Extreme marine events in the western Baltic Sea: a data- and model-based approach

Marine ecosystems are increasingly affected by extreme events such as heat waves, oxygen depletion, and algal blooms. Potential consequences include fish kills due to oxygen depletion and beach closures due to algal blooms. These can cause enormous ecological, social and economic damage. With extreme marine events intensity thresholds, which induce physiological stress or even mortality on marine organisms, are more likely passed with potential consequences ranging from the species to community level, raising concerns over ecosystem stability and habitat preservation (Daru & Rock 2023, Antão et al., 2020).

The Baltic Sea, located in north-eastern Europe, is an ideal location for studying extreme marine events due to its susceptibility to climate change and anthropogenic activities such as excessive nutrient inputs. In order to understand highly dynamic extreme events, high-frequency observations over sufficient time spans are necessary. However, observations are often limited in terms of both space and time. To overcome these limitations we used both available daily resolved station data and high-resolution 3D outputs from the coupled hydrodynamic-biogeochemical model MOM-ERGOM. For the western Baltic Sea in particular, high-frequency measurements from 2011 to 2024 enabled a more detailed analysis of the similarities and differences between the areas, which will be presented at the conference. Despite localized differences in the identification of extreme marine events between the model and measurements, spatial analysis remains a powerful tool for understanding extreme events in coastal areas. The long time series also facilitates the evaluation of potential influences on the monitoring and assessment of water quality. Moreover, we investigated cascading and compounding extreme marine events to improve our understanding of the dynamics to which marine organisms are exposed when subjected to multiple stressors. This knowledge can help us design more realistic multi-stressor experiments and ultimately assess the impact of extreme marine events on organisms.