Deep, hot, and more alive than we thought Marine sediments represent a massive microbial ecosystem, but we still do not fully understand what factors shape and limit life underneath the seafloor. Analyzing samples from a subduction zone off the coast of Japan, Heuer et al. found that microbial life, in particular bacterial vegetative cells, decreases as depth and temperature increases down to ∼600 meters below the seafloor, corresponding to temperatures of ∼70°C. Below this limit, endospores are common—a remnant, and a potential reservoir, of bacterial life. Deeper still is a sterile zone, and below 1000 meters is a scalding realm populated by vegetative cells. At such great depths, high concentrations of acetate and sulfate coexist, and there are also signs of hyperthermophilic methanogenesis. These data provide a fascinating window into an extreme and inhospitable environment that nonetheless supports microbial life. Science , this issue p. 1230

Abstract A constructive back-propagation code that was designed to run as a single-hidden-layer, feed-forward neural network (SLFFNN) has been adapted and used to estimate subsurface temperature from a small volume of magnetotelluric (MT)-derived electrical resistivity data and borehole thermograms. The code was adapted to use a looping procedure in searching for better initialization conditions that can optimally solve nonlinear problems using the random weight initialization approach. Available one-dimensional (1D) MT-derived resistivity data and borehole temperature records from the Tattapani geothermal field, central India, were collated and digitized at 10-m intervals. The two datasets were paired to form a set of input–output pairs. The paired data were randomized, standardized, and partitioned into three mutually exclusive subsets. The various subsets had 52% (later increased to 61%), 30%, and 18% (later reduced to 9%) for training, validation, and testing, respectively, in the first and second training phases. The second training phase was meant to assess the influence of the training data volume on network performance. Standard statistical techniques including adjusted coefficient of determination (R2a), relative error (ɛ), absolute average deviation (AAD), root-mean-square error (RMSE), and regression analysis were used to quantitatively rate network performance. A manually designed two-hidden-layer, feed-forward network with 20 and 15 neurons in the first and second layers was also adopted in solving the same problem. Performance ratings were observed to be 0.97, 3.75, 4.09, 1.41, 1.18, and 1.08 for R2a, AAD, ɛ, RMSE, slope, and intercept, respectively, compared to an ɛ of 20.33 observed with the manually designed network. The SLFFNN is thus a structurally flexible network that performs better in spite of the small volume of data used in testing the network. The network needs to be tested further.

Abstract. Deep subsurface microorganisms constitute over 80 % of Earth's prokaryotic biomass and play an important role in global biogeochemical cycles. Geochemical processes driven by geothermal heating are key factors influencing their biomass and activities, yet their full breadth remains uncaptured. Here, we investigated the microbial community composition and metabolism in microbial-natural-gas-bearing aquifers at temperatures ranging from 38 to 81 °C, situated above nonmicrobial-gas- and oil-bearing sediments at temperatures exceeding 90 °C. Cultivation-based and molecular gene analyses, including radiotracer measurements, of formation water indicated variations in predominant methanogenic pathways across different temperature regimes of upper aquifers: high potential for hydrogenotrophic–methylotrophic, hydrogenotrophic, and acetoclastic methanogenesis at temperatures of 38, 51–65, and 73–81 °C, respectively. The potential for acetoclastic methanogenesis correlated with elevated acetate concentrations with increasing depth, possibly due to the decomposition of sedimentary organic matter. In addition to acetoclastic methanogenesis, in aquifers at temperatures as high as or higher than 65 °C, acetate is potentially utilized by microorganisms responsible for the dissimilatory reduction of sulfur compounds other than sulfate because of their high relative abundance at greater depths. The stable sulfur isotopic analysis of sulfur compounds in water and oil samples suggested that hydrogen sulfide, generated through the thermal decomposition of sulfur compounds in oil, migrates upward and is subsequently oxidized with iron oxides present in sediments, yielding elemental sulfur and thiosulfate. These compounds are consumed by sulfur-reducing microorganisms, possibly reflecting elevated microbial populations in aquifers at temperatures as high as or higher than 73 °C. These findings reveal previously overlooked geothermal-heat-driven geochemical and microbiological processes involved in carbon and sulfur cycling in the deep sedimentary biosphere.

Genetic differentiation in traits is assumed to frequently occur in response to divergent natural selection. For example, developmental traits might respond to differences in climate. However, little is known about when and at which spatial scales environmental differences lead to genetic differentiation, and to what extent there is genetic differentiation also in trait plasticity. Using a crossing design and a greenhouse heating experiment, we investigated genetic differentiation in thermal sensitivity of flowering time in a perennial herb along small-scale gradients in geothermal soil heating in Iceland. We found additive genetic variation in both flowering time and thermal plasticity of flowering time. Genetic differentiation in median flowering date of individuals showed a counter-gradient pattern; flowering being earlier at higher greenhouse temperatures, while at a given temperature individuals originating from warmer soils flowered later than individuals from colder soils. We found no corresponding pattern for plasticity, suggesting that genetic differentiation in phenology in response to soil heating has occurred through changes in trait means rather than in plasticity. Findings such as these, identifying genetic trait differentiation along an environmental gradient are key to understand how environmental variation can drive the process of local adaptation, and to predict responses to future environmental changes.

The Büyük Menderes Graben (BMG) is an E-W oriented active extensional geothermal basin within the Menderes Massif, a metamorphic core complex, in Western Anatolia, Turkey. 1500 (megawatts-energy) MWe of installed geothermal capacity for power production exist as of December 2019 in Western Anatolia, mostly generated in the BMG. While the BMG is a vastly producing geothermal resource, it is predicted that it has higher production potential. However, other studies do not include field scale 3D geologic models or geothermal gradient maps. This study aims to first quantitatively test the geothermal gradients in the Aydın-İncirliova-Osmanbükü Geothermal Field (IGF), then map the information. This study also aims to compare the IGF with a neighboring geothermal field. To complete this study, information from stratigraphic columns, bottom hole temperatures, and continuous temperature logs from 13 geothermal wells is utilized with Leapfrog Geothermal to create 3D models of the geology and subsurface temperature distribution. Then, isothermal contour maps of the field are created. The geologic modeling suggests that synextensional deposition has occurred within the graben. The temperature modeling suggests both that thermal breakthrough may have occurred in the field, and that the IGF has a higher geothermal gradient than the nearby Germencik Geothermal Field

Abstract Geothermal gradient is an important tool in petroleum exploration and critical to several reservoir evaluations. Borehole Temperature data from 14 wells are utilized to find the geothermal tendency of the Western Desert in Iraq. The discrepancies in geothermal gradients throughout the area are a consequence of variability of sediment’s thermal conductivity, direction of groundwater flow, fault pattern, and heat generation. High value converts liquid hydrocarbon to dry gas and low value will not help organic matter to reach maturity level. The lowest gradient within the units above Palaeozoic Era’s section is 12.2 °C/km for well KH-9/7 in the eastern part of the area and the highest is 31.3 °C/km for well KH-5/4 in the middle part of the region. Whereas, the highest geothermal gradient which is 61.0 °C/km within the Palaeozoic section is recorded within Akkas Formation in 2100-2350 m subsurface. The mean geothermal gradient in Western Desert is 26 °C/km within the units younger than the Palaeozoic, but this average rises up to 40 °C/km within Palaeozoic units due to existence of Silurian hot shales and heat flow from the Proterozoic section especially from Halaban Group andesites.

sediments and soils; the climate on the surface, temperature profiles and hydrology also vary. Most of the information on subsurface life comes from a small The deep biosphere is the part of the biosphere that resides below the first few meters of the land surface and seafloor. It extends 10 km (6.2 mi) below the continental surface and 21 km (13 mi) below the sea surface, at temperatures that may reach beyond 120 °C (248 °F) which is comparable to the maximum temperature where a metabolically active organism has been found. It includes all three doma T…