ARTICLE IN PRESS

Quaternary Science Reviews 26 (2007) 405–414

The California current system during the last 136,000 years:
response of the North Paciﬁc High to precessional forcing
Masanobu Yamamotoa,, Masumi Yamamurob, Yuichiro TanakabaFaculty of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japanb
Geological Survey of Japan, AIST, Tsukuba, Ibaraki 305-8567, Japan

Abstract
Alkenone sea surface temperature (SST) records were generated from the Ocean Drilling Program’s (ODP) Sites 1014 and 1016 to
examine the response of the California Current System to global climate change during the last 136 ka. The temperature differences
between these sites (DSSTNEP ¼ SSTODP1014–SSTODP1016) reﬂected the intensity of the California Current and varied between 0.4 and
6.1 1C. A high DSSTNEP (weaker California Current) was found for late marine isotope stage (MIS) 2 and early MIS 5e, while a low
DSSTNEP (stronger California Current) was detected for mid-MIS 5e and MIS 1. Spectral analysis indicated that this variation pattern
dominated 23- (precession) and 30-ka periods. Comparison of the DSSTNEP and SST based on data from core MD01-2421 at the Japan
margin revealed anti-phase variation; the high DSSTNEP (weakening of the California Current) corresponded to the low SST at the Japan
margin (the southward displacement of the NW Paciﬁc subarctic boundary), and vice versa. This variation was synchronous with amodel prediction of the tropical El Niño-Southern Oscillation behavior. These ﬁndings suggest that the intensity of the North Paciﬁc
High varied in response to precessional forcing, and also that the response has been linked with the changes of tropicalocean–atmosphere interactions.
r 2007 Elsevier Ltd. All rights reserved.

1. Introduction
The California current system (CCS) is an easternboundary current system in the North Paciﬁc that consistsof the southward California Current, northward Southern
California Countercurrent, Davidson Current and California Undercurrent, as shown in Fig. 1 (Hickey, 1979).
Previous studies ﬁnding decreased productivity (Lyle et al.,1992) and an increased meridional paleo-SST gradient(Doose et al., 1997; Mangelsdorf et al., 2000; Herbert et al.,2001) have suggested that the California Current declined
during the last glacial maximum. This decline has been
attributed to the depressed summer North Paciﬁc Highinﬂuenced by the semipermanent development of a highpressure cell over the expanded Laurentide ice sheet on the
North American continent (Kutzbach and Wright, 1985;
Lyle et al., 1992). Recently, Yamamoto et al. (2004) notedthat SST variation at the California margin did not fullyCorresponding author. Tel./fax: +81 11 706 2379.

E-mail address: myama@ees.hokudai.ac.jp (M. Yamamoto).
0277-3791/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.quascirev.2006.07.014

agree with the development of the Laurentide ice sheet but
did correspond to SSTs at the Japan margin, suggestingbasin-scale variation in North Paciﬁc SSTs.
The relative intensities of the California Current and theSouthern California Countercurrent are controlled by thedevelopment of the North Paciﬁc High (Hickey, 1979).
California Current water originates from the subarctic
West Wind Drift and the subtropical North Paciﬁc Current(Hickey, 1979). Subarctic water contributions and theintensity of the California Current increase during summer
due to a strengthened North Paciﬁc High (Hickey, 1979).
The Southern California Countercurrent is a northward
ﬂow that occurs during most of the year except for spring;the countercurrent becomes seasonally intensiﬁed in latefall and winter (Hickey, 1979) and annually in El Niñoyears due to the weaker North Paciﬁc High (Bograd and
Lynn, 2001).
In this study, we compared alkenone-derived SST
records at Ocean Drilling Program’s (ODP) Sites 1014
and 1016 to clarify the response of the CCS to global
climate change during the last 136 ka. Sites 1014 and 1016

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406

Neogloboquadrina pachyderma, d18O of planktonic foraminifers, and foraminiferal assemblages have indicated that
the LGM was more than 5 1C cooler than the Holocene(Kahn et al., 1981; Kennett and Ingram, 1995; Kennett and
Venz, 1995; Thunell and Mortyn, 1995; Mortyn et al.,1996). Pollen assemblages at Site 893 agreed with foraminiferal SST estimations (Heusser, 1995). This ‘‘temperature disagreement’’ in the California Borderland remains
an open question. We examined this issue by comparing
variations in the unsaturation parameters of alkenones andalkenoates with planktonic foraminiferal d18O.

40°N
1000m
3000m

4000m

DavidsonCurrent

San Fransisco

Santa Cruz

35°N

2. Materials and methods

Point Conception
Santa Barbara

California
Current

1016

Los Angeles

1014

30°N
125°W

Southern
California
Countercurrent

Cores 167-1014A-1H, 2H and 3H (ODP Site 1014;
0–16.9 m below the sea ﬂoor [mbsf]) were collected in the
Tanner Basin (321480 N, 1181540 W) at a water depth of1165 m (Lyle et al., 1997; Fig. 1). The sediment coresconsisted of dark olive gray to dark gray hemipelagic clay
interbedded nannofossil ooze containing foraminifers
throughout (Lyle et al., 1997). Samples of approximately
10 cm3 in volume were taken every 20 cm and immediately
frozen in N2-ﬁlled Kapack bags. The age model (Table 1
and Fig. 2) was created by Oxygen Isotope Stratigraphy(Martinson et al., 1987) of the benthic foraminifera

120°W

Fig. 1. Locations of ODP Sites 1014 and 1016 and the California Current
System.

Table 1Age-depth model of ODP Site 1014
Depth
(mcd)

were drilled during ODP Leg 167 in 1996 (Lyle et al., 1997).
Site 1014 is inﬂuenced by the northward invasion of theSouthern California Countercurrent into the California
Borderland region. Site 1016 is located along the main pathof the California Current. The temperature difference
between these sites must therefore reﬂect the relative
intensities of the California Current and the Southern
California Countercurrent.
Paleo-SSTs during the last glacial maximum (LGM)
were estimated using alkenones, foraminifers, radiolarians
and pollen at numerous locations along the California
margin. Along the northern and central California margin,
alkenone-derived temperatures (Prahl et al., 1995; Dooseet al., 1997; Mangelsdorf et al., 2000; Seki et al., 2002)
agreed with those estimated using radiolarian assemblages(Sabin and Pisias, 1996) and foraminiferal d18O and theirassemblages (Ortiz et al., 1997); these data indicate thattemperatures were 4 1C lower in the LGM than in the
Holocene. In contrast, at the southern California margin(the California Borderland), alkenone-derived temperatures disagreed with foraminiferal and pollen-derived
temperatures during the LGM. Alkenone temperature
estimations have indicated that the LGM was 0–2 1C
cooler than the Holocene (Herbert et al., 1995; Dooseet al., 1997; Hinrichs et al., 1997), whereas temperature estimations using the sinistral/dextral ratios of

0.25
1.05
1.55
1.95
2.35
2.75
3.05

MethodConventional
age

(7)

Age
(years BP)

Reference

14

2830
7800
11,31013,24016,45017,15018,000

50
60
60
70
80
90
90

2297
8005
12,643
15,102
18,766
19,572
20,550

1
1
1
1
1
1
1

C of BOM
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14

Depth
(mcd)

OIS

Age
(years BP)

Reference

6.20
6.65
7.20
7.45
8.00
8.70
9.80
10.55
11.15
11.80
12.55
13.45
13.75
14.05
14.45
16.75
17.50
18.50

3.13
3.3
3.31
4
4.22
5
5.1
5.2
5.31
5.33
5.4
5.51
5.5
5.53
6
6.3
6.4
6.41

43,88050,21055,45058,96064,09073,91079,25090,95096,210103,290
110,790
122,560
123,820
125,190
129,840
142,280
152,580
161,340

2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2

Reference 1: this study, 2: Hendy and Kennett (2000).

ARTICLE IN PRESS
M. Yamamoto et al. / Quaternary Science Reviews 26 (2007) 405–414

0Table 2Age-depth model of ODP Site 1016

Site 1016
5

Depth (m)407

10Site 1014

15

14

Cages

Oxygen isotope events
δ15N correlations
20
0

50

100

150

Age (Ka)
Fig. 2. Age-depth models of ODP Sites 1014 and 1016.

Uvigerina (Hendy and Kennett, 2000) and by calendar ages
converted from the AMS 14C ages of seven bulk organic
matter samples (2.30–20.55 ka). The 14C ages were converted to calendar ages using the CALIB4.3 marine98
program (Stuiver and Reimer, 1993) and an equation by
Bard (1998) with a 633-year reservoir correction for the
California margin (Ingram and Southon, 1996).
Core 167-1016C-1H (ODP Site 1016; 0–9.2 mbsf) wascollected off the coast of central California (341320 N,
1221170 W) at 3834 m water depth (Lyle et al., 1997; Fig. 1).
Core sediments consisted of gradationally interbedded
dark gray to dark greenish gray diatom ooze and lightgreenish yellow to light olive gray diatom nannofossil ooze
(Lyle et al., 1997). The core was sealed in a N2-ﬁlled
oxygen-impermeable plastic bag immediately after recovery and stored in a refrigerator for 3 months until shorebased sampling. Samples of approximately 10 cm3 involume were taken every 9 cm and immediately frozen.
The age model was created with calendar ages converted from the AMS 14C ages of eleven bulk organic
matter samples (5.66–37.72 ka) using the same program
and reservoir correction method as for cores 167-1014A(Table 2 and Fig. 2). Correlating the d15N values ofthis core with those of Site 1014 established that theage-depth model extended to 135.57 ka, as described in
Section 3.1.
Alkenones and alkenoates were analyzed following themethod of Yamamoto et al. (2000). The separation of allalkenones and alkenoates was enough for accuratequantiﬁcation (Fig. 7 in Yamamoto et al., 2000). The
0alkenone unsaturation index UK
37 was calculated from theconcentrations of di- and tri-unsaturated C37 alken-2-ones

Depth
(mcd)

MethodConventional
age

(7)

Age (years
BP)

Reference

0.18
0.36
0.54
0.63
0.72
0.90
1.17
1.53
1.98
2.43
2.88

14

5550
7900
10,95013,13013,48015,09017,40021,38022,95030,44033,660

40
40
50
70
40
50
60
90
80
200
240

5657
8128
11,941
14,33915,392
17,201
19,86024,513
26,30034,42737,719

1
1
1
1
1
1
1
1
1
1
1

Depth
(mcd)

MethodAge (years
BP)

Reference

3.51
3.78
4.50
5.49
6.66
6.93
7.11
7.83
8.46
8.82
9.00

d15N correlation
d15N correlation
d15N correlation
d15N correlation
d15N correlation
d15N correlation
d15N correlation
d15N correlation
d15N correlation
d15N correlation
d15N correlation

48,10053,54565,91475,852104,290108,290
112,752
123,274
127,050
133,951
135,573

1
1
1
1
1
1
1
1
1
1
1

C of BOM
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14
C of BOM
14

Reference 1: this study.

[C37MK] using the following expression (Prahl et al., 1988):
0UK
37 ¼ ½C37:2 MK=ð½C37:2 MK þ ½C37:3 MKÞ.
Temperature was calculated according to the equation
0UK
37 ¼ 0:034T þ 0:039,

where T is the temperature (1C) based on experimental
results for cultured strain 55a of Emiliania huxleyi (Prahl
et al., 1988); analytical accuracy was 0.24 1C in ourlaboratory. The culture-based calibration (Prahl et al.,1988) was nearly identical to the core-top calibration along
the California margin (Herbert et al., 1998). Additional
unsaturation indices for Ume
36 and K37:4/K37 were calculatedusing the following equations (Prahl et al., 1995):Ume
36 ¼ ½C36:2 ME=ð½C36:2 ME þ ½C36:3 MEÞ,
where [C36ME] is the concentration of C36 fatty acidmethyl ester, andK37:4 =K37 ¼ ½C37:4 MK=ð½C37:2 MK
þ ½C37:3 MK þ ½C37:4 MKÞ.
To determine stable nitrogen isotope ratios, samples
were combusted at 1020 1C in a Fisons Instruments
EA1108 elemental analyzer (Beverly, MA, USA). The
generated N2 was introduced into a Finnigan Delta Plus
isotope-ratio mass spectrometer (Thermo Electron Corp.,
Waltham, MA, USA) by using a He carrier. The ratio of

ARTICLE IN PRESS
M. Yamamoto et al. / Quaternary Science Reviews 26 (2007) 405–414

408
15

N/14N was expressed relative to the N2 in air. Machinedrift during analyses was checked with l-a-alanine(d15N ¼ 7.61%) every three samples. Accuracy was determined using interlaboratory-determined nitroarginine
following the method of Minagawa et al. (1984).
We performed spectral analyses using the Blackman–
Tuckey and Cross–Blackman–Tuckey methods provided in
the Analyseries software package (Paillard et al., 1996).

was consistent with the observation that the isotopic
fractionation of d15N between sinking particles and surface
sediments tends to increase with increasing water bottom
depth (Nakanishi and Minagawa, 2003).
3.2. Paleo-SSTs at the California margin
At Site 1014, SSTs ranged from 12 to 19 1C during thelast 158 ka, whereas at Site 1016, SSTs ranged from 9 to
18 1C during the last 136 ka (Fig. 3). The core-top
temperatures of Sites 1014 and 1016 were 16 and14 1C, respectively, in agreement with present annual
mean SSTs at these sites (Robinson, 1976). This result is0concordant with the observation that core-top UK
37 -derived
temperatures represent the annual mean SSTs along theCalifornia margin (Herbert et al., 1998). At both sites, theSST increase preceded the MIS 1/2 and 5/6 boundaries by8 and 6 ka, respectively (Fig. 3). This early warming
was more evident at Site 1014 than at Site 1016 (Fig. 3),
implying a stronger Southern California Countercurrent(Herbert et al., 2001) analogous to a modern El Niñocondition (Bograd and Lynn, 2001) at the latest glacial
stage. Strong cooling was observed around the MIS 2/3
and 3/4 boundaries (Fig. 3). Coccolithus pelagicus, acoccolithophore speciﬁc to subarctic waters in the North
Paciﬁc (Okada and McIntyre, 1977), was abundant during
the same intervals at Site 1014 (Fig. 4; Tanaka, Y.,
unpublished data). These observations indicate an intensiﬁed California Current analogous to a modern La Niñacondition during those periods.

3. Results and discussion
3.1. Nitrogen isotopes and the age-depth model of Site 1016
Oxygen isotope stratigraphy could not be used toestablish the age-depth model of Site 1016 because
carbonates had dissolved at most intervals. Instead, weestablished that the age-depth model extended to 135.57 ka(Table 2 and Fig. 2) by correlating d15N values of this corewith those of Site 1014 (Fig. 3). Because the d15N values ofcores in the Northeastern Paciﬁc rim from the Mexico to
Oregon margins varied synchronously during the lastglacial age (Kienast et al., 2002), d15N could be used forstratigraphic correlation for the California margin. The
d15N values ranged from 5% to 9% (Fig. 3); thisvariation was synchronous with that in the Mexican
margin (Ganeshram et al., 1995) except that the d15N
maximum for MIS 5a was more enhanced for Sites 1014
and 1016 than that at the Mexican margin. The d15N values
were generally 0–2% higher for the deeper site (Site 1016)
than the shallower site (Site 1014). This differenceδ15N permil
0

4

6

8

VolumeΔSSTNEP (oC) x 106 km3

SST (oC)

10 8

10

12

14

16

18

20 0 2

4

60

20

NINO3

40 -0.4 0

0.4 MIS12

3

Age (ka)50
45aODP1016

5b

100

5c
5d

ODP10165e

150

ODP1014

ODP1014023-kyr filtered Laurentide
ice sheet

6

Fig. 3. Changes in sedimentary d15N and alkenone UK
37 -derived sea surface temperatures (SSTs) of ODP Sites 1014 and 1016 and the DSSTNEP(SSTODP1014–SSTODP1016) during the last 160 ka. Data on SSTs for Sites 1014 and 1016 are from Yamamoto et al. (2000, 2004). The calculated NINO3
index (Clement et al., 1999) and the estimated volume of the Laurentide ice sheet (Boulton et al., 1985) are shown for comparison. Blue and green crosses
indicate the age controls for Sites 1014 and 1016, respectively, by 14C dating and oxygen isotope stratigraphy.

ARTICLE IN PRESS
M. Yamamoto et al. / Quaternary Science Reviews 26 (2007) 405–414

UK37'-SST
(˚C )

Ume36

Uvigerina
δ180 (‰)

K37:4/K37

8 10 12 14 16 18 0.75 0.8 0.85 0

0.04

0.08

4

0

3

G. bulloides
δ180 (‰)
3

2

1

UK37'-SST(˚C )0 10 12 14 16 18 20

409

Ume36
0.8

0.9

0

K37:4/K37

C. pelagicus %0.02 0.04

010 20 30 40

0

1

1

2
2
5

Depth (mcd)

Depth (mbsf)

3

4
5
5a
5b
5c

3

4
5a
10

5b
5c
5d
5e

5d
15
5e

6
6
10

20

ODP Site 1016

ODP Site 1014

0meFig. 4. The UK
37 -derived SST, U36 , and K37:4/K37 indices for Sites 1014 and 1016 and the abundance of Coccolithus pelagicus in relation to total coccoliths
18
at Site 1014. The d O proﬁles of Uvigerina and Globigerina bulloides at Site 1014 (Hendy and Kennett, 2000) are shown for comparison. Data for SST,
Ume
36 , and K37:4/K37 indices at Site 1016, and SST at Site 1014 are from Yamamoto et al. (2000, 2004).

0

In the Tanner Basin, the UK
37 -derived paleo-temperaturesduring the latter half of MIS 2 at Site 1014 were more than
4 1C higher than those indicated by foraminiferal d18O andassemblages in core AHF10164 (Kahn et al., 1981).
Interestingly, the Ume
36 and K37:4/K37 proﬁles were similar
to the d18O proﬁle of planktonic foraminifera Globigerina
bulloides around MIS 2 (Hendy and Kennett, 2000) but
0
differed from the UK
37 proﬁle at Site 1014 (Fig. 4).
However, the Ume
36 and K37:4/K37 proﬁles were similar to0
the UKat Site 1016 (Yamamoto et al., 2000; Fig. 4).
37 proﬁle0
The UK
with Ume
37 proﬁle showed good correlation
36
K0
and K37:4/K37 at Site 1016; however, U37 values from late
MIS 2 samples were higher than those of other intervals at
Site 1014 (Fig. 5). This ﬁnding suggests multiple sources ofalkenones and alkenonates at Site 1014 in late MIS 2.
At least two major sources are indicated. The ﬁrst source
may have been C36ME- and C37:4MK-rich species thatbloomed in cooler water. The second source may have been
C36ME- and C37:4MK-poor species that bloomed inwarmer water. Sediment-trap studies at the Santa Barbara
Basin demonstrated that when the spring upwelling was
reduced under El Niño conditions, coccolithophore export
production was enhanced particularly for the tropical
species Gephyrocapsa oceanica (De Bernardi et al., 2005),
while the export production of the planktonic foraminifers
Globigerina bulloides and N. pachyderma (dextral) was
reduced (Pak et al., 2004). Frequent invasions of subtropical water to the California Borderland during late
MIS 2, which was analogous to modern El Niño conditions(Bograd and Lynn, 2001), may therefore have enhanced
haptophyte blooms possibly by the second type ofalkenone producer noted above and reduced the bloomsof planktonic formaninifers and the ﬁrst type of alkenone0
producer. This ecological setting possibly caused the UK
37 torecord warmer temperatures than those by foraminifers
K0
and Ume36 . The high U37 during late MIS 2 might moreaccurately reﬂect the frequent invasion of warmer water tothe California Borderland.
3.3. Variations of the CCS on orbital timescales
Site 1014 experiences the northward invasion of theSouthern California Countercurrent to the California
Borderland, while Site 1016 is located along the main pathof the California Current. Thus, the temperature difference
between these sites reﬂects the relative intensities of the
California Current and the Southern California Countercurrent. We obtained SST differences for the Sites 1014 and1016 (DSSTNEP) for the last 136 ka by subtracting the SSTof Site 1016 from that of Site 1014 (Fig. 3). The DSSTNEP
varied between 0.4 and 6.1 1C with an average of 2.9 1C. A
high DSSTNEP (weaker California Current) was observedin late MIS 2 and early MIS 5e, while a low DSSTNEP(stronger California Current) was observed in mid-MIS 5eand MIS 1.
We evaluated the effects of time-scale uncertainty on the
DSSTNEP proﬁle by comparing various DSSTNEP proﬁles
obtained under the assumption that the ages of Site 1016
shift in the direction of younger or older. Because thesample intervals of d15N measurement were 1.3 ka at Site
1016, the maximum error in the direct correlation of d15N
must be 1.3 ka, although errors caused by other factors
were not evaluated in detail. Shifting the ages of Site 1016
to younger and older directions within 3 ka did not change
the DSSTNEP proﬁle, which shows high DSSTNEP in late
MIS 2, mid-MIS 3, MIS 5a and early MIS 5e and low
DSSTNEP in MIS 1, early MIS 3, the MIS 4/5a boundary
and MIS 5b. One exception was mid-MIS 5e. Shifting toARTICLE IN PRESS
M. Yamamoto et al. / Quaternary Science Reviews 26 (2007) 405–414

410

Hole 1016C

Hole 1014A
0.9

Ume 36

Ume 36

0.9

0.8

0.8

Ume 36 = 0.666UK' 37

1016C+ 0.491

0.7
0.3

0.4

0.5

0.6

12-20 ka

0.7
0.3

0.7

0.4

0.5

0.6

0.7

UK' 37

UK' 370.08

0.08

Hole 1014A

Hole 1016C2

Ume 36 = 0.863(UK' 37)

0.06

1016C

0.06

12-20 ka

K37:4 / K 37

K37:4 / K 37

-1.11UK' 37 + 0.352

0.04

0.04

0.02

0.02

0

0
0.3

0.4

0.5
U

0.6

0.7

0

0.3

0.4

0.5

0.6

0.7

UK' 37

K' 37
0

me
K
Fig. 5. Plots of UK
37 2U36 and U37  K37:4 =K37 for Sites 1014 and 1016 samples.

the younger direction by 1–3 ka weakened the negative
peak at mid-MIS 5e.
Previous studies have suggested a decline in the
California Current during MIS 2 based on decreased
productivity (Lyle et al., 1992) and an increased meridional
paleo-SST gradient (Doose et al., 1997; Mangelsdorf et al.,2000). Herbert et al. (2001) showed that an early warmingat the California Borderland began 24 ka, and the SST
reached a maximum value at 16 ka (late MIS 2), reﬂecting
weakening of the California Current. This decline wasattributed to a depressed summer North Paciﬁc Highinﬂuenced by the semipermanent development of ahigh-pressure cell over the expanded Laurentide ice sheetover continental North America (Kutzbach and Wright,
1985; Lyle et al., 1992). However, paleo-SST change at Site
1014 did not fully agree with the estimated volume changeof the Laurentide ice sheet (Boulton et al., 1985). In
particular, a low SST and abundant C. pelagicus indicate astrong California Current in late MIS 4; however, thesecond-largest expanse of the Laurentide ice sheet during
the last glacial period also occurred during this time
(Fig. 4). Thus, the volume of the Laurentide ice sheet may
not have been the only factor affecting the CCS.
Spectral analyses indicated that the SST variation
patterns of Sites 1014 and 1016 dominate 100-ka (eccentricity), 41-ka (obliquity), and 23-ka (precession) periods andare highly coherent at these frequencies with the d18O
variation of the benthic foraminifera Uvigerina at Site 1014
(Fig. 6A and B). However, the variation pattern of
DSSTNEP dominated 23-ka and 30-ka periods (Fig. 6C).
Comparing the DSSTNEP and the SST of MD01-2421 at
the Japan margin revealed an anti-phase variation during
the last 136 ka (Fig. 7). Both DSSTNEP and the SST of
MD01-2421 showed variations in 23-ka and 30-ka periods
and lacked a 41-ka period (Fig. 6C and D). Cross-spectral
analysis indicated that DSSTNEP variation is highly
coherent with the SST variation of MD01-2421 at 23-ka
and 30-ka periods, and also indicated that the DSSTNEP
led the SST of MD01-2421 by 169712 and 1277111 at
23- and 30-ka bands, respectively. The high DSSTNEP at the
California margin corresponded to the low SST at theJapan margin, and vice versa (Fig. 7).
At the Japan margin, the alkenone SST variation mainly
reﬂects the latitudinal displacement of the subarctic
boundary in summer (Yamamoto et al., 2004, 2005). The
latitudinal position of the subarctic boundary associatedwith the westerly jet in summer is principally controlled by
the relative intensities of the North Paciﬁc High and the
Okhotsk High (Nitta, 1987; Goes et al., 2001). A low SST
reﬂects the southward displacement of the subarctic
boundary, resulting from the weaker North Paciﬁc High.
The observed SST of alkenone maximum productionARTICLE IN PRESS
M. Yamamoto et al. / Quaternary Science Reviews 26 (2007) 405–414

0

ΔSSTNEP

California
margin0.1

0Benthic δ18O

Power
(E)

0.5

SSTMD01-2421
Japan
marginBenthic δ18O

Coherency

00.01 0.02 0.03 0.04 0.05 0.06 0.07

Frequency (ky-1)

1

ΔSSTNEP
0.5

0

10
1

1
0.10

(D)

100
10

10
1

1

100
10

0
0.01 0.02 0.03 0.04 0.05 0.06 0.07

30 ky 23 ky

Frequency (ky-1)
30 ky 23 ky

Frequency (ky-1)(C)00.01 0.02 0.03 0.04 0.05 0.06 0.07

1

0.5

1

Benthic δ18O
California
margin(B)

Coherency

30 ky 23 ky

10

0.5
10
1

0

Frequency (ky-1)

(A)

Power

0
0.01 0.02 0.03 0.04 0.05 0.06 0.07

1

SSTODP1016

1

Power

0.1

23 ky

Coherency

Benthic δ18O
California SSTODP1014
margin1

100
10

SSTMD01-2421
Japan-California

Coherency

Power

0.5

10
1

41 ky

1

Power

23 ky

Coherency

41 ky
100
10

411

0
0.01 0.02 0.03 0.04 0.05 0.06 0.07

Frequency (ky-1)

Fig. 6. Spectral densities and coherencies of (A) SST versus the d18O of Uvigerina for Site 1014 at the California margin (3–136 ka, bandwidth ¼ 0.011);(B) the SST of Site 1016 versus the d18O of Uvigerina in Site 1014, California margin (3–136 ka, bandwidth ¼ 0.011); (C) DSSTNEP versus the d18O ofUvigerina for Site 1014 at the California margin (3–136 ka, bandwidth ¼ 0.011); (D) the SST versus the d18O of benthic foraminifera Uvigerina for core
MD01-2421, Japan margin (5–142 ka, bandwidth ¼ 0.011) and (E) the DSSTNEP versus the SST in core MD01-2421 (5–136 ka, bandwidth ¼ 0.011). The
horizontal dashed line indicates an 80% level of nonzero coherency.

season (July and August) at the site of MD01-2421 from1950 to 2002 has positive correlation (r ¼ 0.39, n ¼ 53,
po0.05) with the intensity of the summer North Paciﬁc
High (Isono and Yamamoto, unpublished data). Thus, thehigh DSSTNEP at the California margin and the low SST at
the Japan margin both resulted from a weaker North
Paciﬁc High, and vice versa. The anti-phase relationshipbetween DSSTNEP and the SST of MD01-2421 at theprecession band suggests that variation in the CCS at 23-ka
periods is a part of the response of the North Paciﬁc Highto precessional forcing.
A 30-ka period was previously reported in the variationsof atmospheric carbon dioxide concentration recordedin the Vostok ice core (Petit et al., 1999) and in the
paleo-productivity records in the tropical Indo-Paciﬁc(e.g., Beaufort et al., 2001, 2003). At the 30-ka band, theDSSTNEP maxima (the weakest California Current) lagged
the CO2 concentration minima by 117151, and the SST
maxima of MD01-2421 lagged the CO2 concentration

maxima by 397231 (Fig. 8). The phase lag between the
DSSTNEP maxima and the SST maxima of MD01-2421 was
1277111; the relationship was not anti-phase. This phaselag suggests that these variations were not a simple result of
the response of the North Paciﬁc High, but were interferedby an unknown factor at either the California or Japan
margin.
3.4. Linkage between the CCS and tropical Indo-Pacificclimates
Both the DSSTNEP and SST at the Japan margin arecontrolled by the intensity of the North Paciﬁc High. The
North Paciﬁc High is inﬂuenced by modern interannual El
Niño-Southern Oscillation (ENSO) through atmosphericteleconnections (Bograd and Lynn, 2001). In El Niñoyears, the tropical convection center moves to the central
and eastern equatorial Paciﬁc. This process weakens theNorth Paciﬁc High in summer, resulting in a warming of

ARTICLE IN PRESS
M. Yamamoto et al. / Quaternary Science Reviews 26 (2007) 405–414

412

the California Borderland by the intensiﬁcation of theSouthern California Countercurrent (Bograd and Lynn,
2001). At the Japan margin, the depressed North Paciﬁc
High in the summer of El Niño years tend to delay thenorthward shifts of the westerly jet and oceanic subarctic
boundary (Goes et al., 2001) and thus cool the Japan
margin in summer (Nitta, 1987; Kawamura et al., 1998). In
La Niña years, the tropical convection center moves to theMD01-2421

ΔSSTNEP (°C)

SST (°C)

0

12

16

20

24 0 24

NINO3-0.4 0 0.4 MIS

6

1
2

3
50
Age (ka)

4
5a
5b
100

5c
5d
5e
23-kyr filtered6

23-kyr filtered

150

NW PacificTropical
Pacific

NE Pacific0Fig. 7. The UK
37 -derived SST at the Japan margin (core MD01-2421;
Yamamoto et al., 2005), the DSSTNEP at the California margin and thecalculated NINO3 index (Clement et al., 1999) during the last 150 ka.

western equatorial Paciﬁc, intensifying the summer North
Paciﬁc High and the California Current and cooling theCalifornia margin. This process excites the Paciﬁc–Japan
teleconnection pattern in summer (Nitta, 1987) andaccelerates the northward shift of the subarctic boundary,warming the Japan margin (Nitta, 1987; Kawamura et al.,1998).
Zebiak-Cane ENSO model calculations for the past
150 ka demonstrated that seasonal anomalies in insolation
driven by precession could have changed ENSO behaviors(see the calculated NINO3 in Fig. 7; Clement et al., 1999).
In the modern Paciﬁc, the Intertropical Convergence Zone
(ITCZ) nears the equator in spring, generating a zonal
symmetric response in atmospheric heating, while theeastern Paciﬁc ITCZ moves north in autumn, generating
zonal asymmetry in atmospheric heating. The model
calculation assumes that when the perihelion occurs inspring, uniform atmospheric heating of the tropical Paciﬁc
generates a background state giving an El Niño-like
response; for an autumn perihelion, asymmetric atmospheric heating generates a background state creating a La
Niña-like response.
Beaufort et al. (2001) generated late Pleistocene sedimentrecords of nannofossil-derived paleo-productivity along theequator in the Indian and Paciﬁc oceans. Their study
showed that variations in equatorial productivity have beencaused primarily by both glacial–interglacial variability andprecession-controlled changes in the east–west thermocline
slope of the Indo-Paciﬁc. Precession-controlled variations in
productivity were linked to processes similar to the ENSO
phenomenon and preceded changes in the d18O of benthic
foraminifera (Fig. 8), indicating that these changes did not
result from ice sheet ﬂuctuations.
At the precession band, the intensity minima of theNorth Paciﬁc High was in phase with the April perihelion
and the maxima of predicted NINO3 index (Clement et al.,June 21 perihelion

23-kyr0°

Lead

Max. pCO2

30-kyrLead

LagMax. WEP production
Max. SSTODP 10140°Max. SSTODP 1016
Min. δ18O-90°
90°
Max. SSTMD01-2421

Max. ΔSSTNEP
Max. NINO3
90°
Max. δ O
18

Lag
Max. SSTMD01-2421-90oMax. Indian SM
Max. Asian SM
180°

Max. ΔSSTNEP
180°

Dec. 21 perihelion

Fig. 8. Precession and 30-ka wheels showing the phases of the SST maxima in core MD01-2421 at the Japan margin, the SST maxima at Sites 1014 and
1016, the DSSTNEP maxima at the California margin, SPECMAP d18O maxima and minima (Imbrie et al., 1984), the predicted NINO3 (Clement et al.,1999), the maximum Indian summer monsoon (summer monsoon stack by Clemens and Prell, 2003), the maximum East Asian summer monsoon(abundance of Cryptomeria japonica in core MD01-2421, Igarashi and Oba, 2006), and the maximum primary production in the western equatorial Paciﬁc(Beaufort et al., 2001). Positive and negative angles indicate phase leads and lags, respectively, relative to the precession minima (21 June perihelion) or the
pCO2 maxima.

ARTICLE IN PRESS
M. Yamamoto et al. / Quaternary Science Reviews 26 (2007) 405–414

1999; Fig. 8). However, productivity variation in thetropical Indo-Paciﬁc (Beaufort et al., 2001) was out ofphase with the DSSTNEP and the predicted NINO3 (Fig. 8).
The El Niño-like phase of the thermocline slope lagged the
DSSTNEP maxima and the predicted NINO3 maxima by1201 (Fig. 8). Our results and those of the model
prediction indicate that the weakest North Paciﬁc Highand the optimal phase of the El Niño-like condition lagged
the ice volume maxima, while the productivity records(Beaufort et al., 1999) indicate that the optimal El Niñolike phase preceded the ice volume minima (Fig. 8). This
phase discrepancy of long-term ENSO-like variability
remains a key question because little is known about the
behavior of tropical ocean–atmosphere interactions atorbital timescales, although shorter paleo-records in theeastern tropical Paciﬁc and the tropical Andes regions wereconsistent with the model prediction (e.g., Koutavas et al.,
2002; Moy et al., 2002).
The precession wheel in Fig. 8 illustrates that thestrongest North Paciﬁc High (DSSTNEP minima) led by301 (2 ka) with the maxima of the Indian summer
monsoon (based on the summer monsoon stack by
Clemens and Prell, 2003) and East Asian summer monsoon(based on the abundance of a Japanese cedar [Cryptomeria
japonica] pollen in the NW Paciﬁc off Japan by Morley andHeusser, 1997; Igarashi and Oba, 2006). Meteorologicalstudies demonstrated a close linkage between boreal
summer monsoon (BSM) and ENSO; the stronger BSM
corresponds to the La Niña state of the tropical Paciﬁc,and the weaker BSM corresponds to the El Niño state (e.g.,Meehl, 1987; Yasunari, 1991). Heusser and Sirocko (1997)
reported a large centennial-scale ﬂuctuation of pollen
assemblages during the last deglaciation in ODP Site 893,
Santa Barbara Basin, California margin. They suggested
that correlative high-frequency variations for the northeast
Paciﬁc winter and southern Asian summer climates may
reﬂect submillennial-scale ENSO-type forcing involving
water vapor transport over the Indian and Paciﬁc oceans.
These modern and centennial-scale studies suggest thesynchronous climate variations throughout the IndoPaciﬁc region. In contrast, our orbital-timescale records
demonstrated the phase lead of the North Paciﬁc High toboreal monsoon variations, suggesting either that the
ENSO-like variability has been independent of BSM orthat the ENSO-like variability has caused the change of
BSM.
4. Conclusion
The present study presents the new perspective thatvariation of the CCS is part of a basin-scale oceanic andatmospheric response in the North Paciﬁc. The variation
indicates that the North Paciﬁc High varied in response to
precessional forcing. Long-term ENSO-like variability andwave propagation by teleconnection (Heusser and Sirocko,
1997; Clement et al., 1999; Beaufort et al., 2001;
Yamamoto et al., 2004) are potential driving forces of413

the basin-scale climate response. Establishing the linkage
between this basin-scale response and tropical ocean–atmospheric dynamics will be a key toward better understanding
the role of the Indo-Paciﬁc in global climate change.
Acknowledgements
We thank Kazuko Hino for analytical assistance in thelaboratory. Special thanks are due to Ryuji Tada, Itaru
Koizumi, Tomohisa Irino, Yaeko Igarashi, Tadamichi Oba,and Masatoshi Komiya, for valuable discussions. We also
thank Timothy D. Herbert for his helpful comments inreview and Peter Clark for his editorial handling. This
research used samples and data provided by the Ocean
Drilling Program (ODP). The ODP is sponsored by the US
National Science Foundation (NSF) and participating
countries under management of Joint Oceanographic
Institution (JOI), Inc. This study was supported by ﬁnancial
aid from the Science and Technology Agency of Japan.
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