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Ricaud, P., Del Guasta M., Bazile E., Azouz N., Lupi A., Durand P., Attié J.-L., Veron D., Guidard V., Grigioni P. |
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Supercooled Liquid Water Cloud observed, analysed and modelled at the Top of the Planetary Boundary Layer above Dome C |
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Communication |
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2020 |
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Antarctica, SCAR, Visio, Hobart, Australia, August 2020 |
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7839 |
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Philippe Ricaud, Paolo Grigioni, Romain Roehrig, Pierre Durand, Dana E. Veron |
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Title |
Trends in Atmospheric Humidity and Temperature above Dome C |
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Communication |
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2020 |
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Antarctica Evaluated from Observations and Reanalyses, SCAR, Visio, Hobart, Australia, August 2020. |
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7840 |
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Winton V.H.L., Ming A., Caillon N., Hauge L. Jones A.E., Savarino J., Yang X., Frey M.M. |
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Title |
Deposition, recycling, and archival of nitrate stable isotopes between the air–snow interface: comparison between Dronning Maud Land and Dome C, Antarctica |
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2020 |
Publication |
Atmospheric Chemistry and Physics |
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20 |
Issue |
9 |
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5861–5885 |
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The nitrogen stable isotopic composition in nitrate (δ15N-NO−3) measured in ice cores from low-snow-accumulation regions in East Antarctica has the potential to provide constraints on past ultraviolet (UV) radiation and thereby total column ozone (TCO) due to the sensitivity of nitrate (NO−3) photolysis to UV radiation. However, understanding the transfer of reactive nitrogen at the air–snow interface in polar regions is paramount for the interpretation of ice core records of δ15N-NO−3 and NO−3 mass concentrations. As NO−3 undergoes a number of post-depositional processes before it is archived in ice cores, site-specific observations of δ15N-NO−3 and air–snow transfer modelling are necessary to understand and quantify the complex photochemical processes at play. As part of the Isotopic Constraints on Past Ozone Layer Thickness in Polar Ice (ISOL-ICE) project, we report new measurements of NO−3 mass concentration and δ15N-NO−3 in the atmosphere, skin layer (operationally defined as the top 5 mm of the snowpack), and snow pit depth profiles at Kohnen Station, Dronning Maud Land (DML), Antarctica. We compare the results to previous studies and new data, presented here, from Dome C on the East Antarctic Plateau. Additionally, we apply the conceptual 1D model of TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow (TRANSITS) to assess the impact of NO−3 recycling on δ15N-NO−3 and NO−3 mass concentrations archived in snow and firn. We find clear evidence of NO−3 photolysis at DML and confirmation of previous theoretical, field, and laboratory studies that UV photolysis is driving NO−3 recycling and redistribution at DML. Firstly, strong denitrification of the snowpack is observed through the δ15N-NO−3 signature, which evolves from the enriched snowpack (−3 ‰ to 100 ‰), to the skin layer (−20 ‰ to 3 ‰), to the depleted atmosphere (−50 ‰ to −20 ‰), corresponding to mass loss of NO−3 from the snowpack. Based on the TRANSITS model, we find that NO−3 is recycled two times, on average, before it is archived in the snowpack below 15 cm and within 0.75 years (i.e. below the photic zone). Mean annual archived δ15N-NO−3 and NO−3 mass concentration values are 50 ‰ and 60 ng g−1, respectively, at the DML site. We report an e-folding depth (light attenuation) of 2–5 cm for the DML site, which is considerably lower than Dome C. A reduced photolytic loss of NO−3 at DML results in less enrichment of δ15N-NO−3 than at Dome C mainly due to the shallower e-folding depth but also due to the higher snow accumulation rate based on TRANSITS-modelled sensitivities. Even at a relatively low snow accumulation rate of 6 cm yr−1 (water equivalent; w.e.), the snow accumulation rate at DML is great enough to preserve the seasonal cycle of NO−3 mass concentration and δ15N-NO−3, in contrast to Dome C where the depth profiles are smoothed due to longer exposure of surface snow layers to incoming UV radiation before burial. TRANSITS sensitivity analysis of δ15N-NO−3 at DML highlights that the dominant factors controlling the archived δ15N-NO−3 signature are the e-folding depth and snow accumulation rate, with a smaller role from changes in the snowfall timing and TCO. Mean TRANSITS model sensitivities of archived δ15N-NO−3 at the DML site are 100 ‰ for an e-folding depth change of 8 cm, 110 ‰ for an annual snow accumulation rate change of 8.5 cm yr−1 w.e., 10 ‰ for a change in the dominant snow deposition season between winter and summer, and 10 ‰ for a TCO change of 100 DU (Dobson units). Here we set the framework for the interpretation of a 1000-year ice core record of δ15N-NO−3 from DML. Ice core δ15N-NO−3 records at DML will be less sensitive to changes in UV than at Dome C; however the higher snow accumulation rate and more accurate dating at DML allows for higher-resolution δ15N-NO−3 records. |
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1177 |
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Bachelor's thesis |
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1680-7316 |
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yes |
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Serial |
7855 |
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Author |
Alison Ming, V. Holly L. Winton, James Keeble, Nathan L. Abraham, Mohit C. Dalvi, Paul Griffiths, Nicolas Caillon, Anna E. Jones, Robert Mulvaney, Joël Savarino, Markus M. Frey, Xin Yang |
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Title |
Stratospheric Ozone Changes From Explosive Tropical Volcanoes: Modeling and Ice Core Constraints |
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Journal |
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Year |
2020 |
Publication |
Journal of geophysical research: atmospheres |
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Volume |
125 |
Issue |
11 |
Pages |
e2019JD032290 |
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Keywords |
Antarctica chemistry-climate modeling isotopes in ice cores ozone Samalas volcanic eruption |
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Major tropical volcanic eruptions have emitted large quantities of stratospheric sulfate and are potential sources of stratospheric chlorine although this is less well constrained by observations. This study combines model and ice core analysis to investigate past changes in total column ozone. Historic eruptions are good analogs for future eruptions as stratospheric chlorine levels have been decreasing since the year 2000. We perturb the preindustrial atmosphere of a chemistry-climate model with high and low emissions of sulfate and chlorine. The sign of the resulting Antarctic ozone change is highly sensitive to the background stratospheric chlorine loading. In the first year, the response is dynamical, with ozone increases over Antarctica. In the high HCl (2 Tg emission) experiment, the injected chlorine is slowly transported to the polar regions with subsequent chemical ozone depletion. These model results are then compared to measurements of the stable nitrogen isotopic ratio, , from a low snow accumulation Antarctic ice core from Dronning Maud Land (recovered in 2016–2017). We expect ozone depletion to lead to increased surface ultraviolet (UV) radiation, enhanced air-snow nitrate photochemistry and enrichment in in the ice core. We focus on the possible ozone depletion event that followed the largest volcanic eruption in the past 1,000 years, Samalas in 1257. The characteristic sulfate signal from this volcano is present in the ice core but the variability in dominates any signal arising from changes in ultraviolet from ozone depletion. Prolonged complete ozone removal following this eruption is unlikely to have occurred over Antarctica. |
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1177 |
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2169-8996 |
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yes |
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7856 |
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Barbero A. Grilli R., Blouzon C., Caillon N., Savarino, J. |
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Title |
New Observations to Better Constrain NOx (NO + NO2) Concentrations on the Antarctic Plateau and to Resolve the Ambiguity in the NO2:NO Ratio |
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Communication |
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Year |
2020 |
Publication |
AGU Fall Meeting 2020, 1-17 December 2020 San Francisco, USA |
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High southern latitude regions present specificities that are highly relevant for studying the climate in connection with the atmospheric chemistry. Contrary to regions of the rest of the world, Antarctica is still considered as a pristine environment not yet influenced by predominant anthropogenic emissions (with the notable exceptions of GHG) and thus represents the last continental-size natural laboratory. Polar snow-air-radiation interactions and the specific oxidant character of the polar atmosphere are key in order to decipher the right information buried in the ice and the current chemical stability of the polar atmosphere. Previous Antarctic campaigns have shown atmospheric similarities between the Antarctic Plateau (at Dome C, Concordia) and other regions. However, several differences are yet to be explained: the large NO2:NO ratios previously found in ambient air indicates the existence of an unknown source of NO2 above the Antarctic Plateau. These observations question either the reliability of previous measurements or the lack of our understanding of the NOx chemistry. Novel optical instruments based on the incoherent broadband cavity enhanced absorption spectroscopy technique (IBBCEAS) were developed. The instruments can measure simultaneously NO2, NOx and NO with detection limits of 11, 10 and 21 ppt, respectively (1σ) within 22 minutes of measurements. The two compact and transportable instruments were deployed during the 2019/20 Dome C summer campaign. Atmospheric measurements together with flux chamber experiments were performed for determining the snowpack NOx emissions and the NO2:NO ratio. The observations seem to differ from the conclusions of the previous Antarctic campaigns. Assuming steady state and maximum radiations, the theoretical NO2:NO ratio from the period observed in December was calculated to be 0.38 ± 0.15 and 0.31 ± 0.12 in January. The instruments measured a ratio close to steady state in December (0.25 ± 0.25) while the ratio observed in January (1.248 ± 0.792) indicates the presence of a strong NO oxidant or an unknown source of NO2. Flux chamber experiments on different types of snow were done during this campaign, and the results will help deepen our knowledge of Antarctic atmospheric chemistry. |
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1177 |
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yes |
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7864 |
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Ishino S., Hattori S., Savarino J., Legrand M., Albalat E., Albarède F., Preunkert S., Jourdain B., Yoshida N. |
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Title |
Homogeneous sulfur isotope signature in East Antarctica and implication for sulfur source shifts through the last glacial-interglacial cycle |
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Communication |
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Year |
2020 |
Publication |
The Geochemical Society of Japan |
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1177 |
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yes |
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7865 |
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Casado M., Leroy-Dos C., Fourre E., Favier V., Agosta C., Arnaud L., Prié F., Akers P., Janssen L., Savarino J., Landais A. |
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Title |
Water vapor isotopic signature along the EAIIST traverse |
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Communication |
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2020 |
Publication |
EGU General Assembly, 19-30 April 2021 |
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yes |
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7868 |
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Author |
Weisen Shen, Douglas A. Wiens, Andrew J. Lloyd, Andrew A. Nyblade |
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Title |
A Geothermal Heat Flux Map of Antarctica Empirically Constrained by Seismic Structure |
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Year |
2020 |
Publication |
Geophysical Research Letters |
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Volume |
47 |
Issue |
14 |
Pages |
e2020GL086955 |
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Antarctica crust and uppermost mantle geothermal heat flux ice sheet modeling |
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Abstract |
The geothermal heat flux (GHF) is an important boundary condition for modeling the movement of the Antarctic ice sheet but is difficult to measure systematically at a continental scale. Earlier GHF maps suffer from low resolution and possibly biased assumptions in tectonism and crustal heat generation, resulting in significant uncertainty. We present a new GHF map for Antarctica constructed by empirically relating the upper mantle structure to known GHF in the continental United States. The new map, compared with previously seismologically determined one, has improved resolution and lower uncertainties. New features in this map include high GHF in the southern Transantarctic Mountains where warmer uppermost mantle is introduced by lithospheric removal and in the Thwaites Glacier region. Additionally, a modest GHF in the central West Antarctic Rift system near the Siple Coast and an absence of large-scale regions with GHF greater than 90 mW/m2 are found. |
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133 |
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1944-8007 |
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yes |
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7887 |
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J. Díaz, M. Ruiz, J. J. Curto, J. M. Torta, J. Ledo, A. Marcuello, P. Queralt |
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On the observation of magnetic events on broad-band seismometers |
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2020 |
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Earth, planets and space |
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72 |
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1 |
Pages |
109 |
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Anthropogenic sources of magnetic noise Seismic instrumentation Sudden Storm Commencements |
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The objective of this contribution is to get new insights into the effects of magnetic field variations of natural and anthropogenic origin on broad-band seismic stations. Regarding natural sources of magnetic perturbations, we have investigated if the Sudden Storm Commencements (SSC) cataloged during the 24th solar cycle (2008–2019) can be systematically identified in broad-band seismic stations distributed worldwide. The results show that the 23 SSC events with a mean amplitude above 30 nT and most of those with lower energy but still clearly identified in the magnetometer detection network can be observed at broad-band stations’ network using a simple low-pass filter. Although the preliminary impulse of those signals is usually stronger at stations located at high latitudes, major SSC are observed at seismic stations distributed worldwide. Regarding anthropogenic sources, we focus on the short period seismic signals recorded in urban environments which are correlated with the activity of the railway transportation system. We have analyzed collocated measurements of electric field and seismic signals within Barcelona, evidencing that significant changes in the electric field following the activity of the transportation systems can be attributed to leakage currents transmitted to the soil by trains. During space weather events, electric currents in the magnetosphere and ionosphere experience large variations inducing telluric currents near the Earth surface, which in turn generate a secondary magnetic field. In the case of underground trains, leakage currents are transmitted to the soil, which in turn can result in local variations in the magnetic field. The observed signals in modern seismometers can be related to the reaction of the suspension springs to these magnetic field variations or to the effect of the magnetic field variations on the force transducers used to keep the mass fixed. |
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133 |
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ISSN |
1880-5981 |
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yes |
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7888 |
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Author |
Alexey Lyubushin |
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Title |
Global Seismic Noise Entropy |
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2020 |
Publication |
Frontiers in Earth Science |
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Volume |
8 |
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558 |
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Abstract |
Data of continuous records of low-frequency (periods from 2 to 1,000 min) seismic noise on a global network of 229 broadband stations located around the world for 23 years, 1997–2019, are analyzed. The daily values of the entropy of the distribution of the squares of the orthogonal wavelet coefficients are considered as an informative characteristic of noise. An auxiliary network of 50 reference points is introduced, the positions of which are determined from the clustering of station positions. For each reference point, a time series is calculated, consisting of 8,400 samples with a time step of 1 day, the values of which are determined as the medians of the entropy values at the five nearest stations that are operable during the given day. The introduction of a system of reference points makes it possible to estimate temporal and spatial changes in the correlation of noise entropy values around the world. Estimation in an annual sliding time window revealed a time interval from mid-2002 to mid-2003, when there was an abrupt change in the properties of global noise and an intensive increase in both average entropy correlations and spatial correlation scales began. This trend continues until the end of 2019, and it is interpreted as a feature of seismic noise which is connected with an increase in the intensity of the strongest earthquakes, which began with the Sumatran mega-earthquake of December 26, 2004 (M = 9.3). The values of the correlation function between the logarithm of the released seismic energy and the bursts of coherence between length of day and the entropy of seismic noise in the annual time window indicate the delay in the release of seismic energy relative to the coherence maxima. This lag is interpreted as a manifestation of the triggering effect of the irregular rotation of the Earth on the increase in global seismic hazard. |
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133 |
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2296-6463 |
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2296-6463 |
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yes |
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7889 |
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