Seabed geoenvironments of the land uplift coast – a case from the river–sea transect in the Gulf of Bothnia

• Main Author: Sahiluoto, Meri
• Other Authors: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, University of Helsinki, Faculty of Science, Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten
• Format: Master Thesis
• Language: English
• Published: Helsingin yliopisto 2024
• Subjects: ei opintosuuntaa; no specialization; ingen studieinriktning; Geologian ja geofysiikan maisteriohjelma; Master's Programme in Geology and Geophysics; Magisterprogrammet i geologi och geofysik; Sea ice
• Online Access: http://hdl.handle.net/10138/585522

Only a small part of Finnish marine areas has been formally mapped geologically, leaving significant knowledge gaps, especially in the shallow waters. Mapping of coastal marine areas is essential for developing effective strategies for coastal zone management and for mitigating the impact of anthropogenic activities. Geological insights offer a foundation for the protection of valuable ecosystems and resources, and for safe navigation. Geological surveys also provide important information about the structure of the seabed. This thesis encompasses the entire process from acoustic-seismic data collection to sampling, data processing, interpretation, and creation of the final maps. In this study acoustic-seismic shipborne methods, such as swath sonar, sediment echo sounding, side-scan sonar, and reflection seismic sounding, were used to collect data of the characteristics and bathymetry of the seafloor. The study area is in coastal area near Lohtaja along the eastern coast of the Gulf of Bothnia. The surveys were conducted from shore up to 15-meter water depths. The goal is to interpret the seabed structure and explore erosion environments and identify the key factors affecting them. Sediment samples were collected to support the interpretations made from the seismic profiles and to analyse the Caesium-137 activity. The activity measurements were used to estimate sedimentation rates in the depositional area. The findings reveal variations among the study area. Erosional features suggest dynamic environmental conditions, likely influenced by wave action and sea ice. In contrast, more sheltered areas exhibit softer sediments, including thick mud layers indicative of active sediment accumulation. These soft sediments, coupled with shallow depths and sheltered conditions, emerge as potential habitats for dense vegetation. The study is part of SeaMoreEco (Seamless monitoring, restoration, and conservation in the northern Gulf of Bothnia) project. SeaMoreEco is an Interreg Aurora project co-funded by Lapin Liitto and ...