregates rather than monomers trapped in crystalline water-ice when cycled through temperatures that convert amorphous ice to crystalline ice, rendering a better insight into phenomena such as the formation of cometary crust. This aggregate formation also may significantly change the secondary reaction pathways and rates in impurity-doped ices in the lab, on Earth, in the solar system, and in the interstellar medium. PMID:25302532

Lignell, Antti; Gudipati, Murthy S

2015-03-19

202

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

203

Real time thermal imaging of high temperature semiconductor melts  

NASA Technical Reports Server (NTRS)

A real time thermal imaging system with temperature resolution better than + or - 1 C and spatial resolution of better than 0.5 mm was developed and applied to the analysis of melt surface thermal field distributions in both Czochralski and liquid encapsulated Czochralski (LEC) growth configurations. The melt is viewed in near normal incidence by a high resolution charge coupled device camera to which is attached a very narrow bandpass filter. The resulting image is digitized and processed using a pipelined pixel processor operating at an effective 40 million operations per second thus permitting real time high frequency spatial and temporal filtering of the high temperature scene. A multi-pixel averaging algorithm was developed which permits localized, low noise sensing of temperature variations at any location in the hot zone as a function of time. This signial is used to implement initial elements of a feedforward growth control scheme which is aimed at reducing disturbances to the melt caused by the batch nature of the growth process. The effect of magnetic melt stabilization on radial melt temperature distributions was measured using this technique. Problems associated with residual internal reflections and non-optimized path geometry are discussed.

Wargo, Michael J.

1988-01-01

204

Ice melting and downward transport of meltwater by two-phase flow in Europa's ice shell  

NASA Astrophysics Data System (ADS)

With its young surface, very few impact craters, and the abundance of tectonic and cryovolcanic features, Europa has likely been subjected to relatively recent endogenic activity. Morphological analyses of chaos terrains and double ridges suggest the presence of liquid water within the ice shell a few kilometers below the surface, which may result from enhanced tidal heating. A major issue concerns the thermal/gravitational stability of these water reservoirs. Here we investigate the conditions under which water can be generated and transported through Europa's ice shell. We address particularly the downward two-phase flow by solving the equations for a two-phase mixture of water ice and liquid water in one-dimensional geometry. In the case of purely temperate ice, we show that water is transported downward very efficiently in the form of successive porosity waves. The time needed to transport the water from the subsurface region to the underlying ocean varies between ˜1 and 100 kyr, depending mostly on the ice permeability. We further show that water produced in the head of tidally heated hot plumes never accumulates at shallow depths and is rapidly extracted from the ice shell (within less than a few hundred kiloyears). Our calculations indicate that liquid water will be largely absent in the near subsurface, with the possible exception of cold conductive regions subjected to strong tidal friction. Recently active double ridges subjected to large tidally driven strike-slip motions are perhaps the most likely candidates for the detection of transient water lenses at shallow depths on Europa.

Kalousová, Klára; Sou?ek, Ond?ej; Tobie, Gabriel; Choblet, Gaël.; ?adek, Ond?ej

2014-03-01

205

Formation of relief on Europa's surface and analysis of a melting probe movement through the ice  

NASA Astrophysics Data System (ADS)

These days, studies of planetary bodies' are of great interest. And of special interest are the icy moons of the giant planets like Jupiter and Saturn. Analysis of 'Voyager 1', 'Voyager 2', 'Galileo' and 'Cassini' spacecraft data showed that icy covers were observed on Jupiter's moons Ganymede, Europa and Calisto, and Saturn's moons Titan and Enceladus. Of particular interest is the relatively smooth surface of Europa. The entire surface is covered by a system of bands, valleys, and ridges. These structures are explained by the mobility of surface ice, and the impact of stress and large-scale tectonic processes. Also conditions on these moons allow speculation about possible life, considering these moons from an astrobiological point of view. To study the planetary icy body in future space missions, one of the problems to solve is the problem of design of a special device capable of penetrating through the ice, as well as the choice of the landing site of this probe. To select a possible landing site, analysis of Europa's surface relief formation is studied. This analysis showed that compression, extention, shearing, and bending can influence some arbitrarily separated section of Europe's icy surface. The computer simulation with the finite element method (FEM) was performed to see what types of defects could arise from such effects. The analysis showed that fractures and cracks could have various forms depending on the stress-strained state arising in their vicinity. Also the problem of a melting probe's movement through the ice is considered: How the probe will move in low gravity and low atmospheric pressure; whether the hole formed in the ice will be closed when the probe penetrates far enough or not; what is the influence of the probe's characteristics on the melting process; what would be the order of magnitude of the penetration velocity. This study explores the technique based on elasto-plastic theory and so-called 'solid water' theory to estimate the melting velocity and to study the melting process. Based on this technique, several cases of melting probe motion are considered, the velocity of the melting probe is estimated, the influence of different factors are studied and discussed, and an easy way to optimize the parameters of the probe is proposed.

Erokhina, O. S.; Chumachenko, E. N.; Dunham, D. W.; Aksenov, S. A.; Logashina, I. V.

2013-12-01

206

Shock Melting of Permafrost on Mars: Water Ice Multiphase Equation of State for Numerical Modeling and Its Testing  

NASA Technical Reports Server (NTRS)

The presence of water/ice/brine in upper layers of Martian crust affects many processes of impact cratering. Modeling of these effects promises better understanding of Martian cratering records. We present here the new ANEOS-based multiphase equation of state for water/ice constructed for usage in hydrocodes and first numerical experiments on permafrost shock melting. Preliminary results show that due to multiple shock compression of ice inclusions in rocks the entropy jump in shocked ice is smaller than in pure ice for the same shock pressure. Hence previous estimates of ice melting during impact cratering on Mars should be re-evaluated. Additional information is included in the original extended abstract.

Ivanov, B. A.

2005-01-01

207

accumulation, B (positive for melting), and the dif-ference in ice flux between the two gates per unit  

E-print Network

accumulation, B (positive for melting), and the dif- ference in ice flux between the two gates per is thickening (thinning) and ice flow is steady, then B would be lower (higher) than calcu- lated under steady), pp. 322­360. 28. D. S. Russell-Head, Ann. Glaciol. 1, 119 (1980). 29. S. Ushio, T. Takizawa

Palumbi, Stephen

208

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

209

The influence of cryo-hydrologic warming on the ice temperature in the ablation zone - insights from a computational model  

NASA Astrophysics Data System (ADS)

Each summer, a large amount of melt water is produced in the ablation zones of glaciers and ice sheets. This melt water does not travel over long distances on the ice, but a significant fraction enters the glacier and flows through en-glacial and sub-glacial hydrologic channels. Correspondingly, the en-glacial and sub-glacial hydrologic channel wall-temperatures are raised to the pressure melting point of ice. The thermal influence of these hydrologic processes is seldom incorporated in heat transfer models for glaciers and ice sheets. In a warming climate with increased melt water production, en-glacial and sub-glacial hydrologic processes can potentially influence the thermodynamics of ice sheets. Although the role of refreezing melt water in the firn of the accumulation zone is often accounted for to explain warmer near-surface temperatures, the role of melt water flow within a glacier is not considered in large ice sheet models. We propose a simple dual-column flow-line model to simulate the importance of cryo-hydrologic warming. Our approach considers two interacting vertical columns representing ice and the cryo-hydrologic system, with exchange of energy between the two columns. Each ice column is connected to next ice column upstream by means of horizontal advection. However, there is no coupling between adjacent cryo-hydrologic columns. The cryo-hydrologic heat exchange coefficient ? is defined as k/R2, where R is the characteristic spacing between en-glacial passages and k is the thermal conductivity of ice. Correspondingly, the characteristic time scale for cryo-hydrologic heat exchange is ?/R2, where ? is the thermal diffusivity of ice, and depends strongly on R. Our results suggest that for a characteristic spacing between en-glacial passages or R in the range of a few 10’s of meters, cryo-hydrologic warming has the potential to accelerate the warming of ice sheets, and thus increase ice flow velocities as the effective viscosity of ice decreases significantly with increasing temperature. The temperature profile of a flow-line in the Sermeq Avannarleq Glacier in Western Greenland is derived using a steady-state flow-line model incorporating cryo-hydrologic heat exchange. Our results show that for a rising equilibrium line over the last 25 years, the ice temperature rises by 9K to a new steady state temperature within a decade. Correspondingly, the ice velocity at the ice margin can increase by 60% even without invoking the influence of lubrication at the bed. The surface topography of the Sermeq Avannarleq Glacier shows a kink in the vicinity of the equilibrium line that may potentially be explained by cryo-hydrologic warming. The increased ice temperatures downstream of the equilibrium line will decrease the ice viscosity in this region, leading to an increase in ice velocity. Because the region just upstream of the equilibrium line remains cold, a sharp spatial velocity variation will occur, leading to a kink.

Rajaram, H.; Phillips, T. P.; Steffen, K.

2010-12-01

210

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

NASA Astrophysics Data System (ADS)

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

Rasmussen, Tine L.; Thomsen, Erik

2013-11-01

211

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

212

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

Microsoft Academic Search

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

C. C. Karmosky; D. J. Lampkin

2009-01-01

213

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

2002-01-01

214

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

215

Rapid increase in melt rates of Pine Island Glacier ice shelf during early stages of its retreat  

NASA Astrophysics Data System (ADS)

Observations beneath the floating section of Pine Island Glacier have revealed the presence of a subglacial ridge which rises up to 300m above the surrounding bathymetry. This topographic feature has likely served as a steady grounding line position, and Pine Island Glacier was at least partially grounded on the ridge until the early 1970s. Today the grounding line is situated approximately 40km further upstream, following an ongoing phase of rapid retreat. As a result, a large ocean cavity has formed behind the ridge, strongly controlling the ocean circulation beneath the ice shelf and modulating the ocean water properties that cause melting of the ice shelf in the vicinity of the grounding line. In order to understand how melt rates have changed during various phases of cavity formation, we use a high resolution ocean model to simulate the cavity circulation for a series of synthetic geometries. We show that the gap between the ridge and the bottom of the ice shelf strongly controls the inflow of warm bottom waters into the cavity, and hence influences the melt rates. Model results provide evidence for rapidly increasing melt rates at the onset of ice shelf thinning, but a weak change in melt rates once the gap between the ridge and the ice shelf has passed a threshold value of ?150m. At present the gap is well over 150m, suggesting that observed variability in melt rates is primarily controlled by other factors such as the depth of the thermocline.

De Rydt, Jan; Holland, Paul; Dutrieux, Pierre; Jenkins, Adrian

2013-04-01

216

Electric Charge Transfer Associated with Temperature Gradients in Ice  

Microsoft Academic Search

The development of electric potentials in ice crystals under the influence of temperature gradients is investigated both theoretically and experimentally. The maintenance of a steady temperature gradient across a piece of ice is accompanied by concentration gradients of H^+ and OH^- ions; because of the much greater mobility of H^+ ions, these diffuse more rapidly into the colder part of

J. Latham; B. J. Mason

1961-01-01

217

Tropical sea temperatures did not cause glacial melting  

NSDL National Science Digital Library

Three different model scenarios were compared to determine the effect of sea surface temperature (SST) on deglaciation. Results suggest that periods with warmer sea surface temperatures during the last glacial maximum also affected the atmospheric moisture supply, enhancing cloud cover that increased precipitation and decreased solar radiation over the ice sheets. The authors conclude that factors other than SST were more likely to induce the deglaciation.

Rodgers et al.

218

The influence of temperature gradient zone melting on microsegregation  

Microsoft Academic Search

Adding an algorithm for considering temperature gradient zone melting (TGZM) to an existing numerical model for predicting\\u000a microstructure and microsegregation allows the prediction of migration distances of dendrite arms and asymmetric concentration\\u000a distributions in the arms. Provided that detailed information on the time dependence of the temperature gradient as well as\\u000a the cooling rate is available from heat flow calculations,

T. Kraft; O. Pompe; H. E. Exner

1998-01-01

219

Substrate effect on the melting temperature of thin polyethylene films.  

PubMed

Strong dependence of the crystal orientation, morphology, and melting temperature (Tm) on the substrate is observed in the semicrystalline polyethylene thin films. The Tm decreases with the film thickness decrease when the film is thinner than a certain critical thickness, and the magnitude of the depression increases with increasing surface interaction. We attribute the large Tm depression to the decrease in the overall free energy on melting, which is caused by the substrate attraction force to the chains that competes against the interchain force which drives the chains to crystallization. PMID:16486656

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

2006-01-20

220

Velocity of sound in solid methane near melting temperatures  

E-print Network

in these crystals. 6 7 Hersfeld and Goeppert-Mayer and Born and his collaborators have attempted to relate the temperature variation of the elastic constants with the phenomenon of melting. ht the present time, there is no satisfactory theory of melting; however... ~Theor of Solids (McGraw-Hi. ll Book Co, Inc. , New York, 1940), p. 373. Z. Z. Z, ~E1 t' tt I~A1 tt1. IM I 01I. 1ty f Chicago Press, Chicago, 1948), p. 16. 6. K. Herzfeld and M. Goeppert-Mayer, Phys. Rev. 46, 995 (1934). 7. M. Born et al. , J. Chem...

Whitehead, John Martin

1968-01-01

221

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

NASA Astrophysics Data System (ADS)

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

Budke, C.; Koop, T.

2015-02-01

222

Marangoni Flow and Surface Tension of High Temperature Melts  

NASA Astrophysics Data System (ADS)

Marangoni flow plays an important role in the heat and mass transport for highly value-added high-temperature processes, such as crystal growth, welding, casting, and electron beam melting. For silicon single crystal growth, the effect of the oscillatory Marangoni flow on the introduction of growth striation was discussed by Chen and Wilcox for the first time in 1972 [1]. The existence of the Marangoni flow within molten silicon was proved through microgravity experiments in space on board a sounding rocket in 1983 by Eyer et al. [2], who found formation of growth striation in single crystals even under microgravity, where buoyancy-driven flow was suppressed. To explain the Marangoni effect at the melt surface, surface tension is essential. Keene [3] discussed the oxygen contamination in the surface tension measurement and recommended the use of a levitation technique, which is a containerless process and assures the contamination-free condition from measurement devices. It is well known that flow direction in the weld pool is dependent on surface contamination and that this is related to weldability [4, 5]. Flow direction is controlled by the temperature coefficient of surface tension for molten steels; contaminants are oxygen and sulfur. In the electron beam button melting system, the Marangoni flow is dominant because of intense heating at the melt surface [5]. In this chapter, surface tension of high temperature metallic melts is discussed from the viewpoint of the Marangoni effect in the value-added high temperature processes, particularly from the viewpoint of the effect of oxygen and sulfur. Theoretical treatment for oxygen adsorption is also discussed.

Hibiya, Taketoshi; Ozawa, Shumpei

223

Ice-melt rates by steam condensation during explosive subglacial eruptions  

NASA Astrophysics Data System (ADS)

Subglacial volcanism melts cavities in the overlying ice. These cavities may be flooded with meltwater or they may be fully or partially drained. We quantify, for the first time, heat transfer rates by condensation of steam on the walls and roof of a fully or partially drained subglacial eruption cavity. Our calculations indicate that heat fluxes of up to 1 MW m-2 may be obtained when the bulk vapor in the cavity is in free convection. This is considerably smaller than heat fluxes inferred from ice penetration rates in recent subglacial eruptions. Forcing of the convection by momentum transfer from an eruption jet may allow heat fluxes of up to 2 MW m-2, consistent with values inferred for the Gjálp 1996 subglacial eruption. Vapor-dominated cavities in which vapor-liquid equilibrium is maintained have thermal dynamic responses that are an order of magnitude faster than the equivalent flooded cavities.

Woodcock, D. C.; Gilbert, J. S.; Lane, S. J.

2015-02-01

224

Modeling Regolith Temperatures and Volatile Ice Processes (Invited)  

NASA Astrophysics Data System (ADS)

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

Mellon, M. T.

2013-12-01

225

Sea ice concentration, ice temperature, and snow depth using AMSR-E data  

Microsoft Academic Search

A summary of the theoretical basis and initial performance of the algorithms that are used to derive sea ice concentration, ice temperature, and snow depth on sea ice from newly acquired Earth Observing System-Aqua\\/Advanced Microwave Scanning Radiometer-EOS (AMSR-E) radiances is presented. The algorithms have been developed and tested using historical satellite passive microwave data and are expected to provide more

Josefino C. Comiso; Donald J. Cavalieri; Thorsten Markus

2003-01-01

226

Modeling the Influence of Antifreeze Proteins on Three-Dimensional Ice Crystal Melt Shapes using a Geometric Approach  

E-print Network

The melting of pure axisymmetric ice crystals has been described previously by us within the framework of so-called geometric crystal growth. Nonequilibrium ice crystal shapes evolving in the presence of hyperactive antifreeze proteins (hypAFPs) are experimentally observed to assume ellipsoidal geometries ("lemon" or "rice" shapes). To analyze such shapes we harness the underlying symmetry of hexagonal ice Ih and extend two-dimensional geometric models to three-dimensions to reproduce the experimental dissolution process. The geometrical model developed will be useful as a quantitative test of the mechanisms of interaction between hypAFPs and ice.

Jun Jie Liu; Yangzong Qin; Maya Bar Dolev; Yeliz Celik; J. S. Wettlaufer; Ido Braslavsky

2012-07-12

227

Skin Temperature Processes in the Presence of Sea Ice  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

228

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

229

Deposition Ice Nuclei Concentration at Different Temperatures and Supersaturations  

NASA Astrophysics Data System (ADS)

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

López, M. L.; Avila, E.

2013-05-01

230

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

231

High-Temperature Density of Lanthanide-Bearing Silicate Melts  

NASA Astrophysics Data System (ADS)

The lanthanides are of interest in the geosciences, despites usually occurring as minor or trace elements in rock-forming minerals although they can be essential constituents of some minerals. In general, they are partitioned more extremely than major elements making them more sensitive indicators of the petrological processes that occur. Therefore, they are a powerful tool in order to trace the processes involved in the petrogenesis of magmas, in the thermodynamical modelling to accurately predict the crystal-melt phase equilibria in a magma. The development of such models requires a reliable thermodynamic database which includes volumetric data available for both major and trace element oxide liquids.\\Efforts have been made to extend the volumetric database of silicate melts on a variety of multi-component systems for the most naturally abundant oxides. However, experimental data on other significant oxides, such as lanthanides, are lacking. Therefore, in order to fill this gap and to provide a new volumetric dataset, which will allow the available models in the literature to be extended to lanthanide-bearing liquids, we are conducting density measurements on various lanthanide-bearing silicate melts.\\In this paper, we present density measurements obtained in air for various lanthanide-bearing silicate melts (from cerium to lutetium including lanthanum). The present results suggest that the addition of lanthanide leads to an increase in density of the melt. In addition, the melt density at a given lanthanide content increases with increasing atomic number, with the exception of La. This preliminary volumetric dataset allows a first estimation of the partial molar volume of each lanthanide oxide liquids (i.e., the partial molar volumes calculated at 1550 K for the investigated lanthanide oxides range from 15 to 23 cm3/mol for Tm2O3 and Pr6O11, respectively). High-temperature density measurements on new compositions are in progress in order to determine the partial molar volume of lanthanide oxide liquids more accurately.

Courtial, P.; Dingwell, D.

2002-12-01

232

Ice nucleation behavior of biomass combustion particles at cirrus temperatures  

Microsoft Academic Search

Measurements of ice formation by biomass combustion particles generated in controlled laboratory burns were made using a continuous flow diffusion chamber operating in the temperature range between ?45 and ?60°C. These measurements are the first of their kind to investigate the role that such particles may play in ice formation in upper tropospheric clouds. Measurements of aerosol water uptake were

Paul J. DeMott; Markus D. Petters; Anthony J. Prenni; Christian M. Carrico; Sonia M. Kreidenweis; Jeffrey L. Collett; Hans Moosmüller

2009-01-01

233

Syntheses of neptunium trichloride and measurements of its melting temperature  

NASA Astrophysics Data System (ADS)

Neptunium trichloride (NpCl3) of high purity was synthesized by the solid state reaction of neptunium nitride with cadmium chloride. Lattice parameters of hexagonal NpCl3 were determined from the powder X-ray diffraction pattern to be a = 0.7428 ± 0.0001 nm and c = 0.4262 ± 0.0003 nm, which fairly agree with the reported values. The melting temperature of NpCl3 was measured on a sample of about 1 mg, hermetically encapsulated in a gold crucible with a differential thermal analyzer. The value determined was 1070 ± 3 K which is close to the recommended value (1075 ± 30 K) derived from the mean value of the melting temperature of UCl3 and of PuCl3.

Hayashi, Hirokazu; Takano, Masahide; Kurata, Masaki; Minato, Kazuo

2013-09-01

234

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

E-print Network

;2) Lower the pressure ­ Adiabatic rise of mantle with no conductive heat loss ­ Decompression melting could isothermal decompression How does the mantle melt?How does the mantle melt? #12;Why does the mantle melt? ...because of upwelling and isothermal decompression of the melt #12;Magma Formation · Two major mechanisms

Siebel, Wolfgang

235

Human neuronal tau promoting the melting temperature of DNA  

Microsoft Academic Search

The hyperchromic effect of ultraviolet spectroscopy shows that adding recombinant human neuronal tau to the solution of calf\\u000a thymus DNA will promote the melting temperature (T\\u000a m) from 67°C to 81°C. Similar result has been detected when adding tau to plasmid p Bluescript-II SK, by raising Tm from 75°C\\u000a to 85°C. The kinetics of thermal denaturation of DNA with tau

Qian Hua; Rongqiao He

2000-01-01

236

In situ visualization of crystallization inside high temperature silicate melts  

NASA Astrophysics Data System (ADS)

The present work is concerned with the real time in situ visualization of crystallization processes inside strongly supercooled silicate melts using optical projection technique. The crystallization experiments are carried out for forsterite composition under container-less conditions. Starting material is heated above its liquidus temperature (2169 K) using a high power CO2 laser and crystallization is initiated following rapid cooling. Three different values of supercooling (?T ?320, 400, and 500 K, calculated with respect to the liquidus temperature of forsterite composition as reference) are independently employed to initiate the nucleation process by adjusting the output power of CO2 laser. Primary findings of the study show that a suitably designed optical system is capable of imaging melt convection at temperatures as high as near liquidus and presents a novel approach for the prediction of resultant crystallization textures in real time nondestructively. Using the developed optical arrangement, formation of porphyritic-like textures and parallel-barred structures could be successfully visualized during the crystallization process. The results also reveal that for very large values of supercooling, it is possible to initiate nucleation from inside the melt droplet. The in situ predictions of resultant crystalline textures are compared with the textures revealed by photomicrographs of the corresponding thin sections and a good agreement is seen between the two observations.

Srivastava, Atul; Inatomi, Yuko; Tsukamoto, Katsuo; Maki, T.; Miura, Hitoshi

2010-06-01

237

Geophysical controls on C band polarimetric backscatter from melt pond covered Arctic first-year sea ice: Assessment using high-resolution scatterometry  

NASA Astrophysics Data System (ADS)

Geophysical controls on C band polarimetric backscatter from the discrete surface cover types which comprise advanced melt first-year sea ice (FYI): snow covered ice, bare ice, and melt pond; are assessed using polarimetric radar scatterometry from test sites representing high Arctic and marginal ice zones in the Canadian Arctic. Surface characterization data is used to evaluate the interaction of polarized radiation with each feature, and dominant scattering mechanisms are assessed in a regional context. High-resolution time series (diurnal) scatterometry and coincident atmospheric boundary layer profile data are used to explain linkages between ice-atmosphere interactions and polarimetric backscatter in a marginal ice zone. The co-polarization ratio for FYI melt ponds is shown to be distinct from snow covered ice or bare ice during early and peak phases of advanced melt, making it a candidate parameter for the unambiguous detection of pond formation and the inversion of melt pond fraction. The ratio displays an increasing trend with radar incidence angle in a manner consistent with Bragg surface scattering theory, though it is not predictable by a Bragg model. Cross-polarization backscatter intensity shows potential for discriminating the onset and duration of freeze events in a marginal ice zone, due to dominant backscatter from the snow cover adjacent to melt ponds. Preliminary results here outline the potential of covariance matrix derived polarimetric measurements for the inversion of advanced melt sea ice geophysical parameters, and provide a basis for the investigation of distributed targets in late season spaceborne polarimetric SAR scenes.

Scharien, R. K.; Yackel, J. J.; Barber, D. G.; Asplin, M.; Gupta, M.; Isleifson, D.

2012-08-01

238

Low melt rates with seasonal variability at the base of Fimbul Ice Shelf, East Antarctica, revealed by in situ interferometric radar measurements  

NASA Astrophysics Data System (ADS)

Basal melt is a major cause of ice shelf thinning affecting the stability of the ice shelf and reducing its buttressing effect on the inland ice. The Fimbul ice shelf (FIS) in Dronning Maud Land (DML), East Antarctica, is fed by the fast-flowing Jutulstraumen glacier, responsible for 10% of ice discharge from the DML sector of the ice sheet. Current estimates of the basal melt rates of the FIS come from regional ocean models, autosub measurements, and satellite observations, which vary considerably. This discrepancy hampers evaluation of the stability of the Jutulstraumen catchment. Here, we present estimates of basal melt rates of the FIS using ground-based interferometric radar. We find a low average basal melt rate on the order of 1 m/yr, with the highest rates located at the ice shelf front, which extends beyond the continental shelf break. Furthermore, our results provide evidence for a significant seasonal variability.

Langley, Kirsty; Kohler, Jack; Sinisalo, Anna; Øyan, Mats Jørgen; Hamran, Svein Erik; Hattermann, Tore; Matsuoka, Kenichi; Nøst, Ole Anders; Isaksson, Elisabeth

2014-11-01

239

GSA DATA REPOSITORY 2012265 Seasonal Laurentide Ice Sheet melting during the Mystery Interval  

E-print Network

). The second half was pulverized for homogeneity and a 50­80 mg aliquot was analyzed for stable isotope ratios the isotopic effects of temperature with the Mg/Ca-SST proxy and applying the Orbulina universa high for the same isotopic shift in GOM 18 OSW (Fig. DR2). #12;2 The 18 OGOM value is used to identify LIS melting

South Florida, University of

240

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

2013-08-01

241

Landscape transformation under influence of melting buried ice blocks (North Poland)  

NASA Astrophysics Data System (ADS)

The aim of the research was to decipher impacts, how dead ice melting can influence landscape transformation in the Lateglacial and early Holocene in Central Europe. Here, we present the paleoecological results from the middle section of the Wda river located in northern Poland (Central Europe), on the outwash plain formed during the Pomeranian phase of the last (Vistulian) glacial period ca 16,000 14C yrs BP. The Wda river has a typical polygenetic valley in young glacial areas of the northern central European lowlands. We reconstructed environmental changes using biotic proxies (plant macrofossil and pollen analyses) and geomorphological investigations. Abrupt changes in lithology and sediment structures show rapid changes and threshold processes in environmental conditions. The AMS 14C dating of terrestrial plant remains reveals an age for the basal sediments of 11 223 ± 23 cal yr BP coinciding with the Preboreal biozone. The results show the existence of buried ice blocks in northern Poland even at the beginning of the Holocene proving that locally discontinuous permafrost was still present at that time. Our study demonstrates a strong influence of melting buried ice blocks on the geomorphological development, hydrological changes in the catchment, and the biotic environment even in the early Holocene. This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution (ICLEA) of the Helmholtz Association. Financial support by the COST Action ES0907 INTIMATE is gratefully acknowledged. The research was supported by the National Science Centre Poland (grants No. NN 306085037 and NCN 2011/01/B/ST10/07367).

S?owi?ski, Micha?; B?aszkiewicz, Miros?aw; Brauer, Achim; Nory?kiewicz, Bo?ena; Ott, Florian; Tyszkowski, Sebastian

2014-05-01

242

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

243

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

244

Melt-Triggered Seismic Response in Hydraulically-Active Polar Ice: Observations and Methods  

NASA Astrophysics Data System (ADS)

Glacier ice responds to environmental forcing through changes in its sliding speed and mass balance. While these changes often occur on daily time scales or longer, they are initiated by brittle deformation events that establish hydrological pathways in hours or seconds and allow meltwater access to englacial or subglacial depths to facilitate ice motion. In this thesis, we (various contributing authors including myself) use seismic monitoring to detect and locate the creation and growth of some of these hydraulic pathways by monitoring their seismic emissions, or icequakes. More specifically, we address (1) what seismic observables, unavailable from other sensing methods, indicate an initial glaciogenic response to melt- water input and (2) if these comprise evidence of feedbacks that may destabilize polar ice under a warming climate. Supplemental to our scientific contributions, we advance statistical processing methods that demonstrably improve the capability of digital detectors at discriminating icequakes from astationary noise. We begin by interpreting geophysical observations collected from a dry-based, sub-freezing (--17 ° C), polar glacier environment (Taylor Glacier, ANT). By implementing a calibrated surface energy balance model, we estimate the timing and volume of surface meltwater generated during the collection of seismic data from a six-receiver geophone network. We proceed by contrasting these response characteristics with geophysical observations following an early (spring) supraglacial lake drainage within the lake-forming ablation zone of the Western Greenland Ice Sheet. Using measurements from a ˜5km-aperture geophone network, we find that the anticipated post-drainage icequakes are diurnally responsive, largely surficial in origin, and indicative of tensile fracturing from shallow cracks in the ice. The creation of the lake-drainage moulin appears to coincide with a shift in mean icequake source locations, and an increase in icequake occurrence at night relative to that in the day. Contrary to our expectations, we find that the timing of GPS-derived surface speeds do not clearly indicate this seismic activity on any given day. Rather, these icequakes are best explained by peaks in localized strain gradients that develop at night when decreased subglacial water flux likely increases variability in basal traction. Additionally, our results appear comprise the first detailed seismic observations targeted at an actively draining lake. Our last study addresses the apparent deficiency in observed basal icequakes detected from Greenland lake site. To explain the lack of deep icequakes, we compute thresholds on the magnitude of detectable basal events within the network and thereby illustrate that surficial icequakes with similar magnitudes and spectral content are more likely to be observed. By restricting our attention to seismic events that produce lower frequency waveforms, we find a population of nearly monochromatic, sub-1Hz, large magnitude ( M w ? 3) seismic events borne from remote glaciogenic sources. In contrast to surficial icequakes, these events occur without significant bias between day and/or night periods and are best explained as glacial earthquakes generated by sliding episodes or iceberg calving events in the vicinity of Jakobshavn Glacier. These events occur daily and not correlate with the presence of local, surficial seismicity. We conclude with three general assertions regarding melt-triggered response characteristics of polar ice. First, hydraulic connections established by fracture events do not necessarily result in seismogenic basal stick slip, and therefore cannot necessarily be observed with conventional GPS monitoring. This was demonstrated at Taylor Glacier. Here, meltwater input to a hydraulic pathway led to fracture growth deep within a cold glacier without any change in surface speed. Second, the presence of melt-triggered basal sliding does not necessarily induce a clear seismogenic basal response in the lakes regions. This was demonstrated on the Greenland Ice Sheet.

Carmichael, Joshua D.

245

Numerical modeling of the energy balance and the englacial temperature of Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

The surface mass and energy balance of ice sheets links the response of ice sheets to atmospheric forcing. Historically, ice sheet model have relied on empirical parameterizations of these surface processes (e.g., positive degree days). More recently, global and regional climate models (e.g., RACKMO, MAR) have begun to incorporate sophisticated surface process models in an attempt to simulate ice sheet mass balance using a more physically based modeling approach. In this study we explore the limits of simple downscaling techniques to obtain the appropriate atmospheric forcing for surface energy balance models from global reanalysis products and evaluate the partition of uncertainties associated with downscaling and with various albedo, turbulent energy transfer and densification parameterizations. To accomplish this we have developed a simple physically based numerical model of the coupled radiation, snow and ice system has been developed. The model is a one-dimensional multi-layer snow and ice model that accounts for both the surface energy balance and subsurface heating to evaluate the energy and mass balance in the upper part of Greenland Ice Sheet and calculates the surface energy balance, temperature and density evolution in the uppermost part of ice. It is run over the full annual cycle, simulating melting, temperature and density profiles throughout the seasons. We assess uncertainty in the forcing by driving the model using downscaled ECMWF ERA-Interim reanalysis data and comparing this with forcing derived from in situ AWS stations from Greenland Climate Network Automatic Weather Stations (AWS) data and perform sensitivity studies using a suite of parameterizations for the albedo, turbulent fluxes and densification.

Liu, X.; Bassis, J. N.

2012-12-01

246

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

247

The impact of ocean temperature and salinity stratification on buoyancy-driven meltwater flows next to ice shelves and glacier termini  

NASA Astrophysics Data System (ADS)

Melting of the undersides of floating ice shelves can impact the dynamics of ice flow, and this presents the challenge of modelling coupled ice-shelf and ocean interactions to achieve well-quantified predictions of sea level rise. Melting rates are controlled by the supply of heat and salt to the ice-ocean interface, which depend on both the details of turbulence and the temperature and salinity conditions in the underlying ocean. One such feedback on ice melting comes from the buoyancy-driven flow of fresh meltwater rising below the ice shelf, which shares dynamical similarities with meltwater flows rising along steep glacier termini. The strength of this flow and resulting melting rates are sensitive to the vertical stratification of temperature and salinity in the neighbouring ocean. To build theoretical insight into the role of ocean stratification, we apply a plume model to describe buoyancy-driven flow under a planar ice shelf lying above a stratified ocean. A range of background ocean temperature and salinity profiles are studied. Our plume model considers both persistent alongslope flows, or layered flows featuring multiple intrusions into the background ocean, with intrusions occurring after the plume density reaches a neutral buoyancy level compared to the background ocean density stratification. For flows with negligible subglacial discharge into a linear stratification, we develop approximate scaling laws for the dependence of melting rates on the temperature and salinity stratifications. The scaling laws are in good agreement with results from numerical simulations. Under appropriate conditions, these scaling laws may provide a computationally-efficient approximation to ice-shelf melting rates controlled by buoyancy-driven flows, in circumstances where the use of a more detailed ocean model proves impractical.

Magorrian, Samuel; Wells, Andrew

2014-05-01

248

Measurement of the size of intracellular ice crystals in mouse oocytes using a melting point depression method and the influence of intracellular solute concentrations  

Microsoft Academic Search

Characterization of intracellular ice formed during the cooling procedures of cells significantly benefits the development and optimization design of cryopreservation or cryosurgery techniques. In this study, we investigated the influence of the concentration of extracellular non-permeable and permeable solutes on the melting points of the intracellular ice in mouse oocytes using cryomicroscopy. The results showed that the melting points of

Xu Han; John K. Critser

2009-01-01

249

Electrons In Water-ices At Outer Solar System Temperatures  

NASA Astrophysics Data System (ADS)

Solid water-rich ice is an important constituent of our Solar System. The importance of both laboratory and in-situ observational work to make advances in this field cannot be overstated. Over the past several years, we have been studying VUV-radiation processing of organic impurities such as the extraterrestrially abundant polycyclic aromatic hydrocarbons (PAHs) embedded in water-ices between 20 K and 180 K. During these in-situ studies we discovered several counter-intuitive phenomena (See Gudipati and Allamandola, J. Phys. Chem. A 110, 9020, 2006 and references therein for details): 1) PAHs embedded in cryogenic water-ice are easily and efficiently ionized (>80%, i.e., near quantitative ion yields) to the cation form by VUV photons. 2) In water ice, PAH ionization energy is lowered by up to 2 eV compared to the gas-phase, in agreement with recent theoretical predictions. 3) PAH cations are stabilized in water ice to temperatures as high as 120 K. 4) Sequential photoionization leading to the formation and stabilization of doubly positively charged organic (PAH) species in water ice has also been found. Our recent laboratory studies have focused on the fate of electrons that are produced during PAH photoionization in the ice. Careful warm-up experiments suggest that indeed some electrons are stored over several hours in these ices. During warm-up of these ices between 20 K and 70 K, these stored electrons become mobilized and react with positively charged PAH ions in the ice. Taken together, these laboratory findings strongly suggest that ice rich trans-Saturnian icy objects including moons, comets, and KBOs, as well as some of Saturn's rings, can host ionized organic impurities and free electrons. These species have physical and chemical properties that can fundamentally alter ice properties such as color, strength, structure, energy-budget, reaction networks etc. Acknowledgments: Funded by NASA's Exobiology, Astrobiology, LTSA, and PG&G Programs

Gudipati, Murthy; Allamandola, L. J.

2006-09-01

250

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

251

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

PubMed

High-pressure H2O polymorphs among which ice VI and ice VII are abundant in the interiors of large icy satellites and exo-planets. Knowledge of the elastic properties of these pure H2O ices at high-temperature and high-pressure is thus crucial to decipher the internal structure of icy bodies. In this study we assess for the first time the pressure-volume-temperature (PVT) relations of both polycrystalline pure ice VI and ice VII at high pressures and temperatures from 1 to 9 GPa and 300 to 450 K, respectively, by using in situ synchrotron X-ray diffraction. The PVT data are adjusted to a second-order Birch-Murnaghan equation of state and give V0 = 14.17(2) cm(3)?mol(-1), K0 = 14.05(23) GPa, and ?0 = 14.6(14) × 10(-5) K(-1) for ice VI and V0 = 12.49(1) cm(3)?mol(-1), K0 = 20.15(16) GPa, and ?0 = 11.6(5) × 10(-5) K(-1) for ice VII. PMID:25217935

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

2014-09-14

252

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

SciTech Connect

High-pressure H{sub 2}O polymorphs among which ice VI and ice VII are abundant in the interiors of large icy satellites and exo-planets. Knowledge of the elastic properties of these pure H{sub 2}O ices at high-temperature and high-pressure is thus crucial to decipher the internal structure of icy bodies. In this study we assess for the first time the pressure-volume-temperature (PVT) relations of both polycrystalline pure ice VI and ice VII at high pressures and temperatures from 1 to 9 GPa and 300 to 450 K, respectively, by using in situ synchrotron X-ray diffraction. The PVT data are adjusted to a second-order Birch-Murnaghan equation of state and give V{sub 0} = 14.17(2) cm{sup 3}?mol{sup ?1}, K{sub 0} = 14.05(23) GPa, and ?{sub 0} = 14.6(14) × 10{sup ?5} K{sup ?1} for ice VI and V{sub 0} = 12.49(1) cm{sup 3}?mol{sup ?1}, K{sub 0} = 20.15(16) GPa, and ?{sub 0} = 11.6(5) × 10{sup ?5} K{sup ?1} for ice VII.

Bezacier, Lucile; Hanfland, Michael [European Synchrotron Radiation Facility, 6 rue Jules Horowitz, 38000 Grenoble (France); Journaux, Baptiste; Perrillat, Jean-Philippe; Cardon, Hervé; Daniel, Isabelle [Laboratoire de Géologie de Lyon, UMR 5276 CNRS, Ecole Normale Supérieure de Lyon – Université Claude Bernard Lyon 1, 2 rue Raphael Dubois, 69622 Villeurbanne Cedex (France)

2014-09-14

253

Burnup dependence of melting temperature of FBR mixed oxide fuels irradiated to high burnup  

NASA Astrophysics Data System (ADS)

The melting temperatures of FBR MOX fuels with Pu content of 28-30 wt.% irradiated to from 22.5 to 112.5 MWd kg -1 were measured using a rhenium inner capsule to hold the specimens. The rhenium inner capsule could prevent chemical reactions between fuels and tungsten materials which decrease the melting temperature. The melting temperatures were about 30 K higher than the previous data using tungsten capsules. The melting temperature decreases in a linear manner with burnup due to solid solution of fission products in fuels. However, the slopes of the lines plotting melting temperature versus burnup are almost similar to the previous data.

Hirosawa, Takashi; Sato, Isamu

2011-11-01

254

Extremophilic fungi in arctic ice: a relationship between adaptation to low temperature and water activity  

NASA Astrophysics Data System (ADS)

Little is known about fungal diversity in extremely cold regions. Low temperatures induce the formation of ice crystals and therefore also the creation of low water activity ( aw). These are the dominant factors in external chemistry that influence microbial biota in cold regions. Therefore, we have used selective low water activity media plus low incubation temperatures for the isolation of fungi from an Arctic environment. In comparison with the highest values of colony forming units (CFU) obtained on mesophilic media, considerably higher fungal CFU per litre of water were detected on low aw media, ranging from 1000 to 3000 l -1 in seawater, 6000 to 7000 l -1 in melted sea ice and up to 13,000 l -1 in melted glacier ice. The dominant taxa were ascomycetous and basidiomycetous yeasts, melanized fungi, mainly represented by the genera Cladosporium and Aureobasidium plus different species of the genus Penicillium. Preliminary taxonomic analyses revealed several new species and varieties. Further characterisations are needed to determine whether this diversity is due to geographic isolation, ecological conditions or independent evolutionary origin.

Gunde-Cimerman, N.; Sonjak, S.; Zalar, P.; Frisvad, J. C.; Diderichsen, B.; Plemenitaš, A.

255

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

256

The generation of martian floods by the melting of ground ice above dykes.  

PubMed

The surface of Mars is cut by long linear faults with displacements of metres to kilometres, most of which are thought to have been formed by extension. The surface has also been modified by enormous floods, probably of water, which often flowed out of valleys formed by the largest of these faults. By analogy with structures on Earth, we propose here that the faults are in fact the surface expression of dykes, and not of large-scale tectonic movements. We use a numerical model to show that the intrusion of large dykes can generate structures like Valles Marineris. Such dykes can provide a heat source to melt ground ice, and so provide a source of water for the floods that have been inferred to originate in some of the large valleys. PMID:9930697

McKenzie, D; Nimmo, F

1999-01-21

257

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

Microsoft Academic Search

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

M. J. Branney

1995-01-01

258

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

Microsoft Academic Search

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

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

2004-01-01

259

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

NASA Astrophysics Data System (ADS)

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

Budke, C.; Koop, T.

2014-09-01

260

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

261

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

Code of Federal Regulations, 2014 CFR

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

2014-04-01

262

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

Code of Federal Regulations, 2011 CFR

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

2011-04-01

263

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

Code of Federal Regulations, 2013 CFR

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

2013-04-01

264

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

Code of Federal Regulations, 2012 CFR

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

2012-04-01

265

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

Code of Federal Regulations, 2010 CFR

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

2010-04-01

266

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

NASA Astrophysics Data System (ADS)

Photo mapping of melt pond coverage on sea ice was undertaken in the Arctic during the summer of 2004 using an Aerosonde. Aerosondes are small, long endurance UAV designed to undertake a wide range of operations in a highly flexible and inexpensive mode. The Aerosonde conducts a defined mission in a completely autonomous mode. All flights are under the command of a ground controller who can change missions and respond to air traffic control requests, etc. An NSF-funded effort (Office of Polar Programs' Long Term Observations [LTO]) is now underway to deploy Aerosondes for routine mapping and atmospheric sounding missions in the Arctic. Aerosondes were deployed at Barrow, AK, during June, 2004 as part of the LTO effort. During this deployment, several flights were dedicated to examining the fractional coverage of melt ponds over sea ice in the Beaufort and Chukchi Seas, as part of a study funded by NASA. Melt ponds have been identified as a key feature in determining the amount of solar insulation absorbed by sea ice, and hence is a primary controller of the melt rate of the ice through the summer. Sea ice models have, to date, crudely parameterized ponds, due in part to a lack of large-scale observations of their temporal and spatial evolution. The NASA-funded study uses observations from the EOS sensor MODIS to estimate pond fraction over a large portion of the Beaufort and Chukchi, by examining several spectral (visible and near-infrared) MODIS bands and deducing melt pond coverage from the known spectral properties of ponds. The Aerosonde flights dedicated to the melt pond study were necessary to test the validity of the pond coverage estimated using the MODIS data. A downward-looking Olympus C-3030 digital camera was mounted within the Aerosonde to photograph the sea ice. The digital photos are analyzed to classify each photo according to the percentage cover of melt ponds, unponded ice, and open water. These estimates are compared to the values retrieved using MODIS for the same area of coverage. To enhance these comparisons, missions were flown with 10 km x 10 km grid patterns, with overlapping (along-track and cross-track) digital photos, which allow for comparison with 400 MODIS pixels (500 m resolution). Additional missions were designed to examine the evolution of pond coverage over sea ice off the coast of Point Barrow, Alaska. The sea ice in this area of interest was fast ice (i.e. not drifting ice) and served as an area where melt ponds can be observed during formation and their evolution through the summer. The Aerosonde team flew several flights paralleling Point Barrow and overlapping in a pattern that provided contiguous digital camera images of the fast ice from shore to a few km off the coast. These flights were repeated several times during June, providing imagery that will assist investigators in determining how pond fraction changes over this period. The technique and results of pond coverage estimation from airborne digital photography will be presented, as will comparisons to estimates retrieved using MODIS.

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

2004-12-01

267

Regional melt-pond fraction and albedo of thin Arctic first-year drift ice in late summer  

NASA Astrophysics Data System (ADS)

The paper presents a case study of the regional (?150 km) morphological and optical properties of a relatively thin, 70-90 cm modal thickness, first-year Arctic sea ice pack in an advanced stage of melt. The study combines in situ broadband albedo measurements representative of the four main surface types (bare ice, dark melt ponds, bright melt ponds and open water) and images acquired by a helicopter-borne camera system during ice-survey flights. The data were collected during the 8-day ICE12 drift experiment carried out by the Norwegian Polar Institute in the Arctic, north of Svalbard at 82.3° N, from 26 July to 3 August 2012. A set of > 10 000 classified images covering about 28 km2 revealed a homogeneous melt across the study area with melt-pond coverage of ? 0.29 and open-water fraction of ? 0.11. A decrease in pond fractions observed in the 30 km marginal ice zone (MIZ) occurred in parallel with an increase in open-water coverage. The moving block bootstrap technique applied to sequences of classified sea-ice images and albedo of the four surface types yielded a regional albedo estimate of 0.37 (0.35; 0.40) and regional sea-ice albedo of 0.44 (0.42; 0.46). Random sampling from the set of classified images allowed assessment of the aggregate scale of at least 0.7 km2 for the study area. For the current setup configuration it implies a minimum set of 300 images to process in order to gain adequate statistics on the state of the ice cover. Variance analysis also emphasized the importance of longer series of in situ albedo measurements conducted for each surface type when performing regional upscaling. The uncertainty in the mean estimates of surface type albedo from in situ measurements contributed up to 95% of the variance of the estimated regional albedo, with the remaining variance resulting from the spatial inhomogeneity of sea-ice cover.

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

2015-02-01

268

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

269

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

270

Isotopic probes of ice microphysics at cold temperatures  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

271

Ice nucleation behavior of biomass combustion particles at cirrus temperatures  

NASA Astrophysics Data System (ADS)

Measurements of ice formation by biomass combustion particles generated in controlled laboratory burns were made using a continuous flow diffusion chamber operating in the temperature range between -45 and -60°C. These measurements are the first of their kind to investigate the role that such particles may play in ice formation in upper tropospheric clouds. Measurements of aerosol water uptake were used to examine the role of hygroscopicity in low-temperature ice nucleation by biomass combustion particles. Ice formation by the smoke particles at below -45°C and below water saturation followed the temperature and relative humidity dependencies predicted for water activity-based homogeneous freezing within measurement uncertainties. As predicted, relative humidity dependence of homogeneous freezing fractions on hygroscopicity was weak in comparison with the temperature dependence for biomass particles of typical atmospheric sizes. The action of heterogeneous ice nucleation in or on these small smoke particles in the haze particle regime could not be distinguished within measurement uncertainties. Impedance of homogeneous freezing below -50°C was inferred for freezing higher number fractions of predominantly organic smoke particles separately reported to contain an abundance of large organic molecules, consistent with the recently predicted onset conditions for and impact of viscous or glassy aerosol phase states. Finally, we note that precision and accuracy requirements of instrumentation for resolving modest impacts (a few degrees less supercooling or a few percent lower relative humidity) of heterogeneous freezing, as compared with homogeneous freezing in the upper tropospheric temperature regime present difficulties for validating aerosol impacts on cirrus.

Demott, Paul J.; Petters, Markus D.; Prenni, Anthony J.; Carrico, Christian M.; Kreidenweis, Sonia M.; Collett, Jeffrey L.; Moosmüller, Hans

2009-08-01

272

LWC and Temperature Effects on Ice Accretion Formation on Swept Wings at Glaze Ice Conditions  

NASA Technical Reports Server (NTRS)

An experiment was conducted to study the effect of liquid water content and temperature on the critical distance in ice accretion formation on swept wings at glaze ice conditions. The critical distance is defined as the distance from the attachment line to tile beginning of the zone where roughness elements develop into glaze ice feathers. A baseline case of 150 mph, 25 F, 0.75 g/cu m. Cloud Liquid Water Content (LWC) and 20 micrometers in Water Droplet Median Volume Diameter (MVD) was chosen. Icing runs were performed on a NACA 0012 swept wing tip at 150 mph and MVD of 20 micrometers for liquid water contents of 0.5 g/cu m, 0.75 g/cu m, and 1.0 g/cu m, and for total temperatures of 20 F, 25 F and 30 F. At each tunnel condition, the sweep angle was changed from 0 deg to 45 deg in 5 deg increments. Casting data, ice shape tracings, and close-up photographic data were obtained. The results showed that decreasing the LWC to 0.5 g/cu m decreases the value of the critical distance at a given sweep angle compared to the baseline case, and starts the formation of complete scallops at 30 sweep angle. Increasing the LWC to 1.0 g/cu m increases the value of the critical distance compared to the baseline case, the critical distance remains always above 0 millimeters and complete scallops are not formed. Decreasing the total temperature to 20 F decreases the critical distance with respect to the baseline case and formation of complete scallops begins at 25 deg sweep angle. When the total temperature is increased to 30 F, bumps covered with roughness elements appear on the ice accretion at 25 deg and 30 deg sweep angles, large ice structures appear at 35 deg and 40 deg sweep angles, and complete scallops are formed at 45 deg sweep angle.

Vargas, Mario; Reshotko, Eli

2000-01-01

273

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

NASA Astrophysics Data System (ADS)

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

Fischer, Hubertus

2014-05-01

274

Deposition mode ice nucleation reexamined at temperatures below 200 K  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

275

Recrystallization of ice in ice cream during controlled accelerated storage  

Microsoft Academic Search

Accelerated ice recrystallization in a thin film of vanilla ice cream was studied on a cold stage microscope, housed in a refrigerated glove box. Sample temperature was held constant (within ±0.01 °C) or sinusoidally oscillated for 5 days. Changes in ice crystal size distribution were monitored using an image analysis technique. Several recrystallization mechanisms were observed. Melt-refreeze recrystallization was important

Daniel P. Donhowe; Richard W. Hartel

1996-01-01

276

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

277

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

278

Pressure dependence of the melting temperature of solids - Rare-gas solids  

NASA Technical Reports Server (NTRS)

A method presented by Schlosser et al. (1989) for analyzing the pressure dependence of experimental melting-temperature data is applied to rare-gas solids. The plots of the logarithm of the reduced melting temperature vs that of the reduced pressure are straight lines in the absence of phase transitions. The plots of the reduced melting temperatures for Ar, Kr, and Xe are shown to be approximately straight lines.

Schlosser, Herbert; Ferrante, John

1991-01-01

279

Temperature effects on atomic pair distribution functions of melts  

SciTech Connect

Using molecular dynamics simulations, we investigate the temperature-dependent evolution of the first peak position/shape in pair distribution functions of liquids. For metallic liquids, the peak skews towards the left (shorter distance side) with increasing temperature, similar to the previously reported anomalous peak shift. Making use of constant-volume simulations in the absence of thermal expansion and change in inherent structure, we demonstrate that the apparent shift of the peak maximum can be a result of the asymmetric shape of the peak, as the asymmetry increases with temperature-induced spreading of neighboring atoms to shorter and longer distances due to the anharmonic nature of the interatomic interaction potential. These findings shed light on the first-shell expansion/contraction paradox for metallic liquids, aside from possible changes in local topological or chemical short-range ordering. The melts of covalent materials are found to exhibit an opposite trend of peak shift, which is attributed to an effect of the directionality of the interatomic bonds.

Ding, J., E-mail: ding@jhu.edu; Ma, E. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States)] [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Xu, M. [I. Physikalisches Institut IA, RWTH Aachen University, Aachen 52056 (Germany)] [I. Physikalisches Institut IA, RWTH Aachen University, Aachen 52056 (Germany); Guan, P. F. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States) [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Beijing Computational Science Research Center, Beijing 100086 (China); Deng, S. W. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States) [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Department of Chemistry, East China University of Science and Technology, Shanghai 200237 (China); Cheng, Y. Q. [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)] [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2014-02-14

280

Elastic properties of model basaltic melt compositions at high temperatures  

NASA Astrophysics Data System (ADS)

To constrain the effect of composition and temperature on the elasticity of glasses and super-cooled liquids, acoustic velocities of samples in the pseudoternary system anorthite-diopside-forsterite (An-Di-Fo) were measured by Brillouin spectroscopy. Both the longitudinal and shear wave velocities were measured in the glassy state and into the region of super-cooled liquids. The glass transformation temperatures (Tg) inferred from the Brillouin measurements are equal to those obtained by earlier viscosity and thermal expansion measurements on the same samples, within the limits of experimental uncertainties. The variation of the elastic properties with temperature is approximately linear, both for the glassy state (below Tg) and in the super-cooled liquid state (above Tg). The temperature derivative of vibrational contributions to Young's (E), bulk (KS), and shear (G) modulus is approximately 6-12 times greater for super-cooled liquids than for glasses. In the glassy state the elastic moduli and their temperature derivatives are described by ideal mixing of molar properties of oxides. The pronounced variations with composition in the elastic and anelastic properties above the glass transformation can be related to changes in configurational contributions. The configurational contribution for chemically complex glasses (mixtures of the An-Di-Fo end-members) does not affect the overall compressibility at lower temperatures, whereas at higher temperatures they dominate the temperature derivatives of the moduli. In the super-cooled liquid state the temperature dependence of the vibrational elastic moduli for simple end-member compositions (An, Di) is much higher than for complex compositions. On the other hand, the configurational contribution to compressibility is higher for complex compositions than extrapolated from end-member compositions. Therefore the density and elastic properties of complex melts in the basaltic anorthite-diopside-forsterite-system cannot be easily approximated from the behavior of pure anorthite or diopside samples. Our results indicate that with increasing temperature, configurations with a higher bond strength were preferentially occupied. Isothermal relaxation times, varying between ?0.01 and ?1 s at 950°C, show a minimum for intermediate anorthite-diopside-compositions and are related to the maximum in configurational entropy.

Schilling, Frank R.; Sinogeikin, Stanislav V.; Hauser, Markus; Bass, Jay D.

2003-06-01

281

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

282

Femtosecond laser melting and resolidifying of high-temperature powder materials  

NASA Astrophysics Data System (ADS)

Though the development of laser additive manufacturing has achieved great success and has been widely used for various materials, it still has limited applications for materials with high melting temperature. In this report, we explore the feasibility of using femtosecond lasers to melt and resolidify these materials, as femtosecond lasers can generate MW-level peak power and create high local temperature. Tungsten, which has the highest melting point (3,422 ) among all the elements, and several other materials with melting temperature higher than 3,000 are chosen for the proof of concept. For the first time, femtosecond laser melting and resolidification of these high-temperature powder materials is achieved. Fabricated samples are characterized by scanning electron microscope and energy-dispersive X-ray spectroscopy. The results manifest that femtosecond laser melting can be an ideal solution for laser additive manufacturing of high-temperature materials.

Nie, Bai; Huang, Huan; Bai, Shuang; Liu, Jian

2015-01-01

283

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

E-print Network

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

Mills, Peter

2012-01-01

284

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

285

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

286

Arctic ice surface temperature retrieval from AVHRR thermal channels  

NASA Technical Reports Server (NTRS)

The relationship between AVHRR thermal radiances and the surface (skin) temperature of Arctic snow-covered sea ice is examined through forward calculations of the radiative transfer equation, providing an ice/snow surface temperature retrieval algorithm for the central Arctic Basin. Temperature and humidity profiles with cloud observations collected on an ice island during 1986-1987 are used. Coefficients that correct for atmospheric attenuation are given for three Arctic clear sky 'seasons', as defined through statistical analysis of the daily profiles, for the NOAA 7, 9, and 11 satellites. Modeled directional snow emissivities, different in the two split-window (11 and 12 micron) channels, are used. While the sensor scan angle is included explicitly in the correction equation, its effect in the dry Arctic atmosphere is small, generally less than 0.1 K. Using the split-window channels and scan angle, the rms error in the estimated ice surface temperature is less than 0.1 K in all seasons. Inclusion channel 3(3.7 microns) during the winter decreases the rms error by less than 0.003

Key, J.; Haeflinger, M.

1992-01-01

287

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

288

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

NASA Astrophysics Data System (ADS)

The carbon dioxide (CO2)-carbonate chemistry of sea-ice melt and co-located, contemporaneous seawater has rarely been studied in sea-ice-covered oceans. Here, we describe the CO2-carbonate chemistry of sea-ice melt (both above sea-ice as "melt ponds" and below sea-ice as "interface waters") and mixed-layer properties in the western Arctic Ocean in the early summer of 2010 and 2011. At 19 stations, the salinity (∼0.5 to <6.5), dissolved inorganic carbon (DIC; ∼20 to <550 ?mol kg-1) and total alkalinity (TA; ∼30 to <500 ?mol kg-1) of above-ice melt pond water was low compared to the co-located underlying mixed layer. The partial pressure of CO2 (pCO2) in these melt ponds was highly variable (∼<10 to >1500 ?atm) with the majority of melt ponds acting as potentially strong sources of CO2 to the atmosphere. The pH of melt pond waters was also highly variable ranging from mildly acidic (6.1 to 7) to slightly more alkaline than underlying seawater (>8.2 to 10.8). All of the observed melt ponds had very low (<0.1) saturation states (?) for calcium carbonate (CaCO3) minerals such as aragonite (?aragonite). Our data suggest that sea-ice generated alkaline or acidic type melt pond water. This melt water chemistry dictates whether the ponds are sources of CO2 to the atmosphere or CO2 sinks. Below-ice interface water CO2-carbonate chemistry data also indicated substantial generation of alkalinity, presumably owing to dissolution of CaCO3 in sea-ice. The interface waters generally had lower pCO2 and higher pH/?aragonite than the co-located mixed layer beneath. Sea-ice melt thus contributed to the suppression of mixed-layer pCO2, thereby enhancing the surface ocean's capacity to uptake CO2 from the atmosphere. Our observations contribute to growing evidence that sea-ice CO2-carbonate chemistry is highly variable and its contribution to the complex factors that influence the balance of CO2 sinks and sources (and thereby ocean acidification) is difficult to predict in an era of rapid warming and sea-ice loss in the Arctic Ocean.

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

2014-12-01

289

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

290

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

292

Determination of DNA Melting Temperatures in Diffusion-Generated Chemical Gradients  

E-print Network

Determination of DNA Melting Temperatures in Diffusion-Generated Chemical Gradients Tim Liedl-nucleotide resolution in a micro- fluidic setup, stable gradients of the denaturing agent formamide were generated by means of diffusion. Forma- mide lowers the melting temperature of DNA, and a given formamide

Ludwig-Maximilians-Universität, München

293

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

E-print Network

DSC Evidence for Microstructure and Phase Transitions in Polyethylene Melts at High Temperatures polyethylenes of types HDPE, LDPE, and LLDPE. DSC data were obtained for a range of heating and cooling rates previous rheology findings of order and high-temperature transitions in polyethylene melts. Introduction

Hussein, Ibnelwaleed A.

294

Regional scale albedo of first year Arctic drift ice during summer melt estimated from synthesis of in situ measurements and airborne imagery  

NASA Astrophysics Data System (ADS)

The paper presents the results of analysis of the radiative properties of first year sea ice in advanced stages of melt. The presented technique is based on the upscaling in situ point measurements of surface albedo to the regional (150 km) spatial scale using aerial photographs of sea ice captured by a helicopter borne camera setup. The sea ice imagery as well as in situ snow and ice data were collected during the eight day ICE12 drift experiment carried out by the Norwegian Polar Institute in the Arctic north of Svalbard at 83.5 N during 27 July-03 August 2012. In total some 100 ground albedo measurements were made on melting sea ice in locations representative of the four main types of sea ice surface identified using the discriminant analysis -based classification technique. Some 11000 images from a total of six ice survey flights adding up to some 770 km of flight tracks covering about 28 km2 of sea ice surface were classified to yield the along-track distributions of four major surface classes: bare ice, dark melt ponds, bright melt ponds and open water. Results demonstrated a relative homogeneity of sea ice cover in the study area allowing for upscaling the local optical measurements to the regional scale. For the typical 10% open water fraction and 25% melt pond coverage, with a ratio of dark to bright ponds of 2 identified from selected images, the aggregate scale surface albedo of the area was estimated to be 0.42(0.40;0.44). The confidence intervals on the estimate were derived using the moving block bootstrap approach applied to the sequences of classified sea ice images and albedo of the four surface classes treated as random variables. Uncertainty in the mean estimates of local albedo from in situ measurements contributed some 65% to the variance of the estimated regional albedo with the remaining variance to be associated with the spatial inhomogeneity of sea ice cover. The results of the study are of relevance for the modeling of sea ice processes in climate simulations. It particularly concerns the period of summer melt when the optical properties of sea ice undergo substantial changes which the existing sea ice models experience most difficulties to accurately reproduce. That phase of a season is especially crucial for climate and ecosystem processes in the polar regions.

Divine, Dmitry; Granskog, Mats A.; Hudson, Stephen R.; Pedersen, Christina A.; Karlsen, Tor I.; Gerland, Sebastian

2014-05-01

295

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

296

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

Microsoft Academic Search

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

James Marti; Konrad Mauersberger

1993-01-01

297

A Comparison of Sea Ice Type, Sea Ice Temperature, and Snow Thickness Distributions in the Arctic Seasonal Ice Zones with the DMSP SSM/I  

NASA Technical Reports Server (NTRS)

Global climate studies have shown that sea ice is a critical component in the global climate system through its effect on the ocean and atmosphere, and on the earth's radiation balance. Polar energy studies have further shown that the distribution of thin ice and open water largely controls the distribution of surface heat exchange between the ocean and atmosphere within the winter Arctic ice pack. The thickness of the ice, the depth of snow on the ice, and the temperature profile of the snow/ice composite are all important parameters in calculating surface heat fluxes. In recent years, researchers have used various combinations of DMSP SSMI channels to independently estimate the thin ice type (which is related to ice thickness), the thin ice temperature, and the depth of snow on the ice. In each case validation efforts provided encouraging results, but taken individually each algorithm gives only one piece of the information necessary to compute the energy fluxes through the ice and snow. In this paper we present a comparison of the results from each of these algorithms to provide a more comprehensive picture of the seasonal ice zone using passive microwave observations.

St.Germain, Karen; Cavalieri, Donald J.; Markus, Thorsten

1997-01-01

298

The Effect of Prolonged Holding at Pasteurization Temperature on the Properties of an Ice Cream Mix  

Microsoft Academic Search

This investigation was started as a result of a question raised by the Research Committee of the International Association of Ice Cream Manu- facturers, as to what effect prolonged holding of an ice cream mix at pas- teurization temperature would have on the properties of the mix and quality of the ice cream. It is common practice in ice cream

W. H. Martin

1932-01-01

299

Methane efflux from high-latitude lakes during spring ice melt  

Microsoft Academic Search

Ice cores removed from shallow ice-covered tundra lakes near Barrow, Alaska, and taiga lakes near Anchorage, Alaska, exhibit increasing concentrations of methane with depth. Methane concentrations in the ice cores increased from 0 muM in the top 15 cm sections to a maximum of 23 muM in the lowest 15 cm sections of tundra lake ice and to a maximum

Allan R. Phelps; Kim M. Peterson; Martin O. Jeffries

1998-01-01

300

Methane efflux from high-latitude lakes during spring ice melt  

Microsoft Academic Search

Ice cores removed from shallow ice-covered tundra lakes near Barrow, Alaska, and taiga lakes near Anchorage, Alaska, exhibit increasing concentrations of methane with depth. Methane concentrations in the ice cores increased from 0 (tM in the top 15 cm sections to a maximum of 23 (tM in the lowest 15 cm sections of tundra lake ice and to a maximum

Allan R. Phelps; Kim M. Peterson; Martin O. Jeffries

1998-01-01

301

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

302

New borehole-derived results on temperatures at the base of the Fennoscandian ice sheet  

NASA Astrophysics Data System (ADS)

During the last few years, a data base of deep boreholes (>1000 m )in the area of the Fennoscandian ice sheet has been collected, including boreholes from Russia, Poland, Finland, Sweden and Norway. All of these are supposed to have recorded local basal ice conditions during the last glacial cycle. However, at each of these sites we are confronted with particular problems of interpretation. Here, we will concentrate on two very deep boreholes, namely the Outokumpu ICDP borehole (OKU, ?2500 m) and a set of boreholes of intermediate depth (up to 1300 m) in the immediate meighborhood of the Kola superdeep borehole SG3. In the first case, OKU, we have developed a strategy combining the use of a traditional variational inversion of thye Tikhonov type, with a MCMC approach for the exploration of the associated uncertainty. A wide distribution around the result of the variational approach was chosen, with a time dependent temporal correlation length reflecting the loss of resolution back in time. The results fit very well with region independent results from different proxies, multi-proxy reconstructions, and instrumental data. They also are consistent with surface temperatures derived from recent calibrated ice sheet models. The SAT-GST offset independently derived from shallow borehole observations in the area was a crucial step to obtain theses results. The second case, SG3, has been studied a long time, and no final result was obtained regarding the question whether the observed heat flow density profile is caused by paleoclimate, fluid flow, or both. Earlier studies, as well as forward modelling using the results of the aforementioned ice sheet model indicate that paleoclimate alone can not explain the observations. We tested the model derived from the set of shallow boreholes against the temperature log from the main superdeep SG3, which, in contrast to these, transects the main high-permeability zone. The comparison led to a favorable results, and is also qualitatively consistent with other data reported in earlier Russian publications. However, for the SG3 case, which involves fluid flow processes, there are still important open questions. These are related to some of the assumptions made in the modeling and inversion process. The temperature conditions at the base of the ice sheet are surely not it's only effect: the high pressures induced but the ice load are known to drive melt water deep into the subsurface, with unknown temperature effects. Moreover, the crustal deformation related to isostatic effects probably influence large-scale permeability, in particular if older structures can be reactivated. These questions will be discussed in the light or recent modelling results obtained by groups active in nuclear waste disposal research, and which may open new research perspectives in the future.

Rath, Volker; Vogt, Christian; Mottaghy, Darius; Kukkonen, Ilmo; Tarasov, Lev

2014-05-01

303

Subpixel variability of MODIS albedo retrievals and its importance for ice sheet surface melting in southwestern Greenland's ablation zone  

NASA Astrophysics Data System (ADS)

On the Greenland ice sheet, albedo declined across 70% of its surface since 2000, with the greatest reduction in the lower 600 m of the southwestern ablation zone. Because albedo plays a prominent role in the ice sheet surface energy balance, its decline has resulted in near doubling of meltwater production. To characterize ice sheet albedo, Moderate Imaging Spectrometer (MODIS) surface albedo products are typically used. However, it is unclear how the spatial variability of albedo within a MODIS pixel influences surface melting and whether it can be considered a linear function of albedo. In this study, high spatiotemporal resolution measurements of spectral albedo and ice sheet surface ablation were collected along a ~ 1.3 km transect during June 2013 within the Akuliarusiarsuup Kuua (AK) River watershed in southwest Greenland. Spectral measurements were made at 325-1075 nm using a Analytical Spectral Devices (ASD) spectroradiometer, fitted with a Remote Cosine Receptor (RCR). In situ albedo measurements are compared with the daily MODIS albedo product (MCD43A) to analyze how space, time, surface heterogeneity, atmospheric conditions, and solar zenith angle geometry govern albedo at different scales. Finally, analysis of sub-pixel albedo and ablation reveal its importance on meltwater production in the lower parts of the ice sheet margin.

Moustafa, S.; Rennermalm, A. K.; Roman, M. O.; Koenig, L.; Smith, L. C.; Schaaf, C.; Wang, Z.; Mioduszewski, J.

2013-12-01

304

Signal and noise in four ice-core records from the Agassiz Ice Cap, Ellesmere Island, Canada: details of the last millennium for stable isotopes, melt and solid conductivity  

Microsoft Academic Search

Four ice cores and two deep pit\\/auger sequences from the top of the Agassiz Ice Cap have been variously analysed for ?(O18), ECM (solid conductivity) and ice melt-layer stratigraphy. The high- resolution data are presented on time scales covering about the last 1000 years. The 8 time series are compared and the noise examined in terms of snow-drifting and wind-scouring

David A. Fisher; Roy M. Koerner

1994-01-01

305

Alternative ice shelf equilibria determined by ocean environment  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

306

Melting Temperature and Partial Melt Chemistry of H2O-Saturated Mantle Peridotite to 11 Gigapascals  

PubMed

The H2O-saturated solidus of a model mantle composition (Kilborne Hole peridotite nodule, KLB-1) was determined to be just above 1000°C from 5 to 11 gigapascals. Given reasonable H2O abundances in Earth's mantle, an H2O-rich fluid could exist only in a region defined by the wet solidus and thermal stability limits of hydrous minerals, at depths between 90 and 330 kilometers. The experimental partial melts monotonously became more mafic with increasing pressure from andesitic composition at 1 gigapascal to more mafic than the starting peridotite at 10 gigapascals. Because the chemistry of the experimental partial melts is similar to that of kimberlites, it is suggested that kimberlites may be derived by low-temperature melting of an H2O-rich mantle at depths of 150 to 300 kilometers. PMID:9092469

Kawamoto; Holloway

1997-04-11

307

Constraining the equation of state of fluid H2O to 60 GPa using the melting curve of Ice VII and the formation of Mg(OH)2 in the MgO-H2O system.  

NASA Astrophysics Data System (ADS)

The physical properties of fluid H2O are important geologically over a large range of pressure and temperature. Shock-wave data have served as the main resource for the derivations of many equations of state for fluid H2O. Direct measurements of the specific volume of water are required to test the validity of these models; however, direct measurements at elevated pressures and temperatures are difficult and, as a result, rare. The study presented here sought to determine the PVT properties of Ice VII along the melting curve at pressures > 20 GPa using the a Mao-Bell type diamond anvil cell with an external Mo-wire resistance heater. Small grains of MgO, gold and a relatively large volume of H2O were loaded in a sample chamber drilled in a pre-indented Re-gasket. The temperature of the experiment was determined by placing a thermocouple between the diamond anvil and Re-gasket, directly against the surface of the diamond. The experiments were conducted on beam line X17C at the Brookhaven National Synchrotron Light Source using the Energy Dispersive X-ray Diffraction (EDXD) technique. The unit cells of Ice VII, MgO, and gold were monitored during the experiment with gold being used as an internal pressure calibrant. The methodology was to use the disappearance of the diffraction pattern of Ice VII with the production of brucite following the reaction of fluid H2O with MgO. Generally, experiments would follow the following sequence as temperature was increased: 1.) slight drop in pressure, 2.) the appearance of diffraction lines indicative of brucite, and 3.) total disappearance of Ice VII diffraction lines and noticeable drop in pressure (up to ~2 GPa at the highest pressures). The appearance of brucite would always proceed the disappearance of Ice VII diffraction lines. The data suggest that brucite formed as soon as fluid H2O became available whereas Ice VII melted over a small range over temperature (<50 K). The melting curve for Ice VII from 3-60 GPa can be related by: P(GPa)=10.448 - 0.02375*(T)- 4.1826x10-5*(T2) + 1.3114x10-7*(T3) where T is temperature in Kelvin. The molar volume of Ice VII along the melting curve was found to be related by: P (GPa) = -0.1791 + 2017.7*exp(-0.5912*V) where V is the molar volume (cm3/mol). We used the melting curve of Ice VII to constrain the density of fluid H2O along the melting curve by taking the pressure derivative of the Gibbs Free Energy difference between Ice VII and fluid H2O. Comparison of these results suggests that the previously stated equations of state of fluid H2O overestimate the molar volume of water at pressures > 45 GPa.

Frank, M. R.; Fei, Y.

2002-12-01

308

Effect of temperature on condensation equilibrium in synthesis of the copolyester vectra in a melt  

Microsoft Academic Search

It was shown that the equilibrium concentration of CH\\u000a 3COOH in a melt of this copolyester is low and is proportional to the square of its vapor pressure above the polymer melt,\\u000a while the effective distribution constant of CH3COOH between the gas phase and the melt decreases as the temperature increases. Based on an analysis of the experimental data,\\u000a a

A. K. Kuznetsov; L. V. Khanzutina; L. N. Mizerovskii

1997-01-01

309

Measurement of the Melting Point Temperature of Several Lithium-Sodium-Beryllium Fluoride Salt (Flinabe) Mixtures  

SciTech Connect

The molten salt Flibe, a combination of lithium and beryllium fluorides studied for molten salt fission reactors, has been proposed as a breeder and coolant for fusion applications. The melting points of 2LiF-BeF{sub 2} and LiF-BeF{sub 2} are 460 deg. C and 363 deg. C, but LiF-BeF{sub 2} is rather viscous and has less lithium for breeding. In the Advanced Power Extraction (APEX) Program, concepts with a free flowing liquid for the first wall and blanket were investigated. Flinabe (a mixture of LiF, BeF{sub 2} and NaF) was selected for a molten salt design because a melting temperature below 350 deg. C appeared possible and this provided an attractive operating temperature window for a reactor. To confirm that a ternary salt with a low melting temperature existed, several combinations of the fluoride salts, LiF, NaF and BeF{sub 2}, were melted in a stainless steel crucible under vacuum. One had an apparent melting temperature of 305 deg. C. The test system, preparation of the mixtures, melting procedures and temperature curves for the melting and cooling are presented along with the apparent melting points. Thermal modeling of the salt pool and crucible is reported in an accompanying paper.

McDonald, J.M; Nygren, R.E.; Lutz, T.J.; Tanaka, T.J; Ulrickson, M.A.; Boyle, T.J.; Troncosa, K.P. [Sandia National Laboratories (United States)

2005-04-15

310

High Strain-Rate Response of High Purity Aluminum at Temperatures Approaching Melt  

SciTech Connect

High-temperature, pressure-shear plate impact experiments were conducted to investigate the rate-controlling mechanisms of the plastic response of high-purity aluminum at high strain rates (10{sup 6} s{sup -1}) and at temperatures approaching melt. Since the melting temperature of aluminum is pressure dependent, and a typical pressure-shear plate impact experiment subjects the sample to large pressures (2 GPa-7 GPa), a pressure-release type experiment was used to reduce the pressure in order to measure the shearing resistance at temperatures up to 95% of the current melting temperature. The measured shearing resistance was remarkably large (50 MPa at a shear strain of 2.5) for temperatures this near melt. Numerical simulations conducted using a version of the Nemat-Nasser/Isaacs constitutive equation, modified to model the mechanism of geometric softening, appear to capture adequately the hardening/softening behavior observed experimentally.

Grunschel, S E; Clifton, R J; Jiao, T

2010-01-28

311

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

312

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

313

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

314

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

315

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

NASA Astrophysics Data System (ADS)

Understanding the evolution of melt ponds on Arctic sea ice is important for climate model parameterisations, weather forecast models and process studies involving mass, energy and biogeochemical exchanges across the ocean-sea ice-atmosphere interface. A field campaign was conducted in a region of level first-year sea ice (FYI) in the central Canadian Arctic Archipelago (CAA), during the summer of 2012, to examine the potential for estimating melt pond fraction (fp) from satellite synthetic aperture radar (SAR). In this study, 5.5 GHz (C-band) dual co- (HH + VV - horizontal transmit and horizontal receive + vertical transmit and vertical receive) and cross-polarisation (HV + HH - horizontal transmit and vertical receive + horizontal transmit and horizontal receive) radar scatterometer measurements of melt-pond-covered FYI are combined with ice and pond properties to analyse the effects of in situ physical and morphological changes on backscatter parameters. Surface roughness statistics of ice and ponds are characterised and compared to the validity domains of the Bragg and integral equation model (IEM) scattering models. Experimental and model results are used to outline the potential and limitations of the co-polarisation ratio (VV / HH) for retrieving melt pond information, including fp, at large incidence angles (?35°). Despite high variability in cross-polarisation ratio (HV / HH) magnitudes, increases at small incidence angles (<30°) are attributed to the formation of ice lids on ponds. Implications of the results for pond information retrievals from satellite C-, L- and P-band SARs are discussed.

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

2014-11-01

316

Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants: II. Krafft temperature and melting temperature.  

PubMed

The melting temperature T(M) of two series of dimeric (gemini) surfactants, the alkanediyl-alpha,omega-bis(dodecyl and hexadecyl dimethylammonium bromide), referred to as 12-s-12 and 16-s-16, respectively (s = carbon number of the alkanediyl spacer), and the Krafft temperature T(K) of 1 wt% aqueous solutions of these surfactants have been measured. The melting temperature of the solid surfactant increases with the carbon number m of the alkyl chain. For each surfactant series, T(M) goes through a maximum at s close to 5, irrespective of the value of m. For the 12-s-12 series, T(M) goes through a minimum at s = 10 to 12. At a constant value of s, the value of T(K) increases with m. The variations of T(M) and T(K) with s show some correlation, with T(K) decreasing when T(M) increases and vice versa. The results are discussed in relation to the solution properties of the investigated surfactants. PMID:16290787

Zana, Raoul

2002-08-01

317

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

SciTech Connect

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

Emuna, M.; Mayo, M.; Makov, G. [Materials Engineering Department, Ben-Gurion University of the Negev, 84105 Beer-Sheva (Israel)] [Materials Engineering Department, Ben-Gurion University of the Negev, 84105 Beer-Sheva (Israel); Greenberg, Y.; Caspi, E. N.; Yahel, E. [Physics Department, Nuclear Research Centre-Negev, 84190 Beer-Sheva (Israel)] [Physics Department, Nuclear Research Centre-Negev, 84190 Beer-Sheva (Israel); Beuneu, B. [Laboratoire Léon Brillouin CEA/Saclay, 91191 Gif-Sur-Yvette Cedex (France)] [Laboratoire Léon Brillouin CEA/Saclay, 91191 Gif-Sur-Yvette Cedex (France)

2014-03-07

318

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

PubMed

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

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

2011-09-21

319

Thermal Diffusivity for III-VI Semiconductor Melts at Different Temperatures  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

320

Melting temperature of metal polycrystalline nanowires electrochemically deposited into the pores of anodic aluminum oxide.  

PubMed

The arrays of metallic nanowires are considered as promising precursors for 1D semiconductor nanostructures after appropriate treatment at temperatures close to the melting point. Therefore the melting behaviour of the metallic structures in oxide templates is a key parameter for the subsequent conversion process. The present paper focuses on understanding of the effect of mechanical stress generated during heating on the melting point of the metal nanowires deposited into the pores of anodic alumina. Extremely high local compressive stress appears due to the difference in the thermal coefficients of the oxide template and nanowires inside the pores. The effect of the composite structural parameter that may be related to the concentration of nanowires on the melting temperature has been investigated. A numerical model predicting the melting point has been developed for composites with indium, tin, and zinc nanowires. The simulation results obtained using the suggested model were compared with the experimental data. PMID:25101924

Shilyaeva, Yu I; Bardushkin, V V; Gavrilov, S A; Silibin, M V; Yakovlev, V B; Borgardt, N I; Volkov, R L; Smirnov, D I; Zheludkevich, M L

2014-09-28

321

Defects Can Increase the Melting Temperature of DNA-Nanoparticle Assemblies  

E-print Network

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

Harris, Nolan C

2006-01-01

322

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

323

Temperatures in the earth's core from melting-point measurements of iron at high static pressures  

Microsoft Academic Search

The most reliable method for determining the temperature gradient at the earth's core is the estimation of Fe and Fe-rich compounds' melting temperature at the pressure of the inner core boundary. Attention is presently given to melting-point measurements on Fe and Fe-O compounds at up to 2 Mbar. An extrapolation of these results to 3.3 Mbar yields an inner core

R. Boehler

1993-01-01

324

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

Microsoft Academic Search

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

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

2003-01-01

325

Measurement of the melting point temperature of several lithium-sodium-beryllium fluoride salt (FLINABE) mixtures.  

SciTech Connect

The molten salt Flibe, a combination of lithium and beryllium flourides, was studied for molten salt fission reactors and has been proposed as a breeder and coolant for the fusion applications. 2LiF-BeF{sub 2} melts at 460 C. LiF-BeF{sub 2} melts at a lower temperature, 363 C, but is rather viscous and has less lithium breeder. In the Advanced Power Extraction (APEX) Program, concepts with a free flowing ternary molten salt for the first wall surface and blanket were investigated. The molten salt (FLiNaBe, a ternary mixture of LiF, BeF2 and NaF) salt was selected because a melting temperature below 350 C that would provide an attractive operating temperature window for a reactor application appeared possible. This information came from a Russian binary phase diagram and a US ternary phase diagram in the 1960's that were not wholly consistent. To confirm that a ternary salt with a low melting temperature existed, several combinations of the fluoride salts, LiF, NaF and, BeF{sub 2}, were melted in a small stainless steel crucible under vacuum. The proportions of the three salts were selected to yield conglomerate salts with as low a melting temperature as possible. The temperature of the salts and the crucible were recorded during the melting and subsequent re-solidification using a thermocouple directly in the salt pool and two thermocouples embedded in the crucible. One mixture had an apparent melting temperature of 305 C. Particular attention was paid to the cooling curve of the salt temperature to observe evidence of any mixed intermediate phases between the fully liquid and fully solid states. The clarity, texture, and thickness were observed and noted as well. The test system, preparation of the mixtures, and the melting procedure are described. The temperature curves for the melting and cooling of each of the mixtures are presented along with the apparent melting points. Thermal modeling of the salt pool and crucible was also done and is reported in a separate paper.

Boyle, Timothy J.; Troncosa, Kenneth P.; Nygren, Richard Einar; Lutz, Thomas Joseph; McDonald, Jimmie M.; Tanaka, Tina Joan; Ulrickson, Michael Andrew

2004-09-01

326

The Met Office Hadley Centre sea ice and sea surface temperature data set, version 2: 1. Sea ice concentrations  

NASA Astrophysics Data System (ADS)

We present a new version of the sea ice concentration component of the Met Office Hadley Centre sea ice and sea surface temperature data set, HadISST.2.1.0.0. Passive microwave data are combined with historical sources, such as sea ice charts, to create global analyses on a 1° grid from 1850 to 2007. Climatology was used when no information about the sea ice was available. Our main aim was to create a homogenous data set by calculating and applying bias adjustments using periods of overlaps between the different data sources used. National Ice Center charts from 1995 to 2007 have been used as a reference to achieve this. In particular, large bias adjustments have been applied to the passive microwave data in both the Antarctic and Arctic summers. Overall, HadISST.2.1.0.0 contains more ice than HadISST1.1, with higher concentrations, shorter marginal ice zones, and larger extents and areas in some regions and periods. A new method for estimating the concentrations within the ice pack using the distance from the ice edge has been developed and evaluated. This was used when only the extents were known or the original concentration fields were heterogeneous. A number of discontinuities in the HadISST1.1 record are no longer found in HadISST.2.1.0.0.

Titchner, Holly A.; Rayner, Nick A.

2014-03-01

327

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

328

Can changes in the atmospheric circulation make Atlantic Water available for melting Arctic sea ice?  

NASA Astrophysics Data System (ADS)

At the moment the Arctic sea ice is shielded from the warm Atlantic water at mid-depth by a well-developed halocline. If the heat content of the Atlantic layer would become available to the surface of the ocean, that could impact the development of the ice cover enormously. Coupled climate models contributing to the 4th assessment report of the IPCC project an ice free Arctic until the end of this century with this halocline either intact or even thickened. However, given the large sea ice extent reductions in recent years and the apparent inability of most climate models to reproduce the recent sea ice decline, we are exploring mechanisms that could weaken or even dissolve the halocline within a few decades. Before substantially increased fresh water input through precipitation and run-off can strengthen the halocline later in the 21st century, there is the possibility that changing atmospheric pressure patterns can redistribute fresh water such that the halocline in certain areas becomes weak enough to allow tapping of the Atlantic heat reservoir. To investigate this possibility we use experiments with an ocean-sea ice model (NAOSIM) and an atmospheric forcing that reflects e. g. the increasing importance of the Arctic Dipole sea level pressure pattern compared to the annular mode.

Koeberle, Cornelia; Gerdes, Ruediger

2010-05-01

329

Effective Temperature in an Interacting Vertex System: Theory and Experiment on Artificial Spin Ice  

E-print Network

for a range of field step sizes (Hs) and for two lattice geometries, square ice and hexagonal ice,Effective Temperature in an Interacting Vertex System: Theory and Experiment on Artificial Spin Ice [10], and from experiments of Brownian motion in vibrofluidized grains, in which it increases

330

Sea ice trends in the Antarctic and their relationship to surface air temperature during 19792009  

E-print Network

Sea ice trends in the Antarctic and their relationship to surface air temperature during 1979 in the Antarctic. It is found that the SAT variation from Goddard Institute for Space Studies (GISS) is the best ice and SAT in the Antarctic during 1979­2009. The Antarctic sea ice extent (SIE) shows an increased

Wang, Chunzai

331

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

332

A Temperature, Scarp and Ice Flow Model of the Northern Remnant Ice Cap on Mars  

NASA Astrophysics Data System (ADS)

Climate history from several hundreds of thousand years has been recorded in the terrestrial ice sheets. Drilling deep ice cores though the ice sheets and analyzing the ice and the impurities has assessed this climate history. The visible stratification that is seen the troughs in the polar deposits on Mars, indicate that the climate history of Mars has been recorded in the Martian ice cap as it is the case for the terrestrial ice sheets. If the polar caps on Mars accumulate under present climate the accumulation rates are very low and even under high obliquity climates the accumulation rates are much lower than for the terrestrial ice sheets. Lower accumulation rates yield thinner yearly layers and consequently more years are presents in an e.g. 3 km thick ice cap. Several million years of Martian climate history could present in the 3-4 km thick Martian ice caps. Additional information can be found in the original extended abstract.

Larsen, J.

2000-08-01

333

Ice nucleation in the upper troposphere: Sensitivity to aerosol number density, temperature, and cooling rate  

NASA Technical Reports Server (NTRS)

We have investigated the processes that control ice crystal nucleation in the upper troposphere using a numerical model. Nucleation of ice resulting from cooling was simulated for a range of aerosol number densities, initial temperatures, and cooling rates. In contrast to observations of stratus clouds, we find that the number of ice crystals that nucleate in cirrus is relatively insensitive to the number of aerosols present. The ice crystal size distribution at the end of the nucleation process is unaffected by the assumed initial aerosol number density. Essentially, nucleation continues until enough ice crystals are present such that their deposition growth rapidly depletes the vapor and shuts off any further nucleation. However, the number of ice crystals nucleated increases rapidly with decreasing initial temperature and increasing cooling rate. This temperature dependence alone could explain the large ice crystal number density observed in very cold tropical cirrus.

Jensen, E. J.; Toon, O. B.

1994-01-01

334

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

PubMed

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

Ewert, Marcela; Deming, Jody W

2014-08-01

335

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

Microsoft Academic Search

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

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

336

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

337

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

E-print Network

control on the subglacial distribution and flow of water5,62. The geometry is 351 prescribed using a 2008 SPOT surface DEM at 40m-resolution63, and a 500 m bed 352 DEM produced from ice surface and thickness measurements from NASA's 353 Operation Ice... during the past 614 decade. Proceedings of the National Academy of Sciences of the United States 615 of America 108, 8978-8983, doi:10.1073/pnas.1017313108 (2011). 616 617 618 Acknowledgements 619 This project was funded by the UK Natural...

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

2014-09-29

338

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

NASA Astrophysics Data System (ADS)

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

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

339

dnaMATE: a consensus melting temperature prediction server for short DNA sequences.  

PubMed

An accurate and robust large-scale melting temperature prediction server for short DNA sequences is dispatched. The server calculates a consensus melting temperature value using the nearest-neighbor model based on three independent thermodynamic data tables. The consensus method gives an accurate prediction of melting temperature, as it has been recently demonstrated in a benchmark performed using all available experimental data for DNA sequences within the length range of 16-30 nt. This constitutes the first web server that has been implemented to perform a large-scale calculation of melting temperatures in real time (up to 5000 DNA sequences can be submitted in a single run). The expected accuracy of calculations carried out by this server in the range of 50-600 mM monovalent salt concentration is that 89% of the melting temperature predictions will have an error or deviation of <5 degrees C from experimental data. The server can be freely accessed at http://dna.bio.puc.cl/tm.html. The standalone executable versions of this software for LINUX, Macintosh and Windows platforms are also freely available at the same web site. Detailed further information supporting this server is available at the same web site referenced above. PMID:15980538

Panjkovich, Alejandro; Norambuena, Tomás; Melo, Francisco

2005-07-01

340

Melting temperatures of the ZrO{sub 2}-MOX system  

SciTech Connect

Severe accidents occurred at the Fukushima Daiichi Nuclear Power Plant Units 1-3 on March 11, 2011. MOX fuels were loaded in the Unit 3. For the thermal analysis of the severe accident, melting temperature and phase state of MOX corium were investigated. The simulated coriums were prepared from 4%Pu-containing MOX, 8%Pu-containing MOX and ZrO{sub 2}. Then X-ray diffraction, density and melting temperature measurements were carried out as a function of zirconium and plutonium contents. The cubic phase was observed in the 25%Zr-containing corium and the tetragonal phase was observed in the 50% and 75%Zr-containing coria. The lattice parameter and density monotonically changed with Pu content. Melting temperature increased with increasing Pu content; melting temperature were estimated to be 2932 K for 4%Pu MOX corium and 3012 K for 8%Pu MOX corium in the 25%ZrO{sub 2}-MOX system. The lowest melting temperature was observed for 50%Zr-containing corium. (authors)

Uchida, T.; Hirooka, S.; Kato, M.; Morimoto, K. [Japan Atomic Energy Agency, 4-33, Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194 (Japan); Sugata, H.; Shibata, K.; Sato, D. [Inspection Development Company, 4-33, Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194 (Japan)

2013-07-01

341

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

Microsoft Academic Search

Ice creams were prepared that varied only in the percentage of milk fat (0.1, 3, 7, or 10%) and the corresponding total solids. All mixes were formulated to have similar freezing points and percentages of water frozen. Quantitative descriptive analysis was used to develop a ballot, which was then used by a trained sensory panel to assess the appearance, flavor,

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

1999-01-01

342

Melting temperature of heavy quarkonium with a holographic potential up to sub-leading order  

E-print Network

A calculation of the melting temperatures of heavy quarkonium states with the holographic potential was introduced in the work of\\cite{DF}. In this paper, we consider the holographic potential including its sub-leading order, we find this correction lowers the dissociation temperatures of heavy quarkonium.

Zi-qiang Zhang; Yan Wu; De-fu Hou

2015-04-10

343

Study of melting and freezing processes of water for application to ice thermal energy storage system  

Microsoft Academic Search

This thesis presents the results of a study of the solid-liquid phase change process of water in a rectangular enclosure for application to thermal energy storage systems. The work performed combined experimental results with analytical and numerical methods to develop computer models of the system. Experiments were performed to obtain data to verify the models under various melting and freezing

Liang Yong

1993-01-01

344

Characterization of Superhydrophobic Surfaces for Anti-icing in a Low-Temperature Wind Tunnel  

SciTech Connect

In this study, a closed loop low-temperature wind tunnel was custom-built and uniquely used to investigate the anti-icing mechanism of superhydrophobic surfaces in regulated flow velocities, temperatures, humidity, and water moisture particle sizes. Silica nanoparticle-based hydrophobic coatings were tested as superhydrophobic surface models. During tests, images of ice formation were captured by a camera and used for analysis of ice morphology. Prior to and after wind tunnel testing, apparent contact angles of water sessile droplets on samples were measured by a contact angle meter to check degradation of surface superhydrophobicity. A simple peel test was also performed to estimate adhesion of ice on the surfaces. When compared to an untreated sample, superhydrophobic surfaces inhibited initial ice formation. After a period of time, random droplet strikes attached to the superhydrophobic surfaces and started to coalesce with previously deposited ice droplets. These sites appear as mounds of accreted ice across the surface. The appearance of the ice formations on the superhydrophobic samples is white rather than transparent, and is due to trapped air. These ice formations resemble soft rime ice rather than the transparent glaze ice seen on the untreated sample. Compared to untreated surfaces, the icing film formed on superhydrophobic surfaces was easy to peel off by shear flows.

Swarctz, Christopher [Stevens Institute of Technology, Hoboken, New Jersey; Alijallis, Elias [Stevens Institute of Technology, Hoboken, New Jersey; Hunter, Scott Robert [ORNL; Simpson, John T [ORNL; Choi, Chang-Hwan [Stevens Institute of Technology, Hoboken, New Jersey

2010-01-01

345

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

NASA Technical Reports Server (NTRS)

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 of Pb, which shows enrichments up to a factor of 500. An apparent anticorrelation between the Ni-content and trace element concentration was observed in both types of spherules. The fractionation patterns of the iron and chondritic spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

Chevallier, P.; Wang, J.; Jehanno, C.; Maurette, M.; Sutton, S. R.

1986-01-01

346

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

347

Correlation and Trend Studies of the Sea Ice Cover and Surface Temperatures in the Arctic  

NASA Technical Reports Server (NTRS)

Co-registered and continuous satellite data of sea ice concentrations and surface ice temperatures from 1981 to 1999 are analyzed to evaluate relationships between these two critical climate parameters and what they reveal in tandem about the changing Arctic environment. During the 18-year period, the actual Arctic ice area is shown to be declining at a rate of 3.1 +/- 0.4 % /decade while the surface ice temperature has been increasing at 0.4 +/- 0.2 K /decade. Yearly anomaly maps also show that the ice concentration anomalies are predominantly positive in the 1980s and negative in the 1990s while surface temperature anomalies were mainly negative in the 1980s and positive in the 1990s. The yearly ice concentration and surface temperature anomalies are shown to be highly correlated indicating a strong link especially in the seasonal region and around the periphery of the perennial ice cover. The surface temperature data are also especially useful in providing the real spatial scope of each warming (or cooling) phenomenon that usually extends beyond the boundaries of the sea ice cover. Studies of the temporal variability of the summer ice minimum also reveal that the perennial ice cover has been declining at the rate of 6.6% /decade while the summer surface ice temperature has been increasing at the rate of 1.3 K /decade. Moreover, high year-to-year fluctuations in the minimum ice cover in the 1990s may have caused reductions in average thickness of the Arctic sea ice cover.

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

2001-01-01

348

The influence of Greenland ice sheet melting on the Atlantic meridional overturning circulation during past and future warm periods: a model study  

NASA Astrophysics Data System (ADS)

The sensitivity of the climate system to changes in radiative forcing is crucial for our understanding of past and future climates. Especially important are feedbacks related to melting of ice sheets like the Greenland ice sheet (GIS) and its potential impact on the Atlantic meridional overturning circulation (AMOC). These effects are likely to delay and dampen predicted long-term warming trends. Estimates of climate sensitivity may be deduced from palaeoclimate-reconstructions, but this raises the question whether past climate sensitivity is applicable to the future. Therefore we have analysed the impact of GIS melt water on the AMOC strength in two past warm climates (last interglacial and early present interglacial) and three future scenarios with three different model parameter sets. These model parameter sets represent three different model sensitivities to freshwater perturbation: low, moderate and high. In both the moderate and high sensitivity versions, we find for lower GIS melt rates (below 54 mSv, Sv = 106 m3/s) a clear difference between past and future warm climates in the sensitivity of the AMOC to GIS melt. This difference is connected to the convective activity in the Labrador Sea and the amount of additional surface freshening due to sea ice melting. In contrast, for higher GIS melt rates (over 54 mSv) we find similar reductions of the AMOC strength in all cases. Considering the low sensitivity version of our model, we find that for all GIS melt rates the influence of freshwater forcing on the AMOC is independent of the background climate. Our results and implications are thus strongly determined by the parameter set considered in our model. Nonetheless, our results from two out of three model versions suggest that proxy-based reconstructions of past AMOC sensitivity to GIS melt are likely to be misleading if interpreted for future applications.

Blaschek, M.; Bakker, P.; Renssen, H.

2015-04-01

349

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

E-print Network

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

Tamio Yamazaki

2014-10-06

350

Antarctica Ice  

NSDL National Science Digital Library

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

National Geographic

351

Water-melt interaction in hydrous magmatic systems at high temperature and pressure  

NASA Astrophysics Data System (ADS)

Experimental data on the structure and properties of melts and fluids relevant to water-melt interaction in hydrous magmatic systems in the Earth's interior have been reviewed. Complex relationships between water solubility in melts and their bulk composition [Al/Si-ratio, metal oxide/(Al + Si) and electron properties of metal cations] explain why water solubility in felsic magmas such as those of rhyolite and andesite composition is significantly greater than the water solubility in basalt melts. The silicate solubility in aqueous fluid is also significantly dependent on composition with metal oxide/(Al + Si) and electron properties of the metal cations, the dominant variables. Hydrogen bonding is not important in hydrous fluids and melts at temperatures above 500°C to 550°C and does not, therefore, play a role in hydrous magmatic systems. The properties of hydrous melts and aqueous solutions are governed by how the silicate speciation ( Q n species, where n is the number of bridging oxygen in an individual species) varies with bulk composition, silicate composition, temperature, and pressure. The reactions that describe the interactions are similar in melts, fluids, and supercritical fluids. The degree of melt polymerization caused by dissolved water varies with melt composition and total water content. Silicate- and alkali-rich felsic magmatic melts are more sensitive to water content than more mafic magmas. Transport and configurational properties of hydrous magmatic melts can be modeled with the aid of the Q n speciation variations. Liquidus and melting phase relations of hydrous systems also can be described in such terms, as can minor and trace element partition coefficients. Stable isotope fractionation (e.g., D/H) can also be rationalized in this manner. Critical to these latter observations is the high silicate concentration in aqueous fluids. These components can enhance solubility of minor and trace elements by orders of magnitude and change the speciation of H and D complexes so that their fractionation factors change quite significantly. Data from pure silicate-H2O systems cannot be employed for these purposes.

Mysen, Bjorn

2014-12-01

352

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

NASA Astrophysics Data System (ADS)

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 anorthite-wollastonite-gehlenite (An-Wo-Geh) compatibility triangle were determined on glassy and liquid samples using a combination of calorimetry and dilatometry. The melts have either 0.5 or 1 non-bridging oxygens per tetrahedraly coordinated cations. The volumes at room temperature were derived from density measurements using the Archimedean buoyancy method. Each sample had a cooling-heating history of 10-10 K/min at 298K and a precise dimension of the samples allowed calculation of the density from the sample geometry at room temperature. The thermal expansion coefficient of the glass from 298K to the glass transition interval was measured by a dilatometer and the heat capacity was measured using a differential scanning calorimeter over a 298-1135K temperature range The thermal expansion coefficient and the heat flow was determined at a heating rate of 10 K/min on glasses which was previously cooled at 10 K/min. Supercooled liquid molar thermal expansivities were indirectly determined by combining differential scanning calorimetric and dilatometric measurements assuming that kinetics of enthalpy and shear relaxation are equivalent. This low-temperature combined determination of supercooled liquid density, molar volume and molar expansivities was tested against high-temperature data obtained by using the Lange-Carmichael (1987), Lange (1997) and Courtial-Dingwell (1999) model. The best linear fit provides a combination of data presented in this study and high temperature data calculated using the Courtial-Dingwell (CAS) model. This dilatometric/calorimetric method of liquid molar expansivity determination greatly increases the temperature range accessible for thermal expansion measurements. These results contrast strongly with those obtained for geologic multicomponent melts, as well as anorthite-diopside eutectic and diopside melts, which exhibit a clear temperature-dependence of expansivity. The temperature-dependence of the thermal expansivity of melts is herewith confirmed to be a sensitive function of composition. This leads us to speculate that its origins may indeed lie in the temperature-dependence of the coordination number of specific cations with temperature.

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

2004-12-01

353

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

NASA Technical Reports Server (NTRS)

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

Brun, Edmond

1938-01-01

354

Adhesion of Polymer Composite Melt to PTFE at Elevated Temperature  

NASA Astrophysics Data System (ADS)

A novel technique for measuring the adhesive force between a thin molten polyester composite film and a PTFE surface is presented in the paper. The molten film was prepared by first depositing powdery composite particles on a substrate and then heating the powdery film on the substrate to the test temperature through a heated pressure nip between two conformable rollers comprising a PTFE overcoat at a speed up to 400 mm/s. The adhesive force is measured by wedging a bendable metal knife into the interface between the molten film and PTFE near the exit of the heating nip. Strain gauges were mounted on both sides of the metal knife. The differential strain gauge reading resulting from the degree of the knife bending is calibrated against standard weights. The technique was used to investigate the effects of the substrate, substrate roughness, molten film thickness, temperature and type of wax additive on the adhesion of the molten composite film to PTFE. On the effects of temperature and type of wax, we found that the adhesive force remains relatively constant at low temperature, and then drops significantly, in some instances to zero, as the temperature further increases. A phenomenological model is proposed to explain the effects of main temperature and the wax additive. The model is evidenced by the surface segregation of wax from the polyester composite film as determined by XPS.

Pan, David; Debies, Thomas; McVeigh, Dan

2007-03-01

355

Correlation between the surface temperature and thickness of Arctic sea ice  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

356

Ocean rises are products of variable mantle composition, temperature and focused melting  

NASA Astrophysics Data System (ADS)

Ocean ridges, where Earth's tectonic plates are pulled apart, range from more than 5-km depth in the Arctic to 750 m above sea level in Iceland. This huge relief is generally attributed to mantle plumes underlying mantle hotspots--areas of voluminous volcanism marked by ocean islands. The plumes are thought to feed the mantle beneath adjacent ocean ridges. This process results in thickened crust and ridge elevation to form ocean rises. The composition of mid-ocean ridge basalt, a direct function of mantle composition and temperature, varies systematically along ocean rises, but in a unique way for each different rise. Here we use thermodynamic calculations of melt-evolution pathways to show that variations in both mantle temperature and source composition are required to explain the chemical make-up of rise basalts. Thus, lateral gradients in mantle temperature cannot be uniquely determined from basalt chemistry, and ocean rises can be supported by chemically buoyant mantle or by robust mantle plumes. Our calculations also indicate that melt is conserved and focused by percolative flow towards the overlying ridge, progressively interacting with the mantle to shallow depth. We conclude that most mantle melting occurs by an overlooked mechanism, focused melting, whereas fractional melting is a secondary process that is important largely at shallow depth.

Dick, Henry J. B.; Zhou, Huaiyang

2015-01-01

357

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

358

Melting analysis on microbeads in rapid temperature-gradient inside microchannels for single nucleotide polymorphisms detection.  

PubMed

A continuous-flow microchip with a temperature gradient in microchannels was utilized to demonstrate spatial melting analysis on microbeads for clinical Single Nucleotide Polymorphisms (SNPs) genotyping on animal genomic DNA. The chip had embedded heaters and thermometers, which created a rapid and yet stable temperature gradient between 60?°C and 85?°C in a short distance as the detection region. The microbeads, which served as mobile supports carrying the target DNA and fluorescent dye, were transported across the temperature gradient. As the surrounding temperature increased, the fluorescence signals of the microbeads decayed with this relationship being acquired as the melting curve. Fast DNA denaturation, as a result of the improved heat transfer and thermal stability due to scaling, was also confirmed. Further, each individual microbead could potentially bear different sequences and pass through the detection region, one by one, for a series of melting analysis, with multiplex, high-throughput capability being possible. A prototype was tested with target DNA samples in different genotypes (i.e., wild and mutant types) with a SNP location from Landrace sows. The melting temperatures were obtained and compared to the ones using a traditional tube-based approach. The results showed similar levels of SNP discrimination, validating our proposed technique for scanning homozygotes and heterozygotes to distinguish single base changes for disease research, drug development, medical diagnostics, agriculture, and animal production. PMID:25553186

Li, Kan-Chien; Ding, Shih-Torng; Lin, En-Chung; Wang, Lon Alex; Lu, Yen-Wen

2014-11-01

359

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

Microsoft Academic Search

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

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

2010-01-01

360

On the influence of debris in glacier melt modelling: a new temperature-index model accounting for the debris thickness feedback  

NASA Astrophysics Data System (ADS)

The increase of rockfalls from the surrounding slopes and of englacial melt-out material has led to an increase of the debris cover extent on Alpine glaciers. In recent years, distributed debris energy-balance models have been developed to account for the melt rate enhancing/reduction due to a thin/thick debris layer, respectively. However, such models require a large amount of input data that are not often available, especially in remote mountain areas such as the Himalaya. Some of the input data such as wind or temperature are also of difficult extrapolation from station measurements. Due to their lower data requirement, empirical models have been used in glacier melt modelling. However, they generally simplify the debris effect by using a single melt-reduction factor which does not account for the influence of debris thickness on melt. In this paper, we present a new temperature-index model accounting for the debris thickness feedback in the computation of melt rates at the debris-ice interface. The empirical parameters (temperature factor, shortwave radiation factor, and lag factor accounting for the energy transfer through the debris layer) are optimized at the point scale for several debris thicknesses against melt rates simulated by a physically-based debris energy balance model. The latter has been validated against ablation stake readings and surface temperature measurements. Each parameter is then related to a plausible set of debris thickness values to provide a general and transferable parameterization. The new model is developed on Miage Glacier, Italy, a debris cover glacier in which the ablation area is mantled in near-continuous layer of rock. Subsequently, its transferability is tested on Haut Glacier d'Arolla, Switzerland, where debris is thinner and its extension has been seen to expand in the last decades. The results show that the performance of the new debris temperature-index model (DETI) in simulating the glacier melt rate at the point scale is comparable to the one of the physically based approach. The definition of model parameters as a function of debris thickness allows the simulation of the warming/insulating effect suggested by the Ostrem curve. We show that it is important indeed to take into account the effect of debris thickness also in empirical approaches, especially for thin debris mantles. The new DETI model is an innovative approach that can be included in continuous mass balance models of debris-covered glaciers, because of its limited data requirements. As such, we expect its application to lead to an improvement in simulations of the debris covered glacier response to climate.

Carenzo, Marco; Mabillard, Johan; Pellicciotti, Francesca; Reid, Tim; Brock, Ben; Burlando, Paolo

2013-04-01

361

EFFECTS OF HIGH TEMPERATURE MELTING ON FRACTIONATION OF HEAVY METALS IN SEWAGE SLUDGE  

Microsoft Academic Search

Sewage sludge from aerobic treatment plant was found to contain high amounts of heavy metals. Research was carried out to investigate the speciation and leaching behavior of heavy metals when using high temperature melting technology for treatment. This was achieved by conducting a sequential chemical extraction procedure and EP-TOX leaching test. The thermal treatment led to increased shift of metals

Azni Idris; Katayon Saed

2002-01-01

362

Substrate Effect on the Melting Temperature of Thin Polyethylene Films M. Rafailovich,1,* J. Sokolov,1  

E-print Network

Substrate Effect on the Melting Temperature of Thin Polyethylene Films Y. Wang,1 M. Rafailovich,1 polyethylene thin films. The Tm decreases with the film thickness decrease when the film is thinner than that the degree of crystal- linity of polyethylene (PE) remained high even in films as thin as 15 nm [5]. A novel

363

PUBLISHED ONLINE: 8 NOVEMBER 2009 | DOI: 10.1038/NPHYS1438 Melting temperature of diamond at  

E-print Network

LETTERS PUBLISHED ONLINE: 8 NOVEMBER 2009 | DOI: 10.1038/NPHYS1438 Melting temperature of diamond be `diamonds in the sky' in 1981 (ref. 1), the idea of significant quantities of pure carbon existing in giant the evolution and structure of such planets4 . Still, one of the most defining of thermal properties for diamond

Loss, Daniel

364

to be submitted Melting temperature effects on the size of ion-induced craters  

E-print Network

to be submitted Melting temperature effects on the size of ion-induced craters K. Nordlund, K. O. E (September 8, 2001) Recent work on the sizes of craters produced by ion impacts of solids has shown that the size of the crater scales with the inverse square of the cohesive energy. This observation

Nordlund, Kai

365

{sup 3}He melting pressure temperature scale below 25 mK  

SciTech Connect

Using {sup 60}Co {gamma} ray anisotropy radiation as a primary thermometer, with a Pt NMR susceptibility secondary thermometer, the authors have made high precision measurements of the {sup 3}He melting pressure versus temperature from 500 {mu}K to 25 mK. Temperatures obtained for the fixed points on the melting curve are: the superfluid A transition T{sub A} = 2.505 mK, the A-B transition T{sub AB} = 1.948 mK, and the solid ordering temperature T{sub N} = 0.934 mK. The authors provide a functional form for P(T), which, with the fixed points, constitutes a convenient temperature scale, based on a primary thermometer, usable to well below 1 mK.

Adams, E.D.; Ni, W.; Xia, J.S.

1995-04-01

366

Sea ice-albedo climate feedback mechanism  

SciTech Connect

The sea ice-albedo feedback mechanism over the Arctic Ocean multiyear sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice-atmosphere system. In its simplest form, ice-albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature, further decreasing the area cover of snow and ice. It is shown that the sea ice-albedo feedback can operate even in multiyear pack ice, without the disappearance of this ice, associated with internal processes occurring within the multiyear ice pack (e.g., duration of the snow cover, ice thickness, ice distribution, lead fraction, and melt pond characteristics). The strength of the ice-albedo feedback mechanism is compared for several different thermodynamic sea ice models: a new model that includes ice thickness distribution., the Ebert and Curry model, the Mayjut and Untersteiner model, and the Semtner level-3 and level-0 models. The climate forcing is chosen to be a perturbation of the surface heat flux, and cloud and water vapor feedbacks are inoperative so that the effects of the sea ice-albedo feedback mechanism can be isolated. The inclusion of melt ponds significantly strengthens the ice-albedo feedback, while the ice thickness distribution decreases the strength of the modeled sea ice-albedo feedback. It is emphasized that accurately modeling present-day sea ice thickness is not adequate for a sea ice parameterization; the correct physical processes must be included so that the sea ice parameterization yields correct sensitivities to external forcing. 22 refs., 6 figs., 1 tab.

Schramm, J.L.; Curry, J.A. [Univ. of Colorado, Boulder, CO (United States); Ebert, E.E. [Bureau of Meterology Research Center, Melbourne (Australia)

1995-02-01

367

Ice surface temperature retrieval from AVHRR, ATSR, and passive microwave satellite data: Algorithm development and application  

NASA Technical Reports Server (NTRS)

One essential parameter used in the estimation of radiative and turbulent heat fluxes from satellite data is surface temperature. Sea and land surface temperature (SST and LST) retrieval algorithms that utilize the thermal infrared portion of the spectrum have been developed, with the degree of success dependent primarily upon the variability of the surface and atmospheric characteristics. However, little effort has been directed to the retrieval of the sea ice surface temperature (IST) in the Arctic and Antarctic pack ice or the ice sheet surface temperature over Antarctica and Greenland. The reason is not one of methodology, but rather our limited knowledge of atmospheric temperature, humidity, and aerosol vertical, spatial and temporal distributions, the microphysical properties of polar clouds, and the spectral characteristics of snow, ice, and water surfaces. Over the open ocean the surface is warm, dark, and relatively homogeneous. This makes SST retrieval, including cloud clearing, a fairly straightforward task. Over the ice, however, the surface within a single satellite pixel is likely to be highly heterogeneous, a mixture of ice of various thicknesses, open water, and snow cover in the case of sea ice. Additionally, the Arctic is cloudy - very cloudy - with typical cloud cover amounts ranging from 60-90 percent. There are few observations of cloud cover amounts over Antarctica. The goal of this research is to increase our knowledge of surface temperature patterns and magnitudes in both polar regions, by examining existing data and improving our ability to use satellite data as a monitoring tool. Four instruments are of interest in this study: the AVHRR, ATSR, SMMR, and SSM/I. Our objectives are as follows. Refine the existing AVHRR retrieval algorithm defined in Key and Haefliger (1992; hereafter KH92) and applied elsewhere. Develop a method for IST retrieval from ATSR data similar to the one used for SST. Further investigate the possibility of estimating surface temperature from passive microwave data (in conjunction with AVHRR clear sky samples) through the use of 'effective emissivities' and physical relationships between skin temperature and subsurface temperature. Use the general method outlined in MK93 to calculate a 12-year record of clear sky equivalent surface temperatures, or possibly all-sky snow-ice interface physical temperatures, from SMMR and SSM/I, compare these temperatures to climatologies, ECMWF modeled surface temperatures, and surface temperatures predicted by a 2-D ice model. And intercompare several ice