Non-reciprocity in optical fiber links: experimental evidence.

Fundamental limits of fiber link are set by non-reciprocal effects that violate the hypothesis of equality between forward and backward path. Non-reciprocal noise arises technically from the set-up asymmetry, and fundamentally by the Sagnac effect when the fiber link encloses a non-zero area. As a pre-requisite for observation of Sagnac effect in fiber links, we present a study on phase noise and frequency stability contributions affecting coherent optical frequency transfer in bi-directional fiber links. Both technical and fundamental limitations of Two-Way optical frequency transfer are discussed. Our model predicts and our experiments substantially verify that the dominant noise mechanism at low Fourier frequencies is the polarization asymmetry induced by the temperature and relative humidity variations impacted on fiber links. The flicker noise floor due to the non-reciprocal noise arising from polarization mode dispersion is evidenced for the first time. We perform a post-processing approach which enables us to remove this polarization noise, improve the long-term stability and remove a frequency bias. We evaluate the uncertainty contributions of all the effects discussed for our 50 km spooled fiber link, dominated by its non-reciprocal noise induced by polarization mode dispersion with uncertainty of 1.9( ± 0.8)( ± 1.2) × 10-20. After correction, the linear drift of the residual phase is as low as 27 yoctosecond/s, leading to an uncertainty of the frequency transfer of 2.6 ( ± 39) × 10-22, confirming its potential for searching for more fundamental effects such as Sagnac effect or transient frequency variation due to dark matter.

Searching for Dark Matter with an Optical Cavity and an Unequal-Delay Interferometer.

We propose a new type of experiment that compares the frequency of a clock (an ultrastable optical cavity in this case) at time t to its own frequency some time t-T earlier, by "storing" the output signal (photons) in a fiber delay line. In ultralight oscillating dark matter (DM) models, such an experiment is sensitive to coupling of DM to the standard model fields, through oscillations of the cavity and fiber lengths and of the fiber refractive index. Additionally, the sensitivity is significantly enhanced around the mechanical resonances of the cavity. We present experimental results of such an experiment and report no evidence of DM for masses in the [4.1×10^{-11}, 8.3×10^{-10}] eV region. In addition, we improve constraints on the involved coupling constants by one order of magnitude in a standard galactic DM model, at the mass corresponding to the resonant frequency of our cavity. Furthermore, in the model of relaxion DM, we improve on existing constraints over the whole DM mass range by about one order of magnitude, and up to 6 orders of magnitude at resonance.

Unidirectional two-way optical frequency comparison and its fundamental limitations.

High-quality frequency transfer based on existing telecommunication fiber links allows state-of-the-art microwave and optical clocks to be compared on a continental and potentially even intercontinental scale. We present a half-a-year-long data set of unidirectional optical frequency transfer over a 2×43km urban fiber link. We observe a relative frequency instability of 8.0×10-16 at 1 s and at best 6.0×10-18 at 106s integration time. Our results show that the unidirectional two-way method gives the possibility to perform comparisons of international primary standards over fiber links faster than over satellite links. Moreover, we investigate the major limiting factors of such a unidirectional setup.

Patterns and trends of fish mercury in New York State.

In the mid-2000s a survey was conducted to evaluate fish mercury in lakes across New York State. Approximately 10 years later a second survey examining adult sportfish from 103 lakes and reservoirs was conducted to evaluate the response of fish mercury to recent declines in US mercury emissions. Of those lakes, 43 were part of the earlier survey and were examined to determine if mercury concentrations in four popular sport species, Yellow Perch, Walleye, and Small- and Largemouth Bass, declined in response to decreasing emissions. Water samples were also collected at 35 of these lakes and analyzed for mercury, methylmercury and other analytes. The Adirondack and Catskill regions remain biological mercury hotspots with elevated concentrations in fish. The most widely sampled species, Yellow Perch, showed significant increases in mercury in the Northeast and West regions of New York State over the past decade. The increases in Yellow Perch mercury is not consistent with significant reductions in water concentrations of both total and methylmercury observed corresponding in lake water samples. This discrepancy suggests watershed and in-lake processes beyond mercury emissions, such as recovery from acid deposition, impacts from climate change, or changes in food web structure may be controlling fish mercury concentrations. These results demonstrate a need for a consistent, long-term program to monitor fish mercury to inform the status of mercury contamination in New York State.

Reciprocity of propagation in optical fiber links demonstrated to 10-21.

We present a study of the fundamental limit of fiber links using dedicated link architecture. We use an experimental arrangement that enables us to detect the forward and backward propagation noise independently and simultaneously in optical fiber and where the optical phase evolution is expected to be driven by the only contribution of the reference arms of the Michelson interferometer ensemble. In this article, we demonstrate indeed the high correlation between the optical phase evolution and the temperature variation of the interferometer ensemble, leading to a frequency offset of (4.4±2.3)×10-21. Using a simple temperature model and a Bayesian analysis to evaluate the model parameters, we show that the temperature effect can be compensated with post-processing, removing the frequency offset down to (0.5±2.0)×10-21. The residual slope of the optical phase evolution over 33 days is 350 yoctosecond/s. Using a global temperature parameter, we divide these 33 days dataset in four subsets and analyse their uncertainties. We show that they are self-consistent when the temperature is taken into account. This provides an alternative method to evaluate the accuracy of a fiber link, especially when the dataset includes large dead times. The result is finally interpreted as a test of the reciprocity of the propagation delay in an optical fiber. This unprecedented transfer capability could enable the comparisons of future optical clocks with expected performance at 10-20 level and open new possibilities for stringent tests of special and general relativity.

Metal Resistance in Bacteria from Contaminated Arctic Sediment is Driven by Metal Local Inputs.

Anthropogenic impact over the Pasvik River (Arctic Norway) is mainly caused by emissions from runoff from smelter and mine wastes, as well as by domestic sewage from the Russian, Norwegian, and Finnish settlements situated on its catchment area. In this study, sediment samples from sites within the Pasvik River area with different histories of metal input were analyzed for metal contamination and occurrence of metal-resistant bacteria in late spring and summer of 2014. The major differences in microbial and chemical parameters were mostly dependent on local inputs than seasonality. Higher concentrations of metals were generally detected in July rather than May, with inner stations that became particularly enriched in Cr, Ni, Cu, and Zn, but without significant differences. Bacterial resistance to metals, which resulted from viable counts on amended agar plates, was in the order Ni2+>Pb2+>Co2+>Zn2+>Cu2+>Cd2+>Hg2+, with higher values that were generally determined at inner stations. Among a total of 286 bacterial isolates (mainly achieved from Ni- and Pb-amended plates), the 7.2% showed multiresistance at increasing metal concentration (up to 10,000 ppm). Selected multiresistant isolates belonged to the genera Stenotrophomonas, Arthrobacter, and Serratia. Results highlighted that bacteria, rapidly responding to changing conditions, could be considered as true indicators of the harmful effect caused by contaminants on human health and environment and suggested their potential application in bioremediation processes of metal-polluted cold sites.

Studying the fundamental limit of optical fiber links to the 10-21 level.

We present a hybrid fiber link combining effective optical frequency transfer and evaluation of performances with a self-synchronized two-way comparison. It enables us to detect the round-trip fiber noise and each of the forward and backward one-way fiber noises simultaneously. The various signals acquired with this setup allow us to study quantitatively several properties of optical fiber links. We check the reciprocity of the accumulated noise forth and back over a bi-directional fiber to the level of 3.1(±3.9) × 10-20 based on a 160000s continuous data. We also analyze the noise correlation between two adjacent fibers and show the first experimental evidence of interferometric noise at very low Fourier frequency. We estimate redundantly and consistently the stability and accuracy of the transferred optical frequency over 43 km at 4 × 10-21 level after 16 days of integration and demonstrate that a frequency comparison with instability as low as 8 × 10-18 would be achievable with uni-directional fibers in urban area.

Cascaded optical fiber link using the internet network for remote clocks comparison.

We report a cascaded optical link of 1100 km for ultra-stable frequency distribution over an Internet fiber network. The link is composed of four spans for which the propagation noise is actively compensated. The robustness and the performance of the link are ensured by five fully automated optoelectronic stations, two of them at the link ends, and three deployed on the field and connecting the spans. This device coherently regenerates the optical signal with the heterodyne optical phase locking of a low-noise laser diode. Optical detection of the beat-note signals for the laser lock and the link noise compensation are obtained with stable and low-noise fibered optical interferometer. We show 3.5 days of continuous operation of the noise-compensated 4-span cascaded link leading to fractional frequency instability of 4x10(-16) at 1-s measurement time and 1x10(-19) at 2000 s. This cascaded link was extended to 1480-km with the same performance. This work is a significant step towards a sustainable wide area ultra-stable optical frequency distribution and comparison network at a very high level of performance.

Sealworm (Pseudoterranova decipiens) infection in grey seals (Halichoerus grypus), cod (Gadus morhua) and shorthorn sculpin (Myoxocephalus scorpius) in the Baltic Sea.

The anisakid nematode Pseudoterranova decipiens, known as the sealworm or cod worm, can infect the flesh of several fish species. The parasite causes cosmetic problems for the fish industry and can cause abdominal discomfort if consumed by humans. There are only scattered studies on the abundance or distribution of the sealworm in fish and seals in the Baltic Sea. To remedy this situation, the extent of sealworm infection was investigated in cod (Gadus morhua) and shorthorn sculpin (Myoxocephalus scorpius) collected along the Swedish coast. A relative presence of the sealworm was also investigated in samples from grey seal (Halichoerus grypus) stomachs. Up to 100% of the fish were infected in some of the areas. Sculpin were generally worse infected than cod, both in abundance and prevalence of parasites. General linear models showed a significant correlation between the number of seals in an area and the prevalence of sealworms in cod. There was a sharp decrease of infected fish in areas with salinity lower than 7‰. Even though the northern Baltic proper and the southern Bothnian Sea have a high number of grey seals, only one sealworm was found in a sculpin in that region, and none in cod. In grey seal stomachs the sealworm was only found in samples from the central Baltic proper; further north, all anisakid nematodes identified in seals were Contracaecum osculatum. The results indicate that seal presence drives the distribution in the southern parts of the Baltic and that low salinity, or some other variable which correlates with salinity, limits the distribution in the northern part.

Sediment quality classification in freshwater lakes predicted by the history of treatment with copper-based aquatic algaecides.

Copper-based aquatic algaecides have been widely used in the management of aquatic macrophyte and harmful algal blooms for decades due to their effectiveness and low cost. However, repeated treatment of freshwater lakes results in the accumulation of copper in the sediment, which may adversely affect the ecosystem of the lakes through toxicity to benthic invertebrates and other organisms. Consequently, copper-based aquatic herbicides and algaecides have been frequently subjected to regulations aimed at preventing further ecological deterioration in treated waterbodies. Many states in the US are taking or considering taking an approach that limits or prohibits copper treatment in waterbodies. Freshwater lakes with extensive historical copper treatments typically have significantly higher concentrations of copper in the sediment than untreated lakes. However, the correlation between the extent of the treatments and level of copper accumulation in the sediment has not been quantitatively characterized. In the present study, between 2006 and 2017, copper concentrations were measured in the sediment from selected lakes in New York State with different histories of copper-based aquatic algaecide treatment. Analysis of these data confirmed findings from earlier studies conducted by New York State that lakes with histories of copper treatment have significantly higher copper concentrations in the sediment. It also demonstrated that sediment copper concentrations were significantly higher in the sublittoral zone than the littoral zone in treated lakes. Moreover, a positive correlation was detected between sediment copper concentrations and the total number of treatments with copper-based aquatic algaecide for both littoral and sublittoral zones (p-value = 7.94 × 10-8 and 3.1 × 10-13 , respectively). This relationship can be used as a screening tool for regulatory agencies to identify lakes with sediment copper levels possibly higher than the toxicity threshold for aquatic life. Consequently, additional ecological risk assessment may be required before allowing future treatment with copper-based aquatic algaecides. Integr Environ Assess Manag 2024;00:1-12. © 2024 SETAC.

First report on pollutant accumulation and associated microbial communities in the freshwater sponge Spongilla lacustris (Linnaeus, 1759) from the sub-Arctic Pasvik River (Norway).

This explorative study was aimed at first characterizing the sponge Spongilla lacustris (Linnaeus, 1759) from the sub-Arctic Pasvik River (Northern Fennoscandia), in terms of associated microbial communities and pollutant accumulation. Persistent organic pollutants were determined in sponge mesohyl tissues, along with the estimation of the microbial enzymatic activity rates, prokaryotic abundance and morphometric traits, and the analysis of the taxonomic bacterial diversity by next-generation sequencing techniques. The main bacterial groups associated with S. lacustris were Alphaproteobacteria and Gammaproteobacteria, followed by Chloroflexi and Acidobacteria. The structure of the S. lacustris-associated bacterial communities was in sharp contrast to those of the bacterioplankton, being statistically close to those found in sediments. Dieldrin was measured at higher concentrations in the sponge tissues (3.1 ± 0.4 ng/g) compared to sediment of the same site (0.04 ± 0.03 ng/g). Some taxonomic groups were possibly related to the occurrence of certain contaminants, as was the case of Patescibacteria and dieldrin. Obtained results substantially contribute to the still scarce knowledge of bacterial community diversity, activities, and ecology in freshwater sponges. PRACTITIONER POINTS: Microbial community associated with Spongilla lacustris is probably shaped by the occurrence of certain contaminants, mainly dieldrin and heavy metals. A higher accumulation of dieldrin in the sponge mesohyl tissues than in sediment was determined. S. lacustris is suggested as sponge species to be used as a sentinel of pesticide pollution in the Pasvik River. S. lacustris, living in tight contact with soft substrates, harbored communities more similar to sediment than water communities.

Predictors of in-ICU length of stay among congenital heart defect patients using artificial intelligence model: A pilot study.

Objective: This study aims to develop a predictive model using artificial intelligence to estimate the ICU length of stay (LOS) for Congenital Heart Defects (CHD) patients after surgery, improving care planning and resource management. Design: We analyze clinical data from 2240 CHD surgery patients to create and validate the predictive model. Twenty AI models are developed and evaluated for accuracy and reliability. Setting: The study is conducted in a Brazilian hospital's Cardiovascular Surgery Department, focusing on transplants and cardiopulmonary surgeries. Participants: Retrospective analysis is conducted on data from 2240 consecutive CHD patients undergoing surgery. Interventions: Ninety-three pre and intraoperative variables are used as ICU LOS predictors. Measurements and main results: Utilizing regression and clustering methodologies for ICU LOS (ICU Length of Stay) estimation, the Light Gradient Boosting Machine, using regression, achieved a Mean Squared Error (MSE) of 15.4, 11.8, and 15.2 days for training, testing, and unseen data. Key predictors included metrics such as "Mechanical Ventilation Duration", "Weight on Surgery Date", and "Vasoactive-Inotropic Score". Meanwhile, the clustering model, Cat Boost Classifier, attained an accuracy of 0.6917 and AUC of 0.8559 with similar key predictors. Conclusions: Patients with higher ventilation times, vasoactive-inotropic scores, anoxia time, cardiopulmonary bypass time, and lower weight, height, BMI, age, hematocrit, and presurgical oxygen saturation have longer ICU stays, aligning with existing literature.

A systems genetic analysis of high density lipoprotein metabolism and network preservation across mouse models.

We report a systems genetic analysis of high density lipoprotein (HDL) levels in an F2 intercross between inbred strains CAST/EiJ and C57BL/6J. We previously showed that there are dramatic differences in HDL metabolism in a cross between these strains, and we now report co-expression network analysis of HDL that integrates global expression data from liver and adipose with relevant metabolic traits. Using data from a total of 293 F2 intercross mice, we constructed weighted gene co-expression networks and identified modules (subnetworks) associated with HDL and clinical traits. These were examined for genes implicated in HDL levels based on large human genome-wide associations studies (GWAS) and examined with respect to conservation between tissue and sexes in a total of 9 data sets. We identify genes that are consistently ranked high by association with HDL across the 9 data sets. We focus in particular on two genes, Wfdc2 and Hdac3, that are located in close proximity to HDL QTL peaks where causal testing indicates that they may affect HDL. Our results provide a rich resource for studies of complex metabolic interactions involving HDL. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Environmental footprints of farmed chicken and salmon bridge the land and sea.

Food production, particularly of fed animals, is a leading cause of environmental degradation globally.1,2 Understanding where and how much environmental pressure different fed animal products exert is critical to designing effective food policies that promote sustainability.3 Here, we assess and compare the environmental footprint of farming industrial broiler chickens and farmed salmonids (salmon, marine trout, and Arctic char) to identify opportunities to reduce environmental pressures. We map cumulative environmental pressures (greenhouse gas emissions, nutrient pollution, freshwater use, and spatial disturbance), with particular focus on dynamics across the land and sea. We found that farming broiler chickens disturbs 9 times more area than farming salmon (∼924,000 vs. ∼103,500 km2) but yields 55 times greater production. The footprints of both sectors are extensive, but 95% of cumulative pressures are concentrated into <5% of total area. Surprisingly, the location of these pressures is similar (85.5% spatial overlap between chicken and salmon pressures), primarily due to shared feed ingredients. Environmental pressures from feed ingredients account for >78% and >69% of cumulative pressures of broiler chicken and farmed salmon production, respectively, and could represent a key leverage point to reduce environmental footprints. The environmental efficiency (cumulative pressures per tonne of production) also differs geographically, with areas of high efficiency revealing further potential to promote sustainability. The propagation of environmental pressures across the land and sea underscores the importance of integrating food policies across realms and sectors to advance food system sustainability.

A virion-associated protein kinase induces apoptosis.

Apoptosis and inhibition of host gene expression are often associated with virus infections. Many viral polypeptides modulate apoptosis by direct interaction with highly conserved apoptotic pathways. Some viruses induce apoptosis during late stages of the infection cycle, while others inhibit apoptosis to facilitate replication or maintain persistent infection. In previous work, we showed that Chilo iridescent virus (CIV) or CIV virion protein extract induces apoptosis in spruce budworm and cotton boll weevil cell cultures. Here, we characterize the product of a CIV gene (iridovirus serine/threonine kinase; istk) with signature sequences for S/T kinase and ATP binding. ISTK appears to belong to the superfamily, vaccinia-related kinases (VRKs). The istk gene was expressed in Pichia pastoris vectors. Purified ISTK (48 kDa) exhibited S/T kinase activity. Treatment with ISTK induced apoptosis in budworm cells. A 35-kDa cleavage product of ISTK retaining key signature sequences was identified during purification. Pichia-expressed 35-kDa polypeptide, designated iridoptin, induced apoptosis and inhibition of host protein synthesis in budworm and boll weevil cells. A mutation in the ATP-binding site eliminated both kinase and apoptosis activity of iridoptin, suggesting that kinase activity is essential for induction of apoptosis. Analysis with custom antibody confirmed that ISTK is a structural component of CIV particles. This is the first demonstration of a viral kinase inducing apoptosis in any virus-host system and the first identification of a factor inducing apoptosis or host protein shutoff for the family Iridoviridae.

Democratizing education: Open schooling engaged the less privileged in environmental sciences.

Democratizing learning is essential for environmental sustainability. Less privileged areas are crucial in this regard. Informal education has great such potential, but often fails to reach the less privileged, and to document learning. With the objective to identify and counter these issues, we here report on EDU-ARCTIC, an informal open schooling course in environmental science, aimed at European teachers with teenage pupils. Of the 1,181 teachers who enrolled, 73% were females and 43% were from less privileged nations (according to UN Human Development Index). This is a higher share of less privileged (females) than is the case for the general population of Europe. Teachers from less privileged nations also participated in more project activities than did those from more privileged nations, apart from in urban areas. For the project period, the teachers reported a significant increase in all the three categories of aspired learning outcomes for their pupils. We conclude that courses like ours can increase teenagers' literacy and engagement in science and environmental issues, not the least in less privileged areas. Deliberate efforts are required to reach these target groups, who may be less inclined to join on their own.

A 500-km Cascaded White Rabbit Link for High-Performance Frequency Dissemination.

We perform experiments exploring the use of white rabbit precision time protocol (WR-PTP) for time and frequency dissemination over long-distance optical fiber links. We use unidirectional links, to ensure compatibility with active telecommunication networks, and White Rabbit equipment with modifications for improved performance. Using fiber spools, we realize a 500 km, four-span cascaded white rabbit link. We show short term fractional frequency stability of 2×10-12 , averaging down to 2×10-15 at one day of integration time, with no frequency shift within the statistical uncertainty. We demonstrate the impact of increasing the White Rabbit SoftPLL bandwidth and the PTP message rate. We show evidence of the effect of thermal fluctuations acting on the fiber, and finally discuss the limitations of the achieved performance. We show comparisons with experimental data acquired with commercial good quality global positioning system (GPS) receivers and show that the medium- and long- term stability and accuracy are more than one order of magnitude better with a WR-PTP link.

Benthic Microbial Communities in a Seasonally Ice-Covered Sub-Arctic River (Pasvik River, Norway) Are Shaped by Site-Specific Environmental Conditions.

The Pasvik River experiences chemical, physical, and biological stressors due to the direct discharges of domestic sewage from settlements located within the catchment and runoff from smelter and mine wastes. Sediments, as a natural repository of organic matter and associated contaminants, are of global concern for the possible release of pollutants in the water column, with detrimental effects on aquatic organisms. The present study was aimed at characterizing the riverine benthic microbial community and evaluating its ecological role in relation to the contamination level. Sediments were sampled along the river during two contrasting environmental periods (i.e., beginning and ongoing phases of ice melting). Microbial enzymatic activities, cell abundance, and morphological traits were evaluated, along with the phylogenetic community composition. Amplified 16S rRNA genes from bacteria were sequenced using a next-generation approach. Sediments were also analyzed for a variety of chemical features, namely particulate material characteristics and concentration of polychlorobiphenyls, polycyclic aromatic hydrocarbons, and pesticides. Riverine and brackish sites did not affect the microbial community in terms of main phylogenetic diversity (at phylum level), morphometry, enzymatic activities, and abundance. Instead, bacterial diversity in the river sediments appeared to be influenced by the micro-niche conditions, with differences in the relative abundance of selected taxa. In particular, our results highlighted the occurrence of bacterial taxa directly involved in the C, Fe, and N cycles, as well as in the degradation of organic pollutants and toxic compounds.

Ecological risk of methylmercury to piscivorous fish of the Great Lakes region.

Contamination of fish populations with methylmercury is common in the region of the Laurentian Great Lakes as a result of atmospheric deposition and methylation of inorganic mercury. Using fish mercury monitoring data from natural resource agencies and information on tissue concentrations injurious to fish, we conducted a screening-level risk assessment of mercury to sexually mature female walleye (Sander vitreus), northern pike (Esox lucius), smallmouth bass (Micropterus dolomieu), and largemouth bass (Micropterus salmoides) in the Great Lakes and in interior lakes, impoundments, and rivers of the Great Lakes region. The assessment included more than 43,000 measurements of mercury in fish from more than 2000 locations. Sexually mature female fish that exceeded threshold-effect tissue concentrations of 0.20 µg g(-1) wet weight in the whole body occurred at 8% (largemouth bass) to 43% (walleye) of sites. Fish at 3% to 18% of sites were at risk of injury and exceeded 0.30 µg g(-1) where an alteration in reproduction or survival is predicted to occur. Most fish at increased risk were from interior lakes and impoundments. In the Great Lakes, no sites had sexually mature fish that exceeded threshold-effect concentrations. Results of this screening-level assessment indicate that fish at a substantive number of locations within the Great Lakes region are potentially at risk from methylmercury contamination and would benefit from reduction in mercury concentrations.

Studying phenological phenomena in subarctic biomes with international school pupils as citizen scientists.

Citizen science can facilitate in-depth learning for pupils and students, contribute to scientific research, and permit civic participation. Here, we describe the development of the transnational school-based citizen science project Phenology of the North Calotte. Its primary goal is to introduce pupils (age 12-15; grades 7-10) in northern Norway, Russia, and Finland to the local and global challenges of climate change resulting in life cycle changes at different trophic and ecosystem levels in their backyards. Partnerships between regional scientists and staff from NIBIO Svanhovd, State nature reserves, national parks, and teachers and pupils from regional schools aim to engage pupils in project-based learning. The project uses standardized protocols, translated into the different languages of participating schools. The phenological observations are centered around documenting clearly defined life cycle phases (e.g., first appearance of species, flowering, ripening, leaf yellowing, snow fall, and melt). The observations are collected either on paper and are subsequently submitted manually to an open-source online database or submitted directly via a newly developed mobile app. In the long term, the database is anticipated to contribute to research studying changes in phenology at different trophic levels. In principle, guided school-based citizen science projects have the potential to contribute to increased environmental awareness and education and thereby to transformative learning at the societal level while contributing to scientific progress of understudied biomes, like the northern taiga and (sub)arctic tundra. However, differences in school systems and funding insecurity for some schools have been major prohibiting factors for long-term retention of pupils/schools in the program. Project-based and multidisciplinary learning, although pedagogically desired, has been partially difficult to implement in participating schools, pointing to the need of structural changes in national school curricula and funding schemes as well as continuous offers for training and networking for teachers.