23. stable isotope stratigraphy and amino-acid ...23. stable isotope stratigraphy and amino-acid...

23. STABLE ISOTOPE STRATIGRAPHY AND AMINO-ACID EPIMERIZATION FOR THE LAST2.4 M.Y. AT SITE 610, HOLES 610 AND 610A1

Eystein Jansen and Hans Petter Sejrup, Department of Geology, University of Bergen, Norway2

ABSTRACT

A record of carbon and oxygen isotopes in benthic and planktonic foraminifers has been obtained from the intervalcorresponding to the last 2.4 m.y. of Site 610, Holes 610 and 610A, with a sample resolution of about 30 kyr. The recordfrom the late Quaternary (<0.9 Ma) shows large amplitudes and high frequencies in oxygen isotopic variation. Prior to0.9 Ma the isotopic variability record is reduced in amplitude (but not in frequency) compared with the late Quaternary,suggesting lower ice-volume and climatic fluctuations, and higher average eustatic sea level.

Left-coiling (L, polar) Neogloboquadrinapachyderma were not found in samples between 1.0 and 2.2 Ma, indicat-ing less influence of polar front migrations in the Northeast Atlantic. Both polar planktonic faunas and larger isotopefluctuations reappear in the lowermost samples (2.3 to 2.4 Ma), pointing toward a period of larger climatic variability inthe late Pliocene than in the early Quaternary.

The variation in benthic δ13C and hence in deep-water δ13C seems to have been constant through the analyzed sec-tion, reflecting a stable variability in the production of North Atlantic Deep Water (NADW) and possibly in Norwe-gian-Greenland Sea Overflow. Preliminary analyses of amino-acid epimerization in N. pachyderma (L) indicate a con-stant rate of epimerization to approximately 0.3 Ma. Beneath this level the average epimerization rate is much reduced.

INTRODUCTION

The introduction of the hydraulic piston corer (HPC)has offered new possibilities for detailed studies of un-disturbed, unconsolidated sediments covering large partsof the Neogene, and has provided a potential for study-ing cores with high deposition rates far beyond the lim-its of conventional piston coring. Site 610 is located onthe Feni Drift (Fig. 1) at 2417 m depth. The differentHPC-drilled holes at this site constitute an almost com-plete section, down to 200 m sub-bottom depth, reveal-ing a high sedimentation rate of approximately 5.2 cm/kyr.

The main objective of this study was to provide abenthic and planktonic δ13C and δ 1 8 θ record for the up-per 122.5 m at this site in order to elucidate some of themain trends in isotopic variability within the cores. Thisrecord should serve as a pilot study to test the feasibilityof obtaining detailed isotopic records in these sediments.Our sampling interval of 1.5 m (approximately 30 kyr.)should be sufficient to determine the primary amplitudesin climatic variability, and to test whether the Quater-nary climatic oscillations have been variable or constantin amplitude, and if there were intervals when the over-all pattern of climatic variation changed. Studies of DSDPHole 502B in the Caribbean indicate higher-amplitudeclimatic fluctuations within the late Quaternary (Brun-hes Epoch) than in the early Quaternary (Prell, 1982).The carbon isotopic composition of deep-sea benthicforaminifers may be used as an indicator of rates ofdeep-water renewal, and in our case may provide infor-

1 Ruddiman, W. F., Kidd, R. B., Thomas, E., et al., Init. Repts. DSDP, 94: Washington(US. Govt. Printing Office).

2 Address: Dept. of Geology, Section B, University of Bergen, Allégaten 41, N-5000Bergen, Norway.

70°N

60°

50c

40c

30°

552A 116

Gardar Drift Feni Drift

611, 610

'Norfolk

6081 King'sTrough

Azores606

20°80°W 70° 60° 50° 40° 30° 20° 10° 0° 10°E

Figure 1. Location of Leg 94 sites and DSDP Holes 552A and 116.

mation on variations in the production of North AtlanticDeep Water (NADW) and possibly Norwegian-GreenlandSea Overflow. We have also analyzed planktonic fora-minifers in order to study differences in deep-water andsurface isotopic response.

In addition, we report here the first results from anongoing study of the diagenesis in the protein remainsin foraminifers from Site 610, Holes 610 and 610A. Themajor objectives of this study are to: (1) evaluate the po-tential of using amino-acid diagenesis as a geochrono-logical tool in deep-sea cores, and to determine whatprecision level this method has; (2) investigate how iso-leucine epimerization reaction rates for different speciesrelate to each other, and whether they change in time;(3) evaluate the influence of geothermal heat flow on

879

E. JANSEN, H. P. SEJRUP

the results by comparison with results from cores withslower sedimentation rates (King and Neville, 1977; Ba-da and Man, 1980; Müller, 1984); and (4) investigate thepossibility of using amino-acid data to evaluate possibledifferences in bottom-water temperatures in different deep-sea basins.

So far only the epimerization of l^isoleucine to D-al-loisoleucine in the planktonic foraminifer Neogloboquad-rina pachyderma left-coiling (L) has been investigated.

METHODS

Stable Isotope Analysis

Samples were wet-sieved and dried at 30° C. Monospecific sampleswere picked from the > 125-µm fraction, cleaned ultrasonically in meth-anol, and roasted for 40 min. in vacuo at 38O°C. CO2 for analysis wasextracted by reaction with 100% orthophosphoric acid at 50°C on-lineto the mass-spectrometer and cleaned from water by a cold trap at-95°C.

The isotopic measurements were performed on an automated Fin-nigan MAT 251 mass spectrometer. All data are presented with respectto the PDB standard. Calibration to PDB is produced through com-parison with Cambridge, Lamont, and Copenhagen standards as wellas standards supplied by the National Bureau of Standards (NBS 18and NBS 19). The analytical precision is ±O.l‰ for δ 1 8 θ and ±0.07‰for δ 1 3 C. Replicate analyses of the same samples were performed on afew levels that contained enough benthic carbonate, and gave a repro-ducibility within 0.3‰ for δ 1 8 θ and δ 1 3 C.

Amino-Add Analysis

Monospecific samples of N. pachyderma (L) were picked from the> 125-µm fraction. Each sample consisted of about 100 well-preservedspecimens. The samples were repeatedly cleaned with purified water inan ultrasonic bath following the procedure described by Miller et al.(1983). After the tests were dissolved in 7N HC1, using Norleucine asan internal standard, the samples were hydrolyzed at 110°C for 22 hr.,and subsequently dried under vacuum, rehydrated with a pH 2 solu-tion, and analyzed in an automatic ion-exchange HPLC amino-acidanalyzer. The D-alloisoleucine/L-isoleucine ratios presented in this chapterrepresent the ratios between peak heights as determined by a Hewlett-Packard computing integrator. The extent of epimerization, given asthe ratio between D-alloisoleucine and L-isoleucine (alle/Ile), is closeto 0.01 in a modern sample and reaches an equilibrium at a value ofcirca 1.4 in Miocene samples from deep-sea cores (King and Neville,1977; Müller, 1984).

During the same period when the samples from Leg 94 were ana-lyzed, the Bergen Amino Acid Geochronology Laboratory (BAL) ana-lyzed the interlaboratory calibration standards presented by Wehmiller(1984) with the following alle/Ile ratios in the total fraction: 81-ICA-A: 0.167 ± 0.003; 81-ICA-B: 0.540 ± 0.016; 81-ICA-C: 1.20 ± 0.048.

ISOTOPE RESULTS

Both benthic and planktonic foraminiferal assemblagesshow large downcore variations in faunal composition.Consequently it is not possible to base the isotope stratig-raphy on a single species; therefore we analyzed a rangeof different benthic species in order to produce a com-plete record. Because most of these species have been re-ported to show constant oxygen isotopic disequilibria inearlier studies, it is possible to adjust the values for spe-cies-specific departures from oxygen isotopic equilibrium.The factors we have applied are summarized in Table 1.Although there are widely accepted correction factorsfor carbon isotope values from the common benthic spe-cies Uvigerina peregrina and Cibicides wuellerstorfi, thereis a rather large scatter in the values proposed for theother species we have used (Shackleton, 1974; Belangeret al., 1981), which imposes some uncertainties on the

Table 1. Correction factors applied for benthic foraminifers at Site610.

Species δ l öθ Reference

Cibicides wuellerstorfi +0.64 0.00

Melonis barleeanumMelonis pompilioides)

Uvigerina peregrina

Oridorsalis tener

Pyrgo murrhina

Cassidulina teretis

+ 0.40 +0.36

0.00 +0.90

+ 0.36 +1.17

0.00 0.00

Shackleton and Opdyke, 1973;Duplessy et al., 1984

Graham et al., 1981;Woodruff et al., 1980

Shackleton, 1974; Duplessy etal., 1984

CLIMAP Project Members,1984;Graham et al., 1981

Shackleton, 1974; Ganssen,1983;Graham et al., 1981

+ 0.30 +1.17 Jansen, preliminary results

carbon isotope record and may account for some of thelarge peaks. Most notably the values for Pyrgo murrhi-na and Melonis barleeanum may be unreliable.

For the planktonic record we usually analyzed N.pachyderma (L), and in samples where this species wasmissing we analyzed N. pachyderma right-coiling (R)and Globigerina bulloides. With some exceptions thisprovided us with a complete planktonic record.

We have tabulated the isotope results in Tables 2through 5 and have given both the measured values andthe supposed isotopic equilibrium values for benthic for-aminifers. Most samples contained enough specimens ofone benthic species to make an analysis. In some sam-ples we were able to perform analyses on more than onespecies and found them generally to reproduce the knowndifferences in departures from isotopic equilibrium. Insome samples the amount of benthic carbonate avail-able was too small to enable analysis. This situation wasmost serious in Core 610A-12. Although the results dem-onstrate the feasibility of producing a detailed isotopestratigraphy, it might prove difficult to provide a com-plete record with the desired sampling density in someparts of the hole.

Planktonic foraminifers were available in large num-bers in all samples. The primary difficulty with the plank-tonic record is the large variation in the planktonic as-semblages, making it impossible to make a single speciesrecord. The three species we have used were normallypresent in adequate amounts either alone or together;nevertheless it was not possible to obtain measurablenumbers of specimens of these species in some samples.Through large parts of the section we were unable tofind N. pachyderma (L) (Fig. 2). In the samples wherethe normal, coarse-textured and involute N. pachyder-ma (L) was absent it was possible to identify smaller for-aminifers resembling N. pachyderma. These do not oc-cur in polar assemblages, and analyses of their isotopiccomposition display values substantially lighter in δ 1 8 θthan expected values for N. pachyderma. The isotopevalues are lighter than those of both N. pachyderma (R)and G. bulloides from the same samples. We thus con-

880

STABLE ISOTOPE STRATIGRAPHY AND AMINO-ACID EPIMERIZATION

Table 2. Oxygen and carbon isotopic composition of benthic foraminifers at Hole 610A.

Core-section

1-11-2

1-31-41-51-62-12-22-63-13-23-33-43-53-64-24-34-44-54-65-25-35-45-55-66-16-26-26-46-56-67-27-37-57-68-18-28-38-58-69-19-29-39-49-59-610-110-210-310-410-611-211-411-511-612-112-212-413-313-413-513-6

Sampleinterval

(cm)

44-4644-4644-4654-5644-4644-4644-4654-5664-6644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-46

Sub-bottomdepth(m)

0.451.953.455.056.457.959.85

11.0517.1519.0520.5522.0523.5525.0526.5530.1531.6533.1534.6536.1539.7541.2542.7544.2545.7547.8549.3549.3552.3553.8555.3558.9560.4563.4564.9567.0568.5570.0573.0574.5576.6578.1579.6581.1582.6584.1586.2587.7589.2590.7593.7597.35

100.35101.85103.35105.45106.95109.95118.05119.55121.05122.55

Species

C. wuellerstorfiP. murrhinaC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiM. barleeanumC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiM. barleeanumU. peregrinaU. peregrinaU. peregrinaC. wuellerstorfiM. barleeanumM. barleeanumC. wuellerstorfiC. wuellerstorfiM. barleeanumC. wuellerstorfiM. barleeanum/pompilioidesM. barleeanum/pompilioidesM. barleeanum/pompilioidesP. murrhinaM. pompilioidesC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiM. pompilioidesO. tenerC. wuellerstorfiCibicides sp.C. wuellerstorfiC. wuellerstorfiU. peregrinaC. wuellerstorfiP. murrhinaC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiP. murrhinaC. wuellerstorfiM. pompilioidesC. wuellerstorfiP. murrhinaU. peregrinaC. wuellerstorfiC. wuellerstorfiU. peregrinaP. murrhinaM. barleeanumU. peregrinaU. peregrinaC. wuellerstorfiO. tenerC. wuellerstorfiM. barleeanum

δ 1 8 o P D B

+ 2.61+ 4.45+ 3.60+ 3.38+ 3.11+ 3.32+ 3.61+ 4.03+ 3.32+ 3.57+ 2.93+ 2.61+ 4.37+ 4.27+ 3.57+ 3.83+ 3.34+ 2.96+ 3.47+ 4.09+ 3.27+ 3.74+ 2.97+ 2.84+ 3.23+ 3.32+ 4.51+ 3.65+ 3.03+ 3.13+ 3.60+ 3.11+ 3.83+ 3.05+ 3.38+ 2.68+ 2.94+ 3.86+ 2.67+ 2.71+ 2.19+ 2.45+ 3.43+ 3.33+ 2.71+ 4.08+ 2.50+ 3.49+ 3.06+ 3.26+ 3.26+ 2.60+ 2.48+ 2.81+ 3.14+ 3.01+ 3.31+ 3.18+ 2.78+ 4.48+ 2.57+ 2.98

δ 1 8 O P D B

(corr. values)

+ 3.25+ 4.45+ 4.24+ 4.02+ 3.75+ 3.96+ 4.25+ 4.43+ 3.96+ 4.20+ 3.57+ 3.25+ 4.77+ 4.27+ 3.57+ 3.83+ 3.98+ 3.36+ 3.87+ 4.73+ 3.91+ 4.14+ 3.61+ 3.24+ 3.67+ 3.72+ 4.51+ 4.05+ 3.67+ 3.77+ 4.24+ 3.51+ 4.19+ 3.69+ 4.02+ 3.32+ 3.58+ 3.86+ 3.31+ 2.71+ 2.83+ 3.09+ 4.07+ 3.97+ 3.35+ 4.08+ 3.14+ 3.89+ 3.70+ 3.26+ 3.26+ 3.24+ 3.12+ 2.81+ 3.14+ 3.41+ 3.31+ 3.18+ 3.43+ 4.84+ 3.21+ 3.38

δ 1 3 C P D B

+ 0.83+ 1.14+ 0.77+ 0.53+ 0.92+ 0.65+ 0.82-0.06+ 1.06+ 0.11+ 0.77+ 0.90-0.43-0.50+ 0.22-0.35+ 0.48-0.53+ 0.20+ 0.36+ 0.83-0.87-0.16-0.29-0.58-0.42-0.80-1.30+ 0.02+ 0.38+ 0.70+ 0.38-0.63+ 0.41-0.49+ 0.97+ 0.40-0.58+ 0.30+ 0.29+ 0.63+ 0.83+ 0.64+ 0.42+ 0.64+ 0.56+ 1.09-0.14+ 0.57+ 0.21-0.02+ 0.11+ 1.23+ 0.11+ 0.67-1.04-0.16+ 0.24+ 0.52-0.66+ 0.89-0.26

δ 1 3 C P D B

(corr. values)

+ 0.83+ 1.14+ 0.77+ 0.53+ 0.92+ 0.65+ 0.82+ 0.30+ 1.06+ 0.11+ 0.77+ 0.90-0.07+ 0.40+ 1.12+ 0.55+ 0.48-0.17+ 0.16+ 0.36+ 0.83-0.51-0.16+ 0.07-0.22-0.06-0.80-1.11+ 0.02+ 0.38+ 0.70+ 0.74+ 0.54+ 0.41-0.49+ 0.97+ 0.40+ 0.32+ 0.30+ 0.29+ 0.63+ 0.83+ 0.64+ 0.42+ 0.64+ 0.56+ 1.09+ 0.22+ 0.57+ 0.21+ 0.88+ 0.11+ 1.23+ 1.01+ 0.67-0.68+ 0.74+ 1.14+ 0.52+ 0.51+ 0.89+ 0.07

elude that these small variants should not be consideredas N. pachyderma, at least not with regard to their iso-topic composition. Right-coiling N. pachyderma are onthe average lighter in δ1 3C by O.35%o and in δ 1 8 θ byO.45%o than G. bulloides, although the sample-to-sam-ple difference may vary markedly (Fig. 2) (Tables 3 and5). This is in accordance with the isotopic patterns forthese species revealed by a study of their recent distribu-

tion in the Norwegian Sea (T. Johannessen, personal com-munication, 1984).

Coring disturbances are present in some of the uppercores from Hole 610A. A number of samples from Hole610 were thus analyzed in order to fill in gaps in the sed-iment recovery of Hole 610A. A summary of the inter-vals that were reported to show severe coring disturbanceis presented in Figure 2. Some of the uppermost sedi-

881


Table 3. Oxygen and carbon isotopic composition of planktonic fora-minifers at Hole 610A.

Core-section

-1-2

-3-4

-5-6

2-12-2

2-63-13-2

3-3

3-4

3-53-64-24-3

4-4

4-54-65-35-4

5-66-16-26-4

6-5

6-67-2

7-37-4

7-6

8-18-28-38-48-4

8-58-69-19-2

9-3

9-39-59-6

10-110-210-210-310-310-410-410-510-510-611-211-311-411-411-511-612-112-212-312-412-512-513-213-213-313-413-513-6

Sampleinterval

(cm)

44-4644-4644-4644-4644-4644-4684-8654-5664-6644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-46

Sub-bottomdepth

(m)

0.451.953.455.056.457.959.85

11.5517.1519.0520.5522.0523.5525.0526.5530.1531.6533.1534.6536.1541.2542.7545.7547.8549.3552.3553.8555.3558.9560.4561.9564.9567.0568.5570.0571.5571.5573.0574.5576.6578.1579.6579.6582.6584.1586.2587.2587.7589.2589.2590.7590.7592.2592.2593.7597.3598.85

100.35100.35101.85103.35105.45106.95108.45109.95111.45111.45116.55116.55118.05119.55121.05122.55

Species

N. pachyderma (R)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (R)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (R)N. pachyderma (L)N. pachyderma (R)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (R)N. pachyderma (R)N. pachyderma (R)G. bulloidesN. pachyderma (R)N. pachyderma (R)G. bulloidesG. bulloidesG. bulloidesN. pachyderma (R)G. bulloidesN. pachyderma (R)G. bulloidesG. bulloidesG. bulloidesG. bulloidesG. bulloidesN. pachyderma (R)N. pachyderma (R)G. bulloidesN. pachyderma (R)G. bulloidesN. pachyderma (R)G. bulloidesN. pachyderma (R)N. pachyderma (R)N. pachyderma (R)G. bulloidesN. pachyderma (R)G. bulloidesG. bulloidesG. bulloidesG. bulloidesN. pachyderma (R)N. pachyderma (R)N. pachyderma (R)G. bulloidesG. bulloidesN. pachyderma (R)N. pachyderma (R)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)

δ 1 8 O P D B

+ 0.95+ 3.70+ 3.44+ 2.79+ 2.46+ 2.86+ 2.95+ 3.68+ 2.79+ 3.38+ 2.55+ 0.81+ 3.46+ 3.30+ 2.00+ 1.50+ 2.84+ 1.36+ 2.67+ 3.48+ 2.66+ 2.34+ 1.96+ 2.39+ 2.70+ 2.54+ 2.55+ 2.41+ 1.99+ 1.98+ 1.19+ 1.05+ 0.88+ 1.26+ 1.17+ 0.36+ 0.96+ 1.26+ 1.75+ 0.65+ 1.20+ 1.66+ 1.76+ 1.86+ 2.52+ 1.95+ 1.95+ 1.24+ 1.51+ 1.70+ 1.36+ 1.88+ 1.21+ 1.30+ 1.50+ 1.42+ 1.04+ 1.80+ 1.44+ 1.69+ 2.06+ 2.03+ 1.66+ 1.39+ 1.09+ 1.09+ 1.68+ 1.74+ 0.81+ 1.30+ 2.87+ 2.05+ 2.60

δ 1 3 C P D B

+ 0.29-0.42-0.63-0.95+ 0.61+ 0.25-0.18-0.40-0.13-0.62+ 0.03+ 0.26-0.17-0.41+ 0.72+ 0.02-0.72-0.55-0.15-0.13-1.09-0.50-0.64-0.65-1.26+ 0.12+ 0.28+ 0.09-0.28-0.53-0.41+ 0.20+ 0.01-0.75-0.98-0.47-0.57-0.44-0.30-0.43+ 0.26-0.46-0.26+ 0.24+ 0.26+ 0.41+ 0.32-0.97-1.01-0.69-1.03-0.39-0.43-0.13-0.13+ 0.21+ 0.03+ 0.30+ 0.14+ 0.64+ 0.35-1.09-0.76-0.24+ 0.19+ 0.32+ 0.03+ 0.41+ 0.04+ 0.39+ 0.87+ 1.25+ 0.46

ments may have been lost during coring in Hole 610, asthe top sample, taken at 0.45 m in this hole, shows gla-cial planktonic assemblages and isotope values, whereasthe sample from the same level in Hole 610A shows Hol-

ocene assemblages and isotope values. The Brunhes/Ma-tuyama (B/M) magnetic boundary is somewhat shallow-er in Hole 610 than in 610A. These differences make itdifficult to match precisely samples from the two holesin order to form a single record. Ruddiman, Cameron,and Clement (this volume) performed detailed visual cor-relations of the different offset holes at Site 610. Theirresults indicate that corresponding levels in Holes 610and 610A are not offset by a constant factor downhole,but rather that correlative levels are found to be locatedwith a difference in sub-bottom depths ranging between25 and 100 cm. In order to fit the data from Hole 610into the record from Hole 610A we have used the visualcorrelations of Ruddiman et al., and the upper level ofthe Brunhes/Matuyama boundary. By this method thesub-bottom depths of the samples from Hole 610 aremoved downward by the following factors (Figs. 2 and4): 0-5 m—25 cm; 5-15.5 m—60 cm; 15.5-34.5 m—75cm; 34.5-47 m—100 cm. The problems of hole-to-holecorrelations show that it is not an easy task to place asingle sample in its right place. We thus note that themethod we have used may have led to possible errors,and that the composite record we have obtained cannotbe regarded as a continuous one. A correct placing ofthe data is dependent on matching of complete curvesbased on a much higher sampling density than the oneused for this study.

DISCUSSION

Oxygen Isotopes

Oxygen isotopes in benthic foraminifers are believedto be rough measures of global ice volume (Shackleton,1967; Shackleton and Opdyke, 1973). Studies by Du-plessy et al. (1980) indicate that there might be a tempera-ture overprint on benthic δ 1 8θ records from the North-east Atlantic Basin, as a result of lower glacial deep-wa-ter temperatures. The benthic record and the record fromTV. pachyderma (L) follow similar trends, reflecting theproposed deep habitat for N. pachyderma (L) (Kellogget al., 1978; Duplessy et al., 1981). High-amplitude iso-topic peaks are recorded throughout the Brunhes Epochand down to approximately 0.9 Ma, just above the Jara-millo Event on the paleomagnetic time scale (Fig. 2).This reflects the large fluctuations in ice volume and cli-mate known from numerous isotope records from thelate Quaternary. The extreme difference between peakglacial and peak interglacial values is approximately1.8%o, in good accordance with expected values in re-cords with high sedimentation rates. We also note thatice-volume minima coincide with the absence of polarplanktonic foraminiferal species, and thus with warmsurface-water conditions.

According to our records, before 0.9 Ma there was acontinuation of high-frequency climatic variations, butthe severity of these variations were markedly reduced incomparison with those of the late Quaternary. A sum-mary of the mean isotopic values and variability (ex-pressed as the standard deviation about the mean) is pre-sented in Table 6 and Figure 3. The mean benthic oxy-gen isotope value is 0.4‰ lighter prior to 0.9 Ma than

882


Table 4. Oxygen and carbon isotopic composition of benthic foraminifers at Hole 610.

Core-section

1-1

1-2

1-2

1-31-41-62-12-12-22-32-32-32-4

2-5

3-33-4

4-4

4-65-25-25-45-6

Sampleinterval

(cm)

44-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4624-2644-4644-4654-5644-4644-4644-4644-46

Sub-bottomdepth

(m)

0.451.951.953.454.957.95

10.0510.0511.5513.0513.0513.0514.5516.0522.4524.1533.7536.8540.3540.3544.0546.35

Species

M. barleeanumU. peregrinaC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiC. teretisC. wuellerstorfiP. murrhinaC. wuellerstorfiU. peregrinaC. wuellerstorfiM. barleeanumU. peregrinaU. peregrinaC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiC. wuellerstorfiCibicides sp.C. teretisC. wuellerstorfiP. murrhina

δ 1 8 O P D B

+ 3.89+ 4.45+ 3.83+ 3.64+ 3.70+ 4.00+ 3.70+ 4.29+ 2.71+ 3.22+ 2.19+ 2.59+ 4.42+ 4.05+ 2.33+ 3.10+ 2.96+ 3.10+ 3.53+ 3.58+ 2.61+ 3.56

δ 1 8 O P D B

(corr. values)

+ 4.29+ 4.45+ 4.47+ 4.29+ 4.34+ 4.30+ 4.34+ 4.29+ 3.35+ 3.22+ 2.83+ 2.99+ 4.42+ 4.05+ 2.97+ 3.74+ 3.60+ 3.74+ 4.17+ 3.88+ 3.25+ 3.56

δ C P D B

-0.16-0.24+ 0.97+ 0.47+ 1.03-1.52+ 0.13+ 0.68+ 0.98-0.19+ 0.63+ 0.37-0.57-0.34+ 1.06+ 0.73+ 0.34+ 0.73-0.28-1.49+ 0.33+ 0.80

δ 1 3 C P D B

(corr. values)

+ 0.20+ 0.66+ 0.97+ 0.47+ 1.03+ 0.35+ 0.13+ 0.68+ 0.98+ 0.71+ 0.63+ 0.73+ 0.33+ 0.56+ 1.06+ 0.73+ 0.34+ 0.73-0.28-0.24+ 0.33+ 0.80

Table 5. Oxygen and carbon isotopic composition of planktonic fora-minifers at Hole 610.

Core-section

Sampleinterval

(cm)

Sub-bottomdepth

(m) Species1 O 1 -J

δ °PDB δ C PDB

1-11-2

1-3

1-31-41-4

1-5

1-62-12-2

2-32-4

2-53-33-4

4-54-6

4-65-2

5-55-6

44-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4644-4624-2644-4644-4644-4654 5644-4644-4644-46

0.451.953.453.454.954.956.457.95

10.0511.5513.0514.5516.0522.4524.1535.2536.8536.8540.3544.8546.35

N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (R)N. pachyderma (L)N. pachyderma (R)N. pachyderma (R)N. pachyderma (L)N. pachyderma (L)N. pachyderma (R)N. pachyderma (R)N. pachyderma (L)N. pachyderma (L)N. pachyderma (R)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)N. pachyderma (R)N. pachyderma (L)N. pachyderma (L)N. pachyderma (L)

+ 3.94+ 3.43+ 2.59+ 1.27+ 2.62+ 1.29+ 0.63+ 3.71+ 3.59+ 0.91+ 0.83+ 3.35+ 3.41+ 0.59+ 3.45+ 3.51+ 3.04+ 0.84+ 2.98+ 3.16+ 2.42

-0.32-0.39-0.53-0.45+ 0.26-0.13-0.65-0.27-0.36-0.26-0.03-0.30-0.43+ 0.21-0.19-0.98-1.53-0.75-1.29-0.41-0.42

after, showing a generally smaller average terrestrial icevolume and concomittantly higher eustatic sea level forthe early Quaternary/latest Pliocene. The standard de-viation is also lower in the section prior to 0.9 Ma, indi-cating less severe climatic fluctuations in this part. In astudy of the Quaternary section of Hole 502B, Prell (1982)identified a similar pattern showing two modes of cli-matic variability through the Quaternary. He proposedthat the change of modes occurred at about 0.73 Ma,beneath the B/M boundary. Our results seem to indicatethe presence of high-amplitude peaks down to approxi-mately 0.9 Ma, but the exact timing of this change willhave to be further validated by more detailed isotope re-cords. The isotope records of Site 504 (Shackleton andHall, 1983) and Site 552 (Shackleton et al., 1984) mayalso indicate less severe climatic oscillations in a period

before 1 Ma. Hole 552A seems to indicate a return tolarger amplitudes at about 2 Ma, continuing down tothe first indication of large Northern Hemisphere glaci-ations at 2A Ma.

Hole 552A was located on the flank of the RockallBank not far to the west of our Site 610 (Fig. 1). AtHole 610A we note evidence of larger amplitudes in thelowermost samples, at about 2.3 Ma, possibly correla-tive with similar features in the record from Hole 552A.Evidence from marine terraces in New Zealand indicatesthat there was an increase in amplitude of eustatic sea-level fluctuations at about 1 Ma (Beu and Edwards, 1984),a conclusion in agreement with assumptions on sea-levelchanges based on oxygen isotope records.

The first input of ice-rafted detritus into the NorthAtlantic at Hole 5 52A has been rather accurately datedat 2.4 Ma by nannofossil zonation (Shackleton et al.,1984). Blanc et al. (1983) also found that the first ap-pearances of polar foraminiferal assemblages and ice-rafted detritus took place at about 2.5 Ma at Site 116,located in the Rockall Basin area (Fig. 1). We recordnormal N. pachyderma (L) in the lowermost samplesfrom Hole 610A, but have not found this species in sam-ples between this level (approximately 2.3 Ma) and a lev-el slightly beneath the Jaramillo Event (approximately 1Ma). With the caution that polar assemblages might bepresent as high-frequency peaks not detected by our coarsesample spacing, we suggest that this indicates: (1) Oce-anic polar front oscillations across the Northeast Atlan-tic, typical of late Quaternary ocean circulation (Ruddi-man and Mclntyre, 1976), were generally not character-istic of the period between 1 and 2 Ma. This may implythat the role of the North Atlantic Ocean in climaticchange in the late Quaternary, described by Ruddimanand Mclntyre (1984), could have been significantly dif-ferent from that in the early Quaternary. (2) The firstpart of the period recording Northern Hemisphere glaci-ations (approximately 2-2.5 Ma) might, as indicated by

883


Figure 2. Oxygen and carbon isotope record from Holes 610 and 610A. (Open symbols indicate samplesfrom 610, filled symbols indicate samples from 610A; paleomagnetic and nannofossil boundaries afterSite 610 report [this volume]; B = Brunhes, M = Matuyama, J = Jaramillo, O = Olduvai, and R =Reunion.)

Table 6. Mean (x) and standard deviation (σ) of earlyand late Quaternary isotope records.

δ 1 8 θ benthic x

n σ

δ iC benthic x

18 °δ 1 8 θ planktonicx

. , σδliC planktonic x

σ

late Quaternary(0-0.9 Ma)

3.90‰0.470.43‰0.512.53‰0.98

-O.38‰0.47

early Quaternary/latest Pliocene(0.9-2.38 Ma)

3.5O‰0.410.46‰0.521.57‰0.53

-O.IO‰0.55

isotope variability and planktonic foraminifers, be char-acterized by large climatic oscillations and polar frontmigrations into the North Atlantic, analogous with thelate Quaternary record.

Carbon Isotopes

Recent studies have documented the importance ofbenthic carbon isotope variations as an indicator of var-iations in the rates of deep-water renewal (Kroopnick,1980; Shackleton et al., 1983; Duplessy et al., 1984). Fo-raminiferal evidence (Streeter and Shackleton, 1979; Stree-ter et al., 1982; Jansen et al., 1983) and carbon isotopevariations (Duplessy, 1982; Curry and Lohmann, 1982;

884


δ 1 8 θ versus PDB δ 1 3 C versus PDB

+4.0 +3.0 +2.0 +1.0 -1.0 0 +1.0

100-r

110-

120--

Figure 3. Mean carbon and oxygen isotope values in benthic foramini-fers from Holes 610 and 610A (heavy line), standard deviationaround the mean (light line and hachured area), and planktoniccarbon isotopic mean (dotted line). Paleomagnetic boundaries af-ter Site 610 report (this volume); B = Brunhes, M = Matuyama, J= Jaramillo, O = Olduvai, and R = Reunion.

Shackleton et al., 1983) indicate large variations in theproduction rates of NADW and Norwegian-GreenlandSea Overflow in response to Quaternary climatic varia-tions, with an assumed reduction in the production ratesof NADW and hence in deep-water δ13C during glacials.As can be seen in Figure 2 and 3, glacial stages on theδ13C record do not display any notable change in modein the mid-Quaternary, as did the δ 1 8 θ record (Figs. 2and 3, Table 6). This could imply that, despite reducedclimatic variability in the early Quaternary, the varia-tions in the production rates of NADW remained rela-tively constant in magnitude. Hence the δ13C variationsimply that the on-off situation in Northern Hemispherebottom-water formation was a feature in operationthroughout the last 2.3 Ma either as Norwegian-Green-land Sea Overflows or as deep-water formation in theNorth Atlantic itself.

In a study of benthic foraminiferal assemblages incores from the Rio Grande Rise, Peterson and Lohmann(1982) proposed that a major change in South Atlanticdeep-water circulation took place about 700 kyr. ago.The inflow of Antarctic Bottom Water (AABW) was re-duced before this time, whereas the production of NADWdid not seem to be affected. This contention seems to be

in agreement with the carbon isotope record of Hole610A, which does not indicate major changes in NADWvariability across the time level of 0.7 Ma (Figs. 2 and3).

The mean benthic δ13C of + 0.45%0 at Hole 610A con-firms the conclusion of Shackleton et al. (1984) that thedeep waters of the North Atlantic generally have beenbetter ventilated than Pacific deep waters throughout thelate Pliocene/Quaternary. The variability of the δ13C re-cord at Hole 610A is similar to that found at other NorthAtlantic holes (Hole 552A—Shackleton et al., 1984; Hole397—Shackleton and Cita, 1979). The mean δ13C valueis close to that of Hole 552A, whereas the values for Site397 (corrected for the difference in isotopic disequilibri-um between Cibicides and Uvigeriná) indicate lower δ13Clevels for the deep water off West Africa. The differencemight reflect the difference in deep-water residence timebetween the two regions, but may also in part reflect dif-ferences in surface productivity and in the input of or-ganic matter to the bottom.

The planktonic δ13C record indicates variations of thesame order of magnitude as the benthic record. The re-sults for N. pachyderma (L) duplicate some of the trendsin the benthic curve (Fig. 2). The low sampling density,however, does not enable us to investigate further thecorrelation between near-surface and bottom δ13C re-sponse. In an area such as the North Atlantic, with nu-merous rapid changes in surface water masses and pro-ductivity, it is natural to expect large variations in plank-tonic δ13C. Generally the planktonic δ13C values arelighter than the benthic values. More studies of vital ef-fects, habitat, and feeding conditions of the species ana-lyzed will be needed in order to evaluate the implica-tions of this difference, but it might be suggested thatthe depletion reflects low δ13C levels in the productiveupper water masses.

We have also compared mean benthic and planktonicδ13C before and after 0.9 Ma (Fig. 3). The difference be-tween benthic and planktonic δ13C values appears to de-crease before 0.9 Ma, but this might be a result of theuse of another planktonic species in the lower part ofthe record (Table 3).

AMINO-ACID DIAGENESIS—RESULTS ANDDISCUSSION

The isoleucine epimerization in the total fraction (free+ peptide bound) in N. pachyderma (L) is presented asalle/Ile ratios in Table 7 and Figure 4. In the followingdiscussion we assume a constant sedimentation rate of5.2 cm/kyr. Down to about 20 m sub-bottom depth thealle/Ile ratios increase rather linearly to a ratio close to0.3. Further downcore we are able to register an increasein the alle/Ile ratio, but the reaction rate appears to bemuch lower. Similar trends of isoleucine epimerizationhave been demonstrated earlier for other planktonic spe-cies such as Globigerionoides sacculifer and Globorota-lia tumida (King and Neville, 1977) and Orbulina uni-versa and Globorotalia tumida menardii (group) (Mül-ler, 1984). The inflection point in our material occurs ata different alle/Ile ratio than has been reported for oth-er species. This might be due to changes in the natural

885


Table 7. alle/Ile ratios in N. pachyderma (L) fromSite 610.

Sample(core-section,

interval in cm)

610-1-1,44-46610-1-3, 44-46610A-1-4, 54-56610A-1-4, 54-56610A-2-1, 84-86610-2-1, 44-46610-2-5, 44-46610A-3-1, 44-46610A-3-6, 44-46610A-5-6, 44-46610A-7-3, 44-46610A-13-5, 44-46610A-13-6, 44-46

Lab no.

BAL 422BAL 421BAL 423BAL 425BAL 424BAL 445BAL 446BAL 447BAL 448BAL 452BAL 455BAL 544BAL 545

Sub-bottomdepth(m)

0.703.705.055.059.85

10.6516.8017.1526.5545.7560.45

121.05122.55

alle/Ile

0.0650.0380.0680.0690.1650.2270.3150.2870.3620.4100.4920.8500.782

hydrolysis reaction or leaching of isoleucine in the freefraction (Müller, 1984). In order to try to resolve this weplan to perform parallel analyses of the free fractionand more closely study hydrolysis reactions.

Earlier investigations of the isoleucine epimerizationin foraminifers from the deep sea have mostly been basedon material from piston cores from areas with low sedi-mentation rates (King and Neville, 1977; Müller, 1984).Our data might be more influenced by geothermal heatflow than these, especially in the lower part of the hole.To quantify this, more analyses are needed as well ascomparisons with data on TV. pachyderma (L) from areaswith low sedimentation rates.

King (1980), demonstrated that planktonic foraminif-eral species could be divided into two different groupsbased on the overall composition of the protein. Thesegroups parallel the taxonomic distinction between spi-nose and nonspinose forms. It is important to note thatTV. pachyderma's epimerization picture is more similarto the spinose O. universa than the nonspinose G. me-nardii tumida (group), as reported by Müller (1984).

Although we are only able to report preliminary re-sults; it should be possible to draw some conclusions onthe feasibility of using isoleucine epimerization in TV.pachyderma as a geochronological tool in this type ofmaterial. The relatively steep curve back to approximately0.3 Ma indicates that the best possibility for using thismethod for absolute dating of deep-sea sediments is formaterial younger than 0.3 m.y. The method might be ofimportance for older material, but probably with lowerprecision. An accurate kinetic model for isoleucine epi-merization in TV. pachyderma (L) is needed, as this is akey taxon in many deep-sea records from high latitudes,and epimerization ratios have been used to raise ques-tions concerning the difficult problem of the chronol-ogy of Arctic Ocean cores (Sejrup et al., 1984).

CONCLUSIONS1. It should be feasible to produce a detailed stable

isotope stratigraphy from both benthic and planktonicforaminifers through the upper Pliocene/Quaternary inHoles 610 and 610A. The high deposition rates at thissite give a unique opportunity for providing a record

that shows details in climatic response throughout thisperiod.

2. The benthic oxygen isotope record indicates lessclimatic variability before 0.9 Ma than after, with re-duced amplitudes in isotopic fluctuations and generallysmaller continental ice volume during the early Quater-nary than in the late Quaternary.

3. Frequent oscillations of the oceanic polar frontacross the Northeast Atlantic seem to be dramaticallyreduced in the period between 2 and 1 Ma, as comparedwith the late Quaternary.

4. During the period between 2.5 and approximately2.0 Ma, there may have been larger ice-volume fluctua-tions and polar-front oscillations than in the early Qua-ternary/latest Pliocene.

5. The production rates of NADW as indicated byδ13C values were variable throughout the studied period,but the variance of NADW production remained un-changed throughout the Quaternary, unlike the δ 1 8 θ rec-ord.

6. The extent of isoleucine epimerization in TV. pachy-derma (L) suggest that amino-acid diagenesis has its great-est resolution as a geochronological tool over the last300 kyr. Before this age reaction rate was reduced andthe data show greater scatter.

ACKNOWLEDGMENTS

We thank Ida Beyer, Truls Johannessen, Karl-Johan Karlsen, andKjell S0gnen for assistance with sample processing and Jane Ellingsenfor making the drawings. We also gratefully thank Sturla Rolf sen forhis skilled efforts in keeping the mass-spectrometer operative, JulieBrigham-Grette for performing the amino-acid analyses and for herconstructive suggestions concerning the manuscript, and Scott Lehmanfor carefully reading the manuscript, which helped us to improve it.Our reviewers Giff Miller and Warren Prell suggested many valuableimprovements. The National Stable Isotope Laboratory at Bergen Uni-versity is supported by grants from the Norwegian Research Councilfor Science and the Humanities (NAVF), which also supported this re-search through the program "Correlation of Marine and ContinentalQuaternary Stratigraphy."

REFERENCES

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Belanger, P. E., Curry, W. B., and Mathews, R. K., 1981. Core-topevaluation of benthic foraminiferal isotopic ratios for paleo-ocean-ographic interpretations. Paleogeogr. Paleoclimatol. Paleoecol., 33:205-220.

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Blanc, P. L., Fontugne, M. R., and Duplessy, J. C , 1983. The time-transgressive initiation of boreal ice-caps: continental and oceanicevidence reconciled. Paleogeogr. Paleoclimatol. Paleoecol., 43:211-224.

CLIMAP Project Members, 1984. The last interglacial ocean. Quat.Res., 21:123-224.

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Duplessy, J. C , 1982. Circulation des eaux profondes Nord Atlan-tiques au cours du dernier cycle climatique. Bull. Inst. Bass. d'A-quitaine, 31:379-391.

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Duplessy, J. C , Delibrias, G., Turon, J. L., Pujol, C , and Duprat, J.,1981. Deglacial warming of the northeastern North Atlantic Ocean:correlation with the paleoclimatic evolution of the European conti-nent. Paleogeogr. Paleoclimatol. Paleoecol., 35:121-144.

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Date of Initial Receipt: 9 November 1984Date of Acceptance: 28 June 1985

887


ho~-•? ^•à α3 Φ

1 0 -

2 0 -

3 0 -

4 0 -

5 0 -

•

6 0 -

7 0 -

8 0 -

9 0 -

100-

110-

120-

u

a>

P "o 2_Φ Φ

a. ^

TB

0.73M

0.91J

0.98

1.66o

1.88

in

IΛino"oc<nZ

zz

o

1

zz

_

zz

Holes 610 and 610A

/ 1 + alle/Ile \l n l i-0.77a l e / l l e / i n N p a c / I y d β r m a ( L )

0.5 1.0 1.5I I

\

\\\\\\\\\\\\#\\\\\\\\\\\\\\\\\\\\

' 1 1 1 1 1 1 1 10.2 0.4

alle/Ile

0.6 0.8

Figure 4. The alle/Ile ratios in N. pachyderma (L) from Holes 610 (open circles) and Hole 610A(closed circles). Paleomagnetic and nannofossil boundaries after Site 610 report (this volume). B= Brunhes, M = Matuyama, J = Jaramillo, and O = Olduvai.

888

23. stable isotope stratigraphy and amino-acid ...23. stable isotope stratigraphy and amino-acid...

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