Week 2 - Reconstructing Quarternary Environments 3.9

Question 1

Why are lakes, mires and bogs genetically related?

Answer 1

Because all lakes become infilled with sediment to form mires and bogs

Question 2

In what 2 ways do lake, mire and bog deposits reveal information about past environmental conditions?

Answer 2

Fossil flora and fauna provide evidence of both local and regional ecological changes

The character of the sediments offers clues about former environmental conditions

Question 3

In lake sediments, variations in chemical and physical properties reflects developments in the lake ____

Answer 3

Ecosystem

Question 4

What do fossil lacustrine sediments and associated shoreline features reveal during the later part of the Quarternary?

Answer 4

A record of fluctuations in lake levels in response to climatic changes

Question 5

How are Tectonic lakes formed and how long is the sediment record?

Answer 5

In areas of subsidence caused by folding or faulting, and include some of the largest lakes in the world

Some sediment sequences span the whole of Quarternary time

Question 6

How are Volcanic lakes formed and how long is the sediment record?

Answer 6

In calderas and craters

From when volcanic activity ceased

Question 7

How are Glacial lakes formed and how long is the sediment record?

Answer 7

Typically in glaciated regions - kettle lakes develop in hollows created by the melting of buried ice. And lakes damned behind or between glacial landforms as a result of the blocking of drainage outlets

Sediment records span shorts period of time

Question 8

What is lithology?

Answer 8

The study of rocks - a rock formation having a particular set of characteristics

Question 9

When sediments contain nekron mud (gyttja), what can that tell you about the conditions of the lake?

Answer 9

The condition is/was eutrophic - The lake is/was rich in mineral nutrients, organic productivity

Question 10

What plant material will deep water nekron mud (gyttja) contain and what plant material will shallow water nekron mud contain?

Answer 10

Deep - Largely unrecognisable plant material

Shallow - detritus gyttja with recognisable plant macrofossils

Question 11

Where the lake substrate is calcerous, what mineral may be precipitated from the water by aquatic plants and other organisms, and what will accumulate as a result?

Answer 11

Lime

A cream-white clay-rich sediment (marl)

Question 12

In lake sediments, what conditions will result in predominately autochthonous material and what conditions will result in predominantly allochthonous material?

Answer 12

Auto - when sediments are deposited under eutrophic conditions

Allo - when the lake is poor in nutrients and organic productivity is low (oligotrophic)

Question 13

How are diatomites formed?

Answer 13

Under eutrophic or oligotrophic conditions, depending on the ecological affinities of the diatom species

Question 14

What 2 stratified ways can lakes be distinguished?

Answer 14

Chemically and thermally

Question 15

What is epilimnion and hypolimnion?

Answer 15

Warm surface waters

Deeper cooler surface waters

Question 16

When does thermal stratification occur in lakes?

Answer 16

When summer water temperatures exceed 4°C, the epiliminion becomes less dense than the hypolimnion

Also in winter due to surface freezing

Question 17

What are diamictic lakes?

Answer 17

Temperate lakes experience vertical mixing (breakdown of thermal stratification) twice a year

Question 18

What are Monomictic lakes?

Answer 18

High altitude, high latitude lakes where warming does not exceed 4°C. Similarly lakes in low altitude may not cool below 4°C.

Mixing occurs once a year.

Question 19

What are meromicitc lakes?

Answer 19

Lakes that remain stable throughout the year

Question 20

Large and deep lakes tend to be ____ whereas shallow or small lakes tend to be ____

Answer 20

Stratified

Unstratified

Question 21

Why might there be differences in lake chemistry, lake biota and sediment type between epilimnion and hypolimnion?

Answer 21

Because Epilimnion is well oxygenated and Hypolimnion is anoxic (anaerobic)

Question 22

Why might there be large scale die off of algae and diatoms in diamictic lakes and how can this help scientists reconstruct past environments?

Answer 22

Diamictic lakes experience seasonal turnover

Question 23

What are organic varves?

Answer 23

Consists of lateral concentrations of organic matter

Question 24

What are chemical varves?

Answer 24

Seasonal alternation between epiliminion and hypolimnion may lead to seasonal production of calcareous deposits, iron oxides or sulphur-rich sediments

Question 25

What does hydrosere mean?

Answer 25

The succession from open water to mire and bog, where sediments change in character from mud to peats

Question 26

What are the 3 types of peat?

Answer 26

Limnic - form beneath the regional water table

Telmatic - form in the swamp zone

Terrestrial - at or above high water mark

Question 27

How can chemical data from lake sediments help scientists reconstruct lake catchment histories?

Answer 27

Periods of reduced erosion allows for increased aquatic productivity, leading to higher values of organic carbon

Question 28

How do the lake cores in northern England show the effects of deforestation by Neolithic people at 6 ka?

Answer 28

Lake cores show an increase in concentration of base elements, brought about by accelerated soil erosion

Question 29

What 2 reasons might sediments change in magnetic properties?

Answer 29

Because of the types of processes operating around the catchment

Because of human disturbance, such as deforestation

Question 30

Lake level records also enable inferences to be made about changes in ___ circulation patterns

Answer 30

atmospheric