[Xelom]

Then does this mean these volcanoes will slowly shrink the size of the ocean which might contribute to raising sea levels on top of melting glaciers?

[colechristensen]

No.

Land moves around, raises and lowers, plates crash lifting mountains and subduct continents under each other so stuff moves, but stuff goes up and down at the same time. Sometimes the land sinks, sometimes it's pushed up, but these geological processes happen on geological time. Sea level rise is a concern within a few human generations.

These are just much different time and volume scales.

[pulvinar]

It would be extremely unlikely. Instead, it should be close to equilibrium, with as many eroding away as being created.

[1propionyl]

Wouldn't erosion tend to lag exposure by something like an order of magnitude or five? Geological time vs climate time.

That said, I'd also point out that most of these are deep enough we wouldn't see them exposed even if ocean levels dropped a meter worldwide.

[louthy]

Surely the magma, once cooled, would take less physical space than when hot?

[codybontecou]

Wouldn't it just displace the water?

[theelous3]

Yes? That is exactly the commenters concern. Fill a bowl to the brim with water, throw a ball in. It spills over the edges of the bowl by "just displacing" the water.