Water exchange in the Baltic Sea: a historical view of research approaches from basin scales to submesoscale

At the beginning of the 20th century, Knudsen illustrated that the mean observed salinity of the Baltic Sea could be realistically estimated, assuming an inflow of saline Kattegat water equals the net freshwater supply, also called the Knudsen theorem. As given in the historical review, several stud...

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Main Authors: Jüri Elken, Anders Omstedt
Format: Article
Language:English
Published: Frontiers Media S.A. 2025-07-01
Series:Frontiers in Earth Science
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Online Access:https://www.frontiersin.org/articles/10.3389/feart.2025.1598983/full
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author Jüri Elken
Anders Omstedt
author_facet Jüri Elken
Anders Omstedt
author_sort Jüri Elken
collection DOAJ
description At the beginning of the 20th century, Knudsen illustrated that the mean observed salinity of the Baltic Sea could be realistically estimated, assuming an inflow of saline Kattegat water equals the net freshwater supply, also called the Knudsen theorem. As given in the historical review, several studies have followed the approach of well-mixed boxes, including time variations and a division between different sub-basins in the Baltic Sea. The box concept was later developed into mechanistic models by resolving the vertical structure in each sub-basin and adding processes related to vertical mixing, strait flow dynamics, and exchange with the atmosphere. However, as with the box concept, each sub-basin was assumed to be horizontally homogeneous. Early on, it was clear that the Baltic Sea circulation was highly unsteady, with fronts and eddies at different scales, illustrating a typical marine turbulent flow with energy cascade from basin scale to mesoscale, submesoscale, and microscale, where the energy dissipates. Many observational and modeling studies addressing the three-dimensional structure were developed over the last half-century. The approach of mechanistic models is useful for interpreting large-scale effects of meso- and submesoscale processes and for climate and long-term studies. The submesoscale approaches, including in situ observations, remote sensing, and models resolving the three-dimensional structure, may guide parametrizations of exchange between and within the different sub-basins. Recent submesoscale studies suggest localized eddy-rich regions: Arkona Basin, Gulf of Finland, Irbe Strait, Åland Sea connections, and several coastal areas.
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spelling doaj-art-009ca9e030ac41a38178cb772f8ccc3a2025-08-20T03:17:44ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632025-07-011310.3389/feart.2025.15989831598983Water exchange in the Baltic Sea: a historical view of research approaches from basin scales to submesoscaleJüri Elken0Anders Omstedt1Department of Marine Systems, Tallinn University of Technology, Tallinn, EstoniaDepartment of Marine Sciences, University of Gothenburg, Gothenburg, SwedenAt the beginning of the 20th century, Knudsen illustrated that the mean observed salinity of the Baltic Sea could be realistically estimated, assuming an inflow of saline Kattegat water equals the net freshwater supply, also called the Knudsen theorem. As given in the historical review, several studies have followed the approach of well-mixed boxes, including time variations and a division between different sub-basins in the Baltic Sea. The box concept was later developed into mechanistic models by resolving the vertical structure in each sub-basin and adding processes related to vertical mixing, strait flow dynamics, and exchange with the atmosphere. However, as with the box concept, each sub-basin was assumed to be horizontally homogeneous. Early on, it was clear that the Baltic Sea circulation was highly unsteady, with fronts and eddies at different scales, illustrating a typical marine turbulent flow with energy cascade from basin scale to mesoscale, submesoscale, and microscale, where the energy dissipates. Many observational and modeling studies addressing the three-dimensional structure were developed over the last half-century. The approach of mechanistic models is useful for interpreting large-scale effects of meso- and submesoscale processes and for climate and long-term studies. The submesoscale approaches, including in situ observations, remote sensing, and models resolving the three-dimensional structure, may guide parametrizations of exchange between and within the different sub-basins. Recent submesoscale studies suggest localized eddy-rich regions: Arkona Basin, Gulf of Finland, Irbe Strait, Åland Sea connections, and several coastal areas.https://www.frontiersin.org/articles/10.3389/feart.2025.1598983/fullBaltic Seawater budgetwater exchangemodelsfrontseddies
spellingShingle Jüri Elken
Anders Omstedt
Water exchange in the Baltic Sea: a historical view of research approaches from basin scales to submesoscale
Frontiers in Earth Science
Baltic Sea
water budget
water exchange
models
fronts
eddies
title Water exchange in the Baltic Sea: a historical view of research approaches from basin scales to submesoscale
title_full Water exchange in the Baltic Sea: a historical view of research approaches from basin scales to submesoscale
title_fullStr Water exchange in the Baltic Sea: a historical view of research approaches from basin scales to submesoscale
title_full_unstemmed Water exchange in the Baltic Sea: a historical view of research approaches from basin scales to submesoscale
title_short Water exchange in the Baltic Sea: a historical view of research approaches from basin scales to submesoscale
title_sort water exchange in the baltic sea a historical view of research approaches from basin scales to submesoscale
topic Baltic Sea
water budget
water exchange
models
fronts
eddies
url https://www.frontiersin.org/articles/10.3389/feart.2025.1598983/full
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