Philipp Steinmann

Chemical composition, pH, and redox state of sulfur and iron in complete vertical porewater profiles from two Sphagnum peat bogs, Jura Mountains, Switzerland

Complete porewater profiles from two peat bogs in the Jura Mountains were analysed for major and trace inorganic anions and cations. At La Tourbiere des Genevez (TGe) and Etang de la Gruere (EGr), peat formation began approximately 5,000 and 10,000 years bp, respectively. The maximum depths of peat accumulation are 140 cm (TGe) and 650 cm (EGr); previous geochemical studies showed that the ombrogenic sections of the bogs extend to depths of approximately 20 cm (TGe) and 250 cm (EGr). Water samples were obtained using in situ diffusion equilibrium samplers (peepers), which allow filtered (0.2 μm) porewaters to be obtained while preventing degassing and oxidation. These samplers were found to be well suited to bog porewaters and allowed volatile (dissolved CO2, acetate) and redox-sensitive species (HS−, Fe2+) to be quantified without further sample preparation or treatment. Aqueous species concentrations were determined immediately afterwards using ion chromatography with either conductivity (acetate, HCO3−, Cl−, Br−, NO3−, HPO42−, SO42−, Na+, NH4+, K+, Mg2+, Ca2+), amperometry (HS−), or absorbance detection (Fe(III) and Fe(II)). The comprehensive analyses of anions and cations allowed humic substances to be calculated by the difference in electrical charge balance (i.e., the anion deficit). Concentrations of total dissolved CO2 (2–12 mM) showed that carbonate equilibria play a significant role in the acid-base chemistry throughout the profiles. In near surface, ombrogenic porewaters with pH around 4, however, protons (approx. 160 μeq/L) are contributed mainly by the dissociation of humic substances (2–7 mM DOC). In the deepest, minerogenic layers H2CO3 is the predominant acid at both sites. At these depths, carbonate alkalinity (up to 3 meq/L at EGr, up to 8 meq/L at TGe) arises from reaction of the pore fluids with mineral matter in the underlying sediments. In the transition zone between the ombrogenic and minerogenic extremes, organic and inorganic acids are equal in importance. Unidentified organic S species accounted for 90–99% of total dissolved sulfur (ST) in the porewaters at TGe, with SO42− and HS− the dominant inorganic species; S species with intermediate oxidation states such as SO32− and S2O32− were always less than the detection limit of approximately 0.4 μM. At TGe the sulfate concentrations exceeded those of sulfide, with 1.25 and 0.25 μM, respectively, being typical. At EGr, ST and SO42− were comparable to the waters at TGe, but HS− at EGr was always less than the detection limit of 0.15 μM. At both sites dissimilatory sulfate reduction is limited by the low concentrations of sulfate supplied to the bog surfaces (i.e., atmospheric deposition only), and the uptake of sulfate and its conversion to organic S compounds by the living plants. Despite the anoxic condition of the waters, the ratio of Fe(III)T to Fe(II)T was always high: at EGr this ratio was generally 1:1, and even in the sulfidic waters at TGe the ratio was 1:3. PHREEQE was used to calculate the effect of complex-forming organic ligands on {Fe3+} and {Fe2+} in these porewaters. The relatively high ratios of Fe(III)T compared to Fe(II)T can be explained in terms of the much greater thermodynamic stability of the organic complexes of Fe3+ compared to those of Fe2+.

Carbonate and silicate weathering in two presently glaciated, crystalline catchments in the Swiss Alps

Abstract We present a weathering mass balance of the presently glaciated Rhone and Oberaar catchments, located within the crystalline Aar massif (central Switzerland). Annual chemical and physical weathering fluxes are calculated from the monthly weighted means of meltwater samples taken from July, 1999 to May, 2001 and are corrected for precipitation inputs. The meltwater composition issuing from the Oberaar and Rhone catchments is dominated by calcium, which represents 81% and 55% of the total cation flux respectively (i.e. 555 and 82–96 keq km−2 yr−1). The six to seven times higher Ca2+ denudation flux from the Oberaar catchment is attributed to the presence of a strongly foliated gneissic zone. The gneissic zone has an elevated calcite content (as reflected by the 4.6 times higher calcite content of the suspended sediments from Oberaar compared to Rhone) and a higher mechanical erosion rate (resulting in a higher flux of suspended sediment). The mean flux of suspended calcite of the Oberaar meltwaters during the ablation period is 7 times greater than that of the Rhone meltwaters. Taking the suspended calcite as a proxy for the total (including sub-glacial sediments) weathering calcite surface area, it appears that the available surface area is an important factor in controlling weathering rates. However, we also observe an increased supply of protons for carbonate dissolution in the Oberaar catchment, where the sulphate denudation flux is six times greater. Carbonic acid is the second important source of protons, and we calculate that three times as much atmospheric CO2 is drawn down (short term) in the Oberaar catchment. Silica fluxes from the two catchments are comparable with each other, but are 100 kmol km2 yr−1 lower than fluxes from physically comparable, non-glaciated basins.

Beryllium-7 as a tracer to study mechanisms and rates of metal scavenging from lake surface waters

The removal of Be-7 from lake surface waters (Lake Lugano, Switzerland/Italy) was studied from September 1995 to May 1996. During this period the atmospheric input and sedimentary flux of Be-7, as well as concentrations of dissolved ( 1 μm) Be-7 in the epilimnion were measured. The separation of dissolved, colloidal, and particulate fractions of Be-7 was carried out using continuous flow centrifugation (CFC) and tangential flow filtration (TFF) techniques. Lacustrine colloids (log Kc ≈ 6) were shown to be much more efficient sorbents for Be-7 than the suspended particles (log Kp 4–5). Particle concentrations Cp ranged from 0.5 to 2 mg/L. The ratio of colloid (>10 kD) to particle concentration Cc/Cp was close to 0.09 during winter months when detrital inputs are dominant, but was higher (0.16) in summer and in spring after an algal bloom. The Be-7 data were used to estimate coagulation rates of colloids. The highest coagulation rates (λcoag ≈ 0.4 d−1) along with the lowest Kc (log Kc ≈ 5.2) were found after an algal bloom in spring.

Decoupling of P- and Corg-burial following Early Cretaceous (Valanginian–Hauterivian) platform drowning along the NW Tethyan margin

During the Hauterivian three important phases of platform drowning, phosphogenesis and mesotrophic carbonate deposition along the northern margin of the Tethys are not mirrored by positive N 13 Ccarb excursions such as during the Valanginian and Aptian, but rather by decreasing to stable trends. The aim of this study is to understand the decoupling of organic carbon and phosphorus burial during the Hauterivian. For this purpose PO4-concentrations were determined from biogenic limestones from eight sections along a platform to basin transect. Integration with a previously obtained dataset for the Valanginian leads to a biostratigraphically calibrated high resolution phosphorus accumulation rate (mg/cm 2 /kyr) curve based on 575 data points. From the Late Valanginian to Early Hauterivian phosphorus accumulation rates increased nearly threefold from 0.75 mg/cm 2 /kyr to 2.1 mg/cm 2 /kyr. The phosphorus accumulation rate increase obtained in this study correlates well with a compilation based on ODP and DSDP records, indicating that phosphorus accumulation rates along the northern margin of the Tethys reflect global changes in P in- and output. A global rise in continental P input is thought to have resulted from intensified greenhouse climate conditions leading to increased riverine runoff. Coeval sea-level rise led to re-arrangement of circulation and oxygenation of bottom waters, which meant that P was increasingly well retained by means of Fe- and Mnoxyhydroxides. Furthermore, the NW margin of the Tethys may have been especially susceptible to phosphogenesis as it was influenced by cold water exchange with the Boreal Realm and prone to coastal upwelling. The Late Hauterivian witnessed sea-level fall, more sluggish circulation along the NW Tethyan margin and also globally lower weathering and erosion rates, leading to generally lower phosphorus accumulation rates. Increased regeneration of phosphorus might have occurred as circulation stagnated and bottom water oxygen levels decreased. Increased phosphorus input into Early Hauterivian oceans did not lead to the production of organic carbon-rich rocks, but rather to increased carbonate carbon burial, also seen in a decoupling between the N 13 Ccarb record (decreasing) and phosphorus accumulation rates (increasing). Decoupling of these records reflects the ecological recovery of the carbonate system after a prolonged phase of reef destruction during the late Early and Late Valanginian. Carbonate production in the

Dysaerobic conditions during Heinrich events 4 and 5: Evidence from phosphorus distribution in a North Atlantic deep-sea core

Abstract Reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments. The degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions, which may be linked to larger scale phenomena, such as bottom water circulation, water column ventilation, and organic carbon flux. Phosphorus phases of the

Carbonaceous and Phosphate-Rich Sediments of the Miocene Monterey Formation at El Capitan State Beach, California, U.S.A.

ABSTRACT The organic- and phosphate-rich interval of the Monterey Formation at El Capitan State Beach (west of Santa Barbara, California, U.S.A.; late early to early late Miocene in age) is composed of a carbonaceous marl (TOC contents between 1.2 and 23.2 wt %) with intercalated phosphate-rich laminae, lenses, and layers. Subordinate lithologies include ash layers, dolomitized horizons, and siliceous beds. We distinguished five lithological units: (1) a gray marl unit lacking major phosphate accumulations (> 16.3 Ma; average TOC content 2% by weight; average sedimentation rate 75 m/My; average TOC accumulation rate 0.19 mg/cm2/yr); (2) a black marl unit including light-colored phosphatic laminae, lenses, and discrete particles (16.3-14.5 Ma; average TOC content 7.5% by weight; average sedimentation rate 20 m/My; average TOC accumulation rate 0.19 mg/cm2/yr); (3) a red marl unit including light-colored phosphatic laminae, lenses, and commonly reworked particles (14.5-12.7 Ma; average TOC content 15% by weight; average sedimentation rate 20 m/My (14.5-13.3 Ma) and 2 m/My (13.3-12.7 Ma), respectively; average TOC accumulation rate 0.39 mg/cm2/yr (14.5-13.3 Ma) and 0.04 mg/cm2/yr (13.3-12.7 Ma), respectively); (4) a unit of complex and condensed phosphatic beds, interbedded with red marl (12.7-10.8 Ma; average sedimentation rate 3 m/My); and (5) a black marl unit with intercalated phosphatic laminae and lenses (< 10.8 Ma; average sedimentation rate 9 m/My; average TOC accumulation rate 0.09 mg/cm2/yr). Phosphogenesis and accumulation of phosphate were dynamic processes, which started with local phosphogenesis leading to the formation of phosphatized particles, as well as stratigraphically bound phosphogenesis leading to the formation of phosphate laminae and lenses. Phases of subsequent sediment reworking resulted in the concentration of phosphate particles in phosphate-rich layers, and repeated phases of sediment reworking and phosphogenesis ultimately resulted in the formation of the complex phosphate condensed horizons. Preservation of organic matter was favored by high productivity rates and by the development of dysaerobic bottom-water conditions. The dynamic sedimentary environment likely led to the formation of early diagenetic phosphatic lids (which may have sealed off subjacent organic-rich layers) as well as to the rapid deposition of entire layers in the form of mud flows, thereby eventually enhancing the potential of organic-matter preservation. Our new age data suggest that at the El Capitan State Beach section the intervals characterized by high TOC values and maximum TOC accumulation rates (red marl), as well as significant quantities of in situ phosphates appeared in the late middle Miocene, i.e., during and after the major cooling phase at around 14.5 Ma. This implies that deposition of phosphate and organic carbon continued well after this cooling phase, thereby underlining the observation that preservation of organic carbon in the Monterey Formation is not only dependent on climate change during the mid Miocene but also on regional conditions.

Anthropogenic radionuclides in atmospheric air over Switzerland during the last few decades

The atmospheric nuclear testing in the 1950s and early 1960s and the burn-up of the SNAP-9A satellite led to large injections of radionuclides into the stratosphere. It is generally accepted that current levels of plutonium and caesium radionuclides in the stratosphere are negligible. Here we show that those radionuclides are present in the stratosphere at higher levels than in the troposphere. The lower content in the troposphere reveals that dry and wet deposition efficiently removes radionuclides within a period of a few weeks to months. Since the stratosphere is thermally stratified and separated from the troposphere by the tropopause, radioactive aerosols remain longer. We estimate a mean residence time for plutonium and caesium radionuclides in the stratosphere of 2.5-5 years. Our results also reveal that strong volcanic eruptions like Eyjafjallajökull in 2010 have an important role in redistributing anthropogenic radionuclides from the stratosphere to the troposphere.

Atmospheric deposition and migration of artificial radionuclides in Alpine soils (Val Piora, Switzerland) compared to the distribution of selected major and trace elements.

Artificial radionuclides ((137)Cs, (90)Sr, Pu, and (241)Am) are present in soils because of Nuclear Weapon Tests and accidents in nuclear facilities. Their distribution in soil depth varies according to soil characteristics, their own chemical properties, and their deposition history. For this project, we studied the atmospheric deposition of (137)Cs, (90)Sr, Pu, (241)Am, (210)Pb, and stable Pb. We compared the distribution of these elements in soil profiles from different soil types from an alpine Valley (Val Piora, Switzerland) with the distribution of selected major and trace elements in the same soils. Our goals were to explain the distribution of the radioisotopes as a function of soil parameters and to identify stable elements with analogous behaviors. We found that Pu and (241)Am are relatively immobile and accumulate in the topsoil. In all soils, (90)Sr is more mobile and shows some accumulations at depth into Fe-Al rich horizons. This behavior is also observed for Cu and Zn, indicating that these elements may be used as chemical analogues for the migration of (90)Sr into the soil.

Disparity in 90Sr and 137Cs uptake in Alpine plants: phylogenetic effect and Ca and K availability

Background and aimsUptake of 90Sr and 137Cs in plants varies widely between soil types and between plant species. It is now recognized that the radionuclide uptake in plants is more influenced by site-specific and plant-specific parameters rather than the bulk radionuclide concentration in soil. We hypothesized that the stress which Alpine plants experience because of the short growing season may enhance the phylogenetic effect on the 137Cs and 90Sr transfer factors as well as the dependency of the uptake by plant to the concentrations of exchangeable Ca and K of soils.MethodsWe carried out a field study on the 90Sr and 137Cs uptake by 11 species of Alpine plants growing on 6 undisturbed and geochemically different soils in the Alpine valley of Piora, Switzerland.ResultsResults show that a strong correlation exists between the log TF and the log of exchangeable Ca or K of the soils.ConclusionsCs uptake by Phleum rhaeticum (Poales) and Alchemilla xanthochlora (Rosales) is more sensitive to the amount of exchangeable K in the soil than the corresponding uptake by other orders. Moreover, the 90Sr results indicate a phylogenetic effect between Non-Eudicot and Eudicots: the order Poales (Phleum rhaeticum) concentrating much less 90Sr than Eudicots do.

Recent changes in sedimentary organic matter from Lake Neuchâtel (Switzerland) as traced by Rock-Eval pyrolysis

Recent changes in the composition of sedimentary organic material (OM) from a well-oxygenated lake (Lake Neuchâtel, Switzerland) were investigated using the new generation Rock-Eval pyrolysis (Re6). Although Re6 offers a range of new analytical parameters, the classical hydrogen and oxygen indices (HI and OI) prove to be most useful for the kind of material analysed. For a rapid screening of lake sediment cores we propose an additional parameter, POI=S3/(S 1+S2a), which reflects most of the observed changes in the nature of the OM, but can be calculated from the pyrolysis step alone.