The micrometeorology of the Arctic coastal tundra ecosystem near Barrow, Alaska was observed during the summer of 1993, and the characteristics of the heat and water budgets in the active layer were examined.
Direct measurement results of the thawed layer depth at the IBP site indicated that the thawed layer deepened from 10 to 22cm between mid June and mid-August. The effect of the thawing on the soil water content of the thawed layer was analyzed using the water budget model provided. The evapotranspiration (
ET) was much larger than the precipitation during the summer of 1993, and the excess
ET was supplied by the thawed water from the frost soil. Therefore, the excess
ET makes dry the active layer.
The ratio of the latent heat of the thawing,
Qthaw to the soil surface heat flux,
G did not change remarkably until mid-August when it started refreezing and the value
Qthaw/
G ranged within 15-20%. The heat storage in the thawed layer was negligible and about 80% of the heat from the ground surface was transfered to the permafrost which had little porosity and large thermal conductivity. From model analyses the followings were obtained. The drying of the active layer caused by the excess
ET decreases the ice content of the frost soil, which causes the decrease in the heat transfer to the permafrost and the increase of
Qthaw/
G, which might accelerate the thawing.
Global warming accelerate evapotranspiration at the Arctic tundra which makes the soil dry at the deeper part as well as at the surface of the active layer, thus leads the descent of the permafrost table.
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