Fossil coral records of ENSO and

1
Fossil coral records of ENSO and ENSO-like
variability over the last millennium
Kim M. Cobb, Georgia Institute of
Technology Christopher D. Charles, Scripps
Institution of Oceanography R. Lawrence Edwards,
Hai Cheng, UMN
2
ENSO El Niño-Southern Oscillation December
1997 SST Anomalies
Palmyra Island
Locations of annually-resolved climate proxy
records in the tropics that extend to 1500A.D.
ENSO-like ___________ variability
1) change in ENSO characteristics vs. change
in tropical Pacific baseline 2) forced (sun,
volcanoes) vs. intrinsic variability
3
Research Objective To generate gt100-yr-long,
high-resolution, high-fidelity
climate proxy records from the tropical Pacific
Ocean Materials Modern and Fossil
Corals Methods Dating U-Th
Climate proxy Coral skeletal d18O ƒ(SST,
d18Osw)
Site
4
Central tropical Pacific warmer SST - d18O
more precip - d18O
El Niño (La Niña) events are recorded as negative
(positive) anomalies in Palmyra coral d18O.
5
Most Porites corals at Palmyra grow in 10m
water depth.
Large fossil Porites corals are strewn on
ocean-facing beaches.
6
The Palmyra Island Coral Collection
Modern
Already run
Future work
7
Calibrating the Palmyra modern coral d18O record
8
ENSO-like decadal variability
(Evans et al., 1999)
CTP corals
Palmyra Coral d18O (Cobb et al., 2001)
(McPhaden and Zhang., 2002)
(Deser, 2000)
instrumental records
(Mantua et al., 1997)
9
Palmyra Coral Sequences
3-coral splice
Modern
5-coral splice
Single records
2-coral splice
1C
ENSO error
Mean climate error
Decadal error
Cobb et al., 2003b
10
ENSO 2-7yr
El Niño events/30yr La Niña events/30yr
Low-frequency 8yr
MWP little change in ENSO, cooler, drier mean
climate
LIA vigorous ENSO little change in mean
11
Proxy-proxy comparison for last millennium
1C
- rate, magnitude of 20th century climate change
unprecedented - no simple relationship b/t
tropical Pacific climate and NH temp, solar, or
volcanic forcing - changes in the meridional
temperature gradients implied (inc. during LIA,
dec. during MWP)
12
Building an interpretive framework for the
Palmyra fossil coral d18O
Starting assumptions The teleconnections
associated with ENSO-like variability
resemble those of ENSO. The relationship
between CTP temperature anomalies and CTP d18Osw
have remained constant.
Hypothesis (MWP - La Niña-like, LIA - El
Niño-like)
Research Question Is ENSO-like
centennial-scale variability during the last
millennium consistent with evidence from
ENSO-sensitive proxy records?
13
ENSO-like MWP, LIA scorecard
Research Question Is ENSO-like
centennial-scale variability during the last
millennium consistent with evidence from
ENSO-sensitive proxy records?
ENSO-like centennial-scale variability may have
contributed to the MWP and LIA, but firmer
conclusions await more rigorous testing.
14
Conclusions Most intense ENSO activity occurred
during 17th century, no change in the CTP mean
state. Cooler, drier conditions in the CTP
characterized the early centuries of the last
millennium. ENSO characteristics can change
dramatically from decade to decade, absent any
known forcing. No simple relationship emerges
between ENSO character and NH temperature or mean
coral d18O. Changes in the tropical Pacific
zonal SST gradient during the LIA (El Niño-like)
and MWP (La Niña-like) are consistent with some
key paleo-data, but can be more rigorously tested.
Data available at http//www.ngdc.noaa.gov/paleo/
paleo.html
15
(No Transcript)
16
Gunung Buda Speleothem Project Goal to
reconstruct annual to centennial-scale rainfall
variability from an ENSO- sensitive region over
the last glacial cycle Materials 40
speleothems (0.1 1.8m long) Dating U-series
geochemistry Climate proxies growth rate,
d18O, d13C, Sr/Ca, Mg/Ca, optical
properties Approach 1. On-site geochemical
calibration 2. Reproducibility tests
3. billions and billions of datapoints
17
(No Transcript)
18
2.3yr
19
(No Transcript)
20
U/Th Dating Constraints for 17th Century splice
10 years younger than best fit
best fit
Assigned Date (A.D.)
Assigned Date (A.D.)
21
U/Th Dating Constraints for 5-coral splice
10 years younger than best fit
best fit
Assigned Date (A.D.)
Assigned Date (A.D.)
22
(No Transcript)
23
Palmyra Coral d18O ()
Drilled in May 1998
Climate Proxy Coral d18O
1995
Coral d18Oƒ(SST,d18OSW)
1990
Palmyra Coral Calibration
1985
Coral d18O -0.23(SST) R -0.81
26
27
28
29
30
1980
SST (C)
24
Decadal Coherence
(Evans et al., 1999)
Palmyra Coral d18O (Cobb et al., 2001)
(McPhaden and Zhang., 2002)
(Deser, 2000)
(Mantua et al., 1997)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
Reproducibility of 14th-15th century d18O records
Interannual reproducibility good, decadal
reproducibility lower
29
(No Transcript)
30
(No Transcript)
31
Palmyra modern coral
32
Palmyra 17th century spliced coral
33
Palmyra 14th century spliced coral
34
Error of fossil coral d18O records 7 pairs of
overlapping corals Interannual 0.04
(0.2C) Decadal 0.08 (0.4C) Mean
climate 0.12 (0.5C)
Strength of splicing approach When overlapping
corals agree, we have more confidence in the
climate reconstruction.