Subaquatic moraine amphitheatre in Lake Thun

The combination of a recently acquired high-resolution multibeam bathymetric dataset with 2D multichannel reflection seismic data from perialpine Lake Thun reveals new insights into the evolution of the lake basin upon deglaciation and a so far unknown subaquatic moraine. These new data improve our socomprehension of the landforms associated with the ice-contact zone, the facies architecture of the sub- to proglacial units, the related depositional processes, and thus the retreat mechanisms of the Aare Glacier. The overdeepened basin of Lake Thun was formed by a combination of tectonically predefined weak zones and glacial erosion during the last glaciation periods. Seismic stratigraphic analysis of the new data indicates that below the outermost edge of a morphologically distinct platform in the southeastern part of the lake basin (‘Bödeli’), a complex ridge structure marked by strong reflection amplitudes occurs. This structure is interpreted as a stack of several subaquatic terminal moraine crests, most likely created by a slightly advancing or stagnant and grounded Aare Glacier during its overall retreat phase. Packages of overridden moraine crests are distuinguishable, which smoothly transform downstream into prograding clinoforms with foresets with internally recognisable layering. They dip steeply towards the deepest part of the basin, eventually transforming into bottomsets. This stacked succession of subaquatic glacial sequences is overlain by lacustrine deposits formed by Late-Glacial and Holocene laminated muds comprising intercalated turbidites (Wirth et al. 2011). Little is known about the exact timing and behaviour of the retreating Aare Glacier between its recessional phase from the Alpine foreland to the deglaciation of the inner-Alpine ice cap, mostly due to the lack of well-developed moraines that indicate glacier stabilization or slight readvance. Radiocarbon-dated calcareous clay gyttja of Late-Glacial Lake Amsoldingen, located adjacent to the water outlet of Lake Thun, shows a ~16.3 ka BP age (Lotter, 1985), providing a minimum age for the formation of the postglacial small lake. Higher up in the catchment, the oldest 10Be exposure ages from the Grimsel area, the accumulation area of the Aare Glacier, indicate ice-free conditions around 14-11.3 ka BP (Kelly et al., 2006; Wirsig et al., 2016). The emplacement of the subaquatic moraine complex of the Aare Glacier must have occurred between these age constraints, implying high sedimentation rates in the lake basin

Improving Problem-Solving Skills with Smart Personal Assistants: Insights from a Quasi Field Experiment

Problem-solving skills are considered one of the most important learning goals for life. Therefore, educational institutions should help learners gain these skills despite organizational and financial restrictions. Even though there exists a growing body of research about the design and use of Smart Personal Assistants, such as Google’s Assistant or Amazon’s Alexa, little is known about their ability to help learners improve their problem-solving skills. Using a mixed-method approach, we investigate the value of newly emerging Smart Personal Assistants to improve long-term problem solving skills with the help of a pre- and post-test quasi field experiment in a second grade class of a vocational business school in Switzerland. The results indicate that groups interacting with Smart Personal Assistants show significantly better problem-solving skills compared to learners using paper-based support explained by changing learning processes. Our study contributes to existing intelligent tutoring system and technology-enhanced scaffolding research

A subaquatic moraine complex in overdeepened Lake Thun (Switzerland) unravelling the deglaciation history of the Aare Glacier

To investigate the history of the Aare Glacier and its overdeepened valley, a high-resolution multibeam bathymetric dataset and a 2D multi-channel reflection seismic dataset were acquired on perialpine Lake Thun (Switzerland). The overdeepened basin was formed by a combination of tectonically predefined weak zones and glacial erosion during several glacial cycles. In the deepest region of the basin, top of bedrock lies at ~200m below sea level, implying more than 750m of overdeepening with respect to the current fluvial base level (i.e. lake level). Seismic stratigraphic analysis reveals the evolution of the basin and indicates a subaquatic moraine complex marked by high-amplitude reflections below the outermost edge of a morphologically distinct platform in the southeastern part of the lake. This stack of seven subaquatic terminal moraine crests was created by a fluctuating, “quasi-stagnant” grounded Aare Glacier during its overall recessional phase. Single packages of overridden moraine crests are seismically distuinguishable, which show a transition downstream into prograding clinoforms with foresets at the icedistal slope. The succession of subaquatic glacial sequences (foresets and adjacent bottomsets) represent one fifth of the entire sedimentary thickness. Exact time constraints concerning the deglacial history of the Aare Glacier are very sparse. However, existing 10Be exposure ages from the accumulation area of the Aare Glacier and radiocarbon ages from a Late-Glacial lake close to the outlet of Lake Thun indicate that the formation of the subaquatic moraine complex and the associated sedimentary infill must have occurred in less than 1000 years, implying high sedimentation rates and rapid disintegration of the glacier. These new data improve our comprehension of the landforms associated with the ice-contact zone in water, the facies architecture of the sub- to proglacial units, the related depositional processes, and thus the retreat mechanisms of the Aare Glacier

Decreasing gut wall glucose as an early marker of impaired intestinal perfusion

To access publisher full text version of this article. Please click on the hyperlink in Additional Links fieldOBJECTIVE: The aim of this study was to assess the microcirculatory and metabolic consequences of reduced mesenteric blood flow. DESIGN: Prospective, controlled animal study. SETTING: The surgical research unit of a university hospital. SUBJECTS: A total of 13 anesthetized and mechanically ventilated pigs. INTERVENTIONS: Pigs were subjected to stepwise mesenteric blood flow reduction (15% in each step, n = 8) or served as controls (n = 5). Superior mesenteric arterial blood flow was measured with ultrasonic transit time flowmetry, and mucosal and muscularis microcirculatory perfusion in the small bowel were each measured with three laser Doppler flow probes. Small-bowel intramucosal Pco2 was measured by tonometry, and glucose, lactate (L), and pyruvate (P) were measured by microdialysis. MEASUREMENTS AND MAIN RESULTS: In control animals, superior mesenteric arterial blood flow, mucosal microcirculatory blood flow, intramucosal Pco2, and the lactate/pyruvate ratio remained unchanged. In both groups, mucosal blood flow was better preserved than muscularis blood flow. During stepwise mesenteric blood flow reduction, heterogeneous microcirculatory blood flow remained a prominent feature (coefficient of variation, approximately 45%). A 30% flow reduction from baseline was associated with a decrease in microdialysis glucose concentration from 2.37 (2.10-2.70) mmol/L to 0.57 (0.22-1.60) mmol/L (p < .05). After 75% flow reduction, the microdialysis lactate/pyruvate ratio increased from 8.6 (8.0-14.1) to 27.6 (15.5-37.4, p < .05), and arterial-intramucosal Pco2 gradients increased from 1.3 (0.4-3.5) kPa to 10.8 (8.0-16.0) kPa (p < .05). CONCLUSIONS: Blood flow redistribution and heterogeneous microcirculatory perfusion can explain apparently maintained regional oxidative metabolism during mesenteric hypoperfusion, despite local signs of anaerobic metabolism. Early decreasing glucose concentrations suggest that substrate supply may become crucial before oxygen consumption decreases

Decreasing gut wall glucose as an early marker of impaired intestinal perfusion

OBJECTIVE: The aim of this study was to assess the microcirculatory and metabolic consequences of reduced mesenteric blood flow. DESIGN: Prospective, controlled animal study. SETTING: The surgical research unit of a university hospital. SUBJECTS: A total of 13 anesthetized and mechanically ventilated pigs. INTERVENTIONS: Pigs were subjected to stepwise mesenteric blood flow reduction (15% in each step, n = 8) or served as controls (n = 5). Superior mesenteric arterial blood flow was measured with ultrasonic transit time flowmetry, and mucosal and muscularis microcirculatory perfusion in the small bowel were each measured with three laser Doppler flow probes. Small-bowel intramucosal Pco2 was measured by tonometry, and glucose, lactate (L), and pyruvate (P) were measured by microdialysis. MEASUREMENTS AND MAIN RESULTS: In control animals, superior mesenteric arterial blood flow, mucosal microcirculatory blood flow, intramucosal Pco2, and the lactate/pyruvate ratio remained unchanged. In both groups, mucosal blood flow was better preserved than muscularis blood flow. During stepwise mesenteric blood flow reduction, heterogeneous microcirculatory blood flow remained a prominent feature (coefficient of variation, approximately 45%). A 30% flow reduction from baseline was associated with a decrease in microdialysis glucose concentration from 2.37 (2.10-2.70) mmol/L to 0.57 (0.22-1.60) mmol/L (p < .05). After 75% flow reduction, the microdialysis lactate/pyruvate ratio increased from 8.6 (8.0-14.1) to 27.6 (15.5-37.4, p < .05), and arterial-intramucosal Pco2 gradients increased from 1.3 (0.4-3.5) kPa to 10.8 (8.0-16.0) kPa (p < .05). CONCLUSIONS: Blood flow redistribution and heterogeneous microcirculatory perfusion can explain apparently maintained regional oxidative metabolism during mesenteric hypoperfusion, despite local signs of anaerobic metabolism. Early decreasing glucose concentrations suggest that substrate supply may become crucial before oxygen consumption decreases

Subaquatic moraine amphitheatre in Lake Thun

The combination of a recently acquired high-resolution multibeam bathymetric dataset with 2D multichannel reflection seismic data from perialpine Lake Thun reveals new insights into the evolution of the lake basin upon deglaciation and a so far unknown subaquatic moraine. These new data improve our socomprehension of the landforms associated with the ice-contact zone, the facies architecture of the sub- to proglacial units, the related depositional processes, and thus the retreat mechanisms of the Aare Glacier. The overdeepened basin of Lake Thun was formed by a combination of tectonically predefined weak zones and glacial erosion during the last glaciation periods. Seismic stratigraphic analysis of the new data indicates that below the outermost edge of a morphologically distinct platform in the southeastern part of the lake basin (‘Bödeli’), a complex ridge structure marked by strong reflection amplitudes occurs. This structure is interpreted as a stack of several subaquatic terminal moraine crests, most likely created by a slightly advancing or stagnant and grounded Aare Glacier during its overall retreat phase. Packages of overridden moraine crests are distuinguishable, which smoothly transform downstream into prograding clinoforms with foresets with internally recognisable layering. They dip steeply towards the deepest part of the basin, eventually transforming into bottomsets. This stacked succession of subaquatic glacial sequences is overlain by lacustrine deposits formed by Late-Glacial and Holocene laminated muds comprising intercalated turbidites (Wirth et al. 2011). Little is known about the exact timing and behaviour of the retreating Aare Glacier between its recessional phase from the Alpine foreland to the deglaciation of the inner-Alpine ice cap, mostly due to the lack of well-developed moraines that indicate glacier stabilization or slight readvance. Radiocarbon-dated calcareous clay gyttja of Late-Glacial Lake Amsoldingen, located adjacent to the water outlet of Lake Thun, shows a ~16.3 ka BP age (Lotter, 1985), providing a minimum age for the formation of the postglacial small lake. Higher up in the catchment, the oldest 10Be exposure ages from the Grimsel area, the accumulation area of the Aare Glacier, indicate ice-free conditions around 14-11.3 ka BP (Kelly et al., 2006; Wirsig et al., 2016). The emplacement of the subaquatic moraine complex of the Aare Glacier must have occurred between these age constraints, implying high sedimentation rates in the lake basin

Overdeepened glacigenic landforms in Lake Thun (Switzerland) revealed by a multichannel reflection seismic survey

Recently acquired high-resolution multibeam bathymetry, in combination with a 2D multichannel reflection seismic campaign on perialpine Lake Thun (Switzerland) reveals new insights into the diverse geometry of the lake basin and a so far unknown subaquatic moraine crest with unprecedented clarity. These new data will improve our comprehension concerning the retreat phases of the Aare glacier, the morphology of its proximal deposits and the facies architecture of the subglacial units. The overdeepened basin of Lake Thun was formed by a combination of tectonically predefined weak zones and glacial erosion during the last glacial periods. The new data indicate that below the outermost edge of a morphologically distinct platform in the south eastern part of the lake basin, a ridge structure marked by strong reflection amplitudes occurs. This structure is interpreted as a subaquatic terminal moraine crest, most likely created by a slightly advancing or stagnant grounded Aare glacier during its major retreating phase. The terminal moraine smoothly transforms downstream into well distinguishable foresets with internally recognisable layering, which dip steeply towards the deepest part of the basin, eventually transforming into bottomsets. This depositional sequence formed by the fore- and bottomsets represents ~50% of the overall sediment volume that fills the basin and was deposited while the glacier was stagnant, interpreted to represent a rather short period of time of a few hundreds of years. This sequence is overlain by lacustrine deposits formed by late-glacial and Holocene laminated muds comprising intercalated turbidites (Wirth et al. 2011). Little is known about the exact timing and behaviour of retreating glaciers between their recessional phase from the Alpine foreland to the deglaciation of the inner-Alpine ice cap, mostly due to the lack of well-developed moraines that indicate glacial stabilization or slight readvance. Findings from pollen analyses by Ammann (1994) hint at a completely ice-free Northern Alpine foreland during the Oldest Dryas. Radiocarbon-dated calcareous clay gyttja of late-glacial Lake Amsoldingen, located adjacent to the water outlet of Lake Thun, shows a ~16.3 ka BP age (Lotter, 1985) while the oldest 10Be exposure ages from the Grimsel area, the accumulation area of the Aare glacier, indicate ice-free conditions around 14-11.3 ka BP (Kelly et al., 2006). The deposition of the subaquatic moraine of the Aare glacier hence has to fit temporally between these age constraints, implying rather high sedimentation rates, which will be integrated in an appropriate sedimentological concept quantifying subaquatic moraine formation in a recessional overdeepened setting