Volker Rath

Chapter 1 Mediterranean climate variability over the last centuries: A review

Publisher Summary This chapter discusses a necessary task for assessing to which degree the industrial period is unusual against the background of pre-industrial climate variability. It is the reconstruction and interpretation of temporal and spatial patterns of climate in earlier centuries. There are distinct differences in the temporal resolution among the various proxies. Some of the proxy records are annually or even higher resolved and hence record year-by-year patterns of climate in past centuries. Several of the temperature reconstructions reveal that the late twentieth century warmth is unprecedented at hemispheric scales and is explained by anthropogenic, greenhouse gas (GHG) forcing. The chapter discusses the availability and potential of long, homogenized instrumental data, documentary, and natural proxies to reconstruct aspects of past climate at local- to regional-scales within the larger Mediterranean area, which includes climate extremes and the incidence of natural disasters. The chapter describes the role of external forcing, including natural and anthropogenic influences, and natural, internal variability in the coupled ocean–atmosphere system at subcontinental scale.

Thermal conductivity from core and well log data

Abstract The relationships between thermal conductivity and other petrophysical properties have been analysed for a borehole drilled in a Tertiary Flysch sequence. We establish equations that permit us to predict rock thermal conductivity from logging data. A regression analysis of thermal conductivity, bulk density, and sonic velocity yields thermal conductivity with an average accuracy of better than 0.2 W ( m K ) - 1 . As a second step, logging data are used to compute a lithological depth profile, which in turn is used to calculate a thermal conductivity profile. From a comparison of the conductivity–depth profile and the laboratory data, it can be concluded that thermal conductivity can be computed with an accuracy of less than 0.3 W ( m K ) - 1 from conventional wireline data. The comparison of two different models shows that this approach can be practical even if old and incomplete logging data are used. The results can be used to infer thermal conductivity for boreholes without appropriate core data that are drilled in a similar geological setting.

A Review of 2000 Years of Paleoclimatic Evidence in the Mediterranean

The integration of climate information from instrumental data and documentary and natural archives; evidence of past human activity derived from historical, paleoecological, and archaeological records; and new climate modeling techniques promises major breakthroughs for our understanding of climate sensitivity, ecological processes, environmental response, and human impact. In this chapter, we review the availability and potential of instrumental data, less well-known written records, and terrestrial and marine natural proxy archives for climate in the Mediterranean region over the last 2000 years. We highlight the need to integrate these different proxy archives and the importance for multiproxy studies of disentangling complex relationships among climate, sea-level changes, fire, vegetation, and forests, as well as land use and other human impacts. Focusing on dating uncertainties, we address seasonality effects and other uncertainties in the different proxy records. We describe known and anticipated challenges posed by integrating multiple diverse proxies in high-resolution climate-variation reconstructions, including proxy limitations to robust reconstruction of the natural range of climate variability and problems specific to temporal scales from interannual to multicentennial. Finally, we highlight the potential of paleo models to contribute to climate reconstructions in the Mediterranean, by narrowing the range of climate-sensitivity estimates and by assimilating multiple proxies.

Uncertainties and shortcomings of ground surface temperature histories derived from inversion of temperature logs

Analysing borehole temperature data in terms of ground surface history can add useful information to reconstructions of past climates. Therefore, a rigorous assessment of uncertainties and error sources is a necessary prerequisite for the meaningful interpretation of such ground surface temperature histories. This study analyses the most prominent sources of uncertainty. The diffusive nature of the process makes the inversion relatively robust against incomplete knowledge of the thermal diffusivity. Similarly the influence of heat production is small. It turns out that for investigations of the last 1000 to 100 000 years the maximum depth of the temperature log is crucial. More than 3000 m are required for an optimal inversion. Reconstructions of the last one or two millennia require only modestly deep logs (>300 m) but suffer severely from noisy data.

The thermal regime of the Eastern Alps from inversion analyses along the TRANSALP profile

A combination of petrophysical measurements and inverse modeling is used to estimate the 2-D, steady-state conductive thermal regime in the crust and heat flow at the Moho along the N–S trending TRANSALP profile across the continental collision zone of the Eastern Alps. The uncertainty to which each parameter in the simulation is known beforehand is expressed in terms of its variance, entering a Bayesian parameter estimation scheme. This approach is particularly attractive for geological applications–– where often information is available, if only with large uncertainty––because it allows to introduce soft information into a quantitative approach. Our inversion studies show that while the large a priori standard deviation of particularly the heat production rate in the upper crust can be significantly reduced a posteriori, the variance of the middle crust heat production rate remains comparatively large. Using two extreme models with maximum and minimum heat production rates in the middle crust the range of Moho temperatures and heat flow can be estimated. Depending on different assumptions about the composition of the middle crust we obtain maximum temperatures of around 900 C � 30% in the lower most parts of the European crust. In the Alpine root and in the Southern Alps, maximum temperatures are 700–800 C � 10% and 600 C � 10%, respectively. Moho heat flow varies from 5–25 mW m � 2 and is

Ground Surface Temperature Histories Reconstructed from Boreholes in Poland: Implications for Spatial Variability

We present results from inversions for ground surface temperature histories (GSTH), reconstructed from two deep boreholes in Poland. One data set comes from the Udryn borehole, located in northeastern Poland. It implies temperatures during the last glacial maximum (LGM) near −10°C, some 18 K lower than today. Since Udryn is located in a low heat flow region (40 mW m−2), a thick permafrost layer could develop. The associated latent heat effect is important and was considered in the inversions.The second data set originates from Czeszewo which lies in western Poland, about 400 km from Udryn. Here, heat flow is considerably higher (≈90 mW m−2). This prevents the formation of a thick permafrost layer in spite of the high porosities. First results from GSTH inversions suggest about 10 K lower temperatures at the LGM than today. This is considerably less than in Udryn and confirmed by recently published results of the 2.9 km deep temperature log in the Torun borehole (130 km NE of Czeszewo), which shows heat flow values around 60 mW m−2.We discuss possible reasons for this large difference of the temperatures during the LGM within a few 100 km. The most important seems to be the different position with respect to the time-dependent rim of the Eurasian ice sheet.

Estimating Darcy flow velocities from correlated anomalies in temperature logs

Fluid flow in reservoirs can be identified by its characteristic signatures in temperature logs. The method presented here is based on the great sensitivity of the subsurface temperature field with respect to heat advected by fluid flow. This requires that all other temperature perturbations are eliminated. These may be caused, for instance, by heterogeneous thermal properties or paleoclimate transients, both of which may distort an otherwise linear temperature log. We propose a simple geothermal technique for quantifying regional strata-bound flow based on a detailed analysis of borehole temperatures. Depending on the spatial data distribution and the geothermal situation, this method yields results of varying quality. In a case study with data from southern Germany, the method yields a lower bound for the flow magnitude. Another case study from northern Germany yields the magnitude of the regional flow owing to a larger data set and information of the direction of flow from additional independent information. Under optimum conditions, this method also yields an estimate of the direction of regional strata-bound groundwater flow as well as the uncertainty in magnitude and direction. Finally, the full potential of the method is illustrated using a synthetic data set.

A Multidimensional Markov Chain Model for Simulating Stochastic Permeability Conditioned by Pressure Measures

In this paper, we are interested in simulating a stochastic permeability distribution constrained by some pressure measures coming from a steady flow (Poisson problem) over a two-dimensional domain. The permeability is discretized over a regular rectangular gird and considered to be constant by cell but it can take randomly a finite number of values. When such permeability is modeled using a multidimensional Markov chain, it can be constrained by some permeability measures. The purpose of this work is to propose an algorithm that simulates stochastic permeability constrained not only by some permeability measures but also by pressure measures at some points of the domain. The simulation algorithm couples the MCMC sampling technique with the multidimensional Markov chain model in a Bayesian framework.

Multi‐Layer Constrained Identification in Geophysics with Shape Optimization and Level Set Methods

This work shows the use of multiple level set functions with constraints in order to reconstruct multiple geophysical layers from temperature measurements with shape optimization methods. Temperature is measured inside subdomains modeling the boreholes and the interface of the geophysical zones is described with level set functions. Shape optimization techniques are used to derive the adjoint equations and the gradient for the iterative process. The direct and the adjoint equations are solved with the standard finite element method.

Semi-automatic parallelization of direct and inverse problems for geothermal simulation

We describe a strategy for parallelizing a geothermal simulation package using the shared-memory programming model OpenMP. During the code development OpenMP is employed for the direct problem in such a way that, in a subsequent step, the OpenMP-parallelized code can be transformed via automatic differentiation into an OpenMP-parallelized code capable of computing derivatives for the inverse problem. Performance results on a Sun Fire X4600 using up to 16 threads are reported demonstrating that, for the derivative computation, an approach using nested parallelism is more scalable than a single level of parallelism.