26. carbonate accumulation in the indian ocean ......kent, this volume). we used four of these...

Duncan, R. A., Backman, J., Peterson, L. C , et al., 1990Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 115

26. CARBONATE ACCUMULATION IN THE INDIAN OCEAN DURING THE PLIOCENE:EVIDENCE FOR A CHANGE IN PRODUCTIVITY AND PRESERVATION AT ABOUT 2.4 Ma1

William B. Curry,2 James L. Cullen,3 and Jan Backman4

ABSTRACT

We measured carbonate concentrations in Pleistocene and Pliocene sediments deposited at Sites 709, 710, and 711.Carbonate concentrations exhibit low-amplitude, long-wave length (300-400 k.y. period) variations at the shallowestsites (709 and 710). Before 2.47 Ma, all three sites exhibit higher frequency (100 k.y. period) variations. The deepest site(711) exhibited low-amplitude variations and very low concentrations up to the Gauss/Matuyama magnetic reversal(2.47 Ma), then concentrations abruptly increased. After 2.47 Ma, carbonate concentrations at Site 711 exhibited thesame periodic changes as at Site 709. Although a long wave-length periodicity (260-280 k.y.) occurs at these sites after2.47 Ma, the 100 k.y. period is absent. The dominant periods observed in these data are those found in the eccentricitycomponent of the earth's orbital geometry.

Estimates of carbonate accumulation at Sites 709 and 710 document that surface-water productivity decreased nearthe Gauss/Matuyama magnetic reversal whereas accumulation at Site 711 increased. These results indicate that the rateof carbonate preservation in the deep Indian Ocean increased at that time. This increase in preservation may have re-sulted from a decrease in the production rate of carbonate in tropical oceans of the world. Carbonate accumulation esti-mated from sediments in shallow locations ( — 3000-3800 m) of the Atlantic and Pacific oceans also indicates that car-bonate production decreased at this time. A consequence of lowered surface-water productivity is increased carbonateion concentration of the deep ocean and better preservation of carbonate on the seafloor.

INTRODUCTION

One of the principal goals of Ocean Drilling Program (ODP)Leg 115 was to reconstruct the history of carbonate sedimenta-tion in the western Indian Ocean during the Neogene. The drill-ing strategy, to core a series of holes down the northern slope ofthe Madingley Rise, produced a series of three sites (709, 710,and 711) that span the water depth interval from 3000 to 4400 m.We have measured the carbonate concentration of the Pliocenesediments that spanned the interval associated with the most re-cent phase of Northern Hemisphere ice growth ( — 2.4 Ma). Thepurpose of our study is to determine what changes in the car-bonate system occurred in response to this major change in theearth's climate.

Our research strategy is based on studies of late Quaternarysedimentation and sediment geochemistry that have successfullyreconstructed many aspects of late Quaternary deep-water cir-culation and chemistry (Johnson et al., 1977; Curry and Loh-mann, 1983, 1985, in press; Peterson and Prell, 1985a). Thisstrategy invokes a basic assumption that the principal source ofcarbonate in the sediments at this location is from surface-waterproductivity, with little or no lateral input from advection ordown-slope reworking. If this assumption is true, then carbon-ate accumulation in the shallowest sites, if they are always abovethe lysocline, is the best approximation of the past history ofsurface-water carbonate productivity. If the sites are located closeto one another and not near any sharp gradients in surface-wa-ter productivity, then the input rate of carbonate from surfacewater should be nearly equal in all sites. Then the difference inaccumulation between the shallowest and progressively deeper

1 Duncan, R. A., Backman, J., Peterson, L. C , et al., 1990. Proc. ODP, Sci.Results, 115: College Station, TX (Ocean Drilling Program).

2 Department of Geology and Geophysics, Woods Hole Oceanographic Insti-tution, Woods Hole, MA, 02543, U.S.A.

3 Department of Geological Science, Salem State College, Salem, MA 01945,U.S.A.

4 Department of Geology, University of Stockholm, Stockholm, Sweden.

sites is a quantitative estimate of the amount of carbonate lostto dissolution. Thus, our research strategy constrains the his-tory of two important components of the carbonate system:carbonate productivity and dissolution.

METHODSWe employed a new, automated system to measure the car-

bonate concentration of the sediments. The system determinesthe carbonate concentration based on the amount of gas evolvedduring the chemical reaction of a known mass of dried sediment(0.01-0.02 g) in 100% phosphoric acid at a constant tempera-ture of 80°C. The pressure of the evolved gas is converted tomass of carbonate based on the regression line of pressure vs.mass of carbonate determined for pure carbonate samples re-acted in the same system. Thus, the fraction of carbonate equalsthe ratio of the mass of carbonate estimated from this regres-sion and the mass of raw sediment. The system is microproces-sor controlled and interfaced with a digital balance (Ostermannet al., 1990), so that the only manual operations include placingthe sediment samples into the reaction boats and loading theboats into the system. Based on three sets of replicate analysesof marine sediment samples, the precision of these measure-ments ranges from ±0.5% to 0.8% (Fig. 1). We analyzed sam-ples at 10-cm spacing in Site 709 and at 5-cm spacing in Sites710 and 711 for a total of 1097 analyses. The carbonate concen-tration data are presented in the Appendix.

RESULTS

Site 709Two holes at this site (3°55' S, 60°33 'E, 3038 m water depth)

were cored with the advanced piston corer (APC) to a depth ofabout 200 m. We analyzed the section from about 3 m belowseafloor (mbsf) to 37 mbsf in Hole 709B (Fig. 2). The carbonateconcentration throughout this interval is fairly constant with anaverage value of 91.3% ± 2.1% (TV = 335). These values aretypical of shallow cores in this region (e.g., RC12-328) and re-sult from a low input rate of noncarbonate, terrigenous sedi-mentary components and a low dissolution rate. All of the car-

509

W. B. CURRY, J. L. CULLEN, J. BACKMAN

ooo

90

80 4

70

60

50

40

30

20-

10--

EN066 44GGC 1cm Mean 79.40 + 0.86

CaCO3 (%)85 90 95

EN066 24GGC 50 cm Mean 52.62 ±0.88

. . " - . • • • • • • • • • • • • • . .

EN066 27 GGC 100 cm Mean 11.41 ±0.49

" I " " I ' ' " I ' " ' I " " I ' " • I ' ' ' ' I " ' ' I

0 5 10 15 20 25 30 35 40

Sample NumberFigure 1. Replicate analyses of carbonate concentration for sampleswith high, medium, and low concentrations. The sediments are from Gi-ant Gravity Cores (GGC) recovered during cruise Endeavor 066 (EN066)to the Sierra Leone Rise in the eastern equatorial Atlantic (Curry andLohmann, 1985). The data were produced using an automated, digital,gasometric system with a precision of ±0.5%-0.8% (Ostermann et al.,1990).

bonate concentrations fall between 86% and 97%. Within thishole, seven magnetic reversals were identified (Schneider andKent, this volume). We used four of these reversals to producethe time series of carbonate concentration.

Site 710Two holes at this site (4°19'S, 60°59'E, 3812 m water depth)

were cored with the APC. In Hole 710A we analyzed samplesfrom Cores 115-710A-3H and -4H, and in Hole 710B we ana-lyzed samples from Cores 115-710B-4H and -5H (Fig. 3). Car-bonate concentrations in Hole 710A average 12.1'% ± 6.7%(N = 276) and in Hole 710B they average 71.4% ± 7.1% (TV =201). Carbonate concentrations exhibit greater variability in theseholes than in Hole 709B. Minimum concentrations are generally60% whereas maximum concentrations exceed 80%. Magneticreversals in these holes were used to produce a time series of car-bonate concentration from ~5 Ma to ~2.3 Ma with a 200,000yr gap at about 3 Ma.

Site 711This site lies between the Madingley Rise and the Carlsberg

Ridge (2°45'S, 61°10'E, 4430-m water depth). Two holes weredrilled at Site 711, and we measured the carbonate concentra-tion in Cores 115-711A-2H and -3H for Hole 711A and in Core115-711B-3H for Hole 71 IB (Fig. 4). Carbonate concentrationsaverage 27.5% ± 17.9% (TV = 135) in Hole 711A and 6.3% ±7.9% (TV - 150) in Hole 71 IB. Overall, the average carbonateconcentration is 16.3% ± 17.2% (TV = 285). In the deeper sec-tions of these holes, very low carbonate concentrations were ob-served. At about 14 mbsf in Hole 711A, the carbonate concen-tration abruptly increases to values that are consistently greaterthan about 25%. Maximum values at about 9 mbsf reach 75%.Magnetic reversals in these cores were identified (Schneider andKent, this volume), and we have used these reversals to combine

(f)

E

Q _CDQ

Olduvai (T)

Gauss/Matuyama

Kaena (O)

Mammoth (O)

5--

10--

15--

20--

25--

30--

35-

Figure 2. Carbonate concentrations in Hole 709B. Carbonate percent-ages average 91.3% ± 2.1% in this hole. The four magnetic reversalboundaries (Schneider and Kent, this volume) identified in the figurewere used to produce the time series of carbonate concentration pre-sented in Figure 5.

the records to produce a continuous time series of carbonateconcentration for this site for the interval from ~ 5 to —1.4 Ma.

Carbonate Concentration Time SeriesTime series of carbonate concentration are plotted in Figure 5.

Throughout the last 4 m.y., the carbonate concentration in Hole709B does not exhibit any abrupt changes. The changes in con-centration appear periodic with a long wave length ( — 400,000yr). In Site 710, the combined record includes intervals with veryhigh-frequency changes in carbonate concentration. The com-bined record for Site 711 exhibits some very sharp changes incarbonate concentration that correlate with major events in thePliocene isotopic record (Shackleton et al., 1984; Keigwin, 1986).At about 2.8 Ma, carbonate concentration increases from val-ues near 0 to values that average 10%-20%. At about 2.4 Ma,the carbonate concentration increases again to values that aver-age >30%. The increase is very abrupt and, since the event at2.4 Ma occurs entirely within Hole 711 A, it is not a result ofcombining the records from Holes 711A and 71 IB. This increasein concentration correlates with a major increase in 518O ob-served above the Gauss/Matuyama magnetic reversal in manyAPC sites where Pliocene sediments have been recovered (Shack-

510

PLIOCENE CARBONATE ACCUMULATION

CaCO60

1 5 -

2 0 -

_Q

E

Q_CDQ

2 5 -

3 0 -

3 5 -

40--

801-

CaCO3 (%)60 80

Olduvai (T) 1 5 -

Gauss/Matu. 2 0

<r- D. tamalis

25 4

<- Cochiti (O) 30-

35-

<r- Thvera (T)

40-

Kaena (O)Mammoth (O)

<r- Gauss/Gilbert

Cochiti (T)

Cochiti (O)

Sidufjall (T)

<- Thvera (O)

Figure 3. Carbonate concentrations in Holes 710A (left) and 710B (right). Carbonate percentages average72.7% ± 6.7% in Hole 710A and 71.4% ± 7.1% in Hole 710B. The identified magnetic reversals (Schneiderand Kent, this volume) and one biostratigraphic boundary were used to combine the data sets and to producethe time-series record for Site 710, which is presented in Figure 5.

leton et al., 1984; Keigwin, 1986). The earlier increase in con-centration at 2.8 Ma correlates with isotopic events that predatethe increase at 2.4 Ma (Keigwin, 1986).

A low-frequency, periodic signal is apparent in the carbonateconcentration record of Site 709. Decomposing this signal intoits spectral components (Fig. 6) reveals high-amplitude varia-tions at about a 400-k.y. period (frequency = 0.0025 cycles/k.y.) during the interval from 2.47 to 3.40 Ma. After 2.47 Ma,the most prominent period in the carbonate concentration rec-ord is about 267 k.y. (frequency = 0.0037 cycles/k.y.). Thesesame periodic changes are apparent in sections of Sites 710 and711. Before the Gauss/Matuyama magnetic reversal, carbonateconcentrations in Site 710 varied with a period of 333,000-400,000 yr. Following the Gauss/Matuyama magnetic reversal,carbonate concentrations in Site 711 varied with a period ofabout 285 k.y. (In Site 710, the record is too short to resolve anylow-frequency changes in carbonate concentration after 2.47 Ma.In Site 711, low carbonate concentrations of small amplitudeoccurred before 2.47 Ma, so the record of low-frequency varia-tions may be obscured.) Pisias and Prell (1985) also noted low-frequency variations (period = ~ 300 k.y.) in carbonate concen-tration in the Pliocene interval of Pacific Deep Sea DrillingProject (DSDP) Site 572. Periodic variations with a wave lengthof about 100 k.y. occur in all three sites before 2.47 Ma, butthey cannot be resolved after that time (Fig. 6).

Bulk Density and Sediment Accumulation

Shipboard measurements of dry-bulk density (dry wt/wetvol.) are plotted in Figure 7 with respect to their carbonate con-centration. (Note: We used only those shipboard measurementsfrom cores that we analyzed for carbonate concentration. Al-though there are many more bulk density measurements avail-able, they are mostly from deeper sections in these holes andsuffer from compaction because of sediment overburden.) Thecorrelation coefficient between the two variables is 0.95 (TV =25). The slope and intercept are very similar to those found inother equatorial regions (equatorial Pacific: Lyle and Dymond,1976; eastern equatorial Atlantic: Curry and Lohmann, 1985,1986), which indicates that similar sedimentary components havemixed at this location to produce the carbonate concentrationsand bulk densities. In the equatorial Pacific and eastern equato-rial Atlantic, the noncarbonate component is opaline silica,which has a grain density lower than calcium carbonate and ter-rigenous silicates. Addition of silica to the sediment lowers thecarbonate concentration as well as the bulk density. In regionswith low input of opaline silica but high input of terrigenous sil-icates, bulk density is more constant over a wide range of car-bonate concentrations (Curry and Lohmann, in press).

We used the carbonate concentration, bulk density, and sedi-mentation rates to calculate the accumulation rate of carbonate

511


CaCO3

0 50

10-

D

E

Q .CDO

15-

20--

1001

CaC03 (%)0 50 100

—, 1 , 1

Site 709

C. maclntyrei (LO)

Olduvai (T) *10-

15-

- Thvera (O) 20 -

- Olduvai (T)

• Gauss/Matuyama

«- Gilbert/Gauss

- Thvera (T)

Figure 4. Carbonate concentrations in Holes 711A (left) and 71 IB (right).Carbonate percentages average 27.5% ± 17.9% in Hole 711A and6.3% ± 7.9% in Hole 71 IB. The identified magnetic reversals (Sch-neider and Kent, this volume) and one biostratigraphic boundary wereused to combine the records and to produce the time-series record forSite 711, which is presented in Figure 5. Note that the Olduvai (T) rever-sal was not identified in Hole 711A. Its level in this hole was projectedfrom the magnetic reversal record in Hole 71 IB by correlating theirmagnetic susceptibility records.

and noncarbonate sediment components for these sites so thatwe could evaluate the changes in productivity and preservationthat affected this region during the Pliocene (Fig. 8). Averageaccumulation rates are presented for the intervals before and af-ter the Gauss/Matuyama magnetic reversal (Table 1) becausenear this stratigraphic boundary a global increase in 518O oc-curred that marks the most recent phase of Northern Hemi-sphere ice growth (Shackleton et al., 1984; Keigwin, 1986).

Before the Gauss/Matuyama boundary, carbonate accumu-lation in Hole 709B averaged 0.74 g/cm2/k.y. After this mag-netic reversal, the accumulation rate decreased to 0.62 g/cm2/k.y. This decrease in accumulation, if not accompanied by anychange in dissolution at this shallow depth, must reflect a smalldecrease in the production of carbonate in the overlying surfacewater. (Note: The timing of the change in carbonate accumula-tion is not constrained by this data. In Figure 8, it occurs at 2.47Ma only as an artifact because our chronology forces a changein sedimentation rate at that interval. Based on the changes incarbonate concentration at Site 711 that were caused by this de-crease in carbonate productivity, we think that the decrease incarbonate accumulation may have occurred in two steps: at 2.8Ma and 2.4 Ma.) Carbonate accumulation in Site 710 also de-creased at about this time, from pre-Gauss/Matuyama values of0.46 g/cmVk.y. to post-Gauss/Matuyama values of 0.36 g/cm2/k.y. Although Site 710 is only 800 m deeper than Site 709, 0.3 g/cmVk.y. (about 40%) of carbonate on average have been lost todissolution before and after the Gauss/Matuyama magnetic re-versal. At Site 711 very little carbonate is accumulating eitherbefore or after the Gauss/Matuyama magnetic reversal. Morethan 90% of the carbonate that settled through the water col-

CDoO

2 3

Age (Ma)

Figure 5. Time series of carbonate concentration for Sites 709, 710, and711. The carbonate record for Site 709 exhibits low-frequency variationswith a wave length of about 400 k.y. In the deepest site (711), carbonateconcentrations increase at about 2.8 Ma and then very abruptly increaseagain at about 2.4 Ma. The abrupt increase at 2.4 Ma correlates withthe 518O increase that marks the beginning of the latest phase of icegrowth in the Northern Hemisphere (Shackleton et al., 1984). The ear-lier increase in concentration may correlate with the earlier 518O increaseobserved by Keigwin (1986). The chronology is not accurate enough tobe certain of this correlation.

umn to the seafloor has subsequently dissolved. Site 711 is theonly site to exhibit an increase in carbonate accumulation acrossthe Gauss/Matuyama magnetic reversal, increasing from 0 to0.02 g/cm2/k.y. at 2.8 Ma and from 0.02 to 0.06 g/cm2/k.y. at2.4 Ma.

Noncarbonate accumulation was low in all three sites. In theshallowest hole, noncarbonate accumulation averaged 0.08 g/cmVk.y. before 2.47 Ma and 0.06 g/cm2/k.y. after 2.47 Ma. InSite 710 a decrease also occurred, from values of 0.17 g/cm2/k.y. before 2.47 Ma to 0.10 g/cm2/k.y. after 2.47 Ma. In thedeepest site, low values of 0.11 g/cm2/k.y. occurred before andafter the Gauss/Matuyama magnetic reversal. The slight bathy-metric increase in noncarbonate accumulation implies that down-slope reworking or advection of sediment components may haveaffected these sites. In a region with no lateral input of sedi-ment, the refractory noncarbonate material should not exhibitany change in accumulation as a function of water depth (Curryand Lohmann, 1986). In these sites, noncarbonate accumula-tion increases slightly with depth in the water column after 2.47Ma. Before 2.47 Ma, little difference in accumulation occurredbetween the shallowest and deepest site, but the middle site(710) had nearly twice the accumulation of noncarbonate mate-rial. It is difficult to evaluate the significance of these changesin noncarbonate accumulation because the values are so low inall cases. To quantify the extent of downslope or lateral input ofmaterial, it is necessary to measure the carbonate and noncar-bonate accumulation rates in the smaller size fractions, as theyare the sizes most likely to be affected by resuspension and rede-position (Curry and Lohmann, 1986). However, the existence ofan increase in noncarbonate accumulation with depth in the wa-ter column cautions us to be concerned that carbonate may alsohave been transported into the deeper sites at this location byprocesses other than vertical settling. Therefore, our estimatesof carbonate lost to dissolution should be considered "minima."

512

Site 709 (1.66-2.47 Ma)


Site 709 (2.47-3.40 Ma)200-r

! 4-400 k.y.

150- -

1 0 0 - •

200-r

150--

100-1

i 400 k.y.

0.02 0.04 0.06 0.02 0.04 0.06

Site 711 (1.66-2.47 Ma) Site 711 (2.47-3.40) Ma200-r

! I 400 k.y.

150--

100--

200 -r

'. 1400 k.y.

150--

100

0.02 0.04 0.06 0.02 0.04 0.06

Cycles/k.y. Cycles/k.y.

Figure 6. Spectral analysis of Sites 709 and 711. Note that most of the power in these records is concentrated at low frequency. Before 2.47 Ma, Sites709 and 710 (not shown) each exhibit a strong 400 k.y. period and a minor 100 k.y. period. Site 711 also has power at about 100 k.y., but no power at400 k.y. After 2.47 Ma, Sites 709 and 711 each exhibit a strong 260-280-k.y. period. No 100 k.y. period is apparent in any of the sites after 2.47 Ma.

DISCUSSION

History of Carbonate ProductivityIn Site 709, the carbonate accumulation rate decreased by

— 0.1 g/cm2/k.y. after the Gauss/Matuyama magnetic reversal.This change in accumulation, if not caused by any change incarbonate dissolution, reflects a decrease in the production ofcarbonate in the overlying surface water. Dissolution changeshave affected the sediments at this site (Cullen, this volume),but fortunately dissolution decreased after the magnetic rever-sal. Before 2.47 Ma, the ratio of foraminifer test fragments towhole tests was high, indicating that dissolution may have causedat least some loss of carbonate (Cullen, this volume). (Signifi-cant fragmentation of foraminifers can occur without measur-able loss of CaCO3; Peterson and Prell, 1985b.) Therefore, thecarbonate accumulation measured in Hole 709B before 2.47 Mais a minimum estimate of the carbonate productivity rate in thesurface waters at that time. After 2.47 Ma, dissolution (mea-sured as the fragmentation ratio) and carbonate accumulation

decreased, so the decrease in accumulation was not caused bychanges in dissolution. Thus, we are confident that a decreasein productivity occurred at about 2.47 Ma and that ~0.1 g/cmVk.y. (the difference between the pre- and post-2.47 Ma val-ues) is a minimum estimate of the decrease.

Throughout the Pliocene, Site 710 always had a lower car-bonate accumulation than Site 709 (by 0.3 g/cm2/k.y.). Thus,dissolution must have influenced the accumulation rate of car-bonate at Site 710. Its carbonate accumulation also decreasedby ~0.1 g/cm2/k.y. after the Gauss/Matuyama magnetic rever-sal, the same difference observed in Site 709. This decrease inaccumulation may have resulted from the same decrease in sur-face-water productivity implied by the record of Site 709, butunfortunately our conclusion is ambiguous for two reasons.First, we have less confidence in our mean value for the 1.66-2.47-Ma interval because we sampled only a small number ofsediments from just above the Gauss/Matuyama magnetic re-versal. Second, we have no independent control over the changesin dissolution at this depth. We think that the dissolution rate

513


Table 1. Calculated accumulation rates of CaCO3 and non-CaCO3 forSites 709, 710, and 711.

1.00-1

0.50- -

y=0.0053(%CaCO3)+0.36

r=0.95

50

CaCO3

100

Figure 7. Dry-bulk density and carbonate concentration from shipboardmeasurements that were performed during Leg 115. The relationship be-tween carbonate concentration and dry-bulk density is similar to the re-lationships that are observed in other equatorial locations where bio-genic opal is the principal noncarbonate component of the sediment(Lyle and Dymond, 1976; Curry and Lohmann, 1985). Based on thisstrong correlation, we have used the carbonate concentration data topredict sediment bulk density in all of our accumulation rate calcula-tions.

2 3

Age (Ma)

Figure 8. Carbonate accumulation rate variations for Sites 709, 710, and711. Carbonate accumulation in Site 709 decreased on average by about0.1 g/cm2/k.y. at the Gauss/Matuyama magnetic reversal (2.47 Ma). Atthe same time, accumulation in the deepest site (711) increased. Thispattern of carbonate accumulation implies that, in the Indian Ocean,carbonate productivity decreased at 2.47 Ma while dissolution on theseafloor decreased. Parallel decreases in carbonate accumulation in Pli-ocene sediments of the Atlantic and Pacific oceans suggest that carbon-ate productivity may have decreased in many tropical locations at thistime. A mean decrease in carbonate productivity, if it is not accompa-nied by a change in river input of Ca and CO3, would decrease the cor-rosiveness of deep water and increase carbonate preservation on the sea-floor.

Site

709710711

CaCO3

0.62 ±0.020.36±0.050.06 + 0.02

1.66-2.47 Ma

non-CaCO3

0.06 ±0.010.10±0.030.11 ±0.01

NNN

#

= 63= 18= 53

CaCO3

0.74 ±0.040.46 ±0.220.02 ±0.02

2.47-3.40 Ma

non-CaCO3

0.08 + 0.010.17±0.060.11±0.01

#

N =N =N =

688762

Note: The data are presented as averages (in g/cm /k.y.) for the intervals between theOldavai (T) and the Gauss/Matuyama magnetic reversals (1.66-2.47 Ma) and theGauss/Matuyama and Gauss/Gilbert (2.47-3.40 Ma) magnetic reversals.

did not increase since dissolution decreased in Site 709 (Cullen,this volume) and because we observe an increase in preservationin deeper Site 711.

History of Carbonate DissolutionOf the three sites, only Site 711 experienced an increase in

carbonate accumulation after the Gauss/Matuyama magneticreversal. Although the increase is small, it is significant (p <0.005) because of the large number of analyses that have beenused to produce the mean values. Because the accumulation ratein the two shallower sites decreased after the magnetic reversal,Site 711 also probably experienced a decreased input rate of car-bonate because of lower surface-water productivity after 2.47Ma. Thus, the increase in carbonate accumulation in Site 711after 2.47 Ma must have resulted from an increase in the preser-vation of calcium carbonate. (Changes in advection or down-slope reworking of carbonate are not likely the cause of the in-crease in carbonate accumulation because the accumulation rateof the insoluble fraction in Site 711 is the same before and after2.47 Ma.)

Carbonate preservation in the deep sea is controlled by pro-cesses that may act on the ocean as a whole (e.g., changes insurface-water productivity) or locally (changes in the location,chemistry, or production rate of deep water). To determine thecause of this change in preservation in Site 711, we must com-pare the changes in carbonate sedimentation at this location tothose observed in the tropical Pacific and Atlantic oceans. Forthe Pacific, carbonate concentration data of comparable tempo-ral resolution and shallow depth are available from Site 503(4°3'N, 95°38'W, 3672 m water depth), and for the Atlantic(Caribbean), data are available from Site 502 (11°29'N, 79°23'W,3051-m water depth). We used the carbonate data from thesesites (Prell, Gardner, et al., 1982) to determine if there wereglobal changes in carbonate accumulation that may be relatedto changes in carbonate production.

Table 2 summarizes the changes in carbonate accumulationin the Atlantic (Site 502) and Pacific (Site 503) oceans that oc-curred at the Gauss/Matuyama magnetic reversal. Carbonateaccumulation decreased in both sites at this time. In the Atlan-tic location, carbonate accumulation decreased from pre-2.47Ma values of 1.76 g/cm2/k.y. to post-2.47 Ma values of 1.66 g/cmVk.y. In the Pacific Ocean location, carbonate accumulationdecreased from 0.59 to 0.53 g/cm2/k.y. These decreases in accu-mulation occur at water depths that are above the present depthof the carbonate lysocline. The decreases in accumulation ob-served in Sites 502 and 503 are on the same order ( — 0.1 g/cm2/k.y.) as the decrease observed in Site 709. Taken together, thesedata imply that the production rate of carbonate in the surfacewaters of tropical locations decreased near the Gauss/Matu-yama magnetic reversal, in response to the cooling associatedwith Northern Hemisphere ice growth. Although the decrease inaverage productivity rate is clearly evident, the exact timing ofthe decrease is unconstrained by these data; our accumulationrates are forced to change at the magnetic reversal because the

514


Table 2. Calculated accu-mulation rates of CaCO3

for Sites 502 (Atlantic)and 503 (Pacific).

Site1.66-2.47

Ma2.47-3.40

Ma

502503

1.660.53

1.760.59

Note: The carbonate dataused in the calculationsare from Prell, Gardner, etal. (1982). The data arepresented as averages (ing/cm2/k.y.) for the inter-vals between the Olduvai(T) and Gauss/Matuyamamagnetic reversals (1.66-2.47 Ma) and the Gauss/Matuyama and Gauss/Gilbert (2.47-3.40 Ma)magnetic reversals.

reversal provides our sedimentation rate constraint. But on thebasis of the effect of the decrease on carbonate productivity onpreservation at the deepest site, we think that productivity mayhave changed in two steps, one at 2.8 Ma and one at 2.4 Ma.

The increases in carbonate accumulation observed at thistime in the deepest Indian Ocean site (711) most likely resultedfrom a decrease in carbonate productivity of the tropical oceans.In today's ocean, carbonate productivity far exceeds the rate ofcarbonate burial that is needed to balance the river input of cal-cium and carbonate. Consequently, only about a third of thecarbonate produced in surface water survives chemical destruc-tion on the shallow flanks of submarine rises and ridges. If therate of productivity decreased without any net change in riverinput, the lysocline and carbonate compensation depth (CCD)must migrate to deeper locations if the balance of carbonateand calcium in the deep ocean is to be maintained. We thinkthat the evidence presented here supports our hypothesis to ex-plain the pattern of carbonate accumulation in Site 709, 710,and 711: a decrease in carbonate productivity of surface waterslowered the demand for carbonate dissolution needed to bal-ance river input. Consequently, the dissolution rate decreased inSite 711, which in turn increased its carbonate concentrationand carbonate accumulation rate.

CONCLUSIONSCarbonate sedimentation patterns changed near the Gauss/

Matuyama magnetic reversal in response to the major change inthe earth's climate at that time. Based on these changing pat-terns, we conclude:

1. Surface-water productivity of carbonate-producing orga-nisms decreased by about 0.1 g/cm2/k.y. in the western tropicalIndian Ocean. Based on data from shallow APC sites in thetropical Atlantic and Pacific oceans, carbonate accumulationalso decreased. If these sites were shallower than the carbonatelysocline at that time, then the evidence indicates that carbonateproductivity may have decreased in all tropical regions of theoceans.

2. Dissolution decreased in the deepest parts of the westernIndian Ocean, which caused increased carbonate concentrationand accumulation in Site 711 after the Gauss/Matuyama mag-netic reversal. This decrease in dissolution may have been a con-sequence of a decrease in carbonate productivity in the tropicalAtlantic, Indian, and Pacific oceans.

3. Before 2.47 Ma, low-frequency variations with a periodof 400 k.y. dominated the records of carbonate concentration.After 2.47, the low-frequency periodic component was closer to280 k.y. in duration. Before 2.47 Ma, all sites exhibit variationsin carbonate concentrations with a wave length of about 100 k.y.These wave lengths are characteristic of eccentricity variationsin the earth's orbit, implying that orbital variations affected thecarbonate system during the early Pliocene.

ACKNOWLEDGMENTSThe carbonate data presented in this paper were produced by

D. R. Ostermann. This paper benefited from reviews by twoanonymous reviewers. We thank them for many useful com-ments. Although not supported by a specific grant, the researchstrategy used in this paper was developed through grants fromthe National Science Foundation. This is Woods Hole Oceano-graphic Institution Contribution No. 7397.

REFERENCES

Curry, W. B., and Lohmann, G. P., 1983. Reduced advection into At-lantic Ocean deep eastern basins during last glaciation maximum.Nature, 306:577-580.

, 1985. Carbon deposition rates and deep water residence timein the equatorial Atlantic Ocean throughout the last 160,000 years.In Sundquist, E. T., and Broecker, W. S. (Ed.), The Carbon Cycleand Atmospheric CO2: Natural Variations Archean to Present. Am.Geophys. Union Monogr., 32:285-301.

_, 1986. Late Quaternary carbonate sedimentation at the SierraLeone Rise (eastern equatorial Atlantic Ocean). Mar. Geol., 70:223-250.

_, in press. Reconstructing past particle fluxes in the tropicalAtlantic Ocean. Paleoceanography.

Johnson, D. A., Ledbetter, M., and Burckle, L. H., 1977. Vema Chan-nel paleo-oceanography: Pleistocene dissolution cycles and episodicbottom water flow. Mar. Geol., 23:1-33.

Keigwin, L. D., 1986. Pliocene stable-isotope record of Deep Sea Drill-ing Project Site 606: sequential events of 18O enrichment beginningat 3.1 Ma. In Ruddiman, W. F., Kidd, R. B., Thomas, E., et al.,Init. Repts. DSDP, 94, Pt. 2: Washington (U.S. Govt. Printing Of-fice), 911-920.

Lyle, M. W., and Dymond, J., 1976. Metal accumulation rates in thesoutheast Pacific—errors introduced from assumed bulk densities.Earth Planet. Sci. Lett., 30:164-168.

Ostermann, D. R., Karbott, D., and Curry, W. B., 1990. Automatedsystem to measure the carbonate concentration of sediments. WoodsHole Oceanogr. Inst. Tech. Rep. WHOI-90-03.

Peterson, L. C , and Prell, W. L., 1985a. Carbonate preservation andrates of climatic change: an 800 kyr record from the Indian Ocean.In Sundquist, E. T., and Broecker, W. S. (Ed.), The Carbon Cycleand Atmospheric CO2: Natural Variations Archean to Present. Am.Geophys. Union Monogr., 32:251-269.

, 1985b. Carbonate dissolution in Recent sediments of theeastern equatorial Indian Ocean: preservation patterns and carbon-ate loss above the lysocline. Mar. Geol., 64:259-290.

Pisias, N. G., and Prell, W. L., 1985. High resolution carbonate recordsfrom the hydraulic piston cored section of Site 572. In Mayer, L.,Theyer, R, Thomas, E., et al., Init. Repts. DSDP, 85: Washington(U.S. Govt. Printing Office), 711-722.

Prell, W. L., Gardner, J. V., et al., 1982. Init. Repts. DSDP, 68: Wash-ington (U.S. Govt. Printing Office).

Shackleton, N. J., Backman, J., Zimmerman, H. B., Kent, D. V., Hall,M. A., Roberts, D. G., Schnitker, D., Baldauf, J. G., Desprairies,A., Homrighausen, R., Huddleston, P., Keene, J. B., Kaltenback,A. J., Krumsiek, K.A.O. Morton, A.C., Murray, J. W., and West-berg-Smith, J., 1984. Oxygen isotope calibration of the onset oficerafting in DSDP Site 552A: history of glaciation in the North At-lantic region. Nature, 307:620-623.

Date of initial receipt: 11 September 1989Date of acceptance: 22 January 1990Ms 115B-164

515


APPENDIXCarbonate Concentrations for Sites 709, 710, and 711.

Depth Age(msbf) (Ma)

CaCO3

115-709B-2H-

3.843.944.044.144.244.344.444.544.644.744.834.925.045.145.245.345.445.545.645.745.845.946.036.146.246.336.426.546.646.746.846.947.047.147.247.347.447.547.647.747.847.958.048.128.248.388.468.558.648.748.848.949.049.149.259.359.469.559.669.769.889.96

10.0510.1410.2410.3510.4410.5410.6410.7410.8610.9711.0511.1611.26

0.3450.3540.3630.3710.3800.3890.3980.4070.4160.4250.4330.4410.4520.4610.4700.4790.4880.4970.5060.5150.5240.5330.5410.5510.5600.5680.5760.5870.5960.6050.6140.6230.6320.6410.6500.6590.6680.6770.6860.6950.7030.7130.7210.7290.7390.7520.7590.7670.7750.7840.7930.8020.8110.8200.8300.8390.8490.8570.8670.8760.8870.8940.9020.9100.9190.9290.9370.9460.9550.9640.9740.9840.9921.0011.010

92.189.994.092.196.392.393.293.693.793.493.294.093.293.191.391.792.093.092.392.293.293.794.495.193.593.794.495.394.594.994.994.492.091.388.391.590.790.189.287.587.586.485.488.989.686.987.586.788.390.388.089.690.291.190.790.390.690.691.992.793.190.089.188.392.091.391.693.191.389.991.492.489.290.992.4

Depth Age CaCO3

(msbf) (Ma) (%)

115-709B-2H-(Cont.)

Depth Age CaCO3

(msbf) (Ma) (%)

115-709B-2H-(Cont.)

Depth Age CaCO3

(msbf) (Ma) (<%)

115-709B-2H-(Cont.)

Depth Age CaCO3

(msbf) (Ma) (%)

115-709B-2H-(Cont.)

11.4411.5411.6411.7411.8411.9412.0412.1412.2412.3412.4212.5312.6312.7312.8412.9413.0413.1413.2513.3313.4413.5413.6413.7413.8413.9414.0414.1414.2414.3414.4414.5314.6514.7514.8514.9415.0415.1415.2415.3415.4415.5415.6415.7415.8415.9416.0416.1816.2616.3616.4416.5416.6416.7416.8416.9417.0417.1417.2417.3417.4417.5417.6717.7617.8617.9418.0418.1418.2418.3418.4418.5418.6418.7418.84

1.0271.0351.0441.0531.0621.0711.0801.0891.0981.1071.1141.1241.1331.1421.1521.1611.1701.1791.1891.1961.2061.2151.2241.2331.2421.2511.2601.2691.2781.2871.2961.3041.3151.3241.3321.3411.3501.3591.3671.3761.3851.3941.4031.4121.4211.4301.4391.4521.4591.4681.4751.4841.4931.5021.5111.5201.5291.5381.5471.5561.5651.5741.5861.5941.6031.6101.6191.6281.6371.6461.6551.6651.6781.6911.704

91.691.891.890.191.792.891.091.289.892.593.793.792.392.693.194.394.892.892.092.392.794.195.194.894.996.197.593.394.992.697.492.092.590.691.191.690.489.391.792.792.293.793.192.292.793.190.491.393.691.493.593.192.994.093.294.494.793.696.491.694.692.291.089.189.687.489.589.990.191.291.592.589.991.192.3

18.9419.0419.1219.2219.3419.4419.5419.6419.7419.8419.9420.0420.1420.2420.3420.4420.5420.6420.7220.8120.9421.0421.1421.2421.3421.4421.5421.6621.7421.8421.9722.0722.1522.2422.3422.4422.5422.6422.7422.8422.9423.0223.1423.2423.3423.4423.5423.6423.7423.8423.9424.0424.1324.2524.3624.4624.5624.6424.7424.8424.9425.0425.1425.2425.3427.9428.0428.1428.2228.3228.4428.5428.6328.7528.86

.7171.729

::

.740

.753

.768

.781

.7941.8071.8191.8321.8451.8581.8711.8841.8971.9091.9221.9351.9451.9571.9741.9871.9992.0122.0252.0382.0512.0662.0772.0892.1062.1192.1292.1412.1542.1672.1792.1922.2052.2182.2312.2412.2572.2692.2822.2952.3082.3212.3342.3472.3592.3722.3842.3992.4132.4262.4392.4492.4622.4742.4842.4952.5052.5152.5262.7932.8042.8142.8222.8322.8452.8552.8642.8772.888

91.890.892.194.591.693.893.493.893.994.992.893.689.592.692.392.692.692.889.789.088.189.790.087.091.590.891.791.195.494.292.793.392.591.392.289.590.889.689.389.889.188.988.290.890.390.891.991.090.291.489.590.488.291.691.090.292.491.092.991.289.791.891.892.190.991.388.789.091.392.991.592.693.890.991.8

28.9529.0529.1429.3429.4429.5429.6429.7429.8429.9430.0430.1330.2430.3630.4430.5430.6430.7430.8430.9431.0431.1431.2231.3231.4431.5431.6331.7431.8631.9632.0532.1432.2432.3432.4432.5432.6432.7432.8532.8632.9433.0433.1433.2433.3433.4433.5433.6433.7433.8333.9234.0434.1434.2434.3434.4434.5434.6434.7434.8434.9435.0435.1435.2435.3435.4335.5435.6435.7435.9436.0436.1436.2436.3436.44

2.8972.9082.9172.9372.9482.9582.9682.9792.9893.0003.0103.0203.0313.0443.0523.0633.0733.0843.0953.1053.1163.1263.1353.1453.1583.1683.1783.1903.2023.2133.2223.2323.2423.2533.2633.2743.2853.2953.3073.3083.3163.3273.3373.3483.3583.3693.3803.3903.4013.4103.4203.4323.4433.4533.4643.4753.4853.4963.5063.5173.5273.5383.5483.5593.5703.5793.5913.6013.6123.6333.6433.6543.6653.6753.686

91.192.292.791.895.092.292.491.390.994.090.992.591.192.091.490.693.090.188.289.187.289.691.090.690.188.390.890.490.491.391.993.492.291.491.591.992.590.489.091.091.895.391.192.292.492.790.693.291.691.193.392.688.789.689.791.290.789.792.191.087.388.190.287.386.986.687.288.488.489.291.090.586.990.288.0

36.5436.6436.7436.8436.9437.0437.1437.24

115-71OA-3H-

19.2119.2619.3119.3619.4119.4619.5219.5819.6119.6619.7119.7619.8119.8619.9119.9620.0120.0620.1120.1620.2120.2720.3120.3720.4020.4620.5120.5620.6120.6620.7120.7620.8120.8620.9120.9621.0221.0821.1121.1621.2121.2621.3121.3621.4121.4621.5121.5621.6121.6621.7121.7721.8121.8721.9022.2122.2622.3122.3622.4122.4622.5222.5822.61

3.6963.7073.7173.7283.7383.7493.7603.770

2.3172.3252.3342.3422.3512.3602.3702.3802.3862.3942.4032.4112.4202.4292.4372.4462.4542.4632.4712.4752.4792.4852.4882.4932.4962.5012.5052.5092.5142.5182.5222.5272.5312.5352.5392.5442.5492.5542.5572.5612.5652.5692.5742.5782.5822.5872.5912.5952.5992.6042.6082.6132.6172.6222.6242.6512.6552.6592.6642.6682.6722.6772.6832.685

89.689.389.391.190.592.090.789.7

77.780.085.676.181.183.273.884.286.486.175.081.683.178.872.766.868.760.769.871.576.573.969.377.178.682.382.669.383.767.471.175.978.080.278.964.065.874.764.375.481.581.084.176.082.582.082.981.073.570.167.175.375.577.180.669.179.377.175.574.775.765.965.369.4

516


Appendix (continued).

Depth Age CaCO3

(msbf) (Ma) (%)

115-710A-3H-(Cont.)

Depth Age CaCO3

(msbf) (Ma) (<%)

115-710A-4H-(Cont.)

Depth Age CaCO3

(msbf) (Ma) (%)

115-710A-4H-(Cont.)

Depth Age CaCO3

(msbO (Ma) (%)

115-710B-4H-(Cont.)

Depth Age CaCO3

(msbf) (Ma) (%)

115-710B-4H-(Cont.)

22.6622.7122.7622.8122.8622.9122.9623.0123.0623.1123.1623.2123.2723.3123.3723.4023.4623.5123.5623.6123.66

2.6892.6942.6982.7022.7072.7112.7152.7192.7242.7282.7322.7372.7422.7452.7502.7532.7582.7622.7672.7712.775

115-710A-4H-

28.8128.8628.9128.9629.0129.0629.1229.1729.2129.2629.3129.3629.4129.4629.5229.5629.6129.6629.7129.7629.8129.8729.9129.9730.0230.0630.1230.1730.2130.2630.3130.3630.4130.4630.5130.5630.6230.6730.7130.7730.8130.8630.9130.9631.0231.0631.1131.1631.2131.2631.3131.37

3.8873.8913.8953.8993.9023.9063.9113.9153.9183.9213.9253.9293.9333.9373.9413.9443.9483.9523.9563.9593.9633.9683.9713.9753.9793.9823.9873.9913.9943.9974.0014.0054.0094.0134.0164.0204.0254.0284.0324.0364.0394.0434.0474.0514.0554.0584.0624.0664.0694.0734.0774.082

85.063.368.167.975.776.981.684.075.272.072.668.871.369.659.663.864.471.077.673.967.8

73.767.873.978.072.969.272.876.372.268.468.564.668.755.963.069.864.864.170.069.369.572.560.668.865.377.569.469.570.467.374.174.177.771.671.369.570.269.776.179.078.970.371.667.986.265.871.277.867.969.672.771.0

31.4131.4731.5231.5631.6231.6731.7131.7631.8131.8631.9632.0132.0632.1232.1732.2132.2632.3132.3632.4132.4632.5232.5632.6132.6632.7132.7632.8132.8732.9132.9733.0233.0633.1233.1733.2133.2633.3133.3633.4133.4633.5133.5633.6233.6733.7133.7633.8133.8633.9133.9634.0234.0634.1134.1634.2134.2634.3134.3734.4134.4734.5234.5634.6234.6734.7134.7534.8134.8634.9134.9635.0135.0635.1235.1735.21

4.0854.0894.0934.0964.1014.1044.1074.1114.1154.1194.1264.1304.1344.1394.1424.1454.1494.1534.1574.1614.1644.1694.1724.1764.1804.1834.1874.1914.1964.1994.2034.2074.2104.2154.2184.2214.2254.2294.2334.2374.2404.2444.2484.2534.2564.2594.2634.2674.2714.2754.2784.2834.2864.2904.2944.2974.3014.3054.3094.3134.3174.3214.3244.3284.3324.3354.3384.3434.3474.3514.3544.3584.3624.3664.3704.373

68.769.376.276.678.878.478.275.763.468.154.856.555.047.256.464.358.460.459.358.749.866.559.358.970.465.467.469.773.972.470.971.876.076.074.967.577.176.380.877.775.460.771.173.766.569.169.269.266.576.461.368.070.362.373.368.570.273.074.675.667.963.181.479.480.872.765.467.275.778.477.175.576.575.170.066.0

35.2635.3135.3635.4135.4635.5235.5635.6135.6635.7135.7635.8135.8735.9135.9736.0236.0636.1236.1736.2136.2636.3136.3636.4136.4636.5136.5636.6236.6736.7136.7636.8136.8636.9136.9637.0237.0637.1137.1637.2137.2637.3137.3637.4137.4737.5237.5637.6237.6737.7137.7637.8137.8637.9137.9638.0138.0638.1238.1738.2138.2638.3138.36

4.3774.3814.3854.3884.3924.3974.4004.4044.4074.4114.4154.4194.4234.4264.4314.4354.4384.4424.4464.4494.4534.4574.4614.4644.4684.4724.4764.4804.4844.4874.4914.4954.4994.5024.5064.5114.5144.5184.5214.5254.5294.5334.5374.5404.5454.5494.5524.5564.5604.5634.5674.5714.5754.5784.5824.5864.5904.5944.5984.6014.6054.6094.613

115-710B-4H-

25.8125.8625.9125.9626.0126.0626.1026.1626.2126.26

2.9382.9522.9662.9792.9933.0063.0173.0333.0473.061

69.277.280.078.878.878.073.478.569.567.475.978.075.779.381.278.481.876.070.774.472.681.380.569.274.568.062.676.976.078.779.778.282.075.977.858.470.468.166.575.362.075.472.279.179.477.473.169.473.073.266.483.182.078.281.772.277.680.780.176.774.971.783.0

73.463.366.966.064.260.960.458.861.659.3

26.3126.3626.4126.4626.5026.5626.6126.6626.7126.7626.8226.8626.9126.9627.0127.0627.1127.1627.2127.2627.3127.3627.4127.4627.5127.5627.6027.6627.7127.7627.8127.8627.9127.9628.0128.0628.1128.1628.2128.2628.3128.3628.4128.4628.5128.5628.6228.6628.7128.7628.8128.8628.9128.9629.0129.0629.1029.1629.2129.2629.3129.3629.4129.4629.5029.5629.6129.6629.7129.7629.8129.8629.9129.9630.0130.06

3.0743.0883.1013.1153.1263.1423.1563.1693.1813.1883.1963.2023.2093.2163.2233.2303.2363.2433.2503.2573.2643.2713.2783.2843.2913.2983.3043.3123.3193.3263.3333.3403.3463.3533.3603.3673.3743.3813.3883.3953.4013.4083.4143.4213.4273.4343.4423.4473.4533.4603.4663.4733.4793.4863.4923.4993.5043.5123.5183.5253.5313.5383.5443.5503.5563.5633.5703.5763.5833.5893.5963.6023.6093.6153.6223.628

68.169.574.074.967.959.563.866.959.470.170.973.074.275.371.972.671.175.372.268.058.762.260.869.359.563.365.462.471.170.164.465.968.770.658.963.263.165.462.370.870.874.170.874.971.473.070.968.271.369.961.858.067.277.973.672.864.659.558.068.563.663.967.668.468.269.571.172.973.169.464.164.662.457.168.062.7

30.1230.1630.2130.2630.3130.3630.4130.4630.5130.5630.6030.6630.7130.7630.8130.8630.9130.9631.0031.0631.1131.1631.2131.2631.3131.3631.4131.4631.5131.5631.6231.6631.7131.7631.8131.8631.9131.9632.0132.0632.1032.1632.2132.2632.3132.3632.4132.4632.5032.5632.6132.6632.7132.7632.8132.8632.9132.9633.0133.06

115-71OB-5H-

38.1138.1638.2138.2638.3138.3638.4138.4638.5138.5638.6138.6638.71

3.6363.6413.6483.6543.6613.6673.6743.6803.6873.6933.6983.7063.7133.7193.7263.7323.7393.7453.7503.7583.7653.7713.7783.7843.7903.7973.8033.8103.8163.8233.8313.8363.8423.8493.8553.8623.8683.8753.8813.8853.8883.8933.8973.9013.9053.9093.9143.9183.9213.9263.9303.9343.9383.9423.9463.9503.9543.9593.9633.967

4.5574.5614.5654.5694.5734.5784.5824.5864.5904.5944.5984.6024.606

62.464.553.869.969.568.161.868.770.565.564.471.666.566.362.166.858.361.460.256.364.369.867.770.068.671.373.374.673.573.274.875.476.473.175.876.479.177.476.180.679.178.976.776.476.573.873.970.267.967.869.170.970.771.270.972.172.169.368.269.8

82.182.281.183.083.481.983.677.679.984.785.385.982.7

517


Appendix (continued).

Depth(msbf)

Age(Ma)

115-710B-5H-(Cont.)

38.7638.8138.8638.9138.9639.0139.0639.1139.1639.2139.2639.3139.3639.4139.4639.5139.5639.6139.6639.7139.7639.8139.8639.8939.9139.9640.0140.0640.1140.1640.2140.2640.3140.3640.4140.4740.5140.5840.6140.6640.7140.76

4.6104.6154.6194.6234.6274.6314.6354.6394.6434.6474.6524.6564.6604.6644.6684.6724.6764.6804.6844.6894.6934.6974.7014.7034.7054.7094.7134.7174.7214.7264.7304.7344.7384.7424.7464.7514.7544.7604.7634.7674.7714.775

115-711A-2H-

8.208.258.308.358.408.468.518.568.618.658.698.758.808.858.908.959.009.059.109.159.219.309.359.409.509.659.709.759.809.849.90

•

]

:

-

•

:

•

•

'•

L.38U

1.3891.3981.4061.4151.426[.4341.4431.4521.4591.4661.4761.4851.4941.5021.5111.520'•

'•

'•

'•

'

1.5291.5381.5461.5571.5721.5811.5901.6071.6341.6421.6511.6601.6721.690

CaCO3

(%)

83.383.284.881.175.779.383.080.377.979.279.976.376.376.177.379.979.879.376.380.782.584.482.377.475.476.276.273.171.976.879.879.376.877.278.779.378.972.975.975.578.678.2

14.830.832.734.024.828.139.447.035.329.937.247.559.282.673.562.856.167.163.358.134.744.477.373.243.821.434.839.835.431.035.4

Depth(msbf)

Age(Ma)

115-711A-2H-(Cont.)

9.9610.0010.0510.1010.1610.2010.2610.3010.3610.4510.5010.5510.6310.7210.7710.8110.8610.9110.9511.0111.0611.1511.2011.2511.3011.3511.3911.4611.5011.5511.6111.6511.7011.7511.8011.8511.8911.9111.9512.0512.2112.2712.3612.4112.4512.5112.6612.7112.7612.8112.8612.9012.98

1.7071.7191.7341.7491.7671.7781.7961.8081.8261.8531.8671.8821.9061.9321.9471.9591.9741.9892.0012.0182.0332.0602.0752.0892.1042.1192.1312.1522.1642.1782.1962.2082.2232.2382.2522.2672.2792.2852.2972.3262.3742.3922.4182.4332.4452.4632.5072.5222.5372.5522.5662.5782.602

115-711A-3H-

18.1018.1518.2118.2518.3018.4018.4418.5018.5518.5918.6618.7018.8018.8418.9018.9519.0019.0519.1019.15

4.1184.1334.1514.1634.1784.2074.2194.2374.2524.2644.2844.2964.3264.3384.3554.3704.3854.4004.4154.429

CaCO3

(%)

38.348.955.136.434.334.645.024.732.529.522.930.443.532.546.744.254.544.435.131.240.633.843.238.933.839.428.540.330.340.538.032.141.826.934.450.328.524.053.541.515.89.8

13.419.522.722.428.426.727.328.528.228.118.0

12.611.77.49.37.41.65.03.18.84.06.75.45.53.44.33.83.04.97.5

10.8

Depth(msbf)

Age(Ma)

115-711A-3H-(Cont.)

19.2019.2519.3019.3519.4019.4519.5019.5519.6019.6519.7019.7519.8019.8519.9019.9520.0020.0520.1020.1520.2220.2520.3020.3420.4020.4520.5020.5520.6020.6520.70

4.4444.4594.4744.4894.5034.5184.5334.5484.5634.5774.5924.6074.6224.6374.6524.6664.6814.6964.7114.7264.7464.7554.7704.7824.8004.8144.8294.8444.8594.8744.888

115-711B-3H-

11.7511.8011.8511.9011.9512.0012.0512.1012.1512.2012.2512.3012.3512.4012.4512.5012.5512.6012.6512.7012.7512.8012.8512.9012.9513.0013.0513.1013.1513.2013.2513.3013.3513.4013.4513.5013.5513.6013.6513.7113.7513.80

2.4272.4412.4562.4702.4872.5042.5222.5392.5562.5732.5912.6082.6252.6422.6592.6772.6942.7112.7282.7462.7632.7802.7972.8142.8322.8492.8662.8832.9012.9182.9352.9522.9692.9873.0043.0213.0383.0563.0733.0933.1073.124

CaCO3

(%)

12.815.315.318.114.913.713.916.223.721.012.012.625.015.914.616.113.412.69.69.68.27.89.07.58.37.1

10.27.05.56.96.7

26.417.519.613.722.121.510.815.627.831.330.428.419.415.822.015.915.212.811.217.829.230.111.811.19.08.89.07.57.15.78.58.06.33.65.34.32.11.74.92.92.01.8

Depth(msbf)

Age(Ma)

115-711B-3H-(Cont.)

13.8513.9013.9514.0114.0514.1014.1514.2014.2514.3014.3414.4014.4514.5014.5514.6014.6514.7014.7514.8014.8514.9014.9515.0015.0515.1015.1515.2015.2515.3015.3515.4015.4515.5015.5515.6015.6515.7015.7515.8015.8515.9015.9516.0016.0516.1016.1516.2016.2516.3016.3516.4016.4516.5016.5516.6016.6516.7016.7516.8016.8516.9016.9517.0017.0517.1017.1517.2017.2517.3017.3517.4017.4517.5017.5517.60

3.1423.1593.1763.1973.2113.2283.2453.2623.2793.2973.3103.3313.3483.3663.3833.4003.4143.4293.4433.4573.4713.4863.5003.5143.5283.5433.5573.5713.5853.6003.6143.6283.6433.6573.6713.6853.7003.7143.7283.7423.7573.7713.7853.8003.8143.8283.8423.8573.8713.8853.8993.9143.9283.9423.9563.9713.9853.9994.0144.0284.0424.0564.0714.0854.0994.1134.1284.1424.1564.1704.1854.1994.2134.2284.2424.256

CaCO3

(%)

2.02.92.95.14.42.13.91.20.71.22.82.73.13.23.02.24.13.71.10.80.80.70.80.90.60.60.70.50.60.40.50.40.40.40.40.60.50.50.50.40.30.30.40.50.60.60.80.50.60.80.50.50.91.00.51.00.81.20.81.81.90.50.51.11.01.10.80.60.40.40.71.21.21.21.21.5

Depth(msbf)

115-711B-3H-

17.6517.7017.7517.8017.8517.9017.9518.0018.0518.1018.1518.2018.2518.3018.3518.4018.4518.5018.5518.6018.6518.7018.7518.8018.8518.9018.9519.0019.0519.1019.1519.20

Age(Ma)

(Cont.)

4.2704.2854.2994.3134.3274.3424.3564.3704.3854.3994.4134.4274.4424.4564.4704.4844.4994.5134.5274.5414.5564.5704.5844.5994.6134.6274.6414.6564.6704.6844.6984.713

CaCO3

(%)

0.40.82.52.71.91.71.42.42.11.94.36.32.43.16.06.27.99.1

16.618.622.523.912.814.815.315.817.614.114.07.47.76.9

518

26. carbonate accumulation in the indian ocean ......kent, this volume). we used four of these...

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