Climate warming and permafrost dynamics in the Antarctic Peninsula region J. Bockheim a, ⁎, G. Vieira b , M. Ramos c , J. López-Martínez d , E. Serrano e , M. Guglielmin f , K. Wilhelm a , A. Nieuwendam b a Department of Soil Science, University of Wisconsin, Madison, WI 53706-1299, USA b Center of Geographic Studies, IGOT, University of Lisbon, Lisbon, Portugal c Department of Physics, University of Alcalá, Madrid, Spain d Departamento Geología y Geoquímica, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain e Departamento Geografía, Universidad de Valladolid, 47011 Valladolid, Spain f Department of Theoretical & Applied Science, Insubria University, Varese, Italy abstract article info Article history: Received 11 June 2012 Accepted 25 October 2012 Available online 2 November 2012 Keywords: Permafrost Active-layer Ground surface temperature Boreholes Temperature gradient Periglacial features Dramatic warming of the climate over the last several decades has influenced the properties and distribution of permafrost in the Antarctic Peninsula region. Five approaches were used to estimate the distribution of permafrost in the region: (1) correlation of permafrost distribution with mean annual air temperature iso- therms, (2) mapping the distribution of periglacial features indicative of permafrost, (3) summarizing data from shallow excavations and boreholes, (4) detection of permafrost from geophysical techniques, and (5) application of models to predict the occurrence of permafrost. Whereas permafrost is continuous in the South Orkney Islands (60–61° S) and along the eastern Antarctic Peninsula (63–65° S), it is discontinuous in the South Shetland Islands (62–63° S), and occurs only sporadically in the Palmer Archipelago and Biscoe Islands along the western Antarctic Peninsula (64–66° S). Permafrost then becomes continuous on Alexander Island (71–74° S) along the western Antarctic Peninsula as the maritime climate shifts to a more continental climate. Reports prior to 1980 mention the presence of permafrost at depths of 25 to 35 cm in ice-free areas near Palmer Station (64°46′ S; 64°04′ W), where the mean annual air temperature from extrapolation of data from the nearby Vernadsky Station has increased 3.4 °C and the mean winter temperature has increased 6 °C since 1950. Recent measurements suggest that permafrost is absent or close to 0 °C in the upper 14 m of the highest ice-free areas (67 m a.s.l.) near Palmer Station. Permafrost temperatures elsewhere along the western Antarctic Peninsula region range from -0.4 to -1.8 °C in the South Shetland Islands (62–63° S) to -3.1 °C at Adelaide Island (67°34′ S). Permafrost at this temperature is susceptible to thawing, which has resulted in historic increases in active-layer thicknesses and in thermokarst features such as debris flows, and active-layer detachment slides. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Permafrost (permanently frozen ground) underlies 22 million km 2 , approximately 17% of the global land area (Gruber, 2012). Permafrost is most extensive in the circumarctic, but also exists on the Central Asian Plateau and in ice-free areas of Antarctica. Permafrost warming has been measured in recent decades in various boreholes in North America (Smith et al., 2010), Russia (Romanovsky et al., 2010) and Northern Europe (Christiansen et al., 2010), but very little is known about trends in Antarctica, including the Antarctic Peninsula region. Along the west- ern Antarctic Peninsula (WAP), the mean annual air temperature has increased as much as 3.4 °C and the mid-winter temperature has increased 6.0 °C over the past 50 yr, making the region one of the world's climate warming “hotspots” (Vaughan et al., 2003; Turner et al., 2005, 2009). These changes in climate are related to shifts of the Antarctic Circumpolar Current to the south (Böning et al., 2008) and have resulted in a 40% decrease in sea-ice coverage in the Bellingshausen Sea (Ducklow et al., 2008; Stammerjohn et al., 2008) and disintegration of ice shelves along both the eastern and western Antarctic Peninsula (Cook and Vaughan, 2010). Permafrost properties and seasonal thaw-layer (active-layer) dynamics are two key indicators of climate change in the polar region (Anisimov et al., 1997; Burgess et al., 2000). However, the distribu- tion and properties of permafrost and active-layer dynamics in the Antarctic Peninsula region are poorly understood. Early reports of permafrost in this region arise from the study of periglacial features (e.g., Corte and Somoza, 1954), vegetation (e.g., Smith, 1982), and soils (e.g., Holdgate et al., 1967). Bockheim (1995) prepared the first permafrost map of Antarctica, proposing that continuous and discontinuous permafrost boundaries correspond to mean annual air temperature isopleths of -8 °C and Global and Planetary Change 100 (2013) 215–223 ⁎ Corresponding author. E-mail address: bockheim@wisc.edu (J. Bockheim). 0921-8181/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gloplacha.2012.10.018 Contents lists available at SciVerse ScienceDirect Global and Planetary Change journal homepage: www.elsevier.com/locate/gloplacha