Blown Earth A Study of the Parisian Infrastructural Relief

“His mind was like a soup dish—wide and shallow; ...” - Irving Stone on William Jennings Bryan A compilation of the Sr-isotopic stratigraphy of the Bushveld Complex, shows that the evolution of the magma chamber occurred in two major stages. During the lower open-system Integration Stage (Lower, Critical and Lower Main Zone), there were numerous influxes of magma of contrasting isotopic composition with concomitant mixing, crystallisation and deposition of cumulates. Larger influxes correspond to the boundaries of the zones and sub-zones and are marked by sustained isotopic shifts, major changes in mineral assemblages and development of unconformities. During the upper, closed system Differentiation Stage (Upper Main Zone and Upper Zone), there were no major magma additions (other than that which initiated the Upper Zone), and the thick magma layers evolved by fractional crystallisation. The Lower and Lower Critical Zones are restricted to a belt that runs from Steelpoort and Burgersfort in the northeast, to Rustenburg and Northam in the west and an outlier of the Lower and Lower Critical Zone, up to the LG4 chromitite layer, in the far western extension north of Zeerust. It is only in these areas that thick harzburgite and pyroxenite layers are developed and where chromitites of the Lower Critical Zone occur. These chromitites include the economically important c. 1 m thick LG6 and MG1 layers exposed around both the Eastern and Western lobes of the Bushveld Complex. The Upper Critical Zone has a greater lateral extent than the Lower Critical Zone and overlies but also onlaps the floor-rocks to the south of the Steelpoort area . The source of the magmas also appears to have been towards the south as the MG chromitite layers degrade and thin northward whereas the LG layers are very well represented in the North and degrade southward. Sr and Os isotope data indicate that the major chromitite layers including the LG6, MG1 and UG2 originated in a similar way. Extremely abrupt and stratigraphically restricted increases in the Sr isotope ratio imply that there was massive contamination of intruding melt which “hit the roof” of the chamber and incorporated floating granophyric liquid which forced the precipitation of chromite (Kruger 1999; Kinnaird et al. 2002). Therefore, each chromitite layer represents the point at which the magma chamber expanded and eroded and deformed its floor. Nevertheless, this was achieved by in situ contamination by roof-rock melt of the intruding Critical Zone liquids that had an orthopyroxenitic to noritic lineage. The Main Zone is present in the Eastern and Western lobes of the Bushveld Complex where it overlies the Critical Zone, and onlaps the floor-rocks to the south, and the north where it is also the basal zone in the Northern lobe. The new magma first intruded the Northern lobe north of the Thabazimbi–Murchison Lineament, interacted with the floor-rocks, incorporated sulphur and precipitated the “Platreef” along the floor-rock contact before flowing south into the main chamber. This exceptionally large influx of new magma then eroded an unconformity on the Critical Zone cumulate pile, and initiated the Main Zone in the main chamber by precipitating the Merensky Reef on the unconformity. The Upper Zone magma flowed into the chamber from the southern “Bethal” lobe as well as the TML. This gigantic influx eroded the Main Zone rocks and caused very large-scale unconformable relationships, clearly evident as the “Gap” areas in the Western Bushveld Complex. The base of this influx, which is also coincident with the Pyroxenite Marker and a troctolitic layer in the Northern lobe, is the petrological and stratigraphic base of the Upper Zone. Sr-isotope data show that all the PGE rich ores (including chromitites) are related to influxes of magma, and are thus related to the expansion and filling of the magma chamber dominantly by lateral expansion; with associated transgressive disconformities onto the floor-rocks coincident with major zone changes. These positions in the stratigraphy are marked by abrupt changes in lithology and erosional features over which succeeding lithologies are draped. The outcrop patterns and the concordance of geochemical, isotopic and mineralogical stratigraphy, indicate that during crystallisation, the Bushveld Complex was a wide and shallow, lobate, sill-like sheet, and the rock-strata and mineral deposits are quasi-continuous over the whole intrusion.

Chapter 18 - The Built Environment in the Critical Zone: From Pre- to Postindustrial Cities

Abstract. The critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetative canopy through the soil and down to fresh bedrock and the bottom of the groundwater. All humans live in and depend on the CZ. This zone has three co-evolving surfaces: the top of the vegetative canopy, the ground surface, and a deep subsurface below which Earth's materials are unweathered. The network of nine CZ observatories supported by the US National Science Foundation has made advances in three broad areas of CZ research relating to the co-evolving surfaces. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response, in turn, impacts aboveground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences aboveground ecosystems. Third, several new mechanistic models now provide quantitative predictions of the spatial structure of the subsurface of the CZ.Many countries fund critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gases, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each US observatory has succeeded in (i) synthesizing research across disciplines into convergent approaches; (ii) providing long-term measurements to compare across sites; (iii) testing and developing models; (iv) collecting and measuring baseline data for comparison to catastrophic events; (v) stimulating new process-based hypotheses; (vi) catalyzing development of new techniques and instrumentation; (vii) informing the public about the CZ; (viii) mentoring students and teaching about emerging multidisciplinary CZ science; and (ix) discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO enterprise in the United States and identify how such observatories could operate in the future as a network designed to generate critical scientific insights. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a driving question for future CZ science and a hubs-and-campaigns model to address that question and target the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.

Detecting and quantifying geochemical transport through the critical zone at the continental to regional scale requires reliable  statistical procedures that can be uniquely interpreted. We present methods that provide different views on the same data sets and  formulate rules for their application and interpretation. The statistical analysis of cumulative distribution functions (CDFs) uses cumulative probability (CP) plots for spatially representative multi-element and multi-media data sets, preferably containing >1000 sites.Mathematical models demonstrate how contamination can influence elemental CDFs of different  sample media. For example large-scale diffuse soil contamination leads to a distinctive shift of the low-concentration end of the distribution of the studied element in its top-soil CP plot, whereas high local contamination influences the high-concentration end. But also bio-geochemical processes can generate recognizable changes in elemental CDFs.A related and partly unsolved problem is the correct interpretation of compositional data in terms of their transport through  the critical zone.  

The critical zone (CZ) can be conceptualized as an open system reactor that is continually transforming energy and water fluxes into an internal structural organization and dissipative products. In this study, we test a controlling factor on water transit times (WTT) and mineral weathering called Effective Energy and Mass Transfer (EEMT). We hypothesize that EEMT, quantified based on local climatic variables, can effectively predict WTT within—and mineral weathering products from—the CZ. This study tests whether EEMT or static landscape characteristics are good predictors of WTT, aqueous phase solutes, and silicate weathering products. Our study site is located around Redondo Peak, a rhyolitic volcanic resurgent dome, in northern New Mexico. At Redondo Peak, springs drain slopes along an energy gradient created by differences in terrain aspect. This investigation uses major solute concentrations, the calculated mineral mass undergoing dissolution, and the age tracer tritium and relates them quantitatively to EEMT and landscape characteristics. We found significant correlations between EEMT, WTT, and mineral weathering products. Significant correlations were observed between dissolved weathering products (Na+ and DIC), 3H concentrations, and maximum EEMT. In contrast, landscape characteristics such as contributing area of spring, slope gradient, elevation, and flow path length were not as effective predictive variables of WTT, solute concentrations, and mineral weathering products. These results highlight the interrelationship between landscape, hydrological, and biogeochemical processes and suggest that basic climatic data embodied in EEMT can be used to scale hydrological and hydrochemical responses in other sites.

Peatlands, though covering only 3 % of the global land surface, play an active role in the Critical Zone (CZ) by mediating substantial water and carbon exchanges with adjacent aquifers, surface waters, and the atmosphere. These ecosystems provide key services, such as carbon and water storage and local climate regulation, addressing contemporary challenges related to climate change, biodiversity loss, and water resource management. However, peatlands are increasingly threatened by global pressures, including climate change, and local disturbances, such as drainage for agriculture, forestry, and peat extraction. To mitigate these threats, it is essential to understand the hydrological, biogeochemical, and ecological processes governing peatland dynamics across spatiotemporal scales. To explore the factors controlling greenhouse gases sources, production, and transport in peatlands, an interdisciplinary field campaign was conducted at the Frasne peatland (7 ha, 46.826°N, 6.1754°E, 840 m a.s.l.), a long-term observatory since 2008. The site is part of the French CZ research infrastructure (OZCAR) and the long term ecological research site Jurassian Arc, which focuses on the interaction between human and nature. The campaign was supported by the TERRA FORMA project, which develops smart, connected, low-cost, and low-impact environmental sensors to monitor CZ trajectories in the Anthropocene. The fieldwork integrated microbiological analyses of peat material, including membrane lipid profiling to trace microbial metabolisms, combined with detailed hydrogeochemical investigations of peat pore water along lateral flow and depth gradients. Measurements included physicochemical parameters (temperature, electrical conductivity, pH) and major elements, dissolved organic and inorganic carbon (DOC and DIC), CO₂, and CH₄ concentration, as well as their isotopic characterization (δ¹⁸O, δ²H, δ¹³C) . Additionally, greenhouse gases fluxes were quantified at multiple scales, employing methods such as dissolved gas profiling, chamber measurements, eddy covariance, and UAV-based surveys. This multiscale approach aims to tackle critical challenges in peatland research and management, including three-dimensional quantification of carbon fluxes (lateral and vertical) at the ecosystem scale; characterization of hydrological, biogeochemical, and ecological processes that modulate greenhouse gases and dissolved carbon production and transport; and development of accessible and efficient tools for addressing these pressing environmental issues. three-dimensional quantification of carbon fluxes (lateral and vertical) at the ecosystem scale; characterization of hydrological, biogeochemical, and ecological processes that modulate greenhouse gases and dissolved carbon production and transport; and development of accessible and efficient tools for addressing these pressing environmental issues.

Soil is the central interface of Earth's critical zone—the planetary surface layer extending from unaltered bedrock to the vegetation canopy—and is under intense pressure from human demand for biomass, water, and food resources. Soil functions are flows and transformations of mass, energy, and genetic information that connect soil to the wider critical zone, transmitting the impacts of human activity at the land surface and providing a control point for beneficial human intervention. Soil functions are manifest during bedrock weathering and, in fully developed soil profiles, correlate with the porosity architecture of soil structure and arise from the development of soil aggregates as fundamental ecological units. Advances in knowledge on the mechanistic processes of soil functions, their connection throughout the critical zone, and their quantitative representation in mathematical and computational models define research frontiers that address the major global challenges of critical zone resource provisioning for human benefit. ▪ Connecting the mechanisms of soil functions with critical zone processes defines integrating science to tackle challenges of climate change and food and water supply. ▪ Soil functions, which develop through formation of soil aggregates as fundamental eco-logical units, are manifest at the earliest stages of critical zone evolution. ▪ Global degradation of soil functions during the Anthropocene is reversible through positive human intervention in soil as a central control point in Earth's critical zone. ▪ Measurement and mathematical translation of soil functions and critical zone processes offer new computational approaches for basic and applied geosciences research.

Primary stratiform platinum-group element (PGE) mineralizations associated with chromitites in the Critical zone of the Bushveld Complex, South Africa, are confined to cumulate layers that are regionally persistent over tens of kilometers. Four categories ofchromitite are recognized: layers at the bases of cycles in the Lower Critical zone (type I), layers at the bases of cycles in the Upper Critical zone (type II), thin layers in the intermediate parts of cycles (type III), and stringers associated with orthopyroxene pegmatoids (type IV). These latter may not be of primary magmatic origin, nevertheless, probably each type of chromitite contains anomalous concentrations of PGE.Chromitites at the bases of cycles, comprising the Lower Group (LG), Middle Group (MG), and Upper Group (UG), are further categorized into types Ia (LG-1/LG-4), Ib (LG-5/MG-1), IIa (MG-2/UG-1), and IIb (UG-2 and above) on the basis of lithostratigraphy, chromite and PGE chemistry, and sulfide content. Type IIb chromitites contain significant quantities of sulfides and are not investigated here. New whole-rock and electron microprobe chemical analyses of the sulfide-poor type Ia, Ib, and IIa chromitites (Cu contents 1.8, low PGE contents ( 2. Type Ib chromitites occur in pyroxenite cycles and form an intermediate group.These regular variations with increased height are interpreted as a differentiation trend. PGE are concentrated in sulfide-poor chromitites as a result of chromitite control, a process not fully understood but thought to involve a combination of direct nucleation of platinum-group minerals and localized S saturation. It is the crystallization of copious quantities of chromite from hybridized melts close to the crystal-liquid interface that triggers this process, but magma mixing, essential to drive the melt into the chromite field, is the overall cause. Replenishment of the magma chamber was from a single magma batch, because the chromitites below the UG-2 are not associated with major isotopic inflections. Huge volumes of dense hot magma were fed as basal flows along the crystal-liquid interface. The magma chamber was compartmentalized at an early stage, possibly in response to basement tectonics, and lateral mixing over distances of > 150 km is an alternative mechanism for achieving sufficiently high R values.Repeated replenishment of the magma chamber resulted in mixing with resident liquid that became increasingly differentiated with height. Type Ia chromitites are ascribed to replenishment and mixing with the relatively primitive Lower zone residue, type Ib crystallized as a result of mixing with Lower Critical zone resident liquid, and type IIa, due to mixing with more evolved Upper Critical zone resident liquid. Differentiation of PGE with height is a critical part of the process which culminates in the occurrence of higher grade PGE mineralization in sulfide-bearing chromitites (UG-2, Merensky reef) in the uppermost part of the Upper Critical zone.

Different land uses imposed by human activities have affected biotic and abiotic components, modifying the natural environment according to population growth and increasing the environmental impact over time. As a consequence, the relevance of studies to evaluate the magnitude and aspects of environmental changes is increasing. In this context, the Ribeirao do Pinheirinho Basin (Sao Paulo state, southeastern Brazil) was selected for this study, since it is part of a region that recharges a set of drainage channels that provide water to several municipalities (approximately 2 million people), primarily during dry seasons. Additionally, this basin has been intensively used for agricultural purposes over the last 50 years. To determine the current characteristics and to analyze the environmental changes, this study was based on temporal and spatial analyses of the components of the basin’s critical zone at a scale of 1:10,000. In association, due to water availability issues, the HOST (hydrology of soil types) classification was adopted, as well as previous data, satellite images, aerial photos and results of laboratory and field tests. As a result, anthropogenic activities have changed the depth, areal distribution, and environmental functions of geological materials. These activities have affected the relationship between rainfall, infiltration and surface runoff, resulting in a lower groundwater level and decreasing water availability. In conclusion, the adopted methodology aids in the assessment of the changes in the environmental area of study. This could be useful for environmental recovery projects as well as the establishment of environmental policies.

The International Symposium of Molecular Environmental Soil Science at the Interfaces in the Earth’s Critical Zone (ISMESS 2009) was successfully held during 10–14 October 2009 at Zhejiang University in Hangzhou, China. Two hundred sixty-six participants from 21 countries attended the symposium. The scientific program featured 2 plenary lecturers, 19 invited lecturers, 29 oral presentations, and 65 poster presentations. The five main sessions were included in the symposium: (1) The role of mineral colloids in carbon turnover and sequestration and the impact on climate change; (2) Biogeochemical interfacial reactions and the transformation, transport, and fate of vital and toxic elements; (3) Anthropogenic organics, crop protection, and ecotoxicology; (4) Environmental nanoparticles: distribution, formation, transformation, structural, and surface chemistry and biogeochemical and ecological impacts; and (5) Environmental processes and ecosystem health (Xu and Huang 2009). Following the peer reviewing process, a selection of articles arising from the symposium is published in this issue of Journal of Soils and Sediments. This symposium provided a forum for the interactions and communication of soil chemists, mineralogists, microbiologists, and physicists with allied scientists including pure chemists, biologists, environmental scientists, ecologists, and ecotoxicologists to address the current state-ofthe-art on “Molecular Environmental Soil Science”. No doubt this symposium contributed to identification of gaps in knowledge and to future research directions and research on soil processes at the interfaces at the molecular level in the Earth’s critical zone. It is significant to advance the frontiers of knowledge on biophysicochemical processes in soil and related environmental systems and their biogeochemical and ecological impacts and to promote education in this extremely important and challenging area of science for years to come. The symposium was highly evaluated by all the participants, and major knowledge shared include the following: (1) The concept of the Earth’s critical zone was highlighted, which is a system of coupled chemical, biological, physical, and geological processes operating together to support life at the Earth’s surface. (2) Further efforts are required by scientists to cross-disciplines for the study of the interactive processes in the critical zone and their impact on the globe and humankind, ranging in scale from the environmental mineral–organism–humus–water–air interfaces. (3) Discussion on carbon turnover improved the understanding of the role of mineral colloids in carbon transformation, dynamics, and sequestration and their impact on climate change in the environment. (4) Microbes are involved in important natural biogeochemical processes relating to metal–mineral transformations, element cycling, bioweathering, biocorrosion, bioremediation, revegetation, phytoremediation, and containment of pollution in the Earth’s critical zone. (5) The importance of nanoscience as a new frontier in soil science has been emphasized. The resolution is occurring for the study of Responsible editor: Jianming Xu

Bringing ancient loess critical zones into a new era of sustainable development goals

<p>Human activities and climate variability have direct impacts on the dynamic of the Critical Zone (CZ) both in quantitative (increase of the flux of organic and mineral matter) and qualitative way (modification of the biogeochemical cycles). Mountainous areas hold a strong CZ dynamic due to their inherent environmental conditions. Among them, European Alps are of prime interest because they have been impacted by human activities over the last millennia. To understand the CZ trajectories, we need to develop long term monitoring far beyond the current instrumental period. To reach this objective we adopt a source-to-sink approach based on geochemical analyses with i) Nd and Sr isotopic composition to trace sediment sources form the watershed and ii) major and traces elements compositions to reconstruct the evolution of  sources weathering states over this period. The watershed of Lake Iseo, located in the Val Camonica (NW Italy) was chosen for its substantial size (1.777km²), its various geological context, helping the identification of the different sources of sediment inputs, and a well-documented anthropization history. 25 samples of fine fluviatile sediments were sampled on the flood plain of the main tributaries of Lake Iseo and were linked to a 15.5m long lake sediment core, retrieved from the deep basin of the lake and covering the last 2,000 years. The fluctuations of the sediment inputs coming from the different sources is discussed from the  Roman period until the recent warming through Medieval Optimum and Little Ice Age period to disentangle the influence of both climate (precipitation, glacial dynamics) and human activity onto the dynamic of the CZ throughout the erosion and the chemical weathering of the soils in this Mediterranean Alpine region.</p>

Topography affects the distribution and movement of water on Earth, yet new insights about topographic controls continue to surprise us and exciting puzzles remain. Here we combine literature review and data synthesis to explore the influence of topography on the global terrestrial water cycle, from the atmosphere down to the groundwater. Above the land surface, topography induces gradients and contrasts in water and energy availability. Long‐term precipitation usually increases with elevation in the mid‐latitudes, while it peaks at low‐ to mid‐elevations in the tropics. Potential evaporation tends to decrease with elevation in all climate zones. At the land surface, topography is expressed in snow distribution, vegetation zonation, geomorphic landforms, the critical zone, and drainage networks. Evaporation and vegetation activity are often highest at low‐ to mid‐elevations where neither temperature, nor energy availability, nor water availability—often modulated by lateral moisture redistribution—impose strong limitations. Below the land surface, topography drives the movement of groundwater from local to continental scales. In many steep upland regions, groundwater systems are well connected to streams and provide ample baseflow, and streams often start losing water in foothills where bedrock transitions into highly permeable sediment. We conclude by presenting organizing principles, discussing the implications of climate change and human activity, and identifying data needs and knowledge gaps. A defining feature resulting from topography is the presence of gradients and contrasts, whose interactions explain many of the patterns we observe in nature and how they might change in the future.

Water plays a fundamental role in the Critical Zone driving chemical weathering, releasing nutrients, and sustaining ecosystem productivity. In natural systems, river chemistry reflects the balance between solutes dissolved from bedrock and those sequestered by mineral precipitation and/or ecosystem uptake. However, human activities like agriculture have disrupted this balance, altering solute cycling. Silicon (Si), a crucial nutrient that supports primary productivity in terrestrial and aquatic ecosystems, is particularly impacted by agriculture. Crop harvesting alters the fluxes of dissolved and biogenic Si in soils, rivers, and ecosystems. Despite its importance, the effects of these changes on riverine solute exports remain largely unexplored. In this study, we investigated the Si isotope composition (δ³⁰Si) and germanium-silicon (Ge/Si) ratio dynamics across Critical Zone compartments—soil, bedrock, water, and vegetation— within the Kervidy-Naizin agricultural catchment, France. We observed a vertical gradient in δ30Si across the water pool in the Critical Zone, from lighter groundwater (δ30Si = 0.56 ± 0.25 ‰) to heavier soil solutions (δ30Si = 1.50 ± 0.22 ‰). This gradient reflects depth-dependent processes: mineral weathering and clay precipitation control δ30Si signatures in groundwater, while plant uptake and crop removal significantly enrich δ³⁰Si in soil solutions. Using a mass balance that combines δ30Si and Ge/Si ratios, we quantified Si export from the catchment as plant material, both natural and harvested. Additionally, we employed two independent methods to assess Si export through agricultural harvesting: an elemental mass balance based on riverine chemistry and suspended sediments, and a method incorporating isotope fractionation factors and soil Si loss indices. an elemental mass balance based on riverine chemistry and suspended sediments, and a method incorporating isotope fractionation factors and soil Si loss indices. Our results show that plant-mediated Si export—both natural and harvested—is the largest Si flux from the catchment, accounting for ~74 % of the Si solubilized from rock and exceeding dissolved Si export by 3.2 to 5.4 times. Through two independent methods, we estimated that harvesting alone accounts for 37 ± 10 % to 50 ± 19 % of total Si export, depending on crop species, with the harvesting flux being 1 to 4 times greater than the dissolved Si flux. These findings suggest that agricultural activities significantly reduce riverine Si exports, potentially altering downstream ecosystems where Si availability regulates primary productivity. By quantifying Si fluxes and exploring their drivers, this study provides critical insights into the interplay between water partitioning, nutrient cycling, and solute transport in the Critical Zone, highlighting the transformative effects of agriculture.

Abstract. The critical zone (CZ) is the heterogeneous, near-surface layer of the planet that regulates life-sustaining resources. Previous research has demonstrated that a quantification of the influxes of effective energy and mass transfer (EEMT) to the CZ can predict its structure and function. In this study, we quantify how climate variability in the last 3 decades (1984–2012) has affected water availability and the temporal trends in EEMT. This study takes place in the 1200 km2 upper Jemez River basin in northern New Mexico. The analysis of climate, water availability, and EEMT was based on records from two high-elevation SNOTEL stations, PRISM data, catchment-scale discharge, and satellite-derived net primary productivity (MODIS). Results from this study indicated a decreasing trend in water availability, a reduction in forest productivity (4 g C m−2 per 10 mm of reduction in precipitation), and decreasing EEMT (1.2–1.3 MJ m2 decade−1). Although we do not know the timescales of CZ change, these results suggest an upward migration of CZ/ecosystem structure on the order of 100 m decade−1, and that decadal-scale differences in EEMT are similar to the differences between convergent/hydrologically subsidized and planar/divergent landscapes, which have been shown to be very different in vegetation and CZ structure.