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Few studies have been made of the specific importance of waterfowl as food in the Baltic Sea during the late medieval and early modern period. This study shows the seasonal importance of water birds to island and coastal inhabitants living in the middle of the Baltic Sea during the late medieval and early modern periods (ca. CE 1400–1700) and practical implementations for interpretation of cut and chop marks. The paper is based on a bird bone assemblage retrieved from a remote ecclesial site on the island group of Kökar, which is part of the Åland Islands, as well as historical documents and local specialist knowledge. The site was established by Franciscan friars somewhere in the mid‐15th century. Documents indicate that the friars had landownership, income from taxing nearby fisheries, and the right to seal tithe. These assets were taken over by the crown in the mid‐16th century due to the Reformation and a parish church was established on the same site after the friary was dissolved. The bone assemblages from the site include birds, mammals, and fish. The material shows a relatively small number of chicken bones in relation to waterfowl, allowing one to look closer into the structural food economy around water birds for the area. The bones also show several cut and chop marks, which have been analyzed to explore the possible processing of these birds. The results show that fowling was concentrated to a couple of species most likely during spring when these species were abundant. The placement of the cut and chop marks indicates that a large number of birds were likely processed at the same time. [ABSTRACT FROM AUTHOR]

Citizen science is changing society's contribution to research projects worldwide. Non‐experts are no longer just spectators, they are active participants and supporters of scientific work. Using citizen science, that is, data collected by laypeople, the opportunities to collect large‐scale data on the environment are increasing. Such community‐based and citizen scientific approaches can provide useful tools as local people can be trained to accurately take measurements that can be used in scientific studies. However, little is known about how well volunteer‐based non‐standard subjective assessments of the environment based on prior experience only and no training compare with scientifically measured estimates of that environment. In this paper, we tested how well measures of coastal water quality assessed by local inhabitants corresponds with objective water quality data collected using scientific instruments. Our results showed that over 70% of the respondents assessed water quality in the right direction and almost 60% were correct in their estimates. We found that socio‐demographic factors affect the assessments, but do not markedly improve reliability. We conclude that simple questionnaires can be used to assess general coastal water quality. [ABSTRACT FROM AUTHOR]

Recently discovered, ocean submesoscales have attracted considerable attention due to their ability to change the upper ocean stratification, affect vertical transport, and induce a downscale cascade of energy toward dissipation. In this paper, we highlight the effect of submesoscale fronts and filaments on surface layer properties and dynamics during storm events, extending previous idealized simulations toward real‐ocean applications. Here, we use the Baltic Sea as a natural laboratory to study the rich submesoscale activity of this system with the help of realistic high‐resolution numerical simulations. These simulations reveal a wealth of cold submesoscale filaments with sharp lateral buoyancy gradients, strong surface convergence, and high vertical velocities. Highly heterogeneous Mixed Layer Depth (MLD) modulations are associated with these features, maintaining locally reduced MLDs even during storm events due to vigorous submesoscale restratification. The interaction of near‐surface turbulence and submesoscale restratification results in strong and highly efficient mixing inside the submesoscale fronts. Focusing on a typical filament, it is shown that frontogenesis is associated with the convergent cross‐front circulation arising from a turbulent thermal wind balance, consistent with previous studies. We show that the sharp fronts generated by this process may become symmetrically unstable, and show enhanced (modeled) energy dissipation rates that are in good quantitative agreement with existing theoretical estimates. Plain Language Summary: Recent studies have revealed that horizontal density differences on scales of 0.1–10 km (submesoscales) are ubiquitous in the surface mixed layer and play an essential role in its evolution. Submesoscale features can restratify, that is, bring warm water above cold water and shallow the depth of the mixed layer, which along with their high vertical velocities, makes them particularly relevant for biology. In this study, we highlight the effect of submesoscales on the restratification process and near‐surface turbulence during the lifetime of storms, thereby extending previous idealized simulations toward real‐ocean applications. We analyze a realistic high‐resolution numerical simulation focusing on the central Baltic Sea, an area where observations from a field campaign confirm that it constitutes a hotspot of submesoscale activity, hence forming an ideal natural laboratory. The simulation reveals a strong lateral temperature gradient that persists during autumn. The basin is found to be rich in submesoscale features that create shallow and heterogeneous Mixed Layer Depths (MLDs). The MLD presents high temporal variability, with the submesoscales being able to maintain shallow MLDs during storms and induce rapid restratification when the wind subsides. Submesoscale restratification tends to counteract the destratification effect caused by atmospheric forcing, yielding stably stratified patches. Key Points: Using realistic simulations a strong surface front, characterized by intense submesoscale activity, was identified in the central Baltic SeaSubmesoscales maintain shallow mixed layers during storms and induce rapid restratification afterward creating stably stratified patchesThe interaction of near‐surface turbulence and submesoscale restratification results in highly efficient mixing inside submesoscale fronts [ABSTRACT FROM AUTHOR]

ABSTRACT The Baltic Sea region has in recent years become known as a pioneer of new modes of governance, reflecting the dynamic development of the network society. At the same time, the Baltic Sea is considered one of the world's most polluted seas, especially in terms of eutrophication, the accelerated enrichment of nutrients in the water. Overall, there is a contrast between the formally successful governance system and the actual state of the Baltic Sea. This paper describes the existing Baltic Sea environmental governance system, from the regional regime to non-governmental actors, noting that highly institutionalized inter-state and transnational environmental cooperation adds a greater element of hierarchy for environmental governance in the region. Supporting democratic development is a special requirement for governance in the post-Cold War context. The paper explicates governance challenges posed by the emerging network society, on the one hand, and the problem of eutrophication, on the other, and makes suggestions on how to develop the governance system in order to meet the challenges. As a conclusion, a general lesson for the management of international water bodies is given. Institutional diversity with many different scale preoccupations is key, but so is the need for leaders to overcome the challenges of polycentric governance: that is, to reduce opacity of governing and to increase the power of stakeholders to define the problem and its solutions in the first place. Copyright © 2013 John Wiley & Sons, Ltd and ERP Environment. [ABSTRACT FROM AUTHOR]

This paper describes a framework in which artificial extreme sea levels (ESLs) can be generated for use in flood risk analyses. Such analyses require large numbers of events to accurately assess the risk associated with certain return water levels and quantify uncertainties surrounding the temporal variability of ESL events. Stochastic models satisfy this requirement as they are computationally inexpensive, and thus, many thousands of events may be generated over a very short period of time. As a case study, we have developed a stochastic model for the German Baltic Sea coast capable of simulating the temporal behavior of ESLs. To do this, high‐resolution water level data from 45 tide‐gauges have been used as model input. At each location, observed ESLs are identified and parameterized. Artificial ESLs are generated using Monte Carlo simulations based on the parametric distribution functions fitted to the parameterized observed ESLs. We show that the method outlined here provides an accurate representation of ESLs at all tide‐gauges tested. However, the model is limited by the availability, length, and quality of high‐resolution water level data. Due to the rarity of ESLs in the German Baltic Sea, including historical measurements into the stochastic procedure allows for the generation of artificial ESLs more in‐line with past extremes. Plain Language Summary: Extreme sea levels leading to coastal flooding pose a major threat to coastal populations. With global exposure to such events expected to increase due to a number of factors, including sea level rise and population growth, it is important that an accurate assessment of flood risk is conducted to inform future decisions on coastal defenses and adaptation options. However, extreme sea levels are rare and in regions where water level records are short, it is difficult to accurately determine the level of risk. In this study, we develop an extreme sea level model capable of producing thousands of artificial extreme events to be used in flood risk analyses. The modeled events are based on a number of observed extreme sea level statistics and are therefore representative of recorded events. Our results highlight the need for further digitization of past extreme events so that they may contribute to a better understanding of extreme sea levels. Key Points: Artificial extreme sea level events are generated for the German Baltic Sea coast using a stochastic modelThe model generates extreme sea level hydrographs, allowing for an analysis of temporal variability as well as peak water levelModel output is useful for quantifying uncertainties in flood extent due to temporal variability of extreme sea level events [ABSTRACT FROM AUTHOR]

ABSTRACT The increasing transboundary nature of many environmental problems has not only elevated the importance of international environmental governance it has also contributed to shifts in the scales at which these problems are addressed and at which environmental programmes are implemented. The result is that environmental governance is experiencing rescaling which often involves a combination of changes including shifts in powers to other layers of decision-making, the emergence of new scales of policy intervention and alternative forms of intervention, and the appearance of new actor constellations. The emergence of 'soft' policy and programming spaces - multi-area sub-regions in which strategy is being made between or alongside formal institutions and decision-making processes - is another phenomena associated with rescaling. This paper charts the rescaling of environmental governance in part of Europe - the Baltic Sea Region (BSR) - and examines the influence of European macro-regional cooperation initiatives on the changing nature of environmental governance in the region. Copyright © 2014 John Wiley & Sons, Ltd and ERP Environment [ABSTRACT FROM AUTHOR]

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The dramatic increase of bioreactive nitrogen entering the Earth's ecosystems continues to attract growing attention. Increasingly large quantities of inorganic nitrogen are flushed from land to water, accelerating freshwater, and marine eutrophication. Multiple, interacting, and potentially countervailing drivers control the future hydrologic export of inorganic nitrogen. In this paper, we attempt to resolve these land-water interactions across boreal/hemiboreal Sweden in the face of a changing climate with help of a versatile modeling framework to maximize the information value of existing measurement time series. We combined 6,962 spatially distributed water chemistry observations spread over 31 years with daily streamflow and air temperature records. An ensemble of climate model projections, hydrological simulations, and several parameter parsimonious regression models was employed to project future riverine inorganic nitrogen dynamics across Sweden. The median predicted increase in total inorganic nitrogen export from Sweden (2061-2090) due to climate change was 14% (interquartile range 0-29%), based on the ensemble of 7,500 different predictions for each study site. The overall export as well as the seasonal pattern of inorganic nitrogen loads in a future climate are mostly influenced by longer growing seasons and more winter flow, which offset the expected decline in spring flood. The predicted increase in inorganic nitrogen loading due to climate change means that the political efforts for reducing anthropogenic nitrogen inputs need to be increased if ambitions for reducing the eutrophication of the Baltic Sea are to be achieved. [ABSTRACT FROM AUTHOR]

Ferromanganese concretions commonly occur in shallow‐water coastal regions worldwide. In the Baltic Sea, they can record information about past and present underwater environments and could be a potential source for critical raw materials. We report on their microstructural characteristics and magnetic properties and link them to their formation mechanisms and environmental significance. Microstructural investigations from nano‐ and micro‐computed tomography, electron microscopy, and micro‐X‐ray fluorescence elemental mapping reveal diverse growth patterns within concretions of different morphologies. Alternating Fe‐ and Mn‐rich growth bands indicate fluctuating redox conditions during formation. Bullet‐shaped magnetofossils, produced by magnetotactic bacteria, are present, which suggests the influence of bacterial activity on concretion formation. Spheroidal concretions, which occur in deeper and more tranquil environments, have enhanced microbial biomineralization and magnetofossil preservation. Conversely, crusts and discoidal concretions from shallower and more energetic environments contain fewer magnetofossils and have a greater detrital content. Our results provide insights into concretion formation mechanisms and highlight the importance of diagenetic processes, oxygen availability, and bacterial activity in the Baltic Sea. Key Points: Magnetic minerals within shallow water Fe‐Mn concretions can provide valuable environmental information about their formationMagnetic properties are linked to specific growth patterns in Baltic Sea Fe‐Mn concretionsSpheroidal and crust/discoidal concretions are dominated by biogenic and pedogenic magnetic phases, respectively [ABSTRACT FROM AUTHOR]

In the Baltic Sea, sea level variations are often very pronounced. During the winter season, storm surges caused by strong extratropical cyclones (ETCs) can have major societal impacts on coastal cities. In this study, using reanalysis‐based cyclone tracks and in‐situ tide gauge records, we show that serial cyclone clustering (SCC) leads to higher sea levels in the Baltic Sea than situations where only one ETC passes the tide gauge. Consequently, almost half of extreme sea level events in the Baltic Sea are associated with cyclone clustering periods. For example, in Helsinki, 45% of the extreme sea level events coincided with SCC periods of three or more ETCs, while only 6% of the events coincided with a single ETC. Our study represents a significant advance in the understanding of the factors influencing sea level variations in the Baltic Sea. Plain Language Summary: Sea levels in the Baltic Sea can vary a lot. In winter, powerful storms can lead to storm surges that seriously affect coastal towns. Our research studied storm paths and sea level observations. We found that multiple consecutive storms within a week raise sea levels in the Baltic Sea more than when only one storm passes the same location. As a result, most of the high sea level events in the Baltic Sea are linked to periods when several storms pass the region. In Helsinki, for instance, almost half of all analyzed high sea level events co‐occurred with periods when at least three storms occurred, while only 6% of high sea level events occurred due to a single storm. Our analysis is a significant progression in understanding the reasons that impact the Baltic Sea water levels. Hence, these results could aid in preparing for possible coastal floods. Key Points: Serial cyclone clustering (SCC) commonly causes elevated sea levels in the Baltic SeaPeak storm surges during SCC are on average 2–2.7 times (25–48 cm) higher than during single cyclonesThe intensity of the cyclones within the SCC modulates the storm surge levels, with deeper cyclones more likely to induce higher surges [ABSTRACT FROM AUTHOR]

Aim Many studies have quantified and mapped cumulative human impacts on marine ecosystems. These maps are intended to inform management and planning, but uncertainty in them has not been studied in depth. This paper aims to: (1) quantify the uncertainty in cumulative impact maps and related spatial modelling results; (2) attribute this uncertainty to specific model assumptions and problems with data quality; (3) identify and test sound approaches to such analyses. Location We used the Baltic Sea and the Mediterranean and Black Seas as example regions. The methods and conclusions are relevant for human impact mapping anywhere. Methods We conducted computational experiments to test the effects of nine model assumptions and data quality problems (factors) on maps of human impact and related modelling results. The factors were implemented on the basis of a literature review. We quantified aggregate uncertainty using Monte Carlo simulations, and ranked the factors by their influence on modelling results using the elementary effects method. Both methods are well established and theoretically suitable for complex models, but had to be modified for application to spatial human impact models. Results Some, but not all, modelling results were robust. This contradicts previous studies that found only minor effects of the factors they tested. Of the nine factors tested here, eight had a considerable influence on at least one modelling result in at least one of the two study regions. Main conclusions Model assumptions and data quality have larger aggregate effects on maps of human impact than found in previous analyses. These effects depend on the study region and the data that describe it. Future human impact mapping studies should thus include comprehensive uncertainty analyses. Computational experiments allow us to distinguish robust from less reliable modelling results and to prioritize improvements in models and data. [ABSTRACT FROM AUTHOR]

As initiatives are taken in Sweden to evaluate the geological potential for carbon dioxide storage in the adjacent Baltic Sea, experiences from elsewhere may provide lessons about perceptions of and potential opposition toward carbon capture and storage (CCS). A comprehensive analysis of storage feasibility needs to include the issue of social acceptance. The knowledge of CCS is low in Sweden however and there are no Swedish CCS projects to learn from. This paper therefore draws on lessons from other large-scale energy projects that are embedded in similar Baltic Sea contexts to complement lessons on CCS acceptance provided in the literature. The aim of this study is to facilitate an understanding of acceptance of potential future CO2 storage initiatives in the Swedish Baltic Sea region and to analyze what contextual factors are likely to be determinative of the outcome of these and similar projects. The study identifies climate change as one such key contextual factor, which can often be used both to support and oppose a large-scale energy project. Furthermore, the study finds that there are perceptions of uncertainties regarding the regulatory framework that need to be adressed in order to facilitate the planning of CCS projects in the region. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

Eutrophication, increased temperatures and stratification can lead to massive, filamentous, N2‐fixing cyanobacterial (FNC) blooms in coastal ecosystems with largely unresolved consequences for the mass and energy supply in food webs. Mesozooplankton adapt to not top‐down controlled FNC blooms by switching diets from phytoplankton to microzooplankton, resulting in a directly quantifiable increase in its trophic position (TP) from 2.0 to as high as 3.0. If this process in mesozooplankton, we call trophic lengthening, was transferred to higher trophic levels of a food web, a loss of energy could result in massive declines of fish biomass. We used compound‐specific nitrogen stable isotope data of amino acids (CSIA) to estimate and compare the nitrogen (N) sources and TPs of cod and flounder from FNC bloom influence areas (central Baltic Sea) and areas without it (western Baltic Sea). We tested if FNC‐triggered trophic lengthening in mesozooplankton is carried over to fish. The TP of cod from the western Baltic (4.1 ± 0.5), feeding mainly on decapods, was equal to reference values. Only cod from the central Baltic, mainly feeding on zooplanktivorous pelagics, had a significantly higher TP (4.6 ± 0.4), indicating a strong carry‐over effect trophic lengthening from mesozooplankton. In contrast, the TP of molluscivorous flounder, associated with the benthic food web, was unaffected by trophic lengthening and quite similar reference values of 3.2 ± 0.2 in both areas. This suggests that FNC blooms lead to a large loss of energy in zooplanktivorous but not in molluscivorous mesopredators. If FNC blooms continue to trigger the detour of energy at the base of the pelagic food web due to a massive heterotrophic microbial system, the TP of cod will not return to lower TP values and the fish stock not recover. Monitoring the TP of key species can identify fundamental changes in ecosystems and provide information for resource management. [ABSTRACT FROM AUTHOR]

ABSTRACT Beach-ridge systems are important geo-archives providing evidence for past wave climate including catastrophic storm flood events. This study investigates the morphological impacts of the 1872 Baltic storm flood on a beach-ridge system (sandy spit) in south-eastern Denmark and evaluates the frequency of extreme storm flood events in the area over a longer time perspective. This paper combines field studies of morphology and sedimentary deposits, studies of historical maps, digital terrain model, ground-penetrating radar profiles, and luminescence dating. Sea water reached 2.8 m above mean sea level (amsl) during peak inundation and, based on studies of the morphological impacts of the 1872 storm flood, the event can be divided into four phases. Phase 1: increasing mean water levels and wave activity at the beach brought sediments from the beach (intertidal bars and normal berm) higher up in the profile and led to the formation of a storm-berm. Phase 2: water levels further increased and sediment in the upper part of the profile continued to build up the storm-berm. Phase 3: water levels now reached the top of the dune ridge and were well above the storm-berm level. Sea water was breaching the dune ridge at several sites and wash-over fans were generated until a level where the mean water level had dropped too much. Phase 4: the non-vegetated wash-over fans functioned as pathways for aeolian sand transport and relatively high dunes were formed in particular along the margins of the fan where aeolian sand was trapped by existing vegetation. The studied beach-ridge system records about 4500 years of accumulation; the storm flood sediments described are unique suggesting that the 1872 Baltic storm flood event was an extreme event. Thus studies of beach-ridge systems form a new source for understanding storm surge risk. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT The QuikSCAT mission provided valuable daily information on global ocean wind speed and direction from July 1999 until November 2009 for various applications including numerical weather prediction, ocean and atmospheric modelling. One new and important application for wind vector satellite data is offshore wind energy, where accurate and frequent measurements are required for siting and operating modern wind farms. The greatest advantage of satellite observations rests in their extended spatial coverage. This paper presents analyses of the 10 year data set from QuikSCAT, for the overview of the wind characteristics observed in the North and Baltic Seas, where most of Europe's offshore wind farms operate and more will be constructed. Significant issues in data availability are identified, directly related to the flagging schemes. In situ observations from three locations in the North Sea are used for comparisons. Mean biases (in situ minus satellite) are close to zero for wind speed and -2.7° for wind direction with a standard deviation of 1.2 m s − 1 and 15°, respectively. The impact of using QuikSCAT and in situ measurements extrapolated to 10 m for wind power density estimations is assessed, accounting for possible influences of rain-contaminated retrievals, the sample size, the atmospheric stability effects and either fitting the Weibull distribution or obtaining the estimates from the time series of wind speed observations.Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper we reconstructed river runoff to the Baltic Sea since 1500 using temperature and atmospheric circulation indices, showing the important atmospheric processes for river runoff in different regions. Runoff appears to be strongly linked to temperature, wind and rotational circulation components in the northern region and Gulf of Finland, but more associated with rotational and deformation circulation components in the south. No significant long-term change has been detected in total river runoff to the Baltic Sea for 500 years, although decadal and regional variability is large. Analysis of runoff sensitivity to temperature shows that the south region may become drier with rising air temperatures. This is in contrast to the north region and Gulf of Finland where warmer temperatures are associated with more river runoff. Over the past 500 years the total river runoff to the Baltic Sea has decreased by 3% (450 m/s) per degree Celsius increase. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

This paper presents a model of late-glacial and post-glacial deposition for the late-Neogene sedimentary succession of the Archipelago Sea in the northern Baltic Sea. Four genetically related facies associations are described: (i) an ice-proximal, acoustically stratified draped unit of glaciolacustrine rhythmites; (ii) an onlapping basin-fill unit of rotated rhythmite clasts in an acoustically transparent to chaotic matrix interpreted as debris-flow deposits; (iii) an ice-distal, acoustically stratified to transparent, draped unit of post-glacial lacustrine, weakly laminated to homogeneous deposits; and (iv) an acoustically stratified to transparent unit of brackish-water, organic-rich sediment drifts. The debris-flow deposits of the unit 2 pass laterally into slide scars that truncate the unit 1; they are interpreted to result from a time interval of intense seismic activity due to bedrock stress release shortly after deglaciation of the area. Ice-berg scouring and gravitational failure of oversteepened depositional slopes may also have contributed to the debris-flow deposition. Comparisons to other late-Neogene glaciated basins, such as the Hudson Bay or glacial lakes formed along the Laurentide ice sheet, suggest that the Archipelago Sea succession may record development typical for the deglaciation phase of large, low relief, epicontinental basins. The Carboniferous–Permian glacigenic Dwyka Formation in South Africa may provide an ancient analogue for the studied succession. Chronological control for the studied sediments is provided by the independent palaeomagnetic and AMS-14C dating methods. In order to facilitate dating of the organic-poor early post-glacial deposits of the northern Baltic Sea, the 10 000 year long Lake Nautajärvi palaeomagnetic reference chronology ( Ojala & Saarinen, 2002 ) is extended by 1200 years. [ABSTRACT FROM AUTHOR]

We studied how size variation in populations of Diatoma moniliformis Kitz, was influenced by environmental effects on the diatom life cycle. One of the two populations sampled monthly in the northern Baltic Sea grew under natural conditions; the other population was in a cooling water discharge changed of a nuclear power plant, where the temperature and flow rate of the water were artificially higher. The life cycle was synchronous at the natural site, with sexual reproduction accuning in the winter; most of the initial cells were found in March-April. After this, a reduction in cell size occurred, and the vegetative life cycle consisted of two parts. During the first part, cell volume decreased, whereas the surface area to volume ratio increased, and during the second part of the cycle, both of these parameters decreased. No direct evidence was found for the existence of a supra-annual life cycle in D. moniliformis, as convincing modes for large cells were lacking in the size-frequency distributions. It was concluded from extrapolations of the data that the natural life cycle of D. moniliformis probably lasts 2 or 3 years. The changes in cell proportions during the life cycle fit well with included from extrapolations of the data that the natural life cycle of D. moniliformis probably lasts 2 or 3 years. The changes in cell proportions during the life cycle fit well with annual growth cycle of D. moniliformis at the natural site (i.e. the cells had high surface area to volume ratios during the period of optimal growth in late spring (May-June) At the site affected by cooling water discharge, the synchronization of the natural life cycle was disrupted, but some seasonal size variation did occur. Under natural conditions, auxosporulation is probably triggered by a combination of small cell size, low water temperature (0.3°C), and rapidly increasing light intensity or daylength in late winter to early spring. When these conditions were not met (e.g. at the heated site, the required low temperature was absent), auxosporulation did not occur simultaneously. This paper also presents scanning electron photomicrographs showing the typical shape and fine structure of the initial cell of D. moniliformis. These cells are semispherical in cross section, possess a pronounced curvature along the longitudinal axis, and are bent on the pervatuar plane. [ABSTRACT FROM AUTHOR]

The North Eastern Baltic has no copper resources of its own, meaning that Cu alloy was imported either as raw material or as finished objects. The north‐eastern coastline of Estonia during the late pre‐Roman and Roman Iron Age was connected to the south by sea to the long‐distance 'amber' trade route and to the east by Russian river systems. This study quantitatively assesses the direction of the Cu alloy supply in the region before and after brass enters circulation at the beginning of the Roman Iron Age. After an initial portable X‐ray fluorescence (pXRF) survey, 18 objects were chosen for Pb isotope analysis. This isotope analysis resolved a group of nine brass artefacts from the Roman Iron Age amongst a 'melting pot' of other Cu alloys. The similarity between the isotope ratios found in the Roman world suggests the presence of the same 'melting pot' in the North Eastern Baltic, possibly created by a large amount of Roman Cu alloy being traded north. No evidence for Cu alloy from Scandinavia or the Ural Mountains could be found. The hypothesis from this small study is that the Cu alloy entering Estonia was dominated by metal from Southern Europe from the late pre‐Roman Iron Age and the Roman period. [ABSTRACT FROM AUTHOR]

Range expansions can lead to increased contact of divergent populations, thus increasing the potential of hybridization events. Whether viable hybrids are produced will most likely depend on the level of genomic divergence and associated genomic incompatibilities between the different entities as well as environmental conditions. By taking advantage of historical Baltic cod (Gadus morhua) otolith samples combined with genotyping and whole genome sequencing, we here investigate the genetic impact of the increased spawning stock biomass of the eastern Baltic cod stock in the mid 1980s. The eastern Baltic cod is genetically highly differentiated from the adjacent western Baltic cod and locally adapted to the brackish environmental conditions in the deeper Eastern basins of the Baltic Sea unsuitable for its marine counterparts. Our genotyping results show an increased proportion of eastern Baltic cod in western Baltic areas (Mecklenburg Bay and Arkona Basin)—indicative of a range expansion westwards—during the peak population abundance in the 1980s. Additionally, we detect high frequencies of potential hybrids (including F1, F2 and backcrosses), verified by whole genome sequencing data for a subset of individuals. Analysis of mitochondrial genomes further indicates directional gene flow from eastern Baltic cod males to western Baltic cod females. Our findings unravel that increased overlap in distribution can promote hybridization between highly divergent populations and that the hybrids can be viable and survive under specific and favourable environmental conditions. However, the observed hybridization had seemingly no long‐lasting impact on the continuous separation and genetic differentiation between the unique Baltic cod stocks. [ABSTRACT FROM AUTHOR]

Aquaculture is seen as a possible solution to meet the rising demand for fish but only if the sector reduces its use of wild fish in feed as well as its environmental impacts. The cultivation of extractive species along with fish farming (the integrated multi‐trophic aquaculture system) has a potential to mitigate the adverse environmental effects of fish farming. The dynamic energy budget (DEB) modelling is a powerful tool to be used in different aquaculture settings to achieve the Blue Growth goals set by the commission.This study explored the potential of mussel for bioremediation at finfish farms to develop environmentally sustainable finfish farming solutions in the eutrophic Baltic Sea region.The study integrated the DEB models of blue mussels Mytilus edulis/trossulus and rainbow trout Oncorhynchus mykiss and a regional hydrodynamic‐biogeochemical model to explore the potential of mussel farming to fully compensate nutrient discharges from finfish farms.The DEB models demonstrated that despite suboptimal mussel growth conditions (low salinity), mussel farming has a potential to fully compensate for the discharge of nutrients from fish farms and thereby provide a solution for sustainable fish farming in the Baltic Sea region.Synthesis and applications. As such fish farming may become a necessary enabler of economically sustainable mussel farming in the region. Mussel farming facilitates finfish farming licensing whereas finfish farming covers some costs of mussel farming thereby increasing the economic feasibility of this activity in the region. [ABSTRACT FROM AUTHOR]

During the last decades, the Baltic Sea has been among the fastest warming seas in the world. The warming is mainly driven by increasing air temperatures but deeper water layers can also be warmed by lateral advection of heat. By analyzing a 159 years long (1850–2008) hindcast simulation of the Baltic Sea, we link the exceptionally strong bottom water warming in the western Baltic Sea to a shift in the seasonality of saltwater inflows from the North Sea to the Baltic Sea. Over the model period, warm summer and early autumn inflows have increased while cold winter inflows have decreased. Sensitivity experiments reveal that these changes were partly driven by a shift in river runoff seasonality. The strong warming could lead to faster oxygen depletion in the affected layers and thus have ecological consequences. Plain Language Summary: The Baltic Sea is home to various marine and freshwater species and an important economic factor for the surrounding countries. Like other seas, the Baltic Sea is getting warmer due to climate change. The water at the surface warms especially fast because it takes up heat from the warming atmosphere. After some time, temperatures also increase in deeper layers. However, some deep parts in the western Baltic Sea are warming even faster than the sea surface. In our study, we investigate if the exceptional warming can be explained by an increase in warm saltwater inflows from the North Sea. Hence, we use a model simulation of the Baltic Sea for over 150 years to compare long time series of warm inflows and the temperatures in the deep layers of the western Baltic Sea. We find a strong correlation. Thus, we can link the exceptional warming in the deep layers of the western Baltic Sea during the last decades to an increase in warm inflows. The warming has ecological consequences since in warmer water, the oxygen is consumed faster and the deep water layers of the Baltic Sea are suffering from low oxygen concentrations. Key Points: Summer and early autumn salt import into the Baltic Sea increased significantly since 1851 compared to the annual salt importSalt import between June and October is highly correlated with the annual sub‐thermocline temperature maximum in the western Baltic SeaThe shift in inflow seasonality was partly caused by seasonal changes in river runoff [ABSTRACT FROM AUTHOR]

The Baltic Proper harbour porpoise population is listed as Critically Endangered by IUCN, and only a few hundred animals remain. One of the most serious threats to this population is bycatch in static net fisheries. To minimize bycatch, ICES has proposed that acoustic deterrent devices, pingers, should be used on static nets within the population's range.However, there have previously been indications that grey seals learn to associate the pinger sounds with the presence of nets with easily accessible prey, and that pinger use therefore can increase the risk of seal depredation in static net fisheries.In recent years, pingers operating at higher frequencies have been made commercially available, the idea being that harbour porpoises will still be able to hear the sound at 50–120 kHz while this will be above or at the limit of seal hearing. This would mean that such high‐frequency pingers would not induce this so‐called dinner‐bell effect.In this study, data were collected from active commercial static net fisheries in the Baltic Proper, using two types of high‐frequency pingers operating at 50–120 and 70 kHz, respectively. Pingers were attached to nets in accordance with manufacturers' guidelines, and fishers were asked to estimate the catch loss owing to seals in nets with and without pingers.Data were received from 646 deployments made between May 2019 and September 2020. Four generalized mixed effect models were developed with relevant variables.The results suggest using high‐frequency pingers does not increase seal depredation on static nets. It is concluded that pingers could be used as an interim measure to minimize bycatch of the Critically Endangered Baltic Proper harbour porpoise population. [ABSTRACT FROM AUTHOR]

The Centre for Marine Evolutionary Biology (CeMEB) at the University of Gothenburg, Sweden, was established in 2008 through a 10‐year research grant of 8.7 m€ to a team of senior researchers. Today, CeMEB members have contributed >500 scientific publications, 30 PhD theses and have organised 75 meetings and courses, including 18 three‐day meetings and four conferences. What are the footprints of CeMEB, and how will the centre continue to play a national and international role as an important node of marine evolutionary research? In this perspective article, we first look back over the 10 years of CeMEB activities and briefly survey some of the many achievements of CeMEB. We furthermore compare the initial goals, as formulated in the grant application, with what has been achieved, and discuss challenges and milestones along the way. Finally, we bring forward some general lessons that can be learnt from a research funding of this type, and we also look ahead, discussing how CeMEB's achievements and lessons can be used as a springboard to the future of marine evolutionary biology. [ABSTRACT FROM AUTHOR]

Convective sea‐effect snowfall, in the form of snowbands, is observed over the northern Baltic Sea annually. Quasi‐stationary snowbands may last up to several days over the sea and, depending on the wind direction, move towards the coast. This study provides climatology of spatial and temporal occurrence of snowbands in Finland for a 48‐year period (1973–2020). We used a set of detection criteria together with ERA5 reanalysis at off‐shore areas and FMIClimGrid gridded observational data for on‐shore areas to find the days favouring snowband formation. Only those snowband days (SBD) when snow reached the Finnish coastal mainland were considered. The total annual number of SBDs in Finland varied from 6 to 40 with an average of 16. SBDs were detected most frequently over the Gulf of Bothnia near the western coast of the country. The largest increase in snow depth (SDI) during an SBD (67 cm/day) also took place on the western coast, although the long‐term mean of SDI (3–5 cm/day) was highest over the southern coast. Throughout the country, November and December showed the highest frequency of SBDs. However, between the periods 1973–1996 and 1997–2020, the seasonal cycle of SBDs shifted 1 month forward from late autumn to mid‐winter as the decrease in the number of SBDs during December as well as the increase during January and February were statistically significant in Finland. In northern Baltic Sea, long‐term increases in monthly means of sea surface temperature (SST) and air temperature at the atmospheric level of 850 hPa (T850) were in line with the decadal changes in the occurrence of SBDs. The increasing trend in SST favours the formation of snowbands but in late autumn the probability for snowband formation decreased because even larger increases in T850 resulted in diminishing differences between SST and T850. [ABSTRACT FROM AUTHOR]

Baltic cod Gadus morhua otoliths marked with oxytetracycline ( OTC) in 1974-1975 had been sectioned and the sections stored in paper envelopes at room temperature in dry, dark conditions. After 40 years of storage, the historic OTC marks were still clearly visible showing that OTC is suitable for long-term chemical marking of otoliths. They were, however, noticeably paler than marks in recently recaptured and archived Baltic G. morhua otoliths, chemically tagged with tetracycline at similar dosage to the historic otoliths. [ABSTRACT FROM AUTHOR]

Observations from the global ocean have long confirmed the ubiquity of thermohaline inversions in the upper ocean, often accompanied by a clear signal in biogeochemical properties. Their emergence has been linked to different processes such as double diffusion, mesoscale stirring, frontal subduction, and the recently discussed submesoscale features. This study uses the central Baltic Sea as a natural laboratory to explore the formation of salinity inversions in the thermocline region during summer. We use realistic high‐resolution simulations complemented by field observations to identify the dominant generation mechanism and potential hotspots of their emergence. We propose that the strongly stratified thermocline can host distinct salinity minima during summer conditions resulting primarily from the interaction between lateral surface salinity gradients and wind‐induced differential advection. Since this is a generic mechanism, such salinity inversions can likely constitute a typical feature of the upper ocean in regions with distinct thermoclines and shallow mixed layers. Plain Language Summary: The upper ocean is characterized by a well‐mixed surface layer, below which temperature decreases rapidly with depth, forming the so‐called thermocline region. A corresponding salinity increase with depth is typically anticipated for stable density stratification to occur. Temperature and salinity inversions can, however, emerge in the upper ocean. Such thermohaline inversions have been observed in different regions of the world's oceans, and various mechanisms have been proposed to explain their generation. Here, the central basin of the Baltic Sea is used as a natural laboratory to explore the formation of distinct salinity minima in the thermocline region during summer conditions. Using high‐resolution numerical simulations and measurements from a field campaign, we show that inversions are abundant and can emerge throughout the entire basin. They increase with increasing wind speeds and concentrate mainly in regions with strong lateral salinity differences. We propose that thermocline salinity minima can occur during summer when the wind transports saltier water over less saline surface waters. This is a generic mechanism that can therefore be responsible for the formation of the salinity inversions observed worldwide in areas with distinct thermoclines and shallow mixed layers. Key Points: Observations collected in the central Baltic Sea during summer indicate patches of distinct salinity minima in the thermocline regionRealistic high‐resolution simulations are used to explore the origin of the salinity minima and to identify the hotspots of their genesisLateral surface salinity gradients interacting with wind‐induced differential advection are shown to generate most of the inversions [ABSTRACT FROM AUTHOR]

River estuaries are characterized by mixing processes between freshwater discharge and marine water masses. Since the first are depleted in heavier stable isotopes compared with the marine realm, estuaries often show a linear correlation between salinity and water stable isotopes (δ18O and δ2H values). In this study, we evaluated spatial and seasonal isotope dynamics along three estuarine lagoon transects, located at the northern German Baltic Sea coast. The data show strong seasonality of isotope values, even at locations located furthest from the river mouths. They further reveal a positive and linear salinity‐isotope correlation in spring, but ‐in two of the three studied transects‐ hyperbolic and partially reverse correlations in summers. We conclude that additional hydrological processes partially overprint the two‐phase mixing correlation during summers: aside from the isotope seasonality of the riverine inflows, the shallow inner lagoons in the studied estuaries are influenced by evaporation processes. In contrast the estuarine outflow regions are under impact of significant salinity and isotope fluctuations of the Baltic Sea. Deciphering those processes is crucial for the understanding of water isotope and salinity dynamics. This is also of relevance in context of ecological studies, for example, when interpreting oxygen and hydrogen isotope data in aquatic organisms that depend on ambient estuarine waters. [ABSTRACT FROM AUTHOR]

Coastal systems experience strong impacts of ongoing environmental change, affecting fish communities and subsequently fishery yields. In the Baltic Sea, the combined effects of climate‐induced changes and eutrophication‐related pressures constitute major threats to its living resources. Although much work has been devoted to uncovering environmental impacts on the commercially most valuable fish stocks, only little is known about community‐wide responses of fished species and how environmental change may affect their yield. In this study, the authors use a joint species distribution modelling framework to disentangle environmental impacts on species‐specific fishery yields of 16 fished species along the coast of Finland over four decades. The authors show that environmental covariates substantially contributed to variations in fishery yields and are likely to have strong impacts on fished resources also in the future. Salinity and near‐bottom oxygen concentration emerged as the strongest environmental drivers of yields at the community level, whereas temperature was particularly important for cod (Gadus morhua) and sprat (Sprattus sprattus) yields. The authors found shore density to be an important predictor for fisheries resources especially for freshwater fish. The results of this study suggest that the changes in environmental conditions during the past four decades had a positive effect on the yields of freshwater and warm‐affinity species, whereas yields of marine cold‐affinity species have been mainly negatively affected by contracting favourable habitats, becoming warmer and less saline. [ABSTRACT FROM AUTHOR]

Climate change influences the ocean's physical and biogeochemical conditions, causing additional pressures on marine environments and ecosystems, now and in the future. Such changes occur in environments that already today suffer under pressures from, for example, eutrophication, pollution, shipping, and more. We demonstrate how to implement climate change into regional marine spatial planning by introducing data of future temperature, salinity, and sea ice cover from regional ocean climate model projections to an existing cumulative impact model. This makes it possible to assess climate change impact in relation to pre‐existing cumulative impact from current human activities. Results indicate that end‐of‐century projected climate change alone is a threat of the same magnitude as the combination of all current pressures to the marine environment. These findings give marine planners and policymakers forewarning on how future climate change may impact marine ecosystems, across space, emission scenarios, and in relation to other pressures. [ABSTRACT FROM AUTHOR]

Baltic Sea is one of the World's most oxygen‐depletes seas, so the region requires urgent mitigation measures to significantly reduce nitrogen and phosphorus inputs from land through rivers, which cannot be achieved without large‐scale restoration of wetland buffer zones. The manuscript summarizes the findings of the discrete choice experiment aimed at assessment of the preferences of Danish, German, and Polish citizens toward ecosystem services of lowland small rivers of the Baltic Sea basin. Our results suggest that respondents in all the studied countries are willing to pay substantial amounts to improve water quality in rivers and the Baltic Sea, as well as to restore naturally meandering rivers and natural riparian vegetation. Wild marshes and Wetland agriculture were equally valued as the most desirable options. Respondents systematically cared about the appearance of small rivers in their neighborhood. We conclude that re‐meandering, rewetting of floodplains, and restoration of wild marshes (i.e. natural wetland vegetation) or development of wetland agriculture could gain a lot of public support in Europe. [ABSTRACT FROM AUTHOR]

Environmental gradients have emerged as important barriers to structuring populations and species distributions. We set out to test whether the strong salinity gradient from the marine North Sea to the brackish Baltic Sea in northern Europe represents an ecological and genetic break, and to identify life history traits that correlate with the strength of this break. We accumulated mitochondrial cytochrome oxidase subunit 1 sequence data, and data on the distribution, salinity tolerance, and life history for 28 species belonging to the Cnidaria, Crustacea, Echinodermata, Mollusca, Polychaeta, and Gastrotricha. We included seven non‐native species covering a broad range of times since introduction, in order to gain insight into the pace of adaptation and differentiation. We calculated measures of genetic diversity and differentiation across the environmental gradient, coalescent times, and migration rates between North and Baltic Sea populations, and analyzed correlations between genetic and life history data. The majority of investigated species is either genetically differentiated and/or adapted to the lower salinity conditions of the Baltic Sea. Species exhibiting population structure have a range of patterns of genetic diversity in comparison with the North Sea, from lower in the Baltic Sea to higher in the Baltic Sea, or equally diverse in North and Baltic Sea. Two of the non‐native species showed signs of genetic differentiation, their times since introduction to the Baltic Sea being about 80 and >700 years, respectively. Our results indicate that the transition from North Sea to Baltic Sea represents a genetic and ecological break: The diversity of genetic patterns points toward independent trajectories in the Baltic compared with the North Sea, and ecological differences with regard to salinity tolerance are common. The North Sea–Baltic Sea region provides a unique setting to study evolutionary adaptation during colonization processes at different stages by jointly considering native and non‐native species. [ABSTRACT FROM AUTHOR]

Each year, millions of hatchery‐reared sea‐run brown trout Salmo trutta L. (the sea trout) juveniles are released into the natural environment in the Atlantic region. The aim of this work was to investigate the growth responses of sea trout to changing temperature conditions and to compare the growth plasticity between wild and hatchery‐reared fish. Scales were collected from sea trout in a selected river flowing into the southern Baltic Sea. We analyzed the scale increment widths as a proxy of somatic growth and investigated the interannual variabilities and differences in growth between fish groups (wild and hatchery‐reared). We used mixed‐effects Bayesian modeling and ascribed the variances in growth to different sources. Furthermore, we developed indices of interannual (2003–2015) growth variation in the marine and freshwater phases of the life cycle of the fish and analyzed the relationships between trout growth and temperature. Temperature positively affects fish growth, regardless of the origin of the fish. We observed stronger relationships between fish growth and temperature conditions in the marine phase than in the freshwater phase. Additionally, wild sea trout are characterized by stronger responses to temperature variability and higher phenotypic plasticity of growth than those of the hatchery‐reared individuals. Therefore, wild sea trout might be better suited to changing environmental conditions than hatchery‐reared sea trout. This knowledge identifies possible threats in management actions for sea trout with an emphasis on ongoing climate change. [ABSTRACT FROM AUTHOR]

Studying how food web structure and function vary through time represents an opportunity to better comprehend and anticipate ecosystem changes. Yet, temporal studies of highly resolved food web structure are scarce. With few exceptions, most temporal food web studies are either too simplified, preventing a detailed assessment of structural properties or binary, missing the temporal dynamics of energy fluxes among species.Using long‐term, multi‐trophic biomass data coupled with highly resolved information on species feeding relationships, we analysed food web dynamics in the Gulf of Riga (Baltic Sea) over more than three decades (1981–2014). We combined unweighted (topology‐based) and weighted (biomass‐ and flux‐based) food web approaches, first, to unravel how distinct descriptors can highlight differences (or similarities) in food web dynamics through time, and second, to compare temporal dynamics of food web structure and function.We find that food web descriptors vary substantially and distinctively through time, likely reflecting different underlying ecosystem processes. While node‐ and link‐weighted metrics reflect changes related to alterations in species dominance and fluxes, unweighted metrics are more sensitive to changes in species and link richness. Comparing unweighted, topology‐based metrics and flux‐based functions further indicates that temporal changes in functions cannot be predicted using unweighted food web structure. Rather, information on species population dynamics and weighted, flux‐based networks should be included to better comprehend temporal food web dynamics.By integrating unweighted, node‐ and link‐weighted metrics, we here demonstrate how different approaches can be used to compare food web structure and function, and identify complementary patterns of change in temporal food web dynamics, which enables a more complete understanding of the ecological processes at play in ecosystems undergoing change. [ABSTRACT FROM AUTHOR]

The concept of social–ecological knowledge diversity (SEKD) provides a novel way of examining coupled human–environment interactions—it acknowledges differences in knowledge, values, and beliefs of stakeholder groups within social–ecological systems (SES). Thus, understanding and measuring SEKD is an essential component of sustainable management with implications for conflict resolution, collective action and policymaking. However, methods to efficiently define and model knowledge diversity are still underdeveloped. Using a semiquantitative cognitive mapping approach, we collected and analyzed stakeholder‐specific knowledge and perceptions of the Western Baltic cod fishery to model SEKD. Results demonstrate substantial variation in perceptions across different individuals and social groups. SEKD was evident in (a) distinctive meanings attached to social factors relative to ecological factors, (b) causal relationships underlying the understanding of SES dynamics, and (c) social impacts of ecological changes on ecosystems (and vice versa). By identifying and representing knowledge‐specific disparities in SES frameworks, our model explicitly improves the understanding of human–environment interactions with implications that could help reduce conflicts and legitimize management plans. [ABSTRACT FROM AUTHOR]

Global environmental changes have accelerated at an unprecedented rate in recent decades due to human activities. As a consequence, the incidence of novel abiotic conditions and biotic communities, which have been continuously emerging in the Earth system, has rapidly risen. Despite growing attention to the incidence and challenges posed by novelty in terrestrial ecosystems, novelty has not yet been quantified in marine ecosystems. Here, we measured for the rate of novelty (RoN) in abiotic conditions and community structure for three trophic levels, i.e., phytoplankton, zooplankton, and fish, in a large marine system ‐ the Baltic Sea. We measured RoN as the degree of dissimilarity relative to a specific spatial and temporal baseline, and contrasted this with the rate of change as a measure of within‐basin change over time. We found that over the past 35 years abiotic and biotic RoN showed complex dynamics varying in time and space, depending on the baseline conditions. RoN in abiotic conditions was smaller in the open Central Baltic Sea than in the Kattegat and the more enclosed Gulf of Bothnia, Gulf of Riga, and Gulf of Finland in the north. We found a similar spatial pattern for biotic assemblages, which resulted from changes in composition and stock size. We identified sea‐surface temperature and salinity as key drivers of RoN in biotic communities. Hence, future environmental changes that are expected to affect the biogeochemistry of the Baltic Sea, may favor the rise of biotic novelty. Our results highlighted the need for a deeper understanding of novelty development in marine ecosystems, including interactions between species and trophic levels, ecosystem functioning under novel abiotic conditions, and considering novelty in future management interventions. [ABSTRACT FROM AUTHOR]

Forage fish populations often undergo large and rapid fluctuations in abundance. However, most of their predators are buffered against such fluctuations owing to their slower pace of life, which allows them to maintain more stable populations, at least during short periods of food scarcity. In this study, we investigated top‐down processes exerted by seabirds on forage fish stocks in five contrasted marine ecosystems, compiling numerous data sets on seabird counts, diets, energetic needs and prey energy content and abundance. Off Norway, South Africa, Peru, Sweden and Scotland, we found that predation pressure—estimated as the proportion of a fish stock consumed by seabirds—was generally low (median = 1%), but increased sharply at low levels of prey abundance. When prey biomass decreased below 15–18% of its maximum recorded value, predation by seabirds became a source of important additional pressure on prey stocks (~20% of prey biomass is consumed by seabirds). An earlier empirical study advocated for keeping forage stocks from falling below a threshold of 33% of long‐term maximum prey biomass in order to safeguard seabird breeding success, but here we further suggest that a threshold of 18% should be considered as a limit not to be exceeded for the sake of the forage fish themselves, and below which extra cautious management of fisheries may be required. Nevertheless, despite exceptionally high rates of predation on some occasions, predation pressure was not correlated with prey dynamics, suggesting an absence of prey entrapment due to seabirds alone in these five ecosystems. [ABSTRACT FROM AUTHOR]

The sensitivity of the overturning circulation in the Baltic Sea is analyzed with respect to long‐term changes in atmospheric and hydrological conditions by using two state‐of‐the‐art ocean circulation models: RCO (Rossby Centre Ocean model) with a reference simulation and various sensitivity experiments as well as MOM (Modular Ocean Model). Historical reconstructions since 1850 lasting for >150 years are considered in order to identify coherences between the overturning stream function and surface wind, river runoff, major Baltic inflows, salinity, and water temperature. Long‐term time series are evaluated statistically for several subbasins of the Baltic Sea for the two different models and for the sensitivity experiments concerning the interannual, multidecadal, and centennial variability. We found that the simulated overturning circulation has a response time scale with respect to wind or runoff of around 30 years. The overturning circulation will decrease basin‐wide under anomalous wind conditions which hamper the deep water flow within the Baltic Sea, under a warmer climate or when river runoff increases. However, a global sea level rise would reinforce the overturning circulation. Overall, multidecadal variations of the overturning circulation are anticorrelated to and caused by the wind parallel to the cross‐section of the overturning circulation. They are not caused by river runoff and the coherence with major Baltic inflows is small. Hence, the overturning circulation does not act as a good proxy for major Baltic inflows. Plain Language Summary: The Baltic Sea as a semienclosed sea in northern Europe exchanges water masses with the adjacent North Sea. This process is characterized by bottom inflow of saline water into the Baltic Sea and surface outflow of brackish water. The reverse currents drive a circulation within the whole Baltic Sea which transports and turns over large amounts of water, heat, and salt. We analyze this so‐called overturning circulation by using two different ocean circulation models. Besides a model intercomparison, different experiments are done with one of the models for identifying overturning circulation changes due to variations in air temperature, wind, river runoff, and sea level. Changes in wind or runoff affect the circulation after ∼30 years in both models. The circulation reinforces when global sea level rises, but it decreases when the wind hampers the water mass exchange with the North Sea, when river runoff increases or under warmer climate. These counteracting responses allow no clear projection of the future overturning circulation of the Baltic Sea. Overall we found that pronounced 30‐years variations of this circulation are caused by wind hampering surface water outflow of the Baltic Sea but not by river runoff and only little by saltwater inflows. Key Points: Projected warming and increased freshwater supply will decrease the overturning circulation while rising global sea level will increase itThe variability of the strength of the overturning circulation is only partially explained by major Baltic inflowsMultidecadal variations of the overturning circulation are caused mainly by the wind parallel to the overturning circulation [ABSTRACT FROM AUTHOR]

According to ecological theory, two species cannot occupy the same niche. Using nitrogen isotope analyses (δ15N) of amino acids, we tested the extent to which two sympatric deposit‐feeding amphipods, Monoporeia affinis and Pontoporeia femorata, partition their trophic resources. We found that trophic position (TP) and resynthesis index (∑V; a proxy for degradation status of ingested material prior to assimilation by the consumer) differ between species. The surface‐feeding M. affinis had higher TP and intermediate ∑V, both pointing to a large contribution of metazoans in its diet. P. femorata, which feeds in the subsurface layers, had lower TP and a bimodal distribution of the ∑V values, supporting previous experimental evidence of a larger feeding niche. We also evaluated whether TP and ∑V values have consequences for amphipod fecundity and embryo viability and found that embryo viability in M. affinis was negatively linked to TP. Our results indicate that the amino acid‐δ15N data paired with information about reproductive status are useful for detecting differences in the trophic ecology of sympatric amphipods. [ABSTRACT FROM AUTHOR]

Marine food webs are highly compartmentalized, and characterizing the trophic niches among consumers is important for predicting how impact from human activities affects the structuring and functioning of marine food webs. Biomarkers such as bulk stable isotopes have proven to be powerful tools to elucidate trophic niches, but they may lack in resolution, particularly when spatiotemporal variability in a system is high. To close this gap, we investigated whether carbon isotope (δ13C) patterns of essential amino acids (EAAs), also termed δ13CAA fingerprints, can characterize niche differentiation in a highly dynamic marine system. Specifically, we tested the ability of δ13CAA fingerprints to differentiate trophic niches among six functional groups and ten individual species in the Baltic Sea. We also tested whether fingerprints of the common zooplanktivorous fishes, herring and sprat, differ among four Baltic Sea regions with different biochemical conditions and phytoplankton assemblages. Additionally, we investigated how these results compared to bulk C and N isotope data for the same sample set. We found significantly different δ13CAA fingerprints among all six functional groups. Species differentiation was in comparison less distinct, due to partial convergence of the species' fingerprints within functional groups. Herring and sprat displayed region‐specific δ13CAA fingerprints indicating that this approach could be used as a migratory marker. Niche metrics analyses showed that bulk isotope data had a lower power to differentiate between trophic niches than δ13CAA fingerprinting. We conclude that δ13CAA fingerprinting has a strong potential to advance our understanding of ecological niches, and trophic linkages from producers to higher trophic levels in dynamic marine systems. Given how management practices of marine resources and habitats are reshaping the structure and function of marine food webs, implementing new and powerful tracer methods are urgently needed to improve the knowledge base for policy makers. [ABSTRACT FROM AUTHOR]

In this study, we investigate the regional tectonic impact on salt movement at the northeastern margin of the intracontinental North German Basin. We discuss the evolution of salt pillows in the Bay of Mecklenburg in the light of thick‐ and thin‐skinned tectonics, including gravity gliding, and differential loading using seismic imaging. Stratigraphic and structural interpretation of a 170 km long, multichannel seismic line, extending from the Bay of Mecklenburg to northeast of Rügen Island, incorporates well information of nearby onshore wells. This new high‐resolution seismic line completely images the stratigraphic and tectonic pattern of the subsurface, from the base of the Zechstein to the seafloor. Our analysis reveals that subsidence during Late Triassic to Early Cretaceous at the northeastern basin margin was associated with transtensional dextral strike slip movement within the Trans‐European Suture Zone. We reinterpret the Werre and Prerow Fault Zones west of Rügen Island as an inverted, thin‐skinned normal fault system associated with the formation of the Western Pomeranian Fault System. Salt movement in the Bay of Mecklenburg was initiated in the Late Triassic and lasted until the Early Jurassic. A second phase of salt pillow growth occurred during the Coniacian until Cenozoic and correlates with compression‐related regional basin inversion due to the onset of the Africa‐Iberia‐Europe convergence. Thin‐skinned extensional initialization of salt pillow growth and compressional salt remobilization explains salt pillow evolution in the Bay of Mecklenburg. Additionally, we discuss an impact of gravity gliding on salt pillow evolution induced by basin margin tilt. Key Points: A regional high‐resolution seismic profile continuously images the SW Baltic Sea subsurface from the Zechstein salt base to the seafloorLate Triassic salt movement and Late Cretaceous‐Cenozoic remobilization correlate with regional tectonics at the North German Basin marginThe tectonic evolution of salt pillows is discussed in terms of thin‐skinned extensional/compressional deformation and gravity gliding [ABSTRACT FROM AUTHOR]

The role of future forests in global biogeochemical cycles will depend on how different tree species respond to climate. Interpreting the response of forest growth to climate change requires an understanding of the temporal and spatial patterns of seasonal climatic influences on the growth of common tree species. We constructed a new network of 310 tree‐ring width chronologies from three common tree species (Quercus robur, Pinus sylvestris and Fagus sylvatica) collected for different ecological, management and climate purposes in the south Baltic Sea region at the border of three bioclimatic zones (temperate continental, oceanic, southern boreal). The major climate factors (temperature, precipitation, drought) affecting tree growth at monthly and seasonal scales were identified. Our analysis documents that 20th century Scots pine and deciduous species growth is generally controlled by different climate parameters, and that summer moisture availability is increasingly important for the growth of deciduous species examined. We report changes in the influence of winter climate variables over the last decades, where a decreasing influence of late winter temperature on deciduous tree growth and an increasing influence of winter temperature on Scots pine growth was found. By comparing climate–growth responses for the 1943–1972 and 1973–2002 periods and characterizing site‐level growth response stability, a descriptive application of spatial segregation analysis distinguished sites with stable responses to dominant climate parameters (northeast of the study region), and sites that collectively showed unstable responses to winter climate (southeast of the study region). The findings presented here highlight the temporally unstable and nonuniform responses of tree growth to climate variability, and that there are geographical coherent regions where these changes are similar. Considering continued climate change in the future, our results provide important regional perspectives on recent broad‐scale climate–growth relationships for trees across the temperate to boreal forest transition around the south Baltic Sea. [ABSTRACT FROM AUTHOR]

Spatial connectivity is an essential process to consider in the design and assessment of Marine Protected Areas (MPAs). To help maintain and restore marine populations and communities MPAs should form ecologically coherent networks. How to estimate and implement connectivity in MPA design remains a challenge.Here a new theoretical framework is presented based on biophysical modelling of organism dispersal, combined with a suite of tools to assess different aspects of connectivity that can be integrated in MPA design. As a demonstration, these tools are applied to an MPA network in the Baltic Sea (HELCOM MPA).The tools are based on the connectivity matrix, which summarizes dispersal probabilities, averaged over many years, between all considered areas in the geographic target area. The biophysical model used to estimate connectivity included important biological traits that affect dispersal patterns where different trait combinations and habitat preferences will produce specific connectivity matrices representing different species.Modelled connectivity matrices were used to assess local retention within individual MPAs, which offers indications about the adequacy of size when MPAs are considered in isolation. The connectivity matrix also provides information about source areas to individual MPAs, e.g. sources of larvae or pressures such as contaminants. How well several MPAs act as a network was assessed within a framework of eigenvalue perturbation theory (EPT). With EPT, the optimal MPA network with respect to connectivity can be identified. In addition, EPT can suggest optimal extensions of existing MPA networks to enhance connectivity. Finally, dispersal barriers can be identified based on the connectivity matrix, which may suggest boundaries for management units.The assessment of connectivity for the HELCOM MPA are discussed in terms of possible improvements, but the tools presented here could be applied to any region. [ABSTRACT FROM AUTHOR]

Temporal trends from 1981 to 2013 of 28 per‐ and polyfluoroalkyl substances (PFASs) were investigated in liver tissue of cod (Gadus morhua) sampled near southeast Gotland, in the Baltic Sea. A total of 10 PFASs were detected, with ∑28PFAS geometric mean concentrations ranging from 6.03 to 23.9 ng/g ww. Perfluorooctane sulfonate (PFOS) was the predominant PFAS, which increased at a rate of 3.4% per year. Most long‐chain perfluoroalkyl carboxylic acids increased at rates of 3.9 to 7.3% per year except for perfluorooctanoate (PFOA), which did not change significantly over time. The perfluoroalkyl acid precursors perfluorooctane sulfonamide (FOSA) and 6:2 fluorotelomer sulfonic acid were detected, of which the former (FOSA) declined at a rate of –4.4% per year, possibly reflecting its phase‐out starting in 2000. An alternate time trend analysis from 2000 to 2013 produced slightly different results, with most compounds increasing at slower rates compared to the entire study period. An exception was perfluorohexane sulfonate (PFHxS), increasing at a faster rate of 3.7% measured from 2000 on, compared to the 3.0% per year measured starting from 1981. Analysis of the total fluorine content of the samples revealed large amounts of unidentified fluorine; however, its composition (organic or inorganic) remains unclear. Significant negative correlations were found between concentrations of individual PFASs (with the exception of PFOS) and liver somatic index. In addition, body length was negatively correlated with PFOA and perfluorononanoate, but positively correlated with perfluorododecanoate (PFDoDA) and FOSA. Additional studies on endocrine, immunological, and metabolic effects of PFAS in marine fish are essential to assess the environmental risk of these substances. Environ Toxicol Chem 2020;39:300–309. © 2019 SETAC [ABSTRACT FROM AUTHOR]

Marine heatwaves have been observed worldwide and are expected to increase in both frequency and intensity due to climate change. Such events may cause ecosystem reconfigurations arising from species range contraction or redistribution, with ecological, economic and social implications. Macrophytes such as the brown seaweed Fucus vesiculosus and the seagrass Zostera marina are foundation species in many coastal ecosystems of the temperate northern hemisphere. Hence, their response to extreme events can potentially determine the fate of associated ecosystems. Macrophyte functioning is intimately linked to the maintenance of photosynthesis, growth and reproduction, and resistance against pathogens, epibionts and grazers. We investigated morphological, physiological, pathological and chemical defence responses of western Baltic Sea F. vesiculosus and Z. marina populations to simulated near‐natural marine heatwaves. Along with (a) the control, which constituted no heatwave but natural stochastic temperature variability (0HW), two treatments were applied: (b) two late‐spring heatwaves (June, July) followed by a summer heatwave (August; 3HW) and (c) a summer heatwave only (1HW). The 3HW treatment was applied to test whether preconditioning events can modulate the potential sensitivity to the summer heatwave. Despite the variety of responses measured in both species, only Z. marina growth was impaired by the accumulative heat stress imposed by the 3HW treatment. Photosynthetic rate, however, remained high after the last heatwave indicating potential for recovery. Only epibacterial abundance was significantly affected in F. vesiculosus. Hence both macrophytes, and in particular F. vesiculosus, seem to be fairly tolerant to short‐term marine heatwaves at least at the intensities applied in this experiment (up to 5°C above mean temperature over a period of 9 days). This may partly be due to the fact that F. vesiculosus grows in a highly variable environment, and may have a high phenotypic plasticity.Impact of simulated marine heatwaves on foundation macrophytes in the Baltic Sea. [ABSTRACT FROM AUTHOR]

An aggregated sample of 925 Atlantic cod Gadus morhua collected by four countries in different regions of the Baltic Sea during different seasons were measured (total length, LT = 161–890 mm and weighed (mass, M = 45–6900 g) both before freezing and after defrosting. The cod were found to decrease significantly in both LT and M following death and frozen storage. There was an average (±SD) change in LT of −2.91% (±0.05%) following freezing, independent of starting LT. Total M changed by −2.65% (±0.14%), independent of starting mass. Shrinkage of LT and M did not differ significantly between 1 and 4 months frozen storage, though LT shrinkage was significantly greater after 1 or 4 months in the freezer compared with after 5 days. There was significant variation in LT and M shrinkage between regions of capture. A significant negative relationship between condition of cod and LT or M change was also observed. Equations to back‐calculate fresh LT and M from thawed LT, M and standard length (LS), gutted LT, gutted LS and gutted M are provided. [ABSTRACT FROM AUTHOR]

The rear face of the wave spectrum is described by an equilibrium and a saturation subrange. Although accurate information about these ranges are highly relevant for wave modeling and many practical applications, there have been inconsistencies between results originating from temporal and spatial measurements. These discrepancies have been explained by the Doppler shift and the harmonics of nonlinear waves. We present high‐frequency wave measurements from the Baltic Sea gathered with R/V Aranda using a wave staff array, which provided directional frequency‐wavenumber data. In addition to the traditional wavenumber and frequency spectra, F(k) and S(ω), we also define a new spectrum that is a function of the inverse phase speed. We denote this spectrum Q(ν), where ν=kω−1. The properties of this Q‐spectrum were studied using data from four different sites. A strongly forced fetch‐limited case showed an equilibrium‐to‐saturation transition in the Q‐spectrum, with less variations in the equilibrium constants compared to the frequency spectra. The transition to a saturation regime happened around Uν=3 in all spectra where an equilibrium range was identified. Most duration‐limited spectra had no equilibrium range in the inverse phase speed domain. The absence of an equilibrium range was consistent with the wavenumber domain, but the frequency spectra still showed an apparent equilibrium subrange extending to ωU/g=5. The consistency of the saturation ranges between the Q‐spectrum and the wavenumber spectrum indicate a weak Doppler shift effect. We deduced that the main factor distorting the frequency spectra was wave nonlinearities. Plain Language Summary: Surface waves are studied by partitioning them according to their length expressed in wave periods (seconds) or wavelengths (meters). Both approaches should give a similar descriptions of the waves, but in practice they produce inconsistent results. This limits our fundamental knowledge of waves and complicates practical applications. Measuring the wave period and the wavelength simultaneously is difficult, and there are not a lot of good data to study this problem. We measured the waves in the Baltic Sea from the ship R/V Aranda by recording the water level elevations using several thin submerged wires. From these observations we could describe the waves using both wave periods and wavelengths. The central part of our work was presenting the waves in a new way: We combined the wavelength and period measurements and partitioned the waves according to the speed which with they travel. The new partitioning shed light on the physical processes responsible for the discrepancies between the two traditional ways of representing the waves. This new approach might turn out to be useful, since many properties of the waves—such as the energy transfer from the wind—are controlled by their speed relative to the wind. Key Points: A spectrum representing wind waves as a function of their inverse phase speed is defined and examined using wave staff observationsThe new spectrum is consistent with the wavenumber spectrum for the shortest wavesThe inconsistencies observed in the frequency spectra are deduced to mainly be a result of wave nonlinearities [ABSTRACT FROM AUTHOR]

A challenge facing ecologists trying to predict responses to climate change is the few recent analogous conditions to use for comparison. For example, negative relationships between ectotherm body size and temperature are common both across natural thermal gradients and in small‐scale experiments. However, it is unknown if short‐term body size responses are representative of long‐term responses. Moreover, to understand population responses to warming, we must recognize that individual responses to temperature may vary over ontogeny. To enable predictions of how climate warming may affect natural populations, we therefore ask how body size and growth may shift in response to increased temperature over life history, and whether short‐ and long‐term growth responses differ. We addressed these questions using a unique setup with multidecadal artificial heating of an enclosed coastal bay in the Baltic Sea and an adjacent reference area (both with unexploited populations), using before‐after control‐impact paired time‐series analyses. We assembled individual growth trajectories of ~13,000 unique individuals of Eurasian perch and found that body growth increased substantially after warming, but the extent depended on body size: Only among small‐bodied perch did growth increase with temperature. Moreover, the strength of this response gradually increased over the 24 year warming period. Our study offers a unique example of how warming can affect fish populations over multiple generations, resulting in gradual changes in body growth, varying as organisms develop. Although increased juvenile growth rates are in line with predictions of the temperature–size rule, the fact that a larger body size at age was maintained over life history contrasts to that same rule. Because the artificially heated area is a contemporary system mimicking a warmer sea, our findings can aid predictions of fish responses to further warming, taking into account that growth responses may vary both over an individual's life history and over time. [ABSTRACT FROM AUTHOR]

The Baltic Sea is highly impacted by global warming and other anthropogenic changes and is one of the fastest‐warming marginal seas in the world. To detect trends in water temperature and to attribute them to atmospheric parameters, the results of two different ocean circulation models driven by reconstructed atmospheric forcing fields for the period 1850–2008 were analyzed. The model simulations were analyzed at temporal and spatial scales from seasonal to centennial and from intrabasin to basin, respectively. The strongest 150‐year trends were found in the annual mean bottom temperature of the Bornholm Deep (0.15 K/decade) and in summer mean sea surface temperature (SST) in Bothnian Bay (0.09–0.12 K/decade). A comparison of the time periods 1856–2005 and 1978–2007 revealed that the SST trends strengthened tenfold. An attribution analysis showed that most of the SST variability could be explained by the surface air temperature (i.e., sensible heat flux) and the latent heat flux. Wind parallel to the coast and cloudiness additionally explained SST variability in the coastal zone affected by the variations in upwelling and in offshore areas affected by the variations in solar radiation, respectively. In contrast, the high variability in stratification caused by freshwater and saltwater inflows does not impact the long‐term variability in the SST averaged over the Baltic Sea. The strongest SST trends since the 1980s can be explained by the superposition of global warming and a shift from the cold to the warm phase of the Atlantic Multidecadal Oscillation. Key Points: The Baltic Sea SST trend is mainly driven by SAT, which has been reinforced by the positive phase of the AMO since 1980Wind parallel to the coast and cloudiness are important for the SST in upwelling and offshore areas, respectivelyChanging stratification due to inflows from the North Sea do not affect long‐term variability in the SST [ABSTRACT FROM AUTHOR]

To test whether the established B/Cl ratio (0.2414 mg·kg–1·‰–1) derived for the open ocean is applicable to coastal systems globally, we measured the B concentration and salinity of seawater samples (n = 245) collected from the coastal waters of the Yellow, East China, and East Seas. We also measured the B concentration of freshwater samples (n = 10) from six rivers discharging into these seas and analyzed along with the B concentrations of other rivers globally, obtained from literatures. Our results show that the supply of riverine B (2–6 μmol B/kg) did not discernably alter the B/Cl ratio in most estuarine systems. The impact of this riverine B input on the interconversion between total alkalinity ([HCO3–] + 2[CO32–] + [B (OH)4–] + others) and carbonate alkalinity ([HCO3–] + 2[CO32–]) is less than a few micromoles per kilogram for most estuarine and coastal systems, although exceptions in the Baltic Sea do occur. Plain Language Summary: Accurate data on boron (B) concentration (mg/kg) are critical for seawater thermodynamic calculations, including the interconversion between total alkalinity ([HCO3–] + 2[CO32–] + [B (OH)4–] + others) and carbonate alkalinity ([HCO3–] + 2[CO32–]). These conversions are made using the dissociation constant of boric acid and the total B concentration, derived from chlorinity (Cl, in per mil (‰); calculated from salinity) and the ratio of B to Cl (derived from open ocean data). The established B/Cl ratio implicitly assumes a zero B concentration in river discharges entering coastal seas and thus does not reflect riverine B concentrations. The consistent ratio of B to Cl concentrations found in coastal waters of the Yellow, and East China, and East Seas provides compelling evidence that the poorly studied processes (e.g., ocean biology, atmospheric deposition, and river discharges) have nondetectable impacts on the ocean B concentration and thereby do not change the B/Cl ratio established for the open ocean environments. The low B concentration (mean of 3 μmol/kg) measured in all major rivers flowing into the East China, Yellow, and East Seas, along with the low degree of dilution in these areas, supports use of the B/Cl ratio of 0.2414 reported for the open ocean environments. Key Points: Variation in the B concentration from that based on the established B/Cl ratio is common to most coastal areas under riverine influenceThe impact of B concentration variation on the conversion of total alkalinity to carbonate alkalinity (or vice versa) is insignificantThe supply of riverine B was not large enough to alter the B/Cl ratio in the coastal systems of the Yellow, East China, and East Seas [ABSTRACT FROM AUTHOR]