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Climate Data and Paleoclimate Proxies

Climate Data and Paleoclimate Proxies. Ruddiman p. 17-31, Appendices 1 and 2 Paleoclimate at NOAA. Overview. Direct climate information Instrumental Historical Indirect climate information (proxies) Measurement techniques Dating Calibration Quantitative informaiton Types of proxies

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Climate Data and Paleoclimate Proxies

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  1. Climate Data and Paleoclimate Proxies Ruddiman p. 17-31, Appendices 1 and 2 Paleoclimate at NOAA

  2. Overview • Direct climate information • Instrumental • Historical • Indirect climate information (proxies) • Measurement techniques • Dating • Calibration • Quantitative informaiton • Types of proxies • Tree rings • Corals • Sediments • Speleothems • Ice cores

  3. Instrumental Records Land temperature record Ocean temperature record

  4. Historical Records • Written accounts • El Niño events recorded from late 1500's • Crop harvest, migrations, spring blooms • Hurricane landfall • Artwork • Snow/ice in temperate locations during Little Ice Age

  5. Direct Measurements vs. Proxy Records • Direct measurements have limited time frame • Historical records often qualitative, incomplete • Proxies = natural archives of climate information

  6. Dating Techniques • Radioactive dating • Unstable atom decays at known rate (half-life) • 14C, U-Th, 210Pb, 10Be - recent proxies 14C dating curve 1 half-life 2 half-lives 3 half-lives 4 half-lives

  7. Calibration • Make sure the proxy works!  Compare with instrumental data From Lindsley et al., 2000

  8. Quantitative Information • Isotopes • Atom with same # of protons/electrons, differing number of neutrons • Protons – Postive charge • Electrons – Negative charge • Neutrons – No charge (neutral) • Ex.- Oxygen exists as 16O, 17O, 18O • Oxygen = 8 protons • 16O = 8 neutrons, 17O = 9 neutrons, 18O = 10 neutrons

  9. Quantitative Information • Oxygen isotopes - 16O and 18O (stable) • 16O lighter than 18O - distribution changes through time • Evaporation - Lighter 16O more likely to evaporate • Precipitation - Heavier 18O more likely to fall as rain • Proxy for temperature, rainfall in water/carbonate (CaCO3) More 16O at high altitudes More 18O rains out near coast

  10. Quantitative Information • Carbon stable isotopes - 13C, 12C • Information about ecological community (precipitation) • Wet condition plants (C3) - more 12C, dry condition plants (C4, CAM) - more 13C • Trace metal ratios - Sr/Ca, Mg/Ca • Replace one atom with another, usually temperature controlled • Trace metal concentrations - Fe, Ti • Proxy for sediment source (terrestrial) •  Grain size distribution • Runoff, currents

  11. Predominantly temperate (mid-latitudes) Dated using radiocarbon Thick bands during growing season, thin bands during cold/dry months Varying widths of growth bands reflect temperature or precipitation Need stress to vary growth rates U.S. Southwest - desert Tree Rings

  12. Tree Rings

  13. Corals • Skeletons made of aragonite (CaCO3)  • Dated using annual density band, U-Th, 14C   • Recorders of tropical sea  surface conditions:         Temperature, Salinity • Oxygen Isotopes record a  combination of temp and salinity • Strontium/Calcium (Sr/Ca) records mainly temperature

  14. Lake Sediments • Record terrestrial climate variations (temperature,         precipitation) • Varved sediments - annual banding          caused by seasonal changes in          productivity, sediment input • Summer - mostly biological,                  organic-rich • Winter - mostly runoff • Ostracods • Oxygen isotopes              of shells • Pollen/C isotopes • Changing vegetation 

  15. Marine Sediments • Foraminifera •  Temperature, ice volume •  Replacement of Ca with Mg in skeleton - temp • Oxygen isotopes - ice • Ice-rafted debris • Indicative of glacial conditions

  16. Cariaco Basin • Varved marine sediment record (very rare) • Fe, Ti concentrations  changes in precipitation over S. America • Foram record  temp, precipitation • ITCZ

  17. Speleothems • Calcium carbonate (CaCO3 cave deposits • Grow on scale of 10’s of microns per year • Can get continuous record for tens of thousands of years  δ18O  used for paleoclimate reconstructions: Monsoons The δ18O of speleothems is a reflection of the groundwater δ18O, and ultimately the δ18O of rainfall in the region  Changes in δ18O may be attributed to: • Ratio of summer to winter precipitation • The movement of the ITCZ • Changes in ENSO intensity

  18. Ice Cores • Dated with volcanic ash, ice flow models • Located at high latitudes, altitudes • H2O in ice • Oxygen isotopes - temp, precipitation • Dust amounts • Global dryness, wind •  Air Bubbles • Actual samples of trapped air, determine past concentrations of different gases, i.e. CO2, CH4

  19. Air in Ice Cores • Air in bubbles may be 100’s of years younger than surrounding ice • Difficult to determine timing of CO2 increase vs. temp increase

  20. Multiproxy reconstruction Although the proxies we have discussed come from all over the world and tell us about different aspects of past climate, they can be used together to look at the bigger picture Modified from Cheng et al., 2009

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