The Life Inside Sea Ice Guest Scientists Andrew Juhl and Craig Aumack Originally presented 14 Jan content/uploads/2009/07/fondonegro.jpg

Vast areas in the Arctic and Antarctic Oceans are covered with sea ice Freezing seawater demonstrates an array of structures that create the surface cover of polar seas The extent of sea ice varies seasonally and long-term Sea ice provides a vibrant ecosystem /ice_tour/sea_ice_formation/

On average, sea ice cover more than 25 million sq. km (9.5 million sq. mi) Seasonal changes are monitored via satellite by the NSIDC AMNH Science Bulletin “Sea Ice” “Sea Ice” Sep 2010 Mar

Stages in the Formation of Sea Ice Seawater with a salinity of 34 ppt begins to freeze at o C. Frazil ice mm-sized crystals that form sticks which give a greasy appearance to the surface Aggregate into ice chunks that merge to form pancake-shaped ice floes These freeze together, moved by winds and waves, to form the rough surface and rugged bottom of the solid ice cover

“First-Year” vs. “Multiyear” Ice “New Ice” – less than 10 cm (3.9 in.) thick “Young Ice” – 10 – 30 cm thick Sometimes divided into “grey ice” (10-15 cm) and “grey-white ice” (15 – 30 cm) “First-year Ice” – more than 30 cm, but has not yet survived a summer melt “Multiyear Ice” – has survived one or more summer melts may be 2 – 4 m thick

Other Sea Ice Structures Polynyas Persistent open water areas within the ice Important in creating bottom waters of global thermohaline circulation Leads Narrow linear cracks that form when ice floes seaparate

Sea Ice Microstructure Depends on ice formation processes Wind and wave turbulence create granular ice Calm conditions produce columnar ice Usually, both form and can be seen in layers under a microscope Ice crystals consist of pure water, because the dissolved salts are excluded during freezing Salinity of liquid water increases, lowering the freezing point and increasing the density Some remains between crystals as brine channels

Brine Channels Provide Habitats for Diatoms Diatoms have adapted to the conditions in brine channels Red, yellow, and green pigments often produce a brown “stain” on the underside of sea ice

Phytoplankton “blooms” As polar night ends around the equinox, return of sunlight and melting of ice fosters “bloom” of algae that utilize the nutrients in surface waters

Polar Food Webs Phytoplankton and ice algae  zooplankton plankton, amphipods, other small organisms  fish and benthic organisms Fish and benthic organisms  seals, sea lions, penguins and other birds, killer whales, polar bears, as occur in each hemisphere

Aerial view, of ‘dirty ice’ in the Chukchi Sea, from an “Ecology Picture of the Week”