Baltic Sea: Easterly winds cause historically low water levels - and an opportunity

The Baltic Sea is an inland sea with very little water exchange. Nutrients that enter the Baltic Sea from the coasts and via rivers therefore accumulate and ensure that oxygen is completely depleted in some deep areas. Life is then no longer possible there. Scientists therefore speak of so-called dead zones.

This makes it all the more important that fresh and oxygen-rich North Sea water can regularly flow in via the straits between Germany, Sweden and Denmark. However, this requires a special and very rare weather situation - and this is exactly what is happening at the moment.

Easterly wind pushes water out of the Baltic Sea

The reason for this is the easterly wind that has been blowing since the beginning of January, pushing large quantities of seawater westwards and out of the Baltic Sea via the Belts. How the Leibnitz Institute for Baltic Sea Research in Warnemünde (IOW) According to the IOW, measurements at the Landsort-Norra gauge in Sweden confirm the lowest water levels since records began in 1886, with a daily average of more than 67 centimetres below the long-term average water level measured on 5 February.

According to current calculations, the Baltic Sea is currently lacking around 275 cubic kilometres of water compared to the long-term average. In the 140-year series of measurements, similarly low water levels with deviations of more than 60 centimetres below sea level have only been measured in five other years. The last comparable event took place more than four decades ago in March 1980. As the IOW states in a press release, the current extreme value of is an exceptionally good starting point for a major inflow event.

Persistent westerly winds required

In addition to the current water levels, the researchers are currently also looking at the meteorological development expected in the coming days and weeks. For an above-average inflow of North Sea water into the Baltic Sea to occur, the current easterly wind situation must end and be replaced by persistent westerly winds, which would then push salt- and oxygen-rich North Sea water into the Baltic Sea. According to the IOW, this would be of great ecological importance, particularly for the deep water layers of its central basins, as oxygen deficiency often prevails there for years.

Rare opportunity

"The chances of a major inflow in the coming weeks are higher than they have been for a long time," explains Michael Naumann, one of the coordinators of the IOW long-term observation programme. "According to the time series of saltwater inflow events into the Baltic Sea calculated here at the IOW, the probability is currently 80 to 90 per cent."

The long-lasting easterly wind could therefore lead to a noticeable improvement in ecological conditions in the Baltic Sea.