Traces of industrialization in a Baltic Sea sediment core with particular emphasis on marine traffic in Bornholmsgattet

Sammanfattning

Multiple stressors affect the Baltic Sea, such as eutrophication, deoxygenated water and pollution. Almost all stres- sors are heightened or caused by anthropogenic impact. The stressors effect has increased since the beginning of the industrialisation and increased many of the stressors. The area of interest for this thesis is Bornholmsgattet, an area located between Sweden and the Island of Bornholm. The particular interest this area has is that one of the largest sea lanes in the Baltic Sea passes through Bornholmsgattet. This entails that the area should show traces of marine traffic or other anthropogenic indications. The aim for this thesis is therefore to see if it is possible to use marine sediment and marine traffic data in order to trace the industrialisation. The methods include: 1) sediment analysis specifically looking at total carbon, total organic carbon, nitrogen and black carbon, 2) compiling marine traffic data dating back to the 1870 until today. The marine data consists of arriving and departing domestic and internat- ional ships in four harbors in Skåne: Helsingborg, Malmö, Ystad and Simrishamn. 3) attempt to trace historical events and tie them to sedimentary variations in the marine data and black carbon. 4) Using hydrographic data col- lected by SMHI from 1957 to 2024 to provide an overview on some of the stressors water related such as tempera- ture and oxygen. Using a sedimentary accumulation rate of 1.4 mm/year made it possible to estimate the age of the bottom of the core to 1760. This made it possible later to correlate sediment depth with years and opened the possibility to corre- late historical events such as the first and second world war in the marine data as well as the opening of the Öresund bridge in the year 2000. It was noted that there was a general globalization beginning in the 1950 which resulted in a large increase in the number of ships and their net tonnage. We could discern that during the world wars when the marine traffic was low, so were the black carbon levels. Another observation that was made was the C/N ratios decreasing around 1970-1990 and abruptly changing into an increasing quota. Finally we could also see that in the past 67 years the bottom water temperature in Bornholmsgattet has increased and resulted in less oxygen being able to be dissolved, causing the already existing hypoxic and anoxic areas to worsen.