ALBERT

Description: Sensor-to-sensor variability is a source of error common to all geoscientific instruments, which needs to be assessed before comparative and applied research can be performed with multiple sensors. Consistency among sensor systems is especially critical when the signal is an integral value that covers a large volume within complex, urban terrain. Cosmic-Ray Neutron Sensors (CRNS) are a recent technology that is used to monitor large-scale environmental water storages, for which a rigorous comparison study of numerous co-located sensors has never been performed. In this work, nine stationary CRNS probes of type CRS1000 were installed in relative proximity on a grass patch surrounded by complex urban terrain. While the dynamics of the neutron count rates were found to be similar, offsets of a few percent from the absolute average neutron count rates were found. Technical adjustments of the individual detection parameters brought all instruments into good agreement. Furthermore, the arrangement of multiple sensors allowed to find a critical integration time of 6 hours above which all sensors showed consistent dynamics in the data and their RMSE fell below 1 % of gravimetric water content. The residual differences between the nine signals indicated local effects of the complex urban terrain at the scale of several meters. Mobile CRNS measurements and spatial neutron transport simulations in the surrounding area (25 ha) have revealed that CRNS detectors are sensitive to sub-footprint heterogeneity despite their large averaging volume. The paved and sealed areas in the footprint furthermore damp the dynamics of the CRNS soil moisture product. We developed strategies to correct for the sealed-area effect based on theoretical insights about the spatial sensitivity of the sensor. This procedure not only led to reliable soil moisture estimation in drying periods, it further revealed a strong signal of interception and evaporation water that emerged over the sealed ground during and shortly after rain events. The presented arrangement offered a unique opportunity to demonstrate the CRNS performance in complex terrain, and the results indicate great potential for further applications in urban water sciences.

Description: Sensor-to-sensor variability is a source of error common to all geoscientific instruments that needs to be assessed before comparative and applied research can be performed with multiple sensors. Consistency among sensor systems is especially critical when subtle features of the surrounding terrain are to be identified. Cosmic-ray neutron sensors (CRNSs) are a recent technology used to monitor hectometre-scale environmental water storages, for which a rigorous comparison study of numerous co-located sensors has not yet been performed. In this work, nine stationary CRNS probes of type “CRS1000” were installed in relative proximity on a grass patch surrounded by trees, buildings, and sealed areas. While the dynamics of the neutron count rates were found to be similar, offsets of a few percent from the absolute average neutron count rates were found. Technical adjustments of the individual detection parameters brought all instruments into good agreement. Furthermore, we found a critical integration time of 6 h above which all sensors showed consistent dynamics in the data and their RMSE fell below 1 % of gravimetric water content. The residual differences between the nine signals indicated local effects of the complex urban terrain on the scale of several metres. Mobile CRNS measurements and spatial simulations with the URANOS neutron transport code in the surrounding area (25 ha) have revealed substantial sub-footprint heterogeneity to which CRNS detectors are sensitive despite their large averaging volume. The sealed and constantly dry structures in the footprint furthermore damped the dynamics of the CRNS-derived soil moisture. We developed strategies to correct for the sealed-area effect based on theoretical insights about the spatial sensitivity of the sensor. This procedure not only led to reliable soil moisture estimation during dry-out periods, it further revealed a strong signal of intercepted water that emerged over the sealed surfaces during rain events. The presented arrangement offered a unique opportunity to demonstrate the CRNS performance in complex terrain, and the results indicated great potential for further applications in urban climate research.

Description: Die Entwicklung des westantarktischen Eisschildes (WAIS) steht zur Zeit im Fokus des Interesses, da seine mögliche Instabilität zu einem Meeresspiegelanstieg von 3-6 m führen könnte. Der Amundsenmeer-Sektor spielt eine besondere Rolle, denn die gegenwärtig gemessenen Rückzugsraten der Pine- und Thwaites-Gletschersysteme sind die höchsten der antarktischen Eisströme. Mit den Ergebnissen der geophysikalischen und geologischen Untersuchungen der FS Polarstern Expeditionen ANT-XXIII/4 (2006) und ANT-XXVI/3 (2010) wird der Frage nachgegangen, wie sich der WAIS in diesem Sektor seit Beginn der glazialen Entwicklung verhalten hat und was die Ursachen und Prozesse für die Eisschilddynamik sind.

Description: The development of morphologies follow initially the tectonic displacement structures of thebasement and sediments. Such tectonic lineaments are often exploited by surface erosional processes and play an important role in reconstructing past ice sheet dynamics. Observations of bathymetric features of the continental shelf of the Amundsen Sea Embayment and identification of tectonic lineaments from geophysical mapping indicate that erosional processes of paleo-ice stream flows across the continental shelf followed such lineaments inherited from the tectonic history since the Cretaceous breakup between New Zealand and West Antarctica. East-west oriented basement trends correlate with coastline trends and overlay tectonic lineaments caused by former rift activities. Directional trends in northwest-southeast orientation are observed for the glacial troughs of the western embayment outer shelf, the western Pine Island Bay coastal zones, and the inner Pine Island glacial trough and are superposed on a distributed southern plate boundary zone of the former Bellingshausen Plate. The north-south trend of the main Pine Island glacial trough and the NNE-trend of the Abbot Ice Shelf trough follow the predicted lineation trend of an eastern branch of the West Antarctic Rift System extending from the Thwaites drainage basin northward into Pine Island Bay. An understanding of this context helps better constrain the geometries and sea-bed substrate conditions for regional paleo-ice sheet models.

Description: An understanding of the glacial history of the Amundsen Sea Embayment (ASE) and Pine Island Bay (PIB) is essential for proposing models on the future development of the West Antarctic Ice Sheet. This requires an understanding of the tectonic history and knowledge of tectonic features such as lineaments, ridges, sills and basins, because basement morphology and inherited erosional features control the flow direction of ice-sheets and the influx of Circum-Polar Deep Water (CDW). This is an attempt to reconstruct the tectonic history with the aim to search for basement features and crustal boundaries which may be correlated to the flow and dynamics of the ice-sheet. The Amundsen Sea Embayment of West Antarctica is in a prominent location for a series of tectonic and magmatic events from Paleozoic to Cenozoic times. Seismic, magnetic and gravity data from the embayment and PIB reveal the crustal thickness and significant tectonic features. NE-SW trending magnetic and gravity anomalies and the thin crust indicate a former rift zone which was active during or in the run-up to the breakup process between Chatham Rise and West Antarctica before or at 90 Ma. NW-SE trending gravity and magnetic anomalies, following a prolongation of Peacock Sound, indicate the extensional southern boundary to the Bellingshausen Plate which was active between 79 and 61 Ma. It is likely that the prominent Pine Island Trough follows a structural boundary between the crustal blocks of Ellsworth Land and Marie Byrd Land. Data are shown from the ASE and PIB which can be interpreted in context with the reconstruction of the ice advance and retreat history in this area. Differences in the behaviour of the ice-sheet are shown to exist for the western and eastern parts of PIB due to basement structures affecting the inflow of CDW.

Description: In the last years, the Amundsen Sea sector of West Antarctica has attracted increasing attention due to the role of the marine-based West Antarctic Ice Sheet which partly drains into the Amundsen Sea. For instance, the Pine Island and Thwaites glacier systems exhibit an amplifying ice-flow velocity and a retreat of their grounding zones. Arising questions concern the regime of the underlying tectonically and magmatically formed basement which forms the controlling morphology geometry for past ice-sheet dynamics. Accurate models of the geodynamic-tectonic evolution contain some of the most important parameters for understanding and reconstruction of the paleoenvironment. The objectives comprise the identification of the boundaries between suspected crustal blocks and volcanic zones in Pine Island Bay. The glacier troughs and Pine Island Bay are thought to have developed along such tectonic boundaries.During two expeditions with RV Polarstern in the years 2006 and 2010 to West Antarctic continental margin, a considerable amount of magnetic data has been acquired in the Amundsen Sea, particularly in Pine Island Bay. In both years, the data acquisition was conducted with a permanent ship borne magnetometer system and a variable helicopter borne magnetometer system. Helicopter borne magnetic measurements were performed with a caesium vapour magnetometer, towed 30 m below the helicopter to avoid magnetic disturbances. During the flight campaign of 2010, in which 15000 km of flight data was gathered, a densification and supplement of the grid of 2006 containing 20000 km flight data, was achieved. The resulting grid covers an area of about 20000 km² and ranges from Pine Island Bay on the inner shelf to the outer shelf and above continental slope. Shipborne magnetic measurements were made by two fluxgate vector magnetometers, which are permanently mounted at the crow's nest of RV Polarstern. The data were sampled at one-second intervals. To take account of the influence of the metallic bulk of the ship, the ship undertook compensation loops. In the small area of a compensation loop the variation of the magnetic field due to the crustal magnetization are assumed to be negligible. The loops thus provide coefficients that relate the ship's heading, roll, and pitch movements to the variations in magnetometer measurements that they cause. Using these coefficients it is possible to correct the ship borne magnetic measurements in the wider area around the compensation loop.A fundamental division exists between the magnetic styles of the inner, middle and outer shelf. Short wavelength anomalies characterize the inner shelf and adjacent land. These short wavelength anomalies can be associated with the existence of magmatic structures which also can be observed in several magmatic exposures on small islands. In contrast, long wavelength anomalies are visible on the outer shelf. Parallel belts of similar magnetic signature can be identified here. These linear features are up to 500 km long and strike approximately southwest-northeast. Similar but less distinct features strike in a direction perpendicular to these. The magnetic anomaly pattern shows at least two phases of tectonic and magmatic processes in the Amundsen Sea Embayment.