|Résumé||(disponible en anglais seulement)|
Introduction and objectives
The Geological Survey of Canada and the University of Ottawa collaboratively initiated a field project in July 2009 to examine
and quantify the variability in ground thermal regime in the vicinity of Eureka (80°N, 86°W) on the Fosheim Peninsula of Ellesmere Island, Nunavut. The goal was to examine the impact of coastal proximity on ground temperatures in a High Arctic
environment. The region is cold and dry with an average annual air temperature at the Eureka weather station of -18.8°C and total yearly precipitation of 79 mm (1981-2010), about 60% of which falls as snow (Environment Canada, 2015). Previous
research showed that summer air temperatures inland can be as much 10°C higher than in the immediate coastal zone on the Fosheim Peninsula due to the coastal effect (Atkinson and Gajewski, 2002). The latter is mainly due to surface inversions
resulting from cold, dense air over ice-covered waters forming a wedge that moves inland beneath warmer air heated by sensible heat transfer from the ground. In addition, coastal locations often have greater amounts of summer cloud cover. Without
supporting data, Atkinson (2000) assumed that the distance to which coastal air impacts summer air temperatures inland becomes zero at 6 km. In winter, the impact of the coastal effect might reverse, with relatively warm ocean water beneath its ice
cover potentially warming the air and the ground, but again, for an unknown distance inland. Most climate stations in the Canadian High Arctic are located at the coast so estimates of current ground temperatures based on their records could be
inaccurate if there is a strong gradient inland, and in turn this would lead to inaccurate estimates of the impacts of future warming. Our objectives, therefore, were to examine the relative strengths of the seasonal influences of coastal proximity
on air and ground temperatures and to establish the distance to which they penetrate inland.
Study Sites and Methods
Six shallow (5-10 m deep) boreholes were drilled by water-jet in the valley of Station Creek at sites with elevations of 10
to 75 m a.s.l. (EUK-1 ¿ EUK-6). Surficial deposits at the boreholes were mainly ice-rich marine silts and clays with some sandy horizons and vegetation cover was less than 5 %. The sites were located at progressively greater distances from the coast
of Slidre Fiord (100 m to 5 km) and at increasing distances from one another. Each borehole was instrumented with a multi-point thermistor cable and associated logger (RBR; accuracy better than ±0.1°C). In addition, screen-height air and ground
surface temperatures were measured at each site except EUK-1 using Hobo loggers (Onset; accuracy of ±0.2°C) while snow depths were inferred from iButton temperature loggers (Thermochron; accuracy of ±1°C) installed on a wooden stake at 5, 10, 20, 30,
40, 50, 60 and 80 cm above the ground surface.
Results and Discussion
Here we present the results of monitoring between 2009-2015 with a minimum of three years of record for each site. Seasonal and annual means were calculated from monthly
averages, themselves compiled from all available complete months. Air temperatures increased away from the coast on an annual as well as a seasonal basis. Mean annual air temperatures increased logarithmically inland by 1.6°C from -17.2°C to -15.6°C
(Figure 1). The summer months (June, July, August) showed an increase of 2.7°C, from 6.1 to 8.8°C, while in the remainder of the year the average air temperature increased inland by 1.3°C, from -25.0 to -23.7°C. The annual temperature range (July
mean temperature minus the mean temperature of the coldest month (January or February)) also increased inland, from 46.1°C to 48.1°C. Mean ground surface temperatures varied from -13.3°C to -14.3°C and did not show a consistent trend inland on either
an annual (Figure 1) or a seasonal basis. Snow depths at the weather station, close to EUK-1 and 2, average about 10 cm from September to May (Environment Canada, 2015). Snow depths at all sites, inferred from the iButton data loggers, rarely covered
even the lowermost logger at 5 cm above the ground. Annual surface offsets varied from 1.8°C to 3.5°C and showed no consistent trend, but summer surface offsets declined from 2.5°C at EUK-2 to 0.5°C at EUK-6. This suggests that near the coast,
advection results in air warmed by solar heating being replaced by cold air moving in from the fiord whereas inland, air temperatures rise as a result of vertical sensible heat transfer to the air resulting in a smaller offset. Mean ground
temperatures at 0.5 m and 5 m depth increased inland from EUK-2 by up to 3°C and 1.1°C respectively (Figure 1). EUK-2 is slightly colder than EUK-1 even though the latter is closer to the nearest shoreline. EUK-2, however, is on the delta of Station
Creek which extends farther into the fiord than EUK-1 and this probably accounts for its lower temperatures. None of the boreholes reached the depth of zero annual amplitude with the temperature varying annually by about 2°C at 10 m (EUK-3 and 4).
The average temperature for the boreholes increased with depth for EUK- 1-4, and decreased with depth for EUK-5 and 6. Since the latter two were the warmest near the surface, coastal to inland differences in ground temperatures declined with depth.
We conclude that, in the Eureka area, both air and ground temperatures increase inland according to the logarithm of the distance from the coast for at least 5 km. The trends are clear for air and temperatures within the
permafrost but not for ground surface temperatures. Air temperatures are warmer inland in summer, as expected, but are also warmer in winter for reasons that are not yet clear. Permafrost temperatures in the High Arctic are increasing faster than in
many other parts of northern Canada and long-term monitoring of these sites will reveal if coastal and inland locations will warm at the same or different rates.
This project was supported by Natural Resources Canada, the
University of Ottawa, the Federal Government¿s International Polar Year Program and Polar Continental Shelf Program. Additional logistical support was provided by Environment Canada. W. Pollard, M. Ward and A. Cassidy kindly assisted with data
Atkinson, D. E., 2000: Modelling July mean temperatures on Fosheim Peninsula, Ellesmere Island, Nunavut. Geological Survey of Canada Bulletin, 529: 99-111.
Atkinson D.E. and Gajewski K.G. 2002. High-Resolution
Estimation of Summer Surface Air Temperature in the Canadian Arctic Archipelago. Journal of Climate, 15: 3601-3614. DOI: 10.1175/1520-0442(2002)015<3601:HREOSS>2.0.CO;2
Environment Canada. 2015. Climate normals for Eureka weather station
(1981-2010). http://climate.weather.gc.ca/climate normals Accessed Nov 30, 2015.