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Showing papers in "Nature Geoscience in 2012"


Journal ArticleDOI
TL;DR: In this article, an analysis of organic carbon data from just under one thousand seagrass meadows indicates that, globally, these systems could store between 4.2 and 8.4 Pg carbon.
Abstract: Seagrass meadows are some of the most productive ecosystems on Earth. An analysis of organic carbon data from just under one thousand seagrass meadows indicates that, globally, these systems could store between 4.2 and 8.4 Pg carbon.

1,344 citations


Journal ArticleDOI
TL;DR: A review of recent studies emphasizes the importance of wind-driven upwelling in the Southern Ocean for global ocean circulation as discussed by the authors, which plays a central role in the climate and its variability.
Abstract: The meridional overturning circulation of the ocean plays a central role in the climate and its variability. This Review of recent studies emphasizes the importance of wind-driven upwelling in the Southern Ocean for global ocean circulation.

799 citations


Journal ArticleDOI
TL;DR: In this paper, a synthesis of the latest observations suggests that more longwave radiation is received at the Earth's surface than previously thought, and that more precipitation is generated, and the additional precipitation is sustained by more energy leaving the surface by evaporation, that is, in the form of latent heat flux.
Abstract: Climate change is governed by changes to the global energy balance. A synthesis of the latest observations suggests that more longwave radiation is received at the Earth's surface than previously thought, and that more precipitation is generated. Climate change is governed by changes to the global energy balance. At the top of the atmosphere, this balance is monitored globally by satellite sensors that provide measurements of energy flowing to and from Earth. By contrast, observations at the surface are limited mostly to land areas. As a result, the global balance of energy fluxes within the atmosphere or at Earth's surface cannot be derived directly from measured fluxes, and is therefore uncertain. This lack of precise knowledge of surface energy fluxes profoundly affects our ability to understand how Earth's climate responds to increasing concentrations of greenhouse gases. In light of compilations of up-to-date surface and satellite data, the surface energy balance needs to be revised. Specifically, the longwave radiation received at the surface is estimated to be significantly larger, by between 10 and 17 Wm−2, than earlier model-based estimates. Moreover, the latest satellite observations of global precipitation indicate that more precipitation is generated than previously thought. This additional precipitation is sustained by more energy leaving the surface by evaporation — that is, in the form of latent heat flux — and thereby offsets much of the increase in longwave flux to the surface.

678 citations


Journal ArticleDOI
TL;DR: In this article, photoautotrophic communities, which are capable of synthesizing their own food from inorganic substances using sunlight, were analyzed and found to account for nearly half of the biological nitrogen fixation on land.
Abstract: Many terrestrial surfaces are covered by photoautotrophic communities, which are capable of synthesizing their own food from inorganic substances using sunlight. According to an analysis of previously published data, these communities account for nearly half of the biological nitrogen fixation on land.

673 citations


Journal ArticleDOI
TL;DR: In the early Triassic period, Ammonoids and some other groups diversified rapidly, within 1-3 Myr, but extinctions continued through the Early Triassic, and a stable, complex ecosystem did not re-emerge until the beginning of the Middle Triassic 8-9 Myr after the crisis as discussed by the authors.
Abstract: The aftermath of the great end-Permian period mass extinction 252 Myr ago shows how life can recover from the loss of >90% species globally. The crisis was triggered by a number of physical environmental shocks (global warming, acid rain, ocean acidification and ocean anoxia), and some of these were repeated over the next 5-6 Myr. Ammonoids and some other groups diversified rapidly, within 1-3 Myr, but extinctions continued through the Early Triassic period. Triassic ecosystems were rebuilt stepwise from low to high trophic levels through the Early to Middle Triassic, and a stable, complex ecosystem did not re-emerge until the beginning of the Middle Triassic, 8-9 Myr after the crisis. A positive aspect of the recovery was the emergence of entirely new groups, such as marine reptiles and decapod crustaceans, as well as new tetrapods on land, including — eventually — dinosaurs. The stepwise recovery of life in the Triassic could have been delayed either by biotic drivers (complex multispecies interactions) or physical perturbations, or a combination of both. This is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large-scale evolution. from a much more devastated planet and biota than the others. With only some 10% of species surviving, the EPME was much harsher than the other mass extinctions, during which global species diversity reduced to only about 50% of the pre-extinction total 1,2,24-26 . This means that the Triassic recovery has two profound implications: first, it may show qualitative, as well as quantitative, differences from the other post-extinction recoveries; and, second, it can act as an exemplar of what to expect, at its most extreme, when global biodiversity is pushed to the brink. There are obvious implications for current concerns about biodiversity loss and recovery resulting from human impacts 27,28 . In the past ten years, attention has focused on the sedimentary successions in south China. These are enormously laterally extensive, with some formations extending more than 2,000 km from the Zhejiang to Yunnan provinces. The huge exposures, length of the sections and improving dating open up the opportunity to explore physical environmental and biotic changes through the extinction and recovery times in varied marine habitats, and compare these with patterns elsewhere in the world (Fig. 1). A fine- scale, forensic analysis of this extraordinary time in Earth's history now becomes possible. The end-Permian mass extinction The EPME killed 80-96% of marine animal species and 70% of terrestrial vertebrate species

605 citations


Journal ArticleDOI
TL;DR: In this paper, a review of our understanding of groundwater depletion suggests that although the problem is global, solutions must be adapted to specific regional requirements at the aquifer scale, and that the world's largest freshwater resource is groundwater.
Abstract: The world's largest freshwater resource is groundwater. A review of our understanding of groundwater depletion suggests that although the problem is global, solutions must be adapted to specific regional requirements at the aquifer scale.

600 citations


Journal ArticleDOI
TL;DR: In this paper, an analysis of the regional mass balance of Karakoram glaciers by comparison of digital elevation models from 1999 to 2008 reveals a small glacier mass gain in the area.
Abstract: The mass balance of Hindu-Kush–Karakoram–Himalaya glaciers has been debated, partly because of a severe lack of observations from the region. An analysis of the regional mass balance of Karakoram glaciers by comparison of digital elevation models from 1999 to 2008 reveals a small glacier mass gain in the area.

581 citations


Journal ArticleDOI
TL;DR: In this article, the authors suggest that shifts in the large-scale environment could alter the prevalence of mixed-phase clouds, potentially affecting surface radiative fluxes and the Arctic energy budget.
Abstract: Mixed-phase clouds, comprising both ice and supercooled liquid water, have a large impact on radiative fluxes in the Arctic. Interactions between numerous local feedbacks sustain these complex cloud systems, leading to the development of a resilient mixed-phase cloud system. The Arctic region is particularly sensitive to climate change. Mixed-phase clouds, comprising both ice and supercooled liquid water, have a large impact on radiative fluxes in the Arctic. These clouds occur frequently during all seasons in the region, where they often persist for many days at a time. This persistence is remarkable given the inherent instability of ice–liquid mixtures. In recent years it has emerged that feedbacks between numerous local processes, including the formation and growth of ice and cloud droplets, radiative cooling, turbulence, entrainment and surface fluxes of heat and moisture, interact to create a resilient mixed-phase cloud system. As well as the persistent mixed-phase cloud state there is another distinct Arctic state, characterized by radiatively clear conditions. The occurrence of either state seems to be related, in part, to large-scale environmental conditions. We suggest that shifts in the large-scale environment could alter the prevalence of mixed-phase clouds, potentially affecting surface radiative fluxes and the Arctic energy budget.

508 citations


Journal ArticleDOI
TL;DR: The high topography in eastern Tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin this paper. But this was not the case in the early part of the Indo-Asian collision.
Abstract: High topography in eastern Tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin. Thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the Indo-Asian collision, implying that crustal flow alone could not have created the high topography.

453 citations


Journal ArticleDOI
TL;DR: It is suggested that contemporary evolution could help to maintain the functionality of microbial processes at the base of marine food webs in the face of global change.
Abstract: Oc ean acidification, the drop in seawater pH associated with the ongoing enrichment of marine waters with carbon dioxide from fossil fuel burning, may seriously impair marine calcifying organisms. Our present understanding of the sensitivity of marine life to ocean acidification is based primarily on short-term experiments, in which organisms are exposed to increased concentrations of CO2. However, phytoplankton species with short generation times, in particular, may be able to respond to environmental alterations through adaptive evolution. Here, we examine the ability of the world’s single most important calcifying organism, the coccolithophore Emiliania huxleyi, to evolve in response to ocean acidification in two 500-generation selection experiments. Specifically, we exposed E. huxleyi populations founded by single or multiple clones to increased concentrations of CO2. Around 500 asexual generations later we assessed their fitness. Compared with populations kept at ambient CO2 partial pressure, those selected at increased partial pressure exhibited higher growth rates, in both the single- and multiclone experiment, when tested under ocean acidification conditions. Calcification was partly restored: rates were lower under increased CO2 conditions in all cultures, but were up to 50% higher in adapted compared with non-adapted cultures. We suggest that contemporary evolution could help to maintain the functionality of microbial processes at the base of marine food webs in the face of global change.

445 citations


Journal ArticleDOI
TL;DR: In this article, a 5,200-year-long lake sediment record was used to reconstruct the circulation patterns associated with the North Atlantic Oscillation (NAO) in the Arctic and northern Europe.
Abstract: The North Atlantic Oscillation influences climate in the Arctic region and northern Europe. Reconstructions of circulation patterns associated with the North Atlantic Oscillation from a 5,200-year-long lake sediment record suggest that the atmospheric circulation responded to significant transitions in Northern Hemisphere climate.

Journal ArticleDOI
TL;DR: A combination of results from the fields of petrology, numerical modelling, geophysics and geochemistry suggests a two-step process. as mentioned in this paper suggests that intensely mixed metamorphic rock formations (melanges) form along the interface between the subducted slab and the mantle.
Abstract: At subduction zones, crustal material enters the mantle. Some of this material, however, is returned to the overriding plate through volcanic and plutonic activity. Magmas erupted above subduction zones show a characteristic range of compositions that reflect mixing in the magma source region between three components: hydrous fluids derived from the subducted oceanic crust, components of the thin veneer of subducted sediments and peridotite mantle rocks. The mechanism for mixing and transport of these components has been enigmatic. A combination of results from the fields of petrology, numerical modelling, geophysics and geochemistry suggests a two-step process. First, intensely mixed metamorphic rock formations—melanges—form along the interface between the subducted slab and the mantle. As the melange contains the characteristic three-component geochemical pattern of subduction-zone magmas, we suggest that melange formation provides the physical mixing process. Then, blobs of low-density melange material—diapirs—rise buoyantly from the surface of the subducting slab and transport the well-mixed melange material into the mantle beneath the volcanoes. Magma erupted at subduction-zone volcanoes contains mantle rocks and a mixture of fluids and sediments derived from the subducted slab. A synthesis of work over past years provides an integrated physico-chemical framework for subduction zones with mixing at the slab–mantle interface and transport towards the surface volcanoes by buoyant diapirs.

Journal ArticleDOI
TL;DR: In this paper, the authors present a data set of satellite-tracked sea-ice motion for the period of 1992-2010 that reveals large and statistically significant trends in Antarctic ice drift, which, in most sectors, can be linked to local winds.
Abstract: The sea-ice cover around Antarctica has experienced a slight expansion in area over the past decades1, 2. This small overall increase is the sum of much larger opposing trends in different sectors that have been proposed to result from changes in atmospheric temperature or wind stress3, 4, 5, precipitation6, 7, ocean temperature8, and atmosphere or ocean feedbacks9, 10. However, climate models have failed to reproduce the overall increase in sea ice11. Here we present a data set of satellite-tracked sea-ice motion for the period of 1992–2010 that reveals large and statistically significant trends in Antarctic ice drift, which, in most sectors, can be linked to local winds. We quantify dynamic and thermodynamic processes in the internal ice pack and show that wind-driven changes in ice advection are the dominant driver of ice-concentration trends around much of West Antarctica, whereas wind-driven thermodynamic changes dominate elsewhere. The ice-drift trends also imply large changes in the surface stress that drives the Antarctic ocean gyres, and in the fluxes of heat and salt responsible for the production of Antarctic bottom and intermediate waters.

Journal ArticleDOI
TL;DR: Sediment records and climate modelling suggest that the winter monsoon was also affected by millenial scale variability, and that the abrupt changes were driven by changes in the strength of the Atlantic meridional overturning circulation as mentioned in this paper.
Abstract: East Asian summer monsoon precipitation varied on millennial timescales during the last glacial period. Sediment records and climate modelling suggest that the winter monsoon was also affected by millenial scale variability, and that the abrupt changes were driven by changes in the strength of the Atlantic meridional overturning circulation.

Journal ArticleDOI
TL;DR: The Atlantic Ocean has been suggested as an important driver of variability in European climate on decadal timescales as discussed by the authors, and analyses of ocean and atmosphere temperature data from observations suggest that the shift in European Climate during the 1990s was a result of warming in the North Atlantic Ocean.
Abstract: The Atlantic Ocean has been suggested as an important driver of variability in European climate on decadal timescales. Analyses of ocean and atmosphere temperature data from observations suggest that the shift in European climate during the 1990s was a result of warming in the North Atlantic Ocean.

Journal ArticleDOI
TL;DR: In this article, isotopic homogeneity in titanium, a highly refractory element, suggests that the Moon was derived from the mantle of the proto-Earth and not from the Earth.
Abstract: Geochemical evidence continues to challenge giant impact models, which predict that the Moon formed from both proto-Earth and impactor material. Analyses of lunar samples reveal isotopic homogeneity in titanium, a highly refractory element, suggesting lunar material was derived predominantly from the mantle of the proto-Earth.

Journal ArticleDOI
TL;DR: In this paper, a synthesis of research indicates that the mechanisms controlling this growth depend on the size of the growing particle, and that dependence of particle growth mechanisms on particle size needs to be investigated more systematically.
Abstract: The growth of the smallest atmospheric particles to sizes at which they may act as seeds for cloud droplets is a key step linking aerosols to clouds and climate. A synthesis of research indicates that the mechanisms controlling this growth depend on the size of the growing particle. Aerosols have a strong, yet poorly quantified, effect on climate. The growth of the smallest atmospheric particles from diameters in the nanometre range to sizes at which they may act as seeds for cloud droplets is a key step linking aerosols to clouds and climate. In many environments, atmospheric nanoparticles grow by taking up organic compounds that are derived from biogenic hydrocarbon emissions. Several mechanisms may control this uptake. Condensation of low-volatility vapours and formation of organic salts probably dominate the very first steps of growth in particles close to 1 nm in diameter. As the particles grow further, formation of organic polymers and effects related to the phase of the particle probably become increasingly important. We suggest that dependence of particle growth mechanisms on particle size needs to be investigated more systematically.

Journal ArticleDOI
TL;DR: In this paper, an analysis of more than 15,000 landslides in the eastern Himalaya, mapped from satellite images, shows that steep uplands primarily respond to uplift and river incision by increases in landslide erosion rates rather than by steepened hillslope angles.
Abstract: The steep topography of mountain landscapes arises from interactions between tectonic rock uplift, valley incision and landslide erosion on hillslopes. An analysis of more than 15,000 landslides in the eastern Himalaya, mapped from satellite images, shows that steep uplands primarily respond to uplift and river incision by increases in landslide erosion rates rather than by steepened hillslope angles.

Journal ArticleDOI
TL;DR: In this paper, the potential for anaerobic ammonium oxidation coupled to iron(III) reduction, known as Feammox, was investigated in tropical upland soils. And the results showed that Feammoxide can fuel nitrogen losses in ecosystems rich in poorly crystalline iron minerals with low or fluctuating redox conditions.
Abstract: The oxidation of ammonium is a key step in the nitrogen cycle, regulating the production of nitrate, nitrous oxide and dinitrogen. In marine and freshwater ecosystems, anaerobic ammonium oxidation coupled to nitrite reduction, termed anammox, accounts for up to 67% of dinitrogen production 1‐3 . Dinitrogen production through anaerobic ammonium oxidation has not been observed in terrestrial ecosystems, but the anaerobic oxidation of ammonium to nitrite has been observed in wetland soils under iron-reducing conditions 4,5 . Here, we incubate tropical upland soil slurries with isotopically labelled ammonium and iron(III) to assess the potential for anaerobic ammonium oxidation coupled to iron(III) reduction, otherwise known as Feammox 6 , in these soils. We show that Feammox can produce dinitrogen, nitrite or nitrate in tropical upland soils. Direct dinitrogen production was the dominant Feammox pathway, short-circuiting the nitrogen cycle and resulting in ecosystem nitrogen losses. Rates were comparable to aerobic nitrification 7,8 and to denitrification 9 , the latter being the only other process known to produce dinitrogen in terrestrial ecosystems. We suggest that Feammox could fuel nitrogen losses in ecosystems rich in poorly crystalline iron minerals, with low or fluctuating redox conditions.

Journal ArticleDOI
TL;DR: A revised analysis of measured changes in the net radiation imbalance at the top of the atmosphere, and the ocean heat content to a depth of 1,800m, suggests that these two sets of observations are consistent within error margins as mentioned in this paper.
Abstract: Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by the Earth and the thermal radiation emitted back to space. A revised analysis of measured changes in the net radiation imbalance at the top of the atmosphere, and the ocean heat content to a depth of 1,800 m, suggests that these two sets of observations are consistent within error margins.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the effect of the turn-of-the-century drought in western North America on carbon uptake in the region, using reanalysis data, remote sensing observations and data from global monitoring networks.
Abstract: The severity and incidence of climatic extremes, including drought, have increased as a result of climate warming. Analyses of observational and reanalysis data suggest that the strength of the western North American carbon sink declined by 30–298 Tg carbon per year during the drought at the turn of the century. Fossil fuel emissions aside, temperate North America is a net sink of carbon dioxide at present1,2,3. Year-to-year variations in this carbon sink are linked to variations in hydroclimate that affect net ecosystem productivity3,4. The severity and incidence of climatic extremes, including drought, have increased as a result of climate warming5,6,7,8. Here, we examine the effect of the turn of the century drought in western North America on carbon uptake in the region, using reanalysis data, remote sensing observations and data from global monitoring networks. We show that the area-integrated strength of the western North American carbon sink declined by 30–298 Tg C yr−1 during the 2000–2004 drought. We further document a pronounced drying of the terrestrial biosphere during this period, together with a reduction in river discharge and a loss of cropland productivity. We compare our findings with previous palaeoclimate reconstructions7 and show that the last drought of this magnitude occurred more than 800 years ago. Based on projected changes in precipitation and drought severity, we estimate that the present mid-latitude carbon sink of 177–623 Tg C yr−1 in western North America could disappear by the end of the century.

Journal ArticleDOI
TL;DR: In this article, the authors use continuous satellite measurements between 1995 and 2010 to show that the dome in sea surface height associated with the western Arctic Beaufort Gyre has been steepening, indicating spin-up of the gyre.
Abstract: The Arctic Ocean’s freshwater budget comprises contributions from river runoff, precipitation, evaporation, sea-ice and exchanges with the North Pacific and Atlantic. More than 70,000km3 of freshwater are stored in the upper layer of the Arctic Ocean, leading to low salinities in upper-layer Arctic sea water, separated by a strong halocline from warm, saline water beneath. Spatially and temporally limited observations show that the Arctic Ocean’s freshwater content has increased over the past few decades, predominantly in the west. Models suggest that wind-driven convergence drives freshwater accumulation. Here we use continuous satellite measurements between 1995 and 2010 to show that the dome in sea surface height associated with the western Arctic Beaufort Gyre has been steepening, indicating spin-up of the gyre. We find that the trend in wind field curl—a measure of spatial gradients in the wind that lead to water convergence or divergence—exhibits a corresponding spatial pattern, suggesting that wind-driven convergence controls freshwater variability. We estimate an increase in freshwater storage of 8,000±2,000km3 in the western Arctic Ocean, in line with hydrographic observations, and conclude that a reversal in the wind field could lead to a spin-down of the Beaufort Gyre, and release of this freshwater to the Arctic Ocean.

Journal ArticleDOI
TL;DR: In this paper, an analysis of sea snail specimens, extracted live from the Southern Ocean in January and February 2008, showed that the shells of these organisms are already dissolving and aragonite may become undersaturated by 2050 in the upper layers of the Southern ocean.
Abstract: As a result of ocean acidification, aragonite may become undersaturated by 2050 in the upper layers of the Southern Ocean. Analyses of sea snail specimens, extracted live from the Southern Ocean in January and February 2008, show that the shells of these organisms are already dissolving.

Journal ArticleDOI
TL;DR: The authors found that tropical extreme precipitation extremes increase in intensity over many regions of the globe in simulations of a warming climate, but not always consistently, indicating a high sensitivity of tropical extreme rainfall to global warming.
Abstract: Precipitation extremes increase in intensity over many regions of the globe in simulations of a warming climate, but not always consistently. Observational constraints, together with a close relationship between model responses to interannual variability and climate change, suggest a high sensitivity of tropical extreme precipitation to warming.

Journal ArticleDOI
TL;DR: This paper used detrital zircon geochronology, tephro-and magnetostratigraphy, along with analyses of past river flow recorded in sedimentary rocks from the Rukwa Rift Basin, Tanzania, to constrain the timing of rifting, magmatism and drainage development in this part of the western branch.
Abstract: The East African Rift System transects the anomalously high-elevation Ethiopian and East African plateaux that together form part of the 6,000-km-long African superswell structure. Rifting putatively developed as a result of mantle plume activity that initiated under eastern Africa. The mantle activity has caused topographic uplift that has been connected to African Cenozoic climate change and faunal evolution. The rift is traditionally interpreted to be composed of two distinct segments: an older, volcanically active eastern branch and a younger, less volcanic western branch. Here, we show that initiation of rifting in the western branch began more than 14 million years earlier than previously thought, contemporaneously with the eastern branch. We use a combination of detrital zircon geochronology, tephro- and magnetostratigraphy, along with analyses of past river flow recorded in sedimentary rocks from the Rukwa Rift Basin, Tanzania, to constrain the timing of rifting, magmatism and drainage development in this part of the western branch. We find that rift-related volcanism and lake development had begun by about 25 million years ago. These events were preceded by pediment development and a fluvial drainage reversal that we suggest records the onset of topographic uplift caused by the African superswell. We conclude that uplift of eastern Africa was more widespread and synchronous than previously recognized.

Journal ArticleDOI
TL;DR: In this article, the authors apply a regression analysis to an ensemble of coupled climate model simulations to show that the coupling between ocean and atmosphere shapes the distinct storm-track response to greenhouse-gas forcing in the North Atlantic region.
Abstract: A poleward shift of the mid-latitude storm tracks in response to anthropogenic greenhouse-gas forcing has been diagnosed in climate model simulations1, 2. Explanations of this effect have focused on atmospheric dynamics3, 4, 5, 6, 7. However, in contrast to storm tracks in other regions, the North Atlantic storm track responds by strengthening and extending farther east, in particular on its southern flank8. These adjustments are associated with an intensification and extension of the eddy-driven jet towards western Europe9 and are expected to have considerable societal impacts related to a rise in storminess in Europe10, 11, 12. Here, we apply a regression analysis to an ensemble of coupled climate model simulations to show that the coupling between ocean and atmosphere shapes the distinct storm-track response to greenhouse-gas forcing in the North Atlantic region. In the ensemble of simulations we analyse, at least half of the differences between the storm-track responses of different models are associated with uncertainties in ocean circulation changes. We compare the fully coupled simulations with both the associated slab model simulations and an ocean-forced experiment with one climate model to establish causality. We conclude that uncertainties in the response of the North Atlantic storm track to anthropogenic emissions could be reduced through tighter constraints on the future ocean circulation.

Journal ArticleDOI
TL;DR: In this article, the authors analyzed records of daily precipitation and discharge within twelve catchments in Nepal over about 30 years, and inferred that water is stored temporarily in a reservoir with characteristic response time of about 45 days, suggesting a diffusivity typical of fractured basement aquifers.
Abstract: In the course of the transfer of precipitation into rivers, water is temporarily stored in reservoirs with different residence times such as soils, groundwater, snow and glaciers. In the central Himalaya, the water budget is thought to be primarily controlled by monsoon rainfall, snow and glacier melt, and secondarily by evapotranspiration. An additional contribution from deep groundwater has been deduced from the chemistry of Himalayan rivers, but its importance in the annual water budget remains to be evaluated. Here we analyse records of daily precipitation and discharge within twelve catchments in Nepal over about 30 years. We observe annual hysteresis loops--that is, a time lag between precipitation and discharge--in both glaciated and unglaciated catchments and independent of the geological setting. We infer that water is stored temporarily in a reservoir with characteristic response time of about 45 days, suggesting a diffusivity typical of fractured basement aquifers. We estimate this transient storage capacity at about 28km3 for the three main Nepal catchments; snow and glacier melt contribute around 14km3yr-1, about 10% of the annual river discharge. We conclude that groundwater storage in a fractured basement influences significantly the Himalayan river discharge cycle.

Journal ArticleDOI
TL;DR: The Late Ordovician period, ending 444 million years ago, was marked by the onset of glaciations as discussed by the authors, and the expansion of non-vascular land plants accelerated chemical weathering and may have drawn down enough atmospheric carbon dioxide to trigger the growth of ice sheets.
Abstract: The Late Ordovician period, ending 444 million years ago, was marked by the onset of glaciations. The expansion of non-vascular land plants accelerated chemical weathering and may have drawn down enough atmospheric carbon dioxide to trigger the growth of ice sheets.

Journal ArticleDOI
TL;DR: In this article, the authors used the Li-Ca-Sr isotope system to quantitatively constrain the duration of subduction-zone fluid release at ∼ 70 km depth within subducting oceanic lithosphere, now exhumed in the Chinese Tianshan Mountains.
Abstract: During subduction, the seawater-altered lithosphere becomes dehydrated and expels fluids. Isotopic analysis of an exhumed oceanic slab in the Tianshan Mountain Range shows that although subduction can continue for many millions of years, fluids are expelled in short-lived channels over periods of just a few hundred years. At subduction zones, oceanic lithosphere that has interacted with sea water is returned to the mantle, heats up during descent and releases fluids by devolatilization of hydrous minerals. Models for the formation of magmas feeding volcanoes above subduction zones require largescale transport of these fluids into overlying mantle wedges1,2,3. Fluid flow also seems to be linked to seismicity in subducting slabs. However, the spatial and temporal scales of this fluid flow remain largely unknown, with suggested timescales ranging from tens to tens of thousands of years3,4,5. Here we use the Li–Ca–Sr isotope systems to consider fluid sources and quantitatively constrain the duration of subduction-zone fluid release at ∼ 70 km depth within subducting oceanic lithosphere, now exhumed in the Chinese Tianshan Mountains. Using lithium-diffusion modelling, we find that the wall-rock porosity adjacent to the flowpath of the fluids increased ten times above the background level. We show that fluids released by devolatilization travelled through the slab along major conduits in pulses with durations of about ∼ 200 years. Thus, although the overall slab dehydration process is continuous over millions of years and over a wide range of pressures and temperatures, we conclude that the fluids produced by dehydration in subducting slabs are mobilized in short-lived, channelized fluid-flow events.

Journal ArticleDOI
TL;DR: In this paper, a tomographic model for the entire European upper mantle is presented, which identifies northeastward subduction of the Adria plate beneath the Dinarides Mountains, volcanism related to the upwelling Eifel hotspot and mantle delamination beneath Scandinavia.
Abstract: The structure of the European crust and upper mantle is precisely known only in limited regions. A new tomographic model for the entire European upper mantle identifies northeastward subduction of the Adria plate beneath the Dinarides Mountains, volcanism related to the upwelling Eifel hotspot and mantle delamination beneath Scandinavia.