Polar Seas

Question 1

Icebergs

Answer 1

• prominent feature of polar seas

- form when portions of ice sheets or glaciers break off

Question 2

Ice sheets

Answer 2

• form on land from snow accumulation and spread outward until they reach the sea
• Antarctica ice sheet, Greenland ice sheet

Question 3

Sea ice

Answer 3

• is frozen seawater (freezes at -1.8 C)
• in Arctic ocean, multiyear ice is common
• in Southern ocean, first year sea ice is common

Question 4

Pack ice

Answer 4

• mobile as it drifts across ocean surface under influence of wind and currents
• moves vertically under influence of waves, tides, and swells

Question 5

Landfast ice (aka fast ice)

Answer 5

• immobile since it is directly attached to coast or seafloor
• can also be locked in place between grounded icebergs

Question 6

how ice sheets form, step 1

Answer 6

• ice crystals form, float to the top, and aggregate into a thin/soupy layer at the surface

Question 7

Nilas ice

Answer 7

• very thin, fragile layer of aggregated ice crystals

- plankton can get caught and trapped in freezing water

Question 8

Frazil/Grease Ice

Answer 8

• ice continues to stick together forming a thicker layer (few cm thick)
• resembles grease slick on the surface

Question 9

Consolidated pancake ice (1st year ice)

Answer 9

• forms in rougher waters
• wind, waves, and currents move ice around causing collisions, forming the pancake ice
• (20-50 cm diameters) gives rise to first year ice sheet and adds thickness by freezing on the bottom

Question 10

Congelation

Answer 10

more ice forms on the bottom of established ice cover

Question 11

Leads

Answer 11

open areas between ice sheets

Question 12

Polynas

Answer 12

open areas/holes in the middle of an ice sheet

Question 13

pressure ridges

Answer 13

• ice mountains formed when sheets collide and material is forced upward

Question 14

seasonal changes in ice cover

Answer 14

• ocean freezes and sea ice expands in autumn/winter
• period of melting and retreat in spring/summer
  [min and max ice extent varies annually and by decade]
• extent of sea ice cover has significant impact on global climate

Question 15

The Arctic Basin

Answer 15

• enclosed almost entirely by land [except Bering and Fram straits]
• drift of sea ice dominated by Beaufort gyre (clockwise) and Transpolar drift (into Atlantic)
• 1/3 of basin is shallow shelf (<100m)
• high input of freshwater containing suspended solids, DOM, and inorganic nutrients

Question 16

N. Hemisphere sea ice

Answer 16

• extent ranges from approx. 7 million km2 (September) to 14 million km2 (March)
• Arctic sea ice is usually older (1-7 years), thicker, and less saline than Antarctic ice
• extent has declined steadily over last few decades, major ecological implications

Question 17

Sympagic

Answer 17

associated with ice

Question 18

sea ice biota

Answer 18

• sea ice consists of a mixture of ice crystals and brine channels

Question 19

brine channels

Answer 19

• form a 3D network of tubes with diameters a few microns to several cm
• support a sympagic community

Question 20

Brine channel biota (in channels)

Answer 20

• several hundred species of unicellualr algae inhabit brine channels (diatoms)
• produce lots of DOM that supports bacteria, viruses, and fungi
• some protozoans and metazoans (amphipods, copepods, rotifers) feed on ice algae/wastes, may seek refuge in larger channels

Question 21

brine channel biota (surrounding channel)

Answer 21

• small fauna mainly crustaceans (larger copepods) feed on the underside of the ice and release wastes and nutrients
• abundant zooplankton, primarily copepods, support planktivorous fish

Question 22

Consequences of reduced sea ice in the Arctic

Answer 22

• rise in surafce temps, thermal stratification
• higher nutrient input
• primary production increase
• high latitude species disappear, replaced with low latitude ones
• increased commerance and oil drilling
• ice dependent species losing hunting, nesting, and resting grounds
• long-term effects on community structure

Question 23

S. Hemisphere sea ice

Answer 23

• Southern ocean
• circulation dominated by Antarctic circumpolar current
• gryes in Ross and Weddell sea don’t recirculate ice, deflect westward ice north, and meets eastward ice offshore
• ice tends to be younger, thinner, and more saline than Arctic ice
• extent ranges from 4 mil km2 (Feb) to 20 mil km2 (Sept)

Question 24

Marginal Ice zone (MIZ)

Answer 24

• portion of the ice cover that is close enough to the open ocean to be affected by its processes
• algal blooms occur as ice algae, DOM, bacteria, inorganic nutrients, metazoans/protozoans are released from ice as it melts
• rich feeding grounds for zooplankton, swarms of krill gather at edges and attract whales

Question 25

Krill (Euphausia superba)

Answer 25

• small planktonic species that occur in high abundance in the southern ocean
• crucial food source for many species
• abundance is positively correlated w/ sea ice extent
• exploited by humans for aquaculture and omega-3 harvesting
• strong positive correlation w/ krill abundance and duration of sea ice

Question 26

Polar Benthos

Answer 26

• southern ocean is 1.5-6 times greater in species # in taxonomic groups
• dominated by suspension feeders
• soft bottom sediments
• fish and sharks are more common in Arctic
• icebergs scour benthic communities, destroying it, periodic disturbances contribute to high diversity by driving succession and re-colonization

Question 27

Endemism in Polar seas

Answer 27

• Higher endemism in Antarctica than Arctic
• 95% of fish, 57% of polychaetes, and 37% of macroalgae endemic in the Antarctic
• 5% endemic macroalgae and crabs, flatfishes and barnacles are more common in Arctic
• Antarctica isolated for 25 million years due to circumpolar current
• Arctic species shared w/ North Atlantic and Pacific

Question 28

Polar Gigantism

Answer 28

• isopods, sponges, sea spiders, ribbon worms, ctenophores, copepods, anemones, and pteropods all have gigantism around Antarctica
• low metabolism, slow growth, long-lived