Borehole paleoclimatology ? the effect of deep lakes and "heat islands" on temperature profiles

International audienceIt is known that changes in ground surface temperatures could be caused by many non-climatic effects. In this study we propose a method based on utilization of Laplace equation with nonuniform boundary conditions. The proposed method makes possible to estimate the maximum effect of deep lakes and "heat islands" (areas of deforestation, urbanization, farming, mining and wetland drainage) on the borehole temperature profiles

Spatial distribution of Pleistocene/Holocene warming amplitudes in Northern Eurasia inferred from geothermal data

International audienceWe analyze 48 geothermal estimates of Pleistocene/Holocene warming amplitudes from various locations in Greenland, Europe, Arctic regions of Western Siberia, and Yakutia. The spatial distribution of these estimates exhibits two remarkable features. (i) In Europe and part of Asia the amplitude of warming increases toward the northwest and displays clear asymmetry with respect to the North Pole. The region of maximal warming is close to the North Atlantic. A simple parametric dependence of the warming amplitudes on the distance to the warming center explains 91% of the amplitude variation. The Pleistocene/Holocene warming center is located northeast of Iceland. We claim that the Holocene warming is primarily related to the formation (or resumption) of the modern system of currents in the North Atlantic. (ii) In Arctic Asia, north of the 68-th parallel, the amplitude of temperature change sharply decreases from South to North, reaching zero and even negative values. These small or negative amplitudes could be attributed partially to a joint influence of Late Pleistocene ice sheets. Using a simple model of the temperature regime underneath the ice sheet we show that, depending on the relationship between the heat flow and the vertical ice advection velocity, the base of the glacier can either warm up or cool down. Nevertheless, we speculate that the more likely explanation of these observations are warm-water lakes thought of have formed in the Late Pleistocene by the damming of the Ob, Yenisei and Lena Rivers

The maximum effect of deep lakes on temperature profiles – determination of the geothermal gradient

Understanding the climate change processes on the basis of geothermal observations in boreholes is an important and at the same time high-intricate problem. Many non-climatic effects could cause changes in ground surface temperatures. In this study we investigate the effects of deep lakes on the borehole temperature profilesobserved within or in the vicinity of the lakes. We propose a method based on utilization of Laplace equation with nonuniform boundary conditions. The proposed method makes possible to estimate the maximum effect of deep lakes (here the term "deep lake" means that long term mean annual temperature of bottom sediments can beconsidered as a constant value) on the borehole temperature profiles. This method also allows one to estimate an accuracy of the determination of the geothermal gradient

THE MAXIMUM EFFECT OF DEEP LAKES ON TEMPERATURE PROFILES – DETERMINATION OF THE GEOTHERMAL GRADIENT

Understanding the climate change processes on the basis of geothermal observations in boreholes is an important and at the same time high-intricate problem. Many non-climatic effects could cause changes in ground surface temperatures. In this study we investigate the effects of deep lakes on the borehole temperature profilesobserved within or in the vicinity of the lakes. We propose a method based on utilization of Laplace equation with nonuniform boundary conditions. The proposed method makes possible to estimate the maximum effect of deep lakes (here the term "deep lake" means that long term mean annual temperature of bottom sediments can beconsidered as a constant value) on the borehole temperature profiles. This method also allows one to estimate an accuracy of the determination of the geothermal gradient

Heat Exchange between Permafrost and the Atmosphere in the Presence of a Vegetation Cover

The heat exchange between the ground and the atmosphere in the North is extremely important in the formation and continued existence of permafrost. An understanding of this process and how it is influenced by surface terrain features such as vegetation is vital in furthering knowledge of the thermal regime and other characteristics of permafrost having important engineering implication. Investigations in this field are underway in Canada and the U.S.S.R. This article was written by a senior worker at the Permafrost Institute, Academy of Sciences of the U.S.S.R., Yakutsk in Eastern Siberia. It reviews North American and Soviet studies and presents analytical material pertaining to the important role of vegetation in the heat exchange between the permafrost and the atmosphere.SOMMAIRE FRANCAIS A SUIVREPeer reviewed: NoNRC publication: Ye