Towards an Antarctic Active Layer and Permafrost Monitoring Network

Towards an Antarctic active layer and permafrost monitoring network

M. Guglielmin ArpaLombardia, Milan, Italy M. Balks Department of Earth Sciences, University of Waikato, Hamilton, New Zealand R. Paetzold Natural Resource Conservation Service, United States Department of Agriculture, Lincoln, Nebraska, USA

ABSTRACT: This paper is the first step to create a coordinated program for active layer monitoring in Antarctica as instigated by several international panels and programs (GCOS, IGBP). Actually 7 sites located along a latitu- dinal transect in Victoria Land between 77°55S and 74°26S are monitored. At all the sites ground temperatures at depths to 7.8 m and some climatic parameters (e.g. air temperature, incoming radiation), are all year round recorded using dataloggers. The climatic significance of GST in four selected sites (Scott Base, Bull Pass, Boulder Clay and Simpson Crags) is illustrated. The active layer thickness shows a large variability both in space and in time. The southern sites show an active layer thicker (ranging between 22 and 55 cm) than the northern ones (17–39 cm) despite of a warmer GST in the last. This difference can be explained with the higher ice content of the northern sites.

1 INTRODUCTION the main research stations. All the sites were chosen following pedological, geophysical and/or geomor- The thermal state of the active layer and permafrost phological study (Guglielmin et al., 1997a). The sites are key indicators of climate change within the cryo- of Mount Keinath and Oasi are both located on granitic sphere and several international panels and programs outcrops and differ from the other sites, which are char- (GCOS, IGBP, GTN-P) endeavour to monitor these acterized by till deposits. CALM grids of 100 m (121 parameters. The IPA has instigated the Circumpolar measurements points) at Boulder Clay and Simpson Active Layer Monitoring (CALM) program that, until Crags were established in 1998 to monitor the active now, has mainly developed in the Arctic. This paper is layer thickness. Permafrost is continuous in all the the first step to create a coordinated program for sites with a thickness of several hundred meters and a active layer monitoring in Antarctica. Also the impor- ZAA (zero annual amplitude) approximately around tant biological project “Regional Sensitivity to Climate 11 m at Boulder Clay (French and Guglielmin, 2000). Change in Antarctic Terrestrial and Limnetic Ecosys- The ice content within the permafrost is variable. In the tems” (RiSCC) looks forward to integrating its bio- Northern Victoria Land the ice-free areas are mainly logical data with the abiotic data of this project. characterized by massive ice bodies of different ori- In this paper we present the results of the first years gins (Gragnani et al., 1998; Guglielmin et al., 2001) of active layer and near permafrost thermal monitoring. such as at the sites of Boulder Clay and Simpson Crags We also illustrate the methodologic problems related to or ice-rich and ice-bonded permafrost along the raised the active layer monitoring that occurs in Antarctica. beaches and within the older till. The gravimetric moisture content of the active layer of soils in Southern Victoria Land is typically between 2 STUDY AREAS 1 and 10% (Campbell et al., 1994, 1997). There is some seasonal variability at sites where snow-melt has been The study sites are all located in Victoria Land shown to result in an increase in soil moisture content (Antarctica) between 77°50S and 74°44S at altitudes to values of up to 15% for short periods (up to 14 days, ranging from 38 to 1100 m a.s.l. The sites include a Campbell et al., 1997). Within the underlying per- range of geographical, geomorphological, geological mafrost in coastal areas, moisture contents are variable and pedological characteristics (Table 1). The choice ranging from lenses of ice (100% moisture), to mois- of the sites was influenced by the availability of logis- ture contents of 10%, with an average of about tical facilities with Scott Base, Boulder Clay and Oasi 40% (Campbell et al., 1998). In dry inland areas, such adjacent to New Zealand, or Italian Antarctic stations. as the Wright Valley, soil moisture contents, in both The Marble Point, Bull Pass, Mount Keinath and the permafrost and the active layer, are generally less Simpson Crags sites are accessible by helicopter from than 10%.

337 Table 1. Geographical, geomorphological, geological and pedological characteristics of the different sites.

Elevation Geomorphologic Station Coordinates (m a.s.l.) Slope (°) Aspect location Lithology Soil

Scott Base 77°51S 38 6 SE Mid-slope on side of Basalt scoria Hypergelic 166°46E basalt scoria cone dominated till Typic over scoriacious Anhyorthel basalt bedrock Marble Point 77°25S 50 3 S Midslope of a gently Marble dominated Hypergelic 163°41E sloping till/outwash till with granite, Calcic surface dolerite, sandstone, Anhyorthel and gneiss Bull Pass 77°31S 152 3 S Colluvial fan of Granite dominated Hygergillic 161°52E till material. till with dolerite and Nitric sandstone present Anhyorthel Boulder Clay 74°45S 205 5 SE Midslope of a Granite dominated n.a. 164°01E gently sloping till till with dolerite and gneiss Simpson Crags 74°26S 830 6 SE Midslope of a Granite dominated n.a. 162°53E gently sloping till till with gneiss within glacial cirque Mount Keinath 74°33S 1100 3 SW Top of mountain peak Deeply weathered n.a. 163°59E granitic outcrop

In Northern Victoria Land the climate is generally dry Campbell Scientific Incorporated (CSI), Logan, Utah) with snow precipitation of 270 mm/year water equiva- was installed at each site with sensors to record air lent and strong winds, predominantly from the west temperature, relative humidity, solar radiation, and with speeds of over 30 Km/hour recorded for almost a wind speed and direction. Thermistor temperature third of the year. At the sites investigated in Southern probes (Campbell107, CSI) and Vitel moisture probes Victoria Land the climate is generally less windy with (hydra type A, Stevens Vitel Inc, Chantilly, Virginia) lower precipitation than the sites further north. The Bull were installed at depths of 2 cm to 1.2 m. Measurements Pass site is subject to diurnal katabatic winds in summer of atmospheric variables were made at 10 second inter- except for storm events is relatively calm in winter. vals. Soil variables were measured every 15 minutes. All measurements were averaged and recorded hourly with data down-loaded annually. 3 METHODS In this paper we used the data of the two more sur- ficial depths (2 cm, 30 cm) that there are at four sites Data collection at all the sites included solar radiation (Scott Base; Bull Pass; Boulder Clay, and Simpson (pyranometer) and air temperature. Some sites are Crags). The sensors are placed directly in the soil par- better equipped to monitor other climatic elements allel to the ground surface. including wind speed and direction, net radiation, snow In this paper we used the continuous records of height, and long and short wave radiation. In Northern thermal data to determine the 0°C isotherm in the dif- Victoria Land the ground thermal regime is moni- ferent sites. Three methods to determine the active layer tored with thermometers (MTX LTN , with accuracy thickness were used. of 0.15°C) installed at different depths to 7.8 m. The First, the active layer thickness was obtained by the ground temperatures are measured every 10 minutes graphical interception of the curve of the annual max- with the minimum, maximum and average values imum temperature at each depth with the 0°C axes. recorded by datalogger (MTX) every 60 minutes at Second, the active layer was determined as the greater the Boulder Clay Glacier, Mount Keinath and Oasi depth reached by interpolation (using a triangulation sites and every 90 minutes at Simpson Crags. At Oasi with a linear interpolation algorithm) of the all monthly a borehole of 15.5 m deep is monitored with a string of maximum temperatures at each depth, and thirdly 16 thermistors (LTN 0.1°C of accuracy) at the depths using the Gold & Lachenbruch (1973) equation: of 0.02; 0.3, 0.6; 1.6; 2.6; 3.6; 5; 7.6; 10; 11; 12; 13; 14; 14.5; 15; 15.5 m. Al apPln|A/T|/ 00 The soil climate stations in Southern Victoria Land were established in undisturbed areas typical of the where A0 and T0 are respectively the annual amplitude surrounding terrain and soils. A data-logger (CR10X, and average of the ground surface temperature (here

338 we used the 2 cm data as representative of surface and Boulder Clay sites. If we consider only the sum- condition); P is 1 year and (a) is the thermal diffusivity mer period of 1999 (1 January–30 March, then a linear computed according the equation correlation between the mean daily GST and air temperature is evident. The linear regressions between mean K {p/P [(z z )/ln (A /A )]}2 2 1 1 2 daily GST and air temperature for the summer period have a higher R2 especially at Scott Base and Simpson where z2 and z1 are respectively the depths of 30 and Crags (Table 2). 2 cm and A1/A2 are the amplitude of the temperature at these depths. The linear regressions between incoming radiation and mean daily GST are not as good (Table 2) and only at Bull Pass is the R2 is higher than 0.8. If we consider 4 RESULTS the hourly data there is a much stronger correlation with incoming solar in the summer, especially in the The daily mean air temperature and daily mean ground Southern Victoria Land. surface temperature (GST 2 cm) measured during If we compare the linear regressions between mean 1999 shows a direct relationship between the two daily GST and air temperature all year round, and only parameters at all the sites (Figures 1a and b) with an for the summer, we can see that during the winter R2 greater than 0.8 and higher R2 values at the Bull Pass there is some disturbance especially at Scott Base and Simpson Crags. During the winter in all the stations

20 and all the years there are several climatic episodes of sudden warming of the air temperature (and also of the 10 GST) that in the literature are known as the “Coreless 0 Winter”. During the winter, (1 April–30 September) at -10 Scott Base and Simpson Crags, mean daily GST, air

-20 temperature and wind speed indicate that many air- warming events occur with very low wind speeds -30 (Figure 2). There were three episodes in Simpson Crags -40 and 5 episodes at Scott Base where high wind speed -50 a corresponded to increasing air temperature. Moreover -60 BP SC BC SM the GST sometimes shows a reverse trend at both the sites (e.g. see the episodes of 8 and 16/08 of Scott base) where an increase in wind speed corresponded BP 2 cm SC 2 cm BC 2 cm SM 2 cm with a decrease in air temperature. At Simpson Crags 20 it is also remarkable that the GST between the 7 June 10 and 11 July remained almost stable although at least 0 two strong warm air events (19/06 and 3/07) occurred. -10 This may be attributable to the insulating effect of -20 snow cover. At all the times in which the wind speed -30 exceeds 10 m/s, and there is increasing air temperature -40 and GST, the average wind direction at both the sites is from the south or south-east and not from inland. -50 b Figure 3 shows the trend of mean daily air tempera- -60 ture (a) and GST (b) for 1999–2001 at Scott Base and Figure 1. Mean daily temperature of air (a) and ground Boulder Clay. In this figure it is clear that the air tem- surface (2 cm) (b) for the stations of Scott Base, Bull perature is substantially stable while the GST shows a Pass, Boulder Clay and Simpson Crags for 1999. pronounced decrease during the summer 2000.

Table 2. Linear regressions between daily mean GST and air temperature for the stations of Scott Base, Bull Pass, Boulder Clay and Simpson Crags for the entire 1999 (a) and summer 1999 (b). The column c shows the linear regressions between daily mean GST and incoming radiation.

Stations a b c

Scott base y 1.15x 4.08 r2 0.89 y 1.15x 5.91 r2 0.94 y 0.09x 22.03 r2 0.80 Bull Pass y 1.13x 2.40 r2 0.96 y 1.13x 4.01 r2 0.98 y 0.15x 32.00 r2 0.84 Boulder Clay y 0.96x 1.86 r2 0.97 y 0.93x 0.54 r2 0.98 y 0.06x 16.85 r2 0.45 Simpson Crags y 1.16x 3.30 r2 0.84 y 1.19x 6.86 r2 0.95 y 0.06x 15.81 r2 0.67

339 30

20 Ϫ10 10 Ϫ 0 20 -10 Ϫ30 -20

-30 Ϫ40 -40 Ϫ -50 air temp SC Air temp SM 50 SC 2 cm SM 2 cm Ϫ60 Figure 2. Comparison between wind speed and air and 61218243036 ground surface (2 cm) temperature (°C) for the winter 1999 at Scott Base (SC) and Simpson Crags (SM). The upper Figure 4. Thermal regime at Scott Base between part of the plot shows the wind speed (m/s) of Scott Base 1/01/1999 and 31/12/2001. For the legend of the tempera- (dashed line) and Simpson Crags (solid line). The lower ture (°C) interpolations see Figure 5. part of the plot shows the air and 2 cm ground temperature.

20 Ϫ10 10 0 Ϫ20 -10 Ϫ30 -20 -30 Ϫ40 -40 -50 Ϫ a 50

Ϫ60 20 61218243036 10 Ϫ28Ϫ24 Ϫ20 Ϫ16Ϫ12 Ϫ8 Ϫ4048 0

-10 Figure 5. Thermal regime at Boulder Clay between 1/01/1999 and 31/12/2001. Note that in the summer -20 2000–2001 the surface (2 cm) was not above 0°C. -30 -40 radiation can play an important role. It is also clear -50 b that the greater differences between GST and air temperature occur during the winter. These differences can Figure 3. Mean daily temperature of air (a) and ground be related to the effect of the snow cover (Guglielmin & surface (2 cm) (b) for Scott Base (grey thick line) and Dramis, 1999) as, for example, in the case of Simpson Boulder Clay (black thin line) for the period 1/01/1999– 31/12/2001. Note that the marks on the x axes are every 4 Crags during the period between 7 June and 11 July months. 1999. Most of the air warming episodes that occur in the winter could be related to storms that come from the sea accompanied by relatively strong, warm, Figures 4 and 5 summarize the thermal regimes of winds and snow fall. Within the active layer there are Scott Base and Boulder Clay using the method of some comments to do about the different results of the interpolation of the mean monthly maximum temper- processing of the data. The accuracy of the three ature at different depths (using the algorithm of trian- methods depends firstly on the number of sensors gulation with linear interpolation) respectively. placed in the ground, in fact the thermal gradients and the thermal diffusivity can change strongly above all 5 DISCUSSION in the first 10–20 cm. The differences between the three method of data processing (Table 3) show that, in The results illustrated demonstrate clearly that the general, the method of Gold & Lachenbruch (1973) mean daily GST is related to the air temperature even overestimated the depth of the 0°C isotherm compared if during the summer in some places the incoming to the depth calculated with the other two methods.

340 Table 3. Active layer thickness determined by the method The active layer is generally thicker in the southern of intercept (1), interpolation of monthly maximum tempera- sites than in the northern sites probably reflecting the ture (2) and using Gold and Lachenbruch (1973) equation (3) higher ice content of the last. for Scott Base; Bull Pass; Boulder Clay and Simpson Crags.

Stations 1 2r 3 REFERENCES Scott base, 1999 35 45 42 Scott base, 2000 36 39 40 Campbell, I.B., Claridge, G.G.C., Campbell, D.I. & Scott base, 2001 43 22 27 Balks, M.R. 1994. The effect of human activities on Bull Pass, 1999 42 47 50 moisture content of soils and underlying permafrost Bull Pass, 2000 38 43 47 from the McMurdo Sound region, Antarctica. Antarctic Bull Pass, 2001 51 53 55 Science, 6, 307–14. Boulder Clay, 1999 25 27 33 Campbell, I.B., Claridge, G.G.C., Balks, M.R. & Boulder Clay, 2000 19 17 27 Campbell, D.I. 1997. Moisture content in soils of the Boulder Clay, 2001 20* 19* 17* McMurdo Sound and Dry Valley region of Antarctica. Simpson Crags, 1999 31 35 39 In Lyons, W.B., Howard-Williams, C. & Hawes, I. eds. Simpson Crags, 2000 24* 22* 19* Ecosystem Processes in Antarctic ice-free landscapes. Balkema, Rotterdam, 61–76. * uncompleted year. Campbell, I.B., Claridge, G.G.C., Campbell, D.I. & Balks, M.R. 1998. Permafrost Properties in the The maximum thawing depth does not necessarily cor- McMurdo Sound – Dry Valleys Region of Antarctica. respond to the 0°C isotherm in Antarctic areas espe- In Lewkowicz, A.G. & Allard, M. eds. Permafrost. cially where the salinity in the soil is high (e.g. Proceedings of the Seventh International Conference, Boulder Clay, and Bull Pass). June 23–27, 1998, Yellowknife, Canada, 121–126. French, H. & Guglielmin, M. 2000. Permafrost and frozen The active layers in Southern Victoria Land are phenomena of the Northern Foothills (Terra Nova Bay, thicker than in the Northern Victoria Land despite of a Northern Victoria Land, Antarctica). Geographiska lower mean annual GST in the southern area. This dif- Annaler. 82a: 513–526. ference can be explained with the different ice content Gold, L.W. & Lachenbruch, A.H. 1973. Thermal conditions of the sites. At Boulder Clay and Simpson Crags mas- in permafrost: a review of North American literature. sive ice bodies occur at a depth around 35–60 cm and In: 2nd International Permafrost Conference 13–28 July the active layer above is ice rich. Although there aren’t 1973, Yakutsk, U.S.S.R. North American contribution. measurements of water content within the active layer Washington, DC, National Academy of Sciences, 3–25. in the sites of Northern Victoria Land, direct observa- Gragnani, R., Guglielmin, M., Stenni, B., Longinelli, A., Smiraglia, C. & Cimino, L. (1998). Origins of the tion demonstrates that in several cases the entire active ground ice in the ice-free lands of the Northern layer can be saturated during the period of maximum Foothills (Northern Victoria Land, Antarctica). In 7th thawing. The high water content changes the thermal International Conference. on Permafrost, 23–27 June diffusivity of the ground and the energy required for 1998, Yellowknife, N.W.T., Canada, Proceedings. melting the ice smooth the temperature wave penetra- Ottawa, Ont., Collection Nordicana, A.G. Lewkowicz tion, reducing the active layer thickness. and M. Allard Eds 335–340. Guglielmin, M., Biasini, A. & Smiraglia, C. 1997a. The contribution of geoelectrical investigations in the ground ice 6 CONCLUSION analysis of periglacial and glacial landforms in ice-free areas of the Northern Foothills (Northern Victoria Land, Antarctica). Geogr. Ann., 79A(1–2), 17–24. In Antarctica the GST is very well related to the air Guglielmin, M. & Dramis, F. 1999. Permafrost as a climatic temperature although snow cover and incoming radia- indicator in northern Victoria Land, Antarctica. Annals tion can play an important role in the energy balance of of Glaciology. 29: 131–135. the surface. The active layer thickness shows a large variability both in space and in time responding sensi- tively to the climatic changes.

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