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Sample records for ice melting temperature

  1. Arctic temperature amplification and sea-ice melt

    NASA Astrophysics Data System (ADS)

    Graversen, R. G.; Kapsch, M.; Mauritzen, T.; Tjernström, M.

    2012-04-01

    In recent decades, Arctic temperatures increase more than the global average - this has become known as Arctic temperature amplification. At the same time, Arctic sea-ice extent is shrinking with a pace being largest in summer. Reanalysis data show Arctic temperature amplification in the free troposphere above the boundary layer. In summer this warming aloft cannot be attributed to surface processes. This is because the surface-air temperature trends are modest in the Arctic during summer, since the ice-melt keeps the temperatures close to the melting point. Rather the warming in the free troposphere could be due to changes of the heat advection into the Arctic and changes of the cloudiness. The warming aloft induces an increase of the energy flux towards the surface in terms of longwave radiation and turbulent fluxes, which contributes to the sea-ice melt during summer. When the ice melts, surface-based processes start acting, among them the surface-albedo feedback where the sea-ice reduction leads to an increase of absorption of solar radiation. During summer, the excess of energy at the surface is stored in the ocean, both internally as heat, and latently due to the ice melt. This energy is released during the following autumn and winter causing positive surface-air temperature in these seasons. The extreme ice melt in 2007 is an example of this chain of processes. During the summer of 2007 the Arctic sea ice shrank to the lowest extent ever observed. Using the state-of-the-art ERA-Interim reanalysis data, the role of the atmospheric energy transport in this extreme melt event is explored.

  2. The impact of melt ponds on summertime microwave brightness temperatures and sea-ice concentrations

    NASA Astrophysics Data System (ADS)

    Kern, Stefan; Rösel, Anja; Toudal Pedersen, Leif; Ivanova, Natalia; Saldo, Roberto; Tage Tonboe, Rasmus

    2016-09-01

    Sea-ice concentrations derived from satellite microwave brightness temperatures are less accurate during summer. In the Arctic Ocean the lack of accuracy is primarily caused by melt ponds, but also by changes in the properties of snow and the sea-ice surface itself. We investigate the sensitivity of eight sea-ice concentration retrieval algorithms to melt ponds by comparing sea-ice concentration with the melt-pond fraction. We derive gridded daily sea-ice concentrations from microwave brightness temperatures of summer 2009. We derive the daily fraction of melt ponds, open water between ice floes, and the ice-surface fraction from contemporary Moderate Resolution Spectroradiometer (MODIS) reflectance data. We only use grid cells where the MODIS sea-ice concentration, which is the melt-pond fraction plus the ice-surface fraction, exceeds 90 %. For one group of algorithms, e.g., Bristol and Comiso bootstrap frequency mode (Bootstrap_f), sea-ice concentrations are linearly related to the MODIS melt-pond fraction quite clearly after June. For other algorithms, e.g., Near90GHz and Comiso bootstrap polarization mode (Bootstrap_p), this relationship is weaker and develops later in summer. We attribute the variation of the sensitivity to the melt-pond fraction across the algorithms to a different sensitivity of the brightness temperatures to snow-property variations. We find an underestimation of the sea-ice concentration by between 14 % (Bootstrap_f) and 26 % (Bootstrap_p) for 100 % sea ice with a melt-pond fraction of 40 %. The underestimation reduces to 0 % for a melt-pond fraction of 20 %. In presence of real open water between ice floes, the sea-ice concentration is overestimated by between 26 % (Bootstrap_f) and 14 % (Bootstrap_p) at 60 % sea-ice concentration and by 20 % across all algorithms at 80 % sea-ice concentration. None of the algorithms investigated performs best based on our investigation of data from summer 2009. We suggest that those algorithms which are

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

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

    USGS Publications Warehouse

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

    2008-01-01

    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.

  6. Melting of Ice under Pressure

    SciTech Connect

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

    2008-07-31

    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.

  7. Melting of ice under pressure.

    PubMed

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

    2008-09-30

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

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

    NASA Astrophysics Data System (ADS)

    Kanno, Hitoshi; Soga, Makoto; Kajiwara, Kazuhito

    2007-08-01

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

  9. The physical basis of enhanced temperature index ice melt parameterizations in the Nepal Himalaya.

    NASA Astrophysics Data System (ADS)

    Litt, Maxime; Shea, Joseph; Koch, Inka; Wagnon, Patrick

    2016-04-01

    Glacier melt is an important component of seasonal water flows in the Himalayas. Due to scarce data availability and computational convenience, most glaciological projections in the Himalayan region derive ice melt from temperature index (TI) or enhanced temperature index (ETI) parameterizations, which require only temperature and solar radiation as inputs. Still, the processes linking these variables to melt remain poorly documented under high-altitude climates, where the air is cold, and the main input is shortwave radiation. In this study, we question the physical basis of enhanced temperature index (ETI) melt parameterizations in the Nepal Himalayas. Using atmospheric weather station (AWS) installed on Yala glacier at 5090 m a.s.l and Mera glaciers at 6350 m a.s.l., we study the surface energy balance (SEB) during one melt season, i.e, the monsoon and surrounding weeks, in 2014. The SEB estimates provide insights into the atmospheric controls on the glaciers. We study the variability of correlation coefficients linking daily means of temperature, SEB and SEB components. On Yala at 5090 m a.s.l, energy inputs are high during the pre-monsoon due to low surface albedo and strong incoming solar radiation near the solstice, and melt is strong. The temperature correlates moderately with the SEB (R = 0.58) mainly through sublimation and net longwave radiation. During the monsoon snow deposition reduces the magnitude of net shortwave radiation, thus dampening the melt rates. Strong longwave emission from clouds compensates for the surface emission, and the correlation of temperature with the SEB, mainly explained through net shortwave radiation, decreases (R = 0.49). During the post-monsoon, high albedo, heat losses through sublimation and clear-skies favoring longwave losses at the surface lead to a near zero SEB, and reduced melt. Temperature correlates well with the SEB (R = 0.88) through net longwave radiation. On Mera at 6300 m a.s.l, high surface albedo and

  10. A preliminary view on adsorption of organics on ice at temperatures close to melting point

    NASA Astrophysics Data System (ADS)

    Kong, Xiangrui; Waldner, Astrid; Orlando, Fabrizio; Artiglia, Luca; Ammann, Markus; Bartels-Rausch, Thorsten

    2016-04-01

    -level spectroscopies to reveal the behaviour of adsorption and dissociation on ice. Additionally, pure ice and amine doped ice will be compared for their surface structure change at different temperatures, which will indicate the differences of surface disordering caused by different factors. For instance, we will have a chance to know better if impurities will cause local disordering, i.e. forming hydration shell, which challenges the traditional picture of a homogenous disordered doped ice surface. The findings of this study could not only improve our understanding of how acidic organics adsorb to ice, and of their chemical properties on ice, but also have potentials to know better the behaviour of pure ice at temperatures approaching to the melting point.

  11. Melting temperature of ice Ih calculated from coexisting solid-liquid phases

    NASA Astrophysics Data System (ADS)

    Wang, J.; Yoo, S.; Bai, J.; Morris, James R.; Zeng, X. C.

    2005-07-01

    We carried out molecular-dynamics simulations by using the two-phase coexistence method with the constant pressure, particle number, and enthalpy ensemble to compute the melting temperature of proton-disordered hexagonal ice Ih at 1-bar pressure. Four models of water were considered, including the widely used TIP4P [W. L. Jorgensen, J. Chandrasekha, J. D. Madura, R. W. Impey, and M. L. Klein, J. Chem. Phys.79, 926 (1983)] and TIP5P [M. W. Mahoney and W. L. Jorgensen J. Chem. Phys.112, 8910 (2000)] models, as well as recently improved TIP4P and TIP5P models for use with Ewald techniques—the TIP4P-Ew [W. Horn, W. C. Swope, J. W. Pitera, J. C. Madura, T. J. Dick, G. L. Hura, and T. Head-Gordon, J. Chem. Phys.120, 9665 (2004)] and TIP5P-Ew [S. W. Rick, J. Chem. Phys.120, 6085 (2004)] models. The calculated melting temperature at 1bar is Tm=229±1K for the TIP4P and Tm=272.0±0.6K for the TIP5P ice Ih, both are consistent with previous simulations based on free-energy methods. For the TIP4P-Ew and TIP5P-Ew models, the calculated melting temperature is Tm=257.0±1.1K and Tm=253.9±1.1K, respectively.

  12. Use of ice cores from glaciers with melting for reconstructing mean summer temperature variations

    NASA Astrophysics Data System (ADS)

    Nakazawa, Fumio; Fujita, Koji

    This study examines a new method for reconstructing mean summer temperature variations by using an ice core from a wet-snow zone on a summer-accumulation-type glacier. In July 2001, a 25.1 m deep ice core was recovered from the accumulation area of Sofiyskiy glacier (49°47‧ N, 87°43‧ E; 3435 m a.s.l.), located in the southern Chuyskiy range of the Russian Altai mountains, and a 4.5 m deep pit was excavated about 50 m northwest of the drill site. The observation site has a positive balance even during summer when melting occurs. The summer balance for each year from 1990 to 2000 was estimated from Pinaceae and Artemisia pollen peaks in these samples. Pinaceae pollen marks spring, whereas Artemisia pollen marks autumn. Moreover, meltwater intrusion did not reach the previous year's accumulation. Thus, the ice between these pollen peaks in the same year was used to estimate a summer balance. The reconstructed summer balance variations were negatively correlated with mean summer temperature variations (r = -0.72, P < 0.05). This study shows that, for summer-accumulation-type glaciers such as Sofiyskiy glacier, the most important climate factor controlling the glacier's surface mass balance is mean summer temperature. Therefore, the summer layer thickness in an ice core can be used as a proxy for reconstructing mean summer temperature variations.

  13. Water Freezing and Ice Melting.

    PubMed

    Małolepsza, Edyta; Keyes, Tom

    2015-12-08

    The generalized replica exchange method (gREM) is designed to sample states with coexisting phases and thereby to describe strong first order phase transitions. The isobaric MD version of the gREM is presented and applied to the freezing of liquid water and the melting of hexagonal and cubic ice. It is confirmed that coexisting states are well-sampled. The statistical temperature as a function of enthalpy, TS(H), is obtained. Hysteresis between freezing and melting is observed and discussed. The entropic analysis of phase transitions is applied and equilibrium transition temperatures, latent heats, and surface tensions are obtained for hexagonal ice ↔ liquid and cubic ice ↔ liquid with excellent agreement with published values. A new method is given to assign water molecules among various symmetry types. Pathways for water freezing, ultimately leading to hexagonal ice, are found to contain intermediate layered structures built from hexagonal and cubic ice.

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

    NASA Astrophysics Data System (ADS)

    Kimizuka, Norihito; Suzuki, Toru

    We measured the ice nucleation temperature depression , ΔTf , and equilibrium melting points depression, ΔTm, 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 ΔTf ,and ΔTm all samples. In addition the value of λ , which can be obtained from the linear relationship, ΔTf =λ ΔTm, were confirmed to show correlation with the value of λ , as obtained by the W/O emulsion method.

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

    PubMed

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

    2012-11-21

    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-ρ) 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-ρ) curve improves the estimation of the freezing point. We also determined and compared the densities of

  16. Water freezing and ice melting

    DOE PAGES

    Malolepsza, Edyta; Keyes, Tom

    2015-10-12

    The generalized replica exchange method (gREM) is designed to sample states with coexisting phases and thereby to describe strong first order phase transitions. The isobaric MD version of the gREM is presented and applied to freezing of liquid water, and melting of hexagonal and cubic ice. It is confirmed that coexisting states are well sampled. The statistical temperature as a function of enthalpy, TS(H), is obtained. Hysteresis between freezing and melting is observed and discussed. The entropic analysis of phase transitions is applied and equilibrium transition temperatures, latent heats, and surface tensions are obtained for hexagonal ice↔liquid and cubic ice↔liquid,more » with excellent agreement with published values. A new method is given to assign water molecules among various symmetry types. As a result, pathways for water freezing, ultimately leading to hexagonal ice, are found to contain intermediate layered structures built from hexagonal and cubic ice.« less

  17. Water freezing and ice melting

    SciTech Connect

    Malolepsza, Edyta; Keyes, Tom

    2015-10-12

    The generalized replica exchange method (gREM) is designed to sample states with coexisting phases and thereby to describe strong first order phase transitions. The isobaric MD version of the gREM is presented and applied to freezing of liquid water, and melting of hexagonal and cubic ice. It is confirmed that coexisting states are well sampled. The statistical temperature as a function of enthalpy, TS(H), is obtained. Hysteresis between freezing and melting is observed and discussed. The entropic analysis of phase transitions is applied and equilibrium transition temperatures, latent heats, and surface tensions are obtained for hexagonal ice↔liquid and cubic ice↔liquid, with excellent agreement with published values. A new method is given to assign water molecules among various symmetry types. As a result, pathways for water freezing, ultimately leading to hexagonal ice, are found to contain intermediate layered structures built from hexagonal and cubic ice.

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

    ERIC Educational Resources Information Center

    Brady, John B.

    1992-01-01

    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…

  19. Bulk heat transfer coefficient in the ice-upper ocean system in the ice melt season derived from concentration-temperature relationship

    NASA Astrophysics Data System (ADS)

    Nihashi, Sohey; Ohshima, Kay I.

    2008-06-01

    The bulk heat transfer coefficient in the ice-upper ocean system (Kb) in the ice melt season is estimated by a new method at 18 areas that cover much of the Antarctic seasonal ice zone. The method is based on a model in which ice melting is caused only by heat input through open water and is treated in a bulk fashion in the ice-upper ocean system. Kb is estimated by fitting a convergent curve derived from the model to an observed ice concentration-temperature plot (CT-plot). Estimated Kb is 1.15 ± 0.72 × 10-4 m s-1 on average. If Kb can be expressed by the product of the heat transfer coefficient (ch) and the friction velocity (uτ), ch is 0.0113 ± 0.0055. This value is about two times larger than that estimated at the ice bottom. The relationship between Kb and the geostrophic wind speed (Uw), which is roughly proportional to uτ, shows a significant positive correlation, as expected. Further, Kb seems more likely to be proportional to the square or cube of Uw rather than a linear relationship. Since Kb estimated from our method is associated with ice melting in a bulk fashion in the ice-upper ocean system, this relationship likely indicates both the mixing process of heat in the upper ocean (proportional to uτ3) and the local heat transfer process at the ice-ocean interface (proportional to uτ).

  20. Scaling laws for melting ice avalanches.

    PubMed

    Turnbull, B

    2011-12-16

    This Letter describes an investigation of interfacial melting in ice-bearing granular flows. It is proposed that energy associated with granular collisions causes melting at an ice particle's surface, which can thus occur at temperatures well below freezing. A laboratory experiment has been designed that allows quantification of this process and its effect on the dynamics of a granular shear flow of ice spheres. This experiment employs a rotating drum, half filled with ice particles, situated in a temperature controlled laboratory. Capillary forces between the wetted melted particle surfaces lead to the clumping of particles and enhanced flow speeds, in turn leading to further melting. Dimensional analysis defines a parameter space for further experimentation.

  1. Local ice melting by an antifreeze protein.

    PubMed

    Calvaresi, Matteo; Höfinger, Siegfried; Zerbetto, Francesco

    2012-07-09

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

  2. Ice cream structural elements that affect melting rate and hardness.

    PubMed

    Muse, M R; Hartel, R W

    2004-01-01

    Statistical models were developed to reveal which structural elements of ice cream affect melting rate and hardness. Ice creams were frozen in a batch freezer with three types of sweetener, three levels of the emulsifier polysorbate 80, and two different draw temperatures to produce ice creams with a range of microstructures. Ice cream mixes were analyzed for viscosity, and finished ice creams were analyzed for air cell and ice crystal size, overrun, and fat destabilization. The ice phase volume of each ice cream were calculated based on the freezing point of the mix. Melting rate and hardness of each hardened ice cream was measured and correlated with the structural attributes by using analysis of variance and multiple linear regression. Fat destabilization, ice crystal size, and the consistency coefficient of the mix were found to affect the melting rate of ice cream, whereas hardness was influenced by ice phase volume, ice crystal size, overrun, fat destabilization, and the rheological properties of the mix.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  4. Basal melt beneath whillans ice stream and ice streams A and C

    NASA Technical Reports Server (NTRS)

    Joughin, I.; Teluezyk, S.; Engelhardt, H.

    2002-01-01

    We have used a recently derived map of the velocity of Whillans Ice Stream and Ice Streams A and C to help estimate basal melt. Temperature was modeled with a simple vertical advection-diffusion equation, 'tuned' to match temperature profiles. We find that most of the melt occurs beneath the tributaries where larger basal shear stresses and thicker ice favors greater melt (e.g., 10-20 mm/yr). The occurrence of basal freezing is predicted beneath much of the ice plains of Ice Stream C and Whillans Ice Stream. Modelled melt rates for when Ice Stream C was active suggest there was just enough melt water generated in its tributaries to balance basal freezing on its ice plain. Net basal melt for Whillans Ice Stream is positive due to smaller basal temperature gradients. Modelled temperatures on Whillans Ice Stream, however, were constrained by a single temperature profile at UpB. Basal temperature gradients for Whillans B1 and Ice Stream A may have conditions more similar to those beneath Ice Streams C and D, in which case, there may not be sufficient melt to sustain motion. This would be consistent with the steady deceleration of Whillans stream over the last few decades.

  5. Rotation of melting ice disks due to melt fluid flow

    NASA Astrophysics Data System (ADS)

    Dorbolo, S.; Adami, N.; Dubois, C.; Caps, H.; Vandewalle, N.; Darbois-Texier, B.

    2016-03-01

    We report experiments concerning the melting of ice disks (85 mm in diameter and 14 mm in height) at the surface of a thermalized water bath. During the melting, the ice disks undergo translational and rotational motions. In particular, the disks rotate. The rotation speed has been found to increase with the bath temperature. We investigated the flow under the bottom face of the ice disks by a particle image velocimetry technique. We find that the flow goes downwards and also rotates horizontally, so that a vertical vortex is generated under the ice disk. The proposed mechanism is the following. In the vicinity of the bottom face of the disk, the water eventually reaches the temperature of 4°C for which the water density is maximum. The 4°C water sinks and generates a downwards plume. The observed vertical vorticity results from the flow in the plume. Finally, by viscous entrainment, the horizontal rotation of the flow induces the solid rotation of the ice block. This mechanism seems generic: any vertical flow that generates a vortex will induce the rotation of a floating object.

  6. Rotation of melting ice disks due to melt fluid flow.

    PubMed

    Dorbolo, S; Adami, N; Dubois, C; Caps, H; Vandewalle, N; Darbois-Texier, B

    2016-03-01

    We report experiments concerning the melting of ice disks (85 mm in diameter and 14 mm in height) at the surface of a thermalized water bath. During the melting, the ice disks undergo translational and rotational motions. In particular, the disks rotate. The rotation speed has been found to increase with the bath temperature. We investigated the flow under the bottom face of the ice disks by a particle image velocimetry technique. We find that the flow goes downwards and also rotates horizontally, so that a vertical vortex is generated under the ice disk. The proposed mechanism is the following. In the vicinity of the bottom face of the disk, the water eventually reaches the temperature of 4 °C for which the water density is maximum. The 4 °C water sinks and generates a downwards plume. The observed vertical vorticity results from the flow in the plume. Finally, by viscous entrainment, the horizontal rotation of the flow induces the solid rotation of the ice block. This mechanism seems generic: any vertical flow that generates a vortex will induce the rotation of a floating object.

  7. Quantum melting of spin ice

    NASA Astrophysics Data System (ADS)

    Onoda, Shigeki; Tanaka, Yoichi

    2010-03-01

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

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

    USGS Publications Warehouse

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

    2006-01-01

    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.

  9. Melting and crystallization of ice in partially filled nanopores.

    PubMed

    Solveyra, Estefanía González; de la Llave, Ezequiel; Scherlis, Damián A; Molinero, Valeria

    2011-12-08

    We investigate the melting and formation of ice in partially filled hydrophilic and hydrophobic nanopores of 3 nm diameter using molecular dynamics simulations with the mW water model. Above the melting temperature, the partially filled nanopores contain two water phases in coexistence: a condensed liquid plug and a surface-adsorbed phase. It has been long debated in the literature whether the surface-adsorbed phase is involved in the crystallization. We find that only the liquid plug crystallizes on cooling, producing ice I with stacks of hexagonal and cubic layers. The confined ice is wetted by a premelted liquid layer that persists in equilibrium with ice down to temperatures well below its melting point. The liquid-ice transition is first-order-like but rounded. We determine the temperature and enthalpy of melting as a function of the filling fraction of the pore. In agreement with experiments, we find that the melting temperature of the nanoconfined ice is strongly depressed with respect to the bulk T(m), it depends weakly on the filling fraction and is insensitive to the hydrophobicity of the pore wall. The state of water in the crystallized hydrophilic and hydrophobic pores, however, is not the same: the hydrophobic pore has a negligible density of the surface-adsorbed phase and higher fraction of water in the ice phase than the hydrophilic pore. The widths of the ice cores are nevertheless comparable for the hydrophobic and hydrophilic pores, and this may explain their almost identical melting temperatures. The enthalpy of melting ΔH(m), when normalized by the actual amount of ice in the pore, is indistinguishable for the hydrophobic and hydrophilic pores, insensitive to the filling fraction, and within the error bars, the same as the difference in enthalpy between bulk liquid and bulk ice evaluated at the temperature of melting of ice in the nanopores.

  10. Multiscale Models of Melting Arctic Sea Ice

    DTIC Science & Technology

    2014-09-30

    represent sea ice more rigorously in climate models. OBJECTIVES Viewed from high above, the melting sea ice surface can be thought of as a two phase ...composite of ice and melt water. The boundaries between the two phases evolve with increasing complexity and a rapid onset of large scale...connectivity, or percolation of the melt phase . We plan to document this phenomenon with photographic imagery and to develop percolation and other models to

  11. Ice-Shelf Melting Around Antarctica

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Istomina, Larysa; Heygster, Georg

    2014-05-01

    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

  13. Surface melting on ice shelves and icebergs

    NASA Astrophysics Data System (ADS)

    Sergienko, Olga V.

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

  14. Mathematical Modelling of Melt Lake Formation on an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Buzzard, Sammie; Feltham, Daniel; Flocco, Daniela; Sammonds, Peter

    2015-04-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice shelf collapse. The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present results of a 1D mathematical model of heat transfer through an idealised ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation, melt lake development and refreezing are demonstrated through the modelled results. Furthermore, the effect of lateral meltwater transport upon melt lakes is examined. This will be developed through the estimations of meltwater catchment areas and the fraction of the ice shelf where melt lakes are present. Investigating the role of meltwater in ice shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea level rise.

  15. Rapid bottom melting widespread near Antarctic Ice Sheet grounding lines.

    PubMed

    Rignot, Eric; Jacobs, Stanley S

    2002-06-14

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

  16. Greenland Ice Sheet Today: A daily look at surface melt of the Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Leslie, S. R.; Gergely, K. L.; Beitler, J.; Scambos, T. A.; Stroeve, J. C.

    2013-12-01

    An increase in the surface melt of the Greenland ice sheet in recent decades signals the waning of the ice sheet in a changing climate. The unprecedented intense surface melt of the ice sheet in 2012 prompted NASA and NSIDC to launch Greenland Ice Sheet Today, a Web site that offers daily updated satellite data and periodic scientific analysis on surface melting of the Greenland ice sheet. Near-real-time melt data are derived from an algorithm that estimates melt and is applied to DMSP SSMIS brightness temperatures gridded to a 25km EASE-Grid. These data are then used to generate a daily melt image, a cumulative melt days image, and a daily melt graph. Contextual background information on ice sheets as well as scientific discussions about the status of the Greenland ice sheet are posted periodically. Greenland Ice Sheet Today serves to keep a wide range of user communities informed about a crucial part of the Earth's cryosphere and here we examine the development of and reactions to the Web site.

  17. Mathematical Modelling of Melt Lake Formation On An Ice Shelf

    NASA Astrophysics Data System (ADS)

    Buzzard, Sammie; Feltham, Daniel; Flocco, Daniela

    2016-04-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice-shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice-shelf collapse. The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present results of a 1-D mathematical model of heat transfer through an idealized ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation, melt lake development and refreezing are demonstrated through the modelled results. Furthermore, the effect of lateral meltwater transport upon melt lakes and the effect of the lakes upon the surface energy balance are examined. Investigating the role of meltwater in ice-shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea-level rise.

  18. Mathematical Modelling of Melt Lake Formation On An Ice Shelf

    NASA Astrophysics Data System (ADS)

    Buzzard, S. C.; Feltham, D. L.; Flocco, D.; Sammonds, P. R.

    2015-12-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice-shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice-shelf collapse. The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present results of a 1-D mathematical model of heat transfer through an idealized ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation, melt lake development and refreezing are demonstrated through the modelled results. Furthermore, the effect of lateral meltwater transport upon melt lakes and the effect of the lakes upon the surface energy balance are examined. Investigating the role of meltwater in ice-shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea-level rise.

  19. Linking surface energy balance calculations and Temperature Index models of surface melt: Revision of the Positive Degree-Day (PDD) methodology for the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Wake, L. M.; Marshall, S. J.; Lecavalier, B.; Milne, G. A.; Huybrechts, P.; Simpson, M. J. R.; Bayou, N.

    2012-04-01

    Positive Degree-Day (PDD) methodology (Braithwaite and Olesen, 1989; Reeh, 1991) is widely used in conjunction with observationally-derived Degree-Day Factors (DDFs) for snow and ice in order to simulate ice-sheet wide ablation rates using mean monthly temperature as the only input. Monthly PDD totals are calculated using the assumption that the monthly temperature distribution follows a Gaussian relationship with a spatially and temporally invariable standard deviation (σm), typically in the range of 4-5oC. DDFs for snow and ice used in ice sheet modelling are usually fixed at ~3 and 8 mm w.e. oC-1 day-1 respectively, but field observations show that these can vary by at least a factor of two depending on the albedo characteristics of the glacier surface (Hock, 2003). At odds with the assumption of constant σm, it has been shown that temperature variability is reduced at temperatures close to or above the melting point, due to thermal (latent heat) buffering and the maximum temperature of 0oC for a melting snow/ice surface (e.g., Marshall and Sharp, 2009). Analysis of hourly temperature data from 22 GC-Net stations (Steffen and Box, 2001) spanning the period 1995-2010 shows that observed σm follows a quadratic relationship with observed average monthly temperature. Comparisons of calculated and observed monthly PDD totals from GC-Net locations show that current assumptions of σm = 4-5oC can overestimate monthly PDD totals by 25% on average, compared to ~3% for the new methodology using a spatially varying σm. In the absence of extensive field measurements, 'theoretical' daily melt rates are calculated at several GC-Net locations using available field data to estimate the components of the daily surface energy budget (Net radiation, sensible and latent heat and subsurface energy flux). Subsequently, 'theoretical' DDFs are evaluated as a function of surface albedo. Our results suggest that future studies should consider DDFs for snow and ice of 3-7 mm w.e. oC-1

  20. Formation of melt channels on ice shelves

    NASA Astrophysics Data System (ADS)

    Sergienko, Olga

    2013-04-01

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

  1. Greenland ice sheet melt from MODIS and associated atmospheric variability.

    PubMed

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

    2014-03-16

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

  2. Greenland Ice Sheet Melt from MODIS and Associated Atmospheric Variability

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  3. Mathematical Modelling of Melt Lake Formation on an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Feltham, D. L.; Buzzard, S. C.; Flocco, D.; Sammonds, P. R.

    2014-12-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice shelf collapse.The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present preliminary results of a mathematical model of heat transfer through an idealised ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation and melt lake development are demonstrated through the modelled results. Investigating the role of meltwater in ice shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea level rise.

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

    PubMed

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

    2010-04-28

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

  5. Floating ice-algal aggregates below melting arctic sea ice.

    PubMed

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

    2013-01-01

    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.

  6. Basal terraces on melting ice shelves

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  7. Basal Terraces on Melting Ice Shelves

    NASA Astrophysics Data System (ADS)

    Dutrieux, P.; Stewart, C.; Jenkins, A.; Nicholls, K. W.; Corr, H. F. J.; Rignot, E. J.; Steffen, K.

    2014-12-01

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

  8. Indirect measurement of interfacial melting from macroscopic ice observations.

    PubMed

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

    2014-06-01

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

  9. Greenland ice sheet melting during the last interglacial

    NASA Astrophysics Data System (ADS)

    Langebroek, Petra M.; Nisancioglu, Kerim H.

    2016-04-01

    During the last interglacial period (LIG) peak temperatures over Greenland were several degrees warmer than today. The Greenland ice sheet (GIS) retreated causing a global sea-level rise in the order of several meters. Large uncertainties still exist in the exact amount of melt and on the source location of this melt. Here we examine the GIS response to LIG temperature and precipitation patterns using the SICOPOLIS ice sheet model. The LIG climate was simulated by forcing the Norwegian Earth System Model (NorESM) with the appropriate greenhouse gases and orbital settings. The resulting LIG ice volume evolution strongly depends on the chosen value of uncertain model parameters for the ice sheet (e.g. basal sliding parameter, PDD factors, and atmospheric temperature lapse rate). We reduce the uncertainty by evaluating an ensemble of model results against present-day observations of ice sheet size, elevation and stability, together with paleo information from deep ice cores. We find a maximum GIS reduction equivalent to 0.8 to 2.2m of global sea-level rise. In this model set-up most of the melting occurs in southwestern Greenland.

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

    NASA Astrophysics Data System (ADS)

    Flocco, Daniela; Feltham, Daniel; Schroeder, David

    2013-04-01

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

  11. Islands uncovered by melting polar ice

    NASA Astrophysics Data System (ADS)

    Kumar, Mohi

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

  12. Using Melting Ice to Teach Radiometric Dating.

    ERIC Educational Resources Information Center

    Wise, Donald Underkofler

    1990-01-01

    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)

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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

  14. Onset of convective instabilities in under-ice melt ponds.

    PubMed

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

    2012-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Nost, Ole Anders

    2010-05-01

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

  16. Massive Ice Layer Formed by Refreezing of Ice-shelf Surface Melt Ponds: Larsen C Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Kuipers Munneke, P.; Hubbard, B. P.; Luckman, A. J.; Ashmore, D.; Bevan, S. L.; Kulessa, B.; Jansen, D.; O'Leary, M.

    2015-12-01

    Surface melt ponds now form frequently on ice shelves across the northern sector of the Antarctic Peninsula in response to regional warming and local föhn winds. Analysis of a new, 1-year set of observations from an Automatic Weather Station on Larsen C Ice Shelf, Antarctica, reveals that föhn winds are able to cause intense melt in summer, and even into the late austral autumn. A potentially important, but hitherto unknown, consequence of this intense surface melting and ponding is the formation of high-density near-surface ice from the refreezing of that water. We report the discovery of a massive subsurface ice layer located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and ground-based radar measurements with remote sensing and firn modelling to investigate the formation and spatial extent of this layer, found to be tens of kilometres across and tens of metres deep. The presence of this ice layer has the effect of raising local ice shelf density by ~190 kg m-3 and temperature by 5 - 10 °C above values found in areas unaffected by ponding and hitherto used in models of ice-shelf fracture and flow.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    USGS Publications Warehouse

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

    2004-01-01

    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.

  19. Melt onset over Arctic sea ice controlled by atmospheric moisture transport

    NASA Astrophysics Data System (ADS)

    Mortin, Jonas; Svensson, Gunilla; Graversen, Rune G.; Kapsch, Marie-Luise; Stroeve, Julienne C.; Boisvert, Linette N.

    2016-06-01

    The timing of melt onset affects the surface energy uptake throughout the melt season. Yet the processes triggering melt and causing its large interannual variability are not well understood. Here we show that melt onset over Arctic sea ice is initiated by positive anomalies of water vapor, clouds, and air temperatures that increase the downwelling longwave radiation (LWD) to the surface. The earlier melt onset occurs; the stronger are these anomalies. Downwelling shortwave radiation (SWD) is smaller than usual at melt onset, indicating that melt is not triggered by SWD. When melt occurs early, an anomalously opaque atmosphere with positive LWD anomalies preconditions the surface for weeks preceding melt. In contrast, when melt begins late, clearer than usual conditions are evident prior to melt. Hence, atmospheric processes are imperative for melt onset. It is also found that spring LWD increased during recent decades, consistent with trends toward an earlier melt onset.

  20. Impact ejecta-induced melting of surface ice deposits on Mars

    NASA Astrophysics Data System (ADS)

    Weiss, David K.; Head, James W.

    2016-12-01

    Fluvial features present around impact craters on Mars can offer insight into the ancient martian climate and its relationship to the impact cratering process. The widespread spatial and temporal distribution of surface ice on Mars suggests that the interaction between impact cratering and surface ice could have been a relatively frequent occurrence. We explore the thermal and melting effects on regional surface ice sheets in this case, where an impact event occurs in regional surface ice deposits overlying a regolith/bedrock target. We provide an estimate for the post-impact temperature of martian ejecta as a function of crater diameter, and conduct thermal modeling to assess the degree to which contact melting of hot ejecta superposed on surface ice deposits can produce meltwater and carve fluvial features. We also evaluate whether fluvial features could form as a result of basal melting of the ice deposits in response to the thermal insulation provided by the overlying impact ejecta. Contact melting is predicted to occur immediately following ejecta emplacement over the course of hundreds of years to tens of kyr. Basal melting initiates when the 273 K isotherm rises through the crust and reaches the base of the ice sheet ∼0.1 to ∼1 Myr following the impact. We assess the range of crater diameters predicted to produce contact and basal melting of surface ice sheets, as well as the melt fluxes, volumes, timescales, predicted locations of melting (relative to the crater), and the associated hydraulic and hydrologic consequences. We find that the heat flux and surface temperature conditions required to produce contact melting are met throughout martian history, whereas the heat flux and surface temperature conditions to produce basal melting are met only under currently understood ancient martian thermal conditions. For an impact into a regional ice sheet, the contact and basal melting mechanisms are predicted to generate melt volumes between ∼10-1 and 105 km3

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

    NASA Technical Reports Server (NTRS)

    Anderson, Mark R.

    1987-01-01

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

  2. Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

    NASA Astrophysics Data System (ADS)

    Krabbendam, Maarten

    2016-09-01

    Basal ice motion is crucial to ice dynamics of ice sheets. The classic Weertman model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that pressure melting is limited by heat flow through the obstacle and ductile flow is controlled by standard power-law creep. These last two assumptions, however, are not applicable if a substantial basal layer of temperate (T ˜ Tmelt) ice is present. In that case, frictional melting can produce excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. High-temperature ice creep experiments have shown a sharp weakening of a factor 5-10 close to Tmelt, suggesting standard power-law creep does not operate due to a switch to melt-assisted creep with a possible component of grain boundary melting. Pressure melting is controlled by meltwater production, heat advection by flowing meltwater to the next obstacle and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. Ice streaming over a rough, hard bed, as possibly in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.

  3. Ice melting properties of steel slag asphalt concrete with microwave heating

    NASA Astrophysics Data System (ADS)

    Li, Bin; Sun, Yihan; Liu, Quantao; Fang, Hao; Wu, Shaopeng; Tang, Jin; Ye, Qunshan

    2017-03-01

    The ice on the surface of asphalt pavement in winter significantly influences the road transportation safety. This paper aims at the improvement of the ice melting efficiency on the surface of asphalt pavement. The steel slag asphalt concrete was prepared and the high ice melting efficiency was achieved with the microwave heating. A series of experiments were conducted to evaluate the ice melting performance of steel slag asphalt concrete, including the heating test, ice melting test, thermal conductivity test and so on. The results indicated that the microwave heating of steel slag concrete can improve the efficiency of deicing, mainly because the heating rates of steel slag asphalt mixture are much better than traditional limestone asphalt mixture. According to different thickness lever of ice, the final temperatures of each sample were very close to each other at the end of melting test. It is believed the thickness of the ice has a limited impact on the ice melting efficiency. According to the heating tests results, the bonding of ice and asphalt concrete is defined failure at the moment when the surface temperature of the ice reached 3 °C.

  4. Massive Ice Layer Formed by Refreezing of Ice-shelf Surface Melt Ponds: Larsen C Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Hubbard, Bryn; Luckman, Adrian; Ashmore, David; Bevan, Suzanne; Kulessa, Bernd; Kuipers Munneke, Peter; Jansen, Daniela; O'Leary, Martin

    2016-04-01

    Surface melt ponds now form frequently on ice shelves across the northern sector of the Antarctic Peninsula in response to regional warming and local föhn winds. A potentially important, but hitherto unknown, consequence of this surface melting and ponding is the formation of high-density near-surface ice from the refreezing of that water. We report the discovery and physical character of a massive subsurface ice layer located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and ground-based radar measurements with remote sensing and firn modelling to investigate the formation and spatial extent of this layer, found to be tens of kilometres across and tens of metres deep. The presence of this ice layer has the effect of raising local ice shelf density by ~190 kg m^-3 and temperature by 5 - 10 degrees C above values found in areas unaffected by ponding and hitherto used in models of ice-shelf fracture and flow.

  5. Melting beneath Greenland outlet glaciers and ice streams

    NASA Astrophysics Data System (ADS)

    Alexander, David; Perrette, Mahé; Beckmann, Johanna

    2015-04-01

    Basal melting of fast-flowing Greenland outlet glaciers and ice streams due to frictional heating at the ice-bed interface contributes significantly to total glacier mass balance and subglacial meltwater flux, yet modelling this basal melt process in Greenland has received minimal research attention. A one-dimensional dynamic ice-flow model is calibrated to the present day longitudinal profiles of 10 major Greenland outlet glaciers and ice streams (including the Jakobshavn Isbrae, Petermann Glacier and Helheim Glacier) and is validated against published ice flow and surface elevation measurements. Along each longitudinal profile, basal melt is calculated as a function of ice flow velocity and basal shear stress. The basal shear stress is dependent on the effective pressure (difference between ice overburden pressure and water pressure), basal roughness and a sliding parametrization. Model output indicates that where outlet glaciers and ice streams terminate into the ocean with either a small floating ice tongue or no floating tongue whatsoever, the proportion of basal melt to total melt (surface, basal and submarine melt) is 5-10% (e.g. Jakobshavn Isbrae; Daugaard-Jensen Glacier). This proportion is, however, negligible where larger ice tongues lose mass mostly by submarine melt (~1%; e.g. Nioghalvfjerdsfjorden Glacier). Modelled basal melt is highest immediately upvalley of the grounding line, with contributions typically up to 20-40% of the total melt for slippery beds and up to 30-70% for resistant beds. Additionally, modelled grounding line and calving front migration inland for all outlet glaciers and ice streams of hundreds of metres to several kilometres occurs. Including basal melt due to frictional heating in outlet glacier and ice stream models is important for more accurately modelling mass balance and subglacial meltwater flux, and therefore, more accurately modelling outlet glacier and ice stream dynamics and responses to future climate change.

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

    NASA Astrophysics Data System (ADS)

    Schomacker, A.; Kjaer, K. H.

    2007-12-01

    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.

  7. On the phase diagram of water with density functional theory potentials: The melting temperature of ice I(h) with the Perdew-Burke-Ernzerhof and Becke-Lee-Yang-Parr functionals.

    PubMed

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

    2009-06-14

    The melting temperature (T(m)) of ice I(h) was determined from constant enthalpy and pressure (NPH) Born-Oppenheimer molecular dynamics simulations to be 417+/-3 K for the Perdew-Burke-Ernzerhof and 411+/-4 K for the Becke-Lee-Yang-Parr density functionals using a coexisting ice (I(h))-liquid phase at constant pressures of P=2500 and 10,000 bar and a density rho=1 g/cm(3), respectively. This suggests that ambient condition simulations at rho=1 g/cm(3) will rather describe a supercooled state that is overstructured when compared to liquid water.

  8. Percolation blockage: A process that enables melt pond formation on first year Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Polashenski, Chris; Golden, Kenneth M.; Perovich, Donald K.; Skyllingstad, Eric; Arnsten, Alexandra; Stwertka, Carolyn; Wright, Nicholas

    2017-01-01

    Melt pond formation atop Arctic sea ice is a primary control of shortwave energy balance in the Arctic Ocean. During late spring and summer, the ponds determine sea ice albedo and how much solar radiation is transmitted into the upper ocean through the sea ice. The initial formation of ponds requires that melt water be retained above sea level on the ice surface. Both theory and observations, however, show that first year sea ice is so highly porous prior to the formation of melt ponds that multiday retention of water above hydraulic equilibrium should not be possible. Here we present results of percolation experiments that identify and directly demonstrate a mechanism allowing melt pond formation. The infiltration of fresh water into the pore structure of sea ice is responsible for blocking percolation pathways with ice, sealing the ice against water percolation, and allowing water to pool above sea level. We demonstrate that this mechanism is dependent on fresh water availability, known to be predominantly from snowmelt, and ice temperature at melt onset. We argue that the blockage process has the potential to exert significant control over interannual variability in ice albedo. Finally, we suggest that incorporating the mechanism into models would enhance their physical realism. Full treatment would be complex. We provide a simple temperature threshold-based scheme that may be used to incorporate percolation blockage behavior into existing model frameworks.

  9. Methods for Melting Temperature Calculation

    NASA Astrophysics Data System (ADS)

    Hong, Qi-Jun

    Melting temperature calculation has important applications in the theoretical study of phase diagrams and computational materials screenings. In this thesis, we present two new methods, i.e., the improved Widom's particle insertion method and the small-cell coexistence method, which we developed in order to capture melting temperatures both accurately and quickly. We propose a scheme that drastically improves the efficiency of Widom's particle insertion method by efficiently sampling cavities while calculating the integrals providing the chemical potentials of a physical system. This idea enables us to calculate chemical potentials of liquids directly from first-principles without the help of any reference system, which is necessary in the commonly used thermodynamic integration method. As an example, we apply our scheme, combined with the density functional formalism, to the calculation of the chemical potential of liquid copper. The calculated chemical potential is further used to locate the melting temperature. The calculated results closely agree with experiments. We propose the small-cell coexistence method based on the statistical analysis of small-size coexistence MD simulations. It eliminates the risk of a metastable superheated solid in the fast-heating method, while also significantly reducing the computer cost relative to the traditional large-scale coexistence method. Using empirical potentials, we validate the method and systematically study the finite-size effect on the calculated melting points. The method converges to the exact result in the limit of a large system size. An accuracy within 100 K in melting temperature is usually achieved when the simulation contains more than 100 atoms. DFT examples of Tantalum, high-pressure Sodium, and ionic material NaCl are shown to demonstrate the accuracy and flexibility of the method in its practical applications. The method serves as a promising approach for large-scale automated material screening in which

  10. Regional variability in sea ice melt in a changing Arctic.

    PubMed

    Perovich, Donald K; Richter-Menge, Jacqueline A

    2015-07-13

    In recent years, the Arctic sea ice cover has undergone a precipitous decline in summer extent. The sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing. The amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations in both surface and bottom melting. Combined surface and bottom melt ranged from 16 to 294 cm, with a mean of 101 cm. The mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm. On average, surface melting decreases moving northward from the Beaufort Sea towards the North Pole; however interannual differences in atmospheric forcing can overwhelm the influence of latitude. Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, due to decreases in ice concentration. In the central Arctic, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. This suggests that under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover.

  11. Regional variability in sea ice melt in a changing Arctic

    PubMed Central

    Perovich, Donald K.; Richter-Menge, Jacqueline A.

    2015-01-01

    In recent years, the Arctic sea ice cover has undergone a precipitous decline in summer extent. The sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing. The amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations in both surface and bottom melting. Combined surface and bottom melt ranged from 16 to 294 cm, with a mean of 101 cm. The mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm. On average, surface melting decreases moving northward from the Beaufort Sea towards the North Pole; however interannual differences in atmospheric forcing can overwhelm the influence of latitude. Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, due to decreases in ice concentration. In the central Arctic, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. This suggests that under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover. PMID:26032323

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

    PubMed

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

    2014-10-07

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

  13. In-Situ Biological Decontamination of an Ice Melting Probe

    NASA Astrophysics Data System (ADS)

    Digel, Ilya

    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

  14. The Radiation Budget of Sea Ice during the Springtime Melt

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    The energy budget of sea ice in the melt season has significant spatial variability at scales much smaller than a model cell or satellite pixel. This variability results primarily from albedo variation caused by different surface characteristics such as melt ponds of varying depth, snow of varying thickness, and sediment content within the snow, ice, or surface water. There may also be variation in the longwave energy emitted by the surface, mostly resulting from temperature variations. Understanding this variability and how it affects the progress of the melt is necessary for improving energy-budget parameterizations in models or retrievals from satellite sensors. To gain a better understanding of this variability, we have developed a radiation sled that quickly measures the upwelling and downwelling broadband longwave and shortwave radiation, along with the spectral albedo. In addition, it photographs the sky and surface at the time of the measurement, measures the surface temperature with a narrowband infrared thermometer, and records the measurement location and the air temperature and humidity. The sled is set up to allow many measurements in an area to be made during a short period by one or two people. From this we can see the large scale effect of small scale variations in the surface energy budget. This sled was deployed for the first time during the first two weeks of June this year. Data were collected every 5 m along a 200-m line located on fast ice about 3 km southwest of Point Barrow, Alaska. Observations were made around local noon each day from 5 to 13 June, when the progression of the melt forced us to bring the instruments back to land. During most of the observation period, we had refreezing of melt ponds that were prevalent at the start. Midway through, there was some light snowfall, before melt resumed on the last days. The line included a variety of surfaces, including bare ice with a scattering layer, melt ponds of varying depths with a

  15. The Radiation Budget of Sea Ice during the Springtime Melt

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    The energy budget of sea ice in the melt season has significant spatial variability at scales much smaller than a model cell or satellite pixel. This variability results primarily from albedo variation caused by different surface characteristics such as melt ponds of varying depth, snow of varying thickness, and sediment content within the snow, ice, or surface water. There may also be variation in the longwave energy emitted by the surface, mostly resulting from temperature variations. Understanding this variability and how it affects the progress of the melt is necessary for improving energy-budget parameterizations in models or retrievals from satellite sensors. To gain a better understanding of this variability, we have developed a radiation sled that quickly measures the upwelling and downwelling broadband longwave and shortwave radiation, along with the spectral albedo. In addition, it photographs the sky and surface at the time of the measurement, measures the surface temperature with a narrowband infrared thermometer, and records the measurement location and the air temperature and humidity. The sled is set up to allow many measurements in an area to be made during a short period by one or two people. From this we can see the large scale effect of small scale variations in the surface energy budget. This sled was deployed for the first time during the first two weeks of June 2011. Data were collected every 5 m along a 200-m line located on fast ice about 3 km southwest of Point Barrow, Alaska. Observations were made around local noon each day from 5 to 13 June, when the progression of the melt forced us to bring the instruments back to land. During most of the observation period, we had refreezing of melt ponds that were prevalent at the start. Midway through, there was some light snowfall, before melt resumed on the last days. The line included a variety of surfaces, including bare ice with a scattering layer, melt ponds of varying depths with a refrozen

  16. Channelized bottom melting and stability of floating ice shelves

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Steffen, K.

    2008-01-01

    The floating ice shelf in front of Petermann Glacier, in northwest Greenland, experiences massive bottom melting that removes 80% of its ice before calving into the Arctic Ocean. Detailed surveys of the ice shelf reveal the presence of 1-2 km wide, 200-400 m deep, sub-ice shelf channels, aligned with the flow direction and spaced by 5 km. We attribute their formation to the bottom melting of ice from warm ocean waters underneath. Drilling at the center of one of channel, only 8 m above sea level, confirms the presence of ice-shelf melt water in the channel. These deep incisions in ice-shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously.

  17. Abnormal Winter Melting of the Arctic Sea Ice Cap Observed by the Spaceborne Passive Microwave Sensors

    NASA Astrophysics Data System (ADS)

    Lee, Seongsuk; Yi, Yu

    2016-12-01

    The spatial size and variation of Arctic sea ice play an important role in Earth’s climate system. These are affected by conditions in the polar atmosphere and Arctic sea temperatures. The Arctic sea ice concentration is calculated from brightness temperature data derived from the Defense Meteorological Satellite program (DMSP) F13 Special Sensor Microwave/Imagers (SSMI) and the DMSP F17 Special Sensor Microwave Imager/Sounder (SSMIS) sensors. Many previous studies point to significant reductions in sea ice and their causes. We investigated the variability of Arctic sea ice using the daily sea ice concentration data from passive microwave observations to identify the sea ice melting regions near the Arctic polar ice cap. We discovered the abnormal melting of the Arctic sea ice near the North Pole during the summer and the winter. This phenomenon is hard to explain only surface air temperature or solar heating as suggested by recent studies. We propose a hypothesis explaining this phenomenon. The heat from the deep sea in Arctic Ocean ridges and/ or the hydrothermal vents might be contributing to the melting of Arctic sea ice. This hypothesis could be verified by the observation of warm water column structure below the melting or thinning arctic sea ice through the project such as Coriolis dataset for reanalysis (CORA).

  18. Diamond stabilization of ice multilayers at human body temperature.

    PubMed

    Wissner-Gross, Alexander D; Kaxiras, Efthimios

    2007-08-01

    Diamond is a promising material for wear-resistant medical coatings. Here we report a remarkable increase in the melting point of ice resting on a diamond (111) surface modified with a submonolayer of Na+. Our molecular dynamics simulations show that the interfacial ice bilayer melts at a temperature 130 K higher than in free ice, and relatively thick ice films (2.6 nm at 298 K and 2.2 nm at 310 K ) are stabilized by dipole interactions with the substrate. This unique physical effect may enable biocompatibility-enhancing ice overcoatings for diamond at human body temperature.

  19. Directional close-contact melting in glacier ice

    NASA Astrophysics Data System (ADS)

    Kowalski, Julia; Schüller, Kai

    2015-04-01

    The Saturnian moon Enceladus shows incidence of liquid water underneath a thick ice sheet cover and is thought to be a potential candidate for extraterrestrial life. However, direct exploration of these subglacial aquatic ecosystems is very challenging. Within the scope of the joint research project 'Enceladus Explorer' (EnEx) (consisting of FH Aachen, RWTH Aachen, Bergische Universität Wuppertal, Universität Bremen, TU Braunschweig und Bundeswehr Universität München), initiated by the German Space Agency, a maneuverable close-contact melting probe has been developed. The force-regulated and heater-controlled probe is able to melt against gravity or even on a curved trajectory. Hence, it offers additional degrees of freedom in its melting motion, e.g. for target oriented melting or obstacle avoidance strategies. General feasibility of the concept has been demonstrated in various field tests. However, in order to optimize its design and to adopt it to extraterrestrial missions a simulation model is needed, capable of determining melting velocity and efficiency at given environmental conditions and system configurations. Within this contribution, the physical situation is abstracted into a quasi-stationary mathematical model description, and a numerical solution strategy is developed to compute melting velocity and temperature distribution within the probe and the surrounding ice. We present an inverse solution approach, in which a background velocity field of the ice mimics the melting velocity. The fundamental balance laws are solved with the corresponding melting rate. Following Newton's laws, the resulting force acting on the probe has to balance the contact force exerted by the probe and can hence be used for convergence. We present both, analytical results to a simplified head geometry, as well as results from a simulation model implemented into the open source software Elmer for arbitrary head geometries. The latter can deal with the full 3d situation

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

    PubMed

    Koerner, R M

    1989-05-26

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  2. How much can Greenland melt? An upper bound on mass loss from the Greenland Ice Sheet through surface melting

    NASA Astrophysics Data System (ADS)

    Liu, X.; Bassis, J. N.

    2015-12-01

    With observations showing accelerated mass loss from the Greenland Ice Sheet due to surface melt, the Greenland Ice Sheet is becoming one of the most significant contributors to sea level rise. The contribution of the Greenland Ice Sheet o sea level rise is likely to accelerate in the coming decade and centuries as atmospheric temperatures continue to rise, potentially triggering ever larger surface melt rates. However, at present considerable uncertainty remains in projecting the contribution to sea level of the Greenland Ice Sheet both due to uncertainty in atmospheric forcing and the ice sheet response to climate forcing. Here we seek an upper bound on the contribution of surface melt from the Greenland to sea level rise in the coming century using a surface energy balance model coupled to an englacial model. We use IPCC Representative Concentration Pathways (RCP8.5, RCP6, RCP4.5, RCP2.6) climate scenarios from an ensemble of global climate models in our simulations to project the maximum rate of ice volume loss and related sea-level rise associated with surface melting. To estimate the upper bound, we assume the Greenland Ice Sheet is perpetually covered in thick clouds, which maximize longwave radiation to the ice sheet. We further assume that deposition of black carbon darkens the ice substantially turning it nearly black, substantially reducing its albedo. Although assuming that all melt water not stored in the snow/firn is instantaneously transported off the ice sheet increases mass loss in the short term, refreezing of retained water warms the ice and may lead to more melt in the long term. Hence we examine both assumptions and use the scenario that leads to the most surface melt by 2100. Preliminary models results suggest that under the most aggressive climate forcing, surface melt from the Greenland Ice Sheet contributes ~1 m to sea level by the year 2100. This is a significant contribution and ignores dynamic effects. We also examined a lower bound

  3. Continuous melting and ion chromatographic analyses of ice cores.

    PubMed

    Huber, T M; Schwikowski, M; Gäggele, H W

    2001-06-22

    A new method for determining concentrations of organic and inorganic ions in ice cores by continuous melting and contemporaneous ion chromatographic analyses was developed. A subcore is melted on a melting device and the meltwater produced is collected in two parallel sample loops and then analyzed simultaneously by two ion chromatographs, one for anions and one for cations. For most of the analyzed species, lower or equal blank values were achieved with the continuous melting and analysis technique compared to the conventional analysis. Comparison of the continuous melting and ion chromatographic analysis with the conventional analysis of a real ice core segment showed good agreement in concentration profiles and total amounts of ionic species. Thus, the newly developed method is well suited for ice core analysis and has the advantages of lower ice consumption, less time-consuming sample preparation and lower risk of contamination.

  4. Ice-sheet acceleration driven by melt supply variability.

    PubMed

    Schoof, Christian

    2010-12-09

    Increased ice velocities in Greenland are contributing significantly to eustatic sea level rise. Faster ice flow has been associated with ice-ocean interactions in water-terminating outlet glaciers and with increased surface meltwater supply to the ice-sheet bed inland. Observed correlations between surface melt and ice acceleration have raised the possibility of a positive feedback in which surface melting and accelerated dynamic thinning reinforce one another, suggesting that overall warming could lead to accelerated mass loss. Here I show that it is not simply mean surface melt but an increase in water input variability that drives faster ice flow. Glacier sliding responds to melt indirectly through changes in basal water pressure, with observations showing that water under glaciers drains through channels at low pressure or through interconnected cavities at high pressure. Using a model that captures the dynamic switching between channel and cavity drainage modes, I show that channelization and glacier deceleration rather than acceleration occur above a critical rate of water flow. Higher rates of steady water supply can therefore suppress rather than enhance dynamic thinning, indicating that the melt/dynamic thinning feedback is not universally operational. Short-term increases in water input are, however, accommodated by the drainage system through temporary spikes in water pressure. It is these spikes that lead to ice acceleration, which is therefore driven by strong diurnal melt cycles and an increase in rain and surface lake drainage events rather than an increase in mean melt supply.

  5. Investigating evaporation of melting ice particles within a bin melting layer model

    NASA Astrophysics Data System (ADS)

    Neumann, Andrea J.

    Single column models have been used to help develop algorithms for remote sensing retrievals. Assumptions in the single-column models may affect the assumptions of the remote sensing retrievals. Studies of the melting layer that use single column models often assume environments that are near or at water saturation. This study investigates the effects of evaporation upon melting particles to determine whether the assumption of negligible mass loss still holds within subsaturated melting layers. A single column, melting layer model is modified to include the effects of sublimation and evaporation upon the particles. Other changes to the model include switching the order in which the model loops over particle sizes and model layers; including a particle sedimentation scheme; adding aggregation, accretion, and collision and coalescence processes; allowing environmental variables such as the water vapor diffusivity and the Schmidt number to vary with the changes in the environment; adding explicitly calculated particle temperature, changing the particle terminal velocity parameterization; and using a newly-derived effective density-dimensional relationship for use in particle mass calculations. Simulations of idealized melting layer environments show that significant mass loss due to evaporation during melting is possible within subsaturated environments. Short melting distances, accelerating particle fall speeds, and short melting times help constrain the amount of mass lost due to evaporation while melting is occurring, even in subsaturated profiles. Sublimation prior to melting can also be a significant source of mass loss. The trends shown on the particle scale also appear in the bulk distribution parameters such as rainfall rate and ice water content. Simulations incorporating observed melting layer environments show that significant mass loss due to evaporation during the melting process is possible under certain environmental conditions. A profile such as the

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  7. Circulation and melting beneath the ross ice shelf.

    PubMed

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

    1979-02-02

    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.

  8. Dissociative melting of ice VII at high pressure

    SciTech Connect

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

    2009-04-02

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

  9. Dissociative melting of ice VII at high pressure

    NASA Astrophysics Data System (ADS)

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

    2009-03-01

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

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

    PubMed

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

    2014-01-10

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

  11. Basal Melt Under the Interior of the Greenland Ice Sheet: Comparison of Models, Deep Ice Cores, and Radar Observations

    NASA Astrophysics Data System (ADS)

    Rezvanbehbahani, S.; Stearns, L. A.; van der Veen, C. J.

    2014-12-01

    Basal ice temperature is a critical boundary condition for ice sheet models. It modulates the basal melt rate and sliding conditions, and also affects the ice hardness which alters the deformational velocity. Therefore, in order to obtain reliable estimates on the future mass loss of the ice sheets using numerical models, basal ice temperature is of paramount importance. In this study, the basal temperature and basal melt rate under the Greenland Ice Sheet are estimated using the Robin temperature solution. The analytical Robin solution is obtained by solving the heat conservation equation for steady state conditions, assuming that advection and diffusion are significant only in the vertical direction. In this study, the sensitivity of the basal temperature obtained from the Robin solution to changes in input parameters, including changes in atmospheric conditions, ice thickness, and geothermal heat flux is tested. Although the Robin solution is frequently used in glaciology, there has been no quantitative study to estimate the effect of neglecting the horizontal advection on basal temperatures in regions of higher velocity. Here, a two-dimensional model is applied to quantify the effect of horizontal heat advection on basal temperatures. Overall, horizontal heat advection lowers the basal temperature except in regions where surface mass balance gradients are negative along the flow. Comparing the results from the 2D temperature model to the Robin solution along multiple flowlines of the Greenland Ice Sheet suggest that the horizontal heat advection alters the basal temperatures by less than 3°C up to 30-45% of the flow distance away from the ice divide; at greater distances this difference increases rapidly. All simulations using the Robin solution predict substantial basal melting under the northeast drainage basin of the ice sheet. Our 2D model results also show that because of the negative surface mass balance gradient, horizontal heat advection increases the

  12. Experimental and theoretical evidence for bilayer-by-bilayer surface melting of crystalline ice

    PubMed Central

    Sánchez, M. Alejandra; Kling, Tanja; Ishiyama, Tatsuya; van Zadel, Marc-Jan; Mezger, Markus; Jochum, Mara N.; Cyran, Jenée D.; Smit, Wilbert J.; Bakker, Huib J.; Shultz, Mary Jane; Morita, Akihiro; Donadio, Davide; Nagata, Yuki; Bonn, Mischa; Backus, Ellen H. G.

    2017-01-01

    On the surface of water ice, a quasi-liquid layer (QLL) has been extensively reported at temperatures below its bulk melting point at 273 K. Approaching the bulk melting temperature from below, the thickness of the QLL is known to increase. To elucidate the precise temperature variation of the QLL, and its nature, we investigate the surface melting of hexagonal ice by combining noncontact, surface-specific vibrational sum frequency generation (SFG) spectroscopy and spectra calculated from molecular dynamics simulations. Using SFG, we probe the outermost water layers of distinct single crystalline ice faces at different temperatures. For the basal face, a stepwise, sudden weakening of the hydrogen-bonded structure of the outermost water layers occurs at 257 K. The spectral calculations from the molecular dynamics simulations reproduce the experimental findings; this allows us to interpret our experimental findings in terms of a stepwise change from one to two molten bilayers at the transition temperature. PMID:27956637

  13. Experimental and theoretical evidence for bilayer-by-bilayer surface melting of crystalline ice.

    PubMed

    Sánchez, M Alejandra; Kling, Tanja; Ishiyama, Tatsuya; van Zadel, Marc-Jan; Bisson, Patrick J; Mezger, Markus; Jochum, Mara N; Cyran, Jenée D; Smit, Wilbert J; Bakker, Huib J; Shultz, Mary Jane; Morita, Akihiro; Donadio, Davide; Nagata, Yuki; Bonn, Mischa; Backus, Ellen H G

    2017-01-10

    On the surface of water ice, a quasi-liquid layer (QLL) has been extensively reported at temperatures below its bulk melting point at 273 K. Approaching the bulk melting temperature from below, the thickness of the QLL is known to increase. To elucidate the precise temperature variation of the QLL, and its nature, we investigate the surface melting of hexagonal ice by combining noncontact, surface-specific vibrational sum frequency generation (SFG) spectroscopy and spectra calculated from molecular dynamics simulations. Using SFG, we probe the outermost water layers of distinct single crystalline ice faces at different temperatures. For the basal face, a stepwise, sudden weakening of the hydrogen-bonded structure of the outermost water layers occurs at 257 K. The spectral calculations from the molecular dynamics simulations reproduce the experimental findings; this allows us to interpret our experimental findings in terms of a stepwise change from one to two molten bilayers at the transition temperature.

  14. Ocean circulation and basal melting below the Fimbul Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Hattermann, T.; Nøst, O. A.; Smedsrud, L. H.; Lilly, J. M.

    2012-04-01

    The mechanisms by which oceanic heat is delivered to Antarctic ice shelves are a major source of uncertainty when assessing the response of the Antarctic ice sheet to climate change. Here, we combine observations below the Fimbul Ice Shelf with high resolution ocean modeling to study the heat exchange of the ice shelf cavity with the open ocean and quantify ice shelf basal melting. Situated at the prime meridian, the Fimbul Ice Shelf is the sixth largest ice shelf in Antarctica, being fed by Jutulstraumen, the largest ice stream in western Dronning Maud Land. Its oceanographic configuration is typical for the ice shelves along the coast of the Eastern Weddell Sea, where only a narrow continental shelf protects the glaciated coast from intrusions of Warm Deep Water and estimates of melting has varied widely over a number of studies. Our results reveal an unexpected level of complexity to supply of oceanic heat for basal melting. Two different water masses reach the ice base at different times of the year: (i) bursts of Modified Warm Deep Water access the cavity at depth in late winter and, (ii) fresher surface water flushes large parts of the ice base with temperatures above freezing during late summer. This suggests a "bi-modal" cavity circulation, rather than a steady ice-pump mechanism, where the strength of basal melting is controlled by both solar heating at the surface as well as by the eddy-driven on-shore transport of warm water at depth. Hence, we find that that successful modeling of basal melt rates in this sector of Antarctica crucially depends achieving a more realistic representation of the coastal processes and water masses involved.

  15. Detecting ice lenses and melt-refreeze crusts using satellite passive microwaves (Invited)

    NASA Astrophysics Data System (ADS)

    Montpetit, B.; Royer, A.; Roy, A.

    2013-12-01

    With recent winter climate warming in high latitude regions, rain-on-snow and melt-refreeze events are more frequent creating ice lenses or ice crusts at the surface or even within the snowpack through drainage. These ice layers create an impermeable ice barrier that reduces vegetation respiration and modifies snow properties due to the weak thermal diffusivity of ice. Winter mean soil temperatures increase due to latent heat being released during the freezing process. When ice layers freeze at the snow-soil interface, they can also affect the feeding habits of the northern wild life. Ice layers also significantly affect satellite passive microwave signals that are widely used to monitor the spatial and temporal evolution of snow. Here we present a method using satellite passive microwave brightness temperatures (Tb) to detect ice lenses and/or ice crusts within a snowpack. First the Microwave Emission Model for Layered Snowpacks (MEMLS) was validated to model Tb at 10.7, 19 and 37 GHz using in situ measurements taken in multiple sub-arctic environments where ice layers where observed. Through validated modeling, the effects of ice layer insertion were studied and an ice layer index was developed using the polarization ratio (PR) at all three frequencies. The developed ice index was then applied to satellite passive microwave signals for reported ice layer events.

  16. Impact of ice-shelf sediment content on the dynamics of plumes under melting ice shelves

    NASA Astrophysics Data System (ADS)

    Wells, A.

    2015-12-01

    When a floating ice shelf melts into an underlying warm salty ocean, the resulting fresh meltwater can rise in a buoyant Ice-Shelf-Water plume under the ice. In certain settings, ice flowing across the grounding line carries a basal layer of debris rich ice, entrained via basal freezing around till in the upstream ice sheet. Melting of this debris-laden ice from floating ice shelves provides a flux of dense sediment to the ocean, in addition to the release of fresh buoyant meltwater. This presentation considers the impact of the resulting suspended sediment on the dynamics of ice shelf water plumes, and identifies two key flow regimes depending on the sediment concentration frozen into the basal ice layer. For large sediment concentration, melting of the debris-laden ice shelf generates dense convectively unstable waters that drive convective overturning into the underlying ocean. For lower sediment concentration, the sediment initially remains suspended in a buoyant meltwater plume rising along the underside of the ice shelf, before slowly depositing into the underlying ocean. A theoretical plume model is used to evaluate the significance of the negatively buoyant sediment on circulation strength and the feedbacks on melting rate, along with the expected depositional patterns under the ice shelf.

  17. Rapid bottom melting widespread near Antarctic ice sheet grounding lines

    NASA Technical Reports Server (NTRS)

    Rignot, E.; Jacobs, S.

    2002-01-01

    As continental ice from Antartica reaches the grounding line and begins to float, its underside melts into the ocean. Results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  19. Applying Archimedes' Law to Ice Melting in Sea Water

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  20. Observed anomalous atmospheric patterns in summers of unusual Arctic sea ice melt

    NASA Astrophysics Data System (ADS)

    Knudsen, Erlend M.; Orsolini, Yvan J.; Furevik, Tore; Hodges, Kevin I.

    2015-04-01

    The Arctic sea ice retreat has accelerated over the last decade. The negative trend is largest in summer, but substantial interannual variability still remains. Here we explore observed atmospheric conditions and feedback mechanisms during summer months of anomalous sea ice melt in the Arctic. Compositing months of anomalous low and high sea ice melt over 1979-2013, we find distinct patterns in atmospheric circulation, precipitation, radiation, and temperature. Compared to summer months of anomalous low sea ice melt, high melt months are characterized by anomalous high sea level pressure in the Arctic (up to 7 hPa), with a corresponding tendency of storms to track on a more zonal path. As a result, the Arctic receives less precipitation overall and 39% less snowfall. This lowers the albedo of the region and reduces the negative feedback the snowfall provides for the sea ice. With an anticyclonic tendency, 12 W/m2 more incoming shortwave radiation reaches the surface in the start of the season. The melting sea ice in turn promotes cloud development in the marginal ice zones and enhances downwelling longwave radiation at the surface toward the end of the season. A positive cloud feedback emerges. In midlatitudes, the more zonally tracking cyclones give stormier, cloudier, wetter, and cooler summers in most of northern Europe and around the Sea of Okhotsk. Farther south, the region from the Mediterranean Sea to East Asia experiences significant surface warming (up to 2.4°C), possibly linked to changes in the jet stream.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    SciTech Connect

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

    2009-06-11

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

  3. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica

    NASA Astrophysics Data System (ADS)

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M.; Seroussi, Helene; Schodlok, Michael P.; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C.; Velicogna, Isabella

    2016-10-01

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300-490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica.

  4. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica

    PubMed Central

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M.; Seroussi, Helene; Schodlok, Michael P.; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C.; Velicogna, Isabella

    2016-01-01

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300–490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica. PMID:27780191

  5. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica.

    PubMed

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M; Seroussi, Helene; Schodlok, Michael P; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C; Velicogna, Isabella

    2016-10-25

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300-490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica.

  6. A simple equation for the melt elevation feedback of ice sheets

    NASA Astrophysics Data System (ADS)

    Levermann, Anders; Winkelmann, Ricarda

    2016-08-01

    In recent decades, the Greenland Ice Sheet has been losing mass and has thereby contributed to global sea-level rise. The rate of ice loss is highly relevant for coastal protection worldwide. The ice loss is likely to increase under future warming. Beyond a critical temperature threshold, a meltdown of the Greenland Ice Sheet is induced by the self-enforcing feedback between its lowering surface elevation and its increasing surface mass loss: the more ice that is lost, the lower the ice surface and the warmer the surface air temperature, which fosters further melting and ice loss. The computation of this rate so far relies on complex numerical models which are the appropriate tools for capturing the complexity of the problem. By contrast we aim here at gaining a conceptual understanding by deriving a purposefully simple equation for the self-enforcing feedback which is then used to estimate the melt time for different levels of warming using three observable characteristics of the ice sheet itself and its surroundings. The analysis is purely conceptual in nature. It is missing important processes like ice dynamics for it to be useful for applications to sea-level rise on centennial timescales, but if the volume loss is dominated by the feedback, the resulting logarithmic equation unifies existing numerical simulations and shows that the melt time depends strongly on the level of warming with a critical slowdown near the threshold: the median time to lose 10 % of the present-day ice volume varies between about 3500 years for a temperature level of 0.5 °C above the threshold and 500 years for 5 °C. Unless future observations show a significantly higher melting sensitivity than currently observed, a complete meltdown is unlikely within the next 2000 years without significant ice-dynamical contributions.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    PubMed

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

    2014-06-03

    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.

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

    PubMed

    Mishima, Osamu

    2011-12-08

    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.

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

    PubMed

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

    2014-11-26

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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

  12. Mechanical sea-ice strength parameterized as a function of ice temperature

    NASA Astrophysics Data System (ADS)

    Hata, Yukie; Tremblay, Bruno

    2016-04-01

    Mechanical sea-ice strength is key for a better simulation of the timing of landlock ice onset and break-up in the Canadian Arctic Archipelago (CAA). We estimate the mechanical strength of sea ice in the CAA by analyzing the position record measured by the several buoys deployed in the CAA between 2008 and 2013, and wind data from the Canadian Meteorological Centre's Global Deterministic Prediction System (CMC_GDPS) REforecasts (CGRF). First, we calculate the total force acting on the ice using the wind data. Next, we estimate upper (lower) bounds on the sea-ice strength by identifying cases when the sea ice deforms (does not deform) under the action of a given total force. Results from this analysis show that the ice strength of landlock sea ice in the CAA is approximately 40 kN/m on the landfast ice onset (in ice growth season). Additionally, it becomes approximately 10 kN/m on the landfast ice break-up (in melting season). The ice strength decreases with ice temperature increase, which is in accord with results from Johnston [2006]. We also include this new parametrization of sea-ice strength as a function of ice temperature in a coupled slab ocean sea ice model. The results from the model with and without the new parametrization are compared with the buoy data from the International Arctic Buoy Program (IABP).

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

    NASA Astrophysics Data System (ADS)

    Gradinger, Rolf; Bluhm, Bodil; Iken, Katrin

    2010-01-01

    The abundances and distribution of metazoan within-ice meiofauna (13 stations) and under-ice fauna (12 stations) were investigated in level sea ice and sea-ice ridges in the Chukchi/Beaufort Seas and Canada Basin in June/July 2005 using a combination of ice coring and SCUBA diving. Ice meiofauna abundance was estimated based on live counts in the bottom 30 cm of level sea ice based on triplicate ice core sampling at each location, and in individual ice chunks from ridges at four locations. Under-ice amphipods were counted in situ in replicate ( N=24-65 per station) 0.25 m 2 quadrats using SCUBA to a maximum water depth of 12 m. In level sea ice, the most abundant ice meiofauna groups were Turbellaria (46%), Nematoda (35%), and Harpacticoida (19%), with overall low abundances per station that ranged from 0.0 to 10.9 ind l -1 (median 0.8 ind l -1). In level ice, low ice algal pigment concentrations (<0.1-15.8 μg Chl a l -1), low brine salinities (1.8-21.7) and flushing from the melting sea ice likely explain the low ice meiofauna concentrations. Higher abundances of Turbellaria, Nematoda and Harpacticoida also were observed in pressure ridges (0-200 ind l -1, median 40 ind l -1), although values were highly variable and only medians of Turbellaria were significantly higher in ridge ice than in level ice. Median abundances of under-ice amphipods at all ice types (level ice, various ice ridge structures) ranged from 8 to 114 ind m -2 per station and mainly consisted of Apherusa glacialis (87%), Onisimus spp. (7%) and Gammarus wilkitzkii (6%). Highest amphipod abundances were observed in pressure ridges at depths >3 m where abundances were up to 42-fold higher compared with level ice. We propose that the summer ice melt impacted meiofauna and under-ice amphipod abundance and distribution through (a) flushing, and (b) enhanced salinity stress at thinner level sea ice (less than 3 m thickness). We further suggest that pressure ridges, which extend into deeper, high

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Perol, T.; Rice, J. R.

    2011-12-01

    Could the 40 to 80 km widths of West Antarctic (Ross Shelf) ice streams be controlled by onset of melting within the ice sheet at the stream margins? The streams are driven by gravity which is resisted by basal drag, inferred to be small, and by shear stress at the lateral margins, assuming longitudinal stress gradients are unimportant [Whilans & van der Veen, JG'93]. Lateral shear stress in the sheet scales with the difference between gravitational stress and basal drag, and increases linearly with the lateral distance X from the center of a stream. With increasing X, that lateral shear stress times the creep strain rate it induces becomes a significant heat source within the ice sheet (proportional to X4 using Glen's law), and must ultimately induce internal melting. We study this possibility using data for a set of 5 ice stream profiles (A, WNar, C, D, E) of Joughin et al. [JGR'02]. They used measured lateral shear strain rates at the margins, and a depth-averaged values of the Glen's law creep parameter, based on a 1-D conduction-advection heat transfer analysis, without internal heating, to estimate the lateral drag. We find that when we incorporate the product of their drag stress and strain rate as a source in a conductive heat transfer model, the predicted margin temperatures are in excess of melting over some depth range for all five profiles. This supports the possibility that internal melting within the ice sheet is indeed related to why the margins are where they are. Next, we reformulated the 1-D vertical heat flux problem allowing some lower depth range of the of ice sheet to be partially melted ice at the melting temperature, with the rest of the sheet frozen and undergoing conductive heat transfer. The sheet was subjected to a uniform lateral shear rate, allowing the Glen's law parameter and local shear stress to be different for the two zones. The predicted fraction of the thickness that is molten, if any, depends on the lateral shear strain rate

  16. Large melt channels discovered underneath Antarctic ice shelves

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Atreyee

    2012-10-01

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

  17. Development of a Passive Microwave Surface Melt Record for Antarctica and Antarctic Ice Shelves

    NASA Astrophysics Data System (ADS)

    Karmosky, C. C.; Reasons, J.; Morgan, N. J.

    2015-12-01

    Antarctica contains the largest mass of ice in the world and much time and energy has gone into researching the ice-ocean-atmosphere-land dynamics that, in a warming climate, have the potential to significantly affect sea levels throughout the world. While there are many datasets currently available to researchers examining sea ice extent and volume, glacier thickness, ice shelf retreat and expansion, and atmospheric variables such as temperature and wind speeds, there is not currently a dataset that offers surface melt extent of land ice in the southern hemisphere. The database outlined here uses the Cross-Polarized Gradient Ratio (XPGR) to show surface melt extent on a daily basis for all of Antarctica. XPGR utilizes passive microwave satellite imagery in the 19 GHz and 37GHz frequencies to determine the presence or absence of greater than 1% liquid water in the top layers of ice. Daily XPGR melt occurrence (1987-2014) was calculated for both the ice sheet as well as ice shelves on Antarctica, and is available as a GIS shapefile or asci text file.

  18. Spontaneous rotation of an ice disk while melting on a solid plate

    NASA Astrophysics Data System (ADS)

    Dorbolo, S.; Vandewalle, N.; Darbois Texier, B.

    2016-12-01

    Ice disks were released at the surface of a thermalised aluminium plate. The fusion of the ice creates a lubrication film between the ice disk and the plate. The situation is similar to the Leidenfrost effect reported for a liquid droplet evaporating at the surface of a plate which temperature is above the boiling temperature of the liquid. An analogy is depicted between the Leidenfrost phenomenon and the rapid fusion of a solid at the contact of a hot plate. Similarly to Leidenfrost droplet, we observe that, while the ice disks were melting, the disks were very mobile: translation and rotation. A hole was drilled in the plate and allowed the canalising of the melted liquid. Under these conditions, we discover that the rotation of the ice disk is systematic and persistent. Moreover, the rotation speed increases with the temperature of the plate and with the load put on the ice disk. A model is proposed to explain the spontaneous rotation of the ice disk. We claim that the rotation is due to the viscous drag of the liquid that flows around the ice disk.

  19. Satellite Gravity Measurements Confirm Accelerated Melting of Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

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

    2006-09-01

    Using time-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite mission, we estimate ice mass changes over Greenland during the period April 2002 to November 2005. After correcting for the effects of spatial filtering and limited resolution of GRACE data, the estimated total ice melting rate over Greenland is -239 +/- 23 cubic kilometers per year, mostly from East Greenland. This estimate agrees remarkably well with a recent assessment of -224 +/- 41 cubic kilometers per year, based on satellite radar interferometry data. GRACE estimates in southeast Greenland suggest accelerated melting since the summer of 2004, consistent with the latest remote sensing measurements.

  20. Forced convective melting at an evolving ice-water interface

    NASA Astrophysics Data System (ADS)

    Ramudu, Eshwan; Hirsh, Benjamin; Olson, Peter; Gnanadesikan, Anand

    2015-11-01

    The intrusion of warm Circumpolar Deep Water into the ocean cavity between the base of ice shelves and the sea bed in Antarctica causes melting at the ice shelves' basal surface, producing a turbulent melt plume. We conduct a series of laboratory experiments to investigate how the presence of forced convection (turbulent mixing) changes the delivery of heat to the ice-water interface. We also develop a theoretical model for the heat balance of the system that can be used to predict the change in ice thickness with time. In cases of turbulent mixing, the heat balance includes a term for turbulent heat transfer that depends on the friction velocity and an empirical coefficient. We obtain a new value for this coefficient by comparing the modeled ice thickness against measurements from a set of nine experiments covering one order of magnitude of Reynolds numbers. Our results are consistent with the altimetry-inferred melting rate under Antarctic ice shelves and can be used in climate models to predict their disintegration. This work was supported by NSF grant EAR-110371.

  1. Divergent trajectories of Antarctic ice shelf surface melt under 21st century climate scenarios

    NASA Astrophysics Data System (ADS)

    Trusel, L. D.; Frey, K. E.; Das, S. B.; Kuipers Munneke, P.; van Meijgaard, E.

    2014-12-01

    Antarctic ice shelves represent a critical interface between continental ice masses and the surrounding ocean. Breakup events of several ice shelves in recent decades have been linked to an increase in intense surface melting, and have in turn lead to cascading effects including accelerated glacier discharge into the ocean. In this study, we utilized sophisticated regional and global climate models (GCMs) to assess potential future surface melt trajectories across Antarctica under two climate scenarios (RCP4.5 and RCP8.5). RACMO2.1, a polar-adapted regional atmospheric climate model, was forced by the ERA-Interim reanalysis (1980-2010) and by two GCMs, EC-EARTH and HadGEM2-ES (2007-2100). Using RACMO2.1, we observed an exponential growth function well represents the relationship between ice shelf surface meltwater production and mean summer (DJF) 2-meter air temperature (t2m). We employed this melt-t2m relationship to project melt using t2m output from an ensemble of five CMIP5-based GCMs incorporating the NCAR Community Land Model 4 (CLM4), following spatial downscaling and bias correction using t2m from ERA-Interim-forced RACMO2.1. Our resulting GCM-derived melt projections provide an independent and methodologically unique perspective into potential future melt pathways, complementary to those derived from RACMO2.1. Most notably, both RACMO2.1 and the CMIP5 ensemble reveal divergent trajectories of meltwater production beyond 2050 under the two climate scenarios. For many ice shelves in RCP4.5, meltwater production through 2100 remains at levels comparable to present. Conversely, under RCP8.5 all methods indicate non-linear melt intensification, resulting in a four-fold increase in the Antarctic-wide meltwater volume by the end of the 21st century. For some ice shelves, including Larsen C and Wilkins (Antarctic Peninsula), and Shackleton and West (Wilkes Land), spatially averaged end-of-century meltwater production within RCP8.5 approaches or surpasses levels

  2. Cold Model Investigations of Melting of Ice in a Gas-Stirred Vessel

    NASA Astrophysics Data System (ADS)

    Shukla, Ajay Kumar; Dmitry, Ryabov; Volkova, Olena; Scheller, Piotr R.; Deo, Brahma

    2011-02-01

    The melting of steel scrap in high temperature liquid iron melt is investigated by conducting cold model experiments of the melting of ice sample of different geometries and sizes in an argon-stirred vessel containing water. The melting process of ice samples is observed using a high-speed camera. Design of experiments is based on similarity criteria. The relationships between non-dimensional groups related to heat transfer (Nu, Re, Pr, and Gr) are derived for different experimental conditions. The results are compared with those reported in the literature. The heat transfer coefficient is estimated as a function of mixing power and is found to be in good agreement with the calculated values obtained by using reported relationships in literature.

  3. Quantifying signal dispersion in a hybrid ice core melting system.

    PubMed

    Breton, Daniel J; Koffman, Bess G; Kurbatov, Andrei V; Kreutz, Karl J; Hamilton, Gordon S

    2012-11-06

    We describe a microcontroller-based ice core melting and data logging system allowing simultaneous depth coregistration of a continuous flow analysis (CFA) system (for microparticle and conductivity measurement) and a discrete sample analysis system (for geochemistry and microparticles), both supplied from the same melted ice core section. This hybrid melting system employs an ice parcel tracking algorithm which calculates real-time sample transport through all portions of the meltwater handling system, enabling accurate (1 mm) depth coregistration of all measurements. Signal dispersion is analyzed using residence time theory, experimental results of tracer injection tests and antiparallel melting of replicate cores to rigorously quantify the signal dispersion in our system. Our dispersion-limited resolution is 1.0 cm in ice and ~2 cm in firn. We experimentally observe the peak lead phenomenon, where signal dispersion causes the measured CFA peak associated with a given event to be depth assigned ~1 cm shallower than the true event depth. Dispersion effects on resolution and signal depth assignment are discussed in detail. Our results have implications for comparisons of chemistry and physical properties data recorded using multiple instruments and for deconvolution methods of enhancing CFA depth resolution.

  4. Melting by temperature-modulated calorimetry

    SciTech Connect

    Wunderlich, B.; Okazaki, Iwao; Ishikiriyama, Kazuhiko; Boller, A. |

    1997-09-01

    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.

  5. Thermodynamic origin of surface melting on ice crystals.

    PubMed

    Murata, Ken-Ichiro; Asakawa, Harutoshi; Nagashima, Ken; Furukawa, Yoshinori; Sazaki, Gen

    2016-11-01

    Since the pioneering prediction of surface melting by Michael Faraday, it has been widely accepted that thin water layers, called quasi-liquid layers (QLLs), homogeneously and completely wet ice surfaces. Contrary to this conventional wisdom, here we both theoretically and experimentally demonstrate that QLLs have more than two wetting states and that there is a first-order wetting transition between them. Furthermore, we find that QLLs are born not only under supersaturated conditions, as recently reported, but also at undersaturation, but QLLs are absent at equilibrium. This means that QLLs are a metastable transient state formed through vapor growth and sublimation of ice, casting a serious doubt on the conventional understanding presupposing the spontaneous formation of QLLs in ice-vapor equilibrium. We propose a simple but general physical model that consistently explains these aspects of surface melting and QLLs. Our model shows that a unique interfacial potential solely controls both the wetting and thermodynamic behavior of QLLs.

  6. Thermodynamic origin of surface melting on ice crystals

    NASA Astrophysics Data System (ADS)

    Murata, Ken-ichiro; Asakawa, Harutoshi; Nagashima, Ken; Furukawa, Yoshinori; Sazaki, Gen

    2016-11-01

    Since the pioneering prediction of surface melting by Michael Faraday, it has been widely accepted that thin water layers, called quasi-liquid layers (QLLs), homogeneously and completely wet ice surfaces. Contrary to this conventional wisdom, here we both theoretically and experimentally demonstrate that QLLs have more than two wetting states and that there is a first-order wetting transition between them. Furthermore, we find that QLLs are born not only under supersaturated conditions, as recently reported, but also at undersaturation, but QLLs are absent at equilibrium. This means that QLLs are a metastable transient state formed through vapor growth and sublimation of ice, casting a serious doubt on the conventional understanding presupposing the spontaneous formation of QLLs in ice-vapor equilibrium. We propose a simple but general physical model that consistently explains these aspects of surface melting and QLLs. Our model shows that a unique interfacial potential solely controls both the wetting and thermodynamic behavior of QLLs.

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

    PubMed

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

    2012-04-25

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

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

    NASA Technical Reports Server (NTRS)

    Abdalati, Waleed; Steffen, Konrad

    2000-01-01

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

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

    SciTech Connect

    Oerlemans, J. ); Vugts, H.F. )

    1993-03-01

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

  10. Melt ponds and marginal ice zone from new algorithm of sea ice concentration retrieval

    NASA Astrophysics Data System (ADS)

    Repina, Irina; Tikhonov, Vasiliy; Komarova, Nataliia; Raev, Mikhail; Sharkov, Evgeniy

    2016-04-01

    Studies of spatial and temporal properties of sea ice distribution in polar regions help to monitor global environmental changes and reveal their natural and anthropogenic factors, as well as make forecasts of weather, marine transportation and fishing conditions, assess perspectives of mineral mining on the continental shelf, etc. Contact methods of observation are often insufficient to meet the goals, very complicated technically and organizationally and not always safe for people involved. Remote sensing techniques are believed to be the best alternative. Its include monitoring of polar regions by means of passive microwave sensing with the aim to determine spatial distribution, types, thickness and snow cover of ice. However, the algorithms employed today to retrieve sea ice characteristics from passive microwave sensing data for different reasons give significant errors, especially in summer period and also near ice edges and in cases of open ice. A new algorithm of sea ice concentration retrieval in polar regions from satellite microwave radiometry data is discussed. Beside estimating sea ice concentration, the algorithm makes it possible to indicate ice areas with melting snow and melt ponds. Melt ponds are an important element of the Arctic climate system. Covering up to 50% of the surface of drifting ice in summer, they are characterized by low albedo values and absorb several times more incident shortwave radiation than the rest of the snow and ice cover. The change of melt ponds area in summer period 1987-2015 is investigated. The marginal ice zone (MIZ) is defined as the area where open ocean processes, including specifically ocean waves, alter significantly the dynamical properties of the sea ice cover. Ocean wave fields comprise short waves generated locally and swell propagating from the large ocean basins. Depending on factors like wind direction and ocean currents, it may consist of anything from isolated, small and large ice floes drifting over a

  11. Turbulent convection driven by internal radiative heating of melt ponds on sea ice

    NASA Astrophysics Data System (ADS)

    Wells, Andrew; Langton, Tom; Rees Jones, David; Moon, Woosok

    2016-11-01

    The melting of Arctic sea ice is strongly influenced by heat transfer through melt ponds which form on the ice surface. Melt ponds are internally heated by the absorption of incoming radiation and cooled by surface heat fluxes, resulting in vigorous buoyancy-driven convection in the pond interior. Motivated by this setting, we conduct two-dimensional direct-numerical simulations of the turbulent convective flow of a Boussinesq fluid between two horizontal boundaries, with internal heating predicted from a two-stream radiation model. A linearised thermal boundary condition describes heat exchange with the overlying atmosphere, whilst the lower boundary is isothermal. Vertically asymmetric convective flow modifies the upper surface temperature, and hence controls the partitioning of the incoming heat flux between emission at the upper and lower boundaries. We determine how the downward heat flux into the ice varies with a Rayleigh number based on the internal heating rate, the flux ratio of background surface cooling compared to internal heating, and a Biot number characterising the sensitivity of surface fluxes to surface temperature. Thus we elucidate the physical controls on heat transfer through Arctic melt ponds which determine the fate of sea ice in the summer.

  12. Melting and Freezing of Ice in Relation to Iron Oxidation of Meteorites

    NASA Astrophysics Data System (ADS)

    Hruba, J.; Kletetschka, G.

    2015-07-01

    Meteorites discovered in the Antarctic ice sheet are better preserved than specimens elsewhere as the ice protects them. But ice or snow adhering to their surfaces may melt or sublimate directly on them, which may cause their oxidation.

  13. Observation of melt onset on multiyear Arctic sea ice using the ERS 1 synthetic aperture radar

    NASA Technical Reports Server (NTRS)

    Winebrenner, D. P.; Nelson, E. D.; Colony, R.; West, R. D.

    1994-01-01

    We present nearly coincident observations of backscattering from the Earth Remote-Sensing Satellite (ERS) 1 synthetic aperture radar (SAR) and of near-surface temperature from six drifting buoys in the Beaufort Sea, showing that the onset of melting in snow on multiyear sea ice is clearly detectable in the SAR data. Melt onset is marked by a clean, steep decrease in the backscattering cross section of multiyear ice at 5.3 GHz and VV polarization. We investigate the scattering physics responsible for the signature change and find that the cross section decrease is due solely to the appearance of liquid water in the snow cover overlying the ice. A thin layer of moist snow is sufficient to cause the observed decrease. We present a prototype algorithm to estimate the date of melt onset using the ERS 1 SAR and apply the algorithm first to the SAR data for which we have corresponding buoy temperatures. The melt onset dates estimated by the SAR algorithm agree with those obtained independently from the temperature data to within 4 days or less, with the exception of one case in which temperatures oscillated about 0 C for several weeks. Lastly, we apply the algorithm to the entire ERS 1 SAR data record acquired by the Alaska SAR Facility for the Beaufort Sea north of 73 deg N during the spring of 1992, to produce a map of the dates of melt onset over an area roughly 1000 km on a side. The progression of melt onset is primarily poleward but shows a weak meridional dependence at latitudes of approximately 76 deg-77 deg N. Melting begins in the southern part of the study region on June 13 and by June 20 has progressed to the northermost part of the region.

  14. Experimental validation of a numerical model for an internal melt ice-on-coil thermal storage tank

    SciTech Connect

    Neto, J.H.M.; Krarti, M.

    1997-12-31

    An internal melt ice-on-coil thermal storage tank was instrumented and tested over various inlet conditions of secondary fluid temperature and flow rate in a full-scale heating, ventilating, and air-conditioning (HVAC) laboratory. Five charging/discharging cycle tests were performed. The measured data for one typical charging/discharging cycle were used to validate a numerical model developed for analyzing internal melt ice-on-coil ice storage tanks. The validation analysis was based on the secondary fluid temperature leaving the tank, the secondary fluid heat transfer rates, the inventory of ice, the temperature of the secondary fluid at four representative locations along the coil, the temperature of the water and the ice at three representative locations inside the tank, and secondary fluid pressure drop through the tank. In general, good agreement was found between the predicted and the measured data.

  15. Distinguishing snow and glacier ice melt in High Asia using MODIS

    NASA Astrophysics Data System (ADS)

    Rittger, Karl; Brodzik, Mary J.; Bair, Edward; Racoviteanu, Adina; Barrett, Andrew; Jodha Khalsa, Siri; Armstrong, Richard; Dozier, Jeff

    2016-04-01

    In High Mountain Asia, snow and glacier ice contribute to streamflow, but the contribution of each of these hydrologic components is not fully understood. We generate daily maps of snow cover and exposed glacier ice derived from MODIS at 500 m resolution as inputs to melt models to estimate daily snow and glacier ice contributions to streamflow. The daily maps of 1) exposed glacier ice (EGI), 2) snow over ice (SOI) and 3) snow over land (SOL) between 2000 and 2014 are generated using fractional snow cover, snow grain size, and annual minimum ice and snow from the MODIS-derived MODSCAG and MODICE products. The method allows a systematic analysis of the annual cycle of snow and glacier ice extents over High Mountain Asia. We compare the time series of these three types of surfaces for nine sub-basins of the Upper Indus Basin (UIB) and characterize the variability over the MODIS record. Results show that the Dras Nala, Astore, and Zanskar sub-basins located in the eastern part of the UIB have the highest annual fraction of SOL driven by mid-winter westerly storms. Sub-basins in the northwestern extent of the UIB with relatively high mean elevations, the Hunza, Shigar, and Shyok show the highest annual fraction of both SOI and EGI (i.e. accumulation and ablation zones of the glacier). The largest sub-basin, Kharmong has the smallest annual fraction of SOL, SOI, and EGI, and a smaller SOI and EGI than the mouth of the river (Tarbela). Using these maps, snow and ice melt contributions are then estimated for the nine Upper Indus sub-basins using two melt models: a calibrated temperature-index (TI) model and an uncalibrated energy balance (EB) model. Near-surface air temperatures for the TI model are downscaled from ERA-Interim upper air temperatures, bias corrected using observed temperatures, and aggregated to 100 m elevation bands. We calibrate the seasonally variable degree-day factors for ice and snow by comparing streamflow to the sum of melt (SOL+SOI+EGI) and

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

    PubMed

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

    2016-06-10

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

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    Stubai Alps in a north to south aligned valley, with 12 rockglaciers of different activities between elevations of 2400 m and 2800 m a.s.l.. Beside the rockglaciers, a big dead ice body (approx. at 2800 m to 2850 m a.s.l.) next to the terminus of the southern Schrankarferner was identified. For the quantification of dead-ice melting, ALS data was used from 2006 - 2009. Additionally, a time series of digital elevation models (DEM) derived from aerial images of different periods (1953 -2003) were integrated in the analysis. In recent years, high-accuracy DEMs from ALS altimetry are emerging as an additional data source to existing field measurements. We present inter annual and annual trends of topographic changes caused by dead-ice melting. These trends are determined from multitemporal DEM differencing. The DEMs are generated from aerial images and ALS data. First results on the three dead-ice bodies of Hintereisferner show significant changes (-0.48 m and -2.24 m respectively per year). The derived melt rates are discussed, summarized and assessed in relation to climate parameters, like mean annual air temperature, mean summer air temperature, mean annual precipitation, mean summer precipitation, and annual sum of positive degree days.

  19. AMOC projections driven by global warming and Greenland Ice Sheet melt

    NASA Astrophysics Data System (ADS)

    Bakker, Pepijn; Schmittner, Andreas; Lenaerts, Jan; Abe-Ouchi, Ayako; Bi, Dave; van den Broeke, Michiel; Hu, Aixue; Beadling, Rebecca Lynn; Marsland, Simon; Mernhild, Sebastian H.; Ohgaito, Rumi; Rodehacke, Christian; Saenko, Oleg; Swingedouw, Didier; Yang, Shuting; Yin, Jianjun

    2016-04-01

    The evolution of the Atlantic meridional overturning circulation (AMOC) is one of the key uncertainties of future climate projections. State-of-art climate models that took part in the CMIP5 project show that over the 21st century the AMOC might reduce by 20-30% under the intermediate RCP4.5 scenario and by 36-44% under the high end RCP8.5 scenario relative to preindustrial values. However, these projections neglect enhanced meltwater input from the Greenland Ice Sheet and lack a thorough uncertainty assessment. We present results of a community effort to use state-of-the-science climate models to simulate the impact of the partial melt of the Greenland Ice Sheet on the AMOC under future global warming up to the year 2300 (AMOCMIP). A probabilistic uncertainty assessment is presented based on a physics-based AMOC emulator and includes uncertainties in the AMOC's sensitivity to temperature and salinity changes, as well as uncertainties of future global warming, regional temperature amplification and melt rates of the Greenland Ice Sheet. We find that the impact of increased Greenland Ice Sheet melt on the AMOC strength is non-negligible, albeit strongly model dependent. The uncertainty analysis shows that the chance of an collapse of the AMOC is negligible if global temperature change remains below 2°C, but becomes more probable for larger warming.

  20. Thermodynamic origin of surface melting on ice crystals

    PubMed Central

    Murata, Ken-ichiro; Asakawa, Harutoshi; Nagashima, Ken; Furukawa, Yoshinori; Sazaki, Gen

    2016-01-01

    Since the pioneering prediction of surface melting by Michael Faraday, it has been widely accepted that thin water layers, called quasi-liquid layers (QLLs), homogeneously and completely wet ice surfaces. Contrary to this conventional wisdom, here we both theoretically and experimentally demonstrate that QLLs have more than two wetting states and that there is a first-order wetting transition between them. Furthermore, we find that QLLs are born not only under supersaturated conditions, as recently reported, but also at undersaturation, but QLLs are absent at equilibrium. This means that QLLs are a metastable transient state formed through vapor growth and sublimation of ice, casting a serious doubt on the conventional understanding presupposing the spontaneous formation of QLLs in ice–vapor equilibrium. We propose a simple but general physical model that consistently explains these aspects of surface melting and QLLs. Our model shows that a unique interfacial potential solely controls both the wetting and thermodynamic behavior of QLLs. PMID:27791107

  1. Thermooptical properties of gold nanoparticles embedded in ice: characterization of heat generation and melting.

    PubMed

    Richardson, Hugh H; Hickman, Zackary N; Govorov, Alexander O; Thomas, Alyssa C; Zhang, Wei; Kordesch, Martin E

    2006-04-01

    We investigate the system of optically excited gold NPs in an ice matrix aiming to understand heat generation and melting processes at the nanoscale level. Along with the traditional fluorescence method, we introduce thermooptical spectroscopy based on phase transformation of a matrix. With this, we can not only measure optical response but also thermal response, that is, heat generation. After several recrystallization cycles, the nanoparticles are embedded into the ice film where the optical and thermal properties of the nanoparticles are probed. Spatial fluorescence mapping shows the locations of Au nanoparticles, whereas the time-resolved Raman signal of ice reveals the melting process. From the time-dependent Raman signals, we determine the critical light intensities at which the laser beam is able to melt ice around the nanoparticles. The melting intensity depends strongly on temperature and position. The position-dependence is especially strong and reflects a mesoscopic character of heat generation. We think that it comes from the fact that nanoparticles form small complexes of different geometry and each complex has a unique thermal response. Theoretical calculations and experimental data are combined to make a quantitative measure of the amount of heat generated by optically excited Au nanoparticles and agglomerates. The information obtained in this study can be used to design nanoscale heaters and actuators.

  2. Calving fluxes and basal melt rates of Antarctic ice shelves.

    PubMed

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

    2013-10-03

    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.

  3. A simple parameterisation of melting near the grounding lines of ice shelves and tidewater glaciers

    NASA Astrophysics Data System (ADS)

    Jenkins, A.

    2012-04-01

    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. It is generally assumed that the accelerations have been driven by the ocean, probably through changes in the submarine melt rate. However, the processes that drive melting, particularly in the region close to the grounding line are difficult to observer and quantify. The rapid flow of the outlet glaciers is almost always associated with an active sub-glacial hydrological system, so in the key regions where the glaciers either discharge into ice shelves or terminate in fjords there will be a flow of freshwater draining across the grounding line from the glacier bed. The input of freshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice-ocean interface. This process is modelled using the theory of buoyant plumes that has previously been applied to the study of the larger-scale circulation beneath ice shelves. The plume grows through entrainment of ocean waters, and the heat brought into the plume as a result drives melting at the ice-ocean interface. The equations are non-dimensionalised using scales appropriate for the region where the sub-glacial drainage, rather than the subsequent addition of meltwater, supplies the majority of the buoyancy forcing. It is found that the melt rate within this region can be approximated reasonably well by a simple expression that is linear in ocean temperature, has a cube root dependence on the flux of sub-glacial meltwater, and a more complex dependency on the slope of the ice-ocean interface. The model is used to investigate variability in melting induced by changes in both ocean temperature and sub-glacial discharge for a number of realistic examples of ice shelves and tidewater glaciers. The results show how warming ocean waters and increasing sub-glacial drainage both generate increases in melting near the

  4. Radar measurements of melt zones on the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  5. AMOCMIP: Probabilistic projections of future AMOC evolution driven by global warming and Greenland Ice Sheet melt.

    NASA Astrophysics Data System (ADS)

    Bakker, P.; Ohgaito, R.; Abe-Ouchi, A.; Swingedouw, D.; Saenko, O.; Marsland, S. J.; Bi, D.; Schmittner, A.; Hu, A.; Mernild, S. H.; Yin, J.; Beadling, R. L.; Lenaerts, J.; van den Broeke, M.

    2015-12-01

    We present results of a community effort to use state-of-the-science climate models to simulate the impact of the partial melt of the Greenland Ice Sheet on the Atlantic Meridional Overturning Circulation (AMOC) under future global warming: the AMOC Model Intercomparison Project (AMOCMIP). The evolution of the AMOC is one of the key uncertainties of future climate projections. Climate models taking part in CMIP5 showed that over the 21st century the AMOC might reduce by 20-30% under the intermediate Representative Concentration Pathways (RCP) 4.5 scenario and by 36-44% under the high-end RCP8.5 scenario relative to preindustrial values. However, these projections didn't include the predicted partial melting of the Greenland Ice Sheet. Using a combination of observations and regional climate model experiments, realistic scenarios of the future mass loss of the Greenland Ice Sheet are constructed for different RCPs that span the next three centuries. These melt water scenarios have been included in various climate models to investigate its role in the simulated future evolution of the climate in general and more specifically the AMOC. To rigorously quantify the uncertainties of the AMOC projections and the probability of a future AMOC collapse we have used an AMOC emulator. This physics-based approach allows us to include uncertainties in the AMOC's sensitivity to temperature and salinity changes, as well as uncertainties of future global warming, polar amplification and melt rates of the Greenland Ice Sheet. Based on the first AMOCMIP simulations of future AMOC evolution forced by changes in greenhouse-gas concentrations and Greenland Ice Sheet melt, we will present probabilistic projections of future AMOC changes and the probability of an AMOC collapse.

  6. Passive microwave-derived snow melt regions on the Greenland ice sheet

    NASA Technical Reports Server (NTRS)

    Abdalati, Waleed; Steffen, Konrad

    1995-01-01

    By comparing data from the Special Sensor Microwave Imager (SSM/I) to field data, a melt threshold of the cross-polarized gradient ratio (XPGR), which is a normalized difference between the 19 GHz horizontally-polarized and 37 GHz vertically polarized brightness temperatures, is determined. This threshold, XPGR = -0.025, is used to classify dry and wet snow. The annual areal extent of melt is mapped for the years 1988 through 1991, and inter-annual variations of melt extent are examined. The results show that the melt extent varied from a low of 38.3% of the ice sheet (1990) to a high of 41.7% (1991) during the years 1988-1991.

  7. Surface melt-induced acceleration of Greenland ice-sheet flow.

    PubMed

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

    2002-07-12

    Ice flow at a location in the equilibrium zone of the west-central Greenland Ice Sheet accelerates above the midwinter average rate during periods of summer melting. The near coincidence of the ice acceleration with the duration of surface melting, followed by deceleration after the melting ceases, indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice-bedrock interface. Interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting, with larger increases accompanying higher amounts of summer melting. The indicated coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    PubMed

    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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  13. Isotope thermometry in melt-affected ice cores

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    A statistically significant relationship is observed between stable water isotopes (δ18O) 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 δ18O 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.

  14. Effect of microorganism on Greenland ice sheet surface temperature change

    NASA Astrophysics Data System (ADS)

    Shimada, R.; Takeuchi, N.; Aoki, T.

    2012-12-01

    Greenland ice sheet holds approximately 10% of the fresh water on earth. If it melts all, sea level rises about 7.2meter. It is reported that mass of Greenland ice sheet is decreasing with temperature rising of climate change. Melting of the coastal area is particularly noticeable. It is established that 4 to 23% of the sea level rising from 1993 to 2005 is caused by the melting of Greenland ice sheet. In 2010, amount of melting per year became the largest than the past. However many climate models aren't able to simulate the recent melting of snow and ice in the Arctic including Greenland. One of the possible causes is albedo reduction of snow and ice surface by light absorbing snow impurities such as black carbon and dust and by glacial microorganisms. But there are few researches for effect of glacial microorganism in wide area. So it is important to clarify the impact of glacial microorganisms in wide area. The purpose of this study is to clarify the effect of microorganism on Greenland ice sheet surface temperature change using satellite images of visible, near infrared and thermal infrared wavelength range and observation carried out in northwestern Greenland. We use MODIS Land Surface Temperature Product as ice sheet surface temperature. It estimates land surface temperature based on split window method using thermal infrared bands. MODIS data is bound to cover the whole of Greenland, and calculated the ratio of the temperature change per year. Analysis period is from December 2002 to November 2010. Results of calculating Greenland ice sheet surface temperature change using the MODIS data, our analysis shows that it is upward trend in the whole region. We find a striking upward trend in northern and western part of Greenland. The rate is 0.33±0.03 degree Celsius per a year from 47.5°W to 49°W. While in the coastal area from 49°W to 50.7°W, the rate is 0.26±0.06 degree Celsius per a year. This large upward trend area is the same area as dark region

  15. Bottom melting of Arctic Sea Ice in the Nansen Basin due to Atlantic Water influence

    NASA Astrophysics Data System (ADS)

    Muilwijk, Morven; Smedsrud, Lars H.; Meyer, Amelie

    2016-04-01

    Our global climate is warming, and a shrinking Arctic sea ice cover remains one of the most visible signs of this warming. Sea Ice loss is now visible for all months in all regions of the Arctic. Hydrographic and current observations from a region north of Svalbard collected during the Norwegian Young Sea Ice Cruise (N-ICE2015) are presented here. Comparison with historical data shows that the new observations from January through June fill major gaps in available observations, and help describing important processes linking changes in regional Atlantic Water (AW) heat transport and sea ice. Warm and salty AW originating in the North Atlantic enters the Arctic Ocean through the Fram Strait and is present below the Arctic Sea Ice cover throughout the Arctic. However, the depth of AW varies by region and over time. In the region north of Svalbard, we assume that depth could be governed primarily by local processes, by upstream conditions of the ice cover (Northwards), or by upstream conditions of the AW (Southwards). AW carries heat corresponding to the volume transport of approximately 9 SV through Fram Strait, varying seasonally from 28 TW in winter to 46 TW in summer. Some heat is recirculated, but the net annual heat flux into the Arctic Ocean from AW is estimated to be around 40 TW. The Atlantic Water layer temperature at intermediate depths (150-900m) has increased in recent years. Until recently, maximum temperatures have been found to be 2-3 C in the Nansen Basin. Studies have shown that for example, in the West Spitsbergen Current the upper 50-200m shows an overall AW warming of 1.1 C since 1979. In general we expect efficient melting when AW is close to the surface. Previously the AW entering through Fram Strait has been considered as less important because changes in the sea ice cover have been connected to greater inflow of Pacific Water through Bering Strait and atmospheric forcing. Conversely it is now suggested that AW has direct impact on melting of

  16. Winter ocean-ice interactions under thin sea ice observed by IAOOS platforms during N-ICE2015: Salty surface mixed layer and active basal melt

    NASA Astrophysics Data System (ADS)

    Koenig, Zoé; Provost, Christine; Villacieros-Robineau, Nicolas; Sennéchael, Nathalie; Meyer, Amelie

    2016-10-01

    IAOOS (Ice Atmosphere Arctic Ocean Observing System) platforms, measuring physical parameters at the atmosphere-snow-ice-ocean interface deployed as part of the N-ICE2015 campaign, provide new insights on winter conditions North of Svalbard. The three regions crossed during the drifts, the Nansen Basin, the Sofia Deep, and the Svalbard northern continental slope featured distinct hydrographic properties and ice-ocean exchanges. In the Nansen Basin, the quiescent warm layer was capped by a stepped halocline (60 and 110 m) and a deep thermocline (110 m). Ice was forming and the winter mixed layer salinity was larger by ˜0.1 g/kg than previously observed. Over the Svalbard continental slope, the Atlantic Water (AW) was very shallow (20 m from the surface) and extended offshore from the 500 m isobath by a distance of about 70 km, sank along the slope (40 m from the surface) and probably shed eddies into the Sofia Deep. In the Sofia Deep, relatively warm waters of Atlantic origin extended from 90 m downward. Resulting from different pathways, these waters had a wide range of hydrographic characteristics. Sea-ice melt was widespread over the Svalbard continental slope and ocean-to-ice heat fluxes reached values of 400 W m-2 (mean of ˜150 W m-2 over the continental slope). Sea-ice melt events were associated with near 12 h fluctuations in the mixed-layer temperature and salinity corresponding to the periodicity of tides and near-inertial waves potentially generated by winter storms, large barotropic tides over steep topography, and/or geostrophic adjustments.

  17. Antarctic icebergs melt over the Southern Ocean : Climatology and impact on sea ice

    NASA Astrophysics Data System (ADS)

    Merino, Nacho; Le Sommer, Julien; Durand, Gael; Jourdain, Nicolas C.; Madec, Gurvan; Mathiot, Pierre; Tournadre, Jean

    2016-08-01

    Recent increase in Antarctic freshwater release to the Southern Ocean is suggested to contribute to change in water masses and sea ice. However, climate models differ in their representation of the freshwater sources. Recent improvements in altimetry-based detection of small icebergs and in estimates of the mass loss of Antarctica may help better constrain the values of Antarctic freshwater releases. We propose a model-based seasonal climatology of iceberg melt over the Southern Ocean using state-of-the-art observed glaciological estimates of the Antarctic mass loss. An improved version of a Lagrangian iceberg model is coupled with a global, eddy-permitting ocean/sea ice model and compared to small icebergs observations. Iceberg melt increases sea ice cover, about 10% in annual mean sea ice volume, and decreases sea surface temperature over most of the Southern Ocean, but with distinctive regional patterns. Our results underline the importance of improving the representation of Antarctic freshwater sources. This can be achieved by forcing ocean/sea ice models with a climatological iceberg fresh-water flux.

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

    PubMed

    Knopf, Daniel Alexander; Lopez, Miguel David

    2009-09-28

    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.

  19. FAST TRACK COMMUNICATION: Growth melt asymmetry in ice crystals under the influence of spruce budworm antifreeze protein

    NASA Astrophysics Data System (ADS)

    Pertaya, Natalya; Celik, Yeliz; Di Prinzio, Carlos L.; Wettlaufer, J. S.; Davies, Peter L.; Braslavsky, Ido

    2007-10-01

    Here we describe studies of the crystallization behavior of ice in an aqueous solution of spruce budworm antifreeze protein (sbwAFP) at atmospheric pressure. SbwAFP is an ice binding protein with high thermal hysteresis activity, which helps protect Choristoneura fumiferana (spruce budworm) larvae from freezing as they overwinter in the spruce and fir forests of the north eastern United States and Canada. Different types of ice binding proteins have been found in many other species. They have a wide range of applications in cryomedicine and cryopreservation, as well as the potential to protect plants and vegetables from frost damage through genetic engineering. However, there is much to learn regarding the mechanism of action of ice binding proteins. In our experiments, a solution containing sbwAFP was rapidly frozen and then melted back, thereby allowing us to produce small single crystals. These maintained their hexagonal shapes during cooling within the thermal hysteresis gap. Melt-growth-melt sequences in low concentrations of sbwAFP reveal the same shape transitions as are found in pure ice crystals at low temperature (-22 °C) and high pressure (2000 bar) (Cahoon et al 2006 Phys. Rev. Lett. 96 255502) while both growth and melt shapes display faceted hexagonal morphology, they are rotated 30° relative to one another. Moreover, the initial melt shape and orientation is recovered in the sequence. To visualize the binding of sbwAFP to ice, we labeled the antifreeze protein with enhanced green fluorescent protein (eGFP) and observed the sbwAFP-GFP molecules directly on ice crystals using confocal microscopy. When cooling the ice crystals, facets form on the six primary prism planes (slowest growing planes) that are evenly decorated with sbwAFP-GFP. During melting, apparent facets form on secondary prism planes (fastest melting planes), leaving residual sbwAFP at the six corners of the hexagon. Thus, the same general growth-melt behavior of an apparently rotated

  20. Processes controlling surface, bottom and lateral melt of Arctic sea ice in a state of the art sea ice model.

    PubMed

    Tsamados, Michel; Feltham, Daniel; Petty, Alek; Schroeder, David; Flocco, Daniela

    2015-10-13

    We present a modelling study of processes controlling the summer melt of the Arctic sea ice cover. We perform a sensitivity study and focus our interest on the thermodynamics at the ice-atmosphere and ice-ocean interfaces. We use the Los Alamos community sea ice model CICE, and additionally implement and test three new parametrization schemes: (i) a prognostic mixed layer; (ii) a three equation boundary condition for the salt and heat flux at the ice-ocean interface; and (iii) a new lateral melt parametrization. Recent additions to the CICE model are also tested, including explicit melt ponds, a form drag parametrization and a halodynamic brine drainage scheme. The various sea ice parametrizations tested in this sensitivity study introduce a wide spread in the simulated sea ice characteristics. For each simulation, the total melt is decomposed into its surface, bottom and lateral melt components to assess the processes driving melt and how this varies regionally and temporally. Because this study quantifies the relative importance of several processes in driving the summer melt of sea ice, this work can serve as a guide for future research priorities.

  1. Deterministic model for an internal melt ice-on-coil thermal storage tank

    SciTech Connect

    Neto, J.H.M.; Krarti, M.

    1997-12-31

    A deterministic numerical model, based on a quasi-steady-state approach, is developed for an internal melt ice-on-coil thermal storage tank with a built-in spiral coil tubing heat exchanger having a counterflow configuration and quiescent water around the coils. This model is able to simulate both charging and discharging modes, taking into account the overlapping phenomenon that occurs due to the superposition of the ice layers during freezing as well as the superposition of the water layers during melting. The developed model accounts for the cooldown of the water earlier during the charging period and the warm-up of the water later during the discharging period. The input parameters include the geometric dimensions of the tank, the secondary fluid temperature and its flow rate entering the tank, the number of segments along the coil, and the time step. The model determines the heat transfer rates, the inventory of the ice, and other output parameters such as temperatures and ice/water radius. This model can be used by manufacturers and engineers for design and simulation purposes.

  2. Ice melting properties of steel fiber modified asphalt mixtures with induction heating

    NASA Astrophysics Data System (ADS)

    Fang, Hao; Sun, Yihan; Liu, Quantao; Li, Bin; Wu, Shaopeng; Tang, Jin

    2017-03-01

    In this paper, the ice melting performance of asphalt concrete with steel fibers was studied. Steel fiber modified asphalt mixtures were prepared, five different fiber amount of steel fiber modified asphalt mixtures were mixed to study their induction heating rate. The samples covered with different thickness of ice were heated with induction heating to study their ice melting efficency. It was proved that the induction heating of steel fiber modified asphalt mixtures could significantly improve their ice melting efficency compared with the natural condition. And it was found that the thickness of the ice had little influence on the induction heating rate of the asphalt concrete.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    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

  4. Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting

    NASA Astrophysics Data System (ADS)

    Gladstone, Rupert Michael; Warner, Roland Charles; Galton-Fenzi, Benjamin Keith; Gagliardini, Olivier; Zwinger, Thomas; Greve, Ralf

    2017-01-01

    Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence.A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line.Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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

  6. The melting sea ice of Arctic polar cap in the summer solstice month and the role of ocean

    NASA Astrophysics Data System (ADS)

    Lee, S.; Yi, Y.

    2014-12-01

    The Arctic sea ice is becoming smaller and thinner than climatological standard normal and more fragmented in the early summer. We investigated the widely changing Arctic sea ice using the daily sea ice concentration data. Sea ice data is generated from brightness temperature data derived from the sensors: Defense Meteorological Satellite Program (DMSP)-F13 Special Sensor Microwave/Imagers (SSM/Is), the DMSP-F17 Special Sensor Microwave Imager/Sounder (SSMIS) and the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) instrument on the NASA Earth Observing System (EOS) Aqua satellite. We tried to figure out appearance of arctic sea ice melting region of polar cap from the data of passive microwave sensors. It is hard to explain polar sea ice melting only by atmosphere effects like surface air temperature or wind. Thus, our hypothesis explaining this phenomenon is that the heat from deep undersea in Arctic Ocean ridges and the hydrothermal vents might be contributing to the melting of Arctic sea ice.

  7. Interfacial melting of ice under a high-speed slider: real-time visualization and friction modeling

    NASA Astrophysics Data System (ADS)

    Kim, Hyung-Seok; Yun, Chang-Ho; Kim, Dong-Jo; Kim, Ho-Young

    2016-11-01

    When a solid plate slides on ice, frictional heat melts asperities on the ice surface causing the real contact area to increase. Previous studies indicate the significance of contact area growth for ice friction, yet its quantitative understanding is far from clear mainly because the direct observation of the melting process at the interface has been extremely difficult. Here we describe a novel experimental setup that visualizes the interface of a rapidly rotating ice disc (up to the linear velocity of 10 m/s) and a transparent quartz surface in real time using the total internal reflection. We find that the melted area of the ice surface is a sensitive function of both sliding speed and temperature. We rationalize such quantitative measurements numerically and analytically, which allows us to predict the friction coefficient of ice as a function of relative velocity and temperature. This work can be used to develop friction-controlling mechanisms on ice surface, which are important in traffic safety as well as winter sports.

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

    SciTech Connect

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

    2008-11-12

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

  9. Documenting Melting Features of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Tedesco, M.

    2011-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Holt, B.; Digby, S. A.

    1985-01-01

    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.

  11. Strong isotope effects on melting dynamics and ice crystallisation processes in cryo vitrification solutions.

    PubMed

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

    2015-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

    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.

  13. The effect of basal friction on melting and freezing in ice shelf-ocean models

    NASA Astrophysics Data System (ADS)

    Gwyther, David E.; Galton-Fenzi, Benjamin K.; Dinniman, Michael S.; Roberts, Jason L.; Hunter, John R.

    2015-11-01

    The ocean is an important control on the mass budget of the Antarctic ice sheet, through basal melting and refreezing underneath the floating extensions of the ice sheet known as ice shelves. The effect of the ice surface roughness (basal roughness) on melting and refreezing is investigated with idealised ice shelf-ocean numerical simulations. Both "hot" ocean forcing (e.g. Pine Island Glacier; high basal melting) and "cold" ocean forcing (e.g. Amery Ice Shelf; low basal melting, stronger refreezing) environments are investigated. The interaction between the ocean and ice shelf is further explored by examining the contributions to melt from heat exchange across the ice-ocean interface and across the boundary layer-ocean interior, with a varying drag coefficient. Simulations show increasing drag strengthens melting. Refreezing increases with drag in the cold cavity environment, while in the hot cavity environment, refreezing is small in areal extent and decreases with drag. Furthermore, melting will likely be focussed where there are strong boundary layer currents, rather than at the deep grounding line. The magnitude of the thermal driving of the basal melt decreases with increasing drag, except for in cold cavity refreeze zones where it increases. The friction velocity, a function of the upper layer ocean velocity and the drag coefficient, monotonically increases with drag. We find friction-driven mixing into the boundary layer is important for representing the magnitude and distribution of refreezing and without this effect, refreezing is underestimated. Including a spatially- and temporally-varying basal roughness (that includes a more realistic, rougher refreezing drag coefficient) alters circulation patterns and heat and salt transport. This leads to increased refreezing, altered melt magnitude and distribution, and a pattern of altered vertical flow across the entire ice shelf. These results represent a summary of melting and freezing beneath ice shelves and

  14. Comparisons of Cubed Ice, Crushed Ice, and Wetted Ice on Intramuscular and Surface Temperature Changes

    PubMed Central

    Dykstra, Joseph H; Hill, Holly M; Miller, Michael G; Cheatham, Christopher C; Michael, Timothy J; Baker, Robert J

    2009-01-01

    Context: Many researchers have investigated the effectiveness of different types of cold application, including cold whirlpools, ice packs, and chemical packs. However, few have investigated the effectiveness of different types of ice used in ice packs, even though ice is one of the most common forms of cold application. Objective: To evaluate and compare the cooling effectiveness of ice packs made with cubed, crushed, and wetted ice on intramuscular and skin surface temperatures. Design: Repeated-measures counterbalanced design. Setting: Human performance research laboratory. Patients or Other Participants: Twelve healthy participants (6 men, 6 women) with no history of musculoskeletal disease and no known preexisting inflammatory conditions or recent orthopaedic injuries to the lower extremities. Intervention(s): Ice packs made with cubed, crushed, or wetted ice were applied to a standardized area on the posterior aspect of the right gastrocnemius for 20 minutes. Each participant was given separate ice pack treatments, with at least 4 days between treatment sessions. Main Outcome Measure(s): Cutaneous and intramuscular (2 cm plus one-half skinfold measurement) temperatures of the right gastrocnemius were measured every 30 seconds during a 20-minute baseline period, a 20-minute treatment period, and a 120-minute recovery period. Results: Differences were observed among all treatments. Compared with the crushed-ice treatment, the cubed-ice and wetted-ice treatments produced lower surface and intramuscular temperatures. Wetted ice produced the greatest overall temperature change during treatment and recovery, and crushed ice produced the smallest change. Conclusions: As administered in our protocol, wetted ice was superior to cubed or crushed ice at reducing surface temperatures, whereas both cubed ice and wetted ice were superior to crushed ice at reducing intramuscular temperatures. PMID:19295957

  15. Freshwater - the key to melt pond formation atop first year sea ice

    NASA Astrophysics Data System (ADS)

    Polashenski, C.; Golden, K. M.; Skyllingstad, E. D.; Perovich, D. K.

    2014-12-01

    Melt pond formation atop Arctic sea ice is a primary control of shortwave energy balance and light availability for photosynthesis in the upper Arctic Ocean. The initial formation process of melt ponds on first year ice typically requires that melt water be retained on the surface of ice several to tens of centimeters above sea level for several days. Albedo feedbacks during this time period create below-sea-level depressions which remain ponds later in summer. Both theory and observations, however, show that sea ice is so highly porous and permeable prior to the formation of melt ponds that retention of water tens of centimeters above hydraulic equilibrium for multiple days should not be possible. Here we present results of percolation test experiments that identify the mechanism allowing above-sea level melt pond formation. The infiltration of fresh water from snowmelt into the pore structure of the ice is responsible for plugging the pores with fresh ice, sealing the ice against further water percolation, and allowing water to pool above freeboard. Fresh meltwater availability and desalination processes, therefore, exert considerable influence over the formation of melt ponds. The findings demonstrate another mechanism through which changes in snowfall on sea ice, already being observed, are likely to alter ice mass balance and highlight the importance of efforts to improve treatment of ice salinity in models.

  16. Drag Moderation by the Melting of an Ice Surface in Contact with Water

    NASA Astrophysics Data System (ADS)

    Vakarelski, Ivan U.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.

    2015-07-01

    We report measurements of the effects of a melting ice surface on the hydrodynamic drag of ice-shell-metal-core spheres free falling in water at a Reynolds of number Re ˜2 ×104- 3 ×105 and demonstrate that the melting surface induces the early onset of the drag crisis, thus reducing the hydrodynamic drag by more than 50%. Direct visualization of the flow pattern demonstrates the key role of surface melting. Our observations support the hypothesis that the drag reduction is due to the disturbance of the viscous boundary layer by the mass transfer from the melting ice surface.

  17. Drag Moderation by the Melting of an Ice Surface in Contact with Water.

    PubMed

    Vakarelski, Ivan U; Chan, Derek Y C; Thoroddsen, Sigurdur T

    2015-07-24

    We report measurements of the effects of a melting ice surface on the hydrodynamic drag of ice-shell-metal-core spheres free falling in water at a Reynolds of number Re~2×10^{4}-3×10^{5} and demonstrate that the melting surface induces the early onset of the drag crisis, thus reducing the hydrodynamic drag by more than 50%. Direct visualization of the flow pattern demonstrates the key role of surface melting. Our observations support the hypothesis that the drag reduction is due to the disturbance of the viscous boundary layer by the mass transfer from the melting ice surface.

  18. Numerical analysis on thermal characteristics and ice melting efficiency for microwave deicing vehicle

    NASA Astrophysics Data System (ADS)

    Wang, Can; Yang, Bo; Tan, Gangfeng; Guo, Xuexun; Zhou, Li; Xiong, Shengguang

    2016-05-01

    In the high latitudes, the icy patches on the road are frequently generated and have a wide distribution, which are difficult to remove and obviously affect the normal usage of the highways, bridges and airport runways. Physical deicing, such as microwave (MW) deicing, help the ice melt completely through heating mode and then the ice layer can be swept away. Though it is no pollution and no damage to the ground, the low efficiency hinders the development of MW deicing vehicle equipped without sufficient speed. In this work, the standard evaluation of deicing is put forward firstly. The intensive MW deicing is simplified to ice melting process characterized by one-dimensional slab with uniform volumetric energy generation, which results in phase transformation and interface motion between ice and water. The heating process is split into the superposition of three parts — non-heterogeneous heating for ground without phase change, heat transfer with phase change and the heat convection between top surface of ice layer and flow air. Based on the transient heat conduction theory, a mathematical model, combining electromagnetic and two-phase thermal conduction, is proposed in this work, which is able to reveal the relationship between the deicing efficiency and ambient conditions, as well as energy generation and material parameters. Using finite difference time-domain, this comprehensive model is developed to solve the moving boundary heat transfer problem in a one-dimensional structured gird. As a result, the stimulation shows the longitudinal temperature distributions in all circumstances and quantitative validation is obtained by comparing simulated temperature distributions under different conditions. In view of the best economy and fast deicing, these analytic solutions referring to the complex influence factors of deicing efficiency demonstrate the optimal matching for the new deicing design.

  19. Spatial and Temporal Observations of Summer Ice Melt Using ERS-1 SAR Imagery

    NASA Technical Reports Server (NTRS)

    Holt, B.; Martin, S.

    1995-01-01

    The complete understanding of the heat and mass balance of the polar oceans includes the melting of sea ice in the summer and the reinjection of fresh water into the upper ocean. This study examines the spatial and temporal character of ice melt. Using ERS-1 SAR imagery, the development of small floes formed by melt and deforma- tion, and changes in the fraction of open water and floes is examined.

  20. Massive Cellular Automata in Geosimulation: Antarctica Ice Melting as Example

    NASA Astrophysics Data System (ADS)

    Lan, H.; Torrens, P.; Lin, J.; Han, R.

    2015-12-01

    One of the essential features of the cellular automata (CA) model is its high scalability: CA lattices can be theoretically run at gargantuan size to represent intricacies of complex phenomena. However, one barrier in the use of cellular automata for scientific simulations is the issue of scalability in terms of the number of cells, to either model phenomena at finer granularities or at larger scales. Some researchers have developed parallel CA algorithms using MapReduce to eke out efficiency, but MapReduce may not provide the ideal scheme to address messy parallelism in large CA when they require complex rule-sets and broker a lot of state exchange across large solution-space lattices. In this research, we take advantage of the Bulk Synchronous Parallel (BSP) model of distributed computation, via the Giraph open-source implementation, to implement large-scale cellular automata simulations. Additionally, this study also describes a scientifically interesting example, in which ice dynamics in Antarctic is simulated using a melting model. Short-term and medium-term ice sheet dynamics are driven by a variety of forces. We do not fully understand what they might be and how they interplay, and simulation is an important medium for building the science to guide us in finding answers. In our experiments, using a voxel CA comprising 1 trillion cells—by far the largest scale voxel-based CA model reported in literature—which took only 2.48 minutes for per step for processing.

  1. When glaciers and ice sheets melt: consequences for planktonic organisms

    PubMed Central

    SOMMARUGA, RUBEN

    2016-01-01

    The current melting of glaciers and ice sheets is a consequence of climatic change and their turbid meltwaters are filling and enlarging many new proglacial and ice-contact lakes around the world, as well as affecting coastal areas. Paradoxically, very little is known on the ecology of turbid glacier-fed aquatic ecosystems even though they are at the origin of the most common type of lakes on Earth. Here, I discuss the consequences of those meltwaters for planktonic organisms. A remarkable characteristic of aquatic ecosystems receiving the discharge of meltwaters is their high content of mineral suspensoids, so-called glacial flour that poses a real challenge for filter-feeding planktonic taxa such as Daphnia and phagotrophic groups such as heterotrophic nanoflagellates. The planktonic food-web structure in highly turbid meltwater lakes seems to be truncated and microbially dominated. Low underwater light levels leads to unfavorable conditions for primary producers, but at the same time, cause less stress by UV radiation. Meltwaters are also a source of inorganic and organic nutrients that could stimulate secondary prokaryotic production and in some cases (e.g. in distal proglacial lakes) also phytoplankton primary production. How changes in turbidity and in other related environmental factors influence diversity, community composition and adaptation have only recently begun to be studied. Knowledge of the consequences of glacier retreat for glacier-fed lakes and coasts will be crucial to predict ecosystem trajectories regarding changes in biodiversity, biogeochemical cycles and function. PMID:26869738

  2. When glaciers and ice sheets melt: consequences for planktonic organisms.

    PubMed

    Sommaruga, Ruben

    2015-05-01

    The current melting of glaciers and ice sheets is a consequence of climatic change and their turbid meltwaters are filling and enlarging many new proglacial and ice-contact lakes around the world, as well as affecting coastal areas. Paradoxically, very little is known on the ecology of turbid glacier-fed aquatic ecosystems even though they are at the origin of the most common type of lakes on Earth. Here, I discuss the consequences of those meltwaters for planktonic organisms. A remarkable characteristic of aquatic ecosystems receiving the discharge of meltwaters is their high content of mineral suspensoids, so-called glacial flour that poses a real challenge for filter-feeding planktonic taxa such as Daphnia and phagotrophic groups such as heterotrophic nanoflagellates. The planktonic food-web structure in highly turbid meltwater lakes seems to be truncated and microbially dominated. Low underwater light levels leads to unfavorable conditions for primary producers, but at the same time, cause less stress by UV radiation. Meltwaters are also a source of inorganic and organic nutrients that could stimulate secondary prokaryotic production and in some cases (e.g. in distal proglacial lakes) also phytoplankton primary production. How changes in turbidity and in other related environmental factors influence diversity, community composition and adaptation have only recently begun to be studied. Knowledge of the consequences of glacier retreat for glacier-fed lakes and coasts will be crucial to predict ecosystem trajectories regarding changes in biodiversity, biogeochemical cycles and function.

  3. High basal melting forming a channel at the grounding line of Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Marsh, Oliver J.; Fricker, Helen A.; Siegfried, Matthew R.; Christianson, Knut; Nicholls, Keith W.; Corr, Hugh F. J.; Catania, Ginny

    2016-01-01

    Antarctica's ice shelves are thinning at an increasing rate, affecting their buttressing ability. Channels in the ice shelf base unevenly distribute melting, and their evolution provides insight into changing subglacial and oceanic conditions. Here we used phase-sensitive radar measurements to estimate basal melt rates in a channel beneath the currently stable Ross Ice Shelf. Melt rates of 22.2 ± 0.2 m a-1 (>2500% the overall background rate) were observed 1.7 km seaward of Mercer/Whillans Ice Stream grounding line, close to where subglacial water discharge is expected. Laser altimetry shows a corresponding, steadily deepening surface channel. Two relict channels to the north suggest recent subglacial drainage reorganization beneath Whillans Ice Stream approximately coincident with the shutdown of Kamb Ice Stream. This rapid channel formation implies that shifts in subglacial hydrology may impact ice shelf stability.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Sawada, Hisashi; Okada, Masashi; Nakagawa, Shinji

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  7. Analysis of Summer 2002 Melt Extent on the Greenland Ice Sheet using MODIS and SSM/I Data

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Williams, Richard S., Jr.; Steffen, Konrad; Chien, Y. L.; Foster, James L.; Robinson, David A.; Riggs, George A.

    2004-01-01

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

  8. Analysis of Summer 2002 Melt Extent on the Greenland Ice Sheet using MODIS and SSM/I Data

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Williams, Richard S.; Steffen, Konrad; Chien, Janet Y. L.

    2004-01-01

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

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

    USGS Publications Warehouse

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

    2004-01-01

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

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

    PubMed

    Kim, Jun Soo; Yethiraj, Arun

    2008-09-28

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    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

  12. Non-eruptive ice melt driven by internal heat at glaciated stratovolcanoes

    NASA Astrophysics Data System (ADS)

    Hemmings, Brioch; Whitaker, Fiona; Gottsmann, Joachim; Hawes, Molly C.

    2016-11-01

    Mudflows, floods and lahars from rapid snow and ice melting present potentially devastating hazards to populations surrounding glacial stratovolcanoes. Most ice-melt induced lahars have resulted from eruptive processes. However, there is evidence for non-eruptive hydrothermal volcanic unrest generating rapid and hazardous glacial melt. Here, we use TOUGH2 numerical fluid flow simulations to explore ice melt potential associated with hydrothermal perturbation. Our simulations are loosely based on Cotopaxi Volcano, Ecuadorian Andes. We show that dynamic permeability has a strong control on ice melt response to perturbation. In the absence of concurrent permeability increases, the delay time between onset of a deep hydrothermal perturbation and a response in surface heat flow is on the order of many 10s of years. When increased hot fluid influx at depth is combined with permeability enhancement, the surface heat flow response can be immediate. However, our results suggest that melt rates resulting from such hydrothermal perturbation are still orders of magnitude lower than those induced by eruptive processes; potentially hazardous melt volumes take many months to accumulate, compared to minutes for eruption induced melting. Additional mechanisms, such as glacier destabilisation, meltwater impounding and hydrothermal outburst, may be required to generate volumes of water similar to those associated with catastrophic eruption initiated ice-melt lahars.

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

    PubMed

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

    2011-01-27

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

  14. Melting temperature of water: DFT-based molecular dynamics simulations with D3 dispersion correction

    NASA Astrophysics Data System (ADS)

    Seitsonen, Ari P.; Bryk, Taras

    2016-11-01

    Extensive ab initio simulations of ice-water basal interface at seven temperatures in the range 250-400 K were performed in NVT and NPT ensembles with a collection of 389 water molecules in order to estimate the melting point of ice from direct liquid-solid two-phase coexistence. Density functional theory with the BLYP (Becke-Lee-Yang-Parr) exchange-correlation functional and the D3 dispersion correction were used in the expression of total energy. Analysis of density profiles and the evolution of the total potential, or Kohn-Sham plus D3, energy in the simulations at different temperatures resulted in an estimate for melting temperature of ice of 325 K.

  15. Response of Arctic Snow and Sea Ice Extents to Melt Season Atmospheric Forcing Across the Land-Ocean Boundary

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Little research has gone into studying the concurrent variations in the annual loss of continental snow cover and sea ice extent across the land-ocean boundary, however, the analysis of these data averaged spatially over three study regions located in North America and Eastern and Western Russia, reveals a distinct difference in the response of anomalous snow and sea ice conditions to the atmospheric forcing. This study compares the monthly continental snow cover and sea ice extent loss in the Arctic, during the melt season months (May-August) for the period 1979-2007, with regional atmospheric conditions known to influence summer melt including: mean sea level pressures, 925 hPa air temperatures, and mean 2 m U and V wind vectors from NCEP/DOE Reanalysis 2. The monthly hemispheric snow cover extent data used are from the Rutgers University Global Snow Lab and sea ice extents for this study are derived from the monthly passive microwave satellite Bootstrap algorithm sea ice concentrations available from the National Snow and Ice Data Center. Three case study years (1985, 1996, and 2007) are used to compare the direct response of monthly anomalous sea ice and snow cover areal extents to monthly mean atmospheric forcing averaged spatially over the extent of each study region. This comparison is then expanded for all summer months over the 29 year study period where the monthly persistence of sea ice and snow cover extent anomalies and changes in the sea ice and snow conditions under differing atmospheric conditions are explored further. The monthly anomalous atmospheric conditions are classified into four categories including: warmer temperatures with higher pressures, warmer temperatures with lower pressures, cooler temperatures with higher pressures, and cooler temperatures with lower pressures. Analysis of the atmospheric conditions surrounding anomalous loss of snow and ice cover over the independent study regions indicates that conditions of warmer temperatures

  16. Estimating the time of the melt onset and freeze onset over arctic sea-ice area using satellite active and passive microwave data

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

    Calculating the time of melt onset, freeze onset and melt duration over Arctic sea-ice area is critical for climate and global change studies because they are combined with accuracy of surface energy balance estimates. Our studies compare 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 (Tb) using Drobot and Anderson's (2001) 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 Surface air temperatures (IABP/POLES); 3) an elaborated version of the AHRA that uses IABP/POLES to avoid anomalous results (PMSTA); 4) another elaborated version of the AHRA that uses Tb variance to avoid anomalous results (MDSDA); 5) Smith's (1998) vertically-polarized Tb algorithm for estimating melt onset in multiyear (MY) ice (SSM/I 19V-37V); and 6) analyses of concurrent backscattering cross section (sigma zero) and Tb in MY ice using data from OKEAN. 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 calibrations coefficients and algorithm threshold values. Compared to the PMSTA method, the AHRA method tended to estimated significantly earlier melt dates, likely caused by the AHRA's susceptibility to prematurely identify melt onset conditions. In contrast, the IABP/POLES air surface 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

  17. Simulation of Melting Ice-Phase Precipitation Hydrometeors for Use in Passive and Active Microwave Remote-Sensing Algorithms

    NASA Astrophysics Data System (ADS)

    Johnson, B. T.

    2014-12-01

    The Global Precipitation Measurement (GPM) mission, with active and passive microwave remote-sensing instruments, was designed to be sensitive to precipitation-sized particles. The shape of these 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 the GPM DPR at Ku- and Ka-band. We also compute the top-of-the-atmosphere brightness temperatures at GPM GMI channels for the same vertical profiles, and discuss the sensitivities to variances in the aforementioned physical properties.

  18. Changes in Arctic Melt Season and Implications for Sea Ice Loss

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

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

    PubMed

    Mochizuki, Kenji; Matsumoto, Masakazu; Ohmine, Iwao

    2013-06-20

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  1. Widespread Refreezing of Both Surface and Basal Melt Water Beneath the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Bell, R. E.; Tinto, K. J.; Das, I.; Wolovick, M.; Chu, W.; Creyts, T. T.; Frearson, N.

    2013-12-01

    The isotopically and chemically distinct, bubble-free ice observed along the Greenland Ice Sheet margin both in the Russell Glacier and north of Jacobshavn must have formed when water froze from subglacial networks. Where this refreezing occurs and what impact it has on ice sheet processes remain unclear. We use airborne radar data to demonstrate that freeze-on to the ice sheet base and associated deformation produce large ice units up to 700 m thick throughout northern Greenland. Along the ice sheet margin, in the ablation zone, surface meltwater, delivered via moulins, refreezes to the ice sheet base over rugged topography. In the interior, water melted from the ice sheet base is refrozen and surrounded by folded ice. A significant fraction of the ice sheet is modified by basal freeze-on and associated deformation. For the Eqip and Petermann catchments, representing the ice sheet margin and interior respectively, extensive airborne radar datasets show that 10%-13% of the base of the ice sheet and up to a third of the catchment width is modified by basal freeze-on. The interior units develop over relatively subdued topography with modest water flux from basal melt where conductive cooling likely dominates. Steps in the bed topography associated with subglacial valley networks may foster glaciohydraulic supercooling. The ablation zone units develop where both surface melt and crevassing are widespread and large volumes of surface meltwater will reach the base of the ice sheet. The relatively steep topography at the upslope edge of the ablation zone units combined with the larger water flux suggests that supercooling plays a greater role in their formation. The ice qualities of the ablation zone units should reflect the relatively fresh surface melt whereas the chemistry of the interior units should reflect solute-rich basal melt. Changes in basal conditions such as the presence of till patches may contribute to the formation of the large basal units near the

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

    NASA Astrophysics Data System (ADS)

    Fastook, James L.; Head, James W.

    2015-02-01

    Geological evidence for extensive non-polar ice deposits of Amazonian age indicates that the current cold and dry climate of Mars has persisted for several billion years. The geological record and climate history of the Noachian, the earliest period of Mars history, is less certain, but abundant evidence for fluvial channels (valley networks) and lacustrine environments (open-basin lakes) has been interpreted to represent warm and wet conditions, including rainfall and runoff. Alternatively, recent atmospheric modeling results predict a "cold and icy" Late Noachian Mars in which moderate atmospheric pressure accompanied by a full water cycle produce an atmosphere where temperature declines with elevation following an adiabatic lapse rate, in contrast to the current situation on Mars, where temperature is almost completely determined by latitude. These results are formulated in the Late Noachian Icy Highlands (LNIH) model, in which these cold and icy conditions lead to the preferential deposition of snow and ice at high elevations, such as the southern uplands. What is the fate of this snow and ice and the nature of glaciation in such an environment? What are the prospects of melting of these deposits contributing to the observed fluvial and lacustrine deposits? To address these questions, we report on a glacial flow-modeling analysis using a Mars-adapted ice sheet model with LNIH climate conditions. The total surface/near-surface water inventory is poorly known for the Late Noachian, so we explore the LNIH model in a "supply-limited" scenario for a range of available water abundances and a range of Late Noachian geothermal fluxes. Our results predict that the Late Noachian icy highlands (above an equilibrium line altitude of approximately +1 km) were characterized by extensive ice sheets of the order of hundreds of meters thick. Due to extremely cold conditions, the ice-flow velocities in general were very low, less than a few mm/yr, and the regional ice

  3. Loss of Arctic Snow Cover and Sea Ice Extent Across the Land-Ocean Boundary During the Melt Season

    NASA Astrophysics Data System (ADS)

    Bliss, A.; Anderson, M. R.

    2010-12-01

    Concern over the rapid changes in the Arctic cryosphere in recent years has spurred much research into the response of sea ice and snow cover to warming temperatures and the resulting climate feedbacks. However, the vast majority of Arctic climate studies do not assess the response of both continental snow cover and sea ice in concert through the data record. This study is designed to compare the monthly Northern Hemispheric continental snow cover extent data available from Rutgers University Global Snow Lab and the passive microwave derived monthly Bootstrap algorithm sea ice extent data available from the National Snow and Ice Data Center (NSIDC) in the Arctic during the melt season (March-August) over the 29-year study period 1979-2007. Since these data are stored in incompatible formats, little research has gone into studying the concurrent variations in the annual loss of continental snow cover and sea ice extent across the land-ocean boundary. However, with a creation of a snow and ice extent climate data record (CDR) incorporating different data formats, one would allow analysis of these data to investigate conditions during the melt season. As a CDR example three autonomous study regions located in Siberia, North America, and Western Russia were determined to reveal any differences in the response of snow and sea ice extents during melt. Each study domain extends from over land, northward, into an Arctic marginal sea, containing a land-ocean boundary that is roughly parallel to latitude and is subject to considerable inter-annual variability in the extent and retreat of both snow and sea ice during the warm season. Each domain area was also selected to include a minimal extent of mountainous areas where persistent snow cover throughout the year could misrepresent the seasonal northward progression of snow cover lost, relative to other land domains in the study. The results show on average, sea ice extent is lost earlier in the year, in May, than snow cover

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  5. Ocean heat drives rapid basal melt of the Totten Ice Shelf.

    PubMed

    Rintoul, Stephen Rich; Silvano, Alessandro; Pena-Molino, Beatriz; van Wijk, Esmee; Rosenberg, Mark; Greenbaum, Jamin Stevens; Blankenship, Donald D

    2016-12-01

    Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 10(6) m(3) s(-1) of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level.

  6. Ocean heat drives rapid basal melt of the Totten Ice Shelf

    PubMed Central

    Rintoul, Stephen Rich; Silvano, Alessandro; Pena-Molino, Beatriz; van Wijk, Esmee; Rosenberg, Mark; Greenbaum, Jamin Stevens; Blankenship, Donald D.

    2016-01-01

    Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106 m3 s−1 of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level. PMID:28028540

  7. Ice shelf basal melt rates around Antarctica from simulations and observations

    NASA Astrophysics Data System (ADS)

    Schodlok, M. P.; Menemenlis, D.; Rignot, E. J.

    2016-02-01

    We introduce an explicit representation of Antarctic ice shelf cavities in the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) ocean retrospective analysis; and compare resulting basal melt rates and patterns to independent estimates from satellite observations. Two simulations are carried out: the first is based on the original ECCO2 vertical discretization; the second has higher vertical resolution particularly at the depth range of ice shelf cavities. The original ECCO2 vertical discretization produces higher than observed melt rates and leads to a misrepresentation of Southern Ocean water mass properties and transports. In general, thicker levels at the base of the ice shelves lead to increased melting because of their larger heat capacity. This strengthens horizontal gradients and circulation within and outside the cavities and, in turn, warm water transports from the shelf break to the ice shelves. The simulation with more vertical levels produces basal melt rates (1735 ± 164 Gt/a) and patterns that are in better agreement with observations. Thinner levels in the sub-ice-shelf cavities improve the representation of a fresh/cold layer at the ice shelf base and of warm/salty water near the bottom, leading to a sharper pycnocline and reduced vertical mixing underneath the ice shelf. Improved water column properties lead to more accurate melt rates and patterns, especially for melt/freeze patterns under large cold-water ice shelves. At the 18 km grid spacing of the ECCO2 model configuration, the smaller, warm-water ice shelves cannot be properly represented, with higher than observed melt rates in both simulations.

  8. Melting at the base of the Greenland ice sheet explained by Iceland hotspot history

    NASA Astrophysics Data System (ADS)

    Rogozhina, Irina; Petrunin, Alexey G.; Vaughan, Alan P. M.; Steinberger, Bernhard; Johnson, Jesse V.; Kaban, Mikhail K.; Calov, Reinhard; Rickers, Florian; Thomas, Maik; Koulakov, Ivan

    2016-05-01

    Ice-penetrating radar and ice core drilling have shown that large parts of the north-central Greenland ice sheet are melting from below. It has been argued that basal ice melt is due to the anomalously high geothermal flux that has also influenced the development of the longest ice stream in Greenland. Here we estimate the geothermal flux beneath the Greenland ice sheet and identify a 1,200-km-long and 400-km-wide geothermal anomaly beneath the thick ice cover. We suggest that this anomaly explains the observed melting of the ice sheet’s base, which drives the vigorous subglacial hydrology and controls the position of the head of the enigmatic 750-km-long northeastern Greenland ice stream. Our combined analysis of independent seismic, gravity and tectonic data implies that the geothermal anomaly, which crosses Greenland from west to east, was formed by Greenland’s passage over the Iceland mantle plume between roughly 80 and 35 million years ago. We conclude that the complexity of the present-day subglacial hydrology and dynamic features of the north-central Greenland ice sheet originated in tectonic events that pre-date the onset of glaciation in Greenland by many tens of millions of years.

  9. The effect of basal channels on oceanic ice-shelf melting

    NASA Astrophysics Data System (ADS)

    Millgate, Thomas; Holland, Paul R.; Jenkins, Adrian; Johnson, Helen L.

    2013-12-01

    The presence of ice-shelf basal channels has been noted in a number of Antarctic and Greenland ice shelves, but their impact on basal melting is not fully understood. Here we use the Massachusetts Institute of Technology general circulation model to investigate the effect of ice-shelf basal channels on oceanic melt rate for an idealized ice shelf resembling the floating tongue of Petermann Glacier in Greenland. The introduction of basal channels prevents the formation of a single geostrophically balanced boundary current; instead the flow is diverted up the right-hand (Coriolis-favored) side of each channel, with a return flow in the opposite direction on the left-hand side. As the prescribed number of basal channels is increased the mean basal melt rate decreases, in agreement with previous studies. For a small number of relatively wide channels the subice flow is found to be a largely geostrophic horizontal circulation. The reduction in melt rate is then caused by an increase in the relative contribution of weakly melting channel crests and keels. For a larger number of relatively narrow channels, the subice flow changes to a vertical overturning circulation. This change in circulation results in a weaker sensitivity of melt rates to channel size. The transition between the two regimes is governed by the Rossby radius of deformation. Our results explain why basal channels play an important role in regulating basal melting, increasing the stability of ice shelves.

  10. Warm winds from the Pacific caused extensive Arctic sea-ice melt in summer 2007

    NASA Astrophysics Data System (ADS)

    Graversen, Rune G.; Mauritsen, Thorsten; Drijfhout, Sybren; Tjernström, Michael; Mårtensson, Sebastian

    2011-06-01

    During summer 2007 the Arctic sea-ice shrank to the lowest extent ever observed. The role of the atmospheric energy transport in this extreme melt event is explored using the state-of-the-art ERA-Interim reanalysis data. We find that in summer 2007 there was an anomalous atmospheric flow of warm and humid air into the region that suffered severe melt. This anomaly was larger than during any other year in the data (1989-2008). Convergence of the atmospheric energy transport over this area led to positive anomalies of the downward longwave radiation and turbulent fluxes. In the region that experienced unusual ice melt, the net anomaly of the surface fluxes provided enough extra energy to melt roughly one meter of ice during the melting season. When the ocean successively became ice-free, the surface-albedo decreased causing additional absorption of shortwave radiation, despite the fact that the downwelling solar radiation was smaller than average. We argue that the positive anomalies of net downward longwave radiation and turbulent fluxes played a key role in initiating the 2007 extreme ice melt, whereas the shortwave-radiation changes acted as an amplifying feedback mechanism in response to the melt.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  12. Early 2016 Winter Storm Melts Arctic Sea Ice

    NASA Video Gallery

    Arctic sea ice grows during the winter months, reaching its largest extent sometime in March. When something disrupts the cold, dry, winter Arctic atmosphere, sea ice can feel the effects, and thes...

  13. Enhanced High-Temperature Ice Nucleation Ability of Crystallized Aerosol Particles after Pre-Activation at Low Temperature

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Moehler, O.; Saathoff, H.; Schnaiter, M.

    2014-12-01

    The term pre-activation in heterogeneous ice nucleation describes the observation that the ice nucleation ability of solid ice nuclei may improve after they have already been involved in ice crystal formation or have been exposed to a temperature lower than 235 K. This can be explained by the retention of small ice embryos in cavities or crevices at the particle surface or by the capillary condensation and freezing of supercooled water, respectively. In recent cloud chamber experiments with crystallized aqueous ammonium sulfate, oxalic acid, and succinic acid solution droplets, we have unraveled a further pre-activation mechanism under ice subsaturated conditions which does not require the preceding growth of ice on the seed aerosol particles (Wagner, R. et al., J. Geophys. Res. Atmos., 119, doi: 10.1002/2014JD021741). First cloud expansion experiments were performed at a high temperature (267 - 244 K) where the crystallized particles did not promote any heterogeneous ice nucleation. Ice nucleation at this temperature, however, could be triggered by temporarily cooling the crystallized particles to a lower temperature. This is because upon crystallization, residuals of the aqueous solution are trapped within the crystals. These captured liquids can freeze when cooled below their respective homogeneous or heterogeneous freezing temperature, leading to the formation of ice pockets in the crystalline particles. When warmed again to the higher temperature, ice formation by the pre-activated particles occurred via depositional and deliquescence-induced ice growth, with ice active fractions ranging from 1 to 4% and 4 to 20%, respectively. Pre-activation disappeared above the eutectic temperature, which for the organic acids are close to the melting point of ice. This mechanism could therefore contribute to the very small fraction of atmospheric aerosol particles that are still ice active well above 263 K.

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

    PubMed

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

    2008-01-01

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

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

    PubMed

    Ogawa, Shigesaburo; Asakura, Kouichi; Osanai, Shuichi

    2012-12-21

    Phase transition behavior of lyotropic liquid crystals of an octyl β-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.

  16. Investigating methods to estimate melting event parameters over Arctic sea- ice using SSM/I, OKEAN, and RADARSAT Data

    NASA Astrophysics Data System (ADS)

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

    The melting events (early melt, melt onset, melt ponding, freeze-up onset) over Arctic sea-ice area are critical for climate and global change studies. They are combined with accuracy of surface energy balances estimates (due to contrasts in the short wave albedo of snow and ice, open water or melt ponds) and drives a number of important processes (onset of snow melt, thawing of boreal forest, etc). M icrowave measurements identify seasonal transition zones due to large differences in emissivity during melt onset, melt ponding and freeze-up periods. This report presents near coincident observation of backscatter cross section (0 ) and brightness temperature (Tb) from Russian OKEAN 01 satellite series, backscatter cross section (0) from RADARSAT-1, brightness temperatures (Tbs) from SSM/I sensors, and near-surface temperature derived from the International Arctic Buoy Program data (IABP) (Belchansky and Douglas, 2000, 2002). To determine the melt duration (time of freeze-up onset minus time of melt onset) passive and active microwave methods were developed. These methods used differences between SSM /I 19.3GHz,H and SSM/I 37.0 GHz, H channels (SSM/I Tb), OKEAN 0 (9.52GHz, VV) and Tb (37.47 GHz, H) channels, RADARSAT-1 0 (5.3GHz, HH), and a threshold technique. An evolution of the SSM/I Tb, OKEAN-01 0 and Tb, RADARSAT ScanSAR 0, MEAN ( 0), SD(0) and SD(0 ) / MEAN(0 ) as function of time was investigated along FY and MY dominant type ice areas during January 1996 through December 1998. The SSM/I, OKEAN and RADARSAT melt onset and freeze up onset algorithms were constructed. The SSM/I algorithm was based- on analysis of the SSM/I Tb. The OKEAN and RADARSAT ScanSAR algorithms were based, respectively, on analysis of OKEAN 0 and Tb of MY and FY sea ice at each MY and FY ice region (200 km by 200 km) determined in OKEAN imagery prior to melting period and changes in RADARSAT SD(0 ) / MEAN(0) of sea-ice during different stages of melting processes at each ice site (75 km

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

    NASA Astrophysics Data System (ADS)

    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

    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

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    The interior plateau of northern Baffin Island in the eastern Canadian Arctic is home to several small (< 50 km2) ice caps whose melt has been well recorded since 1949. Modern equilibrium line altitude (ELA) is well above all existing ice and a continuation of current climatic conditions will lead to the disappearance of all ice on the plateau in the future. Between 2000 and 2005, approximately 1 km2 of ice was lost per year, equivalent to ~1.3% of the total ice cover on the plateau. To put this current melt into a larger picture of ice-cap history on the plateau since deglaciation 6 ka, several techniques have been used in concert. The recent extent of the ice caps during the Little Ice Age can be estimated from the preservation of lichen trimlines across much of the plateau. These trimlines represent previous multi-year snow or ice cover and their aerial extent can be measured via satellite imagery. Based on these measurements, modern ice caps represent only ~3% of ice-cap extent during the Little Ice Age. Radiocarbon dating of moss, preserved beneath the ice caps due to their cold-based nature, suggests a sudden expansion of ice cover around 520 calendar years before present (cal BP), indicated by a mode of 7 dates of approximately this age. This coincides with a pulse of global volcanic activity; predicted cooling from increased aerosol loading may have triggered rapid ice-cap growth. However, dead moss emerging at three sites is more than 1000 years old, with a maximum age of 1326±15 cal BP, indicating that portions of the remaining ice caps have remained intact from more than 1000 years Further constraints on ice cap size are provided by 14C cosmogenic exposure dating. 14C concentrations in rocks at the modern ice margin are too low to be the result of continuous exposure since deglaciation followed by shielding for 500-1000 years by ice cover. Exposure history modeling indicates at least one additional prior period of ice cover of approximately 1000 years

  3. Modeling of ocean-induced ice melt rates of five west Greenland glaciers over the past two decades

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Xu, Y.; Menemenlis, D.; Mouginot, J.; Scheuchl, B.; Li, X.; Morlighem, M.; Seroussi, H.; den Broeke, M. van; Fenty, I.; Cai, C.; An, L.; Fleurian, B. de

    2016-06-01

    High-resolution, three-dimensional simulations from the Massachusetts Institute of Technology general circulation model ocean model are used to calculate the subaqueous melt rate of the calving faces of Umiamako, Rinks, Kangerdlugssup, Store, and Kangilerngata glaciers, west Greenland, from 1992 to 2015. Model forcing is from monthly reconstructions of ocean state and ice sheet runoff. Results are analyzed in combination with observations of bathymetry, bed elevation, ice front retreat, and glacier speed. We calculate that subaqueous melt rates are 2-3 times larger in summer compared to winter and doubled in magnitude since the 1990s due to enhanced subglacial runoff and 1.6 ± 0.3°C warmer ocean temperature. Umiamako and Kangilerngata retreated rapidly in the 2000s when subaqueous melt rates exceeded the calving rates and ice front retreated to deeper bed elevation. In contrast, Store, Kangerdlugssup, and Rinks have remained stable because their subaqueous melt rates are 3-4 times lower than their calving rates, i.e., the glaciers are dominated by calving processes.

  4. Energy harvesting in pavement from passing vehicles with piezoelectric composite plate for ice melting

    NASA Astrophysics Data System (ADS)

    Faisal, Farjana; Wu, Nan; Kapoor, Kartik

    2016-04-01

    An energy harvester in the road pavement made from a piezoelectric composite plate is designed and studied to collect energy from the passing vehicles for the ice melting aim. Piezoelectric material has the ability to produce electric charge on its surface when strain takes place due to any external loading. Based on this property, a rectangular composite plate harvester is developed consisting of piezoelectric material as the energy generation coating layer and A514 steel as the substrate layer to realize the energy harvesting process from the variable pressure generated in the road pavement by passing vehicles. Based on Westergaards stress model, a numerical model is developed to calculate the three dimensional stress distribution in the pavement. Numerical simulations are conducted to study the optimization of various parameters of the harvester, such as depth of the harvester in the pavement, length and width as well as thicknesses of piezoelectric layer and the substrate. By taking in to consideration the maximum stress that can be sustained by both of the piezoelectric material and also the substrate material, an optimum design of the piezoelectric couple composite plate energy harvester is suggested. It is seen that the maximum output power, which can be generated by a single patch of 0.2m*0.2m*0.0026m dimension with a vehicle passing at 22.2 m/s, can reach up to 23.36 W. With the well-designed pavement energy harvesters, it is feasible to collect enough energy to rise the temperature of the ice with the thickness of 1cm covering a 5m width road by 20 degree Celsius within 2.5 hours. This technique can be applied to melt the ice on the roads and bridges especially in cold countries.

  5. Mechanisms and implications of α-HCH enrichment in melt pond water on Arctic sea ice.

    PubMed

    Pućko, M; Stern, G A; Barber, D G; Macdonald, R W; Warner, K-A; Fuchs, C

    2012-11-06

    During the summer of 2009, we sampled 14 partially refrozen melt ponds and the top 1 m of old ice in the pond vicinity for α-hexachlorocyclohexane (α-HCH) concentrations and enantiomer fractions (EFs) in the Beaufort Sea. α-HCH concentrations were 3 - 9 times higher in melt ponds than in the old ice. We identify two routes of α-HCH enrichment in the ice over the summer. First, atmospheric gas deposition results in an increase of α-HCH concentration from 0.07 ± 0.02 ng/L (old ice) to 0.34 ± 0.08 ng/L, or ~20% less than the atmosphere-water equilibrium partitioning concentration (0.43 ng/L). Second, late-season ice permeability and/or complete ice thawing at the bottom of ponds permit α-HCH rich seawater (~0.88 ng/L) to replenish pond water, bringing concentrations up to 0.75 ± 0.06 ng/L. α-HCH pond enrichment may lead to substantial concentration patchiness in old ice floes, and changed exposures to biota as the surface meltwater eventually reaches the ocean through various drainage mechanisms. Melt pond concentrations of α-HCH were relatively high prior to the late 1980-s, with a Melt pond Enrichment Factor >1 (MEF; a ratio of concentration in surface meltwater to surface seawater), providing for the potential of increased biological exposures.

  6. Temperature dependence of crystal growth of hexagonal ice (I(h)).

    PubMed

    Rozmanov, Dmitri; Kusalik, Peter G

    2011-09-14

    The transformations between water and ice have many implications across numerous fields of study. A better understanding of this process would benefit many areas of science and technology such as medicine, biology, and atmospheric and material sciences. In the present work the temperature dependence of the rate of growth (melting) of the basal face of hexagonal ice I(h) and the effect of system size are investigated in molecular dynamics simulations. Using an effective pair potential model of water, systems are studied over temperatures ranging from T(M) - 40 to T(M) + 16 K, where T(M) is the melting temperature of the model. It is found that the growth rates reach a maximum value of 0.7 Å ns(-1) (7 cm s(-1)) at about 12 K below the melting temperature. A noticeable effect of the system size on the melting temperature and ice growth rates is observed; it is shown that the size effect arises in smaller systems due to the artificial ordering under periodic conditions. The decrease in melting entropy in the smallest system by 0.4 J (mol K)(-1) relative to the largest system results in an up-shift in the melting temperature by about 2 K. An almost 60% increase in the maximum growth rate is observed for the smallest system.

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

    SciTech Connect

    Hwang, Yong Seok; Levitas, Valery I.

    2014-06-30

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

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Macayeal, D. R.

    1984-01-01

    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.

  10. Monitoring southwest Greenland's ice sheet melt with ambient seismic noise.

    PubMed

    Mordret, Aurélien; Mikesell, T Dylan; Harig, Christopher; Lipovsky, Bradley P; Prieto, Germán A

    2016-05-01

    The Greenland ice sheet presently accounts for ~70% of global ice sheet mass loss. Because this mass loss is associated with sea-level rise at a rate of 0.7 mm/year, the development of improved monitoring techniques to observe ongoing changes in ice sheet mass balance is of paramount concern. Spaceborne mass balance techniques are commonly used; however, they are inadequate for many purposes because of their low spatial and/or temporal resolution. We demonstrate that small variations in seismic wave speed in Earth's crust, as measured with the correlation of seismic noise, may be used to infer seasonal ice sheet mass balance. Seasonal loading and unloading of glacial mass induces strain in the crust, and these strains then result in seismic velocity changes due to poroelastic processes. Our method provides a new and independent way of monitoring (in near real time) ice sheet mass balance, yielding new constraints on ice sheet evolution and its contribution to global sea-level changes. An increased number of seismic stations in the vicinity of ice sheets will enhance our ability to create detailed space-time records of ice mass variations.

  11. Export of algal biomass from the melting Arctic sea ice.

    PubMed

    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

    2013-03-22

    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.

  12. Methane excess in Arctic surface water-triggered by sea ice formation and melting.

    PubMed

    Damm, E; Rudels, B; Schauer, U; Mau, S; Dieckmann, G

    2015-11-10

    Arctic amplification of global warming has led to increased summer sea ice retreat, which influences gas exchange between the Arctic Ocean and the atmosphere where sea ice previously acted as a physical barrier. Indeed, recently observed enhanced atmospheric methane concentrations in Arctic regions with fractional sea-ice cover point to unexpected feedbacks in cycling of methane. We report on methane excess in sea ice-influenced water masses in the interior Arctic Ocean and provide evidence that sea ice is a potential source. We show that methane release from sea ice into the ocean occurs via brine drainage during freezing and melting i.e. in winter and spring. In summer under a fractional sea ice cover, reduced turbulence restricts gas transfer, then seawater acts as buffer in which methane remains entrained. However, in autumn and winter surface convection initiates pronounced efflux of methane from the ice covered ocean to the atmosphere. Our results demonstrate that sea ice-sourced methane cycles seasonally between sea ice, sea-ice-influenced seawater and the atmosphere, while the deeper ocean remains decoupled. Freshening due to summer sea ice retreat will enhance this decoupling, which restricts the capacity of the deeper Arctic Ocean to act as a sink for this greenhouse gas.

  13. Methane excess in Arctic surface water- triggered by sea ice formation and melting

    PubMed Central

    Damm, E.; Rudels, B.; Schauer, U.; Mau, S.; Dieckmann, G.

    2015-01-01

    Arctic amplification of global warming has led to increased summer sea ice retreat, which influences gas exchange between the Arctic Ocean and the atmosphere where sea ice previously acted as a physical barrier. Indeed, recently observed enhanced atmospheric methane concentrations in Arctic regions with fractional sea-ice cover point to unexpected feedbacks in cycling of methane. We report on methane excess in sea ice-influenced water masses in the interior Arctic Ocean and provide evidence that sea ice is a potential source. We show that methane release from sea ice into the ocean occurs via brine drainage during freezing and melting i.e. in winter and spring. In summer under a fractional sea ice cover, reduced turbulence restricts gas transfer, then seawater acts as buffer in which methane remains entrained. However, in autumn and winter surface convection initiates pronounced efflux of methane from the ice covered ocean to the atmosphere. Our results demonstrate that sea ice-sourced methane cycles seasonally between sea ice, sea-ice-influenced seawater and the atmosphere, while the deeper ocean remains decoupled. Freshening due to summer sea ice retreat will enhance this decoupling, which restricts the capacity of the deeper Arctic Ocean to act as a sink for this greenhouse gas. PMID:26553610

  14. Response of a Coupled Ocean-Atmosphere Model to Greenland Ice Melting

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    We investigate the transient response of the global coupled ocean-atmosphere system to enhanced freshwater forcing representative of melting of the Greenland ice sheets. A 50-year long simulation by a coupled atmosphere-ocean general circulation model (CGCM) is compared with another of the same length in which Greenland melting is prescribed. To highlight the importance of coupled atmosphere-ocean processes, the CGCM results are compared with those of two other experiments carried out with the oceanic general circulation model (OGCM). In one of these OGCM experiments, the prescribed surface fluxes of heat, momentum and freshwater correspond to the unperturbed simulation by the CGCM; in the other experiment, Greenland melting is added to the freshwater flux. The responses by the CGCM and OGCM to the Greenland melting have similar patterns in the Atlantic, albeit the former having five times larger amplitudes in sea surface height anomalies. The CGCM shows likewise stronger variability in all state variables in all ocean basins because the impact of Greenland melting is quickly communicated to all ocean basins via atmospheric bridges. We conclude that the response of the global climate to Greenland ice melting is highly dependent on coupled atmosphere-ocean processes. These lead to reduced latent heat flux into the atmosphere and an associated increase in net freshwater flux into the ocean, especially in the subpolar North Atlantic. The combined result is a stronger response of the coupled system to Greenland ice sheet melting.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  17. Physical Mechanisms Controlling Interannual and Seasonal Variations in Melt Pond Evolution on First-Year Sea Ice in the Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Landy, J.; Ehn, J. K.; Shields, M.; Barber, D. G.

    2014-12-01

    At the transition between spring and summer, melt ponds form and evolve at the surface of Arctic sea ice, significantly modifying energy exchanges between the ice, atmosphere and ocean. Past observations have demonstrated that the fractional coverage of melt ponds on Arctic sea ice can vary widely over the course of a melt season, between years in the same location, and between regions. Here we present two years of melt pond observations from landfast, first-year sea ice in the Canadian Arctic, and analyze which physical mechanisms were responsible for considerable interannual variations in melt pond coverage. In general, the key factors affecting pond coverage were: (1) premelt surface topography, (2) the number of drainage features in the ice and locations of drainage channels, (3) the evolution of ice temperature, and (4) the surface energy balance. Terrestrial LiDAR measurements showed that the premelt topography was rougher in 2011 than in 2012, which led to interannual variations in maximum pond coverage and hydraulic head of 20 pp and 7 cm, respectively. 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. The LiDAR measurements also demonstrated that premelt topography was modified due to preferential melting under meltwater drainage channels. Some melt ponds in areas of low-lying premelt topography were unexpectedly drained as the ponds became elevated above deepening channels. Although the sea ice cover was 0.35 m thinner in 2012 than in 2011, ice interior temperatures remained colder later into June, delaying a transition in ice permeability that would allow vertical meltwater drainage from ponds. This permeability transition was observed in 2011 and contributed to a significant drop in pond coverage. For more information see: Landy, J., J. Ehn, M. Shields, and D. Barber (2014), Surface and melt pond evolution on landfast first-year sea ice in the

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

    PubMed

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

    2013-09-13

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

  19. Sea ice melt onset associated with lead opening during the spring/summer transition near the North Pole

    NASA Astrophysics Data System (ADS)

    Vivier, Frédéric; Hutchings, Jennifer K.; Kawaguchi, Yusuke; Kikuchi, Takashi; Morison, James H.; Lourenço, Antonio; Noguchi, Tomohide

    2016-04-01

    In the central Arctic Ocean, autonomous observations of the ocean mixed layer and ice documented the transition from cold spring to early summer in 2011. Ice-motion measurements using GPS drifters captured three events of lead opening and ice ridge formation in May and June. Satellite sea ice concentration observations suggest that locally observed lead openings were part of a larger-scale pattern. We clarify how these ice deformation events are linked with the onset of basal sea ice melt, which preceded surface melt by 20 days. Observed basal melt and ocean warming are consistent with the available input of solar radiation into leads, once the advent of mild atmospheric conditions prevents lead refreezing. We use a one-dimensional numerical simulation incorporating a Local Turbulence Closure scheme to investigate the mechanisms controlling basal melt and upper ocean warming. According to the simulation, a combination of rapid ice motion and increased solar energy input at leads promotes basal ice melt, through enhanced mixing in the upper mixed layer, while slow ice motion during a large lead opening in mid-June produced a thin, low-density surface layer. This enhanced stratification near the surface facilitates storage of solar radiation within the thin layer, instead of exchange with deeper layers, leading to further basal ice melt preceding the upper surface melt.

  20. Temperature dependence of ice-on-rock friction at realistic glacier conditions.

    PubMed

    McCarthy, C; Savage, H; Nettles, M

    2017-02-13

    Using a new biaxial friction apparatus, we conducted experiments of ice-on-rock friction in order to better understand basal sliding of glaciers and ice streams. A series of velocity-stepping and slide-hold-slide tests were conducted to measure friction and healing at temperatures between -20°C and melting. Experimental conditions in this study are comparable to subglacial temperatures, sliding rates and effective pressures of Antarctic ice streams and other glaciers, with load-point velocities ranging from 0.5 to 100 µm s(-1) and normal stress σn = 100 kPa. In this range of conditions, temperature dependences of both steady-state friction and frictional healing are considerable. The friction increases linearly with decreasing temperature (temperature weakening) from μ = 0.52 at -20°C to μ = 0.02 at melting. Frictional healing increases and velocity dependence shifts from velocity-strengthening to velocity-weakening behaviour with decreasing temperature. Our results indicate that the strength and stability of glaciers and ice streams may change considerably over the range of temperatures typically found at the ice-bed interface.This article is part of the themed issue 'Microdynamics of ice'.

  1. Temperature dependence of ice-on-rock friction at realistic glacier conditions

    NASA Astrophysics Data System (ADS)

    McCarthy, C.; Savage, H.; Nettles, M.

    2017-02-01

    Using a new biaxial friction apparatus, we conducted experiments of ice-on-rock friction in order to better understand basal sliding of glaciers and ice streams. A series of velocity-stepping and slide-hold-slide tests were conducted to measure friction and healing at temperatures between -20°C and melting. Experimental conditions in this study are comparable to subglacial temperatures, sliding rates and effective pressures of Antarctic ice streams and other glaciers, with load-point velocities ranging from 0.5 to 100 µm s-1 and normal stress σn = 100 kPa. In this range of conditions, temperature dependences of both steady-state friction and frictional healing are considerable. The friction increases linearly with decreasing temperature (temperature weakening) from μ = 0.52 at -20°C to μ = 0.02 at melting. Frictional healing increases and velocity dependence shifts from velocity-strengthening to velocity-weakening behaviour with decreasing temperature. Our results indicate that the strength and stability of glaciers and ice streams may change considerably over the range of temperatures typically found at the ice-bed interface. This article is part of the themed issue 'Microdynamics of ice'.

  2. Method For Synthesizing Extremely High-Temperature Melting Materials

    DOEpatents

    Saboungi, Marie-Louise; Glorieux, Benoit

    2005-11-22

    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.

  3. Method for synthesizing extremely high-temperature melting materials

    DOEpatents

    Saboungi, Marie-Louise; Glorieux, Benoit

    2007-11-06

    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.

  4. Method for Synthesizing Extremeley High Temperature Melting Materials

    DOEpatents

    Saboungi, Marie-Louise and Glorieux, Benoit

    2005-11-22

    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.

  5. Melting West Antarctic ice-shelves: role of coastal warming versus changes in cavity geometries

    NASA Astrophysics Data System (ADS)

    Jourdain, Nicolas; Mathiot, Pierre; Durand, Gael; Le Sommer, Julien; Spence, Paul

    2015-04-01

    The mass loss of West Antarctic glaciers has accelerated over the last 15 years, most likely in response to ocean warming in Antarctic coastal waters. This oceanic warming in Antarctic coastal waters has recently been suggested to be caused by the positive trend of the Southern Annular Mode. But the mechanisms controlling he changes in melt rates underneath outlet glaciers are still poorly understood. For instance, despite recent developments in glacier modeling, melt rates are usually prescribed in glacier models. This strongly limits the ability of glacier models to predict the future evolution of West Antarctic glaciers. Several ocean models are now able to simulate ocean circulation beneath ice-shelves, therefore allowing a direct study of the mechanisms controlling the changes in melting rates underneath outlet glaciers. Building upon these developments, we here investigate the relative influence of ocean warming in coastal waters and changes in ice-shelves cavern geometries on melting rates underneath West Antarctic glaciers. To this purpose, we use a regional ocean/sea-ice model configuration based on NEMO, centered on the Admundsen sea, that explicitly represents flows in ice-shelves cavities. A series of sensitivity experiments is conducted with different cavern geometries and under different atmospheric forcing scenarios in order to identify the leading mechanism controlling the changes in melt rates underneath West Antarctic glaciers over the 21st century. Our results provide a first assessment on the importance of coupling glacier models to ocean models for predicting the future evolution of outlet glaciers.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    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

  8. Melt anomalies on the Greenland Ice Sheet and large scale modes of atmospheric circulation

    NASA Astrophysics Data System (ADS)

    Huff, Russell

    The relationships between inter annual melt variability in Greenland and large scale atmospheric circulation are explored based on an empirical orthogonal function (EOF) analysis of melt in Greenland derived from passive microwave satellite observations. The first EOF of the melt anomalies was found to be highly representative of the spatial and temporal distribution of melt anomalies accounting for over 34% of the variability and the principal component (PC) time series is 98% correlated with the annual total melt extent time series. The leading melt PC is highly correlated with key features of the large scale atmospheric circulation both in the vicinity of Greenland and regions that are well removed. Some aspects of the atmospheric pressure anomaly fields related to melt in Greenland are congruent with the summer expression of the AO/NAO including the main center of action east of Greenland, however there are features of the melt related anomaly field that are not. During peak melt years there is a decrease in the pressure gradient between the Bearing Sea and more southerly latitudes resulting in a redistribution of the central Arctic low pressure toward the Pacific side of the Arctic basin. This pattern is expressed as a 50% correlation between melt in Greenland and the phase of planetary pressure wave #1 and #2 north of 50° N. The storm tracks related to increased melt in Greenland result in increased summer storm activity to the south and west of Greenland balanced by decreased cyclonic activity to the east and north. Comparison with the NAO related storm track highlights key differences relative to the melt related atmospheric circulation that lead to increased southerly flow directly into Greenland during years with increased melt. The pattern of summer sea ice concentration anomalies linked to the melt PC is remarkably similar to the spatial pattern of recent sea ice decline. The pattern of circulation anomalies associated with increased melt in Greenland

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

    PubMed

    English, Niall J

    2014-12-21

    Ice crystallisation and melting was studied via massively parallel molecular dynamics under periodic boundary conditions, using approximately spherical ice nano-particles (both "isolated" and as a series of heterogeneous "seeds") of varying size, surrounded by liquid water and at a variety of temperatures. These studies were performed for a series of systems ranging in size from ∼1 × 10(6) to 8.6 × 10(6) molecules, in order to establish system-size effects upon the nano-clusters" crystallisation and dissociation kinetics. Both "traditional" four-site and "single-site" and water models were used, with and without formal point charges, dipoles, and electrostatics, respectively. Simulations were carried out in the microcanonical and isothermal-isobaric ensembles, to assess the influence of "artificial" thermo- and baro-statting, and important disparities were observed, which declined upon using larger systems. It was found that there was a dependence upon system size for both ice growth and dissociation, in that larger systems favoured slower growth and more rapid melting, given the lower extent of "communication" of ice nano-crystallites with their periodic replicae in neighbouring boxes. Although the single-site model exhibited less variation with system size vis-à-vis the multiple-site representation with explicit electrostatics, its crystallisation-dissociation kinetics was artificially fast.

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

    NASA Astrophysics Data System (ADS)

    English, Niall J.

    2014-12-01

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

  11. Increased Arctic sea ice volume after anomalously low melting in 2013

    NASA Astrophysics Data System (ADS)

    Tilling, Rachel L.; Ridout, Andy; Shepherd, Andrew; Wingham, Duncan J.

    2015-08-01

    Changes in Arctic sea ice volume affect regional heat and freshwater budgets and patterns of atmospheric circulation at lower latitudes. Despite a well-documented decline in summer Arctic sea ice extent by about 40% since the late 1970s, it has been difficult to quantify trends in sea ice volume because detailed thickness observations have been lacking. Here we present an assessment of the changes in Northern Hemisphere sea ice thickness and volume using five years of CryoSat-2 measurements. Between autumn 2010 and 2012, there was a 14% reduction in Arctic sea ice volume, in keeping with the long-term decline in extent. However, we observe 33% and 25% more ice in autumn 2013 and 2014, respectively, relative to the 2010-2012 seasonal mean, which offset earlier losses. This increase was caused by the retention of thick sea ice northwest of Greenland during 2013 which, in turn, was associated with a 5% drop in the number of days on which melting occurred--conditions more typical of the late 1990s. In contrast, springtime Arctic sea ice volume has remained stable. The sharp increase in sea ice volume after just one cool summer suggests that Arctic sea ice may be more resilient than has been previously considered.

  12. EOS Aqua AMSR-E Arctic Sea Ice Validation Program: Intercomparison Between Modeled and Measured Sea Ice Brightness Temperatures

    NASA Technical Reports Server (NTRS)

    Stroeve, J.; Markus, T.; Cavalieri, D. J.; Maslanik, J.; Sturm, M.; Henrichs, J.; Gasiewski, A.; Klein, M.

    2004-01-01

    During March 2003, an extensive field campaign was conducted near Barrow, Alaska to validate AQUA Advanced Microwave Scanning Radiometer (AMSR) sea ice products. Field, airborne and satellite data were collected over three different types of sea ice: 1) first year ice with little deformation, 2) first year ice with various amounts of deformation and 3) mixed first year ice and multi-year ice with various degrees of deformation. The validation plan relies primarily on comparisons between satellite, aircraft flights and ground-based measurements. Although these efforts are important, key aspects such as the effects of atmospheric conditions, snow properties, surface roughness, melt processes, etc on the sea ice algorithms are not sufficiently well understood or documented. To improve our understanding of these effects, we combined the detailed, in-situ data collection from the 2003 field campaign with radiance modeling using a radiative transfer model to simulate the top of the atmosphere AMSR brightness temperatures. This study reports on the results of the simulations for a variety of snow and ice types and compares the results with the National Oceanographic and Atmospheric Administration Environmental Technology Laboratory Polarimetric Scanning Radiometer (NOAA) (ETL) (PSR) microwave radiometer that was flown on the NASA P-3.

  13. Melting Arctic Sea Ice Dries the American West

    NASA Astrophysics Data System (ADS)

    Sewall, J. O.; Sloan, L. C.

    2003-12-01

    Over the last century, Arctic sea ice cover has decreased dramatically and many researchers expect that future greenhouse warming will exacerbate this trend. The prospect of a warmer Arctic with less ice raises many environmental and economic questions, one of which is: How will reduced Arctic ice cover effect extrapolar climates? Using the fully coupled NCAR CCSM we completed a multi-century simulation of global climate responses to reduced Arctic sea ice cover. While the global average climate response is muted, regional responses to the imposed forcing are significant. One of the more striking regional responses is a shift in storm tracks that drives a 50-100% increase in annual evaporation minus precipitation over the American West, a region where limited water resources are already a significant problem. This result highlights two well-known aspects of climate change: (1) relatively small global changes can be composed of significant regional changes and (2) changes in one region can have a large impact on distant locations. Both of these facts will become increasingly important as researchers and policy makers attempt to untangle the looming thicket of climate change impacts and feedbacks.

  14. Direct Observations of Melt-Water Lake Drainage and the Establishment of an Efficient Surface to Basal Water Connection on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Das, S. B.; Joughin, I.; Behn, M. D.; Howat, I.; King, M. A.; Lizarralde, D.; Bhatia, M. P.

    2007-12-01

    Melt water lakes are recurrent features on the surface of the Greenland Ice Sheet margin that collect a large fraction of the annual surface melt across the ablation region. Many of these lakes fill and drain seasonally and are hypothesized to be a significant source of surface melt water to the ice sheet bed. We present results from field campaigns during the summers of 2006 and 2007 to investigate the filling and draining of two lakes, and the dynamic response of the ice sheet to drainage events. Measurements include air temperature, lake-water level, seismicity and local ice motion. One of the instrumented lakes was observed to be actively discharging water through a meltwater-cut channel in the side of the lake basin, which followed a deeply incised (5-10 m) supraglacial stream for nearly a kilometer before cascading into a moulin. The second instrumented lake drained catastrophically through a series of fractures and moulins that opened beneath the lake and that were subsequently mapped in the field following drainage. At this site, the 2.7-km-diameter lake, holding on the order of 0.03 km3 of water, drained entirely through 1 km of ice thickness in less than 2 hours. The peak rate of water flow during this event exceeds the average flow over Niagara Falls. This drainage event coincided with increased seismicity as well as rapid glacier uplift (1.2 m) and horizontal acceleration to nearly 8 km/yr as measured on the ice surface near the lake shoreline. Subsequent subsidence and deceleration of the ice sheet occurred over the following 24 hours. These observations provide evidence for the injection of surface melt water directly to the ice sheet bed, and also indicate the presence of an efficient basal drainage system that can quickly disperse large inputs of surface melt water.

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

    PubMed Central

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

    2012-01-01

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

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

    PubMed

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

    2012-12-07

    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.

  17. Effect of Frozen Storage Temperature on the Quality of Premium Ice Cream.

    PubMed

    Park, Sung Hee; Jo, Yeon-Ji; Chun, Ji-Yeon; Hong, Geun-Pyo; Davaatseren, Munkhtugs; Choi, Mi-Jung

    2015-01-01

    The market sales of premium ice cream have paralleled the growth in consumer desire for rich flavor and taste. Storage temperature is a major consideration in preserving the quality attributes of premium ice cream products for both the manufacturer and retailers during prolonged storage. We investigated the effect of storage temperature (-18℃, -30℃, -50℃, and -70℃) and storage times, up to 52 wk, on the quality attributes of premium ice cream. Quality attributes tested included ice crystal size, air cell size, melting resistance, and color. Ice crystal size increased from 40.3 μm to 100.1 μm after 52 wk of storage at -18℃. When ice cream samples were stored at -50℃ or -70℃, ice crystal size slightly increased from 40.3 μm to 57-58 μm. Initial air cell size increased from 37.1 μm to 87.7 μm after storage at -18℃ for 52 wk. However, for storage temperatures of -50℃ and -70℃, air cell size increased only slightly from 37.1 μm to 46-47 μm. Low storage temperature (-50℃ and -70℃) resulted in better melt resistance and minimized color changes in comparison to high temperature storage (-18℃ and -30℃). In our study, quality changes in premium ice cream were gradually minimized according to decrease in storage temperature up to-50℃. No significant beneficial effect of -70℃ storage was found in quality attributes. In the scope of our experiment, we recommend a storage temperature of -50℃ to preserve the quality attributes of premium ice cream.

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

    PubMed

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

    2014-09-29

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

  19. Austral Summer Sea Ice Melt Revealed in Antarctic ERS-1/2 and NSCAT Scatterometer Data

    NASA Technical Reports Server (NTRS)

    Drinkwater, M.; Liu, X.

    1999-01-01

    The first in-situ field observations of Antarcic austral summer sea-ice melt were made in the Bellingshausen Sea by Arctowski (1908) on Belgica in 1899, and later by Wordie (1921) during the ill-fated drift of Endurance in the Weddell Sea from 1914-1916.

  20. Modeling the Temperature Fields of Copper Powder Melting in the Process of Selective Laser Melting

    NASA Astrophysics Data System (ADS)

    Saprykin, A. A.; Ibragimov, E. A.; Babakova, E. V.

    2016-08-01

    Various process variables influence on the quality of the end product when SLM (Selective Laser Melting) synthesizing items of powder materials. The authors of the paper suggest using the model of distributing the temperature fields when forming single tracks and layers of copper powder PMS-1. Relying on the results of modeling it is proposed to reduce melting of powder particles out of the scanning area.

  1. Ionic conductivity measurements of H2O ice at high pressure and temperature and superionic ice in the mantle of ice giants

    NASA Astrophysics Data System (ADS)

    Sugimura, E.; Komabayashi, T.; Ohta, K.; Hirose, K.; Sata, N.; Ohishi, Y.; Shimizu, K.; Dubrovinsky, L. S.

    2011-12-01

    The experimental evidence for the superionic conduction in H2O ice at high pressure (P) and temperature (T) has been long-searched since its theoretical prediction. Melting experiments reported a steep rise of the melting curve at P-T range of 35-43 GP and 1000-1600 K, which could be due to a first-order phase transition in the solid phases, namely the presence of the triple point of water, ice VII, and a high-T phase which was assumed superionic. Nonetheless, there has still been no report on direct experimental evidence for superionic conduction (ca. 0.1 S/cm) in ice at high pressure. Here we examined ionic conductivity and isothermal molar volume of ice at high-P-T based on impedance spectroscopy (IS) and x-ray diffraction measurements in an externally-resistive heated diamond anvil cell. In situ IS measurements up to 62 GPa and 920 K demonstrated that ice exhibits superionic conduction (> 0.1 S/cm) above 580-720 K at 20-60 GPa. This suggests that superionic conduction occurs at sufficiently lower P-T than the triple point. Isothermal P-V data collected at P = 33-101 GPa and T = 873 K revealed that an anomalous volume reduction occurs at P = 50-53 GPa. This compression manner corresponds to the previously reported highly compressible regime at P = 40-60 GPa, T = 300 K, which were attributed to hydrogen bond symmetrization. There is no volume discontinuity in the isothermal compression, which contradicts the proposed first order P-T boundary between ice VII and superionic ice. Furthermore, all the conductivity data is expressed by a single Arrhenius equation so that the superionic conduction occurs regardless of the ongoing hydrogen bond symmetrization upon compression. We suggests that the previously reported steep rise of the melting temperature of ice above 35-43 GPa is independent of superionic transition, and is a consequence of the hydrogen bond symmetrization. Combining above results with the existing planetary isentropes, superionic conduction in H2O ice

  2. Aragonite undersaturation in the Arctic Ocean: effects of ocean acidification and sea ice melt.

    PubMed

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

    2009-11-20

    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 to be a direct consequence of the recent extensive melting of sea ice in the Canada Basin. In addition, the retreat of the ice edge well past the shelf-break has produced conditions favorable to enhanced upwelling of subsurface, aragonite-undersaturated water onto the Arctic continental shelf. Undersaturation will affect both planktonic and benthic calcifying biota and therefore the composition of the Arctic ecosystem.

  3. Radar-Inference of the Basal Properties and Englacial Temperature of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Bamber, J. L.; Jordan, T.; Williams, C.; Paden, J. D.; Siegert, M. J.

    2015-12-01

    Measurements of the basal properties (primarily the presence of basal melting, and bed roughness) are important for defining the lower boundary condition for thermomechanical models of ice sheets. Additionally, constraining the englacial temperature provides a test of the steady state solution of such models. Whilst direct measurements of the basal properties and temperature can only be made at a limited number of borehole sights, radio echo sounding provides a means to infer the spatial distribution of both throughout entire ice sheets. The radar-inference of basal melt is possible due to a wet basal interface having a ~10-15 decibel higher reflection coefficient than an ice-bedrock interface, and the radar-inference of englacial temperature is possible due to there being an exponential Arrhenius relationship with the radar attenuation rate. In our study we use ~10 years of radio echo sounding data to map the spatial distribution of basal melt and depth-averaged temperature for the Greenland ice sheet. A necessary precursor to our investigation has been the development of a refined algorithm to infer the radar attention rate using the variation in bed-returned power with ice thickness. The algorithm is conditioned using a prior Arrhenius model calculation of the attenuation rate, and enables sample regions to be selected that are not significantly biased by an inhomogeneous bed. We demonstrate that, for the first time, this algorithm approaches the necessary accuracy to distinguish basal melt directly, with the uncertainty for the radar-inferred attenuation loss less than the decibel separation in reflection coefficients for wet and dry beds. We further cross-validate our method by using the radar-inferred attenuation loss as a constraint to predict the spatial distribution of geothermal heat flux, and to reconstruct temperature profiles that are closer to borehole measurements than zeroth order thermomechanical ice sheet models.

  4. Surface and basal sea ice melt from autonomous buoy arrays during the 2014 sea ice retreat in the Beaufort/Chukchi Seas

    NASA Astrophysics Data System (ADS)

    Maksym, T. L.; Wilkinson, J.; Hwang, P. B.

    2014-12-01

    As the Arctic continues its transition to a seasonal ice cover, the nature and role of the processes driving sea ice retreat are expected to change. Key questions revolve around how the coupling between dynamics and thermodynamic processes and potential changes in the role of melt ponds contribute to an accelerated seasonal ice retreat. To address these issues, 44 autonomous platforms were deployed in four arrays in the Beaufort Sea in March, 2014, with an additional array deployed in August in the Chukchi Sea to monitor the evolution of ice conditions during the seasonal sea ice retreat. Each "5-dice" array included four or five co-sited ice mass balance buoys (IMB) and wave buoys with digital cameras, and one automatic weather station (AWS) at the array center. The sensors on these buoys, combined with satellite imagery monitoring the large-scale evolution of the ice cover, provide a near-complete history of the processes involved in the seasonal melt of sea ice. We present a preliminary analysis of the contributions of several key processes to the seasonal ice decay. The evolution of surface ponding was observed at several sites with differing ice types and surface morphologies. The records of surface melt and ice thickness demonstrate a key role of ice type in driving the evolution of the ice cover. Analysis of the surface forcing and estimates of solar energy partitioning between the surface and upper ocean is compared to the surface and basal mass balance from the IMBs. The role of ice divergence and deformation in driving sea ice decay - in particular its role in accelerating thermodynamic melt processes - is discussed.

  5. Low melting temperature alloy deployment mechanism and recent experiments

    NASA Technical Reports Server (NTRS)

    Madden, M. J.

    1993-01-01

    This paper describes the concept of a low melting temperature alloy deployment mechanism, U.S. Patent 4,842,106. It begins with a brief history of conventional dimethyl-silicone fluid damped mechanisms. Design fundamentals of the new melting alloy mechanism are then introduced. Benefits of the new over the old are compared and contrasted. Recent experiments and lessons learned complete this paper.

  6. Substrate effect on the melting temperature of thin polyethylenefilms

    SciTech Connect

    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

    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.

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

    USGS Publications Warehouse

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

    2004-01-01

    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

  8. Biopolymers form a gelatinous microlayer at the air-sea interface when Arctic sea ice melts.

    PubMed

    Galgani, Luisa; Piontek, Judith; Engel, Anja

    2016-07-20

    The interface layer between ocean and atmosphere is only a couple of micrometers thick but plays a critical role in climate relevant processes, including the air-sea exchange of gas and heat and the emission of primary organic aerosols (POA). Recent findings suggest that low-level cloud formation above the Arctic Ocean may be linked to organic polymers produced by marine microorganisms. Sea ice harbors high amounts of polymeric substances that are produced by cells growing within the sea-ice brine. Here, we report from a research cruise to the central Arctic Ocean in 2012. Our study shows that microbial polymers accumulate at the air-sea interface when the sea ice melts. Proteinaceous compounds represented the major fraction of polymers supporting the formation of a gelatinous interface microlayer and providing a hitherto unrecognized potential source of marine POA. Our study indicates a novel link between sea ice-ocean and atmosphere that may be sensitive to climate change.

  9. Biopolymers form a gelatinous microlayer at the air-sea interface when Arctic sea ice melts

    NASA Astrophysics Data System (ADS)

    Galgani, Luisa; Piontek, Judith; Engel, Anja

    2016-07-01

    The interface layer between ocean and atmosphere is only a couple of micrometers thick but plays a critical role in climate relevant processes, including the air-sea exchange of gas and heat and the emission of primary organic aerosols (POA). Recent findings suggest that low-level cloud formation above the Arctic Ocean may be linked to organic polymers produced by marine microorganisms. Sea ice harbors high amounts of polymeric substances that are produced by cells growing within the sea-ice brine. Here, we report from a research cruise to the central Arctic Ocean in 2012. Our study shows that microbial polymers accumulate at the air-sea interface when the sea ice melts. Proteinaceous compounds represented the major fraction of polymers supporting the formation of a gelatinous interface microlayer and providing a hitherto unrecognized potential source of marine POA. Our study indicates a novel link between sea ice-ocean and atmosphere that may be sensitive to climate change.

  10. Unusually loud ambient noise in tidewater glacier fjords: A signal of ice melt

    NASA Astrophysics Data System (ADS)

    Pettit, Erin Christine; Lee, Kevin Michael; Brann, Joel Palmer; Nystuen, Jeffrey Aaron; Wilson, Preston Scot; O'Neel, Shad

    2015-04-01

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

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

    USGS Publications Warehouse

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

    2015-01-01

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

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

    USGS Publications Warehouse

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

    1998-01-01

    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

  13. Exceptional melt pond occurrence in the years 2007 and 2011 on the Arctic sea ice revealed from MODIS satellite data

    NASA Astrophysics Data System (ADS)

    RöSel, Anja; Kaleschke, Lars

    2012-05-01

    Melt ponds contribute to the ice-albedo feedback as they reduce the surface albedo of sea ice, and hence accelerate the decay of Arctic sea ice. Here, we analyze the melt pond fraction, retrieved from the MODIS sensor for the years 2000-2011 to characterize the spatial and temporal evolution. A significant anomaly of the relative melt pond fraction at the beginning of the melt season in June 2007 is documented. This is followed by above-average values throughout the entire summer. In contrast, the increase of the relative melt pond fraction at the beginning of June 2011 is within average values, but from mid-June, relative melt pond fraction exhibits values up to two standard deviations above the mean values of 30 ± 1.2% which are even higher than in Summer 2007.

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

    NASA Astrophysics Data System (ADS)

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

    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

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

    PubMed

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

    2015-03-01

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

  16. Real time thermal imaging of high temperature semiconductor melts

    NASA Technical Reports Server (NTRS)

    Wargo, Michael J.

    1988-01-01

    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.

  17. Monitoring the temperature-dependent elastic and anelastic properties in isotropic polycrystalline ice using resonant ultrasound spectroscopy

    NASA Astrophysics Data System (ADS)

    Vaughan, Matthew J.; van Wijk, Kasper; Prior, David J.; Hamish Bowman, M.

    2016-11-01

    The elastic and anelastic properties of ice are of interest in the study of the dynamics of sea ice, glaciers, and ice sheets. Resonant ultrasound spectroscopy allows quantitative estimates of these properties and aids calibration of active and passive seismic data gathered in the field. The elastic properties and anelastic quality factor Q in laboratory-manufactured polycrystalline isotropic ice cores decrease (reversibly) with increasing temperature, but compressional-wave speed and attenuation prove most sensitive to temperature, indicative of pre-melting of the ice. This method of resonant ultrasound spectroscopy can be deployed in the field, for those situations where shipping samples is difficult (e.g. remote locations), or where the properties of ice change rapidly after extraction (e.g. in the case of sea ice).

  18. Liquidus Temperature Depression in Cryolitic Melts

    NASA Astrophysics Data System (ADS)

    Solheim, Asbjørn

    2012-08-01

    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-}.

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

    SciTech Connect

    Yoo, Soohaeng; Xantheas, Sotiris S.

    2011-03-28

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

  20. Arctic Ocean stability: The effects of local cooling, oceanic heat transport, freshwater input, and sea ice melt with special emphasis on the Nansen Basin

    NASA Astrophysics Data System (ADS)

    Rudels, Bert

    2016-07-01

    The Arctic loses energy to space and heat is transported northward in the atmosphere and ocean. The largest transport occurs in the atmosphere. The oceanic heat flux is significantly smaller, and the warm water that enters the Arctic Ocean becomes covered by a low-salinity surface layer, which reduces the heat transfer to the sea surface. This upper layer has two distinct regimes. In most of the deep basins it is due to the input of low-salinity shelf water, ultimately conditioned by net precipitation and river runoff. The Nansen Basin is different. Here warm Atlantic water is initially in direct contact with and melts sea ice, its upper part being transformed into less dense surface water. The characteristics and depth of this layer are determined as functions of the temperature of the Atlantic water and for different energy losses using a one-dimensional energy balance model. The amount of transformed Atlantic water is estimated for two different sea ice melt rates and the assumption of a buoyant boundary outflow. To create the upper layer sea ice formed elsewhere has to drift to the Nansen Basin. With reduced ice cover, this ice drift might weaken and the ice could disappear by the end of winter. The surface buoyancy input would disappear, and the upper layer might eventually convect back into the Atlantic water, reducing the formation of less dense Polar water. The created ice-free areas would release more heat to the atmosphere and affect the atmospheric circulation.

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    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.

  2. Investigation of the effects of summer melt on the calculation of sea ice concentration using active and passive microwave data

    NASA Technical Reports Server (NTRS)

    Cavalieri, Donald J.; Burns, Barbara A.; Onstott, Robert G.

    1990-01-01

    The effects of ice surface melt on microwave signatures and errors in the calculation of sea ice concentration are examined, using active and passive microwave data sets from the Marginal Ice Zone Experiment aircraft flights in the Fram Strait region. Consideration is given to the possibility of using SAR to supplement passive microwave data to unambiguously discriminate between open water areas and ponded floes. Coincident active multichannel microwave radiometer and SAR measurements of individual floes are used to describe the effects of surface melt on sea ice concentration calculations.

  3. 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)

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

    2012-05-01

    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.

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

    USGS Publications Warehouse

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

    2004-01-01

    Accurate calculation of the time of melt onset, freeze onset, and melt duration over Arctic sea-ice area is crucial for climate and global change studies because it affects accuracy of surface energy balance estimates. This comparative study evaluates several methods used to estimate sea-ice melt and freeze onset dates: (1) the melt onset database derived from SSM/I passive microwave brightness temperatures (Tbs) using Drobot and Anderson's [J. Geophys. Res. 106 (2001) 24033] Advanced Horizontal Range Algorithm (AHRA) and distributed by the National Snow and Ice Data Center (NSIDC); (2) the International Arctic Buoy Program/Polar Exchange at the Sea (IABP/POLES) surface air temperatures (SATs); (3) an elaborated version of the AHRA that uses IABP/POLES to avoid anomalous results (Passive Microwave and Surface Temperature Analysis [PMSTA]); (4) another elaborated version of the AHRA that uses Tb variance to avoid anomalous results (Mean Differences and Standard Deviation Analysis [MDSDA]); (5) Smith's [J. Geophys. Res. 103 (1998) 27753] vertically polarized Tb algorithm for estimating melt onset in multiyear (MY) ice (SSM/I 19V - 37V); and (6) analyses of concurrent backscattering cross section (rj) and brightness temperature (Tb) from OKEAN-01 satellite series. Melt onset and freeze onset maps were created and compared to understand how the estimates vary between different satellite instruments and methods over different Arctic seaice regions. Comparisons were made to evaluate relative sensitivities among the methods to slight adjustments of the Tb calibration coefficients and algorithm threshold values. Compared to the PMSTA method, the AHRA method tended to estimate significantly earlier melt dates, likely caused by the AHRA's susceptibility to prematurely identify melt onset conditions. In contrast, the IABP/POLES surface air temperature data tended to estimate later melt and earlier freeze in all but perennial ice. The MDSDA method was least sensitive to small

  5. Revisiting the potential of melt pond fraction as a predictor for the seasonal Arctic sea ice extent minimum

    NASA Astrophysics Data System (ADS)

    LIU, J.; Song, M.; Horton, R. M.; Hu, Y.

    2015-12-01

    Seasonal sea ice prediction is challenging because of high variability in diverse atmospheric and oceanic influences, and because the Arctic climate is changing in ways without precedent for at least the past millennium. A recent modeling study that employed a prognostic melt pond model in a stand-alone sea ice model found that September Arctic sea ice extent can be accurately predicted from the melt pond fraction in May. Here we show that satellite observations do not support the model-based finding that the melt pond fraction in May has the strongest impact on September sea ice extent. Instead, we see no evidence of predictive skill in May. We find that a significantly strong relationship first emerges as the melt pond fraction is integrated from early May to late June, with a persistent strong relationship only occurring after late July. Our results highlight that late spring to mid summer melt pond information is required to improve the prediction skill of the seasonal sea ice minimum. Furthermore, satellite observations indicate a much higher percentage of melt pond formation in May than does the aforementioned model simulation, which points to the need to reconcile model simulations and observations, in order to better understand key mechanisms of melt pond formation and evolution and their influence on sea ice state.

  6. 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)

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

    2014-05-01

    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

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

    USGS Publications Warehouse

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

    2004-01-01

    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

  8. High productivity in an ice melting hot spot at the eastern boundary of the Weddell Gyre

    NASA Astrophysics Data System (ADS)

    Geibert, W.; Assmy, P.; Bakker, D. C. E.; Hanfland, C.; Hoppema, M.; Pichevin, L. E.; Schröder, M.; Schwarz, J. N.; Stimac, I.; Usbeck, R.; Webb, A.

    2010-09-01

    The Southern Ocean (SO) plays a key role in modulating atmospheric CO2 via physical and biological processes. However, over much of the SO, biological activity is iron-limited. New in situ data from the Antarctic zone south of Africa in a region centered at ˜20°E-25°E reveal a previously overlooked region of high primary production, comparable in size to the northwest African upwelling region. Here, sea ice together with enclosed icebergs is channeled by prevailing winds to the eastern boundary of the Weddell Gyre, where a sharp transition to warmer waters causes melting. This cumulative melting provides a steady source of iron, fuelling an intense phytoplankton bloom that is not fully captured by monthly satellite production estimates. These findings imply that future changes in sea-ice cover and dynamics could have a significant effect on carbon sequestration in the SO.

  9. Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming is highly dangerous

    NASA Astrophysics Data System (ADS)

    Hansen, J.; Sato, M.; Hearty, P.; Ruedy, R.; Kelley, M.; Masson-Delmotte, V.; Russell, G.; Tselioudis, G.; Cao, J.; Rignot, E.; Velicogna, I.; Kandiano, E.; von Schuckmann, K.; Kharecha, P.; Legrande, A. N.; Bauer, M.; Lo, K.-W.

    2015-07-01

    There is evidence of ice melt, sea level rise to +5-9 m, and extreme storms in the prior interglacial period that was less than 1 °C warmer than today. Human-made climate forcing is stronger and more rapid than paleo forcings, but much can be learned by combining insights from paleoclimate, climate modeling, and on-going observations. We argue that ice sheets in contact with the ocean are vulnerable to non-linear disintegration in response to ocean warming, and we posit that ice sheet mass loss can be approximated by a doubling time up to sea level rise of at least several meters. Doubling times of 10, 20 or 40 years yield sea level rise of several meters in 50, 100 or 200 years. Paleoclimate data reveal that subsurface ocean warming causes ice shelf melt and ice sheet discharge. Our climate model exposes amplifying feedbacks in the Southern Ocean that slow Antarctic bottom water formation and increase ocean temperature near ice shelf grounding lines, while cooling the surface ocean and increasing sea ice cover and water column stability. Ocean surface cooling, in the North Atlantic as well as the Southern Ocean, increases tropospheric horizontal temperature gradients, eddy kinetic energy and baroclinicity, which drive more powerful storms. We focus attention on the Southern Ocean's role in affecting atmospheric CO2 amount, which in turn is a tight control knob on global climate. The millennial (500-2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change, thus the time scale for paleo global climate, ice sheet and sea level changes. This millennial carbon cycle time scale should not be misinterpreted as the ice sheet time scale for response to a rapid human-made climate forcing. Recent ice sheet melt rates have a doubling time near the lower end of the 10-40 year range. We conclude that 2 °C global warming above the preindustrial level, which would spur more ice shelf melt, is highly dangerous. Earth's energy imbalance, which

  10. Correlation Studies of Sea Ice Concentration with Surface Temperature and Meltponding

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Slovák, Jan; Tanaka, Hideki

    2005-05-01

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

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

    PubMed

    Slovák, Jan; Tanaka, Hideki

    2005-05-22

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

  13. The Gibbs-Thomson effect and intergranular melting in ice emulsions: Interpreting the anomalous heat capacity and volume of supercooled water

    NASA Astrophysics Data System (ADS)

    Johari, G. P.

    1997-12-01

    Calculations for the Gibbs-Thomson effect and the intergranular melting of the ice droplets in (water) emulsions at temperatures below 273.16 K show that water and ice coexist at thermodynamic equilibrium in an apparently frozen emulsion. The fraction of water at this equilibrium increases on heating, which alters further the thermodynamic properties of the emulsion. As some of the ice in the emulsion has already melted, the increase in the enthalpy, H, and heat capacity, Cp, and the decrease in the volume measured on the normal melting at 273.16 K, are less than the values anticipated. The ratio of this increase in H, or Cp, on melting of the emulsion to the corresponding value for pure ice, underestimates the emulsion's water content which, when used for scaling the difference between the Cp of the unfrozen and frozen emulsion at lower temperatures, as in earlier studies, leads to a larger Cp of supercooled water than the actual value. Similar scaling of the corresponding difference between the volume leads to higher volume, or lower density, than the actual value. A formalism for this premelting effect is given for both the adiabatic and differential scanning calorimetry (DSC), and its magnitude is calculated. New experiments show that the rise in the DSC signal, or equivalently in the apparent Cp observed on heating the frozen emulsion, occurs over a temperature range much wider than the Gibbs-Thomson effect and intergranular melting predict, for which reasons are given. It is shown that Cp of the dispersant phase is also affected by the melting of ice droplets. There are four consequences of the premelting effects for all finely dispersed materials, for frozen water emulsions below 273.16 K: (i) water and ice coexist in the emulsion, (ii) its apparent Cp will increase with increase in the heat input used to measure it, (iii) the apparent Cp will increase with decrease in the average size of the droplets, and (iv) the apparent Cp will decrease on annealing the

  14. The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay

    NASA Astrophysics Data System (ADS)

    Williams, G. D.; Herraiz-Borreguero, L.; Roquet, F.; Tamura, T.; Ohshima, K. I.; Fukamachi, Y.; Fraser, A. D.; Gao, L.; Chen, H.; McMahon, C. R.; Harcourt, R.; Hindell, M.

    2016-08-01

    A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011-2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65-34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate.

  15. The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay.

    PubMed

    Williams, G D; Herraiz-Borreguero, L; Roquet, F; Tamura, T; Ohshima, K I; Fukamachi, Y; Fraser, A D; Gao, L; Chen, H; McMahon, C R; Harcourt, R; Hindell, M

    2016-08-23

    A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011-2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65-34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate.

  16. The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay

    PubMed Central

    Williams, G. D.; Herraiz-Borreguero, L.; Roquet, F.; Tamura, T.; Ohshima, K. I.; Fukamachi, Y.; Fraser, A. D.; Gao, L.; Chen, H.; McMahon, C. R.; Harcourt, R.; Hindell, M.

    2016-01-01

    A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate. PMID:27552365

  17. 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)

    Gauthier, Francis; Hétu, Bernard; Allard, Michel

    2013-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Kalousová, Klára; Souček, Ondřej; Tobie, Gabriel; Choblet, Gaël.; Čadek, Ondřej

    2014-03-01

    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.

  19. Radar attenuation and temperature within the Greenland Ice Sheet

    USGS Publications Warehouse

    MacGregor, Joseph A; Li, Jilu; Paden, John D; Catania, Ginny A; Clow, Gary D.; Fahnestock, Mark A; Gogineni, Prasad S.; Grimm, Robert E.; Morlighem, Mathieu; Nandi, Soumyaroop; Seroussi, Helene; Stillman, David E

    2015-01-01

    The flow of ice is temperature-dependent, but direct measurements of englacial temperature are sparse. The dielectric attenuation of radio waves through ice is also temperature-dependent, and radar sounding of ice sheets is sensitive to this attenuation. Here we estimate depth-averaged radar-attenuation rates within the Greenland Ice Sheet from airborne radar-sounding data and its associated radiostratigraphy. Using existing empirical relationships between temperature, chemistry, and radar attenuation, we then infer the depth-averaged englacial temperature. The dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry. Where radar transects intersect boreholes, radar-inferred temperature is consistently higher than that measured directly. We attribute this discrepancy to the poorly recognized frequency dependence of the radar-attenuation rate and correct for this effect empirically, resulting in a robust relationship between radar-inferred and borehole-measured depth-averaged temperature. Radar-inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice-sheet model, particularly in southern Greenland. This pattern suggests that past changes in surface boundary conditions (temperature and accumulation rate) affect the ice sheet's present temperature structure over a much larger area than previously recognized. This radar-inferred temperature structure provides a new constraint for thermomechanical models of the Greenland Ice Sheet.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Paleoclimate data are often extracted from ice cores by careful geochemical analysis of meltwater samples. The analysis of the microparticles found in ice cores can also yield unique clues about atmospheric dust loading and transport, dust provenance and past environmental conditions. Determination of microparticle concentration, size distribution and chemical makeup as a function of depth is especially difficult because the particle size measurement either consumes or contaminates the meltwater, preventing further geochemical analysis. Here we describe a microcontroller-based ice core melting system which allows the collection of separate microparticle and chemistry samples from the same depth intervals in the ice core, while logging and accurately depth-tagging real-time electrical conductivity and particle size distribution data. This system was designed specifically to support microparticle analysis of the WAIS Divide WDC06A deep ice core, but many of the subsystems are applicable to more general ice core melting operations. Major system components include: a rotary encoder to measure ice core melt displacement with 0.1 millimeter accuracy, a meltwater tracking system to assign core depths to conductivity, particle and sample vial data, an optical debubbler level control system to protect the Abakus laser particle counter from damage due to air bubbles, a Rabbit 3700 microcontroller which communicates with a host PC, collects encoder and optical sensor data and autonomously operates Gilson peristaltic pumps and fraction collectors to provide automatic sample handling, melt monitor control software operating on a standard PC allowing the user to control and view the status of the system, data logging software operating on the same PC to collect data from the melting, electrical conductivity and microparticle measurement systems. Because microparticle samples can easily be contaminated, we use optical air bubble sensors and high resolution ice core density

  2. Mixing of the immiscible: hydrocarbons in water-ice near the ice crystallization temperature.

    PubMed

    Lignell, Antti; Gudipati, Murthy S

    2015-03-19

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

  3. Temperature Distribution Measurement of The Wing Surface under Icing Conditions

    NASA Astrophysics Data System (ADS)

    Isokawa, Hiroshi; Miyazaki, Takeshi; Kimura, Shigeo; Sakaue, Hirotaka; Morita, Katsuaki; Japan Aerospace Exploration Agency Collaboration; Univ of Notre Dame Collaboration; Kanagawa Institute of Technology Collaboration; Univ of Electro-(UEC) Team, Comm

    2016-11-01

    De- or anti-icing system of an aircraft is necessary for a safe flight operation. Icing is a phenomenon which is caused by a collision of supercooled water frozen to an object. For the in-flight icing, it may cause a change in the wing cross section that causes stall, and in the worst case, the aircraft would fall. Therefore it is important to know the surface temperature of the wing for de- or anti-icing system. In aerospace field, temperature-sensitive paint (TSP) has been widely used for obtaining the surface temperature distribution on a testing article. The luminescent image from the TSP can be related to the temperature distribution. (TSP measurement system) In icing wind tunnel, we measured the surface temperature distribution of the wing model using the TSP measurement system. The effect of icing conditions on the TSP measurement system is discussed.

  4. Revisiting the Potential of Melt Pond Fraction as a Predictor for the Seasonal Arctic Sea Ice Extent Minimum

    NASA Technical Reports Server (NTRS)

    Liu, Jiping; Song, Mirong; Horton, Radley M.; Hu, Yongyun

    2015-01-01

    The rapid change in Arctic sea ice in recent decades has led to a rising demand for seasonal sea ice prediction. A recent modeling study that employed a prognostic melt pond model in a stand-alone sea ice model found that September Arctic sea ice extent can be accurately predicted from the melt pond fraction in May. Here we show that satellite observations show no evidence of predictive skill in May. However, we find that a significantly strong relationship (high predictability) first emerges as the melt pond fraction is integrated from early May to late June, with a persistent strong relationship only occurring after late July. Our results highlight that late spring to mid summer melt pond information is required to improve the prediction skill of the seasonal sea ice minimum. Furthermore, satellite observations indicate a much higher percentage of melt pond formation in May than does the aforementioned model simulation, which points to the need to reconcile model simulations and observations, in order to better understand key mechanisms of melt pond formation and evolution and their influence on sea ice state.

  5. Optical Measurements and Analysis of Sea Ice in the Chukchi Sea during the Onset of 2014 Melt

    NASA Astrophysics Data System (ADS)

    Arntsen, A. E.; Stwertka, C.; Polashenski, C.; Perovich, D. K.

    2014-12-01

    Partitioning of solar radiation by the sea ice-ocean system controls sea ice melt and light availability for primary production in the upper ocean. Morphological changes occurring as the Chukchi Sea transitions to a first year ice cover with a higher melt pond fraction are likely altering the surface radiation budget and thereby impacting physical and biological systems. Field observations were conducted from the onset of snowmelt to the formation of melt ponds at several locations in the Chukchi Sea from May 18 to June 17, 2014. The state and variability of incident, reflected, and transmitted spectral irradiance as well as vector and scalar photosynthetically active radiation (PAR) were measured coincident with snow depth and ice thickness. These in situ observations were combined with coincident satellite imagery to describe the radiation budget and solar partitioning at an aggregate scale. Results show decreasing albedo and increasing transmission as melt progressed with trends interrupted by a late season snowfall. Albedo declined steadily from a high of 85% to a low of 53%, while transmitted light available for primary production remained well below 1% prior to snow melt and when highly absorbing algae was present at the bottom of the ice. Comparison of our solar partitioning observations with similar observations in multiyear ice highlights the profound impact changing ice morphology has on solar partitioning of the Chukchi Sea.

  6. Did accelerated North American ice sheet melt contribute to the 8.2 ka cooling event ?

    NASA Astrophysics Data System (ADS)

    Matero, Ilkka S. O.; Gregoire, Lauren J.; Ivanović, Ruža F.; Tindall, Julia C.; Haywood, Alan M.

    2016-04-01

    The 8.2 ka event was an abrupt cooling of the Northern Hemisphere 8,200 years ago. It is an almost ideal case study to benchmark the sensitivity of climate models to freshening of the North Atlantic by ice sheet melt (Schmidt and LeGrande, 2005). The event is attributed to the outburst of North American proglacial lakes into the Labrador Sea, causing a slow-down in Atlantic overturning circulation and cooling of 1-2.5 °C around the N. Atlantic (Alley and Ágústsdóttir,2005). Climate models fail to simulate the ~150 year duration of the event when forced with a sudden (0.5 to 5 years) drainage of the lakes (Morrill et al., 2013a). This could be because of missing forcings. For example, the separation of ice sheet domes around the Hudson Bay is thought to have produced a pronounced acceleration in ice sheet melt through a saddle collapse mechanism around the time of the event (Gregoire et al., 2012). Here we investigate whether this century scale acceleration of melt contributed to the observed climatic perturbation, using the coupled Ocean-Atmosphere climate model HadCM3. We designed and ran a set of simulations with temporally variable ice melt scenarios based on a model of the North American ice sheet. The simulated magnitude and duration of the cold period is controlled by the duration and amount of freshwater introduced to the ocean. With a 100-200 year-long acceleration of ice melt up to a maximum of 0.61 Sv, we simulate 1-3 °C cooling in the North Atlantic and ~0.5-1 °C cooling in Continental Europe; which are similar in magnitude to the ~1-2 °C cooling estimated from records for these areas (Morrill et al., 2013b). Some of the observed features are however not reproduced in our experiments, such as the most pronounced cooling of ~6 °C observed in central Greenland (Alley and Ágústsdóttir, 2005). The results suggest that the ~150 year North Atlantic and European cooling could be caused by ~200 years of accelerated North American ice sheet melt. This

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

    PubMed

    Rasmussen, Tine L; Thomsen, Erik

    2013-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Ivanov, B. A.

    2005-01-01

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

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

    PubMed

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

    2013-06-01

    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.

  10. An Experimental Investigation of Ice-melting and heat transfer rates from submerged warm water jets upward impinging into ice-blocks as analogous for water-filled cavities formed during subglacial eruptions.

    NASA Astrophysics Data System (ADS)

    Jamshidnia, Hamidreza; Gudmundsson, Magnus Tumi

    2016-11-01

    Rates of energy transfer in water-filled cavities formed under glaciers by geothermal and volcanic activity are investigated by conducting experiments in which hot water jets (10°- 90°C) impinging into an ice block for jet Reynolds numbers in turbulent regime of 10000 -70000. It is found that heat flux is linearly dependent on jet flow temperature. Water jet melts a cavity into an ice block. Cavities had steep to vertical sides with a doming roof. Some of ice blocks used had trapped air bubbles. In these cases that melting of the ice could have led to trapping of air at the top of cavity, partially insulating the roof from hot water jet. The overall heat transfer rate in cavity formation varied with jet temperature from <100 kW m-2 to 900 kW m-2 while melting rates in the vertical direction yield heat transfer rates of 200-1200 kW m-2. Experimental heat transfer rates can be compared to data on subglacial melting observed for ice cauldrons in Iceland. For lowest temperatures the numbers are comparable to those for geothermal water in cool, subglacial water bodies and above subglacial flowpaths of jökulhlaups. Highest experimental rates for 80-90°C jets are 3-10 times less than inferred from observations of recent subglacial eruptions (2000-4000 kW m-2) . This can indicate that single phase liquid water convection alone may not be sufficient to explain the rates seen in recent subglacial eruptions, suggesting that forced 2 or 3 phase convection can be common.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Operational ice information services rely heavily on space-borne synthetic aperture radar (SAR) data for the production of ice charts to meet their mandate of providing timely and accurate sea ice information to support safe and efficient marine operations. During the summer melt period, the usefulness of SAR data for sea ice monitoring is limited by the presence of wet snow and melt ponds on the ice surface, which can mask the signature of the underlying ice. This is a critical concern for ice services whose clients (e.g. commercial shipping, cruise tourism, resource exploration and extraction) are most active at this time of year when sea ice is at its minimum extent, concentration and thickness. As a result, there is a need to further quantify the loss of ice information in SAR data during the melt season and to identify what information can still be retrieved about ice surface conditions and melt pond evolution at this time of year. To date the majority of studies have been limited to analysis of single-polarization C-band SAR data. This study will investigate the potential complimentary and unique sea ice information that polarimetric C- and X-band SAR data can provide to supplement the information available from traditional single co-polarized C-band SAR data. A time-series of polarimetric C- and X-band SAR data was acquired over Jones Sound in the Canadian Arctic Archipelago, in the vicinity of the Grise Fiord, Nunavut. Five RADARSAT-2 Wide Fine Quad-pol images and 11 TerraSAR-X StripMap dual-pol (HH/VV) images were acquired. The time-series begins at the onset of melt in early June and extends through advanced melt conditions in late July. Over this period several ponding and drainage events and two snowfall events occurred. Field observations of sea ice properties were collected using an Ice Mass Balance (IMB) buoy, hourly photos from a time-lapse camera deployed on a coastal cliff, and manual in situ measurements of snow thickness and melt pond depth

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

    PubMed

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

    2002-01-04

    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.

  13. Formation of Recent Martian Debris Flows by Melting of Near-Surface Ground Ice at High Obliquity

    NASA Astrophysics Data System (ADS)

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

    2002-01-01

    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.

  14. Role of melting temperature on the properties of displacement cascades

    SciTech Connect

    Smalinskas, K.; Robertson, I.M.; Averback, R.S. . Dept. of Materials Science and Engineering); Kirk, M.A. )

    1990-04-01

    The defect structure produced in Cu-Ni alloys by room temperature heavy-ion irradiation have been investigated by TEM. This system exhibits complete solid solubility over the entire composition range and therefore allows the role of melting temperature on the properties of displacement cascades to be assessed. The probability of a dislocation loop forming in the Cu-Ni alloy system is highest in pure Cu and decreases with increasing Ni content. However, the change in formation probability with melting temperature is not a simple one as it is found that loops form more readily in pure nickel than in Cu-90%Ni. It was also found that the size of the dislocation loops varies markedly with alloy content. The higher the nickel content the smaller the loops. These results will be correlated with ion-beam mixing experiments to assess the role of vacancy mobility in the loop formation process. 21 refs., 4 figs., 1 tab.

  15. An Experimental Investigation of Ice Melting and Heat Transfer Characteristics from Submerged Jets of Hot Water, Implications for Subglacial Volcanic Eruptions

    NASA Astrophysics Data System (ADS)

    Jamshidnia, H.; Gudmundsson, M. T.

    2014-12-01

    The rates and processes of energy transfer in water-filled cavities formed under glaciers by geothermal and volcanic activity has been investigated by designing, developing, and using an experimental setup in which hot water jets can impinge on an ice block. Systematic sets of experimental runs typically lasting 60-90 seconds with water jet temperatures in the range 10° - 90°C have been performed with initial ice block temparature. It is quantitatively found that heat flux from flowing water to ice is linearly dependent on temperature of the jet flow. The hot water jet meltes out a cavity into the ice block during the process. The cavities had steep to vertical sides with a doming roof. Some of the ice blocks used had trapped air bubbles. In these cases melting of the ice lead to the trapping of air at the top of the cavity, partially insulating the roof from the hot water jet. Such cavities had lower aspect ratios (height/width) and flatter and less dome shaped roofs than did cavities in ice blocks with little or no air bubbles. The overall heat transfer rate in cavity formation varied with jet temperature from <100 kW m-2 to ~900 kW m-2 while melting rates in the vertical direction yield heat transfer rates of 200-1200 kW m-2. The observed experimental heat transfer rates can be compared to data on subglacial melting observed for ice cauldrons in various settings in Iceland. For the lowest experimental temperatures the numbers are comparable to those found for geothermal water in cool, subglacial water bodies and above subglacial flowpaths of jökulhlaups. However, the highest experimental rates for 80-90°C jets are 3-10 times less than inferred from observations of recent subglacial eruptions (2000-4000 kW m-2). This can indicate that single phase liquid water convection alone is not sufficient to explain the rates seen in recent subglacial eruptions in Iceland, suggesting that during such eruptions forced two-phase (liquid and steam) or three phase (liquid

  16. Glacio-hydrological Modeling in the Glacierized Tamor River Basin, Eastern Nepal using Temperature Index Melt Approach.

    NASA Astrophysics Data System (ADS)

    Shrestha, A.; Kayastha, R. B.

    2015-12-01

    In the region with sparse hydro-meteorological data, use of temperature index melt model to estimate snow and ice melt has shown to be an effective method to melt modeling. This study presents the estimation of daily discharge of Tamor River basin located in eastern Nepal with relative contribution of snow and ice melt using this approach, which is based on the relation that the melting of snow or ice during any particular period is proportional to the positive temperature linked by positive degree day factor. The study basin is one of the sub-basins of Koshi River basin that lies in the Himalayan region and has an area of 4001.2 km2 with approximately 9.4 % of the total basin covered by glaciers (debris covered and clean ice type) and approximately 21.5 % of the area lying above 5000 m a.s.l. The model is calibrated from 2001 to 2005 and validated from 2007 to 2010. The model efficiency assessments show good results with Nash - Sutcliffe model efficiency coefficients and volume differences as 0.80 and 4.8 %, respectively in calibration and 0.83 and 1.1 %, respectively in validation periods. The average discharges during these periods are 237.95 m3/s and 231.49 m3/s with 43.3 % and 40.7 % of average snow and ice melt contributions, respectively. The model is also used to project river discharge from 2020 to 2050 with meteorological input data (i.e., temperature and precipitation) projected from Regional Climate Model using Weather Research and Forecasting (V3.5) model of 12 km resolution and boundary conditions from NorESM, which is bias corrected to the basin scale for RCP 4.5 and 8.5 climate scenarios. The model projection shows increase in river discharge by 0.24 m3/s per year with decreasing snow and ice contribution by 0.03 m3/s per year under RCP 4.5 scenario, whereas it shows decrease in total river discharge and snow and ice contribution as well by 0.29 m3/s and 0.28 m3/s per year, respectively under RCP 8.5 scenario. The study indicates that this model can

  17. Estimation of melt pond fraction over high-concentration Arctic sea ice using AMSR-E passive microwave data

    NASA Astrophysics Data System (ADS)

    Tanaka, Yasuhiro; Tateyama, Kazutaka; Kameda, Takao; Hutchings, Jennifer K.

    2016-09-01

    Melt pond fraction (MPF) on sea ice is an important factor for ice-albedo feedback throughout the Arctic Ocean. We propose an algorithm to estimate MPF using satellite passive microwave data in this study. The brightness temperature (TB) data obtained from the Advanced Microwave Scanning Radiometer-Earth observing system (AMSR-E) were compared to the ship-based MPF in the Beaufort Sea and Canadian Arctic Archipelago. The difference between the TB at horizontal and vertical polarizations of 6.9 and 89.0 GHz (MP06H-89V), respectively, depends on the MPF. The correlation between MP06H-89V and ship-based MPF was higher than that between ship-based MPF and two individual channels (6.9 and 89.0 GHz of horizontal and vertical polarizations, respectively). The MPF determined with the highest resolution channel, 89.0 GHz (5 km × 5 km), provides spatial information with more detail than the 6.9 GHz channel. The algorithm estimates the relative fraction of ice covered by water (1) over areas where sea ice concentration is higher than 95%, (2) during late summer, and (3) in areas with low atmospheric humidity. The MPF estimated from AMSR-E data (AMSR-E MPF) in early summer was underestimated at lower latitudes and overestimated at higher latitudes, compared to the MPF obtained from the Moderate Resolution Image Spectrometer (MODIS MPF). The differences between AMSR-E MPF and MODIS MPF were less than 5% in most the regions and the periods. Our results suggest that the proposal algorithm serves as a basis for building time series of MPF in regions of consolidated ice pack.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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

  19. Consistent estimate of ocean warming, land ice melt and sea level rise from Observations

    NASA Astrophysics Data System (ADS)

    Blazquez, Alejandro; Meyssignac, Benoît; Lemoine, Jean Michel

    2016-04-01

    Based on the sea level budget closure approach, this study investigates the consistency of observed Global Mean Sea Level (GMSL) estimates from satellite altimetry, observed Ocean Thermal Expansion (OTE) estimates from in-situ hydrographic data (based on Argo for depth above 2000m and oceanic cruises below) and GRACE observations of land water storage and land ice melt for the period January 2004 to December 2014. The consistency between these datasets is a key issue if we want to constrain missing contributions to sea level rise such as the deep ocean contribution. Numerous previous studies have addressed this question by summing up the different contributions to sea level rise and comparing it to satellite altimetry observations (see for example Llovel et al. 2015, Dieng et al. 2015). Here we propose a novel approach which consists in correcting GRACE solutions over the ocean (essentially corrections of stripes and leakage from ice caps) with mass observations deduced from the difference between satellite altimetry GMSL and in-situ hydrographic data OTE estimates. We check that the resulting GRACE corrected solutions are consistent with original GRACE estimates of the geoid spherical harmonic coefficients within error bars and we compare the resulting GRACE estimates of land water storage and land ice melt with independent results from the literature. This method provides a new mass redistribution from GRACE consistent with observations from Altimetry and OTE. We test the sensibility of this method to the deep ocean contribution and the GIA models and propose best estimates.

  20. Antarctic Sea ice variations and seasonal air temperature relationships

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

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

    SciTech Connect

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

    2010-07-19

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

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  3. Variability of the oceanic environment and basal melting of the Dotson Ice Shelf, West Antarctica, 2000 to 2014

    NASA Astrophysics Data System (ADS)

    Shoosmith, Deb; Jenkins, Adrian; Dutrieux, Pierre; Jacobs, Stan; Kim, Tae Wan; Lee, Sang Hoon; Ha, Ho Kyung; Stammerjohn, Sharon

    2016-04-01

    It is well known that the ocean plays a key role in the process of mass loss from ice sheets through iceberg calving and basal melting. The Amundsen Sea, in the eastern Pacific sector of the Southern Ocean, is a region where the ice shelves are rapidly thinning. The widespread, coherent nature of the thinning suggests oceanic forcing, which has now been well documented for Pine Island Glacier. Studies using satellite data have indicated that Dotson Ice Shelf was melting at a rate of 8 m per year and thinning by about 3 m per year during the 2003 - 2008 period. This study takes a slightly longer term perspective, exploiting oceanographic observations spanning a decade and a half (2000 - 2014) that have been obtained at the Dotson Ice Front. A total of 7 hydrographic sections reveal variability in the oceanographic environment in front of the ice shelf and associated changes in meltwater production over time. We quantify the variability in circulation and net meltwater transport from beneath the ice shelf to produce estimates of the basal melt rate for this 15 year period. We find that changes in ocean heat content in front of the ice shelf drive high variability in melting on multi-annual to decadal time-scales.

  4. Temperature and composition dependencies of trace element partitioning - Olivine/melt and low-Ca pyroxene/melt

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    This paper presents a systematic thermodynamic analysis of the effects of temperature and composition on olivine/melt and low-Ca pyroxene/melt partitioning. Experiments were conducted in several synthetic basalts with a wide range of Fe/Mg, determining partition coefficients for Eu, Ca, Mn, Fe, Ni, Sm, Cd, Y, Yb, Sc, Al, Zr, and Ti and modeling accurately the changes in free energy for trace element exchange between crystal and melt as functions of the trace element size and charge. 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. Moreover, variations in partition coeffeicients during crystallization or melting can be modeled on the basis of changes in temperature and major element chemistry.

  5. Syntheses of neptunium trichloride and measurements of its melting temperature

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  6. Level-Ice Melt Ponds in the Los Alamos Sea Ice Model, CICE

    DTIC Science & Technology

    2012-12-06

    assumed to infiltrate the snow. If there is enough water to fill the air spaces within the snowpack , then the pond becomes visible above the snow...h eff pnd ¼ 0. Otherwise, we assume that the snowpack is saturated with liquid water. Liquid water percolates down very quickly into the snow. Here...Comparing Fig. 14 with Fig. 11, it is clear that effective pond area in July 1998–2007 is larger in central areas (where the snowpack has not melted) for

  7. Making High-Temperature Superconductors By Melt Sintering

    NASA Technical Reports Server (NTRS)

    Golben, John P.

    1992-01-01

    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.

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

    PubMed

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

    2008-07-04

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

  9. Biopolymers form a gelatinous microlayer at the air-sea interface when Arctic sea ice melts

    PubMed Central

    Galgani, Luisa; Piontek, Judith; Engel, Anja

    2016-01-01

    The interface layer between ocean and atmosphere is only a couple of micrometers thick but plays a critical role in climate relevant processes, including the air-sea exchange of gas and heat and the emission of primary organic aerosols (POA). Recent findings suggest that low-level cloud formation above the Arctic Ocean may be linked to organic polymers produced by marine microorganisms. Sea ice harbors high amounts of polymeric substances that are produced by cells growing within the sea-ice brine. Here, we report from a research cruise to the central Arctic Ocean in 2012. Our study shows that microbial polymers accumulate at the air-sea interface when the sea ice melts. Proteinaceous compounds represented the major fraction of polymers supporting the formation of a gelatinous interface microlayer and providing a hitherto unrecognized potential source of marine POA. Our study indicates a novel link between sea ice-ocean and atmosphere that may be sensitive to climate change. PMID:27435531

  10. Basal melt, seasonal water mass transformation, ocean current variability, and deep convection processes along the Amery Ice Shelf calving front, East Antarctica

    NASA Astrophysics Data System (ADS)

    Herraiz-Borreguero, L.; Church, J. A.; Allison, I.; Peña-Molino, B.; Coleman, R.; Tomczak, M.; Craven, M.

    2016-07-01

    Despite the Amery Ice Shelf (AIS) being the third largest ice shelf in Antarctica, the seasonal variability of the physical processes involved in the AIS-ocean interaction remains undocumented and a robust observational, oceanographic-based basal melt rate estimate has been lacking. Here we use year-long time series of water column temperature, salinity, and horizontal velocities measured along the ice shelf front from 2001 to 2002. Our results show strong zonal variations in the distribution of water masses along the ice shelf front: modified Circumpolar Deep Water (mCDW) arrives in the east, while in the west, Ice Shelf Water (ISW) and Dense Shelf Water (DSW) formed in the Mackenzie polynya dominate the water column. Baroclinic eddies, formed during winter deep convection (down to 1100 m), drive the inflow of DSW into the ice shelf cavity. Our net basal melt rate estimate is 57.4 ± 25.3 Gt yr-1 (1 ± 0.4 m yr-1), larger than previous modeling-based and glaciological-based estimates, and results from the inflow of DSW (0.52 ± 0.38 Sv; 1 Sv = 106 m3 s-1) and mCDW (0.22 ± 0.06 Sv) into the cavity. Our results highlight the role of the Mackenzie polynya in the seasonal exchange of water masses across the ice shelf front, and the role of the ISW in controlling the formation rate and thermohaline properties of DSW. These two processes directly impact on the ice shelf mass balance, and on the contribution of DSW/ISW to the formation of Antarctic Bottom Water.

  11. Atmospheric moisture transport: the bridge between ocean evaporation and Arctic ice melting

    NASA Astrophysics Data System (ADS)

    Gimeno, L.; Vázquez, M.; Nieto, R.; Trigo, R. M.

    2015-09-01

    Changes in the atmospheric moisture transport have been proposed as a vehicle for interpreting some of the most significant changes in the Arctic region. The increasing moisture over the Arctic during the last decades is not strongly associated with the evaporation that takes place within the Arctic area itself, despite the fact that the sea ice cover is decreasing. Such an increment is consistent and is more dependent on the transport of moisture from the extratropical regions to the Arctic that has increased in recent decades and is expected to increase within a warming climate. This increase could be due either to changes in circulation patterns which have altered the moisture sources, or to changes in the intensity of the moisture sources because of enhanced evaporation, or a combination of these two mechanisms. In this short communication we focus on the more objective assessment of the strong link between ocean evaporation trends and Arctic Sea ice melting. We will critically analyse several recent results suggesting links between moisture transport and the extent of sea ice in the Arctic, this being one of the most distinct indicators of continuous climate change both in the Arctic and on a global scale. To do this we will use a sophisticated Lagrangian approach to develop a more robust framework on some of these previous disconnecting results, using new information and insights. Results reached in this study stress the connection between two climate change indicators, namely an increase in evaporation over source regions (mainly the Mediterranean Sea, the North Atlantic Ocean and the North Pacific Ocean in the paths of the global western boundary currents and their extensions) and Arctic ice melting precursors.

  12. Skin Temperature Processes in the Presence of Sea Ice

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Budke, C.; Koop, T.

    2015-02-01

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

  14. A calving law for ice sheet models; Investigating the role of surface melt on dynamics of Greenland outlet glaciers

    NASA Astrophysics Data System (ADS)

    Nick, F. M.; van der Veen, C. J.; Vieli, A.

    2008-12-01

    alving of icebergs accounts for perhaps as much as half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. We have formulated a calving model that can be readily incorporated into time-evolving numerical ice-flow models. Our model is based on downward penetration of water-filled surface crevasses and upward propagation of basal crevasses. A calving event occurs when the depth of the surface crevasse (which increases as melting progresses through the summer) reaches the height of the basal crevasse. Our numerical ice sheet model is able to reproduce observed seasonal changes of Greenland outlet glaciers, such as fluctuations in flow speed and terminus positions. We have applied the model to Helheim Glacier on the east coast, and Petermann Glacier in the northwest. Our model suggests that rapid retreat of the claving front is highly affected by the amplified calving rate due to increasing water level in surface crevasses during warmer summers. Our results show little response to seasonally enhanced basal lubrication from surface melt. This modeling study provides insights into the role of surface and basal hydrology to ice sheet dynamics and on how to incorporate calving in ice sheet models and therefore advances our ability to predict future ice sheet change.

  15. High temperature steady shear and oscillatory rheometry of basaltic melt

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

  16. Monitoring South-West Greenland's ice sheet melt with ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Mordret, Aurélien; Mikesell, Dylan; Harig, Christopher; Lipovsky, Brad; Prieto, German

    2016-04-01

    The Greenland ice sheet (GIS) accounts for ~ 70% of global ice sheet mass loss and contributes to sea level rise at a rate of 0.7 mm/yr. Therefore, the GIS needs to be carefully monitored. The spaceborne techniques commonly used to monitor the GIS mass balance contain inherent uncertainties. These uncertainties can be reduced by comparing independent datasets and techniques. However, spaceborne methods remain inadequate in the sense that they offer low spatial and/or temporal resolution. This fact highlights the need for other complementary methods to monitor the GIS more accurately and with greater resolution. Here we use a seismic method: the correlation of seismic noise recorded at South-West Greenland seismic stations to show that the GIS seasonal melt produces significant variations of seismic wave speed in the Greenland crust. The amplitudes of the measured velocity variations during 2012-2013 correlate with the total ice plus atmospheric mass variations measured by the GRACE (Gravity Recovery and Climate Experiment) satellite mission. We explain the phase delay between mass maxima and velocity minima ( 50 days) using a non-linear poroelastic model that includes a 55 cm-thick layer of till between the ice sheet and the bedrock. We, thus, interpret the velocity variations as pore pressure variations in the bedrock resulting from the loading and unloading of the overlying glacier and atmosphere. This method provides a new and independent way to monitor in near real-time the first-order state of the GIS, giving new constraints on its evolution and its contribution to the global sea level rise. By increasing the density of seismic stations in the region it will be possible to increase the spatial and temporal resolution of the method and create detailed maps of ice-mass variations across Greenland.

  17. Monitoring South-West Greenland's ice sheet melt with ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Mordret, A.; Mikesell, T. D.; Harig, C.; Lipovsky, B.; Prieto, G. A.

    2015-12-01

    The Greenland ice sheet (GIS) accounts for ~ 70% of global ice sheet mass loss and contributes to sea level rise at a rate of 0.7 mm/yr. Therefore, the GIS needs to be carefully monitored. The spaceborne techniques commonly used to monitor the GIS mass balance contain inherent uncertainties. These uncertainties can be reduced by comparing independent datasets and techniques. However, spaceborne methods remain inadequate in the sense that they offer low spatial and/or temporal resolution. This fact highlights the need for other complimentary methods to monitor the GIS more accurately and with greater resolution. Here we use a seismic method: the correlation of seismic noise recorded at South-West Greenland seismic stations to show that the GIS seasonal melt produces significant variations of seismic wave speed in the Greenland crust. The amplitudes of the measured velocity variations during 2012-2013 correlate with the total ice plus atmospheric mass variations measured by the GRACE (Gravity Recovery and Climate Experiment) satellite mission. We explain the phase delay between mass maxima and velocity minima ( 50 days) using a non-linear poroelastic model that includes a 55 cm-thick layer of till between the ice sheet and the bedrock. We, thus, interpret the velocity variations as pore pressure variations in the bedrock resulting from the loading and unloading of the overlying glacier and atmosphere. This method provides a new and independent way to monitor in near real-time the first-order state of the GIS, giving new constraints on its evolution and its contribution to the global sea level rise. By increasing the density of seismic stations in the region it will be possible to increase the spatial and temporal resolution of the method and create detailed maps of ice-mass variations across Greenland.

  18. Potential methane emission from north-temperate lakes following ice melt

    USGS Publications Warehouse

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

    1996-01-01

    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.

  19. 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)

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

    2010-12-01

    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.

  20. Impact of ice melting on distribution of particulate sterols in glacial fjords of Chilean Patagonia

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Marcelo H.; Riquelme, Pablo; Pantoja, Silvio

    2016-04-01

    We analyzed variability in abundance and composition of sterols in waters of the fjord adjacent to glacier Jorge Montt, one of the fastest retreated glaciers in Patagonian Icefields. The study was carried out between August 2012 and November 2013 under different meltwater scenarios. Distribution of sterols in surface and bottom waters was determined by Gas Chromatography coupled to Mass Spectrometry. Sterol concentration ranged from 18 to 1726 ng/L in surface and bottom waters and was positive correlated with chlorophyll-a concentration. Under high melting conditions in austral summer, surface meltwaters showed high concentrations of sterols and were dominated by methylene-cholesterol, a representative sterol of centric diatoms. In the area near open ocean and in austral autumn, winter and spring in proglacial fjord, lower sterol concentrations in surface waters were accompanied by other microalgae sterols and an increase in relative abundance of plant sterols, evidencing a different source of organic matter. In autumn, when high meltwater flux was also evidenced, presence of stanols and an uncommon tri-unsaturated sterol suggests influence of meltwaters in composition of sterols in the downstream fjord. We conclude that ice melting can modify sterol composition by setting conditions for development of a singular phytoplankton population able to thrive in surface meltwater and by carrying glacier organic matter into Patagonian glacial fjords. In projected ice melting scenario, these changes in organic matter quantity and quality can potentially affect availability of organic substrates for heterotrophic activity and trophic status of glacial fjords. This research was funded by COPAS Sur-Austral (PFB-31)

  1. Amundsen Sea sector ice shelf thickness, melt rates, and inland response from annual high-resolution DEM mosaics

    NASA Astrophysics Data System (ADS)

    Shean, D. E.; Joughin, I. R.; Smith, B. E.; Alexandrov, O.; Moratto, Z.; Porter, C. C.; Morin, P. J.

    2014-12-01

    Significant grounding line retreat, acceleration, and thinning have occurred along the Amundsen Sea sector of West Antarctica in recent decades. These changes are driven primarily by ice-ocean interaction beneath ice shelves, but existing observations of the spatial distribution, timing, and magnitude of ice shelf melt are limited. Using the NASA Ames Stereo Pipeline, we generated digital elevation models (DEMs) with ~2 m posting from all ~450 available WorldView-1/2 along-track stereopairs for the Amundsen Sea sector. A novel iterative closest point algorithm was used to coregister DEMs to filtered Operation IceBridge ATM/LVIS data and ICESat-1 GLAS data, offering optimal sub-meter horizontal/vertical accuracy. The corrected DEMs were used to produce annual mosaics for the entire ~500x700 km region with focused, sub-annual products for ice shelves and grounding zones. These mosaics provide spatially-continuous measurements of ice shelf topography with unprecedented detail. Using these data, we derive estimates of ice shelf thickness for regions in hydrostatic equilibrium and map networks of sub-shelf melt channels for the Pine Island (PIG), Thwaites, Crosson, and Dotson ice shelves. We also document the break-up of the Thwaites ice shelf and PIG rift evolution leading up to the 2013 calving event. Eulerian difference maps document 2010-2014 thinning over fast-flowing ice streams and adjacent grounded ice. These data reveal the greatest thinning rates over the Smith Glacier ice plain and slopes beyond the margins of the fast-flowing PIG trunk. Difference maps also highlight the filling of at least two subglacial lakes ~30 km upstream of the PIG grounding line in 2011. Lagrangian difference maps reveal the spatial distribution of ice shelf thinning, which can primarily be attributed to basal melt. Preliminary results show focused ice shelf thinning within troughs and large basal channels, especially along the western margin of the Dotson ice shelf. These new data

  2. An 800-kyr Record of Global Surface Ocean δ18Osw and Implications for Ice Volume-Temperature Coupling

    NASA Astrophysics Data System (ADS)

    Shakun, J. D.; Lea, D. W.; Lisiecki, L. E.; Raymo, M. E.

    2014-12-01

    We use 49 paired sea surface temperature (SST)-planktonic δ18O records to extract the mean δ18O of surface ocean seawater (δ18Osw) over the past 800 kyr, which we interpret to dominantly reflect global ice volume, and compare it to SST variability on the same stratigraphy. This analysis suggests that ice volume and temperature contribute to the marine isotope record in ~60/40 proportions, but they show consistently different patterns over glacial cycles. Global temperature cools early during each cycle while major ice sheet growth occurs later, suggesting that ice volume may have exhibited a threshold response to cooling and also had relatively little feedback on it. Multivariate regression analysis suggests that the rate of ice volume change through time is largely determined by the combined influence of orbital forcing, global temperature, and ice volume itself (r2 = 0.70 at zero-lag for 0-400 ka), with sea level rising faster with stronger insolation and warmer temperatures and when there is more ice available to melt. Indeed, cross-spectral analysis indicates that ice volume exhibits a smaller phase lag and larger gain relative to SST at the 41 and 23 kyr periods than at the 100 kyr period, consistent with additional forcing from insolation at the obliquity and precession time scales. Removing the surface ocean δ18Osw signal from the global benthic δ18O stack produces a reconstruction of deep ocean temperature that bears considerable similarity to the Antarctic ice core temperature record (r2 = 0.80 for 0-400 ka), including cooler interglacials before 400 ka. Overall, we find a close association between global surface temperature, deep ocean temperature, and atmospheric CO2. Additionally, we find that rapid cooling precedes the gradual buildup of large continental ice sheets, which may then be instrumental in terminating the cycle.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    We analyze changes in Antarctic Bottom Waters (AABW) around the deep Southern Ocean using repeat section data collected between 1981 and 2012. The international World Ocean Circulation Experiment (WOCE) Hydrographic Program collected a global high-quality baseline of full-depth, accurate oceanographic transects in the 1980s and 1990s. Since the 2000s, some of these transects are being reoccupied, again through international collaboration, as part of GO-SHIP (The Global Ocean Ship-Based Hydrographic Investigations Program). The average dates of the first and last data used to estimate these trends are circa 1991 and 2008. Temperature analyses reveal a nearly global-scale signature of warming in the abyssal ocean ventilated from the Antarctic. In the deep basins around Antarctica, AABW warmed at a rate of 0.02 to 0.05 °C per decade below 4000 m. In addition, the waters between 1000 and 4000 m within and south of the Antarctic Circumpolar Current warmed at a rate of about 0.03 °C per decade. With this warming, cold, deep isotherms are sinking in the Southern Ocean. The 0 °C potential isotherm sinking rate is around 100 m per decade, implying a 8.2 (±2.6) Sv contraction rate of AABW, about 7% per decade. In addition to this contraction, AABW freshening is observed within the Indian and Pacific sectors of the Southern Ocean. The freshening signal is stronger closer to AABW sources. Its spatial pattern implies recent changes in AABW formation, perhaps partly owing to freshening of the shelf waters, which has been linked to increases in glacial ice sheet melt. The observed rate of water-mass freshening for AABW colder than 0°C in the Indian and Pacific Sectors of the Southern Ocean is about half of the estimated increase in mass lost by glacial ice sheets there in recent years. A positive feedback loop might link the AABW contraction and ice sheet melt-influenced freshening as follows: Increased ocean heat flux drives enhanced basal melt of floating ice shelves

  4. Assessment for Melting Temperature Measurement of Nucleic Acid by HRM

    PubMed Central

    2016-01-01

    High resolution melting (HRM), with a high sensitivity to distinguish the nucleic acid species with small variations, has been widely applied in the mutation scanning, methylation analysis, and genotyping. For the aim of extending HRM for the evaluation of thermal stability of nucleic acid secondary structures on sequence dependence, we investigated effects of the dye of EvaGreen, metal ions, and impurities (such as dNTPs) on melting temperature (Tm) measurement by HRM. The accuracy of HRM was assessed as compared with UV melting method, and little difference between the two methods was found when the DNA Tm was higher than 40°C. Both insufficiency and excessiveness of EvaGreen were found to give rise to a little bit higher Tm, showing that the proportion of dye should be considered for precise Tm measurement of nucleic acids. Finally, HRM method was also successfully used to measure Tms of DNA triplex, hairpin, and RNA duplex. In conclusion, HRM can be applied in the evaluation of thermal stability of nucleic acid (DNA or RNA) or secondary structural elements (even when dNTPs are present). PMID:27833775

  5. 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)

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

    2012-08-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    PubMed

    Bower, Jonathan P; Anastasio, Cort

    2013-08-01

    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.

  8. Determining melt regime patterns and changing melt dynamics for Alaskan glaciers and icefields using passive microwave brightness temperatures

    NASA Astrophysics Data System (ADS)

    Semmens, K. A.; Ramage, J. M.

    2012-12-01

    Monitoring and studying glacier melt dynamics is necessary for understanding how the cryosphere responds to climate variability and change. Surface melting is often a driver of enhanced glacier velocities and can affect glacial mass balance. Several decades of remotely sensed passive microwave data provides a means for characterizing and analyzing surface melt dynamics across wide spatial domains with temporal continuity. Specifically, brightness temperatures from passive microwave sensors, Special Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Radiometer for Earth Observing Systems (AMSR-E), enable the detection of melt timing and dynamics over large icefields with relatively high temporal resolution (0.5 to 3 days). The ability to detect melt stems from the distinctness of the melt signal at 36-37 GHz vertical polarization. Further, the sensors collect data in all weather and both day and night providing a complete record. Utilizing these datasets, we focus on large icefields in Alaska including Juneau, St. Elias, and Stikine, as well as on individual glaciers such as the Malaspina, Hubbard, and Bering glaciers to investigate changing melt dynamics and relationships to larger atmospheric circulation patterns and temperatures. A 24 year time series of annual brightness temperature histograms is constructed to determine years that are anomalous from the average and to assess the general melt regime characteristics of the area along with temporal and spatial trends. Potential causative and correlative factors are explored including climate indices, temperature, elevation, distance from coast, and discharge. Diurnal amplitude variations (brightness temperature differences between the day and night) are also calculated to determine melt variability and melt-refreeze duration. Melt regime pattern and type are hypothesized to be largely controlled by distance from coast (maritime versus continental), elevation, and latitude. Melt dynamics and brightness

  9. Numerical evidence of quantum melting of spin ice: quantum-classical crossover

    NASA Astrophysics Data System (ADS)

    Kato, Yasuyuki; Onoda, Shigeki

    2015-03-01

    Unbiased quantum Monte-Carlo simulations are performed on the simplest case of the quantum spin ice model, namely, the nearest-neighbor spin-1/2 XXZ model on the pyrochlore lattice with an antiferromagnetic longitudinal and a weak ferromagnetic transverse exchange couplings, J and J⊥. On cooling across TCSI ~ 0 . 2 J , the specific heat shows a broad peak associated with a crossover to a classical Coulomb liquid regime characterized by a remnant of the pinch-point singularity in longitudinal spin correlations as well as the Pauling ice entropy for | J⊥ | << J , as in classical spin ice. On further cooling, the entropy restarts gradually decaying to zero for J⊥ >J⊥ c ~ - 0 . 104 J , as expected for bosonic quantum Coulomb liquids. With negatively increasing J⊥ across J⊥ c, a first-order transition occurs at a nonzero temperature from the quantum Coulomb liquid to an XY ferromagnet. Relevance to magnetic rare-earth pyrochlore oxides is discussed.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  11. Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse

    NASA Astrophysics Data System (ADS)

    Sutter, Johannes; Gierz, Paul; Grosfeld, Klaus; Thoma, Malte; Lohmann, Gerrit

    2016-03-01

    The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea levels in excess of 7 m in the last warm era, of which probably not much more than 2 m are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3-D thermomechanical ice sheet model forced by an atmosphere-ocean general circulation model (AOGCM). Our results show that high LIG sea levels cannot be reproduced with the atmosphere-ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2-3°C, accounting for a sea level rise of 3-4 m during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming.

  12. Electrons In Water-ices At Outer Solar System Temperatures

    NASA Astrophysics Data System (ADS)

    Gudipati, Murthy; Allamandola, L. J.

    2006-09-01

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

  13. Investigation on recalescence temperatures of deeply undercooled melts

    NASA Astrophysics Data System (ADS)

    Xu, X. L.; Liu, F.; Hou, H.; Zhao, Y. H.; Gu, T.; Wang, S. Y.; Yan, F.

    2016-12-01

    According to the theory of classic thermodynamics, any transformation is driven by the decrease of Gibbs free energy of the system. Solidification pertains to the first order transformation and obeys this basic law. The Gibbs free energy of the condensed phases of metals and alloys is closely related to the temperature and composition of the system. Thus we can describe rapid solidification process in a more precise way by using quantitative thermodynamic calculation. In combination with solidification kinetics theory, we calculated the evolution of the thermodynamic parameters during rapid solidification process. On this basis, we proposed a criterion for the end point of recalescence process and built a physical model for describing rapid solidification process and predicting recalescence temperatures of undercooled melts. Good agreement can be achieved between the present model prediction and experimental data.

  14. Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous

    NASA Astrophysics Data System (ADS)

    Hansen, James; Sato, Makiko; Hearty, Paul; Ruedy, Reto; Kelley, Maxwell; Masson-Delmotte, Valerie; Russell, Gary; Tselioudis, George; Cao, Junji; Rignot, Eric; Velicogna, Isabella; Tormey, Blair; Donovan, Bailey; Kandiano, Evgeniya; von Schuckmann, Karina; Kharecha, Pushker; Legrande, Allegra N.; Bauer, Michael; Lo, Kwok-Wai

    2016-03-01

    We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6-9 m with evidence of extreme storms while Earth was less than 1

  15. Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate Modeling, and Modern Observations that 2C Global Warming Could Be Dangerous

    NASA Technical Reports Server (NTRS)

    Hansen, J.; Sato, Makiko; Hearty, Paul; Ruedy, Reto; Kelley, Maxwell; Masson-Delmotte, Valerie; Russell, Gary; Tselioudis, George; Cao, Junji; Rignot, Eric; Velicogna, Isabella; Tormey, Blair; Donovan, Bailey; Kandiano, Evgeniya; von Schuckmann, Karina; Kharecha, Pushker; Legrande, Allegra N.; Bauer, Michael; Lo, Kwok-Wai

    2016-01-01

    We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to C6-9m with evidence of extreme storms while Earth was less than 1 C

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

    SciTech Connect

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

    2014-09-14

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

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

    PubMed

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

    2014-09-14

    High-pressure H2O polymorphs among which ice VI and ice VII are abundant in the interiors of large icy satellites and exo-planets. Knowledge of the elastic properties of these pure H2O ices at high-temperature and high-pressure is thus crucial to decipher the internal structure of icy bodies. In this study we assess for the first time the pressure-volume-temperature (PVT) relations of both polycrystalline pure ice VI and ice VII at high pressures and temperatures from 1 to 9 GPa and 300 to 450 K, respectively, by using in situ synchrotron X-ray diffraction. The PVT data are adjusted to a second-order Birch-Murnaghan equation of state and give V0 = 14.17(2) cm(3) mol(-1), K0 = 14.05(23) GPa, and α0 = 14.6(14) × 10(-5) K(-1) for ice VI and V0 = 12.49(1) cm(3) mol(-1), K0 = 20.15(16) GPa, and α0 = 11.6(5) × 10(-5) K(-1) for ice VII.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    Regional "clear sky" surface temperature increases since the early 1980s in the Arctic, measured using Advanced Very High Resolution Radiometer (AVHRR) infrared data, range from 0.57+/-0.02 deg C to 72+/-0.10 deg C per decade. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near 0 deg C during the melt season, and is thus vulnerable to rapid melting if temperatures continue to increase. An increase in melting of the ice sheet would accelerate sea-level rise, an issue affecting potentially billions of people worldwide. To quantify the ice-surface temperature (IST) of the Greenland Ice Sheet, and to provide an IST dataset of Greenland for modelers that provides uncertainties, we are developing a climate-data record (CDR) of daily "clear-sky" IST of the Greenland Ice Sheet, from 1982 to the present using AVHRR (1982 - present) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data (2000 - present) at a resolution of approximately 5 km. Known issues being addressed in the production of the CDR are: time-series bias caused by cloud cover (surface temperatures can be different under clouds vs. clear areas) and cross-calibration in the overlap period between AVHRR instruments, and between AVHRR and MODIS instruments. Because of uncertainties, mainly due to clouds, time-series of satellite IST do not necessarily correspond with actual surface temperatures. The CDR will be validated by comparing results with automatic-weather station data and with satellite-derived surface-temperature products and biases will be calculated.

  19. Ice cap melting and low viscosity crustal root explain narrow geodetic uplift of the Western Alps

    NASA Astrophysics Data System (ADS)

    Chery, Jean; Genti, Manon; Vernant, Philippe

    2016-04-01

    More than 10 years of geodetic measurements demonstrate an uplift rate of 1-3 mm/yr of the high topography region of the Western Alps. By contrast, no significant horizontal motion has been detected. Three uplift mechanisms have been proposed so far: (1) the isostatic response to denudation. However this process is responsible for only a fraction of the observed uplift and (2) the rebound induced by the Wurmian ice cap melting. This process leads to a broader uplifting region than the one evidenced by geodetic observations. (3) a deep source motion associated with slab motion or some deep isostatic unbalance. Using a numerical model accounting for crustal and mantle rheology of the Alps and its foreland, we model the response to Wurmian ice cap melting. We show that a crustal viscosity contrast between the foreland and the central part of the Alps, the later being weaker with a viscosity of 1021 Pa.s, is needed to produce a narrow uplift. The vertical rates are enhanced if the strong uppermost mantle beneath the Moho is interrupted across the Alps, therefore allowing a weak vertical rheological anomaly thanks to the continuity between the low viscosity parts of the crust and mantle. References: Champagnac, J.-D., F. Schlunegger, K. Norton, F. von Blanckenburg, L. M. Abbühl, and M. Schwab (2009), Erosion-driven uplift of the modern Central Alps, Tectonophysics, 474(1-2), 236-249. Vernant, P., F. Hivert, J. Chéry, P. Steer, R. Cattin, and A. Rigo (2013), Erosion-induced isostatic rebound triggers extension in low convergent mountain ranges, geology, 41(4), 467-470.

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

    NASA Technical Reports Server (NTRS)

    Ohsaka, K.; Trinh, E. H.

    1992-01-01

    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.

  1. A characterization of Greenland Ice Sheet surface melt and runoff in contemporary reanalyses and a regional climate model

    NASA Astrophysics Data System (ADS)

    Cullather, Richard; Nowicki, Sophie; Zhao, Bin; Koenig, Lora

    2016-02-01

    For the Greenland Ice Sheet (GrIS), large-scale melt area has increased in recent years and is detectable via remote sensing, but its relation to runoff is not known. Historical, modeled melt area and runoff from Modern-Era Retrospective Analysis for Research and Applications (MERRA-Replay), the Interim Re-Analysis of the European Centre for Medium Range Weather Forecasts (ERA-I), the Climate Forecast System Reanalysis (CFSR), the Modèle Atmosphérique Régional (MAR), and the Arctic System Reanalysis (ASR) are examined. These sources compare favorably with satellite-derived estimates of surface melt area for the period 2000-2012. Spatially, the models markedly disagree on the number of melt days in the interior of the southern part of the ice sheet, and on the extent of persistent melt areas in the northeastern GrIS. Temporally, the models agree on the mean seasonality of daily surface melt and on the timing of large-scale melt events in 2012. In contrast, the models disagree on the amount, seasonality, spatial distribution, and temporal variability of runoff. As compared to global reanalyses, time series from MAR indicate a lower correlation between runoff and melt area (r2 = 0.805). Runoff in MAR is much larger in the second half of the melt season for all drainage basins, while the ASR indicates larger runoff in the first half of the year. This difference in seasonality for the MAR and to an extent for the ASR provide a hysteresis in the relation between runoff and melt area, which is not found in the other models. The comparison points to a need for reliable observations of surface runoff.

  2. Effect of gravity wave temperature variations on homogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Dinh, Tra; Podglajen, Aurélien; Hertzog, Albert; Legras, Bernard; Plougonven, Riwal

    2015-04-01

    Observations of cirrus clouds in the tropical tropopause layer (TTL) have shown various ice number concentrations (INC) (e.g., Jensen et al. 2013), which has lead to a puzzle regarding their formation. In particular, the frequently observed low numbers of ice crystals seemed hard to reconcile with homogeneous nucleation knowing the ubuquity of gravity waves with vertical velocity of the order of 0.1 m/s. Using artificial time series, Spichtinger and Krämer (2013) have illustrated that the variation of vertical velocity during a nucleation event could terminate it and limit the INC. However, their study was limited to constructed temperature time series. Here, we carry out numerical simulations of homogeneous ice nucleation forced by temperature time series data collected by isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency (30 s), so gravity wave signals are well resolved in the temperature time series. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentrations (INC) as previously observed in the tropical upper troposphere. The simulations confirm that the dynamical time scale of temperature variations (as seen from observations) can be shorter than the nucleation time scale. They show the existence of two regimes for homogeneous ice nucleation : one limited by the depletion of water vapor by the nucleated ice crystals (those we name vapor events) and one limited by the reincrease of temperature after its initial decrease (temperature events). Low INC may thus be obtained for temperature events when the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result for temperature events is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This

  3. Pressure variation of melting temperatures of alkali halides

    NASA Astrophysics Data System (ADS)

    Arafin, Sayyadul; Singh, Ram N.

    2017-02-01

    The melting temperatures of alkali halides (LiCl, LiF, NaBr, NaCl, NaF, NaI, KBr, KCl, KF, KI, RbBr, RbCl, RbI and CsI) have been evaluated over a wide range of pressures. The solid-liquid transition of alkali halides is of considerable significance due to their huge industrial applications. Our formalism requires a priori knowledge of the bulk modulus and the Grüneisen parameter at ambient conditions to compute Tm at high pressures. The computed values are in very good agreement with the available experimental results. The formalism can satisfactorily be used to compute Tm at high pressures where the experimental data are scanty. Most of the melting curves (Tm versus P) exhibit nonlinear variation with increasing pressure having curvatures downward and exhibit a maximum in some cases like NaCl, RbBr, RbCl and RbI. The values of Tmmax and Pmax corresponding to the maxima of the curves are given.

  4. A snow and ice melt seasonal prediction modelling system for Alpine reservoirs

    NASA Astrophysics Data System (ADS)

    Förster, Kristian; Oesterle, Felix; Hanzer, Florian; Schöber, Johannes; Huttenlau, Matthias; Strasser, Ulrich

    2016-10-01

    The timing and the volume of snow and ice melt in Alpine catchments are crucial for management operations of reservoirs and hydropower generation. Moreover, a sustainable reservoir operation through reservoir storage and flow control as part of flood risk management is important for downstream communities. Forecast systems typically provide predictions for a few days in advance. Reservoir operators would benefit if lead times could be extended in order to optimise the reservoir management. Current seasonal prediction products such as the NCEP (National Centers for Environmental Prediction) Climate Forecast System version 2 (CFSv2) enable seasonal forecasts up to nine months in advance, with of course decreasing accuracy as lead-time increases. We present a coupled seasonal prediction modelling system that runs at monthly time steps for a small catchment in the Austrian Alps (Gepatschalm). Meteorological forecasts are obtained from the CFSv2 model. Subsequently, these data are downscaled to the Alpine Water balance And Runoff Estimation model AWARE running at monthly time step. Initial conditions are obtained using the physically based, hydro-climatological snow model AMUNDSEN that predicts hourly fields of snow water equivalent and snowmelt at a regular grid with 50 m spacing. Reservoir inflow is calculated taking into account various runs of the CFSv2 model. These simulations are compared with observed inflow volumes for the melting and accumulation period 2015.

  5. Spring melt ponds drive Arctic September ice at past, present and future climates in coupled climate simulation

    NASA Astrophysics Data System (ADS)

    Schroeder, David; Feltham, Danny; Rae, Jamie; Flocco, Daniela; Ridley, Jeff; Blockley, Edd

    2016-04-01

    Stand-alone sea ice simulations with a physical based melt pond model reveal a strong correlation between the simulated spring pond fraction and the observed as well as simulated September sea ice extent for the period 1979 to 2014. This is explained by a positive feedback mechanism: more ponds reduce the albedo; a lower albedo causes more melting; more melting increases pond fraction. This feedback process is a potential reason for the acceleration of Arctic sea ice decrease in the last decade and the failure of many climate models (without an implicit pond model) to simulate the observed decrease. We implemented the Los Alamos sea ice model CICE 5 including our physical based melt pond model into the latest version of the Hadley Centre coupled climate model, HadGEM3. The model surface shortwave radiation scheme has been adjusted to account for pond fraction and depth. We performed three 55-year HadGEM3 simulations with constant external forcing for the years 1985, 2010 and 2035. In all three simulations we find a strong correlation between the April/May pond fraction and the September sea ice extent with correlation coefficients R1985 = -0.86, R2010 = -0.83 and R2035 = -0.79. Based on the correlation we can perform forecasts with remarkable skill values of S1985 = 0.50, S2010 = 0.36 and S2035 = 0.40. We calculate the skill as S = 1 - σferr2/ σref2, where σref2 is the variance of the de-trended climatology and σferr2 the forecast error variance. Altogether our three simulations cover a large range of September sea ice extent from maximum values of 8.5 million km2 for the 1985 run down to 1.5 million km2 for the 2035 run. We demonstrate that spring melt ponds are an important driver for summer ice melt and the consequent minimum ice extent for current and future climate conditions.

  6. Relationships linking primary production, sea ice melting, and biogenic aerosol in the Arctic

    NASA Astrophysics Data System (ADS)

    Becagli, S.; Lazzara, L.; Marchese, C.; Dayan, U.; Ascanius, S. E.; Cacciani, M.; Caiazzo, L.; Di Biagio, C.; Di Iorio, T.; di Sarra, A.; Eriksen, P.; Fani, F.; Giardi, F.; Meloni, D.; Muscari, G.; Pace, G.; Severi, M.; Traversi, R.; Udisti, R.

    2016-07-01

    This study examines the relationships linking methanesulfonic acid (MSA, arising from the atmospheric oxidation of the biogenic dimethylsulfide, DMS) in atmospheric aerosol, satellite-derived chlorophyll a (Chl-a), and oceanic primary production (PP), also as a function of sea ice melting (SIM) and extension of the ice free area in the marginal ice zone (IF-MIZ) in the Arctic. MSA was determined in PM10 samples collected over the period 2010-2012 at two Arctic sites, Ny Ålesund (78.9°N, 11.9°E), Svalbard islands, and Thule Air Base (76.5°N, 68.8°W), Greenland. PP is calculated by means of a bio-optical, physiologically based, semi-analytical model in the potential source areas located in the surrounding oceanic regions (Barents and Greenland Seas for Ny Ålesund, and Baffin Bay for Thule). Chl-a peaks in May in the Barents sea and in the Baffin Bay, and has maxima in June in the Greenland sea; PP follows the same seasonal pattern of Chl-a, although the differences in absolute values of PP in the three seas during the blooms are less marked than for Chl-a. MSA shows a better correlation with PP than with Chl-a, besides, the source intensity (expressed by PP) is able to explain more than 30% of the MSA variability at the two sites; the other factors explaining the MSA variability are taxonomic differences in the phytoplanktonic assemblages, and transport processes from the DMS source areas to the sampling sites. The taxonomic differences are also evident from the slopes of the correlation plots between MSA and PP: similar slopes (in the range 34.2-36.2 ng m-3of MSA/(gC m-2 d-1)) are found for the correlation between MSA at Ny Ålesund and PP in Barents Sea, and between MSA at Thule and PP in the Baffin Bay; conversely, the slope of the correlation between MSA at Ny Ålesund and PP in the Greenland Sea in summer is smaller (16.7 ng m-3of MSA/(gC m-2 d-1)). This is due to the fact that DMS emission from the Barents Sea and Baffin Bay is mainly related to the MIZ

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

    NASA Astrophysics Data System (ADS)

    Tuffen, Hugh

    2007-03-01

    Models of the early stages of basaltic eruptions beneath temperate glaciers are presented that consider the evolving sizes of volcanic edifices emplaced within subglacial cavities. The cavity size reflects the competing effects of enlargement by melting and closure by downward ductile deformation of the ice roof, which occurs when the cavity pressure is less than glaciostatic due to meltwater drainage. Eruptions of basaltic magma from fissures and point sources are considered, which form either hemicylindrical or hemispherical cavities. The rate of roof closure can therefore be estimated using Nye's law. The cavity size, edifice size, and depth of meltwater above the edifice are predicted by the model and are used to identify two potential eruption mechanisms: explosive and intrusive. When the cavity is considerably larger than the edifice, hydroclastic fragmentation is possible via explosive eruptions, with deposition of tephra by eruption-fed aqueous density currents. When the edifice completely fills the cavity, rising magma is likely to quench within waterlogged tephra in a predominantly intrusive manner. The models were run for a range of magma discharge rates, ice thicknesses and cavity pressures relevant to subglacial volcanism in Iceland. Explosive eruptions occur at high magma discharge rates, when there is insufficient time for significant roof closure. The models correctly predict the style of historic and Pleistocene subglacial fissure eruptions in Iceland and are used to explain the contrasting sedimentology of basaltic and rhyolitic tuyas. The models also point to new ways of unraveling the complex coupling between eruption mechanisms and glacier response during subglacial eruptions.

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

    NASA Astrophysics Data System (ADS)

    Budke, C.; Koop, T.

    2014-09-01

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

  9. Temperature Effects on Aluminoborosilicate Glass and Melt Structure

    NASA Astrophysics Data System (ADS)

    Wu, J.; Stebbins, J. F.

    2008-12-01

    Quantitative determination of the atomic-scale structure of multi-component oxide melts, and the effects of temperature on them, is a complex problem. Ca- and Na- aluminoborosilicates are especially interesting, not only because of their major role in widespread technical applications (flat-panel computer displays, fiber composites, etc.), but because the coordination environments of two of their main network cations (Al3+ and B3+) change markedly with composition and temperature is ways that may in part be analogous to processes in silicate melts at high pressures in the Earth. Here we examine a series of such glasses with different cooling rates, chosen to evaluate the role modifier cation field strength (Ca2+ vs. Na+) and of non-bridging oxygen (NBO) content. To explore the effects of fictive temperature, fast quenched and annealed samples were compared. We have used B-11 and Al-27 MAS NMR to measure the different B and Al coordinations and calculated the contents of non-bridging oxygens (NBO). Lower cooling rates increase the fraction of [4]B species in all compositions. The conversion of [3]B to [4]B is also expected to convert NBO to bridging oxygens, which should affect thermodynamic properties such as configurational entropy and configurational heat capacity. For four compositions with widely varying compositions and initial NBO contents, analysis of the speciation changes with the same, simple reaction [3]B = [4]B + NBO yields similar enthalpy values of 25±7 kJ/mol. B-11 triple quantum MAS NMR allows as well the proportions of [3]B boroxol ring and non-ring sites to be determined, and reveals more [3]B boroxol ring structures present in annealed (lower temperature) glasses. In situ, high-temperature MAS NMR spectra have been collected on one of the Na-aluminoborosilicate and on a sodium borate glass at 14.1 T. The exchange of boron between the 3- and 4-coordinated sites is clearly observed well above the glass transition temperatures, confirming the

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  11. Late Holocene stable-isotope based winter temperature records from ice wedges in the Northeast Siberian Arctic

    NASA Astrophysics Data System (ADS)

    Opel, Thomas; Meyer, Hanno; Laepple, Thomas; Dereviagin, Alexander Yu.

    2016-04-01

    The Arctic is currently undergoing an unprecedented warming. This highly dynamic response on changes in climate forcing and the global impact of the Arctic water, carbon and energy balances make the Arctic a key region to study past, recent and future climate changes. Recent proxy-based temperature reconstructions indicate a long-term cooling over the past about 8 millennia that is mainly related to a decrease in solar summer insolation and has been reversed only by the ongoing warming. Climate model results on the other hand show no significant change or even a slight warming over this period. This model-proxy data mismatch might be caused by a summer bias of the used climate proxies. Ice wedges may provide essential information on past winter temperatures for a comprehensive seasonal picture of Holocene Arctic climate variability. Polygonal ice wedges are a widespread permafrost feature in the Arctic tundra lowlands. Ice wedges form by the repeated filling of thermal contraction cracks with snow melt water, which quickly refreezes at subzero ground temperatures and forms ice veins. As the seasonality of frost cracking and infill is generally related to winter and spring, respectively, the isotopic composition of wedge ice is indicative of past climate conditions during the annual cold season (DJFMAM, hereafter referred to as winter). δ18O of ice is interpreted as proxy for regional surface air temperature. AMS radiocarbon dating of organic remains in ice-wedge samples provides age information to generate chronologies for single ice wedges as well as regionally stacked records with an up to centennial resolution. In this contribution we seek to summarize Holocene ice-wedge δ18O based temperature information from the Northeast Siberian Arctic. We strongly focus on own work in the Laptev Sea region but consider as well literature data from other regional study sites. We consider the stable-isotope composition of wedge ice, ice-wedge dating and chronological

  12. A synthetic ice core approach to estimate ion relocation in an ice field site experiencing periodical melt: a case study on Lomonosovfonna, Svalbard

    NASA Astrophysics Data System (ADS)

    Vega, Carmen P.; Pohjola, Veijo A.; Beaudon, Emilie; Claremar, Björn; van Pelt, Ward J. J.; Pettersson, Rickard; Isaksson, Elisabeth; Martma, Tõnu; Schwikowski, Margit; Bøggild, Carl E.

    2016-05-01

    Physical and chemical properties of four different ice cores (LF-97, LF-08, LF-09 and LF-11) drilled at Lomonosovfonna, Svalbard, were compared to investigate the effects of meltwater percolation on the chemical and physical stratigraphy of these records. A synthetic ice core approach was employed as reference record to estimate the ionic relocation and meltwater percolation length at this site during the period 2007-2010. Using this method, a partial ion elution sequence obtained for Lomonosovfonna was NO3- > SO42-, Mg2+, Cl-, K+, Na+ with nitrate being the most mobile within the snowpack. The relocation length of most of the ions was on the order of 1 m during this period. In addition, by using both a positive degree day (PDD) and a snow-energy model approaches to estimate the percentage of melt at Lomonosovfonna, we have calculated a melt percentage (MP) of the total annual accumulation within the range between 48 and 70 %, for the period between 2007 and 2010, which is above the MP range suggested by the ion relocation evidenced in the LF-syn core (i.e., MP = 30 %). Using a firn-densification model to constrain the melt range, a MP of 30 % was found over the same period, which is consistent with the results of the synthetic ice core approach, and a 45 % of melt for the last 60 years. Considering the ionic relocation lengths and annual melt percentages, we estimate that the atmospheric ionic signal remains preserved in recently drilled Lomonosovfonna ice cores at an annual or bi-annual resolution when weather conditions were similar to those during the 2007-2010 period.

  13. Temperature effects on atomic pair distribution functions of melts

    SciTech Connect

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

    2014-02-14

    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.

  14. Arctic sea-ice melting: Effects on hydroclimatic variability and on UV-induced carbon cycling

    NASA Astrophysics Data System (ADS)

    Sulzberger, Barbara

    2016-04-01

    Since 1980 both the perennial and the multiyear central Arctic sea ice areas have declined by approximately 13 and 15% per decade, respectively (IPCC, 2013). Arctic sea-ice melting has led to an increase in the amplitude of the Northern Hemisphere jet stream and, as a consequence, in more slowly moving Rossby waves which results in blocking of weather patterns such as heat waves, droughts, cold spells, and heavy precipitation events (Francis and Vavrus, 2012). Changing Rossby waves account for more than 30% of the precipitation variability over several regions of the northern middle and high latitudes, including the US northern Great Plains and parts of Canada, Europe, and Russia (Schubert et al., 2011). From 2007 to 2013, northern Europe experienced heavy summer precipitation events that were unprecedented in over a century, concomitant with Arctic sea ice loss (Screen, 2013). Heavy precipitation events tend to increase the runoff intensity of terrigenous dissolved organic matter (tDOM) (Haaland et al., 2010). In surface waters tDOM is subject to UV-induced oxidation to produce atmospheric CO2. Mineralization of DOM also occurs via microbial respiration. However, not all chemical forms of DOM are available to bacterioplankton. UV-induced transformations generally increase the bioavailability of tDOM (Sulzberger and Durisch-Kaiser, 2009). Mineralization of tDOM is an important source of atmospheric CO2 and this process is likely to contribute to positive feedbacks on global warming (Erickson et al., 2015). However, the magnitudes of these potential feedbacks remain unexplored. This paper will discuss the following items: 1.) Links between Arctic sea-ice melting, heavy precipitation events, and enhanced tDOM runoff. 2.) UV-induced increase in the bioavailability of tDOM. 3.) UV-mediated feedbacks on global warming. References Erickson, D. J. III, B. Sulzberger, R. G. Zepp, A. T. Austin (2015), Effects of stratospheric ozone depletion, solar UV radiation, and climate

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  16. Pd-modified Reactive Air Braze for Increased Melting Temperature

    SciTech Connect

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

    2005-03-01

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

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

    NASA Technical Reports Server (NTRS)

    Vargas, Mario; Reshotko, Eli

    2000-01-01

    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.

  18. Self-consistent ice-sheet properties: ice dynamics, temperature, accumulation, delta-age and chronologies for ice cores and radar isochrones

    NASA Astrophysics Data System (ADS)

    Lundin, J.; Waddington, E. D.; Conway, H.

    2011-12-01

    Ice sheet behavior has not previously been modeled to force self-consistency, to determine histories of accumulation, temperature, and ice dynamics that incorporate the ice-age/gas-age offset (delta-age) and sparse depth-age measurements from ice cores. An iterative scheme is used to combine several modular components into one self-consistent model. The goal is to determine a suite of histories constrained by the depth-age data from ice cores and ice radar that are part of a physically self-consistent ice sheet. The model is tested using a synthetic data set resembling WAIS divide. Using synthetic data provides proof of concept that histories of accumulation, temperature and ice dynamics can be recovered by the self-consistent model, and that the depth-age from ice cores and ice radar can be matched. Results from synthetic data show we can recover the ice-sheet properties used to generate the data and we can improve the depth-age chronologies by interpolating with an ice-flow model where data are sparse. When this self-consistent model can be applied to field data, results will (1) improve chronologies for ice cores and radar layers, (2) determine histories of accumulation for GCM modelling, and (3) improve estimates of past ice sheet configurations, incorporating data from ice cores and ice radar.

  19. Studying regimes of convective heat transfer in the production of high-temperature silicate melts

    NASA Astrophysics Data System (ADS)

    Volokitin, O. G.; Sheremet, M. A.; Shekhovtsov, V. V.; Bondareva, N. S.; Kuzmin, V. I.

    2016-09-01

    The article presents the results of theoretical and experimental studies of the production of high-temperature silicate melts using the energy of low-temperature plasma in a conceptually new setup. A mathematical model of unsteady regimes of convective heat and mass transfer is developed and numerically implemented under the assumption of non-Newtonian nature of flow in the melting furnace with plasma-chemical synthesis of high-temperature silicate melts. Experiments on melting silicate containing materials were carried out using the energy of low-temperature plasma. The dependence of dynamic viscosity of various silicate materials (basalt, ash, waste of oil shale) was found experimentally.

  20. 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)

    Fischer, Hubertus

    2014-05-01

    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 δ18O (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 δ11B 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

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

    PubMed

    Zelent, B; Vanderkooi, J M

    2009-07-15

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

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

    PubMed

    Liu, Minglu; Wang, Robert Y

    2013-08-21

    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.

  3. Numerical modeling of inward and outward melting of high temperature PCM in a vertical cylinder

    NASA Astrophysics Data System (ADS)

    Riahi, S.; Saman, W. Y.; Bruno, F.; Tay, N. H. S.

    2016-05-01

    Numerical study of inward and outward melting of a high temperature PCM in cylindrical enclosures were performed, using FLUENT 15. For validation purposes, numerical modeling of inward melting of a low temperature PCM was initially conducted and the predicted results were compared with the experimental data from the literature. The validated model for the low temperature PCM was used for two high temperature cases; inward melting of a high temperature PCM in a cylindrical enclosure and outward melting in a cylindrical case with higher aspect ratio. The results of this study show that the numerical model developed is capable of capturing the details of melting process with buoyancy driven convection for Ra<108, i.e. laminar flow, for a high temperature PCM and can be used for the design and optimization of a latent heat thermal storage unit.

  4. Melt pond fraction and spectral sea ice albedo retrieval from MERIS data - Part 1: Validation against in situ, aerial, and ship cruise data

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    The presence of melt ponds on the Arctic sea ice strongly affects the energy balance of the Arctic Ocean in summer. It affects albedo as well as transmittance through the sea ice, which has consequences for the heat balance and mass balance of sea ice. An algorithm to retrieve melt pond fraction and sea ice albedo from Medium Resolution Imaging Spectrometer (MERIS) data is validated against aerial, shipborne and in situ campaign data. The results show the best correlation for landfast and multiyear ice of high ice concentrations. For broadband albedo, R2 is equal to 0.85, with the RMS (root mean square) being equal to 0.068; for the melt pond fraction, R2 is equal to 0.36, with the RMS being equal to 0.065. The correlation for lower ice concentrations, subpixel ice floes, blue ice and wet ice is lower due to ice drift and challenging for the retrieval surface conditions. Combining all aerial observations gives a mean albedo RMS of 0.089 and a mean melt pond fraction RMS of 0.22. The in situ melt pond fraction correlation is R2 = 0.52 with an RMS = 0.14. Ship cruise data might be affected by documentation of varying accuracy within the Antarctic Sea Ice Processes and Climate (ASPeCt) protocol, which may contribute to the discrepancy between the satellite value and the observed value: mean R2 = 0.044, mean RMS = 0.16. An additional dynamic spatial cloud filter for MERIS over snow and ice has been developed to assist with the validation on swath data.

  5. Aureimonas glaciistagni sp. nov., isolated from a melt pond on Arctic sea ice.

    PubMed

    Cho, Yirang; Lee, Inae; Yang, Yoon Y; Baek, Kiwoon; Yoon, Soo J; Lee, Yung M; Kang, Sung-Ho; Lee, Hong K; Hwang, Chung Y

    2015-10-01

    A Gram-staining-negative, motile, aerobic and rod-shaped bacterial strain, PAMC 27157T, was isolated from a melt pond on sea ice in the Chukchi Sea. Phylogenetic analysis of the 16S rRNA gene sequence of strain PAMC 27157T revealed an affiliation to the genus Aureimonas with the closest sequence similarity (96.2 %) to that of Aureimonas phyllosphaerae. Strain PAMC 27157T grew optimally at 30 °C and pH 7.0 in the presence of 3.5 % (w/v) NaCl. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, phosphatidylmonomethylethanolamine, sulfoquinovosyldiacylglycerol and an unidentified aminolipid. The major cellular fatty acid was summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c, 83.1 %) and the major respiratory quinone was Q-10. The genomic DNA G+C content was 69.1 mol%. The combined phylogenetic, phenotypic and chemotaxonomic data showed that strain PAMC 27157T could be clearly distinguished from species of the genus Aureimonas with validly published names. Thus, strain PAMC 27157T should be classified as representing a novel species in the genus Aureimonas, for which the name Aureimonas glaciistagni sp. nov. is proposed. The type strain is PAMC 27157T ( = KCCM 43049T = JCM 30183T).

  6. Arctic ice surface temperature retrieval from AVHRR thermal channels

    NASA Technical Reports Server (NTRS)

    Key, J.; Haeflinger, M.

    1992-01-01

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

  7. Martian north pole summer temperatures: dirty water ice.

    PubMed

    Kieffer, H H; Chase, S C; Martin, T Z; Miner, E D; Palluconi, F D

    1976-12-11

    Broadband thermal and reflectance observations of the martian north polar region in late summer yield temperatures for the residual polar cap near 205 K with albedos near 43 percent. The residual cap and several outlying smaller deposits are water ice with included dirt; there is no evidence for any permanent carbon dioxide polar cap.

  8. Martian north pole summer temperatures - Dirty water ice

    NASA Technical Reports Server (NTRS)

    Kieffer, H. H.; Martin, T. Z.; Chase, S. C., Jr.; Miner, E. D.; Palluconi, F. D.

    1976-01-01

    Broadband thermal and reflectance observations of the Martian north polar region in late summer yield temperatures for the residual polar cap near 205 K with albedos near 43 percent. The residual cap and several outlying smaller deposits are water ice with included dirt; there is no evidence for any permanent carbon dioxide polar cap.

  9. Ocean Profile Measurements During the Seasonal Ice Zone Reconnaissance Surveys

    DTIC Science & Technology

    2014-09-30

    Chukchi sea seasonal sea ice zone (SIZ) utilizing US Coast Guard Arctic Domain Awareness (ADA) flights of opportunity. This report covers our grant... ice cover in 2014. The consequent reduced melting early in the summer delays the onset of sea- ice -albedo feed back in accelerating melt throughout the...season and thus reduces the melt -back of the ice edge. The reduction in upper ocean temperatures may also explain our 2014 visual observations of

  10. Entropic changes in liquid gallium clusters: understanding the anomalous melting temperatures

    NASA Astrophysics Data System (ADS)

    Gaston, Nicola; Steenbergen, Krista

    Melting in finite-sized materials differs in two ways from the solid-liquid phase transition in bulk systems. First, there is an inherent scaling of the melting temperature below that of the bulk, known as melting point depression. Secondly, at small sizes, changes in melting temperature become non-monotonic, and show a size-dependence that is sensitive to the structure of the particle. Melting temperatures that exceed those of the bulk material have been shown to occur in vacuum, but have still never been ascribed a convincing physical explanation. Here we find answers in the structure of the aggregate liquid phase in small gallium clusters, based on molecular dynamics simulations that reproduce the greater-than-bulk melting behavior observed in experiments, and demonstrate the critical role of a lowered entropy in destabilising the liquid state.

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

    USGS Publications Warehouse

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

    2001-01-01

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

  12. Aerosolization of two strains (ice+ and ice-) of Pseudomonas syringae in a Collison nebulizer at different temperatures

    NASA Astrophysics Data System (ADS)

    Pietsch, Renee; David, Ray; Marr, Linsey; Vinatzer, Boris; Schmale, David

    2015-04-01

    The aerosolization of microorganisms from aquatic environments is understudied. In this study, an ice nucleation active (ice+) strain and a non-ice nucleation active (ice-) strain of the bacterium Pseudomonas syringae were aerosolized from aqueous suspensions under artificial laboratory conditions using a Collison nebulizer. The aerosolization of P. syringae was not influenced by water temperatures between 5° and 30°C. In general, the culturability (viability) of P. syringae in aerosols increased with temperature between 5 and 30°C. The ice+ strain was aerosolized in greater numbers than the ice- strain at all temperatures studied, suggesting a possible connection between the ice nucleation phenotype and aerosol production. Together, our results suggest that P. syringae has the potential to be aerosolized from natural aquatic environments, such as streams, rivers, ponds, and lakes; known reservoirs of P. syringae. Future work is needed to elucidate the mechanisms of aerosolization of P. syringae from natural aquatic systems.

  13. Temperature and Runback Ice Prediction Method for Three-Dimensional Hot Air Anti-Icing System

    NASA Astrophysics Data System (ADS)

    Zhou, Ying; Lin, Guiping; Bu, Xueqin; Mu, Zuodong; Pan, Rui; Ge, Qimo; Qiao, Xudong

    2017-03-01

    A prediction method of surface temperature and runback ice for a three-dimensional hot air anti-icing system was proposed. Computational approach to realize this method was introduced. Both the external and internal flows were separately calculated, results of which were set as boundary conditions of heat conduction computation in airfoil skin. The results of external and internal flow calculations show that the effect of surface temperature on convective heat transfer coefficients and local droplet collection efficiency is negligible and the calculations can be decoupled. The prediction method based on heat flux was used to calculate surface temperature and runback ice results. The results show that, the effects of LWC and Mach number are much more significant than the effect of external flow temperature. The surface temperature at impinging interaction point is more sensitive to the change of external conditions than that at stagnation point. The surface temperature changes significantly with changing Mach number because both the mass rate of droplet and the impact limit are changed.

  14. Dislocation Creep of Ice At Glaciological Pressures and Temperatures

    NASA Astrophysics Data System (ADS)

    Qi, C.; Goldsby, D. L.

    2015-12-01

    The Glen law, a power law between effective strain rate ɛdot and effective stress τ of the form ɛdot=Aτn, where A is a temperature-dependent parameter, and n is the stress exponent of value 3, attributed to dislocation creep, has underpinned models and calculations of glacier flow for over six decades. Compilations of ice creep data from tests at ambient and elevated confining pressures, however, suggest that dislocation creep of ice is characterized by a value of n=4, not 3. While high-pressure experiments on ice provide the best constraints on the dislocation creep regime and have consistently yielded a stress exponent of ~4, most of these tests have been conducted at much-lower-than-glaciological temperatures (Durham et al., 1992). To investigate dislocation creep of ice at glaciological conditions, we deformed samples at temperatures ≥264 K and elevated confining pressures up to ~30 MPa, the maximum cryostatic pressure in the ice sheets. Samples were formed by flooding evacuated cylindrical compacts of distilled-water seed ice of particle sizes 0.18-0.25 mm or 1-1.6 mm at 273 K, followed by freezing at 243 K. Each indium-jacketed specimen was deformed in compression in a gas-medium apparatus at a single constant displacement rate to ~20% strain, at nominally constant strain rates of from 10-6 to 10-3 s-1. In each test, we obtain the peak stress after ~2-3% strain and the steady-state flow stress at larger strains. Plots of strain rate vs. both peak stress and flow stress yield a value of n=4, consistent with previous data from higher-pressure, lower-temperature tests (Durham et al., 1992) and from some ambient pressure experiments (Goldsby and Kohlstedt, 2001), and with models of climb-limited dislocation creep (Weertman, 1968). At stresses <3 MPa, tests on the finer-grained samples show a slight decrease in n to a value <4, while data for the coarser-grained samples show no such transition, consistent with the onset of dislocation-accommodated grain

  15. Correlation between average melting temperature and glass transition temperature in metallic glasses

    NASA Astrophysics Data System (ADS)

    Lu, Zhibin; Li, Jiangong

    2009-02-01

    The correlation between average melting temperature (⟨Tm⟩) and glass transition temperature (Tg) in metallic glasses (MGs) is analyzed. A linear relationship, Tg=0.385⟨Tm⟩, is observed. This correlation agrees with Egami's suggestion [Rep. Prog. Phys. 47, 1601 (1984)]. The prediction of Tg from ⟨Tm⟩ through the relationship Tg=0.385⟨Tm⟩ has been tested using experimental data obtained on a large number of MGs. This relationship can be used to predict and design MGs with a desired Tg.

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  17. The melting temperature of liquid water with the effective fragment potential

    SciTech Connect

    Brorsen, Kurt R.; Willow, Soohaeng Y.; Xantheas, Sotiris S.; Gordon, Mark S.

    2015-09-17

    Direct simulation of the solid-liquid water interface with the effective fragment potential (EFP) via the constant enthalpy and pressure (NPH) ensemble was used to estimate the melting temperature (Tm) of ice-Ih. Initial configurations and velocities, taken from equilibrated constant pressure and temperature (NPT) simulations at T = 300 K, 350 K and 400 K, respectively, yielded corresponding Tm values of 378±16 K, 382±14 K and 384±15 K. These estimates are consistently higher than experiment, albeit to the same degree with previously reported estimates using density functional theory (DFT)-based Born-Oppenheimer simulations with the Becke-Lee-Yang-Parr functional plus dispersion corrections (BLYP-D). KRB was supported by a Computational Science Graduate Fellowship from the Department of Energy. MSG was supported by a U.S. National Science Foundation Software Infrastructure (SI2) grant (ACI – 1047772). SSX acknowledges support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle.

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

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

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

    PubMed

    Kawamoto; Holloway

    1997-04-11

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

  20. A Thermal Melt Probe System for Extensive, Low-Cost Instrument Deployment Within and Beneath Ice Sheets

    NASA Astrophysics Data System (ADS)

    Winebrenner, D. P.; Elam, W. T.; Carpenter, M.; Kintner, P., III

    2014-12-01

    More numerous observations within and beneath ice sheets are needed to address a broad variety of important questions concerning ice sheets and climate. However, emplacement of instruments continues to be constrained by logistical burdens, especially in cold ice a kilometer or more thick. Electrically powered thermal melt probes are inherently logistically light and efficient, especially for reaching greater depths in colder ice. They therefore offer a means of addressing current measurement problems, but have been limited historically by a lack of technology for reliable operation at the necessary voltages and powers. Here we report field tests in Greenland of two new melt probes. We operated one probe at 2.2 kilowatts (kW) and 1050 volts (V), achieving a depth of 400 m in the ice in ~ 120 hours, without electrical failure. That depth is the second greatest achieved thus far with a thermal melt probe, exceeded only by one deployment to 1005 m in Greenland in 1968, which ended in an electrical failure. Our test run took place in two intervals separated by a year, with the probe frozen at 65 m depth during the interim, after which we re-established communication, unfroze the probe, and proceeded to the greater depth. During the second field test we operated a higher-power probe, initially at 2.5 kW and 1500 V and progressing to 4.5 kW and 2000 V. Initial data indicate that this probe achieved a descent rate of 8 m/hr, which if correct would be the fastest rate yet achieved for such probes. Moreover, we observed maintenance of vertical probe travel using pendulum steering throughout both tests, as well as autonomous descent without operator-intervention after launch. The latter suggests potential for crews of 1-2 to operate several melt probes concurrently. However, the higher power probe did suffer electrical failure of a heating element after 7 hours of operation at 2000 V (24 hours after the start of the test), contrary to expectations based on laboratory

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

    SciTech Connect

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

    2010-01-28

    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.

  2. Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

    PubMed Central

    Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E.

    2016-01-01

    TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1−xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now. PMID:27905481

  3. Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

    NASA Astrophysics Data System (ADS)

    Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E.

    2016-12-01

    TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1‑xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now.

  4. Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system.

    PubMed

    Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D; Konings, Rudy J M; Reece, Michael J; Lee, William E

    2016-12-01

    TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1-xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now.

  5. Near Ice Oceanographic Observations of the Breiðamerkurjökull Glacier Melt Plume in Jökulsárlón Lagoon, Iceland

    NASA Astrophysics Data System (ADS)

    Brandon, M. A.; Hodgkins, R.

    2014-12-01

    The Breiðamerkurjökull glacier flows down from the Vatnajökull ice cap and it has a marine terminus in a lagoon connected to the North Atlantic Ocean. The lagoon waters have characteristics determined by the Atlantic water, subglacial run-off and the local melting of ice calved from the glacier. The lagoon is not a fjordic environment, but many similar physical processes are operating. We conducted four hydrographic sections within the lagoon to determine the effects of the ocean on the glacier. Three of the sections across the lagoon allow us to determine the pathway of Atlantic water towards the glacial ice. One hydrographic section of 16 stations along the Breiðamerkurjökull glacier face was always within 3 to 30m from the ice face. This very near ice section showed both the warmest and coldest water sampled in the lagoon. The coldest water was close to the maximum depth of our measurements and was formed through contact with the ice. A heat and salt conservation model has enabled the relative contributions of the inflowing Atlantic derived saline water, the sub glacial fresh water run-off and the melt from the ice face to be determined. Overall the dominant freshwater contribution to the lagoon in the upper 20 m is from the sub-glacial freshwater. Beneath 20 m the dominant factor is modified North Atlantic water. The contribution from melting ice is observed below 10 m, and below 40 m depth this is in layers. Individual CTD measurements show that within the layers of higher ice melt there are strong peaks of increased melt, and so there is a 3 dimensional structure to the melt. The highest resolution data we obtained show that the water at these depths is in places statically unstable.

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  7. Ab initio calculations of the melting temperatures of refractory bcc metals.

    PubMed

    Wang, L G; van de Walle, A

    2012-01-28

    We present ab initio calculations of the melting temperatures for bcc metals Nb, Ta and W. The calculations combine phase coexistence molecular dynamics (MD) simulations using classical embedded-atom method potentials and ab initio density functional theory free energy corrections. The calculated melting temperatures for Nb, Ta and W are, respectively, within 3%, 4%, and 7% of the experimental values. We compare the melting temperatures to those obtained from direct ab initio molecular dynamics simulations and see if they are in excellent agreement with each other. The small remaining discrepancies with experiment are thus likely due to inherent limitations associated with exchange-correlation energy approximations within density-functional theory.

  8. Fifteen Year Record of Land Surface Temperature and Surface Albedo over Ice Caps in the Queen Elizabeth Islands, Arctic Canada, 2000-2014

    NASA Astrophysics Data System (ADS)

    Mortimer, C.

    2015-12-01

    This study investigates the relationship between changes in land surface temperature (LST) and surface albedo over ice caps in the Queen Elizabeth Islands (QEI), Arctic Canada, for the period 2000-2014. Higher mean summer LST can indicate a more intense and/or longer melt season. Higher LST has been tied to higher rates of glacier mass loss as well as a reduction in surface albedo. A lower albedo means more solar radiation is absorbed which can increase the LST, leading to more melt and further reductions in albedo. Recent work on the Greenland Ice Sheet, immediately east of the QEI, has found recent reductions in ice sheet albedo to be consistent with documented increases in summer air and ice temperatures as well as melt and mass loss. No studies documenting large-scale trends in surface albedo and their relationship to land surface temperatures, surface melt and glacial mass balance exist for the QEI. Data from the Moderate Resolution Imaging Spectroradiometer (MODIS) are used to determine mean summer clear-sky land surface temperature over QEI ice caps and glaciers from 2000 to 2014 (MOD11A2), and mean and minimum shortwave broadband white-sky and black-sky albedo from 2001 to 2014 (MCD43A3). Preliminary results reveal 14yr (2001-2014) mean summer melt season white-sky and black-sky surface albedos, of 0.547 and 0.562, respectively, averaged across all ice masses in the QEI. Mean summer QEI-wide ice surface temperature, averaged over the period 2000-2014 was 269.2K with a maximum of 270.4K in 2007. Manson Icefield and Sydkap Ice Cap, situated on southern Ellesmere Island had both the lowest mean summer albedo and the highest mean summer LST whilst the ice masses on northern Ellesmere and Axel Heiberg Islands, in the northwest sector of the QEI, had both the highest mean summer albedo and the lowest mean summer LST. Expanding on these preliminary results, the spatial and temporal trends in LST and albedo over ice caps in the QEI will be presented and the

  9. Diazotroph Diversity in the Sea Ice, Melt Ponds, and Surface Waters of the Eurasian Basin of the Central Arctic Ocean.

    PubMed

    Fernández-Méndez, Mar; Turk-Kubo, Kendra A; Buttigieg, Pier L; Rapp, Josephine Z; Krumpen, Thomas; Zehr, Jonathan P; Boetius, Antje

    2016-01-01

    The Eurasian basin of the Central Arctic Ocean is nitrogen limited, but little is known about the presence and role of nitrogen-fixing bacteria. Recent studies have indicated the occurrence of diazotrophs in Arctic coastal waters potentially of riverine origin. Here, we investigated the presence of diazotrophs in ice and surface waters of the Central Arctic Ocean in the summer of 2012. We identified diverse communities of putative diazotrophs through targeted analysis of the nifH gene, which encodes the iron protein of the nitrogenase enzyme. We amplified 529 nifH sequences from 26 samples of Arctic melt ponds, sea ice and surface waters. These sequences resolved into 43 clusters at 92% amino acid sequence identity, most of which were non-cyanobacterial phylotypes from sea ice and water samples. One cyanobacterial phylotype related to Nodularia sp. was retrieved from sea ice, suggesting that this important functional group is rare in the Central Arctic Ocean. The diazotrophic community in sea-ice environments appear distinct from other cold-adapted diazotrophic communities, such as those present in the coastal Canadian Arctic, the Arctic tundra and glacial Antarctic lakes. Molecular fingerprinting of nifH and the intergenic spacer region of the rRNA operon revealed differences between the communities from river-influenced Laptev Sea waters and those from ice-related environments pointing toward a marine origin for sea-ice diazotrophs. Our results provide the first record of diazotrophs in the Central Arctic and suggest that microbial nitrogen fixation may occur north of 77°N. To assess the significance of nitrogen fixation for the nitrogen budget of the Arctic Ocean and to identify the active nitrogen fixers, further biogeochemical and molecular biological studies are needed.

  10. Diazotroph Diversity in the Sea Ice, Melt Ponds, and Surface Waters of the Eurasian Basin of the Central Arctic Ocean

    PubMed Central

    Fernández-Méndez, Mar; Turk-Kubo, Kendra A.; Buttigieg, Pier L.; Rapp, Josephine Z.; Krumpen, Thomas; Zehr, Jonathan P.; Boetius, Antje

    2016-01-01

    The Eurasian basin of the Central Arctic Ocean is nitrogen limited, but little is known about the presence and role of nitrogen-fixing bacteria. Recent studies have indicated the occurrence of diazotrophs in Arctic coastal waters potentially of riverine origin. Here, we investigated the presence of diazotrophs in ice and surface waters of the Central Arctic Ocean in the summer of 2012. We identified diverse communities of putative diazotrophs through targeted analysis of the nifH gene, which encodes the iron protein of the nitrogenase enzyme. We amplified 529 nifH sequences from 26 samples of Arctic melt ponds, sea ice and surface waters. These sequences resolved into 43 clusters at 92% amino acid sequence identity, most of which were non-cyanobacterial phylotypes from sea ice and water samples. One cyanobacterial phylotype related to Nodularia sp. was retrieved from sea ice, suggesting that this important functional group is rare in the Central Arctic Ocean. The diazotrophic community in sea-ice environments appear distinct from other cold-adapted diazotrophic communities, such as those present in the coastal Canadian Arctic, the Arctic tundra and glacial Antarctic lakes. Molecular fingerprinting of nifH and the intergenic spacer region of the rRNA operon revealed differences between the communities from river-influenced Laptev Sea waters and those from ice-related environments pointing toward a marine origin for sea-ice diazotrophs. Our results provide the first record of diazotrophs in the Central Arctic and suggest that microbial nitrogen fixation may occur north of 77°N. To assess the significance of nitrogen fixation for the nitrogen budget of the Arctic Ocean and to identify the active nitrogen fixers, further biogeochemical and molecular biological studies are needed. PMID:27933047

  11. A Two-Dimensional Liquid Structure Explains the Elevated Melting Temperatures of Gallium Nanoclusters.

    PubMed

    Steenbergen, Krista G; Gaston, Nicola

    2016-01-13

    Melting in finite-sized materials differs in two ways from the solid-liquid phase transition in bulk systems. First, there is an inherent scaling of the melting temperature below that of the bulk, known as melting point depression. Second, at small sizes changes in melting temperature become nonmonotonic and show a size-dependence that is sensitive to the structure of the particle. Melting temperatures that exceed those of the bulk material have been shown to occur for a very limited range of nanoclusters, including gallium, but have still never been ascribed a convincing physical explanation. Here, we analyze the structure of the liquid phase in gallium clusters based on molecular dynamics simulations that reproduce the greater-than-bulk melting behavior observed in experiments. We observe persistent nonspherical shape distortion indicating a stabilization of the surface, which invalidates the paradigm of melting point depression. This shape distortion suggests that the surface acts as a constraint on the liquid state that lowers its entropy relative to that of the bulk liquid and thus raises the melting temperature.

  12. 46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 5 2012-10-01 2012-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20...

  13. 46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20...

  14. 46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20...

  15. 46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 5 2014-10-01 2014-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20...

  16. A Simple Scheme for Estimating Turbulent Heat Flux over Landfast Arctic Sea Ice from Dry Snow to Advanced Melt

    NASA Astrophysics Data System (ADS)

    Raddatz, R. L.; Papakyriakou, T. N.; Else, B. G.; Swystun, K.; Barber, D. G.

    2015-05-01

    We describe a dynamic-parameter aggregation scheme to estimate hourly turbulent heat fluxes over landfast sea ice during the transition from winter to spring. Hourly albedo measurements are used to track the morphology of the surface as it evolved from a fairly smooth homogeneous dry snow surface to a rougher heterogeneous surface with spatially differential melting and melt ponds. The estimates of turbulent heat fluxes for 928 h are compared with eddy-covariance measurements. The model performance metrics (W m) for sensible heat flux were found to be: mean bias , root-mean-square error 6 and absolute accuracy 4, and for latent heat flux near zero, 3 and 2, respectively. The correlation coefficient between modelled and measured sensible heat fluxes was 0.82, and for latent heat fluxes 0.88. The turbulent heat fluxes were estimated more accurately without adjustments than with adjustments for atmospheric stability based on the bulk Richardson number. Overall, and across all metrics for both sensible and latent heat fluxes, the dynamic-parameter aggregation scheme outperformed the static Community Ice (C-ICE) scheme, part of the Community Climate System model, applied to the same winter-to-spring transition period.

  17. Recovering Paleo-Records from Antarctic Ice-Cores by Coupling a Continuous Melting Device and Fast Ion Chromatography.

    PubMed

    Severi, Mirko; Becagli, Silvia; Traversi, Rita; Udisti, Roberto

    2015-11-17

    Recently, the increasing interest in the understanding of global climatic changes and on natural processes related to climate yielded the development and improvement of new analytical methods for the analysis of environmental samples. The determination of trace chemical species is a useful tool in paleoclimatology, and the techniques for the analysis of ice cores have evolved during the past few years from laborious measurements on discrete samples to continuous techniques allowing higher temporal resolution, higher sensitivity and, above all, higher throughput. Two fast ion chromatographic (FIC) methods are presented. The first method was able to measure Cl(-), NO3(-) and SO4(2-) in a melter-based continuous flow system separating the three analytes in just 1 min. The second method (called Ultra-FIC) was able to perform a single chromatographic analysis in just 30 s and the resulting sampling resolution was 1.0 cm with a typical melting rate of 4.0 cm min(-1). Both methods combine the accuracy, precision, and low detection limits of ion chromatography with the enhanced speed and high depth resolution of continuous melting systems. Both methods have been tested and validated with the analysis of several hundred meters of different ice cores. In particular, the Ultra-FIC method was used to reconstruct the high-resolution SO4(2-) profile of the last 10,000 years for the EDML ice core, allowing the counting of the annual layers, which represents a key point in dating these kind of natural archives.

  18. An Investigation of Climate Change Impact on Snow/Ice Melts Runoff in Himalayas

    NASA Astrophysics Data System (ADS)

    Selvan, M. T.; Ahmad, S. S.

    2005-12-01

    system. Apart from atmospheric processes, snow cover also plays important role in hydrological cycle. The hydrological response of the basin was simulated under changed climatic scenarios. The adopted changes in temperature and precipitation covered a range from 1 to 3°C and from -10 to +10 percent respectively. It was found that annual snowmelt runoff, glacier melt runoff and total stream flow for the Himalayan basin increased linearly with changes in temperature, but the most prominent effect of increase in temperature was noticed on glacier melt runoff. Contours extracted from geocoded toposheet were used to generate the Digital Elevation Model(DEM), which in turn was used for carrying out terrain analysis including generation of slope, aspect and shaded relief maps. Both slope and aspect maps were classified using density slicing, which is useful for hazardous zonation.

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

    PubMed Central

    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

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

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

    PubMed

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

    2002-06-11

    Airborne radar has detected approximately 100 lakes under the Antarctic ice cap, the largest of which is Lake Vostok. International planning is underway to search in Lake Vostok for microbial life that may have evolved in isolation from surface life for millions of years. It is thought, however, that the lakes may be hydraulically interconnected. If so, unsterile drilling would contaminate not just one but many of them. Here we report measurements of temperature vs. depth down to 2,345 m in ice at the South Pole, within 10 km from a subglacial lake seen by airborne radar profiling. We infer a temperature at the 2,810-m deep base of the South Pole ice and at the lake of -9 degrees C, which is 7 degrees C below the pressure-induced melting temperature of freshwater ice. To produce the strong radar signal, the frozen lake must consist of a mix of sediment and ice in a flat bed, formed before permanent Antarctic glaciation. It may, like Siberian and Antarctic permafrost, be rich in microbial life. Because of its hydraulic isolation, proximity to South Pole Station infrastructure, and analog to a Martian polar cap, it is an ideal place to test a sterile drill before risking contamination of Lake Vostok. From the semiempirical expression for strain rate vs. shear stress, we estimate shear vs. depth and show that the IceCube neutrino observatory will be able to map the three-dimensional ice-flow field within a larger volume (0.5 km(3)) and at lower temperatures (-20 degrees C to -35 degrees C) than has heretofore been possible.

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

    PubMed

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

    2014-03-07

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

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

    SciTech Connect

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

    2014-03-07

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

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

    NASA Astrophysics Data System (ADS)

    Frank, M. R.; Fei, Y.

    2002-12-01

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

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

    PubMed

    Meierbachtol, T; Harper, J; Humphrey, N

    2013-08-16

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

  5. Thermal Diffusivity for III-VI Semiconductor Melts at Different Temperatures

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  6. Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  7. THE RATIO OF THE GLASS TEMPERATURE TO THE MELTING POINT IN POLYMERS.

    DTIC Science & Technology

    PLASTICS , MELTING POINT, TRANSITION TEMPERATURE, POLYETHYLENE PLASTICS , VINYL PLASTICS , BUTADIENES, FLUORINE COMPOUNDS, STYRENE PLASTICS , POLYMERS...NYLON, PHYSICAL PROPERTIES, MOLECULAR STRUCTURE, CARBONATES, ESTERS, ACRYLIC RESINS, PHENOLIC PLASTICS , ANHYDRIDES, CARBOXYLIC ACIDS, PHTHALATES, UNITED KINGDOM.

  8. Thermophysical properties of liquid Ni around the melting temperature from molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Rozas, R. E.; Demiraǧ, A. D.; Toledo, P. G.; Horbach, J.

    2016-08-01

    Thermophysical properties of liquid nickel (Ni) around the melting temperature are investigated by means of classical molecular dynamics (MD) simulation, using three differe