EVSC10001 Lecture Notes - Lecture 32: Thermohaline Circulation, Atmospheric Circulation, Oxygen-18
10 Jun 2018
School
Department
Course
Professor
Quaternary
Last 2 million years
-
Human history developed
-
Characterised by multiple glacial-interglacial cycles
-
Glacial cycles
Global temps reconstructed from O isotopes in ice sheets and ocean
sediment cores
Glacial
Lower sea-level
§
16O evaporates -> snowfall -> H216O accumulates in ice
§
18O enrichment in water
§
○
Interglacial
Higher sea level
§
16O evaporates -> precipitation + run-off -> 16O returns to
oceans
§
Decrease of 18O/16O ratio
§
○
-
Glacial cycle: cold stage - but internally variable
-
Global LGM (last glacial max) - 20 ka
-
When shelves are exposed -> continents grow + global dust increases
-
120m lower sea level during LGM
-
Facilitated by expansion of humans
-
Modified thermo-haline circulation
Ocean currents blocked off
○
-
Glacial climate
Different ocean-land constellation
-
Modified thermohaline circulation
-
Large polar ice sheets - contraction of global atmospheric circulation
-
Larger temp differences - wind intensification
-
Global glacial landscapes
Predictions
-
Temp reduction1.
Glacier growth in temperate zone
-
Also affecting river systems
-
Increase temp gradient -> stronger wind systems and equatorward shifts 2.
Hydrologic cycle in tropics less intensive due to colder temps -> weaker
monsoon
3.
Exposed shelves -> higher continentality -> expansion of drylands4.
Not much evidence in reality
-
Climate proxy: indirect indicatory of past climate
-
Landscape reconstruction
Geomorphology - remote sensing (recognition and analysis of change)1.
Sediment archives - field + labwork (depositional and transport processes)2.
Chronology - laboratory (timing and rates eg. Luminescence)3.
Glaciation - Loess (fine grained dust)
Can find loess intercolated with orange soils
Dust + soil = cycles b/w glacial and interglacial conditions
○
Orang soil = interglacial
○
-
Outburst floods
A lot of energy
-
Low frequency not often
-
Glacial damming
-
Glacial landscapes in Australia
Snowy mountains - small glaciers
-
WESTERLY WINDS bring moisture should have shifted nORTH -> affect lower
Murray river
-
The murray in the Ice Age
Long-term lateral variability
-
Avulsion: shift in channel direction
-
Larger + wider rivers
-
Source-bordering dune - point bar -> probs shallow
-
Australian tropics - dry or wet?
Monsoon: dominant driver of precipitation
-
Waterfalls from escarpment
-
Less intense, temps lower -> weaker system
When weak, sed builds up in pools
○
-
Swamps - extract sediment core
-
Clay (dry) -> peat (wet)
After ice age becomes peat
○
Interglacial wet periods
○
Peat requires moisture - Holocene
○
-
A green desert
Wasn’t always a desert in the middle - LAKE FULL CONDITIONS DURING
LGM
○
Core - sedimentology, mineralogy, geochemistry, pollen macrofossils
○
Large lake systems started to dry up 45ka
○
-
Earth Surface Dynamics
Earth-surface dynamics - water vs. sediment 1.
Earth is a system - processes are inter-related 2.
Earth-surface dynamics depend on multiple controls (climate, tectonics,
humans, time)
3.
Glacial-Interglacial Cycles
Thursday, 7 June 2018
10:33 pm
Document Summary
Global temps reconstructed from o isotopes in ice sheets and ocean sediment cores. 16o evaporates -> snowfall -> h216o accumulates in ice. 16o evaporates -> precipitation + run-off -> 16o returns to oceans. Glacial cycle: cold stage - but internally variable. Global lgm (last glacial max) - 20 ka. When shelves are exposed -> continents grow + global dust increases. Large polar ice sheets - contraction of global atmospheric circulation. Increase temp gradient -> stronger wind systems and equatorward shifts. Hydrologic cycle in tropics less intensive due to colder temps -> weaker monsoon. Exposed shelves -> higher continentality -> expansion of drylands. Geomorphology - remote sensing (recognition and analysis of change) Sediment archives - field + labwork (depositional and transport processes) Chronology - laboratory (timing and rates eg. luminescence) Dust + soil = cycles b/w glacial and interglacial conditions. Westerly winds bring moisture should have shifted north -> affect lower. Source-bordering dune - point bar -> probs shallow.
