Missing citation for sea ice thickness plots

We don't have a citation for the observations used in the sea-ice thickness plots.  The ones for the Arctic are perhaps the same as the citation we have for the NH time series of sea-ice volume (but perhaps not).

For Antarctica, a likely candidate is:
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2012JC008141
https://earth.gsfc.nasa.gov/cryo/data/antarctic-sea-ice-thickness