Magnetic imaging of the Kurungnakh Island ice complex upper layer structure, Lena Delta, Russia

Ground-based detailed magnetic surveys have so far been minimally used in permafrost research but they have a great potential to explore near-surface structures and to reveal their hidden features. This study presents the results of a two-elevation magnetic survey on a Pleistocene ice complex covered by Holocene deposits and penetrated by ice wedges. A polygonal pattern, which is not distinctly visible on the surface, is successfully identified in the anomalous magnetic field. Obtained data allow to confidently allocate polygon distribution and to discriminate ice wedges of different thicknesses. Typical values of total magnetic field anomalies related to ice wedges and frozen sediments in between are about several nanoteslas measured at the elevations of 0.4 and 1.15 m above the surface. Magnetic susceptibility of permafrost samples is of the order of 10-4. Observed data were modelled using a numerical magnetic model to estimate quantitatively geometrical and magnetic parameters of the ice complex structure. The best fitting model provides the following results: the upper part of Pleistocene and Holocene ice wedges shows a thickness of 8 and 3 m, respectively, and the upper boundary of the Pleistocene ice wedges where they contact with Holocene wedges rests at 1 m depth. The magnetic susceptibility of frozen sediments between ice wedges is about 0.14 × 10-3. An anomalous high vertical gradient within the study area has been observed. The presumable sources for this anomaly sources were considered. Our results suggest that detailed magnetometry could be efficient as it is a rapid and non-invasive reconnaissance permafrost research.