Impact of shallow water bodies on the permafrost temperature and estimation of risk of thermokarst development at the Barrow Environmental Observatory area.

Abstract:

Extension of the thermokarst features such as lakes and ponds had been noticed in many regions of the Arctic affected by the modern climate warming. Thermokarst is a process of permafrost thawing under the water bodies with depths larger than maximal thickness of seasonal ice in the area, i.e. with permanent positive temperature at the bottom. This process is most probable in the areas where massive ice bodies (wedges, lenses, layers etc) or ice rich deposits exist close to ground surface and even insignificant increasing of thaw depth can lead to its melting and surface subsidence. Local depressions such as low-centered polygonal ponds or interpolygonal troughs can potentially become triggers of thermokarst development. Current research was aimed on determination of warming impact of small water bodies on the permafrost temperature and seasonal thawing and estimation of risk of thermokarst development at Barrow Environmental Observatory area.

Comparison of temperature measurements under shallow (10 – 40 cm deep) with relatively dry spots and active layer thickness survey show that warming impact of small water bodies (mean annual temperature at the permafrost table here is up to 2^oC higher then under “dry” geomorphological features) is not realized in increasing of the thawing depth. Active layer thickness does not exceed values of 45 cm under polygonal ponds and 35 cm under troughs that is less then thickness of protective layer above ice wedges in the area.

For estimation of risk of thermokarst development we used analytical equations developed by V.Kudryavtsev (1974). Results of calculations show that in this area crucial depth of water bodies required for mean annual temperature at the bottom of the pond became higher then freezing point consists of 0.95 cm.

Current research was supported by US DOE as a part of research project Next Generation of Ecosystem Experiment (NGEE).