Lecture 5

Question 1

Features of polar waters

Answer 1

• Cold
• Rich in dissolved gases (dissolve better in cooler water)
• Rich in nutrients
• Weak thermocline
• Weak pycnocline (density gradient)
• Primary production light-limited

Question 2

Biological differences between Arctic and Antarctic Oceans: macrobenthic diversity

Answer 2

• Arctic: low

- Antarctic: high (6 times higher than Arctic)

Question 3

Biological differences between Arctic and Antarctic Oceans: endemism

Answer 3

• Arctic: low, benthos similar to cold-temperate Atlantic and Pacific
• Antarctic: extremely high (95% fish species)

Question 4

Biological differences between Arctic and Antarctic Oceans: biomass

Answer 4

Arctic: low
Antarctic: High (10-100x higher at given depth)

Question 5

Biological differences between Arctic and Antarctic Oceans: benthos characteristics

Answer 5

Arctic: typically infaunal species that feed in particulate organic matter suspended in the water or settled on the bottom
Antarctic: large numbers of epifaunal and infaunal species

Question 6

Biological differences between Arctic and Antarctic Oceans: biotic disturbance

Answer 6

Arctic: high (many large mammals)
Antarctic: low

Question 7

Why is the ice margin important in the Antarctic?

Answer 7

Important foraging area

Question 8

What are macrobenthos?

Answer 8

Organisms living on, or in, the sea bottom which are larger than 1mm

Question 9

Biological differences between the Arctic and Antarctic Oceans: biotic disturbance

Answer 9

• Arctic: biotic disturbance very high due to bioturbation of sediment and skeleton-crushing (durophagous predators)
• Antarctic: less disturbance and harder sediment

Question 10

Physical differences between Arctic and Antarctic Oceans: ocean form

Answer 10

Antarctic: circumpolar ring
Arctic: almost enclosed by land

Question 11

Physical differences between Arctic and Antarctic Oceans: current system

Answer 11

Arctic: transpolar current
Antarctic: circular currents that cause upwelling in the convergence zone

Question 12

Physical differences between Arctic and Antarctic Oceans: river input

Answer 12

Arctic: high (low saline stratified surface + sediments)
Antarctic: None

Question 13

Physical differences between Arctic and Antarctic Oceans: euphotic zone nutrients

Answer 13

Arctic: seasonally depleted
Antarctic: high all year round

Question 14

Physical differences between Arctic and Antarctic Oceans: pack ice cover

Answer 14

Arctic: little seasonality - 90% in winter, 80% in summer, 3.5m thick
Antarctic:high seasonality - 50% in winter, 10% in summer, 1.5m thick, melted ice leads to high productivity

Question 15

Physical differences between Arctic and Antarctic Oceans: continental shelves

Answer 15

Arctic: wide continental shelves, large river discharge, two shallow straits into Pacific and Atlantic Oceans
Antarctic: narrow, open to all oceans, exchange with deep ocean

Question 16

Where is the convergence zone of the Antarctic?

Answer 16

A transition region of the Southern Hemisphere separating the Antarctic and sun-antarctic regions. Major area of upwelling so huge phytoplankton blooms

Question 17

Physical differences between Arctic and Antarctic Oceans: temperature

Answer 17

Antarctic: waters coldest of anywhere in Earth (0 to -1.9 degrees Celsius)

Question 18

Types of ice

Answer 18

Sea ice (pack ice): formed from saltwater freezing into base of pack ice
Ice shelf (continental ice sheet or glacier): formed on land from snow but extends into sea

Question 19

Sea ice community features

Answer 19

Diatoms live within brine channels in sea ice - chlorophyll concentrations 1000x that of open surface waters in southern ocean
Provide a highly concentrated food source for grazing zooplankton in winter
As it melts in spring it provides a seed population of plankton for blooms along the ice edge - important grazing grounds

Question 20

What is the word for organisms capable of growth and reproduction in cold temperatures?

Answer 20

Psychrophilic

Question 21

Antarctic krill

Answer 21

Euphausia superba
Dominant herbivore in Antarctic pelagic ecosystem
Grow up to 6cm
Occupy all layers in the water column which makes them prey to surface, pelagic and benthic feeders
Whole food web based on them - form dense swarms covering miles

Question 22

How to krill depend on sea ice?

Answer 22

Extensive winter sea ice means plentiful winter food from ice algae
Promotes larval recruitment, replenishing krill population

Question 23

Krill versus Salps

Answer 23

Salps are free-floating tunicates which move and feed by pumping water through hollow gelatinous body.
They are the primary competitor of krill for phytoplankton, but can’t feed on ice algae.
In the absence of krill, salps can exploit spring phytoplankton blooms and undergo extensive population growth.
In years following low sea ice cover in winter, they reach high densities.
They can tolerate warmer water than krill

Question 24

What is the benthic ecosystem dominated by in ice habitats

Answer 24

Suspension feeders - they are dependent on highly seasonal pulses of food from waters above

Question 25

Benthos and ice scours

Answer 25

• Icebergs or hard pack ice scours the benthic species at the bottom
• High faunal mortality and skewed population structures result, with dominance of mobile secondary consumers
• At the regional scale, this promotes biodiversity and habitat heterogeneity

Question 26

What grows where there is low ice disturbance?

Answer 26

Giant slow-growing sponges

Question 27

What colonises after ice shelf collapse?

Answer 27

Fast growing ascidians

Question 28

What is a polynya?

Answer 28

An area of persistent open water surrounded by sea ice.

Caused by upwelling of circumpolar deep water which is warmer and melts the sea ice.

Question 29

Polynyas and Emperor and Adélie penguins

Answer 29

• Polynyas provide ideal conditions for early and intense phytoplankton blooms
• 90% of these penguins are sited next to recurrent coastal polynyas
• Breeding success of Emperor and Adélie penguins depends on distance of breeding colony to open water foraging ground
• To adapt to the unpredictable length of foraging trips, there is great flexibility in chuck rearing/feeding