On the influence of kriging parameters on the cartographic output—A study in mapping subglacial topography

Geostatistics provides a suite of methods, summarized as kriging, to analyze a finite data set to describe a continuous property of the Earth. Kriging methods consist of moving window optimum estimation techniques, which are based on a least-squares principle and use a spatial structure function, usually the variogram. Applications of kriging techniques have become increasingly wide-spread, with ordinary kriging and universal kriging being the most popular ones. The dependence of the final map or model on the input, however, is not generally understood. Herein we demonstrate how changes in the kriging parameters and the neighborhood search affect the cartographic result. Principles are illustrated through a glaciological study. The objective is to map ice thickness and subglacial topography of Storglaciären, Kebnekaise Massif, northern Sweden, from several sets of radio-echo soundings and hot water drillings. New maps are presented.     

On the potential for CO2 mineral storage in continental flood basalts - PHREEQC batch- and 1D diffusion-reaction simulations

ABSTRACT: Continental flood basalts (CFB) are considered as potential CO2 storage sites because of their high reactivity and abundant divalent metal ions that can potentially trap carbon for geological timescales. Moreover, laterally extensive CFB are found in many place in the world within reasonable distances from major CO2 point emission sources.Based on the mineral and glass composition of the Columbia River Basalt (CRB) we estimated the potential of CFB to store CO2 in secondary carbonates. We simulated the system using kinetic dependent dissolution of primary basalt-minerals (pyroxene, feldspar and glass) and the local equilibrium assumption for secondary phases (weathering products). The simulations were divided into closed-system batch simulations at a constant CO2 pressure of 100?bar with sensitivity studies of temperature and reactive surface area, an evaluation of the reactivity of H2O in scCO2, and finally 1D reactive diffusion simulations giving reactivity at CO2 pressures varying from 0 to 100?bar.Although the uncertainty in reactive surface area and corresponding reaction rates are large, we have estimated the potential for CO2 mineral storage and identified factors that control the maximum extent of carbonation. The simulations showed that formation of carbonates from basalt at 40?C may be limited to the formation of siderite and possibly FeMg carbonates. Calcium was largely consumed by zeolite and oxide instead of forming carbonates. At higher temperatures (60 - 100?C), magnesite is suggested to form together with siderite and ankerite. The maximum potential of CO2 stored as solid carbonates, if CO2 is supplied to the reactions unlimited, is shown to depend on the availability of pore space as the hydration and carbonation reactions increase the solid volume and clog the pore space. For systems such as in the scCO2 phase with limited amount of water, the total carbonation potential is limited by the amount of water present for hydration of basalt.     

Benthic Phosphorus Dynamics in the Gulf of Finland, Baltic Sea

Benthic fluxes of soluble reactive phosphorus (SRP) and dissolved inorganic carbon (DIC) were measured in situ using autonomous landers in the Gulf of Finland in the Baltic Sea, on four expeditions between 2002 and 2005. These measurements together with model estimates of bottom water oxygen conditions were used to compute the magnitude of the yearly integrated benthic SRP flux (also called internal phosphorus load). The yearly integrated benthic SRP flux was found to be almost 10 times larger than the external (river and land sources) phosphorus load. The average SRP flux was 1.25?±?0.56?mmol?m^?2?d^?1 on anoxic bottoms, and ?0.01?±?0.08?mmol?m^?2?d^?1 on oxic bottoms. The bottom water oxygen conditions determined whether the SRP flux was in a high or low regime, and degradation of organic matter (as estimated from benthic DIC fluxes) correlated positively with SRP fluxes on anoxic bottoms. From this correlation, we estimated a potential increase in phosphorus flux of 0.69?±?0.26?mmol?m^?2?d^?1 from presently oxic bottoms, if they would turn anoxic. An almost full annual data set of in situ bottom water oxygen measurements showed high variability of oxygen concentration. Because of this, an estimate of the time which the sediments were exposed to oxygenated overlying bottom water was computed using a coupled thermohydrodynamic ocean?Csea and ecosystem model. Total phosphorus burial rates were calculated from vertical profiles of total phosphorus in sediment and sediment accumulation rates. Recycling and burial efficiencies for phosphorus of 97 and 3%, respectively, were estimated for anoxic accumulation bottoms from a benthic mass balance, which was based on the measured effluxes and burial rates.     

Characterisation of rock aggregate breakage properties using realistic texture‐based modelling

Realistic texture‐based modelling methods, that is microstructural modelling and micromechanical modelling, are developed to simulate the rock aggregate breakage properties on the basis of the rock actual microstructure obtained using microscopic observations and image analysis. The breakage properties of three types of rocks, that is Avja, LEP and Vandle taken from three quarries in Sweden, in single aggregate breakage tests and in inter‐aggregate breakage tests are then modelled using the proposed methods. The microstructural modelling directly integrates the microscopic observation, image analysis and numerical simulation together and provides a valuable tool to investigate the mechanical properties of rock aggregates on the basis of their microstructure properties. The micromechanical modelling takes the most important microstructure properties of rock aggregates into consideration and can model the major mechanical properties. Throughout this study, it is concluded that in general, the microstructure properties of rock aggregate work together to affect their mechanical properties, and it is difficult to correlate a single microstructure property with the mechanical properties of rock aggregates. In particular, for the three types of rock Avja, LEP and Vandle in this study, crack size distribution, grain size and grain perimeter (i.e. grain shape and spatial arrangement) show good correlations with the mechanical properties. The crack length and the grain size negatively affect the mechanical properties of Avja, LEP and Vandle, but the perimeter positively influences the mechanical properties. Besides, the modelled rock aggregate breakage properties in both single aggregate and inter‐aggregate tests reveal that the aggregate microstructure, aggregate shape and loading conditions influence the breakage process of rock aggregate in service. For the rock aggregate with the same microstructure, the quadratic shape and good packing dramatically improve its mechanical properties. During services, the aggregate is easiest to be fragmented under point‐to‐point loading condition, and then in the sequence of multiple‐point, point‐to‐plane and plane‐to‐plane loading conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Petrogenesis and geotectonic setting of early Svecofennian arc cumulates in the Roslagen area,east‐central Sweden

Several intrusions of ultrabasic to basic composition occur in the Roslagen area of east‐central Sweden in close spatial and temporal association with the surrounding 1.90–1.87 Ga old early orogenic Svecofennian granitoids. An imprecise Sm‐Nd WR errorchron yields an age of 1895 ± 71 Ma. In spite of the penetrative deformation in the granitoids, the basic–ultrabasic rocks mostly appear undeformed and largely preserve magmatic textures with plagioclase, olivine (in some rock types), orthopyroxene and clinopyroxene, and amphibole as major constituents. The plagioclase is typically very anorthitic (ca. An₉₀). The Roslagen intrusions range in composition from primitive to evolved (Mg# 80 to 49) but contain only 40–50 wt% SiO₂. Many samples are highly elevated in Al₂O₃ (up to 30 wt%), CaO (up to 16 wt%) and Sr (up to 800 ppm), with strongly positive Eu and Sr anomalies, in line with being plagioclase cumulates. Although masked by cumulus effects, the relative trace element contents indicate a volcanic arc signature. The initial Nd isotope composition is homogeneously ‘mildly depleted’, with ε_Nd of +0.3 to +1.1, and the initial Sr isotope composition ‘mildly enriched’, with ε_Sr of +8 to +15. Non‐cumulus rocks with small Eu and Sr anomalies can be used to deduce the composition of the parental magma. This LILE‐ and LREE‐enriched and HFSE‐depleted high‐alumina basalt magma, with Mg# of ca. 50–60 and Ca# of ca. 80, most likely formed by partial melting of mantle material, enriched by fluids in a subduction environment, at 1.9 Ga. The cumulate rocks apparently crystallized from a somewhat more evolved water‐rich magma with Mg# of ca. 40. Crystallization was followed by the development of late‐magmatic to post‐magmatic coronas between olivine and plagioclase in the presence of H₂O‐rich fluids. The subduction‐related setting would make these intrusions Palaeoproterozoic counterparts of Alaskan‐type ultramafic intrusions, but they differ from those in being plagioclase enriched, possibly reflecting different levels of exposure. Copyright © 2012 John Wiley & Sons, Ltd.     

An OSL‐dated sediment sequence at Idre,west‐central Sweden,indicates ice‐free conditions in MIS 3

In central and northern Sweden, glacial sediments and landforms, formed during Early and Middle Weichselian stadials and their transition into interstadials, are often preserved in spite of having been overridden by later glacial advances. This study presents an OSL‐dated glacial stratigraphy from Idre in west‐central Sweden, expanding the area in which Middle Weichselian ice‐free conditions have been identified. Three sedimentary units were identified, with the lowermost unit consisting of glaciolacustrine sand, deposited in a stagnant water‐body. Nine OSL samples gave ages ranging from 54 to 41 ka, suggesting deposition during a deglacial phase in MIS 3. Normal faults and silt veins, formed after deposition, indicate that the area was ice‐free for a prolonged period, enabling the melting of buried stagnant ice. Above an erosional unconformity is a sediment unit characterized by gravels and sands deposited in a proximal braided‐river environment. OSL ages range from 180 to 41 ka, indicating poor sediment bleaching during deposition. We thus consider them to give a maximum age of the sedimentation, indicating deposition at or after 41 ka. The uppermost unit consists of a stacked succession of subglacial traction tills and glaciotectonite beds, representing the Late Weichselian glaciation of the area, probably during the inception phase with a wet‐based glacier regime. At the last deglaciation of the area there was extensive meltwater erosion, eroding all sedimentary units and forming a landscape with terraces and channels, and erosional remnants of the uppermost diamict as free‐standing hummocks.     

Analysis of limestone micromechanical properties by optical microscopy

Four dense Scandinavian limestones were analyzed to determine their mechanical properties. The generation of dust (? 10 μm) and fines (? 90 μm) during a closed circuit vertical roller mill comminution process was correlated with the calcite crystal size distributions of each limestone. Thin sections were analyzed and by means of stereology the calcite crystal size distributions for each limestone was measured. The dust generation of limestones is governed by a surface abrasive mechanism (R² = 0.99) and the production of fines is governed by the mechanical strength of limestones (R² = 0.99). The overall limestone degradation mechanism is predominantly controlled by the calcite cleavage planes which reduce the power consumption during the comminution process. This study is the first step in determining the influence of limestone texture on the wear rates in heterogenous raw mixes used in closed circuit comminution equipment.     

Signal and distribution of volatile Mercury (Hg0) in the Marine High Arctic During Polar Summer in the Sequel of Enhanced Atmospheric Deposition of HgⅡ

1 Introduction It has been elucidated that high levels of neurotoxic mercury (Hg) in the Arctic is related to a rapid, near-compete depletion of Hg0 (MDE) in the atmospheric boundary-layer occurring episodically during the Polar spring[1].     

Continental margin magmatism and migmatisation in the west-central Fennoscandian Shield

The Ljusdal Batholith (LjB) is a major component of the central Svecofennian Domain in Sweden. It is separated from the Bothnian Basin to the north by the 1.82–1.80 Ga crustal-scale Hassela Shear Zone (HSZ). The LjB has emplacement ages of 1.86–1.84 Ga, is mainly alkali-calcic, metaluminous, has _Nd values between − 0.3 and + 1.2 and was formed in a magmatic arc setting.

During the Svecokarelian orogeny the LjB was affected by at least three fold episodes. Large-scale folded screens of migmatised metasedimentary rocks occur in the eastern part of the batholith, and to the north of the HSZ, there is a 50 km wide diatexite belt. The Transition Belt (TrB), consisting of 1.88–1.85 Ga granitoids, is located at the northwestern extension of this belt. A calc-alkaline and peraluminous composition combined with negative _Nd values (− 1.7 to − 0.8) indicates a large proportion of metasediments in the source for these granitoids.

U–Pb SIMS data on zircon rims from migmatites and leucogranites to the north and east of LjB yield ages of 1.87–1.86 Ga, i.e. coeval with the granitoids of the LjB and the TrB. There is thus a close relationship between the LjB, the TrB and the migmatites in both space and time. Syn-migmatitic shearing along the HSZ indicates that a proto-HSZ was initiated already at c. 1.86 Ga, and the location of the proto-HSZ is inferred to be controlled by two older nuclei present in the lower parts of the crust. As crustal-scale shear zone systems are known to act as ascent pathways for sheet-like flow in active orogenies the TrB may represents accumulations of melts that were attracted and extracted by the proto-HSZ and intruded in a block that was not pervasively affected by subsequent shear along the HSZ.

An active continental margin setting for the LjB implies subduction at c. 1.86 Ga, and provides a heat source for both the migmatites and the TrB.

A later migmatisation at 1.82 Ga has been recorded to the south of the HSZ. Within the LjB the 1.82 Ga stromatic migmatites are folded by F₂ folds, and the fabric is truncated by 1.80 Ga pegmatites.     

Middle Ordovician subduction of continental crust in the Scandinavian Caledonides: an example from Tjeliken,Seve Nappe Complex,Sweden

The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430–400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between ~ 505 and ~ 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jämtland). New age determinations were performed on eclogite and garnet–phengite gneiss at Tjeliken in northern Jämtland. Thermodynamic modelling yielded peak metamorphic conditions of 25–27 kbar/680–760 °C for the garnet–phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25–26 kbar/650–700 °C). Metamorphic rims of zircons from the garnet–phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 ± 2.5 Ma. Lu–Hf garnet-whole rock dating yielded 458 ± 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm–Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jämtland during the Middle Ordovician in a fast subduction–exhumation cycle.