Coastal Upwelling Dynamics in the Baltic Sea

Coastal upwelling in the Baltic Sea arises predominantly under offshore wind conditions when surface waters are displaced and deeper, nutrient-rich waters ascend to the coastal zone. The interplay of wind stress, Earth’s rotation and basin geometry governs the onset, intensity and spatial extent of these events. During spring and summer, prevailing westerly or north-westerly winds drive an Ekman transport of surface layers away from the shore, triggering cold, nutrient-laden waters to rise. This process can induce sharp sea surface temperature (SST) gradients, form narrow filaments extending tens of kilometres offshore and alter local stratification. In winter, variations in atmospheric forcing and ice cover may lead to anomalous warm upwelling, further complicating seasonal patterns. Observation techniques range from satellite-derived SST and ocean colour imagery to in situ gliders and high-resolution hydrodynamic modelling. These methods collectively reveal that upwelling frequency and magnitude vary interannually in response to shifts in wind regimes, large-scale climate modes and regional bathymetry. Ecologically, coastal upwelling boosts primary productivity by supplying nutrients, yet rapid cooling and stratification changes can suppress phytoplankton blooms in near-shore waters and influence oxygen dynamics. A finer understanding of upwelling dynamics carries global significance: comparable processes occur in other semi-enclosed basins and productive eastern boundary systems. Practically, improved forecasting of upwelling events supports fisheries management, pollution dispersion modelling and coastal resilience planning in the face of changing wind patterns and sea-level rise.

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Coastal Upwelling Dynamics in the Baltic Sea publication trend

The graph below shows the total number of articles in coastal upwelling dynamics in the baltic sea across all publications each year (not limited to Nature Index journals).

Technical terms

Coastal upwelling: vertical movement of deeper water to the surface driven by wind stress.

Ekman transport: net movement of surface water at right angles to wind direction due to the Coriolis effect.

Sea surface temperature (SST): the temperature of the ocean’s uppermost layer, often measured by satellite sensors.

Stratification: the layering of water masses with different densities due to variations in temperature and salinity.

Upwelling index: a numerical measure of upwelling intensity derived from wind stress and Ekman transport calculations.

Hydrodynamic model: a computational tool that simulates fluid motion and properties in the marine environment.

Chlorophyll-a: a photosynthetic pigment in phytoplankton used as an indicator of biological productivity.

References

1. Remote Sensing of Coastal Upwelling in the South-Eastern Baltic Sea: Statistical Properties and Implications for the Coastal Environment. Remote Sensing (2018).
2. Summer upwelling at the Boknis Eck time-series station (1982 to 2012) – a combined glider and wind data analysis. Biogeosciences (2014).
3. Combining Satellite Imagery and Numerical Modelling to Study the Occurrence of Warm Upwellings in the Southern Baltic Sea in Winter. Remote Sensing (2019).