Record-low water levels in the Baltic Sea – causes and effects of the phenomenon

The Polish sea is experiencing an extraordinary anomaly: the average water level in the Baltic Sea is 67 cm below the long-term norm. It is also the lowest level recorded in the history of measurements, that is, since 1886. Scientists from Poland, Sweden and Germany are closely analyzing this unusual phenomenon, examining its potential consequences.

Why is the Baltic Sea lacking water?

Seas are governed by different rules than rivers and lakes, whose levels depend on precipitation frequency and air temperature. As experts from the Institute of Oceanology of the Polish Academy of Sciences explain, the Baltic has very limited natural outflow and inflow from land, and its level depends primarily on the strength and direction of the wind.

Strong easterly winds prevailing since January have pushed enormous masses of water through the Danish Straits into the North Sea. Until atmospheric conditions change, the water from the Baltic will remain trapped in the neighboring basin.

According to scientists from the Leibniz Institute for Baltic Sea Research Warnemünde (IOW), the Baltic Sea is currently missing 275 km3 of water. Over the past 140 years, the water level in our sea has fallen by more than 60 cm relative to the long-term average only five times. This year’s measurements recorded at the Landsort-Norra tide gauge off the coast of Sweden constitute an absolute historical minimum.

Less water means more ice

Such a dramatic loss of water in the Baltic has direct consequences for maritime navigation. In many ports, a drop in sea level of more than 0.5 m significantly hinders or even prevents safe mooring and maneuvering along the quay.

Currently, the situation is further complicated by severe frost – shallower water freezes more easily, which promotes ice formation in bays. As reported last week by Portal Morski, many operators are canceling ferry crossings to avoid dangerous situations. Last Friday, the ferry Epsilon became stuck in ice 25 km from Świnoujście and only resumed its journey after the intervention of a large German ferry that managed to break through the ice cover.

Ice-covered coasts and bays can also prove disastrous for curious thrill-seekers. As we wrote a week ago in Wodne Sprawy, walking on ice is dangerous and irresponsible – at sea, the threat is exceptionally high.

Ice near maritime infrastructure is particularly dangerous. Thickness and load-bearing capacity vary greatly – even with differences of just a few centimeters, cracks, gaps and weak spots may occur, warn scientists from the Institute of Oceanology of the Polish Academy of Sciences.

Hope for winter regeneration of the Baltic Sea

The lowering of the Baltic Sea’s water level is also a tremendous ecological opportunity. As soon as the wind direction changes, oceanographers expect a massive inflow of cold and saline water from the North Sea. Why is this important?

As Volker Mohrholz from IOW explains, cold water absorbs much more oxygen than warm water, creating a unique opportunity to oxygenate the deep waters of the Baltic. This will be crucial for marine ecosystems suffering from oxygen deficiency.

A second potential benefit results from the cooling effect of the anticipated inflow. For two decades, elevated temperatures have been observed in the deep waters of the central basins of the Baltic Sea, which favor increased microbiological activity and accelerate the decomposition of organic matter. As a result, oxygen consumption rises, threatening many species of marine organisms and increasing the risk of nutrient loading in the Baltic Sea. Lowering the water temperature may halt these negative processes, or at least slow them down.

The scale of the potentially unprecedented inflow of saline water from the North Sea into the Baltic will be studied by the IOW research vessel Elisabeth Mann Borgese, which is setting out on an eight-week voyage.