Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

Author ORCID Identifier

Timothy Hodson:https://orcid.org/0000-0003-0962-5130

Publication Title

Journal of Geophysical Research: Oceans

ISSN

21699275

E-ISSN

21699291

Document Type

Article

Abstract

Mass loss from the Antarctic ice sheet is sensitive to conditions in ice shelf grounding zones, the transition between grounded and floating ice. To observe tidal dynamics in the grounding zone, we moored an ocean pressure sensor to Ross Ice Shelf, recording data for 54 days. In this region the ice shelf is brought out of hydrostatic equilibrium by the flexural rigidity of ice, yet we found that tidal pressure variations at a constant geopotential surface were similar within and outside of the grounding zone. This implies that the grounding zone ocean cavity was overpressurized at high tide and underpressurized at low tide by up to 10 kPa with respect to glaciostatic pressure at the ice shelf base. Phase lags between ocean pressure and vertical ice shelf motion were tens of minutes for diurnal and semidiurnal tides, an effect that has not been incorporated into ocean models of tidal currents below ice shelves. These tidal pressure variations may affect the production and export of meltwater in the subglacial environment and may increase basal crevasse heights in the grounding zone by several meters, according to linear elastic fracture mechanics. We find anomalously high tidal energy loss at the K1 constituent in the grounding zone and hypothesize that this could be explained by seawater injection into the subglacial environment at high tide or internal tide generation through interactions with topography. These observations lay the foundation for improved representation of the grounding zone and its tidal dynamics in ocean circulation models of sub–ice shelf cavities.

Publication Date

4-1-2020

DOI

10.1029/2019JC015562

Keywords

ice fracture, Ross Ice Shelf, Ross Sea, subglacial hydrology, tide, Whillans Ice Stream

Department

Department of Geology and Environmental Geosciences

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