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  1. Article: Turbulence Observations Beneath Larsen C Ice Shelf, Antarctica

    Davis, Peter E.D. / Nicholls, Keith W.

    Journal of geophysical research. 2019 Aug., v. 124, no. 8

    2019  

    Abstract: Increased ocean‐driven basal melting beneath Antarctic ice shelves causes grounded ice to flow into the ocean at an accelerated rate, with consequences for global sea level. The turbulent transfer of heat through the ice shelf‐ocean boundary layer is ... ...

    Abstract Increased ocean‐driven basal melting beneath Antarctic ice shelves causes grounded ice to flow into the ocean at an accelerated rate, with consequences for global sea level. The turbulent transfer of heat through the ice shelf‐ocean boundary layer is critical in setting the basal melt rate, yet the processes controlling this transfer are poorly understood and inadequately represented in global climate models. This creates large uncertainties in predictions of future sea level rise. Using a hot‐water drilled access hole, two turbulence instrument clusters (TICs) were deployed 2.5 and 13.5 m beneath Larsen C ice shelf in December 2011. Both instruments returned a yearlong record of turbulent velocity fluctuations, providing a unique opportunity to explore the turbulent processes within the ice shelf‐ocean boundary layer. Although the scaling between the turbulent kinetic energy (TKE) dissipation rate and mean flow speed varies with distance from the ice shelf base, at both TICs the TKE dissipation rate is balanced entirely by the rate of shear production. The freshwater released by basal melting plays no role in the TKE balance. When the upper TIC is within the log‐layer, we derive an under‐ice drag coefficient of 0.0022 and a roughness length of 0.44 mm, indicating that the ice base is smooth. Finally, we demonstrate that although the canonical three‐equation melt rate parameterization can accurately predict the melt rate for this example of smooth ice underlain by a cold, tidally forced boundary layer, the law of the wall assumption employed by the parameterization does not hold at low flow speeds.
    Keywords climate ; cold ; drag coefficient ; freshwater ; geophysics ; heat ; ice ; ice shelf ; kinetic energy ; research ; roughness length ; sea level ; turbulent flow ; Antarctic region ; Antarctica
    Language English
    Dates of publication 2019-08
    Size p. 5529-5550.
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 161667-5
    ISSN 2169-9291 ; 2169-9275 ; 0148-0227 ; 0196-2256
    ISSN (online) 2169-9291
    ISSN 2169-9275 ; 0148-0227 ; 0196-2256
    DOI 10.1029/2019JC015164
    Database NAL-Catalogue (AGRICOLA)

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  2. Article ; Online: Observations of Modified Warm Deep Water Beneath Ronne Ice Shelf, Antarctica, From an Autonomous Underwater Vehicle

    Davis, Peter E. D. / Jenkins, Adrian / Nicholls, Keith W. / Dutrieux, Pierre / Schröder, Michael / Janout, Markus A. / Hellmer, Hartmut H. / Templeton, Rob / McPhail, S. D.

    Journal of Geophysical Research: Oceans. 2022 Nov., v. 127, no. 11 p.e2022JC019103-

    2022  

    Abstract: Filchner‐Ronne Ice Shelf (FRIS) is the world's largest ice shelf by volume. It helps regulate Antarctica's contribution to global sea level rise, and water mass transformations within the sub‐ice‐shelf cavity produce globally important dense water masses. ...

    Abstract Filchner‐Ronne Ice Shelf (FRIS) is the world's largest ice shelf by volume. It helps regulate Antarctica's contribution to global sea level rise, and water mass transformations within the sub‐ice‐shelf cavity produce globally important dense water masses. Rates of ice shelf basal melting are relatively low, however, as the production of cold (−1.9°C) and dense High Salinity Shelf Water over the Weddell Sea continental shelf isolates the ice shelf from large‐scale inflow of warm water. Nevertheless, a narrow inflow of relatively warm (−1.4°C) Modified Warm Deep Water (MWDW) that hugs the western flank of Berkner Bank is observed to reach Ronne Ice Front, although the processes governing its circulation and fate remain uncertain. Here we present the first observations taken within the ice shelf cavity along this warm water inflow using the Autosub Long Range autonomous underwater vehicle. We observe a core of MWDW with a south‐westward velocity of 4 cm s⁻¹ that reaches at least 18 km into the sub‐ice cavity. The hydrographic properties are spatially heterogeneous, giving rise to temporal variability that is driven by tidal advection. The highest rates of turbulent dissipation are associated with the warmest MWDW, with the vertical eddy diffusivity reaching 10⁻⁴ m² s⁻¹ where the water column is fully turbulent. Mixing efficiency is close to the canonical value of 0.2. Modeling studies suggest MWDW may become the dominant water mass beneath FRIS in our changing climate, providing strong motivation to understand more fully the dynamics of this MWDW inflow.
    Keywords advection ; climate ; cold ; continental shelf ; diffusivity ; geophysics ; ice ; ice shelf ; motivation ; research ; salinity ; sea level ; temporal variation ; Antarctica
    Language English
    Dates of publication 2022-11
    Publishing place John Wiley & Sons, Ltd
    Document type Article ; Online
    Note JOURNAL ARTICLE
    ZDB-ID 161667-5
    ISSN 2169-9291 ; 2169-9275 ; 0148-0227 ; 0196-2256
    ISSN (online) 2169-9291
    ISSN 2169-9275 ; 0148-0227 ; 0196-2256
    DOI 10.1029/2022JC019103
    Database NAL-Catalogue (AGRICOLA)

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  3. Article: Propagation and Vertical Structure of the Tidal Flow in Nares Strait

    Davis, Peter E. D. / Johnson, Helen L. / Melling, Humfrey

    Journal of geophysical research. 2019 Jan., v. 124, no. 1

    2019  

    Abstract: The southward freshwater flux through Nares Strait is an important component of the Arctic's freshwater budget. On short time scales, flow through the strait is dominated by the tides, and tidal dynamics may be important for the magnitude of the ... ...

    Abstract The southward freshwater flux through Nares Strait is an important component of the Arctic's freshwater budget. On short time scales, flow through the strait is dominated by the tides, and tidal dynamics may be important for the magnitude of the freshwater flux over longer periods. Here we build upon our existing knowledge of the tides in the region by exploring their propagation and vertical structure using data from four bottom‐mounted Acoustic Doppler Current Profilers deployed in Nares Strait between 2003 and 2006. We observe that propagating barotropic semidiurnal tidal waves interact to create a standing wave pattern, explaining the abnormally large tidal amplitudes that are observed in this region. In the along‐strait direction, semidiurnal tidal currents exhibit strong variations with depth. In contrast, the diurnal tides propagate northward through the strait as progressive waves, and the tidal currents are broadly depth invariant. Proximity of Nares Strait to the semidiurnal critical latitude and the topographical restriction imposed by the steep side wall of Ellesmere Island are primary drivers behind the observed vertical variability. In the upper part of the water column, baroclinic activity increases the tidal current amplitude by up to 25%. In the across‐strait direction, a two‐layer structure exists in both the diurnal and semidiurnal tidal flow, with a phase lag of approximately a quarter of a tidal cycle across the strait for the semidiurnal tide. Our results suggest that strong vertical motion exists against the side walls of Nares Strait, as the across‐strait flow interacts with the steeply sloping bathymetry.
    Keywords acoustics ; freshwater ; geophysics ; latitude ; research ; tides ; Arctic region
    Language English
    Dates of publication 2019-01
    Size p. 281-301.
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 161667-5
    ISSN 2169-9291 ; 2169-9275 ; 0148-0227 ; 0196-2256
    ISSN (online) 2169-9291
    ISSN 2169-9275 ; 0148-0227 ; 0196-2256
    DOI 10.1029/2018JC014122
    Database NAL-Catalogue (AGRICOLA)

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  4. Article ; Online: Observed interannual changes beneath Filchner-Ronne Ice Shelf linked to large-scale atmospheric circulation.

    Hattermann, Tore / Nicholls, Keith W / Hellmer, Hartmut H / Davis, Peter E D / Janout, Markus A / Østerhus, Svein / Schlosser, Elisabeth / Rohardt, Gerd / Kanzow, Torsten

    Nature communications

    2021  Volume 12, Issue 1, Page(s) 2961

    Abstract: Floating ice shelves are the Achilles' heel of the Antarctic Ice Sheet. They limit Antarctica's contribution to global sea level rise, yet they can be rapidly melted from beneath by a warming ocean. At Filchner-Ronne Ice Shelf, a decline in sea ice ... ...

    Abstract Floating ice shelves are the Achilles' heel of the Antarctic Ice Sheet. They limit Antarctica's contribution to global sea level rise, yet they can be rapidly melted from beneath by a warming ocean. At Filchner-Ronne Ice Shelf, a decline in sea ice formation may increase basal melt rates and accelerate marine ice sheet mass loss within this century. However, the understanding of this tipping-point behavior largely relies on numerical models. Our new multi-annual observations from five hot-water drilled boreholes through Filchner-Ronne Ice Shelf show that since 2015 there has been an intensification of the density-driven ice shelf cavity-wide circulation in response to reinforced wind-driven sea ice formation in the Ronne polynya. Enhanced southerly winds over Ronne Ice Shelf coincide with westward displacements of the Amundsen Sea Low position, connecting the cavity circulation with changes in large-scale atmospheric circulation patterns as a new aspect of the atmosphere-ocean-ice shelf system.
    Language English
    Publishing date 2021-05-20
    Publishing country England
    Document type Journal Article
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-021-23131-x
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Suppressed basal melting in the eastern Thwaites Glacier grounding zone.

    Davis, Peter E D / Nicholls, Keith W / Holland, David M / Schmidt, Britney E / Washam, Peter / Riverman, Kiya L / Arthern, Robert J / Vaňková, Irena / Eayrs, Clare / Smith, James A / Anker, Paul G D / Mullen, Andrew D / Dichek, Daniel / Lawrence, Justin D / Meister, Matthew M / Clyne, Elisabeth / Basinski-Ferris, Aurora / Rignot, Eric / Queste, Bastien Y /
    Boehme, Lars / Heywood, Karen J / Anandakrishnan, Sridhar / Makinson, Keith

    Nature

    2023  Volume 614, Issue 7948, Page(s) 479–485

    Abstract: Thwaites Glacier is one of the fastest-changing ice-ocean systems in ... ...

    Abstract Thwaites Glacier is one of the fastest-changing ice-ocean systems in Antarctica
    Language English
    Publishing date 2023-02-15
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 120714-3
    ISSN 1476-4687 ; 0028-0836
    ISSN (online) 1476-4687
    ISSN 0028-0836
    DOI 10.1038/s41586-022-05586-0
    Database MEDical Literature Analysis and Retrieval System OnLINE

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    In stock of ZB MED Cologne/Königswinter

    Zs.A 26: Show issues Location:
    Je nach Verfügbarkeit (siehe Angabe bei Bestand)
    bis Jg. 1994: Bestellungen von Artikeln über das Online-Bestellformular
    Jg. 1995 - 2021: Lesesall (1.OG)
    ab Jg. 2022: Lesesaal (EG)
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  6. Article: Variability in Basal Melting Beneath Pine Island Ice Shelf on Weekly to Monthly Timescales

    Davis, Peter E. D. / Jenkins, Adrian / Nicholls, Keith W. / Brennan, Paul V. / Abrahamsen, E. Povl / Heywood, Karen J. / Dutrieux, Pierre / Cho, Kyoung‐Ho / Kim, Tae‐Wan

    Journal of geophysical research. 2018 Nov., v. 123, no. 11

    2018  

    Abstract: Ocean‐driven basal melting of Amundsen Sea ice shelves has triggered acceleration, thinning, and grounding line retreat on many West Antarctic outlet glaciers. Here we present the first year‐long (2014) record of basal melt rate at sub‐weekly resolution ... ...

    Abstract Ocean‐driven basal melting of Amundsen Sea ice shelves has triggered acceleration, thinning, and grounding line retreat on many West Antarctic outlet glaciers. Here we present the first year‐long (2014) record of basal melt rate at sub‐weekly resolution from a location on the outer Pine Island Ice Shelf. Adjustment of the upper thermocline to local wind forced variability in the vertical Ekman velocity is the dominant control on basal melting at weekly to monthly timescales. Atmosphere‐ice‐ocean surface heat fluxes or changes in advection of modified Circumpolar Deep Water play no discernible role at these timescales. We propose that during other years, a deepening of the thermocline in Pine Island Bay driven by longer timescale processes may have suppressed the impact of local wind forcing on high‐frequency upper thermocline height variability and basal melting. This highlights the complex interplay between the different processes and their timescales that set the basal melt rate beneath Pine Island Ice Shelf.
    Keywords advection ; geophysics ; ice shelf ; research ; sea ice ; wind ; Antarctic region
    Language English
    Dates of publication 2018-11
    Size p. 8655-8669.
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 161667-5
    ISSN 2169-9291 ; 2169-9275 ; 0148-0227 ; 0196-2256
    ISSN (online) 2169-9291
    ISSN 2169-9275 ; 0148-0227 ; 0196-2256
    DOI 10.1029/2018JC014464
    Database NAL-Catalogue (AGRICOLA)

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