The article is actually talking about volcanic activity building things up. I.e. active volcanoes building up relative to the seafloor immediately around them.

The article is actually talking about volcanic activity building things up. I.e. active volcanoes building up relative to the seafloor immediately around them. Isostatic rebound is also occurring for the overall area, though. It's just a smaller effect (millimeters to centimeters per year) vs the meters to hundreds of meters that can occur from an eruption. (For those who don't know, isostatic rebound is occurring for large areas where the ice sheets were very thick during the last ice age. The lithosphere (rigid portion of the earth) "flexed" downward as a result, and it's currently still flexing back now that the ice is gone. The mantle has a very high viscosity, though, and needs to "flow" into the space as the lithosphere flexes back. That means it's a process that takes tens of thousands of years to equalize. "Flow" is in quotes, because most folks don't think of solids flowing. The mantle is solid rock, but solid rock does flow.)