Vladimír Čermák

Underground temperature and inferred climatic temperature of the past millenium

Abstract There is considerable evidence from different fields of investigation that the world climate has undergone significant variations, even during the last 1,000 years. The effect of the change of temperature on the earths surface in the past may be preserved at depths of several hundred feet below the surface. The relation between underground and surface temperature is the reaction of the internal field in a semi-infinite medium to the boundary conditions. Any change at the surface is propagated downwards, and it is shown that the detailed record of temperature with depth can be used to trace the past climatic history. The theory of climatic correction of heat flow is used, and the data is obtained from two boreholes in northeastern Ontario. After analysis the measured underground temperature clearly confirmed the notably warm climate that lasted a few hundred years around A.D. 1000–1200 and the following cold period after 1500. Both these recent climatic extremes, for which the terms “Little Climatic Optimum” and “Little Ice Age” were coined, are well substantiated, but the magnitude of the temperature variations is uncertain. The relation between mean annual air temperature and surface (ground) temperature depends very much on the precipitation character and the duration of snow cover. The calculated magnitudes of the surface temperature changes probably correspond to the minimum changes of the annual air temperatures, which might have been more pronounced. The results presented indicate for the Kapuskasing area a surface temperature during the Little Climatic Optimum at least 1.5°C higher than the reference value; the mean temperature during the Little Ice Age was about 1°C below this reference value. A remarkable increase since about 1850 reaches value in excess of 3°C.

Heat Flow Map of Europe

The heat flow map of Europe was derived from 3076 existing observations, which for this purpose were supplemented by numerous results of deep borehole temperatures, gradients, and local heat flow patterns. In areas without data the heat flow field was estimated on the basis of the regional tectonic structure and the observed correlation of heat flow with the age of the last tectono-thermal event. The heat flow pattern as shown on the map may be described by two components: (1) the regional part and (2) the local part of the measured surface geothermal activity. The regional part of the heat flow field in Europe is dominated on the whole by a general “north-east to south-west” increase of the geothermal activity, which is an obvious consequence of the tectonic evolution. The major heat flow provinces correspond thus to the principal tectonic units. The geothermal fine structure (local part) superimposing the former is mainly controlled by local tectonics, especially by the distribution of the deep-reaching fracture zones and by the hydrogeological parameters. The paper gives a brief introductory description of the map, together with some remarks to the problem of preparing the map, corrections to the measured heat flow values and data obtained by numerous authors in all individual European countries. The correlation between the heat flow pattern and the crustal structure allows some preliminary geophysical implications: (1) areas of the increased seismicity may be connected with the zones of high horizontal temperature gradient, (2) increased surface heat flow may be generally observed in the areas of weakened crustal thickness, (3) there are considerable regional variations in the calculated temperature on the Mohorovicic discontinuity, as well as in the upper mantle heat flow contribution, (4) upper mantle heat flow must be of fundamental importance for the understanding of large-scale and long-term crustal evolution.

Air‐ground temperature coupling and subsurface propagation of annual temperature signals

[1] Borehole-based reconstructions of ground surface temperature (GST) have been widely used as indicators of paleoclimate. These reconstructions assume that heat transport within the subsurface is conductive. Climatic interpretations of GST reconstructions also assume that GST is strongly coupled to surface air temperature (SAT) on timescales of decades and longer. We examine these two assumptions using records of SAT and subsurface temperature time series from Fargo, North Dakota; Prague, Czech Republic; Cape Henlopen State Park, Delaware; and Cape Hatteras National Seashore, North Carolina. The characteristics of downward propagating annual temperature signals at each site clearly indicate that heat transport can be described as one-dimensional conduction in a homogeneous medium. Extrapolations of subsurface observations to the ground surface yield estimates of annual GST signals and allow comparisons to annual SAT signals. All annual GST signals are modestly attenuated and negligibly phase shifted relative to SAT. The four sites collectively demonstrate that differences between annual GST and SAT signals arise in both summer and winter seasons, in amounts dependent on the climatic setting of each site. INDEX TERMS: 1645 Global Change: Solid Earth; 1875 Hydrology: Unsaturated zone; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 3367 Meteorology and Atmospheric Dynamics: Theoretical modeling; KEYWORDS: heat transport, air-ground termperature coupling, paleoclimate

Two-dimensional temperature modelling along five East-European geotraverses

Abstract A two-dimensional numerical solution of the heat conductivity equation is applied to five long-run profiles crossing all the major tectonic provinces of Central and Eastern Europe. The relations between surface heat flow, Moho heat flow, thermal conductivity and heat production are described by a linear algebraic system. The results of explosion seismology are used to define individual crustal blocks of specific seismic velocities. An experimental relationship between seismic velocity and radiogenic heat production is applied and the heat production exponentially decreases with depth in each block. Thermal conductivity is temperature dependent. Low crustal temperatures are typical of the Precambrian East European Platform (Moho temperature 350–500°C) with a clear minimum beneath the Ukrainian shield. Moho temperatures increase slightly beneath Variscan units (500–600°C) and attain 600–800°C in the Alpine realm. The highest temperatures may exist beneath hyperthermal basins, such as the Pannonian Basin (over 800°C). The results clearly confirm the possible existence of the astenosphere at depths as shallow as 60 km in the areas of very high heat flow. The regional variations of the Moho heat flow may range from 15–20 to 40–50 mW.m − 2.

Daily, seasonal, and annual relationships between air and subsurface temperatures

[1] Inversions of borehole temperature profiles that reconstruct past ground surface temperature (GST) changes have been used to estimate historical changes in surface air temperature (SAT). Paleoclimatic interpretations of GST reconstructions are based on the assumption that GST and SAT changes are closely coupled over decades, centuries, and longer. This assumption has been the subject of some debate because of known differences between GST and SAT at timescales of hours, days, seasons, and years. We investigate GST and SAT relationships on daily, seasonal, and annual timescales to identify and characterize the principal meteorological changes that lead to short-term differences between GST and SAT and consider the effects of those differences on coupling between the two temperatures over much longer time periods. We use observational SAT and subsurface data from Fargo, North Dakota; Prague, Czech Republic; Cape Henlopen State Park, Delaware; and Cape Hatteras National Seashore, North Carolina. These records comprise intradaily observations that span parts of one or two decades. We compare subsurface temperature observations to calculations from a conductive subsurface model driven with daily SAT as the surface boundary condition and show that daily differences exist between observed and modeled subsurface temperatures. We also analyze year-to-year spectral decompositions of daily SAT and subsurface temperature time series and show that dissimilarities between mean annual GST and SAT are attributable to differences in annual amplitudes of the two temperature signals. The seasonal partitioning of these amplitude differences varies from year to year and from site to site, responding to variable evapotranspiration and cryogenic effects. Variable year-to-year differences between mean annual GST and SAT are closely estimated using results from a multivariate regression model that associates the partial influences of seasonal meteorological conditions with the attenuation of annual GST amplitudes.

Terrestrial Heat Flow and the Lithosphere Structure

General Lithospheric Geothermics.- Regional Variations in Lithosphere Rheology from Heat Flow Observations.- Radioactive Heat Production in the Continental Crust and Its Depth Dependence.- Determination of the Past Heat Flow from Subsidence Data in Intracontinental Basins and Passive Margins.- Are Granites Representative of Heat Flow Provinces?.- Regional Lithospheric Geothermics.- Lithosphere Structure, Heat Flow, Gravity, and Other Geoparameters in Central Europe.- Heat Flow, Regional Geophysics and Lithosphere Structure in Czechoslovakia and Adjacent Part of Central Europe.- Crustal Geothermics of Some Geotraverses of the Former GDR.- Regional Geothermal Gradients and Lithosphere Structure in Spain.- Heat Flow and Lithospheric Structure in Romania.- Heat Flow and Analysis of the Thermal Structure of the Lithosphere in the European Part of the USSR.- Heat Field of the Lithosphere of Northeast Asia and the Northwestern Sector of the Asia-Pacific Transition Zone.- Heat Flow as an Indicator of the Dynamics of Deep Processes Occurring in Marginal Seas and Island Arcs of the Northwestern Pacific.- Heat Flow Pattern and Lithospheric Thickness of Peninsular India.- Crust and Upper Mantle Thermal Structure of Xizang (Tibet) Inferred from the Mechanism of High Heat Flow Observed in South Tibet.- The Thickness of the Thermal Lithosphere in the Panxi Paleorift Zone, Southwestern China.- Heat Flow in the Canadian Shield and Its Relation to Other Geophysical Parameters.- Terrestrial Heat Flow and Lithospheric Geothermal Structure of New Zealand.- Worldwide Heat Flow Density Studies.- Geothermal Regime of Italy and Surrounding Seas.- Heat Flow and Thermal Structure of the Aegean Sea and the Southern Balkans.- Trends of Heat Flow Density from West Africa.- Review of Siberian Heat Flow Data.- Compilation of Heat Flow Data in Southeast Asia and Its Marginal Seas.- Terrestrial Heat Flow in Canada.- Terrestrial Heat Flow in Mexico.- Heat Flow and Regional Geophysics in Australia.- Geographical and Geological Index.

Lithospheric thermal regimes in Europe

Abstract The heat flow pattern of Europe, derived from more than 8000 observations, is dominated by a general northeast to southwest increase in geothermal activity, which is the consequence of the tectonic evolution of the whole continent. This paper reviews the history of the geothermal mapping of Europe, and describes the recently compiled set of geothermal maps of Europe. Surface heat flow is correlated with the age of the last tectonothermal event, with the near-surface heat production and with the crustal thickness. Deep temperature distributions within the crust-lithosphere are calculated for 1-D, 2-D and simple 3-D models. Characteristic temperature-depth curves are given for some of the major tectonic provinces, and the results of various techniques are compared. The value of the crustal heat contribution is assessed and a regional Moho heat flow pattern is proposed. The Mohorovicic discontinuity is clearly not an isothermal surface, neither is the heat flow from below the crust constant.

Heat flow models across the Trans-European Suture Zone in the area of the POLONAISE’97 seismic experiment

Abstract Heat flow data from the Polish basin show a sharp change in the transition from the East European Craton (EEC) and Teisseyre–Tornquist Zone (TTZ) in the north-east to the accreted terranes in the south west (Paleozoic Platform). The analysis of this data and numerical modelling of the crustal temperatures show evidence of extensive crustal–mantle warming in the area between the Sudetes to the south and the Trans-European Suture Zone to the north. The change in heat flow is 100% when compared with values for the EEC. Heat flow in the anomalous zone is also higher than in the Sudetes. The axis of the anomaly is aligned with the Dolsk Fault and Variscan deformation front. Low crustal/mantle temperatures derived from the relationship between temperature and P n velocities (more than 8.2 and as high as 8.4 km/s) are at odds with high crustal temperatures calculated from surface heat flow, seismic velocity based heat generation models and thermal conductivity. High heat flow (Variscan platform) and related high temperatures of the crust coincide with small crustal thickness (30–35 km). The opposite is the case for the low heat flow EEC (45–50 km). High heat flow above thin crust and low heat flow above thick crust with no major variation in elevation is supported by a simple isostatic balance model. Crustal heat generation explains part of the high heat flow within the zone with thick meta-sediments reaching down to 20 km depth, however, it is far from explaining high heat flow in Variscan crust and in the transition zone into a cold EEC. 2D numerical models of heat flow based on new seismic data require a contrast of 15 mW/m 2 in mantle heat flow. High mantle heat flow (35–40 mW/m 2 ) is likely to occur in the high heat flow zone while cold crust and cold and high-density mantle (mantle heat flow of 20–30 mW/m 2 ) is typical of the EEC. Thermal lithosphere thickness for the craton is 200 km while it is only 100 km in the accreted terranes to the southwest of the TTZ. The TTZ in Poland appears as a relatively cold area.

Crustal heat production and mantle heat flow in Central and Eastern Europe

Abstract The conversion of seismic velocity ( υ p ) into radiogenic heat production ( A ) enables the distribution of crustal heat sources to be estimated. This technique was used to assess the mantle (Moho) heat flow for 49 seismic velocity-depth profiles located along five continental traverses in Central and Eastern Europe. The effect of pressure and temperature on υ p was taken into account, as was the age dependence of A . The uppermost part of the crust is dominated by microcracks that may have allowed a certain redistribution of radioactive elements by deep groundwater migration. Furthermore, owing to the highly variable value of the pressure derivative of v p in the uppermost crust, the use of a A−υ p relationship is problematic within this depth range. This radioactivity enriched zone, the thickness of which can be determined from the parameters of the heat flow-heat production relationship, was therefore treated separately. According to the model adopted for the upper crust, the Moho heat flow ranges from 14 to 26 mW m−2 in the stable continental areas such as the shields or ancient platforms. Younger terrains are characterized by elevated Moho heat flows of 20 to 40 mW m−2 and the Moho heat flow may eventually attain values over 50 mW m−2 in regions characterized by very high surface heat flow, such as the Pannonian Basin for example. The present data were compared with crustal models proposed by other authors. Moho heat flow estimates based on a simple exponential distribution of heat sources valid for the whole crust might be too high if applied to stable continental crust. Our data confirm a considerable variability in the mantle heat flow corresponding to the large-scale tectonothermal evolution, with a generally lower Moho heat flow typical of consolidated stable continental crust. The discrepancy in relation to the above estimates can be accounted for by a heat generation hump beneath an upper zone of exponential decline.

Heat flow, heat generation and crustal temperature in the kapuskasing area of the Canadian Shield☆

Abstract Combined heat flow and heat production measurements in three boreholes in the Superior Province of the Canadian Shield were made to test the geothermal consequences of the Kapuskasing fault zone. The evidence of gravity and geomagnetic investigation suggests that this zone is a deeply eroded remnant of a crustal rift. A linear relation between heat flow (q) and surface heat production (P), q = qo + bP, where qo and b are empirical constants, has been found by F. Birch, R. Roy and A. Lachenbruch for different heat-flow provinces over the North American continent. The results from the Kapuskasing zone clearly confirmed this relation, giving qo = 0.63 μcal. · cm−2 · sec−1 and b = 13.5 km. The significance of these parameters for the crustal structure study and the probable temperature-depth distribution are discussed in the paper. The influence of different surface temperature during the past on the underground temperature is mentioned. The consistent elimination of the climatic effect on measured heat flow is necessary when a geothermal model is to be constructed.