Ice Types 101

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 26^th. Photo credit: A. Margolin.

—Peter

PS – We would also like to note that Gianluca had his birthday during this project on February 10^th. 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/

Microbial Sampling for the TRACERS Project on the NBP

Working on behalf of Gerhard Herndl’s lab at the University of Vienna in Austria, Santiago Gonzalez and I are sampling the microbes in the water column as part of the TRACERS project.  Prokaryotic microbes (specifically bacteria and archaea) are present all throughout the water column in all the world’s oceans, with as many as millions of cells in a single milliliter of seawater at the surface and tens or hundreds of thousands at depth.  So there are lots and lots of microbes present, and we’re studying their role in the cycling of organic matter and nutrients.  As the phytoplankton responsible for photosynthesis in surface waters sink down into the water column, it’s the microbes that work to degrade and recycle this organic material and we expect the high flux of sinking particles following an algal bloom to provide lots of ‘food’ for the microbes down below.

Sampling seawater from the rosette, which can collect water at twenty different depths throughout the water column. From left to right: Dave, Cassandra, Sarah and Roberta collecting water, with Amanda and Christina in the background. Photo credit: A. Margolin.

When sampling from the Niskin bottles on the CTD, I first take small samples for determining the abundance of microbes in the water -- just a few milliliters of seawater are fixed with glutaraldehyde and then frozen.  We’ll ship these back to Vienna and count the prokaryotes and viruses in these samples using flow cytometry.  I then collect a much larger amount of seawater (usually ~10L) and filter it through a 0.2µm filter to collect the microbes in the water.  I store these filters in small tubes and freeze them, and will also send these back to Vienna.  Back in the lab there, we’ll extract the DNA from the microbes collected on the filter and use that DNA for various analyses like PCR, T-RFLP to determine community composition, cloning and sequencing of 16S rRNA genes, and qPCR of particular functional genes of interest.  This will give us an idea of what organisms are present in our samples, how the microbial communities differ at different depths and stations, and to some extent what metabolic capabilities these microbes have.  For all these analyses, I am just collecting the samples here at sea but most of the work will be done back home in Vienna.

The filtration setup in the Bio Lab that Roberta uses to collect particles from seawater samples, for the extraction of microbe DNA back in Vienna. Photo credit: R. Hansman.

On board, Santiago is working to make some metabolic rate measurements.  He collects seawater and then adds two different radioactively-labeled substrates (³H-leucine and ¹⁴C-bicarbonate) to separate samples that the microbes use in two different ways, either as heterotrophs (taking up ³H-leucine) or autotrophs (fixing ¹⁴C-bicarbonate).  After adding the substrates to a set volume of seawater and incubating the microbes in the seawater for a fixed amount of time at in situ temperature, he then filters these samples to collect the microbes on 0.2µm filters.  Any of the labeled substrates that were incorporated by the microbes are now part of cellular material that is collected on the filter.  By using a scintillation counter to determine the amount of radioisotope on each filter, he can calculate how much substrate was utilized.  And using the set volume and fixed incubation time, he can further calculate the rate of heterotrophic production (for the ³H-leucine samples) or autotrophy (for the ¹⁴C-bicarbonate samples).  Because the radioisotopes are considered hazardous, Santiago has special training to work with these materials and does all his work in an isolated container called the rad van located up on the helo deck of the NBP.

Santiago enjoying his work in the rad van. Photo credit: R. Hansman.

The incubators on the helo deck that Santiago uses. Photo credit: A. Margolin.

The helo deck, with the rad van and incubators. Photo credit: A. Margolin.

After the cruise, we’ll combine our data from sampling the microbes with the many other types of measurements also being done by other groups on board to help get a better picture of what’s happening in the Ross Sea.

--Roberta

P.S. Hello to Mrs. Hansman’s 3^rd grade class at Glen Arden Elementary!