The rise and evolution of large vascular land plants (mainly trees) during the mid-to-late Palaeozoic resulted in increased consumption of atmospheric CO2 by accelerated silicate rock weathering followed by further consumption due to increased terrestrially-derived organic matter burial in sediments, with the latter accompanied by increased production of O2. Changes in CO2 and O2 have been treated theoretically in terms of carbon- and sulphur-cycle modelling (Berner and Kothavala, 2001; Berner, 2006a,b). The CO2 modelling rests on the palaeobotanical record, field observations of the effect of trees on the rate of modern silicate weathering, and calculation of global organic matter burial based on the carbon isotopic record derived from carbonate fossils.

We present a dust flux (g m-2yr-1) record for the East Mediterranean Sea constructed using 87Sr/86Sr ratio measurements on the fine fraction of carbonate-free sediment from core 9501 from the north Levantine basin. The Saharan dust flux profile shows a first order correspondence with Atlantic dust-flux records in showing: (1) small dust fluxes during the last glacial maximum, a dust pulse associated with the Heinrich 1 (H1) event; (2) a small peak corresponding with the younger dryas (YD); (3) a decrease during the African Humid Period (AHP); and (4) an abrupt return to dustier conditions between ~5.7—5.2 ky BP.

In oxic waters, dissolved Fe exists dominantly as Fe(III) complexes with strongly coordinating, siderophore-like ligands. In this study, we have determined an equilibrium Fe isotope fractionation of 0.6% (∆56Fe) between inorganic Fe(III) and Fe(III) siderophore complexes using the siderophore desferrioxamine B as a model compound. The 57Fe tracer experiments show that the Fe isotopes ofthe siderophores exchange readily with dissolved inorganic Fe. The results indicate that organic ligands are likely to be important in the generation ofFe isotope signatures in oxic environments. For example, the isotopic composition ofmarine Fe-Mn nodules may largely be due to the presence of strongly coordinating ligands.

Long-term climate moderation is commonly attributed to chemical weathering; the greater the temperature and precipitation the faster the weathering rate. To test this widely-held hypothesis, we performed a field study and determined the weathering rates of eight nearly pristine north-east Iceland river catchments with varying glacial cover over 44 y. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all eight catchments and between mean annual temperature and mechanical weathering and runoff in seven of the eight catchments. The runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14%, respectively, depending on the catchment for each degree of temperature increase. Positive correlations were found between time and mechanical and chemical weathering for all catchments. In summary, these results demonstrate a significant feedback between climate and Earth surface weathering, and suggest that this weathering rate is currently increasing with time due to global warming.

U-series were investigated in groundwaters from two water bodies of the Eocene sands aquifer, southwest France. The 234U/238U activity ratios are always larger than the equilibrium value, some waters being highly enriched in 234U (as large as 13.5). In the southern water body, 234U/238U ratios correlate with 14C ages (with one exception). Such U isotopic signatures may allow the evaluation of the residence time of groundwaters within their aquifer using an open-system model based on U activity ratios and concentrations. It is suggested that the ‘oldest’ groundwaters from the southern water body are no older than 38 ky, whereas the maximum ‘age’ of groundwaters from the northern water body, though overall of the same order of magnitude, could be slightly younger (25 ky).

The Costa Rican forearc is characterized by active fluid venting related to mud diapirism and volcanism. The geochemical compositions of fluids obtained from dewatering sites indicate that mineral precipitation or dehydration is the major driver of fluid mobilization and upward migration. The peculiar situation at the latter sites is that Ca concentrations in the upward migrating fluids are well above seawater levels. In turn, these Ca-enriched fluids could offer a potential reason for widespread carbonate caps on top of the mounds.

The essential state of the Phanerozoic ocean-atmosphere system with respect to major lithophile and organic components can be bounded by sedimentary observational data and relatively few model assumptions. The model assumptions are in turn sufficient to constrain and compute the remaining fluxes that result in a comprehensive model describing atmospheric and oceanic evolutionary history over the past 500 m.y. that is in accord with the sedimentary observational data. Two central themes emerge. First, there is a strong coupling of the state of various reservoirs throughout the entire system imposed mainly by negative physical, chemical and biological feedbacks. Second, there is a significant overprint of ‘physical’ processes, such as weathering, by biologically-mediated processes and ecosystem evolution. Ultimately, the Phanerozoic is characterized by two modes of seawater major-ion chemistry, pH and carbonate saturation state, and atmospheric CO2. Importantly, the transition between these two modes may result from the previous state of the system whose impacts lag by tens of millions of years. Thus, the instantaneous state of the system at any given point in time may reflect in part the ‘memory’ ofa previous period when fluxes and processes were not in balance. The modern-day problem of ocean acidification mainly reflects the fact that human activities of fossil fuel burning and land use changes are resulting in geologically rapid releases of CO2 to the atmosphere and its absorption by the surface ocean and does not reflect the longer term processes and feedbacks that led to the acidic oceans of the past.

Results from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as well as chain character and length. The analysed crystals showed a narrow size range (~14—67 nm) with an average diameter of 46±6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range.

A survey of the surface-area-normalized dissolution rates of major phosphate bearing minerals shows these rates to vary by >8 orders of magnitude with a general dissolution-rate trend sturvite > britholite ∼ fluoroapatite > variscite > monazite ∼ rhabdophane. This trend reflects the relative strength of the metal-oxygen bonds holding together the phosphate tetrahedra in the mineral structure. Due to the high surface-area-normalized reactivity of fluoroapatite, and the high surface area of natural variscite and rhabdophane, it seems likely that these minerals buffer the concentration of P and the rare-earth elements in many natural waters. As such, the solubility of these minerals plays a significant role in the global phosphorus cycle, and may potentially provide clues for future sustainable phosphorus use.

Our study focused on the investigation of climate change and the fate of lead in soils from the Low Volga region of Russia over 3500 years. We used a comparative analysis of the modern soils and palaeosols preserved under burial mounds, which date back to the Middle Ages and the Early Iron and Bronze Ages. A climate reconstruction showed periodic changes, with the most humid climate conditions occurring during Golden Horde period. However, we could not find any consistent changes in Pb concentration and profile distribution following the climate change. We observed a clear difference in Pb isotopic ratios between the lower and upper horizons both for the modern and buried profiles, reflecting the influence of atmospheric lead depositions. However, there is no statistically significant difference in Pb isotopic ratios between the upper horizons of buried and modern soils (except modern soils collected in the vicinity of a motorway). This means that either anthropogenic input due to long range air transport was insignificant, or that airborne anthropogenic lead and natural airborne lead have similar isotopic composition.

Ice-hosted sediments in glaciers and icebergs from Antarctica and Svalbard contain authigenic nanoparticulates of schwertmannite, ferrihydrite and goethite that formed during sulphide oxidation. These phases indicate the existence of subglacial biogeochemical hotspots containing fluids of low pH (2—4), rich in dissolved Fe(III) and sulphate. Nanophase Fe is partially bioavailable and potentially important to global biogeochemical cycles, since the flux delivered by icebergs to the Southern Ocean is comparable to the flux of soluble, bioavailable Fe from aeolian dust.

The dissolution rates of natural well-crystallized variscite (AlPO4.2H2O) were measured from the evolution of aqueous Al and P concentrations in closed and mixed-flow through reactors at 25°C and from 1.5 to 9 pH. Measured dissolution rates decrease with increasing pH from 5.05x10-16 mol/cm2/s at pH = 1.51 to 4.92x10-17 mol/cm2/s at pH = 5.89 and then increase with increasing pH to 1.64x10-17 mol/cm2/s at pH = 8.99. Estimates of the time required to equilibrate a mildly acidic, initially Al- and P-free solution with variscite based on measured dissolution rates and solubility products suggests it takes no more than several weeks to equilibrate this mineral with soil pore fluids. This result suggests that variscite can buffer aqueous phosphate concentrations in a significant number of near surface environments.

Preliminary atomic force microscopy investigations of the {104} calcite surface cleaved in ethanol indicate a different surface behaviour than that of the {104} surface cleaved in air. The results are consistent with recent theoretical studies and suggest strong ordering of ethanol over the termination of the bulk calcite structure.

Over the last ∼200 years, since the start of the industrial revolution, the increase in the burning of fossil fuels, cement manufacturing and changes to land use has increased atmospheric CO2 concentrations from ∼80 to 385 ppm. These are the highest levels experienced on Earth for at least the last 800,000 years, possibly for the past 10’s of millions of years. The 2007 IPCC report on climate change predicts a continued rapid rise in atmospheric CO2 leading to significant temperature increases in the atmosphere and ocean in the coming decades, as well as other climate changes. The IPCC (2007) also reports, for the first time, that increasing anthropogenic CO2 will result in increased acidity of the world’s surface oceans. This process is already happening and further rapid decreases in ocean pH will occur this century, concomitantly with warming seas, creating multiple threats to the marine environment. The future addition of massive amounts of CO2 to surface waters will have a profound impact on ocean chemistry and could have an equally profound impact on biogeochemical cycles, marine organisms, ecosystems and the services they provide. ‘Ocean acidification’ is a strong additional argument to that of climate change for urgent and substantial reduction of CO2 emissions.

Two sediment cores retrieved at the northern slope of Sakhalin Island, Sea of Okhotsk, were analysed for biogenic opal, organic carbon, carbonate, sulphur, major element concentrations, mineral contents and dissolved substances including nutrients, sulphate, methane, major cations, humic substances and total alkalinity. Down-core trends in mineral abundance suggest that plagioclase feldspars and other reactive silicate phases (olivine, pyroxene, volcanic ash) are transformed into smectite in the methanogenic sediment sections. The element ratios Na/Al, Mg/Al and Ca/Al in the solid phase decrease with sediment depth indicating a loss of mobile cations with depth and producing a significant down-core increase in the chemical index of alteration.

Assessing metal contamination of soils has been a difficult task because the metal concentration in soil is not directly correlated to its potential effects. We review an approach, termed the Terrestrial Biotic Ligand Model (TBLM), in which partitioning of metal from soil to soil solution is modelled and the metal in solution interacts with an organism, the biotic ligand, to cause toxicity. The toxicity is modulated by other cations in the soil solution, principally H+, Ca2+, and Mg2+. New results for the model using Ni as the toxic species and barley root elongation as the biological response are presented.

Water supplies from chalk aquifers in northern Europe can be contaminated by semi-metals such as As and metals such as Cr, Ni and many more, as a result of leaks from landfills, industrial sites and from natural oxidation of pyrite in the chalk, releasing trace elements. Chalk, which is predominantly calcite (CaCO3), has the ability to immobilize Ni, but its uptake by chalk is sometimes greater than expected. In an attempt to identify the controls on metal uptake, chalk samples from Klintholm I/S (Fyn, Denmark) were decalcified in EDTA solution and the residue was examined with transmission electron microscopy (TEM) for morphology and composition. Energy dispersive X-ray spectrometry (EDXS) revealed minor Si and Al (probably clay) and major Mn and Fe as (hydr)oxides. These natural nanoparticles have very large surface areas contributing to chalk’s uptake capacity for Ni and other metals from groundwater.

Nickel can cause allergic reactions so it is often considered to be a toxic metal. In some areas of Denmark and northern Europe, where drinking water comes predominantly from chalk aquifers, Ni concentrations in groundwater are higher than safety limits. The contamination is natural in the sense that it comes from oxidation of small grains of pyrite in the chalk that contain Ni as a trace element (Larsen and Postma, 1997). Because of Danish water-treatment practice, the most politically acceptable water-supply protocol is not to use secondary water treatment, so in order to minimize allergy risks for consumers, high-Ni water is either mixed with low-Ni water to bring concentrations below the Danish limit, or new, uncontaminated wells are drilled. Some recent efforts focused on finding a method to minimize nickel concentration while the water is still in the ground, before it is pumped to the primary treatment facility and distributed.

Unfortunately, only a few experimental studies of the interactions between Ni and calcite have been published (Lakshtanov and Stipp, 2007; Zachara et al., 1991; Hoffmann and Stipp, 2001) and we found no previous work on Ni uptake by chalk. Experiments with calcite show that Ni forms surface complexes and it is incorporated into the solid as solid solution. Chalk aquifers often contain as much as 99% calcite, so the same processes ought to control Ni uptake, but some very preliminary experiments suggested that chalk behaviour might not be what one would expect by analogy with calcite (Stipp et al., 2005). The aim of this study was to examine the Ni-uptake capacity of chalk and compare it with that of synthetic, pure calcite.

Uranium is a redox-sensitive element and can be immobilized by reduction from soluble U(VI) to insoluble U(IV). By performing flow-through experiments, uranium mobility was observed under different redox conditions. Inflow solutions with different electron acceptors, nitrate and sulphate, and a control inflow solution were used to obtain different sedimentary redox conditions. Uranium was about one order more mobile when nitrate was used than when sulphate or the control was used. The difference in uranium mobility is attributed to the reduction of uranium. Even though uranium mobility is heavily dependent on the redox state of uranium, sedimentary concentrations of organic matter argue that organic matter is the most important complexing agent and that this determines the retardation of uranium.

In this paper, the kinetics of Mo and V (100 μM) uptake on ferrihydrite (FHY) were evaluated in batch, mono-sorbate systems at pH between 4 and 9, and in bi-sorbate systems in the presence of P (100 μM) at pH 7. In the Mo and V single-sorbate experiments, 100% adsorption was observed at pH values below 6 and 8, respectively. Above the point of zero charge (PZC = 7.97) of FHY, the adsorption efficiency for Mo dropped dramatically (20% at pH 8) while V showed high uptake efficiencies even at pH 9 (60% efficiency). The results from the bi-sorbate experiments (Mo-P and V-P) showed that at pH 7, P out-competed (97%) Mo for binding sites on FHY, while in the V-P binary system only ∼44% of the binding sites are occupied by P with the remaining sites being occupied by V.