Lec 8 - Deglaciation and other climate fluctuations Flashcards
What are ocean currents?
- horizontal motion of surface waters (often found along rims of ocean basins)
- created by wind stress (drag), so influenced by Coriolis force and geography of ocean basins
Where do ocean gyres occur?
in the middle of ocean basins (deep parts)
How do the east and west edges of ocean basins compare?
western edges carry warmer water
- due to these being the areas carrying water from the equator to the poles
When does upwelling in the ocean occur?
when strong offshore winds along a coastal regions drag warm surface water seaward
- draws up cooler water from below
Give an example of a place that is influenced by cold water upwelling
The Western coast of S America, cold water upwelling helps create the Atacama desert (driest desert on earth)
What is ocean downwelling?
when warm water is cooled and forced downward
Give an example of how ocean downwelling can have climatic effects
North Atlantic – North Atlantic drift loses a lot of heat to the atmosphere and sinks deeper
How much did sea level rise after the last glacial max?
110-125m
What geographic effects did deglaciation have?
- submerged links between continents/islands
- flooded basins
- formed meltwater lakes
- forests and tundra moved north
What triggered the melting of northern ice sheets?
- precession of the equinoxes - tilt and location of perihelion maximized summer insolation
- as ice sheets melted, their impacts on climate diminished
- also a shift in CO2 concentrations
When did our orbit maximize summer insolation in the N hemisphere?
about 10kya
What archive is considered the best record of ice sheete melting?
corals!
- since some corals only grow just below sea level
Do ice sheets grow and melt at a steady rate?
No!
- melting had two big pulses
What were the causes of the first meltwater pulses that caused a burst of sea level rise at the start of deglaciation?
- pulse from Barents ice sheet (Northern marine sheet) which was vulnerable to melt as a seawater icesheet below sea level
- Gulf of Mexico - meltwater rapidly flowing from Laurentide Ice sheet
What was the Mid-Deglacial Cooling?
- the Younger Dryas period
- from pollen records, we know things cooled down again during deglaciation
What caused the Younger Dryas?
- low salinity meltwater might have disturbed the ocean temperature conveyer belt
What feedbacks are relevant to deglaciation?
- albedo (ice)
- bedrock/elevation (delayed rebound from ice sheets)
- greenhouse gases
what are proglacial lakes?
lakes formed from meltwater in the depressed bedrock left by ice sheets
How did deglaciation affect monsoons?
monsoon effects grew (more insolation/land heating)
What is a no-analog community/climate?
a community/climate that is compositionally different from any modern baseline
How does the Walker circulation work?
warm surface water is carried from east to west Pacific (Americas to Oceania)
- warm water evaporates, is carried back eastward by winds?
What is an El Nino event?
- reversal of Walker circulation
- warm surface waters transported eastward
- movement of warm water causes cold upwelling along South American coast
What are changes to the Walker circulation called?
ENSO - El Nino Southern Oscillation
What happens after an El Nino event?
a strengthened normal phase, or La Nina
- colder
What is the Pacific Decadal Oscillation?
PDO is a large oscillation pattern (20-30yrs) in the Pacific
What is Arctic Oscillation?
AO is as index of pressure differences between Arctic and Southerly latitudes
- affects weather over North America
What happens in a positive AO (Arctic Oscillation)
- cold stratosphere
- warmer, wetter troposphere in NA
What happens in a negative AO (Arctic Oscillation)?
- less cold stratosphere
- colder, drier in NA
What is the North Atlantic Oscillation?
Pressure difference between Iceland and Bermuda
- positive when there is a greater pressure difference
- negative when there is a lower pressure difference than normal
What does the North Atlantic Oscillation influence?
- location and intensity of jet stream in NA and Europe
- positive phase = stormy in Europe, mild/wet in NA
What can we learn from climate oscillations?
everything is interconnected? lots to consider when predicting future climate
