| Description |
The environment of Antarctic ice-free areas (oasis) is characterized by extreme range of temperature, aridity and short summer season. Evaluation of thermal properties of soil and vegetation cover in the Antarctic oases is of crucial importance for calculation of energy balace and prediction of stability of these ecosystems under ongoing global climate change. The paper presented focuses on the role of vegetation cover in thermal regime of such ecosystems. In February 2002, microclimatological measurements were held on a stony terrace in close proximity to the Peruvian Antarctic station Machu Picchu (58deg 28.5 W, 62deg 05.5 S), Admiralty Bay, King George Island, South Shetlands. In order to characterize temperat ure differentiation between atmosphere, vegetation cover and soil, data loggers HFX06 and MiniCube VX (EMS, Czech Republic) equipped with temperature sensors were used. The sensors were placed at the height of (a) 2 m, (b) 10 cm, (c) 6 cm, and (d) 2 cm above ground level. The sensor (b) was located at the upper surface of a lichen clump, while the (c) and (d) sensors were located in the clump. Another sensor (e) was placed 2 cm into sandy soil. Heat flux from/to soil was measured using self-calibrating sensors HFP01SC (Hukseflux, the Netherlands). Within the period, days showing contrasting types of local austral summer climate were selected and denoted as (I) cloudy+wet, (II) cloudy+dry, (III) sunny+dry. For these days, temperature regimes within lichen clumps, soil, and heat fluxes from atmosphere to soil were evaluated and compared. No apparent temperature shift (compared to reference temperature measured 2 m above vegetation) was found in cloudy+wet day within lichen clump. Daily (9:00-18:00) mean temperature reached a constant value of 2.0 oC. In cloudy+dry day, however, daily mean temperature within a lichen clumps was significantly higher (4.7 - Usnea antarctica, 3.5 oC - Usnea aurantiaco-atra) than reference temperature (2.1 oC). The most significant increase in daily mean temperature was found in lichen clumps within sunny+dry day. It reached 15.9 oC (U. antarctica) and 10.9 oC (U. aurantiaco-atra), while reference temperature reached 7.2 oC. Daily mean temperature of upper soil layer differed from mean air temperature by +3.0 and +4.2 oC in cloudy+wet and cloudy+dry days, respectively. Much higher difference were found in sunny+dry day: +9.5 oC. These temperature differences were also reflected in heat exchange between soil and atmosphere in these days. Daily (9:00-18:00) means of heat flux to the soil were very low and independent on vegetation cover during cloudy+wet and cloudy+dry days (4-8 and 6-16 W m-2 d-1, resp.). It reached much higher values in sunny+dry day and was dependent on presence and character of vegetation cover: 91 W m-2 d-1 (bare soil), 75 and 65 W m-2 d-1 (two moss species forming a carpet).
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