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Students predict what will happen when salt water is frozen. Will the ice be salty or fresh? Experimentation and a study of the plight of the crew of the Jeannette will bring home the right answer.

Students will learn that through experimentation disaster could have been avoided. They will also learn about the physical chemistry of sea ice and its formation.

Grade Level/Discipline
Middle School/ Earth Science/ Physical Science

Students will use inquiry and good experimental technique to get the answer to a problem, an answer which may surprise them.

National Standards
UCP1,2,5:: A1,2; B 1,2,3; C 4, 5; E 1,2; F 3,5; G 1,2,3.

Teacher Preparation for Activity


Cake pans in which water will be frozen, beakers, salt, water, balances, graduated cylinders, freezer space, world map.

Optional are Seatest Salinity measuring devices available at tropical fish stores, CBL devices, salinity titration equipment.

Pre-activity set-up
The teacher should assemble the lab materials.

Time Frame
Two periods and internet research time.

Teaching Sequence

Engagement and Exploration (Student Inquiry Activity)
Teacher should use a map for the little lecture on the Jeannette Expedition below.

Read or recite the history of the Jeannette below:

The Jeannette (http://www.uss-salem.org/danfs/steamers/jeannett.txt) left San Francisco in July,1879. Her mission was to sail through the Bering Sea to the Arctic Ocean and then to sail to the North Pole. Her captain, U.S. Navy Lt. George Washington DeLong, believed that this was possible thinking that a warm water part of the Kuroshio current should keep the pack ice from forming along his route. He was wrong, and after twenty months frozen in the ice pack, the Jeannette was crushed by sea ice . Later her wreckage was found 135 degrees to the east in Baffin Bay. This astounding find caused Nansen to believe that if he had a ship able to withstand the crushing effects of moving sea ice, and which could be fitted out for a crew for three years, that he could perhaps drift with the ice to or near the North Pole, the goal of goals of the Heroic Age. Being a biologist by training, and a generalist by intellectual bent, Nansen saw the potential of the scientific research that could be done on such an exploration. He then designed and had Archer build the FRAM.

But what of the Jeannette. What is her story? Why did most of the survivors nearly die on their walk back to land? Their diaries relate that they had no water to drink. But isn't sea ice fresh water? Why did they find it too salty to drink?

Divide the class into small groups. Students will prepare salt water solutions, 35 parts per thousand. Have them relate this to percent (3.5 % salt by weight, perhaps 35 grams of salt dissolved in one liter of water.) Have the students taste the water. Test the salinity of the water. You may use CBL ion probes to test the salinity, or determine salinity through titration, or better and much less expensive, use Seatest density/salinity monitors available in most home hobbyist aquarium shops.

Tell your students that we are going to freeze the water so that there's a crust of ice on top and that we will taste it to see if it's fresh water ice.

Before you begin, have the students fill out the following worksheet.

Student Name(s) ______________ Period _____

Jeannette Salinity Predictions

Draw diagrams of your set-up.

1) at outset

2) halfway frozen

3) fully frozen

On each diagram predict where you think you would find salty water, fresh water, salty ice, freshwater ice.

After tasting the ice and water in the halfway frozen state (and or measuring its salinity) , write a few words about how successful your predictions were.

Now have the students freeze the water until there's an ice crust, a thin layer of ice on top. Don't use glass containers. As in the Lesson "FRAM", cake pans are ideal freezing vessels. Also a large clean plastic basin will work well. A clear plastic container will allow the successive freezing to be observed.

The students should now test the salinity of the unfrozen water and also the salinity of the ice crust after melting it. Have them record their results in a small table.

Explanation (Discussing)
Sea ice may be up to 2 meters thick. It freezes from the top down. TEA Peter Amatti relates that on video taken under the pack ice in the Antarctic he saw cones of ice forming at the bottom of the ice as sea water was freezing. These cones coalesce into the next layer of ice. Out of these cones, which are the ends of "brine channels" forming in the ice comes streaming hypersaline (very salty) water . This is easily observable because of the diffraction they cause in the light surrounding them. Peter mentions, by the way, that visibility under the ice is extremely good during the Antarctic summer ( austral summer) objects being brightly visible over 200 meters away. So here is the mechanism for the removal of salt from the sea ice. How then can one explain that natural sea ice is too salty to drink?

Have your students think of mechanisms to explain this. Have them design an experiment (full lab report form or a descriptive set of hypotheses to test) showing that in the natural environment the ice remains too salty to drink.

Elaboration (Polar Applications)
TEA Peter Amatti says that the reasons are two-fold. First, sea spray and wind carries salt onto the surface of the already frozen ice making it salty, and, secondly, sometimes the ice freezes so quickly that pockets of salt water are encapsulated in the fresh ice later to freeze making the whole body of the ice salty to taste.- see what your students come up with. TEA Charlotte Kelchner adds that when ice forms it is slightly concave towards the center of the floe thus trapping and freezing and spray that comes onto the floe. Also, she continues, sea ice is constantly moving causing pressure ridges and depressions which scoop up or splash up large quantities of sea water onto the floes.

Exchange (Students Draw Conclusions)
In a class discussion, brainstorm to consensus why natural sea ice has so much salt in it (occasionally or always?? Is sea ice ever fresh, pure? ) Discriminate between sea ice and icebergs. Icebergs are the floating remnants of glaciers which have calved into the sea and they contain fresh water only having formed on the continent.

Evaluation (Assessing Student Performance)
Teacher can assess the quality of work on the worksheet and the lab report. A first person report on the Jeannette expedition can be included in a portfolio document which may also include the lab report, the worksheet and other art work . Some writing about the Heroic Age is requisite in the portfolio.

Additional work and research that may be included in an authentic assessment mode might include an essay with maps about why DeLong may have thought that the Kuroshio current would have carried him to the pole. Map work showing the extent of the Arctic and Antarctic ice sheets , including data from this year and last would be of interest.

Larry Rose, Science Teacher, TEA Associate, Pleasanton Middle School, Pleasanton, California

Students can explore the journals of TEA Besse Dawson who worked on the poor areal development of the ice pack during the El Nino year of 1997-98, and how this negatively affected the development of the phytoplankton in Antarctic seas. At high latitudes, phytoplankton are frozen in the ice and survive in that fashion. Icebreakers churning through pack ice leave a wake of brown ice behind them, the brown color due to masses of phytoplankton embedded in the ice. If they are not frozen into the pack ice they sink and die. Phytoplankton are the base of the food chain in the oceans. The El Nino year's poor development of sea ice bodes poorly for the krill population and thus for the populations of krill-eating penguins and cetaceans and all throughout the food chain.

Phytoplankton which depend on the development of the pack ice for their survival also, perhaps, are the most efficient way that nature removes carbon dioxide from the atmosphere. Student research on the carbon cycle, the greenhouse effect and global warming and its intimate relationship with pack ice development should provide your students with many avenues for research into the global ecological importance of polar studies.


Some web sites to start with include:

Some fine photos of the arctic pack along with personal descriptions at http://www.voicenet.com/~jstewart/nwt

A paper on the reduction of the size of ice packs overall since 1978 is at http://www.greenpeace.org/~comms/97/arctic/library/climate/packice.html

Japanese research in the Sea of Ohkotsk on pack ice physics and distribution is at http://clim.lowtem.hokudai.ac.jp/teion/sirl-e.html.

Student Reproducible Masters

We look forward to hearing from you! Please review this activity.

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