Lec9: Antarctic Lakes and Rivers Flashcards Preview

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Flashcards in Lec9: Antarctic Lakes and Rivers Deck (20):
1

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

Taylor Glacier, Bonney, Hoare, Canada Glacier, Fryxell

2

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

No, remarkably similar.

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.

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

4

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

1. Salt remains
2. Nutrients move slowly up column

5

In which Valley is Lake Vanda located?

Wright Valley.

6

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

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

7

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

Onyx river, from the east.

8

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

Surface layer = oxygen saturated.

9

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

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

10

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

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

11

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

Because it precipitates as hydroxyapatite.
Allows nitrifying bacteria and algae to live.

12

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

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

13

What is the Don Juan Pond water composed of?

Calcium chloride brine.

14

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

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

15

What is Antarcticite and where is it found?

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

16

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

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

17

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

1. Northern end is melting, which frees nutrients.
2. Southern end is freezing, forms accretion ice.

18

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

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

19

Why is there no life in lake Vostok?

1. Contamination - especially from drilling fluids
2. Extremely oligotrophic: High temp, no sunlight, supersaturated with nitrogen and oxygen

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

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