Eiriksdottir E.S.,Institute of Earth science |
Gislason S.R.,Institute of Earth science |
Oelkers E.H.,University Paul Sabatier
Applied Geochemistry | Year: 2011
The rate of chemical denudation is controlled by both temperature and runoff. The relative role of these two factors in the rivers of NE Iceland is determined through the rigorous analysis of their water chemistry over a 5-a period. River catchments are taken to be analogous to laboratory flow reactors; like the fluid in flow reactors, the loss of each dissolved element in river water is the sum of that of the original rainwater plus that added from kinetically controlled dissolution and precipitation reactions. Consideration of the laboratory determined dissolution rate behaviour of basalts and measured water chemistry indicates that the maximum effect of changing temperature on chemical denudation in the NE Icelandic rivers was 5-25% of the total change, whereas that of runoff was 75-95%. The bulk of the increased denudation rates with runoff appear to stem from an increase in reactive surface area for chemical weathering of catchment solids. © 2011 Elsevier Ltd.
Oelkers E.H.,University Paul Sabatier |
Gislason S.R.,Institute of Earth science |
Eiriksdottir E.S.,Institute of Earth science |
Jones M.,Institute of Earth science |
And 2 more authors.
Applied Geochemistry | Year: 2011
A review of the relative masses of continental weathering products transported to the oceans indicates that particulate fluxes dominate dissolved fluxes for most elements. The degree to which this particulate material plays a role in the compositional evolution of seawater depends on its dissolution rate, which appears to be rapid due to its high surface area. Consideration of the results of batch experiments and mineral saturation state calculations suggest that much of the mass dissolved into seawater from particulate material dissolution is rapidly removed by the precipitation of secondary minerals. Although this process limits the degree to which the overall concentration of elements in seawater are affected by the addition of particulate material, the dissolution of isotopically distinct particulate phases may affect the isotopic composition of seawater over remarkably short timescales. © 2011 Elsevier Ltd.
Watts A.B.,University of Oxford |
Nomikou P.,National and Kapodistrian University of Athens |
Moore J.D.P.,University of Oxford |
Parks M.M.,Institute of Earth science |
Alexandri M.,Hellenic Center for Marine Research
Geochemistry, Geophysics, Geosystems | Year: 2015
Historical bathymetric charts are a potential resource for better understanding the dynamics of the seafloor and the role of active processes, such as submarine volcanism. The British Admiralty, for example, have been involved in lead line measurements of seafloor depth since the early 1790s. Here, we report on an analysis of historical charts in the region of Santorini volcano, Greece. Repeat lead line surveys in 1848, late 1866, and 1925-1928 as well as multibeam swath bathymetry surveys in 2001 and 2006 have been used to document changes in seafloor depth. These data reveal that the flanks of the Kameni Islands, a dacitic dome complex in the caldera center, have shallowed by up to ∼175 m and deepened by up to ∼80 m since 1848. The largest shallowing occurred between the late 1866 and 1925-1928 surveys and the largest deepening occurred during the 1925-1928 and 2001 and 2006 surveys. The shallowing is attributed to the emplacement of lavas during effusive eruptions in both 1866-1870 and 1925-1928 at rates of up to 0.18 and 0.05 km3 a-1, respectively. The deepening is attributed to a load-induced viscoelastic stress relaxation following the 1866-1870 and 1925-1928 lava eruptions. The elastic thickness and viscosity that best fits the observed deepening are 1.0 km and ∼1016 Pa s, respectively. This parameter pair, which is consistent with the predictions of a shallow magma chamber thermal model, explains both the amplitude and wavelength of the historical bathymetric data and the present day rate of subsidence inferred from InSAR analysis. © 2015. The Authors.
Lin K.-C.,National Taiwan University |
Lin K.-C.,Seismological Observation Center |
Hu J.-C.,National Taiwan University |
Ching K.-E.,National Cheng Kung University |
And 6 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2010
Using data at 110 continuous GPS stations from 1 January 2003 to 31 December 2005, we characterized the surface deformation in Taiwan after the Mw = 7.6 Chi-Chi earthquake of 21 September 1999. In continuous GPS (CGPS) data, the maximum coseismic deformation of the Chengkung earthquake and Ilan double earthquakes reached 165.5 0.5 mm and 35.4 0.5 mm in horizontal displacement and 181.7 1.1 mm and 12.6 1.5 mm in vertical displacement, respectively. With respect to Paisha station, S01R, the stations of the Coastal Range and Lanhsu showed an average displacement of 40.5-93.6 mm/yr with directions of 307-333. The stations in the Longitudinal Valley and Central Range revealed velocities in the range 19.0-49.3 mm/yr with directions of 285-318. In western Taiwan, the velocities in the inner fold-and-thrust belt range from 14.2 to 45.5 mm/yr with directions of 284-304. Extensional strain affects the Ilan and Pingtung plains near belt tips, revealing lateral extrusion toward the adjacent subduction zones. Extensional strain also affects the southern Central Range because of the rapid uplift related to the southward propagating collision process. Large and medium size earthquakes affect the strain pattern revealed by CGPS, albeit in different ways: regional extension and displacement were large and rotations were small regarding the Mw = 7.6 Chi-Chi earthquake. In contrast, the limited size of the affected area, moderate displacement, and large rotations characterized the 2003 Mw = 6.8 Chengkung earthquake. The impact of smaller earthquakes such as the 2005 M w = 5.9 Ilan double earthquakes and the 2005 Mw = 5.6 Hualien earthquake was locally significant but regionally minor. The CGPS data provide a snapshot of the deformation that is generally consistent with the long-term history of the collision but should not be directly extrapolated because thrust deformation is migrating along the tectonic boundary. Regarding the Chi-Chi earthquake, the new CGPS data show that the Chi-Chi hanging wall is still recognizable as a kinematic block, whereas in the previous pattern the hanging wall was not discernable. © 2010 by the American Geophysical Union.
McRoberts W.C.,Agri Food and Biosciences Institute of Northern Ireland |
Keppler F.,Institute of Earth science |
Harper D.B.,Queen's University of Belfast |
Hamilton J.T.G.,Queen's University of Belfast
Environmental Chemistry | Year: 2015
Environmental context Chloromethane is the most abundant naturally produced chlorine-containing organic compound, responsible for ∼16% of chlorine-catalysed stratospheric ozone destruction. A significant source of this gas is emission from biomass by reaction between chloride ion and methoxyl groups of the biopolymers pectin and lignin. The seasonal changes in the chlorine and methoxyl pools observed in leaves of several deciduous tree species have implications for understanding chlorine volatilisation during biomass burning and estimation of the global chloromethane budget. Abstract Atmospheric chloromethane (CH3Cl) plays a role in the destruction of stratospheric ozone. Previous studies suggest an important source of this gas is emission from leaves and leaf litter at ambient and elevated (150-350°C) temperatures. In this study, the total chlorine and OCH3 content of leaves of the deciduous temperate tree species ash, beech, Norway maple and oak were measured throughout the 2004 and 2005 growing seasons. The total chlorine content increased with leaf age. The overall seasonal accumulation varied between five- and twenty-one fold, dependent on both year and species. Throughout the 2004 growing season, the OCH3 pool and the release of CH3Cl and methanol (CH3OH) from leaves of ash and Norway maple were monitored on heating to 350°C. The amounts of CH3Cl released increased linearly as leaf chlorine accumulated whereas emissions of CH3OH did not substantially change. Conversion of chlorine to CH3Cl was lower in the spring than during the summer and autumnal senescence period, ranging from 22 to 58%. No correlation was found between leaf OCH3 content and either CH3Cl or CH3OH release. The percentage conversion of OCH3 to the summed concentrations of CH3OH and CH3Cl ranged from 41 to 66%. The plant components pectin and lignin were identified as two major sources of the CH3 group in CH3Cl and CH3OH and emissions ceased when the OCH3 pool contributing the methyl moiety was exhausted (>350°C). These findings have implications for estimation of CH3Cl release during biomass burning and for our understanding of chlorine volatilisation during energy production from biomass.
Rae J.G.L.,UK Met Office |
Aoalgeirsdottir G.,Danish Meteorological Institute |
Aoalgeirsdottir G.,Institute of Earth science |
Edwards T.L.,University of Bristol |
And 14 more authors.
Cryosphere | Year: 2012
Four high-resolution regional climate models (RCMs) have been set up for the area of Greenland, with the aim of providing future projections of Greenland ice sheet surface mass balance (SMB), and its contribution to sea level rise, with greater accuracy than is possible from coarser-resolution general circulation models (GCMs). This is the first time an intercomparison has been carried out of RCM results for Greenland climate and SMB. Output from RCM simulations for the recent past with the four RCMs is evaluated against available observations. The evaluation highlights the importance of using a detailed snow physics scheme, especially regarding the representations of albedo and meltwater refreezing. Simulations with three of the RCMs for the 21st century using SRES scenario A1B from two GCMs produce trends of between-5.5 and-1.1 Gt yr-2 in SMB (equivalent to +0.015 and +0.003 mm sea level equivalent yr-2), with trends of smaller magnitude for scenario E1, in which emissions are mitigated. Results from one of the RCMs whose present-day simulation is most realistic indicate that an annual mean near-surface air temperature increase over Greenland of ∼ 2° C would be required for the mass loss to increase such that it exceeds accumulation, thereby causing the SMB to become negative, which has been suggested as a threshold beyond which the ice sheet would eventually be eliminated. © 2012 Author(s).
Vrijmoed J.C.,Institute of Earth science |
Vrijmoed J.C.,ETH Zurich |
Podladchikov Y.Y.,Institute of Earth science
Contributions to Mineralogy and Petrology | Year: 2015
Recent advances in metamorphic petrology point out the importance of grain-scale pressure variations in high-temperature metamorphic rocks. Pressure derived from chemical zonation using unconventional geobarometry based on equal chemical potentials fits mechanically feasible pressure variations. Here, a thermodynamic equilibrium method is presented that predicts chemical zoning as a result of pressure variations by Gibbs energy minimization. Equilibrium thermodynamic prediction of the chemical zoning in the case of pressure heterogeneity is done by constrained Gibbs minimization using linear programming techniques. In addition to constraining the system composition, a certain proportion of the system is constrained at a specified pressure. Input pressure variations need to be discretized, and each discrete pressure defines an additional constraint for the minimization. The Gibbs minimization method provides identical results to a geobarometry approach based on chemical potentials, thus validating the inferred pressure gradient. The thermodynamic consistency of the calculation is supported by the similar result obtained from two different approaches. In addition, the method can be used for multi-component, multi-phase systems of which several applications are given. A good fit to natural observations in multi-phase, multi-component systems demonstrates the possibility to explain phase assemblages and zoning by spatial pressure variations at equilibrium as an alternative to pressure variation in time due to disequilibrium. © 2015, Springer-Verlag Berlin Heidelberg.
Nandedkar R.H.,ETH Zurich |
Ulmer P.,ETH Zurich |
Muntener O.,Institute of Earth science
Contributions to Mineralogy and Petrology | Year: 2014
Differentiation of mantle-derived, hydrous, basaltic magmas is a fundamental process to produce evolved intermediate to SiO2-rich magmas that form the bulk of the middle to shallow continental and island arc crust. This study reports the results of fractional crystallization experiments conducted in a piston cylinder apparatus at 0.7 GPa for hydrous, calc-alkaline to arc tholeiitic magmas. Fractional crystallization was approached by synthesis of starting materials representing the liquid composition of the previous, higher temperature experiment. Temperatures ranged from near-liquidus at 1,170 °C to near-solidus conditions at 700 °C. H2O contents varied from 3.0 to more than 10 wt%. The liquid line of descent covers the entire compositional range from olivine-tholeiite (1,170 °C) to high-silica rhyolite (700 °C) and evolves from metaluminous to peraluminous compositions. The following crystallization sequence has been established: olivine → clinopyroxene → plagioclase, spinel → orthopyroxene, amphibole, titanomagnetite → apatite → quartz, biotite. Anorthite-rich plagioclase and spinel are responsible for a marked increase in SiO2-content (from 51 to 53 wt%) at 1,040 °C. At lower temperatures, fractionation of amphibole, plagioclase and Fe-Ti oxide over a temperature interval of 280 °C drives the SiO2 content continuously from 53 to 78 wt%. Largest crystallization steps were recorded around 1,040 °C and at 700 °C. About 40 % of ultramafic plutonic rocks have to crystallize to generate basaltic-andesitic liquids, and an additional 40 % of amphibole-gabbroic cumulate to produce granitic melts. Andesitic liquids with a liquidus temperature of 1,010 °C only crystallize 50 % over an 280 °C wide range to 730 °C implying that such liquids form mobile crystal mushes (<50 % crystals) in long-lived magmatic systems in the middle crust, allowing for extensive fractionation, assimilation and hybridization with periodic replenishment of more mafic magmas from deeper magma reservoirs. © 2014 Springer-Verlag Berlin Heidelberg.
Jakobsson S.,Institute of Earth science |
Blundy J.,University of Bristol |
Moore G.,University of Michigan
Contributions to Mineralogy and Petrology | Year: 2014
Jakobsson (Contrib Miner Petrol 164(3):397-407, 2012) investigated a double capsule assembly for use in piston-cylinder experiments that would allow hydrous, high-temperature, and high-pressure experiments to be conducted under controlled oxygen fugacity conditions. Using a platinum outer capsule containing a metal oxide oxygen buffer (Ni-NiO or Co-CoO) and H2O, with an inner gold-palladium capsule containing hydrous melt, this study was able to compare the oxygen fugacity imposed by the outer capsule oxygen buffer with an oxygen fugacity estimated by the AuPdFe ternary system calibrated by Barr and Grove (Contrib Miner Petrol 160(5):631-643, 2010). H2O loss or gain, as well as iron loss to the capsule walls and carbon contamination, is often observed in piston-cylinder experiments and often go unexplained. Only a few have attempted to actually quantify various aspects of these changes (Brooker et al. in Am Miner 83(9-10):985-994, 1998; Truckenbrodt and Johannes in Am Miner 84:1333-1335, 1999). It was one of the goals of Jakobsson (Contrib Miner Petrol 164(3):397-407, 2012) to address these issues by using and testing the AuPdFe solution model of Barr and Grove (Contrib Miner Petrol 160(5):631-643, 2010), as well as to constrain the oxygen fugacity of the inner capsule. The oxygen fugacities of the analyzed melts were assumed to be equal to those of the solid Ni-NiO and Co-CoO buffers, which is incorrect since the melts are all undersaturated in H2O and the oxygen fugacities should therefore be lower than that of the buffer by 2 log aH2O. © 2014 Springer-Verlag Berlin Heidelberg.
Lepori F.,Institute of Earth science |
Pozzoni M.,Institute of Earth science |
Pera S.,Institute of Earth science
River Research and Applications | Year: 2015
We investigated the effects of climate warming and land-use changes on the temperature and discharge of seven Swiss and Italian streams in the catchment of Lake Lugano. In addition, we attempted to predict future stream conditions based on regional climate scenarios. Between 1976 and 2012, the study streams warmed by 1.5-4.3°C, whereas discharge showed no long-term trends. Warming trends were driven mainly by catchment urbanization and two large-scale climatic oscillations, the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. In comparison, independent influences by radiative forcing due to increased atmospheric CO2 were uncertain. However, radiative forcing was predicted to further increase stream temperature (to +3-7°C), reduce summer discharge (to -46%) and increase winter discharge (to +96%) between the present and 2070-2099. These results provide new insights into the drivers of long-term temperature and discharge trends in European streams subject to multiple impacts. The picture emerging is one of transition, where greenhouse-gas forcing is gaining ground over climate oscillations and urbanization, the drivers of past trends. This shift would impress a more directional nature upon future changes in stream temperature and discharge, and extend anthropogenic warming to rural streams. Diffusing future impacts on stream ecosystems would require adaptation measures at local to national scales and mitigation of greenhouse-gas emissions at the global scale. © 2014 John Wiley & Sons, Ltd.