And no, the graph presented does not apply to melt. During melt times, there is the Sun, which is very, very major factor - deciding factor; there is secondary heat from the Sun - re-radiated by air, by GHGs in the air, by water in any currents which go directly under the ice and even - to lesser extent, - from deeper yet warm currents (Gulfstream remains in the Arctic are known to get somewhat deep at places, for example), etc. Melt is happening completely differently. It's more like "pulsing mode", instead of "rapid first, slows to crawl later" or "crawl first, accelerates to rapid melt later". There is, if you will, "breathing" when Arctic melts - it goes in somewhat rhytmic big chunks, quite often. The main "initiating melt" mechanic is, afaik, warm water and air currents (significantly above 0C), which "intrude" into cold enough "so far" areas. Air currents warm them up to the point of melt ponds on the surface (albedo plummets - direct insolation starts to work full-time). Water currents warm them up "from below", decreasing thickness of ice and fragmenting ice fields into "chunks", with bits and pieces of open water (which does not refreeze as long as warm water current is there), and then the more open water there is, the more direct sunlight absorbtion kicks in. When strong warm air and water currents "attack" an ice-covered region, it often "bursts" into open water incredibly fast. If it's clear sky and the time is May...August, then it can be amazingly fast.