Contributions of Volatiles to the Venus Atmosphere from the Observed Extrusive Volcanic Record: Implications for the History of the Venus Atmosphere

<p>One of the most important questions in planetary science is the origin of the current Venus atmosphere, its relationship and coupling to Venus’ geologic and geodynamic evolution, andwhy it is so different from that of the Earth. We specifically address the following question:Does the eruption of the total volume of extrusive volcanic deposits observed in the exposed geologic record of Venus contribute significantly to the current atmosphere through volatile release during emplacement of the extruded lavas? To address this question, we used the observed geologic and stratigraphic record of volcanic units and features, and their volumes, as revealed by Magellan (1; their Fig. 26 and Table 5).  We converted the volumes of the main volcanic units to lava/magma masses using a density of 3000 kg m<sup>-3</sup>. Next, we chose the upperthickness values, and added the contributions from allof the units; summing the values of the "total eruptives" gives the absolute upper limit estimate of the mass of documented volcanics that could contribute to the atmosphere, 7.335 x 10<sup>20 </sup>kg. We then compare this with the current mass of the Venus atmosphere (4.8 x 10<sup>20 </sup>kg). We find that in order to make the current atmosphere from the above volcanics, the magma would have to consist of 65.4% by mass volatiles, which is, of course, impossible. We conclude that the grand totalof the currently documented volcanics can not have produced other than a very small fraction of the current atmosphere.</p><p>Exsolution of volatiles during volcanic eruptions is significantly dependent on surface atmospheric pressure (2-3). However, the total volumeof lava erupted in the period of global volcanic resurfacingis still insufficient to produce the CO<sub>2</sub>atmosphere observed today, even if the ambient atmospheric pressure at that time was only 50% of what it is today. Therefore, a very significant part of the current CO<sub>2</sub>atmosphere must have been inherited from a time prior to the observed geologic record, sometime in the first ~80% of Venus history. Furthermore, the total volumeof lava erupted in the stratigraphically youngest period of the observed record (1) is insufficient to account for the current abundance of SO<sub>2 </sub>in the atmosphere; thus, it seems highly unlikely that current and recently ongoing volcanism could be maintaining the currently observed ‘elevated’ levels of SO<sub>2 </sub>in the atmosphere (4).  In addition, because of the fundamental effect of atmospheric pressure on the quantity of volatiles that will be degassed, varying the nature of the mantle melts over a wide range of magma compositions and mantle fO<sub>2 </sub>appears to have minimal influence on the outcome.  We conclude that the current Venus atmosphere must be a “fossil atmosphere”, largely inherited from a previous epoch in Venus history, and if so, may provide significant insight into the conditions during the first 80% of Venus history.</p><p>(1) Ivanov and Head (2013) Plan. Space Sci. 84, 66; (2) Gaillard & Scaillet, 2014, EPSL 403, 307; (3) Head & Wilson, 1986, JGR 91, 9407;(4)Esposito, 1984, Science 223, 1072.</p>

Quantitative Detection of Iodine in the Stratosphere

<p>Ozone in the extrapolar lower stratosphere is currently declining for reasons that are not well understood. Iodine is emitted mostly from marine sources, and changing iodine emissions provide a possible chemical reason for why ozone in the lower stratosphere continues to decline (Koenig et al., 2020). Previous stratospheric measurements had detected iodine qualitatively in particles. More recently, IO observations in the daytime tropical tropopause layer (TTL) have suggested that between 0.25 to 0.70 pptv Iy are injected into the stratosphere, which is 1.6 to 3.5 times the WMO2014 upper limit. These indirect observations have led to revised estimates of 0 - 0.8 pptv Iy stratospheric injection in the WMO2018 report. This presentation discusses first quantitative measurements of IO radicals and of submicron particulate iodine from aircraft in the stratosphere that support 0.77 pptv Iy stratospheric injection. Our observations support the WMO2018 upper limit estimate, and clearly are incompatible with zero iodine injection. The implications of the obseved iodine concentrations for ozone loss in the lower stratosphere are discussed, also in light of climate records that find increasing iodine in recent decades, observed ozone trends, and ongoing and future research needs to better quantify iodine's contribution to explain these trends. </p>

Assessing Ensemble Forecasts of Low-Level Supercell Rotation within an OSSE Framework

Under the envisioned warn-on-forecast (WoF) paradigm, ensemble model guidance will play an increasingly critical role in the tornado warning process. While computational constraints will likely preclude explicit tornado prediction in initial WoF systems, real-time forecasts of low-level mesocyclone-scale rotation appear achievable within the next decade. Given that low-level mesocyclones are significantly more likely than higher-based mesocyclones to be tornadic, intensity and trajectory forecasts of low-level supercell rotation could provide valuable guidance to tornado warning and nowcasting operations. The efficacy of such forecasts is explored using three simulated supercells having weak, moderate, or strong low-level rotation. The results suggest early WoF systems may provide useful probabilistic 30–60-min forecasts of low-level supercell rotation, even in cases of large radar–storm distances and/or narrow cross-beam angles. Given the idealized nature of the experiments, however, they are best viewed as providing an upper-limit estimate of the accuracy of early WoF systems.

Characterization of Chemical Bonding in Ion-Implanted Polymers by Means of Mid-Infrared Reflectivity

An optical approach for structural characterization of the modified surface layer in ion-implanted polymers is proposed. The mid-infrared reflectivity from the implanted surface is analyzed in terms of an oscillator dispersion model combined with the theory of differential reflection spectroscopy. The degree of destruction of a specific chemical bond is determined by the relative drop of the oscillator strengths associated with the corresponding vibrational modes. As an example, this methodology is applied to poly(methylmethacrylate) (PMMA) implanted with 50 keV silicon ions at fluences in the range 3 × 1014 to 1 × 1017 ions/cm2. The scission rates for the C=O, C–O–C, and C–H bonds, as well as the static dielectric constant of the ion-modified material, are calculated as a function of the ion fluence. Further, a lower-limit estimate of 120 nm for the thickness of the ion-modified layer is obtained.

Impact of Additional Cytogenetic Changes and FLT3 Mutations on the Outcome of Patients with Newly Diagnosed Acute Promyelocytic Leukaemia Treated with Single Agent Arsenic Trioxide.

The efficacy of single agent arsenic trioxide (ATO) in the management of relapsed and newly diagnosed patients with acute promyelocytic leukaemia (APL) has been established. The impact of FLT3 activating mutations and additional cytogenetic changes in newly diagnosed patients with APL treated with single agent ATO has never been reported. Between January 1998 and April 2005, 98 newly diagnosed cases of PML-RARα positive APL were treated with a regimen of single agent ATO at our centre. FLT3 activating mutations were seen in 33% (FLT3-ITD - 21.3%, D835V- 11.7%). Of the 69 patients evaluated for additional cytogenetic findings, 76.8% had an isolated t(15;17) while 23.2% had t(15;17) along with additional cytogenetic findings. The presence of a FLT3 mutation was significantly associated with a higher mean white cell count (18.11±23.74 vs. 8.04±21.44, P=0.024) and a bcr3 PML-RARα isoform (48.4% vs. 20.6%, P=0.006). There was also a significant delay in achieving a molecular remission (MR) among patients with a FLT3 mutation as noted by the number of patients who were in MR prior to onset of consolidation therapy (60.9% vs. 85.7%, P=0.031). There was no significant difference in the hematological remission rate (CR), time to CR or early mortality between the group with and without a FLT3 mutation. At a median follow up of 20 months (range: 4 – 97), the 3 year Kaplan-Meier estimate of OS, EFS and DFS for patients with a FLT3 mutation was 82.51±7.24, 77.01±8.6, 88.82±7.48 percent while for those without a FLT3 mutation it was 92.06±3.4, 80.45±5.86, 89.02±5.31 percent. Statistical analysis of these survival curves by a log rank test did not reveal any significant difference between the two groups [Figure 1]. The presence of additional cytogenetic changes was not associated with any significant differences in the clinical or laboratory parameters at presentation. It also did not have an impact on the CR, MR, EFS, DFS or OS. Neither FLT3 activating mutations nor additional cytogenetic changes have a significant impact on the outcome of newly diagnosed patients with APL treated with single agent ATO in the short term. Whether either of these two parameters will affect long term outcome remains to be seen. Figure 1: Kaplan-Meier product limit estimate of EFS based on FLT3 mutation status (n=94). Figure 1:. Kaplan-Meier product limit estimate of EFS based on FLT3 mutation status (n=94).

Use of small-sample-based reference limits on a group basis

The evaluation of a biochemical or hematological quantity measured in a study group of employees during occupational health assessments involves a comparison with a reference sample group. Part of this evaluation consists of checking whether the percentage of values larger than a predetermined upper reference limit is significantly larger than the percentage normally expected (2.5%, if the 97.5 percentile is used as the upper reference limit). The reference limit, however, is estimated from a random reference sample, the size of which, for many reasons, may be relatively small; as a consequence, the reference limit estimate will be imprecise. In situations in which the reference sample size is smaller than or not much larger than the study sample size, this imprecision results in the usual binomial test of significance being highly inappropriate. We provide an exact nonparametric test valid for all reference sample sizes.

Stucture of 1/2 Dislocations In γ-Tial by High Resolution Tem and Embedded Atom Method Modelling

High Resolution TEM (HRTEM) observations of a dislocation in γ-TiAl are compared directly with atomistic calculations of dislocation structures performed with atomistic potentials in order to obtain an estimate of the Complex Stacking Fault Energy (γcsf). A value of between 470 and 620 mJ/M2 was obtained. HRTEM observations are presented of a Ti-52AI sample, containing a dislocation with Burgers vector 1/2<110> and 60° line orientation. This image is matched against images simulated from the outputs of Embedded Atom Method (EAM) simulations, using potentials that were fit to bulk γ-TiAl properties. Two atomistic simulation methods were employed in order to give the range of values for γcsf. In the first of these methods, three EAM potentials were used to simulate the stress-free core structure. These were fit so as to produce three different values of γcsf, all other properties being roughly the same as the literature values for γ-TiAI. All of these potentials produced cores that were more extended than the experimental observation. Thus a value of 470 mJ/M2, being the highest value of γcsf obtainable for the EAM potentials, is reported as a low limit estimate of γcsf for γ-TiAl. An upper limit estimate of the value of γcsf was obtained by applying an external ‘Escaig’ stress that forced the Shockley partials to further constrict, simulating the effect of an increase in γcsf, The preliminary value calculated from this procedure was 620 mJ/M2.