Quasi-steady circulation regimes in the Baltic Sea

Liblik, Taavi; Väli, Germo; Salm, Kai; Laanemets, Jaan; Lilover, Madis‐Jaak; Lips, Urmas

doi:10.5194/os-2021-123

Cited by 4 publications

(4 citation statements)

References 46 publications

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“…On the one hand, a possible explanation could be that the northern BP is the accumulation zone, where the discharge and buoyant particles from different basins (the GOF, GOR, Bothnian region, and south-and eastern BP) are concentrated. Secondly, the mean cyclonic current structure of the BP (Placke et al, 2018;Liblik et al, 2022) recirculates/traps the surface water in the basin for a longer period. In addition, MPs exhibit different buoyancy characteristics based on their density, shape, size, and biofouling rate (Adamopoulou et al, 2021).…”

Section: Discussionmentioning

confidence: 99%

Spatiotemporal Variability of Microplastics in the Eastern Baltic Sea

et al. 2022

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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/m3 (0.002–0.43 counts/m2), and the mean was 0.49 counts/m3 (0.08 counts/m2). 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/m3) (0.11 counts/m2) 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.

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Section: Discussionmentioning

confidence: 99%

Spatiotemporal Variability of Microplastics in the Eastern Baltic Sea

et al. 2022

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“…Data availability. The data used can be found at Zenodo: https://doi.org/10.5281/zenodo.6616795 (Liblik et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

Quasi-steady circulation regimes in the Baltic Sea

et al. 2022

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Abstract. Circulation plays an essential role in the creation of physical and biogeochemical fluxes in the Baltic Sea. The main aim of the work was to study the quasi-steady circulation patterns under prevailing forcing conditions. A total of 6 months of continuous vertical profiling and fixed-point measurements of currents, two month-long underwater glider surveys, and numerical modeling were applied in the central Baltic Sea. The vertical structure of currents was strongly linked to the location of the two pycnoclines: the seasonal thermocline and the halocline. The vertical movements of pycnoclines and velocity shear maxima were synchronous. The quasi-steady circulation patterns were in geostrophic balance and highly persistent. The persistent patterns included circulation features such as upwelling, downwelling, and boundary currents, as well as a sub-halocline gravity current. The patterns had a prevailing zonal scale of 5–60 km as well as considerably higher magnitude and different direction than the long-term mean circulation pattern. A northward (southward) geostrophic boundary current in the upper layer was observed along the eastern coast of the central Baltic in the case of southwesterly (northerly) wind. The geostrophic current at the boundary was often a consequence of wind-driven, across-shore advection. The sub-halocline quasi-permanent gravity current with a width of 10–30 km from the Gotland Deep to the north over the narrow sill separating the Fårö Deep and Nothern Deep was detected in the simulation, and it was confirmed by an Argo float trajectory. According to the simulation, a strong flow, mostly to the north, with a zonal scale of 5 km occurred at the sill. This current is an important deeper limb of the overturning circulation of the Baltic Sea. The current was stronger with northerly winds and restricted by the southwesterly winds. The circulation regime had an annual cycle due to seasonality in the forcing. The boundary current was stronger and more frequent northward during the winter period. The sub-halocline current towards the north was strongest in March–May and weakest in November–December.

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“…For comparison with the high-resolution model version (HR2D-250m and HR3D-250m), a medium resolution setup (HR2D-1km) for the Baltic Sea based on GETM with horizontal grid spacing of 0.5 nautical miles (approximately 926 m) is used within the study. A detailed description of this configuration is given by Zhurbas et al (2018) and Liblik et al (2020Liblik et al ( , 2022. Model simulations and their setups are summarized in Table 1.…”

Section: Numerical Modelmentioning

confidence: 99%

Investigating the influence of sub-mesoscale current structures on Baltic Sea connectivity through a Lagrangian analysis

Hariri,

Meier,

Väli

2024

Front. Mar. Sci.

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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.

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Quasi-steady circulation regimes in the Baltic Sea

Cited by 4 publications

References 46 publications

Spatiotemporal Variability of Microplastics in the Eastern Baltic Sea

Spatiotemporal Variability of Microplastics in the Eastern Baltic Sea

Quasi-steady circulation regimes in the Baltic Sea

Investigating the influence of sub-mesoscale current structures on Baltic Sea connectivity through a Lagrangian analysis

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