- 1Department of Earth and Environmental Sciences, Dalhousie University, Halifax, Nova Scotia, Canada (irena.schulten@dal.ca)
- 2Department of Chemical and Geological Sciences, University of Modena and Reggio Emilia, Modena, Italy
- 3GEOMAR Helmholtz Centre for Ocean Research Kiel, RD2/Marine Geosystems, RD4/Marine Geodynamic, Kiel, Germany
- 4Natural Resources Canada (NRCan), Geological Survey of Canada Atlantic, Dartmouth, Nova Scotia, Canada
- 5Department Hydrogeology, Helmholtz Centre for Environmental Research GmbH - UFZ, Leipzig, Germany
- 6Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, California, USA
- 7Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada
- 8Department of Geoscience, Aarhus University, Aarhus C, Denmark
- 9Fisheries and Marine Institute, Memorial University of Newfoundland, Newfoundland and Labrador, Canada
- 10Department of Civil and Resource Engineering and Centre for Water Resources Studies, Dalhousie University, Halifax, Nova Scotia, Canada
- 11Department of Earth Sciences, University of Delaware, Newark, Delaware, USA
- 12Department of Civil and Environmental Engineering, University of Delaware, Newark, Delaware, USA
Geochemical and oceanographic studies using in-situ measurements have long established the presence of groundwater flow to the seafloor, which likely originates in the deeper sub-bottom. This raises the question: What is the impact of such a flow on the sediment stratigraphy as imaged by high-resolution seismic data? In this study from the Gulf of St. Lawrence (Atlantic Canada), high-resolution seismic data indicate the presence of localized dome-shaped, semi-transparent features (50-200 m-wide, <15 m-long) that do not extend to the seafloor. In proximity to these structures, low-salinity pore water has been extracted from a 3-m-long gravity core. A pore water transport model constrained using geophysical and geochemical data indicates a potential freshwater source at 60-80 m depth, but also suggests freshwater advection from a depth of 30 m sub-bottom depth, which is where the seismic structures are visible. We, therefore, interpret the dome-shaped features as a consequence of sediment deformation caused by groundwater fluid flow. In this regard, the dome-shaped features resemble fluid plumes observed in seismic reflection profiles elsewhere, but here they are often of large dimensions (1 km-wide), extend through the sediment package to the seafloor and are often related to gas. Furthermore, similar features in sub-bottom profiles often appear to be neglected in descriptions and interpreted as artefacts. Given that the dome-shaped features are only present in specific parts of the basin where the advection is supposed to be strongest, we argue that similar features observed elsewhere are possibly not artifacts and should be considered as deformational features related to fluid flow and potentially even offshore freshened groundwater. Easy access to freshwater resources becomes increasingly challenging nowadays in many parts of the world, particularly in coastal regions. It is therefore important to have additional indicators that can help detecting the presence of offshore freshened groundwater and especially locations with active advection, which can then be sampled in more detail.
How to cite: Schulten, I., Maselli, V., Hensen, C., King, E., Schmidt, M., Müller, T. H., Micallef, A., Berndt, C., Brown, C. J., Cordoba-Ramirez, F., Elger, J., Hölz, S., Kotliarov, A., Kurylyk, B., Michael, H., Robert, K., Yu, S., and Nedimovic, M.: Can offshore groundwater flow within shelf sediments generate fluid deformation structures?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12205, https://doi.org/10.5194/egusphere-egu25-12205, 2025.
