On Friday, 27 February 2015 17:49:38 UTC, General wrote:
Just idle curiosity, but can anyone who understands these things kindly
explain:

If I look at the map of _Antarctic_ sea ice (not the graph, the map) at:

http://nsidc.org/arcticseaicenews/

then I'm looking at the Ross Sea - the major inlet right below the S pole:

1. What is the mass of ice apparently floating away from the continent - it
looks huge but completely unconnected to and some considerable distance from
the nearest coastline.

I can't see and Antarctic sea ice on the page you linked but this map shows the current state of sea ice in the Antarctic.
http://polar.ncep.noaa.gov/seaice/sh.html

The mass you mention is an island of sea ice that has formed during the SH summer melt.

2. What's happened to the Ross Ice Shelf? Isn't that meant to fill a large
area of the Ross Sea? But the median extent line for what is presumably the
minimum ice extent at about this time of year shows largely open water for
the Ross Sea. Or is the ice shelf drawn to be part of the Antarctic land
mass in this presentation?

Yes, the ice shelf is mapped as part of the Antarctic land mass. Sea ice is a few feet thick and reforms each year. Ice shelves are about 1000 feet or more thick.

(Not uninteresting looking at this map: much of the slight excess of
Antarctic sea ice seems to concentrated in the Weddell Sea for some reason,
whereas the coastal area from the Peninsula round to the Ross Sea seems well
below 'normal'. Looks like a very marked change away from the median
distribution, or is this just a one-year picture - ie every year shows a
different distribution and this just happens to be the picture this year?)

The Weddell Sea is sheltered from the circumpolar current by the Antarctic Penisula so the sea-ice melt is less there.

On the map I linked you can animate the last month of sea ice and sea that island form. You can also click to see the se-ice this time last year.