Deep exposures of soil profiles on Miocene or Mio-Pliocene alluvial deposits were studied along a 500 km N-S transect in the Atacama Desert. These ancient deposits, with excellent surface preservation, now stand many meters above a broad incised PlioPleistocene alluvial terrain. Total geochemical analyses and mass balance calculations allowed the establishment of elemental gains, losses, and redistribution in the soils. From north to south (presently hyperarid to arid), the ancient soils reveal an increase in losses of rock-forming elements (Si, Al, Fe, K, Mg). Additionally, rare earth elements (REE) show losses with increasing southerly latitude and systematic patterns with soil depth. Some REEs appear to be unique chemical tracers of exogenous dust and aerosol additions to the soils. The removal of major elements and REEs is impossible in the present climate (one of salt and dust accumulation), revealing that for a significant period following the deposition of the alluvium, soils were exposed to rainfall, chemical weathering, and mass loss-with a geographical pattern that mirrors the present rainfall gradient in the region. Following the cessation of weathering, the pre-weathered soils have undergone enormous dust and salt accumulations, with the rates and types of salt accumulation consistent with latitude: (1) carbonate in the south and (2) sulfate, chlorides, and nitrates to the north. The quantity, and apparent rates, of salt accumulation have a strong latitudinal trend. Isotopes of sulfate have predictable depth patterns based on isotope fractionation via vertical reaction and transport. The relict hyperarid soils are geochemically similar to buried Miocene soils (ca. 10-9 Ma) in the region, but they differ from older Miocene soils, which formed in more humid conditions. The overall soil record for the Atacama Desert appears to be the product of changes in Pacific Ocean sea surface temperatures over time, and resulting changes in rainfall. The mid-Miocene was relatively humid based on buried soil chemistry and evidence of fluvial activity. The mid to late Miocene cooling (ca. 10-5.5 Ma) appears to have aridified the region based on paleosol soil chemistry. Pliocene to earliest Pleistocene conditions caused weathering of the relict soils examined here, and regional fluvial activity. Since the earliest Pleistocene, the region has largely experienced the accumulation of salts and, except for smaller scale oscillations (glacial-interglacial), has experienced protracted hyperaridity.

The radiocarbon content of soil organic carbon (C) is assumed to reflect the carbon’s biological reactivity. Large soil radiocarbon ages are interpreted to mean that the C will have a slow response to environmental perturbations such as the effects of warming on the soil microbial C decomposition rate. Here we show that downward advective transport of soil C is an important process affecting soil C ages, leading to an inevitable increase in radiocarbon age with depth even if the decomposition rates remain constant. Thus, the increasing radiocarbon ages of C with depth do not directly imply a corresponding decrease in C reactivity as a function of depth. On the basis of theory and an independent assessment of soil C decomposition rates, the radiocarbon profiles (and content for a given depth) were calculated for over 3,000 soils in the USA and were compared to observational results based on measured soil radiocarbon. The first-order coherence between the two entirely differing approaches suggests the fundamental importance of transport and the implication that the soil C decomposition rate constant may be relatively invariant with depth. These insights may serve to reduce biases in Earth system models that presently do not match the observed depth patterns in soil C or its radiocarbon content. A reassessment of soil radiocarbon profiles, which shows a strong influence of vertical transport processes, suggests that soil organic carbon is similarly responsive to environmental changes regardless of depth.

AbstractAfter 4.5 billion years as an evolving and dynamic planet, the Earth continues to evolve but with human‐altered dynamics. Earth scientists have special opportunities and responsibilities to accelerate our understanding of Earth's changes that are transforming our most remarkable home.

Total geochemical analyses of the soils examined.

Carbon (C), nitrogen (N), and sulfur (S) are elements strongly influenced by biological cycling and redox reactions in soils, but few comparative analyses have investigated the behaviors of these elements with time. Thus, we examined changes in content and isotope composition of soil profiles along a chronosequence (58–212 kyr) of marine terraces on the central California coast, in an area with significant background geochemical research. Unlike in other chronosequences in more humid locations, the total C, N, and S in these soils did not vary strongly with age, possibly due to the retention of phosphorus (P). The total pools of soil N and S cannot be explained by wet deposition of NO3 and SO4 alone, suggesting other sources of atmospheric inputs such as NH4+ and dimethyl sulfide. Total C and N declined in a characteristic logarithmic pattern with depth, while S did not. The ratio of extractable soil nitrate (NO3) to total N declined with depth, suggesting strong biological demand via various avenues. In contrast, the ratio of extractable sulfate (SO4) to total S increased with depth, suggesting that S was in biological excess. We used a simple reactive transport model to integrate the depth profiles of total C and N and their isotope values. The depth trends of total concentrations suggested one-pool residence times of approximately 500 to 1000 y, consistent with turnover times calculated by mass balance. Depth trends of stable isotope values indicated that N is isotopically fractionated at a magnitude twice that of C, consistent with observed 15N-depleted nitrous oxide (N2O) emissions during the dry summer months. The isotope composition of S (total and SO4) suggests some isotope enrichment during biogeochemical cycling, but far less than observed for N. Thus, despite significant chemical weathering and elemental loss over time, the biogeochemical cycles of C, N, and S remain relatively unaffected by soil age in this climatic setting.

The genus Celtis includes widespread trees that produce drupes with aragonite endocarps, or "hackberries." These carbonate endocarps are preserved in the fossil record, often in cave deposits or packrat middens, and thus are targets for paleoclimate reconstructions. Stable oxygen isotopes in Celtis endocarps have been used as proxies for oxygen isotopic composition of past stream water and for paleothermometry. Here, we explore the suitability of hackberry carbonates for paleoclimate reconstructions based on carbonate clumped-isotope thermometry. We sampled modern hackberries grown at sites across North America (n = 37) for stable and clumped isotope analyses. Measured clumped-isotope temperatures are found to be within the range of measured local modern growing season surface temperatures and typically in dual clumped-isotope equilibrium. As such, we propose that hackberry clumped-isotope measurements can be used to reconstruct past Earth-surface air temperatures.

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

The stable N and O isotope composition of soil and soil‐respired N 2 O is increasingly measured, yet a solid theoretical framework for interpreting the data remains to be developed. Here, the physical processes that affect soil N 2 O and its isotopes are embedded in a diffusion/reaction model. Numerical experiments are compared to data to demonstrate how various soil processes influence depth profiles and surface fluxes of soil N 2 O, δ 15 N N2O , and δ 18 O N2O . Model predictions and data suggest that the isotope composition of the net N 2 O soil flux, in soils that have N 2 O consumption, is a function of the net flux rate, and the isotope differences between the atmosphere and the biological source. Asymptotically large negative or positive δ 15 N flux and δ 18 O flux values occur as the net soil N 2 O flux approaches zero from positive or negative flux rates, respectively. This implies that the isotopic imprint of soil fluxes on the global atmospheric N 2 O pool is more variable than previously suggested. Additionally, the observed isotope values in static flux chambers are possibly complicated by the fact that consumption fluxes increase as the concentration in the chambers increases. This work reveals that even simple chamber flux measurements may possess isotope effects imparted by consumption during the chamber measurement and suggests ways to experimentally test this possibility. Additionally, simple methods to estimate depth‐dependent net production/consumption and its isotope effects are suggested. However, understanding the gross rates of the production and consumption of soil N 2 O remains an elusive goal.

The Mojave Desert has warmed >2°C, and aridified, in the past 50 years, making it a strategic location to investigate climate change impacts on arid soil processes. We resampled a climosequence of soils in the Mojave first sampled in 1973 and compared current soil properties to those 45+ years earlier. Radiocarbon changes revealed that C is cycling rapidly through the soils, particularly near the surface, with a temperature‐sensitive decomposition rate (Arrhenius E a = 66 kJ/mol). Significant decreases in soil C/N ratios and increases in δ 15 N values occurred, suggestive of enhanced rates of soil C and N cycling and their losses. Covariation between changes in soil radiocarbon, δ 13 C, δ 15 N, and C/N point toward emerging chemical impacts on the coupled C and N cycles in response to climate change.

Microbial communities are found throughout the biosphere, from human guts to glaciers, from soil to activated sludge. Understanding the statistical properties of such diverse communities can pave the way to elucidate the common mechanisms ...Multiple ecological forces act together to shape the composition of microbial communities. Phyloecology approaches—which combine phylogenetic relationships between species with community ecology—have the potential to disentangle such forces but are often ...

Soil and other Earth scientists who conduct research on C management found themselves, in the past decade within a swirl of efforts concerning climate mitigation, economic and business investments in carbon markets, and political aspirations. All these external pressures are issues with which soil science is largely unfamiliar. As a result, science has responded without deeply considering the landscape in which it finds itself, and some of the unanticipated challenges these issues present. Here, we suggest soil C scientists now consider and respond to these issues. The first order challenge is to transition from the concept of technical carbon sequestration potentials, made in the absence of social and policy contexts, to societally achievable sequestration estimates based on highly transdisciplinary teams of natural and social sciences and scientists. To achieve this will requires re-thinking national science funding programs, in which climate-relevant social science is under-funded. In addition, the science of soil C itself is in need of a priority shift. Presently, publications in soil C sequestration out-strip papers on soil feedbacks to climate change, and on how to adapt soil to climate change: two areas of research which may well be more societal important in the next few decades than sequestering C. Most seriously, given the urgent nature of our collective societal climate problem, our profession must not find itself a decade from now continuing the now 20-year-old narrative that soil C can potentially mitigate climate change and compensate for greenhouse gas emissions. We must consider the possibility that other options and expenditures of resources are more viable, and we must reframe our science's objectives to expand into the many other urgent needs that confront humanity.

Microbial communities are found throughout the biosphere, from human guts to glaciers, from soil to activated sludge. Understanding the statistical properties of such diverse communities can pave the way to elucidate the common mechanisms ...Multiple ecological forces act together to shape the composition of microbial communities. Phyloecology approaches—which combine phylogenetic relationships between species with community ecology—have the potential to disentangle such forces but are often ...

21st Century soil science must deeply grapple with the enormity of the agricultural impact on soils, and the complex ways in which this impacts soil sustainability. The first step is to remove the cloud of mysticism that sometimes surrounds soil and farming, reframe the narrative, and be clear about the enormous difficulty of creating a truly steady state and/or C-neutral soil management system. The objective of this paper is to examine the global footprint of agriculture on soils, and its impact on soil erosion, carbon, and nutrients. Stabilizing any one of these 3 mass balances globally will require complex and highly integrated collaborations between social scientists, policy experts, engineers, farmers, politicians, and natural scientists. There are no magical or simple solutions. Yet, there are untapped opportunities for research and solution-driven activities that can help to create a new framework for more effective efforts by our science to address wicked societal problems.

The year 2021 marks the 80th anniversary of the publication of Factors of Soil Formation. A System of Quantitative Pedology by Hans Jenny. Given the exponential surge in annual citations of the book over the past 30 years, and this important milestone in its history, it is an opportune time to examine what the book presents, and how it is relevant to transdisciplinary research in the 21st Century. The book did not originate the concept of soil forming factors, which were by then already widely accepted in soil science, but instead translated it into a quantitative scientific framework through rigorous definition of the soil system, and the identification and separation of dependent and independent variables. The initial formulation of the theoretical framework was inspired by thermodynamics, but with pedologically-relevant state variables. Subsequent formulations of the model by Jenny articulated the connection and utility to examining energy and mass fluxes through the soil system, a point of departure for recent efforts to bring open system, non-equilibrium thermodynamic methods to bear on soil research. The State Factor theory is a powerful lens to examine a number of academic and societally relevant issues in the 21st century, such as the role of the biotic factor and its interplay with the physical soil environment. However, the most critical, and understudied, state factor is the effect of humans on soil systems. Earth science must embrace the challenge, and obligation to society, to explore the human footprint on the planet, and devise ways to remediate its impact.

The Atacama Desert contains the driest regions on Earth, with significant rain occurring only a few times per century, based on sparse historical records. However, the frequency and magnitude of rainfall remains speculative. On March 24-26 of 2015, an unusual storm caused rainfall rates and quantities to exceed many historical records. Of interest is whether this storm was able to activate geomorphic processes whose impacts are evident on numerous landscape features. Here, the results of a reconnaissance from N to S transecting through the plant-free expanse of the Atacama Desert, between 22 and 26 degrees S, are examined in relation to evidence of past runoff activity coupled with soil architecture and soil hydraulic properties. The results suggest the rain initiated some minor runoff processes on the upper hillslopes. However, the rainfall was too small to reactivate many features that appear to be driven by larger, less frequent storms. The field evidence suggests that larger scale rainfalls have occurred throughout the Quaternary, and that there are fossilized (or infrequently active) features in various stages of "repair" that provide evidence of rainfall re-occurrence. The landscapes largely escaped overland flow alteration due to the high infiltration rate capacity caused by the salt-rich soils, which we estimated to average 78 mm h(-1) for hillslopes and 244 mm h(-1) for alluvial soils, based on disc infiltrometer measurements. This gives a resilience, and potential rainfall threshold, to alteration by intensive rainfall events. Published paleoclimatic records coupled with evidence from soil examined at the arid/hyperarid periphery of the desert show evidence of a cessation of carbonate formation since similar to 11 ka, a time of aridification similar to the drying of lakes and marshlands in the hyperarid region. Thus, the past fluvial alteration features are likely to be, at least partially, remnant Pleistocene features which have been largely unaffected by Holocene events, whose magnitudes were similar to that of 2015. (C) 2021 Elsevier Ltd. All rights reserved.

The stable isotopic composition of pedogenic carbonate forms in equilibrium with environmental parameters and, thus, records palaeoenvironmental signals. The aims of this study are to synthesize available data on the stable isotopic composition of Quaternary pedogenic carbonates in calcareous parent materials of Iran and to decipher paleoenvironmental implications of the isotopic data for the country. Isotopic composition and microfabric of pedogenic carbonates in 18 pedons in both gravelly (calcareous alluvium in central Iran) and non-gravelly deposits (calcareous loess in northeastern Iran) have been investigated. The results indicate that in limestone-derived soils of central Iran in situ weathering of calcareous pebbles is a major source of Ca for genesis of the carbonates, and carbonate features consist of micritic calcite crystals. In the loessic soils of northeastern Iran, pedogenic carbonates show a dominance of nodule morphology and are classified as orthic nodules. Microfabric analysis reveals that most of the carbonates have not been altered by diagenetic processes, especially the Holocene carbonates, and are suitable for isotopic study and palaeoreconstructions. In limestone-derived soils within the arid region of central Iran, the delta O-18 and the delta C-13 values of carbonates indicate their enrichment due to the effects of evaporative water loss, a decline in plant density and the entrance of atmospheric CO2 into the soils. In semi-arid ecosystems of central and northeastern Iran, most of the Holocene carbonates have formed in equilibrium with the ambient environment and are suitable for palaeoenvironmental reconstructions. The combination of carbon and oxygen isotopic data demonstrates the dominant role of climate in determining the delta C-13 values of carbonates. There is a strong relationship between the delta C-13 values of carbonates and rainfall, and between O isotopes and aridity indices. Stable isotope patterns in Holocene soils appear to provide data for models that can then be used to interpret the many localities where Pleistocene-aged soils and associated carbonate exist.

When I was a young professor at Berkeley, my colleagues and I would frequently run into Jean Jenny, the wife of Hans Jenny, at various events on campus.Jean, a formidable force of nature with a deep interest in the future of soil science (and in the 1980's, its state of languishing in the backwaters of popular science), would frequently walk directly up to me and say, literally pointing her finger at me, ''you guys need to make soil sexy!!''.I would laugh, but I pondered the issue many times.As a young and then minor participant in the field, it seemed well beyond my ability, or even vision, that soil science would somehow be the stuff of popular appeal.Yet, here we are today.In the past decade or so, we have had high-end soil documentaries narrated by Jamie Lee Curtis (Dirt!The Movie) and Woody Harrelson (Kiss the Ground), with cameo appearances by people like Gisele Bu ¨ndchen and Tom Brady.How much sexier can we get!? Soil