Sluggish hydrodynamic escape of early Martian atmosphere with reduced chemical compositions

<p>   Mars may have obtained a proto-atmosphere enriched in H<sub>2</sub>, CH<sub>4</sub>, and CO during accretion. Such a reduced proto-atmosphere would have been largely lost by hydrodynamic escape, but its flux is highly uncertain. To estimate the evolution of the proto-atmosphere of Mars correctly, an exact escape modeling including exact radiative balance and chemical processes is required partly because those reduced species and their photochemical products may act as an effective coolant that suppresses the escape of atmosphere. Here we develop a one-dimensional hydrodynamic escape model that includes radiative processes and photochemical processes for a multi-component atmosphere and apply to the reduced proto-atmosphere on Mars.</p><p>   Under the enhanced XUV flux suggested for young Sun, the escape flux decreases by more than one order of magnitude with increasing the mixing fraction of CH<sub>4</sub> and CO<span>  </span>from zero to > 10 % mainly because of the energy loss by radiative cooling by these infrared active chemical molecules. Concurrently, the mass fractionation between H<sub>2</sub> and other heavier species becomes to be enhanced. Given that the proto-Mars initially obtained > 10 bar of H<sub>2</sub> and carbon species equivalent to 1 bar of CO<sub>2</sub> was then left behind after the end of the hydrodynamic escape of H<sub>2</sub>, the total amount of carbon species lost by hydrodynamic escape is estimated to be equivalent to 20 bar of CO<sub>2</sub> or more. Such a severe loss of carbon species may explain the paucity of CO<sub>2</sub> on Mars compared to Earth and Venus. If the proto-Mars obtained > 100 bar of H<sub>2</sub>, the timescale for H<sub>2</sub> escape exceeds ~100 Myr. This implies that an atmosphere with reduced chemical compositions allowing the production of organic matter deposits may have been kept on early Mars traceable by geologic records.</p>

Characterization of Fluid Connectivity in Reservoirs using Strontium Isotopes

<p>Routine measurements of formation pressure while drilling reservoirs can indicate the presence of internal barriers to vertical fluid movement when there is a sudden shift in the pressure data. However, pinpointing the location of a barrier is often not possible since the density of pressure measurements is low and irregular. The aim of this contribution is to show how the Strontium isotopic system can help characterize the fluid connectivity and pinpoint the precise location of low permeability barriers in reservoir units and sedimentary sequences. As an example, we use a 25 m thick interval within the Middle Jurassic Hugin reservoir unit of the Langfjellet oil discovery on the Norwegian Continental Shelf. The location of the barrier is constrained by the upper and lower pressure measurements and could correspond to any of the several layers of silt, shale or coal layers in this interval. In this study, we collected every 2-4 m a total of 40 samples from a 110 m long cored section of a technical side-track well over the available. Each sample was prepared and analyzed using the SrRSA method (Strontium Residual Salt Analysis), which measures the <sup>87</sup>Sr/<sup>86</sup>Sr ratio in salt residue that precipitated in the pore space after the core dried out. The <sup>87</sup>Sr/<sup>86</sup>Sr is a natural tracer because the ratio is not affected by mass fractionation. The <sup>87</sup>Sr/<sup>86</sup>Sr in rocks is mostly acquired by water-rock interactions during diagenesis and evolves through mixing and equilibration of different water bodies, unless low-permeability barriers prevent equilibration. Therefore, the SrRSA patterns observed in the well represent a 1D snapshot of the fluid dynamics at the time of oil filling, which is a frozen image of competing equilibrium vs disequilibrium conditions. The SrRSA data follow a smooth trend of content values at 0.713 and display a sudden jump to lighter 0.709 values near the top of the 25 m thick interval that suggests the presence of a potential barrier. The lithological core log shows that the SrRSA step change corresponds to a coal-shale unit, which is interpreted to represent the barrier. The SrRSA data further demonstrate the reservoir unit at Langfjellet does not contain any other barriers to fluid flow, since pressure equilibration could have masked a possible compartmentalization. This study shows that the SrRSA method is a powerful tool that should be routinely applied for the characterization of fluid connectivity of storage units.</p>

Mass fractionation of Rb and Sr isotopes during laser ablation-multicollector-ICPMS: in situ observation and correction

Background One of the most critical issues concerning in situ mass spectrometry lies in accounting for elements and molecules that overlap target isotopes of analytical interest in a sample. This study traced the instrumental mass fractionation of Rb and Sr isotopes during laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) to obtain reliable 87Sr/86Sr ratios for high-Rb/Sr samples. Findings In the LA-MC-ICPMS analysis, Kr interferences were corrected using Ar and He gas blanks measured without ablating material. Contributions from doubly charged Er and Yb ions were corrected using the intensities of half masses and isotopic compositions reported in the literature. After Kr correction, the calculated 166Er2+ intensity of NIST SRM 610 approached the measured intensity at mass 83, and the 173Yb2+/171Yb2+ ratio agreed with the recommended value within error ranges. Kr- and REE2+-stripped peak intensities were further corrected for Rb interference. Use of the Sr mass bias factor for the calculation of measured 87Rb/85Rb yielded 87Sr/86Sr ratios consistent with the recommended and expected values for low-Rb/Sr materials, such as NIST SRM 616, modern shark teeth, and plagioclase collected from Jeju Island, but failed to account for the 87Rb interference from high-Rb/Sr materials including NIST SRM 610 and SRM 612. We calculated in situ mass bias factor of Rb from the known 87Sr/86Sr ratios of the standards and observed a correlation between Rb and Sr mass fractionation, which allowed inference of the Rb bias from the standard run. Reliable 87Sr/86Sr and 85Rb/86Sr ratios were obtained for SRM 610 and SRM 612 using the inferred mass bias factor of Rb calculated by the standard bracketing method. Conclusions This study revealed that Rb and Sr isotopes behave differently during LA-MC-ICPMS and suggests the potential usefulness of the standard bracketing method for measuring the Rb–Sr isotopic compositions of high-Rb/Sr materials.

In situ oxygen isotopic analysis of aragonite by secondary ion mass spectrometry with a new reference material

Accurate oxygen isotopic analysis of aragonite by secondary ion mass spectrometry (SIMS) requires appropriate reference materials to calibrate systems for instrumental mass fractionation. Several hundred SIMS oxygen isotopic analyses were...

Changes of Indicators in Fiber and Cotton Seed Quality in Separating Cut Fractions on Cotton Fiber Mass

This article describes the fourth type of medium-fiber Hampor, currently widely used in the Surkhandarya region, the lengnth is about 160-170 mg, 171-180 mg, 181-190 mg, 191-200 mg, 201-205 mg, 206-210 mg was divided into fractions by mass of fibers, the LKM equipment was cleaned of fine and dirty particles in the laboratory of the ginnery, DL-10 was isolated from the fiber on the ginning equipment, and the physical and mechanical properties of the seeds, the strength of the breakage, the modal mass, the length of the staple mass, the average mass, the ripening, the length and the squared irregularity were determined by the equipment. The optimal option for fiberglass mass fractionation was proposed to obtain high quality products.

Innovative Detection Strategies on Large Geometry SIMS open new challenging applications for light isotope ratio analyses

<p>Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS), operating in multicollection mode, allows high precision light isotope ratio measurements at high lateral resolution (tens of μm down to sub-μm range). For some challenging applications involving fine scale analysis of low abundance isotopes (i.e. <sup>17</sup>O or <sup>36</sup>S) or low-concentration elements (i.e. nitrogen in diamonds) measurement of low signal intensities is required. Traditionally, count rates between the upper level of pulse counting systems ~10<sup>5</sup> c/s and the lower level of Faraday Cup (FC) measurements ~10<sup>6</sup> c/s are considered to be in a “gap area” where neither detection protocol can achieve performance better than the 1‰ level.</p><p>Faraday Cup detectors (FC) offer high precision with no need for gain monitoring, however the uncertainty of FC measurements depends on the signal to noise ratio. One approach for measuring low signal intensities is to use FCs coupled to electrometers with high ohmic resistors. CAMECA LG-SIMS can now be equipped with low noise 10<sup>12</sup> Ω resistor FC preamplifier boards for measuring signal intensities down to the ~ 3 x 10<sup>5</sup> c/s range with precision better than the 0.5‰ level (1SD).</p><p>For measurement of low-abundance isotopes, a complementary approach consists of using discrete-dynode pulse counting electron multiplier (EM) detectors, for which drift and aging effects are minimized using a fast automated EM high voltage adjustment routine.</p><p>During this PICO presentation, we will discuss the relevance of the detector choice (FC 10<sup>12</sup> Ω vs EM) for few examples of innovative applications.</p><p>Example of mass independent fractionation:</p><p>In addition to classical isotopic ratio measurements (e.g. δ<sup>13</sup>C, δ<sup>15</sup>N, δ<sup>18</sup>O or δ<sup>34</sup>S), for which the instrumental mass fractionation (IMF) correction is mostly limited by the natural heterogeneity (chemical and isotopic) of the reference material, SIMS is particularly well suited for the measurement of mass independent fractionation (MIF, e.g. ∆<sup>33</sup>S, ∆<sup>36</sup>S and ∆<sup>17</sup>O). Along with classical geochemical processes, the degree of isotopic fractionation scales with the difference in mass of the isotopes involved (i.e. δ<sup>33</sup>S ≈ 0.515 * δ<sup>34</sup>S). MIF refers to non-conventional ratios that depart from these mass dependent rules. As instrumental mass fractionation has been shown to be strictly mass dependent, MIF measurements are not subject to IMF correction and are therefore measured directly. The use of SIMS in this specific case is particularly well suited and allows to fully explore the rich phenomenology of MIF source processes. We will discuss the advantages and disadvantages of using FC 10<sup>12</sup> Ω for the minor Sulphur isotope (<sup>36</sup>S) measurement.</p><p>Carbon and Nitrogen in diamond:</p><p>We will also show a recent analytical development aiming to measure δ<sup>13</sup>C in diamonds at mass resolution of ~5000 (allowing the full separation of <sup>13</sup>C- and <sup>12</sup>CH-) as well as N-content and N-isotopes in diamonds at a mass resolution of ~9000 (full separation of <sup>12</sup>C<sup>14</sup>N- and <sup>13</sup>C<sup>13</sup>C-).  For this purpose, the use of FC 10<sup>12</sup> Ω greatly improves the data quality and allows the simultaneous measurement of N-content and δ<sup>15</sup>N.</p>

The Archean atmosphere

The atmosphere of the Archean eon—one-third of Earth’s history—is important for understanding the evolution of our planet and Earth-like exoplanets. New geological proxies combined with models constrain atmospheric composition. They imply surface O2 levels <10−6 times present, N2 levels that were similar to today or possibly a few times lower, and CO2 and CH4 levels ranging ~10 to 2500 and 102 to 104 times modern amounts, respectively. The greenhouse gas concentrations were sufficient to offset a fainter Sun. Climate moderation by the carbon cycle suggests average surface temperatures between 0° and 40°C, consistent with occasional glaciations. Isotopic mass fractionation of atmospheric xenon through the Archean until atmospheric oxygenation is best explained by drag of xenon ions by hydrogen escaping rapidly into space. These data imply that substantial loss of hydrogen oxidized the Earth. Despite these advances, detailed understanding of the coevolving solid Earth, biosphere, and atmosphere remains elusive, however.