The water observed in the Bornholm Deep from 80 meters depth down to the area's maximum depth of 104 meters is the same water that flowed into the Baltic Sea between February 8 and March 5, according to multiple reports. This inflow increased the Baltic Sea level by half a meter, equivalent to around 100 cubic kilometers of water. From the turn of the year until a week into February, the water level in the Baltic Sea continuously dropped due to easterly winds pushing water out through the Öresund and the Belts, multiple reports indicate.
The high-pressure blockage then eased, currents turned southward, and began refilling the Baltic Sea with cold, salty, oxygen-rich water originating from the Kattegat, Skagerrak, and North Sea. The properties of the different waters have evened out slightly, with the quality of the inflow deteriorating as salt and oxygen content decreased, according to multiple reports. The salinity has decreased from 28 per mille at the inflow through the Öresund two months ago to the current 17 per mille when it reached the Bornholm Deep.
The oxygen content has not decreased as much, from 7 milliliters of oxygen per liter of water when it flowed through the Öresund to now 6 milliliters per liter in the Bornholm Deep. Compared to the ice extent at the same time last year, the difference is large, as then the ice extent was 67,000 square kilometers, multiple reports indicate. The weather situation this year compared to last year has been quite different, with last year being milder and windier with regular bouts of southwesterly winds that compressed the ice in the north against the Finnish side.
This year, since the high pressure moved in over Scandinavia, it has been cold and relatively little wind, which has allowed the ice to grow more freely. Based on the season's largest recorded ice extent so far, the season could be classified as a normal ice winter, meaning the maximum ice extent has been between 115,000–230,000 square kilometers. It remains unknown whether the water inflow will reach the Gotland Deep or remain in the Bornholm Deep, and the long-term ecological impact of the decreased salinity and oxygen levels is not yet clear.
According to Vetenskapsradion, the unusually low water levels in the Baltic Sea could open up for a larger inflow of cold and oxygen-rich water from the North Sea now that a low pressure has moved in, though the specific timing and magnitude of this potential inflow are uncertain.