There also seems to be a fair chunk gone from that region towards the bottom left. Is that significant?

Haven't read all comments but I came to this study through the Guardian online. I punted a question to Dr Shakhova and received a helpful reply. The gist is that the Siberian continental margin contains a lot of coal and this, along with geothermal heat is producing heat from below. And specifically that groundwater provides a significant mechanism for melting from below. It may be that if sediments are sufficiently continuous, permafrost melting may reach through to this groundwater and cause circulation from the surface to the bottom of the underwater permafrost layer. Then you'd have melting from top and bottom. This may be a quicker process than simply warming seas would suggest.

Interestingly enough the southern UK has had its first decent summer since the melt started in earnest in 2007 or so. Maybe the weather conditions have changed this year. Any thoughts on the summer where everyone else is? PS in your poll I reckoned on a less than severe melt this year. Just wait till WUWT wakes out of his coma!