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A hydrodynamic model coupled with a particle tracking model was used to identify the pathways and accumulation areas of microplastics (MP) in the Gulf of Finland (GoF) over a three-year period (2018-2020). Two key sources, wastewater treatment plants (WWTPs) and rivers, were considered, focusing on polypropylene (PP)/polyethylene (PE) and polyethylene terephthalate (PET) particles sized 20-500 μm. Rivers contribute 76% of total MP entering the gulf, while WWTPs account for the remaining 24%. Most of the MP accumulates inside the gulf and does not drift to the Baltic Proper. The eastern part of the gulf exhibits the highest surface concentrations of particles influenced by the Neva River. In the water column, MP concentrations were notably high in shallow coastal areas, decreasing gradually offshore. Potential MP accumulation zones were identified primarily between longitudes 28°E and 30°E, particularly near the major rivers Narva and Kymi and in the easternmost gulf related to the Neva River discharge. The MP concentrations in the surface layer and water column were higher in winter while settling was more intense in summer. Short-term variability in the surface layer was caused by (sub)mesoscale advection and divergence/convergence, while in the near-bottom layer, strong bottom currents and consequent resuspension elevated the concentrations. [ABSTRACT FROM AUTHOR]

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Phytoplankton blooms exhibit varying patterns in timing and number of peaks within ecosystems. These differences in blooming patterns are partly explained by phytoplankton:nutrient interactions and external factors such as temperature, salinity and light availability. Understanding these interactions and drivers is essential for effective bloom management and modelling as driving factors potentially differ or are shared across ecosystems on regional scales. Here, we used a 22-year data set (19 years training and 3 years validation data) containing chlorophyll, nutrients (dissolved and total), and external drivers (temperature, salinity, light) of the southern Baltic Sea coast, a European brackish shelf sea, which constituted six different phytoplankton blooming patterns. We employed generalized additive mixed models to characterize similar blooming patterns and trained an artificial neural network within the Universal Differential Equation framework to learn a differential equation representation of these pattern. Applying Sparse Identification of Nonlinear Dynamics uncovered algebraic relationships in phytoplankton:nutrient:external driver interactions. Nutrients availability was driving factor for blooms in enclosed coastal waters; nutrients and temperature in more open regions. We found evidence of hydrodynamical export of phytoplankton, natural mortality or external grazing not explicitly measured in the data. This data-driven workflow allows new insight into driver-differences in region specific blooming dynamics. [ABSTRACT FROM AUTHOR]

Background: Zostera marina is an important ecosystem engineer influencing shallow water environments and possibly shaping the microbiota in surrounding sediments and water. Z. marina is typically found in marine systems, but it can also proliferate under brackish conditions. Changes in salinity generally have a strong impact on the biota, especially at the salty divide between salinity 6 and 9. To better understand the impact of the salty divide on the interaction between Z. marina and the surrounding sediment and water microbiota, we investigated the effects of Z. marina meadows on the surrounding microbiota across a salinity range of 6–15 in the Baltic Sea during the summer using 16S and 18S rRNA gene amplicon sequencing. Results: Salinity was the most important factor for structuring the microbiota within both water and sediment. The presence of Z. marina affected the composition of the bacterial and eukaryotic community and bacterial alpha diversity in the sediment. However, this effect was confined to alpha-mesohaline conditions (salinity 9–15). The impact of Z. marina below salinity 9 on water and sediment microbiota was insignificant. Conclusions: Increasing salinity was associated with a longer leaf length of Z. marina, causing an increased canopy height, which affects the sediment microbiota through reduced water velocity. Hence, we propose that the canopy effect may be the major predictor explaining Z. marina's interactions with the surrounding microbiota at salinity 9–15. These findings emphasize the importance of the physical effects of Z. marina meadow ecosystem services and have important implications for Z. marina management under brackish conditions in a changing climate. [ABSTRACT FROM AUTHOR]

In 2023, exceptionally few salmon (Salmo salar) ascended from the Baltic Sea to spawn in the Rivers Tornionjoki and Simojoki, regardless of the proper number of smolts descending to the sea in preceding years. We investigated how the numbers of age-0 and young herring (Clupea harengus) and sprat (Sprattus sprattus), which are the principal prey species of salmon in the Baltic Proper, the main feeding area of these salmon, as well as the amount of lipid obtained from them and their protein-to-lipid ratio, correlated with the number of returning salmon and the thiamine (vitamin B1) status of spawning salmon. The fewer the 0-year-old herring were and the more abundant were the youngish sprat in the Baltic Proper when the post-smolts arrived there, and the greater the lipid content and lower the protein-to-lipid ratio of the prey fish, the fewer salmon returned to the Rivers Tornionjoki and Simojoki to spawn two years later. The number of returning salmon was lowest with a high ratio of youngish sprat, 1–3 years old, regarding the River Tornionjoki and 1–2 years old regarding the River Simojoki post-smolts, to 0-year-old herring, which were of a suitable size to be the prey for the post-smolts upon their arrival in the Baltic Proper. In 2021, the ratios were lowest due to the record-low number of 0-year-old herring. The poor thiamine status of spawning salmon was also associated with the high lipid content of available prey fish and with the abundance of youngish sprat, which have twice the lipid content of age-0 herring. Our findings parallel the observations in the early 1990s when post-smolt survival declined concurrently with the outbreak of thiamine deficiency, M74. We conclude that consuming high-lipid marine fish reduces the survival of post-smolts and, thus, the number of returning salmon, in addition to causing thiamine deficiency. [ABSTRACT FROM AUTHOR]

Hypoxia is a major environmental threat for coastal seas, including the strongly-stratified Baltic Sea in northern Europe. There, a pronounced increase in nutrient loads since the 1950s led to the development of one of the largest hypoxic areas worldwide. So far, other drives of hypoxia, like the increase in water temperatures due to global warming, have been considered minor compared to eutrophication. We show, by analyzing 159-years long hindcast simulations of three different Baltic Sea models, that exceptional warming trends in deep water layers of the western Baltic Sea deteriorated the local oxygen conditions. The above-average warming is only to a small extent attributed directly to global warming, but mainly to a shift in the seasonality of saltwater inflows from the North Sea towards more warm summer and early autumn inflows. Hence, we identify a so far unknown driver of oxygen depletion in the western Baltic Sea with potentially serious ecological consequences. [ABSTRACT FROM AUTHOR]

This study aims to reconstruct the changes in storminess during the past 7600 years in the northeastern Baltic Sea region. For storminess reconstructions, aeolian sand influx (ASI) in coastal peat bog deposits was applied as an indicator of the past storminess. We analyzed cores from four peat bogs in the western and northern coastal areas of Estonia: the cores from Hiiumaa N, Hiiumaa SW, Saaremaa and Juminda study sites covered the past 3700, 3750, 2400, and 8400 years, respectively. The sediment chronologies were established using 36 14C dates. Image-analysis method (ImageJ) was used to count and measure the grain size of all sand particles at every centimeter to gain high-resolution ASI records. Although minor site-to-site variations exist, all four ASI records were in general consistent, suggesting that stormier periods occurred around 7300, 6600, 5900, 4600, 3600, 2900, 2400, 2100, and 1600 cal yr BP and over the last 1200 years. The results and comparisons with other storminess and climate studies indicate a shift in climatic conditions around 2500 cal yr BP when stormy periods became more frequent. The ASI values were also high during the last millennium, suggesting either higher storminess or more suitable transport mechanisms for sand into the coastal bogs: the niveo-aeolian transport mode could have been favored in winters, especially during the Little Ice Age, and human impact on landscapes has probably increased over the past centuries. [ABSTRACT FROM AUTHOR]

Knowledge of the structure and spatial distribution of coastal water habitats is crucial for understanding coastal water systems. However, spatial habitat data are largely lacking, hampering ecological and ecosystem service assessments as required by EU policies. Mapping the structure, spatial distribution, and temporal dynamics of macrophytes is a particular challenge. In this study, we combined long-term macrophyte data with remote sensing methods (i.e., aerial and underwater drones, as well as SENTINEL-2 data) to assess their potential for spatial macrophyte monitoring and habitat-based ecosystem service assessments, in which ecosystem services were linked to habitats using the expert-based Baltic Ecosystem Service Potential Matrix. Greifswald Bay in the German Baltic Sea served as the case study for this research. Our aerial drone detected macrophytes up to a depth of 3 m that could be integrated into the existing macrophyte monitoring scheme of the Water Framework Directive. Reliable data from SENTINEL-2 were only obtained in optically shallow waters and could therefore only be used as proxy indicators to assess changes at a water body level. Despite the uncertainties and inaccuracies of the SENTINEL-2-based macrophyte maps, they were crucial for filling data gaps and enabled a spatially differentiated ecosystem service assessment for Greifswald Bay. However, we have shown that the commonly used matrix approach does not allow for the assessment of spatiotemporal changes at the water body level and is thus not suitable for supporting coastal and marine policy implementation. [ABSTRACT FROM AUTHOR]

In the coastal zone, two types of habitats—linear and areal—are distinguished. The main differences between both types are their shape and structure and the hydro- and litho-dynamic, salinity, and ecological gradients. Studying linear littoral habitats is essential for interpreting the 'coastal squeeze' effect. The study's main objective was to assess short-term behavior of soft cliffs as littoral linear habitats during calm season storm events in the example of the Olandų Kepurė cliff, located on a peri-urban protected seashore (Baltic Sea, Lithuania). The approach combined the surveillance of the cliff using unmanned aerial vehicles (UAVs) with the data analysis using an ArcGIS algorithm specially adjusted for linear habitats. The authors discerned two short-term behavior forms—cliff base cavities and scarp slumps. The scarp slumps are more widely spread. It is particularly noticeable at the beginning of the spring–summer period when the difference between the occurrence of both forms is 3.5 times. In contrast, cliff base cavities proliferate in spring. This phenomenon might be related to a seasonal Baltic Sea level rise. The main conclusion is that 55 m long cliff cells are optimal for analyzing short-term cliff behavior using UAV and GIS. [ABSTRACT FROM AUTHOR]

In this study, we investigate the interplay between relative sea‐level changes, the development of human settlements and land‐cover changes in the Västervik–Gamlebyviken region on the southeast coast of Sweden, an important archaeological area from the Mesolithic until recent times. The reconstruction of shore displacement was based on diatom analysis of radiocarbon‐dated sediment cores from three lake basins combined with previously published lake isolation data. The resulting curve was used to construct palaeogeographical maps for selected time windows. Land‐cover changes were inferred from pollen data from three lakes using the Landscape Reconstruction Algorithm with its two models REVEALS and LOVE. Our data suggest that people took advantage of the land gained due to an overall fall in relative sea level from ~35 to ~3 metres above sea level (m a.s.l.) over the last 10 000 years, interrupted by periods of transgression and highstands. A sea‐level regression of ~16 m occurred between 10 000 and 8500 cal a bp followed by an ~3–4‐m sea‐level rise, reaching ~22 m a.s.l. at ~7500 cal a bp, which corresponds to the maximum Littorina Sea shoreline in the area. The available archaeological findings for the Mesolithic and Early Neolithic (8950–5450 cal a bp) agree well with the shore displacement curve showing that settlements and human activities were concentrated along or above the shorelines as defined from our study. During the transgression after 8500 cal a bp, however, seasonal settlements were submerged (as shown by findings of polished stone tools and hearths buried in sand) and used again during the subsequent regression after 4600 cal a bp. The Iron Age (2450–900 cal a bp) corresponds partly to a highstand at ~11 m a.s.l. between 3600 and 2000 cal a bp and partly to a rapid regression of ~8 m between 2000 and 1500 cal a bp, and both periods coincide with known human activities along the contemporaneous shoreline. The rapid regression after 2000 cal a bp corresponds to an increase of both regional and local landscape openness and the beginning of a continuous record of crop cultivation. [ABSTRACT FROM AUTHOR]

The incidental capture (bycatch) of seabirds is a global conservation issue and a top threat to European species that demands urgent conservation and management action. Here, we present the first European review of seabird bycatch data, considering all fishing gears and data collection methods available in the region. We calculate seabird bycatch numbers per species, family, country and European marine region and assess the reliability of the data available. The cumulative bycatch estimate extracted from this review suggests that about 195,000 seabirds (ranging from around 130,000 to 380,000) are bycaught in European waters annually. The most affected seabird species is the Common Guillemot Uria aalge with over 31,000 birds killed per year. The marine region with the highest bycatch estimate is the Northeast Atlantic (over 115,000 seabirds year−1). Gillnet fisheries are responsible for the highest bycatch levels, with over 95,000 seabirds year−1, followed by longline fisheries. The families most affected by bycatch are Anatidae and Alcidae. These numbers are likely an underestimation since we were unable to find bycatch estimates, or to extrapolate estimates from available bycatch data for 12 (out of 34) European coastal states. Our assessment also identified significant data gaps in key areas such as Gran Sol (in the north‐east Atlantic), the central and Eastern Mediterranean and the Black Sea. Combining systematic data collection with immediate implementation of mitigation measures will be crucial to fill in knowledge gaps, reduce current mortality levels and meet international conservation commitments such as those of the European Union and the Convention on Migratory Species. [ABSTRACT FROM AUTHOR]

During fish larvae development functional, morphological, and physiological adaptations are key in larval survival strategies and can determine mortality bottlenecks. For many fish groups such as needlefish, which play crucial roles in marine food webs, studies on early life stages are almost lacking. Herein, the development, with focus on the postcranial skeleton, of the garfish Belone belone (Linnaeus, 1761) is described and a staging system is introduced. Ten larval and juvenile life stages are proposed in three main phases: yolk sac, larval, and juvenile development. During the yolk sac phase the garfish deplete their yolk reservoirs and finish the development of their unpaired fins. During the larval period the lower jaw elongates and the needlenose stage is reached. In the juvenile phase, the upper jaw elongates until both jaws are almost equally long. Since B. belone larvae develop much of their postcranial skeleton in the late embryonic and yolk sac phases they might not experience a severe bottleneck in this early stage such as many other marine fish species. Therefore, young garfish could be more resilient to environmental changes. [ABSTRACT FROM AUTHOR]

In 2012, a well-preserved wooden sailing vessel was found near Tallinn, Estonia. Initial research suggested it to be a fluit, a merchant vessel from the first half of the 17th century. New and more thorough research was carried out in 2022 and this article summarises the results of the later fieldwork. New finds and measurements suggest a later dating than the initial one – construction in the second half of 17th century and sinking somewhere during the last quarter of the century. The vessel has a lot of similarities with other well-preserved fluit wrecks that are used here as a comparison. The origin of the vessel is yet unknown, but clay analysis of the brick used in the galley suggests a location somewhere around Lübeck – a well-known trading partner of Tallinn (then called Reval). [ABSTRACT FROM AUTHOR]

The Maderö wreck was discovered in the 1960s in the Stockholm Archipelago, Sweden. An archaeological investigation undertaken in 2022 included the inspection and documentation of visible ship parts, sampling for dendrochronological analysis and sampling for ICP analysis from the brick cargo. The results show that the wood originates from the Baltic Sea area and was felled after 1467, while the clay for the brick originates from the Mecklenburg-Vorpommern area. The ship's technical analysis shows that it is a large clinker-built merchant ship. Traces of iron on a recovered stone shot indicate that the ship was armed when it sank. [ABSTRACT FROM AUTHOR]

This article analyzes underwater surveillance and monitoring technologies aimed at enhancing security and environmental management, using a hypothetical underwater data center in the Baltic Sea as a case study. It explores cutting-edge solutions such as remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs), and smart buoys, focusing on their integration for monitoring underwater infrastructure and safeguarding against infrastructural threats. With rising concerns over maritime security due to recent events like the Nord Stream outage, this research highlights the need for advanced technological systems to address such a kind of vulnerabilities. The analysis also considers multi-layered potential of these systems for security, safety, and environmental resilience. Consequently, this study provides insights into the feasibility, challenges, and future directions for deploying underwater data centers as a sustainable alternative to traditional land-based facilities of this type, contributing to the broader discourse on securing critical underwater infrastructure and promoting eco-friendly data storage solutions. [ABSTRACT FROM AUTHOR]

New data are presented on the distribution of the alien species the Chinese mitten crab Eriocheir sinensis in the basin of the eastern part of the Gulf of Finland, the Baltic Sea. The fact of widespread occurrence of E. sinensis in bottom communities has been confirmed. During the period from 2021 to 2023, 81 adult individuals of the mitten crab were recorded; 32 of them were studied in the laboratory. Of the studied individuals, males were dominant; the sex ratio (males : females) was 3.6 : 1; females with exterior egg sacs were not found. The carapace width of the studied crabs (n = 32) ranged from 46.6 to 85 mm, averaging to 63.2 ± 1.7 mm. Males were slightly larger than females; however, statistically significant differences in carapace width between males and females were not detected. The paper further discusses issues related to the origin of crabs inhabiting the eastern part of the Baltic Sea and the possibility of naturalization of this species in the basin of the eastern part of the Gulf of Finland, the Baltic Sea. The conclusion is drawn about the importance of systematic monitoring of E. sinensis in the Gulf of Finland basin. [ABSTRACT FROM AUTHOR]

Ecosystem accounting provides a standardised framework for evaluating the economic value of ecosystems to society. Following the international accounting standard, System of Environmental Economic Accounting – Ecosystem Accounting (SEEA EA), we present first marine ecosystem extent pilot accounts for Finland, based on three habitat classification systems: the Marine Strategy Framework Directive (MSFD), the EU Habitats Directive (HD) and the IUCN Red List of Ecosystems (RLE). We assess their condition using indicators from the Water Framework Directive, which measure ecosystem quality through biological, ecological and physico-chemical parameters.We found that MSFD habitats have the largest extent, exceeding the areas covered by HD and RLE habitats. A large portion of the assessed habitats, particularly in the inner archipelago and shallow areas close to shore, were in poor condition, reflecting the eutrophication status of coastal waters. We identify considerable challenges in reporting marine ecosystem extent and condition accounts, which most likely recur across (European) countries. For instance, MSFD habitats are rather coarse for accurately reporting ecosystem extents, potentially overlooking declines in ecosystem condition, while HD habitats cover only a subset of habitats. RLE habitats provide more ecological detail, although they may be less compatible with classifications used in other countries.Our research provides a baseline for future ecosystem accounts and emphasises the need for improved data and methods to enhance the accuracy and comparability of marine ecosystem assessments. Additionally, we discuss the compatibility of SEEA EA with EU policy reporting requirements, the spatial scale of reporting ecosystem extents and condition and highlight the limitations of current habitat classifications in representing the full diversity of marine ecosystems. The findings underscore the importance of integrating multiple habitat classification systems, development of crosswalks between habitat classifications and monitoring frameworks to ensure comprehensive and accurate ecosystem accounts.

Commercial small-scale fisheries along the Baltic Sea coasts have declined over the years although these fisheries are viewed as important for coastal development and food security at the local, national, and EU levels. The viability and future of small-scale fisheries are severely challenged by problems caused by grey seals. The conflict, occurring between Baltic Sea coastal fisheries and conservation of the grey seals, has been severe since the mid-1990s and continues despite attempts to find a more balanced situation. Resting on reviews of multiple material, this paper explores the state-of-the-art opportunities for mitigating the seal-fisheries conflict and asks how these are related to social struggles and social justice. Our paper concludes that co-existence of coastal fisheries and the grey seal is possible but necessitates political will and co-designed seal management plans that help implement context-specific measures. Seal deterrents, for instance, give hope as a supplementary conflict mitigation measure – along with seal-proof fishing gear – but provide only partial relief. From the fisheries sector's position, influencing the size of the seal population is a logical solution. The lifting of the EU trade ban of seal products as a regional derogation would allow sustainable management of seal populations so that they be used as renewable natural resource. Monitoring changes in the seal population is crucial for maintaining a balanced population. Reaching co-existence is timely, because – unlike the seal – the diverse Baltic coastal fishing culture is increasingly endangered. [ABSTRACT FROM AUTHOR]

Abstract Coastal ecosystems are affected by a multitude of anthropogenic stressors. As the Baltic Sea ecosystems rank among the most altered marine ecosystems worldwide, they represent ideal model regions to study ecosystem responses to anthropogenic pressures. Our statistical analysis of data including dissolved organic carbon and nitrogen, as well as bacterial abundance and -biomass production from the time-series station Boknis Eck in the southwestern Baltic Sea reveals that bacterial biomass production intensifies towards summer following the phytoplankton spring bloom. Moreover, warming, especially very high temperatures in summer, enhances stratification and bacterial biomass production despite long-term reduction in nutrient input. A strong decrease in oxygen in the bottom layer is possibly linked to this. We detect an increasing trend in bacterial biomass production along with intensifying warming and stratification, and more frequently occurring hypoxia despite ongoing restoration efforts. If this trend continues, the coastal Baltic Sea ecosystem is likely to be altered even further. Coastal ecosystems play pivotal roles in mitigating impacts of climate change but if destroyed, they may amplify climate change further calling for stronger ecosystem management strategies.

Wave parameters form the base for the design of coastal structures. For this purpose, commonly modelled wave properties are employed. This approach is usually adequate in open ocean conditions where spatial variations in wave properties are normally quite limited. The situation is different in nearshore areas of complicated shapes, where wave properties can be highly variable. In such instances, long and sufficiently detailed wave measurements for model validation are usually unavailable. The use of default settings of wave models means that possible errors remain unknown, and employing data with substantial uncertainties could lead to overdimensioned structures or structural failures. We address the magnitude of possible errors in such conditions by comparing the output of simple wave models (such as the fetch-based SPM model or the SWAN model forced with one-point homogenous wind) and the sophisticated multi-nested SWAN wave model forced with ERA5 winds with recent wave measurements in various nearshore locations in the eastern Baltic Sea. We use records of different length spanning over more than ten years. While in some locations simple models or models forced with homogenous wind yield acceptable results, in most areas more sophisticated models are needed to adequately replicate wave properties. The outcomes of our analysis provide several site-specific hints for practical coastal engineering.

Abstract This study examined Baltic Sea Marine Heatwaves (MHWs) using 42 years of satellite-derived sea surface temperature (SST) data. We found that MHWs in warmer months are more intense but shorter compared to MHWs in cooler months. Also, MHWs predominantly affect offshore areas in warmer months, whereas MHWs predominantly impacting coastal seas in cooler months, especially along the eastern coast. Our analysis of interannual variability revealed that, unlike in many other basins worldwide, Baltic MHWs tend to maintain a constant intensity, while their spatial extent has significantly increased over the last few decades. Shortwave radiation notably influences MHW intensity and spatial extent, with additional impacts from longwave radiation in cooler months and latent heat flux in warmer months. Northern Hemisphere teleconnections exhibit stronger correlations with MHWs in the Baltic Sea compared to global-scale climate oscillations, with the Eastern Atlantic pattern having a particularly significant effect on MHW variability in the region.

This study examined Baltic Sea Marine Heatwaves (MHWs) using 42 years of satellite-derived sea surface temperature (SST) data. We found that MHWs in warmer months are more intense but shorter compared to MHWs in cooler months. Also, MHWs predominantly affect offshore areas in warmer months, whereas MHWs predominantly impacting coastal seas in cooler months, especially along the eastern coast. Our analysis of interannual variability revealed that, unlike in many other basins worldwide, Baltic MHWs tend to maintain a constant intensity, while their spatial extent has significantly increased over the last few decades. Shortwave radiation notably influences MHW intensity and spatial extent, with additional impacts from longwave radiation in cooler months and latent heat flux in warmer months. Northern Hemisphere teleconnections exhibit stronger correlations with MHWs in the Baltic Sea compared to global-scale climate oscillations, with the Eastern Atlantic pattern having a particularly significant effect on MHW variability in the region. [ABSTRACT FROM AUTHOR]

The impact of freshwater sources like surface river runoff and submarine groundwater discharge (SGD) on coastal waters is currently in focus of intense debate and investigation. One of the ongoing challenges in SGD research is the characterization and quantification of the freshwater endmember contributions to the subsurface mixing zone and their influences on element balance and biogeochemical transformations. Long-term investigations of the sediment porewater composition provide characterization and understanding of the physical, hydrological and biogeochemical processes controlling the substance exchanges. In this study, we focus on the hydrochemical and stable isotope (δ2H, δ18O) compositions of sediment porewaters along the coastline of a southern Baltic Sea peatland. Coastal surface water and groundwater dynamics were monitored at two coastal sites using 5-m-long stationary lances over a 5-year period.The vertical compositional gradients were used to extrapolate to zero-salinity (ZS) components applying a binary mixing model on the salinity and water isotope composition. The results characterize a subterranean estuary (STE) with three potential mixing endmembers: two fresh groundwaters and the brackish Baltic Sea. Tritium–helium (3H–3He) porewater dating gave ages of more than about 20 years for the freshwater components. The ZS components were compared with other SGD sites along the southern Baltic Sea and North Sea and highlight the importance of local SGD studies for a proper groundwater endmember characterization as basis to understand hydrological and biogeochemical developments at the land–ocean continuum in times of current climate change. [ABSTRACT FROM AUTHOR]

The monitoring of coastal waters using satellite data, from sensors such as Sentinel-3 OLCI, has become a vital tool in the management of these water environments, especially when it comes to improving our understanding of the effects of climate change on these regions. In this study, the latest Level-2 water products derived from different OLCI Sentinel-3 processors were validated against a comprehensive in situ dataset from the NW Baltic Sea proper region through a matchup analysis. The products validated were those of the regionally adapted Case-2 Regional Coast Colour (C2RCC) OLCI processor (v1.0 and v2.1), as well as the latest standard Level-2 OLCI Case-2 (neural network) products from Sentinel-3's processing baseline, listed as follows: Baseline Collection 003 (BC003), including "CHL_NN", "TSM_NN", and "ADG443_NN". These products have not yet been validated to such an extent in the region. Furthermore, the effect of the current EUMETSAT system vicarious calibration (SVC) on the Level-2 water products was also validated. The results showed that the system vicarious calibration (SVC) reduces the reliability of the Level-2 OLCI products. For example, the application of these SVC gains to the OLCI data for the regionally adapted v2.1 C2RCC products resulted in RMSD increases of 36% for "conc_tsm"; 118% for "conc_chl"; 33% for "iop_agelb"; 50% for "iop_adg"; and 10% for "kd_z90max" using a ±3 h validation window. This is the first time the effects of these SVC gains on the Level-2 OLCI water products has been isolated and quantified in the study region. The findings indicate that the current EUMETSAT SVC gains should be applied and interpreted with caution in the region of study at present. A key outcome of the paper recommends the development of a regionally specific SVC against AERONET-OC data in order to improve the Level-2 water product retrieval in the region. The results of this study are important for end users and the water authorities making use of the satellite water products in the Baltic Sea region. [ABSTRACT FROM AUTHOR]

This study examines the impact of storm surges, infragravity waves, wider area seiches and natural harbour oscillations (harbour seiches) on port operations in the Baltic Sea, with a particular emphasis on the Port of Klaipėda, all during the severe storm that occurred from November 22–24, 2023. The study examines the interplay between meteorological factors, such as changes in air pressure and wind speed and direction, and the coastal geography of the area. Wind speeds during the storm reached a maximum of 29.7 m/s, and air pressure dropped for f ~ 50 hPa, with a corresponding sea level rise of approximately 40 cm due to the combined effects of storm surges and long waves. The research findings indicate that it was precisely long waves, which were generated offshore and amplified by the port's distinctive resonance characteristics and coastal topography, that were the primary cause of operational disruptions, creating hazardous conditions that necessitated the closure of the port. The port's elongated and narrow inlet played a pivotal role in the amplification of these waves, rendering it particularly vulnerable to resonance-induced oscillations. The research yielded several key findings, including identifying long waves (long ocean waves, wider area seiches, harbour seiches, and infragravity waves) with periods ranging from 12 to 13 h to 2–4 min, which posed significant risks to vessels moored at the port. Furthermore, the occurrence of simultaneous sea level fluctuations between Klaipėda and Karlshamn indicated the presence of seiches with period of 12,4 h across the Baltic Sea, thereby further complicating port operations. These results underscore the critical need for improved forecasting and mitigation strategies to enhance the safety and efficiency of port activities during severe weather events. [ABSTRACT FROM AUTHOR]

This study aims to investigate the seasonal and spatial distribution of surface phytoplankton communities in the Baltic Sea, using pigment analysis and hydrological parameters. Data were collected during six oceanographic campaigns between 2005 and 2008, including high-performance liquid chromatography (HPLC) pigment characterization and hydrological measurements. The first part of this comprehensive study was focused on the HPLC phytoplankton pigment dataset in relation to hydrological conditions. The research highlighted the importance of high-quality input data for accurate taxonomic analysis. Several unsupervised machine learning approaches, such as hierarchical cluster analysis (HCA), principal component analysis (PCA), and network-based community detection analysis (NCA), were used to analyze the data and identify phytoplankton communities based on biomarker pigments. Five main phytoplankton communities were identified: diatoms, dinoflagellates, cryptophytes, green algae, and cyanobacteria. The results evidenced distinct seasonal patterns, with diatom blooms dominating in spring, cyanobacterial blooms in mid-summer, and haptophyte and dinoflagellate peaks occurring in late summer and autumn. While PCA and NCA provided consistent insights into community structure, HCA offered less clarity in distinguishing between groups. The results of the statistical analysis were then compared with those of traditional approaches such as CHEMTAX and region-specific bio-optical algorithms, providing new perspectives on the taxonomic composition of phytoplankton groups. This study provides valuable insights into phytoplankton dynamics in the Baltic Sea and the effectiveness of different analytical approaches in understanding community structure, providing metrics that can enhance current and future advancements in remote sensing, including support for hyperspectral ocean color remote sensors. [ABSTRACT FROM AUTHOR]

Plastic production and plastic waste have increased to such an extent that it has become globally ubiquitous. Several studies already have investigated the mesoand microplastic pollution along the German Baltic and North Sea coasts, but were all limited to a few locations. To obtain representative bulk samples from sandy beaches along the entire German coast, we initiated a citizen-science project entitled "Microplastic Detectives." Here, we describe in detail 1) how we recruited, instructed, and engaged citizen scientists, 2) why we chose bulk sampling over reduced-volume sampling, and 3) the laboratory methods we used. The citizen scientists collected 1,139 samples from 71 locations along the German coast, totalling 2.2 tons of sand. After drying, sieving with a 1 mm sieve, and visual inspection of the retained fraction under a binocular microscope, all putative plastic particles =1 mm were analysed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. 177 out of 1,139 samples (15.5%) contained a total of 260 plastic particles, with a large right-skewed variation among locations. Most of the particles were fragments, foils, foams, fibres, and pellets (96.2% in total), and 89.6% of the particles were made of polyethylene, polypropylene, polyester, and polystyrene. The unweighted mean pollution densities were 4.12 particles m-2, 0.17 particles kg-1 and 0.27 particles L-1, and the weighted mean pollution densities were 3.77 particles m-2, 0.11 particles kg-1 and 0.18 particles L-1. These densities are lower than in other similar studies, but previous studies had important methodological differences. We discuss how these differences could have influenced the results and make recommendations for improving future studies. Two important recommendations are 1) to use random or stratified random sampling and 2) to run transects perpendicular (rather than parallel) to the waterline. Our study highlights that large-scale, scientifically rigorous monitoring of meso- and microplastic pollution is possible at the national level, and possibly even at much larger spatial and temporal scales. With the help of local authorities, such a monitoring program could be established. [ABSTRACT FROM AUTHOR]

In the Baltic Sea, the dinoflagellates Apocalathium malmogiense, Biecheleria baltica, and Gymnodinium corollarium are important contributors to the spring bloom. However, their relative contribution to the bloom community cannot be unambiguously determined by conventional light microscopy due to a lack of resolution of distinctive morphological features of the three species. Here, we describe a molecular approach based on a quantitative real-time polymerase chain reaction (qPCR) primer and probe system, targeting the ITS1 and ITS2 regions of the rRNA gene for all three species and enabling their quantification. The specificity of the method was demonstrated using monocultures of A. malmogiense, B. baltica, G. corollarium as well as three other dinoflagellate species co-occurring in the Baltic Sea during spring and validated using field-collected phytoplankton samples. [ABSTRACT FROM AUTHOR]

A new member of the family Flavobacteriaceae (termed Hal144T) was isolated from the marine breadcrumb sponge Halichondria panicea. Sponge material was collected in 2018 at Schilksee which is located in the Kiel Fjord (Baltic Sea, Germany). Phylogenetic analysis of the full-length Hal144T 16S rRNA gene sequence revealed similarities from 94.3 to 96.6% to the nearest type strains of the genus Maribacter. The phylogenetic tree of the 16S rRNA gene sequences depicted a cluster of strain Hal144T with its closest relatives Maribacter aestuarii GY20T (96.6%) and Maribacter thermophilus HT7-2T (96.3%). Genome phylogeny showed that Maribacter halichondriae Hal144T branched from a cluster consisting of Maribacter arenosus, Maribacter luteus, and Maribacter polysiphoniae. Genome comparisons of strain Maribacter halichondriae Hal144T with Maribacter sp. type strains exhibited average nucleotide identities in the range of 75–76% and digital DNA-DNA hybridisation values in the range of 13.1–13.4%. Compared to the next related type strains, strain Hal144T revealed unique genomic features such as phosphoenolpyruvate-dependent phosphotransferase system pathway, serine-glyoxylate cycle, lipid A 3-O-deacylase, 3-hexulose-6-phosphate synthase, enrichment of pseudogenes and of genes involved in cell wall and envelope biogenesis, indicating an adaptation to the host. Strain Hal144T was determined to be Gram-negative, mesophilic, strictly aerobic, flexirubin positive, resistant to aminoglycoside antibiotics, and able to utilize N-acetyl-β-D-glucosamine. Optimal growth occurred at 25–30 °C, within a salinity range of 2–6% sea salt, and a pH range between 5 and 8. The major fatty acids identified were C17:0 3-OH, iso-C15:0, and iso-C15:1 G. The DNA G + C content of strain Hal144T was 41.4 mol%. Based on the polyphasic approach, strain Hal144T represents a novel species of the genus Maribacter, and we propose the name Maribacter halichondriae sp. nov. The type strain is Hal144T (= DSM 114563T = LMG 32744T). [ABSTRACT FROM AUTHOR]

The release of dissolved organic matter (DOM) from sediments serves as an important part of the carbon cycle. Here, we address pore water DOM quality and its release from shallow sediments (0-10 cm) of the central and southern Baltic Sea - Gdansk, Bornholm, and Eastern Gotland Basins - using excitation-emission matrix spectroscopy and size-exclusion chromatography. DOM release from sediments displayed spatial variability, with diffusive DOC fluxes ranging from 0.02 to 1.06 mmol m-2 d-1, and basin-averaged fluxes increased in the order Gotland < Bornholm < Gdansk. DOM qualitative characteristics also varied among investigated basins. In the oxygen-limited study sites from the Gdansk Basin, we observed elevated abundances of low apparent molecular weight DOM fraction and proteinaceous-like fluorescent DOM, while in the Bornholm Basin, pore water DOM was generally more humic-like and of higher apparent molecular weight. Pore waters from the deepest study sites in the Gotland Basin were qualitatively very similar to those of the pore waters from the upper sediment layers (0-4 cm) from all other investigated sites, suggesting little organic matter reworking at depth at those stations. Our results suggest that the spatial variability in the magnitude of DOM release may be linked to the qualitative differences of DOM in sediments. [ABSTRACT FROM AUTHOR]

The present study aimed to investigate 1) whether country categories and type of DLD predict the type of therapy (direct, indirect, and mixed) the child receives, and 2) whether there is an association between country categories, type of therapy, and type of DLD (receptive, expressive, and mixed). European countries were categorised based on Sapir's typology into Continental, AngloSaxon, Nordic and Mediterranean groups. A fifth group i.e. Central European (including Baltic countries) was added. The data to address these questions comes from an online survey, translated and adapted into 30 languages, and is based on reports by 4685 professionals delivering services for children with DLD. This survey was developed by the COST Action IS1406 members and distributed online among practitioners in the year 2017 across European countries. Results indicated that country categories and type of DLD predicted type of therapy. It was suggested that cultural and contextual factors might play a key role in driving clinical practice above and beyond language profiles, patient characteristics and evidence-based practice. [ABSTRACT FROM AUTHOR]