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Seasonal changes in bay water column properties and their influence on the distribution of dissolved and particulate substances along the south coast of Curaçao (Caribbean Sea)
No full textAs endpoints of watersheds, bays concentrate erosion- and human-derived substances such as dissolved inorganic nutrients and pollutants. We investigated the water movement and biogeochemistry of two bays in Curaçao: Piscadera Bay and Spaanse Water, during the dry (May 2022 and 2023) and wet seasons (November 2021 and 2023). Bay-ocean exchange was limited during the dry season, enhancing nutrient concentrations in the bays. The wet season showed increased mixing between bay and offshore water. Extreme rainfall from the 2023 El Niño event led to heavy runoff and wastewater influx, particularly in Piscadera Bay, where enriched δ15N and total xenobiotic concentrations were over 1.5 times higher than in the dry season. Elevated δ15N and δ13C values reflected greater terrestrial influence in Piscadera Bay. These findings show how extreme weather, likely under future climate scenarios, can enhance nutrient and pollutant export from bays to reefs.</span
Identification of clear-sky periods and cloudiness using diffuse-to-direct spectral ratios of hyperspectral solar irradiance and sky radiance measurements
No full textAccurate identification of clear-sky and cloudy periods from hyperspectral radiometric data is essential for atmospheric and remote sensing studies. Traditional approaches that rely on single-wavelength spectral ratios often fail under broken-clouds due to rapid irradiance fluctuations and aerosol interference. This study introduces a new method based on the spectrally integrated diffuse-to-direct irradiance ratio (IDR), which is derived from modeled hyperspectral components and provides a robust indicator of sky conditions. The model is developed using 15-year hyperspectral measurements of solar downwelling irradiance (ES(λ), mW m-2 nm-1) and sky radiance (LS(λ), mW m-2 nm-1 sr-1) collected in a fixed coastal station located at the Marsdiep tidal inlet in the Dutch Wadden Sea. The model is validated against reference clear-sky periods identified using established clear-sky models and detection algorithms based on simultaneous Global Horizontal Irradiance (GHI) measurements. Results show that IDR thresholds of ≤ 0.35 for clear skies and ≥ 0.70 for overcast conditions achieve high agreement (95% and 92%, respectively) with reference sky classifications. The IDR effectively accounts for the influence of rapidly changing cloud cover in intermediate conditions, ensuring robust classification of clear-sky and overcast periods. The classification is further supported by spectral analysis using Principal Component Analysis, which confirm the stability of diffusive component to ES(λ) features and the interferences of LS(λ)/ES(λ) ratio across different sky conditions. This work highlights the importance of the diffuse irradiance component role in hyperspectral sky classification. Future research should validate IDR with direct diffuse irradiance measurements to enhance the proposed model under diverse atmospheric conditions.</span
Microbial and nutrient enrichments in Brine and Nilas during the first 24 h of open water lead refreezing
No full textOpen water leads in the sea ice covering the Polar regions are becoming more frequent and cover larger areas as a result of the warming and thinning of the ice. Refreezing of the leads advances the occurrence of young and newly formed sea ice (nilas), which has a thickness of < 10 cm and is characterized by a highly saline surface brine. Due to the growth of fragile frost flowers exposed at its surface, nilas can become a significant source of bromine, mercury, sea salt aerosols, bioaerosols, and ice nucleating particles for the atmosphere. Here we report the results of a study where we investigated the initial formation phase of a 3–6 mm–thick nilas in cleared sea ice ponds. Samples for quantifications of macronutrients, microorganisms, Chlorophyll a (Chl a) and photobiology were collected from seawater, nilas, and brine 5 and 24 h, after the experiment commenced. The concentration changes between constituents were scaled relative to changes in salinity with the enrichment index (I). Nilas was enriched in microalgae and Chl a and the brine was highly enriched in bacteria, virus like particles (VLPs) and algae after only 5 h. We did not find a significant further enrichment between 5 and 24 h of nilas formation. This indicates that the initial formation phase of the nilas is an important step in distributing nutrients and microorganisms in nilas and brine. Only particulate matter was enriched in nilas and brine and none of the macronutrients. Photosynthetic microalgae were strongly impaired in the nilas and the brine, where no fluorescence signal could be detected supposedly due to a combination of excessive light at the surface and high brine salinity. The reasons for the observed differences in enrichments are evaluated and discussed including concentration of particulate matter, evaporation of surface brine, microbial growth and concentration of microorganisms in the sea surface microlayer (SML). Further studies are needed to decipher which of the proposed mechanisms were predominantly responsible for the observed enrichments as well as how these enrichments affect firstly the frost flowers and secondly the atmosphere.</span
Spatial variability of the coastal Wadden Sea fish community as revealed by environmental DNA
No full textPrevious studies have suggested the occurrence of spatial variability in the fish food web structure in the temperate Wadden Sea. However, these studies were carried out in different years and with different fishing devices. To eliminate interannual variability in fish abundance and the impact of sampling design, an environmental DNA (eDNA) study was performed monthly at eight locations over the spatial scale of the Dutch Wadden See year-round in 2018–2019. In total, 40 different individual fish species and 8 fish groups were identified. The number of fish species identified in the samples varied over time and among locations between three and 19 different fish species. Over the year, 20 species were identified at all locations; eight species were found at 6–7 locations and the remaining 30 species were found only incidentally. The spatial variability found in the Wadden Sea fish community is the result of the variability in presence of rare (transient) species, due to location specific differences in hydrographical and geomorphological characteristics.</span
Diel rhythmicity of activity and corticosterone metabolites in Arctic barnacle geese during breeding
No full textBirds that migrate from temperate areas to the Arctic to breed lose their strongest Zeitgeber of circadian organization when they cross the Arctic circle in spring – the 24h light-dark cycle. Under continuous daylight, diverse behavioral and physiological patterns have been detected in both free-ranging and laboratory animals. To better understand the evolution of plasticity in circadian clocks, it is essential to study behavioral and physiological rhythmicity in the context of a species’ ecology. Employing a multifaceted approach, which included wildlife cameras, accelerometers, and noninvasive sampling of hormone metabolites, we investigated activity patterns and corticosterone rhythmicity in a migratory herbivore, the barnacle goose (Branta leucopsis), during its Arctic breeding season on Svalbard. We found that females showed a combination of both ultradian and diel rhythmicity in nest recesses and sleep during incubation. In both parents, these rhythms in activity continued also during the gosling rearing phase. During molt, many geese aligned activity with the prevailing tidal rhythm. Barnacle geese showed weak diel rhythmicity in excreted corticosterone metabolites (CORTm). This suggests that while Arctic geese may adopt an alternative Zeitgeber during the Arctic summer to maintain a diel rhythm, ultradian rhythmicity remains essential, allowing the geese to flexibly adjust their rhythms to environmental conditions
Organic carbon uptake and mineralization in slow sand filters and their relation to process variables
No full textSlow sand filtration (SSF) is a widely used biofiltration method for drinking water treatment, yet quantitative measures of biological activity, specifically in terms of carbon uptake and mineralization, are not well established. This study assessed biological activity in mature SSF systems operated by three Dutch drinking water companies using carbon concentration measurements, isotopic signature analyses, and 13C-labeled glucose tracer experiments. Our results revealed measurable differences in carbon concentrations and isotopic signatures between influent and effluent waters. Specifically, DOC concentrations decreased by up to 0.13 mmol L−1, while DIC concentrations increased by up to 0.84 mmol L−1. Additionally, δ13C-DOC and δ13C-DIC values exhibited shifts of up to +1.9 ‰ and 2.9 ‰, respectively, indicative of carbon uptake and mineralization. Biological activity varied across filters, as reflected in the time required for complete removal of glucose, which ranged from 5 to over 48 h and correlated with assimilable organic carbon (AOC) removal rates. AOC loading appeared to be the primary driver of bioactivity, with the lowest activity found in a filter fed with dune-infiltrated water and the highest in a filter receiving ozonated influent water. These findings highlight the importance of considering source water characteristics and the preceding treatment chain to understand their potential impact on biological activity in SSF.</span
Unusual plastoquinones in non‐phototrophic nitrifying bacteria
No full textIsoprenoid quinones are important compounds in most organisms. They are essential in electron and proton transport in respiratory and photosynthetic electron transport chains, and additional functions include oxidative stress defence. The biologically most relevant quinones are naphthoquinones including menaquinone and benzoquinones including ubiquinone and plastoquinone. They differ in their polar headgroup structures, physicochemical properties, and distribution among organisms. Menaquinone is the most widespread quinone in prokaryotes, ubiquinone occurs only in bacteria of the phylum Pseudomonadota and eukaryotes, and plastoquinone exists in phototrophic Cyanobacteria and plants. We found that chemolithoautotrophic nitrifying bacteria of the genus Nitrospira (phylum Nitrospirota) exclusively possess unusual methyl-plastoquinones with a standard redox potential below that of canonical plastoquinone and ubiquinone but above menaquinone, suggesting functional roles in reverse electron transport, ammonia oxidation, alternative energy metabolisms, and oxidative stress mitigation. This extends the known diversity of quinones and suggests that plastoquinone derivatives are essential in ecologically important, non-phototrophic bacteria.</span
Bacteriohopanepolyols and glycerol dialkyl glycerol tetraethers record Holocene redox regime shifts in a marine inlet in eastern Prydz Bay, Antarctica
No full textPrydz Bay is located at the terminus of one of the largest marine-terminating glacial systems of East Antarctica. Consequently, its sedimentary record may hold information on the response of marine biogeochemical cycling to changes in Antarctic palaeoceanography and palaeoclimate. Bacteriohopanepolyols (BHPs) and glycerol dialkyl glycerol tetraethers (GDGTs) offer great potential for tracing such changes, as these membrane lipids have been linked to distinct biogeochemical processes and environmental niches. Here, we present the BHP and GDGT inventory of a Holocene sediment record, recovered from a marine basin in eastern Prydz Bay. BHP and GDGT lipidomics were complemented with (organic) geochemical tools to reconstruct palaeoenvironmental conditions. GDGT-based indices suggest terrestrial organic matter influx was insignificant. Our results show elevated nucleoside-BHPs in early Holocene sediments from ∼9.1 to 10.7 cal ka BP. Their presence is interpreted to reflect autochthonous production under hypoxic-anoxic water column conditions, as inferred from BHT-x ratios of ≥0.2. The record is characterized by a large diversity of rare and novel unsaturated BHPs and BHP isomers. Their occurrence is potentially related to homeoviscous adaptations of the membranes of predominantly aerobic bacteria to cold conditions (i.e., reconstructed sea surface temperatures are −2.4 to −0.8 °C based on ). Increased abundance and diversity of these BHPs between ∼5.5–7.5 and ∼8.9–9.8 cal ka BP is likely associated with an oxygenation of the basin at this time. During the late Holocene (<3.0 cal ka BP), the water column experienced photic zone euxinia, high rates of nitrogen loss and methanogenesis, as indicated by the presence of isorenieratene, enriched δ15N values and high GDGT-0/cren ratios, respectively. BHPs in these sediments likely derive from two different ecological niches: i) the uppermost oxygenated to suboxic waters where aerobic methane oxidation occurred and ii) the deeper sulfidic waters. More reducing conditions in the late Holocene coincide with increased brGDGT cyclization and methylation, and is proposed to indicate a shift in the source bacterial niche from sediments to the water column. This study shows that GDGT and BHP distributions can be linked to distinct redox regime shifts within the basin, which appear regulated by changes in sea level and sea ice in Prydz Bay. Our findings highlight the potential use of these lipids as tracers for biogeochemical cycling in marine polar regions.</span
Search for quantum decoherence in neutrino oscillations with six detection units of KM3NeT/ORCA
No full textNeutrinos described as an open quantum system may interact with the environment which introduces stochastic perturbations to their quantum phase. This mechanism leads to a loss of coherence along the propagation of the neutrino - a phenomenon commonly referred to as decoherence - and ultimately, to a modification of the oscillation probabilities. Fluctuations in space-time, as envisaged by various theories of quantum gravity, are a potential candidate for a decoherence-inducing environment. Consequently, the search for decoherence provides a rare opportunity to investigate quantum gravitational effects which are usually beyond the reach of current experiments. In this work, quantum decoherence effects are searched for in neutrino data collected by the KM3NeT/ORCA detector from January 2020 to November 2021. The analysis focuses on atmospheric neutrinos within the energy range of a few GeV to 100 GeV. Adopting the open quantum system framework, decoherence is described in a phenomenological manner with the strength of the effect given by the parameters Γ21 and Γ31. Following previous studies, a dependence of the type Γij ∝ (E/E0)n on the neutrino energy is assumed and the cases n = -2,-1 are explored. No significant deviation with respect to the standard oscillation hypothesis is observed. Therefore, 90% CL upper limits are estimated as Γ21 < 4.6· 1021GeV and Γ31 < 8.4· 1021GeV for n = -2 and Γ21 < 1.9· 10-22GeV and Γ31 < 2.7· 10-22GeV for n = -1, respectively.</span
Migration, land loss and costs to 2100 due to coastal flooding under the IPCC AR6 sea-level rise scenarios and plausible adaptation choices
No full textSea-level rise (SLR) through the twenty-first century and beyond is inevitable, threatening coastal areas and their inhabitants unless there is appropriate adaptation. We investigate coastal flooding to 2100 under the full range of IPCC AR6 (2021) SLR scenarios, assuming plausible adaptation. The adaptation selects the most economically robust adaptation option: protection or retreat. People living in unprotected coastal areas that are frequently inundated (below 1-in-1-year flood level) are assumed to migrate, and the land is considered lost. Globally, across the range of SLR and related socioeconomic scenarios, we estimate between 4 million and 72 million people could migrate over the twenty-first century, with a net land loss ranging from 2,800 to 490,000 km2. India and Vietnam consistently show the highest absolute migration, while Small Island Developing States are the most affected when considering relative migration and land loss. Protection is the most robust adaptation option under all scenarios for 2.8% of the global coastline, but this safeguards 78% of the global population and 91% of assets in coastal areas. Climate stabilisation (SSP1–1.9 and SSP1–2.6) does not avoid all coastal impacts and costs as sea levels still rise albeit more slowly. The impacts and costs are also sensitive to the socioeconomic scenario: SSP3–7.0 experiences higher migration than SSP5–8.5 despite lower SLR, reflecting a larger population and lower GDP. Our findings can inform national and intergovernmental agencies and organisations on the magnitude of SLR impacts and costs and guide assessments of adaptation policies and strategies