Leaching of nitrate from arable land into groundwater in Sweden

The agricultural influence on the quality of the groundwater in Sweden is mostly associated with infiltration areas. The local conditions here determine the extent of the nitrate leakage. It is evident that certain combinations of factors in normal cropping can give unduly high nitrate concentrations in the groundwater.     

A Late Pleistocene coarse-grained spit-platform sequence in northern Jylland, Denmark

Several well-preserved Late Pleistocene spit systems occur uplifted in northern Jylland, Denmark. Their present-day morphological expression allows detailed study of spit growth patterns while the internal sedimentological organisation can be examined in a series of pits distributed along the length of the spits. Two characteristic vertical sequences are recognized in the systems. The first (Sequence I) consists of a giant-scale cross-bedded foreset unit, overlain by topset and beach units, while the second (Sequence II) consists of the foreset unit overlain by bar-trough and beach units. The two sequence types pass laterally into each other with a short overlap zone. They can be interpreted in terms of Meistrell's (1966, 1972) model for spit-platform growth based on scaled wave tank experiments. The giant-scale cross-bedded unit corresponds to prograding of a coarse-grained subaqueous spit-platform while the topset, bar-trough and beach units reflect the growth of the subaerial spit. The alternation between sequence I and II reflects the inversely related growth of the spit and platform structures: when the rate of subaqueous platform progradation declines, the subaerial spit grows uniformly, and when the platform progrades uniformly spit growth declines. The model is probably only valid for relatively coarse-grained systems because only these deposits would have a relatively steep front. The water depth in which the spit system progrades and thus bottom topography, determines the thickness of the giant-scale cross-bedded foreset unit because the water depth over the top of the platform is relatively constant. If the water is less than a few metres deep the spit-platform is not developed as seen where the Late Pleistocene spit systems prograded over elevations of the sea bottom. Conversely, the correct recognition of spit-platform sequences allows precise determination of sea-level and water depth at the time of formation. Finally, the model adds one further mode of formation of giant-scale cross-bedding to those already known from fluvial transverse, lateral and point bars, subtidal sand waves and Gilbert deltas.     

Inherent gravitational instability of thickened continental crust with regionally developed low- to medium-pressure granulite facies metamorphism

Petrological arguments show that regionally developed low- to medium-pressure, high-temperature granulite facies metamorphism may critically enhance the lowering of crustal density with depth. This leads to gravitational instability of homogeneously thickened continental crust, mainly due to changes in mineral assemblages and the thermal expansion of minerals in conjunction with the exponential lowering of the effective viscosity of rocks with increasing temperature. It is argued that crustal processes of gravitational redistribution (crustal diapirism) contributing to the exhumation of granulite facies rocks may be activated in this way.     

On the foundation of collocation in physical geodesy

The boundary value problem in physical geodesy is nowadays mostly presented with the use of an advanced stochastic model by Krarup-Moritz. This model includes a primary Gauss-Markov model and an adjoining Wiener-Hopf model. Degenerations of the Wiener-Hopf section are found in thesingular auto-covariance matrix of the residuals. The non-singular inverse of the auto-covariance matrix of the signal is proved to be a generalized inverse of the singular auto-covariance matrix of the residuals. The joint model is given a non-stochastic evaluation for a case with spherical external surface (using a non-singular inverse). These findings will not prevent a successful application of the model, which has important merits, specially when using suitablea priori values for the stochastic parameters in the covariance functions. A method for quadratic unbiased estimation ofa priori variances is presented in an introductory section. It is meant to be of value when using a solution of the boundary value problem with the collocation technique based on the classical Gauss-Markov solution. (Bjerhammar (1963).)     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.     

Coordinated Ocean-ice Reference Experiments (COREs)

Coordinated Ocean-ice Reference Experiments (COREs) are presented as a tool to explore the behaviour of global ocean-ice models under forcing from a common atmospheric dataset. We highlight issues arising when designing coupled global ocean and sea ice experiments, such as difficulties formulating a consistent forcing methodology and experimental protocol. Particular focus is given to the hydrological forcing, the details of which are key to realizing simulations with stable meridional overturning circulations.The atmospheric forcing from [Large, W., Yeager, S., 2004. Diurnal to decadal global forcing for ocean and sea-ice models: the data sets and flux climatologies. NCAR Technical Note: NCAR/TN-460+STR. CGD Division of the National Center for Atmospheric Research] was developed for coupled-ocean and sea ice models. We found it to be suitable for our purposes, even though its evaluation originally focussed more on the ocean than on the sea-ice. Simulations with this atmospheric forcing are presented from seven global ocean-ice models using the CORE-I design (repeating annual cycle of atmospheric forcing for 500 years). These simulations test the hypothesis that global ocean-ice models run under the same atmospheric state produce qualitatively similar simulations. The validity of this hypothesis is shown to depend on the chosen diagnostic. The CORE simulations provide feedback to the fidelity of the atmospheric forcing and model configuration, with identification of biases promoting avenues for forcing dataset and/or model development.     

Slow drift oscillations of a ship in irregular waves

A procedure to calculate horizontal slow drift excitation forces on an infinitely long horizontal cylinder in irregular beam sea waves is presented. The hydrodynamic boundary-value problem is solved correctly to second order in wave amplitude. Results in the form of second order transfer functions are presented for different two-dimensional shapes. It is concluded that Newman's approximative method is a practical way to calculate slow drift excitation forces on a ship in beam sea and suggested that it may be used in a more general case. Applications of the results for moored ships are discussed.     

GHG mitigation of agricultural peatlands requires coherent policies

As soon as peat soil is drained for agricultural production, the peat starts to degrade, which causes emissions to the atmosphere. In countries with large peatland areas, the GHG mitigation potential related to management of these soils is often estimated as the highest amongst the measures available in agriculture. Although the facts are well known, the policies leading to diminished emissions are often difficult to implement. We have analysed the reasons why the mitigation potential is not fully utilized and what could be done better in national implementation of climate policies. Four cases are used to illustrate the necessary steps to reach mitigation targets: determining the amount and properties of peat soils, estimating the potential, costs and feasibility of the mitigation measures, and selecting and implementing the best measures. A common feature for all of the cases was that national and international climate policies have increased the public interest in GHG emissions from peat soils and increased the pressure for mitigation. Basically the same factors restrict the implementation of mitigation measures in all countries with significant peat soil areas. The most important of these is lack of policy coherence, e.g. ignoring climate policies when planning land use or agricultural policies. We conclude that GHG mitigation is achieved only if other policies, especially national regulations and strategies, are in line with climate policies.

Policy relevance

Agricultural peat soils could be used to help reach GHG mitigation goals in many countries, but the full potential of mitigation of peat soils is not used. Although peatland cultivation inevitably leads to loss of the whole peat layer and high emissions, there are few incentives or regulation to effectively minimize these losses. This article discusses the possibilities to reduce GHG emissions from agricultural peat soils, with specific emphasis on the barriers of implementing mitigation measures nationally. The lessons learned from the selected cases emphasize the role of all policy makers and their cooperation in planning coherent policies for achieving the goals determined by climate policies.     

Amorphous silicates as a record of solar nebular and parent body processes—A transmission electron microscope study of fine‐grained rims and matrix in three Antarctic CR chondrites

Renazzo‐type (CR) carbonaceous chondrites belong to one of the most pristine meteorite groups containing various early solar system components such as matrix and fine‐grained rims (FGRs), whose formation mechanisms are still debated. Here, we have investigated FGRs of three Antarctic CR chondrites (GRA 95229, MIL 07525, and EET 92161) by electron microscopy techniques. We specifically focused on the abundances and chemical compositions of the amorphous silicates within the rims and matrix by analytical transmission electron microscopy. Comparison of the amorphous silicate composition to a matrix area of GRA 95229 clearly shows a compositional relationship between the matrix and the fine‐grained rim, such as similar Mg/Si and Fe/Si ratios. This relationship and the abundance of the amorphous silicates in the rims strengthen a solar nebular origin and rule out a primary formation mechanism by parent body processes such as chondrule erosion. Moreover, our chemical analyses of the amorphous silicates and their abundance indicate that the CR rims experienced progressive alteration stages. According to our analyses, the GRA 95229 sample is the least altered one based on its high modal abundance of amorphous silicates (31%) and close‐to‐chondritic Fe/Si ratios, followed by MIL 07525 and finally EET 92161 with lesser amounts of amorphous silicates (12% and 5%, respectively) and higher Fe/Si ratios. Abundances and chemical compositions of amorphous silicates within matrix and rims are therefore suitable recorders to track different alteration stages on a submicron scale within variably altered CR chondrites.