Effects of sea surface warming, irradiance, and grazer abundance on organic matter cycling in a plankton community

Ocean warming affects all components of the food-web. Autotrophic processes, however, are less temperature sensitive than those conducted by heterotrophs, and changes in their balance can thus be expected, likely changing biogeochemical cycling in the oceans. The combined response of all food-web processes to temperature and other factors will thus determine the future direction of the biological carbon pump, which transports photosynthetically fixed CO2 to deeper parts of the ocean via sinking biogenic particles or dissolved organic matter. The aim of this study was to investigate the temperature-dependent partitioning of organic matter between dissolved and particulate matter pools and the changes in their stoichiometry, with emphasis on the impact of changes in irradiance or zooplankton abundance. To elucidate these questions, indoor-mesocosm studies were conducted with natural winter plankton communities from Kiel Bight (Baltic Sea) containing all trophic levels from bacteria to mesozooplankton. Chapter 1 addresses the effects of temperature in combination with different irradiance levels. Rising temperature accelerated the production rate of particulate and dissolved organic matter (POM and DOM), while light intensity played a comparatively minor role for the bloom development. Maximum accumulation of POM was significantly reduced at elevated compared to ambient temperature. Although, heterotrophic loss processes were enhanced by temperature, also an increased formation of transparent exopolymer particles (TEP) was observed. This suggests that in a warmer ocean the accumulation of POM is controlled by two counteracting mechanisms: 1) enhanced heterotrophic remineralization processes, leading to a weakening of the biological pump; and 2) enhanced particle aggregation due to TEP and strengthened transport of POM to deeper parts of the ocean. Chapter 2 describes the effects of temperature in combination with three different overwintering zooplankton grazer (copepod) densities. Increasing copepod abundance decreased the ratio of particulate organic carbon to nitrogen and phosphorus. DOC was positively affected by temperature, but when normalized to Chlorophyll a concentration, showed a tendency to decrease with increasing copepod abundance. This study indicates that the enhanced inorganic carbon consumption relative to N and P by phytoplankton under nutrient stress, which was suggested for a warmer sea surface ocean, could be counteracted by the effect of consumer-driven nutrient recycling. Chapter 3 is a comparative data analysis that aims to identify recurrent patterns of biogeochemical parameters in response to an increase in water temperature. Warming stimulated heterotrophic bacterial processes in particular and had an accelerating effect on the temporal development of phytoplankton blooms. Warming increased the rate of POM and DOC accumulation, whereas the magnitude of POM decreased with rising temperature. Chapter 4 presents results on the effects of high and low light conditions during the months January and February. It was shown that it was possible to induce a diatom phytoplankton bloom in January, comparable to one in February. POM accumulation increased with increasing light levels, whereas DOM, TEP and “Coomassie stainable particles (CSP) remained unaffected by the different irradiance levels. However, CSP were found to occur at the same magnitude and size as TEP and might hence be as important for the partitioning of N as TEP are for the partitioning of C, and should receive more attention in future studies on organic matter cycling. The results presented here show that temperature induced changes in biogeochemical cycling can have strong implications for the biological pump, which plays a vital role in Earth’s climate. Additionally, they demonstrate the strong potential for interactive effects by the interplay of temperature with changes in irradiance and grazer abundance

Assessment of noticing of classroom disruptions: a multi-methods approach

Teachers’ noticing as a basic precondition for effective teaching is characterized by focusing on relevant events in the classroom and ignoring the irrelevant. In recent years, many researchers have used eye-tracking methodology in classroom observations to gather information about the continuous attentional processes of teachers. Despite the general validity of the eye–mind assumption, methodological triangulation is necessary to draw conclusions about the where and why of the focus of attention. Although in previous studies, different data sources like gaze and verbal data have been used, the analyses were mostly conducted separately, instead of directly combining the data. In our study, we collected verbal data (retrospective think-aloud; RTA) and a reaction-based concurrent measure (keystroke) to assess the noticing process of novice and experienced teachers (N  =  52) while they watched staged videos of classroom situations. For a direct triangulation, we combined these data with eye-tracking data. The aim of the study was to combine both measures with eye-tracking parameters that indicate attentional processes (fixation count, mean fixation duration, and revisits), and with expertise. We found that participants who were aware of the critical incidents in the videos (they gave a keystroke or mentioned the incident in the RTA), showed—as expected—a higher number of fixations and more revisits to the appropriate area, but a comparable mean fixation duration. However, expertise differences regarding accuracy in both measures could not be shown. We discuss methodological issues regarding the implementation of RTA and keystroke as measurements for the noticing process because—despite only partially significant results—both methods are promising as they allow complementation and possible correction of eye-movement-only data

Professional Vision and the Compensatory Effect of a Minimal Instructional Intervention: A Quasi-Experimental Eye-Tracking Study With Novice and Expert Teachers

The early recognition of potential disruptions in learning environments is of great importance for the proactive control of the teaching process and maximizing learning outcomes. The professional competence of (prospective) teachers is required for successful classroom management. Teachers’ professional vision (PV) serves as a link between their knowledge and classroom management behavior. Expertise research in different domains has shown that experts and novices show differences in visual perception based on their expertise level; however, research results to date are heterogeneous and often based on small samples. An eye-tracking study using a quasi-randomized experimental design was performed to investigate how German prospective (n = 29) and experienced (n = 35) teachers perceived different teaching situations. The goal of the study was to determine whether previous results from expertise research could be replicated in a standardized experimental setting. Moreover, the impact of a minimal intervention (specific instruction) on PV of potential classroom disruptions was investigated. In contrast to the hypotheses, no expertise-dependent differences on various eye-tracking parameters can be found. Furthermore, the minimal intervention does not lead to an improvement in PV for experts or novices. The results are discussed with regard to the discrepancy with previously published findings and possible explanations are offered (e.g., the salience of disruptions, internal personal factors, and external environmental influences)

Effects of rising temperature on pelagic biogeochemistry in mesocosm systems: a comparative analysis of the AQUASHIFT Kiel experiments

A comparative analysis of data, obtained during four indoor-mesocosm experiments with natural spring plankton communities from the Baltic Sea, was conducted to investigate whether biogeochemical cycling is affected by an increase in water temperature of up to 6 °C above present-day conditions. In all experiments, warming stimulated in particular heterotrophic bacterial processes and had an accelerating effect on the temporal development of phytoplankton blooms. This was also mirrored in the build-up and partitioning of organic matter between particulate and dissolved phases. Thus, warming increased both the magnitude and rate of dissolved organic carbon (DOC) build-up, whereas the accumulation of particulate organic carbon (POC) and phosphorus (POP) decreased with rising temperature. In concert, the observed temperature-mediated changes in biogeochemical components suggest strong shifts in the functioning of marine pelagic food webs and the ocean’s biological carbon pump, hence providing potential feedback mechanisms to Earth’s climate system

Prozessbasierte Erfassung professioneller Wahrnehmung der Klassenführung bei (angehenden) Lehrkräften. Ein systematisches Review

Effective classroom management is seen as a fundamental component of teachers’ professional competence. The early detection of potential disturbances is of great importance for proactive control of the teaching process. Thus, professional vision serves as a link between teacher’s knowledge and his or her actions in the event of deviations. Professional vision can be split into two aspects: noticing and reasoning. Previous research, based on subjective test procedures (i.e. video analysis or interviews), has primarily focused on the process of reasoning, whereas only a few studies have focused on the basal process of noticing, i.e. the recognition of possible disturbing situations. It is known from expertise research in different domains using process-based methods, such as eye-tracking, that experts and novices show differences in noticing processes. Therefore, to examine eye-tracking research for the teaching profession – especially noticing in classroom management – a systematic literature search was carried out between the years of 1999 to 2019. A total of 12 studies were found that recorded professional vision in the field of classroom management using eye-tracking. Overall, there were stable differences in the eye movement patterns of experts and novices for different parameters. However, some questions about the indicators used and possible influencing factors on expertise dependent perception remain unsettled. (DIPF/Orig.)Effektive Klassenführung wird als grundlegender Bestandteil professioneller Kompetenz von Lehrkräften angesehen. Für eine proaktive Steuerung des Unterrichtsgeschehens ist das frühzeitige Erkennen von potentiellen Störungen von großer Bedeutung. Professionelle Wahrnehmung gilt als Bindeglied zwischen Wissen und Handeln der Lehrkraft und kann in die Aspekte Noticing und Reasoning unterteilt werden. Bisherige Arbeiten nutzten häufig subjektive Testverfahren (z. B. Interviews auf Basis von Videostimuli) zur Erfassung des Reasoning-Prozesses. Nur wenige Studien fokussieren auf den basaleren Prozess des Noticing. Aus der Expertiseforschung in unterschiedlichen Domänen, die prozessbasierte Methoden wie Eye-Tracking nutzen, ist bekannt, dass sich Novizen und Experten systematisch in der Erkennung potentieller Störsituationen unterscheiden. Das systematische Review gibt einen Überblick über die Arbeiten, die mit Eye-Tracking-Verfahren den Noticing-Prozess im Bereich der Klassenführung erfasst haben. Dafür wurde eine Literaturrecherche für den Zeitraum von 1999 bis 2019 durchgeführt. Insgesamt konnten 12 Studien identifiziert werden. Es zeigen sich stabile Unterschiede zwischen Experten und Novizen bei den meisten untersuchten Parametern. Sowohl die verwendeten Parameter als auch weitere mögliche Einflussfaktoren auf den Noticing-Prozess werden im Review diskutiert. (DIPF/Orig.

Effect of CO2 on the properties and sinking velocity of aggregates of the coccolithophore Emiliania huxleyi.

Coccolithophores play an important role in organic matter export due to their production of the mineral calcite that can act as ballast. Recent studies indicated that calcification in coccolithophores may be affected by changes in seawater carbonate chemistry. We investigated the influence of CO2 on the aggregation and sinking behaviour of the coccolithophore Emiliania huxleyi (PML B92/11) during a laboratory experiment. The coccolithophores were grown under low (~180 μatm), medium (~380 μatm), and high (~750 μatm) CO2 conditions. Aggregation of the cells was promoted using roller tables. Size and settling velocity of aggregates were determined during the incubation using video image analysis. Our results indicate that aggregate properties are sensitive to changes in the degree of ballasting, as evoked by ocean acidification. Average sinking velocity was highest for low CO2 aggregates (~1292 m d−1) that also had the highest particulate inorganic to particulate organic carbon (PIC/POC) ratio. Lowest PIC/POC ratios and lowest sinking velocity (~366 m d−1) at comparable sizes were observed for aggregates of the high CO2 treatment. Aggregates of the high CO2 treatment showed a 4-fold lower excess density (~4.2×10−4 g cm−3) when compared to aggregates from the medium and low CO2 treatments (~1.7 g×10−3 cm−3). We also observed that more aggregates formed in the high CO2 treatment, and that those aggregates contained more bacteria than aggregates in the medium and low CO2 treatment. If applicable to the future ocean, our findings suggest that a CO2 induced reduction of the calcite content of aggregates could weaken the deep export of organic matter in the ocean, particularly in areas dominated by coccolithophores