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Geomorphological Observations of Permafrost and Ground-Ice Degradation on Deception and Livingston Islands, Maritime Antarctica Gonçalo Vieira Centre of Geographical Studies, University of Lisbon, Portugal Jerónimo López-Martínez Autonomous University of Madrid, Spain Enrique Serrano Department of Geography, University of Valladolid, Spain Miguel Ramos Department of Physics, University of Alcalá de Henares, Spain Stephan Gruber Department of Geography, University of Zurich, Switzerland Christian Hauck University of Karlsruhe, Germany Juan José Blanco Department of Physics, University of Alcalá de Henares, Spain Abstract The Antarctic Peninsula is experiencing one of the fastest increases in mean annual air temperatures (ca. 2.5ºC in the last 50 years) on Earth. If the observed warming trend continues as indicated by climate models, the region could suffer widespread permafrost degradation. This paper presents field observations of geomorphological features linked to permafrost and ground-ice degradation at two study areas: northwest Hurd Peninsula (Livingston Island) and Deception Island along the Antarctic Peninsula. These observations include thermokarst features, debris flows, activelayer detachment slides, and rockfalls. The processes observed may be linked not only to an increase in temperature, but also to increased rainfall, which can trigger debris flows and other processes. On Deception Island some thermokarst features may be related to anomalous geothermal heat flux from volcanic activity. Keywords: active layer; Antarctic; debris flow; permafrost; thermokarst. Introduction The Antarctic Peninsula is experiencing the strongest warming signal in the Southern Hemisphere, with mean annual air temperatures (MAAT) increasing ca. 3ºC since 1951 (Marshall et al. 2002, Meredith & King 2005, Turner et al. 2005). However, the region of strongest warming is limited in area, with the highest increases near Faraday/ Vernadsky Stations and lesser increases near the northern tip of the Peninsula and the Orcadas Islands (King & Comiso 2003, Turner et al. 2007). Global Climate Model (GCM) projections for 2001–2100 suggest that the strongest warming will extend into the Antarctic continent, with values even greater than those expected on the Antarctic Peninsula (Chapman & Walsh 2007). The strong atmospheric warming in the Antarctic Peninsula region has had a substantial effect on glaciers in the last few decades, especially on ice-shelves along the eastern coast (Scambos et al. 2003). The collapse of Larsen-B in 2002 is the most well-known example, but the retreat of mountain and outlet glaciers has been also reported. On Livingston Island (Hurd Peninsula) glaciers have been retreating and equilibrium-line elevations increasing (Ximenis et al. 1999, Molina et al. 2007). Permafrost is central to the carbon cycle and to the climate system, especially due to CH4 and CO2 release following permafrost degradation in organic-rich sediments (Anisimov et al. 1997, Osterkamp 2003). The active-layer thickness and dynamics are also important factors in polar ecology. Since most exchanges of energy, moisture, and gases between the atmospheric and terrestrial systems occur through the active layer, its thickening has important ramifications on geomorphic, hydrologic and biological processes (Nelson & Anisimov 1993). Furthermore, permafrost degradation can cause terrain instability and increase geomorphological hazards and damage to infrastructures. According to the International Panel on Climate Change (IPCC), regions underlain by permafrost have been reduced in extent, and a warming of the ground has been observed in many areas (Anisimov et al 2001, Lemke et al 2007). Permafrost is, therefore, recognized by the (World Climate Research Programme/World Meteorological Organization (WCRP/ WMO) as a key element of the Earth System in which research efforts should focus. However, compared with the Arctic, very little is known about the distribution, thickness, and properties of permafrost in Antarctica. The scarcity of data on Antarctic permafrost is reflected in the last IPCC 1839 1840 Ninth International Conference on Permafrost D E C E P TI O N ISLAN D 0 3 km Figure 1. Location of Deception and Livingston Islands in the Antarctic. report (Lemke et al. 2007) where it is not even mentioned. The main problem is the limited network of boreholes for monitoring permafrost temperatures and the paucity of active-layer monitoring sites. Turner et al. (2007) mention a reduction in permafrost extent in the Antarctic Peninsula region. In general, increasing air temperatures will have a direct influence on ground-temperature regimes and, therefore, on permafrost and ground ice. A major consequence of warming of the lower atmosphere is an increase in activelayer thickness, which induces permafrost degradation and amplifies the rates of geomorphic processes. As a consequence, thermokarst features are prone to occur in icerich and unconsolidated sediments, active-layer detachment slides and debris flows on sloping ground, and an increase in rockfall activity may occur in rocky terrain. The northerly location of the Antarctic Peninsula region and the oceanic setting result in a milder and moister climate than in the interior of the Antarctic continent. The northern Antarctic Peninsula is roughly located between the MAAT isotherms of -1 to -8ºC at sea level and, therefore, the northern tip of the Peninsula and especially the South Shetland islands are close to the environmental limits of permafrost occurrence (Bockheim 1995). If the observed warming trend continues, as indicated by climate models, the region might suffer widespread permafrost degradation. Monitoring of ground temperatures is essential for assessing the reaction of permafrost to global change, but in remote areas the drilling and maintenance of boreholes is problematic. Geomorphological surveying enables identification of the processes related to permafrost degradation and provides important information for assessing the influence of climate change on ground temperatures. However, other techniques are needed, such as geophysical surveying, monitoring of active-layer depths, micrometeorological measurements, and modelling to achieve a more complete overview of the response of permafrost to regional warming. This paper joins together inputs from two groups researching in the South Shetlands. The group of the Autónoma de Madrid and Valladolid universities (i.e., Serrano & López-Martínez 2000, Smellie et al. 2002, Serrano 2003) has been focusing on geomorphological surveying and mapping of the periglacial processes in the South Shetlands (Fig. 1). The group at the universities of Alcalá de Henares, Lisbon, Zurich, and Karlsruhe (Ramos & Vieira 2003, Vieira & Ramos 2003, Ramos et al. 2007, Hauck et al. 2007) has been monitoring ground temperatures and modelling spatial distribution of permafrost. In this paper a synthesis of observations on geomorphic processes that are seemingly related to permafrost and ground-ice degradation from Hurd Peninsula (Livingston Island) and Deception Island is presented. The next step is a geomorphological and climatological monitoring programme, which is planned to start in 2008–09. Climate of the South Shetlands The climate of the South Shetlands is cold-oceanic at sea level with frequent summer rainfalls and a moderate annual temperature range. Mean annual air temperatures are close to -2ºC at sea level and average relative humidity is very high, ranging from 80 to 90% (Simonov 1977, RakusaSusczewski 1993). The weather conditions are dominated by the influence of the polar frontal systems, and atmospheric circulation is variable, with the possibility of winter rainfall occurring as far south as Rothera Station (Turner et al. 2007). Temperature data from Hurd Peninsula recorded by our group for the period of 2003–05 at 20 m a.s.l. show values comparable to those at Arctowski Station on King George Island. From April to November average daily temperatures stay generally below 0ºC and from December to March temperatures are generally slightly above 0ºC. Two contrasting seasons in terms of freezing and thawing are, therefore, defined. At 275 m a.s.l. on Reina Sofia Hill the recorded mean annual air temperatures were of ca. -4.2ºC. This corresponds to a lapse rate of -0.8 ºC/100 m and to a freezing season that is about one month longer than at sea level. The climate on Deception Island is similar to Hurd Peninsula. Geomorphological Setting and Permafrost Distribution Deception Island Deception Island is an active stratovolcano with a large collapsed caldera; the most recent eruptions occurred in 1967, 1969, and 1970 (Smellie et al. 2002). In some places there are fumaroles and ground temperature anomalies from continued volcanic activity. Mean annual air temperature at sea level is close to -2ºC. The volcano rim rises to 539 m a.s.l. at Mount Pond, and the island is glaciated to a large extent. As a result of recent eruptions, the island has been covered by volcanic ash and debris, and many of the glaciers remain ash-covered today. Pyroclastic deposits covered snow, and buried snow is still present at some sites. The pyroclastic deposits are very porous and insulating, and give rise to a thin active layer, which varies from 30 to 90 cm in thickness. Vieira et al. 1841 Figure 2. Thermokarst bumpy terrain in Deception Island (arrow). Figure 3. Thermokarst hollows in Deception Island. On lower valley slopes, exposures of fossil snow (buriedice) with perennially frozen ice-cemented volcanic debris on top can be observed, testifying to post-eruption aggradation of permafrost. At these sites, ice-cemented permafrost also occurs under the buried-ice layer. Buried-ice is widespread on Deception Island, especially along the lower slopes, and ice-cemented permafrost occurs down to sea level. Geophysical surveying and trenches show that the permafrost inside the caldera thins near sea level and is absent on beaches near the shore. limit between continuous and discontinuous permafrost in bedrock is probably located between these two altitudinal limits, 115 and 275 m a.s.l. However, it is possible that at 115 m the active layer is thicker than 1 m. At 35 m a.s.l. ground temperature data indicate that permafrost may be absent in bedrock, or that the active layer is thicker than 2.3 m. Ice-cored sediments are widely distributed on Hurd Peninsula and occur down to sea level. These are likely of glacigenic origin, but in several cases still show active deformation giving origin to rockglaciers, mostly of the protalus or moraine-derived types. Hurd Peninsula (Livingston Island) Hurd Peninsula is comprised of mountainous terrain and is located on the southern coast of Livingston Island. About 90% of the island is glaciated, with ice-free areas occurring at low altitude, generally on small peninsulas with rugged relief. Our study focused on ice-free areas of the northwestern part of Hurd Peninsula in the vicinity of the Spanish Antarctic Station Juan Carlos I. The bedrock is a low-grade metamorphic turbidite sequence with alternating layers of quartzite and shales; conglomerates and breccias occur in some areas (Miers Bluff Formation). Dolerite dykes and quartz veins are frequent (Arche et al., 1992), with the surficial lithology being very heterogeneous (Pallàs 1996). The geological setting on Hurd Peninsula is substantially different to that of Deception Island. On the former, bedrock outcrops are prevalent, with only a thin cover of diamictite. Therefore, studying permafrost distribution is much more complex than at Deception, since frozen bedrock is very difficult to identify without a good network of boreholes. Observations from boreholes and geophysical surveying (Electrical Resistivity Tomography and Refraction Seismics Tomography) will allow a first insight into permafrost distribution, and a dense network of boreholes is planned for installation in 2007/08. The observations indicate that continuous permafrost is present in diamictite and bedrock at least at 275 m a.s.l. At 115 m a.s.l. permafrost probably occurs only at some locations and seems to be controlled by late-lying snow patches. At this altitude in diamictite deposits, during summer, the ground thaws at least down to 1 m depth. On Hurd Peninsula, the Permafrost and Ground-Ice Degradation Features Thermokarst Thermokarst features have been observed at different sites on Deception Island. Two types of features occur, including thermokarst bumpy terrain and thermokarst hollows. Bumpy terrain consists on a series of depressions with a small depth/width ratio that cover the terrain continuously (Fig. 2). They appear on the upper parts of the slopes inside the caldera. Preliminary observations suggest that they are more frequent on slopes below 100–150 m a.s.l. Bumpy terrain is related to the thaw of buried-ice derived from buried snow patches. It is not yet clear if the depressions are solely the consequence of atmospheric warming or if they relate to a dynamic situation mainly induced by the thinning of the insulating layer of pyroclastic material being eroded. The thinning of the sedimentary cover, which is stronger in upper sector of the slopes, induces a decrease of the thermal insulation of the buried-ice layer, allowing for thawing. On the lower slope, the sedimentary cover is thickest due to the accumulation of material transported from upslope. There, a permafrost layer above the buried-ice layer can be observed which is probably linked to an increasing insulation effect due to sediment accretion. Thermokarst hollows are features of decimetric to metric size and occur isolated or in small groups (Fig. 3). Their depth/width ratio is larger than the bumpy terrain, but they were not studied in detail yet. They appear in flat or 1842 Ninth International Conference on Permafrost Figure 4. Debris-flow tracks in a talus slope on Hurd Peninsula (Livingston Island). Figure 6. Debris flow tracks in Deception Island. Figure 5. Debris flows depositing over the surface of the Las Palmas Glacier in Hurd Peninsula (Livingston Island). gentle sloping terrain. No trenches were excavated, nor was geophysical surveying conducted in these features. They are probably related to localized degradation of massive ice. Their origin is not clear yet, since they can result from a climatic influence, but may also relate to changes in ground heat flux due to the volcanic activity. Geophysical surveying of these thermokarst hollows will be conducted in 2007/08. Debris flows Sub-aerial present-day debris-flow activity is a geomorphic process that has been poorly analysed in the literature for maritime Antarctica. Recent debris-flow tracks and deposits have been observed at several sites both on Livingston (Vieira & Ramos 2003) and Deception Islands (Figs. 4, 5, 6). Debris-flow activity is initiated by the saturation of surface unconsolidated material that flows along a channel in the slope, reworking the slope material. In several mountain regions in the northern hemisphere an increase or altitudinal change in debris-flow activity has been linked to permafrost degradation (Jomelli et al. 2004). In maritime Antarctica, the widespread distribution of permafrost, together with the mountainous terrain and its proximity to the climatic limits of permafrost, a similar consequence of increasing air temperatures is to be expected. Figure 7. Active layer detachment slide on Deception Island. However, rainfall episodes may also be a triggering mechanism for debris flows. The lack of monitoring data does not allow us to precisely define the origin of the debris-flow activity and, therefore, in 2008/09 a monitoring programme for debris-flows will be implemented. On Deception Island debris-flow tracks are widespread, at least in the inner slopes of the caldera. These are erosional slopes built up of volcanoclastic material. The debris flows form on the upper parts of the slopes and seem to be related to permafrost degradation, since this area is also at a similar geomorphological setting to the bumpy terrain features. The tracks are tens to a few hundred metres long. The predominantly gravely grain-size of the slope material and moderate slope angle limit the downslope movement of the flow; therefore, the debris generally does not contribute significantly to the valley floors. In the 2007/08 campaign a systematical mapping of the debris-flow tracks will be conducted in order to detect their spatial pattern and controlling factors. On Hurd Peninsula several debris-flow tracks have been Vieira et al. 1843 observed and one of them is known to have occurred in late spring. Debris flows on Hurd affect mainly talus slopes and lateral moraines. Due to the steep slope angles and slope length they reach more than a hundred metres in length and have been observed being deposited on top of glaciers (Fig. 5). Active-layer detachment slides Active-layer detachment slides form from the presence of an impermeable frozen layer at depth. Several small slides of metric dimension have been observed affecting the surface of the ice-cored moraine of the Argentine lobe of Hurd glacier in January 2000 and are related to the degradation of the icerich till on the very steep inner slope of the moraine. Other ice-cored moraines near sea level have been detected using electrical resistivity tomography and refraction seismics tomography and they can be subject to these processes of degradation in the near future if the current climate trend continues. On Deception Island small detachment slides were also found on steep slopes. The mass movements were under 40 m2 in area (Fig. 7). Rockfalls Rockfalls in the mountain permafrost zone have been pointed out as a consequence of permafrost degradation, especially relating to the melting of ice filling rock wall fractures (Davies et al. 2001, Kaab et al. 2005, Gruber & Haeberli 2007). Rockfalls occur on both Hurd Peninsula and Deception Island; however, without proper monitoring it is difficult to access the influence of permafrost degradation on their origin. Conclusions The South Shetland Islands are a privileged area to study climate change and its effects on landscape dynamics. Permafrost is widespread and occurs down to sea level. On Deception Island permafrost is continuous throughout most of the area, but on the Hurd Peninsula continuous permafrost likely occurs only above ca. 150 m a.s.l. In the same area discontinuous and sporadic permafrost exist down to sea level, especially in the form of ice-cored moraines and rock glaciers. The mean annual air temperatures at sea level are close to -2ºC, positioning the archipelago near the climatic limit of permafrost. This fact, together with the warming that affects the Antarctic Peninsula region should be responsible for permafrost degradation. This paper describes landforms and geomorphic processes related to permafrost and ground-ice degradation that seem to result from climate change. Where ground-ice occurs, thermokarst hollows, bumpy terrain, and active-layer detachment slides have been found. The first occurs on flat or gentle sloping ground and the latter on moderate to steep slopes. Debris-flow activity was observed to be widespread on slopes of both. Their genesis has still to be assessed, since they can be linked either to ground warming or to heavy rainfall events. On Deception Island heat flux anomalies caused by volcanic activity can also generate permafrost degradation features. These anomalies are of small areal extent and their locations are known. The observations presented here are preliminary and constitute a starting point for a new approach that will emphasize monitoring of geomorphological activity in order to detect the influence of climate change on present-day processes. Another interesting issue to be analysed is the control of changing geothermal heat fluxes on permafrost degradation in Deception Island and to assess on the possibility of using permafrost degradation features as indicators of changes in volcanic activity. Acknowledgments This study was conducted as part of the project PERMAMODEL within the Spanish Antarctic Program CICyT (CGL2004-20896-E/ANT). This research is included in the IPY project ANTPAS – Antarctic and Sub-Antarctic Permafrost, Soils and Periglacial Processes. G. Vieira was funded by the Fundo de Apoio à Comunidade Científica (FCT) and Fundação Calouste Gulbenkian. References Anisimov., O. A., Shiklomanov., N. I. & Nelson, F.E. 1997. Global warming and active layer thickness: results from transient general circulation models. Global and Planetary Change 15: 61-67. Arche, A., López-Martínez, J. & Martínez de Pisón, E. 1992. 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