Transcript Document

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 14C, U-Th, 210Pb, 10Be - recent proxies
14C
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
o
o
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
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 16O at high
altitudes
More 18O rains
out near coast
Quantitative Information
• Carbon stable isotopes - 13C, 12C
o 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, 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
(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 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
• H2O 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. 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