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  • Artikel  (9)
  • Artikel (Open Access)  (9)
  • Antarctica  (5)
  • Mixing  (4)
  • John Wiley & Sons  (8)
  • Copernicus  (1)
  • National Academy of Sciences
  • 2010-2014  (9)
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  • 1
    Publikationsdatum: 2017-04-04
    Beschreibung: During the 2007-2008 antarctic campaign, the Italian PNRA installed a Low Power Magnetometer within the framework of the AIMNet (Antarctic International Magnetometer Network) project, proposed and coordinated by BAS. The magnetometer is situated at Talos Dome, around 300 km geographically North-West from Mario Zucchelli Station (MZS), and approximately at the same geomagnetic latitude as MZS. In this work we present a preliminary analysis of the geomagnetic field 1-min data, and a comparison with simultaneous data from different Antarctic stations.
    Beschreibung: Published
    Beschreibung: Vienna, Austria
    Beschreibung: 1.6. Osservazioni di geomagnetismo
    Beschreibung: open
    Schlagwort(e): daily variation ; AIMNet project ; Antarctica ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: Poster session
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  • 2
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    John Wiley & Sons
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 1239–1256, doi:10.1002/jgrc.20138.
    Beschreibung: A three-dimensional circulation model with a relatively simple dissolved oxygen model is used to examine the role that physical forcing has on controlling hypoxia and anoxia in Chesapeake Bay. The model assumes that the biological utilization of dissolved oxygen is constant in both time and space, isolating the role that physical forces play in modulating oxygen dynamics. Despite the simplicity of the model, it demonstrates skill in reproducing the observed variability of dissolved oxygen in the bay, highlighting the important role that variations in physical forcing have on the seasonal cycle of hypoxia. Model runs demonstrate significant changes in the annual integrated hypoxic volume as a function of river discharge, water temperature, and wind speed and direction. Variations in wind speed and direction had the greatest impact on the observed seasonal cycle of hypoxia and large impacts on the annually integrated hypoxic volume. The seasonal cycle of hypoxia was relatively insensitive to synoptic variability in river discharge, but integrated hypoxic volumes were sensitive to the overall magnitude of river discharge at annual time scales. Increases in river discharge were shown to increase hypoxic volumes, independent from the associated biological response to higher nutrient delivery. However, increases in hypoxic volume were limited at very high river discharge because increased advective fluxes limited the overall length of the hypoxic region. Changes in water temperature and its control on dissolved oxygen saturation were important to both the seasonal cycle of hypoxia and the overall magnitude of hypoxia in a given year.
    Beschreibung: The funding for this research was obtained from NSF Grant OCE-0954690 and supported by NOAA via the U.S. IOOS Office (Award Numbers NA10NOS0120063 and NA11NOS0120141) and managed by the Southeastern Universities Research Association.
    Beschreibung: 2013-09-14
    Schlagwort(e): Hypoxia ; Stratification ; Mixing ; Wind
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 3
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 118 (2013): 2774–2792, doi:10.1002/jgrc.20217.
    Beschreibung: The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Mid-depth turbulent dissipation rates are found to increase from inline image in the Southeast Pacific to inline image in the Scotia Sea, typically reaching inline image within a kilometer of the seabed. Enhanced levels of turbulent mixing are associated with strong near-bottom flows, rough topography, and regions where the internal wavefield is found to have enhanced energy, a less-inertial frequency content and a dominance of upward propagating energy. These results strongly suggest that bottom-generated internal waves play a major role in determining the spatial distribution of turbulent dissipation in the ACC. The energy flux associated with the bottom internal wave generation process is calculated using wave radiation theory, and found to vary between 0.8 mW m−2 in the Southeast Pacific and 14 mW m−2 in the Scotia Sea. Typically, 10%–30% of this energy is found to dissipate within 1 km of the seabed. Comparison between turbulent dissipation rates inferred from finestructure parameterizations and microstructure-derived estimates suggests a significant departure from wave-wave interaction physics in the near-field of wave generation sites.
    Beschreibung: The DIMES experiment is supported by the Natural Environment Research Council (NERC) of the U.K. and U.S. National Science Foundation. K.L.S. and J.A.B. are supported by NERC.
    Beschreibung: 2013-12-04
    Schlagwort(e): Turbulent dissipation ; Internal wave ; Antarctic Circumpolar Current ; Mixing
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 4
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 118–130, doi:10.1029/2012JC008077.
    Beschreibung: Our understanding of past sea-ice variability is limited by the short length of satellite and instrumental records. Proxy records can extend these observations but require further development and validation. We compare methanesulfonic acid (MSA) and chloride (Cl–) concentrations from a new firn core from coastal West Antarctica with satellite-derived observations of regional sea-ice concentration (SIC) in the Amundsen Sea (AS) to evaluate spatial and temporal correlations from 2002–2010. The high accumulation rate (~39 g∙cm–2∙yr–1) provides monthly resolved records of MSA and Cl–, allowing detailed investigation of how regional SIC is recorded in the ice-sheet stratigraphy. Over the period 2002–2010 we find that the ice-sheet chemistry is significantly correlated with SIC variability within the AS and Pine Island Bay polynyas. Based on this result, we evaluate the use of ice-core chemistry as a proxy for interannual polynya variability in this region, one of the largest and most persistent polynya areas in Antarctica. MSA concentrations correlate strongly with summer SIC within the polynya regions, consistent with MSA at this site being derived from marine biological productivity during the spring and summer. Cl– concentrations correlate strongly with winter SIC within the polynyas as well as some regions outside the polynyas, consistent with Cl– at this site originating primarily from winter sea-ice formation. Spatial correlations were generally insignificant outside of the polynya areas, with some notable exceptions. Ice-core glaciochemical records from this dynamic region thus may provide a proxy for reconstructing AS and Pine Island Bay polynya variability prior to the satellite era.
    Beschreibung: This research was supported by an award from the Department of Energy Office of Science Graduate Fellowship Program (DOE SCGF) to ASC, a James E. and Barbara V. Moltz Research Fellowship to SBD, and by grants from NSF-OPP (#ANT-0632031 & #ANT-0631973); NSF-MRI (#EAR-1126217); NASA Cryosphere Program (#NNX10AP09G); and a WHOI Andrew W. Mellon Foundation Award for Innovative Research.
    Beschreibung: 2013-07-25
    Schlagwort(e): Sea ice ; Polynyas ; Antarctica ; Amundsen Sea ; Pine Island Bay ; Methanesulfonic acid
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 5
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 6148–6153, doi:10.1002/2013GL058138.
    Beschreibung: This study generates novel satellite-derived estimates of Antarctic-wide annual (1999–2009) surface meltwater production using an empirical relationship between radar backscatter from the QuikSCAT (QSCAT) satellite and melt calculated from in situ energy balance observations. The resulting QSCAT-derived melt fluxes significantly agree with output from the regional climate model RACMO2.1 and with independent ground-based observations. The high-resolution (4.45 km) QSCAT-based melt fluxes uniquely detect interannually persistent and intense melt (〉400 mm water equivalent (w.e.) year−1) on interior Larsen C Ice Shelf that is not simulated by RACMO2.1. This supports a growing understanding of the importance of a föhn effect in this region and quantifies the resulting locally enhanced melting that is spatially consistent with recently observed Larsen C thinning. These new results highlight important cryosphere-climate interactions and processes that are presently not fully captured by the coarser-resolution (27 km) regional climate model.
    Beschreibung: This research was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program (grant NNX12AO01H), the NASA Cryospheric Sciences Program (grant NNX10AP09G), and the NSF Antarctic Sciences Section (grant ANT-063203).
    Beschreibung: 2014-06-04
    Schlagwort(e): Antarctica ; Surface melt ; Ice shelves ; Remote sensing
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: text/plain
    Format: application/pdf
    Format: application/postscript
    Format: application/msword
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  • 6
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    John Wiley & Sons
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 118 (2013): 5322–5332, doi:10.1002/jgrc.20379.
    Beschreibung: By analyzing global data, we find that over large scales, surfaces of constant nitrate are often better aligned with isopycnals than with isobars, particularly below the euphotic zone. This is unexplained by the movement of isopycnal surfaces in response to eddies and internal waves, and is perhaps surprising given that the biological processes that alter nitrate distributions are largely depth dependent. We provide a theoretical framework for understanding the orientation of isonitrate surfaces in relation to isopycnals. In our model, the nitrate distribution results from the balance between depth-dependent biological processes (nitrate uptake and remineralization), and the along-isopycnal homogenization of properties by eddy fluxes (parameterized by eddy diffusivity). Where the along-isopycnal eddy diffusivity is relatively large, nitrate surfaces are better aligned with isopycnals than isobars. We test our theory by estimating the strength of the eddy diffusivity and biological export production from global satellite data sets and comparing their contributions. Indeed, we find that below the euphotic zone, the mean isonitrate surfaces are oriented along isopycnals where the isopycnal eddy diffusivity is large, and deviate where the biological export of organic matter is relatively strong. Comparison of nitrate data from profiling floats in different regions corroborates the hypothesis by showing variations in the nitrate-density relationship from one part of the ocean to another.
    Beschreibung: We acknowledge the support of the National Science Foundation (Grant OCE-0928617) and NASA (Grant NNX- 08AL80G).
    Beschreibung: 2014-04-15
    Schlagwort(e): Nitrate ; Export ; Mixing ; Isopycnal ; Alignment ; Large-scale
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 7
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 496-508, doi:10.1002/2013JC009346.
    Beschreibung: Observational studies have shown that an unprecedented warm anomaly has recently affected the temperature of the Atlantic Water (AW) layer lying at intermediate depth in the Arctic Ocean. Using observations from four profiling moorings, deployed in the interior of the Canada Basin between 2003 and 2011, the upward diffusive vertical heat flux from this layer is quantified. Vertical diffusivity is first estimated from a fine-scale parameterization method based on CTD and velocity profiles. Resulting diffusive vertical heat fluxes from the AW are in the range 0.1–0.2 W m−2 on average. Although large over the period considered, the variations of the AW temperature maximum yields small variations for the temperature gradient and thus the vertical diffusive heat flux. In most areas, variations in upward diffusive vertical heat flux from the AW have only a limited effect on temperature variations of the overlying layer. However, the presence of eddies might be an effective mechanism to enhance vertical heat transfer, although the small number of eddies sampled by the moorings suggest that this mechanism remains limited and intermittent in space and time. Finally, our results suggest that computing diffusive vertical heat flux with a constant vertical diffusivity of ∼2 × 10−6 m2 s−1 provides a reasonable estimate of the upward diffusive heat transfer from the AW layer, although this approximation breaks down in the presence of eddies.
    Beschreibung: C. Lique acknowledge support from JISAO and the Program on Climate Change of the University of Washington. J. Guthrie and J. Morison are supported by National Science Foundation grants ARC-0909408 and ARC-0856330. M. Steele is supported by the Office of Naval Researches Arctic and Global Prediction Program, by NSFs Division of Polar Programs, and by NASAs Cryosphere and Physical Oceanography programs. Support for the BGOS program and R. Krishfield was provided by the National Science Foundation (under grants ARC-0806115, ARC-0631951, ARC-0806306, and ARC-0856531) and Woods Hole Oceanographic Institution internal funding. For A. Proshutinsky, this research is supported by the National Science Foundation Office of Polar Programs, awards ARC-1203720 and ARC-0856531.
    Beschreibung: 2014-07-22
    Schlagwort(e): Arctic Ocean ; Atlantic water ; Mixing
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 8
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 6803–6810, doi:10.1002/2014GL061266.
    Beschreibung: We use autonomous gas measurements to examine the metabolic balance (photosynthesis minus respiration) of coastal Antarctic waters during the spring/summer growth season. Our observations capture the development of a massive phytoplankton bloom and reveal striking variability in pCO2 and biological oxygen saturation (ΔO2/Ar) resulting from large shifts in community metabolism on time scales ranging from hours to weeks. Diel oscillations in surface gases are used to derive a high-resolution time series of net community production (NCP) that is consistent with 14C-based primary productivity estimates and with the observed seasonal evolution of phytoplankton biomass. A combination of physical mixing, grazing, and light availability appears to drive variability in coastal Antarctic NCP, leading to strong shifts between net autotrophy and heterotrophy on various time scales. Our approach provides insight into the metabolic responses of polar ocean ecosystems to environmental forcing and could be employed to autonomously detect climate-dependent changes in marine primary productivity.
    Beschreibung: This study was supported by funds from the U.S. National Science Foundation (OPP awards ANT-0823101, ANT-1043559, ANT-1043593, and ANT-1043532) as well as support for PDT and ECA from the National Science and Engineering Research Council of Canada.
    Beschreibung: 2015-04-03
    Schlagwort(e): Photosynthesis ; Respiration ; Net community production ; DO2/Ar ; CO2 ; Antarctica
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 9
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Atmospheres 119 (2014): 9168–9182, doi:10.1002/2013JD020720.
    Beschreibung: The sources and transport pathways of aerosol species in Antarctica remain uncertain, partly due to limited seasonally resolved data from the harsh environment. Here, we examine the seasonal cycles of major ions in three high-accumulation West Antarctic ice cores for new information regarding the origin of aerosol species. A new method for continuous acidity measurement in ice cores is exploited to provide a comprehensive, charge-balance approach to assessing the major non-sea-salt (nss) species. The average nss-anion composition is 41% sulfate (SO42−), 36% nitrate (NO3−), 15% excess-chloride (ExCl−), and 8% methanesulfonic acid (MSA). Approximately 2% of the acid-anion content is neutralized by ammonium (NH4+), and the remainder is balanced by the acidity (Acy ≈ H+ − HCO3−). The annual cycle of NO3− shows a primary peak in summer and a secondary peak in late winter/spring that are consistent with previous air and snow studies in Antarctica. The origin of these peaks remains uncertain, however, and is an area of active research. A high correlation between NH4+ and black carbon (BC) suggests that a major source of NH4+ is midlatitude biomass burning rather than marine biomass decay, as previously assumed. The annual peak in excess chloride (ExCl−) coincides with the late-winter maximum in sea ice extent. Wintertime ExCl− is correlated with offshore sea ice concentrations and inversely correlated with temperature from nearby Byrd station. These observations suggest that the winter peak in ExCl− is an expression of fractionated sea-salt aerosol and that sea ice is therefore a major source of sea-salt aerosol in the region.
    Beschreibung: This work was supported by grants from the NSF Antarctic Program (0632031 and 1142166), NSF-MRI (1126217), the NASA Cryosphere Program (NNX10AP09G), and by an award from the Department of Energy Office of Science Graduate Fellowship Program (DOE SCGF) to ASC.
    Beschreibung: 2015-01-21
    Schlagwort(e): Antarctica ; Ice cores ; Biomass burning ; Sea ice ; Nitrate ; Acidity
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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