NWT RESEARCH DATABASE

Regions: Inuvialuit Settlement Region

Tags: physical sciences, geological mapping, climate change, permafrost thaw, permafrost mapping

Objective(s): To map the extent and depth to the top of ice-bearing permafrost (IBP) offshore of Tuktoyaktuk Island.

Project Description: This licence has been issued for the scientific research application No.5561. Through ERT and PS methods, the extent and depth will be mapped to the top of ice-bearing permafrost (IBP) offshore of Tuktoyaktuk Island. On land, ERT surveys will also reveal information on permafrost characteristics like ice content, but offshore, tools can only reliably map the thickness of the unfrozen body (talik) above the IBP. By performing repeat ERT and PS surveys at our 2018 and 2021 sites, we can investigate the capability of our tools to detect nearshore thaw-induced IBP depth changes from 2018 to 2023. Subsea permafrost thaw results in subsidence, which can affect wave dynamics and coastal erosion rates. This study may provide new insights for engineers about how the permafrost beneath Tuktoyaktuk Island can be stabilized in the coming decades. Electrical Resistivity Tomography (ERT) is a geophysical technique for imaging subsurface structures, such as permafrost, from electrical resistivity measurements made at the surface. We plan to deploy ERT both on land and in the coastal waters using a floating cable (~100 m long) attached to a small boat. The resistivity of the ground depends on sediment type, porewater salinity, temperature, moisture content, and especially its state (unfrozen or frozen). Therefore, ERT is capable of detecting unfrozen/frozen interfaces in the ground. The passive seismic (PS) technique measures natural vibrations in the Earth. This allows detection of interfaces with shear wave velocity contrasts. Similar to the resistivity of the ground, the shear wave velocity is higher for frozen sediment compared to unfrozen sediment. Compared to the ERT, the PS method is easier to deploy in the water because it consists of only one housing unit for the instrument. It can be deployed at specific locations by lowering the sensor to the seabed with a cable from a small boat. Provided there are shallow boreholes for calibration, PS may also yield better resolution of the IBP depth, which is important for repeat measurements over a five-year period. Perhaps most importantly, passive seismic does not disturb wildlife, because no signals are emitted. To complement our geophysical surveys, we will take active layer measurements with a permafrost probe on land. Offshore, we will deploy conductivity, temperature, and depth (CTD) sensors in the water to produce vertical profiles of seawater properties. We will also equip our boat with an echo sounder to measure water depth. Both the water depth and water resistivity are crucial for ERT data processing. Further, we will deploy a small Van Veen sampler to collect sediment samples from the seabed. These samples will be returned to Germany for grain size testing in the laboratory. The fieldwork for this study will be conducted from: July 01 - August 31, 2023