Winter growth and tidal variability of the sub-ice platelet layer observed with electromagnetic induction soundings

• Main Authors: Brett, Gemma M., Leonard, Gregory H., Rack, Wolfgang, Haas, Christian, Langhorne, Patricia J., Irvin, Anne
• Format: Text
• Language: English
• Published: 2021
• Subjects: McMurdo Sound; Ross Ice Shelf; Ice Shelf
• Online Access: https://doi.org/10.5194/tc-2021-61; https://tc.copernicus.org/preprints/tc-2021-61/

Here, we present the first electromagnetic induction time-series measurements of ice shelf-influenced fast ice and sub-ice platelet layer thickness over winter and in late spring in McMurdo Sound. Significant increases in sub-ice platelet layer thickness (~0.5–1 m) co-occurred with strong southerly wind events and satellite-observed polynya activity suggesting wind-driven surface circulation of supercooled Ice Shelf Water outflow from the McMurdo-Ross ice shelf cavity. Temporal variability observed in sub-ice platelet layer thickness on diurnal timescales correlated with tidally-induced current patterns previously observed in McMurdo Sound. The thickness of the sub-ice platelet layer increased on spring and neap ebb tides corresponding with northward currents circulating out from the ice shelf cavity. The late spring spatial distributions of first-year and second-year fast ice and sub-ice platelet layer thickness in McMurdo Sound were assessed with drill hole and electromagnetic induction surveys and were comparable to a previous four-year dataset. We resolved second-year fast ice thicknesses of 4 m with a substantial sub-ice platelet layer beneath of up to 11 m using electromagnetic induction techniques suggesting that the longer temporal persistence of the two-year-old fast ice allowed a substantially thicker sub-ice platelet layer to form. The variability observed in the sub-ice platelet layer indicates that a combination of the tides, wind-driven polynya activity and the presence of multi-year ice influences the circulation of Ice Shelf Water in the upper surface ocean and consequently sub-ice platelet layer formation over a range of timescales.