Sea temperature statistics

Sea water temperature vary according to seasons, but if compared to air temperature variations, the changes are relatively slow. In addition, surface water warms up and cools down quite fast, but deeper in the sea, the temperature may differ a lot from the surface temperature. That´s why the measuring depth has a great impact on the result. In addition sea currents move warmer and cooler sea masses causing local differences in temperatures.

For example, on a sunny summer day the sea surface layer warms up quickly, but underneath there is chiller water. If the water temperature measurement is then made from the surface water, the value may be several degrees higher than measuring with a temperature buoy, where the sensor is some tenths of centimetres below the surface. Also, the water in a sheltered bay may warm up faster than in the open sea.

Sea surface temperatures 30-year statistics

The sea surface temperature statistics were calculated for two stations on the graphs below, Seili in the Archipelago Sea and Harmaja in the Gulf of Finland. The measurements have been made manually by an observer and by an automatic measuring instrument. The statistics are calculated from the observations from the period 1991-2020.