[wonderer (OP)]

I understand that if the arctic sea ice were to melt from general climate change, it would be accompanied by the melting of ice on land as well causing a general rise in sea levels.

However, I understand that water is one of the few substances we know of that grows as it freezes and shrinks as it melts, so if by some means we melted JUST the arctic sea ice would there be a measurable change in sea levels?

Maybe someone put a big parabolic mirror in space to focus extra sunlight onto the arctic ice cap for instance, or a bunch of boats go up with blow torches... Regardless of the mechanism, would sea levels drop measurably (and by how much) or is there some balancing act that happens due to the fact that a small portion of the ice currently floats above the water line that would cancel out?  Does the salinity of seawater cause the ice to float higher than we would otherwise expect (in the way that people are extra buoyant in the Dead Sea)?  Would the salinity of global oceans change appreciably?  Would that cause a further difference in results as the ice continued to melt and completed melting?

Thanks for your thoughts!

[alancalverd]

Since the arctic land ice is mostly surrounded by sea ice, all of which is below 0°C, land ice cannot run off into the sea, or indeed anywhere, until all the sea ice has melted.

As the sea ice is below the maximum density temperature for water, and floating on water, melting sea ice will initially decrease sea levels.

However the concept of "sea level" is pretty meaningless in this context. Mariners are interested in local tides, which vary by anything up to 40 ft in a day and are different every day, and aviators use a nominal mean sea level as a reference ± 1 ft or so to ensure vertical separation and reasonably smooth landings - and in seismically active areas we resurvey the runway every few months. Since the solid crust is moving all the time (up to 50 m in a few seconds at the Fukushima epicenter) any better accuracy can only be obtained by radar altimetry and GPS, which need to be reviewed daily. So the question is "sea level relative to what?"