Lecture 11/12 - Sea Ice & Chemistry Intro

Question 1

What is the geographical distribution of ice in the Arctic and Antarctic regions?

Answer 1

Arctic Basin around 3000m deep covered by a thin 4m shell of ice.

Antarctic similar in extent but is a continent with a permanent ice cap, up to 3000m thick and accounts for about 90% of permanent ice caps.

Question 2

What happens to the ice in Antarctica during summer?

Answer 2

Its obviously melts. Large proportion of the pack ice which forms around Antarctica melts during the Summer.

Question 3

Other than sea ice, what are other forms of ice can be found at sea? (2)

Answer 3

Icebergs and River Ice

Question 4

What is different about freezing in fresh water compared to saline water?

Answer 4

Saline waters are not the same as Fresh, as density/salinity effects the rate of freezing.
Increased salinity lowers the temperature at which water freezes and also increases density

Question 5

What is the process of delaying salt water freezing?

Answer 5

Convection of cold water down continues unlike fresh water which becomes stratified easily
This convection or overturning delays onset of ice formation
Delay in some areas may prevent ice freezing at all

Question 6

How does sea ice develop?

Answer 6

First indication ice speckles in top few cms of water column
As cooling continues new ice is formed, with further cooling sheets of ice form.
Ice grows in thickness by freezing from below and the sides and coalescence

Question 7

What is the importance of snowfall in the development of sea ice?

Answer 7

Snowfall especially important in the Antarctic with gradual freezing taking place of waterlogged snow.

Question 8

What are the processes involved in the deformation of ice?

Answer 8

Constant motion caused by wind current and internal stresses
The toughness/irregularity of ice depends upon
- Age
- Ridging (Deforms quickly under pressure)
- Coastal areas

Question 9

In what ways are ice sheets melted? (4)

Answer 9

1. ) Summer heat
2. ) Gaps in ice/algae patches reduce albedo & increase melt
3. ) Meltwater percolates ice and increases rate of melting
4. ) Mixing with surrounding seawater

Question 10

What are the different processes that are involved in the movement of Ice? (6)

Answer 10

1. ) Pack ice moves under influence of Wind and Currents
2. ) Fast ice is immobile
3. ) Pack ice moves downwind (Subject to Coriolis effect)
4. ) Onshore winds tend to concentrate pack ice
5. ) Offshore winds open it up
6. ) Currents

Question 11

How are icebergs formed?

Answer 11

These icebergs fall off seaward flowing glaciers/ice cliffs etc
Their size is reduced by calving (breaking), melting, erosion by wind and rain

Question 12

What is the importance of Arctic icebergs?

Answer 12

Predominantly Greenland Ice Cap glaciers
90% of land ice in N Hemisphere
Large number from the E Coast Glaciers

Question 13

What is the importance of Antarctic icebergs?

Answer 13

Vast number of bergs produced, much more than Arctic
Antarctic bergs tend to be in several distinct forms
Weddell sea bergs have been used as an indicator of global warming

Question 14

What are icebergs effect on shipping?

Answer 14

Grounding of ships
Dangers of becoming fast ice
Must maintain very good alert radar/visual look out
Ice Patrol - Joint US Canada venture with regular ice reports
and regular sea ice charts

Question 15

The total salinity varies, does the major element composition of seawater vary as well or is the chemistry of seawater constant?

Answer 15

Relative proportion of all the major elements remain constant

Question 16

What are the variations of composition through different marine systems?

Answer 16

1. ) Enclosed seas or estuaries e.g. major river draining limestone terrain will have high Ca loading
2. ) Anoxic Basins e.g. lack of O2, microbes will use SO4 as a source of energy = SO4 decline
3. ) Shallow Seas e.g. Bahamas Bank – lots of CaCO3 ppt so Ca is reduced in surface waters
4. ) Hydrothermal Vents e.g. low Mg
5. ) Pore Waters

Question 17

What is conservative and non-conservative behaviour?

Answer 17

Conservative behaviour - usually from major ions (only affected by physical mixing)
Non-conservative behaviour - minor ions (nutrients) concentration affected by bio/chem processes

Question 18

What is the residence time?

Answer 18

This is the average amount of time that a particle spends in a particular system.
Gives an idea as to how long an element will remain in solution before being removed