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1

Melting Ice  

NSDL National Science Digital Library

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

Consortium, The C.

2011-12-13

2

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

3

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

4

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

USGS Publications Warehouse

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

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

2008-01-01

5

Melting of Ice under Pressure  

SciTech Connect

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

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

2008-07-31

6

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.

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

2008-01-01

7

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

8

Melting ice cubes  

NSDL National Science Digital Library

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

Glessmer, Mirjam

9

Melting Sea Ice  

NSDL National Science Digital Library

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

Domain, Wgbh E.

10

Melting artificial spin ice  

Microsoft Academic Search

Artificial spin ice arrays of micromagnetic islands are a means of engineering additional energy scales and frustration into magnetic materials. Here we demonstrate a magnetic phase transition in an artificial square spin ice and use the symmetry of the lattice to verify the presence of excitations far below the ordering temperature. We do this by measuring the temperature-dependent magnetization in

Vassilios Kapaklis; Unnar B Arnalds; Adam Harman-Clarke; Evangelos Th Papaioannou; Masoud Karimipour; Panagiotis Korelis; Andrea Taroni; Peter C W Holdsworth; Steven T Bramwell; Björgvin Hjörvarsson

2012-01-01

11

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

12

Melting of ice cubes under controlled conditions  

Microsoft Academic Search

Weight variations with time during the melting of suspended ice cubes under controlled conditions at various temperatures\\u000a ranging from 10–45°C have been experimentally studied. The melting data have been used to determine certain parameters leading\\u000a to the calculation of complete melting time, thickness of the water film on ice surface and the temperature at the interface\\u000a of air and water

R Pratap Singh; Vijay Kumar Upadhyay

1979-01-01

13

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

14

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

15

Dissociation behavior of C2H6 hydrate at temperatures below the ice point: melting to liquid water followed by ice nucleation.  

PubMed

The dissociation of C(2)H(6) hydrate particles by slow depressurization at temperatures slightly below the ice melting point was studied using optical microscopy and Raman spectroscopy. Visual observations and Raman measurements revealed that ethane hydrates can be present as a metastable state at pressures lower than the dissociation pressures of the three components: ice, hydrate, and free gas. However, they decompose into liquid water and gas phases once the system pressure drops to the equilibrium boundary for supercooled water, hydrate, and free gas. Structural analyses of obtained Raman spectra indicate that structures of the metastable hydrates and liquid water from the hydrate decay are fundamentally identical to those of the stable hydrates and supercooled water without experience of the hydration. These results imply a considerably high energy barrier for the direct hydrate-to-ice transition. Water solidification, probably induced by dynamic nucleation, was also observed during melting. PMID:21744826

Ohno, Hiroshi; Oyabu, Ikumi; Iizuka, Yoshinori; Hondoh, Takeo; Narita, Hideo; Nagao, Jiro

2011-08-18

16

Why does salt melt ice?  

NSDL National Science Digital Library

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

Senese, Fred

17

Isotope thermometry in melt-affected ice cores  

Microsoft Academic Search

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

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

2011-01-01

18

How Does Melting Ice Affect Sea Level?  

NSDL National Science Digital Library

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

Dahlman, Luann; Andrill

19

Melting artificial spin ice  

Microsoft Academic Search

Artificial spin ice arrays of micromagnetic islands are a means of engineering additional energy scales and frustration into magnetic materials. Despite much progress in elucidating the properties of such arrays, the `spins' in the systems studied so far have no thermal dynamics as the kinetic constraints are too high. Here we address this problem by using a material with an

Vassilios Kapaklis; Unnar B. Arnalds; Adam Harman-Clarke; Evangelos Th. Papaioannou; Masoud Karimipour; Panagiotis Korelis; Andrea Taroni; Peter C. W. Holdsworth; Steven T. Bramwell; Björgvin Hjörvarsson

2011-01-01

20

MELTING OF ICE AROUND A HORIZONTAL ISOTHERMAL CYLINDRICAL HEAT SOURCE  

Microsoft Academic Search

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

JORG HERRMANN; WOLFGANG LEIDENFROST; RAYMOND VISKANTA

1984-01-01

21

Results from a lab study of melting sea ice  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

22

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

USGS Publications Warehouse

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

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

2006-01-01

23

Sensitivity of Arctic warming to sea surface temperature distribution over melted sea-ice region in atmospheric general circulation model experiments  

NASA Astrophysics Data System (ADS)

Substantial reduction in Arctic sea ice in recent decades has intensified air-sea interaction over the Arctic Ocean and has altered atmospheric states in the Arctic and surrounding high-latitude regions. This study has found that the atmospheric responses related to Arctic sea-ice melt in the cold season (October-March) depend on sea-ice fraction and are very sensitive to in situ sea surface temperature (SST) from a series of atmospheric general circulation model (AGCM) simulations in which multiple combinations of SSTs and sea-ice concentrations are prescribed in the Arctic Ocean. It has been found that the amplitude of surface warming over the melted sea-ice region is controlled by concurrent in situ SST even if these simulations are forced by the same sea-ice concentration. Much of the sensitivity of surface warming to in situ SST are related with large changes in surface heat fluxes such as the outgoing long-wave flux in early winter (October-December) and the sensible and latent heat fluxes for the entire cold season. Vertical extension of surface warming and moistening is sensitive to these changes as well; the associated condensational heating modulates a static stability in the lower troposphere. This study also indicates that changes in SST fields in AGCM simulations must be implemented with extra care, especially in the melted sea-ice region in the Arctic. The statistical method introduced in this study for adjusting SSTs in conjunction with a given sea-ice change can help to model the atmospheric response to sea-ice loss more accurately.

Jun, Sang-Yoon; Ho, Chang-Hoi; Kim, Baek-Min; Jeong, Jee-Hoon

2014-02-01

24

Ice-shelf melting around Antarctica.  

PubMed

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. PMID:23765278

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

2013-07-19

25

Monitoring Antarctic ice sheet surface melting with TIMESAT algorithm  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

26

Cloud screening and melt water detection over melting sea ice using AATSR/SLSTR  

NASA Astrophysics Data System (ADS)

With the onset of melt in the Arctic Ocean, the fraction of melt water on sea ice, the melt pond fraction, increases. The consequences are: the reduced albedo of sea ice, increased transmittance of sea ice and affected heat balance of the system with more heat passing through the ice into the ocean, which facilitates further melting. The onset of melt, duration of melt season and melt pond fraction are good indicators of the climate state of the Arctic and its change. In the absence of reliable sea ice thickness retrievals in summer, melt pond fraction retrieval from satellite is in demand as input for GCM as an indicator of melt state of the sea ice. The retrieval of melt pond fraction with a moderate resolution radiometer as AATSR is, however, a non-trivial task due to a variety of subpixel surface types with very different optical properties, which give non-unique combinations if mixed. In this work this has been solved by employing additional information on the surface and air temperature of the pixel. In the current work, a concept of melt pond detection on sea ice is presented. The basis of the retrieval is the sensitivity of AATSR reflectance channels 550nm and 860nm to the amount of melt water on sea ice. The retrieval features extensive usage of a database of in situ surface albedo spectra. A tree of decisions is employed to select the feasible family of in situ spectra for the retrieval, depending on the melt stage of the surface. Reanalysis air temperature at the surface and brightness temperature measured by the satellite sensor are analyzed in order to evaluate the melting status of the surface. Case studies for FYI and MYI show plausible retrieved melt pond fractions, characteristic for both of the ice types. The developed retrieval can be used to process the historical AATSR (2002-2012) dataset, as well as for the SLSTR sensor onboard the future Sentinel-3 mission (scheduled for launch in 2015), to keep the continuity and obtain longer time sequence of the product. Cloud detection over melting sea ice is a non-trivial problem as well. The sensitivity of AATSR 3.7 micron band to atmospheric reflectance is used to screen out clouds over melting sea ice.

Istomina, Larysa; Heygster, Georg

2014-05-01

27

What controls dead-ice melting under different climate conditions?  

NASA Astrophysics Data System (ADS)

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

Schomacker, A.

2008-12-01

28

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

NASA Astrophysics Data System (ADS)

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

Schomacker, A.; Kjaer, K. H.

2007-12-01

29

Greenland ice sheet melt from MODIS and associated atmospheric variability  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

30

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.

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

2013-01-01

31

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.

32

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

NASA Astrophysics Data System (ADS)

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

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

1998-04-01

33

Calving fluxes and melt rates of Antarctic ice shelves  

NASA Astrophysics Data System (ADS)

Iceberg calving has been assumed to be the dominant mass loss term for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000 Gt yr-1. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. To date, however, no study has reliably quantified the volume of bottom (sub-shelf) melt (BM) and the calving flux (CF) for the whole of Antarctica. The distribution of freshwater in the Southern Ocean and its partitioning between liquid and solid phase is, therefore, poorly constrained. Here, we estimate the mass budget of Antarctic ice shelves using satellite measurements of calving flux, grounding line flux and modelled ice shelf accumulation rates. We obtain a total calving flux of 938 ± 109 Gt yr-1 and a total net bottom melt of 1,130 ± 241 Gt yr-1. Thus, about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front and the calving flux is less than half the estimate derived from iceberg tracking. Calving is therefore not the most important term in the mass loss of the continent. In addition, the fraction of mass loss from bottom melt varies dramatically from ~10 to 90% between ice shelves. We find that ice shelves with high melt ratios correlate well with those experiencing thinning and enhanced discharge, suggesting that a high melt ratio may be a good indicator of ice shelf vulnerability to changes in ocean temperature.

Depoorter, Mathieu A.; Griggs, Jennifer A.; Lenaerts, Jan T. M.; van den Broeke, Michiel R.; Bamber, Jonathan L.

2013-04-01

34

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

35

A PIV and CFD Analysis of Natural Convection Ice Melting  

Microsoft Academic Search

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

T J Scanlon; M T Stickland; M Lacombe

36

Using Melting Ice to Teach Radiometric Dating.  

ERIC Educational Resources Information Center

Presented is an activity in which a mystery setting is used to motivate students to construct their own decay curves of melting ice used as an analogy to radioactive decay. Procedures, materials, apparatus, discussion topics, presentation, and thermodynamics are discussed. (CW)

Wise, Donald Underkofler

1990-01-01

37

Causes and Effects of Melting Ice  

NSDL National Science Digital Library

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

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

2012-11-14

38

Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion  

NASA Astrophysics Data System (ADS)

Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded, with record extent in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica's ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.

Bintanja, R.; van Oldenborgh, G. J.; Drijfhout, S. S.; Wouters, B.; Katsman, C. A.

2013-05-01

39

Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion  

NASA Astrophysics Data System (ADS)

Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded, with record extent in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica's ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.

Bintanja, R.; Oldenborgh, G. V.; Drijhout, S.; Wouters, B.; Katsman, C. A.

2013-12-01

40

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

41

Duration of the Arctic Sea Ice Melt Season: Regional and Interannual Variability, 1979 2001.  

NASA Astrophysics Data System (ADS)

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

42

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

43

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

44

Simulated melt rates for the Totten and Dalton ice shelves  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

45

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

46

Separation of melting and environmental signals in an ice core with seasonal melt  

Microsoft Academic Search

We examine the impact of melt water percolation on the soluble ion chemical record from the Lomonosovfonna ice core. Principle component analysis shows that melting produces only simple changes between bubbly and clear ice facies, due to elution of ions. The data can be naturally split into four groups: pre-industrial, immediately before, and after the end of the Little Ice

John C. Moore; Aslak Grinsted; Teija Kekonen; Veijo Pohjola

2005-01-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

48

Study on Heat Transfer and Melt Mechanism of Arctic Sea Ice  

NASA Astrophysics Data System (ADS)

Sea ice is one of the most important natural phenomena in the Arctic Ocean and controls the heat transfer between ocean and atmosphere. In this study, We provide a theoretical reference in revealing the processes of heat transfer and melting mechanism of Arctic sea ice. Field measurements of sea ice physical and heat transfer data of sea ice during the summer 2010 Chinese National Arctic Research Expedition are used to establish a three-dimensional model of sea ice using numerical simulation of FLUENT software, with full consideration of (1) the influence of atmosphere and sea water to the convective heat transfer of sea ice and (2) the influence of solar radiative heat transfer to sea ice. Through virtual temperature field of sea ice in different thermal environments we expect to reveal the internal heat transfer mechanism of the composite structure of arctic sea ice. Based on the above simulation, the melting mechanism of sea ice can be theoretically examined. Under the energy conservation principle, the latent heat of melting sea ice is then measured in laboratory setting. Through both laboratory and theoretical analyses, we expect to provide important data and information for better understanding the heat transfer and melting mechanism process of Arctic sea ice

Qian, Z.; Xie, H.

2011-12-01

49

High density amorphous ice at room temperature  

PubMed Central

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

Chen, Jing-Yin; Yoo, Choong-Shik

2011-01-01

50

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

51

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

52

H/D exchange kinetics in pure and HCl doped polycrystalline ice at temperatures near its melting point: structure, chemical transport, and phase transitions at grain boundaries.  

PubMed

We report the results of a fast thermal desorption spectroscopy study of the H/D isotopic exchange kinetics in a few micrometer thick, pure polycrystalline ice film and in ice films doped with HCl. Using the isotopic exchange reaction as a probe of transport processes in ice, we determined the effective H/D interdiffusion coefficients, D(eff), in pure and doped polycrystalline ice at temperatures ranging from -18 to -1 degree C. In the case of pure polycrystalline ice, D(eff) demonstrates an Arrhenius dependence on temperature with an effective activation energy of 69+/-3 kJ mol(-1) and a pre-exponential of 10(9+/-0.5) microm(2) ms(-1) up to -2 degrees C. According to our analysis, H/D interdiffusion coefficient at the grain boundaries also shows an Arrhenius dependence on temperature with an activation energy of 69+/-3 kJ mol(-1) and a pre-exponential of 10(11+/-1) microm(2) ms(-1). However, the addition of 0.04% of HCl results in a marked deviation of D(eff) from Arrhenius law at -8 degrees C, which is attributed to premelting at intersections of grain boundaries. We discuss the structure and transport properties of condensed aqueous phase at grain boundaries in polycrystalline ice at various temperatures. PMID:19206978

Lu, Haiping; McCartney, Stephanie A; Sadtchenko, Vlad

2009-02-01

53

Pine Island glacier ice shelf melt distributed at kilometre scales  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

54

Southern Ocean warming: Increase in basal melting and grounded ice loss  

NASA Astrophysics Data System (ADS)

We apply a global finite element sea ice/ice shelf/ocean model (FESOM) to the Antarctic marginal seas to analyze projections of ice shelf basal melting in a warmer climate. 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. Results 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. While trends in sea ice coverage, ocean heat content, and ice shelf basal melting are small in simulations forced with ECHAM5 data, a substantial shift towards a warmer regime is found in experiments forced with HadCM3 output. A strong sensitivity of basal melting to increased ocean temperatures is found for the ice shelves in the Amundsen Sea. For the cold-water ice shelves in the Ross and Weddell Seas, decreasing convection on the continental shelf in the HadCM3 scenarios leads to an erosion of the continental slope front and to warm water of open ocean origin entering the continental shelf. As this water reaches 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. Highest melt rates at the deep FRIS grounding line causes a retreat of > 200km, equivalent to an land ice loss of 110 Gt/yr.

Determann, J.; Hellmer, H. H.; Timmermann, R.; Thoma, M.

2013-12-01

55

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

Microsoft Academic Search

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

Chuansi Gao; John Abeysekera; Mikko Hirvonen; Carita Aschan

2003-01-01

56

Circulation and melting beneath the ross ice shelf.  

PubMed

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

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

1979-02-01

57

Heat transfer during the melting of ice around a horizontal, isothermal cylinder  

Microsoft Academic Search

An experimental investigation of the melting of ice around a horizontal, isothermal cylinder is performed. Emphasis is placed on interpreting the heat transfer mechanisms which control solid-liquid interface position. Flow visualization and interferometric techniques are employed to study the transient flow patterns and corresponding temperature distributions in the melted region.

D. White; R. Viskanta; W. Leidenfrost

1986-01-01

58

Ion fractionation and percolation in ice cores with seasonal melting  

Microsoft Academic Search

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

John C. Moore; Aslak Grinsted

59

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

Microsoft Academic Search

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

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

2010-01-01

60

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

PubMed Central

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.

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

2014-01-01

61

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

62

Melting of the precipitated ice IV in LiCl aqueous solution and polyamorphism of water.  

PubMed

Melting of the precipitated ice IV in supercooled LiCl-H(2)O solution was studied in the range of 0-0.6 MPa and 160-270 K. Emulsified solution was used to detect this metastable transition. Ice IV was precipitated from the aqueous solution of 2.0 mol % LiCl (or 4.8 mol % LiCl) in each emulsion particle at low-temperature and high-pressure conditions, and the emulsion was decompressed at different temperatures. The melting of ice IV was detected from the temperature change of the emulsified sample during the decompression. There was an apparently sudden change in the slope of the ice IV melting curve (liquidus) in the pressure-temperature diagram. At the high-pressure and high-temperature side of the change, the solute-induced freezing point depression was observed. At the low-pressure and low-temperature side, ice IV transformed into ice Ih on the decompression, and the transition was almost unrelated to the concentration of LiCl. These experimental results were roughly explained by the presumed existence of two kinds of liquid water (low-density liquid water and high-density liquid water), or polyamorphism in water, and by the simple assumption that LiCl dissolved maily in high-density liquid water. PMID:21736291

Mishima, Osamu

2011-12-01

63

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

PubMed

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

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

2011-11-01

64

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

65

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

NASA Astrophysics Data System (ADS)

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

Schomacker, Anders

2008-11-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

67

Growth kinetics of CO 2 hydrate just below melting point of ice  

Microsoft Academic Search

CO2 gas hydrate formation was clearly observed through Raman spectroscopy, when CO2 interacted with ice under high pressures of 1.6MPa. The CO2 hydrate formation rate, which was measured by the change of the CO2 gas volume consumed by the CO2 hydrate formation, was found to be remarkably dependent on the temperature, especially at around the melting point of ice. At

Taro Kawamura; Takeshi Komai; Yoshitaka Yamamoto; Kazushige Nagashima; Kotaro Ohga; Kiyoshi Higuchi

2002-01-01

68

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

69

Quantum melting of spin ice: emergent cooperative quadrupole and chirality.  

PubMed

Quantum melting of spin ice is proposed for pyrochlore-lattice magnets Pr2TM2O7 (TM=Ir, Zr, and Sn). The quantum superexchange Hamiltonian having a nontrivial magnetic anisotropy is derived on the basis of atomic non-Kramers magnetic doublets. The ground states exhibit a cooperative ferroquadrupole and pseudospin chirality, forming a magnetic analog of smectic liquid crystals. Our theory accounts for dynamic spin-ice behaviors experimentally observed in Pr2TM2O7. PMID:20867877

Onoda, Shigeki; Tanaka, Yoichi

2010-07-23

70

Ranking spatially and temporally variable Greenland ice surface melt factors  

NASA Astrophysics Data System (ADS)

Greenland ice sheet surface melt water production is evaluated via a spatially distributed surface energy budget analysis of the 14 summers spanning 2000-2013. Key ingredients are DMI HIRHAM5 5km x 5km output and NASA MOD10A1 daily albedo. The HIRHAM5 simulated downward solar and infrared fluxes and turbulent fluxes are compared with in-situ data from the Danish PROMICE.org automatic weather stations. The seasonally and spatially evolving relative importance of individual surface energy budget components yields detailed insight into physical processes driving melt variability with some surprising implications to ice sheet surface mass balance sensitivity to climate change.

Box, Jason; Mottram, Ruth; Langen, Peter; Boberg, Fredrik; Promice Team

2014-05-01

71

Sea level change due to Greenland ice sheet melting  

NASA Astrophysics Data System (ADS)

One major source of global and regional sea level change in the recent past is the mass loss of continental ice sheets. Therefore, the contribution of Greenland ice sheet melting to the sea level change in the North Atlantic is investigated within this study. Several melting scenarios, which are derived from different studies, are included into the Finite Element Sea-Ice Ocean Model (FESOM, Timmermann et al., 2009) to estimate changes in ocean circulations. The self-gravitational effect is implemented into the mass conserving FESOM model, to more realistically simulate the response of the ocean. The loss of Greenland ice mass also results in a decrease of gravitational attraction of the ice sheet, which has to be taken into account as it affects the regional sea level. First results are presented, showing a global sea level change of about 0.6mm if 200Gt of Greenland ice is molten. Simulations using different melting scenarios show similar patterns of regional sea level change in the North Atlantic.

Brunnabend, Sandra-Esther; Schroeter, Jens; Timmermann, Ralph; Rietbroek, Roelof; Kusche, Juergen

2010-05-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

73

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

74

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

NASA Astrophysics Data System (ADS)

A new meltpond parameterization has been developed for the CICE sea ice model, taking advantage of the level ice tracer available in the model. The ponds evolve according to physically based process descriptions, assuming a depth-area ratio for changes in pond volume. A novel aspect of the new scheme is that the ponds are carried as tracers on the level ice area of each thickness category, thus limiting their spatial extent based on the simulated sea ice topography. This limiting is meant to approximate the horizontal drainage of melt water into depressions in ice floes. Simulated melt pond processes include collection of liquid melt water and rain into ponds, drainage through permeable sea ice or over the edges of floes, infiltration of snow by pond water, and refreezing of ponds. Furthermore, snow that falls on top of ponds whose top surface has refrozen blocks radiation from penetrating into the ponds and sea ice below. Along with a control simulation, we present a range of sensitivity tests to parameters related to each subprocess described by the parameterization. With the exception of one parameter that alters the albedo of snow-covered pond ice, results are not highly sensitive to these parameters unless an entire process is removed. The snow simulation itself is critical, because the volume of snow deposition and rate of snow melt largely determine the timing and extent of the simulated melt ponds. Nevertheless, compensating effects moderate the model's sensitivity to precipitation changes. For instance, infiltration of the snow by melt water postpones the appearance of ponds and the subsequent acceleration of melting through albedo feedback, while snow on top of refrozen pond ice also reduces the ponds' effect on the radiation budget. By construction, the model simulation of level and ridged ice is also important for this parameterization. We find that as sea ice thins, either through time or when comparing sensitivity tests, the area of level ice increases. This leads to an enhanced thinning feedback in the model, because a greater ice area may be exposed to ponding and further thinning due to lowered albedo.

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

2013-11-01

75

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

76

Enhanced Sea Ice Concentration and Ice Temperature Algorithms for AMSR  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

77

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

78

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

79

Changing sea ice melt parameters in the Canadian Arctic Archipelago: Implications for the future presence of multiyear ice  

Microsoft Academic Search

Estimates of annual sea ice melt onset, freeze onset, and melt duration are made within the Canadian Arctic Archipelago (CAA) using SeaWinds\\/QuikSCAT data from 2000 to 2007. The average date of melt onset occurred on day 150, the average freeze onset occurred on day 266, and the average number of days of melt was 116. Melt onset occurred first, and

Stephen E. L. Howell; Adrienne Tivy; John J. Yackel; Brent G. T. Else; Claude R. Duguay

2008-01-01

80

Getz Ice Shelf, West Antarctica: Little glacier speed increase despite basal ice shelf melting  

NASA Astrophysics Data System (ADS)

The Getz Ice Shelf, stretching along ~500 km of coastline in the Amundsen Sea Sector of West Antarctica, occupies a region of changing climatic and oceanic conditions. Climatically, the region is influenced by the Amundsen Sea Low, a mean atmospheric circulation feature of West Antarctica that has slowly increased in intensity over the past several decades. Oceanographically, the shelf is affected by intrusions of Antarctic Circumpolar Deep Water, which are currently melting the shelf from below at a rate of 4.3 × 0.4 meters of water per year. Recent results from gravity-based assessments of mass change in the region indicate significant mass loss for the entire Getz ice drainage area, and altimetry studies of grounded ice in the Getz Ice Shelf catchment area show significant elevation loss since the 1990s. Our study examines the history of ice velocities from 1972-present on the Getz Ice Shelf, with particular attention to the ice shelf edge and the grounding zone area during the last decade. The shelf and grounded ice are characterized by relatively narrow zones of faster outflow and steep grounded ice surface slopes. The fastest outflow speeds are found toward the western edge at DeVicq Glacier, typically 800-1000 ma-1 near the ice edge and 400-800 ma-1 at the grounding line. Slower speeds towards the east are generally 250-500 ma-1 at the ice edge and 150-400 ma-1 near the grounding line. Despite significant basal melt and thinning of grounded ice, the Getz Ice Shelf has exhibited only modest accelerations: ~20% near the grounding line in the DeVicq Glacier region, ~35% at the far eastern edge, and <10% across central sections of the shelf. This contrasts with the nearly 50% flow speed increase of Pine Island Glacier between 1972 and 2012, and >100% for the adjacent Smith Glacier between 1992 and 2008. We postulate that steep slopes in the grounded ice flow just above the grounding line imply high basal shear stresses for the feeder glaciers and therefore relative insensitivity to thinning of the shelf. With steep initial surface slope, the increase in driving stress caused by grounding line melting is minor. We also examine the potential connection between the measured elevation loss of grounded ice feeding the Getz Ice Shelf with changes (decreases) in annual snow accumulation associated with the evolution of the Amundsen Sea Low.

Alley, K. E.; Scambos, T. A.

2013-12-01

81

Changes in the Arctic Melt Season and Implications for Sea Ice Loss  

NASA Astrophysics Data System (ADS)

The Arctic melt season has lengthened by 6 days dec-1 from 1979 to 2012, dominated by later autumn freeze-up within the Kara, Laptev, East Siberian, Chukchi and Beaufort seas between 5 and 12 days dec-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 the summer melt season. The additional heat stored in the upper ocean during the last decade increases sea surface temperatures and largely explains the one to two week delay in autumn freeze-up within the Arctic basin. Cumulative anomalies in total absorbed solar radiation from May through September for the most recent pentad locally exceed 300-400 MJ m-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, Julienne; Markus, Thorsten; Boisvert, Linette

2014-05-01

82

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

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

83

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

84

Rapid ice melting drives Earth's pole to the east  

NASA Astrophysics Data System (ADS)

Space geodetic observations of polar motion show that around 2005, the average annual pole position began drifting toward the east, an abrupt departure from the drift direction seen over the past century. Satellite gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) show that about 90% of this change is due to accelerated melting of polar ice sheets and mountain glaciers and related sea level rise. The close relationship between long-term polar motion and climate-related mass redistribution established using GRACE data indicates that accurately measured polar motion data offer an additional tool for monitoring global-scale ice melting and sea level rise and should be useful in bridging the anticipated gap between GRACE and follow-on satellite gravity missions.

Chen, J. L.; Wilson, C. R.; Ries, J. C.; Tapley, B. D.

2013-06-01

85

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

86

Testing alternative parameterizations of lateral melting and upward basal heat flux in a thermodynamic sea ice model  

SciTech Connect

A zonally averaged, physically based sea ice model is coupled to an energy balance climate model with prescribed observed atmospheric temperatures and used to investigate the sea ice model sensitivity to alternative parameterizations of (1) the upward heat flux F{sub b} to the ice base, and (2) lateral melting of ice from open water. The parameterizations tested here are taken from the climate and sea ice modeling literature. The different parameterizations for each of these processes can lead to dramatically different results in simulated sea ice area, sea ice thickness, or both. Parameterizing F{sub b} by prescribing (or computing) an upward heat flux at the mixed layer base and either constraining the subice mixed layer temperature to equal the freezing point of seawater or parameterizing F{sub b} as a function of subice mixed layer temperature has the advantage of incorporating the effects on heat fluxes to the ice base of both convective overturning and meridional oceanic heat flux convergence. Parameterizing lateral melting as a function of lead temperature T{sub lead}, rather than making it depend on {partial derivative}T{sub lead}/{partial derivative}t, has relatively little impact on simulated winter ice extent, and no impact on summer ice extent.

Harvey, L.D.D. (Univ. of Toronto, Ontario (Canada))

1990-05-15

87

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

88

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

89

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

90

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

NASA Astrophysics Data System (ADS)

Meltwater from the Greenland Ice Sheet (GIS) has been a major contributor to sea level change in the recent past. Global and regional sea level variations caused by melting of the GIS are investigated with the finite element sea-ice ocean model (FESOM). We consider changes of local density (steric effects), mass inflow into the ocean, redistribution of mass, and gravitational effects. Five melting scenarios are simulated, where mass losses of 100, 200, 500, and 1000 Gt/yr are converted to a continuous volume flux that is homogeneously distributed along the coast of Greenland south of 75°N. In addition, a scenario of regional melt rates is calculated from daily ice melt characteristics. The global mean sea level modeled with FESOM increases by about 0.3 mm/yr if 100 Gt/yr of ice melts, which includes eustatic and steric sea level change. In the global mean the steric contribution is one order of magnitude smaller than the eustatic contribution. Regionally, especially in the North Atlantic, the steric contribution leads to strong deviations from the global mean sea level change. The modeled pattern mainly reflects the structure of temperature and salinity change in the upper ocean. Additionally, small steric variations occur due to local variability in the heat exchange between the atmosphere and the ocean. The mass loss has also affects on the gravitational attraction by the ice sheet, causing spatially varying sea level change mainly near the GIS, but also at greater distances. This effect is accounted for by using Green's functions.

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

2012-09-01

91

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

92

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.

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

2014-01-01

93

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.

94

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):P(T,XNaCl)=9.27+0.996XNaCl-(6.99×10-2+7.6×10-3XNaCl)·T+(1.414×10-4+1.541×10-5XNaCl)·T2 P(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

95

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

PubMed

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

Knopf, Daniel Alexander; Lopez, Miguel David

2009-09-28

96

Estimation of Greenland's Ice Cover Melting Area Using the Atmospheric Infrared Sounder (AIRS)  

NASA Astrophysics Data System (ADS)

Using the Atmospheric Infrared Sounder (AIRS), we are able to detect the melting of Greenland's ice cover for the July 12, 2012 warming event and estimate the corresponding fractional melted area. We collect all of AIRS' overpasses above Greenland, using the reflected solar radiation to avoid cloudy scenes. We perform a retrieval of the skin surface temperature in order to classify a scene as likely frozen (skin temperature well below the freezing point), likely melted (skin temperature well above freezing point), or thawing. Using empirical snow and water emissivity data we retrieve an effective scene snow/water fraction. For this day we estimate that 90% of the ice cover exhibits some thawing and that 53% of the ice cover area was effectivelly covered with liquid water. For contrast we also look at July 8, 2012, and verify that most of the island, 68%, was frozen at that date. We also see a correlation of the thawing area with the solar angle as the day progresses.

Imbiriba, B.; Desouza-Machado, S. G.; Hannon, S.; Strow, L. L.

2012-12-01

97

Recent Changes in Arctic Sea Ice Melt Onset, Freeze-Up, and Melt Season Length  

NASA Technical Reports Server (NTRS)

In order to explore changes and trends in the timing of Arctic sea ice melt onset and freeze-up and therefore melt season length, we developed a method that obtains this information directly from satellite passive microwave data, creating a consistent data set from 1979 through present. We furthermore distinguish between early melt (the first day of the year when melt is detected) and the first day of continuous melt. A similar distinction is made for the freeze-up. Using this method we analyze trends in melt onset and freeze-up for 10 different Arctic regions. In all regions except for the Sea of Okhotsk, which shows a very slight and statistically insignificant positive trend (O.4 days/decade), trends in melt onset are negative, i.e. towards earlier melt. The trends range from -1.0day/decade for the Bering Sea to -7.3 days/decade for the East Greenland Sea. Except for the Sea of Okhotsk all areas also show a trend towards later autumn freeze onset. The Chukchi/Beaufort Seas and Laptev/East Siberian Seas observe the strongest trends with 7 days/decade. For the entire Arctic, the melt season length has increased by about 20 days over the last 30 years. Largest trends of over 1O days/decade are seen for Hudson Bay, the East Greenland Sea the Laptev/East Siberian Seas, and the Chukchi/Beaufort Seas. Those trends are statistically significant a1 the 99% level.

Markus, Thorsten; Stroeve, Julienne C.; Miller, Jeffrey

2010-01-01

98

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

NASA Astrophysics Data System (ADS)

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

Greuell, W.

99

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

100

Melting and refreezing beneath Roi Baudouin Ice Shelf (East Antarctica) inferred from radar, GPS, and ice core data  

NASA Astrophysics Data System (ADS)

Ice-penetrating radar profiles across the grounding line of a small ice-rise promontory located within the Roi Baudouin Ice Shelf in the Dronning Maud Land sector of East Antarctica show downward dipping englacial radar-detected reflectors. Model results indicate that this reflector pattern is best fit by including basal melting of at least 15 cm a-1. This rate of melting is low compared with rates observed on larger ice shelves in both West and East Antarctica. Ice cores extracted from a rift system close to the ice-rise promontory show several meters of marine ice accreted beneath the shelf. These observations of low rates of basal melting, and limited distribution of accreted marine ice suggest that either Antarctic surface water may reach the ice shelf base or that circulation beneath the shelf is likely dominated by the production of high salinity shelf water rather than the incursion of circumpolar deep water, implying a weak sub-shelf circulation system here. Many of the ice shelves located along the coast of Dronning Maud Land are, like Roi Baudouin Ice Shelf, characterized by frequent ice rises and promontories. Therefore, it is highly likely that these are also of shallow bathymetry and are subject to similarly weak side-shelf basal melting and refreezing.

Pattyn, F.; Matsuoka, K.; Callens, D.; Conway, H.; Depoorter, M.; Docquier, D.; Hubbard, B.; Samyn, D.; Tison, J. L.

2012-12-01

101

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

Microsoft Academic Search

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

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

2011-01-01

102

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

103

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

104

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

105

Combining Modis and Quikscat Data to Delineate Surface and Near-Surface Melt on the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

Over the last two decades, increasing melt has been measured on the Greenland Ice Sheet, along with mass loss as determined from satellite data, Monitoring the state of the Greenland Ice Sheet becomes critical especially because it is actively losing mass, and the ice sheet has a sea-level rise potential of 7 in. However measurement of the extent of surface melt varies depending on the sensor used, whether it is passive or active microwave or visible or thermal infrared. We have used remote-sensing data products to study surface and near-surface melt characteristics of the Greenland Ice Sheet. We present a blended MODIS-QS melt daily product for 2007 [1]. The products, including Moderate Resolution Imaging Spectroradiometer (MODIS) daily land-surface temperature (LST) and a special daily melt product derived from the QuikSCAT (QS) scatterometer [2,3] show consistency in delineating the melt boundaries on a daily basis in the 2007 melt season [I], though some differences are identified. An assessment of maximum melt area for the 2007 melt shows that the QSCAT product detects a greater amount of melt (862,769 square kilometers) than is detected by the MODIS LST product (766,184 square kilometers). The discrepancy is largely because the QS product can detect both surface and near-surface melt and the QS product captures melt if it occurred anytime during the day while the MODIS product is obtained from a point in time on a given day. However on a daily bases, other factors influence the measurement of melt extent. In this work we employ the digital-elevation model of Bamber et al. [4] along with the National Centers for Environmental Prediction (NCEP) data to study some areas and time periods in detail during the 2007 melt season. We focus on times in which the QS and MODIS LST products do not agree exactly. We use NCEP and elevation data to analyze the atmospheric factors forcing the melt process, to gain an improved understanding of the conditions that lead to melt and melt persistence, and our ability to capture surface melt accurately using MODIS and QS data.

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

2010-01-01

106

Processes and imagery of first-year fast sea ice during the melt season  

NASA Technical Reports Server (NTRS)

In June and July 1982, a field program was conducted in the Canadian Arctic on Prince Patrick Island to study sea ice during the melt season with in situ measurements and microwave instrumentation operated near the surface and from aircraft. The objective of the program was to measure physical characteristics together with microwave backscatter and emission coefficients of sea ice during this major period of transition. The present paper is concerned with a study of both surface measurements and imagery of first-year fast ice during the melt season. The melting process observed in first-year fast ice was found to begin with the gradual reduction of the snow cover. For a two- to three-day period in this melt stage, a layer of superimposed ice nodules formed at the snow/ice interface as meltwater froze around ice and snow grains.

Holt, B.; Digby, S. A.

1985-01-01

107

Heat of Freezing and Melting of Sea Ice.  

National Technical Information Service (NTIS)

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

D. Anderson

1966-01-01

108

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

109

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

110

Modelling Feedbacks between Ocean Stratification, Atmospheric Forcing, Sea-Ice Growth, and Glacier Terminus Melting in Fjords  

NASA Astrophysics Data System (ADS)

In many locations, ice sheets discharge into the ocean via marine-terminating glaciers. This provides a coupling where the ice-sheet mass balance can respond to changing ocean forcing, which is of interest for predictions of sea level rise. Models and observations suggest that the melting of a marine glacier terminus depends critically on the ocean temperature and salinity stratification. However, there is uncertainty about which processes provide the dominant control on the ocean conditions in fjords. I develop a simplified conceptual model of a fjord circulation coupled to a melting glacier terminus. This provides a tool to assess the impact of a range of processes on glacial melting, including the inflow of ocean waters at the fjord mouth, the estuarine circulation of glacial meltwater, vertical mixing driven by atmospheric forcing, and sea ice formation. The model describes the seasonal evolution of vertical profiles of temperature, salinity, and velocity in the fjord, using a horizontally-averaged finite volume method. The temperature and salinity stratification control the glacial melting rate via a meltwater plume rising along the glacier terminus, which in turn drives an estuarine-style circulation in the fjord interior. Further advective transport and vertical mixing are driven by atmospheric forcing, via winds and surface buoyancy fluxes. Finally, modelled sea ice growth enhances the buoyancy-driven mixing as a result of brine rejection from growing sea ice, but reduces the transmission of wind stresses through fast ice into the ocean. A scaling analysis reveals the relative significance of each of these processes for transport and mixing in the fjord over a range of forcing conditions. The model is applied to simulate the seasonal evolution of glacial melting for several case studies that are representative of Greenland fjords, and the inherent coupled feedback mechanisms are explored. If the ocean is weakly stratified at the fjord mouth, then vertical mixing plays a significant role in modulating both the fjord stratification, and the vertical distribution and magnitude of glacier terminus melting.

Wells, A.

2013-12-01

111

Contribution of ice sheet and mountain glacier melt to recent sea level rise  

NASA Astrophysics Data System (ADS)

Changes in global mean sea level primarily reflect the sum of three contributions: water mass changes in the oceans, water density changes, and variations in the volume of the ocean basins. Satellite altimetry data suggest that sea level rose by about 2.39+/-0.48mmyr-1 between 2005 and 2011. However, previous estimates of sea level rise from density and ocean mass changes were lower than the altimeter data indicate. Here we show that the gap in the sea level budget disappears when we combine gravity data from the GRACE (Gravity Recovery and Climate Experiment) satellite mission and temperature and salinity observations from the Argo programme collected between 2005 and 2011. The Argo data indicate a density-driven sea level rise of 0.60+/-0.27mmyr-1 throughout this period. To estimate ocean mass change from the gravity data, we developed a forward modelling technique that reduces the bleeding of terrestrial signals into the ocean data. Our reassessment suggests an ocean mass contribution of 1.80+/-0.47mmyr-1, for a total sea level rise of 2.40+/-0.54mmyr-1, in agreement with the altimeter-based estimates. On the basis of the GRACE data, we conclude that most of the change in ocean mass is caused by the melting of polar ice sheets and mountain glaciers. This contribution of ice melt is larger than previous estimates, but agrees with reports of accelerated ice melt in recent years.

Chen, J. L.; Wilson, C. R.; Tapley, B. D.

2013-07-01

112

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

113

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

NASA Astrophysics Data System (ADS)

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

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

2004-01-01

114

Surface and melt pond evolution on landfast first-year sea ice in the Canadian Arctic Archipelago  

NASA Astrophysics Data System (ADS)

evolution of landfast sea ice melt pond coverage, surface topography, and mass balance was studied in the Canadian Arctic during May-June 2011 and 2012, using a terrestrial laser scanner, snow and sea ice sampling, and surface meteorological characterization. Initial melt pond formation was not limited to low-lying areas, rather ponds formed at almost all premelt elevations. The subsequent evolution of melt pond coverage varied considerably between the 2 years owing to four principle, temporally variable factors. First, the range in premelt topographic relief was 0.5 m greater in 2011 (rougher surface) than in 2012 (smoother surface), such that a seasonal maximum pond coverage of 60% and maximum hydraulic head of 204 mm were reached in 2011, versus 78% and 138 mm in 2012. A change in the meltwater balance (production minus drainage) caused the ponds to spread or recede over an area that was almost 90% larger in 2012 than in 2011. Second, modification of the premelt topography was observed during mid-June, due to preferential melting under certain drainage channels. Some of the lowest-lying premelt areas were subsequently elevated above these deepening channels and unexpectedly became drained later in the season. Third, ice interior temperatures remained 1-2°C colder later into June in 2012 than in 2011, even though the ice was 0.35 m thinner at melt onset, thereby delaying permeability increases in the ice that would allow vertical meltwater drainage to the ocean. Finally, surface melt was estimated to account for approximately 62% of the net radiative flux to the sea ice cover during the melt season.

Landy, Jack; Ehn, Jens; Shields, Megan; Barber, David

2014-05-01

115

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

Microsoft Academic Search

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 MODIS using a spectral unmixing algorithm. The unmixing was implemented using a multilayer perceptron (MLP) to reduce

A. Rösel; L. Kaleschke; G. Birnbaum

2011-01-01

116

Albedo and the Mechanisms of Melt Pond Evolution on Seasonal Ice  

NASA Astrophysics Data System (ADS)

On undeformed seasonal ice, melt pond formation and evolution is the predominate driver of albedo shifts after the onset of melt. Due to the low topographic relief of this ice type, small variations in melt water balance can drive large changes in pond coverage. These changes in total pond coverage regularly exceed 50% and occur over time spans of just a few days or less. A field program was conducted on seasonal landfast ice in northern Alaska from March to late June 2009 to track the formation and evolution of melt ponds as well as the corresponding changes in the ice surface albedo. The observations were framed around monitoring the melt water balance on the ice surface through the principal stages of pond flooding, drainage, and lateral widening, with the intent of developing a mechanistic understanding of the processes which force these rapid changes in pond coverage on seasonal ice. Time series surface based LiDAR surveys, aerial photographs, albedo surveys, and radiation measurements provide high resolution information on the surface mass balance, energy budget, pond area, and pond growth rate over two representative study areas. A floe-wide water balance was conducted to determine the dominant water balance terms during early melt. Aerial photographs were obtained to confirm the generality of the findings over a larger area of both shorefast ice and nearby pack ice. Pond formation and early season evolution are found to be strongly dependent on melt rate and the horizontal transport of surface melt water to macroscopic ice flaws. Later in the season, pond evolution is found to be controlled largely by lateral melting at the pond perimeter and changes in freeboard caused by thinning. Key findings of this experiment demonstrate i) the importance of over-ice horizontal melt water transport and ice topography in the early-season coverage of melt ponds; ii) a phenomena of brine drainage channels widening to produce macroscopic drainage points in otherwise impermeable ice, and iii) the role of lateral melt rates in pond evolution later in the melt season. The results enhance a mechanistic understanding of melt pond evolution which may serve as a framework for improving albedo modeling on seasonal ice.

Polashenski, C.; Courville, Z.; Perovich, D. K.; Finnegan, D. C.; Sturm, M.; Druckenmiller, M.; Eicken, H.; Petrich, C.

2009-12-01

117

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

118

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

NASA Astrophysics Data System (ADS)

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

Korhonen, Meri; Rudels, Bert; Zhou, Jinping

2010-05-01

119

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

120

How long has the central-northern Greenland Ice Sheet been melting at the base?  

NASA Astrophysics Data System (ADS)

Ice-penetrating radar studies (Fahnestock et al., 2001) and the deep ice core project NGRIP (Anderson et al., 2004) have identified extensive areas of rapid basal melt under the central-northern Greenland Ice Sheet (GIS). Our new reconstruction of the lithosphere structure in Greenland reveal that strong anomalies in geothermal heat flux are responsible for much of the estimated ice loss through basal melt. We use our coupled lithosphere-GIS model to study the history of basal ice conditions since the Pliocene period and find that the anomalous heat flow has been maintaining basal ice melt throughout the history of Greenland glaciation. Persistence of basal melt water over the course of ~3.5 million years and periodic development of paleo ice streams originating at the anomaly have likely caused considerable erosion of the subglacial bedrock. The erosion is revealed by ice-penetrating radar measurements, and now exerts a geometric control on ice sheet streaming in the eroded region, and possibly the overall geometry of the GIS. Anderson, K. K., et al. (2004), High-resolution record of Northern Hemisphere climate extending into the last interglacial period, Nature, 431(7005), 147-151 Fahnestock, M., W. Abdalati, I. Joughin, J. Brozena, and P. Gogineni (2001), High geothermal heat flow, basal melt, and the origin of rapid ice flow in central Greenland, Science, 294, 2338-2342

Rogozhina, Irina; Petrunin, Alexey G.; Johnson, Jesse V.; Vaughan, Alan P. M.

2014-05-01

121

Analysis of Interannual Variations of Snow Melt on Arctic Sea Ice Mapped from Meteorological Satellite Imagery,  

National Technical Information Service (NTIS)

The seasonal progression of snow melt on the Arctic ice pack was mapped from shortwave satellite imagery for 1977, 1979, 1984 and 1985. The four years showed substantial differences in the timing of the melt interval. The progression of melt in May and Ju...

D. A. Robinson G. Scharfen R. G. Barry G. Kukla

1987-01-01

122

Parameterizing Arctic sea-ice melt pond characteristics for radiation budgets and climate modeling  

Microsoft Academic Search

Solar heating in the Arctic atmosphere-ice-ocean system plays a key role in the recently observed decline of the Arctic sea-ice cover and is key to ice-albedo feedback. The summertime absorption and transmission of shortwave radiation by Arctic sea ice is strongly affected by the areal extent and optical properties of melt ponds. As part of an effort to arrive at

H. Eicken; D. K. Perovich; S. V. Nghiem; J. P. Harbeck; B. Light

2006-01-01

123

Scaling laws for the melt rate and overturning circulation beneath ice shelves derived from simple plume theory  

NASA Astrophysics Data System (ADS)

Both the Antarctic and Greenland ice sheets are experiencing rapid change, at least in part as a result of acceleration of some of their larger, marine-terminating outlet glaciers that has been driven in turn by the ocean, through changes in the submarine melt rate. Much progress has been made in incorporating the key ocean processes into Ocean General Circulation Models and the coupling of these to dynamic ice sheet models is now an active area of research. However, at the resolutions currently used in global ocean models, some of the smaller ice shelves and almost all marine-terminating outlet glaciers will be sub-grid-scale features. Parameterisations of the ice-ocean interactions will therefore be needed for the foreseeable future. Those currently available in the literature rely on the specification of a length scale over which the ice-ocean interaction takes place or the strength of the overturning circulation that results. These unknown parameters must be chosen to match current melt rates, and the implicit assumption made that those choices remain valid as ocean temperatures evolve. However, within a coupled model the length-scale of the interaction and the overturning strength are parameters that will almost certainly change. One-dimensional plume theory provides the simplest physical description of the overturning circulation appropriate for the sub-grid-scales of interest. In this presentation it is shown how the melt rates and overturning strength produced by a plume model scale quite simply with ocean temperature and with the depth and slope of the ice-ocean interface. The simple scalings mean that plume model results can be well represented by a single polynomial expression that is accurate to about 20% for melt rates that range over many orders of magnitude. Such a polynomial could provide the basis for a powerful and versatile parameterisation of the interaction between an ocean model and sub-grid-scale features generated at the marine margins of an ice sheet model.

Jenkins, Adrian

2014-05-01

124

The Moulin Explorer: A Novel Instrument to Study Greenland Ice Sheet Melt-Water Flow.  

NASA Astrophysics Data System (ADS)

Recent data shows that the Greenland ice sheet has been melting at an accelerated rate over the past decade. This melt water flows from the surface of the glacier to the bedrock below by draining into tubular crevasses known as moulins. Some believe these pathways eventually converge to nearby lakes and possibly the ocean. The Moulin Explorer Probe has been developed to traverse autonomously through these moulins. It uses in-situ pressure, temperature, and three-axis accelerometer sensors to log data. At the end of its journey, the probe will surface and send GPS coordinates using an Iridium satellite tracker so it may be retrieved via helicopter or boat. The information gathered when retrieved can be used to map the pathways and water flow rate through the moulins. This work was performed at the Jet Propulsion Laboratory- California Institute of Technology, under contract to NASA. Support was provided by the NASA Earth Science, Cryosphere program

Behar, A.; Wang, H.; Elliott, A.; O'Hern, S.; Martin, S.; Lutz, C.; Steffen, K.; McGrath, D.; Phillips, T.

2008-12-01

125

Predicting melting temperature directly from protein sequences.  

PubMed

Proteins of both hyperthermophilic and mesophilic microorganisms generally constitute from the same 20 amino acids; however, the extent of thermal tolerance of any given protein is an inherent property of its amino acid sequence. The present study is the first to report a rapid method for predicting Tm (melting temperature), the temperature at which 50% of the protein is unfolded, directly from protein sequences (the Tm Index program is available at http://tm.life.nthu.edu.tw/). We examined 75 complete microbial genomes using the Tm Index, and the analysis clearly differentiated hyperthermophilic from mesophilic microorganisms on this global genomic basis. These results are consistent with the previous hypothesis that hyperthermophiles express a greater number of high Tm proteins compared with mesophiles. The Tm Index will be valuable for modifying existing proteins (enzymes, protein drugs and vaccines) or designing novel proteins having a desired melting temperature. PMID:19896904

Ku, Tienhsiung; Lu, Peiyu; Chan, Chenhsiung; Wang, Tsusheng; Lai, Szuming; Lyu, Pingchiang; Hsiao, Naiwan

2009-12-01

126

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

NASA Astrophysics Data System (ADS)

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

Gauthier, Francis; Hétu, Bernard; Allard, Michel

2013-04-01

127

Changes in Arctic melt season and implications for sea ice loss  

NASA Astrophysics Data System (ADS)

Arctic-wide melt season has lengthened at a rate of 5 days decade-1 from 1979 to 2013, dominated by later autumn freezeup within the Kara, Laptev, East Siberian, Chukchi, and Beaufort seas between 6 and 11 days decade-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 752 MJ m-2 during the last decade increases sea surface temperatures by 0.5 to 1.5 °C and largely explains the observed delays in autumn freezeup 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-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.

2014-02-01

128

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

NSDL National Science Digital Library

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

Landis, Carol

129

Influence of melt ponds on the formation of the multiyear sea ice cover  

Microsoft Academic Search

The features of the sea ice growing and melting under the modern climatic conditions are considered with the use of the thermodynamic\\u000a model of sea ice taking into account the seasonal melting and recrystallization of its upper layers. The evolution of the\\u000a snowy and icy cover for the North Pole geographic point is estimated quantitatively on the basis of the

P. V. Bogorodskii; A. V. Pnyushkov

2011-01-01

130

Surface melt on the Greenland Ice Sheet in the Nuuk and Kangerlussuaq regions  

NASA Astrophysics Data System (ADS)

We use automatic weather station data to produce surface melt maps for the regions of the Greenland Ice Sheet that drain into the Kangerlussuaq and Nuuk fjords. These regions are characterized by relatively low amounts of wintertime accumulation and high summertime melt. Since 2007, weather stations have been monitoring the ablation zone in these regions as part of the PROMICE and GAP observational networks. We use the station data to run a surface energy and mass budget model, which includes MODIS albedo, iterative turbulent heat flux calculations, solar radiation penetration in snow and ice, refreezing of melt water, etc. The results show yearly net ablation values of 5 m at low elevation: a considerable increase compared to observations from the 1980s. We present melt maps and run-off time series, and attempt to link surface melt to both fjord hydrology and ice dynamics.

van As, D.; Hubbard, A.; Ahlstrom, A. P.; Mikkelsen, A.; Hasholt, B.; van den Broeke, M. R.; Andersen, M. L.; Nielsen, S.; Rysgaard, S.

2010-12-01

131

Temperature Dependent Thermal Expansivities for Volcanic Melts  

NASA Astrophysics Data System (ADS)

The thermal expansivities of three volcanic melts (Etna 1992, Vesuvius 1631 and Slapany) have been obtained from room temperature up to 1800K. The compositions are tephriphonolite, trachybasalt and basanite. The low temperature volumes were derived from measurements of the glass density of each sample having 5-5 K.min-1 cooling-heating history at 298 K, followed by measurements of the glass thermal expansion coefficient from 298 K to the respective glass transition interval. Supercooled liquid volumes and molar thermal expansivities were indirectly determined by combining scanning calorimetric and dilatometric measurements assuming that kinetics of enthalpy and shear relaxation are equivalent (Webb et al. 1992). High temperature densities were measured using Pt double bob Archimedean densitometry. In addition, oxidation state of iron has been analyzed using wet chemistry method. Small amount of samples has been taken from the liquids using "dip" technique at regular temperature step during high temperature densitometry. The measured high temperature densities have been compared with calculated densities at same temperature interval using Lange & Carmichael model (1987) and multicomponent density model of Lange (1997), respectively, incorporating the necessary correction for oxidation state. The resulting data for liquid volumes near glass transition temperature (950 - 990 K) and at super-liquidus temperature (1512 - 1803 K) are combined to yield thermal expansivities over the entire supercooled to stable liquid range. This study confirms that the temperature-dependent thermal expansivities previously obtained for synthetic aluminosilicate melts are also observed for natural compositions. The temperature-dependence increases from basanite to tephriphonolite composition.

Potuzak, M.; Dingwell, D. B.

2004-12-01

132

Changing sea ice melt parameters in the Canadian Arctic Archipelago: Implications for the future presence of multiyear ice  

NASA Astrophysics Data System (ADS)

Estimates of annual sea ice melt onset, freeze onset, and melt duration are made within the Canadian Arctic Archipelago (CAA) using SeaWinds/QuikSCAT data from 2000 to 2007. The average date of melt onset occurred on day 150, the average freeze onset occurred on day 266, and the average number of days of melt was 116. Melt onset occurred first, and freeze onset occurred last within the Amundsen, Western Arctic Waterway, and Eastern Parry Channel regions, whereas the reverse occurred in the Queen Elizabeth Islands (QEI) and the M'Clure and Viscount-Melville regions. Multiyear sea ice (MYI) increases occurred from 2000 to 2004 because of dynamic import and first-year sea ice (FYI) being promoted to MYI, but this replenishment virtually stopped from 2005 to 2007, coincident with longer melt seasons. Only after two consecutive long melt seasons (2005-2006) and almost no replenishment were regions to the south of the QEI cleared of MYI. We argue that this is because MYI must slowly ablate on the underside while in transit within the CAA from the small oceanic heat flux and can therefore survive for several years in southern regions without replenishment. Net positive dynamic MYI import into the CAA was observed in 2007 following MYI removal during 2005-2006. Longer melt seasons will continue to reduce the inventory of FYI in the CAA following the melt season. Longer melt seasons within the CAA will likely not reduce MYI dynamic import, but it remains to be seen whether or not this MYI will be able to survive longer melt seasons as it migrates to the southern regions.

Howell, Stephen E. L.; Tivy, Adrienne; Yackel, John J.; Else, Brent G. T.; Duguay, Claude R.

2008-09-01

133

The Melting of Spherical Ice Particles Falling at Terminal Velocity in Air: AN Experimental and Theoretical Study.  

NASA Astrophysics Data System (ADS)

This study utilized the UCLA cloud physics wind tunnel and the IBM 3033 computer. The wind tunnel experiments were conducted using two separate procedures, depending on the size of the spherical particle. Particles less than 1 mm diameter, were melted in free fall while experiencing a time varying environmental temperature, similar to the variation of temperature it would encounter while freely falling in the atmosphere. Particles larger than 1 mm diameter have a tendency to wander towards the tunnel walls, requiring restraint by a thin nylon fiber frozen halfway through the particle. Using this fiber, the particle was suspended from above. Although attached to a thread, the particle's terminal velocity was constantly maintained during melting by keeping the fiber slack. Particles less than 1 mm diameter usually undergo "sailing" motions upon melting due to the melting of surface protuberances. Once the protuberances are melted, the particle falls with no horizontal drift. The melting ice core was observed to remain tangent with the downstream end of the particle, resulting in an eccentric melting location. The meltwater itself was also observed to circulate due to the external shear of the air on the meltwater surface. For these small particles, no meltwater was shed. Particles larger than 9 mm diameter were found to shed meltwater, with the fraction shed increasing with particle size. Particles between 9 mm and 5 mm diameter did not shed their meltwater, and did not develop an internal circulation. Particles between 1 mm and 5 mm, however, did develop a significant internal circulation, resulting in a conically shaped ice core. For each of the above size ranges, melting theories are developed which are able to quantitatively describe the melting rates of these particles.

Rasmussen, Roy Martin

134

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

135

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

NASA Astrophysics Data System (ADS)

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

Jin, ZheYan; Jin, SongYue; Yang, ZhiGang

2013-11-01

136

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

Microsoft Academic Search

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

Steven M. Jepsen; Edward E. Adams

2008-01-01

137

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

Microsoft Academic Search

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

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

2008-01-01

138

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

139

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

Microsoft Academic Search

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

Jun Inoue; Takashi Kikuchi; Donald K. Perovich

2008-01-01

140

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

Microsoft Academic Search

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

Byron R. Parizek; Richard B. Alley

2004-01-01

141

Oceanic Heat Contribution to Arctic Sea Ice Melt  

Microsoft Academic Search

The recent warming and record breaking summer reduction of sea ice cover in the Arctic Ocean have gained attention of both the scientific community as well as the general public. However, most of these changes have been so far primarily associated with the atmospheric forcing and ice-albedo feedback. We analyze output from a high resolution coupled ice-ocean model of the

W. Maslowski; J. Clement Kinney; J. Jakacki

2009-01-01

142

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

143

The Moulin Explorer: A Novel Instrument to Study Greenland Ice Sheet MeltWater Flow  

Microsoft Academic Search

Recent data shows that the Greenland ice sheet has been melting at an accelerated rate over the past decade. This melt water flows from the surface of the glacier to the bedrock below by draining into tubular crevasses known as moulins. Some believe these pathways eventually converge to nearby lakes and possibly the ocean. The Moulin Explorer Probe has been

A. Behar; H. Wang; A. Elliott; S. O'Hern; S. Martin; C. Lutz; K. Steffen; D. McGrath; T. Phillips

2008-01-01

144

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

National Technical Information Service (NTIS)

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....

C. B. Schaaf D. K. Hall G. Neumann N. E. DiGirolamo S. V. Nghiem

2010-01-01

145

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

146

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

147

Application of Aerosondes to melt-pond observation over Arctic sea ice  

NASA Astrophysics Data System (ADS)

Continuous observation of sea ice using a small robotic aircraft called the Aerosonde was made over the Arctic Ocean from Barrow, Alaska, on 20-21 July 2003. Over a region of 350 km off the coast of Barrow, ice concentration data that consists of ice and ponded areas was made using images taken by the aircraft. Melt- pond fraction (A_p) increased northward from 15 % to 30 % as the ice fraction (A_i) increased. However, the fraction of the ice that is ponded (A_p/(A_i+A_p)) was over 30 % in the perennial ice zone while about 25 % in the first year ice zone, suggesting the different stages of melt-pond evolution in each regions. AMSRE-derived ice concentration was underestimated 7% as compared with the observed one (A_i+A_p). These analyses demonstrate new technology for monitoring the spatial variations in the sea ice with melt ponds that would be very difficult to measure using satellites.

Inoue, J.; Curry, J. A.

2006-12-01

148

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

149

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

150

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

151

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

152

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

153

A model of the three-dimensional evolution of Arctic melt ponds on first-year and multiyear sea ice  

NASA Astrophysics Data System (ADS)

During winter the ocean surface in polar regions freezes over to form sea ice. In the summer the upper layers of sea ice and snow melts producing meltwater that accumulates in Arctic melt ponds on the surface of sea ice. An accurate estimate of the fraction of the sea ice surface covered in melt ponds is essential for a realistic estimate of the albedo for global climate models. We present a melt-pond-sea-ice model that simulates the three-dimensional evolution of melt ponds on an Arctic sea ice surface. The advancements of this model compared to previous models are the inclusion of snow topography; meltwater transport rates are calculated from hydraulic gradients and ice permeability; and the incorporation of a detailed one-dimensional, thermodynamic radiative balance. Results of model runs simulating first-year and multiyear sea ice are presented. Model results show good agreement with observations, with duration of pond coverage, pond area, and ice ablation comparing well for both the first-year ice and multiyear ice cases. We investigate the sensitivity of the melt pond cover to changes in ice topography, snow topography, and vertical ice permeability. Snow was found to have an important impact mainly at the start of the melt season, whereas initial ice topography strongly controlled pond size and pond fraction throughout the melt season. A reduction in ice permeability allowed surface flooding of relatively flat, first-year ice but had little impact on the pond coverage of rougher, multiyear ice. We discuss our results, including model shortcomings and areas of experimental uncertainty.

Scott, F.; Feltham, D. L.

2010-12-01

154

Surface melting of the (0001) face of TIP4P ice  

NASA Astrophysics Data System (ADS)

The onset of surface melting of the basal plane (0001) face of TIP4P ice is studied in the temperature range T = 190-250 K using the molecular dynamics (MD) method. The disordering of the surface seen in the calculations can be explained in terms of the disruption of the hydrogen bonding network at the surface. At T = 210 K and lower the surface remains solid-like, as evidenced by non-zero order parameters and no calculable self-diffusion, although the reorientational correlation time (ca. 100 ps) is closer to that of the liquid than that of bulk ice. On the other hand, at T = 230 K (-43°C) and higher the surface is liquid-like, as shown by low order parameters and a high translational and rotational mobility of the molecules. At all temperatures, there is an orientational preference for the water molecule pointing its protons down, which is in agreement with experiment. The polarisation of the surface increases with increasing temperature. For the transition layer, the calculated reorientational correlation times are in rough agreement with NMR experiments, but for T ? 230 K the calculated self-diffusion coefficients are much higher than the values obtained in NMR experiments.

Kroes, Geert-Jan

1992-09-01

155

Comparison of DMSP SSM/I and Landsat 7 ETM+ Sea Ice Concentrations During Summer Melt  

NASA Technical Reports Server (NTRS)

As part of NASA's EOS Aqua sea ice validation program for the Advanced Microwave Scanning Radiometer (AMSR-E), Landsat 7 Enhanced Thematic Mapper (ETM+) images were acquired to develop a sea ice concentration data set with which to validate AMSR-E sea ice concentration retrievals. The standard AMSR-E Arctic sea ice concentration product will be obtained with the enhanced NASA Team (NT2) algorithm. The goal of this study is to assess the accuracy to which the NT2 algorithm, using DMSP Special Sensor Microwave Imager radiances, retrieves sea ice concentrations under summer melt conditions. Melt ponds are currently the largest source of error in the determination of Arctic sea ice concentrations with satellite passive microwave sensors. To accomplish this goal, Landsat 7 ETM+ images of Baffin Bay were acquired under clear sky conditions on the 26th and 27th of June 2000 and used to generate high-resolution sea ice concentration maps with which to compare the NT2 retrievals. Based on a linear regression analysis of 116 25-km samples, we find that overall the NT2 retrievals agree well with the Landsat concentrations. The regression analysis yields a correlation coefficient of 0.98. In areas of high melt ponding, the NT2 retrievals underestimate the sea ice concentrations by about 12% compared to the Landsat values.

Cavalieri, Donald J.; Markus, Thorsten; Ivanoff, Alvaro; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

156

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

157

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

NASA Technical Reports Server (NTRS)

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

Macayeal, D. R.

1984-01-01

158

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

159

Isotope thermometry in melt-affected ice cores  

Microsoft Academic Search

A statistically significant relationship is observed between stable water isotopes (delta18O) 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

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

2011-01-01

160

Export of Algal Biomass from the Melting Arctic Sea Ice  

NASA Astrophysics Data System (ADS)

In the Arctic, under-ice primary production is limited to summer months and is restricted not only by ice thickness and snow cover but also by the stratification of the water column, which constrains nutrient supply for algal growth. Research Vessel Polarstern visited the ice-covered eastern-central basins between 82° to 89°N and 30° to 130°E in summer 2012, when Arctic sea ice declined to a record minimum. During this cruise, we observed a widespread deposition of ice algal biomass of on average 9 grams of carbon per square meter to the deep-sea floor of the central Arctic basins. Data from this cruise will contribute to assessing the effect of current climate change on Arctic productivity, biodiversity, and ecological function.

Boetius, Antje; Albrecht, Sebastian; Bakker, Karel; Bienhold, Christina; Felden, Janine; Fernández-Méndez, Mar; Hendricks, Stefan; Katlein, Christian; Lalande, Catherine; Krumpen, Thomas; Nicolaus, Marcel; Peeken, Ilka; Rabe, Benjamin; Rogacheva, Antonina; Rybakova, Elena; Somavilla, Raquel; Wenzhöfer, Frank; aff1

2013-03-01

161

Dip-Pen Nanolithography of High Melting-Temperature Molecules  

PubMed Central

Direct nanopatterning of a number of high melting-temperature molecules have been systematically investigated by Dip-Pen Nanolithography (DPN). By tuning DPN experimental conditions, all of the high melting-temperature molecules transported smoothly from the AFM tip to the surface at room temperature without tip pre-heating. Water meniscus formation between the tip and substrate is found to play a critical role in patterning high melting-temperature molecules. These results show that heating an AFM probe to a temperature above the ink's melting temperature is not a prerequisite for ink delivery, which extends the current “ink-substrate” combinations, available to DPN users.

Huang, Ling; Chang, Yu-Hsu; Kakkassery, Joseph J.; Mirkin, Chad A.

2008-01-01

162

September Arctic sea-ice minimum predicted by spring melt-pond fraction  

NASA Astrophysics Data System (ADS)

The area of Arctic September sea ice has diminished from about 7 million km2 in the 1990s to less than 5 million km2 in five of the past seven years, with a record minimum of 3.6 million km2 in 2012 (ref. ). The strength of this decrease is greater than expected by the scientific community, the reasons for this are not fully understood, and its simulation is an on-going challenge for existing climate models. With growing Arctic marine activity there is an urgent demand for forecasting Arctic summer sea ice. Previous attempts at seasonal forecasts of ice extent were of limited skill. However, here we show that the Arctic sea-ice minimum can be accurately forecasted from melt-pond area in spring. We find a strong correlation between the spring pond fraction and September sea-ice extent. This is explained by a positive feedback mechanism: more ponds reduce the albedo; a lower albedo causes more melting; more melting increases pond fraction. Our results help explain the acceleration of Arctic sea-ice decrease during the past decade. The inclusion of our new melt-pond model promises to improve the skill of future forecast and climate models in Arctic regions and beyond.

Schröder, David; Feltham, Daniel L.; Flocco, Daniela; Tsamados, Michel

2014-05-01

163

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

164

Methane efflux from high-latitude lakes during spring ice melt  

NASA Astrophysics Data System (ADS)

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 ?M in the top 15 cm sections to a maximum of 23 ?M in the lowest 15 cm sections of tundra lake ice and to a maximum of 147 ?M in taiga lake ice. Methane concentrations in the water beneath the ice reflect a similar pattern, with values near 5 ?M early in the ice-covered season, increasing up to 42 ?M in the tundra lakes, and up to 730 ?M in the taiga lakes. Methane levels increase in the water beneath the ice during the course of the winter due to decreasing water volume, exclusion from growing ice, and continued methane production in thawed sediments. Since the ice layer prohibits gas exchange with the atmosphere, the methane is not oxidized, as it would be during the summer months, allowing the winter accumulation and storage of methane in the ice and lake waters. Efflux measurements, taken with floating chambers on the taiga lakes, indicated a large pulse of methane released during the period of ice melt and spring turnover. The efflux from one lake ranged from 2.07 g CH4 m-2 in 1995 to 1.49 g CH4 m-2 in 1996 for the 10 day period immediately after ice melt. Estimation of methane efflux using a boundary layer diffusion model and surface water concentrations during the entire ice-free period in 1996 predicted an efflux of 1.79 g CH4 m-2 during the same 10 day period, compared with 2.28 g CH4 m-2 for the remainder of the summer season. This observation suggests that almost as much methane efflux can occur during a brief period immediately after ice melt as occurs during the remainder of the ice-free season. Since measurements of methane efflux from high-latitude-lakes are generally made after this breakup period, the overall contribution to atmospheric methane from high-latitude lakes may be twice that of current estimates.

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

1998-11-01

165

On the link between SAR?derived sea ice melt and development of the summer upper ocean mixed layer in the North Open Water Polynya  

Microsoft Academic Search

We examine the ability of SAR?derived landfast sea ice thermodynamic state surrounding the North Water Polynya to predict the timing of a shallow, stably stratified summer ocean mixed layer in the region. Radarsat?1 ScanSAR is used to derive melt and pond onset dates over landfast sea ice surrounding the polynya, describing its thermodynamic evolution. Salinity and temperature profiles, connected in

R. J. Galley; D. G. Barber; J. J. Yackel

2007-01-01

166

MODIS-Derived Surface Temperatures of the Greenland Ice Sheet, 2000 to 2006  

NASA Astrophysics Data System (ADS)

Ground and satellite measurements have shown increasing melt in recent years on the Greenland Ice Sheet (GIS). However, many questions remain about the magnitude, timing, and characteristics of the melt. Is the ice sheet melting earlier? Is the melt season lengthening? Is the average surface temperature of the ice sheet changing? Has the ice-sheet surface temperature increased in eastern, western, and/or northern Greenland? These questions can be addressed through analysis of satellite-derived, ice-sheet surface temperatures using the Moderate-Resolution Imaging Spectroradiometer (MODIS) flown on-board NASA's Terra and Aqua satellites. A standard, 1-km resolution, land-surface temperature (LST) daily product, MOD11A1 (Wan et al., 2002), is available from February 2000 to the present. Previous work using MOD11C2, a 5-km resolution, 8- day composite LST product, showed that the years 2002 and 2005 experienced the highest average ice-sheet temperatures during the peak of the 2000 2005 melt seasons when mean, clear-sky LSTs were studied for the entire ice sheet (Hall et al., 2006). This was in agreement with other studies showing extensive melt in 2002 and 2005 from passive-microwave and gound data (Steffen et al., 2004 and Steffen and Huff, 2005). Mean LSTs of the GIS were recalculated with the finer-resolution, 1-km daily data and results still show that the warmest mean LSTs of the 6-year period, 8.1 deg C and 8.2 deg C, occurred in 2002 and 2005, respectively. Other results using the MOD11A1 dataset show that the dates of first melt for seven years of MODIS data (2000 2006) are variable; for example unusually-large areas of the northeastern and northwestern sectors of the GIS began melting in June of 2002 and 2005. Also an extensive area of surface melt was observed for a few days in June of 2004, and not in the other six years. Automatic weather station data from Dye-2, Saddle and South Dome corroborate the satellite measurements, showing higher air temperatures on those days in June 2004. Additional work is underway to address the key questions, above. Though the MODIS record is not yet long enough to provide information about trends in LST of the GIS, MODIS-derived LSTs can be used to learn more about ice-sheet surface-temperature variability and its relationship to other climate indicators. References Hall, D.K., R.S. Williams, Jr., K.A. Casey, N.E. DiGirolamo and Z. Wan, 2006: Satellite-Derived, Melt-Season Surface Temperature of the Greenland Ice Sheet (2000-2005) and its Relationship to Mass Balance, Geophysical Research Letters, 33, L11501, doi:10.1029/2006GL026444. Steffen, K. S. V. Nghiem, R. Huff, and G. Neumann, 2004: The melt anomaly of 2002 on the Greenland Ice Sheet from active and passive microwave satellite observations, Geophysical Research Letters, 31, L20402, doi:10.1029/2004GL020444. Steffen, K. and R. Huff, 2005: http://cires.colorado.edu/science/groups/steffen/greenland/melt2005/ Wan, Z., Y. Zhang, Q. Zhang, and Z.-L. Li, 2002: Validation of the land-surface temperature products retrieved from Terra Moderate Resolution Imaging Spectroradiometer data, Remote Sensing of Environment, 83:163- 180.

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

2006-12-01

167

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

Microsoft Academic Search

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

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

2011-01-01

168

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

169

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

170

New insights into ice growth and melting modifications by antifreeze proteins  

PubMed Central

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

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

2012-01-01

171

Can Marine Microorganisms Influence Melting of the Arctic Pack Ice?  

Microsoft Academic Search

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

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

2004-01-01

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

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

174

Large-Scale Patterns of Snow Melt on Arctic Sea Ice Mapped from Meteorological Satellite Imagery,  

National Technical Information Service (NTIS)

The seasonal progression of snow melt on Arctic pack ice is mapped from satellite shortwave imagery (0.4-1.1 micrometers) for four spring/summer seasons (1977, 1979, 1984 and 1985). This provides the first detailed information on the temporal change of th...

G. Scharfen R. G. Barry D. A. Robinson G. Kukla M. C. Serreze

1987-01-01

175

Mesospheric trends of temperatures and ice clouds  

NASA Astrophysics Data System (ADS)

The Leibniz-Institute Middle Atmosphere Model LIMA is used to study mesospheric trends in summer during the last decades. In order to account for realistic atmospheric conditions LIMA adapts several observational data sets, amongst others the tropospheric and stratospheric temperatures and winds from ECMWF, daily Lyman alpha fluxes, carbon dioxide concentrations, and total ozone. With a coupled microphysical model (LIMA-ICE) the effects on noctilucent clouds (NLC) are investigated since they are considered to be tracers for changes in the mesosphere. We present several comparisons of simulated trends with observations regarding the background atmosphere (temperatures, ionospheric reflection heights) and mesospheric ice clouds. In general there is good agreement between trends from LIMA and observations. Cooling in the mesosphere is on the order of 2-4 K/decade. The magnitude of the mesospheric temperature trend varies during the last five decades. In particular, the period from 1979-1997 shows large mesospheric cooling of 3-5 K/decade. This large cooling is primarily caused by long term changes of ozone in the upper stratosphere in combination with an increase of carbon dioxide. From our model results we identify sources of trends and their effects on ice layers. We critically discuss the role of mesospheric ice clouds as indicators for global change.Summerly averaged temperature anomalies at 70 km altitude derived from LIMA at 50°N, 7°E. Linear trends (red lines) are determined for run 1 from multiple regression which considers solar activity. Ozone anomalies (black) are taken from SBUV at 0.70~hPa and from WMO for the period 1961-1978 (from Berger and Lübken, Geophys. Res. Lett., 2011).

Luebken, F.; Berger, U.

2012-12-01

176

Hydrograph peaks caused by ice channel melt in Black Hills streams  

SciTech Connect

The Black Hills has an average annual precipitation of approximately 20 inches, most of which occurs in early summer. The winters are typically cold and fairly dry. Most streams within the Precambrian central Black Hills have perennial and ephemeral reaches which are related to the presence of surficial deposits. During the winter, ice accumulates in the channels of some stream reaches, completely filling the channels, particularly in shady locations below springs or seeps. High discharges occur during warm spells in late winter and early spring. These high discharges are not due to snow melt because many watersheds are often void of snow. Ice-channel surveys were conducted on Spring, Battle, French, Slate, and Grace Coolidge Creeks during 1988. High discharges occurred during the warm spells at the end of March. Since no precipitation occurred during this time, and the watersheds were barren of snow, the discharge peaks are believed due to melting of ice stored in the channels. This hypothesis is supported by the fact that the volume of the water stored as ice was approximately the same as the volume of water represented by the discharge anomaly. The ice stored in channels primarily results from ground water discharge over the winter. It is not due to melting snow or surface water runoff per se. Separation of the hydrograph into surface and ground water components should take into account this phenomena.

Rahn, P.H. (South Dakota School of Mines and Technology, Rapid City, SD (United States). Dept. of Geology and Geological Engineering)

1992-01-01

177

Melting dynamics of large ice balls in a turbulent swirling flow  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

178

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

179

The influence of double-diffusive processes on the melting of ice in the Arctic Ocean: laboratory analogue experiments and their interpretation  

NASA Astrophysics Data System (ADS)

This study has been motivated by two oceanographic observations: an increased rate of melting of sea ice in the Arctic Ocean, and the advance of an anomalously warm tongue of Atlantic water across the Arctic below the halocline over the last few decades. A series of laboratory experiments has been carried out in order to explore the physical principles underlying these phenomena, and the possibility that the extra heating at depth is responsible for the enhanced melting rate. A tank was filled with salt solution having various constant vertical density gradients. A block of ice one third of the length of the tank was floated on the surface at one end, and the rest of the surface and the walls of the tank were insulated. When no extra heat was supplied the melting rate (loss of weight of the ice in 1 h) systematically decreased as the stratification was changed from homogeneous fluid to increasingly large density gradients, while keeping the salinity of the solution in contact with the ice constant. An analogue of the intruding Atlantic water was produced by heating the lower portion of the vertical end wall at the end of the tank opposite to the ice end, keeping its temperature constant, and using the same range of salinity gradients as in the unheated experiments. Again the melting rate decreased as the density gradient was increased, but for low gradients it was larger than that in the unheated experiments. Above a certain intermediate gradient there was no significant difference in melting rate between the unheated and heated runs. The melting data were supplemented by photographs and vertical temperature and salinity profiles. The upward transfer of heat from the body of the fluid to melt the ice was clearly double-diffusive: overturning layers, separated by 'diffusive' interfaces, were visible on shadowgraphs, and the thickness of the layers decreased as the density gradient increased. The mean thickness of the layers through the depth of the tank also systematically decreased as the density gradient increased. With weak gradients an extra heat flux to the ice came from the intruding heated layer, but at large gradients this tongue of warm water at depth did not add to the flux near the surface. Though they were obtained in a simple, arbitrary and fixed geometry, we believe that the results of these experiments can be used as the basis for a better physical understanding of the melting rates of ice in the Arctic under various conditions.

Turner, J. S.; Veronis, G.

2004-03-01

180

Snow/ice melt precipitation runoff modelling of glaciers in the Bhutan himalaya  

NASA Astrophysics Data System (ADS)

After the 1994 outburst of the Luggye glacier lake in Northern Bhutan, the Royal Bhutanese Government initiated a project on GLOF risk reduction and mitigation measures in the Pho River headwaters. The approach to model snow/ice melt and precipitation of this high mountain system with few measured data only was a request of this integrated geoscientific project. The size of the test area for runoff modelling is about 50 km2 and comprises an interlinked glacier system of 3 glaciers and moraine dammed glacier lakes. The model proposed for the Luggye catchment area is based on records from a nearby weather station at Thanza (4150 m altitude) available for the years 2000-2001, a high resolution digital elevation model and the total surface discharge of the Luggye test area, calculated from the Luggye outlet hydrograph. Using the digital elevation model, the catchment area and the surface of the glaciers, up to 7000 m altitude, was divided into 100-meter elevation layers. Precipitation and mean air temperature from Thanza were extrapolated according to the best fitting results. Prominent single temperature and precipitation “events” recorded at Thanza can be related to discharge “events” in the Luggye hydrograph and allow for calculation of time lag and lapse rates. The modelled discharge is calculated as the total of the three simulated components, namely base flow, melt water from snow and ice, and precipitation. The model proposed can be interactively evaluated by best fitting of the model hydrograph to the measured hydrograph. This simulation was achieved using temperature lapse rates of -0.4 to -0.45 °C/100 m during the summer monsoon period, a degree/day factor of 6 to 8 l/(m2*day*°C), and the decrease of precipitation with approximately 7% per 100-meter altitude. Although many assumptions have to be taken for non-extreme weather conditions, the very good correlation of 0.97 between runoff modelling and the real discharge hydrograph highlights the quality of the simulation model. This encourages for testing it in other Himalayan regions. Furthermore such a model could act as a low-cost, data-driven early warning system for the glaciated regions in the Himalayas, when meteorological data reaches dangerous threshold values, which may precede a glacial lake outburst.

Payer, T.; Leber, D.; Haeusler, H.; Brauner, M.; Wangda, D.

2003-04-01

181

Advances in Determining First-year Sea Ice Melt Pond Fraction Using C-band Polarimetric SAR  

NASA Astrophysics Data System (ADS)

Greater sea ice melt pond fractions arising from an increase in first-year sea ice relative to multiyear ice may contribute to decreasing Arctic summer sea ice extents observed in recent years. Regions of higher melt pond fraction experience enhanced absorption of shortwave energy into the ice-ocean system which accelerates ice decay and a decrease in ice volume in successive years. Understanding regional variations in melt pond fraction, and determining linkages to competing interactions such as snow depth, sea ice type, and warming/cooling trends, requires an effective sea ice monitoring tool during the critical summer melt period. Optical remote sensing data are of limited use due to the ubiquity of cloud cover over the Arctic during summer months. First results are presented on C-band (5.3 GHz) radar scattering signatures and polarimetric discriminants from a surface-based, fully-polarimetric, scatterometer deployed over melt pond covered first-year sea ice in the Canadian Arctic. Scattering properties of melt ponds, sea ice, and composite surfaces are evaluated for varying radar parameters and changing surface geophysical properties. Coincident high-resolution C-band dual-polarised (HH+VV or HH+HV) radar image data from ENVISAT-ASAR are used to demonstrate the utility of wide swath SAR data for the inversion of melt pond fraction and the proxy estimation of climatological á from Arctic first-year sea ice. The optimal combination of polarimetric discriminants and radar parameters for achieving this technique using fully polarimetric SAR data, e.g. from the recently launched RADARSAT-2, is outlined.

Scharien, R.; Geldsetzer, T.; Yackel, J.

2008-12-01

182

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

USGS Publications Warehouse

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

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

1998-01-01

183

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

NASA Astrophysics Data System (ADS)

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

Timmermann, Ralph; Hellmer, Hartmut H.

2013-10-01

184

Predicting a protein's melting temperature from its amino acid sequence.  

PubMed

Melting temperature is an important characteristic feature of a protein and is used for various purposes such as in drug development. Currently protein melting temperature is determined by laboratory methods such as Differential Scanning Calorimetry, Circular Dichroism, Fourier transform infrared spectroscopy and several other methods. These methods are laborious and costly. Therefore, we propose a novel bioinformatics based method for predicting protein melting temperature from amino acid sequence of a protein. This is not only a challenging task but has been previously unexplored. For this study, melting temperature of 230 proteins from a range of organisms was collected along with their sequence information from the published literature. The melting temperature of these proteins represents a very large spectrum and varies between 25°C and 113°C. The protein sequences are then used to derive two sets of sequence-driven features, namely amino acid composition (AAC) and pseudo-amino acid composition (PseudoAAC) to characterise the proteins. In order to predict the melting temperature, two different computational intelligence methods, namely artificial neural networks (ANN) and adaptive network-fuzzy inference system (ANFIS) were utilized. Amongst over 100 different models generated, the ANN produced the best model with the least error (0.01087 for the AAC and 0.01086 for the pseudoAAC). As both feature sets yielded quite similar error and computation of pseudoAAC is costly when compared to that of AAC, traditional AAC seems to be an effective feature set for predicting melting temperature. The results obtained in this study are very promising and, for the first time, shows that the melting temperature of a protein can be predicted from its amino acid sequence only. Therefore, costly lab-based experiments may not be required to measure the melting temperature and the bioinformatics models can help speed up laboratory processes such as in drug development. PMID:21095941

Gorania, Malde; Seker, Huseyin; Haris, Parvez I

2010-01-01

185

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

186

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

SciTech Connect

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

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

1997-07-01

187

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

188

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

189

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

190

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

191

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

192

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

193

Melting probes as a means to access the subsurface of Mars' polar caps and Jupiter's ice moons  

NASA Astrophysics Data System (ADS)

There is a high scientific interest in exploring certain planetary icy environments in the solar system (Mars' polar caps, Europa and other icy satellites) motivated by the search for traces of life in these extreme environments as well as interest in planetary climate history as in the case of Mars. A promising technique to penetrate thick ice layers with small and reliable probes which do not require the heavy, complex and expensive equipment of a drilling rig is by melting. Contamination avoidance with respect to planetary protection requirements can be fulfilled using melting probes, since the melting channel refreezes behind the probe and shuts off the contact to the surface; also, in-situ decontamination of the probe is possible. Melting probes can be equipped with a suite of scientific instruments that are capable e.g. of determining the chemical and isotopic composition of the embedded or dissolved materials, of the ices themselves, of the dust content and possible traces of indigenous biological activity. Due to the still rather high energy demand to overcome the melting enthalpy, in case of extraterrestrial application (e.g. Europa or polar caps of Mars), only heating with radioactive isotopes seems feasible for reaching greater depths. The necessary power is driven by the desired penetration velocity (linearly) and the dimensions of the probe (proportional to the cross section). On Mars, however, solar cells could be used to power small tethered melting probes in polar summer. While such probes have successfully been used for terrestrial applications, e.g., in Antarctica in the 1990ies, the technology is not yet mature for space applications; for example, the behaviour in vacuum (below the triple point pressure of water, i.e., 611 Pa) needs to be assessed. We will report briefly on our laboratory tests with melting probes in vacuum and under very low temperatures to this end. Practical issues (impact of dust on the performance, gravity dependence, prevention of blocking, attitude control, power supply, communications) and engineering concepts will be discussed. For future missions to Europa (in particular in view of the ESA Cosmic Vision Programme), if planned to include a Surface Package, a melting probe may be the most adequate (and most easily realized) way to access the subsurface areas, protected from the intense ionising radiation in the Jovian system and most interesting from a biochemical and biological point of view.

Biele, J.; Ulamec, S.; Funke, O.; Engelhardt, M.

194

Correlation Studies of Sea Ice Concentration with Surface Temperature and Meltponding  

NASA Technical Reports Server (NTRS)

The spatial and temporal variability of sea ice concentrations derived from passive microwave data is studied in conjunction with co-registered high resolution infrared and visible satellite data. Cloud free infrared and visible data provide surface temperature and large scale surface characteristics, respectively, that can be used to better understand regional and seasonal fluctuations in ice concentrations. Results from correlation analysis of ice concentration versus surface temperature data show the intuitively expected negative relationship but the strength in the relationship is unexpectedly very strong. In the Antarctic, the correlation is consistently very high spatially when yearly anomalies are used, and not so high in some areas when seasonal anomalies are used, especially during spring and summer. In the monthly anomalies, the correlation is also good, especially in dynamically active regions. The expanse in the anomalies in surface temperature are shown to go way beyond the sea ice regions into the open ocean and continental areas, suggesting strong atmospheric forcing. Weak correlations are normally found in highly consolidated areas, where large changes in temperature do not cause large changes in ice concentration on a short term, and in open ocean polynya areas, where the change in ice concentration may be cause by melt from the underside of the ice. In the Arctic, strong correlations between surface temperature and ice concentration are evident for all seasons except during the summer. In the summer, factors such as meltponding, surface wetness, and ice breakup, as detected by high resolution visible data, contributes to larger uncertainties in the determination of ice concentration and the lack of good correlation of the variables.

Comiso, J. C.; Zukor, Dorothy J. (Technical Monitor)

2001-01-01

195

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

196

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

USGS Publications Warehouse

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

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

2004-01-01

197

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

198

Early Mars climate near the Noachian-Hesperian boundary: Independent evidence for cold conditions from basal melting of the south polar ice sheet (Dorsa Argentea Formation) and implications for valley network formation  

NASA Astrophysics Data System (ADS)

Currently, and throughout much of the Amazonian, the mean annual surface temperatures of Mars are so cold that basal melting does not occur in ice sheets and glaciers and they are cold-based. The documented evidence for extensive and well-developed eskers (sediment-filled former sub-glacial meltwater channels) in the south circumpolar Dorsa Argentea Formation is an indication that basal melting and wet-based glaciation occurred at the South Pole near the Noachian-Hesperian boundary. We employ glacial accumulation and ice-flow models to distinguish between basal melting from bottom-up heat sources (elevated geothermal fluxes) and top-down induced basal melting (elevated atmospheric temperatures warming the ice). We show that under mean annual south polar atmospheric temperatures (-100 °C) simulated in typical Amazonian climate experiments and typical Noachian-Hesperian geothermal heat fluxes (45-65 mW/m2), south polar ice accumulations remain cold-based. In order to produce significant basal melting with these typical geothermal heat fluxes, the mean annual south polar atmospheric temperatures must be raised from today's temperature at the surface (-100 °C) to the range of -50 to -75 °C. This mean annual polar surface atmospheric temperature range implies lower latitude mean annual temperatures that are likely to be below the melting point of water, and thus does not favor a "warm and wet" early Mars. Seasonal temperatures at lower latitudes, however, could range above the melting point of water, perhaps explaining the concurrent development of valley networks and open basin lakes in these areas. This treatment provides an independent estimate of the polar (and non-polar) surface temperatures near the Noachian-Hesperian boundary of Mars history and implies a cold and relatively dry Mars climate, similar to the Antarctic Dry Valleys, where seasonal melting forms transient streams and permanent ice-covered lakes in an otherwise hyperarid, hypothermal climate.

Fastook, James L.; Head, James W.; Marchant, David R.; Forget, Francois; Madeleine, Jean-Baptiste

2012-05-01

199

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

200

Temperature Measurements Reveal Accretion Of Ice On Airfoils  

NASA Technical Reports Server (NTRS)

Method of detecting accretion of ice on airfoil based on measurement of difference between temperatures at icing and nonicing locations on airfoil. Release of latent heat of fusion gives rise to characteristic gradient of temperature. Temperatures and difference between them measured by use of contact sensors or remote sensor. Measurements used to trigger alarms and/or deicing equipment.

Hansman, Robert J., Jr.; Dershowitz, Adam Lee

1995-01-01

201

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

202

InSAR and GPS Observations Show Seasonal Speedup of Ice Flow in Greenland Following the Onset of Summer Melting  

Microsoft Academic Search

We have assembled a comprehensive set of InSAR and GPS observations that reveal both spatial and temporal changes in velocity during the summer melt season along a several-hundred kilometer stretch of the ice-sheet margin near Jakobshavn Isbrae, Greenland. In the bare ice zone, we obtain InSAR (speckle\\/feature tracking) results throughout the melt season that agree well with results from two

I. Joughin; S. B. Das; M. A. King; B. Smith; I. Howat; T. Moon

2007-01-01

203

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

204

Regulation of algal blooms in Antarctic Shelf Waters by the release of iron from melting sea ice  

NASA Astrophysics Data System (ADS)

During summer 1995-96, we measured iron in the water column and conducted iron-enrichment bottle-incubation experiments at a station in the central Ross Sea (76°30?S, 170°40?W), first, in the presence of melting sea ice, and 17 days later, in ice-free conditions. We observed a striking temporal change in mixed-layer dissolved iron concentrations at this station, from 0.72-2.3 nM with sea ice present, to 0.16-0.17 nM in ice-free conditions. These changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal (diatom) biomass. Our incubation experiments suggest that conditions were iron-replete in the presence of sea ice, and iron-deficient in the absence of sea ice. We surmise that bioavailable iron was released into seawater from the melting sea ice, stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer, until iron-limited conditions developed. These observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production, particularly ice-edge blooms, in seasonally ice-covered Antarctic waters.

Sedwick, Peter N.; DiTullio, Giacomo R.

1997-10-01

205

The Relationship between East Greenland Current Temperature and Southern Greenland Ice Sheet Runoff during the Last Two Deglaciations  

Microsoft Academic Search

Recent observations of outlet glaciers of the Greenland Ice Sheet (GIS) suggest that they are sensitive to subsurface water warming, but these observations are limited to only the past decade. Here we investigate past changes in East Greenland Current temperature and their relationship to southern GIS melting. We use Neogloboquadrina pachyderma (sinistral) Mg\\/Ca as a proxy for pycnocline temperatures, and

K. Winsor; A. E. Carlson; G. P. Klinkhammer; B. A. Haley; J. S. Stoner; C. Hillaire-Marcel

2009-01-01

206

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

PubMed

The climate of the last glaciation was interrupted by numerous abrupt temperature fluctuations, referred to as Greenland interstadials and stadials. During warm interstadials the meridional overturning circulation was active transferring heat to the north, whereas during cold stadials the Nordic Seas were ice-covered and the overturning circulation was disrupted. Meltwater discharge, from ice sheets surrounding the Nordic Seas, is implicated as a cause of this ocean instability, yet very little is known regarding this proposed discharge during warmings. Here we show that, during warmings, pink clay from Devonian Red Beds is transported in suspension by meltwater from the surrounding ice sheet and replaces the greenish silt that is normally deposited on the north-western slope of Svalbard during interstadials. The magnitude of the outpourings is comparable to the size of the outbursts during the deglaciation. Decreasing concentrations of ice-rafted debris during the interstadials signify that the ice sheet retreats as the meltwater production increases. PMID:24264767

Rasmussen, Tine L; Thomsen, Erik

2013-01-01

207

Effects of locust bean gum and mono- and diglyceride concentrations on particle size and melting rates of ice cream.  

PubMed

The objective of this study was to determine how varying concentrations of the stabilizer, locust bean gum (LBG), and different levels of the emulsifier, mono- and diglycerides (MDGs), influenced fat aggregation and melting characteristics of ice cream. Ice creams were made containing MDGs and LBG singly and in combination at concentrations ranging between 0.0% to 0.14% and 0.0% to 0.23%, respectively. Particle size analysis, conducted on both the mixes and ice cream, and melting rate testing on the ice cream were used to determine fat aggregation. No significant differences (P < 0.05) were found between particle size values for experimental ice cream mixes. However, higher concentrations of both LBG and MDG in the ice creams resulted in values that were larger than the control. This study also found an increase in the particle size values when MDG levels were held constant and LBG amounts were increased in the ice cream. Ice creams with higher concentrations of MDG and LBG together had the greatest difference in the rate of melting than the control. The melting rate decreased with increasing LBG concentrations at constant MDG levels. These results illustrated that fat aggregation may not only be affected by emulsifiers, but that stabilizers may play a role in contributing to the destabilization of fat globules. PMID:23772704

Cropper, S L; Kocaoglu-Vurma, N A; Tharp, B W; Harper, W J

2013-06-01

208

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

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

An optimized estimate of glacial melt from the Ross Ice Shelf using noble gases, stable isotopes, and CFC transient tracers  

Microsoft Academic Search

Isotopes of helium and neon and the H218O\\/H216O ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts. Their high concentrations in glacial meltwater, compared to other environmental sources, make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior. We combine

B. Loose; P. Schlosser; W. M. Smethie; S. Jacobs

2009-01-01

211

An optimized estimate of glacial melt from the Ross Ice Shelf using noble gases, stable isotopes, and CFC transient tracers  

Microsoft Academic Search

Isotopes of helium and neon and the H2 18O\\/H2 16O ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts. Their high concentrations in glacial meltwater, compared to other environmental sources, make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior.

B. Loose; P. Schlosser; W. M. Smethie; S. Jacobs

2009-01-01

212

GNET detected an anomalous 'spike' in ice loss in Greenland during the 2010 melting season  

NASA Astrophysics Data System (ADS)

The Greenland GPS Network (GNET) uses GPS geodesy to measure the displacement of bedrock exposed near the margins of the Greenland Ice Sheet. The amplitudes of the observed vertical velocities indicate that over most of coastal Greenland these displacements are dominated by the solid earth's instantaneous elastic response to contemporary losses in ice mass. Superimposed on longer term trends, an anomalous 'pulse' of uplift accumulated at many GNET stations during a ~5 month period in 2010, and we will show that this anomalous uplift is spatially correlated with the 2010 melting day anomaly (Tedesco et al., 2011). This result confirms the ability of GPS networks in Greenland, Antarctica and elsewhere to directly sense ice mass changes at sub-annual as well as longer timescales. GNET and similar GPS networks can therefore mitigate the loss of ice mass measurements following the anticipated termination of the GRACE satellite mission. This result also suggests that ice mass varies over a range of time scales, rather like sea level.

Bevis, M. G.; Wahr, J. M.; Khan, S. A.; Madsen, F.; Brown, A. K.; Willis, M. J.; Kendrick, E. C.; Knudsen, P.; van Dam, T. M.; Box, J. E.; Caccamise, D. J.; Johns, B.; Nylen, T.; Abbott, R.; White, S.; Forsberg, R.; Zhou, H.; Francis, O.; Wang, J.; Wilson, T. J.

2011-12-01

213

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

214

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

215

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

216

Spatial and Temporal Variation of Multiyear Sea Ice Distributions: Relationships among Melt Duration, Recruitment, Export, Clouds, and Greenhouse Gases  

NASA Astrophysics Data System (ADS)

We present the spatial and temporal variation of multiyear (MY) sea ice distributions: relationships among melt duration, recruitment, export, clouds, and greenhouse gases in the Arctic. Melt onset dates, freeze onset dates were estimated over Arctic sea-ice for the past 25-years using standardized SMMR-SSM/I data sets (1979-2002). Sea ice melt dynamics were compared between annual and perennial ice, and between different geographic regions. 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, coinciding with cyclonic low pressure and ice motion anomalies associated with the AO's high-index phase (1989-2002). In the northern Chukchi and East Siberian Seas, mean annual melt duration increased 2-3 weeks following the positive AO phase shift, compared to prior years (1979-1988). Different methods of MY sea ice inversions from SSM/I Tb data were compared using different multilayer perceptron (MLP) neural networks (NN) constructed with learning data based on ERS SAR and OKEAN-01 MY ice map products. Monthly Arctic MY sea ice concentration maps (1979 - 2003) were generated from SSM/I Tbs (19 GHz V, 19 GHz H and 37 GHz V) using a modified MLP with error back propagation, and then compared with respective MY sea ice concentration maps derived with the NASA Team algorithm. Three MLP NN ice-type classification methods utilizing SSM/I passive microwave data were originally developed and compared. Each used the same OKEAN-derived MY sea ice learning data, but each used a different learning algorithm: error back propagation with simulated annealing, dynamic learning with polynomial basis functions, and dynamic learning with two-step optimization. For MY sea ice inversions, the modified MLP NN with error back propagation was determined more efficient. NN analyses of MY sea ice distribution revealed considerable interannual dynamics and variability. Linear trends in MY sea ice area during 1979-2003 were negative and most significant for the NN estimates. MY sea ice distribution revealed considerable interannual dynamics and regional variability. Overall decreases in MY ice area over the 14-year period resulted from average net losses in the far western and near eastern Arctic, however, the losses were partially compensated by increases in the central Siberian sector. In conclusion of our studies we estimated Fram Strait MY sea ice export, constructed January MY ice area concurrently regressed on the previous winter's AO index and the previous year's average sea level pressure gradient across the Fram Strait, and correlation between melting events, clouds, and greenhouse gases.

Belchansky, G. I.; Douglas, D. C.; Eremeev, V. A.; Platonov, N. G.

2004-05-01

217

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

NASA Technical Reports Server (NTRS)

We have developed a climate-data record (CDR) of "clear-sky" ice-surface temperature (IST) of the Greenland Ice Sheet using Moderate-Resolution Imaging Spectroradiometer (MODIS) data. The CDR provides daily and monthly-mean IST from March 2000 through December 2010 on a polar stereographic projection at a resolution of 6.25 km. The CDR is amenable to extension into the future using Visible/Infrared Imager Radiometer Suite (VIIRS) data. Regional "clear-sky" surface temperature increases since the early 1980s in the Arctic, measured using Advanced Very High Resolution Radiometer (AVHRR) infrared data, range from 0.57 +/- 0.02 to 0.72 +/- 0.1 c per decade. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near O C during the melt season, and is thus vulnerable to rapid melting if temperatures continue to increase. An increase in melting of the ice sheet would accelerate sea-level rise, an issue affecting potentially billions of people worldwide. The IST CDR will provide a convenient data set for modelers and for climatologists to track changes of the surface temperature of the ice sheet as a whole and of the individual drainage basins on the ice sheet. The daily and monthly maps will provide information on surface melt as well as "clear-sky" temperature. The CDR will be further validated by comparing results with automatic-weather station data and with satellite-derived surface-temperature products.

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

2011-01-01

218

Emissivities of High Temperature Metallic Melts  

Microsoft Academic Search

The mathematical modeling of heat flow in high temperature processes has been a useful means of obtaining more efficient process\\u000a design and stricter process control. At high temperatures heat can be transferred by three mechanisms, that is, conduction,\\u000a convection, and radiation. Analysis of heat transfer requires physical property data of a medium through which heat is transferred,\\u000a relevant to the

Masahiro Susa; Rie K Endo

2009-01-01

219

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

220

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

221

A phenomenological model for predicting melting temperatures of DNA sequences.  

PubMed

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

Khandelwal, Garima; Bhyravabhotla, Jayaram

2010-01-01

222

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

223

Eutectic melting temperature of the lowermost Earth's mantle  

NASA Astrophysics Data System (ADS)

Partial melting of the Earth's deep mantle probably occurred at different stages of its formation as a consequence of meteoritic impacts and seismology suggests that it even continues today at the core-mantle boundary. Melts are important because they dominate the chemical evolution of the different Earth's reservoirs and more generally the dynamics of the whole planet. Unfortunately, the most critical parameter, that is the temperature profile inside the deep Earth, remains poorly constrained accross the planet history. Experimental investigations of the melting properties of materials representative of the deep Earth at relevant P-T conditions can provide anchor points to refine past and present temperature profiles and consequently determine the degree of melting at the different geological periods. Previous works report melting relations in the uppermost lower mantle region, using the multi-anvil press [1,2]. On the other hand, the pyrolite solidus was determined up to 65 GPa using optical observations in the laser-heated diamond anvil cell (LH-DAC) [3]. Finally, the melting temperature of (Mg,Fe)2SiO4 olivine is documented at core-mantle boundary (CMB) conditions by shock wave experiments [4]. Solely based on these reports, experimental data remain too sparse to draw a definite melting curve for the lower mantle in the relevant 25-135 GPa pressure range. We reinvestigated melting properties of lower mantle materials by means of in-situ angle dispersive X-ray diffraction measurements in the LH-DAC at the ESRF [5]. Experiments were performed in an extended P-T range for two starting materials: forsterite and a glass with chondrite composition. In both cases, the aim was to determine the onset of melting, and thus the eutectic melting temperatures as a function of pressure. Melting was evidenced from drastic changes of diffraction peak shape on the image plate, major changes in diffraction intensities in the integrated pattern, disappearance of diffraction rings, and changes in the relation between sample-temperature and laser-power. In this work, we show that temperatures higher than 4000 K are necessary for melting mean mantle at the 135 GPa pressure found at the core mantle boundary (CMB). Such temperature is much higher than that from estimated actual geotherms. Therefore, melting at the CMB can only occur if (i) pyrolitic mantle resides for a very long time in contact with the outer core, (ii) the mantle composition is severely affected by additional elements depressing the solidus such as water or (iii) the temperature gradient in the D" region is amazingly steep. Other implications for the temperature state and the lower mantle properties will be presented. References (1) Ito et al., Phys. Earth Planet. Int., 143-144, 397-406, 2004 (2) Ohtani et al., Phys. Earth Planet. Int., 100, 97-114, 1997 (3) Zerr et al., Science, 281, 243-246, 1998 (4) Holland and Ahrens, Science, 275, 1623-1625, 1997 (5) Schultz et al., High Press. Res., 25, 1, 71-83, 2005.

Andrault, D.; Lo Nigro, G.; Bolfan-Casanova, N.; Bouhifd, M.; Garbarino, G.; Mezouar, M.

2009-12-01

224

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

225

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

226

The ‘Little Ice Age’ – only temperature?  

Microsoft Academic Search

Understanding the climate of the last few centuries, including the ‘Little Ice Age’, may help us better understand modern-day natural climate variability and make climate predictions. The conventional view of the climate development during the last millennium has been that it followed the simple sequence of a ‘Mediaeval Warm Period’, a cool ‘Little Ice Age’ followed by warming in the

Atle Nesje; Svein Olaf Dahl

2003-01-01

227

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

Microsoft Academic Search

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

D. G. Barber; J. Yackel

228

Surface deformation induced by present-day ice melting in Svalbard  

NASA Astrophysics Data System (ADS)

The vertical movement of the Earth's surface is the result of a number of internal processes in the solid Earth, tidal forces and mass redistribution in the atmosphere, oceans, terrestrial hydrosphere and cryosphere. Close to ice sheets and glaciers, the changes in the ice loads can induce large vertical motions at intraseasonal to secular timescales. The Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) antennas in Ny-Ålesund, Svalbard that started observations in 1991 and 1995, respectively, observe vertical uplift rates on the order of 8 +/- 2 mmyr-1, which are considerably larger than those predicted by postglacial rebound (PGR) models (order 2 mmyr-1). The observations also indicate increased uplift rates starting some time in 2000. A local GPS campaign network that has been reoccupied annually since 1998, reveals a tilting away from the neighbouring glaciers. The Svalbard glaciers have been undergoing melting and retreat during the last century, with increased melting since about 2000. We compared the observed vertical motion to the motion predicted by loading models using a detailed ice model with annual time resolution as forcing. The model predictions correlate well with the observations both with respect to the interannual variations and the spatial pattern of long-term trends. The regression coefficients for predicted and observed interannual variations in height is 1.08 +/- 0.38, whereas the regression coefficient for the predicted and observed spatial pattern turns out to be 1.26 +/- 0.42. Estimates of the predicted secular trend in height due to PGR and present-day melting are on the order of 4.8 +/- 0.3 mmyr-1 and thus smaller than the observed secular trend in height. This discrepancy between predictions and observations is likely caused by the sum of errors in the secular rates determined from observations (due to technique-dependent large-scale offsets) and incomplete or erroneous models (unaccounted tectonic vertical motion, errors in the ice load history, scale errors in the viscoelastic PGR models and the elastic models for present-day melting).

Kierulf, H. P.; Plag, H.-P.; Kohler, J.

2009-10-01

229

Abundance and variability of microorganisms and transparent exopolymer particles across the ice–water interface of melting first-year sea ice in the Laptev Sea (Arctic)  

Microsoft Academic Search

The distribution and abundance of transparent exopolymer particles (TEP) was determined in and below pack ice of the Laptev\\u000a Sea from July to September 1995. Samples were collected from the lowermost 10?cm of ice floes and at 10?cm below the ice–water\\u000a interface. Abundance of bacteria, protists and TEP was determined, and the sea ice–water boundary layer was characterized\\u000a using temperature,

C. Krembs; A. Engel

2001-01-01

230

Exploring the Influence of Ice Temperature in Alpine Glaciers on the Evolution of Longitudinal Valley Profiles  

NASA Astrophysics Data System (ADS)

The erosional signature of a glacier is often characterized by a longitudinal valley profile that exhibits a stepped morphology, decreased valley floor slope, and overdeepened basin. Numerical modeling experiments have demonstrated that the evolution of such profiles is highly dependent on ice discharge, and hence subglacial water pressure-dependent sliding speed, as well as the material properties of the underlying bedrock. While there are abundant examples of landscapes that demonstrate the valley profile characteristic of efficient glacial erosion, some highly glaciated mountain ranges such as the Himalayas maintain exceptionally tall peaks. These exceptionally tall peaks may be interpreted as evidence for the absence of efficient glacial erosion. One possible explanation for the absence of efficient glacial erosion is the presence of cold-based glacial conditions. Alternatively, the presence of erosionally resistant bedrock with wide fracture spacing may limit erosion. In temperate glaciers, in which basal ice temperatures are warm, or at the pressure melting point (PMP), sliding and erosion occur whenever and wherever high subglacial water pressures exist. In polythermal glaciers, by contrast, erosion efficiency is strongly modulated by basal ice temperature. Sliding, and hence erosion, is prevented when and where basal ice temperatures are cold, or below the PMP. To date, the influence of spatial and temporal variations in basal ice temperature on the efficiency of glacial erosion over long timescales (>1 Ma) remains largely unexplored. We present numerical model results in which we explore the influence of glacier ice temperature on the longitudinal valley profile that emerges during long-term glacial erosion. We focus on identifying conditions that maintain polythermal glaciers in which the basal ice at high elevations is cold, while the basal ice at lower elevations is at the PMP. These unique conditions limit sliding and erosion to low elevations. In cases in which rock uplift outpaces the limited high elevation glacial erosion, exceptionally high peaks emerge, and a knickpoint forms along the longitudinal valley profile at the transition between cold and warm-based ice. These simulations allow a more formal means of discrimination between the conditions in which cold-based ice may be invoked to explain low glacial erosion rates, versus the conditions in which a high bedrock resistance to erosion may be alternatively invoked. Establishing whether basal ice temperature or bedrock erodibility exerts the dominant control on the longitudinal valley profile produced by glacial erosion has significant implications for the interpretation of past climate inferred from glacial geomorphology.

Duhnforth, M.; Anderson, R. S.; Colgan, W.

2012-12-01

231

Anomalous Temperature Dependence of Vibrational Lifetimes in Water and Ice  

NASA Astrophysics Data System (ADS)

We have used femtosecond two-color midinfrared spectroscopy to determine the temperature dependence of the OH-stretching lifetime in dilute HDO:D2O solution, both in the liquid and solid (ice Ih) state. Like many other properties of water, the vibrational lifetime shows a remarkable temperature dependence: In liquid water the vibrational relaxation of the OH-stretching mode is twice as slow as in ice, and becomes even slower with increasing temperature.

Woutersen, Sander; Emmerichs, Uli; Nienhuys, Han-Kwang; Bakker, Huib J.

1998-08-01

232

A Study of Hexagonal and Cubic Ice at Low Temperatures.  

National Technical Information Service (NTIS)

The formation of hexagonal and cubic forms of ice was studied by the use of a cold stage in an electron microscope within the temperature range of -190 to 170 degrees C. Ice crystal specimens were made on cold substrates, i.e., a collodion film, gold foil...

M. Kumai

1967-01-01

233

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

NASA Astrophysics Data System (ADS)

Since 2007, there has been a succession of surface melt records over the Greenland Ice Sheet (GrIS) in continuity of the trend towards increasing melt observed since the end of the 1990s. But, these last two decades are characterized by an increase of negative phases of the North-Atlantic Oscillation (NAO) favouring warmer and drier summers than normal over GrIS. In this context, we use a circulation type classification based on the daily 500 hPa geopotential height to evaluate the role of the atmospheric dynamics in this surface melt acceleration for the last two decades. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June-July-August) mean temperature from reanalyses at 700 hPa over Greenland; analogous atmospheric circulations in the past show that ~70% of the 1993-2012 warming at 700 hPa over Greenland has been driven by changes in the atmospheric flow frequencies. Indeed, the occurrence of anticyclones centred over the GrIS at the surface and at 500 hPa has doubled since the end of 1990s, which induces more frequent southerly warm air advection along the Western Greenland coast and over the neighbouring Canadian Arctic Archipelago (CAA). These changes in the NAO modes explain also why no significant warming has been observed these last summers over Svalbard, where northerly atmospheric flows are twice as frequent as before. Therefore, the recent warmer summers over GrIS and CAA cannot be considered as a long term climate warming but are rather a consequence of the NAO variability impacting the atmospheric heat transport. While no global model from the CMIP5 database projects consequent changes in NAO through this century, we cannot exclude that these changes in NAO are due to global warming. Indeed, we have performed several sensitivity experiments performed with the regional climate model MAR over an integration domain large enough for allowing MAR to simulate its own general circulation independently of the forcing (ERA-INTERIM). These MAR simulations seem to suggest that the NAO anomalies over summers 2007-2012 are due to changes in the Sea Ice Cover (SIC) and Sea Surface Temperatures (SST) in the Arctic.

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

2013-04-01

234

Radiance Temperature of Tantalum at Its Melting Point.  

National Technical Information Service (NTIS)

Radiance temperature (at two wavelengths, 653 and 995 nm) of tantalum at its melting point was measured with the use of a subsecond-duration pulse heating technique. Specimens in the form of strips with initially different surface roughnesses were used. T...

A. Cezairliyan J. L. McClure L. Coslovi F. Righini A. Rosso

1976-01-01

235

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

PubMed

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. PMID:20867188

Udagawa, Masafumi; Ishizuka, Hiroaki; Motome, Yukitoshi

2010-06-01

236

Surface melt magnitude retrieval over Ross Ice Shelf, Antarctica using coupled MODIS near-IR and thermal satellite measurements  

NASA Astrophysics Data System (ADS)

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 is sparse coverage of automatic weather stations. Satellite based assessments of melt from passive microwave systems are limited in that they only provide an indication of melt occurrence and have coarse spatial resolution. An algorithm was developed to retrieve surface melt magnitude using coupled near-IR/thermal surface measurements from MODIS were calibrated by estimates of liquid water fraction (LWF) in the upper 1 cm of the firn derived from a one-dimensional physical snowmelt model (SNTHERM89). For the modeling phase of this study, SNTHERM89 was forced by hourly meteorological data from automatic weather station data at reference sites spanning a range of melt conditions across the Ross Ice Shelf during a relatively intense melt season (2002). Effective melt magnitude or LWF were derived for satellite composite periods covering the Antarctic summer months at a 4 km resolution over the entire Ross Ice Shelf, ranging from 0-0.5% LWF in early December to areas along the coast with as much as 1% LWF during the time of peak surface melt. Spatial and temporal variations in the magnitude of surface melt are related to both katabatic wind strength and advection during onshore flow.

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

2009-12-01

237

Potential methane emission from north-temperate lakes following ice melt  

USGS Publications Warehouse

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

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

1996-01-01

238

Electronic Desorption from Internal Surfaces of Porous Low Temperature Ice  

NASA Astrophysics Data System (ADS)

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

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

2006-05-01

239

High temperature strength and thermal stability for melt growth composite  

Microsoft Academic Search

Melt growth composites (MGCs) have a microstructure, in which continuous networks of single-crystal Al2O3 phases and single-crystal oxide compounds (YAG (Y3Al5O12), GAP (GdAlO3)) interpenetrate without grain boundaries. Therefore, the MGCs have excellent high-temperature strength characteristics, creep resistance, superior oxidation resistance and thermal stability in the air atmosphere at very high temperature. To achieve ultra-high thermal efficiency and low NOx emission

Narihito Nakagawa; Hideki Ohtsubo; Atsuyuki Mitani; Kazutoshi Shimizu; Yoshiharu Waku

2005-01-01

240

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

241

Effects of Present-Day Ice Melting on the Geodetic Measurements in Southeast Alaska  

NASA Astrophysics Data System (ADS)

It is known that the southeast Alaska (SE-AK) is undergoing a rapid land uplift, which is considered to be mainly due to the effect of melting of past ice, especially in the last two hundred years after the little ice age (LIA). The crustal deformation caused by the post-glacial rebound (PGR) has been clearly detected by GPS and tidal gauge measurements and modeled (Larsen et al., 2004 and 2005). On the other hand, it is considered also that the observed uplift rate is affected by the present-day ice melting (PDIM), which is considered to be the effect of recent global warming (Larsen et al., 2005; Sato et al., 2006). The displacement measurements provide us useful information to evaluate the ice-melting rate and to discuss the viscosity of the earth. However, usually, it is difficult to separate the uplift rate due to the long- term viscous response of the earth by only using displacement observations, because the two effects (i.e. the elastic and viscous deformations) are mixed in the observed data. Related to this problem, Wahr et al. (1995) demonstrated a method to separate the viscous contribution from the observed data by collocating position and gravity measurements. Considered this, since 2006, we, a joint team of Japanese and U.S. researchers are carrying out the absolute gravity (AG) measurements once a year adding to the temporal and continuous GPS observations in SE-AK. Combining the AG measurements and GPS measurements is useful because the attraction part of gravity measurement is sensitive to a mass change of the present-day ice melting, while the past-ices should have no effect to the attraction part of the observed gravity change. In this context of the discussion, precise numerical estimation of the PDIM effect is important (Sato et al., 2007). Based on the two kinds of DEM (Digital Elevation Model), i.e. one is from the 2000 Shuttle Radar Topography Mission (SRTM) and other is that from air photo dating data which were obtained in the period of 1948-1987, Larsen et al. (2007) estimate the volume changes in SE-AK and adjoining area of Canada. Their results show that the glacier surface elevations lowered by a rate of about -1.1 m/yr as an average over the area of 14,580 square km glacier-covered area. According to the Farrell"fs method (1972) and using this thinning data, we have evaluated the effects of PDIM on our AG and GPS measurements in SE-AK. The gravity effect consists of two parts (i.e. the attraction and the effect of elastic deformation). Different from the elastic part, the computation results for the attraction part are sensitive to the assumed mean thickness of the glaciers and the elevation of glacier mass. Therefore, although the computation is still preliminary one, our results indicate that, the maximum gravity effect for our 6 AG sites is -1.4 micro Gal/yr as sum of the two parts mentioned above. Compared with the observed gravity rate of -5 micro Gal/yr, we may say that the PDIM effect is not negligible. On the other hand, for the vertical displacement, it is estimated at the order of +2.4 mm/yr at the most. Therefore, compared the observed maximum uplift rate of +30 mm/yr, the magnitude of the PDIM effect is not so large.

Sato, T.; Larsen, C. F.; Miura, S.; Ohta, Y.; Fujimoto, H.; Sun, W.; Sugano, T.; Kaufman, A. M.; Freymueller, J. T.

2008-12-01

242

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

243

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

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

Dynamic and static equilibrium sea level effects of Greenland Ice Sheet melt: An assessment of partially-coupled idealized water hosing experiments (Invited)  

NASA Astrophysics Data System (ADS)

Regional sea level can deviate from mean global sea level because of both dynamic sea level (DSL) effects, resulting from oceanic and atmospheric circulation and temperature and salinity distributions, and changes in the static equilibrium (SE) sea level configuration, produced by the gravitational, elastic, and rotational effects of mass redistribution. Both effects will contribute to future sea level change, but because they are studied by two different subdisciplines -- climate modeling and glacial rebound modeling -- projections that attempt to combine both have to date been scarce. To compare their magnitude, we simulated the effects of Greenland Ice Sheet (GIS) melt by conducting idealized North Atlantic "water-hosing" experiments in a climate model unidirectionally coupled to a SE sea level model. At current rates of GIS melt, freshwater hosing experiments in fully coupled atmosphere-ocean general circulation models (AOGCMs) do not yield clear DSL trends but do generate DSL variability; comparing that variability to expected static equilibrium "fingerprints" suggests that at least about 40 years of observations are needed to detect the "fingerprints" of ice sheet melt at current Greenland melt rates of about 0.3 mm equivalent sea level (esl)/year. Accelerated melt rates of about 2--6 mm esl/y, as may occur later in the century, should be detectable above background DSL variability within less than a decade of their onset. At these higher melt rates, AOGCMs do yield clear DSL trends. In the GFDL CM 2.1 model, DSL trends are strongest in the western North Atlantic, while SE effects come to dominate in most of the ocean when melt exceeds about 20 cm esl.

Kopp, R. E.; Mitrovica, J. X.; Griffies, S. M.; Yin, J.; Hay, C. C.; Stouffer, R. J.

2010-12-01

246

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

Microsoft Academic Search

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

Douglas Reed MacAyeal

1984-01-01

247

Analysis of surface roughness and morphology of first-year sea ice melt ponds: implications for microwave scattering  

Microsoft Academic Search

Variations in wind forcing over summer first-year sea ice (FYI) melt ponds occur at hourly to weekly scales and are a significant contributor to microwave backscatter (?°) variability observed from spaceborne synthetic aperture radar (SAR) platforms (e.g., ENVISAT-ASAR and RADARSAT-1). This variability impairs our ability to use SAR to derive information on summer sea ice thermodynamic state and energy balance

Randall K. Scharien; John J. Yackel

2005-01-01

248

Modeling the dependence of alumina solubility on temperature and melt composition in cryolite-based melts  

NASA Astrophysics Data System (ADS)

The solubility of alumina in NaF-AlF3 melts was calculated and modeled thermodynamically for the temperature range of 1240 to 1300 K (967 °C to 1027 °C). The solute complexes of alumina in the cryolite melts were identified to be Na2Al2OF6 (acidic solute), Na2Al2O2F4 (neutral solute), and Na4Al2O2F6 (basic solute). The assumption that the oxygen-free solute species in solution were Na3AlF6 and NaAlF4 was supported by the modeling results. The equilibrium constants for the formation reactions of the solutes were calculated and the corresponding ? G {/f 0} values were evaluated as a function of temperature. The interaction derivatives (? ln a NaF/? x add, ? ln a NaF/? x add, and ? ln a AlF3/? x add) for small additions of LiF, CaF2, and MgF2 to the NaF-AlF3-Al2O3 ternary system were also estimated as a function of temperature and melt composition.

Zhang, Yunshu; Rapp, Robert A.

2004-06-01

249

Destruction of polychlorinated naphthalenes by a high-temperature melting treatment (GeoMelt process).  

PubMed

A series of treatment experiments were carried out to evaluate the applicability of a high-temperature melting treatment (GeoMelt process) to the destruction of polychlorinated naphthalene (PCN) formulation. We started with 10-kg-scale experiments in which a small melting furnace was used and then scaled up to a 1-t-scale experiment in which a melting furnace that resembled an actual treatment system was used. These runs were evaluated whether destruction efficiency (DE) of total PCNs was more than 99.999% and whether concentrations of PCNs and polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/DFs) in vitrified materials, emission gas, and scrubber water were below the target levels. Because DE values and the target levels of PCNs and PCDDs/DFs in these runs were satisfactory, then we carried out a demonstrative experiment using the actual treatment system and confirmed destruction of PCNs. Based on good results of the demonstrative experiment, stock of PCN formulation was successfully treated continuously. PMID:24595750

Yamamoto, Takashi; Kai, Yasufumi; Nakauchi, Hiroaki; Abuku, Toshiaki; Noma, Yukio

2014-06-01

250

Use and Limitations of a Climate-Quality Data Record to Study Temperature Trends on the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

Enhanced melting of the Greenland Ice Sheet has been documented in recent literature along with surface-temperature increases measured using infrared satellite data since 1981. Using a recently-developed climate-quality data record, 11- and 12-year trends in the clear-sky ice-surface temperature (IST) of the Greenland Ice Sheet have been studied using the Moderate-Resolution Imaging Spectroradiometer (MODIS) IST product. Daily and monthly MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 are now available at 6.25-km spatial resolution on a polar stereographic grid as described in Hall et al. (submitted). This record will be elevated in status to a climate-data record (CDR) when more years of data become available either from the MODIS on the Terra or Aqua satellites, or from the Visible Infrared Imager Radiometer Suite (VIIRS) to be launched in October 2011. Maps showing the maximum extent of melt for the entire ice sheet and for the six major drainage basins have been developed from the MODIS IST dataset. Twelve-year trends of the duration of the melt season on the ice sheet vary in different drainage basins with some basins melting progressively earlier over the course of the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. IST 12-year trends are compared with in-situ data, and climate data from the Modern Era Retrospective-Analysis for Research and Applications (MERRA) Reanalysis.

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

2011-01-01

251

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

252

Mixture models for analysis of melting temperature data  

PubMed Central

Background In addition to their use in detecting undesired real-time PCR products, melting temperatures are useful for detecting variations in the desired target sequences. Methodological improvements in recent years allow the generation of high-resolution melting-temperature (Tm) data. However, there is currently no convention on how to statistically analyze such high-resolution Tm data. Results Mixture model analysis was applied to Tm data. Models were selected based on Akaike's information criterion. Mixture model analysis correctly identified categories in Tm data obtained for known plasmid targets. Using simulated data, we investigated the number of observations required for model construction. The precision of the reported mixing proportions from data fitted to a preconstructed model was also evaluated. Conclusion Mixture model analysis of Tm data allows the minimum number of different sequences in a set of amplicons and their relative frequencies to be determined. This approach allows Tm data to be analyzed, classified, and compared in an unbiased manner.

Nellaker, Christoffer; Uhrzander, Fredrik; Tyrcha, Joanna; Karlsson, Hakan

2008-01-01

253

Melt trends above the equilibrium line of the Greenland Ice Sheet during the period of 2003-2012 (Invited)  

NASA Astrophysics Data System (ADS)

Warming in the Arctic has raised concern about the effects that increased fresh water input from Greenland and other ice caps into the oceans could have on sea level rise and on the thermohaline ocean circulation. Melt over the Greenland Ice Sheet (GIS) has been increasing steadily over the last 20 years, and although mass loss has been limited to the margins, the departure from the 1979-1999 mean melt rate in the last decade has become particularly large in the interior. This has resulted in variable conditions that make ice volume changes derived from remote sensing measurements difficult to interpret, and an equilibrium line that is continuously migrating. We present a combined analysis of field measurements obtained in western Greenland and results from the Regional Atmospheric Climate Model to estimate trends in melt and refreezing rates over the interior of the Greenland ice sheet. The combined dataset show the evolution of melt intensity in regions with little or no meltwater runoff during the last 20 years. We estimated a threefold increase in the total area experiencing significant melt in the last decade, and an amount of refrozen meltwater larger than the total mass balance of the ice sheet. Conditions observed after the extreme melt event of July 2012 at and above the 2000 m elevation line contrast sharply with previous studies, and illustrate the current and future state of the Greenland interior if warming trends continue. We will discuss changes during the last decade in surface mass balance conditions, and the melting and refreezing processes occurring above the equilibrium line of the GIS. Additionally, we will summarize some implications these processes may have in estimating mass balance from altimetry techniques, and how in-situ data and models can help improving altimetry-derived results. The intensity of melt and the huge ice reservoirs found in the field are an indication that percolation facies are no longer just an interesting feature with no real relevance other than their effects in radar altimetry signals, but rather the result of an intense melting process of at least the same scale as the total mass imbalance of the GIS.

de la Peña, S.; Howat, I. M.; van den Broeke, M. R.; Price, S. F.; Nienow, P. W.; Mosley-Thompson, E. S.

2013-12-01

254

Making High-Temperature Superconductors By Melt Sintering  

NASA Technical Reports Server (NTRS)

Melt-sintering technique applied to YBa2Cu3O7-x system and to Bi/Ca/Sr/Cu-oxide system to produce highly oriented bulk high-temperature-superconductor materials extending to macroscopically usable dimensions. Processing requires relatively inexpensive and simple equipment. Because critical current two orders of magnitude greater in crystal ab plane than in crystal c direction, high degree of orientation greatly enhances critical current in these bulk materials, making them more suitable for many proposed applications.

Golben, John P.

1992-01-01

255

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.

256

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

257

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

258

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

259

InSAR and GPS Observations Show Seasonal Speedup of Ice Flow in Greenland Following the Onset of Summer Melting  

NASA Astrophysics Data System (ADS)

We have assembled a comprehensive set of InSAR and GPS observations that reveal both spatial and temporal changes in velocity during the summer melt season along a several-hundred kilometer stretch of the ice-sheet margin near Jakobshavn Isbrae, Greenland. In the bare ice zone, we obtain InSAR (speckle/feature tracking) results throughout the melt season that agree well with results from two continuous GPS stations located at roughly 1000 meters elevation. Over much of the slow-moving (100 m/yr) bare-ice zone, the InSAR data show summer speedups of 50-to-100 m/yr averaged over 24 days. We also detect seasonal speedups of similar magnitude on Jakobshavn Isbrae and several smaller fast moving (> 1 km/yr) outlet glaciers. In relative terms, however, the outlet glaciers speedups represent increases of less than 10 % relative to their annual means. Thus, proportionately the slow-moving inland ice is far more sensitive to seasonal speedup than are the rapidly flowing outlet glaciers, making it unlikely that recently reported large (> 1 km/yr) speedups on Jakobshavn and other outlet glaciers can be directly attributed to enhanced basal lubrication from increased surface melt. Similarly, the GPS data also reveal a period of generally enhanced flow extending through the melt season, punctuated by shorter-term speedups lasting a few days. These shorter-term accelerations correlate well with periods of increased surface melt that we inferred from positive-degree-day values measured at the GPS sites. In addition, the short-term accelerations coincide well with GPS-measured periods of peak uplift rates of the ice-sheet surface. The strong correlation of seasonal velocity with melt and uplift rates suggests that surface melt makes its way to bed rapidly, providing enhanced lubrication to regions of the ice sheet extending up to at least 1000 meters elevation. Furthermore, the spatially uniform nature of the speedup in the upper bare-ice zone, where a sparse distribution of moulins delivers water to the bed, suggests the presence of a well distributed sub-glacial drainage network.

Joughin, I.; Das, S. B.; King, M. A.; Smith, B.; Howat, I.; Moon, T.

2007-12-01

260

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

261

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

262

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

263

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

264

Antarctic temperatures over the past two centuries from ice cores  

Microsoft Academic Search

We present a reconstruction of Antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high-resolution, precisely dated ice cores. Both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability, with the dominant pattern being anti-phase anomalies between the main Antarctic continent and the Antarctic Peninsula region. Comparative analysis of the instrumental

David P. Schneider; Eric J. Steig; Tas D. van Ommen; Daniel A. Dixon; Paul A. Mayewski; Julie M. Jones; Cecilia M. Bitz

2006-01-01

265

Antarctic Temperatures Over the Past Two Centuries from Ice Cores  

Microsoft Academic Search

We present a reconstruction of Antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high-resolution, precisely dated ice cores. Both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability, with the dominant pattern being anti-phase anomalies between the main Antarctic continent and the Antarctic Peninsula region. Comparative analysis of the instrumental

David P. Schneider; Eric J. Steig; Tas D. van Ommen; Daniel A. Dixon; Paul Andrew Mayewski; Julie M. Jones; Cecilia M. Bitz

2006-01-01

266

First-year sea ice spring melt transitions in the Canadian Arctic Archipelago from time-series synthetic aperture radar data, 1992-2002  

NASA Astrophysics Data System (ADS)

This paper synthesizes 10-years' worth of interannual time-series space-borne ERS-1 and RADARSAT-1 synthetic aperture radar (SAR) data collected coincident with daily measurement of snow-covered, land-fast first-year sea ice (FYI) geophysical and surface radiation data collected from the Seasonal Sea Ice Monitoring and Modeling Site, Collaborative-Interdisciplinary Cryospheric Experiment and 1998 North Water Polynya study over the period 1992 to 2002. The objectives are to investigate the seasonal co-relationship of the SAR time-series dataset with selected surface mass (bulk snow thickness) and climate state variables (surface temperature and albedo) measured in situ for the purpose of measuring the interannual variability of sea ice spring melt transitions and validating a time-series SAR methodology for sea ice surface mass and climate state parameter estimation. We begin with a review of the salient processes required for our interpretation of time-series microwave backscatter from land-fast FYI. Our results suggest that time-series SAR data can reliably measure the timing and duration of surface albedo transitions at daily to weekly time-scales and at a spatial scales that are on the order of hundreds of metres. Snow thickness on FYI immediately prior to melt onset explains a statistically significant portion of the variability in timing of SAR-detected melt onset to pond onset for SAR time-series that are made up of more than 25 images. Our results also show that the funicular regime of snowmelt, resolved in time-series SAR data at a temporal resolution of approximately 2.5 images per week, is not detectable for snow covers less than 25 cm in thickness. Copyright

Yackel, J. J.; Barber, D. G.; Papakyriakou, T. N.; Breneman, C.

2007-01-01

267

High temperature steady shear and oscillatory rheometry of basaltic melt  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

268

Glacial cycles and ice-sheet modelling  

Microsoft Academic Search

An attempt is made to simulate the Pleistocene glacial cycles with a numerical model of the Northern Hemisphere ice sheets. This model treats the vertically-integrated ice flow along a meridian, including computation of bedrock adjustment and temperature distribution in the ice. Basal melt water is traced and controls ice-mass discharge.

J. Oerlemans

1982-01-01

269

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

270

Force-dependent melting of supercoiled DNA at thermophilic temperatures.  

PubMed

Local DNA opening plays an important role in DNA metabolism as the double-helix must be melted before the information contained within may be accessed. Cells finely tune the torsional state of their genomes to strike a balance between stability and accessibility. For example, while mesophilic life forms maintain negatively superhelical genomes, thermophilic life forms use unique mechanisms to maintain relaxed or even positively supercoiled genomes. Here, we use a single-molecule magnetic tweezers approach to quantify the force-dependent equilibrium between DNA melting and supercoiling at high temperatures populated by Thermophiles. We show that negatively supercoiled DNA denatures at 0.5 pN lower tension at thermophilic vs. mesophilic temperatures. This work demonstrates the ability to monitor DNA supercoiling at high temperature and opens the possibility to perform magnetic tweezers assays on thermophilic systems. The data allow for an estimation of the relative energies of base-pairing and DNA bending as a function of temperature and support speculation as to different general mechanisms of DNA opening in different environments. Lastly, our results imply that average in vivo DNA tensions range between 0.3 and 1.1 pN. PMID:24486433

Galburt, E A; Tomko, E J; Stump, W T; Ruiz Manzano, A

2014-01-01

271

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

Microsoft Academic Search

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

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

2008-01-01

272

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

273

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

274

Arctic Melting  

NSDL National Science Digital Library

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

2011-06-15

275

Formation of high temperature superconductors from the solidified melt  

NASA Astrophysics Data System (ADS)

The drop tube experiments with the YBa2Cu3O(7 - delta) (Y123) material have illustrated that the particle size, temperature and atmosphere during decomposition, melting and solidification is critical to the formation of the desired decomposition phases. Temperatures above 1450 C and small size, -75 +53 micro-m, particulate are necessary to produce complete decomposition of the Y123 and melting of all phases with the exception of Y2O3 (200). The importance of the atmosphere is demonstrated by the presence of the low P(sub O2) stable BaCu2O2 (012) phase in the solidified spheres produced in a nitrogen atmosphere and the cubic phase (phi) in the solidified spheres produced in an oxygen atmosphere. The as solidified microstructure of the spheres where the liquids temperature was not obtained, are relatively similar. The major features of the phase composition and microstructure are primarily attributed to what happens upon heating and depend relatively little upon the solidification rate.

Merkle, B.

1992-01-01

276

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

277

Greenland ice sheet hydrology: insights from an isotope mixing model during the 2011 and 2012 melt seasons  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet (GrIS) is the Northern Hemisphere's largest terrestrial permanent ice mass. Each summer, subglacial drainage systems are altered by sustained inputs of meltwater from the ice sheet surface (Bartholomew et al., 2010). Prior to the development of an efficient subglacial channel system, constrained and inefficient meltwater flow paths at the glacier-bed interface cause hydrological forcing that results in the fastest annual rates of acceleration. However, most land terminating glaciers in Greenland slow down appreciably after the development of an efficient subglacial hydrological system. We used naturally-occurring radioactive and stable isotopes (7Be, 222Rn, 18O, D) as passive flow tracers to construct a high-resolution time series model of meltwater sourced from recent surface snow, glacial ice and delayed-flow basal meltwater during 2011 and 2012. Our field site is Leverett Glacier, a large outlet glacier (600 km2) on the western Greenland margin that discharges through a single, large proglacial river. Our isotope mixing model is complemented by concurrent stream discharge measurements that constrain the magnitude, timing, and routing of meltwater discharge. Furthermore, global positioning systems (GPS) were deployed within the catchment area to continuously measure changes in ice velocity. Our model results show diurnal changes in each meltwater component. Furthermore, we observe episodic outburst events of delayed-flow basal meltwater, snowmelt, and ice melt. The volume of delayed-flow basal meltwater co-varies with ice velocity during both diurnal cycles and episodic speed up and uplift events. For example in July 2011, a large ice uplift and acceleration event was preceded by a decrease in delayed-flow basal meltwater, followed by ice acceleration and a release of an abnormally large volume of delayed-flow basal meltwater. Similar analyses will be presented for the 2012 melt season, which included extreme ice melting conditions in July as recorded by satellite measurements and stream discharge measurements at our field site. These results demonstrate the intimate relationship between subglacial hydrology and glacial dynamics in the GrIS. Bartholomew, I., Nienow, P., Mair, D., Hubbard, A., King, M.A., Sole, A., 2010. Seasonal evolution of subglacial drainage and acceleration in a Greenland outlet glacier. Nat Geosci 3, 408-411.

Linhoff, B.; Charette, M. A.; Butler, C. E.; Tedstone, A.; Cowton, T.; Sole, A. J.; Nienow, P. W.; Wadham, J. L.

2012-12-01

278

A Self-consistent Estimation Method of Melting Condition Based on Major Elements in Volcanic Rocks: Degree of Melting, Pressure, H2O Content and Melting Temperature  

NASA Astrophysics Data System (ADS)

Estimation of magma generation conditions, including degree of partial melting, melting pressure, H2O content, and melting temperature, is a key step to better understand the magmatism of various tectonic settings including mid ocean ridges, hot spots, and subduction zones. There are many studies that estimated magma generation conditions on the basis of chemical compositions of volcanic rocks, but the most of them are neither comprehensive nor self-consistent in that a part of melting conditions was estimated or assumed to estimate the rest. Moreover, they are mostly applicable only to a specific tectonic setting and are not universal. Chemical compositions of volcanic rocks are results of integration of various magmatic processes that take place in the upper mantle and the crust. Therefore, estimation of melting condition in the mantle is inevitably coupled with estimation of magma evolution during fractional crystallization in the crust. In other words, conditions for melting and fractional crystallization must be determined all together by dealing with all the relevant magmatic processes. Based on this idea, a rigorous least-squares approach to estimate melting conditions in the upper mantle from major element composition of a single volcanic rock, in which crystallization and melting parameters are simultaneously and consistently determined, is proposed. Melting in the mantle was modeled based on the batch melting experiments of KLB-1 peridotite (Takahashi, 1986; Hirose and Kushiro, 1993), and fractional crystallization in the crust was modeled by MELTS program (Ghiorso and Sack, 1995). Unknown parameters are degree of partial melting, melting pressure, and H2O content for mantle melting, and pressure and final temperature of crystallization for fractional crystallization in the crust. The melting temperature is estimated from the relationships among degree of melting, melting pressure, and H2O content. In optimization of these parameters, not only olivine but also plagioclase, clinopyroxene, and orthopyroxene are considered as fractionated phases. This approach is applicable to more differentiated rocks, which are not suitable for olivine addition methods widely used in estimation of primary magmas. Because the amounts and compositions of fractionated phases and degree of partial meting are determined without using trace element data, we can estimate trace element abundances in the source mantle from those of a volcanic rock basically without any assumptions. This method is very general and applicable to wider compositional range of volcanic rocks irrespective of their tectonic settings. Application of this method to several sets of multiple rock samples from a volcano gave consistent melting conditions, substantiating robustness of this approach. If this method is applied to volcanoes distributed in a volcanic region, it is possible to investigate two- or three-dimensional variation of melting conditions, which are strong constraints to understand melting mechanisms, thermal structure, and material transport in the mantle. This method was applied to a frontal volcano of the Izu arc, Aogashima Volcano, and volcanoes distributed in its back arc region in order to understand the across arc variation of magma generation conditions. The melting conditions of the Izu arc shows increases in melting temperature and melting pressure toward the volcanic front from the back-arc side.

Ogitsu, I.; Ozawa, K.

2008-12-01

279

Micro Temperature Loggers: A Cost Effective Technology to Derive Input Data for Distributed Snow Melt Models  

Microsoft Academic Search

In snow dominated forested watersheds the quantification of snow melt is the most important process in hydrological modelling. The simplicity and in general satisfying accuracy of air temperature index or degree day models make them the most commonly used method to estimate snow melt rates when snow melt is based on radiation (and not on rain on snow events). Temperature

M. Weiler; G. Jost; Y. Alila

2005-01-01

280

Low-temperature-SEM study of dihedral angles in the ice-I/sulfuric acid partially molten system.  

PubMed

The transport and mechanical properties of partially molten materials are influenced by the wetting behaviour of the melt with respect to the crystalline solid. The equilibrium microstructure of an ice + melt system was examined using low-temperature scanning electron microscopy. The samples were prepared by spraying a liquid solution of H(2) O-H(2) SO(4) into liquid nitrogen and packing the frozen particulates into aluminium capsules. Samples were then sintered at -35°C or -55°C (above the eutectic temperature, T(E) =-62°C) for various durations and were quenched in liquid nitrogen to capture the equilibrium microstructure. This paper reports the first quantitative measurements of dihedral angle in this system. The measured median dihedral angle between the solid and vitrified melt is approximately 26 ± 2° at -35°C and increases slightly as temperature decreases and approaches the solidus (32 ± 3° at -55°C). PMID:23252882

McCarthy, C; Blackford, J R; Jeffree, C E

2013-02-01

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

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

Microsoft Academic Search

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

Paul R. Holland; Daniel L. Feltham

2006-01-01

283

Evidence for Past Melting at the Base of the GISP2 Ice Core from Uranium-Thorium Disequilibrium Measurements  

NASA Astrophysics Data System (ADS)

We measured 238U-234U-230Th disequilibria by mass spectrometric methods for silty ice samples from the base of the GISP2 Greenland ice core, at a depth of 3040-3052 m. The expected age of these samples is >150 kyr based on counting ice layers. We separated the samples into several fractions by filtration and analyzed the <50 nm (truly dissolved + particulate) and >200 nm (particulate) filtered fractions. In the <50 nm fractions, low Th/U mass ratios of 0.51-0.65 indicate that a large portion (86-89%) of U is truly dissolved and not associated with particles. In addition, 230Th/234U activity ratios are quite low (0.18-0.24), suggesting either recent 230Th loss and/or 234U addition to the samples. This Th/U fractionation is not consistent with an age >150 kyr. Since liquid water is characterized by 230Th/234U activity ratios <<1, these results suggest that recent melting/freezing event(s) have occurred at the base of the GISP2 core. The particulate (>200 nm) fraction is characterized by Th/U ratios of ~4.4-4.9, 234U/238U activity ratios of 1.049-1.056, and 230Th/234U activity ratios of 1.12-1.23. The U-Th disequilibrium in the particles is consistent with recent (<350 kyr) fractionation of U-Th in these ice samples. We have modeled these results using a two component mass balance calculation, with dissolved and particulate pools for each radionuclide. The main assumption is that all of the 232Th in the <50 nm fraction is due to particles, due to the low aqueous solubility of 232Th. By mass balance, 230Th/234U activity ratios for the truly dissolved fraction are 0.031-0.062, and dates for when the samples were last frozen are 3.5-6.9 kyr. These results are consistent with the notion of ice melting at the base of large continental ice sheets, with recent evidence of large sub-glacial lakes in Antarctica and active melting at the base of the nearby N-GRIP Greenland ice core. There also appears to be a significant difference in age for the deepest ice sample (3.5 kyr; 3052 m) and the other samples (5.2-6.9 kyr; 3040-3048 m), suggesting that the deepest part of the ice core adjacent to bedrock at 3053.3 m depth may have existed as liquid water for at least several hundred - few thousand years.

Goldstein, S. J.; Lee, V. E.; Nishiizumi, K.; Murrell, M. T.; Amato, R. S.; Nunn, A. J.

2011-12-01

284

Temperature and ice layer trends in the summer middle atmosphere  

NASA Astrophysics Data System (ADS)

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

Lübken, F.-J.; Berger, U.

2012-04-01

285

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

286

On the melting temperatures of low-temperature phases of polymorphic metals  

NASA Technical Reports Server (NTRS)

An improved analytical formula for determining the melting temperatures of the low-temperature phases of polymorphic metals is proposed which uses the specific heat differences at the equilibrium transition temperatures. The formula is solved by an iterative method, with no more than one iteration necessary to converge. The results obtained using the formula proposed here are generally in good agreement with the analytical solution.

Ohsaka, K.; Trinh, E. H.

1992-01-01

287

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

NASA Astrophysics Data System (ADS)

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

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

2001-03-01

288

Invention of Ozone Inclusion Ice Using Low-Temperature Plasma  

NASA Astrophysics Data System (ADS)

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

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

289

Melt ponds on sea ice in the Canadian Archipelago 2. On the use of RADARSAT-1 synthetic aperture radar for geophysical inversion  

Microsoft Academic Search

Microwave scattering from a first-year sea ice (FYI) melt ponded surface is examined using RADARSAT-1 synthetic aperture radar (SAR) data collected during the 1997 Collaborative-Interdisciplinary Cryospheric Experiment (C-ICE'97) near Resolute Bay, Nunavut. This paper (1) investigates the utility of time series of microwave scattering to detect melt pond formation and (2) investigates approaches toward geophysically inverting information on the physical

J. J. Yackel; D. G. Barber

2000-01-01

290

The influence of temperature gradient zone melting on microsegregation  

SciTech Connect

Adding an algorithm for considering temperature gradient zone melting (TGZM) to an existing numerical model for predicting microstructure and microsegregation allows the prediction of migration distances of dendrite arms and asymmetric concentration distributions in the arms. Provided that detailed information on the time dependence of the temperature gradient as well as the cooling rate is available from heat flow calculations, accurate predictions of the type and amount of secondary phases or dendrite arm spacings are possible for cooling conditions at which TGZM is active. Parameter studies are performed to investigate the influence of TGZM for typical temperature gradients (0.01 to 10 K/mm). Sawtoothlike concentration distributions are predicted for high-temperature gradients. A binary Al-6.8 wt pct Cu alloy is solidified unidirectionally and asymmetrical concentration profiles are measured. Considering TGZM in the simulation results in good agreement of model predictions with experimental measurements in the position of the minimum concentration and the asymmetric shape of the concentration profile as well as dendrite arm spacings and amount of second phase.

Kraft, T.; Pompe, O.; Exner, H.E. [Technical Univ. of Darmstadt (Germany). Dept. of Materials Science

1998-01-01

291

Fluid and deformation induced partial melting and melt volumes in low-temperature granulite-facies metasediments, Damara Belt, Namibia  

NASA Astrophysics Data System (ADS)

Fluid-present partial melting has generally been regarded a poor candidate for effecting crustal differentiation. In this study we report on granulite-grade metasediments from the Pan-African Damara Belt in Namibia that have undergone fluid-present biotite melting at a relatively low-temperature, yet appear to have lost a significant volume of melt. In situ anatectic features have been identified on the basis of the existence of new generations of cordierite and/or garnet produced as the solid products of incongruent anatexis within or adjacent to leucosomes. Leucosomes occur in lens-shaped pods that are orientated at high angles to the regional stretching lineation that formed during orogen-parallel extrusion of the rocks during the main collisional event in the Damara Belt. Within these sites biotite underwent incongruent melting via the reaction Bt + Qtz + Pl + H 2O = Melt + Grt + Crd. Cordierite nucleated on pre-existing crystals within the bounding gneiss; garnet nucleated within the fracture sites (leucosomes) and typically occurs as individual, large (50 to 120 mm) poikiloblastic crystals. Thermobarometry applied to the anatectic assemblage yields low-temperature, granulite-facies peak conditions of 750 °C, 0.5 GPa. This temperature is approximately 100 °C lower than the accepted conditions for the onset of fluid-absent biotite melting. This, coupled to the focussing of anatexis on dilational sites, suggests that anatexis occurred through water-present biotite incongruent melting. In order to better understand this process, both fluid-absent and water-present partial melting experiments were conducted within the temperature interval 700 to 900 °C at 0.7 GPa. In the fluid-absent experiments, biotite incongruent melting started between 800 and 850 °C to produce melt coexisting with peritectic garnet and cordierite. In contrast, in water-saturated experiments, biotite melted via the reaction Bt + Qtz + Pl + H 2O = Melt + Grt + Crd, between 700 and 750 °C, to produce melt, cordierite and garnet in the proportions 73:24:3. The garnet compositions produced in these low-temperature experiments match very well with the relatively high spessartine content (10%), low Mg# garnets formed with the leucosomes, confirming the water-saturated, low-temperature nature of anatexis in the study area. Mass balance calculations indicate that melting in typical dilational sites has produced 6 dm 3 of melt. This melt has been sourced from some 0.08 m 3 of rock, a volume that coincides well with the typical frequency of extensional fracture spacing. This was probably important in enabling efficient melt extraction which has caused a slight shift towards more refractory compositions in the granulite-facies metapelites over amphibolite-facies equivalents. However, the attendant expansion in chemical equilibration volume has resulted in a marked compositional homogenization of the high-grade gneisses over the rhythmically bedded amphibolite-facies metapelites.

Ward, Robert; Stevens, Gary; Kisters, Alex

2008-10-01

292

Temperature and composition dependencies of trace element partitioning: olivine/melt and low-Ca pyroxene/melt  

SciTech Connect

Trace element distribution coefficients between olivine and melt and between low-Ca pyroxene and melt have been determined by microprobe analysis of synthetic olivine, low-Ca pyroxene, and quenched basaltic glass equilibrated in 1-atm gas mixing furnaces. Experiments were conducted in several compositional systems, with a wide range of Fe/Mg, at 1180/sup 0/C-1420/sup 0/C. Partition coefficients were determined for Eu, Ca, Mn, Fe, Ni, Sm, Gd, Y, Yb, Sc, Al, Zr, and Ti. The values of ..delta..H and ..delta..S for reactions involving several trace elements were determined by linear regression for data from this study as well as additional data from the literature. This data set included partition coefficients determined in anhydrous systems of basanitic to near-andesitic composition. Despite uncertainties in the definition of activity-composition relationships for the melt, most of the temperature and composition dependence of partition coefficients is accounted for without recourse to complex melt structure modeling. Free energy changes (..delta..G) for trace element exchange between crystal and melt are accurately modeled as functions of trace element size and charge. This permits prediction of the temperature and composition dependence of partition coefficients for elements not experimentally investigated. On the basis of this model, partition coefficients for olivine/melt and low-Ca pyroxene/melt can be predicted for a wide range of elements over a variety of basaltic bulk compositions and temperatures. More importantly, variations in partition coefficients during crystallization or melting can be modeled on the basis of changes in temperature and major element chemistry.

Colson, R.O.; McKay, G.A.; Taylor, L.A.

1988-02-01

293

Fingerprint-based estimates of polar ice sheet mass change: The application of a Kalman smoother to identify ice melt contributions to 20th century sea level change  

NASA Astrophysics Data System (ADS)

Rapidly melting ice sheets generate a spatial pattern of sea level change that is unique to the location and geometry of the melt region. Using these so-called "fingerprint" patterns in combination with sea-level observations, it is possible, at least in principle, to estimate the individual sources of meltwater. We describe the application of a Kalman smoother in the estimation of the meltwater contributions to sea level change over the last century via the assimilation of tide gauge observations. Contributions to the observed sea level from thermosteric effects and glacial isostatic adjustment are accounted for in the estimation procedure using a multi-model likelihood technique that minimizes the residuals between the observations and the Kalman smoother states. We present estimates of the melt contributions from polar ice sheets and select mountain glaciers, together with their associated uncertainties, as well as an updated time series of the global mean sea level change through the 20th century and up to the present day.

Morrow, E.; Hay, C.; Kopp, R. E.; Mitrovica, J. X.

2012-12-01

294

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

295

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

296

Temperature effects on atomic pair distribution functions of melts.  

PubMed

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. PMID:24527926

Ding, J; Xu, M; Guan, P F; Deng, S W; Cheng, Y Q; Ma, E

2014-02-14

297

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

298

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

299

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

300

The 2012 melting record and 21st century sea level rise projections for major drainage systems of the Greenland ice sheet  

NASA Astrophysics Data System (ADS)

At the time of the submission of this abstract melting over the Greenland ice sheet estimated from spaceborne microwave observations and modeled by the regional climate model MAR (Modèle Atmosphérique Régional) are close to previously breaking-record values set in 2010 and 2011 (for the period 1979 - 2011). With August still to come, 2012 is very likely going to set a new record for the whole season. For the period June - July, melting detected from spaceborne observations was already above two standard deviations the 1979 - 2011 mean, setting a new record for that period. In this study, we compare the 2012 melting season with those previously setting a new record and analyze some of the potential drivers for the new record. To put things in the context of future projections, we analyze MAR outputs to study 21st century projected surface mass balance (SMB) over six major drainage basins of the Greenland Ice Sheet (GrIS). The regional model is forced with the outputs of three different Earth System Models (CanESM2, NorESM1 and MIROC5) obtained when considering two greenhouse gas future scenarios with levels of CO2 equivalent of, respectively, 850 and > 1370 ppm by 2100. First, we study whether the MAR future projections starting in 2006 (using the historical period 1980 - 2005) are capable of identifying the recently observed melting records. We also find that, by the end of the century, the increase in runoff due to warming will exceed the increased precipitation deriving from the increase in evaporation for all basins, with the amount of net loss of mass at the surface varying spatially. Basins along the southwest and north coast are projected to have the highest sensitivity of SMB to increasing temperatures. For these basins, the global temperature anomaly corresponding to a decrease of the SMB below the 1980 - 1999 average (when the ice sheet was near the equilibrium) ranges between +0.60 deg C and +2.16 deg C. For the basins along the northwest and northeast, these values range between +1.50 deg C and +3.40 deg C. The projected sea level rise from each basin under the different scenarios is discussed at the end.

Tedesco, M.; Fettweis, X.

2012-12-01

301

Vibration for controlling of temperature and dopant distributions in melt  

NASA Astrophysics Data System (ADS)

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

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

302

High-Temperature Vibrational Properties and Melting Curve of Aluminum  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

303

Future increase of west African monsoon due to sea ice melt  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

304

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

305

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

PubMed Central

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

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

2002-01-01

306

Phase change nanocomposites with tunable melting temperature and thermal energy storage density.  

PubMed

Size-dependent melting decouples melting temperature from chemical composition and provides a new design variable for phase change material applications. To demonstrate this potential, we create nanocomposites that exhibit stable and tunable melting temperatures through numerous melt-freeze cycles. These composites consist of a monodisperse ensemble of Bi nanoparticles (NPs) embedded in a polyimide (PI) resin matrix. The Bi NPs operate as the phase change component whereas the PI resin matrix prevents nanoparticle coalescence during melt-freeze cycles. We tune melting temperature and enthalpy of fusion in these composites by varying the NP diameter. Adjusting the NP volume fraction also controls the composite's thermal energy storage density. Hence it is possible to leverage size effects to tune phase change temperature and energy density in phase change materials. PMID:23835614

Liu, Minglu; Wang, Robert Y

2013-08-21

307

Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

308

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

Microsoft Academic Search

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

Ruzica Dadic; Bonnie Light; Stephen G. Warren

2010-01-01

309

Effect of melting temperature and time on iron valence and crystallization of iron phosphate glasses  

Microsoft Academic Search

The effect of melting temperature and time on iron valence, dissolution rate (DR) in deionized water, and crystallization of iron phosphate glasses was investigated using a 40Fe2O3–60P2O5, mol%, batch composition. The concentration of Fe2+ ions in these glasses increased from 17% to 57% as melting temperature increased from 1150°C to 1450°C, but remained nearly constant at about 20% for melting

C. S Ray; X Fang; M Karabulut; G. K Marasinghe; D. E Day

1999-01-01

310

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

Microsoft Academic Search

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

James E. Gardner; Richard A. Ketcham

2011-01-01

311

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

Microsoft Academic Search

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

James E. GardnerRichard; Richard A. Ketcham

312

Phase change nanocomposites with tunable melting temperature and thermal energy storage density  

NASA Astrophysics Data System (ADS)

Size-dependent melting decouples melting temperature from chemical composition and provides a new design variable for phase change material applications. To demonstrate this potential, we create nanocomposites that exhibit stable and tunable melting temperatures through numerous melt-freeze cycles. These composites consist of a monodisperse ensemble of Bi nanoparticles (NPs) embedded in a polyimide (PI) resin matrix. The Bi NPs operate as the phase change component whereas the PI resin matrix prevents nanoparticle coalescence during melt-freeze cycles. We tune melting temperature and enthalpy of fusion in these composites by varying the NP diameter. Adjusting the NP volume fraction also controls the composite's thermal energy storage density. Hence it is possible to leverage size effects to tune phase change temperature and energy density in phase change materials.Size-dependent melting decouples melting temperature from chemical composition and provides a new design variable for phase change material applications. To demonstrate this potential, we create nanocomposites that exhibit stable and tunable melting temperatures through numerous melt-freeze cycles. These composites consist of a monodisperse ensemble of Bi nanoparticles (NPs) embedded in a polyimide (PI) resin matrix. The Bi NPs operate as the phase change component whereas the PI resin matrix prevents nanoparticle coalescence during melt-freeze cycles. We tune melting temperature and enthalpy of fusion in these composites by varying the NP diameter. Adjusting the NP volume fraction also controls the composite's thermal energy storage density. Hence it is possible to leverage size effects to tune phase change temperature and energy density in phase change materials. Electronic supplementary information (ESI) available: Experimental details and additional DSC data on nanocomposites and pure PI resin. See DOI: 10.1039/c3nr02842a

Liu, Minglu; Wang, Robert Y.

2013-07-01

313

Physical and polarimetric C-band microwave scattering properties of first-year Arctic sea ice during the advanced melt season  

NASA Astrophysics Data System (ADS)

In this thesis, the physical, dielectric, and polarimetric microwave C-band properties of first-year sea ice (FYI) during the advanced melt season are investigated. Advanced melt is the most dynamic and least understood season in the annual cycle of Arctic sea ice due to rapid, small-scale, phase changes associated with melt processes and the occurrence of melt ponds on the ice surface. Measurements of the physical, structural, and dielectric properties of advanced melt FYI, combined with in-situ and spaced-based measurements of C-band microwave scattering, form the basis of this research. A physical model of the medium is created and physical controls on its C-band, like-polarized, backscatter response are evaluated using a multi-layer surface and volume scattering model and in-situ scattering observations. C-band microwave scattering from bare FYI is shown to be dominated by volumetric moisture content driven fluctuations in the dielectric properties, as well as structural variability, of desalinated upper ice layers. The C-band polarimetric scattering properties of surface features---wet snow, bare ice, and melt ponds---are investigated for high-Arctic and marginal ice environments, and dominant scattering mechanisms are theorized. Results demonstrate the potential for the exploitation of polarization diversity for the detection of advanced melt FYI geophysical information using spaceborne synthetic aperture radar (SAR). This knowledge is extended to the application of ENVISAT-ASAR imagery for the regional scale mapping of advanced melt FYI surface albedo using a multi-scale, object-based image analysis (OBIA) approach.

Scharien, Randall

314

Spin liquid regimes at nonzero temperature in quantum spin ice  

NASA Astrophysics Data System (ADS)

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

Savary, Lucile; Balents, Leon

2013-05-01

315

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

316

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

Microsoft Academic Search

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

Jiakuan Yang; Bo Xiao; Aldo R. Boccaccini

2009-01-01

317

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

318

Impacts of metals and nutrients released from melting multiyear Arctic sea ice  

Microsoft Academic Search

Nutrients (C, N, and P) and metals (iron, molybdenum, nickel, zinc, vanadium, copper, and cobalt) were determined in water and multiyear ice sampled along the Greenland current and Fram Strait in July 2007. Total metal and nutrient concentrations in ice varied fivefold to tenfold, for most elements, across the area sampled. Data show that some nutrients (i.e., NH4+) and metals

Antonio Tovar-Sánchez; Carlos M. Duarte; Juan C. Alonso; Silvia Lacorte; Romà Tauler; Cristobal Galbán-Malagón

2010-01-01

319

Ice velocities near the terminus of the Matanuska Glacier, Alaska, during an unseasonably warm melt season  

Microsoft Academic Search

Horizontal ice motion in the western terminus region of the Matanuska Glacier, AK, was tracked over an 18-day period during June-July 2004. The movement of 23 stakes anchored into the ice was monitored using total station surveying equipment, which was set up over a temporary benchmark on an end moraine. The summer of 2004 was unique in that there was

Monica Z. Bruckner

320

Arctic sea ice conditions in spring 2009-2013 prior to melt  

NASA Astrophysics Data System (ADS)

from NASA IceBridge airborne surveys in March/April 2009-2013 over the western Arctic Ocean are presented in the context of previous observations to assess changes in the characteristics of the sea ice cover during the last decade, taking into account spatial and temporal limitations in the available data. Following a precipitous drop in the amount and thickness of multiyear (MY) ice in 2007-2008, the characteristics of the ice cover have remained largely consistent through March 2013. The central Arctic continues to be dominated by MY ice with mean and modal thicknesses of 3.2 m and 2.4 m, respectively. The southern Beaufort and Chukchi Sea region is a complex mixture of ~75% first-year ice and 25% MY ice. IceBridge observations indicate that the mean thickness in the Beaufort and Chukchi Seas may have decreased from ~2.5 m to as low as 1.6 m over the 5 year period.

Richter-Menge, Jacqueline A.; Farrell, Sinead L.

2013-11-01

321

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

322

Complex network of channels beneath an Antarctic ice shelf  

NASA Astrophysics Data System (ADS)

shelves play an important role in stabilizing the interior grounded ice of the large ice sheets. The thinning of major ice shelves observed in recent years, possibly in connection to warmer ocean waters coming into contact with the ice-shelf base, has focused attention on the ice-ocean interface. Here we reveal a complex network of sub ice-shelf channels under the Fimbul Ice Shelf, Antarctica, mapped using ground-penetrating radar over a 100 km2 grid. The channels are 300-500 m wide and 50 m high, among the narrowest of any reported. Observing narrow channels beneath an ice shelf that is mainly surrounded by cold ocean waters, with temperatures close to the surface freezing point, shows that channelized basal melting is not restricted to rapidly melting ice shelves, indicating that spatial melt patterns around Antarctica are likely to vary on scales that are not yet incorporated in ice-ocean models.

Langley, K.; Deschwanden, A.; Kohler, J.; Sinisalo, A.; Matsuoka, K.; Hattermann, T.; Humbert, A.; Nøst, O. A.; Isaksson, E.

2014-02-01

323

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

NASA Astrophysics Data System (ADS)

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

324

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

NASA Astrophysics Data System (ADS)

Since 2007, there has been a series of surface melt records over the Greenland ice sheet (GrIS), continuing the trend towards increased melt observed since the end of the 1990's. The last two decades are characterized by an increase of negative phases of the North Atlantic Oscillation (NAO) favouring warmer and drier summers than normal over GrIS. In this context, we use a circulation type classification based on daily 500 hPa geopotential height to evaluate the role of atmospheric dynamics in this surface melt acceleration for the last two decades. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June-July-August) mean temperature from reanalyses at 700 hPa over Greenland; analogous atmospheric circulations in the past show that ~70% of the 1993-2012 warming at 700 hPa over Greenland has been driven by changes in the atmospheric flow frequencies. Indeed, the occurrence of anticyclones centred over the GrIS at the surface and at 500 hPa has doubled since the end of 1990's, which induces more frequent southerly warm air advection along the western Greenland coast and over the neighbouring Canadian Arctic Archipelago (CAA). These changes in the NAO modes explain also why no significant warming has been observed these last summers over Svalbard, where northerly atmospheric flows are twice as frequent as before. Therefore, the recent warmer summers over GrIS and CAA cannot be considered as a long-term climate warming but are more a consequence of NAO variability affecting atmospheric heat transport. Although no global model from the CMIP5 database projects subsequent significant changes in NAO through this century, we cannot exclude the possibility that the observed NAO changes are due to global warming.

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

2013-02-01

325

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

326

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

327

Serum separation in molten ice creams produced by low temperature extrusion processes  

Microsoft Academic Search

The microstructure and kinetics of serum separation due to creaming of air bubbles in molten ice creams produced using the novel twin and single screw low temperature extrusion processes are investigated. The measured fat globule size distributions are bimodal for both ice creams. However, the concentration of primary fat globules is much larger for the twin screw extruded ice cream

H. Wildmoser; S. A. K. Jeelani; E. J. Windhab

2005-01-01

328

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

329

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

Microsoft Academic Search

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

R. L. Brown; E. E. Adams

2002-01-01

330

Long-term ocean simulations in FESOM: evaluation and application in studying the impact of Greenland Ice Sheet melting  

NASA Astrophysics Data System (ADS)

The Finite Element Sea-ice Ocean Model (FESOM) is formulated on unstructured meshes and offers geometrical flexibility which is difficult to achieve on traditional structured grids. In this work, the performance of FESOM in the North Atlantic and Arctic Ocean on large time scales is evaluated in a hindcast experiment. A water-hosing experiment is also conducted to study the model sensitivity to increased freshwater input from Greenland Ice Sheet (GrIS) melting in a 0.1-Sv discharge rate scenario. The variability of the Atlantic Meridional Overturning Circulation (AMOC) in the hindcast experiment can be explained by the variability of the thermohaline forcing over deep convection sites. The model also reproduces realistic freshwater content variability and sea ice extent in the Arctic Ocean. The anomalous freshwater in the water-hosing experiment leads to significant changes in the ocean circulation and local dynamical sea level (DSL). The most pronounced DSL rise is in the northwest North Atlantic as shown in previous studies, and also in the Arctic Ocean. The released GrIS freshwater mainly remains in the North Atlantic, Arctic Ocean and the west South Atlantic after 120 model years. The pattern of ocean freshening is similar to that of the GrIS water distribution, but changes in ocean circulation also contribute to the ocean salinity change. The changes in Arctic and sub-Arctic sea level modify exchanges between the Arctic Ocean and subpolar seas, and hence the role of the Arctic Ocean in the global climate. Not only the strength of the AMOC, but also the strength of its decadal variability is notably reduced by the anomalous freshwater input. A comparison of FESOM with results from previous studies shows that FESOM can simulate past ocean state and the impact of increased GrIS melting well.

Wang, Xuezhu; Wang, Qiang; Sidorenko, Dmitry; Danilov, Sergey; Schröter, Jens; Jung, Thomas

2012-12-01

331

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

PubMed

Ice cream quality is dependent on many factors including storage temperature. Currently, the industry standard for ice cream storage is -28.9 °C. Ice cream production costs may be decreased by increasing the temperature of the storage freezer, thus lowering energy costs. The first objective of this research was to evaluate the effect of 4 storage temperatures on the quality of commercial vanilla-flavored light and full-fat ice cream. Storage temperatures used were -45.6, -26.1, and -23.3 °C for the 3 treatments and -28.9 °C as the control or industry standard. Ice crystal sizes were analyzed by a cold-stage microscope and image analysis at 1, 19.5, and 39 wk of storage. Ice crystal size did not differ among the storage temperatures of light and full-fat ice creams at 19.5 or 39 wk. An increase in ice crystal size was observed between 19.5 and 39 wk for all storage temperatures except -45.6 °C. Coldness intensity, iciness, creaminess, and storage/stale off-flavor of the light and full-fat ice creams were evaluated at 39 wk of storage. Sensory evaluation indicated no difference among the different storage temperatures for light and full-fat ice creams. In a second study, light and full-fat ice creams were heat shocked by storing at -28.9 °C for 35 wk and then alternating between -23.3 and -12.2 °C every 24h for 4 wk. Heat-shocked ice creams were analyzed at 2 and 4 wk of storage for ice crystal size and were evaluated by the sensory panel. A difference in ice crystal size was observed for light and full-fat ice creams during heat-shock storage; however, sensory results indicated no differences. In summary, storage of light or full-fat vanilla-flavored ice creams at the temperatures used within this research did not affect quality of the ice creams. Therefore, ice cream manufacturers could conserve energy by increasing the temperature of freezers from -28.9 to -26.1 °C. Because freezers will typically fluctuate from the set temperature, usage of -26.1 °C allows for a safety factor, even though storage at -23.3 °C did not affect ice cream quality. PMID:21524511

Buyck, J R; Baer, R J; Choi, J

2011-05-01

332

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

Microsoft Academic Search

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

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

1984-01-01

333

Effects of Culture, pH and Fat Concentration on Melting Rate and Sensory Characteristics of Probiotic Fermented Yellow Mombin (Spondias mombin L) Ice Creams  

Microsoft Academic Search

Twelve fermented yellow mombin ice creams were produced with different starter cultures (Lactobacillus acidophilus 74-2, L. acidophilus LAC 4 and yoghurt starter culture), final pH (4.5 and 5) and concentrations of added cream (5 and 10%). Probiotic culture stability, melting properties and sensory acceptance were evaluated in ice cream samples. The mixes were frozen and stored for 105 days at

C. S. Favaro-Trindade; J. C. de Carvalho Balieiro; P. Felix Dias; F. Amaral Sanino; C. Boschini

2007-01-01

334

Coincident high resolution optical-SAR image analysis for surface albedo estimation of first-year sea ice during summer melt  

Microsoft Academic Search

The parameterization of sea ice albedo during summer, when fluctuations in the fractional coverage of melt ponds change on a variety of spatial and temporal scales, represents a significant challenge for both the modelling and remote sensing communities. Ubiquitous cloud cover in summer inhibits the use of optical sensors for providing large-scale estimates of sea ice surface albedo. C-band (5.3 GHz)

Randall K. Scharien; John J. Yackel; Mats A. Granskog; Brent G. T. Else

2007-01-01

335

Comparative study on size dependence of melting temperatures of pure metal and alloy nanoparticles  

NASA Astrophysics Data System (ADS)

A comparative study on the size dependence of the melting temperatures of pure metal and alloy nanoparticles has been carried out. It was found that the melting temperatures of Bi-Sn, In-Sn, and Pb-Sn alloy nanoparticles decreased more rapidly with decreasing particle size than those of the constituent metal nanoparticles (Bi, In, Pb, Sn). Namely, the size dependence of the melting temperature was stronger for the alloy nanoparticles than that for the constituent metal nanoparticles. Results calculated with a thermodynamic model were in good agreement with the experimental observations.

Chen, C. L.; Lee, J.-G.; Arakawa, K.; Mori, H.

2011-07-01

336

Comparative study on size dependence of melting temperatures of pure metal and alloy nanoparticles  

SciTech Connect

A comparative study on the size dependence of the melting temperatures of pure metal and alloy nanoparticles has been carried out. It was found that the melting temperatures of Bi-Sn, In-Sn, and Pb-Sn alloy nanoparticles decreased more rapidly with decreasing particle size than those of the constituent metal nanoparticles (Bi, In, Pb, Sn). Namely, the size dependence of the melting temperature was stronger for the alloy nanoparticles than that for the constituent metal nanoparticles. Results calculated with a thermodynamic model were in good agreement with the experimental observations.

Chen, C. L. [Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); WPI Research Center, Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Lee, J.-G. [Functional Materials Division, Korea Institute of Materials Science, 531 Changwondaero, Changwon, Gyeongnam 641-831 (Korea, Republic of); Arakawa, K.; Mori, H. [Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)

2011-07-04

337

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

338

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

339

A 1700-year Record of Tropical Sea Surface Temperatures and High-altitude Andean Climate Derived from the Quelccaya Ice Cap, Peru (Invited)  

NASA Astrophysics Data System (ADS)

Stable isotopic, aerosol, and physical stratigraphy provided by new ice-core records from the Quelccaya ice cap (5670 masl) in Peru provide annual time series of tropical climatic and environmental variations extending back to 315 AD. These records present an opportunity to extract new information about links between rising temperatures on Andean tropical glaciers and sea surface temperatures (SSTs) in El Niño-Southern Oscillation (ENSO) indicator regions and in the Intertropical Convergence Zone (ITCZ) in the eastern Pacific and western Atlantic Oceans. ENSO is a dominant force for tropical climate variability on interannual time scales. It is linked with the position of the ITCZ and the associated teleconnections affect the strength and direction of air masses and storm tracks, variations in convective activity that control flooding and drought, and modulation of tropical storm intensities. The Quelccaya ice core record may be considered as the “Rosetta Stone” for high resolution climate records extracted from tropical glaciers, relating stable isotopic variations with tropical SSTs and freezing level heights. The ice core histories from Quelccaya also provide the longer term context needed to assess the significance of the magnitude and rate of its current ice loss. The cores provide a detailed description of climate conditions in the tropical Andes during the "Little Ice Age" and "Medieval Climate Anomaly” periods. They show that the recent acceleration of ice retreat in this Andean region is not driven solely by precipitation changes and that over decadal and longer time scales stable isotopic ratios are not significantly correlated with precipitation. The well-documented accelerating ice loss on Quelccaya in the Andes, as well as that on Naimona’nyi in the Himalayas, on Kilimanjaro in eastern Africa, and on ice fields near Puncak Jaya, Papua, Indonesia point to an overarching, larger scale driver. The ongoing melting of these ice fields is consistent with model predictions for a vertical amplification of temperature in the tropics, and has serious implications for the people who live in these areas.

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

2010-12-01

340

Low temperature biodegradation of airport de-icing fluids.  

PubMed

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

Revitt, D M; Worrall, P

2003-01-01

341

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

342

Spin Ice: a Laboratory for Low Temperature Physics  

Microsoft Academic Search

Pauling's model of hydrogen disorder in water ice illustrates how zero point entropy can occur in a practical system. `Spin Ice' is a precise analogue of Pauling's model in which hydrogen displacement vectors are replaced by Ising spins and the `ice rules' are enforced by ferromagnetic coupling. The model is approximated almost ideally by several rare earth pyrochlore magnets of

S. T. Bramwell; T. Fennell

2006-01-01

343

Antarctica Ice  

NSDL National Science Digital Library

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

Geographic, National

344

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

Microsoft Academic Search

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

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

2009-01-01

345

Spatial and temporal melt variability at Helheim Glacier, East Greenland, and its effect on ice dynamics  

Microsoft Academic Search

Understanding the behavior of large outlet glaciers draining the Greenland Ice Sheet is critical for assessing the impact of climate change on sea level rise. The flow of marine-terminating outlet glaciers is partly governed by calving-related processes taking place at the terminus but is also influenced by the drainage of surface runoff to the bed through moulins, cracks, and other

M. L. Andersen; T. B. Larsen; M. Nettles; P. Elosegui; D. van As; Gordon S. Hamilton; Leigh A. Stearns; J. L. Davis; A. P. Ahlstrøm; J. de Juan; G. Ekström; L. Stenseng; S. A. Khan; R. Forsberg; D. Dahl-Jensen

2010-01-01

346

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

Microsoft Academic Search

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

Christopher Swarctz; Elias Alijallis; Scott Robert Hunter; John T Simpson; Chang-Hwan Choi

2010-01-01

347

Existence of a Quasiliquid Film on the Surface of Ice.  

National Technical Information Service (NTIS)

The hypothesis of existence of a quasiliquid film on the surface of ice at temperatures below its melting point (T(melt)) was first stated by M. Faraday for explanation of a number of mechanical properties of ice. In this report the authors describes the ...

L. A. Ushakova V. F. Kiselev V. I. Kvlividze

1971-01-01

348

Debye-Hückel theory for spin ice at low temperature  

NASA Astrophysics Data System (ADS)

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

Castelnovo, C.; Moessner, R.; Sondhi, S. L.

2011-10-01

349

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

350

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