The hypothesis of the bottom of the permafrost in Spitsbergen and its overall "shape" - a case study from Hornsund

The permafrost-covered areas in polar regions face rapid changes in the current climate. While the active layer and permafrost zone near the surface are well-studied, the precise boundaries of the bottom permafrost remain unclear. Consequently, there is insufficient accuracy in understanding the overall shape of permafrost between the upper and lower boundaries. The evolution of deep cryotic structures, influenced by subsurface factors, is also relatively unknown.

In this study, based on the results of seismic reflection imaging we propose a hypothesis regarding the permafrost shape in the coastal area of Svalbard, Southern Spitsbergen. Additional Ground penetrating radar survey using a low-frequency antenna, as well as results of previous researches based on multiple geophysical methods, allowed for correlation of the obtained seismic results with surface observations. The entire methods were complemented by synthetic modeling, in order to better understand the obtained data. The work emphasizes the importance of recognizing not only the upper active layer but also the bottom permafrost boundary and its transition zone due to the underestimated potential role in observing climatic changes. The estimated bottom permafrost border ranges from 70 m below the surface near the shore to 180 m deep further inland, with a continuous frozen matrix layer identified between 40 m and 100 m depth. We also present a hypothesis about the possible presence of subsea permafrost in the Hornsund.

Factors such as seawater intrusions, isostatic uplift of deglaciated areas, and surface-related processes influencing permafrost evolution may lead to extensive changes in the hydrology and geology of polar regions in the future. Therefore, global attention and scientific efforts are essential for monitoring, geophysical imaging, and understanding the characteristics and evolution of deep permafrost structures. The research presented here forms the basis for a full understanding of permafrost evolution and degradation, and should be repeated across the globe to monitor climate change on a worldwide scale.