Icebergs: carbon offsetters?

Yes: it may be true'; while warming may increase iceberg formation, it could be that the bergs generate enough life-related activity to offset some carbon:

Icebergs that break off Antarctica and drift away are hotspots of life and may help reduce the amount of carbon dioxide in the world's atmosphere ... The icebergs hold nutrients that they release far out to sea as they melt, sustaining a community of seabirds, krill, fish and phytoplankton spread over a radius of up to two miles around each one.

I guess the issue is how much. Well,

Based on their new understanding, they estimate icebergs are raising the biological productivity of nearly 40% of the Weddell Sea's area.

Unfortunately, I don't know what that means in relation to the wider global carbon scene, but I'll keep an eye open for it.