A moderate heat wave has been taking effect along Finland’s entire coast since the beginning of September, the Finnish Meteorological Institute said on Friday.
The anomalous temperatures were first detected by measurement buoys in the Gulf of Finland off the south coast and more recently in the Bothnian Bay, to the west.
In particular, there have been exceptional temperature readings from a wave buoy on the Gulf of Finland and at Harmaja island near Helsinki.
This past week, both sites reported the highest September temperatures ever recorded in approximately 30 years of measurements. Average daytime temperatures have been more than five degrees higher Celsius than the average, and previous records have been shattered by 1–2 degrees.
"This is the second marine heat wave observed this year. The first was in late May and early June. In terms of Baltic Sea temperatures, this summer season has been exceptionally long, compared to the past 30 years," says Veera Haapaniemi, a doctoral researcher at the FMI.
New tool deepens understanding of changes in marine nature
The FMI is gaining new insight into marine heat waves through a new tool it has developed, which identifies and classifies marine heat waves according to their intensity.
Seawater temperature changes have many effects on biogeochemical processes. The most visible examples include algal blooms and the proliferation of moon jellyfish along the coast.
On a daily basis, the tool compares real-time observations with background data from 1991–2020. FMI scientists say that a heatwave is in progress when the temperature remains above the rarest 10 percent threshold that period over at least five consecutive days.
While the warm sea water may signal a dangerous disruption for plants and animals in the marine environment, there has also been an unusually long swimming season. Southern coastal waters are still around 18-20 degrees.
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