PERMAFROST AND PERIGLACIAL PROCESSES Permafrost and Periglac. Process. (2015) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/ppp.1871 Short Communication Effect of Snow Cover on the Active-Layer Thermal Regime – A Case Study from James Ross Island, Antarctic Peninsula Filip Hrbáček,1* Kamil Láska1 and Zbyněk Engel2 1 Masaryk University, Faculty of Science, Department of Geography, Brno, Czech Republic 2 Charles University in Prague, Department of Physical Geography and Geoecology, Praha, Czech Republic ABSTRACT The response of active-layer thickness and the ground thermal regime to climatic conditions on the Ulu Peninsula (James Ross Island, northeastern Antarctic Peninsula) in 2011–13 is presented. The mean air temperature over this period was –8.0°C and ground temperature at 5 cm depth varied from –6.4°C (2011–12) to –6.7°C (2012–13). The active-layer thickness ranged between 58 cm (January 2012) and 52 cm (February 2013). Correlation analyses indi- cate that air temperature affects ground temperature more significantly on snow-free days (R2 = 0.82) than on snow cover days (R2 = 0.53). Although the effect of snow cover on the daily amplitude of ground temperature was observ- able to 20 cm depth, the overall influence of snow depth on ground temperature was negligible (freezing n-factor of 0.95–0.97). Copyright © 2015 John Wiley & Sons, Ltd. KEY WORDS: active-layer; ground temperature; snow cover; air temperature; Antarctic Peninsula; active layer thickness INTRODUCTION et al., 2014). In this paper, we evaluate the effect of air tem- perature and snow cover on active-layer temperature in the The Antarctic Peninsula (AP) has experienced the largest northern part of James Ross Island (JRI) from March 2011 atmospheric warming of all regions on Earth over the last to April 2013, one of the largest permafrost regions in the 50 years (Turner et al., 2002), with the temperature increase northeastern AP. accelerating downwasting of ice sheets on the AP (Vaughan, 2006) and causing the collapse of ice shelves along its eastern coast (Cook and Vaughan, 2010). The response of regional REGIONAL SETTINGS permafrost to this warming remains unknown and represents one of the most important topics in climate modelling, The study site (63°48′S 57°52′W) is located in the Ulu because numerical models suggest that permafrost may Peninsula, northern JRI (Figure 1), approximately 100 m become the dominant contributor of CO2 and CH4 into the south of the Johann Gregor Mendel Station at 10 m asl. atmosphere in the 21st century (Schaefer et al., 2011). Glaciers started to retreat from the Ulu Peninsula before Despite the increasing number of periglacial studies focusing 12.9 ka (Nývlt et al., 2014), leaving low-lying areas ice-free on the AP in the last decade (Vieira et al., 2010; Guglielmin at the beginning of the Holocene. At present, small glaciers et al., 2014; Bockheim et al., 2013; De Pablo et al., 2014; persist only on high-altitude volcanic plateaus and in valley Almeida et al., 2014; Goyanes et al., 2014), thermal condi- heads (Engel et al., 2012). Permafrost in the northern part of tions in the active layer and its interaction with meteorologi- JRI can approach 95 m in thickness and the ALT is highly var- cal factors are not well known. In particular, the influence of iable, ranging from 22 to 150 cm (Borzotta and Trombotto, snow on active-layer thickness (ALT) and the thermal regime 2004; Engel et al., 2010; Bockheim et al., 2013). The study is relatively poorly understood, despite being a major modu- site is located on a Holocene marine terrace (Figure 2) lating factor to the atmosphere (Boike et al., 2008; Vieira formed by beach deposits composed of gravelly sand (Stachoň et al., 2014). *Correspondence to: F. Hrbáček, Masaryk University, Faculty of The climate of JRI is dominated by the advection of air Science, Department of Geography, Kotlářská 2, 611 37 Brno, Czech masses, which are strongly influenced by the position of Republic. E-mail: hrbacekfi[email protected] the AP relative to the circumpolar trough of low pressure Received 11 September 2014 Revised 31 July 2015 Copyright © 2015 John Wiley & Sons, Ltd. Accepted 5 August 2015 F. Hrbáček et al. Figure 1 Location of the study site in the northern part of James Ross Island, close to the eastern coast of the Antarctic Peninsula. Figure 2 (A) Detailed view of the study site and (B, C) its geomorphological position on the northern coast of the Ulu Peninsula. The red arrow marks the study site near Mendel Station. This figure is available in colour online at wileyonlinelibrary.com/journal/ppp (Domack et al., 2003). A complex orography causes fre- long-term observations on the northern AP, the temperature quent variation between two main advection patterns: (1) was 0.2°C colder in 2011–13 than over the reference period cold and dry southerly winds blowing along the eastern of 1961–2000, with a MAAT of –5.2°C (Turner et al., coast of the AP, and (2) westerly winds bringing relatively 2004). Precipitation is mostly snow and estimated to range warm maritime air masses across the peninsula to northern from 300 to 500 mm water equivalent per year (Van Lipzig JRI (King et al., 2003; Zvěřina et al., 2014). The mean an- et al., 2004). nual air temperature (MAAT) at Mendel Station is –6.8°C (2006–11) and the extremes of mean daily air temperatures vary between around 8°C in January and –30°C in METHODS July/August (Láska et al., 2012). Mean daily temperatures above 0°C typically occur only for 2 months each summer Temperature in the active layer was measured at depths of 5, (December–January), with hourly maximum and minimum 10, 20, 30, 50 and 75 cm using Pt100/Class A platinum re- values of 10°C and –5°C, respectively (Láska et al., 2011). sistance thermometers (EMS, Brno, Czech Republic). Air According to data from Esperanza, the nearest station making temperature was measured 2 m above ground level using Copyright © 2015 John Wiley & Sons, Ltd. Permafrost and Periglac. Process., (2015) Active Layer Monitoring on James Ross Island an EMS33 sensor (EMS Brno) with a Pt100/Class A plati- RESULTS num resistance thermometer placed inside a solar radiation shield. Both ground and air temperatures were measured Air and Ground Temperatures with an accuracy of ± 0.15°C and data were recorded at 30 min intervals with an EdgeBox V12 datalogger (EMS The MAAT over the whole 2 year study period was –8.0°C; Brno). We then calculated mean daily air temperatures, the although the individual MAAT values for the 2 years were cumulative sum of mean daily air temperatures above 0°C equal, the temperature range differed from 44.0°C (2011– – (the thawing-degree days – TDDa) and the cumulative 12) to 42.3°C (2012 13). The larger temperature extreme sum of mean daily air temperatures below 0°C (the in 2011–12 was documented by a lower mean temperature – freezing-degree days – FDDa), according to Guglielmin of the coldest month (July 2011, 18.5°C) and a higher et al. (2008) and De Pablo et al. (2014). Incoming and mean temperature of the warmest month (December 2011, reflected shortwave radiation (used to estimate albedo) were 2.0°C) compared to those for 2012–13 (–15.0°C and 0.2° measured using EMS-11 (EMS Brno) and CM6B (Kipp & C, respectively). The maximum air temperature recorded Zonen, Delft, The Netherlands) pyranometers, respectively, during the entire study period was 11.6°C on 23 February at 10 s time intervals and stored as 30 min average values. 2013; the minimum recorded was –34.1°C on 26 July 2011. Snow depth was recorded every 2 h using an ultrasonic depth The MAGT at 5 cm depth was –6.4°C in 2011–12 and – sensor (Judd Communication, Salt Lake City, UT, USA) 6.7°C in 2012–13. The mean monthly ground temperature with an accuracy of ± 1 cm. All meteorological parameters at 5 cm depth varied between –16.3°C (July 2011) and – and ground temperature data were analysed during the period 6.1°C (December 2011). Minimum ( 26.3°C) and maxi- from 1 March 2011 to 30 April 2013. MAAT and mean mum (16.0°C) 5 cm ground temperatures over the study annual ground temperature (MAGT) were also calculated period were recorded on 1 August 2011 and 18 December for a period of 2 years from March 2011 to February 2013, 2012, respectively. The MAGT at 50 cm depth, which rep- referred to in the text as the 2011–12 and 2012–13 periods. resents active-layer conditions close to the permafrost table, – – – – The ground thermal regime for the period of 2011–13 was ranged between 6.1°C in 2011 12 and 6.0°C in 2012 13. – evaluated in accordance with recent studies investigating Minimum ( 16.3°C) and maximum (1.3°C) ground temper- Maritime Antarctic (Guglielmin et al., 2008; Michel et al., atures at 50 cm were recorded on 5 August 2011 and 26 2012; De Pablo et al., 2014), using the following parameters: January 2012, respectively. The MAGT at 75 cm depth, which represents the uppermost part of the permafrost zone, (1) mean annual and monthly ground temperatures; (2) the cu- – mulative sum of mean daily ground temperatures above 0°C reached 5.8°C, while maximum and minimum tempera- tures for the greatest depth were –1.0°C and –14.4°C, (the thawing-degree days – TDDg); (3) the cumulative sum of mean daily ground temperatures below 0°C (the freezing- respectively.