"Zoltan"North Sea storm a stroke of luck for the Baltic Sea

Andreas Fritsch

 · 02.01.2024

"Zoltan": North Sea storm a stroke of luck for the Baltic SeaPhoto: dpa/ap
Walkers during storm surge on the banks of the Weser estuary in Bremerhaven as storm "Zoltan" passed through
Winter storm "Zoltan" brought two high storm surges to the North Sea coast - and at the same time became a blessing for the Baltic Sea, which urgently needs the water from the North Sea

It may sound strange to many, but if the Baltic Sea is to do well, it needs the water from the North Sea. More precisely, the very oxygen-rich, more saline deep water. As an inland sea, which is also often shallow, the Baltic Sea has been suffering from increasing oxygen depletion for centuries. This occurs because the excessively nutrient-rich water forms a lot of algae in summer, which then die off later in the year, sink to the bottom and begin to rot there. This results in a lack of oxygen. This has been a huge problem in the Baltic Sea for years and has led to square kilometre-sized "death zones" at the bottom where life is no longer possible. This is also dramatically decimating fish stocks, such as cod.

This is why the Baltic Sea is biologically dependent on a regular, strong influx of cold, much saltier North Sea water. Especially at depth. This mixes and displaces the oxygen-poor water at the bottom.

Largest saltwater intrusion since 2014

It is precisely this process that the Leibniz Institute before Christmas, as reported by the BSH: " The autonomous measuring station Darßer Schwelle operated by the BSH has been measuring a strong inflow of salty water in the entire water column since 20 December 2023. This is one of the strongest saltwater intrusions since 2014. "

Shortly after the storm, even the surface water off Skagen pushed strongly into the Baltic Sea.Photo: Nobletec Time ZeroShortly after the storm, even the surface water off Skagen pushed strongly into the Baltic Sea.

On top of this, long south-easterly winds prevailed before "Zoltan", which had previously pushed the water out of the Baltic Sea and significantly lowered the water level. The return current, fuelled by the hurricane, was all the stronger. This allowed oxygen-poor deeper basin areas such as the Gotland Basin to be aerated with oxygen. This at least temporarily prevented the formation of toxic hydrogen sulphide at the bottom.

Spread of low oxygen zones in the Baltic Sea over the decadesPhoto: HansenAndersson et. alSpread of low oxygen zones in the Baltic Sea over the decades

For decades, marine biologists had observed that these inflow events had become fewer and weaker and that the formation of algae in the Baltic Sea was becoming increasingly dramatic at the same time because too many nutrients were being introduced from agriculture and wastewater. We can only hope that the current strong influx will perhaps improve the situation somewhat.


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