Projections for future radiocarbon content in dissolved inorganic carbon in hardwater lakes: a retrospective approach

Inland water bodies contain significant amounts of carbon in the form of dissolved inorganic carbon (DIC) derived from a mixture of modern atmospheric and pre-aged sources, which needs to be considered in radiocarbon-based dating and natural isotope tracer studies. While reservoir effects in hardwater lakes are generally considered to be constant through time, a comparison of recent and historical DI14C data from 2013 and 1969 for Lake Constance reveals that this is not a valid assumption. We hypothesize that changes in atmospheric carbon contributions to lake water DIC have taken place due to anthropogenically forced eutrophication in the 20th century. A return to more oligotrophic conditions in the lake led to reoxygenation and enhanced terrigenous organic matter remineralization, contributing to lake water DIC. Such comparisons using DI14C measurements from different points in time enable nonlinear changes in lake water DIC source and signature to be disentangled from concurrent anthropogenically induced changes in atmospheric 14C. In the future, coeval changes in lake dynamics due to climate change are expected to further perturb these balances. Depending on the scenario, Lake Constance DI14C is projected to decrease from the 2013 measured value of 0.856 Fm to 0.54–0.62 Fm by the end of the century

Dynamic e-learning modules for student lecture preparation

We have developed and demonstrated the effectiveness of a set of online interactive learning modules to accompany physics courses at first- and second-year university levels. Students access the modules prior to attending lectures to familiarize themselves with content which is then discussed and reaffirmed in class. Student surveys and access data show that students were much more likely to use material presented in this form, rather than a textbook, when preparing for lectures given in an active learning format. The students found that interactive simulations, videos of problem-solving approaches prepared by course staff, and quick-check immediate feedback questions were all useful tools for lecture preparation–none of which are available when using a traditional textbook for lecture preparation

Widespread dispersal and aging of organic carbon in shallow marginal seas

The occurrence of pre-aged organic carbon (OC) in continental margin surface sediments is a commonly observed phenomenon, yet the nature, sources, and causes of this aged OC remain largely undetermined for many continental shelf settings. Here we present the results of an extensive survey of the abundance and radiocarbon content of OC in surface sediments from the northern Chinese marginal seas. Pre-aged OC is associated with both coarser (>63 µm) and finer (<63 µm) sedimentary components; measurements on specific grain-size fractions reveal that it is especially prevalent within the 20–63 µm fraction of inner shelf sediments. We suggest that organic matter associated with this sortable silt fraction is subject to protracted entrainment in resuspension-deposition loops during which it ages, is modified, and is laterally dispersed, most likely via entrainment within benthic nepheloid layers. This finding highlights the complex dynamics and predepositional history of organic matter accumulating in continental shelf sediments, with implications for our understanding of carbon cycling on continental shelves, development of regional carbon budgets, and interpretation of sedimentary records

Active learning using online interactivity

Preparation for classes and interactivity are core components of active learning. Both of these components can be implemented in ways enabled by technology, using online resources and activities. This presentation will discuss a range of online strategies to support active learning, from the viewpoint of at least a decade’s work on implementing active learning in a variety of university physics courses. A particular focus has been the development and evaluation of online learning modules.  “Five Minute Physics” was originally envisaged as lecture preparation material. Its concise text, videos/animations and quizzes with instant feedback are designed to provide students with a fundamental understanding of course material, preparing them for interactive in-class activities. Once it was proven that students actually use this resource, its content was extended.  An introductory-level service course has a complete suite of Five Minute Physics modules covering the course material. These have been consistently nominated by students over many semesters (pre-COVID, at the height of the pandemic crisis, and now), as one of the best aspects of the course.  Initially, student engagement with interactive simulations that were incorporated in Five Minute Physics varied widely. We have since integrated simulations in learning tasks, for example, small-group worksheets for tutorials. Students across a number of courses have responded very positively to use of online simulations, reporting gains from simulation-based activities, and describing how simulations helped their learning. In the rapid transition to new delivery modes prompted by COVID-19, we attempted to retain advantages of active learning – supported by technology. In recent semesters, for a first-year course with hundreds of students, consisting of lectures, tutorials and practicals, most students experienced a blend of online and face-to-face teaching. Interactive lectures have been achieved online, and in simultaneous face-to-face/online mode. Tutorials on-campus and online have used the same activities, based on online interactive simulations and small-group discussion. Student attitudes to the use of online simulations in both situations have been overwhelmingly positive. Student engagement in in-person tutorials was relatively high. In online tutorial sessions, engagement was generally lower, the productive student discussion varied dramatically, but engagement improved over the semester with tutors working to encourage discussion. As we aim to address contemporary and future challenges in physics education, technology-enabled strategies will continue to offer interesting possibilities to support active learning. REFERENCE Five Minute Physics. http://teaching.smp.uq.edu.au/fiveminutephysics

The effect of an interdisciplinary science course on student perceptions of computer programming

Interdisciplinary courses are being offered and recommended by many academic institutions as part of a science degree. In one such first year interdisciplinary science course with a large enrollment we measured attitudes to and perceptions of computer programming at the start and end of semester. For those students with prior computer programming experience, there was a significant positive change in their attitudes to and perceptions of computer programming. The aspects of the course that effected this change were examined. Most students reported that the regular tutorials and the summative assignment, each of which integrated scientific modelling, communication and computer programming, had a positive effect on their attitudes to and perceptions of computer programming. This suggests that an interdisciplinary course can be an effective way to introduce skills such as computer programming

Temporal variability in composition and fluxes of Yellow River particulate organic matter

This study examines temporal variations of the abundance and carbon isotopic characteristics of particulate organic carbon (POC) and specific-source compounds in the context of hydrological variability in the Yellow River. The content and bulk carbon isotopic characteristics (13C and 14C) of POC were relatively uniform over the hydrologic (seasonal) cycle. We attribute these temporally invariant geochemical characteristics to the dominant contribution of loess material to the suspended particulate matter (SPM). In contrast, molecular-level signals revealed that hydrologic conditions exert a significant influence on the proportional contributions of petrogenic and especially fresh plant-derived OC, while pre-aged soil OC is mobilized via deeper erosion processes (e.g., gully erosion, mudslides) and is independent of hydrodynamics and surface runoff. A coupled biomarker-isotope mixing model was applied to estimate the time-varying supply of contemporary/modern biomass, pre-aged soil, and fossil OC components to Chinese marginal seas from the Yellow River. We found that natural (e.g., precipitation) and human-induced (e.g., water and sediment regulation) variations in hydrological regime strongly influence the flux with the magnitude of the corresponding annual fluxes of POC ranging between 0.343 ± 0.122 Mt yr−1 and 0.581 ± 0.213 Mt yr−1, but less strongly infleunce proportions of the different OC constituents. Inter-annual differences in pre-aged soil and fossil OC fluxes imply that extreme climate events (e.g., floods) modulate the exhumation and export of old carbon to the ocean, but the OC homogeneity in the pre-aged mineral soil-dominated watersheds facilitates robust predictions in terms of OC transport dynamics in the past (sediment cores) and in the future

Student experiences of virtual reality - a case study in learning special relativity

We present a study of student learning through the use of virtual reality. A software package is used to introduce concepts of special relativity to students in a game-like environment where users experience the effects of travelling at near light speeds. From this new perspective, space and time are significantly different to that experienced in everyday life. The study explores how students have worked with this environment and how these students have used this experience in their study of special relativity. A mixed method approach has been taken to evaluate the outcomes of separate implementations of the package at two universities. Students found the simulation to be a positive learning experience and described the subject area as being less abstract after its use. Also, students were more capable of correctly answering concept questions relating to special relativity, and a small but measurable improvement was observed in the final exam

Hydrologic controls on seasonal and inter-annual variability of Congo River particulate organic matter source and reservoir age

We present dissolved organic carbon (DOC) concentrations, particulate organic matter (POM) composition (δ13C, δ15N, ∆14C, N/C), and particulate glycerol dialkyl glycerol tetraether (GDGT) distributions from a 34-month time-series near the mouth of the Congo River. An end-member mixing model using δ13C and N/C indicates that exported POM is consistently dominated by C3 rainforest soil sources, with increasing contribution from C3 vegetation and decreasing contribution from phytoplankton at high discharge. Large C4 inputs are never observed despite covering ≈ 13% of the catchment. Low and variable ∆14C values during 2011 [annual mean = (− 148 ± 82) ‰], when discharge from left-bank tributaries located in the southern hemisphere reached record lows, likely reflect a bias toward pre-aged POM derived from the Cuvette Congolaise swamp forest. In contrast, ∆14C values were stable near − 50‰ between January and June 2013, when left-bank discharge was highest. We suggest that headwater POM is replaced and/or diluted by C3 vegetation and pre-aged soils during transit through the Cuvette Congolaise, whereas left-bank tributaries export significantly less pre-aged material. GDGT distributions provide further evidence for seasonal and inter-annual variability in soil provenance. The cyclization of branched tetraethers and the GDGT-0 to crenarchaeol ratio are positively correlated with discharge (r ≥ 0.70; p-value ≤ 4.3 × 10− 5) due to the incorporation of swamp-forest soils when discharge from right-bank tributaries located in the northern hemisphere is high. Both metrics reach record lows during 2013, supporting our interpretation of increased left-bank contribution at this time. We conclude that hydrologic variability is a major control of POM provenance in the Congo River Basin and that tropical wetlands can be a significant POM source despite their small geographic coverage

Numerical Prediction of Radiation Measurements Taken in the X2 Facility for Mars and Titan Gas Mixtures

Thermochemical relaxation behind a normal shock in Mars and Titan gas mixtures is simulated using a CFD solver, DPLR, for a hemisphere of 1 m radius; the thermochemical relaxation along the stagnation streamline is considered equivalent to the flow behind a normal shock. Flow simulations are performed for a Titan gas mixture (98% N2, 2% CH4 by volume) for shock speeds of 5.7 and 7.6 km/s and pressures ranging from 20 to 1000 Pa, and a Mars gas mixture (96% CO2, and 4% N2 by volume) for a shock speed of 8.6 km/s and freestream pressure of 13 Pa. For each case, the temperatures and number densities of chemical species obtained from the CFD flow predictions are used as an input to a line-by-line radiation code, NEQAIR. The NEQAIR code is then used to compute the spatial distribution of volumetric radiance starting from the shock front to the point where thermochemical equilibrium is nominally established. Computations of volumetric spectral radiance assume Boltzmann distributions over radiatively linked electronic states of atoms and molecules. The results of these simulations are compared against experimental data acquired in the X2 facility at the University of Queensland, Australia. The experimental measurements were taken over a spectral range of 310-450 nm where the dominant contributor to radiation is the CN violet band system. In almost all cases, the present approach of computing the spatial variation of post-shock volumetric radiance by applying NEQAIR along a stagnation line computed using a high-fidelity flow solver with good spatial resolution of the relaxation zone is shown to replicate trends in measured relaxation of radiance for both Mars and Titan gas mixtures