L7 - The Holocene Flashcards
The Holocene is Stage 1 covering which years?
10,000 years ago to the Present
What was the 8.2kyr event?
The largest amplitude event in the Holocene
Sub-Orbital timescales are what timescales?
Millenial
How much higher is SL that it was at the LGM?
120m
What are the 2 main drivers for Eustatic SL change?
- G-IG Melt
2. Thermal Expansion
Which sea was flooded at the end of the last deglaciation?
The Black Sea
Glacial rebound occurs on what timescale and where is it shown in the UK?
1,000s of years
The North is rising (Firth of Forth)
The South is falling (Dungess, Kent)
What is the Climatic Optimum?
A dominant Northern Hemisphere Summer Event
When was there warming in the Holocene?
Early (Pre 8.2 event)
More recently (Post 8.2 event) what has the general trending temperature been in the Holocene?
Gradual Cooling
Give 6 methods for evidencing Holocene temperature trends?
- Greenland Ice Cores
- European Pollen Assemblages
- Low Latitude Ice Cores
- Western Equatorial Pacific Forams
- Antarctic Ice Core
- Tropical Atlantic Forams
What has happened to the Northern Hemisphere snowline throughout the Holocene?
It has lowered
What do colder summers in the North mean for monsoons?
They are weaker
What do warmer summers in the South mean for monsoons?
They are stronger
What does a southwards shift of the ITCZ cause?
Drying in the North and increase pptn in the South
What has happened to the ITCZ throughout the Holocene?
It has been shifting Southwards
In the early Holocene, there was high obliquity which meant what?
Closer to the sun in summer (perihelion) – stronger summers and more seasonal contrast
(It is the opposite today)
What dominates insolation today?
Precession
In the last how many years has methane risen? and what are the 2 theories?
~5000 years
- Paddy Fields
- Natural Changes in Tropical Hydrology
How many years have we got a well-documented rise in CO2 and what are the 2 main reasons for this when it should be falling?
~8000 years
- Forset Clearance
- Fossil Fuels
What has the Greenland Ice Core shown about the 8.2 event?
Less snow accumulation, lower temperatures, winder, increased fires, decreased methane
What have speleothem records shown about the 8.2 event?
Dryer in the North and Wetter in the South
What have North Atlantic Marine Sediments shown about the 8.2 event?
Similarities with the Stage 3 stadial – reduced SST, reduced surface salinity, lower bottom current flow speeds
What are the 3 centennial to millennial variabilities to occur during the Holocene?
- Fluctuations in IRD (1500 year periodicity)
- Asian Monsoon Variations (small bond events = weaker and match IRD events)
- South American Monsoon Variations (stronger but we aren’t confident)
When was the Maunder Minimum?
During the Little Ice Age
How long are solar cycles?
11 years + some longer variations
How does TSI change globally with increased sunspot activity?
~0.1%
What can be used as a proxy for solar variability?
C-14 and Be-10 and cosmic ray intensity records
What does a decreased TSI mean for monsoons?
Weaker in the Northern Hemisphere and Stronger in the Southern Hemisphere
What does a decreased TSI mean for SST?
Colder SST
