Abstract. The Utö Atmospheric and Marine Research Station introduced in
this paper is located on Utö Island
(59∘46.84′ N, 21∘22.13′ E) at the outer edge of the Archipelago
Sea, by the Baltic Sea towards the Baltic Proper. Meteorological observations at
the island started in 1881 and vertical profiling of seawater temperature
and salinity in 1900. Since 1980, the number of observations at Utö has
rapidly increased, with a large number of new meteorological, air quality,
aerosol, optical and greenhouse gas parameters, and recently, a
variety of marine observations. In this study, we analyze long-term changes
of atmospheric temperature, cloudiness, sea salinity, temperature and ice
cover. Our main dataset consists of 248 367 atmospheric temperature
observations, 1632 quality-assured vertical seawater temperature and salinity
profiles and 8565 ice maps, partly digitized for this project. We also use
North Atlantic Oscillation (NAO), major Baltic inflow (MBI) and Baltic Sea
river runoff data from the literature as reference variables to our data. Our
analysis is based on a statistical method utilizing a dynamic linear model. The
results show an increase in the atmospheric temperature at Utö, but the
increase is significantly smaller than on land areas and has taken place only
since the early 1980s, with a rate of
0.4 ∘C decade−1 during the last 35 years. We also see an increase in
seawater temperatures, especially on the surface, with an increase of
0.3 ∘C decade−1 for the last 100 years. In deeper water
layers, the increase is smaller and influenced by vertical mixing, which is modulated
by inflow of saline water from the North Sea and freshwater inflow from
rivers and by wind-driven processes influenced by the local bathymetry. The date
when air temperature in the spring exceeds +5 ∘C became 5 days
earlier from the period 1951–1980 to the period 1981–2010 and the date when sea
surface water temperature exceeds +4 ∘C changed to 9 days earlier.
Sea ice cover duration at Utö shows a decrease of approximately 50 %
during the last 35 years. Based on the combined results, it is possible that
the climate at Utö has changed into a new phase, in which the sea ice
no longer reduces the local temperature increase caused by the global
warming.
Holocene saline water inflow changes into the Baltic Sea, ecosystem responses and future scenarios