And said ice functions as a barrier for the land ice, greatly slowing down its ability to progress into the ocean.
Also, it's an example of Bad Amateur Science that floating icebergs shed by glaciers don't affect sea level. What's true in the case of a glass of water in your kitchen is not true in the ocean. Freshwater ice, melted and diffused in seawater, results in an elevated sea level. It's a small impact (only about 3% that of land-based ice melting), but still meaningful.
Basically: a chunk of ice, floating in water, displaces its own weight in water. At 0C, Freshwater ice is .9167g/cc, and freshwater is 0.998g/cc. If 0.998g of freshwater (1cc) is displaced, then the volume of the ice is 0.998/0.9167cc, or 1.0887cc - 1cc below the waterline, 0.0887cc above it. As it melts, it shrinks back to 1cc, equaling the formerly displaced water.
Seawater at 0CC however is 1,028g/cc, aka 3% more. For a given amount of displacement, there's an extra 3% of freshwater ice volume and mass. This melts to a volume 3% larger than than the displaced volume.
Think of it using a extreme example. Pretend that neutron stars were stable containable liquids and not highly explosive condensed states maintained by gravity, and that you had a bucket containing a thin layer of it at the bottom. You fill the rest of the bucket with a giant chunk of ice. The neutron star "sea level" rise from having the ice atop it is basically immeasurable. That's your starting point. Now let the ice melt. Now the entire bucket is full of liquid. The "sea level" has risen dramatically.
Of course, it's even more complicated than this in reality, because you don't have a separation of saltwater and freshwater, but rather they merge, and the net density isn't exactly a linear weighted average between the two. Close, but not exactly.