When talking about the sea and
ice, one can easily think of Kate Winslet and Leonardo DiCaprio standing on the
bow of RMS Titanic as it meets its
destiny in the shape of an iceberg in North Atlantic, or Bering Sea fishermen
dodging ice floes to catch snow crab, or Happy Feet dancing his way to
happiness. But ice is more than a
mere backdrop to a movie or TV show, it defines the environment that we study
and shapes the world that we live in.
It is home to a multitude of creatures ranging from penguins (in
Antarctica) to polar bears, walrus, narwhal and beluga (in the Arctic). In Antarctica, the formation of sea-ice
around Antarctica during winter doubles the size of the Antarctic
continent. Yet ice on the ocean is
simply not a big chunk of frozen seawater and not all ice on the ocean is
sea-ice. There are a variety of
names given to different types of sea-ice and different ice features. And we’ll get back to the ice on the
ocean that is not sea-ice!
Sea-ice formation starts with the
formation of small ice crystals called frazil ice. If the sea is calm, the
frazil ice congeles into a thin film called grease ice, so named because it has the appearance of an oil
slick on the sea surface. As the
grease ice film grows, it thickens into a thin ice sheet called nilas. Wind
and currents can push the nilas sheets on to each other in a process called rafting. As the
nilas ice thickens, it becomes congelation ice. If the
sea is rough, the frazil ice is pushed together to form circular shaped pancake
ice (or simply pancakes). If
the wave action is strong enough, the pancakes can be rafted together. Eventually, the pancakes freeze together
to form an ice sheet called consolidated pancake ice. On
this trip, we have seen lots of pancake ice.
Small
pancakes (up to 1 foot, or 30 cm, in diameter) with a thick slurry of
frazil ice between them, or as someone on the boat described it, pancakes and
syrup! Photo credit: P. Lee.
The newly formed sea-ice sheets
are under constant pressure from winds and currents. These pressures result in fracturing of the ice sheet. The broken sheets are pushed backed
together and pile on top of each other creating a pressure ridge. The
part of the ridge above the sea surface is called the sail, and the part below the sea surface is called the keel. If the
ice is grounded on the on the sea floor then it is said to be fast-ice. Ice
that does not melt during the following summer and survives into the next
winter (or beyond) is called multiyear ice. Chunks of ice that
protrude up to 3 feet (1 m) above the sea surface are called growlers. They
get their name from the (animal-like) growling sound that they occasionally
make as trapped air escapes when they melt. Next on the size scale are bergy bits, which rise 3-12 feet (1-4 m) out of the water. Because of their relatively low
profile, bergy bits have a small radar cross-section and can be difficult to
see, making them a hazard to shipping (even icebreakers are on constant lookout
for them and avoid them whenever possible!). Anything bigger than 12 feet (4 m) is called a floeberg.
A
tabular iceberg that was once part of the nearby Ross Ice Shelf. Photo
credit: A. Margolin.
What about the ice on the ocean
that is not sea-ice you ask?
Icebergs, which are synonymous with polar oceans and the source of
Titanic’s demise, are in fact formed from freshwater and not seawater. Icebergs start as snow falling in the
mountains that accumulates to eventually become glaciers. As with all ice formation, any salts
present are expelled from the freshly formed ice but in the case of glaciers,
extra time and pressure causes more impurities to be forced from the ice,
leaving the characteristic “crystal clear” blue color associated with glaciers
and icebergs. When the glaciers
slide down hill and finally reach the ocean, they break off (or calve) to form an iceberg.
A
small iceberg surrounded by a mixture of multiyear-ice growlers and first year
ice. Photo credit: P. Lee.
A
mixture of frazil ice, pancakes, growlers, bergy bits and icebergs near Cape
Washington. The clouds billowing from Cape Washington are in fact blowing snow
from near hurricane force katabatic winds! Photo credit: A. Lee.
But perhaps the most important
type of ice is not the ice that occurs outside and all around the Nathaniel
B. Palmer, but inside our steel home away
from home. It comes in three basic
forms, tubs, bars and homemade. Yes, I speak of none
other than ice cream! Whether as
an Almond Magnum Bar or stirred up in a bowl, its morale-boosting properties
are undeniable! With a compliment
of 55 crew and scientists onboard for a 53-day expedition, there will be a few
birthday celebrations along the way and nothing says Happy Birthday like an
ice-cream cake! Enjoy!!
A
batch of morale-boosting mint chocolate-chip ice cream is whipped up by Amy,
Christina and Julia as Alexander documents the experience! Photo credit: A.
Margolin.
Julia, Amy and Jacob
enjoy some of the freshly-made liquid nitrogen ice cream after Jack gave his
approval. Photo credits: A. Margolin.
David
enthusiastically cuts his ice cream birthday cake before eating half of it for
lunch on February 26th. Photo credit: A. Margolin.
—Peter
PS – We would also like to note
that Gianluca had his birthday during this project on February 10th.
We all plan to buy him many beers in Punta Arenas to celebrate properly once we
arrive… which is only one month away from today!!! ALSO, check out Cassandra’s
new post! Here’s the link: http://newswatch.nationalgeographic.com/2013/02/28/a-gift-of-an-antarctic-sunset-and-the-start-of-a-long-dark-winter/
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