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Bown J, Boye M, Laan P, Bowie A R, Park Y-H, Jeandel C, Nelson D M, . (2012). Imprint of a dissolved cobalt basaltic source on the Kerguelen Plateau
. Biogeosciences, 9(12), 5279–5290.
Abstract: Processes of cobalt (Co) entrainment from shelf sediments over the Kerguelen Plateau were studied during the KEOPS (Kerguelen Ocean Plateau compared Study) cruise data to assess the potential use of dissolved Co as a tracer for estimating natural iron fertilization over the plateau. Lateral advection and dissolution of Co contained in basalt sediments around Heard Island, a main source of lithogenic Co in the study area, were shown to imprint the process of surface enrichment over the plateau. Sedimentary Co inputs were estimated to be much higher than biological Co uptake in phytoplankton blooms, resulting in strong inputs of dissolved Co to surface waters, which allows the use of Co as an efficient tracer of sedimentary inputs. Based on a simple, steady state balance equation of the external input of dissolved iron over the plateau, the fertilization of iron inferred by using Co as a tracer of basalt sources is estimated to be 28 x102 ± 21 x102 ton y-1 in surface waters of the Kerguelen Plateau. This estimate is consistent with the advective iron supply matching with phytoplankton demand, strengthening our idea of using Co as a new tracer for the natural fertilization over the plateau.
Programme: 1061
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Landais A, Dreyfus G, Capron E, Pol K, Loutre M F, Raynaud D, Lipenkov V Y, Arnaud L, Masson-Delmotte V, Paillard D, Jouzel J, Leuenberger M, . (2012). Towards orbital dating of the EPICA Dome C ice core using δO2/N2
. Clim. Past, 8(1), 191–203.
Abstract: Based on a composite of several measurement series performed on ice samples stored at -25 °C or -50 °C, we present and discuss the first δO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core covering the period between 300 and 800 ka (thousands of years before present). The samples stored at -25 °C show clear gas loss affecting the precision and mean level of the δO2/N2 record. Two different gas loss corrections are proposed to account for this effect, without altering the spectral properties of the original datasets. Although processes at play remain to be fully understood, previous studies have proposed a link between surface insolation, ice grain properties at close-off, and δO2/N2 in air bubbles, from which orbitally tuned chronologies of the Vostok and Dome Fuji ice core records have been derived over the last four climatic cycles. Here, we show that limitations caused by data quality and resolution, data filtering, and uncertainties in the orbital tuning target limit the precision of this tuning method for EDC. Moreover, our extended record includes two periods of low eccentricity. During these intervals (around 400 ka and 750 ka), the matching between δO2/N2 and the different insolation curves is ambiguous because some local insolation maxima cannot be identified in the δO2/N2 record (and vice versa). Recognizing these limitations, we restrict the use of our δO2/N2 record to show that the EDC3 age scale is generally correct within its published uncertainty (6 kyr) over the 300–800 ka period.
Programme: 902
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Dommergue A, Barret M, Courteaud J, Cristofanelli P, Ferrari C P, Gallée H, . (2012). Dynamic recycling of gaseous elemental mercury in the boundary layer of the Antarctic Plateau
. Atmos. Chem. Phys., 12(22), 11027–11036.
Abstract: Gaseous elemental mercury (Hg0) was investigated in the troposphere and in the interstitial air extracted from the snow at Dome Concordia station (alt. 3320 m) on the Antarctic Plateau during January 2009. Measurements and modeling studies showed evidence of a very dynamic and daily cycling of Hg0 inside the mixing layer with a range of values from 0.2 ng m−3 up to 2.3 ng m−3. During low solar irradiation periods, fast Hg0 oxidation processes in a confined layer were suspected. Unexpectedly high Hg0 concentrations for such a remote place were measured under higher solar irradiation due to snow photochemistry. We suggest that a daily cycling of reemission/oxidation occurs during summer within the mixing layer at Dome Concordia. Hg0 concentrations showed a negative correlation with ozone mixing ratios, which contrasts with atmospheric mercury depletion events observed during the Arctic spring. Unlike previous Antarctic studies, we think that atmospheric Hg0 removal may not be the result of advection processes. The daily and dramatic Hg0 losses could be a consequence of surface or snow induced oxidation pathways. It remains however unclear whether halogens are involved. The cycling of other oxidants should be investigated together with Hg species in order to clarify the complex reactivity on the Antarctic plateau.
Programme: 1028
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Gazeaux J, Bekki S, Naveau P, Keckhut P, Jumelet J, Parades J, David C, . (2012). Detection of particle layers in backscatter profiles: application to Antarctic lidar measurements
. 1680-7316, 12(7), 3205–3217.
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Pison I, Ringeval B, Bousquet P, Prigent C, Papa F, . (2013). Stable atmospheric methane in the 2000s: key-role of emissions from natural wetlands
. Atmos. Chem. Phys., 13(23), 11609–11623.
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Cavitte M G P, Blankenship D D, Young D A, Siegert M J, Le Meur E, . (2013). Radar stratigraphy connecting Lake Vostok and Dome C, East Antarctica, constrains the EPICA/DMC ice core time scale
. The Cryosphere Discuss., 7(1), 321–342.
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Gallet J-C, Domine F, Savarino J, Dumont M, Brun E, . (2014). The growth of sublimation crystals and surface hoar on the Antarctic plateau
. The Cryosphere, 8(4), 1205–1215.
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Slemr F, Angot H, Dommergue A, Magand O, Barret M, Weigelt A, Ebinghaus R, Brunke E-G, Pfaffhuber K A, Edwards G, Howard D, Powell J, Keywood M, Wang F, . (2015). Comparison of mercury concentrations measured at several sites in the Southern Hemisphere
. Atmos. Chem. Phys., 15(6), 3125–3133.
Abstract: Our knowledge of the distribution of mercury concentrations in air of the Southern Hemisphere was until recently based mostly on intermittent measurements made during ship cruises. In the last few years continuous mercury monitoring has commenced at several sites in the Southern Hemisphere, providing new and more refined information. In this paper we compare mercury measurements at several remote sites in the Southern Hemisphere made over a period of at least 1 year at each location. Averages of monthly medians show similar although small seasonal variations at both Cape Point and Amsterdam Island. A pronounced seasonal variation at Troll research station in Antarctica is due to frequent mercury depletion events in the austral spring. Due to large scatter and large standard deviations of monthly average median mercury concentrations at Cape Grim, no systematic seasonal variation could be found there. Nevertheless, the annual average mercury concentrations at all sites during the 2007–2013 period varied only between 0.85 and 1.05 ng m−3. Part of this variability is likely due to systematic measurement uncertainties which we propose can be further reduced by improved calibration procedures. We conclude that mercury is much more uniformly distributed throughout the Southern Hemisphere than the distributions suggested by measurements made onboard ships. This finding implies that smaller trends can be detected in shorter time periods. We also report a change in the trend sign at Cape Point from decreasing mercury concentrations in 1996–2004 to increasing concentrations since 2007.
Programme: 1028
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Barral H, Genthon C, Trouvilliez A, Brun C, Amory C, . (2014). Blowing snow at D17, Adélie Land, Antarctica: atmospheric moisture issues
. The Cryosphere Discuss., 8(3), 2759–2798.
Abstract: Three years of blowing snow and meteorological observations have been collected along a 7 m mast at site D17 in coastal Adélie Land, Antarctica. This is a region particularly exposed to katabatic winds. The atmospheric surface layer is often close to saturation because of the sublimation of the airborne snow particles. A systematic dry bias results in atmospheric models that ignore blowing snow and its moistening effects, and in meteorological analyses that use such model. The Crocus snow-pack model, including a parameterization for the erosion of surface snow by wind, reproduces the observed march of snow accumulation and ablation if the observed meteorology is used as input. Because of subsaturation, a 2.5 fold increase in surface sublimation is obtained if analyzed surface air meteorology is used. The sublimation obtained in the Crocus model poorly agrees with the moisture fluxes evaluated using the profile method along the mast. Moisture gradients are very weak, particularly when blowing snow saturates the air, to a point where measurement accuracy is an issue. Using the profile method, the measurement uncertainties are strongly amplified in case of strong wind. In such conditions, a single level bulk parameterization with surface energy balance closure as in the Crocus model is preferred. At D17, more than half of the total snow fall is removed by erosion and sublimation, both at the surface and, mainly, of airborne snow particles.
Programme: 411
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Gorodetskaya I V, Kneifel S, Maahn M, Van Tricht K, Schween J H, Crewell S, Van Lipzig N P M, . (2014). Cloud and precipitation properties from ground-based remote sensing instruments in East Antarctica
. The Cryosphere Discuss., 8(4), 4195–4241.
Abstract: A new comprehensive cloud-precipitation-meteorological observatory has been established at Princess Elisabeth base, located in the escarpment zone of Dronning Maud Land, East Antarctica. The observatory consists of a set of ground-based remote sensing instruments (ceilometer, infrared pyrometer and vertically profiling precipitation radar) combined with automatic weather station measurements of near-surface meteorology, radiative fluxes, and snow accumulation. In this paper, the observatory is presented and the potential for studying the evolution of clouds and precipitating systems is illustrated by case studies. It is shown that the synergetic use of the set of instruments allows for distinguishing ice, mixed-phase and precipitating clouds, including some information on their vertical extent. In addition, wind-driven blowing snow events can be distinguished from deeper precipitating systems. Cloud properties largely affect the surface radiative fluxes, with liquid-containing clouds dominating the radiative impact. A statistical analysis of all measurements (in total 14 months mainly occurring in summer/autumn) indicates that these liquid-containing clouds occur during as much as 20% of the cloudy periods. The cloud occurrence shows a strong bimodal distribution with clear sky conditions 51% of the time and complete overcast conditions 35% of the time. Snowfall occurred 17% of the cloudy periods with a predominance of light precipitation and only rare events with snowfall > 1 mm h-1 water equivalent (w.e.). Three of such intensive snowfall events occurred during 2011 contributing to anomalously large annual snow accumulation. This is the first deployment of a precipitation radar in Antarctica allowing to assess the contribution of the snowfall to the local surface mass balance. It is shown that on the one hand large accumulation events (>10 mm w.e. day-1) during the measurement period of 26 months were always associated with snowfall, but that on the other hand snowfall did not always lead to accumulation. In general, this promising set of robust instrumentation allows for improved insight in cloud and precipitation processes in Antarctica and can be easily deployed at other Antarctic stations.
Programme: 411
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