Ground Temperature History Research Articles

Recent climate variations in Chile: constraints from borehole temperature profiles

Abstract. We have compiled, collected, and analyzed 31 temperature–depth profiles from boreholes in the Atacama Desert in central and northern Chile. After screening these profiles, we found that only nine profiles at four different sites were suitable to invert for ground temperature history. For all the sites, no surface temperature variations could be resolved for the period 1500–1800. In the northern coastal region of Chile, there is no perceptible temperature variation at all from 1500 to present. In the northern central Chile region, between 26 and 28∘ S, the data suggest a cooling from ≈ 1850 to ≈ 1980 followed by a 1.9 K warming starting ≈ 20–40 years BP. This result is consistent with the ground surface temperature histories for Peru and the semiarid regions of South America. The duration of the cooling trend is poorly resolved and it may coincide with a marked short cooling interval in the 1960s that is found in meteorological records. The total warming is greater than that inferred from proxy climate reconstructions for central Chile and southern South America, and by the PMIP3-CMIP5 surface temperature simulations for the north-central Chile grid points. The differences among different climate reconstructions, meteorological records, and models are likely due to differences in spatial and temporal resolution among the various data sets and the models.

Numerical Simulation of Diagenetic Stage in Sandstone Reservoir of Huagang Formation in Xihu Sag

To predict distribution of diagenetic stages of Xihu Sag Huagang Formation sandstone reservoir and secondary pore development zone, and research original pore reservation and secondary pore increase and decrease in reservoir evolution process, combining traditional diagenesis research and numerical simulation technique, and based on interaction model and effect model, this paper establishes a aggregative model on numerical simulation of diagenetic stages. In diagenesis simulation process, based on process response principle, and restricted by current diagenetic stage distribution and type, diagenetic stage distribution and type of reservoir during geological historical evolution period is back stripped through diagenetic temperature. Taking single well diagenetic stage data as constraint condition, and combining with research area burial history, ground temperature history, and diagenetic stage division basis, and scheme, plane distribution of diagenetic stages of the whole research area during each geological historical period is finally obtained.

The environment and permafrost of the Mackenzie Delta area

AbstractThe Mackenzie Delta, prograding northwestwards into the Beaufort Sea, is North America's largest arctic delta. This Holocene feature is bounded by rolling uplands to the east and the Richardson Mountains to the west. Treeline traverses the region, separating the subarctic boreal forest in southern parts from low‐shrub tundra and sedge wetlands at the coast. The region is experiencing rapid climate change, and mean annual air temperature has increased by more than 2.5°C since 1970. The area was at the margin of the Wisconsinan ice sheet, so that in the uplands the mean annual ground temperature and glacial history control permafrost thickness, which varies from >700 m to <100 m. Ground temperatures in the delta are distinct from the uplands due to the thermal influence of numerous lakes and shifting channels. In the uplands, ground temperatures decrease northwards across treeline in association with a decrease in the thickness of snow cover. Ground temperatures have increased since 1970 in the uplands by approximately 1.5°C in association with rising annual mean air temperature. The increase has been less in the delta south of treeline due to the extensive thermal influence of water bodies on ground temperature. However, in the outer delta, the ground is currently more than 2.5°C warmer than in 1970. The impact of climate change on permafrost is also evident in the thickness of the active layer, which increased on average by 8 cm at 12 tundra sites on northern Richards Island from 1983–2008. Copyright © 2009 John Wiley & Sons, Ltd. and Her Majesty the Queen in right of Canada.

On the relationship between ground temperature histories and meteorological records: a report on the Pomquet station

An experimental air–ground climate station is operating in Pomquet, Nova Scotia, monitoring meteorological (surface air temperatures at three heights, wind velocity and direction, incoming solar radiation, precipitation, snow depth and relative humidity) and ground thermal variables (soil temperatures at depths of 0, 5, 10, 20, 50 and 100 cm). Readings are taken every 30 s and 5 min averages are stored, in order to characterize the energy exchanges at the air ground interface. Here, I report on the first year of operation. For spring, summer and fall, we find that soil temperatures track surface air temperatures with amplitude attenuation and phase lag with depth confirming that heat conduction adequately describe the soil thermal field at the Pomquet site. For winter conditions, we find that heat transfer is dominated by latent heat released during soil freezing and to a lesser extent by the insulating affect of snow cover. A numerical model of heat conduction was used in order to estimate the magnitude of the heat released by freezing during the winter months. I also show that there is an inverse correlation for the difference between soil (100 cm) and air temperatures and the incoming solar radiation at the site.

Ground temperature history in Romania inferred from borehole temperature data

Geothermal observations (temperature-depth data and thermal property measurements) from a suite of boreholes in the Romanian Carpathians area are used to infer ground surface temperature (GST) history. Temperature observations in boreholes are combined with meteorological data at nearby weather stations to test that temperature in the earth's subsurface contains a record of recent climate change. The subsurface temperature profiles are consistent with the air temperature records. The GST histories that can be extracted by inversion of perturbed temperature data from boreholes ranging in depth between 190 and 520 m cover the past 200–400 years. Results of inversion indicate for the last 150 years a cooler episode for the inner region of the Carpathian Mts. and a warmer time in the Carpathian foreland. The GST histories for this southeastern part of Europe are slightly different from those obtained in western and central Europe. These differences are consistent with the spatial variability of climatic trends.

Reconstruction of remote climate changes from borehole temperatures

Data from temperature measurements in drillholes are indicators of the temperature variations associated with past climate change. The aim of this paper is to investigate the maximum extent of ground temperature history which can be extracted from geothermal data. We discuss ground surface temperature histories reconstructed from borehole temperature measurements in twelve deep holes (∼ 700 to 6000 m) in the Czech Republic. The study has identified climatic episodes back to the last glaciation period. The reconstructed climatic histories exhibit features similar to those extracted from borehole temperature logs by other inversion techniques and also found by independent climate reconstruction methods. Results confirm the possibility to identify long-term climatic trends from the borehole temperature-depth profiles and to integrate it into the assemblage of traditional paleoclimatological records.

Simultaneous inversion of borehole temperature data for determination of ground surface temperature history

Recent variations of the ground surface temperature, recorded in the Earth's subsurface, can be inverted from borehole temperature data. The resolution of the inversion of borehole temperature logs is poor, even when the noise level is low. This report concerns the potential improvement in the resolution of ground surface temperature history when temperature logs from several boreholes are inverted simultaneously. For an inversion algorithm based on singular value decomposition, the singular values obtained for simultaneous inversion of several boreholes do not decrease as rapidly as the singular values for a single borehole. With the same value of the cut-off or of the damping parameter, more eigenvectors remain in the solution and give higher resolution for several boreholes than for one. Tests conducted with synthetic data for 15 boreholes show that the improvement in resolution is real but not spectacular. These tests indicate that borehole temperature logs should have approximately the same sampling interval. Temperature profiles over different depth ranges can be inverted if the reference heat flows and ground temperatures are included in the parameters determined by the inversion. Tests also show that no consistent ground-temperature history (GTH) is obtained when inverting data from boreholes that have experienced different surface-temperature variations. Simultaneous inversion can be applied to: (1) obtain a local GTH for a single site with several boreholes having identical surface conditions, or (2) obtain regional averages with data from different sites that have experienced the same variations in ground temperature. Temperature profiles measured in four boreholes near Belleterre, in eastern Canada, appear to have recorded the same perturbation. Inversion of the temperature data from individual boreholes yields similar, but not identical, GTHs. The GTH obtained by simultaneous inversion of these four boreholes indicates a cool period, with minimum temperatures at ca. 1800 AD, followed by warming above the reference level. It is consistent with other analyses indicating recent warming in eastern Canada.

A geothermal climate change observatory: First year results from Emigrant Pass in northwest Utah

Temperature‐depth profiles, measured in boreholes, contain a temporal record of past changes in surface ground temperature and provide valuable constraints on climatic variations over the last few centuries. However, the linkage between ground temperature and meteorological variables including air temperature is imperfectly known. To understand that linkage better and to document in detail how the surface ground temperature changes propagate into the subsurface where they are later measured in temperature‐depth logs in boreholes, we have designed and installed a geothermal climate change observatory. Installed in arid northwest Utah, our Emigrant Pass Observatory (EPO) consists of an array of thermistor strings in the subsurface and a meteorological station at the borehole collar. Results from our first complete annual cycle, November 1, 1993, though October 31, 1994, are presented. Ground and air temperatures generally track each other but with important time‐varying offsets. The mean surface ground temperatures for the period are 11.3°C on the granite outcrop and 9.5°C for the partially shaded regolith site; mean air temperature at a 2‐m mast height above the ground is 8.8°C. The ground‐air temperature differences are variable on timescales from days to seasons, largely governed by level of absorbed solar radiation. Marginal precipitation (8.6 mm) and ephemeral snow cover did not significantly disturb the ground‐air temperature difference during the year monitored. Instrumental measurement of air temperature has nonrandom sampling biases that present problems for observing long term changes. The calculation of average annual air temperature at EPO decreases by 0.34 K as the sampling rate of air temperature is decreased from 60 s to every 12 hours. The attenuation and phase lag of thermal waves with depth confirm that heat conduction theory adequately describes the transient temperature field at this site, and yield in situ estimates of thermal diffusivity, a quantity needed to reconstruct surface ground temperature histories. Thermal diffusivity for the granite and regolith is 0.88 × 10−6 m2 s−1 and 0.45 × 10−6 m2 s−1, respectively. Energy flux calculations for the Emigrant Pass Observatory site suggest that a geothermal climate change observatory has the capability of detecting a century scale energy perturbation that is one part in a million of the instantaneous flux.

Palaeoclimate and structure: the most important factors controlling subsurface temperatures in crystalline rocks. A case history from Outokumpu, eastern Finland

SUMMARY The present work contributes to the study of heat-transfer mechanisms in crystalline bedrock. We present evidence from a thoroughly investigated case history in Outokumpu, eastern Finland, in the Fennoscandian (or Baltic) Shield, which shows that the subsurface temperature field is controlled by the thermal conductivity structure and downward diffusion of palaeoclimatic ground-temperature variations. The subsurface temperature profiles from three continuously cored boreholes (790-1 100 m deep) were used for a detailed 2-D modelling of structural, hydrogeological and palaeoclimatic effects on the subsurface temperature field. The boreholes are situated in a subdued topography and they intersect Early Precambrian folded lithologies, such as mica gneisses, black schists, skarn rocks, quartzites and serpentinite-talc rocks. Finitedifference techniques were used in the numerical solution of the heat- and masstransport equations. The 2-D models of thermal conductivity and hydraulic permeability that were compiled were based on an extensive set of data relating to geological structure, in situ hydraulic permeability, groundwater composition and thermal conductivity of drill-core samples down to about 1 km depth. It was found that the thermal effect of topographically driven groundwater convection is very small, with Peclet numbers typically of the order of 10-4-10-5. The effect of anisotropy of thermal conductivity was found to be one order of magnitude smaller than the effects of heatflow refraction in the inclined rock layers which produce horizontal components of heat-flow density ranging from - 15 to 5 mW m-' (basal heat flow 35 mW m-'). Since the advective heat transfer could be neglected, we tried to find a palaeoclimatic groundtemperature history that would explain the measured data. First, an inversion algorithm based on heat conduction in laterally homogeneous media was used for the reconstruction of palaeoclimatic ground-temperature history, but it yielded spurious results because of the strong 2-D conductivity effects. The only means to reconstruct the past ground-temperature changes was forward modelling using a conductive transient 2-D model with time-dependent surface-temperature variations. The surface temperatures at different times (between 100000 yr BP and the present) and the basal heat-flow density were varied in order to reach a reasonable fit between the modelled and measured borehole temperatures. To reach this goal, the ground-temperature history must include the main climatic events during the last 100000 yr, such as the last glacial epoch and the Little Ice Age (from about 1300 AD to 1700 AD), followed by warmer temperatures in more recent times. Our results suggests that subsurface temperatures in conditions similar to those of the Outokumpu case can yield a wealth of palaeoclimatic information when an appropriate approach for modelling heat transfer in the bedrock is chosen.

Reconstruction of high resolution ground temperature histories combining dendrochronological and geothermal data

In an attempt to obtain robust records of past climatic variations, geothermal temperature-depth data have been combined with dendrochronological data to yield high resolution ground temperature histories. Since the resolution of the dendrochronological record and the ground temperature history inferred from geothermal data are different, comparison of these records is made possible by multiplying the dendrochronological data by the model resolution matrix for the geothermal data inversion. Under this condition, we find that a simple transformation between tree-ring indices and ground temperature changes allows us to interpret tree-ring widths in terms of ground temperatures, thus yielding a high resolution ground temperature history which explains the observed subsurface temperature regime. The linear transformation relating the ground temperature changes and average variations from the tree-ring chronology was found to beΔ T g = 9.93 I average.

Records of climatic change in the Canadian Arctic: towards calibrating oxygen isotope data with geothermal data

Borehole temperature-depth data have been combined with oxygen isotope data from an ice core at a nearby location in the Canadian Arctic to calibrate the oxygen isotope data to ground temperature histories. The relationship of oxygen isotope data to ground surface temperature history is δ 18O = 0.42 ΔT g and this reproduces the main features of the observed subsurface temperature profile measured at the borehole site. These results suggests that oxygen isotope data are a good representation of the regional, long term climatic variations at these latitudes. Discrepancies between the observed subsurface profile and the theoretical profile calculated from the calibrated oxygen isotope time series may be explained in terms of the different character of the records, in particular snow cover, and active layer processes.

Ground temperature history in central Europe from borehole temperature data

SUMMARY Ground temperature histories (GTH) are inferred from temperature measurements in several boreholes of south-eastern Germany and western Bohemia (Czech Republic). The GTHs that can be extracted from these boreholes, ranging in depth between 150 and 700m, cover the past 250yr. Both data sets were inverted separately and yield consistent GTHs. They were also inverted jointly to yield a regional GTH of the past 250yr for this part of Europe. The results indicate two main episodes in the mean ground temperature with (1) a cooling period from 1750-1800 to 1930-1950, followed by (2) short colder and warmer periods until now. The same trends are found in the meteorological records at four nearby weather stations (Bayreuth, Jena, Munchen and Praha), but the meteorological record in Berlin is clearly distinct. The GTH for this part of Europe is also markedly different from one obtained in central France. These differences are consistent with the spatial variability of climatic trends.

Resolution of ground temperature histories inverted from borehole temperature data

Inversion methods have been used to determine ground temperature history from borehole temperature data. This paper examines the resolution of an inversion method based on singular value decomposition. The method includes in the constraints the rate of change of subsurface if available. The response of the Earth to a unit pulselike change in surface temperature and the model resolution were calculated to determine the details of ground temperature variations obtainable from geothermal data. The model parameters estimated by the inversion correspond to averages over time intervals of increasing length with time. For a unit impulse temperature change occurring at time t before present, the estimated ground temperature history shows the event “spread” over at least 60% the time of occurrence. In practice, the resolution is not improved by increasing the sampling frequency of the data. Likewise, the simultaneous inversion of the temperature profile and of its time derivative does not significantly improve the resolution. Selection of a particular parametrization may improve resolution of the chosen parameters, but not the actual resolution since the parameters represent longer time averages. Temperature data from the Minchin Lake borehole in western Ontario, which was logged twice over 15 years, have been inverted to illustrate these conclusions.

Climate change on the Colorado Plateau of eastern Utah inferred from borehole temperatures

Temperature profiles from boreholes on the Colorado Plateau of southeastern Utah have been examined for evidence of climate change. Because these boreholes penetrate layered sedimentary rocks with different thermal conductivities, Bullard plots (temperature versus integrated thermal resistance) are used to estimate background heat flow and surface temperature intercepts. Reduced temperatures, which represent departures from a constant heat flow condition, are inverted for a surface ground temperature history at each borehole site using a singular value decomposition algorithm. Singular value cutoffs are selected by analyzing the spectral energy and the standard deviation of the model fit to the data as a function of the number of eigenvalues; solutions are constructed from areas of large spectral energy and a cutoff where additional eigenvalues fail to improve the solution significantly. The solution is parameterized in terms of 13 time steps increasing in duration and going back 400 years. Eight of nine borehole sites indicate between 0.4 and 0.8°C (±0.2° C) warming over the past 200 years with some evidence for accelerated warming in this century; one borehole indicates local cooling over the same time period. The amplitude of the warming inferred from borehole temperatures is less than that deduced from analysis of 100‐year surface air temperature records at four of the five weather stations surrounding the borehole sites.

Heat advection versus conduction at the KTB: possible reasons for vertical variations in heat-flow density

SUMMARY Data from the 4 km deep KTB pilot hole (VB) show a strong vertical variation in heat-flow density (HFD) by as much as 50 per cent. This may be caused both by heat conduction, by advection, and by transient diffusion. At the moment it is not possible to quantify exactly the contribution of each of these. However, 2-D simulations help to define the parameter ranges and structural features required if these processes are to be thermally efficient. The main results are: (1) thermal conductivity contrasts combined with structural heterogeneities as seen in the drilled profile give rise to steady-state, lateral refraction of heat. 2-D simulations of heat conduction indicate that this effect alone is sufficiently strong to account for the observed variation of HFD with depth. (2) Vertical PCclet number analyses of T-logs in shallow boreholes and the KTB-VB indicate a NE-SW flow of meteoric water across the Franconian Line (FL). However, average PCclet numbers of -0.37f0.13 in the potential recharge zone east of the FL are compatible with 2-D, steady-state simulations of heat and fluid flow only up to a distance of about 10 km east of the FL, and only if a crystalline permeability k, = m2 is assumed. (3) A permeability this high, however,' is not confirmed by a comparison of temperature and HFD from numerical simulations and data from the KTB boreholes, neither for a model focusing on shallow flow systems nor a deep structural model investigating potential contributions of convection in the entire upper crust. (4) Alternatively, a joint inversion of T-logs from the same shallow holes yields a ground-temperature history (GTH) that is in remarkably good agreement with long-term meteorological records. (5) It appears, therefore, as if the thermal regime at the KTB was generally dominated by conduction, with additional advective, topography-driven contributions mainly at shallow depths. The conductive regime, however, is a complicated one, characterized by lateral heat flow due to structural heterogeneity (and possibly anisotropy), and, at least at shallower depths, by transient diffusion of paleoclimatic temperature signals into the subsurface.

Ground temperature changes in eastern Canada: borehole temperature evidence compared with proxy data

ABSTRACTBorehole temperature logs have been inverted to infer ground temperature histories (GTH) in eastern and central Canada. Regional ground temperature histories were obtained by simultaneous inversion of several temperature profiles from the same areas. Simultaneous inversion of 21 temperature logs sampled across all of eastern and central Canada yielded an average solution for this region. All but three of the studied sites show signs of warming in the last 150 years. This period of warming, which started after 1800 AD, was found throughout this part of Canada. The warming followed a cooler period corresponding to the little Ice Age. The inferred ground temperature histories exhibit long‐term trends similar to those obtained from treering growth indices in nearby regions and stable isotope data in the southern hemisphere. The modern warming appears correlated with the atmospheric concentration of CO2 as measured in ice cores.

Ground temperature history from two deep boreholes in Central France

Ground temperature histories were inverted from temperature measurements in two deep boreholes (700 and 1000 m) in central France. The study has identified three main climatic episodes over the past 1500 years: (1) a climatic optimum at ca 1000 AD, (2) the little ice ages with a minimum at ca 1600–1700 AD, and AD, and (3) recent warming over the past 150–200 years. The results, which confirm a previously published analysis of past climate in France, exhibit trends similar to those found in other parts of the world.

Ground temperature history from two deep boreholes in Central France

Ground temperature histories were inverted from temperature measurements in two deep boreholes (700 and 1000 m) in central France. The study has identified three main climatic episodes over the past 1500 years: (1) a climatic optimum at ca 1000 AD, (2) the little ice ages with a minimum at ca 1600–1700 AD, and AD, and (3) recent warming over the past 150–200 years. The results, which confirm a previously published analysis of past climate in France, exhibit trends similar to those found in other parts of the world.

Ground temperature histories in eastern and central Canada from geothermal measurements: evidence of climatic change

Inverse and direct methods have been used to analyze a large number of borehole temperature logs in order to infer past climatic changes. Results indicate a warming of 1–2°C in eastern and central Canada during the past 150 years. A period of cooling between 500 and 200 years before present, corresponding to the time of the “Little Ice Age”, has also been identified in the same areas. A regional ground temperature history is estimated for eastern and central Canada from the simultaneous inversion of several temperature logs. The inferred temperature changes appear correlated with the concentration of atmospheric carbon dioxide as reported from a Greenland ice core, and agree with existing meteorological and dendrochronological records for the area.

Ground temperature histories in eastern and central Canada from geothermal measurements: evidence of climatic change

Inverse and direct methods have been used to analyze a large number of borehole temperature logs in order to infer past climatic changes. Results indicate a warming of 1–2°C in eastern and central Canada during the past 150 years. A period of cooling between 500 and 200 years before present, corresponding to the time of the “Little Ice Age”, has also been identified in the same areas. A regional ground temperature history is estimated for eastern and central Canada from the simultaneous inversion of several temperature logs. The inferred temperature changes appear correlated with the concentration of atmospheric carbon dioxide as reported from a Greenland ice core, and agree with existing meteorological and dendrochronological records for the area.