Goncalo Teles Vieira

Ground temperature regimes and geomorphological implications in a Mediterranean mountain (Serra da Estrela, Portugal)

Air and shallow ground temperatures from two monitoring sites at the Serra da Estrela (Portugal) are analysed. The Cantaro Gordo site is located at 1875 m ASL and the Fraga das Penas at 1640 m ASL. The climate of the study area is Mediterranean and very irregular, both on a yearly and monthly basis. This is particularly significant during winter, when differences in snow cover have direct influence on the ground thermal regimes and therefore on geocryological processes. To assess the significance of the ground thermal regimes for the geomorphological dynamics, bi-hourly records of temperature are studied at a daily basis. Eight types of daily regime were identified: isothermal unfrozen, non-isothermal unfrozen, surficial freeze-thaw, surficial freeze-thaw and subsurficial frost, surficial and subsurficial freeze-thaw, subsurficial frost, surficial and subsurficial frost and surficial frost but no daily rhythm. The occurrence of these regimes is analysed and their geomorphological significance is presented. Based on the altitudinal differences of the two monitoring sites, on the occurrence of the different regimes and on field observations, a conceptual model for the altitudinal and seasonal zoning of the daily thermal regimes of the ground is presented. This model was prepared for the Serra da Estrela, but it can be used in other Mediterranean or tropical areas if altitude and seasonal precipitation differences are taken in explanation. D 2002 Elsevier Science B.V. All rights reserved.

Interannual active layer variability at the Limnopolar Lake CALM site on Byers Peninsula, Livingston Island, Antarctica

Abstract In order to monitor the evolution of the active layer in the South Shetland Islands, in February 2009 we established a new Circumpolar Active Layer Monitoring (CALM) site in the Limnopolar Lake basin on Byers Peninsula, Livingston Island. We monitored air, surface and ground (two boreholes of 135 and 80 cm deep) temperatures and Active Layer Thickness (ALT) was measured by mechanical probing in early February 2009, 2010 and 2011. The mean ALT was 44 cm with a range of about 92 cm, but where permafrost existed it was deeper than 1.0 m, as could be inferred from the borehole temperatures. ALT at this site was very dependent on air temperature and snow cover thickness, the ALT spatial distribution presenting the same pattern as soil penetration resistance, and higher values ALT coinciding with sites where patterned ground, ponds, and a near surface ground water saturation were observed. Additionally, ground temperature data provided an excellent tool for understanding the relationship between the ALT measured during the thaw season and the thermal evolution of the ground throughout the year.

VARIAÇÕES DA FRENTE DA GELEIRA POLAR CLUB, PENÍNSULA POTTER (ILHA REI GEORGE, ANTÁRTICA MARÍTIMA) ENTRE 1986 E 2011

Environmental changes, especially in the cryosphere, can result in large global consequences. Studies of glaciers in the Polar Regions are strategic for analyzing climate change sensitive areas. This work analyzed the glaciers front change rates of the Polar Club and compared with inter-seasonal variability of air temperature at Potter Peninsula, King George Island, in order to understand direct impact of the climate change on the local ice-free areas dynamics. We used a series of ten Landsat satellite imagery scenes and atmospheric temperature data from 1986 to 2011. The results show an increasing trend of 0.04 oC per year, which resulted in an increment of 1.03 oC in average temperatures for the 26-year analyzed period. The front of the glacier over the past 26 years showed progressive withdrawal mapped, resulting in an increase of 1.63 km2 of ice-free area at Potter Peninsula. The influences of atmospheric temperature at the glaciers retreat demonstrate delay of about one year. Despite the evidence of increased average air temperatures in recent decades in the region, the series of atmospheric temperatures alone is not sufficient to explain the variation observed for the Polar Club glacier front. These phenomena may be associated with re-accommodation of the ice sheet stresses across King George, changes in rainfall rates and climate conditions.