Paleoclimate research at the University of Arizona

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Paleoclimate research at the University of Arizona

• Michael N. Evans
• Laboratory of Tree-Ring Research
• CICESE
• 22 October 2004
• Motivating questions
• Overview of recent results

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Paleoclimate researchers at the University of
Arizona(partial list...)

• J.W. Beck (Physics, Geosciences) wbeck_at_physic
  s.arizona.edu
• J.L. Betancourt (USGS/Geosciences) jlbetanc_at_us
  gs.gov
• A.S. Cohen (Geosciences) acohen_at_geo.arizona.
  edu
• J.E. Cole (Geosciences) jcole_at_geo.arizona.e
  du
• O.K. Davis (Geosciences) palynolo_at_geo.arizo
  na.edu
• M.N. Evans (Tree-Ring Lab) mevans_at_ltrr.arizo
  na.edu
• K.W. Flessa (Geosciences) kflessa_at_geo.arizon
  a.edu
• M.K. Hughes (Tree-Ring Lab) mhughes_at_ltrr.ari
  zona.edu
• A.J.T. Jull (Physics, Geosciences) ajtjull_at_ph
  ysics.arizona.edu
• S.W. Leavitt (Tree-Ring Lab) sleavitt_at_ltrr.a
  rizona.edu
• J.T. Overpeck (Geosciences) jto_at_u.arizona.ed
  u
• J. Quade (USGS/Geosciences) jquade_at_geo.arizo
  na.edu

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A paleo-proxy menu
Archive timescales locales proxies uncert
ainty reef corals 10-1-103yr tropics growth
rate , ?18Of(T,?18Osw) chronology min.
el. f(T), ?14C f(mixing) calibration
'green box' tree rings 100-103yr extra
tropics RW,Df(T,P,G,D), ?14C, ?18O,
?13C calibration 'green
box' ice cores 100-105yr poles, high CO2, CH4,
isotopes, dust, ions,... chronology alt.
tropics f(atm gas conc., T,P, circulation...)
spatial scale packrat 101-105yr arid
regions macrofossils spatial
scale, middens lake seds. 101-105yr lakes, sed
color, CaCO3, isotopes, chron,
calib, anoxic marker species (pollen,
macrofossils) chronology, deep sea mar.
seds f(prod(nutr(T)),S), stratigraphy, mixing, s
ediments 103-107yr gl. oceans minor elements
f(T),... 'green box' rock record 105-108yr gl
oceans sed/strat, stable/radioisotopes
unconformities hist data 10-2-102yr global(t,x
) SAT, SST, SLP, rain,... meas bias,
gaps models 100-108yr global T,P,u,???????
physics, param, paleo bc/ic's
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Two views of paleoclimatology
Paleoclimate is climate that existed before
humans began collecting instrumental measurements
of weather... By analyzing records taken from
trees, reefs, glaciers, sediments, and other
proxy sources, scientists can extend our
understanding far beyond the 140-year
instrumental record... the paleoclimate
perspective allows us to evaluate climate change
many decades and centuries into the past, in
order to develop a more reliable estimate of how
climate may change in the future. -excerpted
from the National Geophysical Data Center web
pages, c. 2001
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Two views of paleoclimatology
Paleoclimate is climate that existed before
humans began collecting instrumental measurements
of weather... By analyzing records taken from
trees, reefs, glaciers, sediments, and other
proxy sources, scientists can extend our
understanding far beyond the 140-year
instrumental record... the paleoclimate
perspective allows us to evaluate climate change
many decades and centuries into the past, in
order to develop a more reliable estimate of how
climate may change in the future. -excerpted
from the National Geophysical Data Center web
pages, c. 2001 Paleoclimatology The study of
past climates from the traces left behind in the
geologic record. It is assumed that the
uniformitarian principle has obtained, but this
may not be the case, and the geologic data are
always insufficient for paleoclimatological purpos
es. Dating methods and paleogeographic
reconstructions are suspect, and often fossil
floras and faunas cannot be related easily in
terms of time. Most glacial strata can be dated
only within wide limits and many climatic
criteria leave no mark in the rocks. -Oxford
Dictionary of the Earth Sciences, c. 1990
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Geochronology

• Radiometric measurements Radiocarbon, Th/U
• Dating of archive materials
• Timing of events
• Rates
• Periodicities
• Annual to geologic timescales
• Archives carbonates, organics
• Corals, marine/lake sediments, tree-rings,
  pollen, macrofossils, charcoal ...

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Radiocarbon calibration using Th/U, tree-ring,
varved sediment, speleothem, marine sediment data
to 50Ky BP
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Palynology of the southwest US
How is Great basin paleoclimate/ecology connected
to global events, on glacial timescales?
Owen Davis (Geosciences)
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• Great Salt Lake, US
• Multiple half-graben Basins (up to 6Km seds)
• Saline/hypersaline lake (4360Km2, highly
  variable)
• 1285m ASL, 13m max. depth

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• Lake level cycles
• Open, saline, low lake level
• Rapid crash to hypersaline, evaporative lake
• Open, fresh lake
• Marsh with lake level below coring site
• Correspondence of cycles with paleoshorelines and
  marine ?18O record?

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Julio Betancourt USGS Desert Laboratory
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Records of drought from speleothems Initial
results from Arizona caves
Layered CaCO3 deposits stable isotopes, U/Th,
(14C) Age range actively growing to several
hundred millennia Resolution up to
interannual Isotopic records from last
millennium, mid-Holocene, stage 2-3 (10-50
ka) Ongoing water and CO2 sampling for
calibration Replication a high priority!
Cave of the Bells
Blue stars mark additional caves under study
Jennifer Wagner, Julie Cole, Geosciences W.
Beck, Physics/AMS
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North Atlantic warmer
North Atlantic cooler
GISP2???18O (PDB)
Jennifer Wagner, Julie Cole, Geosciences W.
Beck, Physics/AMS
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A thousand year record
Number of shells
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Tree-ring records of southwest regional climate
Vertical axis annual precipitation in S.D.
units, smoothed. Blue line from one site (MWK)
red line from all 6. Grey bars low stands of
Mono Lake (Stine, 1994).
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Correlation with high resolution marine records
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• ??18Orain correlated with local T,P
• ???18Orain , T, P correlated with ETP specific
  humidity (and SST)
• Same relationship can be derived from ?18O from
  summertime growth of trees in Catalina Mtns

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Pacific decadal variability Is the mechanism in
the tropics or extratropics?
M.N. Evans (Tree-Ring Lab)
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Pacific decadal variability Is there a
preferred timescale?
M.N. Evans (Tree-Ring Lab)
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Paleoclimate researchers at the University of
Arizona(partial list...)

• J.W. Beck (Physics, Geosciences) wbeck_at_physic
  s.arizona.edu
• J.L. Betancourt (USGS/Geosciences) jlbetanc_at_us
  gs.gov
• A.S. Cohen (Geosciences) acohen_at_geo.arizona.
  edu
• J.E. Cole (Geosciences) jcole_at_geo.arizona.e
  du
• O.K. Davis (Geosciences) palynolo_at_geo.arizo
  na.edu
• M.N. Evans (Tree-Ring Lab) mevans_at_ltrr.arizo
  na.edu
• K.W. Flessa (Geosciences) kflessa_at_geo.arizon
  a.edu
• M.K. Hughes (Tree-Ring Lab) mhughes_at_ltrr.ari
  zona.edu
• A.J.T. Jull (Physics, Geosciences) ajtjull_at_ph
  ysics.arizona.edu
• S.W. Leavitt (Tree-Ring Lab) sleavitt_at_ltrr.a
  rizona.edu
• J.T. Overpeck (Geosciences) jto_at_u.arizona.ed
  u
• J. Quade (USGS/Geosciences) jquade_at_geo.arizo
  na.edu