Precipitation Of Mirabilite Research Articles

Analysis of the Hydrochemical Characteristics and the Evolutionary Stages of Brine in Mahai Salt Lake in the Qaidam Basin

The objective of this study was to contribute to the understanding of the hydrochemical processes and evolution of brine in the Qaidam basin, in order to provide a theoretical basis for the application of brine resources in the region. The hydrochemical characteristics and evolutionary stages of brine in Mahai Salt Lake were investigated using factor analysis on brine chemistry data from 109 sampling points. Our results showed that the centre of the Salt Lake has the highest concentration of total dissolved solids (TDS), and the hydrochemical type of brine is chloride-magnesium. The brine at the centre of the lake is at the later stages of mirabilite precipitation, and the content of K+ is relatively stable. Comparatively, the hydrochemical type of brine in the slope area of the Salt Lake is Cl-Na-Mg, and is at the early stages of brine evolution. It is of guiding significance to further develop and utilize brine resources, especially to evaluate its resource development potential.

Frost flowers and sea-salt aerosols over seasonal sea-ice areas in northwestern Greenland during winter–spring

Abstract. Sea salts and halogens in aerosols, frost flowers, and brine play an important role in atmospheric chemistry in polar regions. Simultaneous sampling and observations of frost flowers, brine, and aerosol particles were conducted around Siorapaluk in northwestern Greenland during December 2013 to March 2014. Results show that water-soluble frost flower and brine components are sea-salt components (e.g., Na+, Cl−, Mg2+, K+, Ca2+, Br−, and iodine). Concentration factors of sea-salt components of frost flowers and brine relative to seawater were 1.14–3.67. Sea-salt enrichment of Mg2+, K+, Ca2+, and halogens (Cl−, Br−, and iodine) in frost flowers is associated with sea-salt fractionation by precipitation of mirabilite and hydrohalite. High aerosol number concentrations correspond to the occurrence of higher abundance of sea-salt particles in both coarse and fine modes, and blowing snow and strong winds. Aerosol number concentrations, particularly in coarse mode, are increased considerably by release from the sea-ice surface under strong wind conditions. Sulfate depletion by sea-salt fractionation was found to be limited in sea-salt aerosols because of the presence of non-sea-salt (NSS) SO42−. However, coarse and fine sea-salt particles were found to be rich in Mg. Strong Mg enrichment might be more likely to proceed in fine sea-salt particles. Magnesium-rich sea-salt particles might be released from the surface of snow and slush layer (brine) on sea ice and frost flowers. Mirabilite-like and ikaite-like particles were identified only in aerosol samples collected near new sea-ice areas. From the field evidence and results from earlier studies, we propose and describe sea-salt cycles in seasonal sea-ice areas.

The effect of mirabilite precipitation on the absolute and practical salinities of sea ice brines

The sea ice cover of high latitude oceans contains concentrated brines which are the site of in-situ chemical and biological reactions. The brines become supersaturated with respect to mirabilite (Na2SO4·10H2O) below −6.4°C, and the associated removal of Na+ and SO42− from the brine results in considerable non-conservative changes to its composition. The changes are reflected in the brine salinity, which is a fundamental physico-chemical parameter in the sea ice brine system. Here, measurements of electrical conductivity and brine composition in synthetic sea ice brines between −1.8 and −20.6°C, obtained during a comprehensive investigation of the brine-mirabilite equilibrium at below-zero temperatures reported elsewhere, are combined with modelled estimates to assess the behaviour of the absolute (SA) and practical (SP) salinities of sea ice brines. Results display substantial divergence of SP from SA below −6.4°C, reaching a 7.2% difference at −22.8°C. This is shown to create inaccuracies when SP is assumed to be equivalent to SA, firstly by misrepresenting the conditions inhabited by sea ice biota, whilst also creating errors in the calculation of physical sea ice parameters. Our measured and modelled data are used to refine the SA−T relationship for sea ice brines, implicit of mirabilite precipitation, which is crucial in estimating brine properties in absence of salinity data. Furthermore, because SP is the parameter measured in field studies, we provide an SP−T relationship for sea ice brines to −22.8°C, which aids in explaining the trends observed in available SP−T data from sea ice brines in the Southern Ocean, demonstrating the importance of the mirabilite-brine equilibrium in natural sea ice. Finally, we initiate the development of a conversion factor for the estimation of SA from SP measurement in sea ice brines, and produce an equation that can calculate SA from modelled brine density. This work ultimately highlights careful consideration of salinity concepts when applied to the sea ice system.

Is sheer thenardite attack impotent compared with cyclic conversion of thenardite–mirabilite mechanism in laboratory simulation tests?

The precipitation of mirabilite during the wetting stage of a cyclic total immersion test has widely been implicated as the main damage mechanism of sodium sulfate. We, however, hypothesized that the damage contribution from thenardite cannot be discounted in laboratory tests. To verify the supposition, a series of laboratory experiments was undertaken by subjecting three types of rocks to the sodium sulfate attack. To unambiguously demonstrate the potency of thenardite, in addition to cyclic total immersion tests, continuous partial immersion tests were also performed under different environmental conditions, which allowed either sheer thenardite precipitation or reversible thenardite–mirabilite conversion. Although rock breakdown occurred only during immersion, the results clearly indicated that thenardite alone could induce significant damage in both cyclic total immersion and continuous partial immersion tests. In most cases, tests that involved mirabilite precipitation, however, were more destructive than sheer thenardite tests, regardless of the type of salt supply technique. With the same duration and temperature of the immersion stage, the difference in drying temperature influenced the degree of damage, revealing the damage contribution from thenardite even in the tests with cyclic phase conversion. The reason why mirabilite is generally credited to be more destructive than thenardite and the effect of test duration on the damage potency of thenardite are also discussed.

Mineralogy of saline perennial cold springs on Axel Heiberg Island, Nunavut, Canada and implications for spring deposits on Mars

In recent years evidence for spring deposits on Mars has been mounting. It seems increasingly likely that groundwater upwelling and surfacing as springs may be responsible for some mineral deposits on Mars’ surface. In order to more easily detect and better understand potential spring deposits on Mars, it is pertinent that we gain a better understanding of the distribution of minerals at cold spring systems on Earth. Here, we report on the detailed mineralogy and distribution of precipitates in crusts and sediments of three non-volcanic perennial saline cold spring systems associated with gypsum/anhydrite diapirs on Axel Heiberg Island, Canada: Wolf spring (WS; also known as Lost Hammer), Colour Peak springs (CP), and Gypsum Hill springs (GH). At these sites permafrost, frigid winter temperatures, and arid atmospheric conditions approximate conditions of present-day, as well as past, Mars. Mineralogy of the three springs is dominated by halite (NaCl), calcite (CaCO3), gypsum (CaSO4·2H2O), thenardite (Na2SO4), mirabilite (Na2SO4·10H2O), and elemental sulfur (S°). Minerals at WS are more sodium-rich than at the other two sites, and water salinity is much higher, suggesting water flows through halite in the subsurface. Mirabilite is likely deposit at WS during winter months and dehydrates to thenardite during summer months. Elemental sulfur is typically associated with gypsum, and may be related to microbial metabolism. Spring sediments are home to thriving microbial communities in winter and summer months, and presumably year round. If spring systems did exist on the surface of Mars, they may represent environments capable of supporting microbial life. It is not known to what extent mineral crusts in cold saline spring systems on Earth preserve evidence of microbial life, or if they ever did on Mars. Therefore, studying terrestrial saline spring mineral deposits such as those on Axel Heiberg Island may help us to better understand cold spring precipitation on Mars and guide us in the search for minerals that may have been precipitated in spring systems and that may contain evidence of life. Additionally, spectral data from Europa indicates the presence of mirabilite. While the depositional environment on Europa differs from Axel Heiberg Island, the springs may still be a good mineralogical analogue, given the precipitation of mirabilite by the upwelling of cold, salty subsurface water, in a cold, semi-arid desert environment.

Seasonal variation of fractionated sea‐salt particles on the Antarctic coast

Aerosol sampling was conducted at Syowa Station, Antarctica (coastal station) in 2004–2006. SO42−depletion by mirabilite precipitation was identified from April through November. The fractionated sea‐salt particles were distributed in ultrafine– coarse modes. Molar ratios of Mg2+/Na+ and K+/Na+ were higher than in bulk seawater ratio during winter–spring. The Mg2+/Na+ ratio in aerosols greatly exceeded the upper limit in the case only with mirabilite precipitation. The temperature dependence of Mg2+/Na+ ratio strongly suggested that higher ratios of Mg2+/Na+ and K+/Na+were associated with sea‐salt fractionation by precipitation of mirabilite at −9°C, hydrohalite at ca. −23°C and other salts such as ikaite at ca. −5°C and gypsum at ca. −22°C during winter–spring. Mg‐salts with lower deliquescence relative humidity can be enriched gradually in the fractionated sea‐salt particles. Results suggests that sea‐salt fractionation can alter aerosol hygroscopicity and atmospheric chemistry in polar regions.

Chemical composition of the snowpack during the OASIS spring campaign 2009 at Barrow, Alaska

The chemical composition of the seasonal snowpack was determined close to Barrow, an Arctic coastal location in northern Alaska. One hundred and twelve samples of different snow types including fresh snow, surface hoar, diamond dust, blowing snow, rounded snow grains, and depth hoar were collected and analyzed for major sea salt components, bromide, and nitrate. Sodium, chloride, sulfate, and potassium are mainly introduced into the snowpack by the deposition of sea salt, while magnesium and calcium result from a combination of sea salt and dust. Sulfate was strongly depleted in most samples compared to other sea salt components. This is attributed to the precipitation of mirabilite in newly formed sea ice and frost flowers that leads to an efficient fractionation of sulfate. Uptake of volatile but soluble species from the gas phase also contributed to the observed chloride, sulfate, and nitrate in the snow. However, for chloride and sulfate the input from the marine sources was overwhelming and the uptake from the gas phase was only visible in the samples with low concentrations like fresh snow, diamond dust, and surface hoar. Nitrate concentrations in the snowpack were less variable and for aged snow nitrate was related to the specific surface area of the snow indicating the adsorption of nitric acid can be an important nitrate source in the aged snow. Bromide was also introduced into the snowpack from marine sources, but due to its high reactivity it was partly transferred back to the atmosphere in the form of reactive species. The result of these processes was evident in bromide concentrations, which were both enriched and depleted at the snowpack surface while deeper layers were mostly depleted. Blowing snow also exhibited a depleted bromide composition. For all compounds except nitrate, many depth hoar samples exhibited the greatest concentrations, probably as a result of higher input earlier in the season as well as increases due to the sublimation of water during the metamorphism of the snow.

Cryogenic origin for brine in the subsurface of southern McMurdo Sound, Antarctica

Sampling of interstitial fluids during deep coring in southern McMurdo Sound, Antarctica, revealed the presence of seawater-sourced, hypersaline brine at depths >200 m below the seafloor. Na-Cl-Br and SO 4 -Cl-Br relationships are consistent with a concentration mechanism that involves the removal of pure H 2 O as ice and precipitation of mirabilite (Na 2 SO 4 ·10H 2 O) during progressive freezing of seawater. The brine is in Neogene subglacial, glacimarine, and marine facies that record advance and retreat of glaciers through the Ross Sea embayment. In this environment, sea ice formation in semi-isolated marine basins that occupied flexural troughs along ice sheet margins produced dense brines that sank and infiltrated the permeable subglacial sediment. Repeated cycles of glacial advance and retreat provided multiple opportunities for batches of seawater to be transformed into brine that now is in the subsurface of southern McMurdo Sound. Results demonstrate the feasibility of brine formation via seawater freezing and attest to the potential of a cryogenic origin for subsurface brines in high-latitude regions of the Northern Hemisphere, as proposed by some workers.

Saline rhythm and climatic change since 20.6 kyr bp from the Qiulinanmu Playa Lake in Tibet

A rare lacustrine rhythmite from the Qiulinanmu Playa Lake in Tibet is presented, which was composed of distinct layers of mirabilite, borax, and clay with thickness measuring 1.5–75 cm, 0.5–20 mm, and 0.5–30 mm, respectively. The thickness of each layer was measured in the field and dating was performed using 14C and U data. The lake was previously supplied by river water, groundwater, and hot springs enriched in sodium, sulfur, and boron. Control factors on the rhythmite were climate oscillations and compositional differences of water. The adsorption of boron by clay minerals could be attributed to the alternation between clay and borax layers. Low temperature, high pH, and high evaporation exerted significant influences on the precipitation of original borax and mirabilite. In the evaporative lake, the precipitation of mirabilite (a mineral indicative of a cold-dry environment) was dominant and produced the asymmetric couplets. The lake water was poor in chloride and rich in sodium sulfate, and an abrupt change was observed at 11.4 cal. kyr bp. According to the laminated sediment and the thickness of the minerals, the climate was dry-cold with four sub-warm phases before 11.4 kyr bp (after 20.6–11.4 kyr bp), and wet-warm with four sub-cold pulses after 11.4 kyr bp (11.4–5.2 kyr bp). The two thickest mirabilite layers suggested extremely hard conditions after 20.6 kyr bp, and before 11.4 kyr bp, respectively.

Frost flower chemical composition during growth and its implications for aerosol production and bromine activation

Frost flowers have been proposed to be the major source of sea‐salt aerosol to the atmosphere during polar winter and a source of reactive bromine during polar springtime. However little is known about their bulk chemical composition or microstructure, two important factors that may affect their ability to produce aerosols and provide chemically reactive surfaces for exchange with the atmosphere. Therefore, we chemically analyzed 28 samples of frost flowers and parts of frost flowers collected from sea ice off of northern Alaska. Our results support the proposed mechanism for frost flower growth that suggests water vapor deposition forms an ice skeleton that wicks brine present on newly grown sea ice. We measured a high variability in sulfate enrichment factors (with respect to chloride) in frost flowers and seawater from the vicinity of freezing sea ice. The variability in sulfate indicates that mirabilite precipitation (Na2SO4 · 10 H2O) occurs during frost flower growth. Brine wicked up by frost flowers is typically sulfate depleted, in agreement with the theory that frost flowers are related to sulfate‐depleted aerosol observed in Antarctica. The bromide enrichment factors we measured in frost flowers are within error of seawater composition, constraining the direct reactive losses of bromide from frost flowers. We combined the chemical composition measurements with temperature observations to create a conceptual model of possible scenarios for frost flower microstructure development.

Seasonal variability of crustal and marine trace elements in the aerosol at Neumayer station, Antarctica

Atmospheric trace element concentrations were measured from March 1999 to December 2003 at the Air Chemistry Observatory of the German Antarctic station Neumayer, by inductively coupled plasma–quadrupol mass spectrometry (ICP–QMS) and ion chromatography (IC). This continuous five-year long record derived from weekly aerosol sampling revealed a distinct seasonal summer maximum for elements linked with mineral dust entry (Al, La, Ce, Nd) and a winter maximum for the mostly sea salt derived elements Li, Na, K, Mg, Ca and Sr. The relative seasonal amplitude was around 1.7 and 1.4 for mineral dust (La) and sea salt aerosol (Na), respectively. On average, a significant deviation regarding mean ocean water composition was apparent for Li, Mg and Sr, which could hardly be explained by mirabilite precipitation on freshly formed sea ice. In addition, we observed all over the year, a not clarified high variability of element ratios Li/Na, K/Na, Mg/Na, Ca/Na and Sr/Na. We found an intriguing co-variation of Se concentrations with biogenic sulphur aerosols (methane sulphonate and non-sea salt sulphate), indicating a dominant marine biogenic source for this element, linked with the marine biogenic sulphur source.

PChemistry and stratification of Antarctic meltwater ponds I: Coastal ponds near Bratina Island, McMurdo Ice Shelf

The geochemistry and vertical stratification of shallow meltwater ponds at 78°S near Bratina Island (McMurdo Ice Shelf) have been determined for late winter (October) and summer (January) conditions as part of the Latitudinal Gradient Project. Of the five frozen ponds investigated in October, all were stratified with respect to conductivity, and three had highly saline basal brines beneath the ice at temperatures of −16 to −20°C. In the ice column, inclusions of saline fluid were observed in channels between ice crystals; the abundance increasing with depth and decreasing ice crystal size. In January, seven of the ten ponds investigated (including ponds sampled in October) retained conductivity stratification, whereas significant thermal stratification was observed in only three ponds (maximum ΔT = 5.5°C). Basal brines, ice and meltwaters were Na-Cl or Na-SO4 dominated. FREZCHEM52 modelling, supported by changes in ion ratios, indicated that the precipitation of mirabilite (Na2SO4.10H2O) and gypsum (CaSO4.2H2O) during progressive freezing is an important determinant in chemical evolution of the basal brine. High pH (8.8–11.2) and over-saturation with respect to dissolved oxygen (> 20 mg L−1) in summer, and the presence of sulphide ions in basal brines in winter, occurred in those ponds which experienced high biological productivity during the summer months.

Year‐round records of bulk and size‐segregated aerosol composition and HCl and HNO3 levels in the Dumont d'Urville (coastal Antarctica) atmosphere: Implications for sea‐salt aerosol fractionation in the winter and summer

Year‐round composition of bulk and size‐segregated aerosol was examined at a coastal Antarctic site (Dumont d'Urville). Sea‐salt particles display a summer depletion of chloride relative to sodium, which reaches ∼10%. The mass chloride loss is maximum on 1‐ to 3‐μm‐diameter particles, nitrate being often the anion causing the chloride loss. The summer SO42−/Na+ ratio exceeds the seawater value on submicron particles due to biogenic sulfate and on coarse particles due to ornithogenic (guano‐enriched soils) sulfate and to heterogeneous uptake of SO2 (or H2SO4). HCl levels range from 47 ± 28 ng m−3 in the winter to 130 ± 110 ng m−3 in the summer, being close to the mass chloride loss of sea‐salt aerosols. In the winter, sea‐salt particles exhibit Cl−/Na+ and SO42−/Na+ mass ratios of 1.9 ± 0.1 and 0.13 ± 0.04, respectively. Resulting from precipitation of mirabilite during freezing of seawater, this sulfate‐depletion‐relative sodium takes place from May to October. From March to April, warmer temperatures and/or smaller sea ice extent offshore the site limit the phenomenon. A range of 14–50 ng m−3 of submicron sulfate is found, confirming the existence of nssSO42− in the winter at a coastal Antarctic site, highest values being found in the winters of 1992–1994 due to the Pinatubo volcanic input. Apart from these three winters, nssSO42− levels range between 15 and 30 ng m−3, but its origin is still unclear (quasi‐continuous SO2 emissions from the Mount Erebus volcano or local wintertime dimethyl sulfide [DMS] oxidation, in addition to long‐range transported by‐product of DMS oxidation).

Salt weathering: influence of evaporation rate, supersaturation and crystallization pattern

Micro- and macroscale experiments which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations. Previously unexplained differences are found in crystal morphology, crystallization patterns, kinetics and substrate damage when comparing the growth of mirabilite (Na2SO4. 10H2O) and thenardite (Na2SO4) versus halite (NaCl). The crystallization pattern of sodium sulphate was strongly affected by relative humidity (RH), while a lesser RH effect was observed for sodium chloride. Macroscale experiments confirmed that mirabilite (crystallizing at RH > 50 per cent) and thenardite (crystallizing at RH < 50 per cent) tend to form subflorescence in highly localized areas under conditions of constant RH and temperature. This crystallization pattern was more damaging than that of halite, since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion, a result which contradicts Wellman and Wilson's theoretical model of salt damage. Low RH promoted rapid evaporation of saline solutions and higher supersaturation levels, resulting in the greatest damage to the stone in the case of both sodium sulphate and sodium chloride crystallization. At any particular crystallization condition, sodium chloride tended to reach lower supersaturation levels (resulting in the crystallization of isometric crystals) and created negligible damage, while sodium sulphate reached higher supersaturation ratios (resulting in non-equilibrium crystal shapes), resulting in significant damage. ESEM showed no damage from sodium sulphate due to hydration. Instead, after water condensation on thenardite crystals, rapid dissolution followed by precipitation of mirabilite took place, resulting in stone damage by means of crystallization pressure generation. It is concluded that salt damage due to crystallization pressure appears to be largely a function of solution supersaturation ratio and location of crystallization. These key factors are related to solution properties and evaporation rates, which are constrained by solution composition, environmental conditions, substrate properties, and salt crystallization growth patterns. When combined with a critical review of salt damage literature, these experiments allow the development of a model which explains variations in damage related to combinations of different salts, substrates and environmental conditions.

Sea‐salt aerosol in coastal Antarctic regions

Continuous year round records of atmospheric sea‐salt concentrations have been recovered at three coastal Antarctic stations (Halley, Dumont D'Urville, and Neumayer) at temporal resolutions typically between 1 day and 2 weeks. The records were evaluated in terms of their spatial and seasonal variability as well as with respect to changes in the relative ion composition of airborn sea‐salt particles. Annual mean sea‐salt concentrations vary between 1400 ng m−3 at Dumont D'Urville, 850 ng m−3 at Neumayer, and 200 ng m−3 at Halley, respectively. They are thus considerably lower than the mean levels previously observed at the north tip of the Antarctic Peninsula but are, at their lower end, comparable to the level previously reported from Mawson. The representativeness of the atmospheric sea‐salt data appears to be weak due to their high temporal variability, strong impacts of site specific aspects (such as site topography) but also due to the nonuniform sampling techniques applied so far. In accordance with the ice core evidence, the seasonal change in the atmospheric sea‐salt load is found to be clearly out of phase with the seasonal cycle of the open water fraction offshore from the station as (with the exception of Dumont D'Urville) the lowest concentrations are generally observed during the local summer months. Major ion analyses of bulk aerosol and concurrently sampled fresh snow show a strong, systematic depletion of the SO42− to Na+ (Cl−) ratios with respect to bulk sea water, which appeared to be confined to the local winter half year. During that time, sea‐salt SO42− was found to be depleted typically by 60–80% along with a concurrent Na+ deficit, which is in accordance with the precipitation of mirabilite. No significant fractionation of Mg2+, K+, and Ca2+ between seawater and sea‐salt particles is observed. Laboratory experiments failed to simulate the SO42− fractionation in airborne seawater droplets or in the skin of seawater bubbles at low air temperatures. They gave, however, SO42− depletion factors, similar to the field observation in air and snow, in the remaining brine of seawater which was partly frozen below −8°C to an artificial sea ice surface. It is suggested therefore that the mobilization of brine from the sea ice surface constitutes an important sea‐salt source in winter which may dominate the atmospheric sea‐salt load at high latitudes of coastal Antarctica.

Geoquímica de las lagunas saladas de los Monegros (Zaragoza). l. determinación experimental de los efectos del reequilibrio mirabilita-solucion con la temperatura en un sistema natural

Geochemical evolution of Los Monegros playa-lakes is affected by temperature fluctuations in the brine body at different time scales. Temperature shifts promote seasonally, daily and even during minor cycles mineralogical and compositional changes. Seasonal impacts of temperature change the brine composition and the crystallized mineral sequences (Pueyo, 1978-79). So, during summer cycle minerals crystallize according to the sequence: carbonates-gypsum-halite; and during winter the sequence of precipitation changes to carbonates-gypsum-mirabilite. Daily cycles also exist during winter brine evolution: mirabilite crystallization occurs during spring nights by lowering temperature, whereas diurnal temperatures promote its dissolution. And when high saturation levels are reached by evaporative concentration and the amount of precipitated mirabilite is important in the system (mirabilite stage, at spring), diurnal temperature fluctuations induce quick mirabilite-solution reequilibrium processes. Sampling of brines during this stage and thermodynamic calculations through the extended HMW model (Harvie, Moller and Weare, 1984) enclosed in the PHRQPITZ code (Plummer et al., 1988) indicate that mirabilite equilibrium holds in spite of variations in the concentration degree and temperature of samples. Field observations confirm that the reequilibrium process is efective in a few minutes when temperature varies only sorne degrees. Experimental determination of mirabilite solubility between Oand 30oC, using a natural brine sampled in advanced concentration stage, allows to isolate temperature effects on solution composition from those of evaporative concentration. Results indicate that modifications of mirabilite solubility produce their maximum effects between 20-30oC, fluctuation common in the natural system during spring: several hundreds of grams/kg water of mirabilite are mobilized, brine ionic strength changes from 4 to 8 molal and water activity varies from 0.943 to 0.896. Thenardite, bloedite and glauberite saturation states are affected by that reequilibrium process but those of gypsum and halite are almost insensitive to it. Predicted brine evolution by means of classical chemical divide or generalized residual alkalinity rules fails because of the special characters of these systems (high concentration solutions and evolution paths under variable temperature conditions). This non-isothermal evolution must be taken into account in more elaborated physicochemical approaches to brine evolution: the normal simplification using isothermal conditions (25oC) in thermodynamic calculations leads to important discrepancies in the predicted timing of mirabilite precipitation refered to field observations. Partial validation of the extended HMW model by comparison of laboratory and field solubility data appear to be confirmed.

Chemical Fractionation of Brine in the McMurdo Ice Shelf, Antarctica

AbstractDuring the austral summers of 1976–77 and 1978–79, several ice cores were taken from the McMurdo Ice Shelf brine zone to investigate its thermal, physical, and chemical properties. This brine zone consists of a series of superimposed brine layers (waves) that originate at the seaward edge of the ice shelf and migrate at various rates, depending on their age and position in the ice shelf. The brine in these layers becomes increasingly concentrated as the waves migrate inland through the permeable ice-shelf firn. Chemical analyses of brine samples from the youngest (uppermost) brine wave show that, except for the advancing front, it contains sea salts in normal sea-water proportions. Further inland, deeper and older brine layers, though highly saline (S &gt; 200°/00), are severely depleted in SO42-, with the SO42-/Na+ ratio being an order of magnitude less than that of normal sea-water. Consideration of the solubility of alternative salts, together with analyses of Na+, K+, Ca2+, Mg2+, SO42-, and Cl- concentrations, shows that the sulfate depletion is probably due to selective precipitation of mirabilite, Na2SO4·10H2O. The location of the inland boundary of brine penetration is closely related to the depth at which the brine encounters the firn/ice transition. However, a small but measureable migration of brine is still occurring in otherwise impermeable ice; this is attributed to eutectic dissolution of the ice by concentrated brine as it moves into deeper and warmer parts of the McMurdo Ice Shelf.

Chemical Fractionation of Brine in the McMurdo Ice Shelf, Antarctica

AbstractDuring the austral summers of 1976–77 and 1978–79, several ice cores were taken from the McMurdo Ice Shelf brine zone to investigate its thermal, physical, and chemical properties. This brine zone consists of a series of superimposed brine layers (waves) that originate at the seaward edge of the ice shelf and migrate at various rates, depending on their age and position in the ice shelf. The brine in these layers becomes increasingly concentrated as the waves migrate inland through the permeable ice-shelf firn. Chemical analyses of brine samples from the youngest (uppermost) brine wave show that, except for the advancing front, it contains sea salts in normal sea-water proportions. Further inland, deeper and older brine layers, though highly saline(S&amp;gt; 200°/00), are severely depleted in SO42-, with the SO42-/Na+ratio being an order of magnitude less than that of normal sea-water. Consideration of the solubility of alternative salts, together with analyses of Na+, K+, Ca2+, Mg2+, SO42-, and Cl-concentrations, shows that the sulfate depletion is probably due to selective precipitation of mirabilite, Na2SO4·10H2O. The location of the inland boundary of brine penetration is closely related to the depth at which the brine encounters the firn/ice transition. However, a small but measureable migration of brine is still occurring in otherwise impermeable ice; this is attributed to eutectic dissolution of the ice by concentrated brine as it moves into deeper and warmer parts of the McMurdo Ice Shelf.