Climate Data and Paleoclimate Proxies Ruddiman p 17

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

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

Instrumental Records Land temperature record Ocean temperature record

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

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

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

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

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

Quantitative Information • Oxygen isotopes - 16 O and 18 O (stable) o 16 O lighter than 18 O - distribution changes through time § Evaporation - Lighter 16 O more likely to evaporate § Precipitation - Heavier 18 O more likely to fall as rain o Proxy for temperature, rainfall in water/carbonate (Ca. CO 3) More 16 O at high altitudes More 18 O rains out near coast

Quantitative Information • Carbon stable isotopes - 13 C, 12 C o Information about ecological community (precipitation) o Wet condition plants (C 3) - more 12 C, dry condition plants (C 4, CAM) - more 13 C • Trace metal ratios - Sr/Ca, Mg/Ca o Replace one atom with another, usually temperature controlled • Trace metal concentrations - Fe, Ti o Proxy for sediment source (terrestrial) • Grain size distribution o Runoff, currents

Tree Rings • 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 o Need stress to vary growth rates o U. S. Southwest - desert

Tree Rings

Corals • Skeletons made of aragonite (Ca. CO 3) • Dated using annual density band, U -Th, 14 C • Recorders of tropical sea surface conditions: Temperature, Salinity • Oxygen Isotopes record a combination of temp and salinity • Strontium/Calcium (Sr/Ca) records mainly temperature

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

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

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

Speleothems • Calcium carbonate (Ca. CO 3 cave deposits • Grow on scale of 10’s of microns per year • Can get continuous record for tens of thousands of years δ 18 O used for paleoclimate reconstructions: Monsoons The δ 18 O of speleothems is a reflection of the groundwater δ 18 O, and ultimately the δ 18 O of rainfall in the region Changes in δ 18 O may be attributed to: 1. Ratio of summer to winter precipitation 2. The movement of the ITCZ 3. Changes in ENSO intensity

Ice Cores • Dated with volcanic ash, ice flow models • Located at high latitudes, altitudes • H 2 O in ice o Oxygen isotopes - temp, precipitation • Dust amounts o Global dryness, wind • Air Bubbles o Actual samples of trapped air, determine past concentrations of different gases, i. e. CO 2, CH 4

Air in Ice Cores • Air in bubbles may be 100’s of years younger than surrounding ice • Difficult to determine timing of CO 2 increase vs. temp increase

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