Ground surface temperature history in central Canada inferred from 10 selected borehole temperature profiles
Résumé
Among the 57 temperature-depth profiles recently measured in Manitoba and Saskatchewan(C anada), 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.