Temperature and heat flux changes at the base of Laurentide ice sheet inferred from geothermal data (evidence from province of Alberta, Canada) (original) (raw)
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Holocene paleotemperatures deduced from geothermal measurements
Palaeogeography Palaeoclimatology Palaeoecology, 1983
Vasseur, G., Bernard, Ph., Van de Meulebrouck, J., Kast, Y. and Jolivet, J., 1983. Holocene paleotemperatures deduced from geothermal measurements. Palaeogeogr., Palaeoclimatol., Palaeoecol., 43 : 237--259.
Tectonophysics, 1998
Calculations of the present geothermal gradient and terrestrial heat flow were made on 156 deep wells of the Canadian Arctic Archipelago. Corrected bottom hole temperature (BHT) data and drill stem test (DST) temperatures were used to determine the thermal gradients for sites for which the quality of data was sufficient. Thermal gradients evaluated for depths below the base of permafrost for the onshore wells and below sea bottom for the offshore wells were combined with the estimates of effective thermal conductivity to approximate heat flow for these sites. The present geothermal gradient is in the 15-50 mK/m range (mean = 31 4-7 mK/m). Present heat flow is mainly in the 35-90 mW/m 2 range (mean = 53 4-12 mW/m2). Maps of the present geothermal gradient and present heat flow have been constructed for the basin. The analysis of vitrinite reflectance profiles and the calculation of logarithmic coalification gradients for 101 boreholes in the Sverdrup Basin showed large variations related in many cases to regional variations of present terrestrial heat flow. Paleo-geothermal gradients estimated from these data are mostly in the range of 15-50 mK/m (mean = 28 5= 9 mK/m) and paleo-heat flow is in the 40-90 mW/m 2 range (mean = 57 ± 18 mW/m 2) related to the time of maximum burial in the Early Tertiary. Mean values of the present heat flow and paleo-heat flow for the Sverdrup Basin are almost identical considering the uncertainties of the methods used (53 + 12 versus 57 4-18 mW/m 2, respectively). Present geothermal gradients and paieo-geothermal gradients are also close when means are compared (31 4-7 versus 28 4-9 mK/m respectively). A zone of high present heat flow and a paleo-heat flow zone coincide in places with the northeastern-southwestern incipient rift landward of the Arctic margin first described by . Correlation between present heat flow and paleo-heat flow for the time of maximum burial in the earliest Tertiary suggests that the high heat flow zone has prevailed since that time.
Journal of Geophysical Research, 1998
Among the 57 temperature-depth profiles recently measured in Manitoba and Saskatchewan (Canada), only 10 are suitable for inferring recent changes in ground surface temperature. Many of the rejected temperature profiles show an apparent climatic signal but are affected by topography, changes in vegetation, or the proximity of lakes. At the northernmost site, near Lynn Lake, Manitoba, shallow horizontal variations in temperature have been identified that are related to intermittent permafrost. Such variations can induce an apparent "climatic" perturbation. In areas where lateral thermal conductivity contrasts have been measured, heat refraction effects can also incorrectly be interpreted as ground surface temperature histories. The analysis suggests that forest fires that occurred at some of the sites have had little influence on the temperature profiles. The 10 selected temperature profiles cover a wide area in northern Manitoba and Saskatchewan. They have been independently and jointly inverted by a singular value decomposition method. The ground surface temperature history shows two main episodes. A cold period, tentatively identified as Little Ice Age, with a minimum around 1820 A.D., was followed by marked warming after 1920. These trends are similar to those recognized in eastern Canada. GUILLOU-FROTTIER ET AL' GROUND TEMPERATURE HISTORY IN CANADA m 0.5 ø-1.0øC decrease in temperature, at m 1700 A.D. in These differences between European and American temperatures in the 18 tn and 19 tn centuries are supported by tree ring chronologies [Fritts and Lough, 1985]. Temporal variations in ground surface temperature were first inferred from borehole data in northern Ontario by Beck and Judge [1969] and Cermak [1971]. These authors recognized that a cold period, identified as Little Ice Age (LIA), had preceded the current warming trend. These results were later confirmed by several studies in eastern Canada that identified the LIA and the recent warming in borehole temperature
Geothermal evidence of very low glacial temperatures on a rim of the Fennoscandian ice sheet
Geophysical Research Letters, 2004
1] The mean ground temperature as low as À10°C and the existence of more than 500 m thick permafrost during the last glacial are apparent from the analysis of deep borehole temperature profiles in north-eastern Poland. The largest thickness of the permafrost and its survival deep into the Holocene was restricted to a region known for its low terrestrial heat flow, where the negative temperature gradient is observed in the uppermost 400 m. We have shown that the profiles are consistent with warming from the glacial mean of À10°C to the Holocene mean of +7°C 14 ka ago and to +8°C in the last 150 years.
The research into a geothermal energy option for Northern Alberta basin is currently underway. Correct estimates of heat flow and geothermal gradient for the sedimentary strata (direct heat energy option) and deeper crystalline basement are needed. A series of detailed geophysical logs and boreholes studies have recently been collected in the Hunt well AOC GRANITE 7-32-89-10. The well was drilled 2.36 km into basement granitic rocks just west of Fort McMurray. A temperature log acquired as part of the University of Alberta Helmholtz-Alberta Initiative (HAI) geothermal energy project in 2010-2011shows that there is a significant increase in thermal gradient in the granites. Inversion of the measured T-z profile between 550 m -2320 m indicates a temperature increase of 9.6+/-0.3 o C, at 13.0 +/-0.6 ka and that the glacial base surface temperature was -4.4+/-0.3 o C. This inversion computation accounted for granite heat production of 3 W/m 3 . We find from the Hunt well study that heat flow in the basin has been underestimated for wells shallower than 2 km due to the paleoclimatic effect. A significant increase in surface temperatures since the end of the last ice age in northern North America causes a perturbation of shallow <2 km heat flows. For this reason, estimates of gradient based on single or numerous data from different depths are not necessarly characteristic of the whole sedimentary column and can lead to spurious predictions of temperature at depth needed for geothermal energy or hydrocarbon models.
Canadian Journal of Earth Sciences, 1980
Temperature measurements were made in seven boreholes, ranging in depth from 50-276 m, in the Barnes Ice Cap. Holes B4, D4, and TO975 are approximately 1 km from the margin and an average of 8 km apart. Holes T091, T081, T061, and TO20 lie along a 10.2 km flow line passing through T0975. Temperature profiles are convex upward in all holes except T020, reflecting the combined effects of longitudinal and upward vertical advection, and frictional heating. The profile in TO20 is concave near the bottom of the hole, as a result of downward vertical advection, but convex above mid-depth, owing to a 2.X cooling of the near-surface ice in the early 1940's.
Annals of Glaciology, 2000
Analyses of the geothermal gradient in permafrost areas constitute a key signal of the ground-surface temperature history. Permafrost temperatures in selected areas are particularly well suited to reconstructing past surface-temperature changes, mainly because there is no thermal disturbance due to circulating groundwater. One year of temperature data from an instrumented 102 m deep borehole in permafrost on Janssonhaugen, Svalbard, is presented. Ground thermal properties are calculated. The average value for the thermal conductivity is 1.85 ±0.05 W m–1 K–1 , and the average value for the thermal diffusivity is 1.1m2 s–1, which gives a phase speed for the annual wave of 5.65 × KT2 m d–1. The depth of zero annual amplitude is 18 m The permafrost thickness is estimated as approximately 220 m. Analysis of the temperatures reveals an increasing temperature gradient with depth. Using a heat-conduction inversion model, a palaeoclimatic reconstruction is presented, showing a warming of the...