L4 Polar seas

Question 1

Why are Polar sea surfaces rich in dissolves gases and nutrients?

Answer 1

Weak thermoclines

Question 2

What nutrients are continually recycled in polar seas?

Answer 2

PO4 3- and NO3 -

Due to weak thermo and pyrocline

Question 3

What limits productivity in polar seas?

Answer 3

Light

Peaks in summer

Question 4

How do arctic and antarctic differ geographically?

Answer 4

Arctic - N, almost enclosed sea surrounded by icy land

Antarctic - S, Isolated icy land, surrounded by ocean

Question 5

How does macrobenthos diversity differ in the Arctic and antatctic?

Answer 5

Arctic - low diversity, mainly infaunal species.
Antarctic - High diversity, epifaunal and infaunal species, sediment type affects organism composition. Many ascidians, holothurians, echinoderms, crustaceans, sponges and polychaetes.

Question 6

how do suspension feeders and deposit feeders differ?

Answer 6

Suspension - feed on particles falling down from upper layers. active pumping of water and passive feeding using cilia.
Deposit - feed on particles on sea floor. many infaunal species eg Macoma clam, polychaete worms. Dominate Arctic benthos

Question 7

Where is there more bioturbation and what causes it?

Answer 7

Arctic
Organisms causing turbidity eg walrus.
Skeleton crushing predatos cause bioturbation on a small scale.

Question 8

Where has the most biomass?

Answer 8

Antarctic - 10-100 x that of atlantic and arctic

Question 9

What goes on at the ice margin at both arctic and antarctic?

Answer 9

Arctic - no specific community associated with ice margin

Antarctic - v. important foraging area

Question 10

Which has river discharge?

Answer 10

Arctic, brings sediment and disch`arge

Question 11

Describe physical aspects of Arctic

Answer 11

Wide continental shelves
soft sediment habitat
low salinity surface waters (due to river discharge) causes more stratification and nutrient depletion.
Shallow exits into Atlantic and Pacific.

Question 12

Describe physical aspects of Antarctic

Answer 12

v. narrow continental shelves, rapid drop into deep
98% continent covered in 2km thick ice.
Barrier of deep cold water prevents other organisms entering antarctic.
Continental shelves found at 600m depth, compared to 150m in arctic.

Question 13

What is the dominant primary producer in the North Pacific?

Answer 13

Neodenticula senunae
(Diatom)
in 1999 abundant in Atlantic for the first time in 800,000 years as it was trandported across the arctic in the ice free conditions.

Question 14

What is the Brinicle?

Answer 14

“Finger of death”

As ice on surface freezes, all salts move out and sink. Particles are so cold that they freeze the water they touch.

Question 15

Why are species in Antarctic isolated and trapped there?

Answer 15

If reliant on continental shelf

Question 16

what causes upwelling in the southern ocean?

Answer 16

2 circumpolar currents - E and W wind drift creates convergence zone
Summer phytoplankton blooms occur here

Question 17

How does ice cover in arctic and antarctic differ?

Answer 17

Arctic - permanent ice cover, average 10 years old. 100% coverage in winter
Antarctic - more seasonal variation. -19m km2 ocean freezes in winter. annual variations in pack ice extent.

Question 18

What 3 types of ice are there?

Answer 18

1. Sea/pack ice - frozen salt water
2. Icebergs - Large chunks of ice shelves/glaciers which calve into the ocean
3. Ice shelf - Continental ice sheet/glacier. Formed on land and extends into the sea. FW

Question 19

3 things about sea ice communities

Answer 19

1. If brown ice - dominated by diatoms
2. complicated food webs
3. Krill is fundamental to pelagic ecosystems, dominant herbivore in antarctic

Question 20

What does Psychrophilic mean?

Answer 20

Orgs can only survive in narrow band of nutrients and temp found in polar regions.
May also survive in other regions but not as competitive so not found there.

Question 21

How does sea ice affect productivity?

Answer 21

Sea ice chlorophyll conc is 1000x that of open surface waters. Diatoms live in microscopic brine channels made by microbes, form 10-30% volume of ice.
In spring when it melts, ‘seed’ population for plankton blooms along ice edge.

Question 22

describe krill

Answer 22

Euphasia superba
live about 5 years, 6cm. Occupy all layers of water column and high density of up to >10,000 krill per m3 water, important to predatorz.
Whole food web based on krill

Question 23

What does krill density depend on?

Answer 23

Extent of sea ice

more ice=more krill, as plentiful winter food from ice algae which promotes larval recruitment.

Question 24

What is a predator of phytoplankton that competes with krill?

Answer 24

Salps - free living, colonial tunicates. Feed by pumping water through hollow gelatinous body.
Explosive population growth following absence of krill, so high densities following low ice cover. Can tolerate warmer water than Krill.

Question 25

What causes ice scours in the southern ocean?

Answer 25

Icebergs and hard pack ice scraping along the benthos

Question 26

What are the impacts of ice scours in the southern ocean?

Answer 26

Local high faunal mortality which skews population structures. Dominance by mobile secondary consumers (eg echinoderms and crustaceans).
Regional level - promotes biodiversity and habitat heterogeneity.

Question 27

What is a polynya?

Answer 27

stretch of open water surrounded by ice.

Question 28

Why does upwelling occur at polynyas?

Answer 28

katabatic winds blow over glaciers bringing FW into sea. FW pushes SW down into deep ocean and flows off continental shelf. displaces deep water causing upwelling.

Question 29

What was discovered at the Ross ice shelf in 2014?

Answer 29

new ecosystem on underside of ice shelf. Fish swim upside down, ‘eggroll’ holothurian uses appendages to swim. anemone - anchored upside down.

Question 30

case study of polynya

Answer 30

Mertz Glacier polynya

• Emperor and Adelie penguin breeding success depends on sea ice extent. As distance to open water foraging ground increases, chick survival decreases.
• need flexibility of chick feeding/rearing due to unpredictability of foraging.
• Pairs take turns to incubate egg. Antimicrobial peptide present in stomach to prevent digestion for about 20 days. Preserved stomach content can sustain chick for 10 days.
• 4 scenarios: ideal if female returns after egg hatches. 40% survive if female is late back. Male returns late from foraging. Egg is deserted and death of chick.