Maps showing temperature anomalies in the Baltic Sea glow angry red. But the ongoing heat wave does not cover the entire sea, but it is the northern parts of the Gulf of Bothnia that have been suffering from temperatures far above normal since mid-July.
Scientists in Umeå believe it is the longest sustained marine heat wave with the highest temperatures ever measured in the area. Near Luleå and in some bays along the coast further south, surface water is up to 3-4 degrees warmer than the average temperature during the same period 1985-2012.
– It has lasted for several days in some places and in others for several weeks, says Nicholas Kamenos, professor at the Department of Ecology, Environment and Geosciences at Umeå University and director of the Umeå Marine Research Center.
– We believe that the heat wave is now coming to an end. Then we can start to see what effects this has had, if the ecosystems have changed and, if so, if they can recover.
Bacteria thrive
It is normal for sea temperatures to go up and down due to natural variations. But this summer’s heat wave in the northern Baltic worries scientists, as persistent heat does
harder for ecosystems and organisms to recover.
– They can cope with shorter periods of heat, but if it persists, it creates new conditions that the species in the northern Baltic Sea are not adapted to, says Kamenos.
– It could be that parts of the ecosystems do not function as they should or are taken over by other species that are more used to living in warmer water. The heat can also make certain bacteria more active, which can upset the bacterial balance in the Baltic Sea.
Sea carbon sink
Since the 1990s, the temperature in the entire Baltic Sea has risen on average by around 1-1.5 degrees, especially in the surface water.
One concern when the water gets warmer is that it may impair the ocean’s ability to absorb carbon dioxide from the atmosphere, according to Kamenos.
– That the oceans absorb carbon dioxide reduces the pace of climate change, he says.
– It is largely thanks to the ocean’s ecosystem. If we start to change its structure, it may happen that the ocean is no longer as good at absorbing carbon dioxide as before. And then it risks increasing the speed of climate change instead.