The calving process results in ice already floating in water moving. Archimedes' law means the effect is very limited ~ the height the ice sticks above the surface and the little change in density.
More importantly, the article mentions removing annual effects on Polar Motion. They are averaging - somehow - to look at permanent changes. The annual effects may be an order of magnitude greater, it is not relevant.
More importantly, the article mentions removing annual effects on Polar Motion. They are averaging - somehow - to look at permanent changes. The annual effects may be an order of magnitude greater, it is not relevant.