Showing papers in "Nature Geoscience in 2020"
University of California, Irvine1, Alfred Wegener Institute for Polar and Marine Research2, University of Texas at Austin3, University of Tübingen4, University of Bremen5, British Antarctic Survey6, National Space Institute7, Northumbria University8, Polar Research Institute of China9, Ohio State University10, Norwegian Polar Institute11, University of Kansas12, Université libre de Bruxelles13, University of Tasmania14, Institute for Geosciences and Natural Resources15, California Institute of Technology16, Utrecht University17
TL;DR: In this paper, a high-resolution and physically based description of Antarctica bed topography using mass conservation is presented, revealing previously unknown basal features with major implications for glacier response to climate change.
Abstract: The Antarctic ice sheet has been losing mass over past decades through the accelerated flow of its glaciers, conditioned by ocean temperature and bed topography. Glaciers retreating along retrograde slopes (that is, the bed elevation drops in the inland direction) are potentially unstable, while subglacial ridges slow down the glacial retreat. Despite major advances in the mapping of subglacial bed topography, significant sectors of Antarctica remain poorly resolved and critical spatial details are missing. Here we present a novel, high-resolution and physically based description of Antarctic bed topography using mass conservation. Our results reveal previously unknown basal features with major implications for glacier response to climate change. For example, glaciers flowing across the Transantarctic Mountains are protected by broad, stabilizing ridges. Conversely, in the marine basin of Wilkes Land, East Antarctica, we find retrograde slopes along Ninnis and Denman glaciers, with stabilizing slopes beneath Moscow University, Totten and Lambert glacier system, despite corrections in bed elevation of up to 1 km for the latter. This transformative description of bed topography redefines the high- and lower-risk sectors for rapid sea level rise from Antarctica; it will also significantly impact model projections of sea level rise from Antarctica in the coming centuries.
433 citations
TL;DR: In this article, the authors examined global N and P limitation using the ratio of site-averaged leaf resorption efficiencies of the dominant species across 171 sites and evaluated their predictions using a global database of N- and P-limitation experiments based on nutrient additions at 106 and 53 sites, respectively.
Abstract: Nitrogen (N) and phosphorus (P) limitation constrains the magnitude of terrestrial carbon uptake in response to elevated carbon dioxide and climate change. However, global maps of nutrient limitation are still lacking. Here we examined global N and P limitation using the ratio of site-averaged leaf N and P resorption efficiencies of the dominant species across 171 sites. We evaluated our predictions using a global database of N- and P-limitation experiments based on nutrient additions at 106 and 53 sites, respectively. Globally, we found a shift from relative P to N limitation for both higher latitudes and precipitation seasonality and lower mean annual temperature, temperature seasonality, mean annual precipitation and soil clay fraction. Excluding cropland, urban and glacial areas, we estimate that 18% of the natural terrestrial land area is significantly limited by N, whereas 43% is relatively P limited. The remaining 39% of the natural terrestrial land area could be co-limited by N and P or weakly limited by either nutrient alone. This work provides both a new framework for testing nutrient limitation and a benchmark of N and P limitation for models to constrain predictions of the terrestrial carbon sink. Spatial patterns in the phosphorus and nitrogen limitation in natural terrestrial ecosystems are reported from analysis of a global database of the resorption efficiency of nutrients by leaves.
426 citations
Institute of Arctic and Alpine Research1, University of Guelph2, Brigham Young University3, United States Geological Survey4, University of Alaska Fairbanks5, University of Alberta6, Northern Arizona University7, Alfred Wegener Institute for Polar and Marine Research8, University of Potsdam9, Stockholm University10, Lawrence Berkeley National Laboratory11, National Center for Atmospheric Research12
TL;DR: In this article, the authors synthesize the best available information and develop inventory models to simulate abrupt thaw impacts on permafrost carbon balance, and they conclude that models considering only gradual thaw are substantially underestimating carbon emissions.
Abstract: The permafrost zone is expected to be a substantial carbon source to the atmosphere, yet large-scale models currently only simulate gradual changes in seasonally thawed soil. Abrupt thaw will probably occur in <20% of the permafrost zone but could affect half of permafrost carbon through collapsing ground, rapid erosion and landslides. Here, we synthesize the best available information and develop inventory models to simulate abrupt thaw impacts on permafrost carbon balance. Emissions across 2.5 million km2 of abrupt thaw could provide a similar climate feedback as gradual thaw emissions from the entire 18 million km2 permafrost region under the warming projection of Representative Concentration Pathway 8.5. While models forecast that gradual thaw may lead to net ecosystem carbon uptake under projections of Representative Concentration Pathway 4.5, abrupt thaw emissions are likely to offset this potential carbon sink. Active hillslope erosional features will occupy 3% of abrupt thaw terrain by 2300 but emit one-third of abrupt thaw carbon losses. Thaw lakes and wetlands are methane hot spots but their carbon release is partially offset by slowly regrowing vegetation. After considering abrupt thaw stabilization, lake drainage and soil carbon uptake by vegetation regrowth, we conclude that models considering only gradual permafrost thaw are substantially underestimating carbon emissions from thawing permafrost. Analyses of inventory models under two climate change projection scenarios suggest that carbon emissions from abrupt thaw of permafrost through ground collapse, erosion and landslides could contribute significantly to the overall permafrost carbon balance.
399 citations
California Institute of Technology1, Cornell University2, ETH Zurich3, University of British Columbia4, Planetary Science Institute5, Institut Universitaire de France6, Institut de Physique du Globe de Paris7, University of Paris8, German Aerospace Center9, Universities Space Research Association10, University of California, Los Angeles11, University of Oxford12, Colorado School of Mines13, Max Planck Society14, Imperial College London15, Université catholique de Louvain16, Royal Observatory of Belgium17, University of California, Berkeley18, Institut supérieur de l'aéronautique et de l'espace19, Goddard Space Flight Center20, Smithsonian Institution21, Princeton University22, Austrian Academy of Sciences23, Virginia Tech24, University of Cologne25, Space Science Institute26, Johns Hopkins University Applied Physics Laboratory27, Paul Sabatier University28, Stony Brook University29, École normale supérieure de Lyon30, University of Nantes31, Texas Tech University32, University of California, Santa Cruz33, Spanish National Research Council34, University of Maryland, College Park35, Southern Methodist University36, Johns Hopkins University37, University of Bristol38, State University of New York at Geneseo39, Marshall Space Flight Center40
TL;DR: For example, the first ten months of the InSight lander on Mars revealed a planet that is seismically active and provided information about the interior, surface and atmospheric workings of Mars as mentioned in this paper.
Abstract: NASA’s InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018. It aims to determine the interior structure, composition and thermal state of Mars, as well as constrain present-day seismicity and impact cratering rates. Such information is key to understanding the differentiation and subsequent thermal evolution of Mars, and thus the forces that shape the planet’s surface geology and volatile processes. Here we report an overview of the first ten months of geophysical observations by InSight. As of 30 September 2019, 174 seismic events have been recorded by the lander’s seismometer, including over 20 events of moment magnitude Mw = 3–4. The detections thus far are consistent with tectonic origins, with no impact-induced seismicity yet observed, and indicate a seismically active planet. An assessment of these detections suggests that the frequency of global seismic events below approximately Mw = 3 is similar to that of terrestrial intraplate seismic activity, but there are fewer larger quakes; no quakes exceeding Mw = 4 have been observed. The lander’s other instruments—two cameras, atmospheric pressure, temperature and wind sensors, a magnetometer and a radiometer—have yielded much more than the intended supporting data for seismometer noise characterization: magnetic field measurements indicate a local magnetic field that is ten-times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected, hosting baroclinic and gravity waves and convective vortices. With the mission due to last for an entire Martian year or longer, these results will be built on by further measurements by the InSight lander. Geophysical and meteorological measurements by NASA’s InSight lander on Mars reveal a planet that is seismically active and provide information about the interior, surface and atmospheric workings of Mars.
299 citations
Cornell University1, Technische Universität München2, Woods Hole Oceanographic Institution3, University of Vienna4, Oregon State University5, Stanford University6, Stockholm University7, University of Paris8, Max Planck Society9, University of California, Santa Barbara10, Lawrence Berkeley National Laboratory11, Institute of Arctic and Alpine Research12, National Center for Atmospheric Research13
TL;DR: In this article, the authors propose that soil carbon persistence can be understood through the lens of decomposers as a result of functional complexity derived from the interplay between spatial and temporal variation of molecular diversity and composition, which suggests soil management should be based on constant care rather than one-time action to lock away carbon in soils.
Abstract: Soil organic carbon management has the potential to aid climate change mitigation through drawdown of atmospheric carbon dioxide. To be effective, such management must account for processes influencing carbon storage and re-emission at different space and time scales. Achieving this requires a conceptual advance in our understanding to link carbon dynamics from the scales at which processes occur to the scales at which decisions are made. Here, we propose that soil carbon persistence can be understood through the lens of decomposers as a result of functional complexity derived from the interplay between spatial and temporal variation of molecular diversity and composition. For example, co-location alone can determine whether a molecule is decomposed, with rapid changes in moisture leading to transport of organic matter and constraining the fitness of the microbial community, while greater molecular diversity may increase the metabolic demand of, and thus potentially limit, decomposition. This conceptual shift accounts for emergent behaviour of the microbial community and would enable soil carbon changes to be predicted without invoking recalcitrant carbon forms that have not been observed experimentally. Functional complexity as a driver of soil carbon persistence suggests soil management should be based on constant care rather than one-time action to lock away carbon in soils. Dynamic interactions between chemical and biological controls govern the stability of soil organic carbon and drive complex, emergent patterns in soil carbon persistence.
289 citations
Institut de Physique du Globe de Paris1, Institut Universitaire de France2, California Institute of Technology3, Imperial College London4, ETH Zurich5, Max Planck Society6, Institut supérieur de l'aéronautique et de l'espace7, University of Cologne8, University of Toulouse9, University of California, Santa Cruz10, Claude Bernard University Lyon 111, University of Paris12, University of Nantes13, University of California, Los Angeles14, University of Zurich15, Free University of Berlin16, University of Maryland, College Park17, Centre national de la recherche scientifique18, University of Stuttgart19, Colorado School of Mines20, École des ponts ParisTech21, German Aerospace Center22, University of Bristol23, Princeton University24, Johns Hopkins University Applied Physics Laboratory25, École normale supérieure de Lyon26, University of Oxford27, Centre National D'Etudes Spatiales28, International Space Science Institute29, Kaiserslautern University of Technology30, Marshall Space Flight Center31, Cornell University32, University of British Columbia33, Planetary Science Institute34, Instituto Nacional de Técnica Aeroespacial35
TL;DR: In this paper, the authors measured the crustal diffusivity and intrinsic attenuation using multiscattering analysis and found that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles.
Abstract: Mars’s seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth’s microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight’s Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8–11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles. The crust beneath the InSight lander on Mars is altered or fractured to 8–11 km depth and may bear volatiles, according to an analysis of seismic noise and wave scattering recorded by InSight’s seismometer.
221 citations
Planetary Science Institute1, Space Science Institute2, Johns Hopkins University Applied Physics Laboratory3, Institut supérieur de l'aéronautique et de l'espace4, Spanish National Research Council5, Institut de Physique du Globe de Paris6, Institut Universitaire de France7, Royal Observatory of Belgium8, University of Bristol9, Jet Propulsion Laboratory10, Swiss Seismological Service11, ETH Zurich12, University of Stuttgart13
TL;DR: The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander is measuring Mars's atmosphere with unprecedented continuity, accuracy and sampling frequency.
Abstract: The atmosphere of Mars is thin, although rich in dust aerosols, and covers a dry surface. As such, Mars provides an opportunity to expand our knowledge of atmospheres beyond that attainable from the atmosphere of the Earth. The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander is measuring Mars’s atmosphere with unprecedented continuity, accuracy and sampling frequency. Here we show that InSight unveils new atmospheric phenomena at Mars, especially in the higher-frequency range, and extends our understanding of Mars’s meteorology at all scales. InSight is uniquely sensitive to large-scale and regional weather and obtained detailed in situ coverage of a regional dust storm on Mars. Images have enabled high-altitude wind speeds to be measured and revealed airglow—faint emissions produced by photochemical reactions—in the middle atmosphere. InSight observations show a paradox of aeolian science on Mars: despite having the largest recorded Martian vortex activity and dust-devil tracks close to the lander, no visible dust devils have been seen. Meteorological measurements have produced a catalogue of atmospheric gravity waves, which included bores (soliton-like waves). From these measurements, we have discovered Martian infrasound and unexpected similarities between atmospheric turbulence on Earth and Mars. We suggest that the observations of Mars’s atmosphere by InSight will be key for prediction capabilities and future exploration.
181 citations
ETH Zurich1, Institut de Physique du Globe de Paris2, Institut Universitaire de France3, California Institute of Technology4, Imperial College London5, Max Planck Society6, Swiss Seismological Service7, Institut supérieur de l'aéronautique et de l'espace8, University of Zurich9, Cornell University10, University of Nantes11, University of Bristol12, University of Paris13, Centre National D'Etudes Spatiales14, Brown University15, Russian Academy of Sciences16, University of Maryland, College Park17, Virginia Tech18, Free University of Berlin19, University of Cologne20, University of Toulouse21, University of California, Santa Cruz22, Royal Observatory of Belgium23, Instituto Nacional de Técnica Aeroespacial24, Centre national de la recherche scientifique25, Spanish National Research Council26, University of Oxford27, Marshall Space Flight Center28
TL;DR: The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander was deployed in Elysium Planitia on Mars on 26 November 2018 and fully deployed its seismometer by the end of February 2019 as mentioned in this paper.
Abstract: The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018 and fully deployed its seismometer by the end of February 2019. The mission aims to detect, characterize and locate seismic activity on Mars, and to further constrain the internal structure, composition and dynamics of the planet. Here, we present seismometer data recorded until 30 September 2019, which reveal that Mars is seismically active. We identify 174 marsquakes, comprising two distinct populations: 150 small-magnitude, high-frequency events with waves propagating at crustal depths and 24 low-frequency, subcrustal events of magnitude Mw 3–4 with waves propagating at various depths in the mantle. These marsquakes have spectral characteristics similar to the seismicity observed on the Earth and Moon. We determine that two of the largest detected marsquakes were located near the Cerberus Fossae fracture system. From the recorded seismicity, we constrain attenuation in the crust and mantle, and find indications of a potential low-S-wave-velocity layer in the upper mantle. Mars is seismically active: 24 subcrustal magnitude 3–4 marsquakes and 150 smaller events have been identified up to 30 September 2019, by an analysis of seismometer data from the InSight lander.
178 citations
TL;DR: Glaciers in the Karakoram region, with their balanced or slightly positive mass balance, stand out from global glacier shrinkage, but this anomaly is not expected to persist in the long term, according to an overview of the possible explanations.
Abstract: Global-scale glacier shrinkage is one of the most prominent signs of ongoing climatic change. However, important differences in glacier response exist at the regional scale, and evidence has accumulated that one particular region stands out: the Karakoram. In the past two decades, the region has shown balanced to slightly positive glacier budgets, an increase in glacier ice flow speeds, stable to partially advancing glacier termini and widespread glacier surge activity. This is in stark contrast to the rest of High Mountain Asia, where glacier retreat and slowdown dominate, and glacier surging is largely absent. Termed the Karakoram Anomaly, recent observations show that the anomalous glacier behaviour partially extends to the nearby Western Kun Lun and Pamir. Several complementary explanations have now been presented for the Anomaly’s deeper causes, but our understanding is far from complete. Whether the Anomaly will continue to exist in the coming decades remains unclear, but its long-term persistence seems unlikely in light of the considerable warming anticipated by current projections of future climate. Glaciers in the Karakoram region, with their balanced or slightly positive mass balance, stand out from global glacier shrinkage, but this anomaly is not expected to persist in the long term, according to an overview of the possible explanations.
175 citations
TL;DR: In this paper, the authors present that long-range transport and aerosol-boundary layer feedback may interact rather than act as two isolated processes as traditionally thought by investigating typical regional haze events in northern and eastern China.
Abstract: Although air quality in China has substantially improved since 2013 as a consequence of the clean air action, severe haze events still frequently strike megacities despite strict local emissions reduction efforts. Long-range transport and local accumulation as well as chemical transformation have been deemed as key factors of heavy haze pollution; however, the formation mechanisms of regional long-lasting haze and the physical and chemical connections between different megacities clusters are still poorly understood. Here we present that long-range transport and aerosol–boundary layer feedback may interact rather than act as two isolated processes as traditionally thought by investigating typical regional haze events in northern and eastern China. This interaction can then amplify transboundary air pollution transport over a distance of 1,000 km and boost long-lasting secondary haze from the North China Plain to the Yangtze River delta. Earlier emission reduction before the pollution episodes would provide better air pollution mitigation in both regions. Our results show an amplified transboundary transport of haze by aerosol–boundary layer interaction in China and suggest the importance of coordinated cross-regional emission reduction with a focus on radiatively active species like black carbon. Secondary air pollution events are enhanced in the Yangtze River delta, China, due to the interaction of long-range transport and aerosol–boundary layer feedback, according to a combination of observations and simulations of haze events from 2013 to 2018.
163 citations
TL;DR: For the four largest ‘cold-water’ ice shelves, meltwater fluxes are partitioned into deep and shallow sources to reveal distinct signatures of temporal variability, providing insights into climate forcing of basal melting and the impact of this melting on the Southern Ocean.
Abstract: Ocean-driven basal melting of Antarctica's floating ice shelves accounts for about half of their mass loss in steady-state, where gains in ice shelf mass are balanced by losses. Ice shelf thickness changes driven by varying basal melt rates modulate mass loss from the grounded ice sheet and its contribution to sea level, and the changing meltwater fluxes influence climate processes in the Southern Ocean. Existing continent-wide melt rate datasets have no temporal variability, introducing uncertainties in sea level and climate projections. Here, we combine surface height data from satellite radar altimeters with satellite-derived ice velocities and a new model of firn-layer evolution to generate a high-resolution map of time-averaged (2010-2018) basal melt rates, and time series (1994-2018) of meltwater fluxes for most ice shelves. Total basal meltwater flux in 1994 (1090±150 Gt/yr) was not significantly different from the steady-state value (1100±60 Gt/yr), but increased to 1570±140 Gt/yr in 2009, followed by a decline to 1160±150 Gt/yr in 2018. For the four largest "cold-water" ice shelves we partition meltwater fluxes into deep and shallow sources to reveal distinct signatures of temporal variability, providing insights into climate forcing of basal melting and the impact of this melting on the Southern Ocean.
TL;DR: This paper found that 85% of sediment-hosted base metals, including all giant deposits (>10 megatonnes of metal, occur within 200 kilometres of the transition between thick and thin lithosphere.
Abstract: Sustainable development and the transition to a clean-energy economy drives ever-increasing demand for base metals, substantially outstripping the discovery rate of new deposits and necessitating dramatic improvements in exploration success. Rifting of the continents has formed widespread sedimentary basins, some of which contain large quantities of copper, lead and zinc. Despite over a century of research, the geological structure responsible for the spatial distribution of such fertile regions remains enigmatic. Here, we use statistical tests to compare deposit locations with new maps of lithospheric thickness, which outline the base of tectonic plates. We find that 85% of sediment-hosted base metals, including all giant deposits (>10 megatonnes of metal), occur within 200 kilometres of the transition between thick and thin lithosphere. Rifting in this setting produces greater subsidence and lower basal heat flow, enlarging the depth extent of hydrothermal circulation available for forming giant deposits. Given that mineralization ages span the past two billion years, this observation implies long-term lithospheric edge stability and a genetic link between deep Earth processes and near-surface hydrothermal mineral systems. This discovery provides an unprecedented global framework for identifying fertile regions for targeted mineral exploration, reducing the search space for new deposits by two-thirds on this lithospheric thickness criterion alone. Major sediment-hosted base metal deposits are located within 200 km of the border between thick and thin lithosphere, according to statistical comparisons between global lithospheric thickness and known deposit locations.
TL;DR: In this article, the authors used 789 radiocarbon (∆14C) profiles, along with other geospatial information, to create globally gridded datasets of mineral soil and mean age.
Abstract: Soils contain more carbon than the atmosphere and vegetation combined An increased flow of carbon from the atmosphere into soil pools could help mitigate anthropogenic emissions of carbon dioxide and climate change Yet we do not know how quickly soils might respond because the age distribution of soil carbon is uncertain Here we used 789 radiocarbon (∆14C) profiles, along with other geospatial information, to create globally gridded datasets of mineral soil ∆14C and mean age We found that soil depth is a primary driver of ∆14C, whereas climate (for example, mean annual temperature) is a major control on the spatial pattern of ∆14C in surface soil Integrated to a depth of 1 m, global soil carbon has a mean age of 4,830 ± 1,730 yr, with older carbon in deeper layers and permafrost regions In contrast, vertically resolved land models simulate ∆14C values that imply younger carbon ages and a more rapid carbon turnover Our data-derived estimates of older mean soil carbon age suggest that soils will accumulate less carbon than predicted by current Earth system models over the twenty-first century Reconciling these models with the global distribution of soil radiocarbon will require a better representation of the mechanisms that control carbon persistence in soils Soils may accumulate less carbon and with a slower turnover than Earth system models predict, according to analysis of the age distribution of global soil carbon, which finds that the mean age of soil carbon is older than that in simulated in models
TL;DR: In this article, the authors use Landsat imagery and a detailed correction to the Randolph Glacier Inventory to show that 7.3% of mountain glacier area is debris covered and over half of Earth’s debris is concentrated in three regions: Alaska (38.6%), Southwest Asia (12.6%).
Abstract: Rock debris can accumulate on glacier surfaces and dramatically reduce glacier melt. The structure of a debris cover is unique to each glacier and sensitive to climate. Despite this, debris cover has been omitted from global glacier models and forecasts of their response to a changing climate. Fundamental to resolving these omissions is a global map of debris cover and an estimate of its future spatial evolution. Here we use Landsat imagery and a detailed correction to the Randolph Glacier Inventory to show that 7.3% of mountain glacier area is debris covered and over half of Earth’s debris is concentrated in three regions: Alaska (38.6% of total debris-covered area), Southwest Asia (12.6%) and Greenland (12.0%). We use a set of new metrics, which include stage, the current position of a glacier on its trajectory towards reaching its spatial carrying capacity of debris cover, to quantify the state of glaciers. Debris cover is present on 44% of Earth’s glaciers and prominent (>1.0 km2) on 15%. Of Earth’s glaciers, 20% have a substantial percentage of debris cover for which the net stage is 36% and the bulk of individual glaciers have evolved beyond an optimal moraine configuration favourable for debris-cover expansion. Use of this dataset in global-scale models will enable improved estimates of melt over 10.6% of the global glacier domain. A global map of rock-debris cover on mountain glaciers shows its spatial distribution and evolution.
TL;DR: In this article, the authors analyzed regional and global seismic and deformation data to provide a one-year-long detailed picture of a deep, rare magmatic process and identified about 7,000 volcano-tectonic earthquakes and 407 very-long-period seismic signals.
Abstract: The dynamics of magma deep in the Earth’s crust are difficult to capture by geophysical monitoring. Since May 2018, a seismically quiet area offshore of Mayotte in the western Indian Ocean has been affected by complex seismic activity, including long-duration, very-long-period signals detected globally. Global Navigation Satellite System stations on Mayotte have also recorded a large surface deflation offshore. Here we analyse regional and global seismic and deformation data to provide a one-year-long detailed picture of a deep, rare magmatic process. We identify about 7,000 volcano-tectonic earthquakes and 407 very-long-period seismic signals. Early earthquakes migrated upward in response to a magmatic dyke propagating from Moho depth to the surface, whereas later events marked the progressive failure of the roof of a magma reservoir, triggering its resonance. An analysis of the very-long-period seismicity and deformation suggests that at least 1.3 km3 of magma drained from a reservoir of 10 to 15 km diameter at 25 to 35 km depth. We demonstrate that such deep offshore magmatic activity can be captured without any on-site monitoring. Recent seismicity near Mayotte in the Indian Ocean is due to dyke propagation from and drainage of a 25–35 km deep magma reservoir, according to an analysis of earthquake and deformation data.
TL;DR: In this article, a combination of in situ and satellite-based datasets and conducted meteorological model simulations is analyzed to show that intensive irrigation in the region cools the land surface by 1°C and the air by 0.5°C.
Abstract: Intensive irrigation in India has been demonstrated to decrease surface temperature, but the influence of irrigation on humidity and extreme moist heat stress is not well understood. Here we analysed a combination of in situ and satellite-based datasets and conducted meteorological model simulations to show that irrigation modulates extreme moist heat. We found that intensive irrigation in the region cools the land surface by 1 °C and the air by 0.5 °C. However, the decreased sensible heat flux due to irrigation reduces the planetary boundary layer height, which increases low-level moist enthalpy. Thus, irrigation increases the specific and relative humidity, which raises the moist heat stress metrics. Intense irrigation over the region results in increased moist heat stress in India, Pakistan, and parts of Afghanistan—affecting about 37–46 million people in South Asia—despite a cooler land surface. We suggest that heat stress projections in India and other regions dominated by semi-arid and monsoon climates that do not include the role of irrigation overestimate the benefits of irrigation on dry heat stress and underestimate the risks. Intensive irrigation in India cools the land surface, but increases the moist heat stress in South Asia, according to an analysis of observational datasets and meteorological models.
TL;DR: In this article, the role of water migrating from slab to surface during subduction has been underappreciated, but the origin of these magmatic systems is not well understood.
Abstract: Continental arcs are the sites of production of continental crust, but the origin of these magmatic systems is not well understood. Although a number of processes have been suggested to be important, the role of water migrating from slab to surface during subduction has been underappreciated. Directly below the Moho, hot (approximately 1,100 °C), hydrous basaltic magmas fractionate as they cool to the regional geotherm at 750 to 800 °C, ultimately solidifying as mafic underplates. Cooling and fractionation cause water to exsolve and ascend, triggering fluid-fluxed melting of overlying mafic underplates and other crust. Melting of prior mafic underplates buffers temperatures and generates the voluminous, juvenile low-K magmas of Cordilleran batholiths. These granitoid magmas comprise a low-temperature slurry of melt and residue, and recrystallize into silicic mush during adiabatic ascent. Such hydrous mushes are intermittently infused by hotter, more mafic magmas, which hybridize and facilitate ascent and, potentially, eruption. Fluid-fluxed melting overcomes many of the general petrological and geochemical problems associated with models dominated by fractional crystallization. The role of water during repeated episodes of mafic underplating is critical to generate the juvenile granitoid infrastructure of the continents. Migration of water from the slab to the surface during subduction is highlighted as a key process in the formation of continental crust.
TL;DR: In this paper, the authors show that the geochemical diversity of TTG plutons from South Africa do not represent liquids but fossil, crystal-rich magma reservoirs left behind by the eruption of silicic volcanic rocks, being possibly coeval at the million-year scale as constrained by high-precision uranium-lead geochronology.
Abstract: Granitoids of the tonalite–trondhjemite–granodiorite (TTG) series dominate Earth’s earliest continental crust. The geochemical diversity of TTGs is ascribed to several possible geodynamic settings of magma formation, from low-pressure differentiation of oceanic plateaus to high-pressure melting of mafic crust at convergent plate margins. These interpretations implicitly assume that the bulk-rock compositions of TTGs did not change from magma generation in the source to complete crystallization. However, crystal–liquid segregation influences the geochemistry of felsic magmas, as shown by the textural and chemical complementarity between coeval plutons and silicic volcanic rocks in the Phanerozoic Eon. We demonstrate here that Paleoarchean (ca. 3,456 million years old) TTG plutons from South Africa do not represent liquids but fossil, crystal-rich magma reservoirs left behind by the eruption of silicic volcanic rocks, being possibly coeval at the million-year scale as constrained by high-precision uranium–lead geochronology. The chemical signature of the dominant trondhjemites, conventionally interpreted as melts generated by high-pressure melting of basalts, reflects the combined accumulation of plagioclase phenocrysts and loss of interstitial liquid that erupted as silicic volcanic rocks. Our results indicate that the entire compositional diversity of TTGs could derive from the upper crustal differentiation of a single, tonalitic magma formed by basalt melting and/or crystallization at <40 km depth. These results call for a unifying model of Hadean–Archean continent nucleation by intracrustal production of TTG magmas. The chemical diversity of Earth’s early continental building blocks can be explained by differentiation of a single melt, without complex geodynamic settings, according to petrological and geochemical analysis of samples from South Africa.
TL;DR: In this paper, the authors employ data-driven and land-surface models to produce observation-based global reconstructions of water availability from 1902 to 2014, a period during which our planet experienced a global warming of approximately 1°C.
Abstract: Human-induced climate change impacts the hydrological cycle and thus the availability of water resources However, previous assessments of observed warming-induced changes in dryness have not excluded natural climate variability and show conflicting results due to uncertainties in our understanding of the response of evapotranspiration Here we employ data-driven and land-surface models to produce observation-based global reconstructions of water availability from 1902 to 2014, a period during which our planet experienced a global warming of approximately 1 °C Our analysis reveals a spatial pattern of changes in average water availability during the driest month of the year over the past three decades compared with the first half of the twentieth century, with some regions experiencing increased and some decreased water availability The global pattern is consistent with climate model estimates that account for anthropogenic effects, and it is not expected from natural climate variability, supporting human-induced climate change as the cause There is regional evidence of drier dry seasons predominantly in extratropical latitudes and including Europe, western North America, northern Asia, southern South America, Australia and eastern Africa We also find that the intensification of the dry season is generally a consequence of increasing evapotranspiration rather than decreasing precipitation Regional changes in dry-season water availability over recent decades can be attributed to human-induced climate change, according to analyses of global reconstructions
TL;DR: In this paper, the authors study an As-contaminated aquifer in Van Phuc, Vietnam, located ~10 km southeast of Hanoi on the banks of the Red River, which is affected by large-scale groundwater abstraction.
Abstract: Geogenic groundwater arsenic (As) contamination is pervasive in many aquifers in south and southeast Asia. It is feared that recent increases in groundwater abstractions could induce the migration of high-As groundwaters into previously As-safe aquifers. Here we study an As-contaminated aquifer in Van Phuc, Vietnam, located ~10 km southeast of Hanoi on the banks of the Red River, which is affected by large-scale groundwater abstraction. We used numerical model simulations to integrate the groundwater flow and biogeochemical reaction processes at the aquifer scale, constrained by detailed hydraulic, environmental tracer, hydrochemical and mineralogical data. Our simulations provide a mechanistic reconstruction of the anthropogenically induced spatiotemporal variations in groundwater flow and biogeochemical dynamics and determine the evolution of the migration rate and mass balance of As over several decades. We found that the riverbed–aquifer interface constitutes a biogeochemical reaction hotspot that acts as the main source of elevated As concentrations. We show that a sustained As release relies on regular replenishment of river muds rich in labile organic matter and reactive iron oxides and that pumping-induced groundwater flow may facilitate As migration over distances of several kilometres into adjacent aquifers. The interface between riverbed and aquifer is a biogeochemical reaction hotspot for arsenic release from river sediments, according to numerical simulations of groundwater flow and biogeochemical reaction processes.
TL;DR: In this article, the authors argue that progress towards diversification can only come with a concerted shift in mindsets and a deeper understanding of the complexities of race in the United States.
Abstract: Geoscientists in the United States are predominantly White. Progress towards diversification can only come with a concerted shift in mindsets and a deeper understanding of the complexities of race.
TL;DR: In this article, the authors used three-dimensional thermomechanical numerical simulations of impingement of a thermal mantle plume on the Venusian lithosphere to assess the origin and diversity of large Venusian coronae.
Abstract: In the absence of global plate tectonics, mantle convection and plume–lithosphere interaction are the main drivers of surface deformation on Venus. Among documented tectonic structures, circular volcano-tectonic features known as coronae may be the clearest surface manifestations of mantle plumes and hold clues to the global Venusian tectonic regime. Yet, the exact processes underlying coronae formation and the reasons for their diverse morphologies remain controversial. Here we use three-dimensional thermomechanical numerical simulations of impingement of a thermal mantle plume on the Venusian lithosphere to assess the origin and diversity of large Venusian coronae. The ability of the mantle plume to penetrate into the Venusian lithosphere results in four main outcomes: lithospheric dripping, short-lived subduction, embedded plume and plume underplating. During the first three scenarios, plume penetration and spreading induce crustal thickness variations that eventually lead to a final topographic isostasy-driven topographic inversion from circular trenches surrounding elevated interiors to raised rims surrounding inner depressions, as observed on many Venusian coronae. Different corona structures may represent not only different styles of plume–lithosphere interactions but also different stages in evolution. A morphological analysis of large existing coronae leads to the conclusion that at least 37 large coronae (including the largest Artemis corona) are active, providing evidence for widespread ongoing plume activity on Venus. Thermomechanical modelling shows that the formation and diverse morphologies of coronae on Venus can be explained by interactions between the lithosphere and impinging mantle plumes. Some corona structures are consistent with ongoing plume activity.
TL;DR: In this article, the authors show that during the peak of the 2015-2016 El Nino anomaly, temperature fluctuations associated with internal waves reduced cumulative heat exposure by up to 88%.
Abstract: Coral reefs are among the most species-rich, productive and economically valuable ecosystems on Earth but increasingly frequent pantropical coral bleaching events are threatening their persistence on a global scale. The 2015–2016 El Nino led to the hottest sea surface temperatures on record and widespread bleaching of shallow-water corals. However, the causes of spatial variation in bleaching are poorly understood, and near-surface estimates of heat stress, such as those inferred from satellites, cannot be generalized across the broad depth ranges occupied by corals. Here, using in situ temperatures recorded across reefs from the near surface to 30–50 m depths in the western, central and eastern Pacific, we show that during the peak of the 2015–2016 anomaly, temperature fluctuations associated with internal waves reduced cumulative heat exposure by up to 88%. The durations of severe thermal anomalies above 8 °C-days, at which point widespread coral bleaching and mortality are likely, were also decreased by >36% at some sites and were prevented entirely at others. The impact of internal waves across depths on coral reefs has the potential to create and support thermal refuges in which heat stress and coral bleaching risk may be modulated, but future effects depend on the response of internal wave climates to continued warming and strengthening ocean stratification. Internal waves can relieve coral reef heat stress, according to an analysis that isolates the effect at different depths using a compilation of high-resolution temperature records.
TL;DR: In this paper, the authors performed a multicountry assessment of the links between large-scale land acquisitions and tropical forest loss by combining a new georeferenced database of 82,403 individual land deals with data on annual forest cover and loss between 2000 and 2018.
Abstract: Tropical forests are vital for global biodiversity, carbon storage and local livelihoods, yet they are increasingly under threat from human activities Large-scale land acquisitions have emerged as an important mechanism linking global resource demands to forests in the Global South, yet their influence on tropical deforestation remains unclear Here we perform a multicountry assessment of the links between large-scale land acquisitions and tropical forest loss by combining a new georeferenced database of 82,403 individual land deals—covering 15 countries in Latin America, sub-Saharan Africa and Southeast Asia—with data on annual forest cover and loss between 2000 and 2018 We find that land acquisitions cover between 6% and 59% of study-country land area and between 2% and 79% of their forests Compared with non-investment areas, large-scale land acquisitions were granted in areas of higher forest cover in 11 countries and had higher forest loss in 52% of cases Oil palm, wood fibre and tree plantations were consistently linked with enhanced forest loss while logging and mining concessions showed a mix of outcomes Our findings demonstrate that large-scale land acquisitions can lead to elevated deforestation of tropical forests, highlighting the role of local policies in the sustainable management of these ecosystems Tropical deforestation rates are linked to large-scale land investments, according to georeferenced land deal records and remote sensing of forest loss over the past two decades
TL;DR: In this paper, the authors present a case study of Chile's copper mining and show that the direct and indirect greenhouse gas emissions from mining for green technologies need to be accurately and transparently accounted for.
Abstract: The climate change impacts of mining are often not fully accounted for, although the environmental impact of mineral extraction more generally is widely studied. Copper mining can serve as a case study to analyse the measurable pathways by which mining contributes to climate change through direct and indirect greenhouse gas emissions. For example, mining, processing and transportation require fuel and electricity, and the decomposition of carbonate minerals, employed to reduce environmental impacts, also releases carbon dioxide. Overall, we estimate that greenhouse gas emissions associated with primary mineral and metal production was equivalent to approximately 10% of the total global energy-related greenhouse gas emissions in 2018. For copper mining, fuel consumption increased by 130% and electricity consumption increased by 32% per unit of mined copper in Chile from 2001 to 2017, largely due to decreasing ore grade. This trend of increasing energy demand to produce the same quantity of some metals compounds the problems of increased metal demand due to the pressures of new technologies and increasing population. For green technologies to be implemented effectively, it is necessary that the mining industry and regulators accurately and transparently account for greenhouse gas emissions to implement mitigation strategies. Direct and indirect greenhouse gas emissions from mining for green technologies need to be accurately and transparently accounted for, as highlighted by a case study of Chilean copper mining.
TL;DR: In this article, the authors quantify the widespread peat carbon loss by using InSAR remote sensing to map subsidence at 90-m resolution across 2.7 million hectares of tropical peatland area from 2007 to 2011.
Abstract: Over the last three decades, most of the 25 million hectares of tropical peatlands in Southeast Asia have been deforested and drained. As a consequence, declining water tables are exposing peat to oxidation, converting plant material accumulated over millennia to carbon dioxide, and causing land subsidence. Here, we quantify the widespread peat carbon loss by using InSAR remote sensing to map subsidence at 90-m resolution across 2.7 Mha of peatland area from 2007 to 2011. Over 90% of the surveyed area is subsiding, with a mean rate of 2.2 cm yr−1. Consequently, the region now faces loss of productive land and flooding because many peatlands are near sea level. Our measurements reveal that smallholder agricultural areas and degraded peatlands are subsiding at rates comparable to those of plantations, and that subsidence rates increase away from rivers and decrease over time following drainage. Because of its detailed spatial resolution, InSAR provides a valuable tool to identify emissions by land use and geography and to target hotspots for better management. Finally, we use remotely sensed maps to update IPCC emissions factors and calculate regional CO2 emissions from peat oxidation of 155 ± 30 MtC yr−1 in 2015, similar in magnitude to both regional fossil-fuel emissions and peat fires. Subsidence and carbon emissions in tropical peatlands are primarily linked to drainage history, not land-use type, according to large-scale high-resolution remote sensing in Southeast Asia.
TL;DR: In this paper, the authors used a global analysis of active meander migrations that includes previously ignored unvegetated rivers from the arid interiors of modern continents to demonstrate how profoundly vegetation transformed the pace of change for Earth's landscapes, and at last offer a mechanistic explanation for the radically distinct stratigraphic records of barren and vegetated rivers.
Abstract: Meandering rivers are diagnostic landforms of hydrologically active planets, and their migration regulates the continental component of biogeochemical cycles that stabilize climate and allow for life on Earth. The rise of river meanders on Earth has been linked to riverbank stabilization driven by the Palaeozoic evolution of plant life about 440 million years ago. Here we provide a fundamental test for this hypothesis using a global analysis of active meander migrations that includes previously ignored unvegetated rivers from the arid interiors of modern continents. When normalized by channel size, unvegetated meanders universally migrate an order of magnitude faster than vegetated ones. While providing irrefutable evidence that vegetation is not required for meander formation, we demonstrate how profoundly vegetation transformed the pace of change for Earth’s landscapes, and we at last offer a mechanistic explanation for the radically distinct stratigraphic records of barren and vegetated rivers. We posit that the migration slowdown driven by the rise of land plants dramatically impacted biogeochemical fluxes and rendered Earth’s landscapes even more hospitable to life. Therefore, the tenfold faster migration of unvegetated rivers may be key to deciphering the environments of barren worlds such as early Earth and Mars. River meanders migrate much faster in barren than in vegetated landscapes, according to global analyses of active meander migration of both unvegetated and vegetated rivers. The difference in migration rates suggests that the rise of land plants had a significant influence on landscapes.
Umeå University1, University of Gothenburg2, Stockholm University3, Aalto University4, University of Greifswald5, Swiss Federal Institute for Forest, Snow and Landscape Research6, Leibniz University of Hanover7, Sukachev Institute of Forest8, Lawrence Berkeley National Laboratory9, Swedish University of Agricultural Sciences10, International Institute for Applied Systems Analysis11, University of Vienna12, Government College University, Faisalabad13, VU University Amsterdam14
TL;DR: In this article, the authors combine high-resolution spatial and depth-resolved datasets of key plant and permafrost properties with empirical relationships of priming effects from living plants on microbial respiration.
Abstract: As global temperatures continue to rise, a key uncertainty of climate projections is the microbial decomposition of vast organic carbon stocks in thawing permafrost soils. Decomposition rates can accelerate up to fourfold in the presence of plant roots, and this mechanism—termed the rhizosphere priming effect—may be especially relevant to thawing permafrost soils as rising temperatures also stimulate plant productivity in the Arctic. However, priming is currently not explicitly included in any model projections of future carbon losses from the permafrost area. Here, we combine high-resolution spatial and depth-resolved datasets of key plant and permafrost properties with empirical relationships of priming effects from living plants on microbial respiration. We show that rhizosphere priming amplifies overall soil respiration in permafrost-affected ecosystems by ~12%, which translates to a priming-induced absolute loss of ~40 Pg soil carbon from the northern permafrost area by 2100. Our findings highlight the need to include fine-scale ecological interactions in order to accurately predict large-scale greenhouse gas emissions, and suggest even tighter restrictions on the estimated 200 Pg anthropogenic carbon emission budget to keep global warming below 1.5 °C.
TL;DR: In this article, the authors investigate the interplay between sediment consolidation, faulting and the evolution of stress and pore fluid pressure in response to seamount subduction, using a numerical model that couples mechanical and hydrological processes and is constrained by laboratory and field observations.
Abstract: Subduction of rough seafloor and seamounts is thought to impact a broad range of geodynamic processes, including megathrust slip behaviour, forearc fluid flow and long-term structural evolution in the overriding plate. Although there are many conceptual models describing the effects of seamount subduction, our quantitative and mechanistic understanding of the underlying deformation and fluid processes remains incomplete. Here we investigate the interplay between sediment consolidation, faulting and the evolution of stress and pore fluid pressure in response to seamount subduction, using a numerical model that couples mechanical and hydrological processes and is constrained by laboratory and field observations. Our results show that subducting topography drives marked spatial variations in tectonic loading, sediment consolidation and megathrust stress state. Downdip of a subducting seamount on its leading flank, enhanced compression and drainage lead to large fault-normal stress and overconsolidated wall rocks. A stress shadow in the seamount’s wake leads to anomalously high sediment porosity. These variations help explain observed patterns of megathrust slip, with earthquakes and microseismicity favoured at the downdip edge of seamounts and aseismic or slow slip in the updip stress shadow. Changing stresses and pore fluid pressures during subduction of seamounts, as simulated with a numerical model that couples mechanical and hydrological processes, help explain observed patterns of megathrust slip.
TL;DR: In this article, the authors investigate the tropical response to Antarctic sea-ice loss and compare it with the response to Arctic sea ice loss using a fully coupled climate model, and find that future Antarctic seaice loss will exert a profound influence on the tropics.
Abstract: Arctic and Antarctic sea-ice extent are both projected to dramatically decline over the coming century. The effects of Arctic sea-ice loss are not limited to the northern high latitudes, and reach deep into the tropics. Yet little is known about the effects of future Antarctic sea-ice loss outside of the southern high latitudes. Here, using a fully coupled climate model, we investigate the tropical response to Antarctic sea-ice loss and compare it with the response to Arctic sea-ice loss. We show that Antarctic sea-ice loss, similar to Arctic sea-ice loss, causes enhanced warming in the eastern equatorial Pacific and an equatorward intensification of the Intertropical Convergence Zone. We demonstrate that Antarctic sea-ice loss causes a mini global warming signal comparable to the one caused by Arctic sea-ice loss, and reminiscent of the response to greenhouse gases. We also show that ocean dynamics are key to capturing the tropical response to sea-ice loss. In short, we find that future Antarctic sea-ice loss will exert a profound influence on the tropics. Combined Arctic and Antarctic sea-ice losses will account for 20–30% of the projected tropical warming and precipitation changes under the high-emissions scenario Representative Concentration Pathway 8.5. Antarctic sea-ice loss causes enhanced warming in the eastern equatorial Pacific, and together with Arctic sea-ice loss accounts for 20–30% of projected warming and rainfall changes in the tropics, suggest climate model simulations.