Are open fractures necessarily aligned with maximum horizontal stress?

Fluid flow in fractured rock is an increasingly central issue in recovering water and hydrocarbon supplies and geothermal energy, in predicting flow of pollutants underground, in engineering structures, and in understanding large-scale crustal behaviour. Conventional wisdom assumes that fluids prefer to flow along fractures oriented parallel or nearly parallel to modern-day maximum horizontal compressive stress, or S_Hmax. The reasoning is that these fractures have the lowest normal stresses across them and therefore provide the least resistance to flow. For example, this view governs how geophysicists design and interpret seismic experiments to probe fracture fluid pathways in the deep subsurface. Contrary to these widely held views, here we use core, stress measurement, and fluid flow data to show that S_Hmax does not necessarily coincide with the direction of open natural fractures in the subsurface (>3 km depth). Consequently, in situ stress direction cannot be considered to predict or control the direction of maximum permeability in rock. Where effective stress is compressive and fractures are expected to be closed, chemical alteration dictates location of open conduits, either preserving or destroying fracture flow pathways no matter their orientation.     

The influence of systematic errors in the Southeast Pacific on ENSO variability and prediction in a coupled GCM

The impact of the warm SST bias in the Southeast Pacific (SEP) on the quality of seasonal and interannual variability and ENSO prediction in a coupled GCM is investigated. The reduction of this bias is achieved by means of empirical heat flux correction that is constant in time. It leads to a wide range of changes in the tropical Pacific climate including enhanced southeast trades, well-defined dry zone in the SEP, better simulation of the South Pacific Convergence Zone and stronger cross-equatorial asymmetry of the mean state in the eastern Pacific. As a result of the mean climate correction, significant improvements in the simulation of the seasonal cycle of the oceanic and atmospheric states are also observed both at the equator and basin-wide. Due to more realistic simulation of the seasonal evolution of the cold tongue, tropical convection and surface winds in the corrected version of the model, phase-lock of ENSO to the annual cycle looses its strong semi-annual component and becomes quite similar to the observed, although the amplitude of ENSO is reduced. Zonal wind stress response to the SST anomalies in the central-eastern Pacific also becomes more realistic. ENSO retrospective forecast experiments conducted with the directly coupled and the flux-corrected versions of the model demonstrate that deficiencies in the seasonal evolution of the cold tongue/Inter-Tropical Convergence Zone complex (that were largely due to the SEP bias in this model) and the related errors in the ENSO phase-lock to the annual cycle can seriously degrade ENSO prediction. By reducing these errors, ENSO predictive skill in the coupled model was substantially enhanced.     

Natural variability of summer rainfall over China in HadCM3

Summer rainfall over China has shown decadal variability in the past half century, which has resulted in major north–south shifts in rainfall with important implications for flooding and water resource management. This study has demonstrated how multi-century climate model simulations can be used to explore interdecadal natural variability in the climate system in order to address important questions around recent changes in Chinese summer rainfall, and whether or not anthropogenic climate change is playing a role. Using a 1,000-year simulation of HadCM3 with constant pre-industrial external forcing, the dominant modes of total and interdecadal natural variability in Chinese summer rainfall have been analysed. It has been shown that these modes are comparable in magnitude and in temporal and spatial characteristics to those observed in the latter part of the twentieth century. However, despite 1,000 years of model simulation it has not been possible to demonstrate that these modes are related to similar variations in the global circulation and surface temperature forcing occurring during the latter half of the twentieth century. This may be in part due to model biases. Consequently, recent changes in the spatial distribution of Chinese summer rainfall cannot be attributed solely to natural variability, nor has it been possible to eliminate the likelihood that anthropogenic climate change has been the driving factor. It is more likely that both play a role.     

Luminescence dating of ice‐marginal deposits in northern Germany: evidence for repeated glaciations during the Middle Pleistocene (MIS 12 to MIS 6)

The exact number, extent and chronology of the Middle Pleistocene Elsterian and Saalian glaciations in northern Central Europe are still controversial. This study presents new luminescence data from Middle Pleistocene ice‐marginal deposits in northern Germany, giving evidence for repeated glaciations during the Middle Pleistocene (MIS 12 to MIS 6). The study area is located in the Leine valley south of the North German Lowlands. The data set includes digital elevation models, high‐resolution shear wave seismic profiles, outcrop and borehole data integrated into a 3D subsurface model to reconstruct the bedrock relief surface. For numerical age determination, we performed luminescence dating on 12 ice‐marginal and two fluvial samples. Luminescence ages of ice‐marginal deposits point to at least two ice advances during MIS 12 and MIS 10 with ages ranging from 461±34 to 421±25 ka and from 376±27 to 337±21 ka. The bedrock relief model and different generations of striations indicate that the older ice advance came from the north and the younger one from the northeast. During rapid ice‐margin retreat, subglacial overdeepenings were filled with glaciolacustrine deposits, partly rich in re‐worked Tertiary lignite and amber. During MIS 8 and MIS 6, the study area may have been affected by two ice advances. Luminescence ages of glaciolacustrine delta deposits point to a deposition during MIS 8 or early MIS 6, and late MIS 6 (250±20 to 161±10 ka). The maximum extent of both the Elsterian (MIS 12 and MIS 10) and Saalian glaciations (MIS 8? and MIS 6) approximately reached the same position in the Leine valley and was probably controlled by the formation of deep proglacial lakes in front of the ice sheets, preventing a further southward advance.     

A framework for addressing the lack of diversity in the Geosciences through evaluating the current structure of institutional efforts

How can universities build institutional partnerships through supporting community geography projects? This paper details the case of university members seeking to achieve a community goal of expanding Geosciences education opportunities, while also targeting a long-range goal of improving diversity within the university Geosciences. Over the course of one year, two Ph.D students collaborated with community members affiliated with a local middle school to design and organize the School of Earth, Society, and Environment (SESE) Geosciences Camp for Middle School Girls, held in August 2019. This paper deconstructs and critiques the camp organizing process and its outcomes. The conclusion addresses what worked and what did not as a model for future attempts at more sustainable institutional partnerships serving community geography projects.