Lec9: Antarctic Lakes and Rivers

Question 1

What are the 3 major lakes in Taylor Valley in order from left to right (and also include the names of any glaciers)?

Answer 1

Taylor Glacier, Bonney, Hoare, Canada Glacier, Fryxell

Question 2

Does the thickness of the ice sheet vary between the 3 Taylor Valley Lakes?

Answer 2

No, remarkably similar.

Question 3

What three functions of the ice cover of the Taylor Valley lakes lead to reduced photosynthesis, supersaturation with gases that enter but cannot leave, and a stable water column.

Answer 3

1. Reflects solar radiation
2. Prevents gas exchange with atmosphere
3. Minimises wind-induced mixing

Question 4

What is the consequence of a stable (as opposed to active) water column in the Taylor Valley lakes?

Answer 4

1. Salt remains

2. Nutrients move slowly up column

Question 5

In which Valley is Lake Vanda located?

Answer 5

Wright Valley.

Question 6

What is the length, width and depth of Lake Vanda?

Answer 6

L = 5.5km
W = 1.4km
D = 75m

Question 7

Which river feeds Lake Vanda and from which direction does it flow?

Answer 7

Onyx river, from the east.

Question 8

Lake Vanda is a meromitric (two layer) system. Which layer is oxygen saturated?

Answer 8

Surface layer = oxygen saturated.

Question 9

The bottom layer of Lake Vanda is increasingly salinic, anoxic and temperature. Describe the reasons for each.

Answer 9

Salinic = saline stratification from past low levels 
Anoxic = no mixing of oxygen by convection
Temperature = infrared radiation is adsorbed by bottom sediments

Question 10

What is Crystal Clear Lake Vanda ice, and what does it allow?

Answer 10

Vertical ice crystals.
18% of phosynthetically active radiation penetrates, and infrared radiation is adsorbed by bottom sediments, thus warming the bottom.

Question 11

Why is Lake Vanda low in phosphorous? Also, which organisms can exist here since the lake is high in nitrogen?

Answer 11

Because it precipitates as hydroxyapatite.

Allows nitrifying bacteria and algae to live.

Question 12

What are dry-bottomed lakes compared to hypersaline ponds, and name an example for each.

Answer 12

Lake = Lake Vida = permentantly frozen. 
Pond = Don Juan Pond = never freezes.

Question 13

What is the Don Juan Pond water composed of?

Answer 13

Calcium chloride brine.

Question 14

How did the Don Juan Pond water come to be comprised of calcium cholride brine?

Answer 14

Deposition by sea spray, and then concentrated by evaporation and sublimation of water.

Question 15

What is Antarcticite and where is it found?

Answer 15

Calcium chloride hexahydrate crystals precipitate around the edge of Don Juan Pond.

Question 16

Why does Lake Vostok never freeze? (Two reasons).

Answer 16

1. Extreme pressure of the overlying ice sheet keeping it at pressure melting point.
2. Radioactive decay of bedrock is hot

Question 17

At which end is the ice-sheet melting, and which end is freezing? What does this mean for each end?

Answer 17

1. Northern end is melting, which frees nutrients.

2. Southern end is freezing, forms accretion ice.

Question 18

How do Subglacial lakes, such as Lake Vostok, form?

Answer 18

Ice-sheet traps geothermal heat produced by bedrock , and it heats the basal ice until it exceeds pressure melting point.

Question 19

Why is there no life in lake Vostok?

Answer 19

1. Contamination - especially from drilling fluids

2. Extremely oligotrophic: High temp, no sunlight, supersaturated with nitrogen and oxygen

Question 20

With reagards to Lake Vostok, what is the:

1. Surface area
2. Depth (and which end is deeper)
3. Thickness of overlying ice sheet

Answer 20

1. 14 million km2
2. 750m
3. 4km