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

Climate Data and Paleoclimate Proxies

Ruddiman p. 17-31, Appendices 1 and 2

Paleoclimate at NOAA

Overview• Direct climate information

o Instrumentalo 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

  Ocean temperature recordLand temperature record

Historical Records

• Written accountso El Niño events recorded

from late 1500'so 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 14C, U-Th, 210Pb, 10Be - recent proxies

14C dating curve

1 half-life

2 half-lives3 half-lives

4 half-lives

Calibration

• Make sure the proxy works!  Compare with instrumental data

From Lindsley et al., 2000

Quantitative Information

• Isotopeso Atom with same # of protons/electrons, differing number

of neutronso Protons – Postive chargeo Electrons – Negative chargeo Neutrons – No charge (neutral)

o Ex.- Oxygen exists as 16O, 17O, 18O Oxygen = 8 protons 16O = 8 neutrons, 17O = 9 neutrons, 18O = 10 neutrons

Quantitative Information• Oxygen isotopes - 16O and 18O (stable)

o 16O lighter than 18O - distribution changes through time Evaporation - Lighter 16O more likely to evaporate Precipitation - Heavier 18O more likely to fall as rain

o Proxy for temperature, rainfall in water/carbonate (CaCO3)

More 18O rains out near coast

More 16O at high altitudes

Quantitative Information

• Carbon stable isotopes - 13C, 12Co Information about ecological community (precipitation)o Wet condition plants (C3) - more 12C, dry condition plants

(C4, CAM) - more 13C• Trace metal ratios - Sr/Ca, Mg/Ca

o Replace one atom with another, usually temperature controlled

• Trace metal concentrations - Fe, Tio Proxy for sediment source (terrestrial)

•  Grain size distributiono 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 precipitationo Need stress to vary

growth rateso U.S. Southwest - desert

Tree Rings

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

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 (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: 1. Ratio of summer to winter precipitation2. The movement of the ITCZ3. Changes in ENSO intensity

Ice Cores

• Dated with volcanic ash, ice flow models

• Located at high latitudes, altitudes

• H2O in iceo 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. CO2, CH4

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

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