Page 13 - living-ice

A frozen Swiss cheese
Seawater becomes heavier as temp- eratures get colder. The freezing point at typical ocean salinity (35 grams of dissolved salts per litre of water) is -1.8 ˚C. Large bodies of water need to cool down to this temperature before sea ice forms. Consequently, the winter must be cold and long for a solid sea ice cover to establish. The sea ice itself is composed almost en- tirely of fresh water because the salt is separated from the water when the ice forms. The salt in turn concentrates in a brine with such a high concentration of salt that it cannot freeze. As the ice matrix grad- ually forms, the brine is left in a series of holes and channels between the ice crystals. This creates a unique and dynamic habitat for algae, bacteria, viruses and small crustaceans. The brine can be three times saltier than the ocean, which can explain
why the inside of the sea ice resembles a Swiss cheese.
NAUPLII COPEPODA
FLATWORMS
AMPHIPODA
BACTERIA
POLYCHAETA
ROTIFERA
ALGAE NEMATODA
ALGAE
FUNGI
FLAGELLATES
ALGAE
CILIATES
HYDROZOA
PHOTO: Christopher Krembs, UW