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  • 1
    Online Resource
    Online Resource
    Data_Sheet_1.PDF
    Frontiers Media SA ; 2021
    In:  Frontiers in Marine Science Vol. 8 ( 2021-12-24)
    Details
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 8 ( 2021-12-24)
    Abstract: Dissolved oxygen in the sea is essential for marine fauna and biogeochemical processes. Decline in the sea water oxygen concentration is considered to be an effect of eutrophication, also exacerbated by climate change. The Baltic Sea is one of the most eutrophic seas in the world and is located in northern Europe. It is a vulnerable, brackish, semi-enclosed sea, suffering from high pressures from human activity. This leads to increased hypoxic and anoxic areas, which can be used as a measure of the environmental state. In the present study the extent of anoxic (O 2 & lt; 0 ml l –1 ) and hypoxic (O 2 & lt; 2 ml l –1 ) areas were estimated for the autumns in 1960–2019 using vertical profiles of observed oxygen concentrations in the Baltic proper and four sub-areas of the Baltic proper: the Bornholm Basin, the western, northern and eastern Gotland basins. From vertical profiles of observed salinity, the annual average of the halocline depths in the four sub-basins were estimated. The results imply regime shifts toward increased anoxic area extents in the Gotland basins around the turn of the 20th century. In autumn 2018, the extent of anoxic bottom areas in the Baltic Sea was record high since the start of the data series. During the later part of the studied period the depths of the halocline coincide with the depth of the hypoxia in the Gotland basins. This implies that in these basins a worst-case scenario for the extent of hypoxic areas seems to be reached.
    Type of Medium: Online Resource
    ISSN: 2296-7745
    URL: Article
    URL: Article
    DOI: 10.3389/fmars.2021.799936
    DOI: 10.3389/fmars.2021.799936.s001
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2021
    detail.hit.zdb_id: 2757748-X
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  • 2
    Online Resource
    Online Resource
    DataSheet_1.docx
    Frontiers Media SA ; 2022
    In:  Frontiers in Marine Science Vol. 9 ( 2022-5-23)
    Details
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 9 ( 2022-5-23)
    Abstract: Microplastic (MP) pollution is present in all aquatic environments and is gaining critical concern. We have conducted sea surface MP monitoring with a Manta trawl at 16 sampling stations in the eastern Baltic Sea in 2016–2020. The concentrations varied from 0.01 to 2.45 counts/m 3 (0.002–0.43 counts/m 2 ), and the mean was 0.49 counts/m 3 (0.08 counts/m 2 ). The fibers and fragments had, on average, an approximately equal share in the samples. Correlation between the concentration of fibers and fragments was higher near the land and weaker further offshore. The following spatial patterns were revealed: higher mean values were detected in the Baltic Proper (0.65 counts/m 3 ) (0.11 counts/m 2 ) and the Gulf of Finland (0.46–0.65) (0.08–0.11) and lower values were detected in the Gulf of Riga (0.33) (0.06) and Väinameri Archipelago Sea (0.11) (0.02). The difference between the latter three sub-basins and the meridional gradient in the Gulf of Riga can likely be explained by the degree of human pressure in the catchment areas. The MP concentration was higher in autumn than in summer in all regions and stations, probably due to the seasonality of the biofouling and consequent sinking rate of particles. A weak negative correlation between the wind speed and the MP concentration was detected only in the central Gulf of Finland, and positive correlation in the shallow area near river mouth. We observed a 60-fold difference in MP concentrations during coastal downwelling/upwelling. Divergence/convergence driven by the (sub)mesoscale processes should be one of the subjects in future studies to enhance the knowledge on the MP pathways in the Baltic Sea.
    Type of Medium: Online Resource
    ISSN: 2296-7745
    URL: Article
    URL: Article
    DOI: 10.3389/fmars.2022.875984
    DOI: 10.3389/fmars.2022.875984.s001
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2757748-X
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  • 3
    Online Resource
    Online Resource
    Wind-Controlled Transport of Saltwater in the Southeastern Baltic Sea: A Model Study
    Frontiers Media SA ; 2022
    In:  Frontiers in Marine Science Vol. 9 ( 2022-3-16)
    Details
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 9 ( 2022-3-16)
    Abstract: We hypothesized that the saltwater transport in a system of the southeastern Baltic basins including the Gdańsk and Gotland deeps connected by the Hoburg Channel, is greatly controlled by wind forcing, which has a clear physical explanation. Namely, the westerly winds develop the Ekman transport in the upper layer to the south from the Gotland Deep to the Gdańsk Deep which causes a compensatory saltwater countercurrent in the deep layer to the north from the Gdańsk Deep toward the Gotland Deep, and, vice versa, the easterly winds develop the Ekman transport to the north from the Gdańsk Deep toward the Gotland Deep causing a compensatory saltwater countercurrent in the deep layer to the south from the Gotland Deep to the Gdańsk Deep. To confirm the hypothesis, results of numerical modeling of the Baltic Sea circulation for a 10-year period (2010–2019) are applied. The daily saltwater transport to the northeast through a cross-section of the Hoburg Channel is found to be highly correlated with the wind stress component toward southeast (the correlation coefficient is 0.812) which can be considered as a straightforward confirmation of the hypothesis indicating the strong wind-driven circulation also in the deep layers of the Baltic Sea. Estimates of the daily saltwater transport through the above-mentioned and several other cross-sections of the southeastern Baltic Sea basins confirm a rule stating that the maximum correlation takes place between the saltwater transport and a wind stress component directed perpendicularly to the right relative to the direction of saltwater transport.
    Type of Medium: Online Resource
    ISSN: 2296-7745
    URL: Article
    DOI: 10.3389/fmars.2022.835656
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2757748-X
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  • 4
    Online Resource
    Online Resource
    Image_1.pdf
    Frontiers Media SA ; 2024
    In:  Frontiers in Marine Science Vol. 11 ( 2024-4-11)
    Details
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 11 ( 2024-4-11)
    Abstract: This study explores the impact of sub-mesoscale structures and vertical advection on the connectivity properties of the Baltic Sea using a Lagrangian approach. High-resolution flow fields from the General Estuarine Transport Model (GETM) were employed to compute Lagrangian trajectories, focusing on the influence of fine-scale structures on connectivity estimates. Six river mouths in the Baltic Sea served as initial positions for numerical particles, and trajectories were generated using flow fields with varying horizontal resolutions: 3D trajectories with 250m resolution as well as 2D trajectories with 250m and 1km resolutions. Several Lagrangian indices, such as mean transit time, arrival depths, and probability density functions of transit times, were analyzed to unravel the complex circulation of the Baltic Sea and highlight the substantial impact of sub-mesoscale structures on numerical trajectories. Results indicate that in 2D simulations, particles exhibit faster movement on the eastern side of the Gotland Basin in high-resolution compared to coarse-resolution simulations. This difference is attributed to the stronger coastal current in high-resolution compared to coarse-resolution simulations. Additionally, the study investigates the influence of vertical advection on numerical particle motion within the Baltic Sea, considering the difference between 3D and 2D trajectories. Findings reveal that denser water in the eastern and south-eastern areas significantly affects particle dispersion in 3D simulations, resulting in increased transit times. Conversely, regions in the North-western part of the basin accelerate particle movement in 3D compared to the 2D simulations. Finally, we calculated the average residence time of numerical particles exiting the Baltic Sea through the Danish strait. Results show an average surface layer residence time of approximately 790 days over an eight-year integration period, highlighting the relatively slow water circulation in the semi-enclosed Baltic Sea basin. This prolonged residence time emphasizes the potential for the accumulation of pollutants. Overall, the study underscores the pivotal role of fine-scale structures in shaping the connectivity of the Baltic Sea, with implications for understanding and managing environmental challenges in this unique marine ecosystem.
    Type of Medium: Online Resource
    ISSN: 2296-7745
    URL: Article
    URL: Article
    DOI: 10.3389/fmars.2024.1340291
    DOI: 10.3389/fmars.2024.1340291.s001
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2024
    detail.hit.zdb_id: 2757748-X
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