scholarly journals Localized Basal Freezing Within George VI Ice Shelf, Antarctica

1988 ◽  
Vol 34 (116) ◽  
pp. 71-77 ◽  
Author(s):  
M. Pedley ◽  
J.G. Paren ◽  
J.R. Potter
Keyword(s):  
Freezing Point ◽  
Saline Water ◽  
Thick Layer ◽  
Ice Shelf ◽  
Low Salinity ◽  
Ice Surface ◽  
Salinity Water ◽  
Basal Melting ◽  
Surface Ice

AbstractHobbs Pool is an area of thin ice shelf situated within George VI Ice Shelf, Antarctica. Thicker ice shelf surrounding Hobbs Pool isolates the upper 155 m of the water column from water lying at the same depth else-where under the ice shelf. Summer melt-water lakes drain through crevasses at Hobbs Pool forming a 155 m thick layer of low-salinity water close to its freezing point. Colder and more saline water in the lower part of this layer leads to in-situ freezing of fresher water lying above it. Below 155 m depth, the water temperature and salinity are linearly related by basal melting which is observed elsewhere under the ice shelf. The surface ice shows areas of deformation and deposits of subglacial rock debris which may result from upward particle paths in the area. The raising of subglacial rock debris on to the ice surface may provide a mechanism for the transport of erratics across the ice shelf to Alexander Island from the base of Palmer Land glaciers.

scholarly journals Localized Basal Freezing Within George VI Ice Shelf, Antarctica

1988 ◽  
Vol 34 (116) ◽  
pp. 71-77 ◽  
Author(s):  
M. Pedley ◽  
J.G. Paren ◽  
J.R. Potter
Keyword(s):  
Freezing Point ◽  
Saline Water ◽  
Thick Layer ◽  
Ice Shelf ◽  
Low Salinity ◽  
Ice Surface ◽  
Salinity Water ◽  
Basal Melting ◽  
Surface Ice

AbstractHobbs Pool is an area of thin ice shelf situated within George VI Ice Shelf, Antarctica. Thicker ice shelf surrounding Hobbs Pool isolates the upper 155 m of the water column from water lying at the same depth else-where under the ice shelf. Summer melt-water lakes drain through crevasses at Hobbs Pool forming a 155 m thick layer of low-salinity water close to its freezing point. Colder and more saline water in the lower part of this layer leads toin-situfreezing of fresher water lying above it. Below 155 m depth, the water temperature and salinity are linearly related by basal melting which is observed elsewhere under the ice shelf. The surface ice shows areas of deformation and deposits of subglacial rock debris which may result from upward particle paths in the area. The raising of subglacial rock debris on to the ice surface may provide a mechanism for the transport of erratics across the ice shelf to Alexander Island from the base of Palmer Land glaciers.

scholarly journals Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Masahiro Minowa ◽  
Shin Sugiyama ◽  
Masato Ito ◽  
Shiori Yamane ◽  
Shigeru Aoki
Keyword(s):  
Freezing Point ◽  
East Antarctica ◽  
Ice Shelf ◽  
Rate Estimate ◽  
Ice Shelves ◽  
Plume Water ◽  
Warm Deep Water ◽  
Glacier Ice ◽  
Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

scholarly journals Evaluation of basal melting parameterisations using in situ ocean and melting observations from the Amery Ice Shelf, East Antarctica

2021 ◽  
Author(s):  
Madelaine Gamble Rosevear ◽  
Benjamin Keith Galton-Fenzi ◽  
Craig Stevens
Keyword(s):  
Freezing Point ◽  
Acoustic Doppler Current Profiler ◽  
Current Speed ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Amery Ice Shelf ◽  
Current Profiler ◽  
Basal Melting

Abstract. Ocean driven melting of Antarctic ice shelves is causing grounded ice to be lost from the Antarctic continent at an accelerating rate. However, the ocean processes governing ice shelf melting are not well understood, contributing to uncertainty in projections of Antarctica's contribution to sea level. Here, we analyse oceanographic data and in situ measurements of ice shelf melt collected from an instrumented mooring beneath the centre of the Amery Ice Shelf, East Antarctica. This is the first direct measurement of basal melting from the Amery Ice Shelf, and was made through the novel application of an upwards-facing Acoustic Doppler Current Profiler (ADCP). ADCP data were also used to map a region of the ice base, revealing a steep topographic feature or “scarp” in the ice with vertical and horizontal scales of ~20 m and ~40 m respectively. The annually-averaged ADCP-derived melt rate of 0.51 ± 0.18 m yr−1 is consistent with previous modelling results and glaciological estimates, and there is significant seasonal variation in melting with a maximum in May and a minimum in September. Melting is driven by temperatures ~0.2 °C above the local freezing point and background and tidal currents, which have typical speeds of ~3.0 cm s−1 and 10.0 cm s−1 respectively. We use the coincident measurements of ice shelf melt and oceanographic forcing to evaluate parameterisations of ice-ocean interactions, and find that parameterisations in which there is an explicit dependence of the melt rate on current speed beneath the ice tend to overestimate the local melt rate at AM06 by between 200 % and 400 %, depending on the choice of drag coefficient. A convective parameterisation in which melting is a function of the slope of the ice base is also evaluated and is shown to under-predict melting by 20 % at this site. Using available observations from other ice shelves, we show that a common current speed-dependent parameterisation overestimates melting at all but the coldest, most energetic cavity conditions.

scholarly journals Growth and gas exchange of corn under salt stress and nitrogen doses

2021 ◽  
Vol 25 (3) ◽  
pp. 174-181
Author(s):  
Henderson C. Sousa ◽  
Geocleber G. de Sousa ◽  
Carla I. N. Lessa ◽  
Antonio F. da S. Lima ◽  
Rute M. R. Ribeiro ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Gas Exchange ◽  
Leaf Area ◽  
Plant Height ◽  
Saline Water ◽  
Saline Stress ◽  
Low Salinity ◽  
Salinity Water ◽  
Hybrid Maize ◽  
The University

ABSTRACT The excess of salts can affect several processes in the crops, and nitrogen (N) can attenuate the depressive effect of salinity. The objective was to evaluate the influence of nitrogen doses on the growth and gas exchange of corn crop irrigated with saline water. The experiment was conducted from June to September 2019 at the University of International Integration of Afro-Brazilian Lusophony, Redenção, CE, Brazil. The experimental design was completely randomized, in a 2 x 3 factorial scheme (supply water of 0.3 dS m-1 and saline solution of 3.0 dS m-1) and three nitrogen doses, 0, 80, and 160 kg ha-1, corresponding to 0, 50, and 100% of the recommended dose respectively, with six repetitions. At 30 and 45 days after sowing (DAS), plant height, leaf area, number of leaves, photosynthesis, transpiration, and stomatal conductance were evaluated. Saline stress affects plant height, leaf area, photosynthesis, transpiration, and conductance at 30 DAS. The doses of 80 and 160 kg ha-1 provide greater performance in plant height, leaf area, photosynthesis, transpiration, and conductance at 30 DAS. The use of low salinity water and doses of 80 and 160 kg ha-1 were more efficient in terms of plant height, leaf area, photosynthesis, transpiration, and conductance at 45 DAS. The dose of 160 kg ha-1 of N attenuates the harmful effects of salts in AG 1051 hybrid maize plants, providing higher values of photosynthesis, transpiration, and stomatal conductance at 45 DAS when irrigated with water of 3.0 dS m-1.

scholarly journals Partitioning Effects during Terminal Carbon and Electron Flow in Sediments of a Low-Salinity Meltwater Pond near Bratina Island, McMurdo Ice Shelf, Antarctica

1999 ◽  
Vol 65 (12) ◽  
pp. 5493-5499 ◽  
Author(s):  
Douglas O. Mountfort ◽  
Heinrich F. Kaspar ◽  
Malcolm Downes ◽  
Rodney A. Asher
Keyword(s):  
Sulfate Reduction ◽  
Methane Production ◽  
Electron Flow ◽  
Fold Increase ◽  
Cyanobacterial Mats ◽  
Ice Shelf ◽  
Physiological Conditions ◽  
Low Salinity ◽  
Methane Production Rate

ABSTRACT A study of anaerobic sediments below cyanobacterial mats of a low-salinity meltwater pond called Orange Pond on the McMurdo Ice Shelf at temperatures simulating those in the summer season (<5°C) revealed that both sulfate reduction and methane production were important terminal anaerobic processes. Addition of [2-14C]acetate to sediment samples resulted in the passage of label mainly to CO2. Acetate addition (0 to 27 mM) had little effect on methanogenesis (a 1.1-fold increase), and while the rate of acetate dissimilation was greater than the rate of methane production (6.4 nmol cm−3 h−1compared to 2.5 to 6 nmol cm−3 h−1), the portion of methane production attributed to acetate cleavage was <2%. Substantial increases in the methane production rate were observed with H2 (2.4-fold), and H2 uptake was totally accounted for by methane production under physiological conditions. Formate also stimulated methane production (twofold), presumably through H2 release mediated through hydrogen lyase. Addition of sulfate up to 50-fold the natural levels in the sediment (interstitial concentration, ∼0.3 mM) did not substantially inhibit methanogenesis, but the process was inhibited by 50-fold chloride (36 mM). No net rate of methane oxidation was observed when sediments were incubated anaerobically, and denitrification rates were substantially lower than rates for sulfate reduction and methanogenesis. The results indicate that carbon flow from acetate is coupled mainly to sulfate reduction and that methane is largely generated from H2 and CO2 where chloride, but not sulfate, has a modulating role. Rates of methanogenesis at in situ temperatures were four- to fivefold less than maximal rates found at 20°C.

scholarly journals Formation, Flow, and Disintegration Of Ice Shelves

1979 ◽  
Vol 24 (90) ◽  
pp. 259-271 ◽  
Author(s):  
G. De Q. Robin
Keyword(s):  
Sea Ice ◽  
Thick Layer ◽  
Big Bang ◽  
Bottom Surface ◽  
Minor Importance ◽  
Ice Shelf ◽  
Creep Failure ◽  
Ice Shelves ◽  
Basal Melting ◽  
Inland Ice

AbstractIce shelves may develop either by continued thickening of sea ice that is held fast to the shore, or by the seaward extension of inland ice. For both processes, as well as for an understanding of ablation and of accumulation at the bottom surface of ice shelves, we need to understand melting and freezing processes in relation to salinity, temperature, and pressure. Consideration of these factors shows that basal melting beneath the thicker parts of ice shelves is much greater than is generally appreciated. This could be sufficient to bring the estimated mass balance of Antarctica into approximate equilibrium. It appears that most Antarctic ice shelves are dependent on the supply of inland ice for their continued existence. However the thick layer of sea ice beneath the Amery Ice Shelf is readily explained in terms of sub-ice water circulation.Transport of heat and mass by water motion beneath ice shelves has the potential to change ice thicknesses by similar amounts to that caused by internal deformation of the ice shelf. Bottom freezing due to thermal conduction throughout the ice shelf is of minor importance.While attention is drawn to the basic equations for flow of ice shelves, it is pointed out that they have yet to be applied satisfactorily to the problem of iceberg calving. This appears from field observations to be due primarily to creep failure of spreading ice shelves, possibly aided by impact from floating icebergs. Recent observations show the effectiveness and likely quantitative importance of this “big bang” theory of iceberg formation in Antarctica.A brief discussion of the effects of climatic change on the disintegration of ice shelves is presented.

scholarly journals Enhanced Wettability Modification and CO2 Solubility Effect by Carbonated Low Salinity Water Injection in Carbonate Reservoirs

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Ji Ho Lee ◽  
Kun Sang Lee
Keyword(s):  
Oil Recovery ◽  
Saline Water ◽  
Water Injection ◽  
Carbonate Reservoirs ◽  
Viscosity Reduction ◽  
Low Salinity ◽  
Low Salinity Water ◽  
Geochemical Reactions ◽  
Salinity Water ◽  
Low Salinity Water Injection

Carbonated water injection (CWI) induces oil swelling and viscosity reduction. Another advantage of this technique is that CO2 can be stored via solubility trapping. The CO2 solubility of brine is a key factor that determines the extent of these effects. The solubility is sensitive to pressure, temperature, and salinity. The salting-out phenomenon makes low saline brine a favorable condition for solubilizing CO2 into brine, thus enabling the brine to deliver more CO2 into reservoirs. In addition, low saline water injection (LSWI) can modify wettability and enhance oil recovery in carbonate reservoirs. The high CO2 solubility potential and wettability modification effect motivate the deployment of hybrid carbonated low salinity water injection (CLSWI). Reliable evaluation should consider geochemical reactions, which determine CO2 solubility and wettability modification, in brine/oil/rock systems. In this study, CLSWI was modeled with geochemical reactions, and oil production and CO2 storage were evaluated. In core and pilot systems, CLSWI increased oil recovery by up to 9% and 15%, respectively, and CO2 storage until oil recovery by up to 24% and 45%, respectively, compared to CWI. The CLSWI also improved injectivity by up to 31% in a pilot system. This study demonstrates that CLSWI is a promising water-based hybrid EOR (enhanced oil recovery).

Evolution of supercooling under coastal Antarctic sea ice during winter

2011 ◽  
Vol 23 (4) ◽  
pp. 399-409 ◽  
Author(s):  
Gregory H. Leonard ◽  
Patricia J. Langhorne ◽  
Michael J.M. Williams ◽  
Ross Vennell ◽  
Craig R. Purdie ◽  
...  
Keyword(s):  
Sea Ice ◽  
Freezing Point ◽  
Circulation Pattern ◽  
Late Winter ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
The North ◽  
Antarctic Sea Ice ◽  
Ice Production

AbstractHere we describe the evolution through winter of a layer of in situ supercooled water beneath the sea ice at a site close to the McMurdo Ice Shelf. From early winter (May), the temperature of the upper water column was below its surface freezing point, implying contact with an ice shelf at depth. By late winter the supercooled layer was c. 40 m deep with a maximum supercooling of c. 25 mK located 1–2 m below the sea ice-water interface. Transitory in situ supercooling events were also observed, one lasting c. 17 hours and reaching a depth of 70 m. In spite of these very low temperatures the isotopic composition of the water was relatively heavy, suggesting little glacial melt. Further, the water's temperature-salinity signature indicates contributions to water mass properties from High Salinity Shelf Water produced in areas of high sea ice production to the north of McMurdo Sound. Our measurements imply the existence of a heat sink beneath the supercooled layer that extracts heat from the ocean to thicken and cool this layer and contributes to the thickness of the sea ice cover. This sink is linked to the circulation pattern of the McMurdo Sound.

Low salinity frazil ice generation at the base of a small Antarctic ice shelf

1993 ◽  
Vol 5 (3) ◽  
pp. 309-322 ◽  
Author(s):  
J.-L. Tison ◽  
D. Ronveaux ◽  
R. D. Lorrain
Keyword(s):  
Interstitial Water ◽  
Sea Water ◽  
Freezing Point ◽  
Free Water ◽  
Ice Crystals ◽  
Ice Shelf ◽  
Apparent Contradiction ◽  
Ice Shelves ◽  
Frazil Ice ◽  
Low Salinity

Chemical, isotopic and crystallographic characteristics of marine ice formed at the base of the Hells Gate Ice Shelf, Terra Nova Bay, allow a better understanding of the dynamics of marine ice accretion under small ice shelves. The observed properties of the different types of frazil ice found in the area immediately behind the ice shelf front, result from a progressive evolution of the individual frazil ice crystals initially accreted at the base of the ice-shelf. Basal melting caused by the descending plumes of water masses at a temperature above their local freezing point, initiates partial melting of the frazil ice crystals. This dilutes the interstitial water and initiates chemical sorting effects as diffusion proceeds from the normal sea water in the free water column to the diluted interstitial water in the loose frazil layer. Different environmental conditions will result in contrasting properties. Where the subglacial interface is sculptured with domes or inverted channels, it will favour the accumulation of thick units of frazil ice, in a calm environment, that will be further protected from convection mixing over long time periods. This will result in the formation of orbicular frazil showing c-axes at random, strong dilution and important sorting effects. On the contrary, where no channel or dome exist, or where those are already filled with frazil, rectangular or wave-like banded frazil will form with properties showing interfacial streaming effects induced by water currents. Strong c-axes concentration at a single maximum, less dilution and weaker chemical sorting effects are then observed. These findings provide a tentative explanation for the apparent contradiction between the very low salinity levels detected in marine ice at the base of ice shelves and the comparatively minor salinity fluctuations in sea water profiles near ice shelves.

scholarly journals Effect of saline water and shading on dragon fruit (‘pitaya’) seedling growth

2021 ◽  
Vol 25 (8) ◽  
pp. 547-552
Author(s):  
Geocleber G. de Sousa ◽  
Sinara B. Sousa ◽  
Ana C. da S. Pereira ◽  
Virna B. Marques ◽  
Maria L. G. da Silva ◽  
...  
Keyword(s):  
Plant Height ◽  
Root Length ◽  
Plant Biomass ◽  
Saline Water ◽  
Semiarid Region ◽  
Saline Stress ◽  
Higher Plant ◽  
Low Salinity ◽  
Dry Biomass ◽  
Salinity Water

ABSTRACT ‘Pitaya’ (Hylocereus undatus) is a fruit-bearing, climbing cactus with great food potential for the semiarid region. This study aimed to evaluate the production of ‘pitaya’ seedlings irrigated with low and high salinity water and grown in different light intensities. The experiment was conducted in a completely randomized design, in a 2 × 2 factorial arrangement, with two electrical conductivities of irrigation water: S1 - 0.3 dS m-1 (low salinity) and S2 - 5.0 dS m-1 (moderate salinity) in two environments: A1 - black net with 50% shading, and A2 - full sun, with ten replicates. The variables evaluated were plant height, main cladode diameter, above-ground biomass, root biomass, total plant biomass, number of secondary cladodes, root length, and length of secondary cladodes. The 50% shading (black net) promoted higher plant height, number of secondary shoots, and root length of the ‘pitaya’ plants. The irrigation with moderate saline water (5.0 dS m-1) reduced the number of secondary cladodes, length of root, and length of secondary cladodes. The ‘pitaya’ seedlings grown under 50% shading (black net) showed greater root dry biomass when irrigated with low-salinity water. Greater values of diameter of the primary cladode, above-ground dry biomass, and total dry biomass were observed under full sunlight and elevated saline stress.

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