Evaluation of frozen ground conditions along a coastal topographic gradient at Byers Peninsula (Livingston Island, Antarctica) by geophysical and geoecological methods
Introduction
Frozen ground conditions exert a key control on geomorphological dynamics in ice-free areas of periglacial environments, which have been broadly defined as those regions with mean annual temperatures ranging from − 2 to 3 °C (French, 2007). However, frozen ground conditions can be permanent (permafrost) or seasonal (seasonal frost). The soil frost regime has large implications on soil, hydrological, biological and geomorphological processes prevailing in cold-climate environments (Oliva et al., 2014).
In some cases, though, it may be difficult to identify the spatial boundary between seasonal frost and permafrost conditions. With the purpose of detecting this limit, increasing number of boreholes and shallow drillings are recently been established for monitoring permafrost and active layer dynamics in mid-latitude mountain regions as well as in polar environments (e.g. Harris et al., 2003, Haeberli et al., 2010, Romanovsky et al., 2010). Also, two international programmes (Global Terrestrial Network for Permafrost and Circumpolar Active Layer Monitoring System), led by the International Permafrost Association, have been implemented in order to establish protocols to monitor permafrost and active layer parameters worldwide. In the case of Antarctica, by 2010 there were 73 boreholes and 28 CALM sites (Vieira et al., 2010) although this is clearly insufficient for a vast continent, exceeding 14 million km2.
Permafrost in Antarctica is both present in ice-free areas of Maritime (Vieira et al., 2010, Bockheim et al., 2013) and Continental Antarctica (Bockheim and Hall, 2002), as well as beneath the ice-sheet where subglacial permafrost exists (Bockheim and Hall, 2002). However, it is in ice-free environments of Maritime Antarctic where permafrost conditions are found in boundary climatic conditions. In the case of the South Shetland Islands (SSI), permafrost has not been generally detected in elevations below 20 m a.s.l. but has been found widespread above 40 m a.s.l. (Serrano, 2003, Serrano et al., 2008, Ramos et al., 2009, Vieira et al., 2010). Therefore, a transition belt with sporadic or discontinuous was established in the SSI between 20 and 40 m a.s.l. Nevertheless, local factors can induce changes in this general distribution. In the SSI geomorphological landforms features related to permafrost conditions, such as rock glaciers, protalus lobes or moraines with ice-rich permafrost, have been observed close to sea level (López-Martínez et al., 2012, Oliva and Ruiz-Fernández, 2015).
Vegetation cover also can generate a strong control on permafrost distribution and active layer dynamics. In discontinuous permafrost regions there is a close relationship between vegetation assemblages and the existence or absence of permafrost conditions in the area (Dingman et al., 1974). A tundra-type vegetation has also a strong impact on active layer thaw since it intercepts incoming radiation (Kelley et al., 2004). Besides, the distribution of snow across the landscape can alter active layer dynamics and induce changes on the vegetation communities (Johansson et al., 2013). However, it is necessary to note that in the Maritime Antarctic the vegetation forms an open tundra (Serrano, 2003), sparser than other types of tundra.
Most of these studies have used geomorphological indicators or boreholes data to determine the permafrost conditions. However, there are other methods that can provide accurate data on the distribution of permanent frozen ground conditions. In this regard geoelectrical methods can be useful in detecting and delineating permafrost and/or frozen ground and space and time evolution (Hauck and Kneisel, 2008). Field and laboratory data indicates that electrical resistivity of rocks and soil increase several times after freezing temperature is reached (Hoekstra et al., 1975, Olhoeft, 1978, Scott et al., 1990, Vanhala et al., 2009). Depending on the salts content freezing can take place at temperatures lower than 0 °C and the electrical resistivity increases slowly until all water is frozen; after complete freezing rocks and soil generally present very high electrical resistivities. The use of geoelectrical methods for detecting permafrost must also consider that electrical resistivities depend on ground ice content.
The main objective of this research is to evaluate the present-day distribution of permafrost conditions in Byers Peninsula (Livingston Island), the largest ice-free environment in the SSI archipelago, along a topographic gradient from sea level to Sealer Hill, a summit plateau at 91 m a.s.l. in the SE area of Byers Peninsula. We analysed the geoecological settings along this transect in order to understand the relationship between the geomorphic features and the biological activity. The geophysical surveying was carried out along the raised beaches transect of this profile to infer the distribution of frozen ground conditions at the coastal zone. Also, we discussed how the distribution of permafrost conditions in Byers fits the geographical pattern of frozen ground conditions in the SSI.
Section snippets
Study area
The study area is located in Byers Peninsula (between 62°34′35″S–62°40′35″S latitude and 60°54′14″W–61°13′07″W longitude) in Livingston Island. With ~ 60 km2, this ice-free environment is the largest of the SSI. This archipelago is composed of 11 main islands located 120–130 km NW of the tip of the Antarctic Peninsula (AP) (Fig. 1). About 90% of these islands is covered by glaciers (Serrano, 2003). The ice-free environments correspond mostly to nunataks and small peninsulas distributed along the
Materials and methods
Field work was conducted in late January 2015 after a snowy year in the SSI, which conditioned research activities in the field as well as the results obtained and presented in this paper. A geomorphological sketch of the landforms along a transect from sea level to Sealer Hill was carried out in the field together with the support of a high resolution WorldView2 satellite image of Byers Peninsula from 2-1-2011. These data were compared also with geoecological observations conducted in the
Geophysical transect
Fig. 3 shows the electrical resistivity model obtained by inversion of apparent electrical resistivities measured along the transect shown in Fig. 2. The data showed a good quality; the RMS of the inversion of the three merged ERTs is 2.8% and the individual RMS of each ERT is lower than 2%. Besides this, the measurements showed high stability and reproducibility during the field work.
From the model (Fig. 3) it is apparent that high electrical resistivities are located near the surface of the
Permafrost distribution based on geophysical methods
In general terms there is an average slow increase of the size and thickness of the more resistive patches observed along the geoelectrical model of Fig. 3 inland. These high electrical resistivity patches reached values of about 2000 Ω·m, which are interpreted as sporadic permafrost conditions. As a matter of fact, frozen ground was detected by eye inspection when trying to decrease the electrical contact resistance between the stainless electrodes and the ground when doing the field work.
It is
Conclusions
Permafrost plays a key role on geomorphological and geoecological processes prevailing in ice-free environments in Maritime Antarctic. However, data on permafrost distribution across the AP region are scarce and only limited to geomorphological observations and monitoring data from a reduced number of sites. With the purpose of complementing the existing knowledge on permafrost distribution in the lowland areas of the SSI, in January 2015 we conducted a geoelectrical survey on the Late Holocene
Acknowledgements
This research has been funded by the Portuguese Science Foundation (PTDC/CTE-GIX/119582/2010) through the research project HOLOANTAR (Holocene environmental change in the Maritime Antarctic. Interactions Between permafrost and the lacustrine environment) and the Portuguese Polar Program (PROPOLAR). We are grateful to the Chilean Antarctic Institute (INACH) for providing logistic support of field work activities. M. Oliva acknowledges the AXA Research Fund for funding his research activities in
References (56)
- et al.
Climate warming and permafrost dynamics in the Antarctic Peninsula region
Glob. Planet. Chang.
(2013) - et al.
Warming permafrost in European mountains
Glob. Planet. Chang.
(2003) - et al.
The Upper Jurassic-Lower Cretaceous Byers Group, South Shetland Islands, Antarctica: revised stratigraphy and regional correlations
Cretac. Res.
(1998) - et al.
Periglacial processes and landforms in the South Shetland Islands (northern Antarctic Peninsula region)
Geomorphology
(2012) - et al.
Distribution and characterization of soils and landform relationships in Byers Peninsula, Livingston Island
Maritime Antarctica Geomorphology
(2012) - et al.
Rock glaciers in the South Shetland Islands, Western Antarctica
Geomorphology
(2000) - et al.
Timing of the most recent Neoglacial advance and retreat in the South Shetland Islands, Antarctic Peninsula: insights from raised beaches and Holocene uplift rates
Quat. Sci. Rev.
(2012) - et al.
A proxy for snow cover and winter ground surface cooling: mapping Usnea sp. communities using high resolution remote sensing imagery (Maritime Antarctica)
Geomorphology
(2014) - et al.
Marine landforms and deposits
- et al.
Regional weather survey on Byers Peninsula, Livingston Island, South Shetland Islands
Antarctica. Antarctic Sci.
(2013)