Depositional and organic carbon-controlled regimes during the Coniacian-Santonian event: First results from the southern Tethys (Egypt)

ABSTRACT The direct dating of rock paintings is not always possible due to the lack of organic carbon compounds in pigments, or because sampling from a heritage site is often restricted. To overcome these limitations, dating laboratories have to develop new approaches. In this study, we consider sampling calcium oxalate crusts covering the painted artworks as a way to indirectly date the rock art. This stratigraphic approach includes isolating and extracting pure oxalate from the crusts. The approach was tested on natural bulk accretions collected in the open-air sites of Erongo Mountains in Namibia. The accretions were separated into two phases (pure oxalate and the remaining residues) with a special pretreatment. This process removes carbonates through acidification (HCl 6N) and dissolves the oxalate into the supernatant, leaving the minerals and windblown organic compounds in the residue. The efficiency of the separation was checked on the two phases by FTIR analyses and by 14C dating and showed that pure oxalate powders were indeed obtained. AMS radiocarbon results of various accretions on the same art panels provided ages from modern periods to 2410 ± 35 BP. From these first results, more targeted sampling campaigns can be considered to provide a terminus ante quem for the rock art.

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Effects of intermittency and land use on the in-stream phosphorus and organic carbon uptake

10.5194/egusphere-egu2020-2337 ◽

2020 ◽

Author(s):

Gabriele Weigelhofer ◽

Matthias Pucher

Keyword(s):

Land Use ◽

Organic Carbon ◽

Dissolved Organic Carbon ◽

Hyporheic Zone ◽

Agricultural Land ◽

Headwater Streams ◽

Phosphorus Release ◽

Nutrient Concentrations ◽

Agricultural Land Use ◽

First Results

Understanding the consequences of the interplay between land use and climate change is among the most pressing challenges of the 21st century for river managers. Over the past decades, agricultural land use has altered nutrient concentrations and stoichiometric ratios in stream ecosystems, thereby affecting aquatic biogeochemical cycles and the coupling among carbon, phosphorus, and nitrogen. In addition, the frequency and duration of droughts has increased dramatically across Europe, causing perennial streams to shift to intermittency and changing the capacity of sediments for the uptake and storage of macronutrients.Our study aims to understand the effects of drying and re-wetting on the uptake, storage, and release of phosphorus and organic carbon from the benthic and the hyporheic zone of headwater streams under the additional stressor of agricultural land use. In specific, we are interested in the potential coupling and decoupling of phosphorus and dissolved organic carbon cycling in autotrophic and heterotrophic benthic biofilms. We sampled headwater streams before, during, and after the dry period in 2018 and 2019 and performed laboratory experiments with artificial drying and re-wetting and additions of dissolved organic carbon. We measured nutrient uptake and release, microbial biomass, respiration, and the activity of extra-cellular enzymes. The first results show an increased phosphorus release from the sediments immediately after re-wetting, foolowed by a reduced uptake capacity. The uptake of DOC was correlated with phosphorus in autotrophic biofilms, but not in heterotrophic ones.

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Towards the estimation of DOC from space in the open ocean

10.5194/egusphere-egu2020-7342 ◽

2020 ◽

Author(s):

Ana Gabriela Bonelli ◽

Hubert Loisel ◽

Vincent Vantrepotte ◽

Daniel Jorge ◽

Antoine Mangin ◽

...

Keyword(s):

Organic Carbon ◽

Temporal Dynamics ◽

Open Ocean ◽

Colored Dissolved Organic Matter ◽

Ocean Water ◽

Chl A ◽

First Results ◽

Spatio Temporal ◽

Input Variables ◽

Global Carbon

The Dissolved Organic Carbon (DOC) represents the largest pool of organic carbon and the most active carbon compartment in the ocean. Describing the spatio-temporal dynamics of the oceanic DOC in response to variation in the physical of biological forcings is therefore crucial for better understanding the global carbon cycle. The DOC distribution and its temporal dynamics is however currently not well known.In the recent years several works have demonstrated the possibility to assess from space the DOC distribution in the coastal ocean thanks to direct relationships between DOC and the optical properties of colored dissolved organic matter (CDOM). Such CDOM-DOC relationships are not applicable for the open ocean water due making more complex the DOC estimation from space in the latter environments. Here we present first results documenting an alternative method for estimating DOC from satellite imagery which rely on the use of a neural network which combines different physical and biogeochemical input variables (SST, SSS, PAR, aCDOM and Chl-a).

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Stable carbon isotopic composition of biomass burning emissions – implications for estimating the contribution of C3 and C4 plants

10.5194/egusphere-egu2020-10484 ◽

2020 ◽

Author(s):

Ulrike Dusek ◽

Roland Vernooij ◽

Anupam Shaikat ◽

Chenxi Qiu ◽

Elena Popa ◽

...

Keyword(s):

Organic Carbon ◽

Biomass Burning ◽

Stable Carbon Isotope ◽

Carbon Isotopic Composition ◽

Combustion Process ◽

C4 Plants ◽

C3 Plants ◽

Stable Carbon ◽

C3 And C4 Plants ◽

First Results

Biomass burning on the African continent emits large amounts of CO2, CO, and aerosols. Our aim is to use measurements of the stable carbon isotope 13C in organic carbon, CO and CO2 in biomass burning smoke to estimate the contribution of C3 plants (trees and bushes) and C4 plants (mainly Savannah grass), which have very distinct 13C/12C ratios. This is possible, if 13C/12C ratios are not significantly altered by the combustion process. This assumption is investigated in a series of laboratory experiments, where C3 and C4 plants (corn and willow wood), or C3-C4 plant mixtures are burned. The laboratory results are used to interpret the results of pilot studies of smoke sampled in African savannah fires.&#160;First results from the laboratory studies indicate that organic carbon (OC) from combustion of willow or corn shows 13C/12C ratios comparable to the burned plant material. For combustion of willow (C3), the 13C/12C ratios in OC tend to be slightly higher than in the wood fuel, depending on combustion conditions. For combustion of corn 13C/12C ratios of OC tend to be slightly lower than in the fuel. For mixtures of willow and corn the relationship between 13C/12C ratios in the emitted organic carbon and the fuel mixture is slightly non-linear: For a 50-50% oak wood and corn mixture the 13C/12C ratio in OC is closer to that of corn than that of willow. First results from pilot field studies indicate that a larger fraction of OC comes from trees and bushes, although mainly Savannah grass is burned in the investigated fires.

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Distribution of 14C and 13C in Forest Soils of the Dinghushan Biosphere Reserve

Radiocarbon ◽

10.1017/s0033822200041321 ◽

2001 ◽

Vol 43 (2B) ◽

pp. 671-678 ◽

Cited By ~ 17

Author(s):

Chengde Shen ◽

Weixi Yi ◽

Yanmin Sun ◽

Changping Xing ◽

Ying Yang ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Forest Soil ◽

Forest Soils ◽

Biosphere Reserve ◽

Subtropical Forest ◽

Lower Section ◽

Broad Leaf ◽

First Results ◽

The Mean

We report here first results on the bulk soil organic carbon (SOC), apparent radiocarbon ages and δ13C characteristics of the tropical and subtropical forest soil in Dinghushan Biosphere Reserve (DHSBR). The forest oxisol in Dinghushan has developed during the Holocene. The δ13C variation curves in all three profiles may be divided into two sections. The upper section from 0 to 40 cm has δ13C values varying from −27.4 to −24.1‰, −27.5 to −22.2‰, and −24.4 to −20.1‰. in the Wukesong, Qingyunsi and Kengkou profiles, respectively. The lower section, including the 40–160 cm horizons, has a uniform δ13C. The mean δ13C values of the soil organic carbon could be used not only to discriminate between C3 and C4 plants, but also to distinguish between coniferous and broad-leaf plants.

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Discussion of the Oblique Rotator Model Cases Of 108 Aqr and x Serp.

International Astronomical Union Colloquium ◽

10.1017/s0252921100080891 ◽

1976 ◽

Vol 32 ◽

pp. 577-588

Author(s):

C. Mégessier ◽

V. Khokhlova ◽

T. Ryabchikova

Keyword(s):

Mathematical Formulation ◽

The Other ◽

Rotator Model ◽

Oblique Rotator ◽

First Results

My talk will be on the oblique rotator model which was first proposed by Stibbs (1950), and since received success and further developments. I shall present two different attempts at describing a star according to this model and the first results obtained in the framework of a Russian-French collaboration in order to test the precision of the two methods. The aim is to give the best possible representation of the element distributions on the Ap stellar surfaces. The first method is the mathematical formulation proposed by Deutsch (1958-1970) and applied by Deutsch (1958) to HD 125248, by Pyper (1969) to α2CVn and by Mégessier (1975) to 108 Aqr. The other one was proposed by Khokhlova (1974) and used by her group.

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Meridional Circulation, Turbulence, and Diffusion Processes in Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100080477 ◽

1976 ◽

Vol 32 ◽

pp. 109-116 ◽

Cited By ~ 1

Author(s):

S. Vauclair

Keyword(s):

Convection Zone ◽

Diffusion Processes ◽

Meridional Circulation ◽

Diffusion Time ◽

Work In Progress ◽

First Results ◽

Stellar Envelopes ◽

And Diffusion ◽

Turbulence And Diffusion ◽

Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

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Investigation of cluster layers of small netal particles by TEM, SEM, EELS and by photoacoustic spectroscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100174382 ◽

1990 ◽

Vol 48 (4) ◽

pp. 250-251

Author(s):

H. Seiler ◽

U. Haas ◽

K.H. Körtje

Keyword(s):

Bulk Material ◽

High Vacuum ◽

Optical Methods ◽

Metal Particles ◽

Silver Particles ◽

Low Loss ◽

Plasmon Excitation ◽

First Results ◽

Diffraction Patterns ◽

Small Metal Particles

The physical properties of small metal particles reveal an intermediate position between atomic and bulk material. Especially Ag has shown pronounced size effects. We compared silver layers evaporated in high vacuum with cluster layers of small silver particles, evaporated in N2 at a pressure of about 102 Pa. The investigations were performed by electron optical methods (TEM, SEM, EELS) and by Photoacoustic (PA) Spectroscopy (gas-microphone detection).The observation of cluster layers with TEM and high resolution SEM show small silver particles with diameters of about 50 nm (Fig. 1 and Figure 2, respectively). The electron diffraction patterns of homogeneous Ag layers and of cluster layers are similar, whereas the low loss EELS spectra due to plasmon excitation are quite different. Fig. 3 and Figure 4 show first results of EELS spectra of a cluster layer of small silver particles on carbon foil and of a homogeneous Ag layer, respectively.

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Towards 1-Ångstrom-resolution STEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100150812 ◽

1993 ◽

Vol 51 ◽

pp. 996-997

Author(s):

H.S. von Harrach ◽

D.E. Jesson ◽

S.J. Pennycook

Keyword(s):

High Resolution ◽

Field Emission ◽

Phase Contrast ◽

Spherical Aberration ◽

A Priori ◽

Dark Field ◽

Image Resolution ◽

Objective Lens ◽

Annular Dark Field ◽

First Results

Phase contrast TEM has been the leading technique for high resolution imaging of materials for many years, whilst STEM has been the principal method for high-resolution microanalysis. However, it was demonstrated many years ago that low angle dark-field STEM imaging is a priori capable of almost 50% higher point resolution than coherent bright-field imaging (i.e. phase contrast TEM or STEM). This advantage was not exploited until Pennycook developed the high-angle annular dark-field (ADF) technique which can provide an incoherent image showing both high image resolution and atomic number contrast.This paper describes the design and first results of a 300kV field-emission STEM (VG Microscopes HB603U) which has improved ADF STEM image resolution towards the 1 angstrom target. The instrument uses a cold field-emission gun, generating a 300 kV beam of up to 1 μA from an 11-stage accelerator. The beam is focussed on to the specimen by two condensers and a condenser-objective lens with a spherical aberration coefficient of 1.0 mm.

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