Deglaciation and Postglacial Flashcards
What period of time was the last deglaciation?
The LR04 ocean core stack
present day tp 5.3 Ma BP
What are climate archives?
- Sediment cores
- Ice cores
> annually resolved layers (although the layers get thinner with depth
> Gives very precise chronology (i.e. age) - constrained by volcanic eruptions and ice flow models
What is the global ocean thermohaline circulation?
Network of ocean currents driven by contrasting temperature and salinity ( ie density)
- Helps redistribute energy around the globe
What are the general principles of the thermohaline circulation?
- Cold/saline water is dense - sinks - flow at depth
- Warm/ fresh water is less dense - flows close to the surface
What is the thermohaline circulation driven by?
Cold water sinking in the polar regions
What is the main focus of the THC?
Atlantic meridional overturning circulation (AMOC)
What happened to the AMOC during the last glacial?
Was suppressed by presence of ice sheets and supply of melt into N Atlantic - Gluf stream cannot transport heat as far North
What caused rapid warming into the Bølling–Allerød?
- AMOC strengthened abruptly, causing warm surface waters to be transported further northwards
- But at a time when the melting of N Hemisphere ice sheets were significant (which tends to weaken the AMOC)
What went on during the Bolling-Allerod period?
- A sudden reduction in meltwater input to N. Atlantic
- reduced iceberg production in the Barents Sea
- Interactions with Southern Ocean/Antarctica?
- Freshwater input into the Gulf of Mexico
Facts about the Svalbard-Barents Sea Ice Sheet
- Mostly grounded below sea level
- Which makes it less stable than ice grounded above sea
- Will have deglaciated more rapidly than other ice sheets, through iceberg calving
- Icebergs melt in the N Atlantic, supressing the AMOC
What happened during the transition from BA to YD?
Rapid cooling
- Warmer Bolling-Allerod was followed by rapid cooling into the Younger Dryas
- Caused by another change to the THC
What did the catastrophic drainage of N American ice cause?
Glacial Lake Agassiz
- Freshwater input to the ocean
- Old theory suggests that between BA and YD, the route switched from southern to eastern
- Geochronological evidence for the northern route into Arctic Ocean
What was the impact on the AMOC
- Freshwater covered surface of N. Atlantic, preventing the formation of NADW
- Then means the overturning happens further south
- Warmer surface waters from lower latitudes do not reach as far north
- therefore climate cooling
How did the Holocene begin?
- YD ended with abrupt warming 11.7 ka before present
- Strengthening of the AMOC - overturning circulation happens further north
What does a post-glacial landscape look like?
- Sediment and scoured bedrock
- No vegetation/ little obvious life
What was Britain like during these periods?
- Proxy evidence of environmental change is British sediments
- Sediments from peat bogs and lakes are best
What was Britain like during the Bolling-Allerod interstadial?
Hawes Water record indicated significant environmental change
What was Britain like during the Younger Dryas?
Glaciers
- By the end of the BA interstadial, most/all of the glaciers in Britain had disappeared
- But the Younger Dryas triggered cooling sufficient to allow glaciers to return
- Very clear glacial geomorphological evidence
Britain during the Younger Dryas: Climate
BA to YD saw British temperatures drop by 4C
Britain at the start of the Holocene: Temperatures
Rapid warming of around 3-4C
British environment at the start of the Holocene
- Climate warms
- Glaciers disappear
- Landscape could be recolonised by a larger wider variety of vegetation compared to the tundra grassland of the YD
- Vegetation succession
What was the Mid-late Holocene like?
5-6,000 years ago, mixed deciduous woodland was established as the dominant vegetation type
- Britain should be covered in this vegetation…
The Anthropocene?
- From the mid-late Holocene, the British landscape has been dominated by humans
- Evidence of tree clearance and beginnings of agriculture
- Evidence of grass begins to dominate in the pollen record
- A new epoch?
- Currently being considered for official epoch status, alongside the Pleistocene
(2.588Ma-11.7ka BP) and the Holocene (11.7ka to present) - Debate as to when it should start (mid-Holocene agricultural boom, industrial
revolution, nuclear age?)
