Jacek A. Majorowicz

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.

Large ground warming in the Canadian Arctic inferred from inversions of temperature logs

Abstract The simultaneous functional space inversion applied for the first time to the set of precise temperature logs from 61 wells located between 60° and 82°N in northern Canada shows evidence of large ground surface temperature (GST) warming. These results include highest latitude locations of the well temperature profiles known in the Northern Hemisphere. There is strong evidence that GST warming started in the late-18th century and lasted until the 20th century. Simultaneous inversion of all well temperature data suggests that the cumulative ground surface temperature change over the past five centuries amounts to about 2°C significantly exceeding recent estimates from conventional climate proxies. This large GST warming is also present in other circumpolar locations in the Northern Hemisphere.

Measured versus simulated transients of temperature logs—a test of borehole climatology

We report the results of repeated temperature, T, measurements with depth (z) for two borehole sites located in the Western Canadian Sedimentary Basin, in central Alberta and south central Saskatchewan. These were logged at three different times within the time period of 1986 AD to 2004 AD. Subsurface temperature transient changes of 0.1 to 0.4 °C observed between the repeated temperature logs over the last two decades agree only partially with the changes derived from the synthetic profiles in which surface temperature time series were used as forcing signals. The surface temperature forcing is responsible for the majority of the observed deviation of temperature with depth. In some cases, differences higher than the error of measurement are observed between the model and measurements. This can be an indication that factors other than the surface temperature change also influence the subsurface thermal regime.

The Climate of Europe in Recent Centuries in the Context of the Climate of Mid to High Latitude Northern Hemisphere from Borehole Temperature Logs

I present results from inversions for ground surface temperature histories reconstructed from deep borehole temperatures in Europe in the context of mid to high latitude Northern Hemisphere data. Precise deep borehole temperature logs provide information about the average warming and preceding colder period and average timing of the onset and magnitude of the recent warm period. Analysis of the borehole temperature-depth data from the mid to high latitude Northern Hemisphere using a simple ramp function model indicates that the timing of the onset of warming and its amplitude varies spatially. This large spatial variation explains large standard deviation of the average ground surface temperature histories derived from stack of individual ground surface temperature reconstructions from borehole temperature logs. Such averaged continental and N Hemisphere histories are commonly used to compare with other proxy. Central and Northern European borehole temperatures point to high ground temperature warming (0.5°–2°C) in recent two centuries. This warming is generally less than in northern parts of North America including high Arctic and less than most of Asia (1°–3°C). Timing of the onset of Central European recent warm period is circa 100–150 years and is compatible with that in the northern N. America and especially western Canada and Alaska. It is more than 200 years for the start of the recent warming period in south-central N. America and in Asia. Warming signal from Earth’s subsurface is apparent for the Polish borehole temperature logs. Large warming observed in central–northern Europe is the main feature seen from the available european data.