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.