ORCID Profile
0000-0003-4123-3305
Current Organisations
Max Planck Institute for Meteorology
,
ETH Zürich
,
Colorado State University
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Publisher: Proceedings of the National Academy of Sciences
Date: 22-07-2021
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-12043
Abstract: & & The Northern Apennines of Italy are a young orogen comprised of mixed siliciclastic and carbonate lithologies. Young orogens are typically characterized by marine sedimentary sequences that contain important volumes of carbonate, which can dominate chemical weathering, as carbonate weathers a factor of 3 times faster than silicates. However, most models that address the interplay between erosion and weathering have focused on silicate lithologies. & Carbonate weathering is typically limited by the availability of acid rather than dissolution kinetics, and more tightly linked to soil and sub-surface CO& sub& & /sub& concentrations than silicate weathering. Therefore, it remains unclear if the same processes that control the partitioning of denudation between erosion and weathering in actively uplifting, silicate-rich lithologies are also active in orogens comprised of mixed carbonate-silicate lithologies. The partitioning of denudation between physical erosion and chemical weathering in mixed silicate-carbonate landscapes remains a fundamental knowledge gap that has implications for landscape development and the carbon cycle. Here we address two key questions: (1) how is the total denudation separated into carbonate and silicate fluxes, and (2) how is carbonate denudation partitioned into erosion and weathering in an active orogenic setting? We partition denudation fluxes from & sup& & /sup& Be concentrations into carbonate and silicate chemical weathering and physical erosion fluxes, using major dissolved ions from water chemistry, the percent of carbonate sand from each catchment, and annual discharge measurements. Denudation fluxes in the Northern Apennines are dominated by physical erosion of both silicate and carbonate lithologies. Chemical weathering fluxes are 1-2 orders of magnitude lower than physical erosion fluxes and are dominated by carbonate dissolution. Despite a number of studies that have shown a strong positive correlation between denudation and chemical weathering fluxes, we find only a weakly positive correlation. Relative to a global dataset from silicate-rich orogenic settings, the Northern Apennines have similar denudation fluxes as the eastern side of the New Zealand Southern Alps. However, rivers from the Northern Apennines generally have higher total weathering fluxes relative to the Southern Alps, consistent with the exposure of a large volume of carbonate lithologies in the Northern Apennines.& &
Publisher: Springer Science and Business Media LLC
Date: 26-10-2020
Publisher: Elsevier BV
Date: 05-2023
Publisher: Copernicus GmbH
Date: 28-11-2022
Publisher: American Geophysical Union (AGU)
Date: 03-05-2011
DOI: 10.1029/2011EO180013
Publisher: Springer Science and Business Media LLC
Date: 07-2019
DOI: 10.1038/S41586-019-1332-Y
Abstract: The long-term cooling, decline in the partial pressure of carbon dioxide, and the establishment of permanent polar ice sheets during the Neogene period
Publisher: Copernicus GmbH
Date: 20-08-2019
DOI: 10.5194/CP-2019-88
Abstract: Abstract. During the late Palaeocene to the middle Eocene (57.5 to 46.5 Ma) a total of 39 hyperthermals – periods of rapid global warming recorded by prominent negative carbon isotope excursions (NCIEs) as well as peaks in iron content – have been recognized in marine cores. Understanding how the Earth system responded to rapid warming during these hyperthermals is fundamental because they represent potential analogues, in the geological record, to the ongoing anthropogenic modification of global climate. However, while hyperthermals have been well documented in the marine sedimentary record, only few have been recognized and described in continental deposits, thereby limiting our ability to understand the effect and record of global warming on terrestrial surficial systems. Hyperthermals in the continental record could be a powerful correlation tool to help connect marine and continental records, addressing issues of environmental signal propagation from land to sea. In this study, we generate new stable carbon isotope data (δ13C values) across the well-exposed and time-constrained fluvial sedimentary succession of the early Eocene Castissent Formation in the South-Central Pyrenees (Spain). The δ13C values of pedogenic carbonate reveal – similarly to the global records – stepped NCIEs, culminating in a minimum δ13C value that we correlate with the hyperthermal event U at ca. 50 Ma. This general trend towards more negative values is most probably linked to higher primary productivity leading to an overall higher respiration of soil organic matter during these climatic events. The relative enrichment in immobile elements (Zr, Ti, Al) and higher estimates of mean annual precipitation together with the occurrence of small iron-oxides/hydroxides nodules during the NCIEs suggest intensification of chemical weathering and/or longer exposure of soils in a highly seasonal climate. The results show that even relatively small-scale hyperthermals compared with their prominent counterparts, such as PETM, ETM2 and 3, have left a recognizable trace in the stratigraphic record, providing insights into the dynamics of the carbon cycle in continental environments during these events.
Publisher: American Geophysical Union (AGU)
Date: 05-2022
DOI: 10.1029/2021PA004392
Abstract: We explore the effects of the Pliensbachian–Toarcian Boundary Event (P–ToBE) on tropical carbonate productivity in the interior to margin and slope of the Venetian Platform (Northern Italy). We document the P–ToBE for the first time in the shallow‐water platform margin, and we bio‐ and chemostratigraphically tie it to transgressive/regressive cycles. Following the latest Pliensbachian sea‐level drop and emersion, transgressive grainstones at the platform edge record the P–ToBE negative carbon isotope excursion (CIE) of 1–1.5‰, also found in marl/limestone couplets on the slope. Recovery of platform productivity was ephemeral, as the platform drowned right after the peak negative CIE and was covered by deep‐sea thin‐bedded micritic limestones. The end of the P–ToBE correlates with a regression and renewed recovery of carbonate productivity. The negative CIE of the subsequent Toarcian Oceanic Anoxic Event is recorded in open‐sea cherty limestones both at the marginal and interior platform. These limestones document an even wider transgression and the renewed partial drowning of the platform in the Serpentinus Zone. We investigate the causes of the carbon perturbation at the P–ToBE, using a simple carbon cycle model. The duration and magnitude of the CIE suggest a rapid release of methane in driving the CIE, perhaps related to the preceding sea‐level drop and associated cryosphere perturbation, or to thermogenic alteration of coals near the Karoo‐Ferrar Large Igneous Province (LIP). The extent of the warming and the magnitude of the P–ToBE CIE implies a contribution of volcanogenic carbon dioxide from the Karoo‐Ferrar LIP.
Publisher: Elsevier BV
Date: 08-2020
Publisher: Resilience Alliance, Inc.
Date: 2013
Publisher: Elsevier BV
Date: 10-2018
Publisher: Wiley
Date: 25-10-2022
Publisher: Elsevier BV
Date: 07-2019
Publisher: Geological Society of America
Date: 15-02-2018
DOI: 10.1130/G39962.1
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-1937
Abstract: & & Spatial compilations of stable isotopes may be used to disentangle the competing effects of mountain uplift and paleoclimate change. Because both changes in paleoelevation and changes in paleoclimate result in fluctuations in the & #948 & sup& & /sup& O recorded in authigenic materials, large-scale spatial compilations of oxygen isotope data are required to discern the main driver of isotopic change in the past. Spatially limited studies may lack sufficient geographic range to robustly attribute isotopic shifts to either climate or tectonics. To elucidate potential hydroclimate changes or orographic changes across Eurasia in the Cenozoic, we compile previously published analyses of oxygen isotopes, recorded in authigenic materials such as paleosol, lacustrine, and speleothem carbonates, and mammal tooth enamel, to generate a dataset of over 14,500 & #948 & sup& & /sup& O datapoints spanning Cenozoic Eurasia. Compiled Quaternary & #948 & sup& & /sup& O data across Europe indicate that different proxy materials reliably record the same or similar local meteoric water signatures, signifying the validity of a multi-proxy approach. Across the continent, these Quaternary data capture the decrease in & #948 & sup& & /sup& O with increasing longitude that is observed in modern waters, indicating that the same proxies can be applied to reconstruct meteoric & #948 & sup& & /sup& O during the Cenozoic. Preliminary results from pre-Quaternary Cenozoic proxy data show that the longitudinal & #948 & sup& & /sup& O& gradient is not markedly reduced or steepened relative to the modern, even during globally warmer periods such as the Miocene. This result suggests that westerly moisture transport across Eurasia during the Cenozoic resembled modern-day moisture transport processes, despite large changes in atmospheric CO& sub& & /sub& and paleogeography. Although this first-order isotopic trend appears throughout the Cenozoic record, many sites& #8212 articularly those nearer to the Paratethys& #8212 have elevated estimated paleo-precipitation & #948 & sup& & /sup& O& relative to modern. Disparities between the Cenozoic record and modern data may reflect elevation changes due to multiple small orogens that developed during the Cenozoic along the Tethyan margin, changes in moisture sources as the Paratethys shrank, differences in the seasonality of authigenic mineral formation, and changes in atmospheric CO& sub& & /sub& that affect moisture transport. Nevertheless, given the constancy of the overall decrease in & #948 & sup& & /sup& O with increasing longitude, we find that tectonics and paleogeographic changes appear to be a secondary control on continental-scale moisture transport, as there are large changes in paleogeography and orography in the Cenozoic that are not substantially reflected in large-scale spatial patterns of & #948 & sup& & /sup& O. These paleogeographic changes appear to have local impacts, but do not drive continental-scale changes in & #948 & sup& & /sup& O. Consequently, we attribute first-order changes in & #948 & sup& & /sup& O& gradients to climatic effects rather than changes in paleogeography or topography.& &
Publisher: Springer Science and Business Media LLC
Date: 21-05-2012
DOI: 10.1038/SREP00413
Publisher: Elsevier BV
Date: 10-2015
Publisher: Copernicus GmbH
Date: 04-10-2023
Publisher: Copernicus GmbH
Date: 20-08-2019
Publisher: Springer Science and Business Media LLC
Date: 24-06-2010
Publisher: Geological Society of America
Date: 21-08-2015
DOI: 10.1130/G36999.1
Publisher: American Geophysical Union (AGU)
Date: 08-10-2015
DOI: 10.1002/2015GL064829
Publisher: European Respiratory Society (ERS)
Date: 20-04-2023
DOI: 10.1183/13993003.00499-2023
Abstract: Tuberculosis (TB) elimination and pre-elimination, with thresholds of 1 and 10 incident cases per million population, respectively, were considered achievable for low TB incidence countries in the 1990s, when they were conceived. However, it has since become clear that, even in low TB incidence settings with effective programmes and sufficient resources, achieving pre-elimination in the next decade will require a dramatic acceleration of efforts. In this review, we describe the history of the TB elimination concept and existing country experiences, as well as the interventions available to accelerate the progress towards this threshold. We then propose a framework for near-term progress towards the more aspirational goal of TB pre-elimination. This framework consists of five stages (high incidence, moderate incidence, low incidence, nearing pre-elimination and pre-elimination) that are benchmarked to specific levels of TB incidence in each country. Using this framework, countries can set 5-year targets of achieving certain reductions in TB incidence and/or reaching the next stage, through the use of strategies tailored to both local epidemiology and available organisation and infrastructure. TB elimination remains as an aspirational goal in all stages, but certain activities can be prioritised in the short term to make more rapid progress, ensure local-level buy-in and increase accountability. As TB pre-elimination is approached, certain ethical and social concerns are likely to rise in importance these concerns are also discussed. Our aim in setting this framework is to guide clinicians, public health experts and decision makers in taking actionable next steps in the trajectory towards TB pre-elimination and elimination.
Publisher: Elsevier BV
Date: 10-2016
Publisher: Springer Science and Business Media LLC
Date: 14-05-2021
DOI: 10.1038/S43247-021-00160-4
Abstract: Simple and complex climate models suggest a hard snowball – a completely ice-covered planet – is one of the steady-states of Earth’s climate. However, a seemingly insurmountable challenge to the hard-snowball hypothesis lies in the difficulty in explaining how the planet could have exited the glaciated state within a realistic range of atmospheric carbon dioxide concentrations. Here, we use simulations with the Earth system model MPI-ESM to demonstrate that terminal deglaciation could have been triggered by high dust deposition fluxes. In these simulations, deglaciation is not initiated in the tropics, where a strong hydrological cycle constantly regenerates fresh snow at the surface, which limits the dust accumulation and snow aging, resulting in a high surface albedo. Instead, comparatively low precipitation rates in the mid-latitudes in combination with high maximum temperatures facilitate lower albedos and snow dynamics that – for extreme dust fluxes – trigger deglaciation even at present-day carbon dioxide levels.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-19916
Abstract: & & Geological evidence suggests that Earth's past featured periods during which the planet was largely or even entirely covered by ice, a state termed & quot snowball Earth& quot .& Model based studies confirm that one of Earth's equilibrium states is a fully glaciated planet (hard snowball) but it is not clear how this state could have been left once it had been established. We use simulations with the Max-Planck-Institute for Meteorology's Earth system model to investigate the conditions that enable the transition out of the snowball-state. We show that the high albedo of pure snow would have prevented deglatiation, even for extremely high atmospheric CO2 concentrations. Terminal deglaciation is only triggered for surface albedos corresponding to old, darkened snow or sea-ice. Here, increasing snowfall rates, resulting from the intensification of the hydrological cycle with rising CO2 concentrations, would have prohibited the gradual build-up of dust that leads to a darkening of the surface.& Only when assuming dust deposition fluxes at least similar to present-day fluxes, can the deglation be triggered for plausible atmospheric CO2 concentrations.& &
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-9221
Abstract: & & The supply of fresh minerals to Earth& #8217 s surface by erosion is thought to modulate global climate by removing atmospheric carbon dioxide (CO& sub& & /sub& ) through silicate weathering. In turn, weathering of accessory carbonate and sulfide minerals is a geologically-relevant CO& sub& & /sub& source, which may d en or reverse the effect of silicate weathering on climate. Although these weathering pathways commonly operate side by side, we lack quantitative constraints on their co-evolution across erosion-rate gradients. Using stream-water chemistry across a 3 order-of-magnitude erosion-rate gradient in shales and sandstones of southern Taiwan, here, we demonstrate that silicate, sulfide, and carbonate weathering are linked: Increasing sulfide oxidation generates sulfuric acid and boosts carbonate solubility whereas silicate weathering kinetics remain constant or even decline, perhaps due to buffering of the pH by carbonates. On timescales shorter than marine sulfide compensation, CO& sub& & /sub& emission rates from weathering in rapidly-eroding terrain are more than twice the CO& sub& & /sub& sequestration rates in slow-eroding terrain. On longer timescales, CO& sub& & /sub& emissions are compensated, but CO& sub& & /sub& sequestration rates do not increase with erosion, in contrast to assumptions in carbon cycle models. We posit that these patterns are broadly applicable to many Cenozoic mountain ranges that expose dominantly siliciclastic metasediments.& &
Publisher: Elsevier BV
Date: 11-2022
DOI: 10.1016/J.IJID.2022.02.043
Abstract: Multidrug-resistant tuberculosis (MDR-TB) is a life-threatening condition needing long poly-chemotherapy regimens. As no systematic reviews/meta-analysis is available to comprehensively evaluate the role of delamanid (DLM), we evaluated its effectiveness and safety. We reviewed the relevant scientific literature published up to January 20, 2022. The pooled success treatment rate with 95% confidence intervals (CI) was assessed using a random-effect model. We assessed studies for quality and bias, and considered P 0.05). The overall pooled treatment success rate in DLM and bedaquiline-containing regimens was 75.2% (95% CI 68.1-81.1) with no evidence of publication bias (Begg's test P >0.05). In experimental studies the pooled treatment success rate of DLM-containing regimens was 72.5 (95% CI 44.2-89.8, P <0.001, I In MDR-TB patients receiving DLM, culture conversion and treatment success rates were high despite extensive resistance with limited adverse events.
Publisher: Copernicus GmbH
Date: 04-02-2020
Abstract: Abstract. The late Palaeocene to the middle Eocene (57.5 to 46.5 Ma) recorded a total of 39 hyperthermals – periods of rapid global warming documented by prominent negative carbon isotope excursions (CIEs) as well as peaks in iron content – have been recognized in marine cores. Documenting how the Earth system responded to rapid climatic shifts during hyperthermals provides fundamental information to constrain climatic models. However, while hyperthermals have been well documented in the marine sedimentary record, only a few have been recognized and described in continental deposits, thereby limiting our ability to understand the effect and record of global warming on terrestrial systems. Hyperthermals in the continental record could be a powerful correlation tool to help connect marine and continental deposits, addressing issues of environmental signal propagation from land to sea. In this study, we generate new stable carbon isotope data (δ13C values) across the well-exposed and time-constrained fluvial sedimentary succession of the early Eocene Castissent Formation in the south central Pyrenees (Spain). The δ13C values of pedogenic carbonate reveal – similarly to the global records – stepped CIEs, culminating in a minimum δ13C value that we correlate with the hyperthermal event “U” at ca. 50 Ma. This general trend towards more negative values is most probably linked to higher primary productivity leading to an overall higher respiration of soil organic matter during these climatic events. The relative enrichment in immobile elements (Zr, Ti, Al) and higher estimates of mean annual precipitation together with the occurrence of small iron oxide and iron hydroxide nodules during the CIEs suggest intensification of chemical weathering and/or longer exposure of soils in a highly seasonal climate. The results show that even relatively small-scale hyperthermals compared with their prominent counterparts, such as PETM, ETM2, and ETM3, can leave a recognizable signature in the terrestrial stratigraphic record, providing insights into the dynamics of the carbon cycle in continental environments during these events.
Publisher: American Geophysical Union (AGU)
Date: 28-02-2022
DOI: 10.1029/2021AV000566
Abstract: The shift from denser forests to open, grass‐dominated vegetation in west‐central North America between 26 and 15 million years ago is a major ecological transition with no clear driving force. This open habitat transition (OHT) is considered by some to be evidence for drier summers, more seasonal precipitation, or a cooler climate, but others have proposed that wetter conditions and/or warming initiated the OHT. Here, we use published ( n = 2,065) and new ( n = 173) oxygen isotope measurements ( δ 18 O ) in authigenic clays and soil carbonates to test the hypothesis that the OHT is linked to increasing wintertime aridity. Oxygen isotope ratios in meteoric water ( δ 18 O p ) vary seasonally, and clays and carbonates often form at different times of the year. Therefore, a change in precipitation seasonality can be recorded differently in each mineral. We find that oxygen isotope ratios of clay minerals increase across the OHT while carbonate oxygen isotope ratios show no change or decrease. This result cannot be explained solely by changes in global temperature or a shift to drier summers. Instead, it is consistent with a decrease in winter precipitation that increases annual mean δ 18 O p (and clay δ 18 O ) but has a smaller or negligible effect on soil carbonates that primarily form in warmer months. We suggest that forest communities in west‐central North America were adapted to a wet‐winter precipitation regime for most of the Cenozoic, and they subsequently struggled to meet water demands when winters became drier, resulting in the observed open habitat expansion.
Publisher: Springer Science and Business Media LLC
Date: 2020
Publisher: Wiley
Date: 14-09-2016
DOI: 10.1111/BRE.12213
Publisher: American Geophysical Union (AGU)
Date: 22-03-2011
DOI: 10.1029/2011EO120008
Publisher: American Journal of Science (AJS)
Date: 2019
DOI: 10.2475/01.2019.01
Publisher: Geological Society of America
Date: 12-09-2016
DOI: 10.1130/G38267.1
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-14888
Abstract: & & Long-term cooling, pCO& sub& & /sub& decline, and the establishment of permanent, polar ice sheets in the Neogene& sup& & /sup& has frequently been attributed to increased uplift and erosion of mountains and consequent increases in silicate weathering, which removes atmospheric CO& sub& & /sub& . However, an increasing weathering flux is incompatible with a balanced atmospheric CO& sub& & /sub& budget [1]. For ex le, a weathering increase scaled to frequently invoked erosional increase [2] would have removed nearly all carbon from the atmosphere. Further, the marine & sup& & /sup& Be/& sup& & /sup& Be proxy indicates constant silicate weathering fluxes over the past 10 Ma [3].& & & & Rather, as volcanic CO& sub& & /sub& emissions have been largely constant yet atmospheric CO& sub& & /sub& decreased, as indicated by the marine & sup& & /sup& B/& sup& & /sup& B proxy, an increase in & #8220 land surface reactivity& #8221 has likely driven global cooling [4]. Land surface reactivity quantifies the likelihood of weathering zone material to react with carbon derived from atmospheric CO& sub& & /sub& and represents the degree of coupling between weathering and climate. That surface reactivity has increased during the Neogene is confirmed by the stable & sup& & /sup& Li/& sup& & /sup& Li seawater proxy, which increases during the Neogene. The question we now need to address is thus: what has caused the increase in land surface reactivity? What is needed is an increased availability of Ca and Mg-rich primary minerals in the global critical zone. This could have come about by 1) an increased exposure of mafic volcanic rock 2) supply of fresh glacial debris 3) widespread rejuvenation of the continental land surface by faulting 4) more efficient mineral dissolution by biota or 5) an increase in erosion rate with or without mountain uplift. Only explanation 1) can be discounted as this hypothesis fails to satisfy the marine Sr and Os radiogenic isotope records. Explanations 2 & #8211 5 remain. In all of these the role of erosion is to remove weathered material. Indeed, parsimonious geochemical models are roughly compatible with a doubling in global erosional mass flux since 10 Ma [1].& & & & (1) Caves Rugenstein, J.K., D.E. Ibarra, and F. von Blanckenburg, Neogene cooling driven by land surface reactivity rather than increased weathering fluxes. Nature, 2019.& & & & (2) Molnar, P., Late Cenozoic increase in accumulation rates of terrestrial sediment: how might climate change have affected erosion rates? Ann. Rev. Earth Planet. Sc., 2004.& & & & (3) Willenbring, J.K. and F. von Blanckenburg, Long-term stability of global erosion rates and weathering during late-Cenozoic cooling. Nature, 2010.& & & & (4) Kump, L.R. and M.A. Arthur, Global chemical erosion during the Cenozoic: Weatherability balances the budgets, in Tectonic Uplift and Climate Change. 1997.& &
Publisher: Copernicus GmbH
Date: 28-11-2022
DOI: 10.5194/EGUSPHERE-2022-1000
Abstract: Abstract. Models of the carbon cycle and climate on geologic ( year) timescales have improved tremendously in the last 50 years due to parallel advances in our understanding of the Earth system and the increase in computing power to simulate its key processes. Despite these advances, balancing the Earth System's vast complexity with a model's computational expense is a primary challenge in model development. Running longer simulations spanning hundreds of thousands of years or more generally requires reducing the complexity of the modeled climate system. However, simpler model frameworks often leave out certain features of the climate system, such as radiative feedbacks, shifts in atmospheric circulation, and the expansion and decay of ice sheets, which can have profound effects on the long-term carbon cycle. Here, we present a model for climate and the long-term carbon cycle that captures many fundamental features of global climate while retaining the computational efficiency needed to simulate millions of years of time. The Carbon-H2O Coupled HydrOlOgical model with Terrestrial Runoff And INsolation, or CH2O-CHOO TRAIN, couples a one-dimensional (latitudinal) moist static energy balance model of climate with a model for rock weathering and the long-term carbon cycle. The key advantages of this framework are (1) it simulates fundamental climate forcings and feedbacks (2) it accounts for geographic configuration and (3) it is highly customizable, equipped to easily add features, change the strength of feedbacks, and prescribe conditions that are often hard-coded or emergent properties of more complex models, such as climate sensitivity and the strength of meridional heat transport. The CH2O-CHOO TRAIN is capable of running million-year-long simulations in about thirty minutes on a laptop PC. This paper outlines the model equations, presents a sensitivity analysis of the climate responses to varied climatic and carbon cycle perturbations, and discusses potential applications and next stops for the CH2O-CHOO TRAIN.
Publisher: Elsevier BV
Date: 11-2014
Publisher: Geological Society of America
Date: 11-01-2017
DOI: 10.1130/GSATG305A.1
Publisher: Geological Society of America
Date: 04-2015
DOI: 10.1130/G36427.1
Publisher: American Journal of Science (AJS)
Date: 2022
DOI: 10.2475/01.2022.02
Publisher: Springer Science and Business Media LLC
Date: 12-05-2017
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-11141
Abstract: & & The North American Great Plains are characterized by a sharp aridity gradient at around the 100& sup& th& /sup& meridian with a more humid climate to the east and a more arid climate to the west. This aridity gradient shapes the region's agriculture and economy, and recent work suggests that arid conditions on the Great Plains may expand eastward with global warming. The abundant Neogene sediments of the Ogallala Formation in the Great Plains present an opportunity to reconstruct regional hydroclimate conditions at a time when & em& & /em& CO& sub& & /sub& and global temperatures were much higher than today, providing insight into the aridity and ecosystem response to warming. We present new paleosol carbonate & #948 & sup& & /sup& C and & #948 & sup& & /sup& O& data (n=366) across 37 sites spanning the Great Plains and compile previously published measurements (n=381) to evaluate the long-term hydroclimatic and ecosystem changes in the region during the late Neogene. This study combines a spatial and temporal analysis of carbon and oxygen isotope data with reactive-transport modeling of oxygen isotopes constrained by climate model output, providing critical constraints on the paleoenvironmental and paleoclimatological evolution of the Neogene Great Plains. Carbonate & #948 & sup& & /sup& O demonstrate remarkable similarity between the spatial pattern of paleo-precipitation & #948 & sup& & /sup& O and modern precipitation & #948 & sup& & /sup& O. Today, modern precipitation & #948 & sup& & /sup& O over the Great Plains is set by the mixing between moist, high-& #948 & sup& & /sup& O moisture delivered by the Great Plains Low-Level Jet and drier, low-& #948 & sup& & /sup& O westerly air masses. Thus, in the absence of countervailing processes, we interpret this similarity between paleo and modern & #948 & sup& & /sup& O to indicate that the proportional mixing between these two air masses has been minimally influenced by changes in global climate and that any changes in the position of the 100& sup& th& /sup& meridian aridity gradient has not been forced by dynamical changes in these two synoptic systems. In contrast, prior to the widespread appearance of C& sub& & /sub& plants in the landscape of the Great Plains, paleosol carbonate & #948 & sup& & /sup& C show a robust east-to-west gradient, with higher values to the west. We interpret this gradient as reflective of lower primary productivity and hence soil respiration to the west. Close comparison with modern primary productivity data indicates that primary productivity has declined and shifted eastward since the late Neogene, likely reflecting declining precipitation and/or a reduction in CO& sub& & /sub& fertilization during the late Neogene. Finally, & #948 & sup& & /sup& C increases across the Miocene-Pliocene boundary, which, consistent with previous studies, we interpret as a shift from a C& sub& & /sub& to a C& sub& & /sub& dominated landscape. We conclude that, to first order, the modern aridity gradient and the hydrologic processes that drive it are not strongly sensitive to changes in global climate and any shifts in this aridity gradient in response to rising CO& sub& & /sub& will be towards the west, rather than towards the east.& &
Publisher: Geological Society of America
Date: 21-01-2016
DOI: 10.1130/G37574Y.1
Publisher: American Journal of Science (AJS)
Date: 22-09-2014
DOI: 10.2475/08.2014.01
Publisher: American Association for the Advancement of Science (AAAS)
Date: 20-09-2019
Abstract: Valdes et al . contest our results, suggesting failings in our modeling approach as well as in our comparison with data. Although their comment points to interesting ideas of improvement, we find that their critique reflects an incomplete understanding of our methods and is not supported by the material they provide.
Publisher: Proceedings of the National Academy of Sciences
Date: 08-08-2022
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-20554
Abstract: & & Long-term cooling, pCO& sub& & /sub& decline, and the establishment of permanent, polar ice sheets in the Neogene has frequently been attributed to increased uplift and erosion of mountains and consequent increases in silicate weathering, which removes atmospheric CO& sub& & /sub& . However, geological records of erosion rates are potentially subject to averaging biases and the magnitude of the increase in weathering fluxes, and even its existence, remain debated. Moreover, a weathering increase scaled to the hypothesized erosional increase would have removed nearly all carbon from the atmosphere, leading to proposals of compensatory carbon fluxes in order to preserve carbon cycle mass balance. In contrast, increasing land surface reactivity& #8212 resulting from greater fresh mineral surface area or an increase in the supply of reactive minerals& #8212 rather than an increase in the weathering flux, has been proposed to reconcile these disparate views. We develop a parsimonious carbon cycle model that tracks two weathering-sensitive isotopic tracers (stable & sup& & /sup& Li/& sup& & /sup& Li and cosmogenic & sup& & /sup& Be/& sup& & /sup& Be) to show that an increase in land surface reactivity is necessary to simultaneously decrease atmospheric CO& sub& & /sub& , increase seawater & sup& & /sup& Li/& sup& & /sup& Li, and retain constant seawater & sup& & /sup& Be/& sup& & /sup& Be since 16 Ma. We find that the global silicate weathering flux remained constant, even as the global silicate weathering intensity& #8212 the fraction of the total denudation flux derived from silicate weathering& #8212 decreased, sustained by an increase in erosion. Thus, long-term cooling during the Neogene reflects a change in the partitioning of denudation into weathering and erosion. Variable partitioning of denudation and consequent changes in silicate weathering intensity reconcile marine isotope and erosion records with the need to maintain mass balance in the carbon cycle and without increases in the silicate weathering flux. These changes in land surface reactivity through time suggest that the Earth system& #8217 s response to carbon cycle perturbations is not constant and that today& #8217 s Earth can more efficiently remove excess carbon than during analogous perturbations observed in the geologic record.& & &
Publisher: Informa UK Limited
Date: 22-06-2017
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-7187
Abstract: & & The uplift and erosion of active mountain ranges and the consequent weathering of minerals modulates the global carbon cycle and impacts Earth& #8217 s climate on geologic timescales. However, the link between erosion and weathering is complex because weathering rates can be limited by the supply of minerals to the weathering zone, by the supply of acidic fluids, or by the kinetics of mineral weathering. Existing approaches that model the carbon cycle over geologic timescales assume that with increasing erosion rates, weathering transitions from a supply limit where weathering rates scale linearly with erosion to an & #8216 acid& #8217 or a kinetic limit where weathering is insensitive to erosion. Alternative models fit a single power-law to the relationship between erosion and weathering across multiple orders of magnitude. The validity of these two approaches remains difficult to assess at the landscape scale because existing data do not cover all limits or because co-variation between runoff and erosion obscures the driver of changes in weathering rates. Here, we compile five datasets of solute concentrations in streams that span well-defined erosion rate gradients in relatively uniform lithologies and with limited or well-constrained variations in runoff. Across 2-3 orders of magnitude of erosion rates, and for both metasedimentary and granitic lithologies, we find that silicate weathering rates are insensitive to erosion rates. In turn, weathering of sulfide and carbonate minerals increase with erosion rates, consistent with a limitation by mineral supply. However, contrary to existing models of supply-limited weathering, we observe a non-linear increase of sulfide and carbonate weathering rates with erosion. These new findings suggests that supply-limited and kinetically limited zones of weathering co-exist within a single landscape across multiple orders of magnitude of erosion rate. The distribution of these zones is most likely controlled by erosion processes. As a consequence, existing weathering models that assume a linear relationship between erosion and weathering at the supply limit may overestimate the sensitivity of weathering rates to erosion and underestimate the impact of climate on these reactions, with implications for the effect of mountain building on the carbon cycle and on Earth& #8217 s climate.& &
Publisher: American Geophysical Union (AGU)
Date: 08-2021
DOI: 10.1029/2021JF006064
Abstract: Mixed siliciclastic‐carbonate active orogens are common on Earth's surface, yet most studies have focused on erosion and weathering in silicate‐rich landscapes. Relative to purely siliciclastic landscapes, the response of erosion and weathering to uplift may differ in mixed‐lithology regions. However, our knowledge of weathering and erosion in mixed carbonate‐silicate lithologies is limited and, thus, so is our understanding of the mechanistic coupling between uplift, weathering, and the carbon cycle. Here, we partition denudation fluxes into erosion and weathering fluxes of carbonates and silicates in the Northern Apennines—a mixed carbonate‐siliciclastic active orogen—using dissolved solutes, the carbonate sand fraction, and existing 10 Be denudation rates. Erosion generally dominates total denudation fluxes relative to weathering by an order of magnitude. Carbonate and silicate contributions to erosion vary between lithologic units, but weathering fluxes are systematically dominated by carbonates. Silicate weathering may be kinetically limited, whereas carbonate weathering may be limited by acid supply. Carbonate re‐precipitation estimated by comparing ion ratios (Sr, Ca, Na) from rivers and bedrock suggests that up to 90% of dissolved Ca 2+ is lost from carbonate‐rich catchments. Corresponding [Ca 2+ ] estimates for the weathering zone are high, likely driven by high soil CO 2 partial pressures ( p CO 2 ) however, re‐equilibration with atmospheric p CO 2 in rivers converts solutes back into grains that become part of the physical denudation flux. Weathering limits in this landscape therefore differ between the subsurface weathering zone and riverine exports, and our findings suggest that carbon cycle models may overestimate the sensitivity to erosion of solute exports (Ca 2+ and HCO 3 − ) derived from carbonate weathering.
Publisher: American Geophysical Union (AGU)
Date: 10-05-2011
DOI: 10.1029/2011EO190006
Publisher: Springer Science and Business Media LLC
Date: 04-2021
DOI: 10.1038/S41561-021-00714-3
Abstract: Global climate is thought to be modulated by the supply of minerals to Earth’s surface. Whereas silicate weathering removes carbon dioxide (CO 2 ) from the atmosphere, weathering of accessory carbonate and sulfide minerals is a geologically relevant source of CO 2 . Although these weathering pathways commonly operate side by side, we lack quantitative constraints on their co-variation across erosion rate gradients. Here we use stream-water chemistry across an erosion rate gradient of three orders of magnitude in shales and sandstones of southern Taiwan, and find that sulfide and carbonate weathering rates rise with increasing erosion, while silicate weathering rates remain steady. As a result, on timescales shorter than marine sulfide compensation (approximately 10 6 –10 7 years), weathering in rapidly eroding terrain leads to net CO 2 emission rates that are at least twice as fast as CO 2 sequestration rates in slow-eroding terrain. We propose that these weathering reactions are linked and that sulfuric acid generated from sulfide oxidation boosts carbonate solubility, whereas silicate weathering kinetics remain unaffected, possibly due to efficient buffering of the pH. We expect that these patterns are broadly applicable to many Cenozoic mountain ranges that expose marine metasediments.
Publisher: Elsevier BV
Date: 09-2016
Publisher: Copernicus GmbH
Date: 28-09-2023
Publisher: American Association for the Advancement of Science (AAAS)
Date: 03-2019
Abstract: The elevation of the Tibetan Plateau has a major impact on climate, affecting the monsoons and regional weather patterns. Although some isotope proxies have suggested a roughly equivalent height for the plateau as far back as the Eocene (∼40 million years ago), other lines of evidence suggest a lower elevation in the distant past. Botsyun et al. used a model to show that several previously overlooked factors contribute to the isotopic record from the Eocene (see the Perspective by van Hinsbergen and Boschman). The results harmonize the isotopic record with other proxies and argue for a Tibetan Plateau that was about 1000 meters lower than it is today. Science , this issue p. eaaq1436 see also p. 928
Publisher: Springer International Publishing
Date: 2022
No related grants have been discovered for Jeremy Rugenstein.