L4 Polar seas Flashcards
Why are Polar sea surfaces rich in dissolves gases and nutrients?
Weak thermoclines
What nutrients are continually recycled in polar seas?
PO4 3- and NO3 -
Due to weak thermo and pyrocline
What limits productivity in polar seas?
Light
Peaks in summer
How do arctic and antarctic differ geographically?
Arctic - N, almost enclosed sea surrounded by icy land
Antarctic - S, Isolated icy land, surrounded by ocean
How does macrobenthos diversity differ in the Arctic and antatctic?
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.
how do suspension feeders and deposit feeders differ?
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
Where is there more bioturbation and what causes it?
Arctic
Organisms causing turbidity eg walrus.
Skeleton crushing predatos cause bioturbation on a small scale.
Where has the most biomass?
Antarctic - 10-100 x that of atlantic and arctic
What goes on at the ice margin at both arctic and antarctic?
Arctic - no specific community associated with ice margin
Antarctic - v. important foraging area
Which has river discharge?
Arctic, brings sediment and disch`arge
Describe physical aspects of Arctic
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.
Describe physical aspects of Antarctic
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.
What is the dominant primary producer in the North Pacific?
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.
What is the Brinicle?
“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.
Why are species in Antarctic isolated and trapped there?
If reliant on continental shelf
what causes upwelling in the southern ocean?
2 circumpolar currents - E and W wind drift creates convergence zone
Summer phytoplankton blooms occur here
How does ice cover in arctic and antarctic differ?
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.
What 3 types of ice are there?
- Sea/pack ice - frozen salt water
- Icebergs - Large chunks of ice shelves/glaciers which calve into the ocean
- Ice shelf - Continental ice sheet/glacier. Formed on land and extends into the sea. FW
3 things about sea ice communities
- If brown ice - dominated by diatoms
- complicated food webs
- Krill is fundamental to pelagic ecosystems, dominant herbivore in antarctic
What does Psychrophilic mean?
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.
How does sea ice affect productivity?
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.
describe krill
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
What does krill density depend on?
Extent of sea ice
more ice=more krill, as plentiful winter food from ice algae which promotes larval recruitment.
What is a predator of phytoplankton that competes with krill?
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.
What causes ice scours in the southern ocean?
Icebergs and hard pack ice scraping along the benthos
What are the impacts of ice scours in the southern ocean?
Local high faunal mortality which skews population structures. Dominance by mobile secondary consumers (eg echinoderms and crustaceans).
Regional level - promotes biodiversity and habitat heterogeneity.
What is a polynya?
stretch of open water surrounded by ice.
Why does upwelling occur at polynyas?
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.
What was discovered at the Ross ice shelf in 2014?
new ecosystem on underside of ice shelf. Fish swim upside down, ‘eggroll’ holothurian uses appendages to swim. anemone - anchored upside down.
case study of polynya
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.
