fossil coral records of enso and “enso-like” variability over the last millennium kim m. cobb,...
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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
“ENSO-like” ___________variability
Palmyra Island
ENSO “El Niño-Southern Oscillation”
December 1997 SST Anomalies
Locations of annually-resolved climate proxy records in the tropics that extend to 1500A.D.
1) change in ENSO characteristicsvs.
change in tropical Pacific baseline
2) forced (sun, volcanoes) vs. intrinsic variability
Research Objective: To generate >100-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 18O ƒ(SST, 18Osw)
Site
ENSO and coral 18O at Palmyra
+4°
+2°
0°
-2°
16°N
8°N
0°
8°S
16°S
Palmyra
180°150°E 150°W 120°W 90°W
SST and rainfall anomalies for the 82-83 El Niño eventColor = SST anomaly (°C), contours = rain anomaly (CI 10 cm/month)
El Niño (La Niña) events are recorded as negative (positive) anomalies in Palmyra coral 18O.
Central tropical Pacific warmer SST = - 18O more precip = - 18O
Most Porites corals at Palmyra grow in ~10m water depth.
Large fossil Porites corals are strewn on ocean-facing beaches.
Modern
The Palmyra Island Coral Collection
Little Ice Age (LIA)Medieval Warm Period (MWP)
Already runFuture work
SS
T A
nom
oly
(°C
)
3
2
1
0
-1
-2
18 O
(‰
)
-0.6
-0.4
-0.2
0.0
0.2
NIÑO3.4 SSTPalmyra coral
Year (A.D.)
1900 1920 1940 1960 1980 2000
SS
T A
nom
oly
(°C
) 1
0
-1
-2
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
R = -0.66
R = -0.84
18 O
(‰
)
Calibrating the Palmyra modern coral 18O record
(Evans et al., 1999)
(McPhaden and Zhang., 2002)
(Deser, 2000)
(Mantua et al., 1997)
“ENSO-like” decadal variability
Palmyra Coral 18O (Cobb et al., 2001)
CTPcorals
instrumentalrecords
5-coral splice
3-coral splice Modern
Single records
Me
an
clim
ate
err
or E
NS
O e
rro
r
De
cad
al e
rro
r
1°C
Palmyra Coral Sequences
Cobb et al., 2003b
2-coral splice
930 960
-5.2
-4.8
-4.4
930 960
18O
(‰)
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
1170 1200 1230 1320 1350 1380 1410 1440 1650 1680 1890 1920 1950 1980
Num
ber o
f Eve
nts
(per
30y
r)
0
2
4
6
Year (A.D.)
1320 1350 1380 1410 1440 1650 1680 1890 1920 1950 1980
18O
(‰)
1170 1200 1230
1090 1120
1090 1120
ENSO2-7yr
# El Niño events/30yr# La Niña events/30yr
Low-frequency8yr+
MWP: little change in ENSO,cooler, drier mean climate
LIA: vigorous ENSOlittle change in mean
Proxy-proxy comparison for last millennium
1°C
- 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)
Dai
and
Wig
ley,
200
0
Building an interpretive frameworkfor the Palmyra fossil coral 18O
Starting assumptions:The teleconnections associated with “ENSO-like” variability resemble those of ENSO.
The relationship between CTP temperature anomaliesand CTP 18Osw have remainedconstant.
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?
“ENSO-like” MWP, LIA scorecard
“ENSO-like” centennial-scale variability may have contributed to the MWP and LIA, but firmer conclusions await more rigorous testing.
Research Question:Is “ENSO-like” centennial-scale variability during the last millennium consistent with evidence from ENSO-sensitive proxy records?
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 18O.
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
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, 18O, 13C, Sr/Ca, Mg/Ca, optical properties
Approach: 1. On-site geochemical calibration 2. Reproducibility tests 3. billions and billions of datapoints
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Spe
ctra
l Den
sity
101
102
103
104
101
102
103
104
Spe
ctra
l Den
sity
101
102
103
104
Frequency (cycles/yr)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0101
102
103
104
Spe
ctra
l Den
sity
Spe
ctra
l Den
sity
1635-1703 A.D.
1317-1458 A.D.
1145-1217 A.D.
1886-1998 A.D.11-
16yr
5.5y
r
3.5y
r
2-3y
r
1.8y
r
5yr
2.2y
r
16-2
4yr
8-10
yr
5.5y
r
4.2y
r
8-13
yr
5.3y
r
2.3
yr
Absolute Date
1880 1900 1920 1940
U/T
h D
ate
1880
1900
1920
1940
Fossil NB9Modern
Splice Date
1620 1640 1660 1680 1700
U/T
h D
ate
1620
1640
1660
1680
1700
SB3SB13SB8
U/Th Dating Constraints for 17th Century splice
10 years younger than best fit
Splice Date
1620 1640 1660 1680 1700
U/T
h D
ate
1620
1640
1660
1680
1700
SB3SB13SB8
best fit
Assigned Date (A.D.) Assigned Date (A.D.)
Splice Date
1300 1350 1400 1450 1500
U/T
h D
ate
1300
1350
1400
1450
1500
Fossil CH9Fossil SB7Fossil SB5Fossil CH5Fossil SB6
Splice Date
1300 1350 1400 1450 1500
U/T
h D
ate
1300
1350
1400
1450
1500
Fossil CH9Fossil SB7Fossil SB5Fossil CH5Fossil SB6
U/Th Dating Constraints for 5-coral splice
best fit 10 years younger than best fit
Assigned Date (A.D.) Assigned Date (A.D.)
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1860 1880 1900 1920 1940 1960 1980 2000
Tem
pera
ture
(°C
)
-2
-1
0
1
2
Palmyra Island
Christmas Island
NIÑO3.4SST
18O
(‰)
18O
(‰)
Year
1860 1880 1900 1920 1940 1960 1980 2000
18O
(‰)
-1.0-0.8-0.6-0.4-0.20.00.20.40.60.8
Maiana Island
1990
1995
1985
1980
Palmyra Coral O (‰)
SST ( C)
3029282726
-4.7 -5.1 -5.5 -5.9
Building a Chronology from the Coral Oxygen Isotopic Record
SST (°C)
Palmyra Coral 18O (‰)
1995
1990
1985
26 27 28 29 301980
Coral 18O = -0.23(SST)R = -0.81
1000
/
)/(/1618
1618161818 x
OO
OOOOO
std
stdspl
Coral 18O=ƒ(SST,18OSW)
Climate Proxy: Coral 18O
Palmyra Coral Calibration
Drilled inMay 1998
T
empe
ratu
re (
°C)
26.7
26.9
27.1
27.3
1900 1920 1940 1960 1980 2000
Cor
al
18O
(‰)
-4.8
-4.9
-5.0
-5.1
-5.2
-5.3
Rai
nfal
l (s.
d. u
nits
) -0.50
-0.25
0.00
0.25
0.50
Year
1900 1920 1940 1960 1980 2000
PD
O In
dex
(s.d
. uni
ts)
-1.0
-0.5
0.0
0.5
1.0
Christmas Coral
Tropical Pacific SST
South Pacific Convergence Zone
Pacific DecadalOscillation
(Evans et al., 1999)
(McPhaden and Zhang., 2002)
(Deser, 2000)
(Mantua et al., 1997)
Decadal Coherence
Palmyra Coral 18O (Cobb et al., 2001)
CTP warmer
CTP colder
1330 1335 1340 1345 1350 1355
18 O
(‰
)
-5.4
-5.2
-5.0
-4.8
-4.6
-4.4SB7CH9
18O
(‰
)
-0.2
-0.1
0.0
0.1
0.2
1330 1335 1340 1345 1350 1355
18 O
(‰
)
-5.2
-5.0
-4.8
-4.6
-4.4
Month of Year2 4 6 8 10 12
18O
(‰
)
-5.0
-4.9
-4.8
-4.7
1330 1335 1340 1345 1350 1355
18 O
(‰
)
-5.4
-5.2
-5.0
-4.8
-4.6
-4.4SB7CH9
18 O
(‰
)
-0.2
-0.1
0.0
0.1
0.2
1330 1335 1340 1345 1350 1355
18 O
(‰
)
-5.2
-5.0
-4.8
-4.6
-4.4
R = 0.68
R = 0.78
R = 0.72
a)
b)
c)
1410 1420 1430 1440 1450
18 O
(‰
)
-5.4
-5.2
-5.0
-4.8
-4.6
-4.4
-4.2
SB5CH5SB6
18 O
(‰
)
-0.2
-0.1
0.0
0.1
0.2
1410 1420 1430 1440 1450
18 O
(‰
)-5.0
-4.8
-4.6
-4.4
R = 0.69R = 0.71
R = 0.69 R = 0.74
R = 0.86R = 0.86
Reproducibility of 14th-15th century 18O records
Interannual reproducibility good, decadal reproducibility lower
1410 1420 1430 1440 1450
18O
(‰
)
-5.4
-5.2
-5.0
-4.8
-4.6
-4.4
-4.2
SB5CH5SB6
18O
(‰
)
-0.2
-0.1
0.0
0.1
0.2
1410 1420 1430 1440 1450
18O
(‰
)
-5.0
-4.8
-4.6
-4.4
Month of Year2 4 6 8 10 12
18 O
(‰
)
-5.0
-4.9
-4.8
-4.7
Month of Year2 4 6 8 10 12
-5.0
-4.9
-4.8
-4.7
1660 1670 1680 1690
18O
(‰
)
-5.6
-5.4
-5.2
-5.0
-4.8
-4.6
SB3SB13SB8
18O
(‰
)
-0.4
-0.2
0.0
0.2
0.4
1660 1670 1680 1690
18O
(‰
)
-5.2
-5.0
-4.8
-4.6
Month of Year2 4 6 8 10 12
18 O
(‰
)
-5.0
-4.9
-4.8
-4.7
Month of Year2 4 6 8 10 12
-5.0
-4.9
-4.8
-4.7
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
18 O
(‰)
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
Palmyra modern coral
1640 1650 1660 1670 1680 1690 1700
18 O
(‰)
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
Palmyra 17th century spliced coral
1320 1340 1360 1380 1400 1420 1440 1460
18 O
(‰)
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
Palmyra 14th century spliced coral
Error of fossil coral 18O records
7 pairs of overlapping corals
Interannual ±0.04‰ (±0.2°C)Decadal ±0.08‰ (±0.4°C)Mean climate ±0.12‰ (±0.5°C)
Strength of splicing approach:When overlapping corals agree, we have more confidence in the climate reconstruction.