EGU25-10537, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-10537
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Resistivity anomalies in buried subglacial landforms and Plio-Pleistocene sediments of the southeastern North Sea revealed by surface-towed time-domain CSEM measurements
Arne Lohrberg1, Amir Haroon2, Nils Moosdorf3,1, and Sebastian Krastel1
Arne Lohrberg et al.
  • 1Christian-Albrechts-Universität zu Kiel, Institute of Geosciences, Geophysics, Kiel, Germany (arne.lohrberg@ifg.uni-kiel.de)
  • 2University of Hawai‘i at Manoa, Honolulu, Hawaii, United States
  • 3Leibniz Centre for Tropical Marine Research, Bremen, Germany

The role of large subsurface landforms produced during glaciations of the Pleistocene is still poorly understood with respect to groundwater flow. In particular, so-called tunnel valleys formed beneath ice sheets, acted as drainage systems of glacial meltwater. Their dimensions (up to 5 km width, 400 m depth, 100s of km length) reflect the massive amount of meltwater that incised into and flushed the subsurface beneath ice sheets.

To understand the potential of tunnel valleys as preferential flow pathways of offshore freshened groundwater (OFG) in the southeastern North Sea, we sailed 320 km of marine time-domain controlled-source electromagnetic surveys on 10 profiles using the surface-towed SWAN system on R/V ALKOR. In particular, we aim to answer the following questions: (1) Does the distribution of electrical resistivities indicate the presence of freshened groundwater in the subsurface of the North Sea? and (2) Can we delineate different resistivity distributions inside tunnel valleys?

Here we show our data acquisition and processing workflow as well as the subsurface electrical resistivity distribution from 2D inversions of the TD-CSEM data both for minimal constraints and for structural constraints inferred from a dense net of high-resolution 2D seismic reflection data. We use additional information from core data in similar geological setting in the interpretation to integrate geophysical and geological data.

The subsurface electrical resistivities show good correlation with the structures prevalent in the 2D seismic reflection data, where correlation is strongest for the upper and lower parts of the tunnel valleys. Plio-Pleistocene sediments show a widespread region of significantly increased electrical resistivities, which are interpreted to represent remnant offshore freshened groundwater from the flushing of meltwater below ice sheets during the Pleistocene.

How to cite: Lohrberg, A., Haroon, A., Moosdorf, N., and Krastel, S.: Resistivity anomalies in buried subglacial landforms and Plio-Pleistocene sediments of the southeastern North Sea revealed by surface-towed time-domain CSEM measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10537, https://doi.org/10.5194/egusphere-egu25-10537, 2025.