Just a stupid question: What is counted as Antarctic Sea Ice?
1. We have a lot of thin floes of sea ice (mostly 1-year ice), some of them packed together by winds or currents, but principally mobile
2. We have fast ice around the coast of the continent and between the coastline and the little islands around Antarctica, some of it grounded to submarine hills
3. We have large broken-off ice bergs (originating from shelves or fast ice), some of them dozens of km² large, floating around and slowly melting
4. We have ice shelves (like Ross, Rønne/Filchner, Getz, Larsen) etc.
The latter one do probably not count into "Antarctic Sea Ice", even thogh there is water beneath them. What is with fast ice?
M understanding is that:
-Sea ice is frozen sea water.
- Ice formed by freezing freshwater (mostly snowfall) is not.
So, in theory,
- if the origin of the ice is the sea, it is sea ice,
- if the origin of the ice is from land / snow, it is not sea ice.
In practice, 1. and 2. are sea ice.
3. , the bergs, even though they are mostly frozen freshwater, are included as how can the satellites cope with hundreds, thousands, of moving objects? I wonder if berg A-68 (5,000 km2) is masked out? But with sea ice in the range from 2 to 20 million, and daily ice loss of around 200,000 or more per day at the moment, it is not significant.
4. The ice shelves are frozen freshwater formed from glaciers moving into the ocean plus a few 10s of thousands of years of snowfall on top. I wonder if some have sea ice at their base from when they first formed?
Both NSIDC and JAXA use a mask to exclude the continent and the ice shelves from the measurements.