Flashcards in Lecture 5 Deck (29)
Features of polar waters
-Rich in dissolved gases (dissolve better in cooler water)
-Rich in nutrients
-Weak pycnocline (density gradient)
-Primary production light-limited
Biological differences between Arctic and Antarctic Oceans: macrobenthic diversity
-Antarctic: high (6 times higher than Arctic)
Biological differences between Arctic and Antarctic Oceans: endemism
-Arctic: low, benthos similar to cold-temperate Atlantic and Pacific
-Antarctic: extremely high (95% fish species)
Biological differences between Arctic and Antarctic Oceans: biomass
Antarctic: High (10-100x higher at given depth)
Biological differences between Arctic and Antarctic Oceans: benthos characteristics
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
Biological differences between Arctic and Antarctic Oceans: biotic disturbance
Arctic: high (many large mammals)
Why is the ice margin important in the Antarctic?
Important foraging area
What are macrobenthos?
Organisms living on, or in, the sea bottom which are larger than 1mm
Biological differences between the Arctic and Antarctic Oceans: biotic disturbance
-Arctic: biotic disturbance very high due to bioturbation of sediment and skeleton-crushing (durophagous predators)
-Antarctic: less disturbance and harder sediment
Physical differences between Arctic and Antarctic Oceans: ocean form
Antarctic: circumpolar ring
Arctic: almost enclosed by land
Physical differences between Arctic and Antarctic Oceans: current system
Arctic: transpolar current
Antarctic: circular currents that cause upwelling in the convergence zone
Physical differences between Arctic and Antarctic Oceans: river input
Arctic: high (low saline stratified surface + sediments)
Physical differences between Arctic and Antarctic Oceans: euphotic zone nutrients
Arctic: seasonally depleted
Antarctic: high all year round
Physical differences between Arctic and Antarctic Oceans: pack ice cover
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
Physical differences between Arctic and Antarctic Oceans: continental shelves
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
Where is the convergence zone of the Antarctic?
A transition region of the Southern Hemisphere separating the Antarctic and sun-antarctic regions. Major area of upwelling so huge phytoplankton blooms
Physical differences between Arctic and Antarctic Oceans: temperature
Antarctic: waters coldest of anywhere in Earth (0 to -1.9 degrees Celsius)
Types of ice
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
Sea ice community features
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
What is the word for organisms capable of growth and reproduction in cold temperatures?
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
How to krill depend on sea ice?
Extensive winter sea ice means plentiful winter food from ice algae
Promotes larval recruitment, replenishing krill population
Krill versus Salps
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
What is the benthic ecosystem dominated by in ice habitats
Suspension feeders - they are dependent on highly seasonal pulses of food from waters above
Benthos and ice scours
-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
What grows where there is low ice disturbance?
Giant slow-growing sponges
What colonises after ice shelf collapse?
Fast growing ascidians
What is a polynya?
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.