AD 2017 Q4

Divers often have to wait their turn
to use the dive holes, as Weddell
seals (Leptonychotes weddellii) refill
their lungs for another breath-hold
dive under the ice
by five different manufacturers, and we collected data
following every dive.
On the surface, we assembled the rebreathers and
performed predive tasks under differing conditions.
At one end of the spectrum, we used heated shelters;
at the other extreme, we pretested the units outdoors
in the wind and ambient temperature (cold!). Based
on this experience, we conducted all subsequent
preparation in shelters and conducted dives from dive
shelters erected over the dive holes.
The best part of the project was the diving. We
conducted all the dives on the ice covering the Ross
Sea. The ice averaged about 8 feet thick in the locations
we dived. While our primary focus was on the
equipment and its performance, we had plenty of time
to enjoy other aspects of the environment around us.
Our dives begin by descending through a vertical
shaft 4 feet in diameter, a hole in the ice drilled from
the surface using a giant auger.
As I slide out the bottom of the shaft, a white ceiling
stretches out to infinity. The first thing that strikes
me upon emerging is the visibility — gazing in any
direction I can easily see more than 500 feet.
Everything is a shade of blue. The cerulean ice exhibits
a multitude of hues as the 24-hour sunlight filters down
through varying thicknesses of snow and solid ice. Azure
cracks shine in the gloom where the ice plates meet.
Brinicles (brine icicles) extend from the ceiling,
sometimes reaching 30 feet toward the bottom. These
hollow stalactitelike features form as seawater freezes,
extruding salts and forming freshwater ice (seawater
freezes at a lower temperature than freshwater). It is
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