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Aquatic Geochemistry (v.3, #4)
Carbonyl Sulfide (COS) in the Surface Ocean and the Atmospheric COS Budget by V.S. Ulshöfer; M.O. Andreae (pp. 283-303).
Carbonyl sulfide (COS) mixing ratioswere measured in the marine atmosphere and in airequilibrated with surface sea water during severalcruises in the North Sea and western NorthAtlantic. In April 1994, North Sea waters weresupersaturated with respect to the atmosphere,resulting in oceanic emissions of COS. Saturationratios varied between the equilibrium value of one inthe central North Sea and high values of >15 in theElbe Estuary. We observed weak diel cycles of surfacewater COS during a three day drift station. During theunderway parts of the cruise, diel COS variations weremasked by the high geographical variability of COSconcentrations in the German Bight. In August 1994, weobserved a pronounced diel cycle of COS off theFlorida coast with saturation ratios varying betweenthe equilibrium value of one in the early morning andmaximum values of four to five in the afternoon. InMarch 1995, we found COS supersaturation as well asextensive undersaturation in the western NorthAtlantic between Norfolk, VA, and Bermuda. Suchundersaturation in marine surface waters results inregional and seasonal uptake of atmospheric COS. Basedon our data and those of other researchers, weestimate the global oceanic COS net emission to bebetween 1.3 and 2.5 Gmol yr-1. This estimate is significantly smaller than previous ones which had notconsidered the possibility of COS uptake by theoceans. COS hydrolysis in the ocean has a significantinfluence on the atmospheric turnover time of COS,which we estimate to be 5.7 yr. This may contribute tothe lack of an observable increase in atmospheric COSlevels despite substantial anthropogenic emissions.
Origin of Dissolved Groundwater Sulphate in Coastal Plain Sediments of the Rio de la Plata, Eastern Argentina by Williams S. Logan; Ronald V. Nicholson (pp. 305-328).
Groundwater of the coastal plain of the Rio de La Plata, Argentina,contains up to 17 g L-1 SO4 and 37 gL-1 TDS. Some of this SO4 is from paleo-seawater intrusion; however, SO4 : Cl ratios can be>2 : 1, and most of the SO4 must, therefore, have another source. Three possible sources were investigated: gypsum, organic matter,and iron sulphides.Dissolved SO4 showed δ34S valuesfrom -7 to 0‰, typical values for S from iron sulphides or organicmatter, but distinct from that of seawater (+22‰). To test whetherthe SO4 was derived from oxidation of reduced S, four 4-mcores were taken from marine sediments of the coastal plain. Two were takenfrom higher, drier areas where the highest dissolved SO4values were encountered, and two were taken from lower, wetter areas thathad much lower SO4 concentrations. Pore waterSO4, Cl and alkalinity were determined; solids were analyzedfor SO4, sulphide-S and organic-S.Sulphide-S was the dominant form of reduced S, averaging about0.5% S in the lower interval (2.5–4 m) of the cores. Sulphidewas absent in the upper 2.5 m in both topographically higher and lowerareas. Sulphate was present in the entire unit in the higher, drier areas,but almost absent in lower areas. Organic-S was insignificant.Our model for the origin of dissolved SO4 is: fine-grainedpyrite was oxidized during hotter or drier periods. Some resulting dissolvedSO4 was precipitated as gypsum. Iron from the pyriteprecipitated as FeOOH. Lower, wetter areas formed over time where recharginggroundwater dissolved most of the gypsum. In higher areas with low hydraulicgradients and high net evapotranspiration, SO4 remained asgypsum and in the dissolved phase.
Keywords: Rio de la Plata; La Plata; Argentina; Postpampeano; sedimentary pyrite oxidation; sulfur cycling; coastal plain; sulfur isotopes; oxygen isotopes
The Source of Silica and Trace Metals in Particulate Matter in Framvaren Fjord by David W. Dyrssen (pp. 329-343).
The lake and streams in the Framvarenwatershed were sampled and analyzed in September 1983.The results can be explained by the precipitation ofacid rain containing some sea salts and thedissolution of Farsundite, the dominating rock in thecatchment area. The runoff supplies the surface waterof Framvaren with silica, aluminium, manganese, iron,copper, zinc, cadmium and lead. Reasonablecalculations show that the runoff most likely is themain source for the particulate matter found insediment traps and by filtering off suspendedparticles. Thus the calculations supplement recentstudies of Skei et al. (1996).
Keywords: Framvaren; Farsundite; watershed; runoff; silica; aluminium; trace metals; sulfides; particulate matter
Interaction of B $$(OH)_3^0 $$ and $$HCO_3^ - $$ in Seawater: Formation of B $$(OH)_2 CO_3^ - $$ by Sean McElligott; Robert H. Byrne (pp. 345-356).
Boron is known to interact with a wide variety of protonated ligands(HL) creating complexes of the form B(OH)2L-.Investigation of the interaction of boric acid and bicarbonate in aqueoussolution can be interpreted in terms of the equilibrium $$B(OH)_3^0 + HCO_3^ -
ightleftharpoons B(OH)_2 CO_3^ - + H_2 O$$ The formation constant for this reaction at 25 °C and 0.7 molkg-1 ionic strength is $$K_{BC} = left[ {B(OH)_2 CO_3^ - }
ight]left[ {B(OH)_3^0 }
ight]^{ - 1} left[ {HCO_3^ - }
ight]^{ - 1} = 2.6 pm 1.7$$ where brackets represent the total concentration of each indicatedspecies. This formation constant indicates that theB(OH)2 $$CO_3^ - $$ concentration inseawater at 25 °C is on the order of 2 μmol kg-1. Dueto the presence of B(OH)2 $$CO_3^ - $$ , theboric acid dissociation constant ( $$Kprime _B $$ ) in natural seawaterdiffers from $$Kprime _B $$ determined in the absence of bicarbonate byapproximately 0.5%. Similarly, the dissociation constants of carbonicacid and bicarbonate in natural seawater differ from dissociation constantsdetermined in the absence of boric acid by about 0.1%. Thesedifferences, although small, are systematic and exert observable influenceson equilibrium predictions relating CO2 fugacity, pH, totalcarbon and alkalinity in seawater.
Keywords: boron; boric acid; carbonate; CO2 system; complexation; spectrophotometric pH
The Influence of Redox Reactions on the Uptake of Dissolved Ce by Suspended Fe and Mn Oxide Particles by Eric Heinen De Carlo; Xi-Yuan Wen; Mark Irving (pp. 357-389).
Laboratory experiments were conducted to evaluate the partitioning ofrare earth elements (REE) between solution and suspended particles. Becauseof their strong tendency to complex, the REE can be used to study a varietyof marine processes and in particular particle scavenging. In this study, anemphasis was placed on examining abiotic redox processes that influence theuptake of dissolved Ce by particles. Batch sorption experiments wereconducted with REE and synthetic mineral phases over the range of pH4–9. The solutions varied in ionic strength between 0 and 0.7 M andconsisted of individual solutes (NaNO3, NaCl, andNa2SO4), ionic mixtures that duplicate theseawater composition, and natural seawater. The uptake of REE from solutionwas also studied at a Pt electrode coated with $$delta { ext{ - MnO}}_{ ext{2}} $$ using cyclic voltametry.Experimental results are consistent with uptake of dissolved Ce onto $$delta { ext{ - MnO}}_{ ext{2}} $$ occurring by a combination of oxidativescavenging and surface complexation. The contribution of oxidativescavenging to the removal of Ce from solution is most pronounced at acidicpH, where the strictly trivalent REE exhibit little propensity for sorptiononto $$delta { ext{ - MnO}}_{ ext{2}} $$ . Sorption of dissolved Ce onto FeOOH occursin a manner analogous to that of the other strictly trivalent REE and nocontribution from oxidative scavenging is observed on this mineral phase atlow pH. Our work also substantiates the hypothesis that anions in solution,particularly $${ ext{SO}}_{ ext{4}}^{{ ext{2}} - } $$ and Cl-, aswell as those adsorbed on the surface of the particles, influence the extentof Ce uptake by $$delta { ext{ - MnO}}_{ ext{2}} $$ .
Keywords: Iron oxide; manganese oxide; oxidation-reduction; particles; rare earth elements; scavenging; seawater