Arctic sea ice extent meltdown

Arctic sea ice extent meltdown has come 9% of the way from Winter Maximum to a Blue Ocean Event per April 6th. The lowest extent year ever, 2016, by the same date, was at 5%.

Q: Where’s the data source for this plot?
A: Here: https://ads.nipr.ac.jp/vishop/#/extent
Q: How can anyone know if there is a Blue Ocean Event?
A: Easy. Use a computer. If you have less than 1 million km² sea ice extent in the Arctic, then you have a Blue Ocean Event.
Q: Why would I even do that?
A: Let’s say you want to know when the Arctic Ocean goes ice–free. Basing this on satellite measurements instead of gut feeling makes your conversations more interesting.