Geophysical Research Letters
Supporting Information for
Identification of frequent La Niña events during the early 1800s
in the east equatorial Pacific
Ellen R.M. Druffel1*, Sheila M. Griffin1, Desiree Vetter1,
Robert B. Dunbar2, and Dave Mucciarone2
1
Department of Earth System Science, University of California, Irvine, CA 92697-3100
2
Environmental Earth System Science, Stanford University, Stanford, CA 94305
*to whom correspondence should be addressed; Email: edruffel@uci.edu
Contents of this file
Text S1
Text S2
Figures S1 to S5
Text S1. Comparison of near-monthly coral isotope data with SOI
Another ENSO record we use is the Southern Oscillation Index (SOI), which is the
difference in surface air pressure between the high at Tahiti and the low at Darwin, Australia.
The annual SOI extends from 1650–1980 [Mann et al., 2000] and was rescaled to the observed
mean and variance over 1867–1977 for October to March [Jones and Mann, 2004]. A linear
regression of annual SOI values and cool season ∆14C values reveals a significant inverse
correlation (r=–0.29, p=.03, n=49). Likewise, a linear regression of annual SOI and warm season
∆14C values reveals a significant inverse correlation (r=–0.30, p=.03, n=49). These correlations
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indicate that a high SOI (strong southeast trade winds) occurs when upwelling is strong in the
EEP (low ∆14C), and that a low SOI (weak winds) occurs when upwelling is weak or absent (high
∆14C).
A linear regression of annual SOI and cool season 18O values yields a positive
correlation (r=.30, p=.03, n=50). Additionally, annual SOI and warm season 18O values are
positively correlated (r=.49, p=.0003, n=49). These results show that cool season 18O values
are high (low SST) when southeast trade winds are strong (high SOI), and low (high SST) when
winds are weak or absent, e.g. during El Niño. It appears that both cool and warm season ∆14C
and 18O values are correlated with the annual SOI, which is an indicator of ENSO (both La
Niña and El Niño phases). These results agree with correlations in our calibration study for this
coral between near-monthly ∆14C and 18O [Druffel et al., 2014] with a monthly SST Niño 3.4
record [Kao and Yu, 2009].
Text S2. Comparison of near-monthly coral isotope data with PDO record of Biondi et al.
(2001)
The annual PDO index is available for the period AD 1661-1991 using tree ring
chronologies [Biondi et al., 2001]. A linear regression of this annual PDO index and cool season
∆14C values from 1783-1835 yields a positive correlation (r=0.31, p=.02, n=52). This agrees
with our analysis using the PDO record of MacDonald and Case (2005) [MacDonald and Case,
2005]. A positive correlation was also obtained for a linear regression of the annual PDO and
warm season ∆14C values between 1783 and 1835 (r=0.39, p=.003, n=53). The annual PDO
index and cool season 18O values from 1783–1835 is negatively correlated (r=–0.29, p=.03,
n=51), again agreeing our analysis using the PDO record of MacDonald and Case (2005).
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Figure S1. Seasonal Galapagos coral ∆14C (black circles), 18O (black open circles) and 13C
(grey circles) measurements for (a) 1602-1611, b) 1637-1647, and (c) 1783-1835. Annual bands
were assigned mainly using 13C seasonality. These band assignments are 2 years later in bands
older than 1799, compared to those made previously [Druffel et al., 2007; Dunbar et al., 1994],
based on the seasonal 13C values in the period 1790-1800.
Figure S2. Annual tree ring ∆14C [Stuiver et al., 1986] (open circles) and seasonal Galapagos
coral ∆14C values (filled circles) for (a) 1602-1611, (b) 1637-1647, (c) 1783-1835.
Figure S3. Seasonal Galapagos coral ∆14C (black circles), and 18O (black open circles)
measurements for (a) 1783-1805, and (d) 1806-1835. Cool season ∆14C and 18O values are blue
open circles, and warm season ∆14C (18O) values are red circles. These cool and warm season
values are used in Sections 4.3 and 4.4 of the text for comparison with climate indices.
Figure S4. Wavelet spectral density of the ∆14C and 18O records (interpolated to 12 or 13
measurements per year) from coral bands from 1602-1611 (a,b), 1637-1647 (c,d), and 1783-1835
(e,f), respectively. The greyness scale shows that 75%, 50%, 25% and 5% of the wavelet power
is above each level (white, grey, dark grey, darkest grey), respectively. The black lines show the
20% significance level using a red-noise (autoregressive lab 1) background spectrum. The crosshatched region is the cone of influence where boundary effects are significant [Torrence and
Compo, 1998].
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Figure S5. Cross spectral analyses [Howell et al., 2006] of the ∆14C and 18O measurements
from the time periods (a) 1602-1611, (b) 1637-1647, (c) 1783-1835, and iterative cross spectral
analyses of these measurements from the time periods d) 1783-1800, e) 1800-1818, and f) 18181835.
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Figure S1a,b,c.
(a)
(b)
(c)
5
Figure S2a,b,c.
(a)
(b)
(c)
6
Figure S3a,b.
(a)
(b)
7
Figure S4a,b,c,d,e,f.
(a)
(b)
(c)
(d)
(e)
(f)
8
Figure S5a,b,c.
(a)
(b)
(c)
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Figure S5d,e,f.
(d)
(e)
(f)
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