Preserved landscapes underneath the Antarctic Ice Sheet reveal the geomorphological history of Jutulstraumen Basin

The landscape of Antarctica, hidden beneath kilometre-thick ice in most places, has been shaped by the interactions between tectonic and erosional processes. The flow dynamics of the thick ice cover deepened pre-formed topographic depressions by glacial erosion, but also preserved the subglacial landscapes in regions with moderate to slow ice flow. Mapping the spatial variability of these structures provides the basis for reconstruction of the evolution of subglacial morphology. This study focuses on the Jutulstraumen Glacier drainage system in Dronning Maud Land, East Antarctica. The Jutulstraumen Glacier reaches the ocean via the Jutulstraumen Graben, which is the only significant passage for draining the East Antarctic Ice Sheet through the western part of the Dronning Maud Land mountain chain. We acquired new bed topography data during an airborne radar campaign in the region upstream of the Jutulstraumen Graben to characterise the source area of the glacier. The new data show a deep relief to be generally under-represented in available bed topography compilations. Our analysis of the bed topography, valley characteristics and bed roughness leads to the conclusion that much more of the alpine landscape that would have formed prior to the Antarctic Ice Sheet is preserved than previously anticipated. We identify an active and deeply eroded U-shaped valley network next to largely preserved passive fluvial and glacial modified landscapes. Based on the landscape classification, we reconstruct the temporal sequence by which ice flow modified the topography since the beginning of the glaciation of Antarctica.     

Quaternary tephrachronology on the Iceland Plateau,north of Iceland

Four major ash zones recorded in piston cores raised from the Iceland Plateau north of Iceland are shown to be coincident with the last four interglacial isotopic stages. Their geochemical composition links the ashes to volcanic events on Iceland. The occurrence of these ash layers, which record events orders of magnitude larger than the ‘normal’ Holocene volcanic eruptions, can not be explained by changes in sea ice cover and atmospheric circulation alone. It is suggested that these events are related to pressure releases in the magma chambers resulting from major deglaciations of the Icelandic Ice Cap.     

Reduced-order optimal control of water flooding using proper orthogonal decomposition

Model-based optimal control of water flooding generally involves multiple reservoir simulations, which makes it into a time-consuming process. Furthermore, if the optimization is combined with inversion, i.e., with updating of the reservoir model using production data, some form of regularization is required to cope with the ill-posedness of the inversion problem. A potential way to address these issues is through the use of proper orthogonal decomposition (POD), also known as principal component analysis, Karhunen–Loève decomposition or the method of empirical orthogonal functions. POD is a model reduction technique to generate low-order models using ‘snapshots’ from a forward simulation with the original high-order model. In this work, we addressed the scope to speed up optimization of water-flooding a heterogeneous reservoir with multiple injectors and producers. We used an adjoint-based optimal control methodology that requires multiple passes of forward simulation of the reservoir model and backward simulation of an adjoint system of equations. We developed a nested approach in which POD was first used to reduce the state space dimensions of both the forward model and the adjoint system. After obtaining an optimized injection and production strategy using the reduced-order system, we verified the results using the original, high-order model. If necessary, we repeated the optimization cycle using new reduced-order systems based on snapshots from the verification run. We tested the methodology on a reservoir model with 4050 states (2025 pressures, 2025 saturations) and an adjoint model of 4050 states (Lagrange multipliers). We obtained reduced-order models with 20–100 states only, which produced almost identical optimized flooding strategies as compared to those obtained using the high-order models. The maximum achieved reduction in computing time was 35%.     

A Novel Method for Removal of Emitter Noise in SAR Images

Traditionally, interfering emitter signatures have been removed through notched filtering in the range (fast-time) dimension. This works well when a narrowband emitter interferes with a wideband radar pulse; however, when the emitter and radar signal bandwidths are comparable, then this approach fails since the noise is distributed throughout the pulse and the image as well. In cases where the interfering signal is localized in the cross range, joint time-frequency methods can often focus this interference signal, thereby transforming the image. In this transformed image, the interferer is the foreground, and the desired synthetic aperture radar image is blurred and now the background. The focused compressed interferer can be analyzed and censored from the transformed image. Back transformation restores the image with the interference removed. This technique has been fully automated and applied to an Electromagnetics Institute Synthetic Aperture Radar (EMISAR) image contaminated by a nonstationary emitter. The cleansed image is virtually free of the emitter interference     

Inception of the Northern European ice sheet due to contrasting ocean and insolation forcing

About 115,000 yr ago the last interglacial reached its terminus and nucleation of new ice-sheet growth was initiated. Evidence from the northernmost Nordic Seas indicate that the inception of the last glacial was related to an intensification of the Atlantic Meridional Overturning Circulation (AMOC) in its northern limb. The enhanced AMOC, combined with minimum Northern hemisphere insolation, introduced a strong sea-land thermal gradient that, together with a strong wintertime latitudinal insolation gradient, increased the storminess and moisture transport to the high Northern European latitudes at a time when the Northern hemisphere summer insolation approached its minimum.     

Trace-element behavior in the W---Sn granite of Regoufe, Portugal

Vein-type W-Sn deposits occur both in and around the Regoufe granite. The muscovite-albite granite hosts several roof pendants of schist along its eastern and northern margins. Biotite, tourmaline and K-feldspar megacrysts are virtually absent from the roof zone of the granite but sulphides are abundant. These sulphides disappear through a transition zone and the granite becomes a tourmaline-bearing porphyritic two-mica granite. Fifty-five rock samples were collected within the granite resulting in a sample density of about 10 samples per km². The analytical results show that the granite is extremely rich in Sn, W, Li and Cs, rich in P, Ta, Rb, F and U, about normal in Cu, Zn and Nb and low in Sr, Ti and Zr in comparison with the global averages for low-Ca granites. Factor analysis was applied to the data and the resulting three factor model could be correlated to the field relations. Factor 1 reflects greisenization and albitization processes. Factor 2 scores are high in the mineralized areas and factor 3 appears to be connected with the transition zone.     

Metamorphism of siliceous dolomites at Naxos,Greece

Siliceous dolomitic marbles at Naxos, Greece, are crystallized in a range of metamorphic temperatures, estimated from 350 to 700 °C and a total pressure of about 6 kb. A number of low variant assemblages of this rock-system have been studied. The sequence of these metamorphic assemblages is a function of increasing metamorphism, and this is in agreement with other fielddata and with experimental data for the chemical system CaO-MgO-SiO₂-H₂O-CO₂ (-HF). The composition of the associated fluid inclusions may be considered reasonably correct in the light of experimentally obtained X _CO2 values for the mineral equilibria, extrapolated for a total pressure of about 6 kb at the interpolated temperatures at the sample locations.     

Predicting sediment yield from climate and topography

Linear regression models relating annual average sediment yield with a number of climatic and topographic variables, are developed for rivers (basin area >5,000 km²) in bach of the world's major climatic zones. The models are seen to be of value as a predictive cool to assess the scale of the sediment problem in rivers where no sediment data exist. Despite the limitations imposed by the use of numerical optimisation in their development, the relative significance of different climatic and topographic factors is demonstrated, and an estimate of the annual global denudation, based on the equations, compares satisfactorily with existing figures.