A bibliographic research on permafrost occurrence and distribution in the sub-antarctic islands

Transcription

1 A bibliographic research on permafrost occurrence and distribution in the sub-antarctic islands Clémence Golinelli Bachelor s thesis University of Fribourg Under the supervision of Faculty of Sciences Prof. Christian Hauck Department of Geosciences Summer 2016

2 1. INTRODUCTION RESEARCH QUESTION 5 2. PRESENTATION OF THE STUDY SITE THE SUB-ANTARCTIC REGION THE SOUTHERN OCEAN ANTARCTIC CIRCUMPOLAR CURRENT (ACC) THE ANTARCTIC CONVERGENCE AND DIVERGENCE SUBTROPICAL FRONT (OR SUBTROPICAL CONVERGENCE) CLIMATE IN THE ANTARCTIC AND THE SUB-ANTARCTIC REGION 11 3 METHODOLOGY 12 4 PERMAFROST DEFINITION THE ACTIVE LAYER DISTRIBUTION OF PERMAFROST 14 5 LANDFORMS PERIGLACIAL ENVIRONMENT FROST ACTION GRAVITATIONAL MASS MOVEMENT: SOLIFLUCTION GLACIAL ENVIRONMENT COLD BASED GLACIERS CIRQUES 20 6 DATA PRESENTATION MARION AND PRINCE EDWARD ISLANDS CROZET ISLANDS KERGUELEN ISLANDS HEARD AND MCDONALD ISLANDS MACQUARIE ISLAND BALLENY ISLANDS SCOTT ISLAND PETER 1ST ISLAND DIEGO RAMIREZ ISLANDS SOUTH GEORGIA ISLANDS SOUTH SANDWICH ISLANDS BOUVET ISLAND 37 6 DISCUSSION 39 7 CONCLUSION 42 8 BIBLIOGRAPHY 45 (Cover picture: A glacier on Bouvet island; François Guerraz, (2011)) 2

3 1. Introduction This research is based on the proposed travel plan of the Antarctic circumnavigation expedition through the sub-antarctic islands which was planned for 2016/2017 (fig. 1). The Swiss Polar Institute (SPI) is an interdisciplinary center based at the EPFL (Swiss Federal Institute of Technology in Lausanne) in association with other Swiss Universities as well as the Swiss Federal Institute for Forest, Snow and Landscape Research. The SPI is dedicated to researching the South and North poles, and other extreme environments. The SPI organizes an international scientific expedition through the sub-antarctic circumpolar waters. It will mandate 55 scientific researchers from 30 different countries, who will work on 22 research projects. The main purpose of the circumnavigation expedition is to measure the impact of climate change on the Southern Ocean (Perrin, 2016). Figure 1. The Antarctic circumnavigation expedition - Indicative travel plan (Swiss Polar Institute, 2016) 3

4 The Antarctic continent, located on the geographic south pole is an important international scientific field with approximately 35 permanent scientific base on its ground. Its unique characteristics makes it one of the most interesting place to study Earth, ice and climate change. Being the fifth largest continent, it contains 90% of all the ice on the planet as it is almost completely ice-covered less than 1% is ice free. It is also the coldest, windiest and driest continent, making it one of the most desolated region on Earth (Taylor Redd, 2012). Nevertheless, permafrost researches are diverse and precise as the Antarctic continent is nowadays relatively easy to access by plane. As stated above, it has also been an important region for researches on climate change: being ice covered, increasing temperatures have direct impacts on the many glaciers and ice sheets. The western part of the continent especially the Antarctic peninsula has shown rapid shrinkage, causing sea level to increase and impacting the surrounding biological environment (Taylor Redd, 2012). The sub-antarctic region is located in the southern hemisphere, north of the Antarctic continent. The region, situated in the Southern Ocean, is characterised by isolated remote islands and extreme climatic conditions (Convey, 2007). Numbers vary, but it is approximately located between 46 and 60 latitude south of the Equator. Due to the remote situation of the sub-antarctic islands, only few researches on permafrost have been conducted there. In addition, Antarctic and Sub-Antarctic waters can be difficult to navigate due to strong polar easterlies. Therefore, most of the expeditions have taken place on more accessible islands such as the South Shetland islands, a group of small islands situated north of the Antarctic peninsula, very close to both the Argentinian continent about ½ day cruise and the Antarctic continent (see fig. 1). Research have shown that permafrost is present on both the South Shetland islands and the Antarctic peninsula. Therefore, the sub-antarctic islands should present similar results, although many of the sub-antarctic islands are subject to extreme winds, local climates and other processes that are very likely to affect permafrost differently than on the South Shetland islands and on the Antarctic peninsula. 4

5 1.1. Research question The purpose of this research is to collect all the published information available regarding permafrost on the sub-antarctic Islands. The aim is to establish a record of the occurrence and distribution of permafrost on those Islands, according to local climates, oceanography and topography. The main question of this research is: Is there permafrost on the sub-antarctic islands and if there is, what is its distribution and what are the limits of the available information? In order to answer those questions, the following sub-questions arise: o What are the permafrost s characteristics in the region? o Is the climate similar on every island? o Do the islands have similar topographic features? o Are glaciers, volcanoes or other phenomena present? If yes, what impact do they have on permafrost distribution? o How does (and will) climate change impact permafrost distribution in the sub- Antarctic region? The thesis is composed of eight chapters. The first three chapters are about introducing the subject and the main research question, presenting the study site as well as presenting the methodology used in the research. The fourth chapter is about permafrost, first in a general way, followed by a more precise aim on the sub-antarctic region. It presents all the information needed to properly understand the data exposed further on in the research. Landforms linked to the presence of permafrost are presented in the fifth chapter, followed by the data presentation. The data is, as stated above, all the published information on permafrost, in addition to information about climate, altitude, wind and other processed that can influence the permafrost occurrence. Lastly, the two chapter following the data are about discussing the presented information and answering the research question and sub-questions. 5

6 2. Presentation of the study site 2.1 The Sub-Antarctic Region As explained in the introduction, the sub-antarctic region is characterised by extreme climates and currents, as well as strong mostly westerly winds. These characteristics differentiate most of the sub-antarctic islands from other well researched areas such as the Antarctic peninsula and the South Shetland islands. Although some sub-antarctic islands are easily accessible from the continent Balleny island from the Antarctic continent and Diego Ramirez from the Argentinian continent, others are very remote and are very difficult to access for research purpose. The study area selected for this research consists of twelve sub-antarctic islands, all located around the Antarctic continent. There are about a hundred islands considered being located inside the sub-antarctic region, and many more located in the overall Antarctic region. The twelve islands chosen for this research have been selected to be the same as the Antarctic circumnavigation expedition of the Swiss Polar Institute (fig. 1) and therefore are: 1. Marion / Prince Edward 2. Crozet 3. Kerguelen 4. Heard / McDonald 5. Macquarie 6. Balleny 7. Scott 8. Peter 1 st 9. Diego Ramirez 10. South Georgia 11. South Sandwich 12. Bouvet For the purpose of this research, the twelve islands were divided into four groups. They represent the geographic proximity of the islands, which hypothetically also represent climatic similarities and therefore also permafrost similarities. The four groups are, as shown in figure 2: 1. Marion/ Prince Edward; Crozet; Kerguelen; Heard/ McDonald 2. Macquarie; Balleny; Scott 3. Peter 1 st ; Diego Ramirez 4. South Georgia; South Sandwich; Bouvet 6

7 Figure 2. Map of the Antarctic and sub-antarctic region, specifying the four groups of sub-antarctic islands (Modified from Rogers, 2007) 7

8 2.2 The Southern Ocean The Southern Ocean, also known as the Antarctic Ocean or Austral Ocean, comprises all the southern parts of the Pacific, Atlantic and Indian ocean. It surrounds the Antarctic continent entirely (Rosenberg, 2016) Antarctic Circumpolar Current (ACC) The motor of global water circulation is determined by a difference of density in water masses called thermohaline circulation. Salinity and temperature are the two primary factors involved in influencing seawater density globally. Locally, salinity is controlled by the balance between precipitation and evaporation (Emerson & Hedges, 2008). Salty water is denser than less salty water, similar to cold water being denser than warmer water. This results in the sinking of dense water masses to the bottom of the ocean, flowing northward, inducing the moving of water masses and bringing water masses in the world s oceans to circulate (Ward, 2001). The ACC is an eastward current induced by wind driven circulation on the water surface as opposed to deep waters, driven by a difference of density in water masses (Fig. 3). Unequal temperatures around the Globe create different wind circulations. Easterly winds and high polar pressure are dominant in the poles, between 60 and 90, as in subpolar regions, between 30 and 60, low pressures and westerly winds prevail (Emerson & Hedges, 2008). In addition to wind stress, thermohaline circulation plays a significant role in the moving of water masses as the water balance below 1500 meters is conducted by the sinking of water in the polar region (Emerson & Hedges, 2008) The Antarctic Convergence and Divergence The Antarctic continent continually contributes to cooling its surrounding waters by inducing katabatic winds (cold dense air masses going down slopes under the force of gravity also known as fall winds) and reinforcing the Albedo effect as the sun radiation reflects on the white ice, cooling down the surface. Due to their high density, cold waters sink down to the ocean floor and flow in opposite direction to the Antarctic continent. Moving up north, cold water masses meet warmer, less dense waters in the sub-antarctic region, moving down south from the Pacific, Atlantic and Indian oceans. This particular zone is the Antarctic convergence, also known as the Polar Front, a crucial and primal 8

9 source of life on earth (Encyclopædia Britannica, 2015). Conditions created by the meeting point of cold and warm water masses benefit the development of phytoplankton, the first element of all oceanic food chain (Encyclopædia Britannica, 2015). Although the Antarctic convergence does not have a definite line, its frontier rarely varies more than half a degree of latitude from its 60 S mean position; it is situated at a point of sudden change in water temperature. The line of the Antarctic convergence (Fig. 2) is correlated with the presence of strong westerly winds (Encyclopædia Britannica, 2016). The Antarctic divergence, closer to the continent than the convergence, is a region of transition between waters of high and low salinity. The line of divergence is situated where the maximum salinity can be found below a depth of 150 meters. It is caused by the upwelling of highly saline waters coming from the North Atlantic. Stagnation of saline waters below 150 meters is due to high precipitations induced by the continent s topography and the melting of ice, resulting in strong presence of freshwater. The deeper salty and cold waters are denser and therefore flows along the bottom under the effect of gravity in addition to the difference of density between water masses. The divergence is also partially explained by the demarcation between the easterly winds and the westerly winds as they induce currents to meet each other towards the divergence line (Baum, 2011) Subtropical Front (or Subtropical Convergence) The subtropical front is the boundary that separates warm and salty subtropical waters from cold sub-antarctic waters as a result of difference of density in water masses. It is the northern line of demarcation between the sub-polar and polar waters and the subtropical waters, as shown in figure 3. In addition, the subtropical front plays an important role in the global climate system as it acts as a saline regulator between the Atlantic and Indian ocean (Graham & De Boer, 2013). A wind induced shift in water masses is being researched as to being the reason for a widen salt water gateway to the Indian ocean and a smaller gateway to the Atlantic (Graham & De Boer, 2013). 9

10 Figure 3. The Antarctic circumpolar current, polar front and sub-antarctic front in relation to the position of the Antarctic continent (Stevens & Chiswell, 2013) Figure 4. The average monthly temperatures in degres Celcius for the different climate zones in the Antarctic and sub-anatrctic region (Ward, 2001) 10

11 2.3 Climate in the Antarctic and the sub-antarctic region The climate in Antarctica and the sub-antarctic region is not overall similar; the Antarctic continent itself has several local climates induced by many elements such as the proximity to water, the altitude and the exposure to winds and currents. The closest to the South pole is the coldest, the Vostok station being one of the coldest in the world as is it situated on the continental high plateau of the Antarctic continent (fig. 4). The continental high plateau is situated all around the center of the continent and has an altitude of about meters. It is exposed to extremely cold temperatures all year round, ranging between - 20 C and -60 C (Ward, 2001). These extreme temperatures are due to its close location to the South pole, its altitude, and the constant cold and dry winds. The Vostok station has an average temperature of -55 C because of its close location to the center of the continent (Ward, 2001). The further away from the South pole, the more temperatures warm up (fig. 4); on the Antarctic peninsula the climate is maritime, it is exposed to cold winters and warmer summers with a monthly temperature average ranging from +1 C to -15 C (Ward, 2001). The Antarctic peninsula is lower in altitude than the high plateau, with only 5 meters of altitude. Because of the difference of altitude between the center of the continent and its coasts, the Antarctic peninsula is exposed to strong katabatic winds, bringing regular precipitations coming from the continent. The Antarctic islands also have a maritime climate, although with warmer temperatures: from +1 C to -10 C monthly average (Ward, 2001). Winter temperatures are mainly induced by the presence of sea-ice (frozen seawater floating on the ocean s surface) cooling their surroundings, in addition to strong winds. The sub-antarctic islands are for most situated above the northern limit of sea-ice, and are therefore not subject to the same temperatures as for the Antarctic islands. An oceanic climate with mild summers and cooler winters causes the monthly average temperature to be between +4 C and -1.5 C (Ward, 2001). Strong for most westerly winds induce precipitation in the form of rain in summer and snow in winter. Winds in the Antarctic and sub-antarctic region are mostly westerly because of the Coriolis force induced by the rotation of the Earth (Ward, 2001). 11

12 3 Methodology This thesis is based on a bibliographic methodology. All the data used in this research was found in published books or articles, such as on scientific websites. In order to carry out a bibliographic research, a few methodological steps need to be followed. Firstly, the subject itself, the research area and the subject s limits have to be well defined. Is the subject limited in time, is it limited in space, or geographically? For this particular research, the geographical frontier is the sub-antarctic region, including the Antarctic continent since some islands are very close to it and may hypothetically be influenced by winds, currents or other climate processes. But it is not limited in time as all the information available are being discussed, nor is it limited in space as winds and climates are also one of the main part of the research. Secondly, key words have to be well chosen especially when searching data on a web platform. For this particular research the key words used were primarily Permafrost, Sub- Antarctic, the sub-antarctic Islands, as well as all the precise names of all the studied islands: Marion / Prince Edward, Crozet, Kerguelen, Heard / McDonald, Macquarie, Balleny, Scott, Peter 1 st, Diego Ramirez, South Georgia, South Sandwich and Bouvet. The next step is to identify which type of document is relevant to the research. Here, only scientific data was relevant. Books, encyclopaedias, dictionaries, revues and thesis were mostly used. As for the specific information, a lot of researches that were not directly linked to the subject, such as fauna and flora researches were also of interest. The main difficulty when using a bibliographic methodology is to be able and to be sure to find every relevant information available on the subject. By the time of this research a lot of information has not yet been published although it presumably exists, in addition to the fact that a lot of research may not have published any data at all. Furthermore, some publications can be private. 12

13 4 Permafrost 4.1 Definition Permafrost is ground (soil and/or rock) that remains at or below 0 C for a minimum of two consecutive years (French, 2007). The definition of permafrost is therefore purely based on its thermal characteristics. Therefore, permafrost is not automatically ice since the freezing point of water can be below 0 C. Frozen ground processes occur in periglacial environments, such as high mountain regions or high continental latitudes like the Arctic or Antarctic regions. Permafrost occurs after consecutive long periods of cold, and short periods of warm temperatures, creating climatic conditions for the ground not to warm up above 0 C during warmer periods (French, 2007). According to French (2007), it is important to differentiate the thermal condition from the state condition of permafrost. The terms cryotic and non-cryotic refer directly to the temperature of permafrost, not indicating anything about water or ice content. The soil is considered cryotic when below the temperature of 0 C, and non-cryotic when above 0 C. In opposition to that, permafrost can be stated as unfrozen, partially frozen or frozen depending only on its water-to-ice ratio (French, 2007). Unfrozen permafrost has little to no ice, partially frozen ground has both water and ice and frozen permafrost mainly contains ice, also called dry permafrost. The presence of permafrost is primarily determined by temperature, as stated in its definition, but it is however influenced by many other factors, such as earth materials, snow cover, topography, precipitation and sun exposure, to cite only the most dominant factors. Nevertheless, more than 20% of the world s land area is underlain by permafrost (French, 2007), which makes it an important research subject for the understanding of the world s glacial and periglacial dynamics. 13

14 4.2 The active layer During warmer periods, mostly in summer, the uppermost layer of permafrost thaws forming the so-called active layer. The latter is thinner in polar regions than in lower latitudes, due to cold temperatures during summer periods, even though it is important to point out that the thickness of the active layer may vary from year to year. This thickness depends directly on air temperature, snow cover, slope orientation and solar radiation, as well as vegetation, drainage and water content (French, 2007).The transient layer is the layer which is in between the active layer and the main permafrost body. The transient layer is generally an ice-rich layer defined as the upper part of permafrost. This layer may thaw and refreeze, but only very rarely, usually during very warm summers. During these unusual warm periods, the active layer expands beyond its habitual depth which causes part of the ice-rich layer to thaw. This extreme thawing of permafrost can result in soil instability, increased solifluction activity as well as rapid mass movements. It is a serious matter as the climate continues to change and temperatures tend to increase, which means that the ice-rich layer will continue to thaw as the active layer progressively thickens with years to come (French, 2007). The lower layer of permafrost is a long term perennially-frozen ground which only freezes and thaws on a century or millennial scale (French, 2007). Permafrost forms when outside air temperatures are low and soil materials are predisposed to freezing. The latter grows when climatic conditions reflect a negative heat balance at the surface of the earth. It therefore aggrades when the thickness of the active layer is inferior to the thickness of the transient layer. If the thermal conditions allow, permafrost will thicken repeatedly over the years and will expand downwards from the surface. Nevertheless, other factors need to be taken into consideration. For instance, large bodies of water around the surface exercise a warming effect, which is why permafrost is less present in coastal locations. Another factor is climate stability. It is difficult to predict permafrost thickness when the overall climate variates continuously. This explains why it is also important to take past climatic conditions and changes into consideration (French, 2007). 4.3 Distribution of permafrost Permafrost occurs in different environments. It is present at high altitudes, at both midand low latitudes, as well as at low altitudes at high latitudinal sites. It may sometimes be 14

15 difficult to differentiate Alpine (or mountain) permafrost from Polar (or latitudinal) permafrost as it can intermix in mountain chains such as the Western Cordillera in North America. In both Polar and Alpine permafrost, climate is the most important factor, to which other characteristics such as snow cover, inclination of slope and altitude should be added. Polar permafrost is present at high latitudes, or in other terms, in both the Arctic and the Antarctic. In the northern hemisphere, more than 50% of both Canada and Russia are underlain by frozen ground, while this number reaches more than 80% in Alaska. Latitudinal permafrost is predominantly present in the Northern hemisphere and varies greatly in terms of thickness: from a couple of centimeters to hundreds of meters (Heginbottom et al., 2012). Current periglacial environments were mainly established during the many glacial intervals happening during the Pleistocene Epoch. During this Epoch, the sea level was much lower than in the Quaternary, which resulted in more land areas being exposed to negative air temperatures. In the northern hemisphere, the Arctic continental shelves were more exposed to glacial and periglacial processes (Heginbottom, et al., 2012). Periglacial processes and permafrost distribution in the southern hemisphere are more complicated to analyze due to the thickness of ice that covers big parts of high latitudinal sites. In 1995, J. Bockheim (1995) published a map representing the permafrost distribution in Antarctica. It indicates that permafrost is pervasive in the ice-free areas of the continent and on its offshore islands (lat. 50 S), but is believed to be missing in the sub-antarctic islands, except at high elevations. The thickness of the active layer in the Antarctic continent ranges between 15 and 50 centimeters, but in the Antarctic islands and east Antarctica it is said to range between 50 and 150 centimeters, as those regions are largely influenced by marine processes (Bockheim, 1995). A particularity of the sub-antarctic islands is that the climatic conditions of the region is resemble more the climatic conditions of Alpine permafrost than to those of Polar permafrost. Nevertheless, this varies depending on the location of the islands. 15

16 5 Landforms 5.1 Periglacial environment Periglacial environments refer to a range of cold, non-glacial conditions where frost-action and permafrost-related processes dominate. Even though several periglacial zones exist, based on their climatic conditions, they all have two common criteria. The first is the continuous freezing and thawing of the ground, usually in association with the presence of water in the subsurface. The second is the presence of perennially frozen ground. Permafrost is indeed the main criteria for the definition of periglacial environments. Nevertheless some areas experience continuous freeze-thaw oscillations, but are not underlain by permafrost. An estimated 25% of the present Earth s land surface experience periglacial conditions, and an estimated 25% more experienced periglacial conditions at some point in time, especially during the cold periods of the Pleistocene (French, 2007). Periglacial processes are usually associated with the formation of frost and ice in the soil. Permafrost is unique to periglacial environments, while other high magnitude or high frequency processes that are not necessarily limited to periglacial environments can also be important. These processes are mainly related to frost action and rapid mass movements (French, 1996). In this chapter, only landforms observed on the different sub-antarctic islands will be presented, namely frost action and gravitational mass movements Frost action The freezing process of water in soils depend on many factors, the first one being that soils don t cool down at the same rate depending on the material of the soils. The second factor to take into consideration is that soils don t necessarily all freeze below 0 C. Saline water, for example, is known for lowering the freezing point of a given subsurface. The third important factor is that depending on the duration and intensity at which temperatures drop below 0 C, it will affect the rate as well as the amount of frozen soil (French, 2007). 16

17 Freeze-thaw processes are frequent in periglacial environments, generally in the form of seasonal temperature variations. Furthermore, regions with a cold oceanic climate and a low annual air temperature range are the most exposed to freeze-thaw processes as there is a lot of moisture in the subsurface. In opposition, alpine periglacial environments are more exposed to diurnal freeze-thaw cycles rather than seasonal cycles. As explained in the previous chapter (4), the sub-antarctic islands freezing processes are more likely to be compared with those of alpine regions, even though the influence of the maritime climate and the proximity to the Antarctic continent also have an influence. Therefore, the islands are subject to both seasonal and diurnal frost action (French, 2007). Seasonal frost action occurs when temperatures vary from negative to positive values between summer and winter. Seasonally frozen ground is defined as the soil near the surface that freezes from 1 to 15 days per year. The active layer of permafrost (see chapter 4.3.2) is considered seasonally frozen ground as it freezes and thaws yearly. Unlike permafrost, intermittently frozen ground extends to lower altitudes as well as lower latitudes. The maximum extent of seasonally frozen ground in the Northern Hemisphere is in January (Zhang, Barry, Knowles, Ling, & Armstrong, 2003) and in July in the Southern Hemisphere. Diurnal frost action is a freeze-thaw mechanism that occurs within 24 hours only (Gerrard, 1990). Short term frost cycles relate to the changing solar radiation and surface heating due to variations in the angle of the sun (French, 2007). The number and extent of the different frost cycles are very important to understand the variability of the environment and the energy exchange occurring in the soils (Gerrard, 1990). Furthermore, frozen water is more voluminous and therefore exerts pressure on the materials surrounding it. This can lead to the cracking of rocks, and deformation of soils (Gerrard, 1990). Recurrent landforms observed with freeze-thaw cycles are called patterned ground. The formation of ice lenses in freezing soil displaces stones in the soil with the movement of water and ice: the soil is displaced toward soil-rich domains and stones are displaced toward stone-rich domains (Kessler & Werner, 2003). Depending on the freezing process, different forms will be formed. Polygons are formed when the squeezing and confinement of stones are high and stripes form when a hillslope gradient is high (Kessler & Werner, 2003). Other forms can also be observed, as shown in figure 5, with sorted circles and sorted labyrinth also being recurrent in cold regions. 17

18 Figure 5. Different forms of patterned ground (A) sorted circles and (B) sorted labyrinths; (C) sorted stripes, and (D) sorted polygons (Kessler & Werner, 2003) Another process found in periglacial environments, due to the freezing and thawing of ice in the soil is called needle ice. A capillary mechanism induced by low surrounding air temperatures forms ice crystals growing upward, sometimes pushing away particles of the soil (fig. 6). When the air temperatures stay low for a long period of time, the ice needles can grow up to forty centimeters long (National Snow & Ice Data Center, 2013). Figure 4. Needle ice formed on frozen ground ( J. Brew) 18

19 5.1.2 Gravitational mass movement: solifluction Lots of different landforms induced by gravitational mass movements can be observed, but one in particular is regarded as one of the most widespread processes in periglacial environments (French, 2007). Solifluction processes are induced by the saturation of the soil with water, creating flowage pulled downslope. Soils underlain by permafrost are highly exposed to solifluction processes as the perennial ice creates an impermeable layer. In areas with no permafrost, solifluction processes are also highly present as the soil is weakened by the freeze-thaw cycles (Encyclopaedia Britannica, 2016). 5.2 Glacial environment Glacial environments are characterized by areas that are covered in ice, meaning areas with glaciers, ice sheet and icebergs. The world s main ice masses are at high latitudes, on the Antarctic continent for the Southern Hemisphere and in Greenland for the Northern Hemisphere, but also at high altitudes, mainly in the Alps and the Himalayas (Nagle & Witherick, 2002). For the purpose of this research, only the relevant information regarding the occurrence and distribution of permafrost will be presented Cold based glaciers Two main types of glaciers can be found in the glacial areas of the world: the warm-based and the cold-based glaciers. The first is mainly found at high altitudes in temperate regions, as the second type is found in polar regions. This chapter will only be about the second type, as it is relevant to the development of permafrost. Cold-based glaciers are slow moving, as they are located in areas where precipitations are low and temperatures are well below the freezing point, inducing a limited ablation and accumulation process. The glacier is very often frozen to the bedrock, the ablation mainly being the loss of mass through icebergs and evaporation (Nagle & Witherick, 2002). In these conditions the temperature of the soil being below 0 C, permafrost can form in the soil below the glacier. As shown in figure 7, the base of the cold based glacier is at or below 0 C, creating favorable conditions for permafrost. 19

20 Figure 5. Temperature profiles of both types of glaciers; (a) Cold-based glacier; (b) Warm-based glacier (Nagle & Witherick, 2002, p.11) Cirques Cirques, also called corrie, are semi-circular hollows surrounded by ridges called arêtes. They are typical of characteristics of glacial highlands, that vary greatly in size and shape. They vary from a few hundred meters to 15 kilometers wide, the biggest being in Antarctica (Nagle & Witherick, 2002). The formation of cirques is complex and involves a number of processes and characteristics. The main characteristic is that the surrounding rocks need to be hard enough to resist complete destruction, but weak enough to erode with freeze-thaw weathering. A shallow pre-glacial hollow is formed with a rapid accumulation of snow, enlarging with freeze-thaw cycles. The continuing ablation movement of the mass of ice at the bottom creates a large basin, continually eroding with the accumulation of snow added to frost action. When the ice and snow finally melt, a lake usually forms at the bottom of the basin, leaving a circular hollow with steep ridges of rocks. Most of the cirques were formed in the early glacial phase (Nagle & Witherick, 2002) and are now completely free of ice. 20

21 6 Data presentation As mentioned above, the studied islands will be presented in four different groups in order to simplify the presentation of the data. Within every group, each island will then be individually presented. Group 1 includes the Islands south between Cape Town, SA and Hobart, AUS: Marion/Prince Edward; Crozet Islands; Kerguelen Islands and Heard/McDonald Marion and Prince Edward islands Location S, E Position from Antarctic convergence North Number of island 2 Surface / Area 290km 2 & 40km 2 Altitude Max meters Temperature indication Mean annual air temp.: 6 C Precipitation indication Extensive: 2500 mm / year Wind Strong westerly Landforms Frost action: seasonal frost; needle ice Permafrost Strong probability above 1000 m.a.s.l. Marion and Prince Edward refer to two small peaks emerging from a submerged volcano located north of the Antarctic convergence. They are respectively 290 km 2 and 40 km 2 in total (Hall K., 2002) and are South African territories, situated 1,920 km southeast of Cape Town (Encyclopædia Britannica, 2016). The local climate in the Prince Edward islands is characterized by intensive year-round precipitations and strong constant westerly winds. It rains about 2,500 mm annually, the islands being cloud covered almost all year round. The climate is considered isothermal, which implies temperate temperatures all year long, the mean annual temperature being 6 C (Boelhouwers, Holness, & Sumner, 2002). Marion and Prince Edward islands were extensively glaciated though the beginning of the Quaternary Epoch, and show very little receding ice at the top. Permafrost is present, although only at the highest altitudes, namely above 1000 m.a.s.l. (Hall K., 2002). As shown in figure, only Marion island has a peak higher than 1000 m. 21

22 Permafrost has only been found on Marion island, although a number of periglacial landforms and active processes were found on both islands. Sorted stripes, which are usually associated with the presence of permafrost were found on both islands (Hall K., 2002). This can be explained by two different factors. First, the latitudinal location of the islands (north of the AC) and its temperate climate also prevents the forming of permafrost. Furthermore, frost action is present on both islands under the 1000 m.a.s.l. limit due to diurnal frost cycles. The presence of ice in the soil and the active periglacial processes are therefore explained by these frost cycles, reinforced by the presence of water in the soil, due to strong precipitations. At highest elevations frost action is due to seasonal freezing, which allows permafrost to form and grow throughout the years. Other active periglacial processes are explained by the variety of downslope movements due to the lack of vegetation on the islands steep slopes. Figure 8. Map of Marion & Prince Edward Islands (Wikipédia, public domaine) 22

23 6.1.2 Crozet islands Location S, E Position from Antarctic convergence North Number of island 5 Surface / Area Total landmass: 500 km 2 Altitude Max. 934 m.a.s.l. Temperature indication Mean annual air temperature: 7 C Precipitation indication Wind Landforms Permafrost Extensive: 2400 mm annually Strong westerly Small-scale sorted stripes; polygons None to weak Crozet is an archipelago composed of five islands situated north of the Antarctic convergence. They are situated half way between the Marion/ Prince Edward Islands and Kerguelen Islands (Hall K., 2002), and are French territory. All the islands are from volcanic origin and have a total landmass of 500 km 2 (World Wildlife Fund, 2016). The archipelago is very similar to Marion/ Prince Edward in many ways. It is subject to the same oceanic mild climate. The overall archipelago has an annual mean temperature of 7 C (Boelhouwers, Holness, & Sumner, 2002) and monthly average temperatures ranging between 2.9 C in winter and 7.9 C in summer (World Wildlife Fund, 2016). Precipitations are extensive, with an annual rainfall of 2400 mm, and strong westerly winds impact Crozet as much as they do Marion/Prince Edward. No permanent snow or ice cover is found on the archipelago, but just like Marion / Prince Edward islands, they probably experienced a full glaciation in the past since landforms suggesting an ice cap were discovered. Freeze-thaw diurnal cycles are active on the islands, forming small-scale sorted stripes and polygons. Other processes are active, such as solifluction (Hall K., 2002). The reason for the presence of mass movements on the islands is mainly the extensive precipitations coupled with temperatures above 0 C, preventing long term ice from forming and from stabilizing the slopes. For the same reasons, no permafrost can from on the islands, not even on high elevations since the highest peak is under the 1000 m.a.s.l., being 934 m.a.s.l. (fig. 9). 23

24 Figure 9. Location of the five Crozet islands (Wikipédia : Public domaine) Figure 10. Map of the Kerguelen islands and the Cook Ice Cap (Wikipédia : Public domaine) 24

25 6.1.3 Kerguelen islands Location S, E Position from Antarctic convergence North Number of island 300 Surface / Area km 2 in total Altitude Max m.a.s.l (on Grand Terre) Temperature indication Mean annual air temp. (main island): 4.6 C Precipitation indication >1100 mm annually Wind Strong westerly & katabatic wind Landforms Polygons ; sorted stripes Permafrost Probable at high elevations Kerguelen is a big archipelago composed of 300 islands. Its total area is about km 2, but the main island Grand Terre has already an area of km 2 alone, which makes it the biggest of all the sub-antarctic Islands (Hall K., 2002). The Kerguelen archipelago is, just like Marion/ Prince Edward and Crozet Islands, situated north of the Antarctic convergence. Another similarity with its neighboring islands is the presence of strong westerly winds. However, the Kerguelen Islands are also subject to katabatic winds induced by the high iced peak on Grand Terre. The mean annual air temperature for Grand Terre is approximately 4.6 C (measured at the Port-aux-Français base (fig.10)), but temperatures in winter drop below 0 C (Hall K., 2002). Precipitations are extensive, attaining about 1100 mm per year (Boelhouwers, Holness, & Sumner, 2002). Grand Terre is home to the Cook Ice Cap which covers approximately 750 km 2 of land (fig. 10). It peaks at an altitude of m.a.s.l., has 40 outlet glaciers and covers 10% of the land on Grand Terre (Hall K., 2002). The archipelago still shows residual volcanic activity from the early Quaternary as fumaroles are still present on some parts of the islands. Periglacial landforms were observed on the islands, mainly small-scale patterned ground including polygons and sorted stripes. At an elevation of 613 m.a.s.l. a special phenomenon occurs: small stripes develop within large-scale stripes. This indicates that annual freeze cycles form large-scale stripes, coupled with diurnal cycles forming smallscale stripes. But other signs of past periglacial processes such as solifluction are very rare, probably due to longer glaciations than on the other sub-antarctic islands, as well as glacier regrowth during the Little Ice Age (Hall K., 2002). Low winter temperatures and annual freeze cycles indicate that permafrost could form at high elevations. 25

26 6.1.4 Heard and McDonald islands Location Position from Antarctic convergence Number of island S, E South 1 archipelago & 1 small island Surface / Area ~370 km 2 Altitude Max m.a.s.l. Temperature indication Mean annual air temp. : 0.5 C Precipitation indication Strong: days per year Wind Westerly Landforms Sorted polygons ; sorted stripes Permafrost None to weak The Heard and McDonald Islands are located south of the Antarctic convergence. They are exposed to a cold climate, the mean annual air temperature on the coasts being approximately 0.5 C, with very short summers and limited temperature fluctuations. Precipitations are extremely frequent and present almost all year long, with rainy days per year. The ground is rarely exposed to the sun because of the continuous cloud cover and almost all-year-round precipitations. Therefore, 81% of the islands are estimated to being permanently covered in snow and ice (Hall K., 2002). Heard island is known for being home to an active volcano called Big Ben (Fig. 9), with a peak at m. Cryogenic activity occurs at low elevations where vegetation can grow, under the snowline, so under 300 m.a.sl. (Hall K., 2002). McDonald is a smaller active volcanic island, whose size recently doubled due to a volcanic eruption. The site is of great interest since it is an active volcanic location (UNESCO, 2016). Sorted polygons and sorted stripes were found on Heard island, even though permafrost is not present on the island. The volcanic activity on McDonald island prevents ice from accumulating on a long term on the ice-free land, and the ice cap on Heard island is located on the 1000 m.a.s.l. limit and above, where permafrost could have occurred (Hambrey, et al., 2013). Figure 11. The map of Heard Island and McDonald Island (Perry-Castañeda Library, 1976) 26

27 Group 2 includes Macquarie Island, Balleny Island and Scott Island Macquarie island Location S, E Position from Antarctic convergence North Number of island 1 small island Surface / Area ~128 km 2 Altitude 433 m.a.s.l. Temperature indication Mean annual air temp.: 4.9 C Precipitation indication Very frequent: 900 mm annually Wind Strongest force of westerly winds Landforms Sorted polygons; sorted stripes; solifluction Permafrost Unlikely but not proven Macquarie is a small island situated north of the Antarctic convergence, low in altitude, and exposed to the strongest force of westerly winds (Hall K., 2002). Temperatures on the island are mild, the mean annual air temperature being 4.9 C (Boelhouwers & al. 2002). But temperatures can drop below 0 C temperatures in July and August, the coldest months. The water temperatures act as moderator for the air temperatures, and range between 3 C and 5 C. The winter months are very cloudy and present frequent precipitations of rain and snow, with an average of 900 mm of rainfall per year. Wind is constant on the island, but can becomes very strong when exposed to low pressure systems, reaching up to 170 km/h (Australian Government, 2016). The island is very low in altitude, being only 433 meters above sea level. The modern snowline is approximately at 500 m.a.s.l., therefore snow never stays more than a few days before melting (Selkirk, Seppelt, & Selkirk, 1990). The island is ice free and could only sustain small glaciers during the Quaternary Epoch because of its low altitude. Although no glacier is present on the island many cryogenic processes and landforms were observed, similar to the ones on Marion/ Prince Edward islands and Crozet islands. Sorted polygons and sorted stripes were observed, as well as solifluction processes. But these do no indicate the presence of permafrost as they are explained to being the result of the interaction between needle ice and water action. Solifluction processes are due to a strong presence of water in the soils because of the strong precipitations (Hall K., 2002). The average air temperatures being above 0 C and the low altitude of the island give indications that permafrost could not form on Macquarie even though frost action is present. 27

28 Figure 6. The Macquarie island (source: Australian Antarctic Data Center, Map 13620) Figure 13. Figure 11. The Balleny islands (National Science Foundation, 2001) 28

29 6.2.2 Balleny islands Location Position from Antarctic convergence Number of island Surface / Area Altitude Temperature indication Precipitation indication Wind Landforms Permafrost S S, E E South 3 main & few other small 30 km long / 3-15 km wide Max m.a.s.l. <1 month positive per year Heavy Strong westerly & easterly No data Probable although not proven Three main islands are part of the Balleny Islands, surrounded by a few other small islands forming a chain (Fig. 11). Young, Buckle and Sturge are all approximately the same size, 30km long and from 3 to 15 km wide, depending on the island. The chain of islands is roughly 160 km long and is oriented north-west to south-east. They are all volcanic islands, believed to be still active as smoke and steam were seen on these islands. The islands are too far south to have any vegetation as they are only a couple of kilometers away from the Antarctic continent. Because of their steep cliffs, the islands are difficult to access by sea. Especially the northern part of the chain, as it is almost impossible to access by boat, because of the lack of beaches or flat land. Sturge island has a peak that culminates at m.a.s.l. called Brown Peak. In March 1998 the north-western part of the island witnessed an 8.1 magnitude earthquake, therefore pointing towards the presence of active volcanoes. A particularity of Balleny Islands is that it is at the junction of two opposing current and wind systems. To the north come strong westerly winds, and to the south polar easterly winds prevail. The two opposite wind directions influence the current surrounding the islands, creating extremely stormy weather from the meeting of opposite air and water masses. The islands are subject to heavy precipitations and frequent mist (Biswell, 2007). Being close to the eastern part of the Antarctic continent, the islands are exposed to extreme negative temperatures. The mean monthly temperatures are positive less than one month per year. It is exposed to the same climate as on the east coasts of the Antarctic continent (Riffenburgh, 2007). Although no research has published any data on the presence of permafrost, it is possible that it is present as the temperatures are below 0 C almost all year round and one of the islands has a high peak. 29

30 6.2.3 Scott island Location 67 24'S, 'W Position from Antarctic convergence South Number of island 1 Surface / Area 500 m. long / m. wide Altitude Haggits Pillar : 62 m.a.s.l. Temperature indication 2002: min C; max 1.6 C Precipitation indication Hypothesis: same as Balleny Wind Hypothesis: same as Balleny Landforms Ice covered Permafrost Probable since is ice covered Scott Island is a volcanic island located south of the Antarctic convergence, very close to the Antarctic continent, west to the the Balleny islands (Fig. 12). It is 500 m long and m wide. Very few expeditions have gone to the island, even though it is well known for its bird population. The island has many steep cliffs with a few cove and beaches on the northeastern and western coasts. More than half of the area above the cliffs is covered with ice, and the beaches are probably also ice-covered for most of the year, but they regularly get washed by high waves during storms. West of the island is Haggits Pillar, a sea stack, which culminates at 62 m.a.s.l. (Wilson & Harper, 1996). Because of its remote location and its difficulty to access, there are only little data available regarding the climate of the island. The Antarctic Meteorological Research Center archived climatic data for Scott island from the year 1980 to Two climatic stations have been installed on the island, the first one, Siple Dome, shows more extreme temperatures than the second one, Byrd, unfortunately no indication on the altitude is given. In 2002 at Siple Dome, for the maximum temperatures, only the two months of January and February were above 0 C, as for the minimum temperatures for the same year, the two months of June and July were the coldest, reaching -51 C (The Antarctic Meteorological Research Center, 2013). There is no indication on precipitations nor winds, but given the close location of the island to the Balleny islands, it is probable that they experience similar climatic conditions. This would mean that the Scott island is subject to strong winds and heavy precipitations. No data on permafrost has yet been published, but the climatic conditions are favorable for perennial ice. 30

31 Figure 14. Scott island and the Haggits Pillar (right) Rolf Stange Group 3 only contains Peter 1 st Island and Diego Ramirez Island, situated south of the South American coasts Peter 1st island Location S, W Position from Antarctic convergence South Number of island 1 Surface / Area 209 km 2 Altitude Peak: m.a.s.l. Temperature indication No data Precipitation indication No data Wind No data Landforms Ice covered Permafrost Probable since is ice covered 31

32 The island of Peter 1 st is situated opposite to Ellsworth Land, Antarctica. It is a 209 km 2 volcanic island, with a 100-meter-wide crater at the top. An extensive ice cover is present even during the summer months, making the island difficult to access (Global Volcanism Program, 2016). Peter 1 st has a few high mountains, the highest being Lars Christensentoppen that peaks at meters and is completely ice-covered (Fig. 13). The coastline is almost inaccessible by land, as it mostly consists of 40 m high steep cliffs. A few beaches can be accessed by sea, but the terrain is unstable and changes regularly due to cliff erosion, rockfalls and waves (Stange, 2014). There is no record of temperatures, precipitations, winds, nor permafrost for Peter 1 st island, but temperatures are probably below 0 C most of the year as it is located close to the Antarctic peninsula. Therefore, permafrost is probably present in the ice free areas of the island. Figure 15. Map of Peter 1st Island from the Norwegian Polar Institute as they spent a few days on the island in

33 6.3.2 Diego Ramirez islands Location S, W Position from Antarctic convergence North Number of island 2 main & other small ones Surface / Area 0.93 km 2 & 0.38 km 2 for main islands Altitude 190 m.a.s.l.; 140 m.a.s.l. Temperature indication Mean annual air temp.: 5.2 C Precipitation indication mm Wind No data Landforms No data Permafrost Unlikely The Diego Ramirez Archipelago is located 112 km southwest of the Cape Horn, in South America. The islands are very close to the Antarctic Polar Front, creating a favorable environment for fishes and birds to breed. The two biggest islands are Bartolomé Island which has an area of 0.93 km 2 and a peak at 190 m.a.s.l., and Gonzalo Island, 0.38 km 2, with the highest point at 140 m.a.s.l. (Arata & Xavier, 2003) (Fig. 14). Águila Islet, a small island part of the Diego Ramirez Archipelago is, as most people ignore, the most southern point of South America (Nolan, 2014). The mean annual air temperature on the islands are 5.2 C, the warmest month being February with an average temperature of 7.5 C, and the coldest month is July, with an average of 3.2 C. Annual precipitations are mm, which indicate heavy precipitations in form of rain and snow. The heaviest precipitations are during the months of February, March and April (ClimaTemps, 2015). There is no scientific information available on the force or direction of winds on the islands, but being located between Cape Horn and the Antarctic peninsula where strong winds prevail, there is a high probability that the islands are subject to strong winds. Furthermore, no data is available on periglacial landforms nor on permafrost. Looking at the mean annual air temperature -being above 0 C- and the altitudes being low-, it is very unlikely to find permafrost on the islands. Figure 16. The Diego Ramirez Islands (Wikipedia :public domaine) 33

34 Group 4 assembles South Georgia islands, South Sandwich islands and Bouvet island South Georgia islands Location S, W Position from Antarctic convergence South Number of island 1 main & other small Surface / Area 160 km long, 5-30 km wide Altitude Peak: m.a.s.l. Temperature indication Mean annual air temp.: 1.7 C Precipitation indication Mean annual: 1395 mm. Wind Westerly wind Landforms Permafrost Cirques & ice covered Probable at high elevations on the western part of the island South Georgia islands, located south of the Antarctic convergence, is a British oversea territory and the largest island on the Scotia arc (island forming an arc system in the Scotia sea) (Fig. 14). It is home to a central mountain range which has a west-north-west to eastsouth-east direction. The plateau summit of Mount Paget is the highest of the mountainous chain, peaking at m.a.s.l. The islands have been eroded by glaciers and sea action, shortening the coastlines of weak bedrock and exposing steep sea cliffs. The climate is directly influenced by the position of the islands within the sub-antarctic cyclonic zone. The mean annual air temperature is 1.7 C and the mean annual precipitation is 1395 mm (Clapperton, 1971). Because of the topography of the islands, the orographic effect is strong, which creates frequent rain and snowfall. A Föhn effect on the east side of the island prevents it from becoming glaciated. The western part of the island is extensively covered in ice, with a cover reaching 58% of the area of the island (Fig. 15). Cumberland bay is a glacier valley on the northern coast of the island, which presents an impressive amount of glacier cirques. Above 800 meters high, most cirques contain glaciers. Georgia Island is a great study site for glacial, periglacial and marine processes and landforms (Clapperton, 1971). Since the main island presents a very high plateau summit, temperatures at high elevations are below 0 C most of the year. These conditions indicate that permafrost could form in the non-glaciated areas of the island, at high elevations. 34

35 Figure 17. The Scotia Arc (source: National Oceanic and Atmospheric Administration) Figure 18. South Georgia and the South Sandwich islands (source: Ian Macky for the open source portable atlas, 2015) 35

36 6.4.2 South Sandwich islands Location S, W Position from Antarctic convergence South Number of island 11 Surface / Area Biggest: 10 km by 12 km Altitude Mount Belinda Peak: m.a.s.l. Temperature indication No data Precipitation indication No data Wind Westerly wind Landforms Ice covered Permafrost Probable in ice free areas with no volcanic activity South Sandwich, situated south of the Antarctic convergence, is a volcanic arc of 11 small uninhabited islands (Fig. 16). They lie between S and W, east of the Scotia sea, close to the South Georgia islands. They are approximately km north from the Antarctic continent. The South Sandwich islands are recent volcanic islands still very active as fumaroles have regularly been seen (Bonner & Walton, 1985 ; Patrick, et al., 2005). There has nevertheless been a decrease of heat emission in the islands, observed with the loss of heat-associated plants (Convey, Lewis Smith, Hodgson, & Peat, 2000). The neighboring location to the South Georgia islands indicate they are exposed to the same maritime climatic conditions. Montagu Island is the largest of all the islands measuring approximately 10 km by 12 km (Patrick, et al., 2005). Mount Belinda peaks at m.a.s.l. and is a small summit caldera (volcanic crater formed by the collapse of the empty central magma chamber) which is filled with permanent ice. The depth of the ice extent on Mount Belinda is unknown, as the island is difficult to access 90% of the island is covered in ice, and the remaining 10% of exposed rocks mainly consist of vertical sea cliffs- resulting in only few researches (Patrick, et al., 2005). No scientific data is available for the mean annual air temperatures and mean annual precipitations, but the islands being located south of the Antarctic convergence in addition to being south of the South Georgia islands, indicate that temperatures are likely to be below 0 C most of the year. The island could have permafrost in the ice-free areas where there is no heat emission from the residual volcanic activity. 36

37 6.4.3 Bouvet island Location S, 3 21 E Position from Antarctic convergence South Number of island 1 Surface / Area 9.5 km long / 7 km wide Altitude 780 m.a.s.l. Temperature indication MAAT range at sea level -2.7 C / -1.6 C Precipitation indication Frequent Wind Westerly Landforms Diurnal frost Permafrost Probable since ice covered Bouvet island, an uninhabited Norwegian island (Atlas Obscura, 2016), is situated 500 kilometers south of the Antarctic convergence (Hall K., 2002) and km south-west of the coasts of South Africa (Huyser, 2001). It is a 9.5 km long and 7 km wide volcanic island (Huyser, 2001) very difficult to access due to its steep glacial cliffs (Atlas Obscura, 2016). Because of its particularly southern location, 93% of the island is covered in ice (Fig. 16) and has almost no vegetation except for fungi and lichens. The mean annual air temperature range at sea level is between -2.7 C and -1.6 C, the islands is therefore exposed to a polar maritime climate, which is characterized by small daily and seasonal temperature variations (Huyser, 2001) and westerly winds. The island rises to 780 m.a.s.l., but its surface is very irregular (Huyser, 2001). The main periglacial process on the island is diurnal frost action (Hall K., 2002). The cold temperatures and the climatic conditions of the island indicate that permafrost could form on the island in the non-glaciated areas. Although in 1978, a temperature of 25 C was measured only 30 cm below the surface because of remaining emission of volcanic gases (Norwegian Polar Institute, 2016). There is no available information indicating if emissions of gases are still active nowadays, and if they have an impact on the development of permafrost on the island, but it is probable that permafrost is present on the island. 37

38 Figure 19. Picture of a glacier on Bouvet island (source: François Guerraz, 2011) Figure 20. The Bouvet island (Norwegian Polar Institute, 2011) 38

39 6 Discussion During the Last Glacial Maximum the whole sub-antarctic region was subject to glaciations as periglacial signs show on many islands (Bonner & Walton, 1985). Frost action processes are still present on all of the islands located north of the Antarctic convergence, with the presence of sorted stripes and sorted polygons on most of them. Both diurnal and seasonal frost action processes are present, as they are exposed to oceanic climates, but are as well influenced by cold winds from the Antarctic region. High precipitations and frequent cloud cover result in a high frequency of short freeze-thaw cycles (Boelhouwers, 2003) All the islands of the sub-antarctic region lie either within or close to the Antarctic Convergence. The Balleny, Scott, Peter 1 st, South Georgia, Bouvet and the South Sandwich islands, are all within the Antarctic convergence zone, subject to cold temperatures, strong westerly winds and frequent snowfall. They all have permanent ice caps and/or snowfields, even though the South Sandwich, Kerguelen, Heard and McDonald and Bouvet islands are still part of active volcanic regions (Bonner & Walton, 1985). Kerguelen is located on the convergence zone, making it limited in glaciated superficies. Macquarie, Crozet, Diego Ramirez and Marion/ Prince Edward islands show no glacier nor permanent snowfields, as they all lie north of the Antarctic convergence and are subject to milder temperatures. Local climates are directly influenced by the amount of ice and snow cover, which are therefore influenced by the topography of the islands. Bouvet, Peter 1 st and Heard have severe climates, with very strong winds and precipitations. The Heard and McDonald islands have cold and short summers, followed by long and very cold winters due to its southern position, in proximity to the Antarctic continent. On the other hand Macquarie island has cool and long summers and mild winter temperatures (Bonner & Walton, 1985). Scott island has the coldest air temperature of all the islands, reaching C in 2002 (The Antarctic Meteorological Research Center, 2013). Only three out of the twelve researched islands have scientific information on permafrost presence. Marion island has permafrost at high altitude, mainly above m.a.s.l. (Hall K., 2002). Crozet has no permafrost as it is often exposed to temperatures above 0 C and has no high peak like Marion island. As for Heard and McDonald islands, they don t have 39

40 permafrost either since the volcanic activity on McDonald prevents ice from accumulating, and the ice cap on Heard is where permafrost could have occurred (Hambrey, et al., 2013). The other nine islands show enough information on air temperatures, precipitations and topography to estimate the presence and distribution of permafrost. Most of the islands located south of the Antarctic convergence are estimated to have permafrost, due to the cold air temperatures they are exposed to, and the ice covers that are present on the islands. Only Heard and McDonald islands are situated south of the convergence and are proven not to have permafrost (Hambrey, et al., 2013). Kerguelen, Balleny and South Georgia islands are estimated to have permafrost at high elevations, on the basis of Marion island, namely above m.a.s.l. This estimation is based on the fact that there is a loss of 5 C to 10 C for each 1000 meters up in altitude, as for when air rises it cools down (depending on the adiabatic gradient: the moist adiabatic cooling rate has a lesser value as condensation prevents the air from cooling rapidly; the dry adiabatic gradient has a value of 10 C per 1000 m.) (Strahler, 2011). The mean annual air temperatures are usually measured at sea level or slightly above, therefore, Kerguelen can have permafrost above m.a.s.l as the islands show a MAAT of 4.6 C and an elevation of m.a.s.l. (Hall K., 2002). Pure scientific data is difficult to to find for such remote islands, as most of them are difficult to access and do not have scientific bases. Aside from the information on the presence of permafrost, a lot of remote islands show missing data on temperature, precipitation and wind. In particular, for the islands that are extensively ice covered and therefore difficult to access. Scott island has no data for precipitation and wind, the South Sandwich islands have no data for temperature and precipitation, and Peter 1 st has no data for temperature, precipitation and wind (fig. 21). As they are ice covered, it is estimated that permafrost is present on the ice-free areas of the islands, but it makes it difficult to estimate the the extent of permafrost. Furthermore, there is only little information on the presence of glaciers, in particular on the type of glacier. As explained above, cold based glaciers are a good indication for the presence of permafrost in the ground. Nevertheless, the number of research on past and present periglacial processes and landforms in the continental and maritime Antarctica have been increasing in the past years (Hauck, Vieira, Gruber, Blanco, & Ramos, 2007). The missing data for each individual island is stated below in figure 21, creating a state of the art for further researches. 40

41 Figure 21. The available data for the position to the Antarctic convergence, the altitude, the temperature, precipitations, wind and permafrost for the twelve researched sub-antarctic islands 41