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https://doi.org/10.5194/tc-2020-249
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-249
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  12 Oct 2020

12 Oct 2020

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This preprint is currently under review for the journal TC.

Dynamics of Large Pelagic Ice Crystals in an Antarctic Ice Shelf Water Plume Flowing Beneath Land-Fast Sea Ice

Craig Stevens1,2, Natalie Robinson1, Gabby O'Connor2, and Brett Grant1 Craig Stevens et al.
  • 1National Institute of Water and Atmospheric Research, Greta Point, Wellington, New Zealand
  • 2University of Auckland, New Zealand

Abstract. Observations of boundary-layer processes and ice crystal behaviour in an outflow region from the Ross/McMurdo Ice Shelves are presented. From a fast ice field camp, we captured the kinematics of free-floating relatively large (many 10s of mm in scale) ice crystals that were advecting as well as aggregating in a depositional layer on the sea ice underside (SIPL, sub-ice platelet layer). Simultaneously, we measured the background oceanic temperature, salinity, currents and turbulence structure. At the camp location the total water depth was 536 m, with the uppermost 50 m being in-situ super-cooled. Tidal flow speeds had an amplitude of around 0.1 m s−1 and the resulting under-ice boundary layer sustained turbulent dissipation rates as large as ϵ = 10−6 W kg−1. Acoustic sampling (200 kHz) identified three classes of backscatter (1) large individual highly mobile targets, (2) echoes from large, individually identifiable suspended crystals and (3) a varying background, presumably of very small (frazil) crystals. This second class of backscatter was associated with crystal sizes far larger than typical, certainly larger than anything normally described as frazil, and some individuals at least were depositing close to fully grown. Measurement indicated crystal scales of the range 30–80 mm. The existence and settlement of this scale of crystal has implications for understanding SIPL evolution and the processes controlling the fate of Ice Shelf Water.

Craig Stevens et al.

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Craig Stevens et al.

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Latest update: 25 Oct 2020
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Short summary
Along Antarctica's coastal margin melting ice shelves create plumes of very cold sea water. In some circumstances the water is so cold that ice crystals exist in suspension. We present evidence from near the McMurdo Ice Shelf of ice crystals far larger than normal (by an order of magnitude or more). The crystal behaviour is examined by combining measurements of the crystal motion with ocean flow and turbulence data. This helps us make links between ice shelf melting and sea ice formation.
Along Antarctica's coastal margin melting ice shelves create plumes of very cold sea water. In...
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