Science.gov

Sample records for ice melting temperature

  1. 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.

  2. 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.

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

    USGS Publications Warehouse

    Hall, D.K.; Williams, R.S., Jr.; 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.

  4. Melting of ice under pressure

    PubMed Central

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

    2008-01-01

    The melting of ice under pressure is investigated with a series of first-principles molecular dynamics simulations. In particular, a two-phase approach is used to determine the melting temperature of the ice-VII phase in the range of 10–50 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 and 40 GPa, ice melts as a molecular solid. For pressures above ≈45 Gpa, there is a sharp increase in the slope of the melting curve because of the presence of molecular dissociation and proton diffusion in the solid before melting. The onset of significant proton diffusion in ice-VII as a function of increasing temperature is found to be gradual and bears many similarities to that of a type-II superionic solid. PMID:18809909

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  7. 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

  8. 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.

  9. Water Freezing and Ice Melting.

    PubMed

    Małolepsza, Edyta; Keyes, Tom

    2015-12-01

    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. PMID:26642983

  10. 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.

  11. Water freezing and ice melting

    DOE PAGESBeta

    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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

    Karacali, H.; Yurtseven, H.

    2007-02-01

    We reexamine the Pippard relations in this study by relating the specific heat CP to the Raman frequency shifts 1/ν∂ and the thermal expansivity αp to the 1/ν∂, when the mode Grüneisen parameter depends on the temperature and pressure close to the melting point in hexagonal ice. From linear relations between them, the values of the slope {dP}/{dT} are deduced in this crystal. Our slope values calculated here do not change significantly compared to those obtained when the mode Grüneisen parameter is taken as a constant close to the melting point in hexagonal ice.

  14. 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…

  15. Developing Temperature Forcing for Snow and Ice Melt Runoff Models in High Mountain Regions

    NASA Astrophysics Data System (ADS)

    Barrett, A. P.; Armstrong, R. L.; Brodzik, M. J.; Khalsa, S. J. S.; Raup, B. H.; Rittger, K.

    2014-12-01

    Glaciers and snow cover are natural storage reservoirs that delay runoff on seasonal and longer time-scales. Glacier wastage and reduced snow packs will impact the volume and timing of runoff from mountain basins. Estimates of the contributions of glacier and snow melt to runoff in river systems draining mountain regions are critical for water resources planning. The USAID funded CHARIS project aims to estimate the contributions of glacier and snow melt to streamflow in the Ganges, Indus, Brahmaputra, Amu Darya and Syr Darya rivers. Most efforts to estimate glacier and snow melt contributions use temperature-index or degree-day approaches. Near-surface air temperature is a key forcing variable for such models. As with all mountain regions, meteorological stations are sparse and may have short records. Few stations exist at high elevations, with most stations located in valleys below the elevations of glaciers and seasonal snow cover. Reanalyses offer an alternative source of temperature data. However, reanalyses have coarse resolution and simplified topography, especially in the Himalaya. Surface fields are often biased. Any reanalysis product must be both bias-corrected and "downscaled" to the resolution of the melt-runoff model. We present a combined empirically-based bias-correction and downscaling procedure that uses near-surface air temperature from global atmospheric reanalyses to generate near-surface temperature forcing fields for the five river basins in the CHARIS study area. We focus on three 3rd Generation reanalyses; NASA MERRA, NCEP CFSR and ECMWF ERA-Interim. Evaluation of reanalysis temperature fields reveals differences between seasonal means of 500 hPa air temperatures for the three products are of the order of 1 °C, indicating choice of reanalysis can impact model results. The procedure accounts for these seasonal variations in biases of the reanalysis products and in lapse rates.

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

    NASA Astrophysics Data System (ADS)

    Steffen, K.; McGrath, D.

    2013-12-01

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

  17. 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.

  18. 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.

  19. 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., Jr.; 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.

  20. Ice-shelf melting around Antarctica.

    PubMed

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

    2013-07-19

    We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines. PMID:23765278

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  3. 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

  4. 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.

  5. 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. PMID:12065835

  6. Ice-shelf melting around Antarctica

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Jacobs, S.

    2008-12-01

    The traditional view on the mass balance of Antarctic ice shelves is that they loose mass principally from iceberg calving with bottom melting a much lower contributing factor. Because ice shelves are now known to play a fundamental role in ice sheet evolution, it is important to re-evaluate their wastage processes from a circumpolar perspective using a combination of remote sensing techniques. We present area average rates deduced from grounding line discharge, snow accumulation, firn depth correction and ice shelf topography. We find that ice shelf melting accounts for roughly half of ice-shelf ablation, with a total melt water production of 1027 Gt/yr. The attrition fraction due to in-situ melting varies from 9 to 90 percent around Antarctica. High melt producers include the Ronne, Ross, Getz, Totten, Amery, George VI, Pine Island, Abbot, Dotson/Crosson, Shackleton, Thwaites and Moscow University Ice Shelves. Low producers include the Larsen C, Princess Astrid and Ragnhild coast, Fimbul, Brunt and Filchner. Correlation between melt water production and grounding line discharge is low (R2 = 0.65). Correlation with thermal ocean forcing from the ocean are highest in the northern parts of West Antarctica where regressions yield R2 of 0.93-0.97. Melt rates in the Amundsen Sea exhibit a quadratic sensitivity to thermal ocean forcing. We conclude that ice shelf melting plays a dominant role in ice shelf mass balance, with a potential to change rapidly in response to altered ocean heat transport onto the Antarctic continental shelf.

  7. 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.

  8. 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.

  9. 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.

  10. Turbulent plumes from ice melting into a linearly stratified ocean

    NASA Astrophysics Data System (ADS)

    Wells, Andrew; Magorrian, Samuel

    2015-11-01

    The melting of submerged marine glacier termini and ice shelves floating atop the ocean has important implications for ice sheet dynamics and sea level rise. When vertical or inclined ice faces melt into a warm salty ocean, the fresh meltwater rises in a buoyant plume along the ice-ocean interface and the resulting turbulent heat transfer provides a feedback on melting rates. We apply a turbulent plume model to consider the dynamics of well-mixed meltwater plumes rising along planar ice faces through a linearly stratified ocean, with vertical gradients of background ocean temperature and salinity. When the driving buoyancy force is dominated by salinity differences, the flow develops in a repeating series of layers, with the meltwater plume accelerating along the slope, rising past its neutral density level, and then separating from the ice face and intruding into the background ocean. We determine approximate scaling laws for the layer heights, melting rates and flow properties as a function of the background ocean temperature and salinity. These scaling laws provide a good collapse across a range of numerical solutions of the plume model, and may prove useful as a simple parameterisation of glacial melting in stratified Greenland fjords.

  11. 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. PMID:24204642

  12. Floating Ice-Algal Aggregates below Melting Arctic Sea Ice

    PubMed Central

    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. PMID:24204642

  13. Calving fluxes and melt rates of Antarctic ice shelves

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  14. 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. PMID:25019705

  15. 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.

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

    PubMed Central

    Häkkinen, 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 500 hPa height. Blocking activity with a range of time scales, from synoptic waves breaking poleward (<5 days) to full-fledged blocks (≥5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the years with the greatest melt (2002 and 2012) during the MODIS era, the area-average temperature anomaly of 2 standard deviations above the 14 year June-July mean results in a melt fraction of 40% or more. Though the summer of 2007 had the most blocking days, atmospheric temperature anomalies were too small to instigate extreme melting. Key Points Short-term atmospheric blocking over Greenland contributes to melt episodes Associated temperature anomalies are equally important for the melt Duration and strength of blocking events contribute to surface melt intensity PMID:25821277

  17. Radiatively-driven convection in melt ponds on sea ice

    NASA Astrophysics Data System (ADS)

    Wells, Andrew; Moon, Woosok; Rees Jones, David; Kim, Joo-Hong; Wilkinson, Jeremy

    2016-04-01

    Melt ponds have a significant impact on the energy budget of sea ice, and the predictability of the evolving summer sea ice cover. Recent observations of melt-pond temperature show complex vertical structure, with significant diurnal variability. To understand the driving physical mechanisms, we use two-dimensional direct numerical simulations of turbulent convection in a relatively fresh melt pond. We quantify the competition between internal radiative heating and surface fluxes in controlling the strength of convective flow. We explore variability in the resulting energy balance for a range of forcing, including effects of the diurnal cycle. The results are evaluated in light of the strong sensitivity of sea-ice thickness to net energy flux perturbations of order of a few watts per square metre.

  18. 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.

  19. 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)

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. Sea ice melt onset dynamics in the northern Canadian Arctic Archipelago from RADARSAT

    NASA Astrophysics Data System (ADS)

    Mahmud, M. S.; Howell, S.; Geldsetzer, T.; Yackel, J.

    2015-12-01

    Sea ice melt onset, the appearance of liquid water in its snow cover, decreases surface albedo which increases shortwave absorption and thereby accelerates snow and sea ice melting. Earlier melt onset leads to the earlier formation of open water which enhances the ice-albedo feedback. Sea ice melt onset timing and duration vary considerably, both spatially and temporally, owing to variability in atmospheric forcing; this in turn influences the September sea ice extent. Sea ice melt onset variability has been investigated using coarse resolution passive microwave observation in Canadian Arctic Archipelago (CAA); however, this does not provide sufficient information about sea ice melt dynamics. We developed a new melt onset algorithm using high resolution synthetic aperture radar (SAR) images from RADARSAT to better understand sea ice melt onset dynamics in northern Canadian Arctic Archipelago (fig 1) from 1997 to 2014. The algorithm is based on the temporal evolution of the SAR backscatter coefficient (σo), using separate thresholds for seasonal first-year ice and multi-year ice. Results indicated that the mean annual average melt onset date in the northern CAA was on year day 164 (mid-June) with a standard deviation of 4 days over the 18 year period. No significant trend for melt onset date was found over the 18 year period (fig: 2) but extreme early melt onset was detected in 1998 and 2012 associated with anomalous atmospheric forcing. Spatially, sea ice onset over the entire northern CAA varied from a 10-day minimum in 2007, to a 35-day maximum in 2011 and exhibited negative correlation (r=0.70) with the rate of increase in surface air temperature (fig 3) derived from Extended AVHRR Polar Pathfinder (APP-x) dataset. An earlier (later) melt onset also results in light (heavier) September sea ice area in the northern CAA (fig 4).

  5. Strong thermodynamic coupling between sub-ice-shelf melting and sea ice in a high-resolution global sea-ice-ocean isopycnal model

    NASA Astrophysics Data System (ADS)

    Sergienko, O. V.

    2015-12-01

    Sub-ice-shelf melting(freezing) of the Antarctic ice shelves acts as a source(sink) of freshwater, therefore, affects ocean water properties and circulation. In its turn, sub-ice-shelf melting/freezing is controlled by the ocean water properties that reach the sub-ice-shelf cavities. The properties of these water masses are determined by heat and fresh-water exchange with sea ice and atmosphere. Simulations of a high-resolution (1/8 deg) global sea-ice-ocean isopycnal model capable to resolve the ocean circulation in sub-ice-shelf cavities of Antarctic ice shelves and account for the thermodynamic interaction of the circulation with ice shelves show that melting/freezing rates have a strong seasonal cycle with highest melting rates observed in the Austral Fall. On the continental shelf, subsurface ocean temperatures (100-300 m) have a similar seasonal cycle which is lagged with respect to the surface. Shelf temperatures peak in the summertime, followed by rapid cooling towards the freezing point as seasonal ice cover increases. The lagged warming in the subsurface is attributable to reduced heat loss to the atmosphere in the presence of seasonal sea ice. This suggests that the seasonal cycle in melt rates is controlled by the phasing of subsurface temperatures on the continental shelf, which is in turn dominated by sea ice. The outflowing fresh, cold and light meltwater formed in sub-ice-shelf cavities remains in the mixed layer and promotes formation of sea ice and its longer persistence into the Austral Summer. These processes suggest the presence of strong mutual feedbacks between sub-ice-shelf melting and sea ice formation around Antarctic ice shelves.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Antarctic Ice Sheet melting in the southeast Pacific

    NASA Astrophysics Data System (ADS)

    Jacobs, Stanley S.; Hellmer, Hartmut H.; Jenkins, Adrian

    The first oceanographic measurements across a deep channel beneath the calving front of Pine Island Glacier reveal a sub-ice circulation driven by basal melting of 10-12 m yr-1. A salt box model described here gives a melt rate similar to that of ice balance and numerical models, 5-50 times higher than averages for the George VI and Ross Ice Shelves. Melting is fueled by relatively warm Circumpolar Deep Water that floods the deep floor of the Amundsen and Bellingshausen Sea continental shelves, reaching the deep draft of this floating glacier. A revised melt rate for ice shelves in the Southeast Pacific sector raises circumpolar ice shelf melting to 756 Gt yr-1. Given prior estimates of surface accumulation and iceberg calving, this suggests that the Antarctic Ice Sheet is currently losing mass to the ocean.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  14. Optical properties of melting first-year Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Light, Bonnie; Perovich, Donald K.; Webster, Melinda A.; Polashenski, Christopher; Dadic, Ruzica

    2015-11-01

    The albedo and transmittance of melting, first-year Arctic sea ice were measured during two cruises of the Impacts of Climate on the Eco-Systems and Chemistry of the Arctic Pacific Environment (ICESCAPE) project during the summers of 2010 and 2011. Spectral measurements were made for both bare and ponded ice types at a total of 19 ice stations in the Chukchi and Beaufort Seas. These data, along with irradiance profiles taken within boreholes, laboratory measurements of the optical properties of core samples, ice physical property observations, and radiative transfer model simulations are employed to describe representative optical properties for melting first-year Arctic sea ice. Ponded ice was found to transmit roughly 4.4 times more total energy into the ocean, relative to nearby bare ice. The ubiquitous surface-scattering layer and drained layer present on bare, melting sea ice are responsible for its relatively high albedo and relatively low transmittance. Light transmittance through ponded ice depends on the physical thickness of the ice and the magnitude of the scattering coefficient in the ice interior. Bare ice reflects nearly three-quarters of the incident sunlight, enhancing its resiliency to absorption by solar insolation. In contrast, ponded ice absorbs or transmits to the ocean more than three-quarters of the incident sunlight. Characterization of the heat balance of a summertime ice cover is largely dictated by its pond coverage, and light transmittance through ponded ice shows strong contrast between first-year and multiyear Arctic ice covers.

  15. Seasonal evolution of melt ponds on Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Webster, Melinda A.; Rigor, Ignatius G.; Perovich, Donald K.; Richter-Menge, Jacqueline A.; Polashenski, Christopher M.; Light, Bonnie

    2015-09-01

    The seasonal evolution of melt ponds has been well documented on multiyear and landfast first-year sea ice, but is critically lacking on drifting, first-year sea ice, which is becoming increasingly prevalent in the Arctic. Using 1 m resolution panchromatic satellite imagery paired with airborne and in situ data, we evaluated melt pond evolution for an entire melt season on drifting first-year and multiyear sea ice near the 2011 Applied Physics Laboratory Ice Station (APLIS) site in the Beaufort and Chukchi seas. A new algorithm was developed to classify the imagery into sea ice, thin ice, melt pond, and open water classes on two contrasting ice types: first-year and multiyear sea ice. Surprisingly, melt ponds formed ˜3 weeks earlier on multiyear ice. Both ice types had comparable mean snow depths, but multiyear ice had 0-5 cm deep snow covering ˜37% of its surveyed area, which may have facilitated earlier melt due to its low surface albedo compared to thicker snow. Maximum pond fractions were 53 ± 3% and 38 ± 3% on first-year and multiyear ice, respectively. APLIS pond fractions were compared with those from the Surface Heat Budget of the Arctic Ocean (SHEBA) field campaign. APLIS exhibited earlier melt and double the maximum pond fraction, which was in part due to the greater presence of thin snow and first-year ice at APLIS. These results reveal considerable differences in pond formation between ice types, and underscore the importance of snow depth distributions in the timing and progression of melt pond formation.

  16. 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. PMID:26032323

  17. 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

  18. 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

    2014-10-01

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

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

    PubMed Central

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

    2014-01-01

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

  20. 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

  1. The impact of under-ice melt ponds on Arctic sea ice volume

    NASA Astrophysics Data System (ADS)

    Smith, Naomi; Flocco, Daniela; Feltham, Daniel

    2016-04-01

    A one-dimensional, thermodynamic model of Arctic sea ice [Flocco et al, 2015] has been adapted to study the evolution of under-ice melt ponds, pools of fresh water that are found below the Arctic sea ice, and false bottoms, sheets of ice that form at the boundary between the under-ice melt pond and the oceanic mixed layer. Over time, either the under-ice melt pond freezes or the false bottom is completely ablated. We have been investigating the impact that these features have on the growth or ablation of sea ice during the time that they are present. The sensitivity of our model to a range of parameters has been tested, revealing some interesting effects of the thermodynamic processes taking place during the life-cycle of these phenomena. For example, the under-ice melt pond and its associated false bottom can insulate the sea ice layer from ocean, increasing the thickness of sea ice present at the end of the time frame considered. A comparison of the results of the model of under-ice melt pond evolution with that of sea ice with a bare base has been used to estimate the impact of under-ice melt ponds on sea ice volume towards the end of the melt season. We find that the under-ice melt ponds could have a significant impact on the mass balance of the sea ice, suggesting that it could be desirable to include a parameterisation of the effects of under-ice melt pond in the sea ice components of climate models.

  2. Diamond stabilization of ice multilayers at human body temperature

    NASA Astrophysics Data System (ADS)

    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 130K higher than in free ice, and relatively thick ice films ( 2.6nm at 298K and 2.2nm at 310K ) are stabilized by dipole interactions with the substrate. This unique physical effect may enable biocompatibility-enhancing ice overcoatings for diamond at human body temperature.

  3. 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

  4. 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

  5. Melting of ice stuck on cylinders placed horizontally in a water flowing duct

    NASA Astrophysics Data System (ADS)

    Sugawara, M.; Komatsu, Y.; Beer, H.

    2016-04-01

    Melting of ice stuck on seven in-lined cooling cylinders placed horizontally in a water flowing duct is investigated by means of a numerical analysis on the PHOENICS Code. The numerical results are validated compared with the experiment of an ice sphere melting. Parameters for calculations are inlet temperature, inlet velocity and clearance between the cylinders. The most concern of the melting is a finding of a curious behavior that is the melting in small inlet velocity on the long clearance between the cylinders.

  6. Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf

    NASA Astrophysics Data System (ADS)

    Jacobs, Stanley S.; Jenkins, Adrian; Giulivi, Claudia F.; Dutrieux, Pierre

    2011-08-01

    In 1994, ocean measurements near Antarctica's Pine Island Glacier showed that the ice shelf buttressing the glacier was melting rapidly. This melting was attributed to the presence of relatively warm, deep water on the Amundsen Sea continental shelf. Heat, salt and ice budgets along with ocean modelling provided steady-state calving and melting rates. Subsequent satellite observations and modelling have indicated large system imbalances, including ice-shelf thinning and more intense melting, glacier acceleration and drainage basin drawdown. Here we combine our earlier data with measurements taken in 2009 to show that the temperature and volume of deep water in Pine Island Bay have increased. Ocean transport and tracer calculations near the ice shelf reveal a rise in meltwater production by about 50% since 1994. The faster melting seems to result mainly from stronger sub-ice-shelf circulation, as thinning ice has increased the gap above an underlying submarine bank on which the glacier was formerly grounded. We conclude that the basal melting has exceeded the increase in ice inflow, leading to the formation and enlargement of an inner cavity under the ice shelf within which sea water nearly 4°C above freezing can now more readily access the grounding zone.

  7. Melting in temperature sensitive suspensions

    NASA Astrophysics Data System (ADS)

    Alsayed, Ahmed M.

    We describe two experimental studies about melting in colloidal systems. In particular we studied melting of 1-dimensional lamellar phases and 3-dimensional colloidal crystals. In the first set of experiments we prepared suspensions composed of rodlike fd virus and the thermosensitive polymer, poly(N-isopropylacrylamide). The phase diagram of this systems is temperature and concentration dependent. Using video microscopy, we directly observed melting of lamellar phases and single lamellae into nematic phase. We found that lamellar phases swell with increasing temperature before melting into the nematic phase. The highly swollen lamellae can be superheated as a result of topological nucleation barriers that slow the formation of the nematic phase. In another set of experiments we prepared colloidal crystals from thermally responsive microgel spheres. The crystals are equilibrium close-packed three-dimensional structures. Upon increasing the temperature slightly above room temperature, particle volume fraction decreased from 0.74 to less than 0.5. Using video microscopy, we observed premelting at grain boundaries and dislocations within bulk colloidal crystals. Premelting is the localized loss of crystalline order at surfaces and defects at sample volume fractions above the bulk melting transition. Particle tracking revealed increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. In total these observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and in atomic scale crystals.

  8. 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. PMID:11452998

  9. 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

  10. Circulation and melting beneath the ross ice shelf.

    PubMed

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

    1979-02-01

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

  11. Ice shelf melt rates and 3D imaging

    NASA Astrophysics Data System (ADS)

    Lewis, Cameron Scott

    Ice shelves are sensitive indicators of climate change and play a critical role in the stability of ice sheets and oceanic currents. Basal melting of ice shelves plays an important role in both the mass balance of the ice sheet and the global climate system. Airborne- and satellite based remote sensing systems can perform thickness measurements of ice shelves. Time separated repeat flight tracks over ice shelves of interest generate data sets that can be used to derive basal melt rates using traditional glaciological techniques. Many previous melt rate studies have relied on surface elevation data gathered by airborne- and satellite based altimeters. These systems infer melt rates by assuming hydrostatic equilibrium, an assumption that may not be accurate, especially near an ice shelf's grounding line. Moderate bandwidth, VHF, ice penetrating radar has been used to measure ice shelf profiles with relatively coarse resolution. This study presents the application of an ultra wide bandwidth (UWB), UHF, ice penetrating radar to obtain finer resolution data on the ice shelves. These data reveal significant details about the basal interface, including the locations and depth of bottom crevasses and deviations from hydrostatic equilibrium. While our single channel radar provides new insight into ice shelf structure, it only images a small swatch of the shelf, which is assumed to be an average of the total shelf behavior. This study takes an additional step by investigating the application of a 3D imaging technique to a data set collected using a ground based multi channel version of the UWB radar. The intent is to show that the UWB radar could be capable of providing a wider swath 3D image of an ice shelf. The 3D images can then be used to obtain a more complete estimate of the bottom melt rates of ice shelves.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    The dynamics of melt pond development on sea ice were studied on a well-defined patch of level land-fast sea ice off the coast of Barrow, Alaska in 2008. The pond development was correlated with both sea ice properties and the history of snow distribution during the ice growth season. In mid January, the ice was covered by an almost level snow layer of 4~cm thickness. We observed an increase in snow depth and development of snow dunes since February. At least some snow dunes stayed in place, and at the end of April ice thickness was negatively correlated with the thickness of compacted snow dunes. Snow salinity remained above 5~psu in the bottom 4 to 5~cm of the snow pack throughout the ice growth season. In comparison, snow more than 5~cm above the snow--ice interface was almost devoid of salt. The air temperature increased rapidly in early May and started to exceed 0°C on May 15. From this day on, thermistor string data show that the sea ice temperature profile deviated from linear with the lowest temperature inside the body of ice rather than at the surface. Superimposed ice was present with certainty after May 24. The superimposed ice investigated in early June exhibited a rough texture consistent with meltwater percolation columns in the snow pack. It was found only under snow dunes; no superimposed ice was observed under thin snow (2~cm) or melt ponds. Meltwater collected at topographic low points that surrounded distinct ice islands. Aerial photography and surface LiDAR measurements at various times during the early melt season showed that the location of these ice islands coincided with the locations of wind packed snow dunes that had been tracked since February. The lateral movement of surface waters was relatively slow during the very early stages of melt pond formation. However, we observed a significant lateral redistribution of meltwater under the ice surface; this redistribution happened through distinct veins. The sea ice salinity profiles showed

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

    NASA Astrophysics Data System (ADS)

    Keegan, K. M.; Albert, M. R.; McConnell, J.; Baker, I.

    2014-12-01

    The Greenland ice sheet experiences melting at low elevations near the coastline annually. However, surface melt is rare over the dry snow region in its center. In July 2012, over 97% of the Greenland ice sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. It had been previously unknown when the ice sheet had experienced melt events of this magnitude, or what caused them. Here we show that the most recent previous widespread melt occurred in 1889, and demonstrate that warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold, permitting the melt events in both 1889 and 2012. Furthermore, 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 ice sheet may begin to occur almost annually by the end of century.

  14. Daily Accumulated Area of Snow Melt Onset on Arctic Sea Ice

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The ice and snow in the Arctic are vital components of the global climate system, which has seen record-breaking changes in recent years. Changes in the onset of melting in the Arctic during the spring and summer months greatly changes the surface albedo of snow and ice covered surfaces, impacting sea ice loss through the remainder of the melt season. The present study utilizes the date on which melting begins in the snow atop sea ice, derived from passive microwave brightness temperatures from the DMSP SMMR, SSM/I (F08-F13), and SSMIS (F17) platforms, to analyze regional and inter-annual variability in the onset of melting in the Arctic. The Advanced Horizontal Range Algorithm (AHRA) snowmelt onset dates used in this study exploit the changes between 19 GHz (18 GHz for SMMR) and 37 GHz brightness temperatures to derive snow melt onset dates over Arctic sea ice from 1979-2011. Each annual AHRA snowmelt onset date grid indicates the day from the first of the year that melting occurred at each grid point. To analyze snowmelt onset on a daily basis, the annual grids are partitioned by date. A melt onset area is calculated by summing the number of grid points experiencing melt on individual dates then multiplying by the grid resolution to produce an areal extent of melt onset for each date during the melt seasons throughout the study period. By totaling the daily areal extent of melt onset, an accumulation is calculated by summing the area of melt each day throughout the melt season. Variations observed in the melt accumulation pattern through a melt season can be attributed to the weather conditions present at the time of melt onset. Analysis of the daily accumulation of melt area indicates high variability in the timing of snowmelt onset over the 1979-2011 record and a trend towards earlier melt onset dates for the Arctic region as a whole and sub-regionally. The accumulation of melt area through the melt season shows the SMMR years (1979-1987) to generally be below

  15. 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. PMID:24385606

  16. 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.

  17. Dissociative melting of ice VII at high pressure.

    PubMed

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

    2009-03-28

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

  18. The extreme melt across the Greenland ice sheet in 2012

    NASA Astrophysics Data System (ADS)

    Nghiem, S. V.; Hall, D. K.; Mote, T. L.; Tedesco, M.; Albert, M. R.; Keegan, K.; Shuman, C. A.; DiGirolamo, N. E.; Neumann, G.

    2012-10-01

    The discovery of the 2012 extreme melt event across almost the entire surface of the Greenland ice sheet is presented. Data from three different satellite sensors - including the Oceansat-2 scatterometer, the Moderate-resolution Imaging Spectroradiometer, and the Special Sensor Microwave Imager/Sounder - are combined to obtain composite melt maps, representing the most complete melt conditions detectable across the ice sheet. Satellite observations reveal that melt occurred at or near the surface of the Greenland ice sheet across 98.6% of its entire extent on 12 July 2012, including the usually cold polar areas at high altitudes like Summit in the dry snow facies of the ice sheet. This melt event coincided with an anomalous ridge of warm air that became stagnant over Greenland. As seen in melt occurrences from multiple ice core records at Summit reported in the published literature, such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the Medieval Warm Period. Given its rarity, the 2012 extreme melt across Greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research.

  19. Numerical simulation of melting ice around a floating by microwaves

    NASA Astrophysics Data System (ADS)

    Lakzian, Esmail; Parsian, Armin; Lakzian, Kazem

    2016-03-01

    In this paper a new method in using microwaves is provided for melting the ice around a floating equipment in a freezing condition in cold regions. The numerical simulation's results for validation are compared with the simple model's experimental data. Using microwave in melting the ice around a floating equipment is caused by lack of the mechanical wear, low energy dissipation factor and acceptable defrosting process speed in small lakes.

  20. Observing ice-shelf channels and basal melting from space

    NASA Astrophysics Data System (ADS)

    Berger, Sophie; Drews, Reinhard; Helm, Veit; Rack, Wolfgang; Lenaerts, Jan; Ligtenberg, Stefan; Pattyn, Frank

    2016-04-01

    Ice-shelf channels (along-flow lineations in which ice is thinner) are ubiquitous in Antarctic ice shelves. Although these features are readily visible in satellite imagery, ice-thickness and ice-velocity variations in their surrounding are typically heavily undersampled. Ice-shelf channels focus channelized melting and significantly alter the basal mass balance (and hence ice-shelf stability) on short horizontal scales. Here we use interferometrically-derived TandDEM-X digital elevation models and ice-flow velocities with a horizontal gridding of 125 m illustrating the ice-shelf dynamics of the Roi Baudouin Ice Shelf, Dronning Maud Land (East Antarctica) in unprecedented detail. Using ground-based GPS surface elevation, we demonstrate that TanDEM-X is an ideal sensor to map the channel morphology at the ice-shelf surface. We find velocity anomalies surrounding the channels along the entire ice shelf potentially indicating the presence of locally elevated basal melt rates. Using mass conservation in a Lagrangian framework, we find basal melt rates averaging 0.4 m/a in the middle of the ice shelf and peaking at 12 m/a inside some channels. We illustrate the sensitivity of the method with respect to systematic biases in elevation/velocity and also with respect to lateral variations of the depth-density relationship. With the increased availability of high-resolution radar satellites (such as Sentinel1), the techniques presented here could be applied on an pan-Antarctic scale to map basal melting both in space and time at high-resolution.

  1. 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.

  2. The melting of floating ice raises the ocean level

    NASA Astrophysics Data System (ADS)

    Noerdlinger, Peter D.; Brower, Kay R.

    2007-07-01

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

  3. 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.

  4. 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.

  5. 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.

  6. Superheated ice: true compression fractures and fast internal melting.

    PubMed

    Knight, C A; Knight, N C

    1972-11-10

    Internal melt figures can be nucleated in ice without the presence of a vapor bubble. Their form and growth are fracture-like, different from the normal Tyndall stars, which do contain vapor bubbles. Normal Tyndall figures that grow rapidly are not oriented in the basal plane, and very rapid internal melting gives a peculiar, systematic growth of clouds of Tyndall figures. PMID:17793685

  7. 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

  8. Quantitative Links between Amundsen Sea Heat and Pine Island Ice Shelf Melt

    NASA Astrophysics Data System (ADS)

    Bindschadler, R.; Vaughan, D. G.; Vornberger, P.

    2010-12-01

    Previous researchers have established the strong connection between the Amundsen Sea and basal melt of Pine Island Glacier’s ice shelf in Antarctica. In this presentation we extend this work by focusing on a strong spatial pattern of ice thickness undulations observed on the ice shelf and the predicted temporal pattern of pulses of Circumpolar Deep Water (CDW) upwelled onto the Amundsen Sea continental shelf by variable surface winds (Thoma et al., 2008). After converting the temporal pattern to spatial position on the ice shelf, we show a remarkable correlation over the last decade of these records that allows us to quantitatively associate an amount of heat at the front of the ice shelf, with an amount of melt that occurs at the grounding line. By considering the excess melting driven by pulses of CDW separately from the background melting, we extract a set of heat vs. melt values that suggest a linear relationship supporting the results of Rignot and Jacobs (2002) and disputing the non-linear relationship suggested by Holland et al. (2008). We infer that the current delivering the ocean’s heat is approximately 3.4 cm/sec , that most of the heat is expended by melt, and that the majority of melting is spatially limited to the grounding line vicinity. References cited: Holland, P.R., A. Jenkins and D.M. Holland, 2008. The Response of Ice Shelf Basal Melting to Variations in Ocean Temperature. Journal of Climate, Vol. 21, pp. 2558-2572, DOI: 10.1175/2007JCLI1909.1 Rignot E. and S.S. Jacobs, 2002. Rapid bottom melting widespread near Antarctic ice sheet grounding lines, Science, Vol. 296, No. 5575, p. 2020-2023. Thoma, M., A. Jenkins, D. Holland, and S. Jacobs, 2008. Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica, Geophysical Research Letters, Vol. 35, No. 18, L18602, doi: 10.1029/2008GL034939

  9. 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.

  10. 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

    2014-06-01

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

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

    PubMed Central

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

    2014-01-01

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

  12. Impact of ice temperature on microwave emissivity of thin newly formed sea ice

    NASA Astrophysics Data System (ADS)

    Hwang, Byong Jun; Ehn, Jens K.; Barber, David G.

    2008-02-01

    This study examines the impact of ice temperature on microwave emissivity over thin, newly formed sea ice at 6, 19, and 37 GHz during October 2003 in the southern Beaufort Sea, where the physical properties of newly formed sea ice were coincidently measured with microwave emissions. Six ice stations with distinct properties were selected and divided according to ice surface temperature into warm (above -3°C) or cold (below -3°C) stations. The warm stations had a lower emissivity at the vertical polarization by 0.1 than the cold stations and a corresponding difference in brine volume and dielectric properties. Significant correlations were observed between brine volume and ice emissivity (R2 = 0.8, p value < 0.05). A sensitivity study showed that decreasing ice temperatures from -2.1° to -5.0°C explained the observed difference of 0.1 in ice emissivity between warm and cold stations. The results suggest that the temperature of thin bare ice could be the critical factor in determining ice emissivity near the melting point (about -2°C). Furthermore, a slight decrease in ice temperature (i.e., from -2° to -5°C) significantly reduces the brine volume, thus resulting in high ice emissivity. Finally, we demonstrate the potential of newly formed ice to cause errors in estimating sea ice concentrations using Advanced Microwave Scanning Radiometer-E data.

  13. Experimental study of natural convection melting of ice in salt solutions

    SciTech Connect

    Fang, L.J.; Cheung, F.B.; Linehan, J.H.; Pedersen, D.R.

    1984-01-01

    The solid-liquid interface morphology and the micro-physical process near the moving phase boundary during natural convection melting of a horizontal layer of ice by an overlying pool of salt solution were studied experimentally. A cathetometer which amplifies the interface region was used to measure the ice melting rate. Also measured were the temperature transients of the liquid pool. Within the temperature and the density ratio ranges explored, the ice melting rate was found to be very sensitive to the ratio of pool-to-ice melt density but independent of pool-to-ice temperature difference. By varying the density ratio, three different flow regimes and morphologies of the solid-liquid interface were observed, with melt streamers emanating from the crests of the wavy interface into the pool in all three cases. The measured wavelengths (spacing) between the streamers for four different pairs of materials were correlated with the density ratio and found to agree favorably with the predictions of Taylor instability theory.

  14. 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

  15. 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.

  16. 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. PMID:25353109

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

    SciTech Connect

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

    1987-01-01

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

  18. The "blob of death", or how warm air advection causes rapid ice melt

    NASA Astrophysics Data System (ADS)

    Tjernström, Michael; Shupe, Matthew; Achtert, Peggy; Brooks, Barbara; Brooks, Ian; Johnston, Paul; Persson, Ola; Prytherch, John; Salisbury, Dominic; Sedlar, Joseph; Sotiropoulou, Georgia; Wolfe, Dan

    2015-04-01

    The Arctic Clouds in Summer Experiment (ACSE) program obtained measurements of surface energy fluxes, boundary-layer structure, cloud macro- and micro-physical structure, and upper-ocean thermal and salinity structure from pack-ice and open-water regions in the eastern Arctic from early July to early October 2014. ACSE was divided into two legs. The first took a route from Tromsö, Norway, to Barrow, Alaska, during late summer (early July to late August) mostly on the Siberian Shelf, while the second leg was from traversed back mostly north of the shelf during September and early October. This paper will present ACSE and show examples of some results. Energy fluxes at the surface determine the annual summer melt and autumn freeze-up of Arctic sea ice, but are strongly modulated by interactions between atmospheric, ocean, and sea-ice processes. ACSE summer measurements showed energy flux surpluses leading to significant surface melt, while late August and September measurements showed deficits, leading to freeze-up of sea ice and the ocean surface. A weeklong episode with intensive melt resulting from warm air advection from continental Russia will be presented and discussed. During this episode, temperatures up to 20 °C was observed aloft while near surface temperatures over the ice remained near melting. In the surface inversion dense fog formed that enhanced the downward longwave radiation. Together with a downward turbulent sensible heat flux this caused a rapid melt in this area.

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

    PubMed Central

    Sartor, G; Mayer, E

    1994-01-01

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

  20. Water isotopic ratios from a continuously melted ice core sample

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

    A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We built an interface between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of δ18O and δD on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub μl amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100% efficiency in a~home made oven at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW-SLAP scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on the water concentration in the optical cavity. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1‰ and 0.5‰ for δ18O and δD, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the temporal resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of δ18O and δD, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present

  1. Ranking spatially and temporally variable Greenland ice surface melt factors

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  2. 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.

  3. Warm-air advection, air mass transformation and fog causes rapid ice melt

    NASA Astrophysics Data System (ADS)

    Tjernström, Michael; Shupe, Matthew D.; Brooks, Ian M.; Persson, P. Ola G.; Prytherch, John; Salisbury, Dominic J.; Sedlar, Joseph; Achtert, Peggy; Brooks, Barbara J.; Johnston, Paul E.; Sotiropoulou, Georgia; Wolfe, Dan

    2015-07-01

    Direct observations during intense warm-air advection over the East Siberian Sea reveal a period of rapid sea-ice melt. A semistationary, high-pressure system north of the Bering Strait forced northward advection of warm, moist air from the continent. Air-mass transformation over melting sea ice formed a strong, surface-based temperature inversion in which dense fog formed. This induced a positive net longwave radiation at the surface while reducing net solar radiation only marginally; the inversion also resulted in downward turbulent heat flux. The sum of these processes enhanced the surface energy flux by an average of ~15 W m-2 for a week. Satellite images before and after the episode show sea-ice concentrations decreasing from > 90% to ~50% over a large area affected by the air-mass transformation. We argue that this rapid melt was triggered by the increased heat flux from the atmosphere due to the warm-air advection.

  4. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  6. Sea ice melting in the marginal ice zone.

    USGS Publications Warehouse

    Josberger, E.G.

    1983-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  9. 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

    2012-04-26

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

  10. Simulating Ice Particle Melting using Smooth Particle Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Kuo, Kwo-Sen; Pelissier, Craig

    2015-04-01

    To measure precipitation from space requires an accurate estimation of the collective scattering properties of particles suspended in a precipitating column. It is well known that the complicated and typically unknowable shapes of the solid precipitation particles cause much uncertainty in the retrievals involving such particles. This remote-sensing problem becomes even more difficult with the "melting layer" containing partially melted ice particles, where both the geometric shape and liquid-solid fraction of the hydrometeors are variables.. For the scattering properties of these particles depend not only on their shapes, but also their melt-water fraction,and the spatial distribution of liquid and ice within. To obtain an accurate estimation thus requires a set of "realistic" particle geometries and a method to determine the melt-water distribution at various stages in the melting process. Once this is achieved, a suitable method can be used to compute the scattering properties. In previous work, the growth of a set of astoundingly realistic ice particles has been simulated using the "Snowfake" algorithm of Gravner and Griffeath. To simulate the melting process of these particles, the method of Smooth Particle Hydrodynamics (SPH) is used. SPH is a mesh-less particle-based approach where kinematic and thermal dynamics is controlled entirely through two-body interactions between neighboring SPH particles. An important property of SPH is that the interaction at boundaries between air/ice/water is implicitly taken care of. This is crucial for this work since those boundaries are complex and vary throughout the melting process. We present the SPH implementation and a simulation, using highly parallel Graphic Processing Units (GPUs), with ~1 million SPH particles to represent one of the generated ice particle geometries. We plan to use this method, especially its parallelized version, to simulate the melting of all the "Snowfake" particles (~10,000 of them) in our

  11. 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

  12. Enhanced Sea Ice Concentration and Ice Temperature Algorithms for AMSR

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  13. 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.

  14. Comparison of 2013 and 2012 Greenland Ice Sheet Surface Melt and Associated Mechanisms

    NASA Astrophysics Data System (ADS)

    Chen, Zhiqiang; Liu, Jiping

    2016-04-01

    We examine the characteristics of the Greenland Ice Sheet surface melt in summer 2013 and compare the results with 2012. The atmospheric dynamic and thermodynamic differences between these two cases and their impacts on the Greenland Ice Sheet surface melt are also examined. Results show that the maximum surface melt extent is only 44% in 2013, which is far less than 97% in 2012. The averaged extent and duration of the surface melt in 2013 are close to the climatology. The summer atmospheric circulation anomalies in 2013 are nearly opposite to those observed in 2012. Greenland and the surrounding areas show anomalously low pressure, particularly a negative height at 500-hPa, which leads to a more zonal pattern than that in 2012. The corresponding anomalous cyclonic circulation in the north and south areas of Greenland is favorable for advecting cold Arctic air to Greenland. Moreover, the surface downward radiation pattern in 2013 is oriented in a southwest-northeast direction over Greenland, which differs from the north-south distribution in 2012. The net downward radiation is small due to the cancellation of downward shortwave and longwave components in 2013. However, downward shortwave dominates from the distribution perspective, leading to an insignificant impact on surface temperatures over Greenland. The combination of dynamic effects of atmospheric circulation and thermodynamic effects of the radiation budget contribute to the surface melt of the Greenland Ice Sheet. We further find that a positive feedback between the variability in the extent of summer Arctic sea ice and melt area of the summer Greenland ice sheet, which affects the Greenland ice sheet mass balance.

  15. 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.

  16. 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

  17. 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

    2016-01-01

    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. 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.

  19. 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.

  20. 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

  1. 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.

  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

    2013-10-01

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

  3. 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.

  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. Organochlorine compounds in ice melt water from Italian Alpine rivers.

    PubMed

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

    2006-01-01

    Organochlorine chemicals (OCs) (dichlorodiphenyltrichloroethanes, hexachlorocyclohexanes, and hexachlorobenzene) were measured in ice melt water from five glaciers in the Italian Alps. Even though the data collected may not be sufficient for a precise description of persistent organic pollutant release patterns from glacier melting, they have, however, highlighted the potential for surface water contamination. Concentrations were of the same order of magnitude in all glacial streams, indicating comparable contamination levels in different glaciers of the alpine region. OC levels in nonglacial springs sampled in the same areas are usually lower. Even if differences during the melting season (from spring to autumn) have been identified, a regular seasonal pattern in OC concentrations was not observed. Risk for the aquatic environment is excluded through direct water exposure, but it is likely to occur through biomagnification and secondary poisoning exposure. PMID:16054693

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  7. 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.

  8. 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.

  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. PMID:24497990

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

    PubMed Central

    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. PMID:24497990

  11. Heat-transfer analysis of the basal melting of Antarctic ice shelves

    SciTech Connect

    Minale, M.; Astarita, G.

    1993-12-01

    Basal melting of Antarctic ice shelves is an important element in the overall balance of Antarctic ice. A heat-transfer model for the basal melting of the Drygalski Ice Tongue is presented. The model does not contain any adjustable parameter. The calculated basal melting rate agrees very well with the value estimated from an overall ice balance on the ice tongue. It is concluded that relatively simple concepts of transport phenomena may be used to model some important features of the dynamics of the Antarctic ice sheet.

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

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

    Basal thermal regimen of West Antarctic Ice Sheet (WAIS) plays the key role in determining the dynamics and stability of this ice sheet. Basal melt water lubricates the ice base allowing fast ice streaming while basal freeze-on increases basal resistance to ice flow. Within WAIS, basal melting is dominant in the interior, where geothermal heat is trapped underneath ~2-to-4-km-thick layer of ice. Basal freeze-on is dominant beneath the slow moving, ~1-km-thick interstream ridges separating fast-moving ice streams. There, conductive heat escape through exceeds the geothermal flux and basal frictional heating is low. Using a time-dependent basal energy balance model (Vogel et al., in press) we examined spatial and temporal distribution of basal melting and freezing in the catchment areas of Whillans Ice Stream and Ice Stream C since the Last Glacial Maximum (LGM, ~20,000 years ago). Model results indicate that basal melting peaked despite lower surface temperatures during late LGM (~15,000), due to a thickened ice sheet (Steig et al., 2001). This widespread and abundant basal lubrication may have initiated the retreat and thinning of the ice sheet that continued through the Holocene. However, the ice-sheet thinning itself caused gradually a general decrease in basal melting rates in spite of higher Holocene surface temperatures. This reduction in basal water production may be responsible for the recent stoppage of Ice Stream C and slow down of the Whillans Ice Stream. Our modeling results indicate that WAIS is still adjusting to the significant climate warming that marked the end of the LGM and the beginning of Holocene. Only the thinnest portions of the Whillans Ice Stream and Ice Stream C (<1 km) might have adjusted enough to cause locally significant basal freeze-on and to, at least temporarily, slow the ice sheet decay (Joughin and Tulaczyk, 2002). Basal thermal regimen of the rest of WAIS is changing in such a way as to favor increased basal melting, and

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  15. 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.

  16. 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

  17. 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

  18. Flow of Ice near a Large Melt Channel in the Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    Conway, H.; Hindmarsh, R. C. A.; Koutnik, M. R.; Stevens, C.; Winberry, J. P.

    2014-12-01

    There is increasing evidence for the existence of large channels incised beneath ice shelves in West Antarctica. However, the genesis of these channels is still not clear. Measurements from the floating tongue of Pine Island Glacier show that sub-shelf channels formed by localized melting (Stanton et al., 2013); oceanographic models of flow in sub-ice-shelf cavities are capable of producing sub-shelf channels through non-linear feed-back mechanisms (Gladish et al. 2012; Sergienko, 2013). On the other hand, other evidence suggests that sub-shelf channels can initiate at locations where melt water beneath grounded ice crosses the grounding line (Le Brocq et al. 2013). Here we use ground-based radar to map a channel incised into the base of the Ross Ice Shelf proximal to the grounding zone of Beardmore Glacier, West Antarctica. Results show that in the grounding zone (ice thickness is 1150m), the channel is 100m deep and 0.5 km wide. On the shelf, the channel widens and deepens down stream; 8km down from the grounding line (ice thickness is 600-800 m), the channel is 200m deep and 1 km wide (see Figure); apparently in this case, the channel originates from beneath the grounded ice. Although there is some indication of radar-detected internal stratigraphy dipping toward the channels indicative of meltin, the pattern of the stratigraphy suggests significant accumulated strain (see Figure). Further, vertical strain-rates calculated from repeat measurements using phase-sensitive radar (pRES), show a more complex pattern over melt-channels than is usually assumed for ice shelves. Specifically, 57 of the 69 pRES measurements exhibit a pattern of compression in the upper 75% of the ice column and extension in the lower 25%. This observation is important because such a pattern affects the ratio of surface- to mean-velocity, which is usually assumed to be unity in shelf-mass balance calculations. FIGURE CAPTION: Unmigrated, across-channel radar profile 8km downstream from the

  19. 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.

  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. PMID:26347538

  1. Modelling Antarctic ice shelf melting under LGM and doubled CO2 climate using ice shelf-ocean model and climate model

    NASA Astrophysics Data System (ADS)

    Obase, T.; Abe-Ouchi, A.; Kusahara, K.; Hasumi, H.

    2014-12-01

    Ice-ocean interaction is thought to be a responsible process on long-term Antarctic ice sheet variations, such as retreat of West Antarctic Ice Sheet during Eemian interglacial. Numerical simulation of Antarctic ice sheet require melt rate at ice shelf base as a boundary condition, but the relation between climate and melt rate is unclear. We calculate Antarctic ocean and basal melting of Antarctic ice shelves under Last Glacial Maximum(LGM) and doubled CO2(2xCO2) climate at equilibrium as well as present-day(CTL). We use circumpolar ice shelf-ocean general circulation model(OGCM, based on COCO) and outputs of climate model(MIROC). For the CTL case, we drive OGCM with surface atmospheric climatology based on reanalysis(OMIP) and present-day ocean temperature and salinity for restoration at northern boundary, placed at around latitude of 40S. The surface boundary conditions for LGM(or 2xCO2) is computed from the outputs from climate model simulations. Annual mean marine 2m air temperature anomaly averaged for south of 60S is -7.3℃ for LGM and +6.0℃ for 2xCO2. LGM (or 2xCO2) anomalies of surface atmospheric variables are superimposed to OMIP to make LGM (or 2xCO2) atmospheric boundary conditions. We modify the ocean temperature and salinity column for restoration at northern boundary by superimposing anomaly to present-day ocean climatology. Present-day geometry of ice sheet and ice shelf is used in all experiments to test the sensitivity to climate. We show that melting amount of Antarctic ice shelves show 23% reduction for the LGM and 3.5 times increase for the 2xCO2 compared to the CTL case. We perform a series of additional sensitivity experiments to investigate the role of surface change in sea surface atmospheric variables (temperature, wind) and ocean structures in the Southern Ocean on melt rate of ice shelves. Water mass, ocean circulation and sea ice production on continental shelf are analyzed.

  2. 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

  3. 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

  4. 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

  5. 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.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    PubMed Central

    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. PMID:25815751

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  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. 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.

  15. 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.

  16. 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. PMID:26252689

  17. 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

  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. Stochastic dynamics of melt ponds and sea ice-albedo climate feedback

    NASA Astrophysics Data System (ADS)

    Sudakov, Ivan

    Evolution of melt ponds on the Arctic sea surface is a complicated stochastic process. We suggest a low-order model with ice-albedo feedback which describes stochastic dynamics of melt ponds geometrical characteristics. The model is a stochastic dynamical system model of energy balance in the climate system. We describe the equilibria in this model. We conclude the transition in fractal dimension of melt ponds affects the shape of the sea ice albedo curve.

  1. 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.

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  5. Seasonal changes in ice sheet motion due to melt water lubrication

    NASA Astrophysics Data System (ADS)

    Hewitt, I.

    2012-12-01

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

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

    PubMed

    Tuffen, Hugh

    2010-05-28

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

  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.; 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.

  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., 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.

  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., Jr.; 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. Antarctic sea ice and temperature variations

    SciTech Connect

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

    1992-03-01

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

  11. 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.

  12. Potassium-Rich Ices at High Pressures and Temperatures

    NASA Astrophysics Data System (ADS)

    Frank, M. R.; Scott, H. P.; Aarestad, E.; Prakapenka, V.

    2014-12-01

    Accurate modeling of planetary interiors requires that the pressure-volume-temperature properties of phases present within the body be well understood. The high-pressure polymorphs of H2O have been studied extensively, due to the abundance of ice phases in icy moons and likely vast number of extra-solar planetary bodies, with only select studies evaluating impurity-laden ices. In this study, ice formed from a 1.6 mole percent KCl-bearing aqueous solution was studied up to 33 GPa and 650 K, and the incorporation of K+ and Cl- into the ice VII structure was documented. The compression data at 300 K were fit with a third order Birch-Murnaghan equation of state and yielded K, K/, and V0 of 24.7±0.9 GPa, 4.44±0.09, and 39.17±0.15 Å3, respectively. Thermal expansion coefficients were also determined for several isothermal compression curves at elevated temperatures, and a P-V-T equation of state will be presented. The melting of ice VII with incorporated K+ and Cl- was determined up to 625 K and 10.6 GPa and was fit by using a Simon-Glatzel equation. The melting curve is systematically depressed relative to the melting curve of pure H2O by approximately 45 K and 80 K at 4 and 11 GPa, respectively. Interestingly, a portion of the K+ and Cl- contained within the ice VII structure was observed to exsolve with increasing temperature and pressure. This suggests that an internal differentiating process could concentrate a K-rich phase deep within H2O-rich planets, and we speculate that this could supply an additional source of heat through the radioactive decay of 40K. Birch (1951; JGR, 56, 107-126) has estimated that 40K contributes 2.7 μcal/g.year for each wt.% of K, and our results suggest at least 3.33 wt.% can be incorporated into the structure of ice VII, thus making it a source of heat rather than just a conductive layer. In conclusion, our data illustrate a mechanism that may concentrate K at depth and impact the supposed pressure and temperature within moderate

  13. 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

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

    NASA Astrophysics Data System (ADS)

    Wei, Xing

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

  15. 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.

  16. Honeycomb artificial spin ice at low temperatures

    NASA Astrophysics Data System (ADS)

    Zeissler, Katharina; Chadha, Megha; Cohen, Lesley; Branford, Will

    2015-03-01

    Artificial spin ice is a macroscopic playground for magnetically frustrated systems. It consists of a geometrically ordered but magnetically frustrated arrangement of ferromagnetic macros spins, e.g. an arrangement of single domain ferromagnetic nanowires on a honeycomb lattice. Permalloy and cobalt which have critical temperature scales far above 290 K, are commonly used in the construction of such systems. Previous measurements have shown unusual features in the magnetotransport signature of cobalt honeycomb artificial spin ice at temperatures below 50 K which are due to changes in the artificial spin ice's magnetic reversal. In that case, the artificial spin ice bars were 1 micron long, 100 nm wide and 20 nm thick. Here we explore the low temperature magnetic behavior of honeycomb artificial spin ice structures with a variety of bar dimensions, indirectly via electrical transport, as well as, directly using low temperature magnetic imaging techniques. We discuss the extent to which this change in the magnetic reversal at low temperatures is generic to the honeycomb artificial spin ice geometry and whether the bar dimensions have an influence on its onset temperature. The EPSRC (Grant No. EP/G004765/1; Grant No. EP/L504786/1) and the Leverhulme Trust (Grant No. RPG 2012-692) funded this scientific work.

  17. 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.

    2011-10-01

    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 MODIS using a spectral unmixing algorithm. The unmixing was implemented using a multilayer perceptron (MLP) 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 (RMSE) 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 correlations coefficients ranging from R2 = 0.28 to R2 = 0.45. The mean annual cycle of the melt pond fraction 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 from the geographical latitude, and has its maximum in mid-July in 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 ASI-, 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.

  18. 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.

  19. 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.

  20. 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.

  1. Ocean Properties and Submarine Melt of Ice Shelves in a High-Arctic Fiord (Milne Fiord)

    NASA Astrophysics Data System (ADS)

    Hamilton, A.; Mueller, D.; Laval, B.

    2014-12-01

    The role of ambient stratification, the vertical distribution of heat, and fiord circulation on submarine melt rates in glacial fiords in the Canadian Arctic are largely unknown despite recent widespread collapse of ice shelves in this region. A 3-year field study was conducted to investigate ocean influence on ice loss from an ice shelf and glacier tongue in Milne Fiord (82oN), Ellesmere Island. Direct ocean observations of the sub-ice cavities from through-ice profiles showed a vertically stratified water column consisting of a perennial fresh ice-dammed epishelf lake at the surface, above cold relatively fresh Polar Water, and warm saline waters from the upper halocline of the Atlantic layer at depth. The broad continental shelf and a topographic sill prevented the warmest waters of the Atlantic layer from entering the 450 m deep fiord. Meltwater concentrations were highest near the glacier grounding line, with meltwater exported at depth due to the strong ambient stratification. There was little evidence of increased buoyancy-driven melt in summer from subglacial discharge as observed in sub-Arctic fiords (e.g. southern Greenland), suggesting that circulation in high-latitude fiords is largely melt-driven convection with less pronounced seasonality. Basal melt rates estimated using three methods, meltwater flux, divergence of ice flux, and an ocean thermodynamic model, were broadly consistent. Average melt rates of 0.75 ± 0.46 m a-1 and 1.14 ± 0.83 m a-1 were found for the Milne Ice Shelf and Milne Glacier Tongue, respectively, although showed high spatial variability. The highest melt rates (~4 m a-1) were found near the glacier grounding line and were driven by warm upper halocline waters. Similar melt rates occurred in near-surface waters driven by solar heating of the epishelf lake, enhancing melt along the margins of the glacier tongue and the landward edge of the ice shelf. The Milne Ice Shelf and Milne Glacier Tongue are in a state of negative mass

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  3. Structure and decompression melting of a novel, high-pressure nanoconfined 2-D ice.

    PubMed

    Wang, Jianwei; Kalinichev, Andrey G; Kirkpatrick, R James

    2005-08-01

    Molecular dynamics (MD) simulations of water confined in nanospaces between layers of talc (system composition Mg(3)Si(4)O(10)(OH)(2) + 2H(2)O) at 300 K and pressures of approximately 0.45 GPa show the presence of a novel 2-D ice structure, and the simulation results at lower pressures provide insight into the mechanisms of its decompression melting. Talc is hydrophobic at ambient pressure and temperature, but weak hydrogen bonding between the talc surface and the water molecules plays an important role in stabilizing the hydrated structure at high pressure. The simulation results suggest that experimentally accessible elevated pressures may cause formation of a wide range of previously unknown water structures in nanoconfinement. In the talc 2-D ice, each water molecule is coordinated by six O(b) atoms of one basal siloxane sheet and three water molecules. The water molecules are arranged in a buckled hexagonal array in the a-b crystallographic plane with two sublayers along [001]. Each H(2)O molecule has four H-bonds, accepting one from the talc OH group and one from another water molecule and donating one to an O(b) and one to another water molecule. In plan view, the molecules are arranged in six-member rings reflecting the substrate talc structure. Decompression melting occurs by migration of water molecules to interstitial sites in the centers of six-member rings and eventual formation of separate empty and water-filled regions. PMID:16852798

  4. 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

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    Inoue, J.; Curry, J. A.

    2006-12-01

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

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. Cumulates, Dykes and Pressure Solution in the Ice-Salt Mantle of Europa: Geological Consequences of Pressure Dependent Liquid Compositions and Volume Changes During Ice-Salt Melting Reactions.

    NASA Astrophysics Data System (ADS)

    Day, S.; Asphaug, E.; Bruesch, L.

    2002-12-01

    Water-salt analogue experiments used to investigate cumulate processes in silicate magmas, along with observations of sea ice and ice shelf behaviour, indicate that crystal-melt separation in water-salt systems is a rapid and efficient process even on scales of millimetres and minutes. Squeezing-out of residual melts by matrix compaction is also predicted to be rapid on geological timescales. We predict that the ice-salt mantle of Europa is likely to be strongly stratified, with a layered structure predictable from density and phase relationships between ice polymorphs, aqueous saline solutions and crystalline salts such as hydrated magnesium sulphates (determined experimentally by, inter alia, Hogenboom et al). A surface layer of water ice flotation cumulate will be separated from denser salt cumulates by a cotectic horizon. This cotectic horizon will be both the site of subsequent lowest-temperature melting and a level of neutral buoyancy for the saline melts produced. Initial melting will be in a narrow depth range owing to increasing melting temperature with decreasing pressure: the phase relations argue against direct melt-though to the surface unless vesiculation occurs. Overpressuring of dense melts due to volume expansion on cotectic melting is predicted to lead to lateral dyke emplacement and extension above the dyke tips. Once the liquid leaves the cotectic, melting of water ice will involve negative volume change. Impact-generated melts will drain downwards through the fractured zones beneath crater floors. A feature in the complex crater Mannan'an, with elliptical ring fractures around a conical depression with a central pit, bears a close resemblance to Icelandic glacier collapse cauldrons produced by subglacial eruptions. Other structures resembling Icelandic cauldrons occur along Europan banded structures, while resurgence of ice rubble within collapse structures may produce certain types of chaos region. More general contraction of the ice mantle

  13. Ice Regime and Melt-out Timing Cause Divergent Hydrologic Responses among Arctic Lakes

    NASA Astrophysics Data System (ADS)

    Bondurant, A.; Arp, C. D.; Jones, B. M.; Liljedahl, A. K.; Hinkel, K. M.; Welker, J. M.

    2015-12-01

    Lakes are prevalent in the Arctic and thus play a key role in regional hydrology. Because many lakes are shallow and ice grows thick (historically 2-m or greater), lakes often freeze solid (bedfast ice) and this condition fundamentally alters lake energy balance and melt-out processes compared to deeper lakes with perennial liquid water below floating ice. Our analysis of lakes in northern Alaska indicated that ice-off in bedfast ice lakes occurred on average 17 days earlier (22-June) than ice-off in adjacent floating ice lakes (9-July). Earlier melt in bedfast ice lakes caused higher open-water evaporation, 28 % on average, relative to floating ice lakes and this divergence increased in lakes closer to the coast and in cooler summers. Specific conductivity and water isotopes (18O and 2H) indicated similar differences in evaporation between these lake types. Our analysis suggests that ice regimes and associated ice-out timing currently create a strong hydrologic divergence among Arctic lakes, which makes understanding the distribution and dynamics of lakes by ice regime essential for predicting regional hydrology. An observed trend towards more floating ice lakes due to thinner ice growth may initially offset lake drying because of lower evaporative loss from this lake type. This potential negative feedback caused by winter processes is in spite of an overall projected increase in evapotranspiration as the Arctic climate warms. The unusually warm spring observed in 2015 caused much earlier lake ice-out throughout Arctic Alaska, thus providing perfect conditions to test these hypotheses concerning differential lake hydrologic responses.

  14. 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.

  15. Continued Melting of Greenland Ice-Sheet Regulated Northern Hemisphere Climate During the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Govin, A.; Michel, E.; Marti, O.; Braconnot, P.; Jansen, E.; Labeyrie, L.; Landais, A.; Mosquet, E.; Risebrobakken, B.; Swingedouw, D.; Waelbroeck, C.

    2008-12-01

    The evolution of Northern Hemisphere climate during the Last Interglacial (LIG) (129--118 ka) is significant for the study of future climate changes as it may provide information on the climate system responses and feedbacks to radiative forcing (Jansen et al. 2007). We present here a comparison of foraminiferal records from high latitude deep-sea cores with model simulations over the LIG period. We compare high-resolution benthic oxygen and carbon isotope composition records, Sea Surface Temperature (SST) and Ice-Rafted Detritus (IRD) records from a Southern Ocean core with three North Atlantic cores at different water--depth, and one Norwegian Sea core. Our strategy is to correlate in details high latitude sea surface records from both hemispheres with corresponding ice isotopic records using atmospheric markers for the interhemispheric correlation (e.g. Blunier et al 1998; Landais et al 2003). We observe persistent iceberg melting at the beginning of the LIG which maintained relatively cold and fresh surface-water conditions in the North Atlantic and the Nordic Seas between 129 and 125 ka. Similarly, benthic δ13C data indicate different LIG deep-water ventilation patterns, with North Atlantic Deep Waters sinking shallower during the 129--125 ka interval than during the later climatic optimum. The establishment of peak interglacial conditions in the high northern latitudes and associated strengthening of North Atlantic thermohaline circulation were delayed in consequence. Simulations with the IPSL--CM4 ocean--atmosphere coupled model (Marti et al. 2005) suggest that our results are consistent with the impact of a continued melting of Greenland ice sheet on Northern Hemisphere climate, in response to a particularly high boreal summer insolation.

  16. 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.

  17. Laurentide Ice Sheet basal temperatures at the Last Glacial Cycle as inferred from borehole data

    NASA Astrophysics Data System (ADS)

    Mareschal, Jean-Claude; Pickler, Carolyne; Beltrami, Hugo

    2016-04-01

    We measured and inverted thirteen temperature-depth profiles (≥1500 m) in boreholes in eastern and central Canada to determine the ground surface temperature histories during and after the last glacial cycle. The sites are located in the southern part of the region covered by the Laurentide Ice Sheet. The inversions yield ground surface temperatures ranging from -1.4 to 3.0oC throughout the last glacial cycle. These temperatures, near the pressure melting point of ice, demonstrate that the southern portion of the Laurentide Ice Sheet was not frozen to the bed, allowing for basal flow and fast flowing ice streams at the base. Despite such conditions, which have been inferred from geomorphological data and models, the ice sheet persisted throughout the last glacial cycle. Our results suggest some regional trends in basal temperatures with possible control by internal heat flow.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  19. 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.

  20. 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. PMID:27386524

  1. 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. PMID:23413190

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  3. 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.

  4. Does ice accretion temperature and geothernmal heating pace the change from ~40 kyr to ~100 kyr glacial cycles?

    NASA Astrophysics Data System (ADS)

    Buck, W. R.

    2008-12-01

    The growth and decay of ice sheets are clearly linked to cycles of the Earth's orbit, particularly the ~41 kyr obliquity cycle. Early Pleistocene ice ages appear to have grown and decayed on a timescale close to the obliquity period, while the period for late Pleistocene ice ages averages closer to 100 kyr. The thermal state of an ice sheet may control whether the climatic changes produced by orbital changes are can lead to the termination of an ice age. Numerous model studies indicate that the termination of ice ages requires glacial flow that is faster than expected for cold-based ice sheets. Fast flow likely requires that the base of the ice sheet be partially melted. Large ice sheets probably accrete cold, but geothermal heating can melt the base of an ice sheet if the surface of the ice is not too cold (as it may be in Antarctica) or if the accretion rate is not too high (as it may be in Greenland). The timescale for basal melting depends on the initial temperature structure of the ice sheet and on the rate of geothermal heating. For example the melting timescale depends on the square of the initial temperature of the ice sheet base. Although some workers assume parameters that give a melting timescale of less than 10 kyrs, reasonable values of ice temperature and terrestrial heatflow could give a timescale several times longer. One-dimensional numerical ice sheet flow models with a rate of ice accretion/ablation paced at 41 kyrs show a periodicity of the glacial cycles that depends on the period of basal melting. If the melting period is short (say <~30 kyrs) then the base of the ice sheet will be partially melted in time for the obliquity maximum that could produce a termination. The ice sheet then disappears at this first obliquity maximum after ice sheet initiation because it can flow fast enough to melt at lower latitudes and elevations. For longer basal melting periods the entire ice sheet may not be warm enough to flow fast enough to lead to termination

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

    PubMed

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

    2015-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  7. 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

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

    PubMed

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

    2003-04-01

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

  9. Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall

    NASA Astrophysics Data System (ADS)

    Doyle, Samuel H.; Hubbard, Alun; van de Wal, Roderik S. W.; Box, Jason E.; van As, Dirk; Scharrer, Kilian; Meierbachtol, Toby W.; Smeets, Paul C. J. P.; Harper, Joel T.; Johansson, Emma; Mottram, Ruth H.; Mikkelsen, Andreas B.; Wilhelms, Frank; Patton, Henry; Christoffersen, Poul; Hubbard, Bryn

    2015-08-01

    Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available. Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change.

  10. Springtime melt onset on arctic sea ice from satellite observations and related atmospheric conditions

    NASA Astrophysics Data System (ADS)

    Bliss, Angela C.

    The timing of snowmelt onset (MO) on Arctic sea ice derived from passive microwave satellite data is examined by determining the melting area (in km 2) on a daily basis for the spring and summer melt season months over the 1979 -- 2012 data record. The date of MO on Arctic sea ice has important implications for the amount of total solar energy absorbed by the ice-ocean system in a given year. Increasingly early mean MO dates have been recorded over the 34-year data record. Statistically significant trends indicate that MO is occurring 6.6 days decade-1 earlier in the year over all Arctic sea ice extent. Larger trends exist in sub-regions of the Arctic Ocean including the Barents, Kara, Laptev, East Siberian, Chukchi, and Beaufort Seas and in the Central Arctic region. The Bering Sea is the only sub-region of the Arctic that has a positive trend in mean MO date indicating that melting is occurring later in the year. Temporal and spatial variability in melting events are examined in the time series of daily MO areas via the identification of several types of melting events. These melting events are characterized based on the magnitude of area melted and duration of the event. Daily maps of MO during melting events are compared with the atmospheric conditions from reanalysis data to investigate the nature of spatial variability in melting area. The occurrence of transient cyclones tends to produce large, contiguous areas of melting on sea ice located in the warm sector of the cyclone. By contrast, high pressure and attendant clear sky conditions tend to produce sporadic, discontinuous areas of melting area. Interannual variability in daily MO area is assessed using an annual accumulation of daily MO area for each melt season. Trends in mean MO dates are evident in the annual accumulations, however, regional variability is high and outlier events can occur. This work illustrates the need for a better understanding of the synoptic weather conditions leading to specific

  11. Contribution of glacial melt water to the recent Southern Ocean sea ice increase

    NASA Astrophysics Data System (ADS)

    Haid, Verena; Iovino, Dorotea

    2015-04-01

    In recent years climate change and global warming are topics that are discussed everywhere. Big concerns are the melting of land ice, the reduced summer sea ice cover in the Arctic Ocean, and the general decline of the cryosphere. In contrast to those scenarios, the response of Antarctic sea ice to a warming climate is elaborate and puzzling: sea ice extent has been slightly increasing on a circumpolar scale during the last decades. Atmospheric data analysis ascribed this expansion to changes in the wind dynamics; simulations with climate-scale ocean model suggest that accelerated basal melting of ice shelves plays a major role. We investigate the influence of the glacial melt water on the sea ice of the Southern Ocean on the circumpolar and regional scales employing the ocean/sea ice NEMO-LIM coupled system at eddy-permitting resolution. The forcing of the sea ice-ocean model is supplied from the ERA-Interim data set. After a 25-year spin-up period the reference run supplies a realistic simulation of the period 2004-2013. Different volumes and distributions of melt water are applied in individual model runs spanning the same period and results are compared with the reference run. The results of this study will increase our understanding of the effect of climate change on the Southern Ocean at present and thus also of the future development. Questions like how long the increasing trend in sea ice will last or how fast it will be reversed once the tipping point is reached will be able to be addressed with more accuracy.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-08-01

    Isotopes of helium and neon and the H218O/H216O ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts. Their high concentrations in glacial meltwater, compared to other environmental sources, make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior. We combine noble gas and stable isotopes with temperature, salinity, and dissolved oxygen measurements from three cruises (along the Ross Ice Shelf during the austral summers of 1993-1994 and 1999-2000 and to the Ross Sea in 2000-2001) and use optimal multiparameter analysis to compute the water mass concentration, including glacial meltwater. The distribution of meltwater at the front of the Ross Ice Shelf extended east from 180°W, with the highest concentrations found near 165°W in both 1994 and 2000. The mean meltwater concentration at the ice shelf front was 2.0 ± 0.33‰ in 1994, 2.2 ± 0.36‰ in 2000, and 0.25 ± 0.1‰ in the western Ross Sea in 2001. Water mass concentrations are used to correct for bias in the CFC age, introduced by mixing with CFC-free waters, an effect revealed by comparing CFC age with transit time distribution curves. The water residence time within the ice shelf cavity, using CFCs and the mean meltwater concentration, implies a basal melt rate of 33-50 km3 a-1.

  14. 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.

  15. 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. PMID:24031016

  16. 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.

  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. Reducing the uncertainty in projections of future ice shelf basal melting

    NASA Astrophysics Data System (ADS)

    Timmermann, Ralph; Kauker, Frank

    2014-05-01

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

  19. 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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

  1. Physical Basis for the Temperature-Based Melt-Index Method.

    NASA Astrophysics Data System (ADS)

    Ohmura, Atsumu

    2001-04-01

    The close relationship between air temperature measured at standard screen level and the rate of melt on snow and ice has been widely used to estimate the rate of melt. The parameterization of the melt rate using air temperature usually takes a simple form as a function of either the mean temperature for the relevant period or positive degree-day statistics. The computation provides the melt rate with sufficient accuracy for most practical purposes. Because of its simplicity, it is often called a crude method and is rated as inferior to other more sophisticated methods such as the energy balance method. The method is often used with the justification that temperature data are easily available or that obtaining energy balance fluxes is difficult. The physical process responsible for the temperature effect on the melt rate is often attributed to the sensible heat conduction from the atmosphere. The simulation capacity of the temperature-based melt-index method, however, is too good to be called crude and inferior. The author investigated physical processes that make the air temperature so effective a parameter for melt rate. Air temperature has a more profound influence on melt than previously has been acknowledged. The influence of air temperature through the turbulent sensible heat flux is limited, however. The air temperature information is transferred to the surface mainly through longwave atmospheric radiation, which is by far the most important heat source for melt. Under cloudless-sky conditions, as much as 60% of the atmospheric emission is derived from within the first 100 m and 90% from the first 1 km of the atmosphere. When the sky is overcast with the cloud bottom within the first 1 km, more than 90% originates within this layer between the surface and the bottom of the cloud. When the sky is overcast with the cloud bottom higher than 1 km, the first 1 km of the atmosphere still makes up about 70% of the longwave irradiance at the surface, for which the

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

    PubMed Central

    Park, Sung Hee; Jo, Yeon-Ji; Chun, Ji-Yeon; Hong, Geun-Pyo

    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. PMID:26877639

  3. 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. PMID:26877639

  4. 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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    Ice shelf stability is of crucial importance in the Antarctic because shelves serve as buttresses to glacial ice advancing from the Antarctic Ice Sheet. Surface melt has been increasing over recent years, especially over the Antarctic Peninsula, contributing to disintegration of shelves such as Larsen. Unfortunately, we are not realistically able to quantify surface snowmelt from ground-based methods because there is sparse coverage in automatic weather stations. Satellite based assessments of melt from passive microwave systems are limited in that they only provide an indication of melt occurrence and have coarse resolution. Though this is useful in tracking the duration of melt, melt amount of magnitude is still unknown. Coupled optical/thermal surface measurements from MODIS were calibrated by estimates of liquid water fraction (LWF) in the upper 1cm of the firn derived from a one-dimensional thermal snowmelt model (SNTHERM). SNTHERM was forced by hourly meteorological data from automatic weather station data at reference sites spanning a range of melt conditions across the Ross Ice Shelf during a particularly intense melt season. Melt intensities or LWF were derived for satellite composite periods covering the Antarctic summer months at a 4km resolution over the entire Ross Ice Shelf, ranging from 0-2 percent LWF in early December to areas along the coast with upwards of 10 percent LWF during the time of peak surface melt. Spatial and temporal variations in the amount of surface melt are seen to be related to both katabatic wind strength and wind shifts due to the progression of cyclones along the circumpolar vortex. Sea ice concentration along the ice shelf front, specifically the formation of polynyas, are also thought to be driving factors for surface melt as latent and sensible heat fluxes increase by one to three orders of magnitude as polynyas form. A future application of surface melt mapping using this empirical retrieval model is to determine melt

  6. 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.

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

    PubMed Central

    Lampkin, Derrick; Peng, Rui

    2008-01-01

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

  8. Ice-melt rates in liquid-filled cavities during explosive subglacial eruptions

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    Subglacial eruptions are often associated with rapid penetration of overlying ice and release of large flow rates of water as jökulhlaups. Observations of recent subglacial eruptions indicate rapid syn-eruptive ice melting within liquid-filled subglacial cavities, but quantitative descriptions of possible heat transfer processes need to be developed. Calculations of heat flux from the ice cavity fluid to the melting ice surface indicate that up to 0.6 MW m-2 may be obtained for fluids undergoing single-phase free convection, similar to minimum estimates of heat flux inferred from observations of recent eruptions. Our model of boiling two-phase free convection in subglacial cavities indicates that much greater heat fluxes, in the range 3-5 MW m-2, can be obtained in the vent region of the cavity and may be increased further by momentum transfer from the eruption jet. Rapid magma-water heat transfer from fragmented magma is needed to sustain these heat fluxes. Similar heat fluxes are anticipated for forced convection of subcooled cavity water induced by momentum transfer from an eruption jet. These heat fluxes approach those required to explain jökulhlaup flow rates and rapid ice penetration rates by melting in some, but not all recent eruptions.

  9. Light reflection from a sea-ice cover during the onset of summer melt

    NASA Astrophysics Data System (ADS)

    Perovich, Donald K.; Govoni, John W.

    1992-12-01

    A knowledge of the reflection of light from a sea ice cover is important for both the interpretation of remote sensing imagery at visible and near-infrared wavelengths and for climatological studies involving the energy balance of the polar regions. Spectral measurements of albedo, bidirectional reflectance function (BDRF), and polarized reflectance were made for sea ice conditions found during the onset of melt in the Canadian Arctic. The wavelength region studied was from the ultraviolet to the near infrared (370 - 1000 nm). Results for five surface types are presented: (1) dry snow, (2) dry snow with a glazed surface, (3) bare ice, (4) blue ice, and (5) a melt pond. Results indicate that spectral albedos decrease at all wavelengths as the melt season progresses and the surface conditions evolve from (1) through (5), and that the decrease is most pronounced at longer wavelengths. Reflectance data suggest that (1) at most angles reflectance has the same spectral shape as albedo, (2) at 30 degree(s) elevation reflectance is for the most part azimuthally isotropic and (3) at 60 degree(s) elevation a significant specular component was evident at 0 degree(s) azimuth, especially for the bare ice case.

  10. Hydrograph peaks caused by ice channel melt in Black Hills streams

    SciTech Connect

    Rahn, P.H. . Dept. of Geology and Geological Engineering)

    1992-01-01

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

  11. Investigations of the temperature regimes of the selective laser melting

    NASA Astrophysics Data System (ADS)

    Chivel, Yu.

    2012-06-01

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

  12. 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. PMID:19965425

  13. Chemistry and nanoparticulate compositions of a 10,000 year-old ice core melt water.

    PubMed

    Murr, L E; Esquivel, E V; Bang, J J; de la Rosa, G; Gardea-Torresdey, J L

    2004-11-01

    Particulates extracted from a single section of a 10,000 year-old ice core melt sample exhibited characteristics of contemporary, airborne fine particulates: a majority were microcrystalline particulates and aggregated microcrystals, including some mixtures of microcrystals and carbonaceous matter. Particularly significant were the presence of carbon nanotubes and fullerene nanocrystals composing aggregated particulates reflecting global combustion products similar to contemporary, airborne carbon nanocrystal aggregates. ICP elemental analysis of the melt water showed significant concentrations of Ca, K and especially Na (corresponding to K, NaCl), S, Si, Se, and Zn. Overall, the elemental analysis of the melt water is similar to local tap water. However, lead was absent in the local tap water and only half the concentration of selenium was present in the tap water in contrast to the ice core water. While these observations cannot be generalized, the methodology illustrates the potential to characterize and compare airborne particulate regimes and water chemistries in antiquity. PMID:15491674

  14. Method for Synthesizing Extremeley High Temperature Melting Materials

    SciTech Connect

    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.

  15. Method for synthesizing extremely high-temperature melting materials

    SciTech Connect

    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.

  16. Method For Synthesizing Extremely High-Temperature Melting Materials

    SciTech Connect

    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.

  17. Satellite observation of winter season subsurface liquid melt water retention on the Greenland ice sheet using spectroradiometer and scatterometer data

    NASA Astrophysics Data System (ADS)

    Miller, J. Z.; Forster, R. R.; Long, D. G.; Brewer, S.

    2013-12-01

    controlled by surface heat flux and the detection of subsurface liquid water content controlled by the retention process. Surface freeze-up is identified using MODIS-derived ice surface temperatures. We then identify distinct microwave signatures suggesting the presence of subsurface liquid water content, characterize the stratigraphy and geophysical processes controlling the observed response, and derive a retrieval algorithm using a simple radiative transfer model. Over the 4 year time series (2009-2013), results indicate subsurface liquid melt water persists within Ku-band penetration depth up to ~1 month and within C-band penetration depth between ~1-5 months following surface-freeze-up. Detection occurs exclusively in regions where the PFA has previously been mapped using field (Arctic Circle Traverse) and airborne (IceBridge) observations and the spatial extent is consistent with regional climate model (RACMO2) simulations.

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

    NASA Astrophysics Data System (ADS)

    Turner, J. S.; Veronis, G.

    2004-03-01

    This study has been motivated by two oceanographic observations: an increased rate of melting of sea ice in the Arctic Ocean, and the advance of an anomalously warm tongue of Atlantic water across the Arctic below the halocline over the last few decades. A series of laboratory experiments has been carried out in order to explore the physical principles underlying these phenomena, and the possibility that the extra heating at depth is responsible for the enhanced melting rate. A tank was filled with salt solution having various constant vertical density gradients. A block of ice one third of the length of the tank was floated on the surface at one end, and the rest of the surface and the walls of the tank were insulated. When no extra heat was supplied the melting rate (loss of weight of the ice in 1 h) systematically decreased as the stratification was changed from homogeneous fluid to increasingly large density gradients, while keeping the salinity of the solution in contact with the ice constant. An analogue of the intruding Atlantic water was produced by heating the lower portion of the vertical end wall at the end of the tank opposite to the ice end, keeping its temperature constant, and using the same range of salinity gradients as in the unheated experiments. Again the melting rate decreased as the density gradient was increased, but for low gradients it was larger than that in the unheated experiments. Above a certain intermediate gradient there was no significant difference in melting rate between the unheated and heated runs. The melting data were supplemented by photographs and vertical temperature and salinity profiles. The upward transfer of heat from the body of the fluid to melt the ice was clearly double-diffusive: overturning layers, separated by 'diffusive' interfaces, were visible on shadowgraphs, and the thickness of the layers decreased as the density gradient increased. The mean thickness of the layers through the depth of the tank also

  19. 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.

  20. 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.

  1. Estimation of the diversity between DNA calorimetric profiles, differential melting curves and corresponding melting temperatures.

    PubMed

    Chang, Chun-Ling; Fridman, Alexander S; Grigoryan, Inessa E; Galyuk, Elena N; Murashko, Oleg N; Hu, Chin-Kun; Lando, Dmitri Y

    2016-11-01

    The Poland-Fixman-Freire formalism was adapted for modeling of calorimetric DNA melting profiles, and applied to plasmid pBR 322 and long random sequences. We studied the influence of the difference (HGC -HAT ) between the helix-coil transition enthalpies of AT and GC base pairs on the calorimetric melting profile and on normalized calorimetric melting profile. A strong alteration of DNA calorimetrical profile with HGC -HAT was demonstrated. In contrast, there is a relatively slight change in the normalized profiles and in corresponding ordinary (optical) normalized differential melting curves (DMCs). For fixed HGC -HAT , the average relative deviation (S) between DMC and normalized calorimetric profile, and the difference between their melting temperatures (Tcal -Tm ) are weakly dependent on peculiarities of the multipeak fine structure of DMCs. At the same time, both the deviation S and difference (Tcal -Tm ) enlarge with the temperature melting range of the helix-coil transition. It is shown that the local deviation between DMC and normalized calorimetric profile increases in regions of narrow peaks distant from the melting temperature. PMID:27422497

  2. Modeling the melting temperature of nanoscaled bimetallic alloys.

    PubMed

    Li, Ming; Zhu, Tian-Shu

    2016-06-22

    The effect of size, composition and dimension on the melting temperature of nanoscaled bimetallic alloys was investigated by considering the interatomic interaction. The established thermodynamics model without any arbitrarily adjustable parameters can be used to predict the melting temperature of nanoscaled bimetallic alloys. It is found that, the melting temperature and interatomic interaction of nanoscaled bimetallic alloys decrease with the decrease in size and the increasing composition of the lower surface energy metal. Moreover, for the nanoscaled bimetallic alloys with the same size and composition, the dependence of the melting temperature on the dimension can be sequenced as follows: nanoparticles > nanowires > thin films. The accuracy of the developed model is verified by the recent experimental and computer simulation results. PMID:27292044

  3. 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.

  4. 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.

  5. 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.

  6. 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

  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. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    SciTech Connect

    St. Germain, K.M.; Cavalieri, D.J.

    1997-07-01

    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.

  11. 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

  12. Effects of melting ice sheets and orbital forcing on the early Holocene warming in the extratropical Northern Hemisphere

    NASA Astrophysics Data System (ADS)

    Zhang, Yurui; Renssen, Hans; Seppä, Heikki

    2016-05-01

    temperatures with proxy records illustrate uncertainties related to the reconstruction of ice-sheet melting, and such a kind of comparison has the potential to constrain the uncertainties in ice-sheet reconstruction. Overall, our results demonstrate the variability of the climate during the early Holocene, both in terms of spatial patterns and temporal evolution.

  13. 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.

  14. 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

  15. 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

  16. Cenozoic ice volume and temperature simulations with a 1-D ice-sheet model

    NASA Astrophysics Data System (ADS)

    de Boer, B.; van de Wal, R. S. W.; Bintanja, R.; Lourens, L. J.; Tuenter, E.

    2009-04-01

    Ice volume and temperature for the past 35 Million years is investigated with a 1-D ice-sheet model, simulating ice-sheets on both hemispheres. The simulations include two continental Northern Hemisphere (NH) ice-sheets representative for glaciation on the two major continents, i.e. Eurasia (EAZ) and North America (NAM). Antarctic glaciation is simulated with two separate ice-sheets, respectively for West and East Antarctica. The surface air temperature is reconstructed with an inventive inverse procedure, forced with benthic δ18O data. The procedure linearly relates the temperature to the difference between the modelled and observed marine δ18O 100 years later. The derived temperature, representative for the NH, is used to run the ice-sheet model over 100 years, to obtain a mutually consistent record of marine δ18O, sea level and temperature for the last 35 Ma of the Cenozoic. For Northern Hemispheric glaciations results are good compared to similar simulations performed with a much more comprehensive 3-D ice-sheet model. On average, differences are only 1.9 ˚ C for temperature and 6.1 m for sea level. Results with ice-sheets on both hemispheres are very similar. Most notably, the reconstructed ice volume as function of temperature shows a transition from climate dominated by Antarctic ice volume variation towards NH ice-sheets controlled climate. The transition period falls within the range of interglacials (about -2 to +8 ˚ C with respect to present day) and is thus characterized by lower ice volume changes per ˚ C. The relationship between temperature, sea level and δ18O input is tested with an equilibrium experiment, which results in a linear and symmetric relationship for both temperature and total sea level, providing limited evidence for hysteresis, though transient behaviour is still important. Furthermore results show a rather good comparison with other simulations of Antarctic ice volume and observed sea level and deep-sea temperature.

  17. 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

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  20. Variability of sea ice melt and meteoric water input in the surface Labrador Current off Newfoundland

    NASA Astrophysics Data System (ADS)

    Benetti, M.; Reverdin, G.; Pierre, C.; Khatiwala, S.; Tournadre, B.; Olafsdottir, S.; Naamar, A.

    2016-04-01

    The respective contributions of saline (Atlantic and Pacific water) and freshwater (sea ice melt, meteoric water) components in the surface Labrador Current are quantified using salinity, δ18O, and nutrient data collected between 2012 and 2015 east of Newfoundland to investigate the seasonal variability of salinity in relation with the different freshwater contributions. Nutrient data indicate that the surface saline water is composed on average over 2012-2015 of roughly 62% Atlantic Water and 38% Pacific Water. A large salinity seasonal cycle of ≈ 1.5 peak-to-peak amplitude is found over the middle continental shelf, which is explained by the freshwater input seasonal variability: 2/3 of the amplitude of the salinity seasonal cycle can be explained by meteoric water input and 1/3 by the sea ice melt. A smaller seasonal salinity cycle (≈1.3) is observed over the inner shelf compared to the middle shelf, because of smaller variability in the large meteoric water inputs. Furthermore, the data reveal that sea ice melt (SIM) input was particularly important during July 2014, following a larger extension of sea ice over the Labrador shelf during the 2013/2014 winter season, compared to both previous winter seasons. Some patches of large SIM contribution observed during July 2014 and April 2015 were located on the continental slope or further offshore. The comparison of 2012-2015 data with data collected in 1994-1995 shows that the surface water over the Newfoundland shelf and slope is strongly affected by sea ice processes in both periods and suggests a larger contribution of brines over the slope during 1994-1995.

  1. 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.

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  5. 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

  6. 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

    2016-01-01

    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

  7. Modelling the impact of submarine frontal melting and ice melange on glacier dynamics

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Submarine melting of the calving face of tidewater glaciers and the mechanical back force applied by the ice melange layer are two mechanisms generally proposed to explain seasonal variations at the calving front of tidewater glaciers. However, the way these processes affect the calving rate and glacier dynamics remains uncertain. In this study, we used a finite element-based model that solves the full Stokes equations to simulate the impact of these forcings on two-dimensional theoretical flow line glacier configurations. The model, which includes calving processes, suggests that frontal melting affects the position of the terminus only slightly (less than a few hundred metres) and does not affect the multiannual glacier mass balance at all. However, the ice melange has a greater impact on the advance and retreat cycles of the glacier front (more than several kilometres) and its consequences for the mass balance are not completely negligible, stressing the need for better characterization of forcing properties. We also show that ice melange forcing against the calving face can mechanically prevent crevasse propagation at sea level and hence prevent calving. Results also reveal different behaviours in grounded and floating glaciers: in the case of a floating extension, the strongest forcings can disrupt the glacier equilibrium by modifying its buttressing and ice flux at the grounding line.

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

    NASA Astrophysics Data System (ADS)

    Waythomas, C. F.

    2013-12-01

    Recent eruptions in Alaska (Redoubt 2009; Pavlof 2007, 2013; Veniaminof 2013) all involved ice eruptive-product interactions that led to variable amounts of melt water generation. Production of melt water during explosive eruptions is the primary mechanism for lahar generation, which is a significant and sometimes-deadly hazard at snow and ice clad volcanoes. During the 2009 eruption of Redoubt Volcano, pyroclastic flows produced by explosive destruction of lava domes swept across and eroded glacier ice and generated large quantities of melt water that formed correspondingly large lahars (107-109 m3) in the Drift River valley north of the volcano. Three of the twenty lahars generated during the eruption were large enough to threaten an oil storage facility 40 km from the volcano. During eruptions of Pavlof Volcano in 2007 and 2013 spatter-fed lava flows and minor pyroclastic flows descended over snow and ice on the upper flanks of the volcano and produced some melt water that generated lahars in the associated drainages. These lahars were smaller than those associated with the 2009 eruption of Redoubt Volcano because the melt water generation mechanism was different. At Veniaminof Volcano, a low-level eruption beginning in June 2013 produced small lava flows that flowed passively over glacier ice and produced only limited amounts of melt water. Although melt pits surrounding the lava flows eventually developed, the rate of melt water production was gradual and no significant outflows of water occurred. These eruptions and comparison with past events highlight the various mechanisms for melt water production during eruptive activity at snow and ice clad Alaskan volcanoes. Dynamic emplacement of eruptive products over glacier ice that involves significant erosion of ice and snow leads to production of large volumes of melt water. Less dynamic, but still energetic interactions such as those that have occurred at Pavlof Volcano, produce smaller amounts of melt and

  9. Fuel Rod Melt Progression Simulation Using Low-Temperature Melting Metal Alloy

    SciTech Connect

    Seung Dong Lee; Suh, Kune Y.; GoonCherl Park; Un Chul Lee

    2002-07-01

    The TMI-2 accident and various severe fuel damage experiments have shown that core damage is likely to proceed through various states before the core slumps into the lower head. Numerous experiments were conducted to address when and how the core can lose its original geometry, what geometries are formed, and in what processes the core materials are transported to the lower plenum of the reactor pressure vessel. Core degradation progresses along the line of clad ballooning, clad oxidation, material interaction, metallic blockage, molten pool formation, melt progression, and relocation to the lower head. Relocation into the lower plenum may occur from the lateral periphery or from the bottom of the core depending upon the thermal and physical states of the pool. Determining the quantities and rate of molten material transfer to the lower head is important since significant amounts of molten material relocated to the lower head can threaten the vessel integrity by steam explosion and thermal and mechanical attack of the melt. In this paper the focus is placed on the melt flow regime on a cylindrical fuel rod utilizing the LAMDA (Lumped Analysis of Melting in Degrading Assemblies) facility at the Seoul National University. The downward relocation of the molten material is a combination of the external film flow and the internal pipe flow. The heater rods are 0.8 m long and are coated by a low-temperature melting metal alloy. The electrical internal heating method is employed during the test. External heating is adopted to simulate the exothermic Zircaloy-steam reaction. Tests are conducted in several quasi-steady-state conditions. Given the variable boundary conditions including the heat flux and the water level, observation is made for the melting location, progression, and the mass of molten material. Finally, the core melt progression model is developed from the visual inspection and quantitative analysis of the experimental data. As the core material relocates

  10. 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.

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  16. 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.

  17. Pressure dependence of the melting temperature of metals

    NASA Technical Reports Server (NTRS)

    Schlosser, Herbert; Vinet, Pascal; Ferrante, John

    1989-01-01

    A new method for the analysis of the experimental data for the pressure dependence of the melting temperature of metals is presented. The method combines Lindemann's law, the Debye model, and a first-order equation of state with the experimental observation that the Grueneisen parameter divided by the volume is constant. It is observed that, based on these assumptions, in the absence of phase transitions, plots of the logarithm of the normalized melting temperature versus the logarithm of the normalized pressure are straight lines. It is found that the normalized-melting--temperature versus normalized-pressure curves accurately satisfy the linear relationship for Al, Ag, Au, Cs, Cu, K, Na, Pt, and Rb. In addition, this technique provides a sensitive tool for detecting phase transitions.

  18. Probing the microscopic flexibility of DNA from melting temperatures

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

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

  19. 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. PMID:24264767

  20. 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

  1. 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.

  2. 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-}.

  3. 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

  4. The implication of nonradiative energy fluxes dominating Greenland ice sheet exceptional ablation area surface melt in 2012

    NASA Astrophysics Data System (ADS)

    Fausto, Robert S.; As, Dirk; Box, Jason E.; Colgan, William; Langen, Peter L.; Mottram, Ruth H.

    2016-03-01

    During two exceptionally large July 2012 multiday Greenland ice sheet melt episodes, nonradiative energy fluxes (sensible, latent, rain, and subsurface collectively) dominated the ablation area surface energy budget of the southern and western ice sheet. On average the nonradiative energy fluxes contributed up to 76% of daily melt energy at nine automatic weather station sites in Greenland. Comprising 6% of the ablation period, these powerful melt episodes resulted in 12-15% of the south and west Greenland automatic weather station annual ablation totals. Analysis of high resolution (~5 km) HIRHAM5 regional climate model output indicates widespread dominance of nonradiative energy fluxes across the western ablation area during these episodes. Yet HIRHAM5 still underestimates melt by up to 56% during these episodes due to a systematic underestimation of turbulent energy fluxes typical of regional climate models. This has implications for underestimating future melt, when exceptional melt episodes are expected to occur more frequently.

  5. Acceleration of sea-ice Melt Addition Into the Northern North Atlantic

    NASA Astrophysics Data System (ADS)

    Cox, K. A.; Stanford, J. D.; McVicar, A. J.; Rohling, E. J.; Bacon, S.; Bolshaw, M.; de La Rosa, S.; Wilkinson, D.

    2008-12-01

    Observations over the last decade suggest both a thinning of the Arctic sea-ice cover (Rothrock et al., 1999; Laxon et al., 2003) and a dramatic reduction in its spatial extent (Comiso, 2002; Stroeve et al., 2005). We detect a positive change of ~10 ‰ between 1998 and 2005 in the stable oxygen isotope composition of the net freshwater component in the East Greenland Current (EGC) and East Greenland Coastal Current (EGCC), key carriers of freshened surface waters out of the Arctic. This isotopic signal is unique in the context of oxygen isotope measurements in the northern North Atlantic region dating back to the early 1960s. We show that this signal reflects a remarkable increase in the sea-ice melt water transport within these currents, to the equivalent of a net minimum volumetric loss of multi-year ('permanent') Arctic sea-ice of 10 ± 3% per decade. This independent measurement therefore complements and corroborates the sea-ice reduction inferred from satellite data, and places it in a longer-term multi-decadal context. Our findings suggest that a large proportion of the sea-ice meltwater resulting from the rapid reduction of Arctic sea-ice between 1998 and 2005 is exported from the Arctic via the EGC/EGCC into the northern North Atlantic. Additionally it appears that this sea-ice meltwater export is not in phase with atmospheric circulation regimes such as the North Atlantic Oscillation and the Arctic Oscillation. These findings could have important ramifications for the global thermohaline circulation (e.g. Rahmstorf, 2005).

  6. 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

  7. 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.

  8. Measurements of seismic attenuation in ice: A potential proxy for englacial temperature?

    NASA Astrophysics Data System (ADS)

    Peters, L. E.; Anandakrishnan, S.

    2010-12-01

    Constraints on seismic attenuation in ice are key to determining conditions at the ice-bed interface and below. Variations in this value by as little as a factor of two can make the difference between identifying a soft, deformable sediment bed or hard bedrock stratum from seismic data (both of which have quite different effects on ice dynamics), making the need to understand this parameter imperative for accurate seismic analysis of the subglacial environment. While laboratory tests have demonstrated that seismic attenuation in ice is quite sensitive to englacial temperature, especially as the pressure-melting point is approached, little validation has been performed in the field to confirm this. The results presented here are from a series of wide-angle common midpoint (CMP) seismic datasets across Antarctica and Greenland, where both englacial and basal seismic reflections are observed, each having calculated englacial seismic attenuation values that exhibit a positive correlation with observed and predicted englacial temperatures. We investigate the effects of energy losses due to dissipation as a seismic wave propagates through the ice. Various seismic signals are analyzed in both the time and frequency domains to determine the frequency-dependency of seismic attenuation with respect to depth in the ice column, source-receiver offset, and the frequency spectra of both the source and observed seismic signal. Surface wave data from ten locations across Antarctica and Greenland are analyzed in the time domain to determine near-surface frequency-dependent seismic attenuation, focusing on the upper 100 - 500 m of the ice column where englacial temperatures are indicative of the mean annual surface temperature. These data yield lower attenuation values in the colder regions of Antarctica and higher attenuation values at the warmer locations. Spectral analysis of the basal reflection at each location produces similar results: regions where the bulk temperature of the

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

    NASA Astrophysics Data System (ADS)

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

    2004-05-01

    We present the spatial and temporal variation of multiyear (MY) sea ice distributions: relationships among melt duration, recruitment, export, clouds, and greenhouse gases in the Arctic. Melt onset dates, freeze onset dates were estimated over Arctic sea-ice for the past 25-years using standardized SMMR-SSM/I data sets (1979-2002). Sea ice melt dynamics were compared between annual and perennial ice, and between different geographic regions. Average annual melt dates, freeze dates, and melt durations in annual ice were significantly correlated with seasonal strength of the Arctic oscillation (AO). Following high-index AO winters (January-March), spring melt tended to be earlier and autumn freeze later, leading to longer melt season durations. The largest increases in melt duration were observed in the eastern Siberian Arctic, coinciding with cyclonic low pressure and ice motion anomalies associated with the AO's high-index phase (1989-2002). In the northern Chukchi and East Siberian Seas, mean annual melt duration increased 2-3 weeks following the positive AO phase shift, compared to prior years (1979-1988). Different methods of MY sea ice inversions from SSM/I Tb data were compared using different multilayer perceptron (MLP) neural networks (NN) constructed with learning data based on ERS SAR and OKEAN-01 MY ice map products. Monthly Arctic MY sea ice concentration maps (1979 - 2003) were generated from SSM/I Tbs (19 GHz V, 19 GHz H and 37 GHz V) using a modified MLP with error back propagation, and then compared with respective MY sea ice concentration maps derived with the NASA Team algorithm. Three MLP NN ice-type classification methods utilizing SSM/I passive microwave data were originally developed and compared. Each used the same OKEAN-derived MY sea ice learning data, but each used a different learning algorithm: error back propagation with simulated annealing, dynamic learning with polynomial basis functions, and dynamic learning with two-step optimization

  10. 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.

  11. 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.

  12. A Shift to Melted Sea Ice From Runoff as the Major Component of Chukchi Shelf Open Water Freshwater Fractions, 1993-2013

    NASA Astrophysics Data System (ADS)

    Cooper, L. W.; Frey, K. E.; Logvinova, C. L.; Biasatti, D. M.; Grebmeier, J. M.

    2014-12-01

    The freshwater fraction of water that is derived from melted sea ice has increased significantly on the Chukchi shelf relative to runoff within the past decade, based upon analysis of salinity and δ18O mixing lines from a number of research cruises from 1993-2013. The shift to summertime dominance of melted sea ice (freshwater end-member δ18O >-10 per mil) relative to runoff occurred within the past ten years with a transition primarily observed from runoff dominance to sea ice melt after 2004. This shift is localized to the Chukchi shelf and does not reflect large amounts of melted sea ice flowing north through Bering Strait, which still largely transports a freshwater component with runoff origins (freshwater end-member δ18O ~-20 per mil). These observations have implications for understanding high latitude shelf biogeochemical cycling as melted sea ice carries much lower fractions of dissolved organic carbon (DOC) than runoff, allowing for greater light penetration, including through melt ponds in sea ice, and potential changes in productivity. Lower alkalinity and buffering capacity in melted sea ice compared to runoff will also increase the vulnerability of shelf organisms to water column acidification. Melted sea ice, with low DOC relative to runoff can dominate the freshwater budget in Chukchi shelf waters even under apparently continuous ice coverage. The higher transmission of light through melted sea ice with low DOC may be in part responsible for recent reported under-ice blooms on the Chukchi shelf. Since these blooms occur in waters with the freshwater budget dominated by melted sea ice, they can reasonably interpreted as being part of a continuum with other ice melt-associated blooms and not independent of sea ice retreat and dissolution.

  13. 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.

  14. High-temperature oxygen sensors for glass-forming melts.

    PubMed

    Baucke, F G

    1996-09-01

    Electrochemical sensors are reported for the on-line measurement of oxygen partial pressures of oxidic glass-forming melts on a laboratory and technical scale. Based on the principle of solid electrolyte cells without transference, they are principally simple units. The extreme chemical and temperature conditions of their applications, however, demanded extensive fundamental investigations and resulted in specific forms of reference and measuring electrodes, a thermo-dynamic procedure of verifying the correct functioning of such cells, and a method of measuring thermoelectric voltages of non-isothermal glass melts. PMID:15048355

  15. 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

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

    PubMed

    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

  17. Modeling Regolith Temperatures and Volatile Ice Processes (Invited)

    NASA Astrophysics Data System (ADS)

    Mellon, M. T.

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

    Understanding the behavior of large outlet glaciers draining the Greenland Ice Sheet is critical for assessing the impact of climate change on sea level rise. The flow of marine-terminating outlet glaciers is partly governed by calving-related processes taking place at the terminus but is also influenced by the drainage of surface runoff to the bed through moulins, cracks, and other pathways. To investigate the extent of the latter effect, we develop a distributed surface-energy-balance model for Helheim Glacier, East Greenland, to calculate surface melt and thereby estimate runoff. The model is driven by data from an automatic weather station operated on the glacier during the summers of 2007 and 2008, and calibrated with independent measurements of ablation. Modeled melt varies over the deployment period by as much as 68% relative to the mean, with melt rates approximately 77% higher on the lower reaches of the glacier trunk than on the upper glacier. We compare melt variations during the summer season to estimates of surface velocity derived from global positioning system surveys. Near the front of the glacier, there is a significant correlation (on >95% levels) between variations in runoff (estimated from surface melt) and variations in velocity, with a 1 day delay in velocity relative to melt. Although the velocity changes are small compared to accelerations previously observed following some calving events, our findings suggest that the flow speed of Helheim Glacier is sensitive to changes in runoff. The response is most significant in the heavily crevassed, fast-moving region near the calving front. The delay in the peak of the cross-correlation function implies a transit time of 12-36 h for surface runoff to reach the bed.

  19. 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.

  20. Self-optimizing MPC of melt temperature in injection moulding.

    PubMed

    Dubay, R

    2002-01-01

    The parameters in plastic injection moulding are highly nonlinear and interacting. Good control of plastic melt temperature for injection moulding is very important in reducing operator setup time, assuring consistent product quality, and preventing thermal degradation of the melt. Step response testing was performed on the barrel heating zones on an industrial injection moulding machine (IMM). The open loop responses indicated a high degree of process coupling between the heating zones. From these experimental step responses, a multiple-input-multiple-output model predictive control strategy was developed and practically implemented. The requirement of negligible overshoot is important to the plastics industry for preventing material overheating and wastage, and reducing machine operator setup time. A generic learning and self-optimizing MPC methodology was developed and implemented on the IMM to control melt temperature for any polymer to be moulded on any machine having different electrical heater capacities. The control performance was tested for varying setpoint trajectories typical of normal machine operations. The results showed that the predictive controller provided good control of melt temperature for all zones with negligible oscillations, and, therefore, eliminated material degradation and extended machine setup time. PMID:12014805

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

    NASA Astrophysics Data System (ADS)

    Rikiishi, K.

    2008-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Zhang, Yunshu; Rapp, Robert A.

    2004-06-01

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

  3. Melting of Temperature-Sensitive 3D Colloidal Crystals

    NASA Astrophysics Data System (ADS)

    Alsayed, Ahmed; Han, Yilong; Yodh, Arjun

    2006-03-01

    We employ thermally responsive monodisperse microgel colloidal spheres to study the melting mechanisms of colloidal crystals [1]. The particle diameter decreases with increasing temperature and leads to volume fraction changes that drive phase-transitions. We will describe observations of a variety of phenomena. Premelting, the localized loss of crystalline order near defects (e.g. grain boundaries) at volume fractions above the bulk melting transition, is directly observed by video microscopy, and is characterized by monitoring the first peak position of the particle pair correlation function. We find the position of the first peak shifts toward smaller particle separations at the onset of premelting. After Delaunay triangulation, mean square rotational and translational fluctuations of bonds were measured close to and away from defects. The behavior of all such quantities exhibits increased disorder near the defects. By locally heating the material within a crystal domain, we also studied the superheating and melting of a perfect 3D crystal. Finally, the introduction of weak attractions between spheres reveals free-floating 3D crystal `blobs' which can be made to melt and recrystallize by tuning the temperature. [1] A. M. Alsayed, M. F. Islam, J. Zhang, P. J. Collings, A. G. Yodh, Science 309, 1207 (2005). This work was supported by grants from NSF (DMR-0505048 and MRSEC DMR05-20020) and NASA (NAG8-2172).

  4. Viscosity and Density Measurements of High Temperature Melts

    NASA Astrophysics Data System (ADS)

    Sato, Yuzuru

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

  5. 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.

  6. 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.

  7. Response of the ice sheets to fluctuating temperatures

    NASA Astrophysics Data System (ADS)

    Bøgeholm Mikkelsen, Troels; Grinsted, Aslak; Ditlevsen, Peter

    2016-04-01

    Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing tempera- tures. Using coupled climate and ice sheet models long time forecasting is often made computationally feasible by running the ice sheet model in off-line mode, such that the temperature and precipitation fields govern- ing the mass balance of the ice sheets are taken to be constant over time. As the temperature and precipitation fluctuates, the asymmetry in the typical time scales for accumulation and ablation would result in a bias in the resulting mass balance of the ice sheet. We show that the steady state of the ice sheet is biased toward larger size of the ice sheet, if the short time scale fluctuations in temperature are not taken into account. This could potentially imply that the critical global temperature increase for ice sheet collapse is overestimated, thus the risk of collapse in a given climate change scenario underestimated. Our results highlight the need to consider the variability and not only the mean of the forcing of the mass balance of the ice sheet. We estimate that the effect of temperature variability on surface mass balance of the Greenland Ice Sheet in recent ensemble forecasting should be adjusted downward by as much as 10 percent of the present day observed value, if assuming a 2 degree warming. We are thus closer to a potential tipping point, than previously anticipated. Many predicted scenarios of the future climate show an increased variability in temperature over much of the Earth. In light of the findings presented here, it is important to gauge the extent to which this increased variability will further influence climate change.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The erosional signature of a glacier is often characterized by a longitudinal valley profile that exhibits a stepped morphology, decreased valley floor slope, and overdeepened basin. Numerical modeling experiments have demonstrated that the evolution of such profiles is highly dependent on ice discharge, and hence subglacial water pressure-dependent sliding speed, as well as the material properties of the underlying bedrock. While there are abundant examples of landscapes that demonstrate the valley profile characteristic of efficient glacial erosion, some highly glaciated mountain ranges such as the Himalayas maintain exceptionally tall peaks. These exceptionally tall peaks may be interpreted as evidence for the absence of efficient glacial erosion. One possible explanation for the absence of efficient glacial erosion is the presence of cold-based glacial conditions. Alternatively, the presence of erosionally resistant bedrock with wide fracture spacing may limit erosion. In temperate glaciers, in which basal ice temperatures are warm, or at the pressure melting point (PMP), sliding and erosion occur whenever and wherever high subglacial water pressures exist. In polythermal glaciers, by contrast, erosion efficiency is strongly modulated by basal ice temperature. Sliding, and hence erosion, is prevented when and where basal ice temperatures are cold, or below the PMP. To date, the influence of spatial and temporal variations in basal ice temperature on the efficiency of glacial erosion over long timescales (>1 Ma) remains largely unexplored. We present numerical model results in which we explore the influence of glacier ice temperature on the longitudinal valley profile that emerges during long-term glacial erosion. We focus on identifying conditions that maintain polythermal glaciers in which the basal ice at high elevations is cold, while the basal ice at lower elevations is at the PMP. These unique conditions limit sliding and erosion to low elevations. In

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The Greenland Ice Sheet (GrIS) contains the largest store of fresh water in the northern hemisphere, equivalent to ~7.4m of eustatic sea level rise, but its impacts on current, past and future sea level, ocean circulation and European climate are poorly understood. Previous estimates of GrIS melt, from 26 years of satellite observations and temperature driven melt-models over 48 years, show a trend of increasing melt. There are however no runoff data of comparable duration with which to validate temperature-based runoff models, or relationships between the spatial extent of melt and runoff. Further, longer runoff records that extend GrIS melt records to centennial timescales will enable recently observed trends to be put into a better historical context. We measured Mg/Ca, δ18O and structural cell size in annual growth bands of red coralline algae to reconstruct: (1) near surface sea water temperature; and, (2) melt/runoff from the GrIS. (1) Temperature: we reconstructed the longest (1821-2009) sub-annual resolution record of water temperature in Disko Bugt (western Greenland) showing an abrupt change in temperature oscillation patterns during the 1920s which may be attributable to the interaction between atmospheric temperature and mass loss from Jakobshavn Isbrae glacier. (2) GrIS runoff: using samples from distal parts of Søndre Strømfjord we produced the first reconstruction of decadal (1939-2002) GrIS runoff. We observed significant negative relationships between historic runoff, relative salinity and marine summer temperature. Our reconstruction shows a trend of increasing reconstructed runoff since the mid 1980s. In situ summer marine temperatures followed a similar trend. We suggest that since 1939 atmospheric temperatures have been important in forcing runoff. Subject to locating in situ coralline algae samples, these methods can be applied across hundreds to thousands of years. These results show that our technique has significant potential to enhance

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    It is known that the southeast Alaska (SE-AK) is undergoing a rapid land uplift, which is considered to be mainly due to the effect of melting of past ice, especially in the last two hundred years after the little ice age (LIA). The crustal deformation caused by the post-glacial rebound (PGR) has been clearly detected by GPS and tidal gauge measurements and modeled (Larsen et al., 2004 and 2005). On the other hand, it is considered also that the observed uplift rate is affected by the present-day ice melting (PDIM), which is considered to be the effect of recent global warming (Larsen et al., 2005; Sato et al., 2006). The displacement measurements provide us useful information to evaluate the ice-melting rate and to discuss the viscosity of the earth. However, usually, it is difficult to separate the uplift rate due to the long- term viscous response of the earth by only using displacement observations, because the two effects (i.e. the elastic and viscous deformations) are mixed in the observed data. Related to this problem, Wahr et al. (1995) demonstrated a method to separate the viscous contribution from the observed data by collocating position and gravity measurements. Considered this, since 2006, we, a joint team of Japanese and U.S. researchers are carrying out the absolute gravity (AG) measurements once a year adding to the temporal and continuous GPS observations in SE-AK. Combining the AG measurements and GPS measurements is useful because the attraction part of gravity measurement is sensitive to a mass change of the present-day ice melting, while the past-ices should have no effect to the attraction part of the observed gravity change. In this context of the discussion, precise numerical estimation of the PDIM effect is important (Sato et al., 2007). Based on the two kinds of DEM (Digital Elevation Model), i.e. one is from the 2000 Shuttle Radar Topography Mission (SRTM) and other is that from air photo dating data which were obtained in the period of

  13. 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.

  14. 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

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

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

  16. 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)

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  18. 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

  19. 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.

  20. Taking a balanced approach to estimating snow and ice melt contributions to High Asia runoff

    NASA Astrophysics Data System (ADS)

    Barrett, A. P.

    2015-12-01

    We assess the magnitude and variability of glacier and snow melt input to rivers draining the major glacierized and snow covered river basins of High Asia. The water budget provides a basic framework for hydrological analysis. Measurements of all components of the water budget allow the accuracy of estimates of each component to be checked. In glacierized catchments, the water budget is the balance between runoff, precipitation inputs (as rain or snow), loss by evaporation, and the release or uptake of water by soil moisture and ground water stores, snow cover, glaciers and permafrost, as well as by engineered reservoirs and lakes. In this paper, we estimate these components of the water budgets of the Syr Darya, Amu Darya, Indus, Ganges and Brahmaputra rivers using a combination of station observations, satellite remote sensing and reanalysis output, mass balance measurements, and simple snow cover and glacier models. We estimate the errors for each of these terms with a view to answering the question; how well can we assess glacier and snow melt contributions. Monthly changes in land surface moisture storage are estimated from the difference between runoff and net precipitation (P-E) and also from GRACE. Net precipitation (P-E) is estimated from upper air fields from the NASA MERRA reanalysis using the aerological method and from observations and reanalysis fields of precipitation and evaporation. The challenge is to separate land surface moisture storage into the component reservoirs. Estimates of glacier mass balance in each basin are based on in situ measurements, satellite altimetry, and DEM differencing. Changes in snow storage and contributions from ice melt are estimated using simple accumulation and melt models. Estimates of soil moisture, groundwater and permafrost storage are taken from the literature.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    High-pressure H2O polymorphs among which ice VI and ice VII are abundant in the interiors of large icy satellites and exo-planets. Knowledge of the elastic properties of these pure H2O ices at high-temperature and high-pressure is thus crucial to decipher the internal structure of icy bodies. In this study we assess for the first time the pressure-volume-temperature (PVT) relations of both polycrystalline pure ice VI and ice VII at high pressures and temperatures from 1 to 9 GPa and 300 to 450 K, respectively, by using in situ synchrotron X-ray diffraction. The PVT data are adjusted to a second-order Birch-Murnaghan equation of state and give V0 = 14.17(2) cm3 mol-1, K0 = 14.05(23) GPa, and α0 = 14.6(14) × 10-5 K-1 for ice VI and V0 = 12.49(1) cm3 mol-1, K0 = 20.15(16) GPa, and α0 = 11.6(5) × 10-5 K-1 for ice VII.

  2. 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.

  3. 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. PMID:25217935

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

    NASA Astrophysics Data System (ADS)

    Carmichael, Joshua D.

    Glacier ice responds to environmental forcing through changes in its sliding speed and mass balance. While these changes often occur on daily time scales or longer, they are initiated by brittle deformation events that establish hydrological pathways in hours or seconds and allow meltwater access to englacial or subglacial depths to facilitate ice motion. In this thesis, we (various contributing authors including myself) use seismic monitoring to detect and locate the creation and growth of some of these hydraulic pathways by monitoring their seismic emissions, or icequakes. More specifically, we address (1) what seismic observables, unavailable from other sensing methods, indicate an initial glaciogenic response to melt- water input and (2) if these comprise evidence of feedbacks that may destabilize polar ice under a warming climate. Supplemental to our scientific contributions, we advance statistical processing methods that demonstrably improve the capability of digital detectors at discriminating icequakes from astationary noise. We begin by interpreting geophysical observations collected from a dry-based, sub-freezing (--17 ° C), polar glacier environment (Taylor Glacier, ANT). By implementing a calibrated surface energy balance model, we estimate the timing and volume of surface meltwater generated during the collection of seismic data from a six-receiver geophone network. We proceed by contrasting these response characteristics with geophysical observations following an early (spring) supraglacial lake drainage within the lake-forming ablation zone of the Western Greenland Ice Sheet. Using measurements from a ˜5km-aperture geophone network, we find that the anticipated post-drainage icequakes are diurnally responsive, largely surficial in origin, and indicative of tensile fracturing from shallow cracks in the ice. The creation of the lake-drainage moulin appears to coincide with a shift in mean icequake source locations, and an increase in icequake

  5. 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.

  6. Melting and Frustration in Temperature-Sensitive Colloids

    NASA Astrophysics Data System (ADS)

    Yodh, Arjun

    2009-03-01

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

  7. 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.

  8. On the role of submarine melting of tidewater glaciers in driving the Greenland ice sheet out of balance (Invited)

    NASA Astrophysics Data System (ADS)

    Rignot, E. J.; Koppes, M. N.; Velicogna, I.

    2009-12-01

    The Greenland ice sheet is losing mass and the rate of mass loss has been increasing with time. A recent comparison of the components contributing to the mass balance of the ice sheet suggests that half of the signal is caused by an increase in runoff and half by ice dynamics, i.e. the acceleration of outlet glaciers. The root cause of the glacier acceleration is a de-stabilization of the glacier frontal regions, i.e. an un-grounding of the frontal parts which reduces buttressing and allows faster rates of ice sliding to sea. While the role of surface melt water on the lubrication of the glacier bed has been highly publicized, detailed study of the effect of melt water on glacier flow suggest that it can only account for a moderate acceleration of glaciers. De-stabilization of glaciers from vertical thinning is key, yet the increase in runoff is not large enough to explain the observations. We propose instead that submarine melting of the glacier submerged faces has been the main trigger and control. In August 2008, we collected CTD and current measurements in the front of 4 glaciers, 100 km north of Jakobshavn Isbrae, in West Greenland. Calculation of heat and mass flow reveal submarine melt rates ranging from 1 to 3 meters per day, or 100 times larger than the rates of surface melt. Large variations exist from one glacier to the next, but the results suggest that submarine melting is a large contributor to glacier thinning, capable of explaining glacier un-grounding and de-stabilization. Submarine melting removes from 20% to 90% of the ice that reaches the ocean, the rest being discharged as icebergs. Prior studies totally ignored the role of submarine melting in Greenland and only considered iceberg calving. We conclude than more detailed studies of ice-ocean interactions in tidewater glacier environments are absolutely critical to better understand present-day and future evolutions of the Greenland ice sheet in a warming climate.

  9. 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

  10. 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

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

    NASA Astrophysics Data System (ADS)

    Magorrian, Samuel; Wells, Andrew

    2014-05-01

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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  14. 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.

  15. 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

  16. Tectonics of icy satellites driven by melting and crystallization of water bodies inside their ice shells

    NASA Astrophysics Data System (ADS)

    Johnston, Stephanie Ann

    Enceladus and Europa are icy satellites that currently support bodies of liquid water in the outer solar system Additionally, they show signs of being geologically active. Developing numerical models informed by observations of these icy satellites allows for the development of additional constraints and an improved understanding of the tectonics and evolution of icy satellites. The formation mechanisms for both chaos and ridges on Europa are thought to involve water as albedo changes observed in association with them imply the deposition of salt-rich water near these features. Ridges are the most ubiquitous feature on Europa and are described as central troughs flanked by two raised edifices, range in height from tens to hundreds of meters. Europan ridges can extend hundreds of km continuously along strike but are only about 2 km across. A model of a crystallizing dike--like water intrusion is able to match the overall morphology of ridges, and is consistent the long continuous strike. However, the intrusion of a large volume of water is required to match the most common heights of the ridges. Chaos on Europa is defined as a large area of disrupted ice that contain blocks of pre-existing material separated by a hummocky matrix. A proposed mechanism for the formation of Chaos is that a region of heterogeneous ice within the shell is melted and then recrystallizes. Comparing the model results with the geology of Thera Macula, a region where it has been proposed that Chaos is currently forming, suggests that additional processes may be needed to fully understand the development of Chaos. Water-rich plumes erupt from the south pole of Enceladus, suggesting the presence of a pressurized water reservoir. If a pressurized sea is located beneath the south polar terrain, its geometry and size in the ice shell would contribute to the stress state in the ice shell. The geometry and location of such an ocean, as well as the boundary conditions and thickness of an ice shell

  17. 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

  18. 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.

  19. Liquidus Temperatures of Cryolite Melts With Low Cryolite Ratio

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

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

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  2. 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

  3. 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.

  4. Deposition Ice Nuclei Concentration at Different Temperatures and Supersaturations

    NASA Astrophysics Data System (ADS)

    López, M. L.; Avila, E.

    2013-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Udagawa, Masafumi; Ishizuka, Hiroaki; Motome, Yukitoshi

    2010-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  7. 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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  9. 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.

  10. 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.

  11. Short Communication: 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.

    2015-06-01

    If we could choose a region where the effects of global warming are likely to be pronounced and considerable, and at the same time one where the changes could affect the global climate in similarly asymmetric way with respect to other regions, this would unequivocally be the Arctic. The atmospheric branch of the hydrological cycle lies behind the linkages between the Arctic system and the global climate. Changes in the atmospheric moisture transport have been proposed as a vehicle for interpreting the most significant changes in the Arctic region. This is because the transport of moisture from the extratropical regions to the Arctic 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 assessing more objectively the strong link between ocean evaporation trends and Arctic Sea ice melting. We will critically analyze 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 disconnect ng results, using new information and insights. Among the many mechanisms that could be involved are hydrological (increased Arctic river discharges), radiative (increase of cloud cover and water vapour) and meteorological (increase in summer storms crossing the Arctic, or increments in precipitation).

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  13. Satellite-derived surface type and melt area of the Greenland ice sheet using MODIS data from 2000 to 2005

    NASA Astrophysics Data System (ADS)

    Fausto, Robert S.; Mayer, Christoph; Ahlstrøm, Andreas P.

    2007-10-01

    A new surface classification algorithm for monitoring snow and ice masses based on data from the moderate-resolution imaging spectroradiometer (MODIS) is presented. The algorithm is applied to the Greenland ice sheet for the period 2000-05 and exploits the spectral variability of ice and snow reflectance to determine the surface classes dry snow, wet snow and glacier ice. The result is a monthly glacier surface type (GST) product on a 1 km resolution grid. The GST product is based on a grouped criteria technique with spectral thresholds and normalized indices for the classification on a pixel-by-pixel basis. The GST shows the changing surface classes, revealing the impact of climate variations on the Greenland ice sheet over time. The area of wet snow and glacier ice is combined into the glacier melt area (GMA) product. The GMA is analyzed in relation to the different surface classes in the GST product. The results are validated with data from weather stations and similar types of satellite-derived products. The validation shows that the automated algorithm successfully distinguishes between the different surface types, implying that the product is a promising indicator of climate change impact on the Greenland ice sheet.

  14. Stability of blood gases in ice and at room temperature.

    PubMed

    Liss, H P; Payne, C P

    1993-04-01

    Arterial blood samples from 75 patients were analyzed for PO2, PCO2, and pH at 0, 15, and 30 min. After the baseline analysis, 60 samples were kept in ice while 59 samples were left at room temperature. There was a statistically significant increase in the PO2 at 15 min and again at 30 min in both groups. There was a statistically significant decrease in the PCO2 at 15 min in both groups. There were no further changes in the PCO2 at 30 min in either group. There was a statistically significant decrease in the pH at 15 min in both groups. There was a further statistically significant decrease in the pH at 30 min in the group of blood samples left at room temperature but not in those in ice. There is no reason to keep arterial blood in ice if blood gas analysis is done within 30 min. PMID:8131450

  15. Two decades of ice melt reconstruction in Greenland and Antarctica from time-variable gravity

    NASA Astrophysics Data System (ADS)

    Talpe, M.; Nerem, R. S.; Lemoine, F. G.

    2014-12-01

    In this study, we present a record of ice-sheet melt derived from space-borne gravity that spans over two decades—beyond the time-frame of the GRACE mission. GRACE fields are merged with conventional tracking data (SLR/DORIS) spanning 1992 to the present. They are provided as weekly global fields of degree and order five without C50 and S50 but with C61 and S61. Their multi-decade timespan complements the monthly fields of GRACE of degree and order 60 that start in 2003 and will end when the GRACE mission terminates. The two datasets are combined via an empirical orthogonal function analysis, whereby the conventional tracking data temporal modes are obtained by fitting the SLR/DORIS coefficients to the GRACE spatial modes via linear least squares. Combining those temporal modes with GRACE spatial modes yields the reconstructed global gravity fields. The error budget of the reconstructions is composed of three components: the SLR/DORIS covariances, the errors estimated from the assumption that GRACE spatial modes can be mapped over the SLR/DORIS timeframe, and the covariances from the least squares fit applied to obtain the SLR/DORIS temporal modes. The reconstructed surface mass changes in Greenland and Antarctica, predominantly captured in the first mode, show a rate of mass loss that is increasing since 1992. The trend of mass changes in Greenland over various epochs match with an overarching study assembling altimetry, gravimetry, and interferometry estimates of ice-sheet balance over a 1992-2011 time-frame [Shepherd et al., 2012]. Antarctica shows a trend that is different because of updated GIA models [A et al., 2013] compared to the other studies. We will also show regional mass changes over various other basins, as well as the influence of each SLR/DORIS coefficient on the reconstructions. The consistency of these results underscores the possibility of using low-resolution SLR/DORIS time-variable gravity solutions as a way to continuously monitor the

  16. Using pan-Arctic, springtime, surface radiation observations to quantify atmospheric preconditioning processes that impact the sea ice melt season

    NASA Astrophysics Data System (ADS)

    Cox, Christopher; Uttal, Taneil; Starkweather, Sandy; Intrieri, Janet; Maturilli, Marion; Kustov, Vasily; Konopleva, Elena; Crepinsek, Sara; Long, Chuck

    2015-04-01

    Accurate, seasonal-scale forecasts of sea ice extent and distribution are critical for weather forecasting, transportation, the energy industry and local Arctic communities. Current forecasting methods capture an overall trend of decreasing sea ice on decadal scales, but do not reliably predict inter-annual variability. Recent work using satellite observations identified a relationship between spring-time, cloud modulated, shortwave radiation, and late season sea-ice extent; this relationship suggested an atmospheric preconditioning process that modulates the ice-albedo feedback and sets the stage for the melt season. Due to a general lack of emphasis on the role of the atmosphere on the evolution of the summer sea-ice, compounded by biases in cloud properties within models, this preconditioning process is poorly represented in current forecasting methods. Longwave and shortwave radiation data collected at the surface from stations surrounding the Arctic Basin as part of the Baseline Surface Radiation Network (BSRN) provide high-quality, continuous observations of the surface radiation budget. This includes downwelling fluxes and surface-cloud radiative interactions which cannot be directly acquired by satellites. These BSRN data are used to investigate the role of the atmosphere and clouds in seasonal scale variability of sea ice conditions, and the potential for improving predictability by incorporating these atmospheric observations into prediction strategies. We find that the downwelling fluxes measured at the land stations in spring are well correlated with sea ice conditions in September, especially in regions of the Arctic Ocean where late summer sea ice concentration has large inter-annual variability. Using observations of the total radiative flux (longwave + shortwave) at the surface, it is possible to make a seasonal sea-ice extent forecast that is within the range of uncertainty of forecasts currently incorporated into the Sea Ice Prediction Network

  17. 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.

  18. Temperature effects on atomic pair distribution functions of melts

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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.

  19. 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.

  20. 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). PMID:26296341

  1. Effect of sea-ice melt on inherent optical properties and vertical distribution of solar radiant heating in Arctic surface waters

    NASA Astrophysics Data System (ADS)

    Granskog, Mats A.; Pavlov, Alexey K.; Sagan, Sławomir; Kowalczuk, Piotr; Raczkowska, Anna; Stedmon, Colin A.

    2015-10-01

    The inherent optical properties (IOPs) of Polar Waters (PW) exiting the Arctic Ocean in the East Greenland Current (EGC) and of the inflowing Atlantic waters (AW) in the West Spitsbergen Current (WSC) were studied in late summer when surface freshening due to sea-ice melt was widespread. The absorption and attenuation coefficients in PW were significantly higher than previous observations from the western Arctic. High concentrations of colored dissolved organic matter (CDOM) resulted in 50-60% more heat deposition in the upper meters relative to clearest natural waters. This demonstrates the influence of terrigenous organic material inputs on the optical properties of waters in the Eurasian basin. Sea-ice melt in CDOM-rich PW decreased CDOM absorption, but an increase in scattering nearly compensated for lower absorption, and total attenuation was nearly identical in the sea-ice meltwater layer. This suggests a source of scattering material associated with sea-ice melt, relative to the PW. In the AW, melting sea-ice forms a stratified surface layer with lower absorption and attenuation, than well-mixed AW waters in late summer. It is likely that phytoplankton in the surface layer influenced by sea-ice melt are nutrient limited. The presence of a more transparent surface layer changes the vertical radiant heat absorption profile to greater depths in late summer both in EGC and WSC waters, shifting accumulation of solar heat to greater depths and thus this heat is not directly available for ice melt during periods of stratification.

  2. 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.

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

    NASA Technical Reports Server (NTRS)

    Schlosser, Herbert; Ferrante, John

    1991-01-01

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

  4. 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.

  5. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  7. Invention of Ozone Inclusion Ice Using Low-Temperature Plasma

    NASA Astrophysics Data System (ADS)

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

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

  8. Temperature-Dependent Pore Space of Sea Ice: X-ray Computed-Tomography and Dual Model Network Analysis

    NASA Astrophysics Data System (ADS)

    Pringle, D.; Miner, J.; Glantz, R.; Hilpert, M.; Eicken, H.

    2006-12-01

    Sea ice provides a mechanical and thermal barrier between the atmosphere and ocean at high latitudes and is an important component of the climate system. It is a composite material with temperature- and salinity- dependent volume fractions of ice, brine and air. Our present interest is the microstructural control of the (hydraulic) permeability, which affects the melt-season albedo (shortwave reflectance) of sea ice by enabling or restricting the drainage of surface meltwater, and is also relevant for other processes including nutrient delivery to microorganisms colonizing the lower layers of the ice sheet. At low temperatures, the relative brine volume (porosity) is small, the inclusions are disconnected, and the permeability is small. The relative brine volume increases with temperature, and the permeability increases strongly above a porosity of ~5%. We have imaged the pore space of natural and laboratory-grown sea ice with x-ray micro-computed tomography (CT) over a temperature range typical of that in the Arctic ( - 25°C to -3°C) and which spans corresponding changes in the permeability by several orders of magnitude. Based on our `Dual Model' approach, we identify pore bodies and throats from the segmented CT data to eventually derive a pore network. We characterize the temperature-dependence of the pore space connectivity and apply critical path analysis to investigate the dependence of permeability on pore microstructural evolution.

  9. 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.

  10. 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

  11. Sea surface temperature control on the distribution of far-traveled Southern Ocean ice-rafted detritus during the Pliocene

    NASA Astrophysics Data System (ADS)

    Cook, C. P.; Hill, D. J.; Flierdt, Tina; Williams, T.; Hemming, S. R.; Dolan, A. M.; Pierce, E. L.; Escutia, C.; Harwood, D.; Cortese, G.; Gonzales, J. J.

    2014-06-01

    The flux and provenance of ice-rafted detritus (IRD) deposited in the Southern Ocean can reveal information about the past instability of Antarctica's ice sheets during different climatic conditions. Here we present a Pliocene IRD provenance record based on the 40Ar/39Ar ages of ice-rafted hornblende grains from Ocean Drilling Program Site 1165, located near Prydz Bay in the Indian Ocean sector of the Southern Ocean, along with the results of modeled sensitivity tests of iceberg trajectories and their spatial melting patterns under a range of sea surface temperatures (SSTs). Our provenance results reveal that IRD and hence icebergs in the Prydz Bay area were mainly sourced from (i) the local Prydz Bay region and (ii) the remote Wilkes Land margin located at the mouth of the low-lying Aurora Subglacial Basin. A series of IRD pulses, reaching up to 10 times background IRD flux levels, were previously identified at Site 1165 between 3.3 and 3.0 Ma. Our new results reveal that the average proportion of IRD sourced from distal Wilkes Land margin doubles after 3.3 Ma. Our iceberg trajectory-melting models show that slower iceberg melting under cooling SSTs over this middle Pliocene interval allowed Wilkes Land icebergs to travel farther before melting. Hence, declining SSTs can account for a large part of the observed IRD provenance record at Site 1165. In early Pliocene IRD layers, sampled at suborbital resolution around 4.6 Ma, we find evidence for significant increases in icebergs derived from Wilkes Land during very warm interglacials. This is suggestive of large-scale destabilization of the East Antarctic Ice Sheet in the Aurora Subglacial Basin, as far-traveled icebergs would have to overcome enhanced melting in warmer SSTs. Our results highlight the importance of considering SSTs when interpreting IRD flux and provenance records in distal locations.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  16. The temperature jump at a growing ice-water interface

    NASA Astrophysics Data System (ADS)

    Elif Genceli Güner, F.; Wåhlin, Johan; Hinge, Mogens; Kjelstrup, Signe

    2015-02-01

    During an ice growth rate of around 0.02 mm/s, we report a temperature jump at an ice-water interface above 0 °C up to 1.68 °C (0.01 ± °C), as measured with thermochromatic-liquid-crystals. This gives experimental proof for the existence of an interfacial temperature jump during a liquid-solid phase transition, confirming similar results for liquid-vapour transition, and supporting idea of the surface as a separate thermodynamic system. The fact that there is no continuity in intensive variables across the interface, unlike what is assumed in standard engineering models, has a bearing on the understanding and modelling of coupled heat and mass transport at interfaces in nature and man-made applications.

  17. 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.

  18. Melting and casting processes for high-temperature intermetallics

    SciTech Connect

    Sen, Subhayu; Stefanescu, D.M. )

    1991-05-01

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

  19. Effects of cryoprotectants and ice-seeding temperature on intracellular freezing and survival of human oocytes.

    PubMed

    Trad, F S; Toner, M; Biggers, J D

    1999-06-01

    The accurate determination of the freezing conditions that promote intracellular ice formation (IIF) is crucial for designing cryopreservation protocols for cells. In this paper, the range of temperatures at which IIF occurs in human oocytes was determined. Fresh oocytes with a germinal vesicle, failed-to-fertilize (metaphase I and metaphase II stages) and polyspermic eggs were used for this study. The occurrence of IIF was first visualized at a cooling rate of 120 degrees C/min using a programmable thermal microscope stage connected to a videomicroscope. Then, with a cooling rate of 0.2 degrees C/min, the seeding temperature of the extracellular ice was modified to decrease the incidence of IIF and increase the survival rate of frozen-thawed human oocytes. After adding different cryoprotectants, the median temperature of IIF (TMED) was decreased by approximately 23 degrees C in mouse and only by approximately 6.5 degrees C in human oocytes. Using 1.5 M propylene glycol and seeding temperatures of -8.0, -6.0 and -4.5 degrees C, the incidence of IIF was 22/28 (78%), 8/24 (33%) and 0/33 (0%) and the 24 h post-thaw survival rate was 10/31(32%), 19/34 (56%) and 52/56 (93%) respectively. The results show that IIF occurs more readily in human oocytes, and that ice seeding between -6 degrees C and -8 degrees C triggers IIF in a large number of human oocytes. Undesirable IIF can be prevented and survival rates maximized by raising the seeding temperature as close as possible to the melting point of the solution, which in our instrument was -4.5 degrees C. PMID:10357978

  20. 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.

  1. Doped Artificial Spin Ice

    NASA Astrophysics Data System (ADS)

    Olson Reichhardt, Cynthia; Libal, Andras; Reichhardt, Charles

    We examine square and kagome artificial spin ice for colloids confined in arrays of double-well traps. Unlike magnetic artificial spin ices, colloidal and vortex artificial spin ice realizations allow creation of doping sites through double occupation of individual traps. We find that doping square and kagome ice geometries produces opposite effects. For square ice, doping creates local excitations in the ground state configuration that produce a local melting effect as the temperature is raised. In contrast, the kagome ice ground state can absorb the doping charge without generating non-ground-state excitations, while at elevated temperatures the hopping of individual colloids is suppressed near the doping sites. These results indicate that in the square ice, doping adds degeneracy to the ordered ground state and creates local weak spots, while in the kagome ice, which has a highly degenerate ground state, doping locally decreases the degeneracy and creates local hard regions.

  2. 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. PMID:9092469

  3. 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.

  4. Investigating Crevasse Structure Impact on Glacial Sub-Surface Ice Temperature Distribution with Implications for Moulin Formation

    NASA Astrophysics Data System (ADS)

    Hurley, A.; Lampkin, D.

    2008-12-01

    Ice flow acceleration in the ablation zone of outlet glaciers in Greenland has been linked to an increase in infiltration of surface melt through moulins. In order to understand the potential for moulin formation within cracks and crevasses in glacial ice and their impact on melt infiltration rates it is important to gain knowledge about how crevasse structure influences sub-surface ice cold content. A tower of seven wireless sensors was deployed in a moulin at the base of a crevasse in Svinasfellsjokull, glacier in Iceland as an analog to those in Greenland to measure temperature and incoming solar radiation at depth. Seven Crossbow® Environmental Motes (MEP410 Models) measuring temperature and irradiance (integrated from 0.4- 0.6μm) were deployed and inserted in a moulin at a depth of 156.8 cm for three days. Temperature measurements indicate greater diurnal fluctuations near the surface of 0.39 °C from the near surface mote, while sub-surface temperature remain stable near mean temperature of -0.05 °C at a depth of 139.8 cm. Incoming solar radiation measurements showed diurnal variation as expected near the surface at 5.30 W/m2 in the top of the sensor tower, whereas no variation occurred at other depths as the average was 0 W/m2. A computational fluid dynamic model has been calibrated by measured mote temperatures. The model was run accounting for diffusion and convective processes and forced with meteorological data to explore how crevasse density, depth, and geometry influence sub-surface ice temperature distribution.

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

    SciTech Connect

    Bentley, C.R.

    1995-12-31

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

  6. Airborne Remote Sensing of Sea Surface Temperature Using the Ball Experimental Sea Surface Temperature (BESST) Radiometer With A Discussion of the 2013 Marginal Ice Zone Observation Processes EXperiment.

    NASA Astrophysics Data System (ADS)

    Tooth, M.; Emery, W. J.

    2014-12-01

    Airborne remote sensing has opened up new possibilities for scientists to study oceanic and atmospheric problems that are relevant to industry, environmental groups, and the scientific community as a whole. Data obtained from these platforms can provide much higher resolution imagery in comparison to satellite observations that allow for more detailed analyses of important regions. Sea surface temperature (SST) data obtained from instruments like the BESST radiometer can be used to provide more insight into issues like natural disasters and oceanographic problems of interest; such as the influence of melting sea ice on SST. During the 2013 Marginal Ice Zone Observation Processes EXperiment (MIZOPEX), BESST was flown on a Scan Eagle UAS in the Alaskan Marginal Ice Zone to acquire SST data. These observations will be discussed, along with possible future uses for the BESST radiometer.

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

    NASA Astrophysics Data System (ADS)

    Scharien, Randall

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

  8. The Sahelian agro-ecosystem vulnerability to an acceleration of ice-sheet melting during the 21st century

    NASA Astrophysics Data System (ADS)

    Defrance, Dimitri; Ramstein, Gilles; Charbit, Sylvie; Sultan, Benjamin; Dumas, Christophe; Vrac, Mathieu; Swingedouw, Didier; Gemenne, François; Alvarez-Solas, Jorge; Vanderlinden, Jean-Paul

    2016-04-01

    During the 20th century, Sahelian drought episodes like those between 1972 and 1982 showed the vulnerability of the Sahelian agro-ecosystem provoking significant intraregional southward human migrations, to or near the coast. According to the latest IPCC report, the Sahel could become increasingly impacted by climate change during the 21st century because of a lagged and shorter rainfall season having the potential to induce a drastic destabilization of the Sahelian agro-ecosystem and to heavily impact the population. Such effects could be further amplified by a net increase of the Sahelian population. Drastic climate changes over tropical areas also occurred in the past: weakening of the West African Monsoon and megadrought Sahelian episodes have been reported with a close correspondence between the large rainfall decrease and the massive freshwater discharges following ice-sheet melting or iceberg surges. During the last decades a continuous acceleration of ice-sheet mass loss has been observed and post IPCC-AR5 studies suggest the ice-sheet contribution to future sea-level rise could be revised upward due partly to the lack of an accurate representation of ice-ocean interactions. The release of freshwater discharge in response to ice-sheet instability could have large consequences on the most vulnerable regions, such as the tropical areas. To investigate the impacts of large ice-sheet instability during the 21st century, we first explore the climatic signature of Greenland or Antarctic ice-sheet collapse scenarios corresponding to 0.5 to 1.5 meter of sea-level rise, superimposed to the RCP8.5 scenario. We show that a freshwater discharge coming from Greenland melting induces a significant decrease of summer monsoon rainfall, that may lead to changes in agricultural practices. Combined with increasing demography, this has the potential to induce important human migration flows. Without adaptation measures, we estimate that tens to hundreds million people could be

  9. Interactions of adsorbed CO₂ on water ice at low temperatures.

    PubMed

    Karssemeijer, L J; de Wijs, G A; Cuppen, H M

    2014-08-01

    We present a computational study into the adsorption properties of CO2 on amorphous and crystalline water surfaces under astrophysically relevant conditions. Water and carbon dioxide are two of the most dominant species in the icy mantles of interstellar dust grains and a thorough understanding of their solid phase interactions at low temperatures is crucial for understanding the structural evolution of the ices due to thermal segregation. In this paper, a new H2O-CO2 interaction potential is proposed and used to model the ballistic deposition of CO2 layers on water ice surfaces, and to study the individual binding sites at low coverages. Contrary to recent experimental results, we do not observe CO2 island formation on any type of water substrate. Additionally, density functional theory calculations are performed to assess the importance of induced electrostatic interactions. PMID:24955794

  10. Potential positive feedback between Greenland Ice Sheet melt and Baffin Bay heat content on the west Greenland shelf

    NASA Astrophysics Data System (ADS)

    Castro de la Guardia, Laura; Hu, Xianmin; Myers, Paul G.

    2015-06-01

    Greenland ice sheet meltwater runoff has been increasing in recent decades, especially in the southwest and the northeast. To determine the impact of this accelerating meltwater flux on Baffin Bay, we examine eight numerical experiments using an ocean-sea ice model: Nucleus for European Modelling of the Ocean. Enhanced runoff causes shoreward increasing sea surface height and strengthens the stratification in Baffin Bay. The changes in sea surface height reduces the southward transport through the Canadian Arctic Archipelago and strengthens the gyre circulation within Baffin Bay. The latter leads to further freshening of surface waters as it produces a larger northward surface freshwater transport across Davis Strait. Increasing the meltwater runoff leads to a warming and shallowing of the west Greenland Irminger water on the northwest Greenland shelf. These warmer waters can now more easily enter fjords on the Greenland coast and thus provide additional heat to accelerate the melting of marine-terminating glaciers.

  11. 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.

  12. Monitoring southwest Greenland’s ice sheet melt with ambient seismic noise

    PubMed Central

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

    2016-01-01

    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. PMID:27386524

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  14. Arctic sea ice melt, the Polar vortex, and mid-latitude weather: Are they connected?

    NASA Astrophysics Data System (ADS)

    Vihma, Timo; Overland, James; Francis, Jennifer; Hall, Richard; Hanna, Edward; Kim, Seong-Joong

    2015-04-01

    The potential of recent Arctic changes to influence broader hemispheric weather is a difficult and controversial topic with considerable skepticism, as time series of potential linkages are short (<10 years) and the signal-to-noise ratio relative to chaotic weather events is small. A way forward is through further understanding of potential atmospheric dynamic mechanisms. Although not definitive of change in a statistical or in a causality sense, the exceptionally warm Arctic winters since 2007 do contain increased variability according to some climate indices, with six negative (and two positive) Arctic Oscillation atmospheric circulation index events that created meridional flow reaching unusually far north and south. High pressure anomalies developed east of the Ural Mountains in Russia in response to sea-ice loss in the Barents/Kara Seas, which initiated eastward-propagating wave trains of high and low pressure that advected cold air over central and eastern Asia. Increased Greenland blocking and greater geopotential thickness related to low-level temperatures increases led to northerly meridional flow into eastern North America, inducing persistent cold periods. Arctic connections in Europe and western North America are less clear. The quantitative impact of potential Arctic change on mid-latitude weather will not be resolved within the foreseeable future, yet new approaches to high-latitude atmospheric dynamics can contribute to improved extended range forecasts as outlined by the WMO/Polar Prediction Program and other international activities.

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

    PubMed

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

    2011-09-21

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

  16. A two-dimensional thermodynamic model for sea ice advance and retreat in the Newfoundland marginal ice zone

    NASA Astrophysics Data System (ADS)

    Tang, C. L.

    1991-03-01

    A time dependent two-dimensional ice-ocean coupled thermodynamic model is developed to study the ice edge advance and retreat, development of the oceanic mixed layer, and oceanic response to ice movement, ice melt, and heat balance in the Newfoundland marginal ice zone. The model domain is a vertical section of the ocean along the direction of the ice velocity. Initially, the ocean is free of ice and has a deep mixed layer formed by winter surface cooling. An ice sheet then moves into the domain from the upstream boundary at constant velocity. It melts from the bottom and a shallow mixed layer beneath the ice is developed. Heat and buoyancy fluxes at the air-sea and ice-water interfaces and at the bottom of the mixed layer determine the melt rate and change of the mixed layer properties. The ice edge reaches a maximum distance and starts to retreat when the ice is being melted by the warm water faster than it is being advected into the area. The oceanic properties change with the ice movement. During the advancing phase of the ice movement, the heat loss to the ice bottom from ice melting exceeds the heat gain by surface heating and entrainment, causing the mixed layer temperature to drop. But since the buoyancy created by the melting is not sufficient to overcome the effect of wind mixing, the mixed layer deepens rapidly. During the retreating phase, the mixed layer becomes shallower and warmer because of the increasing surface heating and buoyance production by ice melting. The most important factors controlling the melt rate and the excursion distance are the air temperature and the ambient water temperature. Higher wind speeds increase the mixed layer depth but do not have a strong effect on the melt rate.

  17. 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...

  18. 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...

  19. 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...

  20. 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...

  1. Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  2. Predictions of depth-to-ice on asteroids based on an asynchronous model of temperature, impact stirring, and ice loss

    NASA Astrophysics Data System (ADS)

    Schorghofer, Norbert

    2016-09-01

    Water ice near the surface of main belt asteroids is gradually lost to space. A mantle of low thermal conductivity causes large surface temperature amplitudes, and thus increased cooling by thermal re-radiation, lowering temperatures well below the fast-rotator limit. A computational barrier for modeling this ice loss is the multi-scale character of the problem: accurate temperatures require many time steps within a solar day, but ice retreats slowly over billions of years. This barrier is overcome with asynchronous coupling: Models of temperature, ice loss, and impact stirring each use their own time steps and are coupled with one another. The model is applied to 1 Ceres and 7968 Elst-Pizarro. On Ceres, ice can be expected in the top half meter poleward of 60° latitude on both hemispheres, even if excursions of the axis tilt took place, and even in the presence of impact gardening. At the poles, ice can be expected within a centimeter of the surface. The retreating ice crust leads to emission of water from the surface, mainly at the equator; the gradually retreating ice supplies a water exosphere less dense than has been observed by the Herschel telescope. For Main Belt Comet Elst-Pizarro, depths to ice depend on the properties of the surface mantle. For a dust mantle estimated depths are on the order of a decimeter; for a rocky surface the depth at the pole is on the order of one meter. Hence, it could have been activated by a small impact that exposed buried ice.

  3. 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.

  4. Monitoring of soil temperatures in an Atlantic high mountain environment: The Forcadona buried ice patch (Picos de Europa, NW Spain).

    NASA Astrophysics Data System (ADS)

    Ruiz-Fernández, Jesus; Vieira, Gonçalo; Oliva, Marc; Gallinar, David; García-Hernández, Cristina

    2015-04-01

    Ground temperatures in the area of a buried ice mass located at Western Massif of the Picos de Europa (Cantabrian Mountains, Northwestern Spain) are studied. Ground temperatures were measured at depths of 10 to 50 cm at intervals 2-hour intervals from 2006 to 2011. Ground temperatures showed two distinct seasonal periods: 1) continuous thaw with diurnal oscillation, from late summer to early autumn, and 2) near-0°C, isothermal regime from mid-autumn to late summer. Snow cover thickness controls freeze-thaw cycles in the latter. Transition periods are of very short duration. The small annual number of freeze-thaw cycles in the soil (0 to 16) was controlled by the depth of the snow cover. Extreme minimum temperatures in the soil oscillated between 0.3 and -6.3°C. Monitoring of soil temperatures on the ice patch resulted in slightly negative mean annual temperatures about 0°C. These conditions may reveal that the buried ice is close to melting point and in disequilibrium with the current environmental conditions of the massif.

  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. Effects of the past- and present-day ice melting on observed uplift rates in Southeast Alaska

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    A joint Japanese-US observation project called ISEA (International geodetic project in South-Eastern Alaska) was initiated in 2005 to follow up the work of the University of Alaska Fairbanks (UAF) by adding new geodetic data sets (Miura et al., 2007). Based on 91 improved GPS velocities and the proposed ice loss models by Larsen et al. (2004, 2005, 2007) and by Tushingham and Peltier (1991), we estimated three effects: present-day ice melting (PDIM), post-little ice age (LIA) melting, and deglaciation following the last glacier maximum (LGM). We also have reevaluated the thickness of lithosphere and the viscosities of the mantle including that of asthenosphere in the region. The effects of LGM deglaciation were computed based on the ICE3G model (Tushingham and Peltier, 1991). Although the effect of LGM ice is small in SE-AK (i.e. 2 mm/yr at the maximum), we have confirmed that, by comparing with the misfits obtained by correcting for only two effects of PDIM and LIA, correcting for the LGM effect can improve the chi^2 of misfits by about 0.5 %. We estimated the effect of post-LIA ice melting based on the melting history proposed by Larsen et al. (2004, 2005). For the viscoelastic structure, we have tested two different kinds of mantle viscosity structure: a two-layer model similar to the model used by Larsen et al. (2005) and a 4-layer model. To search the best combination of the lithosphere thickness and the mantle viscosities, the combinations of the rheological parameters tested here were 161 in total number. To test the sensitivity of the estimated rheological parameters to the elastic PDIM effects, we have compared two PDIM models; one is EPSL2005 model (Larsen et al., 2005) and the other is JGR2007 model (Larsen et al., 2007). Statistical examinations of the misfits between observations and model predictions, which were based on the magnitudes of the minimum chi^2 and the mean of residuals fitting to a Gaussian function, indicate that the JGR2007 model gives

  7. Size and shape dependent melting temperature and thermal expansivity of metallic and semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Patel, Ghanshyam R.; Thakar, Nilesh A.; Pandya, Tushar C.

    2016-05-01

    Liquid drop model is used to predict the size dependent melting temperature of low dimensional systems. In the present work we have modified liquid drop model for predicting shape and size dependent melting temperature of nanoparticles of Pb and Si. The new modified liquid drop model gives good agreement between calculated and experimental data which demonstrate the validity of the present work. It is found that the particle shape can affect the melting temperature of nanoparticles and this effect on the melting temperature becomes larger with decreasing of particle size. In the present study relationship for size and shape dependent of thermal expansivity is deduced for metallic and semiconductor nanoparticles. The present relationship for thermal expansivity may be used to predict the coefficient of thermal expansion for nanoparticles.

  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 different embedded atom method potentials to model the interactions between the Ni atoms. Melting temperature, enthalpy, static structure factor, self-diffusion coefficient, shear viscosity, and thermal diffusivity are compared to recent experimental results. Using ab initio MD simulation, we also determine the static structure factor and the mean-squared displacement at the experimental melting point. For most of the properties, excellent agreement is found between experiment and simulation, provided the comparison relative to the corresponding melting temperature. We discuss the validity of the Hansen-Verlet criterion for the static structure factor as well as the Stokes-Einstein relation between self-diffusion coefficient and shear viscosity. The thermal diffusivity is extracted from the autocorrelation function of a wavenumber-dependent temperature fluctuation variable.

  9. The effect of sudden ice sheet melt on ocean circulation and surface climate 14-16 ka

    NASA Astrophysics Data System (ADS)

    Ivanovic, Ruza; Gregoire, Lauren; Wickert, Andrew; Valdes, Paul

    2016-04-01

    Collapse of ice sheets can cause significant sea-level rise and widespread climate change. Around 14.6 thousand years ago, global sea level rose by ˜15 m in less than 350 years[1] during an event known as Meltwater Pulse 1a. Modelling work[2,3] has suggested that approximately half of this ˜50 mm yr‑1 sea level rise came from a North American ice Saddle Collapse that drained into the Arctic and Atlantic Oceans. However, dating uncertainties make it difficult to determine the sequence of events and their drivers, leaving many fundamental questions. For example, did the abrupt ice melting and subsequent ocean freshening have any detectable climatic impact? Was melting from the Northern American ice sheets responsible for the Older-Dryas[4] or other cooling events? And how were all these signals linked to changes in Atlantic Ocean overturning circulation[e.g.5]? To address these questions, we examined the effect of the North American ice Saddle Collapse using a newly developed high resolution network drainage model coupled to an atmosphere-ocean-vegetation General Circulation Model. Here, we present the first quantitative routing estimates of the consequent meltwater discharge and its impact on climate. The results show that approximately 50% of the Saddle Collapse meltwater pulse was routed down the Mackenzie River into the Arctic Ocean, and around half was discharged directly into the Atlantic via the St. Lawrence River. This meltwater flux, equivalent to a total of 7 m of sea-level rise, caused a strong weakening of Atlantic Meridional Overturning Circulation (AMOC) and widespread Northern Hemisphere cooling. The greatest cooling is in the Arctic, but there is also significant warming over North America. We find that AMOC (and climate) is most sensitive to meltwater discharged to the Arctic Ocean. [1] Deschamps et al. (2012) Nature 483, 559-564. [2] Gregoire et al. (2012) Nature 487, 219-222. [3] Gomez et al. (2015) GRL 42(10), 3954-3962. [4] Menviel et al

  10. A comparison between the effect of ice packs on the forehead and ice cubes in the mouth on nasal submucosal temperature.

    PubMed

    Porter, M J

    1991-03-01

    The submucosal temperature in the inferior turbinate was measured in 13 subjects. It was found that giving ice cubes to suck produced a significantly greater fall in nasal temperature than did the application of ice packs to the forehead. In only seven out of the 13 subjects did an ice pack reduce nasal temperature. PMID:2038651

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

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

    PubMed

    Erbe, Eric F; Rango, Albert; Foster, James; Josberger, Edward G; Pooley, Christopher; Wergin, William P

    2003-09-01

    Methods to collect, transport, and store samples of snow and ice have been developed that enable detailed observations of these samples with a technique known as low-temperature scanning electron microscopy (LTSEM). This technique increases the resolution and ease with which samples of snow and ice can be observed, studied, and photographed. Samples are easily collected in the field and have been shipped to the electron microscopy laboratory by common air carrier from distances as far as 5,000 miles. Delicate specimens of snow crystals and ice grains survive the shipment procedures and have been stored for as long as 3 years without undergoing any structural changes. The samples are not subjected to the melting or sublimation artifacts. LTSEM allows individual crystals to be observed for several hours with no detectable changes. Furthermore, the instrument permits recording of photographs containing the parallax information necessary for three-dimensional imaging of the true shapes of snowflakes, snow crystals, snow clusters, ice grains, and interspersed air spaces. This study presents detailed descriptions of the procedures that have been used successfully in the field and the laboratory to collect, ship, store, and image snow crystals and ice grains. PMID:12938115

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

    USGS Publications Warehouse

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

    2003-01-01

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

  14. Photodesorption and physical properties of CO ice as a function of temperature

    NASA Astrophysics Data System (ADS)

    Muñoz Caro, G. M.; Chen, Y.-J.; Aparicio, S.; Jiménez-Escobar, A.; Rosu-Finsen, A.; Lasne, J.; McCoustra, M. R. S.

    2016-05-01

    Context. Ice photodesorption has been the topic of recent studies that aim to interpret the abundances of gas-phase molecules, in particular CO, toward cold interstellar regions. But little is known about the effect of the ice's physical properties on the photodesorption rate. The linear decrease observed in the photodesorption rate, as a function of increasing CO ice deposition temperature, was provisionally attributed to a more compact CO ice structure. Aims: The goal of this work is to monitor the physical properties of solid CO as a function of ice deposition temperature. Then, we evaluate the possible link between the structure of ice and the ice's photodesorption rate. Methods: Infrared spectroscopy is an efficient tool to monitor the structural evolution of pure ices during warm-up or irradiation. The infrared absorption bands of molecular ice components observed toward various space environments allow for the detection of H2O, CO, CO2, CH3OH, NH3, etc. Typically, a pure ice that is composed of one of these species displays significant changes in their mid-infrared band profiles as a result of warm-up. But, at most, only very subtle changes appear in the narrow CO ice infrared absorption band as the result of warm-up. We, therefore, also used vacuum-ultraviolet spectroscopy of CO ice to monitor the effect of temperature in the physical properties of the ice. Finally, temperature-programmed desorption and photo-desorption experiments for different CO ice deposition temperatures were performed. Results: Mid-infrared and vacuum-ultraviolet spectroscopy showed that warm-up of CO ice that is deposited at 8 K did not lead to structural changes. Only CO ice samples deposited at temperatures above 20 K displayed different spectroscopic properties compared to lower deposition temperatures. The observed gradual and linear drop in the photodesorption rate of CO ice, as a function of increasing ice deposition temperature in the 7 to 20 K range, is, therefore, not due to

  15. Photodesorption and physical properties of CO ice as a function of temperature

    NASA Astrophysics Data System (ADS)

    Muñoz Caro, G. M.; Chen, Y.-J.; Aparicio, S.; Jiménez-Escobar, A.; Rosu-Finsen, A.; Lasne, J.; McCoustra, M. R. S.

    2016-04-01

    Context. Ice photodesorption has been the topic of recent studies that aim to interpret the abundances of gas-phase molecules, in particular CO, toward cold interstellar regions. But little is known about the effect of the ice's physical properties on the photodesorption rate. The linear decrease observed in the photodesorption rate, as a function of increasing CO ice deposition temperature, was provisionally attributed to a more compact CO ice structure. Aims: The goal of this work is to monitor the physical properties of solid CO as a function of ice deposition temperature. Then, we evaluate the possible link between the structure of ice and the ice's photodesorption rate. Methods: Infrared spectroscopy is an efficient tool to monitor the structural evolution of pure ices during warm-up or irradiation. The infrared absorption bands of molecular ice components observed toward various space environments allow for the detection of H2O, CO, CO2, CH3OH, NH3, etc. Typically, a pure ice that is composed of one of these species displays significant changes in their mid-infrared band profiles as a result of warm-up. But, at most, only very subtle changes appear in the narrow CO ice infrared absorption band as the result of warm-up. We, therefore, also used vacuum-ultraviolet spectroscopy of CO ice to monitor the effect of temperature in the physical properties of the ice. Finally, temperature-programmed desorption and photo-desorption experiments for different CO ice deposition temperatures were performed. Results: Mid-infrared and vacuum-ultraviolet spectroscopy showed that warm-up of CO ice that is deposited at 8 K did not lead to structural changes. Only CO ice samples deposited at temperatures above 20 K displayed different spectroscopic properties compared to lower deposition temperatures. The observed gradual and linear drop in the photodesorption rate of CO ice, as a function of increasing ice deposition temperature in the 7 to 20 K range, is, therefore, not due to

  16. [Relationships between temperature change and microbial amount in inactive ice wedges in Yitulihe, Northeast China].

    PubMed

    Yang, Si-Zhong; Jin, Hui-Jun; Wen, Xi; Luo, Dong-Liang; Yu, Shao-Peng

    2009-11-01

    Ice-wedge is an indicator of paleoclimate change. The delta18 O concentration in different layers could reflect the change of paleotemperature during ice-wedge growth. In the late 1980s, inactive ice wedges were found in Yitulihe, Northeast China, which were the south-most ones so far and were important in climatic and environmental research. In this paper, the delta18 O concentration and microbial number in the inactive ice-wedges were analyzed by using stable isotope, fluorescence microscopy counting, and flow cytometer (FCM). During the ice-wedge growth in Yitulihe area, there were three short-term paleotemperature fluctuation, and three times of fluctuation in microbial amount in different ice-wedge layer. Correlation analysis indicated that there was a converging relationship between the temperature change and microbial amount in the ice-wedges. The lower the temperature when ice-wedge layer formed, the less the microbes survived in the layer. PMID:20136017

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

    PubMed

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

    2011-05-01

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

  18. 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, J. C.; DiGirolamo, N. E.; Shuman, C. A.

    2011-01-01

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

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

    SciTech Connect

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

    1994-09-01

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

  20. Determination of the melting temperature of palladium nanoparticles by X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Vlasenko, V. G.; Podsukhina, S. S.; Kozinkin, A. V.; Zubavichus, Ya. V.

    2016-02-01

    The anharmonicity parameters of the interatomic potential in ~4-nm palladium nanoparticles deposited on poly(tetra)fluoroethylene microgranules 0.2-0.5 μm in average size were studied by X-ray absorption spectroscopy from an analysis of temperature-dependent EXAFS Pd K edges. The parameters of the interatomic potential obtained were used to calculate melting temperature T melt = 1591 K and Debye temperature ΘD = 257 K of palladium nanoparticles; these temperatures are significantly lower than those in metallic palladium: 277 K and 1825 K, respectively.

  1. Low temperature biodegradation of airport de-icing fluids.

    PubMed

    Revitt, D M; Worrall, P

    2003-01-01

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

  2. The melting curve of iron to 250 gigapascals - A constraint on the temperature at earth's center

    NASA Technical Reports Server (NTRS)

    Williams, Quentin; Jeanloz, Raymond; Bass, Jay; Svendsen, Bob; Ahrens, Thomas J.

    1987-01-01

    The melting curve of iron, the primary constituent of earth's core, has been measured to pressures of 250 gigapascals with a combination of static and dynamic techniques. The melting temperature of iron at the pressure of the core-mantle boundary (136 GPa) is 4800 + or - 200 K, whereas at the inner core-outer core boundary (330 GPa), it is 7600 + or - 500 K. A melting temperature for iron-rich alloy of 6600 K at the inner core-outer core boundary and a maximum temperature of 6900 K at earth's center are inferred. This latter value is the first experimental upper bound on the temperature at earth's center, and these results imply that the temperature of the lower mantle is significantly less than that of the outer core.

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

    PubMed

    Ewert, Marcela; Deming, Jody W

    2014-08-01

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

  4. Paraffin Phase Change Material for Maintaining Temperature Stability of IceCube Type of CubeSats in LEO

    NASA Technical Reports Server (NTRS)

    Choi, Michael K.

    2015-01-01

    The MLA and IFA of the instrument on the IceCube require a 20 C temperature and a thermal stability of +/-1 C. The thermal environment of the ISS orbit for the IceCube is very unstable due to solar beta angles in the -75deg to +75deg range. Additionally the instrument is powered off in every eclipse to conserve electrical power. These two factors cause thermal instability to the MLA and IFA. This paper presents a thermal design of using mini paraffin PCM packs to meet the thermal requirements of these instrument components. With a 31 g mass plus a 30% margin of n-hexadecane, the MLA and IFA are powered on for 32.3 minutes in sunlight at a 0deg beta angle to melt the paraffin. The powered-on time increases to 38 minutes at a 75deg (+/-) beta angle. When the MLA and IFA are powered off, the paraffin freezes.

  5. Experimental investigations of melting at ultra-high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Kavner, Abby

    The laser-heated diamond anvil cell is an important experimental tool used to access the high pressures and temperatures existing in the interior of the Earth and other planets. The ability to measure a temperature at high pressures is established, and the melting curves of elemental platinum and a complex aggregate, Allende meteorite, are determined. The melting curve of platinum was determined using a laser-heated diamond anvil cell in the pressure range of 12 to 70 GPa. The melting temperature at a given pressure is bracketed by a combination of visual observations and corresponding temperature measurements. The complete melting curve is built up from a series of melting experiments as a function of pressure, performed under different experimental conditions in the diamond cell; however, the placement of the phase boundary is inherently uncertain, due to an experimental "region of indifference" as the phase boundary is approached. To quantify the uncertainties, a statistical method using the logistic model is presented to provide best-fit phase boundaries to the platinum melting data, and can be generalized to fit phase boundary data of any sort. The high-pressure high-temperature phase diagram of Allende meteorite, a chondritic meteorite serving as a model of a primordial terrestrial planet, was investigated in the pressure and temperature ranges of 15 to 70 GPa and 1000 to 4000 K. The melting curve determined here overlaps and is in excellent agreement with previous piston-cylinder and multi-anvil measurements on the same material (Agee, et al., 1995). X-ray diffraction analysis of phases quenched from high pressure and temperature, and high pressure phases both before and after heating, are in good agreement with previous work. The phase diagram of Allende meteorite can be used to constrain events in the early geological evolution of the terrestrial planets.

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    Synchrotron X-ray fluorescence spectra of unpolished iron and chondritic spheres extracted from sediments collected on the melt zone of the Greenland ice cap allow the analysis of Ni, Cu, Zn, Ga, Ge, Pb, and Se with minimum detection limits on the order of several parts per million. All detected elements are depleted relative to chondritic abundance with the exception of Pb, which shows enrichments up to a factor of 500. An apparent anticorrelation between the Ni-content and trace element concentration was observed in both types of spherules. The fractionation patterns of the iron and chondritic spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

  7. Ice cap melting and low-viscosity crustal root explain the narrow geodetic uplift of the Western Alps

    NASA Astrophysics Data System (ADS)

    Chéry, J.; Genti, M.; Vernant, P.

    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. Two uplift mechanisms have been proposed: (1) the isostatic response to denudation responsible for only a fraction of the observed uplift and (2) the rebound induced by the Wurmian ice cap melting which predicts a broader uplifting region than the one evidenced by geodetic observations. Using a numerical model to fit the geodetic data, we show that a crustal viscosity contrast between the foreland and the central part of the Alps, the latter being weaker with a viscosity of 1021 Pa s, is needed. 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 over the entire lithosphere.

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

    NASA Astrophysics Data System (ADS)

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

    1987-03-01

    Synchrotron X ray fluorescence spectra of unpolished iron and chondritic spheres extracted from sediments collected on the melt zone of the Greenland ice cap allow the analysis of Ni, Cu, Zn, Ga, Ge, Pb, and Se with minimum detection limits on the order of several parts per million. All detected elements are depleted relative to chondritic abundance with the exception of Pb, which shows enrichments up to a factor of 500. An apparent anticorrelation between the Ni-content and the element concentration was observed in both types of spherules. The fractionation patterns of the iron and chondritic spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from the ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

  9. Trace element analyses of spheres from the melt zone of the Greenland Ice Cap using synchrotron X ray fluorescence

    NASA Astrophysics Data System (ADS)

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

    Synchrotron X ray fluorescence spectra of unpolished iron and chondritic spheres extracted from sediments collected on the melt zone of the Greenland ice cap allow the analysis of Ni, Cu, Zn, Ga, Ge, Pb, and Se with minimum detection limits on the order of several parts per million. All detected elements are depleted relative to chondritic abundance with the exception of Pb, which shows enrichments up to a factor of 500. An apparent anticorrelation between the Ni-content and trace element concentration was observed in both types of spherules. The fractionation patterns of the iron and chondritic spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from the ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

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

    NASA Astrophysics Data System (ADS)

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

    1987-09-01

    Synchrotron X ray fluorescence spectra of unpolished iron and chondritic spheres extracted from sediments collected on the melt zone of the Greenland ice cap allow the analysis of Ni, Cu, Zn, Ga, Ge, Pb, and Se with minimum detection limits on the order of several parts per million. All detected elements are depleted relative to chondritic abundance with the exception of Pb, which shows enrichments up to a factor of 500. An apparent anticorrelation between the Ni-content and trace element concentration was observed in both types of spherules. The fractionation patterns of the iron and chondrite spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from the ejection of globules of Fe/Ni from parent chondritic micrometeroids. © American Geophyscial Union 1987

  11. What happens when the ice melts? Belugas, contaminants, ecosystems and human communities in the complexity of global change.

    PubMed

    Lennert, Ann Eileen

    2016-06-15

    In general, it is important to examine the whole spectrum of interrelated fields while comprehending pollution, climate change or the environment, because some of their relevances are expected and others not. This study aims at comparatively examining different but interrelated ways of acquiring and communicating information on environmental changes, focusing on pollution in the Arctic, in particular Greenland. In the context of climate change, it discusses how heavily polluted and stressed Arctic marine ecosystems may be affected when ice melts. Bridging cultures of knowledge, this study claims that traditional knowledge together with natural science and studies of contaminants in Arctic marine ecosystems can indicate behavioural factors, elements acting as additional stressors on animals and communities relying on them. Furthermore, it explains the role of scientific engagement with local communities in not only the identification and verification of stressors, enhancing our understanding of them, but also the proposal of solutions to related problems. PMID:27062887

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

    NASA Astrophysics Data System (ADS)

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

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

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

    SciTech Connect

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

    2010-01-01

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

  14. Effect of Hydrogen and Carbon on the Melting Temperature of the Core

    NASA Astrophysics Data System (ADS)

    Nakajima, Y.; Sakamaki, K.; Takahashi, E.; Fukai, Y.; Suzuki, T.; Funakoshi, K.

    2007-12-01

    The temperature of the Earth's outer core has been discussed based on the melting temperature of Fe- O-S alloys (e.g., Boehler, 1996). Although hydrogen and carbon are the possible candidates of the core component, their effects on the melting temperature of iron at high-pressures are unclear. Using a Kawai-type multi-anvil apparatus at SPring-8 synchrotron, we carried out a series of melting experiments on FeH and Fe3C up to 20 and 28 GPa, respectively. In the experiments on FeH, Fe sponge mixed with MgO was packed into a NaCl container with a hydrogen source, LiAlH4 (e.g., Fukai et al., 1989). During heating under high-pressures, hydrogenation of iron was observed by volume change. The phase boundary between ɛ'-phase (low-temperature phase) and γ-phase (high-temperature phase) of iron-hydride was determined using both cooling and heating experiments. Hydrogen concentrations in the γ-FeHx and ɛ'-FeHx were calculated based on the excess volume data from that of pure iron. It is found that γ-FeHx and ɛ'-FeHx synthesized in our experiments at pressures between 10 and 20 GPa are nearly stoichiometric FeH. Melting temperature of the γ-FeH was determined by the abrupt change in the X-ray diffraction patterns (crystalline to amorphous). The melting temperatures were determined to be 1473, 1473, 1493, 1573 and 1593 K at 10, 11.5, 15, 18 and 20 GPa, respectively. In the experiments using Fe3C, the synthesized Fe3C powder was encapsulated in a MgO container. In the diffraction sequences during heating, the peaks of Fe3C disappeared, and the new peaks identified as those of Fe7C3 were observed with halo caused by liquid. Finally, the Fe7C3 peaks disappeared, and only the halo pattern was observed. Based on these observations, the incongruent melting of Fe3C to Fe7C3 and liquid is estimated to occur at 1823 and 1923 K at 19.7 and 27.0 GPa, respectively. The liquidus temperatures of the Fe3C composition are found to be at 2098 and 2198 K at 19.5 and 26.8 GPa

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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