Permafrost extent on the Alaskan Beaufort shelf from surface-towed controlled-source electromagnetic surveys

Image of porpoise device superimposed on permafrost map
TitlePermafrost extent on the Alaskan Beaufort shelf from surface-towed controlled-source electromagnetic surveys
Publication TypeJournal Article
Year of Publication2018
AuthorsSherman D., Constable S.C
JournalJournal of Geophysical Research-Solid Earth
Volume123
Pagination7253-7265
Date Published2018/09
Type of ArticleArticle
ISBN Number2169-9313
Accession NumberWOS:000447858800004
Keywordscontrolled-source electromagnetics; Geochemistry & Geophysics; hydrate; hydrate deposits; ice-bearing permafrost; inversion; sea; subsea permafrost; thickness; zones
Abstract

We have developed a surface-towed electric dipole-dipole system capable of operating in shallow water and deployable from small vessels. Our system uses electromagnetic energy from a modulated manmade source to interrogate the underlying resistivity structure of the seafloor. We used this system in the summers of 2014 and 2015 to map subsea ice-bearing permafrost on the Beaufort shelf along 200km of coastline, from Tigvariak Island to Harrison Bay. Permafrost is resistive and was found to be anisotropic, likely due to interbedded layers of frozen and unfrozen sediment. Maps of depth to permafrost and its thickness were produced from electrical resistivity inversions and results compared to borehole logs in the area. We observed elevated resistivity values offshore the Sagavanirktok River outflow, supporting the idea that fresh groundwater flow has a preserving effect on submerged permafrost. This system provides a cost effective method that could be used to further quantify permafrost extent, provide a baseline for measurements of future degradation, and provide observational constraints to aid in permafrost modeling studies.

DOI10.1029/2018jb015859
Impact: 

We have demonstrated that our surface‐towed CSEM system can produce maps of the extent of offshore permafrost, which are consistent with well logs. Our surveys were conducted for less than the cost of drilling one borehole, making the surface‐towed CSEM system a cost‐effective method for mapping IBPF in regions without well logs.

Further work could include returning to this location when the Beaufort Sea is ice‐free further offshore, which would allow towing across the edge of IBPF to capture the transition to unfrozen sediments. This will give us a baseline extent to monitor future degradation. Additional data collection very nearshore will be useful inputs to models of coastal erosion, where the state of nearshore subsea permafrost will help determine how quickly the coastline erodes.

Student Publication: 
Yes
Student: 
Research Topics: