Search results for "carbon (C)"
showing 10 items of 156 documents
Ensemble reconstruction constraints on the global carbon cycle sensitivity to climate
2010
The processes controlling the carbon flux and carbon storage of the atmosphere, ocean and terrestrial biosphere are temperature sensitive and are likely to provide a positive feedback leading to amplified anthropogenic warming. Owing to this feedback, at timescales ranging from interannual to the 20-100-kyr cycles of Earth's orbital variations, warming of the climate system causes a net release of CO(2) into the atmosphere; this in turn amplifies warming. But the magnitude of the climate sensitivity of the global carbon cycle (termed gamma), and thus of its positive feedback strength, is under debate, giving rise to large uncertainties in global warming projections. Here we quantify the med…
Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle Toarcian in the Paris…
2014
Abstract Lower Toarcian strata (Lower Jurassic) have been extensively studied with a view to understanding the oceanographic, climatic and biological processes that drove the Earth's system into an Oceanic Anoxic Event (OAE). For this time period, the evolution of the European marine seaways is now relatively well constrained owing to multiple geochemical studies, but investigations regarding climatic trends in the continental realm remain sparse. In the present study, we test the clay mineralogy as a continental climate-sensitive proxy in the well-documented Sancerre core (southern Paris Basin). We compare variations in the kaolinite content with p CO 2 fluctuations (derived from paired ca…
Comprehensive dataset of shotgun metagenomes from stratified freshwater lakes and ponds
2020
AbstractStratified lakes and ponds featuring steep oxygen gradients are significant net sources of greenhouse gases and hotspots in the carbon cycle. Despite their significant biogeochemical roles, the microbial communities, especially in the oxygen depleted compartments, are poorly known. Here, we present a comprehensive dataset including 267 shotgun metagenomes from 41 stratified lakes and ponds mainly located in the boreal and subarctic regions, but also including one tropical reservoir and one temperate lake. For most lakes and ponds, the data includes a vertical sample set spanning from the oxic surface to the anoxic bottom layer. The majority of the samples were collected during the o…
Impact of woody encroachment on soil organic carbon and nitrogen in abandoned agricultural lands along a rainfall gradient in Italy
2011
Land use changes represent one of the most important components of global environmental change andhave a strong influence on carbon cycling. As a consequence of changes in economy during the last century, areas of marginal agriculture have been abandoned leading to secondary successions. The encroachment of woody plants into grasslands, pastures and croplands is generally thought to increase the carbon stored in these ecosystems even though there are evidences for a decrease in soil carbon stocks after land use change. In this paper, we investigate the effects of woody plant invasion on soil carbon and nitrogen stocks along a precipitation gradient (200–2,500 mm) using original data from pa…
The Valanginian positive carbon isotope event in Arctic Russia: Evidence from terrestrial and marine isotope records and implications for global carb…
2010
The data presented here comprise Ryazanian–Valanginian carbon isotope ratios analyzed from fossil wood and belemnites from the shallow marine Boyarka River succession in Siberia. Additional belemnite carbon isotope ratios from the Izhma River succession (also Ryazanian–Valanginian) in Russia are also presented. The wood-derived and belemnite-derived isotope ratios are considered to primarily reflect changes in the terrestrial and marine carbon isotope reservoirs respectively. The δ13Ccarb and δ13Cwood records reveal a distinct mid-Valanginian positive carbon isotope excursion, with the initiation occurring near the Boreal Russian michalskii–polyptychus zone boundary, which is broadly time-e…
Comprehensive dataset of shotgun metagenomes from oxygen stratified freshwater lakes and ponds
2021
Stratified lakes and ponds featuring steep oxygen gradients are significant net sources of greenhouse gases and hotspots in the carbon cycle. Despite their significant biogeochemical roles, the microbial communities, especially in the oxygen depleted compartments, are poorly known. Here, we present a comprehensive dataset including 267 shotgun metagenomes from 41 stratified lakes and ponds mainly located in the boreal and subarctic regions, but also including one tropical reservoir and one temperate lake. For most lakes and ponds, the data includes a vertical sample set spanning from the oxic surface to the anoxic bottom layer. The majority of the samples were collected during the open wate…
Rotational coherence imaging and control for CN molecules through time-frequency resolved coherent anti-Stokes Raman scattering
2011
Numerical wave packet simulations are performed for studying coherent anti-Stokes Raman scattering (CARS) for CN radicals. Electronic coherence is created by femtosecond laser pulses between the X²Σ and B²Σ states. Due to the large energy separation of vibrational states, the wave packets are superpositions of rotational states only. This allows for a specially detailed inspection of the second- and third-order coherences by a two-dimensional imaging approach. We present the time-frequency domain images to illustrate the intra- and intermolecular interferences, and discuss the procedure to rationally control and experimentally detect the interferograms in solid Xe environment. peerReviewed
One- and Two-Dimensional Diffusion of Metal Atoms in Graphene
2008
In the present work, individual Au or Pt atoms in layersconsisting of one or twographene planes have been monitoredin real time at high temperature by high-resolution TEM. Weobtain information about the location of metal atoms ingrapheneandthediffusionmechanisms.Activationenergiesfordiffusion are obtained in a temperature range close to thetemperature of the technically important metal-assisted CVDprocess.Thematerialwassynthesizedinanarcdischarge
Phase Stability of Natural Ni0.75Mg0.22Ca0.03CO3 Gaspeite Mineral at High Pressure and Temperature
2020
[EN] Divalent metal carbonates play an important role in Earth's carbon cycle, but the effect of chemical substitution is still poorly known. In this work, we have studied the structural and vibrational properties of natural mineral gaspeite (Ni0.75Mg0.22Ca0.03CO3) under high pressure and temperature using in situ synchrotron X-ray diffraction and Raman spectroscopy in diamond-anvil cells. These experiments have been complemented by ab initio simulations. Synchrotron high-pressure XRD measurements at room temperature using He as the pressure transmitting medium have shown that the calcite-type structure is stable up to 23.3 GPa. A bulk modulus at zero pressure of B-0 = 105(2) GPa with B-0' …
Decreasing Phanerozoic extinction intensity as a consequence of Earth surface oxygenation and metazoan ecophysiology
2021
The decline in background extinction rates of marine animals through geologic time is an established but unexplained feature of the Phanerozoic fossil record. There is also growing consensus that the ocean and atmosphere did not become oxygenated to near-modern levels until the mid-Paleozoic, coinciding with the onset of generally lower extinction rates. Physiological theory provides us with a possible causal link between these two observations-predicting that the synergistic impacts of oxygen and temperature on aerobic respiration would have made marine animals more vulnerable to ocean warming events during periods of limited surface oxygenation. Here, we evaluate the hypothesis that chang…