Browsing by Subject "Antarctica"

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  • Tison, J. -L.; Schwegmann, S.; Dieckmann, G.; Rintala, J. -M.; Meyer, H.; Moreau, S.; Vancoppenolle, M.; Nomura, D.; Engberg, S.; Blomster, L. J.; Hendrickx, S.; Uhlig, C.; Luhtanen, A. -M.; de Jong, J.; Janssens, J.; Carnat, G.; Zhou, J.; Delille, B. (2017)
    Sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean. However, proper understanding of its annual impact on exchanges, and therefore potentially on the climate, notably suffer from the paucity of autumnal and winter data sets. Here we present the results of physical and biogeochemical investigations on winter Antarctic pack ice in the Weddell Sea (R. V. Polarstern AWECS cruise, June-August 2013) which are compared with those from two similar studies conducted in the area in 1986 and 1992. The winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southward from the open Southern Ocean. These conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover (brine tubes), favoring relatively high chlorophyll-a (Chl-a) concentrations. We discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions. Large-scale sea ice model simulations also suggest a context of increasingly deep snow, warm ice, and large brine fractions across the three observational years, despite the fact that the model is forced with a snowfall climatology. This lends support to the claim that more severe Antarctic sea ice conditions, characterized by a longer ice season, thicker, and more concentrated ice are sufficient to increase the snow depth and, somehow counterintuitively, to warm the ice.
  • Heinonen, Jussi S.; Luttinen, Arto V.; Spera, Frank J.; Bohrson, Wendy A. (2019)
    Karoo continental flood basalt (CFB) province is known for its highly variable trace element and isotopic composition, often attributed to the involvement of continental lithospheric sources. Here, we report oxygen isotopic compositions measured with secondary ion mass spectrometry for hand-picked olivine phenocrysts from similar to 190 to 180 Ma CFBs and intrusive rocks from Vestfjella, western Dronning Maud Land, that form an Antarctic extension of the Karoo province. The Vestfjella lavas exhibit heterogeneous trace element and radiogenic isotope compositions (e.g., epsilon(Nd) from -16 to +2 at 180 Ma) and the involvement of continental lithospheric mantle and/or crust in their petrogenesis has previously been suggested. Importantly, our sample set also includes rare primitive dikes that have been derived from depleted asthenospheric mantle sources (epsilon(Nd) up to + 8 at 180 Ma). The majority of the oxygen isotopic compositions of the olivines from these dike rocks (delta O-18 = 4.4-5.2%; Fo = 78-92 mol%) are also compatible with such sources. The olivine phenocrysts in the lavas, however, are characterized by notably higher delta O-18 (6.2-7.5%; Fo = 70-88 mol%); and one of the dike samples gives intermediate compositions (5.2-6.1%, Fo = 83-87 mol%) between the other dikes and the CFBs. The oxygen isotopic compositions do not correlate with radiogenic isotope compositions susceptible to crustal assimilation (Sr, Nd, and Pb) or with geochemical indicators of pyroxene-rich mantle sources. Instead, delta O-18 correlates positively with enrichments in large-ion lithophile elements (especially K) and Os-187. We suggest that the oxygen isotopic compositions of the Vestfjella CFB olivines primarily record large-scale subduction-related metasomatism of the sub-Gondwanan mantle (base of the lithosphere or deeper) prior to Karoo magmatism. The overall influence of such sources to Karoo magmatism is not known, but, in addition to continental lithosphere, they may be responsible for some of the geochemical heterogeneity observed in the CFBs.
  • Heinonen, Jussi S.; Luttinen, Arto V.; Whitehouse, M.J. (2018)
    Karoo continental flood basalt (CFB) province is known for its highly variable trace element and isotopic composition, often attributed to the involvement of continental lithospheric sources. Here, we report oxygen isotopic compositions measured with secondary ion mass spectrometry for hand-picked olivine phenocrysts from similar to 190 to 180 Ma CFBs and intrusive rocks from Vestfjella, western Dronning Maud Land, that form an Antarctic extension of the Karoo province. The Vestfjella lavas exhibit heterogeneous trace element and radiogenic isotope compositions (e.g., epsilon(Nd) from -16 to +2 at 180 Ma) and the involvement of continental lithospheric mantle and/or crust in their petrogenesis has previously been suggested. Importantly, our sample set also includes rare primitive dikes that have been derived from depleted asthenospheric mantle sources (epsilon(Nd) up to + 8 at 180 Ma). The majority of the oxygen isotopic compositions of the olivines from these dike rocks (delta O-18 = 4.4-5.2%; Fo = 78-92 mol%) are also compatible with such sources. The olivine phenocrysts in the lavas, however, are characterized by notably higher delta O-18 (6.2-7.5%; Fo = 70-88 mol%); and one of the dike samples gives intermediate compositions (5.2-6.1%, Fo = 83-87 mol%) between the other dikes and the CFBs. The oxygen isotopic compositions do not correlate with radiogenic isotope compositions susceptible to crustal assimilation (Sr, Nd, and Pb) or with geochemical indicators of pyroxene-rich mantle sources. Instead, delta O-18 correlates positively with enrichments in large-ion lithophile elements (especially K) and Os-187. We suggest that the oxygen isotopic compositions of the Vestfjella CFB olivines primarily record large-scale subduction-related metasomatism of the sub-Gondwanan mantle (base of the lithosphere or deeper) prior to Karoo magmatism. The overall influence of such sources to Karoo magmatism is not known, but, in addition to continental lithosphere, they may be responsible for some of the geochemical heterogeneity observed in the CFBs.
  • Pilla, Rachel M.; Mette, Elizabeth M.; Williamson, Craig E.; Adamovich, Boris V.; Adrian, Rita; Anneville, Orlane; Balseiro, Esteban; Ban, Syuhei; Chandra, Sudeep; Colom-Montero, William; Devlin, Shawn P.; Dix, Margaret A.; Dokulil, Martin T.; Feldsine, Natalie A.; Feuchtmayr, Heidrun; Fogarty, Natalie K.; Gaiser, Evelyn E.; Girdner, Scott F.; González, María J.; Hambright, K. David; Hamilton, David P.; Havens, Karl; Hessen, Dag O.; Hetzenauer, Harald; Higgins, Scott N.; Huttula, Timo H.; Huuskonen, Hannu; Isles, Peter D. F.; Joehnk, Klaus D.; Keller, Wendel Bill; Klug, Jen; Knoll, Lesley B.; Korhonen, Johanna; Korovchinsky, Nikolai M.; Köster, Oliver; Kraemer, Benjamin M.; Leavitt, Peter R.; Leoni, Barbara; Lepori, Fabio; Lepskaya, Ekaterina V.; Lottig, Noah R.; Luger, Martin S.; Maberly, Stephen C.; MacIntyre, Sally; McBride, Chris; McIntyre, Peter; Melles, Stephanie J.; Modenutti, Beatriz; Müller-Navarra, Dörthe C.; Pacholski, Laura; Paterson, Andrew M.; Pierson, Don C.; Pislegina, Helen V.; Plisnier, Pierre-Denis; Richardson, David C.; Rimmer, Alon; Rogora, Michela; Rogozin, Denis Y.; Rusak, James A.; Rusanovskaya, Olga O.; Sadro, Steve; Salmaso, Nico; Saros, Jasmine E.; Sarvala, Jouko; Saulnier-Talbot, Émilie; Schindler, Daniel E.; Shimaraeva, Svetlana V.; Silow, Eugene A.; Sitoki, Lewis M.; Sommaruga, Ruben; Straile, Dietmar; Strock, Kristin E.; Swain, Hilary; Tallant, Jason M.; Thiery, Wim; Timofeyev, Maxim A.; Tolomeev, Alexander P.; Tominaga, Koji; Vanni, Michael J.; Verburg, Piet; Vinebrooke, Rolf D.; Wanzenböck, Josef; Weathers, Kathleen; Weyhenmeyer, Gesa A.; Zadereev, Egor S.; Zhukova, Tatyana V. (Nature, 2021)
    Scientific Data 8 (2021), 200
    Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change.
  • Leppäranta, Matti; Luttinen, Arto; Arvola, Lauri (2020)
    Shallow Antarctic surface lakes belong to the most extreme aquatic environments on the Earth. In Vestfjella, proglacial surface lakes and ponds are characterized by a 2-5 month long period with liquid water and depths <2 m. We give a detailed description of nine seasonal lakes and ponds situating at three nunataqs (Basen, Plogen and Fossilryggen) in western Dronning Maud Land. Their physical and geochemical properties are provided based on observations in four summers. Three main 'lake categories' were found: 1) supraglacial lakes, 2) epiglacial ponds and 3) nunataq ponds. Category 3 lakes can be divided into two subgroups with regards to whether the meltwater source is glacial or just seasonal snow patches. Supraglacial lakes are ultra-oligotrophic (electrical conductivity <10 mu S cm(-1), pH <7), while in epiglacial ponds the concentrations of dissolved and suspended matter and trophic status vary over a wide range (electrical conductivity 20-110 mu S cm(-1), pH 6-9). In nunataq ponds, the maxima were an electrical conductivity of 1042 mu S cm(-1)and a pH of 10.1, and water temperature may have wide diurnal and day-to-day fluctuations (maximum 9.3 degrees C) because snowfall, snow drift and sublimation influence the net solar irradiance.
  • Ruosteenoja, Kimmo; Jylhä, Kirsti; Räisänen, Jouni; Mäkelä, Antti (2018)
    The commentators regard a categorical truncation of supersaturations with respect to ice in climate model output as an inappropriate solution to the supersaturation issue. This view is supported by observational evidence from the East Antarctic Plateau. We accept this criticism to a certain degree. Even so, it is necessary to make a clear distinction between the true supersaturations measured in the atmosphere and the spurious supersaturations existing in archived model output data sets: the latter result, for example, from inconsistencies in the interpolation of temperature and specific humidity to the near-surface level. In the CMIP5 model output data sets, the largest relative humidities in near-surface air are far above those observed. Moreover, supersaturations given at the 2-m height are generally much larger than those at the lowermost tropospheric isobaric levels. Projections of relative humidity for the future may be considerably distorted if founded on unmodified output data sets.
  • Evans, Claire; Brandsma, Joost; Meredith, Michael; Thomas, David Neville; Venables, Hugh; Pond, David; Brussaard, Corina (2021)
    The relative flow of carbon through the viral shunt and the microbial loop is a pivotal factor controlling the contribution of secondary production to the food web and to rates of nutrient remineralization and respiration. The current study examines the significance of these processes in the coastal waters of the Antarctic during the productive austral summer months. Throughout the study a general trend towards lower bacterioplankton and heterotrophic nanoflagellate (HNF) abundances was observed, whereas virioplankton concentration increased. A corresponding decline of HNF grazing rates and shift towards viral production, indicative of viral infection, was measured. Carbon flow mediated by HNF grazing decreased by more than half from 5.7 μg C L−1day−1 on average in December and January to 2.4 μg C L−1 day−1 in February. Conversely, carbon flow through the viral shunt increased substantially over the study from on average 0.9 μg C L−1day−1 in December to 7.6 μg C L−1 day−1 in February. This study shows that functioning of the coastal Antarctic microbial community varied considerably over the productive summer months. In early summer, the system favors transfer of matter and energy to higher trophic levels via the microbial loop, however towards the end of summer carbon flow is redirected towards the viral shunt, causing a switch towards more recycling and therefore increased respiration and regeneration.
  • Sinclair, V. A.; Dacre, H. F. (2019)
    Predicted changes in Southern Hemisphere (SH) precipitation and Antarctic ice mass correspond to variations in the meridional moisture flux (MMF). Thirty-five years of ERA-Interim reanalysis data are combined with an extratropical cyclone (ETC) identification and tracking algorithm to investigate factors controlling SH MMF variability in the midlatitudes and near Antarctica. ETC characteristics which exert the strongest control on ETC MMF are determined thus identifying which ETCs contribute most to SH moisture transport. ETC poleward propagation speed exerts the strongest control on the ETC MMF across the Antarctic coastline. In SH winter, ETCs with the largest poleward propagation speeds transport 2.5 times more moisture than an average ETC. In the midlatitudes, ETC genesis latitude and poleward propagation speed have a similar influence on ETC MMF. Surprisingly, ETC maximum vorticity has little control on ETC MMF. Cyclone compositing is used to determine the reasons for these statistical relationships. ETCs generally exhibit a dipole of poleward and equatorward MMF downstream and upstream of the cyclone center, respectively. However, ETCs with the largest poleward propagation speeds resemble open frontal waves with strong poleward moisture transport downstream of the cyclone center only and thus result in the largest MMF. These results suggest that inhomogeneous trends and predicted changes in precipitation over Antarctica may be due to changes in cyclone track orientation, associated with changes to the large-scale background flow, in addition to changes in cyclone number or intensity.