25 Jul 2023
 | 25 Jul 2023
Status: this preprint is open for discussion.

Transport dynamics in a complex coastal archipelago

Elina Miettunen, Laura Tuomi, Antti Westerlund, Hedi Kanarik, and Kai Myrberg

Abstract. The Archipelago Sea (in the Baltic Sea) is characterised by the complex geometry of thousands of islands and steep gradients of the bottom topography. Together with the much deeper Åland Sea, the Archipelago Sea acts as pathway to the water exchange between the neighbouring basins, Baltic proper and Bothnian Sea. We studied circulation and water transports in the Archipelago Sea using a new high-resolution NEMO configuration that covers the Åland Sea–Archipelago Sea area with horizontal resolution of around 500 m. The results show that currents in the area are steered by the geometry of the islands and straits and the bottom topography. Currents are strongest and strongly aligned in the narrow channels in the northern part of the area, the directions alternating between south and north. In more open areas, the currents are weaker with wider directional distribution. During our study period of 2013–2017, southward currents were more frequent in the surface layer. In the bottom layer in areas deeper than 25 m, northward currents dominated in the southern part of the Archipelago Sea, while in the northern part, southward and northward currents were more evenly represented. Due to the variation in current directions, both northward and southward transports occur. During our study period, the net transport in the upper 20 m layer was southward. Below 20 m depth, the net transport was southward at the northern edge and northward at the southern edge of the Archipelago Sea. There were seasonal and inter-annual variation in the transport volumes and directions in the upper layer. Southward transport was usually largest in spring and summer months and northward transport was largest in autumn and winter months. Our results demonstrate the complexity of the transport dynamics in the Archipelago Sea. No single transect can be chosen to represent water transport through the whole area. Further studies on the water exchange processes between the Baltic proper and the Bothnian Sea through the Archipelago Sea would benefit from using a two-way nested model setup for the area.

Elina Miettunen et al.

Status: open (until 11 Oct 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Elina Miettunen et al.

Data sets

ERA5 hourly data on single levels from 1979 to present H. Hersbach, B. Bell, P. Berrisford, G. Biavati, A. Horányi, J. Muñoz Sabater, J. Nicolas, C. Peubey, R. Radu, I. Rozum, D. Schepers, A. Simmons, C. Soci, D. Dee, and J.-N. Thépaut

Model code and software

nemo-archs A. Westerlund and E. Miettunen

NEMO ocean engine G. Madec and NEMO System Team

Elina Miettunen et al.


Total article views: 220 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
158 51 11 220 6 5
  • HTML: 158
  • PDF: 51
  • XML: 11
  • Total: 220
  • BibTeX: 6
  • EndNote: 5
Views and downloads (calculated since 25 Jul 2023)
Cumulative views and downloads (calculated since 25 Jul 2023)

Viewed (geographical distribution)

Total article views: 215 (including HTML, PDF, and XML) Thereof 215 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 03 Oct 2023
Short summary
We studied the circulation and transports in the Archipelago Sea with a high-resolution hydrodynamic model. Transport dynamics in this area are complex and no single transect can represent transport through the area. The net transport in the surface layer is southward and follows the alignment of the deeper channels. Our results demonstrate the nature of the Archipelago Sea as a buffer zone between the Baltic Proper and the Bothnian Sea.