GEOG 401: Tectonic Changes in Climate. Dr. John Abatzoglou Spring 2013

Transcription

1 GEOG 401: Tectonic Changes in Climate Dr. John Abatzoglou Spring 2013

2 The Long View Early Earth s history (4.5BY- 570MY): 3.7 BY: 10C warmer BY: widespread glaciers, snowball earth BY: warm and ice- free, catastrophic events MY: at least two ice ages 2

3 Why all the Wiggles? Global Climate changes naturally Long Term: consnent posison, carbon cycling, changes in atm CO2 due to tectonics Short Term: orbital Forcing, ocean- atmosphere circulason, asteroid impact Energy Balance of Planet Driven by - Earth/Sun relasonships - Changes in Albedo - Changes in Atmospheric Gases 3

4 Paleoclimate Paleoclimate: past climate, the science of reconstrucsng climate If we want to know about future we must first try to understand the past Hurdles for paleoclimatology - Thermometer invented in 17 th century, with limited observasons - Wri]en records can be useful, albeit subjecsve SoluMon Instead of thermometers and rain gauges, look for environmental records or imprints that correlate strongly with climate elements

5 Why Care About the Past? Understanding of Past Changes in Climate - mechanisms - spasal and Sme scales - abrupt change - rates of change - natural climate experiments and resiliency Earth System Response to Climate Change - feedback systems - biosphere response Backdrop against which to view current climate evolu&on

6 Climate record resoluson (years) 1,000, ,000 10, mon 1day Satellite, in- situ observason Historical data Tree rings Lake core, pollen Ice core Ocean sediment, isotopes Fossils, geologic evidence Be]er ResoluSon/Understanding 1,000, ,000 10, mon 1day

7 ReconstrucSng the Past Proxy data: indicators that infer climate properses back in Sme Changes in growth/deposison (tree ring, ice cores, sediments) Changes in ecological distribusons (pollen, middens) Changes in chemical makeup of gasses (isotopes) General rule: - the older the proxy data, the lower the temporal resoluson that can be measured - some proxy data are global indicators, other localized - Isolated study of changes observed at one locason typically don t provide sufficient informason for understanding change

8 Tectonics and Long- term Climate Four Main Processes: 1. Land- ocean spasal configurason: control where ice sheets form 2. Spread of sea floor: volcanoes and oxidason of organic carbon in sedimentary rocks, control release of CO 2 in the atmosphere 3. Chemical weathering: control CO 2 removal process, a thermostat of the earth s climate 4. Uplii- mountain effect: expose fragmented and fresh rock for chemical weathering Note: We can reconstruct plate tectonics (i.e., consnent posison) using paleomagnesc reconstrucsons

9 Carbon Reservoirs Most C locked away Carbon was once living, therefore the term fossil fuel comes from the fossilized sediments in rock

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12 Polar PosiSon Hypothesis H1: Ice sheets preferensally form over high- lastude consnents. H2: Ice sheets won t form if land- masses do not reach high lastudes. What physical processes would favor ice formason over land v. ocean? Good hypothesis, but does not explain everything Problem: No ice found between Mya despite large SH landmass suggests something else controlled the surface energy balance

13 Seafloor Spreading Rate Hypothesis Carbon inputs from lithosphere to atmosphere occur through tectonic acsvity visa- vi volcanic erupsons and seafloor spreading Changes in the rate of seafloor spreading alter the carbon flux into the atmosphere, and the greenhouse effect

14 EsSmaSng Atmospheric Carbon Burdens Lithosphere- Atmosphere Exchanges Volcanic Outgassing 0.1 Gt/yr Atmospheric CO2 600 Gtons Weathering 0.1 Gt/yr Volcanic Outgassing 0.11 Gt/yr Atmospheric CO2 X Gtons Oceans take ½ excess atm CO2 Weathering 0.1 Gt/yr If this imbalance persists over 1 million years

15 MY: climate was generally colder MY: climate was generally warmer 65-0MY: Earth s climate became colder with Sme.

16 Mesozoic Period ( mya) Indicators 1. No evidence of glacial condisons 2. Faunal/floral record suggest poleward shiis in species 3. Sea level m higher than present 4. Global Temperatures: 5-7C warmer than present 24

17 Causes 1. Post Pangea, a period of high tectonic acsvity!!! 2. Hypothesized to have increased atmospheric CO2 concentrasons to 4-10x present values 3. Flooding of land surface à decrease albedo 4. ConSnent posisons

18 Effect of CO2 on Global Temperatures Very sensisve during cold periods (e.g., ice- albedo feedback useless in ice- free planet >1000pm) Infill of atmospheric window (CO2 saturason) Note that other feedback processes may become more important at warmer temperatures

19 Return to the Greenhouse Paleocene- Eocene Thermal Maximum Strong warming 55MYa Lasted 70kya, abrupt for tectonic change Large warming (6C in 20,000 years) resulted in acidificason of ocean and widespread mortality Abrupt climate feedbacks are implicated here in releasing large amounts of carbon into the atmosphere

20 Methane Clathrates Methane accumulates in sea bo]om sediments/permafrost Considered to be a stable state of methane Warming decreases the density of water in shallow sediment beds and may allow them to disassociate and be released into the upper ocean and atmosphere

21 Global Climate cools Proxy Evidence Aier Deep Impact 1. Ice raied debris sediment in S.H. 35MYa 2. Greenland first evidence 7MYa 3. Fossil record show change in high- lastude vegetason from broadleaf (ill- adapted to cold)à needle- leaf (modern veg. record) Greater % of broadleaf veg in warmer climates 34

22 Proxy records: Life aier death Carbonate shells from marine life contain carbon and oxygen of ambient surface ocean condisons (equilibrium w/air) Carbon falls into deep ocean and into inorganic C Sediments to bo]om of ocean laying down a layer of isotopic informason on Oxygen and C Persistence of sediment record allows for long- term reconstrucson over veg/ice sheet records Foraminifera: provides info on carbon/oxygen

23 Isotopes Atom of the same element with a different numbers of neutrons: Greek for same, but different

24 RadioacSve isotopes: a proxy for age RadioacSve isotopes: logarithmic decay over Sme Rare isotopes, release energy through decay process Half- life: Sme required for 50% of the original atoms to decay to Nitrogen- 14 Carbon 14 (made via cosmic- rays in stratosphere, and release in Nuclear bombs) Half life = 5700 years If you know the raso of 14- C to 14- N, you can then deduce age of given object per mil

25 Stable isotopes of oxygen: a proxy for temperature Stable isotopes: do not decay over Sme 16 O (about 99.8% of total) and 18 O (most of the rest). Which isotope weighs more??? The normal raso of 18 O/ 16 O is about 1/400, so when we express variasons in this raso, it is usually mulsplied by a large number (1000), we call this δ 18 O ramo For ( 18 O/ 16 O) SMOW δ 18 O = 0. Standard Mean Ocean Water δ 18 O = 18 O/ 16 O of sample - 18 O/ 16 O of standard per mil 18 O/ 16 O of standard 1000

26 Making Sense of Oxygen Isotopes Surface ocean water is the standard (SMOW) Deep ocean tends to be enriched in delta (+3-4 per mil) High lastude ice sheets depleted in delta (- 40 per mil) Climate records suggest delta in oceans is sensisve to: (a) Changes in ocean temperature Increase 1 per mil for every 4.2C decrease in ocean temps (b) Changes in the size of ice sheets Increases as ice sheets grow, heavier isotopes stay in ocean

27 Why: FracSonaSon of Isotopes FracSonaSon: Natural processes tend to preferensally take up the lighter isotope, and preferensally leave behind the heavier isotope. Oxygen isotopes are fracsonated during evaporason and precipitason of H 2 O H 2 16 O evaporates more readily than H 2 18 O H 2 18 O precipitates more readily than H 2 16 O 18 O is heavier than 16 O H 2 18 O is heavier than H 2 16 O Oxygen isotopes are also fracsonated by marine organisms that secrete CaCO 3 shells. The organisms preferensally take up more 16 O as temperature increases.

28 Oxygen isotopes and paleoclimate PrecipitaSon favors H 2 18 O Cloud is depleted in O-18 EvaporaSon favors H 2 16 O tropics H 2 16 O, H 2 18 O CaCO 3 H 2 18 O H 2 16 O Ocean Carbonate sediments record a δ 18 O signal of upper- ocean water. H 2 18 O H 2 16 O Ice pole δ 18 O signal in ice reflects temperature and source from evaporason. Colder condisons depleted oxygen- 18

29 DisSllaSon of Oxygen Isotopes Another Viewpoint Water evaporates near the equator, transported poleward through many ET/PPT cycles. PrecipitaSon favors d 18 O, leaves residual h20 vapor depleted in d 18 O. d 16 O falling at high lastudes over land surface is locked away, leaving ocean rich in d 18 O. When land ice melts, O- 16 returns to oceans and d 18 O decreases d 18 O of seawater (or ice core water) proxy for global ice sheets.

30 If we collect a shell/sediment made out of CaCO 3 delta O 18 = [(O 18 /O 16 sample/o 18 /O 16 standard) - 1 ] x1000 Note: The sample is compared to SMOW. PosiSve delta O 18 values mean that your sample is enriched in the heavy O isotope; negasve delta O 18 values mean it s depleted in the heavy O 18. What could you deduce about global climate if you saw sediments from 50 mya were depleted in d018?

31 Thermometers are todays Seashells Increases in d 18 O (bo]om h20) Water enriched in heavy isotope of oxygen Today s deep water forms at about 2C This data suggests deep water was 16C 50Mya! (1 per mil : 4C) Polar climates were much warmer. Why? Deep water forms at high- lastudes!

32 Suspect #1 The Indian plate slams into the Eurasian plate - uplii and mountain building 47

33 Chemical Weathering Hypothesis Strongest w/precip

34 Suspect #2 Reduced Ocean Spreading Rates

35 Suspect #3 Sea Gateways Isthmus of Panama More heat to atmosphere More water to atmosphere Hypothesis is that this would INCREASE glaciason