The current green line, the border between thin and thicker sea ice

~Obviously, top of snow melts more when over thinner sea ice
~Let's take a look

 First we find ESA Maxima picture of the icescape.

Then we look at latest NASA EOSDIS greening of Arctic sea ice:

   With June 2 to 15 2018 animation we can clearly define deep greening zones from the colder highly reflective top white surface ....

   It seems all the Arctic Ocean changed colour, however basically where there is greater surface melting there is a stronger greening,  caused by water ponds, closely outlining the thicker sea ice areas. Ice having a colder core temperature allows top of snow to further resist melting surface temperatures,  top of snow temperature is a reflection of sea ice core minimum.   We can see here the rough outline of beginning of August open water limits,  deeply influenced by thick ice in great part created by Gyre circulation compaction.

2012 to 2018 comparison

     At same June 15 date, 2012 sea ice melt was stronger in the Beaufort,  but 2018 Bering Sea open water is much more prominent:

    Along  North of Russia 2018 has a greater ongoing melt ,  despite 2012 and 18 deeper greening being similar,  but with 18 having more open water,  one must factor the clouds as having an impact over true colours.    2012 can be recognized by next to Wrangle Island open spot.

WD June 17 2018