Wm.Berry Lyons

Formation of alunite, jarosite and hydrous iron oxides in a hypersaline system: Lake Tyrrell, Victoria, Australia

Abstract Alunite (KAl 3 (SO 4 ) 2 (OH) 6 ) and jarosite (KFe 3 (SO 4 ) 2 (OH) 6 ) are common weathering products of aluminosilicates and pyrite. Long-range transport of the constituents forming these minerals and the subsequent deposition of alunite and jarosite in an evaporite setting have not been previously documented. Such conditions for the occurrence of alunite and jarosite were investigated in a hypersaline system where acid groundwater enriched in K, Al, Fe(III) and SO 4 enter a saltplaya lake. Sediment cores were studied by thin section, XRD and SEM-EDS. Groundwater and pore-water chemistries were also analyzed. The results show that alunite and jarosite occur together or as individual layers and cements within the top 20 cm of the sediments, where the groundwater is most concentrated due to evaporation. Hydrous Fe-oxides also occur as cements or vein fillings with the alunite and jarosite, but are distributed throughout the 70-cm sediment column studied. The results are consistent with a model in which alunite and jarosite precipitate as a result of the evaporation of water. Thermodynamic modeling indicates that the pore water in the playa sediments maybe in equilibrium with alunite, jarosite and hydrous Fe-oxides.

Seasonal and spatial trends in South Greenland snow chemistry

Abstract The spatial, temporal, source and physical controls on chloride, nitrate, sulfate and sodium in south Greenland snow are presented in this paper based on chemical data from snowpit and fresh snow samples. The snowpit samples cover the period June 1982–June 1984 and the fresh surface snow samples represent one storm event sampled over a 38-km traverse from Dye 3 to the southwest. Oxygen isotope dated records of chloride, sodium, excess sulfate and nitrate are discussed with respect to input timing and source. Notably the anthropogenic influx of excess sulfate is apparent in addition to an influx of excess sulfate that coincides with and is attributed to the arrival of the El Chichon cloud in S Greenland. The El Chichon event is also marked by highs in chloride and nitrate. Examination of fresh surface snow reveals geographic, temperature and moisture controls on deposition. Some excess sulfate close to Dye 3 can be attributed to local pollution.

Geochemistry of acid brines : Lake Tyrrell, Victoria, Australia

Pore water, groundwater and sediments were collected from Lake Tyrrell to study the evolution of brines in an acidic environment. Lake Tyrrell is a 150-km2 inland salt playa. Acid-saline groundwater enters the playa through springs along the lake margin and is evapo-concentrated past halite precipitation. The brines were found to contain sea salts, but some solutes do not follow the seawater evaporation curve. Processes that occur in neutral-alkaline systems (e.g., gypsum formation) occur here, but precipitation of alunite (KAl3(SO4)2(OH)6), jarosite (KFe3(SO4)2(OH)6) and Fe-oxides also affect solute behavior. Processes that occur in the recharge area and along the groundwater flow path (K uptake, calcrete and gypcrete formation) affect the brines chemical signature. Regardless of the chemical variability found among the samples, solutes have evolved from a common source (sea salt). Acidification, which appears to occur early in the evolution of the groundwater, is related to pyrite oxidation and may be enhanced by precipitation of Fe-oxides, alunite and jarosite, and evaporation. Acidity is maintained in the system because of the lack of buffering capacity of aquifer minerals. We suggest that this acid brine from Australia is another end-member in the Eugster-Jones-Hardie model for the evolution of water by evaporation in closed basins.

The scavenging of atmospheric sulfate by arctic snow

Scavenging ratios for sulfate on the south-central Greenland Ice Sheet at Dye 3 have been computed for 1982–1984. The ratios are based on measured concentrations in snow and estimated concentrations in air. The snow data have been obtained from snowpit samples which were dated by comparing δ18O values with meteorological records. The airborne concentrations have been estimated from data collected at coastal Greenland sites. Scavenging ratios resulting from this process are found to be in the range ~ 100–200 in winter and ~ 200–400 in summer. The greater summer values are attributed to increased riming, resulting in scavenging of sulfate as condensation nuclei and possible oxidation of SO2 in cloudwater droplets. Using the airborne and snowpit concentrations with assumed dry deposition velocities of 0.02–0.05 cms−, it is estimated that dry deposition is responsible for roughly 10–30% of the total sulfate deposition on a year-round basis at Dye 3. During portions of the Arctic winter, however, when the snow is unrimed and when there is less precipitation, dry deposition may be dominant.

Seasonal metal remobilization in the sediments of Great Bay, New Hampshire

Abstract Concentrations of dissolved iron, manganese, molybdenum, copper, and organic carbon (DOC) were measured in the pore waters from surficial sediments of a temperate estuary to delineate seasonal metal remobilization from 1978 through 1980. Iron and DOC data were collected for 31 months and covaried inversely and exponentially. Iron dissolution occurred during the spring and during periods of active bioturbation with concentrations as high as 18 mg 1 −1 . Iron values were low during winter due to oxidation to ferric oxides. The lack of active bioturbation during the summer of 1978 allowed for the nearly complete removal of iron as a monosulfide precipitate. However, bioturbation resumed during the summer of 1979 and 1980 and dissolved iron concentrations as high as 10 mg 1 −1 were observed at those times. The iron and DOC data were a qualitative measure of bioturbation activity. Dissolved manganese, molybdenum, and copper data were collected for 18 months during 1978 and 1979. All three metals displayed spring maxima covariate with iron, suggesting that they behaved chemically like iron and/or were associated with iron- or manganese-rich phases during this time of the year. In general, manganese and molybdenum varied temporally with iron while copper concentrations mimicked iron variations only during the spring.

Trace metal fluxes to nearshore Long Island Sound sediments

Abstract Sediments are very important as trace metal ‘sinks’ in coastal areas. In this paper we present data on the concentrations and calculated fluxes of the trace metals, Fe, Mn, Cu, Pb, Zn, Cd and Ag at nearshore sites in Long Island Sound. In both areas a percentage of the metal accumulation can be ascribed to local human activities with the highest anthropogenic metal fluxes occurring closest to their source.

A Northern Hemisphere Volcanic Chemistry Record (1869-1984) and Climatic Implications using a South Greenland Ice Core

The effect of volcanic emISSIOn of acidic aerosols on climate is well documented. The presence of acid droplets in the stratosphere can reduce transmissivity and hence decrease surface temperatures. Since the amount and chemical composition of erupted material has important effects on regional climate, knowledge of past volcanic events is of extreme importance. Detailed glaciochemical records provide the only milieu wherein the geochemistry of paleovolcanic events can be fully documented. We present a detailed sulfate and chloride record from an ice core drilled at site 20 D, 40 km SW of Dye 3 in southern Greenland. The record spans the time period 1869-1984 with chemical analyses of approximately eight samples per year. Time series decomposition and locally weighted scatter plot smoothing techniques were used to extract long term trends from the data so that individual volcanic eruptions could be documented. A number of events identified here have been unnoticed previously and a high percentage of the major chemical signatures documenting these events is associated with large decreases in temperature in the latitudinal zone 60-90 oN. Many authors have pointed out that the amount of volcanic acids such as HCI and H2S04 injected into the atmosphere has a very important influence on global climate, yet this volcanic input has been difficult to quantify prior to -1960. Our data help to alleviate this problem. These individual events can be compared to available frost tree ring data from North America, further establishing a volcanism--climatic linkage.

Dissolved organic matter in pore water of carbonate sediments from Bermuda

Abstract Pore water samples from seven nearshore areas in Bermuda were obtained under in situ conditions and analyzed for dissolved organic carbon, dissolved carbohydrates, dissolved free amino acids and dissolved humic substances. The concentration of dissolved organic carbon is higher than in the overlying nearshore waters indicating significant diagenetic remobilization of carbon in these recently deposited carbonate sediments. Dissolved carbohydrates decrease with depth due to microbial utilization.

Sulfate reduction and the nature of organic matter in estuarine sediments

Abstract The reduction of sulfate by sulfate reducing bacteria in the anoxic zone is an extremely important process during early diagenesis of marine sediments. Our data from Great Bay, NH reinforce the proposal that the rate of sulfate reduction is directly proportional to the reactivity of the organic matter or the amount of readily metabolizable organic matter present in the sediment and, hence, the source of the organic material in the anoxic zone. It appears that organic matter rich in marine organic remains is more easily degraded in the anoxic zone and that sulfate reduction rates can vary considerably in an estuarine system where many types of organic material may be deposited.

Sedimentary biogeochemistry of an acidic, saline groundwater discharge zone in Lake Tyrrell, Victoria, Australia

Abstract The chemical composition of saline, acidic pore waters at a groundwater discharge zone were investigated to delineate the biogeochemical conditions which occur within this zone. The discharge area was a surface exposure of a subsurface gradient where regional groundwaters of low pH and salinities similar to seawater were mixing with anoxic, sulfidic brines which were refluxing after evaporation within the lake. Shallow pore-water samples collected along transects from the lake edge into the lake revealed large increases in nitrate and iron and small increases in manganese. Ratios of sulfate to chloride near the shore were similar to those found in seawater while ratios increased further into the lake. The mixing of the regional groundwaters with the reflux brines apparently resulted in nitrification, sulfur oxidation and iron reduction. The sulfide in the brines appeared to have been generated at some remote location, probably on the eastern side of the lake where neutral and saline groundwaters discharge and cyanobacterial mats proliferate. Hence, biogeochemical processes occurring in the western discharge zone were fueled primarily by microbial activities in an area situated a few kilometers away.