False bottom (sea ice)

Being located under ice, false bottoms are not easy to investigate, and the current observations are quite variable.

[1] Both physical modelling[5][6] and in situ observations[7] suggest that false bottoms may decrease sea ice melt up to 8%.

[8] The salinity and temperature of under-ice meltwater and false bottoms are controlled by both ice melt and desalination.

[14] False bottoms may create errors in estimates of sea ice thickness from its draft measurements.

They can be investigated manually using ice coring and drilling,[1] hotwire thickness gauges[8] or remotely using underwater sonars.

[7] Ground-based upward-looking sonar cannot distinguish "normal" or parental sea ice from false bottoms.

Scheme of false bottom formed under sea ice [ 1 ]
Typical temperature profile of false bottom
False bottom coverage at the surface plot of sea ice draft estimated using multibeam sonar measurements
Areal coverage of false bottoms (blue-shaded areas) during MOSAiC expedition
Temporal evolution of false bottom thickness and salinity during MOSAiC expedition