A simplified numerical model for ground temperature receptive to the global environmental changes to assess the erosion by thermodenudation in the Arctic coasts

Abstract:

Ground temperature measurements are available along the Baydaratskaya Bay in the Kara Sea from the year 2013. The bluffs at the end of the beach are consisting of continuous permafrost. About nine months of the year the bay remains under snow covers. The open sea season starts at the end of May, and the summer ends around October. The study area has two distinctive zones; a high marine terrace consists of 12m~15m bluff heights and a low marine terrace consist of 3m~6m bluff heights. Observations reveal both the thermoabrasion and thermodenudation erosion process are active on the sites.

Boreholes are constructed phase by phase during the yearly field measurements from the year 2013. The boreholes are equipped with thermal sensors (Geoprecision GmbH) to measure the temperature at every six to twelve hours intervals. The boreholes are 6m to 9m deep. Temperature sensors are placed 0.1m apart near the surface and 0.5m apart after 1.7m depth. The permafrost layer lies around 0.5m depth during the summer. The ground temperature shows a very high correlation with the surface temperature; Pearson ‘r’ value was found to be close to 1 during most of the season, anomalies in the ‘r’ values are observed during the beginning of the summer and winter seasons. The bluffs get exposure of on average 200 W/m² heat flux ( daily mean) from solar radiation in the summer, out of which around 35 W/m² travels downward in the shallow permafrost zones (around 2m to 5m deep).

In ground temperature model, we correlate the heat flux from shortwave solar radiation, cloud clearance, wind speed and ground temperature to estimate the position of the permafrost beneath the active layers (organic and transitional layer). An estimated 25 days phase lag per meter of depth was observed. The numerical model considers the water level, available solar radiation, heat conduction by soil, heat convection by air, surface temperature, wind speeds, seawater temperature, vegetation cover ( simplified categories) and physical characteristics of the soil particles to estimate the thawing rate and slope stability of the exposed bluffs to measure the retreat of the bluff crest.