Pliocene-Pleistocene oxygen isotope record Site 586, Ontong Java Plateau

MarineMicropaleontology, 18 (1992) 171-198

171

Elsevier Science Publishers B.V., Amsterdam

Pliocene-Pleistocene oxygen isotope record Site 586, Ontong Java Plateau Jill M. Whitman and W.H. Berger Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA (Received July 16, 1990; revision received September 3, 1991, and accepted September 6, 1991 )

ABSTRACT Whitman, J.M. and Berger, W.H., 1992. Pliocene-Pleistoceneoxygen isotope record Site 586, Ontong Java Plateau. Mar. Micropal., 18: 171-198. Oceanographic changes in the western equatorial Pacific during the past 6 Ma are inferred from oxygen isotopic analyses of planktic and benthic foraminifera from Ontong Java Plateau (DSDP Site 586). The taxa are Globigerinoides sacculifer, Pulleniatina, Cibicidoides wuellerstorfi, and Oridorsalis umbonatus. Cooling and ice buildup are indicated by an tsO enrichment of 0.3%0 in the planktic species near 3.4 Ma. This shift apparently is compensated in the benthic data by a warming of the deep waters by between 1° and 2 °C. We suggest that the dominant source of upper deep water supply to the Pacific changed from Antarctic to North Atlantic at that time, the North Atlantic-derived water being warmer. Near 2.8 Ma (approximately) the planktic foraminifera again record an enrichment in ~sO (AJ~sO=0.25%e). We suggest ice buildup in the northern hemisphere as the cause, because of subsequent sharp increase in fluctuations of the J~sO signal, that is, instability.The enrichment is magnified in the benthic foraminifera (AJ ~sO= 0.5%) by a cooling of the deep water by 1.5 ° at the time, presumably signallinga glacial-type reduction of North Atlantic Deep Water (NADW) production. Episodic divergence between the signals of G. sacculifer and Pulleniatina in the Pleistocene apparently reflects periods of increased upwelling in the western equatorial Pacific. The amplitude of ice volume fluctuations cannot be reconstructed from Jt~sO data alone, unless there are constraints on temperature variations. The increase in amplitude of fluctuation of the benthic and planktic signals during the Pleistocene may be attributed either to an increase in maximum ice volume, or to an increase in the fractionation of continental ice, or a combination of both causes.

Introduction The last 6 million years were a time of major reorganization of deep and shallow water circulation, in response to climatic changes brought about by mountain-building and regression, by the closing of the Central American Seaway, and by ice-buildup in northern and southern polar regions. It is of great interest to reconstruct this most recent portion of Cenozoic ocean history. One excellent place to proceed with this task is the Ontong Java PlaCorrespondence to: J.M. Whitman, Dept. of Earth Sciences, Pacific Lutheran University, Tacoma, WA 98447, USA.

teau in the western equatorial Pacific. Here the signals recorded in biogenic sediments should have a strong global component, far from the influence of margins or special conditions, other than equatorial upwelling, which is itself a phenomenon of global significance. We have studied the stable isotope record of planktic and benthic foraminifera from this region, using cores recovered at Site 586 of Leg 89 of the Deep Sea Drilling Project. Ontong Java Plateau is a large elevated area in the western Pacific bearing calcareous sediments. Site 586 is close to the equator, at a depth of 2218 m (Fig. 1 ). This portion of the Ontong Java Plateau is bathed in General Pacific Deep Water, about 500 to 700 m below

0377-8398/92/$05.00 © 1992 Elsevier Science Publishers B.V. All fights reserved.

172

J.M. W H I T M A N AND W.H. BERGER

30"N

a

.~1¢'~

~

P~',...~ ~

~"

ONTONG O"

120"E

150"

180"

20"S 50"W

amine the paleoceanographic changes associated with the onset of the m o d e m ice age climate. Analogous changes have been studied in some detail in the North Atlantic by a number of workers (Berggren, 1972; Shackleton and Opdyke, 1977; Backman, 1979; Shackleton et al., 1984; Raymo et al., 1987). The present study examines the oxygen isotope record of four species of foraminifera, two planktic, and two benthic. Our aim is to document the record, and to interpret it in terms of oceanographic changes that have occurred during the Pliocene and Pleistocene, in response to major climatic events.

Stratigraphy Site 586, drilled in 1982 by the Glomar Challenger, is located on the northeastern up-

155"E

160'E

Fig. 1. (a) Western Pacific bathymetry from Apgova et al. ( 1984); location of map (b) indicated by dotted box, (b) Ontong Java Plateau with bathymetry from Mammerickx and Smith (1984). Locations of DSDP Site 586 (00°29.84'S, 158°29.89'E, 2218 m), Site 289 (00°29.92'S, 158°30.69'E, 2206 m), and Site 64 (01 °44.56'N, 158°36.51 'E, 2052 m) indicated.

the Intermediate Waters of the Pacific (Reid, 1965; Dietrich et al., 1980). Sedimentation rates are quite high, ranging from about 20 to 40 m/m.y., due to high productivity along the equatorial divergence. The site is located well above the present depth of the foraminifer lysocline in this region (3400 m; Berger and Johnson, 1976; Berger et al., 1982). Thus, the isotopic record should be largely unaffected by differential dissolution. The 6 Ma record here presented provides a good opportunity to ex-

per slope of Ontong Java Plateau (00 ° 29.84' S, 158°29.89'E, 2218 m), about one nautical mile northwest of DSDP Site 289 (Fig. 1 ). Our study concerns the upper 195 m of sediments, recovered by hydraulic piston coring in Holes 586 and 586A. They constitute a continuous and undisturbed record of the last 6.1 Ma, from the latest Miocene to the present. The sediments recovered in this interval are composed of a single lithologic unit (Moberly et al., 1986): pale green to white foraminifernannofossil ooze and foraminifer-bearing nannofossil ooze (Fig. 2). The sediments of the Pleistocene (0-38 m ) contain a larger percentage of foraminifera (up to 60%) compared to those of the Pliocene (less than 20%). The remainder consists mainly of nannofossils. Biogenic siliceous components (radiolarians and diatoms) are present in minor amounts ( < 5%) and a small contribution of non-biogenic material (volcanic glass, zeolites, pyrite ) is observed throughout the section. The age assignments (Fig. 2) are based on magnetobiostratigraphy. Barton and Bloemendal (1986) place the Brunhes/Matuyama boundary between 15.0 and 15.75 m sub-bottom (msb) in Hole 586B (586B-2-3 and 586B-

PLIOCENE-PLEISTOCENE O X Y G E N ISOTOPE RECORD: O N T O N G JAVA PLATEAU

17 3

Pulleniatina Coiling

Core Age Lithology

.o,o 586 °I;ll

Age

. ~ o o o

0

t

2

3

4

5

6

I

I

I

I

I

I

_______ ~ -:_--~-.,,--~.-.l.

/rny

(

~ ~ ..- - , - - "~ m . ~ - - , , - -

f

22.8

Hole 586A

40

~,,-~ ~ - ~

so

(Ma)

% Right

re~my

J

......~_-. ~ .

d~ .J.--

E

35.0

rn

0

== _o

100

. . a.

I

=.4.

.0 w-

CL G)

a

,

m

T

~.k 4-" - t . ...t.

4 . - t - . . t . -t-

150

• ...k.

=.4.

•,P-

.t_ --I.. -J-t,t_ ,p--I--d_-L

-t--_.t..~

H- . - J - ,

200

-------'~ Fotaminlfet-nsnnofo$silo~ nannofossil-

fotaminifet

ooze

~'~

Nannofos$il ooze

Fig. 2. Lithologic and stratigraphic column for Site 586. Stratigraphy from Moberly et al. (1986). Pulleniatina coiling direction determinedin this study. Sediment rates determinedusing age controlpoints of Table 1.

2-4-25 cm). Thus, the base o f the Brunhes Chron (0.73 Ma) is taken to be 15.4 msb in Hole 586. The biostratigraphic control is based on both shipboard analyses o f core catcher samples (Moberly et al., 1986) and onshore refinements (by J.M.W.) using additional samples to better define the range o f certain

foraminifera. Ages of first and last appearances were taken from Bergren et al. (1985). The age control points for this study are listed in Table 1. A comparison of the foraminiferal stratigraphy o f Holes 586/586A with that o f 586B (Jenkins and Srinivasan, 1986) shows very good agreement between the studies.

174

J.M. WHITMANAND W.H. BERGER

TABLE 1 Age control points/events: site 586 Depth 0.0 15.4 36.6 55.0 64.8 85.8 96.3 160.2 181.5

m m .2 rn m m .2 m m .2 m m .2

Age*~

Event

From interpolation

0.0 Ma 0.73 Ma 1.66 Ma 2.47 Ma 2.9 Ma 3.4 Ma 3.8 Ma 5.3 Ma 5.8 Ma

Top of core Brunhes/Matuyama boundary Pliocene/Pleistocene boundary Matuyama/Gauss boundary Last appearance G. altispira Gauss/Gilbert Boundary Coiling change Pulleniatina Miocene/Pliocene boundary First appearance Pulleniatina

*JDates based on Berggren et al., 1985. *21ndicates age control points identified in Site 586 sediments. Brunhes/Matuyama boundary from Barton and Bloemendal (1986), other controls based on foraminifer stratigraohy (shipboard data and subsequent refinement by J.M.W. ).

Sedimentation rates varied considerably during the last 6 Ma, showing a remarkable decrease in the Late Pliocene, from values near 40 m/m.y, in the Late Miocene and Early Pliocene, to values approaching 20 m/m.y, in the latest Pliocene and Pleistocene times. Similar fluctuations in sedimentation rates were noted at other western Pacific sites by Kennett et al. ( 1986 ). Any smaller scale fluctuations in the sedimentation rate are not resolved here due to the coarseness of the age control. Using the sedimentation rates in Fig. 2, the sampling interval of 1.5 m corresponds to 70 ka in the Late Pliocene and Pleistocene, to 43 ka in the latest Early Pliocene, and to 35 ka in the early part of the record.

Methods

Isotope measurements The cores at Site 586 were sampled at 1.5 m intervals from 0 to 195 m. Each bulk sediment sample of approximately 10 cm 3 was dried and weighed. The samples were soaked overnight in a buffered Calgon solution to promote disaggregation. The sediment was then washed in deionized water, oxidized in 3.5% HzO2, ultrasonified to complete the disaggregation, and

wet sieved at 63 pm, 149 pm and 250 pm (for grain size analysis). Oxygen (and carbon) isotopes were measured on four taxa of foraminifera: two planktic taxa (Globigerinoides sacculifer and the Pulleniatina lineage, including Pulleniatina obliquiloculata, Pulleniatina primalis and Pulleniatina spectabilis) and two benthic species (Oridorsalis umbonatus and Cibicidoides wuellerstorfi). The planktic species were picked from the size fraction 355-425 /tm and the benthic species from the fraction > 250/~m. The sample size for isotopic measurement was 250-1000 #g, depending upon availability of specimens; planktic samples usually contained 15-25 individuals, benthic samples 5-10 individuals. At some intervals, there were insufficient numbers of one or both of the benthic species for analysis. In a few instances, duplicate measurements were made on one of the planktic species. Measurements were made on a VG Micromass 602C mass spectrometer. The samples were reacted with 100% phosphoric acid at 50°C in an in-line vacuum system. CO2 was measured relative to a known reference gas (FIS) and then calculated as standardized difference to PDB (a belemnite from the Pee Dee Formation ), by the procedure of Craig ( 1957 ). The carbon isotope results (Whitman, 1989)

PLIOCENE-PLEISTOCENEOXYGENISOTOPERECORD:ONTONGJAVAPLATEAU

will be discussed in a companion paper to this one (Whitman and Berger, in prep. ).

Interpretation of oxygen isotopes The interpretation of oxygen isotopes in foraminifera is discussed in a number of reviews (e.g., Berger, 1981; Vincent and Berger, 1981 ). The following outline pertains to the approach taken in this study, which differs from the convention by incorporating a salinity effect directly into the coversion ofd01sO to AT. The difference (A) between the isotopic composition of the calcite in two samples of foraminifera (Or) can be expressed as a sum of the change in several factors (of. Berger and Gardner, 1975): /10f = / 1 0 T + / [ 0 G "JI-/10E + / l &

+/10D

+/10A

( 1)

where 0T is the temperature effect, 0~ the glacial ice volume effect, 0E the evaporation and precipitation effect, 6v the vital effect (growthrelated fractionation, or from symbiotic algae), 0o the depth habitat effect, OR the effect due to differential dissolution and 0A the effect due to diagenesis. We assume that diagenesis and dissolution effects are negligible in these samples. Also, we assume that depth- and vital effects stay constant in each species, unless the data dictate otherwise. Thus, changing differences between the oxygen isotope values for coexisting benthic foraminifera are taken to be due to changing vital effects. As long as differences are constant through time, a simple "correction" can map one species onto the other. In the ease of adult planktic forms, consistent differences in signals suggest differences with respect to season or depth of growth. The temperature equation we use is that of Epstein and Mayeda ( 1953 ): T = 16.5-4.3 (0f-0w) + 0.14(0f-0w) 2

(2)

where Of is the isotopic composition of fora-

175

miniferal calcite and 0w is the isotopic composition of seawater. The equation implies that 0w is known or can be constrained. The isotopic composition of the ocean waters varies with salinity due to the effects of evaporation and precipitation as well as runoff, freezing and mixing. The data of Craig and Gordon ( 1965 ) suggest a relationship as follows: A0w = 0 . 4 / i S

(3)

linking a change in isotopic composition of the water to a change in salinity. The salinity of the oceans varies as a function of temperature. For the South Pacific, the data of Sverdrup et al. (1942) can be approximated by the relationship: AS=0.125 AT

(4)

Combining eqns. (3) and (4) yields an estimate of the isotopic composition of seawater as a function of temperature: A0w = 0 . 0 5 / i T

(5)

The equation expresses the fact that warm water is enriched in the heavy isotope (because of excess evaporation) and cold water in the light one (as the evaporated water condenses here). Combining eqn. (2), without the last term, with eqn. ( 5 ), we derive: AT= - 5.5 Art

(6)

and Art = - - 0 . 1 8 AT

(7)

The two equations suggest that the planetary temperature gradient as conventionally calculated from contemporaneous differences in oxygen isotopes is considerably too small (see Berger and Mayer, 1987). The magnitude of the ice effect (dOG) has been examined in various studies since the work of Emiliani (1955, 1966), the most important evidence resulting from the analysis of Greenland ice (Dansgaard and Tauber, 1969). Shackleton and Opdyke ( 1973 ), in their study of late Pleistocene sediments on Ontong Java

176

J.M. WHITMAN A N D W.H. BERGER

Plateau, proposed 1.2%0 for the glacial/interglacial difference, which leads to a change of 0.1%00 per 10 m of sea-level change, for a response ratio of 0.01%00/m, here called "SO-ratio" (for sea level and oxygen). The value of 1.2%o was discussed and defended by Berger and Gardner ( 1975 ), and (after much controversy) is again close to the current consensus (Bender et al., 1985; Chappell and Shackleton, 1986; Fairbanks, 1989). For the late Pleistocene we set, therefore: A ~ =0.01 ASL

(8)

For late Pleistocene sediments, benthic records tend to show a larger amplitude than that of the ice effect alone, thus, glacial cooling of bottom waters is indicated (Chappell and Shackleton, 1986; Labeyrie et al., 1987 ). The isotopic composition of the ice sheets during Pleistocene glacial maxima is readily estimated from the sea-level drop and the SOratio. The drop during the last glacial was ca. - 1 3 0 m (Milliman and Emery, 1968; Shepard, 1973; Chappell and Shackleton, 1986; Fairbanks, 1989), corresponding to a reduction in ocean volume by 3.3%. The isotopic composition of the ice emerges from the isotopic balance between the glacial ocean, ice and interglacial ocean, yielding values between -34%0 and -38%0 (cf. Broecker, 1975; -35%0). In a core where more (or less) than the full amplitude of the isotopic excursion is recorded, the relationship between A~f and sea level is scaled appropriately assuming that local conditions (temperature etc.) change in harmony with the ice mass. Assuming that A/~, AdiA, At~v, and AJ D c a n be neglected, eqn. (1) can now be rewritten to read: A6f =A6~ --O.18 AT

(9)

The maximum value of A8G is 1.3%o for the Pleistocene. We assume that the SO-ratio changes through time. When ice masses are smaller, warmer, and less elevated at the site

of precipitation than in the Pleistocene, this ratio should be smaller than now. Thus the zlSL corresponding to a given/IJG is then larger. A comparison of the magnitude of short-term sealevel changes in the Pleistocene and corresponding fluctuations in J~80 could help constrain the zing value for the more distant past. However, information on sea-level changes may not be sufficiently accurate to do this with a high degree of confidence.

Isotopic data and comparison with other studies Data The oxygen isotope data for Site 586 are given in the Appendix and are plotted versus depth and age in Fig. 3 (using the age control points from Table 1 ). Several events and general trends are apparent, including shifts in average values, and in differences between species, reflecting changes in habitats or vital effects, or both. Changes in the amplitude of fluctuation through time also are discernible. General trends Our data show three isotopic shifts: Event A at 62 m (2.8 Ma, enrichment), Event B at 85 m (3.4 Ma, enrichment), and Event C at 105 m (4.0 Ma, depletion). Between Event C and Event B there is a period of maximum depletion. Also there is a marked increase in the range of fluctuations younger than 2.5 Ma. Numerous workers have commented on analogous events in the oxygen isotope stratigraphy of the Early to Middle Pliocene (Shackleton and Opdyke, 1977; Shackleton and Cita, 1979; Keigwin, 1979, 1982a,b, 1986; Hodell et al., 1983, 1985; Leonard et al., 1983; Shackleton et al., 1984; Elmstrom and Kennett, 1986; Loubere and Moss, 1986; Stein and Bleil, 1986 ). We cannot demonstrate that the events seen in our data are identical to those identified at other locations, since the biostratigraphic resolution at Site 586 is uncertain

PLIOCENE-PLEISTOCENE

177

O X Y G E N I S O T O P E R E C O R D : O N T O N G JAVA P L A T E A U

-2.0

a

A: ....

• •

a 0 ~g

i$

oo

::::::::

1.0

i

~.o

iili :i:i

3 . 0 r-.

"It. ~

•

[

.

0.'_0

~

~

,%.0

~

~

eeo

o

A ~

:iii!

40

I ao

'

~

•

,~,,.

~

•

4,,

,

• 4 4

o

A

-

•

.I "

•

I l

•

I

•

,

~

mo

Depth

b

Oi° |¢1

•

~,,,,

i:i: ,

5.0 o

-1,0

°o-

::::

I,,~

-2.0

•

~,,,,,~

(m)

B

C

i:i: ::::

•

200

~60

•

•

~ 8 ~

o-

0.0 i:i" 10

:+

o

i:i

'~2.0

..:'..;'.,-,:,::

3.0 4.0

:,. ::,. 4

4A ~ 44

~

~

~

~

44~

•

.. . ," •

•

::::

5.0 0

Age

(Ma)

Fig. 3. Oxygen isotope data from Site 586. Symbols are: open diamond ( O ) for G. sacculifer, filled square ( I ) for Pulleniatina, filled circle ( • ) for C. wuellerstorfi, and open triangle ( A ) for O. umbonatus. (a) Data plotted versus depth in the core. Isotopic events are indicated: A (62 m, 2.8 Ma), B (85 m, 3.4 Ma), and C ( 105 m, 4.0 Ma). Open triangles along the x-axis mark the boundaries between the Pleistocene, Pliocene and Miocene; (b) Data plotted versus age in the core (see text for explanation of age assignments). Isotopic events labeled the same as in part (a).

(about 10% of age assigned). However, the major cooling events between 3.2 and 3.4 Ma, and near 2.5 Ma (2.8 Ma in our scale) are well established for the North Atlantic (Shackleton et al., 1984) and numerous other locations throughout the world oceans. A compilation of the documented shifts shows two peaks of occurrence, at 2.5 and 3.2 Ma, but with a spread of + 0.2 Ma for each event (Whitman, 1989).

We do not claim that our shifts are different, rather that it is likely that the events are contemporaneous globally and differences in age result from stratigraphic uncertainties. The labels A, B, and C are used on all figures displaying isotopic data, to aid the reader in orientation (rather than to make a claim regarding their significance). The difference between G. sacculifer and C.

178

J.M. WHITMAN AND W.H. BERGER

wuellerstorfi ranges from 3.7%0 at the bottom to 4.3%o at the top of the sequence. G. sacculifer is believed to deposit its shell in isotopic equilibrium with seawater (Shackleton and Vincent, 1978), while C. wuellerstorfi is depleted in lsO by 0.64 %o0 relative to seawater (Shackleton, 1974). The difference in temperature between the surface and bottom waters should agree with eqn. (6), when adding the deviation of C. wuellerstorfi from equilibrium (0.64%0) to the difference between the two species. The present-day difference is 27°C (Reid, 1969; Craig et al., 1981 ), which agrees with the coefficient of - 5 . 5 in eqn. (6). The smaller difference in the Early Pliocene (by o

~

j

o ~°o

-06

o~o

~ - 0

Benthic foraminiferal record The oxygen isotope values of O. umbonatus are distinctly heavier than those of C. wuellerstorfi, the average difference being 0.64%0 +_0.14 (Fig. 4a, Table 2 ), and the total range 0.34-0.94°/00. The value of 0.64%o agrees with that given by Shackleton and Hall ( 1984 ) and Pisias et al. (1985). Berger and Vincent ( 1986 ) found a difference of 0.600/00 for an Atlantic site (INMD l l5 Bx) and 0.75%0 for a

A

• - 0 8

C)

0.6%0, see Fig. 4) presumably is due to the deep water being warmer by some 3.5 °C (or more, if the evaporation factor was less strong).

o

o °°

o °°°

° °

-I0 K +

-0 8

~c

~

:

°°

:

:

°o

~"

~

^

IP c

-., !!i

C.sacculifer

°

o %

o° o

~ o

oo ° o

5 P-

o

':':~

°+ (Ma)

,

a

1

V

oO~ ~il

o°

:::i

oo~% o

!!i

I

°o

o oo ¢

o

~o°°o%°ooo°o o

o c %

o

o

od~

o

°°

+,

a

co

.........

Mean

-

o o%°

benthics

o 0°-o ~o o o

c o ooo~

<;

° c °s

~ : o 0+:o OOO,+

o

+:

o

00

+ a

4

3

A

o

o ~°

°:"

I

~'

d

o

o

0o%O~

C

±

Age

=o_4S~_oOOO

Pullenialina

o

4

.....

o

o

B

::::

i:i:

!

' u

~ ga

-

i!::i g + s a c c u l i ? e r

-4.o~

F

o

Age A

°0

o o oo o

35!

O.umbonatus

(Ms)

o

o

_ss c o

-

'~

:: o ~+° 0o%%o°o Oo~: : °% °o° °~ooo~ OCbov®

~

k° . . . . -5oF o f'~ / =

oo

. . . .

oo

~ 5 m0

~

"3

2

++ :

02

-55|

°c

C wuellerstorfi 1

o

aa

c° °

°

Age

-4

o

o

o

4

000

<

o

o ~

-02

-

Q

o c

o

°o

c:

c

I

o °

6

5

(Ma)

yB Pulleniattna--

-

oliii li

oi~i~o0°~,~,~oo

Mean

benthics

o

iiil

O~

o

°*% °

o+o o o q ,

o

Age (Ms) Fig. 4. Oxygen isotopedifferencedata (pairsof compared taxa indicatedon each graph). IsotopiceventsA, B and C and epoch boundaries as in Fig. 3.

PLIOCENE-PLEISTOCENEOXYGENISOTOPERECORD:ONTONG JAVAPLATEAU TABLE 2 Oxygen isotope differences. All values given in per mil (%0) Mean

Std. Dev.

N

For entire core: C. wuellerstorfi - 0 . umbonatus G. sacculifer-Pulleniatina

- 0.64 -0.31

0.14 0.19

66 115

For selected intervals: G. sacculifer - Pulleniatina <38m(38 m ( > 1.8 Ma) 38-85 m (1.8-3.4 Ma) 85-122 m (3.4-4.4 Ma) 122-160 m (4.4-5.3 Ma) > 160m ( > 5 . 3 Ma)

-0.48 -0.26 -0.18 -0.34 -0.20 -0.42

0.22 0.14 0.11 0.12 0.10 0.12

25 90 29 23 24 14

Pacific core (ERDC 112 Bx). The offset is ascribed to vital effects: both species live on the seafloor, at the same temperature. Similar offsets have been observed in other benthic species (Shackleton and Opdyke, 1973; Woodruff et al., 1980; Graham et al., 1981; Shackleton and Hall, 1984; Grossman, 1984). The two benthic species show parallel isotopic trends over the entire time interval (0-6 Ma), although data for O. umbonatus are sparse in the lower 560 m due to the scarcity of specimens (Fig. 5a). The correlation coefficient is 0.94 and the best fit through the data points has a slope close to 45 °. The scatter can be attributed to the error of each analysis ( ___0.1%oo) which sums to an error of _ 0.2%0 for each of the points in this plot. Almost all of the points fall within this limit indicating that the difference between the oxygen isotope values of the two benthic species is stable for the period studied. This stability provides a strong argument for the use of either species as a reliable signal carrier. The fact that the records of the benthic foraminifera are parallel (while those of the planktics foraminifera are not) emerges readily when smoothing the data (Fig. 6 ). Smoothing for Fig. 6a was done by a 5-point triangle filter (weighting 1-2-3-2-1 ), corresponding to a 6 m window. Prior to filtering, any depth level with more than one isotopic value per species

179

was averaged to produce a single value. Several filters were considered, the triangle with the 6 m base provided satisfactory reduction in noise with good retention of the fluctuations in the signal. A different smoothing technique was used for the age plot (Fig. 6b ). These sequences were generated by plotting the average of data points within a 0.5 Ma interval at the mid-point of the window and incrementing the window in 0.1 Ma steps. No weighting was applied. This method of smoothing the data eliminates many of the smaller scale variations shown in the curves of Fig. 6a (particularly above 40 m); however, the longer term trends are still apparent.

Planktic foraminiferal record The values of Pulleniatina are distinctly heavier than those of G. sacculifer (Fig. 3 ) reflecting the difference in depth habitats (Berger et al., 1978; Vincent and Berger, 1981). Shackleton and Vincent (1978) believe that both of these foraminifera calcify their tests in isotopic equilibrium with seawater. The difference in the present day values of 0.7%0 would then correspond to a temperature difference of 3.9 ° C. An offset of similar magnitude between the two taxa was found in the southwest Indian Ocean (Shackleton and Vincent, 1978 ). The records on the two planktic species do not vary in parallel as do the benthic ones, and there are distinct trends and fluctuations in the differences between them (Figs. 3b and 4b). The Late Pliocene, for example, is characterized by small differences, the late Pleistocene by large ones, with a large range of variation. Linear regression does not express this complicated pattern well (Fig. 5b), although a positive correlation is retained (corr. coeff. = 0.70 ). The best fit line through the data points makes an angle of less than 45 °, thus changes affecting the values of G. sacculifer tend to be amplified in Pulleniatina. We interpret this as indicating fluctuations in the thickness of the mixed

,I.M. W H I T M A N AND W.H. BERGER

180

co b 4.5 i a ,~

4.0

@5 -

b

%

r. 35 i :

i

•

• ee

30 ~ ,

Z~

°"o o i

0

I

•

Z

/ .oe

je 2 5

20

/

~

-.20

,

3 5

30

4.0

4 ~5

'C

/

,

• _

d'aO P~llerLlat!n~

;

40 ~

*o |

•

-~

a

•

4~ d

/~

-

"1 40

e/ • i0

-

°o

oe

35 •

3o

•/

o

-20

-15

eeoe~ o o z

~

°o

da

"~ ;°Oj

2.5 ~//

- i7

/"

e~ ° ,

I~4..

i

~e

•

50

d'80 O.ttmbonattzs 45

• •

o

-I'0

-05

O0

6'a0 G s a c c u l z f e r

25

r~ e

20

-15

-i0

-05

00

~'80 P u l t e m a t ~ n c t

Fig. 5. Correlation plots of oxygen isotope data sets. Solid lines indicate 45 ° slope through the data points. In (a) and (b), dashed lines are best fit linear regressions through all the data points. In (b), the points above 38 m (Pleistocene) are representedby open squares while the points below 38 m are represented by filled circles. In (c) and (d), the dashed lines are best fit linear regressions through the data points above 105 m ( < 4 Ma). In (c) and (d), the points above 105 m ( < 4 Ma) are representedby filled circles while the points below 105 m ( > 4 Ma) are represented by open squares. layer, which go parallel with changes in surface water temperature and with the ice effect. Thus, upon cooling, Pulleniatina records three correlated effects (cooling, ice buildup, rise of thermocline), G. sacculifer only two (co•ling, ice buildup). The difference is especially apparent in the Pleistocene portion o f the record, Suggesting a threshold effect for sensing the thermocline. The average offset between the two foraminifera over the entire length o f the section is 0.32°/00 (s.d.=0.20; Table 2). However, the large differences in the mean o f the offset for different periods, and also the large differences in the range of fluctuations about this mean (Figs. 4b and 6) presumable reflect substantial differences in oceanic conditions between

these intervals. Statistical tests on homogeneity (using the method of Koch and Link, 1980), confirm this proposition, by demonstrating a lack o f overlap in properties between selected intervals. Below a depth of 38 m (older than 1.8 Ma), the mean value for the difference between the two species is 0.26%0 ( s . d . = 0 . 1 4 ) . Unlike in the benthic data, the scatter about the mean difference is larger than expected from measurement error. Also, there are certain intervals where the average difference is distinctly larger than the overall mean ( 8 5 - 1 2 2 m, 3.5-4.4 Ma; > 160 m, > 5.3 Ma), while other intervals have means much smaller than the overall mean ( 3 8 - 8 5 m, 1.8-3.5 Ma; 122-160 m, 4.4-5.3 Ma). Above 38 m ( < 1.8 Ma), the mean differ-

181

P L I O C E N E - P L E I S T O C E N E O X Y G E N I S O T O P E R E C O R D : O N T O N G JAVA P L A T E A U

-2.0

a

^

B

....

v w

-I.0

C oooooo v '~,"~_.~ooooo~oo~o~oo~..~o~o~ooo

°

0.0 1.0 0 ' ~ ~-.0 3.0 4.0 i!i! i:i:

A j

5.0 0

J

40

J

80

Depth

-2.0

b

-1.0

i

,

120

ix

,

160

(m)

200

e

am i a ° e l ° °

°n°

ii~i

ooemm

0.0 1.0 0 "Q 2.0 oOooooooOoOOOOOOOO°Oooooooooo

3.0 4,0 5.0 0

ooo,,,,o,,,

....

°°o.°° ....

• ........

o.o°°° ....

t

1

&

, " i::i::

.................

•

go

*~*. . . . . *. . . . .

o.....

I

2

;q" i

1

3

4

I

5

ix

l

6

Age (Ma) Fig. 6. Smoothed oxygen isotope data. Symbols for species, isotopic events A, B and C, and epoch boundaries as in Fig. 3. (a) Smoothed data ( 5-term triangle filter) versus depth; (b) Age-averaged data (0.5 Ma window) versus age.

ence between the oxygen values of the two planktic taxa shows a dramatic increase, to a value of 0.49%o and there is a large increase in the scatter about the mean (s.d. = 0 . 2 2 ) . This pattern results from a divergence, such that the m a x i m u m values of Pulleniatina become increasingly heavier than those of G. sacculifer towards the present (Fig. 3). The divergence

implies an overall strengthening a n d / o r shallowing of the thermocline at this location (especially during glacial intervals), with the values p f Pulleniatina reflecting an increasingly colder habitat. The large range of difference values in this interval, with some data points showing almost no offset and others reaching a m a x i m u m 1.0%o offset, suggests that upwell-

182

ing intensity varied greatly through time. Before 1.8 Ma ( > 38 m ) , the variations in the difference between the planktic foraminiferal records may also be attributed to fluctuations in upwelling intensity on a smaller scale. The times of less offset presumably represent warmer times, that is, periods of global transgressions when the temperature gradients are weakened, and when trade winds and equatorial upwelling lose strength, as a consequence.

Benthic versus planktic foraminiferal records To examine the trends in the difference between the records of the benthic and planktic foraminifera, we compare each planktic foraminifera with the mean of the benthic ones. The values of C. wuellerstorfi are adjusted to those of O. umbonatus by adding 0.64%0 before a mean is calculated for each interval of depth-in-hole. The adjustment should yield a difference in terms of equilibrium values. Resuits are plotted in Fig. 4c and d. The fact that differences between the values of the planktic and benthic foraminifera change markedly over the section is reflected in weak correlation coefficients (0.49 for G. sacculifer and 0.65 for Pulleniatina ). The difference between the oxygen values of G. sacculifer, and the mean of the values of the benthics (Fig. 4c) increases by about 0.6%o since the Early Pliocene, corresponding to a temperature change of 3.5°C. The final increase occurs just before 2 million years ago. Before 4.0 Ma, the offset is nearly constant, with a mean of 4.32%o (suggesting a deep water temperature of around 5 ° C ). After 2 Ma, most of the increase in offset has taken place and additional separation is moderate. The difference increases quite rapidly between 4.3 to 3.5 Ma (at Event C in Fig. 4c), decreases near 3.4 Ma (Event B ), and increases again near 2.8 Ma (Event A). Presumably, these events mark corresponding changes in deep water temperatures.

J.M. WHITMAN AND W.H. BERGER

The differences between the oxygen values of Pulleniatina and the mean of the benthics (Fig. 4d) show much the same pattern. The overall increase of nearly 0.5%0 in the offset is slightly less than that for G. sacculifer: as the deep water cools, the thermocline rises. Steps are seen at 4.0 and 2.8 Ma. The interval between 4.0 and 2.8 Ma does not show the same structure in detail as for the G. sacculifer data. Also, there is no increase in separation after 2.8 Ma, indicating that deep water and thermocline water cooled together. The covariance plots of the data of the benthic and planktic foraminifera (Fig. 5c and d) show a substantial scatter, much greater than can be attributed to measurement error alone. This indicates much room for independent variation of the two signals, that is, weak coupling (especially for the time before 4 Ma ). A regression for the entire data set has little meaning, therefore. Above 105 m ( < 4 Ma), the covariance between data of the benthic and planktic foraminifera is considerably increased over the means (corr. coeff. 0.78 for G. sacculifer and 0.88 for Pulleniatina). Presumably, the increased covariance reflects the strengthening of an external driving mechanism involving the entire water column, that is, the waxing and waning of polar ice. The steep slope of the post-4 Ma fit (dashed line, Fig. 5c and d), shows the greater sensitivity of the benthic foraminifera to a large-scale change, consistent with an assumption that surface temperature varies less than deep water temperature. The pattern for the Pulleniatina data is similar to that for G. sacculifer, but the coupling to deep water variability is stronger, for reasons mentioned.

Events and trends A distinct change occurs in the oxygen isotopes of benthic and planktic foraminifera at about 62 m (2.8 Ma, Event A, Fig. 3). For both benthic species, the mean of the values directly above this level is greater than that of those be-

PLIOCENE-PLEISTOCENE OXYGEN ISOTOPE RECORD: ONTONG JAVA PLATEAU

low, by about 0.5%o (Table 3). In each case, the first point following Event A falls well outside the range of the values preceding it. In the planktic foraminifera, the 180 enrichment is of a smaller magnitude; in G. sacculifer it is 0.25°/0o, and in Pulleniatina only 0.15o/oo. At 85 m (3.4 Ma), the records of both planktic foraminifera show a permanent positive change of0.15%o (Event B ), with little apparent effect on the benthic species (Fig. 3). For the entire section below 62 m ( > 2.8 Ma), the isotopic values of the benthic species fluctuate very little about a rather constant average (Table 3). Although both benthic species show a temporary enrichment in 180 at 85 m (3.4 Ma), there is a rebound to lighter values within l0 m (by 3.2 Ma). Aliasing makes the interpretation of such excursions difficult (Pisias and Mix, 1988). At 105 m (4.0 Ma), the Pulleniatina data show a positive shift of 0.3%o (Event C, Fig. 3), from a sequence of near-constant values toward an interval of greater variability, at lighter values. A shift of the same magnitude occurs in the G. sacculifer data at 115 m (4.2 Ma), resulting in a temporarily increased separation between the two signals over the l 0 m interval which appears on the plot of difference data as a small peak before Event C (3 samples, Fig. 4b). The mean of the values for G. sacculifer below 115 m (4.2 Ma) is the same as that above 62 m (2.8 Ma; Table 3 ). In between the values are relatively light. For Pulleniatina, values above 62 m (2.8 Ma) are heavier on average than the values below 105 m (4.0 Ma). Between these two levels, the oxygen values of Pulleniatina likewise are relatively light. Because the changes in benthic and planktic foraminiferal isotopic records are not identical (Fig. 6 ), more than one factor must be responsible. The magnitude of the possible changes in the variables of ice volume, temperature, and salinity can be constrained (tentatively) using the relationships summarized earlier. Options

183

for interpreting the data are outlined in Table 4 and will be discussed later. In the interval above 62 m ( < 2 . 8 Ma), all of the records show an increase in the variability of the data (Fig. 7). For this plot, the difference between adjacent points, averaged within each 6 m interval, was plotted at the midpoint of each (gliding) interval. Aside from the trend of increasing variability in the upper part of the section, especially in post-Event A time, there is very little synchroneity in the amplitude of fluctuations between the records of the benthic and planktic foraminifera. Either the variability of the surface and deep water signals is not linked or, more likely, our sampiing density is not high enough to detect parallelism at the appropriate frequencies. The increase in variability after the 2.8 Ma (62 m ) enrichment (Event A) appears to be gradual with a noticeable acceleration occurring at 1.8 Ma (40 m ) (aliasing may interfere in the recovery of the time trend). For the benthic species, the variability in the upper portion of the core (above 60 m ) reaches values more than double that of the lower part of the core. The factor of increase in variability in the planktic is much greater than in the benthic species. In three cases (C. wuellerstorfi, O. umbonatus and Pulleniatina), the greater post-A variability is due to a proliferation of heavier values in the younger samples while the other limit for the range remains nearly constant (Table 3). For G. sacculifer, both sides of the range expand in the younger samples. This trend results in the divergence of the ranges of the two planktic foraminifera since Event A, which we attribute to a rise of the thermocline and increased upwelling, as mentioned. Effects of changing sedimentation rate on the amplitude of the glacial to interglacial excursion of oxygen isotopes, from mixing (e.g., Peng et al., 1977 ), are readily discounted: sedimentation rates decrease upwards and thus benthic mixing should oppose the trend seen. In any case, the effect of sedimentation rate on

184

J.M. WHITMAN AND W.H. BERGER

TABLE 3 Statistics on oxygen isotope data. All values given in per mil (%0) Benthic species

Mean

Max

Min

Range

Std. Dev.

N

0-38 m (0-1.8 Ma)

C wuellerstorfi O. umbonatus C o m b i n e d benthic species* 38-62 m ( 1.8-2.8 Ma)

C wuellerstorfi O. urnbonatus C o m b i n e d benthic species* > 6 2 m ( > 2 . 8 Ma)

C. wuellerstorfi O. umbonatus C o m b i n e d benthic species* 62-85 m (2.8-3.4 M a )

C. wuellerstorfi O. umbonatus C o m b i n e d benthic species* 85-105 m (3.4-4.0 Ma)

C. wuellerstorfi O. umbonatus C o m b i n e d benthic species* > l 1 5 m (>4.2 Ma)

C. wuellerstorfi O. umbonatus C o m b i n e d benthic species*

3.17 3.83 3.82

3.69 4.54 4.54

2.66 3.22 3.22

1.03 1.32 1.32

0.28 0.26 0.27

25 22 47

3.00 3.63 3.64

3.15 4.10 4.10

2.75 3.32 3.39

0.40 0.78 0.71

0.15 0.22 0.20

11 15 26

2.48 3.06 3.14

2.81 3.39 3.45

2.14 2.78 2.78

0.67 0.61 0.67

0.14 0.14 0.15

53 39 92

2.54 3.20 3.19

2.80 3.47 3.47

2.23 3.05 3.87

0.57 0.42 0.60

0.18 0.13 0.15

11 12 23

2.44 3.02 3.05

2.63 3.23 3.27

2.19 2.83 2.83

0.44 0.40 0.44

0.15 0.13 0.14

11 11 22

2.51

2.81

2.14

0.67

O. 17

36

3.01 3.11

3.27 3.45

2.78 2.78

0.49 0.67

0. l 5 0.17

15 51

- 1.22 - 0.74

-0.83 - 0.13

- 1.75 - 1.16

0.92 1.03

0.22 0.26

25 25

- 1.18 - 1.03

- 1.00 -0.85

- 1.37 - 1.23

0.37 0.38

0.14 0.11

14 14

- 1.47 - 1.26

- 1.29 - 1.18

- 1.77 - 1.43

0.48 0.25

0.12 0.06

15 15

- 1.67 - 1.38

- 1.49 - 1.19

- 1.89 - 1.51

0.40 0.32

0.12 0.10

13 13

- 1.21 - 0.94

-0.97 - 0.60

- 1.44 - 1.26

0.47 0.66

0.09 0.14

50 42

Planktic taxa 0-38 m (0-1.8 M a )

G. sacculifer Pulleniatina 38-62 m (1.8-2.8 Ma)

G. sacculifer Pulleniatina 62-85 m (2.8-3.4 Ma)

G. sacculifer Pulleniatina 85-105 m (3.4-4.0 Ma)

G. sacculifer Pulleniatina >l15m

( > 4 . 2 Ma)

G. sacculifer Pulleniatina Covariance of raw oxygen data

G. sacculifer

Pulleniatina

C wuellerstorfi

O. umbonatus

1.000 0.944

1.000

1.000 0.843

1.000

Entire interval

G. sacculifer Pulleniatina C. wuellerstorfi O. urnbonatus

1.000 0.698 0.606 0.580

1.000 0.701 0.685

0-38 m (0-1.8 Ma)

G. sacculifer Pulleniatina C. wuellerstorfi O. umbonatus

1.000 0.559

1.000

0.607 0.657

0.703 0.706

PLIOCENE-PLEISTOCENE OXYGEN ISOTOPE RECORD: ONTONG JAVA PLATEAU

18 5

TABLE 3 (continued) Covariance of raw oxygen data G. sacculifer

Pulleniatina

C. wuellerstorfi

O. umbonatus

38-62 m (1.8-2.8 Ma) G. sacculifer Pulleniatina C. wuellerstorfi O. umbonatus

1.000 0.939 0.685 0.482

1.000 0.557 0.325

1.000 0.737

1.000

62-85 m (2.8-3.4 Ma) G. sacculifer Pulleniatina C. wuellerstorfi O. umbonatus

1.000 0.033 - 0.213 -0.112

1.000 O.318 0.496

1.000 0.8.36

1.000

85-105 m (3.4-4.0 Ma) G. sacculifer Pulleniatina C. wuellerstorfi O. umbonatus

1.00 0.124 - 0.055 0.172

1.00 O. 141 0.471

1.000 0.768

1.000

< 105 m ( <4.0 Ma) G. sacculifer Pulleniatina C. wuellerstorfi O. umbonatus

1.000 0.722 0.766 0.785

1.000 0.847 0.867

1.000 0.941

1.000

> l 1 5 m ( > 4 . 2 Ma) G. sacculifer Pulleniatina C. wuellerstorfi O. umbonatus

1.000 0.292 -0.459 -0.454

1.000 0.027 -0.294

1.000 0.697

1.000

*Combined benthic species - the values of C. wuellerstorfi and the values of 0. umbonatus, with C. wuellerstorfi values adjusted to the mean ofO. umbonatus, by adding 0.64 %0.

~180 amplitude probably has been overstated in the literature, since intensity of bioturbation (i.e., mixed layer thickness) goes parallel to sedimentation rate (i.e., productivity), which introduces a compensating factor. Dissolution effects can cause a reduction in the amplitude of the oxygen isotope signal, by removal of those specimens in a population which lived in the warmest waters, and hence have the lightest isotopic values (Berger, 1971; Savin and Douglas, 1973; Shackleton and Opdyke, 1976; Berger et al., 1978; Erez, 1979; Wu and Berger, 1989). However, Site 586 is located well above the lysocline; thus, dissolution effects are not likely to affect the patterns seen. Instead they must be ascribed to changes in ice volume, temperature variation, and ice composition.

The sampling frequency at Site 586 does not allow resolution of individual glacial/interglacial cycles, but the data should largely preserve the amplitudes in the fluctuations of the 81sO signals. By the time of the Pleistocene (the upper 38 m, < 1.8 Ma), the amplitude is near 1.3%o for the combined benthic, and somewhat less for the planktic species (ca. 1%; Table 3 ). For the deeper part of the section, the range of variability in the records of both the benthic and planktic species is much smaller: 0.7%o for the combined benthics and near 0.5%o for the planktic foraminifera. Sea level variation and ice composition

Shackleton and Opdyke ( 1973 ) proposed a ratio of change in isotopic composition to

186

J.M. WHITMAN

a

0.6

AND W.H. BERGER

C

0.5 0.4 0

0.3

" • ,% ,,~ ii!! ,-o 0,2 4 " " """ " - • -.- J ." "~."" . ~.:~::..,-__-" ..:.'.-..-"~.-'. 0,1 o

0.0 o

~

A

t

~:

***

I

80

40

"L

_N [

I

i

.:.

•

A

~eo

p.dr-

~ - -

~6o

~oo

Depth (m) b

00.8 5

o

A

•

o~

,

•

0.2 o.1

"°* °

B

i!i

;*

C

~"

P"u" l l e n i a t i n a

.......

•

"..'::,'v.

-:.

*** ,*'.. ~, i:: °'° . ,~'. i! . . . . .." " ~ . ~ , ~ , , ~ . . ]', a

oo o

. "

..% ,,...., - _.,; ~ / * ~,,, ..,7-',~; ,~.,...'"" .." .'~.'"

i

°*~.'r

J

, , ~ _ _

'm~....,-'~IRlt

40

.

".~"

"

~2o

8o

b

[

/x

~6o

eoo

Depth ( m )

06

0

.

0.4

o

c

.

A.

.

0

.

.

5~ J

~*

0 1 ~

.. .. .~.., "T o ~

...~ • ::: ! : . . . .

. . . . . . o :i: ~ o , * . . . . ° , °" A i ° * * * . _ ° ~ ' .. 40 . . . . 80

~0

. ..

~-

d

A

05 • 04 0

E

.

.

.

,,

.~. • . • "~ ,"

***%

Depth

06

.

,,

0.3 .4 °o.o. 0.2 ~ 00

.

C.wuellerstorfi

.%

B

.

~*-'-* L . . . . ,°*o** 120

.m

• J * °.'~'-o &,.., ~-'~°°~ 160 .....

g00

(m) C

0 umbortatus

•.

0.3

,-o 0 2

% ,% ~'.°oo, o.oooo..O *°°o,,oo°o %,

oO -

..-

01 00

:-~ o

40

0o~o. i

8'0"-

.%. m o.Bo0 l.po.. 120

Depth

A •It "

160

t

3~

(m)

Fig. 7. Variability o f o x y g e n i s o t o p e s p l o t t e d v e r s u s d e p t h . I s o t o p i c e v e n t s A, B a n d C a n d e p o c h b o u n d a r i e s as in Fig. 3. Large filled circles are the v a l u e s o f the difference b e t w e e n a d j a c e n t points, a v e r a g e d w i t h i n each 6 m interval. Small o p e n circles are the s t a n d a r d d e v i a t i o n v a l u e s for each a v e r a g e d interval.

change in sea level of 0.1%o per 10 m for the late Pleistocene. This ratio, which we call the SO-ratio (for sea level and oxygen isotopes), must change through time. As high latitudes cool in the Late Neogene and as ice caps buildup to higher elevations, the fractionation of the water vapor feeding the polar ice should have increased. Thus, the SO-ratio should itself be correlated with total ice mass. Without constraints on temperature fluctuations, 5'80 values cannot be converted to ice mass or sealevel change. Simplifying assumptions need to be made, so that the reconstruction of sea level from 51sO, in essence, guesswork (e.g., see

Matthews and Poore, 1980). If one assumes, for the sake of conservative estimation, that the signal with the smallest amplitude reflects the ice effect, then the range of the (tropical) planktic signal records changes in global ice volume and thus tracks sea level. If sea level were given from an independent source, changes in the SO-ratio could be reconstructed. The amplitude of variability in the oxygen isotope data of the earlier part of the section is small compared to the latest Pliocene and Pleistocene. For the Pleistocene, the amplitude of 3180 variability is between 1.1 and 1.3%0. The sea-level data o f H a q et al. (1987)

P L I O C E N E - P L E I S T O C E N E O X Y G E N I S O T O P E R E C O R D : O N T O N G JAVA P L A T E A U

L

1

4

5

+100

(1.) _J U3

k,,.,,

-100

I

I

1

2

3

zk

I

6

7

Time (Ma)

Fig. 8. Age-averaged oxygen isotope data for Pulleniatina (from Fig. 6b) compared to sea-level curve modified from Haq et al. (1987).

and many others suggests an amplitude of ca. 100 m for the Pleistocene. The resulting SOratio (ASc/ASL) is close to the 0.01 given in eqn. (8). In the lower portion of the section ( > 1.8 Ma), the oxygen isotopic amplitude is 55% of that above. There are two options for interpreting this: sea-level fluctuations in the Pliocene were of the magnitude of 55 m or the amplitude of sea-level excursions was constant and the SO-ratio was less. Sea-level data is needed to evaluate the magnitude of the SOratio for the earlier time interval. The overall pattern of the planktic foraminiferal 5180 record shows a general agreement with a sea-level reconstruction by Haq et al. (1987) (Fig. 8 ). In the earliest Pliocene, fluctuation of sea level and of 5~80 values is reduced, there is a high stand (and light oxygen values) somewhere near 4 Ma, a drop near 3 Ma, and large fluctuations since. In detail,

187

however, the records do not agree. The sea-level curve of Haq et al. ( 1987 ) may not be applicable over the entire time span considered, but it can be used to illustrate of how the SO-ratio may have changed through time. The smaller amplitude of variability in the oxygen isotope data of the earlier part in the section can be explained if the early Pliocene polar ice was less depleted in 180 than present polar ice: an extraction of a certain volume of water into ice would have produced a smaller change in the isotopic signal of the foraminifera. If the range of sea-level variation does not change much in post-Miocene time, we can deduce the change in isotopic composition of the ice. During the m a x i m u m glacial stages of the Pleistocene, the isotopic composition of the ice was near -36%o, as discussed earlier. In the lower part of the section ( > 6 2 m, >2.8 Ma), the amplitude of the fluctuations of both the benthic and planktic isotopic signals is about one half (55%) of that in the Pleistocene ( < 38 m, < 1.8 Ma). Thus, the composition of the ice in the Pliocene must have been about one half of the present, that is, near -20%o and the SOratio was a little over one half of that value for the Pleistocene, that is, 0.0055%o/m. Such a change in composition of continental ice, as mentioned, would be expected from a change in size of the ice sheets and the change in the planetary temperature gradient of the late Cenozoic, which is particularly well documented in the Miocene (see Kennet, 1982, 1985, for references). The fractionation of oxygen in water vapor is a function of temperature, distance of travel and altitude (Dansgaard, 1964). as water vapor is transported from warm ocean regions towards cold continental interiors, and from sea level upwards, the vapor becomes increasingly depleted in 180. At a time when ice sheets were smaller and lower, less fractionation occurred. As the ice sheet grew in size and height, the temperature gradient from the equator to the poles also increased. The fractionation then increased due to the greater temperature differential from site

188

J.M. WHITMANAND W.H. BERGER

TABLE 4

Scenarios for magnitudes of effects on seawater composition and/or sea level due to oxygen isotopic shifts at Site 586. Event A, 2.8 Ma; Event B, 3.4 Ma, Event C, 4.0 Ma. For explanation of symbols, see text Magnitude of change from below shift to above shift Observed

Assumed

,d~f

A~G

Residual

Necessary change AT

OR

~S

Sea-level change ( m ) ,4d~;=O.O1ASL ,Jd~=O.OO55,JSL

Scenario # 1: G. sacculifer records ice volume only Shift A G. sacculifer Pulleniatina

+ O. 25 +0.15 +0.5

+ 0.25 +0.25 +0.25

0 -0.1 +0.25

0 +0.6 - 1.55

0 -0.08 +0.20

- 25 -25 - 25

- 45 -45 -45

Shift B Planktic species Benthic species

+ 0.3 0

0.3 -0.3

0 -0.3

0 + 1.9

0 -0.23

- 30 -30

- 55 -55

Shift C Planktic species Benthic species

-0.3 0

-0.3 -0.3

0 +0.3

0 -1.9

0 +0.23

+30 +30

+55 +55

Benthic species

Scenario # 2: Benthic species record ice volume only Shift A Benthic species

+ 0.5 +0.25 +0.15

+ 0.5 +0.5 +0.5

0 -0.25 -0.35

0 + 1.55 +2.2

0 -0.2 -0.27

- 50 -50 -50

- 90 -90 -90

Shift B Benthic species Planktic species

0 +0.3

0 0

0 +0.3

0 - 1.9

0 +0.23

0 0

0 0

Shift C Benthic species Planktic species

0 -0.3

0 0

0 -0.3

0 + 1.9

0 -0.23

() 0

0 0

G. sacculifer Pulleniatina

of evaporation to site of precipitation as well as increased altitude and size of the ice sheets. The implication would be that even as the ice buildup proceeded, a similar amount of ice (more or less) was involved in the episodic melting. The uninvolved or "background" ice mass would keep on increasing, which would account for the overall drop in sea level in the latest Miocene. A change in the SO-ratio clearly makes sea-level reconstruction more difficult (Table 4 ). When the planktic variability is interpreted entirely in terms o f ice volume, the greater amplitude of the record of the benthic foramini-

fera must be attributed to an additional temperature signal in deep waters. Throughout the last 6.0 Ma, the range of the benthic foraminiferal data was 0.2%o greater than that of the planktic foraminiferal data ( 1.3%0 for benthic versus 1.1%oofor planktic species in the Pleistocene and 0.7%0 for benthic versus 0.5%o for planktic species for data from earlier periods ). This would imply that the deep waters were colder by 1 ° C, whenever sea level dropped to glacial levels throughout the section, in agreement with the assessment of Chappell and Shackleton ( 1986 ), for the last 150 ka.

PLIOCENE-PLEISTOCENE OXYGEN ISOTOPE RECORD: ONTONG JAVA PLATEAU

Implications of the isotopic data Site 586 in the western equatorial Pacific provides an excellent record for examining the ocean's response to the evolution of northern hemisphere glaciation in the Pliocene. Much of the work on this evolution, naturally, was carried out on sediments of the North Atlantic (Berggren, 1972; Backman, 1979; Keigwin, 1982b; Shackleton et al., 1984), and the central problem which emerged is the question of ice volume buildup versus cooling. A number of arguments bear on this question (Berger and Gardner, 1975; Matthews and Poore, 1980; Prell, 1984). In the present context, with material from the tropical western Pacific, two extreme options of interpretation available: ( 1 ) the planktic foraminifera grow in constant temperature water and record the ice effect (and nothing else), and (2) the benthic foraminifera grow in constant temperature water and record the ice effect (and nothing else). Both positions have been advanced in the literature (in cases by the same author, with equally persuasive arguments). The implications of choosing between the two extreme options are summarized in Table 4. Intermediate options exist, of course, and maybe more attractive than the extremes. One option is to assume, for the sake of keeping estimates of sea-level change on the conservative side, that, whenever the planktic and benthic signals indicate the same direction of change, the signal with the smaller amplitude will be the true ice volume signal. Using this " m i n i m u m option", Event A marks the only distinct increase in ice volume. Here at 2.8 Ma (Event A, Fig. 3 ) the ice volume change then would be recorded by G. sacculifer and the greater amplitude of the benthic record is attributed to a temperature decrease in the deep waters, analogous to glacial deepwater cooling of 1.5 ° proposed by Chappell and Shackleton (1986). The differences in age of this shift between this work and previous studies is probably due to stratigraphic resolution,

189

as discussed in an earlier section. The cooling experienced by the deep waters would be on the order of 1.4 ° C, implying a coincident decrease in the temperatures at the latitude (s) (or periods) of deep water formation. A decrease in salinity would be expected to go parallel to such a decrease in temperature. Zagwijn (1974) noted a distinct cooling around 2.5 Ma indicated by high latitude terrestrial flora and fauna. Similar trends in the interval between 3.2 and 2.5 Ma were noted at lower latitudes by Van der Hammen et al. (1971), Bonnefille (1983) and Suc (1984). The magnitude of the shift in the Pulleniatina record at 2.8 Ma is smaller than that of G. sacculifer. If the latter species records the ice effect, this effect should also be the same in Pulleniatina. Thus Pulleniatina would have experienced a warming coincident with the postulated global enrichment of ~ 8 0 due to ice buildup. A smaller amplitude signal for deepliving planktic foraminifera between glacial and interglacial times relative to shallow species has been noted previously by Emiliani (1955) who proposed that the difference was due to the upward migration of the species (to warmer waters) during glacials. Such vertical migration could conceivably explain the discrepancy in signal amplitude between G. sacculifer and Pulleniatina at the time of Event A. Another possibility is that the warm mixed layer thickened due to increased supply of warm surface waters from the east, by strengthened trade winds. If we retain G. sacculifer as a proxy-maker for the true record of ice volume, going back in time, we must then explain the lack of a permanent offset in the values of benthic foraminifera at 3.4 Ma (Event B, Fig. 3 ). Because the benthic forms (if anything) record only a temporary enrichment at 3.4 Ma, an increase in deep water temperature would be required. Such a temperature increase during global cooling is conceivable: a change in the dominant source of bottom waters, from the colder Antarctic Bottom Waters (AABW) to the more

190

distant and warmer North Atlantic Deep Waters (NADW; Von Arx, 1962) may be indicated. The isotopic change implies a warming of the bottom waters of 1.65°C or more. The difference in temperature between the two water masses (before mixing) is almost 5 °C (AABW - 1 . 9 ° C ; NADW 3°C; Von Arx, 1962 ) which could readily account for the observed isotopic difference, even after mixing reduced the extremes of the values observed. The strengthening of NADW production presumably was linked to cooling and ice buildup in the North Atlantic realm. The " m i n i m u m option", on the other hand, would simply suggest no change in ice volume at Event B, but a cooling of tropical surface waters (without increased equatorial upwelling: note the small separation of G. sacculifer and Pulleniatina in Fig. 6 ). Event C is recorded in the data of the planktic foraminifera between 4.2-4.0 Ma, but not in the record of the benthic foraminifera (Fig. 3 ). If we apply the " m i n i m u m option" in this case, the benthic signal (the signal of the smallest amplitude) indicates a minor global ice effect, and thus the planktic records reflect changes in the regional surface water mass, presumably a warming by 1.65°C (Scenario # 2, Table 3 ). Such a warming of tropical surface waters, already at the upper range of temperatures for the open ocean (29°C), is difficult to achieve because of the strong negative feedback from increased evaporation. Migration of this site with the northward moving Pacific plate, into a warmer region, is not the answer. The rate of northward motion of the plate is 3 cm/y. or roughly 3 ° per 10 m.y. (Winterer, 1973; Gordon and Cape, 1981 ). Thus, at 4.0 Ma, the site was located at least one degree further south, say, at a latitude of 01 °40'S. However, the 29°C isotherm includes more than 2 ° of latitude on either side of the equator (Reid, 1969). It is unlikely, therefore, that the t80 depletion of plank-tic foraminifera at Event C is in any way connected to plate migration. Two scenarios seem likely candidates for ex-

J.M. WHITMAN AND W.H. BERGER

plaining the shift in planktic foraminiferal 8 ~80, at Event C: ( 1 ) a pile-up of warm water in the western Pacific, from increased trade winds, and (2) a substantial ice effect component. The lag between the shift in the G. sacculifer values at 115 m (4.2 Ma) and the shift in the Pulleniatina values at 105 m (4.0 Ma) presumably favors the first hypothesis - - a local explanation rather than a global one. The implication is that no change occurred in the conditions of the habitat of Pulleniatina while the surface waters warmed, that is, the thermocline stayed at the same depth, and hence Pulleniatina continued to record the same temperature and salinity. Subsequently, the mixed layer thickened and the water at the depth of the habitat of Pulleniatina was affected also. A summary of the oxygen isotope data from Site 586 is given in Fig. 9a, which shows the combined data sets of the benthic and planktic foraminifera. The values of C. wuelterstorfi were mapped on those of O. umbonatus using the average difference value for the data (Table 2 ). Analogously, the values of Pulleniatina were adjusted to those of G. saccul(fer using average differences for several portions of the section (Table 2 ). Within the period studied, the first major accumulation of ice could have occurred at 3.4 Ma (Event B seen in the records of both planktic and benthic species). If it did (which we think likely) it was not ice which readily responded to short-term climatic fluctuation ("Milankovitch lce"). We note that scatter about the mean is small between Events B and A, and we interpret this as a lack of ice which accumulated and melted in response to glacial and interglacial cycles. Since climate amplification is favored in the North Atlantic (due to the Gulf Stream Extension, see Ruddiman et al., 1986), we presume that much of this ice which did not respond to short-term climatic fluctuation formed in Antarctica (see Webb et al., 1984). Increased NADW production, invoked earlier for this purpose, may be respon-

191

PLIOCENE-PLEISTOCENEOXYGENISOTOPERECORD:ONTONGJAVAPLATEAU

a

-2.0

A

°°° ~+ ,<, °, ***

-1.0

° ,

iili

i

O 2.0

•. :.::.+u".'..:+¢ |

•

d'd

~l I

5 0

,

• •

•

, •

-&

,

~."

i:::

n,

"~!~

40

•

-2.0

o

i+ :~:~

1.0

4•0

G

qni!i!

0.0

3.0

B

+!_

b

do

i~o D e p t h (m)

A

,

zx

2oo

160

tt

• .. . .... ....

, . ........... ~oo+oo°'+O~'~'~<}i,t,o,<~oo
-1.0

I

i

i

I I

I I

i i

I

I

l

**

0.0

1.0 0 •o 2.0

3.0

4.0

5.0

,; . . ,.* * . ..a . . . . • . .

......'"".::.";"":'7" o

1

~

?t.

•

~

Age (Ma) Fig. 9. Combined oxygen isotope data sets (a) benthic data (filled circle) adjusted to range of O. umbonatus and planktic data (open diamond ) corrected to range of G. sacculifer (see text for explanation of method); (b) age averaged combined data (with 0.5 Ma window) shown with large symbols and variability of the data points (calculated as in Fig. 7 ) shown with small symbols• Isotopic events A, B and C as in Fig. 3.

sible for the subdued response of the benthic foraminifera (that is, warming of deep water in the Pacific). Subsequently, at Event A (2.8 Ma in the present time scale), there was an increase in the volume of the northern hemisphere ice involved in the glacial and intergla-

cial cycles. A similar two-step ice-buildup scenario was proposed by Shacldeton and Opdyke (1977) who reported on benthic foraminifera only. Shackleton et al. (1984) have recently repudiated that earlier model, claiming cooling for the first step and ice buildup for the

192

second. They do not consider ice buildup in Antarctica. The implications for sea level reconstruction are pertinent. As indicated in Table 4, the total sea-level drop implied by the isotopic shifts at Events A and B is large: - 55 m when eqn. (8) is used. However, considering the likelihood of a decreased SO-ratio (less isotopic fractionation during times with less ice ) the total sea-level drop consistent with the data of the planktic foraminifera could well have been as much as 100 m. If such a change were to be effected by northern ice buildup alone, we would have to postulate Pleistocene-type conditions. But this would then negate the argument regarding the reduced 31 sO difference between ice and ocean. Thus, if both the evidence for substantial sea level change and for reduced 3180 variation is accepted, fluctuations in ice mass in the southern hemisphere must be involved. It seems reasonable that in pre-Pleistocene times the southern ice was less stable than during the Quaternary (being available for producing large sealevel change ), but yet did not respond to Milankovitch forcing in the fashion of northern ice (being less willing to follow northern seasonal patterns ).

Conclusions An overview of major trends in the oxygen isotope signals of Site 586 for the last 6 Ma is shown in Fig. 9b. The combined data sets (Fig. 9a) were averaged in 0.5 Ma windows (as in Fig. 6b) and combined with the variability data from Fig. 7. An increasing separation between the values of the surface and bottom water masses is obvious, almost 1.0%0 in 6 Ma. The difference increases in steps, centered near 4.0 and 2.8 Ma. The step at 4.0 Ma results from warming of surface waters (conceivably aided by melting

J.M. W H I T M A N A N D W.H. BERGER

of Antarctic ice), with no change in the signal of the benthic foraminifera (hence possibly cooling of deep waters). The re-initiation of glaciation at 3.4 Ma, following the early Pliocene warm spell, is recorded as an 180 enrichment in the planktic foraminifera. This shift is not mirrored in the benthic species because of a warming of deep waters, due to strengthening of deep water production in the North Atlantic (NADW). The step at 2.8 Ma results from the global 180 enrichment of ocean waters due to ice buildup, magnified in the benthic record by a cooling of deep waters at the same time. This last major step of cooling and ice buildup (Event A) is associated with a substantial increase in the amplitude of variability, first in the record of the benthic and then in the record of the planktic species. The signal of the benthic foraminifera reflects, in part, changing NADW production during the Pleistocene ice age cycles, while the record of the planktic taxa largely mirrors the waxing and waning of northern ice masses since the last 2.4 Ma. A signal of fluctuating upwelling may also be contained in this record, in the changing differences of the records of the two planktic foraminifera.

Acknowledgments We thank E. Vincent and R.S. Keir for encouragement and advice during the initial stages of this study, and M. Delaney and G. Wefer for comments on an earlier draft of the manuscript. Two anonymous reviewers made useful suggestions. The National Science Foundation supported the work on Ontong Java Plateau during the period of this study (OCE 85-01578 and OCE 89-00074).

193

PLIOCENE-PLEISTOCENE OXYGEN ISOTOPE RECORD: O N T O N G JAVA PLATEAU

Appendix Hole

586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A

Core, section 1,1 2,1 2,2 2,3 2,4 2,5 2,6 3,1 3,1 3,2 3,2 3,3 3,3 3.4 3,4 3,5 3,5 3,6 4,1 4,1 4,2 4,3 4,4 4,4 4,5 4,6 5,1 5,2 5,3 5,4 5,5 5,6 1,1 1,1 1,2 1,3 1,4 1,5 1,6 2,1 2,2 2,2 2,3 2,4 2,5 2,6 2,6 3,1

Interval

49-52 50-52 55-57 55-57 55-57 55-57 55-57 50-52 50-52 49-50 49-50 50-52 50-52 50-52 50-52 50-52 50-52 51-53 50-52 50-52 51-53 50-52 50-52 50-52 50-52 51-53 60-62 60-62 58-60 60-62 60-62 60-62 50-52 50-52 48-50 50-52 50-52 50-52 48-50 50-52 48-50 48-50 50-52 50-52 50-52 48-50 48-50 50-52

Depth

Age

G.~

p.2

C.3

0.4

0.50 1.81 3.36 4.86 6.36 7.86 9.36 11.32 11.32 12.81 12.82 14.31 14.31 15.81 15.81 17.31 17.31 18.82 20.81 20.81 22.32 23.81 25.31 25.31 26.81 28.32 30.41 31.91 33.39 34.91 36.41 37.91 39.81 39.81 41.29 42.81 44.31 45.81 47.29 49.41 50.89 50.89 52.41 53.91 55.41 56.89 56.89 59.01

0.02 0.09 0.16 0.23 0.30 0.37 0.44 0.54 0.54 0.61 0.61 0.68 0.68 0.75 0.75 0.81 0.81 0.88 0.97 0.97 1.03 1.10 1.17 1.17 1.23 1.30 1.39 1.46 1.52 1.59 1.65 1.72 1.80 1.80 1.87 1.93 2.00 2.07 2.13 2.22 2.29 2.29 2.36 2.42 2.49 2.55 2.55 2.65

- 1.48 - 0.83 - 1.49 -0.83 - 1.07 - 1.23 - 1.05 - 1.29

-0.77 - 0.13 - 0.75 -0.24 -0.68 -0.90 -0.73 -0.84 -0.80 -0.96 - 1.10 -0.64 - 0.58 - 0.18 - 0.28 -0.87 - 0.91 -0.79 - 0.80 -0.88 - 1.02 -0.81 - 1.16

2.90 3.61 3.04 3.69 3.30 3.29 3.20 3.08

3.73 4.54

3.29

3.86

- 1.44 - 1.13 - 0.91 - 1.36 - 1.16 - 1.75 -

1.06 1.28 1.28 1.64 1.23 1.33 1.36 1.15 1.17 1.30 0.92 1.27 0.83 1.24 1.31 1.00 1.16 1.13 1.37 1.10 1.20 1.54 1.00 1.16 1.01 1.33 1.26 1.27

3.93 3.92 3.83 3.93

3.54 3.69

4.09

2.83

3.69

3.10 2.66

3.67 3.22

2.85 3.23 2.94

3.67 4.13 3.46

-0.47 - 1.03 -0.43 -0.88 -0.68 -0.90 -0.64 -0.98 --0.87

3.37 2.98 3.39 3.01 2.92 2.92 3.18 3.24 3.06

3.89 3.65 4.12 3.78 3.67 3.73 3.93 3.77 3.58

-- 1.18 -- 0.85 -- 1.04 -- 1.05 - 1.23 - 1.03 - 1.10

2.75

3.47 4.10 3.44 3.96 3.60 3.69 3.43

--0.89 --0.97 --0.98 -- 1.06

3.15

-- 1.08

2.89

2.88 3.09 2.98 3.10

3.21

3.90 3.40 3.68 3.63 3.32

194

A p p e n d i x

Hole

586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A

J M. W H I T M A N A N D W H . BERGER

(continued)

Core, section 3,2 3,3 3,4 3,4 3,5 3,6 4,1 4,2 4,3 4,4 4,5 4,6 5,1 5,1 5,2 5,3 5,4 5,5 5,6 5,6 6,1 6,1 6,2 6,3 6,4 6,5 6,5 6,6 6,6 7,1 7,1 7,2 7.3 7.4 7.5 7,6 8,1 8,1 8,2 8,3 8.4 8,5 8,6 9.1 9,2

9,3 9,4 9,5 9,6 10,1 10.2

Interval

48-50 50-52 50-52 50--52 50-52 48-50 50-52 48-50 50-52 50-52 50-52 48-50 50-52 50-52 48-50 50-52 50-52 50-52 48-50 48-50 50-52 50-52 48-50 50-52 50-52 50-52 50-52 50-52 50-.52 50-52 50-52 48-50 50-52 50-52 50-52 48-50 50-52 50-52 48-50 50-52 50-52 50-52 48-50 50-52 48-50 50-52 50-52 50-52 48-50 50-52 48-50

Depth

60.49 62.01 63.51 63.51 65.01 66.49 68.61 70.09 71.61 73.11 74.64 76.09 78.21 78.21 79,69 81.21 82.71 84.21 85.69 85.69 87.81 87.81 89.29 90.81 92.31 93.81 93.81 95.31 95.31 97.41 97.41 98.89

Age

( i, ~

t'.::

C. ~

0.4

2.71 2.78 2.84 2.84 2.91 2.95 3.01 3.05 3.09 3.14 3.18 3.22 3.28 3.28 3.33 3.37 3.41 3.45 3.50 3.50 3.56 3.56 3.60 3.64 3.69 3.73 3.73 3.77 3.77 3.83 3.83 3.86

--1.26 - ].49 -I,43 -- 1.67 .... 1.53 1.53 -- 1.32 1.44 1.35

- 1.12 - 1.24 --I.18

3.10 2.80

3.7t 3.47

--

.22

-

1,46

-

.28

1.41

....

,25

100.41

3.90

101.91 103.41 104.89 107.01 107.01 108.49 10,0l 11.51 13.01 14.49 16,61 18,09 19,61 121,11 122.61 124.09 126.21 127.69

3.93 3.97 4.00 4.05 4.05 4.09 4.12 4.16 4.19 4.23 4.28 4.31 4.35 4.38 4.42 4.45 4.50 4.54

-

- .26 .... . 2 I - .27 .2i)

1.4'7 1.36 --1.34 - 1.29 - 1,58 1,77 -

-

1.48 -

1.47

•- 1 . 7 6 -- 1.73 -I.51 -

1.89

-1.80

1.73

-

1.65

-

1.42

.... 1.55 . 1.65 . . -- 1.67 ..... 1.50 - 1.70 .... 1.62 - 1.30 -1.55 -1.39

-- 1.65 -- 1,49 --1.54 1.28 -

I. 18

---1.24 -- 1,29 -- 1.31 - 1.17 - 1.11

-1,17 -1.22

3.18 3.17 3.10 3.39 3.13 3.(/6 3.05 3.21

.... ,30 - ,,4

2.65 2.40 2.23 2.55 2.62

--I.26 --1.29 ..... 1.25 1.43 - 1,40

2.74 2.68 2.40 2.19

3.30 3.08 2.86

- 1.51 - 1.46 --1.41 --1.2~ ..... [.15 1.35 .- t.35 1.2tl

2.42 2.55 2.62 2.46

3.08 3.03 3.07

2.60

3.23

l .29 - 1.43 - I, ~3 -. 1 4 3 -- 1.40 -0.99

2.37 2.28 2.63 2.32 2.44 2.54

3.12 2.92 3.17 2.83 2.93 3.06

-- 1.04 - 1.00 -0.95 - 1.10 1.00 .....(1.85 -0.94 -0.87 --0.99 --0.93

2.44

2.96 3.15 3.21 3.(18 3.10

3.24

- 1.48

- 1~73 -

2.44 2.35

.

-.0.91

.1.09 o,99

3.02

2.39 2.36 2.44 2.71 2.41 2.38 2.42 2.58

3.09 3.27 3.05 2.92

19 5

PLIOCENE-PLEISTOCENE OXYGEN ISOTOPE RECORD: ONTONG JAVA PLATEAU

Appendix (continued) Hole

Core, section

Interval

Depth

Age

G.~

p.2

C.3

0.4

586A 586A 586A 596A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A 586A

10,3 10,4 10,5 10,6 11,1 11,2 11,3 11,4 11,5 11,6 12,1 12,2 12,3 12,4 12,5 12,6 13,1 13,2 13,3 13,4 13,5 14,1 14,2 14,3 15,1 15,2 15,3 15,4 15,5 15,6 16,1 16,2 16,3 16,4 16,5 16,6 17,1 17,2 17,3 17,4 t7,5 17,6

50-52 50-52 50-52 48-50 50-52 48-50 50-52 50-52 50-52 48-50 50-52 48-50 50-52 50-52 50-52 48-50 50-52 48-50 50-52 50-52 50-52 50-52 48-50 50-52 50-52 48-50 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52 50-52

129.21 130.71 132.21 133.69 135.81 137.29 138.81 140.31 141.81 143.31 145.41 146.89 148.41 149.91 151.41 152.89 155.01 156.49 158.01 159.51 161.01 162.80 163.79 165.31 167.21 168.69 170.21 171.71 173.21 174.71 175.70 177.71 179.21 180.71 182.21 183.71 185.81 ! 87.31 188.81 190.31 191.81 193.31

4.57 4.61 4.64 4.68 4.73 4.76 4.80 4.83 4.87 4.90 4.95 4.99 5.02 5.06 5.09 5.13 5.18 5.21 5.25 5.28 5.32 5.36 5.38 5.42 5.46 5.50 5.53 5.57 5.61 5.64 5.66 5.71 5.75 5.78 5.82 5.85 5.90 5.94 5.97 6.01 6.04 6.08

- 1.24 - 1.24 - 1.08 - 1.10 - 1.24 - 1.34 - 1.31 - 1.34 - 1.22 - 1.38 - 1.19 - 1.33 - 1.17 - 1.24 - 1.26 - 1.14 -0.97 - 1.20 - 1.06 - 1.40 - 1.17 - 1.44 - 1.21 - 1.20 - 1.20 - 1.18 - 1.19 - 1.21 - 1.20 - 1.16 - 1.22 - 1.32 - 1.23 - 1.24 - 1.24 - 1.20 - 1.19 - 1.18 - 1.10 - 1.13 - 1.05 - 1.06

- 1.01 - 1.18 - 1.09 - 1.11 - 1.00 -0.95 - 1.10 -0.94 -0.95 - 1.14 -0.96 - 1.21 -0.91 -0.90 - 1.00 - 0.95 -0.79 - 1.01 -0.95 - 1.26 -0.71 - 0.92 -0.84 - 1.07 -0.88 - 0.83 - 0.87 - 0.74 -0.75 - 0.60 - 0.86 - 0.67 -0.80 - 0.80

2.47 2.40 2.27

2.98

G. = Globigerinoides sacculifer. 2p. = Pulleniatina. 3C. = Cibicidoides wuellerstorfi. 40. = Oridorsalis umbonatus.

2.53 2.57 2.41 2.30 2.45 2.37 2.43 2.46 2.81 2.80 2.55 2.40 2.80 2.60 2.38 2.50 2.41 2.48 2.42

2.80 3.05

2.81 2.78

3.27 2.95 2.99 3.04

2.78 2.69

2.61 2.81

2.65

2.44 2.32 2.49

3.10 2.99

2.14

196

References Apgova, G. et al., 1984. General Bathymetric Chart of the Oceans. Can. Hydrogr. Office, Ottawa, Ont., Sheet 5.00, scale 1 : 35,000,000 at equator. Backman, J., 1979. Pliocene biostratigraphy of DSDP Sites 111 and 116 from the North Atlantic Ocean and the age of northern hemisphere glaciation. J. Stockh. Contrib. Geol., 32:115-137. Barton, C.E. and Bloemendal, J., 1986. Paleomagnetism of sediments collected during Leg 90, Southwest Pacific. In: J.P. Kennett, C.C. yon der Borch et al. (Editors), Init. Rep. DSDP, 90 (II): 1273-1316. Bender, M., Labeyrie, L.D., Raynaud, D. and Lorius, C., 1985. Isotopic composition of atmospheric 02 in ice linked with deglaciation and global primary productivity. Nature, 318: 349-352. Berger, W.H., 1971. Sedimentation of planktonic foraminifera. Mar. Geol., 11: 325-358. Berger, W.H., 1981. Paleoceanography: the deep-sea record. In: C. Emiliani (Editor), The Sea: The Oceanic Lithosphere, Vol. 7. Wiley, New York, pp. 1437-1519. Berger, W.H. and Gardner, J.V., 1975. On the determination of Pleistocene temperatures from planktonic foraminifera. J. Foraminiferal Res,, 5:102-113. Berger, W.H. and Johnson, T.C., 1976. Deep-sea carbonates: dissolution and mass wasting on Ontong-Java Plateau. Science, 192: 785-787. Berger, W.H. and Mayer, L.A., 1987. Cenozoic paleoceanography 1986: An introduction. Paleoceanography, 2: 613-623. Berger, W.H. and Vincent, E., 1986. Sporadic shutdown of North Atlantic deep water production during the Glacial-Holocene transition. Nature, 324: 53-55. Berger, W.H., Killingley, J.S. and Vincent, E., 1978. Stable isotopes in deep-sea carbonates: Box Core ERDC92, west equatorial Pacific. Oceanol. Acta, 1: 203-216. Berger, W.H., Bonneau, M.-C. and Parker, F.L., 1982. Foraminifera on the deep-sea floor; lysocline and dissolution rate. Oceanol. Acta, 5: 249-258. Berggren, W.A., 1972. Late Pliocene-Pleistocene glaciation. In: A, Laughton, W.A. Berggren et al. (Editors), Init. Rep. DSDP, 12: 953-963. Berggren, W.A., Kent, D.V. and Van Couvering, J.A., 1985. Neogene geochronology and chronostratigraphy. In: N.J. Snelling (Editor), The Chronology of the Geological Record. Geol. Soc. London Mem., 10:211260. Bonnefille, R., 1983. Evidence for a cooler and drier climate in the Ethiopian uplands towards 2.5 Myr ago. Nature, 303:487-491. Broecker, W.S., 1975. Floating ice caps in the Arctic ocean. Science, 188:1116-1118. Chappell, J. and Shacldeton, N.J., 1986. Oxygen isotopes and sea level. Nature, 324:137-140.

J.M. WHITMAN AND W.H. BERGER

Craig, H., 1957. Isotopic standards for carbon and oxygen and correction factors for mass-spectrometric analysis of carbon dioxide. Geochim. Cosmochim. Acta, 12: 133-149. Craig, H. and Gordon, L.I., 1965. Deuterium and oxygen ~80 variations in the ocean and marine atmosphere. In: E. Tongiorgi (Editor), Stable Isotopes in Oceanographic Studies and Paleotemperatures, Spoleto. Consiglio Nazionale Ric., Lab. Geol. Nucl., Pisa, pp. 9130. Craig, H., Broecker, W.S. and Spencer, D., 1981. GEOSECS Pacific Expedition Vol. 4. Natl. Sci. Found., Washington, D.C., 251 pp. Dansgaard, W., 1964. Stable isotopes in precipitation. Tellus, 16: 436-468. Dansgaard, W. and Tauber, H., 1969. Glacier oxygen- 18 and Pleistocene ocean temperatures. Science, 166: 499502. Dietrich, G., Kalle, K., Krauss, W. and Siedler, G., 1980. General Oceanography, An Introduction. 2nd ed. Wiley-Interscience, New York, 626 pp. Elmstrom, K.M. and Kennett, J.P., 1986. Late Neogene paleoceanographic evolution of Site 590: southwest Pacific. In: J.P. Kennett, C.C. v o n d e r Borch et al. (Editors), lnit. Rep. DSDP, 90:1361-1381, Emiliani, C., 1955. Pleistocene temperatures. J. Geol., 63: 538-578. Emiliani, C., 1966. Paleotemperature analysis of Caribbean cores P6304-8 and P6304-9 and a generalized temperature curve for the past 425,000 years. J. Geol., 74: 109-126. Epstein, S. and Mayeda, T., 1953. Variation of 180 content of waters from natural sources. Geochim. Cosmochim. Acta, 4: 213-224. Erez, J., 1979. Modification of the oxygen isotope record in deep-sea cores by Pleistocene dissolution cycles. Nature, 281: 535-538. Fairbanks, R.G., 1989. A 17,000-year glacio-eustatic sea level record: Influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation. Nature, 342: 637-642. Gordon, R.G. and Cape, C.D., 1981. Cenozoic latitudinal shift of the Hawaiian hotspot and its implications for true polar wander. Earth Planet. Sci. Lett., 55: 37-47. Graham, D.W., Corliss, B.H., Bender, M.L. and Keigwin, L.D., Jr., 198 !. Carbon and oxygen isotopic disequilibria of recent deep-sea benthic foraminifera. Mar. Micropaleontol., 6: 483-497. Grossman, E.L., 1984. Stable isotope fractionation in live benthic foraminifera from the southern California Borderland. Palaeogeogr., Palaeoclimatol., Palaeoecol., 47: 301-327. Haq, B.U., Hardenbol, J. and Vail, P.R., 1987. Chronology of fluctuating sea levels since the Triassic. Science, 235: 1156-1167.

PLIOCENE-PLEISTOCENE OXYGEN ISOTOPE RECORD: ONTONG JAVA PLATEAU

Hodell, D.A., Kennett, J.P. and Leonard, K.A., 1983. Climatically induced changes in vertical water mass structure of the Vema Channel during the Pliocene: evidence from Deep Sea Drilling Project Holes 516A, 517 and 518. In: P.F. Barker, R.L. Carlson and D.A. Johnson (Editors), Init. Rep. DSDP, 72:907-919. Hodell, D.A., Williams, D.F. and Kennett, J.P., 1985. Late Pliocene reorganization of deep vertical water-mass structure in the western South Atlantic: faunal and isotopic evidence. Geol. Soc. Am. Bull., 96: 495-503. Jenkins, D.G. and Srinivasan, M.S., 1986. Cenozoic planktonic foraminifera from the equator to the subAntarctic of the southwest Pacific. In: J.P. Kennet, C.C. vonder Botch et al. (Editors), Init. Rep. DSDP, 90: 795-834. Keigwin, L.D., Jr., 1979. Late Cenozoic stable isotope stratigraphy and paleoceanography of DSDP Sites from the east equatorial and central north Pacific Ocean. Earth Planet. Sci. Lett., 45: 361-382. Keigwin, L.D., Jr., 1982a. Isotopic paleoceanography of the Caribbean and east Pacific: role of Panama uplift in the late Neogene time. Science, 217: 350-353. Keigwin, L.D., Jr., 1982b. Stable isotope stratigraphy and paleoceanography of Sites 502 and 503. Init. Rep. DSDP, 68: 445-453. Keigwin, L.D., Jr., 1986. Pliocene stable-isotope record of Deep Sea Drilling Project Site 606: sequential events of ~ 8 0 enrichment beginning at 3.1 Ma. In: W.F. Ruddiman, W.F. Kidd, E. Thomas et al. (Editors), Init. Rep. DSDP, 94:911-920. Kennett, J.P., 1982. Marine Geology. Prentice-Hall, Englewood Cliffs, N.J., 813 pp. Kennett, J.P. (Editor), 1985. The Miocene Ocean: Paleoceanography and Biogeography. (Memoir 163) Geol. Soc. Am., Boulder, Co., 337 pp. Kennett, J.P., vonder Borch, C.C. et al. (Editors), 1986. Init. Rep. DSDP, 90, 1517 pp. Koch, G.S., Jr. and Link, R.F., 1980. Statistical Analysis of Geologic Data, Vol. I. Dover, New York, 375 pp. Labeyrie, L.D., Duplessy, J.C. and Blanc, P.L., 1987. Variations in mode of formation and temperature of oceanic deep waters over the past 125,000 years. Nature, 327: 477-482. Leonard, K.A., Williams, D.F. and Thunnel, R.C., 1983. Pliocene paleoclimatic and paleoceanographic history of the South Atlantic Ocean: stable isotopic records from Leg 72 DSDP Holes 516A and 517. In: P.F. Barker, R.L. Carlson and D.A. Johnson (Editors), Init. Rep. DSDP, 72: 895-906. Loubere, P. and Moss, K., 1986. Late Pliocene climatic change and the onset of northern hemisphere glaciation as recorded in the northeast Atlantic Ocean. Geol. Soc. Am. Bull., 97: 818-828. Mammerickx, J. and Smith, S.M., 1984. Bathymetry of the North-Central Pacific. Geol. Soc. Am. Map Chart Ser. MC-52, Scale 1:6,442,194 at Equator.

19 7

Matthews, R.K. and Poore, R.Z., 1980. Tertiary (~180 record and glacioeustatic sea-level fluctuations. Geology, 8: 501-504. Milliman, J.D. and Emery, K.O., 1968. Sea levels during the past 35,000 years. Science, 162:1121-1123. Moberly, R., Schlanger, S.O. et al. (Editors), 1986. Site 586. Init. Rep. DSDP, 89: 213-281. Peng, T.H., Broecker, W.S., Kipphut, G. and Shackleton, N., 1977. Benthic mixing in deep sea cores as determined by ~4C dating and its implications regarding climate stratigraphy and the fate of fossil fuel CO2. In: N.R. Anderson and A. Malahoff (Editors), The Fate of Fossil Fuel CO2. Plenum, New York pp. 355-373. Pisias, N.G. and Mix, A.C., 1988. Aliasing of the geological record and the search for long-period Milankovitch cycles. Paleoceanography, 3:613-619. Pisias, N.G., Shacldeton, N.J. and Hall, M.A., 1985. Stable isotope and calcium carbonate records from hydraulic piston cored Hole 574A: high-resolution records from the middle Miocene. In: L. Mayer, F. Theyer et al. (Editors), Init. Rep. DSDP, 85: 735-748. Prell, W.L., 1984. Covariance patterns of foraminiferal ~gO: an evaluation of Pliocene ice volume changes near 3.2 million years ago. Science, 226: 692-694. Raymo, M.E., Ruddiman, W.F. and Clement, B.M., 1987. Pliocene-Pleistocene paleoceanography of the North Atlantic at DSDP Site 609. In: W.F. Ruddiman, R.B. Kidd, E. Thomas et al. (Editors), Init. Rep. DSDP, 94: 895-901. Reid, J.L., Jr., 1965. Intermediate Waters of the Pacific Ocean. (Johns Hopkins Oceanographic Studies, 2) Johns Hopkins Univ. Press, Baltimore, MD, 85 pp. Reid, J.L., Jr., 1969. Sea-surface temperature, salinity, and density of the Pacific Ocean in summer and in winter. Deep-Sea Res., 16:215-224. Ruddiman, W.F., Shackleton, N.J. and McIntyre, A., 1986. North Atlantic sea-surface temperatures for the last 1.1 million years. In: C.P. Summerhayes and N.J. Shackleton (Editors), North Atlantic Paleoceanography. Geol. Soc. Spec. Publ., 21: 155-173. Savin, S.M. and Douglas, R.G., 1973. Stable isotope and magnesium geochemistry of recent planktonic foraminifera from the South Pacific. Geol. Soc. Am. Bull., 84: 2327-2342. Shackleton, N.J., 1974. Attainment of isotopic equilibrium between ocean water and the benthonic foraminifera genus Uvigerina: isotopic changes in the ocean during the last glacial. Colloq. Int. D.N.R.S., 219: 203209. Shackleton, N.J. and Cita, M.B., 1979. Oxygen and carbon isotope stratigraphy of benthic foraminifers at Site 397: detailed history of climatic change during the Late Miocene. In: U. von Rad, W.B.F. Ryan et al. (Editors), Init. Rep. DSDP, 47 (1): 433-445. Shackleton, N.J. and Hall, M.A., 1984. Oxygen and carbon isotope stratigraphy of Deep Sea Drilling Project Hole 552A: Plio-Pleistocene glacial history. In: D.G.

198

Roberts, D. Schnitker et al. (Editors), Init. Rep. DSDP, 81 : 599-609. Shackleton, N.J. and Opdyke, N.D., 1973. Oxygen isotope and plaeomagnetic stratigraphy of equatorial Pacific core V28-238P: oxygen isotope temperatures and ice volume on a 105 year and 106 year scale. Quat. Res., 3: 39-55. Schackleton, N.J. and Opdyke, N.D., 1976. Oxygen-isotope and paleomagnetic stratigraphy of Pacific core V28-239 late Pliocene to latest Pleistocene. In: R.M. Cline and J.D. Hays (Editors), CLIMAP: Investigation of Late Quaternary Paleoceanography and Paleoclimatology. Geol. Soc. Am. Mem., 145: 449-464. Shackleton, N.J. and Opdyke, N.D., 1977. Oxygen isotope and paleomagnetic evidence for early Northern hemisphere glaciation. Nature, 270:216-219. Shackleton, N.J. and Vincent, E., 1978. Oxygen and carbon isotope studies in Recent Foraminifera from the southwest Indian Ocean. Mar. Micropaleontol., 3: 113. Shackleton, N.J., Backman, J., Zimmerman, H., Kent, D.V., Hall, M.A., Roberts, D.G., Schnitker, D., Baldauf, J.G., Desprairies, A., Homrighausen, R., Huddlestun, P., Keene, J.B., Kaltenback, A.J., Krumsiek, K.A.O., Morton, A.C., Murray, J.W. and WestburgSmith, J., 1984. Oxygen isotope calibration of the onset of ice-rafting and history of glaciation in the North Atlantic region. Nature, 307: 620-623. Shepard, F.P., 1973. Submarine Geology, 3rd ed. Harper & Row, New York, 517 pp. Stein, R. and Bleil, U., 1986. Deep-water circulation in the Northeast Atlantic and climate changes during the late Neogene (DSDP Site 141 ). Mar. Geol., 70: 191209. Suc, J.-P., 1984. Origin and evolution of the Mediterranean vegetation and climate in Europe. Nature, 307: 429-432. Sverdrup, H.U., Johnson, M.W. and Fleming, R.H., 1942.

J.M. WHITMAN AND W.H. BERGER

The Oceans: Their Physics, Chemistry and General Biology. Prentice-Hall, Englewood Cliffs, N.J., 1087 pp. Van der Hammen, T., Wijmstra, T.A. and Zagwijn, W.H., t971. The floral record of the late Cenozoic of Europe. In: K. Turekian (Editor), The Late Cenozoic Glacial Ages. Yale Univ. Press, New Haven, Conn., pp. 391324. Vincent, E. and Berger, W.H., 1981. Planktonic foraminifera and their use in paleoceanography. In: C. Emiliani (Editor), The Sea, The Oceanic Lithosphere, Vol. 7. Wiley, New York, pp, 1025-1119. Von Arx, W.S., 1962. An Introduction to Physical Oceanography. Addison-Wesley, London, 422 pp. Webb, P.N., Harwood, D.M., McKelvey, B.C., Mercer, J.H. and Scott, L.D., 1984. Cenozoic marine sedimentation and ice-volume variation on the East Antarctic craton. Geology, 12:287-291. Whitman, J.M., 1989. Stable isotope record of foraminifera from Ontong Java Plateau for the last 6 million years. Ph.D. Thesis, Scripps Inst. Ocean., Univ. California, San Diego, 254 pp. Whitman, J.M. and Berger, W.H., in preparation. Pliocene-Pleistocene carbon isotope record-Site 586, Ontong Java Plateau. Winterer, E i . , 1973. Sedimentary facies and plate tectonics of equatorial Pacific. Am. Assoc. Pet. Geol. Bull., 57: 265-282. Woodruff, F., Savin, S.M. and Douglas, R.G., 1980. Biological fractionation of oxygen and carbon isotopes by recent benthic foraminifera. Mar. Micropaleontol., 5: 3-11. Wu, G. and Berger, W.H., 1989. Planktonic foraminifera: Differential dissolution and the Quaternary stable isotope record in the west equatorial Pacific. Paleoceanography, 4:181-198. Zagwijn, W.H., 1974. The Pliocene-Pleistocene boundary in western and southern Europe. Boreas, 3: 75-97.