Ice front blocking in a laboratory model of the Antarctic ice shelf

Mass loss from the Antarctic Ice Sheet to the ocean has increased in recent decades, largely because the thinning of its floating ice shelves has allowed the outflow of grounded ice to accelerate. Enhanced basal melting of the ice shelves is thought to be the ultimate driver of change, motivating a recent focus on the processes that control ocean heat transport onto and across the seabed of the Antarctic continental shelf towards the ice. However, the shoreward heat flux typically far exceeds that required to match observed melt rates, suggesting other critical controls. By laboratory experiments on the Coriolis rotating platform, we show that the depth-independent component of the flow towards an ice shelf is blocked by the dramatic step shape of the ice front, and that only the depth-varying component, typically much smaller, can enter the sub-ice cavity. These results are consistent with direct observations of the Getz Ice Shelf system, as shown by Wahlin et al. (Nature 2019, in press).

The selected data are velocity fields from a selection of 6 experiments, described in Wahlin et al. (2019), supplementary material, fig 4 and 9.

•   EXP26,30,34 correspond to Fig. 4 a,b,c respectively (barotropic case)
•   EXP44,50,51 correspond to Fig. 9 a,b,c respectively (baroclinic case)

The velocity fields are measured by PIV from short image series (bursts) obtained by laser sheet illumination in several quasi-horizontal planes (for Fig 4, N=12 planes vertically separated by 6.2 cm, with 25 images per level, for Fig 9, N=7 planes vertically separated by 5.8 cm, with 19 images per level). The quasi-horizontal planes are parallel to the channel, slanted downward toward the iceshelf with an angle of 1.15 degree.

For each experiment, the whole series of velocity fields is provided in /PCO1.png.sback.civ-PCO2.png.sback.civ.mproj (those are obtained by merging velocity fields from the images of two cameras denoted PCO1 and PCO2) velocity fields averaged inside each burst are provided in PCO1.png.sback.civ-PCO2.png.sback.civ.mproj.stat. Each velocity field is in a single netcdf file labeled by two indices denoting respectively the time and the index in the burst. Planes are scanned in a cyclic way, so that the same position is reached again after each increment of N in the first index.

The average of these averaged velocity fields over 4 volumes when the current is fully established are provided in PCO1.png.sback.civ-PCO2.png.sback.civ.mproj.stat.stat. Details of the set-up and experimental conditions are provided in http://servforge.legi.grenoble-inp.fr/projects/pj-coriolis-17iceshelf