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Tectonics And Climate Notes

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ESD: Past Climate ChangeTectonics and Climate Notes to discuss the relationship between tectonics and climate change, including evidence used to understand the relationship. Contents

1. Tectonic Scale Climate Change (CC)
 Nature of CC
 Evidence for CC
 Drivers of CC
 BLAG Hypothesis
 Weathering and carbon cycles

2. Relationship between geomorphological processes and climate change

3. Testing the Hypotheses for Cenozoic Cooling
 Cenozoic Era
 Evidence base
 Uplift-Erosion Theory

4. Key Texts

1. Tectonic scale Climate Change

Image: Veizer et al (1999)

Nature of Long Term (LT) Climate Change (CC):

Large scale climate has changed on timescales of 10-100s of Ma (Millions of years) Large scale oscillations (major changes in past climate), but the range of conditions experienced is relatively narrow, with no runaway- so feedbacks dampen the excursions

Evidence used for LT CC:

Fossils providing evidence of species present- indicative of climate o Fossils of forests, conifer trees only in warmer climates o Fossil soil formations Geomorphological evidence- identifying locations of former glacial activity (often in present warm areas): Tillite and scratches, Glacial erosional features- grinding of rock surfaces, drop stones- deposited in deep ocean, dropped into the middle of the deep ocean by an iceberg, recognised as fluvial sediments as fine grained sediment from slow fluvial movement Geochemical/isotope data - Ocean water isotope ratios as a proxy for global ice volume

Drivers of LT CC:

Tectonics - Plate boundary reorganisations operate over these timescales of CC and are important drivers of environmental changes at the tectonic scale. Plate boundary reorganisations have implications for: o Tectonic uplift of mountain ranges or plateaus o Opening/closing of sea-ways o Changing location of continents
 Use evidence from palaeomagnetism, as rocks cool the particles align with poles so can determine where poles where in relation to the rock to map location - Continued generation of palaeomagnetic data constantly revises ideas (Kent and Van der Voo, 1990)
 Aligning timings suggests that ice sheets are only present when continents are near the poles, but don't form every time continents are near the poles (ie warm sometimes when should be cold due to position)- position is necessary but not sufficient to drive large scale glaciation
 Does plate movement affect global climate= Yes role to play but other mechanisms involved o Changing sea level
    Atmospheric Carbon Dioxide o Recognised as the key long term temperature control, particularly important is where the carbon is- altering balance of inputs/outputs significant enough to yield big differences in carbon reserve sizes o Both BLAG and Uplift-erosion mechanisms account for changes in CO2

BLAG Hypothesis = Berner et al, (1983)

CO2 concentration in the atmosphere is highly sensitive to changes in seafloor spreading rates and continental land area, and to a much lesser extent masses of calcite/dolomite (Berner et al, 1983) When ocean crust is subducted, and when ridges spread, CO2 is released. Increased spreading rates= Increased release of CO2 into the atmosphere. Subduction- CO2 released during heating/decarbonation Spreading- influences area of continents- influencing rate of XO2 removal from atmosphere This process must be REGULATED somehow- BLAG release of CO2 into the atmosphere and subsequent warming doesn't result in a runaway GH effect .. Answer= Removal from atmosphere via WEATHERING Evidence: Rates deduced from dating seafloor rock, noting distance from plate boundary Rates concur with CO2 levels and cooling periods up until 10Ma ago, when seafloor spreading rates increased but the earth did not warm Cooling in the Cenozoic required a progressive reduction in spreading ratebut rates of spreading increased at 15ya Issues in the evidence o Kent and Muttoni (2013)- Conflicting estimates of global ocean floor production rates over this time period .. Muller et al (2008) and Seton et al (2009)= high production in Late Cretaceous and decreasing production in Cenozoic (AGREES with BLAG), but Humler (2004/6) show reduced production in Late Cretaceous and increasing production over Cenozoic o Reconstructions of oceanic lithosphere history are invariably based on substantial and often poorly constrained extrapolations (Rowley, 2008) o Kent and Muttoni (2013)- Assume constant seafloor production rates in model because view this as better representative due to absence of compelling evidence for LT secular changes in global ocean floor production rates

Weathering and carbon cycles

Weathering of silicate bedrock and carbonic acid in the soils- hydrolosis of silicate rocks is the main mechanism , whereas dissolution W of carbonate rocks has little net effect on CO2 Carbonate-Silicate cycle: Weathering of rocks, washed into oceans, CO2 dissolved into oceans, become sediment in seabed. Slow transition of C from seabed back to the atmosphere- occurs over 10s Ma Relationship between weathering and climate state- NEGATIVE FEEDBACK o Co2 increases temperatures, increased temperatures= more rain, more vegetation and faster chemical reactions = more Co2 drawdown

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