2012 Annual Report - Jesus College - University of Cambridge

38 MEMOIR I Jesus College Annual Report 2012
scouting the immediate surroundings for
leads through the ice, and reading the sky for
darker shades where there may be distant
open water. Sometimes we used pick axes
ahead of the ship and – what was much more
fun – dynamite. After several days in the pack
we became beset near 77°S. It was the
furthest south Shackleton had reached, on
this same course, locked in the ice from
which he never recovered the ship. Our
instructions from the Royal Society read:
‘find a site for a fixed observatory south of 75°
in the Vahsel Bay area of the Weddell Sea’.
So no time was lost in setting out extra
charges of dynamite to gain our release from
the ice and to turn back north, searching the
coastline for a landing site.
Pack ice, is the frozen surface of the sea
comprising floes, large and small, with
occasional leads of open water where the floes
part, or pressure ridges where compressive
forces bring the floes together. The outer
parts of the pack break up in the summer,
drift north, and melt. Sea ice which is several
years old may be many metres thick and, if
attached to the ‘land’, is known as fast ice.
Falling snow inland, on the continent,
compacts over many years, forming firn, and
reaching depths in the Antarctic which
completely obliterate the topography of the
native rock. Then the gradual discharge of the
ice from the centre of the continent to the
coastline is on a very broad front in the form
of an ice sheet which thins as it creeps towards
the coast. If this sheet floats out over the sea,
as much of it does in Antarctica, it is known