Extent is below whole record average but similar to 2007
A few plots of FFTs from JAXA data for Arctic Sea Ice extent data - only 10 years of data so FFT info is unreliable for periods of around a couple of years or more.
Data is daily (with a few infills).
I see no 28 day lunar events:
There are periods of:
652 day (possibly)
2 weeks (possibly)