I thought most of the ice was under the surface of the sea!…..Tip of the iceberg!  Water expands when it freezes, so if it melts, sea levels will drop. 🤔
		
		
	 
An ice berg floats because as the water freezes it expands which reduces its density and thus increases its buoyancy.  The tip of the iceberg  represents the excess buoyancy of the iceberg.
However when a fully  floating iceberg melts,  the H20 increases its density and thus the melted iceberg would assume exactly the same volume as the submerged part of the frozen iceberg,  so there would be no  change in the depth of the water.
You  can prove this with a glass water add an ice cube and mark the depth of water. Recheck when the ice cube has melted -  no  change.
The difference with ice from the Antarctica and other  land based glaciers is these masses are on land presently  above mean sea level,  and any  melt  water  finds its way into the sea which adds to the  volume of the sea,  so the sea level must  rise to accommodate it just as OC stated in #125
Whilst  the above summarises the general  effect  well  enough, The reality  is a little more complex,  becasue most  glacial ice pure water H2O,  but  sea water has  natural  salt and a splattering  of other  minerals in it which  gives it a slightly  different  density.  Coupled with different  temperatures between the sea water  and ice melt,  the ice melt water will often sink to the bottom and not  mix immediately with the salt water above. Not  only  is ice  melt  raising  average sea levels,  but  it  is cooling the  sea bed eco system an creating  different  underwater currents which  is changing the water heat energy  conveyer distribution  across our oceans.