Polar Seas Flashcards
1
Q
Icebergs
A
- prominent feature of polar seas
- form when portions of ice sheets or glaciers break off
2
Q
Ice sheets
A
- form on land from snow accumulation and spread outward until they reach the sea
- Antarctica ice sheet, Greenland ice sheet
3
Q
Sea ice
A
- is frozen seawater (freezes at -1.8 C)
- in Arctic ocean, multiyear ice is common
- in Southern ocean, first year sea ice is common
4
Q
Pack ice
A
- mobile as it drifts across ocean surface under influence of wind and currents
- moves vertically under influence of waves, tides, and swells
5
Q
Landfast ice (aka fast ice)
A
- immobile since it is directly attached to coast or seafloor
- can also be locked in place between grounded icebergs
6
Q
how ice sheets form, step 1
A
- ice crystals form, float to the top, and aggregate into a thin/soupy layer at the surface
7
Q
Nilas ice
A
- very thin, fragile layer of aggregated ice crystals
- plankton can get caught and trapped in freezing water
8
Q
Frazil/Grease Ice
A
- ice continues to stick together forming a thicker layer (few cm thick)
- resembles grease slick on the surface
9
Q
Consolidated pancake ice (1st year ice)
A
- 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
10
Q
Congelation
A
more ice forms on the bottom of established ice cover
11
Q
Leads
A
open areas between ice sheets
12
Q
Polynas
A
open areas/holes in the middle of an ice sheet
13
Q
pressure ridges
A
- ice mountains formed when sheets collide and material is forced upward
14
Q
seasonal changes in ice cover
A
- 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
15
Q
The Arctic Basin
A
- 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
16
Q
N. Hemisphere sea ice
A
- 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
17
Q
Sympagic
A
associated with ice
18
Q
sea ice biota
A
- sea ice consists of a mixture of ice crystals and brine channels
19
Q
brine channels
A
- form a 3D network of tubes with diameters a few microns to several cm
- support a sympagic community
20
Q
Brine channel biota (in channels)
A
- 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
21
Q
brine channel biota (surrounding channel)
A
- 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
22
Q
Consequences of reduced sea ice in the Arctic
A
- 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
23
Q
S. Hemisphere sea ice
A
- 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)
24
Q
Marginal Ice zone (MIZ)
A
- 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
25
Krill (Euphausia superba)
- 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
26
Polar Benthos
- 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
27
Endemism in Polar seas
- 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
28
Polar Gigantism
- isopods, sponges, sea spiders, ribbon worms, ctenophores, copepods, anemones, and pteropods all have gigantism around Antarctica
- low metabolism, slow growth, long-lived
