Geographical persistence of surface-layer water properties in the Archipelago Sea, SW Finland

The Archipelago Sea in the Northern Baltic Sea has a complex water quality regime. The region consists of islands and underwater thresholds that separate interconnected sub-basins, where the waters from the adjacent sea areas and discharges from the mainland are mixed. Thus, the water properties in the region are exceptionally varying by season and location. We studied the seasonal developments of five surface-layer water variables – temperature, salinity, Secchi depth, chlorophyll and acidity – and the persistence of their geographical patterns in a network of 20 sampling stations in the eastern part of the Archipelago Sea during a period from May to October in 2007. Furthermore, the inter-annual persistence of the late summer observations of three of these variables were analysed within the same network. Although preconceptions about the general gradation patterns from the mainland towards the open sea were found realistic, we also identified geographically divergent seasonal developments and found out that the inter-annual persistence of the studied three variables were not geographically as strong as expected.