|
|
Tournadre Jean, Girard-Ardhuin Fanny, Legrésy Benoit, . (2012). Antarctic icebergs distributions, 20022010
. Journal of Geophysical Research: Oceans, 117(C5), C05004–.
Abstract: Interest for icebergs and their possible impact on southern ocean circulation and biology has increased during the recent years. While large tabular icebergs are routinely tracked and monitored using scatterometer data, the distribution of smaller icebergs (less than some km) is still largely unknown as they are difficult to detect operationally using conventional satellite data. In a recent study, Tournadre et al. (2008) showed that small icebergs can be detected, at least in open water, using high resolution (20 Hz) altimeter waveforms. In the present paper, we present an improvement of their method that allows, assuming a constant iceberg freeboard elevation and constant ice backscatter coefficient, to estimate the top-down iceberg surface area and therefore the distribution of the volume of ice on a monthly basis. The complete Jason-1 reprocessed (version C) archive covering the 20022010 period has been processed using this method. The small iceberg data base for the southern ocean gives an unprecedented description of the small iceberg (100 m2800 m) distribution at unprecedented time and space resolutions. The iceberg size, which follows a lognormal distribution with an overall mean length of 630 m, has a strong seasonal cycle reflecting the melting of icebergs during the austral summer estimated at 1.5 m/day. The total volume of ice in the southern ocean has an annual mean value of about 400 Gt, i.e., about 35% of the mean yearly volume of large tabular icebergs estimated from the National Ice Center database of 19792003 iceberg tracks and a model of iceberg thermodynamics. They can thus play a significant role in the injection of meltwater in the ocean. The distribution of ice volume which has strong seasonal cycle presents a very high spatial and temporal variability which is much contrasted in the three ocean basins (South Atlantic, Indian and Pacific oceans). The analysis of the relationship between small and large (>5 km) icebergs shows that a majority of small icebergs are directly associated with the large ones but that there are vast regions, such as the eastern branch of the Wedell Gyre, where the transport of ice is made only through the smaller ones.
Keywords: altimetry, climatology, freshwater, icebergs, 0732 Icebergs, 0758 Remote sensing,
Programme: 1050
|
|
|
|
Gouttevin I, Menegoz M, Dominé F, Krinner G, Koven C, Ciais P, Tarnocai C, Boike J, . (2012). How the insulating properties of snow affect soil carbon distribution in the continental pan-Arctic area
. Journal of Geophysical Research: Biogeosciences, 117(G2), G02020–.
Abstract: We demonstrate the effect of an ecosystem differentiated insulation by snow on the soil thermal regime and on the terrestrial soil carbon distribution in the pan-Arctic area. This is done by means of a sensitivity study performed with the land surface model ORCHIDEE, which furthermore provides a first quantification of this effect. Based on field campaigns reporting higher thermal conductivities and densities for the tundra snowpack than for taiga snow, two distributions of near-equilibrium soil carbon stocks are computed, one relying on uniform snow thermal properties and the other using ecosystem-differentiated snow thermal properties. Those modeled distributions strongly depend on soil temperature through decomposition processes. Considering higher insulation by snow in taiga areas induces warmer soil temperatures by up to 12 K in winter at 50 cm depth. This warmer soil signal persists over summer with a temperature difference of up to 4 K at 50 cm depth, especially in areas exhibiting a thick, enduring snow cover. These thermal changes have implications on the modeled soil carbon stocks, which are reduced by 8% in the pan-Arctic continental area when the vegetation-induced variations of snow thermal properties are accounted for. This is the result of diverse and spatially heterogeneous ecosystem processes: where higher soil temperatures lift nitrogen limitation on plant productivity, tree plant functional types thrive whereas light limitation and enhanced water stress are the new constrains on lower vegetation, resulting in a reduced net productivity at the pan-Arctic scale. Concomitantly, higher soil temperatures yield increased respiration rates (+22% over the study area) and result in reduced permafrost extent and deeper active layers which expose greater volumes of soil to microbial decomposition. The three effects combine to produce lower soil carbon stocks in the pan-Arctic terrestrial area. Our study highlights the role of snow in combination with vegetation in shaping the distribution of soil carbon and permafrost at high latitudes.
Keywords: Arctic, land-surface model, permafrost, snow, snow insulation, soil carbon, 0414 Biogeochemical cycles, processes, and modeling, 0475 Permafrost, cryosphere, and high-latitude processes, 1622 Earth system modeling,
Programme: 1042
|
|
|
|
Ferrari Ramiro, Provost Christine, Renault Alice, Sennéchael Nathalie, Barré Nicolas, Park Young-Hyang, Lee Jae Hak, . (2012). Circulation in Drake Passage revisited using new current time series and satellite altimetry: 1. The Yaghan Basin
. JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 117(C12).
Keywords: 4512 Currents, 4515 Deep recirculations, 4520 Eddies and mesoscale processes, 4528 Fronts and jets, 4532 General circulation, Antarctic circumpolar current, current meter mooring, Drake Passage, eddies, meanders, Yaghan Basin,
Programme: 1061
|
|
|
|
H. W. Jacobi, D. Voisin, J. L. Jaffrezo, J. Cozic, T. A. Douglas. (2012). Chemical composition of the snowpack during the OASIS spring campaign 2009 at Barrow, Alaska (Vol. 117).
Abstract: The chemical composition of the seasonal snowpack was determined close to Barrow, an Arctic coastal location in northern Alaska. One hundred and twelve samples of different snow types including fresh snow, surface hoar, diamond dust, blowing snow, rounded snow grains, and depth hoar were collected and analyzed for major sea salt components, bromide, and nitrate. Sodium, chloride, sulfate, and potassium are mainly introduced into the snowpack by the deposition of sea salt, while magnesium and calcium result from a combination of sea salt and dust. Sulfate was strongly depleted in most samples compared to other sea salt components. This is attributed to the precipitation of mirabilite in newly formed sea ice and frost flowers that leads to an efficient fractionation of sulfate. Uptake of volatile but soluble species from the gas phase also contributed to the observed chloride, sulfate, and nitrate in the snow. However, for chloride and sulfate the input from the marine sources was overwhelming and the uptake from the gas phase was only visible in the samples with low concentrations like fresh snow, diamond dust, and surface hoar. Nitrate concentrations in the snowpack were less variable and for aged snow nitrate was related to the specific surface area of the snow indicating the adsorption of nitric acid can be an important nitrate source in the aged snow. Bromide was also introduced into the snowpack from marine sources, but due to its high reactivity it was partly transferred back to the atmosphere in the form of reactive species. The result of these processes was evident in bromide concentrations, which were both enriched and depleted at the snowpack surface while deeper layers were mostly depleted. Blowing snow also exhibited a depleted bromide composition. For all compounds except nitrate, many depth hoar samples exhibited the greatest concentrations, probably as a result of higher input earlier in the season as well as increases due to the sublimation of water during the metamorphism of the snow.
Keywords: Alaska Arctic Barrow Chemistry Snow
Programme: 1017
|
|
|
|
Jean-Luc Baray, Valentin Duflot, Françoise Posny, Jean-Pierre Cammas, Anne M. Thompson, Franck Gabarrot, Jean-Louis Bonne, Guang Zeng. (2012). One year ozonesonde measurements at Kerguelen Island (49.2°S, 70.1°E): Influence of stratosphere-to-troposphere exchange and long-range transport of biomass burning plumes (Vol. 117).
Abstract: We analyze a 1 year campaign of 17 ozonesondes launched in 2008–2009 at Kerguelen Island (49.2°S, 70.1°E), the first such soundings performed at this location. Tropospheric ozone presents a large variability in austral summer (December to February) and austral winter (June to September). The baseline tropospheric ozone is higher in winter (between 30 and 50 ppbv) than in summer (between 20 and 40 ppbv). We compare these observations to a data set obtained during the same period at Lauder (45.0°S, 169.7°E), which presents a marked seasonal pattern. The analysis of trajectory runs and reanalysis output help identify two significant contributors to the tropospheric ozone level at Kerguelen: the stratosphere-to-troposphere air mass transport and the long-range transport of biomass burning plumes. The stratosphere-to-troposphere transport is exemplified by a case study of a dry and enriched ozone layer over Kerguelen (70 ppbv at an altitude of 6 km on 28 February 2009). Using Lagrangian model simulations, we show that wintertime enhancement of the tropospheric ozone baseline can be partially attributed to the long-range transport of ozone precursors from biomass burning plumes originating in southern America and Africa. However, owing to limited data and to the many factors that can cause this wintertime baseline ozone enhancement, further investigations are needed to fully explain it. Additional measurements are also needed to establish an ozone climatology, to further characterize the ozone annual cycle and wintertime enhancement, and to better compare Kerguelen with other midlatitude sites.
Keywords: stratosphere to troposphere exchange tropospheric ozone
Programme: 109
|
|
|
|
Ponchon A, Grémillet D, Christensen-Dalsgaard S, Erikstad K E, Barrett R T, Reiertsen T K, McCoy K D, Tveraa T, Boulinier T, . (2014). When things go wrong: intra-season dynamics of breeding failure in a seabird
. Ecosphere, 5(1), art4–.
Abstract: During breeding, long-lived species face important time and energy constraints that can lead to breeding failure when food becomes scarce. Despite the potential implications of intra-season dynamics in breeding failure for individual behavior, carry-over effects, dispersal decisions and population dynamics, little information is currently available on these dynamics at fine temporal scales. Here, we monitored the foraging behavior and the proportion of successful black-legged kittiwake pairs from nest construction to chick fledging in a colony of the southern Barents Sea, to relate foraging effort to the dynamics of breeding failure over an entire breeding season, and to infer the environmental conditions leading to this failure. Specifically, we tracked kittiwakes with GPS and satellite tags during incubation and early chick-rearing to document nest attendance, foraging range, time budgets and daily energy expenditures (DEE). We also monitored diet changes over time. We predicted that breeding failure would follow a non-linear trend characterized by a break point after which breeding success would drop abruptly and would be related to a substantial increase in foraging effort. Kittiwakes showed contrasting foraging patterns between incubation and chick-rearing: they extended their foraging range from 20 km during incubation to more than 450 km during chick-rearing and switched diet. They also increased their DEE and readjusted their time budgets by increasing time spent at sea. These changes corresponded to a break point in breeding dynamics beyond which the proportion of successful pairs abruptly dropped. At the end of the season, less than 10% of kittiwake pairs raised chicks in the monitored plots. This integrative study confirms that breeding failure is a non-linear process characterized by a threshold beyond which individuals face an energetic trade-off and cannot simultaneously sustain high reproductive and self-maintenance efforts. In this way, the occurrence of sudden environmental changes complicates our ability to predict population dynamics and poses conservation challenges.
Programme: 333
|
|
|
|
Hindell Mark A., McMahon Clive R., Bester Marthán N., Boehme Lars, Costa Daniel, Fedak Mike A., Guinet Christophe, Herraiz-Borreguero Laura, Harcourt Robert G., Huckstadt Luis, Kovacs Kit M., Lydersen Christian, McIntyre Trevor, Muelbert Monica, Patterson Toby, Roquet Fabien, Williams Guy, Charrassin Jean-Benoît. (2016). Circumpolar habitat use in the southern elephant seal: implications for foraging success and population trajectories. Ecosphere, 7(5).
|
|
|
|
Mathilde Poirier, Dominique Fauteux, Gilles Gauthier, Florent Domine, Jean-François Lamarre. (2021). Snow hardness impacts intranivean locomotion of arctic small mammals (Vol. 12).
Abstract: Fossorial locomotion is often considered as the most energetically costly of all terrestrial locomotion. Small arctic rodents, such as lemmings, dig tunnels not only in the soil but also through the snowpack, which is present for over 8 months of the year. Lemmings typically dig in the softest snow layer called the depth hoar but with climate change, melt-freeze and rain-on-snow (ROS) events are expected to increase in the Arctic, leading to a higher frequency of hardened snowpacks. We assessed the impacts of snow hardness on the locomotion of two lemming species showing different morphological adaptations for digging. We hypothesized that an increase in snow hardness would (1) decrease lemming performance and (2) increase their effort while digging, but those responses would differ between lemming species. We exposed four brown lemmings (Lemmus trimucronatus) and three collared lemmings (Dicrostonyx groenlandicus) to snow of different hardness (soft, hard, and ROS) during 30-min trials (n = 63 trials) in a cold room and filmed their behavior. We found that the digging speed and tunnel length of both species decreased with snow hardness and density, underlining the critical role of snow properties in affecting lemming digging performance. During the ROS trials, time spent digging by lemmings increased considerably and they also started using their incisors to help break the hard snow, validating our second hypothesis. Overall, digging performance was higher in collared lemmings, the species showing more morphological adaptations to digging, than in brown lemmings. We conclude that the digging performance of lemming is highly dependent on snowpack hardness and that the anticipated increase in ROS events may pose a critical energetic challenge for arctic rodent populations.
Keywords: Arctic burrowing behavior digging fossorial hardness lemming locomotion rain-on-snow rodent snow subnivean tunnel
Programme: 1042
|
|
|
|
Van de Vijver Bart, . (2014). Four Achnanthidium species (Bacillariophyta) formerly identified as Achnanthidium minutissimum from the Antarctic Region
. 2118-9773 , 79(79), 1–19.
Abstract: Four taxa belonging to the complex of species around Achnanthidium minutissimum were found during the ongoing taxonomic revision of the Antarctic freshwater and limno-terrestrial diatom flora. Two taxa were previously described as Achnanthidium lailae and A. sieminskae . Two others were formerly identified as A. minutissimum but detailed light and scanning electron microscopical observations revealed sufficient morphological differences compared to the type of A. minutissimum , to justify their separation and description as new taxa: Achnanthidium indistinctum and A. maritimo-antarcticum . The morphology and ecology of all four taxa are discussed comparing the species with morphologically similar taxa. The biogeographical consequences of the splitting of the former A. minutissimum complex in the Antarctic Region are discussed.
Keywords: Achnanthidium, Antarctic Region, Bacillariophyta, biogeography, new species,
Programme: 136
|
|
|
|
Barbora Chattová, Marc Lebouvier, Myriam De Haan, Bart Van de Vijver. (2017). The genus Luticola (Bacillariophyta) on Ile Amsterdam and Ile Saint-Paul (Southern Indian Ocean) with the description of two new species.
Abstract: Five species of the terrestrial diatom genus Luticola D.G.Mann were found during a taxonomic survey of two small volcanic islands, Ile Amsterdam and Ile Saint-Paul (Southern Indian Ocean). Apart from the two already known Luticola species L. beyensii Van de Vijver et al. and L. subcrozetensis Van de Vijver et al., two new species are described: L. ivetana Chattová & Van de Vijver sp. nov. and L. vancampiana Chattová & Van de Vijver sp. nov. Finally, one, up to now unknown, Luticola species is briefly discussed and illustrated. Detailed morphological descriptions of these taxa are provided based on both light and scanning electron microscopy observations. Morphological features of the new species are compared to morphologically similar taxa, and notes on their ecology and biogeography are added.
Keywords: Bacillariophyta diatoms Luticola morphology new species
Programme: 136
|
|
