Elsevier

CATENA

Volume 149, Part 2, February 2017, Pages 529-537
CATENA

Evaluation of frozen ground conditions along a coastal topographic gradient at Byers Peninsula (Livingston Island, Antarctica) by geophysical and geoecological methods

https://doi.org/10.1016/j.catena.2016.08.006Get rights and content

Highlights

  • We examined frozen ground conditions in Byers Peninsula, South Shetland, Antarctica.

  • Geomorphological and geophysical methods were used in this ice-free environment.

  • High resistivity values suggest patchy permafrost conditions in the marine terraces.

  • Permafrost is confirmed by geomorphic features (i.e. active blockstreams) at 18 m.

  • Clear correlation between moss beds and frozen ground conditions

Abstract

Geophysical surveying and geoelectrical methods are effective to study permafrost distribution and conditions in polar environments. Geoelectrical methods are particularly suited to study the spatial distribution of permafrost because of its high electrical resistivity in comparison with that of soil or rock above 0 °C. In the South Shetland Islands permafrost is considered to be discontinuous up to elevations of 20–40 m a.s.l., changing to continuous at higher altitudes. There are no specific data about the distribution of permafrost in Byers Peninsula, in Livingston Island, which is the largest ice-free area in the South Shetland Islands. With the purpose of better understanding the occurrence of permanent frozen conditions in this area, a geophysical survey using an electrical resistivity tomography (ERT) methodology was conducted during the January 2015 field season, combined with geomorphological and ecological studies. Three overlapping electrical resistivity tomographies of 78 m each were done along the same profile which ran from the coast to the highest raised beaches. The three electrical resistivity tomographies are combined in an electrical resistivity model which represents the distribution of the electrical resistivity of the ground to depths of about 13 m along 158 m. Several patches of high electrical resistivity were found, and interpreted as patches of sporadic permafrost. The lower limits of sporadic to discontinuous permafrost in the area are confirmed by the presence of permafrost-related landforms nearby. There is a close correspondence between moss patches and permafrost patches along the geoelectrical transect.

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

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