Surface nuclear magnetic resonance observations of permafrost thaw below floating, bedfast, and transitional ice lakes

Abstract

Lakes in Arctic systems contribute to hydrologic storage, biogeochemical cycling, and permafrost thaw. Here, we have used surface nuclear magnetic resonance (NMR) measurements on lakes of Alaska’s North Slope to investigate the extent of permafrost thaw below lakes with different annual ice conditions. Our purpose is to understand if annual lake ice conditions are related to development of thawed permafrost below lakes. We investigated 10 lakes and two terrestrial permafrost control sites using surface NMR and direct measurement under spring conditions when lake ice is nearly at its thickest. We did not observe unfrozen water below our surveyed bedfast ice lakes, whereas unfrozen water (indicating permafrost thaw) was measured below floating ice lakes. We found that transitional ice lakes, ones that alternate between floating and bedfast ice conditions over multiyear timescales depending on winter ice growth and lake level conditions, have complex vertical unfrozen water content profiles attributed to sporadic periods of thaw. Based on that finding, we speculate that predicting the presence of talik based on remotely sensed lake ice conditions is unreliable. We applied a scheme to subtract the lake water signal from the NMR data and found the resulting inversions to be improved.

Seasonal Subsurface Thaw Dynamics of an Aufeis Feature Inferred From Geophysical Methods

“…Surface NMR has been used for almost three decades study groundwater (e.g., Trushkin et al, 1995) and cryosphere systems (e.g., Legchenko et al, 2014;Lehmann-Horn et al, 2011), as well as freeze-thaw dynamics in permafrost (Keating et al, 2018;Parsekian et al, 2013Parsekian et al, , 2019. While GPR measurements allow fast acquisition of high-resolution profile lines, surface NMR is typically implemented as a static measurement, with data averaging at one location to generate an individual sounding.…”

“…Given the successful performance of NMR during maximum freeze, it is likely that NMR would also be helpful for delineating the AP boundary during maximum thaw at the Kuparuk site. Indeed, surface (Keating et al, 2018;Parsekian et al, 2019) and borehole (Kass et al, 2017;Minsley et al, 2016) NMR has seen growing use for observing freeze-thaw dynamics in the Arctic.…”

Random Noise Suppression of Magnetic Resonance Sounding Data with Intensive Sampling Sparse Reconstruction and Kernel Regression Estimation

“…Ignoring the approximate calculation process influence, comparing the three sparse reconstruction methods according to Equations (8), (10), and (12), we can get: When f s H / f prop is small, the order of noise suppression effect from superior to secondary is trapezoidal sparse reconstruction, rectangular sparse reconstruction, and Simpson sparse reconstruction. In addition, when f s H / f prop is large, the noise elimination effect of rectangular sparse reconstruction is close to that of trapezoidal sparse reconstruction, and the noise elimination effect of Simpson sparse reconstruction is the worst.…”

“…The method proposed in this paper will be verified by simulation experiments and field experiments. In order to clearly compare the noise suppression in the experiments, the SNR for power, the mean squared error (MSE) and the SNIR for power (Equations (8), (10) and (12)) are utilized as indicators for evaluating the method effectiveness. SNR and MSE are defined as follows:…”

“…So far, the MRS method and instrument have been further researched and developed in many countries such as France, the United States, Germany, China and other countries [6][7][8]. The MRS method has been applied to hydrological investigation, observation of permafrost thaw, monitoring the cavity in glacier, water-induced disaster 2 of 32 detection, and infiltrating water surveys [9][10][11][12][13]. However, when the MRS instrument is exploited for groundwater exploration, the received signal is particularly weak and easily degraded in ambient electromagnetic interference [14].…”