Complete Revision Notes
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I produced these notes before my first year examinations at Cambridge University as I wrote out a broad overview of the course to help me understand it. They explain many of the basics of physical geography from long-term climate change to contemporary processes. References are included and useful references to remember are listed at the end.
General Concepts Schumm & Lichty 1965 – Interlinked nature of time and space within nested hierarchy of scales. Maslin et. al. 2001 – Feedbacks (positive & negative) in process of environmental change – Responses may be linear and synchronous – muted or limited (buffered) – delayed or non-linear – or threshold responses. They may also be ‘overshoot’ extreme responses returning to stability (Zachos & Kump 2005). Look for life/environmental processes interactions – the Earth-life system ties together physical and biogeochemical processes surprisingly closely, ie through seawater subduction into volcanoes; carbon interactions (melting ice triggering volcanic activity); geological carbon cycle. How does the Earth work? Mantle, then lithosphere (including crust and upper viscous mantle). Oceans have dense thin crust and continents have thick light crust hence are more buoyant than the oceans – continents are also old (as they are more difficult to destroy) while ocean floors are rarely older than a few hundred mya. Seafloor spreading from deep ocean ridges driven by mantle convection (Hess, refined by Matthews and Vine). Plates floating around driven by internal energy (Wegener), with three kinds of boundaries:
- Divergent (ie spreading), creating light oceanic crust out of mantle. If it happens in the middle of the continent it creates rift vallies and eventually seas/oceans (breaking up continents ie India). Where it fails it creates good conditions for oil.
- Collision – one plate forced under another. When continent reaches the edge it cannot go down so the seafloor is subducted under the continent (ie Pacific Coast of Americas). One pushing up the other making mountains (orogeny).
- Slip/parallel faults – creating strike/slip Earthquakes. Continental drift measurable by palaeomagnetism and geological evidence but now GPS too. Long-Term Environmental Change History of the History of environmental change: Uniformitarianism/catastrophism – James Ussher of Armagh (6000 years). Lyell (correspondent with Croll, both Scottish enlightenment figures), with Agassiz, associate of Humboldt, hypothesizing ‘Ice Age’ from glacial features all throughout Europe (predecessor of Snowball Earth – 700 mya?). Penck and Bruckner suggested four Ice Ages – Bretz scablands – Slaymaker (neocatastrophism). Both gradual/catstrophic concepts combined in ideas of threshold etc. change Tectonics affects climate on largest scale with drift (poleward – importance of high latitude continents – critical ‘Milankovitch-sensitive’ latitude recently of 60-80 N). Cooling of ~15 c in Cenozoic. India collided with Asia 40-55 mya (debate about exactly when) – 2000 km of movement (at c. 4 cm a year), about half upwards and half inwards. Pushing some movement outwards ‘like a slab of brie’ (geomorph: cheesewires! Use cheese metaphor in exam) creating linear mountain ranges as well as Tibetan Plateau. ‘Unprecedented’ but is it really? One day Australia will do the same. Modelling past climate change: Berner, Lasaga and Garrels (1983) – BLAG mdoels –
measuring climate change, CO2 over geological timespan, couldn’t account for Cenozoic cooling. Kutzbach et. al. 1991 – Influence of Laramide orogeny (Rocky Mountains) and Tibetan Plateau on reorganizing circulation patterns (interrupting jetstream), radiating heat to higher altitudes but could only account for 1.5 c cooling. Isthmus of Panama 3mya –
reorganizing oceanic circulation, increasing moisture to Northern Europe (gulfstream without which Europe would be 10 c cooler), as well as increased freshwater output from Siberian rivers causing sea ice formation/albedo feedback. Raymo & Ruddiman 1992: Increase in chemical weathering of silicate rock and organic carbon burial (sedimentary runoff – Gangetic fan) – responsible for cenozoic cooling – 20% of global solute flux from this area. Strengthened monsoonal patterns a positive feedback (increased vegetation, chemical and sediment erosion). Zachos & Kump 2005 – Oligocene transition ~35 mya with an abrupt (c. 50,000 year) reorganization of climate system associated with growth of Antarctic Ice Sheet –
intensifying circulation – aridity in continental interiors. Marked by overshoot to “transient”
extreme sate. Positive feedback of increased productivity and oceanic overturn (thermohaline intensification ½ ice sheet cover – phosphate upwelling and carbon burial)
– negative feedback of decreased weathering due to icecap (would this offset increased weathering triggered by Tibet?). Molnar et. al. 1993 – Strengthening/altering monsoonal patterns by sucking air up at mid-latitudes, reversal of normal Hadley cell direction (heating at equator) – at 8mya. Croll suggested orbital periodicity, refined by Milankovitch (early 20th C) into 100ky (eccentricity), 41ky (obliquity) and 19/23 – 21ky (precession) cycles affecting Northern Hemisphere Summer Insolation. Revived in 1970s with evidence from deep ocean cores (CLIMAP project – LGM) – Hays et. al. 1976 “Variations in the Earth’s Orbit: Pacemaker of the Ice Ages” used spectral analysis to show strong relationship between periodicities and ice ages, later shown to be not just in timing but also size of fluctions – but
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