Magnetotelluric image of the fluid cycle in the Costa Rican subduction zone

Fluids entering the subduction zone are a key factor in the subduction process. They determine the onset of melting, weakening and changes in the dynamics and thermal structure of subduction zones and trigger earthquakes when being released from the subducting plate in a series of metamorphic processes. However, the amount of water carried into the subduction zone and its distribution are not well constrained by existing data and are subject of vigorous current research in SFB574 (Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters). Electromagnetic methods like magnetotellurics have been used widely to recognize fluid release and melt production through enhanced electrical conductivities. Here we present an image of the hydration and dehydration cycle down to 120 km depth in one setting derived by an onshore-offshore transect of magnetotelluric soundings in Costa Rica. An electrically conductive zone in the incoming plate outer rise is associated with sea water penetrating down extensional faults and cracks into the upper mantle possibly causing serpentinization. Along the downward subducting plate distinct conductive anomalies identify fluids from dehydration of sediments, crust and mantle. A conductivity anomaly at a depth of approx. 12 km and at a distance of 65 km from the trench is associated with a first major dehydration reaction of minerally-bound water. This is of importance in the context of mid-slope fluid seeps which are thought to significantly contribute to the recycling of minerally-bound water. The position of the conductivity anomaly correlates with geochemical and seismic evidence stating that mid-slope fluids are originated at >=12 km depth before rising up through deep faults to the seeps. The conductivity anomaly is therefore associated with a fluid accumulation feeding the mid-slope seeps. Another fluid accumulation is revealed by a conductivity anomaly at 20-30 km depth and a distance of approximately 30 km seaward from the volcanic arc. This lower crustal fluid accumulation could likely be caused by trapping of fluids released due to de-serpentinization processes or due to other mineral dehydration processes. While we are at the moment not able to attribute one specific process causing the anomaly based on electromagnetic data alone, this feature is however of fundamental importance. A comparison with other electromagnetic studies from subduction zones around the world reveal that such a conductivity anomaly is a global feature suggesting the presence of a global fluid sink. Based on very simplified assumptions we are able derive rough estimates for the amount of water being stored in the overriding plate. Relating seismic evidence as well as petrological results collected in the multi-disciplinary study on the Costa Rican subduction zone we introduce budget estimations for the water cycle in the subduction zone

Magnetotelluric image of the fluid cycle in the Costa Rican subduction zone

Fluids entering the subduction zone play a key role in the subduction process. They cause changes in the dynamics and thermal structure of the subduction zone1, and trigger earthquakes when released from the subducting plate during metamorphism. Fluids are delivered to the subduction zone by the oceanic crust and also enter as the oceanic plate bends downwards at the plate boundary. However, the amount of fluids entering subduction zones is not matched by that leaving through volcanic emissions4 or transfer to the deep mantle, implying possible storage of fluids in the crust. Here we use magnetotelluric data to map the entire hydration and dehydration cycle of the Costa Rican subduction zone to 120 km depth. Along the incoming plate bend, we detect a conductivity anomaly that we interpret as sea water penetrating down extensional faults and cracks into the upper mantle. Along the subducting plate interface we document the dehydration of sediments, the crust and mantle. We identify an accumulation of fluids at ~20–30 km depth at a distance of 30 km seaward from the volcanic arc. Comparison with other subduction zones5–14 indicates that such fluid accumulation is a global phenomenon. Although we are unable to test whether these fluid reservoirs grow with time, we suggest that they can account for some of the missing outflow of fluid at subduction zones

Helplessness among university students: an empirical study based on a modified framework of implicit personality theories

Due to the COVID-19 pandemic, and within a very short period of time, teaching in the 2020 summer term changed from predominantly on-site to online instruction. Students suddenly faced having to adapt their learning process to new demands for which they may have had both insufficient digital skills and a lack of learning resources. Such a situation carries the risk that a substantial number of students become helpless. The aim of our empirical study was to test a hybrid framework of helplessness that includes both objective causes of helplessness and students’ subjective interpretations of them. Before lectures or courses began, students of a full-scale university were invited to participate in an online survey. The final sample consists of 1690 students. Results indicate that objective factors as well as their subjective interpretations contributed to the formation of helplessness

The webcam and student engagement in synchronous online learning: visually or verbally?

Given that video conferencing serves as a crucial means for remote teaching, the current study investigated higher education students’ (non)use of webcams and engagement in synchronous online courses. Three phases were studied: (1) A state of engagement; (2) antecedents that influence it; and (3) consequences of engagement. The cross-sectional online survey encompassed 3,610 students. Results indicated that visual and verbal engagement were only slightly related to each other. Structural equation modelling revealed different direct and indirect influences on either visual or verbal engagement in synchronous online higher education courses. Due to the novelty of the research scope, results of this study provide a foundation for further investigation

Verfügen Studierende über die Mittel und Wege, um während der Coronaviruspandemie zu lernen? Bedarfe für Online-Lehre in einer plötzlich digitalisierten Landschaft

Across the globe, 2020 terms began under conditions incited by the corona pandemic. Within a relatively short amount of time, universities started to develop and implement online courses for distance learning. The current study is about an online survey at a German university investigating the unique circumstances under which students began the digital 2020 summer term. Of approximately 38 500 students, N = 5563 students from across all institutional faculties took part in the survey. Results indicate how well students are equipped with devices for digital learning, what kind of experiences they have already made with online learning, and how competent they reported feeling regarding digital learning. The study provides important insights into digital higher education during the exceptional pandemic situation. The results are intended to feed into student counselling systems via support by way of access to devices or courses regarding digital skills, or through counselling for students with special social burdens. (DIPF/Orig.)Weltweit begann das Jahr 2020 unter dem Einfluss der Coronapandemie. Innerhalb sehr kurzer Zeit begannen Universitäten, Online-Kurse für den Fernunterricht zu entwickeln und implementieren. Die vorliegende Studie untersuchte anhand einer Online-Umfrage an einer deutschen Universität die besonderen Umstände, unter denen Studierende das digitale Sommersemester 2020 begannen. Von etwa 38 500 Studierenden nahmen N = 5563 Studierende aller Fakultäten an der Umfrage teil. Die Ergebnisse zeigen, wie gut die Studierenden mit Geräten für das digitale Lernen ausgestattet sind, welche Erfahrungen sie zuvor bereits mit dem Online-Lernen gemacht hatten und wie kompetent sie sich in Bezug auf das digitale Lernen fühlen. Die Studie liefert wichtige Einblicke in die digitale Hochschulbildung während der außergewöhnlichen Pandemiesituation. Die Ergebnisse können in studentische Beratungssysteme einfließen, sei es durch Unterstützung beim Zugang zu Geräten, durch Kurse zu digitalen Schlüsselkompetenzen oder durch Beratung von Studierenden mit besonderen sozialen Belastungen. (DIPF/Orig.

Self-regulated resource management in emergency remote higher education: status quo and predictors

Because of the COVID-19 pandemic in the spring term 2020, students faced a sudden change from on-campus learning to online learning with synchronous and asynchronous online courses (emergency remote teaching). To study successfully, students not only needed to be prepared in terms of digital readiness (workspace, IT equipment, previous online learning experiences, and sharing information online), they also faced challenges that pertained to the self-regulated management of external resources (environment structuring, time management, and help-seeking). In the current study, we investigated students’ digital readiness for the sudden switch to online learning; differences between students’ intended and actual use of external resource management strategies; and the influence of students’ digital readiness on their actual use of resource management strategies. Students enrolled in a full-scale, German university (N = 662) answered two online questionnaires (before and in the middle of the term). Descriptive statistics indicated that students seemed to be ready to study online. However, repeated measures ANOVA showed that students were not able to manage their resources during the term as frequently as intended. Finally, separate regression analyses revealed that availability of workspace and IT equipment predicted the use of environment structuring strategies. Additionally, IT equipment and information sharing behavior predicted students’ help-seeking. Based on the current results, we discuss implications for the promotion of student self-regulated learning (SRL) in online emergency remote teaching based on both external resources and digital readiness

"Generation invisible?. Higher education students' (non)use of webcams in synchronous online learning

The pandemic situation continues to influence teaching and learning in higher education, with students oftentimes participating in synchronous videoconferencing sessions as a means to interact with peers and instructors. The frequently noted non-use of webcams by students incited the current study, investigating usage behavior as well as potentially related course variables and individual characteristics. N = 3,527 students from a German university took part in an online survey at the end of the regular summer term 2020 (August 2020). Findings indicate that students’ webcam usage behavior was related to personal thoughts and feelings (e.g., privacy), to course characteristics (e.g., group cohesion), and it differed due to specific groups (gender, study level). With the ongoing importance of videoconferencing in higher education, this study provides a foundation for further investigation into this synchronous learning context

Preservice teachers' online self-regulated learning: does digital readiness matter?

(1) Background: Teaching in today’s schools asks teachers to foster self-regulated learning and digital competences in children and young people. In order to do so, teachers first need to acquire and use these competences themselves. (2) Methods: Based on a mixed-methods approach, the study investigates self-regulated learning in online courses of N = 129 preservice teachers at a German university. (3) Results and conclusions: Perceiving their digital readiness as generally high, preservice teachers appear to not overly self-regulate their learning in the online environment. Finally, preservice teachers’ digital readiness was related only weakly to their online self-regulated learning. A discussion is offered which shows teacher education as a broader phenomenon and implies the need for professional development for teacher educators. Additionally, it is argued to link research on self-regulated learning more closely to research on online learning environments in teacher education