I’ve confirmed that there was a non-reproducible error of some sort in the original 01deg_jra55v140_iaf_cycle4 experiment, so it’s the ocean data that’s bad, not the sea ice.
The difference starts as a very small perturbation, so as far as I can see the ocean data is still credible (a different sample from the same statistical distribution in this turbulent flow). We probably should retain this data despite this flaw, as it has been used in publications such as @LaurieM’s. This is an analogous situation to the glitch in 01deg_jra55v140_iaf_cycle3, which affected all subsequent runs.
It’s unclear as yet what field had the initial error. sea_level first loses reproducibility on 2011-09-27 (almost the end of the run starting 2011-07-01). Other fields would also have lost reproducibility by that time, due to sea_level being coupled directly or indirectly to everything else.