Beautiful Icebergs provide photo opportunities
March 27, 2009
Sea temperature: -1.2°C
Air temperature: -4°C
Today began as one of the chilliest yet, with a -23°C wind chill, but
the colder, drier air and peeks of sunlight were a welcome relief from
the foggy and wet days that have been more common.
The next iceberg target continues to elude the research team. We’ve been
pursuing possible icebergs identified through satellite measurements,
but we can’t see until we arrive whether the satellite image is a large
iceberg or a conglomeration of many small icebergs and pack ice. We also
have been on the lookout opportunistically for icebergs smaller than
satellites can detect, but that are at least a few kilometers long.
Today we investigated several potential targets and passed through an
area with more icebergs than we’ve seen yet—affording many photo
opportunities—but none was large enough or isolated enough for study.
Layers of white and blue show seasonal freeze/thaw cycles in
this iceberg fragment.
Photo by Debbie Nail Meyer
The icebergs and growlers that we passed today have been many shapes,
sizes, and color variations. White, blue, green, and streaks of brown
make each one unique. An iceberg’s life cycle determines many of these
characteristics as it drifts through the sea. Flat, tabular icebergs
break off (calve) from the Antarctic ice shelf and begin with this
composition and structure. Accumulation, freezing, and melting cycles
can be seen as annual layers on icebergs. The freeboard of an iceberg,
the part that can be seen above the water, is mostly compressed snow or
ice particles and air, giving the iceberg its overall white color. Solid
ice is formed tens of meters under the snow where high pressure
compresses air bubbles so completely that air no longer scatters light,
resulting in a blue color. This compressed air is sealed from the
atmosphere and is what scientists measure in ice cores to learn about
the Earth’s atmosphere thousands of years ago.
Some iceberg fragments reveal liquid blue colors.
Photo by Debbie Nail Meyer
Veins of gray are crushed rock materials from the continent that were
incorporated into the parent ice shelf. Stripes can form where meltwater
from the surface freezes into cracks and crevices, with colors dependent
on its composition. Browns and greens come from biological organisms.
Green ice forms when algae-rich seawater freezes along the ice shelf
where the iceberg originated or from pools created as the iceberg melts;
this process results in blue colors if the freezing seawater lacks algae.
As icebergs melt and break apart, shapes change and color variations are
revealed. Waves can carve out hollows and arches, and smaller icebergs
can even be tumbled by rough seas like boulders in a river. Seeing the
range of iceberg shapes and colors today was a reminder that the large,
flat icebergs targeted in this study may conceal an inner beauty under
layers of white.
— Debbie Nail Meyer