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See detailWhere does the methane entrapped in Antarctic sea ice come from?
Jacques, C.; Sapart, Célia Julia ULiege; Carnat, G. et al

Poster (2017, July)

Methane (CH4) atmospheric concentrations have increased by a factor of 2.5 since the beginning of the Industrial Era, mainly because of anthropogenic activities. However, between 1999 and 2006, CH4 growth ... [more ▼]

Methane (CH4) atmospheric concentrations have increased by a factor of 2.5 since the beginning of the Industrial Era, mainly because of anthropogenic activities. However, between 1999 and 2006, CH4 growth rate declined to a near-zero level, suggesting that an equilibrium had been reached. But, from 2007 on, atmospheric concentrations underwent a renewed growth, implying major ongoing changes in the CH4 global budget (Nisbet et al., 2016). These changes challenge our understanding on the contribution of existing sources, and in particular natural sources. Sea ice can strongly affect emissions of CH4 from the ocean, but the precise mechanisms are not well understood. Sea ice has long been considered as an inert and impermeable barrier, but recent studies have highlighted the existence of gas fluxes at the atmosphere-sea ice and sea ice-seawater interfaces (Kort et al., 2012; He et al., 2013; Zhou et al., 2014; Sapart et al., 2016). However, these fluxes are to date poorly understood and quantified. To improve future climate projections, we aim to investigate the control exerted by sea ice on the CH4 atmospheric budget. To unravel the impacts of the Antarctic sea ice physical environment on biogeochemical cycles, the AWECS (Antarctic Winter Ecosystem Climate Study) expedition was conducted between the 8th of June and the 12th of August 2013 in the Weddell Sea. Such an expedition provides a rare opportunity to obtain insights on the behaviour of sea ice during winter. Ice cores specifically dedicated to the investigation of gas dynamics were collected at ten different stations. In order to determine CH4 formation and removal pathways in sea ice, we used concentration and stable isotope analysis, which can help to distinguish different processes. Here, we present and discuss our first results of the isotopic composition of CH4 (δ13C and δ D) on sea ice cores from the Weddell Sea and the Ross Ice Shelf. This new dataset will help to determine the origin of the CH4 entrapped in Antarctic sea ice and its potential impact on the current and future atmospheric CH4 budget. [less ▲]

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See detailThe Size, Shape, Albedo, Density, and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations
Braga-Ribas, F.; Sicardy, B.; Ortiz, J. L. et al

in Astrophysical Journal (2013), 773

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation ... [more ▼]

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R [SUB]equiv[/SUB] = 555 ± 2.5 km and geometric visual albedo p[SUB]V[/SUB] = 0.109 ± 0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of \epsilon = 0.087^{+0.0268}_{-0.0175}, an equatorial radius of 569^{+24}_{-17} km, and a density of 1.99 ± 0.46 g cm[SUP]–3[/SUP]. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere. [less ▲]

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See detailUse of Staby technology for development and production of DNA vaccines free of antibiotic resistance gene
Reschner; Scohy, S.; Vandermeulen, G. et al

in Human Vaccines (2013), 9

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See detailAlbedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation
Ortiz, J. L.; Sicardy, B.; Braga-Ribas, F. et al

in Nature (2012), 491

Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris ... [more ▼]

Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos. Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto, and is currently at a distance to the Sun intermediate between the two. Although Makemake's size (1,420+/-60km) and albedo are roughly known, there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere. Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430+/-9km (1σ) and 1,502+/-45km, implying a V-band geometric albedo p[SUB]V[/SUB] = 0.77+/-0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4-12nanobar (1σ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7+/-0.3gcm[SUP]-3[/SUP] is inferred from the data. [less ▲]

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See detailA Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation
Sicardy, B.; Ortiz, J. L.; Assafin, M. et al

in Nature (2011), 478

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 ... [more ▼]

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163+/-6kilometres, density 2.52+/-0.05 grams per cm[SUP]3[/SUP] and a high visible geometric albedo, . No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ~1nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun. [less ▲]

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See detailStellar Occultations by TNOs: the January 08, 2011 by (208996) 2003 AZ84 and the May 04, 2011 by (50000) Quaoar
Braga-Ribas, F.; Sicardy, B.; Ortiz, J. L. et al

in EPSC-DPS Joint Meeting 2011, held 2-7 October 2011 in Nantes, France. <A href="http://meetings.copernicus.org/epsc-dps2011">http://meetings.copernicus.org/epsc-dps2011</A>, p.1060 (2011, October 01)

Between February 2010 and May 2011, our group has observed five stellar occultations by Trans-Neptunian Objects (TNOs), giving the size and shape for some of the biggest TNO's: Varuna, Eris, 2003 AZ84 ... [more ▼]

Between February 2010 and May 2011, our group has observed five stellar occultations by Trans-Neptunian Objects (TNOs), giving the size and shape for some of the biggest TNO's: Varuna, Eris, 2003 AZ84, Makemake and Quaoar. Here we present two of them: the January 08 stellar occultation by 2003 AZ84, and the May 04 by Quaoar. For the event of 2003 AZ84 we obtained one positive and another negative occultation chords in Chile. We give a lower limit to the diameter of the TNO. The event of Quaoar was observed from 16 sites distributed in Uruguay, Argentina, Chile and Brazil. Five of them yielded positive detection of the occultation. A preliminary analysis shows that the body is probably elongated and significantly bigger than the size determined by Fraser & Brown 2010, with a diameter of 890km. Using the size determined by the occultation, we will discuss the implications for the body density and albedo determination. The upper limit of the atmosphere is also studied. [less ▲]

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