Ice Meltwater Research Articles

Long-term geochemical evolution of the near field repository: Insights from reactive transport modelling and experimental evidences

The KBS-3 underground nuclear waste repository concept designed by the Swedish Nuclear Fuel and Waste Management Co. (SKB) includes a bentonite buffer barrier surrounding the copper canisters and the iron insert where spent nuclear fuel will be placed. Bentonite is also part of the backfill material used to seal the access and deposition tunnels of the repository. The bentonite barrier has three main safety functions: to ensure the physical stability of the canister, to retard the intrusion of groundwater to the canisters, and in case of canister failure, to retard the migration of radionuclides to the geosphere. Laboratory experiments (< 10 years long) have provided evidence of the control exerted by accessory minerals and clay surfaces on the pore water chemistry. The evolution of the pore water chemistry will be a primordial factor on the long-term stability of the bentonite barrier, which is a key issue in the safety assessments of the KBS-3 concept. In this work we aim to study the long-term geochemical evolution of bentonite and its pore water in the evolving geochemical environment due to climate change. In order to do this, reactive transport simulations are used to predict the interaction between groundwater and bentonite which is simulated following two different pathways: (1) groundwater flow through the backfill in the deposition tunnels, eventually reaching the top of the deposition hole, and (2) direct connection between groundwater and bentonite rings through fractures in the granite crosscutting the deposition hole. The influence of changes in climate has been tested using three different waters interacting with the bentonite: present-day groundwater, water derived from ice melting, and deep-seated brine. Two commercial bentonites have been considered as buffer material, MX-80 and Deponit CA-N, and one natural clay (Friedland type) for the backfill. They show differences in the composition of the exchangeable cations and in the accessory mineral content. Results from the simulations indicate that pore water chemistry is controlled by the equilibrium with the accessory minerals, especially carbonates. pH is buffered by precipitation/dissolution of calcite and dolomite, when present. The equilibrium of these minerals is deeply influenced by gypsum dissolution and cation exchange reactions in the smectite interlayer. If carbonate minerals are initially absent in bentonite, pH is then controlled by surface acidity reactions in the hydroxyl groups at the edge sites of the clay fraction, although its buffering capacity is not as strong as the equilibrium with carbonate minerals. The redox capacity of the bentonite pore water system is mainly controlled by Fe(II)-bearing minerals (pyrite and siderite). Changes in the groundwater composition lead to variations in the cation exchange occupancy, and dissolution–precipitation of carbonate minerals and gypsum. The most significant changes in the evolution of the system are predicted when ice-melting water, which is highly diluted and alkaline, enters into the system. In this case, the dissolution of carbonate minerals is enhanced, increasing pH in the bentonite pore water. Moreover, a rapid change in the population of exchange sites in the smectite is expected due to the replacement of Na for Ca.

Pacific freshwater, river water and sea ice meltwater across Arctic Ocean basins: Results from the 2005 Beringia Expedition

Pacific water, sea ice meltwater, and river water are the primary sources of freshwater in the Arctic Ocean. We have determined their relative fractions on a transect across the Arctic Ocean Section 2005 Expedition onboard IB Oden, which took place from 21 August to 23 September 2005. The transect began north of Alaska, continued through the central Canada Basin to the Alpha Ridge and into the Makarov Basin, and ended in Amundsen Basin. Pacific freshwater and river water were the major sources of freshwater throughout the central Canada Basin and into Makarov Basin, with river water fractions sometimes considerably higher than Pacific water in the top ∼50 m. Pacific freshwater extended to depths of about 200 m. Pacific water found over the Alpha Ridge and in the Amundsen Basin is suggested to have been transported there in the Transpolar Drift. The inventories of Pacific freshwater and river water were roughly constant along the section through most of the Canada and Makarov basins. River water fractions were greater than those of Pacific freshwater in the Amundsen Basin. Sea ice meltwater fractions were negative (reflecting net ice formation) or near zero throughout most of the section. A comparison of freshwater inventories with those at stations occupied during expeditions in 1991, 1994, and 1996 indicated an increase in river water inventories in the Makarov and Amundsen basins on the Eurasian side of the Arctic Ocean.

Worldwide potential of riverbank filtration

As the demand for piped drinking water is increasing in developing economies, water utilities are facing the challenge of treating surface water that is often polluted. Furthermore, many cities in developing countries are examining the feasibility of providing a continuous pressurized supply on a 24 h basis to reduce cross contamination. This practice is adding further stresses to treatment capacities in many cities. Riverbank filtration (RBF) is considered to be an excellent treatment (or pretreatment) technology for drinking water production. When wells are placed sufficiently close to a river and pumped, a part of the pumpage is induced infiltration water from the river. In the case of a lake, the process is called lake-bank filtration. As the induced surface water filters through the riverbed sediments and aquifer materials, most suspended and dissolved contaminants, including pathogenic bacteria and viruses are filtered out. RBF has been used in Europe for more than a century to supply drinking water to communities along the Rhine, Elbe, Danube, and Seine rivers. RBF systems have also been supplying drinking water to several communities in the US for nearly half a century. In post-World War II Europe, when the rivers were significantly polluted with municipal and industrial effluents, RBF was the most efficient method of producing high quality drinking water. Pollution in the Rhine in 1960s and 1970s was so severe that the river was termed the ‘‘Sewer of Europe’’ in the Netherlands. At that time, RBF and filtration of river water through dune sand provided drinking water to many communities in the Netherlands. Many of these systems are still functioning well. As late as 1980s, rivers such as the Elbe that passed through the former Czechoslovakia, East Germany, and West Germany contained significant amounts of industrial waste, particularly from the pulp and paper industry. Water quality was poor. RBF systems on the Elbe around the City of Dresden were able to remove most of the surface water contaminants. Recent studies show that RBF is capable of removing many pharmaceutical compounds, pesticides, and endocrine disrupting chemicals that are present in surface water. Removal of natural organic carbon also reduces the formation of disinfection byproducts during chlorination. Some of the most densely populated countries are located in Asia. Drinking water supplies in large cities in those countries mostly come from surface sources. For example, in India and China, a large number of cities are located along rivers, and provide potable water to hundreds of millions of people. In the Ganges Plains, many rivers are perennial, fed by snow and ice-melt waters from the Himalayan mountains. The major rivers of China also receive snow-melt runoff. The perennial nature of these rivers attracted the development of cities along their banks. Many of these cities are large with millions of people living in them. Subsequently, irrigation systems were developed to produce crops during the summer months. Reduction of flow due to irrigation diversion, and discharge of municipal and industrial effluent (often receiving only primary treatment) have caused tremendous water quality degradation in these rivers. For example, the City of Kanpur, India, located on the bank of the Ganges, has a metropolitan population of about 5 million. Before the construction of a new barrage and treatment plant, a diversion canal brought water to the treatment plant. The main industries in Kanpur are textiles and leather tanning. Often blood-red dyes can be seen in the river from the railway bridges. The treatment C. Ray (&) Faculty of Engineering, Driftmier Engineering Center, University of Georgia, Athens, GA 30602, USA e-mail: cray@engr.uga.edu

Oxygen isotope values from high-latitudes: Clues for Permian sea-surface temperature gradients and Late Palaeozoic deglaciation

The Permian was a period of waning large-scale continental glaciations in the southern Hemisphere. The waning of these ice sheets during the Early Permian led to discharge of 18O-depleted ice–melt water into the oceans. This, coupled with rising seawater temperatures, resulted in a concomitant decline of about 2.5‰ in the δ 18O of seawater, as recorded by brachiopod shells from low-latitude (< 30°) habitats. The transition from ice- to greenhouse conditions is reflected also in the oxygen isotope data of unaltered brachiopods and bivalves from high high-latitudes. Moreover, the high-latitude specimens have consistently more positive δ 18O, by about 2.5‰, than their coeval low-latitude counterparts, suggesting a Permian sea-surface temperature (SST) gradient of about 9 to 12 °C between tropical–subtropical (< 30°) and high southern (55 ±10°) latitude localities, apparently irrespective of whether in a greenhouse or an icehouse mode. This Permian SST gradient is comparable to the modern SST gradient of about 14 °C. The δ 18O seawater records suggest that the global warming that resulted in the waning of the Permo-Carboniferous ice sheets during the Sakmarian was followed by another cooling during the late Kungurian and by renewed warming during the Mid- and Late Permian.

To the theory of underwater ice evolution, or nonlinear dynamics of “false bottoms”

We present a mathematical model describing evolution of false bottoms often met between an under-ice melt pond and the underlying ocean during summer. The model treats a false bottom as the region of mixed phase (mushy layer) whose coordinates depend on time and determine the phase transition area. As the heat and the salt fluxes in the ocean are strongly influenced by turbulence and the ice meltwater accumulating underneath the ice cover is practically fresh, we use modified boundary conditions for heat and mass fluxes at the interfaces of phase transition. Explicit analytical solutions (thickness of false bottom and growth rates of its boundaries, temperature and salinity distributions, solid phase fraction and ocean-to-ice heat flux) of the nonlinear model under consideration are found. Model predictions are in good agreement with existing experimental data and physical concepts of phenomena under study.

Sources and distribution of fresh water in the East Greenland Current

Fresh water flowing from the Arctic Ocean via the East Greenland Current influences deep water formation in the Nordic Seas as well as the salinity of the surface and deep waters flowing from there. This fresh water has three sources: Pacific water (relatively fresh cf. Atlantic water), river runoff, and sea ice meltwater. To determine the relative amounts of the three sources of fresh water, in May 2002 we collected water samples across the East Greenland Current in sections from 81.5°N to the Irminger Sea south of Denmark Strait. We used nitrate–phosphate relationships to distinguish Pacific waters from Atlantic waters, salinity to obtain the sum of sea ice melt water and river runoff water, and total alkalinity to distinguish the latter. River runoff contributed the largest part of the total fresh water component, in some regions with some inventories exceeding 12 m. Pacific fresh water (Pacific source water S ∼ 32 cf. Atlantic source water S ∼ 34.9) typically provided about 1/3 of the river runoff contribution. Sea ice meltwater was very nearly non-existent in the surface waters of all sections, likely at least in part as a result of the samples being collected before the onset of the melt season. The fresh water from the Arctic Ocean was strongly confined to near the Greenland coast. We thus conjecture that the main source of fresh water from the Arctic Ocean most strongly impacting deep convection in the Nordic Seas would be sea ice as opposed to fresh water in the liquid phase, i.e., river runoff, Pacific fresh water, and sea ice meltwater.

Chlorophyll blooms in the Antarctic Zone south of Australia and New Zealand in reference to the Antarctic Circumpolar Current fronts and sea ice forcing

Using new high‐resolution maps of the frontal structure of the Antarctic Circumpolar Current (ACC) derived from satellite altimetry, the relationship between circulation, sea ice concentrations, availability of light, and surface chlorophyll in the Southern Ocean south of Australia and New Zealand is investigated. South of the Polar Front, in the Antarctic Zone (AZ), there is a distinct spring bloom, which occurs earlier, persists for longer, and reaches higher maximum values farther south near Antarctica. The seasonal changes in chlorophyll pattern in this zone are predominantly driven by the sea ice meltwater flux which improves the irradiance‐mixing regime via formation of a very shallow mixed layer and provides an additional source of iron which triggers the chlorophyll blooms. There is a clear and consistent increase of about fivefold in both mean and maximum chlorophyll concentrations in regions of largest decrease in monthly mean sea ice concentrations. The seasonal signal in chlorophyll concentrations related to the ice melting is particularly strong between the southern ACC front and the southern boundary of the ACC. The changes in wind‐driven mixed layer depth in the AZ in summer do not explain adequately the elevated surface chlorophyll concentrations observed between these two ACC fronts. Reduction in the cloud cover and consequent increase in photosynthetically active radiation near the Antarctic coast in the summer could also support higher phytoplankton concentrations within the seasonal sea ice zone and costal polynyas.

The mean residence time of river water in the Canada Basin

Seawater was collected from the western Arctic Ocean for measurements of 18O, 226Ra and 228Ra. The fractions of river runoff and sea ice melt-water in water samples were estimated by using δ 18O-S-PO* tracer system. The mean residence time of river water in the Canada Basin was calculated based on the relationship between 228Ra/226Ra)A.R. and the fractions of river runoff in the shelf and deep ocean. Our results showed that the river runoff fractions in the Canada Basin were significantly higher than those in the shelf regions, suggesting that the Canada Basin is a major storage region for Arctic river water. 228Ra activity concentrations in the Chukchi shelf and the Beaufort shelf ranged from 0.16 to 1.22 Bq/m3, lower than those reported for shelves in the low and middle latitudes, indicating the effect of sea ice melt-water. A good positive linear relationship was observed between 228Ra/226Ra)A.R. and the fraction of river runoff for shelf waters, while the 228Ra/226Ra)A.R. in the Canada Basin was located below this regressive line. The low 228Ra/226Ra)A.R. in the Canada Basin was ascribed to 228Ra decay during shelf waters transporting to the deep ocean. The residence time of 5.0–11.0 a was estimated for the river water in the Canada Basin, which determined the time response of surface freshening in the North Atlantic to the river runoff into the Arctic Ocean.

Picophytoplankton and nanophytoplankton abundance and distribution in the southeastern Beaufort Sea (Mackenzie Shelf and Amundsen Gulf) during Fall 2002

The distribution of picophytoplankton (0.2–2 µm) and nanophytoplankton (2–20 µm) in the Beaufort Sea–Mackenzie Shelf and Amundsen Gulf regions during autumn, 2002 is examined relative to their ambient water mass properties (salinity, temperature and nutrients: nitrate + nitrite, phosphate, and silicate) and to the ratio of variable to maximum fluorescence, Fv/Fm. Total phytoplankton and cell abundances (< 20 µm) were mainly correlated with salinity. Significant differences in picophytoplankton cell numbers were found among waters near the mouth of the Mackenzie River, ice melt waters and the underlying halocline water masses of Pacific origin. Picophytoplankton was the most abundant phytoplankton fraction during the autumnal season, probably reflecting low nitrate concentrations (surface waters average ~ 0.65 µM). The ratio Fv/Fm averaged 0.44, indicating that cells were still physiologically active, even though their concentrations were low (max Chl a = 0.9 mg m − 3 ). No significant differences in Fv/Fm were evident in the different water masses, indicating that rate limiting conditions for photosynthesis and growth were uniform across the whole system, which was in a pre-winter stage, and was probably already experiencing light limitation as a result of shortening day lengths.

Infiltration of melting saline ice water in soil columns: Consequences on soil moisture and salt content

A soil column experiment was conducted to study the water and salt redistribution in a coastal saline soil under infiltration of saline ice meltwater. Four salinity levels (0, 5000, 10,000, and 15,000 mg l −1 diluted seawater) and three volumes (1800, 2700, and 3600 ml) of source water were used. The results indicated that the soil water content increased with the volume of applied ice. In the top soil layers, water content was higher under salt-free ice treatment than under saline ice treatments. In the deeper soil layers, however, the saline ice treatments showed higher water content than the salt-free ice treatment. While infiltration of meltwater reduced the salt content of the surface layer of all the treatments, the desalting depths of the saline ice treatments were greater than the desalting depth of the salt-free ice treatment. The results demonstrated that in the monsoon regions, saline soils could be improved through infiltration with meltwater of saline ice.

Freshwater budget of the Canada Basin, Arctic Ocean, from salinity, δ18O, and nutrients

The contribution of freshwater components (e.g., meteoric, sea ice, and Pacific water) in the Canada Basin is quantified using salinity, δ18O, and nutrient data collected in 2003 and 2004. The penetration depth of sea ice meltwater is limited to the upper 30 m, and brine, rejected during sea ice formation, is observed from 30 to 250 m depth. The fraction of meteoric water is high in the upper 50 m and decreases with depth. Pacific water entering via Bering Strait is the main source of freshwater below 50 m depth. Bering Strait throughflow, which transports Pacific water with salinity 32.5 together with meteoric water supplied upstream of the Bering Strait, contributes up to 75% of freshwater input (&gt;3200 km3 a−1) to the Canada Basin. The mean residence time of Pacific water in the Canada Basin is estimated to be 11 years. Precipitation and river runoff from both North American and Eurasian continents add &gt;800 km3 a−1 and sea ice formation removes &lt;900 km3 a−1 (&lt;0.6 m a−1) of fresh water. The export of ice and liquid fresh water from the Canada Basin contributes ∼40% of the freshwater flux from the Arctic Ocean to the North Atlantic Ocean.

East–west differences in water mass, nutrient, and chlorophyll a distributions in the sea ice reduction region of the western Arctic Ocean

The R/V Mirai conducted hydrographic surveys in the western Arctic Ocean during summer 2004 across a front between cold Arctic water and warm water from the Pacific Ocean where sea ice cover has been largely reduced in recent summers. The hydrographic data indicate a new type of vertical temperature minimum water west of the front along isohaline surfaces with approximate salinity (S) of 32, which is fresher than the typical temperature minimum (S ≈ 33) caused by spreading of Pacific winter water (PWW) mainly to the east of the front. Both of the temperature minimum waters are characterized by low potential vorticity with near‐freezing temperature, suggesting that they are formed by winter convection with sea ice formation. A difference between the waters results from a large contribution of sea ice meltwater to the fresh temperature minimum (frTmin) water of S ≈ 32. The distributions of the sea ice meltwater contribution and nitrogen deficit suggest that summer shelf water, largely influenced by the sea ice melt in the Chukchi Sea, is modified by winter convection on its way to the Chukchi Abyssal Plain to form the frTmin water. This water supplies nutrients through the water distribution to the west of the front at depths shallower than the nutrient maximum layer caused by the PWW spreading. The shallower nutrient supply by the frTmin water combined with light penetration without sea ice cover could produce a prominent chlorophyll a maximum layer west of the front.

A Description of Seven Antarctic Marine Gymnamoebae Including a New Subspecies, Two New Species and a New Genus: Neoparamoeba aestuarina antarctica n. subsp., Platyamoeba oblongata n. sp., Platyamoeba contorta n. sp. and Vermistella antarctica n. gen. n. sp.

Seven marine gymnamoebae were isolated from different environments of seawater, slush (pack ice meltwater), and sediment in the Ross Sea area of Antarctica. All amoebae were isolated and maintained at temperatures below 4 degrees C. Growth, rate of locomotion, and general morphology were observed at an environmentally appropriate temperature (1 degrees C) and at room temperature (approximately 25 degrees C). Molecular (srDNA sequences) and microscopical techniques were used to identify the gymnamoebae and establish their phylogenetic affinities. Three isolates (S-131-2, SL-200, and W4-3) were assigned to a psychrophilic subspecies of Neoparamoeba aestuarina, N. aestuarina antarctica n. subsp., one isolate (S-205) was assigned to a new species of Platyamoeba, P. oblongata n. sp., two isolates (W51C#4 & W51C#5) were also assigned to a new species of Platyamoeba, P. contorta n. sp., and one isolate (S-241) was a novel psychrophilic gymnamoeba Vermistella antarctica n. gen. n. sp. Molecular and morphological results revealed that V. antarctica was not related to any described family of gymnamoebae. Strains S-205, W51C#4, and W51C#5 were capable of locomotion at room temperature, while strains SL-200, S-131-2, W4-3, and S-241 exhibited locomotion only below approximately 10 degrees C. Our results imply that the Antarctic environment is host both to cosmopolitan gymnamoebae that have acquired adaptations for existence at low environmental temperature and to apparently novel psychrophilic amoebae described here for the first time.

Amino acid analyses of Antarctic CM2 meteorites using liquid chromatography-time of flight-mass spectrometry

Abstract— Amino acid analyses of the Antarctic CM2 chondrites Allan Hills (ALH) 83100 and Lewis Cliff (LEW) 90500 using liquid chromatography-time of flight-mass spectrometry (LC-ToF-MS) coupled with UV fluorescence detection revealed that these carbonaceous meteorites contain a suite of indigenous amino acids not present in Antarctic ice. Several amino acids were detected in ALH 83100, including glycine, alanine, β-alanine, γ-amino-n-butyric acid (γ-ABA), and α-aminoisobutyric acid (AIB) with concentrations ranging from 250 to 340 parts per billion (ppb). In contrast to ALH 83100, the CM2 meteorites LEW 90500 and Murchison had a much higher total abundance of these amino acids (440–3200 ppb). In addition, ALH 83100 was found to have lower abundances of the α-dialkyl amino acids AIB and isovaline than LEW 90500 and Murchison. There are three possible explanations for the depleted amino acid content in ALH 83100: 1) amino acid leaching from ALH 83100 during exposure to Antarctic ice meltwater, 2) a higher degree of aqueous alteration on the ALH 83100 parent body, or 3) ALH 83100 originated on a chemically distinct parent body from the other two CM2 meteorites. The high relative abundance of ɛ-amino-n-caproic acid (EACA) in the ALH 83100 meteorite as well as the Antarctic ice indicates that Nylon-6 contamination from the Antarctic sample storage bags may have occurred during collection.

Combined modeling of thermal evolution and accretion of trans-neptunian objects—Occurrence of high temperatures and liquid water

We have calculated the early thermal evolution of trans-neptunian objects by means of a thermal evolution code that takes into account simultaneous accretion. The set of coupled partial differential equations for 26Al radioactive heating, transformation of amorphous to crystalline ice and melting of water ice was solved numerically for small porous icy (cometary-like) bodies growing to final radii between 2 and 32 km and accreting between 20 and 44 AU. Accretion within a swarm of gravitationally interacting small bodies was calculated self-consistently with a simple accretion algorithm and thermal evolution of a typical member of the swarm was tracked in a parameter-space survey. We find that including accretion in numerical modeling of thermal evolution leads to a broad variety of thermally processed icy bodies and that the early occurrence of liquid water and extended crystalline ice interiors may be a very common phenomenon. The pristine nature of small icy bodies becomes thus restricted to a particular set of initial conditions. Generally, long-period comets should be more thermally affected than short-period ones.

Polycystine radiolarians in surface sediments from the Bering Sea Green Belt area and their ecological implication for paleoenvironmental reconstructions

Radiolarians in surface sediments along transects from the shelf edge, along the slope into the deep basin of the northern Bering Sea are dominated by Stylochlamydium venustum, Antarctissa? sp. 1, the Spongodiscidae (juvenile), Pseudodictyophimus gracilipes, Ceratospyris borealis, the Plagoniidae ( Phormacantha group and Plectacantha group), Siphocampe arachnea, Cycladophora davisiana and Spongotrochus glacialis. This dominance is most extreme on the shelf edge and slope, where S. venustum, Antarctissa? sp. 1, the Spongodiscidae (juvenile), the Plagoniidae and S. glacialis have their highest relative abundance. There is thus a close relation between radiolarian distribution and the high productivity of the “Bering Sea Green Belt” (BSGB) due to periodic sea ice melt. The radiolarian depth distribution patterns indicate that some radiolarian species have specific ecological preferences. S. venustum, the Spongodiscidae (juvenile), and S. glacialis live close to the surface water under relatively low-temperature and low-salinity conditions due to sea ice melting or melt water influx. Antarctissa? sp. 1 appears to dwell mainly in surface to subsurface waters, but has not been recorded in trap samples of the Bering Sea. The Plagoniidae probably live in subsurface and intermediate waters. S. arachnea and C. davisiana are intermediate to deep dwellers. The close association of these radiolarians with the BSGB and specific water depths provides a valuable reference for paleoenvironmental reconstruction in the region.

Freshwater and brine behaviors in the Arctic Ocean deduced from historical data of δ18O and alkalinity (1929–2002 A.D.)

The long‐term data sets of total alkalinity (TA) (1929–2002 A.D.) and δ18O (1966–2002 A.D.) are used to investigate freshwater and brine distributions in the Arctic Ocean. Fractions of sea ice meltwater and other freshwaters (OF) (precipitation, river runoff, and freshwater carried by Pacific water implied as salinity deficit) are calculated on the basis of salinity‐TA and salinity‐δ18O relationships. Rejected brine during sea ice growth resides in surface water in the central Arctic Ocean, while net melting is found along the surface flow of water from the Pacific and Atlantic oceans. Distribution of OF at 10 m water depth suggests that Russian runoff leaves the shelf mainly west of the Mendeleyev Ridge, enters into the deep basin, and exits from the ocean through the western part of Fram Strait. The influence of Mackenzie River water is limited in the region and in depth. Accumulation of freshwater in the Canadian Basin is caused by deep penetration of OF with brine, indicating the transport of freshwater by shelf‐derived water. The major origin of shelf‐derived water entering into the upper halocline layer in the Canadian Basin should be the Chukchi and East Siberian Sea shelves, and the main freshwater sources are the salinity deficit of Pacific water and/or Russian runoff. An increase in OF inventory accompanied by an increase in brine content may suggest an increase of the shelf‐derived water supply into the western Canadian Basin in anticyclonic years.

Organochlorine compounds in ice melt water from Italian Alpine rivers

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.

Using laser‐light scattering to measure impurities, bubbles, and imperfections in ice cores

Laser‐light scattering (LLS) on polar ice, or on polar ice meltwater, is an accepted method for measuring the concentration of water‐insoluble aerosol deposits (dust) in the ice. LLS on polar ice can also be used to measure water‐soluble aerosols, as well as imperfections (air bubbles and cavities) in the ice. LLS was originally used for measuring the dust concentration in polar ice meltwater, but was later also applied to solid ice for measuring the dust concentration profile along the deep, bubble‐free sections of the Greenland Ice Sheet Project 2 (GISP2) ice core from central Greenland. In this paper, we extend the usability of LLS on ice into the realm of the nontransparent, bubbly polar ice, and put previous empirical findings on a theoretical footing. For LLS on clear, bubble‐free polar ice, we studied numerically the scattering of light by soluble and insoluble aerosol particles embedded in the ice to complement previous experimental studies. For air bubbles in polar ice, we calculated the effects of multiple light scattering using Mie theory and Monte Carlo simulations, and found a method for determining the bubble size and number concentration using LLS on bubbly ice. We also demonstrated that LLS can be used on bubbly ice to rapidly measure annual layers.

A tracer study of ventilation in the Japan/East Sea

During the Circulation Research in East Asian Marginal Seas (CREAMS) summer cruises in 1999, a suite of samples was collected for tracer analysis. Oxygen isotopes combined with tritium-helium ventilation timescales and noble gas measurements give unique insights into the ventilation of water masses in the Japan/East Sea (JES). In particular, noble gases and oxygen isotopes are indicators of brine rejection, which may assist in explaining the recent changes observed in the ventilation of the JES. Oxygen isotope data presented here indicate that both thermally driven convection and brine rejection have played significant roles in deep-water formation but that brine rejection is unlikely to be a significant contributor at the moment. A 6-box ventilation model of the JES, calibrated with tritium and helium-3 measurements, performed better when a significant decrease of dense-water formation rates in the mid-1960s was incorporated. However, the model calculations suggest that Japan Sea Intermediate Water formation is still occurring. Subduction of sea–ice melt water may be a significant ventilation mechanism for this water mass, based on an argon saturation minimum at the recently ventilated salinity minimum in the northwestern sector of the JES. The salinity and oxygen isotope budgets imply a potential bottom-water formation rate of 3.97±0.89×1012 m3 yr−1 due to brine rejection, which could account for a time averaged fraction of between 25% and 35% of the ventilation of subsurface water formation in the JES.